The Daniphos Ligands Synthesis and Catalytic Applications

This indicates an ideal setup for the abstraction of the desired pro-R proton. The chromiumtricarbonyl moiety also facilitates the two consecutive nucleophiic substitutions of the reaction pathway, which both proceed with retention of configuration, by shielding the bottom of the molecule sterically and also by stabihzing the benzylic carbocationic intermediate [6, 7]. 

As mentioned above, this synthetic route enables a modular approach to ligand design. The concept of modularity, as introduced for the Josiphos ligands by Togni [17], is sketched schematically in Fig. 1.4.2 for the Daniphos ligands. 

While the backbone of the ligand provides the stereochemical information, the two different donor groups (DJ can be introduced independently of one another in consecutive steps and therefore make a fine-tuning of the ligand s steric and electronic features possible. So with a stock of electro- and nucleophiles at hand an enormous number of ligands is accessible by employing the same synthetic procedure and workup, while the synthesis is not limited to phosphines other functionalities such as Hal, C, Si, S, O, and N can also be introduced [7b-d,i]. 

D Fine tuning of steric and electronic features of the ligand Fig. 1.4.2 The concept of modularity. 

For the further discussion of the catalytic applications it is important to note the acronym system which we apply to designate each ligand easily and unequivocally. According to the general label R/PR 2/PR , R denotes the substituent in the paro-position to the chiral a-chain (when R = H, it is omitted), PR 2 stands for the group in the ortho-position and finally PR for the phosphino group in the a-chain itself (see Fig. 1.4.4). The abbreviations PbA and PbB refer to the regioisomeric phobane skeletons (PbA = phosphabicyclo[3.3.1]nonane, PbB = phosphabicyclo[4.2.1]nonane), Ind stands for indane and the (R,R)-2,5-dimethylphospholane unit is abbreviated to (R,R)-DMP . 

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I 1.4 The "Daniphos Ligands Synthesis and Catalytic Applications Table 1.4.2 Results of the hydrogenation of the MEA imine. 

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