I. P. Stolyarov

A novel giant palladium cluster

Electron microscopy, electron diffraction, EXAFS, and ultracentrifuging data show that a new catalytically active cluster prepared by reduction of Pd(OAc)2 by H2 in the presence of L = 1,10-phenanthroline, or 2,2′-bipyridine, followed by O2 treatment, contains a close-packed metal nucleus (570 ± 30 Pd atoms) bearing 60 ± 3 co-ordinated L and 180 ± 10 OAc– in the outer sphere of the cluster.

Hydroperoxide Oxidation of Difficult-to-Oxidize Substrates: An Unprecedented C–C Bond Cleavage in Alkanes and the Oxidation of Molecular Nitrogen

In the V(V)H2O2/AcOH system, C5–C20n-alkanes, isooctane, and neohexane undergo oxidation to ketones and alcohols; the oxidation products of branched alkanes are indicative of a C–C bond cleavage in these substrates. A concept is developed, according to which the peroxo complexes of vanadium(V) are responsible for alkane oxidation. These complexes can transfer the oxygen atom or the O+· radical cation to a substrate. The formation of nitrous oxide was found in the oxidation of molecular nitrogen in the H2O2/V(V)/CF3COOH system.

The route to heteronuclear nanoclusters from the viewpoint of coordination chemistry

We propose a new approach to the synthesis of heterobimetallic nanoclusters and materials proceeding from structurally related simple heterobinuclear carboxylato complexes [Pd(μ-OOCR)4M] (R = Me or t-Bu) containing PdII together with transition (ZnII, CuII, NiII, CoII, MnII), alkaline-earth (CaII, SrII, BaII), and rare-earth (NdIII, SmIII, EuIII, TmIII, YbIII) complementary metals. We studied effect of the complementary metal on the molecular geometry, the reaction with N-bases, and the products of thermal transformations of the heterobinuclear complexes, which are building blocks of complex polynuclear structures. We demonstrate, using the palladium(II) zinc(II) acetate complex as an example, that the catalytically active nanoparticles produced by the reductive thermolysis of palladium(II)-based heterometallic complexes far exceed conventional catalysts in their activity and selectivity.

Structure of the Ligand and Solvation Shells of the Giant Pd561Phen60(OAc)180 Cluster

In an IR spectroscopic study, we have investigated the ligand and solvation shells of the giant Pd561Phen60(OAc)180 cluster, where Phen = 1,10-phenanthroline and OAc- are acetate anions, in the solid state and in colloid solutions of acetic acid. Based on the data obtained, we revised the previous idealized model of the cluster which concerns the palladium nucleus-liquid interface. In the solid, the ligand shell of the cluster consists of coordinated Phen and OAc- ligands with a very low content of noncoordinated outer-spheric acetate anions. In acetic acid colloid solutions, interaction of HOAc molecules with coordinated OAc- anions results in quantitative removal of the latter from the ligand shell, forming (OAcċnHOAc)-ċkHOAc complex anions with n≈8 or 9 and k≈20. The anions comprise the outer-spheric solvation shell of the cluster, while the coordination shell contains only phenanthroline ligands.

Unusual selective allylation of norbornadiene in the presence of palladium nanoclusters

The reaction of norbornadiene (NBD) with allyl acetate in the presence of the nanocluster Pd147phen32O60(OCOBut)30 (Pd-147; phen is 1,10-phenanthroline) and PPh3 in acetonitrile is nonselective and is accompanied by the decomposition of the cluster, affording the same allylation products of NBD as the reaction with Pd3(OAc)6 or Pd(dba)2 (dba is dibenzylideneacetone) combined with PPh3. In contrast, in the ionic liquid [bmim][BF4] (bmim is 1-butyl-3-methylimidazolinium), the Pd-147 is not decomposed and the reaction occurs selectively to give methylidene(vinyl)norbornene as the sole product. The data obtained suggest that in an ionic liquid, the reaction under study is catalyzed by the nanocluster Pd-147 rather than by the products of its decomposition.

New palladium nanoclusters. Synthesis, structure, and catalytic properties

The reduction of palladium(ii) carboxylates Pd3(OCOR)6 (R = Me, Et, CHMe2, CMe3) with hydrogen in alcohol solutions containing 1,10-phenanthroline (phen) and subsequent oxidation with oxygen gave new palladium nanoclusters, mainly particles with a nearly spherical metal core and an average size of 18 Å. Based on elemental analysis, NMR, X-ray photoelectron spectroscopy, and EXAFS, nanoclusters were described by the idealized formula Pd147phen32O60(OCOR)30. The specimens contained up to ∼25% smaller 55-atomic Pd clusters with a ∼10 Å metal core. New nanoclusters catalyze hydrogenation of alkynes and alkenes, reduction of nitriles with formic acid, oxidation of aliphatic and benzylic alcohols, oxidative esterification of ethylene and propylene, and disproportionation of benzyl alcohol into toluene and benzaldehyde.

Formation of palladium hydride complexes upon the reduction of Pd(II) by hydrogen

ConclusionsThe reduction of palladium(II) acetate by hydrogen in the presence of 1,10-phenanthroline or 2,2′-dipyridyl gives palladium hydride clusters containing a massive metal-like nucleus with interstitial hydrogen atoms. The ligands are found to be peripheral palladium atoms, while the acetate groups are found in the external sphere.