The catalysts [Ir(COD)(κ³-P,C,P′-PC^NHCP)]BF₄ and [Ir(COD)(κ²-P,C-PC^NHCO)]BF₄ proved to be active in the solventless dehydrogenation of formic acid. The impact of various cosolvents on the activity was evaluated, showing an outstanding improvement of the catalytic performance of [Ir(COD)(κ²-P,C-PC^NHCO)]BF₄] in “green” organic carbonates: namely, dimethyl carbonate (DMC) and propylene carbonate (PC). The TOF_1h value for [Ir(COD)(κ²-P,C-PC^NHCO)]BF₄ increases from 61 to 988 h^–1 upon changing from solventless conditions to a 1/1 (v/v) DMC/HCOOH mixture. However, in the case of [Ir(COD)(PC^NHCP)]BF₄, only a marginal improvement from 156 to 172 h^–1 was observed under analogous conditions. Stoichiometric experiments allowed the identification of various key reaction intermediates, providing valuable information on their reactivity. Experimental data and DFT calculations point to the formation of dinuclear species as the catalyst deactivation pathway, which is prevented in the presence of DMC and PC.

中文翻译：

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绿色助溶剂对甲酸催化脱氢的影响：以含 NHC-磷烷配体的铱催化剂为例

催化剂[Ir(COD)(κ ³ - P , C , P′ -PC ^NHC P)]BF ₄和[Ir(COD)(κ ² - P,C -PC ^NHC O)]BF ₄被证明是有活性的用于甲酸的无溶剂脱氢。评估了各种助溶剂对活性的影响，表明 [Ir(COD)(κ ² - P,C -PC ^NHC O)]BF ₄ ] 在“绿色”有机碳酸酯中的催化性能显着提高：即，碳酸二甲酯 (DMC) 和碳酸亚丙酯 (PC)。该TOF _1H对于物[Ir（COD）值（κ ²- P,C -PC ^NHC O)]BF ₄在从无溶剂条件变为 1/1 (v/v) DMC/HCOOH 混合物时从 61 增加到 988 h ^–1。然而，在 [Ir(COD)(PC ^NHC P)]BF _{4 的情况下}，在类似条件下仅观察到从 156 到 172 h ^–1的边际改善。化学计量实验可以鉴定各种关键的反应中间体，提供有关其反应性的宝贵信息。实验数据和 DFT 计算表明双核物质的形成是催化剂失活途径，这在 DMC 和 PC 存在下被阻止。