Synthesis and characterization of the bromide and hydride derivatives of rhenium(I) 1,2-bis(diphenylphosphinite)ethane complexes

Article abstract of DOI:10.1016/S0277-5387(99)00002-9

The reaction of [ReX(CO)₅] (X=Br, H) with the bidentate phosphinite ligand 1,2-bis(diphenylphosphinite)ethane (L-L), synthesized by reaction of PPh₂Cl and ethylene glycol in a 2:1 ratio in the presence of NEt₃, at room temperature, affords the mononuclear rhenium(I) complexes fac-[ReBr(CO)₃(L-L)] (1) and fac-[ReH(CO)₃(L-L)] (2). The coordination geometry of the complexes was established by diffraction studies and confirmed by spectroscopic data of both complexes. Compound 1 crystallizes in the P2₁/c (No. 14) monoclinic space group while the hydride complex does so in P2₁ (No. 4). The coordination polyhedron around the rhenium atom in both cases is a slightly distorted octahedron with three carbonyl groups in facial positions. The link of the bidentate ligand to the metal atom leads to a seven-membered ReP₂O₂C₂ ring, adopting a conformation better described as a twisted chair.

Full text of DOI:10.1016/S0277-5387(99)00002-9

Polyhedron 18 (1999) 1431–1436
Synthesis and characterization of the bromide and hydride derivatives of
rhenium(I) 1,2-bis(diphenylphosphinite)ethane complexes
a
a
a
a,1
b
˜
´
´
Sandra Bolano , Jorge Bravo , Rosa Carballo , Soledad Garcıa-Fontan , Ulrich Abram ,
a,
*
´
´
Ezequiel M. Vazquez-Lopez
a
´
´
Departamento de Quımica Inorganica, Facultade de Ciencias, Universidade de Vigo, E-36200 Vigo, Galicia, Spain
b
¨
Institut fur Radiochemie des Forschungszentrums Rossendorf, D-01062 Dresden, Germany
Received 20 September 1998; accepted 21 December 1998
Abstract
The reaction of [ReX(CO)5] (X5Br, H) with the bidentate phosphinite ligand 1,2-bis(diphenylphosphinite)ethane (L–L), synthesized
by reaction of PPh2Cl and ethylene glycol in a 2:1 ratio in the presence of NEt3, at room temperature, affords the mononuclear rhenium(I)
complexes fac-[ReBr(CO)3(L–L)] (1) and fac-[ReH(CO)3(L–L)] (2). The coordination geometry of the complexes was established by
diffraction studies and confirmed by spectroscopic data of both complexes. Compound 1 crystallizes in the P21 /c (No. 14) monoclinic
space group while the hydride complex does so in P21 (No. 4). The coordination polyhedron around the rhenium atom in both cases is a
slightly distorted octahedron with three carbonyl groups in facial positions. The link of the bidentate ligand to the metal atom leads to a
seven-membered ReP2O2C2 ring, adopting a conformation better described as a twisted chair.
reserved.
1999 Elsevier Science Ltd. All rights
Keywords: Rhenium(I) 1,2-bis(diphenylphosphinite)ethane complexes
1. Introduction
characterization of rhenium(I) carbonyl bromide and hy-
dride derivatives of the bidentate ligand bis(diphenylphos-
phinite)ethane, Ph2PO–CH2CH2 –OPPh2.
The coordination chemistry of rhenium(I) derivatives
with monodentate and bidentate phosphine ligands is well
developed. Recently, studies of the phosphite complexes
have also received attention due to the different electronic
and steric properties of these ligands [1–11]. However, the
coordination chemistry of bidentate phosphites has been
explored much less thoroughly than that of the phosphine
analogs, probably due to the lack of stability and difficulty
of isolating the former [12].
On the other hand, an increasing number of studies have
been undertaken to evaluate the effects on structure,
bonding and chemical properties of the hydride and the
corresponding h2–H2 rhenium complexes [13,14] when an
oxygen atom, near the phosphorous belonging to an
ancillary ligand, is introduced.
