Metal Carbon Triple Bond Research Articles

Metallacycle Expansion and Annulation: Access to Tetrazolo‐Fused Osmacycles by Reaction of Cyclic Osmium Carbyne with Sodium Azide

Main observation and conclusionThe reaction of a cyclic osmacarbyne complex with sodium azide led to the formation of a ring expansion‐annulation product, a unique tetrazole annulated polycyclic metallacycle. The reaction proceeds by insertion of a nitrogen atom into the metal carbon triple bond and the second azide participating in the [2+3] cycloaddition. The successful isolation and characterization of metalla‐azirine complex and metallapyridinium derivative strongly validated the mechanism for the formation of the title complex. The work demonstrates a new strategy to enrich the varieties of aza‐metallacyclic species.

Terminal, Open-Shell Mo Carbide and Carbyne Complexes: Spin Delocalization and Ligand Noninnocence.

Open-shell compounds bearing metal-carbon triple bonds, such as carbides and carbynes, are of significant interest as plausible intermediates in the reductive catenation of C1 oxygenates. Despite the abundance of closed-shell carbynes reported, open-shell variants are very limited, and an open-shell carbide has yet to be reported. Herein, we report the synthesis of the first terminal, open-shell carbide complexes, [K][1] and [1][BArF4] (1 = P2Mo(≡C:)(CO), P2 = a terphenyl diphosphine ligand), which differ by two redox states, as well as a series of related open-shell carbyne complexes. The complexes are characterized by single-crystal X-ray diffraction and NMR, EPR, and IR spectroscopies, while the electronic structures are probed by EPR studies and DFT calculations to assess spin delocalization. In the d1 complexes, the spin is primarily localized on the metal (∼55-77% Mo dxy) with delocalization on the triply bonded carbon of ∼0.05-0.09 e-. In the reduced carbide [K][1], a direct metal-arene interaction enables ancillary ligand reduction, resulting in reduced radical character on the terminal carbide (⩽0.02 e-). Reactivity studies with [K][1] reveal the formation of mixed-valent C-C coupled products at -40 °C, illustrating how productive reactivity manifolds can be engendered through the manipulation of redox states. Combined, the results inform on the electronic structure and reactivity of a new and underrepresented class of compounds with potential significance to a wide array of reactions involving open-shell species.

Recent Advances in the Reactions of Cyclic Carbynes.

The acyclic organic alkynes and carbyne bonds exhibit linear shapes. Metallabenzynes and metallapentalynes are six- or five-membered metallacycles containing carbynes, whose carbine-carbon bond angles are less than 180°. Such distortion results in considerable ring strain, resulting in the unprecedented reactivity compared with acyclic carbynes. Meanwhile, the aromaticity of these metallacycles would stabilize the ring system. The fascinating combination of ring strain and aromaticity would lead to interesting reactivities. This mini review summarized recent findings on the reactivity of the metal–carbon triple bonds and the aromatic ring system. In the case of metallabenzynes, aromaticity would prevail over ring strain. The reactions are similar to those of organic aromatics, especially in electrophilic reactions. Meanwhile, fragmentation of metallacarbynes might be observed via migratory insertion if the aromaticity of metallacarbynes is strongly affected. In the case of metallapentalynes, the extremely small bond angle would result in high reactivity of the carbyne moiety, which would undergo typical reactions for organic alkynes, including interaction with coinage metal complexes, electrophilic reactions, nucleophilic reactions and cycloaddition reactions, whereas the strong aromaticity ensured the integrity of the bicyclic framework of metallapentalynes throughout all reported reaction conditions.

Addition of alkynes and osmium carbynes towards functionalized d\u03c0\u2013p\u03c0 conjugated systems

The metal-carbon triple bonds and carbon-carbon triple bonds are both highly unsaturated bonds. As a result, their reactions tend to afford cycloaddition intermediates or products. Herein, we report a reaction of M≡C and C≡C bonds that affords acyclic addition products. These newly discovered reactions are highly efficient, regio- and stereospecific, with good functional group tolerance, and are robust under air at room temperature. The isotope labeling NMR experiments and theoretical calculations reveal the reaction mechanism. Employing these reactions, functionalized dπ-pπ conjugated systems can be easily constructed and modified. The resulting dπ-pπ conjugated systems were found to be good electron transport layer materials in organic solar cells, with power conversion efficiency up to 16.28% based on the PM6: Y6 non-fullerene system. This work provides a facile, efficient methodology for the preparation of dπ-pπ conjugated systems for use in functional materials.

