Tetrachloro(h5-cyclopentadienyl)niobium-Magnesium1

(CpNbCl4)

[33114-15-7]  · C5H5Cl4Nb  · Tetrachloro(h5-cyclopentadienyl)niobium-Magnesium  · (MW 299.81) (Mg)

[7439-95-4]  · Mg  · Tetrachloro(h5-cyclopentadienyl)niobium-Magnesium  · (MW 24.31)

(catalyst for cyclotrimerization of alkynes1)

Solubility: sol THF.

Preparative Method: generated, in situ, from CpNbCl4 and Magnesium.

Handling, Storage, and Precautions: is prepared and used under an inert atmosphere of nitrogen or argon.1 Use in a fume hood.

Cyclotrimerization.

It has been demonstrated1 that catalytic amounts of CpNbCl4-Mg (i.e. 1 mol %) will effect the cyclotrimerization of terminal alkynes. A mixture of 1,3,5- and 1,2,4-trisubstituted benzenes are obtained as products, with the 1,3,5-trisubstituted isomer being slightly favored (eq 1; Table 1). The reaction proceeds in 83-91% yield with aryl- and alkyl-substituted alkynes; trimethylsilylacetylene, however, does not react. In contrast to the reaction with terminal alkynes, internal alkynes do not undergo cyclotrimerization or polymerization when treated with catalytic amounts of CpNbCl4-Mg.

Alkyne-Diyne Annulation.

CpNbCl4-Mg catalyzes an annulation reaction between diynes and internal alkynes or sterically hindered terminal alkynes (eqs 2 and 3). These annulations, which lead to indanane ring systems, are conducted at 50 °C with 0.35 equiv of CpNbCl4-Mg. Higher reaction temperatures are required because of the less reactive alkyne component, and greater than catalytic amounts of niobium are needed due to decomposition of the niobium intermediates at the higher temperature.


1. Williams, A. C.; Sheffels, P.; Sheehan, D.; Livinghouse, T. OM 1989, 8, 1566.

Carrie A. Roskamp & Eric J. Roskamp

Northwestern University, Evanston, IL, USA



Copyright 1995-2000 by John Wiley & Sons, Ltd. All rights reserved.