Mixed halide/phosphine complexes of the dirhenium core. Part 7. Reactions of [Re2I8]2- with monodentate phosphines

Article abstract of DOI:10.1016/S0277-5387(01)00688-X

Reactions of the octaiododirhenate anion [Re₂I₈]^2- with monodentate phosphines (PR₃ = PMe₃ (1), PMe₂Ph (2), PEt₃ (3), and PEt₂Ph (4)) have been studied in two different solvents, ethanol and benzene, at room temperature. The reactions in ethanol resulted in two-electron reduction products having the Re⁴⁺₂ core, Re₂I⁴(PR₃)₄ (R₃ = Me₃ (1a) and Me₂Ph (2a)), for which X-ray diffraction study revealed a 1,3,6,8 isomer type. The reaction of [Re₂I₈]^2- with PMe₃ in benzene led to an intermediate edge-sharing bioctahedral dirhenium(III) complex, Re₂(μ-I)₂I₄(PMe₃)₄ (1b), with no metal-metal bond. The interaction of PEt₃ with [Re₂I₈]^2- in benzene again yielded a kinetic product with a different stoichiometry and a Re⁵⁺₂ core, [Buⁿ₄N][Re₂I₆ (PEt₃)₂] (3c). The analogous reactions of [Re₂I₈]^2- with PMe₂Ph and PEt₂Ph in benzene involved two-electron reductions and gave complex 2a and Re₂I₄(PEt₂Ph)₄ (4a), as products. Reduction of 1b with KC₈ gave 1a as the main product along with a few crystals of 1,3,6-Re₂I₅(PMe₃)₃ (1d). Mixed iodide/phosphine complexes of the dirhenium core Reⁿ⁺₂, where n = 4 (1a, 2a, 4a), 5 (1d, 3c), and 6 (1b) have for the first time been characterized by X-ray crystallography. In addition, these products have been further identified by a combination of mass spectrometry and cyclic voltammetric measurements.

Full text of DOI:10.1016/S0277-5387(01)00688-X

Polyhedron 20 (2001) 755–765
www.elsevier.nl/locate/poly
Mixed halide/phosphine complexes of the dirhenium core.
Part 7. Reactions of [Re2I8]2− with monodentate phosphinesꢀ
Panagiotis Angaridis, F. Albert Cotton *, Evgeny V. Dikarev, Marina A. Petrukhina
Laboratory for Molecular Structure and Bonding, P.O. Box 30012, Department of Chemistry, Texas A&M Uni6ersity,
College Station, TX 77842-3012, USA
Received 13 March 2000; accepted 18 April 2000
Abstract
Reactions of the octaiododirhenate anion [Re2I8]2− with monodentate phosphines (PR3=PMe3 (1), PMe2Ph (2), PEt3 (3), and
PEt2Ph (4)) have been studied in two different solvents, ethanol and benzene, at room temperature. The reactions in ethanol
resulted in two-electron reduction products having the Re24+ core, Re2I4(PR3)4 (R3=Me3 (1a) and Me2Ph (2a)), for which X-ray
diffraction study revealed a 1,3,6,8 isomer type. The reaction of [Re2I8]2− with PMe3 in benzene led to an intermediate
edge-sharing bioctahedral dirhenium(III) complex, Re2(m-I)2I4(PMe3)4 (1b), with no metal–metal bond. The interaction of PEt3
with [Re2I8]2− in benzene again yielded a kinetic product with a different stoichiometry and a Re25+ core, [Bu4nN][Re2I6(PEt3)2]
(3c). The analogous reactions of [Re2I8]2− with PMe2Ph and PEt2Ph in benzene involved two-electron reductions and gave
complex 2a and Re2I4(PEt2Ph)4 (4a), as products. Reduction of 1b with KC8 gave 1a as the main product along with a few crystals
of 1,3,6-Re2I5(PMe3)3 (1d). Mixed iodide/phosphine complexes of the dirhenium core Re2n+, where n=4 (1a, 2a, 4a), 5 (1d, 3c),
and 6 (1b) have for the first time been characterized by X-ray crystallography. In addition, these products have been further
identified by a combination of mass spectrometry and cyclic voltammetric measurements. © 2001 Published by Elsevier Science
Ltd.
Keywords: Dirhenium complexes; Phosphine complexes; Iodides; Crystal structures; Metal–metal bonds; Edge-sharing bioctahedral complexes
quire prolonged reflux to give the Re24+ core products,
1. Introduction
1,3,6,8-Re2Cl4(PR3)4 (Scheme 1). In addition, depend-
The chemistry and reactivity of the [Re2I8]2− ion is
much less developed [1] than that of [Re2Cl8]2−. It was
noticed earlier that reactions of these two octa-
halodirhenate anions with monodentate phosphine lig-
ands proceed differently [2]. The octaiododirhenate (III)
anion upon reaction with tertiary phosphines in ethanol
or acetone at room temperature affords two-electron
reduction products Re2I4(PR3)4 (R=Et, Prn, Bun) [2]
within a few minutes. The structures of those com-
pounds have not been reported, although some spectro-
scopic and electrochemical characteristics were
measured [3]. Analogous reactions of [Re2Cl8]2− re-
ing on the choice of reaction conditions (temperature,
time, solvent, concentration of Cl− anions) mixed chlo-
ride/phosphine complexes of the Re26+ and Re25+ cores
of types Re2Cl6P2 and Re2Cl5P3 (Scheme 1) can be
produced [4,5]. These stoichiometries have not yet been
seen for the iodides.
We have recently reported on the reactivity of the
[Re2Cl8]2− ion toward a number of monodentate phos-
phines [5] that vary in basicity and cone angle. These
studies led to the discovery of a new stereochemistry
(1,2,7,8 or cis, cis; Scheme 1) for the type Re2Cl4(PR3)4
(R3=Me3 [5a], Me2Ph [5b] and Et2H [5c]), which can
be preserved under very mild experimental conditions.
We also found different reaction pathways when the
reactions of [Re2Cl8]2− with PMe3, PEt3 and PPrn3 were
carried out in ethanol/acetone and benzene media
[5a,e]. In ethanol/acetone the reduction process was
found to proceed smoothly, while in benzene a dispro-
ꢀ This article was presented at the Second Contemporary Inorganic
Chemistry Conference (CIC-II) held at Texas A&M University, Col-
lege Station, TX, USA, on March 12–15, 2000.
* Corresponding author. Tel.: +1-979-8454432; fax: +1-979-
8459351.
E-mail address: cotton@tamu.edu (F.A. Cotton).
0277-5387/01/$ - see front matter © 2001 Published by Elsevier Science Ltd.
PII: S0277-5387(01)00688-X

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P. Angaridis et al. / Polyhedron 20 (2001) 755–765
portionation mechanism, 3Re26+ “2Re4+ +2Re25+
,
2.2. Physical measurements
was confirmed and several intermediate species, includ-
ing an edge-sharing bioctahedral complex of the type
Re2Cl6P4 (Scheme 1) were observed and isolated.
