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RESEARCH PRODUCT

Diastereospecific control in the synthesis of enantiomerically pure bis-equatorial rhodium(II) catalysts by chiral phosphanes

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The reaction of Rh2(O2CR)4 [R = CH3, CF3] with the chiral phosphane (1S,2S,5R)-(2-hydroxy-5-isopropenyl-2-methylcyclohexyl)(diphenyl)phosphane, (+)PPh2(CH−R*−OH) or its enantiomer (1R,2R,5S)-(2-hydroxy-5-isopropenyl-2-methylcyclohexyl)(diphenyl)phosphane, (−)-PPh2(CH−R*−OH), results in the specific formation of the products (P)-Rh2(μ-O2CR)2(η1-O2CR)2{η2-(+)PPh2(CH−R*−OH)}2 [P(+)1, R = CH3; P(+)2 R = CF3] and (M)-Rh2(μ-O2CR)2(η1-O2CR)2{η2-(−)-PPh2(CH−R*−OH)}2 [M(−)1, R = CH3; M(−)2, R = CF3] in a high yield. Their synthesis, characterisation and catalytic behaviour in metal−carbenoid reactions are reported. X-ray analysis of P(+)2 and M(−)2 shows, in each case, a Rh24+ unit supported by two bridging and two monodentate trifluoroacetates; two phosphanes, (+)PPh2(CH−R*−OH) or (−)PPh2(CH−R*−OH) respectively, acting as chelating equatorial (P) and axial (O) donor ligands, complete the coordination sphere. These compounds are a pair of enantiomers. The crystallographic parameters are as follow: for P(+)2, space group P3121 (trigonal) with a = b = 13.0366(8), c = 29.756(2) A, Z = 6 and R = 0.0499; for M(−)2 space group P32 (trigonal) with a = b = 12.9751(9), c = 29.685(3) A, Z = 3 and R = 0.0747.