Isolable Tetragold(0) Clusters with Polarity-Tunable exo-Au-Au Bond via Intramolecular σ-Aromatization.

Intramolecular π-aromatization is a trait of many organic compounds that enhances the stability of their structures and polarizes related C-C π bonds. In contrast, rare study is focused on this phenomenon in metal clusters. Many existing homometallic clusters exhibit aromaticity, often characterized by nonpolar metal-metal bonds and a high degree of symmetry. However, synthesizing low-symmetric homometallic clusters with high-polar metal-metal bonds is challenging due to their limited thermodynamic stability. Herein, we report a facile strategy for the synthesis of [Au(µ2 -ER2 )]3 -AuPMe3 (E=Ge, Sn; R2 =1,1,4,4-tetrakis(trimethylsilyl)butane-1,4-diyl) clusters and reveal a novel stabilization mode, intramolecular σ-aromatization. Our electronic structure analyses show that these low-symmetric clusters possess a ten-electron σ-aromatic system, which is achieved via intramolecular σ-aromatization. Moreover, the strength of σ-aromaticity gives rise to a polarity-tunable exo-Au-Au bond.

Trinuclear anionic gold clusters bridged by dialkylsilylene and dialkylgermylene.

While the chemistry of gold clusters has been developed rapidly, the knowledge of trinuclear gold clusters with low-valent gold remains scarce. Herein, we report the synthesis, structural characterization, and density functional theory (DFT) calculations of trinuclear anionic gold clusters 3a and 3b ligated by dialkylsilylene (1a) and dialkylgermylene (1b), respectively.

Structure and reactivity of germylene-bridged digold complexes.

The bonding between gold and main-group metallic elements (M) featuring Auδ--Mδ+ polarity, has been studied recently. The gold in the bonds is expected to have the oxidation number of -1, and hence, nucleophilic. However, the knowledge of the reactivity of the gold-metal bonds remains limited. Here, we report digold-substituted germanes of the form of R'2Ge(AuPR3)(AuGeR'2) (3a; R = Me, 3b; R = Et), featuring two Au-Ge(IV) and one Au-Ge(II) bonds. DFT calculations of 3a revealed the existence of high-lying σ(Ge-Au) type HOMO and low-lying LUMO with germylene pπ nature. A pendular motion of AuPR3 group between Ge(IV) and Ge(II) of 3 occurs in the NMR time scale, suggesting that the Ge(II) center has an enhanced electrophilicity to be attacked by the nucleophilic gold (-I) atom. 3a reacts with nucleophilic Cl- and electrophilic MeOTf reagents at Ge(II) and Ge(IV) centers, respectively.

Diverse reactions of a fluorostannylenoid towards ethynes.

Fluoro(dialkyl)stannylenoid 2 exhibits unique reactivity towards ethynes with acetylenic hydrogen and those with trimethylsilyl groups, though the corresponding free dialkylstannylene 1 is inactive against those ethynes. Stannylenoid 2 reacts smoothly with gaseous ethyne and phenylethyne at room temperature, giving the corresponding diethynylstannanes, di(phenylethynyl)stannane 3 and diethynylstannane 6, respectively, in good yields with the concomitant evolution of H2. Trimethylsilyl-substituted ethynes such as 1-trimethylsilyl-(2-phenyl)ethyne and 1,2-bis(trimethylsilyl)ethyne react similarly to give 3 and bis(trimethylsilylethynyl)stannane 8, respectively. Rather unexpectedly, the reaction of 2 with (trimethylsilyl)ethyne affords 1,2-bis(ethenylstannyl)ethyne 7 in a good yield. The reactions of 2 with methyl and ethyl propynoates give the same products 4 and 5 as those obtained during the reaction of dialkylstannylene 1 without CsF. Pathways involving the nucleophilic attack of cesium acetylide to an ethyne-complexed stannylene were proposed, while the detailed mechanisms remain unknown. The structure of 7 was studied by single crystal X-ray diffraction analysis.

