Synthesis and X-ray Crystal Structure of a Triple-Stranded Helical Supramolecular Complex Formed between Tris(3-(pyridin-2-yl)pyrazole)ruthenium(II) and Copper(I)

Abstract

Self-assembly of supramolecules with helical structures has been one of the focuses in supramolecular chemistry. 1 The general synthetic strategy involves the use of multidentate ligands to wrap around one or more metal centers to produce single-, 2-4 double-, 5-8 and triple-stranded 9-15 metal helicates. We have tried a different approach in which smaller building blocks of metal complexes containing only bidentate ligands are linked together to form the desired supramolecular structure. In this work, the synthesis of a triple-stranded ruthenium helicate, {[Ru(py-pz ) 3 ] 2 Cu 3 }(ClO 4 ) (2), from [Ru(py-pzH) 3 ]-(ClO 4 ) 2 (1) (where py-pzH ) 3-(pyridin-2-yl)pyrazole) and Cu-(ClO 4 ) 2 is reported.The coordination chemistry of the 3-(pyridin-2-yl)pyrazole (py-pzH) ligand and its analog has been studied by a number of researchers. 16 Complex 1 was synthesized from py-pzH 17 and RuCl 3 ‚3H 2 O. 18 An acetonitrile solution of 1 shows three absorption bands at 400 nm ( ) 1.74 × 10 4 M -1 cm -1 ), 279 nm ( ) 5.05 × 10 4 M -1 cm -1 ), and 243 nm ( ) 5.00 × 10 4 M -1 cm -1 ), in the UV-vis spectrum. The first absorption is the MLCT transition, while the last two are intraligand in origin. The MLCT band is red-shifted to 430 nm ( ) 1.08 × 10 4 M -1 cm -1 ) upon deprotonation of the pyrazole by the addition of 3 equiv of triethylamine. Such lowering in MLCT energies has also been reported by Meyer et al. in their studies of pyrazole/ pyrazolyl complexes of ruthenium(II). 19 It was concluded that the pyrazolyl moiety possessed much better π-donating ability comparing to that of the pyrazole ligand.Complex 1, after deprotonation by the addition of excess NEt 3 , reacts with Cu(I) or Cu(II) ions in methanol to give a supramolecular structure containing two tris(3-(pyridin-2-yl)pyrazolyl)ruthenium(II) units linked together by three Cu(I) ions: 20 The structure of 2 is shown in Figure 1. 21 2 possesses a C 3 rotation axis. Each Ru center is coordinated to three 3-(pyridin-

Noncovalent Ligand Strands for Transition‐Metal Helicates: The Straightforward and Stereoselective Self‐Assembly of Dinuclear Double‐Stranded Helicates Using Hydrogen Bonding

“…Given the obvious advantages of this noncovalent self‐assembly step, it is somewhat surprising that noncovalent approaches to step 1, the construction of the ligand strands, have been reported only rarely. In these few cases metal ions were used as structural units in the ligand strands of triple helicates4 and mesocates 5. 6 In the present paper we would like to report on a novel, noncovalent strategy for the construction of ligand strands for a series of dinuclear double helicates.…”

From Hierarchical Helicates to Functional Supramolecular Devices

“…[6] Hierarchicalh elicates of type [{(2) 3 Co} 2 M] n + and [{(2) 3 Co} 2 Ag 3 ] 3 + have been described in recent years by different groups with somer epresentative examples 3-7 shown in Figure2. [7,8] Related cluster helicates in which the bridging proceeds not by isolated metal ions but by small metal oxide clusters have been also published. [9] In particular,t he complexes 6 describedb yRaymond [10] and 7 by Shionoya [11] should be mentioned here.…”

1-Acetyl-3-ferrocenyl-5-methyl-1H-pyrazole and 1-acetyl-5-ferrocenyl-3-(2-pyridyl)-1H-pyrazole

“…Acylation of tautomeric 3(5)-ferrocenyl-5(3)-methyl-1Hpyrazole with acetyl chloride afforded the ®rst of the title compounds, (I) (Shi et al, 2006), while 5(3)-ferrocenyl-3(5)-(2pyridyl)-1H-pyrazole, synthesized by our group after acylation of the pyrazolyl NH group, generated the second of the title compounds, (II). Since 3-(2-pyridyl)-1H-pyrazole acts as a multifunctional ligand having several coordination modes (Hu et al, 2006) and exhibiting plentiful coordination chemistry from dinuclearity to multinuclearity (Lam et al, 1997), compound (II) is expected to afford an interesting coordination chemistry via the set of N 2 O donor atoms, viz. one pyridine N atom, one pyrazole N atom and one carbonyl O atom, whereas (I) can act as an N,O-bidentate organometallic ligand on coordination to a metal ion.…”