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Interactions of Aziridines with Nickel Complexes:  Oxidative-Addition and Reductive-Elimination Reactions that Break and Make C−N Bonds

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journal contribution
posted on 2002-03-03, 00:00 authored by Beatrice L. Lin, Christopher R. Clough, Gregory L. Hillhouse
Reaction of the N-tosylaziridines (p-CH3C6H4SO2)NCH2CHR (1a, R = H; 1b, R = Me; 1c, R = n-Bu; 1d, R = i-Pr) with (bpy)Ni(cod) (2; bpy = 2,2‘-bipyridine; cod = 1,5-cyclooctadiene) or (bpy)NiEt2 (3) results in elimination of cod or butane from 2 and 3, respectively, and oxidative addition of an aziridine C−N bond to give the azametallacyclobutane complexes (bpy)Ni(NTosCHRCH2) (4a, R = H; 4b, R = Me; 4c, R = n-Bu; 4d, R = i-Pr) as maroon solids in 50−70% isolated yields. The structure of 4b exhibits a puckered four-membered azametallacycle containing a pyramidal nitrogen and with Ni−N(1) = 1.911(5) Å; the tosyl group on N and the methyl substituent on the adjacent C are disposed in an anti conformation. The monodeuterated aziridine syn-(p-CH3C6H4SO2)NCHDCH-n-Bu (1e) reacts with either 2 or 3 to give (bpy)Ni{NTosCH(n-Bu)CHD} (4e) in 60−65% yield, having an anti arrangement of the methine and methylene protons in the azametallacycle, and indicates that >95% inversion of stereochemistry has occurred at the methylene carbon during the oxidative-addition reaction. When the azametallacyclobutane complexes 4ae are exposed to oxygen, oxidatively induced reductive elimination ensues, giving the free aziridines in 30−60% isolated yields. In the oxidation of 4e, the product aziridine is spectroscopically identical to its parent, 1e, indicating the elimination that forms the C−N bond also proceeds with inversion of stereochemistry (∼92% by 1H NMR) at the methylene carbon.