63262-06-6

Basic information

• Product Name: 1,4-DIBROMO-2,5-DIIODOBENZENE
• Synonyms: 1,4-DIBROMO-2,5-DIIODOBENZENE;1,4-dibroMo-2,5-diiodobenzenex;1,4-Dibromo-2,5-diiodobenzene 99%;1,4-Dibromo-2,5-diiodobenzene99%;Benzene, 1,4-dibromo-2,5-diiodo-;OC1702, 1,4-Dibromo-2,5-diiodobenzene
• CAS NO: 63262-06-6
• Molecular Formula: C₆H₂Br₂I₂
• Molecular Weight: 487.7
• Product Categories: Aryl;Organohalides
• Mol File: 63262-06-6.mol
• Article Data: 33

Chemical Properties

• Melting Point: 163-165℃
• Boiling Point: 377.174°C at 760 mmHg
• Flash Point: 181.909°C
• Appearance: /
• Density: 2.938
• Vapor Pressure: 0mmHg at 25°C
• Refractive Index: 1.748
• Storage Temp.: 2-8°C(protect from light)
• Solubility: soluble in Toluene
• Sensitive: Light Sensitive
• CAS DataBase Reference: 1,4-DIBROMO-2,5-DIIODOBENZENE(CAS DataBase Reference)
• NIST Chemistry Reference: 1,4-DIBROMO-2,5-DIIODOBENZENE(63262-06-6)
• EPA Substance Registry System: 1,4-DIBROMO-2,5-DIIODOBENZENE(63262-06-6)

Safety Data

• Hazard Codes: Xi
• Hazardous Substances Data: 63262-06-6(Hazardous Substances Data)

Usage

Description

1,4-DIBROMO-2,5-DIIODOBENZENE is an organic compound with the molecular formula C6Br2I2. It is a halogenated aromatic compound characterized by the presence of two bromine atoms at the 1,4-positions and two iodine atoms at the 2,5-positions on a benzene ring. 1,4-DIBROMO-2,5-DIIODOBENZENE is known for its unique chemical properties and reactivity, making it a valuable building block in the synthesis of various advanced materials and compounds.

Uses

Used in Organic Synthesis:
1,4-DIBROMO-2,5-DIIODOBENZENE is used as a synthetic intermediate for the preparation of Benzo[1,2-b:4,5-b'']dithiophene (B200100), a compound with potential applications in the development of novel materials and chemicals.
Used in Organic Photovoltaic Cells:
1,4-DIBROMO-2,5-DIIODOBENZENE is used as a reagent in the synthesis of high-crystalline medium-band-gap polymers, which are essential components in the fabrication of organic photovoltaic cells. These polymers contribute to the efficiency and performance of the solar cells by facilitating the absorption of sunlight and the generation of electric current.
Used in Organic Electroluminescence Devices:
Benzo[1,2-b:4,5-b'']dithiophene, derived from 1,4-DIBROMO-2,5-DIIODOBENZENE, serves as a precursor in the preparation of benzodithiophene derivatives. These derivatives are valuable materials in the field of organic electroluminescence devices, where they can be utilized as hole injection materials, hole transport materials, or fluorescent materials. These applications are crucial for the development of advanced display technologies and lighting systems with improved energy efficiency and performance.

InChI:InChI=1/C6H2Br2I2/c7-3-1-5(9)4(8)2-6(3)10/h1-2H

Synthetic route

1.4-dibromobenzene (106-37-6) → 1,4-dibromo-2,5-diiodobenzene (63262-06-6)

Conditions	Yield
With sulfuric acid; iodine at 125 - 135℃; for 48h; Inert atmosphere;	84%
With sulfuric acid; iodine at 125 - 135℃; for 24h;	81%
With sulfuric acid; iodine at 130℃; for 8h;	80%

2,5-dibromo-4-iodoaniline → 1,4-dibromo-2,5-diiodobenzene (63262-06-6)

Conditions	Yield
Stage #1: 2,5-dibromo-4-iodoaniline With sulfuric acid; acetic acid; sodium nitrite In water at 0 - 50℃; for 1h; Stage #2: With potassium iodide In water at 20 - 25℃; for 2h;	83.3%

1,4-dibromo-2-nitrobenzene (3460-18-2) → 1,4-dibromo-2,5-diiodobenzene (63262-06-6)

