Ultrafast studies of metal-metal bond cleavage in Fe 3(CO) 12 in solution

Abstract

The ultrafast dynamics following metal-metal bond breaking in Fe 3(CO) 12 have been investigated. Following excitation at 590 nm, the ground state Fe 3(CO) 12 is converted to a coordinatively unsaturated isomer with bridging COs, Fe 3(CO) 12(unsat.), within the instrument response of 1.5 ps. The unsaturated isomer then returns to the ground state with an exponential time constant of 150 ps. This rate of isomerization back to the ground state implies a barrier of 4.3 kcal mol −1. This is in agreement with the results of Cotton and Hunter who put an upper limit of 6 kcal mol −1 on the isomerization of Fe 3(CO) 12 from an all terminal structure to a bridging structure. A portion (20%) of the excited molecules do not return to the ground state on the time scale of this experiment (< 1 ns). This is attributed to fermentation of Fe 3(CO) 12 to mono- and dinuclear species. Faster disapperance of the Fe 3(CO) 12(unsat.) at longer wavelengths indicates that fragmentation is promoted by excess vibrational energy.