BINAP-DPEN catalyst

Catalysts for ketone hydrogenation continue to be developed but one of the best systems is still the BINAP-DPEN catalyst first reported by Ohkuma et al. in 1995. " In this system ruthenium is combined with both a chiral diphosphine and a chiral diamine, forming an octahedral complex which gives a high degree of enantioselectivity. This stereoselectivity is considered to be a result of the synergistic effect of the chiral diphosphine and diamine ligands. 

Immobilized catalysts on solid supports inherently have benefits because of their easy separation from the products and the possibility of recycling. They are also expected to be useful for combinatorial chemistry and high-throughput experimentation. The polystyrene-bound BINAP/DPEN-Ru complex (beads) in the presence of (CH3)3COK catalyzes the hydrogenation of l -acetonaphthone with an SCR of 12 300 in a 2-propanol-DMF mixture (1 1, v/v) to afford the chiral alcohol in 97% ee (Fig. 32.35) [113]. This supported complex is separable... 

Fig. 32.35 Hydrogenation of I -acetonaphthone with the polymer-bound BINAP/DPEN-Ru catalyst.

The hydrogenation of a number of aromatic ketones is shown in Figure 37.30. Noyori s very effective Ru-diphosphine-diamine technology was developed by several companies. It is not clear on which scale the processes developed by Takasago (dm-binap = 3,5-xylyl-binap) [16] and Dow/Chirotech [109-111] for the reduction of substituted acetophenones are actually applied commercially. Using the Xyl-PhanePhos-dpen catalyst, a highly efficient bench-scale process was developed for the hydrogenation of p-fluoroacetophenone (ee 98%, TON 100000, TOF 50000 IT1 at r.t., 8 bar) [109]. Ru-P-Phos (licensed to Johnson Matthey [112]) achieved ee-values >99.9% and TON up to 100000 for sev-... 

In a related approach, Fan et al. synthesized a series of dendritic BINAP-Ru/chiral diamine ((R,R)-l,2-diphenylethylenediamine DPEN) catalysts for the asymmetric hydrogenation of various simple aryl ketones (Fig. 15) [42]. The resulting systems displayed high catalytic activity and enantioselectivity and allowed facile catalyst recycling. In the case of 1-acetonaphthone and... 

We later developed an analogous enantioselective hydrogenation of aldehydes to the corresponding -branched alcohols using [RuCl2 (xylyl-BINAP) (DPEN or DACH)] as the catalyst (Li and List 2007 for an independent study, see Xie et al. 2007). 

Table 7-4. Asymmetric activation of racemic binaps-RuCiT catalyst (3) by enantio-pure dpen ) ...

Zr[Ru(L -H,)(DPEN)Cl,]4Hp (20) and Zr[Ru(Lj,-H,)(DPEN)Cl,]4Hp (21), respectively. adsorption measurements indicated that both 20 and 21 are highly porous with rather wide pore size distributions. The enantioselective catalytic activity of 20 and 21 for the hydrogenation of aromatic ketones was studied (Table 5). Only 0.1 mol% loading of catalyst 20 in isopropanol was sufficient to hydrogenate acetophenone with complete conversion and 96.3% ee, which is significantly higher than that observed for the parent Ru-BINAP-DPEN homogeneous catalyst (-80% ee) under similar conditions [89,90]. 

Noyori et al. recently used ESI-MS to characterize species present in catalytically active solutions during the hydrogenation of aryl-alkyl ketones using their base-free catalyst precursors trans-[Ru((R)-tol-BINAP)((R, RJ-dpenJfHXf/ -BH ] (tol-BI-NAP = 2,2 -bis(ditolylphosphino) -1, T-binaphthyl dpen = 1,2-diphenylethylenedia-mine) in 2-propanol [9b]. Based upon ESI-MS observations, deuterium-labeling studies, kinetics, NMR observations, and other results, the authors proposed that the cationic dihydrogen complex trans-[Ru((R)-tol-BINAP)((R, R)-dpen)(H)( 2-H2)]+ is an intermediate in hydrogenations carried out in the absence of base. 

A remarkable match-mismatch effect is observed. The difference in reactivity of the matched catalyst—for example, Ru(R-BINAP)(S,S-DPEN)Cl2—can be 120 times more reactive than the mismatched catalyst, Ru(S-BINAP)(S,S-DPEN)Cl2.196 197... 

The use of an activation/deactivation protocol with a chiral poison, (R)-DM-DABN (148), has been achieved with ruthenium catalysts that contained rac-xyl-BINAP and rac-tol-BINAP with chiral diamine (S,S)-DPEN. Asymmetric hydrogenation of 2-napthyl methyl ketone (128, Ar = 2-Naph, R = Me) without 148 gave the alcohol with 41% ee, whereas an enantioselectivity of 91% ee is obtained with deactivator 148 present (Scheme 12.58).197... 

The discovery by the recent Nobel-laureate, Ryoji Noyori, of asymmetric hydrogenation of simple ketones to alcohols catalyzed by raras-RuCl2[(S)-binap][(S,S)-dpen] (binap = [l,l -binaphthalene-2,2/-diyl-bis(diphenylphosphane)] dpen = diphenylethylenediamine) is remarkable in several respects (91). The reaction is quantitative within hours, gives enantiomeric excesses (ee) up to 99%, shows high chemoselecti-vity for carbonyl over olefin reduction, and the substrate-to-catalyst ratio is >100,000. Moreover, the non-classical metal-ligand bifunctional catalytic cycle is mechanistically novel and involves heterolytic... 

The stability of (BIPHEP)PtX2 compounds with respect to racemization over several hours at room temperature suggested that these compounds could be employed as catalysts at room temperature or below. To explore this possibility, [BlPHEP]Pt(OTf)2 was employed in the asymmetric Diels-Alder reaction as illustrated in equation (6). Freshly generated [(l )-BlPHEP]Pt(OTf)2 promoted the asynunetric Diels Alder reaction forming the product in 94 6 endo exo ratio with the ee of the major diastereomer of 92 94%. The enantiomeric excess of the catalyst [(l )-BlPHEP]Pt(OTf)2 was not diminished over the course of the reaction, as determined by quenching the reaction at >90% conversion with (5, 5 )-DPEN and subsequent P NMR analysis of the resulting mixture. The facial selectivity of the asymmetric Diels-Alder reaction catalyzed by [(/f)-BlPHEP]Pt(OTf)2 was the same as observed with [(/ )-BINAP]Pt(OTf)2 with the same... 

The catalyst composed of the mismatched ligands, (f )-Xyl-BlNAP and (5,5)-DPEN, was much slower and furnished the (5)-alcohol with 56% ee (equation 10). Employing racemic Xyl-BINAP and (5, 5 )-DPEN gave a 50 50 mixture of diastereomeric ruthenium complexes that reduced I -acetylnaphthone to the (f )-alcohol with excellent enantioselectivity (90%). 

Interestingly, when the precatalyst RuCl2[(5 )-Tol-BINAP][(S,5)-DPEN] (Tol = d-CeELi-Me) was employed in the reduction of 9-acetylanthracene the enantioselectivity was only 40% (equation 11). In contrast, use of RuCl2 [(/ )-Tol-BINAP][(5,5)-DPEN] resulted in a reduction of the ketone with 81% ee. Employing racemic Tol-BINAP and (5,5 )-DPEN gave (/f)-alcohol with essentially the same enantioselectivity as the enantioenriched (/f)/(5, 5 )-catalyst. 

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