Synthesis of five-coordinate manganese(I) carbonyl complex [(CO)3Mn (-S,-Se-C6H3-4-Me)]−: influences of non-innocent ligand to the structure, reactivity and electrochemical property

Abstract

Oxidative addition of Br2 to [Mn(CO)5]− leads to the formation of [(CO)4MnBr], followed by the ligand exchange of bromide to [S,Se-C6H3-4-Me] 2 2− to form complex (CO)3Mn (µ-ŋ 4-SC6H3-4-(CH3)Se-SeC6H3-4-(CH3)S)Mn(CO)3 (1). A new five-coordinate complex [(CO)3Mn(-S,-Se-C6H3-4-CH3)]− (2) can be synthesized through two different routes: (a) oxidative addition of diselenide [HS,Se-C6H3-4-Me]2 to the [Mn(CO)5]− followed by deprotonation and ligand dissociation to generate complex 2; (b) reduction of diselenide bonds of complex 1 by [BH4]− to produce 2. Drop-wise addition of HBF4·OEt2 at 0 °C results in the formation of complex 1. The X-ray analysis shows that complex 2 has relative short Mn–Se and Mn–S bond distances compare to the published structures of cis-[(CO)4Mn(EPh)2]− (E = S and Se; Liaw et al. in J. Chin. Chem. Soc. 43:427–431, 1996; Liaw et al. in Inorg. Chem. 35:2530, 1996). Interestingly, exposure of the coordinated unsaturated complex 2 under CO(g) atmosphere resulted in complex cis-[(CO)4Mn(-S,-Se-C6H3-4-Me)]− (3) being formed. After purging the solution of complex 3 with N2, it was reconverted completely back to complex 2; this observation was characterized by FTIR. The cyclic voltammetry scan of complex 2 shows a quasi-reversible redox couple with E 1/2 = −1.94 V and I pa/I pc = 0.68. Ligand [HS, Se-C6H3-4-CH3]2 and complexes 1 and 2 are all characterized by IR, UV–Vis, NMR, EA and X-ray single crystal diffraction.