John S. Bradley

Clusters, colloids and catalysis

Abstract Metal cluster molecules containing easily displaceable ligands have been successfully exploited in organometallic cluster synthesis and to a lesser extent in homogeneous catalysis. We have extended this concept to elemental metal clusters in a fluid medium, by stabilizing colloidal transition metal particles in non-polar hydrocarbon solutions using polymers as tenuous ligands to prevent aggregation of the metal. The colloids were prepared by condensation of the metal vapor into a cold solution of the stabilizing polymer. In the absence of polymer, the metal atoms agglomerate into

The Chemistry of Carbidocarbonyl Clusters

100 μm aggregates of microcrystalline metal, containing crystallites of the order of 20–50 A in diameter. In the presence of polymer, agglomeration of the metal proceeds only to the 20–50 A stage, at which point the polymer sterically stabilizes the metal cluster and prevents further aggregation. The colloidal solutions thus obtained exhibit considerable thermal stability. The homogeneous catalytic properties of these solutions have been investigated in the hydrogenation of acenaphthylene. Colloidal metals prepared in this way also serve as sources of heterogeneous metal catalysts; copper-nickel colloids have been used in this way to probe the particle size dependency of filamentous carbon formation from ethane.

Surface chemistry on transition metal colloids—an infrared and NMR study of carbon monoxide adsorption on colloidal platinum

Publisher Summary This chapter discusses the chemistry of carbidocarbonyl clusters. The rapid expansion in carbidocarbonyl cluster chemistry has enabled the chemistry of these compounds to be addressed in its own right rather than as a subgroup of cluster chemistry as a whole. The first carbidocarbonyl transition metal cluster to be recognized was Fe 5 C(CO) 15 ,which was isolated in very low yield from the reaction of tri-iron dodecacarbonyl with methylphenylacetylene and characterized by X-ray diffraction by Dahl and coworkers. The lowest nuclearity carbidocarbonyl clusters of ruthenium and osmium are Ru 5 C(CO) 15 and Os 5 C(CO) 15 . The chemistry of the carbidocarbonyl clusters of cobalt and rhodium is predominantly the work of Italian school of the late Paolo Chini and colleagues. Pyrolysis of Et 4 N[ReH 2 (CO)] at 250°C in n-tetradecane yields a mixture of polynuclear products from which two carbidocarbonyl clusters of rhenium have been isolated. The application of spectroscopic techniques familiar in organometallic chemistry to the unique features of carbidocarbonyl clusters has become more evident since the previous review of this field. Since the completion of this review (mid 1982), the chemistry of carbidocarbonyl clusters has continued to expand rapidly.

The synthesis and molecular structure of η6-carbidohexadecacarbonylhexaruthenate(-2): a high yield route into Ru6C chemistry[1]

Highly dispersed (<10{angstrom}) platinum has been prepared in colloidal solution by condensing platinum vapor into a solution of triisobutylaluminoxane in methylcyclohexane. Carbon monoxide, adsorbed in a linear mode on the surface of the colloidal metal, has been characterized by infrared spectroscopy and {sup 13}C NMR. The chemical shift of the adsorbed CO is 192 ppm, and the absence of a Knight shift is interpreted in terms of a pseudomolecular description of the highly dispersed platinum particles, which are not large enough to exhibit metallic properties. The CO covered colloid is converted by hydrolysis into the molecular platinum carbonyl anion clusters (Pt{sub 3}(CO){sub 6}){sub n}{sup 2 {minus}}, n = 3, 4.

The Reaction of acetylenes with bis(η5-cyclopentadienyl)dicarbonylchromium]

Abstract Ru 6 C(CO) 16 2- is produced in reproducibly high yield by the reduction of Ru 3 12 with Mn(CO) 5 in refluxing diglyme. 13 C NMR evidence identifies carbon monoxide as the source of the encapsulated carbon atom. The facile prototype synthesis of an organometallic derivative of the Ru 6 C core is described.

The syntheses, molecular and electronic structures of two μ4-vinylidene tetrairon clusters

Abstract The reaction between [η-5-C5H5Cr(CO)2]2 and acetylenes proceeds readily in refluxing toluene, to produce a series of binuclear chromacyclopentadiene complexes, the first examples of chromium metallacycles to be isolated.

The characterization of adsorbed carbon monoxide on colloidal palladium by infrared and high resolution 13C nuclear magnetic resonance spectroscopy

Abstract The syntheses, crystal structures and electronic structures of the new μ4-vinylidene clusters, Fe4(CO)12(CC(OCH3)2) and Fe4(CO)12(CC(OCH3)CH3), are reported. Fe4(CO)12(CC(OCH3)2) was prepared by the methylation of [Fe4(CO)12(CCO2CH3)]− with trimethyloxonium fluoroborate in methylene chloride at 25°C. Fe4(CO)12(CC(OCH3)CH3) was prepared in an analogous manner from [Fe4(CO)12(CC(O)CH3)]−. Fe4(CO)12(CC(OCH3)2) crystallizes in the monoclinic space group P21/c (C2h5 No. 14) with a = 13.900(2), b = 8.909(2), c = 17.116(4) A, β = 94.59(2)°; pcalc = 2.03 g cm−3 for mol. wt 645.6 and Z = 4. Fe4(CO)12(CC(OCH3)CH3) crystallizes in the monoclinic space group P21/c (C2h5 No. 14) with a = 28.441(6), b = 9.204(2), c = 17.466(4) A, β = 108.51(2)°; pcalc = 1.93 g cm−3 for mol. wt = 629.6 and Z = 8. Both clusters have an open butterfly core of four iron atoms with the vinylidene ligand bound to all four metal atoms. Molecular orbital calculations using the Fenske—Hall method were carried out for the two clusters. The molecular and electronic structures of the molecules are compared with each other and with those of μ4-methylidyne clusters. Although both of these clusters contain a formal CC double bond in the vinylidene ligand, the presence of oxygen atoms in these ligands leads to a delocalized π system and only partial double bond character in this CC bond. Changes in the structure of the cluster framework can be correlated with the oxygen content and thus double bond character in the vinylidene ligand.

Synthesis and molecular structure of .mu.4-carbido-.mu.2-carbonyl-dodecacarbonyltetrairon, a neutral iron butterfly cluster bearing an exposed carbon atom

Carbon monoxide adsorbed on a stabilized 20 A palladium colloid in methylcyclohexane has been characterised by solution IR and high resolution NMR spectroscopy.