Phosphinite ligand

Agbossou E., Carpentier J. E. Hapiot E., Suisse I., Mortreux A. The Aminophos-phine-Phosphinites and Related Ligands Synthesis, Coordination Chemistry and Enantioselective Catalysis Coord. Chem. Rev. 1998 I78-I80 1615-1645 Keywords stereoselective Diels-Alder reaction catalysts, aminophosphine-phosphinites, enantioselective catalysts... 

Since carbohydrates constitute an inexpensive and highly modular chiral source for preparing chiral ligands," Claver et al. have reported the use of a series of thioether-phosphite" and thioether-phosphinite furanoside ligands" in the test palladium-catalysed allylic substitution reaction. In the first type of ligand, a systematic variation of the donor group attached to the carbon atom C5 indicated that the presence of a bulky phosphite functionality had a positive effect on the enantioselectivity. Indeed, the enantioselectivity was controlled mainly by the phosphite moiety. This was confirmed by the use of a ligand... 

Test reaction with furanoside thioether-phosphite or -phosphinite ligands. 

Furanoside thioether-phosphinite ligand for Pd-catalysed allylic substitutions of acyclic and cyclic allylic substrates. 

Scheme 1.19 Test reaction with phosphinite thioglycoside ligands.

Scheme 2.10 Cu-catalysed 1,4-additions of ZnEt2 and AlEt3 to 2-cyclohexenone with thioether-phosphinite ligands and diphosphinite ligands bearing xylo-furanose backbone.

In general, of the mixed phosphorus-thioether ligands that have been used in the asymmetric hydrogenation of prochiral olefins, the thioether-phosphinite ligands have provided some of the best results. As an example, a new class of thioether-phosphinite ligands developed by Evans et al. has recently proved to be very efficient for the rhodium-catalysed asymmetric hydrogenation of a... 

Scheme 8.4 Hydrogenations of olefins with furanoside thioether-phosphinite ligands.

Other S/P ligands derived from carbohydrates and depicted in Scheme 8.5 were found by Khiar et al. to be efficient catalysts for the rhodium-catalysed methyl ot-acetamidocinnamate hydrogenation, leading to protected (5)-phe-nylalanine in a quantitative yield and with an enantioselectivity of 92% ee. On the other hand, the use of 2-phosphinite tert-butyl-thioarabinoside as the ligand afforded the corresponding (2 )-isomer in 92% ee. 

Scheme 8.6 Hydrogenation of methyl a-acetamidocinnamate with bis(phosphinites) ligands.

Another approach in the use of chiral S/P ligands for the hydrosilylation reaction of ketones was proposed more recently by Evans et Thus, in 2003, these workers studied the application of new chiral thioether-phosphinite ligands to enantioselective rhodium-catalysed ketone hydrosilylation processes. For a wide variety of ketones, such as acyclic aryl alkyl and dialkyl ketones as well as cyclic aryl alkyl ketones and also cyclic keto esters, the reaction gave high levels of enantioselectivity of up to 99% ee (Scheme 10.44). 

Scheme 10.45 Rh-catalysed hydrosilylations of ketones with D-xylose-derived thioether-phosphinite ligand.

In a study of the reactions oi acyclic o-methoxyphenyl-phosphinites (45a), phosphonites (45b) and phosphites (45c) with halogens,the intermediate halogenophosphonium salts (46) are stabilised either by ligand exchange with starting material (not shown) or by elimination of methyl halides to form cyclic phosphoranes ( 47 ) 3 7. ... 

Palladium complexes of inexpensive, easily synthesized bis(phosphinite) PCP -pincer ligands show good activity in the Suzuki coupling of deactivated and sterically hindered aryl bromides.256... 

A reaction of the first type, in a broad sense, uses the mixture obtained from n-BuLi and the phosphinic acid (mes)2P(H)=0 (mes = 2,4,6-trimethylphenyl) in thf/hexane to which the Cd amide Cd[N(SiMe3)2]2 is added a mixed amide-phosphinite is obtained, namely [ MeSi)2N Cd (mes)2PO 2Li-2 thf]. The structure analysis (153 K) reveals that the two phosphinite ligands act as a double bridge between Cd and Li to give a six-membered, twisted ring with two independent Cd—P bonds (rav(Cd—P) 259.4 pm) the exocyclic Cd—N bond is rather short (213.6 pm).226... 

The Heck reaction has proven to be an extremely useful method for the formation of C-C bond at a vinyl carbon centre. There are numerous reported examples of enantioselctive Pd catalyzed C-C bond forming reactions.10"13 Surprisingly, reports of Heck transformations using amino acid based phosphine, phosphinite ligands are rare. Recently Gilbertson reported a proline derived phosphine-oxozoline ligand in a catalytic asymmetric Heck reaction.5 In this paper we present some novel amino acids derived ligands as part of a catalytic system for use in asymmetric Heck reactions. 

Scheme 2 Synthesis of dipeptido phosphinite ligands 1-4 and corresponding metal complexes, 5-12 (i) ClPPh2, CH2C12, Et3N, DMAP (ii) (BzCN)2MC12, CH2C12, M = Pt, Pd.

All ligands and metal complexes were characterized spectroscopically. The 31P-NMR spectra of ligands 1-4 appear in a region of 5 111.6-140.6. Upon metal complexation an upfield shift is observed. Table 1 summarizes the selected spectroscopic properties of the new phosphinite ligands (1-4) and corresponding metal complexes (5-12). With exception of 8 and 12 all complexes have a cis coordination geometry as judged from JP.Pt and the IR spectra (341 cm"1 and 355 cm"1 for 8 and 12, respectively). Due to the steric pressure imposed on the... 

Pd complexes 9-12 were tested for their catalytic behavior in the asymmetric Heck reaction involving the phenylation of 2,3-dihydrofuran (Scheme 3). The results are summarized in Table 2. The two isomeric products of 2-phenyl-2,5-dihydrofuran are formed with varying yields from 80% to 0%. The obtained ee s are high. Complex 12 is shown to be catalytically inactive. The lack of catalysis in complex 12 is rationalized by differences in the steric requirements between the diphenylphosphinites 1-3 (cone angle >140°) and the more sterically hindered cyclohexyl-phosphinite 4 (cone angle >170°) and the resulting stereochemistry on the Pd center. The ligands in complex 12 adopt a... 

Recent developments in chirality induced by ligands, and in efficient synthetic methods for ligands such as diphosphines, chiral diamines, amino-phosphine-phosphinites, phosphino-oxazolines and diimino-diphosphines, are available in the literature.105-107... 

Since the mid-1980s bidentate phosphines and phosphites have become very popular as ligands in hydroformylation and many compounds have been spectroscopically identified. The bidentate ligand PPh2NMeCHMeCHPhOPPh2 shown in (57), having two very distinct absorptions for the amido phosphorus and the phosphinite phosphorus nuclei, gives and 31P spectra that are readily interpreted.187... 

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