Mixed chloride-phosphine complexes of the dirhenium core - 9. The first mixed monodentate phosphine complex, 1,2,7,8-Re2Cl4(PMe2Ph)3(PEt 2H)

Article abstract of DOI:10.1016/S0020-1693(01)00740-X

The reduction of the Re₂⁵⁺ core in 1,2,7-Re₂Cl₅(PR₃)₃ molecules, followed by addition of 1 equiv. of a different phosphine ligand, PR₃′, allows the preparation of the mixed monodentate phosphine compounds of the Re₂⁴⁺ type, namely 1,2,7,8-Re₂Cl₄(PR₃)₃(PR ₃′). The stereochemistry of the starting materials dictates the stereochemistry of the final products. The one-electron reduction of the 1,2,7-isomer of Re₂Cl₅(PMe₂Ph)₃ with KC₈ to the corresponding anion, [1,2,7-Re₂Cl₅(PMe₂Ph)₃] ^- (1), followed by non-redox substitution of one chloride ion by one diethylphosphine, PEt₂H, afforded the first mixed monodentate phosphine compound of the dirhenium(II) core, Re₂Cl₄(PMe₂Ph)₃(PEt₂H) (2), in good yield. Crystal structure determination as well as other physical methods and elemental analysis unambiguously confirmed the formation of 2. The related system 1,2,7-Re₂Cl₅(PMe₃)₃-Co(C ₅H₅)₂-PEt₂H leads to several products, one of which is 1,2,7,8-Re₂Cl₄(PMe₃)₃(PEt ₂H) (3).

Full text of DOI:10.1016/S0020-1693(01)00740-X

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Inorganica Chimica Acta 330 (2002) 173–178
Mixed chloride–phosphine complexes of the dirhenium core
9. The first mixed monodentate phosphine complex,
1,2,7,8-Re2Cl4(PMe2Ph)3(PEt2H)
Panagiotis A. Angaridis a, F. Albert Cotton a,*, Evgeny V. Dikarev a,b,
Marina A. Petrukhina a,b
a Department of Chemistry, Laboratory for Molecular Structure and Bonding, Texas A&M Uni6ersity, College Station, P.O. Box 30012,
Texas, TX 77842-3012, USA
b Department of Chemistry, State Uni6ersity of New York at Albany, Albany, NY 12222, USA
Received 11 September 2001; accepted 12 October 2001
Dedicated to the memory of Professor Luigi Venanzi
Abstract
The reduction of the Re25+ core in 1,2,7-Re2Cl5(PR3)3 molecules, followed by addition of 1 equiv. of a different phosphine
ligand, PR3%, allows the preparation of the mixed monodentate phosphine compounds of the Re24+ type, namely 1,2,7,8-
Re2Cl4(PR3)3(PR3%). The stereochemistry of the starting materials dictates the stereochemistry of the final products. The
one-electron reduction of the 1,2,7-isomer of Re2Cl5(PMe2Ph)3 with KC8 to the corresponding anion, [1,2,7-Re2Cl5(PMe2Ph)3]−
(1), followed by non-redox substitution of one chloride ion by one diethylphosphine, PEt2H, afforded the first mixed monodentate
phosphine compound of the dirhenium(II) core, Re2Cl4(PMe2Ph)3(PEt2H) (2), in good yield. Crystal structure determination as
well as other physical methods and elemental analysis unambiguously confirmed the formation of 2. The related system
1,2,7-Re2Cl5(PMe3)3ꢀCo(C5H5)2ꢀPEt2H leads to several products, one of which is 1,2,7,8-Re2Cl4(PMe3)3(PEt2H) (3). © 2002
Elsevier Science B.V. All rights reserved.
Keywords: Dirhenium(II,II) complex; cis-Isomer; Mixed phosphine complex; Crystal structures
only a few mixed phosphine complexes have been re-
ported, all of which have been prepared by stepwise
1. Introduction
substitution reactions of Re2Cl4P4 core compounds.
