Chromium Hexacarbonyl Research Articles

Structure of films prepared from polystyrene-block-polybutadiene and poly(aryleneoxysulphone)-block-polybutadiene copolymers modified by carbonyls of transition metals

Films prepared from polystyrene-block-polybutadiene and poly(aryleneoxysulphone)-block-polybutadiene modified by reacting the starting block copolymer with tungsten acetonitrile pentacarbonyl or chromium acetonitrile pentacarbonyl, but also with chromium hexacarbonyl, were studied by IR spectroscopy, electron microscopy, and X-ray diffraction methods. The metal-containing component was found to be dispersed as a discrete phase in a continuous polymeric matrix. The results led us to the conclusion that the dispersed phase contains chromium carbonyl or tungsten carbonyl in the form of π-complexes with polymeric ligands.

Photodissociation of chromium hexacarbonyl in 1-propanol and 2-propanol: effect of solvent structure on the mechanisms of formation of Cr(CO)5(OHR) from photogenerated Cr(CO)5(ROH)

Photodissociation of chromium hexacarbonyl in 1-propanol and 2-propanol: effect of solvent structure on the mechanisms of formation of Cr(CO)5(OHR) from photogenerated Cr(CO)5(ROH)

Formate reduction of aldehydes using a photogenerated chromium carbonyl catalyst

The aldehydes RCHO (R = p-tolyl, p-anisyl, n-hexyl) are reduced to the corresponding alcohols RCH 2OH by sodium formate in 95% aqueous methanol in the presence of a catalyst photogenerated from Cr(CO) 6.

NMR and visible spectroscopic study of chromium carbonyl supported on Na-X zeolite and alumina

Solid-state /sup 13/C NMR spectroscopy and diffuse-reflectance visible spectroscopy (DRS) have been used to study samples prepared from Cr(CO)/sub 6/ and Na-X zeolite or ..gamma..-alumina. A rose-colored surface carbonyl with Cr(CO)/sub 3/ stoichiometry is formed when Cr(CO)/sub 6/ reacts with the zeolite at 393 K. The /sup 13/C chemical shift of 247 ppm found by using NMR with magic-angle spinning indicates an anionic tricarbonyl. DRS absorption bands at 460 and 540 nm are from this surface species. With the addition of CO, the 540-nm band is removed and a 460-nm band from an intermediate carbonyl, Cr(CO)/sub 4/ or Cr(CO)/sub 5/, appears. The addition of oxygen was monitored with NMR spectroscopy and DRS and showed that the CO liberated when chromium is oxidized reacts with the remaining Cr(CO)/sub 3/ to form the intermediate carbonyl and finally physisorbed Cr(CO)/sub 6/. Samples prepared from Cr(CO)/sub 6/ and alumina at 393 K produce small /sup 13/C NMR peaks at 225, 216, and 207 ppm although some of the chromium is oxidized. 24 references, 5 figures, 1 table.

Arene Displacement Reactions of (η6−Arene)chromium(0) Carbonyl Compounds

Abstract The development of organometallic chemistry over the past 25 years has led to extremely selective catalytic systems and to a greater understanding of their mechanisms. One area of particular interest has been the study of hydrogenation reactions (e.g. dienes to monoenes) using (η6−arene)tricarbonylchromium(0) complexes as catalysts. 1–4 The possibility of the catalytic liberation of functionalized arenes from the chromium centers in such compounds has also attracted the attention of synthetic organic chemists.5−6 The mechanisms involved in catalytic hydrogenation by (η6−arene)tricarbonylchromium compounds are only just becoming understood despite the fact that these reactions have been investigated since the early sixties. The first step is believed to be partial (or complete) displacement of the arene ring from the chromiummetal center.1−7 Moreover, the catalytic rate is highly dependent on the nature of the arene involved, i.e. on the strength of the arene-Cr bond.2 In this Comment, the work th...

ESCA Studies of N,N′-Thiobisamines and of Some of its Chromium Carbonyl Complexes

Abstract The X-ray photoelectron spectra of some N,N′-thiobisamines and of two of its complexes with Cr(CO)5 have been studied. The S(2p) binding energies are found to correlate with the effective nuclear charge on the sulfur atom as well as with the double bond character of the S-N linkage. The effect of the coordination on the N(1s) and S(2p) binding energies agree with sulfur coordination as well as with a π acceptor behaviour characteristic for thiobisamine ligands.

ChemInform Abstract: Preparation and Characterization of Oxochromium(IV) and Nickel(II) Complexes with 5,14‐Dihydro‐7,16‐diethyl‐(E)‐ or ‐(Z)‐dipyrido(b,i) (1,4,8,11)tetraazacyclotetradecine.

