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Abstract

The tetra-halides of zirconium and hafnium were reacted with one equivalent of the potentially tridentate hybrid ligand, N(SiMe₂CH₂PR₂)2-, (R = Me, i-Pr, t-Bu) to generate the corresponding mono-ligand complexes MCl₃{N(SiMe₂CH₂PR₂)₂), (M = Zr, Hf). Based on the results obtained from the solution spectroscopic data and the single crystal X-ray diffraction analyses of HfCI₃{N(SiMe₂CH₂PMe₂)₂> and ZrCl₃{N(SiMe₂CH₂P(i-Pr)₂)₂) the stereochemistries of all the MCI ₃{N(SiMe ₂CH₂PR₂) ₂) complexes were found to be meridional in solution, but both facial and meridional geometries were displayed in the solid state dependent on the ligand. The mono-ligand derivatives served as useful starting materials for the generation of zirconium- and hafnium-carbon bonds. Thus the addition of three equivalents of MeMgCl to one equivalent of MCl₃{N(SiMe₂CH₂PR₂)₂} generated the trimethyl complexes M(CH₃)₃{N(SiMe₂CH₂PR₂)₂}. When two equivalents of MeMgCl was added to the mono-ligand complexes, an inseparable mixture of the monomethyl and dimethyl derivatives was obtained. The stereochemistry of Hf(CH₃)₃{N(SiMe₂CH₂PMe₂)₂} is facial in the solid state but displays unusual fluxional behaviour in solution. This behaviour is observed for all the trimethyl derivatives as a consequence of the dissociative nature of the phosphine donors. Several possible rearrangement pathways for these compounds are discussed in an attempt to interpret this behaviour in solution.