Re2(CO)10-mediated carbon-hydrogen and carbon-sulfur bond cleavage of dibenzothiophene and 2,5-dimethylthiophene

Ultraviolet photolysis of Re-2(CO)lo and excess dibenzothiophene (DBT) in the noncoordinating solvent hexanes produces the S-bound eq-Re-2(CO)(9)(eta (1)(S)-DBT) (1) and the novel. C-H-cleaved DBT complex Re-2(CO)(8)(mu -C12H7S)(mu -H) (2) Under similar conditions, Re-2(CO)lo reacts with excess 2,5-dimethylthiophene (2,5-Me2T) to give the interesting C-S-cleaved 2,5-Me2T complex Re-2(CO)(7)(mu -2,5-Me2T) (3). The photolysis reactions of Re-2(CO)(10) with DBT and 2,5Me(2)T were inhibited by CO (1 atm)and also by the radical scavenger TEMPO, which suggests that both CO dissociation and homolytic Re-Re bond cleavage are involved. The eta (1)(S)-bound thiophene complexes 1 and Re-2(CO)(9)(eta (1)(S)-2,5-Me2T) (5) were prepared from Re2(CO)S(THF) (4). The DBT ligand in 1 is labile and rapidly (<2 min) reacts with CO (1 atm) to form Re-2(CO)(10) in 1,2-DCE. On the basis of its X-ray structure, complex 1 has one of the smallest tilt angles (<theta> = 113 degrees) observed for a metal-thiophene complex, which may be understood in terms of pi -back-bonding arguments. Complexes 1-3 were characterized by spectroscopic (IR, NMR) methods and by their structures that were determined by X-ray crystallography. Mechanisms for the formation of 1-3 are presented and discussed.