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Quadruple C–H Bond Activations of Methane by Dinuclear Rhodium Carbide Cation [Rh2C3]+

ABSTRACT: The structure of

SUBMITTER: Wu H

PROVIDER: S-EPMC8549038 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Heterobimetallic complexes of rhodium dibenzotetramethylaza[14]annulene [(tmtaa)Rh-M]: formation, structures, and bond dissociation energetics.

Project description:A rhodium(II) dibenzotetramethylaza[14]annulene dimer ([(tmtaa)Rh]2) undergoes metathesis reactions with [CpCr(CO)3]2, [CpMo(CO)3]2, [CpFe(CO)2]2, [Co(CO)4]2, and [Mn(CO)5]2 to form (tmtaa)Rh-M complexes (M = CrCp(CO)3, MoCp(CO)3, FeCp(CO)2, Co(CO)4, or Mn(CO)5). Molecular structures were determined for (tmtaa)Rh-FeCp(CO)2, (tmtaa)Rh-Co(?-CO)(CO)3, and (tmtaa)Rh-Mn(CO)5 by X-ray diffraction. Equilibrium constants measured for the metathesis reactions permit the estimation of several (tmtaa)Rh-M bond dissociation enthalpies (Rh-Cr = 19 kcal mol(-1), Rh-Mo = 25 kcal mol(-1), and Rh-Fe = 27 kcal mol(-1)). Reactivities of the bimetallic complexes with synthesis gas to form (tmtaa)Rh-C(O)H and M-H are surveyed.

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Carbide Dihydrides: Carbonaceous Species Identified in Ta4 + -Mediated Methane Dehydrogenation.

Project description:The products of methane dehydrogenation by gas-phase Ta4 + clusters are structurally characterized using infrared multiple photon dissociation (IRMPD) spectroscopy in conjunction with quantum chemical calculations. The obtained spectra of [4Ta,C,2H]+ reveal a dominance of vibrational bands of a H2 Ta4 C+ carbide dihydride structure over those indicative for a HTa4 CH+ carbyne hydride one, as is unambiguously verified by studies employing various methane isotopologues. Because methane dehydrogenation by metal cations M+ typically leads to the formation of either MCH2 + carbene or HMCH+ carbyne hydride structures, the observation of a H2 MC+ carbide dihydride structure implies that it is imperative to consider this often-neglected class of carbonaceous intermediates in the reaction of metals with hydrocarbons.

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Project description:Through relatively subtle changes in reaction conditions, we have been able to isolate four distinct Rh/Sn cluster compounds, [Rh@Sn10]3-, [Rh@Sn12]3-, [Rh2@Sn17]6- and [Rh3@Sn24]5-, from the reaction of K4Sn9 with [(COE)2Rh(?-Cl)]2(COE = cyclooctene). The last of these has a hitherto unknown molecular topology, an edge-fused polyhedron containing three Rh@Sn10 subunits, and represents the largest endohedral Group 14 Zintl cluster yet to have been isolated from solution. DFT has been used to place these new species in the context of known cluster chemistry. ESI-MS experiments on the reaction mixtures reveal the ubiquitous presence of {RhSn8} fragments that may play a role in cluster growth.

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Di-?-carbonyl-bis-[bis-(triphenyl-phos-phane)rhodium(0)](Rh-Rh) acetone disolvate.

Project description:The dirhodium complex, [Rh(2)(C(18)H(15)P)(4)(CO)(2)]·2(CH(3))(2)CO, has crystallographic twofold symmetry and the Rh-Rh distance is 2.6266?(8)?Å. The four atoms proximate to each Rh atom [Rh-P = 2.3222?(7) and 2.3283?(8)?Å, and Rh-C = 1.961?(3) and 2.045?(3)?Å] form a distorted tetra-hedron with large deviations from the putative tetra-hedral angles [r.m.s. deviation = 23?(1)°]. The six angles more closely approximate those of a trigonal bipyramid [r.m.s. deviation = 14?(1)°] with one missing equatorial ligand. The two bridging carbonyl ligands are much more linearly coordinated to one Rh [Rh-C O = 151.0?(2)°] than to the other [127.0?(2)°], and the two Rh(2)CO planes form a dihedral angle of 45.43?(5)°. The two acetone solvent mol-ecules are disordered, and their estimated scattering contribution was subtracted from the observed diffraction data using the SQUEEZE routine in PLATON [Spek (2009 ?). Acta Cryst.D65, 148-155].

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Consecutive C-F bond activation and C-F bond formation of heteroaromatics at rhodium: the peculiar role of FSi(OEt)3.

Project description:C-F activation of 2,3,5,6-tetrafluoropyridine at [Rh{Si(OEt)3}(PEt3)3] (1) yields [Rh{2-(3,5,6-C5F3HN)}(PEt3)3] (2) and FSi(OEt)3, but in an unprecedented consecutive reaction FSi(OEt)3 acts as a fluoride source to give [Rh(4-C5F4N)(PEt3)3] (4) by regeneration of the C-F bond and C-H activation. Analogous refluorination steps were observed for other 2-pyridyl rhodium complexes. NMR spectroscopic studies revealed a delicate balance between the feasibility for C-F bond formation accompanied by a C-H activation and the occurrence of competing reactions such as hydrodefluorinations induced by the intermediary presence of H2.

