769959-01-5Relevant articles and documents
Exploring CH-activation pathways in bifunctional zirconocene/borane systems
Hill, Michael,Erker, Gerhard,Kehr, Gerald,Froehlich, Roland,Kataeva, Olga
, p. 11046 - 11057 (2007/10/03)
The dimethylsilanediyl-bridged ansa-zirconocene dichloride 1, that contains a pendent allyl substituent at a Cp-ring, adds HB(C6F 5)2 to the vinyl group to yield the bifunctional zirconocene/borane complex 2. Substituted benzimidazoles were added to the strongly electrophilic borane moiety as protective groups, which allowed subsequent chloride versus -CH2SiMe3 exchange at zirconium to take place by treatment with the respective alkyllithium reagent. Alternatively, the introduction of active σ-ligands at zirconium is carried out first, followed by the hydroboration reaction. This route was followed for the synthesis of the diphenyl-ansa-zirconocene/borane complex 12. Complex 12 reacts slowly in solution by intramolecular electrophilic attack of the borane at its adjacent Cp-ring, followed by deprotonation using a [Zr]-Ph group to yield the zwitterionic complex 14 featuring a borata-tetrahydroindenyl moiety as part of the ansametallocene framework. Complex 14 was characterized by X-ray diffraction. It adds PMe3 at zirconium to yield 15. Thermolysis of 12 with excess PMe3 leads to the formation of the (aryne)zirconocene complex 18, which is stabilized by PMe3 coordination to zirconium and PMe3 addition to boron. N-Methylbenzimidazole adds to the -B(C6F5)2 unit of 12 to give the 1:1 adduct 19. Thermolysis of 19 at 80 °C in benzene solution in the presence of one additional equivalent of N-methylbenzimidazole results in deprotonation of the substrate to yield the σ-N- methylbenzimidazolyl zirconium complex 20 (as a mixture of two diastereoisomers). An additional N-methylbenzimidazole ligand is bonded to the B(C6F5)2 unit in this product.
