Organic-inorganic hybrids based on polyoxometalates. 6. Syntheses, structure, and reactivity of the bis(tert-butylsilyl)decatungstophosphate [(gamma-PW10O36)(t-BuSiOH)2]3-.

Abstract

Bis(tert-butylsilyl)decatungstophosphate (n-Bu4N)3[(gamma-PW10O36)(t-BuSiOH)2] (1) has been synthesized through phase-transfer conditions, by reaction of t-BuSiCl3 with Cs7[(gamma-PW10O36)].xH2O. This new hybrid anion has been characterized by elemental analysis, X-ray crystallography, multinuclear solution and solid-state NMR, and infrared spectroscopy. Crystals of 1 are monoclinic, space group C2/c, with lattice constants a = 44.762(10) A, b = 19.032(4) A, c = 22.079(8) A, beta = 98.9(2) degrees, and Z = 8. Anion 1 has nominal Cs symmetry and displays an "open structure" with two t-BuSiOH groups anchored to the (gamma-PW10O36) framework. The two t-BuSiOH units are nonequivalent as confirmed by 29Si CP-MAS NMR and by diffuse reflection infrared spectroscopy. The two OH groups are linked through one H-bond (dO-O = 2.63 A). According to 29Si and 183W NMR, 1 adopts a more symmetrical conformation (C2v) in solution. Anion 1 reacts cleanly in homogeneous conditions with Me2SiCl2 to yield (n-Bu4N)3[(gamma-PW10O36)(t-BuSiO)2(SiMe2)] (2). The structure of 2 has been inferred from multinuclear NMR and infrared spectroscopy. The hybrid "closed-structure" anion 2 consists of the (gamma-PW10O36) framework on which is grafted a heterosilylated network composed of a capping fragment, Si(CH3)2, linked to the t-BuSi groups through two siloxane bridges.