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Asphaltenes comprise the heaviest and least understood fraction of crude petroleum. The asphaltenes are a diverse and complex mixture of organic and organometallic molecules in which most of the molecular constituents are tightly aggregated into more complicated suprastructures. The bulk properties of asphaltenes arise from a broad range of polycyclic aromatics, heteroatoms, and polar functional groups. Despite much analytical effort, the precise molecular architectures of the material remain unresolved. To understand asphaltene characteristics and reactivity, the field has turned to synthetic model compounds that mirror asphaltene structure, aggregation behavior, and thermal chemistry, including the nucleation of coke. Historically, molecular asphaltene modeling was limited to commercial compounds, offering little illumination and few opportunities for hypothesis-driven research. More recently, however, rational molecular design and modern organic synthesis have started to impact this area. This review provides an overview of commercially available model compounds but is principally focused on the design and synthesis of structurally advanced and appropriately functionalized compounds to mimic the physical and chemical behavior of asphaltenes. Efforts to model asphaltene aggregation are briefly discussed, and a prognosis for the field is offered. A referenced tabulation of the synthetic compounds reported to date is provided.

Here, we report the first study to use Fe2S2(CO)6 as a well-defined petroleum-soluble precatalyst for partial hydrogenation of polycyclic aromatic and heteroaromatic compounds, including pyrene, ph...

The structurally unique saddle-shaped paramagnetic tetrametallic clusters of Co(I) and Ni(I) with phosphoranimide ligands have been synthesized and proposed as catalyst precursors. The analogous Cu(I) nanocluster is planar and diamagnetic. These notable variations in geometry and ground electronic states indicate that the effect of metal and ligand substituents on the structure and electronic properties of these complexes requires investigation. We present a computational study of a series of these novel homoleptic complexes containing Co(I), Ni(I), and Cu(I) as well as Fe(I) coordinated to phosphoranimides with electron-donating and withdrawing substituents, conducted at the relativistic density functional theory level using ZORA-PBE/TZP. The optimized structures of the saddle-shaped Co(I) and Ni(I) and planar Cu(I) tetramers with linear N–M–N coordination are validated with respect to X-ray diffraction determinations. The ground-state analysis indicates that Cu(I) complexes are diamagnetic, whereas Ni(I) and Co(I) complexes are in high-spin states, in agreement with magnetic susceptibility measurements. The computational results show that Fe(I) complexes are saddle shaped and high spin. The Co(I) complex is stabilized by a metal macrocycle distortion from square to diamond, as elucidated from its Walsh diagram. The effects of metals and ligand substituents on the ground electronic state, metal center coordination environment, and energy of the complexes are investigated. The bulky tertiary butyl substituent causes the largest saddle-shape distortion of the tetramer marcocycle, which partially offsets its electron-donating effect. Macrocycle distortions with N–M–N site angles ranging from obtuse to alternating obtuse reflex are correlated with the increasing number of unpaired electrons. The phenyl-substituted complexes are expected to have the highest reactivity toward electrophiles. Understanding the interplay between structural and electronic parameters is intended to guide the development of synthetic cooperative systems for multielectron redox reactions, models of biological systems, and molecular magnets.

Petroleum asphaltenes are surface-active compounds found in crude oils, and their interactions with surfaces and interfaces have huge implications for many facets of reservoir exploitation, including production, transportation, and oil-water separation. The asphaltene fraction in oil, found in the highest boiling-point range, is composed of many different molecules that vary in size, functionality, and polarity. Studies done on asphaltene fractions have suggested that they interact via polyaromatic and heteroaromatic ring structures and functional groups containing nitrogen, sulfur, and oxygen. However, isolating a single pure chemical structure of asphaltene in abundance is challenging and often not possible, which impairs the molecular-level study of asphaltenes of various architectures on surfaces. Thus, to further the molecular fundamental understanding, we chose to use functionalized model asphaltenes (AcChol-Th, AcChol-Ph, and 1,6-DiEtPy[Bu-Carb]) and model self-assembled monolayer (SAM) surfaces with precisely known chemical structures, whereby the hydrophobicity of the model surface is controlled. We applied solutions of asphaltenes to these SAM surfaces and then analyzed them with surface-sensitive techniques of near-edge X-ray absorption fine structure (NEXAFS) and X-ray photoelectron spectroscopy (XPS). We observe no adsorption of asphaltenes to the hydrophobic surface. On the hydrophilic surface, AcChol-Ph penetrates into the SAM with a preferential orientation parallel to the surface; AcChol-Th adsorbs in a similar manner, and 1,6-DiEtPy[Bu-Carb] binds the surface with a bent binding geometry. Overall, this study demonstrates the need for studying pure and fractionated asphaltenes at the molecular level, as even within a family of asphaltene congeners, very different surface interactions can occur.

