Synthesis and Stereochemistry of Cobalt(III) Complexes with the New Optically Active Phosphine Ligand, N,N'-Bis[2-(diphenylphosphanyl)ethyl]-(1R,2R)-cyclohexane-1,2-diamine (ch-PNNP). Crystal Structure of Lambda-Cisbeta-[Co(acac)(ch-PNNP)](ClO4)2.
摘要:
A new optically active tetradentate phosphine ligand, N,N'-bis[2-(diphenylphosphanyl)ethyl]-(1R,2R)-cyclohexane-1,2-diamine (ch-PNNP), was prepared from (1R,2R)-cyclohexane-1,2-diamine and purified through the nickel(II) complex. Three new ch-PNNP complexes of cobalt(III) were prepared: trans-[CoCl2(ch-PNNP)](+), trans-[Co(NCS)(2)(ch-PNNP)](+) and Delta-cis beta-[Co-(acac)(ch-PNNP)](2+). The geometrical structures of the complexes were assigned on the basis of NMR, CD and absorption spectra. The molecular structure and the absolute configuration of Delta-cis beta-[Co(acac)(ch-PNNP)](ClO4)(2) were determined by X-ray analysis. The orthorhombic cell (P2(1)2(1)2(1)) has a = 12.721(4), b = 17.073(3), c = 18.26(3) Angstrom, V = 3966(7) Angstrom(3) and Z = 4. The X-ray analysis shows that the three chelate rings from the ch-PNNP ligand form distorted gauche (delta lambda lambda) conformations.
Reversal of enantioselectivity using catalysts containing multiple stereogenic centres
作者:Alexander J.A. Cobb、Charles M. Marson
DOI:10.1016/s0957-4166(01)00290-7
日期:2001.7
N-methylation of ligands with multiple stereogenic centres is shown to provide the product of the opposite configuration in significant enantiomeric excess (e.e), in the addition of diethylzinc to aldehydes. The catalysts possess stereogenic centres appended to a trans-1,2-cyclohexanediamine core. (C) 2001 Elsevier Science Ltd. All rights reserved.