Mixed chloride-phosphine complexes of the dirhenium core. Part 11. Reactions of [Re2Cl8]2- with secondary phosphines, PCy2H and PPh2H

Article abstract of DOI:10.1016/S0020-1693(01)00789-7

The reaction between the dirhenium(III,III) anion, [Re₂Cl₈]^2-, and the secondary phosphine, PCy₂H, yields a mixture of products as a result of disproportionation, namely, a dirhenium(II,III) chloride-phosphine complex 1,3,6-Re₂Cl₅(PCy₂H)₃ (1) and a dirhenium(IV) face-sharing bioctahedral compound with bridging phosphido groups, [Bu₄ⁿN][Re₂(μ-PCy₂) ₃Cl₆] (2). The diphenylphosphine analogue of 2, [Bu₄ⁿN][Re₂(μ-PPh₂) ₃Cl₆] (3) has been similarly prepared from the reaction of [Re₂Cl₈]^2- with PPh₂H. An interesting dirhenium(III,III) complex, [Bu₄ⁿN]₂[Re₂(μ-PPh ₂)₂(PPh₂H)₂Cl₆] (4) having both neutral terminal phosphines and anionic phosphido bridges, has also been isolated as an intermediate in the latter system. Crystal structures of 1-4 have been determined by X-ray crystallography. The compounds were also characterized by cyclic voltammetry, IR and ³¹P NMR spectroscopy.

Full text of DOI:10.1016/S0020-1693(01)00789-7

Inorganica Chimica Acta 332 (2002) 47–53
www.elsevier.com/locate/ica
Mixed chloride–phosphine complexes of the dirhenium core. Part
11. Reactions of [Re2Cl8]2− with secondary phosphines, PCy2H
and PPh2H
Panagiotis A. Angaridis a, F. Albert Cotton a,*, Evgeny V. Dikarev a,b,
Marina A. Petrukhina a,b
a Laboratory for Molecular Structure and Bonding, Department of Chemistry, Texas A&M Uni6ersity, PO Box 30012, College Station,
TX 77842-3012, USA
b State Uni6ersity of New York at Albany, Department of Chemistry, Albany, NY 12222, USA
Received 10 September 2001; accepted 15 October 2001
Abstract
The reaction between the dirhenium(III,III) anion, [Re2Cl8]2−, and the secondary phosphine, PCy2H, yields a mixture of
products as a result of disproportionation, namely, a dirhenium(II,III) chloride–phosphine complex 1,3,6-Re2Cl5(PCy2H)3 (1) and
a dirhenium(IV) face-sharing bioctahedral compound with bridging phosphido groups, [Bun4 N][Re2(m-PCy2)3Cl6] (2). The
diphenylphosphine analogue of 2, [Bun4 N][Re2(m-PPh2)3Cl6] (3) has been similarly prepared from the reaction of [Re2Cl8]2− with
PPh2H. An interesting dirhenium(III,III) complex, [Bu4n N]2[Re2(m-PPh2)2(PPh2H)2Cl6] (4) having both neutral terminal phosphines
and anionic phosphido bridges, has also been isolated as an intermediate in the latter system. Crystal structures of 1–4 have been
determined by X-ray crystallography. The compounds were also characterized by cyclic voltammetry, IR and 31P NMR
spectroscopy. © 2002 Published by Elsevier Science B.V.
Keywords: Phosphine/chloride complexes; Dirhenium(II,III) complexes; X-ray crystallography
diate rhenium species has been of special interest for us
since then. Therefore, we extended this study to two
1. Introduction
monodentate secondary phosphines, namely PCy2H
and PPh2H. It is known that not only can secondary
phosphines react in the same manner as tertiary phos-
phines, but, also, a deprotonation may occur affording
a dialkyl or diaryl phosphido group capable of acting
as either a terminal or bridging ligand. This expands
the structural possibilities in rhenium chemistry and
might stabilize some intermediates in the above-men-
tioned reactions of [Re2Cl8]2− when using secondary
phosphine ligands.
