Electronic structure and electrophilic reactivity of discrete copper diphenylcarbenes

The beta-diketiminato Cu(I) arene adduct {[Me3NN]Cu}(2)(mu-toluene) (3) is prepared in 62% isolated yield by addition of the neutral beta-diketimine H(Me3NN] to copper t-butoxide in toluene. An X-ray structure of 3 shows that the bridging toluene ligand exhibits eta(2)- bonding to each Cu center via four contiguous C atoms. Reaction of the dicopper 3 with 1 equiv. N2CPh2 provides {[Me3NN]-Cu }2(mu-CPh2) (4) as purple crystals in 70% isolated yield. Dicopper carbene 4 possesses a Cu-Cu distance of 2.485(l) A in the solid state and dissociates a [Me3NN]Cu fragment in arene solvents to provide low concentrations Of [Me3NN]Cu=CPh2 (2) and (Me3NN]Cu(arene). DFT calculations performed on terminal carbene 2 and dicopper carbene 4 illustrate relationships between these two bonding modes and suggest electrophilic reactivity at the carbene carbon atom bound to Cu. Dicopper carbene 4 undergoes efficient carbene transfer to HC CPh and PPh3 resulting in the formation of 1,3,3-triphenylcyclopropene and Ph(3)p=CPh2 while reaction with the isocyanide CNAr (Ar = 2,6-Me2C6H3) results in loss of the carbene as Ph2C=CPh2. In each case, the [Me3NN]Cu fragment is trapped by the incoming nucleophile as the three-coordinate [Me3NN]Cu(L). Reaction of 4 with 0, rapidly generates benzophenone and {[Me3NN]Cu}(2)(mu-OH)(2) (c) 2005 Elsevier B.V. All rights reserved.