Nicholas Dyck

Topic

Exploring P–H Activation Facilitated by the [Mo–PR2]+ Fragment

Department of Chemistry

Date & location

• Monday, August 18, 2025
• 10:00 A.M.
• Clearihue Building, Room B007

Examining Committee

Supervisory Committee

• Dr. Lisa Rosenberg, Department of Chemistry, University of Victoria (Supervisor)
• Dr. Neil Burford, Department of Chemistry, UVic (Member)
• Dr. David Leitch, Department of Chemistry, UVic (Member)
• Dr. Roberta Hamme, School of Earth and Ocean Sciences, UVic (Outside Member)

External Examiner

• Dr. Warren Piers, Department of Chemistry, University of Calgary

Chair of Oral Examination

• Dr. Jason Lee, Department of Mechanical Engineering, UVic

Abstract

This thesis reports the synthesis, characterization, and reactivity of metal complexes used to investigate and exploit hydridic P–H activation. This method has been used by our group to achieve stoichiometric hydrophosphination of electron-rich unsaturated substrates, demonstrating a step forward in expanding the limited substrate scope of metal-mediated hydrophosphination reactions.

Chapter 2 evaluates the Lewis acidic behaviour of a new series of Mo(0) phosphenium complex, [Mo(CO)₃(PR₂H)₂(PR₂)]⁺ (4), in comparison to a previous series of these complexes, [Mo(CO)₄(PR₂H)(PR₂)]⁺ (2), to determine how adjusting the “ancillary” coordinated metal fragment could modulate phosphenium ligand reactivity. These studies show that the greater electron density of the Mo fragment in 4 attenuates the Lewis acidity at the phosphenium ligand, but also impacts the behaviour of the complex after formation of a Lewis adduct, leading to additional reactivity such as labilization of other ligands upon phosphenium adduct formation. These differences were examined in the context of the catalytic hydrosilylation of ketones as a model electrophilic reaction.

Chapter 3 investigates the substitutional lability of the P–P bond in a phosphinephosphonium adduct complex, [Mo(CO)₄(PR₂H)(PR₂–PR₂H)]⁺ ([2·PR₂H]⁺), to determine if phosphenium-catalyzed electrophilic hydrophosphination could be achieved via these compounds, an extension of the group’s previous work on the stoichiometric version of this process. While there is evidence of P–P bond cleavage of [2·PR₂H]⁺ through substitution by incoming Lewis bases ([PF₆]^–, PR₂H, and unsaturated substrates), catalytic anti-Markovnikov hydrophosphination mediated by a phosphenium ligand remains inaccessible from this system. Instead, these adduct complexes do act as a Bronsted acid catalyst, catalyzing the Markovnikov hydrophosphination of a 1,1-disubstituted alkene substrate. During these studies, phosphenium complex 2 was also shown to catalyze the dehydrocoupling of secondary phosphines via the formation of [2·PR₂H]⁺.

Chapter 4 describes the development of another series of Mo phosphenium complexes, [Mo(CO)₃(bpy)(PR₂)]+ (7). In the presence of substrate phosphine and alkene, these complexes exhibit no activity for phosphenium-mediated reactivity at the alkene substrate that might lead to hydrophosphination, but they react with phosphines to give the new complexes [Mo(CO)₂(bpy)(PR₂H)(PR₂)]⁺ (8) and [MoH(CO)₂(bpy)(PR₂H)₂)]⁺ (9). This mixture of 8 and 9 reacts with phosphines and 1,1-diphenylethylene to give mostly P–P bond formation and alkene hydrogenation, with some Bronsted acid-mediated hydrophosphination.

In Chapter 5, I have investigated the ability of hydride complex 9 to act as a (pre)catalyst for a phosphenium-catalyzed phosphine dehydrocoupling reaction. Based on stoichiometric reactivity studies, I have determined that this complex can transfer hydrogen to unsaturated substrates such as azobenzene, which generates phosphenium complex 8. When this phosphenium complex reacts with substrate phosphines, P–P bond formation occurs. The resulting P–P-bonded product is substituted from Mo by additional phosphine, regenerating hydride complex 9 and achieving catalytic turnover. This new, electrophilic mechanism for phosphine dehydrocoupling shows very high catalytic activity compared to other transition metal phosphine dehydrocoupling catalysts, providing conversion and catalytic activity at room temperature that are comparable to other systems at elevated temperatures (75 – 120°C).