Cyclopentadienylvanadium tetracarbonyl

Cyclopentadienylvanadium tetracarbonyl (21, 97) and cyclopentadienylchro-mium dicarbonyl nitrosyl (22) can also be acylated under Friedel-Crafts conditions. 

The only known syntheses of cyclopentadienylvanadium tetracarbonyl, C6H6V(CO)4, are based on the reaction of bis(cyclopentadienyl)vanadium with carbon monoxide under pressure. The procedure given below is based on this reaction but avoids isolation of pyrophoric bis-(cyclopentadienyl)vanadium by direct carbonylation of the solution obtained from vanadium(III) chloride and cyclopentadienylsodium. 

Cyclopentadienylvanadium tetracarbonyl is an orange crystalline solid. On prolonged exposure to air, especially when slightly impure, it darkens in color, finally becoming black. It is therefore best stored under a nitrogen atmos-... 

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. 

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