Transition metal carbene complex

Last updated

A transition metal carbene complex is an organometallic compound featuring a divalent carbon ligand, itself also called a carbene. [1] Carbene complexes have been synthesized from most transition metals and f-block metals, [2] using many different synthetic routes such as nucleophilic addition and alpha-hydrogen abstraction. [1] The term carbene ligand is a formalism since many are not directly derived from carbenes and most are much less reactive than lone carbenes. [2] Described often as =CR2, carbene ligands are intermediate between alkyls (−CR3) and carbynes (≡CR). Many different carbene-based reagents such as Tebbe's reagent are used in synthesis. They also feature in catalytic reactions, especially alkene metathesis, and are of value in both industrial heterogeneous and in homogeneous catalysis for laboratory- and industrial-scale preparation of fine chemicals. [1] [3] [4]

Contents

Classification

Metal carbene complexes are often classified into two types. The Fischer carbenes, named after Ernst Otto Fischer, feature strong π-acceptors at the metal and are electrophilic at the carbene carbon atom. Schrock carbenes, named after Richard R. Schrock, are characterized by more nucleophilic carbene carbon centers; these species typically feature higher oxidation state (valency) metals. N-Heterocyclic carbenes (NHCs) were popularized following Arduengo's isolation of a stable free carbene in 1991. [5] Reflecting the growth of the area, carbene complexes are now known with a broad range of different reactivities and diverse substituents. Often it is not possible to classify a carbene complex solely with regards to its electrophilicity or nucleophilicity. [1]

Fischer carbenes

Example Fisher carbene with chromium(0) centre and diethylamine donor. Fisher Carbene 2.png
Example Fisher carbene with chromium(0) centre and diethylamine donor.

The common features of Fisher carbenes are: [6]

Examples include (CO)5W=COMePh and (OC)5Cr=C(NR2)Ph.

Orbital interaction in a Fisher carbene. The carbene electrons are donated to a sigma bond, and weak pi-backbonding occurs. Fisher Orbitals.png
Orbital interaction in a Fisher carbene. The carbene electrons are donated to a sigma bond, and weak pi-backbonding occurs.

Fisher carbene complexes are related to the singlet form of carbenes, where both electrons occupy the same sp2 orbital at the carbon. This lone pair donates to a metal-based empty d orbital, forming a σ bond. π-backbonding from a filled metal d orbital to the empty p orbital of the carbon atom is possible. However this interaction is generally weak since the alpha donor atoms also donate to this orbital. As such, fisher carbenes are characterized as having partial double bond character. The major resonance structures of Fisher carbenes put the negative charge on the metal centre, and the positive on the carbon atom, making it electrophilic. [6]

Major resonance structures of (CO)5W=COMePh. Structures with a positive charge on carbon are significant and make the carbon electrophilic. Fisher Resonance V2.png
Major resonance structures of (CO)5W=COMePh. Structures with a positive charge on carbon are significant and make the carbon electrophilic.

Fischer carbenes can be likened to ketones, with the carbene carbon atom being electrophilic, like the carbonyl carbon atom of a ketone. This can be seen from the resonance structures, where there is a significant contribution from the structure bearing a positive carbon centre. [6] Like ketones, Fischer carbene species can undergo aldol-like reactions. The hydrogen atoms attached to the carbon atom α to the carbene carbon atom are acidic, and can be deprotonated by a base such as n-butyllithium, to give a nucleophile, which can undergo further reaction. [7]

Schrock carbenes

Structure of (C5H5)2TaCH3(CH2), as determined by X-ray crystallography. The Ta-CH3 and Ta=CH2 distances are 2.37 and 2.04 A, respectively. Color code: blue = Ta, gray = C, white = H. CSD CIF CPMTAA10.png
Structure of (C5H5)2TaCH3(CH2), as determined by X-ray crystallography. The Ta−CH3 and Ta=CH2 distances are 2.37 and 2.04 Å, respectively. Color code: blue = Ta, gray = C, white = H.

Schrock carbenes do not have π-accepting ligands on the metal centre. They are often called alkylidene complexes. Typically this subset of carbene complexes are found with: [6]

Examples include ((CH3)3CCH2)Ta=CHC(CH3)3 [9] and Os(PPh3)2(NO)Cl(=CH2). [10]

Orbital interaction in the bonding of a Schrock carbene. Both the metal and carbon provide 2 unpaired electron each, forming the double bond. Schrock Orbitals.png
Orbital interaction in the bonding of a Schrock carbene. Both the metal and carbon provide 2 unpaired electron each, forming the double bond.