Conditions	Yield
Multi-step reaction with 3 steps 1.1: iron; acetic acid / water / 3 h / 50 °C / pH 4 - 5 2.1: N-iodo-succinimide / dimethyl sulfoxide / 2 h / 20 - 30 °C 3.1: sodium nitrite; sulfuric acid; acetic acid / water / 1 h / 0 - 50 °C 3.2: 2 h / 20 - 25 °C View Scheme

1,3-dichloro-2-ethynyl-benzene (6575-25-3) + 1,4-dibromo-2,5-diiodobenzene (63262-06-6) → C22H8Br2Cl4

Conditions	Yield
With bis-triphenylphosphine-palladium(II) chloride; copper(l) iodide; triethylamine In toluene at 20℃; for 5h; Sonogashira Cross-Coupling; Inert atmosphere;	99%

2-octyl-1-ethynylbenzene + 1,4-dibromo-2,5-diiodobenzene (63262-06-6) → 2,2'-((2,5-dibromo-1,4-phenylene)bis(ethyne-2,1-diyl))bis(octylbenzene)

Conditions	Yield
With piperidine; bis-triphenylphosphine-palladium(II) chloride; copper(l) iodide; triethylamine at 20℃; Inert atmosphere;	99%

1,4-dibromo-2,5-diiodobenzene (63262-06-6) + 2-methyl-but-3-yn-2-ol (115-19-5) → 4,4‘-(2,5-dibromo-1,4-phenylene)bis(2-methylbut-3-yn-2-ol) (1191421-83-6)

Conditions	Yield
With bis-triphenylphosphine-palladium(II) chloride; copper(l) iodide; diisopropylamine In benzene at 20℃; Sonogashira coupling; Inert atmosphere;	98%
With bis-triphenylphosphine-palladium(II) chloride; copper(l) iodide; triethylamine for 17h; Inert atmosphere; Reflux;	9.3 g

C18H28OSi + 1,4-dibromo-2,5-diiodobenzene (63262-06-6) → C42H56Br2O2Si2

Conditions	Yield
With bis-triphenylphosphine-palladium(II) chloride; copper(l) iodide; diisopropylamine In tert-butyl methyl ether at -78 - 60℃; for 7h; Sonogashira Cross-Coupling;	98%

1,4-dibromo-2,5-diiodobenzene (63262-06-6) + trimethylsilylacetylene (1066-54-2) → 1,4-dibromo-2,5-bis-(trimethylsilylethynyl)benzene (478190-79-3)

Conditions	Yield
With bis-triphenylphosphine-palladium(II) chloride; copper(l) iodide; diisopropylamine In benzene at 20℃; for 1h; Sonogashira coupling;	97%
With (1,1'-bis(diphenylphosphino)ferrocene)palladium(II) dichloride; copper(l) iodide; diethylamine at 0 - 20℃; for 8h; Inert atmosphere;	92%
With copper(l) iodide; diisopropylamine; bis-triphenylphosphine-palladium(II) chloride In tetrahydrofuran at 20℃; for 12h; Sonogashira cross-coupling;	90%

1,4-dibromo-2,5-diiodobenzene (63262-06-6) + phenylboronic acid (98-80-6) → 2’,5’-dibromo-1,1’:4’,1’’-terphenyl (1089173-60-3)

Conditions	Yield
With tris-(dibenzylideneacetone)dipalladium(0); potassium carbonate; tris-(o-tolyl)phosphine In water; toluene for 12h; Suzuki-Miyaura Coupling; Inert atmosphere; Schlenk technique; Heating;	96%
With tris-(dibenzylideneacetone)dipalladium(0); potassium carbonate; tris-(o-tolyl)phosphine In water; toluene at 90℃; for 12h;	96%
With bis-triphenylphosphine-palladium(II) chloride; potassium carbonate; triphenylphosphine In water; toluene for 24h; Suzuki Coupling; Reflux; Inert atmosphere;	90%

tributyl(thien-2-yl)stannane (54663-78-4) + 1,4-dibromo-2,5-diiodobenzene (63262-06-6) → 1,4-bis(2-thienyl)-2,5-dibromobenzene (1049822-69-6)

