Complexed nitrogen heterosuperbenzene: The coordinating properties of a remarkable ligand

Tetra-peri-(tert-butyl-benzo)-di-peri-(pyrimidino)-coronene 1, the parent compound of the nitrogen heterosuperbenzene family N-HSB, is employed as a novel monotopic ligand in the formation of [Pd(eta(3)-C3H5)(1)]PF6 2 and [Ru(bpy)(2)(1)](PF6)(2) (where bpy = 2,2'-bipyridine 3a and d(8)-2,2'-bipyridine 3b). These N-coordinated complexes are fully characterized by H-1 NMR and IR spectroscopy and ESI-MS. Metal coordination has a profound effect on both the absorption and the emission properties of 1. Pd(II) coordination causes a red-shift in the low-energy absorptions, a decrease in the intensity of the n-pi* absorptions, and a quenching of the emission. Ru(II) coordination causes absorption throughout the visible region and creates two new complexes that join an elite group of compounds known as "black" absorbers. 3a and 3b possess two discernible (MLCT)-M-1 bands. The one of exceptionally low energy (lambda(max) = 615 nm) has an associated (MLCT)-M-3 emission ( lambda(max) = 880 nm) due to the unprecedented electron delocalization and acceptor properties of the rigid aromatic N-HSB 1. Both Ru(II) complexes are near-IR emitters with unusually protracted emission lifetimes of 320 ns at 77 K. They are photochemically inert, and their electrochemical properties are consistent with the presence of a low-lying pi* orbital on 1. The first two reversible reductions (E-1/2 (CH3CN), -0.54 V, -1.01 V vs SCE) are due to the stepwise reduction of 1 and are anodically shifted as compared to [Ru(bpy)(3)](2+). Temperature- and concentration-dependent NMR studies on 2 and 3a suggest extensive aggregation is occurring in solution.