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.