Photoaddition of N‐Substituted Piperazines to C₆₀: An Efficient Approach to the Synthesis of Water‐Soluble Fullerene Derivatives

Abstract

An oxidative radical photoaddition of mono N-substituted piperazines to [60]fullerene was systematically investigated. Reactions of C60 with piperazines bearing bulky electron-withdrawing groups (2-pyridyl, 2-pyrimidinyl) were found to be the most selective and yielded C60(amine)4O as major products along with small amounts of C60(amine)2. In contrast, interactions of fullerene with N-methylpiperazine and N-(tert-butoxycarbonyl)piperazine were found to have low selectivity due to different side reactions. Tetraaminofullerene derivative C60(N-(2-pyridyl)piperazine)4O was found to react readily with organic and inorganic acids to yield highly water-soluble salts (solubility approximately 150 mg mL(-1)). In contrast, C60(N-(2-pyrimidinyl)piperazine)4O undergoes hydrolysis under the same conditions and results in a complex mixture of compounds with an average composition of C60(N-(2-pyrimidinyl)piperazine)2(OH)2O. Radical photoaddition of N-(2-pyridyl)piperazine to fullerene derivatives can be used as a facile route for their transformation into water-soluble compounds. Two model fullerene cycloadducts (a methanofullerene and a pyrrolidinofullerene) were easily converted into mixtures of regioisomers of A=C60(N-(2-pyridyl)piperazine)4O (A=cyclic addend) that give highly water-soluble salts under acid treatment.

Luminescent Tags on Fullerenes: Eu3+ Complexes with Pendant Fullerenes

“…2) were prepared according to the literature procedures. [43,45] The reference complex Eu(TFAcAcN) 3 phen 1 was synthesized according to the conventional route [46] as follows: by adding a solution of EuCl 3 in ethanol dropwise to a mixture of 4,4,4-trifluor-1-(2-naphtyl)-1,3-butandione and [1,10] phenathroline in ethanol a precipitate of 1 is formed ( Fig. 3).…”

“…[43] However, to obtain solid AmF Á nHCl, the excess of hydrochloric acid must be removed at room temperature without additional heating (to avoid degradation of AmF), that usually takes quite a long time. Here, we developed an improved procedure for rapid conversion of AmF to water-soluble hydrochloride: for this purpose AmF was dissolved in acetic …”

“…To obtain solid AmF Á nHCl 4, acetic acid used as a solvent and other volatile components were removed with a stream of N 2 (alternatively, this can be done in vacuum). The composition of the salt obtained was assumed to be AmF Á ($8HCl) as determined in previous studies [43].…”

“…A lot of research has been done in this field to overcome this problem and to construct fullerene derivatives highly soluble in water. [41][42][43][44] As a result, a number of fullerene-based watersoluble compounds was designed for use in biomedical research.…”

“…3). [43] To obtain a water-soluble protonated AmF Eu 3þ complex a solution of 4 in water and a solution of 2 in ethanol were mixed in appropriate volumes (Fig. 3).…”