Chromium Hexacarbonyl Research Articles

Homoleptic binuclear chromium carbonyls: why haven’t they been synthesized as stable molecules?

Density functional theory has been used to explore possible homoleptic binuclear Cr carbonyls Cr 2(CO) n ( n = 11, 10, 9, and 8) using the pure DFT method BP86 and the hybrid Hartree–Fock DFT method B3LYP. The binuclear Cr 2(CO) 11 is computed to be thermodynamically unstable with respect to dissociation into mononuclear fragments in contrast to the experimentally known Cr 2(CO) 10(μ-H) −. This may account for the failure to synthesize Cr 2(CO) 11 as a stable compound. Optimized structures for the formally unsaturated Cr 2(CO) 10 are a singlet with two four-electron donor bridging CO groups and no formal metal–metal bonding and a triplet with no bridging CO groups and a Cr Cr double bond similar to the O O bond in O 2. The more highly unsaturated homoleptic binuclear chromium carbonyls Cr 2(CO) 9 and Cr 2(CO) 8 are computed to be stable with respect to dissociation into mononuclear fragments in contrast to Cr 2(CO) 11 and Cr 2(CO) 10. The optimized structure for Cr 2(CO) 9 is a singlet Cr 2(CO) 6(μ-CO) 3 with a short metal–metal distance (∼2.3 Å) consistent with the Cr≡Cr triple bond required for an 18-electron configuration for each Cr atom. The global minimum for Cr 2(CO) 8 is a closely related Cr 2(CO) 5(μ-CO) 3 structure derived from the Cr 2(CO) 6(μ-CO) 3 global minimum by loss of one of the terminal CO groups with little change in the Cr≡Cr distance. Higher energy minima for Cr 2(CO) 8 include two different Cr 2(CO) 6(μ-CO) 2 structures, one formulated with two four-electron donor μ-CO groups bridging two Cr(CO) 3 groups and the other with similar μ-CO groups bridging a Cr(CO) 4 and a Cr(CO) 2group.

Dissociative ionization at high laser intensities: importance of resonances and relaxation for fragmentation

We investigated dissociative single and double ionization of the metal carbonyls Ni(CO)4, Fe(CO)5 and Cr(CO)6 in the gas phase by means of laser pulses of different durations (30–110 fs) and wavelengths (0.8 and 1.35 µm) at intensities of 2 × 1012–2 × 1014 W cm−2. The mass spectra show striking differences: for example, Fe(CO)5 strongly fragments at 0.8 µm but little at 1.35 µm, whereas for Ni(CO)4 fragmentation is higher at 1.35 µm than at 0.8 µm; chromium carbonyl shows little fragmentation at both wavelengths. In other cases, fragmentation first decreases and then increases again with intensity. These and other phenomena, also published ones, can readily be understood from long-known principles, namely resonances in the parent ions, sometimes also in the neutral molecules, in particular if relaxations are also taken into account. We emphasize that fragmentation and ionization are two separate processes. We also point out that in the process of dissociative ionization in intense laser radiation, one should generally consider intermediate states, even if there is no one-photon resonance.

Low temperature deposition of crystalline chromium phosphide films using dual-source atmospheric pressure chemical vapour deposition

Thin films of crystalline chromium phosphide (CrP) have been produced from the dual-source atmospheric pressure CVD reaction of chromium hexacarbonyl and cyclohexylphosphine. Analysis of the films using EDAX, SEM, glancing angle XRD and XPS is presented.

Toward an Organometallic Molecular Brake with a Metal Foot Pedal: Synthesis, Dynamic Behavior, and X-ray Crystal Structure of [(9-Indenyl)triptycene]chromium Tricarbonyl

The potential use of haptotropic shifts to control rotational barriers has been initiated by the synthesis of (9-indenyl)triptycene (12) and its chromium tricarbonyl derivative (13). Both complexes have been characterized by X-ray crystallography and variable-temperature NMR spectroscopy, revealing barriers to rotation of 12 and 13 kcal mol-1, respectively. In the metal complex, the chromium carbonyl moiety coordinates to one of the blades of the triptycene unit rather than to the more crowded indenyl group.