In view of the very extensive chemistry that arose
from the reactions of phosphines with [Re2Cl8]2− under
various conditions, and bearing in mind that from the
early work of Walton and coworkers [2,3] the [Re2I8]2−
ion might be expected to display both similarities and
differences, we thought it worthwhile to explore further
the chemistry of the latter. For this purpose we chose
four phosphines, PMe3, PMe2Ph, PEt3, and PEt2Ph,
and used two rather different solvents, namely, ethanol
and benzene. Six of the products obtained have been
characterized by X-ray crystallography, and also by
mass spectroscopy and electrochemical measurements.
Scheme 1 shows all the possible products, and their
isomers, of the reactions with which we are concerned
in this paper.
Electrochemical measurements were carried out on
dichloromethane solutions that contained 0.1 M tetra-
n-butylammonium hexafluorophosphate (TBAH) as the
supporting electrolyte. A stream of nitrogen was bub-
bled through the solution during the measurements.
E1/2 values, determined as (Ep,a+Ep,c)/2, were refer-
enced to the Ag/AgCl electrode at room temperature.
Under 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 positive and negative FAB/DIP mass
spectra were acquired using a VG Analytical 70S high-
resolution, double-focusing, sectored (EB) mass spec-
trometer. Samples for analyses were prepared by mixing
a solution of each compound in CH2Cl2 or CHCl3 with
an NBA matrix on the direct insertion probe tip.
2. Experimental
2.3. Syntheses
2.1. General procedures
2.3.1. Preparation of [Bun4N]2[Re2I8]
The starting material, [Bun4N]2[Re2I8], was prepared
according to the published procedure [6]. An excess of
HI (19 ml, 0.75–1.00 M solution in CHCl3) was added
to a suspension of [Bu4nN]2[Re2Cl8] (0.230 g, 0.2 mmol)
in 8 ml of CH2Cl2. The color of the mixture turned
brown-black immediately. This was stirred for 4 h at
room temperature (r.t.) without any further noticeable
change. An excess of isomeric hexanes (120 ml) was
then added to the mixture and it was kept at −10°C
overnight to yield a black-purple crystalline precipitate.
The product was collected by filtration; it was washed
with hexanes until the washings were almost colorless,
and dried. Yield: 0.307 g (78.2%).
All the syntheses and purifications were carried out
under an atmosphere of N2 in standard Schlenkware.
All solvents were freshly distilled under N2 from suit-
able drying agents. The starting materials,
[Bun4N]2[Re2Cl8] (Aldrich); PMe3, PMe2Ph, PEt3 and
PEt2Ph (Strem Chemicals); and HI (0.75–1.00 M in
CHCl3) (Alfa Aesar) were used as received.
Note: Both an excess of HI during the reaction and
the extensive washing of the product with hexanes are
crucial for the preparation of the octaiododirhenate.
Otherwise, chloride-containing products such as
[Re2Cl4(PMe3)4]I may be obtained later.1
1 Crystal data for [1,3,6,8-Re2Cl4(PMe3)4]I·CH2Cl2; brown-green
crystal, 0.12 mm×0.09 mm×0.05 mm, Re2P4Cl6I1C13H38
, or-
thorhombic space group Pnma (No. 62), a=17.193(3), b=13.686(2),
3
,
,
c=13.562(1) A, V=3191.2(8) A , Z=4, T= −60°C. A total of
13 231 independent reflections were measured with 4.7452q5
45.26°; 2219 independent reflections of which 1969 were observed
[I]2|(I)]. Final full-matrix least-squares refinement on F2 converged
to R1=0.0390, wR2=0.0781 for all data, and R1=0.0329, wR2=
,
0.0734 for data with I]2|(I), GOF=1.141. ReꢀRe=2.2122(7) A.
Scheme 1.
See Section 4 for other structure details.

P. Angaridis et al. / Polyhedron 20 (2001) 755–765
757
2.3.2. Reaction of [Bun4N]2[Re2I8] with PMe3 in ethanol
to gi6e Re2I4(PMe3)4 (1a)
at ꢀ10°C. The color of the reaction mixture turned
black-purple immediately. It was stirred for 40 min,
keeping the temperature at ꢀ10°C, and after that the
mixture was filtered. The dark brown filtrate was evap-
orated to dryness, leaving a dark red-brown solid.
Yield: 0.103 g (68.2%). Black-red crystals of 1b·2C6H6
were obtained from the benzene solution (9 ml) layered
with 17 ml of hexanes at r.t. in a few days. FAB/DIP
(NBA/CH2Cl2, m/z): 1437 ([M]+), 720 ([M−Re−
3I−2PMe3]+), 593 ([M−Re−4I−2PMe3]+).
PMe3 (0.8 ml) was added to a suspension containing
[Bun4N]2[Re2I8] (0.196 g, 0.10 mmol) in 15 ml of ethanol.
The reaction mixture, which turned dark brown imme-
diately, was stirred at r.t. for 3 h. During this time a
dark green solid precipitated. The mixture was reduced
to half of its original volume and was then filtered. A
dark green solid was isolated and washed with ethanol
(2×10 ml), dried and then dissolved in 10 ml of
dichloromethane. The dichloromethane solution was
layered with 18 ml of isomeric hexanes at r.t. Dark
green crystals of 1a·CH2Cl2 appeared in one day. Yield:
0.080 g (65.1%). CV (CH2Cl2, 22°C, V versus Ag/
AgCl): E1/2(ox)(1)= −0.02, E1/2(ox)(2)= +0.98. FAB/
DIP (NBA/CH2Cl2, m/z): 1184 ([M]+), 1107
([M−PMe3]+), 1031 ([M−2PMe3]+), 904 ([M−I−
2PMe3]+), 803 ([M−3I]+).
2.3.6. Reaction of [Bun4N]2[Re2I8] with PMe2Ph in
benzene to gi6e Re2I4(PMe2Ph)4 (2a)
PMe2Ph (0.3 ml) was added to a suspension contain-
ing [Bun4N]2[Re2I8] (0.111 g, 0.06 mmol) in 10 ml of
benzene at 5–10°C. The mixture was stirred at that
temperature for 1 h. During this time a green-brown
solid precipitated. It was isolated by filtration, washed
with hexanes (3×10 ml), dried, and dissolved in 10 ml
of dichloromethane. The dichloromethane solution was
layered with 20 ml of hexanes at r.t. Green crystals
were grown over a few days. Yield: 0.037 g (43%). It
was identified as complex 2a by CV measurements and
by X-ray diffraction.