Bonding in such complexes can be viewed as the coupling of a triplet state metal and triplet carbene, forming a true double bond. Both the metal and carbon atom donate 2 electrons, one to each bond. Since there is no donation to the carbene atom from adjacent groups, the extent of pi backbonding is much greater, giving a strong double bond. These bonds are weakly polarized towards carbon and therefore the carbene atom is a nucleophile. Furthermore, the major resonance structures of Schrock carbene put the negative charge on the carbon atom, making it nucleophilic. [6] Complexes with the methylidene ligand (=CH2) are the simplest Schrock-type carbenes.

Major resonance structures of a Schrock carbene. The negative charge at the carbon atom renders it nucleophilic. Schrock Resonance V2.png
Major resonance structures of a Schrock carbene. The negative charge at the carbon atom renders it nucleophilic.

N-Heterocyclic carbenes

IMes is a common NHC ligand. 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (aka IMes).png
IMes is a common NHC ligand.

N-Heterocyclic carbenes (NHCs) are particularly common carbene ligands. [11] They are popular because they are more readily prepared than Schrock and Fischer carbenes. In fact, many NHCs are isolated as the free ligand, since they are persistent carbenes. [12] [13] Being strongly stabilized by π-donating substituents, NHCs are powerful σ-donors but π-bonding with the metal is weak. [14] For this reason, the bond between the carbon and the metal center is often represented by a single dative bond, whereas Fischer and Schrock carbenes are usually depicted with double bonds to metal. Continuing with this analogy, NHCs are often compared with trialkylphosphine ligands. Like phosphines, NHCs serve as spectator ligands that influence catalysis through a combination of electronic and steric effects, but they do not directly bind substrates. [15] [16]

Bimetallic carbene complexes

An early example of this bonding mode was provided by [C5Me5Mn(CO)2]2(μ−CO) prepared from diazomethane:

2 C5Me5Mn(CO)2(thf) + CH2N2 → [C5Me5Mn(CO)2]2(μ−CH2] + N2 + 2 thf

Another example of this family of compounds is Tebbe's reagent. It features a methylene bridge joining titanium and aluminum. [17]

Application of Metal Carbenes

Metal carbene complexes have applications in hetereogeneous and homogeneous catalysis, and as reagents for organic reactions.

Catalysis

Catalytic cycle of olefin metathesis. The metal complex alternated between a metallocyclobutane ring and carbene complex, catalyzing the formation of new carbon-carbon double bonds. Olefin Metathesis Catalytic Cycle.png
Catalytic cycle of olefin metathesis. The metal complex alternated between a metallocyclobutane ring and carbene complex, catalyzing the formation of new carbon-carbon double bonds.

The dominant application of metal carbenes involves none of the above classes of compounds, but rather heterogeneous catalysts used for alkene metathesis for the synthesis of higher alkenes. A variety of related reactions are used to interconvert light alkenes, e.g. butenes, propylene, and ethylene. [18] Carbene complexes are invoked as intermediates in the Fischer–Tropsch route to hydrocarbons. [3]

A variety of homogeneous carbene catalysts, especially the Grubbs' ruthenium and Schrock molybdenum-imido catalysts have been used for olefin metathesis in laboratory-scale synthesis of natural products and materials science. [4]

Stoichiometric reactions

Homogeneous Schrock-type carbene complexes such as Tebbe's reagent can be used for the olefination of carbonyls, replacing the oxygen atom with a methylidene group. The nucleophilic carbon atom behaves similarly to the carbon atom of the phosphorus ylide in the Wittig reaction, attacking the electrophilic carbonyl atom of a ketone, followed by elimination of a metal oxide. [1]

Olefination of an ester using Tebbe's reagent as a methylidene source. Tebbe's Reaction.png
Olefination of an ester using Tebbe's reagent as a methylidene source.

In the nucleophilic abstraction reaction, a methyl group can be abstracted from the donating group of a Fischer carbene, making it a strong nucleophile for further reaction. [6]

Nucleophilic abstraction of the methyl group of a Fisher carbene. The negatively charge oxygen is a nucleophile which can undergo further reaction. Abstraction Reaction.png
Nucleophilic abstraction of the methyl group of a Fisher carbene. The negatively charge oxygen is a nucleophile which can undergo further reaction.

