Simultaneous double N-inversion pathway

Journal of Molecular Structure: …, 2001

Chemical Communications, 2013

Inorganica Chimica Acta, 2018

The Schiff base ligands N-2-(R-pyridyl)-2-hydroxy-1-naphthaldimine (HL) react with the zinc(II) nitrate or acetate to give the Λ-and ∆-bis[N-2-(R-pyridyl)-2-oxo-1naphthaldiminato-κ 2 N,O]zinc(II), [Zn(L) 2 ] {R = H (1), 4/6-CH 3 (2/3)}. EI-mass spectra show the molecular ion peaks at 558 (1) and 586 (2 or 3). Molecular structure determination for 2•0.5CH 2 Cl 2 crystal reveals that two molecules of the N^O-chelate ligands form a tetrahedral N 2 O 2-coordination sphere around the zinc atom, in which one of the pyridyl-N atom is located towards the metal atom at a close contact ([Zn1…N2] = 2.674 A˚). Packing analysis explores that one of the Zn-chelate ring metallacycles forms a reciprocal and rather strong π−π interaction (Cg … Cg = 3.517 Å) with the pyridyl ring of an adjacent molecule and vice versa, and results in an inversion-symmetric complex pair with opposite Λ-and ∆-configurations at the metal centre. The packing analysis is further supported by quantitative analysis of intermolecular interactions with the Hirshfeld surface. The optimized structure and excitation state properties by DFT/TDDFT support the solid state molecular structure and electronic spectra in solution, respectively.

Journal of Molecular Modeling, 2000

The quadrupole moment of formaldazine, H 2 C=N-N=CH 2 , has been studied for the trans structure (∠(C-N-N-C) = τ = 180º) and a series of gauche structures (τ > 120º). Restricted Hartree-Fock theory, second-order Møller-Plesset theory, and quadratic CI theory have been used in conjunction with the basis sets 6-31G*, 6-31G**, 6-311G** and 6-311++G**. Formaldazine is a quadrupolar molecule with primitive quadrupole moment tensor components of Q xx = -22.4, Q yy = -20.4 and Q zz = -25.6 DÅ at the theoretical level QCISD/6-311++G**. The examination of the theoretical level dependency shows that the reliable computation of a quadrupole moment requires the use of a flexible basis set. A large part of the component Q zz = -25.6 DÅ is due to the π-system and compares, on a per electron basis, with the Q zz value of benzene. Conformational changes of the azines in the range 120° < τ < 180º have but a minute effect on the energy and are associated with only minor electronic relaxation. These conformational changes alter the quadrupole moment tensor components less than ∆Q xx = +0.4, ∆Q yy = +1.6 and ∆Q zz = -1.0 DÅ at QCISD/6-311++G**//QCISD/6-31G*. The direction of these changes is explained by consideration of the rotation of the CN-π-systems and a small reduction of the CN bond polarity in the gauche structures. The Q zz component of formaldazine is representative of the quadrupole moment tensor component along the direction of the C 2 axis of the azine bridge as such. Hence, the results of this study suggest that azines can engage in strong quadrupole-quadrupole interactions and can be employed as lateral synthons in crystal engineering.

Journal of Molecular Modeling, 2013

The mechanism of the thermal rearrangement of substituted N-acyl-2,2-dimethylaziridines 1 has been studied using quantum chemistry methods. Geometries of reactants, transition states and products have been optimized at the B3LYP/6-311++G(2d,2p) level. Relative energies for various stationary points have been determined and reaction identified by IRC calculations. The results show that thermal rearrangements occur in three ways. Firstly, the transition state TS 1 in which a hydrogen atom of methyl groups migrates from primary carbon to oxygen of amid group to give the Nmethallylamide 2. The second is via the transition state TS 2 in which the attack of oxygen to the tertiary carbon yields the oxazoline 3. The third is via the transition state TS 3 in which a hydrogen migrate from the secondary carbon to oxygen to give the vinylamide 4. In order to get insights into the factors determining the exact nature of its interactions with electrophiles, the application of reactivity parameters derived from density functional theory in a local sense, in particular the softness and Fukui function, to interpret and predict the mechanisms of the thermal decomposition of the N-acyl-2,2dimethylaziridines 1, has been discussed.

