Temperature-dependent reduction pathways of complexes fac-[Re(CO)3(N-R-imidazole)(1,10-phenanthroline)]+ (RÂ =Â H, CH3)

Peculiar reduction pathways of the complexes fac-[Re(imH)(CO)3(phen)]+ and fac-[Re(imCH3)(CO)3(phen)]+ (imH = imidazole, imCH3 = N-methylimidazole and phen = 1,10-phenanthroline) have been unravelled by performing combined cyclic voltammetric and in situ IR spectroelectrochemical experiments. In the temperature range of 293-233 K, the initial reduction of the phen ligand in [Re(imH)(CO)3(phen)]+ results in irreversible conversion of the imidazole ligand to 3-imidazolate by a rapid phen
- − → imH intramolecular electron transfer coupled with NH bond cleavage. This process is followed by second phen-localized 1e− reduction producing [ReI(3-im−)(CO)3(phen
- −)]−, similar to the analogous 2,2′-bipyridine complex. In contrast to the bpy analogue, the stability of the phen
- −-containing complexes is significantly affected by lowering the temperature. At 233 K, a secondary reaction occurs in both [Re(3-im−)(CO)3(phen
- −)]− and [Re(imCH3)(CO)3(phen
- −)]. The resulting products exhibit ν(CO) wavenumbers indistinguishable from those of the parent phen
- − complexes; however, their oxidation occurs at a considerably more positive electrode potential. It is proposed that these species are produced by a new CC bond formation between the C(2) site of 3-im− or imCH3 and the C(2) site of the phen
- − ligand.