Catalyst optimization is currently predominantly done by screening a large number of catalysts, rarely catalysts are designed by either chemical intuition or molecular modelling.In this proposal we will try to develop -by design- a new catalytic protocol using environmental benign reagents for the synthesis of cyclopropanes. The inspiration for this work stems from an interesting historical anomaly.In early work of Nobel prize laureate Georg Wittig cyclopropanation by the reaction of N-C-ylids as methylene donors with olefins was reported. Later these results were retracted. Possibly, traces of transition metals in one of the reagents were responsible for these inconsistent results. This observation prompts us to start an investigation of the interaction of N-C-ylids with transition metals.In this proposal we will combine (in)organic synthesis, mass spectrometry and molecular modelling to study the interaction of N-C-ylids with transition metals. Thorough understanding of these reactive intermediates will lead to novel synthetic (ideally catalytic) routes to cyclopropanes and the use of these intermediates in related synthetic transformations.Thus testing, validating and further developing our tools for design of catalysis and providing a environmentally benign industrial route to cyclopropanes.