2 Homometallic Alkoxides

388 Alkoxo and Aryloxo Derivatives of Metals
Mo2⊲OPr i ⊳8 C 6MoO2⊲OPr i ⊳2 ! Mo6O6⊲OPr i ⊳12 C 2MoO⊲OPr i ⊳4 ⊲5.21⊳
The structures of several of these molybdenum oxo-alkoxides have been determined
andarediscussedinSection5.
Tungsten oxo-alkoxides have been obtained from the reaction of ketones with the
dinuclear [W2⊲OR⊳6⊲py⊳2] compounds (Eq. 5.22). 35
2W2⊲OPr i ⊳6⊲py⊳2 C 2Me2CO ! W4O2⊲OPr i ⊳12 C C2Me4 C 4py ⊲5.22⊳
With the neopentyloxide a stable adduct is formed containing oxo and -propylidene
ligands by reductive cleavage of the ketonic carbonyl group (Eq. 5.23). 36
W2⊲OCH2Bu t ⊳6⊲py⊳2CMe2CO ! W2⊲ -CMe2⊳⊲ -OCH2Bu t ⊳⊲O⊳⊲OCH2Bu t ⊳5⊲py⊳
⊲5.23⊳
This adduct reacted further with acetone to produce tetramethylethylene
and the oxo-complex [W2O2⊲OCH2Bu t ⊳6]. An analogous adduct formed from
[W2⊲OCH2Bu t ⊳6⊲py⊳2] and cyclopropane carboxaldehyde (C3H5CHO) retained the
cyclopropane ring in the bridging cyclopropylmethylidene complex [⊲Bu t CH2O⊳3W⊲ -
CHC3H5⊳⊲ -OCH2Bu t ⊳2W⊲O⊳⊲OCH2Bu t ⊳⊲py⊳] in which the oxo ligand is bound
terminally to one tungsten. 37
The tungsten trialkoxides [W⊲OR⊳3]n ⊲n D 2 or 4) undergo various reactions with
carbon monoxide including cleavage of CO to form carbido- and oxo-alkoxides. The
tetranuclear complex [W4⊲ 4-C⊳⊲ -O⊳⊲OR⊳12] (RD Pr i or CH2Bu t ) were thereby isolated
and characterized. 38
The Ta(III) siloxide [Ta⊲OSiBu t 3 ⊳3] also abstracted an oxo ligand from CO (Eq. 5.24). 39
4Ta⊲OSiBu t 3 ⊳3 C 2CO ! 2[⊲O⊳Ta⊲OSiBu t 3 ⊳3] C [⊲Bu t 3 SiO⊳3TaC2Ta⊲OSiBu t 3 ⊳3]
⊲5.24⊳
Oxygen transfer from nitrosobenzene to [W2⊲OBu t ⊳6] gaverisetothe -oxo complex
[W2⊲ -O⊳⊲ -OBu t ⊳2⊲NPh⊳2⊲OBu t ⊳4] 40 whilst the siloxo complex [W2⊲OSiMe2Bu t ⊳6]
reacted with nitric oxide forming the oxo-complexes trans-[W⊲O⊳⊲OSiMe2Bu t ⊳4⊲py⊳]
and [W2⊲ -O⊳2⊲OSiMe2Bu t ⊳4⊲O⊳2⊲py⊳2]. 41
Finally it is noteworthy that the tetranuclear mixed valency cerium oxo-isopropoxide
[Ce4⊲ 4-O⊳⊲ 3-OPr i ⊳2⊲ -OPr i ⊳4⊲OPr i ⊳7⊲Pr i OH⊳] was obtained by photolysis of
[Ce2⊲ -OPr i ⊳2⊲OPr i ⊳6⊲Pr i OH⊳2]. 42
2.3 Reactions of Metal Oxochlorides with Alkali Alkoxides
An alternative approach to the synthesis of metal oxo-alkoxides involves the reaction
of the metal oxo-chloride with the requisite amount of sodium alkoxide (Eq. 5.25):
MOx Cly C yNaOR ! MOx ⊲OR⊳y C yNaCl ⊲5.25⊳
An early example of this method was its use in the preparation of uranyl dialkoxides
[UO2⊲OR⊳2⊲ROH⊳x ] (Eq. 5.26): 43
UO2Cl2 C 2LiOMe C MeOH ! UO2⊲OMe⊳2, MeOH C 2LiCl ⊲5.26⊳