C−H and C−S Activation of Thiophene by Rhodium Complexes:  Influence of the Ancillary Ligands on the Thermodynamic Stability of the Products

The reaction of thiophene with the rhodium compound [Tp*Rh(C 2 H 4 )(PMe 3 )] ( 1a; Tp* = hydrotris(3,5-dimethyl-1-pyrazolyl)borate) leads to a mixture of the C−H and C−S activation products [Tp*Rh(H)(2-C 4 H 3 S)(PMe 3 )] ( 2a ) and [Tp*Rh(CHCHCHCHS)(PMe 3 )] ( 3a ), respectively. In contrast to previous observations, the former is the thermodynamically preferred isomer. For the PEt 3 derivative [Tp*Rh(C 2 H 4 )(PEt 3 )] ( 1b ), an even higher selectivity toward C−H activation is observed.