Synthesis of methyl acetate from methanol catalyzed by [(η5-C5H5)(phosphine)2RuX] and [(η5-C5H5)(phosphine)2Ru(SnX3)] (X=F, Cl, Br):: ligand effect

Monometallic Ru and heterobimetallic complexes containing Ru-Sn bonds, [(eta (5)-C5H5) P2RuX] and [(eta (5)-C5H5)P2Ru-(SnX3)], where P=PPh3, PPh2Me, P-2=1,2-bis(diphenilphosphine) ethane (dppe), and X=F, Cl, Br, were synthesized and characterized. These complexes were tested as catalysts in a single-step methanol conversion to acetic acid (methyl acetate) in the absence of CO. All complexes showed a high selectivity with their catalytic activity being strongly dependent on the nature of the ligands P and X. The effect of the ligand P showed the order of PPh3> PPh2Me congruent to dppe and the halogen effect: F > Cl congruent to Br and SnF3> SnCl(3)congruent to SnBr3. Heterobimetallic complexes showed ca. doubled activities compared to their monometallic analogues, indicating the importance of the Ru-Sn bond in a catalytic active specie. The order of catalytic activities followed the increase in the positive charge on the ruthenium atom, which was confirmed by P-31 and Sn-119 NMR spectroscopy and X-ray diffraction techniques. The obtained data support the mechanistic view of acetic acid formation by dehydrogenation of methanol giving formaldehyde via the rate-determining P-hydrogen abstraction in the Ru(II)-OMe intermediate, followed by formaldehyde dimerization into acetic acid. (C) 2000 Elsevier Science B.V. All rights reserved.