Akın Azizoglu

Substituent effects on the ring-opening mechanism of lithium bromocyclopropylidenoids to allenes.

The ring-opening reactions of lithium bromocyclopropylidenoids to allenes have been investigated computationally at the B3LYP/6-31G(d) level of theory. Formally, two pathways can be considered: the reaction may either proceed in a concerted fashion or stepwise with the intermediacy of a free cyclopropylidene. In both cases, the loss of the bromide ion determines the kinetic of the reaction. The stability of the reactive intermediate, i.e., the carbene, is dependent on the substituent. Cyclopropylidenes bearing an electron-donating group (+M) are extremely unstable and ring-open readily to the allene. In contrast, bromocyclopropylidenoids with electron-withdrawing groups are particularly stable species. Here, a high energy barrier needs to be overcome in order to split off bromide and to generate the corresponding carbene or allene. Still, for most of the monosubstituted cyclopropylidenes investigated during this study, the activation energy for the cyclopropylidene to allene rearrangement is lower than the energy required for parent compound (X = H) except for X = -SiH3 and -CF3.

Reductive Cleavage of Carbon Monoxide by a Disilenide

The complete reductive cleavage of the triple bond in carbon monoxide was achieved using a lithium disilenide at room temperature. The C-C-coupled product can be regarded as a silanone dimer with pending alkyne and silirene moieties and incorporates two equivalents of CO per disilenide unit. A formation mechanism via ketenyl intermediates is proposed on the basis of DFT calculations and elucidated experimentally by employing Group 6 metal carbonyls as both stabilizing entity and source of CO in the reaction with disilenide. The isolation of cyclic silylene complexes with weakly donating ketenyl donor groups further supports the mechanistic scenario.

Experimental and computational investigations of a Cadmium(II) mononuclear complex with 2,6-Bis(3,5-dimethyl-N-pyrazolyl)pyridine (bdmpp) and selenocyanate as ligands

A new cadmium (II) complex, [Cd(bdmpp)(SeCN)2(H2O)] (1) (where bdmpp = 2,6-bis(3,5-dimethyl-N-pyrazolyl)pyridine), has been synthesized and characterized by elemental and spectral (IR, 1H-NMR and 13C-NMR, UV-Vis) analyses, differential scanning calorimetry, and single crystal X-ray diffraction studies. X-ray analysis showed that the structure was crystallized in the monoclinic space group Cc with a = 9.031(2), b = 13.884(3), c = 16.910(3) Å, and Z = 4. The geometry around the cadmium atom is distorted octahedral with a CdN3Se2O setup. The N atoms of the SeCN are engaged in two strong intermolecular H-bonding interactions forming a 3D supramolecular polymeric network. The geometry and vibrational frequencies of complex 1 computed with the DFT methods (BLYP, B3LYP, B3PW91, MPW1PW91) are in better agreement with experiment than those obtained with the ab-initio method except for the bond angles. The molecular orbital diagram has been also calculated and visualized at the B3LYP/LanL2DZ level of theory.

Synthesis, crystal structure, magnetic properties and computational study of a series of cyano-bridged MnIII-FeIII complexes

Different derivatives of the Schiff base (SB) N,N′-bis(2-hydroxybenzylidene)-2,2,-dimethylpropane-1,3,-diamine, LH2, have been used to obtain a series of compounds of which we here report the synthesis, structural determination and magnetic study. [Mn(SB)(H2O)]ClO4 and [NEt4]3[Fe(CN)6] react in methanol to give the cis-cyano-bridged assemblies, 3D [NEt4][Mn(5-ClL)]2Fe(CN)6]·2(MeOH) 1, 3D [NEt4]3[Mn(5-BrL)]6[Fe(CN)6]3·11(MeOH) 2, and a trans-cyano-bridged trinuclear compound [NEt4][Mn(4-MeOL)(H2O)]2Fe(CN)6]·(EtOH)·(H2O) 3, depending on the Schiff-base used. Complexes 1, 2 and 3 have been characterized by X-ray analyses, magnetic measurements and DFT calculations. The four CN− in the equatorial plane of the [Fe(CN)6]−3 moiety bridge four Mn ions, each in the cis position, which results in a 3D neutral layered structure with a [–M–NC–Fe–CN–M–] linkage for 1 and 2. The two CN− in the equatorial plane of the [Fe(CN)6]−3 moiety bridge two Mn ions in the trans position, which results in a hydrogen bonded 2D neutral layered structure for 3. Magnetic studies reveal that complexes 1 and 2 exhibit antiferromagnetic coupling, while complex 3 displays ferromagnetic interactions between low-spin Fe(III) and high-spin Mn(III) through the cyanide bridges. Complex 3 further displays alternating current (AC) frequency dependent magnetic susceptibility, typical of the presence of slow magnetization relaxation. Density functional theory (DFT) combined with the broken symmetry state method were used to study the magnetic coupling behavior of complexes 1 and 3. DFT computations reveal that the calculated exchange coupling constants Jtheo were in good agreement with the experimental ones.

