Carbenic nitrile imines: Properties and reactivity

Structures and properties of nitrile imines were investigated computationally at B3LYP and CCSD(T) levels. Whereas NBO analysis at the B3LYP DFT level invariably predicts a propargylic electronic structure, CCSD(T) calculations permit a clear distinction between propargylic, allenic, and carbenic structures. Nitrile imines with strong IR absorptions above ca. 2150 cm-1 have propargylic structures with a CN triple bond (RCNNSiMe 3 and R2BCNNBR2), and those with IR absorptions below ca. 2150 cm-1 are allenic (HCNNH, PhCNNH, and HCNNPh). Nitrile imines lacking significant cumulenic IR absorptions at 1900-2200 cm -1 are carbenic (R-(C:)-N=N-R′). Electronegative but lone pair-donating groups NR2, OR, and F stabilize the carbenic form of nitrile imines in the same way they stabilize "normal" singlet carbenes, including N-heterocyclic carbenes. NBO analyses at the CCSD(T) level confirm the classification into propargylic, allenic, and carbenic reactivity types. Carbenic nitrile imines are predicted to form azoketenes 21 with CO, to form [2+2] and [2+4] cycloadducts and borane adducts, and to cyclize to 1H-diazirenes of the type 24 in mildly exothermic reactions with activation energies in the range 29-38 kcal/mol. Such reactions will be readily accessible photochemically and thermally, e.g., under the conditions of matrix photolysis and flash vacuum thermolysis

Accurate vibrational spectra of methylpotassium using a hybrid CCSD(T)/B3LYP approach and a variational treatment

cited By 20International audienceWe present the structural parameters and vibrational spectra of CH 3K computed using a hybrid approach in which CCSD(T) equilibrium values and harmonic wavenumbers are coupled to B3LYP anharmonic cubic and quartic terms in the framework of our variational treatment recently developed and presented for CH3Li. The obtained results confirm the assignment of several observed bands but suggest some revision of experimental assignments, as well. © 2005 Wiley Periodicals, Inc

Vibrational spectra of methyllithium and its aggregates: A new interpretation from ab initio anharmonic calculations

cited By 20International audienceThe complete quartic force field of methyllithium (CH3Li) is computed at the B3LYP/cc-pVTZ level of theory. The vibrational energy levels calculated from a perturbational and a variational procedure are in agreement with the observed spectra except for the C-Li stretching and the symmetric methyl deformation modes for which a disagreement with the experimental assignment given by Andrews is apparent. This discrepancy between experiment and theory is so large that questions are raised either about a correct characterization of, or correct calculations for the monomeric species CH 3Li. Our theoretical study of methyllithium aggregates (CH 3Li)n, with n = 2, 3, 4 and 6, gives a new interpretation of the experimental data. © 2004 Elsevier B.V. All rights reserved

New results on methylalkali systems: Accurate vibrational study of methylsodium

cited By 3International audienceThis paper presents results (structural parameters and anharmonic vibrational spectra) obtained for the methylsodium system at different levels of theory from DFT and post-HF [CCSD(T)] calculations. These theoretical results are faced with the existing experimental data. An interpretation of the experimental reference is proposed from our calculations about the monomer and the dimer compounds. © 2006 Elsevier B.V. All rights reserved

Software news and updates new parallel software (P_Anhar) for anharmonic vibrational calculations: Application to (CH3Li)2

cited By 44International audienceWe present the development of a new parallel computer code (P_Anhar_v1.0) to calculate the vibrational spectrum of medium size molecules using a variational algorithm. The method is applied to the determination of a complete quartic anharmonic force field (B3LYP/cc-pVTZ) for methyllithium, leading to a new interpretation of experimental data

An single program multiple data strategy for calculation of anharmonic vibrations

cited By 3International audienceThis paper presents a general perturbational and variational scheme to calculate solutions of the spectral problem for the vibrational molecular Hamiltonian. A parallel strategy in the ongoing development of our software P_Anhar is presented, in order to calculate the vibrational spectrum of medium sized molecules. The efficiency of this approach is checked on ethylene oxide. © 2006 Springer Science+Business Media, LLC

Nitrile Imines: Matrix Isolation, IR Spectra, Structures, and Rearrangement to Carbodiimides

The structures and reactivities of nitrile imines are subjects of continuing debate. Several nitrile imines were generated photochemically or thermally and investigated by IR spectroscopy in Ar matrices at cryogenic temperatures (Ph-CNN-H 6, Ph-CNN-CH3 17, Ph-CNN-SiMe3 23, Ph-CNN-Ph 29, Ph3C-CNN-CPh3 34, and the boryl-CNN-boryl derivative 39). The effect of substituents on the structures and IR absorptions of nitrile imines was investigated computationally at the B3LYP/6-31G* level. IR spectra were analyzed in terms of calculated anharmonic vibrational spectra and were generally in very good agreement with the calculated spectra. Infrared spectra were found to reflect the structures of nitrile imines accurately. Nitrile imines with IR absorptions above 2200 cm(-1) have essentially propargylic structures, possessing a CN triple bond (typically PhCNNSiMe3 23, PhCNNPh 29, and boryl-CNN-boryl 39). Nitrile imines with IR absorptions below ca. 2200 cm(-1) are more likely to be allenic (e.g., HCNNH 1, PhCNNH 6, HCNNPh 43, PhCNNCH3 17, and Ph3C-CNN-CPh3 34). All nitrile imines isomerize to the corresponding carbodiimides both thermally and photochemically. Monosubstituted carbodiimides isomerize thermally to the corresponding cyanamides (e.g., Ph-N=C=N-H 5 --> Ph-NH-CN 8), which are therefore the thermal end products for nitrile imines of the types RCNNH and HCNNR. This tautomerization is reversible under flash vacuum thermolysis conditions

Covalency in highly polar bonds. Structure and bonding of methylalkalimetal oligomers (CH3M)(n) (M = Li-Rb; n=1, 4)

We have carried out a theoretical investigation of the methylalkalimetal monomers C