A Silylene–Germylene Molecule Containing a SiI−GeI Single Bond

The first isolable silylene–germylene complex 5 was assembled by a salt metathesis reaction between the germylene anion 3 and the N-heterocyclic chlorosilylene 4 , and structurally characterized. The central structure of 5 demonstrates a remarkable gauche-bent geometry with the silylene and germylene units, which are interconnected by a Si−Ge bond with a length of 2.4498(9) Å. This value is not only perceptibly longer than the distances known in doubly bonded germasilenes, and also slightly longer than those in germylsilanes. The DFT calculations on 5 confirmed a nearly nonpolar Si^I−Ge^I single-bond nature and its bonding orbital, as well as the aromaticity of the C₃NGe-rings in 3 and 5 . The latter increases the molecular stability of 3 and 5 , and makes the preparation of silylene–germylene complex 5 a reality.     

Ab initio Study of Mechanism of Cycloaddition Reaction between Germylene Silylene (H2GeSi:) and Acetone

The mechanism of the cycloaddition reaction between singlet germylene silylene (H₂GeSi:) and acetone has been investigated with CCSD(T)/6‐31G*//MP2/6‐31G* method. From the potential energy profile, we could predict that the reaction has two competitive dominant reaction channels. The present rule of this reaction is that the [2+2] cycloaddition reaction of the two (‐bonds in germylene silylene and acetone generates a four‐membered ring silylene with Ge. Because of the unsaturated property of Si atom in the four‐membered ring silylene with Ge, it could further react with acetone, resulting in the generation of a bis‐heterocyclic compound with Si and Ge. Simultaneously, the ring strain of the four‐membered ring silylene with Ge makes it isomerize to a twisted four‐membered ring product.     

A new type of N-heterocyclic silylene with ambivalent reactivity

The synthesis of a novel divalent silicon compound by debromination of the corresponding dibromosilyl precursor is reported. The silylene possesses a unique reactivity toward electrophiles of the type R-X (R = H, silyl; X = halogen, triflate) in comparison with the germanium congener. DFT calculations suggest that this is due to a much higher basicity of the silylene versus that of germylene lone-pair electrons. Thus, addition of Me3SiX to the silylene (X = OSO2CF3, triflate) furnishes the corresponding (kinetically favored) 1,4-adduct which subsequently rearranges to the thermodynamically favored 1,1-adduct.     

EH3 (E=N,P, As) and H2 Activation with N‐Heterocyclic Silylene and Germylene Homologues

DFT calculations have been used to probe the mechanism of the addition reaction of group 15 hydrides EH₃ (E=N, P, As) and H₂ to a N‐heterocyclic silylene and its germylene homologue. Nitrogen lone pair donation into the vacant p‐orbital of Si and Ge is the first step of ammonia activation, whereas silylene and germylene behave as nucleophiles toward dihydrogen, phosphane, and arsane. Formation of 1,4‐addition products is kinetically favoured in all cases. In excess ammonia, the assistance of a second molecule drastically lowers the 1,1‐addition energy barriers, enabling formation of 1,1‐addition products. The participation of a second molecule in the P? H bond activation of phosphane also lowers the 1,1‐addition energy barriers, but not enough to cause inversion.     

Synthesis and properties of a germanium(II) metalloheterocycle derived from 1,8-di(isopropylamino)naphthalene. A novel ligand leading to formation of Ni[Ge[((i)PrN)(2)C(10)H(6)]]4).

A novel mononuclear germylene, Ge[1,8-((i)PrN)(2)C(10)H(6)] (1), was isolated as a stable crystalline solid by the reaction of Li(2)[1,8-((i)PrN)(2)C(10)H(6)] with GeCl(2)(1,4-dioxane). Structural examination of 1 shows that this compound possesses a planar six-membered heterocyclic ring system with a Ge(II) center and that the steric impact of the substituents on the nitrogen centers is greater than that for the related five-membered metalloheterocycles. Compound 1 is readily oxidized with elemental S and Se and the structural details for the dinuclear product [[1,8-((i)PrN)(2)C(10)H(6)]Ge(micro-S)](2) are reported. Furthermore, the lone pair of electrons on the Ge(II) center in 1 allows this species to function as a novel ligand for the preparation of the unique tetrakis(germylene) complex Ni[Ge[((i)PrN)(2)C(10)H(6)]](4) (4). The structural features of 4 are reported and show that the germylene ligand, when coordinated to the Ni(0) center, now exhibited a twisted (nonplanar) heterometallocycle and a cone angle of 145 degrees.     