Experimental and Computational Studies on the 1:1 Complex of Anthranilic Acid with P-Toluenesulfonic Acid

Abstract The proton-transfer compound (3) was synthesized in good yields by the reaction of anthranilic acid with p-toluenesulfonic acid. It was characterized by elemental analysis, infrared spectroscopy, and X-ray single-crystal determination. The crystal structure analysis of 2-carboxyanilinium p-toulenesulfonate (3) has revealed a one-dimensional hydrogen-bonded network structure, involving the tosylate anion, the carboxyl group, and the ammonium group. The H(N)···O distances range from 1.97 to 2.23 Å. The molecular geometry and vibrational frequencies of 3 were calculated using the ab-initio method (HF) with the 6–31G(d) and 6–31+G(d,p) basis sets. The computed results indicate that the optimized geometry reproduces the crystal structure well, and the assignments of fundamental vibrations also agree well with the theoretical frequencies. The intermolecular proton transfer process between the ionic (3) and nonionic (4) structures was also investigated with the theoretical computations. The nonionic form (4) is energetically more stable than the ionic form (3) and TS(3→4) by 9.76 and 7.01 kcal/mol, respectively, including the zero-point vibrational energy correction at the HF/6–31+G(d,p) level. In addition, the atomic charges, the molecular electrostatic potentials, the nucleus-independent chemical shifts, and the frontier molecular orbitals of 3 were carried out at the HF/6–31+G(d,p) level of theory. Supplementary materials are available for this article. Go to the publishers online edition of Phosphorus, Sulfer, and Silicon and the Related Elements for the following free supplemental files: Additional figures and tables GRAPHICAL ABSTRACT

Substituent effects on hydrogen bonding of aromatic amide-carboxylate

N-(p-benzoyl)-anthranilic acid (BAA) derivatives have been synthesized with different substituents (X: Br, Cl, OCH3, CH3), and their crystal structures have been analyzed in order to understand the variations in their molecular geometries with respect to the substituents by using (1)H NMR, (13)C NMR, IR and X-ray single-crystal diffraction. The carboxylic acid group forms classic OH⋯O hydrogen bonded dimers in a centrosymmetric R2(2)(8) ring motifs for BAA-Br and BAA-Cl. However, no carboxylic acid group forms classic OH⋯O hydrogen bonded dimers in BAA-OCH3 and BAA-CH3. The asymmetric unit consists of two crystallographically independent molecules in BAA-OCH3. DFT computations show that the interaction energies between monomer and dimer are in the range of 0.5-3.8kcal/mol with the B3LYP/6-31+G*, B3LYP/6-31++G*, B3LYP/6-31++G**, and B3LYP/AUG-cc-pVDZ levels of theory. The presence of different hydrogen bond patterns is also governed by the substrate. For monomeric compounds studied herein, theoretical calculations lead to two low-energy conformers; trans (a) and cis (b). Former one is more stable than latter by about 4kcal/mol.

Experimental and Theoretical Vibrational Spectra of Sideridiol Isolated from Sideritis Species

Sideridiol (ent-7α,18β-dihydroxykaur-15-ene) one of the ent-kaurene diterpenoid, is isolated from the genus Sideritis L. belongs to the family of Lamiaceae. The vibrational frequencies of sideridiol in the ground state have been calculated using the Density Functional Theory (DFT) method with the 6-31G(d) and 6 31+G(d,p) basis sets. The calculated vibrational frequencies have been compared with that of obtained experimental IR spectrum.

Theoretical investigations on the electronic and structural properties of stannacyclopropylidenoids and plumbacyclopropylidenoids

The theoretical calculations at the MP2 and WB97XD levels have been carried out to investigate the isomeric structures, energies and properties of heavycyclopropylidenoids (C2H4MLiBr, M = Sn or Pb). The theoretical calculations indicate that the inverted (I) forms of Sn and Pb analogues are energetically more stable than others. No tetrahedral structure for the title plumbacyclopropylidenoid has been located as a minimum on the potential energy surface. Moreover, frontier molecular orbitals (FMO) and molecular electrostatic potential maps (MEP) have been achieved at the MP2 level.