Diazo compounds like methyl phenyldiazoacetate can be used for cyclopropanation or to insert into C-H bonds of organic substrates. These reactions are catalyzed by dirhodium tetraacetate or related chiral derivatives. Such catalysis is assumed to proceed via the intermediacy of carbene complexes. [19]

Catalytic cycle for the insertion of carbenes into carbon-hydrogen bonds. The metal carbene is generated by nitrogen elimination from the diazo compound, and then inserts into the C-H bond. Diazo C-H Insertion.png
Catalytic cycle for the insertion of carbenes into carbon-hydrogen bonds. The metal carbene is generated by nitrogen elimination from the diazo compound, and then inserts into the C-H bond.

Wulff-Dötz Reaction

Fischer carbenes are used with alkynes as the starting reagents for the Wulff–Dötz reaction, forming phenols. [20]

General reaction scheme for the Wullf-Dotz reaction, making phenols from Fisher carbene complexes and alkynes. Wulff-Dotz reaction to a chromium half-sandwich complex.png
General reaction scheme for the Wullf-Dötz reaction, making phenols from Fisher carbene complexes and alkynes.

History

The first metal carbene complex, Chugaev's red salt, was not recognized as such until decades after its preparation. Chugaev's Carbene.svg
The first metal carbene complex, Chugaev's red salt, was not recognized as such until decades after its preparation.

The first metal carbene complex to have been reported was Chugaev's red salt, first synthesized as early as 1925, although it was never identified to be a carbene complex. [21] The characterization of (CO)5W(COCH3(Ph)) in the 1960s is often cited as the starting point of the area and Ernst Otto Fischer, for this and other achievements in organometallic chemistry, was awarded the 1973 Nobel Prize in Chemistry. [22] In 1968, Hans-Werner Wanzlick and Karl Öfele separately reported metal-bonded N-heterocyclic carbenes. [6] [23] [24] The synthesis and characterization of ((CH3)3CCH2)Ta=CHC(CH3)3 by Richard R. Schrock in 1974 marked the first metal alkylidene complex. [9] In 1991, Anthony J. Arduengo synthesized and crystallized the first persistent carbene, an NHC with large adamantane alkyl groups, accelerating the field of N-heterocarbene ligands to its current use. [5] [6]

See also

Related Research Articles

<span class="mw-page-title-main">Organometallic chemistry</span> Study of organic compounds containing metal(s)

Organometallic chemistry is the study of organometallic compounds, chemical compounds containing at least one chemical bond between a carbon atom of an organic molecule and a metal, including alkali, alkaline earth, and transition metals, and sometimes broadened to include metalloids like boron, silicon, and selenium, as well. Aside from bonds to organyl fragments or molecules, bonds to 'inorganic' carbon, like carbon monoxide, cyanide, or carbide, are generally considered to be organometallic as well. Some related compounds such as transition metal hydrides and metal phosphine complexes are often included in discussions of organometallic compounds, though strictly speaking, they are not necessarily organometallic. The related but distinct term "metalorganic compound" refers to metal-containing compounds lacking direct metal-carbon bonds but which contain organic ligands. Metal β-diketonates, alkoxides, dialkylamides, and metal phosphine complexes are representative members of this class. The field of organometallic chemistry combines aspects of traditional inorganic and organic chemistry.

In organic chemistry, a carbene is a molecule containing a neutral carbon atom with a valence of two and two unshared valence electrons. The general formula is R−:C−R' or R=C: where the R represents substituents or hydrogen atoms.

<span class="mw-page-title-main">Olefin metathesis</span> Organic reaction involving the breakup and reassembly of alkene double bonds

In organic chemistry, olefin metathesis is an organic reaction that entails the redistribution of fragments of alkenes (olefins) by the scission and regeneration of carbon-carbon double bonds. Because of the relative simplicity of olefin metathesis, it often creates fewer undesired by-products and hazardous wastes than alternative organic reactions. For their elucidation of the reaction mechanism and their discovery of a variety of highly active catalysts, Yves Chauvin, Robert H. Grubbs, and Richard R. Schrock were collectively awarded the 2005 Nobel Prize in Chemistry.

<span class="mw-page-title-main">Organoboron chemistry</span> Study of compounds containing a boron-carbon bond

Organoboron chemistry or organoborane chemistry studies organoboron compounds, also called organoboranes. These chemical compounds combine boron and carbon; typically, they are organic derivatives of borane (BH3), as in the trialkyl boranes.

