Transition metal complexes of 1,10-phenanthroline

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Structure of PtCl2(1,10-phenanthroline). Color code: green = Cl, blue = N, gray = C. CSD CIF JEXXEQ.jpg
Structure of PtCl2(1,10-phenanthroline). Color code: green = Cl, blue = N, gray = C.

Transition metal complexes of 1,10-phenanthroline ("phen") are coordination complexes containing one or more 1,10-phenanthroline ligands. [2] Complexes have been described for many transition metals. In almost all complexes, phen serves as a bidentate ligand, binding metal centers with the two nitrogen atoms. Examples include PtCl2(phen) and [Fe(phen)3]2+.

Contents

Homoleptic complexes

Several homoleptic complexes are known of the type [M(phen)3]2+. Particularly well studied is [Fe(phen)3]2+, called "ferroin." It can be used for the photometric determination of Fe(II). [3] 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. [4] The pink complex [Ni(phen)3]2+ has been resolved into its Δ and Λ isomers. [5]

Copper(I) forms [Cu(phen)2]+, which is luminescent. [6] [7]

Bioinorganic chemistry

Structure of the metallointercalator [Ru(phen)2(dppz)] (dppz = dipyrido[3,2-a:2',3'-c]phenazine). Ru(phen)2(dppz)2+.svg
Structure of the metallointercalator [Ru(phen)2(dppz)] (dppz = dipyrido[3,2-a:2‘,3‘-c]phenazine).

It has long been known that some cationic metal-phen complexes intercalate into DNA. [8] These metallointercalators associate enantioselectively and exhibit distinctive optical properties. [9] [10]

1,10-Phenanthroline is an inhibitor of metallopeptidases, with one of the first observed instances reported in carboxypeptidase A. [11] 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. [12]

Modified phen ligands

A variety of substituted derivatives of phen have been examined as ligands. [7] [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. [14] Phen itself form complexes of the type [M(phen)3]Cl2 when treated with metal dihalides (M = Fe, Co, Ni). By contrast, neocuproine and bathocuproine form 1:1 complexes such as [Ni(neocuproine)Cl2]2. [15]

Basicities of 1,10-Phenanthrolines and 2,2'-Bipyridine [16]
phen derivativepKacomment/alt. namenumbering scheme
1,10-phenanthroline4.86phen Phenanthroline Numbering.png
2,2'-bipyridine 4.30bipy
5-nitro-1,10-phenanthroline3.57
2,9-dimethyl-1,10-phenanthrolineunknown neocuproine [17] [18]
2,9-Dimethyl-4,7-diphenylphenanthrolineunknown Bathocuproine [17] [19]
4,7-dimethyl-1,10-phenanthroline5.97
4,7-diphenyl-1,10-phenanthrolineunknownbathophenanthroline [20]
5,6-dimethyl-1,10-phenanthroline5.205,6-Me2phen
3,4,7,8-tetramethylphenanthroline6.313,4,7,8-Me4phen [21]
4,7-dimethoxy-1,10-phenanthroline6.454,7-(MeO)2phen [22]
2,6-dimesitylphenanthrolineunknownHETPHEN [23] [14]

1,10-Phenanthroline-5,6-dione is a phen-type ligand incorporating an ortho-quinone group. [24]

Comparison with bipyridine

Complexes of phen and those of 2,2'-bipyridine (bipyr) are similar: the metal-ligand ensemble is planar, which facilitates electron delocalization. As a consequence of this delocalization, phen complexes often exhibit distinctive optical and redox properties. With respective pKa's of 4.86 and 4.3 for their conjugate acids, phenanthroline and bipy are of comparable basicity. [25] In phenanthroline, the two nitrogen donors are preorganized for chelation. According to one ligand ranking scale, phen is a weaker donor than bipy. [26]

