Transition metal complexes of substituted alkynes. XI. The reactions of But-2-yne and Hexafluorobut-2-yne with Dicarbonyl(η-cyclopentadieny)-cobalt and -rhodium

Abstract

The thermally initiated reaction of hexafluorobut-2-yne and (q-C5H5)C~(C0)2 gives the 1-4-q- hexakis(trifiuoromethy1)benzene complex (7-C5H5)Co [(CF3C2CF3)3] in addition to the known cyclopentadienone complex (q-C5H5)Co [(CF3C2CF3)2CO]. The related reaction of but-2-yne with (q-CjH j)Co(CO)2 gives several compounds in addition to the cyclopentadienone complex (q-C jHj)C~- [(MeC2Me)2CO] which has been isolated previously from this reaction. Thus, the duroquinone complex (q-C5H5)Co [(MeC2Me)2(C0)2], the maleoyl complex (q-C5H5)Co(MeC2Me)(C0)3, and free duroquinone have been obtained. The yields of the various products are influenced by the reaction conditions. The metallocyclopentadiene complex (q-C jH j)2Rh2(CF3C2CF3)2, which is formed in the reaction between (q-C,H,)Rh(CO), and hexafluorobut-2-yne, exhibits fluxional behaviour in solution at c. 130". Two complexes are formed in the reaction at 100-120' between (q-C5Hj)Rh- (CO)2 and but-2-yne. These are the cyclopentadienone complex (q-C5H5)Rh [(MeC2Me)2CO] and the duroquinone complex (7-CjH5)Rh [(MeC2Me)2(C0)2]. Comparison of the various reactions indicates that: (i) a cyclopentadienone complex (q-CgH5)M- [(MeC2Me)2CO] is generally formed as major product and a duroquinone complex (q-C5Hj)M- [(MeC2Me)2(C0)2] is generally formed as a minor product in reactions between (q-C5H5)M(C0)2, M = Co and Rh, and but-2-yne; and (ii) a tetrahaptobenzene complex (q-C5H5)M [(CF3C2CF3)3] is formed as major product when M = Rh and as a minor product when M = Co in reactions between (q-C5H5)M(CO)2 and hexafluorobut-2-yne.