As a result of this study, we report here synthetic
preparations and the crystal structures of several new
dirhenium complexes, namely: a compound of the
Re52+ core, Re2Cl5(PCy2H)3 (1), two analogous face-
sharing bioctahedral (FSBO) rhenium(IV) complexes,
[Bun4 N][Re2(m-PR2)3Cl6] (R=Cy (2) and Ph (3)), and a
novel rhenium(III) edge-sharing bioctahedral (ESBO)
compound, [Bun4 N]2[Re2(m-PPh2)2(PPh2H)2Cl6] (4).
Our previous work on the reactions of the oc-
tachlorodirhenium anion, [Re2Cl8]2−, and monodentate
phosphines, revealed that the nature of the solvent has
a great influence on the reaction pathway [1,2]. We
have shown that a disproportionation process rather
than reduction occurs in an inert and nonpolar solvent
such as benzene [3]. In the case of tertiary monodentate
phosphines, PEt3 and PPrn3, both the reduced and the
oxidized rhenium species have been isolated [3]. Some
spectroscopic evidence that edge- and face-sharing bioc-
tahedral dirhenium compounds play an important role
in those processes at an early stage of the reactions has
been presented. Further insight into the disproportiona-
tion mechanism as well as identification of the interme-
* Corresponding author. Tel.: +1-979-845 4432; fax: +1-979-845
9351.
E-mail address: cotton@tamu.edu (F.A. Cotton).
0020-1693/02/$ - see front matter © 2002 Published by Elsevier Science B.V.
PII: S0020-1693(01)00789-7

48
P.A. Angaridis et al. / Inorganica Chimica Acta 332 (2002) 47–53
2. Experimental
then refluxed for 2 days affording a very dark brown
precipitate. The mixture was cooled and the solid was
filtered off. It was washed with hexanes, dried, and then
dissolved in 10 ml of CH2Cl2 giving a dark purple
solution. The CH2Cl2 solution was layered with 25 ml
of Et2O. Dark purple, block crystals were grew at the
walls of the tube in a few days. They were recrystallized
from the acetone–hexanes system affording crystals of
3. Yield: 40–45%. 31P NMR {CD2Cl2, 22 °C}: l 215.6
ppm (s).
2.1. General procedures
All syntheses and purifications were carried out un-
der an atmosphere of N2 in standard Schlenkware. All
solvents were freshly distilled under N2 from suitable
drying agents. Chemicals were purchased from the fol-
lowing commercial sources and used as received:
PCy2H and PPh2H, Strem Chemicals; [Bun4 N]2[Re2Cl8],
Aldrich, Inc.
2.5. Preparation of [Bun4 N]2[Re2(v-PPh2)2(PPh2H)2Cl6]
(4)
2.2. Physical measurements
Electrochemical measurements were carried out on
CH2Cl2 solutions that contained 0.1 M tetra-n-buty-
lammonium hexafluorophosphate (TBAH) as the sup-
porting electrolyte. A stream of dinitrogen was bubbled
through the solution during the measurements. E1/2
values, determined as (Ep,a+Ep,c)/2, were referenced to
the Ag ꢀ AgCl electrode at room temperature (r.t.). Un-
der our experimental conditions, E1/2= +0.47 V versus
Ag ꢀ AgCl for the ferrocenium–ferrocene couple.
Voltammetric experiments were done with the use of a
Bioanalytical Systems Inc. electrochemical analyzer,
Model 100. The scan rate was 100 mV s−1 at a Pt disk
electrode. The 31P {1H} NMR data were recorded at
r.t. on a UNITY-plus 300 multinuclear spectrometer
operated at 121.4 MHz and using 85% H3PO4 as an
external standard. The IR spectra were performed in
the range 400–4000 cm−1 on a Perkin–Elmer 16PC
FT-IR spectrophotometer using KBr pellets.
To a solution containing [Bun4 N]2[Re2Cl8] (0.097 g,
0.085 mmol) in 10 ml of CH2Cl2, 0.5 ml of PPh2H was
added. The solution turned brown in a few minutes. It
was stirred for 1 h at r.t.. All volatiles were removed
under reduced pressure to leave a brown oily solid. It
was washed with hexanes (3×15 ml), then dissolved in
8 ml of acetone, and the acetone solution was layered
with 15 ml of hexanes. Several brown crystals of 4 came
out in a week. Yield: approximately 15%. IR (KBr,
cm−1): 3051.7(s), 2960.0(s), 2873.1(s), 1617.6(w,br),
1586.9(w), 1572.8(w), 1468.0(s), 1482.8(s), 1435.9(s),
1380.3(s), 1312.7(w), 1333.7(w), 1189.1(w), 1156.9(w),
1129.9(m), 1100.8(s), 1069.9(m), 1028.5(m), 978.0(m),
885.9(s), 805.6(w), 740.09(s), 693.2(s), 535.1(s), 515.7(s),
492.0(s), 423.9(m).
