Oxo-rhenium(V) complexes with analogs of bis(diphenylphosphino)ethane

Article abstract of DOI:10.1016/j.ica.2005.07.038

Compounds of the types ReOCl₃(L-L) and ReOCl₂(OEt)(L- L) with bis(diphenylphosphino)ethene (dppen) and bis(diphenylphosphino)ferrocene (dppf) were prepared by reacting the diphosphine with ReOCl ₃(OPPh₃)(Me₂S). The ReOCl₃(L-L) compound with bis(diphenylarsino)ethane (dpae) was prepared similarly. Crystallographic work on ReOCl₃(dppen) and ReOCl₃(dpae) confirmed the approximate octahedral environment of the metal and the presence of a Cl ligand trans to the Re=O bond. The ReOCl₂(OEt)(L-L) compounds contain a transO=Re-OEt unit. The visible spectra of both types of compounds include a two-component d-d absorption pattern originating from the spin-allowed excitation of a d electron from the interaxial d orbital in the equatorial plane to the empty d_xz and d_yz orbitals. For ReOCl ₂(OEt)(dppf), these bands are masked by strong transitions taking place in the ferrocene moiety. The absorptions of the other systems are not greatly displaced compared to the similar dppe compounds, a small decrease in the transition energy being noted for the dpae complex.

Full text of DOI:10.1016/j.ica.2005.07.038

Inorganica Chimica Acta 358 (2005) 4489–4496
www.elsevier.com/locate/ica
Oxo-rhenium(V) complexes with analogs
of bis(diphenylphosphino)ethane
*
´
Olivier Sigouin, Andre L. Beauchamp
De´partement de chimie, Universite´ de Montre´al, C.P. 6128 Succ. Centre-ville, Montre´al, QC, Canada H3C 3J7
Received 8 April 2005; received in revised form 30 July 2005; accepted 30 July 2005
Available online 21 September 2005
Abstract
Compounds of the types ReOCl3(L–L) and ReOCl2(OEt)(L–L) with bis(diphenylphosphino)ethene (dppen) and bis(diphenylphosph-
ino)ferrocene (dppf) were prepared by reacting the diphosphine with ReOCl3(OPPh3)(Me2S). The ReOCl3(L–L) compound with
bis(diphenylarsino)ethane (dpae) was prepared similarly. Crystallographic work on ReOCl3(dppen) and ReOCl3(dpae) confirmed the
approximate octahedral environment of the metal and the presence of a Cl ligand trans to the Re@O bond. The ReOCl2(OEt)(L–L) com-
pounds contain a transO@Re-OEt unit. The visible spectra of both types of compounds include a two-component d–d absorption pattern
originating from the spin-allowed excitation of a d electron from the interaxial d orbital in the equatorial plane to the empty dxz and dyz
orbitals. For ReOCl2(OEt)(dppf), these bands are masked by strong transitions taking place in the ferrocene moiety. The absorptions of
the other systems are not greatly displaced compared to the similar dppe compounds, a small decrease in the transition energy being
noted for the dpae complex.
ꢀ 2005 Elsevier B.V. All rights reserved.
Keywords: Rhenium; Diphosphine; Diarsine; Crystal structure; d–d Electron transitions
1. Introduction
Following the initial study which revealed that the
HOMO–LUMO gap is relatively small in ReOCl(P ꢀ O)2
compounds containing bidentate mixed P ꢀ Oꢁ ligands
[1], various series of related compounds were considered
in order to gain insight in the factors affecting the
HOMO–LUMO gap in these system. We examined Re-
OX3(dppe) and ReOX2(OR)(dppe) compounds, where the
coordination sphere remained close to that of the Re-
OCl(P ꢀ O)2 species and the equatorial cis-P,P arrange-
ment was provided by bis(diphenylphosphino)ethane
(dppe) [2]. The presence of a strong p-donor ROꢁ group
trans to the Re@O bond in ReOX2(OR)(dppe) was found
to produce an energy gap greater than those of the Re-
OX3(dppe) compounds, where the trans position is occu-
pied by a halogen. In the present study, we are looking
at related compounds in which the central –CH2–CH2– link
of dppe is replaced by the more rigid –CH@CH– unit or
the relatively large ferrocene unit. An analogous complex
with bis(diphenylarsino)ethane (dpae) is also included.
