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

Abstract

The tridentate (ONNN')-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 trigonal- bipyramidal 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-o- oxyphenylimine towards the imine moiety. © 1946 – 2014: Verlag der Zeitschrift für Naturforschung. All rights reserved.