Synthesis of new chiral phosphine–phosphites and diphosphites and their application in asymmetric hydroformylation
Introduction
In the last years we have observed an impressive expansion of the research devoted to the development of new chiral phosphorus ligands such as phosphine–phosphites [1], [2], [3], [4], [5], [6], [7] and diphosphites [2], [8], [9]. These efforts are due to the failure of simple methods to accurately predict the catalytic efficiency of a new chiral ligand and to the urgency to find appropriate ligands for many reactions. A very challenging example is the asymmetric hydroformylation of olefins. In fact even the most efficient ligands so far tested do not warrant the high regio- and enantioselectivity required for practical applications.
In this paper we report the synthesis of the new phosphine–phosphite (S,R,R)-1 and diphosphites (R,R,R)-2, (S,R,R)-2 (Scheme 1) and some preliminary studies of their catalytic activity.
Section snippets
Results and discussion
(S,R,R)-1 was synthesised by reacting (R,R)-3 [8], [10] with (S)-4 [11]; analogously the diphosphite ligands (R,R,R)-2 and (S,R,R)-2 were prepared by treatment of (R,R)-3 with (R)- or (S)-5 [12], respectively. Analytical and spectroscopic data for the new ligands are reported in Section 3.
The catalytic activity of 1 and 2 was tested in the asymmetric hydroformylation of styrene (Scheme 2).
The catalysts were prepared in situ by mixing [Rh(acac)(CO)2], a widely used Rh(I) precursor, with the
Materials and instruments
All manipulations were carried out under inert atmosphere (argon). Analytical grade solvents were purified following standard methods described in the literature [14].
(R,R)-(+)-1,2-diphenyl-1′,2′-ethandiol [10], 1-chloro-1-phospha-(3R,4R)-3,4-diphenyl-2,5-dioxacyclopentane (R,R)-3 [8], (S)-(-)-2-(diphenylphosphino)-2′-hydroxy-1,1′-binaphthyl (S)-4 [11] and (S)- and (R)-1,1′-binaphthalene-2,2′-diol (S)- and (R)-4 [12] were prepared according to the literature.
- and were obtained on a
Acknowledgements
This work was supported by the Italian C.N.R. Progetto Finalizzato “Beni Culturali” and MURST Ministero Università Ricerca Scientifica e Tecnologica.
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