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

Reactions of diazocyclopentacliene 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) (80degreesC, CF3C6H5) to give (eta(5)-1 2,3-C5HBr3)M(CO)(3) (3; M = a, Re; b, Mn) and (eta(5) -C5HBr4)M(CO)(3) (4a,b) in 75-85% yields. In the case of 4a, the intermediate ill-cyclopentadienyl complex (eta(1)-C5HBr4)Re(CO)(5) (4'a) can be isolated (44%). An isomer of 3b, (eta(5)- 1,2,4-C5H2Br3)Mn(CO)(3), is accessed by desilylating previously reported (eta(5)-1,2,4-C-5(SiMe3)(2)Br-3)Mn(CO)(3) with CsF/MeOH (85%). The reaction of tetrabromodiazocyclopentadiene and BrRe(CO)(5) at 80degreesC in CF3C6H5 gives the eta(1)-cyclopentadienyl complex (eta(1) -C5Br5)Re(CO)(5) (5'a, 74%) which cannot be induced to decarbonylate to (eta(5) -C5Br5)Re(CO)(3) (5a) under a variety of conditions. However, 5a can be isolated (45%) when a similar reaction is conducted at 120degreesC. The IR properties of the preceding complexes are compared, and the crystal structures of 3a, 3b, 5a, and 5'a are determined and analyzed. (C) 2004 Elsevier B.V. All rights reserved.