Ruthenocenyl phosphinated chalcones and their Pt(II) and Pd(II) complexes: Usual bidentate [PO] and unusual tridentate [PCO] coordination

Abstract

New ruthenocenyl phosphinated chalcones β-(2′-diphenylphosphinophenyl)-acrylruthenocene CpRu(C5H4)C(O)–CHCHC6H4PPh2 (2) and β-(2′-ditolylphosphinophenyl)-acrylruthenocene CpRu(C5H4)C(O)–CHCHC6H4P(tolyl)2 (3) and their Pt(II) and Pd(II) complexes [MCl(κ3-PCO)] (4)–(6) were synthesized as the predominant product, where chalcones coordinate in a tridentate fashion to the metal center and present an unusual η1 coordination at the double bond by activation of C–H bond. During the isolation of Pt(II) (6) complex, a new unstable platinum phosphino-alkene complex (7) [PtCl2(κ2-PO)]was also isolated as a minor product. The X-ray crystal structure of (7) confirms that ligand (2) acts as bidentate ligand and coordinates through phosphorus and η2 double bond ligation to Pt(II) metal. Solution NMR and X-ray crystal structure of chalcone confirm the presence of (E)-stereochemistry at the double bond and s-cis conformation of the enone portion and complexes show square planar geometry around the metal center. Complex (7) decomposes to complex (6) and the oxidized product of ruthenocenyl phosphinated chalcone. Quasi-reversible electrochemistry was found for the ruthenocenyl center in these compounds in acetonitrile solvent. Compared to the ligands, the corresponding metal complexes are easier to oxidize at ruthenocenyl center. From quantum chemical calculations of model systems of (6) and (7) where a platinum atom is replaced by a palladium atom, it was observed that the bonding strength in a η1 coordinated complex is stronger than in a η2 coordinated double bond complex, because of the better chelating effect of the ligand in former complex.