Synthesis, structure, and electronic calculations of group VII substituted pyridazines

A series of 5,6-fused ring cyclopentadienyl tricarbonyl manganese and rhenium complexes, [M(CO)(3){eta (5)-1,2-C5H3(1,4-(R)(2)N2C2}] (2a-3d) were isolated by employing an off-metal ring closure route. Reacting thallium cyclopentadienide (Cp) salts (1a-d) with [MBr(CO)(5)] (M = Mn, Re) provided pyridazyl complexes (2a-3d) in high yield (75-99 %). Spectroscopic characterization (NMR, IR, MS) confirmed the identity of the desired organometallic pyridazines. The off-metal synthetic pathway employed did improve upon the isolation of these complexes as compared to previously reported routes. The molecular and electronic structure of complexes 2a-3d and their optimal energy structures have been characterized with quantum chemistry calculations. Vibrational frequencies calculated were compared to their experimental counterparts. The excited state calculations predict that the dominant low-energy transition involves a ligand-to-metal charge transfer.