Germanium Dichloride-Dioxane Complex1

[28595-67-7]  · C4H8Cl2GeO2  · Germanium Dichloride-Dioxane  · (MW 231.60)

(germylene precursor; Lewis acid catalyst; insertion reactions; cycloadditions and polymerizations)

Physical Data: mp 176-178 °C.

Solubility: slightly sol Et2O; sol THF.

Preparative Methods: a 100 mL flask equipped with a reflux condenser, nitrogen inlet, and gas outlet connected to a bubbling tower (for removing HCl) was charged with 21.8 g of germanium tetrachloride (0.102 mol), 18.7 mL of anhydrous 1,4-dioxane (0.220 mol), and 5 mL of hexane. To this solution at rt was slowly added 9.6 mL of 1,1,3,3-tetramethyldisiloxane (0.054 mol) through the condenser. The reaction mixture was heated at reflux for 8 h, cooled to rt, and filtered to remove a precipitated white solid via cannula. The solid was washed with three 20 mL portions of hexane, then dried in vacuo to give 14.5 g (63%) of the germanium dichloride-dioxane complex as a white solid.2

Handling, Storage, and Precautions: should be handled under nitrogen and stored in a refrigerator. Germanium is reputed to be of low toxicity. Use in a fume hood.

Germylene Precursor.

Germanium dichloride is a convenient starting material for the synthesis of germylenes with alkyl or heteroatom substituents, since the chloride ligands can be displaced by both lithium salts3 and organolithium reagents.4

Lewis Acid Catalyst.

Germanium dichloride behaves as a Lewis acid toward aldehydes, and activates the carbonyl group to 1,2-addition by nucleophiles. For example, it catalyzes intramolecular ene reactions, as in the quantitative conversion of citronellal to isopulegol.5 Germanium dichloride also catalyzes the conversion of aldehydes to b-keto esters with Ethyl Diazoacetate (see also Tin(II) Chloride) (eq 1).6 Finally, germanium dichloride has been used to promote self-condensation reactions with both carbonyl compounds and imines.7

Insertion Reactions.

Germanium dichloride can insert into hydrogen-halogen, carbon-halogen, metal-halogen, metal-hydride, and metal-metal bonds.1 Recently, it has been shown that germanium dichloride-dioxane reacts with aldehydes in the presence of alcohols to give a-alkoxygermanes.5 Similar products are obtained when GeCl2.dioxane is added to an acetal of a saturated aldehyde (eq 2). In both cases, the products of these insertion reactions were converted to more stable derivatives using n-Butyllithium, methyl Grignard, or Lithium Aluminum Hydride. Interestingly, the reaction of GeCl2.dioxane with a,b-unsaturated aldehydes and acetals leads to g-germyl enol ethers instead of a-alkoxygermanes (eq 3).8 These g-germyl enol ethers can be stereoselectively converted to tetrasubstituted tetrahydrofurans via reaction with aldehydes in the presence of Boron Trifluoride (eq 4).5

Cycloadditions and Polymerizations.

Germanium dichloride reacts with alkenes, alkynes, and other unsaturated organic molecules to give organogermanium polymers.9 In the case of dienes, 1,4-cycloaddition products are obtained (eq 5).10

Related Reagents.

Allyltrimethylgermane; Ethyl Diazoacetate; Tin(II) Chloride; Trifluoromethanesulfonic Anhydride.

1. Satgé, J. PAC 1984, 56, 137; Riviere, P.; Riviere-Baudet, M.; Satge, J. In Comprehensive Organometallic Chemistry; Wilkinson, G.; Stone, F. G. A.; Abel, E. W., Eds.; Pergamon: New York, 1982; Vol 2, p 399; Nefedov, O. M.; Manakov, M. N. AG(E) 1966, 5, 1021.
2. Adapted from: Viktorov, N. A.; Gar, T. K.; Mironov, V. F. JGU, 1985, 55, 1208.
3. Examples involving alcohols: Meller, A.; Grabe, C. P. CB 1985, 118, 2020; amines: Herrmann, W. A.; Denk, M.; Behm, J.; Scherer, W.; Klingan, F. R.; Bock, H.; Solouki, B.; Wagner, M. AG(E) 1992, 31, 1485; Hitchcock, P. B.; Lappert, M. F.; Thorne, A. J. CC 1990, 1587; sulfides: Karsch, H. H.; Hollstein, M.; Müller, G., A. ZN(B) 1990, 45, 775; Pfeiffer, J.; Noltemeyer, M.; Müller, A. Z. Anorg. Allg. Chem. 1989, 572, 145; selenides: Du Mont, W. W.; Lange, L.; Pohl, S.; Saak, W. OM 1990, 9, 1395; pseudohalides: Onyszchuk, M.; Castel, A.; Riviere, P.; Satge, J. JOM 1986, 317, C35.
4. Karsch, H. H.; Baumgartner, G.; Gamper, S.; Lachmann, J.; Müller, G. CB 1992, 125, 1333. Lange, L.; Meyer, B.; Du Mont, W. W. JOM 1987, 329, C17.
5. Smith L. A.; Zhu, Q.; Roskamp, E. J. Unpublished results.
6. Holmquist, C. R.; Roskamp, E. J. JOC 1989, 54, 3258. Holmquist, C. R.; Roskamp, E. J. TL 1990, 31, 4991.
7. Mironov, V. F.; Gar, T. K. Organomet. Chem. Rev.(A) 1968, 3, 311.
8. Zhu, Q.; Roskamp, E. J. JOC 1992, 57, 5281.
9. Riviere, P.; Riviere-Baudet, M.; Satge, J. JOM 1975, 97, C37.
10. Mironov, V. F.; Gar, T. K. IZV 1966, 482.

Carrie A. Roskamp & Eric J. Roskamp

Northwestern University, Evanston, IL, USA

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