<span class="mw-page-title-main">Persistent carbene</span> Type of carbene demonstrating particular stability

A persistent carbene is an organic molecule whose natural resonance structure has a carbon atom with incomplete octet, but does not exhibit the tremendous instability typically associated with such moieties. The best-known examples and by far largest subgroup are the N-heterocyclic carbenes (NHC), in which nitrogen atoms flank the formal carbene.

In organic chemistry, umpolung or polarity inversion is the chemical modification of a functional group with the aim of the reversal of polarity of that group. This modification allows secondary reactions of this functional group that would otherwise not be possible. The concept was introduced by D. Seebach and E.J. Corey. Polarity analysis during retrosynthetic analysis tells a chemist when umpolung tactics are required to synthesize a target molecule.

The triazol-5-ylidenes are a group of persistent carbenes which includes the 1,2,4-triazol-5-ylidene system and the 1,2,3-triazol-5-ylidene system. As opposed to the now ubiquitous NHC systems based on imidazole rings, these carbenes are structured from triazole rings. 1,2,4-triazol-5-ylidene can be thought of as an analog member of the NHC family, with an extra nitrogen in the ring, while 1,2,3-triazol-5-ylidene is better thought of as a mesoionic carbene (MIC). Both isomers of this group of carbenes benefit from enhanced stability, with certain examples exhibiting greater thermal stability, and others extended shelf life.

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

Organoruthenium chemistry is the chemistry of organometallic compounds containing a carbon to ruthenium chemical bond. Several organoruthenium catalysts are of commercial interest and organoruthenium compounds have been considered for cancer therapy. The chemistry has some stoichiometric similarities with organoiron chemistry, as iron is directly above ruthenium in group 8 of the periodic table. The most important reagents for the introduction of ruthenium are ruthenium(III) chloride and triruthenium dodecacarbonyl.

<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.

Organogold chemistry is the study of compounds containing gold–carbon bonds. They are studied in academic research, but have not received widespread use otherwise. The dominant oxidation states for organogold compounds are I with coordination number 2 and a linear molecular geometry and III with CN = 4 and a square planar molecular geometry.

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.

Metal carbon dioxide complexes are coordination complexes that contain carbon dioxide ligands. Aside from the fundamental interest in the coordination chemistry of simple molecules, studies in this field are motivated by the possibility that transition metals might catalyze useful transformations of CO2. This research is relevant both to organic synthesis and to the production of "solar fuels" that would avoid the use of petroleum-based fuels.

<span class="mw-page-title-main">Carbene radical</span> Special class of organometallic carbenes

Carbene radicals are a special class of organometallic carbenes. The carbene radical can be formed by one-electron reduction of Fischer-type carbenes using an external reducing agent, or directly upon carbene formation at an open-shell transition metal complex using diazo compounds and related carbene precursors. Cobalt(III)-carbene radicals have found catalytic applications in cyclopropanation reactions, as well as in a variety of other catalytic radical-type ring-closing reactions.

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

In coordination chemistry, a transition metal NHC complex is a metal complex containing one or more N-heterocyclic carbene ligands. Such compounds are the subject of much research, in part because of prospective applications in homogeneous catalysis. One such success is the second generation Grubbs catalyst.

<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.

A Fischer carbene is a type of transition metal carbene complex, which is an organometallic compound containing a divalent organic ligand. In a Fischer carbene, the carbene ligand is a σ-donor π-acceptor ligand. Because π-backdonation from the metal centre is generally weak, the carbene carbon is electrophilic.

<span class="mw-page-title-main">Carbones</span> Class of molecules

Carbones are a class of molecules containing a carbon atom in the 1D excited state with a formal oxidation state of zero where all four valence electrons exist as unbonded lone pairs. These carbon-based compounds are of the formula CL2 where L is a strongly σ-donating ligand, typically a phosphine (carbodiphosphoranes) or a N-heterocyclic carbene/NHC (carbodicarbenes), that stabilises the central carbon atom through donor-acceptor bonds. Carbones possess high-energy orbitals with both σ- and π-symmetry, making them strong Lewis bases and strong π-backdonor substituents. Carbones possess high proton affinities and are strong nucleophiles which allows them to function as ligands in a variety of main group and transition metal complexes. Carbone-coordinated elements also exhibit a variety of different reactivities and catalyse various organic and main group reactions.  

