PREPARATION AND CHARACTERIZATION OF SOME DIMERIC ETA(2)-DIYNE COMPLEXES OF COBALT

The organometallic dimers [{Co2(CO)6}2(diyne)] (diyne = HC2C6H4C2H 1, HC2C6H4C6H4C2H 2, HC2C6H4CH2C6H4C2H 3, Me3SiC2C6H4C6H4C2SiMe3 4, Me3SiC2C6H4CH2C6H4C2SiMe3 5 or Me3SnC2C6H4C6H4C2SnMe3 6) have been synthesised from the reaction of octacarbonyldicobalt(0), [Co2(CO)8], with the appropriate diyne. The products have been characterised by infrared spectroscopy, electron impact (EI) mass spectrometry, microanalysis and H-1 NMR spectroscopy. The complexes 1, 3 and 4 have been characterised by single-crystal X-ray crystallography. In all cases both 'yne' fragments of the diyne bond to a Co2(CO)6 fragment with the C=C vector essentially perpendicular to the Co-Co vector. A bonding analysis by a Fenske-Hall calculation using the crystallographically determined coordinates for dimer 1 is consistent with the observed distortion of the Co2C2 bonding pattern away from quasi-tetrahedral geometry.