期刊
JOURNAL OF ORGANOMETALLIC CHEMISTRY
卷 846, 期 -, 页码 129-140出版社
ELSEVIER SCIENCE SA
DOI: 10.1016/j.jorganchem.2017.04.033
关键词
Ring bending; Palladium; Phosphine-amine; Allylic alkylation
资金
- National Excellence Program [TAMOP-4.2.4.A/2-11/1-2012-0001]
- National Research, Development and Innovation Office (NKFIH) [K 115539, K 108966]
Six-membered chelate complexes of type [Pd(1a-e)Cl-2] (2a-e) and [Pd(1a-e)(eta(3)-PhCHCHCHPh)]BF4 (3a-e) of a series of systematically varied chiral phosphine-amine ligands (S,S)-Ph2PCH(CH3)CH2CH(CH3)NHR 1a-e (R = benzyl 1a, R = ethyl 1b, R = (S)-alpha-phenylethyl 1c, R = isopropyl 1d, R = methyl 1e) have been studied. The complexes 2a-e were characterized by X-ray crystallography, DFT analysis and in solution by 1D and 2D NMR spectroscopy. A very good correlation has been observed between the steric demand of the N-substituent and the distortion of the chelate. Furthermore, it has been proved that sterically more demanding N-substituents are capable of distorting the chelate to a larger extent along one single, well defined conformational pathway. The careful variation of the N-substituent thus allows a precise stereochemical fine tuning of the metal's coordination sphere. As a substantiation of this concept, the investigation of complexes 3a-e revealed that the exo/endo ratio as well as the twisting of the allyl moiety around the Pd-allyl axis can easily be modified by the proper choice of the nitrogen substituent. Furthermore, Pd-catalysts with ligands 1a-e provided high enantioselectivities (up to 96%) in asymmetric allylic alkylation reactions. (C) 2017 Elsevier B.V. All rights reserved.
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