A classic type of problem often encountered in inor-
The first of these triply bonded Re24+ species, having
ganic chemistry involves the stepwise control of substi-
both mono- and bidentate phosphine ligands,
tution reactions while at the same time preserving cis or
Re2Cl4(PEt3)2(dppm), was prepared by heating a mix-
trans geometry of the products. In dirhenium chemistry
ture of Re2Cl4(PEt3)4 and dppm in benzene [1]. Later,
the PMe3 complexes Re2Cl4(PMe3)2(PꢀP) (PꢀP=dppm
and dppa) were obtained by a closely related procedure
1
[2]. H and 31P NMR spectroscopy were used to show
[3] that they possess the type of structure drawn in
Scheme 1, and only much later this was confirmed [4]
by X-ray analysis performed on Re2Cl4(PMe3)2-
(m-dppm). So, to date, the mixed phosphine dirhenium
Scheme 1.
chemistry is dominated by the Re2Cl4(PR3)2(PꢀP) type
core in which the Re2 unit is bridged by bidentate
phosphine groups. No mixed monodentate phosphine
analogues of the dirhenium core have yet been re-
* 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 Elsevier Science B.V. All rights reserved.
PII: S0020-1693(01)00740-X

174
P.A. Angaridis et al. / Inorganica Chimica Acta 330 (2002) 173–178
ported. Although the mechanism of the substitutional
lability of the monodentate phosphine groups at
metalꢀmetal bonded units in solutions has been exam-
ined [5], synthetically the problem of controlled substi-
tution of PR3 ligands and the isolation of the desired
mixed phosphine compounds has not been solved. The
work reported here affords an interesting example of
solving such a problem with the result that the first
dimetal complex containing a mixed set of monoden-
tate phosphine ligands has been synthesized. This is
done by the one-electron reduction of an Re2Cl5(PR3)3
species to the corresponding [Re2Cl5(PR3)3]− anions
followed by substitution of a chloride ion by a different
phosphine group PR3%.
2.3. Preparation of [Bun4 N][1,2,7-Re2Cl5(PMe2Ph)3] (1)
1,2,7-Re2Cl5(PMe2Ph)3 (0.101 g, 0.10 mmol) was
mixed with KC8 (0.022 g, 0.16 mmol). Toluene (5 ml)
was added to the mixture of solids, followed by CH2Cl2
(5 ml). The suspension was stirred for 30 min at r.t.,
after which all volatile components were removed under
reduced pressure. The residue was washed with C6H14
(3×10 ml) and then dried overnight. It was dissolved
in 7 ml of CH2Cl2 containing [Bun4 N]Cl (0.025 g, 0.09
mmol), the mixture was filtered and the green filtrate
was layered with 15 ml of C6H14. Large brown block-
shaped crystals came out in a few days in the freezer.
Yield: 0.069 g (57%). For [1,2,7-Re2Cl5(PMe2Ph)3]− (1):
CV (CH2Cl2, 22 °C, V versus Ag/AgCl): E1/2(ox)(1)=
−0.42, E1/2(ox)(2)= +0.76. −FAB/DIP MS (NBA,
CH2Cl2, m/z): 965 ([M]−), 929 ([M−Cl]−), 828 ([M−
PMe2Ph]−), 791 ([M−PMe2PhꢀCl]−).
2. Experimental
2.1. General procedures
2.4. Preparation of 1,2,7,8-Re2Cl4(PMe2Ph)3(PEt2H)
(2)
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: PMe3,
PMe2Ph, PEt2H, and Co(C5H5)2, Strem Chemicals;
[Bun4 N]2[Re2Cl8], [Bu4n N]Cl, Aldrich, Inc. 1,2,7-
Re2Cl5(PMe2Ph)3 [6], 1,2,7-Re2Cl5(PMe3)3 [7], and KC8
[8] were prepared by literature procedures.
