Carbon Dioxide Insertion into Bridging Iron Hydrides: Kinetic and Mechanistic Studies. Issue 15 (15th February 2019)

• Record Type: Journal Article
• Authors: Hong, Dae Ho; Murray, Leslie J.
• Other Names: Sala Xavier guestEditor.; Llobet Antoni guestEditor.
• Is Part Of: European journal of inorganic chemistry. Issue 15(2019)
• Page Start: 2146
• Page End: 2153
• Publication Date: 2019-02-15
• Subjects: Carbon dioxide fixation -- Iron -- Hydrides -- Bridging ligands -- Kinetics -- Diketiminates; Chemistry, Inorganic -- Periodicals; Organometallic chemistry -- Periodicals; Bioinorganic chemistry -- Periodicals; Solid state chemistry -- Periodicals; 546
• DOI: 10.1002/ejic.201801404
• Languages: English
• ISSNs: 1434-1948

Abstract

Abstract : The reduction of CO2 to formic acid by transition metal hydrides is a potential pathway to access reactive C1 compounds. To date, no kinetic study has been reported for insertion of a bridging hydride in a weak‐field ligated complex into CO2 ; such centers have relevance to metalloenzymes that catalyze this reaction. Herein, we report the kinetic study of the reaction of a tri(µ‐hydride)triiron(II/II/II) cluster supported by a tris(β‐diketimine) cyclophane (1 ) with CO2 monitored by 1 H‐NMR and temperature‐controlled UV/Vis spectroscopy. We found that1 reacts with CO2 to traverse the reported monoformate (1‐CO2 ) and a diformate complex (1‐2CO2 ) at 298 K in toluene, and ultimately yields the triformate species (1‐3CO2 ) at elevated temperature. The second order rate constant, H/D kinetic isotope effect, Δ H ‡, and Δ S ‡ for formation of1‐CO2 were determined as 8.4(3) × 10 –4 m –1 s –1, 1.08(9), 11(1) kcal mol –1, and –3(1) × 10 cal mol –1 K –1, respectively at 298 K. These parameters suggest that CO2 coordination to the iron centers does not coordinate prior to the rate controlling step whereas Fe–H bond cleavage does. Abstract : The kinetics and mechanism of the reaction of bridging hydrides with CO2 from a triiron complex are reported. The kinetic parameters suggest the hydride transfer reaction requires Fe‐(µ‐H) bond cleavage and possible opening of the Fe–H–Fe bridge in the rate determining step.