The synthesis and properties of a new polycyclic aromatic hydrocarbon containing eight annulated rings and based on the anthanthrene core is described. An unexpected, nucleophile-dependent Michael addition to a dibenzanthanthrene-1,7-dione is found, giving a product with three triisopropylsilylacetylene units and a remarkable solid-state structure (as determined by X-ray crystallography).

The catalytic hydrodenitrogenation of heavy petroleum fractions is important for the production of high-quality fuels, because the nitrogen-bearing compounds poison acidic catalysts and inhibit sulfur removal. Two families of synthetic nitrogen-containing model compounds representative of asphaltene molecular structures were catalytically hydrogenated over a commercial NiMo/γAl2O3 catalyst under industrial hydrotreating conditions, i.e., 370 °C and 18 MPa of hydrogen for 1 h, in a stainless steel batch reactor. The bridged compounds with pyridine as a center ring gave cracking, hydrogenation, and hydrodenitrogenation products with selectivities that depended on the position of substituents on the central pyridine ring. In contrast, a series of fused cholestane-benzoquinoline compounds gave only hydrogenation of all-carbon aromatic rings.

The preparation of seven-membered carbocycles via traditional organic synthesis is difficult, yet essential, due to the prevalence of these moieties in bioactive compounds. As we report, the Co-mediated pentadienyl/alkyne [5 + 2] cycloaddition reaction generates kinetically stable η2,η3-cycloheptadienyl complexes in high yield at room temperature, which isomerize to the thermodynamically preferred η5-cycloheptadienyl complexes upon heating at 60–70 °C. Here we describe an extended investigation of this reaction manifold, exploring substituent effects and extending the reaction to tandem cycloaddition/nucleophilic cyclizations, generating fused bicyclic compounds. We also describe a new high-yielding photolytic method for the decomplexation of organic cycloheptadienes from Co(I) complexes. Both C5Me5 (Cp*) and C5H5 (Cp) half-sandwich complexes are active in [5 + 2] cycloaddition with alkynes, with Cp* generally providing higher yields of cycloheptadienyl complexes. Cp cycloheptadienyl complexes, however, a...

In this paper, we report a highly efficient, scalable approach to the total synthesis of conformationally unrestricted, electronically isolated arrays of alkyl-tethered polycyclic aromatic chromophores. This new class of modular molecules consists of polycyclic aromatic "islands" comprising significant structural fragments present in unrefined heavy petroleum, tethered together by short saturated alkyl chains, as represented in the "archipelago model" of asphaltene structure. The most highly branched archipelago compounds reported here share an architecture with first-generation dendrimeric constructs, making the convergent, chromatography-free synthesis described herein particularly attractive for further extensions in scope and applications to materials chemistry. The syntheses are efficient, selective, and readily adaptable to a multigram scale, requiring only inexpensive, "earth-abundant" transition-metal catalysts for cross-coupling reactions and extraction and fractional crystallization for purification. This approach avoids typical limitations in cost, scale, and operational practicality. All of the archipelago compounds and synthetic intermediates have been fully characterized spectroscopically and analytically. The solid-state structure of one archipelago model compound has been determined by X-ray crystallography.

The effects of binary interactions on the coke yield and cracking kinetics in mixtures of model compounds were examined to understand the interactions present in multi-component mixtures, such as petroleum residues. Eight model compounds were selected with molecular weights in the range of 398–623 g/mol and structural elements to represent components of vacuum residues, including a pyrene substituted with four alkyl groups and pyrene derivatives tethered to various heterocycles via an ethano bridge. Thermogravimetric analysis of the binary mixtures showed evidence of three distinct modes of behavior with respect to the additive sum of the mass-weighted component contributions: the coke yield was (1) equal to the additive sum, (2) less than the additive sum, or (3) greater than the additive sum. The individual behavior correlated well with the type of compounds present in the specific mixtures and can be explained in terms of three types of interactions between the mixture components: radical stability or ...