Dimetallapoly‐yn‐diylidynes: LnM≡C−(C≡C)x−C≡MLn (x=0–4)

AbstractSynthetic routes to dimetallated Cx carbon wires in which two metals are separated by a linear carbon chain involving terminal metal–carbon triple bonds are described for the complexes [(Tp*)(CO)2W≡C−(C≡C)n−C≡W(CO)2(Tp*)] (Tp*=hydrotris(dimethylpyrazolyl)borate) where n=1, 3 or 4, joining the previously known examples with n=0, 1 and 2 to complete the series as models for linear carbyne C∞.

Dimetallapoly‐yn‐diylidynes: LnM≡C−(C≡C)x−C≡MLn (x=0–4)

Synthetic routes to dimetallated Cx carbon wires in which two metals are separated by a linear carbon chain involving terminal metal-carbon triple bonds are described for the complexes [(Tp*)(CO)2 W≡C-(C≡C)n -C≡W(CO)2 (Tp*)] (Tp*=hydrotris(dimethylpyrazolyl)borate) where n=1, 3 or 4, joining the previously known examples with n=0, 1 and 2 to complete the series as models for linear carbyne C∞ .

Formal [2 + 2 + 2] Cycloaddition Reaction of a Metal–Carbyne Complex with Nitriles: Synthesis of a Metallapyrazine Complex

Although alkynes have been extensively exploited in [2 + 2 + 2] cycloadditions with nitriles to form N-heterocyclic aromatics, the “alkyne-like” metal–carbon triple bond has never been used in [2 +...

Carbolong Chemistry: A Story of Carbon Chain Ligands and Transition Metals.

The construction of metal-carbon bonds is one of the most important issues of organometallic chemistry. However, the chelation of polydentate ligands to a metal via several metal-carbon bonds is rare. Metallapentalyne, which can be viewed as a 7-carbon (7C) chain coordinated to a metal via three metal-carbon bonds, was first reported in 2013. Although metallapentalyne contains a metal-carbon triple bond in a five-membered ring (5MR) and the bond angle around the carbyne carbon is only 129.5°, metallapentalyne exhibits excellent stability to air, moisture, and heat. Metallapentalyne possesses the rare planar Möbius aromaticity, which is in sharp contrast to the Hückel antiaromaticity in pentalyne. The metal fragment not only relieves the large ring strain present in pentalyne but also results in the transformation of the antiaromaticity in pentalyne to aromaticity in metallapentalyne. With the extension of the carbon chain from 7 to 12 carbon atoms, a series of novel polycyclic frameworks were constructed via the formation of several metal-carbon bonds. Some interesting phenomena were observed for these complexes. For instance, (1) the carbyne carbon of the 7C framework could react with both nucleophilic and electrophilic reagents, leading to the formation of 16- and 18-electron metallapentalenes; (2) σ aromaticity was first observed in an unsaturated system in the 8C framework; (3) two classical antiaromatic frameworks, cyclobutadiene and pentalene, were simultaneously stabilized in the 9C framework for the first time; (4) three fused 5MRs bridged by a metal are coplanar in the 10C framework; (5) the first [2 + 2 + 2] cycloaddition of a late transition metal carbyne complex with alkynes was realized during the construction of an 11C framework; (6) the largest number of carbon atoms coordinated to a metal atom in the equatorial plane was observed in the 12C framework; and (7) sharing of the transition metal by multiple aromatic units has seldom been observed in the metalla-aromatics. Therefore, the term carbolong chemistry has been used to describe the chemistry of these novel frameworks. More interestingly, carbolong complexes exhibit diverse properties, which could lead to potential future applications. As the discovery and creation of molecular fragments lead to advancements in chemistry, medical science, and materials chemistry, these novel polydentate carbon chain chelates might have important influences in these fields due to their facile synthesis, high stability, and unique properties.

