Syntheses, spectroscopic properties and photochemistry of [Re(R)(Co)(3)(4,4 '-Me-2-bpy)] (R = alkyl) complexes

The complexes [Re(R)(CO)(3)(dmb)] (dmb = 4,4'-dimethyl-2,2'-bipyridine; R = CH3, CD3, Et, Bz, or iPr) were synthesized and their spectroscopic (H-1, a nd C-13 NMR, IR, UV-Vis, resonance Raman) properties were studied. Accordin g to the resonance Raman spectra the lowest-energy electronic transition ha s mainly MLCT character. It is therefore concluded that the (3)sigma(Re-R)p i*(dmb) state from which these complexes undergo homolysis of the Re-alkyl bond, is occupied by surface crossing from the nonreactive MLCT states. The [Re(CO)(3)(dmb)](.) radicals, formed by the homolysis reaction, were trapp ed by nitrosodurene and PPh3, and their adducts were identified with EPR sp ectroscopy. The thermal reactions of the radicals in different media were f ollowed with IR spectroscopy. (C) 1999 Elsevier Science S.A. All rights res erved.