Exceedingly Facile PhX Activation (X=Cl, Br, I) with Ruthenium(II): Arresting Kinetics, Autocatalysis, and Mechanisms

[(Ph3P)(3)Ru(L)(H)(2)] (where L= H-2 (1) in the presence of styrene, Ph3P(3), and N-2 (4)) cleave the Ph-X bond (X= Cl, Br, I) at RT to give [(Ph3P)(3)RuH(X)] (2) and PhH. A combined experimental and DFT study points to [(Ph3P)(3)Ru(H)(2)] as the reactive species generated upon spontaneous loss of L from 3 and 4. The reaction of 3 with excess PhI displays striking kinetics which initially appears zeroth order in Ru. However mechanistic studies reveal that this is due to autocatalysis comprising two factors: 1) complex 2, originating from the initial PhI activation with 3, is roughly as reactive toward PhI as 3 itself; and 2) the Ph-I bond cleavage with the just-produced 2 gives rise to [(Ph3P)(2)RuI2], which quickly comproportionates with the still-present 3 to recover 2. Both the initial and onward activation reactions involve PPh3 dissociation, PhI coordination to Ru through I, rearrangement to a eta(2)-PhI intermediate, and Ph-I oxidative addition.