Erik M. Townsend

Massachusetts Institute of Technology, Cambridge, Massachusetts, United States

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Publications (5)27.74 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.
    Preview · Article · Oct 2014 · Organometallics
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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.
    No preview · Article · Aug 2013 · Organometallics
  • Erik Matthew Townsend · Richard Royce 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.
    No preview · Article · Jun 2012 · Journal of the American Chemical Society
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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.
    No preview · Article · Aug 2011 · Advanced Synthesis & Catalysis
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    ABSTRACT: The synthesis of a new bidentate anilide ligand and four uranium amide complexes utilizing the ligand are reported. The secondary aniline HN[R]ArMeL (R=C(CD3)2CH3, ArMeL=2-NMe2-5-MeC6H3) is prepared by condensation of H2NArMeL and acetone-d6 followed by alkylation of the resulting imine with MeLi. The ligand precursors (Et2O)Li(N[R]ArMeL) and K(N[R]ArMeL) are prepared through deprotonation of HN[R]ArMeL with n-BuLi and KH, respectively. Treatment of UI3(THF)4 with (Et2O)Li(N[R]ArMeL) (2 equiv) provides the uranium(III) -ate complex Li[I2U(N[R]ArMeL)2] (Li[1]), while treatment of UI3 with three equiv. of K(N[R]ArMeL) provides the neutral uranium(III) complex U(N[R]ArMeL)3 (2). Both uranium(III) complexes are susceptible to 1e oxidation, as is demonstrated by the syntheses of the uranium(IV) derivatives I2U(N[R]ArMeL)2 (1) and [U(N[R]ArMeL)3][OTf] ([2][OTf]; OTf=CF3SO3). The spectroscopic and X-ray structural characterization of all four uranium complexes is described. The structures of 2 and [2][OTf] exhibit a large degree of steric pressure about the uranium center, effectively preventing the [2]+ ion from achieving a seven-coordinate structure.
    No preview · Article · Jun 2010 · Comptes Rendus Chimie