Phospholane ligands, modular

In addition to hydrogenation reactions, modular phospholane ligands are being applied in a growing rank of other useful asymmetric catalytic transformations. For instance, Jiang and Sen reported the discovery of a dicationic Me-DuPhos-Pd catalyst for the alternating copolymerization of aliphatic a-olefins and carbon monoxide (Scheme 13.21).67... 

Burk, M. J. Modular Phospholane Ligands in Asymmetric Catalysis, Acc. Chem. Res. 2000, 33, 363-372. 

Burk, M.J. (2000) Modular phospholane ligands in asymmetric catalysis. AccownW of Chemical Research, 33, 363-372. 

In this chapter, we review a growing family of modular phosphorus heterocycles that have been found broadly useful as chiral ligands in asymmetric catalysis.4 Specifically, the utility of catalysts based on 4-membered phosphetane and 5-membered phospholane ligands will be the focus herein. A description of other types of chiral phosphorus heterocycles can be found in recent review articles4 as well as in Chapters 12 and 15. 

We therefore focused on the development of a modular synthesis of bi- and tridentate chiral phospholane ligands and selected the 2,5-dimethyl (DMP) and 2,5-diphenyl (DPP) substituted phospholanes as stereodirecting groups, as these two privileged chiral units had shown remarkable reactivity and enantioselectivi-ties with special impact in catalytic asymmetric hydrogenations [66]. 

Ligand electronic properties can dramatically influence the reactivity and selectivity of transition metal catalysts, and the electron-rich nature of phospholanes (Figure 13.1) is a unique feature that appears to differentiate these systems from many other available chiral ligands. Another important attribute of phospholanes is associated with the modularity of these systems. The ability to vary the phospholane R-substituents in a systematic fashion allows valuable information to be gathered concerning the steric requirements of the catalytic process. In this manner, the steric environment imposed by the ligand can be tuned to ideally accommodate the steric demands of the reactants and thus facilitate optimization of catalyst efficacy. 

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