<i>N</i>-Heterocyclic carbene boryl anion Isoelectronic structure

An N-heterocyclic carbene boryl anion is an isoelectronic structure of an N-heterocyclic carbene (NHC), where the carbene carbon is replaced with a boron atom that has a -1 charge. NHC boryl anions have a planar geometry, and the boron atom is considered to be sp2-hybridized. They serve as extremely strong bases, as they are very nucleophilic. They also have a very strong trans influence, due to the σ-donation coming from the boron atom. NHC boryl anions have stronger electron-releasing character when compared to normal NHCs. These characteristics make NHC boryl anions key ligands in many applications, such as polycyclic aromatic hydrocarbons, and more commonly low oxidation state main group element bonding.

<span class="mw-page-title-main">Organoberyllium chemistry</span> Organoberyllium Complex in Main Group Chemistry

Organoberyllium chemistry involves the synthesis and properties of organometallic compounds featuring the group 2 alkaline earth metal beryllium (Be). The area remains understudied, relative to the chemistry of other main-group elements, because although metallic beryllium is relatively unreactive, its dust causes berylliosis and compounds are toxic. Organoberyllium compounds are typically prepared by transmetallation or alkylation of beryllium chloride.

A molecular electron-reservoir complex is one of a class of redox-active systems which can store and transfer electrons stoichiometrically or catalytically without decomposition. The concept of electron-reservoir complexes was introduced by the work of French chemist, Didier Astruc. From Astruc's discoveries, a whole family of thermally stable, neutral, 19-electron iron(I) organometallic complexes were isolated and characterized, and found to have applications in redox catalysis and electrocatalysis. The following page is a reflection of the prototypal electron-reservoir complexes discovered by Didier Astruc.

