Organic Nitriles from Acid Chlorides: An Isovalent N for (O)Cl Exchange Reaction Mediated by a Tungsten Nitride Complex

Nitride NW(N[i-Pr]Ar)3 (1, Ar = 3,5-C6H3Me2) was synthesized in two steps from known NW(O-t-Bu)3 (41% overall yield). Complex 1 is the tungsten congener of NMo(N[i-Pr]Ar)3, a known molecule that has been synthesized using N2 as the nitrido nitrogen source, but which undergoes no reaction with pivaloyl chloride. Compound 1 undergoes metathesis with pivaloyl chloride at 25 degrees C to form the corresponding nitrile in 97% yield. Another substrate examined in this work was the labeled acid chloride 1-Ad13C(O)Cl (Ad = adamantyl). The "(O)Cl" moiety is transferred to tungsten forming an oxo-chloride, (Ar[i-Pr]N)3W(O)Cl (3), as the final tungsten product; both 1 and 3 were characterized structurally by X-ray diffraction. An intermediate observed in the nitrile-forming reaction was characterized spectroscopically to be a tungsten acylimido complex. The latter assignment was substantiated by the synthesis and structural characterization of the compound (Ar[i-Pr]N)3W(NC(O)CF3)(O2CCF3) (2m). In addition, density functional theory calculations performed using ADF lent insight into the thermochemistry of the overall process.