Ruthenium‐Indenylidene and Other Alkylidene Containing Olefin Metathesis Catalysts

This chapter describes the most prominent non‐benzylidene families. The chemistry revolving around ruthenium‐indenylidene complexes is one of the fastest growing areas of olefin metathesis, and nowadays these catalysts represents alternative to the benzylidene congeners. The development of Ru‐indenylidene complexes has paralleled the development of ruthenium benzylidene complexes, and the plethora of catalysts developed can be grouped in generations according to structural motifs. An alternative synthetic pathway to Ru‐alkenylcarbene complexes involves cross metathesis of butadiene with first‐generation catalysts. Ru‐vinylidene complexes can be easily accessed by reaction of the appropriate ruthenium source with an alkyne. Most Ru‐allenylidene or Ru‐alkenylcarbyne complexes are prepared following Selegue's protocol. Fürstner and Dixneuf also developed an alternative procedure that circumvents the use of protic solvents and results in a more practical and flexible method for the preparation of Ru‐allenylidene complexes.