Metal-methyl Bond Research Articles

Enthalpy-Controlled Insertion of a "Nonspectator" Tricoordinate Phosphorus Ligand into Group 10 Transition Metal-Carbon Bonds.

Insertion of a tricoordinate phosphorus ligand into late metal-carbon bonds is reported. Metalation of a P^P-chelating ligand (L1), composed of a nontrigonal phosphorous (i.e., P(III)) triamide moiety, P(N(o-N(Ar)C6H4)2, tethered by a phenylene linker to a -PiPr2 anchor, with group 10 complexes L2M(Me)Cl (M = Ni, Pd) results in insertion of the nontrigonal phosphorus site into the metal-methyl bond. The stable methylmetallophosphorane compounds thus formed are characterized spectroscopically and crystallographically. Metalation of L1 with (cod)PtII(Me)(Cl) does not lead to a metallophosphorane but rather to the standard bisphosphine chelate (κ2-L1)Pt(Me)(Cl). These divergent reactivities within group 10 are rationalized by reference to periodic variation in M-C bond enthalpies.

Insertion of Molecular Oxygen into the Metal–Methyl Bonds of Platinum(II) and Palladium(II) 1,3-Bis(2-pyridylimino)isoindolate Complexes

Upon exposure of [(BPI)M(CH3)] (M = Pd, Pt, BPI = 1,3-bis(2-pyridylimino)isoindole) complexes to O2, direct insertion was observed to generate the O2 insertion products (BPI)M(OOCH3). Kinetic and mechanistic analyses of the O2 insertion reaction support a radical chain substitution mechanism. Reproducible kinetics were observed in the presence of a radical initiator. The release of methanol was subsequently observed from the M–OOCH3 products.

Theoretical Study of Two Possible Side Reactions for Reductive Functionalization of 3d Metal–Methyl Complexes by Hydroxide Ion: Deprotonation and Metal–Methyl Bond Dissociation

A DFT study of two possible competitive reactions for reductive functionalization (RF) of metal–methyl complexes ([MII(diimine)2(CH3)(Cl)], MII = VII through CuII) was performed to understand the factors that lower the selectivity of C–O bond forming reactions. One of the possible side reactions is deprotonation of the methyl group, which leads to formation of a methylene complex and water. The other possible side reaction is metal–methyl bond dissociation, which was assessed by calculating the bond dissociation free energies of M–CH3 bonds. Deprotonation was found to be competitive kinetically for most of the first-row transition-metal–methyl complexes (except for CrII, MnII, and CuII) but less favorable thermodynamically in comparison to reductive functionalization for all of the studied first-row transition metals. Metal–carbon bond dissociation was found to be less favorable than the RF reactions for most 3d transition-metal complexes studied. Therefore, this study suggests that Earth-abundant catalys...

Reductive functionalization of 3d metal–methyl complexes: The greater importance of ligand than metal

Selective oxidation of methane, which is the primary component of natural gas, to methanol, as a more easily transportable liquid, using organometallic catalysis, has become more important recently due to the abundance of domestic natural gas. In this regard, reductive functionalization (RF) of methyl ligands in [M(diimine)2(CH3)(Cl)] complexes, where M is a 3d metal with oxidation state of 2+ has been studied computationally using density functional techniques. The metal ions chosen for study were VII (d3) through CuII (d9) in the 3d row of the periodic table to assess changes in RF energetics as a function of d orbital occupation. A SN2 mechanism for the nucleophilic attack of hydroxide on the metal–methyl bond, resulting in the formation of methanol, was studied. Similar highly exergonic pathways with very low energy SN2 barriers were observed for the proposed RF mechanism for all the studied complexes. Changes in spin state occurred through the RF pathway for most of the metals studied. To modulate RF pathways closer to thermoneutral for catalytic purposes, a future challenge, paradoxically, requires finding a way to strengthen the metal–carbon bond. Furthermore, the DFT calculations suggest that for 3d metals, ligand properties will be of greater importance than metal identity in identifying suitable catalysts for alkane hydroxylation in which reductive functionalization is used to form the C–O bond.

