Electronic Effects of the Substituents on the Catalytic Conversion of Thiolates to Alcohols by Carboxylate Bridged Nonheme Binuclear Fe(II) and Co(II) Complexes

Abstract

A detailed study for the catalytic hydrolysis of 10 thiolates and thiobenzoate at RT to alcohols/phenols and benzoic acid, respectively, by three new dicobalt(II) complexes, [Co₂(PhBIMP)(µ-O₂C-C₆H₃-2,6-(R¹)₂)(X)]²⁺ (R¹ = -OMe, X = DMF, 2d; R¹ = -F, X = MeCN, 2e) and [Co₂(PhBIMP)(µ-O₂C-C₆H₂-2,4,6-(OMe)₃)(DMF)]²⁺ (2f), and three new Fe(II) complexes, [Fe₂(PhBIMP)(µ-O₂C-C₆H₃-2,6-(R¹)₂)(X)]²⁺ (R¹ = -OMe, X = DMF, 4b; R¹ = -F, X = MeCN, 4c) and [Fe₂(PhBIMP)(µ-O₂C-C₆H₂-2,4,6-(OMe)₃)(DMF)]²⁺ (4d) is presented. The results showed that, (i) the Co(II) complexes (maximum yield = 94%, maximum TON = 38, 2f) are catalytically more efficient than the Fe(II) complexes (maximum yield = 72%, maximum TON = 29, 4d), and that (ii) the presence of the electron donating (-OMe) and electron withdrawing (-F) groups at the ortho-positions significantly increases and decreases, respectively, the catalytic efficiency. The key intermediates of the catalytic reactions and the fate of the catalysts have been identified and a plausible reaction mechanism has been proposed. The present work, thus, for the first time, demonstrates Fe(II) catalyzed hydrolysis of thiolates in comparison with analogous Co(II) complexes and offers so far the highest TON for the transition metal mediated catalytic hydrolysis of thiolates to alcohols/phenols.