Alkoxo and Aryloxo Derivatives of Metals Elsevier ppt

Alkoxo and Aryloxo Derivatives of
Metals
Elsevier, 2001

Author: D.C. Bradley, R.C. Mehrotra, I.P. Rothwell and A. Singh
ISBN: 978-0-12-124140-7



Foreword, Page xi

1 - Introduction, Pages 1-2

2 - Homometallic Alkoxides, Pages 3-181

3 - Heterometallic Alkoxides, Pages 183-228

4 - X-Ray Crystal Structures of Alkoxo Metal Compounds, Pages 229-382

5 - Metal Oxo-alkoxides, Pages 383-443

6 - Metal Aryloxides, Pages 445-669

7 - Industrial Applications, Pages 671-686

Index, Pages 687-704
Foreword
The value of a book may well be judged by the number of times a person has to
buy it, for, while many books once read gather dust upon a shelf, those more often
sought can sometimes be seldom found. Over 20 years ago, I was fortunate to receive

a complimentary copy of “Metal Alkoxides” by Bradley, Mehrotra and Gaur. As one
interested in alkoxide metal chemistry, this proved a valuable reference for me and
my research group. In fact, I had to purchase two subsequent copies and probably
would have purchased more were it not for the fact that the book became out of print
and unavailable except through the library. Now I have received the galley proofs of
the second edition entitled “Alkoxo and Aryloxo Derivatives of Metals”byBradley,
Mehrotra, Rothwell and Singh. After 20 years, virtually every field of chemistry must
have changed to the extent that a new edition would be appropriate. However, it is
unlikely that any field of chemistry, save computational chemistry, will have changed
as much as that of the chemistry of metal alkoxides and aryloxides during the period
1978–2000. The explosion of interest in metal alkoxides has arisen primarily for two
reasons. First and foremost, we have witnessed the tremendous growth of materials
chemistry spurred on by the discovery of high temperature superconducting oxides
and by the increasingly important role of other metal oxides to technology. Metal
alkoxides, mixed metal alkoxides and their related complexes have played an essential
role in the development of new routes to these materials either by sol-gel or chemical
vapor deposition techniques. In a second area of almost equal magnitude, we have
seen the growth of a new area of organometallic chemistry and catalysis supported
by alkoxide or aryloxide ancillary ligands. As a consequence of these major changes
in chemistry, virtually any issue of a current chemistry journal will feature articles
dealing with metal alkoxides and aryloxides. Thus, although the present book owes its
origins, and to some extent its format, to the first edition, its content is largely new. For
example, while the first edition reported on but a handful of structurally characterized
metal alkoxides, this second edition carries a whole chapter dealing with this topic, a
chapter with over 500 references to publications. The second edition is therefore most
timely, if not somewhat overdue, and will be a most valuable reference work for this
rapidly expanding field of chemistry. I only hope that I can hold on to my copy more
successfully than I did in the first instance.
Malcolm H. Chisholm FRS
Distinguished Professor of Mathematical and Physical Sciences

The Ohio State University
Department of Chemistry
Columbus, OH 43210-1185 USA
January 2001
1
Introduction
In 1978 the book entitled “Metal Alkoxides” was published.
1
It contained over one
thousand references and attempted to summarize most of what was known about metal
alkoxides up to that time. A striking feature was the dearth of X-ray crystal struc-
tures and so structural aspects necessarily involved speculation based on the results of
molecular weight determinations, combined where possible with spectroscopic data.
The intervening years have witnessed a spectacular advance in our knowledge of
the chemistry of the metal alkoxides, a development which has been driven primarily
by research activity resulting from the realization that these compounds have great
potential as precursors for the deposition of metal oxide films for microelectronic
device applications and in bulk for producing new ceramic materials. Simultaneously
a tremendous advance occurred in X-ray crystallography with the advent of computer-
controlled automated diffractometers and with improvements in the techniques for
growing and mounting single crystals of the air sensitive metal alkoxides. Consequently
the number of structures solved has become so large that in this book a separate chapter
with over 500 references has been devoted to crystal structures with much of the data
summarized in tabular form. In addition, considerable advances have been made in the
synthesis and characterization of a range of new alkoxides of the alkali metals, alkaline
earths, yttrium and the lanthanides which together with other new developments has
led to a chapter on Homometallic Alkoxides containing well over 1000 references.
Similarly the chapter on Heterometallic Alkoxides (previously described as Double
Metal Alkoxides) has been expanded to include many novel compounds, with particular
emphasis on the recently authenticated species containing two, three and even four

different metals in one molecule.
Another area that has expanded in recent years concerns the Industrial Applications
of metal alkoxides. Besides the previously mentioned deposition of metal oxides in the
microelectronic and ceramics industries there have also been major developments in
the catalytic activity of early transition metal alkoxo compounds in several important
homogeneous reactions. This has stimulated a growing interest in the mechanisms of
reactions catalysed by metal alkoxides.
Metal Oxo Alkoxides are implicated as intermediates in the hydrolysis of metal
alkoxides to metal oxides and their importance in the sol–gel process has led to much
research activity in this area. Accordingly we have allocated a whole chapter to the
Metal Oxo Alkoxides.
In the 1978 book very little space was devoted to metal aryloxides because this
area had received scant attention, but the intervening years have seen a resurgence of
activity involving the synthesis and characterization of many novel compounds and
2 Alkoxo and Aryloxo Derivatives of Metals
studies on their catalytic activity. Therefore we have added a separate chapter dealing
with this important topic.
In this book we are giving the relevant references at the end of the seven chap-
ters rather than placing them all at the end of the text in the hope that this will be
more convenient for the reader. Finally, the authors acknowledge their indebtedness to
all of their former research students, postdoctoral assistants, and colleagues for their
invaluable contributions to the research which has provided much of the information
collected in this publication.
REFERENCE
1. D.C. Bradley, R.C. Mehrotra, and D.P. Gaur, Metal Alkoxides, Academic Press, London
(1978).
2
Homometallic Alkoxides
1 INTRODUCTION
Metal alkoxides [M(OR)

x
]
n
(where M D metal or metalloid of valency x;RD simple
alkyl, substituted alkyl, or alkenyl group; and n D degree of molecular association),
may be deemed to be formed by the replacement of the hydroxylic hydrogen of an
alcohol (ROH) by a metal(loid) atom.
Historically, the first homoleptic alkoxo derivatives of elements such as boron and
silicon had been described
1,2
as early as 1846, but later progress in the alkoxide
chemistry of only half a dozen metals was rather slow and sporadic till the 1950s;
since then the chemistry of alkoxides of almost all the metals in the periodic table has
been systematically investigated. With a few exceptions, systematic investigations on
the structural aspects of metal alkoxides till the mid-1980s
3–10
were limited to studies
on molecular association, volatility, chemical reactivity, and spectroscopic (IR, NMR
and electronic) as well as magnetic properties. It is only since the early 1980s that
definitive X-ray structural elucidation has become feasible and increasingly revealing.
The rapidly advancing applications
11–16
of metal alkoxides for synthesis of ceramic
materials by sol–gel/MOCVD (metallo-organic chemical vapour deposition) processes
(Chapter 7) have more recently given a new impetus to intensive investigations on
synthetic, reactivity (including hydrolytic), structural, and mass-spectroscopic aspects
of oxo-alkoxide species.
17–21
Some of the exciting developments since 1990 in metal alkoxide chemistry have been
focussing on the synthesis and structural characterization of novel derivatives involving

special types of alkoxo groups such as (i) sterically demanding monodentate (OBu
t
,
OCHPr
i
2
, OCHBu
t
2
,OCMeEtPr
i
, OCBu
t
3
) as well as multidentate (OCR
0
CH
2
OPr
i

2
)
(R
0
D Bu
t
or CF
3
), OCR

00
2
CH
2
X(R
00
D Me or Et, X D OMe, OEt, NMe
2
) ligands,
21–24
(ii) fluorinated tertiary alkoxo (OCMeCF
3

2
,OCMe
2
CF
3
,OCCF
3

3
, etc.) moie-
ties,
21–23
and (iii) ligands containing intramolecularly coordinating substituents
(OCBu
t
2
CH

2
PMe
2
,OCH
2
CH
2
X(XD OMe, OEt, OBu
n
,NR
2
,PR
2
)).
21,22
Compared
to simple alkoxo groups, most of these chelating/sterically demanding ligands possess
the inherent advantages of enhancing the solubility and volatility of the products by
lowering their nuclearities owing to steric factors and intramolecular coordination.
Solubility and volatility are the two key properties of metal alkoxides which provide
convenient methods for their purification as well as making them suitable precursors
for high-purity metal oxide-based ceramic materials.
It is noteworthy that the homoleptic platinum group metal (Ru, Rh, Pd, Os, Ir, Pt)
alkoxides are kinetically more labile possibly owing to ˇ-hydrogen elimination
9,10,21
4 Alkoxo and Aryloxo Derivatives of Metals
type reaction(s) (Eq. 2.1):
M—OCHR
0
R