2.6. X-ray structure determinations
Single crystals of compounds 1·CH2Cl2·1/2C6H14,
2·3/4(CH3)2CO, and 4·31/2(CH3)2CO were obtained as
described above. The X-ray diffraction experiments
were carried out on a Nonius FAST diffractometer
with an area detector using Mo Ka radiation. The
crystals were mounted on the tip of a quartz fiber with
silicone grease, and the setup was quickly placed in the
cold N2 stream (−60 °C) of a low temperature con-
troller. Fifty reflections were used in cell indexing and
about 250 reflections in cell refinement. The data were
corrected for Lorentz and polarization effects by the
MADNES program [4]. Reflection profiles were fitted and
values of F2 and |(F2) for each reflection were obtained
by the program PROCOR [5]. The intensities for 2·3/4
(CH3)2CO and 4·31/2 (CH3)2CO were also corrected for
absorption using a local adaptation of the program
SORTAV [6]. All calculations were done on a DEC
Alpha running VMS. The coordinates of rhenium
atoms were found in direct E maps using the structure
solution program SHELXTL [7]. The positions of the
remaining atoms were located by means of alternating
series of least-squares cycles and difference Fourier
maps [8]. Anisotropic displacement parameters were
2.3. Preparation of Re2Cl5(PCy2H)3 (1) and
[Bun4 N][Re2(v-PCy2)3Cl6] (2)
To a suspension containing [Bun4 N]2[Re2Cl8] (0.226 g,
0.2 mmol) in C6H6, 0.5 ml of PCy2H was added at
about 0 °C. The mixture was slowly warmed to r.t. and
stirred overnight affording a brown solid. It was iso-
lated by filtration, washed with hexanes (2×10 ml),
dried, and then dissolved in 15 ml of CH2Cl2. The
CH2Cl2 solution was layered with 20 ml of hexanes.
Two sorts of crystals appeared in 3 days: brownish
block-shaped crystals of 1 and purple plates of 2, which
were separated manually. For 1: CV (CH2Cl2,
Ag ꢀ AgCl, 22 °C, V): E1/2(red)= −0.66, E1/2(ox)= +
0.52. For 2: 31P NMR {CD2Cl2, 22 °C}: l 221.3 ppm
(s).
2.4. Preparation of [Bun4 N][Re2(v-PPh2)3Cl6] (3)
To a suspension containing [Bun4 N]2[Re2Cl8] (0.222 g,
0.2 mmol) in 15 ml of toluene, 0.6 ml of PPh2H was
added. The mixture was stirred at r.t. for 2 h; it was

P.A. Angaridis et al. / Inorganica Chimica Acta 332 (2002) 47–53
49
Table 1
Crystallographic data for 1,3,6-Re2Cl5(PCy2H)3·CH2Cl2·1/2C6H14 (1·CH2Cl2·1/2C6H14), [Bun4 N][Re2(m-PCy2)3Cl6]·3/4(CH3)2CO (2·3/4(CH3)2CO)
and [Bun4 N]2[Re2(m-PPh2)2Cl6(PPh2H)2]·31/2(CH3)2CO (4·31/2(CH3)2CO)
1·CH2Cl2·1/2C6H14
2·3/4(CH3)2CO
4·31/2(CH3)2CO
Formula
C40H78Cl7P3Re2
1272.48
monoclinic
P21/n
10.721(3)
20.501(9)
24.000(3)
C54.25H106.50Cl6N1O0.75P3Re2
C90.50H135Cl6N2O3.50P4Re2
2015.99
triclinic
Formula weight
Crystal system
Space group
1462.91
monoclinic
P21
13.670(4)
23.350(8)
20.357(5)
(
P1
,
a (A)
14.562(4)
15.074(4)
23.214(4)
90.35(2)
106.91(2)
99.94(2)
4794(2)
,
b (A)
,
c (A)
h (°)
i (°)
k (°)
101.48(2)
90.81(3)
3
,
V (A )
Z
5170(3)
4
1.635
5.160
6497(3)
4
1.496
4.078
2
zcalc (g cm−3
)
1.397
2.803
v (mm−1
)
,
Radiation (u, A)
Temperature (K)
Mo Ka (0.71073)
213(2)
Mo Ka (0.71073)
213(2)
Mo Ka (0.71073)
213(2)
Transmission factors
0.379–0.554
16 185
15 447
0.329–0.580
11 996
10 593
Number of unique data
Number of observed data [I\2|(I)]
Number of parameters refined
6763
5639
455
0.0709, 0.1600
0.0887, 0.1809
1.136
1185
930
b
R1 a, wR2 [I\2|(I)]
0.0435, 0.1041
0.0475, 0.1090
1.114
0.0477, 0.1165
0.0562, 0.1266
1.106
b
R1 a, wR2 (all data)
Quality-of-fit c
a R1=SꢀꢀFoꢀ−ꢀFcꢀꢀ/SꢀFoꢀ.
