Carbon Bond Activation Research Articles

Chelation-assisted carbon-hydrogen and carbon-carbon bond activation by transition metal catalysts.

Herein we describe the chelation-assisted C-H and C-C bond activation of carbonyl compounds by Rh1 catalysts. Hydroacylation of olefins was accomplished by utilizing 2-amino-3-picoline as a chelation auxiliary. The same strategy was employed for the C-C bond activation of unstrained ketones. Allylamine 24 was devised as a synthon of formaldehyde. Hydroiminoacylation of alkynes with allylamine 24 was applied to the alkyne cleavage by the aid of cyclohexylamine.

Nonradical Trapping Pathway for Reactions of Nitroxides with Rhodium Porphyrin Alkyls Bearing β-Hydrogens and Subsequent Carbon−Carbon Bond Activation

A novel nitroxide-induced hydrogen atom abstraction and β-elimination of rhodium porphyrin alkyls has been observed. Subsequent carbon−carbon bond activation of methyl-substituted nitroxides by the...

Density Functional Study of Carbon−Carbon Bond Activation in Curved Polyaromatic Hydrocarbons by Transition-Metal Complexes

Density functional calculations have been performed on the oxidative addition of a Pt(0) fragment, Pt(PH3)2, to one of the rim C−C bonds of semibuckminsterfullerene (C30H12), to give an η2-σ-bonded...

Catalytic C−C Bond Activation in Biphenylene and Cyclotrimerization of Alkynes: Increased Reactivity of P,N- versus P,P-Substituted Nickel Complexes

Reaction of Ni(COD)2 with the bidentate hybrid ligand (iPr)2CH2CH2NMe2 (PN) and PhC⋮CR (R = Ph, tBu, CF3, C⋮CPh) afforded the donor-stabilized mononuclear Ni(0) complexes (PN)Ni(η2-PhC⋮CR) (R = Ph (1), tBu (4), CF3 (5)) and the dinuclear compound (PN)Ni(η2;η2-PhC⋮C−C⋮CPh)Ni(PN) (3), respectively. In the presence of excess alkyne, compounds 1, 3, and 4 turned out to be active species for the catalytic carbon−carbon bond activation in biphenylene and formation of the corresponding 9,10-disubstituted phenanthrenes. However, cyclotrimerization to benzene derivatives instead of C−C bond cleavage occurred with complex 5 in the presence of excess CF3C⋮CPh and biphenylene. In contrast, the corresponding bis-phosphino-substituted species (dippe)Ni(η2-PhC⋮CR) (R = Ph (2), CF3 (9)) showed substantially reduced catalytic activity toward phenanthrene formation or cyclotrimerization reactions.

Theoretical Studies of Inorganic and Organometallic Reaction Mechanisms. 20. Carbon−Hydrogen and Carbon−Carbon Bond Activation of Cyclopropane by Cationic Iridium(III) and Neutral Rhodium(I) and Iridium(I) Complexes

The reactions of cyclopropane with the coordinately unsaturated species produced by mild thermal activation of [Cp*Ir(P(CH3)3)CH3]+L (L = Cl2CH2, OSO2CF3-) and photochemical activation of Cp*Ir(P(C...

ChemInform Abstract: Catalytic Carbon—Carbon Bond Activation of sec‐Alcohols by a Rodium(I) Complex.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Catalytic Carbon−Carbon Bond Activation ofsec-Alcohols by a Rhodium(I) Complex

Various unstrained sec-alcohols, including cycloalkanols, reacted with alkenes under a catalytic system of Rh(I) complex, 2-amino-3-picoline, and K2CO3 to give the alkyl-group-exchanged ketones through transfer hydrogenation and consecutive carbon−carbon bond activation. The presence of base is essential to enhance the rate of the oxidation step, and alkene acts as a hydrogen acceptor and a substrate of the carbon−carbon coupling reaction.

