Access to Metal Centers and Fluxional Hydride Coordination Integral for CO₂ Insertion into [Fe₃(μ-H)₃]³⁺ Clusters

Abstract

CO2 insertion into tri­(μ-hydrido)­triiron­(II) clusters ligated by a tris­(β-diketiminate) cyclophane is demonstrated to be balanced by sterics for CO2 approach and hydride accessibility. Time-resolved NMR and UV–vis spectra for this reaction for a complex in which methoxy groups border the pocket of the hydride donor (Fe3H3 L 2 , 4) result in a decreased activation barrier and increased kinetic isotope effect consistent with the reduced sterics. For the ethyl congener Fe3H3 L 1 (2), no correlation is found between rate and reaction solvent or added Lewis acids, implying CO2 coordination to an Fe center in the mechanism. The estimated hydricity (50 kcal/mol) based on observed H/D exchange with BD3 requires Fe–O bond formation in the product to offset an endergonic CO2 insertion. μ3-hydride coordination is noted to lower the activation barrier for the first CO2 insertion event in DFT calculations.

Synthesis, Structural Characterization, and CO2Reactivity of a Constitutionally Analogous Series of Tricopper Mono-, Di-, and Trihydrides

“…Holistically, these data are most consistent with sequential CO 2 insertions to μ 2 -κO,O′ formate motifs that are, like the hydrides in 3, fluxional across the Cu 3 ensemble (7, Scheme 2); nevertheless, a terminal binding mode cannot be completely discounted. 47 Contrasting related Fe 3 H 3 systems, 93,94 isomerization is proposed to enable insertion chemistry in the polyiron clusters�and aligns well with the thermodynamic hydricity data established for the Cu 3 H x series. The recalcitrance of 4 to insert CO 2 agrees with a hydricity above ca.…”

“…Holistically, these data are most consistent with sequential CO 2 insertions to μ 2 -κO,O′ formate motifs that are, like the hydrides in 3 , fluxional across the Cu 3 ensemble ( 7 , Scheme ); nevertheless, a terminal binding mode cannot be completely discounted . Contrasting related Fe 3 H 3 systems, , 3 and 6 demonstrate rapid sequential hydride insertions. This reactivity may be related to the geometric flexibility of the Cu 3 corehydride isomerization is proposed to enable insertion chemistry in the polyiron clustersand aligns well with the thermodynamic hydricity data established for the Cu 3 H x series.…”

Single‐Crystal to Single‐Crystal Transformations: Stepwise CO2 Insertions into Bridging Hydrides of [(NHC)CuH]2 Complexes

“…Interestingly, computational analysis on the first CO 2 insertion into L[Fe 3 (μ‐H) 3 ] to form L[Fe 3 (μ‐H) 2 (1,1‐μ‐O 2 CH)] suggests the reaction proceeds by initial formation of a 1,3‐μ‐O 2 CH ligand followed by rearrangement to a 1,1‐μ‐O 2 CH ligand with a computed energy barrier of 8.5 kcal mol −1 . The calculated ground‐state structures of L[Fe 3 (μ‐H) 2 (1,3‐μ‐O 2 CH)] and L[Fe 3 (μ‐H) 2 (1,1‐μ‐O 2 CH)] differ in energy by less than 1 kcal mol −1 [30] …”

“…differ in energy by less than 1 kcal mol À 1 . [30] The unexpected observation of two distinct binding modes of formate suggests considerable change of the dicopper core after the first CO 2 insertion. DFT calculations on CO 2 insertion into a Cu 2 (μ-H) core supported by a truncated polydentate phosphine ligand found that the ground-state structure of Cu 2 (μ-1,3-O 2 CH) is preferred over that of Cu 2 (μ-1,1-O 2 CH).…”