Date of Award
Spring 2023
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Chemistry
First Advisor
Holland, Patrick
Abstract
This thesis details the preparation, characterization, and reactivity of iron(I) hydrocarbyl complexes for the exploration of hydrocarbyl migration to N2 at formally iron(IV) centers. While the migratory insertion into CO is a well-established reaction step, the corresponding reaction with isoelectronic and isolobal N2 has not been reported. Chapter 1 describes the binding of N2 to transition metal centers. Methods of characterization and measurements of N–N bond weakening upon coordination are discussed. The most commonly observed binding modes of N2 and the corresponding effects on weakening of the N2 ligand are explained. Additionally, the various routes of N2 functionalization to form N–Si and N–C bonds to N2 are listed. Chapter 2 interrogates the mechanism of apparent aryl migration to N2 upon silylation. Several intermediates are isolated and characterized, including two monosilylated diazenido species and a formally iron(IV) phenyl hydrazido(2–) complex. The kinetics of aryl migration are measured, and steric effects are explored. Density-functional theory (DFT) calculations support our proposed mechanism of concerted aryl group migration. An inverted ligand field is proposed in the formally iron(IV) species by analysis of the quasi-restricted orbitals as well as multi-reference CASSCF calculations. Chapter 3 details the investigation into the reactivity of formally iron(IV) alkyl species analogous to those presented in Chapter 2. A formally iron(IV) alkyl hydrazido(2–) complex is isolated and characterized, and the electronic structure is shown to differ from the previously isolated phenyl derivative through both experimental measurements and DFT calculations. The exploration of different alkyl groups shows that, unlike aryl migration, Fe–C bond homolysis can occur upon formation of the corresponding iron(IV) alkyl species. DFT calculations of the potential energy surfaces for Fe–C bond homolysis and alkyl migration at iron(IV) show that these two reactions can be kinetically competitive. Chapter 4 explores the chemistry of high-spin mono- and bis(alkynyl)iron complexes. A dimeric iron(II) alkynyl complex is isolated and characterized, and is observed to dissociate into a monomeric form upon reduction. The reduced species was shown to bind and subsequently functionalize N2 to yield a formally iron(IV) alkynyl hydrazido(2–) complex. Despite the reactivity discussed in Chapters 2 and 3 of the iron(IV) aryl and alkyl species, the analogous alkynyl complex was not observed to undergo Fe–C bond homolysis or alkynyl migration. Natural bond orbital (NBO) analysis on the isolated formally iron(IV) alkyl, aryl, and alkynyl complexes provides insight into the differing reactivity. Furthermore, the observation of a rare organometallic pi-tweezer complex with a terminally bound N2 ligand is reported, and the electronic structure is investigated by DFT computations. Two other bis(alkynyl)iron complexes are isolated and characterized, and are presented as starting complexes for potential syntheses of homo- and heterobimetallic species.
Recommended Citation
Bhutto, Samuel Marsh, "Investigation of Hydrocarbyl Migration to Dinitrogen" (2023). Yale Graduate School of Arts and Sciences Dissertations. 867.
https://elischolar.library.yale.edu/gsas_dissertations/867
