Alkoxy- and aryloxyboratabenzene complexes of zirconium

Addition of primary and secondary alcohols to C5H5B-PMe3 (2) affords 1-alkoxyboracyclohexa-2,4-dienes hn high yields. Deprotonation of these;boracyclohexadienes, using NaH or lithium diisopropylamide, followed by the reaction with ZrCl4 allows for the coordination of alkoxyboratabenzene ligands to zirconium; Thus, complexes of the type [C5H5B-OR](2)ZrCl2 (R = Et,1; Cy, 3; Ph, 4; and CH2Ph, 5) can be produced in 45-65% overall yield. The crystallographically determined molecular structure of 4 shows evidence for B-O pi orbital overlap. The linked diols 1,2-trans-cyclohexandiol and binaphthol can be used to generate ansa-type zirconium complexes 7 and 9, respectively. When 1, 3, 4, or 5 react with (AlMe3)(2) the organometallic produce is [C5H5B-Me](2)ZrCl2 (10). Cp*[C5H5B-OEt]ZrCl2 (11, Cp* = C5Me5) and (AlMe3)(2) give Cp*[C5H5B-Me]ZrCl2 (13). The complex Cp*[C5H5B(OEt)(AlMe3)]ZrCl2 (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 [C5H5B-Ph](2)ZrCl2 (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.