2.3.3. Reaction of [Bun4N]2[Re2I8] with PMe2Ph in
ethanol to gi6e Re2I4(PMe2Ph)4 (2a)
PMe2Ph (0.5 ml) was added to a suspension contain-
ing [Bun4N]2[Re2I8] (0.411 g, 0.22 mmol) in 15 ml of
ethanol. The mixture was stirred at r.t. for 1 h. During
this time a green-brown solid precipitated. It was iso-
lated by filtration, washed with hexanes (3×10 ml),
dried, and dissolved in 15 ml of dichloromethane. The
dichloromethane solution was layered with 20 ml of
hexanes at r.t. Green crystals of 2a started to grow in a
few hours and the tube was left for a week. Yield: 0.201
g (63.8%). CV (CH2Cl2, 22°C, V versus Ag/AgCl):
E1/2(ox)(1)= −0.01, E1/2(ox)(2)= +0.94. FAB/DIP
(NBA/CH2Cl2, m/z): 1433 ([M]+), 1293 ([M−
PMe2Ph]+), 1154 ([M−2PMe2Ph]+), 1028 ([M−I−
2PMe2Ph]+), 899 ([M−2I−2PMe2Ph]+).
2.3.7. Reaction of [Bun4N]2[Re2I8] with PEt3 in benzene
to gi6e [Bun4N][Re2I6(PEt3)2] (3c)
PEt3 (0.7 ml) was added to a suspension containing
[Bun4N]2[Re2I8] (0.196 g, 0.10 mmol) in 14 ml of ben-
zene. After stirring for 1 h at r.t., the reaction mixture
turned purple and a solid was formed. The mixture was
filtered and the filtrate was evaporated to dryness to
give a purple solid. It was dried, washed with hexanes,
and then dissolved in 8 ml of benzene. The purple
benzene solution was layered with 20 ml of hexanes at
r.t. to give dark green crystals of 3c·(1/3) C6H6 in a
week along with some unidentified solid. Yield: 0.059 g
(36%).
2.3.4. Reaction of [Bun4N]2[Re2I8] with PEt3 in ethanol
to gi6e Re2I4(PEt3)4 (3a)
PEt3 (0.7 ml) was added to a suspension containing
[Bun4N]2[Re2I8] (0.215 g, 0.11 mmol) in 15 ml of ethanol
at r.t. The reaction mixture turned brown immediately.
It was stirred for 4 h at r.t. to give a brown precipitate.
The solid was filtered, washed with hexanes and kept
under vacuum for 18 h. It was then dissolved in 4 ml of
dichloromethane, and the solution was layered with 11
ml of hexanes. Microcrystalline product 3a appeared in
a day. Yield: 0.082 g (55.2%). CV (CH2Cl2, 22°C, V
versus Ag/AgCl): E1/2(ox)(1)= −0.27, E1/2(ox)(2)= +
0.77. FAB/DIP (NBA/CH2Cl2, m/z): 1352 ([M]+), 1233
([M−PEt3]+), 1118 ([M−2PEt3]+), 980 ([M−2I−
2PEt3]+).
2.3.8. Reaction of [Bun4N]2[Re2I8] with PEt2Ph in
benzene to gi6e Re2I4(PEt2Ph)4 (4a)
PEt2Ph (0.6 ml) was added to a suspension contain-
ing [Bun4N]2[Re2I8] (0.12 g, 0.06 mmol) in 12 ml of
benzene at 5–10°C. The mixture turned dark purple
immediately. It was stirred for 30 min, and then all
volatiles were removed under reduced pressure to give
an oily residue. This was washed with hexanes (3×10
ml), dried, and then dissolved in 10 ml of
dichloromethane. The dichloromethane solution was
layered with 18 ml of hexanes. Brown crystals of 4a
appeared over a period of five days. Yield: 0.054 g
(55.8%). FAB/DIP (NBA/CH2Cl2, m/z): 1286 ([M]+),
1120 ([M−PEt2Ph]+), 1032 ([M−2I]+), 905 ([M−
3I]+).
2.3.5. Reaction of [Bun4N]2[Re2I8] with PMe3 in benzene
to gi6e Re2I6(PMe3)4 (1b)
PMe3 (0.7 ml) was added to a suspension containing
[Bun4N]2[Re2I8] (0.196 g, 0.10 mmol) in 10 ml of benzene

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P. Angaridis et al. / Polyhedron 20 (2001) 755–765
Table 1
Crystallographic data for 1,3,6,8-Re2I4(PMe3)4·CH2Cl2 (1a·CH2Cl2), Re2(m-I)2I4(PMe3)4·2C6H6 (1b·2C6H6), 1,3,6-Re2I5(PMe3)3 (1d), 1,3,6,8-
Re2I4(PMe2Ph)4 (2a), [Bun4N][Re2I6(PEt3)2]·(1/3)C6H6 (3c·(1/3)C6H6), and 1,3,6,8-Re2I4(PMe2Ph)4 (4a)
1a·CH2Cl2
1b·2C6H6
1d
2a
3c·(1/3)C6H6
4a
Formula
Crystal system
Space group
Re2P4I4Cl2C13H38 Re2P4I6C24H48
tetragonal monoclinic
I41/acd (No.142) P21/c (No. 14)
Re2P3I5C9H27
orthorhombic
P212121 (No. 19) Fdd2 (No. 43)
Re2P4I4C32H44
orthorhombic
Re2P2I6N1C30H68 Re2P4I4C40H60
monoclinic
orthorhombic
C2/c (No. 15)
Pbca (No. 61)
Unit cell dimensions
,
a (A)
14.1714(4)
30.813(1)
11.720(1)
16.251(4)
11.490(2)
104.17(3)
2121.8(7)
2
9.742(1)
16.003(2)
16.438(2)
18.149(5)
45.47(2)
9.423(2)
38.970(2)
14.378(1)
25.990(1)
104.534(8)
14097(1)
12
16.347(2)
23.212(2)
24.495(3)
,
b (A)
,
c (A)
i (°)
V (A )
3
,
6188.1(3)
8
2562.7(5)
4
7776(4)
8
9295(2)
8
Z
Crystal size (mm)
Temperature (°C)
2q Range (°)
Data/unique/observ.
0.15×0.12×0.10 0.20×0.18×0.15 0.25×0.15×0.13 0.18×0.12×0.08 0.18×0.12×0.10 0.30×0.20×0.10
−60
−60
−60
−60
−60
−60
4.84–45.00
15413/1013/966
5.10–45.04
9153/2769/2624
0/133
4.86–44.96
12171/3296/3221
42/159
4.96–45.08
7534/2480/2448
1/191
4.24–45.02
28413/8942/7072
41/520
4.52–45.10
38841/6038/5357
1/458
Restraints/parameters 0/60
b
R1 a, wR2 [I\2|(I)] 0.0273, 0.0618
0.0272, 0.0723
0.0294, 0.0753
1.118
0.0599, 0.1480
0.0612, 0.1496
1.041
0.0275, 0.0723
0.0279, 0.0728
1.084
0.0550, 0.1137
0.0773, 0.1302
1.102
0.0424, 0.0997
0.0504, 0.1117
1.123
b
R1 a, wR2 (all data)
0.0285, 0.0626
1.207
Goodnes-of-fit c
a R1 =ꢀꢁꢁFoꢁ−ꢁFcꢁꢁ/ꢀꢁFoꢁ.
b wR2=[ꢀ[w(Fo2−Fc2)2]/ꢀ[w(Fo2)2]]1/2
.
c Goodness-of-fit=[ꢀ[w(Fo2−Fc2)2]/(Nobservns−Nparams)]1/2, based on all data.