1,2,7-Re2Cl5(PMe2Ph)3 (0.202 g, 0.21 mmol) was
mixed with KC8 (0.042 g, 0.31 mmol). Toluene (8 ml)
was added to the mixture of solids, followed by CH2Cl2
(10 ml) and approximately 30 mL of PEt2H. The sus-
pension was stirred for 30 min at r.t., after which all
volatile components were removed under reduced pres-
sure. The residue was washed with C6H14 (3×10 ml)
and then dried overnight. It was dissolved in 7 ml of
CH2Cl2, the solution was filtered, and the green filtrate
was layered with 20 ml of C6H14. The green–brown
(dichroic) crystals of 2·CH2Cl2 came out in a few days
in the freezer. Yield: 0.123 g (53%). For 1,2,7,8-
Re2Cl4(PMe2Ph)3(PEt2H) (2): CV (CH2Cl2, 22 °C, V
versus Ag/AgCl): E1/2(ox)(1)= +0.37, E1/2(ox)(2)=
+1.22. 31P NMR {CD2Cl2, 20 °C}: l 3.19 (s), −13.65
(t), −16.55 (t),−24.83 (s). +FAB/DIP MS (NBA,
CH2Cl2, m/z): 1018 ([M]+), 880 ([M−PMe2Ph]+), 742
([M−2PMe2Ph]+), 652 ([M−2PMe2Ph−PEt2H]+).
Anal. Calc. for C29H46Cl6P4Re2: C, 31.59; H, 4.12.
Found, C, 31.76; H, 4.19%.
2.2. Physical measurements
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
(r.t.). Under our experimental conditions, E1/2= +0.47
V versus Ag/AgCl for the ferrocenium/ferrocene cou-
ple. Voltammetric experiments were done with the use
of a Bioanalytical Systems Inc. electrochemical ana-
lyzer, Model 100. The scan rate was 100 mV s−1 at a Pt
disk electrode. Elemental analyses were done by Cana-
dian Microanalytical Services Ltd. The positive and
negative FAB/DIP mass spectra were acquired using a
VG Analytical 70S high-resolution, double-focusing,
sectored (EB) mass spectrometer. Samples for mass
spectral analysis were prepared by mixing a solution of
each compound in CH2Cl2 or CHCl3 with an NBA
matrix on the direct insertion probe tip. 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.
2.5. Preparation of 1,2,7,8-Re2Cl4(PMe3)3(PEt2H) (3)
1,2,7-Re2Cl5(PMe3)3 (0.101 g, 0.13 mmol) was dis-
solved in 10 ml of CH2Cl2 and cobaltocene, Co(C5H5)2,
(0.024 g, 0.13 mmol) was added to the solution. The
reaction mixture was stirred for about 30 min, after
which 0.1 ml of PEt2H was added to the mixture and
the solution was stirred for 2 h at r.t. The volume of the
solution was reduced by half, and 5 ml of benzene was
added to precipitate cobaltocenium chloride. After
filtration the solution was evaporated to leave a brown
residue. The solid was washed with hexanes, redissolved
in dichloromethane and the solution was layered with

P.A. Angaridis et al. / Inorganica Chimica Acta 330 (2002) 173–178
175
Table 1
found in direct E maps using the structure solution
program SHELXTL [13]. The positions of the remaining
atoms were located by means of alternating series of
least-squares cycles and difference Fourier maps [14].
Anisotropic displacement parameters were assigned
to all non-hydrogen atoms. Hydrogen atoms were in-
cluded in the structure factor calculations at idealized
positions. The hydrogen atom connected to the phos-
phorus atom of diethylphosphine in 2 was found in a
difference Fourier map and then refined independently
with an isotropic thermal parameter.
Crystallographic data for [Bun4 N][1,2,7-Re2Cl5(PMe2Ph)3] (1) and
1,2,7,8-Re2Cl4(PMe2Ph)3(PEt2H)·CH2Cl2 (2·CH2Cl2)
1
2·CH2Cl2
Empirical formula
Formula weight
Temperature (K)
Radiation (l, A)
Crystal system
C40H69Cl5N1P3Re2
1206.52
C
29H46Cl6P4Re2
1103.64
213(2)
213(2)
,
Mo Ka (0.71073)
monoclinic
P21/n
9.958(3)
36.879(6)
Mo Ka (0.71073)
triclinic
(
Space group
P1
,
a (A)
11.336(4)
12.431(3)
15.507(5)
104.70(2)
105.54(6)
103.44(3)
1928(1)
2
,
b (A)
Relevant crystallographic data for 1 and 2·CH2Cl2
are summarized in Table 1, and selected bond distances
and angles are given in Table 2.
