Ruthenium Acetylide, Vinylidene, and Carbene Complexes

In contrast to the lithium acetylide reaction, addition of copper(I) phenylacetylide to (i75-C5H5)(PPh3)2RuCl (1) affords the monomeric ruthenium acetylide-copper chloride adduct (62) as the major product. An X-ray crystal structure of this complex reveals an tj1, -bridging acetylide between the ruthenium and copper centers, respectively (62). A small amount of the dimeric chloride bridged complex 61 was also isolated. The copper chloride can be removed from the monomeric complex by the 

Although the reaction of copper acetylides with transition metal halides has been successfully applied to the preparation of a variety of transition metal acetylides (64), the generation of copper-complexed derivatives is not unprecedented (65). A simpler and more general route to ruthenium acetylide complexes involves the deprotonation of ruthenium vinylidene complexes as described in Section VI,C. 

The interaction of an alkyne with (tj5-C5H5)(PR3)2RuX can result in the formation of a wide variety of ruthenium complexes. The nature of the products formed depends on the conditions used and the type of alkyne reacted. Reactions between I and terminal alkynes in the presence of ammonium hexafluorophosphate lead to the formation of cationic monosubstituted ruthenium vinylidene complexes in high yield, as shown for phenylacetylene in Eq. (61) (4,67,68). 

Consiglio and Morandini and co-workers (67) have investigated the stereochemistry involved in the addition of acetylenes to chiral ruthenium complexes. Reaction of propyne with the separated epimer of the chiral ruthenium phosphine complex 34 at room temperature results in the chemo- and stereospecific formation of the respective propylidene complex 64. An X-ray structure of the product (64) proves that the reaction proceeds with retention of configuration at the ruthenium center. The identical reaction utilizing the epimer with the opposite configuration at ruthenium (35) also proceeded with retention of configuration at the metal center, proving that the stereospecificity of the reaction in not under thermodynamic control [Eq. (62)]. 

Similar reactions of 34 and 35 with phenylacetylene at room temperature are also stereospecific, and they are presumed to occur with retention of configuration at the metal center by analogy to the propyne reactions. When these reactions are performed in refluxing methanol, both chemo-selectivity and stereospecificity are lost, with almost equal amounts of the two benzylidene diastereomers (65 and 66) and a small amount (10-15%) of the methanol adducts (67) (vide infra) being formed from 34 [Eq. (63)]. The individual benzylidene epimers 65 and 66 do not epimerize at the ruthenium center in refluxing methanol, which indicates that the loss of stereochemical integrity occurs prior to addition of the acetylene. 

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