Conditions	Yield
With bis-triphenylphosphine-palladium(II) chloride In N,N-dimethyl-formamide at 80℃; for 40h; Inert atmosphere; Schlenk technique;	93%
With bis-triphenylphosphine-palladium(II) chloride In N,N-dimethyl-formamide at 80℃; for 2h; Inert atmosphere;	70%
With bis-triphenylphosphine-palladium(II) chloride In toluene at 110℃;	65%

C17H24O + 1,4-dibromo-2,5-diiodobenzene (63262-06-6) → C40H48Br2O2

Conditions	Yield
With copper(l) iodide; tetrakis(triphenylphosphine) palladium(0); diisopropylamine In tetrahydrofuran at 60℃; for 12h;	93%

1,4-dibromo-2,5-diiodobenzene (63262-06-6) + 4-tert-butylphenylboronic acid (123324-71-0) → 1,4-dibromo-2,5-bis(4-tert-butylphenyl)benzene (608534-46-9)

Conditions	Yield
With tetrakis(triphenylphosphine) palladium(0); potassium carbonate In toluene at 95℃; for 18h; Suzuki cross-coupling reaction;	92%
With tetrakis(triphenylphosphine) palladium(0); potassium carbonate In 1,4-dioxane; water at 90℃; for 24h; Suzuki Coupling;	71.8%
With tetrakis(triphenylphosphine) palladium(0); potassium carbonate In 1,4-dioxane; water at 90℃; for 24h; Suzuki Coupling; Schlenk technique; Inert atmosphere;	68%

1-Heptyne (628-71-7) + 1,4-dibromo-2,5-diiodobenzene (63262-06-6) → 1,4-dibromo-2,5-di(hept-1-yn-1-yl)benzene

Conditions	Yield
With bis-triphenylphosphine-palladium(II) chloride; copper(l) iodide; triethylamine In dichloromethane-d2 at 20℃; Sonogashira Cross-Coupling; Inert atmosphere;	92%

2,6-dimethoxy-4-dodecyl-phenylboronic acid (1252579-70-6) + 1,4-dibromo-2,5-diiodobenzene (63262-06-6) → C46H68Br2O4

Conditions	Yield
Stage #1: 2,6-dimethoxy-4-dodecyl-phenylboronic acid; 1,4-dibromo-2,5-diiodobenzene With sodium carbonate In ethanol; water; toluene at 80℃; for 1h; Inert atmosphere; Stage #2: With tetrakis(triphenylphosphine) palladium(0) In ethanol; water; toluene at 80℃; for 24h; Inert atmosphere;	91%

3',5'-di-tert-butyl-3-[(triisopropylsilanyl)-ethynyl]-4-(4-trimethylsilanyl-buta-1,3-diynyl)-biphenyl (865096-72-6) + 1,4-dibromo-2,5-diiodobenzene (63262-06-6) → C76H92Br2Si2

Conditions	Yield
With potassium hydroxide; copper(l) iodide; diisopropylamine; tetrakis(triphenylphosphine) palladium(0) In tetrahydrofuran; water at 40℃; for 16h; Sonogashira reaction;	90%

(trifluoromethyl)trimethylsilane (81290-20-2) + 1,4-dibromo-2,5-diiodobenzene (63262-06-6) → 1,4-bis(trifluoromethyl)-2,5-dibromobenzene (2375-96-4)

Conditions	Yield
Stage #1: (trifluoromethyl)trimethylsilane With potassium fluoride; copper(l) iodide; 1,10-Phenanthroline In N,N-dimethyl-formamide at 30 - 40℃; for 1h; Inert atmosphere; Stage #2: 1,4-dibromo-2,5-diiodobenzene In N,N-dimethyl-formamide at 60℃; for 3h; Inert atmosphere;	90%

1,4-dibromo-2,5-diiodobenzene (63262-06-6) + N,N-dibutyl-4-((trimethylsilyl)ethynyl)aniline (667865-53-4) → 1,4-dibromo-2,5-bis[(4-(N,N-dibutylamino)phenyl)ethynyl]benzene (478190-81-7)

Conditions	Yield
With potassium hydroxide; copper(l) iodide; diisopropylamine; tetrakis(triphenylphosphine) palladium(0) In tetrahydrofuran; water at 20℃; Sonogashira cross-coupling;	89%

1,4-dibromo-2,5-diiodobenzene (63262-06-6) + N-phenylbenzamidine (1527-91-9) → 1,2,5,6-tetraphenyl-1,5-dihydrobenzo[1,2-d:4,5-d']diimidazole (133531-74-5)