,
c (A)
13.096(2)
h (°)
i (°)
k (°)
91.92(2)
3
,
V (A )
Z
4807(2)
4
Table 2
,
zcalc (g cm−3
)
1.667
1.901
Selected distances (A), angles (°), and torsion angles (°) for [1,2,7-
Re2Cl5(PMe2Ph)3]− in (1) and 1,2,7,8-Re2Cl4(PMe2Ph)3(PEt2H) (2)
m (mm−1
)
5.438
6.876
Transmission factors
Unique data
0.389–0.580
5916
0.397–0.584
4592
1
2
Observed data [I\2|(I)] 5455
4187
374
0.0374, 0.0917
0.0431, 0.0975
1.159
Bond lengths
Re(1)ꢀRe(2)
Re(1)ꢀP(1)
Re(1)ꢀP(2)
Re(1)ꢀCl(1)
Re(1)ꢀCl(2)
Re(2)ꢀP(3)
Re(2)ꢀP(4)
Re(2)ꢀCl(3)
Re(2)ꢀCl(4)
Re(2)ꢀCl(5)
Parameters refined
460
b
2.2388(7)
2.380(3)
2.360(3)
2.422(3)
2.424(3)
2.352(3)
2.247(1)
2.399(3)
2.390(3)
2.407(3)
2.419(2)
2.392(3)
2.348(3)
2.422(3)
2.411(3)
R1 a, wR2 [I\2|(I)]
0.0403, 0.1018
0.0454, 0.1056
1.264
b
R1 a, wR2 (all data)
Quality-of-fit c
a R1=ꢀ ꢁꢁFoꢁ−ꢁFcꢁꢁ/ꢀ ꢁFoꢁ.
b wR2=[ꢀ [w(Fo2−Fc2)2]/ꢀ [w(Fo2)2]]1/2
.
c Quality-of-fit=[ꢀ [w(Fo2−Fc2)2]/(Nobs−Nparams)]1/2, based on all
2.401(3)
2.401(3)
2.386(3)
data.
hexanes. Brown, block shaped crystals were found at
the bottom of the Schlenk tube after a week. The
product was shown by X-ray crystallography to be a
mixture of species, two known complexes [9]: 1,2,7,8-
Re2Cl4(PMe3)4 and [Bun4 N][1,2,7-Re2Cl5(PMe3)3]; and a
new product, Re2Cl4(PMe3)3(PEt2H) (3).
Bond angles
P(1)ꢀRe(1)ꢀP(2)
95.7(1)
151.3(1)
83.6(1)
86.6(1)
153.7(1)
82.0(1)
97.17(7)
96.88(8)
111.00(8)
109.30(8)
94.57(9)
146.10(9)
83.50(9)
84.47(9)
151.02(9)
81.47(9)
102.66(9)
94.22(7)
111.21(9)
114.46(7)
94.31(9)
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)
Re(2)ꢀRe(1)ꢀP(1)
Re(2)ꢀRe(1)ꢀP(2)
Re(2)ꢀRe(1)ꢀCl(1)
Re(2)ꢀRe(1)ꢀCl(2)
P(3)ꢀRe(2)ꢀP(4)
P(3)ꢀRe(2)ꢀCl(5)
P(3)ꢀRe(2)ꢀCl(3)
P(3)ꢀRe(2)ꢀCl(4)
P(4)ꢀRe(2)ꢀCl(3)
Cl(3)ꢀRe(2)ꢀCl(5)
P(4)ꢀRe(2)ꢀCl(4)
Cl(4)ꢀRe(2)ꢀCl(5)
Cl(3)ꢀRe(2)ꢀCl(4)
Re(1)ꢀRe(2)ꢀP(3)
Re(1)ꢀRe(2)ꢀP(4)
Re(1)ꢀRe(2)ꢀCl(3)
Re(1)ꢀRe(2)ꢀCl(4)
Re(1)ꢀRe(2)ꢀCl(5)
P(1)ꢀRe(1)ꢀRe(2)ꢀCl(3)
P(2)ꢀRe(1)ꢀRe(2)ꢀCl(4)
Cl(1)ꢀRe(2)ꢀRe(1)ꢀP(3)
Cl(2)ꢀRe(2)ꢀRe(1)ꢀP(4)
Cl(2)ꢀRe(1)ꢀRe(2)ꢀCl(5)
2.6. X-ray structure determination
Single crystals of compounds 1 and 2·CH2Cl2 were
obtained as described above. The X-ray diffraction
experiments were carried out on a Nonius FAST dif-
fractometer with an area detector using Mo Ka radia-
tion. 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 controller. Fifty reflections were used in
cell indexing and about 250 reflections in cell refine-
ment. The data were corrected for Lorentz and polar-
ization effects by the MADNES program [10]. Reflection
profiles were fitted and values of F2 and |(F2) for each
reflection were obtained by the program PROCOR [11].
