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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.

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 Mobius orbital array as predicted by the perturbation MO and CCSD analysis of 3- .

Digoldgermanes with a gold coordinated by a dialkylgermylene ligand, R’2Ge(AuPR3)(AuGeR’2) (3a; R = Me, 3b; R = Et), were synthesized as green solids through the reactions of stable dialkylgermylene 1 with R3PAuCl followed by the reduction with KC8 at ambient temperatures. The structural characteristics of 3a and 3b were elucidated using NMR spectroscopy, X-ray crystallography, and DFT calculations. An intense absorption maximum was observed at 590 nm in the UV-vis spectrum of 3a in hexane. A pendular motion of AuPR3 group between Ge(IV) and Ge(II) of 3a and 3b occurring in the NMR time scale was found by the dynamic 1H NMR analysis, suggesting that the Ge(II) ligand has an enhanced electrophilicity to be attacked by the nucleophilic gold atom which closes to ‒1 oxidation state. DFT calculations of 3a revealed the existence of high-lying σ(Ge-Au) type HOMO and low-lying LUMO with germylene pπ nature. We show the bond formation and activation alternatively at Au or Ge atom, a methylation of digoldgermane 3a with MeOTf affords methylgermane 5. Moreover, the digoldgermane 3a reacts with Cl− ion of Ph4PCl and CH3C(O)Cl smoothly to form the corresponding chloride-addition product 7 and chlorogoldgermane 9, respectively. Cyclic trimerization reactions of aromatic isocyanates were high-efficiently catalyzed by 3a giving the corresponding 1,3,5-triaryl isocyanurates.

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.

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.

The reactions of isolable dialkylgermylene 1 with benzoyl and substituted benzoyl chlorides afford the corresponding aroyl(chloro)germanes in high yields. While 2,2-dimethylpropanoyl chloride react...

The reactions of stable monomeric dialkylstannylene 1 with methyl and ethyl propynoates give the corresponding 1:2 adducts, alkenyl(alkynyl)stannane 2 and 3 in high yields, while 1 does not react with parent acetylene or common mono- and disubstituted acetylenes such as phenylacetylene, trimethylsilylacetylene, diethyl 2-butynedioate, etc. Notably, 2 and 3 have the Z-configuration of the alkenyl moieties, in contrast to similar adducts obtained by the known reactions of silylenes with terminal acetylenes. It is suggested that the formation of a carbonyl oxygen-coordinate cyclic zwitterion as a key intermediate is essential for the reactions. Stannylene 1 adds to in situ generated benzyne, forming a 1:1 adduct having a unique 3-stanna-1-silaindane ring system.

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.

The reactions of isolable dialkylstannylene 1 with 1-adamantanoyl, 2,2-dimethylpropanoyl, benzoyl, and substituted benzoyl chlorides afford the corresponding acyl(chloro)stannanes in good yields. Similar reactions with more reactive acetyl and propanoyl chlorides do not give the corresponding insertion products but the corresponding dichlorostannane by the overreaction. The benzoyl(chloro)stannane reacts with acetyl chloride to afford the corresponding 1,2-dione and the dichlorostannane quantitatively. Acyl(chloro)stannanes obtained were fully characterized by multinuclear NMR spectroscopy, high-resolution mass spectrometry, and by single-crystal X-ray diffraction studies.

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.

We describe herein the first facile synthesis of silyl- and disilanyl-BODIPYs through transition-metal-catalyzed dehalosilylation of iodo-BODIPYs using a Pd(P(t-Bu)3)2/Et3N/toluene system. Various mono- and bis-silyl-BODIPYs, mono and bis-disilanyl-BODIPYs and bis-BODIPYs linked by silylene and SiOSi groups have been 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 enhanced, whereas the emission spectra of disilanyl-BODIPYs are red-shifted due to the effective sigma(SiSi)-pi(BODIPY) conjugation.

A cyclic (R

The reaction of isolable dialkylstannylene 1 with an excess amount of CS2 produces an isomeric mixture of 3,3′-distanna-2,2′,4,4′-tetrathiabicyclobutylidene 8 and 3,7-distanna-2,4,6,8-tetrathiabicyclo[3.3.0]oct-1(5)-ene 9 with a ratio depending on the reaction conditions. Compounds 8 and 9 are separated by column chromatography and characterized by NMR spectroscopy and X-ray crystallography. Detailed investigation of the reaction has revealed that the initial product is 8, which isomerizes to 9 irreversibly under the catalytic influence of 1 as a Lewis acid. The above view is supported by the theoretical DFT calculations. Treatment of 1 with ArN═C═O [Ar = 2,6-iPr2C6H3] affords the corresponding carbamoyl(hydroxyl)stannane 11 via the hydrolysis of the corresponding silaaziridinone formed by the [1 + 2] cycloaddition reaction of 1 with the N═C double bond of the isocyanate. Stannylene 1 reacts with ArN═C═S, giving a mixture of complex products, while 1 does not react with CO2.

