Synthesis, X‐ray Structure and Properties of a Trinuclear Mixed‐Valence Co^III‐Co^II‐Co^III Complex with Carboxamido N and Sulfinato S Donors

Abstract

Abstract Air oxidation of the six‐coordinate (Et 4 N) 2 [Co(N 2 S 2 )(CN)(CH 3 CN)] complex derived from N , N ′‐(3‐mercapto‐3‐methylbutyryl)‐ o ‐phenylenediamine results in the formation of the trinuclear mixed‐valence complex (Et 4 N) 4 {Co II [Co III {N 2 (SO 2 ) 2 }(CN)(OH)] 2 } ( 3 ) where the thiolates have been oxidized to sulfinates. Its X‐ray structure reveals a linear arrangement of cobalt ions with bridging hydroxides and sulfinates. All cobalt ions are in a distorted octahedral environment. The mixed‐valence nature of this complex has been demonstrated by temperature‐dependent magnetic susceptibility measurements and by EPR spectroscopy both in the solid state and in solution. These data are in agreement with a high‐spin Co II . The IR spectrum shows the typical vibrations of cyanide and sulfinate at 2130 cm −1 (ν CN ), 1175 (ν as/SO2 ) and 1030 cm −1 (ν s/SO2 ). Trapping of Co II by chelex chromatography after treatment with aqueous HCl, or ” in situ” in aqueous solution, yields six‐coordinate low‐spin complexes with two different axial ligands Na 3 [Co{N 2 (SO 2 ) 2 }(CN)(Cl)] ( 5a ) and (Et 4 N) 2 [Co{N 2 (SO 2 ) 2 }(CN)(H 2 O)] ( 5b ). The p K a of the bound water molecule was estimated as 10.1 by pH‐metric titration. While 3 and 5a were inactive toward acetonitrile hydration, 5b catalyzes acetamide formation at 50 °C and pH 4.7 and 7 with low efficiency. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)