2. Experimental
2.1. Materials and instrumentation
All operations were carried out under an atmosphere of
dry dinitrogen or argon, using standard Schlenk tech-
niques. All solvents were dried over appropriate drying
agents, degassed on a vacuum line and distilled in an Ar
atmosphere [15].
Ph2PCl, ethylene glycol (Aldrich, Steinheim, Germany)
and Re2(CO)10 (ABCR, Karlsruhe, Germany) were used
without any further purification. [ReBr(CO)5] and
[ReH(CO)5] were synthesized by reported methods
[16,17].
As a way of continuing with these studies, we report
here on the synthesis and spectroscopic and diffractometric
Elemental analyses were carried out on a Fisons EA-
1108. Melting points (m.p.) were determined on a Gallen-
Kamp MFB-595 and are uncorrected.
*
Corresponding author. Tel.: 134-986-812-319; fax: 134-986-812-
382.
Infrared spectra were recorded on a Bruker Vector 22FT
spectrophotometer. NMR spectra were obtained on a
´
´
E-mail address: ezequiel@uvigo.es (M. Vasquez-Lopez)
1Corresponding co-author.
0277-5387/99/$ – see front matter
PII: S0277-5387(99)00002-9
1999 Elsevier Science Ltd. All rights reserved.

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S. Bolano et al. / Polyhedron 18 (1999) 1431–1436
1432
Bruker AMX 400 spectrometer. 1H and 13Ch1Hj chemical
shifts refer to internal tetramethylsilane (TMS), while
31Ph1Hj chemical shifts are reported with respect to 85%
H3PO4, with downfield shifts considered positive.
Longitudinal relaxation time values of the hydride
resonance were measured in CD2Cl2 solutions at 400 MHz
by the inversion–recovery method using a standard 1808–
t–908 pulse sequence between 183 and 283 K in 2 and
183 and 238 K in 3. The resulting T1 (min) values are
included in Table 3, while plots of T1 (ms) vs. T (K)
parameters corresponding to compound 3 are shown in
Fig. 4.
crystals were obtained by slow evaporation of an EtOH/
CH2Cl2 (10:2, v/v) solution.
2.5. Synthesis of [Re(h2 –H2 )(CO)3(L–L)]1, 3
The complex was prepared by the addition of HBF4?
Et2O (3.78 mL, 0.02 mmol) with a microsyringe to a
solution of hydride compound 2 (0.02 mmol) in 0.5 mL of
CD2Cl2, placed inside a 5-mm NMR tube and cooled to
193 K. The tube was shaken to complete the reaction and
then the NMR spectra (1H and 31P) were registered. The
compound was not isolated as solid due to the easy loss of
hydrogen above 230 K.
2.2. Synthesis of the ligand Ph2PO(CH2 )2OPPh2 (L–L)
2.6. X-ray data collection, structure and refinement
The synthesis of the ligand is based on the method
described by Rabinowitz and Pellon [18]. Ph2PCl (13 mL,
72.4 mmol) was slowly added dropwise (ca. 30 min) to a
cooled (2808C) solution of freshly distilled Et3N (10 mL,
72.1 mmol) and ethylene glycol (2.23 g, 35.9 mmol) in 30
mL of toluene. The solution was stirred for 1 h and the
formation of the ligand was established by the presence of
a unique signal at 132.6 ppm in the 31Ph1Hj spectrum. The
formed solid, [Et3NH]Cl, was filtered off and the resulting
solution was vacuum concentrated to yield a yellow oil.
Attempts to purify this oil (by distillation or column
chromatography) were unsuccessful because the product is
unstable, as shown by the disappearance of the characteris-
tic signal in the 31Ph1Hj spectrum. So, for the synthesis of
the complexes, a toluene solution of the oil was used. This
solution is stable at room temperature for several months
when it is stored under an inert atmosphere.
Crystallographic measurements of both compounds were
performed on a CAD4 Enraf-Nonius diffractometer. Crys-
tal data and experimental conditions are listed in Table 1.
Data were corrected for polarization and Lorentz effects.
C-scan absorption corrections were also applied [19].
Structure analyses for both compounds were carried out
by the heavy atom method [20] followed by difference
Fourier techniques until all non-hydrogen atoms were
located. All non-H atoms were anisotropically refined. The
positions of H-atoms were calculated geometrically and
included in structure factor calculations, except the hydride
ligand in compound 2 that was located and isotropically
refined.
