Influence of cyclopentadienyl ring-tilt on electron-transfer reactions: Redox-induced reactivity of strained 2 and 3 Ruthenocenophanes

In contrast to ruthenocene Ru((5)-C5H5)(2) and dimethylruthenocene Ru((5)-C5H4Me)(2) (7), chemical oxidation of highly strained, ring-tilted 2ruthenocenophane Ru((5)-C5H4)(2)(CH2)(2) (5) and slightly strained 3ruthenocenophane Ru((5)-C5H4)(2)(CH2)(3) (6) with cationic oxidants containing the non-coordinating B(C6F5)(4)(-) anion was found to afford stable and isolable metalmetal bonded dicationic dimer salts Ru((5)-C5H4)(2)(CH2)(2)(2)B(C6F5)(4)(2) (8) and Ru((5)-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 RuRu 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 RuRu bond in 8 was achieved through reaction with the radical source (CH3)(2)NC(S)SSC(S)N(CH3)(2) (thiram), affording unusual dimer (CH3)(2)NCS2Ru((5)-C5H4)((3)-C5H4)C2H4(2)B(C6F5)(4)(2) (9) through a haptotropic (5)-(3) ring-slippage followed by an apparent 2+2 cyclodimerization of the cyclopentadienyl ligand. Analogs of possible intermediates in the reaction pathway C6H5ERu((5)-C5H4)(2)C2H4B(C6F5)(4) E=S (15) or Se (16) were synthesized through reaction of 8 with C6H5EEC6H5 (E=S or Se)