C,C cross-coupling reactions for the synthesis of nonsymmetrical biaryls represent one of the most significant transformations in contemporary organic chemistry. A variety of useful synthetic methods have been developed in recent decades, since nonsymmetrical biaryls play an evident role in natural product synthesis, as ligand systems in homogeneous catalysis and materials science. Transformation of simple arenes by direct C,H activation belongs to the cutting-edge strategies for creating biaryls; in particular the 2-fold C,H activation is of significant interest. However, in most examples very costly noble metal catalysts, ligand systems, and significant amount of waste-producing oxidants are required. Electrochemical procedures are considered as inherently "green" methods, because only electrons are required and therefore, no reagent waste is produced. Here, we report a metal-free electrochemical method for cross-coupling between phenols and arenes using boron-doped diamond (BDD) anodes in fluorinated media. Our sustainable approach requires no leaving functionalities. Employing water or methanol as mediator represents the key improvement for achieving nonsymmetrical biaryls with superb selectivity and synthetic attractive yields.

SiO in a complex: The first silanone that is stable at room temperature (3) is reported. The two-step synthesis involves carbonylation of the silylidyne complex 1 to give the chromiosilylene 2, followed by oxidation of 2 with N2 O. Silanone 3 features a polar, short SiO bond (1.526(3) Å) to a trigonal-planar-coordinated silicon center and reacts with water to give the dihydroxysilyl complex.

Silylene with a carbene carabiner: The synthesis, structure, and some reactions of a stable carbene adduct of dibromosilylene, SiBr2(Idipp) (see picture; Idipp=1,3‐bis(2,6‐diisopropylphenyl)‐ imidazol‐2‐ylidene), are described. SiBr2(Idipp) was characterized by X‐ray crystallography, NMR spectroscopy, and theoretical methods.

Particularly sustainable: The anodic cross‐coupling reaction between phenols and arenes can be performed on boron‐doped diamond electrodes. The arylated products are formed directly and obtained, in some cases, with high selectivity. Since only hydrogen atoms are sacrificed in the course of reaction this methodology opens the door to a novel concept for biaryl formation.

Structural diffraction analysis of an anilino squaraine with branched isobutyl side chains shows crystallization into two polymorphic structures in the bulk and in spin-casted thin films. We observe multipeaked and pleochroic absorption spectra being blue-(red)-shifted for the monoclinic (orthorhombic) polymorph. We understand the packing as Coulombic molecular H-(J)-aggregates supporting Davydov splitting. Pictures of projected Davydov components in oriented thin films fit well to polarization resolved spectro-microscopy and crossed-polarized light microscopy investigations. By comparison with literature on anilino squaraines with linear alkyl side chains, we point out a general trend for steering the thin film excitonic properties by simple side chain and/or processing condition variation. Combined with the ability to locally probe the direction of transition dipole moments, this adds value to the rational design of functional thin films for optoelectronic applications, especially envisioning ultrastrong light–matter interactions.

The reaction of SiCl4 with an excess of (PPN)N3 (PPN+ = [(Ph3P)2N]+) affords selectively (PPN)2[Si(N3)6] (1). Simultaneous thermal analysis (TG-DTA) shows that the hexaazidosilicate salt is remarkably stable, melting at Tonex = 214 degrees C. Melting of 1 is followed by two distinct exothermic decomposition processes at Ton = 256 and 321 degrees C, the first one involving elimination of N2 and the second one degradation of the PPN cations and evolution of Si(N3)4, N2, and some HN3. The crystal structure of 1 consists of discrete PPN+ cations and S2 symmetric [Si(N3)6]2- anions, which have a very rare, octahedral SiN6 framework and the highest nitrogen content (90%) among the hexaazidometallates reported so far. The IR, Raman, 29Si, and 14N NMR spectra of 1 in CH3CN suggest in combination with the calculated spectra the presence of intact [Si(N3)6]2--anions of S6 symmetry in solution. Geometry optimizations with various methods and basis sets show an S6 symmetric structure to be the most stable [Si(N3)6]2- isomer, the calculated bonding parameters comparing well with the experimental values.

