1048008-81-6Relevant articles and documents
Synthesis, structures, and dynamic features of d0 zirconocene-allyl complexes
Vatamanu, Mihaela
, p. 3683 - 3694 (2014)
The reaction of [Cp2ZrMe][MeB(C6F5) 3] (1) with 2,4-dimethyl-1-pentene and 2,4-dimethyl-1-heptene, respectively, in C6D5Cl at 25 °C results in irreversible formation of the cationic Cp2Zr+-allyl complexes [Cp2Zr(η3-CH2C(CH 2R)CH2)]+ (2a, 3a) and [Cp2Zr(η 3-CH2C(Me)CHR)]+ (2b, 3b) (2a,b, R = CH(CH 3)2; 3a,b, R = CH(CH3)CH2CH 2CH3) and release of methane. The Cp2Zr +-allyl complexes were characterized with regard to their structures and rearrangement dynamics of their allyl ligands by NMR spectroscopy. Variable-temperature 1H NMR experiments show that the allyl ligands of complexes 2a,b and 3a,b are fluxional. The fluxional behavior in these complexes is mainly due to a mechanism that involves η3 to η1 isomerization, rotation of the allyl carbon-carbon π unit about the carbon-carbon σ bond, and reversion to the η3- allyl coordination mode, when both the allyl syn/anti hydrogen exchange and apparent Cp ligand exchange occur. The rotation of the C-C unit about the allyl carbon-carbon σ bond also results in a reversal of the η3-allyl coordination face relative to the Cp2Zr + moiety. A second mechanism which may account for the apparent Cp ligand exchange in the Cp2Zr+-allyl complexes under investigation consists of rotation of the η3-coordinated allyl ligand about the metal-allyl bond. The free energy of activation for the exchange processes, as estimated from the coalescence temperature of the two Cp ligands, is between 54 and 60 kJ/mol. Aside from the intramolecular allyl exchange processes described above, this study also shows that the η1- and η3-coordinated allyl forms of a particular Zr-allyl complex coexist in solution and that the equilibrium composition of these species is temperature dependent. The Cp2Zr+-allyl complexes described in this paper serve as models for similar cationic Cp 2Zr+-allyl intermediates implicated in zirconocene-catalyzed alkene polymerization reactions.
