Kinetic study of the reaction of ferrocenes and ferrocenium ions with ground and excited states of tris (2,2\u27-bipyridine) chromium ions and the preparation and homolysis of organocobalt complexes

摘要

The kinetics of quenching of [superscript]*Cr(bpy)[subscript]3[superscript]3+ by d[superscript]6 metallocenes and by ferrocenium ions were studied by laser flash photolysis. The quenching by ferrocenium ions proceeds by energy transfer and is dependent on the donor-acceptor distance, as expected for an electron-exchange mechanism. The rate constants for quenching with d[superscript]6 metallocenes are at or near the diffusion-controlled limit. The reactions partition themselves between electron transfer and energy transfer. The Cr(bpy)[subscript]2[superscript]2+ and the ferroceniums, formed by electron transfer quenching, undergo rapid back electron transfer, k = (3 - 9) x 10[superscript]9 M[superscript]-1s[superscript]-1;The preparations of a series of organocobalt complexes, RCo(Me[subscript]6 (14) 4,11-dieneN[subscript]4)[superscript]2+ and RCo(Me[subscript]6 (14) aneN[subscript]4)[superscript]2+ (R = primary and substituted primary alkyl group), are presented. The complexes were characterized by [superscript]1H NMR spectroscopy, UV-visible spectroscopy and a crystal structure determination for ClCH[subscript]2Co(Me[subscript]6 (14) 4,11-dieneN[subscript]4) (H[subscript]2O) (ClO[subscript]4)[subscript]2;The unimolecular homolysis have been studied for some of these complexes. The Co-C bond energy is about 23 Kcal/mol for these complexes. The rates of the alkyl group transfer from CoL[superscript]2+ to Cr[superscript]2+(L = Me[subscript]6 (14) 4,11-dieneN[subscript]4 and Me[subscript]6 (14) aneN[subscript]4) show a strong dependence of steric effect on the alkyl group, consistent with a S[subscript] H2 mechanism.