(Allyl)zirconium(IV) Complexes with the N,N′ ‐bis(trimethylsilyl)benzamidinato (“siam”) Ligand — Molecular Structures and η¹–η³ Interconversions of the Allyl Groups

Complexes of the type (siam) 2 Zr(allyl) 2 ( 1a ) and (siam)Zr(allyl) n Cl m are described ( 2a : n = 1, m = 2; 2b : n = 2, m = 1; 2c : n = 3, m = 0; siam: N,N′ ‐bis(trimethylsilyl)benzamidinato group). The molecular structure of 1a shows that both allyl groups are differently bonded. One allyl ligand is η 3 ‐, the other η 1 ‐coordinated. The X‐ray crystal structure of the tris‐(allyl) complex 2c shows a chiral molecule with two η 3 ‐allyl ligands. The third allyl ligand is coordinated in a mode intermediate between η 3 and η 1 , thus serving as a model for an intermediate in the η 3 ‐η 1 intramolecular rearrangement of the allyl ligands observed in solution. Temperature‐dependent 1 H‐ and 13 C‐NMR spectra of 1a, 2b and 2c indicate a rapid η 1 ‐η 3 rearrangement of the allyl groups at 60°C. At −50°C two different coordination modes of the allyl groups can be observed in the case of 2b and 2c .