A low-symmetry nickel(II) α-diimine complex for homopolymerization of ethylene: study of interactive effects of polymerization parameters

A low-symmetry nickel(II) α-diimine complex [(2,4,6-trimethylphenyl)imino)-((2,6-diisopropylphenyl)imino)-acenaphthene nickel(II) dibromide] (C1) was synthesized and characterized crystallographically. Response surface method (RSM) was employed to study the interactive effects of critical factors on ethylene polymerization. The maximum activity of C1, when activated by methylaluminoxane (MAO) cocatalyst {4960 kgPE [(mol Ni)−1 h−1]} was achieved at 10 °C, 7 bar and CC (cocatalyst-to-catalyst ratio) equal to 1550, which is higher than most similar counterparts. Considering surface plots of MW, it is concluded that at high levels (>1000) of CC, there is competition between chain transfer to aluminum and reinsertion of macromonomer to newly formed metal-methyl bonds.

DFT study of the reaction of a two-coordinate iron(II) dialkyl complex with molecular oxygen.

DFT studies are reported of a monomeric iron dialkyl for which oxygen atom insertion into metal-methyl bonds occurs with O2: FeMe2 + O2 → Fe(OMe)2. Computation of the reaction coordinate implicates the intermediacy of Fe(III)-peroxo, Fe(VI)-dioxo, and Fe(IV)-oxo intermediates, connected by O2 oxidative addition and two methyl migration steps. Analysis of the reaction of O2 with d(6)-Fe(Me)2 indicates that oxy-insertion for this iron complex occurs with lower free energy barriers than competing homolytic/radical pathways, exploiting "spin-flip" processes via minimum energy crossing points (MECPs).

Oxygen insertion into metal carbon bonds: formation of methylperoxo Pd(II) and Pt(II) complexes via photogenerated dinuclear intermediates.

Platinum(II) and palladium(II) complexes [M(CH3)(L)]SbF6 with substituted terpyridine ligands L undergo light-driven oxygen insertion reactions into metal methyl bonds resulting in methylperoxo complexes [M(OOCH3)(L)]SbF6. The oxygen insertion reactions occur readily for complexes with methyl ligands that are activated due to steric interaction with substituents (NH2, NHMe or CH3) at the 6,6″-positions on the terpyridine ligand. All complexes exhibit attractive intermolecular π···π or M···M interactions in the solid state and in solution, which lead to excited triplet dinuclear M-M complexes upon irradiation. A mechanism is proposed whereby a dinuclear intermediate is generated upon irradiation that has a weakened M-C bond in the excited state, resulting in the observed oxygen insertion reactions.

Density Functional Theory Study of Oxygen-Atom Insertion into Metal–Methyl Bonds of Iron(II), Ruthenium(II), and Osmium(II) Complexes: Study of Metal-Mediated C–O Bond Formation

Metal-mediated C-O bond formation is a key step in hydrocarbon oxygenation catalytic cycles; however, few examples of this reaction have been reported for low-oxidation-state complexes. Oxygen insertion into a metal-carbon bond of Cp*M(CO)(OPy)R (Cp* = η(5)-pentamethylcyclopentadienyl; R = Me, Ph; OPy = pyridine-N-oxide; M = Fe, Ru, Os) was analyzed via density functional theory calculations. Oxygen-atom insertions through a concerted single-step organometallic Baeyer-Villiger pathway and a two-step pathway via a metal-oxo intermediate were studied; calculations predict that the former pathway was lower in energy. The results indicated that functionalization of M-R to M-OR (R = Me, Ph) is plausible using iron(II) complexes. Starting from Cp*Fe(CO)(OPy)Ph, the intermediate Fe-oxo showed oxyl character and, thus, is best considered an Fe(III)O(•-) complex. Oxidation of the π-acid ancillary ligand CO was facile. Substitutions of CO with dimethylamide and NH3 were calculated to lower the activation barrier by ∼1-2 kcal/mol for formation of the Fe(III)O(•-) intermediate, whereas a chloride ligand raised the activation barrier to 26 kcal/mol from 22.9 kcal/mol.