The Mechanism of Carbon−Carbon Bond Activation in Cationic 6-Alkylcyclohexadienyl Ruthenium Hydride Complexes

Carbon−carbon bond activation in cationic 6-endo-methyl-η5-cyclohexadienyl and 6-exo-methyl-η5-cyclohexadienyl ruthenium hydride complexes has been investigated. Contrary to expectations, it is the 6-exo-methyl complex and not the stereoisomeric 6-endo-methyl complex that undergoes selective carbon−carbon bond activation under exceptionally mild conditions, quantitatively converting the 6-exo-methyl substituent and the hydride ligand to methane. The mechanism of the activation reaction involves dissociation of protic acid from the agostic starting complex by reaction with a weak base (typically water), followed by protolytic activation of the alkyl group, with “back-side” assistance from the nucleophilic metal center. Under the same conditions, the corresponding 6-endo-methyl isomer undergoes selective dehydrogenation rather than demethylation, despite the proximity of the endo-methyl substituent to the metal center. For both exo and endo isomers, the cationic ruthenium hydride intermediates were determined by spectroscopic analysis to adopt fluxional agostic structures. The agostic complexes are kinetically stable at room temperature under rigorously anhydrous conditions but convert quantitatively to cationic η6-arene products in the presence of a Brønsted base. The rates of both carbon−carbon bond activation and dehydrogenation are dependent on the identity and concentration of the base and suppressed in the presence of excess acid. The protolytic mechanism for carbon−carbon bond activation is supported by deuterium-labeling studies and by the reactivity of the neutral complexes toward Lewis acids and one-electron oxidants. This mechanism is shown to be relevant to carbon−carbon bond activation reactions observed in less-substituted 6-exo-methyl-η5-cyclohexadienyl complexes and in a steroid-derived 6,6-disubstituted-η5-cyclohexadienyl complex, representative of previously reported cases of dealkylative ligand aromatization. The low kinetic barrier for the protolytic dealkylation mechanism is contrasted to the comparatively high activation barriers reported for carbon−carbon bond activation reactions that occur in structurally related systems that cannot access a protolytic pathway. This investigation provides a consistent basis for rationalizing this potentially important but poorly understood class of metal-mediated reactions.

Carbon−Carbon Bond Activation by Electrophilic Complexes of Cobalt: Anomalous [3 + 2 + 2] Allyl/Alkyne Cycloaddition Reactions and [5 + 2] Cyclopentenyl/Alkyne Insertion−Ring Expansion Reactions

Carbon−Carbon Bond Activation by Electrophilic Complexes of Cobalt: Anomalous [3 + 2 + 2] Allyl/Alkyne Cycloaddition Reactions and [5 + 2] Cyclopentenyl/Alkyne Insertion−Ring Expansion Reactions

Catalytic Carbon−Carbon Bond Activation and Functionalization by Nickel Complexes

The nickel alkyne complexes (dippe)Ni(PhC⋮CPh), 1, (dippe)Ni(MeC⋮CMe), 2, (dippe)Ni(MeO2CC⋮CCO2Me), 3, (dippe)Ni(CH3OCH2C⋮CCH2OCH3), 4, and (dippe)Ni(CF3C⋮CCF3), 5, were synthesized (dippe = bis(diisopropylphosphino)ethane) and characterized by 1H, 31P, and 13C{1H} NMR spectroscopy. Complexes 1, 2, and 3 were characterized by X-ray crystallography. The thermolysis of complex 1 or 2 (120 °C) in the presence of excess biphenylene and excess alkyne results in very slow catalytic formation of the corresponding 9,10-disubstituted phenanthrene. However, addition of ∼6 mol % O2 (based on the metal complex) to the reaction mixture results in an acceleration in catalysis at lower temperatures (∼70−80 °C). The thermolysis of complexes 3 or 4 with excess biphenylene and excess alkyne leads to the alkyne cyclotrimerization product as the major organic species formed in the reaction. Fluorenone was catalytically produced by heating (dippe)Ni(CO)2, biphenylene, and CO. Catalytic insertion of 2,6-xylylisocyanide into the strained C−C bond of biphenylene was also achieved by heating (dippe)Ni(2,6-xylylisocyanide)2, excess biphenylene, and 2,6-xylylisocyanide. Mechanistic schemes are proposed for these reactions.

