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

[(Ph(3)P)(3)Ru(L)(H)(2)] (where L=H(2) (1) in the presence of styrene, Ph(3)P (3), and N(2) (4)) cleave the Ph—X bond (X=Cl, Br, I) at RT to give [(Ph(3)P)(3)RuH(X)] (2) and PhH. A combined experimental and DFT study points to [(Ph(3)P)(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 [(Ph(3)P)(2)RuI(2)], which quickly comproportionates with the still‐present 3 to recover 2. Both the initial and onward activation reactions involve PPh(3) dissociation, PhI coordination to Ru through I, rearrangement to a η(2)‐PhI intermediate, and Ph—I oxidative addition.