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Novel chromium nitrosyl complexes Jandciu, Eric William

Abstract

This thesis investigates the synthesis, structure and characteristic reactivity of a series of novel chromium nitrosyl complexes. Many compounds of the form Cr(NO)(N'Pr₂)R₂ can be prepared by treatment of the bis(benzoate) precursor Cr(NO)(N'Pr₂)(0₂CPh) ₂ with the appropriate MgR₂ reagent. The resulting formally unsaturated bis(hydrocarbyl) complexes exhibit interesting features in their solid-state molecular structures. For example, when R = Bz there exists both an agostic hydrogen interaction from the amide ligand as well as an ƞ²-benzyl interaction. In solution, the bis(hydrocarbyl) complexes are fluxional, demonstrating rotation about the chromium-amide bond. Variable temperature ¹H NMR spectroscopy has been employed to study this phenomenon. In one instance, with R = o-tolyl, a different reaction pathway is followed. Instead of the bis(hydrocarbyl) complex, a nitrosyl-cleaved oxo imido compound Cr(0)(N'Pr₂)(NR)R is isolated. The solid-state molecular structure of this compound exhibits a Cr-N(imido)-C bond angle that is more bent than in any other previously prepared metal-imido complex. The reactivity of the bis(hydrocarbyl) complexes has also been explored. The insertion of isocyanides into one of the Cr-C bonds of these species proceeds smoothly, although reactions with carbon monoxide and ethylene are not as straightforward. Experiments with Lewis bases, Bronsted-Lowry acids, water and dioxygen are also complicated, most likely due to the inherent instability of the complexes. In that regard, the thermolysis of the bis(hydrocarbyl) compounds is investigated. β-Hydrogen elimination from the amide ligand is shown to be a favourable reaction pathway, and this is believed to lead to the decomposition of the bis(hydrocarbyl) compounds. In many cases, computational means have also been utilized as a means of gaining insight into the experimental observations.

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