Clean oxidation of thiolates to sulfinates in a four-coordinate CoIII complex with a mixed carboxamido N-thiolato S donor set: relevance to nitrile hydratase.

Abstract A new [Co(N 2 (SO 2 ) 2 )(CN t Bu) 2 ](Et 4 N) complex 6 was prepared from N,N′ -(3-mercapto-3-methyl-butyryl)- o -phenylenediamine and completely characterized. While the starting square planar complex [Co(N 2 S 2 )](Et 4 N) 4 was destroyed by dioxirane, the Co ligated thiolates of the six-coordinate intermediate [Co(N 2 S 2 )(CN t Bu) 2 ](Et 4 N) complex 5 was readily oxidized to sulfinates with a stoichiometric amount of this oxidant. The resulting complex 6 crystallizes with an octahedral structure. The SO bonds of the SO 2 groups are almost equivalent (≈1.483 and ≈1.453 A). The isonitrile is linearly bonded to the cobalt with a Co–C–N angle of 177.5° and a very short C–N( t Bu) distance of 1.13 A, which has a triple bond character. As expected for six-coordinate Co III complexes, 5 and 6 are diamagnetic in agreement with their 1 H and 13 C NMR spectra. The SO 2 IR bands are located at 1210 cm −1 ( ν as SO 2 ) and 1070 cm −1 ( ν s SO 2 ), while the CN vibration of the isonitrile is observed at 2170 cm −1 in 5 and 2210 cm −1 in 6 . Very recently, it has been reported in the literature that oxidation of the coordinated thiolates was required for activity of both Fe and Co nitrile hydratases. Complex 6 , with two oxidized thiolates trans to two deprotonated carboxamido nitrogens, is the first to have an in-plane closely related to that of the Co-NHase active site.