Transient Terminal Cu−Nitrene Intermediates from Discrete Dicopper Nitrenes

Reaction of the copper(I) β-diketiminate {[Me3NN]Cu}2(μ-toluene) with the aryl azide N3Ar (Ar = 3,5-Me2C6H3) in toluene results in immediate effervescence and formation of the dicopper nitrene {[Me3NN]Cu}2(μ-NAr) (2) in 77% yield. The X-ray structure of 2 shows nearly symmetric bonding of the nitrene to two Cu centers separated by 2.911(1) Å with Cu−N distances of 1.794(5) and 1.808(5) Å along with a Cu−N−Cu angle of 107.8(2)°. This structure is conceptually related to the dicopper carbenes {[MexNN]Cu}2(μ-CPh2) (x = 2 or 3) (Dai, X.; Warren J. Am. Chem. Soc. 2004, 126, 10085. Badiei, Y. M.; Warren J. Organomet. Chem. 2005, 690, 5989.) which exhibit shorter Cu−Cu distances (2.4635(7) or 2.485(1) Å) and acute Cu−C−Cu angles (79.51(14) or 80.1(2)°). Addition of the Cu(I) anilidoimine {[Me2AI]Cu}2 (prepared from CuOtBu and the aniline-imine H[Me2AI] in 77% yield) to a benzene-d6 solution of 2 results in the formation of two new anilidoimine complexes {[Me2AI]Cu(μ- NAr)Cu[Me3NN] (5) and {[Me2AI]Cu}2(μ-NAr) (6) as well as [Me3NN]Cu(benzene) over 3 h. These observations are consistent with the slow dissociation of a [Me3NN]Cu fragment from 2 to generate the transient terminal nitrenes [Me3NN]CuNAr and [Me2AI]CuNAr quickly trapped by the [Me2AI]Cu fragment to form the new unsymmetrical and symmetrical dicopper nitrenes 5 and 6. Preliminary reactivity studies indicate electrophilic reactivity at the nitrene moiety. Dicopper nitrene 2 reacts with 10 equiv PMe3 and CNtBu to give ArNPMe3 and ArNCNtBu in 94% and 92% yields, respectively, with concomitant formation of [Me3NN]Cu(L) (L = PMe3 and CNtBu). Reaction between 2 and 2 equiv PMe3 allows for observation of the structurally characterized Cu(I) phosphaimide [Me3NN]Cu(ArNPMe3) (7).