Synthesis, Structure, and Hydrothiolation Activity of Rhodium Pyrazolylborate Complexes

A series of rhodium pyrazolylborate complexes [TpRRh(PPh3)2] {TpR = HBR‘3, R‘ = 3,5-dimethylpyrazolyl (1), pyrazolyl (3), 3-phenylpyrazolyl (4), or 3-phenyl-5-methylpyrazolyl (5)} and [BpRRh(PPh3)2] {BpR = H2BR‘2, R‘ = 3,5-dimethylpyrazolyl (2)} were prepared from [ClRh(PPh3)3] and KX (X = pyrazolylborate anion). Complexes 2−5 were characterized crystallographically. The solution structures of new complexes 4 and 5 were also examined by variable temperature NMR and IR spectroscopy. The catalytic activity of complexes 1−5 in alkyne hydrothiolation was then examined. It was found that disubstituted tris(pyrazolyl)borate complexes (1 and 5) give the best selectivity and yield in alkyne hydrothiolation with aliphatic thiols.