Phenanthridine-Containing Pincer-like Amido Complexes of Nickel, Palladium, and Platinum

Abstract

Proligands based on bis(8-quinolinyl)amine (L1) were prepared containing one (L2) and two (L3) benzo-fused N-heterocyclic phenanthridinyl (3,4-benzoquinolinyl) units. Taken as a series, L1-L3 provides a ligand template for exploring systematic π-extension in the context of tridentate pincer-like amido complexes of group 10 metals (1-M, 2-M, and 3-M; M = Ni, Pd, Pt). Inclusion of phenanthridinyl units was enabled by development of a cross-coupling/condensation route to 6-unsubstituted, 4-substituted phenanthridines (4-Br, 4-NO, 4-NH) suitable for elaboration into the target ligand frameworks. Complexes 1-M, 2-M, and 3-M are redox-active; electrochemistry and UV-vis absorption spectroscopy were used to investigate the impact of π-extension on the electronic properties of the metal complexes. Unlike what is typically observed for benzannulated ligand-metal complexes, extending the π-system in metal complexes 1-M to 2-M to 3-M led to only a moderate red shift in the relative highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gap as estimated by electrochemistry and similarly subtle changes to the onset of the lowest-energy absorption observed by UV-vis spectroscopy. Time-dependent density functional theory calculations revealed that benzannulation significantly impacts the atomic contributions to the LUMO and LUMO+1 orbitals, altering the orbital contributions to the lowest-energy transition but leaving the energy of this transition essentially unchanged.

Luminescent Platinum(II) Complexes of N^N–^N Amido Ligands with Benzannulated N-Heterocyclic Donor Arms: Quinolines Offer Unexpectedly Deeper Red Phosphorescence than Phenanthridines

“…The crystal structure of 1 is shown in Figure 2 (the structure of 3 was previously reported 35 ). In the solid state, the ligands are rigidly planar and bind meridionally to the metal centre.…”

Site-Selective Benzannulation of N-Heterocycles in Bidentate Ligands Leads to Blue-Shifted Emission from [(P^N)Cu]2(μ-X)2 Dimers

“…5,7 Despite appearing to represent a simple extension of a quinoline  system, the CuBr (Aldrich), CuI (Aldrich) and CuCl (Acros) were purchased from commercial suppliers and used as received. 2-Bromo-4-methylaniline, 48 6-bromo-2-iodo-4methylaniline, 9 4-bromo-2-methylphenanthridine, 9 8-bromo-6-methylquinoline, 48 4diphenylphosphinophenanthridine 8 (L1) and {(4diphenylphosphino)phenanthridine}CuBr (1-Br) 8 were synthesized following published procedures. Organic solvents were dried over appropriate reagents and deoxygenated prior to use, with the exception of 1,2-dimethoxyethane and water, which were simply degassed.…”

Pseudo-octahedral nickel(ii) complexes of strongly absorbing benzannulated pincer-type amido ligands: ligand-based redox and non-Aufbau electronic behaviour

“…15 We have investigated the incorporation of benzannulated phenanthridine (3,4-benzoquinoline) moieties in diarylamido ligands. 16 In addition to producing Pt MCCs that combine strong absorption and red-shied phosphorescence, 17,18 neutral Fe-based MCCs comprised of two such ligands show strong panchromatic absorption and nanosecond charge-transfer lifetimes in their neutral forms, along with a rich redox prole. 19 Similarly strong but narrower absorption bands can also be seen with isoelectronic Co(III) analogues, as well as congeners of redox-silent Zn(II) and Ga(III) ions.…”