Preparation, Properties, and Reactions of Metal‐Containing Hetercycles, XC. Reactivity of Differently Activated Alkynes toward Ruthenium and Osmium Complexes of the Type (η2‐C2H4)M(CO)4

Abstract

Depending on the substituents, the reaction of the activated alkynes ZC≡CZ (2a‐g) [Z = CO2R: R = Me (a), Et (b); Z = R1: R1 = CF3 (c), CH2Cl (d), CH2Br (e); Z = CH2OC(O)R2: R2 = Me (f), CCl3 (g)] with the labile ruthenium complex (η2‐C2H4)Ru(CO)4 (1) results in the formation of three different types of heterocycles. While the reactions of the dialkyl acet‐ylenedicarboxylates 2a, b lead to the dimeric tricarbonylru‐thenacyclopentadienes 3a, b, being catalytically active in the cyclotrimerization of alkynes like 2a, b, the application of the 1,4‐halogeno‐2‐butynes 2c‐e yields the bicyclic heterocycles 4c‐e. The esters of 2‐butyne‐1,4‐diol 2f, g are converted into the tetracarbonylruthenacyclopentadienes 5f, g. Investigation of the primary attack of the alkynes 2a‐g at complex 1 leads to the conclusion, that an ionic mechanism is preferred in the ruthenium‐catalyzed cyclotrimerization of electron‐poor alkynes. If, instead of 1, (η2‐C2H4)Os(CO)4 (6) is allowed to react with the acetylenes 2a, b the osmium complexes (η4‐C6Z6)Os(CO)3 (7a, b) are isolated. In the presence of CO at 2 bar 7a, b release the benzene derivatives C6Z6 (8a, b) with the formation of Os3(CO)12.