Secondary ligand-metal interactions in rhodium(III) and iridium(III) phosphoramidite complexes |
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Authors: | Tina Osswald |
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Institution: | Department of Chemistry and Applied Biosciences, ETH Zürich, CH-8093 Zürich, Switzerland |
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Abstract: | The synthesis, characterization, and application in asymmetric catalytic cyclopropanation of Rh(III) and Ir(III) complexes containing (Sa,RC,RC)-O,O′-1,1′-binaphthyl-2,2′-diyl]-N,N′-bis1-phenyl-ethyl]phosphoramidite (1) are reported. The X-ray structures of the half-sandwich complexes MCl2(C5Me5)(1,κP)] (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 CF3SO3SiMe3 or with CF3SO3Me) and from 2b (with AgSbF6) gives the cationic species MCl(C5Me5)(1,2-η-1,κP)]+ (M = Rh, 3a; M = Ir, 3b), which display a secondary interaction between the metal and a dangling phenethyl group (NCH(CH3)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 Ir2Cl3(C5Me5)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). |
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Keywords: | Secondary interactions Phosphoramidites Rhodium(III) Iridium(III) Cyclopropanation |
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