Synthesis, structure, and spectroscopy of two benzil-based α-diimine ligands and their palladium(II) complexes

• Published in: Journal of coordination chemistry Vol. 66; no. 8; pp. 1350 - 1362
• Main Authors: Kubota, Miles, Covarrubias, Daniel, Pye, Cameron, Fronczek, Frank R., Isovitsch, Ralph
• Format: Journal Article
• Language: English
• Published: Routledge 01.04.2013
• Subjects: Absorption spectra; Band spectra; Bands; Benzil-based α-diimine ligands; Chloroform; Conjugation; Electronic absorption spectra; Electronics; Ligands; Palladium(II) complexes; X-ray crystal structure; X-rays
• ISSN: 0095-8972; 1029-0389
• DOI: 10.1080/00958972.2013.778402

Two α-diimine ligands were prepared in 60-70% yield via p-toluenesulfonic acid-catalyzed condensation reactions from benzil with 4-bromoaniline and with p-anisidine. Palladium(II) complexes were prepared from both ligands in 70-80% yield. X-ray structures were obtained for the ligand prepared from p-anisidine and its palladium(II) complex. A notable feature observed in the former was its unconjugated C-N double bonds, both in the (E)-configuration. The latter structure possessed two molecules of the metal complex in its unit cell, both of which have diimine cores with a degree of conjugation and a nonideal square-planar geometry around palladium caused by the small bite angles (79.61(3) and 79.15(3)°) of the diimine ligands. Solution-phase electronic absorption spectra of the ligands in chloroform have two bands from π→π ∗ and n→π ∗ transitions at 269-345 nm. Absorption spectra of the complexes in chloroform exhibited bands attributed to ligand-centered transitions that were red-shifted as compared to free ligands. Only the spectrum obtained from a chloroform solution of the palladium(II) complex with the diimine ligand prepared from p-anisidine featured a band at approximately 520 nm, which was assigned to a combination of d π (Pd)→π ∗ and n(Cl)→π ∗ transitions.