fbpx
Wikipedia

Transition metal alkyne complex

January 01, 1970

In organometallic chemistry, a transition metal alkyne complex is a coordination compound containing one or more alkyne ligands. Such compounds are intermediates in many catalytic reactions that convert alkynes to other organic products, e.g. hydrogenation and trimerization.[1]

Synthesis edit

Transition metal alkyne complexes are often formed by the displacement of labile ligands by the alkyne. For example, a variety of cobalt-alkyne complexes arise by the reaction of alkynes with dicobalt octacarbonyl.[2]

Co2(CO)8 + R2C2 → (R2C2)Co2(CO)6 + 2 CO

Many alkyne complexes are produced by reduction of metal halides:[3]

Cp2TiCl2 + Mg + Me3SiC≡CSiMe3 → Cp2Ti[(CSiMe3)2] + MgCl2

Structure and bonding edit

 
Structures of various metal-alkyne complexes.

The coordination of alkynes to transition metals is similar to that of alkenes. The bonding is described by the Dewar–Chatt–Duncanson model. Upon complexation the C-C bond elongates and the alkynyl carbon bends away from 180º. For example, in the phenylpropyne complex Pt(PPh3)2(MeC2Ph), the C-C distance is 1.277(25) vs 1.20 Å for a typical alkyne. The C-C-C angle distorts 40° from linearity upon complexation.[4] Because the bending induced by complexation, strained alkynes such as cycloheptyne and cyclooctyne are stabilized by complexation.[5]

The C≡C vibration of alkynes occurs near 2300 cm−1 in the IR spectrum. This mode shifts upon complexation to around 1800 cm−1, indicating a weakening of the C-C bond.

η2-coordination to a single metal center edit

When bonded side-on to a single metal atom, an alkyne serves as a dihapto usually two-electron donor. For early metal complexes, e.g., Cp2Ti(C2R2), strong π-backbonding into one of the π* antibonding orbitals of the alkyne is indicated. This complex is described as a metallacyclopropene derivative of Ti(IV). For late transition metal complexes, e.g., Pt(PPh3)2(MeC2Ph), the π-backbonding is less prominent, and the complex is assigned oxidation state 0.[6][7]

In some complexes, the alkyne is classified as a four-electron donor. In these cases, both pairs of pi-electrons donate to the metal. This kind of bonding was first implicated in complexes of the type W(CO)(R2C2)3.[8]

η2, η2-coordination bridging two metal centers edit

Because alkynes have two π bonds, alkynes can form stable complexes in which they bridge two metal centers. The alkyne donates a total of four electrons, with two electrons donated to each of the metals. And example of a complex with this bonding scheme is η2-diphenylacetylene-(hexacarbonyl)dicobalt(0).[7]

Benzyne complexes edit

Transition metal benzyne complexes represent a special case of alkyne complexes since the free benzynes are not stable in the absence of the metal.[9]

Applications edit

Metal alkyne complexes are intermediates in the semihydrogenation of alkynes to alkenes:

C2R2 + H2 → cis-C2R2H2

This transformation is conducted on a large scale in refineries, which unintentionally produce acetylene during the production of ethylene. It is also useful in the preparation of fine chemicals. Semihydrogenation affords cis alkenes.[10]

Metal-alkyne complexes are also intermediates in the metal-catalyzed trimerization and tetramerizations. Cyclooctatetraene is produced from acetylene via the intermediacy of metal alkyne complexes. Variants of this reaction are exploited for some syntheses of substituted pyridines.

The Pauson–Khand reaction provides a route to cyclopentenones via the intermediacy of cobalt-alkyne complexes.

 
PK reaction

Acrylic acid was once prepared by the hydrocarboxylation of acetylene:[11]

C2H2 + H2O + CO → H2C=CHCO2H

With the shift away from coal-based (acetylene) to petroleum-based feedstocks (olefins), catalytic reactions with alkynes are not widely practiced industrially.

Polyacetylene has been produced using metal catalysis involving alkyne complexes.

 
Ti-catalyzed polymerization of acetylene, inspired by Ziegler–Natta catalysis.

Cuprous chloride also catalyzes the dimerization of acetylene to vinylacetylene, once used as a precursor to various polymers such a neoprene. Mechanistic studies suggest that this reaction proceeds by insertion of acetylene into a copper(I) acetylide complex.[12]

