Synthesis and Characterization of Pyridine Dipyrrolide Iron Complexes Relevant to Nitrene and Carbene Group Transfer

Author

Brett M. Hakey, West Virginia UniversityFollow

Semester

Fall

Date of Graduation

2020

Document Type

Dissertation

Degree Type

PhD

College

Eberly College of Arts and Sciences

Department

Chemistry

Committee Chair

Carsten Milsmann

Committee Member

Jeffrey Petersen

Committee Member

Brian Popp

Committee Member

Brian Dolinar

Committee Member

Mikel Holcomb

Abstract

The synthesis and electronic structures of the square-planar high-spin Fe^II complexes (^MesPDP^Ph)Fe(OEt₂) and (^MesPDP^Ph)Fe(thf) were investigated. Analysis of these compounds using a combination of ¹H NMR and ⁵⁷Fe Mössbauer spectroscopies, in conjunction with computational analysis, has resulted in a rationalization for their unusual electronic structures, which arise from the unique coordination environment enforced by the pyridine dipyrrolide chelate ligand.

The reactivity of (^MesPDP^Ph)Fe(thf) with organic azides has been probed and resulted in the isolation of an array of products that are consistent with the generation of reactive iron nitrene intermediates. Computational analysis has evidenced that the suspected iron nitrene species are intermediate-spin ferric ions engaged in antiferromagnetic coupling to iminyl radical ligands. Increasing the steric bulk of the nitrene source via the use of mesityl azide allowed for the spectroscopic observation of (^MesPDP^Ph)Fe(NMes), which has been identified as a competent intermediate in nitrene transfer to a C-H bond of the pyridine dipyrrolide supporting ligand. In attempts to sequester intraligand C-H amination and leverage intermolecular reactivity, the new high-spin ferrous species (^2,6-Cl2PhPDP^Ph)Fe(thf) has been synthesized. (^2,6-Cl2PhPDP^Ph)Fe(thf) is also capable of generating nitrene adducts, as demonstrated by the isolation of diamagnetic (^2,6-Cl2PhPDP^Ph)Fe(N¹Ad) and paramagnetic (^2,6-Cl2PhPDP^Ph)Fe(NMes) from its reaction with 1-adamantyl azide and mesityl azide, respectively. It is anticipated that these results will provide a foundation for future investigations of the efficacy of pyridine dipyrrolide iron complexes in nitrene group transfer reactions, which may find application in the construction of new carbon-nitrogen bonds from hydrocarbon substrates.

The reaction of (^MesPDP^Ph)Fe(thf) with diphenyldiazomethane has resulted in the isolation of an unprecedented paramagnetic square-planar iron carbene complex, (^MesPDP^Ph)Fe(CPh₂). Physical characterization and computational analysis of (^MesPDP^Ph)Fe(CPh₂) suggests an S = 1 ground state for the compound and an electronic structure which may be described as an intermediate-spin Fe^III ion engaged in antiferromagnetic coupling with a carbene radical ligand. The reactivity of (^MesPDP^Ph)Fe(CPh₂) with CO and isocyanides was explored and yielded the low-spin Fe^II carbene group transfer products (CPh₂^MesPDP^Ph)Fe(CO)₂ and (CPh₂^MesPDP^Ph)Fe(C≡N-2,6-(CH₃)₂Ph)₂, arising from carbene insertion into an iron pyrrolide nitrogen bond.

Recommended Citation

Hakey, Brett M., "Synthesis and Characterization of Pyridine Dipyrrolide Iron Complexes Relevant to Nitrene and Carbene Group Transfer" (2020). Graduate Theses, Dissertations, and Problem Reports. 7939.
https://researchrepository.wvu.edu/etd/7939

Embargo Reason

Publication Pending