00
 ! M—H C R
0
R
00
C
D
O
#
M C
1
2
H
2
2.1
These, therefore, are not generally isolable under ambient conditions unless special
types of chelating alkoxo ligands
21
are used.
Although single crystal X-ray studies presented considerable difficulties in the earlier
stages,
25
the development of more sophisticated X-ray diffraction techniques has led
to the structural elucidation of a number of homo- and heteroleptic alkoxides
17–23
and
actual identification of many interesting metal oxo-alkoxide systems (Chapter 4).
In this chapter we shall discuss the synthesis,
3,4,26
chemistry and properties of

homometallic alkoxides with more emphasis on homoleptic alkoxides [M(OR)
x
]
n
and
M(OR)
x
.L
n
with occasional references to metal oxo-alkoxides MO
y
OR
x 2y
and
metal halide alkoxides M(OR)
xy
X
y
.L
z
(where x D valency of metal, L D neutral
donor ligand, X D halide, and n, y and z are integers). The discussion will generally
exclude organometallic alkoxides and a considerable range of metal-organic compounds
containing alkoxo groups, as in these systems the alkoxo groups play only a subsidiary
role in determining the nature of the molecule.
2 METHODS OF SYNTHESIS
Metal alkoxides in general are highly moisture-sensitive. Stringent precautions are,
therefore, essential during their synthesis and handling; these involve drying of all
reagents, solvents, apparatus, and the environment above the reactants and products.
Provided that these precautions are taken, the preparation of metal alkoxides, although

sometimes tedious and time consuming, is relatively straightforward.
The method employed for the synthesis
3,4,8,17,21
of any metal/metalloid alkoxide
depends generally on the electronegativity of the element concerned. Highly elec-
tropositive metals with valencies up to three (alkali metals, alkaline earth metals, and
lanthanides) react directly with alcohols liberating hydrogen and forming the corre-
sponding metal alkoxides. The reactions of alcohols with less electropositive metals
such as magnesium and aluminium, require a catalyst (I
2
or HgCl
2
) for successful
synthesis of their alkoxides. The electrochemical synthesis of metal alkoxides by anodic
dissolution of metals (Sc, Y, Ti, Zr, Nb, Ta, Fe, Co, Ni, Cu, Pb) and even metalloids
(Si, Ge) in dry alcohols in the presence of a conducting electrolyte (e.g. tetrabutylam-
monium bromide) appears to offer a promising procedure (Section 2.2) of considerable
utility. It may be worthwhile to mention at this stage that the metal atom vapour tech-
nique, which has shown exciting results in organometallics, may emerge as one of the
potential synthetic routes for metal alkoxides also in future.
For the synthesis of metalloid (B, Si) alkoxides, the method generally employed
consists of the reaction of their covalent halides (usually chlorides) with an appropriate
alcohol. However, the replacement of chloride by the alkoxo group(s) does not appear to
proceed to completion, when the central element is comparatively more electropositive.
In such cases (e.g. titanium, niobium, iron, lanthanides, thorium) excluding the strongly
electropositive s-block metals, the replacement of halide could in general be pushed
Homometallic Alkoxides 5
to completion by the presence of bases such as ammonia, pyridine, or alkali metal
alkoxides.
Another generally applicable method, particularly in the case of electronegative

elements, is the esterification of their oxyacids or oxides (acid anhydrides) with alcohols
(Section 2.6), and removing the water produced in the reaction continuously.
In addition to the above, alcoholysis or transesterification reactions of metal alkox-
ides themselves have been widely used for obtaining the targeted homo- and heteroleptic
alkoxide derivatives of the same metal. Since the 1960s, the replacement reactions
of metal dialkylamides with alcohols has provided a highly convenient and versatile
route (Section 2.9) for the synthesis of homoleptic alkoxides of a number of metals,
particularly in their lower valency states.
The metal–hydrogen and metal–carbon bond cleavage reactions have also been
exploited in some instances (Section 2.10.2).
The following pages present a brief summary of the general methods used for the
synthesis of metal and metalloid alkoxides applicable to specific systems. Tables 2.1
and 2.2 in Section 2.1 (pp. 6–14) list some illustrative compounds along with their
preparative routes and characterization techniques.
2.1 Reactions of Metals with Alcohols (Method A)
The facility of the direct reaction of a metal with an alcohol depends on both the
electropositive nature of the metal and the ramification of the alcohol concerned.
In view of the very feeble acidic character of nonfluorinated alcohols [even
weaker than that of water: pK
a
values (in parentheses) of some alcohols
are CH
3
OH(15.8), CH
3
CH
2
OH(15.9), CH
3


2
CHOH(17.1), CH
3

3
COH(19.2),
CF
3
CH
2
OH(12.8), CH
3
CF
3

2
COH(9.6), CF
3

2
CHOH(9.3),  CF
3

3
COH(5.4)], this
route is more facile with lower aliphatic and fluorinated alcohols.
2.1.1 s-Block Metals
2.1.1.1 Group 1 metals (Li, Na, K, Rb, Cs)
The more electropositive alkali metals react vigorously with alcohols by replacement
of the hydroxylic hydrogen (Eq. 2.2):

M C 1 C yROH  !
1
n
[MOR.yROH]
n
C
1
2
H
2
" 2.2
M D Li,Na,K,Rb,Cs;RD Me, Et, Pr
i
, Bu
t
;
3,6,26,27
y D 0.
M D Li; R D Bu
t
, CMe
2
Ph;
28
y D 0.
M D K, Rb, Cs; R D Bu
t
;
29
y D 1.

M D K, Rb; R D Bu
t
;
29
y D 0.
The alkali metals react spontaneously with sterically compact aliphatic alcohols
(MeOH, EtOH, etc.) and the speed of the reaction increases with atomic number of the
metal, Li < Na < K < Rb < Cs, corresponding to a decrease in ionization potential of
the alkali metals. The ramification of the alkyl group is also important, as shown by the
6 Alkoxo and Aryloxo Derivatives of Metals
Table 2.1 Examples of some homoleptic alkoxides
Method of Characterization
Compound
1
preparation
2
techniques
3
Reference
Group 1
[LiOMe]
1
A X-ray 28a
[LiOBu
t
]
6
AIR;
1
H,

13
C,
7
Li
NMR; MW
28
[LiOCMe
2
Ph]
6
AIR;
1
H,
13
C,
7
Li
NMR; MW;
X-ray
28
[LiOCBu
t
3
]
2
J-2
1
H,
13
C,

7
Li NMR;
X-ray
396
[LiOCBu
t
3
thf]
2
J-2 X-ray 230
[LiOCBu
t
2
CH
2
PMe
2
]
2
J-3
1
H,
13
C,
7
Li,
31
P
NMR; X-ray
22

[LiOCBu
t
2
CH
2
PPh
2
]
2
J-3
1
H,
13
C,
7
Li,
31
P
NMR; X-ray
422
[LiOCBu
t
2
CH
2
PPh
2
]
2
Bu

t
2
CO J-3
1
H,
13
C,
7
Li,
31
P
NMR; X-ray
422
[MOMe]
1
(M D Na,K,Rb,Cs) A X-ray a, b, c, d
[NaOBu
t
]
6
A X-ray e, f
[NaOBu
t
]
9
A X-ray e
[MOBu
t
.HOBu
t

]
1
M D K, Rb)
AIR;
1
H,
13
CNMR;
MW; X-ray
29
[MOBu
t
]
4
M D K, Rb, Cs
A
1
H,
13
CNMR;
X-ray
29, g
[NafOCHCF
3

2
g]
4
J-2 IR;
1

H,
19
FNMR;
X-ray
397
Group 2
[BeOMe
2
]
n
E-3, J-2 IR 214, 385
[BeOBu
t

2
]
3
J-2 IR;
1
H NMR; MW 385
[BeOCEt
3

2
]
2
J-2 IR;
1
H NMR; MW 385
[BeOCMe

2
CH
2
OMe
2
]
2
IIR;
1
H NMR; MS 340
[BeOCEt
2
CH
2
OMe
2
]
2
IIR;
1
H NMR; MS 340
[BefOCCF
3
g
2
]
3
.OEt
2
E-2

1
H,
19
F NMR; MW 396
MgOMe
2
.3.5MeOH A X-ray 38
[Ca-ORORthf]
2
.toluene
2
E-2 IR;
1
H,
13
CNMR;
X-ray
147
[CaOR
2
thf
3
].THF E-2 IR;
1
H,
13
CNMR;
X-ray
147
CafOCCF

3

3
g
2
A
19
F NMR 47, 53, 340
Ca
3
OCHBu
t
2

6
I 53, 340
Ca
2
[OCBu
t
CH
2
OPr
i

2
]
4
I IR; MS; X-ray 53, 340
Ca[OCBu

t
CH
2
OPr
i
CH
2
CH
2
NEt
2
]
2
I IR; MS 53, 340
Ca
9
OC
2
H
4
OMe
18
HOC
2
H
4
OMe
2
AIR;
1

H,
13
CNMR;
X-ray
50
Sr[OCCF
3

3
]
2
A
19
FNMR 47
Sr
2
[OCBu
t
CH
2
OPr
i

2
]
4
I IR; MS 53, 340
BaOBu
t


2
A
1
HNMR 47
BaOCEt
3

2
A
1
HNMR 47
BaOCMeEtPr
i

2
A
1
HNMR 47
Homometallic Alkoxides 7
Table 2.1 (Continued )
Method of Characterization
Compound
1
preparation
2
techniques
3
Reference
BaOCHBu
t

2

2
A
1
HNMR 47
Ba[OCHCF
3

2
]
2
A
19
FNMR 47
Ba[OCCF
3

3
]
2
A
19
FNMR 47
[BaOBu
t

2
HOBu
t


2
]
4
I
1
H,
13
CNMR;
X-ray
549
Ba
2
[OCBu
t
CH
2
OEt
2
]
4
E-2 53, 340
Ba
2
[OCBu
t
CH
2
OPr
i


