Synthesis, Structure, and Hydrothiolation Activity of Rhodium Pyrazolylborate Complexes

A series of rhodium pyrazolylborate complexes [Tp R Rh(PPh 3 ) 2 ] {Tp R = HBR‘ 3, R‘ = 3,5-dimethylpyrazolyl ( 1 ), pyrazolyl ( 3 ), 3-phenylpyrazolyl ( 4 ), or 3-phenyl-5-methylpyrazolyl ( 5 )} and [Bp R Rh(PPh 3 ) 2 ] {Bp R = H 2 BR‘ 2, R‘ = 3,5-dimethylpyrazolyl (2)} were prepared from [ClRh(PPh 3 ) 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.