Conditions	Yield
With palladium diacetate; 4,5-bis(diphenylphos4,5-bis(diphenylphosphino)-9,9-dimethylxanthenephino)-9,9-dimethylxanthene; sodium t-butanolate In toluene at 140℃; for 24h; Molecular sieve; Inert atmosphere; regiospecific reaction;	88%

9-(prop-2-yn-1-yl)nonadecane + 1,4-dibromo-2,5-diiodobenzene (63262-06-6) → 1,4-dibromo-2,5-bis(4-octyltetradec-1-yn-1-yl)benzene

Conditions	Yield
With bis-triphenylphosphine-palladium(II) chloride; copper(l) iodide; triethylamine In tetrahydrofuran at 20℃; Inert atmosphere;	88%
With bis-triphenylphosphine-palladium(II) chloride; copper(l) iodide; diisopropylamine In toluene at 100℃; for 16h; Sonogashira Cross-Coupling;	53.6%

9H-carbazole (86-74-8) + 1,4-dibromo-2,5-diiodobenzene (63262-06-6) → 1,4-dicarbazol-9-yl-2,5-dibromobenzene

Conditions	Yield
With copper(I) oxide; 2,2,6,6-tetramethylheptane-3,5-dione; potassium hydroxide In N,N-dimethyl-formamide at 110℃; for 124h; Inert atmosphere;	87.8%

tris-iso-propylsilyl acetylene (89343-06-6) + 1,4-dibromo-2,5-diiodobenzene (63262-06-6) → 1,4-dibromo-2,5-bis[2-(triisopropylsilyl)ethynyl]benzene (478190-86-2)

Conditions	Yield
With bis-triphenylphosphine-palladium(II) chloride; copper(l) iodide; triethylamine; triphenylphosphine In tetrahydrofuran at 25℃; Schlenk technique; Inert atmosphere;	87%
With copper(l) iodide; N-ethyl-N,N-diisopropylamine; bis-triphenylphosphine-palladium(II) chloride In tetrahydrofuran at 20℃; for 40h; Sonogashira coupling;	77%
With copper(l) iodide; (Ph3P)PdCl2; diisopropylamine In tetrahydrofuran at 20℃; for 40h; Sonogashira coupling;	64%
With bis-triphenylphosphine-palladium(II) chloride; copper(l) iodide In diisopropylamine Inert atmosphere;

1,4-dibromo-2,5-diiodobenzene (63262-06-6) + phenylacetylene (536-74-3) → ((2,5-dibromo-1,4-phenylene)bis(ethyne-2,1-diyl))dibenzene (97094-33-2)

Conditions	Yield
With piperidine; bis-triphenylphosphine-palladium(II) chloride; copper(l) iodide In tetrahydrofuran at 20℃; for 10h; Inert atmosphere;	87%
With piperidine; bis-triphenylphosphine-palladium(II) chloride; copper(l) iodide In tetrahydrofuran at 20℃; for 2h;	83%
Sonogashira reaction;	81%

1,4-dibromo-2,5-diiodobenzene (63262-06-6) + dibutyl-[2-nitro-4-[(triisopropylsilanyl)-ethynyl]-5-(4-trimethylsilanyl-buta-1,3-diynyl)-phenyl]-amine (402508-62-7) → C64H84Br2N4O4Si2 (1025402-11-2)

Conditions	Yield
With bis-triphenylphosphine-palladium(II) chloride; copper(l) iodide; potassium carbonate; diisopropylamine In tetrahydrofuran; water at 20℃; for 16h; Sonogashira coupling; Inert atmosphere;	87%

1,4-dibromo-2,5-diiodobenzene (63262-06-6) + 1-Ethynyl-1-cyclohexanol (78-27-3) → C22H24Br2O2 (1191422-03-3)

Conditions	Yield
With bis-triphenylphosphine-palladium(II) chloride; copper(l) iodide; diisopropylamine In benzene at 20℃; Sonogashira coupling; Inert atmosphere;	87%

4-tert-Butylphenylacetylene (772-38-3) + 1,4-dibromo-2,5-diiodobenzene (63262-06-6) → 4,4'-((2,5-dibromo-1,4-phenylene)bis(ethyne-2,1-diyl))bis(tert-butylbenzene) (952676-72-1)

