ROLE OF THE METAL CENTER IN THE HOMOGENEOUS CATALYTIC DECARBOXYLATION OF SELECT CARBOXYLIC-ACIDS - COPPER(I) AND ZINC(II) DERIVATIVES
ROLE OF THE METAL CENTER IN THE HOMOGENEOUS CATALYTIC DECARBOXYLATION OF SELECT CARBOXYLIC-ACIDS - COPPER(I) AND ZINC(II) DERIVATIVES
复制标题
DOI：
10.1021/ja00106a034
复制
发表时间：
1995-01-11
影响因子：
15
通讯作者：
REIBENSPIES, JH
中科院分区：
文献类型：
--
作者：
DARENSBOURG, DJ;HOLTCAMP, MW;REIBENSPIES, JH
通过结构和动力学研究，全面研究了铜（I）影响氰乙酸脱羧反应的机理。正丁酸铜（I）与1当量氰乙酸和2当量磷化氢反应，合成了铜（I）配合物[（R（3）P）（2）CuO_2CCH_2CN]（1，2）。在R = Ph的情况下，复合物被证明是二聚体，无论是在溶液中还是在固体状态下，由两个铜（I）中心桥接的两个氰基乙酸基团，通过羧酸酯官能团和氮结合到铜。另一方面，对于空间位阻的膦（R = Cy），通过X射线晶体学发现配合物（3）是单体的并且含有单齿羧酸根基团。氰基乙酸盐结合的单齿性质被证明是氰基乙酸盐配体吸电子能力的函数，如通过对（Cy（3）P）（2）Cu（butyrate）（4）类似物的固态结构的检查所揭示的，其中更碱性的丁酸盐配体被证明以双齿方式结合。观察到氰基乙酸铜（I）的两种膦衍生物容易进行可逆的脱羧/羧化过程，如它们与（CO2）-C-13的交换反应所证明的。注意到[PPN][O2 CCH 2CN]和eta（3）-HB（3-PhPz）（3）Zn（O2 CCH 2CN）（5）盐与C-13标记的CO2的类似的、慢得多的交换反应。这些（CO2）-C-13交换过程被发现是一级在各自的基板，与Cy（3）P衍生物进行更快的交换比Ph（3）P复合物。此外，氰乙酸铜（I）的膦衍生物是有效的催化剂，用于氰乙酸的脱羧反应，以非常类似于CO2交换过程的速率得到CH 3CN和CO2。这些反应在铜（I）络合物中为一级反应，在氰基乙酸浓度低于0.05 M时为零级反应。在较高的酸浓度下，由于氰乙酸与铜（I）络合，反应被氰乙酸抑制。η（3）-HB（3-PhPz）（3）Zn（O_2CCH_2CN）和[（[12]ane（3））Zn（O_2CCH_3）][Ph（4）B]对氰乙酸的脱羧反应也是有效的催化剂，后者的阳离子衍生物活性更高。催化行为的这种差异归因于阳离子衍生物中较弱的Zn-O键，如通过X射线晶体学测定的，1.941对1.912埃。提出了一种脱羧机制，其涉及从氰基乙酸配体中消除CO2，所述氰基乙酸配体是与金属中心结合的腈，即，亲电催化3的晶体数据：单斜空间群P2（1）/n，a = 10.619（2）埃，B = 20.628（3）埃，c = 18.146（3）埃，β = 93.89（1）度，Z = 2，R = 6.40%。晶体数据4：三斜晶系空间群P1，a = 9.706（2）埃，B = 10.442（2）埃，c = 22.423（4）埃，α = 97.51（2）度，β 92.30（2）度，γ = 116.22（1）度，Z = 2，R = 4.91%。水晶数据5：三斜晶系空间群P1，a = 13.197（2）埃，B = 14.657（2）埃，c = 16.049（3）埃，α = 103.44（1）度，β = 107.10（1）度，γ = 92.19（1）度，Z = 2，R = 4.72%。
The mechanism by which copper(I) influences the decarboxylation of cyanoacetic acid has been studied comprehensively by means of structural and kinetic investigations. The copper(I) complexes, [(R(3)P)(2)CuO2CCH2CN](1,2), have been synthesized from the reaction of copper(I) n-butyrate with 1 equiv of cyanoacetic acid and 2 equiv of phosphine. In the case of R = Ph, the complex is shown to be a dimer, both in solution and in the solid state, consisting of two copper(I) centers bridged by two cyanoacetate groups that are bound to copper through both the carboxylate functionality and the nitrogen. On the other hand, for the sterically encumbered phosphine (R = Cy), the complex (3) is found by X-ray crystallography to be monomeric and to contain a monodentate carboxylate group. The monodentate nature of the cyanoacetate binding was demonstrated to be a function of the electron-withdrawing ability of the cyanoacetate ligand as revealed by an examination of the solid-state structure of the (Cy(3)P)(2)Cu(butyrate) (4) analog, where the more basic butyrate ligand was shown to be bound in a bidentate manner. Both phosphine derivatives of copper(I) cyanoacetate were observed to readily undergo reversible decarboxylation/carboxylation processes as evidenced by their exchange reactions with (CO2)-C-13. A similar, much slower, exchange reaction with C-13-labeled CO2 was noted for the [PPN][O2CCH2CN] and eta(3)-HB(3-PhPz)(3)Zn(O2CCH2CN) (5) salts. These (CO2)-C-13 exchange processes were found to be first-order in the respective substrate, with the Cy(3)P derivative undergoing more rapid exchange than the Ph(3)P complex. Furthermore, the phosphine derivatives of copper(I) cyanoacetate were efficient catalysts for the decarboxylation of cyanoacetic acid to afford CH3CN and CO2 at rates quite similar to the CO2 exchange process. These reactions were first-order in copper(I) complexes and zero-order in cyanoacetic acid concentrations below 0.05 M. At higher acid concentrations the reaction was inhibited by cyanoacetic acid due to its complexation with copper(I). Both eta(3)-HB(3-PhPz)(3)Zn(O2CCH2CN) and [([12]ane(3))Zn(O2CCH3)][Ph(4)B] are effective catalysts as well for the decarboxylation of cyanoacetic acid, with the latter cationic derivative being more active. This difference in catalytic behavior is attributed to the weaker Zn-O bond in the cationic derivative as determined by X-ray crystallography, 1.941 vs 1.912 Angstrom. A mechanism for decarboxylation is proposed which involves CO2 elimination from a cyanoacetic ligand that is nitrile bound to the metal center, i.e., electrophilic catalysis. Crystal data for 3: monoclinic space group P2(1)/n, a = 10.619(2) Angstrom, b = 20.628(3) Angstrom, c = 18.146(3) Angstrom, beta = 93.89(1)degrees, Z = 2, R = 6.40%. Crystal data for 4: triclinic space group P1, a = 9.706(2) Angstrom, b = 10.442(2) Angstrom, c = 22.423(4) Angstrom, alpha = 97.51(2)degrees, beta 92.30(2)degrees, gamma = 116.22(1)degrees, Z = 2, R = 4.91%. Crystal data for 5: triclinic space group P1, a = 13.197(2) Angstrom, b = 14.657(2) Angstrom, c = 16.049(3) Angstrom, alpha = 103.44(1)degrees, beta = 107.10(1)degrees, gamma = 92.19(1)degrees, Z = 2, R = 4.72%.