Cyclopentadienylcobalt dicarbonyl

Subtle differences in the behavior of azoarenes toward cobalt carbonyl derivatives are observed in regard to metal-complex formation. Azobenzene is transformed by dicobalt octacarbonyl in processes of orthometallation and carbonyl insertion into 2-phenylindazolin-3-one (see Section IV,D,2). In contrast, cyclopentadienylcobalt dicarbonyl effects N—N bond cleavage, and carbonylation of the isolable complex 88a provides 1 -phenylbenzimid-azolin-2-one (Scheme 106).171... 

These compounds have been obtained indirectly by reactions of silylated acetylenes with metal carbonyls or olefin complexes. Thus, trimethylsilylphenylacetylene reacts with rj5-cyclopentadienylcobalt dicarbonyl, cobaltocene, or rjs-cyclopentadienyl-(l,3-cyclooctadiene) cobalt, in refluxing xylene, to give a mixture of cis- and trans-bis-(trimethylsilyl)cyclobutadiene complexes (R = Me, R = Ph) 68, 127, 137) ... 

Cyclopentadienyl-modified silica reacts with Co2(CO)g to yield cyclopentadienylcobalt dicarbonyl according to equation (8). The supported complex is characterized by IR spectroscopy by analogy with its homogeneous counterpart. 

Rosenblum et al. 386> reported a very elegant synthesis of cyclobutadiene iron tricarbonyl starting from oc-pyrone. The corresponding reaction with cyclopentadienylcobalt dicarbonyl produces cyclobutadiene-(cyclopentadienyl)cobalt 88S>. 

An elegant modification of this sort of intrmolecular cycloaddition strategy was reported by Funk and Vollhardt in 1980.81 Cooligomerization of bis(trimethylsilyl)acetylene with a substituted diyne under mild reaction conditions catalyzed by cyclopentadienylcobalt dicarbonyl gave a transfused tetracyclic adduct [Eq. (24)]. 

Indanes and tetralins. A general synthesis of indands (3a) and tetralins (3b) involves the cooligomerization of 1,6-heptadiyne (la) or 1,7-octadiyne (lb) with substituted acetylenes (2) catalyzed by cyclopentadienylcobalt dicarbonyl in -octane. In general, yields of (3) are only modest (15-25%) because of... 

Two general methods have been used for the preparation of cyclopentadienylcobalt dicarbonyl the reaction between dicobalt octacarbonyl and cyclopentadiene and the reaction of bis (cyclopentadienyl) cobalt with carbon monoxide at elevated temperatures and pressures. The method given here is a modification of the second method, and as in the preparation of cyclopentadienylvanadium tetracarbonyl described above, avoids isolation of the intermediate pyrophoric bis(cyclopentadienyl)metal derivative. 

The dark solution in the autoclave is removed and filtered with suction. The autoclave is rinsed and the residues are washed with at least an additional 200 ml. of benzene. The filtrate is then distilled through a Vigreux column at reduced pressme. Benzene is removed first at such a pressure as to give a pot temperature of 35 to 45°. The benzene distills over slightly red in color due to the presence of traces of the product. The product is then distilled at 37 to 38.5° at 2 mm. to give 39 g. (25% yield) of cyclopentadienylcobalt dicarbonyl as a deep red liquid. The product is best stored under nitrogen in a refrigerator. 

Cyclopentadienylcobalt dicarbonyl is a deep red liquid, easily miscible with the usual organic solvents. It is somewhat air-sensitive and is best stored under nitrogen. It undergoes a variety of interesting reactions. 

A novel procedure for generation of orthoquinodimethanes, developed and exploited by Vollhardt, is based on the co-oligomerization of a-a>-diacetylenes and monoacetylenes in the presence of cyclopentadienylcobalt dicarbonyl catalyst. " The reaction is carried out by addition of the diacetylene and catalyst to excess refluxing monoacetylene. When n = 2, the benzocyclobutene co-oligomerization product formed in situ is in thermal equilibrium with the corresponding o-quinodimethane, which can undergo Diels-Alder cyclization with an appropriately positioned dienophile. 

Allyl halides add to the more reactive d complexes. Both a- and w-allyl complexes are found, occasionally both in the same system. An example of this reaction with allyl chloride is that of 7r-cyclopentadienylcobalt dicarbonyl discovered by Fischer 58) and reinvestigated by Heck (66). Both cationic (XLI I) and neutral complexes (XLIII) are formed, depending on the conditions. The cationic sr-allyl complex (XLII) is interesting in that this is another example of the stepwise addition of an electrophile to a live-coordinate rf complex. The reader should remember that the formation of the TTrallyl group entails the loss of an additional neutral ligand. 

With ff-cyclopentadienylcobalt dicarbonyl, it has been shown that when allyl iodide is used a neutral complex w-CsH5Co(ir-C3H5)I is formed in 10% yield, as well as the analogous iodide salt of complex (IV) 48). The reaction of chromocene with allyl iodide does not give an allyl complex (26). 

Perfluoroalkyl iodides also react with 7r-cyclopentadienylcobalt dicarbonyl 105), TT-cyclopentadienylnickel carbonyl 102a, 106), l,2-bis(diphenyl-phosphino)ethanenickel dicarbonyl 107), and di[l,2-bis(diphenylphos-phino)ethane]molybdenum dicarbonyl 106) to afford perfluoroalkyl transition metal compounds. 

JT-Cyclopentadienylcobalt dicarbonyl reacts with perfluorobut-2-yne to give a red, air-stable compound, 7r-CsIl5CoC8F 2, m.p. 166° C. This substance is extremely stable chemically, and can be recovered after treatment with butyllithium, concentrated nitric acid, bromine, and several other regents 136). On the basis of its diamagnetism and infrared and NMR... 

FlO. 2. F NMR spectra of the heterocyclic compounds obtained by treating iron pentacarbonyl or ir-cyclopentadienylcobalt dicarbonyl with tetrafluoroethylene. Spectra taken at 56.4 me. Reproduced by permission of the Varian Associates NMR at Work Series, No. 81. 

A new one-stage synthesis of annelated pyridines, involving the cobalt-catalysed co-oligomerization of dialkynes HC=C(CH2)nC=CH (n = 3, 4, or 5) with nitriles RCN (R = alkyl or aryl), has been announced. Under high dilution and in the presence of cyclopentadienylcobalt dicarbonyl, co-oligomerization to pyridines of type (12) takes place in a remarkably selective manner, yields of 43—81% being realised. The process is particularly useful for the preparation of the otherwise not easily accessible 5,6,7,8-tetrahydroquinolines. An interesting extension of the reaction uses ethyl cyanoacetate in place of the nitrile RCN,... 

Thiets react with cyclopentadienylcobalt dicarbonyl to yield complexes of thioacroleins, which are valence tautomers of thiets. Oxidation of 3-ethyl-4-methylthiet and 3-propyl-4-ethylthiet with hydrogen peroxide in acetic anhydride did not give the S-oxides, but instead 2-ethylbut-2-enal and 2-propyl-pent-2-enal, respectively. ... 

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