Search

ABSTRACT Density functional theory (DFT) calculations for the six-membered ring 1,4-(CH2)2(PtBu)4 ( 1), the dimer (PtBu2)2 ( 2) and the 2,5-chalcogenated derivatives of 1, 3a (E = S) and 3b (E = Se), and the corresponding cation radicals and dications predict significant structural changes upon oxidation. The formation of a transannular P-P single bond (ca. 2.25 Å) in the three cyclic dications 12+, 3a2+, and 3b2+ is indicated by geometry and consideration of the frontier orbitals. The calculations also indicate a weak transannular interaction in the cyclic cation radicals. The nature of these transannular P-P bonding interactions is analyzed through a consideration of the molecular orbitals involved. Cyclic Voltammetry studies of 1 and 2 reveal two well-separated oxidation processes. Both processes are irreversible for 1 at normal scan rates, whereas for 2 the first process is quasi-reversible. The cation radical 1+• could not be detected by in situ electron paramagnetic resonance studies of the first electrochemical oxidation, but a spectrum for the radical cation 2+• could be observed. The difference in the redox behavior of 1 and 2 is considered with respect to the structural parameters and DFT calculations. Chemical oxidation of 1 with NO+[Al(ORF)4]− (RF = C(CF3)3) in CH2Cl2 led to a complex mixture; the protonated cation H 1+ (1,4-(CH2)2(PtBu)3(HPtBu)+) was identified as one of the major products on the basis of multinuclear NMR spectra. [ABSTRACT FROM AUTHOR]

The 1,3-dipolar cycloaddition reactions of the cationic 1,3-dipolarophiles of azocarbenium ion 1 with HCN in the gas phase were examined using the density functional theory, QCISD method (Quadratic configuration interaction using single and double substitutions) and CCSD(T) (Coupled cluster calculations with single and double excitations and a perturbative estimate of triple contributions calculations) calculations. The theoretical results revealed that the reaction takes place via an initial formation of a 1:1 complex of the two reactants, mainly driven by charge interaction, followed by an asynchronous concerted cyclization forming the 3H-[1,2,4]-triazolium ion 3, which undergo [1,2]-H shift to provide the 1H-[1,2,4]-triazolium ion 4. The effect of the solvent has been modeled by using the isodensity-surface polarizable continuum (IPCM) model and the calculation showed that the reaction in CH2Cl2 solution proceeds in a similar manner as in gas phase with only a slight derivation of activation barrier. The substituent effects have also been investigated. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [ABSTRACT FROM AUTHOR]