On the transferability of IrI bond enthalpies between [Ir(μ-StBu)(I)2(CO)2]2 and trans-[Ir(X)(I)2(CO)(PPh3)2] (X=F, Cl, Br, I) complexes

The transferability of the IrI bond enthalpies in [Ir(μ-StBu)(I)2(CO)2]2 and trans-[Ir(X)(I)2(CO)(PPh3)2] (X=F, Cl, Br, I) complexes was investigated by theoretical calculations based on the B3LYP HF/DFT hybrid functional. It was concluded that the IrI bond snap enthalpy, Es(IrI), in [Ir(μ-StBu)(I)2(CO)2]2 was 35 kJ mol−1 smaller than in trans-[Ir(X)(I)2(CO)(PPh3)2] and, therefore, not transferable between both types of molecules. The relative magnitude of the obtained Es(IrI) values is in agreement with the slightly longer IrI distance and smaller Wiberg index found, on average, for [Ir(μ-StBu)(I)2(CO)2]2. In this case, however, the computed dIrI and WIIrI do not seem to be sensitive indicators of ‘bond strength’, since a variation of 35 kJ mol−1 in the Es(IrI) values leads to changes of only 0.01 Å in the bond distances and 0.005 in the Wiberg indexes. The calculations reproduce the experimental IrI mean bond dissociation enthalpies, 〈DH°〉(IrI), in the binuclear and mononuclear systems with a maximum deviation of ca. 10 kJ mol−1.