Infrared spectra of monomeric thioformaldehyde in Ar,N2 and Xe matrices

Pyrolysis products of 1,3-dithietane were trapped in low-temperature matrices and their infrared spectra were recorded. The vibrational bands of monomeric H₂CS, which was not perturbed by other decomposition products, were identified in Ar, N₂ and Xe matrices. These results will be useful to evaluate the frequency shifts of H₂CS induced by the interaction with other molecules.     

CuLn complexes with a single μ-oximato bridge

Two original dinuclear (LnYb, 3 and LnEr, 4) and one trinuclear Cu^IILn^IIICu^II (LnGd, 5) complexes derived from a polydentate non symmetrical Schiff base ligand H₂L have been prepared. The ligand possesses two functions (phenol and oxime) able to coordinate the Ln ions, but structural studies (X-ray diffraction and powder X-ray diffraction) show that the Cu^II and Ln^III ions are only bridged by the oximato (NO) pair. The missing phenoxo bridge is replaced by a surprising pseudo-bridge involving one oxygen atom of the nitrato anion linked to the Cu and Ln ions according to a η²: η¹: μ mode. Although this latter contact has no role from the magnetic point of view, it introduces a large deformation of the unique bridging network. The CuYb complex 3 and the trinuclear CuGdCu complex 5 present antiferromagnetic interactions, with a J_CuGd interaction equal to ?1.25 cm^?1 in 5. The genuine single bridge can be considered as responsible for the antiferromagnetic character of the interaction.     

Synthesis of spiro[bicyclo[2.2.1]heptane-2,2′-furan]-3-amines via stereoselective cycloadditions of trimethylenemethane to (1S,3EZ,4R)-3-arylimino-1,7,7-trimethylbicyclo[2.2.1]heptan-2-ones

Stereoselective [3+2] cycloadditions of trimethylenemethane (TMM) to the exocyclic CO and CN double bonds of (1S,3EZ,4R)-3-arylimino-1,7,7-trimethylbicyclo[2.2.1]heptan-2-ones gave the corresponding spiro[bicyclo[2.2.1]heptane-2,2′-furan] and spiro[bicyclo[2.2.1]heptane-3,2′-pyrrolidine] derivatives. Further stereoselective reductions of the CN or CO bond in these cycloadducts furnished new chiral amines, diamines, and a new aminoalcohol. All cycloadditions and reductions of the CN double bonds took place from the less hindered endo-face of the (1S,3EZ,4R)-3-arylimino-1,7,7-trimethylbicyclo[2.2.1]heptan-2-ones, exclusively, thus giving the corresponding products in 100% de. The structures were determined by NMR, NOESY spectroscopy, and by X-ray diffraction.     

Phosphorus-substituted carbene complexes: Chelates,pincers and spirocycles

The syntheses, structural characterizations and reactivity patterns of main group and late transition metal carbene complexes of the bis(phosphoranimino)methandiide, [C(Ph₂PNSiMe₃)₂]²⁻, and the carbodiphosphorane, Ph₃PCPPh₃, are described and compared to previously reviewed early transition metal analogues. Bimetallic spirocyclic aluminum complexes of the former ligand are accessed by spontaneous double deprotonation of the central carbon atom of the parent, CH₂(Ph₂PNSiMe₃)₂, by two equivalents of AlMe₃, whereas the synthesis of platinum complexes requires the intermediacy of the tetralithium dimer, [Li₂C(Ph₂PNSiMe₃)₂]₂, and elimination of LiCl from a metal chloride precursor. In contrast to the early transition metal analogues, which are N,C,N-pincer, Schrock-type alkylidenes, the C,N-chelated platinum complexes are more akin to Fischer carbenes, and their chemistry is dominated by the nucleophilicity of free nitrogen atom and insertions into labile N–Si bonds. Chelated and pincer carbene complexes of rhodium result from single and double orthometallations, respectively, of the phenyl rings in Ph₃PCPPh₃; the latter compounds represent a wholly new class of C,C,C-pincer complexes. Electronic structure calculations show that the metal–carbon interaction in these compounds may be described as a dative, two-electron, C → M σ-bond. The free bis(phosphoranimino)methandiide and carbodiphosphorane ligands, while not having formal six valence electron resonance forms, may be thought of as having “pull–pull” Fischer carbene character, but the metal to which they become coordinated ultimately dictates their chemistry.     

