abstract
Reactions of (Bn(2)Cyclam)ZrCl(2) (1) (where Bn(2)Cyclam = trans-N,N'(PhCH(2))(2)Cyclam) with appropriate alkylating reagents produced (Bn(2)Cyclam)ZrR(2) (R = Me (2), CH(2)Ph (3), (n)Bu (4), CCPh (5)). Activation of the ortho C-H bond of the two macrocycle benzyl substituents in complexes 2, 3, and 4 was thermally induced, leading to the formation of a bis(ortho-metalated) complex, ((C(6)H(4)CH(2))(2)Cyclam)Zr (6). This reaction proceeds along with RH elimination and converts the original dianionic tetracoordinated cyclam in a tetraanionic hexacoordinated ligand where two new Zr-C(Ph) bonds complete the metal sphere. Treatment of 6 with one equivalent of HC equivalent to CPh led to ((C(6)H(4)CH(2))BnCyclam)Zr(CCPh) (7) via protonation of one Zr-C(Ph) bond by phenylacethylene. Further reaction of 7 with an excess of HC equivalent to CPh led to 5. The reactions of 2 and 3 with B(C(6)F(5))(3) are strongly solvent dependent. Solvent-stabilized cationic species of formula [(Bn(2)Cyclam)ZrR(Solv)]-[RB(C(6)F(5))(3)] were obtained from reactions of 2 in CD(2)Cl(2) (10) or d(8)-THF (12) and from 3 in d(8)-THF (9). The reactions of 3 in CD(2)Cl(2) or d(8)-toluene gave [(Bn(2)Cyclam)Zr(eta(2)-CH(2)Ph)][PhCH(2)B(C(6)F(5))(3)] (8). Finally, the reaction of 2 in d(8)-toluene led to [(Bn(2)Cyclam)Zr(C(6)F(5)){CH(2)B(C(6)F(5))(2)}] (14); the precursor of the latter is the zwitterionic [(Bn(2)Cyclam)Zr(CH(3)){CH(3)B(C(6)F(5))(3)}] (11), which then undergoes methane elimination and C(6)F(5) migration from boron to zirconium. The mechanism of this reaction was studied by DFT and revealed that (i) methane elimination is assisted by one alpha-agostic C-H bond and (ii) migration of the C(6)F(5) ring is supported by one bridging fluorine bond between the zirconium and one of the C(6)F(5) rings that remains bonded to boron.
keywords
MOLECULAR-ORBITAL METHODS; OLEFIN POLYMERIZATION CATALYSIS; EFFECTIVE CORE POTENTIALS; EXTENDED BASIS-SETS; VALENCE BASIS-SETS; POLARIZABLE CONTINUUM MODEL; METALLOCENIUM ION-PAIRS; TRANSITION-METAL ATOMS; GAUSSIAN-BASIS SETS; MAIN-GROUP ELEMENTS
subject category
Chemistry
authors
Munha, RF; Antunes, MA; Alves, LG; Veiros, LF; Fryzuk, MD; Martins, AM
our authors
Rui Munhá
Post-doc FellowshipGroups
acknowledgements
We are grateful to Fundacao para a Ciencia e Tecnologia, Portugal, and NSERC for funding. We would like to thank Dr. Brian O. Patrick from University of British Columbia for collecting the data of compound 3. We would also like to thank the Portuguese NMR Network (IST-UTL Centre) for providing access to the NMR.