Heme-Like {CoNO}⁹, (STTP•–2){CoNO}⁹, and {CoNO}¹⁰ Complexes Supported by 21-Thiaporphyrin Macrocycle

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Using a weaker ligand field thiaporphyrin macrocycle (STTP) as a heme-like ligand, we succeeded in the isolation of an unprecedented complete series of {CoNO} n ( n = 9 and 10 in the Enemark–Feltham notation) and a (STTP •–2 ){CoNO} 9 species. Specifically, electrochemical or chemical reduction of a {CoNO} 9 ( S T = 1/2) species by potassium graphite (KC 8 ) results in first ligand-based reduction leading to a {CoNO} 9 moiety antiferromagnetically coupled to a thiaporphyrin dianionic radical yielding an overall S T = 0 ground state, and subsequent metal-based reduction affording an S T = 1/2 complex comprised of a genuine {CoNO} 10 unit ligated by a thiaporphyrin radical. Multiple analytical and spectroscopic measurements using SXRD, IR, NMR, SQUID, and EPR coupled to detailed DFT calculations support the assignment of a high-spin Co II center in {CoNO} 9 and (STTP •–2 ){CoNO} 9 and a high spin Co I center in {CoNO} 10 . Furthermore, the reaction of the {CoNO} 9 complex with Ph 3 CSNO and PhNO was found to furnish cobalt C -diazeniumdiolate heme-like complexes, which provides an alternative route to accessing a hyponitrite-like intermediate in heme models.