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

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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 [NBun 4][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).

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