Structural and kinetic effects of chloride ions in the palladium-catalyzed allylic substitutions
Structural and kinetic effects of chloride ions in the palladium-catalyzed allylic substitutions
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DOI：
10.1016/s0022-328x(03)00791-5
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发表时间：
2003-12-07
影响因子：
2.3
通讯作者：
Jutand, A
中科院分区：
文献类型：
--
作者：
Cantat, T;Génin, E;Jutand, A
配体与[Pd（eta（3）-RCH-CH-CH 2）（μ-Cl）]（2）或氯离子与阳离子[（eta（3）-RCH-CH-CH 2）PdL 2]+ BF 4-的加成诱导中性配合物eta（1）-RCH= CH-CH 2-PdClL 2的形成（R = H，L =（4-Cl-C6H4）（3）P，（4-CH 3-C6 H4）（3）P，（4-CF 3-C6 H4）（3）P或L，= 1 2-双（二苯基膦基）丁烷（dppb），1，1 '-bis（二苯基膦基）二茂铁（dppl）; R =Ph，L =（4-Cl-C6 H4）（3）P），而不是预期的阳离子络合物[（eta（3）-RCH-CH-CH 2，）PdL 2]Cl-+（-）。在氯离子存在下，吗啉与阳离子配合物[（eta（3）-烯丙基）Pd（PAr 3）（2）]+ BF 4-（Ar =4-Cl-C6 H 4，4-CH 3-C6 H 4）的反应进行得较慢，并涉及阳离子[（eta（3）-烯丙基）Pd（PAr 3）（2）]（+）'和中性的eta（1）-烯丙基-PdCl（PAr 3）（2）配合物作为与Cl-平衡的反应物种。阳离子络合物比中性络合物反应性更强。然而，它们在反应中的相对贡献强烈地取决于控制它们的相对浓度的氯化物浓度。在高氯离子浓度下，中性的eta（1）-allyl-PdCl（PAr 3）（2）可能成为主要的反应物种。因此，与配体缔合的[Pd（eta（3）-allyl）（mu-Cl）]（2）或阳离子[（eta（3）-allyl）PdL 2]+ BF 4-（在钯催化的烯丙基取代中无差别地用作前体）是不等价的。在这两种情况下，Pd催化的烯丙基取代的机理取决于氯离子的浓度，所述氯离子由前体递送或有意添加，其决定哪种物质[（η（3）-烯丙基）PdL 2]（+）或/和η（1）-烯丙基-PdClL 2参与亲核攻击，从而影响反应速率并可能影响其区域选择性。因此，催化前体[Pd（eta（3）-allyl）（mu-Cl）]（2）的氯离子不能被认为是“无辜的”配体。(C)2003 Elsevier B. V.保留所有权利。
Addition of ligands to [Pd(eta(3)-RCH-CH-CH2)(mu-Cl)](2) or chloride ions to cationic [(eta(3)-RCH-CH-CH2)PdL2]+BF4- induces the formation of neutral complexes eta(1)-RCH=CH-CH2-PdClL2 (R = H with L = (4-Cl-C6H4)(3)P, (4-CH3-C6H4)(3)P, (4-CF3-C6H4)(3)P or L, = 1 2-bis(diphenylphosphino)butane (dppb), 1,1'-bis(diphenylphosphino)ferrocene (dppl); R =Ph with L = (4-Cl-C6H4)(3)P), instead of the expected cationic complexes [(eta(3)-RCH-CH-CH2,)PdL2]Cl-+(-). In the presence of chloride ions, the reaction of morpholine with the cationic complexes [(eta(3)-allyl)Pd(PAr3)(2)]+BF4- (Ar =4-Cl-C6H4, 4-CH3-C6H4) goes slower and involves both cationic [(eta(3)-allyl)Pd(PAr3)(2)](+)' and neutral eta(1)-allyl-PdCl(PAr3)(2) complexes as reactive species in equilibrium with Cl-. The cationic complex is more reactive than the neutral one. However, their relative contribution in the reaction strongly depends on the chloride concentration, which controls their relative concentration. The neutral eta(1)-allyl-PdCl(PAr3)(2) may become the major reactive species at high chloride concentration. Consequently, [Pd(eta(3)-allyl)(mu-Cl)](2) associated with ligands or cationic [(eta(3)-allyl)PdL2]+BF4-, used indifferently as precursors in palladium-catalyzed allylic substitutions, are not equivalent. In both situations, the mechanism of the Pd-catalyzed allylic substitution depends on the concentration of the chloride ions, delivered by the precursor or purposely added, that determines which species, [(eta(3)-allyl)PdL2](+) or/and eta(1)-allyl-PdClL2 are involved in the nucleophilic attack with consequences on the rate of the reaction and probably on its regioselectivity. Consequently, the chloride ions of the catalytic precursors [Pd(eta(3)-allyl)(mu-Cl)](2) must not be considered as 'innocent' ligands. (C) 2003 Elsevier B.V. All rights reserved.