Synthesis, isolation, and characterization of imidazole-based abnormal N-heterocyclic carbene (aNHC) pincer complexes of group 10 metals (Ni, Pd, Pt): catalysts towards dinitrogen reduction, and materials for organic light-emitting diodes (OLEDs)

Author

Evans Fosu, Mississippi State UniversityFollow

ORCID

https://orcid.org/0000-0003-1770-4453

Issuing Body

Mississippi State University

Advisor

Hollis, T. Keith

Committee Member

Patrick, Amanda

Committee Member

Webster, Charles E.

Committee Member

Creutz, Sidney E.

Committee Member

Wipf, David O.

Date of Degree

12-13-2024

Original embargo terms

Complete embargo 2 years

Document Type

Dissertation - Open Access

Major

Chemistry

Degree Name

Doctor of Philosophy (Ph.D.)

College

College of Arts and Sciences

Department

Department of Chemistry

Abstract

Our group has been developing normal CCC-NHC pincer complexes for catalysis and OLED applications. However, synthesizing the abnormal analogs has been challenging due to the difficulty in accessing the ligand precursors. This study addresses these challenges, marking a significant step in CCC-NHC pincer chemistry. The abnormal CCC-NHC proligands were synthesized through Ullmann-type coupling of 2-phenylimidazole to 1,3-dibromobenzene. The intermediate 1,3-bis(2-phenylimidazole)benzene was alkylated with 1-iodobutane to obtain the 1,3-bis(N-butyl-2-phenylimidazole)benzene diiodide salt. The proligands 1,3-bis(N-butyl-2-phenylimidazole)benzene dichloride/diiodide were metalated with [Zr(NMe2)4] and transmetalated to group 10 metals (Ni, Pd, Pt) using [NiCl2(glyme)], [Pd(COD)Cl2], and [Pt(COD)Cl2]. Electrospray ionization of the CCC-aNHC pincer complexes [(BuCa-iCa-iCBu)MX] (M = Ni, Pd, Pt, X = Cl, I) in acetonitrile generated dinitrogen adducts [(BuCa-iCa-iCBu)M-N2]+, representing a rare example of group 10 dinitrogen complexes. The coordination of N2 to the cationic species means the pincer ligand provides the required electron density to the metals to stabilize the N2 through π-backbonding. The redox chemistry of NiII and PdII complexes bearing the super electron donating CCC-aNHC pincer ligand was investigated. The PdII complexes were cleanly oxidized with two electron oxidants, such as iodobenzene dichloride (PhICl2). The oxidation of the PdII complex with a half equiv of the oxidants gave mixed valent PdII/PdIV dimer as a thermodynamically preferred product. The oxidation of the CCC-aNHC NiII chloride complex with PhCl2 produced unstable NiIII species. However, utilizing anhydrous CuCl2 as the oxidant yielded a bis-ligated NiIV complex, a seemingly common occurrence among the first-row metals (Fe and Co). Emissive square planar Pt complexes have been utilized to produce OLEDs, but those with halides pose potential threats due to the electrochemical instability of halide complexes. Thus, it is highly desirable that halide-free square planar Pt complexes that maintain high molecular rigidity are developed. The CCC-aNHC pincer Pt halide complexes were emissive when irradiated with UV light. The pincer Pt halide complexes were converted to Pt azolate complexes and retained their emission properties. Substituting halides on Pt complexes with azolates increases the PLQY from 7 % to 24 % and the emission lifetimes from 1.0 μs to 1.4 μs in the solid states.

Recommended Citation

Fosu, Evans, "Synthesis, isolation, and characterization of imidazole-based abnormal N-heterocyclic carbene (aNHC) pincer complexes of group 10 metals (Ni, Pd, Pt): catalysts towards dinitrogen reduction, and materials for organic light-emitting diodes (OLEDs)" (2024). Theses and Dissertations. 6368.
https://scholarsjunction.msstate.edu/td/6368