Metal carbido complex

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A metal carbido complex is a coordination complex that contains a carbon atom as a ligand. They are analogous to metal nitrido complexes. Carbido complexes are a molecular subclass of carbides, which are prevalent in organometallic and inorganic chemistry. Carbido complexes represent models for intermediates in Fischer–Tropsch synthesis, olefin metathesis, and related catalytic industrial processes. [1] Ruthenium-based carbido complexes are by far the most synthesized and characterized to date. Although, complexes containing chromium, gold, iron, nickel, molybdenum, osmium, rhenium, and tungsten cores are also known. Mixed-metal carbides are also known. [2] [3]

Contents

Carbido clusters

Structure of .mw-parser-output .template-chem2-su{display:inline-block;font-size:80%;line-height:1;vertical-align:-0.35em}.mw-parser-output .template-chem2-su>span{display:block;text-align:left}.mw-parser-output sub.template-chem2-sub{font-size:80%;vertical-align:-0.35em}.mw-parser-output sup.template-chem2-sup{font-size:80%;vertical-align:0.65em} Fe5C(CO)15. Fe5C(CO)15.png
Structure of Fe 5C(CO)15.

Most molecular carbido complexes are clusters, usually featuring carbide as a six-fold bridging ligand. Examples include [ Rh 6C(CO)15]2−, and [ Ru 6C(CO)16]2−. [5] Though exceptions exist, such as the nonanuclear Ruthenium cluster (μ-C)Ru9(CO)14 (μ3-η5: η2:η2-C9H7)2, containing a tripped trigonal prism geometry around the carbide. [6]

The iron carbonyl carbides exist not only in the encapsulated carbon ([ Fe 6C(CO)16]2−) but also with exposed carbon centres as in Fe5C(CO)15 and Fe4C(CO)13. [7]

Bimetallic and exotic clusters such as metal carbide clusterfullerenes (MCCF's) have also been able to be prepared. [8] [9]

The complex Au6C(PPh3)6], containing a carbon-gold core. Au6C(PPh3)6.png
The complex Au 6C(P Ph 3)6], containing a carbon-gold core.

Doubly bridging carbide ligands

Bridging carbido ligands can be subdivided into three classes:

Cumulenic compounds generally bridge two metal atoms of the same element and are symmetrical. [11] However, there are exceptions to this. [12]

In contrast, metallocarbyne compounds are generally constitutionally heterobimetallic, with complexes containing varying coordination geometries being common. These moieties have been able to serve as precursors to elaborate molecular scaffolds such as porphyrin derivatives. [13]

The polar covalent class is distinguished from metallocarbynes by a very fine line. This carbide-metal interaction is considered labile in nature. Carbon here can be understood fundamentally as being similar to CO ligands, that is, dative (L-type). Although, this class has also been described to some extent being analogous to the behavior of Lewis acid adduct-forming terminal nitrido and oxo complexes e.g. (PMe2Ph)2Cl-Re≡N-BCl3 and tBu(CH2)3(Br)W=O-AlBr3. [14]

Zwitterionic canonical depiction of polar covalent metal-carbide bond PolarCovalent.png
Zwitterionic canonical depiction of polar covalent metal-carbide bond

Terminal carbides

In rare cases, carbido ligands are terminal. One example is RuC(PCy3)2Cl2 with a Ru-C distance of 163 pm, typical for a triple bond. [15] The complex can be obtained by metathesis of vinyl acetate to give [Ru(CH-p-C6H4Me)(PCy3)2Cl2] results in a metastable Ru(Cl2)(PCy3)2C2HOAc complex, which eliminates acetic acid. [16]

Such transition metal, one coordinate-carbon bonded complexes are comparable to carbon monoxide, cyanide, and isonitrile analogues. These carbides can be used as synthons to access a wide range of carbyne complexes, the most notable being Fischer carbynes. [17] American chemist Christopher C. Cummins is one of the pioneers of this area.

Preparative routes and characterization

Carbido clusters

Synthesis of carbido clusters can be accomplished by hydrolysis, thermolysis of labile ligands, thermal rearrangements, and photolysis. Their synthesis has historically been crudely achieved by serendipitous chance following apparent random molecular organization. One example is the following reaction:

CarbidoClusterSynthesis.png

Doubly bridging carbide ligands

Cumulenic

Synthetic routes to cumulenic carbido complexes can be efficient and lead to rapid, near quantitative product formation with simple purifications. [18] This dimerization involves the formation of a vinylidene from an alkyne. Mechanistically, there are various proposed pathways, starting with oxidative addition of the alkyne to the metal core, followed by either intramolecular 1,2-H shifts or intermolecular 1,3-H shifts. [19] For Ruthenium coordination complexes, bridging Ru-Cl bond lengths have been observed to lie in the range of 1.76-1.8 Å. Ru-C bonds can vary significantly as a result of trans effect phenomena which is caused by the respective ethylene and vinylidene ligands.