The intensities were also corrected for anisotropy ef-
fects using a local adaptation of the program SORTAV
[12]. All calculations were done on a DEC Alpha
running VMS. The coordinates of rhenium atoms were
85.0(1)
149.9(1)
86.9(1)
153.2(1)
85.0(1)
80.4(1)
84.9(1)
141.2(1)
142.8(1)
84.2(2)
97.77(7)
83.0(1)
95.94(9)
102.98(7)
110.9(1)
115.73(8)
112.21(8)
112.38(9)
104.70(9)
28.0(1)
24.2(1)
25.1(1)
30.4(1)
27.0(1)
28.68(9)
34.4(1)
23.3(1)

176
P.A. Angaridis et al. / Inorganica Chimica Acta 330 (2002) 173–178
Scheme 2.
Scheme 3.
Complex 2 has been obtained in pure form in moder-
ate yield, and it has been fully characterized by mass-
spectrometry, elemental analysis and cyclic
3. Results and discussion
It was first shown in 1985 by Dunbar and Walton
[15] that one-electron reduction of a 1,3,6-Re2Cl5(PR3)3
molecule, followed by reaction of the resulting anion
with a molar equivalent of PR3 leads to the product
1,3,6,8-Re2Cl4(PR3)4, as shown in Scheme 2. More re-
cently, after we learned to make 1,2,7-Re2Cl5(PR3)3
molecules [6,9], we discovered the existence of 1,2,7,8-
Re2Cl4(PR3)4 molecules by a similar reaction sequence
(Scheme 3, where PR3%=PR3) starting with a 1,2,7-
Re2Cl5(PR3)3 compound. However, because of the cis
relationship of the PR3 ligands in both starting com-
pound and the product, reactions of this second type
can occur only when the phosphines have small cone
angles [16], that is, with PMe3 [9], PMe2Ph [6], and
PEt2H [17].
voltammetry. We have not detected any side-products
in this system. The reaction affording 3 was not so
clean and less efficient, yielding a mixture of dirhenium
complexes with the Re24+ core, from which crystals of
3 were separated manually for X-ray diffraction study.
In addition to stereochemical suitability of the lig-
ands for the synthesis of cis products, it is also impor-
tant that the entering monodentate phosphine have the
same or lower basicity than the three in the starting
material, in order to avoid phosphine ligand redistribu-
tion. For both of these reasons, the system
Re2Cl5(PMe2Ph)3ꢀPEt2H was found to be unique.
When we tried to introduce the sterically suitable but
most basic ligand, PMe3, to [Re2Cl5(PMe2Ph)3]−, even
at a ratio Re2–PMe3=1:1, uncontrolled side reactions
were observed, including complete substitution of
PMe2Ph by PMe3. Conversely, it might seem that
trimethylphosphine ligands in the starting material
should be resistant to replacement by any other phos-
phine, including PMe2Ph and PEt2H. However, when
we tried to extend our approach by using 1,2,7-
Re2Cl5(PMe3)3 as the starting material and PEt2H as
the entering phosphine, we isolated the target mixed
phosphine complex, 1,2,7,8-Re2Cl4(PMe3)3(PEt2H) (3),
only in a low yield.
