1,10-Phenanthroline Explained

1,10-Phenanthroline (phen) is a heterocyclic organic compound. It is a white solid that is soluble in organic solvents. The 1,10 refer to the location of the nitrogen atoms that replace CH's in the hydrocarbon called phenanthrene.

Abbreviated "phen", it is used as a ligand in coordination chemistry, forming strong complexes with most metal ions.[1] [2] It is often sold as the monohydrate.

Synthesis

Phenanthroline may be prepared by two successive Skraup reactions of glycerol with o-phenylenediamine, catalyzed by sulfuric acid, and an oxidizing agent, traditionally aqueous arsenic acid or nitrobenzene.[3] Dehydration of glycerol gives acrolein which condenses with the amine followed by a cyclization.

Coordination chemistry

In terms of its coordination properties, phenanthroline is similar to 2,2'-bipyridine (bipy) with the advantage that the two nitrogen donors are preorganized for chelation. Phenanthroline is a stronger base than bipy. According to one ligand ranking scale, phen is a weaker donor than bipy.[4]

Several homoleptic complexes are known of the type [M(phen)<sub>3</sub>]2+. Particularly well studied is [Fe(phen)<sub>3</sub>]2+, called "ferroin." It can be used for the photometric determination of Fe(II).[5] It is used as a redox indicator with standard potential +1.06 V. The reduced ferrous form has a deep red colour and the oxidised form is light-blue.[6] The pink complex [Ni(phen)<sub>3</sub>]2+ has been resolved into its Δ and Λ isomers.[7] The complex [Ru(phen)<sub>3</sub>]2+ is bioactive.[8]

Copper(I) forms [Cu(phen)<sub>2</sub>]+, which is luminescent.[9]

Bioinorganic chemistry

1,10-Phenanthroline is an inhibitor of metallopeptidases, with one of the first observed instances reported in carboxypeptidase A.[10] Inhibition of the enzyme occurs by removal and chelation of the metal ion required for catalytic activity, leaving an inactive apoenzyme. 1,10-Phenanthroline targets mainly zinc metallopeptidases, with a much lower affinity for calcium.[11]

Related phen ligands

A variety of substituted derivatives of phen have been examined as ligands.[12] [13] Substituents at the 2,9 positions confer protection for the attached metal, inhibiting the binding of multiple equivalents of the phenanthroline. Such bulky ligands also favor trigonal or tetrahedral coordination at the metal. Phen itself form complexes of the type [M(phen)<sub>3</sub>]Cl2 when treated with metal dihalides (M = Fe, Co, Ni). By contrast, neocuproine and bathocuproine form 1:1 complexes such as [Ni(neocuproine)Cl<sub>2</sub>]2.[14]

Basicities of 1,10-Phenanthrolines and 2,2'-Bipyridine[15]
phen derivativepKacomment/alt. namenumbering scheme
1,10-phenanthroline 4.86phen
4.30bipy
5-nitro-1,10-phenanthroline 3.57
2,9-dimethyl-1,10-phenanthroline unknown neocuproine[16] [17]
2,9-Dimethyl-4,7-diphenylphenanthrolineunknownBathocuproine[18]
4,7-dimethyl-1,10-phenanthroline 5.97
4,7-diphenyl-1,10-phenanthroline unknown bathophenanthroline[19]
5,6-dimethyl-1,10-phenanthroline 5.205,6-Me2phen
3,4,7,8-tetramethylphenanthroline 6.313,4,7,8-Me4phen[20]
4,7-dimethoxy-1,10-phenanthroline 6.454,7-(MeO)2phen[21]
2,6-dimesitylphenanthrolineunknownHETPHEN[22] [23]

As an indicator for alkyllithium reagents

Alkyllithium reagents form deeply colored derivatives with phenanthroline. The alkyllithium content of solutions can be determined by treatment of such reagents with small amounts of phenanthroline (ca. 1 mg) followed by titration with alcohols to a colourless endpoint. Grignard reagents may be similarly titrated.[24]

