Metal Carbonyl Hydrides Research Articles

N-Heterocyclic Phosphenium Complex of Manganese: Synthesis and Catalytic Activity in Ammonia Borane Dehydrogenation.

A neutral N-heterocyclic phosphenium complex of manganese was synthesised by a metathesis approach and characterised by IR, NMR, and XRD studies. The short P-Mn distance suggests a substantial metal-ligand double bond character. Reaction with a hydride produced an anionic phosphine complex, which was also characterised by IR and NMR spectroscopy and, after anion exchange, a single-crystal XRD study. Protonation of the anion occurs at the metal to yield a neutral phosphine metal carbonyl hydride, which releases dihydrogen upon irradiation with UV light. These reactions confirm the electrophilic nature of the phosphenium ligand and suggest that the title complex might undergo reactions displaying metal-ligand cooperativity. Surprisingly, reaction with ammonia borane (AB) did not proceed under transfer hydrogenation of the Mn=P double bond but through the catalytic dehydrogenation of AB. The phosphenium complex behaves here as a class II catalyst, which dehydrogenates AB to NH2 BH2 that was trapped with cyclohexene. Computational model studies led to the identification of two possible catalytic cycles, which differ in the regioselectivity of the initial AB activation step. In one case, the activation proceeds as cooperative transfer hydrogenation of the Mn=P bond, whereas in the other case a H+ /H- pair is transferred to the phosphorus atom and a nitrogen atom of the phosphenium unit, resulting in a ligand-centred reaction in which the metal fragment acts merely as stabilising substituent. Unexpectedly, this pathway, which constitutes a new reaction mode for phosphenium complexes, seems to be better in accord with experimental findings on the course of the catalysis.

Catalytic activity of systems based on supported potassium salts of transition metal carbonyl hydrides in hydrogen-deuterium exchange of hydrocarbons

The deposition of K2[Ru4(CO)13], K2[Os3(CO)11], K2[Fe2(CO)8], and K[Re(CO)5] onto graphite-like carbon “Sibunit” followed by the thermal decomposition of the supported carbonylmetallate in a flow of dihydrogen or argon affords systems capable of activating C-H bonds of methane, ethylene, and acetylene and of introducing them into hydrogen-deuterium exchange reactions. In the case of ethylene and acetylene, the isotope exchange proceeds at room temperature, while in the case of methane reaction temperatures not lower than 150 °C are needed.

ChemInform Abstract: Homogeneous Catalytic Hydrogenation of Aromatic Hydrocarbons and Heteroaromatic Nitrogen Compounds: Synthetic and Mechanistic Aspects

The synthetic and mechanistic aspects of the homogeneous catalytic hydrogenation of mono and polynuclear aromatic hydrocarbons and the corresponding heteroaromatic nitrogen compounds will be reviewed. A comparison of the regioselectivities under various hydrogenation conditions for both classes of compounds will be discussed for a wide variety of transition-metal complexes with regard to substrate binding at the metal center and the role of free radical intermediates in metal carbonyl hydride reactions, where substrate does not bind to the metal center prior to hydrogen transfer. The polynuclear heteroaromatic nitrogen compounds appear to hydrogenate more readily, under similar reaction conditions, than the polynuclear aromatic hydrocarbons. The relative rates of hydrogenation of a variety of heteroaromatic nitrogen compounds as well as compounds that inhibit and enhance selective hydrogenation of the nitrogen-containing ring will be addressed. A relatively new spectroscopic technique, high pressure nuclear magnetic resonance spectroscopy, will be shown to be a powerful tool to elucidate the mechanisms of the regioselective hydrogenation of polynuclear heteroaromatic nitrogen compounds.

Photodissociation and electronic spectroscopy of transition metal hydrides carbonyls: quantum chemistry and wave packet dynamics

The photodissociation mechanism of a number of transition metal carbonyl hydrides (HCo(CO) 4, H 2Fe(CO) 4, HM(CO) 3(H-DAB) with M=Mn, Re and H-DAB=1,4-diaza-1,3-butadiene) is followed in a time-dependent approach. The time scale of the primary reactions, the absorption spectra and the branching ratio of the concurrent dissociation pathways are deduced from wave packet propagations performed on two-dimensional ab initio potential energy surfaces connecting the electronic ground and excited states of the irradiated molecule to those of the primary products.

