Photoreactivity of N-Heterocyclic Carbene-Boranes and the Reactivity of Pyrido[2,1-A] Isoindole
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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.