Alkyne Insertion into the Ru−C Bond of a Four-Membered Metallacycle. Insertion Rate and Reaction Pathway

The insertion of HOCH2C⋮CH (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 PhC⋮CH (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.