Abstract:

Density functional theory (DFT) calculations for the six-membered ring 1,4-(CH2)(2)((PBu)-Bu-t)(4) (1), the dimer ((PBu2)-Bu-t)(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 angstrom) in the three cyclic dications 1(2+), 3a(2+), and 3b(2+) 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(+center dot) could not be detected by in situ electron paramagnetic resonance studies of the first electrochemical oxidation, but a spectrum for the radical cation 2(+center dot) 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)]-(R-F = C(CF3)(3)) in CH2Cl2 led to a complex mixture; the protonated cation H1(+) (1,4-(CH2)(2)((PBu)-Bu-t)(3)((HPBu)-Bu-t)(+)) was identified as one of the major products on the basis of multinuclear (C) 2014 Wiley Periodicals, Inc.