Chromium Tricarbonyl Research Articles

Spectroscopic Characterization of Highly Excited Neutral Chromium Tricarbonyl.

Spectroscopic characterization of highly excited neutral transition-metal complexes is important for understanding the multifaceted reaction mechanisms between metals and ligands. In this work, the reactions of neutral chromium atoms with carbon monoxide were probed by size-specific infrared spectroscopy. Interestingly, Cr(CO)3 was found to have an unprecedented 7A2″ septet excited state rather than the singlet ground state. A combination of experiment and theory shows that the gas-phase formation of this highly excited Cr(CO)3 is facile both thermodynamically and kinetically. Electronic structure and bonding analyses indicate that the valence electrons of Cr atoms in the septet Cr(CO)3 are in a relatively stable configuration, which facilitate the highly excited structure and the planar geometric shape (D3h symmetry). The observed septet Cr(CO)3 affords a paradigm for exploring the structure, properties, and formation mechanism of a large variety of excited neutral compounds.

Синтез комплексов хрома с углеводородными и гетероциклическими лигандами и применение их в процессах полимеризации и газофазного получения хромкарбидных пленок в работах

In the works of Professor A.N. Artemov, the synthesis of chromium-containing isoxazolines by the reaction of 1,3-lipolar cycloaddition was studied and an increase in cis/trans selectivity was demonstrated when introducing a tricarbonylchromium group into molecules of dipoles and dipolarophiles. Arentricarbonylchromium derivatives of six–membered heterocycles with N–C–O bonds, like their five-membered analogues, can be obtained by reaction between heterocycles free of the tricarbonylchromium group, as well as a result of condensation of chromium-containing amino alcohols with carbonyl compounds. The synthesis of bi- and polymetallic compounds in the reactions of organometallic halides with various non-transition metals has been studied. Such reactions make it possible in a one-step process to obtain compounds containing covalent bonds of metals of 12–15 groups (Mg, Zn, Cd, In, Tl, Sn, Pb, Bi) with non-transitive elements (Fe, Mo, W). Styrene chromium tricarbonyl, para-methylstyrene chromium tricarbonyl, α-methylstyrene chromium tricarbonyl, stilbene chromium tricarbonyl, allylbenzene chromium tricarbonyl, and diphenylbutadiene chromium tricarbonyl were studied as polymerization regulators by the mechanism of reversible inhibition for vinyl monomers. α-methylstyrene chromium tricarbonyl, diphenylbutadiene chromium tricarbonyl, allylbenzene chromium tricarbonyl. When they are introduced into the polymerizing mass of methyl methacrylate, butyl acrylate, styrene in quantities commensurate with the concentration of the initiator, they control the termination of the polymer chain at temperatures not exceeding 100 °C. At the same time, the process proceeds at a sufficiently high rate, and the control of chain growth follows the mechanism of reversible inhibition. The gas-phase decomposition of bis-ethylbenzenechromium can proceed with the formation of hard and wear-resistant chromium carbide coatings, as well as with the production of chromium films characterized by a low temperature resistance coefficient.

1,2-Diphenyl-o-carborane and Its Chromium Derivatives: Synthesis, Characterization, X-ray Structural Studies, and Biological Evaluations.

The objective of this study is to design and synthesize substituted η6-chromium(0) tricarbonyl metal complexes carrying o-carborane units as potential boron neutron capture therapy (BNCT) agents. In this study, 1,2-diphenyl-o-carborane (1) units were used as starting materials to generate biologically active species. We investigated how the structural changes of 1 substituted with chromium(0) tricarbonyl affect the biological properties, and 1-(Phenyl-η6-chromium(0) tricarbonyl)-2-phenyl-o-carborane (2) and 1,2-bis(phenyl-η6-chromium(0) tricarbonyl)-o-carborane (3) species were produced in moderate yields. The molecular structures of compounds 1-3 were identified and established by infrared (IR); 1H, 11B, and 13C nuclear magnetic resonance (NMR) and X-ray crystallography analyses. Crystal structures of 1,2-diphenyl-o-carborane and the corresponding chromium complexes 1, 2, and 3 were obtained. In an in vitro study using B16 and CT26 cancer cells containing the triphenyl-o-carboranyl chromium(0) complexes Ph3C2BCr2 and Ph3C2BCr3, which we reported previously, compounds 2 and 3 accumulated at higher levels than compounds Ph3C2BCr2 and Ph3C2BCr3. However, the phenylated o-carboranyl chromium complexes have been found to be more cytotoxic than p-boronophenylalanine (BPA).

