Catalysts for alkyne metathesis

Alkyne metathesis. The complex 1 is a valuable catalyst for alkyne metathesis at room temperature. ... 

Zhang, W., Kraft, S., and Moore, J.S. (2003) A reductive recycle strategy for the facile synthesis of molybdenum (VI) alkylidyne catalysts for alkyne metathesis. Chem. Commun., 832-833. 

Increased activity of in situ catalysts for alkyne metathesis. Org. Lett., 4,... 

Bunz has made a very convenient and robust catalyst for alkyne metathesis available simply from combining Mo(CO)6 with P-XC6H4OH (X = Cl or CFj) and heating to 125-150 C the active catalyst is believed to be (ArO)3Mo5CR. 

Alkynes can also undergo metathesis. The preferred catalysts for alkyne metathesis are Schrock catalysts—catalysts that contain molybdenum or tungsten as the transition metal. 

W. Zhang, S. Kraft, J.S. Moore - A Reductive Recycle Strategy for the Facile Synthesis of Mo Alkylidyne Catalysts for Alkyne Metathesis,... 

Alkylidyne complexes can be used as catalysts for the metathesis of alkynes. For a classic review see Schrock [18],... 

Alkyne metathesis is a curious reaction in view of the fact that two alkyne triple bonds are cleaved and reconstructed simultaneously leading to different triple bonds. The first reported effective catalyst is a heterogeneous mixture of tungsten oxide and silica. Then Mortreux found that a catalytic system that consisted of Mo(CO)6 and resorcinol was effective for alkyne metathesis. As reported, the added alkynes come into equilibrium with different product... 

Although the real species of this solution for alkyne metathesis is not clear, this complex is an excellent tool from a preparative point of view. It is very active for the formation of cycloalkynes of different ring sizes from diynes. In contrast to tungsten alkylidyne complex 1, catalyst I4O/CH2CI2 is sensitive toward acidic protons such as amide proton and exhibited remarkable tolerance toward many polar functional groups (Table 6). ... 

Ziegler-Natta catalysts are not active at all in polymerization of disubstituted acetylenes.415 Mo- and W-based systems (for alkynes with small substituents) and Nb- and Ta-based catalysts (for alkynes with bulky groups), in turn, are very effective catalysts used to convert disubstituted acetylenes into polymers with very high molecular weight.414 415 A polymerization mechanism similar to that of metathesis polymerization of cycloalkenes are supported by most experimental observations.414 423 424... 

J. Wolf, W. Stuer, C. Grunwald, H. Werner, P. Schwab, and M. Schulz, Ruthenium Trichloride, Tricyclohexylphosphane, 1-Alkynes, Magnesium, Hydrogen, and Water-Ingredients of an Efficient One-Pot Synthesis of Ruthenium Catalysts for Olefin Metathesis, Angew. Chem. Int. Ed. 37, 1124-1126 (1998). 

Schrock RR, Czekelius C. Recent advances in the syntheses 136. and applications of molybdenum and tungsten alkylidene and alkylidyne catalysts for the metathesis of alkenes and alkynes. 

Well-defined, relatively stable, Lewis acid-free catalysts, such as Mt(=CHCHMe3)(=NC6H3-/-Pr2)[OCMe(CF3)2]2 (Mt = Mo, W), can provide living polymers with very narrow molecular weight distributions. Certain carbene complexes are active catalysts for the metathesis of internal alkynes [59]. W and... 

Bencheick, A., Petit, M., Mortreux, A., Petit, F. New active and selective catalysts for homogeneous metathesis of disubstituted alkynes. J. Mol. Catal. 1982, 15, 93-101. 

Parallel to the development of catalysts for olefin metathesis, the first alkyne metathesis catalysts were W and Mo metal oxides or carbonyls suspended on alumina or silica.65 The first homogeneous catalysts were developed by Mortreux and consisted of a mixture of Mo(CO)6 and substituted phenols.66 It was not until the work of Schrock and his collaborators, however, that a well-defined, isolable alkylidyne catalyst (38) was synthesized, characterized, and shown to catalyze alkyne metathesis.67 Later modifications on 38 included substituting the alkoxy groups with fluorinated analogs, and for the corresponding Mo alkylidynes (39), the fluorinated alkoxy groups are essential for catalytic activity.68... 

The general equation and mechanism for alkyne metathesis is depicted in Scheme 31. Alkyne metathesis is considerably less well developed in comparison to alkene metathesis. Garbyne complexes or carbyne complex precursors are among the most effective alkyne metathesis catalysts representative catalysts are depicted in Scheme 32. Tungsten carbyne complex 276 is one of the earliest alkyne metathesis catalysts, and has frequently been employed to initiate... 

Schrock, R.R. and Czekelius, C. (2007) Recent advances in the syntheses and applications of molybdenum and tungsten alkylidene and alkylidyne catalysts for the metathesis of alkenes and alkynes. Adv. Synth. Catal, 349, 55-77. Zhang, W. and Moore, J.S. (2007)... 

Table 21.2. Effect of phenol structure on the catalyst activity for alkyne metathesis.

However, the exact nature of the catalytically active species formed in the photochemical reaction of W(CO)6 in tetrachlorocarbon remains a matter of speculation. Later, it was observed that the more active and tractable catalyst for the metathesis of alkenes and the polymerisation of alkynes can be photogenerated in reaction of W(CO)6 carried out in alkane solution containing catalytic amounts of Lewis acid such as the halides group four, thirteen and fourteen elements. In such a system even higher catalytic activity is achieved than in tetrachlorocarbon solution (Eq.2) [12, 15, 20]. 

In 1976 Fischer had tested the ROMP reactions of cycloalkanes with carbyne tungsten(O) complexes as catalysts (6). With addition of Lewis acids as cocatalysts the Fischer type carbyne complexes were active in cycloalkane metathesis polymerisation. Fischer type carbyne complexes are also active catalysts for alkyne polymerisations, as found by Katz in 1984 (7). The catalytic reactions of Schrock type carbyne tungsten(VI) or molybdenum(VI) complexes were focussed on alkyne metatheses reactions (8). 

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