We then recognized that by employing Scheme 3,
with PR3% not the same as PR3, it might be possible to
make the first compounds with different phosphines in
the same Re2Cl4(PR3)4 type molecule. We first accom-
plished such
a synthesis by using 1,2,7-Re2Cl5-
(PMe2Ph)3 as a starting material, KC8 as a reducing
agent and diethylphosphine as the entering phosphine
ligand affording the complex 1,2,7,8-Re2Cl4(PMe2Ph)3-
(PEt2H) (2). We confirmed that the intermediate after
one-electron reduction is indeed the [1,2,7-Re2Cl5-
(PMe2Ph)3]− anion (1). It has been isolated in crys-
talline form as its tetrabutylammonium salt. An
analogous reaction scheme has also been applied for
the related system 1,2,7-Re2Cl5(PMe3)3ꢀCo(C5H5)2ꢀ
PEt2H. However, this resulted in a mixture of products,
but one of them was a new mixed monodentate phos-
phine dirhenium complex, 1,2,7,8-Re2Cl4(PMe3)3-
(PEt2H) (3).
The tetrabutylammonium salt of anion 1 forms crys-
tals in the monoclinic space group P21/n with two pairs
of enantiomeric dimetal molecules in the unit cell. The
dirhenium(II,II) anion has C1 virtual symmetry and
exhibits a staggered conformation (Fig. 1). All dimen-
sions of the [1,2,7-Re2Cl5(PMe2Ph)3]−, including the
ReꢀRe bond length and the PꢀReꢀP angle, have small
deviations from the corresponding dimensions of the

P.A. Angaridis et al. / Inorganica Chimica Acta 330 (2002) 173–178
177
Fig. 1. A drawing of the anion [1,2,7-Re2Cl5(PMe2Ph)3]− (1). Atoms
are represented by thermal ellipsoids at the 40% probability level.
Hydrogen atoms are shown as spheres of arbitrary radii.
Fig. 3. A drawing of 1,2,7,8-Re2Cl4(PMe3)3(PEt2H) (3). Only the
major orientation of the Re2 unit is shown. Rhenium and phosphorus
atoms are represented by thermal ellipsoids at the 30% probability
level; other atoms are shown as spheres of arbitrary radii.
Each molecule has C1 virtual symmetry. The structure
determination on Re2Cl4(PMe2Ph)3(PEt2H) (2) con-
firmed that a cis-type of geometry of phosphine groups
had indeed been retained on both rhenium atoms upon
reduction and addition of the diethylphosphine ligand
to yield an 1,2,7,8-isomer (Fig. 2). The PꢀReꢀP angles
at both ends of the dirhenium unit are almost identical
(94.57(9) and 94.31(9)°). The bond distances and angles
in the mixed phosphine complex 2 are compared with
respective characteristics of other 1,2,7,8-species listed
in Table 3. In fact all geometrical parameters are in
good agreement with the corresponding values for the
whole 1,2,7,8-class of molecules. The essential feature
of the molecule 2 is a ‘half-staggered’ conformation as
in the parent anion 1 (Table 2) with the PꢀReꢀReꢀCl
torsion angles spanning the range 27.0(1)–34.4(1)°.
That contrasts with all other complexes of this type
(and Re2Cl4(PR3)4 complexes with monodentate phos-
phines in general) which are known to have an eclipsed
conformation.
Fig. 2. A drawing of 1,2,7,8-Re2Cl4(PMe2Ph)3(PEt2H) (2). Atoms are
represented by thermal ellipsoids at the 35% probability level. Only
the hydrogen atom connected to the phosphorus atom of the PEt2H
group is shown.
neutral dirhenium(II,III) molecule, 1,2,7-Re2Cl5(PMe2-
Ph)3 [6]. The staggered conformation is also retained
with the torsion angles in the range 23.3(1)–
28.0(1)°.
