Synthesis and structure elucidation of triarylmethyl radicals with anthryl substitution

Two stable triarylmethyl radicals with one or two anthryl substitutions are synthesized in gram scale, and are isolated in the crystalline state. Detailed structural elucidation with X-ray crystallographic analysis and DFT calculations revealed that the twisted structure is more energetically favorable than the folded structure, and consequently, the spin density is mainly localized at the methyl carbon. The spin distribution leads to unique physical properties, making them promising open-shell organic materials.

Direct Photocatalyzed Hydrogen Atom Transfer (HAT) for Aliphatic C-H Bonds Elaboration

Direct photocatalyzed hydrogen atom transfer (d-HAT) can be considered a method of choice for the elaboration of aliphatic C–H bonds. In this manifold, a photocatalyst (PC_HAT) exploits the energy of a photon to trigger the homolytic cleavage of such bonds in organic compounds. Selective C–H bond elaboration may be achieved by a judicious choice of the hydrogen abstractor (key parameters are the electronic character and the molecular structure), as well as reaction additives. Different are the classes of PCs_HAT available, including aromatic ketones, xanthene dyes (Eosin Y), polyoxometalates, uranyl salts, a metal-oxo porphyrin and a tris(amino)cyclopropenium radical dication. The processes (mainly C–C bond formation) are in most cases carried out under mild conditions with the help of visible light. The aim of this review is to offer a comprehensive survey of the synthetic applications of photocatalyzed d-HAT.

9,10-Anthraquinones Disubstituted with Linear Alkoxy Groups: Spectroscopy, Electrochemistry, and Peculiarities of Their 2D and 3D Supramolecular Organizations

Spectroscopic, electrochemical, and structural properties of 2,6-dialkoxy-9,10-anthraquinones (Anth-OCn, n = 4, 6, 8, 10, and 12) of increasing alkoxy substituents length were investigated. UV-vis spectroscopy showed a substitution-induced bathochromic shift of the least energetic band from 325 nm in the case of unsubstituted anthraquinone to ca. 350 nm for the studied derivatives. Similarly as unsubstituted anthraquinone, the studied compound showed two reversible one electron reductions to a radical anion and spinless anions, respectively. The first reduction was affected by electron-donating properties of the substituents, its potential being shifted to ca. -1.5 V (vs Fc/Fc⁺), i.e., by 80 to 95 mV as compared to the case of unsubstituted anthraquinone. This corresponded to a decrease of |EA| from 3.27 to 3.19-3.17 eV. The experimental spectroscopic and electrochemical data were in full agreement with the DFT calculations. The introduction of the alkoxy substituent improved solution processibility of the studied compounds and facilitated the formation of their ordered supramolecular 2D aggregation on HOPG as well as single crystal growth from solutions. Comparative structural investigations carried out on single crystals and monolayers deposited on HOPG revealed two, mutually related, effects of the substituent length on the resulting supramolecular organization. The first one concerns both the 2D organization in the monolayers and 3D molecular arrangement in crystals: increasing substituent length evolution of the structure occurs from herringbone-type to lamellar. The second effect, observed in monolayers of the derivatives with longer substituents, concerns gradual evolution of their lamellar structures with increasing substituent length. This evolution is induced by the structure of the graphite substrate and involves increasing correlation of the molecules orientation (anthraquinone cores as well as alkoxy substituents) with the symmetry of the graphite substrate. As a result, their 2D and 3D structures become dissimilar.

Preparation and Characterisation of a Bis-μ-Hydroxo-NiIII 2 Complex

Hydroxide-bridged high-valent oxidants have been implicated as the active oxidants in methane monooxygenases and other oxidases that employ bimetallic clusters in their active site. To understand the properties of such species, bis-μ-hydroxo-Ni^II ₂ complex (1) supported by a new dicarboxamidate ligand (N,N'-bis(2,6-dimethyl-phenyl)-2,2-dimethylmalonamide) was prepared. Complex 1 contained a diamond core made up of two Ni^II ions and two bridging hydroxide ligands. Titration of the 1 e^- oxidant (NH₄ )₂ [Ce^IV (NO₃ )₆ ] with 1 at -45 °C showed the formation of the high-valent species 2 and 3, containing Ni^II Ni^III and Ni^III ₂ diamond cores, respectively, maintaining the bis-μ-hydroxide core. Both complexes were characterised using electron paramagnetic resonance, X-ray absorption, and electronic absorption spectroscopies. Density functional theory computations supported the spectroscopic assignments. Oxidation reactivity studies showed that bis-μ-hydroxide-Ni^III ₂ 3 was capable of oxidizing substrates at -45 °C at rates greater than that of the most reactive bis-μ-oxo-Ni^III complexes reported to date.

