Argon matrix effect on the geometry and infrared spectrum of H2CMH2 (M = Ti, Zr, Hf): A theoretical study

Within the framework of polarizable continuum model with integral equation formalism (IEF-PCM), an argon matrix effect on the geometry and infrared frequencies of the agostic H₂CMH₂ (M = Ti, Zr, Hf) methylidene complexes was investigated at B3LYP level of theory with the 6-311++G(3df,3pd) basis set for C, H, and Ti atoms and Stuttgart/Dresden ECPs MWB28 and MWB60 for the Zr and Hf atoms. At the B3LYP/IEF-PCM level of theory, H₂CTiH₂ was optimized to an energy minimum having a pyramidal structure. The calculated dipole moment of this structure is 3.06 D. The B3LYP/IEF-PCM simulations gave the three complexes’ agostic angle ∠HCM (°), distance r(H?M) (Å), and CM bond length r(CM) (Å) as follows: ∠HCTi = 87.4, r(H?Ti) = 2.079, r(CTi) = 1.803; ∠HCZr = 89.3, r(H?Zr) = 2.243, r(CZr) = 1.956; ∠HCHf = 94.7, r(H?Hf) = 2.343, r(CHf) = 1.972. As a comparison, the B3LYP simulations gave the values as follows: ∠HCTi = 91.5, r(H?Ti) = 2.150, r(CTi) = 1.811; ∠HCZr = 92.9, r(H?Zr) = 2.299, r(CZr) = 1.955; ∠HCHf = 95.6, r(H?Hf) = 2.352, r(CHf) = 1.967. As far as the MH₂ symmetric and asymmetric stretching and CH₂ wagging frequencies are concerned, the IEF-PCM calculated values are in better agreement with the experimental argon matrix ones than those calculated based on a gas phase model.     

DFT study on the unsaturated germylenoid H2CGeNaF

The unsaturated germylenoid H₂CGeNaF was studied by using the DFT B3LYP method in conjunction with the 6-311+G(d, p) basis set. Geometry optimization calculations indicate that H₂CGeNaF has three equilibrium configurations, in which the p-complex is the lowest in energy and is the most stable structure. Two transition states for isomerization reactions of H₂CGeNaF are located and the energy barriers are calculated. For the most stable one, vibrational frequencies and infrared intensities have been predicted.     

Stability of functionalized C60 paramagnetic dimers and monomers

Density functional theory is used to calculate the bond dissociation energy to cleave the C₆₀C₆₀ bond of the paramagnetic X-C₆₀C₆₀-X and X-C₆₀C₆₀ dimers where X is F, OH, O and H. The results show that these dimers would not be stable much above room temperature and therefore cannot constitute the paramagnetic phase needed to form the observed ferromagnetism which has been shown to be stable up to 800 K. The calculated bond dissociation energies to remove an F, OH or H from a single C₆₀ are large suggesting that they could be the source of the unpaired spin needed for the high temperature ferromagnetism.     

Effects of dipole interaction and solvation on the CO stretching band of N,N-dimethylacetamide in nonpolar solutions: Infrared, isotropic and anisotropic Raman measurements

The concentration dependence of the CO stretching (ν_CO) band of N,N-dimethylacetamide (NdMA) in cyclohexane, n-hexane, and CCl₄ has been investigated by infrared (IR) and polarized Raman spectroscopy. For the neat liquid of NdMA, the noncoincidence of the aniso- and isotropic Raman wavenumbers is evident. In the 0.47 M cyclohexane solution of NdMA, the noncoincidence effect almost disappears and the ν_CO envelopes in both the Raman and IR spectra are asymmetric to the low-wavenumber side. When the concentration of NdMA decreases from 0.33 to 0.023 M, the peak of these bands slightly shifts to a higher wavenumber and the band shape becomes symmetric. The shape of the ν_CO envelope does not show any significant change below 0.023 M. These results suggest that the asymmetric shape of the ν_CO band observed for the 0.33 M cyclohexane solution is associated with the intermolecular interaction among NdMA molecules, which vanishes at around 0.02 M. Spectral changes for the CCl₄ solution of NdMA show a similar tendency. However, the shape and peak wavenumber of the ν_CO band observed in a highly diluted CCl₄ solution (≤0.023 M) indicate that the solvation effect of CCl₄ is more complicated than those of cyclohexane and n-hexane. The analyses of the ν_CO band, which is sensitive to the intermolecular interaction between solutes and between solute and solvent for NdMA dissolved in nonpolar solvents, would serve to clarify the electronic property of the molecule in a solution.     