A Stable Cyclic (R2 SnAu)3 Anion Having In-Plane σ-Möbius Aromaticity.

A cyclic (R2 SnAu)3 anion (3- , R2 Sn=2,2,5,5-tetrakis(trimethylsilyl)-1-stannacyclopentane-1,1-diyl) has been synthesized as a stable blue salt with K+ (THF)6 through the reaction of stable dialkylstannylene 1 with R'3 PAuCl (R'=Et, Ph) followed by the reduction with KC8 . Crystallographic and NMR analysis shows that the six-membered (SnAu)3 ring of 3- is planar and highly symmetric with an equal distance of six Au-Sn bonds. A UV/Vis spectrum of 3- in hexane reveals an intense absorption maximum at 598 nm. While cyclic Au3 - with four valence electrons is known as unstable anti-aromatic anion, 3- with three divalent tin ligands is stable σ aromatic anion with an unprecedented Möbius orbital array as predicted by the perturbation MO and CCSD analysis of 3- .

Disilanylene-bridged BODIPY-based D-σ-A architectures: a novel promising series of NLO chromophores.

The synthesis and optical properties of a novel series of disilanylene-bridged BODIPY-based D-σ-A chromophores are reported. Si-Si σ-electrons are useful and impressible for tunable optical properties. The electron-donating group facilitates enhancement of the CT nature of the excited state through σ(Si-Si) orbital, leading to the remarkable two-photon absorption cross-sections.

Cation-Triggered Stannate(II)/Stannylenoid/Stannylene Conversion.

The reaction of dipotassio-tetrasilan-1,4-diide (4) with anhydrous SnCl2 at low temperature results in the formation of a five-membered cyclic potassio chlorostannate(II) ([(18-C-6)K](1)). By careful cation exchange reactions, it was transformed into the sodium chlorostannylenoid 2 (by using Na2 [B12 Cl12 ]) or into the non-stabilized cyclic bissilylstannylene 3 (through applying Li[Al(OC(CF3 )3 )4 ]). The increasing Lewis basicity of the bissilylstannylene 3 was analyzed by combined methods of DFT calculations and NMR spectroscopy and substantiated by the synthesis of the corresponding iron carbonyl complexes 7 and 8 from the chlorostannate 1 and the stannylene 3, respectively.

Strait Gate: Special Issue on Advances in Silicon Chemistry.

Manufacturing high-purity element silicon and organic polysilicones are two major silicon industries, supporting the basis of the modern electronic industry and our daily lives [...].

Dihydrogen Splitting Using Dialkylsilylene-Based Frustrated Lewis Pairs.

Isolable dialkylsilylene 5 reacts with dihydrogen in the presence of a small amount of a conventional Lewis acid (BPh3 , BEt3 ) or a base (PPh3 , PEt3 , NPh3 , NEt3 ) at low temperatures in a hydrocarbon solvent, giving the corresponding dihydrosilane 10 in high yields. Both 5/Lewis acid and Lewis base/5 pairs work as a frustrated Lewis pair (FLP) to split dihydrogen, being in accord with the amphoteric nature of silylene 5.

Silyl- and Disilanyl-BODIPYs: Synthesis via Catalytic Dehalosilylation and Spectroscopic Properties.

We describe herein the first synthesis of silyl- and disilanyl-BODIPYs through transition-metal-catalyzed dehalosilylation of iodo-BODIPYs using a Pd(P(tBu)3 )2 /Et3 N/toluene system. Various mono- and bis-silyl-BODIPYs, mono- and bis-disilanyl-BODIPYs and bis-BODIPYs linked by silylene and SiOSi groups were synthesized by using this straightforward method. Silyl- and disilanyl-substitution significantly modifies the spectroscopic properties of the BODIPY, in which the fluorescence quantum yields of the silyl-BODIPYs are remarkably increased, whereas the emission spectra of disilanyl-BODIPYs are red-shifted due to effective σ(SiSi)-π(BODIPY) conjugation.

