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Iron hydrides are proposed reactive intermediates for N2and CO conversion in industrial and biological processes. Here, we report a reactivity study of a low-coordinate di(μ-hydrido)diiron(II) complex, Fe2(μ-H)2L, where L2–is a bis(β-diketiminate) cyclophane, with isocyanides, which have electronic structures related to N2and CO. The reaction outcome is influenced by the isocyanide substituent, with 2,6-xylyl isocyanide leading to H2loss, to form a bis(μ-1,1-isocyanide)diiron(I) complex, whereas all of the other tested isocyanides insert into the Fe–H bond to give (μ-1,2-iminoformyl) complexes. Steric bulk of the isocyanide substituent determines the extent of insertion (i.e., into one or both Fe–H–Fe units) with tert-butyl isocyanide reacting to yield the mono-(μ-1,2-iminoformyl)diiron(II) complex, exclusively, and isopropyl- and methyl isocyanides affording the bis(μ-1,2-iminoformyl)diiron(II) products. Treatment of Fe2(μ-1,2-CHNtBu)(μ-H)Lwith 2,6-xylyl isocyanide (or XylNC) yields Fe2(μ-XylNC)2Land tert-butylaldimine as one of the organic products.

Ligand non-innocence is ubiquitous in catalysis with ligands in synthetic complexes contributing as electron reservoirs or co-sites for substrate activation. The latter chemical non-innocence is manifested in H+storage or relay at sites beyond the metal primary coordination sphere. Reaction of a competent CO2-to-oxalate reduction catalyst, namely, [K(THF)3](Cu3SL), where L3–is a tris(β-diketiminate) cyclophane, with CS2affords tetrathiooxalate at long reaction times or at high CS2concentrations, where otherwise an equilibrium is established between the starting species and a complex–CS2adduct in which the CS2is bound to the C atom on the ligand backbone. X-ray diffraction analysis of this adduct reveals no apparent metal participation, suggesting an entirely ligand-based reaction controlled by the charge state of the cluster. Thermodynamic parameters for the formation of the aforementioned Cligand–CS2bond were experimentally determined, and trends with cation Lewis acidity were studied, where more acidic cations shift the equilibrium toward the adduct. Relevance of such an adduct in the reduction of CO2to oxalate by this complex is supported by DFT studies, similar effects of countercation Lewis acidity on product formation, and the homocoupled heterocumulene product speciation as determined by isotopic labeling studies. Taken together, this system extends chemical non-innocence beyond H+to effect catalytic transformations involving C–C bond formation and represents the rarest example of metal–ligand cooperativity, that is, spectator metal ion(s) and the ligand as the reaction center.

CO2insertion into tri(μ-hydrido)triiron(II) clusters ligated by a tris(β-diketiminate) cyclophane is demonstrated to be balanced by sterics for CO2approach 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 (Fe3H3L2, 4) result in a decreased activation barrier and increased kinetic isotope effect consistent with the reduced sterics. For the ethyl congener Fe3H3L1(2), no correlation is found between rate and reaction solvent or added Lewis acids, implying CO2coordination to an Fe center in the mechanism. The estimated hydricity (50 kcal/mol) based on observed H/D exchange with BD3requires Fe–O bond formation in the product to offset an endergonic CO2insertion. μ3-hydride coordination is noted to lower the activation barrier for the first CO2insertion event in DFT calculations.

A pair of cyclophane-encapsulated [Cu3(μ3-E)]3+complexes (E = S and Se) were characterized by resonant X-ray diffraction anomalous fine structure (DAFS), revealing unexpected polarization among the three Cu sites attributed to long-range effects of π-stacking interactions with cocrystallized benzene molecules. The resonant K-edge energies of individual Cu sites within the cluster molecules were found to vary as a function of distance from the cocrystallized benzene. This pattern was interpreted in the context of T-shaped, edge-to-face π-stacking with the assistance of theoretical charge density difference calculations.

The designed [3M–3(μ-H)] clusters (M = FeII, CoII) Fe3H3L (1-H) and Co3H3L (2-H) [where L3–is a tris(β-diketiminate) cyclophane] were synthesized by treating the corresponding M3Br3L complexes with KBEt3H. From single-crystal X-ray analysis, the hydride ligands are sterically protected by the cyclophane ligand, and these complexes selectively react with CO2over other unsaturated substrates (e.g., CS2, Me3SiCCH, C2H2, and CH3CN). The reaction of 1-Hor 2-Hwith CO2at room temperature yielded Fe3(OCHO)(H)2L (1-CO2) or Co3(OCHO)(H)2L (2-CO2), respectively, which evidence the differential reactivity of the hydride ligands within these complexes. The analogous reactions at elevated temperatures revealed a distinct difference in the reactivity pattern for 2-Has compared to 1-H; Fe3(OCHO)3L (1-3CO2) was generated from 1-H, while 2-Hafforded only 2-CO2.

Polynuclear manganese compounds have garnered interest as mimics and models of the water oxidizing complex (WOC) in photosystem II and as single molecule magnets. Molecular systems in which composition can be correlated to physical phenomena, such as magnetic exchange interactions, remain few primarily because of synthetic limitations. Here, we report the synthesis of a family of trimanganese(II) complexes of the type Mn3X3L(X = Cl–, H–, and MeO–) where L3–is a tris(β-diketiminate) cyclophane. The tri(chloride) complex (2) is structurally similar to the reported tri(bromide) complex (1) with the Mn3X3core having a ladder-like arrangement of alternating M–X rungs, whereas the tri(μ-hydride) (3) and tri(μ-methoxide) (4) complexes contain planar hexagonal cores. The hydride and methoxide complexes are synthesized in good yield (48% and 56%) starting with the bromide complex employing a metathesis-like strategy. Compounds 2–4were characterized by combustion analysis, X-ray crystallography, X-band EPR spectroscopy, SQUID magnetometry, and infrared and UV–visible spectroscopy. Magnetic susceptibility measurements indicate that the Mn3clusters in 2–4are antiferromagnetically coupled, and the spin ground state of the compounds (S= 3/2 (1, 2) or S= 1/2 (3, 4)) is correlated to the identity of the bridging ligand and structural arrangement of the Mn3X3core (X = Br, Cl, H, OCH3). Electrochemical experiments on isobutyronitrile solutions of 3and 4display broad irreversible oxidations centered at 0.30 V.