Agostic versus Hypervalent Si‐H Interactions in Half‐Sandwich Complexes of Nb and Ta

Abstract

A series of chlorosilyl hydride complexes of tantalum, Cp(ArN)Ta(PMe3)(H)(SiCln3R3-n) (n = 0-3), was prepared and studied by 29Si NMR, X-ray diffraction and DFT calculations. An unprecedented increase of the J(Si-H) coupling constant between the hydride and silyl ligands from 14 Hz for n = 0 to 50 Hz (n = 3) was observed. Reactions of the compounds CpNb(RN)(PR'Me2)2 (RAr, Ar'; R= Me, Ph) with chlorosilanes HSiMe2Cl give agostic complexes Cp(RN(Me2Si—H…))Nb(PR'Me2)(Cl) studied by 29Si NMR and X-ray diffraction, whereas reaction of CpNb(ArN)(PMe3)2 with HSiCl3 gives the silylhydrido complex Cp(ArN)Nb(PMe3)(H)(SiCl3).