The paper reports the preparation, characterization and
Compounds giving rise to electronic transitions between
low-spin and high-spin states at low energy cost present
considerable interest, since they may provide a basis to de-
velop molecular switches and devices for efficient informa-
tion storage. The d2 oxo-rhenium(V) core is a stable unit in
which the ground state is low-spin and diamagnetic, since
the strong p bonds formed via the oxygen px and py orbi-
tals raise the dxz and dyz orbitals (LUMO) above the other
interaxial d orbital (HOMO), in which the two d electrons
are paired. However, if the HOMO–LUMO gap could be
reduced and become comparable with the pairing energy,
the molecule could adopt a high-spin triplet ground state
or possess a readily accessible high-spin excited state that
could be involved in spin-crossover processes.
*
Corresponding author. Tel.: +1 514 343 6446; fax: +1 514 343 7586.
E-mail address: andre.beauchamp@umontreal.ca (A.L. Beauchamp).
0020-1693/$ - see front matter ꢀ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2005.07.038

4490
O. Sigouin, A.L. Beauchamp / Inorganica Chimica Acta 358 (2005) 4489–4496
UV–visible spectra of these complexes, together with crys-
tallographic work on ReOCl3(dppen) and ReOCl3(dpae).
Although substitution of the central unit in the ligand af-
fects the bite of the ligands and the extent of communica-
tion between the two donor atoms, no drastic changes
were detected in the HOMO–LUMO gap.
2.2.3. ReOCl3(dppf)
Reaction time: 9 days. Green solid, yield: 41%. The solid
retains 0.4 mol of diethyl ether. Anal. Calc. for
C
35.6H32Cl3FeO1.4P2Re: C, 47.90; H, 3.61. Found: C,
1
47.99; H, 3.41%. H NMR (acetone-d6) (ppm) d: 7.98 (m,
4H, Ho), 7.77 (m, 4H, Ho), 7.40–7.56 (m, 12H, Hm,p),
5.37 (m, 2H, Hferrocene), 4.94 (m, 2H, Hferrocene), 4.68 (m,
2H, Hferrocene), 4.52 (m, 2H, Hferrocene). 31P{1H} NMR
(acetone-d6) (ppm) d: ꢁ25.90 (s). Similar NMR data were
obtained in CDCl3 [6] or CD2Cl2 [7]. IR (CsI, cmꢁ1): 966
(s) m(Re@O); 326 (w), 278 (w) m(Re–Cl).
2. Experimental
2.1. Reactants and methods
KReO4, the diphosphines, the diarsine and all other
reactants were obtained from Aldrich and used without
further purification. ReOCl3(OPPh3)(Me2S) was prepared
from ReOCl3(PPh3)2 [3] as described in the literature
[4,5]. Deuterated solvents were purchased from Aldrich.
IR spectra were recorded on Perkin–Elmer Spectrum
One (4000–400 cmꢁ1, KBr pellets) or Bio-Rad Excalibur
FTS 3000FX (4000–200 cmꢁ1, CsI pellets) spectrometers.
The NMR spectra were measured with Bruker AV-300,
AMX-300, AV-400 or ARX-400 spectrometers. For the
1H spectra, the residual solvent signal (DMSO-d6,
2.50 ppm; acetone-d6, 2.17 ppm; CDCl3, 7.26 ppm) was
used as internal reference. H3PO4 was used as an external
reference (d = 0) for the 31P{1H} spectra. Electronic spec-
tra of chloroform solutions were recorded in quartz cells
with a UV–Vis-NIR Cary 5E spectrometer. Elemental
2.2.4. ReOCl3(dpae)
Reaction time: 20 h. Blue–green solid, yield: 91%. Anal.
Calc. for C26H24As2Cl3ORe: C, 39.29; H, 3.04. Found: C,
1
39.33; H, 3.12%. H NMR (DMSO-d6) (ppm) d: 7.93 (m,
4H, Ho), 7.77 (m, 4H, Ho), 7.47–7.53 (m, 12H, Hm,p),
3.40 (m, 2H, CH2, partly masked by water peak), 2.95
(m, 2H, CH2). IR (CsI, cmꢁ1): 980 (s) m(Re@O); 320 (w),
278 (w) m(Re–Cl).
