Ab Initio Study of the Mechanism of Cycloaddition Reaction between H2Ge=Ge: and Acetaldehyde

The mechanism of cycloaddition reaction between singlet state H2Ge=Ge: and acetaldehyde has been investigated with the MP2/6-311++G** method. From the potential energy profile, it could be predicted that the reaction has two competitive dominant reaction pathways. The reaction rule presented is that the two reactants firstly form a four-membered Ge-heterocyclic ring germylene through the [2+2] cycloaddition reaction. As the 4p unoccupied orbital of Ge: atom in the four-membered Ge-heterocyclic ring germylene and the π orbital of acetaldehyde form a π→p donor-acceptor bond, the four-membered Ge-heterocyclic ring germylene further combines with acetaldehyde to give an intermediate. Because the Ge atom in intermediate exhibits sp3 hybridization after transition state, the intermediate isomerizes to a spiro-Ge-heterocyclic ring compound via a transition state. Simultaneously, the ring strain of the four-membered Ge-heterocyclic ring germylene makes it isomerize to a twisted four-membered ring product.     

ChemInform Abstract: Ge2H2: A Molecule with a Low-Lying Monobridged Equilibrium Geometry.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.     

The barrier to internal rotation in Ge2H6

High-quality SCF-MO calculations yield a barrier to internal rotation of 1.70 kJ mole^?1 for Ge₂H₆. A new contraction scheme is reported for Dunning's larger Ge basis set. Geometry optimization, although carried out, is unimportant in this particular calculation. Wavefunctions and properties are reported for GeH₄ and the staggered and eclipsed conformers of Ge₂H₆. The magnitude of the calculated barrier is more physically reasonable than those deduced from experimental data. Comparisons are made across the two series X₂H₆ and CH₃XH₃.     

Density functional theory study of mechanism of forming a spiro-Ge-heterocyclic ring compound from H2Ge=Ge: and ethene

The mechanism of the cycloaddition reaction between singlet H₂Ge=Ge: and ethene has been investigated by the B3LYP/6-311 ++G** method. From the potential energy profile and change of Gibbs free energy, it could be predict that the reaction has only one dominant reaction pathway at 298 K and 149.825 kPa. The reaction rule presented is that the two reactants first form a four-membered Ge-heterocyclic ring germylene through the [2 + 2] cycloaddition reaction; because of the 4p unoccupied orbital of Ge: atom in the four-membered Ge-heterocyclic ring germylene and the π orbital of ethene forming a π → p donor–acceptor bond, the four-membered Ge-heterocyclic ring germylene further combines with ethene to form an intermediate; and because the Ge: atom in intermediate happens sp³ hybridization after transition state, then the intermediate isomerizes to a spiro-Ge-heterocyclic ring compound via a transition state.     

Equilibrium Structures and Isomerization Reactions of the Unsaturated Carbenoid H2Ge=CLiF

The novel carbenoid H2Ge=CLiF was studied by using the DFT B3LYP and QCISD methods. Geometry optimization calculations indicate that H2Ge=CLiF has three equilibrium configurations, in which the three-membered structure is the lowest in energy and thus the most stable. Two transition states for isomerization reactions of H2Ge=CLiF were located and the energy barriers were calculated. For the most stable one, the vibrational frequencies and infrared intensities were predicted.     

Equilibrium Structures and Isomerization Reactions of the Unsaturated Carbenoid H2Ge=CIiF

The novel carbenoid H2Ge=CLiF was studied by using the DFT B3LYP and QCISD methods. Geometry optimization calculations indicate that H2Ge=CLiF has three equilibrium configurations, in which the three-membered structure is the lowest in energy and thus the most stable. Two transition states for isomerization reactions of H2Ge=CLiF were located and the energy barriers were calculated. For the most stable one, the vibrational frequencies and infrared intensities were predicted.     