2
]
4
A, I IR; MS 53, 340
Ba
2
OCPh
3

4
thf
3
A
1
H,
13
CNMR;
X-ray
48
Ba[OCH
2
CH
2

x
CH
3
]
2

(x D 2, 3)
AIR;
1
H,
13
CNMR;
MS
52
Scandium, Yttrium, and Lanthanides
[ScfOCHCF
3

2
g
3
NH
3

2
]
2
IIR;
1
H,
19
FNMR;
MS; X-ray
349
LnOPr
i


3
Ln D Y, Pr, Nd, Sm, Eu,
Gd,Tb,Dy,Ho,Et,Tm,Yb,Lu
AIR;
1
HNMR(Y,
La, Lu);
UV-Vis (Pr, Nd,
Sm, Ho, Er)
55
LnOPr
i

3
Ln D Y, Dy, Yb
AIR;
1
HNMR
(Ln D Y)
54
LnOPr
i

3
Ln D Pr, Nd
E-2 MW 153
LnOR
3
Ln D Pr, Nd;

R D Bu
n
,Bu
i
,Bu
s
,Bu
t
,Am
n
,
Am
t
,Pr
n
CH(Me), Pr
n
CMe
2
G MW 153
GdOPr
i

3
E-2 IR; MW 157
ErOPr
i

3
E-2 IR; MW 157

LnOMe
3
Ln D Gd, Er
E-3 IR 157
HoOPr
i

3
E-2 MW 158
[YfOCHCF
3

2
g
3
thf
3
] I IR; MS; X-ray 349
[YfOCMe
2
CF
3
g
3
]
n
I
1
H,
19

F NMR 349a
[YfOCMe
2
CF
3
g
3
thf
2.5
]I
1
H,
19
F,
89
Y NMR 349a
[YfOCMeCF
3

2
g
3
]
n
I
1
H,
19
F,
89

Y NMR 349a
[YfOCMeCF
3

2
g
3
NH
3

0.5
]I
1
H,
19
F,
89
Y NMR 349a
[YfOCMeCF
3

2
g
3
NH
3

3
]I
1

H,
19
F,
89
Y NMR 349a
[YfOCMeCF
3

2
gthf
3
]I
1
H,
19
F,
89
Y NMR 349a
[YfOCMeCF
3

2
g
3
OEt
2

0.33
]I
1

H,
19
F,
89
Y NMR 349a
fYfOCMeCF
3

2
g
3
diglymeg I
1
H,
19
F,
89
Y NMR 349a
[YfOCMeCF
3

2
g
3
HOBu
t

3
]I
1

H,
19
F,
89
Y NMR 349a
fYOCHCF
3

2
g
3
NH
3

0.5
]I
1
H,
19
F,
89
Y NMR 349a
[YfOCHCF
3

2
g
3
thf
3

]I
1
H,
19
F,
89
Y NMR 349a
[Y
3
OBu
t

9
HOBu
t

2
]IIR;
1
H,
13
C,
89
Y
NMR; MS
345
[Y
3
OAm
t


9
HOAm
t

2
]IIR;
1
H,
13
C,
89
Y
NMR; MS
345
(continued overleaf )
8 Alkoxo and Aryloxo Derivatives of Metals
Table 2.1 (Continued )
Method of Characterization
Compound
1
preparation
2
techniques
3
Reference
[YOR
3
]
2

R D CMe
2
Pr
i
,CMeEtPr
i
,CEt
3
IIR;
1
H,
13
C,
89
Y
NMR; MS
345
[YOC
2
H
4
OMe
3
]
10
AIR;
1
H,
13
CNMR;

X-ray
57
[La
3
OBu
t

9
HOBu
t

2
]I
1
H,
13
CNMR;MS;
X-ray
345
[LaOR
3
]
2
R D CMe
2
Pr
i
,CMeEtPr
i
I

1
H,
13
C NMR; MS 345
[La
3
OBu
t

9
thf
2
]E-2
1
H,
13
CNMR;
X-ray
160
[LaOCPh
3

3
]
2
IIR;
1
H,
13
CNMR;

X-ray
346
[LafOCMeCF
3

2
g
3
thf
3
]IIR;
1
H,
13
CNMR;
MS; X-ray
349c
La
4
OCH
2
Bu
t

12
IIR;
1
H,
13
CNMR;

X-ray
348a
[CeOPr
i

4
.Pr
i
OH]
2
E-1 MW 143
E-2
1
H,
13
CNMR;
X-ray
460
CeOCBu
t
3

3
I MW 344
[CeOCHBu
t
2

3
]

2
150
Ž
C, vacuum X-ray 344
CeOR
4
R D Me, Et, Pr
n
,Bu
n
,Bu
i
,
CH
2
Bu
t
G MW 143
CeOBu
t

4
thf
2
E-2 IR;
1
H,
13
C NMR 164
[PrfOCMeCF

3

2
g
3
NH
3

2
]
2
I IR; MS; X-ray 349
[PrfOCMeCF
3

2
g
3
NH
3

4
]IIR;
1
H NMR; X-ray 349b
[PrfOCMe
2
CF
3
g

3
]
3
I IR; MS; X-ray 349
[NdOCBu
t
3

3
thf]IIR;
1
H NMR; X-ray 959
Nd
4
OCH
2
Bu
t

12
IIR;
1
H NMR; X-ray 348a
Nd
2
OCHPr
i
2

6

thf
2
IIR;
1
H NMR; X-ray 348
[NdOPr
i

3
.Pr
i
OH]
4
AIR 56
[EufOCMeCF
3

2
g
3
]
n
I IR 349b
[Eu
2
fOCMeCF
3

2
g

6
NH
3

2
] I IR 349b
[EufOCMeCF
3

2
g
3
thf
3
]I
1
H,
19
F NMR; MS 349c
[EufOCMeCF
3

2
g
3
diglyme]I
1
H,
19
F NMR; MS 349c

[LuOCMe
2
CH
2
OMe
3
]
2
IIR;
1
H,
13
CNMR;
MS; X-ray
355
Actinides
[ThOPr
i

4
]
n
E-2 MW 141
[ThOEt
4
]
n
G MW 141
[ThOR
4

]
n
G MW 143
R D Bu
n
,Pent
n
,CH
2
Bu
t
143
R D CMe
3
,CMe
2
Et, CMeEt
2
,
CMe
2
Pr
n
,CMe
2
Pr
i
,CEt
3
,

CMeEtPr
n
, CMeEt,Pr
i
141a
Th
4
OPr
i

16
Py
2
E-2 IR;
1
H,
13
CNMR;
X-ray
165
Th
2
OCHEt
2

8
Py J-3 IR;
1
H,
13

CNMR;
X-ray
165
[ThOBu
t

4
Py
2
] E-2 IR;
1
H NMR; X-ray 398
Homometallic Alkoxides 9
Table 2.1 (Continued )
Method of Characterization
Compound
1
preparation
2
techniques
3
Reference
Th
2
OBu
t

8
HOBu
t

 J-3 IR;
1
H,
13
CNMR;
X-ray
398
Th
2
OCHPr
i
2

8
J-3
1
HNMR;
thermochemical
data; X-ray
399
UOMe
4
E-3, I 213
UOR
4
R D Et, Bu
t
I 213
U
2

OBu
t

8
HOBu
t
 J-3 IR;
1
H NMR; UV-Vis 330
UOCHBu
t
2

4
E-3
1
HNMR;
eff
; MS 229
UfOCHCF
3

2
g
4
thf
2
E-2
19
FNMR;

eff
h
UfOCCF
3

3
g
4
thf
2
E-2
19
FNMR;
eff
h
UOEt
5
J-1 379
UOR
5
R D Me, Pr
n
,Pr
i
,Bu
s
,Bu
n
,Bu
i

J-1 289
UOBu
t

5
G 289
UOCH
2
CF
3

5
E-1 289
PuOPr
i

4
.Pr
i
OH E-1 144
Group 4
[TiOEt
4
]
4
E-1 134
E-1
1
H NMR 548
X-ray 434

MOR
4
M D Ti, Zr
R D MeCH
2
CH
2

2
CH
2
,
Me
2
CHCH
2
CH
2
,MeCHEtCH
2
,
Me
3
CCH
2
,CHEt
2
,CHMePr
n
,

CHMePr
i
,CMe
2
Et
G MW 273
TiOR
4
R D CMe
2
Et, CMeEt
2
GMW;Lv
Ł
; S 274
[ZrOR
4
]
n
R D Et, Pr
i
,Bu
n
,Bu
s
E-1 MW 145
R D Pr
i
,Pr
n

,Bu
n
,Am
n
E-1 MW 145a
[ZrOPr
i

4
.Pr
i
OH]
2
E-3, I IR;
1
H,
13
CNMR;
X-ray
460
[HfOR
4
]
n
E-1 MW 277
R D Et, Pr
i
R D Me, Et, Pr
i
,Bu

t
,Am
t
G MW 277
[HfOPr
i

4
.Pr
i
OH]
2
E-1 IR;
1
H,
13
CNMR;
X-ray
460
Group 5
VOR
4
E-3, I 331, 333
R D Me, Et, Pr
i
,Bu
t
UV-Vis; 
eff
; ESR 588, 589, 590