2.3.9. Reaction of Re2I6(PMe3)4 with KC8 to gi6e 1a and
Re2I5(PMe3)3 (1d)
polarization effects by the MADNES program [9]. Reflec-
tion profiles were fitted and values of F2 and |(F2) for
each reflection were obtained by the program PROCOR
[10].
All calculations were carried out on a DEC Alpha
running VMS. The structures were solved and refined
The solid Re2I6(PMe3)4 (0.100 g, 0.07 mmol) was
mixed with a twofold excess of KC8 (made according to
the literature procedure [7]). Then 10 ml of toluene was
added to the mixture followed by 5 ml of CH2Cl2. The
mixture was stirred at 0°C for 1 h, and filtered after
that. The brown filtrate was layered with 18 ml of
hexanes. After the layers were mixed the volume was
reduced by half. Next day dark green crystals of 1a
appeared on the walls of the tube, along with a few
brown crystals of 1d.
using the SHELXTL direct methods [11] and the SHELXL
-
93 programs [12]. In all structures hydrogen atoms were
included in the structure factor calculations at idealized
positions. All crystals of 2a appeared to be racemic
twins; therefore twin refinement was used (BASF=
0.66). There was a complication in the structure of
3c·(1/3) C6H6 due to the observation of three-way
disorder (85.7:9.9:4.4 and 82.4:13.2:4.4% for two crys-
tallographically independent anions, respectively) of the
dirhenium units (often encountered with in the species
of the type Re2X6P2 [1]) along with severe disorder of
the tetrabutylammonium cations and benzene solvation
molecules. A second orientation of the Re2 (1.25%) was
also introduced in the refinement of 4a. The dirhenium
unit was also found to be disordered over three orienta-
tions (91.7:6.4:1.9%) in the crystal of 1d. Two sets of
ligands (I and PMe3) were modeled and refined with
equal occupancies in this experiment. The relevant crys-
tallographic data for complexes 1a·CH2Cl2, 1b·2C6H6,
1d, 2a, 3c·(1/3)C6H6, and 4a are summarized in Table 1.
An X-ray experiment was also carried out for a side-
product [1,3,6,8-Re2Cl4(PMe3)4]I·CH2Cl2.1 These data
can be found in Section 4.
2.4. X-ray structure determinations
Single crystals of compounds 1a·CH2Cl2, 1b·2C6H6,
1d, 2a, 3c·(1/3)C6H6, and 4a were obtained as described
above. All X-ray diffraction experiments were carried
out on a Nonius FAST diffractometer with an area
,
detector using Mo Ka radiation (u=0.71073 A). De-
tails concerning the data collection have been fully
described elsewhere [8]. Each crystal was 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 Model FR 558-S low-temperature con-
troller. Fifty reflections were used in cell indexing and
about 250 reflections in cell refinement. Axial images
were obtained to confirm the Laue group and cell
dimensions. The data were corrected for Lorentz and

P. Angaridis et al. / Polyhedron 20 (2001) 755–765
759
3. Results and discussion
[2,3], but were shown in the dirhenium chloride chem-
istry to afford a number of products with a cis location
of ligands at the rhenium atoms. We expected that the
most basic phosphines, PMe3 and PMe2Ph, would as
readily afford Re2I4(PR3)4 products in ethanol as the
more bulky and less basic ones (PEt3, PPrn3, PBu3n)
examined previously [2].
3.1. Syntheses
While it was observed a long time ago [2] that
reactions of [Re2I8]2− with monodentate phosphines in
ethanol or acetone media lead to the two-electron re-
duction products Re2I4(PR3)4 (R=Et, Prn, Bun) within
a few minutes at room temperature, the structures of
these mixed phosphine/iodide compounds have never
been determined. They were assumed to be the 1,3,6,8
isomers, the only type known at that time. In contrast
to this, prolonged reflux is needed to convert the
analogous [Re2Cl8]2− to the Re2Cl4(PR3)4 compounds.
The reactions of [Re2Cl8]2− with the most basic
monodentate phosphines, PMe3 and PMe2Ph, also pro-
ceed at room temperature in ethanol; they require hours
to reach the stage of one-electron reduction products,
namely the 1,2,7-isomers of Re2Cl5(PR3)3 [5b,13]. These
complexes, which have two phosphine ligands located
cis to each other on one rhenium atom (Scheme 1) have
been used recently [5a,b] as starting materials to pre-
pare a new class of 1,2,7,8 isomers of the Re2Cl4(PR3)4
stoichiometry.
These findings on the existence of a previously un-
known cis type of geometry for the Re2Cl4(PR3)4 stoi-
chiometry gave us an incentive to reinvestigate the ‘old’
processes involving [Re2I8]2−. Since transformations of
octaiododirhenate into the Re2I4P4 core compounds
proceed under very mild conditions (room temperature
and short reaction times) it was considered possible
that cis type products might form directly with steri-
cally undemanding ligands. Therefore we choose two
small cone-angle phosphines, PMe3 and PMe2Ph, which
were not studied in reactions with [Re2I8]2− before
We first performed the reactions of [Re2I8]2− with
sterically undemanding ligands, PMe3 and PMe2Ph, in
ethanol so as to isolate the reduced products of the
Re24+ core in crystalline form and to confirm their
stereochemistry by an X-ray diffraction study. Second,
we used benzene as a medium for the reactions of
[Re2I8]2− with a number of different monodentate
phosphines, PMe3, PMe2Ph, PEt3 and PEt2Ph, since
benzene was earlier shown to be a solvent that allows
isolation of some intermediates and/or kinetic products
in the mixed chloride/phosphine dirhenium chemistry
[5]. The key difference between the two solvents is that
ethanol has the potential to be a reducing agent
whereas benzene does not. We note again that stoi-
chiometries different from the Re2I4(PR3)4 have not
been seen in any previously studied reactions involving
[Re2I8]2− [1–3].
For reactions between [Re2I8]2− and PMe3 and
PMe2Ph in ethanol we confirmed the observations
made before [2] that complete transformation of the
[Re2I8]2− in alcohol takes place within minutes at room
temperature in the presence of monodentate phosphines
to give the Re24+ products, Re2I4(PR3)4 (R3=Me3 (1a)
and Me2Ph (2a)) in good yield. The cyclic voltam-
mograms exhibited two reversible oxidations, which is
consistent with the data published before (Table 2), and
the molecular structures in the solid state revealed a
trans geometry of the phosphine ligands for both com-
pounds (vide supra).
Having found that such small-cone angle phosphine
ligands as PMe3 and PMe2Ph afforded only trans prod-
ucts in the iodide case, we then switched to benzene.
The use of benzene as a solvent for the reactions of
[Re2I8]2− with phosphine ligands allowed us, as ex-
pected, to slow down the transformation and to isolate
some intermediate iodide products, much as in the case
of the analogous reactions involving [Re2Cl8]2− [5]. The
use of benzene afforded novel stoichiometries for the
mixed iodide/phosphine complexes that had not been
observed before. Thus, the reaction of [Re2I8]2− with
PMe3 in benzene for 30 min afforded a new dirhenium-
(III) iodide complex, Re2I6(PMe3)4 (1b). It is a kinetic
product of the reaction, which is controlled by tempera-
ture, time, ratio of reagents, etc. The best yields of 1b
were observed when the reaction was performed at
about 10°C under conditions described in Section 2.3.5.