Due to the complexity of the vacuum residue fraction of petroleum and bitumen, a model compound was used to probe cracking and addition reactions in the liquid phase. Hydrogenation reactions were conducted in a batch microreactor at 430 °C, 13.9 MPa H2 for 30 min using a solution of 1,3,6,8-tetrahexylpyrene (THP) in tetralin. Sulfided iron was prepared on α-alumina, γ-alumina, and glass beads as support materials. The hypothesis of this study was that addition reactions can be suppressed under hydrogenation conditions by using iron sulfide as a low-activity catalyst in the presence of hydrogen gas and a hydrogen donor solvent, by saturating olefin intermediates. The products were analyzed by high performance liquid chromatography, gas chromatography, matrix-assisted laser desorption ionization mass spectrometry, and proton nuclear magnetic resonance spectroscopy to investigate conversion and product distribution for different catalysts and without added catalyst. The results show that sulfided iron can gi...

A structurally unique class of hydrocarbon-soluble, ancillary-ligand-free, tetrametallic Co(I) and Ni(I) clusters is reported. The highly unsaturated complexes are supported by simple, sterically bulky phosphoranimide ligands, one per metal. The electron-rich nitrogen centers are strongly bridging but sterically limited to bimetallic interactions. The hydrocarbon-soluble clusters consist of four coplanar metal centers, mutually bridged by single nitrogen atoms. Each metal center is monovalent, rigorously linear, and two-coordinate. The clusters are in essence two-dimensional atomic-scale "molecular squares," a structural motif adapted from supramolecular chemistry. Both clusters exhibit high solution-phase magnetic susceptibility at room temperature, suggesting the potential for applications in molecular electronics. Designed to be catalyst precursors, both clusters exhibit high activity for catalytic hydrogenation of unsaturated hydrocarbons at low pressure and temperature.

Six asphaltene model compounds incorporating the biomarker structure of 5α-cholestane, covalently fused to a range of differentially substituted benzoquinoline groups, were subjected to thermal cracking. Thermogravimetric analysis of the six compounds showed similar cracking kinetics and yields of solid residue (coke), with the heaviest compound, bearing a pyrenyl substituent, forming the largest amount of residue. Analysis of the products formed from thermal cracking of three such model compounds in a stainless steel microreactor showed mainly dehydrogenation of the saturated hydrocarbon rings, along with some peripheral demethylation, and steroid side-chain fragmentation, with no significant ring opening or release of cyclic substructures from the steroid moiety. Some loss of the aromatic substituents appended to the benzoquinoline moiety was also detected. Methylated products and dimers of the parent compounds were formed by addition reactions, which participated in further cracking and addition reacti...

A series of fully-substituted 5,6-benzoquinolines covalently fused to the chlolestane framework has been synthesized to serve as model compounds for the poorly characterized components found in the heaviest fractions of petroleum, namely the asphaltenes. Acid-catalyzed cyclocondensation of an aromatic imine with 5-α-cholestan-3-one gives 5,6-benzoquinoline cycloadducts incorporating the steroidal biomarker fused to the benzoquinoline system at the 3,4-positions, with various pendent substituents in the 2-position. X-ray crystallography of three such derivatives shows that the solid-state geometries of these molecules are quite similar, and packing in the solid state appears to be dominated to a great extent by the nature of the pendent substituent. X-ray crystallography and solution phase circular dichroism spectroscopy together suggest that the conjugated benzoquinoline moiety adopts a helical conformation. Copyright © 2012 John Wiley & Sons, Ltd.

Cracking and coke formation of a series of pyrene-based model compounds were investigated by thermogravimetric analysis (TGA) and microreactor experiments. The structure of the model compounds is that of a three-island archipelago, consisting of two pyrenyl groups joined to a central aromatic or heteroaromatic group by ethano bridges. The molecular weights of these compounds range from 459–679 g/mol and have sufficiently high boiling points to remain liquid under the reaction conditions. TGA measured the cracking kinetics and the coke yield of each compound, where coke yield was defined as the solid residue remaining after a 10 °C/min ramp to 500 °C, followed by isothermal heating at 500 °C for 15 min. Microreactor experiments provided the yield and structure of both cracked and addition products. Analysis of the reaction products by gas chromatography, mass spectrometry (MS), high-pressure liquid chromatography, matrix-assisted laser desorption/ionization MS, and tandem MS/MS show that the initial cracke...