b wR2=[S[w(Fo2−Fc2)2]/S[w(Fo2)2]]1/2
.
c Quality-of-fit=[S[w(Fo2−Fc2)2]/(Nobs−Nparams)]1/2, based on all data.
assigned to all non-hydrogen atoms. Hydrogen atoms
were included in the structure factor calculations at
idealized positions. The hydrogen atoms connected to
the phosphorus atoms of PPh2H in 4 were found in a
difference Fourier map and then refined independently
with an isotropic thermal parameter.
Relevant crystallographic data for 1·CH2Cl2·
1/2C6H14, 2·3/4(CH3)2CO, and 4·31/2(CH3)2CO are
summarized in Table 1, and selected bond distances
and angles are given in Tables 2–4.
atoms. The PꢀReꢀP angle is 164.4(1)° and ReꢀP dis-
,
tances are averaged to 2.451(5) A. The ReꢀRe bond of
,
2.223(1) A is typical for corresponding dirhenium
molecules with bond order of 3.5 [10]. The
a
Re2Cl5(PCy2H)3 molecule exhibits the highest deviation
from the eclipsed geometry among 1,3,6-Re2Cl5(PR3)3
structures with the average PꢀReꢀReꢀCl torsion angle
as high as 12.0(2)°.
3.2. [Bun4 N][Re2(v-PCy2)3Cl6]·3/4(CH3)2CO
(2·3/4(CH3)2CO) and [Bun4 N][Re2(v-PPh2)3Cl6] (3)
3. Results
Compound 2 conforms to the monoclinic space
group P21 with two crystallographically independent
dirhenium anions [Re2(PCy2)3Cl6]− and two tetra-n-
butylammonium cations in the unit cell. In the dirhe-
nium anion (Fig. 2) two rhenium(IV) atoms are bridged
by three dicyclohexylphosphido groups. Three terminal
chloride ligands complete the coordination sphere of
each metal center, thus defining the core structure as a
face-sharing bioctahedral dirhenium complex.
The two complexes 2 and 3 obtained here are close
analogues. The structure of 3 was not completely
refined because the severe disorder of the tetra-n-buty-
lammonium cations in [Bun4 N][Re2(m-PPh2)3Cl6] (3)
The molecular structures of the four compounds are
shown schematically in Chart 1.