Conditions	Yield
With bis-triphenylphosphine-palladium(II) chloride; copper(l) iodide; triethylamine In tetrahydrofuran at 20℃; for 24h; Sonogashira Cross-Coupling;	87%
With bis-triphenylphosphine-palladium(II) chloride; copper(l) iodide; triethylamine In tetrahydrofuran at 20℃; for 24h; Sonogashira Cross-Coupling; Schlenk technique; Inert atmosphere;	87%
With copper(l) iodide; tetrakis(triphenylphosphine) palladium(0); triethylamine at 25℃; for 3h; Sonogashira coupling;	83%
With bis-triphenylphosphine-palladium(II) chloride; copper(l) iodide; triethylamine In tetrahydrofuran Sonogashira Cross-Coupling;	74%
With copper(l) iodide; tetrakis(triphenylphosphine) palladium(0); triethylamine In tetrahydrofuran

C29H36O2Si + 1,4-dibromo-2,5-diiodobenzene (63262-06-6) → C64H72Br2O4Si2

Conditions	Yield
With bis-triphenylphosphine-palladium(II) chloride; copper(l) iodide; triethylamine at 20℃; for 28h; Inert atmosphere; Schlenk technique;	87%

4-hexyl-dodec-1-ynyl (1411985-78-8) + 1,4-dibromo-2,5-diiodobenzene (63262-06-6) → 1,4-dibromo-2,5-bis(4-hexyldodecyl-1-yn-1-yl)benzene

Conditions	Yield
With bis-triphenylphosphine-palladium(II) chloride; copper(l) iodide; triethylamine In tetrahydrofuran at 20℃; Inert atmosphere;	87%

1,4-dibromo-2,5-diiodobenzene (63262-06-6) + (2-bromophenyl)boronic acid (244205-40-1) → 2,2',2",5'-tetrabromo-1,1',4',1"-terphenyl (912922-58-8)

Conditions	Yield
With sodium carbonate; tetrakis(triphenylphosphine) palladium(0) In ethanol; water; toluene at 85℃; for 15h; Product distribution / selectivity;	85%
With sodium carbonate; tetrakis(triphenylphosphine) palladium(0) In ethanol; water; toluene at 85℃; for 15h;	75%
With silver (II) carbonate; tetrakis(triphenylphosphine) palladium(0) In tetrahydrofuran at 45℃; for 3h; Reflux; Inert atmosphere;	74%

benzo[b]thiophene-2-boronic acid (98437-23-1) + 1,4-dibromo-2,5-diiodobenzene (63262-06-6) → 2,2'-(2,5-dibromobenzene-1,4-diyl)bis(1-benzothiophene)

Conditions	Yield
With sodium carbonate; dichloro(1,1'-bis(diphenylphosphanyl)ferrocene)palladium(II)*CH2Cl2 In tetrahydrofuran; water at 65℃; for 12h; Inert atmosphere;	85%

4-ethyl-1-octyne (65351-05-5) + 1,4-dibromo-2,5-diiodobenzene (63262-06-6) → 1,4-dibromo-2,5-bis(4-ethyloct-1-yn-1-yl)benzene

Conditions	Yield
With bis-triphenylphosphine-palladium(II) chloride; copper(l) iodide; triethylamine In tetrahydrofuran at 20℃; Inert atmosphere;	85%

1-tetradecyne (765-10-6) + 1,4-dibromo-2,5-diiodobenzene (63262-06-6) → 1,4-dibromo-2,5-di(tetradec-1-yn-1-yl)benzene

Conditions	Yield
With bis-triphenylphosphine-palladium(II) chloride; copper(l) iodide; triethylamine In N,N-dimethyl-formamide at 20℃; for 72h; Sonogashira Cross-Coupling; Schlenk technique; Inert atmosphere;	85%

2-bromo-1-ethynylbenzene (766-46-1) + 1,4-dibromo-2,5-diiodobenzene (63262-06-6) → 1,4-bis[(2-bromophenyl)ethynyl]-2,5-dibromobenzene (625389-87-9)

Conditions	Yield
With bis-triphenylphosphine-palladium(II) chloride; copper(l) iodide; triethylamine In toluene at 20℃; for 12h;	84%
With copper(l) iodide; triethylamine; bis-triphenylphosphine-palladium(II) chloride In toluene at 20℃; for 12h;	84%
With copper(l) iodide; tetrakis(triphenylphosphine) palladium(0); diisopropylamine In toluene at 20℃; for 12h; Sonogashira coupling; Inert atmosphere;	79%

