Carbyne complexes heteroatomic substituents

As in the case of carbene complexes, 13C NMR spectroscopy is particularly useful in that the carbyne carbon typically resonates to low field (240 and 360 ppm), with heteroatom substituents shifting this to higher field. As noted above for carbene complexes, X-ray crystallography reveals that carbyne complexes have very short metal-carbon bonds, typically the shortest of any metal-carbon multiple bond, but lengthened if heteroatom substituents are present. 

If trans-subsituted carbene complexes containing ligands which have a greater (T-donor/n-acceptor ratio than CO (e.g., PRj, AsRj, SbRj or a Jt-aromatic ) are reacted with electron-pair acceptor acids, these ligands remain in the product complex. Only the heteroatom-containing substituent is removed from the carbene carbon and cationic carbyne complexes are formed ... 

A variety of heteroatom substituted 1-alkynes were polymerized with the three carbyne W(VI) complexes. These catalysts tolerate in alkyne polymerization reactions more heteroatom substituents than in olefin metathesis [4, 5, 6, 7], Table 3. 

The Schrock type carbyne complexes Np3W=C Bu, ( BuO)3W=C Bu and Cl3(dme)WsC Bu are very active catalysts for the polymerization of alkylsubstituted 1-alkynes and also for 1-alkynes with heteroatom containing substituents. The polymerization of disubstituted alkynes was only achieved with Cl3(dme)W=C Bu as catalyst. 

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