Cationic and neutral NiII complexes containing a non-innocent PNP ligand: formation of alkyl and thiolate species

Abstract

The synthesis and characterization of a series of cationic and neutral Ni-complexes with the non-innocent PNP^tBu pincer ligand is discussed. Starting with the dicationic complex 1, [Ni(PNP^tBu)(NCMe)](BF₄)₂, a small series of dicationic and monocationic Ni^II complexes has been prepared. Substitution with tert-butyl isocyanide and azide occurs readily in MeCN solution. IR spectroscopy provided a practical handle to access the formal valence state of the ligand. For the mono- and dicationic tert-butyl isocyanide species 3 and 6 the main vibrational bands in the IR spectra were reproduced quantitatively by DFT theoretical calculations, showing good agreement with the experimentally observed Δν upon dearomatization of the PNP^tBu backbone. Using a selective dearomatization-reprotonation methodology the mononuclear Ni-thiolate species 7 and 8 are cleanly generated and their structures have been determined by X-ray crystal structure determination. Alternatively, starting from the monocationic species [Ni(PNP^tBu)Cl]BF₄, neutral alkyl derivatives are easily available in a two-step procedure, and these species have been spectroscopically characterized.