Iron, Ruthenium, and Osmium Complexes

Sodium dithionite reduction of [(McgCg)2Fe] gave the paramagnetic Fe(I) cation [(MegCg)2Fe] 149). Electron spin resonance studies have 

One of the cyclopentadienyl ligands in ferrocene can readily be replaced by benzene in the presence of AICI3 giving the benzene cyclopentadienyl cation 310, 311)  

The reaction also occurs with a wide variety of substituted arenes (Table V). Electron-donating substituents attached to either the cyclopentadienyl or the arene ring have been shown to enhance the reaction, whereas electron-accepting substituents hinder the reaction 316). The following intramolecular exchange reaction has also been observed 268)  

The effect of cyclopentadienyl or benzene ring substituents on the proton NMR shifts, polarographic half-wave potentials, and Mosshauer quadrupole splittings in the iron compounds have been shown to correlate well with the Hammett-Taft cTp parameters of the substituents (303, 306, 420). 

A compound of stoichiometry [(MeeCe)Fe(CO)2]2 has been prepared by reacting Fe(CO)5 with hexamethyldewarbenzene and is thought to have structure (XVI) 115). Monomeric complexes of the type (arene)Fe-(CO)2 have not yet been reported, but the PF3 analogs (CgHe)Fe(PF3)2 288) and (MeCeH5)Fe(PF3)2 377) have been prepared by cocondensation of iron metal vapor, PF3, and the arene at — 196°C. 

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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. 

Reactions between salts of [m Jo-7-CBioHi3] and [Fc3(CO)i2] afford the mononuclear anionic iron compound [2,2,2-(CO)3-c/o5o-2,l-FeCBioHn], typically isolated as its [N(PPh3)2] salt (11) (Chart 4). No anionic triiron complex analogous to 5 and 7 is formed in this reaction. The anionic mononuclear iron, ruthenium and osmium complexes and the previously mentioned neutral mononuclear ruthenium dicarbollide complex 4, obtained from [Ru3(CO)i2] and /Jo-7,8-C2BgHi3, are iso-lobal with the cyclopentadienide species [Mn(CO)3(ri-C5H5)] and [Fe(CO)3 (il-CsHs)]. ... 

Another interesting application is the study of the kinetics of thermodynamically unfavourable oxidations of a series of iron, ruthenium and osmium complexes with 2,2 -bipyridyl or 1,10-phenanthroline (ML32 ") (equation 28). If E ° for is more positive than E° for the... 

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