Synthesis, Reactivity, and Photophysical Properties of Cyclometalated 6-Arylphenanthridines

Abstract

Cyclometalation reactions proceeding by a concerted metalation-deprotonation mechanism are recognized as efficient routes toward new organometallic compounds. Using this approach, we reacted 6-(4-tolyl)phenanthridine (1) and 6-(4-(trifluoromethyl)phenyl)phenanthridine (2) with [(η5-C5Me5)MCl2]2 (M = Rh and Ir) in the presence of sodium acetate and obtained the respective cyclometalated products [(η5-C5Me5)MCl(1–H)] and [(η5-C5Me5)MCl(2–H)] in varying yields (20–80%). An unexpected product of 2-fold C–H bond activation [Rh(OAc)(1–H)2] (3) was also isolated. The compounds were characterized by NMR spectroscopy and mass spectrometry, and the structures of the representative complexes were determined by single-crystal X-ray diffraction analysis. In addition, the photophysical properties of the cyclometalated compounds were studied using UV–vis and luminescence spectroscopy, and the data were rationalized by DFT calculations. The reaction of [(η5-C5Me5)RhCl(1–H)] with tolane in the presence of a Cu(II) salt as an oxidant afforded 9-methyl-6,7-diphenylisoquinolino[2,1-f]phenanthridin-5-ium tetrafluoroborate, an annulated product, which suggested that the cyclometalated complexes are plausible intermediates of such annulation reactions.