Reduction–oxidation properties of organotransition-metal complexes. Part 21. Synthesis and X-ray structural characterisation of the redox-related pair of cyclohexadienyl complexes [Mn(CO)(dppe)(η5-C6H6Ph)] and [Mn(CO)(dppe)(η5-C6H6Ph)][PF6]·0.5CH2Cl2

Abstract

The cyclohexadienyl complexes [Mn(CO)_3–nL_n(η⁵-C₆H₆Ph)][la, n= 1, L = PPh₃; 1b, n= 2, L₂= Ph₂PCH₂CH₂PPh₂(dppe)], prepared by U.V. photolysis of [Mn(CO)₃(ηC₆H₆Ph)] and L, undergo reversible one-electron oxidation at a platinum electrode in CH₂Cl₂. The paramagnetic salt [Mn(CO)(dppe)(η-⁵C₆H₆Ph)][PF₆](2) is isolable from the reaction between (1b) and [Fe(η-C₅H₅)₂][PF₆]. X-Ray structural studies on (1b) and (2)·0.₅CH₂Cl₂ show the most pronounced effects of oxidation to be on the mean Mn–P distances which change from 2.221 Å in (1b) to 2.338 Å in (2). The effect on the conformation of the Mn(CO)(dppe) unit relative to the cyclohexadienyl moiety is small; in both complexes the CO ligand lies beneath the saturated ring carbon, giving approximate C_s symmetry to (1b) and (2). The structural consequences of one-electron oxidation on the geometry about the metal and within the ligands are discussed with regard to the nature of the highest occupied molecular orbital of (1b) and its depopulation in (2).