Synthesis and structures of vanadium(III) and vanadium(IV) silanolates

The syntheses of the new and partially known vanadium(III)-silanolate compl exes [{V((OSiMe2Bu)-Bu-t)(3)}(2)(THF)] (1), [Li(THF)(2)V((OSiMe2Bu)-Bu-t)(4 )] (2), [V((OSiMe2Bu)-Bu-t)(lut)] (3), V(OSiPh3)(3)(THF)(3) (4), [Li(THF)(4 )][V(OSiPh3)(4)] (THF)(2) (5), [Li(DME)VMes((OSiMe2Bu)-Bu-t)(3)] (7), [Li(T HF)(4)][VMes .(OSiPh3)(3)] (8), [Li(THF)(4)][VMes(3)((OSiMe2Bu)-Bu-t)] (9), and Na[VMes(3)(OSiPh3)](THF)(4) (10) as well as the vanadium(IV) compounds [V(OSiPh3)(4)] (6), [VMes(3)((OSiMe2Bu)-Bu-t)] (11) and [VMes(3)(OSiPh3)] (12) are reported. In most cases the vanadium atom displays a coordination number of four. The dimeric structure of 1 with coordination numbers of fou r and five, respectively, has been deduced from molecular mass measurements , mass spectrometry and its magnetic properties. The crystal structures of compounds 2, 4, 5, 9 and 11 were resolved. Complex 2 resembles a bridged co ntact ion pair in which both metal centres are in a tetrahedral coordinatio n environment. In 4 the ligands are arranged trigonal bipyramidally with th e THF molecules in the axial positions. Complexes 5 and 9 crystallize in se parated ion paires with the vanadium in a tetrahedral coordination sphere. The crystal structure of 11 is analogous to that of 9 but with consequences due to the higher oxidation state. Oxidation of the vanadates(III), e.g. 5 , 9 and 10, yields the corresponding vanadium(IV) compounds 6, 11 and 12.