Synthesis, characterization and spectroscopic properties of 1,2-diiminetricarbonylrhenium(I)chloride complexes with o-benzoquinone diimines as ligands

The novel organometallic complexes Re(BQDI-R)(CO)(3)Cl with BQDI-R = 4,5-su bstituted o-benzoquinone diimines (R = H, Me, OMe, Cl) have been prepared a nd characterized by elemental analysis, IR, MS and H-1-NMR spectroscopic me thods. Their electronic spectra display a long-wavelength absorption band w hich can be ascribed to a metal-to-ligand charge transfer (MLCT) transition from Re(I) to the low-lying pi*-orbitals of the o-benzoquinone diimine lig and, even though a significant degree of metal-ligand orbital mixing is occ urring. The energy of this absorption band correlates very well with the na ture of the substituents R in the 4,5-position of BQDI-R. In solvent series of decreasing polarity, the MLCT absorption maximum is shifted to longer w avelengths (negative solvatochromism). None of the Re(BQDI-R)(CO)(3)Cl comp lexes studied is photoluminescent at 298 or 77 K. (C) 2000 Elsevier Science S.A. All rights reserved.