A comprehensive series of Group 14 derivatives of the plenary mixed-metal polyoxometalate [PNbW11O40]4−

The Group 14 derivatized polyoxometalate series [LNbOEMe3]3− (L=α-{PW11O39}7−; E=Si, Ge, Sn, Pb) can be prepared from the n-Bu4N+ salt of the niobium substituted Keggin ion [LNbO]4− and Me3EOTf (OTf=O3SCF3) (53–76% yield). The t-butyl species [LNbOCMe3]3− was obtained by ligand exchange between [LNbOSiMe3]3− and excess t-butanol. Multinuclear NMR spectroscopic data of the series and a crystallographic study of [LNbOGeMe3]3− indicate that the {Me3E}+ group binds selectively to the terminal ONb oxygen atom. The carbon and silicon derivatives are susceptible to hydrolysis, however, the germanium, tin and lead species are hydrolytically stable. Facile cleavage of the NbO–E bond with acetate or halide (F, Cl, Br, I) restores [LNbO]4−.