REACTION-MECHANISMS OF METAL-METAL BONDED CARBONYLS .20. SUBSTITUTION AND FRAGMENTATION REACTIONS OF UNDECACARBONYL(TRIPHENYLPHOSPHINE) TRIRUTHENIUM AND DECACARBONYLBIS(TRIPHENYLPHOSPHINE)TRIRUTHENIUM

Kinetic studies are reported of reactions in decalin of the complexes Ru3(CO)11(PPh3) and Ru3(CO)10(PPh3)2. At moderate temperatures (25-75 °C) they undergo substitution reactions with triphenylphosphine, but only Ru3(CO)10(PPh3)2 undergoes simple substitution with carbon monoxide. The retarding effect of CO on reactions with PPh3 is quantitatively consistent with a simple CO-dissociative mechanism, but the considerable labilization, compared with Ru3(CO)12, caused by the presence of PPh3 substituents suggests that a more complex mechanism may be operating. Equilibrium constants for the substitution reactions were determined and found to depend very little on temperature. At higher temperatures (130-170 °C) both complexes undergo fragmentation reactions leading to mononuclear complexes at rates that are independent of [CO] and [PPh3], The activation enthalpies for fragmentation of Ru3(CO)12-n(PPh3)n (n = 1, 2, or 3) increase dramatically with n with an almost compensating increase in ΔS*. This trend can be rationalized in terms of steric effects operating in the proposed intermediates Ru2(CO)8-n(PPh3)n (n = 0, 1, or 2). © 1978, American Chemical Society. All rights reserved.