Abstract: Catalyst component for the polymerization of alpha-olefins in solution, in suspension, in gas phase at low and high pressure and temperature or in mass at high pressures and high or low temperatures, characterised in that is defined by general formulas I or II wherein: R, equal to or different from each other, is hydrogen or a radical which contains from 1 to 20 carbon atoms; this group optionally contains heteroatoms of groups 14 to 16 of the periodic table of the elements and boron; at least one group R contains a group OSiR?3, Q is selected from a group comprising: boron or an element from groups 14 or 16 of the periodic table; m value can change from 1 to 4 and it preferably is 1 or 2; L, equal to or different from each other, is a cyclic organic group united to M through a ? bond, or it is an atom from groups 15 or 16 of the periodic table; L1 and L2, equal to or different from each other, have the same meaning of L; M is a metal from groups 3, 4, 10 of the periodic table, lanthanide or actinide.