Silanethione 2a and silaneselenone 2b—stabilized by intramolecular Si ← N coordination— are obtained as shown below. The X‐ray structure analysis of 2a, 1‐naphthyl instead of phenyl, reveals strong zwitterionic character, which might explain the unexpectedly low reactivity toward nucleophiles and electrophiles (a, X = S; b, X = Se).

SYNOPSISDiaryliodonium tetrakis (pentafluorophenyl) borate salts generate a higher reactivity than any other known diaryliodonium salt. The photochemical properties of diaryliodonium tetrakis (pentafluorophenyl) borate salts were compared to those of the diaryliodonium hexafluoroantimonate salt. The results show that these new salts are the most reactive photoinitiators in this family. In addition, diaryliodonium tetrakis (pentafluorophenyl) borate salts are soluble in low polarity media, such as epoxy silicone oils, which are rich in epoxy groups and insensitive to humidity. These salts have the advantage not to contain a heavy metal (such as antimony). The new properties generated by the use of the tetrakis (pentafluorophenyl) borate anion make the future of the cationic photopolymerization promising. 0 1996 John Wiley & Sons, Inc.

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Crystal structure analysis of 2 : Lattice contants a = 2658.5(7), b = 841.6(3), c =779.3(3) pm, orthorhombic space group Pcca, Z = 4, 1291 unique reflections with I > 00 for 65 parameters, numerical absorption correction, R = 0.027. Further details on the crystal structure investigation are available on request from the Fachinformationszentrum Karlsruhe, Gesellschaft fur wissenschaftlich-technische Information mbH, W-7514 Eggenstein-Leopoldshafen 2 (FRG), on quoting the depository number CSD-55574, the name of the author, and the journal citation.(1990) 293. 141 U. Miiller, Acta Crystallogr. Seet. C40 (1984) 915.