The reaction of the copper(I) β-diketiminate copper complex {(Cu(BDIMes))2(μ-C6H6)} (BDIMes = N,N′-bis(2,4,6-trimethylphenyl)pentane-2,4-diiminate) with the low-valent group 13 metal β-diketiminates M(BDIDip) (M = Al or Ga; BDIDip = N,N′-bis(2,6-diisopropylphenyl)pentane-2,4-diiminate) in toluene afforded the complexes {(BDIMes)CuAl(BDIDip)} and {(BDIMes)CuGa(BDIDip)}. These feature unsupported copper–aluminum or copper–gallium bonds with short metal–metal distances, Cu–Al = 2.3010(6) Å and Cu–Ga = 2.2916(5) Å. Density functional theory (DFT) calculations showed that approximately half of the calculated association enthalpies can be attributed to London dispersion forces.