Ionic Hydrogenations of Hindered Olefins at Low Temperature. Hydride Transfer Reactions of Transition Metal Hydrides

Sterically hindered olefins can be hydrogenated at -50[degree]C in dichloromethane using triflic acid (CF[sub 3]SO[sub 3]H) and a hydride donor. Mechanistic studies indicate that these reactions proceed by hydride transfer to the carbenium ion that is formed by protonation of the olefin. Olefins that form tertiary carbenium ions upon protonation are hydrogenated in high yields (90-100%). Styrenes generally produce lower yields of hydrogenated products (50-60%). Suitable hydride donors include HSiE[sub 3] and several transition metal carbonyl hydrides HW(CO)[sub 3]Cp, HW(CO)[sub 3]Cp[sup +], HMo-(CO)[sub 3]Cp, HMn(CO)[sub 5], HRe(CO)[sub 3], and HO[sub 3](CO)[sub 1]Cp*; Cp = [eta][sup 5]-C[sub 3]H[sub 5+], Cp* = [eta][sup 5]-C[sub 5]Me[sub 5]. A characteristic that is required for transition metal hydrides to be effective is that the cationic dihydrides (or dihydrogen complexes) that result from their protonation must have sufficient acidity to transfer a proton to the olefin, as well as sufficient thermal stability to avoid significant decomposition on the time scale of the hydrogenation reaction. Metal hydrides that fall due to insufficient stability of their protonated forms include HMo(CO)[sub 2](PPH[sub 3])Cp, HMo(CO)[sub 3]Cp*, and HFe(CO)[sub 2]Cp*. 62 refs., 2 tabs.

Method for controlling the removal of acidic metal carbonyl hydride from product streams

Method for controlling the removal of acidic metal carbonyl hydride from product streams

Infrared spectroscopic studies of the reactions between Co 2(CO) 8, H 2 and D 2

The reaction of Co 2(CO) 8 with D 2 does not have as product the expected DCo(CO) 4 only but gives rise to a mixture of DCo(CO) 4 and HCo(CO) 4. This phenomenon, observed also with other metal carbonyl hydrides, was explained by the fact that the reaction-vessel walls were covered by a polymeric layer of water which caused a very fast exchange with the deuterium in DCo(CO) 4, and hence this was the source of hydrogen in the formation of HCo(CO) 4. In this present work, we attempt to obtain alkane solutions of DCo(CO) 4 with very high deuteride content in order to study the spectral and chemical properties of this elusive compound. In concentrated solutions of DCo(CO) 4, having only traces of Co 2(CO) 8, an absorption band at 2048 cm −1 was observed, and attributed to a CO stretching fundamental mode of DCo(CO) 4. This band corresponds to the 2052 cm −1 band found in HCo(CO) 4. In both cases it can be assigned to the a 1 mode in which the axial and equatorial CO groups stretch out of phase. Another band, the total symmetric v(CO) mode at 2116.3 cm −1, is only 0.4 cm −1 lower in energy than the corresponding band of HCo(CO) 4. The extinction coefficients for several significant absorption bands of DCo(CO) 4 were calculated. The high pressure IR spectroscopic analysis, previously applied to calculate cobalt carbonyl concentrations in a three-component system, has proven itself to be quite accurate in the present case as well. Using the quantitative data obtained, the equilibrium constants for the reaction between Co 2(CO) 8 and D 2 were obtained. Finally, the effect of the presence of H 2O or D 2O on H/DCo(CO) 4 mixtures was studied and compared to the exchange with H 2 and D 2 in the gas phase.

5091317 Analysis of acidic metal carbonyl hydride containing streams: James L Cooper, Jack Bogle assigned to Eastman Kodak Company

5091317 Analysis of acidic metal carbonyl hydride containing streams: James L Cooper, Jack Bogle assigned to Eastman Kodak Company

Hydrogen atom transfer reactions of transition-metal hydrides. Kinetics and mechanism of the hydrogenation of .alpha.-cyclopropylstyrene by metal carbonyl hydrides

The hydrogenation of {alpha}-cyclopropylstyrene (CPS) by a series of metal carbonyl hydrides (MH) gives a mixture of the unrearranged hydrogenation product Ph(CH{sub 3})(c-C{sub 3}H{sub 5})CH (UN) and the rearranged hydrogenation product (E)-Ph(CH{sub 3})C{double bond}CHCH{sub 2}CH{sub 3} (RE). With the exception of HCr(CO){sub 3}Cp, second-order kinetics are found, conforming to the rate law {minus}d(CPS)/dt = k(CPS)(MH). The proposed mechanism involves hydrogenation by sequential hydrogen atom transfers from the metal hydride to the organic substrate. The rate-determining step is the first hydrogen atom transfer in which a carbon-centered radical and a metal-centered radical are formed. In the case of HCr(CO){sub 3}Cp at 22{degree}C, the equilibrium constant for this step is K {approximately} 10{sup {minus}12}. The effect of the significant amount of 17-electron {sup {sm bullet}}Cr(CO){sub 3}Cp radical formed in the hydrogenation of CPS by HCr(CO){sub 3}Cp is accommodated by the kinetic analysis. Since the initially formed carbon-centered radical undergoes first-order ring-opening rearrangement in competition with second-order trapping by MH, analysis of the product ratio as a function of (MH) concentration provides relative rates of hydrogen atom transfer from metal hydrides to a carbon-centered radical.