We performed density functional theory (DFT) calculations using the WB97Xd functional with a dispersion correction term and the 6-31G(d,p) basis set to study the contributions of π–π stacking and hydrogen-bonding interactions to the aggregation of asphaltene model compounds containing a 2,2′-bipyridine moiety covalently bonded to one (monosubstituted) and two (disubstituted) aromatic hydrocarbon moieties (phenyl, naphthyl, anthracyl, phenanthryl, and pyrenyl) through ethylene tethers. In these compounds, the N atoms of the 2,2′-bipyridine moiety provide lone pairs for hydrogen bonding to water molecules present in solution. The aggregation strength of the homodimers of these model compounds is evaluated in terms of the aggregation energies, enthalpies, and ΔG²⁹⁸, as well as the π–π interaction distances. Geometry optimization and thermochemistry analysis results show that the homodimers of both mono- and disubstituted compounds are stable and have a negative ΔG²⁹⁸ of aggregation because of π–π stacking interactions. Two water bridges containing one, two, or three water molecules per bridge span between two monomers and provide additional stabilization of the homodimers because of hydrogen bonding. The stabilization of the monosubstituted homodimers is the largest with two water molecules per bridge, whereas the stabilization of the disubstituted homodimers is the largest with three water molecules per bridge. The calculated ¹H nuclear magnetic resonance chemical shifts for the monomers and dimers of the three model compounds of this series synthesized to date are in excellent agreement with experimental results for dilute and concentrated solutions in chloroform, respectively (Tan, X.; Fenniri, H.; Gray, M. R.Water enhances the aggregation of model asphaltenes in solution via hydrogen bonding. Energy Fuels 2009, 23, 3687). The ΔH and ΔG²⁹⁸ results show that hydrogen bonding is as important as π–π interactions for asphaltene aggregation.

The components of petroleum asphaltenes exhibit complex bridged structures comprising sulfur, nitrogen, aromatic, and naphthenic groups linked by alkyl chains. These components aggregate in crude o...

A series of model compounds for the large components in petroleum, with molecular weights from 534 to 763 g/mol, was thermally cracked in the liquid phase at 365–420 °C to simulate catagenesis over a very short time scale and reveals the selectivity and nature of the addition products. The pyrolysis of three types of compounds was investigated: alkyl pyrene, alkyl-bridged pyrene with phenyl or pyridine as a central ring group, and a substituted cholestane–benzoquinoline compound. Analysis of the products of reaction of each compound by mass spectrometry, high-pressure liquid chromatography, and gas chromatography demonstrated that a significant fraction of the products, ranging from 26 to 62 wt %, was addition products with molecular weights higher than that of the starting compounds. Nuclear magnetic resonance (NMR) spectroscopic analysis showed that the pyrene compounds undergo addition through the attached alkyl groups, giving rise to bridged archipelago products. These results imply that the same geoc...

We present a computational exploration of five- and six-coordinate Ni(II) and vanadyl porphyrins, including prediction of UV-vis spectroscopic behavior and metalloporphyrin structure as well as determination of a binding energy threshold between strongly bound complexes that have been isolated as single crystals and weakly bound ones that we detect by visible absorption spectroscopy. The excited states are calculated using the tandem of the time-dependent density functional theory (TD-DFT) and the conductor-like polarizable continuum model (CPCM). The excited-state energies in chloroform solvent obtained by using two density functionals are found to correlate linearly with the experimental Soret and alpha-band energies for a known series of five-coordinate vanadyl porphyrins. The established linear correction allows simulation of the excited states for labile octahedral vanadyl porphyrins that have not been isolated and yields Soret and alpha-band bathochromic shifts that are in agreement with our UV-vis spectroscopic results. The PBE0 and PW91 functionals in combination with DNP basis set perform best for both structure and binding energy prediction. The reactivity preferences of Ni(II) and vanadyl porphyrins toward aromatic fragments of large petroleum molecules are explored by using the density functional theory (DFT). Analysis of electrostatic potentials and Fukui functions matching shows that axial coordination and hydrogen bonding are the preferred aggregation modes between vanadyl porphyrins and nitrogen-containing heterocycle fragments. This investigation improves our understanding on the cause for broadening of the Ni and V porphyrin Soret band in heavy oils. Our findings can be useful for the development of metals removal methods for heavy oil upgrading.

Alkyl-substituted η5-pentadienyl complexes of cobalt have been reported to undergo [5 + 2] cycloaddition reactions with alkynes to form substituted η2,η3- and η5-cycloheptadienyl products, providin...

Part of the metalloporphyrin fraction was separated from asphaltenes by a combination of reactive modification and affinity chromatography. The targeted vanadyl porphyrin complexes were modified by reaction with oxalyl chloride followed by a long chain alkylamine or perfluoroalkylaniline to produce an imido vanadium(IV) derivative bearing an octadecyl or perfluoroctyl side chain. This derivatized asphaltene was then chromatographed on C18-silica gel or perfluorous (-C8F17) silica gel to remove the tagged metalloporphyrins from the remaining asphaltene. With the C18-tagging and reverse-phase chromatography method, from 15 to 40% of the total vanadium content together with comparable percentages of nickel was removed, with less than 5% mass loss from the asphaltene fraction. The fluorous tagging process gave better removal of metals on one sample but was limited by the lower recovery of asphaltenes on other samples. This approach requires further optimization for quantitative selective separation of metal c...