For compound 2, the obtained Flack parameter [21], of
0.11(2), refined simultaneously with the other atomic and
crystal parameters, is rather high. However, all attempts to
refine it as a racemic twin did not improve the model.
Scattering factors and anomalous dispersion terms were
taken from Ref. [22]. Most calculations were performed
with programs SHELXS97 [20] and SHELXL97 [23].
Important intramolecular bond distances and angles for
compounds 1 and 2 are given in Table 2.
2.3. Synthesis of fac-[ReBr(CO)3(L–L)], 1
To a suspension of [ReBr(CO)5] (200 mg, 0.5 mmol) in
toluene (20 mL), 4 mL of the ligand solution (0.45 M)
were added and the mixture was stirred for 12 h. The
solvent was removed under vacuum and the resulting oil
was tritured with ethanol (2 mL). The white precipitate that
formed was filtered off, washed with ethanol and vacuum
dried. Yield, 142 mg (37%); m.p., 1608C. Anal. Found: C,
45.4; H, 3.2%. C29H24BrO5P2Re requires C, 44.6; H,
3.1%. Single crystals were obtained by slow evaporation of
an EtOH/CH2Cl2 (10:2, v/v) solution.
3. Results and discussion
The chelating 1,2-bis(diphenylphosphinite)ethane ligand
Ph2PO(CH2)2OPPh2 (L–L) is produced by the reaction of
35.9 mmol of ethylene glycol (HOCH2CH2OH) and 72.4
mmol of diphenylphosphine chloride (Ph2PCl) in the
presence of triethylamine. Attempts to isolate the ligand
from the solution, after separating [Et3NH]Cl, were unsuc-
cessful; therefore, the synthesis of the rhenium derivatives
must always be performed from a toluene solution of L–L
(see Section 2) (Scheme 1).
After treatment of a toluene solution of L–L with
[ReX(CO)5] (X5Br, H), suspended or dissolved in
toluene at room temperature, the corresponding 1:1 com-
plexes were obtained (Scheme 2), as indicated by the
appearance of IR-bands due to the stretching vibrations of
2.4. Synthesis of fac-[ReH(CO)3(L–L)], 2
To 3 mL of the solution of the ligand L–L (0.50 M),
[ReH(CO)5] (230 mg, 0.7 mmol) dissolved in 10 mL of
tetrahydrofuran (THF) was added. After 4 h of stirring, the
resulting solution was vacuum concentrated to ca. 4 mL.
The white precipitate obtained by the addition of 2 mL of
MeOH was filtered off, washed with methanol and vacuum
dried. Yield, 80 mg (16%); m.p.: 1328C. Found: C, 49.8;
H, 3.6%. C29H25O5P2Re requires: C, 49.6; H, 3.6%. Single

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S. Bolano et al. / Polyhedron 18 (1999) 1431–1436
1433
Table 1
Crystallographic data for compounds 1 and 2
1
2
Formula
C29H24BrO5P2Re
780.53
C29H25O5P2Re
701.63
Monoclinic
P21 (No. 4)
12.136(2)
9.244(1)
12.958(1)
110.76(2)
1359.3(3)
2
Molecular weight
Crystal class
Space group
Monoclinic
P21 /c (No. 14)
10.5090(8)
11.2070(10)
24.719(5)
99.456(8)
2871.7(7)
4
˚
a (A)
˚
b (A)
˚
c (A)
b (8)
V (A )
3
˚
Z
Temperature (K)
293(2)
1.805
213(2)
1.714
2
Dc (g cm23
)
Crystal size (mm)
l (A)
m (mm)
0.2530.2530.10
Mo–Ka50.71073
5.771
0.3030.0530.05
Cu–Ka51.54184
10.167
˚
u (8) range
2–31
6–65
h, k, l range
0,14; 0,15; 235,34
9087
8661/0.0707
3812
0.0461/0.0760
1.143/22.202
21,14; 210,10; 215,14
4569
4569/0.0242
4392
0.0528/0.1473
0.807/21.763
Reflections measured
Independent reflections/Rint
No. reflections with I.2s(I)
R1 /wR2[I.2s(I)]a
23
˚
Peak/hole (eA
)
a
Dc5calculated density; R15ouuFou2uFcuu/ouFou; wR25[ow(Fo2Fc)2 /ow(Fo)2]1 / 2
.