Reactions of chromium, molybdenum and tungsten carbonyls with a tetradentate schiff base

Interaction of metal carbonyls M(CO)6 (M = Cr, Mo and W) with the tetradentate Schiff base bis(salicylaldehyde)phenylenediimine (salphenH2) was studied in THF. Under reduced pressure, reaction of salphenH2 with M(CO)6 (M = Cr, Mo) yielded Cr(CO)2(salphen) 1 and MoO(CO)(salphen) 2. The complexes MoO2(salphenH)2 3 and W2O6(salphenH2) 4 were isolated from reactions in air. All the complexes were characterized by elemental analysis, mass spectrometry and IR and 1H NMR spectroscopy. Spectroscopic studies of the reported complexes revealed the proposed structures. The UV-vis spectra of the complexes in different solvents showed bands due to either metal-to-ligand or ligand-to-metal charge transfer. Thermal properties of the chromium and molybdenum complexes were investigated by thermogravimetric techniques.

From α,β‐Unsaturated Fischer Carbene Complexes to Highly Substituted 3‐Ethoxycyclopentadienes, Masked Cyclopentenones

AbstractThe β‐amino‐substituted α,β‐unsaturated Fischer carbene complexes 3 are readily available by a four step one‐pot procedure from terminal alkynes, chromium hexacarbonyl and secondary amines (24 examples with yields of 68−99% and 7 examples with yields of 26−63%). The formal [3+2] cycloadditions of complexes 3 with different alkynes including diynes and enynes performed in donor solvents such as pyridine or acetonitrile afforded highly substituted 5‐(dialkylamino)‐3‐ethoxycyclopentadienes 7, generally in medium to excellent yields (25 examples with yields of 60−95% and 7 examples with yields of 18−53%). The steric and electronic effects of the substituents on the carbene complexes and the incorporated alkynes on the regio‐ and stereoselectivity of the ring‐forming reaction have been elaborated. An interesting 1,5‐ or, more likely, 1,2‐migration of the dimethylamino group was observed for 5‐(dimethylamino)‐3‐ethoxycyclopentadienes with trimethylsilyl and iPr substituents at C‐5. Attempted asymmetric syntheses of cyclopentadienes 7 from complexes 3 with chiral amino groups or substituents were only moderately successful. At a center of chirality in the secondary amino group, complexes of type 3 gave compounds 7 with diastereomeric excesses of, at best, 59% in yields of 54%, and with a stereogenic center in the substituent R1 attached to the vinyl group of 3, diastereomeric excesses as high as 94% could be achieved, but with poor chemical yields (21%). In general, cyclopentenones 21 could be easily obtained from the cyclopentadienes 7 under acidic conditions in very good yields (4 examples with yields of 81−98%, 1 example with an overall yield of 50% from complex 3). Intramolecular aldol reactions of dicarbonyl compounds generated by hydrolysis of cyclopentadienes 7 with acetal‐protected aldehyde or ketone carbonyl groups in either the 5‐substituent R1 or the N‐substituent R2 led to the bicyclic compounds 22 and 23. The dimethylamino group in cyclopentenones 21 could be either eliminated or transformed into other functional groups via the quaternary ammonium salts 24. The elimination product, cyclopentadienone 27 can undergo dimerization either by a formal [4+2] or [2+2] cycloaddition. Cyclopentenone 21naaa with a bromovinyl‐terminated side chain undergoes an intramolecular Heck reaction to form 5‐methyl‐4,6‐dimethylenebicyclo[3.3.0]oct‐1‐en‐3‐one (32) (37% yield). (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Catalytic Oxidation of Cyclohexane with Ozone-Oxygen Mixtures

Selective oxidation of cyclohexane with ozone in the presence of chromium(0) hexacarbonyl and sodium naphthenates-Cr(III) mixtures was studied.