The introduction of sterically isolating ortho-trialkylsilyl, -aryldialkylsilyl, and -diarylalkylsilyl substituents onto the structurally preorganized tetrakis(2-hydroxyphenyl)ethene ligand framework has been accomplished by a 4-fold retro-Brook rearrangement. Installation of the most sterically demanding silyl substituents required the development of an iterative procedure, involving successive double silylation/metalation/migration sequences without the isolation of intermediates. This system was designed to function as a soluble structural model for the planar binding domains of heterogeneous "oxo-surfaces" of silica and alumina supports.

Association of vanadium and nickel petroporphyrin compounds with aromatic groups is commonly invoked as an important mechanism for aggregation of asphaltenes. In this study, the interaction of vanadium and nickel octaethylporphyrin with condensed aromatic compounds and bridged aromatic compounds was investigated. Neither UV−vis nor fluorescence spectroscopy detect any interactions between porphyrins and aromatic ring groups in either the ground or excited states. The lack of detectable binding of these model compounds suggests that the association of the majority of the vanadium and nickel petroporphyrins in crude oils with the asphaltene fraction may be due to other functionality appended to the porphyrin ring, rather than favorable π−π stacking interactions of aromatic rings with the porphyrin core itself.

General methodology for the synthesis of cationic ruthenium(II) η5-pentadienyl compounds stabilized by the (η6-C6Me6)Ru fragment has been developed. Pentadienyl compounds [(η6-C6Me6)Ru{η5-CH2C(R2)CHC(R4)CH(R5)}]BF4 (R2 = R4 = R5 = H, 2-BF4; R2, R4 = H, R5 = Me, 3; R2, R4 = Me, R5 = H, 4) can be prepared in good yields from reactions of the labile dication [(η6-C6Me6)Ru(acetone)3](BF4)2 (1) with 1-trimethylsilyl-2,4-pentadiene, 1-trimethylsilyl-2,4-hexadiene, and 2,4-dimethyl-1-trimethylstannyl-2,4-pentadiene, respectively. Compound 3 is isolated in 90% yield as a mixture of the syn and anti isomers. In contrast, the reaction of pentadienyllithium with [(η6-C6Me6)RuCl2]2 provides a nonselective reaction, which affords a mixture of isomeric η1-, η3-, and η5-coordinated pentadienyl complexes, [(η6-C6Me6)Ru(η5-CH2CHCHCHCH2)]Cl (2-Cl), [(η6-C6Me6)Ru(η3-CH2CHCHCHCH2)Cl] (5), and [(η6-C6Me6)Ru(η1-CH2CHCHCHCH2)Cl]2 (6); the reaction of 1,4-pentadiene and [(η6-C6Me6)RuCl2]2 in ethanolic carbonate similarly gives a...

A multicomponent cyclocondensation reaction between 2-aminoanthracene, aromatic aldehydes, and 5-α-cholestan-3-one has been used to synthesize model asphaltene compounds. The active catalyst for this reaction has been identified as hydriodic acid, which is formed in situ from the reaction of iodine with water, while iodine is not a catalyst under anhydrous conditions. The products, which contain a tetrahydro[4]helicene moiety, are optically active, and the stereochemical characteristics have been examined by VT-NMR and VT-CD spectroscopies, as well as X-ray crystallography.

The synthesis of structurally relevant compounds that model the chemical behavior and supramolecular aggregation of the asphaltenes, the most polar and metal-rich fraction of heavy petroleum, has been extended to include fusions of important petroleum biomarkers. The synthetic protocol features a multicomponent reaction to form a dyad composed of a fused steroidal naphthoquinoline, followed by a pyrrole cyclocondensation reaction to incorporate the dyad into a chiral triad containing a NiII -porphyrin substituent. This synthetic protocol has been used to prepare large molecules that represent both "continental" and "archipelago" models of asphaltene composition. The steroid-naphthoquinoline-porphyrin triads have been studied by UV/Vis and circular dichroism (CD) spectroscopies, and the results suggest that the naphthoquinoline core, a tetrahydro[4]helicene, adopts a helical conformation, producing a CD signal electronically related to the characteristic Soret absorption band of the porphyrin subunit. Finally, supramolecular aspects of asphaltene aggregation have been examined on a molecular level through analysis of axial coordination of pyridine to the Ni-porphyrin. The relative affinity of pyridine for binding to the Ni center of the porphyrin is evaluated by comparing binding propensities in a series of sterically differentiated substituted porphyrins.

