Benzene Chromium Tricarbonyl Research Articles

Selective cytotoxicity of arene tricarbonylchromium towards tumour cell lines

Metals are cytotoxic and could be harmful to human health; however, as their effects are dose dependent, some of them could be used in chemotherapy. In the present work, mineral chromium (VI) showed that it is cytotoxic on both tumour (MCF-7, HeLa, Hep2 and Caco-2) and non-tumour (HEK293) cell lines. Interestingly, among seven complexes of arene tricarbonylchromium, chromium (0) becomes more efficient in targeting tumour cell lines with less toxicity to non-tumour cells. Three of complexes (formyl benzene tricarbonylchromium 1, anisol tricarbonylchromium 2 and trimethoxybenzene tricarbonylchromium 3) show a decrease of IC50 values for all tested tumour cells compared to the non-tumour cells HEK293. The remaining compounds have an opposite effect; they are less toxic to tumour cells compared to HEK293. The present work demonstrates that some arene tricarbonylchromium are selectively active against cancer cells by inducing apoptosis. The role of formyl and methoxy groups in arene tricarbonylchromium is shown in complexes acquiring the selective tumour cytotoxicity.

Dissociative electron attachment to coordination complexes of chromium: chromium(0) hexacarbonyl and benzene-chromium(0) tricarbonyl.

Here we report the results of dissociative electron attachment (DEA) to gas-phase chromium(0) hexacarbonyl (Cr(CO)6) and benzene-chromium(0) tricarbonyl ((η6-C6H6)Cr(CO)3) in the energy range of 0–12 eV. Measurements have been performed utilizing an electron-molecular crossed beam setup. It was found that DEA to Cr(CO)6 results (under the given experimental conditions) in the formation of three fragment anions, namely [Cr(CO)5]−, [Cr(CO)4]−, and [Cr(CO)3]−. The predominant reaction channel is the formation of [Cr(CO)5]− due to the loss of one CO ligand from the transient negative ion. The [Cr(CO)5]− channel is visible via two overlapping resonant structures appearing in the energy range below 1.5 eV with a dominant structure peaking at around 0 eV. The peak maxima of the fragments generated by the loss of two or three CO ligands are blue-shifted and the most intense peaks within the ion yield curves appear at 1.4 eV and 4.7 eV, respectively. (η6-C6H6)Cr(CO)3 shows a very rich fragmentation pattern with decomposition leading to the formation of seven fragment anions. Three of them are generated from the cleavage of one, two or three CO ligand(s). The energy of the peak maxima of the [(C6H6)Cr(CO)2]–, [(C6H6)Cr(CO)]–, and [(C6H6)Cr]− fragments is shifted towards higher energy with respect to the position of the respective fragments generated from Cr(CO)6. This phenomenon is most likely caused by the fact that chromium–carbonyl bonds are stronger in the heteroleptic complex (η6-C6H6)Cr(CO)3 than in homoleptic Cr(CO)6. Besides, we have observed the formation of anions due to the loss of C6H6 and one or more CO units. Finally, we found that Cr−, when stripped of all ligands, is generated through a high-energy resonance, peaking at 8 eV.

Expensive tripodal rotation in η6-chromium tricarbonyl complexes of phosphabenzenes-Insights from DFT study

Tripodal rotation of Cr(CO)3 moiety complexed to mono, di and tri phosphabenzenes have been studied at B3LYP/LANL2DZ level. In most cases, the conformational minima has preferential orientation of Cr(CO)3 moiety in the anti eclipsed position relative to majority of the phosphorus atoms in the ring although instances of staggered minima in 12DPBC, 14DPBC & 124TPBC have also been reported. We observed large torsional barrier of 6.49kcal/mol (36 folds relative to benzene chromiumtricarbonyl complexes) for 1,3,5-triphosphabenzene chromiumtricarbonyl complex. Based on our observations through NBO analysis, we have attempted to provide interesting insights on conformational preferences and the hyperconjugative stabilisations (bonding/backbonding interactions) that decide these conformational preferences and torsional barrier. Furthermore, we also noted correlation between activation hardness and rotational barrier which explains the unique conformation assumed by 1,3,5-triphosphabenzene chromium tricarbonyl complex.

Monitoring equilibrium reaction dynamics of a nearly barrierless molecular rotor using ultrafast vibrational echoes.

