Control of the migratory aptitudes of vinyl and aryl ligands in ruthenium(II) complexes

Abstract

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 phosphorus 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 organic ligands has migrated onto a carbonyl ligand. Vinyl migration products ( 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 structure 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 electron-donating substituents on the vinyl ligand, electron-withdrawing substituents on the aryl ligand, good σ-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) 2 is independent of t BuNC concentration: k =1.5 × 10 −3 s −1 at 20°C. Isomer 3 of complexes Ru(CO) 2 (CH=CHR) (C 6 H 4 X-4)L 2 in which the phosphorus ligands are mutually trans is much less reactive towards migration reactions. The reactivity of isomer 1 is attributed to the steric strain of two mutually cis phosphorus ligands.