Edwin Van Der Eide - A Kinetic and Thermodynamic Analysis of Processes Relevant to Initiation of Olefin Metathesis by Ruthenium Phosphonium Alkylidene Catalysts

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      Publication Details (including relevant citation   information):

      Erin M. Leitao, Edwin F. van der Eide, Patricio E. Romero,   Warren, E. Piers and Robert McDonaldhttp://pubs.acs.org/doi/abs/10.1021/ja910112m#afn2

      Journal   of the American Chemical Society   2010, 132, 2784-2794

      doi:  10.1021/ja910112m

      Abstract:

      Initiation processes in a family of ruthenium phosphonium   alkylidene catalysts, some of which are commercially available,   are presented. Seven 16-electron zwitterionic catalyst precursors   of general formula   (H2IMes)(Cl)3Ru═C(H)P(R1)2R2  (R1 = R2 = C6H11,   C5H9,   i-C3H7,   1-Cy3-Cl,   1-Cyp3-Cl,   1-iPr3-Cl;   R1 = C6H11, R2 =   CH2CH3,   1-EtCy2-Cl;   R1 = C6H11, R2 =   CH3,   1-MeCy2-Cl;   R1 = i-C3H7,   R2 = CH2CH3,   1-EtiPr2-Cl;   R1 = i-C3H7,   R2 = CH3,   1-MeiPr2-Cl)   were prepared. These compounds can be converted to the metathesis   active 14-electron phosphonium alkylidenes by chloride   abstraction with B(C6F5)3. The   examples with symmetrically substituted phosphonium groups exist   as monomers in solution and are rapid initiators of olefin   metathesis reactions. The unsymmetrically substituted phosphonium   alkylidenes are observed to undergo reversible dimerization, the   extent of which is dependent on the steric bulk of the   phosphonium group. Kinetic and thermodynamic parameters of these   equilibria are presented, as well as experiments that show that   metathesis is only initiated through the monomers; thus   dedimerization is required for initiation. In another detailed   study, the series of catalysts   1-R3  were reacted with o-isopropoxystyrene under   pseudo-first-order conditions to quantify second-order olefin   binding rates. A more complex initiation process was observed in   that the rates were accelerated by catalytic amounts of ethylene   produced in the reaction with o-isopropoxystyrene. The   ability of the catalyst to generate ethylene is related to the   nature of the phosphonium group, and initiation rates can be   dramatically increased by the intentional addition of a catalytic   amount of ethylene.

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