The first N-heterocyclic carbene adducts of arylchlorosilylenes are reported and compared with the homologous germanium compounds. The arylsilicon(II) chlorides SiArCl(Im-Me(4)) [Ar=C(6)H(3)-2,6-Mes(2) (Mes=C(6)H(2)-2,4,6-Me(3)), C(6)H(3)-2,6-Trip(2) (Trip=C(6)H(2)-2,4,6-iPr(3))] were obtained selectively on dehydrochlorination of the arylchlorosilanes SiArHCl(2) with 1,3,4,5-tetramethylimidazol-2-ylidene (Im-Me(4)). The analogous arylgermanium(II) chlorides GeArCl(Im-Me(4)) were prepared by metathetical exchange of GeCl(2)(Im-Me(4)) with LiC(6)H(3)-2,6-Mes(2) or addition of Im-Me(4) to GeCl(C(6)H(3)-2,6-Trip(2)). All compounds were fully characterized. Density functional calculations on ECl(C(6)H(3)-2,6-Trip(2))(Im-Me(4)), where E=Si, Ge, at different levels of theory show very good agreement between calculated and experimental bonding parameters, and NBO analyses reveal similar electronic structures of the two aryltetrel(II) chlorides. The low gas-phase Gibbs free energy of bond dissociation of SiCl(C(6)H(3)-2,6-Trip(2))(Im-Me(4)) (Delta(calcd) degrees=28.1 kJ mol(-1)) suggests that the carbene adducts SiArCl(Im-Me(4)) may be valuable transfer reagents of the arylsilicon(II) chlorides SiArCl.

Si 2+ ions are highly reactive, two-valence-electron species that have been generated in laser-induced plasmas and studied by photoabsorption and microwave spectroscopy. [1] The ions have also been employed as implants for waveguide fabrication in lithium niobate crystals, which are of great interest for various photonic applications owing to their physical and electro-optical properties. [2] A possible method of trapping these highly electrophilic ions in the condensed phase, may involve complexation by three strongly basic, neutral ligands (L) to give dications of the general formula [SiL 3 ] 2+ , in which the silicon center attains a noble gas configuration. However, dicationic silicon(II) complexes are presently unknown, in marked contrast to the few germanium homologues, which were reported some years ago by K. M. Baines et al. [3] This difference can be explained by the anomalous low electronegativity of silicon versus germanium, [4] which makes the isolation of silicon(II)-centered dications a highly challenging goal. Even monocationic silicon(II) compounds are very rare, and only the nido-type cluster cation [(C 5 Me 5 )Si] + , [5] [6] and the Si II cation [{C 10 H 6a,a-NP(nBu) 3 }SiCl] + stabilized by a chelating bis(iminophosphorane) ligand [7] have been isolated thus far.Since the first report of the silicon(0) compound [Si 2 -(Idipp) 2 ] (Idipp = 1,3-bis(2,6-diisopropylphenyl)-imidazol-2ylidene) by G. Robinson et al. in 2008, [8] N-heterocyclic carbenes have been shown to be particularly effective ligands for the stabilization of silicon compounds in unusually low oxidation states. Remarkable examples include NHC adducts of the dihalosilylenes SiX 2 (X = Cl, Br), [9] which are very valuable precursors in Si II chemistry, [9c, 10] or NHC adducts of the organohalosilylenes RSiCl (R = m-terphenyl, (2,6-diisopropylphenyl)(trimethylsilyl)amino), [11] which paved the way for the preparation of the first complexes featuring metalsilicon triple bonds. [12] Herein, the exchange of NHC ligands at Si II centers is illustrated for the first time to provide access to unprecedented dicationic NHC complexes of silicon(II) and NHC adducts of the iodosilyliumylidene cation SiI + .The entry into this chemistry started with the triiodosilylimidazolium salt 1 (Scheme 1), which was obtained from the reaction of SiI 4 with Idipp in toluene and isolated as a yellow, thermally robust solid in 96 % yield. Reduction of 1 with potassium graphite (2.3 equiv) in benzene afforded the yellow NHC-diiodosilylene adduct 2-I in 81 % yield (Scheme 1). [13] Under rigorous exclusion of air, the silicon(II) compound 2-I is stable in benzene or toluene solution at ambient temperature for several days, and decomposes in the solid state upon heating above 160 8C.The solid-state structure of 1·3 (CHCl 3 ) was determined by single-crystal X-ray crystallography. [13] It resembles that of [SiBr 3 (Idipp)]Br·3 (CH 2 Cl 2 ) [9b] and reveals that the chloroform trissolvate of 1 is composed of well separated [SiI 3 -(Idipp)] + cations and i...