Carbonylchromium Monotelluride Complexes [Et4N]2[Te{Cr(CO)5}n] (n = 2, 3): Two Important Intermediates

The first isolation of the monotelluride-bridged chromium carbonyl complexes [Et 4 N] 2 [Te-{Cr(CO) 5 } n ] (n = 3, [Et 4 N] 2 [1]; n = 2, [Et 4 N] 2 [2]) has been achieved from the reaction of Te powder with 3 equiv of Cr(CO) 6 in the presence of [Et 4 N]Br in concentrated KOH/EtOH solution. According to X-ray analysis, anion 1 displays a pyramidal geometry with the Te atom bonded to three Cr(CO) 5 fragments and anion 2 exhibits a nonlinear structure with the Te atom coordinated with two Cr(CO) 5 moieties. Complex 1 can transform to 2 in the presence of Cr(CO) 6 /KOH/EtOH solution. Conversely, 2 can convert back to 1 upon the reaction with Cr(CO) 6 in MeCN. Interestingly, the novel C-O activation of MeOH is observed when 1 was treated with NaOH/MeOH solution at 70 °C, giving the Te-methylated product [Et4N] [MeTe{Cr(CO) 5 } 2 ] ([Et 4 N][3]). Complex 2 is reactive toward some organic solvents. It can react with CH 2 Cl 2 to form the CH 2 -bridged tetrachromium complex [Et 4 N] 2 [CH 2 {TeCr 2 -(CO) 1 0 } 2 ] ([Et 4 N] 2 [4]) and can transform to the known tetrachromium tritelluride complex [Et4N] 2 [Te 3 {Cr(CO) 5 } 4 ], in MeOH solution. Besides, we also found that 2 can undergo oxidative coupling with [Cu(MeCN) 4 ]BF 4 in MeOH to form the dimeric open cluster [Te 2 {Cr(CO) 5 } 4 ] 2 - and can react with NaOH in MeOH to give the dimeric ring complex [Te 2 Cr 4 (CO) 1 8 ] 2 - . Complexes 1-4 are fully characterized by spectroscopic methods and single-crystal X-ray analysis. This paper describes that complexes 1 and 2 are important intermediates for a series of tellurium-containing polychromium complexes, and the interesting structural features of the resultant new polychromium carbonyl complexes are compared as well.

Polymer-supported haloarene chromium dicarbonyl isonitrile complexes: a study of their synthesis and reactivity.

Different arene Cr(CO)(3) complexes were supported on a polystyrene isonitrile resin by photochemical-promoted replacement of a chromium carbonyl ligand by the NC group. The supported complexes proved to be stable and were successfully used for further transformations. In particular, the reactivity of dichlorobenzene complexes to different nucleophiles was investigated and found to be comparable with that of the parent Cr(CO)(3) complexes.

FTIR spectroscopic study of CO and NO adsorption on Cr-ZSM-5

Low temperature adsorption of CO on activated Cr-ZSM-5 sample does not lead to formation of any chromium carbonyls. Very small amount of chromium nitrosyls were produced after NO adsorption at ambient temperature. When NO was adsorbed on a hydrogen-reduced sample (773 K) dinitrosyls of Cr 3+(NO) 2 type were produced and evidenced by strong bands at 1908 and 1782 cm −1. Surprisingly, CO fails to detect these Cr 3+ sites even at low temperature. The results are rationalized by assuming that Cr 3+ cations in Cr-ZSM-5 are coordinatively saturated and do not form chemical bonds with weak ligands. Since the Cr 3+(NO) 2 are very stable (they decompose at 323 K), these species are formed with a simultaneous change in the original coordination of the Cr 3+ cations.

