SYNTHESIS AND CRYSTAL-STRUCTURE OF NEW SIGMA-BONDED ALKYNYLCOBALT(III) COMPLEXES OF 1,3-BIS(DIACETYLMONOXIMEIMINO)PROPANE

Sigma-Alkynyl Costa complexes can be readily synthesized from the trans diiodo-1.3-bis(diacetylmonoximeimino)propanecobalt complex 1 and alkynyl Grignard reagents 2a-d. The conversions are carried out under daylight irradiation and give the cobalt acetylides 3a-d in high yields. This photosubstitution method can be used to synthesize sigma-alkynylcobalt(III) complexes with various substituents. The crystal structure of trimethylsilylethynyliodo-1,3-bis(diacetylmonoximeimino)propanecobalt(III) (3a) has been established by an X-ray diffraction study. The reaction of complexes 3a-d with 4-tert-butylpyridine (4) in the presence of AgPF6 gives positively charged complexes having the nitrogen base trans to the alkynyl ligand. Treatment of phenylethynyl-1,3-bis(diacetylmonoximeimino)propanecobalt(III) (3b) with I2 gives quantitatively complex 1 and 1-iodo-2-phenylethyne (6).