Pincer-Ligated Nickel Hydridoborate Complexes: the Dormant Species in Catalytic Reduction of Carbon Dioxide with Boranes
Pincer-Ligated Nickel Hydridoborate Complexes: the Dormant Species in Catalytic Reduction of Carbon Dioxide with Boranes
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DOI：
10.1021/ic300587b
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发表时间：
2013-01-07
影响因子：
4.6
通讯作者：
Guan, Hairong
中科院分区：
文献类型：
--
作者：
Chakraborty, Sumit;Zhang, Jie;Guan, Hairong
[2，6-（R2 PO）（2）C6 H3]NiH（R = Bu-t，1a; R = Pr-i，1b; R =（c）Pe，1c）型镍钳形配合物与BH 3中心点THF反应生成硼氢化物配合物[2，6-（R2 PO）（2）C6 H3]Ni（eta（2）-BH 4）（2a-c），如NMR和IR光谱、X射线晶体学和元素分析所证实。这些反应在室温下是不可逆的，但在60 ℃下是可逆的。化合物1a将其在镍上的氢与9-BBN或HBcat的硼烷氢交换，但不形成任何可观察到的加合物。然而，体积较小的氢化物络合物1b和1c在室温下与9-BBN和HBcat混合时可逆地产生二氢硼酸镍络合物。在这些配合物中，配体采用η（2）-配位模式，如ER所示。光谱学和X射线晶体学。在1a-c的催化影响下，当9-BBN或HBcat用作还原剂时，CO2的还原导致甲醇水平。最好的催化剂，1a，涉及磷供体原子上的大体积取代基。涉及1b和1c的催化反应效率较低，这是因为形成了作为休眠物种的二氢硼酸盐络合物以及硼烷对催化剂的部分分解。
Nickel pincer complexes of the type [2,6-(R2PO)(2)C6H3]NiH (R = Bu-t, 1a; R = Pr-i, 1b; R = (c)Pe, 1c) react with BH3 center dot THF to produce borohydride complexes [2,6-(R2PO)(2)C6H3]Ni(eta(2)-BH4) (2a-c), as confirmed by NMR and IR spectroscopy, X-ray crystallography, and elemental analysis. The reactions are irreversible at room temperature but reversible at 60 degrees C. Compound 1a exchanges its hydrogen on the nickel with the borane hydrogen of 9-BBN or HBcat, but does not form any observable adduct. The less bulky hydride complexes 1b and 1c, however, yield nickel dihydridoborate complexes reversibly at room temperature when mixed with 9-BBN and HBcat. The dihydridoborate ligand in these complexes adopts an eta(2)-coordination mode, as suggested by ER. spectroscopy and X-ray crystallography. Under the catalytic influence of 1a-c, reduction of CO2 leads to the methoxide level when 9-BBN or HBcat is employed as the reducing agent. The best catalyst, 1a, involves bulky substituents on the phosphorus donor atoms. Catalytic reactions involving 1b and 1c are less efficient because of the formation of dihydridoborate complexes as the dormant species as well as partial decomposition of the catalysts by the boranes.