Hydrocarbon-soluble, hexaanionic fulleride complexes of magnesium

A Well-Defined Magnesium Complex of C70 6

Controlling and understanding charge state and metal coordination in carbon nanomaterials is crucial to harnessing their unique properties. Here we describe the synthesis of the well-defined fulleride complex [{(Mesnacnac)Mg}6C70], 2, (Mesnacnac)=HC(MeCNMes)2, Mes=2,4,6-Me3C6H2, from the reaction of the β-diketiminate magnesium(I) complex [{(Mesnacnac)Mg}2] with C70 in aromatic solvents. The molecular structure of complex 2 was determined, providing the first high-quality structural study of a complex with the C70 6- ion. In combination with solution state NMR spectroscopic and DFT computational studies, the changes in geometry and charge distribution in the various atom and bond types of the fulleride unit were investigated. Additionally, the influence of the (Mesnacnac)Mg+ cations on the global and local fulleride coordination environment was examined.

[{SiNDipp}MgNa]2: A Potent Molecular Reducing Agent

The bimetallic species, [{SiNDipp}MgNa]2 [{SiNDipp} = {CH2SiMe2N(Dipp)}2; (Dipp = 2,6-i-Pr2C6H3)], is shown to be a potent reducing agent, able to effect one- or two-electron reduction of either dioxygen, TEMPO, anthracene, benzophenone, or diphenylacetylene. In most cases, the bimetallic reaction products imply that the dissimilar alkaline metal centers react with a level of cooperativity. EPR analysis of the benzophenone-derived reaction and the concurrent isolation of [{SiNDipp}Mg(OCPh2)2], however, illustrate that treatment with such reducible, but O-basic, species can also result in reactivity in which the metals provide independent reaction products. The notable E-stereochemistry of the diphenylacetylene reduction product prompted a computational investigation of the PhC≡CPh addition. This analysis invokes a series of elementary steps that necessitate ring-opening via Mg+ → Na+ amido group migration of the SiNDipp ligand, providing insight into the previously observed lability of the bidentate dianion and its consequent proclivity toward macrocyclization.

Polyanionic cyano-fullerides for CO2 capture: a DFT prediction

The reaction of C₆₀ fullerene with 'n' molecules (n = 1 to 6) of 1,3-dimethyl-2,3-dihydro-2-cyano-imidazole (IMCN) results in the exothermic formation of imidazolium cation-polyanionic fulleride complexes, (IM⁺)_n⋯((C₆₀(CN)_n)^n-). The binding energy of IM⁺ with (C₆₀(CN)_n)^n- in the imidazolium-fulleride ionic complexes increased from -69.6 kcal mol^-1 for n = 1 to -202.9 kcal mol^-1 for n = 6. The energetics of the complex formation and cation-anion interaction energy data suggest the formation of imidazolium-fulleride ionic liquid (IL) systems. Furthermore, the dimer formation of such ionic complexes showed more exergonic nature due to multiple cooperative electrostatic interactions between oppositely charged species and suggested improved energetics for higher order clusters. The molecular electrostatic potential (MESP) analysis has revealed that the extra 'n' electrons in the ionic complex as well as that in the bare (C₆₀(CN)_n)^n- are delocalized mainly on the unsaturated carbon centers of the fullerene unit, while the CN groups remain as a neutral unit. The MESP minimum (V_min) values of (C₆₀(CN)_n)^n- on the carbon cage have shown that the addition of each CN^- unit on the cage enhances the negative character of V_min by ∼54.7 kcal mol^-1. This enhancement in MESP is comparable to the enhancement observed when one electron is added to C₆₀ to produce (^-62.5 kcal mol^-1) and suggests that adding 'n' CN^- groups to the fullerene cage is equivalent to supplying 'n' electrons to the carbon cage. Also the high capacity of the fullerene cage to hold several electrons can be attributed to the spherical delocalization of them onto the electron deficient carbon cage. The interactive behavior of CO₂ molecules with (IM⁺)_n⋯(C₆₀(CN)_n)^n- systems showed that the interaction becomes stronger from -2.3 kcal mol^-1 for n = 1 to -18.6 kcal mol^-1 for n = 6. From the trianionic fulleride onwards, the C⋯CO₂ noncovalent (nc) interaction changes to C-CO₂ covalent (c) interaction with the development of carboxylate character on the adsorbed CO₂. These results prove that cyano-fullerides are promising candidates for CO₂ capture.

Umpolung of an Aliphatic Ketone to a Magnesium Ketone‐1,2‐diide Complex with Vicinal Dianionic Charge

The new β‐diketimine ^iPrDipnacnacH, HC(iPrCNDip)₂H, Dip=2,6‐iPr₂‐C₆H₃, was converted to the magnesium(I) complex [{(^iPrDipnacnac)Mg}₂] and reaction with 2‐adamantanone (OAd) afforded the ketone‐1,2‐diide complex [{(^iPrDipnacnac)Mg}₂(μ‐OAd)]. The complex contains the first stable dianion of an aliphatic ketone with an electropositive metal and shows an OAd²⁻ unit with long C−O bond and pyramidal carbon centre. DFT studies reveal an anionic charge on both neighbouring C and O atoms. Reductions of aliphatic ketones with magnesium(I) complexes show that these likely proceed via highly reactive dianions and afforded a 1 : 1 mixture of an alkoxide and an enolate when an enolisable ketone was used, and rapid CH activations reactions, e.g., of stabilising ligand moieties, when non‐enolisable ketones were employed.

A 1D Mixed-Valence Cuprofullerene Pyrazolate Polymer as a Semiconductor Material

Polymeric {Cu₆[(μ₃-η²:η²:η²)₂-C₆₀](FPz)₆Cl·3C₆H₅Cl}_∞ [FPz = 4-(trifluoromethyl)pyrazolate], synthesized solvothermally with chlorobenzene as the solvent, is a doubly-connecting trans bis-adduct hexanuclear cuprofullerene that has copper in mixed valence. The compound is an example of a metallofullerene having semiconductivity character.

Regioisomeric core-shell cuprofullerene C60@Cu24

The controlled synthesis of high-nuclear regioisomeric core-shell exohedral metallofullerenes (ExMFs) is challenging. Herein, we demonstrated the synthesis of regioisomeric core-shell cuprofullerene C₆₀@Cu^I₂₄ and its 3-D coordination polymer using heteroleptic ligands, realizing high-nuclear regioisomeric ExMFs and a polymeric ExMF structure.

Exohedral Cuprofullerene: Sequentially Expanding Metal Olefin Up to a C60@Cu24 Rhombicuboctahedron

Exohedral cuprofullerenes with 6-, 12-, or 24-nuclearity were obtained by utilizing fluorocarboxylic/dicarboxylic acid under solvothermal conditions. The 24-nuclear molecule presents a C₆₀@Cu₂₄ core-shell structure with a rhombicuboctahedron Cu₂₄ coated on the C₆₀ core, representing the highest nuclearity in metallofullerene. The resultant complexes show an efficient absorption of visible light as opposed to the pristine C₆₀. TD-DFT calculations revealed the charge transfer from Cu(I) and O atoms to the fullerene moiety dominates the photophysical process.

Mechanistic insights of anionic ligand exchange and fullerene reduction with magnesium(i) compounds

Exchange of anionic ligands on the Mg₂²⁺ ion via an associative mechanism can be facile and depends on ligand sterics and shape.