Arene Ruthenium and Osmium Derivatives as Catalyst Precursors

ARENE RUTHENIUM AND OSMIUM DERIVATIVES AS CATALYST PRECURSORS 

Arene ruthenium(II) complexes have been shown to catalyze the re-gioselective addition of ammonium carbamate to terminal alkynes, such as phenylacetylene and 1-hexyne, to produce vinylcarbamates. 

RuCl2(PMe3)(C6Me6) and RuCl2(PMe3)(p-cymene) appear to be much more efficient catalysts than other mononuclear ruthenium complexes, or Ru3(CO)12, for a variety of secondary amines and terminal alkynes, such as diethylamine, morpholine, piperidine, and pyrrolidine (65,201), except for acetylene itself (202,203). The regioselective addition to the terminal carbon suggests that that the reaction proceeds via an arene ruthenium vinyl-idene intermediate that has been characterized (66) (Section II,A,3,d). 

This catalytic reaction is a unique synthesis involving carbon dioxide. RuCl2(PMe3)(p-cymene) also catalyzes the addition of a variety of carboxylic acids to alkynes to give enol esters in one step. The presence of the basic phosphine is necessary to direct the addition of the carboxylate 

Although arene ruthenium complexes appear to be efficient catalyst precursors for the activation of alkynes, no evidence for the role or even the presence of the arene ligand in the active species has been obtained yet. 

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