Silylmethyl and related complexes. Part 6. Preparation, properties, and crystal and molecular structure of tris[bis(trimethylsilyl)methyl]-chromium(III);the chemistry of related compounds of titanium(III), vanadium(III), zirconium(IV), and hafnium(IV)

Abstract

Interaction of Li[CH(SiMe₃)₂] in OEt₂ with respectively CrCl₃, VCl₃, [TiCl₃(NMe₃)₂] or TiCl₄, [VCl₃(NMe₃)₂], ZrCl₄, or HfCl₄ gives [MR₃](M = Cr, V, or Ti) or [M′R₃Cl][M′= Zr or Hf : R = CH(SiMe₃)₂] as crystalline products. The monomeric [CrR₃] is highly reactive, giving RH on hydrolysis or with glacial acetic acid, a maroon dia- magnetic 1:1 adduct with NO {believed to be [CrR₃(NO)]}, and ĊPh₃ and a purple solid {believed to be [CrR₃Cl]} with CPh₂Cl. Crystals of [CrR₃] are bright emerald-green, extremely air-sensitive needles, elongated along c, in the trigonal space group P31c(confirmed by structure refinement) with unit-cell dimensions a=b= 16.120(5), and c= 8.793(2)Å, and trap solvent in the cavities of the lattice so formed. The molecule, which is confirmed as monomeric and three-co-ordinate, is non-planar, the Cr atom lying ca. 0.3 Å above the plane of the three alkyl carbon atoms [Cr–C 2.07(1)Å, C–Cr–C 117.6(4)°]. Full-matrix least-squares refinement using 548 independent intensities (200 K) has converged to R 0.067 (R′ 0.075). Less detailed analytical and spectroscopic (but not X-ray) characterisation is provided for the other new transition-metal alkyls.