Syntheses, Structure, and Derivatization of Potassium Complexes of Penta(organo)[60]fullerene-Monoanion, -Dianion, and -Trianion into Hepta- and Octa(organo)fullerenes

Dimeric and 1D polymeric low-chlorinated C60 fullerenes, (C60Cl5)2 and (C60Cl4)∞

Low-chlorinated fullerenes, dimeric (C₆₀Cl₅)₂ and one-dimensional, polymeric (C₆₀Cl₄)_∞, were obtained by high-temperature (270 °C) chlorination of C₆₀ with a SbCl₅/SbCl₃ mixture, as revealed by X-ray crystallography. The compounds were characterized by IR and Raman spectroscopy and theoretical calculations. This is the first observation of a fullerene polymer with single C-C bonding and neutral building blocks.

Doubly zwitterionic, di-reduced, highly electron-rich, air-stable naphthalenediimides: redox-switchable islands of aromatic-antiaromatic states

The di-reduced state of the naphthalene moiety and its congeners have long captivated chemists as it is elusive to stabilize these intrinsically reactive electron-rich π-systems and for their emergent multifaceted properties. Herein we report the synthesis and isolation of two-electron (2e-) reduced, highly electron-rich naphthalenediimides (NDIs). A doubly zwitterionic structure is observed for the first time in a naphthalene moiety and validated by single crystal X-ray crystallography and spectroscopic methods. The synthesis avoids hazardous reducing agents and offers an easy, high-yielding route to bench-stable di-reduced NDIs. Notably, we realized high negative first oxidation potentials of up to -0.730 V vs. Fc/Fc+ in these systems, which establish these systems to be one of the strongest ambient stable electron donors. The study also provides the first insights into the NMR spectra of the di-reduced systems revealing a large decrease in diatropicity of the naphthalene ring compared to its 2e- oxidized form. The NICS, NICS-XY global ring current, gauge-including magnetically induced current (GIMIC) and AICD ring current density calculations revealed switching of the antiaromatic and aromatic states at the naphthalene and the imide rings, respectively, in the di-reduced system compared to the 2e- oxidized form. Notably, the substituents at the phosphonium groups significantly tune the antiaromatic-aromatic states and donor ability, and bestow an array of colors to the di-reduced systems by virtue of intramolecular through-space communication with the NDI scaffold. Computational studies showed intramolecular noncovalent interactions to provide additional stability to these unprecedented doubly zwitterionic systems.

1,2,4-Diazaphospholide complexes of lanthanum(iii), cerium(iii), neodymium(iii), praseodymium(iii), and samarium(iii): synthesis, X-ray structural characterization, and magnetic susceptibility studies

A few heteroleptic, charge-separated heterobimetallic, and polymeric alkali metalate complexes of 1,2,4-diazaphospholide lanthanum(iii), cerium(iii), neodymium(iii), praseodymium(iii), and samarium(iii) were simply prepared via the metathesis reaction of MCl3 (THF)m (m = 1-2) and K[3,5-R2dp] ([3,5-R2dp](-) = 3,5-di-substituent-1,2,4-diazaphospholide; R = tBu, Ph) in a varied ratio (1 : 3, 1 : 4, and 1 : 5, respectively) at room temperature in tetrahydrofuran. All the complexes were fully characterized by (1)H, (13)C{(1)H}, (31)P{(1)H}, IR, and X-ray single crystal diffraction analysis despite their paramagnetism (excluding La(iii) complexes). The structures of the complexes were found to feature varied coordination modes. The magnetic properties of several compounds were studied by magnetic susceptibility, and the complexes presented the magnetic moments close to or lower than the theoretical values for the free ions in the trivalent oxidation states (Pr(3+), Nd(3+)).

Electrochemical reduction of cationic Li+@C60 to neutral Li+@C60˙-: isolation and characterisation of endohedral [60]fulleride

Li@C₆₀ was synthesised by electrochemical reduction of ionic Li⁺@C₆₀ salt. This is the first report of isolation and unambiguous characterisation of endohedral metallo[60]fullerene.

Lithium-encapsulated [60]fullerene Li@C₆₀, namely, lithium-ion-encapsulated [60]fullerene radical anion Li⁺@C₆₀˙^–, was synthesised by electrochemical reduction of lithium-ion-encapsulated [60]fullerene trifluoromethanesulfonylimide salt [Li⁺@C₆₀](TFSI^–). The product was fully characterised by UV-vis-NIR absorption and ESR spectroscopy as well as single-crystal X-ray analysis for the co-crystal with nickel octaethylporphyrin. In solution Li@C₆₀ exists as a monomer form dominantly, while in the crystal state it forms a dimer (Li@C₆₀–Li@C₆₀) through coupling of the C₆₀ radical anion cage. These structural features were supported by DFT calculations at the M06-2X/6-31G(d) level of theory.

