Trimerisation of acetylenes

The nickel-catalysed co-trimerisation of acetylenes with isocyanates gave good yields of uracils 46, depending on the isocyanate substituents, pyridones being unwanted by-products... 

The mechanism of trimerisation of acetylene on extended surfaces is thought to be similar to that observed in homogeneous catalysis using transition-metal cluster compounds.A stepwise mechanism, shown below is thought to occur ... 

These ruthenium complexes were also investigated as catalysts for the dimerisation of phenylacetylene (Scheme 5.13). ° The trimerisation of acetylene is typically a competitive process and when compared to [RuCl2(/)-cymene)]2, catalysts 53-56 afforded higher dimerisation yields. However, the results obtained did not allow a clear distinction between the effects of the different types and bonding modes of the carbene ligands. 

The co-trimerisation of alkynes with nitriles (eqn.36) is catalysed by Cp Co(COD) complexes and has been described comprehensively.The catalytic activity increases with the electron-withdrawing character of the Cp ligands and gives a linear correlation with the Co NMR chemical shift.2. 2 5 reaction also proceeds in the presence of (Me00C-C5Hi,)Co(C0T).2 The co-trimerisation of trimethylstannyl acetylenes with acetonitrile has been employed for the synthesis of vitamin Bg.2 2... 

While Ni(cod)2 In hydrocarbon solvents trimerises diphenyl acetylene, THF slows the reaction down and allows the interception of intermediates including the nickelacycle L2M1Ci,Phj,.150 The complex L2N1H(BHi,) or catalysts prepared in situ from Ni(II), L and NaBH (L PCy3) are highly active In the cyclotrlmerlsatlon of Me0( 2CECCH20Me. Substrate purity Is of prime... 

What we have outlined above is an experiment that probes the formation of the initial complex between acetylene and the ion at the active site. By repeated experiments with progressively increasing doses of (deuterated) acetylene injected into the Ni-enriched zeolitic catalyst, one would acquire information that would chart the formation of benzene by trimerisation, There is no doubt that, given adequate neutron-beam time — a not inexpensive factor — the NDIS technique could become a powerful in situ technique for exploring active centres in these complex oxide catalysts. What is increasingly apparent, however, is that synchrotron radiation sources at centralised... 

---