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.