Cem B. Yildiz

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.

Regiodiscriminating Reactivity of Isolable NHC-Coordinated Disilenyl Germylene and Its Cyclic Isomer

An isolable NHC-coordinated disilenyl germylene R2Si═SiR-GePh·NHCiPr2Me2 (5b: R = 2,4,6-triisopropylphenyl, NHCiPr2Me2 = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene) is obtained from the reaction of the α-chloro silyl functionalized heavier vinylidene analogue R2(Cl)Si-RSi═Ge·NHCiPr2Me2 with phenyllithium. The disilenyl germylene 5b isomerizes at 40 °C to the NHC-adduct of the corresponding heavier cyclopropylidene analogue 6b. Both 5b and 6b display near perfect regiodiscrimination in their reactions with phenylacetylene and xylyl isocyanide, affording in the case of each reagent two different regioisomers of NHC-coordinated cyclic germylenes. DFT calculations reveal that the Si═Si bond accounts for the high reactivity of 5b even at low temperature while in the case of cyclic 6b the low-valent germanium center requires a considerable thermal activation.

Diverse Reactivity of an Electrophilic Phosphasilene towards Anionic Nucleophiles: Substitution or Metal–Amino Exchange

The reaction of MesLi (Mes=2,4,6-trimethylphenyl) with the electrophilic phosphasilene R2 (NMe2 )Si-RSi=PNMe2 (2, R=Tip=2,4,6-triisopropylphenyl) cleanly affords R2 (NMe2 )Si-RSi=PMes and thus provides the first example of a substitution reaction at an unperturbed Si=P bond. In toluene, the reaction of 2 with lithium disilenide, R2 Si=Si(R)Li (1), apparently proceeds via an initial nucleophilic substitution step as well (as suggested by DFT calculations), but affords a saturated bicyclo[1.1.0]butane analogue as the final product, which was further characterized as its Fe(CO)4 complex. In contrast, in 1,2-dimethoxyethane the reaction of 1 with 2 results in an unprecedented metal-amino exchange reaction.

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

Reactivity of silagermenylidene toward nitrous oxide: a preliminary DFT study

AbstractThe possible reaction mechanism of silagermenylidene and its NHC (N–heterocyclic carbene) coordinated form with N2O were investigated by DFT methods. Mainly, the potential energy surfaces of the five pathways I–IV were explored. Pathways I, II, III, and III’ deal with the oxidation of silagermenylidene, whereas that of NHC coordinated form is associated with pathways I, III, III’, and IV. Pathway I is initiated by the interaction between terminal N atom of N2O and Si atom of silagermenylidene in a stepwise manner. Pathway II details concerted direct oxidation of silagermenylidene. Pathways III and III’ are related to the concerted 1,3–dipolar cycloaddition steps. Pathway IV is about the interaction of terminal atoms of N2O with carbenic Ge atom of silagermenylidene. All the proposed pathways I–IV portray the isomerization of silagermenylidenes to silagermoxiranylidenes. The subsequent N2O addition to the silagermoxiranylidenes was also investigated in the present study. Somehow with a trend similar to silagermenylidenes, the proposed pathways I–IV exist for the second molecule N2O activation by silagermoxiranylidenes. A comparison of the free energy profiles of the proposed pathways gave the important result that pathways III and III’ remain the most facile mechanisms to activate N2O in all cases. We strongly believe that the proposed mechanisms will be effective to better understand the chemistry of heavier vinylidenes and provide further impetus to this field. Graphical AbstractThe possible oxidation reaction mechanism of silagermenylidene with nitrous oxide was investigatedthrough density functional calculations. The concerted 1,3-dipolar cycloadditions are determined to beenergetically most facile pathways.

CCDC 1509723: Experimental Crystal Structure Determination

Related Article: Debabrata Dhara, Debdeep Mandal, Avijit Maiti, Cem B. Yildiz, Pankaj Kalita, Nicolas Chrysochos, Carola Schulzke, Vadapalli Chandrasekhar, Anukul Jana||Dalton Trans.|||doi:10.1039/C6DT04321F

CCDC 1509722: Experimental Crystal Structure Determination

Related Article: Debabrata Dhara, Debdeep Mandal, Avijit Maiti, Cem B. Yildiz, Pankaj Kalita, Nicolas Chrysochos, Carola Schulzke, Vadapalli Chandrasekhar, Anukul Jana||Dalton Trans.|||doi:10.1039/C6DT04321F

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.