At room temperature the thermodynamic product 1a
was formed in a mixture with 1b due to a type of
disproportionation mechanism discovered recently [5e].
Table 2
Voltammetric E1/2 values (V) for the mixed phosphine/halide dirheni-
um(II,II) compounds, 1,3,6,8-Re2X4(PR3)4
X
E1/2(ox)(1)
E1/2(ox)(2)
Ref.
PMe3
Cl
Br
−0.23
−0.11
−0.02
+0.96
+1.01
+0.98
[14]
[14]
this work
I
PMe2Ph
Cl
I
−0.30
−0.01
+0.83
+0.94
[3]
this work
PEt3
Cl
Br
I
−0.42
−0.31
−0.27
+0.80
+0.83
+0.77
[3]
[3]
[3], this work
PPr3
Cl
Br
I
−0.44
−0.38
−0.22
+0.79
+0.84
+0.85
[3]
[3]
[3]

760
P. Angaridis et al. / Polyhedron 20 (2001) 755–765
its analog Re2I4(PEt2Ph)4 (4a), at least in our hands. In
this case the transformation probably proceeds so fast
even at 5°C that we were unable to isolate any interme-
diates. In general, we found that reactions for oc-
taiododirhenium in benzene proceed much faster than
for [Re2Cl8]2− and afford a mixture of products with
quite low yields. Nevertheless, we were able to observe
some new stoichiometries, previously unknown for the
rhenium iodides. We also used product 1b of the Re26+
core as a starting material for reduction by KC8 and
this reaction yielded the formation of 1a and a few
crystals of the new Re25+ core compound,
Re2I5(PMe3)3 (1d), as a result of incomplete reduction.
3.2. Electrochemical data
Fig. 1. A perspective drawing of 1,3,6,8-Re2I4(PMe3)4 (1a). Atoms are
represented by thermal ellipsoids at the 40% probability level. Carbon
and hydrogen atoms are shown as spheres of arbitrary radii.
It is known [1] that the derivatives of dirhenium(II)
Re2X4P4 exhibit a redox chemistry that is both interest-
ing and extensive. Some electrochemical data for the
mixed phosphine/halide complexes of the type 1,3,6,8-
Re2X4(PR3)4 have been already reported [2,3], and now
we extend these series by adding two more iodide
complexes of this type for PR3=PMe3 and PMe2Ph
(Table 2). All the complexes behave in a similar fash-
ion: the cyclic voltammograms show two electrochemi-
cally reversible, one-electron oxidation waves
corresponding
to
two
oxidation
reactions
[Re2X4(PR3)4]/[Re2X4(PR3)4]+ and [Re2X4(PR3)4]+/
[Re2X4(PR3)4]2+. There is an interesting and clear
trend, namely E1/2(ox)(1) for iodides \E1/2(ox)(1) for
the corresponding chlorides, with bromides being an
intermediate case, while the E1/2(ox)(2) values for the
reported halides are close. This implies indirectly that
the second reduction to Re2X4(PR3)4 complexes from
[Re2X4(PR3)4]+ cations, which we found to be a limit-
ing stage in the analogous chloride system [5d], goes
more easily for iodides and can be achieved at room
temperature.
Fig. 2. A perspective drawing of 1,3,6,8-Re2I4(PMe2Ph)4 (2a). Atoms
are represented by thermal ellipsoids at the 40% probability level.
Carbon and hydrogen atoms are shown as spheres of arbitrary radii.
From the reaction of [Re2I8]2− with PEt3 in benzene at
room temperature we isolated another kinetic product,
namely [Bun4N][Re2I6(PEt3)2] (3c). It is the first iodide
complex of Re2I6P2 stoichiometry, although it was crys-
tallized in its monoanionic form as in the analogous
reaction of [Re2Cl8]2− [5e]. We believe that this is just
one of the kinetic intermediates formed in this system
as CV measurements of reaction products in the system
[Re2I8]2−/PEt3 showed the presence of other intermedi-
ates. In addition, the formation of the oxidized
product, ReI4(PEt3)2, in the system was observed by
mass spectroscopy. We were unable to get these com-
pounds in the crystalline form, but nevertheless they
support the disproportionation mechanism of transfor-
mations in benzene, 3Re26+ “2Re25+ +2Re 4+, as pre-
viously observed in the reactions of [Re2Cl8]2− [5e].
In contrast to the above-mentioned reactions, the
reactions of [Re2I8]2− with PMe2Ph and PEt2Ph in
benzene yield only complexes of the Re24+ core, 2a, and
3.3. Crystal structures
Since there was no crystal structure of any dirhenium
iodide other than [Re2I8]2− itself [6b] reported before, it
is interesting to compare those now available with the
structures of the corresponding chlorides so as to deter-
mine the effect of the bulky iodine atoms upon the
overall geometries of the molecules. For two phosphi-
nes, PMe3 and PMe2Ph, from reactions in ethanol we
isolated Re2I4(PR3)4 (R3=Me3 (1a) and Me2Ph (2a)).
One more complex of the same stoichiometry was
obtained from benzene, Re2I4(PEt2Ph)4 (4a). For all of
them the X-ray diffraction study revealed the 1,3,6,8
type of stereochemistry (Figs. 1–3) with trans phos-
phine ligands on both the rhenium atoms. There are
corresponding chloride analogs for 1a [15] and 2a [16],
but not for 4a. The ReꢀRe distances in 1a and 2a

P. Angaridis et al. / Polyhedron 20 (2001) 755–765
761
Table 4
(Table 3) are not significantly different, namely
,
Selected bond distances (A) and angles (deg) for Re2(m-I)2I4(PMe3)4
(1b) and Re2(m-Cl)2Cl4(PMe3)4
,
2.2541(8) and 2.258(1) A, while the ReꢀRe separation
,
in 4a is a bit longer, 2.2698(7) A, but all of them are
a
1b X=I
Re2(m-Cl)2Cl4(PMe3)4
X=Cl
Bond distances
Re(1)···Re(1A)
ReꢀP
4.274(1)
2.403(2)
2.680(1)
2.8130(7)
3.8476(4)
2.375(1)
2.341(1)
2.512(1)
b
ReꢀXt
c
ReꢀXbr
Bond angles
PꢀReꢀP
XtꢀReꢀXt
XbrꢀReꢀXbr
PꢀReꢀXt
PꢀReꢀXbr
XtꢀReꢀXbr
ReꢀXbrꢀRe
95.08(7)
179.00(2)
81.12(2)
85.96(6)–94.26(5)
92.05(5), 171.87(5)
89.32(2)–91.33(2)
98.88(2)
93.91(5)
178.60(5)
80.02(4)
86.57(5)–93.36(4)
92.85(4), 172.01(4)
89.65(4)–90.78(4)
99.98(4)
a From Ref. [5a].
b Xt — terminal halide atom.
c Xbr — bridging halide atom.
