Syntheses and structures of missing links among polybromocyclopentadienyl rhenium and manganese tricarbonyl complexes

Abstract

Reactions of diazocyclopentadiene and NBS at appropriate stoichiometries give 2,5-dibromodiazocyclopentadiene and 2,3,5-tribromodiazocyclopentadiene in 40% and 30% yields, respectively, after chromatography. These react with BrRe(CO) 5 or BrMn(CO) 5 (80 °C, CF 3C 6H 5) to give (η 5-1,2,3-C 5H 2Br 3)M(CO) 3 ( 3; M = a, Re; b, Mn) and (η 5-C 5HBr 4)M(CO) 3 ( 4a, b) in 75–85% yields. In the case of 4a, the intermediate η 1-cyclopentadienyl complex (η 1-C 5HBr 4)Re(CO) 5 ( 4′ a) can be isolated (44%). An isomer of 3b, (η 5-1,2,4-C 5H 2Br 3)Mn(CO) 3, is accessed by desilylating previously reported (η 5-1,2,4-C 5(SiMe 3) 2Br 3)Mn(CO) 3 with CsF/MeOH (85%). The reaction of tetrabromodiazocyclopentadiene and BrRe(CO) 5 at 80 °C in CF 3C 6H 5 gives the η 1-cyclopentadienyl complex (η 1-C 5Br 5)Re(CO) 5 ( 5′ a, 74%) which cannot be induced to decarbonylate to (η 5-C 5Br 5)Re(CO) 3 ( 5a) under a variety of conditions. However, 5a can be isolated (45%) when a similar reaction is conducted at 120 °C. The IR properties of the preceding complexes are compared, and the crystal structures of 3a, 3b, 5a, and 5′ a are determined and analyzed.