2.3. Preparation of the ReOCl2(OEt)(L–L) compounds
These compounds were obtained by the same method as
above, but ethanol was used as the solvent. In a typical run,
ReOCl3(OPPh3)(Me2S) (0.16 mmol) was stirred in a reflux-
ing solution of dppe (0.16 mmol) in ethanol (10 mL). The
initially green suspension turned purple slowly. After 6
days, a purple solid was collected by filtration, washed with
ethanol and diethyl ether, and dried in vacuo.
´
´
analyses were run at the Laboratoire dꢀAnalyse Elemen-
´
´
taire de lꢀUniversite de Montreal.
2.2. Preparation of the ReOCl3(L–L) compounds
2.3.1. ReOCl2(OEt)(dppe)
All compounds were prepared from ReOCl3-
Purple solid, yield: 64%. Anal. Calc. for
C28H29Cl2O2P2Re: C, 46.93; H, 4.08. Found: C, 46.66; H,
3.94%. 1H NMR, 31P{1H} NMR (DMSO-d6) and IR
(CsI, cmꢁ1) data as reported earlier [2].
(OPPh3)(Me2S). In
a
typical run, this precursor
(1.56 mmol) was added to a refluxing solution of the
diphosphine (1.63 mmol) in THF (25 mL). A blue suspen-
sion formed immediately and after stirring for 90 min, a
blue solid was collected by filtration, washed with ethanol
and diethyl ether, and dried in vacuo. Details for each com-
pound are provided below.
2.3.2. ReOCl2(OEt)(dppen)
Reaction time: 9 days. Purple solid, yield: 69%. Anal.
Calc. for C28H27Cl2O2P2Re: C, 47.06; H, 3.81. Found: C,
46.68; H, 3.66%. 1H NMR (CDCl3) (ppm) d: 8.09 (m,
4H, Ho), 7.97 (m, 2H, HC@C, second-order signal, see next
section), 7.80 (m, 4H, Ho), 7.43 (m, 12H, Hm,p), 2.08 (q, 2H,
J = 7.0 Hz, OCH2CH3), ꢁ0.09 (t, 3H, J = 7.0 Hz,
OCH2CH3). 31P{1H} NMR (CDCl3) (ppm) d: 31.50 (s).
IR (CsI, cmꢁ1): 944 (s) m(Re@O); 282 (w) m(Re–Cl).
2.2.1. ReOCl3(dppe)
Reaction time: 90 min. Blue solid, yield: 84%. Anal.
Calc. for C26H24Cl3OP2Re: C, 44.17; H, 3.42. Found: C,
44.10; H 3.33%. 1H NMR, 31P{1H} NMR and IR data cor-
respond to those reported earlier [2].
2.2.2. ReOCl3(dppen)
2.3.3. ReOCl2(OEt)(dppf)
Reaction time: 7 days. Yellow, solid, yield: 41%. Anal.
Calc. for C36H33Cl2FeO2P2Re: C, 49.55; H, 3.81. Found:
Reaction time: 3 h. In this case, the product was soluble.
The mixture was evaporated to dryness and upon addition
of CH2Cl2, a blue solid was obtained from a green solution.
Yield: 44%. Anal. Calc. for C26H22Cl3OP2Re: C, 44.30; H,
3.15. Found: C, 44.13; H, 2.48%. H NMR (DMSO-d6)
(ppm) d: 8.88 (m, 2H, HC@C, second-order signal, see next
1
C, 49.37; H, 3.82%. H NMR (acetone-d6) (ppm) d: 7.99
(m, 4H, Ho), 7.89 (m, 4H, Ho), 7.44–7.55 (m, 12H, Hm,p),
4.84 (m, 2H, Hferrocene), 4.80 (m, 2H, Hferrocene), 4.61 (m,
2H, Hferrocene), 4.48 (m, 2H, Hferrocene), 2.94 (q, 2H,
J = 7.0 Hz, OCH2CH3), 0.34 (t, 3H, J = 7.0 Hz,
OCH2CH3). 31P{1H} NMR (acetone-d6) (ppm) d: ꢁ9.13
(s). IR (CsI, cmꢁ1): 951 (s) m(Re@O); 275 (w) m(Re–Cl).
1
section), 7.94 (m, 4H, Ho), 7.86 (m, 4H, Ho), 7.51 (m, 12H,
H
m,p). 31P{1H} NMR (DMSO-d6) (ppm) d : 20.69 (s). IR
(CsI, cmꢁ1): 989 (s) m(Re@O); 320 (w), 278 (w) m(Re–Cl).

