Rhenium Carbonyl Biradicals. Formation, Recombination, and Halogen Atom Transfer

Article abstract of DOI:10.1021/ja00269a024

The organometallic biradicals .(OC)4ReL<*>LRe(CO)4. (L<*>L = R2P(CH2)_nPR2; R = Me, Ph, Cy; n = 2-6 or cis-Ph2PCH=CHPPh2) have been observed as transient species following laser flash photolysis of the bridging ligand substituted dirhenium octacarbonyls, in which homolytic metal-metal bond cleavage is a dominant primary photoprocess and CO dissociation is negligible.The intramolecular recombination of these biradicals follows simple first-order kinetics.The rate constants for recombination show a slight solvent dependence probably related to viscosity and the sizes of solvent molecules.The rate constants are affected by steric requirements of the substituents on phosphorus atoms and geometry in the ligand backbone.The rate constants for halogen atom transfer to the biradicals, determined either by laser flash photolysis or by continuous photolysis, are characteristic of mononuclear rhenium carbonyl radicals with similar substituent environments.The metal-centered biradicals thus show typical monoradical behavior in their reactions such as recombination, halogen atom transfer, and electron transfer.