Stereoselective coordination

A six-membered P,N-chelate tailored for asymmetric allylic alkylation

Z. Császár, G. Farkas, A. Bényei, G. Lendvay, I. Tóth, J. Bakos

Research output: Contribution to journalArticle

7 Citations (Scopus)

Abstract

Six-membered chelate complexes [Pd(1a-b)Cl2], (2a-b) and [Pd(1a-b)(η3-PhCHCHCHPh)]BF4, (3a-b) of P,N-type ligands 1a, ((2S,4S)-2-diphenyl-phosphino-4-isopropylamino-pentane) and 1b, ((2S,4S)-2-diphenyl-phosphino-4-methylamino-pentane) have been prepared. The Pd-complexes have been characterized in solution by 1D and 2D NMR spectroscopy. The observed structures were confirmed by DFT calculations and in the case of 2a also by X-ray crystallography. Unexpectedly, the coordination of the all-carbon-backbone aminophosphine 1a resulted in not only a stereospecific locking of the donor nitrogen atom into one of the two possible configurations but also the conformation of the six-membered chelate rings containing three alkyl substituents was forced into the same single chair structure showing the axially placed isopropyl group on the coordinated N-atom. The stereodiscriminative complexation of 1a led to the formation of a palladium catalyst with a conformationally rigid chelate having a configurationally fixed nitrogen and electronically different coordination sites due to the presence of P and N donors. The stereochemically fixed catalyst provided excellent ee's (up to 96%) and activities in asymmetric allylic alkylation reactions. In contrast, the chelate rings formed by 1b exist in two different chair conformations, both containing axial methyl groups, but with the opposite configurations of the coordinated N-atom. Pd-complexes of 1b provided low enantioselectivities in similar alkylations, therefore emphasizing the importance of the stereoselective coordination of N-atoms in analogous P-N chelates. The factors determining the coordination of the ligands were also studied with respect to the chelate ring conformation and the nitrogen configuration.

Original languageEnglish
Pages (from-to)16352-16360
Number of pages9
JournalDalton Transactions
Volume44
Issue number37
DOIs
Publication statusPublished - Aug 9 2015

Fingerprint

Alkylation
Conformations
Atoms
Nitrogen
Ligands
Catalysts
Enantioselectivity
X ray crystallography
Palladium
Complexation
Discrete Fourier transforms
Nuclear magnetic resonance spectroscopy
Carbon
diphenyl
pentane

ASJC Scopus subject areas

  • Inorganic Chemistry

Cite this

Stereoselective coordination : A six-membered P,N-chelate tailored for asymmetric allylic alkylation. / Császár, Z.; Farkas, G.; Bényei, A.; Lendvay, G.; Tóth, I.; Bakos, J.

In: Dalton Transactions, Vol. 44, No. 37, 09.08.2015, p. 16352-16360.

Research output: Contribution to journalArticle

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