Quantitatively analyzing metathesis catalyst activity and structural features in silica-supported tungsten imido-alkylidene complexes.
A broad series of fully characterized, well-defined silica-supported W metathesis catalysts with the general formula [(≡SiO)W(═NAr)(═CHCMe2R)(X)] (Ar = 2,6-iPr2C6H3 (AriPr), 2,6-Cl2C6H3 (ArCl), 2-CF3C6H4 (ArCF3), and C6F5 (ArF5); X = OC(CF3)3 (OtBuF9), OCMe(CF3)2 (OtBuF6), OtBu, OSi(OtBu)3, 2,5-dimethylpyrrolyl (Me2Pyr) and R = Me or Ph) was prepared by grafting bis-X substituted complexes [W(NAr)(═CHCMe2R)(X)2] on silica partially dehydroxylated at 700 °C (SiO2-(700)), and their activity was evaluated with the goal to obtain detailed structure-activity relationships. Quantitative influence of the ligand set on the activity (turnover frequency, TOF) in self-metathesis of cis-4-nonene was investigated using multivariate linear regression analysis tools. The TOF of these catalysts (activity) can be well predicted from simple steric and electronic parameters of the parent protonated ligands; it is described by the mutual contribution of the NBO charge of the nitrogen or the IR intensity of the symmetric N-H stretch of the ArNH2, corresponding to the imido ligand, together with the Sterimol B5 and pKa of HX, representing the X ligand. This quantitative and predictive structure-activity relationship analysis of well-defined heterogeneous catalysts shows that high activity is associated with the combination of X and NAr ligands of opposite electronic character and paves the way toward rational development of metathesis catalysts.
†Department of Chemistry and Applied Biosciences, ETH Zürich, Vladimir Prelog Weg 2, 8093 Zürich, Switzerland.
Victor
V
Mougel
‡Department of Chemistry, University of Utah, 315 South 1400 East, Salt Lake City, Utah 84112, United States.
Celine B
CB
Santiago
†Department of Chemistry and Applied Biosciences, ETH Zürich, Vladimir Prelog Weg 2, 8093 Zürich, Switzerland.
Pavel A
PA
Zhizhko
‡Department of Chemistry, University of Utah, 315 South 1400 East, Salt Lake City, Utah 84112, United States.
Elizabeth N
EN
Bess
§XiMo Hungary, Zahony u. 7 H-1031 Budapest, Hungary.
Jeno
J
Varga
§XiMo Hungary, Zahony u. 7 H-1031 Budapest, Hungary.
Georg
G
Frater
‡Department of Chemistry, University of Utah, 315 South 1400 East, Salt Lake City, Utah 84112, United States.
Matthew S
MS
Sigman
†Department of Chemistry and Applied Biosciences, ETH Zürich, Vladimir Prelog Weg 2, 8093 Zürich, Switzerland.
Christophe
C
Copéret
D000475:Alkenes / Q000737:chemistry*; D002384:Catalysis; D007094:Imides / Q000737:chemistry*; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D012822:Silicon Dioxide / Q000737:chemistry*; D014414:Tungsten / Q000737:chemistry*
D000475:Alkenes; D007094:Imides; D009942:Organometallic Compounds; D012822:Silicon Dioxide; D014414:Tungsten