Acetylene-based synthesis of cumulenic carbido complex Synthesis of Cumulenic Complex.png
Acetylene-based synthesis of cumulenic carbido complex
Proposed hydride shift mechanisms for alkyne being transformed into vinylidene Alkynetovinylidene.png
Proposed hydride shift mechanisms for alkyne being transformed into vinylidene

Metallocarbyne

The appropriate halocarbyne precursors of choice can be reacted with organolithium reagents to afford the respective lithiocarbyne derivate by virtue of lithium/halogen exchange. [20] This species can serve as a lynchpin for subsequent carbide linkage with an additional metal complex. Phosphine-based analogues were first introduced by Templeton and co. [21] These types of complexes can be characterized crystallographically and are distinguishable by their Cs symmetry.

Synthesis of Templeton Phosphoniocarbyne Phosphoniocarbyne.png
Synthesis of Templeton Phosphoniocarbyne
Common synthetic route for bridging carbido complex Bridging Carbido Complex.png
Common synthetic route for bridging carbido complex

Polar covalent

Addition of tricyclohexylphosphine to the carbene complex (PPh3)2(Cl)2Ru=C(CHCO2Me)2 results in olefin extrusion and yields an air stable anionic carbido complex. This species displaces a dimethyl sulfide ligand from PdCl2(SMe)2 to give the μ-carbido bimetallic complex (PCy3)2Cl2Ru≡C-PdCl2(SMe2). Spark towards a novel type of bonding was proposed following empirical observations wherein the carbido-palladium interaction could be readily disturbed. Reversible coordination ensues upon exposure of the bimetallic complex to carbon monoxide. Additionally, no coordination occurs if the anionic carbido complex contains bulky ligands such as H2IMes. This indicates that the thermodynamic sink towards making the C-M bond is not very favorable, suggesting a weak interaction. Although not intuitive, characterization of this type of bonding can be inferred if 13C NMR shifts are observed to be far downfield, and C-M bond lengths are similar to those of complexes proven to contain carbon-based σ-donor ligands such as [(Et2H2Im)PdCl(μ-Cl)]2. [22]

Preparation of carbide complex exhibiting polar covalent C-M bonding PolarCovalentSynthesis.png
Preparation of carbide complex exhibiting polar covalent C-M bonding

Terminal carbido ligands

Metathesis using Grubbs-type alkylidene complexes can be used to synthesize terminal carbido-containing complexes. One example is RuC(PCy3)2Cl2 with a Ru-C distance of 163 pm, typical for a triple bond. [23] The complex can be obtained by metathesis of vinyl acetate to give [Ru(CH-p-C6H4Me)(PCy3)2Cl2] results in a metastable Ru(Cl2)(PCy3)2C2HOAc complex, which eliminates acetic acid. [24]

The "naked" carbido ligand is weakly basic, forming complexes with other metal centers. The C-M bond is typically found to be around 1.65 Å. The 13 C NMR resonance values for the carbido carbons vary widely, but range from δ211-406. [25] Another example of a terminal carbido complex is Li[MoC(NR2)3] (Mo-C distance of 172 pm), which forms upon deprotonation of the respective methylidyne precursor. [26]

Synthesis of a terminal carbido complex. Carbenesynthesis.png
Synthesis of a terminal carbido complex.

See also

Related Research Articles

Grubbs catalysts are a series of transition metal carbene complexes used as catalysts for olefin metathesis. They are named after Robert H. Grubbs, the chemist who supervised their synthesis. Several generations of the catalyst have also been developed. Grubbs catalysts tolerate many functional groups in the alkene substrates, are air-tolerant, and are compatible with a wide range of solvents. For these reasons, Grubbs catalysts have become popular in synthetic organic chemistry. Grubbs, together with Richard R. Schrock and Yves Chauvin, won the Nobel Prize in Chemistry in recognition of their contributions to the development of olefin metathesis.

<span class="mw-page-title-main">Metal carbonyl</span> Coordination complexes of transition metals with carbon monoxide ligands

Metal carbonyls are coordination complexes of transition metals with carbon monoxide ligands. Metal carbonyls are useful in organic synthesis and as catalysts or catalyst precursors in homogeneous catalysis, such as hydroformylation and Reppe chemistry. In the Mond process, nickel tetracarbonyl is used to produce pure nickel. In organometallic chemistry, metal carbonyls serve as precursors for the preparation of other organometallic complexes.