Fig. 3. A perspective drawing of 1,3,6,8-Re2I4(PEt2Ph)4 (4a). Atoms
are represented by thermal ellipsoids at the 40% probability level.
Carbon atoms are shown as spheres of an arbitrary radius. Hydrogen
atoms of the ethyl and phenyl groups are omitted for clarity.
appropriate for a rhenium–rhenium triple bond [1].
The only significant difference between the geometric
characteristics of the corresponding chlorides and io-
dides is, naturally, the rhenium–halide distance, which
Table 3
,
Selected mean bond distances (A), angles (°) and torsion angles (°) for
,
is about 0.3 A greater for the latter. All the angles
Re2I4(PR3)4 (R3=Me3 (1a), Me2Ph (2a), and Et2Ph (4a))
ReꢀReꢀL (L=P, X) are also similar. It may be noted
that while the structure of 1a is perfectly eclipsed, the
molecules of 2a and 4a are partially staggered. The
mean PꢀReꢀReꢀI angle for the PMe2Ph compound (2a)
of 12° is the highest for any known molecule of the
1,3,6,8-Re2X4(PR3)4 isomer type. Interestingly, the cor-
responding angle in 1,3,6,8-Re2Cl4(PMe2Ph)4 is the
highest among all the isotypical chlorides.
1a
2a
4a
Bond distances
ReꢀRe
ReꢀP
2.2541(8)
2.427(2)
2.7108(5)
2.258(1)
2.453(3)
2.7157(9)
2.2698(7)
2.475(3)
2.6969(9)
ReꢀI
Bond angles
PꢀReꢀP
PꢀReꢀI
155.0(1)
84.90(5)
131.36(3)
114.32(2)
102.48(5)
0
146.39(9)
85.08(7)
145.23(3)
107.36(2)
106.80(7)
11.95(8)
149.7(1)
84.51(7)
136.96(3)
111.52(3)
105.15(7)
6.92(8)
From the reaction of [Re2I8]2− with PMe3 in benzene
a complex of composition Re2I6(PMe3)4 (1b) was iso-
lated, for which an X-ray structural analysis revealed
an edge-sharing bioctahedral structure with all of the
trimethylphosphine ligands in the same plane as the
metal centers and the bridging iodide ions (Fig. 4).
Complex 1b is a centrosymmetric iodide-bridged dirhe-
nium molecule analogous to the 1,3,5,7-Re2(m-
Cl)2Cl4(PMe3)4 [5a]. Although there was no reduction
process in this case, the Re26+ core has been disrupted
in this complex to give a very long Re···Re separation
IꢀReꢀI
ReꢀReꢀI
ReꢀReꢀP
PꢀReꢀReꢀI
,
of 4.274(1) A (Table 4). This is much greater than the
,
value of 3.8476(4) A in the analogous chloride due to
the considerably larger size of the bridging iodine
,
atoms. As expected, the ReꢀIbr distances of 2.8130(7) A
,
in 1b are significantly greater, by 0.133 A, than the
,
ReꢀIt of 2.680(1) A. In general, the ReꢀI distances in 1b
are about 0.3 A greater than those of the ReꢀCl in the
,
related chloride molecule, while the difference in the
ReꢀP distances is less by an order of magnitude. The
remaining characteristics, including the angles
ReꢀIbrꢀRe, IbrꢀReꢀIbr, and ItꢀReꢀIt are very similar to
Fig. 4. A perspective drawing of Re2(m-I)2I4(PMe3)4 (1b). Atoms are
represented by thermal ellipsoids at the 40% probability level. Carbon
and hydrogen atoms are shown as spheres of arbitrary radii.

762
P. Angaridis et al. / Polyhedron 20 (2001) 755–765
lated [17] to the MꢀM distances and the angular
parameters. The latter, namely the acute angles
MꢀIbrꢀM of 72.04(4) and 71.21(3)° in the Zr and Hf
compounds, respectively, contrasts with the value of
98.88(2)° in 1b. The metal–metal distances of 3.393(2)
,
,
A in Zr and of 3.328(1) A in Hf analogs (which are
considerably shorter than that in 1b) have been as-
signed as long but real MꢀM single bonds [18].
The reaction of [Re2I8]2− with PEt3 in benzene at
room temperature afforded a new kinetic product,
[Bun4N][Re2I6(PEt3)2] (3c). The chloride analog has been
obtained by us using the same approach, but the struc-
tural characterization was not satisfactory because of a
severe disorder problem. The crystal structure of 3c
consists of paramagnetic dirhenium anions of the Re25+
core (Fig. 5) and tetrabutylammonium cations. There
are two crystallographically distinct [Re2I6(PEt3)2]−
units in the structure, only one of which has an inver-
sion center at the midpoint of the ReꢀRe bond. The
centrosymmetric molecule is less disordered and fully
eclipsed, while the noncentrosymmetric one is partially
staggered with a PꢀReꢀReꢀP torsion angle of 166°.
Similar features have been also observed for analogous
chlorides.
Fig. 5. A perspective drawing of one of the two crystallographically
independent [Re2I6(PEt3)2]− anions from 3c. Atoms are represented
by thermal ellipsoids at the 30% probability level. Carbon and
hydrogen atoms are shown as spheres of arbitrary radii. Only the
major orientation of the disordered dirhenium unit and one orienta-
tion of the ethyl groups are depicted.
those of the chloride analog [5a]. It would seem certain
that there is no Re···Re interaction in 1b in view of the
great metalꢀmetal distance and the obtuse ReꢀIbrꢀRe
angle of 98.88(2)° [17].
