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Salen ligand

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Salen ligand
Names
Other names
2,2′-Ethylenebis(nitrilomethylidene)diphenol, N , N ′-Ethylenebis(salicylimine)
Identifiers
3D model ( JSmol )
ChEMBL
ChemSpider
ECHA InfoCard 100.002.161 Edit this at Wikidata
EC Number
  • 202-376-3
UNII
  • InChI=1S/C16H16N2O2/c19-15-7-3-1-5-13(15)11-17-9-10-18-12-14-6-2-4-8-16(14)20/h1-8,11-12,19-20H,9-10H2/b17-11+,18-12+
    Key: VEUMANXWQDHAJV-JYFOCSDGSA-N
  • C1=CC=C(C(=C1)/C=N/CC/N=C/C2=CC=CC=C2O)O
Properties
C 16 H 16 N 2 O 2
Molar mass 268.32
Melting point 126 °C (259 °F; 399 K)
Hazards
GHS labelling :
GHS07: Exclamation mark
Warning
H315 , H319 , H335
P261 , P264 , P271 , P280 , P302+P352 , P304+P340 , P305+P351+P338 , P312 , P321 , P332+P313 , P337+P313 , P362 , P403+P233 , P405 , P501
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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This article is about Salen. For Complexes of salen and related ligands, see Metal salen complexes .

Salen refers to a tetradentate C 2 -symmetric ligand synthesized from salicylaldehyde ( sal ) and ethylenediamine ( en ). It may also refer to a class of compounds, which are structurally related to the classical salen ligand, primarily bis- Schiff bases . Salen ligands are notable for coordinating a wide range of different metals, which they can often stabilise in various oxidation states. [1] For this reason salen-type compounds are used as metal deactivators . Metal salen complexes also find use as catalysts . [2]

Synthesis and properties [ edit ]

H 2 salen may be synthesized by the condensation of ethylenediamine and salicylaldehyde. [3]

Salcomine, a complex of salen with cobalt
Jacobsen's salen-Mn catalyst

Complexes of salen with metal cations may be made without isolating it from the reaction mixture. [4] [5] This is possible because the stability constant for the formation of the metal complexes are very high, due to the chelate effect .

H 2 L + M n+ → ML (n?2)+ + 2 H +

where L stands for the ligand. The pyridine adduct of the cobalt(II) complex Co(salen)(py) ( salcomine ) has a square-pyramidal structure ; it can act as a dioxygen carrier by forming a labile, octahedral O 2 complex. [6] [7]

The name "salen ligands" is used for tetradentate ligands which have similar structures. For example, in salpn there is a methyl substituent on the bridge. It is used as a metal deactivation additive in fuels. [8] The presence of bulky groups near the coordination site may enhance the catalytic activity of a metal complex and prevent its dimerization. Salen ligands derived from 3,5-di- tert -butylsalicylaldehyde fulfill these roles, and also increase the solubility of the complexes in non-polar solvents like pentane . Chiral "salen" ligands may be created by proper substitution of the diamine backbone, the phenyl ring, or both. [5] An example is the ligand obtained by condensation of the C 2 -symmetric trans -1,2- diaminocyclohexane with 3,5-di- tert -butylsalicylaldehyde. Chiral ligands may be used in asymmetric synthesis reactions, such as the Jacobsen epoxidation : [9] [10]

Related ligands [ edit ]

Synthesis and complexation of Jager's ligand. [11]

A class of tetradentate ligands with the generic name acacen are obtained by the condensation of derivatives of acetylacetone and ethylenediamine . [11] Cobalt complexes [Co(acacen)L 2 ] + , selectively inhibit the activities of histidine-containing proteins through exchange of the axial ligands. These compounds show promise for the inhibition of oncogenesis . [12]

The salan and salalen ligands are similar in structure to salen ligands, but have one or two saturated nitrogen-aryl bonds ( amines rather than imines ). They tend to be less rigid and more electron rich at the metal center than the corresponding salen complexes. [13] [14] Salans can be synthesized by the alkylation of an appropriate amine with a phenolic alkyl halide . The “half-salen” ligands have only one salicylimine group. They are prepared from a salicylaldehyde and a monoamine. [15]

The name “salen” or “salen-type” may be used for other ligands that have similar environment around the chelating site, namely two acidic hydroxyls and two Schiff base (aryl- imine ) groups. These include the ligands abbreviated as salph, from the condensation of 1,2-phenylenediamine and salicylaldehyde, and salqu , from the condensation of salicylaldehyde and 2-quinoxalinol . [16]

See also [ edit ]

References [ edit ]