Notes and References

  1. Luman, C.R. and Castellano, F.N. (2003) "Phenanthroline Ligands" in Comprehensive Coordination Chemistry II. Elsevier. .
  2. 10.1039/cs9942300327. 1,10-Phenanthroline: A versatile ligand. 1994. Sammes. Peter G.. Yahioglu. Gokhan. Chemical Society Reviews. 23. 5. 327.
  3. . 155–157 . 1946 . 10.1039/jr9460000155 . 20983293 . 43. Attempts to find new antimalarials. Part XXIV. Derivatives of o-phenanthroline (7 : 8 : 3 : 2-pyridoquinoline). Halcrow . Barbara E. . Kermack . William O. .
  4. Teng. Qiaoqiao. Huynh. Han Vinh. A Unified Ligand Electronic Parameter Based on C NMR Spectroscopy of N-Heterocyclic Carbene Complexes. Dalton Transactions. 2017. 46. 3. 614–627. 10.1039/C6DT04222H. 27924321.
  5. Belcher R . 1973 . Application of chelate Compounds in Analytical Chemistry . Pure and Applied Chemistry . 34 . 13–27 . 10.1351/pac197334010013 . 44054260 . free .
  6. Bellér . G. B. . Lente . G. B. . Fábián . I. N. . Central Role of Phenanthroline Mono-N-oxide in the Decomposition Reactions of Tris(1,10-phenanthroline)iron(II) and -iron(III) Complexes . Inorganic Chemistry . 49 . 9. 3968–3970 . 2010 . 20415494 . 10.1021/ic902554b.
  7. Book: Resolution of the tris-(1,10-Phenanthroline)Nickel(II) Ion . George B. Kauffman . Lloyd T. Takahashi . Inorganic Syntheses . 1966 . 5 . 227–232. 10.1002/9780470132395.ch60 . 978-0-470-13239-5 .
  8. Biological Activity of Complex Ions . . 170 . 190–191 . 1952 . 10.1038/170190a0 . 12982853 . 4318. 1952Natur.170..190D . Dwyer . F. P. . Gyarfas . Eleonora C. . Rogers . W. P. . Koch . Judith H. . 6483735 .
  9. Armaroli N . 2001 . Photoactive Mono- and Polynuclear Cu(I)-Phenanthrolines. A Viable Alternative to Ru(Ii)-Polypyridines? . Chemical Society Reviews . 30 . 2. 113–124 . 10.1039/b000703j .
  10. 10.1021/bi00908a006 . The mechanism of inhibition of carboxypeptidase A by 1,10-phenanthroline . Biochemistry . 1962 . 1 . 231–238 . 13892106 . 2. Felber . Jean-Pierre . Coombs . Thomas L. . Vallee . Bert L. .
  11. Book: Salvesen, GS . Nagase, H . amp . Inhibition of proteolytic enzymes . Proteolytic Enzymes: A Practical Approach. 2nd. 2001 . 1 . 105–130 . Beynon, Rob . Bond, J S . 978-0-19-963662-4. Oxford University Press.
  12. Pallenberg A. J. . Koenig K. S. . Barnhart D. M. . 1995 . Synthesis and Characterization of Some Copper(I) Phenanthroline Complexes . Inorganic Chemistry . 34 . 11. 2833–2840 . 10.1021/ic00115a009 .
  13. 10.1039/B806408N . 1,10-Phenanthrolines: Versatile building blocks for luminescent molecules, materials and metal complexes . 2009 . Accorsi . Gianluca . Listorti . Andrea . Yoosaf . K. . Armaroli . Nicola . Chemical Society Reviews . 38 . 6 . 1690–2300 . 19587962 .
  14. Preston, H. S. . Kennard, C. H. L. . Crystal Structure of di-mu-Chloro-sym-trans-Dichloro-Bis-(2,9-Dimethyl-1,10-Phenanthroline)dinickel(II)-2-Chloroform. J. Chem. Soc. A. 1969. 2682–2685. 10.1039/J19690002682.
  15. Kinetics of the substitution of acetylacetone in acetylactonato-1,5-cyclooctadienerhodium(I) by derivatives of 1,10-phenantrholine and 2,2-dipyridyl . Journal of Organometallic Chemistry. Leipoldt, J.G.. Lamprecht, G.J.. Steynberg, E.C. . 1991. 402. 2 . 259–263 . 10.1016/0022-328X(91)83069-G.
  16. 10.1021/jacs.7b04312. Nickel-Catalyzed C-Alkylation of Nitroalkanes with Unactivated Alkyl Iodides . 2017 . Rezazadeh . Sina . Devannah . Vijayarajan . Watson . Donald A. . Journal of the American Chemical Society . 139 . 24 . 8110–8113 . 28594543 . 5531607 .
  17. Book: 10.1002/047084289X.rn01440. Neocuproine . Encyclopedia of Reagents for Organic Synthesis . 2012 . Nilsson . Peter . 978-0-471-93623-7 .
  18. Book: 10.1002/047084289X.rn01392. Bathocuproine . Encyclopedia of Reagents for Organic Synthesis . 2012 . Liu . Guosheng . Wu . Yichen . 978-0-471-93623-7 .
  19. Book: 10.1002/047084289X.rn01319.pub2. Bathophenanthroline . Encyclopedia of Reagents for Organic Synthesis . 2013 . Vallée . Frédéric . Kühn . Fritz E. . Korinth . Valentina A. . 978-0-471-93623-7 .
  20. Book: 10.1002/047084289X.rn01515. 3,4,7,8-Tetramethyl-1,10-phenanthroline (Tmphen) . Encyclopedia of Reagents for Organic Synthesis . 2013 . Zhu . Lingui . Altman . Ryan A. . 978-0-471-93623-7 .
  21. Encyclopedia: eEROS. Encyclopedia of Reagents for Organic Synthesis. Altman, Ryan A. . 2008. 10.1002/047084289X.rn00918. 1,10-Phenanthroline, 4,7-Dimethoxy. 978-0-471-93623-7.
  22. 10.1039/c6dt00324a. Synthesis, structure, ultrafast kinetics, and light-induced dynamics of CuHETPHEN chromophores. 2016. Kohler. Lars. Hayes. Dugan. Hong. Jiyun. Carter. Tyler J.. Shelby. Megan L.. Fransted. Kelly A.. Chen. Lin X.. Mulfort. Karen L.. Dalton Transactions. 45. 24. 9871–9883. 26924711.
  23. 10.1021/jacs.0c04695. Ni(I)–Alkyl Complexes Bearing Phenanthroline Ligands: Experimental Evidence for CO2 Insertion at Ni(I) Centers. 2020. Somerville. Rosie J.. Odena. Carlota. Obst. Marc F.. Hazari. Nilay. Hopmann. Kathrin H.. Martin. Ruben. Journal of the American Chemical Society. 142. 25. 10936–10941. 32520556. 7351122. 2020JAChS.14210936S .
  24. A Convenient Method for Determining the Concentration of Grignard Reagents. Lin, Ho-Shen . Paquette, Leo A. . Synth. Commun. . 24 . 2503–2506 . 1994 . 10.1080/00397919408010560 . 17.

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