References edit

  1. ^ Elschenbroich, C. ”Organometallics” 2006 Wiley-VCH: Weinheim. ISBN 3-527-29390-6.
  2. ^ Kemmitt, R. D. W.; Russell, D. R.; "Cobalt" in Comprehensive Organometallic Chemistry I; Abel, E.W.; Stone, F.G.A.; Wilkinson, G. eds., 1982, Pergamon Press, Oxford. ISBN 0-08-025269-9
  3. ^ Rosenthal, Uwe; Burlakov, Vladimir V.; Arndt, Perdita; Baumann, Wolfgang; Spannenberg, Anke (2003). "The Titanocene Complex of Bis(trimethylsilyl)acetylene: Synthesis, Structure, and Chemistry". Organometallics. 22 (5): 884–900. doi:10.1021/om0208570.
  4. ^ Davies, B. William; Payne, N. C. (1975). "Studies on Metal-Acetylene Complexes: V. Crystal and Molecular Structure of Bis(triphenylphosphine)(1-phenylpropyne)platinum(0), [P(C6H5)3]2(C6H5CCCH3)Pt0". J. Organomet. Chem. 99: 315. doi:10.1016/S0022-328X(00)88462-4.
  5. ^ Bennett, Martin A.; Schwemlein, Heinz P. (1989). "Metal Complexes of Small Cycloalkynes and Arynes". Angew. Chem. Int. Ed. Engl. 28 (10): 1296–1320. doi:10.1002/anie.198912961.
  6. ^ Hill, A.F. Organotransition Metal Chemistry, 2002, Royal Society of Chemistry, ISBN 0-471-28163-8.
  7. ^ a b Crabtree, R. H. Comprehensive Organometallic Chemistry V, 2009, John Wiley & Sons ISBN 978-0-470-25762-3 [verification needed]
  8. ^ Joseph L. Templeton (1989). "Four-Electron Alkyne Ligands in Molybdenum(II) and Tungsten(II) Complexes". Advances in Organometallic Chemistry'. 29: 1–100. doi:10.1016/S0065-3055(08)60352-4.
  9. ^ William M. Jones, Jerzy Klosin "Transition-Metal Complexes of Arynes, Strained Cyclic Alkynes, and Strained Cyclic Cumulenes" Advances in Organometallic Chemistry 1998, Volume 42, Pages 147–221. doi:10.1016/S0065-3055(08)60543-2
  10. ^ Michaelides, I. N.; Dixon, D. J. (2013). "Catalytic Stereoselective Semihydrogenation of Alkynes to E-Alkenes". Angew. Chem. Int. Ed. 52 (3): 806–808. doi:10.1002/anie.201208120. PMID 23255528.
  11. ^ W. Bertleff; M. Roeper; X. Sava. "Carbonylation". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a05_217. ISBN 978-3527306732.
  12. ^ Trotuş, Ioan-Teodor; Zimmermann, Tobias; Schüth, Ferdi (2014). "Catalytic Reactions of Acetylene: A Feedstock for the Chemical Industry Revisited". Chemical Reviews. 114 (3): 1761–1782. doi:10.1021/cr400357r. PMID 24228942.

