TY - JOUR
T1 - Kinetic and Thermodynamic Analysis of Processes Relevant to Initiation of Olefin Metathesis by Ruthenium Phosphonium Alkylidene Catalysts
AU - Leitao, Erin M.
AU - van der Eide, Edwin F.
AU - Romero, Patricio E.
AU - Piers, Warren E.
AU - McDonald, Robert
PY - 2010/3/3
Y1 - 2010/3/3
N2 - 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 (H(2)IMes)(CI)(3)Ru=C(H)P(R-1)(2)R-2 (R-1 = R-2 = C6H11, C5H9, i-C3H7, 1-Cy-3-Cl, 1-Cyp(3)-Cl, 1-'Pr-3-Cl; R-1 = C6H11, R-2 CH2CH3, 1-EtCy2-Cl; R-1 = C6H11, R-2 = CH3, 1-MeCy2-Cl; R-1 = i-C3H7, R-2 = CH2CH3, 1-Et'Pr-2-Cl; R-1 = i-C3H7, R-2 = CH3, 1-Me'Pr-2-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-R-3 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.
AB - 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 (H(2)IMes)(CI)(3)Ru=C(H)P(R-1)(2)R-2 (R-1 = R-2 = C6H11, C5H9, i-C3H7, 1-Cy-3-Cl, 1-Cyp(3)-Cl, 1-'Pr-3-Cl; R-1 = C6H11, R-2 CH2CH3, 1-EtCy2-Cl; R-1 = C6H11, R-2 = CH3, 1-MeCy2-Cl; R-1 = i-C3H7, R-2 = CH2CH3, 1-Et'Pr-2-Cl; R-1 = i-C3H7, R-2 = CH3, 1-Me'Pr-2-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-R-3 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.
UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-77649312902&partnerID=8YFLogxK
U2 - 10.1021/ja910112m
DO - 10.1021/ja910112m
M3 - Article (Academic Journal)
C2 - 20136131
SN - 0002-7863
VL - 132
SP - 2784
EP - 2794
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
IS - 8
ER -