Kinetics and mechanism of the reaction between dicobalt octacarbonyl and hydrogen

The equilibrium and the rates of the reaction between Co₂(CO)₈ and H₂ to HCo(CO)₄ have been studied in n-heptane at several temperatures. The formation of HCo(CO)₄ is first order in both Co₂(CO)₈ and H₂ and at low partial pressure of CO is inversely proportional to carbon monoxide concentration. The rate determining step is the reaction of dihydrogen with dicobalt heptacarbonyl, where the latter is formed in a fast pre-equilibrium. Numerical values have been estimated for the preequilibrium constant, for the velocity of the rate determining step and for the overall equilibrium constant.     

The stoichiometric hydrogenation of 1,1-diphenylethylene with hydridocobalt tetracarbonyl; differences from the hydroformylation reaction

The kinetics of the stoichiometric hydrogenation of 1,1-diphenylethylene with HCo(CO)₄ is cleanly second order, permitting a determination of the activation parameters. The rate is unaffected by the atmosphere over the reaction and is enhanced by substituting DCo(CO)₄ for HCo(CO)₄. These results contrast sharply with those secured in the hydroformylation of 1-alkenes and thus dual mechanistic pathways are available for the reaction of HCo(CO)₄ with unsaturated systems. It is very possible that the stoichiometric hydrogenation of 1,1-diphenylethylene involves a geminate free radical pair but definitive proof is still lacking.     

Study of the mechanism of hydroformylation at industrial reaction conditions

With a newly developed analytical technique, i.e. high temperature/pressure IR cell coupled to the reactor, it was possible to study the mechanism of hydroformylation at reaction conditions. It has been conclusively found that the hydrogenolysis of the acyl cobalt complex is performed by HCo(CO)₄ and not by molecular H₂, as proposed byHeck andBreslow.Therefore the formation of HCo(CO)₄ from Co₂(CO)₈ is an intermediate step in the sequence of hydroformylation reaction steps. The rate of hydroformylation of any of the olefins is smaller than the rate of formation of HCo(CO)₄ from Co₂(CO)₈. The IR spectra reveal that always more than 30% of the cobalt is in the form of HCo(CO)₄ under the reaction conditions.It is found that the formation of HCo(CO)₄ from Co₂(CO)₈ is the slowest and most temperature-dependent step of the hydroformylation reaction. Also the reaction between olefin and HCo(CO)₄ is slower than the hydrogenolysis of the acyl complex.The experiments were carried out under industrial oxo conditions. The diffusional effects were eliminated.With 6 FiguresPart of the Ph.D. dissertation 1974. N. H. Alemdarolu, J. M. L. Penninger, andE. Oltay, Mechanism of Hydroformylation, Part II. Mh. Chem.107, 1043 (1976).     

[HCo(CO)4]‐Catalyzed Three‐component Cycloaddition of Epoxides,Imines, and Carbon Monoxide: Facile Construction of 1,3‐Oxazinan‐4‐ones

The three‐component [3+2+1] cycloaddition of epoxides, imines, and carbon monoxide to produce 1,3‐oxazinan‐4‐ones has been developed by using [HCo(CO)₄] as the catalyst. The reaction occurs for a wide variety of imines and epoxides, under 60 bar of CO pressure at 50 °C, to produce 1,3‐oxazinan‐4‐ones with different substitution patterns in high yields, and provides an efficient and atom‐economic route to heterocycles from simple and readily available starting materials. A plausible mechanism involves [HCo(CO)₄]‐induced ring‐opening of the epoxide, followed by sequential addition of carbon monoxide and the imine, and then ring closure to form the product accompanied by regeneration of [HCo(CO)₄].     

[HCo(CO)4]‐Catalyzed Three‐component Cycloaddition of Epoxides,Imines, and Carbon Monoxide: Facile Construction of 1,3‐Oxazinan‐4‐ones

The three‐component [3+2+1] cycloaddition of epoxides, imines, and carbon monoxide to produce 1,3‐oxazinan‐4‐ones has been developed by using [HCo(CO)₄] as the catalyst. The reaction occurs for a wide variety of imines and epoxides, under 60 bar of CO pressure at 50 °C, to produce 1,3‐oxazinan‐4‐ones with different substitution patterns in high yields, and provides an efficient and atom‐economic route to heterocycles from simple and readily available starting materials. A plausible mechanism involves [HCo(CO)₄]‐induced ring‐opening of the epoxide, followed by sequential addition of carbon monoxide and the imine, and then ring closure to form the product accompanied by regeneration of [HCo(CO)₄].     

