Synthesis and Characterization of Cobalt NCN Pincer Complexes.

Abstract

A series of cobalt complexes, stabilized by a monoanionic tridentate NCN pincer ligand, was synthetized and characterized. Preparation of the paramagnetic 15 VE complex [Co(NCNCH2−Et)Br] (1) was accomplished by transmetalation of Li[2,6‐(Et2NCH2)2C6H3] with CoBr2 in THF. Treatment of this air‐sensitive compound with NO gas resulted in the formation of the diamagnetic Co(III) species [Co(NCNCH2−Et)(NO)Br] (2) as confirmed by X‐ray diffraction. This complex features a strongly bent NO ligand (Co−N−O∠135.0°). The νNO is observed at 1609 cm−1 which is typical for a bent metal‐N−O arrangement. Coordinatively unsaturated 1 could further be treated with pyridine, isocyanides, phosphines and CO to form five‐coordinate 17 VE complexes. Oxidation of 1 with CuBr2 led to the formation of the Co(III) complex [Co(NCNCH2−Et)Br2]. Treatment of [Co(NCNCH2−Et)Br2] with TlBF4 as halide scavenger in acetonitrile led to the formation of the cationic octahedral complex [Co(NCNCH2−Et)(MeCN)3](BF4)2. A combination of X‐ray crystallography, IR‐, NMR‐ and EPR‐spectroscopy as well as DFT/CAS‐SCF calculations were used to characterize all compounds.