Palladium Complexes of Perylene Diimides: Strong Fluorescence Despite Direct Attachment of Late Transition Metals to Organic Dyes

We prepared the first σ-bonded metal complexes of widely utilized
organic dyes, perylene tetracarboxylic acid diimides (PDIs). These
1,7-dipalladium PDI complexes were synthesized by C−Br oxidative
addition of 1,7-dibromo-N,N‘-dicyclohexyl PDI (Br2PDI) to Pd(0)
phosphine complexes bearing triphenylphosphine and bischelating
1,2-bis(diphenylphosphino)ethane (dppe). The structures of Pd−PDI complexes were elucidated by single-crystal X-ray analysis.
Surprisingly, despite direct attachement of two late transition metal
centers, Pd−PDI systems are highly fluorescent (Φ = 0.65 and
0.22 for triphenylphosphine and dppe systems, respectively). This
is rationalized in terms of weak electronic interactions between
the metal centers and PDI π-system, as revealed by TD-DFT
calculations.