Comparative DFT study of Raman spectra of phosphorus-containing dendrimers built from thiophosphoryl,cyclotriphosphazene and phthalocyanine cores

The FT Raman spectra of the zero and first generations of phosphorus-containing dendrimers built from thiophosphoryl, cyclotriphosphazene and phthalocyanine core with terminal oxybenzaldehyde groups have been recorded and analyzed. The structural optimization and normal mode analysis were performed for dendrimers on the basis of the density functional theory (DFT). The calculated geometrical parameters, harmonic vibrational frequencies and Raman scattering activities are predicted in a good agreement with the experimental data. The experimental Raman spectra of dendrimers were interpreted by means of potential energy distribution. Relying on DFT calculations the lines of the cores, repeating units and terminal groups of dendrimers were assigned.The influence of the encirclement on the line frequencies and intensities was studied and due to the predictable, controlled and reproducible structure of dendrimers the information, usually inaccessible is obtained. The strong line at 1600 cm⁻¹ show marked changes of intensity in dependence of aldehyde (CHO) or azomethyne (CHN) substituents in the aromatic ring. The polarizabilities and lipophilicity of dendrimers were estimated.     

Structural studies of methyl brevifolincarboxylate in solid state by means of NMR spectroscopy and DFT calculations

Methyl brevifolincarboxylate isolated from the herb of Potentilla argentea L. (Rosaceae) is a representative of the naturally occurring polyphenols. The compound is of pharmaceutical interest mainly because of its antiviral and antioxidant properties. ¹³C NMR spectra were recorded for solution and solid phase. ¹³C CPMAS spectra were assigned by comparison with solution data, dipolar dephasing and short contact time experiments. The correctness of assignments was verified by GIAO DFT calculations of shielding constants. The differences between the solution and solid state chemical shift values were explained in terms of orientation of OH groups and intramolecular hydrogen bonds. The splitting of the C1O resonance shows that there exists a polymorphism in the solid phase, which might be due to the formation of intramolecular hydrogen bond involving carbonyl or methoxy oxygen (i.e. C10OH⋯OC or C10OH⋯OCH₃).     

Fourier transformed infrared spectral investigations of molecular interactions in propionic acid–2-propanol binary system

FTIR spectra of propionic acid (PA), 2-propanol (PROH) and its binary mixtures with varying molefraction of the PA were recorded in the region 500–3500 cm^?1, to investigate the formation of hydrogen bonded complexes in a mixed system. The observed features in ν(CO), ν(CO) and δ(COH) of PA, ν(CO) of PROH and δ(COH) of PA + PROH have been explained in terms of the hydrogen bonding interactions between PROH and PA and dipole–dipole interaction. The dipole moment derivative for the above mentioned vibrational modes have also been predicted from the integrated absorbance. The intrinsic linewidth for the vibrational modes ν(CO) and δ(COH) of PA has been elucidated using Bondarev and Mardaeva model.     

A convenient route to six-membered heterocyclic carbene complexes: Reactions of aminoallenylidene complexes with 1,3-bidentate nucleophiles

Pentacarbonyl dimethylamino(methoxy)allenylidene complexes of chromium and tungsten, [(CO)₅MCCC(NMe₂)OMe] (M = Cr (1a), W (1b)), react with 1,3-bidentate nucleophiles such as amidines and guanidine, H₂N–C(NH)R (R = Ph, C₆H₄NH₂-4, C₆H₄NO₂-3, NH₂), by displacing the methoxy substituent to give exclusively dimethylamino(imino)-allenylidene complexes, [(CO)₅MCCC{NC(NH₂)R}NMe₂] (2a–5a, 2b). Treatment of the chromium complexes 2a–5a with catalytic amounts of hydrochloric acid or HBF₄ gives rise to an intramolecular cyclization. Addition of the terminal NH₂ substituent to the C_α–C_β bond of the allenylidene chain affords pyrimidinylidene complexes 6–9 in high yield. In contrast to the chromium complexes 2a–5a, the corresponding tungsten complex 2b could not be induced to cyclize due to the lower electrophilicity of the α-carbon atom in 2b. The dimethylamino(phenyl)allenylidene complex [(CO)₅CrCCC(NMe₂)Ph] (10) reacts with benzamidine or guanidine similarly to 1a. However, the second reaction step – cyclization to give pyrimidinylidene complexes – proceeds much faster. Therefore, the formation of an imino(phenyl)allenylidene complex as an intermediate is established only by IR spectroscopy. The analogous reaction of 10 with 3-amino-5-methylpyrazole affords, via a formal [3+3]-cycloaddition, a pyrazolo[1,5a]pyrimidinylidene complex 13. Compound 13 is obtained as two isomers differing in the relative position of the N-bound proton (1H or 4H). The related reaction of 10 with thioacetamide yields a thiazinylidene complex and additionally an alkenyl(amino)carbene complex.     

