title: Phosphenium Hydride Reduction of [(cod)MX2] (M = Pd, Pt; X = Cl, Br): Snapshots on the Way to Phosphenium Metal(0) Halides and Synthesis of Metal Nanoparticles.
abstract: The outcome of the reduction of [(cod)PtX2] (X = Cl, Br; cod = 1,5-cyclooctadiene) with N-heterocyclic phosphenium hydridesRNHP-H depends strongly on the steric demand of the N-aryl group R and the nature of X. Reaction of [(cod)PtCl2] withDippNHP-H featuring bulky N-Dipp groups produced an unprecedented monomeric phosphenium metal(0) halide [(DippNHP)(DippNHP-H)PtCl] stabilized by a single phosphine ligand. The phosphenium unit exhibits a pyramidal coordination geometry at the phosphorus atom and may according to DFT calculations be classified as a Z-type ligand. In contrast, reaction of [(cod)PtBr2] with the sterically less protectedMesNHP-H afforded a mixture of donor-ligand free oligonuclear complexes [{(MesNHP)PtBr}n] (n = 2, 3), which are structural analogues of known palladium complexes with μ2-bridging phosphenium units. All reductions studied proceed via spectroscopically detectable intermediates, several of which could be unambiguously identified by means of multinuclear (1H,31P,195Pt) NMR spectroscopy and computational studies. The experimental findings reveal that the phosphenium hydrides in these multistep processes adopt a dual function as ligands and hydride transfer reagents. The preference for the observed intricate pathways over seemingly simpler ligand exchange processes is presumably due to kinetic reasons. The attempt to exchange the bulky phosphine ligand in [(DippNHP)(DippNHP-H)PtCl] by Me3P resulted in an unexpected isomerization to a platinum(0) chlorophosphine complex via a formal chloride migration from platinum to phosphorus, which accentuates the electrophilic nature of the phosphenium ligand. Phosphenium metal(0) halides of platinum further show a surprising thermal stability, whereas the palladium complexes easily disintegrate upon gentle heating in dimethyl sulfoxide to yield metal nanoparticles, which were characterized by TEM and XRD studies.
authors.affiliation: Institute of Inorganic Chemistry, University of Stuttgart , Pfaffenwaldring 55, 70550 Stuttgart, Germany.
authors.forename: Jan
authors.initials: J
authors.lastname: Nickolaus
authors.affiliation: Institute of Inorganic Chemistry, University of Stuttgart , Pfaffenwaldring 55, 70550 Stuttgart, Germany.
authors.forename: Dominik A
authors.initials: DA
authors.lastname: Imbrich
authors.affiliation: Institute of Inorganic Chemistry, University of Stuttgart , Pfaffenwaldring 55, 70550 Stuttgart, Germany.
authors.forename: Simon H
authors.initials: SH
authors.lastname: Schlindwein
authors.affiliation: Institute of Inorganic Chemistry, University of Stuttgart , Pfaffenwaldring 55, 70550 Stuttgart, Germany.
authors.forename: Adrian H
authors.initials: AH
authors.lastname: Geyer
authors.affiliation: Department of Chemistry, University of Helsinki , P.O Box 55 (A.I. Virtasen Aukio 1), 00014 Helsinki, Finland.
authors.forename: Martin
authors.initials: M
authors.lastname: Nieger
authors.affiliation: Institute of Inorganic Chemistry, University of Stuttgart , Pfaffenwaldring 55, 70550 Stuttgart, Germany.
authors.forename: Dietrich
authors.identifier: http://orcid.org/0000-0002-9196-0466
authors.initials: D
authors.lastname: Gudat