Synthesis and Characterization of New Organosilyl Derivatives of Polyoxometalates (<i>n</i>Bu₄N)₂[NbW₅O₁₉SiRR′₂] (R = R′ = Et, <i>i</i>Pr, O<i>t</i>Bu, Ph;R = <i>t</i>Bu and R′ = Me) – X‐ray Crystal Structure of (<i>n</i>Bu₄N)₂[NbW₅O₁₉SiPh₃]

Abstract

Abstract Reactions of ( n Bu 4 N) 4 [(NbW 5 O 18 ) 2 O] with trialkyl/arylsilanols in dichloromethane and/or acetonitrile forms respectively ( n Bu 4 N) 2 [NbW 5 O 19 SiRR′ 2 ] [R = R′ = Et ( 1 ), i Pr ( 3 ), O t Bu ( 4 ), Ph ( 5 ); R = t Bu and R′ = Me ( 2 )] in ca. 90–64 % isolated yields. The compounds have been characterized by elemental analysis, IR, Raman, multinuclear NMR in solution ( 1 H, 13 C, 29 Si, 183 W) and in the solid‐state by 29 Si 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 ( n Bu 4 N) 3 [NbW 5 O 19 ]. This is supported by X‐ray crystallographic analysis of ( n Bu 4 N) 2 [NbW 5 O 19 SiPh 3 ] ( 5 ) which crystallizes in the monoclinic system, space group P 2 1 /a with lattice parameters a = 19.884(5), b = 16.801(2), c = 20.644(3) Å, β = 112.050(12)°, V = 6392(2) Å 3 , and Z = 4. Hydrolysis of the alkyl/arylsilyloxide derivatives leads to the back formation of the (NbW 5 O 18 ) 2 O 4– dimer by the cleavage of the Si–O bond. (© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2007)