Syntheses, interconversions and reactivity of heteropalladacycles made from aryl isocyanates and various phenanthroline Pd(II) precursors with small molecules

Abstract The synthesis and full characterisation of new families of palladacycles such as ( o -phen)PdN(Ar)C(O)N(Ar)C(O) ( 2 / 2a – g ), ( o -phen)PdN(Ar)C(O)N(Ar)C(O)N(Ar) ( 3 / 3a – c ) and ( o -phen)PdN(Ar)C(O)N(Ar) ( 4 / 4a – b ) is reported ( o -phen = 2,2’-phenanthroline), as well as the X-ray structure of the six-member palladacycle ( o -phen)PdN(Tol)C(O)N(Tol)C(O)N(Tol) ( 3c ·Et 2 O). The reactivity of these palladacycles with small molecules like CO, PhNCO and H +  is also investigated. This contribution reveals a rich chemistry and provides a complete picture of the possible interconversions existing between members of different families. Analysed in the context of the catalytic carbonylation of nitroaromatics, this study also gives some clues to understanding the disappointing results reported for (Pd/ o -phen/H + ) catalytic systems when the transformation is attempted in the absence of alcoholic solvent. Notably, the formation of five-member palladacycles like 2 under these conditions could be at the origin of the catalyst deactivation.