How a Chromium Tricarbonyl Complex Catalyzes the [3 + 2] Cycloaddition Reaction of N-Substituted Phenylnitrones with Styrene: A Molecular Electron Density Theory Analysis

The reaction mechanisms of [3 + 2] cycloaddition (32CA) between two N-substituted phenylnitrones (NPPN and NtBPN) and styrene (STY) in the presence of a chromium tricarbonyl complex (Cr(CO)3) have been studied within the framework of molecular electron density theory at the MPWB1K/6-311G(d,p) level. Activation energy analysis reveals that these 32CA reactions take place with high activation barriers due to their non-polar character and with the exo/ortho approach as a favorable reaction path. The activation energy of TS1 series (NPPN) is about 5–6 kcal/mol lower than that of the TS2 series (NtBPN), due to the steric hindrance of tert-butyl at the TS2 structures. Coordination of chromium tricarbonyl to each reactant to form the corresponding complex slightly increases the nucleophilic and electrophilic character of NPPN:Cr, NtBPN:Cr, and STY:Cr, which can be considered a strong nucleophile and electrophile able to participate in a polar 32CA reaction. This polar character in the presence of the chromium tricarbonyl complex was verified by the higher (up to 0.20e) values of global electron density transfer for Cr(CO)3-coordinated transition states. Electron localization function analysis along the exo/ortho reaction path reveals the non-concerted mechanism in the formation of a new bond with the initial appearance of a C–C single bond followed by the O–C one.

Benchmarking the Fluxional Processes of Organometallic Piano-Stool Complexes.

The correlation consistent Composite Approach for transition metals (ccCA-TM) and density functional theory (DFT) computations have been applied to investigate the fluxional mechanisms of cyclooctatetraene tricarbonyl chromium ((COT)Cr(CO)3) and 1,3,5,7-tetramethylcyclooctatetraene tricarbonyl chromium, molybdenum, and tungsten ((TMCOT)M(CO)3 (M = Cr, Mo, and W)) complexes. The geometries of (COT)Cr(CO)3 were fully characterized with the PBEPBE, PBE0, B3LYP, and B97-1 functionals with various basis set/ECP combinations, while all investigated (TMCOT)M(CO)3 complexes were fully characterized with the PBEPBE, PBE0, and B3LYP methods. The energetics of the fluxional dynamics of (COT)Cr(CO)3 were examined using the correlation consistent Composite Approach for transition metals (ccCA-TM) to provide reliable energy benchmarks for corresponding DFT results. The PBE0/BS1 results are in semiquantitative agreement with the ccCA-TM results. Various transition states were identified for the fluxional processes of (COT)Cr(CO)3. The PBEPBE/BS1 energetics indicate that the 1,2-shift is the lowest energy fluxional process, while the B3LYP/BS1 energetics (where BS1 = H, C, O: 6-31G(d′); M: mod-LANL2DZ(f)-ECP) indicate the 1,3-shift having a lower electronic energy of activation than the 1,2-shift by 2.9 kcal mol−1. Notably, PBE0/BS1 describes the (CO)3 rotation to be the lowest energy process, followed by the 1,3-shift. Six transition states have been identified in the fluxional processes of each of the (TMCOT)M(CO)3 complexes (except for (TMCOT)W(CO)3), two of which are 1,2-shift transition states. The lowest-energy fluxional process of each (TMCOT)M(CO)3 complex (computed with the PBE0 functional) has a ΔG‡ of 12.6, 12.8, and 13.2 kcal mol−1 for Cr, Mo, and W complexes, respectively. Good agreement was observed between the experimental and computed 1H-NMR and 13C-NMR chemical shifts for (TMCOT)Cr(CO)3 and (TMCOT)Mo(CO)3 at three different temperature regimes, with coalescence of chemically equivalent groups at higher temperatures.

