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

A new [Co(N-2(SO2)(2))(CNtBu)(2)](Et4N) complex 6 was prepared from N,N'-(3 -mercapto-3-methyl-butyryl)-o-phenylenediamine and completely characterized . While the starting square planar complex [Co(N2S2)](Et4N) 4 was destroyed by dioxirane, the Co ligated thiolates of the six-coordinate intermediate [Co(N2S2)(CNtBu)(2)](Et4N) complex 5 was readily oxidized to sulfinates wit h a stoichiometric amount of this oxidant. The resulting complex 6 crystall izes with an octahedral structure. The SO bonds of the SO, groups are almos t equivalent (approximate to1.483 and approximate to1.453 Angstrom). The is onitrile is linearly bonded to the cobalt with a Co-C-N angle of 177.5 degr ees and a very short C-N(tBu) distance of 1.13 Angstrom, which has a triple bond character. As expected for six-coordinate Co-III complexes, 5 and 6 a re diamagnetic in agreement with their H-1 and C-13 NMR spectra. The SO2 IR bands are located at 1210 cm(-1) (v(as)SO(2)) and 1070 cm(-1) (v(s)SO(2)), while the CN vibration of the isonitrile is observed at 2170 cm(-1) in 5 a nd 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 bo th Fe and Co nitrile hydratases. Complex 6, with two oxidized thiolates tra ns to two deprotonated carboxamido nitrogens, is the first to have an in-pl ane closely related to that of the Co-NHase active site. (C) 2001 Elsevier Science B.V. All rights reserved.