Pyrrolyl metal complexes

The nitrogen atom in ri -pyrrolylmanganesetricarbonyl forms a donor-acceptor bond with transition metals. Complexes in which the pyrrolyl ring behaves as a tt ligand for the manganese atom and n-donor for the other metal were synthesized 12 (M = Mn, Re) [78JOM(157)431]. The binuclear heterobimetallic complexes... 

Almost aU of the pyrrole-, indole-, and carbazole-containing systems afforded stable Fe(ll) and Co(II) complexes. The only exceptions are hgands 44 and 47 which contain only aryl substituents. This indicates that two pairs of o-phenyl groups on the N-pyrrolyl substituents impose too much of a steric hindrance and/ or are too electron-withdrawing for the corresponding [N,N,N] metal complex to form. The two Fe(lII) precatalysts 54c, 55c were synthesized to evaluate the dependence of the polymerization performance on the oxidation state of the metal center. In total, twenty-one different N-azolyl complexes were prepared aiming at a thorough structure-activity evaluation (vide infra). 

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. 

Fig. 6.1. Known bonding modes of pyrrole and pyrrolyl ions in metal complexes.

Metal complexes containing the anionic pyn olyl ligands are much more frequent throughout the periodic table, and the Tj N and Tj binding modes are dominant in the coordination chemistry of such anions [1, 13]. ri N-Pyrrolyl complexes may be synthesized by in situ N-H activation of Pyr by a low-valent metal fragment as in Eq. 

Oxidative addition of C-H bonds leading to Tt (C)pyrrolyl(hydride) metal complexes (Eq. 6.3) has also been described [25]. 

Ihe interaction of polynuclear metal complexes with pyrrole-type molecules has also attracted some attention, and it is interesting in connection with possible interactions with surfaces, where vicinal metal atoms may simultaneously interact with the pyrrole molecule. Cluster compounds containing intact coordinated pyrrole ligands are not known, since this reaction invariably involve N-H and/or C-H bond activation to yield derivatives most frequently containing bridging pyrrolyl ligands, as exemplified in Eig. 6.2. 

Table 6.1. Metal complexes of pyrrole and pyrrolyl ligands. 155...

Electropolymerization represents a useful method to control precisely the deposition of thin films of conducting polymers. These thin films have a wide variety of applications in optical devices [29]. Walder and coworkers showed that photocurrents could be generated using a trilayer thin film. The three different electropolymerized polymers were cleverly prepared from a common precursor, 4-methyl-4 -(2-pyrrolyl-1 -ethyl)-2,2 -bipyridine 7 two were alkylated, diquat derivatives and one was the Ru metal complex of this ligand, which acted as a sensitizer. The appropriate ordering of the triad in terms of their redox potentials led to the maximizing of the photocurrent (Scheme 7.2) [30],... 

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