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Abstract

There is disclosed a process for the preparation of compounds of formula I [R Fe R.sup.2 ].sub.q.sup..sym. X.sup.q.crclbar. (I), wherein R is an anion of formula C.sub.5 H.sub.4 R.sup.1 or C.sub.9 H.sub.7, R.sup.1 is hydrogen, C.sub.1 -C.sub.6 -alkyl or halogen, R.sup.2 is a .pi.-arene, X is an anion of valency q and q is 1, 2 or 3, by reacting ferrocene or a ferrocene derivative (C.sub.5 H.sub.4 R.sup.3)Fe(C.sub.5 H.sub.4 R.sup.1) or (C.sub.9 H.sub.7).sub.2 Fe, in which R.sup.3 has one of the meanings of R.sup.1, with at least one mole of a .pi.-arene R.sup.2, followed by the optional replacement of the anion X.sup.q.crclbar. in a manner known per se, the reaction of the ferrocene or ferrocene derivative being carried out in the presence of (a) at least 1.2 mol of a mixture of Al trihalide and Zr(IV) or Hf(IV) tetrahalide, in the presence or absence of a metallic reducing agent, such that at least 0.2 mol of Zr(IV) or Hf(IV) tetrahalide and at least 0.1 mol of Al trihalide are present, or of (b) at least 1.0 mol of a Zr(IV) or Hf(IV) tetrahalide as sole Lewis acid in conjunction with at least 1.0 mol of a metallic reducing agent, the amounts being based in each case on 1 mol of ferrocene or a ferrocene derivative. The compounds of formula I containing non-nucleophilic anions can be used as photoinitiators for cationically polymerizable compounds.

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