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

The triazine and triazolo ligands (general abbreviations, L) used in the present work are pyridyltriazine (L1), pyrazinyltriazine (L2) and triazolopyridine (L3), 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: ReI(CO)3Cl(L1), 433 nm; ReI(CO)3Cl(L2), 451 nm and ReI(CO)3Cl(L3) 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 L3 complex is comparable with Ru(bpy)32+ 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 L1 and L3 complexes have been determined revealing distorted octahedral ReC3N2Cl 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 ReN, ReC and ReCl lengths are unexceptional.

The reaction of ReI(CO)5Cl with pyridyltriazine (L1), pyrazinyltriazine (L2) and triazolopyridine (L3) (general abbreviation L) has furnished complexes of the type ReI(CO)3Cl(L), A, in excellent yield. The X-ray structures of complexes incorporating the L1 and L3 ligands have been determined. The tricarbonylrhenium(I) complex of the triazolopyridine ligand is strongly fluorescent (A) whereas complexes with pyridyltriazine and pyrazinyltriazine ligands exhibit weak fluorescence in solution.Figure optionsDownload as PowerPoint slide