2,6‐Bis(pyrazolyl)pyridine Functionalised with Two Nitronylnitroxide and Iminonitroxide Radicals

Abstract

During the last two decades, growing interest in the field of material chemistry has been focused on the synthetic design of organic high‐spin molecules for use as novel magnetic materials. Conjugated radicals based on the bis(pyrazolyl)pyridine core are very attractive in principle, since they per se combine optical, chelating and magnetic properties on a single molecular entity. The functionalisation of this core via the bis(4′‐formyl) derivatives with Ullman radicals results in novel functional biradicals, which may further be used for supramolecular architectures. In this paper we describe the synthesis, structure and properties of 2,6‐bis[4′‐(3‐oxo‐1‐oxyl‐4,4,5,5‐tetramethylimidazolin‐2‐yl)pyrazol‐1′‐yl]pyridine (Pz2PyNN) and 2,6‐bis[4‐(1‐oxyl‐4,4,5,5‐tetramethylimidazolin‐2‐yl)pyrazolyl]pyridine (Pz2PyIN). The two biradicals can clearly be differentiated by UV/Vis, IR and EPR spectroscopy. The optical absorptions of the blue Pz2PyNN appear around λmax= 610 nm (ϵ ≈︁ 1700 M−1 cm−1) while for Pz2PyIN the orange‐red colour arises from absorptions at λmax= 468 nm (ϵ ≈︁ 1400 M−1 cm−1). A triplet ground state for the bis(nitronylnitroxide) Pz2PyNN with ΔES‐T ≈︁ 11.8 ± 4.8 cm−1 can be deduced from the EPR studies because of the increase of the double integrated intensity times temperature at very low temperatures, indicating complete population of the triplet state. For the related bis(iminonitroxide) Pz2PyIN a much smaller (at least one order of magnitude lower) singlet−triplet energy gap with an upper limit of 0.7 cm−1 has been derived (0.7 ⪖ ΔES‐T ⪖ −0.07 cm−1). The new multifunctional biradicals represent the first example of high‐spin molecules in the bis(pyrazolyl)pyridine family. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Synthesis, Optical Properties and Magnetic Studies of 2,6‐Bis(pyrazolylmethyl)pyridine Functionalized with Two Nitronyl Nitroxide Radicals

“…However, these principles have their limitations [12] as they are not readily extended to non-alternant systems and heteroatom-containing radicals or couplers. Previously we demonstrated that functionalization of the 4Ј,4ЈЈ-positions interaction between spin carriers, although weak (0.06 cm of the bispyrazolylpyridine core A (Figure 1) with neutral NN radical moieties [13] gated intramolecular ferromagnetic exchange interaction (∆E ST = 11.8 Ϯ 4.8 cm -1 ), besides the unfavourable exchange coupling path and the distance between the radical units (ONĈ NO groups ca. 8.3 Å).…”

“…The detailed synthesis of 1 has been reported previously. [13,15] The nucleophilic substitution occurred very quickly (3 h) and provided 2,6-bis[(4-formylpyrazolyl)methyl]pyridine (3) in a fair yield (54 %) after recrystallization from EtOH/H 2 O solution.…”

“…After oxidation of the radical precursor 5, the intense and broad absorption at around 3200 cm -1 originating from the -NH-OH residues (ν NH-OH ) disappears in B and the so-formed aminoxyl oxide moieties show a distinctive strong ν N-O stretching vibration at 1365 cm -1 , which is consistent with literature values, both in frequency and intensity. [13,17,18] …”

An Efficient Synthesis of Novel Pyrazole-Based Heterocycles as Potential Antitumor Agents

“…Additionally, the utility of MCR under microwave irradiation in the synthesis of heterocyclic compounds enhanced the reaction rates and improved the regioselectivity [34,35]. Over the last decade, several research groups adopted a hybridization approach for the design of pyrazole-pyridine hybrid analogs and illuminated their synthetic and medicinal importance [36][37][38][39][40][41][42].…”

Homo‐ and Heterometallic Coordination Oligomers and Polymers Derived from the Preformed Complexes [Cu(bdmpp)(MeCN)2](ClO4)2, [Cu(bdmpp)(N3)2], and [Cu(bdmpp)(N3)(μ‐N3)]2 [bdmpp = 2,6‐bis(3,5‐dimethyl‐1H‐pyrazol‐1‐yl)pyridine]: Syntheses, Structures, and Redox Properties

“…[27][28][29][30] Some metal/bdmpp complexes did show unsaturated coordination geometry around the metal center. [27][28][29][30] However, these compounds have not been used as precursors to further assemble coordination oligomers and polymers. To this end, we prepared three Cu II /bdmpp complexes, [Cu(bdmpp)(MeCN) 2 ](ClO 4 ) 2 (1), [Cu(bdmpp)(N 3 ) 2 ]· 1.5H 2 O (2·1.5H 2 O), and [Cu(bdmpp)(N 3 )(μ-N 3 )] 2 ·2MeOH (3·2MeOH), in high yields.…”