Diphosphite

Peroxide-decomposing antioxidants destroy hydroperoxides, the sources of free radicals in polymers. Phosphites and thioesters such as tris(nonylphenyl) phosphite, distearyl pentaerythritol diphosphite, and dialkyl thiodipropionates are examples of peroxide-decomposing antioxidants. 

Recent patent activity suggests that DuPont is developing a new generation of chelating diphosphite—nickel catalysts for this technology which are significantly more active than the monodentate phosphite based catalyst system used for the last two decades (61—64). 

Trialkyl esters of phosphonic acid exist ia two structurally isomeric forms. The trialkylphosphites, P(OR)2, are isomers of the more stable phosphonates, 0=PR(0R)2, and the former may be rearranged to resemble the latter with catalytic quantities of alkylating agent. The dialkyl alkylphosphonates are used as flame retardants, plasticizers, and iatermediates. The MichaeUs-Arbusov reaction may be used for a variety of compound types, including mono- and diphosphites having aryl as weU as alkyl substituents (22). Triaryl phosphites do not readily undergo the MichaeUs-Arbusov reaction, although there are a few special cases. 

These polymers are subjected to high temperatures, ca 300°C, duting extmsion and iajection molding. Processing stabilizers are used to decrease both the change ia viscosity of the polymer melt and the development of color. A phosphite, such as tris(2,4-di-/ f2 -butyiphenyi)phosphite (25) or bis(2,4-di-/ f2 butyiphenyi)pentaerythritol diphosphite [26741-53-7] ia combination with a phenoHc antioxidant such as octadecyl... 

Kinetic studies of the oxidation of phosphites such as triisopropyl phosphite with BTSP 1949 to give phosphates such as triisopropyl phosphate [177] led to the discovery that oxidation of diphosphite nucleotide intermediates such as 2008 with BTSP 1949 at -20 °C in the presence of TMSOTf 20 (instead of iodine in... 

Remarkably, Claver et al. showed that in a square planar rhodium carbonyl chloride complex, two bulky phosphite ligands (65) were able to coordinate in a trans orientation.214 Diphosphite ligands having a high selectivity for linear aldehyde were introduced by Bryant and co-workers. Typical examples are (67)-(70).215,216... 

Several types of chiral diphosphite ligand have been synthesized and tested in Pt-catalyzed asymmetric hydroformylation.338-341... 

Diastereomeric diphosphites (107)-(110) were prepared by the reaction of enantiomerically pure 2,2 -dihydroxy-5,5, 6,6, 7,7, 8,8 -octahydro-l,l -binaphthyl or 2,2 -dihydroxy-l,l -binaphthyl with chlorophosphites. The structure of R-bis-(4R,6R)-(l 07) was determined by XRD. The diphosphites were tested in the Pt- and Rh-catalyzed asymmetric hydroformylation of styrene. 

The influence of steric and electronic effects of diphosphites (111) and (112) have been studied with regard to their catalytic performance on the hydroformylation of styrene catalyzed by platinum complexes. The highest chemoselectivity to aldehyde (71%) and regioselectivity to branched aldehyde (85%), with an enantiomeric excess of 86%, was obtained with the plat-inum(II)-SnCl2 catalytic system associated with ligand (25, 45)-bis(5)-(lll).340... 

Modified rhodium systems show considerable activity in the hydroformylation of styrene to the branched aldehydes. Chiral diphosphines, diphosphites, and phosphine-phosphites have been the ligands most studied. Hydroformylation experiments have often been performed in situ but the characterization of intermediates has provided an interesting contribution to coordination chemistry.179... 

The first reports on asymmetric hydroformylation using diphosphite ligands revealed no asymmetric induction. In 1992, Takaya et al. published the results of the asymmetric hydroformylation of vinyl acetate (ee = 50%) with chiral diphosphites.358... 

In 1992, an important breakthrough appeared in the patent literature when Babin and Whiteker at Union Carbide reported the asymmetric hydroformylation of various alkenes with ees up to 90%, using bulky diphosphites derived from homochiral (2i ,4R)-pentane-2, 4-diol, UC-PP (1 19).359 360 van Leeuwen et al. studied these systems extensively. The influence of the bridge length, of the bulky substituents and the cooperativity of chiral centers on the performance of the catalyst has been reported.217 218 221 361-363... 

Chiral diphosphites based on (2R,3R)-butane-2,3-diol, (2R,4R)-pentane-2,4-diol, (25, 5S)-hexane-2,5-diol, (lS -diphenylpropane-hS-diol, and tV-benzyltartarimide as chiral bridges have been used in the Rh-catalyzed asymmetric hydroformylation of styrene. Enantioselectivities up to 76%, at 50% conversion, have been obtained with stable hydridorhodium diphosphite catalysts. The solution structures of [RhH(L)(CO)2] complexes have been studied NMR and IR spectroscopic data revealed fluxional behavior. Depending on the structure of the bridge, the diphosphite adopts equatorial-equatorial or equatorial-axial coordination to the rhodium. The structure and the stability of the catalysts play a role in the asymmetric induction.218... 

Bakos et al. reported a series of diastereomeric diphosphites that were used in the Pt- and Rh-catalyzed asymmetric hydroformylation of styrene. Systematic variation in chirality at both the chelate backbone and the terminal groups revealed a remarkable effect on the enantioselect-ivity of the catalysts. These systems have been described in Section 9.3.3.5. 

A chiral diphosphite based on binaphthol, coordinated with rhodium (I) forming a nine-member ed ring, led to an efficient hydroformylation of vinylarenes, although moderate ees were obtained (up to 46%) at mild pressure and temperature reaction conditions.364 Chiral diphosphites and phosphinite-phosphites derived from spiro[4.4]nonane-l,6-diol were synthesized. Using these catalysts in the asymmetric hydroformylation of styrene, high regioselectivity (97%) and... 

Dipropyl adipate, d787 Dipropylene glycol, b204 Dipropyl ketone, hi6 Distearylpentaerythritol diphosphite, b217 Disulfram, t62... 

The first catalytic 1,4-addition of diethylzinc to 2-cyclopentenone with over 90% ee was described by Pfaltz and Escher, who used phosphite 54 with biaryl groups at the 3,3 -positions of the BINOL backbone.46 Chan and co-workers achieved high enantioselectivity in the same reaction (up to 94% ee) by using chiral copper diphosphite catalyst (R,R,R)-41 48,48a 48d Hoveyda and co-workers used ligand 46 to realize excellent enantiocontrol (97% ee) in the 1,4-additions of 2-cyclopentenones,52 which may be used in the practical asymmetric synthesis of some substituted cyclopentanes (including prostaglandins). 

Subsequently, it was shown that rhodium complexes derived from diphosphi-nites, diphosphonites, and diphosphites - as well as hybrid ligands - are similarly active and selective to diphosphines [46 i],... 

Phosphite compounds, which have been discussed in the context of their application in asymmetric hydrogenation reactions (see Section 6.1.2.6), can also be used to effect the copper salt-mediated asymmetric conjugate addition of diethylzinc to enones.74 As shown in Scheme 8-33, in the presence of diphosphite 92 and copper salt [Cu(OTf)2], the asymmetric conjugate addition proceeds smoothly, giving the corresponding addition product with high conversion and ee. In contrast, the monophosphite 93 gave substantially lower ee. 

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