3.1. Re2Cl5(PCy2H)3·CH2Cl2·1/2C6H14
(1·CH2Cl2·1/2C6H14)
Compound 1 crystallizes in the monoclinic space
group P21/n with dichloromethane and hexanes of sol-
vation. The Re2Cl5(PCy2H)3 molecule (Fig. 1) belongs
to a large class of 1,3,6-isomers [9] having two phos-
phine groups trans to each other on one of the metal

50
P.A. Angaridis et al. / Inorganica Chimica Acta 332 (2002) 47–53
could not be modeled1. However, all geometric charac-
teristics of the dirhenium anion [Re2(m-PPh2)3Cl6]− in 3
(Fig. 3) are reliable. Comparison of structural parame-
ters of the two [Re2(m-PR2)3Cl6]− ions where R=Cy or
Ph, revealed a very close similarity of two complexes
(Table 3). For example, the average ReꢀP distances and
Table 4
,
Selected bond distances (A) and Angles (°) for [Re2(m-
PPh2)2(PPh2H)2Cl6]2− anion in (4)
Bond distances
Re(1)ꢀRe(2)
Re(1)ꢀP(1)
Re(1)ꢀP(2)
Re(1)ꢀP(3)
Re(1)ꢀCl(1)
Re(1)ꢀCl(2)
Re(1)ꢀCl(3)
2.7494(7)
2.312(2)
2.322(2)
2.398(2)
2.507(2)
2.438(2)
2.502(2)
Re(2)ꢀP(1)
Re(2)ꢀP(2)
Re(2)ꢀP(4)
Re(2)ꢀCl(4)
Re(2)ꢀCl(6)
Re(2)ꢀCl(5)
2.313(2)
2.321(2)
2.395(2)
2.521(2)
2.441(2)
2.494(2)
,
the ReꢀPꢀRe angles are 2.390(4) and 2.380(6) A and
60.39(9) and 61.5(2)° for 2 and 3, respectively. These
Table 2
Bond angles
,
Selected bond distances (A), angles (°) and torsion angles (°) for
1,3,6-Re2Cl5(PCy2H)3 (1)
P(1)ꢀRe(1)ꢀP(2)
P(1)ꢀRe(1)ꢀP(3)
P(2)ꢀRe(1)ꢀP(3)
P(1)ꢀRe(1)ꢀCl(1)
P(1)ꢀRe(1)ꢀCl(2)
P(1)ꢀRe(1)ꢀCl(3)
P(2)ꢀRe(1)ꢀCl(1)
P(2)ꢀRe(1)ꢀCl(2)
P(2)ꢀRe(1)ꢀCl(3)
P(3)ꢀRe(1)ꢀCl(1)
P(3)ꢀRe(1)ꢀCl(2)
P(3)ꢀRe(1)ꢀCl(3)
Cl(1)ꢀRe(1)ꢀCl(2)
Cl(1)ꢀRe(1)ꢀCl(3)
Cl(2)ꢀRe(1)ꢀCl(3)
Re(2)ꢀRe(1)ꢀP(1)
Re(2)ꢀRe(1)ꢀP(2)
Re(2)ꢀRe(1)ꢀP(3)
Re(2)ꢀRe(1)ꢀCl(1)
Re(2)ꢀRe(1)ꢀCl(2)
Re(2)ꢀRe(1)ꢀCl(3)
Re(1)ꢀP(1)ꢀRe(2)
107.23(7)
90.48(7)
95.93(7)
83.67(7)
99.89(7)
162.68(7)
168.62(7)
93.27(7)
89.14(7)
87.05(7)
163.47(7)
82.04(7)
81.39(7)
80.38(7)
84.40(7)
53.54(5)
53.69(5)
95.34(5)
137.11(5)
101.17(5)
142.44(5)
72.94(6)
P(1)ꢀRe(2)ꢀP(2)
P(1)ꢀRe(2)ꢀP(4)
P(2)ꢀRe(2)ꢀP(4)
P(1)ꢀRe(2)ꢀCl(4)
P(1)ꢀRe(2)ꢀCl(6)
P(1)ꢀRe(2)ꢀCl(5)
P(2)ꢀRe(2)ꢀCl(4)
P(2)ꢀRe(2)ꢀCl(6)
P(2)ꢀRe(2)ꢀCl(5)
P(4)ꢀRe(2)ꢀCl(4)
P(4)ꢀRe(2)ꢀCl(6)
P(4)ꢀRe(2)ꢀCl(5)
Cl(4)ꢀRe(2)ꢀCl(5)
Cl(4)ꢀRe(2)ꢀCl(6)
Cl(5)ꢀRe(2)ꢀCl(6)
Re(1)ꢀRe(2)ꢀP(1)
Re(1)ꢀRe(2)ꢀP(2)
Re(1)ꢀRe(2)ꢀP(4)
Re(1)ꢀRe(2)ꢀCl(4)
Re(1)ꢀRe(2)ꢀCl(6)
Re(1)ꢀRe(2)ꢀCl(5)
Re(1)ꢀP(2)ꢀRe(2)
107.21(7)
90.70(7)
95.30(7)
83.48(7)
99.54(7)
162.88(7)
168.91(7)
93.43(7)
89.14(7)
87.35(7)
163.96(7)
82.56(7)
80.51(7)
81.63(6)
84.14(7)
53.51(5)
53.70(5)
95.10(5)
136.90(5)
100.91(5)
142.54(5)
72.62(6)
Bond distances
Re(1)ꢀRe(2)
Re(1)ꢀP(1)
Re(1)ꢀP(2)
Re(1)ꢀCl(1)