Isomeric pyridylcarbenes and their Si and Ge heavier analogues at DFT: stabilization through π–p or n–p interaction

To realize the effects of the pyridyl group on the stability, multiplicity, and geometry of isomeric pyridylcarbenes and their heavier Si and Ge analogues, a theoretical study was performed at B3LYP/6-311++G(d,p)//B3LYP/6-31G(d). The behavior of nitrogen atom was totally different in each multiplicity (singlet and triplet), structural isomer (ortho-, meta-, and para-), and divalent center (C, Si, and Ge). All pyridylcarbenes have triplet ground states, while the stable silylene and germylene analogues are singlet. The pyridyl group stabilizes both singlet and triplet states divalent centers with more pronounced effects on the singlet states in the order: carbene>germylene>silylene. While all planar species benefit from common π–p conjugative interaction of the pyridyl ring, in the ortho-isomers of 2-pyridylsilylene and 2-pyridylgermylene there is another interaction, n–p, that leads to two stable non-planar conformers. This finding is confirmed by NBO charges, calculated UV–vis spectra, philicity indices (N and ω), and isodesmic reactions.     

Ab initio study of mechanism of forming bis-heterocyclic compound with Si and Ge between silylene germylene (H2Si=Ge:) and formaldehyde

The mechanism of the cycloaddition reaction between singlet state silylene germylene (H₂Si=Ge:) and formaldehyde has been investigated with the CCSD(T)//MP2/cc-pvtz method, from the potential energy profile, it could be predicted that the reaction has one dominant reaction pathway. The reaction rules presented is that [2?+?2] cycloaddition reaction between two reactants firstly generates a Si-heterocyclic four-membered ring germylene. Because of the 4p unoccupied orbital of the Ge atom in (the) Si-heterocyclic four-membered ring germylene and the ?? orbital of formaldehyde forming a ??????p donor?Cacceptor bond, the Si-heterocyclic four-membered ring germylene further combines with formaldehyde to form an intermediate. Because the Ge atom in intermediate happens sp ³ hybridization after transition state, then, intermediate isomerizes to a bis-heterocyclic compound with Si and Ge via a transition state.     

Intermediacy of silylene and germylene in direct synthesis of organosilanes and organogermanes

In the direct synthesis of silicon compounds by reactions of elemental silicon with methyl chloride, methanol and hydrogen chloride, silylene formed on surface of silicon grains during the reaction is an intermediate. The reaction of surface silylene with a variety of unsaturated hydrocarbons provides new direct synthesis of organosilanes. In the direct synthesis of methylchlorogermanes from elemental germanium, surface germylene is not an intermediate, while tetrachlorogermane is synthesized by the direct reaction of germanium with hydrogen chloride via dichlorogermylene intermediate. Various unsaturated hydrocarbons or organic chlorides added to the system of tetrachlorogermane synthesis give new methods for the synthesis of organogermanes.     

Intermediacy of silylene and germylene in direct synthesis of organosilanes and organogermanes

In the direct synthesis of silicon compounds by reactions of elemental silicon with methyl chloride, methanol and hydrogen chloride, silylene formed on surface of silicon grains during the reaction is an intermediate. The reaction of surface silylene with a variety of unsaturated hydrocarbons provides new direct synthesis of organosilanes. In the direct synthesis of methylchlorogermanes from elemental germanium, surface germylene is not an intermediate, while tetrachlorogermane is synthesized by the direct reaction of germanium with hydrogen chloride via dichlorogermylene intermediate. Various unsaturated hydrocarbons or organic chlorides added to the system of tetrachlorogermane synthesis give new methods for the synthesis of organogermanes.     

Can Low‐Valent Germanium Chemistry Be Practiced Under Ambient Conditions? A Tale of a Water‐Stable Yet Reactive Germylene Monochloride Complex

A germylene monochloride complex ((DPM)GeCl, 1 ) that is water stable was isolated for the first time. Interestingly, it reacts with cesium fluoride under ambient conditions (non‐inert atmosphere and water‐containing solvent) to afford water stable germylene monofluoride complex ((DPM)GeF, 2 ). Due to the usage of DPM (dipyrrinate) ligand, germylene monohalides 1 and 2 show fluorescence in the visible region at 555 and 538 nm, respectively. Compounds 1 and 2 are the first fluorescent germylene complexes and were characterized by multinuclear NMR spectroscopy. The structure of compound 1 was also proved by single crystal X‐ray diffraction studies.     

Organic functionalization of diamond (100) by addition reactions of carbene, silylene, and germylene: a theoretical prediction

We present a theoretical prediction of the facile cycloadditions of carbene, silylene, and germylene onto the diamond (100) surface, a new type of surface reaction that can be employed to functionalize diamond surface at low temperature. This finding renders the plausibility that the diamond surface can be chemically modified by the well-known carbene addition chemistry, which might introduce new functionalities to the diamond surface for novel applications in a diversity of fields.     