O. Sigouin, A.L. Beauchamp / Inorganica Chimica Acta 358 (2005) 4489–4496
4491
Table 1
Crystal data
2.4. Crystallographic measurements and structure
determination
ReOCl3(dpae) Æ CHCl3
27H25As2Cl6ORe
914.25
blue–green block
223(2)
Bruker Smart CCD 2K
monoclinic
Pc (no. 7)
11.4708(1)
21.6188(1)
13.6442(1)
90
108.18(1)
90
3214.63(4)
4
ReOCl3(dppen)
Dark-blue plates of ReOCl3(dppen) were obtained by
slow diffusion of CHCl3 into a CH2Cl2 solution. The crys-
tallographic study was carried out with an Enraf-Nonius
CAD-4 diffractometer (Cu Ka radiation) controlled by
the CAD-4 software [8]. The reduced cell was initially
determined from 20 to 25 spots located on a preliminary
rotation photograph and centered in the detector aperture.
Accurate cell parameters were then calculated from the
positions of 25 high-angle reflections centered with the SE-
TANG and DETTH procedures. The intensities were re-
corded by x/2h scan. Possible crystal decomposition was
monitored by measuring five standard reflections every
hour. Space group P21/n was defined unambiguously from
the monoclinic Laue symmetry and systematic absences
(h0l, h + l ¼ 2n and 0k0, k ¼ 2n). All data in the whole
sphere were collected at room temperature. An absorption
correction based on crystal geometry was applied. The data
were finally corrected for the effects of Lorentz and polar-
ization, and averaged to provide the basic two-octant set.
The Re atom was located by the heavy-atom method
and the remaining non-hydrogen atoms were located by
the standard Fourier technique. The SHELXTL system [9]
was used for all calculations. The structure was refined
on F 2o using all reflections. The H atoms were fixed using
a riding model with Uiso = 1.2 · Ueq of the atom to which
they are bonded. The crystal data are listed in Table 1.
Blue–green crystals of ReOCl3(dpae) were obtained by
slow diffusion of CHCl3 into a CH2Cl2 solution. A crystal
was mounted on a Bruker SMART CCD 2K diffractome-
ter (Cu Ka radiation) controlled by the SMART software
[10]. Sets of 30 oscillation frames of 0.3ꢁ over a range of 9ꢁ
were recorded in four regions of the reciprocal space, from
which the reduced cell was determined by least-squares
refinement. For data collection, frames were recorded for
different orientations of the crystal and detector so as to
cover at least 95% of the reciprocal sphere. At the end,
the first 101 frames were remeasured and the intensities
of the 907 reflections did not show any decomposition of
the crystal. The frames were analyzed with the SAINT soft-
ware [11], which determined the intensity and the position
of each spot. Accurate cell parameters were obtained by
least-squares refinement over the positions of the whole
data set. An absorption correction based on crystal geom-
etry was applied.
Formula
C
C26H22Cl3OP2Re
704.94
blue block
293(2)
Formula weight
Crystal shape
T (K)
Diffractometer
Crystal system
Space group
CAD4
monoclinic
P21/n (no. 14)
10.184(5)
15.606(5)
16.202(5)
90
95.15(3)
90
2565(2)
4
˚
a (A)
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
Volume (A )
Z
dcalc (g/cm3)
Reflections cell
parameters
Crystal dimensions
(mm)
3
˚
1.889
30445
1.826
25
0.38 · 0.21 · 0.09
0.32 · 0.20 · 0.12
Radiation Cu Ka, k
1.54178
1.54178
˚
(A)
l (cmꢁ1
)
14.43
38948
13.42
36063
Reflections
measured
Reflections
independent
Reflections
observed (I > 2r)
R(I > 2r)a
10453
(Rint = 0.049)
9566
4866
(Rint = 0.042)
3592
0.0518
0.1237
1.042
0.0344
0.0860
0.887
wR2(I > 2r)a
S(I > 2r)a
P
P
P
P
2
2 1=2
a
R ¼ kF o j ꢁ j F ck= j F o j, wR2 ¼ f ½wðF 2o ꢁ F c2Þ ꢂ= wðF o2Þ g
,
P
2
1=2
S ¼ f ½wðF 2o ꢁ F 2c Þ ꢂ=ðNobs ꢁ NparamÞg
.
then attempted in the P2/c and Pc groups, assuming that
only the h0l l ¼ 2n condition was strictly obeyed. No solu-
tion emerged in P2/c, but a reasonable model was obtained
in Pc. This model was in fact a superstructure of the P21/c
solution, in which the two molecules related by the P21/c
inversion center have become symmetry independent.
