Bromopentacarbonylrhenium(I)

Bromopentacarbonylrhenium(I) is an inorganic compound of rhenium, commonly used for the syntheses of other rhenium complexes.

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Preparation

Bromopentacarbonylrhenium(I) is commercially available. It is also easily and inexpensively synthesized by the oxidation of dirhenium decacarbonyl with bromine:^[1]

Re₂(CO)₁₀ + Br₂ → 2 ReBr(CO)₅

It was first prepared by the "reductive carbonylation" of rhenium(III) bromide:^[2]

ReBr₃ + 2 Cu + 5 CO → BrRe(CO)₅ + 2 CuBr

Reactions

Bromopentacarbonylrhenium(I) is a useful intermediate to other rhenium complexes. For example, it reacts with zinc and acetic acid to give pentacarbonylhydridorhenium (ReH(CO)₅).^[3]

Re(CO)₅Br + Zn + HO₂CCH₃ → ReH(CO)₅ + ZnBrO₂CCH₃

It also reacts with tetraethylammonium bromide in diglyme to give [NEt₄]₂[ReBr₃(CO)₃)], an important precursor to compounds containing the rhenium tricarbonyl fragment.^[4]

Refluxing bromopentacarbonylrhenium(I) in water also provides access to the rhenium tricarbonyl fragment:

ReBr(CO)₅ + 3 H₂O → [Re(H₂O)(CO)₃]Br + 2 CO

This route avoids the formation of the tetraethylammonium bromide byproduct when the tetraethylammonium complex is used. This is desirable because the tetraethylammonium bromide is often difficult to remove from reaction mixtures.^[5]

References

1. ^ Steven P. Schmidt, William C. Trogler, Fred Basolo (1990). "Pentacarbonylrhenium Halides". Inorganic Syntheses 28: 154-159. doi:10.1002/9780470132593.ch42.
2. ^ W. Hieber, Mitarbeitern, Hans Schulten (1939). "XXX. Mitteilung über Metallcarbonyle. Über Rhenium-Kohlenoxyd-Verbindungen". Zeitschrift für anorganische und allgemeine Chemie 243: 164-173. doi:10.1002/zaac.19392430205.
3. ^ Michael A. Urbancic, John R. Shapley (1990). "Pentacarbonylhydridorhenium". Inorganic Syntheses 28: 165-8. doi:10.1002/9780470132593.ch43.
4. ^ R. Alberto, A. Egli, U. Abram, K. Hegetschweiler, V. Gramlich and P. A. Schubiger (1994). "Synthesis and reactivity of [NEt₄]₂[ReBr₃(CO)₃]. Formation and structural characterization of the clusters [NEt₄][Re₃(µ₃-OH)(µ-OH)₃(CO)₉] and [NEt₄][Re₂(µ-OH)₃(CO)₆] by alkaline titration". J. Chem. Soc., Dalton Trans.: 2815-2820. doi:10.1039/DT9940002815.
5. ^ N. Lazarova, S. James, J. Babich and J. Zubieta (2004). "A convenient synthesis, chemical characterization and reactivity of [Re(CO)₃(H₂O)₃]Br: the crystal and molecular structure of [Re(CO)₃(CH₃CN)₂Br]". Inorganic Chemistry Communications 7 (9): 1023-1026. doi:10.1016/j.inoche.2004.07.006.