· (MW 471.8)
(reagent used as an alkyne metathesis catalyst)
Solubility: soluble in organic solvents such as toluene, hexanes, pentane, chloroform, and diethyl ether.
Form Supplied in: colorless flakes; literature preparation (see below).
Purification: recrystallized from diethyl ether with acetonitrile and cooling to -30 °C or sublimed at 50 °C under vacuum.
Preparative Methods: alkylidyne 1 can be prepared by adding LiO-t-Bu to a solution of [NEt4][W(CCMe3)Cl4] in THF at -30 °C (1).2 An alternative procedure utilizes a metathesis reaction between W2(OCMe3)6 and (CH3)3CCN.3
Handling, Storage, and Precautions: alkylidyne 1 is highly unstable to water and slowly decomposes in an atmosphere of air. However, 1 is stable as a solid or in solution under dry inert atmosphere for extended periods of time.
Intermolecular Metathesis Reactions
Alkylidyne 1 serves to initiate a metathesis reaction between two alkynyl species.4 Terminal acetylenes undergo alkyne metathesis with catalyst 1 to the corresponding symmetrical olefins; however, these reactions are accompanied by a significant amount of undesired polymerization.3b,5 Presumably, deprotonation of an intermediate metallacyclobutadiene species gives rise to this destructive pathway.3b,5 The ratio between the metathesis and polymerization products were found to be susceptible to temperature, solvent and additive effects.3b To circumvent these problems, alkylidyne 1 is typically used to catalyze a metathesis reaction between two internal alkynes.6 Reagent 1 was found to initiate acyclic diyne metathesis (ADIMET) with a series of substituted diynes.7 Dodeca-3,9-diyne was treated with 1 to produce a polyhexynylene (2).7 In addition, a bispropynylbenzene derivative was converted to polymeric aromatic species with alkylidyne 1 (3).7 Tungsten-mediated metathesis has also been used in the total synthesis of natural products. Dimerization of an alkynyl butenolide with 1 proceeded smoothly to give the C2-symmetric precursor of dehydrohomoancepsenolide (4).8 Interestingly, alkylidyne 1 displays high chemoselectivity for the alkyne of the butenolide substrate.
Intramolecular Alkyne Metathesis
Alkylidyne 1 initiates RCM of nonterminal diynes (for reasons stated above) to their corresponding cycloalkyne.9 For instance, alkylidyne 1 catalyzes RCM of diesters to the 14-membered cycloalkyne in good yield (5).9a Catalyst 1 was found to tolerate several functional groups including esters, ethers, enoates, amides, silyl ethers, sulfonamides, carbamates, and sulfones.9a However, strongly Lewis basic moieties such as thioethers and basic nitrogen groups hinder RCM reactions catalyzed by 1.9a The robust nature of catalyst 1 was displayed in the RCM of a functionalized diyne, which formed the skeleton of nakadomarin A in excellent yield (6).9a
Alkylidyne 1 reacts with a variety of different nucleophiles such as water,10 caboxylates,11 diols,12 and Grignard reagents13 to make unique tungsten alkylidyne and alkylidene complexes. Alkylidyne 1 was reacted with BINOL to generate a C1-symmetric alkylidene complex at ambient temperature in good yield (7).12a Treatment of alkylidyne 1 with BCl3 and 1,2-dimethoxyethane at -78 °C formed a new tungsten-alkylidyne species in 87% yield (8).12b
- 1. (a) Schrock, R. R., Polyhedron 1995, 14, 3177. (b) Schrock, R. R., Acc. Chem. Res. 1986, 19: 342.
- 2. Schrock, R. R.; Clark, D. N.; Sancho, J.; Wengrovius, J. H.; Rocklage, S. M.; Pederson, S. F., Organometallics 1982, 1, 1645.
- 3. (a) Schrock, R. R.; Listemann, M. L.; Sturgeoff, L. G., J. Am. Chem. Soc. 1982, 104, 4291. (b) Mortreux, A.; Petit, F.; Petit, M.; Szymanska-Buzar, T., J. Mol. Catal. A: Chem. 1995, 96, 95.
- 4. (a) Katz, T. J.; McGinnis, J., J. Am. Chem. Soc. 1975, 97, 1592. (b) Wengrovius, J. H.; Sancho, J.; Schrock, R. R., J. Am. Chem. Soc. 1981, 103, 3932.
- 5. Bray, A.; Mortreux, A.; Petit, F.; Petit, M.; Szymanska-Buzar, T., J. Chem. Soc., Chem. Commun. 1993, 197.
- 6. Bunz, U. H. F.; Kloppenburg, L., Angew. Chem., Int. Ed. Engl. 1999, 38, 478.
- 7. Weiss, K.; Michel, A.; Auth, E.-M.; Bunz, U. H. F.; Mangel, T.; Müllen, K., Angew. Chem., Int. Ed. Engl. 1997, 36, 506.
- 8. Fürstner, A.; Dierkes, T., Org. Lett. 2000, 2, 2463.
- 9. (a) Fürstner, A.; Guth, O.; Rumbo, A.; Seidel, G., J. Am. Chem. Soc. 1999, 121, 11108. (b) Fürstner, A.; Seidel, G., J. Organomet. Chem. 2000, 75. (c) Fürstner, A.; Seidel, G., Angew. Chem., Int. Ed. Engl. 1998, 37, 1734.
- 10. Feinstein-Jaffe, I.; Pedersen, S. F.; Schrock, R. R., J. Am. Chem. Soc. 1983, 105, 7176.
- 11. Freudenberger, J. H.; Schrock, R. R., Organometallics 1985, 4, 1937.
- 12. (a) Heppert, J. A.; Dietz, S. D.; Eilerts, N. W.; Henning, R. W.; Morton, M. D.; Takusagawa, F., Organometallics 1993, 12, 2565. (b) Stevenson, M. A.; Hopkins, M. D., Organometallics 1997, 16, 3572.
- 13. Chisholm, M. H.; Huffman, J. C.; Klang, J. A., Polyhedron 1990, 9, 1271.
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