Re(1)ꢀCl(2)
2.223(1)
2.447(5) Re(2)ꢀP(3)
2.478(5) Re(2)ꢀCl(3)
2.345(4) Re(2)ꢀCl(4)
2.323(4) Re(2)ꢀCl(5)
2.428(4)
2.333(5)
2.313(4)
2.350(4)
Bond angles
P(1)ꢀRe(1)ꢀP(2)
P(1)ꢀRe(1)ꢀCl(1)
P(1)ꢀRe(1)ꢀCl(2)
P(2)ꢀRe(1)ꢀCl(1)
P(2)ꢀRe(1)ꢀCl(2)
Cl(1)ꢀRe(1)ꢀCl(2)
164.4(1)
85.2(2) P(3)ꢀRe(2)ꢀCl(3)
87.2(2) P(3)ꢀRe(2)ꢀCl(4)
91.5(2) P(3)ꢀRe(2)ꢀCl(5)
86.0(2) Cl(3)ꢀRe(2)ꢀCl(5)
81.5(2)
90.2(2)
159.7(2)
87.7(2)
141.8(2) Cl(3)ꢀRe(2)ꢀCl(4) 142.5(2)
Cl(4)ꢀRe(2)ꢀCl(5)
88.1(2)
Torsion angles
P(1)ꢀRe(1)ꢀRe(2)ꢀCl(3)
P(2)ꢀRe(1)ꢀRe(2)ꢀCl(4)
Cl(1)ꢀRe(1)ꢀRe(2)ꢀP(3)
Cl(2)ꢀRe(1)ꢀRe(2)ꢀCl(5)
15.5(2)
8.5(2)
10.9(2)
12.9(2)
Table 3
two anions are also closely similar to the analogous
n
,
Averaged bond distances (A) and angles in [Bu4 N][Re2(m-PCy2)3Cl6]
anion with diethylphosphido groups, [Re2(m-PEt2)3Cl6]-,
(2) and [Bun4 N][Re2(m-PPh2)3Cl6] (3)
,
reported by us [2]: ReꢀRe, 2.406 A; ReꢀPꢀRe, 61.3°.
2
3
3.3. [Bun4 N]2[Re2(v-PPh2)2(PPh2H)2Cl6]·31/2(CH3)2CO
(4·31/2(CH3)2CO)
Bond distances
ReꢀRe
ReꢀP
2.4049(8)
2.390(4)
2.430(3)
2.435(1)
2.380(6)
2.413(5)
(
Compound 4 crystallizes in the triclinic P1 space
ReꢀCl
group
with
one
dirhenium
anion,
[Re2(m-
Bond angles
ReꢀPꢀRe
PꢀReꢀP
ReꢀReꢀP
ClꢀReꢀCl
ReꢀReꢀCl
PꢀReꢀCl
PPh2)2(PPh2H)2Cl6]2−, and two tetra-n-butylammo-
nium cations in the asymmetric unit. Each anion
consists of two rhenium(III) atoms bridged by two
diphenylphosphido groups with the ReꢀP distances av-
eraged to 2.317(2) A (Fig. 4). There are also one
terminal neutral diphenylphosphine group (the average
60.39(9)
96.9(1)
59.80(9)
84.1(1)
129.35(9)
170.8(1)
89.1(1)
61.5(2)
96.2(2)
59.3(1)
83.9(2)
129.5(2)
170.8(2)
89.7(2)
,
,
ReꢀP distance is 2.397(2) A) and three chloride ligands
,
(average ReꢀCl, 2.484(2) A) on each metal center,
which define its structure as an ESBO dirhenium(III)
complex. For the anion in 4 the rhenium–rhenium
1
n
(
Crystal data for [Bu4 N][Re2(m-PPh2)3Cl6] (3): triclinic P1, a=
,
,
,
13.717(5) A, b=20.374(6) A, c=20.575(4) A, h=106.48(2)°, i=
,
separation is 2.7494(7) A, which is close to the value of
3
,
95.02(2)°, k=100.31(2)°, V=5366(3) A , Z=4, zcalc.=1.712
g
,
2.7551(6)
A in the dirhenium(III) ESBO Re2(m-
cm−3, T=138 K, empirical absorption correction (0.3090–0.9918
transmission coefficient), full-matrix refinement on F2 (Enraf–Nonius
PEt2)2Cl4(PEt2H)4 [2] and indicative of the presence of
the ReꢀRe bond. In contrast to the small diethylphos-
phine ligand [11], two bulky PPh2H probably can not
CAD-4S
,
SHELXL-93), R1 (on F0)=0.1061 for 504 parameters and
11305 unique data (I\2|(I)), R2=0.1288 for all 13 955 data.

