FLASH-PHOTOLYSIS STUDIES OF THE REACTIONS OF DINUCLEAR MANGANESE CARBONYL-COMPOUNDS WITH TRIBUTYLTIN HYDRIDE AND TRIETHYLSILANE

The reactions of Mn2(CO)8L2 (L = CO, PMe3, P(n-Bu)3, P(i-Bu)3, P(i-Pr)3, P(C6H11)3) With HSnBu3 and of Mn2(CO)10 with HSiEt3 were studied via flash photolysis, employing a conventional xenon flash lamp apparatus. The flash photolysis results are consistent with the conclusions based on continuous photolysis studies. The predominant reaction involves oxidative addition of the hydride to manganese at the site of CO loss. The rate of oxidative addition decreases as the steric requirements of L increase. Following oxidative addition, reductive elimination occurs. For HSnBu3, HMn(CO)4L and Bu3SnMn(CO)3L are formed. In the reaction of HSiEt3 with Mn2(CO)10, reformation of HSiEt3 dominates over formation of HMn(CO)5. The lifetime of the intermediate product resulting from the initial addition varies greatly with L. For small L, such as CO or PMe3, the intermediate persists for several seconds. With increasing size of L the addition process is slowed and the rate of elimination increases. A complete model for the reaction systems takes account of the semibridging form of the CO-loss product as the prevalent species in a noncoordinating solvent. Detailed modeling of the reaction system indicates that the on-off equilibrium involving coordination of the semibridging CO to the vacant manganese site is kinetically important. Formation of the semibridging form from the open form appears to have a significant energy barrier.