Highly Variable Zr–CH₂–Ph Bond Angles in Tetrabenzylzirconium: Analysis of Benzyl Ligand Coordination Modes

Analysis of a monoclinic modification of Zr­(CH₂Ph)₄ by single-crystal X-ray diffraction reveals that the bond angles Zr–CH₂–Ph in this compound span a range of 25.1°, which is much larger than previously observed for the orthorhombic form (12.1°). In accord with this large range, density functional theory calculations demonstrate that little energy is required to perturb the Zr–CH₂–Ph bond angles in this compound. Furthermore, density functional theory calculations on Me₃ZrCH₂Ph indicate that bending of the Zr–CH₂–Ph moiety in the monobenzyl compound is also facile, thereby demonstrating that a benzyl ligand attached to zirconium is intrinsically flexible, such that its bending does not require a buffering effect involving another benzyl ligand.