Biscyclopentadienylzirconium(IV) η3-propargyl/allenyl complexes

Reactions of each Cp2Zr(Me)Cl and Cp2ZrCl2 with PhCCCH2MgBr afford the η3-propargyl/allenyl complexes Cp2Zr(Me)(η3-CH2CCPh) (1) and Cp2Zr(CH2CCPh)2 (2), respectively. Both products were characterized by a combination of EI mass spectrometry and 1H- and 13C-NMR spectroscopy, and the structure of 1 was elucidated by a single-crystal X-ray analysis. Molecules of 1 contain an unsymmetrically ligated η3-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) Å. Within the CH2CCPh ligand, C(1)C(2)=1.344(5), C(2)C(3)=1.259(4) Å and C(1)C(2)C(3)=155.4(3)°. The latter set of data indicates that a σ, π-allenyl resonance structure makes a relatively large contribution to the bonding description in 1 compared to a σ, π-propargyl resonance structure. The fragment ZrC(10)C(1)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 1H-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 1H-NMR spectra suggest that a rapid exchange of the modes of bonding of η3-propargyl/allenyl and η1-propargyl ligands may occur, with a probable participation of another ZrC3H2Ph bonding mode, possibly η1-allenyl.