The potentially bidentate hybrid ligand
(o-hydroxyphenyl)diphenylphosphine, abbreviated POH,
reacted via ligand-exchange with pentavalent rhenium precursors to give a series of
six-coordinate mono- and dioxo complexes.
Accurate control of the metal:ligand stoichiometric ratio allowed
for the isolation of the mono-substituted
[ReOCl3(PO)]- (1) and
[ReOCl2(PO)(PPh3)] (2)
derivatives. 1 was found to be the key intermediate for
the
syntheses of three more types of bis-substituted compounds: anionic
dioxo [ReO2(PO)2][A] (A =
NBu4 (3),
AsPh4 (4)), neutral monooxo
[ReOX(PO)2] (X = Cl (5), Br
(6), I (7)), and neutral monooxo mixed-ligand
[ReOX(PO)(PNH)] [PNH =
(o-amidophenyl)diphenylphosphine; X = Cl
(8), Br (9), I (10)] complexes.
In the mono-substituted complexes, the P,O-donors of the bidentate ligand spanned an
equatorial (P) and the apical position
(O) trans to the ReO linkage in a distorted octahedral
arrangement. In all of the bis-substituted monooxo
compounds, the second chelate ligated on the equatorial plane almost
orthogonally positioned with respect to the
first one, the two phosphorus donors showing a mutual
cis-(P,P) orientation. Dioxo complexes retained the
cis-(P,P) configuration with the bidentate ligands symmetrically coordinated
on the equatorial plane normal to the
trans-ReO2 core. All the complexes were
characterized by various physical techniques, including IR, MS,
and
1H/31P{1H} NMR. The
X-ray structure of a representative compound for each category, namely
[ReOCl3(PO)][NBu4] (1),
[ReO2(PO)2][AsPh4]
(4), [ReOCl(PO)2] (5), and
[ReOCl(PO)(PNH)] (8), were determined.
Crystals
of 1 were monoclinic,
P21/n, a =
10.840(3) Å, b = 22.167(6) Å, c =
15.210(4) Å, β = 95.91(2)°, and Z =
4;
those of 4 were triclinic, P1̄, a
= 12.679(7) Å, b = 13.082(7) Å, c
= 19.649(8) Å, α = 82.64(4)°, β =
81.16(4)°,
γ = 62.27(3)°, and Z = 2; those of 5
were orthorhombic, a = 10.225(4) Å, b =
14.208(6) Å, c = 21.771(9) Å,
P212121, and
Z = 4; and those of 8 were orthorhombic,
a = 10.199(2) Å, b = 14.147(4) Å,
c = 21.772(6) Å,
P212121, and
Z = 4. The four structures were solved by the
Patterson method and refined by full-matrix least-squares procedures to R = 0.050, 0.063, 0.043, and 0.039
for 1, 4, 5 and 8,
respectively. Both solution state
(31P{1H} NMR) and solid state (X-ray)
demonstrated a cis-(P,P) arrangement for each
bis-substituted complex,
with the Re atom at the center of a highly distorted octahedron.
Detailed analyses of the IR spectra of this series
of Re(V) compounds in the region 900−580
cm-1 allowed us the possibility to
distinguish between symmetrical
and asymmetrical bis-substituted complexes.