Large Kinetic Isotope Effects for the Protonolysis of Metal–Methyl Complexes Are Not Reliable Mechanistic Indicators

Earlier work on protonolyses of several palladium and platinum methyl complexes (with release of methane) had suggested the possibility that observation of an unusually large kinetic isotope effect, consistent with significant contributions from quantum mechanical tunneling, might be diagnostic of a mechanism involving direct protonation of the metal–methyl bond, as opposed to one proceeding via a metal hydride intermediate. By extension of these measurements to a wider set of complexes, we find no support for the proposed correlation.

Computational Studies of the Relative Rates for Migratory Insertions of Alkenes into Square-Planar, Methyl, −Amido, and −Hydroxo Complexes of Rhodium

The relative rates of the migratory insertions of alkenes into the M-X bonds of (PMe(3))(2)Rh(eta(2)-CH(2) horizontal lineCHR)(X) (R = H, Me; X = CH(3), NH(2), OH) have been analyzed by DFT calculations. These insertions are computed to form metallacycles containing a metal-carbon bond and either an agostic interaction, a dative metal-nitrogen bond, or a dative metal-oxygen bond. The computed barriers for migratory insertion into the metal-hydroxo and metal-amido bonds are lower than those for insertion into the metal-methyl bond. Application of Bader's atoms-in-molecules analysis and natural localized molecular orbital analysis implies that the barriers for alkene insertion into M-X bonds are controlled by the degree of M-X bonding in the transition state, which correlates with the degree of M-X bonding in the initial product. The Rh-X bond orders in the transition states for migratory insertion of ethylene into the Rh-NH(2) and Rh-OH bonds in (PH(3))(2)Rh(eta(2)-C(2)H(4))(NH(2)) and (PH(3))(2)Rh(eta(2)-C(2)H(4))(OH) are much larger than that in the transition state for insertion into the Rh-C bond of (PH(3))(2)Rh(eta(2)-C(2)H(4))(CH(3)). The free energy barriers for 1,2- and 2,1-insertions of propene into the rhodium complexes were also calculated, and the barrier for 1,2-insertion was found to be lower than that for 2,1-insertion. Most striking, the DeltaDeltaG(double dagger) values for 1,2- versus 2,1-insertion of propene into these rhodium complexes were calculated to increase in the order X = CH(3) < NH(2) < OH. The increasing stability of the 1,2-insertion product with increasing polarity of the C-X bonds parallels the relative stabilities of linear versus branched alkanes, amines, and alcohols.

Photochemistry of CH3Mn(CO)5: A multiconfigurational ab initio study

The electronic spectroscopy of CH3Mn(CO)5 has been investigated by means of ab initio multiconfigurational MS-CASPT2/CASSCF calculations. The absorption spectrum is characterized by a series of Metal-Centered (MC) excited states in the UV energy domain (below 290 nm) that could be responsible for the observed photoreactivity starting at 308 nm. The upper part of the spectrum is overcrowded between 264 and 206 nm and dominated by a high density of Metal-to-Ligand-Charge-Transfer (MLCT) states corresponding mainly to 3d(Mn) --> pi*(CO) excitations. A non-negligible contribution of Metal-to-sigma-Bond-Charge-Transfer (MSBCT) states corresponding to 3d(Mn) --> sigma*(Mn-CH3) excitations is also present in the theoretical spectrum of CH3Mn(CO)5. However, in contrast to other transition metal hydrides and methyl substituted (HMn(CO)5, HCo(CO)4, and CH3Co(CO)4) these MSBCT transitions do not participate to the lowest bands of the spectrum as main contributions. The photochemistry of CH3Mn(CO)5, namely the loss of a CO ligand vs. the metal-methyl bond homolysis, is investigated by means of MS-CASPT2 states correlation diagrams. This study illustrates the complexity of the photodissociation mechanism of this class of molecules, which involves a large number of nearly degenerate electronic states with several channels for fragmentation.

