Robert J. Angelici

AN OVERVIEW OF MODELING STUDIES IN HDS, HDN AND HDO CATALYSIS

Abstract Recent legislation directed at reducing sulfur levels in petroleum-based fuels has led to numerous studies of commercial hydrotreating, the process whereby sulfur, nitrogen, and oxygen are removed from organic compounds in petroleum feedstocks. The goal of this overview is to highlight organometallic and clean surface model studies that offer realistic ways of understanding details of hydrodesulfurization (HDS), hydrodenitrogenation (HDN) and hydrodeoxygenation (HDO) reactions as they occur on heterogeneous hydrotreating catalysts.

Transition metal complexes with terminal carbyne ligands

Publisher Summary This chapter discusses the chemistry of molecular carbyne complexes; there is also much interest in them as models for species that are possibly present on metal surfaces in catalytic reactions. Surfacebound methine (CH) is a proposed intermediate in the Fischer–Tropsch synthesis, and alkylidyne groups are suggested as intermediates in heterogeneously catalyzed alkyne metathesis reactions. X-Ray structure determinations of carbyne complexes show that they have very short metal–carbon bond lengths consistent with a metal–carbon triple bond. In certain cases, ∞-protons of an alkylidene ligand may be abstracted by a base to give alkylidyne compounds. Addition of electrophiles to terminal isonitrile (CNR) ligands gives aminocarbyne complexes; the analogous reaction of terminal thiocarbonyl (CS) ligands gives thiocarbynes. Fischer and Himmelreich reported the abstraction of oxygen from an anionic carbamoyl compound with SOCl 2 to give an aminocarbyne compound. Reactions of cationic carbyne compounds with nucleophiles proceed exclusively by nucleophilic attack at the carbyne carbon atom, thus providing a synthetically useful route to certain carbene complexes. The field of transition-metal carbyne chemistry has matured to the point where a great deal is known about the structure, bonding, and reactivity of the carbyne ligand.

A convenient synthetic route to complexes of the types (πC5H5Fe(CO)2X and (πC5H5)Fe(CO)2L

Abstract Oxidation of [(πC 5 H 5 Fe(CO) 2 ] 2 by molecular oxygen in acetone and aqueous fluoroboric acid followed by reaction with anionic or neutral ligands provides a convenient route to complexes of the type (πC 5 H 5 )Fe(CO) 2 X and (πC 5 H 5 )Fe (CO) 2 L + (X  Cl, Br, NCO, CN, NO 3 , N 3 , O 2 CH, O 2 C 2 Cl 3 ; L  P(C 6 H 5 ) 3 , C 5 H 5 N, H 2 NNH 2 , S(C 4 H 9 ) 2 ). Spectroscopic evidence indicates that the intermediate in these reactions is the cationic aquo complex, (πC 5 H 5 )Fe(CO) 2 (OH 2 ) + .

Deep desulfurization by selective adsorption of dibenzothiophenes on Ag+/SBA-15 and Ag+/SiO2

Silver (Ag+) salts adsorbed on amorphous silica or mesoporous SBA-15 extract dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-Me2DBT) from simulated, hydrotreated petroleum feedstocks.

Thiophene, 2,3- and 2,5-dihydrothiophene, and tetrahydrothiophene hydrodesulfurization on Mo and Re/γ-Al2O3 catalysts

Abstract Comparative studies of the hydrodesulfurization (HDS) of thiophene, 2,3-dihydrothiophene, 2,5-dihydrothiophene and tetrahydrothiophene were performed using Mo γ- Al 2 O 3 and Re γ- Al 2 O 3 catalysts. Reaction pathways for interconversion of the organosulfur compounds were shown to exist. Both dihydrothiophene compounds were highly reactive and formed significant amounts of 1,3-butadiene at 300 °C over Re catalysts. The dihydrothiophenes are proposed to be possible reaction intermediates for thiophene HDS.

Isocyanide ligands adsorbed on metal surfaces: applications in catalysis, nanochemistry, and molecular electronics.

Knowledge of the coordination chemistry and reactivity of isocyanide ligands in transition-metal complexes forms the basis for understanding the adsorption and reactions of isocyanides on metal surfaces. In this overview, we explore reactions (often catalytic) of isocyanides adsorbed on metal surfaces that reflect their patterns of reactivity in metal complexes. We also examine applications of isocyanide adsorption to the stabilization of metal nanoparticles, the functionalization of metal electrodes, and the creation of conducting organic-metal junctions in molecule-scale electronic devices.