Topological unraveling of the [3+2] cycloaddition (32CA) reaction between N-methylphenylnitrone and styrene catalyzed by the chromium tricarbonyl complex using electron localization function and catastrophe theory

We have investigated the reaction mechanisms of [3+2] cycloaddition (32CA) between N-methylphenylnitrone and styrene catalyzed by the chromium tricarbonyl complex at the MPWB1K/6-311G(d,p) level of approximation.

Metrological Suitability of Functionalized Epitaxial Graphene.

This work presents one solution for long-term storage of epitaxial graphene (EG) in air, namely through the functionalization of millimeter-scale devices with chromium tricarbonyl - Cr(CO)3. The carrier density may be tuned reproducibly by annealing below 400 K due to the presence of Cr(CO)3. All tuning is easily reversible with exposure to air, with the idle, in-air, carrier density always being close to the Dirac point. Precision measurements in the quantum Hall regime indicate no detrimental effects from the treatment, validating the pursuit of developing air-stable EG-based QHR devices.

Synthesis and isomerism of Cr and Mn phosphonioallene complexes

Earlier, we have discovered the UV-promoted four-component reaction between (arene)chromium and cyclopentadienylmanganese tricarbonyl complexes, propargyl alcohol, PPh3, and HBF4 to afford isomeric terminal and internal phosphonioallene complexes. The present study revealed additional details for this reaction and was extended either to similar manganese and chromium complexes, or to propargyl alcohol derivatives (НС≡ССМе2ОН, DC≡CCH2OMe). In particular, the use of d1-propargyl methyl ether allowed us to exclude possible isomerization of propargylphosphonium to allenylphosphonium in the coordination sphere. The photolysis of CpMn(CO)3 and Cp∗Mn(CO)3 in the presence of propargyl alcohols afforded η2-alkyne complexes, which were then reacted in situ with acid and PPh3 under dark conditions. With unsubstituted propargyl alcohols, the terminal anti-isomer was the only product in both cases, while the internal isomer is exclusively produced in the reactions of both Cr and Mn complexes with 2-methylbut-3-yn-2-ol. Issues related to the isomeric ratio are discussed and the data obtained are compared with those for similar known metal complexes. The obtained compounds were characterized by IR, 1H, 31P, and 13C NMR spectroscopy and the structures of complexes IX and XIII were confirmed by X-ray diffraction.

Ag/Pd Cocatalyzed Direct Arylation of Fluoroarene Derivatives with Aryl Bromides.

Diverse C–H functionalizations catalyzed by Pd employ Ag(I) salts added as halide abstractors or oxidants. Recent reports have shown that Ag can also perform the crucial C–H activation step in several of these functionalizations. However, all of these processes are limited by the wasteful requirement for (super)stoichiometric Ag(I) salts. Herein, we report the development of a Ag/Pd cocatalyzed direct arylation of (fluoroarene) chromium tricarbonyl complexes with bromoarenes. The small organic salt, NMe4OC(CF3)3, added as a halide abstractor, enables the use of a catalytic amount of Ag, reversing the rapid precipitation of AgBr. We have shown through H/D scrambling and kinetic studies that a (PR3)Ag-alkoxide is responsible for C–H activation, a departure from previous studies with Ag carboxylates. Furthermore, the construction of biaryls directly from the simple arene is achieved via a one-pot chromium tricarbonyl complexation/C–H arylation/decomplexation sequence using (pyrene)Cr(CO)3 as a Cr(CO)3 donor.