[NbOR
5
]
2
R D Me, Et, Pr
n
,Bu
n
, n-pentyl
E-1, G MW 279, 468
[TaOR
5
]
n
R D Me, Et, Pr
n
,Bu
n
,
MeCH
2
CH
2
CH
2
(and its isomers),
MeCH
2
CH
2

CH
2
CH
2
(and its
isomers)
E-1, G MW 280, 312, 469
(continued overleaf )
10 Alkoxo and Aryloxo Derivatives of Metals
Table 2.1 (Continued )
Method of Characterization
Compound
1
preparation
2
techniques
3
Reference
[NbOPr
i

5
]
2
B, E-1 IR; MS; X-ray 608
[MOEt
5
]
2
BMS 79

M D Nb, Ta E-1 X-ray (M D Nb) 566
[MOR
5
]
2
G
1
H NMR 470
M D Nb, Ta
R D Me, Et, Bu
i
,Pr
i
[TaOR
5
]
2
AIR;MS 81
R D Me, Et, Bu
n
,Pr
i
[TaOC
2
H
4
OMe
5
]GMS81
Group 6

[CrOCHBu
t
2

2
]
2
E-3 X-ray i
UV-Vis; ESR 226
Cr[OCBu
t
CH
2
OPr
i

2
]
2
E-2 IR; MS 340
[CrOCMe
2
CH
2
OMe
3
] I IR; MS; X-ray 340
CrOCHBu
t
2


3
thf E-3 IR; UV-Vis; MS 226
CrOBu
t

4
E-2 UV-Vis; 
eff
; MW 168
I 331
I Thermochemical
data; MS;
UV-Vis; 
eff
467, 471
CrOCHBu
t
2

4
E-3 IR; UV-Vis; 
eff
;
MS; X-ray
226
Mo
2
OR
6

Mo
Á
Mo
R D Bu
t
,CMe
2
Ph, Pr
i
,CH
2
Bu
t
I
1
H NMR; X-ray
(R D CH
2
Bu
t
)
360, 361, 362
Mo
2
[OCMeCF
3

2
]
6

E-2
1
H,
13
CNMR;
X-ray
170
Mo
2
[OCMe
2
CF
3
]
6
E-2
1
H,
13
C NMR 170
[Mo
2
OCMe
2
Et
6
]E-3
1
H,
13

C NMR 170
Mo
2
OPr
i

8
Mo
D
Mo J-1
I
1
HNMR;MW;
X-ray
371, 372
MoOBu
t

4
I
1
H NMR; MW 371
Mo
2
OPr
i

4
HOPr
i


4
Mo
D
D
Mo J-3 IR;
1
HNMR;
UV-Vis; X-ray
375
Mo
2
OR
4
HOR
4
R D c-pentyl, c-hexyl
J-3 IR;
1
HNMR;
UV-Vis; X-ray
(c-pentyl)
375
Mo
2
OCH
2
Bu
t


4
NHMe
2

4
J-3 IR;
1
HNMR;
UV-Vis; X-ray
375
Mo
2
OPr
i

4
Py
4
J-3 IR;
1
HNMR;
UV-Vis; X-ray
375
W
2
OPr
i

6
I X-ray j

W
2
OPr
i

6
Py
2
I(Cpyridine) IR;
1
HNMR;MS;
X-ray
365
W
2
OBu
t

6
W
Á
W IIR;
1
H NMR; MS 365
W
4
OR
12
R D Pr
i

, CH
2
Bu
t
I MW 365
Homometallic Alkoxides 11
Table 2.1 (Continued )
Method of Characterization
Compound
1
preparation
2
techniques
3
Reference
W
4
OPr
i

12
/W
2
OPr
i

6
Crystallization of
W
2

OPr
i

6
from
dimethoxyethane
1
HNMR;MS;
X-ray
M
4
OCH
2
R
12
M D Mo, W
R D c-C
4
H
7
,c-C
5
H
9
,
c-C
6
H
11
,Pr

i
alcoholysis of
M
2
OBu
t

6
IR;
1
H,
13
C,
95
Mo
NMR;
X-ray (M D Mo;
R D c-C
4
H
7
)
k
W
4
OEt
16
I
1
H NMR; X-ray 366

Group 7
[MnOR
2
]
n
R D primary, secondary, and
tertiary alcohols
I Reflectance spectra;

eff
l
[MnOCHBu
t
2

2
]
2
I IR; UV-Vis; ESR;
MW
226
I X-ray 351
Mn[OCBu
t
CH
2
OPr
i

2

]
2
I IR; MS 340
Re
3
OPr
i

9
E-2
1
H NMR; X-ray 173, 174
Group 8
[FefOCBu
t
CH
2
OEt
2
g
2
]
2
I IR; MS 340
Group 9
[CoOCHBu
t
2

2

]
2
I IR; UV-Vis; MW 226
[CoOCPh
3

2
]
2
.n-C
6
H
14
IIR;
1
HNMR;
UV-Vis; X-ray
351a
CoOCPh
3

2
thf
2
I(THFusedas
solvent)
IR;
1
HNMR;
UV-Vis; X-ray

351a
Co[OCBu
t
CH
2
OPr
i

2
]
2
I IR; MS 340
[Co[OCCF
3
CH
2
OPr
i

2
]
2
]
2
I IR; MS 340
Group 10
[NiOR
2
]
n

R D Me, Et, Pr
n
,Pr
i
,Bu
t
,Am
t
,
t-C
6
H
13
E-3 6, 219
Ni[OCBu
t
CH
2
OPr
i

2
]
2
E-2 IR; MS 340
dppePtOMe
2
E-2
1
H,

31
P NMR; X-ray 177, 177a
PtOCH
2
CH
2
PPh
2

2
E-2 IR;
1
H,
31
PNMR;
MS; X-ray
178
PtOCMe
2
CH
2
PPh
2

2
E-2 IR;
1
H,
31
PNMR;

X-ray
178a
PtOCMe
2
CH
2
PPh
2
.3.5H
2
OI
1
H,
31
P NMR; X-ray 178b
Group 11
[CuOCHBu
t
2
]
4
E-3 MW 226
[CuOBu
t
]
4
E-3 m
E-3 IR;
1
HNMR;ESR n, o

CufOCHCF
3

2
gPPh
3

3
J-2 IR;
1
H NMR; X-ray p
CuOCHPh
2
PPh
3

3
J-2 IR;
1
HNMR p
[CuOCEt
3
]
4
E-2
1
H,
13
CNMR;MW 47
(continued overleaf )

12 Alkoxo and Aryloxo Derivatives of Metals
Table 2.1 (Continued )
Method of Characterization
Compound
1
preparation
2
techniques
3
Reference
CuOCEt
3

2
E-2
1
H,
13
CNMR;
UV-Vis
47
Cu[OCHCF
3

2
]
2
L
L D tmeda, teed, bipy, (py)
2

E-2, G UV-Vis; ESR; X-ray
(L D tmeda)
175
Cu[OCMeCF
3

2
]
2
L
L D tmeda, bipy, (py)
2
E-2, G UV-Vis; ESR; X-ray
(L D tmeda)
175
Group 12
M[OCBu
t
CH
2
OPr
i

2
]
2
M D Zn, Cd
I IR; MS 340
[ZnOR
2

]
n
R D CEt
3
,CEtMe,
C
2
H
4
OMe, C
2
H
4
OC
2
H
4
OMe,
C
2
H
4
NMe
2
,CHMeCH
2
NMe
2
,
C

2
H
4
NMeC
2
H
4
NMe
2
IIR;
1
H NMR 339b
Cd
9
OC
2
H
4
OMe
18
HOC
2
H
4
OMe
2
IIR;
1
H,
13

C,
113
Cd
NMR; X-ray
339c
[CdOBu
t

2
]
n
I IR 339c
Group 13
[AlOPr
i

3
]
4
AIR;
1
H,
13
C,
27
Al
NMR; MW; MS
6
X-ray 579, 580
[AlOBu

t

3
]
2
A71
I X-ray 338
[Ga[OR
3
]
n
R D Me, Et, Pr
n
,Pr
i
E-2 IR;
1
H NMR 187
[InfOCMe
2
CF
3
g
3
]
2
IIR;
1
H,
13

CNMR;
X-ray
358
[InOPr
i

3
]
n
E-2 IR;
1
H NMR 187
Group 14
GeOCBu
t
3

2
I
1
H,
13
CNMR;
X-ray
352
[SnOBu
t

2
]

2
I
1
H,
119
Sn NMR 352
[SnOPr
i

4
.Pr
i
OH]
2
E-2
1
H,
13
C,
119
Sn NMR 190
X-ray 190, 191
SnOBu
t

4
I X-ray 190
[PbOBu
t


2
]
n
IIR;
1
H,
207
Pb NMR;
MS
194
[PbOR
2
]
n
R D Pr
i
,Bu
t
,CMe
2
Et, CEt
3
IIR;
1
H,
13
CNMR;
MW; X-ray
(R D Pr
i

,
C
2
H
4
OMe;
n D1.RD Bu
t
,
n D 3)
612
CH
2
CH
2
OMe,
CHMeCH
2
NMe
2
[PbOPr
i

2
]
x
E-2 192
Homometallic Alkoxides 13
Table 2.1 (Continued )
Method of Characterization

Compound
1
preparation
2
techniques
3
Reference
Group 15
BiOR
3
R D Me, Et, Pr
n
,Pr
i
E-2 202
BiOBu
t

