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

Abstract

Ultraviolet photolysis of Re2(CO)10 and excess dibenzothiophene (DBT) in the noncoordinating solvent hexanes produces the S-bound eq-Re2(CO)9(η1(S)-DBT) (1) and the novel C−H-cleaved DBT complex Re2(CO)8(μ-C12H7S)(μ-H) (2). Under similar conditions, Re2(CO)10 reacts with excess 2,5-dimethylthiophene (2,5-Me2T) to give the interesting C−S-cleaved 2,5-Me2T complex Re2(CO)7(μ-2,5-Me2T) (3). The photolysis reactions of Re2(CO)10 with DBT and 2,5-Me2T 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 η1(S)-bound thiophene complexes 1 and Re2(CO)9(η1(S)-2,5-Me2T) (5) were prepared from Re2(CO)9(THF) (4). The DBT ligand in 1 is labile and rapidly (<2 min) reacts with CO (1 atm) to form Re2(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.