SYNTHESIS, REACTIONS, AND CRYSTAL-STRUCTURE OF A STABLE 10-I-4 PERIODONIUM ION

The structure of the 10-I-4 periodonium ion of bis[alpha,alpha-bis(trifluoromethyl)benzenemethanolato(2-)-C2,O(alpha)]iodine(1+) triflate, salt 1a, was confirmed by an X-ray crystallographic structure determination. The periodonium ion of la was the first example of a stable cationic 10-I-4 species lacking fluorine ligands. In contrast to other periodonium ions, that of la is not hydrolyzed by atmospheric moisture nor by water in neutral or acidic media. It does not react with weak nucleophiles such as pyridine or methanol. The unreactivity of 1a is attributed to the stabilizing effects of its spirobicyclic ligand system with electronegative apical oxygen ligands and electropositive equatorial carbon ligands designed to stabilize a pseudo-trigonal-bipyramidal hypervalent species. The periodonium ion of 1a reacts with stronger nucleophiles by attack at iodine. Treatment of the 10-I-3 tetra-n-butylammonium 2-[3,3-bis(trifluoromethyl)-1,2-benziodoxol-1(3H)-yl]-alpha,alpha-bis(trifluoromethyl)-benzenemethanolate (6) with bromine gave the 12-I-5 bis[alpha,alpha-bis(trifluoromethyl)benzenemethanolato(2-)-C2,O(alpha)]bromoiodine (8b), the first example of a stable 12-I-5 bromoperiodinane. Treatment of alkoxydiaryliodinane 6 with chlorine gave 12-I-5 chloroperiodinane 8a. Treatment of 8b with trifluoromethanesulfonic (triflic) anhydride gave the very stable 10-I-4 periodonium salt 1a. Treatment of gb with trifluoroacetic acid gave nearly equal amounts of iodinane 9 and 10-I-4 periodonium trifluoroacetate lb, with oxidation of the bromide to bromine. Reaction with excess hydroxide ion is postulated to produce the 12-I-5 periodinanide oxide anion 10a. Reaction with excess tert-butylamine provides the analogous 12-1-5 adduct 1 la. Reaction with phenyllithium gives the 10-I-4 adduct 12, isolable as a crystalline solid. Addition of triflic acid to a solution of 10a, 11a, or 12 regenerates the periodonium ion of la.