Using rapidly acquired spectral diffusion, a recently developed variation of heterodyne detected infrared photon echo spectroscopy, we observe ∼3 ps solvent independent spectral diffusion of benzene chromium tricarbonyl (C6H6Cr(CO)3, BCT) in a series of nonpolar linear alkane solvents. The spectral dynamics is attributed to low-barrier internal torsional motion. This tripod complex has two stable minima corresponding to staggered and eclipsed conformations, which differ in energy by roughly half of kBT. The solvent independence is due to the relative size of the rotor compared with the solvent molecules, which create a solvent cage in which torsional motion occurs largely free from solvent damping. Since the one-dimensional transition state is computed to be only 0.03 kBT above the higher energy eclipsed conformation, this model system offers an unusual, nearly barrierless reaction, which nevertheless is characterized by torsional coordinate dependent vibrational frequencies. Hence, by studying the spectral diffusion of the tripod carbonyls, it is possible to gain insight into the fundamental dynamics of internal rotational motion, and we find some evidence for the importance of non-diffusive ballistic motion even in the room-temperature liquid environment. Using several different approaches to describe equilibrium kinetics, as well as the influence of reactive dynamics on spectroscopic observables, we provide evidence that the low-barrier torsional motion of BCT provides an excellent test case for detailed studies of the links between chemical exchange and linear and nonlinear vibrational spectroscopy.

Quadratic susceptibility and first hyperpolarizability of the complex of Cr(CO)3 with [2.2]paracyclophane

The peculiarities of chemical bonding and nonlinear optical properties of the complex of Cr(CO)3 with [2.2]paracyclophane (Cr–pCp) have been studied by a combined experimental–theoretical approach. The Cr–pCp complex exhibits second harmonic generation, the efficiency of which was measured by the powder technique at 1064.2nm fundamental wavelength and estimated theoretically. The comparison of electronic structure of the Cr–pCp with benzene tricarbonyl chromium analogue has revealed an important role of intraligand charge transfer state in pCp moiety conditioned by a strong transannular interaction between aromatic rings which is responsible for the enhanced molecular hyperpolarizability of Cr–pCp.

Vibrational Spectra of Benzene Chromium Tricarbonyl and Its Mesityl Analogue: A Study by Neutron Spectroscopy

We have used high resolution neutron vibrational spectroscopy to study the vibrations of the model compound for arene-to-metal bonding, benzene chromium tricarbonyl, and its mesityl analogue. It is shown that all previously published assignment schemes, based on optical spectroscopy alone, are wrong, and new assignments are given in agreement with ab initio calculations.

Metal-benzene and metal-CO bond energies in neutral and ionic C6H6Cr(CO)3 studied by threshold photoelectron-photoion coincidence spectroscopy and density functional theory.

photoelectron-photoion coincidence spectroscopy and density functional theory calculations have been used to investigate the dissociation kinetics of the benzene chromium tricarbonyl ion, BzCr(CO)3+ (Bz = C6H6). The dissociation of the BzCr(CO)3+ ion proceeds by the sequential loss of three CO and benzene ligands. The first and third CO and the benzene loss reactions were associated with metastable precursor ions (lifetimes in the microsecond range). By simulating the resulting asymmetric time-of-flight peak shapes and breakdown diagram, the 0 K appearance energies of the four product ions were determined to be 8.33 +/- 0.05, 8.93 +/- 0.05, 9.97 +/- 0.06, and 11.71 +/- 0.06 eV, respectively. Combined with the ionization energy of BzCr(CO)3, 7.30 +/- 0.05 eV, the three successive Cr-CO bond energies in the BzCr(CO)3+ were found to alternate, with values of 1.03 +/- 0.05, 0.60 +/- 0.05, and 1.04 +/- 0.05 eV, respectively, and the Bz-Cr bond energy in BzCr+ is 1.74 +/- 0.05 eV, a trend confirmed by the density functional theory (DFT) calculations. Using the heats of formation of the fully dissociated products, C6H6, Cr+, and CO, the 298 K heats of formation the ionic BzCr(CO)n+ (n = 03) species were determined. By scaling the DFT calculated bond energies for the neutral molecules, the heats of formation of the neutral BzCr(CO)n (n = 03) were also obtained.

