Photoreactivity of N-Heterocyclic Carbene-Boranes and the Reactivity of Pyrido[2,1-A] Isoindole
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Authors
McDonald, Sean
Date
Type
thesis
Language
eng
Keyword
Boron , Inorganic , Photochemistry , Organometallic
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Abstract
N-heterocyclic carbene (NHC) borane systems have become an important topic in main group chemistry. Finding uses as catalysts, coordinators for radical polymerizations, and reagents in a variety of reactions, NHCs have become a very important ligand for fundamental research. However, there have been relatively few studies on NHC-boranes over the last fifty years. This thesis will make new strides in the understanding and reactivity of NHC-boranes with UV light.
Modeling after a previous result, NHC-BH3 systems were investigated for their photoreactivity. The systems investigated were found to decompose under irradiation.
The systems were shifted to NHC-BH2R where the R group has a b-hydrogen relative to the boron center. When exposed to UV light a facile reaction occurred, akin to a b-hydrogen elimination reaction. The resulting products are an NHC-BH3 and the corresponding alkene from the elimination.
BMes2 moieties chelated by an NHC were synthesized, analogous to previous work. When irradiated by UV light, mesitylene was eliminated, yielding a new B-C pi-bond. This new system contains an imbedded 1,3-azaborine within its multicyclic structure and is the first example of this type. When the precursor was heated, the boron moiety was eliminated and the ring closed to make a new 1H-imidazo[1,2-a]indole. This new compound shows a striking similarity to pyrido[2,1-a]isoindole (iczH). Like iczH, there is a new highly nucleophilic carbon center at the apex of the new 5-membered ring.
Due to synthetic ease, iczH was selected to test nucleophilicity in place of the 1H-imidazo[1,2-a]indole. The reactivity of iczH as a nucleophile was explored with a variety of transition metals and main group elements. A normal adduct was formed when reacted with a platinum(II) center, while an 6 complex was formed with a chromium(0) center. When iczH was reacted with group 11 metals(I), a redox reaction took place, producing the solid metal, protonation iczH, and a dimer of iczH. A chlorophosphines was found to be very reactive with iczH once again resulting in protonated iczH while also producing an icz-functionalized phosphine. Despite the HOMO residing on the carbon of the icz unit, the phosphorous atom (dominant in HOMO-1) was still the favoured nucleophile when reacted with borane, producing a new borane-phosphine adduct. These new compounds were fully characterized by NMR and X-ray crystallographic analysis.
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ProQuest PhD and Master's Theses International Dissemination Agreement
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Copying and Preserving Your Thesis
This publication is made available by the authority of the copyright owner solely for the purpose of private study and research and may not be copied or reproduced except as permitted by the copyright laws without written authority from the copyright owner.