Ruthenium-Amine Electronic Coupling Bridged through Phen-1,3-diyl Versus Phen-1,4-diyl: Reverse of the Charge Transfer Direction

Three tris-bidentate
cyclometalated ruthenium complexes with a
di­(p-anisyl)­amino [5(PF6)],
di­(p-tolyl)­amino [6(PF6)],
or di­(p-chlorophenyl)­amino [7(PF6)] substituent on the cyclometalating phenyl ring have been
prepared, where the amine nitrogen is in the meta position to the
cyclometalated site (bridged through the phen-1,3-diyl unit). The
structure of 6(PF6) has been confirmed by
single-crystal X-ray diffraction analysis. Two consecutive redox waves
are evident at +0.48 and +0.87 V versus Ag/AgCl for 5(PF6), +0.51 and +1.02 V for 6(PF6), and +0.53 and +1.18 V for 7(PF6), respectively.
The first wave is assigned to the Ru­(II/III) process, and the second
wave is attributed to the N­(0/+) process. After one-electron oxidation
using SbCl5, these complexes display distinct absorptions
in the near-infrared region, which are assigned to the nitrogen-to-ruthenium
intervalence charge-transfer (ICVT) transitions. The energies of the
IVCT transitions vary linearly versus the potential splitting of the
Ru­(II/III) and N­(0/+) process. The charge-transfer direction in these
complexes is reversed with respect to a previously reported ruthenium–amine
system where the amine nitrogen is in the para position to the cyclometalated
site (bridged through the phen-1,4-diyl unit).