CONTROL OF THE MIGRATORY APTITUDES OF VINYL AND ARYL LIGANDS IN RUTHENIUM(II) COMPLEXES

Complexes Ru(CO)(2)(CH=CHR) (C(6)H(4)X-4) L(2) (R = (t)Bu, Ph, OEt; X = H, Cl, OMe; L = PMe(3), PMe(2)Ph, P(OMe)(2)Ph) in which the two phos phorus ligands are mutually cis (isomer 1) react readily with ligands (t)BuNC, CO and P(OMe)(3) to give complexes in which one of the organi c ligands has migrated onto a carbonyl ligand. Vinyl migration product s (5) retain the mutually cis geometry of the phosphorus ligands, and are unstable: one of the decomposition products is the ketone RCH=CHC( O) C(6)H(4)X-4. Phenyl migration products (4) are stable and have the phosphorus ligands in mutually trans positions; an X-ray crystal struc ture of Ru(CO) (CN(t)Bu) (C(O)Ph) (CH=CHPh) (PMe(2)Ph)(2) was obtained . In both cases, the incoming ligand enters trans to the newly formed acyl ligand. Vinyl migration is favoured over aryl migration by electr on-donating substituents on the vinyl ligand, electron-withdrawing sub stituents on the aryl ligand, good a-donor phosphorus ligands and use of (t)BuNC as the incoming ligand. The rate of phenyl migration in Ru( CO)(2)(CH=CHPh)Ph(PMe(2)Ph)(,) is independent of (t)BuNC concentration : k = 1.5 X 10(-3) s(-1) at 20 degrees C. Isomer 3 of complexes Ru(CO) (2)(CH=CHR) (C(6)H(4)X-4)L(2) in which the phosphorus ligands are mutu ally trans is much less reactive towards migration reactions. The reac tivity of isomer 1 is attributed to the steric strain of two mutually cis phosphorus ligands.