Rhodium complexes with planar-chiral cyclopentadienyl ligands: synthesis from tert -butylacetylene and catalytic performance in C-H activation of arylhydroxamates.

The rhodium complex [(C 5 H 2 t Bu 2 CH 2 t Bu)RhCl 2 ] 2 with an asymmetric cyclopentadienyl ligand was prepared in 95% yield by the reaction of [(cod)RhCl] 2 with tert -butylacetylene in the presence of AlCl 3 . A similar reaction in the presence of InBr 3 gave the cationic fulvene complex [(C 5 H 2 t Bu 2 = CH t Bu)Rh(cod)]InBr 4 (70%), which can add alcohols ROH and produce more bulky catalysts [(C 5 H 2 t Bu 2 CH(OR) t Bu)RhCl 2 ] 2 . The enantiomers of these planar-chiral complexes were separated by thin-layer chromatography in the presence of L-phenylglycinol. The complexes catalyze the reactions of arylhydroxamates with alkenes giving dihydroisoquinolones in excellent yields (80-90%), but with moderate enantioselectivity (typically 20-50% ee).