The photochemical reactions of several singlet arenecarbonitriles with aliphatic amines have been investigated. The reactions of 9-phenanthrenecarbonitrile with diethylamaine and its N-and α-C-deuterated derivatives result in exclusive N-H atom transfer to yield the diethylaminyl and 9-cyano-9,10-dihydrophenanthren-9-yl radicals in benzene solution. Increased solvent polarity results in the formation of both diethylaminyl and l-(ethylamino)ethyl radical. Similar results are obtained with 9-anthracenecarbonitrile. The competition between aminyl vs. α-aminoalkyl radical formation in this and other reactions is reviewed. Aminyl radical formation is characteristic of relatively nonpolar heteroexcimers in which hydrogen bonding may favor N-H transfer. Pure charge-transfer exciplexes, like alkoxyl radicals, yield predominantly the thermodynamically more stable α-aminoalkyl radical. The dominant reaction of the aminyl-phenanthren-9-yl radical pair in nonpolar solvent is combination to yield arene-amine adducts, which quantitatively lose HCN upon heating or chromatography. In contrast, the α-aminoalkyl-phenanthren-9-yl radical pairs formed in polar solvent disproportionate to yield reduced arene and oxidized amine, plausibly via radical pair electron transfer followed by proton transfer.
ASJC Scopus subject areas
- Colloid and Surface Chemistry