Phosphine aminophosphine ligands

Mixed Phosphine-Phosphoramidites and Phosphine-Aminophosphine Ligands... 

Fig. 27.5 Mixed phosphine-phosphoramidites and phosphine-aminophosphine ligands.

The chiral, hybrid phosphine-aminophosphine ligand (113) has been applied in the Rh-catalyzed asymmetric hydrogenation of various dimethyl a-benzoyloxyethenephosphonates (114) bearing (3-aryl, (3-alkyl and (3-alkoxy substituents in high enantioselectivities (ee up to 97%) (Scheme 39). 

This section essentially catalogs some of the newer catalyst systems that have not been considered in the previous sections. A number of the catalysts are certainly derived from more established ones (e.g., use of chelated aminophosphine ligand instead of two monodentate phosphines... 

Binaphthol-based phosphorus amidite 30 was developed by Feringa to afford 3-ethylcyclohexanone in over 98% ee [64, 65]. However, high enantioselectivity is limited to cyclohexenone, and rather poor selectivity was observed in the reaction of cyclopentenone (10% ee) and cycloheptenone (53% ee). Symmetric aminophosphine ligand 31 was synthesized and the reaction with cyclohexenone was examined in the presence of 5 mol% of copper triflate to afford the product in 55% ee [66]. Amide-phosphine 32 was examined in the reaction to afford the product in 35% ee. Higher selectivity (64%) was observed in the reaction of 4,4-dimethylcyclohexenone [67, 68]. 

Displacements. Nickel complexes can serve as an alternative to the Pd catalysts, e.g., in the synthesis of allylamines and a-allylmalonic esters. A report on the latter reaction states that bis(aminophosphine) ligands are more efficient than dppb and other usual phosphines. 

Cyclodextrins can be modified by thiol substituents and further attachment to phosphine or aminophosphine ligands (see 9) allows the coordination to rhodium catalysts [30], The activity in the hydroformylation reaction of 1-octene is interesting since turnover frequencies near to 180 h can be reached with a selectivity in Cg-aldehydes higher than 99% (31). 

The diastereoselective synthesis of a 7 -chirogenic p-aminophosphine ligand 300 by carbon-carbon bond formation of the ethano bridge in a 3 1 ratio via reaction of an a-metallated f -chiral phosphine borane (5)-297 with a benzaldimine was described. The major diastereoisomeric p-aminophosphine borane (Sp)-298 was separated and decomplexed into the corresponding p-aminophosphine (5p)-300 under neutral conditions and without epimerization by heating at reflux in EtOH (Scheme 100) [198]. 

The bidentate phosphine dppe (l,2-bis(diphenylphosphino)ethane) and the aminophosphine eddp (2-aminoethyl-diphenylphosphine) form mixed ligand (N, P, O) complexes such as Co(acac) (edpp)2 and Co(acac)(en)(dppe). A preference for trans N-Co-P and P-Co-P configurations over N-Co-N was found for the bis(edpp) complexes.925... 

Another ligand, the potential of which has only recently been exploited, is Bo-Phoz (35). This ligand is an aminophosphine as well as a phosphine (see also Section 23.7). It has shown high selectivities and activities with enamides and itaconates [154, 155]. 

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