Olefin metathesis for metal incorporation: Preparation of conjugated ruthenium-containing complexes and polymers

Olefin Metathesis for Metal Incorporation (OMMI) was used for the stoichiometric attachment of ruthenium to both small and large polyenes. The dinuclear complexes (PCy₃)₂C1₂RuCH(CHCH)_nCHRu(PCy₃)₂Cl₂ (n = 1, 2), were prepared by reacting 2 equiv. of the Grubbs first-generation catalyst (PCy₃)₂C1₂Ru(CHPh)) with 1 equiv. of the appropriate polyene (1,3,5-hexatriene for n = 1 and 1,3,5,7-octatetraene for n = 2). Use of excess hexatriene led to the formation of the monoruthenium complex (PCy₃)₂C1₂RuCHCH CHCHCH₂. The mono- and di-ruthenium complexes exhibited marked differences in their spectroscopic and electrochemical properties, in addition to their Z–E isomerization rates. Nucleophilic attack of PCy₃ on the end CH₂ of the mono complex was observed, leading to both isomerization and phosphonium products. Extending the OMMI strategy to the second-generation catalyst was also done, despite the reduced initiation rate. The more reactive catalyst (H₂IMes)RuCl₂(CHPh)(3-bromopyridine)₂ allowed for ruthenium incorporation into polyacetylene, leading to the formation of polymers and oligomers with high ruthenium content.     

Vibrational spectroscopy of lapachol, α- and β-lapachone: Theoretical and experimental elucidation of the Raman and infrared spectra

Raman and infrared spectroscopy were applied for the vibrational characterization of lapachol and its pyran derivatives, α-lapachone and β-lapachone. Experimental spectra of solid state samples were acquired between 4000 and 100 cm⁻¹ in Raman experiments, and between 4000 and 600 cm⁻¹ (mid-infrared) and 600–100 cm⁻¹ (far-infrared) with FTIR spectroscopy, respectively. Full structure optimization and theoretical vibrational wavenumbers were calculated at the B3LYP/6-31 + + G(d,p) level. Detailed assignments of vibrational modes in an experimental and theoretical spectra were based on potential energy distribution analyses, using Veda 4.1 software. Clear differentiation between the three compounds was verified in the region between 1725 and 1525 cm⁻¹, in which the ν(CO) and ν(CC) modes of the quinone moiety were assigned.     

One-pot synthesis of 2,4,5-trisubstituted oxazoles from N-acyl amino acids by a combination of cyclodehydration with N,N′-diisopropylcarbodiimide and Wittig olefination

By a combination of cyclodehydration of N-acyl amino acids with N,N′-diisopropylcarbodiimide (DIC) and non-classical Wittig olefination of the resultant 5(4H)-oxazolones with Ph₃PCHCN and Ph₃PCHCOOEt, 5-oxazoleacetonitriles and 5-oxazoleacetates were synthesized in one-pot in 41–85% and 57–70% yields, respectively.     

Reaction of the RuTp(PR3)Cl fragment with alkynols: Formation of carbene,vinylidene, allenylidene,and carbyne complexes

The reaction of RuTp(COD)Cl (1) with PR₃ (PR₃ = PPh₂ⁱPr, PⁱPr₃, PPh₃) and propargylic alcohols HCCCPh₂OH, HCCCFc₂OH (Fc = ferrocenyl), and HCCC(Ph)MeOH has been studied.In the case of PR₃ = PPh₂ⁱPr, PⁱPr₃ and HCCCPh₂OH, the 3-hydroxyvinylidene complexes RuTp(PPh₂ⁱPr)(CCHC(Ph)₂OH)Cl (2a) and RuTp(PⁱPr₃)(CCHC(Ph₂)OH)Cl (2b) were isolated.With PR₃ = PPh₂ⁱPr and HCCCFc₂OH as well as with PR₃ = PPh₃ and HCCCPh₂OH dehydration takes place affording the allenylidene complexes RuTp(PPh₂ⁱPr)(CCCFc₂)Cl (3b) and RuTp(PPh₃)(CCCPh₂)Cl (3c).Similarly, with PPh₂ⁱPr and HCCC(Ph)MeOH rapid elimination of water results in the formation of the vinylvinylidene complex RuTp(PPh₂ⁱPr)(CCHC(Ph)CH₂)Cl (4).In contrast to the reactions of the RuTp(PR₃)Cl fragment with propargylic alcohols, with HCC(CH₂)_nOH (n = 2, 3, 4, 5) six-, and seven-membered cyclic oxycarbene complexes RuTp(PR₃)(C₄H₆O)Cl (5), RuTp(PR₃)(C₅H₈O)Cl (6), and RuTp(PR₃)(C₆H₁₀O)Cl (7) are obtained. On the other hand, with 1-ethynylcyclohexanol the vinylvinylidene complex RuTp(PPh₂ⁱPr)(CCHC₆H₉)Cl (8) is formed. The reaction of the allenylidene complexes 3a–c with acid has been investigated. Addition of CF₃COOH to a solution of 3a–c resulted in the reversible formation of the novel RuTp vinylcarbyne complexes [RuTp(PPh₂ⁱPr)(C–CHCPh₂)Cl]⁺ (9a), [RuTp(PPh₂ⁱPr)(C–CHCFc₂)Cl]⁺ (9b), and [RuTp(PPh₃)(C–CHCPh₂)Cl]⁺ (9c). The structures of 3a, 3b, and 5b have been determined by X-ray crystallography.     