The first evidence for a transient stibaallene ArSbCCR2

Dechlorofluorination of ArSb(F)-C(Cl)CR₂ (CR₂ = fluorenylidene, Ar = 2,4,6-tri-tert-butylphenyl) by tert-butyllithium afforded a 3,4-bis(fluorenylidene)-1,2-distibacyclobutane. The formation of the latter probably involves the transient stibaallene ArSbCCR₂ followed by a head-to-head dimerization via two SbC double bonds. Molecular orbital calculations at the ab initio and DFT levels support the head-to-head dimerization of ArSbCCR₂ with the formation of a 1,2-distibacyclobutane.     

Molecular complexes of octafluoronaphthalene with catenated chalcogen-nitrogen compounds C6H5-X-NSN-SiMe3 (X = S, Se)

Mismatched molecular 1:1 complexes of C₁₀F₈ with catenated chalcogen-nitrogen compounds C₆H₅-X-NSN-SiMe₃ (X = S, Se) were prepared and characterized by X-ray crystallography. The complexes provide examples of structurally non-rigid polyheteroatom molecules involved in non-covalent arene-polyfluoroarene π-stacking interactions. In going from homocrystals to the co-crystals, the molecular Z, E configuration of the catenated compounds changes from noticeably non-planar to perfectly planar, i.e. C₁₀F₈ acts as “molecular iron”. On the other hand, C₁₀H₈ does not produce complexes with C₆F₅-X-NSN-SiMe₃ (X = S, Se).     

Thermal gas-phase reaction of perfluorobuta-1,3-diene with NO2

The reaction of NO₂ with perfluorobuta-1,3-diene, CF₂CFCFCF₂ (C₄F₆), has been studied at 312.9, 323.0, 333.4, 396.0 and 418.0 K, using a conventional static system. The products formed in the temperature range 312.9-333.4 K were CF₂CFCF(NO₂)CF₂(NO₂) (I), CF₂(NO₂)CFCFCF₂(NO₂) (II), CF₂CFCF(NO₂)C(O)F (III) and CF₂(NO₂)CFCFC(O)F (IV) and FNO. The formation of these compounds was detected performing infrared and Raman spectra. The infrared spectrum shows a band at 1785 cm⁻¹, characteristic to the terminal -CFCF₂ group and the Raman spectrum shows a band located at 1733 cm⁻¹, corresponding to -CFCF- group. It indicates, that in this temperature range, NO₂ attacks initially only one double bound of CF₂CFCFCF₂. Since the intermediate radical CF₂CFCFCF₂(NO₂) formed in this process is allylic in nature, so there is no isomerization involved in this process, but rather the allylic radical is able to add the second NO₂ either to CF₂ or CFCF₂(NO₂) end, forming the corresponding products. At 396.0 and 418.0 K different products were observed: CF₂(NO₂)CF(NO₂)C(O)F (V), NO, CF₃C(O)F, C(O)F₂ and traces of epoxide of tetrafluoroethene, showing that, at these temperatures, both double bonds are attacked by NO₂ and detachment of CF₂ group is produced. The mechanisms consistent with experimental results in the temperature range 312.9-333.4 and at 396.0 and 418 K are proposed.     

Quantification of the push-pull character of the isophorone chromophore as a measure of molecular hyperpolarizability for NLO applications

The push-pull character of a series of para-phenyl substituted isophorone chromophores has been quantified by the ¹³C chemical shift difference of the three conjugated partial CC double bonds and the quotient of the occupations of both the bonding and anti-bonding orbitals of these CC double bonds as well. The correlations of the two push-pull quantifying parameters, and to the corresponding bond lengths, strongly recommend /π_CC as the general parameter to estimate charge alternation and as a very useful indication of the molecular hyperpolarizabilities for NLO application of the compounds studied.     

