Phosphines phosphine/phosphite-ligands

Several papers have appeared recently comparing various properties of carbonyl metal complexes substituted by various phosphines or phosphite ligands or isocyanides. Angelici and Ingemanson (4) studied the equilibrium... 

Much progress has been made on regioselective hydroformylation of terminal alkenes in favor of the linear product. In particular bidentate phosphine or phosphite ligands, which have a natural bite angle 9 of about 110°, will favor the linear product. The most successful ligand types are BISBI [49, 50], BIPHEPHOS [51,52], and XANTPHOS systems (Scheme 8) [53]. 

Zinc(II) porphyrins form stable complexes with nitrogen donors. This complementary binding motif has been used in a number of variations for the self-assembly combinatorial construction of phosphine and phosphite ligand libraries. 

The first examples of five-coordinate platinum(II) complexes of the type [Pt(PR3)L]2+ (L = tris(2-(diphenylphosphino)ethyl)phosphine R = Et, OMe, OEt) (104) containing only P-donor atoms have been prepared by the reaction of [PtClL]+ with an appropriate monodentate tertiary phosphine or phosphite ligand.284 Triaryl phosphines and phosphites do not react with the precursor complex, even at elevated temperatures, most probably due to the considerable steric interactions that would occur upon the approach of the P-donor ligand to the platinum(II) center. 

Figure 3.2. Chiral phosphine-phosphite ligands on a highly cross-linked polystyrene polymer...

Dieguez et al. reported that phosphine-phosphite ligand 88 (Figure 9) gave 62% ee in the reaction of triethyl-aluminum with 2-cyclohexenone.131... 

Methylation of aldehydes with trimethylaluminum is catalyzed by nickel complexes (Equation (80)).438 Phosphine or phosphite ligands considerably accelerate the reactions. 

Scheme 44.10 Phosphine-phosphite ligand in enantioselective hydrogenation.

Abstract This chapter presents the latest achievements reported in the asymmetric hydroformylation of olefins. It focuses on rhodium systems containing diphosphites and phosphine-phosphite ligands, because of their significance in the subject. Particular attention is paid to the mechanistic aspects and the characterization of intermediates in the hydroformylation of vinyl arenes because these are the most important breakthroughs in the area. The chapter also presents the application of this catalytic reaction to vinyl acetate, dihydrofurans and unsaturated nitriles because of its industrial relevance. 

Inspired by the excellent results using the BINAPHOS ligands, new phosphine-phosphite ligands with different backbones have been developed in recent years. Unfortunately, their Rh-catalyzed hydroformylation provided low-to-moderate enantioselectivity (ee s from 20 to 62%) [35,36,65]. 

Based on the precedent of Van Leeuwen and Roobeek, livinghouse and co-workers screened a variety of electron-deficient phosphine/phosphite ligands for the rhodium-catalyzed [4-1-2] reaction, which provided an alternative catalyst system for the formation of 5,6- and 6,6-ring systems [13]. The most notable of these was the tris-(hexafluoro-2-propyl) phosphite-modified rhodium complex, which was applicable to both carbon- and oxygen-tethered substrates, and also provided the first example of a facial-directed diastereoselective intramolecular rhodium-catalyzed [4-i-2] reaction (Eq. 4). 

Figure 7 A rhodium complex of chiral phosphine-phosphite ligand (H,S)-BINAPHOS used as a catalyst for asymmetric hydroformylation.

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