Concerning the reaction pathway of the metathesis reaction involving WW and CN triple bonds: a theoretical study.
The original "chop-chop" reaction reported by Schrock [J. Am. Chem. Soc. 1982, 104, 4291] involving W(2)(O(t)Bu)(6) and organic nitriles, RC[triple bond]N to give the metal alkylidyne and nitride products ((t)BuO)(3)WC[triple bond]R and ((t)BuO)(3)WC[triple bond]N, has been examined by a density functional theory based calculation where the bulky (t)BuO ligands have been substituted by MeO. The reaction between W(2)(OMe)(6) and MeCN proceeds via a ditungstaazacyclobutadiene intermediate having a planar W(2)CN core, I, with a structure related to that seen for Mo(2)(OCH(2)(t)Bu)(6)(mu-NCNMe(2)). Another possible intermediate having a pseudo tetrahedral W(2)CN core, II, a ditungstaazatetrahedrane was examined and shown to have a higher energy. The interconversion of I and II was found to be energetically unfavorable with respect to their formation of metathesis products. The highest energy transition state involving the conversion of I to products was comparable to that for the conversion of II to products but the initial formation of I from the reaction between W(2)(OMe)(6) and MeCN was favored over the formation of II. The related reaction between Mo(2)(OMe)(6) and MeCN was shown to be thermodynamically unfavorable with respect to either adduct formation or metathesis products. However the reaction between Mo(2)(OMe)(6) and Me(2)NCN did yield a thermodynamically favored 1:1 adduct with a structure related to I.
Chen
Shentan
S
Department of Chemistry, The Ohio State University Columbus, Ohio 43210, USA.
Chisholm
Malcolm H
MH