Two different isomeric forms of the Re2Cl6P2 core
(Scheme 1) have been recognized in the solid state by
X-ray crystallography, including an unprecedented 1,6
rotamer with C2 symmetry, which we discovered re-
cently [5f]. Most structures of the Re2Cl6P2 stoichiome-
try, both in the neutral and monoanionic forms, belong
to the presumably more stable 1,7 isomer type with C2h
virtual symmetry. The dirhenium iodide/phosphine an-
ions in 3c also show the 1,7 disposition of the tri-
ethylphosphine ligands. The trans influence of the
phosphine ligands is reflected in the fact that the ReꢀI
In the molecule of 1b the PMe3 ligands are located cis
to each other on each Re(III) center with an angle
P(1)ꢀReꢀP(2) of 95.08(7)°. It is interesting to compare
the characteristics of 1b with the data for two other
bioctahedral edge-sharing iodides of the same 1,3,5,7
structural type, namely Zr2(m-I)2I4(PMe3)4 [18] and
Hf2(m-I)2I4(PMe3)4 [19]. In contrast to 1b, the zirconium
and hafnium iodide-bridged complexes were formu-
lated, based on the structural, spectroscopic and theo-
retical data, as diamagnetic dimers with a substantial
amount of metal–metal bonding. The degree of M–M
interaction for an M2X6 core has been in general corre-
,
bonds (Table 5) trans to the P atoms are about 0.04 A
longer than those trans to the I atoms. There is also a
Table 5
−
,
Selected mean bond distances (A) and angles (°) for [Re2I6(PEt3)2] in 3c
Bond distances
Re(1)ꢀRe(2)
Re(1)ꢀP(1)
Re(1)ꢀI(1)
Re(1)ꢀI(2)
Re(1)ꢀI(3)
2.233(1)
2.452(4)
2.70(2)
2.74(1)
2.70(2)
Re(3)ꢀRe(3%)
Re(3)ꢀP(3)
Re(3)ꢀI(7)
Re(3)ꢀI(9)
Re(3)ꢀI(8)
2.240(1)
2.439(5)
2.699(1)
2.742(2)
2.687(1)
Re(2)ꢀP(2)
Re(2)ꢀI(5)
Re(2)ꢀI(6)
Re(2)ꢀI(4)
2.414(5)
2.71(2)
2.74(2)
2.71(2)
Bond angles
P(1)ꢀRe(1)ꢀI(1)
P(1)ꢀRe(1)ꢀI(2)
P(1)ꢀRe(1)ꢀI(3)
I(1)ꢀRe(1)ꢀI(2)
I(1)ꢀRe(1)ꢀI(3)
I(2)ꢀRe(1)ꢀI(3)
Re(2)ꢀRe(1)ꢀP(1)
Re(2)ꢀRe(1)ꢀI(1)
Re(2)ꢀRe(1)ꢀI(2)
Re(2)ꢀRe(1)ꢀI(3)
P(1)ꢀRe(1)ꢀRe(2)ꢀP(2)
84.3(3)
147.8(4)
88.3(3)
85.6(5)
146.3(6)
83.3(5)
100.4(1)
106.3(4)
111.7(4)
107.4(4)
165.9(2)
P(2)ꢀRe(2)ꢀI(5)
P(2)ꢀRe(2)ꢀI(6)
P(2)ꢀRe(2)ꢀI(4)
I(5)ꢀRe(2)ꢀI(6)
I(4)ꢀRe(2)ꢀI(5)
I(4)ꢀRe(2)ꢀI(6)
Re(1)ꢀRe(2)ꢀP(2)
Re(1)ꢀRe(2)ꢀI(5)
Re(1)ꢀRe(2)ꢀI(6)
Re(1)ꢀRe(2)ꢀI(4)
83.9(6)
144.7(5)
88.7(3)
84.8(6)
148.9(7)
84.3(5)
101.8(1)
106.6(6)
113.6(5)
103.9(4)
P(3)ꢀRe(3)ꢀI(7)
P(3)ꢀRe(3)ꢀI(9)
P(3)ꢀRe(3)ꢀI(8)
I(7)ꢀRe(3)ꢀI(9)
I(7)ꢀRe(3)ꢀI(8)
I(8)ꢀRe(3)ꢀI(9)
Re(3A)ꢀRe(3)ꢀP(3)
Re(3A)ꢀRe(3)ꢀI(7)
Re(3A)ꢀRe(3)ꢀI(9)
Re(3A)ꢀRe(3)ꢀI(8)
P(3)ꢀRe(3)ꢀRe(3A)ꢀP(3A)
86.2(1)
146.2(1)
86.5(1)
83.92(4)
147.81(5)
84.96(2)
98.6(1)
106.05(5)
115.21(6)
106.03(5)
180.0

P. Angaridis et al. / Polyhedron 20 (2001) 755–765
763
3.4. Reacti6ity of [Re2I8]2− 6ersus [Re2Cl8]2−
The reactivity of [Re2I8]2− toward monodentate
phosphine ligands in ethanol contrasts quite strikingly
with that observed for the corresponding chloride,
[Re2Cl8]2−. All processes associated with the transfor-
mation of [Re2I8]2− in the presence of phosphines,
namely, the substitution of I− by PR3 and the reduc-
tion of the Re26+ to the Re24+ core products, are
significantly faster at room temperature for the iodide
than for [Re2Cl8]2−. In all cases the reduction of the
[Re2I8]2− is practically complete in a few minutes. For
the first time products of Re2I4(PR3)4 stoichiometry
have been structurally characterized in this work for
R3=Me3 (1a), Me2Ph (2a), and Et2Ph (4a), and they
are found to be 1,3,6,8 isomers. Formation of the trans,
trans type of products even for the small cone-angle
phosphines, PMe3 and PMe2Ph, lends credibility to the
assignment of 1,3,6,8 geometry to the Re2I4(PR3)4 (R=
Et, Prn, Bun) compounds made long ago by spectro-
scopic and electrochemical techniques [2,3]. Possible
reasons why both substitution and reduction proceed
faster for [Re2I8]2− could be the higher lability of the
iodide compared to the chloride anion, and a general
tendency of iodides to be more easily reduced than
chlorides [20]. It is also possible that I−, in addition to
the alcohol, can assist in the reduction of the dirhenium
unit by oxidation to the I2. It was not possible to
speculate about the mechanism of these processes until
some intermediate species were detected. The reactions
in benzene are very important because they allow us to
observe some kinetic products.
Fig. 6. A drawing showing the three orientations of the Re2 unit for
the 1,3,6,-Re2I5(PMe3)3 (1d) molecule. Only one orientation of the
ligands is presented. Carbon and hydrogen atoms are not labeled for
clarity.
Table 6
,
Selected mean bond distances (A) and angles (°) for 1,3,6,-
Re2I5(PMe3)3 (1d)
Bond distances
Re(1)ꢀRe(2)
Re(1)ꢀP(1)
Re(1)ꢀP(2)
Re(1)ꢀI(1)
Re(1)ꢀI(2)
2.235(1)
2.47(1)
2.47(1)
2.667(4)
2.659(5)
Re(2)ꢀP(3)
Re(2)ꢀI(3)
Re(2)ꢀI(4)
Re(2)ꢀI(5)
2.452(7)
2.653(5)
2.673(6)
2.740(4)
Bond angles
P(1)ꢀRe(1)ꢀP(2)
P(1)ꢀRe(1)ꢀI(1)
P(1)ꢀRe(1)ꢀI(2)
P(2)ꢀRe(1)ꢀI(1)
P(2)ꢀRe(1)ꢀI(2)
I(1)ꢀRe(1)ꢀI(2)
154.5(4)
85.8(4)
82.2(4)
87.4(4)
84.1(4)
131.9(1)
P(3)ꢀRe(2)ꢀI(5)
P(3)ꢀRe(2)ꢀI(3)
P(3)ꢀRe(2)ꢀI(4)
I(3)ꢀRe(2)ꢀI(5)
I(4)ꢀRe(2)ꢀI(5)
I(3)ꢀRe(2)ꢀI(4)
155.5(2)
83.8(2)
83.5(2)
86.8(2)
87.6(2)
135.3(2)
In general, the reactions of [Re2I8]2− with monoden-
tate phosphines in benzene appeared to be similar to
those of [Re2Cl8]2− giving the same kinetic products for
the respective ligands. For PMe3 we have isolated the
edge-sharing bioctahedral dirhenium(III) complex,
1,3,5,7-Re2(m-I)2I4(PMe3)4 (1b), with a long Re···Re sep-
,
aration of 4.274(1) A and a cis, cis disposition of
steric effect that causes the ReꢀReꢀI angles for the
iodine atoms facing the phosphorus ligands to be 10°
greater than the others.