Reactions of Cyclic Osmacarbyne with Coinage Metal Complexes

The reactions of the five-membered cyclic osmacarbyne complex, i.e., osmapentalyne, with a complete set of coinage metal (Cu, Ag, and Au) complexes have been investigated. Osmapentalyne 1 reacts with CuCl or AuCl(PPh3) via its metal–carbon triple bond, leading to the formation of osmapentalyne-copper(I) chloride adduct 2 or osmapentalyne-gold(I)-triphenylphosphine adduct 3, respectively. Moreover, it can react with AgOTf in the presence of 1,10-phenanthroline to give osmapentalyne-silver(I)-phenanthroline adduct 4. All the compounds have been characterized by X-ray diffraction analysis. The formation of these bimetallic adducts can be regarded as the “alkyne-like” interaction of an osmium–carbon triple bond with the coinage metal center. The interaction is weak and these adducts can readily dissociate to regenerate precursor osmapentalyne 1 in essentially quantitative yield with the assistance of PPh3 or chloride ligands.

Hydroboration and Hydrogenation of an Osmium–Carbon Triple Bond: Osmium Chemistry of a Bis-σ-Borane

The complex [OsHCl(≡CPh)(IPr)(PiPr3)]OTf (1; IPr = 1,3-bis(2,6-diisopropylphenyl)imidazolylidene, OTf = CF3SO3) replaces the chloride ligand with a hydroxo group to give [OsH(OH)(≡CPh)(IPr)(PiPr3)]OTf (2), which undergoes hydroboration and hydrogenation of its metal–carbon triple bond. The hydroboration products depend upon the reagent used. Treatment of 2 with Na[BH4] leads to the bis-σ-borane complex OsH2(η2:η2-H2BCH2Ph)(IPr)(PiPr3) (3), whereas pinacolborane (HBPin) affords the arene compound [Os(η6-C6H5CH2Bpin)H(IPr)(PiPr3)]OTf (4). The hydrogenation of the triple bond of 2 occurs under 4 atm of H2 and yields the toluene derivative [Os(η6-C6H5CH3)H(IPr)(PiPr3)]OTf (5).

HRMS studies on the fragmentation pathways of metallapentalyne

The electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS) using collision-induced dissociation (CID) method was applied to investigate the characteristic fragment ions of metalla-aromatic complexes for the first time. The fragmentation process of osmapentalyne, which contained metal-carbon triple bond in a five-membered ring, was discussed in detail. The ESI FT-ICR MS CID experimental results at high resolution mass spectra (HRMS) demonstrated the elemental composition of fragment ions unambiguously, thus a reasonable fragmentation pathway of osmapentalyne was proposed. In addition, the characteristic fragment ions have been investigated, which were specific and useful for the identification of some osmapentalynes complexes. These characteristic fragmentation pathways were helpful to analyze and interpret the stability and property of the parent ion. Also, this method could be used for the characterization of other organometallic complexes, especially containing characteristic isotopic peaks.

Stabilization of anti-aromatic and strained five-membered rings with a transition metal

Anti-aromatic compounds, as well as small cyclic alkynes or carbynes, are particularly challenging synthetic goals. The combination of their destabilizing features hinders attempts to prepare molecules such as pentalyne, an 8π-electron anti-aromatic bicycle with extremely high ring strain. Here we describe the facile synthesis of osmapentalyne derivatives that are thermally viable, despite containing the smallest angles observed so far at a carbyne carbon. The compounds are characterized using X-ray crystallography, and their computed energies and magnetic properties reveal aromatic character. Hence, the incorporation of the osmium centre not only reduces the ring strain of the parent pentalyne, but also converts its Hückel anti-aromaticity into Craig-type Möbius aromaticity in the metallapentalynes. The concept of aromaticity is thus extended to five-membered rings containing a metal-carbon triple bond. Moreover, these metal-aromatic compounds exhibit unusual optical effects such as near-infrared photoluminescence with particularly large Stokes shifts, long lifetimes and aggregation enhancement.

