Terminal tungsten nitride complexes containing bonds have been reported to catalyze nitr...

Terminal tungsten nitride complexes containing bonds have been reported to catalyze nitrile–alkyne cross-metathesis (NACM) by a mechanism that has parallels with the non-pairwise mechanism for olefin metathesis (A. M. Geyer, E. S. Weidner, J. B. Gary, R. L. Gdula, N. C. Kuhlmann, M. J. A. Johnson, B. D. Dunietz, J. W. Kampf, J. Am. Chem. Soc. , 2008 , 130

8984.) When p -methoxybenzonitrile and 3-hexyne were mixed in the presence of catalyst candidate , two principal products attributable to metathesis were observed.

a. Outline the NACM mechanism, as described in the reference.

b. Account for the formation of the two products, and suggest which was formed first.