Benzene chromium tricarbonyl revisited: Theoretical study of the structure and dynamics of (?6-C6H6)Cr(CO)3

The electronic effects of the chromium tricarbonyl fragment on the structure of the benzene ring of (η6-C6H6)Cr(CO)3 is investigated theoretically using ab initio molecular orbital calculations with electron correlation included by using both Moller–Plesset second-order calculations and density functional theory. The results of the calculations showed that the solid-state structure of alternating long and short carbon–carbon distances in the benzene ring is a result of the orientation of the Cr(CO)3 fragment with respect to the benzene ring in which the carbonyl groups lie over the midpoint of alternate carbon–carbon bonds of the benzene ring, called the staggered conformation. A different distortion of the benzene ring is observed even in the eclipsed conformation in which the carbonyls lie over alternate carbon atoms of the benzene ring. The results of these calculations indicate that the distortion of the benzene ring in (η6-C6H6)Cr(CO)3 is a result of the electronic influence of the Cr(CO)3 fragment on the benzene ring. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 77: 152–160, 2000

Benzene chromium tricarbonyl revisited: Theoretical study of the structure and dynamics of (η6-C6H6)Cr(CO)3

Benzene chromium tricarbonyl revisited: Theoretical study of the structure and dynamics of (η6-C6H6)Cr(CO)3

Synthesis of organometallic amines and their coupling to the C-terminus of amino acids and peptides

Abstract This work describes the use of organometallic amines for the labelling of the C-terminus of amino acids and peptides. N-substituted ferrocene-methylamines 2 could be readily prepared and coupled to a variety of amino acids in good yield. The novel ferrocene amino acid derivatives 4 exist in two conformations in solution, which differ in the orientation of the tertiary amide bond and interconvert slowly in solution. For the glycine derivative 4a the activation energy was determined to be 70.3 kJ mol−1 by 1H-NMR spectroscopy. All new compounds were completely characterised spectroscopically including 15N-NMR by indirect detection 2D 1H-15N-NMR. The potential difference of ca. +50 mV between ferrocene derivatives 2 and the ferrocenyl amino acids 4 in cyclic voltammetry was used to monitor the peptide coupling reaction in situ. Also described are attempts towards the synthesis of organometallic amine derivatives of benzene chromium tricarbonyl and η-cyclopentadienyl molybdenum dicarbonyl. The solid state structures of CpMo(CO)2C2H4N(CO)2C6H4 14 and CpFeC5H4CH2NHCH2-p-CH3C6H4 2a (Cp: η-cyclopentadienyl) were determined by single-crystal X-ray diffraction.

Total Synthesis of (−)-Macrocarpal C. Stereoselective Coupling Reaction with a Novel Hexasubstituted Benzene Cr(CO)3 Complex as a Biomimetic Chiral Benzyl Cation Equivalent

The first total synthesis of (−)-macrocarpal C (3) is described. The synthesis features a highly stereoselective coupling reaction of silyldienol ether 6 with biomimetic benzyl cation species (R)- and (S)-B, which were generated from novel hexasubstituted benzene chromium tricarbonyl complexes (R)- and (S)-17. At the final step of the total synthesis, we developed the tris-O-demethylation of macrocarpal C trimethyl ether 34 under basic conditions using lithium p-thiocresolate. Moreover, spectroscopic evidence shows that the synthetic (−)-3 is identical to natural macrocarpal G (4).

Vibrational Overtone Spectroscopy of Cycloheptatriene Chromium Tricarbonyl, Benzene Chromium Tricarbonyl, and Corresponding Hydrocarbon Ligands

The vibrational overtone spectra of gaseous cycloheptatriene chromium tricarbonyl (CHTCT) and benzene chromium tricarbonyl (BCT) were recorded at the third overtone region using photoacoustic spectroscopy and compared to the spectra of the nonbonded ligands, cycloheptatriene (CHT) and benzene. Analysis of the spectra leads to the conclusion that the metal−ligand bonding lengthens the CH bond by 0.007 Å in the cycloheptatriene complex and by 0.003 Å in the benzene complex. The spectrum of BCT exhibits an additional transition which is absent in the spectrum of free benzene. The experimental peaks are assigned to the pure CH overtones and combination bands. The structural information obtained from the spectra is discussed and compared to the results of gas-phase electron diffraction and microwave spectroscopic studies. Analysis of experimental data indicates that μ6-bonding is more favorable for cycloheptatriene chromium tricarbonyl.

