Photosubstitution of carbon monoxide in W(CO)6 by alkyne: NMR detection of thermally unstable alkyne tungsten(0) carbonyl complexes

The NMR method has been used for the identification and characterisation of the unstable terminal alkyne complexes [W(CO)5(η2-HCCR)], [W(CO)4(η2-HCCR)2], [W(CO)(η2-HCCR)3], and vinylidene derivatives [W(CO)5(CCHR)] formed in photochemical reactions of W(CO)6 and each of the alkynes HCCH, HCCMe and HCCCMe3. The terminal alkyne carbonyl complexes formed after sequential substitution of CO by alkyne were shown to be involved in the cyclotrimerisation of alkynes to arenes, which were detected by NMR spectroscopy and GC-MS analysis in the photochemical reaction of W(CO)6 and each terminal alkyne used. Benzene substitute adducts with W(CO)3 moiety were also observed by NMR in the above reactions.