Organotin and organogermanium linkers for simple, direct functionalization of polyoxotungstates

Fifteen Keggin-anion-derived polytungstates TW11O39MCH2CH2X]]n- (T = Si, Ge, Ga; M = Sn, Ge; X = COOH, COOCH3, CONH2, CN; n = 5, 6) were prepared in aqueous or aqueous-organic solution from the corresponding lacunary polytungstates and trichlorotin and -germanium precursors, and were isolated as caesium salts. The derivatized polytungstates were characterized by elemental analysis, multinuclear NMR spectroscopy, and cyclic voltammetry; they are stable in aqueous solution to pH 6-7. NMR spectroscopy revealed the presence of a second (beta1 or beta3) isomer in the tungstogallate derivatives. Acid hydrolysis of the ester and nitrile derivatives could be achieved without decomposition of the polytungstate moieties, and esterification and amidation of the carboxylate functions was straightforward using standard coupling techniques, e.g. the formation, isolation and characterization of SiW11O39Ge(CH2)2CONHCH2COOCH3]]5- from glycine methyl ester. Since the Cl3MCH2CH2X precursors are readily accessible by hydrostannation/germanation reactions with the corresponding alkenes, novel coupled polytungstates, such as (SiW11O39GeCH2CH2COOCH2)4C]20- from pentaerythritol tetraacrylate, can also be prepared.