Mechanism of Ruthenium Based Olefin Metathesis Catalysts

Over the past decade, olefin metathesis has emerged as a powerful method for the formation of carbon-carbon double bonds [1]. In particular, two ruthenium-based catalysts - (PCy_3)_2(Cl)_2Ru=CHPh (1) [2] and IMesH_2(PCY_3)(Cl)_2Ru=CHPh (2) [3] [IMesH_2 = 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene] (Figure 1) - have become important tools for organic and polymer chemists due to their reactivity with olefinic substrates in the presence of most common functional groups [4]. The development of the "second generation" catalyst 2 is especially significant, since this complex shows extremely high activity for olefin metathesis reactions, often comparing favorably to early transition metal catalyst systems without the complications of functional group incompatibility [5]. Catalyst 2 has recently been applied to the preparation of highly functionalized [6] and tri- and tetra- substituted [3] olefins in small molecule substrates (Figure 2). In addition, 2 has proven useful for the ring opening metathesis polymerization of ROD substituted norbomenes (RGD = peptide) to produce bio-active polymers (Figure 2) [7]