Properties of alkynyliodonium salts

All pure alkynyliodonium species are microcrystalline solids. Their solubility is limited to non-nucleophilic polar solvents. They are insoluble in hydrocarbon, aromatic, ether, and other nonpolar solvents. They tend to decompose in methanol and ethanol as well as in dimethyl sulfoxide (DMSO), dimethylformamide (DMF), etc. With the exception of the parent ethynyliodonium salt they are also insoluble in water. The best solvent seems to be acetonitrile. Reactions may also be carried out under initially heterogeneous conditions in solvents like CH2CI2, CHCI3 where the mixture becomes homogeneous as the reaction proceeds. 

The stability of alkynyliodonium species is highly dependent upon both the counter-anion and the -substituent on the alkyne. The more nucleophilic the counter-ion, the less stable the iodonium salt. Hence, the order of stability as a function of counterion is approximately  

In general, the parent ethynyliodonium salts and simple alkyl-substituted compounds ate the most stable and may be indefinitely stored as pure solids in a refrigerator. The P-func-tionalized (11) and bis-iodonium (34-36) compounds are somewhat less stable but may be isolated, characterized, and stored cold for several days in pure form. The stability of both the diynyliodoniums 26 and the dialkynyl compounds 28 are greatly dependent upon the substituents R. The greater the steric bulk of R, the more stable the compound. Perhaps, the least stable, fully characterized species is the bis-iodonium diyne 32, which decomposes rapidly above — 20°C and hence is best made fresh and used in situ. 

The large majority of alkynyliodonium salts, and all alkyl-substituted ones are white or off-white in color. Some P-functionalized (11) and conjugated bis-iodonium (34, 38) compounds are yellow. 

Although a few plosions have been reported [43] with Phi—O —IPh2BF4 and also with perchlorates, we have not experienced any problems to date with any of the alkynyliodonium triflates or tosylates. Nevertheless, it is prudent to exercise due caution in the handling of all iodonium species. 

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