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

The outcome of the reduction of [(cod)­PtX₂] (X = Cl, Br; cod = 1,5-cyclooctadiene) with N-heterocyclic phosphenium hydrides ^RNHP–H depends strongly on the steric demand of the <i>N</i>-aryl group R and the nature of X. Reaction of [(cod)­PtCl₂] with ^DippNHP–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 protected ^MesNHP–H afforded a mixture of donor-ligand free oligonuclear complexes [{(^MesNHP)­PtBr}_<i>n</i>] (<i>n</i> = 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

A Comparative Experimental and Computational Study of Heterometallic Fe-M (M = Cu, Ag, Au) Carbonyl Clusters Containing N-Heterocyclic Carbene Ligands

The [Fe(CO)4{M(NHC)}]\u2013 (M = Cu, NHC = IMes, 1; M = Cu, NHC = IPr, 2; M = Ag, NHC = IMes, 3; M = Ag, NHC = IPr, 4; IMes = C3N2H2(C6H2Me3)2; IPr = C3N2H2(C6H3iPr2)2) mono-anions were obtained from the reaction of Na2[Fe(CO)4]\ub72thf with one equivalent of M(NHC)Cl (M = Cu, Ag; NHC = IMes, IPr) in dmso. Furthermore, the reaction of Na2[Fe(CO)4]\ub72thf with two equivalents of M(NHC)Cl in thf afforded the neutral compounds Fe(CO)4{M(NHC)}2 (M = Cu, NHC = IMes, 11; M = Cu, NHC = IPr, 12; M = Ag, NHC = IMes, 13; M = Ag, NHC = IPr, 14). 2 and 4 further reacted with one equivalent of M(IPr)Cl (M = Cu, Ag, Au) resulting in the trimetallic clusters Fe(CO)4{Cu(IPr)}{Ag(IPr)} (18), Fe(CO)4{Cu(IPr)}{Au(IPr)} (19), and Fe(CO)4{Ag(IPr)}{Au(IPr)} (20). 1-4, 11-14 and 18-20 have been spectroscopically characterized by IR, 1H and13C{1H} NMR techniques. The molecular structures of 2, 12, 18, 19 and 20 have been determined through single crystal X-ray diffraction. The structure, bonding and stability of the copper and silver IMes derivatives were compared to the related Fe-Au clusters previously reported on the basis of theoretical calculations. Stability of the Fe-M bonds decreases in the order Au &gt; Cu &gt; Ag, and the same trend was found for what concerns the M-IMes interactions. The decomposition products of 1-4, 11-14 and 18-20 have been studied allowing, among the others, the structural characterization of the new species [Fe2(CO)8{Ag(IPr)}]\u2013 (10) and Fe(CO)4(CH2IMes) (21)