ChemInform Abstract: Catalytic Carbon—Carbon Bond Activation of Unstrained Ketone by Soluble Transition‐Metal Complex.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Carbon−Carbon Bond Activation in Adsorbed Cyclopropane by Gas-Phase Atomic Hydrogen on the Ni(111) Surface

Gas-phase atomic hydrogen induces C−C bond activation in adsorbed cyclopropane on the Ni(111) surface, while coadsorbed hydrogen does not. Propane is the only desorbing product observed during subsequent temperature-programmed desorption experiments. Three propane formation pathways are observed. Gas-phase atomic hydrogen reacts with adsorbed cyclopropane to form intermediates at 105 K, which are hydrogenated by coadsorbed hydrogen to form propane at 116 and 210 K. The 116 K pathway is similar to previous results obtained on the Ni(100) surface where propyl was determined to be the primary intermediate. The 210 K pathway has no analogue on the Ni(100) surface and is thought to involve a more stable form of propyl on the Ni(111) surface. The reaction of subsurface hydrogen with adsorbed cyclopropane leads to propane formation at 170 K on the Ni(111) surface. The absence of methane and ethane formation indicates that no multiple C−C bond activation processes occur. In contrast, cyclopropane desorption occur...

Catalytic Carbon−Carbon Bond Activation of Unstrained Ketone by Soluble Transition-Metal Complex

Catalytic Carbon−Carbon Bond Activation of Unstrained Ketone by Soluble Transition-Metal Complex

Demethylation of Coordinated Hexamethylbenzene. Carbon−Carbon Bond Activation during Ruthenium-Mediated [3 + 2] Allyl Alkyne Cycloaddition Reactions

The demethylation of coordinated hexamethylbenzene is integrated into [3 + 2] allyl/alkyne cycloaddition reactions mediated by (η6-hexamethylbenzene)Ru(η3-allyl)OTf. The reaction proceeds in high yield at or below room temperature and yields methane and (η6-pentamethylbenzene)ruthenium(1,2-dialkylcyclopentadienyl)+OTf- complexes exclusively. Cycloaddition with carbon−carbon bond activation is general for a range of disubstituted alkynes.

Mechanistic Investigation of Catalytic Carbon−Carbon Bond Activation and Formation by Platinum and Palladium Phosphine Complexes

The complexes Pt(PEt3)3 and Pd(PEt3)3 cleave the C−C bond of biphenylene to give (PEt3)2Pt(2,2‘-biphenyl), 1, and (PEt3)2Pd(2,2‘-biphenyl), respectively. Heating (PEt3)2Pt(2,2‘-biphenyl) in the presence of biphenylene leads to C−C cleavage of a second biphenylene to give (PEt3)2Pt(2,2‘-tetraphenyl), 2, via a Pt(IV) intermediate. 2 reductively eliminates tetraphenylene at 115 °C. At 120 °C the reaction is catalytic; Pt(PEt3)3 or 1 converts biphenylene to tetraphenylene. The intermediates in the catalytic cycle have been identified, and 1 and 2 have been characterized by X-ray analysis. Under catalytic conditions 1 and 2 approach steady-state concentrations. Kinetic analysis reveals that the steady-state concentration ratio, resting state species, and overall rate of catalysis, kobs, depend on the ratio of biphenylene to PEt3. This observation is consistent with loss of PEt3 from 1, resulting in the 14-electron species (PEt3)Pt(2,2‘-biphenyl), I. At 130 °C, I coordinates to PEt3 approximately 130 times fast...

Carbon−Carbon Bond Activation of Cyclopropane by Subsurface Hydrogen on the Ni(111) Surface

Carbon−carbon bond activation by subsurface hydrogen has been observed for adsorbed cyclopropane at 170 K on the Ni(111) surface. Propane was the dominant product, and no multiple C−C bond activation processes were observed. Cyclopropane desorbs at 124 K from both the clean and the hydrogen-coadsorbed Ni(111) surface. Neither coadsorbed hydrogen nor disproportionation induces propane formation. These observations are consistent with previous results that energetic forms of hydrogen are necessary to activate the C−C bond even in strained cyclopropane under ultrahigh-vacuum conditions.

