Tertiary phosphane-diiodine compounds: Are they molecular adducts or iodophosphonium iodides?

The solid-state and solution structures of Ph(3)P . I-2 have been studied in detail by electronic, P-31{H-1}-NMR and Raman spectroscopy as well as conductometric measurements. When 1 : 1 ratios of triphenylphosphane and diiodine are mixed in dichloroethane, the molecular adduct is shown to exist also in solution. On the basis of the overall results, this molecular adduct is best described as a charge-transfer complex of the donor I- with the acceptor Ph(3)PI(+), rather than the charge-transfer complex of the donor Ph(3)P with the acceptor I-2 Or the ionic species [Ph(3)PI]I as previously proposed. When higher diiodine to triphenylphosphane ratios are used, the Ph(3)P . I-2 adduct dissociates to give Ph(3)PI(+) and I-3(-) or I-5(-) depending on the diiodine excess. Previously reported solution data, which were ascribed to the ionic form of the adduct, are instead in agreement with hydrolysis products (Ph(3)PO, PH3POH+) of the very reactive adduct, formed in the presence of traces of water.