C-H activation reactions on Rh(I)-ethylene complexes of the hydrotris(3,5-dimethylpyrazolyl)borate ligand, Tp(Me2)

N-donor Lewis bases such as acetonitrile or pyridine react with the Rh(I) c ompound Tp(Me2)Rh(C2H4)(2) (1) to give the Rh(III) derivatives Tp(Me2)Rh(CH =CH2)(C2H5)(L) (2, 3) as the kinetic products of the reactions. Upon heatin g at 60 degrees C, the acetonitrile adduct 2 converts into Tp(Me2)Rh(C2H4)( NCMe) (5). Under similar conditions, 2 is able to induce the activation of one of the C-H bonds of C6H6, in a process that involves the intermediacy o f 1, as demonstrated by isotopic labeling studies. The phosphine adducts Tp (Me2)Rh(C2H4)(PR3) (R = Me, Et) are also efficient reagents for the C-H bon d activation of C6H6, py, or thiophene. In the latter case, rupture of the C-S bond is also detected, although the C-S bond activation complexes are t hermodynamically disfavored with respect to those derived from the cleavage of one of the alpha-C-H bonds.