Charles U. Pittman

Metal cluster catalysis. 2. Selective reduction of nitrobenzene catalyzed by rhodium carbonyl cluster anions. Evidence for water gas shift reaction

Abstract The rhodium cluster complex, Rh6(CO)16, has been found to catalyze the homogeneous reduction of nitrobenzene to aniline at temperatures above 80 °C in the presence of N,N-dimenthylbenzylamine, using any one of the following reducing gases: (1) H2/CO, (2) H2, (3)CO/H2O. The reductions are highly selective and aniline was the only product detected. The same result was obtained using Amberlyst A-21 resin beads which contained polymerbound N,N-dimethylbenzylamine moieties which, in turn, immobilize the rhodium clusters. It was shown, by using D2O, and following deuterium incorporation into the resulting aniline, that the water is the source of hydrogen when CO/H2O was used. When nitrobenzene is absent, this catalyst system promotes the water—gas shift reaction. Unlike aromatic nitro groups, aliphatic nitro groups were not reduced. However, the water—gas shift reaction was catalyzed. The kinetics of aniline formation were first order in nitrobenzene and the effect of pressure on the reaction is described. Use of the resin catalyst led to lower rates and a remarkably air sensitive catalyst system relative to the homogeneous reactions.

1,3-Butadiene oligomerization catalyzed by polymer-attached palladium complexes. Comparison with homogeneous catalysis

Abstract Palladium chloride, tetrakis (triphenylphosphine) palladium, and palladium acetate have been anchored to diphenylphosphinated styrene-divinylbenzene resins to provide resin catalysts with from 1.1 to 10.9% Pd loadings and P:Pd ratios from 2.1 to 25.7. Butadiene was oligomerized to product mixtures of E-1-acetoxy-2,7-octadiene, 6; 3-acetoxy-1,7-octadiene, 7; E-1,3,7-octadiene, 8; E-1-acetoxy-2-butene, 9; and 3-acetoxybutene, 10; in THF-HOAC at 100 °C in the presence of these anchored catalysts. The product distribution was essentially unchanged as the percentage Pd in the resin was varied at constant P:Pd. The product distribution varied modestly as P:Pd was changed. The product distribution for reactions catalyzed by such resins was the same as those homogeneously catalyzed by PPh 3 plus Pd(OAc) 2 when compared at equal P:Pd ratios. These observations rule out a mechanism involving a bridged bimetallic intermediate in Pd(OAc) 2 catalyzed reactions because the resin matrix effectively isolates Pd sites from one another. Palladium leaching was serious for anchored PdCl 2 and Pd(PPh 3 ) 4 but less so for Pd(OAc) 2 . The effect of the P:Pd ratio on leaching is discussed. In the presence of triethylamine, metallic palladium was precipitated in the resin.

Use of polymer matrices to activate palladium(0) catalysts and reduce catalyst agglomeration

The dimerization–alkylation of butadiene to 1-methoxy-3,7-octadiene and 3-methoxy-1,7-octadiene has been studied in benzene at 100°C using both homogeneous and resin-attached palladium(0) catalysts. Pd(PPh3)4 was used as the homogeneous catalyst. Styrene-divinylbenzene (1% crosslinked) resins, functionalized with diphenylphosphine groups, were treated with Pd(PPh3)4 to give the resin-bound catalysts by ligand exchange. The rates of the homogeneously catalyzed reactions reach a limiting value as the catalyst concentration reaches 4 X 10−3 to 6 X 10−3 M due to equilibrium processes which limit the concentration of active species. The concentration of palladium in the resins is far higher (0.5 X 10−1 to 7 X 10−1 M), yet at similar P/Pd ratios the rates are greater per Pd using the resins. Furthermore, much larger catalyst charges may be employed, with the resin catalysts, without reaching limiting rates. Apparently, the resin retards the ability polymer-attached phosphines to highly coordinate (i.e., 3 or 4) palladium(0) relative to the corresponding situation in homogeneous solution. The resin matrix appears to retard the tendency, exhibited in the homogeneous reactions, for the catalyst to agglomerate and precipitate from solution as an inactive material.

Metal cluster catalysis: III. Selective homogeneous hydrogenations catalyzed by [n5-C5H5)Fe(u3-CO)l4

Abstract The iron cluster, [(n5-C5H5)Fe(μ3-CO)]4, 1, catalyzes the selective hydrogenation of alkynes to alkenes at 100–130° and 100–1000 psig and the selective reduction of terminal alkynes to olefins in the presence of alkenes or internal alkynes. Internal alkynes are slowly reduced to cis olefins, aryl nitro groups to aniline derivatives, and terminal activated carbon-carbon double bonds (methyl acrylate, acrylonitrile) are hydrogenated. The cluster concentration, monitored by high pressure liquid chromatography, was unchanged after 1148 and 1410 turnovers. Cluster 1 was isolated in 95–97% yields after catalytic reduction (1000 turnovers) and no other iron-containing species were detected. After 280 turnovers, the catalyst solution was filtered through an ultrafiltration membrane into a second vessel where hydrogenation of 1-pentyne continued. Fragmentation of 1 tc

The preparation and properties of triferrocenylphosphine derivatives of metal carbonyls

The triferrocenylphosphine monosubstitution products of M(CO)6 (M = Cr, Mo, W), Fe(CO)5 and Mn2(CO)10 have been prepared and characterized. The CO stretching spectra have been compared with those of the triphenylphosphine analogs. Simplified sets of force constants describing the CO stretching vibrations have been computed for the Group VI derivatives according to the method of Cotton and Kraihanzel, and from these the σ-donor and π-acceptor properties of the ligand evaluated. Triferrocenylphosphine is a better donor ligand than triphenylphosphine.

