Synthesis and Coordination Chemistry of Phenanthridine-Containing Monoanionic N^N-^N Pincer Motifs
Date
2020-12
Authors
Mandapati, Pavan
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Abstract
This thesis involves a series of projects that explore the synthesis of phenanthridine-containing monoanionic N^N-^N ‘pincer’ motifs as ancillary ligands which can stabilize group 10 transition metals (Ni, Pd and Pt). Phenanthridines are 14π electron annulated tricyclic aromatic N-heterocycles with extended π-conjugation. Phenanthridines have been reported in the context of chemical synthesis, material synthesis, and catalysis, and show interesting photophysical and luminescence properties which find applications in bio-imaging techniques as fluorescent markers. Compared to its congener quinoline, however, phenanthridines have been rather underexplored in coordination chemistry. This thesis demonstrates how functionalized phenanthridines can be easily accessed in one-pot syntheses via palladium catalyzed Suzuki C-C coupling followed by condensation at high temperatures. With a route to functionalized phenanthridines with electron donating groups (Me, tBu) and electron withdrawing groups (CF3) in hand, they were incorporated into ‘pincer’ ligand frameworks using Buchwald-Hartwig C-N coupling, to isolate a series of phenanthridinyl/quinolinyl containing symmetric and asymmetric monoanionic N^N-^N proligands (L1-L16).
My subsequent work then focused on examining the effects of systematic benzannulation in pincer-type ligands, through studies of the electronic, material and catalytic properties compared to quinoline in the presence of transition metals. To study these properties, a series of square-planar metal complexes of Group 10 metals (Ni, Pd and Pt) were synthesized containing both phenanthridines and quinolines. Platinum(II) complexes of phenanthridinyl/quinolinyl containing symmetric and asymmetric monoanionic N^N-^N ligands are photo-emissive in nature. These emissive complexes with electron donating groups (Me, tBu) and electron withdrawing groups (CF3) provided a platform to study the effect of site selective benzannulation and ring substituent effects on highest occupied molecular orbitals (HOMO) and lowest unoccupied molecular orbitals (LUMO) and their impact on absorption and emission properties. The results from these studies will be discussed in the following chapters. Although these complexes exhibit interesting photophysical properties, the complexes are relatively less soluble when compared to metal complexes of bis(quinolinyl)amine, in common organic solvents due to strong π-π stacking interactions, which hindered the opportunity to explore reactivity of the complexes. To overcome the issue of solubility, a new ligand design approach was made to synthesize proligands with solubilizing NMe2 groups that help break the planarity of their coordination complexes. Divalent nickel and palladium chloride complexes were synthesized with these proligands, the complexes were soluble in common organic solvents. Moreover, phenanthridine-containing nickel(II) chloride complexes of these more soluble ligands were found to be active catalyst for alkylation of azoles.
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Keywords
Phenanthridine, mono anionic 'pincer', N^N-^N pincer frameworks, catalysis, coordination chemistry
Citation
Mandapati, P.; Giesbrecht, P. K.; Davis, R. L.; Herbert, D. E. Phenanthridine-Containing Pincer-like Amido Complexes of Nickel, Palladium, and Platinum. Inorg. Chem. 2017, 56, 3674−3685.
Mandapati, P.; Braun, J. D.; Killeen, C.; Davis, R. L.; Williams, J. A. G.; Herbert, D. E. Luminescent Platinum(II) Complexes of N^N‑^N Amido Ligands with Benzannulated N-Heterocyclic Donor Arms: Quinolines Offer Unexpectedly Deeper Red Phosphorescence than Phenanthridines. Inorg. Chem. 2019, 58, 14808−14817
Mandapati, P.; Braun, J. D.; Lozada, B. L; Williams, G. A. J.; Herbert, D. E. Deep-Red Luminescence from Platinum(II) Complexes of N^N-^N‐Amido Ligands with Benzannulated N‐Heterocyclic Donor Arms. Inorg. Chem. 2020, 59, 12504–12517.
Mandapati, P.; Braun, J. D.; Sidhu, B. K.; Wilson, G.; Herbert, D. E. Catalytic C−H Bond Alkylation of Azoles with Alkyl Halides Mediated by Nickel(II) Complexes of Phenanthridine-Based N^N-^N Pincer Ligands. Organometallics 2020, 39, 1989-1997
Mandapati, P.; Braun, J. D.; Killeen, C.; Davis, R. L.; Williams, J. A. G.; Herbert, D. E. Luminescent Platinum(II) Complexes of N^N‑^N Amido Ligands with Benzannulated N-Heterocyclic Donor Arms: Quinolines Offer Unexpectedly Deeper Red Phosphorescence than Phenanthridines. Inorg. Chem. 2019, 58, 14808−14817
Mandapati, P.; Braun, J. D.; Lozada, B. L; Williams, G. A. J.; Herbert, D. E. Deep-Red Luminescence from Platinum(II) Complexes of N^N-^N‐Amido Ligands with Benzannulated N‐Heterocyclic Donor Arms. Inorg. Chem. 2020, 59, 12504–12517.
Mandapati, P.; Braun, J. D.; Sidhu, B. K.; Wilson, G.; Herbert, D. E. Catalytic C−H Bond Alkylation of Azoles with Alkyl Halides Mediated by Nickel(II) Complexes of Phenanthridine-Based N^N-^N Pincer Ligands. Organometallics 2020, 39, 1989-1997