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.

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.

An isolable dicoordinate dialkylsilylene, 2,2,5,5-tetrakis(trimethylsilyl)silacyclopentane-1,1-diyl (6), was found to react with CO2 and ArN═C═X (X = O, S) smoothly to give the corresponding bis(silyl)carbonate, 4-imino-1,3-dioxasiletane and 4-imino-1,3-dithiasiletane derivatives in high yields, respectively. The molecular structures of these products were determined by X-ray crystallography. All these reactions are parallel to those of a hypercoordinate silylene with η5-pentamethylcyclopentadienyl ligands, decamethylsilicocene, reported by Jutzi et al. and are suggested to involve similarly the formation of the corresponding Si═X doubly bonded compounds (X = O, S) at the initial steps. Mechanistic details of the multistep reaction of a model dialkylsilylene with CO2 were investigated using DFT calculations.

The structural diversity of bicyclo[1.1.0]tetrasilane has been analyzed using perturbation MO theory and DFT calculations. Among its four planar-cis (C2v), planar-trans (C2h), long-bond (C2v), and short-bond isomers (C2v) found theoretically, the first two are derived as the results of second-order Jahn–Teller distortion of the D2h isomer associated with the π–σ* orbital mixing. The last two are formed through orbital mixing in an isomer with a folded ring. The orbital mixing of the two σ*(Si–H) orbitals at the 1- and 3-silicon atoms into a π-type orbital between the atoms plays a crucial role in stabilizing the system by causing pyramidalization at the silicon atoms and by introducing the inverted σ-bond nature between the atoms. The π–σ* orbital mixing model is applied to predicting the structure of related compounds.

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.

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.

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.

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.

Various reactions for a stable dialkylsilylene, 2,2,5,5-tetrakis(trimethylsilyl)silacyclopentane-1,1-diyl (1), are summarized and their mechanisms are discussed. Silylene 1 isomerizes to the corresponding silaethene via the 1,2-trimethylsilyl migration. Reduction of 1 with alkali metals affords the corresponding radical anion 1 . − with a relatively small 29Si hfs constant (2.99 mT) and a large g-factor (g = 2.0077) compared with those for trivalent silyl radicals. Photo-excitation of 1 generates the corresponding singlet excited state (1 1 ∗ ) with the lifetime of 80.5 ns. The excited state reacts with C=C double bond compounds including benzene, naphthalene, and (E)- and (Z)-2-butenes. Although the thermal reactions of 1 with haloalkanes occur via radical mechanisms, the insertion into O–H, Si–H and Si–Cl bonds proceeds concertedly via the three-membered cyclic transition states. The reaction of 1 with H2SiCl2 gives the Si–Cl insertion product exclusively, while the quantitative insertion to Si–H bond occurs when Me2SiHCl is used as a substrate. The origin of the rather unusual Si–H/Si–Cl selectivity is elucidated using DFT calculations. Silylene 1 adds to C=C, C≡C, and C=O π bonds to afford the corresponding silacycles as stable compounds. The importance of the carbonyl silaylides during the reactions of silylenes with aldehydes and ketones is emphasized.

Three distortion modes, trans and cis bending and twisting, of ethylene, disilene, and digermene and their anions are discussed in terms of a generalized π–σ* orbital mixing model using PMO theory. The model predicts that trans- and cis-bent geometries of neutral dimetallenes may be stabilized from the planar geometry but with very small energy gains and that these geometries should be largely stabilized with significant bend angles and stabilization energies in dimetallene anions. Twisting around the double bonds of dimetallenes may lower the energy of the anions. The above prediction is verified by the potential energy surface calculations at the B3LYP/6-311++G(3df,3pd) level.

