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

Peculiar reduction pathways of the complexes fac-[Re(imH)(CO)(3)(phen)](+) and fac-[Re(imCH(3))(CO)(3) (phen)(+) (imH = imidazole, imCH(3) = 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(center dot-) -> imH intramolecular electron transfer coupled with N-H bond cleavage. This process is followed by second phen-localized 1e(-) reduction producing [Re-I(3-im(-))(CO)(3)(phen(center dot-))](-), similar to the analogous 2,2'-bipyridine complex. In contrast to the bpy analogue, the stability of the phen(center dot-)-containing complexes is significantly affected by lowering the temperature. At 233 K, a secondary reaction occurs in both [Re(3-im-)(CO)(3)(phen(center dot-))](-) and [Re(imCH(3))(CO)(3)(phen(center dot-))]. The resulting products exhibit nu(CO) wavenumbers indistinguishable from those of the parent phen(center dot-) complexes; however, their oxidation occurs at a considerably more positive electrode potential. It is-proposed that these species are produced by a new C-C bond formation between the C(2) site of 3-im(-) or imCH(3) and the C(2) site of the phen(center dot-) ligand. (C) 2013 Elsevier Ltd. All rights reserved.