The effects of bulky substituents in the reactions of alkynes with (η-C5H5)M(CO)2, M = Co or Rh

Abstract

The reactions between (η-C5H5)Co(CO)2 and MeC≡CR (R = Bu, Pri) at 120° gave the cyclopentadienone complexes (η-C5H5)Co[C4Me2R2CO] (2) and small amounts of the p-benzoquinone complexes(η-C5H5)Co[C4Me2R2(CO)2] (1); all possible isomers of both complexes were obtained. For R = But, the only products isolated were two isomers of the cyclopentadienone complex (2). The reactions between (η-C5H5)Rh(CO)2 and MeC=CR at 160° gave the cyclopentadienone complexes(η-C5H5)Rh[C4Me2R2CO] (2), and small amounts of the p-benzoquinone complexes (η-C5H5)Rh-[C4Me2R2(CO)2] (1) and of the binuclear complexes (η-C5H5)2Rh2(MeC2R)2CO (3). With R = But, three isomers of (2), two isomers of (1) and three isomers of (3) were identified. The products obtained with R = Pri were three isomers of (2) and three isomers of (3). With R = But, three isomers of(2) and a very small amount of one of the isomers of (3) were separated. Comparisons of these reactions have shown that increasing the bulk of R results in a decrease in the total yields of products, a decrease in the range of products, and a change in the distribution of the isomers (M = Co only).