An investigation into the relative influence of alkoxide and thiolate ligands on the metal–carbon triple bond in X 3MCH compounds, where M=Cr, Mo and W and X=OH, SH, OCH 3, SCH 3, OCF 3 and SCF 3 from electronic structure calculations

Electronic structure calculations using density functional theory with the aid of the gaussian-98 package have been employed on the model Group 6 metal alkylidyne complexes X 3MCH, where M=Cr, Mo and W and X=OH, SH, OCH 3, SCH 3, OCF 3 and SCF 3. Collectively, these calculations reveal that the relative energies of the metal–carbon π-bonding molecular orbitals are greatly influenced by the metal and the ancillary ligand X. In comparing the bonding in related O and S containing molecules, the effect of oxygen is to increase the relative energy of the M–C π bond by approximately 1 eV as a result of M–O π antibonding interactions. In contrast, the ligand-based lone-pair orbitals lie higher in energy for sulfur and for the series where X=SH, SCH 3 and SCF 3, the HOMO is a sulfur lone-pair combination of a 2 symmetry in the C 3 v point group. The relative influence of H, CH 3 and CF 3 within each series is as expected based on their electron releasing properties. A comparison is made with related compounds having metal to metal or metal to nitrogen triple bonds.

Carbene Complexes of Divalent Chromium

The first carbene complexes 1 (R = H, Me; X = Cl, Br) of divalent chromium were obtained selectively by addition of hydrogen halides to the metal–carbon triple bond in [(η5-C5R5)(CO)2Cr≡CNiPr2]. These carbene complexes react with isocyanides, phosphanes, and phosphites to give cationic CrII carbene complexes.

Dinuclear Molybdenum and Tungsten C3-Bridged Complexes with Metal−Carbon Multiple Bonds

In this communication we report the synthesis and characterization of complexes which have C{sub 3} bridging units with metal-carbon triple bonds. In particular, methylene-bridged biscarbyne molecules serve as vehicles to prepare C{sub 3}-bridged complexes Tp`(CO){sub 2} Mo=V@C-C=V@CMo(O){sub 2}Tp`, Tp`(CO){sub 2}W=V@CC=V@CMo(0){sub 2} Tp`, and Tp`(O){sub 2}WC=V@CC=V@Mo(CO){sub 2}Tp` (Tp` = hydridotris(3,5-dimethylpyrazolyl)borate) as well as the ketone complex Tp`(CO){sub 2}W=V@CC(O)C=V@Mo(CO){sub 2}Tp`. This simple synthetic route provides access to dinuclear complexes with different metals. High-yield formation of Tp`(CO){sub 2}M=V@CCH{sub 2} C=V@Mo(CO){sub 2}Tp` provides an exciting generator for derivative dinuclear chemistry with three carbon atoms linking two metals. 24 refs.

Synthese von 3H‐1,2,3,4‐Triazametallol‐Komplexen durch Addition von Azidoameisensäure‐methylester an die Metall – Kohlenstoff‐Dreifachbindung Cyclopentadienyl‐substituierter Carbin‐Komplexe von Molybdän und Wolfram

Synthesis of 3H‐1,2,3,4‐Triazametallole Complexes by the Addition of Methyl Azidoformate to the Metal–Carbon Triple Bond of Cyclopentadienyl‐Substituted Carbyne Complexes of Molybdenum and TungstenN3CO2Me attacks the electron‐rich metal–carbon triple bond in C5H5(CO)2 ‐ n (PMe3)nMCR (M = Mo, W; R = Ph, Tol; n = 0, 1) (1) to provide neutral 3H‐1,2,3,4‐Triazametallole complexes 2.

Darstellung und Struktur kationischer η2-Thiocarbenkomplexe von Molybdän und Wolfram / Synthesis and Structure of Cationic η2-Thiocarbene Complexes of Molybdenum and Tungsten

The reaction of dimethyl(methylthio)sulfonium tetrafluoroborate [(CH3)2S–SCH3][BF4] with η/5-cyclopentadienyl(dicarbonyl)carbyne complexes of molybdenum and tungsten Cp(CO)2M ≡ C–R (M = Mo, W; R = CH3, C6H5, C6H4CH3) 1c, 2a–d results in an electrophilic attack of the SCH3 moiety at the metal carbon triple bond, providing orange to red, diamagnetic, cationic η2-thiocarbene complexes 3c, 4a–d in high yields. The new compounds were identified by X-ray structure analysis, NMR, IR and mass spectra.

