Synthesis, structure and catalytic activity of new iminophenolato complexes of scandium and yttrium

The reaction of equimolar amounts of 2-(2,4,6-Me3C6H2NCH)(6-But)C6H3OH (HL1) with M(CH2SiMe3)3(THF)3 (M=Sc or Y) under mild conditions gives M(CH2SiMe3)2(THF)(L1). The trigonal-bipyramidal structure of these dialkyls was confirmed crystallographically for M=Sc. Whereas the scandium complex is stable in solution at room temperature, the yttrium derivative slowly disproportionates to give Y(L1)3 which is also accessible from Y(CH2SiMe3)3(THF)3 and three HL1. The X-ray structure of Y(L1)3 indicates a chiral tris-chelate complex. While the reaction of the related ligand (2-CyNCH)(6-But)C6H3OH (HL2, Cy=cyclohexyl) with Sc(CH2SiMe3)3(THF)3 gives the expected dialkyl Sc(CH2SiMe3)2(THF)(L2), the reaction with the yttrium analogue affords the six-coordinate monoalkyl product Y(CH2SiMe3)(THF)(L2)2. This product is stable in solution towards disproportionation. The reaction of Y[N(SiMe3)2]3 with (2-C6F5NCH)(6-But)C6H3OH (HL3) affords Y{N(SiMe3)2}(L3)2 and Y(L3)3. Both complexes are seven-coordinate in the solid state due to Y⋯F co-ordination to the C6F5 substituents. The scandium alkyl complexes are efficient catalysts for the ring-opening polymerisation of ε-caprolactone.