Synthesis and characterization of new organosilyl derivatives of polyoxometalates (nBu4N)2[NbW5O19SiRR′2] (R = R′ = Et, iPr, OtBu, Ph; R = tBu and R′ = Me) -: X-ray crystal structure of (nBu4N)2[NbW5O19SiPh3]

Reactions of (nBu(4)N)(4)[(NbW5O18)(2)O] with trialkyl/arylsilanols in dichloromethane and/or acetonitrile forms respectively (nBu(4)N)(2)[NbW5O19SiRR'2] [R = R' = Et (1), iPr (3), OtBu (4), Ph (5); R = tBu and R' = Me (2)] in ca. 90-64 % isolated yields. The compounds have been characterized by elemental analysis, IR, Raman, multinuclear NMR in solution (H-1, C-13, Si-29, W-183) and in the solid-state by Si-29 CP-MAS NMR spectroscopy. Multinuclear NMR and IR spectroscopic data suggest that the SiRR'(+)(2) electrophilic fragment binds selectively to the terminal NbO oxygen atom which appears the most reactive site in (nBu(4)N)(3)[NbW5O19]. This is supported by Xray crystallographic analysis of (nBu(4)N)(2)[NbW5O19SiPh3] (5) which crystallizes in the monoclinic system, space group P2(1)/a with lattice parameters a = 19.884(5), b = 16.801(2), c = 20.644(3) angstrom, ss = 112.050(12)degrees, V = 6392(2) angstrom(3), and Z = 4. Hydrolysis of the alkyl/arylsilyloxide derivatives leads to the back formation of the (NbW5O18)(2) O4- dimer by the cleavage of the Si-O bond.