FIRST-ORDER AND 2ND-ORDER MECHANISMS FOR OXIDATIVE ADDITION FOR BOUNDMETHYL DISULFIDE IN THE COMPLEX W(CO)(3)(PHEN) (MESSME)

The rate of oxidative addition of methyl disulfide in the complex W(CO )(3)(1,10-phenanthroline)(MeSSMe) in methylene chloride has been studi ed. The dominant reaction pathway is second order in metal complex and inhibited by excess methyl disulfide. Formation of a dinuclear comple x [W(CO)(3)(phen)](2)(MeSSMe) is proposed to lead to the transition st ate for cleavage of the sulfur-sulfur bond in the second-order mechani sm. In neat methyl disulfide, or in concentratred solutions of methyl disulfide at low metal complex concentrations, the reaction occurs at reduced rate and follows a first-order mechanism, Addition of Mo(CO)(3 )(1,10-phenanthroline)(MeSSMe) to the corresponding tungsten complex r esults in a ten-fold increase in the rate of oxidative addition of the tungsten complex and production of Mo(CO)(4)(1,10-phenanthroline) as the sole molybdenum-containing product, The faster rate of reaction in the presence of the molybdenum complex is attributed to the faster fo rmation of the heteronuclear dinuclear intermediate by initial loss of MeSSMe from the molybdenum versus tungsten center. Additional kinetic /mechanistic studies are described using a new flow-through FT-IR/micr oscope reaction system designed to allow convenient monitoring of smal l quantities of sensitive/hazardous reactants. (C) 1998 Elsevier Scien ce S.A.