Insights into the making of a stable silylene

Reduction of Cl2Si[(NR)2C6H4-1,2] (R = CH2Bu(t)) with potassium is known to lead to the stable silylene Si[(NR)2C6H4-1,2] (1). However, silylene is now shown to react further with an alkali metal (Na or K) to yield the (1)(2)2-, c-(1)(3)-*, c-(1)(3)2- or c-(1)(4)2- derivatives. Reduction of Cl2Si[(NR)2C6H4-1,2] (R = CH2CH3 or CH2CHMe2) with potassium does not lead to an isolable silylene, but such a silylene is proposed to be an intermediate and, as for 1, reacts further to afford the potassium salts of c-[Si{(NR)2C6H4-1,2}]4-* and c-[Si{(NR)2C6H4-1,2}](4)2-. The pathways leading to the anionic cyclotri- and cyclotetrasilanes are discussed and supported experimentally; including by X-ray structures of relevant intermediates.     

Electronic Structure of Six-Membered N-Heterocyclic Carbenes and Its Heavier Analogues: Reactivity of the Lone Pair versus the Exocyclic Double Bond

Electronic structure of the six-membered N-heterocyclic carbene, silylene, germylene, and stannylene having an exocyclic double bond at the C3 carbon atom as well as the relative reactivity of the lone-pair on the divalent group 14 element and the exocyclic double bond have been studied at the BP86 level of theory with a TZVPP basis set. The geometrical parameters, NICS values, and NBO population analysis indicate that these molecules can be best described as the localized structure 1X(a), where a trans-butadiene (C1-C2-C3-C4) unit is connected with diaminocarbene (N1-X-N2) via N-atoms having a little contribution from the delocalized structure 1X(b). The proton affinity at X is higher than at C4 for 1C, and a reverse trend is observed for the heavier analogues. Hence, the lone pair on a heavier divalent Group 14 element is less reactive than the exocyclic double bond. This is consistent with the argument that, even though the parent six-membered carbene and its heavier analogues are nonaromatic in nature, the controlled and targeted protonation can lead to either the aromatic system 3X having a lone pair on X or the nonaromatic system 2X with readily polarizable C3-C4 π-bond. The energetics for the reaction with BH(3) and W(CO)(6) further suggest that both the lone pair of Group 14 element and the exocyclic double bond can act as Lewis basic positions, although the reaction at one of the Lewis basic positions in 1X does not considerably influence the reactivity at the other. The protonation and adduct formation with BH(3) and W(CO)(5) at X lead to nonaromatic systems whereas similar reactions at C4 lead to aromatic systems due to π-bond polarization at C3-C4. The degree of polarization of the C3-C4 π-bond is maximum in the protonated adduct and reduces in the complexes formed with BH(3) and W(CO)(5).     

An acyclic imino-substituted silylene: synthesis, isolation, and its facile conversion into a zwitterionic silaimine

A new type of Si(II): A novel silylene stabilized by a Cp* and an imidazolin-2-iminato ligand has been prepared using two different methods. The X-ray crystallographic structure shows that the silicon(II) center is coordinated to an η(2) -Cp* ligand and the nitrogen atom of an imidazolin-2-iminato ligand. This silylene easily reacts with B(C(6) F(5) )(3) to give a stable borane adduct having a zwitterionic resonance structure.     

Synthesis of silylene and silyl(silylene)metal complexes

In 1987, two research groups published the first-ever reports on the synthesis of silylene complexes and presented structural evidence. Since then, a range of synthetic methods have been developed and a number of silylene complexes have been prepared. In 1988, we reported on the first base-stabilized bis(silylene) complexes that can be regarded as being masked silyl(silylene) complexes. These complexes occupy a unique position among silylene and silyl(silylene) complexes in that they provide a convenient tool for studying the reactivity of coordinated silylenes. They are stable enough to be isolated, but the bond between the silylene silicon atom and the internal base can easily be cleaved by thermal perturbation to generate real silyl(silylene) complexes. To date, a number of base-stabilized bis(silylene) complexes have been prepared in which the central metals range from group 5 to group 9. Only two base-free silyl(silylene) complexes have been prepared. One is prepared by reacting a platinum complex with a stable silylene; the other is produced by the photolysis of a tungsten complex in the presence of a hydrodisilane.     