References

  1. 1 2 3 4 5 Elschenbroich, Christoph; Elschenbroich, Christoph (2011). Organometallics (3, compl. rev. and extended ed.). Weinheim: WILEY-VCH. ISBN   978-3-527-29390-2.
  2. 1 2 Arnold, Polly L.; Casely, Ian J. (2009-08-12). "F-Block N-Heterocyclic Carbene Complexes". Chemical Reviews. 109 (8): 3599–3611. doi:10.1021/cr8005203. ISSN   0009-2665.
  3. 1 2 Herrmann, Wolfgang A. (February 1982). "Organometallic Aspects of the Fischer‐Tropsch Synthesis". Angewandte Chemie International Edition in English. 21 (2): 117–130. doi:10.1002/anie.198201171. ISSN   0570-0833.
  4. 1 2 Fürstner, Alois (2000-09-01). "Olefin Metathesis and Beyond". Angewandte Chemie. 39 (17): 3012–3043. doi:10.1002/1521-3773(20000901)39:17<3012::AID-ANIE3012>3.0.CO;2-G.
  5. 1 2 Arduengo III AJ, Harlow RL, Kline M (1991). "A stable crystalline carbene". J. Am. Chem. Soc. 113 (1): 361–363. doi:10.1021/ja00001a054.
  6. 1 2 3 4 5 6 7 8 de Frémont, Pierre; Marion, Nicolas; Nolan, Steven P. (April 2009). "Carbenes: Synthesis, properties, and organometallic chemistry". Coordination Chemistry Reviews. 253 (7–8): 862–892. doi:10.1016/j.ccr.2008.05.018. ISSN   0010-8545.
  7. ↑ Crabtree RH (2005). The Organometallic Chemistry of the Transition Metals (4th ed.). New Jersey: Wiley-Interscience. ISBN   978-0-471-66256-3.
  8. ↑ "A neutron diffraction study of bis(cyclopentadienyl)(methyl)(methylene)tantalum(V) at 15 K". Acta Crystallographica Section C Crystal Structure Communications. 44 (3): 439–443. 1988-03-15. doi:10.1107/S0108270187010527. hdl: 1808/17672 .
  9. 1 2 Schrock, Richard R. (October 1974). "Alkylcarbene complex of tantalum by intramolecular .alpha.-hydrogen abstraction". Journal of the American Chemical Society. 96 (21): 6796–6797. doi:10.1021/ja00828a061. ISSN   0002-7863.
  10. ↑ Hill, Anthony F.; Roper, Warren R.; Waters, Joyce M.; Wright, Anthony H. (September 1983). "A mononuclear, low-valent, electron-rich osmium methylene complex". Journal of the American Chemical Society. 105 (18): 5939–5940. doi:10.1021/ja00356a050. ISSN   0002-7863.
  11. ↑ Hahn FE, Jahnke MC (2008). "Heterocyclic carbenes: synthesis and coordination chemistry". Angewandte Chemie. 47 (17): 3122–72. doi:10.1002/anie.200703883. PMID   18398856.
  12. ↑ Aldeco-Perez E, Rosenthal AJ, Donnadieu B, Parameswaran P, Frenking G, Bertrand G (October 2009). "Isolation of a C5-deprotonated imidazolium, a crystalline "abnormal" N-heterocyclic carbene". Science. 326 (5952): 556–9. Bibcode:2009Sci...326..556A. doi:10.1126/science.1178206. PMC   2871154 . PMID   19900893.
  13. ↑ Arduengo AJ, Goerlich JR, Marshall WJ (2002-05-01). "A stable diaminocarbene". J. Am. Chem. Soc. 117 (44): 11027–11028. doi:10.1021/ja00149a034.
  14. ↑ Fillman KL, Przyojski JA, Al-Afyouni MH, Tonzetich ZJ, Neidig ML (February 2015). "N-heterocyclic carbene complexes". Chemical Science. 6 (2): 1178–1188. doi:10.1039/c4sc02791d. PMC   4302958 . PMID   25621143.
  15. ↑ Przyojski JA, Veggeberg KP, Arman HD, Tonzetich ZJ (2015-09-08). "Mechanistic Studies of Catalytic Carbon–Carbon Cross-Coupling by Well-Defined Iron NHC Complexes". ACS Catalysis. 5 (10): 5938–5946. doi:10.1021/acscatal.5b01445.
  16. ↑ Przyojski JA, Arman HD, Tonzetich ZJ (2012-12-18). "NHC Complexes of Cobalt(II) Relevant to Catalytic C–C Coupling Reactions". Organometallics. 32 (3): 723–732. doi:10.1021/om3010756.
  17. ↑ Herrmann, W. A. (1982). "The methylene bridge: A Challenge to Synthetic, Mechanistic and Structural Organometallic Chemistry". Pure and Applied Chemistry. 54: 65–82. doi:10.1351/pac198254010065.
  18. ↑ Mol, J (2004-04-13). "Industrial applications of olefin metathesis". Journal of Molecular Catalysis A: Chemical. 213 (1): 39–45. doi:10.1016/j.molcata.2003.10.049. ISSN   1381-1169.
  19. ↑ Davies, Huw M. L.; Morton, Daniel (2011-03-21). "Guiding principles for site selective and stereoselective intermolecular C–H functionalization by donor/acceptor rhodium carbenes". Chemical Society Reviews. 40 (4): 1857–1869. doi:10.1039/C0CS00217H. ISSN   1460-4744.
  20. ↑ Denmark, Scott E., ed. (2004-04-30). Organic Reactions (1 ed.). Wiley. doi:10.1002/0471264180.or070.02. ISBN   978-0-471-26418-7.
  21. 1 2 Hahn, F. Ekkehardt; Jahnke, Mareike C. (2008-04-14). "Heterocyclic Carbenes: Synthesis and Coordination Chemistry". Angewandte Chemie International Edition. 47 (17): 3122–3172. doi:10.1002/anie.200703883. ISSN   1433-7851.
  22. ↑ Fischer, E. O.; Maasböl, A. (August 1964). "On the Existence of a Tungsten Carbonyl Carbene Complex". Angewandte Chemie International Edition in English. 3 (8): 580–581. doi:10.1002/anie.196405801. ISSN   0570-0833.
  23. ↑ Wanzlick, H.‐W.; Schönherr, H.‐J. (February 1968). "Direct Synthesis of a Mercury Salt‐Carbene Complex". Angewandte Chemie International Edition in English. 7 (2): 141–142. doi:10.1002/anie.196801412. ISSN   0570-0833.
  24. ↑ Öfele, K. (June 1968). "1,3-Dimethyl-4-imidazolinyliden-(2)-pentacarbonylchrom ein neuer übergangsmetall-carben-komplex". Journal of Organometallic Chemistry. 12 (3): P42–P43. doi:10.1016/s0022-328x(00)88691-x. ISSN   0022-328X.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.