Table 2
Selected bond distances and angles
[ReBr(CO)3(L–L)], (1)
[ReH(CO)3(L–L)], (2)
Scheme 1.
Re–C(1)
1.911(9)
1.938(8)
1.962(9)
2.4423(19)
2.4654(18)
2.6259(9)
1.120(8)
1.137(8)
1.130(9)
1.638(5)
1.812(7)
1.821(7)
1.608(5)
1.825(8)
1.834(7)
1.458(8)
1.478(9)
1.436(7)
89.1(3)
92.4(3)
86.2(3)
92.7(2)
95.2(2)
174.8(2)
94.6(2)
174.3(3)
89.4(2)
88.92(6)
178.4(2)
89.8(3)
Re–C(1)
1.961(14)
1.944(14)
1.941(15)
2.425(3)
2.410(3)
1.75(14)
1.149(17)
1.147(17)
1.147(18)
1.623(9)
1.824(13)
1.825(14)
1.631(9)
1.824(13)
1.831(17)
1.428(16)
1.480(19)
1.448(16)
92.1(6)
Re–C(2)
Re–C(3)
Re–P(1)
Re–P(2)
Re–C(2)
Re–C(3)
Re–P(1)
Re–P(2)
CO groups in 1 and the change in the 31Ph1Hj spectrum of
1 and 2. The resulting complexes can be isolated as
air-stable white solids. They can be partially dissolved in
alcohols or completely in solvents such as chloroform,
dichloromethane and dimethylsulfoxide (DMSO).
Re–Br
Re–H(1)
C(1)–O(1)
C(2)–O(2)
C(3)–O(3)
P(1)–O(4)
P(1)–C(11)
P(1)–C(21)
P(2)–O(5)
P(2)–C(31)
P(2)–C(41)
C(4)–O(4)
C(4)–C(5)
C(5)–O(5)
C(1)–Re–C(2)
C(1)–Re–C(3)
C(2)–Re–C(3)
C(1)–Re–P(1)
C(2)–Re–P(1)
C(3)–Re–P(1)
C(1)–Re–P(2)
C(2)–Re–P(2)
C(3)–Re–P(2)
P(1)–Re–P(2)
C(1)–Re–Br
C(2)–Re–Br
C(3)–Re–Br
P(1)–Re–Br
P(2)–Re–Br
C(1)–O(1)
C(2)–O(2)
C(3)–O(3)
P(1)–O(4)
P(1)–C(11)
P(1)–C(21)
P(2)–O(5)
P(2)–C(31)
P(2)–C(41)
C(4)–O(4)
C(4)–C(5)
C(5)–O(5)
C(1)–Re–C(2)
C(1)–Re–C(3)
C(2)–Re–C(3)
C(1)–Re–P(1)
C(2)–Re–P(1)
C(3)–Re–P(1)
C(1)–Re–P(2)
C(2)–Re–P(2)
C(3)–Re–P(2)
P(1)–Re–P(2)
C(1)–Re–H(1)
C(2)–Re–H(1)
C(3)–Re–H(1)
P(1)–Re–H(1)
P(2)–Re–H(1)
93.2(6)
89.1(6)
96.8(4)
91.5(4)
Scheme 2.
170.0(5)
90.7(4)
176.1(4)
88.1(4)
90.78(10)
177(5)
90(5)
89(5)
81(5)
87(5)
The nature of the complexes as fac-[ReX(CO)3(L–L)]
was established by spectroscopic and diffractometric
studies of both complexes (vide infra).
