Synthesis of Aryl‑, Benzoyl‑, and Iminobenzoyl-Palladium(II) Complexes Derived from N‑Phenyl Formamide. Synthesis of a Homoleptic Ball-Shaped Tetranuclear Palladium Complex

The complex [Pd­{C6H4NHCHO-2}­I­(tBubpy)] (A, tBubpy = 4,4′-di-tert-butyl-2,2′-bipyridine) reacts with CO or XyNC, affording the benzoyl or iminobenzoyl complexes [Pd­{C­(O)­C6H4­NHCHO-2}­I­(tBubpy)] (1) or [Pd­{C­(NXy)­C6H4­NHCHO-2}­I­(tBubpy)] (2), respectively. Dehydroiodination of 2 with Tl­(acac) (acacH = acetylacetone) produced the iminobenzoyl­(amide) complex [Pd­{C,N-C­(NXy)­C6H4­NCHO-2}­(tBubpy)] (3) from which complex [Pd­{C,N-C­(NXy)­C6H4­NCHO-2}­(CNXy)2] (4) was obtained upon substitution of the tBubpy ligand with 2 equiv of XyNC. Heating complex 3 in mesitylene at 160 °C for 3 h caused tBubpy loss, and the generated coordination vacancies were occupied by the amido oxygen and the iminobenzoyl nitrogen atoms, both acting as bridging ligands to give the tetranuclear species [Pd4{N,O-{C,N-C­(NXy)­C6H4­NCHO-2}4] (5). Removal of the iodo ligand in A by reacting it with TlOTf (OTf = trifluoromethanesulfonate, triflate) caused coordination of the amido oxygen atom to give the cationic complex [Pd­{C,O-C6H4­NHCHO-2}­(tBubpy)]­OTf (6) in which the Pd–O bond was split by reaction with XyNC to give [Pd­{C­(NXy)­C6H4­NHCHO-2}­(CNXy)­(tBubpy)]­OTf (7). The crystal structures of 3, 5, and 6 have been determined by X-ray diffraction methods.