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References

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  11. ↑ Felber, Jean-Pierre; Coombs, Thomas L.; Vallee, Bert L. (1962). "The mechanism of inhibition of carboxypeptidase A by 1,10-phenanthroline". Biochemistry. 1 (2): 231–238. doi:10.1021/bi00908a006. PMID   13892106.
  12. ↑ Salvesen, GS & Nagase, H (2001). "Inhibition of proteolytic enzymes". In Beynon, Rob & Bond, J S (eds.). Proteolytic Enzymes: A Practical Approach. Vol. 1 (2nd ed.). Oxford University Press. pp. 105–130. ISBN   978-0-19-963662-4.
  13. ↑ Accorsi, Gianluca; Listorti, Andrea; Yoosaf, K.; Armaroli, Nicola (2009). "1,10-Phenanthrolines: Versatile building blocks for luminescent molecules, materials and metal complexes". Chemical Society Reviews. 38 (6): 1690–2300. doi:10.1039/B806408N. PMID   19587962.
  14. 1 2 Somerville, Rosie J.; Odena, Carlota; Obst, Marc F.; Hazari, Nilay; Hopmann, Kathrin H.; Martin, Ruben (2020). "Ni(I)–Alkyl Complexes Bearing Phenanthroline Ligands: Experimental Evidence for CO2 Insertion at Ni(I) Centers". Journal of the American Chemical Society. 142 (25): 10936–10941. Bibcode:2020JAChS.14210936S. doi:10.1021/jacs.0c04695. PMC   7351122 . PMID   32520556.
  15. ↑ Preston, H. S.; Kennard, C. H. L. (1969). "Crystal Structure of di-mu-Chloro-sym-trans-Dichloro-Bis-(2,9-Dimethyl-1,10-Phenanthroline)dinickel(II)-2-Chloroform". J. Chem. Soc. A: 2682–2685. doi:10.1039/J19690002682.
  16. ↑ Leipoldt, J.G.; Lamprecht, G.J.; Steynberg, E.C. (1991). "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. 402 (2): 259–263. doi:10.1016/0022-328X(91)83069-G.
  17. 1 2 Rezazadeh, Sina; Devannah, Vijayarajan; Watson, Donald A. (2017). "Nickel-Catalyzed C-Alkylation of Nitroalkanes with Unactivated Alkyl Iodides". Journal of the American Chemical Society. 139 (24): 8110–8113. doi:10.1021/jacs.7b04312. PMC   5531607 . PMID   28594543.
  18. ↑ Nilsson, Peter (2012). "Neocuproine". Encyclopedia of Reagents for Organic Synthesis. doi:10.1002/047084289X.rn01440. ISBN   978-0-471-93623-7.
  19. ↑ Liu, Guosheng; Wu, Yichen (2012). "Bathocuproine". Encyclopedia of Reagents for Organic Synthesis. doi:10.1002/047084289X.rn01392. ISBN   978-0-471-93623-7.
  20. ↑ Vallée, Frédéric; Kühn, Fritz E.; Korinth, Valentina A. (2013). "Bathophenanthroline". Encyclopedia of Reagents for Organic Synthesis. doi:10.1002/047084289X.rn01319.pub2. ISBN   978-0-471-93623-7.
  21. ↑ Zhu, Lingui; Altman, Ryan A. (2013). "3,4,7,8-Tetramethyl-1,10-phenanthroline (Tmphen)". Encyclopedia of Reagents for Organic Synthesis. doi:10.1002/047084289X.rn01515. ISBN   978-0-471-93623-7.
  22. ↑ Altman, Ryan A. (2008). "1,10-Phenanthroline, 4,7-Dimethoxy". Encyclopedia of Reagents for Organic Synthesis. eEROS. doi:10.1002/047084289X.rn00918. ISBN   978-0-471-93623-7.
  23. ↑ Kohler, Lars; Hayes, Dugan; Hong, Jiyun; Carter, Tyler J.; Shelby, Megan L.; Fransted, Kelly A.; Chen, Lin X.; Mulfort, Karen L. (2016). "Synthesis, structure, ultrafast kinetics, and light-induced dynamics of CuHETPHEN chromophores". Dalton Transactions. 45 (24): 9871–9883. doi:10.1039/c6dt00324a. PMID   26924711.
  24. ↑ Wendlandt, Alison E.; Stahl, Shannon S. (2014). "Modular o -Quinone Catalyst System for Dehydrogenation of Tetrahydroquinolines under Ambient Conditions". Journal of the American Chemical Society. 136 (34): 11910–11913. Bibcode:2014JAChS.13611910W. doi:10.1021/ja506546w. PMC   4151779 . PMID   25109345.
  25. ↑ J. G. Leipoldt; G. J. Lamprecht; E. C.Steynberg (1991). "Kinetics of the Substitution of Acetylacetone in Acetylactonato-1,5-cyclooctadienerhodium(I) by Derivatives of 1,10-Phenanthroline and 2,2′-Dipyridyl". Journal of Organometallic Chemistry. 402 (2): 259–263. doi:10.1016/0022-328X(91)83069-G.
  26. ↑ Teng, Qiaoqiao; Huynh, Han Vinh (2017). "A Unified Ligand Electronic Parameter Based on C NMR Spectroscopy of N-Heterocyclic Carbene Complexes". Dalton Transactions. 46 (3): 614–627. doi:10.1039/C6DT04222H. PMID   27924321.
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