The Utility Of Low-Valent Niobium In Small Molecule Activation And The Study Of First Row Transition Metal Complexes Supported By Tetradentate Redox Active Ligands

Other Titles


The low-valent complex (silox)3NbPMe3 (silox = tBu3SiO) was synthesized and tested for reactivity towards small molecules. It was discovered that exposure to CO generated the complexes (silox)3Nb=C=C=O (3-Nb), (silox)3Nb=O (2-Nb), and [(silox)3Nb]2([mu]-C2) (4-Nb) in various ratios depending on reaction stoichiometry. The formation of [(silox)3Nb]2([mu]-CO) (5-Nb) was discovered as a byproduct in most reactions. Treatment of (silox)3NbPMe3 with potassium under a dinitrogen atmosphere afforded the dinitrogen complex (silox)3NbNNNb(silox)3 (8-Nb). Reaction of (silox)3NbCl (10-Nb) with NH3 afforded (silox)3NbIV(NH3)Cl, with ammonia binding parameters of [INCREMENT]H = 20.4 ± 2.3 kcal/mol and [INCREMENT]S = 39 ± 7 e.u. The nickel complex {dmp(PI)2}Ni (dmp(PI)2 = Me2C(CH2=Npy)2) was synthesized and subjected to chemical oxidation and reduction to synthesize a 5membered redox series. Through electronic structure study, it was determined that in these complexes the metal center typically remained NiII, with the possible exception of the cationic complex {dmp(PI)2}Ni, and redox changes were primarily ligand-centered. The chemistry of dmp(PI)2 was extended to iron, and {dmp(PI)2}FePMe3 was synthesized. As with the nickel analogue, the complex was determined to be a MII center bound to a dianionic ligand framework, with similar redox behavior as the nickel species. A related tetradentate [beta]-diketiminate-based ligand incorporating two pyridinemethylene units, 2,4-bis[(E)-(2-pyridyl)methylideneamino]pentane (H{nn(PM)2}), was synthesized and metallated to form {nn(PM)2}FeN(TMS)2 (1-N(TMS)2). 1-N(TMS)2 could be further derivatized to form {nn(PM)2}FeX (X = Cl, N3). One of the methylene fragments of the ligand backbone was prone to facile deprotonation and allowed synthesis of {nn(PM)(PI)}FeLL' (LL' = (PMe3)2, (PMe2Ph)2, (PMe3)CO; 2LL') and {nn(PM)(PI)}FeL (L = PMe3, PMePh2, PPh3, CO; 3-L). Electronic structure studies suggested 2-LL' and 3-L existed as FeII metal centers bound to dianionic {nn(PM)(PI)}2-, with strong metal-ligand covalency in 3-L. Oxidation studies on 2(PMe3)2 showed two successive ligand-based 1e- oxidations. The same tetradentate [beta]diketiminate-based ligand was applied to other transition metals of the first row and allowed synthesis of {nn(PM)2}VCl2 (1-VCl2) and {nn(PM)2}Co (1-Co), both of which formed through unusual ligand exchange or disproportionation events, and {nn(PM)(PI)}M (M = Cr, 4-Cr; M = Ni, 4-Ni), which were generated through double deprotonation of the H{nn(PM)2} ligand.

Journal / Series

Volume & Issue



Date Issued




Redox-Active; Low-valent Niobium; First-row Transition metal


Effective Date

Expiration Date




Union Local


Number of Workers

Committee Chair

Wolczanski, Peter Thomas

Committee Co-Chair

Committee Member

Collum, David B
Coates, Geoffrey

Degree Discipline

Chemistry and Chemical Biology

Degree Name

Ph. D., Chemistry and Chemical Biology

Degree Level

Doctor of Philosophy

Related Version

Related DOI

Related To

Related Part

Based on Related Item

Has Other Format(s)

Part of Related Item

Related To

Related Publication(s)

Link(s) to Related Publication(s)


Link(s) to Reference(s)

Previously Published As

Government Document




Other Identifiers


Rights URI


dissertation or thesis

Accessibility Feature

Accessibility Hazard

Accessibility Summary

Link(s) to Catalog Record