KINETIC AND THERMODYNAMIC STUDIES OF CARBON-MONOXIDE INSERTION IN ALKYLOSMIUM(II) COMPLEXES AND COMPARISON WITH IRON(II) AND RUTHENIUM(II) ISOELECTRONIC COMPLEXES

The equilibrium constants of the reaction of cis,trans-[Os(CO)(2)(PMe3 )(2)(Me)I] 1c with carbon monoxide to give ris,trans-[Os(CO)(2)(PMe3)( 2)(COMe)I] 2e have been measured and compared with the values obtained for the isoelectronic complexes of iron and ruthenium. The kinetics o f the above reaction as well as of the analogous insertion reaction wi th C6H11NC, which affords trans-[Os(CO)(PhMe3)(2)(C6H11NC)(COMe)I] 3, has been investigated. The results are interpretable by the methyl mig ration mechanism. The crystal structure of the new complex 3 has been determined. Furthermore, the isomer trarzs,trans-[Os(CO)(2)(PMe3)(2)(M e)I] 1t has been synthesized by the photochemical isomerization of 1c in the solid state. The spectroscopic properties of the cis,trans (c) and trans,trans (t) isomers for the triad Fe, Ru and Os are compared.