Novel Ruthenium Indenylidene Catalysts: From Homogeneous To Heterogeneous

The olefin metathesis was discovered incidentally and independently in 1950s by different researchers on their attempt to polymerize olefins by the Ziegler process [1-5]. The earliest discoveries were the basic exchange olefin metathesis of the inter-conversion of propylene, ethylene and butane-2 as well as ROMP of norbornene and cylcopentene. However, the connection between the two types of reactions was not immediately apparent mainly because different catalysts and conditions were generally involved. The discovery of the tungsten based catalyst by Calderon and co-workers that bring about both rapid polymerization of cyclooctene and cyclooctadiene [6] and the disproportionation of pent-2- ene [7-9] provided the connection that led to the realization that both ring-opening polymerization and the disproportionation of acyclic olefins were the same kind of reaction. Henceforward, the reaction became known as olefin metathesis, to mean the metal-catalyzed redistribution of carbon-carbon double bonds. The most common variations of olefin metathesis are represented in Scheme 1. Cross metathesis (CM) where groups between acyclic olefins are exchanged [10,11], ring closing metathesis (RCM) where acyclic dienes are ring closed [12], ring-opening metathesis (ROM) where dienes are formed from cyclic olefins [13], ring-opening metathesis polymerization (ROMP) where cyclic olefins are polymerized [14,15] and acyclic diene metathesis polymerization (ADMET) where acyclic dienes are polymerized [16].