A Trinuclear Double-Helical Metal Complex of a Quinquepyridine Analog

Abstract

A double-helical metal complex of an oligopyridine analog (i.e. with heterocycles other than pyridinyl rings) has been fully structurally characterized. This complex is the first example of a trinuclear double-helical complex containing quinquedentate and monodentate ligands and is of a type that has not been observed with the oligopyridines. In the rhetoric of metallosupramolecular chemistry much is said about the “design” of complexes of specific structure. Our work invites molecular engineers to consider pyrazolyl ligands as useful additions to their “tool kit”.

Helicates as Versatile Supramolecular Complexes

“…The dinuclear unsaturated helicate (HH)-[Cu 2 ( 20 ) 2 (OAc)] 3+ can be reduced to give the trinuclear complex [Cu 3 ( 20 ) 2 ] 3+ which is supposed to adopt a double-helical structure reminiscent of that found in [Cu 2 ( 47 ) 2 ] 2+ (Figure a) . The crystal structure reported for the unsaturated heterotopic trinuclear double-stranded helicate (HT)-[Cu 3 ( 113 ) 2 (CH 3 CN) 2 ] 3+ strongly supports this hypothesis although the trinuclear structure is not maintained in solution according to ES−MS data (Figure b) …”

“…The introduction of ferrocenyl substituents into the ligand strand 22 does not sterically limit the formation of double-helical complexes and the unsaturated double-stranded helicate [Ni 2 ( 22 ) 2 (OH 2 )] 4+ has been characterized in solution 38 (a) Coordination behavior of quinquepyridine 20 with Cu(II) and Cu(I) 107 and (b) X-ray crystal structure of the unsaturated double-stranded helicate (HT)-[Cu 3 ( 113 ) 2 ] 3+ .…”

Application of Transition‐Metal Complexes in Cyclohexane Oxidation: Synthesis, Structure, and Properties of Copper and Nickel Complexes with a Pincer N‐Heterocyclic Ligand

“…[9] As a member of N-containing heterocyclic families, derivatives of 2,6-di(pyrazol-1-yl)pyridine are commercially available or straightforwardly synthesized, especially those substituted at the 3,4,5-position on the pyrazolyl moiety, and the introduction of pyrazole rings onto the 2-and 6-positions of pyridine is a common strategy to synthesize tridentate ligands that are analogous to substituted derivatives of 2,6-di(pyrazol-1-yl)pyridine. [10][11][12] In addition, the 2,6-di(pyrazol-1-yl)pyridine ligand can bind to various valence-state metal ions in a tridentate manner, [13][14][15] which is widely studied in coordination chemistry. [16][17][18][19][20] Furthermore, transition-metal complexes with 2,6-bis(pyrazol-1-yl)pyridine and their derivatives are of great interest owing to their biological activity [21,22] and rich applications in materials science, [23] semiconductors, [24] photoluminescence, [25][26][27] magnetism, [28,29] and especially in homo-and heterogeneous catalytic oxidation reactions.…”

Chapter 19. The co-ordination chemistry of open-chain polydentate ligands

“…355 The pentadentate ligand L"' mimics the metal-binding domain of the anti-tumour drug bleomycin; its Fe" complex catalyses alkane oxidation by Bu'OOH or 02. 354 The tetrapodal Iigand L172 acts as a capping Iigand for a square-pyramidal array of five-co-ordination sites; [CoCl(LI 7 2 ) ] 2 + is ~c t a h e d r a l . ~~'…”