January 01, 1970
transition, metal, alkyne, complex, organometallic, chemistry, transition, metal, alkyne, complex, coordination, compound, containing, more, alkyne, ligands, such, compounds, intermediates, many, catalytic, reactions, that, convert, alkynes, other, organic, pr. In organometallic chemistry a transition metal alkyne complex is a coordination compound containing one or more alkyne ligands Such compounds are intermediates in many catalytic reactions that convert alkynes to other organic products e g hydrogenation and trimerization 1 Contents 1 Synthesis 2 Structure and bonding 2 1 h2 coordination to a single metal center 2 2 h2 h2 coordination bridging two metal centers 2 3 Benzyne complexes 3 Applications 4 ReferencesSynthesis editTransition metal alkyne complexes are often formed by the displacement of labile ligands by the alkyne For example a variety of cobalt alkyne complexes arise by the reaction of alkynes with dicobalt octacarbonyl 2 Co2 CO 8 R2C2 R2C2 Co2 CO 6 2 CO Many alkyne complexes are produced by reduction of metal halides 3 Cp2TiCl2 Mg Me3SiC CSiMe3 Cp2Ti CSiMe3 2 MgCl2Structure and bonding edit nbsp Structures of various metal alkyne complexes The coordination of alkynes to transition metals is similar to that of alkenes The bonding is described by the Dewar Chatt Duncanson model Upon complexation the C C bond elongates and the alkynyl carbon bends away from 180º For example in the phenylpropyne complex Pt PPh3 2 MeC2Ph the C C distance is 1 277 25 vs 1 20 A for a typical alkyne The C C C angle distorts 40 from linearity upon complexation 4 Because the bending induced by complexation strained alkynes such as cycloheptyne and cyclooctyne are stabilized by complexation 5 The C C vibration of alkynes occurs near 2300 cm 1 in the IR spectrum This mode shifts upon complexation to around 1800 cm 1 indicating a weakening of the C C bond h2 coordination to a single metal center edit When bonded side on to a single metal atom an alkyne serves as a dihapto usually two electron donor For early metal complexes e g Cp2Ti C2R2 strong p backbonding into one of the p antibonding orbitals of the alkyne is indicated This complex is described as a metallacyclopropene derivative of Ti IV For late transition metal complexes e g Pt PPh3 2 MeC2Ph the p backbonding is less prominent and the complex is assigned oxidation state 0 6 7 In some complexes the alkyne is classified as a four electron donor In these cases both pairs of pi electrons donate to the metal This kind of bonding was first implicated in complexes of the type W CO R2C2 3 8 h2 h2 coordination bridging two metal centers edit Because alkynes have two p bonds alkynes can form stable complexes in which they bridge two metal centers The alkyne donates a total of four electrons with two electrons donated to each of the metals And example of a complex with this bonding scheme is h2 diphenylacetylene hexacarbonyl dicobalt 0 7 Benzyne complexes edit Transition metal benzyne complexes represent a special case of alkyne complexes since the free benzynes are not stable in the absence of the metal 9 Applications editMetal alkyne complexes are intermediates in the semihydrogenation of alkynes to alkenes C2R2 H2 cis C2R2H2 This transformation is conducted on a large scale in refineries which unintentionally produce acetylene during the production of ethylene It is also useful in the preparation of fine chemicals Semihydrogenation affords cis alkenes 10 Metal alkyne complexes are also intermediates in the metal catalyzed trimerization and tetramerizations Cyclooctatetraene is produced from acetylene via the intermediacy of metal alkyne complexes Variants of this reaction are exploited for some syntheses of substituted pyridines The Pauson Khand reaction provides a route to cyclopentenones via the intermediacy of cobalt alkyne complexes nbsp PK reaction Acrylic acid was once prepared by the hydrocarboxylation of acetylene 11 C2H2 H2O CO H2C CHCO2H With the shift away from coal based acetylene to petroleum based feedstocks olefins catalytic reactions with alkynes are not widely practiced industrially Polyacetylene has been produced using metal catalysis involving alkyne complexes nbsp Ti catalyzed polymerization of acetylene inspired by Ziegler Natta catalysis Cuprous chloride also catalyzes the dimerization of acetylene to vinylacetylene once used as a precursor to various polymers such a neoprene Mechanistic studies suggest that this reaction proceeds by insertion of acetylene into a copper I acetylide complex 12 References edit Elschenbroich C Organometallics 2006 Wiley VCH Weinheim ISBN 3 527 29390 6 Kemmitt R D W Russell D R Cobalt in Comprehensive Organometallic Chemistry I Abel E W Stone F G A Wilkinson G eds 1982 Pergamon Press Oxford ISBN 0 08 025269 9 Rosenthal Uwe Burlakov Vladimir V Arndt Perdita Baumann Wolfgang Spannenberg Anke 2003 The Titanocene Complex of Bis trimethylsilyl acetylene Synthesis Structure and Chemistry Organometallics 22 5 884 900 doi 10 1021 om0208570 Davies B William Payne N C 1975 Studies on Metal Acetylene Complexes V Crystal and Molecular Structure of Bis triphenylphosphine 1 phenylpropyne platinum 0 P C6H5 3 2 C6H5CCCH3 Pt0 J Organomet Chem 99 315 doi 10 1016 S0022 328X 00 88462 4 Bennett Martin A Schwemlein Heinz P 1989 Metal Complexes of Small Cycloalkynes and Arynes Angew Chem Int Ed Engl 28 10 1296 1320 doi 10 1002 anie 198912961 Hill A F Organotransition Metal Chemistry 2002 Royal Society of Chemistry ISBN 0 471 28163 8 a b Crabtree R H Comprehensive Organometallic Chemistry V 2009 John Wiley amp Sons ISBN 978 0 470 25762 3 verification needed Joseph L Templeton 1989 Four Electron Alkyne Ligands in Molybdenum II and Tungsten II Complexes Advances in Organometallic Chemistry 29 1 100 doi 10 1016 S0065 3055 08 60352 4 William M Jones Jerzy Klosin Transition Metal Complexes of Arynes Strained Cyclic Alkynes and Strained Cyclic Cumulenes Advances in Organometallic Chemistry 1998 Volume 42 Pages 147 221 doi 10 1016 S0065 3055 08 60543 2 Michaelides I N Dixon D J 2013 Catalytic Stereoselective Semihydrogenation of Alkynes to E Alkenes Angew Chem Int Ed 52 3 806 808 doi 10 1002 anie 201208120 PMID 23255528 W Bertleff M Roeper X Sava Carbonylation Ullmann s Encyclopedia of Industrial Chemistry Weinheim Wiley VCH doi 10 1002 14356007 a05 217 ISBN 978 3527306732 Trotus Ioan Teodor Zimmermann Tobias Schuth Ferdi 2014 Catalytic Reactions of Acetylene A Feedstock for the Chemical Industry Revisited Chemical Reviews 114 3 1761 1782 doi 10 1021 cr400357r PMID 24228942 Retrieved from https en wikipedia org w index php title Transition metal alkyne complex amp oldid 1222609967 Applications, wikipedia, wiki, book, books, library,

article

, read, download, free, free download, mp3, video, mp4, 3gp, jpg, jpeg, gif, png, picture, music, song, movie, book, game, games.