Versatile synthesis of chiral 6-oxoverdazyl radical ligands – new building blocks for multifunctional molecule-based magnets

Abstract

A versatile synthetic methodology to access the first family of chiral verdazyl N,N'-chelate ligands is described and exemplified by N,N'-dimethyl-, N,N'-di-isopropyl-and N,N'-diphenyl oxoverdazyls bearing two isomers of the pinene-pyridine functional group. Their physical properties were probed by X-band EPR spectroscopy, cyclic voltammetry and DFT calculations. Preliminary reactivity studies show they can act as N,N'-chelate ligands affording a chiral 1 : 1 complex (3b) with CuCl 2 , which was characterized by single-crystal X-ray diffraction. Variable temperature EPR studies on (3b) confirm the presence of antiferromagnetic interactions between the spins of the Cu(II) ion and the verdazyl radical.The unique properties associated with chiral molecules and their interaction with light inter alia has a rich history that today plays a central role in many areas of chemistry that include organometallic, coordination compounds, metal nanoparticles and molecule-based materials.1 The marriage of chirality with free radical chemistry has also found applications in diverse fields ranging from enantioselective catalysis 2 to the development of chiral radicals as building blocks for chiral organic, or hybrid organic/inorganic magnets. 3 In the latter case, crystallization of chiral molecules into non-centrosymmetric space groups can confer unique physical phenomena that include ferroelectric, piezoelectric, second harmonic generation (SHG) and/or non-linear optical (NLO) properties. 4 Furthermore, in select examples, when magnetic chirality coexists with nuclear chirality, the spatial and temporal symmetry is simultaneously broken affording a range of magneto-optical properties that includes magneto-chiral dichroism (MChD).5

The syntheses, structures and spectroelectrochemical properties of 6-oxo-verdazyl derivatives bearing surface anchoring groups

“…1a and b) to create radical ligands, including chelating and pincer-type structures, for use as spin labels. [3][4][5][6][7][8][9][10][11] In addition, verdazyl-based compounds have been used in the design of a variety of organic magnetic 12 and conductive materials. 13 These potential applications have prompted renewed interest in the synthetic chemistry associated with verdazyl-based structures, 14,15 including demonstrations of Sonogashira cross-coupling reactions that have been used to extend the conjugation of aryl groups at either the 1-or 3-positions.…”

Tautomerism and Self-Association in the Solution of New Pinene-Bipyridine and Pinene-Phenanthroline Derivatives

“…Ligands with an annellated pinene backbone have been used extensively for chiral induction in coordination compounds of d and f metal ions, giving rise to well defined, enantiopure supramolecular structures [1][2][3][4][5]. Their ability to control the metal centers' chirality makes them attractive not only in the field of supramolecular chemistry [2], but also for various applications like enantioselective catalysis or single chiral molecular magnets [6][7][8][9]. Among the pinene containing ligands, the most studied ones possess a bipyridine unit connected to the pinene moiety through either the 4,5 or 5,6 carbon atoms on the pyridine ring.…”

Cobalt(II) Coordination Polymers Assembled from Unexplored Pyridine-Carboxylic Acids: Structural Diversity and Catalytic Oxidation of Alcohols

“…Design and synthesis of new coordination polymers and metal–organic frameworks (abbr. CPs and MOFs, respectively) has recently attracted an enormous attention due to an unlimited diversity of their structural types, architectures, topologies, as well as important properties and applications of these functional solids. − In particular, the use of CPs in catalysis became a recognized research area, − which is primarily associated with the high porosity, crystallinity, inorganic–organic hybrid structures, thermal stability, and tunable physicochemical properties of such compounds. − …”