Cobalt complex cluster

In organometallic systems in particular, clusters with bridging alkylthiolates are well known, as exemplified by Co2(Cp)2(/i-SCH3)2, which undergoes reactions with alkyne-cobalt complexes to yield trinuclear clusters.170... 

A few clusters of interest containing germanium and transition metals have been reported.136-138 Dimethylgermane was found to replace only the bridging carbonyls between cobalt in a mixed germanium/cobalt/iron cluster complex (Equation (107)), and replacement of the carbonyl bridging the iron metal centers was not observed.137 A similar reaction leads to replacement of a bridging carbonyl in a mixed cobalt/silicon cluster (Equation (108)).136... 

Dinuclear clusters ferrous site distortion, 38 175 spin ladder, 38 182-183 Dinuclear cobalt complex, 45 291-293 Dinuclear complexes osmium, electrochemistry, 37 321-323 quadruply bridged, 40 187-235 axial ligand substitution properties, 40 232-234... 

Hydridotris(pyrazolyl)borates, as cobalt complex ligands, 44 274-278 Hydroboration, 16 230-234 chain lenghtening, 16 231-232 role in sythesis, 16 231, 232 Hydrocarbons clusters, 18 57-59... 

Involvement of two nucleophilic nitrogen atoms is thus typical for the amino heterocycles. The mutual disposition of the pyridine and amine nitrogen atoms allows the formation of chelate structures for the cobalt complexes of purine, 221 and 222. Structures with the N, iV -five-membered metal cycles were proven for the tri- and tetranuclear complexes of silver ) with 8-aminoquinoline (223) (92IC4370), and polymeric copper- and rhodium-acetate clusters (224). Another coordination mode can be found in the complexes of 4-amino-3,5-bis(pyridin-2-yl)-l,2,4-triazole, (225 or... 

There are a sufficiently large number of complexes, mainly of germanium, containing more than one type of transition metal, to warrant a separate discussion some examples have already been mentioned (viz. 38 and 57). Mackay and Nicholson (89,91) have described the reaction between [Fe2-(CO)8(//-GeH2)2] and [Co2(CO)8], which affords the mixed cobalt-iron clusters [Fe2(CO)8 /i-Ge(Co2(CO)7) 2], 82, and [Fe2(CO)7 /i-Ge(Co2-(CO)7) 2], 83, the latter having been characterized by X-ray diffraction. This is isoelectronic with the iron-germanium cluster, 63, and both adopt very similar structures. 

No terminal fluoromethylidyne complexes have been reported, but triply bridging CF ligands are observed in the cobalt complex 14 (45), in various substituted analogues (46-49), and in the osmium complex 15 (50). An iron cluster 16 containing two triply bridging CF ligands has also been reported... 

Indoline, in trinuclear Ru and Os clusters, 6, 725 Indolizidine, via cyclization-hydrosilylation, 11, 389-390 Industrial processes, in Ziegler-Natta polymerizations, 4,1040 Inflammation, drugs for, 12, 460 Infrared spectroscopy applications, 1, 501 cobalt complexes, 1, 488... 

Formal silylcarbonylation and silylformylation reactions are mainly catalyzed by cobalt and rhodium complexes (clusters) yet, Chatani et al. [158] have found a new type of carbonylation of diynes with trialkylsilanes leading to catechols (Eq. 100). 

This reaction was first reported in the early 1970s as an unexpected result in search for the synthesis of new organometallic cobalt complexes [13-18]. Dicobalt octacarbonyl was the only cluster used in its beginnings, although now, many cobalt species and other metal complexes are able to mediate or catalyze this reaction. Thus, the stoichiometric reaction has been performed with Zr, Ni, Fe, Ti, W and Mo derivatives. In addition, heterobimetallic Co - W and Co - Mo complexes (1), are suitable precursors for the PKR and impart a high degree of selectivity in the process giving exclusively endo adducts 2 (Scheme 2) [19,20]. 

Modified carbonylcobalt complexes can catalyze the PKR. One or more CO can be substituted by phosphines, and these can be immobilized in resins thus giving anchored cobalt complexes (27), that were able to catalyze the reaction of 28 giving 29 with good yield and minor amounts of 30 (Scheme 10) [76]. Other cobalt metal clusters like Co4(CO)i2 [77] or methyl-idynetricobalt nonacarbonyl [78] have exhibited high reactivity in the catalytic PKR. 

Our group has used a combined metathesis-PKR for the synthesis of tricyclic compounds in one step. The process starts from pure cobalt complexed dienynes 52. The cobalt cluster acts first as a protecting group to avoid undesired enyne metathesis processes. The methodology allows the formation of tricyclic [6.5.5] (53) and [7.5.5] (54) structures including, in some examples, oxygen or nitrogen. Tricycles 53 are obtained in a total stereoselective manner, while compounds 54 are formed as mixtures of two diastereomers (Scheme 17) [110]. 

Keese envisioned the use of a tandem PKR for the synthesis of fenestranes. The second cycloaddition was in principle problematic as it involved an al-kene conjugated with a ketone. They were surprised when they observed the direct formation of the tetracyclic unit 136 from the endiyne 135 although with low yield [ 148]. Further studies from this group led to a mechanistic proposal that explained this result. It was clear from the fact that compound 140 failed to react, that the second PKR had to start from an intermediate metal-lacycle rather than from the uncomplexed final cyclopentenone. Thus, cobalt complex 137 would lead to 138 were both metal clusters would interact giving intermediate 139 which would evolve in the usual way to the final product (Scheme 42) [149]. These systems have been obtained later by Chung s group using cobalt nanoparticles as commented above (Sect. 2.4) [131]. 

The chemistry and synthetic utility of cobalt complexed propargyl cations have been demonstrated by Nicholas in an impressive series of papers, and the area was reviewed in 1987.72 More recently, reviews of cluster-stabilized cations73 and propargylium complexes74 have appeared. Two general routes for the synthesis of dicobalt-propargylium complexes have been developed. The most commonly used method is the treatment of an alkynic ether or alkynic alcohol-hexacarbonyldicobalt complex with a Lewis or Bronsted acid [Eq. (7)]. 

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