Organometallic anionic

An interesting example of a spin-admixed nonheme iron(lll) complex with S - (3/2, 5/2) ground state is the organometallic anion [Fe CeCls) which has four pentachloro phenyl ligands in tetrahedrally distorted planar symmetry [122]. 

Keywords Cation-radical salts, Molecular conductors, Organic superconductors, Organometallic anions, Tetrakis(trifluoromethyl)metallates, Tetrathiafulvalene... 

Scheme 1 Electron-donor molecules that have been utilized as components of cation radical salts with organometallic anions...

Among organometallic anions, those of the M(CF3)4 (M = Cu, Ag and Au) family have the been most studied as components of cation radical salts. These anions were originally chosen because of their surprising stability and solubility in organic... 

Organometallic anions react with halophosphazenes to replace halogen atoms by organometallic units. The first reactions of this type discovered are illustrated in Scheme 5. The metallophosphazenes are surprisingly stable. Moreover, as shown below, hexachlorocyclotrlphosphazene reacts with an organometallic dl-anlon to yield both a dlmetallo derivative (XXXI) and a trl-metallic cluster derivative (XXXII). The latter compound is... 

The formation of the heterocycle 1 from the xylylene-bis-phosphonium salt 2 and PCI3 proceeds via a detectable intermediate 3 in a cascade of condensation reactions that is terminated by spontaneous heterolysis of the last remaining P-Cl bond in a cyclic bis-ylide-substituted chlorophosphine formed (Scheme 1) [15]. The reaction scheme is applicable to an arsenic analogue of 1 [15] and to bis-phosphonio-benzophospholides with different triaryl-, aryl-alkyl- and aryl-vinyl-phosphonio groups [16, 18, 19], but failed for trialkylphosphonio-substituted cations here, insufficient acidity prohibited obviously quantitative deprotonation of the phosphonium salts, and only mixtures of products with unreacted starting materials were obtained [19]. The cations were isolated as chloride or bromide salts, but conversion of the anions by complexation with Lewis-acids or metathesis was easily feasible [16, 18, 19] and even salts with organometallic anions ([Co(CO)4] , [CpM(CO)3] (M=Mo, W) were accessible [20]. 

In the most general sense, any anion radical produced by reduction with a metal, or by electrolytic reduction in the presence of a metallic counterion could be considered an organometallic anion radical. Any review based on such a definition would be monumental. To achieve a manageable volume of material, with a content suitable to the context of this series, we have limited this chapter to anion radicals produced from organometallic compounds. Anion radicals for which the metal is present solely as the reducing agent or counterion have, for the most part, been excluded. 

A variety of preparations for these complexes have been developed, one of which is the reaction of ally I bromide with an organometallic anion ... 

Beer PD, Hayes EJ. Transition metal and organometallic anion complexation agents. Coord Chem Rev 2003 240 167-89. 

The net charge on the complex is also an important factor, and organometallic anions are among the most effective electron donors currently available (10). Conversely, the positively charged organometallic cations are useful electron acceptors in measure with the magnitudes of their electron affinities (11). 

The establishment of electron-transfer equilibria is allowed by the unique stabilizations inherent in the organometallic anion TpMo(CO)3 [where Tp = hydridotris(3,5-dimethylpyrazolyl)borate] (85), in which the 17-electron radical (m20 is persistent (56). Since other members of the group VIB metals, namely, TpW(CO)3 and TpCr(CO)3-, are also available (87), this triad of anions enables the structural effects to be systematically examined,... 

Electron-transfer equilibria of the organometallic anions TpM(CO)3- can be examined by coupling them with a graded series of triarylpyrylium cations (TaP+) for which 1-electron reduction potentials are known to be strongly dependent on the substituents (88). The evaluation of the constant K for the electron-transfer equilibrium in Eq. (39) requires the quantitative analysis of the anionic organometallic redox couple in Eq. (38), as well as that of triarylpyrylium cation. 

Direct evidence for the involvement of the organometallic anions TpM(CO)3 in contact ion pairs obtains from the electronic transitions associated from proximate cation-anion pairs and delineated as charge-transfer excitations by Mulliken (7). This consideration is brought out by the dramatic colors obtained on the exposure of the TpM(CO)3- anions to selected pyridinium cations with reduction potentials °d that are sufficiently negative to obviate spontaneous electron transfer. Thus, the mixing of a dilute, pale yellow solution of Bu4N+ TpMo(CO)3 in dichloromethane with a colorless solution of A-methyl-4-phenylpyridinium (MPP+) triflate with an value of —1.3 V versus SCE immediately produces a deep purple coloration. The quantitative effect of this color change is... 

The isostructural pyrazolylborate complexes TpM(CO)3 thus form a graded series of organometallic anions with donor strengths increasing in... 

Several good reviews (3-10) and books (11,12) have been published on phase-transfer catalysis, should the reader desire a more detailed examination of the phase-transfer process. Although hundreds of examples of the application of phase-transfer catalysis to organic chemistry have appeared in the literature (13), there were, prior to 1976, no such examples in organometallic chemistry despite acceptance of the pivotal role played by organometallic anions in many stoichiometric and catalytic reactions. Since the first publication on organometallic phase-transfer catalysis (14), the field has developed sufficiently rapidly to justify an account at this time. A brief review was published by Cassar (15), and another by the same author is in press. 

The organometallic anions [Mn2(CO)gCl2(NCSe)2] and [Mn2(CO)g-(NCSe) ] are each believed to contain terminal A-selenocyanato groups, and the latter also has two bridging selenocyanates (278). 

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