Crystal structures of 1-hy-droxy-4-prop-yloxy-9,10-anthra-quinone and its acetyl derivative

1-Hy-droxy-4-prop-yloxy-9,10-anthra-quinone, C17H14O4, (I), and its acetyl derivative, 4-acet-yloxy-4-prop-yloxy-9,10-anthra-quinone, C19H16O5, (II), were synthesized from the commercially available dye quinizarin. In both compounds, the anthra-quinone frameworks are close to planarity. There is a large difference in the conformation of the prop-yloxy group; the mol-ecule of (I) adopts a gauche conformation [O-C-C-C = -64.4 (2)°], although the mol-ecule of (II) takes a trans-planar conformation (zigzag) [O-C-C-C = 176.1 (3)°]. In the mol-ecule of (I), there is an intra-molecular O-H⋯O hydrogen bond. In both crystals, the mol-ecules are linked by C-H ⋯O hydrogen bonds. A difference in the mol-ecular arrangements of (I) and (II) is found along the stacking directions.

1,4-Dihydroxy-2,3-dinitro-9,10-anthraquinone

In the title compound, C14H6N2O8, the anthraquinone unit is essentially planar [maximum deviation = 0.0645 (10) Å], and there are two intramolecular O–H...O hydrogen bonds formingS(6) motifs. The planes of the two nitro substituents make dihedral angles of 54.77 (8) and 55.60 (3)° with the anthraquinone ring system. In the crystal, molecules are linked by short intermolecular O...O contacts, leading to a three-dimensional network structure.

4-(3-Bromopropyloxy)-1-hydroxy-9,10-anthraquinone

In the molecule of the title compound, C17H13BrO4, the anthraquinone ring system is slightly bent, with a dihedral angle of 169.99 (7)° between the planes of the two benzene rings. The side chain (O—C—C—C—Br) has agauche–gaucheconformation, as indicated by the O—C—C—C and C—C—C—Br torsion angles of −66.9 (2) and −65.8 (2)°, respectively. In addition, there is an intramolecular O—H...O hydrogen bond enclosing anS(6) ring motif. The hydrogen-bond donor is bifurcated; in the crystal, a pair of O—H...O hydrogen bonds connects two molecules, forming an inversion dimer with anR22(12) ring motif.

Crystal structure of 1,4-dieth-oxy-9,10-anthra-quinone

The asymmetric unit of the title compound, C18H16O4, contains two crystallographically independent mol-ecules. The anthra-quinone ring systems are slightly bent with dihedral angles of 2.33 (8) and 13.31 (9)° between the two terminal benzene rings. In the crystal, the two independent mol-ecules adopt slipped-parallel π-overlap with an average inter-planar distance of 3.45 Å, forming a dimer; the centroid-centroid distances of the π-π inter-actions are 3.6659 (15)-3.8987 (15) Å. The mol-ecules are also linked by C-H⋯O inter-actions, forming a tape structure along the a-axis direction. The crystal packing is characterized by a dimer-herringbone pattern.

2,6-Dimeth-oxy-9,10-anthraquinone

The title compound, C₁₆H₁₂O₄, crystallizes with two half-mol­ecules in the asymmetric unit, each of which is completed by a crystallographic inversion center. The two crystallographically independent mol­ecules have almost the same geometry and are almost planar [maximum deviations = 0.018 (3) and 0.049 (3) Å]. They adopt a conformation in which the C_meth­yl—O bonds are directed along the mol­ecular short axis [C—C—O—C torsion angles of 179.6 (2) and 178.0 (2)°]. In the crystal, the mol­ecular packing is characterized by a combination of a columnar stacking and a herringbone-like arrangement. The mol­ecules form slipped π-stacks along the b axis, in which there are two kinds of columns differing from each other in their slippage. The inter­planar distances between neighboring mol­ecules are 3.493 (3) for one column and 3.451 (2) Å for the other.

2,3,6,7-Tetra-meth-oxy-9,10-anthra-quinone

Mol-ecules of the title compound, C(18)H(16)O(6), are almost planar [maximum deviation = 0.096 (4) Å] and reside on crystallographic centres of inversion. They adopt a conformation in which the C(meth-yl)-O bonds are directed along the mol-ecular short axis [C-C-O-C torsion angles of -175.3 (3) and 178.2 (3)°]. In the crystal, mol-ecules adopt a slipped-parallel arrangement with π-π stacking inter-actions along the a axis with an inter-planar distance of 3.392 (4) Å. Weak C-H⋯O inter-actions link the mol-ecules into sheets parallel to (10-2).