Reactions of anionic transition metal carbonyl hydrides with electrophilic metal carbonyls: Nucleophilic addition (hydride transfer) vs. electron transfer mechanisms

The relative reactivity of anionic transition metal carbonyl hydrides towards hydride transfer to monomeric metal carbonyls is consistent with an ionic route, generating, in the best-matched cases of electrophilic carbonyls (highest f CO or average v(CO)) and most nucleophilic hydrides (such as HW(CO) 4P(OMe) 3 −), metal formyls as sole product. With the metal carbonyl dimers Co 2(CO) 8, [(η 5-C 5H 5)M(CO) 3] 2 (M = Mo, W), and Mn 2(CO) 10 reductive cleavage to the respective anions occurs at rates which correlate with the nucleophilicity of the metal hydride, without observation of intermediate formyls. No reaction occurs with Re 2(CO) 10 or [(η 5-C 5H 5)Fe(CO) 2] 2.

ChemInform Abstract: Solution Homolytic Bond Dissociation Energies of Organotransition‐Metal Hydrides.

AbstractThe homolytic bond dissociation energies (BDE) of the mononuclear metal carbonyl hydrides (I)‐(VI) are estimated in MeCN solution by use of a thermochemical cycle that requires knowledge of the metal hydride pKa and the oxidation potential of its conjugate base (anion) (BDE: 50‐67 kcal/mol).

Hydroformylation of the C.tplbond.C bond of (C5H5)(PMe3)2RuC.tplbond.CCH3 by HRe(CO)5 to give an .eta.1-aldehyde complex of rhenium

The chemistry of aldehydes bonded to transition metals is not well-developed but has been attracting increasing attention. Most of the previously reported aldehyde complexes exhibit {eta}{sup 2}({pi})-bonding. The authors report an unprecedented hydroformylation of the C{triple bond}C bond of a metal alkynyl complex by a metal carbonyl hydride, which results in an {alpha},{beta}-unsaturated aldehyde {eta}{sup 1}({sigma})-bonded to Re{sub 2}(CO){sub 9}.

The mechanism of phosphine-modified rhodium-catalyzed hydroformylation studied by CIR-FTIR

The mechanism of phosphine-modified rhodium-catalyzed hydrofonnylation of 1-hexene was studied by in situ infrared spectroscopy using high pressure autoclaves equipped with embedded cylindrical internal reflectance crystals (CIR-FTIR). A series of RhH(CO) 2(PR 3) 2 complexes 1 were synthesized using p-substituted triarylphosphines where the electron density on rhodium was varied by using p-N(CH 3) 2, p-OCH 3, p-H, p-F, p-Cl or p-CF 3. The metal carbonyl and metal hydride infrared stretching frequencies were correlated by a standard Hammett treatment of the data. Reaction rates and selectivities for linear aldehydes both increased with increasingly electron-withdrawing phosphines. The IR spectra, measured under autogenous conditions of 70 †C and 200 psi (1.38 MPa), showed the presence of various intermediates in the catalytic cycle depending upon the phosphine modification, P/Rh ratio, total syngas pressure, and degree of olefin conversion. The rate and spectroscopic data permitted the assignment of a reaction mechanism involving CO dissociation from RhH(CO) 2L 2 1 as the primary selective hydroformylation pathway.

Reactivity of anionic metal carbonyl hydrides toward bis(diphenylphosphino)methane complexes of palladium and platinum

The reaction between [PPN][HFe(CO) 4] or [PPN][HFeCr(CO) 9] and [PdPt(μ-dppm) 2Cl 2] ( 3) in THF have been shown to give the trimetallic cluster [FePdPt(μ-dppm) 2(CO) 4]; because of the residual acidity of the H ligand in the starting anions, they behave as precursors of [Fe(CO) 4] 2−. Hydride transfer followed by molecular rearrangement takes place in the reaction between [Et 4N][HM(CO) 5] (M  Cr, W) and [PtCl 2(dppm)], which give [Pt 2 (μ-H)(μ-dppm) 2H 2][MCl(CO) 5]. Products resulting from redox exchange and intermolecular dppm (and sometimes CO) transfer were isolated from the reactions of [Pd 2(μ-dppm) 2Cl 2] with Na 2[Cr 2(CO) 10] or [Et 4N][HCr(CO) 5], and of the latter anion with 3. Whereas reaction of this anion with trans-[PdCl 2(PEt 3) 2] led to reduction to palladium metal, trans-[PtCl 2(PEt 3 2] was converted into [Pt 4(μ-CO) 5(PEt 3 4] (79% yield).