Electronic and steric substituent effects on the insertion reactions of dimethylsilylene (1) and 2,2,5,5-tetrasilylsilacyclopentane-1,1-diyl (2′) into Si–H bonds are compared with those into Si–Cl bonds using DFT calculations at the B3LYP/6-31++G(d,p) level. For both 1 and 2′, the ΔG⧧ value for the insertion into a Si–H bond of SiH4 is close to and only ca. 1.5 kcal mol–1 lower than that into the Si–Cl bond of H3SiCl. Effects of in-plane substituents on the ΔG⧧ values for both Si–H and Si–Cl insertion reactions are mainly electronic and electron-withdrawing substituents lower the ΔG⧧ values. Sensitivity of the Si–H insertion to the substituent effects is similar to that of the Si–Cl insertion. Effects of out-of-plane substituents are largely steric, and their sensitivity for the Si–H insertion is close to that for the Si–Cl insertion. The ΔG⧧ values for the insertion reactions of sterically bulky 2′ are significantly larger than those of 1. The puzzling prior observation that a bulky isolable silylene ins...

The reactions of an isolable dialkylsilylene, 2,2,5,5-tetrakis(trimethylsilyl)silacyclopentan-1,1-diyl (1) with ethylene, (Z)-2-butene, acetylene, bis(trimethylsilyl)acetylene, and 2,3-dimethylbutadiene at room temperature gave the corresponding silacycles as isolable compounds. Because of the large steric hindrance, the reaction of 1 with (E)-2-butene gave a complex mixture, indicating no formation of the corresponding silirane. The reaction of 1 with 2,3-dimethylbutadiene afforded the corresponding [1 + 4] cycloadduct without contamination of the [1 + 2] cycloadduct. Stable C-unsubstituted silirane and silirene produced by the reactions of 1 with ethylene and acetylene were analyzed by X-ray crystallography. © 2011 Wiley Periodicals, Inc. Heteroatom Chem 22:432–437, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/hc.20705

Tetra(t-butyldimethylsilyl)germasilene (8b) was synthesized using di(t-butyldimethylsilyl)hydridogermyllithium prepared by the germa-metallation of the corresponding dihydridogermane. Tetrasilylgermasilene 8b was obtained as single crystals by recrystallization from hexane at rt. The molecular structure of 8b is similar to those of the corresponding disilene 8a and digermene 8c but with an intermediate unsaturated bond length and twist angle between those of 8a and 8c. The reactions of 8b with methanol and 2,3-dimethylbutadiene gave the corresponding adducts. Equilibrium between 8b and the corresponding (trisilylsilyl)(silyl)germylene is suggested by the reaction of 8b with triethylsilane giving the germylene insertion product into the Si–H bond.

The reactions of isolable dialkylsilylene 2,2,5,5-tetrakis(trimethylsilyl)-1-silacyclopentane-1,1-diyl with different types of ketones such as adamantanone, acetone, benzophenone, and cyclopropenones proceed smoothly at room temperature to afford the corresponding siloxirane, silyl enol ether, 2-oxa-silacyclopentene, and unusual cyclopropenylsilanes, respectively, without formation of any secondary or side-reaction products. The electronic structure of various types of model carbonyl silaylides was investigated using DFT calculations. The diversity of the reaction modes is explained by invoking the substituent effects on the electronic nature of the initially formed carbonyl silaylides.

Silylenecyclotetrasilane 4 synthesized as marginally stable orange crystals undergoes ring expansion to give cyclopentasilene 5 quantitatively with the activation parameters of ΔH⧧ = 24.8 ± 1.0 kcal mol−1 and ΔS⧧ = +6.5 ± 3.2 cal mol−1 K−1. The activation parameters and DFT calculations support that the isomerization of 4 to 5 proceeds through stepwise double 1,2-silyl migrations.

The synthesis, X-ray and spectroscopic analysis, and unusual bonding and structure among heavy group-14 element congeners of allene (heavy allenes) [R(2)M=M'=MR(2); M = M' = Si (1a), M = Si, M' = Ge (1b), M = Ge, M' = Si (1c), and M = M' = Ge (1d)] are comparatively discussed. Using DFT calculations and PMO theory, the origin of the bent and fluxional skeleton of the heavy allenes is ascribed to the Jahn-Teller distortion associated with the effective pi-sigma* mixing (pi-sigma* distortion). This type of distortion is suggested to be a key concept for qualitative description of the unusual bonding of unsaturated compounds of heavy main-group elements.

