Iminoacylcobalt Compounds as Starting Materials for the Synthesis of Alkynylcobalt Halfsandwiches and Cobaltaheterocycles

The iminoacylcobalt compound [C 5 H 5 Co(C(CH 3 )=NCH 3 )(PMe 2 Ph)] ( 3 ) reacts with propargylic acid ester HC=CCO 2 R (R = Me, Et) to give the alkynylcobalt halfsandwich‐type complexes [C 5 H 5 Co(C(CH 3 )=NHCH 3 )(C=CCO 2 R)‐(PMe 2 Ph)]I ( 5, 6 ). With HC=CCO 2 Me as the substrate, besides 6 (R = Me) the five‐membered cobaltaheterocycle [C 5 H 5 Co{K 2 ( N , C)‐N(CH 3 )C(CH 3 )CHC(CO 2 Me)}(PMe 2 Ph)]I ( 7 ) is also obtained. The reactions of 3 and the analogous benzyl derivative 4 with terminal alkynes HC=CR' (R' = CH 2 OH, CMe 2 OH, [CH 2 ] 2 OH, CH 2 OMe, H, Me, n Bu, Ph) afford exclusively the heterocyclic complexes [C 5 H 5 Co(K 2 ( N ,C)‐N(R)C(CH 3 CHCR')(PMe 2 Ph)]I (R = CH 3 , CH 2 Ph) ( 8–18 ) in 60–70% yield. The molecular structures of 5 (R = Et) and 16 (R = Me, R' = Ph) have been determined by X‐ray crystallography.