Synthesis, Characterization, and Reactivity Studies of Pyridine Dipyrrolide Iron-Carbene Complexes with Electronically Distinct Carbene Moieties

Author

Jose G. Rodriguez, West Virginia UniversityFollow

Author ORCID Identifier

https://orcid.org/0000-0001-9867-4676

Semester

Fall

Date of Graduation

2024

Document Type

Dissertation

Degree Type

PhD

College

Eberly College of Arts and Sciences

Department

Chemistry

Committee Chair

Brian Dolinar

Committee Co-Chair

Carsten Milsmann

Committee Member

Brian Popp

Committee Member

Fabien Goulay

Committee Member

Benoit Driesschaert

Abstract

First, three (^MesPDP^Ph) iron carbene complexes with electronically distinct carbene moieties were synthesized. These transitional iron carbene complexes were first characterized by ¹H nuclear magnetic resonance (NMR) spectroscopy as their spectra showed paramagnetically shifted resonances. Additionally, their respected solid state structures were collected via X-ray diffraction. The two donor/acceptor iron carbene complexes [(^MesPDP^Ph)Fe(C(CO₂Me)(4-FPh) and (^MesPDP^Ph)Fe(C(CO₂Me)(4-MeOPh)] demonstrated a weak Fe-O interaction between the iron center and ester function group while the (^MesPDP^Ph)Fe(IMe) displayed a C_2v symmetric structure in the solid state structure. Furthermore, the electronic structure and magnetic properties for the three complexes were explored by the following characterization methods: Magnetic susceptibility balance measurements, Zero-field and VTVH ⁵⁷Fe Mössbauer spectroscopy, and SQUID magnetometry. The two donor/acceptor carbene complexes showed suppression of the orbital angular momentum portrayed by published (^MesPDP^Ph)Fe(CPh₂). In addition, the (^MesPDP^Ph)Fe(IMe) demonstrated unique magnetic behavior comparable to the (^MesPDP^Ph)Fe(CPh₂) complex. However, these observed phenomena did not sway that the best electronic description of the three transitional iron carbene complexes is an intermediate spin Fe(II) system coordinated to singlet (Fischer-Type) carbene fragments.

Second, the implementation of the two donor/acceptor iron carbene complexes in organic transformations showed enormous potential. As the (^MesPDP^Ph)Fe(C(CO₂Me)(4-FPh) initiated ketenimine formation from 2,6-dimethyl isocyanide (CN-dmp) via carbene group transfer at a faster reaction rate paired with room temperature conditions. Furthermore, the organic ketenimine product as well as the (^MesPDP^Ph)Fe(CN-dmp)₃ byproduct was observed via ¹H NMR spectroscopy. Additionally, the (^MesPDP^Ph)Fe(C(CO₂Me)(4-MeOPh) showed the enhanced carbene reactivity as it was capable of the stoichiometric C-H insertion of N,N-dimethyl aniline as the desired product was isolated and confirmed via ¹H NMR spectroscopy. Moreover, the (^MesPDP^Ph)Fe(C(CO₂Me)(4-MeOPh) showed great promise as it was the proposed active iron carbene catalyst in the catalytic C-H insertion of N,N-dimethylaniline. Numerous ¹H NMR time-course studies showed the detailed observation of the formation of the (^MesPDP^Ph)Fe(C(CO₂Me)(4-MeOPh) catalyst as well as gradual product formation of the C-H inserted product. Further manipulation of the diazomethane concentration showed accelerated rate of formation as well as higher NMR yield (63%: 6.3 TON) confirmed by the internal NMR standard, 1,4-bis(trimethylsilyl)benzene. The combination of the stoichiometric ¹H NMR data as well as the catalytic time course studies allowed for the construction of a proposed catalytic mechanism where the C-H inserted product is “trapped” on the iron center only to be alleviated by another molecule of diazomethane to regenerate the active carbene catalyst.

Lastly, two (^Cl2PhPDP^Ph) iron carbene complexes were synthesized. The two complexes were characterized by ¹H NMR spectroscopy as they were compared to their (^MesPDP^Ph) counterparts. Initial observation showed similar spectra that demonstrated paramagnetically shifted resonance. Further observation showed that the two sets of (^ArPDP^Ph) iron carbene derivates possess similar electronic structures, however the (^Cl2PhPDP^Ph) derivatives are slightly influenced by a potential Fe-Cl interaction portrayed by its iron starting material, (^Cl2PhPDP^Ph)Fe(THF). The synthesis, isolation, and characterization of the five (^ArPDP^Ph) iron carbene complexes showed advancements in fundamental organometallic chemistry while the two iron carbene complexes [(^MesPDP^Ph)Fe(C(CO₂Me)(4-FPh) and (^MesPDP^Ph)Fe(C(CO₂Me)(4-MeOPh)] showed their advancements in carbene group transfer reactivity rarely seen in literature known transitional iron carbene complexes

Recommended Citation

Rodriguez, Jose G., "Synthesis, Characterization, and Reactivity Studies of Pyridine Dipyrrolide Iron-Carbene Complexes with Electronically Distinct Carbene Moieties" (2024). Graduate Theses, Dissertations, and Problem Reports. 12679.
https://researchrepository.wvu.edu/etd/12679