Regioselective electrophilic substitution and addition reactions at an N-coordinated pyrrolyl ligand in (PMe2Ph)(3)Cl2Re(NC4H4)

The reaction of excess pyrrolyllithium with mer-(PMe2Ph)(3)ReCl3 leads to t he formation of the air-stable product mer-(PMe2Ph)(3)Cl2Re(NC4H4) (1), whi ch has been characterized by spectroscopic techniques and by an X-ray diffr action study. Complex 1 reacts with electrophiles to form new Re(III) compl exes with regioselectively substituted pyrrolyl ligands. For example, react ion with 1 equiv of N-chlorosuccinimide forms the complex with a 3-chloropy rrolyl ligand, while reaction with excess reagent produces the 3,4-dichloro pyrrolyl and 2,3,4-trichloropyrrolyl complexes. The regiochemistry of the r eactions has been established from the H-1 NMR data, and the structure of t he dibrominated product (PMe2Ph)(3)Cl2Re(3,4-NC4H2Br2) (5) has been confirm ed by X-ray diffraction. Reaction of 1 with methyl triflate produces after workup (PMe2Ph)(3)Cl2Re(3-NC4H3Me) (6), and further reaction of 6 with meth yl triflate yields (PMe2Ph)(3)Cl2Re(3,4-NC4H2(Me)(2)) (7). In contrast, tri flic acid protonates the pyrrolyl ligand of 1 at the alpha-carbon to form [ (PMe2Ph)(3)Cl2Re(NC4H5)]OTf (8), which has been isolated and identified by an X-ray diffraction study. The Michael addition of dimethyl acetylenedicar boxylate to the beta-carbon of the pyrrolyl ligand in 1 has also been chara cterized. Methods for the removal of the substituted pyrrolyl ligands from the rhenium center are described.