2 Homometallic Alkoxides

Industrial Applications 679
The molybdenum neopentylidene complex Mo⊲CHBu t ⊳⊲NR⊳⊲OBu t ⊳2 is the active
catalyst used in a fascinating development for the synthesis of II–VI semiconductor
clusters (ZnS, CdS, PbS) and silver and gold nanoclusters of predictable size within
microdomains in films of block copolymers prepared by ROMP. 97 Block copolymers of
norbornene and a functionalized norbornene that will complex with a metal-containing
compound were prepared and characterized as monodisperse materials. The functionalized
component (amine, alkoxide, or thiolate) then sequestered the metal and the
metallated block copolymer was cast into a film which was subsequently treated with
H2S to convert the metal into the sulfide. The molybdenum complexes have also
featured in the development of the synthesis of side-chain liquid crystal polymers by
living ROMP. 98,99
4.5 Miscellaneous Reactions Catalysed by Metal Alkoxides
Alkali metal alkoxides in association with transition metal carbonyls (e.g. Ni⊲CO⊳4)
have featured in several patents covering the synthesis of methanol from synthesis gas
(Eq. 7.6). 100
2H2 C CO ! CH3OH ⊲7.6⊳
In the absence of hydrogen, a catalytic reaction of carbon monoxide and an alcohol
produces alkyl formate (Eq. 7.7). The catalyst involved is an alkali metal alkoxide
alone 101 or together with a transition metal carbonyl cluster, e.g. Ru3⊲CO⊳12. 102
ROH C CO ! HCO2R ⊲7.7⊳
Another process featuring alkali metal alkoxides is the conversion of methanol to
hydrogen and formaldehyde (Eq. 7.8). 103
CH3OH ! H2 C H2CO ⊲7.8⊳
Lithium alkoxides play an important role in the oligomeric cyclization of dinitriles
in the synthesis of phthalocyanines. 104 The combination of potassium alkoxide-crown
ether complex in a hydrocarbon solvent gives a very powerful catalyst for production
of vinyl ethers from alcohols and acetylene (Eq. 7.9). 105
ROH C HC CH ! ROCHDCH2 ⊲7.9⊳
Sodium alkoxides have also been used for the isomerization of 1,3-dienes in diene
polymers 106 and in the aldol condensation of acetone. 107
Bimetallic oxoalkoxides are excellent catalysts for the ring-opening-polymerization
of lactones, oxiranes, and thioranes. 108
Aluminium alkoxides have long been used as catalysts for the reduction of aldehydes
or ketones by secondary alcohols and recently lanthanide alkoxides were reported to act
similarly 109 in addition to catalysing the epoxidation of allylic alcohols with tert-butyl
hydroperoxide. Aluminium alkoxides have also been used to catalyse the conversion
of aldehydes to alkylesters (Tischtchenko reaction). 110 Areview 111 gives a fascinating
account of the use of heterometal alkoxides in asymmetric catalysis.
Titanium alkoxides feature as catalysts in the esterification of succinic, adipic,
azelaic, and sebacic acids with 2-ethyl hexanol 112 and in the production of acetate