Alkoxy- and Aryloxyboratabenzene Complexes of Zirconium

Addition of primary and secondary alcohols to C 5 H 5 B−PMe 3 ( 2 ) affords 1-alkoxyboracyclohexa-2,4-dienes in high yields. Deprotonation of these boracyclohexadienes, using NaH or lithium diisopropylamide, followed by the reaction with ZrCl 4 allows for the coordination of alkoxyboratabenzene ligands to zirconium. Thus, complexes of the type [C 5 H 5 B−OR] 2 ZrCl 2 (R = Et, 1; Cy, 3; Ph, 4; and CH 2 Ph, 5 ) can be produced in 45−65% overall yield. The crystallographically determined molecular structure of 4 shows evidence for B−O π orbital overlap. The linked diols 1,2- trans -cyclohexanediol and binaphthol can be used to generate ansa-type zirconium complexes 7 and 9, respectively. When 1, 3, 4, or 5 react with (AlMe 3 ) 2 the organometallic product is [C 5 H 5 B Me] 2 ZrCl 2 ( 10 ). Cp*[C 5 H 5 B−OEt]ZrCl 2 ( 11, Cp* = C 5 Me 5 ) and (AlMe 3 ) 2 give Cp*[C 5 H 5 B Me]ZrCl 2 ( 13 ). The complex Cp*[C 5 H 5 B(OEt)(AlMe 3 )]ZrCl 2 ( 12 ) appears to be an intermediate in the conversion of 11 to 13 . A comparison of the molecular structures of 11 and 12 shows that the B−O interaction weakens and the Zr−B distance contracts upon adduct formation. Complexes 1, 3, 4, 9, 10, and [C 5 H 5 B−Ph] 2 ZrCl 2 ( 14 ) react with excess methylaluminoxane (MAO) and ethylene (1 atm) to give a Flory−Shultz distribution of olefins. For 7 /MAO, ethylene addition results in the formation of polyethylene. The overall activity toward monomer and selectivity for linear 1-alkenes of the catalyst solutions are determined by the exocyclic group of the alkoxyboratabenzene zirconium precursor.