Synthesis and Characterization of Cobalt NCN Pincer Complexes

Jan Pecak; Wolfgang Eder; Gerald Tomsu; Berthold Stöger; Marc Pignitter; Karl Kirchner

doi:10.1002/ejic.202100643

Synthesis and Characterization of Cobalt NCN Pincer Complexes

Eur J Inorg Chem. 2021 Nov 8;2021(41):4280-4285. doi: 10.1002/ejic.202100643. Epub 2021 Oct 11.

Authors

Jan Pecak¹, Wolfgang Eder¹, Gerald Tomsu¹, Berthold Stöger², Marc Pignitter³, Karl Kirchner¹

Affiliations

¹ Institute of Applied Synthetic Chemistry Vienna University of Technology Getreidemarkt 9 A-1060 Wien Austria.
² X-Ray Centre Vienna University of Technology Getreidemarkt 9 1060 Wien Austria.
³ Department of Physiological Chemistry, Faculty of Chemistry University of Vienna Althanstraße 14 1090 Wien Austria.

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(NCN^CH2-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(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 CuBr₂ led to the formation of the Co(III) complex [Co(NCN^CH2-Et)Br₂]. Treatment of [Co(NCN^CH2-Et)Br₂] with TlBF₄ as halide scavenger in acetonitrile led to the formation of the cationic octahedral complex [Co(NCN^CH2-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.

Keywords: Cobalt; DFT studies; EPR studies; Nitrosyl ligand; Pincer complexes.