Phosphinite catalysts

Recently, a breakthrough in the hydrogenation of unfunctionalized olefins was made [51]. For the first time, high enantioselectivities with purely alkyl-substituted alkenes such as 72-74 could be achieved using pyridine-phosphinite catalysts 75 and 76. 

The asymmetric hydrogenation of enol esters can also be catalyzed by chiral amidophosphine phosphinite catalysts derived from chiral amino acids, but the enantioselectivity of these reactions has thus far been only moderate.35... 

Phosphinite pincer iridium systems have also been shown to have a lower tendency to oxidatively add TEE to give (vinyl)(hydride) complexes similar to 3 [18]. While this has been identified as one of the major catalyst deactivation processes in phosphine pincer iridium catalysis, apparently with complexes such as 5, only olefin coordination can occur. However, this is a considerably weaker bonding and is less detrimental to catalyst activity. Eased on steric arguments, product olefin coordination (e.g. COE) is favored over TEE coordination, and therefore at a high TON and high product concentrations the phosphinite catalysts 5 are markedly less active than the phosphine analogues 1. 

Bhanage and coworkers [62] investigated the reaction in polyethylene glycol and used the recycled rhodium phosphinite catalyst up to five times. Wasserscheid s group performed HAM in a continuous reactor operating with supported ionic liquid phase (SILP) catalysts [49]. A particular feature was that, by using a SILP catalyst based on neutral oxide and porous carbon supports and ILs of low basicity, aldol condensation could be fully suppressed. Alternatively, the reaction has been run with the assistance of a rhodium catalyst immobilized in a sol-gel matrix [73]. 

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... 

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. 

The results of unsymmetrical 7r-acid bidentate ligands, e.g., (81), have in the hydroformylation of ra-octenes was described. The preparation of seven such ligands was described. Thus, [Rh-(acac)(cod)]-catalyzed hydroformylation of ra-octene in the presence of a phosphinite ligand gave 94% ra-nonanal.295 A new upper-rim phosphacalix[4]arene 5,17-bis(diphenylphosphinomethyl)-25,26,27,28-tetrapropoxycalix[4]arene has been prepared. It reacted with [(cod)RhCl]2 to give a dirhodium complex that is an active catalyst for the hydroformylation of 1-octene and styrene.296 Rhodium complexes of [l-propyl-3-methylimidazolium+]2 [PhP(C6H4SO%)2] dissolved in the... 

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... 

The introduction of electronic asymmetry into this class of bis(diaryl)phosphinites has been used to design catalysts that can afford both enantiomers of naproxen nitrile. If the carbohydrate scaffold is based on methyl o-D-fructol uranosidc (29), (i )-naproxen nitrile is produced. In a similar manner to the results above, electron-donating aryl substituents on phosphorus afford... 

The directed synthesis of biaryls can be achieved using rhodium-based catalysts along with a phosphinite co-ligand (Equation (143)). 

The rhodium-catalyzed arylation of phenols with aryl halides occurs in the presence of phosphinites [PR2(OAr)] as a co-catalyst (Equation (59)).66 The phosphorus atom coordinates to the rhodium atom to facilitate the electrophilic substitution with the rhodium(m) species at the ortho-pos i on. 

BPPM Scheme 1.17) was used as catalyst [60]. The enantioselective hydrogenation of functionalized ketones was also efficiently achieved by a series of rhodium(I) aminophosphine- and amidophosphine-phosphinite complexes [61]. 

In contrast to the extensive studies on phosphine-phosphites, the corresponding phosphine-phosphinites are rarely exploited. Laschat introduced this design with a bicydic chiral skeleton derived from (lS)-(+)-camphorsulfonic acid [127]. The Rh-complex based on dimesitylphosphinite 154b was found to be the most reactive catalyst, and was used to produce methyl N-2-acetamidodnnamate, with 89% ee. 

The oxazoline-derived P,N ligands can be classified into four groups according to structure phosphino-oxazolines phosphite- and phosphinite-oxazolines catalysts containing a P-N bond and structurally related non-oxazoline catalysts. 

Finally, the phosphinite-oxazole catalyst 29 (Fig. 29.16) was recently reported and used to hydrogenate a series of functionalized and unfunctionalized alkenes [31]. It was anticipated that the planar oxazole unit and the fused ring system would improve the enantioselectivity compared to the PHOX catalyst by increasing rigidity in the six-membered chelating ring [32]. Indeed, these catalysts... 

The oxazole-phosphinite complexes 14 (Fig. 30.14) proved to be highly selective catalysts, comparable to the best catalysts developed so far (see entries in Tables 30.9 and 30.11-30.13) [26]. 

In summary, the most efficient catalysts for substrates 36-40 are the Ser-PHOX and ThrePHOX complexes 46 and 12, as well as the recently reported oxazole-phosphinite complexes 14. 

Catalysts Based on Fluorous Alkylphosphines, -Phosphinites, -Phosphonites, and -Phosphites... 

Rhodium (I) complexes of chiral phosphines have been the archetypical catalysts for the hydrocarbonylation of 1-alkenes, with platinum complexes such as (61) making an impact also in the early 1990s[1461. More recently, rhodium(I)-chiral bisphosphites and phosphine phosphinites have been investigated. Quite remarkable results have been obtained with Rh(I)-BINAPHOS (62), with excellent ee s being obtained for aldehydes derived for a wide variety of substrates1 471. For example, hydroformylation of styrene gave a high yield of (R)-2-phenylpropanal (94% ee). The same catalyst system promoted the conversion of Z-but-2-ene into (5)-2-methylbutanal (82% ee). 

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