cis, trans – or Both: Steric Bulk Determines Coordination Mode of Dimeric Palladium Complexes with Bridging Pyridine‐Phosphane Ligands

Abstract

The coordination mode in a metal complex is critically dependent on the ligands surrounding the metal, on the precursors used, and on the conditions during synthesis. Our goal was to obtain palladium compounds with pyridine-phosphane ligands for catalysis. Therefore, we synthesized ligands 1a-d, which differ in the bulky aryl substituent at the pyridyl moiety. The palladium complexes 6a-d of these ligands are insoluble and have been characterized by various techniques, including solid-state NMR and (for 6a, b, and d) single-crystal X-ray diffraction, showing that bimetallic complexes are formed in which two ligands span two palladium centers. The configuration around these centers is determined by the steric bulk of the ligand. In complexes 6c,d,

Uncovering the Mechanism of Homogeneous Methyl Methacrylate Formation with P,N Chelating Ligands and Palladium: Favored Reaction Channels and Selectivities

“…P,N ligands are known to coordinate in a number of binding modes. While monocoordination and multiple unidentate coordination are typically through the softer phosphorus atom, many structures have been isolated that show chelation. − 2-PyPPh 2 may also coordinate metal (hetero)­dimers, ,− and structures involving iridium suggest that two 2-PyPPh 2 ligands should be able to coordinate in both unidentate and chelating fashion around a single metal center …”

The synthesis of, and characterization of the dynamic processes occurring in Pd(ii) chelate complexes of 2-pyridyldiphenylphosphine

“…7,17,22,24-27 Elsevier has recently developed variants of the pyridylphosphine ligand for catalysis in supercritical CO 2 22 and Doherty has described polymer bound Pd/pyridylphosphine catalysts. 28 The explanation for the enhanced catalytic activity of Ph 2 Ppy vs. PPh 3 is still open to debate since a general consensus regarding the catalytic reaction mechanism has, as yet, not been reached with both Pd(0) [13][14][15] and Pd(II) 7,17, 25 intermediates being proposed in which the pyridylphosphine ligands adopt monodentate, [24][25][26] or mixed mono-and bi-dentate 7,17 coordination, or in which the coordination mode of the ligand is not defined. 27 Thus, although there appears general agreement that the ligand may act as a proton relay, the possibility that the hemilability of the ligand is also important has received little attention, indeed the coordination chemistry of 2-pyridyldiphenylphosphine with palladium(II) and the potential for hemilability of Ph 2 Ppy at Pd(II) has been little explored.…”

Complexes of hydrophilic triphenylphosphines modified with gem-bis(phosphonate) moiety. An unusual simultaneous cis and trans arrangements in the Pt(ii) dinuclear complex

“…This simultaneous cis/trans coordination arrangement has been only very recently observed in dinuclear Pd(II) complexes with ligands derived from [2-(pyridin-2-yl)ethyl]diphenylphosphine. 25 Depending on the steric demands of other substituents on the ligand skeleton, cis/trans or trans/trans configurations were found. It was explained by the presence of a rather flexible three-atom chain between pyridine nitrogen and phoshine phosphorus donor atoms.…”