Radical hydroformylation and hydrogenation of cyclopropenes with HCo(CO)4 and HMn(CO)5

The results of a study of the reactions of HCo(CO)₄ and HMn(CO)₅ with a variety of a substituted cyclopropenes are consistent with the formation of the intermediate caged radical pairs; recombination in the cage of the radical pair leads to hydroformylation, and cage escape leads to hydrogenation. Steric factors play an important role in determining rates as well as the stereochemistry of the products.     

A new stoichiometric hydroformylation of olefins mediated by HCo3(CO)9

3,3-Dimethylbutene is converted into 4,4-dimethylpentanal at ?15°C in the presence of HCo₃(CO)₉ and HCo(CO)₄ under argon. Under the same conditions there is no reaction in the presence of HCo(CO)₄ alone. Labeling experiments show that in the formed aldehyde the hydrogen atom of the formyl group has come from the mononuclear complex, and the hydrogen atom of the alkyl moiety from the trinuclear cluster.     

On the mechanism of the Co2(CO)8 catalyzed hydroformylation of olefins in hydrocarbon solvents. A high pressure UV and IR study

High pressure IR and UV spectroscopic experiments confirm the Heck and Breslow mechanism of the hydroformylation of 1-octene and cyclohexene with Co₂(CO)₈ as the starting catalyst. The major repeating unit is HCo(CO)₄, which is formed via the reaction of acylcobalt tetracarbonyl with H₂. The rates are 6.7 × 10^?4 mol l^?1 min^?1 and 8.8 × 10^?5 mol l^?1 min^?1 for 1-octene and cyclohexene, respectively at 80°C and 95 bar CO/H₂ = 1 in methylcyclohexane. The alternative reaction of RCOCo(CO)₄ with HCo(CO)₄ is only a minor pathway, with rates of 1.8 × 10^?5 mol l^?1 min^?1 and 1.1 × 10^?5 mol l^?1 min^?1 for 1-octene and cyclohexene, respectively. It represents an exit from the catalytic cycle. The activation of the catalyst precursor Co₂(CO)₈ is the slowest step of the reaction.     

Mechanism of hydroformylation,part II Study of the formation of hydrocobalttetracarbonyl by the reaction of Co2(CO)8 and H2

The kinetics and the position of the equilibrium of the reaction Co₂(CO)₈+H₂2 HCo(CO)₄ were studied in the range of 80–160 °C and 50–100 atm. by means of in situ IR spectroscopy.The reaction is reversible first order with respect to CO₂(CO)₈ and HCo(CO)₄ and the energies of activation of the forward and the reverse reaction are found to be 17,3 cal/mole, and 11.0 kcal/mole resp.The reaction is slightly endothermic with H=6.6 kcal/mole and S=14.6 e.u. The heat of formation of HCo(CO)₄ and the bond strength between hydrogen and cobalt in HCo(CO)₄ were found to be—146.1 kcal/mole and 54.7 kcal/mole resp.With 8 FiguresPart of the Ph.D. Dissertation 1974.Part I see Ref.¹³     

Theoretical investigation on hydroformylation reactions : I. Structures and reactivities of cobalt carbonyls and hydrocarbonyls

Extended Hückel Theory calculations have been carried out in a study of the most important cobalt carbonyls and hydrocarbonyls involved in the hydroformylation reaction. The geometries of the stable isomers of Co₂(CO)₈, Co₂(CO)₇, Co(CO)₄, Co(CO)₃ have been calculated and used to interpret the changes in the IR spectrum of Co₂(CO)₈ observed on varying the temperature. The reaction paths for the interconversions of the stable isomers have also been investigated. The optimized geometry of HCo(CO)₄ agrees well with the experimental structure. The C_s symmetry found for the most stable isomer of HCo(CO)₃ is of much interest, serves to explain the formation of the complex with olefins.     

Transition metal-catalyzed tandem isomerization and cationic polymerization of allyl ethers. II. Structural and mechanistic studies

In the presence of organosilanes, dicobalt octacarbonyl catalyzes the polymerization of alkyl allyl ethers to give high molecular weight polymers. This article reports the results of a detailed mechanistic study of this new polymerization reaction. The evidence obtained in this study supports a stepwise process involving first, the reaction of dicobalt octacarbonyl with an organosilane to form HCo(CO)₄ and R₃SiCo(CO)₄. In subsequent steps, HCo(CO)₄ isomerizes the allyl ether to a 1-propenyl ether and then this compound is polymerized by the formal transfer of a silyl cation from R₃SiCo(CO)₄. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 1985–1997, 1997     

Transient species of importance in the stoichiometric hydroformylation reaction I. Evidence for HCo(CO)3 by matrix isolation

Spectra of HCo(CO)₄ in a low temperature argon matrix show a weak band at 2018 cm^?1. On irradiation, this band grows rapidly and additional bands (previously too weak to be readily observable) appear at 2025 and 485 cm^?1. These three bands are assigned to HCo(CO)₃, a coordinatively unsaturated species persistently proposed as an intermediate in the hydroformylation reaction but not previously characterized.     

