Biscyclopentadienylzirconium(IV) η3-propargyl/allenyl complexes

Reactions of each Cp2Zr(Me)Cl and Cp2ZrCl2 with PhC=CCH2MgBr afford the eta(3)-propargyl/allenyl complexes Cp2Zr(Me)(eta(3)-CH2CCPh) (I) and Cp2Zr(CH2CCPh)(2) (2), respectively. Both products were characterized by a combination of EI mass spectrometry and H-1- and C-13-NMR spectroscopy, and the structure of 1 was elucidated by a single-crystal X-ray analysis. Molecules of 1 contain an unsymmetrically ligated eta(3)-propargyl/allenyl group C(1)H2C(2)C(3)Ph with Zr-C(1)=2.658(4), Zr-C(2) = 2.438(3) and Zr-C(3) = 2.361(3) Angstrom. Within the CH2CCPh ligand, C(1)-C(2) = 1.344(5), C(2)-C(3) = 1.259(4) Angstrom and C(1)-C(2)-C(3)= 155.3(3)degrees. The latter set of data indicates that a sigma, pi-allenyl resonance structure makes a relatively large contribution to the bonding description in 1 compared to a sigma, pi-propargyl resonance structure. The fragment ZrC(10)C(I)C(2)C(3) (C(10)= C of Me) is contained essentially in the mirror plane that reflects the two Cp rings. Complex 1 shows no fluxional behavior in its H-1-NMR spectra over the temperature range 303-223 K. In contrast, 2 is fluxional, and its dynamic behavior persists on cooling even to 180 K. The H-1-NMR spectra suggest that a rapid exchange of the modes of bonding of eta(3)-propargyl/allenyl and eta(1)-propargyl ligands may occur, with a probable participation of another Zr-C3H2Ph bonding mode, possibly eta(1)-allenyl. (C) 2000 Elsevier Science S.A. All rights reserved.