Synthesis of Monophasic Hybrid Organic−Inorganic Solids Containing [η6-(Organosilyl)arene]chromium Tricarbonyl Moieties

Silica gel containing benzenechromium tricarbonyl units have been obtained from molecular organosilicon precursors. The hydrolytic sol−gel polymerization of [η6-C6H5Si(OMe)3]Cr(CO)3 (1), [η6-1,4-C6H4RR‘]Cr(CO)3 [R = R‘ = Si(OMe)3 (2), R = R‘ = CH2Si(OMe)3 (3), R = R‘ = CH2CH2Si(OMe)3 (4)], {η6-1,3,5-C6H3[Si(OMe)3]3}Cr(CO)3 (5), under nucleophilic catalysis by fluoride ion (NH4F), have led quantitatively to new monophasic hybrid organic−inorganic silica gels. The derived xerogels X were characterized by FT IR, 13C and 29Si solid state CP MAS NMR spectroscopies. The silicon−carbon bond and the tricarbonylchromium ligand were retained within the gel. The major environment of the Si atoms corresponded to a T2:CSi(OR)(OSi)2 substructure for X2−X4, a T3:CSi(OSi)3 one for X1 and a Ts:CSi(OR)2(OSi) in the case of X5. In most cases, these were amorphous materials that exhibited low specific surface areas (∼10 m2 g-1). Upon heating the xerogels X1, X2, and X4 at 400 °C under an argon flow, weight losses corresponding to complete carbon monoxide elimination were obtained, leading to chromium in a low oxidation state within the solid.

Vapour phase far-infrared studies of η-bonded metal carbonyls, (1,3-butadieneiron tricarbonyl, cyclopentadienylmanganese tricarbonyl and methylcyclopentadienylmanganese tricarbonyl)

Far-infrared spectra of 1,3-butadieneiron tricarbonyl, C 4H 6Fe(CO) 3, cyclopentadienyl-manganese tricarbonyl, C 5HMn(CO) 3 and methylcyclopentadienylmanganese tricarbonyl, CH 3C 5H 4Mn(CO) 3 in the vapour phase have been reported first time in the region 500-10 cm −1. An assignment of the frequencies on the basis of local symmetry of Fe(CO) 3 fragment explain most of the observations, but the FeCO stretching modes of E symmetry are split. The C 4H 6 vibrations are assigned on the basis of C S symmetry. For CpMn(CO) 3 and MeCpMn(CO) 3 particular reference is made to the assignment of the metal-ring modes. This assignment has been discussed in term of previous assignment given for (in liquid phase and Nujoll mull) other ν-cyclopentadienyl and related compounds, including ferrocene, dimethylferrocene, benzenechromium tricarbonyl and toluenechromium tricarbonyl.

An EXAFS study of methyl-substituted benzene chromium tricarbonyl complexes

An extended X-ray absorption fine structure (EXAFS) study is presented of the complexes ( η 6-C 6H 6− n Me n )Cr(CO) 3, where n = 0–6, to determine the molecular structures and explore the variation in electron charge density on chromium with sequential arene methylation. Structural parameters for the complexes, determined by EXAFS analysis, are found to agree closely with literature data from X-ray crystal structures. The structure of ( η 6- p-xylene)Cr(CO) 3 is described, for which no previous determination has been reported. From analysis of the K-edge absorptions, chromium ls electron threshold energies were obtained; a small increase in these energies is observed with each methyl insertion on the benzene ring. This trend is interpreted to indicate a progressive accumulation of electron density on the chromium atom. The results agree with a bonding model previously constructed from vibrational spectral and XPS studies.

First stereoselective total synthesis of macrocarpal C: structure elucidation of macrocarpal G

The first stereoselective total synthesis of macrocarpal C is achieved via a coupling reaction of a silyl dienol ether with a novel hexasubstituted benzene chromium tricarbonyl complex as an optically active benzyl cation equivalent, thereby clarifying the identity of macrocarpal C and G.

Synthesis of some phosphino- and arsinobenzenechromium tricarbonyl derivatives and metal carbonyl clusters

