Vinylacetylene (butenyne) derivatives as precursors of alkenylcarbene ruthenium complexes via allenylidene metal intermediates

Abstract

Complexes (η⁶-arene)(PR₃)RuCl₂(1a—c) react with HCC–C(R¹)CHR² derivatives in methanol to afford in one step the alkenylcarbene–ruthenium cations [(η⁶-arena)(PR₃)ClRuC(OMe)CHC(R¹)CH₂R²]⁺(2)–(6)(R¹ and R²= H or Me) which on deprotonation give cyclometallacarbenes (7)–(8); on the basis of labelling experiments the formation of (2)–(6) involves an allenylidene intermediate RuCCC(R¹)(CH₂R²)⁺ instead of the expected allylcarbene moiety RuC(OMe)CH₂C(R¹)(CHR²)⁺.