Phosphorus–carbon bond activation of PMe3 at a dimolybdenum center: synthesis and structure of [Cp*Mo(μ-O2CMe)]2(μ-PMe2)(μ-Me)

The reaction of Mo2(µ-O2CMe)4 with KCp* in the presence of PMe3 yields [Cp*Mo(µ-O2CMe)]2(µ-PMe2)(µ-Me) as a result of cleavage of the P–CH3 bond.

A PCN Ligand System. Exclusive C−C Activation with Rhodium(I) and C−H Activation with Platinum(II)

Reaction of the new aromatic aminophosphine ligand 1-((diethylamino)methyl)-3-((di-tert-butylphosphino)methyl)-2,4,6-trimethylbenzene (4) with [Rh(COE)2Cl]2 (COE = cyclooctene) or with [Rh(ethylene)2Cl]2 at room temperature results in selective carbon−carbon bond activation, yielding the complex ClRh(CH3)[C6H(CH3)2(CH2N(C2H5)2)(CH2P(t-Bu)2)] (5). No competing C−H activation was observed during the course of the reaction. When 4 was reacted with (COD)PtCl2 (COD = cyclooctadiene), selective C−H activation of the methyl group situated between the phosphine and amine groups took place, with concomitant intramolecular H transfer to the amine ligand, resulting in the zwitterionic Pt(II) complex Cl2PtCH2(C6H(CH3)2(CH2NH(C2H5)2)(CH2P(t-Bu)2) (11).

Gas Phase Atomic Hydrogen Induced Carbon−Carbon Bond Activation in Cyclopropane on the Ni(100) Surface

Carbon−carbon bond activation in adsorbed cyclopropane is observed following exposure to gas phase atomic hydrogen on the Ni(100) surface for temperatures as low as 100 K. Exposure to either gas phase atomic hydrogen or deuterium results in formation of adsorbed propyl. In both cases subsequent reaction between adsorbed propyl and coadsorbed hydrogen/deuterium produces propane at 121 K. The activation of a single C−C bond in adsorbed cyclopropane dominates as indicated by the fact that propane is the only product observed. No multiple C−C bond activation which would result in methane or ethane formation was ever observed. These reactions and their mechanisms have been investigated using temperature-programmed reaction (TPR) and vibrational spectroscopy using high-resolution electron energy loss spectroscopy (HREELS). The reactivities of hydrogen and deuterium were indistinguishable during these experiments so we have used the generic term hydrogen or gas phase atomic hydrogen to describe the reactions of ...

Gas-Phase Organolanthanide (Ln) Chemistry: Formation of Ln+−{Benzene} and Ln+−{Benzyne} Complexes by Reactions of Laser-Ablated Ln+ with Cyclic Hydrocarbons

Nascent laser-ablated lanthanide metal ions, Ln+, were reacted with cyclohexacarbons, C6H6+2n (n = 0, 1, 2, or 3), and the resulting organometallic complex ions, {Ln+}−{CpHq}, were identified by time-of-flight mass spectrometry. Cyclohexane and cyclohexadiene were especially reactive, primarily undergoing one or more dehydrogenations to produce adduct ions corresponding to the benzene and benzyne complexes, {Ln+}−{C6H6} and {Ln+}−{C6H4}. Also identified as minor products were the “sandwich” complexes, {C6H6}−{Ln+}−{C6H6}. Carbon−carbon bond activation was generally an unimportant reaction channel, with small yields of {Ln+}−{CpHq} for p ≤ 5. Significant differences were observed in product yields and distributions between the several Ln+ studied, providing the following comparative reactivities: Ce+ ≳ Tb+ ≳ Gd+ ≈ Pr+ ≳ Ho+ ≳ Dy+ ≳ Lu+ > [Sm+/Tm+/Eu+/Yb+ unreactive]. These differences are explained by the metal ion ground state electronic configurations (typically 4fn-1 6s1) and promotion energies (PE) fo...