Synthesis of Ruthenium Olefin Metathesis Catalysts with Linear Alkyl Carbene Complexes

Second-generation ruthenium olefin metathesis catalysts with linear alkyl carbenes were needed to install a linear alkyl end group on ROMP polymers. The ethylidene complexes RuCl2(PCy3)(SIMes)CHMe (PCy3 = tricyclohexylphosphine; SIMes = 1,3-bis(mesityl)imidazolidin-2-ylidene) and RuCl2(3BP)2(SIMes)CHMe (3BP = 3-bromopyridine) were readily accessible by reaction of RuCl2(PCy3)(SIMes)CHPh with 2-butene. Synthesis of higher alkyl analogues, such as propylidene and heptylidene, are complicated by the intervention of olefin isomerization. Although slightly less reactive than the parent complex, these complexes are suitable catalysts for both ADMET and ROMP.