Metal complexes tricarbonyls

In a number of cases, alkenes that are too unstable for isolation have been isolated in the form of metal complexes. As example is norbomadienone, which was isolated in the form of its iron-tricarbonyl complex (11). The free dienone spontaneously decomposes to carbon monoxide and benzene (see 17-29). 

Optical Stability of Triorganostanny 1-Transit ion Metal Complexes [Methylphenyl(2-phenylpropyl)stannyl](triphenylphosphine)tricarbonyl cobalt (76)... 

One may also resort here to organotransition metal complexes. For example, benzene rings can be selectively activated to nucleophilic attack by complexation to chromium tricarbonyl (Scheme 12.8) [21]. Similarly, an allylic acetate can also be selectively activated in the presence of a bromide (29 versus 3Q) by addition of a palladium(O) catalyst in THF, which coordinates with the double bond [22] (Scheme 12.9). 

Orgel (23). Subsequently, Hubei and co-workers (24) obtained, among other products, tricarbonyl-7r-tetraphenylcyclobutadiene iron by the reaction of tolane with iron carbonyls. More recently, a general synthesis of tetra-phenylcyclobutadiene-metal complexes using ligand transfer from tetra-phenylcyclobutadiene palladium(II) halides (25) to a metal carbonyl has been described (26). It is also possible to obtain complexes containing... 

Several transition-metal complexes of cyclobutadiene have been prepared, and this is all the more remarkable because of the instability of the parent hydrocarbon. Reactions that logically should lead to cyclobutadiene give dimeric products instead. Thus, 3,4-dichlorocyclobutene has been de-chlorinated with lithium amalgam in ether, and the hydrocarbon product is a dimer of cyclobutadiene, 5. However, 3,4-dichlorocyclobutene reacts with diiron nonacarbonyl, Fe2(CO)9, to give a stable iron tricarbonyl complex of cyclobutadiene, 6, whose structure has been established by x-ray analysis. The 7r-electron system of cyclobutadiene is considerably stabilized by complex formation with iron, which again attains the electronic configuration of krypton. 

One of the most fascinating developments in borazine chemistry has been the recent isolation of hexaalkylborazine chromiumtricarbonyl complexes. A reaction was observed when hexamethylborazine was reacted Mo(CO)e but no definite products could be isolated 1S8>. However, with extremely pure starting materials using (CO)3Cr(CHaCN)3 or (CO)3(NH3)3Cr as reactants, the preparation of a borazine-metal complex has been effected iss.ieo). Solvents other than dioxane did not lead to the desired product, and it has been suggested that the reaction proceeds via a dioxane-chromium tricarbonyl complex. The reaction appears to proceed by altering the existing equilibria, indicated in the reaction as depicted in Eq. (43). 

Osmium di- and tricarbonyls on y-Al2C>3, supported metal complexes, 61 Osteoblasts... 

Under conditions of low methyl/iridium ratios, in media with low levels of water and ionic iodide, the major species in solution was found to be Ir(CO)3I, and the carbonylation reaction was found to be inhibited by increasing CO pressure. In separate experiments involving reaction of this complex with methyl iodide, the product was found to be the dicarbonyl iridium(III) species, Ir(CH3XCO)2I2. Apparently, the presence of three carbonyl ligands on the iridium(I) center is sufficient to completely inhibit any nucleophilic behavior by the tricarbonyl complex. Prior dissociation of one of the carbonyl ligands produces a metal complex capable of this type of reactivity. 

Diene complexes containing alkene or diene substituents undergo Diels Alder reactions in good yields. Hetero-Diels Alder reactions have also been reported. Chirahty transfer is observed upon reaction of chiral diene iron tricarbonyl complexes. Reaction of the chiral complex (101) with cyclopentadiene in the presence of a Lewis acid give (102) with a relatively high chirahty transfer from the metal complex (Scheme 162). 

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