Synthesis of the spiroacetal fragment of broussonetine H

(2S,6S)-2-(3-Bromopropyl)-1,7-dioxaspiro[5.5]undecane 3 was prepared by the addition of the acetylide derived from (4S)-4-benzyloxy-7-tert-butyldiphenylsilyloxyhep-1-yne 8 to δ-valerolactone 6 followed by treatment with hydrogen and palladium on charcoal which effected hydrogenation of the alkyne, hydrogenolysis of the benzyl ether and subsequent spiroacetal formation. The (4S)-stereochemistry in acetylene 8 was established by addition of trimethylsilylacetylene 10 to (2S)-epoxide 9, which in turn is derived from l-glutamic acid 11.     

Digermanium polycobalt carbonyls formed by addition reactions of GeH bonds: [Co4(CO)13Ge(GeMe2)] and [Co6(CO)20Ge2]

GeMe₂H₂ reacts under mild conditions with [{Co₂(CO)₇}₂Ge] to replace one bridging CO and give [Co₄(CO)₁₃Ge(GeMe₂)]. GeH₄ similarly yields a trace of [Co₆(CO)₂₀Ge₂], which may be made in high yield from [Co₂(CO)₈] and Ge₂H₆ or Me₂Si(GeH₃)₂. Spectroscopic evidence suggests structures of linked GeCo₂ triangles.     

Study of adsorption and decomposition of H2O on Ge(100)

The adsorption and decomposition of water on Ge(100) have been investigated using real-time scanning tunneling microscopy (STM) and density-functional theory (DFT) calculations. The STM results revealed two distinct adsorption features of H2O on Ge(100) corresponding to molecular adsorption and H-OH dissociative adsorption. In the molecular adsorption geometry, H2O molecules are bound to the surface via Ge-O dative bonds between the O atom of H2O and the electrophilic down atom of the Ge dimer. In the dissociative adsorption geometry, the H2O molecule dissociates into H and OH, which bind covalently to a Ge-Ge dimer on Ge(100) in an H-Ge-Ge-OH configuration. The DFT calculations showed that the dissociative adsorption geometry is more stable than the molecular adsorption geometry. This finding is consistent with the STM results, which showed that the dissociative product becomes dominant as the H2O coverage is increased. The simulated STM images agreed very well with the experimental images. In the real-time STM experiments, we also observed a structural transformation of the H2O molecule from the molecular adsorption to the dissociative adsorption geometry.     

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.     

ChemInform Abstract: Complex Intermetallic Compounds: CaNi5Ge3, Ca15Ni68Ge37, and Ca7Ni49Ge22. Three Multifaceted Ni—Ge Framework Structures Combining the Structural Motifs of Ni3Ge and CaNi2Ge2.

The title compounds are prepared by arc‐melting of the elements followed by heating in Ta ampules (950—1150 °C, 1—12 h).     

Germanium(II) pseudohalides: Ge(CN)2, Ge(NCO)2 and Ge(NCS)2; syntheses and reactivities

The hitherto unknown germanium(II) pseudohalides: Ge(CN)₂, Ge(NCO)₂ and Ge(NCS)₂, have been prepared by reactions of germanium(II) halides with corresponding silver or potassium salts; they are stable in tetrahydrofuran or acetone solution in which they are extremely sensitive to moisture, and they undergo cycloaddition, insertion, and Lewis acid-base reactions characteristic of highly reactive germylenes. Infrared spectra indicate that in tetrahydrofuran solution Ge(CN)₂ is the normal cyanide, whereas Ge(NCO)₂ and Ge(NCS)₂ are the isocyanate and isothiocyanate, respectively.     

Ge, C and H NMR spectra of methylethynylgermanes

The ⁷³Ge, ¹³C and ¹H NMR spectra of methylethynylgermanes have been studied. The chemical shifts were compared with those of the corresponding isostructural tin compounds and a good correlation has been found. The origin of the chemical shifts could not simply be attributed to the electron densities as estimated by MNDO calculations.