Munz Dominik
Friedrich-Alexander Universität Erlangen-Nürnberg , Egerlandstr. 1 , 91058 Erlangen , Germany . Email:
Chem Sci. 2017 Dec 13;9(5):1155-1167. doi: 10.1039/c7sc05034h. eCollection 2018 Feb 7.
The isolation of terminal oxo complexes of the late transition metals promises new avenues in oxidation catalysis like the selective and catalytic hydroxylation of unreactive CH bonds, the activation of water, or the upgrading of olefins. While terminal oxo ligands are ubiquitous for early transition metals, well-characterized examples with group 10 metals remain hitherto elusive. In search for palladium terminal oxo complexes, the relative stability/reactivity of such compounds are evaluated computationally (CASSCF/NEVPT2; DFT). The calculations investigate only well-known ligand systems with established synthetic procedures and relevance for coordination chemistry and homogeneous catalysis. They delineate and quantify, which electronic properties of ancillary ligands are crucial for taming otherwise highly reactive terminal oxo intermediates. Notably, carbene ligands with both strong σ-donor and strong π-acceptor properties are best suited for the stabilization of palladium(ii) terminal oxo complexes, whereas ligands with a weaker ligand field lead to highly reactive complexes. Strongly donating ligands are an excellent choice for high-valent palladium(iv) terminal oxo compounds. Low coordinate palladium(ii) as well as high-valent palladium(iv) complexes are best suited for the activation of strong bonds.
分离晚期过渡金属的末端氧配合物有望为氧化催化开辟新途径，如对惰性碳氢键进行选择性催化羟基化、活化水或烯烃升级。虽然末端氧配体在早期过渡金属中普遍存在，但迄今仍难以找到具有第10族金属的特征明确的例子。为了寻找钯末端氧配合物，通过计算（CASSCF/NEVPT2；DFT）评估了这类化合物的相对稳定性/反应活性。计算仅研究具有既定合成方法且与配位化学和均相催化相关的知名配体体系。它们描绘并量化了辅助配体的哪些电子性质对于驯服原本高活性的末端氧中间体至关重要。值得注意的是，兼具强σ供体和强π受体性质的卡宾配体最适合稳定钯（II）末端氧配合物，而具有较弱配体场的配体则会导致高活性配合物。强给电子配体是高价钯（IV）末端氧化合物的绝佳选择。低配位钯（II）以及高价钯（IV）配合物最适合活化强键。