The structure determination on Re2Cl4(PMe3)3-
(PEt2H) (3) [18] also proved that a cis-type of phos-
phine disposition is preserved (Fig. 3). The structure
(
Compound 2 crystallizes in triclinic group P1 with
two Re2Cl4(PMe2Ph)3(PEt2H) molecules in the unit cell.
solution of 3 was complicated by the disorder
Table 3
,
Selected bond distances (A) and angles (°) for 1,2,7,8-Re2Cl4(PR3)4 type complexes
(PR3)4,
(Reference)
(PMe3)4
([9])
(PMe2Ph)4
([6])
(PEt2H)4
([17])
(PMe2Ph)3(PEt2H) (2)
(this work)
(PMe3)3(PEt2H) (3)
(this work)
Bond distances
ReꢀRe
ReꢀP
2.2414 (8)
2.373 (7)
2.410 (9)
2.260 (1)
2.407 (3)
2.411 (3)
2.2533 (8)
2.366 (2)
2.414 (2)
2.247 (1)
2.382 (3)
2.415 (3)
2.253 (2)
2.353 (8)
2.416 (7)
ReꢀCl
Bond angles
PꢀReꢀP
PꢀReꢀReꢀCl
93.2 (7)
1.1–3.7
93.6 (1)
1.8–4.4
93.12 (6)
0.11–1.16
94.44 (9)
27.0–34.4
95.8 (3)
3.0

178
P.A. Angaridis et al. / Inorganica Chimica Acta 330 (2002) 173–178
of the phosphine groups. Each phosphine position is
occupied by 3/4 of PMe3 and 1/4 of PEt2H. Such a
distribution stems from the fact that trimethyl and
diethyl phosphines match closely in size. Unfortunately,
we were unable to completely model the location of
partially occupied carbon atom positions in the crystal
structure of 3. However, the positions of the heavy
atoms (Re, Cl, and P) were well-refined and the princi-
pal dimensions shown in Table 3 are reliable. As ex-
pected, the core distances and angles in the structure of
1,2,7,8-Re2Cl4(PMe3)3(PEt2H) are very close to those in
corresponding homo-phosphine complexes.
In conclusion, complexes 2 and 3 constitute the first
structurally characterized examples of mixed monoden-
tate phosphine compounds of the multiply bonded din-
uclear core for M2X4(PR3)4−x(PR3%)x, where M=Mo,
W, Tc, Re; X=halide. The suggested synthetic route is
an alternative strategy to a stepwise substitution [19,20],
and opens a door for further research on synthetic
techniques that will allow the formation of mixed phos-
phine derivatives of the dimetal core with controlled
stoichiometry and stereochemistry. We also note that
while the two-step procedure described here might also
be thought to allow conversion of 1,3,6-Re2Cl5(PR3)3
compounds to 1,3,6,8-Re2Cl4(PR3)3(PR3%) compounds,
more complex and not well understood reactions occur
instead.
References
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4. Supplementary material
Crystallographic data (excluding structure factors)
for 1 and 2·CH2Cl2 have been deposited with the Cam-
bridge Crystallographic Data Centre as supplementary
publication nos. CCDC 163592 and 163591. Copies of
the data can be obtained free of charge on application
to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK
(fax: +44-1223-336-033; e-mail: deposit@ccdc.cam.
ac.uk or www:http://www.ccdc.cam.ac.uk).
[18] Crystallographic data for 1,2,7,8-Re2Cl4(PMe3)3(PEt2H) (3):
green–brown block, 0.18×0.23×0.25 mm, orthorhombic, Pbca
,
(No. 61), a=13.884(3), b=13.772(6), c=13.565(3) A, V=
2593.8(3) A , Z=4, T=243 K. The experiment was performed
3
,
on a Nonius FAST diffractometer with an area detector using
Mo Ka radiation in the range 4B2qB50°. Total 2095 reflec-
tions were observed (1103 reflections with I\2|(I)). The princi-
pal metal to ligand distances are given in Table 3. Two
orientations of the Re2 unit were refined (96.6:3.4%)
[19] F.A. Cotton, B. Hong, Inorg. Chem. 32 (1993) 2354.
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Acknowledgements
We acknowledge support by the National Science
Foundation.