Abstract
Pentacarbonyl- and tricarbonyl-rhenium bromide complexes react with AgAsF6 and AgBF4 in
dichloromethane to form the respective aqua species, [Re(CO)5(OH2)]+ Y- (where, Y = AsF6-,
BF4-) and [Re(CO)(L2)(OH2)]+ BF4- [where L2 = bpy, dppe, P(OPh)3].* A variable-temperature
19F nuclear magnetic resonance study of the [Re(CO),3(tmen)(OH2)]+ BF4- system establishes
that an equilibrium exists between the coordinated and 'free' tetrafluoroborate anion in solution
(CD2Cl2):
Re(CO)3(tmen)FBF3 + H2O ℰ [Re(CO)3(tmen)(OH2)]+ + BF4-
This equilibrium is forced to the right by low temperature (c. -10°C) and by removing the water
with phosphorus pentoxide. Thus, under controlled reaction conditions (c. - 10°C, dry nitrogen
atmosphere), AsF6- and BF4- are seen by infrared spectra to be coordinated in the complexes
Re(CO)3(bpy)FAsF5.δ(H2O) and Re(CO)3(tmen)FBF3.δ(H2O). The species [Re(CO)3(L2)(OH2)]+
Y- [where (i), L2 = 2CO, Y = AsF6-; (ii), L2 = tmen, Y = AsF6-, BF4-] have been characterized
by their crystal structures. Crystals of [Re(CO)5(OH5)]+ AsF6- are monoclinic, space group C2/c
with a 27.085(5), b 7.208(1), c 13.404(3) Ǻ and β 105.50(1)°. A full-matrix least-squares refinement
when using the absorption corrected data converged with R = 0.027 and R, = 0.028. The species
[Re(CO)3(tmen)(OH2)] + AsF6- crystallizes in the monoclinic space group P2, with a 7.858(1),
b 15,68(1), c 7.887(2) Ǻ and β 117.11(1)°. The final full-matrix refinement converged with
R = 0.021 and Rw = 0.022. [Re(CO)3(trnen)(OH2)]+ BF4- crystallizes in themonoclinic space group
C2/m with a 14.134(4), b 16.010(4), c 7.729(1) Ǻ and β 113.16(2)°. In these structures the water
molecule coordinates to the rhenium(1) at an average distance of 2,246(5) Ǻ. This is significantly
larger than the rhenium-fluoride bond length of 2.040(4) Ǻ.
Similar manganese aqua complexes, [Mn(CO)3 {P(OPh)3}2(H2O)]+ Y- (where, Y- = AsF6-,
BF4-), also exhibit the same infrared features characteristic of coordinated water [i.e. the presence
of sharp δ(H-O-H) bending absorption near 1600 cm-1]. This feature is absent from all the species
which only have lattice water and a coordinated fluoro anion.