Refinement proceeded slowly, but normally, in space group
Pc. Peaks for C and Cl atoms of two independent CHCl3
solvent molecules were found in the DF map and these
positions were refined isotropically. Anisotropic refinement
of the remaining non-hydrogen atoms, with the hydrogens
constrained as above, converged to R = 0.052. The crystal
data are listed in Table 1.
Relatively large thermal ellipsoids in phenyl rings sug-
gest that a general disorder could exist in the structure
and there is indeed evidence that the trans Cl–Re@O seg-
ment is involved in a subtle disorder. For molecule 2, the
Structure resolution required considerable effort because
both pseudo-symmetry and disorder are present. Space
group P21/c was considered first on the basis of the mono-
clinic Laue symmetry and systematic absences (h0l, l ¼ 2n
and 0k0, k ¼2 n), although uncertainty remained concern-
ing the 0k0 k odd condition, a few of these reflections
showing intensity somewhat above background. A reason-
able solution was obtained in P21/c, but all phenyl rings
showed disorder or very large thermal ellipsoids. The R
factor could not be reduced below 0.12. Resolution was
˚
abnormally long Re(2)@O(2) bond (1.890(13) A) and short
˚
Re(2)–Cl(4) bond (2.196(6) A) indicate that these two
bonds a randomly interchanged over the crystal, as re-
ported earlier for related compounds [2,12,13]. Attempts
to describe the O(2) and Cl(4) sites as a combination of
non-coincident fractional O and Cl atoms did not result

4492
O. Sigouin, A.L. Beauchamp / Inorganica Chimica Acta 358 (2005) 4489–4496
in any significant improvement of the crystallographic re-
sult. A similar effect is noted for molecule 1, although the
bond lengths indicate that the extent of disorder is not as
large. In a search for missed symmetry, the PLATON soft-
ware [14] detected a certain similarity, but very significant
differences between the two independent molecules.
Fast inversion of the puckered chelate ring across the
equatorial plane (perpendicular to Re@O) of the dppe or
dpae complexes renders the two methylene groups equiva-
lent on the NMR time scale. Since both sides of the equa-
torial plane are non-equivalent, two 1H multiplets are
observed between 2.9 and 3.8 ppm. For the same reason,
the ferrocenyl protons of the dppf complexes show four sig-
nals between 4.48 and 5.37 ppm. Because of the anisotropic
effect of the Re@O bond, the protons on the oxo side are
believed to be the most deshielded [18,19]. The presence
of an alkoxo group brings the multiplets closer together.
The Dd value of 0.55 ppm of ReOCl3(dppe) decreases to
0.17 for the ReOCl2(OEt)(dppe) [2]. For the ReOCl3(dppf)
and ReOCl2(OEt)(dppf) pair, a similar reduction of Dd
from ꢀ0.55 to ꢀ0.27 ppm is noted.
3. Results and discussion
In previous reports, ReOCl3(PPh3)2 or ReOCl3(AsPh3)2
were used as starting materials to prepare the ReOCl3(L–L)
compounds [2,3,6,7,15]. In the present cases, the reactions
(Scheme 1) were carried out in THF starting from mer,
trans-O,O-ReOCl3(OPPh3)(Me2S) (I), which reduced reac-
tion time and made purification easier. To obtain the eth-
oxo compounds, the reaction was run in ethanol instead
of THF. Despite the fact that positions the two labile
groups are cis to one another in the precursor (I), rear-
rangement occurred and the fac-trichloro (II) and trans-
oxo-ethoxo products (III) were isolated.
For the dppen complexes, the protons are part of an
AA0XX0 system and they generate the second-order pattern
shown in Fig. 1. Simulation [20] was used to fit the spectra
and a perfect fit was obtained for both ReOCl3(dppen) and
ReOCl2(OEt)(dppen) with the coupling constants listed in
Table 2.
