Previous papers recently published in this Journal have highlighted the role and scope of platinum group metals in the development of metathesis catalysts (1, 2). Following the seminal discovery of the highly active and stereoselective tungsten and molybdenum imido alkylidene metathesis catalysts, for example, 1 and 2 (R = alkyl groups) by Schrock and coworkers (3, 4), an important class of ruthenium bisphosphane alkylidene catalysts, for example, 3 and 4, have been disclosed and successfully

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... plied in metathesis reactions by Grubbs and coworkers (5, 6). R = phenyl (Ph), isopropyl (iPr) or cyclohexyl (Cy) R' = phenyl (Ph) or tert-butyl (tBu) groups Mes = mesityl R = phenyl (Ph), isopropyl (iPr) or cyclohexyl (Cy) R' = phenyl (Ph) or tert-butyl (tBu) groups