Organometallic Polymers. XXVII. Radical-Initiated Polymerization and Copolymerization of π-(2, 4-Hexadien-1-yl Acrylate) tricarbonyliron

Abstract The novel monomer, π-(2, 4-hexadiene- l-yl acrylate) tricarbonyliron (HATI), has been prepared by two routes. It was homopolymerized and copolymerized with acrylonitrile, vinyl acetate, styrene, and methyl acrylate in benzene solutions. In all cases azobisisobutyronitrile was the initiator. The relative reactivity ratios, where HATI is defined as M1, were determined: r1 = 0.34, r2 = 0.74, M2 = acrylonitrile; r1 = 2.0, r2 = 0.05, M2 = 0.74, M2 = acrylonitrile; r1 = 2.0, r2 = 0.05, M2 = vinyl acetate; r1 = 0.26, r2 = 1.81, M2 = styrene; and r1 = 0.30, r2 = 0.74, M2 = methyl acrylate. The homo-and copolymers had high values of Tg. When polymerizations are carried out at high concentrations, a very high molecular weight tail is observed in HATI hompolymerizations and in HATI-methyl acrylate copolymerizations. The polymers were characterized by IR, gel permeation chromatography, viscosity, and differential scanning calorimetry studies. Finally, thermal decompositions carried out in air resulted in dec...

2-Pentene hydroformylation catalyzed by polymer-anchored versus homogeneous cobalt complexes: the effect of chelating phosphine

Abstract Polymer-anchored cobalt carbonyl phosphine complexes have been synthesized for use as hydroformylation catalysts. Three types of structures were prepared, including ℘-C6H4PPh2Co(CO)3Co(CO)3Ph2PC6H4-℘, 2, ℘-C6H4CH2PPh2Co(CO)3Co(CO)3Ph2PCH2C6H4-℘, 4; and the chelated species ℘-C6H4P(Ph)CH2CH2PPh2Co(CO)3Co(CO)3, 5. 2-Pentene hydroformylations were studied using both the resin-anchored catalysts and the corresponding homogeneous species. Resin catalysts containing the diphos unit (i.e., 5) displayed a higher selectivity to n-hexanal when compared with the corresponding homogeneous catalytic species (all experiments were performed with H2/CO = 1/1 at 1100–1150 psi and 40 °C. Resins with structures 2 and 4 gave about the same selectivities as their homogeneous analogs (i.e., Co2(CO)8 plus PPh3) when compared at equivalent P/Co ratios, except when the phosphine loading on the resin was either very high or very low.

Search for a Steric Penultimate Effect: Copolymerization of 2,3,4-Trimethyl-3-pentyl Methacrylate with Styrene

Abstract The hindered monomer, 2,3,4-trimethyl-3-pentyl methacrylate (I), was synthesized for penultimate effect studies. Since it readily homopoiymerized (km111≠ 0) and readily copolymerized with styrene, copolymerizations of I with styrene were carried out at 60°C in benzene with AIBN as initiator. The conversion to copolymer and the copolymer composition were determined by using GLC techniques. Composition-conversion data was analyzed by performing a computerized nonlinear least-squares fitting to the integrated form of the penultimate model equation. The experimental design included the use of optimized M1°/M2° ratios. The penultimate reactivity ratios calculated from these data were r1′ = 0.23, r1′= 0.59, r2 = 0.59, r2′ = 1.34. Thus, when I is the penultimate unit, a terminal styryl radical prefers to add styrene, whereas when styrene is the penultimate unit, terminal styryl radicals prefer to add I. These results constitute the best evidence for a steric penultimate effect yet available in the liter...

Homogenizing Metal Oxide Catalysts

Abstract Metal oxide particles have been prepared which are “soluble” in hydrocarbon solvents. The reaction of either a metal (or its metal oxide) with water, mineral spirits, and a mixture of carboxylic acids can result in hydrocarbon-miscible metal oxide core particles of 20-1000A diameter sizes which are coated with a layer of hydrophobic carboxylates. This will only occur if the metal:acid ratio exceeds one. The particle size increases as the metaltacid ratio increases. The surface carboxylate groups are in equilibrium, preventing the use of colligative property measurements in determining molecular weights. Sedimentation velocity studies confirmed that particle aggregation equilibria occur which are solvent dependent. Aggregation is more serious in polar solvents. The distribution of carboxylic acids used did not effect the particle size. Cobalt and manganese oxide particles have been used in oxidations of cyclohexane, toluene, and xylenes. Cobalt oxides were used in hydroformylations of 1-pentene, N...

Characterization of Hydrocarbon Soluble Metal Oxides. Precursors to Supported Catalysts

Abstract The metal oxide carboxylate complexes described in the previous chapter have been characterized by infrared spectroscopy, x-ray diffraction, electron microscopy, and analytical ultracentrifugation. The molecular weights and solution particle diameters have been determined for a number of the hydrocarbon soluble particles by analytical ultracentrifugation methods, and the use of a spherical model consistent with the particulate shape observed by electron microscopy. The size of the soluble complexes has been studied as a function of: metal, metal/acid ratio, acid composition, and solvent. The molecular weights for the ultimate particles are reasonably independent of the metal employed in the synthesis and are relatively constant for materials with similar metal/acid equivalents ratios. The single particle molecular weights for the complexes studied ranged from approximately 5×104 to 1.5×106g mole−1. The solution size distribution was polydisperse in all cases, with aggregates of the ultimate parti...