1,2,4-Diazaphospholide complexes of yttrium(iii), dysprosium(iii), erbium(iii), and europium(ii,iii): synthesis, X-ray structural characterization, and EPR analysis

Several structurally characterized heteroleptic, charge-separated heterobimetallic, and polymeric alkali metal ate complexes of 1,2,4-diazaphospholide Y(iii), Dy(iii), Er(iii), Eu(iii), and Eu(ii) were prepared via the reaction of MCl3 and K[3,5-R2dp] in varied ratios at 200-220 °C (M = Y, Dy, Er, Eu; R = tBu, Ph).

Ferrocene/fullerene hybrids showing large second-order nonlinear optical activities: impact of the cage unit size

Ferrocene/fullerene complexes through face-to-face fusion enjoy the merits of both ferrocene and fullerene due to their strong donor–acceptor interactions.

Diradical character and nonlinear optical properties of buckyferrocenes: focusing on the use of suitably modified fullerene fragments

Buckyferrocenes, made up of suitably modified fullerenes fragments having an uninterrupted π-electron network, show intermediate diradical character and robustly large third-order nonlinear optical responses.

Magnetic coupling and optical properties of the S6-dodecakis(trifluoromethyl)fullerene radical anions in the layered salt (PPN(+))[C60(CF3)12(·-)]

Poly(trifluoromethyl)fullerene S6-C60(CF3)12 was reduced by sodium fluorenone ketyl in the presence of (PPN)Cl (PPN = bis(triphenylphosphine)iminium) to afford the salt (PPN)[C60(CF3)12] (1), which contains C60(CF3)12(·-) radical anions. In the crystal structure of 1, C60(CF3)12(·-) layers alternate with the PPN(+) cations. There are short F⋅⋅⋅F contacts between C60(CF3)12(·-) radical anions within the layers but no C⋅⋅⋅C contacts. DFT calculations revealed that the negative charge on C60(CF3)12(·-) is distributed mainly between sp(2) carbon and fluorine atoms, whereas spin density is localized mainly on the fullerene-cage sp(2) carbon atoms. IR and UV/Vis/NIR spectra in the solid state and solution showed characteristic changes relative to those of neutral S6-C60(CF3)12 due to the formation of radical anions. The solid-state electronic spectrum of 1 exhibits a single broad band at 738 nm attributed to C60(CF3)12(·-). Crystals of 1 show a narrow EPR signal with g = 2.0025 (ΔH = 0.45 mT) at 300 K. The temperature dependence of the integral intensity follows the Curie-Weiss law with a negative Weiss temperature of -11.8 K (30-300 K) indicating antiferromagnetic interaction of spins. This dependence was approximated by the Heisenberg model for one-dimensional chains of antiferromagnetically interacting spins with exchange interaction J/kB = -9.1 K. It was assumed that magnetic interaction between the C60(CF3)12(·-) spins in the layers is mediated by short F⋅⋅⋅F contacts.

An elusive fulvene 1,7,11,24-C60(CF3)4 and its unusual reactivity

The X-ray crystal structure of a trifluoromethylfullerene (TMF), 1,7,11,24-C60(CF3)4, is reported for the first time. This elusive intermediate, while highly air stable as a solid, exhibits highly regioselective reactivity towards molecular oxygen in polar solvents, and only when exposed to light.

Regioselective synthesis of 1,4-di(organo)[60]fullerenes through DMF-assisted monoaddition of silylmethyl Grignard reagents and subsequent alkylation reaction

Monoaddition of Grignard reagents, in particular tri(organo)silylmethylmagnesium chlorides, to [60]fullerene took place smoothly in the presence of dimethylformamide to produce (organo)(hydro)[60]fullerenes, C60R(1)H, in good yield (up to 93% isolated yield). The hydrofullerene was then deprotonated to generate the corresponding anion, C60R(-), which was then alkylated to obtain 58pi-electron di(organo)[60]fullerenes, C60R(1)R(2), in good to high yield (up to 93% overall yield). The two-step methodology provides a wide variety of 1,4-di(organo)[60] fullerenes bearing the same or different organic addends on the [60] fullerene core. By changing the addends, one can control the chemical and physical properties of the compounds at the molecular and bulk levels.