A Ni(II) porphyrin functionalized with an alkyl carboxylic acid (3) has been synthesized to model the chemical behavior of the heaviest portion of petroleum, the asphaltenes. Specifically, porphyrin 3 is used in spectroscopic studies to probe aggregation with a second asphaltene model compound containing basic nitrogen (4), designed to mimic asphaltene behavior. NMR spectroscopy documents self-association of the porphyrin and aggregation with the second model compound in solution, and a Job's plot suggests a 1 : 2 stoichiometry for compounds 3 and 4.

The direct synthesis of sterically hindered, partially etherified derivatives of tetrakis(2-hydroxyphenyl)ethene is reported by using the McMurry reductive olefination reaction on a range of differentially substituted 2,2′-dialkoxy benzophenone substrates. Three orthogonal protection strategies are demonstrated, incorporating β-silylethyl, 3-butenyl, and tert-butyl protecting groups, respectively, into the starting benzophenones. The latter proved most efficient, with both the McMurry coupling and deprotection steps occurring concomitantly under the McMurry conditions to directly yield the desired bis(2-hydroxyphenyl)-bis(2-methoxyphenyl)ethene as a 1:1 mixture of E- and Z-diastereoisomers.Key words: preorganized polyaryloxide ligands, McMurry olefination, titanium trichloride, supramolecular chemistry, tetrakis(2-hydroxyphenyl)ethene, 2,2′-disubstituted benzophenone.

The first s-trans-1,3-diene complexes of a first-row transition metal have been prepared and characterized both in solution and in the solid state. The unexpected s-trans configuration was obtained from photolytic decarbonylation of Cp'Cr-(NO)(CO) 2 (Cp' = η 5 -C 5 H 5 and η 5 -C 5 Me 5 ) in the presence of conjugated dienes. Related η 2 -olefin and η 2 -2-alkyne complexes have also been prepared.

The first thermally stable chromium(III) η3-allyl complexes have been prepared. Oxidation of neutral cyclopentadienylchromium(II) dicarbonyl η3-allyl, η3-crotyl, and η3-cyclohexenyl complexes 1−3, ...

The crystal structures of magnesium, aluminum, and titanium coordination complexes of the structurally preorganized tetrakis(2-hydroxyphenyl)ethene are reported. As a result of the absence of steric shielding and the conformational flexibility of the ligand, pseudo-dimeric complexes are formed instead of crown- or raft-like compounds. The unsubstituted tetrakis(2-hydroxyphenyl)ethene ligand thus emulates the complexation characteristics of the sterically open calix[4]arene system.Key words: coordination chemistry, polymetallic, titanium complexes, magnesium complexes, aluminum complexes, tetrakis(2-hydroxyphenyl)ethene ligands, crystal structures.

Stereoselective syntheses of (E)- and (Z)-1,2-bis(2'-hydroxyphenyl)-bis(2'-methoxyphenyl)ethene have been developed, the former by convergent coupling of an orthogonally protected 2,2'-benzophenone derivative and the latter by selective partial dealkylation of tetrakis(2-methoxyphenyl)ethene. Selective single demethylation has also been demonstrated in the 5-tert-butyl series. Thus, divalent and monovalent derivatives of the preorganized tetrakis(2-hydroxyphenyl)ethene ligand system are now available for use in coordination chemistry, analogous to corresponding calix[4]arene systems. [structure: see text]

Thermally stable chromium(II) dicarbonyl complexes bearing substituted η3-allyl and η5-cyclopentadienyl ligands have been prepared via oxidative addition of the allyl bromide to tris(acetonitrile)t...