The catalysis of solid state intercalation processes by organic solvents

It is widely thought that the intercalation of ionic species in solids is unaffected by non-ionic species in solution. But in the present work we report that, in some rare cases, low concentrations of non-ionic species in solution can actually catalyse the intercalation of ionic species in the solid state. Cyclic voltammetry, quartz crystal gravimetry, X-ray diffraction, and molecular modelling are used to confirm the existence of this remarkable effect. The origin of the effect is traced to the co-incorporation of the non-ionic species in the solid state, which causes the crystal structure to expand. The rapid incorporation of the ionic species can then occur. This discovery suggests that other solid state reactions might be catalysed in a similar way. The solid state species which are shown to exhibit the catalytic effect include three rhenium carbonyl complexes, namely trans-Re(Br)(CO)(dppe)2, trans-Re(Br)(CO)(dppe)(dppm) (dppe=Ph2P(CH2)2PPh2; dppm=Ph2PCH2PPh2), and trans-Re(Br)(CO)(dpbz)(dppm) (dpbz=o-(Ph2P)2(C6H4); a chromium carbonyl complex, namely trans-Cr(CO)2(dppe)2; the high-stability electron shuttle tetraphenylviologen dichloride; and the propeller-shaped redox reagent decaphenylferrocene. The solvents which can act as catalysts include acetonitrile, acetone, methanol and ethanol.

Aerosol behavior in chromium waste incineration

Cr 2O 3 is considered as the dominant incineration product during the combustion disposal of chromium waste. A hydrogen/air diffusion flame was employed to simulate the industrial process of incineration. Cr 2O 3 aerosols were generated inside the flame by the gas phase reaction of chromium and oxygen. Chromium came from the rapid decomposition of chromium hexacarbonyl (Cr(CO) 6) at room temperature and was carried into the combustion chamber by hydrogen. Aerosol and clusters can then be easily formed in the flame by nucleation and coagulation. A two dimensional Discrete-Sectional Model (DSM) was adopted to calculate the Cr 2O 3 aerosol behavior. The experimental measurement method was Dynamic Light Scattering. The numerically predicted results agreed well with those of the experimental measurement. Both results show that the Cr 2O 3 aerosol size reached about 70 nanometers at the flame top.

Anionic polymerization of methyl methacrylate in the presence of chromium carbonyl [Cr(CO)6

The presence of Cr(CO)6 in nBuLi-initiated anionic polymerization of methyl methacrylates (MMA) was found to effectively enhance stereoselectivity of the polymerization in toluene at 0°C. nBuLi/Cr(CO)6 afforded an isotactic PMMA with 86 % of mm triad, and the polymers obtained with nBuLi/Cr(CO)6/tBuOK were rich in heterotactic structures (mr = ca. 54%). In both cases, the selectivity was improved in ca. 10% compared to those of the polymerization conducted under the similar conditions without Cr(CO)6.

Stereospecific 1,4‐cis‐Hydrogenation of Conjugated Dienes, Dienynes, and Dienediynes Catalyzed by Chromium Carbonyl Complexes in Stereocontrolled Syntheses of Physiologically Active Olefins

AbstractFor Abstract see ChemInform Abstract in Full Text.

New Chromium Carbonyl Catalysts for [6 + 2] Cycloaddition Reactions.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Reactions of Laser-Ablated Chromium Atoms, Cations, and Electrons with CO in Excess Argon and Neon: Infrared Spectra and Density Functional Calculations on Neutral and Charged Unsaturated Chromium Carbonyls

Laser-ablated Cr atoms react with CO (12C16O, 13C16O, 12C18O) in excess argon to give the same Cr(CO)3,4,5 species observed from the photodissociation of Cr(CO)6. Similar reactions in excess neon give neon matrix fundamentals between argon matrix and gas-phase values. The dicarbonyl Cr(CO)2 is bent with 1970.8, 1821.5 cm-1 and 1982.1, 1832.9 cm-1 C−O stretching fundamentals in solid argon and neon, respectively. The high-spin CrCO molecule appears at 1975.6 and 2018.4 cm-1 in solid argon and neon, respectively, and exhibits a strong matrix interaction. The CrCO+ cation and Cr(CO)2- anion are observed in laser-ablation experiments in solid neon at 2200.7 and 1705.0 cm-1, respectively. The Cr2(CO)2 complex absorbs strongly at 1735.4 cm-1 and gives several combination bands in neon. Density functional theory calculations support the vibrational assignments.

