Boratabenzene complexes of zirconium, hafnium and chromium

Boratabenzene (C₅H₅B-R) ligands have been used as cyclopentadienyl (Cp) substitutes in the preparation of complexes of zirconium, hafnium and chromium. The reaction of 2 Na(C₅H₅B-OEt) with ZrCl₄ results in the formation of (C₅H₅B-OEt) ₂ZrCl₂ in good yield. This complex can be activated using methylaluminoxane (MAO) to give a catalyst which oligomerizes ethylene to straight chain α-olefins. Other M(C₅H₅B-OR) (M = Li, Na) ligands were prepared by the reaction of R′OH (R′ = Cy, Ph, CH₂Ph, SiPh₃) with C₅H₅B-PMe₃ followed by deprotonation with NaH or LDA. The corresponding zirconium complexes were prepared by the reaction of 2 M(C₅H₅B-OR′) with ZrCl ₄. Linked structures were prepared starting with ±-binaphthol, trans-1,2-cyclohexanediol and Ph₂Si(OH)₂. All of the metal complexes were studied for ethylene oligomerization upon activation with MAO and were compared against (C₅H₅B-R) ₂ZrCl₂/MAO (R = Me, Ph). (C₅H₅B-OEt) ₂ZrCl₂ and CP*(C₅H₅B-OEt)ZrCI ₂ were studied for OEt/Me exchange reactions with trimethylaluminum. An intermediate, CP[C₅H₅B-OEt(AlMe₃)]ZrCl ₂ was isolated and characterized by X-ray crystallography.; The reactions involving (C₅H₅B-R)₂ZrCl ₂/MAO (R = Me, OEt, OCH₂Ph) were investigated using 11B NMR. The data suggests that exchange with Al-Me occurs for R = OCH₂Ph, but not R = OEt. This led to the development of the selective (C₅H₅B-OMe)₂ZrCl₂ and non-selective (C₅H₅B-OtBu)₂ZrCl₂ precatalysts as a result of their ability to undergo exchange. Mixtures of (C₅H₅B-OMe)₂ZrCl₂/MAO were studied for their reactions with 1-decene as a function of MAO composition.; A new reaction for the formation of boratabenzene zirconium and hafnium complexes was developed. This involves the direct reaction of a neutral Lewis base adduct of borabenzene C₅H₅B-L and a transition metal alkyl or amide. A similar reaction was used to prepare alkylcyclopentadienyl group 4 complexes from M(CH₂Ph)₄ and a fulvene. 6,6-Dimethylfulvene reacts with M(NMe₂)₄ to give a 2-propenyl(cyclopentadienyl) metal complexes and dimethylamine.; The reaction of boratabenzene anions and their surrogates with CrCl ₃(THF)₃ leads to reduction of the metal. The reaction of α-complexes of Cr(III) with C₅H₅B-L gives the expected products (C₅H₅B-R)CrX₂(L) (R = Me, Ph; X = Cl, R; L = PMe₃, Py). These can be activated to give catalysts for the polymerization of ethylene. Preliminary studies on the copolymerization of ethylene and 1-hexene are presented.