Reversible heterolytic CH cleavage by intramolecular CH activation at diazabutadiene ligands at iridium

Abstract

Reactions between [Cp ∗IrCl 2] 2 and diaryl-substituted diazabutadienes (dab) ArNCR′CR′NAr (R′=H: Ar=4-MeC 6H 4, 2,6-Me 2C 6H 3, 2,6- i Pr 2 C 6 H 3 ; R′=Me: Ar=4-MeC 6H 4) proceed straightforwardly to give the dab complexes Cp ∗Ir(dab)Cl +Cl −. Sterically more encumbered dab ligands (R′=Me: Ar=2,6-Me 2C 6H 3, 2,6- i Pr 2 C 6 H 3 , 2,4,6-Me 2C 6H 3) instead give products Cp ∗ IrClCH 2 C( NHAr) CMe N ( Ar) + Cl − in which the dab ligand has undergone CH activation at one of methyl groups of the dab bridge. The CH cleavage reaction is reversible in the sense that thermally, the cyclometalated Ir complex decomposes to regenerate the free ligand.