Journal of Molecular Structure, 2005

The Journal of Physical Chemistry A, 2008

Using a combination of NMR methods we have detected and studied fluxional motions in the slip-sandwich structure of solid decamethylzincocene (I, [(η 5 -C 5 Me 5 )Zn(η 1 -C 5 Me 5 )]). For comparison, we have also studied the solid iminoacyl derivative [(η 5 -C 5 Me 5 )Zn(η 1 -C(NXyl)C 5 Me 5 )] (II). The variable temperature 13 C CPMAS NMR spectra of I indicate fast rotations of both Cp* rings in the molecule down to 156 K as well as the presence of an order-disorder phase transition around 210 K. The disorder is shown to be dynamic arising from a fast combined Zn tautomerism and η 1 /η 5 reorganization of the Cp* rings between two degenerate states A and B related by a molecular inversion. In the ordered phase, the degeneracy of A and B is lifted; that is, the two rings X and Y are inequivalent, where X exhibits a larger fraction of time in the η 5 state than Y. However, the interconversion is still fast and characterized by a reaction enthalpy of ∆H ) 2.4 kJ mol -1 and a reaction entropy of ∆S ) 4.9 J K -1 mol -1 . In order to obtain quantitative kinetic information, variable temperature 2 H NMR experiments were performed on static samples of I-d 6 and II-d 6 between 300 and 100 K, where in each ring one CH 3 is replaced by one CD 3 group. For II-d 6 , the 2 H NMR line shapes indicate fast CD 3 group rotations and a fast "η 5 rotation", corresponding to 72°rotational jumps of the η 5 coordinated Cp* ring. The latter motion becomes slow around 130 K. By line shape analysis, an activation energy of the η 5 rotation of about 21 kJ mol -1 was obtained. 2 H NMR line shapes analysis of I-d 6 indicates fast CD 3 group rotations at all temperatures. Moreover, between 100 and 150 K, a transition from the slow to the fast exchange regime is observed for the 5-fold rotational jumps of both Cp* rings, exhibiting an activation energy of 18 kJ mol -1 . This value was corroborated by 2 H NMR relaxometry from which additionally the activation energies 6.3 kJ mol -1 and 11.2 kJ mol -1 for the CD 3 rotation and the molecular inversion process were determined.

Organometallics, 1986

2a, M = Fe b. M = R u C=C bonds7, is not involved in the reaction. The available evidence suggests that the inner carbon atom in 1, i.e., the one which is attached to three metal atoms, is the one which is attacked by oxygen, and the resulting CO unit is lost subsequently by decarbonylation. In view of the possibilities of alkyne ligand scissions with7 and without8 chemical attack at the alkyne C atoms two types of possible reaction intermediates come into mind. Adhering to the 18-electron rule 3 could result from C e scission followed by oxidation whereas 4 would represent initial oxidation and loss of one CO ligand. Although at the moment this mechanism is purely speculative, in both cases the emergence of the CPh ligand which has to become p 3 bridging can be visualized. 3 I W) 3 4 Cluster model systems related to surface-catalyzed CO interconversions have focused on the deoxygenation of CO ligands forming carbide speciesg which then undergo CC couplingslO. The reactions presented herein represent the reversal of such sequences and underline our proposition that by variation of its metal constituents a polymetallic system can be tuned such that it supports organic reactions in its ligand sphere in both possible directions.'l Further work will elucidate the course of the reaction by isotopic labeling studies and test the possible generalization of this approach.

