Metal complexes ferrocene

M. C. Zerner, G. H. Loew, R. F. Kirchner, and U. T. Mueller-Westerhoff, /. Am. Cbem. Soc., 102, 589 (1980). An Intermediate Neglect of Differential Overlap Technique for Spectroscopy of Transition-Metal Complexes. Ferrocene... 

In 2006, for the first time, the decoration of viral particles with redox-active moieties was reported [83,96]. The decoration of CPMV with a redox-active organo-metallic complex, ferrocene, and also with an organic redox-active compound, viologen, was achieved. Both approaches led to the generation of monodisperse redox-active nanoparticles the redox centers were presented in multiple copies on the solvent-exposed outer surface. 

Cyclopentadiene [542-92-7] (CPD), CsHe, (1), and its more stable dimer, dicy-clopentadiene [77-73-6] (DCPD), C10H12, (2), are the major constituents of hydrocarbon resins, cyclic olefin polymers, and a host of specialty chemicals. They can be transformed into many chemical intermediates used in the production of pharmaceuticals, pesticides, perfumes, flame retardants, and antioxidants. Because of their wide industrial uses, their chemistry has been extensively investigated and documented. Numerous reviews (1-12) have been published on the subject. The production processes and industrial uses of CPD and DCPD are summarized in Reference 13. In addition to the classical organic reactions, CPD forms organic metallic complexes, ferrocene, with transition metals (14). Some of these complexes have been established as excellent olefin polymerization catalysts. Several reviews have been published on this rapid growing field (15-19) (see Single-Site Catalysts). 

Section 14 14 Transition metal complexes that contain one or more organic ligands offer a rich variety of structural types and reactivity Organic ligands can be bonded to a metal by a ct bond or through its it system Metallocenes are transition metal complexes m which one or more of the ligands is a cyclopentadienyl ring Ferrocene was the first metallocene synthesized Its electrostatic potential map opens this chapter... 

On the basis of these results it seems to the present author that inner and outer complexes can reasonably be assumed for the electron transfer to the diazonium ion, but that an outer-sphere mechanism is more likely for metal complexes with a completely saturated coordination sphere of relatively high stability, such as Fe(CN) (Bagal et al., 1974) or ferrocene (Doyle et al., 1987 a). Romming and Waerstad (1965) isolated the complex obtained from a Sandmeyer reaction of benzenediazonium ions and [Cu B ]- ions. The X-ray structural data for this complex also indicate an outer-sphere complex. 

Transition metal complexes containing Si-OH groups have been isolated in low yield after hydrolysis of the products formed in the reaction between (Me2N)2SiCl2 and ferrocene under Friedel-Crafts conditions [Eq. (25)] (151). 

The effects of metal-to-metal electronic coupling are observed for several complexes where a ferrocene moiety is bound to transition-metal complexes with a -conjugated chain, 68 (167), 69 (168), and 70 (169). Tertiary amine-ferrocene conjugated molecules, 71, show two-step le oxidation, and their monocationic forms exhibit strong LMCT bands at 600-700 nm (170). 

Of course, commercially available transition metal complexes are stable at room temperature because they have achieved an 18-electron noble gas-like electronic configuration. Thus, molecules like iron pentacarbonyl [Fe(CO)s], ferrocene [Fe(C5H5)2], as well as piano-stool complexes such as C5H5Co(CO)2 are chemically quite inert. In order to study bimolecular reactions, it is necessary to first prepare unsaturated complexes. For studies using molecular beams, one approach is through photolysis of a stable volatile precursor in a supersonic nozzle. 

Dendrimers built around a metal complex as a core. These compounds can be considered metal complexes of ligands carrying dendritic substituents (Fig. 1 a). The most commonly used metal complex cores are porphyrin complexes, polypyridine complexes, and ferrocene-type compounds. 

The electroactive units in the dendrimers that we are going to discuss are the metal-based moieties. An important requirement for any kind of application is the chemical redox reversibility of such moieties. The most common metal complexes able to exhibit a chemically reversible redox behavior are ferrocene and its derivatives and the iron, ruthenium and osmium complexes of polypyridine ligands. Therefore it is not surprising that most of the investigated dendrimers contain such metal-based moieties. In the electrochemical window accessible in the usual solvents (around +2/-2V) ferrocene-type complexes undergo only one redox process, whereas iron, ruthenium and osmium polypyridine complexes undergo a metal-based oxidation process and at least three ligand-based reduction processes. 

The discovery in 1951 of the transition metal rr-complex, ferrocene or bis-cyclopentadienyl-iron, Fe(Cp)2, (1, 2) led to enormous interest being shown in the possible structures of such compounds and in the nature of the metal-ring bonding. Within a year the sandwich type structure (Fig. 1) had been proposed (2), and an outline treatment of the metal 3d-ligand 7r-orbital interaction by Jaffe (4) was soon followed by a more detailed molecular... 

