Preparation of rhenium(VII) monoimido alkylidyne complexes and metathesis of acetylenes via rhenacyclobutadiene intermediates

Metathesis of acetylenes by d/sup 0/ molybdenum and tungsten alkylidyne complexes of the type M(CR)(OR')/sub 3/ (R is alkyl, R' is alkyl, fluoroalkyl, or aryl) has been established in the last few years. An interesting question is whether a related rhenium(VII) acetylene metathesis catalyst can be designed, since although acetylene metathesis by rhenium is unknown, rhenium-based catalysts for metathesizing olefins are well-known. They report here several four-coordinate monoimido bisalkoxide neopentylidyne complexes, the metathesis of several internal acetylenes by one of them, and the X-ray structure of a rhenacyclobutadiene complex.