Cu(I) complex bearing a PNP-pincer-type phosphaalkene ligand with a bulky fused-ring Eind group: properties and applications to FLP-type bond activation and catalytic CO2 reduction
Cu(I) complex bearing a PNP-pincer-type phosphaalkene ligand with a bulky fused-ring Eind group: properties and applications to FLP-type bond activation and catalytic CO2 reduction
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DOI：
10.1039/d0dt00276c
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发表时间：
2020-03-21
影响因子：
4
通讯作者：
Choi, Jun-Chul
中科院分区：
文献类型：
--
作者：
Takeuchi, Katsuhiko;Tanaka, Yuto;Choi, Jun-Chul
本文报道了[Cu（Eind（2）-BPEP）][PF_6]（2）（Eind（2）-BPEP = 2，6-双（2-Eind-2-磷乙烯基）吡啶，Eind = 1，1，3，3，5，5，7，7-八乙基-1，2，3，5，6，7-六氢-s-引达省-4-基）的合成。Gutmann-Beckett测试显示，配合物2是高度刘易斯酸，并且在强度上与B（C6 F5）（3）相当，B（C6 F5）（3）是相对强的刘易斯酸。此外，2比[Cu（Mes*（2）-BPEP）][PF 6]（3）更刘易斯酸性，[Cu（Mes*（2）-BPEP）][PF 6]（3）是具有较小体积的Mes* 而不是Eind基团的类似络合物。使用模型化合物的DFT计算显示，与3相比，2的更高的刘易斯酸性不是由于配体的电子效应，而是由于由庞大的Eind基团的空间效应引起的LUMO能量的降低。当与叔胺结合时，高度刘易斯酸性和庞大的2表现出受抑的刘易斯对（FLP）的反应性，并且可以活化氢和苯乙炔。配合物2和3在DBU的存在下，在相对温和的条件下催化CO2的氢化和硅氢加成反应。
Herein, we report the synthesis of [Cu(Eind(2)-BPEP)][PF6] (2) (Eind(2)-BPEP = 2,6-bis(2-Eind-2-phosphaethenyl)pyridine, Eind = 1,1,3,3,5,5,7,7-octaethyl-1,2,3,5,6,7-hexahydro-s-indacen-4-yl), a three-coordinated Cu(I) complex bearing a PNP-pincer-type phosphaalkene ligand with bulky fused-ring Eind groups. The Gutmann-Beckett test revealed that complex 2 is highly Lewis acidic and comparable in strength to B(C6F5)(3), which is a relatively strong Lewis acid. In addition, 2 is more Lewis acidic than [Cu(Mes*(2)-BPEP)][PF6] (3), the analogous complex with less-bulky Mes* instead of Eind groups. DFT calculations using model compounds revealed that the higher Lewis acidity of 2 compared to 3 is not due to the electronic effects of the ligand, but due to a reduction in the LUMO energy caused by the steric effect of the bulky Eind groups. When combined with a tertiary amine, the highly Lewis acidic and bulky 2 exhibits the reactivity of a frustrated Lewis pair (FLP) and can activate hydrogen and phenylacetylene. Complexes 2 and 3 were found to catalyze the hydrogenation and hydrosilylation of CO2 in the presence of DBU under relatively mild conditions.