Catalyst components and catalysts for the polymerization of alpha-olefins

Components of catalysts for polymerizing olefins comprising the solid product of the reaction of:

• (a) a halogenated Ti compound containing at least a Ti-halogen bond, and
• (b) an electron-donor compound not containing active hydrogen atoms (ED) reacted as such or as a complex with product (c), said complex being obtained without cogrinding, and employing in such amount, that from 0.2 to 4 moles of compound (ED) per gram atom of Ti of component (a) are present in the catalytic component with
• (c) the solid product, prepared without cogrinding, of the reaction between at least an electron-donor compound containing active hydrogen atoms (HED), selected from aliphatic, cycloaliphatic and aromatic alcohols and thioalcohols having 1 to 20 C, phenols and thiophenols having 6 to 20 C and the silanols having 1 to 20 C, and a Mg dihalide, or complexes thereof with an (ED) compound, said Mg dihalide being obtained by decomposition, with halogenating agents other than the Ti compounds of (a), of reaction product (d) of an organometallic Mg compound of general formula R.sub.m MgX.sub.n, in which R is an alkyl, aryl, cycloalkyl or alkenyl radical having 1 to 20 C, or a group OR, and X is a halogen, R, OR in which R has the meaning as specified or COX' in which X' is a halogen, m is 0<m.ltoreq.2, n is 0<n<2 and M+n=2;
• with a silicium compound selected from polysiloxanes, hydropolysiloxanes, silanols and polysilanols, product (c) being reacted as such without any intermediate pretreatment with an Al-alkyl compound.