Diphosphine, modification

L-Dopa was produced industrially by Hoffrnann-LaRoche, using a modification of the Erlenmeyer synthesis for amino acids. In the 1960s, research at Monsanto focused on increasing the L-Dopa form rather than producing the racemic mixture. A team led by William S. Knowles (1917—) was successful in producing a rhodium-diphosphine catalyst called DiPamp that resulted in a 97.5% yield of L-Dopa when used in the Hoffrnann-LaRoche process. Knowles s work produced the first industrial asymmetric synthesis of a compound. Knowles was awarded the 2001 Nobel Prize in chemistry for his work. Work in the last decade has led to green chemistry synthesis processes of L-Dopa using benzene and catechol. 

In the synthesis of specially substituted methylene diphosphines, made from secondary phosphines and carbonyl derivatives (7), a carbenium ion adjacent to trivalent phosphorus as the transition state has been discussed. The transfer of this reaction principle to primary phosphines and suitable carbonyl compound revealed a further pathway to derivatives of dicoordinated phosphorus (8). Aromatic phosphines react with carboxylic acid amide acetals under elimination of alcohol giving dialkylamino-alkylidene phosphines (Scheme 5). A modification of the synthesis... 

Later, these studies were developed in work [64, 65] in which Pt(II) diphosphine complex was used as the catalyst of oxidation with hydrogen peroxide. Modifications of the catalytic system mentioned were applied to enantioselective oxidation [66], However, these catalytic systems find limited application, because they are active in transformations of cyclic ketones only [67],... 

Recently, a series of polymer-anchored tungsten carbonyl catalysts based on modified polystyrenes was prepared [86]. Polymer modification was carried out by reaction of chloromethylated polystyrene (2% cross-linked with DVB) with diphosphines, di- and triamines, pyrazine, 4,4 -bipyridine, and imidazole. The polymers were treated with W(CO)6(TEIF) and their catalytic performance was evaluated in the epoxidation of cyclooctene. Different solvents and oxidants were tested and epoxide yields up to 98% were obtained using the system CH3CN/ H2O2. A detailed catalyst recycling study was carried out and the catalyst containing 4,4 -bipyridine units kept constant activity over 10 reactions whereas other catalysts revealed deactivation. 

Since the diphosphine is appreciably more electron-rich than is BINAP, the major ruthenium complex is a more active hydrogenation catalyst than the parent. Increased electron-rich ligation may be the reason for the success of heterocyclic analogues of BINAP in which the binaphthalene is replaced by a bi(ben-zothiophene) or biindolyl the resulting Ru complexes are effective both in terms of enantioselectivity and reactivity [139]. Readers of the related Chapter 6.1 on the asymmetric hydrogenation of carbonyl compounds will encounter the Ru complexes of ligands in the DUPHOS family, where the ease of modification of the alkyl substituents of the phospholane enhances the power of the system, since it permits the easy optimization of ee for any substrate [140]. 

Whereas the polyketones were usually reported to precipitate from the aqueous phase, under emulsion conditions latexes of ethylene-undecenoic acid-CO ter-polymers and of 1-alkene-CO copolymers can be obtained, which are film-forming at room temperature [12]. Using a miniemulsion technique (cf. Section 6.12.3), water-insoluble diphosphine ligands can be employed without the necessity for hydrophilic modification. 

There have been many reports that described protein composites containing metal complexes [1-3, 5, 6], Three different approaches for the incorporation of synthetic metal complexes into protein cavities have been reported (i) modification of natural snbstrates, (ii) covalent anchoring, and (iii) non-covalent insertion. For example, Whiteside et al. constructed artificial metaUoenzymes by the conjugation of a Rh diphosphine complex with biotin, which strongly binds to avidin [8], Ward et al. have improved this method to increase the reaction activities [25]. They optimized the reaction conditions by screening the structures of metal complexes and protein environments. Finally, optimized composites catalyzed asymmetric hydrogenation with np to 97% ee (Fig. 2a) [2, 3, 26],... 

Figure 13 Synthesis of a diphosphine G2 polypropyleneimine dendrimer by polymer-analogous modification [46],...

Several further modifications of the general reaction type depicted in equation (1) and documented last year have appeared. Thus, reactions of R MgBr with BrCR =CR OR (R = Et or SiMea) in the presence of a Ni diphosphine complex give R R C=CR OR" in respectable yields. ... 

Further structural modifications have been made to these amido diphosphine-or phosphinimine-based nickel pincer complexes to tune the catalytic activity. Complexes 14-19 depicted in Figure 5.3 represent a new class of pincer complejKs lacking the enamine moiety that is characteristic of complexes 8-13 [19]. The reactivity order in couplingp-MeC H4MgBr withp-MeOCgH4l (0.005 or 0.01 mol% catalyst) is 14 17 19>15>16 18. When PhCl is used as the coupling partner forp-MeC H4MgBr (2 or4 mol% catalyst), the reactivity order is somewhat different ... 

The choice of chelating diphosphines or diphosphites gives additional variations to the coordination chemistry of the catalyst complexes. Beyond their particular coordinating ability and steric demand, these ligands are characterized by their natural bite angle (see the section Theoretical Calculations). By using chiral modificators, the hydroformylation of prochiral olefins can become stereoselective (3-6). Beside the addition of modifiers, the variation of the application phase has been the subject of intense research. For reviews of this topic, see Refs. (242-244). 

Chiral diphosphines such as 17,18, and 19 as modificators in platinum-tin systems were found to lead to high enantiomeric excesses (80-96%) in styrene hydroformylation, but the chemo- and regioselectivity is generally low (121 122)... 

FIGURE 15.15 DFT analysis of the model complex 18g. (Reprinted with permission from Crespo, O. et al., Luminescent nido-carborane-diphosphine anions [(PR2>2C2B9H,o]-(R = Ph, iPr). Modification of their luminescence properties upon formation of three-coordinate gold(l) complexes. Inorg. Ghent, 42, 2061-2068. Copyright 2003 American Chemical Society.)... 

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