Studies of the mechanism of thiophene hydrodesulfurization: Conversion of 2,3- and 2,5-dihydrothiophene and model organometallic compounds

Catalytic hydrodesulfurization (HDS), the process by which organically bound sulfur is removed from crude oils, is one of the largest-scale chemical processes practiced in the world. Thiophene is typical of the organosulfur compounds found in petroleum, and considerable effort has been directed toward investigating the mechanism for thiophene hydrodesulfurization. Recently, the authors have reported new kinetic information involving the HDS of thiophene, 2,3- and 2,5- dihydrothiophenes, and tetrahydrothiophene. These studies were performed with both Re/{gamma}-Al{sub 2}O{sub 3} and Mo/{gamma}-Al{sub 2}O{sub 3} catalysts using a flow microreactor system; in particular, rhenium studies provided new information data concerning reaction intermediates. They have also been able to prepare and characterize thiophene-related organometallic compounds which serve as plausible models for bonding and conversion on catalytic surfaces. The combination of these studies has led to new insights concerning alternate mechanistic pathways for thiophene HDS. This comprehensive mechanism, which is based on kinetic studies using model HDS catalysts and on the synthesis and characterization of relevant transition metal complexes, is offered as a plausible route for thiophene HDS.

Synthesis and reactions of carbamoyl carbonyl complexes of rhenium(I)

Abstract Re(CO)5Br reacts with primary and secondary aliphatic amines, NHRR′, to form the carbamoyl complex,cis-Re(CO)4(NHRR′)(CONRR′). Anhydrous HCl removes -NRR′ from the carbamoyl group to yield the cation, [Re(CO)5(NHRR′)]+. This cation reacts with NHRR′ to regenerate the carbamoyl complex. With hydrazine, [Re(CO)5(NH2CH3)]+ initially yields the carbazoyl compound,cis-Re(CO)4(NH2CH3)(CONHNH2), which loses NH3 to give the isocyanate complexcis-Re(CO)4(NH2CH3)(NCO) as the Final product. Reactions with some methylsubstituted hydrazines proceed in the same manner. The isocyanate complex may also be prepared by reaction of the cation with azide ion, N−3. With I−, the cation yields Re(CO)5I. IR and PMR spectra of the new compounds and mechanisms of their reactions are discussed.

Reactions of cyclopentadienyliron carbonyl cations with amines

[C 5 H 5 Fe(CO) 2 L] + (L = CO, P(C 6 H 5 ) 3 ) reacts with primary and secondary amines to form carboxamido complexes, C 5 H 5 Fe(CO)(L)(CONHR): [C 5 H 5 Fe(CO) 2 L] + + 2RNH 2 → C 5 H 5 Fe(CO)(L)(CONHR) + RNH 3 + Their reaction with HCl removes the -NHR group from the carboxamido group: C 5 H 5 (CO)(L)(CONHR)+HCl → [C 5 H 5 Fe(CO) 2 L] + Cl − +RNH 2 The [C 5 H 5 Fe(CO) 3 ] + cation reacts with NaOCH 3 to form the alkoxycarbonyl derivative, C 5 H 5 Fe(CO) 2 C(O)OCH 3 , according to the equation: [C 5 H 5 Fe(CO) 3 ] + +OCH 3 − → C 5 H 5 Fe(CO) 2 C(O)OCH 3 A mechanism of nucleophilic attack at the carbonyl carbon is proposed for the formation of the carboxamido and alkoxycarbonyl derivatives. The properties of the new compounds are listed, and the carbonyl stretching frequencies are discussed.

Thioketone complexes of chromium, molybdenum, and tungsten carbonyls

Abstract A series of thioketone complexes of the type M(CO) 5 (S=CR 2 ), where M = Cr, Mo or W, and R = Me, Et or Ph, have been prepared by the reaction of M(CO) 5 I − with Ag + in the presence of the ketone (O = CR 2 ) and H 2 S. Coordination to the metal stabilizes thioketones such as thioacetone which, otherwise, is unstable and polymerizes rapidly. Infrared, 1 H and 13 C NMR spectra of the compounds are consistent with the ligands being coordinated through the sulfur atom. The W(CO) 5 (S=CR 2 ) complexes react with MeCN, I − , N 3 − and C 6 H 11 NH 2 (in CCl 4 ) to give the thioacetone-displaced products, W(CO) 5 L. With C 6 H 11 NH 2 in pentane, another product is obtained which apparently results from amine addition to the thioketone ligand. This compound reacts with MeI and Et 3 O + to give the dialkyl sulfide complexes, W(CO) 5 (SMe 2 ) and W(CO) 5 (SEt 2 ).