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

ABSTRACT 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 [( Ar Nacnac)Zn─Al(Cp*)(X)] (Ar = Dep, X = Cl, Br, I; Ar = Dipp, X = Cl, Br; Ar Nacnac = {HC[C(Me)N(Ar)] 2 }; Ar = Dep, C 6 H 3 Et 2 ‐2,6; Dipp, C 6 H 3 i Pr‐2,6; Cp* = C 5 Me 5 ), by insertion of in situ‐generated “AlCp*” into the Zn─X bonds of parent dimeric zinc Ar Nacnac halide complexes [Zn( Ar Nacnac)(μ‐X)] 2 . We find that the reactions of the newly formed Al─Zn complexes with N,Nʹ ‐dicyclohexylcarbodiimide (DCC) proceed by migratory insertion into the Al─Zn bond to give [Zn( Ar Nacnac){μ 2 ‐C(NCy) 2 ‐κ 1 ‐ C ,κ 2 ‐ N , N ʹ}Al(Cp*)(X)] (Ar = Dep, X = Cl, Br, I; Ar = Dipp, X = Cl, Br) as expected, but for the Dipp Nacnac derivatives a second equivalent of DCC inserts into the Al─Cp* moiety to afford [Zn( Dipp Nacnac){μ 2 ‐C(NCy) 2 ‐κ 1 ‐ C ,κ 2 ‐ N , N ʹ}Al(Cl){κ 2 ‐(NCy) 2 C‐η 1 ‐Cp*‐κ 2 ‐ N , N ʹ}] or [Zn( Dipp Nacnac)(Br){μ 2 ‐C(NCy) 2 ‐κ 1 ‐ C ,κ 2 ‐ N , N ʹ}Al{κ 2 ‐(NCy) 2 C‐η 1 ‐Cp*‐κ 2 ‐ N , N ʹ}], 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.