ChemInform Abstract: Transition Metal Complexes with Terminal Carbyne Ligands

Publisher Summary This chapter discusses the chemistry of molecular carbyne complexes; there is also much interest in them as models for species that are possibly present on metal surfaces in catalytic reactions. Surfacebound methine (CH) is a proposed intermediate in the Fischer–Tropsch synthesis, and alkylidyne groups are suggested as intermediates in heterogeneously catalyzed alkyne metathesis reactions. X-Ray structure determinations of carbyne complexes show that they have very short metal–carbon bond lengths consistent with a metal–carbon triple bond. In certain cases, ∞-protons of an alkylidene ligand may be abstracted by a base to give alkylidyne compounds. Addition of electrophiles to terminal isonitrile (CNR) ligands gives aminocarbyne complexes; the analogous reaction of terminal thiocarbonyl (CS) ligands gives thiocarbynes. Fischer and Himmelreich reported the abstraction of oxygen from an anionic carbamoyl compound with SOCl 2 to give an aminocarbyne compound. Reactions of cationic carbyne compounds with nucleophiles proceed exclusively by nucleophilic attack at the carbyne carbon atom, thus providing a synthetically useful route to certain carbene complexes. The field of transition-metal carbyne chemistry has matured to the point where a great deal is known about the structure, bonding, and reactivity of the carbyne ligand.

The electronic and geometric structures of the transition-metal carbyne cations ScCH+, TiCH+, VCH+, and CrCH+

The electronic and geometric structures of several transition-metal carbyne cations have been studied by ab initio methods (MCSCF and MCSCF+1+2). CrCH/sup +/(/sup 3/..sigma../sup -/), VCH/sup +/(/sup 2/..delta..), and TiCH/sup +/(/sup 1/..sigma../sup +/) are all characterized by a metal-carbon triple bond of remarkably similar length (1.772, 1.745, 1.758 A, respectively). Relative to the spin allowed dissociation products (the metal ion in its ground state and CH in the excited /sup 4/..sigma../sup -/ state) the metal-carbon bond energies are calculated (in kcal/mol) to be CrCH/sup +/ (70.8), VCH/sup +/ (108.0), and TiCH/sup +/ (113.0). Relative to the /sup 2/II ground state of CH these bond energies become 53.7, 90.8, and 95.9 kcal/mol. The experimental VC bond energy in VCH/sup +/ is 115 kcal/mol, approximately 24 kcal/mol higher than our calculated value of 90.8. Analysis of the exchange energy loss of the metal ion upon bond formation suggests that there is an intrinsic metal-carbon bond energy for these species given by the sum of the exchange energy loss and the calculated bond energy. The /sup 2/II state of ScCH/sup +/ is characterized by a double bond between Sc and C, with a bond length of 1.940 A and D/sub e/ of 96.3/79.2 kcal/molmore » relative to the /sup 4/..sigma../sup -///sup 2/II state of CH. The electron distribution in the metal-carbon bond is analyzed for each of the titled molecules.« less

ChemInform Abstract: CATALYSIS BY TRANSITION METALS: METAL‐CARBON DOUBLE AND TRIPLE BONDS

Several well-characterized transition metal catalysts contain a metal-carbon double bond or a metal-carbon triple bond. In other homogeneous (or heterogeneous) catalyst systems in which the metal is likely to be in a relatively high oxidation state, such as molybdenum(VI) or tungsten(VI), metal-carbon multiple bonds may play an important role. Some recent results suggest that even supposedly well understood reactions such as ethylene polymerization may actually involve catalysts that behave as if they contained a metal-carbon double bond instead of a metal-carbon single bond. The chemistry of metal-carbon double and triple bonds should eventually complement and perhaps. overlap the known chemistry of complexes containing metal-oxygen double bonds or metal-nitrogen triple bonds, respectively; unique catalytic reactions involving carbon, nitrogen, and oxygen ligands multiply bonded to transition metals are therefore possible.