Protonation of some cyclic triphosphenium ions

Several cyclic triphosphenium ions of various ring sizes have been successfully protonated to form the corresponding triphosphane di-ium dications, either by a (BuCl)-Bu-t/AlO3 mixture and/or by triflic acid. The latter reagent appears to be harsher, however sometimes leading to decomposition. The new dications have been identified in solution by P-31 NMR spectroscopy; recording the spectra proton coupled as well as decoupled has enabled (1)J(PH) as well as (1)J(PP) to be evaluated in most cases. The protonated derivatives of three compounds could not be observed, with only decomposition products being detected. In the case of the triphosphenium ion derived front bis-1,4diphenylphosphinobutane (dppb), clear spectroscopic evidence for an intermediate in the decomposition process of the di-ium dication has been obtained, enabling a plausible mechanism to be proposed. In addition, a novel triphosphorus-containing trication with a norbornane-like structure has been detected, and characterized by single crystal X-ray diffraction, as a minor product from the protonation of the triphosphenium ion derived from cis-bis-1,2-diphenylphosphinoethene (dppE). (c) 2005 Wiley Periodicals, Inc.