Alkyne insertion into the Ru-C bond of a four-membered metallacycle. Insertion rate and reaction pathway

The insertion of HOCH2CCH (ha) into the Ru-C bond of RuII(RL1)(PPh3)2(CO)Cl, 1, has afforded RuII(RL3)(PPh3)2(CO)Cl, 3, which has been structurally characterized. Insertion rates in CH2Cl2-MeOH for ha as well as for PhCCH (pa), which inserts similarly into 1 affording RuII(RL2)(PPh3)2(CO)Cl, 2, are proportional to the product of the concentrations of alkyne and methanol. The insertion rate of ha is nearly 5 times faster than that of pa, and for a given alkyne the rate increases as R becomes more electron-withdrawing (OMe < Me < Cl). A reaction model implicating the adduct 1·MeOH, which binds and activates the alkyne via displacement of MeOH, is proposed