The stoichiometric hydrogenation of 9-methylidenefluorene and related compounds with hydridocobalt tetracarbonyl

9-Methylideneflourene (IIa) reacts rapidly with HCo(CO)₄ at -67° C to give a quantitative yield of 9-methylfluorene (IIIa); k₂  (13.4 ± 0.5) × 10^-2 l mol^-1_S^-1. Although the internal olefin, 9-ethylidenefluorene (IIb) reacts more slowly than IIa, it is hydrogenated about 2.5 times as fast as the terminal olefin, 1,1-diphenylethylene (I). Measurement of the rate of the reaction of IIb with DCo(CO)₄ and comparison with HCo(CO)₄ shows a very large inverse isotope effect k_H/k_D of 0.43.     

From laser control of vibrationally mediated photodissociation to photodesorption: Model simulations of breaking metal-ligand bonds in organometallic molecules,clusters, and adsorbates at surfaces

Three specific model systems, HCo(CO)₄, Na · NH₃, and NO/Pt(111), are used to extend the strategy of vibrationally mediated photodissociations of organometallics, via small clusters of metal atoms and small molecules, to photodesorption of small molecules from metal surfaces. All systems and strategies are similar with respect to breaking metal-ligand bonds by means of infrared IR and visible or ultraviolet UV photons. Specific properties of the systems call, however, for different implementations of the overall tools. In the case of HCo(CO)₄, traditional continuous wave (CW ) IR + UV 2-photon excitations enhance the rates of HCo bond homolysis. A detailed analysis discovers three effects which result from Franck-Condon transitions in the domains of vibrationally excited wave functions: (i) ultrafast (≈ 20 fs) bond rupture starting from the steeply repulsive wall of the potential energy surface of the excited singlet state; (ii) efficient fast (≈ 200 fs) predissociation via tunneling through neighboring potential barriers; and (iii) decreasing contributions from indirect dissociations via slow (≈ 46 ps) intersystem crossing induced by spin-orbit coupling. In the case of Na · NH₃, we suggest a vibrationally mediated pump-and-dump scheme, similar to the strategy of Tannor, Rice, and Kosloff, with proper control of the delay (ca. 70 fs) between ultrashort (ca. 30 fs) pump-and-dump laser pulses. Ultimately, this strategy shifts specific lobes of the vibrationally excited wave packets into a steeply repulsive wall of the potential energy surface of the electronic ground state, with subsequent fast (ca. 100 fs) ruptures of the NA(SINGLEBOND)NH₃ bond, similar to effect (i) for HCo(CO)₄. Finally, we show that a similar, vibrationally mediated pump-and-dump scheme may also support photodesorption of NO from Pt(111), with an intrinsic relaxation step for the electronically excited system NO/Pt(111) instead of active pump-and-dump control for Na · NH₃. All strategies are simulated by fast Fourier transform propagations of representative wave packets on two potential energy surfaces. © 1996 John Wiley & Sons, Inc.     

Dynamics of photochemical reactions: Simulation by quantum calculations for transition metal hydrides

The photodissociation dynamics of some organometallic molecules in the lowest repulsive electronically states are reported for the following concurrent primary reactions: (i) the homolysis of a metal–hydrogen bond vs. the heterolytic loss of a carbonyl ligand in HCo(CO)₄; (ii) the photoinduced elimination of molecular hydrogen vs. the loss of a carbonyl ligand in H₂Fe(CO)₄; and (iii) the photoinduced elimination of molecular hydrogen vs. the loss of a mesithylene ligand in H₂Os(CO)Mes (Mes = C₆H₃(CH₃))₃. The dynamics are simulated quantum mechanically using a time-dependent wavepacket propagation technique on potential energy surfaces obtained from CASSCF /CCI calculations for HCo(CO)₄ and H₂Fe(CO)₄ and from SCF -INO /MRCI calculations for H₂Os(CO)Mes. This approach gives a rather detailed view of some important elementary processes that contribute to the photochemistry of these complexes. The nature of the photoactive excited states is determined without ambiguity, as well as the time scales, the branching ratio of the different primary dissociation pathways, and some features of the absorption spectra. © 1994 John Wiley & Sons, Inc.     

