Reactivity of Zn(ii), Mg(ii) and Al(iii) chlorides with a phosphinimine ligand: new tetrameric inverse crown ether structures

Abstract

Reaction of [Me₃SiNPPh₂CH₃] 1 with ZnCl₂ yields the dimer [ClZn(μ-Cl)(Me₃SiNPPh₂CH₃)]₂2 whereas treatment of 1 with AlCl₃ in THF leads to the monomeric N adduct [Cl₃Al(Me₃SiNPPh₂CH₃)] 3. Compounds 2 and 3 were found to be thermally stable and were fully characterized by NMR spectroscopy, X-ray diffraction, and elemental analysis. On the other hand, treatment of phosphinimine 1 with ⁿBuLi/ZnCl₂ or (CH₃)₂CHMgCl yields the zinc and magnesium complexes [M₄(Me₃SiNPPh₂CH₂)₄(μ₄-O)(μ₂-Cl)₂] 5 (M = Zn) and 6 (M = Mg), respectively. These compounds can be considered as new examples of inverse crown ethers in which the oxygen atom is encapsulated by polar organometallic complexes in a tetrameric arrangement. In contrast, reaction of 1 with ⁿBuLi/AlCl₃ in Et₂O under inert atmospheric conditions leads to the formation of the dimeric species [Cl₂Al(Me₃SiNPPh₂CH₂O)]₂7, which displays oxygen insertion into the C–Al bond, while the same reaction in the presence of air yields the compound [μ-(AlCl₂)(NPPh₂CH₃)]₂8 with loss of ClSiMe₃ and without oxygen insertion into the C–Al bond.