Abstract The reaction of 5,14-dihydro-7,16-diethyl-( E ) or -( Z )-dipyrido[b,i][1,4,8,11]tetraazacyclotetradecine with chromium hexacarbonyl produced the corresponding oxochromium(IV) complexes. These compounds had intense bands in the infrared region at 985 cm −1 , which are attributed to the CrO stretching modes. The two complexes gave mass spectra with prominent parent and parent-O peaks. On the other hand the mass spectra for the nickel(II) complexes showed parent and parent-CH 3 peaks. The absorption bands appearing in the energy range greater than 19 000 cm −1 were attributable to the π→π* and CT transitions. Consistent with their diamagnetism, the oxochromium complexes gave well-resolved proton NMR and carbon-13 NMR spectra. The magnitude of downfield shifts for the oxochromium(IV) complex is much larger than that observed for the corresponding nickel(II) complex. This is due to the fact that the positive charge provided by chromium(IV) is greater in magnitude than that by nickel(II).

Nature of the hydrogen bridge in transition metal complexes: II. Molecular orbital calculations of binuclear carbonyls of Mn, Re, Cr, Mo and W with double hydrogen bridges

To throw more light on the nature and character of the metalhydrogenmetal bond we carried out the electronic structure calculations by use of the parameter-free Fenske-Hall method and the semi-empirical EHT method for ▪ complexes (M = Mn, Re, Cr, Mo, W and n = −2,0). The character and stability of the double hydrogen bridges in these complexes and in ▪ and ▪ were compared. The effects that type of transition metal has on the character and stability of double hydrogen bridges in carbonyl dimers are described. The electronic structures of the bridge cores in the double-and single-hydrogen bridge binuclear carbonyls of chromium and molybdenum were compared.

Stereoselective synthesis of arenechromium tricarbonyl complexes: Origins of the benzylic oxygen directing effects for 1-tetralol derivatives

Thermolysis of chromium hexacarbonyl with 1-tetralol ( 10) or 1-methoxytetralin ( 12) yields the corresponding syn-chromium tricarbonyl complexes ( 9 and 11) via an oxygen chelation controlled mechanism. Complexation of the t-butyldimethylsilyl protected 1-tetralol ( 14) gives a mixture of syn- and anti-diastereoisomers ( 16 and 15), with the latter favoured because the steric effect of the O-silyl group outweighs any chelation effect.

ChemInform Abstract: Structural Consequences of Electron‐Transfer Reactions. Part 15. Mixed‐Valent Cations of Dinuclear Chromium Aryl Complexes: Electrochemical, Spectroscopic, and Structural Considerations.

AbstractThe oxidation of the dinuclear chromium carbonyl complexes (I)‐(IV) is studied by electrochemistry, IR and ESR spectroscopy and X‐ray crystallography.

Characterization of the temporary anion states of metal carbonyl complexes: an MS-X.alpha. and ETS study of chromium hexacarbonyl and iron pentacarbonyl

The electron affinities in the 0-5 eV energy range have been determined for chromium hexacarbonyl and iron pentacarbonyl by means of multiple scattering X..cap alpha.. calculations. The total electron scattering cross sections have been estimated with the continuum MS-X..cap alpha.. method. The computational results are compared with the electron transmission spectra and used for the assignment of the experimental features. The ET spectrum of Fe(CO)/sub 5/ is presented and assigned for the first time and that of Cr(CO)/sub 6/ is reassigned. For both complexes, all the anion states associated with electron capture into the orbitals deriving from the ligand 2..pi..* MOs and into the metal empty d orbitals are assigned to resonances occurring in the 0.4-2.6 eV energy region of the ET spectra. A charge density analysis reveals that a net electronic charge transfer occurs from the ligands to the metal, owing to the acceptor capability of the metal 4s and 4p orbitals. This is consistent with the experimentally observed average stabilization of the anion states localized at the CO ligands with respect to the II anion state of free CO.

Elementary Rate Processes in the Dissociative CO for C2H4 Substitution Reactions of Organometallic Complexes in the Gas Phase

Dissociative substitution mechanisms abound in organometallic chemistry. For certain systems, such processes can be isolated in the gas phase, where, as sequences of elementary unimolecular and bimolecular reactions, their kinetics can convey information on fundamental energetics and dynamics of metal-centered chemical transformations. Methods of competitive kinetics, using time-resolved infrared absorption spectrometry, provide relative and absolute rate constants for comparatively fast reactions. Work yielding unimolecular decay and relative bimolecular production rate constants for selected bis- and tris-ethylene complexes of iron and chromium carbonyls is summarized together with a report of new work on the CO-for-C2H4 substitution kinetics of (C2H4)Cr(CO)5.