Microkinetic modelling of the formation of C 1 and C 2 products in the Fischer–Tropsch synthesis over cobalt catalysts

The heats of adsorption of different C 1 and C 2 molecules assumed to be present during the initial steps of the Fischer–Tropsch synthesis and activation energies for elementary steps envisioned to occur in the synthesis are calculated for Co by using the unity bond index-quadratic exponential potential (UBI-QEP) method. The preexponential factors for the elementary steps are calculated from transition-state theory, and the rate constants are calculated according to the Arrhenius equation. The activation barrier for hydrogenation of CO is found to be lower compared to hydrogen assisted dissociation of CO, which has a smaller activation barrier than direct dissociation of CO. The reaction steps with high activation barriers are eliminated. Based on this elimination two sets of elementary steps for formation of C 1 and C 2 alkenes and alkanes in the Fischer–Tropsch synthesis are established: one based on hydrogen assisted CO dissociation (carbide mechanism) and one based on CO hydrogenation (CO insertion mechanism). In addition, one mechanism of producing CO 2 from the water–gas shift reaction is proposed. The resulting mechanisms are combined and used in the microkinetic model, which are fitted to experimental results at methanation conditions ( T = 483 K or 493 K, p = 1.85 bar and H 2/CO = 10) over a Co/Al 2O 3 Fischer–Tropsch catalyst. A good tuning is obtained by adjusting the C–Co and H–Co binding strengths. The microkinetic modelling based on these assumptions indicates that CO is mainly converted through hydrogenation of CO and that C 2 compounds are mainly produced by insertion of CO into a metal–methyl bond. Thus, from the surface coverages and reaction rates predicted by the microkinetic modelling the mechanism can be further reduced to only include the CO insertion mechanism. Hydrogenation of CHO to CH 2O is found to be the rate determining initiation step, and insertion of CO into a metal–methyl bond is found to be the rate determining step for chain growth. By using the UBI-QEP method for calculation of activation energies, the activation barriers for dissociation of CO and hydrogenation of surface carbon are found to be too large for the carbide mechanisms to occur. However, experimental data or another theoretical method is necessary in order to support or disprove the calculated activation energies in this work.

Aspects of coordination polymerization in heterogeneous and homogeneous catalysis. A computational survey

Theoretical studies on ethylene polymerization by single site homogeneous catalysts, as well as by Ziegler–Natta heterogeneous catalysts, have been reviewed. Studies on cation–anion interactions in ion-pair systems of the type [LL′MR]+[A]− [L, L′=Cp, NCR2, NPR3; M=Ti, Zr; A=MeB(C6F5) 3 − , MAOMe−, B(C6F5) 4 − ] provided indications as to which ancillary ligands on the cation acted as good electron donors, and also revealed the importance of having a weakly coordinating anion to enable the ion-pair to separate more easily in solution. Subsequent calculations of barriers to ethylene insertion into the metal-methyl bond in ion-pair systems of the type LL′MeM-μ-B(C6F5)3[M=Ti, Zr] revealed that the ease of separation of the anion from the cation in solution was an important criterion in determining the activity of the catalysts. The barrier to insertion was found to be the rate determining step during the first insertion of ethylene into the metal–methyl bond, but second insertion studies conducted for two different ion-pair systems showed that the barrier to uptake of the monomer became the rate determining step during the second insertion of the ethylene monomer. Theoretical studies conducted on TiCl4/MgCl2 heterogeneous Ziegler–Natta catalysts provided insights into the nature of the binding of the titanium catalysts (with the Ti in different oxidation states) on to the MgCl2 support. The results indicated that the support worked best when a few Ti atoms replaced Mg atoms in the crystal lattice of the support. Ethylene polymerization studies, along with investigations on chain termination, led to the conclusion that the TiCl3-based edge site on MgCl2 would be the most promising model for the actual catalytic species. Studies on addition of tetrahydrofuran (THF) to the active sites showed that the presence of the base would lead to higher molecular weights of the polymers, as it acted to increase the barrier to termination (by chain transfer to monomer) more than the barrier to insertion.

