Abstract: Transition metal complexes of the formula IL.sub.m MX.sub.n I,whereL is a ligand of the formula II ##STR1## m is 1 or 2, M is a titanium, zirconium, hafnium, vanadium, niobium, tantalum, or a rare earth metal,X is fluorine, chlorine, bromine, iodine, hydrogen, C.sub.1 -C.sub.10 -alkyl, C.sub.6 -C.sub.15 -aryl or OR.sup.1,n is 1, 2, 3, or 4 as defined herein, andR.sup.1, R.sup.2, R.sup.3, R.sup.4, and A are as defined herein,and the use of these complexes as catalysts for olefin polymerization are described herein.

Abstract: Organometallic compounds of the general formula L.sub.r M(CH.sub.2 SiR.sup.1 R.sup.2 R.sup.3).sub.m (1) where M is a transition metal of Groups IIIA to VIA of the Periodic Table of Elements, m is an integer from 1 to the prevailing valency of the metal M, L.sub.r represents the sum of any other incidental ligands attached to the metal M, r being 0 or an integer, and R.sup.1, R.sup.2 and R.sup.3 represent substituted or unsubstituted hydrocarbyl groups or hydrogen atoms, at least one of said groups having the general formula ##SPC1##Where n is an integer from 1 to 5 and Y is a group capable of donating electrons to the metal M are useful as catalysts for olefin polymerization. The compounds may be used as catalysts alone or when supported upon a matrix for example of alumina. Particularly useful compounds are those in which the transition metal M has a valency lower than the maximum valency for that metal.