氧供体铱（III）配合物的合成、结构与反应性：苯的C-H活化研究

Synthesis, structure, and reactivity of O-donor Ir(III) complexes: C-H activation studies with benzene.

作者信息

Bhalla Gaurav, Liu Xiang Yang, Oxgaard Jonas, Goddard William A, Periana Roy A

机构信息

Donald P. and Katherine B. Loker Hydrocarbon Research Institute and Department of Chemistry, University of Southern California, Los Angeles, California 90089-1661, USA.

出版信息

J Am Chem Soc. 2005 Aug 17;127(32):11372-89. doi: 10.1021/ja051532o.

DOI:10.1021/ja051532o

PMID:16089467

Abstract

Various new thermally air- and water-stable alkyl and aryl analogues of (acac-O,O)2Ir(R)(L), R-Ir-L (acac-O,O = kappa2-O,O-acetylacetonate, -Ir- is the trans-(acac-O,O)2Ir(III) motif, R = CH3, C2H5, Ph, PhCH2CH2, L = Py) have been synthesized using the dinuclear complex [Ir(mu-acac-O,O,C3)-(acac-O,O)(acac-C3)]2, [acac-C-Ir]2, or acac-C-Ir-H2O. The dinuclear Ir (III) complexes, [Ir(mu-acac-O,O,C3)-(acac-O,O)(R)]2 (R = alkyl), show fluxional behavior with a five-coordinate, 16 electron complex by a dissociative pathway. The pyridine adducts, R-Ir-Py, undergo degenerate Py exchange via a dissociative mechanism with activation parameters for Ph-Ir-Py (deltaH++ = 22.8 +/- 0.5 kcal/mol; deltaS++ = 8.4 +/- 1.6 eu; deltaG++298 K) = 20.3 +/- 1.0 kcal/mol) and CH3-Ir-Py (deltaH++ = 19.9 +/- 1.4 kcal/mol; deltaS++ = 4.4 +/- 5.5 eu; deltaG++298 K) = 18.6 +/- 0.5 kcal/mol). The trans complex, Ph-Ir-Py, undergoes quantitatively trans-cis isomerization to generate cis-Ph-Ir-Py on heating. All the R-Ir-Py complexes undergo quantitative, intermolecular CH activation reactions with benzene to generate Ph-Ir-Py and RH. The activation parameters (deltaS++ =11.5 +/- 3.0 eu; deltaH++ = 41.1 +/- 1.1 kcal/mol; deltaG++298 K = 37.7 +/- 1.0 kcal/mol) for CH activation were obtained using CH3-Ir-Py as starting material at a constant ratio of [Py]/[C6D6] = 0.045. Overall the CH activation reaction with R-Ir-Py has been shown to proceed via four key steps: (A) pre-equilibrium loss of pyridine that generates a trans-five-coordinate, square pyramidal intermediate; (B) unimolecular, isomerization of the trans-five-coordinate to generate a cis-five-coordinate intermediate, cis-R-Ir- square; (C) rate-determining coordination of this species to benzene to generate a discrete benzene complex, cis-R-Ir-PhH; and (D) rapid C-H cleavage. Kinetic isotope effects on the CH activation with mixtures of C6H6/C6D6 (KIE = 1) and with 1,3,5-C6H3D3 (KIE approximately 3.2 at 110 degrees C) are consistent with this reaction mechanism.

摘要

已使用双核配合物[Ir(μ - acac - O,O,C3)-(acac - O,O)(acac - C3)]2、[acac - C - Ir]2或acac - C - Ir - H2O合成了(acac - O,O)2Ir(R)(L)、R - Ir - L（acac - O,O = κ2 - O,O - 乙酰丙酮，-Ir-为反式-(acac - O,O)2Ir(III)结构单元，R = CH3、C2H5、Ph、PhCH2CH2，L = Py）的各种新型热稳定的烷基和芳基类似物。双核Ir(III)配合物[Ir(μ - acac - O,O,C3)-(acac - O,O)(R)]2（R = 烷基）通过解离途径表现出五配位、16电子配合物的动态行为。吡啶加合物R - Ir - Py通过解离机制进行简并的Py交换，其Ph - Ir - Py的活化参数为（ΔH++ = 22.8 ± 0.5 kcal/mol；ΔS++ = 8.4 ± 1.6 eu；ΔG++298K = 20.3 ± 1.0 kcal/mol），CH3 - Ir - Py的活化参数为（ΔH++ = 19.9 ± 1.4 kcal/mol；ΔS++ = 4.4 ± 5.5 eu；ΔG++298K = 18.6 ± 0.5 kcal/mol）。反式配合物Ph - Ir - Py加热时定量地发生反式 - 顺式异构化生成顺式 - Ph - Ir - Py。所有R - Ir - Py配合物与苯发生定量的分子间CH活化反应生成Ph - Ir - Py和RH。以CH3 - Ir - Py为起始原料，在[Py]/[C6D6] = 0.045的恒定比例下获得了CH活化的活化参数（ΔS++ = 11. +/ - 3.0 eu；ΔH++ = 41.1 ± 1.1 kcal/mol；ΔG++298K = 37.7 ± 1.0 kcal/mol）。总体而言，R - Ir - Py的CH活化反应已被证明通过四个关键步骤进行：(A)吡啶的预平衡损失，生成反式五配位、四方锥中间体；(B)反式五配位的单分子异构化，生成顺式五配位中间体，顺式 - R - Ir - 方形；(C)该物种与苯的速率决定配位，生成离散的苯配合物，顺式 - R - Ir - PhH；以及(D)快速的C - H裂解。C6H6/C6D6混合物（KIE = 1）和1,3,5 - C6H3D3（110℃时KIE约为3.2）对CH活化的动力学同位素效应与该反应机制一致。