  1. ^ Cozzi, Pier Giorgio (2004). "Metal?Salen Schiff base complexes in catalysis: practical aspects". Chem. Soc. Rev . 33 (7): 410?421. doi : 10.1039/B307853C . PMID   15354222 .
  2. ^ Shaw, Subrata; White, James D. (11 June 2019). "Asymmetric Catalysis Using Chiral Salen?Metal Complexes: Recent Advances". Chemical Reviews . 119 (16): 9381?9426. doi : 10.1021/acs.chemrev.9b00074 . PMID   31184109 . S2CID   184486101 .
  3. ^ Tsumaki, T. (1938). "Nebenvalenzringverbindungen. IV. Uber einige innerkomplexe Kobaltsalze der Oxyaldimine" . Bulletin of the Chemical Society of Japan (in German). 13 (2): 252?260. doi : 10.1246/bcsj.13.252 .
  4. ^ Diehl, Harvey; Hach, Clifford C. (1950). "Bis( N,N '-Disalicylalethylenediamine)-μ - Aquodicobalt(II)". Inorganic Syntheses . Vol. 3. pp. 196?201. doi : 10.1002/9780470132340.ch53 . ISBN   978-0-470-13234-0 . {{ cite book }} : |journal= ignored ( help )
  5. ^ a b Pier Giorgio Cozzi (2004). "Metal-Salen Schiff base complexes in catalysis: Practical aspects". Chem. Soc. Rev . 33 (7): 410?421. doi : 10.1039/B307853C . PMID   15354222 .
  6. ^ Appleton, T. G. (1977). "Oxygen Uptake by a Cobalt(II) Complex". J. Chem. Educ. 54 (7): 443. doi : 10.1021/ed054p443 .
  7. ^ Yamada, Shoichiro (1999). "Advancement in stereochemical aspects of Schiff base metal complexes". Coordination Chemistry Reviews . 190?192: 537?555. doi : 10.1016/S0010-8545(99)00099-5 .
  8. ^ Dabelstein, W.; Reglitzky A.; Schutze A.; Reders, K. "Automotive Fuels". Ullmann's Encyclopedia of Industrial Chemistry . Weinheim: Wiley-VCH. doi : 10.1002/14356007.a16_719.pub2 . ISBN   978-3527306732 . {{ cite encyclopedia }} : CS1 maint: multiple names: authors list ( link )
  9. ^ Larrow, J. F.; Jacobsen, E. N. (2004). "( R , R )- N , N'- Bis(3,5-Di- tert -Butylsalicylidene)-1,2-Cyclohexanediamino Manganese(III) Chloride, A Highly Enantioselective Epoxidation Catalyst" . Organic Syntheses ; Collected Volumes , vol. 10, p. 96 .
  10. ^ Yoon, TP; Jacobsen, EN (2003). "Privileged Chiral Catalysts". Science . 299 (5613): 1691?1693. Bibcode : 2003Sci...299.1691Y . doi : 10.1126/science.1083622 . PMID   12637734 . S2CID   27416160 .
  11. ^ a b Weber, Birgit; Jager, Ernst-G. (2009). "Structure and Magnetic Properties of Iron(II/III) Complexes with N
    2     O 2?
    2     -Coordinating Schiff Base-Like Ligands". Eur. J. Inorg. Chem. : 455. doi : 10.1002/ejic.200990003 .
  12. ^ Bajema, Elizabeth A.; Kaleigh F. Roberts; Meade, Thomas J. (2019). "Chapter 11. Cobalt-Schiff Base Complexes:Preclinical Research and Potential Therapeutic Uses". In Sigel, Astrid; Freisinger, Eva; Sigel, Roland K. O.; Carver, Peggy L. (Guest editor) (eds.). Essential Metals in Medicine:Therapeutic Use and Toxicity of Metal Ions in the Clinic . Vol. 19. Berlin: de Gruyter GmbH. pp. 267?301. doi : 10.1515/9783110527872-017 . ISBN   978-3-11-052691-2 . PMID   30855112 . S2CID   73727460 . {{ cite book }} : |editor4-first= has generic name ( help ) ; |journal= ignored ( help )
  13. ^ Atwood, David A.; Remington, Michael P.; Rutherford, Drew (1996). "Use of the Salan Ligands to Form Bimetallic Aluminum Complexes". Organometallics . 15 (22): 4763. doi : 10.1021/om960505r .
  14. ^ Berkessel, Albrecht; Brandenburg, Marc; Leitterstorf, Eva; Frey, Julia; Lex, Johann; Schafer, Mathias (2007). "A Practical and Versatile Access to Dihydrosalen (Salalen) Ligands: Highly Enantioselective Titanium. In Situ Catalysts for Asymmetric Epoxidation with Aqueous Hydrogen Peroxide". Adv. Synth. Catal. 349 (14?15): 2385. doi : 10.1002/adsc.200700221 .
  15. ^ Pang, Xuan; Duan, Ranlong; Li, Xiang; Sun, Zhiqiang; Zhang, Han; Wang, Xianhong; Chen, Xuesi (2014). "Synthesis and characterization of half-salen complexes and their application in the polymerization of lactide and ε-caprolactone". Polymer Chemistry . 5 (23): 6857?6864. doi : 10.1039/C4PY00734D .
  16. ^ Wu, Xianghong, Gorden, A. V. E. (2009). "2-Quinoxalinol Salen Copper Complexes for Oxidation of Aryl Methylenes". Eur. J. Org. Chem. 2009 (4): 503?509. doi : 10.1002/ejoc.200800928 . {{ cite journal }} : CS1 maint: multiple names: authors list ( link )
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