2 Homometallic Alkoxides

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 structures
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 computercontrolled
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