Unusual Reactivity of a Heterobimetallic Al─Zn Complex With a Carbodiimide.

p-Block complexes containing unsupported metal─metal bonds can activate small molecules via mechanisms that complement and contrast with those of d-block metal complexes. Here we report the synthesis of a new family of heterobimetallic Al─Zn complexes [(ArNacnac)Zn─Al(Cp*)(X)] (Ar = Dep, X = Cl, Br, I; Ar = Dipp, X = Cl, Br; ArNacnac = {HC[C(Me)N(Ar)]2}; Ar = Dep, C6H3Et2-2,6; Dipp, C6H3 iPr-2,6; Cp* = C5Me5), by insertion of in situ-generated "AlCp*" into the Zn─X bonds of parent dimeric zinc ArNacnac halide complexes [Zn(ArNacnac)(μ-X)]2. We find that the reactions of the newly formed Al─Zn complexes with N,N'-dicyclohexylcarbodiimide (DCC) proceed by migratory insertion into the Al─Zn bond to give [Zn(ArNacnac){μ2-C(NCy)2-κ1-C,κ2-N,N'}Al(Cp*)(X)] (Ar = Dep, X = Cl, Br, I; Ar = Dipp, X = Cl, Br) as expected, but for the DippNacnac derivatives a second equivalent of DCC inserts into the Al─Cp* moiety to afford [Zn(DippNacnac){μ2-C(NCy)2-κ1-C,κ2-N,N'}Al(Cl){κ2-(NCy)2C-η1-Cp*-κ2-N,N'}] or [Zn(DippNacnac)(Br){μ2-C(NCy)2-κ1-C,κ2-N,N'}Al{κ2-(NCy)2C-η1-Cp*-κ2-N,N'}], with concomitant halide migration giving a Zn─Br bond in the latter complex. These results show that non-innocent reactivity of Al─Cp*, widely assumed to be a spectator ligand in heterobimetallic complexes, can be switched on by subtly tuning ligand steric bulk about Al─Zn bonds.