Erik M Townsend

Massachusetts Institute of Technology, Cambridge, Massachusetts, United States

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Publications (4)25.49 Total impact

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    ABSTRACT: Imido alkylidene complexes of Mo and W and oxo alkylidene complexes of W that contain thiophenoxide ligands of the type S-2,3,5,6-Ph4C6H (STPP) and S-2,6-(mesityl)2C6H3 (SHMT = S-hexamethylterphenyl) have been prepared in order to compare their metathesis activity with that of the analogous phenoxide complexes. All thiolate complexes were significantly slower (up to ∼10× slower) for the metathesis homocoupling of 1-octene or polymerization of 2,3-dicarbomethoxynorbornene, and none of them was Z-selective. The slower rates could be attributed to the greater σ-donating ability of a thiophenoxide versus the analogous phenoxide and consequently a higher electron density at the metal in the thiophenoxide complexes.
    Organometallics 10/2014; 33(19):5334-5341. DOI:10.1021/om500655n · 4.25 Impact Factor
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    ABSTRACT: Reactions between Mo(NAr)(CHR)(Me2Pyr)-(OTPP) (Ar = 2,6-i-Pr2C6H3, R = H or CHCMe2Ph, Me2Pyr = 2,5-dimethylpyrrolide, OTPP = O-2,3,5,6-Ph4C6H) and CH2=CHX where X = B(pin), SiMe3, N-carbazolyl, N-pyrrolidinonyl, PPh2, OPr, or SPh lead to Mo(NAr)(CHX)-(Me2Pyr)(OTPP) complexes in good yield. All have been characterized through X-ray studies (as an acetonitrile adduct in the case of X = PPh2). The efficiencies of metathesis reactions initiated by Mo(NAr)(CHX)(Me2Pyr)(OTPP) complexes can be rationalized on the basis of steric factors; electronic differences imposed as a consequence of X being bound to the alkylidene carbon do not seem to play a major role. Side reactions that promote catalyst decomposition do not appear to be a serious limitation for Mo=CHX species.
    Organometallics 08/2013; 32(16):4612-4617. DOI:10.1021/om400584f · 4.25 Impact Factor
  • Erik M Townsend, Richard R Schrock, Amir H Hoveyda
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    ABSTRACT: Molybdenum or tungsten monoaryloxide pyrrolide (MAP) complexes that contain OHIPT as the aryloxide (hexaisopropylterphenoxide) are effective catalysts for homocoupling of simple (E)-1,3-dienes to give (E,Z,E)-trienes in high yield and with high Z selectivities. A vinylalkylidene MAP species was shown to have the expected syn structure in an X-ray study. MAP catalysts that contain OHMT (hexamethylterphenoxide) are relatively inefficient.
    Journal of the American Chemical Society 06/2012; 134(28):11334-7. DOI:10.1021/ja303220j · 11.44 Impact Factor
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    ABSTRACT: A new tungsten alkylidene complex, W(NAr)(CHCMe2Ph)(OHIPT-NMe2)(pyrrolide) {Ar=2,6-(i-Pr)2C6H3; HIPT-NMe2=2,6-[2,4,6-(i-Pr)3C6H2]2-4-NMe2-C6H2}, has been synthesized and shown to be highly selective for Z homocoupling metathesis of selected terminal olefins in pentane, as is W(NAr)(CH2CH2CH2)(OHIPT)(pyrrolide) (5). Both 5 and W(NAr)(CHCMe2Ph)(OHIPT-NMe2)(pyrrolide) (6) are adsorbed onto calcined alumina. Control experiments and metathesis homocoupling of four substrates lead to the conclusions that 5 is largely adsorbed in a reaction that liberates HIPTOH, while 6 is adsorbed largely through an interaction between the dimethylamino group and an acidic site on the surface. There is no evidence that any adsorbed catalyst can give rise to Z selectivity of a magnitude equal to that found in a homogeneous reaction involving 5 or 6.
    Advanced Synthesis & Catalysis 08/2011; 353(11‐12):1985 - 1992. DOI:10.1002/adsc.201100200 · 5.54 Impact Factor