The synthesis of a number of new phosphino- and arsinobenzenechromium tricarbonyl ligands ER2C6H5Cr(CO)3 (ER2 = PEt2, PPri2, PBut2, PPh2, AsPh2 AsMe2), ER[C6H5Cr(CO)3]2 (ER = PEt, PBut, PPh, AsPh) has been achieved by reacting lithium derivatives of benzenechromium tricarbonyl with appropriate chlorphosphines or iodoarsines. The spectroscopic properties of these ligands are described. The structure of Pri2PC6H5Cr(CO)3 was determined by an X-ray crystallographic study. This is the first solid state structure to be reported for a phosphinobenzenechromium tricarbonyl derivative. The structures of four metal carbonyl cluster complexes were also determined. Crystals of Pri2PC6H5Cr(CO)3 (3, C15H19CrO3P) are monoclinic, space group P21/c, a = 8.150(2) Å, b = 13.490(2) Å, c = 15.125(1) Å, β = 100.19(1)°, Z = 4; those of Ru3(CO)11[PPri2C6H5Cr(CO)3] (15, C26H19CrO14PRu3) are monoclinic, space group P21/n, a = 8.565(2) Å, b = 21.808(3) Å, c = 17.167(3) Å, β = 97.41(2)°, Z = 4; those of Ru3(CO)10[PPh2C6H5Cr(CO)3]2 (19, C32H15CrO14PRu3) are orthorhombic, space group Pbca, a = 17.367(4) Å, b = 24.471(5) Å, c = 16.096(3) Å, Z = 8; those of Ru3(CO)10[PPri2C6H5Cr(CO)3]2•CH2Cl2 (16, C40H38Cr2O16P2Ru3•CH2Cl2) are orthorhombic, space group P21212, a = 13.832(3) Å, b = 17.558(2) Å, c = 10.144(1) Å, Z = 2; and those of Os3(CO)9[PEt2C6H5Cr(CO)3]3 (26, C48H45Cr3O18Os3P3) are trigonal, space group [Formula: see text], a = 15.7558(4) Å, c = 12.662(1) Å, Z = 2. The structures were solved by the Patterson method and were refined by full-matrix least-squares procedures to R = 0.031,0.027, 0.029, 0.025, and 0.029 (Rw = 0.027, 0.024, 0.024, 0.023, and 0.025) for 2326, 4110, 3878, 3046, and 4093 reflections with I ≥ 3σ(I), respectively. Key words: metal carbonyl clusters, phosphinobenzenechromium tricarbonyl derivatives, arsinobenzenechromium tricarbonyl derivatives, crystal structures.

An X-ray photoelectron spectroscopic study of arene chromium tricarbonyl complexes at 170K

Core and valence region XPS spectra of methyl-substituted benzene chromium tricarbonyl complexes have been measured at low (170K) temperature. The core levels were found to be unchanged by the addition of the electron-donating groups on the ring, whilst the shifts in the valence bands have been related to the bonding mechanisms within these compounds.

Infrared and Raman spectra of (η6-C6H6−nXn)Cr(CO)3 complexes where X = Me (n = 0–6) or OMe (n = 0–2). A study of metal—ligand interactions

A systematic study is reported of the infrared and Raman spectra of methyl and methoxy substituted benzene chromium tricarbonyl complexes (η6-C6H6−nXn)Cr(CO)3 where X = Me (n = 0–6) or OMe (n = 0–2). Bands have been assigned and intensities calculated for a number of vibrational modes. Trends in the wavenumbers and band intensities of the arenemetal, metalcarbonyl and carbonyl bonds are examined to gain an insight into metal—ligand interactions and intramolecular electron rearrangements with progressive substitution on the arene. The results are discussed with regard σ-, π- and δ-contributions to arenemetal bonding and of σ- and π-components in metal-carbonyl and carbonyl bonding. The intensities are related to the polarities and polarizabilities of individual bonds within the molecules, and variations in these bond electronic properties with arene substitution are examined.

Measurements of the microwave spectrum and structural parameters for benzene chromium tricarbonyl

Microwave spectra for four isotopomers of benzene chromium tricarbonyl were measured in the 4–17 GHz range using a Flygare–Balle type pulsed beam spectrometer. Rotational constants obtained are B(52Cr)=732.8886(6) MHz and B(53Cr)=732.8966(3) MHz. Asymmetric top spectra were observed for a single 13C substitution on the benzene ring giving B(13C–bz)=729.9606(3) and C(13C–bz)=727.9024(2) MHz. For a single 13C substitution on one of the carbonyl carbons B(13CO)=731.9036(8) and C(13CO)=729.1657(8) MHz. Since no effects of possible internal rotation were observed on the 13C asymmetric top spectra, we can place a lower limit on the V6 potential for internal rotation of V6≳4.0 THz (=1.6 kJ/mole). The centrifugal distortion constants are small, DJ=0.05 kHz and DJK=−0.05 kHz, indicating a fairly rigid structure. The 53Cr quadrupole coupling strength is low, eqQ(53Cr)=−12.11(1) MHz, indicating a near octahedral charge distribution around the Cr atom. Structural parameters obtained are the center of the benzene chromium distance r(Cr–bz)=1.67(2) Å, the chromium–carbonyl bond length r(Cr–CO)=1.86(1) Å and the OC–Cr–CO interbond angle α=88(1)°.