Synthesis and structure of luminescent Re I(CO) 3Cl complexes incorporating pyridyltriazine, pyrazinyltriazine and triazolopyridine chelation

Abstract

The triazine and triazolo ligands (general abbreviations, L) used in the present work are pyridyltriazine (L 1), pyrazinyltriazine (L 2) and triazolopyridine (L 3), respectively. The reaction of Re(CO) 5Cl with a slight excess of L in boiling benzene has furnished complexes of the type Re(CO) 3Cl(L). In dichloromethane solution the complexes display a band of moderate intensity in the visible region: Re I(CO) 3Cl(L 1), 433 nm; Re I(CO) 3Cl(L 2), 451 nm and Re I(CO) 3Cl(L 3) 440 nm. This band is tentatively assigned to a π(Re) → π ∗(L) MLCT excitation. The solutions are also fluorescent, the emission peaks lying at 679, 671 and 592 nm, respectively. The fluorescence is believed to originate from the 3MLCT state. The quantum yield in the three cases are 5.6 × 10 −4, 5.5 × 10 −4 and 0.036, respectively. Interestingly the L 3 complex is comparable with Ru ( bpy ) 3 2 + with regard to quantum yield. The IR and 1H NMR spectra of the chelates are reported. The complexes are electroactive in acetonitrile solution wherein an irreversible one-electron anodic oxidation (1.30–1.50 V ) is observed cyclic voltammetrically. The X-ray structures of the L 1 and L 3 complexes have been determined revealing distorted octahedral ReC 3N 2Cl coordination spheres. The carbon monoxide ligands are facially disposed. In both complexes the chelate rings make a satisfactory plane (mean deviation 0.03 Å). The average Re N, Re C and Re Cl lengths are unexceptional.