[33636-93-0] C108H96Cu6P6 (MW 1961.16) InChI = 1S/6C18H15P.6Cu.6H/c6*1-4-10-16(11-5-1)19(17-12-6-2-7-13-17)18-14-8-3-9-15-18;;;;;;;;;;;;/h6*1-15H;;;;;;;;;;;;/q;;;;;;6*+1;6*-1 InChIKey = ULHDRBNWPMPZLA-UHFFFAOYSA-N (chemo- and stereoselective stoichiometric and catalytic conjugate reduction2, 3, 17, 18; catalytic, hydride-mediated, reduction of enones and ketones4; 1,2-reduction of enals/enones,19-21 reduction and hydrosilylation of aldehydes/ketones19, 20, 22, 23; cis-reduction of alkynes5, 41; hydrostannation/hydroboration of electron-deficient alkynes,24-26 reductive cyclization27-31) Alternative Names: triphenylphosphine copper hydride hexamer; Stryker's reagent. Physical Data: mp 111 °C (dec).1b Solubility: sol benzene, toluene, THF (∼1 g/10 mL); reacts with CH2Cl2 and CHCl3. Form Supplied in: bright red crystals to dark red powders; commercially available. Analysis of Reagent Purity: assay by means of hydrogen evolution.1b1H NMR spectroscopy (deaerated benzene-d6) shows ligated and, if present, free Ph3P. Typical 1H NMR data for pure sample (400 MHz, C6D6):32 7.67 (36H, t, J = 8.1 Hz), 6.95 (18H, t, J = 7.3 Hz), 6.74 (36H, t, J = 7.5 Hz), 3.51 (6H, br s). Preparative Method: prepared by hydrogenolysis of Ph3P-stabilized Copper(I) tert-Butoxide,1c,d which can be generated in situ from Copper(I) Chloride1e and tBuONa or tBuOK (but not tBuOLi, as the use of Li salt is detrimental).1e Precipitation and isolation under an oxygen-free atmosphere yields [(Ph3P)CuH]6. More recently, preparations under homogeneous conditions by reduction using silanes,32 and employing anhydrous Cu(OAc)2 instead of CuOtBu, have been reported.33 There are also an increasing number of recent examples in which [(Ph3P)CuH]6 is generated in situ and used without isolation.14-16. Purification: Ph3P is removed by recrystallization from benzene layered with hexanes or acetonitrile under anaerobic conditions, or by trituration with deaerated hexanes or acetonitrile.1e Handling, Storage, and Precautions: has an indefinite shelf life if stored under an inert atmosphere; can be handled briefly in the air without harm and is stable toward water. The reagent is highly air sensitive in solution; thus only rigorously deoxygenated solvents should be used. For bench top manipulation, transfer of the bulk reagent to a Schlenk tube that can be easily opened under a purge of inert gas and evacuated and backfilled after each use is recommended.

Substituted allyl complexes of bis(2-N,N-dialkylaminoindenyl)titanium(III) undergo highly regioselective central carbon alkylation upon treatment with organic free radicals, providing a general synthesis of 2,3-disubstituted titanacyclobutane complexes. This reactivity contrasts that of the corresponding bis(pentamethylcyclopentadienyl)titanium(III) series, for which titanacyclobutane formation is observed only in reactions of the unsubstituted allyl complex. Unexpectedly, the radical alkylation is more general for complexes of bis(2-N,N-dimethylaminoindenyl)titanium than complexes of the closely analogous bis(2-piperidinoindenyl)titanium, despite only subtle differences between the two ancillary ligands. In addition, the 2-methyl-3-alkyltitanacyclobutane complexes derived from alkylation of bis(2-N,N-dimethylaminoindenyl)titanium(η3-crotyl) are more thermally robust than those derived from the 2-piperidinoindenyl ligand system, resisting decomposition via β-hydride elimination from the α-methyl substitue...

A base metal hydrogenation catalyst composed of the phenyldimethylphosphine-stabilized copper(I) hydride complex provides for the highly chemoselective hydrogenation of unsaturated ketones and aldehydes to unsaturated alcohols, including the regioselective 1,2-reduction of α,β-unsaturated ketones and aldehydes to allylic alcohols. The active catalyst can be derived in situ by phosphine exchange using commercial [(Ph 3 P)CuH] 6 or from the reaction of copper(I) chloride, sodium tert -butoxide, and dimethylphenylphosphine under hydrogen. The catalyst derived from 1,1,1-tris(diphenylphosphinomethyl)ethane is mechanistically interesting but less synthetically useful.

The stereoselectivity and regioselectivity of the catalytic hydrogenation of ketones and α,β-unsaturated ketones and aldehydes using soluble copper(I) hydride catalysts have been investigated as a function of the ancillary phosphine ligand. While a relatively narrow range of aryldialkylphosphine ligands produce active hydrogenation catalysts, some ligands provide higher selectivity for 1,2-reduction of acyclic unsaturated carbonyl substrates than observed using the previously reported dimethylphenylphosphine-stabilized catalyst. The synthetic utility of this class of hydridic hydrogenation catalysts is illustrated by the hydrogenation of decalin and steroidal ketones and enones, the latter giving allylic alcohols with high selectivity.

