Bromopentacarbonylrhenium(I)
# Bromopentacarbonylrhenium(I)

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

## Preparation

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

    $Re_2(CO)_{10}$ + $Br_2$ → 2 $ReBr(CO)_5$

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

    $ReBr_3$ + 2 Cu + 5 CO → $BrRe(CO)_5$ + 2 CuBr

Copper(I) bromide is a byproduct.

## Reactions

Bromopentacarbonylrhenium(I) is a precursor to other rhenium complexes. It reacts with zinc and acetic acid to give pentacarbonylhydridorhenium $(HRe(CO)_5).$

    $Re(CO)_5Br$ + Zn + $HO_2CCH_3$ → $ReH(CO)_5$ + $ZnBrO_2CCH_3$

It also reacts with tetraethylammonium bromide in diglyme to give $[NEt_4]_2[ReBr_3(CO)_3)],$ an important precursor to compounds containing the rhenium tricarbonyl fragment.

Heating bromopentacarbonylrhenium(I) in water give the triaquo complex:

    $ReBr(CO)_5$ + 3 $H_2O$ → $[Re(H_2O)_3(CO)_3]Br$ + 2 CO

This route avoids the formation of the tetraethylammonium bromide byproduct, which is often difficult to remove from reaction mixtures.

