Ethyl diazoacetate reacts with [PtX2L2] [X = Cl, Br, I; L2 = 1,5-cyclooctadiene (cod), 2 PPh3, Ph2P-(CH2)nPPh2, n = 1 (dppm), 2 (dppe), 3 (dppp), 4 (dppb)] to give the corresponding [PtX(CHXCO2Et)L2] as a racemic mixture in high yields. The cod ligands in [PtX(CHXCO2Et)(cod)] are readily displaced by PPh3 or diphosphines. When optically active complexes [PtX2L*] (X = Cl, I; L* = R,R-diop, S,S-chiraphos, S,S-skewphos) were treated with ethyl diazoacetate, the products [PtX(CHXCO2Et)L*] were mixtures of diastereoisomers in different proportions. The major diastereoisomer of [PtCl(CHClCO2Et) (R,R-diop)] was readily separated by fractional crystallization, and its crystal structure revealed that the configuration at the α-carbon was R. This compound is configurationally stable for at least 14 d in CDCl3 solution as shown by 31P NMR spectroscopy. Treatment of pure [PtCl(CHClCO2Et)(R,R-diop)] with S,S-skewphos led to exchange of diphosphines and thereby the assignment of the S configuration at the α-carbon of the major product of the reaction of [PtCl2(S,S-skewphos)] with ethyl diazoacetate. With the aim of optimizing the diastereoeelectivity of the insertion reaction, the chiral diazo ester N2CHCO2R (R = R,R-menthyl) was used as the reagent but it was found that the diastereoselectivities were similar to those with N2CHCO2Et. The highest diastereoselectivities (up to 7:1) were obtained with N2CHCOPh. © 1992, American Chemical Society. All rights reserved.
Diastereoselective Carbene Insertions into Platinum–Halogen bonds. Crystal Structure of [PtCl(R-CHClCO2Et)(R,R-diop)]
BERGAMINI, Paola;COSTA, Emiliana;SOSTERO, Silvana;
1992
Abstract
Ethyl diazoacetate reacts with [PtX2L2] [X = Cl, Br, I; L2 = 1,5-cyclooctadiene (cod), 2 PPh3, Ph2P-(CH2)nPPh2, n = 1 (dppm), 2 (dppe), 3 (dppp), 4 (dppb)] to give the corresponding [PtX(CHXCO2Et)L2] as a racemic mixture in high yields. The cod ligands in [PtX(CHXCO2Et)(cod)] are readily displaced by PPh3 or diphosphines. When optically active complexes [PtX2L*] (X = Cl, I; L* = R,R-diop, S,S-chiraphos, S,S-skewphos) were treated with ethyl diazoacetate, the products [PtX(CHXCO2Et)L*] were mixtures of diastereoisomers in different proportions. The major diastereoisomer of [PtCl(CHClCO2Et) (R,R-diop)] was readily separated by fractional crystallization, and its crystal structure revealed that the configuration at the α-carbon was R. This compound is configurationally stable for at least 14 d in CDCl3 solution as shown by 31P NMR spectroscopy. Treatment of pure [PtCl(CHClCO2Et)(R,R-diop)] with S,S-skewphos led to exchange of diphosphines and thereby the assignment of the S configuration at the α-carbon of the major product of the reaction of [PtCl2(S,S-skewphos)] with ethyl diazoacetate. With the aim of optimizing the diastereoeelectivity of the insertion reaction, the chiral diazo ester N2CHCO2R (R = R,R-menthyl) was used as the reagent but it was found that the diastereoselectivities were similar to those with N2CHCO2Et. The highest diastereoselectivities (up to 7:1) were obtained with N2CHCOPh. © 1992, American Chemical Society. All rights reserved.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