Polyfluoroaromatic compounds with a NCClR group—a reactive type of polyfluoroarene

This review deals with syntheses and reactivity of polyfluoroarenes with a NCClR group (including those with RCl). The most promising and convenient methods of synthesis of these type compounds are based on co-pyrolysis reactions of low-basic polyfluoroaromatic amines with RCCl₃ type derivatives and the interaction of such amines and polyfluoroaromatic hydrazines with RCX₃ (XCl,F) compounds in the presence of AlCl₃ at moderate temperature; they have no analogues in the nonfluorinated series. Reactions with different nucleophilic reagents, the formation of electrophilic intermediates of the nitrilium cation type and reactions of the latter with aromatic and fluoroaromatic hydrocarbons, amines, and compounds with CN, C≡N and CO multiple bonds are described. It is shown that polyfluoroaromatic compounds with a NCClR group are promising precursors for syntheses of a wide range of compounds of various classes, including heterocyclic derivatives.     

Preparation of fluorine compounds of groups 13 and 14: a study case for the diagonal relationship of aluminum and germanium

The synthesis of carbaalanes of composition [(AlF)₆(AlNMe₃)₂(CR)₆] containing terminal fluorine atoms is described. The clusters have in common that the central core consists of eight aluminum and six carbon atoms. Six of the eight aluminum atoms are bearing six terminal fluorine atoms. The fluorination of (t-BuNCH₂AlH)₄ results in the formation of the aggregate (t-BuNCH₂AlF)₄. In group 14, the fluorine containing unsaturated compounds LGeF, LGeS(F), LGeSe(F), and LGeNSiMe₃(F) were prepared (LHC(CMeNAr)₂), Ar = 2,6-iPr₂C₆H₃ and Ar = 2,6-Me₂(C₆H₃)).     

Functionalized fluoroalkyl and alkenyl silanes: Preparations, reactions, and synthetic applications

Preparations, reactions, and synthetic applications of functionalized fluoroalkyl and alkenyl silanes have been summarized. This review focuses mainly on the chemistries of (1) 1-substituted difluoromethylsilanes (XCF₂SiR₃), (2) 1-substituted 2,2-difluorovinylsilanes (CF₂CXSiR₃), (3) trifluoroisopropenyl, trifluoroacetimidoyl, and trifluoroacetyl silanes [CF₃C(SiR₃)X, XCH₂, NAr, O] and (4) other fluorinated alicyclic silanes.     

Solvent and phosphine dependency in the reaction of cis-RuCl2(P-P)2 (P-P = dppm or dppe) with terminal alkynes

Reaction of cis-[RuCl₂(dppm)₂] (dppm = 1,2-bis(diphenylphosphino)methane) with PhCCH and NaPF₆ utilising methanol as solvent results in the formation of the η³-butenynyl complex [Ru(η³-PhCCCCHPh)(dppm)₂][PF₆] in good yield. Similar reactions with Bu^tCCH and PrⁿCCH resulted in the corresponding alkyl-substituted complexes and all three of these compounds have been characterised by NMR spectroscopy and X-ray crystallography. The mechanism of this reaction has been probed by employing labelling experiments with both PhCCD and PhC¹³CH allowing the identity of possible intermediates in the reaction to be determined. Furthermore, [Ru(η³-PhCCCCHPh)(dppm)₂][PF₆] has been shown to be an effective regio- and stereo-selective catalyst for the dimerisation of PhCCH to Z-PhCCCHCHPh in the absence of solvent. In contrast, no evidence for the formation of alkyne coupling was obtained from the reaction of cis-[RuCl₂(dppe)₂] (dppe = 1,2-bis(diphenylphosphino)ethane) with PhCCH and NaPF₆.     

Theoretical studies on the imine germylenoid HNGeNaF and its insertion reaction with R-H (R = F, OH, NH2, CH3)

The geometries and isomerization of the imine germylenoid HNGeNaF as well as its insertion reactions with R-H (R = F, OH, NH₂, CH₃) have been systematically investigated at the B3LYP/6-311+G^∗ level of theory. The potential barriers of the four insertion reactions are 117.2, 172.6, 219.7, and 322.3 kJ/mol, respectively. Here, all the mechanisms of the four reactions are identical to each other, i.e., an intermediate has been formed first during the insertion reaction. Then, the intermediate could dissociate into the substituted germylene (HNGeHR) and NaF with a barrier corresponding to their respective dissociation energies. Correspondingly, the reaction energies for the four reactions are 185.0, 208.1, 224.4, and 266.9 kJ/mol, respectively, which are linearly correlated with the calculated barrier heights. Compared with the insertion reaction of HNGe: and R-H, the introduction of NaF makes the insertion reaction occur easily though it is more difficult to proceed than that of insertion reaction between H₂GeNaF and R-H. Furthermore, the effects of halogen (F, Cl, Br) substitution and inorganic salts employed on the reaction activity have also been discussed. As a result, the relative reactivity among the four insertion reactions should be as follows: H-F > H-OH > H-NH₂ > H-CH₃.     

