Chelation-Controlled Regioselectivity in the Synthesis of Substituted Pyrazolylpyridine Ligands. 3. Unsymmetrically Substituted Tridentates and Ditopic Bis(tridentates) en Route to Singly Stranded Helicates

Abstract

A strategy for the synthesis of helical multinuclear complexes (helicates) of any length is outlined, making use of ditopic ligands to bridge between metals and monotopic ligands to cap the chain's termini. We present the syntheses of both ditopic and monotopic ligands with tridentate binding units for octahedral metals, in liposoluble and functionalized varieties. Of special interest are ligands bearing benzoic acid or toluic acid side-chains which can ionize and serve as counteranions. Several singly N(1)-substituted 2,6-bis(4,5,6,7-tetrahydroindazol-3-yl)pyridines were prepared by regioselective, chelation-controlled mono-N-alkylation or -arylation of the tautomeric N,N‘-H2 parent compound. These were then either coupled with CH2 linkages to provide the ditopic ligands or were further N-functionalized to give unsymmetrically substituted capping ligands. The regiochemistry of the N-substitutions and the ring-to-ring conformations were ascertained by 1H NMR spectra with and without added complexands (H+, D+, Zn2+, and Na+). The formation of a bis(ZnBr2) adduct confirmed the independence of the metal binding sites while Na+ formed the 2:2 helicate.

Mono- and Dinuclear Ruthenium(II) Complexes of 2,6-Di(pyrazol-3-yl)pyridines: Deprotonation, Functionalization, and Supramolecular Association

“…The 1 H NMR spectra fully supported the formulations and structures of the complexes described herein. In our experience with the in situ binding of Na + , Zn II , Ti IV , or D + by our tridentates, , as well as with Ru II complexes of the bidentate analogues, a comparison of the relative positioning of the pyridine signals from the complexes with that from the free ligands can reveal the regiochemistry of N-substitution and can confirm the formation of a complex through the occurrence of conformational changes about the inter-ring bonds. Thus, out N-substitution (i.e.…”

“…This facility has enabled us to prepare a variety of substituted tridentates 8,11,12 and a ditopic bis(tridentate) 11 as well as novel pentadentate and macrocyclic 7 ligands. We have also demonstrated how these ligands can bind alkali metal ions, Fe(III), Ru(II), ,, Zn(II), and Co(II). , The liposolubilities of H 1 and H 2 2 and their derivatives and complexes have proven to be synthetically very advantageous.

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Substituent Control of Hydrogen Bonding in Palladium(II)−Pyrazole Complexes

“…Synthesis. The number of pyrazole-containing ligands in which both ring nitrogens are unsubstituted and a side chain is attached at a ring carbon is rather small, − ,,,− probably because it is relatively difficult to make such systems. However, we recently reported a method to construct precursors 3 (Scheme ) in which substituent R can be methyl, i -propyl, phenyl, tert -butyl, or adamantyl and the side-chain length can be varied .…”

Reactions of 1-aryl- and 2,3-diaryl- 5-diazo-6,6-dimethyl-4-oxo-4,5,6,7-tetra- hydroindazoles with N-ethyl- and N-phenyl-substituted maleimides

“…Among them have been discovered agonists and antagonists of estrogen receptors [9,10], dopamine D-3 [11,12], corticotropin [13], and adenosine [14]; derivatives have been found with antitumor [15], antiinflammatory [16], and antimicrobial [17] action; inhibitors of HIV proteases [18] and membrane-active substances [19] have been discovered. Indazole derivatives have also been used as ligands [20].…”