Pyrroles transition metal complexes

Template and capping reactions feature in recent work. A number of sterically hindered H20 and N4 ligands have been prepared in which a quadridentate Schiff base is capped by condensation of salicylaldehyde or pyrrole-2-carbaldehyde with a series of bis(8-aminonaphthyl)alkyl ethers. These ligands combine the versatility of the Schiff base with the protective features well known for certain model porphyrin systems, and appear to be of some interest. The zinc(II) complex and other transition metal complexes have been prepared.340... 

RAs) and multiple bonds to carbon such as RC=As, R 2C=AsR, RAs=AsR, R 3As=CR, pyridine (C5H5AS), and pyrrole (C4H4ASR) analogues and their transition metal complexes. ... 

A number of transition metal complexes containing weakly basic (5-member ring) HDN-related ligands are known. The authenticated bonding modes of pyrrole (Pyr) and pyrrolyl ions (Pyl) -or their alkylated analogues- in mononuclear metal complexes are summarized in Fig. 6.1. Pyrrole is a 5-member aromatic heterocycle in which the lone pair is delocalized over the n system of the ring, and it is therefore an electron rich molecule that reacts readily with electrophiles but is not susceptible to nucleophilic attack. 

Murakami Y, Yamada S, Matsuda Y, Sakata K (1978) Transition-metal complexes of pyrrole pigments XV coordination of pyridine bases to the axial sites of cobalt corroles. Bull Chem Soc Jpn 51 123-129... 

Different examples of hydrogenation of organic molecules with conducting polymer modified electrodes have been described rather recently in the literature. Two different kinds of modification have been considered for this application insertion of metallic particles, and functionalization of pyrrole with transition metal complexes leading, after electropolymerization, to active electrodes. 

With transition metal complexes (typically rhodium compounds), it is possible to functionalize pyrrole and to obtain active electrodes for the hydrogenation of ketones. An example showing the behaviour of a film of poly(pyiTole-Rh(lll)bipyridyl) is the reduction of cyclohexanone into cyclohexanol with a chemical yield of 79% [110], This molecular electrode is also suitable for the reduction of water in hydrogen, Electrocatalytic hydrogenation of other ketones, unsaturated ketones or aldehydes, has been studied recently [174-176], These hydrogenation reactions are performed in an aqueous medium and the modified electrodes are obtained after electropolymerization of pyrrole substituted 2,2 -bipy-ridine or 1,10-phenanthroline complexes of Pd(Il) or of Rh(Ill). More precisely, with the Pd(ll) complex... 

Transition-metal complex Solvent Pyrrole cone (M) Electrolyte cone. (M) E.PP (V) Current density (mA/cm ) Condtictivity (S/cm) Reference... 

The majority of the anionic transition-metal complexes discussed above are electrostatically bound to the charged PPy moiety. An interesting alternative can be found in the work of Bidan et al. [25]. These workers synthesized Cu(dpp)2, which contained two entwined dpp ligands covalently attached to pyrrole units. Electropolymerization of the complex yielded an... 

The number of anionic transition-metal complexes that may be electrochemically incorporated into PPy is limited and depends primarily on the electrochemical stability of the species. In order to maintain its chemical integrity upon incorporation into the polymer, the complex should not undergo irreversible oxidation (at the anode) or reduction (at the cathode) during the electropolymerization of pyrrole. The transition-metal complexes shown in Figures 12.2 and 12.3 satisfy these criteria. The following consists of a review of the work performed within our laboratories at Monash University on PPy containing transition-metal complexes. 

PPy films containing transition-metal complexes should find applications in areas similar to those in which conventional PPy films are used [1]. In addition, the films discussed in this chapter may possess unique biosensing/chemical sensing properties. This area of research is being actively pursued at Monash University [101]. A different approach for the incorporation of transition-metal complexes into PPy, that has already received some attention [25,35], involves using chemically modified pyrrole monomers. This method should enable a wider range of transition-metal complexes to be incorporated into PPy than has been possible previously. 

For the first time the phenomenon of significant rise of not only initial rate (W j), but also the selectivity (S = [PEH] / A[RH] 100%) and conversion degree (C = A[RH]/[RH]p 100%) of oxidation of alkylarens (ethylbenzene, cumene,) into ROOH by molecular O2 under catalysis by transition metals complexes M(L )2 (M = Ni(ll), Co(ll), L =acac ) in the presence of additives of electron-donor monodentate ligands (L = HMPA (hexameth-ylphosphorus triamide), dimethyl fomiamide (DMF), N-methyl pyrrol-idone-2 (MP)), MSt (M = Li, Na, K) was found by authors of the articles [55-57]. 

Other noteworthy studies on the polymerization of pyrrole in aqueous solutions under different conditions have been performed. Oxygen and water molecules were found to participate in electropolymerization and introduce carbonyl and hydroxyl groups into the films as identified by XPS and FT-IR spectra [56]. Pyrrole films containing transition metal complex anions (a = 100 S cm ) [57] and dodecyl-benzenesulfonate (cr up to 120 S cm ) [58] have been grown in aqueous solutions. 

J. Ridley and M. Zerner, Theoret. Chim. Acta, 32, 111 (1973). An Intermediate Neglect of Differential Overlap Technique for Spectroscopy Pyrrole and the Azines A. D. Bacon and M. C. Zerner, Theoret. Chim. Acta, S3,21 (1979). An Intermediate Neglect of Differential Overlap Theory for Transition Metal Complexes Fe, Co, and Cu Chlorides W. D. Edwards and M. C. Zerner, Theoret. Chim. Acta, 72, 347 (1987). A Generalized Restricted Open-Shell Fock Operator. 

A similar transition-metal-complex template, a Co porphyrin with a single pendant pyrrole group also shown in Fig. 5-23 was used by Bedioui and coworkers [55] to prepare a Co-porphyrin-derivatized P(Py), inunobilized on a carbon electrode, which... 

---