Bidentate phosphonites

The separation between [Cr04] and [CrfCOls] (1795 ppm as usual, the carbonyl is the more shielded species) is comparable to that of other [M04]" / [M(CO)g] pairs (M = W, Re excluded Table 7). Phosphine derivatives of [Cr(CO)j] have not yet been studied by Cr NMR but y( Cr- P) = 153 Hz was obtained from the satellite system of the P resonance of carbonylchromium complexes with bidentate phosphonites. It is likely that satellite systems have been overlooked in and P NMR spectra of chromium compounds. 

Zhao B, Peng X, Wang Z, Xia C, Ding K (2008) Modular chiral bidentate phosphonites design, synthesis, and application in catalytic asymmetric hydroformylation reactions. (2hem Eur J 14 7847-7857... 

Bidentate phosphorus ligands based on BINOL, such as phosphonite 23, phosphites 24 and 25, and phosphoramidite 26 (Tab. 7.2), with various bridging units were introduced by the groups of Reetz, Chan, and Waldmann [48-50]. Excellent enantioselectivities - up to 96% for ligand 23, for instance - were found. 

The use of copper catalysts based on chiral phosphorus ligands to assist 1,4-additions of dialkylzinc reagents has in recent years produced major breakthroughs, with excellent enantioselectivities. A number of monodentate and bidentate phos-phoramidites, phosphites, phosphonites, and phosphines are now available as chiral ligands for alkyl transfer to a variety of cyclic and acyclic enones. So far. 

Whereas bidentate phosphites and phosphonites are excellent ligands for rhodium-catalyzed asymmetric hydrogenation, bidentate phosphoramidites (not shown) gave very poor results with low reaction rates and enantioselectivities. Results of a number of other monodentate phosphoramidites in the asymmetric hydrogenation of. V-acetyl dehydrophenylalanine derivatives are shown in Table 14.7.31-35-36-39-40... 

One of the drawbacks of the use of bisphosphines is the elaborate syntheses necessary for their preparation. Many efforts have been directed towards the development of bis-phosphonites and bis-phosphites. However, surprisingly mono-dentate phosphinates, phosphates and phosphoramidates recently emerged as effective alternatives for bidentate phosphines (Fig. 3.29). This constitutes an important breakthrough in this area as these can be synthesized in one or two steps, and the cost of these ligands is an order of magnitude lower Monophos can be made in a single step from BINOL and HMPT. 

Cobalt(—I) complexes arsenic ligands, 769 bipyridyl, 691 cyanides, 646 phenanthroline, 691 phosphines bidentate, 728 monodentate, 718 multidentate, 738 tridentate, 738 phosphinites, 747 phosphites, 747 phosphonites, 747 terpyridyl, 691 Cobalt(O) Complexes arsenic ligands, 769 bipyridyl, 691 carbon disulfide, 646 cyanides, 646 phenanthroline, 691 phosphines, 718 bidentate, 728 multidentate, 738 tridentate, 738... 

Rh4(CO)i2 in the hydroformylation of 2,3-dihydrofuran produced mainly tetrahydrofuran-2-carbaldehyde (Scheme 4.24) [18]. Also, modification of the metal by monodentate phosphites or phosphoramidites and bidentate phosphites favors a-regioselective hydroformylation as well as higher temperatures, low syngas pressure, and low P/Rh ratios [17, 19, 20]. PPhj or mixed bidentate phosphine phosphites and phosphine phosphonites stimulate isomerization and hence the formation of the fi-isomeric aldehyde [19, 21, 22]. There was no clear... 

The first example of catalytic hydroformylation of vinyl acetate was published in 1949 by Adkins and Krsek [26] [CojfCO), CO/H2 = 100-150 atm, 120-125°C] (Scheme 4.25). Rh as a catalytically active metal was tested first by Brown and Wilkinson in 1969 [27]. In general, Rh-catalyzed hydroformylation of vinyl acetate occurs with extremely high iso-regioselectivity with simple monodentate phosphines [28], phosphonites [20], phosphinites [29], and phosphites [30]. Also, with bidentate diphosphine or diphosphite ligands the a-product is predominantly formed [31]. Therefore, this substrate is frequently screened as a model... 

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