Photochemically generated t-butoxyl radicals react with the primary amine-boranes PNH2-+BH, (R = M e or But) to form, initially, the nucleophilic amine-boryl radical RNH,+BH,, which subsequently abstracts bydrogen from the parent amine-borane to give the more stable isomeric aminyl-borane radical RNH-BH,.The amine-boryl radicals can be intercepted by alkyl bromides or chlorides or by nitriles, with which they react by halogen-atom abstraction or by addition t o the CN group to give irninyl radicals, respectively. The e.s.r. spectra of the aminyl-borane radicals show the presence of extensive hyperconjugative delocalisation of the unpaired electron onto the BH, group [a(3BH) 64-66 GI. Monoalkylaminyl-borane radicals react readily with alkenes, with arenes, and with conjugated or cumulated dienes t o transfer a P-hydrogen atom from boron to give alkyl, cyclohexadienyl, . or ally1 radicals, respectively. Hydrogen atom transfer t o alkenes from the electrophilic MeNHhBH, takes place with high regioselectivity to give the more stable alkyl radical when t w o adducts are possible; the rate of transfer increases as the ionisation potential of the alkene decreases along the series CHFCH, < MeCH=CH, < Me, (+CH, = Me,C=CHMe -= Me,C=CMe,.The absolute rate coefficient for reduction of propene by MeNH+BH, to give the isopropyl radical was determined to be ca. 2 x 10, dm3 mol-l s-' at 282 K. Competition experiments haye been caJried out t o determine the relative rates of the various reactions undergone by RNH,-+BH, and RNH-+BH,. The results are. interprpted with the aid of ab initio molecular-orbital calculations at the 6-31G"" level for RNH,-+BH,, RNH-BH,, RNH,-+BH,, and RNHeBH, (R = H or Me), together with similar calculations for the isoelectronic organic counterparts in which the NB moiety is replaced by a CC grouping. * Analogous trends are, of course, shown by the isoelectronic hydrocarbons Me,CH, -,CH,.5 54 1 282 K only the e.s.r. spectrum of the t-butyl radical was detected.
