Abstract: | In aqueous acetonitrile (AN), Cu (I) forms the complexes Cu(AN)L+ and CuL with a series of substituted imidazoles (L). Stability constants logK of Cu(AN)+ + L ? Cu(AN)L+ and logβ2 were near 5 and 12, resp., log units for all ligands. The rate of autoxidation is described by ?dO2]/dt=CuL]2O2](ka/(1+kbCuL]) + (kcL]+kd)/(CuL] + keCu])), implying competition between one- or two-electron reduction of O2. The value of kc decreases from 5500M ?2S ?1 for unsubstituted imidazole to about 40M ?2S ?1 for 2-methylimidazole or 1,2-dimethyl-imidazole and essentially zero for the corresponding 2-ethyl-derivatives. On the other hand, ka and kb are much less influenced by the nature of the ligands, all values being near 5 · 104M ?2S ?1 and 103M ?1, respectively, for the complexes with the last four bases. Thus rather subtle sterical changes may strongly influence the relative importance of different pathways in the reduction of dioxygen by cuprous complexes. |