Carbonylation. 9. Alkoxycarbonylation of pent-3-ene nitrile with homogeneous Co−Ru catalysts: The respective roles of cobalt and ruthenium

Addition of ruthenium compounds (Ru(acac)₃, Ru₃(CO)₁₂) to cobalt catalysts for pent-3-ene nitrile alkoxycarbonylation increases both activity and selectivity in the production of cyanoesters by (i) reducing the amount of Co(II) and facilitating the generation of the active carbonylation species, HCo(CO)_n, and (ii) improving the isomerisation of pentene nitriles, providing significant amounts of pent-4-ene nitrile for the formation of the ω-ester.     

Reactions of 1,1,3,3-tetramethyldisilazane with dicobalt octacarbonyl and iron pentacarbonyl. Thermal decomposition of the cobalt and iron carbonyl silazane complexes

The reaction of (HMe₂Si)₂NH with Co₂(CO)₈ gives the complex [Co₂(CO)₇(SiMe₂)₂NH₂]⁺[Co(CO)₄]⁻. Its thermal decomposition starts with dissociation into the “acid” HCo(CO)₄ and the “base” Co₂(CO)₇(SiMe₂)₂NH. After that, the base and the initial complex decompose further under the action of HCo(CO)₄. The final products of this reaction are CO, NH₃, Co, volatile dimethylcyclosilazane, and a solid residue consisting of cobalt particles encapsulated into a polymethylsiloxane matrix and possessing properties of mixed para- and ferromagnetics with an ultimate specific magnetization of 64–74 G g⁻¹. Tetramethyldisilazane reacts with iron pentacarbonyl under UV irradiation to give relatively stable 1,3-bis(tetracarbonylthydrideiron)-1,1,3,3-tetramethyldisilazane. This product contains Fe−H…N hydrogen bonds, which stabilize it against dehydrogenation and cyclization to diironcyclodisilazane. Thermal decomposition of this product was investigated. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2537–2544, December, 1998.     

Hydrido cyclopentadienyliron dicarbonyl and its role in olefin hydroformylation

The compound hydrido cyclopentadienyliron dicarbonyl has been shown by infrared and proton NMR to be present in substantial quantities during hydroformylation of propene and 1-pentene in the presence of [(η⁵-C₅H₅)Fe(CO)₂]₂. This and related observations strongly suggest that the hydride is an important link in the catalytic cycle as is HCo(CO)₄ in Co₂(CO)₈-catalyzed olefin hydroformylation.     

Reactions of conjugated dienes with cobalt carbonyls under hydroformylation conditions. a high pressure i.r. spectroscopic study

Summary The chemistry of cobalt carbonyls in the presence of dienes and high pressure of synthesis gas was studied by online i.r. spectroscopy. Dicobalt octacarbonyl reacts with butadiene under 95 bar CO/H₂ and 80°C to give [³-C₄H₇Co(CO)₃] (1) and [⁴-C₄H₆)₂Co₂(CO)₄] (2). Hydrogenation or hydroformylation are observed only with [HCo(CO)₄] as the starting catalyst, and only at the beginning of the reaction. The results are explained by formation of an alkenyl complex, [-C₄H₇Co(CO)₄], which either reacts with [HCo(CO)₄] to give butene and [Co₂(CO)₈], or loses CO to give (1), depending on the [HCo(CO)₄] concentration. The butene is hydroformylated. At temperatures >100°C (1) is transformed into a CO-free species, which catalyzes the oligomerisation of butadiene. Addition of tributylphosphine (L) leads to the formation of [³-C₄H₇Co(CO)₂L] (5) and [Co₂(CO)₆L₂] (6). In (5) the -allyl moiety is more labile than in (1) and a slow hydrogenation and hydroformylation of the butadiene is observed. In methanol solution the reaction of the cobalt carbonyls to give (1) is incomplete and the remaining H⁺ and [Co(CO)₄]^– catalyze the hydroformylation of butadiene. Isoprene is less reactive than butadiene but otherwise behaves similarly.     

Synthese und charakterisierung eines stabilen heterobimetallischen TitanCobalt komplexes mit unverbrückter TiCo-bindung

Unusually stable [(^tC₄H₉O)₃Ti-Co(CO)₄] has been prepared by treating the appropriate carbonylmetallate anion with chloro titanium t-butoxide as well as by protolysis of CH₃Ti(O^tC₄H₉)₃ with HCo(CO)₄. Spectroscopic data indicate that the alkoxide and carbonyl ligands are nonbridging, establishing C_3v-symmetry at the cobalt atom.