Synthesis of methyl acetate from methanol catalyzed by [(eta(5)-C5H5)(phosphine)(2)RuX] and [(eta(5)-C5H5)(phosphine)(2)Ru(SnX3)] (X=F, Cl, Br): ligand effect

Monometallic Ru and heterobimetallic complexes containing Ru-Sn bonds, [(et a (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 synthesi zed 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 o f the ligand P showed the order of PPh3> PPh2Me congruent to dppe and the h alogen 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 ca talytic active specie. The order of catalytic activities followed the incre ase 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 obtain ed data support the mechanistic view of acetic acid formation by dehydrogen ation of methanol giving formaldehyde via the rate-determining P-hydrogen a bstraction in the Ru(II)-OMe intermediate, followed by formaldehyde dimeriz ation into acetic acid. (C) 2000 Elsevier Science B.V. All rights reserved.