Phosphinite complexes

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]. 

Initially, research focused on the use of C2-symmetric rhodium and ruthenium-phosphine and phosphinite complexes a rhodium-phosphine complex 3 (Fig. 30.2) was used in the first reported enantioselective hydrogenation of substrate 1 (Table 30.1, entry 1) [1],... 

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. 

This is markedly higher than the TONs typically observed for phosphine-based Ir—PCP systems (ca. 250 under identical conditions). Electron-withdrawing substituents such as C5F5 (5e) and 3,5-(CF3)2-C6H3 (5f) considerably improve the catalytic activity (Table 12.1). Notably, the MeO-substituted Ir—PCP complex 5c seems to operate differently, and remains active over a longer time range than the other phosphinite complexes, thus reaching final TONs that are comparable to those of 5f. 

The reduced donor ability of the phosphinite complexes such as 5e and 5f has an impact beyond the catalyst activation stipulated above. Apparently, the decreased tendency to undergo oxidative addition reactions also disfavors catalyst deactivation via oxidative olefin addition. Accordingly, (vinyl) (hydride) complexes such as 3 are less relevant. Simultaneously, product oxidative addition is restricted and, as... 

The chemistry of phosphite, phosphonite and phosphinite complexes of palladium(II) generally resembles that of their phosphine analogues. Its description here will therefore be brief, attention being paid to those areas where differences in behaviour are apparent. 

Table 41 Preparations Phosphite, Phosphonite and Phosphinite Complexes...

RajanBabu et al. has deeply explored the chemistry of carbohydrate phosphinite complexes [84, 95]. While the carbohydrate backbone provided the necessary stereochemical diversity, substitution patterns around phosphoms were used to vary the steric and electronic properties of the ligand. 

One of the most successful asymmetric catalytic reactions is the asymmetric hydrogenation of amino acid precursors by means of optically active rho-dium(I)phosphine or phosphinite complexes [55]. Usually, the reaction is carried out in methanol as solvent. When water is used the activity and enantiose-lectivity decrease significantly [16], but the addition of micelle forming surfactants leads to a solubilization of catalyst and substrate and increases activity and enantioselectivity. The results are somewhat better than the ones obtained with methanol as solvent [56]. Table 2 shows the effect with different types of surfactants. 

Fogassy, G., Tangier, A., Levai, A. (2003) Enantioselective hydrogenation of exocyclic alpha,beta-unsaturated ketones. Part 111. Hydrogenation with Pd in the presence of cinchonidine, y. Mol. Catal. A. Chem. 192, 189-194. Hapiat, F., Agboussou, F., Mortreux, A. (1994) Synthesis of new chiral arene Ru(ll) aminophosphine-phosphinite complexes and use in asymmetric hydrogenation of an activated keto compounds. Tetrahedron Asymm. 5, 515-518. 

Modification of the well known diop-Rh catalyst by the inclusion of o-methoxy-groups on the phenyl substituents results in a reversal of the R S ratio in the amino-acid products, relative to diop itself. Overall enantiomeric enrichments are comparable with those obtained with diop-Rh It has been shown that in some cases, chiral Rh -phosphinite complexes derived from sugars are more effective in asymmetric hydrogenations than the corresponding phosphine complexes. ... 

Zargarian and co-workers synthesized and characterized ortho-nickelated phosphinite complex 97, and investigated the C-H metalation of aromatic substrates, determining the importance of aryl substituents... 

Streubel reported the synthesis of phosphinite complexes 107, via reaction of transient Li/Cl phosphinidenoid complexes, prepared from dichloro(organo)phosphane complexes with different alcohols. NMR studies on deprotonation reactions of P-CgMcs- and P-CPhs-substituted methojyphosphinite complexes provided new insights into formation and stability of Li/OMe phosphinidenoid complexes. 

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