BINDING AND ACTIVATION OF HALOCARBONS BY IRON(II) AND RUTHENIUM(II)

A series of cyclopentadienylruthenium(II) and -iron(II) complexes contain intact iodoalkanes, p-iodotoluene, or chelating (P, X) (ohalophenyl)diphenylphosphine (X = Cl, Br) ligands. The halocarbons coordinate via -donation of a halogen lone pair and retain their carbon-halogen bonds. The complexes are synthesized from the halocarbon, metal halide, and silver® ion. Full characterization shows that they are Ru(II) complexes of intact halocarbons rather than Ru(IV) products of oxidative addition. The crystal and molecular structure of one such complex, [Cp(CO)(PPh3)Ru(IC6H4-p-CH3)]PF6, is reported (P⥘, a =10.976 (3) Å, b = 11.329 (3) Å, c = 13.666 (4) Å, β = 102.62 (3)°, Z = 2, Rl = 0.054, R2 = 0.065). The iodoalkanes are activated by coordination, and the complexes cleanly and rapidly alkylate a wide range of inorganic and organic nucleophiles. In particular, carbon-carbon bonds can be formed with C-nucleophiles such as enamines. The halocarbon complex can be much more selective than free halocarbon for C-alkylation over N-alkylation. The iodoalkane complexes undergo ligand substitution with common coordinating solvents to produce the corresponding solvento complexes. The haloarene complexes are displaced only by nucleophiles. Equilibrium experiments demonstrate that the order of binding is chelated o-bromoarene > chelated o-chloroarene > iodomethane > p-iodotoluene. The presence of carbonyl groups on Ru makes the metal more electrophilic, resulting in slower ligand exchange and less selective alkylations. © 1990, American Chemical Society. All rights reserved.