Novel Metalla-Heterocycles Formed By [3+2], [2+2], and [2+3] Cycloaddition Reactions of Cyclopentadienyl Cobalt and Rhodium Complexes

Following the discovery that the cyclopentadienyl cobalt bis(phosphine) complexes C₅H₅Co(PR₃)₂ are strong metal bases [1], we became interested to find out whether also derivatives of the general composition C₅H₅Co(PR₃)₂, in which L is a n-acceptor ligand, despite of the reduced electron density at the metal atom still show the same type of behavior. After the carbonyl compound C₅H₅Co(PMe₃)C0 had been investigated [2], the isocyanide cobalt complexes C₅H₅Co(PMe₃)CNR were prepared and found not only to be good nucleophiles but also useful starting materials for the synthesis of four- and five-membered metalla-heterocycles.