Arborols Based on Luminescent and Redox‐Active Transition Metal Complexes
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Carter F. L., 1988, Molecular Electronic Devices
E.Buchlein W.Wehner F.Vögtle Synthesis 1978155;
For recent papers see (a)T.Nagasaki M.Ukon S.Arimori S.Shinkai J. Chem. Soc. Chem. Commun. 1992 608;
(a)S.Campagna G.Denti L.Sabatino S.Serroni M.Ciano V.Balzani J. Chem. Soc. Chem. Commun.19891500;
Denti G., Perspectives in Coordination Chemistry, 153
That is a species containing 22 metal ions;
Block P. B., 1990, Inorganic Chemical Nomenclature
S.Serroni G.Denti Inorg. Chem. in press.
NMR:1H NMR spectrum of2and3in [D3]acetonitrile solution showed several signals between δ = 4.20 and 4.47 that can be attributed toN‐methyl groups of different stereoisomers. These signals completely disappear on demethylation and are in fact absent in4.Conductivity values (Ω−1cm−1mol−1; l.0 × 10−3M solutions in acetonitrile 20 °C):2 364.0;3 874.7;4 472.3. IR [5 9 11]: the most characteristic bands are those of bridged (system of four bands between 1470 and 1390 cm−1) unbridged (990 cm−1) andN‐methylated (1626 cm−1) 2 3‐dpp ligands. UV/VIS spectra (acetonitrile solutions) [5 11]: ligand‐centered 2 3‐dpp bands: λmax[nm] (ϵ [M−1cm−1]):2 304 (25100);3 296 (137000);4 264 (108000); metal‐to‐ligand charge transfer bands: λmax[nm] (ϵ [M−1cm−1]):2 575 (8490);3 456 (42600);4 461 (38 200). Luminescence at 298 K (in acetonitrile solution) [5]: λmax[nm]:3 714;4 722; at 77 K (methanol/ethanol 4:1 (v/v) rigid matrix) [5]: λmax[nm]:3 700;4 698. Compound2is not emissive. Electrochemical oxidation (potentials [V] vs. SCE; number of electrons involved; ΔEp[mV] [12]: 2: +0.63 1 70 3: +1.70 3 110; electrochemical analysis of4was prevented by adsorption of the compound at the electrodes.
Acetonitrile was used as solvent and tetrabutylammonium tetrafluoroborate as supporting electrolyte. Cyclic voltammograms were usually obtained at a scan rate of 20 mVs−1. Differential‐pulse voltammetry was performed with a scan rate of 20 mV s−1 a pulse height of 50 mV and a duration of 50 ms. Ferrocene (5×10−4M) was employed as a reference. The multielectron nature of some peaks was elucidated as in ref. [5b].
[Ru{μ‐2 3‐dpp)Ru(bpy)2}2Cl2](PF6)4(7) (0.084 g 0.042 mmol) in water/ethanol 1:1 (v/v) (5 mL) was treated with silver nitrate (0.014 g 0.084 mmol). After the mixture had been stirred at room temperature for 2 h a solution of [Ru{(μ‐2 3‐dpp)Ru(2 3‐dpp)2}3](PF6)8(4) (0.025 g 0.007 mmol) in ethylene glycol (3 mL) was added. The reaction mixture was refluxed for seven days then cooled to room temperature. AgCl was separated by repeated centrifugations the mother liquor concentrated by evaporation in vacuum and an excess of solid NH4PF6 methanol (2 mL) and die thy 1 ether (10 mL) were added. The crude product was filtered off and then purified by SEC on Sephadex G‐75 (acetonitrile eluant). The eluate was concentrated in a rotary evaporator to 2 mL and the product6was recovered as a cyclamen (very dark reddish purple) powder by addition of diethyl ether (about 15 mL). Yield: 0.086 g (73%) after purification. Anal.: Calcd. including 25 H2O: C 36.2 H 2.6 N 10.0. Found: C 35.9 H 2.3 N 10.4. Conductivity [Ω−1cm−1mol−1] (1.0 × 10−3Msolution in acetonitrile 20 °C): 2297.4. IR: system of four bands between 1470 and 1390 cm−1 typical of bridged 2 3‐dpp. No typical band for unbridged 2 3‐dpp at 990 cm−1is present.
In principle the complexes 1–7 can exist as different isomers depending on the arrangement of the ligands around the metal ions. A careful analysis of the 2D‐COSY 400 MHz1H NMR spectrum of the [Ru(2 3‐dpp)3]2+ precursor that permitted a complete assignment of the signals [15] has shown that the purified material was obtained as a mixture of themerandfacisomers in which the mer isomer was predominant (92%). The oligometallic complexes can also be a mixture of several diastereoisomeric species since each metal center is also a stereogenic center. For these reasons structural investigations on these systems are difficult [11e]. Differences arising from the presence of isomeric species are not expected to be large in the electrochemical and spectroscopic results described in this paper [16].
G.Predieri C.Vignali G.Denti S.Serroni unpublished.
Balzani V., 1991, Supramolecular Photochemistry, Ellis Horwood