tert-Butylimido complexes of chromium and vanadium. X-Ray crystal structures of Cr(NBut)Cl3(MeOCH2CH2OMe), Cr[C6H4(NH)2-o]Cl2(PMe2Ph)2, Cr(NBut)2(OSiPh3)2, Cr(NBut)-Cl(OC9H6N)2 and [(PPh3)2][Cr(NBut){S2C2(CN)2}2]

Abstract

The compound Cr(NBu^t)Cl₃, isolated as its adducts with tetrahydrofuran (thf) and 1,2-dimethoxyethane (dme), has been prepared by chlorination of Cr(NBu^t)₂Cl₂. These materials have been used as sources of other chromium compounds such as the neutral adducts Cr(NBu^t)Cl₃(PR₃)₂(R₃= Me₃, Et₃, Me₂Ph or EtPh₂) or Cr(NBu^t)Cl₂(NC₇H₁₃)(NC₇H₁₃= quinuclidine) or anionic complexes such as [PPh₄][Cr(NBu^t)Cl₄]. The tertiary phosphine complexes in the presence of excess of phosphine are photochemically or thermally reduced to CrCl₃(PR₃)₃ and the tertiary phosphinimine. Halide-substitution reactions on Cr(NBu^t)Cl₃(dme) or [Cr(NBu^t)Cl₄]^– with O,N, (O,N) and S ligands give rise to compounds such as cis-Cr(NBu^t)Cl(OC₉H₆N)₂(OC₉H₆N = quinolin-8-olate), [Cr(NBu^t)(mnt)₂]^–(mnt = maleonitriledithiolate) and Cr(NBu^t)Cl(S₂CNEt₂)₂; cyclic voltammetry of the last two complexes is reported. Evidence for the disproportionation 2Cr^V→ Cr^VI+ Cr^IV in reactions of alkoxides is given. Reduction of Cr(NBu^t)Cl₃(dme) in the presence of 1,2-bis(dimethylphosphino)ethane (dmpe) gives the chromium(IV) species [Cr(NBu^t)(dmpe)₂Cl]Cl. The EPR (X-band) spectra of chromium(V) species at room temperature show hyperfine splitting for ⁵³Cr, ¹⁴N and ³¹P in appropriate compounds with g_iso values at 77 K of ca. 2.00. The compounds [V(NBu^t)(NHBu^t)(µ-NBu^t)]₂ and [V(µ-NBu^t)(OSiMe₃)₂]₂ are also described. The X-ray structures of five compounds have been determined: Cr(NBu^t)Cl₃(dme) is octahedral with a mer arrangement of the three chlorines; Cr[C₆H₄(NH)₂-o]Cl₂(PMe₂Ph)₂ is also octahedral, having C₂ symmetry with trans phosphines and cis chlorines; Cr(NBu^t)₂(OSiPh₃)₂ is distorted tetrahedral; Cr(NBu^t)Cl(OC₉H₆N)₂ is octahedral with the chelating quinolin-8-olato groups arranged to give trans O,O and cis N,N geometry; and [Cr(NBu^t)(mnt)₂]^– has a square-pyramidal structure with an axial imido group.