Cyclen (1,4,7,10-tetraazacyclododecane) is an aza-crown ether with the formula (CH2CH2NH)4. It is a white solid. It forms coordination complexes with metal cations and is used to synthesize the chelating agentDOTA which has several medical applications. Being structurally simple, symmetrical, and polyfunctional, cyclen has been widely investigated.[1]
Some syntheses exploit the Thorpe-Ingold effect to facilitate ring-formation. Illustrative is the reaction of the deprotonated tosylamides with ditosylates:[2]
Structure of [Ni(cyclen)(OH2)2] . Color code: O = red, N = blue, Ni = dark blue, white = H, gray = C.
Coordination complexes of cyclen have been studied extensively.[5][6] With a 12-membered ring, it tends to bind to four contiguous sites on octahedral metal centers, forming four 4-membered rings (see example figure). In contrast the larger cyclam ligand forms complexes consisting of 4 coplanar rings.
Cyclen also forms complexes of the type [Ln(cyclen)2]3+ where Ln = lanthanide.[7]
↑ Atkins, T. J.; Richman, J. E.; Oettle, W. F. (1978). "1,4,7,10,13,16-Hexaazacyclooctadecane". Org. Synth. 58: 86. doi:10.15227/orgsyn.058.0086.
↑ Reed, David P.; Weisman, Gary R. (2002). "1,4,7,10-Tetraazacyclododecane". Org. Synth. 78: 73. doi:10.15227/orgsyn.078.0073.
↑ Scott, Brian; Brewer, Karen J.; Spreer, Larry O.; Craig, Carl A.; Otvos, John W.; Calvin, Melvin; Taylor, Scott (1990). "A Novel Conformation for a Coordinated Macrocycle: The Crystal Structure of [Ni(12-aneN4)(OH2)2](CIO4)2·H2O; (12-aneN4= 1,4,7,10-Tetraazacyclododecane)". Journal of Coordination Chemistry. 21 (4): 307–313. doi:10.1080/00958979009408193.
↑ Gunnlaugsson, Thorfinnur; Leonard, Joseph P. (2005). "Responsive lanthanide luminescent cyclen complexes: From switching/Sensing to supramolecular architectures". Chemical Communications (25): 3114–3131. doi:10.1039/b418196d. PMID15968347.
↑ Joshi, Tanmaya; Graham, Bim; Spiccia, Leone (2015). "Macrocyclic Metal Complexes for Metalloenzyme Mimicry and Sensor Development". Accounts of Chemical Research. 48 (8): 2366–2379. doi:10.1021/acs.accounts.5b00142. PMID26244894.
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