Synthesis and Characterization of Cobalt NCN Pincer Complexes

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(NCN CH2 −Et)Br] ( 1 ) was accomplished by transmetalation of Li[2,6‐(Et 2 NCH 2 ) 2 C 6 H 3 ] with CoBr 2 in THF. Treatment of this air‐sensitive compound with NO gas resulted in the formation of the diamagnetic Co(III) species [Co(NCN CH2 −Et)(NO)Br] ( 2 ) as confirmed by X‐ray diffraction. This complex features a strongly bent NO ligand (Co−N−O∠135.0°). The ν NO 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 CuBr 2 led to the formation of the Co(III) complex [Co(NCN CH2 −Et)Br 2 ]. Treatment of [Co(NCN CH2 −Et)Br 2 ] with TlBF 4 as halide scavenger in acetonitrile led to the formation of the cationic octahedral complex [Co(NCN CH2 −Et)(MeCN) 3 ](BF 4 ) 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.