Reactions of an Isolable Dialkylsilylene with Aroyl Chlorides. A New Route to Aroylsilanes.

The reactions of isolable dialkylsilylene 1 with aromatic acyl chlorides afforded aroylsilanes 3a-3c exclusively. Aroylsilanes 3a-3c were characterized by ¹H-, 13C-, and 29Si-NMR spectroscopy, high-resolution mass spectrometry (HRMS), and single-crystal molecular structure analysis. The reaction mechanisms are discussed in comparison with related reaction of 1 with chloroalkanes and chlorosilanes.

Reversible Stannylenoid Formation from the Corresponding Stannylene and Cesium Fluoride.

A fluorostannylenoid (Cs+ [R2 SnF]- (9), R2 =(TMS)2 CCH2 CH2 C(TMS)2 ) was prepared by reacting a stable dialkylstannylene (R2 Sn (8), R2 =(TMS)2 CCH2 CH2 C(TMS)2 ) with cesium fluoride at room temperature in THF. While 9 is stable in THF and DME, removal of the solvent leads to the regeneration of stannylene 8. No reaction occurred when 8 was treated with CsF in a hydrocarbon solvent. Addition of dibenzo-21-crown-7 ether to the THF solution of stannylenoid 9 followed by usual workup affords the corresponding crystalline stannylenoid crown ether complex, the X-ray structural analysis of which revealed a fluorine-bridged contact ion-pair structure. The reaction of 9 with excess phenylacetylene gives the corresponding di(phenylethynyl)stannane.

1,3-Diazasilabicyclo[1.1.0]butane with a Long Bridging N-N Bond.

A 1,3-diazasilabicyclo[1.1.0]butane (1) is synthesized as thermally stable crystals by using the cycloaddition reaction of an isolable dialkylsilylene with aziadamantane. The bridge N-N bond length of 1 (1.70 Å) is the longest among those of known N-N singly-bonded compounds, including side-on bridged transition-metal dinitrogen complexes. The compound 1 is intact in air but moisture sensitive. No reaction occurs with hydrogen, even under pressure at 0.5 MPa. Irradiation of 1 with light gives an isomer quantitatively by N-N and adamantyl C-C bond cleavage. The origin of the remarkable N-N bond elongation is ascribed to significant interaction between a Si-C σ* and Ν-Ν π and σ orbitals as determined by DFT calculations of model compounds.

Persistent Dialkylsilanone Generated by Dehydrobromination of Dialkylbromosilanol.

A persistent dialkylsilanone was synthesized by the dehydrobromination of a dialkylbromosilanol with tris(trimethylsilyl)silyl potassium in solution at -80 °C: It was characterized by NMR and IR spectroscopy, and was tested in several reactions. In (29) Si NMR spectrum in [D8 ]toluene, the signal due to the unsaturated silicon nuclei was observed at 128.7 ppm. Reactions of the dialkylsilanone with water and mesitonitrile oxide gave a silanediol and a [2+3] cycloadduct, respectively. The silanone remains intact in [D8 ]toluene below -80 °C for at least two days, while it undergoes unprecedented isomerization to give a siloxysilene by means of 1,3-silyl migration at higher temperatures.

Elusive 2H-1,2-oxasiletes through reactions of an isolable dialkylsilylene with diazocarbonyl compounds.

