Formation and Structures of [1,2–Bis(N-tert-butylcarbamoyl)cyclopentadienyl]zirconium Complexes – Coordination Chemistry of a “Fulvenologous” Malonic Amide Anion Ligand System

Abstract

Treatment of sodium cyclopentadienide with two molar equivalents of tert-butyl isocyanate yields sodium 1,2-bis(N-tert-butylcarbamoyl)cyclopentadienide (6). The [C5H3(1,2-CONHCMe3)2]Na reagent 6 adds to Cp2Zr(CH3)Cl (8) to yield Cp2Zr(CH3)[C5H3(CONHCMe3)2] (9). In 9 the C5H3(CONHCMe3)2 ligand is bonded to zirconium through one of its carboxamido-oxygen atoms (ĸO-coordination). Treatment of 6 with CpZrCl3(THF)2 yields CpZrCl2[C5H3(CONHCMe3)2](THF) 11. In 11 the 1,2-bis(N-tert-butylcarbamoyl)cyclopentadienide moiety serves as a Cs-symmetric chelate ligand, binding to zirconium through both carbamoyl oxygens (ĸ2O,O′-coordination). The same seven-membered metallacyclic structural type is found in the reaction products of 6 with ZrCl4(THF)2 in 1:1 and 2:1 molar ratios. The former yields the distorted octahedral complex ZrCl3[C5H3(CONHCMe3)2](THF) (12), the latter gives the chiral octahedral system ZrCl2[C5H3(CONHCMe3)2]2 (13). In solution, complex 13 undergoes a thermally induced enantiomerization process (Λ → Δ interconversion), for which a Gibbs activation energy of ΔG‡enant = 14.0 ± 0.3 kcal mol−1 was determined by dynamic 1H-NMR spectroscopy. The ĸ2O,O′-coordination of the [C5H3(1,2-CONHCMe3]− ligand in the complexes 11, 12, and 13 was secured by X-ray crystal structure analyses.