Catalytic Nitrile-Alkyne Cross-Metathesis

The first catalytic cross-metathesis reaction of an alkyne with a nitrile is described. The nitride complex N⋮W(OC(CF3)2CH3)3(DME) undergoes reversible triple-bond metathesis reactions with alkynes (RC⋮CR; R = Et, 4-C6H4OMe), forming the alkylidyne complexes RC⋮W(OC(CF3)2CH3)3(DME) (R = Et, 4-C6H4OMe) along with the corresponding nitrile RC⋮N. This has been exploited to effect catalytic cross-metathesis of nitriles with alkynes, in which the organic CR fragments of two nitriles are coupled to yield an alkyne. A simple “sacrificial” alkyne (3-hexyne) acts as the N-atom acceptor, forming two equivalents of nitrile byproduct (propionitrile).