Author ORCID Identifier

https://orcid.org/0000-0001-5887-1747

Semester

Fall

Date of Graduation

2022

Document Type

Dissertation

Degree Type

PhD

College

Eberly College of Arts and Sciences

Department

Chemistry

Committee Chair

Carsten Milsmann

Committee Co-Chair

Jeffrey Petersen

Committee Member

Jeffrey Petersen

Committee Member

Brian Popp

Committee Member

Bjorn Soderberg

Committee Member

Alan Bristow

Abstract

The chemistry of coordination complexes of vanadium supported by pyridine di-pyrrolide pincer ligands was probed via the synthesis and investigation of a variety of compounds from the trivalent starting material, (MesPDPPh)VCl(thf)2. Under reducing conditions and subsequent addition of terpyridine, a redox transfer series (1-, 0, 1+) stemming from the neutral product (MesPDPPh)V(terpy) was isolated and characterized by X-ray crystallography. The precise bond lengths, in conjunction with bulk magnetic susceptibility, allowed for a detailed study of the redox non-innocence of polypyridyl ligands in these systems.

Metathesis of the halide starting material with azide salts allowed for the isolation of [Na(18-crown-6)][(MesPDPPh)V(N3)2(thf)], which could be thermolyzed to produce the mixed nitride/azide salt, [Na(18-crown-6)][(MesPDPPh)VN(N3)]. Following characterization of the resulting vanadium-nitrogen triple bond, the activation of this species with electrophilic reagents was explored. The PDP supported vanadium nitride proved a competent nucleophile toward trimethylsilyl chloride, resulting in the imido complex (MesPDPPh)V(NTMS)(N3). This product was then subjected to reducing conditions as a first step toward silylation-coupled electron transfer, as a model analogue for homogeneous ammonia production, resulting in the isolation of the cobaltocenium salt of the parent complex.

The vanadium-imido complex (MesPDPPh)V(N-1Ad)(N3) was prepared by thermolysis of 1-adamantyl azide in the presence of the trivalent halide starting material, followed by metathesis with azide salts. This product, along with [Na(18-crown-6)][(MesPDPPh)VN(N3)] and (MesPDPPh)V(NTMS)(N3), were then subjected to photolytic conditions to generate transient diradical nitrene intermediate from the decomposition of the pendant azide ligand on the d0 V(V) metal center. Irradiation with green light lead to the generation of the intra-ligand C-H activated products [(Na(18-crown-6)][(MesPDPPh-NH)VN] and (MesPDPPh-NH)V(NTMS). Following the study of this reactivity, computations revealed an unusual lowest lying excited state, which may be responsible for a divergent deazotation mechanism for the preconceived unimolecular pathway.

In order to contrast work in this lab with the photosensitizer Zr(MesPDPPh)2, a new ligand was prepared and appended to a variety of early metals including titanium, zirconium, vanadium, and niobium. The pyridine di-amine (PDA) ligand scaffold was directly compared to the PDP ligand, and its reactions with metals gave several interesting products during the course of this study. However, none of these were luminescent. This result was investigated by empirical techniques and computational chemistry.

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