Selective reductions of carbonyl compounds with group 6 metal carbonyl hydrides

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSelective reductions of carbonyl compounds with group 6 metal carbonyl hydridesDorothy H. Gibson and Yekhlef S. El-OmraniCite this: Organometallics 1985, 4, 8, 1473–1475Publication Date (Print):August 1, 1985Publication History Published online1 May 2002Published inissue 1 August 1985https://doi.org/10.1021/om00127a035RIGHTS & PERMISSIONSArticle Views145Altmetric-Citations26LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (454 KB) Get e-Alerts Get e-Alerts

HYDROGENOLYSIS OF ACYLCOBALT CARBONYL WITH METAL CARBONYL HYDRIDES

Abstract Investigation of dinuclear reductive elimination reactions between hexanoylcobalt tetracarbonyl and various ruthenium and cobalt metal carbonyl hydrides showed that [HRu(CO)4]− reacts much faster to form hexanal than HCo(CO)4. Other hydrides such as [HRu3(Co)11]−, [H2Ru4(CO)12]2−, HRuCo3(CO)12 and HFeCo3(CO)12 are less reactive and compared with the above hydrides.

H ligand charges in HMn(CO)5, H2Fe(CO)4, and HCo(CO)4

The Xα method has been used to calculate the charges carried by the H ligands in some transition metal carbonyl hydride complexes. Employing a H 1s STO with an exponent of 1.0, Mulliken population analyses of the PXα LCAO-MOs, which represent specifically those SCF-Xα-SW MOs with significant H ligand character, give respective H atomic charges of −0.26, −0.27, and −0.33 for HMn(CO)5, HCo(CO)4, and H2Fe(CO)4. These numerical values are consistent with previous theoretical estimates of H ligand charges and observed 1H chemical shifts.

Reaktionen von Metallkomplexen mit kleinen Ringen, XI [1] Ringöffnung von Aziridinen mit Metallcarbonylhydriden; β-Aminoacylchelat-Komplexe von Mangan, Molybdän, Wolfram und Cobalt / Reactions of Metal Complexes with Small Rings, XI [1] Ring Opening of Aziridines by Metal Carbonyl Hydrides; β-Aminoacyl Chelate Complexes of Manganese, Molybdenum, Tungsten and Cobalt

The metal carbonyl hydrides HM(CO)3(π-C5H5) (M = Mo, W), HMn(CO)4L, HCo(CO)3L (L - CO, PPh3) react with aziridines by protonation of aziridine, nucleophilic attack of the corresponding carbonyl metallate and CO insertion to give the β-aminoacyl complexes 2-7. The ring opening of C-substituted aziridines is regiospecific. With alkyl substituted aziridines the nucleophilic attack of the carbonyl metallate occurs at the sterically less hindered carbon atom, with phenyl substituted aziridines at the phenyl substituted carbon atoms. From the reactions of HM(CO)3(π-C5H5) with optically active aziridines, which afford complexes with an asymmetric metal atom, only one diastereomer could be observed. The mechanism of these reactions is discussed and the spectral data (IR, 1H NMR, MS) of the complexes are reported. β-Aminoacyl complexes have also been obtained by addition of amines to [(π-C5H5)(CO)3M(alkene)]+BF4 - (M = Mo, W). The methyl complex H3CMn(CO)5 reacts with aziridine to give the acetyl complexes H3CC(O)Mn(CO)4(aziridine) and H3CC(O)Mn(CO)3(aziridine)2, respectively

Evidence for a negative charge on hydrogen for some metal carbonyl hydrides

Because of the acidity of hydrogen on several metal carbonyl hydrides, it has been presumed that the hydrogen bears a positive charge in the molecule. Matrix isolation studies have led to the characterization of neutral metal carbonyl fragments either directly from hydrogen loss from the related hydride or by independent routes. A comparison of the energy factored force fields of the fragment with those of the hydride containing molecule supports the conclusion that the hydrogen does bear a negative charge in spite of the acidity of the molecule in polar solvents. The acidity of the hydrides is less a function of the charge on hydrogen than a reflection of the weakness of the metalhydrogen bond.

Interaction of metal carbonyl hydrides with Lewis acids

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTInteraction of metal carbonyl hydrides with Lewis acidsThomas G. Richmond, Fred Basolo, and Duward F. ShriverCite this: Organometallics 1982, 1, 12, 1624–1628Publication Date (Print):December 1, 1982Publication History Published online1 May 2002Published inissue 1 December 1982https://doi.org/10.1021/om00072a014RIGHTS & PERMISSIONSArticle Views232Altmetric-Citations19LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (679 KB) Get e-Alerts Get e-Alerts