Reduction–oxidation properties of organotransition-metal complexes. Part 29. Pentaphenylcyclopentadienyl complexes of ruthenium

Abstract

The complex [Ru₃(CO)₁₂] reacts with C₅Ph₅Br in toluene under reflux to give [RuBr(CO)₂(η-C₅Ph₅)](1) which undergoes carbonyl substitution with P-donor ligands, in acetone in the presence of ONMe₃·2H₂O, to yield [RuBr(CO)L(η-C₅Ph₅)][2; L = PPh₃, PEt₃, or P(OMe)₃]. The halide abstraction reactions of (2) with AgPF₆ and L¹ afford [Ru(CO)L(L¹)(η-C₅Ph₅)][PF₆][3; L = PEt₃ or P(OMe)₃; L¹= CO, C₂H₄, or MeCCMe], and the dicarbonyls [Ru(CO)₂L(η-C₅Ph₅)][PF₆][L = PEt₃ or P(OMe)₃] react with L¹, in acetone with ONMe₃·2H₂O, to give [3; L = L¹= PEt₃ or P(OMe)₃]. Complexes (1) and (2; L = PEt₃) react with LiMe in tetrahydrofuran, giving [RuMe(CO)₂(η-C₅Ph₅)](4) and [RuR(CO)(PEt₃)(η-C₅Ph₅)](5; R = Me) respectively, and (5; R = Et, COMe, or CMeCMe₂) are prepared from (3; L = PEt₃, L¹= C₂H₄) and [NBuⁿ₄][BH₄] or from (3; L = PEt₃, L¹= CO or MeCCMe) and LiMe. The neutral compounds (1), (2), (4), and (5) undergo diffusion-controlled one-electron oxidation at a platinum bead electrode in CH₂Cl₂. In most cases the electron-transfer process is fully reversible, but (1), (4), and [FeMe(CO)₂(η-C₅Ph₅)] show only irreversible cyclic voltammetric waves. The chemical oxidation of (2) with [N(C₆H₄Br-p)₃][SbCl₆] in CH₂Cl₂ gives the 17-electron cation (2⁺), and (5⁺) have also been characterised in solution after generation from (5) by AgPF₆ oxidation. Complexes (1) and (3) undergo diffusion-controlled but chemically irreversible reduction at the platinum electrode; reduction by [Co(η-C₅H₅)₂](i) of [3; L = P(OMe)₃, L¹= CO] gives a mixture of (4), [Ru{P(O)(OMe)₂}(CO)₂(η-C₅Ph₅)], and [RuCl(CO){P(OMe)₃}(η-C₅Ph₅)], (ii) of [3; L = P(OMe)₃, L¹= MeCCMe] gives [RuH(CO){P(OMe)₃}(η-C₅Ph₅)], and (iii) of (1) gives trans-[{Ru(µ-CO)(CO)(η-C₅Ph₅)}₂](6).