<span class="mw-page-title-main">Hapticity</span> Number of contiguous atoms in a ligand that bond to the central atom in a coordination complex

In coordination chemistry, hapticity is the coordination of a ligand to a metal center via an uninterrupted and contiguous series of atoms. The hapticity of a ligand is described with the Greek letter η ('eta'). For example, η2 describes a ligand that coordinates through 2 contiguous atoms. In general the η-notation only applies when multiple atoms are coordinated. In addition, if the ligand coordinates through multiple atoms that are not contiguous then this is considered denticity, and the κ-notation is used once again. When naming complexes care should be taken not to confuse η with μ ('mu'), which relates to bridging ligands.

In organic chemistry, carbon–hydrogen bond functionalization is a type of organic reaction in which a carbon–hydrogen bond is cleaved and replaced with a C−X bond. The term usually implies that a transition metal is involved in the C−H cleavage process. Reactions classified by the term typically involve the hydrocarbon first to react with a metal catalyst to create an organometallic complex in which the hydrocarbon is coordinated to the inner-sphere of a metal, either via an intermediate "alkane or arene complex" or as a transition state leading to a "M−C" intermediate. The intermediate of this first step can then undergo subsequent reactions to produce the functionalized product. Important to this definition is the requirement that during the C−H cleavage event, the hydrocarbyl species remains associated in the inner-sphere and under the influence of "M".

<span class="mw-page-title-main">Metallacycle</span>

In organometallic chemistry, a metallacycle is a derivative of a carbocyclic compound wherein a metal has replaced at least one carbon center; this is to some extent similar to heterocycles. Metallacycles appear frequently as reactive intermediates in catalysis, e.g. olefin metathesis and alkyne trimerization. In organic synthesis, directed ortho metalation is widely used for the functionalization of arene rings via C-H activation. One main effect that metallic atom substitution on a cyclic carbon compound is distorting the geometry due to the large size of typical metals.

<span class="mw-page-title-main">Germylene</span> Class of germanium (II) compounds

Germylenes are a class of germanium(II) compounds with the general formula :GeR2. They are heavier carbene analogs. However, unlike carbenes, whose ground state can be either singlet or triplet depending on the substituents, germylenes have exclusively a singlet ground state. Unprotected carbene analogs, including germylenes, has a dimerization nature. Free germylenes can be isolated under the stabilization of steric hindrance or electron donation. The synthesis of first stable free dialkyl germylene was reported by Jutzi, et al in 1991.

Transition metal carbyne complexes are organometallic compounds with a triple bond between carbon and the transition metal. This triple bond consists of a σ-bond and two π-bonds. The HOMO of the carbyne ligand interacts with the LUMO of the metal to create the σ-bond. The two π-bonds are formed when the two HOMO orbitals of the metal back-donate to the LUMO of the carbyne. They are also called metal alkylidynes—the carbon is a carbyne ligand. Such compounds are useful in organic synthesis of alkynes and nitriles. They have been the focus on much fundamental research.

<span class="mw-page-title-main">Cyclopentadienyliron dicarbonyl dimer</span> Chemical compound

Cyclopentadienyliron dicarbonyl dimer is an organometallic compound with the formula [(η5-C5H5)Fe(CO)2]2, often abbreviated to Cp2Fe2(CO)4, [CpFe(CO)2]2 or even Fp2, with the colloquial name "fip dimer". It is a dark reddish-purple crystalline solid, which is readily soluble in moderately polar organic solvents such as chloroform and pyridine, but less soluble in carbon tetrachloride and carbon disulfide. Cp2Fe2(CO)4 is insoluble in but stable toward water. Cp2Fe2(CO)4 is reasonably stable to storage under air and serves as a convenient starting material for accessing other Fp (CpFe(CO)2) derivatives (described below).

<span class="mw-page-title-main">Jaqueline Kiplinger</span> American inorganic chemist

Jaqueline Kiplinger is an American inorganic chemist who specializes in organometallic actinide chemistry. Over the course of her career, she has done extensive work with fluorocarbons and actinides. She is currently a Fellow of the Materials Synthesis and Integrated Devices group in the Materials Physics and Applications Division of Los Alamos National Laboratory (LANL). Her current research interests are focused on the development of chemistry for the United States’ national defense and energy needs.

