Air-stable, room-temperature emissive di(2-naphthyl)disilene, protected by the bulky 1,1,3,3,5,5,7,7-octaethyl-s-hydrindacen-4-yl (Eind) groups, can emit light in an organic light-emitting diode, thus providing the first experimental demonstration of electroluminescence from the heavy group 14 unsaturated compounds.

A room-temperature dynamic equilibrium between dibromodisilenes and bromosilylenes has been demonstrated by taking advantage of the steric protection using the fused-ring bulky 1,1,3,3,5,5,7,7-octa-R-s-hydrindacen-4-yl (Rind) groups. Although the bromosilylenes cannot be directly observed by spectroscopic methods, the thermal homolytic cleavage of the Si═Si double bond has been confirmed by a pseudo-first-order kinetics for the trapping with bis(trimethylsilyl)acetylene and a crossover reaction using two kinds of Rind-substituted dibromodisilenes. The addition of 4-pyrrolidinopyridine (PPy) to the dibromodisilene leads to an equilibrium mixture between the dibromodisilene and a PPy adduct of bromosilylene, the latter being isolated and characterized. The substitution of the bromine atom in the dibromodisilene by the Grignard reagent is significantly accelerated by the addition of PPy.

Diborane(6) as a H-bridged dimer of monoborane can be converted cleanly by two-electron reduction into diborane(6) dianion, which is isoelectronic with ethane, through B–B σ-bond formation when each boron atom has a bulky ligand on it. The existence of the B–B σ bond is supported by the X-ray molecular structure [B–B bond length of 1.924(3) Å], NMR studies, magnetic susceptibility measurements, and DFT calculations. Stepwise hydride abstraction reactions of the diborane(6) dianion produce the corresponding H-bridged diborane(5) anion and doubly H-bridged diborane(4) without B–B bond scission.

p-Monothiobenzoquinones incorporated in a fused-ring octaalkyl-s-hydrindacene skeleton have been synthesized as air- and moisture-stable reddish orange crystals by the oxidation of mercaptophenol derivatives with DDQ, which have been characterized by X-ray crystallography to show a planar quinoid framework.

A series of neutral and cationic Au(I) complexes incorporating π-conjugated phosphasilene ligands stabilized by the bulky 1,1,3,3,5,5,7,7-octa-R-substituted s-hydrindacen-4-yl (Rind) groups have been synthesized. X-ray crystallographic studies show the η1-coordination mode of the phosphasilene ligand, accommodating the linear trans two-coordinate geometry around the gold center. While the metal coordination slightly enhances the intensity of the strong π–π* absorption of the phosphasilene chromophores, the phosphashilene π-conjugation is not extended through the Au atom.

π-Conjugated disilenes with 2-naphthyl or 2-fluorenyl groups on the silicon atoms have been synthesized as air-stable emissive red solids using the bulky 1,1,3,3,5,5,7,7-octaethyl-s-hydrindacen-4-yl (Eind) groups. The strong π−π* absorptions and distinct emission at room temperature, both in solution and in the solid state, have been observed due to the substantial contribution of the 3pπ*(Si−Si)−2pπ*(carbon π-electron system) conjugation.

In contrast to the common multiple bonding between carbon atoms, multiply bonded boron compounds have still been a synthetic challenge due to the electron deficiency of boron. We now report that a stable doubly hydrogen-bridged diborane(4), EindB(μ-H)2BEind, is produced by the two-electron oxidation of a hydrogen-substituted diborane(4) dianion [Li+(thf)]2[Eind(H)BB(H)Eind]2−, where Eind denotes the 1,1,3,3,5,5,7,7-octaethyl-s-hydrindacen-4-yl. The X-ray crystallography reveals a short B−B distance of 1.4879(7) Å in comparison with the normal B−B single bond length (1.72 Å), the presence of two hydrogen atoms bridged perpendicular to the B−B bond with a butterfly shape having a dihedral angle of the two BHB triangles of 113(1)°, and a linear geometry around the B−B bond with a C−B−B bond angle of 178.92(4)°. These structural data, experimental electron density analysis, and computational studies confirm the 3-fold bonding (a σ and two π-like bonds) between the two boron atoms incorporating the two bridging hydrogen atoms.

Recent advances in the chemistry of π-conjugated disilenes stabilized by the newly developed bulky groups based on a fused-ring octa-R-substituted s-hydrindacene skeleton (Rind groups) are described. The synthesis and characterization of the disilenes with various aryl substituents on the silicon atoms are covered. The highly co-planar π-frameworks stabilized by the perpendicularly-fixed Rind groups are demonstrated by the X-ray crystallographic analysis. The extension of the π-conjugation over the diaryldisilene framework is visualized by the photophysical properties such as the UV-vis absorption spectra and the distinct emission both in solution and in the solid state at an ambient temperature.

Isolable mixed diorganocopper(I) complexes have been synthesized and structurally characterized by introducing a variety of bulky “Rind” groups based on a fused-ring octa-R-substituted s-hydrindacene skeleton. Treatment of RindLi with CuBr produced organobromocuprate dimers [Cu(Rind)/CuBr]2 or monomers Li[Cu(Rind)Br], depending on the steric bulkiness of the Rind ligands. Subsequent substitution of the bromine atoms in these complexes by lithium trimethylsilylacetylide gave dimeric and monomeric aryl(alkynyl)copper(I) complexes A and B, respectively. Complex B is the first isolable mixed diorganocuprate monomer formulated as LiCuRR′ and was found to selectively undergo oxidative cross-coupling of two different organic groups on copper.

π-Conjugated phosphasilenes with a variety of aryl substituents on the silicon atom have been synthesized by the use of a 1,1,3,3,5,5,7,7-octaethyl-s-hydrindacen-4-yl (Eind) group. X-ray structural analysis shows the highly coplanar π-framework stabilized by the perpendicularly fixed Eind groups. The strong π−π* absorptions have been observed, demonstrating the extension of π-conjugation over the skeleton. The DFT calculations indicate that the LUMO involves the substantial contribution of the 3pπ*(Si−P)−2pπ*(carbon π-electron system) conjugation. The electrochemical properties of the phosphasilens are also presented.

Recent advances in the chemistry of π-conjugated disilenes stabilized by the newly developed bulky groups based on a fused-ring octa-R-substituted s-hydrindacene skeleton (Rind groups) are described. The synthesis and characterization of the disilenes with various aryl substituents on the silicon atoms are covered. The highly co-planar π-frameworks stabilized by the perpendicularly-fixed Rind groups are demonstrated by the X-ray crystallographic analysis. The extension of the π-conjugation over the diaryldisilene framework is visualized by the photophysical properties such as the UV-vis absorption spectra and the distinct emission both in solution and in the solid state at an ambient temperature.

Air-stable, room-temperature emissive di(2-naphthyl)disilene, protected by the bulky 1,1,3,3,5,5,7,7-octaethyl-s-hydrindacen-4-yl (Eind) groups, can emit light in an organic light-emitting diode, thus providing the first experimental demonstration of electroluminescence from the heavy group 14 unsaturated compounds.