3.1. X-ray structure of the [ReX(CO)3(L–L)] complexes
86.4(2)
88.55(5)
86.41(5)
Figs. 1 and 2 show ZORTEP plots [24] of asymmetric
units of the structures, together with the numbering scheme

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S. Bolano et al. / Polyhedron 18 (1999) 1431–1436
1434
plexes [25–30]. It is worth mentioning that the distance
˚
Re–C(1) in compound 2 [1.961(14) A] is significantly
˚
longer than in compound 1 [1.911(9) A]. This fact can be
explained in terms of a stronger trans influence of H
ligand compared to Br. The position of the hydride ligand
in 2 was determined from an analysis of the Fourier map
˚
and the distance H(1)–Re51.75(14) A is similar to that
found in other rhenium terminal hydride complexes
[14,31] and, like the bromine atom in 1, is located in the
trans position to a carbonyl group.
˚
The Re–P distances [2.443(2) and 2.466(2) A in 1 and
˚
2.425(3) and 2.410(3) A in 2] fall into the range observed
in rhenium(I) complexes with bidentate phosphorus donor
ligands [32], although an increase in the bite ligand angle
in our complexes does not impose geometric restrictions.
This bite angle is slightly deviated from the ideal value
[P–Re–P588.92(7)8 in 1 and 90.78(10)8 in 2].
The coordination of the bidentate ligand to rhenium
leads to a seven-membered ReP2O2C2 ring. The torsion
angles and the distances of the atoms to the ideal plane
involving the chelate ring are represented in Fig. 3. Study
of these data suggests that, in both complexes, the ring
conformation is better described as a twisted chair [32].
Fig. 1. ZORTEP plot of the molecular structure of compound 1. The
thermal ellipsoids correspond to 30% probability.
used for [ReBr(CO)3(L–L)] and [ReH(CO)3(L–L)] com-
pounds, respectively.
The complexes exist as discrete molecules in the unit
cells, with no unusually short intermolecular contacts.
The coordination polyhedron around the rhenium atom
can be described as distorted octahedron (main distortions
involving Br–Re–P angles, 88.55(5) and 86.41(5)8 and,
C(2)–Re–C(3), 86.2(3)8 in compound 1; H(1)–Re–P(1)5
81(5)8, H(1)–Re–P(2)587(5)8 and C(3)–Re–P(1)5
170.0(5)8 angles in compound 2; Table 2). The distances
Re–C in both compounds and Re–Br in 1 are similar to
those found in other rhenium(I) bromide–carbonyl com-
3.2. Spectroscopic results
The IR spectrum of the bromide derivative in toluene
solution shows three strong bands at 2034, 1951 and 1907
cm21 with similar intensity, corresponding to n(CO), and
at similar positions to those observed in the complexes
fac-[ReX(CO)3(L)2] (L5phosphine or phosphite ligand)
[33]. When the bromide ligand is replaced by the hydride
ligand, the first two bands shift to lower wavelength
numbers and a contrary effect is observed with respect to
Fig. 2. ZORTEP plot of the molecular structure of compound 2. The
Fig. 3. Distances to ideal plane and torsion angles (in italics) of the
thermal ellipsoids correspond to 30% probability.
seven-membered chelate ring of compounds 1 (bold) and 2.

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S. Bolano et al. / Polyhedron 18 (1999) 1431–1436
1435
the third band (2019, 1939 and 1923 cm21). However, the
3.3. Protonation of hydride complex 2
net result is the shift towards smaller wavenumbers, in
agreement with the structural data obtained by X-ray
diffraction (C–O distances shorter in 1 than 2). In complex
2, the Re–H band, which usually appears as a weak band
around 1990 cm21, is obscured by the presence of
carbonyl bands.
The reaction of 2 with HBF4?Et2O at 2808C gives the
non-classical dihydrogen complex [Re(h2–H2)(CO)3(L–
L)]1, 3 (Scheme 3). This cationic compound is fairly
stable in solution at low temperatures but was not isolated
as a solid because of easy dihydrogen release (around 233
1
1
The H-NMR spectrum of compound 2 shows the signal
K). The H NMR spectrum exhibits a broad resonance in
due to the hydride ligand at 24.87 ppm; it appears as a
triplet due to its coupling with the two phosphorus atoms
of the phosphinite ligand (2J(1H–31P)526 Hz). For both
complexes, the signals corresponding to –CH2 – groups of
the bidentate ligand appear as two groups of multiplets at
around 3.9 and 4.68 (1) and 4.29 ppm (2).
the hydride region at 23.5 ppm, due to a more deshielded
nuclide than in 2 (24.87 ppm) and close to those chemical
shifts observed in [Re(h2–H2)(CO)3(L)2]1 (L5P(OEt)3,
PPh(OMe)2, PPh(OEt)2, PPh2(OMe) and PPh2(OEt)) [14].
