A process for preparing dihalide or monohalide metallocene compounds comprising contacting a compound of formula (II) (Cp)(ZR.sup.1.sub.m).sub.n(A).sub.rML'.sub.y (II) wherein Cp is a cyclopentadienyl radical; (ZR.sup.1.sub.m).sub.n is a divalent bridging group between Cp and A; A is a cyclopentadienyl radical or O, S, NR.sup.2, PR.sup.2 wherein R.sup.2 is an hydrocarbon radical, M is zirconium, titanium or hafnium. L' is an hydrocarbon radical, r ranges from 0 to 2 and y is equal to 4; with an halogenating agent selected from the group consisting of: T.sup.1L.sub.w.sup.1 wherein T.sup.1 is a metal of groups 3 13 of the periodic table; L is halogen and w.sup.1 is equal to the oxidation state of the metal T.sup.1; T.sup.2L.sub.w.sup.2 wherein T.sup.2 is a nonmetal element of groups 13 16 of the periodic table (new IUPAC version); and w.sup.2 is equal to the oxidation state of the element T.sup.2; O=T.sup.3L.sub.w.sup.3 where T.sup.3 is a selected from the group consisting of C, P and S; O is an oxygen atom bonded to T.sup.3 through a double bond; and w.sup.3 is equal to the oxidation state of the element T.sup.3 minus 2; R.sup.6C(O)L, wherein R.sup.6 is an hydrocarbon radical; L.sub.2 and HL.