OXIDATION OF RUTHENIUM HYDRIDES (ETA(5)-C5H4R)RU(PPH3)(2)H (R=H, TBU,CH2PH, CTOL(3)) - X-RAY CRYSTAL-STRUCTURE DETERMINATION OF (ETA(5)-C5H4(CTOL(3)))RU(PPH3)(2)H AND AN ELECTROCHEMICAL STUDY OF ITS STABLE CATION-RADICAL

The oxidation of a series of cyclopentadienylruthenium hydrides (eta(5 )-C5H4R)Ru(PPh3)(2)H (R=H, tBu, CH2Ph, CTol(3), CPh2(p-MeOC6H4)) has b een investigated by cyclic voltammetry. For R=H, tBu and CH2Ph, uncomp licated reversible oxidation processes are observed. For the trityl-su bstituted species (R = CTol(3), CPh2(p-MeOC6H4)), the cyclic voltammog rams indicate the presence of two isomeric cation radicals that exist in a dynamic equilibrium. It is suggested that this may be the result of an interaction between the 17-electron Ru center in the cation radi cal and the pi system in one aromatic ring to yield a weakly bonded 19 -electron adduct of the cation radical. The first ESR spectroscopic da ta for a 17-electron cyclopentadienylruthenium hydride cation radical are reported for (eta(5)-C5H(CTol(3)))Ru(PPh3)(2)H.+. The anisotropic ESR spectra showed no hyperfine structure. The X-ray crystal structure of the neutral hydride (eta(5)-C5H4(CTol(3)))Ru(PPh3)(2)H reveals a s terically crowded molecule in which the trityl group eclipses the hydr ide ligand. Two tolyl groups on the CTol(3) ring substituent are on th e same side of the Cp ring plane as the metal and induce steric repuls ions in the molecule. Crystal data for (eta(5)-C5H4(CTol(3)))Ru(PPh3)( 2)H: space group P-1, a=11.3505(3), b=14.3263(3), c=17.3172(4) Angstro m, alpha=102.005(1), beta=98.348(1), gamma=112.321(1)degrees, T=170 K, R-1(F>4 sigma(F))=0.067, wR(2)(I>2 sigma(I))=0.128.