Insertion reactions of dimethylsilylene (Me(2)Si:) into the silicon-chlorine bond of various substituted chlorosilanes have been computationally studied by using DFT calculations with a 6-31++G(d,p) basis set. All of the insertions investigated herein were exothermic (more than 40 kcal mol(-1)) and proceeded via three-membered cyclic transition states (TS) with one substituent of a chlorosilane in the ring plane and two other substituents out of the plane. Among the two possible concerted insertion pathways, the pathway via a TS with a silylene lone-pair orbital approaching a chlorosilane silicon atom was preferred. Important nucleophilic interactions of silylene lone-pair orbitals with anti-bonding sigma orbitals of Si-Y (in plane) were supported by carrying out a natural bond orbital (NBO) analysis of the reaction. A radical pathway through the initial abstraction of chlorine from chlorosilane by the silylene cannot compete with the preferred concerted pathway. Systematic calculations for SiMe(2) insertion into various chlorosilanes (YR(2)SiCl; Y (in-plane substituent) = H, Me, NH(2), OH, F, SiH(3), PH(2), SH and Cl; R (out-of-plane substituent) = H, Me, iPr and tBu) have revealed remarkable substituent effects on activation free energies (DeltaG(double dagger)). In-plane (Y) substituent effects were mostly electronic. Electron-withdrawing substituents accelerate the insertion through enhanced nucleophilic interaction between silylene lone-pair orbitals with the sigma*(Si-Y) orbital at the TS. The DeltaG(double dagger) values correlate with the sigma(I) constants as a scale of the inductive effect of Y. Out-of-plane (R) substituent effects are mainly steric, and bulky substituents increase the activation free energy . Correlation of the DeltaG(double dagger) values with Taft's steric substituent constants (E(s)) was observed. There was no significant difference in the out-of-plane substituent effects between the electron-withdrawing Cl and the electron-donating Me groups.

Hexakis(tert-butyldimethylsilyl)bicyclo[1.1.0]tetrasilane (3), which is known to isomerize to the corresponding cyclotetrasilene 4 above 0 °C, was synthesized via an alternative synthetic route and isolated at low temperatures as air-sensitive yellow crystals. The short-bond structure of 3 was disclosed by X-ray analysis and DFT calculations, and facile ring flipping of 3 below 0 °C with the activation parameters of ΔH‡ = 6.67 ± 0.18 kcal mol−1 and ΔS‡ = −22.7 ± 0.8 cal mol−1 K−1 was observed.

Ethynylsilyllithiums [R1R2(R3CC)SiLi: R1 = R2 = t-BuMe2Si, R3 = Me3Si (5a); R1 = R2 = t-BuMe2Si, R3 = Ph (5b); R1 = R2 = R3 = Me3Si (5c); R1 = t-BuMe2Si, R2 = Ph, R3 = Me3Si (5d); R1 = t-BuMe2Si, ...

A number of the distinctive reactions of trisilaallene 1 and 2-germadisilaallene 4 with various reagents including water, alcohols, acetone, and haloalkanes were studied. The addition reactions of 1 to water and alcohols occur in a regiospecific manner to afford 1,3-dioxytrisilanes in high yields. The additions are explained by a stepwise mechanism involving the initial nucleophilic attack of a hydroxy oxygen to a terminal allenic silicon to give an intermediate unsymmetric disilene. The regiospecificity is rationalized by the shape of the frontier molecular orbitals and the NPA charge distribution of trisilaallene 1 and the intermediate disilene.

The solvent reorientation dynamics of the intramolecular charge-transfer (ICT) process of the (p-cyanophenyl)pentamethyldisilane-H(2)O (CPDS-H(2)O) cluster was investigated by transient infrared (IR) absorption spectroscopy. Transient IR bands of two distinct charge-transfer (CT) states appeared in both the OH and the CN-stretching vibration regions. Analyses of the IR spectra and the time profiles of the transient bands revealed that the ICT process of the CPDS-H(2)O cluster proceeds in two steps. The first step is a transition from a photo-prepared locally excited (LE) state to the CT state, which is accompanied by a minor reorientation of the H(2)O moiety. In contrast, the second step is an extensive reorientation process of the H(2)O molecule in the CT state. These two reorientation processes exhibit very distinct pico- and nano-second time scales. In the latter case, a relatively slow time constant of 2 ns was related to a large geometric change in the orientation.

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.

We successfully synthesized silicon- and germanium-based allenes as isolable crystalline compounds. These allenes were found to have bent and fluxional structure in sharp contrast to carbon allenes having rigid linear structure. Remarkable red-shifts of the absorption bands of these allenes indicate the significant interactions between two cumulative double bonds.