Heme-Like {CoNO}, (STTP){CoNO}, and {CoNO} Complexes Supported by 21-Thiaporphyrin Macrocycle.

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} ( = 9 and 10 in the Enemark-Feltham notation) and a (STTP){CoNO} species. Specifically, electrochemical or chemical reduction of a {CoNO} ( = 1/2) species by potassium graphite (KC) results in first ligand-based reduction leading to a {CoNO} moiety antiferromagnetically coupled to a thiaporphyrin dianionic radical yielding an overall = 0 ground state, and subsequent metal-based reduction affording an = 1/2 complex comprised of a genuine {CoNO} 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 center in {CoNO} and (STTP){CoNO} and a high spin Co center in {CoNO}. Furthermore, the reaction of the {CoNO} complex with PhCSNO and PhNO was found to furnish cobalt -diazeniumdiolate heme-like complexes, which provides an alternative route to accessing a hyponitrite-like intermediate in heme models.