3
E-2 IR;
1
H,
13
C NMR 203
[BiOC
2
H
4
OMe
3

] E-2; I IR;
1
H,
13
CNMR;
MS; X-ray, MW
205, 339
[BiOCHCF
3

2
]
3
thf]
2
E-2 IR;
1
H,
19
FNMR;
X-ray
206, 206a
[BifOCCF
3

3
g
3
]BiC
3CF

3

3
CCOCl
IR;
19
FNMR q
Group 16
SeOR
4
R D Me,Et E-1,E-2
1
H,
13
C,
77
Se NMR r, s
R D CH
2
CF
3
E-1
1
H,
13
C,
77
Se,
19
F

NMR
s
TeOR
4
R D Me, Et, Pr
i
E-2 r
R D CH
2
CF
3
E-1
1
H,
13
C,
125
Te,
19
F
NMR
R D CCF
3

3
Te C
4CF
3

3

CCOCl
IR;
19
FNMR q
Ł
Lv D Latent heat of vaporization.
1
bpy D 2,2
0
-bipyridine; diglyme D bis (2-methoxyethyl) ether (ligand); dppe D 1,2-bis
(diphenylphosphino)ethane, Py D pyridine (ligand); teed D N,N,N
0
,N
0
-tetraethylethylenediamine
(ligand); tmeda D N,N,N
0
,N
0
-tetramethylethylenediamine (ligand);
2
Methods A–J (J-1–J-7) as
described in text;
3
ESR D electron spin resonance; 
eff
D magnetic moment; MS D mass
spectrum; MW D molecular weight; UV-Vis D ultraviolet and visible.
a
E.Weiss, Helv. Chim. Acta, 46, 2051 (1963);

b
E. Weiss and W. Bi
¨
ucher, Angew. Chem., 75,
1116 (1963);
c
E. Weiss, Z. Anorg. Allg. Chem., 332, 197 (1964);
d
E. Weiss and H. Alsdorf, Z.
Anorg. Allg. Chem., 372, 2061 (1970);
e
J.E. Davies, J. Kopf, and E. Weiss, Acta Crystallogr., 38,
2251 (1982);
f
E.Weiss, Angew. Chem., Int. Ed. Engl., 32, 1501 (1993);
g
E. Weiss, H. Alsdorf,
and H. K
¨
uhr, Angew. Chem. Int. Ed. Engl., 6, 801 (1967);
h
R.A. Andersen, Inorg. Nucl. Chem.,
Lett., 15, 57 (1979);
i
B.D. Murray, H. Hope, and P.P. Power, J. Am. Chem. Soc., 107, 169
(1985);
j
M.H. Chisholm, D.L. Clark, J.C. Huffman, and M. Hampden-Smith, J. Am. Chem.
Soc., 109, 7750 (1987);
k

M.H. Chisholm, K.Folting, C.E. Hammond, M.J. Hampden-Smith, and
K.G. Moodley, J. Am. Chem. Soc., 111, 5300 (1989);
l
B. Horvath, R. Moseler, and E.G. Horvath,
Z. Anorg. Allg. Chem., 449, 41 (1979);
m
T. Greiser and E. Weiss, Chem. Ber., 104, 3142 (1976);
n
T. Tsuda, T. Hashimoto, and T. Saegusa, J. Am. Chem. Soc., 94, 658 (1972);
o
T.H. Lemmen,
G.V. Goeden, J.C. Huffman, R.L. Geerts, and K.G. Caulton, Inorg. Chem., 29, 3680 (1990);
p
K.
Osakada, T. Takizawa, M. Tanaka, and T. Yamamoto, J. Organomet Chem., 473, 359 (1994);
q
J.M. Canich, G.L. Gard, and J.M. Shreeve, Inorg. Chem., 23, 441 (1984);
r
N.Temple and W.
Schwarz, Z. Anorg. Allg. Chem., 474, 157 (1981);
s
D.B. Denny, D.Z. Denny, P.T. Hammond,
and Y.F. Hsu, J. Am. Chem. Soc., 103, 2340 (1981).
14 Alkoxo and Aryloxo Derivatives of Metals
Table 2.2 Examples of a few selected heteroleptic alkoxides
Method of Characterization
Compound
1
preparation
2

techniques
3
References
[Y
5
OOPr
i

13
]A
1
H,
13
C,
89
YNMR;MW; 59
MS; X-ray
[Ln
5
OOPr
i

13
] A; E-2 IR;
1
HNMR;MS; 58
Ln D Sc,Y,Yb X-ray(LnD Yb)
[Nd
5
OOPr

i

3
HOPr
i

2
] A IR; X-ray 60
[Y
3
OBu
t

7
Cl
2
thf
2
]E-2
1
H,
13
C NMR; X-ray 161
[Y
3
OBu
t

8
Clthf

2
] E-2 IR;
1
H,
13
C NMR; X-ray 160
[CeOCBu
t
3

2
OBu
t

2
]CeOCBu
t
3

2
1
H,
13
C NMR 383
C Bu
t
OOBu
t
[NdOCBu
t

3

2
Clthf]
2
E-3 IR;
1
H NMR; X-ray 959
[Nd
6
OPr
i

17
Cl] E-2 X-ray 159
Bu
t
3
CO
2
UCl
2
thf
2
E-3
1
H NMR 227
UO
2
OBu

t

2
Ph
3
PO
2
E-2 IR;
1
H NMR; X-ray a
Bu
t
3
CO
2
MCl
2
E-3
1
H,
13
C NMR 228
M D Ti, Zr
TiOPr
i

2
[OCHCF
3


2
]
2
G IR 272
Ti[OCH(CF
3
)
2
]
2
(OEt)
2
(HOEt) G IR,
1
H,
19
F NMR; X-ray 272
[TiCl
3
OPr
i
HOPr
i
]
2
DIR;
1
H,
13
C NMR; X-ray 108

[TiCl
2
OPr
i

2
HOPr
i
]
2
DIR;
1
H,
13
C NMR; X-ray 108
[TiCl
2
OCH
2
CH
2
Cl
2
HOCH
2
CH
2
Cl]
2
DIR;

1
H,
13
C NMR; X-ray 108a
VClOMe
2
E-3 IR; reflectance spectra; 
eff
592
VOOPr
i

3
E-3 IR;
1
H, NMR; MW 235
CrO
2
OR
2
E-3 IR;
1
H,
19
F NMR; MW 233
R D CH
2
CCl
3
, CH

2
CF
3
,CH
2
CH
2
Cl
Mo
4
OPr
i

10
OMe
2
G
1
H NMR; X-ray b
[WOCH
2
CF
3

2
Cl
2
PMe
2
Ph

2
]WCl
4
PMe
2
Ph
2
IR;
1
H,
13
C,
31
P NMR; X-ray 171
C TlOCH
2
CF
3
Re
3
OCHEt
2

8
H E-2 IR;
1
H,
13
C NMR 174
Re

3
OPr
i

8
Hˇ-Hydrogen IR;
1
H,
13
C NMR; X-ray 174
elimination
from Re
3
OPr
i

9
CoBrOMe.2MeOH E-3 IR; reflectance spectra; 
eff
595
Ni(OMe)Cl E-3 IR; reflectance spectra; 
eff
541
[CuOMefOCHCF
3

2
g]
n
G IR 175

Cu
3
OBu
t

4
[OCCF
3

3
]
2
GIR;
1
H,
19
F NMR; UV-Vis; 651

eff
; X-ray
Cu
4
OBu
t

6
[OCCF
3

3

]
2
GIR;
1
H,
19
F NMR; UV-Vis; 651

eff
; X-ray
[ZnOCEt
3
fNSiMe
3

2
g]
2
IIR;
1
H NMR; MW; X-ray 688
[Zn
2
OOCMe
3
OMe]ZnOAc
2
IR;
1
H NMR; X-ray 431a

C Bu
n
2
SnOMe
2
[AlOPr
i
OBu
t

2
]
2
G
1
H NMR; MW; MS 492
[AlOPr
i

2
acac]
2
AlOPr
i

3
C acacH
1
H,
13

C,
27
Al NMR; X-ray 726
In
5
OOPr
i

13
E-2 IR;
1
H,
13
C NMR; MS; X-ray 58
[SnOBu
t

3
OAcpy]SnOBu
t

4
1
H,
13
C,
17
O,
119
Sn NMR; 431

C Me
3
SiOAc C Py X-ray
1
acac D acetylacetonate; py D pyridine; thf D tetrahydrofuranligand;
2
For methods see text (Section 2);
3
For abbreviations see footnote of Table 2.1.
a
C.J. Burns, D.C. Smith, A.P. Sattelberger, and H.B. Gray, Inorg. Chem., 31, 3724 (1992);
b
M.H. Chisholm,
C.E. Hammond, M. Hampden-Smith, J.C. Huffman, and W.G. Van der Sluys, Angew. Chem., Int. Ed. Engl.,
26, 904 (1987).
Homometallic Alkoxides 15
reactivity sequence of alcohols, MeOH > EtOH > Pr
i
OH > Bu
t
OH, towards an alkali
metal. This order of reactivity is understandable from an electronic viewpoint which
predicts a decrease in the acidity of the hydroxyl hydrogen in the same order.
2.1.1.2 Group 2 metals (Be, Mg, Ca, Sr, Ba)
Group 2 metals, being less electropositive than group 1 metals, react sluggishly even
with sterically compact alcohols and require a catalyst (iodine or mercury(
II) chloride)
particularly in cases of lighter group 2 metals (Be and Mg)
30–34
to yield insoluble,

polymeric, and nonvolatile metal dialkoxides.
The reaction of magnesium with methanol had been reported
26
to form solvates of dif-
ferent compositions: MgOCH
3

