Hetero Cu(III)–Pd(II) Complex of a Dibenzo[<i>g</i>,<i>p</i>]chrysene-Fused Bis-dicarbacorrole with Stable Organic Radical Character

Abstract

Bis-dicarbacorrole (bis-H₃) with two adj-CCNN subunits was synthesized by incorporating a dibenzo[g,p]chrysene moiety into the macrocyclic structure. The two trianionic cores in bis-H₃ can stabilize two Cu(III) ions (bis-Cu) or concurrently a Cu(III) cation and a Pd(II) ion in the form of a hetero bis-metal complex (mix-Cu/Pd). As prepared, mix-Cu/Pd displays organic π radical character, as confirmed by various techniques, including electron paramagnetic resonance spectroscopy, cyclic voltammetry, femtosecond transient absorption measurements, and DFT calculations. Radical formation is ascribed to one-electron transfer from the dicarbacorrole backbone to the Pd center allowing the d⁸ Pd(II) center to be accommodated in a square planner coordination geometry. Nucleus-independent chemical shift and anisotropy of the induced current density calculations provide support for the conclusion that bis-H₃ and bis-Cu both display antiaromatic character and contain two formally 16 π-electron dicarbacorrole subunits. On this basis, we suggest that mix-Cu/Pd is best considered as containing a fused 15 π-electron nonaromatic radical subunit and a 16 π-electron antiaromatic subunit. The spectroscopic observations are consistent with these assignments.