Benzonitrile Extrusion from Molybdenum(Ⅳ) Ketimide Complexes Obtained via Radical C-E (E = O, S, Se) Bond Formation: Toward a New Nitrogen Atom Transfer Reaction

摘要

Beta-elimination is explored as a possible means of nitrogen-atom transfer into organic molecules. Molybdenum(Ⅳ) ketimide complexes of formula (Ar[t-Bu]N)_3Mo(N=C(X)Ph), where Ar = 3,5-Me_2C_6H_3 and X = SC_6F_5, SeC_6F_5, or O_2CPh, are formally derived from addition of the carbene fragment [:C(X)Ph] to the terminal nitrido molybdenum(Ⅳ) complex (Ar[t-Bu]N)_3Mo≡N in which the nitrido nitrogen atom is installed by scission of molecular nitrogen. Herein the pivotal (Ar[t-Bu]N)_3Mo(N=C(X)Ph) complexes are obtained through independent synthesis, and their propensity to undergo beta-X elimination, i.e., conversion to (Ar-[t-Bu]N)_3MoX + PhC≡N, is investigated. Radical C-X bond formation reactions ensue when benzonitrile is complexed to the three-coordinate molybdenum(Ⅲ) complex (Ar[t-Bu]N)_3Mo and then treated with 0.5 equiv of X_2, leading to facile assembly of the key (Ar[t-Bu]N)_3Mo(N=C(X)Ph) molecules. Treated herein are synthetic, structural, thermochemical, and kinetic aspects of (ⅰ) the radical C-X bond formation and (ⅱ) the ensuing beta-X elimination processes. Beta-X elimination is found to be especially facile for X = O_(2~-)CPh, and the reaction represents an attractive component of an overall synthetic cycle for incorporation of dinitrogen-derived nitrogen atoms into organic nitrile (R—C≡N) molecules.