Heterolytic activation of dihydrogen by platinum and palladium complexes

Abstract

Compounds Pt2a-d are potential candidates for dihydrogen bonding because they possess a protonated pyridyl moiety (hydrogen bond donor) and a metal hydride (hydrogen bond acceptor) in close proximity. The presence of a dihydrogen interaction has been characterized in the solid state by X-ray crystallography 1 and neutron diffraction, 2,3,4 and in solution by NMR and IR spectroscopy. 5 Normally, the infrared spectra of hydrogen bonded systemsshows that the metal-hydride and the NH or OH vibration bands broaden and shift to lower frequencies compared to compounds in which no hydrogen bonding occurs. 6 The 1 H NMR spectrum usually displays low field shifts for the X-H resonance (X= O or N), low minimumT 1 values and sometimes even hydride-proton couplings. 7,8In order to investigate whether dihydrogen bonding occurred in the platinum compounds

Late Transition Metal Complexes of Pyridyldiphosphines

“…spectrum to the 31 P NMR signal at 3.32 ppm indicated that this was the signal for the methyl protons in the acyl group. The 1 H NMR spectrum was consistent with those of the other unsymmetrical complexes (27)(28)(29)(30)(31)(32)(33)(34)(35)(36)(37). The IR spectrum of complex 38 contained a C=O stretch at 1638 cm −1 consistent with the presence of an acyl group, 71 while the C=N stretches at 1573 and 1562 cm −1 indicated the pyridyl nitrogens were not coordinated to the platinum.…”

“…Another method for the synthesis of complexes with a P,N chelated PPh 2 Py ligand is shown in Scheme 1.5. 35 When the complex with the chelated PPh 2 Py ligand was put under hydrogen pressure the pyridyl nitrogen dissociates to create a vacant site at the metal centre. However, this example illustrates a further advantage of pyridylphosphine ligands, the ability of the pyridyl nitrogen to act as an internal base.…”

“…24 There are also several examples where the same trend is observed when PPy 3 behaves as a chelating P,N ligand in platinum and palladium complexes. 35 Also when pyridine ligands are coordinated to a metal the signals due to the pyridyl protons become deshielded and shift to higher ppm in the 1 H NMR spectra, particularly the signal of the proton next to the nitrogen. 35,127 As none of the expected changes in the NMR data were observed it was concluded that a pyridyl nitrogen atom had not coordinated to the platinum.…”

“…In 2013, van Leeuven and co-workers reported the heterolytic activation of hydrogen by platinum and palladium complexes containing pyridylphosphine ligands. 35 The platinum complexes used in that work were of the type [Pt(PP*)(PN)]OTf where PP* = 9,9-dimethyl-4,5-bis(diphenylphosphino)xanthene (Xantphos), bis(2-(diphenylphosphino)phenyl)ether (DPEphos) and PN = a chelating PPh 2 Py ligand. While no reaction was observed when solutions of the complexes were put under 1 bar of hydrogen gas, when this was increased to 4 bar of hydrogen a reaction was observed.…”

Theoretical Study of Rhodium‐Catalyzed C−C Activation of Cyclobutanones: Origin of Ligand‐Controlled Product Selectivity

“…All stationary points were optimized without any constraints in the solvent phase at the B3LYP level of theory . The use of B3LYP for geometry optimizations and M06 for single‐point energy calculations effectively provides appropriate descriptions of metal‐catalyzed C−C functionalization reactions . Solvent effects were dealt with by using the SMD solvation model, with 1,4‐dioxane as the solvent.…”