Influence of Cyclopentadienyl Ring-Tilt on Electron-Transfer Reactions: Redox-Induced Reactivity of Strained [2] and [3]Ruthenocenophanes

In contrast to ruthenocene [Ru(η5-C5H5)2] and dimethylruthenocene [Ru(η5-C5H4Me)2] (7), chemical oxidation of highly strained, ring-tilted [2]ruthenocenophane [Ru(η5-C5H4)2(CH2)2] (5) and slightly strained [3]ruthenocenophane [Ru(η5-C5H4)2(CH2)3] (6) with cationic oxidants containing the non-coordinating [B(C6F5)4]− anion was found to afford stable and isolable metal[BOND]metal bonded dicationic dimer salts [Ru(η5-C5H4)2(CH2)2]2[B(C6F5)4]2 (8) and [Ru(η5-C5H4)2(CH2)3]2[B(C6F5)4]2 (17), respectively. Cyclic voltammetry and DFT studies indicated that the oxidation potential, propensity for dimerization, and strength of the resulting Ru[BOND]Ru bond is strongly dependent on the degree of tilt present in 5 and 6 and thereby degree of exposure of the Ru center. Cleavage of the Ru[BOND]Ru bond in 8 was achieved through reaction with the radical source [(CH3)2NC(S)S[BOND]SC(S)N(CH3)2] (thiram), affording unusual dimer [(CH3)2NCS2Ru(η5-C5H4)(η3-C5H4)C2H4]2[B(C6F5)4]2 (9) through a haptotropic η5–η3 ring-slippage followed by an apparent [2+2] cyclodimerization of the cyclopentadienyl ligand. Analogs of possible intermediates in the reaction pathway [C6H5ERu(η5-C5H4)2C2H4][B(C6F5)4] [E=S (15) or Se (16)] were synthesized through reaction of 8 with C6H5E[BOND]EC6H5 (E=S or Se).status: publishe