Cooperative Activation of CO2 and N2O by Heterometallic Complexes Stabilized by N-Heterocyclic Carbenes

The motivation to transform gaseous small molecules, CO2 and N2O, into useful chemicals requires a fundamental understanding of how such molecules can be captured and activated. In biological systems, several metalloenzymes feature multimetallic active sites that can capture these gases and cooperatively convert them into useful chemicals or fuels. We have developed heterometallic catalysts featuring (NHC)M-[Mco] (NHC = N-heterocycliccarbene; M = Cu, Ag, Au, ZnCl; [Mco] = e.g. FeCp(CO)2, Mn(CO)5, WCp(CO)3, Co(CO)4, etc.), with metal-metal bond polarity that was tuned by changing monoanionic [Mco]- with a dianionic metal carbonyl nucleophile. Herein, this thesis reports synthesis, structural characterization, and small molecule reactivity of two heterobimetallic complexes, trinuclear [(IPr)Cu]2Fe(CO)4 and tetranuclear [(IPr)ZnFe(CO)4]2 (IPr = N,N’-bis(2,6-diisoporpylphenyl)imidazol-2-ylidine). Studied reactivity of the trinuclear heterometallic Cu-Fe complex towards N2O resulted in formation of carbonate complex [(IPr)Cu]2(μ-CO3) determined by X-ray crystallography. Byproduct was stoichiometrically expected to be 1/n [Fe(CO)3]n, which could be trapped with phosphine ligand to form trans-Fe(CO)3(PPh3)2. Due to this unexpected oxidation of CO to carbonate, catalytic turnover was prevented. Additionally, synthesis and characterization of a novel paramagnetic Ni/W heterobimetallic catalyst supported by a bidentate NHC ligand were studied alongside preliminary reactivity towards these gaseous molecules. Activation of N2O by Ni-W complex resulted in formation of (Npy-NHC)W(CO)4 determined by X-ray crystallography, albeit with other unidentified Ni complexes. Moreover, independent reactivity between N2O and LiWCp*(CO)3 showed formation of dimeric (µ-O)WII2(Cp*)2(CO)4, which might provide clues about the reaction between N2O and Ni/W complex. The fundamental studies on structure, bonding, and reactivity presented in this thesis will inform future designs of compounds for cooperative activation of inert small molecules.