(Iodoethynyl)trimethylsilane

[18163-47-8]  · C5H9ISi  · (Iodoethynyl)trimethylsilane  · (MW 224.13)

(alkyne coupling reagent predominantly used in conjunction with organocopper species or palladium catalysis)

Physical Data: bp 96 °C, 55 °C/20 mmHg; n20D 1.5110.

Form Supplied in: not commercially available.

Preparative Methods: all involve iodination of trimethylsilylacetylenes. Direct iodination of metalated (lithium or magnesium) trimethylsilylacetylene has been largely supplanted due to the modest yields obtained.1 Utilizing Trimethylsilylacetylene and Bis(trimethylsilyl) Peroxide in the presence of Copper(I) Iodide gives good yields.2 Substituting Zinc Iodide requires using the lithium acetylide.3 Copper(I) iodide (0.05 equiv.) in the presence of iodine, sodium carbonate, and a phase-transfer catalyst gives good yields without having to use n-butyllithium or a Grignard reagent to first deprotonate the trimethylsilylacetylene.4 The most popular procedure uses Bis(trimethylsilyl)acetylene, treating it with Iodine Monochloride in dichloromethane at 25 °C to obtain excellent yields of (iodoethynyl)trimethylsilane.5,6

Handling, Storage, and Precautions: use in a fume hood.

Introduction.

(Iodoethynyl)trimethylsilane has been largely confined to aryl- and vinylcopper coupling, where it serves well since the reverse procedure, i.e. coupling with alkynylcopper reagents, is not straightforward due to the lack of reactivity of alkynyl moieties bound to copper.

Cross Coupling with Organocopper Reagents.

Vinylcopper species, prepared by the copper-catalyzed addition of Ethylmagnesium Bromide to monosubstituted alkynes, react with (iodoethynyl)trimethylsilane (eq 1) in the presence of 1.2-2 equiv of TMEDA to afford the enyne in good yield.7 In the absence of TMEDA, iodine exchange to the vinyl group occurs instead of alkynyl-vinyl coupling. In a similar fashion,8 addition of lithium tributylstannyl(cyano)cuprate across the alkyne gave a vinylcuprate which required the addition of Lead(IV) Acetate-Copper(II) Acetate to couple successfully with (iodoethynyl)trimethylsilane. In the absence of zinc(II) chloride, very low yields of the desired product are obtained.

Allenylcopper species, prepared by n-Butyllithium deprotonation of substituted allenes followed by addition to Copper(I) Bromide, have been coupled with (iodoethynyl)trimethylsilane to give allenyne products (eq 2).9

Arylcopper(I) adducts, prepared by adding an aryllithium or Grignard reagent to a slight excess of copper(I) bromide in ethereal solvent, give rise to arylalkynes when treated with (iodoethynyl)trimethylsilane (eq 3).10 Yields are modest to good, with Phenylcopper giving 64%. It was noted that substitution of a catalytic amount of copper(I) bromide, with either Phenyllithium or Phenylmagnesium Bromide, or using Lithium Diphenylcuprate, gives iodine transfer to the phenyl group, resulting in the copper acetylide which undergoes coupling with the reactive (iodoethynyl)trimethylsilane to give bis(trimethylsilyl)butadiyne. Although yields are modest, the above sequence is complementary to the Stephens-Castro coupling where aryl iodides are heated in the presence of relatively unreactive copper acetylides to obtain arylalkynes.

Both (bromo- and (iodoethynyl)trimethylsilane undergo base-induced desilylation, followed by decomposition, when subjected to Cadiot-Chodkiewicz coupling conditions. Switching to the more stable (bromoethynyl)triethylsilane affords good yields of the terminal diynes after protodesilylation (eq 4).11

Palladium-Catalyzed Coupling.

Palladium catalysis (eq 5) has been successfully applied to the coupling of (iodoethynyl)trimethylsilane and acrylate esters. Palladium(II) Acetate (0.004 equiv.), reduced in situ to palladium(0), in the presence of the alkyne, methyl acrylate, carbonate base, and a phase-transfer salt at 25 °C, gave a 40% yield of the coupled product.12

At some point, cleavage of the alkynyl-silane bond is generally desired, which can be accomplished quickly and almost quantitatively by treatment with alkali in methanol at 25 °C.13


1. Buchert, H.; Zeil, W. Spectrochim. Acta 1962, 18, 1043.
2. Casarini, A.; Dembech, P.; Reginato, G.; Ricci. A.; Seconi, G. TL 1991, 32, 2169.
3. Ricci, A.; Taddei, M.; Dembech, P.; Guerrini, A.; Seconi, G. S 1989, 461.
4. Jeffery, T. CC 1988, 909.
5. Walton, D. R. M.; Waugh, F. JOM 1972, 37, 45.
6. Walton, D. R. M.; Webb, M. J. JOM 1972, 37, 41.
7. Normant, J. F.; Commercon, A.; Villieras, J. TL 1975, 1465.
8. (a) Magriotis, P. L.; Scott, M. E.; Kim, K. D. TL 1991, 32, 6085. (b) Westmijze, H.; Ruitenberg, K.; Meijer, J.; Vermeer, P. TL 1982, 23, 2797.
9. Ruitenberg, K.; Meijer, J.; Bullee, R. J.; Vermeer, P. JOM 1981, 217, 267.
10. Oliver, R.; Walton, D. R. M. TL 1972, 5209. Luteyn, J. M.; Spronck, H. J. W.; Salemink, C. A. RTC 1978, 97, 187.
11. Eastmond, R.; Walton, D. R. M. T 1972, 28, 4591.
12. Jeffery, T. S 1987, 70.
13. Eaborn, C.; Walton, D. R. M. JOM 1965, 4, 217.

Arthur G. Romero

The Upjohn Company, Kalamazoo, MI, USA



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