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

Abstract

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 (ST = 1/2) species by potassium graphite (KC8) results in first ligand-based reduction leading to a {CoNO}9 moiety antiferromagnetically coupled to a thiaporphyrin dianionic radical yielding an overall ST = 0 ground state, and subsequent metal-based reduction affording an ST = 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 CoII center in {CoNO}9 and (STTP•-2){CoNO}9 and a high spin CoI center in {CoNO}10. Furthermore, the reaction of the {CoNO}9 complex with Ph3CSNO 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.