Intramolecular alkene–alkyne metathesis and 1,4-cis-hydrogenation as a stereocontrolled route to compounds with exocyclic double bonds

Intramolecular alkene-alkyne metathesis of diethyl (but-3-en-1-yl)(propargyl)malonate affords diethyl 3-vinylcyclohex-3-ene-1,1-dicarboxylate whose conjugated diene system was 1,4-cis-hydrogenated in the presence of η6-(naphthalene)chromium tricarbonyl. The exocyclic double bond of thus formed diethyl 3-ethylidenecyclohexane-1,1-dicarboxylate is strictly (E)-configured.

Reaction of phenyl-containing N-substituted 1,3-oxazolidines and 1,3-oxazinanes with triammine(tricarbonyl)chromium

New heterocyclic compounds with phenyl chromium tricarbonyl substituents were synthesized by the reaction of triammine(tricarbonyl)chromium with phenyl-substituted 1,3-oxazacy-cloalkanes bearing acetyl, tert-butyloxycarbonyl, or phenyl group at the nitrogen atom. The resulting compounds were isolated in the individual state and characterized by physicochemical methods of analysis.

Chromium(III) and Chromium(II) Phenolate Complexes with Bulky Alkylcyclopentadienyl Ligands

The chromium(II) tricarbonyl methyl complex [Cp′′′Cr(CO)3CH3] (1, Cp′′′ = η5‐C5H2tBu3‐1,2,4) was obtained from chromium hexacarbonyl, NaCp′′′, and methyl iodide. 1 was found to establish an equilibrium with the dicarbonyl acetyl isomer [Cp′′′Cr(CO)2(COCH3)] in solution via reversible, slightly endothermic methyl migration from chromium to a carbonyl ligand with ΔH ca. 3.6 kJ/mol and Ea ca. 49.5 kJ/mol. Phosphorus pentachloride oxidized 1 to the green, dinuclear tetrachloro complex [Cp′′′CrCl(µ‐Cl)]2 (2), which was crystallized as the blue‐green chromium(III) half sandwich complex [Cp′′′CrCl2(THF)] (3) in the presence of tetrahydrofuran vapor. Attempted sublimation of the known chromium(II) iodo complex [4CpCr(µ‐I)]2 resulted in a redox reaction with formation of the chromium(III) iodo dimer [4CpCrI(µ‐I)]2, whose tri(tert‐butyl)cyclopentadienyl derivative [Cp′′′CrI(µ‐I)]2 (4) could also be prepared by oxidation of [Cp′′′Cr(µ‐I)]2 with iodine. The chromium(III) bis(2,6‐diisopropylphenolate) complex [4CpCr(OC6H3iPr2‐2,6)2] (5) was obtained from chromium trichloride in a one pot reaction with sodium tetraisopropylcyclopentadienide, followed by sodium 2,6‐diisopropylphenolate. The chromium(III) starting compound 2 reacted with 2,6‐diisopropylphenolate to the Cp′′′ derivative [Cp′′′Cr(OC6H3iPr2‐2,6)2] (6). The chromium(II) starting compound [Cp′′′Cr(µ‐Br)]2 afforded the phenolate‐bridged chromium(II) dimer [Cp′′′Cr(µ‐OC6H5)]2 (7) upon treatment with sodium phenolate, while the product of the analogous reaction with 2,6‐di(tert‐butyl)phenolate was the mononuclear tetrahydrofuran adduct [Cp′′′Cr(OC6H3tBu2‐2,6)(THF)] (8).

Gateless and reversible Carrier density tunability in epitaxial graphene devices functionalized with chromium tricarbonyl

Monolayer epitaxial graphene (EG) has been shown to have clearly superior properties for the development of quantized Hall resistance (QHR) standards. One major difficulty with QHR devices based on EG is that their electrical properties drift slowly over time if the device is stored in air due to adsorption of atmospheric molecular dopants. The crucial parameter for device stability is the charge carrier density, which helps determine the magnetic flux density required for precise QHR measurements. This work presents one solution to this problem of instability in air by functionalizing the surface of EG devices with chromium tricarbonyl - Cr(CO)3. Observations of carrier density stability in air over the course of one year are reported, as well as the ability to tune the carrier density by annealing the devices. For low temperature annealing, the presence of Cr(CO)3 stabilizes the electrical properties and allows for the reversible tuning of the carrier density in millimeter-scale graphene devices close to the Dirac point. Precision measurements in the quantum Hall regime show no detrimental effect on the carrier mobility.

