Hydrolytic pathways of the organometallic aqua ion[Re(CO)
3(H
2O)
3]
+(
2) in aqueous mediawere in
vestigated by means of potentiometric titration experiments.The aqua complex
2was obtained quantitati
vely by dissol
ving(NEt
4)
2[Re(CO)
3Br
3](
1) in water. Con
ventionalalkalimetric titrations (0.1 M KNO
3, 25
![](/images/entities/deg.gif)
C) allowed thedetermination of the formationconstants of[Re
3(CO)
9(
2-OH)
3(
3-OH)]
-(
3) and[Re
2(CO)
6(
2-OH)
3]
-(
4). The neutraldinuclear[Re
2(CO)
6(
2-OH)
2(H
2O)
2](
5) was obser
ved as a minor species. A fasttitrationtechnique was used to in
vestigate a rapid preequilibrium, consisting ofthe formation of themononuclear deprotonation products[Re(CO)
3(OH)(H
2O)
2](
6) and[Re(CO)
3(OH)
2(H
2O)]
-(
7).The corresponding p
Ka values are7.5(2) and 9.3(3). The immediate extraction of anaqueoussolution of
2 with diethyl ether after base addition (1equi
v) led to the quantitati
ve isolationof the well-known cubane cluster[Re(CO)
3(OH)]
4 (
8),which was obtained as a DMF (
8b) orOPPh
3 adduct (
8c). Attempts to isolate theaqua complex
2 as a crystalline material byprecipitating the bromo ligands of
1 withAgCF
3COO resulted in the formation of(NEt
4)
2[Re(CO)
3(CF
3COO)
3](
9). The structures of
8b,
8c,and
9 were elucidated by single-crystal X-ray analysis.