Transformation of Carbon Dioxide to Formic Acid and Methanol by Wan-Hui Wang Xiujuan Feng & Ming Bao

Author:Wan-Hui Wang, Xiujuan Feng & Ming Bao
Language: eng
Format: epub
Publisher: Springer Singapore, Singapore

Guan and co-workers further investigated other nickel bis(phosphinite) pincer complex [2,6-(R2PO)2C6H3]NiH (LRNiH, 13b R = isopropyl, 13c R = cyclopentyl) which was synthesized from [2,6-(R2PO)2C6H3]NiCl with LiAlH4 [12]. The reaction of LRNiH (R = t Bu, i Pr, and cPe) with CO2 at room temperature gave respectively the LRNiOCHO 14 (R = t Bu, i Pr, and cPe) as the sole products. The formato complexes 14 reacted with HBCat to form LRNiH, CH3OCat, and CatBOBCat. The reaction of LRNiOCHO (R = t Bu) 14a is faster than reactions of other formate derivatives, which indicated that the reaction of formate derivatives bearing bulky substitutes had a better performance on the formation of CH3OCat. It was supposed that complex bearing a smaller substituent is favorable for the interaction of LRNiH and HBCat, resulting in concentration decrease of active LRNiH. To investigate the scope of reducing reagents for reduction of CO2, the reaction of LRNiOCHO (R = t Bu) 14a with 9-borabicyclo[3.3.1]nonane (9-BBN), pinacolborane (HBpin) or PhSiH3, was carried out respectively under the same conditions (Scheme 4.10). They found that the reducing reagent significantly affects the reaction outcome. 9-BBN provided a methoxide, while HBpin gave only formate species even large excess of HBpin was used. No reaction was observed when PhSiH3 was employed.

Scheme 4.10Reaction of LRNiOCHO (R = t Bu) 14 with 9-BBN, HBpin or PhSiH3

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