Carbon−carbon bond activation in cationic 6-endo-methyl-η5-cyclohexadienyl and 6-exo-methyl-η5-cyclohexadienyl ruthenium hydride complexes has been investigated. Contrary to expectations, it is the 6-exo-methyl complex and not the stereoisomeric 6-endo-methyl complex that undergoes selective carbon−carbon bond activation under exceptionally mild conditions, quantitatively converting the 6-exo-methyl substituent and the hydride ligand to methane. The mechanism of the activation reaction involves dissociation of protic acid from the agostic starting complex by reaction with a weak base (typically water), followed by protolytic activation of the alkyl group, with “back-side” assistance from the nucleophilic metal center. Under the same conditions, the corresponding 6-endo-methyl isomer undergoes selective dehydrogenation rather than demethylation, despite the proximity of the endo-methyl substituent to the metal center. For both exo and endo isomers, the cationic ruthenium hydride intermediates were determin...

We applied a multiscale modeling approach that involves the statistical-mechanical three-dimensional reference interaction site model with the Kovalenko-Hirata closure approximation (3D-RISM-KH molecular theory of solvation) as well as density functional theory (DFT) of electronic structure to study the role of water in aggregation of the asphaltene model compound 4,4'-bis(2-pyren-1-yl-ethyl)-2,2'-bipyridine (PBP) [X. Tan, H. Fenniri and M. R. Gray, Energy Fuels, 2008, 22, 715]. The solvation free energy and potential of mean force predicted by 3D-RISM-KH reveal favorable pathways for disaggregation of PBP dimers in pure versus water-saturated chloroform solvent. The water density distribution functions elucidate hydrogen bonding preferences and water bridge formation between PBP monomers. The ΔG(298) values of -5 to -7 kcal mol(-1) for transfer of water molecules in chloroform to a state interacting with PBP molecules are in agreement with experimental results. Geometry optimization and thermochemistry analysis of PBP dimers with and without water bridges using WB97Xd/6-31G(d,p) predict that both PBP dimerization and dimer stabilization by water bridges are spontaneous (ΔG(298) < 0). The (1)H NMR chemical shifts of PBP monomers and dimers predicted using the gauge-independent atomic orbital method and polarizable continuum model for solvation in chloroform are in an excellent agreement with the experimental results for dilute and concentrated PBP solutions in chloroform, respectively [X. Tan, H. Fenniri and M. R. Gray, Energy Fuels, 2009, 23, 3687]. The DFT calculations of PBP dimers with explicit water show that bridges containing 1-3 water molecules lead to stabilization of PBP dimers. Additional water molecules form hydrogen bonds with these bridges and de-shield the PBP protons, negating the effect of water on the (1)H(C3) NMR chemical shift of PBP, in agreement with experiment. The ΔG(298) results show that hydrogen bonding to water and water-promoted polynuclear assembly bridging is as important as π-π interactions for asphaltene aggregation.

Alkyl-substituted η(5)-pentadienyl half-sandwich complexes of cobalt have been reported to undergo [5+2] cycloaddition reactions with alkynes to provide η(2),η(3)-cycloheptadienyl complexes under kinetic control. DFT studies have been used to elucidate the mechanism of the cyclization reaction as well as that of the subsequent isomerization to the final η(5)-cycloheptadienyl product. The initial cyclization is a stepwise process of olefin decoordination/alkyne capture, C-C bond formation, olefin arm capture, and a second C-C bond formation; the initial decoordination/capture step is rate-limiting. Once the η(2),η(3)-cycloheptadienyl complex has been formed, isomerization to η(5)-cycloheptadienyl again involves several steps: olefin decoordination, β-hydride elimination, reinsertion, and olefin coordination; also here the initial decoordination step is rate limiting. Substituents strongly affect the ease of reaction. Pentadienyl substituents in the 1- and 5-positions assist pentadienyl opening and hence accelerate the reaction, while substituents at the 3-position have a strongly retarding effect on the same step. Substituents at the alkyne (2-butyne vs. ethyne) result in much faster isomerization due to easier olefin decoordination. Paths involving triplet states do not appear to be competitive.

Isonitrile migratory insertion into substituted titanacyclobutane complexes provides for the stereocontrolled synthesis of synthetically valuable organic cyclobutanimines. Using the sterically crowded permethyltitanocene system, the intermediate iminoacyl complex is isolable and can be diverted by carbonylation to yield five-membered-ring enamidolate complexes.