Ligands amidophosphine

A C2 symmetric bis(amidophosphine) ligand was used by Trost to prepare the natural nucleoside adenosine (see Chapter 49 for nucleosides) in similar fashion to the carbocyclic analogue described above. The key enantioselective step was the first allylic alkylation that selected between two cnan-tiotopic benzoates in the meso dihydrofuran derivative to give one enantiomer the expected cis product. 

Regarding the use of well-defined nickel complexes as catalysts for reduction of carbonyl groups, only three examples are described in the literature. In 2009, Guan and coworkers [77] described the efficiency of a nickel PCP-pincer complex performing the hydrosilylation of aldehydes. In the same year, the catalytic hydrosilylation of ketones via a transient Ni-H complex supported by a monoanionic bidentate amidophosphine ligand was reported by Mindiola [78]. Later, Jones investigated well-defined PNP nickel pincer complexes, which catalyzed the hydrosilylation of aldehydes [79] (Fig. 10.16). 

Several efficient amidophosphine- and aminophosphine-phosphinite ligands have been reported by Agbossou and Carpentier.148,148a 148g Amidophosphine-phosphinite ligands (.9)-Cy.Cy-oxoProNOP and (.V)-Cp,Cp-oxoProNOP... 

Lithiation of the dicarboxamide 365 is similarly diastereoselective, and after two successive n-BuLi-(—)-sparteine lithiations C2-symmetric products such as 367 can be made with high ee (Scheme 156) Attempted double lithiation of 365 in one pot fails with n-BuLi with s-BuLi-(—)-sparteine the major product is the meso isomer of 367 ". The amidophosphine 366 has been used as a chiral ligand for Pd chemistry the amides can be reduced to amino groups with BHsiTHF . 

Amido phosphine-donor complexes, with Zr(IV), 4, 799 Amidophosphines, chelating, in hydrogenations, 10, 14 Amido-supporting ligands... 

Leautey, M. Castelot-Deliencourt, G. Jubault, P. Pannecoucke, X. Quirion, J.-C. Synthesis of a-substituted /i-amidophosphines by diastereoselective alkylation. A new access to chiral ligands for asymmetric catalysis. 

As final examples of potentially P,0 bitopic ligands, amidophosphines have been applied with success to various enantioselective transformations, e. g., addition of arylboronic acids, Grignard reagents, and organocuprates to enones in the presence of Rh and Cu catalysts (10) (>96% ee) [40]. 

Based on the metal-differentiating coordination concept, proline-derived biden-tate amidophosphines 23-25 were developed. The carbonyl oxygen and phosphorus atoms of the ligand selectively coordinate to lithium and copper atoms of an organocopper species, which discriminate the reaction face of the complex as shown in 26. The reaction of dimethylcopper lithium with chalcone gave the adduct in 84% ee [52]. Enantioselectivity was later improved to 90% with the more bulky amidophosphine 25 based on the model 26 (Eq. (12.26)) [53]. 

Owing to strategic reasons, Lonza exited the dextrometorphan business before the process could be transferred. Subsequently a further study of the hydrogenation of 10, using iridium complexes with chiral amidophosphine-phosphonite ligands, was published by another group [14]. An enantioselectivity of 86% ee was reached, but the chemoselectivity was low. 

A brief overview on the very recent use of Cr complexes bearing [F/VJ bidentate ligands as ethylene oligomerization precatalysts should also be mentioned. As summarized in Scheme 40, Cr(II) amidophosphine complexes 110-114 were... 

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