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Carbon Dioxide Insertion into Bridging Iron Hydrides: Kinetic and Mechanistic Studies
Author(s) -
Hong Dae Ho,
Murray Leslie J.
Publication year - 2019
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.201801404
Subject(s) - chemistry , hydride , formic acid , reaction rate constant , inorganic chemistry , kinetic isotope effect , metal , medicinal chemistry , photochemistry , crystallography , kinetics , organic chemistry , deuterium , physics , quantum mechanics
The reduction of CO 2 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 CO 2 ; 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 CO 2 monitored by 1 H‐NMR and temperature‐controlled UV/Vis spectroscopy. We found that 1 reacts with CO 2 to traverse the reported monoformate ( 1‐CO 2 ) and a diformate complex ( 1‐2CO 2 ) at 298 K in toluene, and ultimately yields the triformate species ( 1‐3CO 2 ) at elevated temperature. The second order rate constant, H/D kinetic isotope effect, Δ H ‡ , and Δ S ‡ for formation of 1‐CO 2 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 CO 2 coordination to the iron centers does not coordinate prior to the rate controlling step whereas Fe–H bond cleavage does.