Transition metal complexes with heterocyclic analogs of fluorene 1. Synthesis, structures, and haptotropic rearrangements of tricarbonylchromium complexes of dibenzothiophene

The complex formation of dibenzothiophene with chromium carbonyl complexes of the general formula L3Cr(CO)3 (L = Py, NH3, or CO) afforded η6-C12H8SCr(CO)3 (1). In the presence of tetramethylethylenediamine, complex 1 was selectively metallated with BuLi at position 4 of the coordinated ring to form η6-4-LiC12H8SCr(CO)3 (2). In decane, the tricarbonylchromium group is reversibly and intramolecularly migrates from the unsubstituted to substituted ring due to the inter-ring haptotropic rearrangement (IRHR) at 130 °C for 100 h. In decane, the rate constant of IRHR was estimated experimentally by 1H NMR spectroscopy and theoretically by the density functional theory (DFT).

New Chromium Carbonyl Catalysts for [6+2] Cycloaddition Reactions

The complexes, (benzene)chromiumdicarbonyl(methyl acrylate) and chromiumdicarbonylbis(cyclohexadiene), are precursors for the highly coordinatively unsaturated chromium dicarbonyl fragment 3, a catalyst for the cycloaddition of activated olefins to cycloheptatriene.

Thermal stability of organo-chromium or chromium organic complexes and vapor pressure measurements on tris(2,4-pentanedionato)chromium(III) and hexacarbonyl chromium(0) by TG-based transpiration method

Thirteen different organo-chromium and chromium organic complexes were synthesized and thermogravimetric studies had been carried out on these complexes in order to search for materials exhibiting high vapor pressure for chemical vapor deposition applications. These studies revealed only two complexes namely tris(2,4-pentanedionato)chromium(III), Cr(acac) 3 and hexacarbonyl chromium(0), Cr(CO) 6 to be vaporizing congruently even at temperatures as low as 500 K , without any decomposition and identifying themselves to be promising candidate materials for coating purposes. A horizontal thermo analyzer was adopted as a transpiration apparatus to measure the vapor pressure of Cr(acac) 3 and Cr(CO) 6 after ascertaining the equilibrium nature of these measurements and by exploiting Dalton's law of partial pressure for ideal gas mixtures. The vapor pressures of Cr(acac) 3 and Cr(CO) 6 were computed to be log(p/ Pa)=14.16(±0.07)−5830(±157) K/T and log(p/ Pa)=11.54(±0.04)−3308(±110) K/T , valid over the ranges 374– 418 K and 309– 347 K and yielding values of 111.6±3.0 and 63.3±2.1 kJ/ mol for their standard enthalpies of sublimation, respectively.

Unimolecular Decomposition in Ion Cyclotron Resonance Traps: Kinetic Energy Release and Microsecond-Scale Kinetics

A method of recovering information about the kinetics and dynamics of gas-phase ion-molecule reactions which occur on a microsecond time scale inside a Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR-MS) cell is presented. In FT-ICR experiments, the typical time-scale of the ion detection is of the order of milliseconds to seconds and the microsecond-scale reactions usually run to completion before the detection takes place. However, axial oscillation inside the ICR cell can be made very fast and the efficiency of the dynamic voltage trapping depends on the axial position of the ions. We present a theoretical model which relates experimental ion abundance to the life-times and kinetic energy releases, illustrating it with an example of fast-decomposing chromium hexacarbonyl molecular cation activated by collision with a fluorinated self-assembled monolayer surface in a 7-Tesla FT-ICR cell. General formalism, quantitative limitations and application of this method to measure lifetimes and the kinetic energy releases of less-studied ionic systems are addressed in detail.