Re2(CO)10-Mediated Carbon−Hydrogen and Carbon−Sulfur Bond Cleavage of Dibenzothiophene and 2,5-Dimethylthiophene

Ultraviolet photolysis of Re 2 (CO) 10 and excess dibenzothiophene (DBT) in the noncoordinating solvent hexanes produces the S-bound eq -Re 2 (CO) 9 (η 1 ( S )-DBT) ( 1 ) and the novel C−H-cleaved DBT complex Re 2 (CO) 8 (μ-C 12 H 7 S)(μ-H) ( 2 ). Under similar conditions, Re 2 (CO) 10 reacts with excess 2,5-dimethylthiophene (2,5-Me 2 T) to give the interesting C−S-cleaved 2,5-Me 2 T complex Re 2 (CO) 7 (μ-2,5-Me 2 T) ( 3 ). The photolysis reactions of Re 2 (CO) 10 with DBT and 2,5-Me 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 η 1 (S)-bound thiophene complexes 1 and Re 2 (CO) 9 (η 1 ( S )-2,5-Me 2 T) ( 5 ) were prepared from Re 2 (CO) 9 (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 (θ = 113°) observed for a metal−thiophene complex, which may be understood in terms of π-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.