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

Complexes Ru(CO)2 (CH=CHR) (C6H4X-4)L2 (R=tBu, Ph, OEt; X=H, Cl, OMe; L=PMe3, PMe2Ph, P(OMe)2Ph) in which the two phosphorus ligands are mutually cis (isomer 1) react readily with ligands tBuNC, 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)C6H4X-4. Phenyl migration products (4) are stable and have the phosphorus ligands in mutually trans positions; an X-ray crystal structure of Ru(CO) (CNtBu) {C(O)Ph} (CH=CHPh) (PMe2Ph)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 tBuNC as the incoming ligand. The rate of phenyl migration in Ru(CO)2(CH=CHPh)Ph(PMe2Ph)2 is independent of tBuNC concentration: k=1.5 × 10−3 s−1 at 20°C. Isomer 3 of complexes Ru(CO)2(CH=CHR) (C6H4X-4)L2 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.