Radical anion of isolable dialkylsilylene

By the reduction of an isolable dialkylsilylene, 2,2,5,5-[tetrakis(trimethylsilyl)]-1-silacyclopentane-1,1-diyl (1), with cesium, rubidium, potassium, sodium, and lithium 4,4'-di(tert-butyl)biphenylide in DME at low temperatures, the corresponding silylene radical anion 2 was generated as the first persistent silylene radical anion in solution and characterized by ESR spectroscopy. Radical anion 2 is rather stable at -70 degrees C in DME but decomposes rapidly at room temperature with a half-life time of ca. 20 min. The g-factor and 29Si hyperfine splitting constants (hfs's) of 2 are almost independent of the countercations, indicating that 2 exists as a free ion or a solvent-separated ion pair in a polar DME solution. A very small hfs due to the 29Si nucleus of the divalent silicon (3.0 mT) as well as a very large g-factor (2.0077) indicates that an unpaired electron is accommodated in the vacant 3ppi orbital of silylene 1.     

Germabenzenylpotassium: A Germanium Analogue of a Phenyl Anion

Reduction of the stable germabenzene, 1‐Tbt‐2‐tert ‐butyl‐germabenzene (Tbt=2,4,6‐tris[bis(trimethylsilyl)methyl]phenyl), with KC₈ resulted in the formation of 2‐tert ‐butylgermabenzenylpotassium, that is, the germanium analogue of phenylpotassium, under concomitant elimination of the aryl group from the Ge atom. Under an inert atmosphere, this germabenzenylpotassium could be isolated in the form of stable yellow crystals. In the crystalline state, as well as in solution, the germabenzenyl moiety adopts a monomeric form, even though the X‐ray diffraction analysis suggests the presence of highly reactive Ge=C double bonds. The spectroscopic and X‐ray crystallographic analyses, in combination with theoretical calculations indicate an ambident character for this germabenzenyl anion, with contributions from aromatic and germylene resonance structures.     

Quantum chemical study of interactions of carbenes and their analogs of the EH2 and EHX types (E = Si, Ge, Sn; X = F, Cl, Br) with HX and H2, respectively: the insertion and substituent exchange reactions

Interactions of carbenes and carbene analogs EH₂ and EHX with HX and H₂ (E = C, Si, Ge, Sn; X = F, Cl, Br), respectively, were studied by quantum chemical methods. Theoretical analysis of the carbene and silylene systems was carried out at the G3 level of theory using the MP2(full)/6?C31G(d) calculated geometries and vibrational frequencies. The stannylene systems were examined at the MP2 level using a modified LANL2DZ basis set for the Sn atoms and the 6?C31+G(d,p) basis sets for other atoms. Transformations in the germylene systems were studied within the framework of both approaches, which gave similar results. This allowed one to compare the reaction pathways and their energy profiles for the whole series of systems. In addition to the insertions into the H-X and H-H bonds, the exchange reactions resulting in interconversions of EH₂ and EHX can proceed in the systems under consideration. The effects of the nature of the E and X atoms on the reaction barriers and exothermicity of both the insertion and exchange reactions are analyzed. Possible role of radical processes in these systems is assessed.     

A stable Schrock-type hafnium-silylene complex

The first stable hafnium-silylene complex, (eta-C5H4Et)2(PMe3)Hf=Si(SiMetBu2)2 (6) was obtained in the form of the phosphine adduct as red crystals by the coupling reaction of 1,1-dilithiosilane (1) with 0.9 equiv of (eta-C5H4Et)2HfCl2 in dry toluene at -50 degrees C, followed by treatment with an excess of PMe3 at -50 degrees C. In the 29Si NMR spectrum of 6, the signal from the silylene ligand is shifted greatly downfield at 295.4 ppm, with a JSiP coupling constant of 15.0 Hz. X-ray crystallographic analysis of 6 revealed that the Si-Hf bond length (2.6515(9) A) is about 5% shorter than typical Si-Hf single bonds, obviously indicating the double-bond character between the silicon and hafnium atoms. The compound 6 was found to be a Schrock-type silylene complex, a conclusion that was supported by the natural population analysis (NPA) charge distribution for the model complex, (eta-C5H4Et)2(PMe3)Hf=Si(SiMe3)2 (8), showing a negative charge on the silicon atom (-0.34).     

Striking reactivity of ylide-like germylene toward terminal alkynes: [4+2] cycloaddition versus C-H bond activation

The isolable ylide-like N-heterocyclic germylene LGe: (2) {L = CH[(C=CH(2))CMe][N(aryl)](2), aryl = 2,6-(i)Pr(2)C(6)H(3)} shows an unprecedented dual reactivity toward terminal alkynes: its reaction with acetylene leads via [4+2] cycloaddition to the novel intramolecular donor stabilised germylene 3, while conversion of phenylacetylene furnishes the analogous cycloadduct 4 along with a C-H bond activation product, the novel N-donor stabilised alkynyl germylene 5.