P.A. Angaridis et al. / Inorganica Chimica Acta 332 (2002) 47–53
51
be accommodated at one ReIII center in 4, so the
compositions of these two ESBO complexes are
different.
4. Discussion
In the course of studying reactions of the [Re2Cl8]2−
ion with monodentate phosphines [1–3] we have found
that benzene is an interesting reaction medium in which
Fig. 2. A perspective drawing of the [Re2(m-PCy2)3Cl6]− in 2. Atoms
are represented by thermal ellipsoids at the 35% probability level.
Carbon atoms are shown as spheres of arbitrary radii. Hydrogen
atoms are omitted.
Chart 1. Schematic representation of the structures reported here.
Fig. 3. A perspective drawing of the [Re2(m-PPh2)3Cl6]− in 3. Atoms
are represented by thermal ellipsoids at the 35% probability level.
Carbon atoms are shown as spheres of arbitrary radii. Hydrogen
atoms are omitted.
disproportionation reactions proceed affording both
oxidized and reduced rhenium products [3]. We previ-
ously studied the reaction of [Re2Cl8]2− with the small
cone-angle secondary phosphine, PEt2H. Both dirheni-
um(II,II) and dirhenium(IV,IV) products were isolated
from the same reaction as a result of disproportiona-
tion [2]:
Fig. 1. A perspective drawing of 1,3,6-Re2Cl5(PCy2H)3 (1). Atoms are
represented by thermal ellipsoids at the 35% probability level. Carbon
atoms and hydrogen atoms attached to the phosphorus atoms are
shown as spheres of arbitrary radii. Hydrogen atoms of cyclohexyl
groups are omitted.
2[Bun4 N]2[Re2Cl8]+10PEt2H
“Re2Cl4(PEt2H)4+[Bun4 N][Re2(m-PEt2)3Cl6]
+3 [Bun4 N]Cl+3 [PEt2H2]Cl
(1)

52
P.A. Angaridis et al. / Inorganica Chimica Acta 332 (2002) 47–53
Schematically this disproportionation process can be
written as: 2Re26+ “Re24+ +Re28+
The unusual ESBO compound, Re2(m-PEt2)2Cl4-
(PEt2H)4, containing both terminal phosphines and
phosphido bridges, was also obtained by carrying out a
reaction in benzene under mild conditions [2]:
oxidized products, all monomeric rhenium(IV) com-
plexes of the ReCl4(PR3)2 type [3], since a tertiary
phosphine cannot easily give rise to R2P bridges.
As crystals of 1 and 2 have distinctively different
colors, they were separated manually and characterized
individually. Both compounds are air-stable, but they
lose solvents of crystallization so quickly at room tem-
perature that accurate chemical analysis data could not
be obtained.
.
[Bun4 N]2[Re2Cl8]+8PEt2H
“Re2(m-PEt2)2Cl4(PEt2H)4+2[Bun4 N]Cl+2[PEt2H2]Cl
For the system [Re2Cl8]2− –PPh2H, the reaction was
performed in toluene at reflux conditions affording
(2)
It was proposed that the overall disproportionation
process proceeds through this intermediate:
analogous to 2 the dirhenium(IV) complex with
diphenylphosphido bridges, [Bun4 N][Re2(m-PPh2)3Cl6]
(3). We did not isolate the reduced dirhenium complex
from this system, but we believe there is a dispropor-
tionation reaction analogous to that shown in eq. (4).
