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

The synthesis and characterization of a series of cationic and neutral Ni-complexes with the non-innocent PNPtBu pincer ligand is discussed. Starting with the dicationic complex 1, [Ni(PNPtBu)(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 Delta nu upon dearomatization of the PNPtBu 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(PNPtBu)Cl]BF4, neutral alkyl derivatives are easily available in a two-step procedure, and these species have been spectroscopically characterized.