Transition metal complexes of substituted alkynes. IX. Factors that influence the formation of Tris(alkyne)cobalt complexes

Reactions involving p-alkyne-hexacarbonyldioobalt complexes and an excess of an alkyne have been investigated systematically to determine some of the factors affecting the formation and stabilization of CO,(CO)~C,(CF,)~R,-, complexes. Systems have been studied in which the value of n has been varied through all values from 0 to 6. The new tris(a1kyne)tetracarbonyldioobalt complex CO,(CO),C,(CF,),(CH~)~- Hz, formed from Co,(CO),(CH,C,CH,) and an excess of CF,C=_CH, has been characterized by elementary and spectroscopic analysis. Tris(a1kyne)tetracarbonyldi- cobalt compIexes have not been isolated from the systems [Co,(CO),(CF3C,CF3)+2- CH,C=CCH,], [Co,(CO),(CF,C,CF,) + 2CH3CzCH], [Co,(CO),(CF,C,CH,) + 2CH3C~C- CH,], [Co,(CO),(CH,C,CH,) + 2CF3CKXF3], [Co,(CO),(CH3C,CH,) + 2CH3C~CCH3], and [Co,(CO),(CH3C,CH,)+2CH3C~CH]. Rather, significant amounts of various CF,- and/or CH,-substituted benzenes are obtained in these reactions. These sub- stituted benzenes are presumably formed by decomposition of unstable tris(a1kyne)- tetracarbonyldicobalt complexes. The accumulated results indicate that two principal factors influence the stability of the CO,(CO)~C,(CF,),R,-, complexes. Stable complexes are isolated only when (i) at least two CF, groups are incorporated as substituents in the C,-bridging fragment, and (ii) CF, substituents are attached to the two terminal carbon atoms of the bridging fragment.