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Updated: Jun 19, 2026

Accessing Valuable Ligand Supports for Transition Metals: A Modified, Intermediate Scale Preparation of 1,2,3,4,5-Pentamethylcyclopentadiene
Published on: March 20, 2017
A mixed-valent pentanuclear Cu(II)(4)Cu(I) compound containing a radical-anion ligand
Tiddo J Mooibroek1, Guillem Aromí, Manuel Quesada
1Leiden Institute of Chemistry, Leiden University, P.O. Box 9502, 2300 RA Leiden, The Netherlands.
Abstract:
Reaction of 2,4-(2,2'-dipyridylamino)-6-(2-pyridylhydrazino)-1,3,5-triazine, abbreviated dppht (5), with copper(II) chloride in methanol yields a mixed-valent Cu(II)(4)Cu(I) compound (6), also involving the presence of a radical anion. The single-crystal structure determination for [Cu(5)(5(M))(5(MR))Cl(8)] (6) reveals that the original dppht ligand (5) has been monochlorinated at one of its pyridine rings and oxidized at its hydrazyl moiety, generating the ligand 2,4-(2,2'-dipyridylamino)-6-(2-(5-chloropyridyl)azo)-1,3,5-triazine (5(M)). Moreover, the molecular structure of 6 indicates that one of the two coordinated ligands 5(M) is in a radical-anion state, symbolized as 5(MR), characterized by a typical N-N bond length of about 1.33 A for a one-electron reduced azo group. The nature of this unique [Cu(II)(4)Cu(I)(radical)] assembly is corroborated by X-ray absorption spectroscopy, electron paramagnetic resonance, and magnetic susceptibility measurements. Density-functional theory calculations are consistent with the unprecedented structural features and support the spectroscopic data.
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