2,2'-Dipyrromethene, often called just dipyrromethene or dipyrrin, is a chemical compound with formula whose skeleton can be described as two

pyrrole Pyrrole is a heterocyclic aromatic organic compound, a five-membered ring with the formula C4 H4 NH. It is a colorless volatile liquid that darkens readily upon exposure to air. Substituted derivatives are also called pyrroles, e.g., ''N''-meth ...

rings connected by a methyne bridge =CH– through their nitrogen-adjacent (position-2) carbons; the remaining bonds being satisfied by hydrogen atoms. It is an unstable compound that is readily attacked by

nucleophyl In chemistry, a nucleophile is a chemical species that forms bonds by donating an electron pair. All molecules and ions with a free pair of electrons or at least one pi bond can act as nucleophiles. Because nucleophiles donate electrons, they are ...

ic compounds above −40 °C. 2,2'-Dipyrromethene and its more stable and easily prepared derivatives—formally obtained by replacing one or more hydrogen atoms by other functional groups—are important precursors for the family of BODIPY fluorescent dies. The derivatives include salts of the dipyrrinato anion and of the

cation An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...

Preparation

2,2'-Dipyrromethene and its derivatives can be obtained from suitable pyrrole derivatives by several methods. The unsubstituted compound can be prepared by oxidation of

2,2'-dipyrrolemethane The comma is a punctuation mark that appears in several variants in different languages. It has the same shape as an apostrophe or single closing quotation mark () in many typefaces, but it differs from them in being placed on the baseline ...

with

2,3-dichloro-5,6-dicyano-1,4-benzoquinone 2,3-Dichloro-5,6-dicyano-1,4-benzoquinone (or DDQ) is the chemical reagent with formula C6Cl2(CN)2O2. This oxidant is useful for the dehydrogenation of alcohols, phenols, and steroid ketones. DDQ decomposes in water, but is stable in aqueous mine ...

(DDQ) at −78 °C in dry

dichloromethane Dichloromethane (DCM or methylene chloride, methylene bichloride) is an organochlorine compound with the formula . This colorless, volatile liquid with a chloroform-like, sweet odour is widely used as a solvent. Although it is not miscible with ...

solution. An alternative synthesis that avoids the oxidation step is the condensation of 2-formyl pyrrole and pyrrole catalyzed by trifluoroacetic acid, followed by deprotonation with N,N-diisopropylethylamine. More generally, one starts with a pyrrole with suitable substituents at positions 3, 4, or 5 (but not 2). Condensation of two such molecules at their 2 positions with a bridging compound gives the corresponding 2,2'-dipyrromethane. The condensation may use, for example, the Knorr pyrrole synthesis, with an aromatic aldehyde in the presence of TFA. The dipyrromethane core is then oxidized to dipyrromethene using a

quinone The quinones are a class of organic compounds that are formally "derived from aromatic compounds

uch as benzene or naphthalene Uch ( pa, ; ur, ), frequently referred to as Uch Sharīf ( pa, ; ur, ; ''"Noble Uch"''), is a historic city in the southern part of Pakistan's Punjab province. Uch may have been founded as Alexandria on the Indus, a town founded by Alexand ...

by conversion of an even number of –CH= groups into –C(=O)– groups with any necessary rearrangement of double ...

oxidant such as

DDQ 2,3-Dichloro-5,6-dicyano-1,4-benzoquinone (or DDQ) is the chemical reagent with formula C6Cl2(CN)2O2. This oxidant is useful for the dehydrogenation of alcohols, phenols, and steroid ketones. DDQ decomposes in water, but is stable in aqueous mi ...

or p-chloranil. Dipyrromethene synthesis

Alternatively, one may use an activated

carboxylic acid In organic chemistry, a carboxylic acid is an organic acid that contains a carboxyl group () attached to an R-group. The general formula of a carboxylic acid is or , with R referring to the alkyl, alkenyl, aryl, or other group. Carboxylic ...

derivative, usually an acyl chloride. As another possibility, one may condense a substituted pyrroles with a 2-acylpyrrole; this route allows the synthesis of unsymmetrical dipyrromethenes.

Reactions

Dipyrrin is unstable above −40 °C. However, its acts as a base, and its chloride [] [] is sufficiently stable in solution. The so-called BODIPY, BODIPY dyes can be obtained by reacting 2,2'-dipyrromethene or its derivatives with boron trifluoride-diethyl ether complex (·) in the presence of triethylamine or 1,8-diazabicyclo .4.0ndec-7-ene (DBU). Dipyrrin and its derivatives for coordination complexes with transition metals. For example, the derivative anion 5-phenyl dipirrinato (pdp) forms the neutral iron(III) complex (dark green monoclinic crystals, soluble in benzene, orange solution in

), where the ion is coordinated to six nitrogen atoms of the dipyrrin cores in distorted octahedral geometry. A similar cobalt(III) complex has also been reported, as well as a complex with copper(II)

References

Seth M Cohen and Sara R Halper (2002): "Dipyrromethene complexes of iron". ''Inorganica Chimica Acta'', volume 341, pages 12-16. Sara R. Halper, Mitchell R. Malachowski, Heather M. Delaney, and Seth M. Cohen (2004): "Heteroleptic copperdipyrromethene complexes: synthesis, structure,and coordination polymers". ''Inorganic Chemistry'', volume 43, pages 1242−1249 =K. Tram, H. Yan, H. A. Jenkins, S. Vassiliev, and D. Bruce (2009): "The synthesis and crystal structure of unsubstituted 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY)". ''Dyes and Pigments'', volume 82, issue 3, pages = 392–395. A. Schmitt, B. Hinkeldey, M. Wild , and G. Jung (): "Synthesis of the core compound of the BODIPY dye class: 4,4′-difluoro-4-bora-(3a,4a)-diaza-s-indacene". ''Journal of Fluorescence'', volume = 19, issue = 4, pages = 755–759 Brandon R. Groves, Sarah M. Crawford,a Travis Lundrigan, Chérif F. Matta, Shahin Sowlati-Hashjin, and Alison Thompson (2013): "Synthesis and characterisation of the unsubstituted dipyrrin and 4,4-dichloro-4-bora-3a,4a-diaza-s-indacene: improved synthesis and functionalisation of the simplest BODIPY framework." ''Chemical Communications'', volume 49, pages 816-818. pyrroles {{DEFAULTSORT:Dipyrromethene, 2,2'-