The Raman spectra of serine and 3,3-dideutero-serine in aqueous solution

The Raman spectra of serine [α-amino-β-hydroxypropionic acid; HOCH₂CH(NH₃)⁺COO⁻] and 3,3-dideutero-serine [HOCD₂CH(NH₃)⁺COO⁻] in aqueous solution were studied in the range 4000–300 cm⁻¹. The data obtained for the deuterated compound are novel and provide compelling evidence that previously reported assignments for the undeuterated amino acid should be revised.     

Mechanism of thermal energy charge transfer reactions: rare gas ions reacting with NH3 and PH3

Absolute rate constants and approximate product distributions are presented for the reactions of He⁺, Ne⁺, Ar⁺, Kr⁺, Xe⁺, CO⁺ and CO⁺₂ with NH₃ and PH₃. In all cases, electron transfer is the dominant reaction channel. Hydrogen atom transfer is observed in several systems, but only as a minor product, even when this channel is very exothermic. The magnitude of the absolute rate constants can be correlated with the Franck-Condon factors associated with the reactions in most cases. Several exceptions to this general rule are observed that could not be readily predicted a priori. It is speculated that these reactions proceed via a collision complex.     

Spectroscopic and theoretical studies of N-trichlorophosphazotrifluoroacetyl,CF3C(O)NPCl3 and N-trichlorophosphazotrichloroacetyl,CCl3C(O)NPCl3

FTIR, Raman and NMR spectra of N-trichlorophosphazotrifluoroacetyl, CF₃C(O)NPCl₃ (1) and N-trichlorophosphazotrichloroacetyl, CCl₃C(O)NPCl₃ (2) were obtained. The experimental data are compared with results of ab initio and density functional theory (DFT) calculations. According the theoretical studies the main conformer for both molecules possesses C_s symmetry (CO bond syn respect to the NP bond). The preference of the syn conformation has been rationalized based on the natural bond orbital formalism. The vibrational spectra of 1 in the liquid phase and 2 in the solid phase are in good agreement with theoretical results.     

Spectral additive properties of phosphorus-containing dendrimers

The FT-Raman and FTIR spectra of 12 generations of phosphorus-containing dendrimers:

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with terminal aldehyde and PCl groups have been recorded and analyzed. Their spectral pattern is determined by the ratio T/R (T, the number of terminal groups; R, the number of repeating units). The influence of the encirclement on the band frequencies and intensity was studied and due to the predictable, controlled and reproducible structure of dendrimers the information usually inaccessible was obtained. Bands assigned to the core, repeated units and terminal groups of dendrimers were separated by the differential spectroscopy method. The strong band at 1600 cm⁻¹ show marked changes of optical density in dependence of the aldehyde (CHO) or azomethyne (CHN) substitution in aromatic ring. From the differential IR and Raman spectra of dendrimers it follows that for the generations higher than 6, the steric congestion disturbs the conformations of the terminal groups. The rather rigid repeated units with little conformational flexibility define the perfect microstructure of phosphorus-containing dendrimers up to 11 generation. FT-Raman and FTIR spectroscopy provides the unique detailed information about the structure of technologically relevant materials, which could not be obtained before with any other technique.     

