The structure and chemistry of tris(pentafluorophenyl)borane protected mononuclear nitridotitanium complexes

Abstract

Treatment of TiCl(NMe₂)₃ with H₃N·B(C₆F₅)₃ results in N–H activation and ligand exchange to yield the structurally characterised salt [TiCl(NMe₂)₂(NMe₂H)₂]⁺[TiNB(C₆F₅)₃(Cl)₂(NMe₂H)₂]⁻. Cation exchange with [Me₄N]Cl, [Ph₄P]Cl and [(PhCH₂)Ph₃P]Cl yields the respective ammonium and phosphonium salts of the [TiNB(C₆F₅)₃(Cl)₂(NMe₂H)₂]⁻ anion. X-ray crystallography reveals that the essential trigonal bipyramidal geometry and composition of the anion is retained in each of these salts despite some minor variations in the Ti–N–B angle and the nature of the interionic interactions. Electronic investigation by DFT calculations confirmed the Ti–N triple bond character implied by the experimentally determined bond length, with the HOMO and HOMO-1 having Ti–N π-bonding character. The dimethylamine ligands of the anion resist substitution by moderate bases but can be displaced by pyridine to give a pentacoordinate anion. In contrast, addition of 2,2′-bipyridyl gives a neutral octahedral complex. Treatment of the pyridine complex with TlCp results in the formation of a four coordinate anionic cyclopentadienyl complex.