Secondary ligand―metal interactions in rhodium(III) and iridium(III) phosphoramidite complexes

Abstract The synthesis, characterization, and application in asymmetric catalytic cyclopropanation of Rh(III) and Ir(III) complexes containing ( S a ,R C ,R C )-O,O′-[1,1′-binaphthyl-2,2′-diyl]-N,N′-bis[1-phenyl-ethyl]phosphoramidite ( 1 ) are reported. The X-ray structures of the half-sandwich complexes [MCl 2 (C 5 Me 5 )( 1 ,κ P )] (M = Rh, 2a ; M = Ir, 2b ) show that the metal–phosphoramidite bond is significantly shorter in the Ir(III) analog. Chloride abstraction from 2a (with CF 3 SO 3 SiMe 3 or with CF 3 SO 3 Me) and from 2b (with AgSbF 6 ) gives the cationic species [MCl(C 5 Me 5 )(1,2-η- 1 ,κ P )] + (M = Rh, 3a ; M = Ir, 3b ), which display a secondary interaction between the metal and a dangling phenethyl group (NCH(CH 3 )Ph) of the phosphoramidite ligand, as indicated by NMR spectroscopic studies. Complexes 3a and 3b slowly decompose in solution. In the case of 3b , the binuclear species [Ir 2 Cl 3 (C 5 Me 5 ) 2 ] + is slowly formed, as indicated by an X-ray study. Preliminary catalytic tests showed that 3a cyclopropanates styrene with moderate yield (35%) and diastereoselectivity (70:30 trans : cis ratio) and with 32% ee (for the trans isomer).