A ruthenium(II) allenylidene complex with a 4,5-diazafluorene functional group: A new building-block for organometallic molecular assemblies

The synthesis of the new ruthenium(II) allenylidene complex [ClRu(dppe)₂CCC₁₁H₆N₂][OTf] (4) (dppe = 1,2-bis(diphenylphosphino)ethane) terminated with a 4,5-diazafluorene ligand is reported. Further coordination of that metal allenylidene to ruthenium and rhenium moieties leads to the bimetallic adducts [ClRu(dppe)₂CCC₁₁H₆N₂{Ru(bpy)₂}][B(C₆F₅)₄]₃ (5a), [ClRu(dppe)₂CCC₁₁H₆N₂{Ru(^tBu-bpy)₂}][PF₆]₃ (5b) and [ClRu(dppe)₂CCC₁₁H₆N₂{Re(CO)₃Cl}][OTf] (6). Their optical and electrochemical properties show that the allenylidene moiety is an attractive molecular clip for the access to larger original redox-active homo/heteronuclear multi-component supramolecular assemblies. The X-ray crystal structure of the allenylidene metal building block is also described.     

Highly chemo- and stereoselective glycosidation of permethacrylated O-glycosyl trichloroacetimidate reagents promoted by TMSNTf2

TMSNTf₂ has been used efficiently as a promoter in glycosidation reaction involving permethacrylated Schmidt reagents. While TMSNTf₂ is known to be a powerful activator for CO double bonds, we have discovered that this reagent can activate CN double bond selectively, even in the presence of excess CO groups of permethacrylated O-glycosyl trichloroacetimidate substrates. Glycosides are synthesized in moderate to reasonable yields with an excellent overall β-stereoselectivity.     

Further chemistry of ruthenium butatrienylidene complexes

Several complexes have been obtained from reactions carried out in early attempts to prepare the diynyl complexes Ru(CCCCR)(dppe)Cp* (R = H, SiMe₃). These have been identified crystallographically as the acyl complex Ru{CCC(O)Me}(dppe)Cp* (3), the cationic imido complex [Ru{CCC(NH₂)Me}(dppe)Cp*]PF₆ (4), the binuclear butenynylallenylidene [{Ru(dppe)Cp*}₂{μ-CCC(OMe)CHCMeCC}]PF₆ (5), and the bis(ethynyl)cyclobutenylidene [{Ru(dppe)Cp*}₂{μ-CCC₄H₂(SiMe₃)CC}]PF₆ (6). NMR studies of 5 have revealed the existence of two isomers. Plausible routes for their formation from the putative butatrienylidene intermediate [Ru(CCCCH₂)(dppe)Cp*]⁺ (A) are discussed.     

Ferrole-type compounds containing thiophenic or thiepinic rings in the 3,4-positions of the metallacycle

The new ferrole Fe₂(CO)₆[μ-η²,η⁴-(Fc)CC{C(H)C(R)S}CC(SiMe₃)] [R = SiMe₃ (1) and R = Fc (2)] and ruthenoles Ru₂(CO)₆[μ-η²,η⁴-(Me₃Si)CC{SC(Fc)C(H)}CC(Fc)] 3 and Ru₂(CO)₆[μ-η²,η⁴-(Me₃Si)CC(SCCFc)C(H)C(Fc)] 4, have been obtained from the reactions of M₃(CO)₁₂ (M = Fe, Ru) and FcCCSCCSiMe₃ through S-C bond activations and C-C coupling reactions. Thermolysis of Ru₂(CO)₆[μ₃-η²,η⁴,η³-(Me₃Si)CC{SC(Fc)C(SCCSiMe₃}Ru(CO)₃}CC(Fc)] alone and in the presence of HCCFc, yielded the compounds Ru₂(CO)₆[μ-η²,η⁴-(Me₃Si)CC{SC(Fc)C(SCCSiMe₃)}CC(Fc)] 5 and Ru₂(CO)₆[μ-η²,η⁴-(Me₃Si)CC{SC(Fc)C(SCCSiMe₃)C(H)C(Fc)}CC(Fc)] 6, respectively. The crystal structures of the compounds 1, 3, 4 and 6 are reported.