Carbon-carbon vs carbon-hydrogen bond activation by ruthenium(II) and platinum(II) in solution

Reaction of RuCl2(PPh3)(3) with the bisphosphine {1,3,5-(CH3)(3)-2,6-((Pr2P CH2)-Pr-i)(2)C6H} (1) under 30 psi H-2 results in quantitative C-C activati on of an Ar-CH3 bond to afford Ru(Cl)(PPh3){2,6-((Pr2PCH2)-Pr-i)(2)-3,5-(CH 3)(2)C6H} (2) and CH4, whereas reaction of RuCl2(PPh3)(3) with 1 in the pre sence of (NaOBu)-Bu-t results in selective ArCH2-H bond activation to affor d the benzylic complex Ru(Cl)(PPh3){1-CH2-2,6-((Pr2PCH2)-Pr-i)(2)-3,5-(CH3) (2)C6H} (7). The identity of the 16-electron complex 2 was confirmed by rea ction of the bisphosphine {2,6-((Pr2PCH2)-Pr-i)(2)-3,5(CH3)(2)C6H2} (3, lac king the Ar-CH3 group between the phosphine arms, with RuCl2(PPh3)(3). Meta l insertion into an Ar-Et bond was observed as well. Follow-up of the react ion of RuHCl(PPh3)(3) with 1 by NMR and deuterium labeling studies reveal t hat the kinetic products of ArCH2-H bond activation (7 and Hz) are irrevers ibly converted into the thermodynamically more stable products of Ar-C bond activation (2 and CH4) via reversal of the C-H activation process. Reactio n of(COD)PtCl2 (COD = cycloocta-1,5-diene) with a stoichiometric amount of 1 at room temperature results in the exclusive formation of the benzylic Pt (II) complex Pt(Cl){1-CH2-2,6-((Pr2PCH2)-Pr-i)(2)-3,5-(CH3)(2)C6H} (8) and HCl. The iodide analogue of 8 has been characterized by X-ray analysis. Rea ction of 8 with a 10-fold excess of HCl results in selective C-C bond activ ation to afford Pt(Cl(2,6-((Pr2PCH2)-Pr-i)(2)-3,5-(CH3)(2)C6H} (10) and MeC l. The activation parameters for the overall process are Delta H double dag ger = 10.6 kcal/mol, Delta S double dagger = - 40.1 eu, and Delta G double dagger((298)) = 23.1 kcal/mol in a benzene/dioxane solution (5.5:1 v/v) and Delta H double dagger = 2.1 kcal/mol, Delta S double dagger = -65.4 eu, an d Delta G double dagger((298)) = 21.6 kcal/mol in dioxane.