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 ofa) 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 ofb) at least 1.

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.

Abstract: A process is described for preparing compounds of the formula I[R Fe R.sup.2 ].sub.q .sym.X.sup.q.crclbar. (I)in which R is an anion of the 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 a q-valent anion and q is 1, 2, 3 or 4, 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 in the presence of at least 1.4 moles, of a mixture of Al halide and Ti(IV) halide or (C.sub.5 H.sub.4 R.sup.1)-Ti(IV) halide if desired in the presence of a metallic reducing agent, followed if desired by the replacement of the anion X.sup.q- in a manner known per se, with the proviso that the Lewis acid mixture contains at least 0.1 mole of Al halide and at least 0.