Reactivity of the Latent 12-Electron Fragment [Rh(P i Bu 3 ) 2 ] + with Aryl Bromides: Aryl?Br and Phosphine Ligand C?H Activation
Reactivity of the Latent 12-Electron Fragment [Rh(P i Bu 3 ) 2 ] + with Aryl Bromides: Aryl?Br and Phosphine Ligand C?H Activation
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潜在 12 电子片段 [Rh(P i Bu 3 ) 2 ] 与芳基溴化物的反应性：Aryl?Br 和膦配体 C?H 活化
DOI：
10.1002/chem.201000554
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发表时间：
2010
期刊：
影响因子：
--
通讯作者：
Townsend N
中科院分区：
文献类型：
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作者：
Townsend N
溴代芳烃与12电子[Rh（PiBu 3）2][BArF 4]（ArF= 3，5-（CF 3）2C 6 H3）的氧化加成反应形成多种产物。使用对甲苯基溴，Rh III二聚体络合物产生[Rh（PiBu 3）2（o/p-MeC 6 H4）（μ-Br）]2[BArF 4]2。类似地，与p-ClC 6 H4 Br反应得到[Rh（PiBu 3）2（p-ClC 6 H4）（μ-Br）]2[BArF 4]2。相比之下，使用o-BrC 6 H4 Me得到其中甲苯已被消除并且异丁基膦已经历C2 H3活化的产物：[Rh{PiBu 2（CH 2CHCH 3CH 2）}（PiBu 3）（μ-Br）]2[BArF 4]2。用邻溴苯甲醚或邻溴茴香硫醚的捕获实验表明，该过程的可能中间体是低配位的RhIII络合物，然后进行C-OH活化。苯甲醚和硫代苯甲醚配合物已被分离，它们的结构显示OMe或SMe与金属中心的相互作用，以及支持agostic相互作用，[Rh（PiBu 3）2（C6 H4 OMe）Br][BArF 4]（报告了5-甲基取代类似物的固态结构）和[Rh（PiBu 3）2（C6 H4 SMe）Br][BArF 4]。苯甲醚衍生的络合物继续得到[Rh{PiBu 2（CH 2CHCH 3CH 2）}（PiBu 3）（μ-Br）]2[BArF 4]2，而苯硫醚络合物是不反应的。[Rh（PiBu 3）2（C6 H4 OMe）Br][BArF 4]的分离及其向前的反应性，以得到C12 H活化和芳基消除的产物，表明它涉及σ-键复分解反应的途径，DFT计算加强了这一假设。计算还表明，通过膦辅助的非agostic键的去质子化的C = OH键裂解也是竞争性的，尽管随后的芳基配体的质子化的能量太高而不能解释产物的形成。基于这些计算，也排除了通过氧化加成的C-OH活化。这些新的配合物已经通过溶液NMR/ESIMS技术和固态X射线晶体学进行了表征。
Oxidative addition of aryl bromides to 12‐electron [Rh(PiBu3)2][BArF4] (ArF=3,5‐(CF3)2C6H3) forms a variety of products. Withp‐tolyl bromides, RhIIIdimeric complexes result [Rh(PiBu3)2(o/p‐MeC6H4)(μ‐Br)]2[BArF4]2. Similarly, reaction withp‐ClC6H4Br gives [Rh(PiBu3)2(p‐ClC6H4)(μ‐Br)]2[BArF4]2. In contrast, the use ofo‐BrC6H4Me leads to a product in which toluene has been eliminated and an isobutyl phosphine has undergone CH activation: [Rh{PiBu2(CH2CHCH3CH2)}(PiBu3)(μ‐Br)]2[BArF4]2. Trapping experiments withortho‐bromo anisole orortho‐bromo thioanisole indicate that a possible intermediate for this process is a low‐coordinate RhIIIcomplex that then undergoes CH activation. The anisole and thioanisole complexes have been isolated and their structures show OMe or SMe interactions with the metal centre alongside supporting agostic interactions, [Rh(PiBu3)2(C6H4OMe)Br][BArF4] (the solid‐state structure of the 5‐methyl substituted analogue is reported) and [Rh(PiBu3)2(C6H4SMe)Br][BArF4]. The anisole‐derived complex proceeds to give [Rh{PiBu2(CH2CHCH3CH2)}(PiBu3)(μ‐Br)]2[BArF4]2, whereas the thioanisole complex is unreactive. The isolation of [Rh(PiBu3)2(C6H4OMe)Br][BArF4] and its onward reactivity to give the products of CH activation and aryl elimination suggest that it is implicated on the pathway of a σ‐bond metathesis reaction, a hypothesis strengthened by DFT calculations. Calculations also suggest that CH bond cleavage through phosphine‐assisted deprotonation of a non‐agostic bond is also competitive, although the subsequent protonation of the aryl ligand is too high in energy to account for product formation. CH activation through oxidative addition is also ruled out on the basis of these calculations. These new complexes have been characterised by solution NMR/ESIMS techniques and in the solid‐state by X‐ray crystallography.