2
.3CH
3
OH and MgOCH
3

2
.4CH
3
OH,
35,36
which have
beenshown byX-ray diffractionstudiestohave thecompositionsMgOCH
3

2
.2CH
3
OH
37
and MgOCH
3


2
.3.5CH
3
OH,
38
respectively.
With sterically less demanding alcohols, alkoxides of the heavier alkaline earth
metals (Ca, Sr, Ba) [M(OR)
2
]
n
R D Me, Et, Pr
i
 had been prepared by a number
of workers
39–44
by reactions of metals with alcohols. These are also oligomeric or
polymeric, and nonvolatile.
Interest in the synthesis and chemistry of soluble and volatile alkaline earth metal
alkoxides experienced a sudden upsurge in the 1990s,
21–23
owing to the discovery of
superconducting ceramics
45,46
containing Ba and Ca.
Reactions of sterically demanding monodentate alcohols
47
with heavier alkaline earth
metals (M
0

) have been reported to yield soluble derivatives:
M
0
C 2R
0
OH  ! M
0
OR
0

2
C H
2
" (2.3)
M
0
D Ba; R
0
D CMe
3
, CEt
3
, CHMe
2
, CHCF
3

2
. M
0

D Ca, Sr; R
0
D CCF
3

3
.
By contrast, reaction of barium granules with Ph
3
COH does not appear to take place,
even in the presence of I
2
or HgCl
2
as a catalyst, in refluxing tetrahydrofuran (THF)
over three days. However, the same reaction in the presence of ammonia as a catalyst
yields X-ray crystallographically characterized dimeric derivative [H
3
Ba
6
OOBu
t

11
OCEt
2
CH
2
O(thf)
3

].
48
It may be inferred that ammonia reacts initially with barium
to form BaNH
2

2
, which undergoes proton transfer and anion metathesis to yield the
desired alkoxide derivative.
Although the reactions of heavier alkaline earth metals with alcohols are generally
straightforward, yielding the expected homoleptic derivatives, in some instances it
has been reported that the reaction follows a different course to yield an intriguing
product as in the case of the formation of X-ray crystallographically characterized
49
oxo-alkoxide cluster of the composition H
3
Ba
6
OOBu
t

11
OCEt
2
CH
2
O(thf), in the
reaction of Ba with Bu
t
OH in THF. The reasons for the formation of such an unusual

product in a simple reaction of the above type (Eq. 2.3) are not yet well understood,
but it tends to indicate that either adventitious hydrolysis or alkene/ether elimination
may be the main factor. Furthermore, the formation of OCEt
2
CH
2
O ligated product
in this reaction indicates that the diolate ligand is probably formed in a side-reaction
involving the solvent tetrahydrofuran molecules.
2-Methoxyethanol (a chelating alcohol) has been shown
50
to react with calcium
filings in refluxing n-hexane to yield an X-ray crystallographically authenticated product
16 Alkoxo and Aryloxo Derivatives of Metals
according to the following reaction:
Ca C 4HOC
2
H
4
OMe
n-hexane
!
1
9
[Ca
9
OC
2
H
4

OMe
18
].2HOC
2
H
4
OMe C H
2
" 2.4
By contrast, a similar reaction with barium granules followed a different course
51
to yield [H
4
Ba
6
OOCH
2
CH
2
OMe
14
] which has been characterized by single-crystal
X-ray diffraction studies.
Recently, it has been reported that monomeric Ba[OCH
2
CH
2
O
n
CH

3
]
2
(n D 2or3)
products are obtained in the reactions of barium granules with an oligoether alcohol
52
in tetrahydrofuran (Eq. 2.5):
Ba C 2HOCH
2
CH
2
O
n
CH
3
THF
 ! Ba[OCH
2
CH
2
O
n
CH
3
]
2
C H
2
" 2.5
where n D 2or3.

The factor(s) determining the variation in the nature of products in the reaction of
Ca/Ba with chelating alcohols obviously require further investigations.
Interestingly, the reaction of barium with a sterically demanding alcohol having
donor functionality yields a volatile derivative
53
with excellent solubility (even in
n-pentane) (Eq. 2.6):
Ba C 2HOCBu
t
CH
2
OPr
i

2
THF/NH
3
 !
H
2

Ba[OCBu
t
CH
2
OPr
i

2
]

2
2.6
2.1.2 Group 3 and the f-block Metals
The method involving direct reaction of a metal with alcohol was extended by Mazdi-
yasni et al .
54
for the formation of scandium, yttrium, and lanthanide alkoxides using
mercuric chloride (10
3
–10
4
mol per mol of metal) as a catalyst:
Ln C 3Pr
i
OH
(excess)
HgCl
2
cat.
!
heat
1
n
[LnOPr
i

3
]
n
C

3
2
H
2
" 2.7
Ln D Sc,Y,Dy,andYb.
Mercuric chloride appears to form an amalgam with the metal which reacts with
isopropyl alcohol to yield the triisopropoxide. Mazdiyasni et al .
54
also noticed that the
use of HgCl
2
in stoichiometric ratio resulted in the formation of alkenoxide contami-
nated with chloride. For example, the reaction of yttrium metal, isopropyl alcohol, and
mercuric chloride in 1:3:4 molar ratio yielded yttrium isopropeneoxide
55
and hydrogen
chloride:
Y C 3HOCHCH
3

2
C 4HgCl
2
 ! Y[OCCH
3

D
CH
2

]
3
C 4Hg C 8HCl C
1
2
H
2
2.8
The above route has also been utilized for the synthesis of neodymium
56
and
yttrium
57
alkoxides as shown by Eqs (2.9) and (2.10):
4Nd C 16Pr
i
OH  ! [NdOPr
i

3
.Pr
i
OH]
4
C 6H
2
" 2.9
10Y C 30HOC
2
H

4
OMe  ! [YOC
2
H
4
OMe
3
]
10
C 15H
2
" 2.10
Homometallic Alkoxides 17
By contrast, interesting oxo-isopropoxides of the type Ln
5
OOPr
i

13
,whereLnD
Sc,
58
Y,
58,59
Nd,
60
and Yb
58
have been isolated from the reaction mixtures resulting
from the interaction of metal chips and isopropyl alcohol, out of which, the last three

have been characterized by X-ray crystallography.
In restrospect, the isolation of oxo-alkoxide products, in the straightforward reactions
of metals with alcohols has generated a new interest in metal oxo-alkoxide products
(Chapter 5), a large number of which have been reported in the extensive investiga-
tions of Turova et al.
61–63
employing the solubility and vapour pressure studies of
M(OR)
x
–ROH systems.
Bradley et al.
58
have suggested that the formation of Ln
5
OOPr
i

13
occurs by
the mechanism of metal alkoxide decomposition involving elimination of an ether,
64
according to Eq. (2.11):
5LnOPr
i

3
 ! Ln
5
OOPr
i


13
C Pr
i
2
O 2.11
Obviously, more quantitative work is essential to explore the extent and course
of side-reactions in the interactions of metals with different alcohols under varying
experimental conditions.
2.1.3 p-Block Elements
Aluminium alkoxides may be prepared
65–74
by reaction of an alcohol with aluminium
activated by I
2
,HgCl
2
,orSnCl
4
under refluxing conditions, for example:
2Al C 6ROH
(excess)
1%HgCl
2
!

2Al(OR)
3
C 3H
2

" 2.12
where R D primary, secondary, or tertiary alkyl groups.
Aluminium triethoxide was first prepared in 1881 by Gladstone and Tribe
65
by
the reaction of aluminium metal with ethanol in the presence of iodine as a catalyst.
Wislicenus and Kaufman
66
in 1893 reported an alternative method of preparing normal
as well as isomeric higher alkoxides of aluminium by reacting amalgamated aluminium
with excess of refluxing alcohol. Hillyer
67
prepared aluminium trialkoxides by the
reaction of metal with alcohols in the presence of SnCl
4
as a catalyst. Tischtschenko
68
in 1899, however, pointed out that the above reactions involving catalysts were useful
for the preparation of primary and secondary alkoxides of aluminium, but the reaction
of metal with tert-butyl alcohol was very slow even in the presence of catalysts. A
successful synthesis of aluminium tri-tert-butoxide described by Adkins and Cox
71
in 1938, involved the reaction of amalgamated aluminium with refluxing tert-butyl
alcohol.
By contrast, in a reaction similar to Eq. (2.12), indium forms In
5
OOPr
i

13

,the
structure of which has been established by X-ray crystallography.
58
Although metallic thallium did not appear to react with alcohols
75
even under
refluxing conditions, the reaction of ethyl alcohol with the metal partly exposed to
air does occur, resulting in the formation of liquid thallous ethoxide, for which the
following course of reactions has been suggested: (Eqs 2.13–2.15):
2Tl C
1
2
O
2
 ! Tl
2
O 2.13
18 Alkoxo and Aryloxo Derivatives of Metals
Tl
2
O C EtOH ! TlOEt C TlOH 2.14
TlOH C EtOH


