William C. Kaska

A highly active alkane dehydrogenation catalyst: stabilization of dihydrido rhodium and iridium complexes by a P–C–P pincer ligand

The novel P–C–P pincer complex, [IrH2{C6H3(CH22PBut2)2}] has long-term stability and 200 ° C and catalyses the transfer dehydrogenation of cyclooctnane to cyclooctene at the rate of 12 turnovers min1 min–1.

Transition metal complexes of hexaphenylcarbodiphosphorane

Abstract The displacement of tetrahydrofuran (THF) from W(CO) 5 (THF) with hexaphenylcarbodiphosphorane yields a compound with a carbon-metal bond (CO) 5 W C[P(C 6 H 5 ) 3 ] 2 . The in situ photolysis of tungsten hexacarbonyl and hexaphenylcarbodiphosphorane, however, yields a product (CO) 5 W − CC + P(C 6 H 5 ) 3 . Ethylenebis(triphenylphosphine)platinum and hexaphenylcarbodiphosphorane in benzene yield a platinum containing heterocycle [(C 6 H 5 ) 3 P] 2 PtC[ P(C 6 H 5 ) 3 ]P -(C 6 H 5 ) 3 .

How carbon monoxide bonds to alumina-supported rhodium particles. Tunneling spectroscopy measurements with isotopes

Carbon monoxide chemisorbs in at least three different ways on alumina-supported rhodium particles: There are two different linear-bonded species and at least one bridge-bonded species. These conclusions from tunneling measurements on a model catalyst surface are based on isotope shifts with 13CO and C18O. They are in agreement with the conclusions from infrared measurements on dispersed metal catalysts.

Rhodium pincer complexes of 2,2′-bis(diphenylphosphino)diphenylamine

Abstract The novel pincer ligand 2,2′-bis(diphenylphosphino)diphenylamine (1) has been synthesized by treatment of 2,2′-dibromodiphenylamine with n-butyl lithium and subsequent reaction with diphenylchlorophosphine. When ligand 1 is treated with RhCl3 hydrate the dinuclear complex 1a forms which can be converted into the square planar carbonyl complex 1c upon reduction with Na/Hg in the presence of CO. Depending on the reaction conditions two different complexes were isolated when 1 reacts with [(COE)2RhCl]2. In THF the hydrochloro complex 1b and with n-butyl lithium the COE complex 1d is generated. Interestingly, the formation of 1b represents a rare case of N–H oxidative addition to a late transition metal complex fragment. Compound 1c is observed upon reaction of the COE complex 1d with carbon monoxide. Quantum chemical calculations at different levels of theory are in good agreement with the experimental structure of 1c.

Crystal and molecular structure of bis(pentamethylcyclopentadienyl)dicarbonyldicobalt

The compound (η 5 -Me 5 C 5 )Co(μ-CO) 2 Co(η 5 -Me 5 C 5 ) has been prepared and characterized. The crystal structure has been determined and the CoCo distance found to be 2.327(2) A. This structure completes the information on MM distances in the series of compounds CpM(EO)(E′O)MCp, where Cp = C 5 H 5 or Me 5 C 5 , M = Fe or Co and E = C or N, several members of which were previously studied by others. The EAN rule would predict a double bond here as in the isoelectronic compound CpFe(NO) 2 FeCp and the MM distances are virtually identical in the two molecules. Disordered packing of the molecules limits the accuracy with which the molecular dimensions, other than CoCo, may be determined. However, the structure is in generally close agreement with those of the other molecules in the set previously mentioned. The crystals are monoclinic with a 7.433(2) A, b 14.704(8) A, c 9.671(2) A, β 101.84(2)° and V 1034.6(7) A 3 ; Z = 2. The structure was refined to R 1 = 0.062 and R 2 = 0.074 using a disordered model in space group P 2 1 / m .

Formation of hydrocarbons from carbon monoxide on rhodium/alumina model catalysts

Abstract When tunnel junctions containing carbon monoxide adsorbed on alumina-supported Rh are heated in hydrogen the vibrational peaks due to carbon monoxide decrease and a new set of vibrational peaks grows. Shifts in the positions of some of these new peaks are observed if the normal 12C16O is replaced by 13C16O, but not if it is replaced by 12C18O. This suggests that the new surface species includes the carbon from the CO, but not the oxygen. The set of new peaks grows together and is in one-to-one correspondence with the peaks of ethylidene as extrapolated between published spectra of halogenated derivatives. A different surface species, tentatively identified as formate ions, can be produced by heating without hydrogen.

Thermochemical alkane dehydrogenation catalyzed in solution without the use of a hydrogen acceptor

(PCP)IrH2 [PCP = η3-C6H3(PBut2)2-1,3] catalyzes the efficient (several hundred mol product/mol catalyst) dehydrogenation of alkanes under reflux to give the corresponding alkenes and dihydrogen.

Low energy vibrational modes of carbon monoxide on iron

The energy range 300 to 600 cm−1 contains bending and metal–carbon stretching vibrations for carbon monoxide chemisorbed on transition metals. Tunneling spectroscopy reveals vibrations at 436, 519, and 569 cm−1 for carbon monoxide chemisorbed on alumina‐supported iron particles. Measured vibrational mode shifts with the isotopes 13C16O and 12C18O suggest that the lower two are bending vibrations and that the highest one is an iron–carbon stretching vibration for the structure Fe=C=O. Comparisons with infrared data on supported iron particles, iron particles in oil, and iron carbonyls suggest the complementary nature of infrared and tunneling spectroscopy in deducing the nature of adsorbed species.

A novel functionalized P,C,P pincer ligand complex

Abstract Reaction of 3,5-di(bromomethyl)nitrobenzene with di-t-butylphosphine and subsequent treatment with sodium acetate gives the novel functionalized P,C,P pincer ligand 2. Heating an isopropanol/water solution of 2 with iridium(III)chloride results in the iridium hydrochloride complex 3. This complex was characterized by X-ray structure analysis in the solid state, NMR spectroscopy in solution, and density functional calculations in the gas phase.

Vibrational spectra of carbon monoxide chemisorbed on alumina‐supported nickel particles: A tunneling spectroscopy study

Tunneling spectroscopy is used to study the chemisorption of CO on small nickel particles. The particles are grown from vapor on a thermally oxidized aluminum substrate. Carbon monoxide is observed to chemisorb in at least four distinct ways, giving CO stretching frequencies of 256.5, 246, 222, and 207 meV. The 256.5 meV species has low frequency modes at 45.5 and 59.5 meV. The low frequency modes of the remaining three species are not resolved sufficiently for identification. The frequencies of all modes were found to have some coverage dependence. The largest shift is seen in a CO stretching vibration that moves from 200 to 207 meV with increasing coverage. The effect of hydrogen coadsorption is examined and evidence for the presence of oxygen on the particles is presented. The reaction of hydrogen with the CO chemisorbed on these nickel particles is found to produce very little surface hydrocarbon in contrast to results found previously for rhodium particles under similar conditions.