Through-space intramolecular palladium rearrangement in substituted aryl complexes: theoretical study of the aryl to alkylpalladium migration process

DFT/B3LYP calculations have been carried out to study intramolecular 1,n palladium shifts (n = 3-5) between sp2 and sp3 carbon atoms in alkylarylpalladium systems. Such shifts, which also involve a concomitant exchange with a hydrogen atom of the alkylaryl ligand, are quite often a pivotal step of several organic transformations mediated by palladium complexes. We show that the intimate mechanism for the 1,3 shift corresponds to a Pd(IV) pathway, whereas a Pd(II) pathway is favored in the case of 1,5 migrations. In the case of 1,4 migrations, both mechanisms are competitive. The Pd(IV) pathway can involve either a true Pd(IV) intermediate (oxidative addition/reductive elimination mechanism) or a Pd(IV) transition state (oxidative hydrogen migration mechanism). The energy barrier is very high for the 1,3 palladium shift, making this process very unlikely, in contrast to the other ones which have enthalpy barriers ranging between 22.8 kcal mol-1 (for the 1,5 shift) and 31.9 kcal mol-1 (for the least favorable 1,4 shift studied here). All of these results are in line with our previous results for palladium shifts between two sp2 carbon atoms. In addition, the sp2 to sp3 shifts have been found to be rather exothermic owing to the possibility for the alkylaryl ligand in the product to achieve a eta3 coordination mode. This eta3 coordination mode results either from the shift itself (1,3 case) or from a subsequent rearrangement that comprises a chain-running mechanism within the alkyl chain bound to the metal (for n > 3).     

Newton's method for overdetermined systems of equations

Complexity theoretic aspects of continuation methods for the solution of square or underdetermined systems of polynomial equations have been studied by various authors. In this paper we consider overdetermined systems where there are more equations than unknowns. We study Newton's method for such a system.

     

Antibacterial Mode of Action of the Daucus carota Essential Oil Active Compounds against Campylobacter jejuni and Efflux-Mediated Drug Resistance in Gram-Negative Bacteria

Today, an alarming rise of bacterial gastroenteritis in humans resulting from consuming Campylobacter-tainted foods is being observed. One of the solutions for mitigating this issue may be the antibacterial activity of essential oils. In the present research, we propose to study the antibacterial activity against Campylobacter and other Gram-negative bacteria of Daucus carota essential oil and its active molecules. In addition, a few chemically synthesized molecules such as (E)-methylisoeugenol, Elemicin, and eugenol were also studied. The results showed that the essential oil itself and its most active component, (E)-methylisoeugenol, exhibited bactericidal effects. Similar effects were detected using purified and chemically synthesized molecules. Also, it was observed that the Daucus carota essential oil and its active molecules affected intracellular potassium and intracellular ATP contents in Campylobacter cells. Inhibition of the membrane bound F_OF₁-ATPase was also observed. Eventually, for the first time, the efflux mechanism of active molecules of Daucus carota essential oil was also identified in gamma proteobacteria and its specific antibacterial activity against Campylobacter jejuni was associated with the lack of this efflux mechanism in this species.     

Theoretical investigation of the hydride migration to coordinated carbon monoxide

SCF and Cl calculations for the hydride migration to the carbonyl ligand of the HMn(CO)₅ system are reported. A rather high barrier, obtained from     

Rotational isomerism inbis carbene MOL4 complexes: A theoretical study

LCAO-MO-SCF calculations are reported for the different stereoisomers of the Mo(CO)₄(CH₂)₂ and Mo(CO)₄[C(NH₂)₂]₂ systems. The substitution of the hydrogen atoms by the amino groups in the carbene ligands leads to an almost zero rotational barrier. Steric interactions are therefore expected to govern the barrier for diaminocarbene ligands which are more bulky than C(NH₂)₂. The rotational isomerism in thesebis carbene MoL₄ systems is also discussed in connection with the isolobal analogy between CH₂ and C₂H₄.     

Can weak interactions modify the binding properties of a strong nitrogen donor? Unusual N-coordination of a phosphoranylidene-substituted pyrazolone unit towards palladium(II) centres: an experimental and theoretical study

Selective N(2)-binding of 3-methyl-1-phenyl-4-(triphenylphosphoranylidene)-2-pyrazolin-5-one (L) has been found in two palladium(II) complexes, [PdCl(2)L(2)](2) and [Pd(o-C(6)H(4)CH(2)NMe(2))Cl](3). X-Ray diffraction studies show that the pyrazole rings lie almost perpendicular to the coordination plane. In both complexes the metal atom is located out of the plane defined by the pyrazole ring(s)(dihedral angle between the plane and the Pd-N vector approximately 30 degrees). To investigate the origin of this distortion, a theoretical study was carried out on a simplified model of complex , where a single pyrazolone ligand was replaced by NH(3). From this study it could be inferred that the out-of-plane distortion mainly involves weak, electrostatic interactions between a chlorine atom and an ortho-aromatic H atom of the N(1)-linked phenyl group, as well as between the other chlorine atom and an ortho-aromatic H atom of the PPh(3) group.     

End-on versus side-on coordination of dioxygen model ab initio calculations for the adducts of Co(acacen)

From ab initio calculations, the ground state electronic configuration is found for the three possible structures (linear, bent or perpendicular) of the cobalt-dioxygen unit in the adducts Co(acacen) LO₂(L=none, H₂O, CN^?, CO). The bent structure is energetically the most favourable, being slightly more stable than the linear one (by 4–26 kcal/mole depending on the fifth ligand L) but much more stable than the perpendicular one (by 46–82 kcal/mole). These results are rationalized in terms of the main metal-ligand interactions, with the bent structure stabilized by a 3d _z ²-1π _g ^/a interaction and the perpendicular structure destabilized by a four-electron destabilizing interaction 3d _xz -1π _g ^/a .