The stereochemical course of electrophilic cleavage of metal–carbon bonds at a chiral ruthenium centre. X-Ray crystal structure of [(S)Ru-RuBr(CO)PPh3{η-C5H4(neomenthyl)}

The stereochemical course of the cleavage of the metal–methyl bond in [RuMe(CO)PPh3{η-C5H4(neomenthyl)}] by electrophiles has been investigated. Cleavage by hydrogen halides occurs predominantly with retention of configuration at the ruthenium whereas cleavage by halogens shows little stereoselectivity. These results have been rationalised by proposing that the reactions proceed via an oxidative addition mechanism involving a configurationally labile seven co-ordinate ruthenium(IV) intermediate. In the case of hydrogen halides, rapid reductive elimination of methane from the ruthenium(IV) intermediate does not allow significant epimerisation of the ruthenium centre whereas with halogens a slower reductive elimination of methyl halide results in significant epimerisation. The crystal structure of [(S)Ru-RuBr(CO)PPh3{η-C5H4(neomenthyl)}] is also reported.

Carbonyl insertion into metal-hydrogen and metal-methyl bonds for second-row transition metal atoms

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTCarbonyl insertion into metal-hydrogen and metal-methyl bonds for second-row transition metal atomsMargareta R. A. Blomberg, Christina A. M. Karlsson, and Per E. M. SiegbahnCite this: J. Phys. Chem. 1993, 97, 37, 9341–9350Publication Date (Print):September 1, 1993Publication History Published online1 May 2002Published inissue 1 September 1993https://doi.org/10.1021/j100139a015RIGHTS & PERMISSIONSArticle Views180Altmetric-Citations28LEARN 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 (3 MB) Get e-Alerts

The Ziegler—Natta olefin insertion reaction into a metal—alkyl bond for second-row transition metal atoms

The Ziegler—Natta olefin insertion reaction into a metal—alkyl bond has been studied for the second-row transition metal atoms, without additional ligands and with two hydride ligands added. Correlation effects of all valence electrons are included in the calculations using reasonably large basis sets. The results are compared to the corresponding insertion into a metal—hydride bond which has been studied previously. For most metals the barrier height for the olefin insertion into the metal—alkyl bond is about 20 kcal/mol higher than for insertion into the metal—hydride bond. The origin of this difference is the directional character of the methyl bond. The hydride can continuously change the direction of its bond from the metal to the olefin, but for the methyl group a large part of the metal—methyl bond has to be broken before the methyl group can start to bind towards the olefin. For the reaction mechanism, the d character of the bond at the transition state and the importance of repulsion between non-bonding electrons on the metal and the electrons on the olefin is emphasized.

Theoretical studies of CO adsorption and dissociation on Ru in presence of Cl or MoO x

Using the extended Huckel molecular orbital method we studied the adsorption and dissociation of CO over a Ru cluster with Cl or MoO preadsorbed onto it. Previous experimental information oriented us to think that the remaining Cl present in Ru/SiO2 and RuMo/SiO2 catalysts could influence their chemisorptive and catalytic properties. On this basis our theoretical model explains the observed activity and selectivity during the CO + H2 reaction, that is, Cl decreases the adsorption of CO and hinders its dissociation. This could lead to the appearance of methanol as a synthesis product. On the other hand, our theoretical calculations indicate that the presence of MoO on top of the Ru cluster favors the adsorption of CO parallel to the cluster surface. They also predict an energy barrier for its dissociation which is interpreted in terms of the possible insertion of this CO molecule into a metal-methyl bond thereby forming the ethanol precursor.

New neutral and ionic methyl and chloro palladium and platinum complexes containing hemilabile phosphorus-nitrogen ligands. Study of the insertion of carbon monoxide into the metal-methyl bond

New neutral and ionic methyl and chloro palladium and platinum complexes containing hemilabile phosphorus-nitrogen ligands. Study of the insertion of carbon monoxide into the metal-methyl bond

Theoretical study on the difference in the relative strengths of metal-hydrogen and metal-methyl bonds in complexes of early transition metals and complexes of middle to late transition metals

Theoretical study on the difference in the relative strengths of metal-hydrogen and metal-methyl bonds in complexes of early transition metals and complexes of middle to late transition metals

Theoretical study on the relative strengths of the metal-hydrogen and metal-methyl bonds in complexes of middle to late transition metals

Theoretical study on the relative strengths of the metal-hydrogen and metal-methyl bonds in complexes of middle to late transition metals