Ferrocene is a very stable compound that melts at 173 °C and can be sublimed without disruption of the metal complex. Many reactions exhibited by ferrocene are essentially those of an aromatic organic compound. For example, sulfonation of ferrocene can be achieved as follows ... 

The dithiophosphonic acid monoesters, RP(OR )(S)SH can be conveniently prepared by cleavage of dimeric, cyclic diphosphetane disulfides, [RP(S)S]2 with alcohols, silanols, or trialkylsilylalcohols180 and then can be converted into metal complexes M[SPR(OR )]2 without isolation.181 The substituted ferrocenyl anion, (N3C6H4CH20)(CpFeC5H4)PS2 has been prepared in two steps from P4Sio, ferrocene and hydroxymethylbenzotriazole (and its salt was used for the preparation of some nickel and rhodium complexes).182 Zwitter-ionic ferrocenylditiophosphonates,... 

Over the past decade a number of new covalently bonded TTF/ferrocene adducts have been reported [77, 78]. The crystal structure of the l,l -bis(l,3-dithiole-2-ylidine)-substituted ferrocene derivative has been published [77]. In this complex, ferrocene has essentially been incorporated as a molecular spacer between the two l,3-dithole-2-ylidene rings forming a stretched TTF molecule. This adduct, and its methyl-substituted derivative, have been combined with TCNQ to form charge-transfer complexes with room temperature powder conductivities of 0.2 S cm-1. Similar diferrocenyl complexes have been prepared with bis (dithiolene) metal complexes [79, 80]. 

Until now, only two families of ligands have been realized where both P groups are attached to side chains, probably because the resulting metal complexes have relatively large chelate rings which usually are not suitable for enantioselective catalysis. A cursory inspection of the ligands depicted in Fig. 25.14 shows that, due to steric bulk of the ferrocene backbone, both diphosphines probably have sufficiently restricted flexibility so that good stereocontrol is still possible. 

However, because of the mostly very slow electron transfer rate between the redox active protein and the anode, mediators have to be introduced to shuttle the electrons between the enzyme and the electrode effectively (indirect electrochemical procedure). As published in many papers, the direct electron transfer between the protein and an electrode can be accelerated by the application of promoters which are adsorbed at the electrode surface [27], However, this type of electrode modification, which is quite useful for analytical studies of the enzymes or for sensor applications is in most cases not stable and effective enough for long-term synthetic application. Therefore, soluble redox mediators such as ferrocene derivatives, quinoid compounds or other transition metal complexes are more appropriate for this purpose. 

As mentioned in Chapter 4, Section 1, to date, several hundred ferrocene derivatives have been synthesized. A further increase in their number has occurred in recent years due to the use of ferrocene derivatives as ligands in metal complexes.2 Since some examples of metallic centres branched by several ferrocene units have already been presented in Chapter 4, Section 1.4.2 (when dealing with dendrimers), we will limit our discussion... 

We like to conclude the present section with an example which points out the role played by the electronic effects of ferrocene ligands in stabilizing uncommon oxidation states in metal complexes rather than their electrochemical properties. Figure 10 shows the molecular structure of the Ir(I) monocation [Ir(dppf)2]+ (dppf= l,l -bis(diphenylphosphi-no)ferrocene)7 and its electrochemical behaviour in thf solution.8... 

Sihcon chemistry also provides a means for preparing dendrimers capped with metal ions [3,65]. For example, ferrocene [78,79], Co +, [80], Ru [81], and [9] have been hnked to the periphery of sihcon-based dendrimers. These materials are prepared by displacing reactive Si-Cl functional groups with any of a variety of nucleophiles, such as amines, alcohols, or Grignard reagents, containing the metal complexes or hgands. 

Abstract This review describes recent results in the field of poly(aryleneethynylene)s (PAEs) that contain metal ions in the polymer backbone, or in the polymer side chain. This work is focused primarily on polymers possessing ligands of metal complexes as part of the aryle-neethynylene chain. PAEs with porphyrinylene in the backbone have also been addressed. Synthetic routes toward the polymers, as well as their photochemical, photophysical, and electrochemical properties, are presented. Monodisperse oligo(phenyleneethynylene)s with terminal metal complexes or with a ferrocene and thiol at each end are mentioned. 

Bielawski et al. described the synthesis and properties of NHC 15 introducing a novel carbene architecture incorporating a l,l -disubstituted ferrocene moiety as backbone [71 ]. In its metal complexes [71,72] this carbene ligand supported a long-range electronic communication between the iron center and the carbene coordinated transition metal. 

---