Catalysis of Organic..

Pugin et al. 295ferrocene binding modes dominate or if the one or both of the additional phosphinegroups interact with the complexed metal. While a mixture of complexes may bepresent, in any catalysis reaction it may be expected that each complex will behaveindependently and therefore the observed product distribution will represent the sumof the contributions of the individual catalytically active species. Given that activity,selectivity, and productivity of the various species will differ, the observed productdistribution will not necessarily reflect the population distribution of the differentspecies. In fact, such an outcome would be unexpected.The six ligands studied in these investigations are shown in Figure 3. For eachnew ferrocene tetraphosphine prepared, we evaluated the hydrogenation behaviorrelative to the corresponding diphosphine of the “Josiphos” 7 or “Bophoz” 8 type.H 3CHCyHex 2PPh 2PFe(MOD) 2PtBu 2PH 3C HFePh 2PPh 2PNH 3CH 3C HFe1Josiphos(SL-J001-2)3Josiphos(SL-J013-1)5Bophoz(SL-F122-1)H 3CHCyHex 2PPh 2PFe2(SL-J851-2)H 3CHHtBuCH 2P3(MOD) 2PPCyHex 2PPh 2Fe4(SL-J853-2)H 3CH CH 3 Ph 2PPtBu 2P(MOD) 2H 3HNCHPhCHFe32PN CH 3PPh 2PPh 26(SL-F011-2)Figure 3. Structures of ligands used in this study (Cyh = cyclohexyl, Ph = phenyl,MOD = 3,5-dimethyl-4-methoxyphenyl, tBu = 2-methyl-2-propyl).For our initial studies we chose to evaluate the hydrogenation of two unsaturatedcarbonyl model prochiral substrates with rhodium complexes of chiral ferrocenediphosphine and tetraphosphine ligands using a standard set of conditions. Thesubstrates screened were methyl α-acetamido cinnamate (MAC) and dimethyliticonate (DIMI). The substrates, catalysts, conditions, and experimental results areshown in Table 1.