Divergent CO₂ Activation by Tuning the Lewis Acid in Iron‐Based Bimetallic Systems

Abstract

Bimetallic motifs mediate the selective activation and functionalization of CO 2 in metalloenzymes and some recent synthetic systems. In this work, we build on the nascent concept of bimetallic frustrated Lewis pairs (FLPs) to investigate the activation and reduction of CO 2 . Using the Fe 0 fragment [(depe) 2 Fe] (depe = 1,2-bis(diethylphosphino)ethane) as base, we modify the nature of the partner Lewis acid to accomplish a divergent and highly chemoselective reactivity towards CO 2 . [Au(PMe 2 Ar)] + irreversibly dissociates CO 2 , Zn(C 6 F 5 ) 2 and B(C 6 F 5 ) 3 yield different CO 2 adducts stabilized by push-pull interactions, while Al(C 6 F 5 ) 3 leads to a rare heterobimetallic CÀ O bond cleavage, and thus to contrasting reduced products after exposure to dihydrogen. Computational investigations provide a rationale for the divergent reactivity, while Energy Decomposition Analysis-Natural Orbital for Chemical Valence (EDA-NOCV) method substantiates the heterobimetallic bonding situation.

[AsCCAs]-Coordinated Rhenium Hydrides and Their Reactivities Toward Unsaturated Hydrocarbons, Heterocumulenes, and CO2

“…Figure ). The resulting mixture was then reacted with lutidinium chloride ([LutH]­Cl, 1 equiv), which led to the generation of lutidinium formate in the form of its stable B­(C 6 F 5 ) 3 adduct. The latter organic product was produced in nearly quantitative conversions and unambiguously identified by means of 1 H, 19 F, and 11 B NMR spectroscopy (see the Supporting Information for details).…”

Polarized Au(i)/Rh(i) bimetallic pairs cooperatively trigger ligand non-innocence and bond activation

“…When the reaction is monitored at −20 °C in the NMR probe the resonances narrow, as previously observed for other bimetallic FLPs investigated in our group. 10 The reluctance to form a stable Rh → Au dative bond in this case is most likely due to steric reasons. In fact, treating compound 6d with the smaller gold complex 2 Me does yield the corresponding bimetallic pair 7d Me , which was fully characterized by spectroscopic means (see ESI † for details).…”

“…The very small but positive enthalpic value, along with the only moderately positive entropic component, enable the persistence of variable amounts of the monometallic fragments in solution, a prerequisite for exhibiting bimetallic FLP reactivity. 10 …”

“…We have previously demonstrated the importance of accessing monometallic fragments in highly polarized and unsupported bimetallic pairs to enhance their cooperative reactivity. 10,22 As such, we promptly explored the reactivity of the non-bonded pair 6d:2 Cyp towards a variety of small molecules containing both non-polar or weakly polarized (H 2 , C 2 H 2 , C 2 H 4 ) and polar bonds (NH 3 , H 2 O, MeOH). However, instead of the foreseen FLP-type bond activation, we rapidly detected the formation of the heteroleptic gold compound [Au(PCyp 2 Ar Xyl2 )(PPh 3 )] ( 8 ) (Scheme 4), defined by two distinctive doublets ( 2 J PP = 309 Hz) at 59.4 and 44.3 ppm by 31 P{ 1 H} NMR spectroscopy.…”

“…Thus, as highly constrained metallic fragments of opposed Lewis character, they may behave as bimetallic frustrated Lewis pairs (FLPs), 9 a nascent topic to which we have contributed in recent years. 10 Nonetheless, the Cp* non-innocence described herein advises for the exploration of alternative aromatic capping ligands in our continuous search for bimetallic FLPs.…”