Inorganic Chemistry, 1997

A series of dinuclear M(III) (M) Fe or Ga) catecholate complexes has been prepared using bisbidentate catecholate ligands (L). The products contain discrete, dinuclear M 2 (L) 3 6anions featuring pseudo-octahedral coordination centers. The helical nature of the dinuclear complexes has been established by CD spectroscopy and X-ray crystallography. The salt (N(CH 3) 4) 6 Ga 2 (L 3) 3 (L 3) N,N′-bis(2,3-dihydroxy-4-carbamoylbenzoyl)-1,4-phenylenediamine) has been characterized by X-ray diffraction; crystals are hexagonal, space group P3 h1c with unit cell dimensions a) 14.283(2) Å, c) 42.966(2) Å, V) 7591 Å 3 , and Z) 2. Variable-temperature 1 H NMR experiments demonstrate that the configuration inversion of the enantiomers of K 6 Ga 2 (L 4) 3 (L 4) N,N′-bis(2,3dihydroxy-4-(isopropylcarbamoyl)benzoyl)-1,4-phenylenediamine) and K 6 Ga 2 (L 5) 3 (L 5) N-(2,3-dihydroxy-4-(isopropylcarbamoyl)benzoyl)-N′-(2,3-dimethoxy-4-(methylcarbamoyl)benzoyl)-1,4-phenylenediamine) is facile in D 2 O or DMSO-d 6. The mechanism of inversion has been probed by dynamic NMR spectroscopy, using the complex K 6 Ga 2 (L 5) 3 which exists in two isomeric forms in solution, cis-and trans. The intramolecular inversion of the dinuclear helicates occurs without cis-trans isomerization and proceeds by independent trigonal twisting of each metal center, affording the heterochiral meso complex as an intermediate. The free energy of activation for the inversion of K 6 Ga 2 (L 4) 3 in D 2 O at p[D]) 12.1 is ∆G q 298) 79(2) kJ mol-1 , with ∆H) 75(2) kJ mol-1 and ∆S q)-12(6) J mol-1 K-1. Under slightly acidic conditions a proton-assisted pathway becomes dominant and the rate of inversion shows a second-order dependence in [D + ]. The heterochiral meso complex of Ga 2 (L 4) 6 3is shown to be a transient kinetic intermediate in the (Λ,Λ) T (∆,∆) inversion process of the helicate complex.

The Journal of Organic Chemistry, 2010

The uncatalyzed, thermal N-inversion reactions were studied of pyrimidin-4(3H)-imine (PMI), pyridin-2(1H)-imine (PYI), and 1H-purine-6(9H)-imine (PUI). Relevant regions of the potential energy surfaces were explored with second-order Mo 9 ller-Plesset perturbation theory (MP2(full)/ 6-31G(d)) and with coupled cluster theory (CCSD/6-31G(d), CCSD/6-31þG(d)). The thermochemistry of stationary structures was evaluated at the MP2 level and their energies also were computed at the levels CCSD(T)/6-311þG(d,p) and CCSD(T)/6-311þG(2df,2p) and with structures optimized at lower CCSD levels. The best estimates for the (E)-preference free enthalpies ΔG 298 (Z vs. E) are 2.6 (PMI), 2.3 (PYI), and 6.0 (PUI) kcal/mol and for the free enthalpies of activation ΔG 298 (Z f E) they are 21.6 (PMI), 21.1 (PYI) and 19.7 (PUI) kcal/mol. Nonplanar N-inversion transition state (ITS) structures occur along enantiomeric reaction paths and stationary structures for in-plane N-inversion correspond to second-order saddle points (SOSP) on the potential energy surface. The deformation energy ΔE def = E(SOSP)-E(ITS) is less than 0.5 kcal/mol for PMI and PUI, but it is as high as ΔE def ≈ 2 kcal/mol for PYI. The detailed study of structures and electronic structures along the entire N-inversion path of the isomerization (Z)-PMI a (E)-PMI revealed a remarkable stabilization due to asymmetry in the ascent region from the (E)-isomer to ITS. Structures in this region of the potential energy surface allow best for additional bonding overlaps in the HOMO, and this amidine effect predicts lower N-inversion barriers in analogous imines with (Z)-preference energies. The discussion of the halogen-bonded aggregate PMI 3 ClCH 3 exemplifies that the asymmetry in N-inversion paths is retained and perhaps even enhanced in chlorinated solvents of low polarity.