title: Hypervalent hydridosilicates: synthesis, structure and hydride bridging.
abstract: A range of hydridosilicate anions has been prepared and characterised by spectroscopic, structural and computational methods. The general approach involved reaction of KH with a neutral silane precursor in the presence of [18]crown-6. In this manner, [K([18]crown-6)]+ salts of [Ph3SiH2](-) (1), [Ph3SiF2](-) (9), and [(p-FC6H4)3SiHF](-)/[(p-FC6H4)3SiH2](-) (12) were stabilised and characterized by NMR spectroscopy and X-ray diffraction. In each case, the anion adopts a trigonal bipyramidal (TBP) geometry with three equatorial phenyl groups eclipsing the axial Si-H/Si-F bonds. The Si-H[dot dot dot]K distances, along with DFT calculations on 1, indicate an electrostatic interaction that does not dictate the geometry adopted by the anion. A [H2SiOiPr3](-) salt (7) has also been crystallised in the same way; X-ray diffraction shows in this case a distorted TBP array with axial hydride ligands, and both Si-H[...]K and Si-O[...]K interactions. 1H NMR exchange experiments show 1 to undergo facile hydride exchange with Ph3SiH. Compound 1 acts as a good hydride transfer reagent to a variety of substrates, but its high reactivity often results in redistribution and other side reactions.
authors: Department of Chemistry, King's College London, Strand, London, UKWC2R 2LS.
authors: Paul D
authors: PD
authors: Prince
authors: Michael J
authors: MJ
authors: Bearpark
authors: G Sean
authors: GS
authors: McGrady
authors: Jonathan W
authors: JW
authors: Steed