Phenylcyanamidoruthenium Scorpionate Complexes

Nine [Ru­(Tp)­(dppe)­L] complexes, where Tp is hydrotris­(pyrazol-1-yl)­borate, dppe is ethylenebis­(diphenylphosphine), and L is (4-nitrophenyl)­cyanamide (NO2pcyd–), (2-chlorophenyl)­cyanamide (2-Clpcyd–), (3-chlorophenyl)­cyanamide (3-Clpcyd–), (2,4-dichlorophenyl)­cyanamide (2,4-Cl2pcyd–), (2,3-dichlorophenyl)­cyanamide (2,3-Cl2pcyd–), (2,5-dichlorophenyl)­cyanamide (2,5-Cl2pcyd–), (2,4,5-trichlorophenyl)­cyanamide (2,4,5-Cl3pcyd–), (2,3,5,6-tetrachlorophenyl)­cyanamide (2,3,5,6-Cl4pcyd–), and (pentachlorophenyl)­cyanamide (Cl5pcyd–), and the dinuclear complex [{Ru­(Tp)­(dppe)}2(μ-adpc)], where adpc2– is azo-4,4-diphenylcyanamide, have been prepared and characterized. The crystal structures of [Ru­(Tp)­(dppe)­(Cl5pcyd)] and [{Ru­(Tp)­(dppe)}2(μ-adpc)] reveal the RuII ion to occupy a pseudooctahedral coordination sphere in which the cyanamide ligand coordinates to RuII by its terminal nitrogen atom. For both complexes, the cyanamide ligands are planar, indicating significant π mixing between the cyanamide and phenyl moieties as well as the azo group in the case of adpc2–. The optical spectra of the nominally ruthenium­(III) species [Ru­(Tp)­(dppe)­L]+ were obtained through spectroelectrochemistry measurements and showed an intense near-IR absorption band. Time-dependent density functional theory calculations of these species revealed that oxidation of the ruthenium­(II) species led to species where partial oxidation of the cyanamide ligand had occurred, indicative of noninnocent character for these ligands. The spin densities reveal that while the 3-Clpycd species has substantial RuII(3-Clpycd0) character, the Cl5pycd species is a much more localized ruthenium­(III) complex of the Cl5pycd monoanion. Some bond order and charge distribution data are derived for these ruthenium­(III) species. The near-IR band is assigned as a quite complex mixture of d–d, 4dπ to L­(NCN) MLCT, and L­(NCN) to Ru 4d LMCT with even a scorpionate ligand component. Spectroelectrochemistry was also performed on [{Ru­(Tp)­(dppe)}2(μ-adpc)] to generate the mixed-valence state. The intense intervalence transition that is observed in the near-IR is very similar to that previously reported for [{Ru­(trpy)­(bpy)}2(μ-adpc)]2+, where trpy is 2,2′:6′,2″-terpyridine and bpy is 2,2′-bipyridine, and by analogy identifies [{Ru­(Tp)­(dppe)}2(μ-adpc)]+ as a delocalized mixed-valence complex.