Mortreux system, alkyne metathesis

Comparison of the Schrock versus the Mortreux-Bunz Alkyne Metathesis Systems... 

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... 

A particularly interesting example is the synthesis of alkyne-bridged oligomers and polymers, which are attractive materials for optical and electronic applications. Bunz and coworkers were able to modify the Mortreux catalyst system [Mo(CO)6 and a suitable phenol]11 and reaction conditions to perform acyclic alkyne metathesis of 1,4-dipropynylated benzenes to produce high-molecular-weight poly(p-... 

Stephens-Castro coupling of 12a generated 14a in 4.6% isolated yield [62]. Almost 30 years later, Bunz reported the preparation of 14b from 13b in 6% yield with the Mortreux catalyst system, clearly demonstrating the potential of alkyne metathesis for the preparation of macrocycles [63]. However, isolation of the desired [6]cycle from linear polymers was reported to be rather tedious. In 2004, the preparation was reported of 14b from 13b in 61% yield with EtC=Mo[N(Ar)(CMe3)]3/4-nitrophenol in 1,2,4-trichlorobenzene at 1 mmHg [59]. 

It is believed that the Mortreux system, Mo O a phenol best phenols - 1 hOH, -F3 hOH and -F hOH involves some form of Mo R OAr 3 as well as catalytically active species with the alkylidyne ligand coming from O or the alkyne. 11 24 improvement of such a system with a polyether best efficiency 1, -diphenoxyethane over a bed of molecular sieves leads to metathesis of phenylpropyne at 5 Another improvement of this system is... 

FIGURE 24.6. Mortreux system and tungsten alkyUdyne complex for the alkyne metathesis. 

Finally, one may note the curious behaviour of alkynes. If Mo(CO)6/non-4-yne is irradiated at room temperature and an excess of 3-chlorophenol then added, there is rapid metathesis to give oct-4-yne and dec-5-yne with nearly 100% selectivity (Mortreux 1977). In contrast, W(CO)6/CCl4//iv (350 ran) induces polymerization of hept-2-yne while causing metathesis of pent-2-ene present in the same reaction mixture (Stockel 1978). The difference in behaviour of the two systems presumably lies in the ability of Mo(CO)6/non-4-yne// v to generate a metal carbyne on addition of the phenol, whereas W(CO)6/CCl4/Av gives only a metal carbene. Photoassisted polymerization of terminal alkynes takes place with WCV/iv in hydrocarbon solutions (Landon 1985) photocatalyzed polymerization of substituted alkynes is induced by W(CO)6/SnCl4// v (Tamura 1994). For related systems, see Ch. 10. 

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