The fac-geometry of the complexes can also be pro-
posed by the study of the 13Ch1Hj spectra. The spectra
show two signals, a triplet (1, 187.0 ppm; 2, 194.3 ppm)
due to a carbonyl group trans to X ligand (cis to
phosphinites groups, J(13C–31P).7 Hz) and a multiplet
2
Scheme 3.
(collapsed double doublet) at a lower field (1, 188.9; 2,
195.1 ppm), corresponding to carbonyl groups at trans
positions with respect to phosphorous atoms. At the same
time, the methylene carbons are magnetically equivalent,
showing a unique signal around 66 ppm.
Experiments of longitudinal relaxation times measured
at different temperatures of hydride resonance were per-
formed to establish the nature of the H2 –Re bond [34–36]
in compound 3 but also in compound 2 for comparative
purposes. The plotting of T1 (ms) versus T (K) in both
compounds shows a well defined V-shaped curve, shown
in Fig. 4, from which the T1 (min) can easily be de-
termined. The T1 (min) values and the corresponding
Finally, the 31Ph1Hj spectra of both compounds present
a single signal at positions close to those corresponding to
the free ligand (132.6 ppm), suggesting the magnetic
equivalence of the two phosphorus nuclei at room tempera-
ture.
Table 3
Relevant spectral data
[ReBr(CO)3(L–L)], (1)
[ReH(CO)3(L–L)], (2)
[Re(h2–H2)(CO)3(L–L)]1, (3)
IR spectraa
n(CO)
2034 s
2019 s
1951 s,b
1907 s,b
1939 s,b
1923 s,b
NMR spectrab
Solvent
CDCl3
CD2Cl2
CD2Cl2
1H
d(H–Re)
24.87 t
2J(1H–31P)526
218
23.5 br
T (K)c
225
T1 (min) ms
T stability (K)d
d(CH2)
267.7
15.3
233
3.9 m, 4.2 m
(4H)
3.97 m, 4.68 m;
3.99 m, 4.29 m;
3J(1H–31P)56–7
(4H)
3J(1H–31P)57 (4H)
d(Ph)
13C
7.1–8 m (20H)
7.3–7.8 m (20H)
7.3–7.8 m (20H)
d(CO)
187.0 t
194.3 t
2J(13C–31P)57.2
188.9 m
2J(13C–31P)57.4
195.1 m
31P
122.3 s
135.5 s
129.3 s
a
1 in toluene, 2 in dichloromethane. n in cm21. b5broad and s5strong.
d in ppm and J in Hz. m5multiplet; s5singlet; t5triplet.
Temperature (K) for T1 (min).
b
c
d
Limit for thermal stability.

˜
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S. Bolano et al. / Polyhedron 18 (1999) 1431–1436
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´
´
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´
´
Compound 2 shows a T1 (min) value of 267.7 ms at 218
K, which is similar to those found in [ReH(CO)3(L)2]
complexes [14]. The value for derivative 3 is 15.3 ms at
225 K, in agreement with the existence of h2–H2 ligand
[34–36], although it is slightly greater than those observed
in cationic complexes [Re(h2–H2)(CO)3(L)2]1 (3–7 ms).
On the other hand, the dihydrogen complex 3 shows a
lesser stability, to the loss of H2, than similar complexes
with phosphinite ligands [14]. It seems that, as several
authors had previously reported [14,37], the stability of
rhenium dihydrogen complexes depends on a set of
different factors, amongst which, the number of carbonyl
groups and the nature of the ancillary ligands are outstand-
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Supplementary data available
Supplementary data are available from the Cambridge
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Acknowledgements
¨
We thank Professor J. Strahle for granting access to the
X-ray diffraction facilities at the University of Tubingen
(Germany).
¨
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