· (MW 402.84)
(couples with alkynes1)
Alternate Name: trans-bromotetracarbonyl(methylmethylidyne)tungsten.
Physical Data: solid at 25 °C; mp dec; yellow crystals.
Solubility: sol pentane, THF, Et2O.
Form Supplied in: not commercially available.
Preparative Methods: prepared from the reaction of pentacarbonyl(1-methoxyethylidene)tungsten and Boron Tribromide2 or tetramethylammonium acetyl(pentacarbonyl)tungstate and Oxalyl Bromide.3
Purification: after synthesis, trans-bromotetracarbonyl(ethylidyne)tungsten is purified by chromatography on silica gel at -30 °C using 1:1 pentane-dichloromethane as an eluent, followed by recrystallization from pentane at -78 °C. Purification by extensive washing with pentane at low temperature is apparently sufficient for use in alkyne coupling reactions.1
Handling, Storage, and Precautions: unstable above 35 °C; decomposes in air.
Reactions with Alkenes and Alkynes.
Coupling of diynes and trans-bromotetracarbonyl(ethylidyne)tungsten leads to ring-fused phenol derivatives in moderate yield (eq 1).1 The reaction is most efficient for the construction of indanols, and less so for preparation of tetrahydronaphthols and benzocyclobutanols. A similar reaction pathway is observed for the analogous carbene complex;4 involvement of carbene complexes in these processes has not been ruled out. Cyclization of enynes is less efficient, leading to pentadienyltungsten complexes having the sickle geometry (eq 2).5 Enynes having methylene group tethers did not display the reactivity depicted in eq 2. Additional reactions of trans-bromotetracarbonyl(ethylidyne)tungsten with unsaturated hydrocarbons include alkyne polymerization and ring opening metathesis polymerization (ROMP) of cycloalkenes.6
A limited number of synthetic transformations have been reported employing trans-bromotetracarbonyl(ethylidyne)tungsten; however, substitution of the CO ligands for phosphine ligands provides a more stable carbyne complex (eq 3). These ligand-modified complexes have been the focus of considerable investigation.7
- 1. Sivavec, T. M.; Katz, T. J. TL 1985, 26, 2159.
- 2. Fischer, E. O.; Kreis, K.; Kreiter, C. G.; Müller, J.; Huttner, G.; Lorenz, H. AG(E) 1973, 12, 564.
- 3. McDermott, G. A.; Dorries, A. M.; Mayr, A. OM 1987, 6, 925.
- 4. Wulff, W. D.; Kaesler, R. W.; Peterson, G. A.; Tang, P.-C. JACS 1985, 107, 1060.
- 5. Sivavec, T. M.; Katz, T. J.; Chiang, M. Y.; Yang, G. X.-Q. OM 1989, 8, 1620.
- 6. Katz, T. J.; Ho, T. H.; Shih, N. Y.; Ying, Y. C.; Stuart, V. I. W. JACS 1984, 106, 2659.
- 7. Mayr, A.; Hoffmeister, H. Adv. Organomet. Chem. 1987, 27, 51.
James W. Herndon
University of Maryland, College Park, MD, USA
Copyright © 1995-2000 by John Wiley & Sons, Ltd. All rights reserved.