Carbon−Carbon vs Carbon−Hydrogen Bond Activation by Ruthenium(II) and Platinum(II) in Solution

Abstract

Reaction of RuCl2(PPh3)3 with the bisphosphine {1,3,5-(CH3)3-2,6-(iPr2PCH2)2C6H} (1) under 30 psi H2 results in quantitative C−C activation of an Ar−CH3 bond to afford Ru(Cl)(PPh3){2,6-(iPr2PCH2)2-3,5-(CH3)2C6H} (2) and CH4, whereas reaction of RuCl2(PPh3)3 with 1 in the presence of NaOtBu results in selective ArCH2−H bond activation to afford the benzylic complex Ru(Cl)(PPh3){1-CH2-2,6-(iPr2PCH2)2-3,5-(CH3)2C6H} (7). The identity of the 16-electron complex 2 was confirmed by reaction of the bisphosphine {2,6-(iPr2PCH2)2-3,5-(CH3)2C6H2} (3), lacking the Ar−CH3 group between the phosphine arms, with RuCl2(PPh3)3. Metal insertion into an Ar−Et bond was observed as well. Follow-up of the reaction of RuHCl(PPh3)3 with 1 by NMR and deuterium labeling studies reveal that the kinetic products of ArCH2−H bond activation (7 and H2) are irreversibly converted into the thermodynamically more stable products of Ar−C bond activation (2 and CH4) via reversal of the C−H activation process. Reaction of (COD)PtCl2 (COD = ...