Upstream product

• 106-37-6 1.4-dibromobenzene 
• 3460-18-2 1,4-dibromo-2-nitrobenzene 

Downstream Products

• 190371-83-6 1,4-dibromo-2,5-bis([4-(dodecyloxy)phenyl]ethynyl)benzene 
• 625389-87-9 1,4-bis[(2-bromophenyl)ethynyl]-2,5-dibromobenzene 
• 608534-54-9 1,4-bis-(2'-biphenyl)yl-2,5-dibromobenzene 
• 922736-78-5 1,4-dibromo-2,5-bis{[2-(ethoxydimethylsilyl)phenyl]ethynyl}benzene 
• 478190-81-7 1,4-dibromo-2,5-bis[(4-(N,N-dibutylamino)phenyl)ethynyl]benzene 
• 618119-20-3 2,5-bis(3,3-dimethylbutynyl)-4-bromobenzaldehyde 
• 618119-21-4 2,5-bis(3,3-dimethylbutynyl)-4-(1,3-dioxolan-2-yl)bromobenzene 
• 618119-22-5 2,5-bis(3,3-dimethylbutynyl)-4-(1,3-dioxolan-2-yl)iodobenzene 
• 618904-86-2 2-[2,5-bis-(3,3-dimethyl-but-1-ynyl)-4-(3,5-di-pent-1-ynyl-phenylethynyl)-phenyl]-[1,3]dioxolane 
• 133531-74-5 1,2,5,6-tetraphenyl-1,5-dihydrobenzo[1,2-d:4,5-d']diimidazole 

Relevant articles and documents

Benzodipyrrole-2,6-dione-3,7-diylidenedimalononitrile Derivatives for Air-Stable n-Type Organic Field-Effect Transistors: Critical Role of N-Alkyl Substituent on Device Performance

Benzodipyrrole-2,6-dione-3,7-diylidenedimalononitriles (BDPMs) were synthesized as active materials for the use in air-stable n-type organic field-effect transistors (OFETs), whose optical and electrochemical properties were examined. BDPM-based small molecules exhibit deep lowest unoccupied molecular orbital levels, which are required in air-stable n-type OFETs. An OFET device that was based on BDPM-But and fabricated by vapor deposition provided a maximum electron mobility of 0.131 cm2 V-1 s-1 under ambient conditions.

Green synthesis method for 2,5-dibromo-1,4-diiodobenzene intermediate

The invention discloses a green synthesis method for a 2,5-dibromo-1,4-diiodobenzene intermediate, belonging to the technical field of intermediates of organic photoelectric materials. According to the method, organic cyclic high-valence iodine is used as an iodination reagent, metal organic phosphorus is used as a catalyst, trifluoromethanesulfonic acid is used as an additive, and 1,2-dichloroethane is used as a solvent; an ortho-position C-H bond is activated through a weak positioning group, namely a bromine group, and an ortho-position iodination reaction of p-dibromobenzene is experimented; and after the reaction is finished, the solvent is removed to directly obtain 2,5-dibromo-1,4-diiodobenzene. According to the method, the problems of poor iodination reaction purity and poor selectivity of traditional methods are solved, and high-purity, high-efficiency and high-selectivity iodination reaction of p-dibromobenzene is realized. By adopting the above optimized synthetic route, themethod has the advantages of greatly improved yield, reduced cost, enhanced safety, conservation of energy and the like, and meets the modern chemical production requirements on green reaction.

The kinetics and mechanism of interconversion within a system of [Fe2L 3]4+helicates and [Fe4L 6]8+cages

Nature builds simple molecules into highly complex assemblies, which are involved in all fundamental processes of life. Some of the most intriguing biological assemblies are those that can be precisely reconfigured to achieve different functions using the same building blocks. Understanding the reconfiguration of synthetic self-assembled systems will allow us to better understand the complexity of proteins and design useful artificial chemical systems. Here we have prepared a relatively simple system in which two distinct self-assembled structures, a [Fe2L3]4+ helicate and a [Fe4L6]8+ cage that are formed from the same precursors, coexist at equilibrium. We have measured the rates of interconversion of these two species and propose a mechanism for the transformation.