Mixed Chloride/Phosphine Complexes of the Dirhenium Core. 2. New Reactions Involving Dimethylphenylphosphine

Two geometrical isomers of the composition
Re2Cl5(PMe2Ph)3,
namely 1,2,7 and 1,3,6, have been prepared.
The unusual paramagnetic
1,2,7-Re2Cl5(PMe2Ph)3
(1a), the first analogue of the previously reported
trimethylphosphine complex
1,2,7-Re2Cl5(PMe3)3,
has been synthesized by carrying out the reaction of
octachlorodirhenium
anions with PMe2Ph in benzene at room temperature.
A different reaction product,
1,3,6-Re2Cl5(PMe2Ph)3
(1b),
was obtained when
[Bun4N]2Re2Cl8
was reacted with PMe2Ph under the same conditions in
acetonitrile.
Electrochemical studies revealed that both 1a and
1b, as expected for the Re25+
core, are capable of undergoing
a one-electron reduction and a one-electron oxidation to yield the
respective Re24+ and
Re26+ dinuclear complexes.
Both processes have been accomplished chemically for the
1,2,7-isomer in the present work. One-electron
reduction
of 1a by cobaltocene followed by nonredox substitution of a
chloride ligand in the resulting anionic species by
PMe2Ph affords triply bonded
1,2,7,8-Re2Cl4(PMe2Ph)4
(2), only the second example of this rare
stereochemistry
with a cis-configuration of monodentate phosphines at both metal atoms
in the large
M2X4(PR3)4 class
of
compounds. One-electron oxidation of 1a in the presence
of a chloride source, Bun4NCl, resulted in
a quadruply
bonded
Re2Cl6(PMe2Ph)2
(3), completing the full series of
Re2Cl8-x(PMe2Ph)x
(x = 2, 3, 4) compounds with
Re2n+ (n
= 6, 5, 4) cores. The crystal structures of all complexes
1−3 have been investigated by X-ray
diffraction.
The crystallographic parameters for these structures are as
follows: 
1,2,7-Re2Cl5(PMe2Ph)3
(1a), triclinic space
group P1̄ with a = 9.350(3) Å,
b = 11.102(1) Å, c = 14.558(3) Å,
α = 101.34(2)°, β = 92.81(2)°, γ =
90.80(2)°, and Z = 2;
1,3,6-Re2Cl5(PMe2Ph)3
(1b), monoclinic space group
P21/c with a =
11.202(4) Å, b = 14.357(6) Å, c = 19.509(5) Å, β = 97.84(3)°, and
Z = 4;
1,2,7,8-Re2Cl4(PMe2Ph)4
(2), triclinic space group P1̄
with
a = 11.847(4) Å, b = 12.094(3) Å,
c = 13.056(5) Å, α = 76.111(8)°, β =
88.523(9)°, γ = 88.95(2)°, and Z
=
2;
1,7-Re2Cl6(PMe2Ph)2,
(3), triclinic space group P1̄ with
a = 9.209(1) Å, b = 11.480(2) Å,
c = 13.389(2) Å,
α = 81.74(2)°, β = 69.89(2)°, γ =
66.35(2)°, and Z = 2. The Re−Re bond lengths
in the Re24+ (2),
Re25+ (1a
and 1b), and Re26+ (3)
centered molecules (2.260(1), 2.2313(4), 2.219(1), and
2.214(1) Å) are consistent with
bond orders of 3.0, 3.5, and 4.0, respectively.