TlOEt C H
2
O 2.15
2.2 Electrochemical Technique (Method B)
The possibility of synthesizing metal alkoxides by the anodic dissolution of metals
into alcohols containing conducting electrolytes was demonstrated for the first time

by Szilard
76
in 1906 for the methoxides of copper and lead. Since then this technique
has proved to be most promising. For example, the electrochemical method for the
preparation of ethoxides of Ti, Zr, Ta, Si, and Ge
77
was patented by the Monsanto
Corporation in 1972, and was later applied by Lehmkuhl et al.
78
for the synthesis of
Fe(
II), Co, and Ni alkoxides M(OR)
2
(R D Me, Et, Bu
n
,andBu
t
).
Turova et al.
79
have substantially widened the scope of this technique by the synthesis
of a wide variety of homoleptic metal alkoxides and oxo-metal alkoxides: (i) soluble
M(OR)
n
,MD Sc, Y, La, lanthanide,
80
Ti, Zr, Hf, Nb,
79
Ta
81

when R D Me, Et, Pr
i
,
Bu
n
; MO(OR)
4
,MD Mo, W when R D Me, Et, Pr
i
;
82–86
2-methoxyethoxides of Y,
lanthanide, Zr, Hf, Nb, Ta, Fe(
III), Co, Ni, Sn(II),
87
and (ii) insoluble metal alkoxides
such as Bi(OMe)
3
;
88
Cr(OR)
3
,RD Me, Et, MeOC
2
H
4
;
89
V(OR)
3

;
86
Ni(OR)
2
,RD Me,
Pr
n
,Pr
i
;
90
Cu(OR)
2
,RD Bu
n
,C
2
H
4
OMe;
91
Re
4
O
2
(OMe)
16
.
92
Besides the above, Banait et al . have also employed the electrochemical reactions

of some (including polyhydroxy) alcohols for the synthesis of alkoxides of copper
93
and mercury.
94
In 1998, the anodic oxidation of molybdenum and tungsten
95
in alcohols in the pres-
ence of LiCl (as electroconductive additive) was found to yield a variety of interesting
oxo-metal alkoxide complexes, some of which have been authenticated by single-
crystal X-ray crystallograpy.
The electrode ionization reactions of alcohols and anode polarized metals in the
presence of an electroconductive additive, followed by the interaction of the generated
intermediate species and the formation of the final products can by illustrated
96
by the
following reactions (Eqs 2.16 and 2.17):
M  ! M
nC
C ne

anode2.16
nROH C ne

 ! nRO

C nH
ž
nH
ž
 !

n
2
H
2
cathode2.17
M
nC
C nRO

 ! M(OR)
n
where M D anode metal and ROH D an appropriate alcohol.
This process has great promise for the direct conversion of the less electropositive
metals to their alkoxides owing to its simplicity and high productivity as well as its
continuous and non-polluting character (with hydrogen as the major by-product).
The electrochemical technique appears to have been successfully employed in Russia
for the commercial production
96
of alkoxides of Y, Ti, Zr, Nb, Ta, Mo, W, Cu, Ge,
Sn, and other metals.
Homometallic Alkoxides 19
2.3 Reactions of Metal Atom Vapours with Alcohols (Method C)
Although the development of metal atom vapour technology over the past three decades
has shown tremendous utility for the synthesis of a wide range of organometallic
compounds (many of which were inaccessible by conventional techniques),
97
the use
of this technique for the synthesis of metal alkoxides and related derivatives does not
appear to have been fully exploited.
98

In 1990, Lappert et al.
99
demonstrated the utility
of this technique for the synthesis of M—O—C bonded compounds by the isolation
of alkaline earth metal aryloxides.
2.4 Direct Reactions of Metal Halides with Alcohols (Method D)
By far the most common synthetic technique for metal alkoxides (Eq. 2.18) is the
replacement of halides from an appropriate metal halide by alkoxo groups.
MCl
n
C x C yROH


MCl
nx
(OR)
x
(ROH)
y
C xHCl " 2.18
Halides of alkaline earth, lanthanide, actinide, and later 3d (Mn, Fe, Co, Ni) metals on
interactions with alcohols form crystalline molecular adducts like MgBr
2
.6MeOH,
100
CaBr
2
.6MeOH,
100
LnCl

3
.3Pr
i
OH
101–103
where Ln is a lanthanide metal,
ThCl
4
.4EtOH,
104,105
MCl
2
.2ROH (M D Mn,Fe,Co,Ni;RD Me, Et, Pr
n
,Pr
i
).
106
Apart
from the alkaline earth metal (Ca, Sr, Ba) halides, all of these undergo alcoholysis in
the presence of a suitable base to yield the corresponding homoleptic alkoxide or
chloride-alkoxide derivatives (Sections 2.5.1, 2.5.2, and 2.5.3).
Interesting variations in the extent of alcoholysis reactions of tetravalent metal (Ti,
Zr, Th, Si) chlorides may be represented
107
by Eqs (2.20–2.23), to which CCl
4
has
been added for comparison.
CCl

4
C ROH (excess)  !no reaction 2.19
SiCl
4
C 4ROH  !Si(OR)
4
C 4HCl " 2.20
TiCl
4
C 3ROH (excess)  !TiCl
2
(OR)
2
.ROH C HCl " 2.21
2ZrCl
4
C 6ROH (excess)  !ZrCl
2
(OR)
2
.ROH
C ZrCl
3
(OR).2ROH C 3HCl " 2.22
ThCl
4
C 4ROH (excess)  !ThCl
4
.4ROH 2. 23
Depending on the nature of the metal (M), the initial metal chloride (MCl

n
)ora
product MCl
xy
(OR)
y
forms an addition complex with alcohol molecules (ROH)
without enough perturbation of electronic charges for the reaction to proceed further.
The reactions of metal tetrachlorides MCl
4
(M D Ti, Zr, Th) towards ethyl alcohol
show a gradation TiCl
4
> ZrCl
4
> ThCl
4
.
107
Although no clear explanation is available for the varying reactivity of different metal
chlorides with alcohols, it is interesting to note that final products of similar compo-
sitions have been isolated in the reactions of tetraalkoxides of these metals with HCl.
For example, the reaction of TiOPr
i

4
with HCl leads finally to TiOPr
i

2

Cl
2
.Pr
i
OH
(Section 4.11.2).
20 Alkoxo and Aryloxo Derivatives of Metals
Specific intermediate products according to Eq. (2.18) may be isolated by controlling
the conditions (solvent, stoichiometry, or temperature). For example, the equimolar
reaction of TiCl
4
with Pr
i
OH in dichloromethane at room temperature has been
shown
108
to yield the dimeric complex [TiCl
3
HOPr
i
-Cl]
2
. The above reaction
in 2–3 molar ratios gives the dimeric complexes [TiCl
2
OPr
i
HOPr
i
-Cl]

2
and
[TiCl
2
OPr
i
HOPr
i
-OPr
i
]
2
as outlined in Scheme 2.1 on the basis of X-ray
structures of the products.
− 2HCl
Cl
Ti
Cl
Ti
O
H
O
H
Cl
Cl
Pr
i
OPr
i
ClPr

i
O
Cl
Pr
i
Pr
i
O
Ti
O
H
Cl
Cl
Pr
i
OPr
i
Cl
H
4HOPr
i
+
Pr
i
Pr
i
Cl
Ti
O
Ti

O
H
O
H
Cl
O
Pr
i
OPr
i
ClPr
i
O
Cl
Pr
i
2TiCl
4
+ 2HOPr
i
− 2HCl
Scheme 2.1
Interestingly, the reaction of metallic uranium in isopropyl alcohol in the presence of
stoichiometric amounts of iodine
109
has been shown to afford a mixed iodide–isoprop-
oxide of uranium(IV), UI
2
OPr
i


2
Pr
i
OH
2
(Eq. 2.24):
U C 2I
2
C 4Pr
i
OH
Pr
i
OH
! UI
2
OPr
i

2
Pr
i
OH
2
C 2HI 2.24
This type of reaction appears to have considerable promise for the preparation of other
polyvalent metal–iodide–isopropoxide complexes.
Out of the p-block elements, anhydrous chlorides of electronegative elements
boron,

110–112
silicon,
2,113–117
and phosphorus
118,119
react vigorously with alcohols to
yield homoleptic alkoxo derivatives [M(OR)
x
] (Eq. 2.25). Although no detailed studies
have been made, AlCl
3
120,121
and NbCl
5
122,123
undergo only partial substitution, while
GeCl
4
124,125
does not appear to react at all with alcohols.
MCl
x
C xROH  ! M(OR)
x
C nHCl " 2.25
M D B, x D 3; Si, x D 4; P,As x D 3
The reactions indicated above occur with primary and secondary alcohols only, and
have been studied mainly with ethyl and isopropyl alcohols. With a tertiary alcohol
(Bu
t

OH), silicon tetrachloride yields almost quantitatively Si(OH)
4
and Bu
t
Cl.
126
This
Homometallic Alkoxides 21
has been shown by Ridge and Todd
127
to be due to facile reactivity of HCl initially
evolved to yield Bu
t
Cl and H
2
O, which hydrolyses SiCl
4
.
SiCl
4
C 4Bu
t
OH  ! Si(OH)
4
C 4Bu
t
Cl " 2.26
The reaction of AsCl
3
with an excess of CF

3
CH
2
OH
128
gives AsOCH
2
CF
3

3
,which
could be oxidized with chlorine in the presence of CF
3
CH
2
OH to AsOCH
2
CF
3

