Synthetic routes to zinc complexes supported by sterically demanding bis(phosphinimino)methyl ligands are reported. Two aryl-substituted ligand precursors have been utilised, [CH2(Ph2P=NC6H2Me3-2,4,6) 2], 1, and [CH2(Ph2P=NPh)(Ph2P=NC6H2 Me3-2,4,6)], 2. The second of these is the first example of an asymmetric bis(phosphinimino)methane. These ligands are converted to three-coordinate RZnX complexes (R = 1; X = Me, N(SiMe3)2; R = 2; X = Me) with either C2 or Cs symmetry in solution by reaction with either ZnMe2 or Zn[N(SiMe3)2]2 in toluene. All three derivatives have been shown to exist as three-coordinate monomers in the solid state by X-ray diffraction analysis. Protonolysis of these compounds with the bulky phenol 2,4-tBu2C6H3OH or triphenylmethanol resulted in the isolation of a series of three-coordinate aryloxy or alkoxyzinc derivatives. In contrast, reaction with less sterically demanding alcohols resulted in protonation of the bis(phosphinimino)methyl ligand. A similar result was obtained from reaction of RZnMe (R = 1) and triphenylsilanol and the product is the first example of a bis(triorganosiloxy)zinc compound to be structurally characterised. All the compounds have been examined for activity in ring opening polymerisation catalysis of rac-lactide. The aryloxy and triphenylmethoxy derivatives are active catalysts; however, no evidence of true 'living' behaviour or stereocontrol of diastereomer insertion has been observed.
|Number of pages||9|
|Journal||Journal of the Chemical Society. Dalton Transactions|
|Publication status||Published - 21 Dec 2002|
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