Diphosphine ferrocene derived

While Josiphos 41 also possessed an element of atom-centered chirality in the side chain, Reetz reported a new class of ferrocene-derived diphosphines which had planar chirality only ligands 42 and 43, which have C2- and C -symmetry, respectively.87 Rhodium(i)-complexes of ligands (—)-42 and (—)-43 were used in situ as catalysts (0.75 mol%) for the hydroboration of styrene with catecholborane 1 for 12 h in toluene at — 50 °C. The rhodium/ i-symmetric (—)-43 catalyst system was the more enantioselective of the two - ( -l-phenylethanol was afforded with 52% and 77% ee with diphosphines (—)-42 and (—)-43, respectively. In both cases, the regioselectivity was excellent (>99 1). With the same reaction time but using DME as solvent at lower temperature (—60 °C), the rhodium complex of 43 afforded the alcohol product with an optimum 84% ee. 

Ligand effects of diphosphines have been reported by Unruh and Christensen. They studied the hydroformylation of 1-hexene using substituted ferrocene derived diphosphines Fe sHiPRah (Fig. 6.4). 

Reaction of phosphinite borane 42 (Table 4.2, entry 43) with 1-bromo-l -lithioferrocene afforded the monophosphine borane 43 (Table 4.4, entry 50), which still possesses a bromine atom susceptible to metallation on the non-phosphinated Cp ring. After lithiation, the ferrocenyl anion reacted with the second phosphinite borane 44 (Table 4.2, entry 44), affording the desired optically pure dissymmetric diphosphine borane 45 in 29% yield from 42. During the synthesis impurities such as undesired monosubstituted ferrocene derivatives could be separated by column chromatography. 

Josiphos Chiral diphosphine ligand derived from ferrocene... 

Another interesting example was reported by Hayashi in the form of asymmetric rhodium-catalyzed hydrogenations of tetrasubstituted acrylic acids, such as 109. In the presence of Rh complexes prepared from the ferrocene-derived diphosphine ligand 110 (Equation 30) [82], 111 is produced in quantitative yield and excellent enantioselectivity. 

The ferrocene-derived Josiphos ligands (137) first reported by Togni and Spindler [99] are another class of chiral diphosphine ligands that are of immense importance both in asymmetric hydrogenations and in other asymmetric transformations. A variety of substrates can be reduced with high enantioselectivity in the presence of chiral metal complexes derived from these ligands. The reduction of dimethyl itaconate (136) furnishes 138 in quantitative yield and 98-99 % ee (Equation 39) [99]. 

Hartwig reported that ferrocene-based diphosphine 13 catalyzes the arylation of aniline at room temperature, Eq. (91) [72]. Additionally, the (f-BuljP/Pd-based system effects the room-temperatuxe condensation of anilines and aryl bromides. However, the (f-BuljP/Pd-catalyst is considerably more active [50]. While the reaction with 4-bromotoluene and anihne proceeded in 20 h using 5 mol% 15/Pd(dba)2, the reaction between bromoben-zene and aniline was complete in 1 h using only 1 mol% of the (f-BuljP-derived catalyst. 

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