Hoop-Shaped Condensed Aromatic Systems: Synthesis and Structure of Iron– and Ruthenium–Hepta(organo)[60]fullerene Complexes

Potassium reduction of iron- and ruthenium-penta(organo)[60]fullerene complexes, [M(eta(5)-C60R5)(eta(5)-Cp)] (1 a: M = Fe, R = Ph; 1 b: M = Fe, R = Me; 1 c: M = Ru, R = Ph; 1 d: M = Ru, R = Me; Cp = C5H5) gave mono- and dianions of these complexes. Treatment of the dianion 1 a with alpha-bromodiphenylmethane gave three different iron-hepta(organo)[60]fullerenes, [Fe{eta(5)-C60Ph5(CHPh2)2}(eta(5)-Cp)], as a mixture of regioisomers. All three compounds were fully characterized by physical methods, including X-ray crystallography and electrochemical measurements. One of the three compounds contains a new hoop-shaped condensed aromatic system.

Chiral Ruthenium–Allenylidene Complexes That Bear a Fullerene Cyclopentadienyl Ligand: Synthesis, Characterization, and Remote Chirality Transfer

Ruthenium complexes that bear both a fullerene and an allenylidene ligand, [Ru(C60Me5)((R)-prophos)=C=C=CR1R2]PF6 (prophos = 1,2-bis(diphenylphosphanyl)propane), were prepared by the reaction of [Ru(C60Me5)Cl((R)-prophos)] and a propargyl alcohol in better than 90% yields, and characterized by 1H, 13C, and 31P NMR, IR, and UV/Vis/NIR spectroscopy and MS. Cyclic voltammograms of these complexes showed one reversible or irreversible reduction wave due to the allenylidene part, and two reversible reduction waves due to the fullerene core. Nucleophilic addition of RMgBr or RLi proceeded regioselectively at the distal carbon atom of the allenylidene array. The reaction took place with a 60:40-95:5 level of diastereoselectivity with respect to the original chirality in the (R)-prophos ligand, which is located six atoms away from the electrophilic carbon center.

Singly-bonded fullerene dimers: neutral (C60Cl5)2 and cationic (C70)22+?

C(60)Br(24) and C(70)Br(10) react with TiCl(4), splitting out bromine, and, after Br/Cl exchange, forming singly-bonded dimeric structures (C(60)Cl(5))(2) and [(C(70))(2)](Ti(3)Cl(13))(2), respectively, the latter consisting of dimeric [(C(70))(2)](2+) dications and (Ti(3)Cl(13))(-) anions.

Synthesis and Structural, Electrochemical, and Stacking Properties of Conical Molecules Possessing Buckyferrocene on the Apex

A series of conical molecules featuring a [60]fullerene/ferrocene hybrid and five aralkyl side chains (Fe[C60{C6H4-(OCO-C6H3-(OR)2-3,4)-4}5]Cp) have been synthesized and examined for their structural and electrochemical properties as well as their ability to form supramolecular structures in crystals and liquid crystals. When the R group on the side is a methyl group, the compound forms crystals in which the dipolar conical molecules are stacked head-to-tail to form a columnar structure. When the R group is as long as a C18H38 group, the compound forms liquid crystals. Oxidation of the liquid crystalline compound by an aminium salt [(4-BrC6H4)3N][SbCl6] produces the corresponding paramagnetic Fe(III) compound that also exhibits liquid crystalline properties.

Synthesis and Electrochemistry of Double-Decker Buckyferrocenes

D5d- and C5v-symmetric double-decker buckyferrocene Fe2(C60R10)Cp2 (R10 = Me5Ph5 and Me10) represents a new type of diiron complexes featuring conjugative connection of two ferrocene groups by a hoop-shaped [10]cyclophenacene. The compounds exhibit two-electron oxidation and two-electron reduction behavior, generating dicationic and dianionic species. The two iron atoms interact with each other through the pi-conjugation of the cyclophenacene, as revealed by differential pulse voltammetric analysis of the D5d Fe2(C60Me10)Cp2.

Convergent Synthesis of a Polyfunctionalized Fullerene by Regioselective Five-Fold Addition of a Functionalized Organocopper Reagent to C60

[reaction: see text] A method for one-step preparation of polyfunctionalized fullerene derivatives by regioselective penta-addition of an organocopper reagent is described. A functionalized aryl iodide is first converted to the corresponding Grignard reagent and then to a copper reagent and finally is allowed to react with C(60). The method allows introduction of five functional groups to the C(60) skeleton in a convergent manner. The shuttlecock-like molecules crystallize into a columnar packing structure.