In an effort to detect intermediates in the present
reactions, we studied the transformations in the system
[Re2Cl8]2− –PPh2H in dichloromethane under mild ex-
perimental conditions and short reaction times. For
diphenylphosphine we found an interesting and novel
dirhenium(III) ESBO compound, [Bun4 N]2[Re2(m-
PPh2)2(PPh2H)2Cl6] (4), which is formed at an early
stage:
2Re2(m -PEt2)2Cl4(PEt2H)4+2Cl−+[PEt2H2]+
“Re2Cl4(PEt2H)4+[Re2(m-PEt2)3Cl6]−+6PEt2H (3)
From the reaction of [Re2Cl8]2− with PCy2H in
benzene at room temperatures we have also isolated
both reduced and oxidized dirhenium products from
one pot:
3 [Bun4 N]2[Re2Cl8]+12PCy2H
“2Re2Cl5(PCy2H)3 (1)+[Bun4 N][Re2Cl6(PCy2)3] (2)
+5[Bun4 N]Cl+3[PCy2H2]Cl
(4)
[Bun4 N]2[Re2Cl8]+6PPh2H
This disproportionation reaction can be schemati-
cally presented as 3 Re26+ “2 Re25+ +Re28+. The
difference from the PEt2H reaction is that the reduced
product in reaction (4) contains the Re25+ core rather
than the Re24+ core, while the oxidized product is still
of the [Re2(m-PR2)3Cl6]1− type, typical for secondary
phosphines. In reactions with tertiary phosphines we
found the same Re25+ reduced products, but different
“[Bun4 N]2[Re2Cl6(PPh2)2(PPh2H)2]+2[PPh2H2]Cl (5)
We believe this ESBO complex may be an intermedi-
ate in the disproportionation process, according to the
following reaction, to give the dirhenium(IV) complex 2
or 3 and the reduced dirhenium(II,III) species (for
R=Ph, Cy):
3[Bun4 N]2[Re2Cl6(PR2)2(PR2H)2]
“[Bun4 N][Re2Cl6(m -PR2)34]+2Re2Cl5(PR2H)3
+5[Bun4 N]+3PR−2 +2 Cl−
(6)
In conclusion, our present results again provide evi-
dence in favor of a disproportionation mechanism for
the reaction system [Re2Cl8]2− –PR2H when the solvent
itself, e.g. benzene, toluene, hexane and dichloro-
methane, cannot be the actual reducing agent.
5. Supplementary material
Crystallographic
data
(excluding
structure
factors) for 1·CH2Cl2·1/2C6H14, 2·3/4(CH3)2CO, and
4·31/2(CH3)2CO have been deposited with the Cam-
bridge Crystallographic Data Centre as supplementary
publications no. CCDC 166881, 166882 and 166883.
Copies of the data can be obtained free of charge on
application to The Director, CCDC, 12 Union
Road, Cambridge CB21EZ, UK (fax: +44-1223-336
033; e-mail: deposit@ccdc.cam.ac.uk or www: http://
www.ccdc.cam.ac.uk).
Fig. 4. A perspective drawing of the [Re2(m-PPh2)2(PPh2H)2Cl6]2− in
4. Atoms are represented by thermal ellipsoids at the 35% probability
level. Carbon atoms and hydrogen atoms attached to the phosphorus
atoms are shown as spheres of arbitrary radii. Hydrogen atoms of
phenyl groups are omitted.

P.A. Angaridis et al. / Inorganica Chimica Acta 332 (2002) 47–53
53
description of MADNES appears in: A. Messerschmitt, J. Pflu-
grath, J. Appl. Crystallogr. 20 (1987) 306.
Acknowledgements
[5] (a) W. Kabsch, J. Appl. Crystallogr. 21 (1988) 67;
(b) W. Kabsch, J. Appl. Crystallogr. 21 (1988) 916.
[6] R.H. Blessing, Acta Crystallogr. A51 (1995) 33.
[7] SHELXTL V.5; Siemens Industrial Automation Inc.: Madison,
WI, 1994.
We acknowledge support by the National Science
Foundation.
[8] G.M. Sheldrick, in: H.D. Flack, L. Parkanyi, K. Simon (Eds.),
Crystallographic Computing 6, Oxford University Press, Oxford,
UK, 1993, p. 111.
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A