Oxidative Coordination versus C3−C(O)Me Bond Cleavage in Acetylacetonate Iridium Complexes

Iridabicycles [Ir{κ3‐N,C,O‐(pyC(H)=C(C(O)Me)2}(Cl)(L−L)](L−L=cod (cod=1,5‐cyclooctadiene), 1 a; bipy (bipy=2,2’‐bipyridine), 1 b) have been obtained by oxidative coordination of 3‐(pyridine‐2‐yl‐methylene)pentane‐2,4‐dione L1, to the complexes [{Ir(μ‐Cl)(cod)}2] and [{Ir(μ‐Cl)(coe)2}2] (coe=cis‐cyclooctene), the latter in the presence of bipy. Remarkably, cleavage of the C3−C(O)Me bond of L1 has instead been achieved in the reaction with [Ir(Cl)(dmb)2] (dmb=2,3‐dimethylbutadiene), yielding a compound formulated as [Ir{κ2‐N,C‐(pyC(H)C(C(O)Me))}(CO)(μ‐Cl)(Me)]2, 2. Treatment of dimer 2 with DMSO or PMe3 produced the complexes[Ir{κ2‐N,C‐(pyC(H)C(C(O)Me)}(CO)Cl(Me)L] (L=DMSO, 3 a; PMe3, 3 b). Plausible mechanisms for the reactions leading to complexes 1 and 2 are proposed by means of DFT calculations. The key role of olefin co‐ligands in the reactivity of IrI precursors toward alkylidenediketone, pyCH=C(COMe)2, is shown. In this regard, 1,5‐cyclooctadiene and cyclooctene induce the oxidative coordination of the above‐mentioned alkylidenediketone, leading to the formation of new iridabicyclic complexes. By contrast, dimethylbutadiene promotes at room temperature C3−COMe bond cleavage of the alkylidenediketone.