Beniwal Naveen, Sharma Nidhi, Singh Lovjeet, Rekha Pawan
Department of Chemistry, Malaviya National Institute of Technology Jaipur, Rajasthan-302017, India.
Department of Chemistry, Shiv Nadar Institution of Eminence, NCR Delhi, UP-201314, India.
Nanoscale. 2025 Sep 11;17(35):20123-20134. doi: 10.1039/d5nr02036k.
Developing efficient and sustainable catalytic systems for carbon dioxide utilization is crucial in tackling the challenges posed by increasing greenhouse gas emissions. This study investigates the co-catalyst- and solvent-free cycloaddition of CO with epoxides using a series of iron-based metal phosphonates, FePPA (iron phenylphosphonate), FeHEDP (iron hydroxyethylidene diphosphonate), and FeEDTMP (iron ethylenediamine tetramethylene phosphonate), with the aim of elucidating the role of acidic-basic sites in enhancing their catalytic performance. These catalysts, prepared using phosphonic acids with various functional groups, offer a platform for examining how structural modifications influence CO fixation efficiency. Among them, FeEDTMP demonstrated superior catalytic performance, attributed to its bifunctional nature. Coordinatively unsaturated iron centers (Fe/Fe) provide Lewis acidity and N-containing moieties introduce basicity to activate epoxides and CO synergistically. Unlike many metal phosphonates that require halogen-based co-catalysts, such as tetrabutylammonium bromide (TBAB), which pose environmental concerns and often complicate product separation, this work employs a truly co-catalyst-free and solvent-free system. The reaction mechanism is proposed without invoking external nucleophiles, highlighting the intrinsic bifunctionality of FeEDTMP in facilitating both CO activation and epoxide ring opening. Extensive parameter optimization was performed to study the influence of catalyst loading, temperature, pressure, and reaction time. Under optimized conditions (30 mg of catalyst, 100 °C, 7 bar CO, and 24 h), FeEDTMP achieved 99% yield and ∼100% selectivity, with 100% epoxide conversion of CO. The catalyst also exhibited broad substrate scope, with steric and electronic factors influencing the reactivity of different epoxides while retaining its structural stability after catalysis. This work provides fundamental insights into structure-activity relationships and offers a promising route for designing green, halogen-free catalytic systems for CO utilization.
开发高效且可持续的二氧化碳利用催化体系对于应对温室气体排放增加带来的挑战至关重要。本研究使用一系列铁基金属膦酸盐，即FePPA（苯基膦酸铁）、FeHEDP（羟基亚乙基二膦酸铁）和FeEDTMP（乙二胺四亚甲基膦酸铁），研究了CO与环氧化物的无共催化剂和无溶剂环加成反应，旨在阐明酸碱位点在提高其催化性能中的作用。这些使用具有不同官能团的膦酸制备的催化剂，为研究结构修饰如何影响CO固定效率提供了一个平台。其中，FeEDTMP表现出优异的催化性能，这归因于其双功能性质。配位不饱和铁中心（Fe/Fe）提供路易斯酸性，含氮部分引入碱性以协同活化环氧化物和CO。与许多需要基于卤素的共催化剂（如四丁基溴化铵（TBAB））的金属膦酸盐不同，TBAB存在环境问题且常常使产物分离复杂化，本工作采用了真正无共催化剂和无溶剂的体系。提出的反应机理无需引入外部亲核试剂，突出了FeEDTMP在促进CO活化和环氧化物开环方面的内在双功能性质。进行了广泛的参数优化以研究催化剂负载量、温度、压力和反应时间的影响。在优化条件下（30 mg催化剂、100 °C、7 bar CO和24 h），FeEDTMP的产率达到99%，选择性约为100%，CO对环氧化物的转化率为100%。该催化剂还表现出广泛的底物范围，空间和电子因素影响不同环氧化物的反应性，同时在催化后保持其结构稳定性。这项工作为结构 - 活性关系提供了基本见解，并为设计用于CO利用的绿色、无卤素催化体系提供了一条有前景的途径。
