N,N 0 -diethyl and N-ethyl,N 0 -methyl glyoxal-bridged cyclams: synthesis, characterization, and bleaching activities of the corresponding Mn(II) complexes Giovanni Di Mauro 1 • Alfonso Annunziata 1 • Maria Elena Cucciolito 1 • Matteo Lega 2 • Stefano Resta 2 • Angela Tuzi 1 • Francesco Ruffo 1 Received: 15 March 2017 / Accepted: 3 April 2017 Ó Springer International Publishing Switzerland 2017 Abstract The synthesis and characterization of N,N 0 -di- ethyl (L-Et,Et) and N-ethyl,N 0 -methyl (L-Et,Me) glyoxal- bridged cyclam ligands are described, together with the X-ray crystal structure of the complex [MnCl 2 (L-Et,Me)]. Bleaching of morine in the presence of hydrogen peroxide by the corresponding Mn catalysts [MnCl 2 (L-Et,Et)], [MnCl 2 (L-Et,Me)] and [MnCl 2 (L-Me,Me)] has been studied in aqueous solution at three different pH values (8.0, 8.75, and 9.0). The results clearly show that increas- ing pH has a different effect on the three catalysts, and that the dimethyl derivative is by far the most active. Introduction Glyoxal-bridged cyclam-based ligands (L-R,R 0 ) have attracted much interest [1–9] in the last decades, due to their ability to coordinate mid–late transition metals (Scheme 1). These macrocycles can be easily N-functionalized with various groups, allowing the preparation of a wide range of ligands suitable for important applications such as for catalysis [4, 8], and the development of metal-based imaging and therapeutic agents in medicine [10]. In particular, manganese(II) complexes of formula [MnCl 2 (L-R,R 0 )] show well-proven peroxide-based bleaching activity, which has been the object of extensive studies documented in the patent literature [11–17]. These complexes were initially targeted as potential oxidation catalysts because the rigid cross-bridged ligand strongly binds the manganese ion and prevents it from being deactivated in the form of MnO 2 . Additional distinctive properties are the presence of the alkyl groups R and R 0 , which preclude dimerization and consequent deactivation of the catalyst, and the all-tertiary nature of the nitrogen atoms, which minimizes the possibility of ligand oxidation and catalyst destruction. Both [MnCl 2 (L-Me,Me)] and [MnCl 2 (L-Et,Et)] are patented bleach catalysts, which have been heavily inves- tigated by the laundry detergent industry because of their ability to activate O 2 /H 2 O 2 in water and remove stain molecules from cloth. The crystal structures of both com- plexes [5, 18] have been recently reported, demonstrating also the academic interest [19, 20] toward this class of compounds. Despite this attention, the detailed synthesis of L-Et,Et has never been reported in the literature, as well as the preparation of the mixed L-Et,Me species, which has also been mentioned in the patent literature. Aiming to fill this gap, this paper presents the synthesis of L-Et,Et and L-Et,Me (Scheme 1) along with their NMR characterization. In addition, the preparation of the corre- sponding MnCl 2 complexes, which have been tested in the bleaching of morine with hydrogen peroxide, in compar- ison with [MnCl 2 (L-Me,Me)], and the crystal structure of [MnCl 2 (L-Et,Me)] are reported. Electronic supplementary material The online version of this article (doi:10.1007/s11243-017-0146-8) contains supplementary material, which is available to authorized users. & Francesco Ruffo ruffo@unina.it 1 Dipartimento di Scienze Chimiche, Universita ` di Napoli Federico II, Complesso Universitario di Monte S. Angelo, Via Cintia 21, 80126 Naples, Italy 2 Fater SpA, Via Ardeatina 100, 00040 Pomezia, Rome, Italy 123 Transit Met Chem DOI 10.1007/s11243-017-0146-8