Compounds for use in catalyst compositions for the production of polyolefins

The present invention relates to compds. according to formula I, wherein: R1 is a cyclopentadienyl moiety or a moiety comprising a cyclopentadienyl ring structure; R2 is a moiety M(R5)​2 or MR5, wherein M is a metal selected from hafnium, titanium or zirconium, and R5 is F, Cl, I, Br or an alkyl-​moiety comprising 1 to 10 carbon atoms, preferably Me, benzyl, butadiene or pentadiene; R3 is H, an alkyl or aryl moiety comprising 1 to 10 carbon atoms, or a moiety comprising N or O and 1 to 15 carbon atoms; R4 is H, an alkyl or aryl moiety comprising 1 to 10 carbon atoms, or a moiety comprising N or O and 1 to 15 carbon atoms, or a halogen; wherein if R3 is H, R4 is a moiety other than H, and if R4 is H, R3 is a moiety other than H; each R6 is individually selected from H, a halogen, an alkyl moiety, an aryl moiety, a halogen-​substituted alkyl moiety, a halogen-​substituted aryl moiety, an alkoxy moiety, a siloxy-​moiety, or a nitrogen-​contg. moiety, preferably H. Such compds. may be used in a catalyst system for olefin polymn., particularly ethylene copolymn., providing at least one of a high catalyst activity, a high comonomer incorporation, and​/or a high mol. wt. polymer.