Recent Developments in Catalytic Asymmetric Hydrogenation Employing P‐Chirogenic Diphosphine Ligands

Abstract

Rhodium‐ and ruthenium‐catalyzed asymmetric hydrogenations reactions employing C2‐symmetric chiral diphosphine ligands have a long history, and exceedingly high enantioselectivities have been reported. On the other hand, metal complexes containing P‐chirogenic, electron‐rich diphosphine ligands such as 1,2‐bis(alkylmethylphosphino)ethane (BisP*) and bis(alkylmethylphosphino)methane (MiniPHOS) have been tested only recently, and proved greatly successful. These results prompted intensive research amongst organic chemists, and the scope and limitations of the use of ligands bearing the chiral center at phosphorus atoms is presented in this review. The most recent data have been collected and summarized. In terms of ligand design, it is necessary to address an important question: “which properties are responsible for very high enantioselectivity in hydrogenation reactions?”. To this extent, a full discussion of new aspects on the mechanism, in particular the demonstration of a dihydride mechanism for enantioselective hydrogenation as opposed to the unsaturated mechanism widely accepted so far, also constitutes an important part of this review.

Conservation of helicity and helical character matching in chiral interactions

“…Also, independent of the size variations of R 1 and R 2 , catalysts of comparable helical characters, such as 1d -h, 1i -m, and 1n -p, give comparable ee values, further highlighting the control of catalyst -substrate helical character matching on the magnitude of enantioselectivity. By contrast, application of conventional steric theories, such as the diene twist rule 18 or the quadrant rule, 19 to these systems seem not to lead to correct predictions either of the senses of asymmetric induction or of the variations in ee. That certain catalyst structural properties can be related to the magnitudes of the ee they induce should have practical utility.…”

Synthesis of unsymmetrical P-stereogenic oligophosphines and chemoselective cleavage of phosphine-borane coordinate bonds

“…The organic layer was extracted with ethyl acetate (100 ml  3). The combined organic layers were washed with brine and dried over MgSO 4 . After filtration, the solvent was removed in vacuo.…”

“…1 In fact, several such P-stereogenic phosphines have been prepared, and in particular, P-stereogenic bisphosphines have been widely employed as chelate ligands for transition metal-catalyzed asymmetric reactions. [2][3][4][5][6] However, despite the widespread use of P-stereogenic phosphines, polymers containing chiral phosphorus atoms in their backbones have rarely been prepared. 7 Recently, we synthesized P-stereogenic optically active polymers [8][9][10][11][12][13] and oligomers [14][15][16] using P-stereogenic bisphosphines as chiral building blocks.…”

Recent progress in the development of advanced element-block materials

“…110 Therefore, their complexes are widely used as chiral catalysts. [111][112][113] There are several optically active polymers whose structures are highly controlled by repeating asymmetric reactions; however, optically active polymers including chiral heteroatoms in the main chain are limited. In our group, we have successfully reported oligomers, [114][115][116][117] polymers, 118-123 dendrimers 124 and macrocycles, [125][126][127][128][129][130][131][132][133] including chiral phosphorus atoms in the main chain, and we have revealed their properties and potential applications.…”