The reactions of isolable dialkysilylene 1 with 2-diazo-1,2-diphenylethanone and ethyl 2-diazo-2-phenylacetate gave elusive silacycles, 2H-1,2-oxasiletes 2 and 3, respectively, in high yields. Because these reactions occur at low temperatures of ca.-30 °C, initial complexation of the silylene to the carbonyl oxygen of the diazocarbonyl compounds is suggested to trigger dinitrogen elimination followed by cyclization. In contrast, a six-membered cyclic diazo compound 8 and 1-sila-2,3-diazabicyclo[3.3.0]oct-3-ene 10 were obtained in good yields by the reaction of 1 with less reactive ethyl 2-diazo-3-oxo-3-phenylpropanoate 7 and trimethylsilyldiazomethane 9. Molecular structures of 2, 3, 8 and 10 were determined by X-ray crystallography.

Kinetic stabilization against the oxidation reaction induced by a silaalkane cage in a thiophene-bridged molecular gyroscope.

Macrocage molecules with a bridged rotor have been synthesized as molecular gyroscopes. The kinetics of the oxidation reaction of the thiophene-bridged molecular gyroscope, whose thiophene ring was bridged inside a silaalkane cage, was investigated. A remarkable kinetic stabilization against the oxidation of the thiophene moiety induced by the molecular cage framework was observed.

Reactions of an isolable dialkylsilylene with aromatic nitriles providing a new type of heterosilole.

The 1 : 2 reactions of isolable dialkylsilylene with nitriles having electron-donating aromatic substituents gave 1,4-diaza-2-siloles with a hitherto-unknown type of ring system, in contrast to the previous studies showing exclusive formation of the corresponding 1,3-diaza-2-siloles; the reactions of with aromatic nitriles bearing electron-withdrawing substituents afforded the latter ring system. The remarkable diversity of the reactions is explained by invoking the corresponding nitrile silaylides as key intermediates whose polarity switches depending on the substituents of nitriles.

Diverse reactivity of an isolable dialkylsilylene toward imines.

The reactions of isolable dialkylsilylene 10 with various aldimines proceed smoothly at low temperatures to give diverse products depending on the substituents on the imine. The reactions of 10 with 4-XC(6)H(4)CH=NPh [X = H (11a), MeO (11b), and Cl (11c)] give the corresponding silaaziridines 12a-12c in high yields, which are thermally very stable and remain intact in the air and moisture for a long time. In contrast, the reactions of 10 with 4-F(3)CC(6)H(4)CH=NPh (11d) and 3,5-(F(3)C)(2)C(6)H(3)CH=NPh (11e) having strong electron-withdrawing aryl substituents on imine carbon are accompanied by 1,2-trimethylsilyl migration rather unexpectedly to give silaazetidines 13d-13e incorporated into a bicyclo[3.2.0]heptane ring. The reaction of 10 with N-benzylbenzaldimine 11f affords the corresponding (dibenzylamino)silane 14f in a moderate yield. Molecular structures of 12a-12c, 13d-13e and 14f were determined by X-ray crystallography. All these reactions are proposed to occur via the initial formation of the corresponding imine silaylides, while the subsequent reactions leading to the final products are controlled by the electronic structure of the ylide depending on the substituents. N-phenylbenzophenimine 11g does not react with 10.

New isolable dialkylsilylene and its isolable dimer that equilibrate in solution.

The new isolable dialkylsilylene 3 bearing a bidentate alkyl substituent was synthesized. Recrystallization of silylene 3 gave yellow crystals of 3 and orange-red crystals of tetraalkyldisilene 4, a dimer of 3. In the solid state, 3 exists as a monomer with a closest distance of 6.745 Å between dicoordinate silicon atoms, while disilene 4 has a remarkably long Si═Si double bond distance of 2.252 Å. An equilibrium between 3 and 4 in solution was observed by NMR and UV-vis spectroscopies, and the thermodynamic parameters of the equilibrium were estimated to be ΔH = -36 ± 3 kJ mol(-1) and ΔS = -170 ± 15 J mol(-1) K(-1). Analysis of the percent buried volume, a measure of the steric demand around the divalent silicon, showed that the flexible steric bulkiness of the alkyl substituent of 3 and 4 allows the reversible dimerization of silylene 3 to disilene 4 and the isolation of both species.