Asymmetric synthesis of secondary benzylic alcohols via arene chromium tricarbonyl complexes

(Aryl aldehyde)- and (aryl ketone)-chromium tricarbonyl complexes ortho-substituted with the chiral auxiliary O-methyl-N-(α-methylbenzyl)hydroxylamine undergo diastereoselective addition of Grignard reagents and Super-Hydride®, respectively, to give the corresponding secondary alcohols in high diastereoisomeric purity. These compounds may be easily decomplexed and deprotected to give the corresponding enantiopure amino alcohols.

Coordination complexes of chromium(0) with a series of 1,3-diphenyl-6-aryl-fulvenes.

The synthesis and structural properties of a series of chromium tricarbonyl 'piano-stool' complexes bearing substituted penta-fulvene ligands were studied. The complexes, tricarbon-yl(1,3,6-tri-phenyl-fulvene)chromium(0) benz-ene hemisolvate, [Cr(C24H18)(CO)3]·0.5C6H6 (I), tricarbon-yl[1,3-di-phen-yl-6-(3-vinyl-phen-yl)fulvene]chromium(0), [Cr(C26H20)(CO)3] (II), and tricarbon-yl[1,3-diphenyl-6-(pyren-1-yl)fulvene]chromium(0), [Cr(C34H22)(CO)3] (III), each have a distorted octa-hedral geometry, with the fulvene coordinated in a π-η2:π-η2:π-η2 fashion. Significant deviation of the exocyclic fulvene double bond from the cyclo-penta-diene plane accompanies coordination. Evidence of non-covalent π-π inter-actions was observed in both (I) and (III), with centroid-to-centroid distances ranging from 3.330 (8) to 3.494 (8) Å.

Synthesis and properties of Fischer carbene complexes of N,N-dimethylaniline and anisole π-coordinated to chromium tricarbonyl

The reaction of lithiated N,N-dimethylaniline π-coordinated to Cr(CO)3 with W(CO)6 and alkylation with [Et3O][BF4] afforded the o-, m- and p-isomers of the σ,π-bimetallic complexes {η6-Me2NC6H4C(OEt)W(CO)5}Cr(CO)3 (o-, 1, m-, 2 and p-isomer, 3). A by-product of the reaction is found by the substitution of a carbonyl ligand in 1 by the aniline nitrogen atom to give {η6-C,N-o-Me2NC6H4C(OEt)W(CO)4}Cr(CO)3 (4). As a result, the W-chelate ring dominates the HOMO rather than the{η6-arene Cr(CO)3} fragment, affecting the site of the first oxidation. Enhanced activation of anisole by π-coordination to Cr(CO)3, and subsequent reactions with nBuLi, W(CO)6 and [Et3O][BF4] gave only o-substituted products {μ,η6:1-o-MeOC6H4C(OEt)W(CO)5}Cr(CO)3 (5), the monocarbene chelate {μ,η6:2-C,O-o-MeOC6H4C(OEt)W(CO)4}Cr(CO)3 (6) by carbonyl substitution, and by reaction of two molar equivalents of these reagents, the unique σ,π-heterotrimetallic biscarbene complex {μ3,η6:1:1-o,o-MeOC6H3(C(OEt)W(CO)5)2}Cr(CO)3 (7). Attempts to synthesise the m- and p-isomers of 5 were unsuccessful due to transmetallation of the lithiated precursors. NMR data confirmed that lithiation and subsequent reactions of m- or p-bromoanisole chromiumtricarbonyl afforded only the o-isomer 5 and {η6-MeOC6H5}Cr(CO)3. Crystal structure determinations of complexes 1–7 confirmed their molecular structures. Spectroscopic data, electrochemistry studies and DFT calculations of the complexes are reported and are in line with a shifting of the HOMO from the Cr(CO)3 to the W(CO)4 chelate entity and with an unusually large delocalization of the HOMO of the other complexes onto the π-coordinated arene ligand and the carbene-bonded metal atom.

