This journal is © The Royal Society of Chemistry and the Chinese Chemical Society 2018 Mater. Chem. Front., 2018, 2, 591--596 | 591 Cite this: Mater. Chem. Front., 2018, 2, 591 A direct synthetic method for (nitronyl nitroxide)- substituted p-electronic compounds via a palladium-catalyzed cross-coupling reaction with a zinc complex† Shuichi Suzuki, * Fumiya Nakamura and Takeshi Naota * We have developed an efficient synthetic method for (nitronyl nitroxide)-substituted (NN-substituted) p-electronic compounds via palladium-catalyzed cross-coupling reactions with a zinc complex of the parent nitronyl nitroxide radical anion. Various aryl iodides can be directly converted to the desired coupling compounds with high efficiency. The utility of the present method has been demonstrated by direct synthesis of a newly prepared radical species, NN-substituted phenothiazine 15P, which could not be obtained from the corresponding aldehyde compound by typical condensation-oxidation methods. The molecular structure and characteristic electronic nature of 15P were examined by single-crystal X-ray diffraction analysis and cyclic voltammetry, indicating that 15P is a promising candidate as a precursor for a triplet ground state species by one-electron oxidation. Introduction Open-shell p-electronic compounds are promising components for next-generation electronic devices because of their wide diversity in molecular design, structural flexibility, and process- ability. 1–3 In the past few decades, nitronyl nitroxides (NN-Rs) and their related radicals have been especially utilized for organic spin sources and their unique spin-related properties have been investigated in view of purely organic ferromagnets, 1 hybrid ferrimagnets, 4 and negative magnetoresistance. 5 NN-Rs are generally prepared via the condensation reactions of N,N 0 -dihydroxy-2,3-dimethylbutane-2,3-diamine with various aldehydes and subsequent oxidation with a stoichiometric amount of oxidant (Scheme 1a). 6 However, the condensation reactions with highly electron-donating 5,6b,7 and electron- accepting 6b,8 aromatic aldehydes were sometimes unsuccessful, probably due to the low reactivity of the substrates and low stability of the products. Some modified methods using the corresponding dimethyl acetals 7 and butanediamine 4b,9 have been reported for the syntheses of NN-Rs with specified func- tionalities. One of the significant aspects to be improved in these conventional methods is the stoichiometric use of strong oxidants, such as lead dioxide 6 and m-chloroperbenzoic acid, 4b,9 since the use of these oxidants frequently leads to the undesired decomposition of product NN-Rs, especially with electron-rich p-electronic systems. The direct introduction of the NN group to organic platforms using a parent NN (NN-H) as a synthetic unit is an alternative but promising method for the unlimited synthesis of a variety of NN derivatives. A number of nucleophilic coupling reactions of NN-H have been performed with various electrophiles such as MeOCH 2 Cl, 10 MeOTf, 11 CO 2 , 11 pyridine-oxide and related- N-oxide, 12 2-methyl-2-nitrosopropane, 13 nitrone, 14 and penta- fluorocyanobenzene, 15 although the methods are limited to using well-developed p-electronic systems due to preparations of reactants with suitable substituents. Recently, Okada and coworkers reported that a gold(I) complex of the NN radical Scheme 1 Synthetic methods of NN derivatives: (a) typical condensation– oxidation method and (b) palladium-catalyzed cross-coupling method with NN-Zn. Department of Chemistry, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan. E-mail: suzuki-s@chem.es.osaka-u.ac.jp, naota@chem.es.osaka-u.ac.jp † Electronic supplementary information (ESI) available: ESR spectra of isolated products, detailed UV-vis spectra during reaction, and calculated results. CCDC 1588474 (14P) and 1588475 (15P). For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c7qm00565b Received 7th December 2017, Accepted 17th January 2018 DOI: 10.1039/c7qm00565b rsc.li/frontiers-materials MATERIALS CHEMISTRY FRONTIERS RESEARCH ARTICLE