Silicon(IV) Chelates of an (ONN')-Tridentate Pyrrole-2-Carbaldimine Ligand: Syntheses, Structures and UV/Vis Properties

Abstract

The tridentate (ONN_)-chelator properties of the pyrrole-2-(o-hydroxyphenyl)carbaldimine dianion (L2−) were explored for the neutral penta-coordinate diorganosilicon complexes LSiRR' (R,R' = Ph, Ph; Ph, Me; Ph, tBu) where the ligand L occupies the ax-eq-ax sites in a distorted trigonalbipyramidal arrangement arround the silicon atom, and for the neutral hexa-coordinate L2Si, that has a mer-coordination. Single-crystal X-ray diffraction analyses show an almost planar ligand backbone with a Si-N bond to the imine group that is shorter in hexa-coordinate L2Si than in pentacoordinate LSiRR'. In sharp contrast to the almost colorless neutral ligand LH2, both complexes show pronounced UV/Vis absorptions in the red-brown region that originate from HOMO- LUMO and HOMO-1 -LUMO transitions, and that are due to intra-ligand π-π∗ transitions from the N-ooxyphenylimine towards the imine moiety