Infrared Spectral Assignment of Pyrimidine and Pyrazine in the CH Stretching Region by an Effective Spectroscopic Hamiltonian

Mid-Infrared spectra of pyrimidine (PM) and pyrazine (PZ) were recorded in the gas phase using a multi-pass long path gas cell. The IR band structure of these compounds above and below 3000 cm⁻¹ is very broad and contains many humps and shoulders. These humps and shoulders are due to various higher quantum excitation of low-frequency vibrational modes, which participate in Fermi resonance with the nearby CH stretch fundamentals and appears in this region. We constructed an Effective Spectroscopic Hamiltonian (ESH) in a mixed local mode (LM) normal mode (NM) basis to assign the various overtone and combination bands in the CH stretching region of these compounds. The CH stretching vibrations of both PZ and PM were treated as symmetrized anharmonic Morse oscillators in local coordinates and the in-plane deformations down to 1000 cm⁻¹ were treated as normal coordinates. The ESHs were diagonalized and the resulting eigenvalues were subsequently fitted in a given parameter space with the experimentally observed bands. The eigenvalues of the converged Hamiltonian are the anharmonic frequencies and the transition intensities were obtained by summing the squared eigenvector components. The overtone and combination transitions near 3000 cm⁻¹ of both PM and PZ were identified and assigned from the eigenvector coefficients of the ESH matrix. The wavefunctions of a pure CH stretch, overtone of the HCC in-plane bend and due to Type 1 Fermi coupling (resonance between a fundamental with an overtones of a low frequency mode, in this case resonance between the CH strech and the overtone of HCC in-plane bending modes) has been demonstrated pictorially.     

Toward the catalytic synthesis of phosphiranes. A computational study

Reaction pathways for the formation of zirconocene phosphinidene complex Cp₂Zr(PR₃)PR from Cp₂ZrCl₂ and LiH and LiPRH and its reactivity to 1,2-dichloroethane are explored with density functional theory using model structures that are devoid of substituents. After the initial Cp₂Zr(Cl)PH₂ is generated with LiPH₂ reaction with LiH is likely to eliminate HCl in a single step to give directly the 16-electron complex Cp₂ZrPH, which is stabilized by the PH₃ phosphine ligand. The intermediate formation of a phosphine hydride complex, Cp₂Zr(H)PH₂ resulting from hydride substitution, is unlikely both on the basis of unfavorable reaction energies and calculated ³¹P NMR chemical shifts that indicate that such a species cannot have been observed experimentally. It is likely that a diphosphine complex, Cp₂Zr(PH₂)₂, results on using an excess of the lithium phosphide, which on H-transfer gives directly the phosphine-stabilized phosphinidene complex. The reactivity of this species is dominated by the release of its stabilizing phosphine ligand to give a highly reactive 16-electron phosphinidene complex, Cp₂ZrPH, which reacts with 1,2-dichloroethane after coordination to one of the chlorine atoms in two asynchronous metathesis steps to the three-membered phosphirane ring. In this process, ZrCl₂ is reformed enabling its recycling to regenerate the phosphinidene complex. This study highlights the special reactivity of the 16-electron Cp₂ZrPH and suggests that related complexes may be generated similarly, thereby expanding the synthetic potential of these nucleophilic reagents.     

Theoretical study on the potential energy surface of SiC2O

The DFT/B3LYP/6-311G(d) and CCSD(T)/6-311G(2df) (single-point) methods have been used to investigate the potential energy surface of SiC₂O. A total of 11 isomers are located, which are connected by 13 interconversion transition states. The global minimum is the linear SiCCO with ¹Σ⁺ electronic state whose structure can be described as cumulenic double bonding form :SiCCÖ:. The isomer O-cSiCC possessing SiCC three-membered ring with an exocyclic OSi bond also shows considerable stability. Both SiCCO and O-cSiCC are kinetically stable towards isomerization and dissociation. Further calculations are performed at the CCSD(T)/6-311G(2df)//QCISD/6-311G(2d) level to obtain more reliable energies, geometrical parameters, harmonic vibrational frequencies and infrared intensities of the isomers. The energies and geometrical parameters are also calculated with the CASPT2//CASSCF methods.     

Concentration dependent Raman study of 1,4-diethynylbenzene on gold nanoparticle surfaces

Concentration dependent adsorption behaviors of 1,4-diethynylbenzene (DEB) on gold nanoparticle surfaces have been investigated by means of surface-enhanced Raman scattering (SERS). The spectral features including the multiple peaks in the ν(CC)_bound stretching region were found to vary as the bulk concentration of DEB in gold nanoparticles. At a low concentration of 10⁻⁶ M, only the multiple ν(CC)_bound band was conspicuous at ∼2000 cm⁻¹ and the free CC stretching band was barely detected in the SERS spectra. When the bulk concentration was increased, the ν(CC)_free band became prominent at ∼2104 cm⁻¹. These splitting bands may provide the evidence that DEB is adsorbed on gold mainly through one of the two acetylene groups with the other CC groups being pendent with respect to the gold surface. Ab initio density functional theory (DFT) calculations of DEB were performed to check the vibrational assignment.