phosphine ligands. In the case of PEt3 we have found a
kinetic product with Re2I6P2 stoichiometry and a Re25+
core, namely [Bu4nN][Re2I6(PEt3)2] (3c). No intermedi-
ates have been detected for the PMe2Ph and PEt2Ph
ligands. However, it is clear that those kinetic products
are significantly less stable for iodides than for chlorides
and their disproportionation products appear to be
different. Thus, for PMe3 and PMe2Ph those are
1,3,6,8-Re2I4(PR3)4 versus 1,2,7-Re2Cl5(PR3)3. The reac-
tivity of these intermediates is also different: the reduc-
tion of Re2X6(PMe3)4 gives trans products of the Re25+
and Re24+ for X=I (1d, 1a) versus the corresponding
cis complexes for X=Cl [5g].
Another Re25+ core compound is represented by the
1,3,6-isomer of Re2I5(PMe3)3 (1d) having two phos-
phine ligands trans to each other on one of the rhenium
atoms (the PꢀReꢀP angle is 154.5(4)°). As is common
for this type of structure, the molecule of 1d is eclipsed
and shows a three-way disorder of the dimetal unit.
Note that for all three orientations we have the same
,
1,3,6-isomer (Fig. 6). The ReꢀRe distance of 2.235(1) A
(Table 6) is the same as for the chloride analogs [13b]
and is typical for the bond order of 3.5. Again, we
should mention the trans effect of the phosphine groups
We believe that the different results of substitutions
on the [Re2I8]2− ion and the [Re2Cl8]2− ion can be well
accounted for by recognizing that Cl− has a higher
trans effect than I−. Thus, the order of trans effects is
,
leading to the elongation of the ReꢀI (ꢀ0.08 A) and
,
the ReꢀP (ꢀ0.02 A) bonds trans to the P atoms in
relation to those which are trans to the I atoms.

764
P. Angaridis et al. / Polyhedron 20 (2001) 755–765
Scheme 2.
Cl−\PR3\I−. The consequences of this are shown in
Scheme 2. Both [Re2X8]2− ions first react in the same
way with two molecules of PR3 to give 1,7-Re2X6P2
intermediates, but then there is a difference depending
on whether X−=Cl− or I−. The higher trans effect of
Cl− leads to the successive formation of 1,2,7 and
1,2,7,8 products, while the lower trans effect of I− leads
to the formation of 1,3,6 followed by 1,3,6,8 products.
There are, of course, further complications, but this
much at least seems to make sense.
[3] P. Brant, D.J. Salmon, R.A. Walton, J. Am. Chem. Soc. 100
(1978) 4424.
[4] (a) J.R. Ebner, R.A. Walton, Inorg. Chem. 14 (1975) 1987. (b)
K.R. Dunbar, R.A. Walton, Inorg. Chem. 24 (1985) 5. (c) F.A.
Cotton, Inorg. Chem. 37 (1998) 5710.
[5] (a) F.A. Cotton, E.V. Dikarev, M.A. Petrukhina, J. Am. Chem.
Soc. 119 (1997) 12 541. (b) F.A. Cotton, E.V. Dikarev, M.A.
Petrukhina, Inorg. Chem. 37 (1998) 1949. (c) F.A. Cotton, E.V.
Dikarev, M.A. Petrukhina, Inorg. Chem. 37 (1998) 6035. (d)
F.A. Cotton, E.V. Dikarev, M.A. Petrukhina, Inorg. Chem.
Commun. 2 (1999) 28. (e) F.A. Cotton, E.V. Dikarev, M.A.
Petrukhina, Inorg. Chem. 38 (1999) 3384. (f) F.A. Cotton, E.V.
Dikarev, M.A. Petrukhina, Inorg. Chem. 38 (1999) 3899. (g)
F.A. Cotton, E.V. Dikarev, M.A. Petrukhina, in preparation.
[6] (a) W. Preetz, L. Rudzik, Angew. Chem., Int. Ed. Engl. 18
(1979) 150. (b) F.A. Cotton, L.M. Daniels, K. Vidyasagar,
Polyhedron 7 (1988) 1667.
4. Supplementary material
Crystallographic data (excluding structure factors)
for the structures reported in this paper have been
deposited with the Cambridge Crystallographic Data
Center, CCDC Nos. 141439–141445 for 1a·CH2Cl2,
1b·2C6H6, 1d, 2a, 3c·(1/3)C6H6, 4a, and [Re2Cl4-
(PMe3)4]I·CH2Cl2, respectively. Copies of the data can
be obtained free of charge from The Director, CCDC,
12 Union Road, Cambridge CB2 1EZ, UK (fax: +44-
1223-336033; e-mail: deposit@ccdc.cam.ac.uk or www:
http://www.ccdc.cam.ac.uk).
[7] (a) A. Fu¨rstner, Angew. Chem., Int. Ed. Engl. 32 (1993) 164. (b)
M.A. Schwindt, T. Lejon, L.S. Hegedus, Organometallics 9
(1990) 2814.
[8] F.A. Cotton, E.V. Dikarev, X. Feng, Inorg. Chim. Acta 237
(1995) 19.
[9] J. Pflugrath, A. Messerschmitt, MADNES, Munich Area Detector
(New EEC) System, version EEC 11/9/89, with enhancements by
Enraf-Nonius Corp., Delft, The Netherlands. A description of
MADNES appears in: A. Messerschmitt, J. Pflugrath, J. Appl.
Crystallogr. 20 (1987) 306.
[10] (a) W. Kabsch, J. Appl. Crystallogr. 21 (1988) 67. (b) W.
Kabsch, 21 (1988) 916.
[11] SHELXTL V.5; Siemens Industrial Automation Inc., Madison,
WI, 1994.
[12] G.M. Sheldrick, in: H.D. Flack, L. Parkanyi, K. Simon (Eds.),
Crystallographic Computing 6, Oxford University Press, Oxford,
1996, p. 111.
[13] (a) F.A. Cotton, A.C. Price, K. Vidyasagar, Inorg. Chem. 29
(1990) 5143. (b) F.A. Cotton, E.V. Dikarev, Inorg. Chem. 35
(1996) 4738.
Acknowledgements
We acknowledge support by the National Science
Foundation.
[14] D.R. Root, C.H. Blevins, D.L. Lichtenberger, A.P. Sattelberger,
R.A. Walton, J. Am. Chem. Soc. 108 (1986) 953.
[15] F.A. Cotton, J.G. Jennings, A.C. Price, K. Vidyasagar, Inorg.
Chem. 29 (1990) 4138.
[16] F.A. Cotton, K.R. Dunbar, L.R. Falvello, M. Tomas, R.A.
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