Dinuclear hexamethylbenzene ruthenium cations containing η1:η2-2-(ferrocenyl)ethen-1-yl ligands: Synthesis, structure, electrochemistry

The cationic ferrocenyl-containing complexes [(η6-C6Me6)2Ru2(μ-η1:η2-CH–CHFc)2(μ-H)]+ (3) and [(η6-C6Me6)2Ru2(μ-PPh2)(μ-η1:η2-CH–CHFc)(μ-H)]+ (4) have been synthesised in ethanol from ethynylferrocene and the dinuclear precursors [(η6-C6Me6)2Ru2(μ-H)3]+ (1) and [(η6-C6Me6)2Ru2(μ-PPh2)(μ-H)2]+ (2) respectively, and isolated as tetrafluoroborate salts. The spectroscopic data of 3 and 4 as well as the single-crystal X-ray diffraction analysis of [4][BF4] show that the alkyne function of ethynylferrocene has been converted to a σ/π-ethenyl ligand by transfer of a bridging hydride from the diruthenium backbone onto the α-carbon of the triple bond in ethynylferrocene. The ferrocenyl-containing diruthenium compounds [3][BF4] and [4][BF4] as well as their parent compounds [1][BF4] and [2][BF4] have been studied by voltammetric techniques: Whereas 1 shows only an irreversible Ru(II)/Ru(III) oxidation, the phosphido-bridged derivative 2 displays two well-separated one-electron redox processes. In the case of 3 and 4, the ferrocenyl substituents give rise to additional reversible ferrocene/ferrocenium waves.