Organotransition‐Metal Complexes of Multidentates 2. Synthesis and Allyl Bromination of N, N‐Bis(3,5‐Dimethylpyrazol‐1‐YL)Methane Derivatives of the Group VI Metal Carbonyls

AbstractN,N‐Bis(3,5‐dimethylpyrazol‐1‐yl)methane (H2CPz'2) reacts with the hexacarbonyls of chromium, molybdenum, and tungsten to give cis‐(H2CPz'2)M(CO)4 derivatives with M=Cr, Mo, W. The direct allyl bromination of these complexes is also investigated and only the molybdenum complex is converted into (H2CPz'2)Mo(CO)2(π‐C3H3)(Br).

Preparation and characterization of oxochromium(IV) and nickel(II) complexes with 5,14-dihydro-7,16-diethyl-( E)- or -( Z)-dipyrido[b,i][1,4,8,11]tetraazacyclotetradecine

The reaction of 5,14-dihydro-7,16-diethyl-( E) or -( Z)-dipyrido[b,i][1,4,8,11]tetraazacyclotetradecine with chromium hexacarbonyl produced the corresponding oxochromium(IV) complexes. These compounds had intense bands in the infrared region at 985 cm −1, which are attributed to the CrO stretching modes. The two complexes gave mass spectra with prominent parent and parent-O peaks. On the other hand the mass spectra for the nickel(II) complexes showed parent and parent-CH 3 peaks. The absorption bands appearing in the energy range greater than 19 000 cm −1 were attributable to the π→π* and CT transitions. Consistent with their diamagnetism, the oxochromium complexes gave well-resolved proton NMR and carbon-13 NMR spectra. The magnitude of downfield shifts for the oxochromium(IV) complex is much larger than that observed for the corresponding nickel(II) complex. This is due to the fact that the positive charge provided by chromium(IV) is greater in magnitude than that by nickel(II).

Lsocyanide derivatives of ferrocene. Preparation, complexation and redox properties

Syntheses and properties of 11 isocyanides containing the ferrocene moiety, including 7 chiral compounds, are described. The redox properties and spectroscopic data of some of these isocyanides are discussed together with those of their chromium carbonyl complexes.

ESR spectra of ion-radical complexes of chromium and molybdenum with 1-H-1-oxo-2,4,6,8-tetrakis(tert-butyl)phenoxazine ligand

1. The formation of bis-1-oxo-2,4,6,8-tetrakis(tert-butyl)phenoxazinyl complexes of chromium, molybdenum, and tungsten has been detected. 2. In the chromium complexes, the ligands are in the anion-radical form, but in the molybdenum complexes they are in the dianion form. 3. A staged mechanism has been established for the addition of Φ-K+ to carbonyls of chromium, molybdenum, and tungsten.

ChemInform Abstract: Synthesis of Leaf Alcohol from Methyl Sorbate.

AbstractReduction of methyl sorbate (I) with lithium aluminum hydride gives sorbic alcohol (II) which is subsequently hydrogenated in the presence of chromium hexacarbonyl, producing leaf alcohol (III).

Reaction of bulky monosubstituted phosphorus(III) halides with disodium tetracarbonylferrate. Steric and electronic factors in the synthesis of Fe(CO)4 complexes of diphosphene and phosphinidene ligands

Reaction of Na/sub 2/Fe(CO)/sub 4/ with a bulky monosubstituted phosphorus(III) halide RPCl/sub 2/ where R = Mes (2,4,6-Me/sub 3/C/sub 6/H/sub 2/), CH/sub 2/SiMe/sub 3/, CH(SiMe/sub 3/)/sub 2/, N(SiMe/sub 3/)/sub 2/, -OC/sub 6/H/sub 2/-2,6-t-Bu/sub 2/-4-Me, or -OC/sub 6/H/sub 2/-2,4,6-t-Bu/sub 3/ yields products in which the phosphorus center behaves as either a diphosphene or a bridging phosphinidene group. The type of product depends on the substituent used. The synthesis of two precursor ligands, 2,4,6,-t-Bu/sub 3/C/sub 6/H/sub 2/OPCl/sub 2/ and 4-Me-2,6-t-Bu/sub 2/C/sub 6/H/sub 2/OPCl/sub 2/, and eight iron carbonyl complexes involving various diphosphene and phosphinidene ligand are described and discussed in the context of the corresponding chromium carbonyl complexes.

ChemInform Abstract: Diastereoselective Complexation of Benzyl Alcohols by Chromium Hexacarbonyl. Different Reactivities of the Diastereomers in an Acidic Medium.

AbstractThe benzylic alcohols (I) react with chromium hexacarbonyl, producing the isomeric chromocarbonyl compounds (III) and (IV).

ChemInform Abstract: Contributions to the Chemistry of Silicon‐Sulphur Compounds. Part 42. Bis(1‐methyldibenzosilole)sulphide: Its Synthesis, Crystal Structure, and Reaction with Chromium hexacarbonyl.

Abstract1‐Methyldibenzosilole (I) reacts with elemental sulphur to give the sulphide (III) via the intermediate thiol (II).