Chiral platinum and palladium complexes containing functionalized C2-symmetric bisaminoaryl 'Pincer' ligands

被引:97
作者
Albrecht, M
Kocks, BM
Spek, AL
van Koten, G
机构
[1] Univ Utrecht, Dept Crystal & Struct Chem, Bijvoet Ctr Biomol Res, NL-3584 CH Utrecht, Netherlands
[2] Univ Utrecht, Debye Inst, Dept Met Mediated Synth, NL-3584 CH Utrecht, Netherlands
关键词
asymmetric synthesis; homogeneous catalysis; pincer N ligand; ligand tuning; platinum;
D O I
10.1016/S0022-328X(01)00667-2
中图分类号
O61 [无机化学];
学科分类号
070301 ; 081704 ;
摘要
The synthesis of enantiopure (oxo-functionalized) C-2-symmetric NCN pincer ligands is described. A key step is the symmetric functionalization of the benzylic positions, which was achieved by enantioselective ketone reduction and subsequent stereoselective substitution protocols. The introduction of alpha -alkyl substituents has a pronounced effect on the cavity for metal binding. For example, lithiation of the alpha -ethyl-functionalized pincer ligand afforded mixed (alkyl)(aryl)lithium aggregates rather than dinuclear bis(aryl) lithium [Li(NCN)](2) species as usually observed for NCN-lithium complexes. Similar effects were established or the (trans)-metalation reaction, which proceeded significantly slower when the steric demand of the alpha -substituent is increased. The potential of the corresponding enantiopure palladium and ruthenium complexes as enantioselective catalyst has been probed in the asymmetric aldol condensation and hydrogen transfer reactions. The low enantiomeric excess of the products of both reactions indicated that face-discrimination of substrates is not induced by these catalysts and that the chiral information must be located in closer proximity to the metal center. (C) 2001 Elsevier Science B.V. All rights reserved.
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页码:271 / 286
页数:16
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