5
as
shown by the following reaction (Eq. 2.27):
AsCl
3
C 3CF
3
CH
2

OH !
3HCl
AsOCH
2
CF
3

3
CCl
2
, C2HOCH
2
CF
3
! AsOCH
2
CF
3

5
C 2HCl " 2.27
Following the earlier observations of Fischer,
129
Klejnot
130
observed that the reaction
of WCl
6
with ethyl alcohol can be represented by Eqs (2.28) and (2.29):
WCl

6
C 2C
2
H
5
OH  ! WCl
3
(OEt)
2
C
1
2
Cl
2
C 2HCl " 2.28
Cl
2
C C
2
H
5
OH  ! CH
3
CHO C 2HCl " 2.29
Chloro-alkoxo derivatives of W(V) can be prepared by the direct reactions of WCl
5
with alcohols at 70
Ž
C.
131,132

The reaction between WCl
4
and the alcohols ROH
(R D Me, Et) leads to the (W
D
W
8C
-containing derivatives W
2
Cl
4
(OR)
4
(HOR)
2
,
133
which have been characterized by X-ray crystallography.
2.5 Reactions of Simple and Complex Metal Chlorides or Double Nitrates
with Alcohols in the Presence of a Base (Method E)
On the basis of the earlier observations,
3,4,26
it appears that except for a few metal(loid)
halides, most of these undergo only partial solvolysis or no solvolysis even under
refluxing conditions. Thus in order to achieve the successful preparation of pure
homoleptic metal alkoxides, the use of a base such as ammonia, pyridine, trialkyl-
amines, and alkali metal alkoxides appears to be essential. While alkali alkoxides
provide anions by direct ionization, the role of other bases (
ž
ž

B) could be to increase
the concentration of alkoxide anions according to Eqs (2.30)–(2.32):
ž
ž
B C ROH


(HB)
C
C OR

2.30
OR

C M—Cl  ! M—OR C Cl

2.31
(HB)
C
C Cl

 ! (BH)
C
Cl

2.32
Of the commonly employed bases (NH
3
, NaOR, KOR) for completion of the reac-
tions and preparation of soluble metal alkoxides, NH

3
appears to have some distinct
advantages including: (i) passage of anhydrous ammonia in a reaction mixture of an
anhydrous metal chloride and alcohol produces heat by neutralization of the liberated
HCl with NH
3
; the cooling of the reaction mixture is an index of the completion of the
reaction, (ii) precipitated NH
4
Cl can be filtered easily, (iii) excess NH
3
can be easily
removed by evaporation, whereas (iv) heterobimetallic alkoxides like NaAl(OR)
4
and
KZr
2
(OR)
9
tend to be formed with excess of alkali alkoxides.
22 Alkoxo and Aryloxo Derivatives of Metals
2.5.1 The Ammonia Method (E-1)
The addition of a base, typically ammonia, to mixtures of metal(loid) halides and
alcohols allows the synthesis of homoleptic alkoxides for a wide range of metals and
metalloids. Anhydrous ammonia appears to have been employed for the first time by
Nelles
134
in 1939 for the preparation of titanium tetra-alkoxides (Eq. 2.33):
TiCl
4

C 4ROH C 4NH
3
(excess)
benzene
! Ti(OR)
4
C 4NH
4
Cl # 2.33
Zirconium tetra-alkoxides were prepared for the first time in 1950 by the ammonia
method,
135
as earlier attempts
136
to use the alkali alkoxide method did not give a
pure product, owing to the tendency of zirconium to form stable heterobimetallic
alkoxides
137
(Chapter 3) with alkali metals.
The ammonia method has, therefore, been successfully employed
3,4,21,26
for the
synthesis of a large number of alkoxides of main-group and transition metals according
to the following general reaction (Eq. 2.34):
MCl
x
C xROH C xNH
3
benzene
! M(OR)

x
C xNH
4
Cl # 2.34
Owing to the highly hydrolysable nature of most of the alkoxide derivatives, strin-
gently anhydrous conditions are essential for successful preparation of the alkoxides.
Apart from careful drying of all the reagents as well as solvents, gaseous ammonia
should be carefully dried by passage through a series of towers packed with anhy-
drous calcium oxide, followed preferably by bubbling through a solution of aluminium
isopropoxide in benzene.
Benzene has been reported to be a good solvent for the preparation of metal alkoxides
by the ammonia method, as its presence tends to reduce the solubility of ammonium
chloride, which has a fair solubility in ammoniacal alcohols. In addition, the ammo-
nium chloride precipitated tends to be more crystalline under these conditions, making
filtration easier and quicker. Although most of the earlier laboratory preparations have
been carried out in benzene, the recently emphasized carcinogenic properties of this
solvent suggests that the use of an alternative solvent should be explored.
2.5.1.1 Group 3 and f-block metals
To date no unfluorinated alkoxides of scandium, yttrium, and lanthanides
18,21
in the
common C3 oxidation state appear to have been prepared by the ammonia method.
By contrast, yttrium and lanthanides (Ln) fluoroalkoxide derivatives of the types
LnfOCHCF
3

2
g
3
138

and LnfOCHCF
3

2
g
3
.2NH
3
139
have been isolated by this route.
It might appear that the ammonia method is applicable to the synthesis of a large
number of metal alkoxides, but there are certain limitations. For example, metal chlo-
rides (such as LaCl
3
)
140
tend to form a stable and insoluble ammoniate MNH
3

y
Cl
n
instead of the corresponding homoleptic alkoxide derivative. Difficulties may also arise
if the metal forms an alkoxide which has a base strength comparable with or greater than
that of ammonia. Thorium provides a good example of this type where the ammonia
method has not been found to be entirely satisfactory.
141
For example, during the
preparation of thorium tetra-alkoxides from ThCl
4

and alcohols, Bradley et al.
142
could
Homometallic Alkoxides 23
obtain only thorium trialkoxide monochlorides owing to the partial replacement of chlo-
rides. These workers observed that the alcoholic solutions of Th(OEt)
4
or ThOPr
i

4
were alkaline to thymolphthalein. On the other hand anhydrous ammoniacal alcohols
were acidic to this indicator. Thus thorium tetra-alkoxides tend to be more basic than
ammonia and the following feasible equilibria (Eqs 2.35 and 2.36) may be responsible
for the formation of Th(OR)
3
Cl instead of the expected tetra-alkoxides.
Th(OR)
4
C NH
4
C


Th(OR)
3
C
C NH
3
C ROH 2.35

Th(OR)
3
C
C Cl



Th(OR)
3
Cl 2.36
However, it was observed
141
that treatment of alcoholic solutions of thorium tetra-
chloride with sodium alkoxides gave thorium tetra-alkoxides.
In search of a convenient method for the synthesis of tetra-alkoxides of cerium(
IV)and
plutonium(
IV), which do not form stable chlorides, the complex chlorides C
5
H
6
N
2
MCl
6
(M D Ce(IV), Pu(IV); C
5
H
6
N D pyridinium) method proved to be convenient starting

materials:
C
5
H
6
N
2
MCl
6
C 6NH
3
C 4ROH  ! M(OR)
4
C 6NH
4
Cl # 2C
5
H
5
N 2.37
where M D Ce
143
or Pu
144
and R D Pr
i
.
Bradley et al.
145
had earlier reported that dipyridinium hexachlorozirconate

C
5
H
6
N
2
ZrCl
6
, which can be prepared from the commonly available ZrOCl
2
.8H
2
O,
also reacted smoothly with alcohol in the presence of ammonia to form the tetra-
alkoxides Zr(OR)
4
.
During an attempt to prepare tetra-tert-alkoxides of zirconium and cerium by the
reactions of C
5
H
6
N
2
MCl
6
(M D Zr, Ce) with tert-butyl alcohol, Bradley and co-
workers
143,144
had noticed the formation of MClOBu

t

3
.2C
5
H
5
N as represented by
Eq. (2.38):
C
5
H
6
N
2
MCl
6
C 3Bu
t
OH C 5NH
3
 ! MClOBu
t

3
.2C
5
H
5
N C 5NH

4
Cl # 2.38
As the product reacts with primary alcohols (Eq. 2.39) in the presence of ammonia to
give heteroleptic alkoxides, M(OR)OBu
t

3
, steric reasons have been suggested as a
possible explanation for the partial replacement reactions with tert-butyl alcohol:
MClOBu
t

3
.2C
5
H
5
N C EtOH C NH
3
 ! M(OEt)OBu
t

3
C 2C
5
H
5
N C NH
4
Cl #

2.39
It is, however, somewhat intriguing that dipyridinium hexachloro derivatives of
zirconium and cerium
146
undergo complete replacement with Cl
3
C.CMe
2
OH, which
should apparently be an even more sterically hindered alcohol than Bu
t
OH:
C
5
H
6
N
2
MCl
6
C 4Cl
3
C.CMe
2
OH C 6NH
3
 ! MOCMe
2
CCl
3


4
C 2C
5
H
5
N C 6NH
4
Cl # 2.40
Reactions ofMCl
4
(M D Se, Te) with avariety of alcohols(MeOH, EtOH, CF
3
CH
2
OH,
Bu
t
CH
2
OH, Me
2
CHOH) in 1:4 molar ratio in THF using Et
3
N as a proton acceptor afford
corresponding tetra-alkoxides.
146a