Novel Bidentate [N,S] Palladacycle Metalloligands. 1H–15N HMBC as a Decisive NMR Technique for the Structural Characterization of Palladium–Rhodium and Palladium–Palladium Bimetallic Complexes

Treatment of tetranuclear palladacycles with 2-(diphenyl­phosphino)­pyridine, Ph2Ppy, in acetone at room temperature for 10 h, gave the new bidentate [N,S] palladacycle metalloligands 1–7. Treatment of [Rh2Cl2­(CO)4] with AgClO4 in acetone at room temperature for 10 min, followed by addition of 1–7 and stirring at room temperature for 10 h, gave the novel heterobimetallic palladium–rhodium compounds 1a–7a as 1:1 electrolytes, where the new bidentate [N,S] palladacycle metalloligands are bonded to the second metal through the pyridine nitrogen atom, and the sulfur atom of the thiosemicarbazone moiety; they exhibit a six-membered bimetallic central ring of differing atoms. In a similar manner, reaction of [PdBr2­(Ph2PR4­PPh2)] (R4 = CH2, CCH2, (CH2)2, cis-CHCH) with AgClO4 in acetone at room temperature, followed by addition of 1–7, gave the homobimetallic palladium–palladium compounds, 2b, 3b, 5b–7b, and 5c–7c, as 1:2 electrolytes, also with [N,S] coordination of the corresponding metalloligand. 1H–15N HMBC experiments were a most valuable tool in helping to unequivocally ascertain rhodium–nitrogen and palladium–nitrogen coordination in the bimetallic species. The crystal and molecular structures of 3, 6, 2b, and 3b have been determined by X-ray crystallography; for compounds 3 and 3b, inter- and intramolecular interactions in the solid state result in crystal self-organization, leading to chains and/or layers in the molecular array.