Asymmetric catalysis with the normally unresolvable, conformationally dynamic 2,2′-bis(diphenylphosphino)-1,1′-biphenyl (biphep)
Asymmetric catalysis with the normally unresolvable, conformationally dynamic 2,2′-bis(diphenylphosphino)-1,1′-biphenyl (biphep)
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DOI：
10.1021/ja016167p
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发表时间：
2001-09-26
影响因子：
15
通讯作者：
Gagné, MR
中科院分区：
文献类型：
--
作者：
Becker, JJ;White, PS;Gagné, MR
在不对称催化中实现高的对映选择性通常需要刚性的、构象受限的手性配体（例如BINAP、DuPhos）。1最近出现了一种新的方法，其中有意地使用构象灵活的配体来放大其他手性配体的作用。2例如，Et 2 Zn与醛的加成可以用含有柔性双（磺酰胺）配体与通常无效的手性醇盐配体的组合的钛催化剂进行对映选择性。2a提出手性醇盐通过在磺酰胺配体中诱导选择性构象来放大其手性。类似地，手性胺或胺N-氧化物添加剂诱导在其他非手性（salen）锰（II）络合物中的手性构象，并导致对映选择性烯烃环氧化催化。2b-d 1，1′-双（二苯基膦基）联苯（biphep）在两种atrop形式之间相互转化，当与手性钌片段Cl 2 Ru（S，S-dpeda），（S，S-dpeda）（S，S）-1，2-二苯基乙二胺）配位时，其中一种是有利的（3：1）。2 e-f这3：1的混合物选择性氢化酮在高达92%ee。上述每种情况下利用灵活的配体放大立体化学诱导的手性催化剂。更罕见的是利用被锁定在亚稳态的柔性配体来提供催化的唯一不对称性来源。Brintzinger的联苯桥连的bisCp钛催化剂以这种方式起作用。3在这种独特的情况下，非对映异构体混合物的热处理产生单一复合物，其中BINOL对一种反式形式的柄型配体的偏好提供了对映和非对映纯的二茂钛预催化剂，在去除BINOL后，该催化剂以高达98%ee氢化1-苯基吡咯啉。该催化剂中立体控制的唯一来源来自联苯桥连配体。将这一策略扩展到在催化中具有广泛用途的手性配体（例如，二膦），有望将手性配体基础扩展到通常被认为是可拆分的基础之外。
Achieving high enantioselectivites in asymmetric catalysis usually requires rigid, conformationally restricted chiral ligands (eg, BINAP, DuPhos). 1 Recently a new approach has emerged where conformationally flexible ligands are intentionally used to magnify the effect of other chiral ligands. 2 For example, Et2Zn addition to aldehydes can be made enantioselective with titanium catalysts containing flexible bis (sulfonamide) ligands in combination with a normally ineffective chiral alkoxide ligand. 2a The chiral alkoxide is proposed to magnify its chirality by inducing a selective conformation in the sulfonamide ligand. Similarly, chiral amine or amine N-oxide additives induce chiral conformations in otherwise achiral (salen) manganese (II) complexes and lead to enantioselective alkene epoxidation catalysis. 2b-d 1, 1′-Bis (diphenylphosphino) biphenyl (biphep) interconverts between two atrop forms, one of which is favored (3: 1) when coordinated to the chiral ruthenium fragment, Cl2Ru (S, S-dpeda),(S, S-dpeda)(S, S)-1, 2-diphenylethylenediamine). 2e-f This 3: 1 mixture selectively hydrogenates ketones in up to 92% ee. Each of the above cases utilizes a flexible ligand to magnify the stereochemical induction of a chiral catalyst. More rare is the utilization of a flexible ligand that is locked into a metastable state to provide the only source of asymmetry for catalysis. Brintzinger’s biphenyl-bridged bisCp titanium catalyst functions in this manner. 3 In this unique case, thermolysis of a mixture of diastereomers leads to a single complex where BINOL’s preference for one atrop form of the ansa ligand provides an enantioand diastereopure titanocene precatalyst, which after BINOL removal hydrogenates 1-phenylpyrroline in up to 98% ee. The sole source of stereocontrol in this catalyst comes from the biphenyl-bridged ligand. Expanding this strategy to chiral ligands with broad utility in catalysis (eg, diphosphines) promises to expand the chiral ligand base beyond those normally considered resolvable.