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Conversion of Methane with Oxygen to Produce Hydrogen Catalyzed by Triatomic Rh3 - Cluster Anion.

Project description:Metal catalysts, especially noble metals, have frequently been prepared upon downsizing from nanoparticles to subnanoclusters to catalyze the important reaction of partial oxidation of methane (POM) in order to optimize the catalytic performance and conserve metal resources. Here, benefiting from mass spectrometric experiments in conjunction with photoelectron spectroscopy and quantum chemical calculations, we successfully determine that metal cluster anions composed of only three Rh atoms (Rh3 -) can catalyze the POM reaction with O2 to produce 2H2 + CO2 under thermal collision conditions (∼300 K). The interdependence between CH4 and O2 to protect Rh3 - from collapse and to promote conversion of CH4 → 2H2 has been clarified. This study not only provides a promising metal cluster displaying good catalytic behavior in POM reaction under mild conditions but also reveals a strictly molecular-level mechanism of direct partial oxidation for the production of hydrogen, a promising renewable energy source in the 21st century.

| S-EPMC8790732 | biostudies-literature

Silicon carbide formation from methane and silicon monoxide.

Project description:Silicon carbide (SiC) formation plays an important role during the production of elemental silicon. SiC forms through a high temperature reaction between silicon monoxide gas (SiO) and carbon. Currently, the carbon sources are solids, however finding a way of substituting the solid carbon with methane could have several advantages. SiC formation was studied in argon, hydrogen and methane containing atmospheres at 1650 °C and 1750 °C. SiO gas was generated from pellets of a 1:2 molar ratio of SiC and silica (SiO2). The reactions were investigated through CO off-gas analysis in conjunction with measuring the weight change. After each experiment, the reaction products were examined in a scanning electron microscope with secondary electrons and through energy-dispersive X-ray spectroscopy. It was confirmed that SiC may form from SiO and methane. Increasing the methane content to 5% caused a significant increase in SiC formation. Furthermore, the SiC structure was also highly sensitive to the methane content that was used. In addition, the SiO producing reaction was affected by hydrogen. The hydrogen lead to an increased rate of SiO formation relative to what was seen in argon. The effect of hydrogen was most pronounced at 1750 °C which is right after the melting of silica.

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Versatile Reaction Pathways of 1,1,3,3,3-Pentafluoropropene at Rh(I) Complexes [Rh(E)(PEt3 )3 ] (E=H, GePh3 , Si(OEt)3 , F, Cl): C-F versus C-H Bond Activation Steps.

Project description:The reaction of the rhodium(I) complexes [Rh(E)(PEt3 )3 ] (E=GePh3 (1), H (6), F (7)) with 1,1,3,3,3-pentafluoropropene afforded the defluorinative germylation products Z/E-2-(triphenylgermyl)-1,3,3,3-tetrafluoropropene and the fluorido complex [Rh(F)(CF3 CHCF2 )(PEt3 )2 ] (2) together with the fluorophosphorane E-(CF3 )CH=CF(PFEt3 ). For [Rh(Si(OEt)3 )(PEt3 )3 ] (4) the coordination of the fluoroolefin was found to give [Rh{Si(OEt)3 }(CF3 CHCF2 )(PEt3 )2 ] (5). Two equivalents of complex 2 reacted further by C-F bond oxidative addition to yield [Rh(CF=CHCF3 )(PEt3 )2 (μ-F)3 Rh(CF3 CHCF2 )(PEt3 )] (9). The role of the fluorido ligand on the reactivity of complex 2 was assessed by comparison with the analogous chlorido complex. The use of complexes 1, 4 and 6 as catalysts for the derivatization of 1,1,3,3,3-pentafluoropropene provided products, which were generated by hydrodefluorination, hydrometallation and germylation reactions.

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Versatile deprotonated NHC: C,N-bridged dinuclear iridium and rhodium complexes.

Project description:Bearing the versatility of N-heterocyclic carbene (NHC) ligands, here density functional theory (DFT) calculations unravel the capacity of coordination of a deprotonated NHC ligand (pNHC) to generate a doubly C2,N3-bridged dinuclear complex. Here, in particular the discussion is based on the combination of the deprotonated 1-arylimidazol (aryl = mesityl (Mes)) with [M(cod)(?-Cl)] (M = Ir, Rh) generated two geometrical isomers of complex [M(cod){µ-C3H2N2(Mes)-?C2,?N3}]2). The latter two isomers display conformations head-to-head (H-H) and head-to-tail (H-T) of C S and C 2 symmetry, respectively. The isomerization from the H-H to the H-T conformation is feasible, whereas next substitutions of the cod ligand by CO first, and PMe3 later confirm the H-T coordination as the thermodynamically preferred. It is envisaged the exchange of the metal, from iridium to rhodium, confirming here the innocence of the nature of the metal for such arrangements of the bridging ligands.

| S-EPMC4734348 | biostudies-literature

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