Martín Marta, Torres Olga, Oñate Enrique, Sola Eduardo, Oro Luis A
Departamento de Compuestos de Coordinación y Catálisis Homogénea, Instituto de Ciencia de Materiales de Aragón, Universidad de Zaragoza-CSIC and Instituto Universitario de Catálisis Homogénea, Universidad de Zaragoza, 50009 Zaragoza, Spain.
J Am Chem Soc. 2005 Dec 28;127(51):18074-84. doi: 10.1021/ja0557233.
In the presence of ligands such as acetonitrile, ethylene, or propylene, the Ir(I) complex [Ir(1,2,5,6-eta-C8H12)(NCMe)(PMe3)]BF4 (1) transforms into the Ir(III) derivatives [Ir(1-kappa-4,5,6-eta-C8H12)(NCMe)(L)(PMe3)]BF4 (L = NCMe, 2; eta2-C2H4, 3; eta2-C3H6, 4), respectively, through a sequence of C-H oxidative addition and insertion elementary steps. The rate of this transformation depends on the nature of L and, in the case of NCMe, the pseudo-first-order rate constants display a dependence upon ligand concentration suggesting the formation of five-coordinate reaction intermediates. A similar reaction between 1 and vinyl acetate affords the Ir(III) complex [Ir(1-kappa-4,5,6-eta-C8H12){kappa-O-eta2-OC(Me)OC2H3}(PMe3)]BF4 (7) via the isolable five-coordinate Ir(I) compound [Ir(1,2,5,6-eta-C8H12){kappa-O-eta2-OC(Me)OC2H3}(PMe3)]BF4 (6). DFT (B3LYP) calculations in model complexes show that reactions initiated by acetonitrile or ethylene five-coordinate adducts involve C-H oxidative addition transition states of lower energy than that found in the absence of these ligands. Key species in these ligand-assisted transformations are the distorted (nonsquare-planar) intermediates preceding the intramolecular C-H oxidative addition step, which are generated after release of one cyclooctadiene double bond from the five-coordinate species. The feasibility of this mechanism is also investigated for complexes [IrCl(L)(PiPr3)2] (L = eta2-C2H4, 27; eta2-C3H6, 28). In the presence of NCMe, these complexes afford the C-H activation products [IrClH(CH=CHR)(NCMe)(PiPr3)2] (R = H, 29; Me, 30) via the common cyclometalated intermediate [IrClH{kappa-P,C-P(iPr)2CH(CH3)CH2}(NCMe)(PiPr3)] (31). The most effective C-H oxidative addition mechanism seems to involve three-coordinate intermediates generated by photochemical release of the alkene ligand. However, in the absence of light, the reaction rates display dependences upon NCMe concentration again indicating the intermediacy of five-coordinate acetonitrile adducts.
在乙腈、乙烯或丙烯等配体存在下，Ir(I)配合物[Ir(1,2,5,6-η-C8H12)(NCMe)(PMe3)]BF4 (1)通过一系列C-H氧化加成和插入基本步骤分别转化为Ir(III)衍生物[Ir(1-κ-4,5,6-η-C8H12)(NCMe)(L)(PMe3)]BF4 (L = NCMe, 2；η2-C2H4, 3；η2-C3H6, 4)。这种转化的速率取决于配体L的性质，对于乙腈的情况，准一级速率常数显示出对配体浓度的依赖性，这表明形成了五配位反应中间体。1与醋酸乙烯酯之间的类似反应通过可分离的五配位Ir(I)化合物[Ir(1,2,5,6-η-C8H12){κ-O-η2-OC(Me)OC2H3}(PMe3)]BF4 (6)得到Ir(III)配合物[Ir(1-κ-4,5,6-η-C8H12){κ-O-η2-OC(Me)OC2H3}(PMe3)]BF4 (7)。模型配合物中的DFT (B3LYP)计算表明，由乙腈或乙烯五配位加合物引发的反应涉及比在没有这些配体时更低能量的C-H氧化加成过渡态。这些配体辅助转化中的关键物种是分子内C-H氧化加成步骤之前的扭曲（非平面正方形）中间体，它们是在从五配位物种释放一个环辛二烯双键后产生的。对于配合物[IrCl(L)(PiPr3)2] (L = η2-C2H4, 27；η2-C3H6, 28)也研究了该机制的可行性。在乙腈存在下，这些配合物通过常见的环金属化中间体[IrClH{κ-P,C-P(iPr)2CH(CH3)CH2}(NCMe)(PiPr3)] (31)得到C-H活化产物[IrClH(CH=CHR)(NCMe)(PiPr3)2] (R = H, 29；Me, 30)。最有效的C-H氧化加成机制似乎涉及由烯烃配体的光化学释放产生的三配位中间体。然而，在没有光照的情况下，反应速率再次显示出对乙腈浓度的依赖性，这再次表明五配位乙腈加合物的中间体性质。