1,4-cis-Hydrogenation of butyl sorbate in supercritical carbon dioxide

Hydrogenation of butyl sorbate into butyl Z-hex-3-enoate in supercritical carbon dioxide proceeds at high conversion and selectivity of 93–96% under catalysis with chromium hexacarbonyl at 180 °C and on using (methyl benzoate)chromium tricarbonyl as a catalyst at 160 °C.

Recognition of Melamine by Chromium Tricarbonyl (Thio)barbituric Acid Derivatives: Theoretical Insight into Multiple Hydrogen‐Bond Modes

AbstractMelamine‐contaminated milk products continually emerge in recent years and cause disease. Therefore, how to swiftly and efficiently differentiate melamine from protein becomes an urgent issue. In this work, three neutral receptors p‐dimethylaminobenzaldehyde‐barbituric acid chromium tricarbonyl (PBC), p‐dimethylaminobenzaldehyde‐2‐thiobarbituric acid chromium tricarbonyl (2‐PTC), and p‐dimethylaminobenzaldehyde‐4‐thiobarbituric acid chromium tricarbonyl (4‐PTC) were constructed for recognition of melamine, and their non‐covalent interactions were systematically studied using density functional theory and several theoretical analysis methods. Our results suggest that melamine can be theoretically recognized by receptors PBC and 2‐/4‐PTC due to the formation of multiple hydrogen bonds upon complexation, indicating the good detecting capability of the Cr(CO)3‐based (thio)barbituric acid moiety. Nevertheless, the IR analysis results show the receptors 2‐/4‐PTC cannot distinctly detect melamine by evident frequency shift of metal carbonyl. Therefore, we further proposed a structural modification strategy by introducing the cyano group into the (thio)barbituric acid moiety, and the corresponding IR analysis exhibits large frequency shift of metal carbonyl, indicating the potential of modified receptors in the infrared neutral molecular recognition of melamine. The results reported herein will be very useful in the design of potent receptors distinguishing melamine from protein.

A Direct Arylation-Cyclisation Reaction for the Construction of Medium-Sized Rings.

A strategy for assembling biaryls linked through a medium-sized ring is herein presented. π-Complexation of fluoroarenes to chromium tricarbonyl activates the molecule towards both C-H activation and nucleophilic aromatic substitution without covalently altering the molecular connectivity of the arene. The construction of bridged biaryl molecules with 6-10-membered core rings is achieved through a one-pot C-H arylation/nucleophilic aromatic substitution sequence. The methodology is applicable to the synthesis of heterocyclic as well as fully carbocyclic rings.

DFT study of chromium tricarbonyl complexes of coronene and kekulene

A quantum chemical study of the mechanism and determination of the activation barriers of intramolecular η6,η6-inner-ring haptotropic rearrangements (IHR), consisting in moving a chromium tricarbonyl group Cr(CO)3 from one six-membered aromatic ring to another, are carried out using the density functional theory (DFT) for the respective η6-complexes of coronene I and kekulene II. The stationary states on the potential energy surface, determining the mechanism of η6,η6-IHR, have a lower hapticity, which is of interest for catalysis because of the possibility of coordinating an additional substrate and reagent around the transition metal during the rearrangement. The processes of η6,η6-IHR complexes I and II occur with similar energy barriers (ΔG≠ ≈ 20–25 kcal/mol) that are lower than the barriers (ΔG≠ ≈ 30 kcal/mol) of similar transformations previously calculated or measured for naphthalene complexes and a number of small polyaromatic hydrocarbons.