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)]+ (<b>3</b>) and [(η⁶-C₆Me₆)₂Ru₂ (μ-PPh₂)(μ-η¹:η²-CH–CHFc)(μ-H)]⁺ (<b>4</b>) have been synthesised in ethanol from ethynylferrocene and the dinuclear precursors [(η⁶-C₆Me₆)₂Ru₂ (μ-H)₃]⁺ (<b>1</b>) and [(η⁶-C₆Me₆)₂Ru₂(μ-PPh₂)(μ-H)₂]⁺ (<b>2</b>) respectively, and isolated as tetrafluoroborate salts. The spectroscopic data of <b>3</b> and <b>4</b> as well as the single-crystal X-ray diffraction analysis of [<b>4</b>][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 [<b>3</b>][BF4] and [<b>4</b>][BF4] as well as their parent compounds [<b>1</b>][BF₄] and [<b>2</b>][BF₄] have been studied by voltammetric techniques: Whereas <b>1</b> shows only an irreversible Ru(II)/Ru(III) oxidation, the phosphido-bridged derivative <b>2</b> displays two well-separated one-electron redox processes. In the case of <b>3</b> and <b>4</b>, the ferrocenyl substituents give rise to additional reversible ferrocene/ferrocenium waves.