<span class="mw-page-title-main">Transition-metal allyl complex</span>

Transition-metal allyl complexes are coordination complexes with allyl and its derivatives as ligands. Allyl is the radical with the connectivity CH2CHCH2, although as a ligand it is usually viewed as an allyl anion CH2=CH−CH2−, which is usually described as two equivalent resonance structures.

Russell P. Hughes an American/British chemist, is the Frank R. Mori Professor Emeritus and Research Professor in the Department of Chemistry at Dartmouth College. His research interests are in organometallic chemistry, with emphasis on the chemistry of transition metal complexes interacting with fluorocarbons. His research group’s work in this area led to several creative syntheses of complexes of transition metal and perfluorinated hydrocarbon fragments.

T. Don Tilley is a professor of chemistry at the University of California, Berkeley.

<span class="mw-page-title-main">Cyclic alkyl amino carbenes</span> Family of chemical compounds

In chemistry, cyclic(alkyl)(amino)carbenes (CAACs) are a family of stable singlet carbene ligands developed by the research group of Guy Bertrand in 2005 at UC Riverside. In marked contrast with the popular N-heterocyclic carbenes (NHCs) which possess two "amino" substituents adjacent to the carbene center, CAACs possess one "amino" substituent and an sp3 carbon atom "alkyl". This specific configuration makes the CAACs very good σ-donors and π-acceptors when compared to NHCs. Moreover the reduced heteroatom stabilization of the carbene center in CAACs versus NHCs also gives rise to a smaller ΔEST.

<span class="mw-page-title-main">Decamethylsilicocene</span> Chemical Compound

Decamethylsilicocene, (C5Me5)2Si, is a group 14 sandwich compound. It is an example of a main-group cyclopentadienyl complex; these molecules are related to metallocenes but contain p-block elements as the central atom. It is a colorless, air sensitive solid that sublimes under vacuum.

Metal arene complexes are organometallic compounds of the formula (C6R6)xMLy. Common classes are of the type (C6R6)ML3 and (C6R6)2M. These compounds are reagents in inorganic and organic synthesis. The principles that describe arene complexes extend to related organic ligands such as many heterocycles (e.g. thiophene) and polycyclic aromatic compounds (e.g. naphthalene).

<span class="mw-page-title-main">Plumbylene</span> Divalent organolead(II) analogues of carbenes

Plumbylenes (or plumbylidenes) are divalent organolead(II) analogues of carbenes, with the general chemical formula, R2Pb, where R denotes a substituent. Plumbylenes possess 6 electrons in their valence shell, and are considered open shell species.

<span class="mw-page-title-main">Lanthanocene</span>

A lanthanocene is a type of metallocene compound that contains an element from the lanthanide series. The most common lanthanocene complexes contain two cyclopentadienyl anions and an X type ligand, usually hydride or alkyl ligand.

A transition metal phosphido complex is a coordination complex containing a phosphido ligand (R2P, where R = H, organic substituent). With two lone pairs on phosphorus, the phosphido anion (R2P−) is comparable to an amido anion (R2N−), except that the M-P distances are longer and the phosphorus atom is more sterically accessible. For these reasons, phosphido is often a bridging ligand. The -PH2 ion or ligand is also called phosphanide or phosphido ligand.

β-Carbon elimination is a type of reaction in organometallic chemistry wherein an allyl ligand bonded to a metal center is broken into the corresponding metal-bonded alkyl (aryl) ligand and an alkene. It is a subgroup of elimination reactions. Though less common and less understood than β-hydride elimination, it is an important step involved in some olefin polymerization processes and transition-metal-catalyzed organic reactions.

Metal-ligand cooperativity (MLC) is a mode of reactivity in which a metal and ligand of a complex are both involved in the bond breaking or bond formation of a substrate during the course of a reaction. This ligand is an actor ligand rather than a spectator, and the reaction is generally only deemed to contain MLC if the actor ligand is doing more than leaving to provide an open coordination site. MLC is also referred to as "metal-ligand bifunctional catalysis." Note that MLC is not to be confused with cooperative binding.

