The complexes Cp*Ru(NO)(CH2Cl)Cl and Cp*Ru(NO)(CH2Cl)2 are formed in a stepwise fashion by treating Cp*Ru(NO)Cl2 with ethereal diazomethane in the presence of Cu powder (Cp* = eta-5-C5Me5). Photolysis or thermolysis of Cp*Ru(NO)(CH2Cl)2 leads to the formation of ethylene and the reformation of Cp*Ru(NO)Cl2. Deuterium labeling studies show the ethylene to originate by an intramolecular coupling of CH2 groups. An X-ray analysis of Cp*Ru(NO)(CH2Cl)2 reveals a nearly symmetric C(s) molecular geometry, with a ''vertical'' face-to-face orientation of the cis-bis(chloromethyl) ligands. The (C-Ru-C) angle of 79.4 (5)degrees between the chloromethyl ligands is somewhat acute, placing the nonbonded methylene carbon atoms at a separation of 2.68 angstrom: monoclinic space group P2(1)/n, a = 7.083 (4) angstrom, b = 17.723 (4) angstrom, c = 12.055 (5) angstrom; beta = 94.27 (4)degrees; R/R(w) = 5.50%/5.50%. H-1 NOE NMR experiments on the bis(chloromethyl) complex indicate that the ''vertical'' chloromethyl methylene orientation seen in the solid state is also preferred in solution. The mechanistic aspects of ethylene extrusion are discussed in terms of a transition state, where one CH2Cl ligand undergoes migratory insertion to an ''ionized'' chloromethyl ligand, represented as Ru = CH2-delta+Cl-delta-. The beta-chloroethyl complex Cp*Ru(NO)Cl(CH2CH2Cl) expected from this process is apparently unstable to beta-Cl elimination, leading to ethylene extrusion and the reformation of Cp*Ru(NO)Cl2. Frontier orbital analysis based on the established theory of the CpRu(NO)R2 System suggests that the observed face-to-face orientation of the chloromethyl ligands is conducive to the migratory insertion. A filled metal d-pi orbital is correctly oriented for stabilizing the metal-methylidene-like Ru = CH2-delta+Cl-delta- interaction in the transition state.
