Synthesis and structure of some group VII 1,2-diacyl cyclopentadiene complexes and their pyridazine derivatives

A series of 1,2-diacyl cyclopentadienyl tricarbonyl manganese and rhenium complexes, [M(CO)(3){eta(5)-1,2-C5H3(CO-(R)(2)}] (3a-c and 4a-b), were isolated utilizing a straightforward, 3-step route. The synthetic pathway began with a 1,2-diacyl cyclopentadiene (fulvene), followed by the formation of its corresponding thallium salt and transmetallation with the appropriate pentacarbonyl metal bromide. X-ray crystallographic analysis and high-accuracy mass spectrometry confirmed the structures of the both the 4-methoxyphenyl and 4-chlorophenyl diacyl rhenium complexes, [Re(CO)(3){eta(5)-1,2-C5H3(CO-(4-OCH3) C6H4)(2)}] (4a) and [Re(CO)(3){eta(5)-1,2-C5H3(CO-(4-Cl)C6H4)(2)}] (4b). Diacyl complexes 3a-c and 4a-b were then ring-closed with hydrazine hydrate to form their corresponding pyridazine complexes,[M(CO)(3){eta(5)-1,2-C5H3(1,4-(R)(2)N2C2}] (5a-c and 6a-b), in good yields (60-83%). The pyridazyl ligands were found to be relatively labile, and recrystallization of the target complexes 5a-c and 6a-b afforded only the free pyridazine ligands.