References

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  2. ↑ Zhao, Lili; Chai, Chaoqun; Petz, Wolfgang; Frenking, Gernot (2020-10-26). "Carbones and Carbon Atom as Ligands in Transition Metal Complexes". Molecules. 25 (21): 4943. doi: 10.3390/molecules25214943 . ISSN   1420-3049. PMC   7663554 . PMID   33114580.
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  4. ↑ Emile H. Braye; Lawrence F. Dahl; Walter. Hubel; Dale L. Wampler (1962). "The Preparation, Properties and Structure of the Iron Carbonyl Carbide Fe5(CO)15C". J. Am. Chem. Soc. 84 (24): 4633–4639. doi:10.1021/ja00883a004.
  5. ↑ Wang, Ruiyao; Zheng, Zhiping; Koknat, Friedrich W.; Marko, David J.; Müller, Achim; Das, Samar K.; Krickemeyer, Erich; Kuhlmann, Christoph; Therrien, Bruno (2004-04-21), Shapley, John R. (ed.), "Cluster and Polynuclear Compounds", Inorganic Syntheses, Hoboken, NJ, USA: John Wiley & Sons, Inc., pp. 184–232, doi:10.1002/0471653683.ch5, ISBN   978-0-471-64750-8 , retrieved 2023-03-25
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  7. ↑ Hill, Ernestine W.; Bradley, John S.; Cassidy, Juanita; Whitmire, Kenton H. (2007-01-05), Ginsberg, Alvin P. (ed.), "Tetrairon Carbido Carbonyl Clusters", Inorganic Syntheses, Hoboken, NJ, USA: John Wiley & Sons, Inc., pp. 182–188, doi:10.1002/9780470132586.ch36, ISBN   978-0-470-13258-6 , retrieved 2023-03-25
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  9. ↑ Saha, Sumit; Zhu, Lei; Captain, Burjor (2013-03-04). "Bimetallic Octahedral Ruthenium–Nickel Carbido Cluster Complexes. Synthesis and Structural Characterization". Inorganic Chemistry. 52 (5): 2526–2532. doi:10.1021/ic302470w. ISSN   0020-1669. PMID   23421564.
  10. ↑ Hill, Anthony; Sharma, Willis (2012). "Heterodinuclear Bridging Carbido and Phosphocarbyne Complexes". Organometallics. 31 (7): 2538–2542. doi:10.1021/om201057c.
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  13. ↑ Frogley, Benjamin J.; Hill, Anthony F. (2020). "Carbyne decorated porphyrins". Dalton Transactions. 49 (35): 12390–12400. doi:10.1039/D0DT02809F. hdl: 1885/217011 . ISSN   1477-9226. PMID   32852027. S2CID   221347588.
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  15. ↑ Carlson, Robert G.; Gile, Melanie A.; Heppert, Joseph A.; Mason, Mark H.; Powell, Douglas R.; Vander Velde, David; Vilain, Joseph M. (2002). "The Metathesis-Facilitated Synthesis of Terminal Ruthenium Carbide Complexes: A Unique Carbon Atom Transfer Reaction". Journal of the American Chemical Society. 124 (8): 1580–1581. doi:10.1021/ja017088g. PMID   11853424.
  16. ↑ Caskey, Stephen (11 November 2005). "Two General Routes to Terminal Carbido Complexes". J. Am. Chem. Soc. 127 (48): 16750–16751. doi:10.1021/ja0453735. PMID   16316197.
  17. ↑ Enriquez, Alejandro E.; White, Peter S.; Templeton, Joseph L. (2001-05-01). "Reactions of an Amphoteric Terminal Tungsten Methylidyne Complex". Journal of the American Chemical Society. 123 (21): 4992–5002. doi:10.1021/ja0035001. ISSN   0002-7863. PMID   11457327.
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  19. ↑ Grotjahn, Douglas B.; Zeng, Xi; Cooksy, Andrew L. (2006-03-01). "Alkyne-to-Vinylidene Transformation on trans -(Cl)Rh(phosphine) 2: Acceleration by a Heterocyclic Ligand and Absence of Bimolecular Mechanism". Journal of the American Chemical Society. 128 (9): 2798–2799. doi:10.1021/ja058736p. ISSN   0002-7863.
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  21. ↑ Jamison, G. M.; White, P. S.; Templeton, J. L. (June 1991). "Synthesis of Group 6 (aryloxy)carbyne and phosphoniocarbyne complexes from chlorocarbyne precursors". Organometallics. 10 (6): 1954–1959. doi:10.1021/om00052a048. ISSN   0276-7333.
  22. ↑ Liu, Shiuh-Tzung; Hsieh, Tung-Ying; Lee, Gene-Hsiang; Peng, Shie-Ming (1998-03-01). "Carbene Transfer between Transition-Metal Ions". Organometallics. 17 (6): 993–995. doi:10.1021/om9709897. ISSN   0276-7333.
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  26. ↑ C. Peters, Jonas; L. Odom, Aaron; C. Cummins, Christopher (1997). "A terminal molybdenum carbide prepared by methylidyne deprotonation". Chemical Communications (20): 1995–1996. doi:10.1039/a704251e. ISSN   1359-7345.
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