3.1. IR and NMR spectroscopies
The phenyl rings above the equatorial plane are not
equivalent with those below and they should lead to two
sets of H signals. This is not detected in the spectra of
the dppe complexes, where only two complicated multiplets
appear in a 2:3 intensity ratio and are assigned to the ortho
and to the meta/para protons, respectively [2]. However,
for the other ligands, although the meta/para protons re-
1
The IR spectra of the trichloro complexes show the
strong IR m(Re@O) band at 966–989 cmꢁ1 expected for
mono-oxo systems [16]. Two m(Re–Cl) bands are observed
at 278–280 and 320–326 cmꢁ1 [13]. For the oxo-ethoxo
complexes, the m(Re@O) band appears in the 944–
951 cmꢁ1 range and a single m(Re–Cl) vibration is found
between 275 and 285 cmꢁ1
.
A singlet in the 31P{1H} NMR spectra of the trichloro
compounds is clear evidence for bidentate coordination
of the diphosphine and for the fac-trichloro arrangement
(II) observed in the crystal structures of the compounds
with dppe [2], dppf [15] and dppen (see below). The ethoxo
complexes (III) also give a 31P{1H} NMR singlet, in agree-
ment with the Cl ligand trans to the Re@O bond being dis-
placed, as observed for dppe complexes with various
alkoxo groups [2,17]. The singlets are downfield from those
of the corresponding trichloro complexes.
Hm,p
Ho
HC=C
O
Ph2
Cl
Cl
P
Re
P
Ph2
9.00
8.75
8.50
8.25
8.00
7.75
7.50
(ppm)
δ
Cl
O
1
Fig. 1. Low-field H NMR spectral region of ReOCl3(dppen) in DMSO-
d6. The complex second-order signal at ꢀ8.9 ppm is due to the –
C(H)@C(H)– protons.
(II)
Cl
Cl
Cl
Re
SMe2
O
Ph2
P
OPPh3
Cl
Cl
Table 2
Re
P
Ph2
Coupling constants (Hz) for the –C(H)@C(H)– protons in ReOCl3(dppen)
(I)
3
0
JHH
9.3
51.5
7.8
OEt
2JHP
3
(III)
0
JHP
3
0
JPP
7.5
Scheme 1.

O. Sigouin, A.L. Beauchamp / Inorganica Chimica Acta 358 (2005) 4489–4496
4493
3.2.1. ReOCl3(dppen)
The structure of ReOCl3(dppen) is actually very close to
that of ReOCl3(dppe) [21]. As expected, replacing the –
CH2–CH2– connecting segment by –C(H)@C(H)– reduces
˚
the central C–C distance from 1.537 to 1.327 A, but the
P(1)–Re–P(2) bite angle is not appreciably affected (82.0ꢁ
vs. 83.3ꢁ for dppe) [21]. The bond lengths in the O@Re–
Cl unit remain close to those of the dppe compound. Sig-
nificant differences in the Re–Cleq distances (and various
other distortions) ascribed to ring puckering in the dppe
compounds [2] are no longer observed here, the Re–Cleq
˚
distances being 2.385 A. The P–C@C–P atoms are coplanar
within experimental error, but the chelate ring is not pla-
˚
nar, since the Re atom lies 0.359 A away from this plane.
The torsion angles in Table 3 show that replacing the puck-
ered chelate ring of ReOCl3(dppe) by the relatively flat ring
in ReOCl3(dppen) results in a considerable modification of
the van der Waals envelope of the complex, not only be-
cause the P–Ph bonds are differently positioned, but also
because the phenyl rings adopt different orientations. This
Fig. 2. ORTEP drawing of the ReOCl3(dppen) molecule. Ellipsoids
correspond to 30% probability. Hydrogens are omitted for simplicity. In
the phenyl ring numbering scheme, the last digit corresponds to the
position around the ring, starting with 1 for the ipso position.
is particularly clear for ring #1, where the Re–P–Cipso
Cortho torsion angles differ by 44ꢁ.
–
main unresolved, the eight ortho protons split into two sig-
nals with the same intensity.
3.2.2. ReOCl3(dpae)
3.2. X-ray diffraction studies
The unit cell of ReOCl3(dpae) contains two symmetry
independent molecules, which are actually very similar to
one another and to ReOCl3(dppe) [21] (Table 3). The con-
formations of the puckered chelate rings are actually very
close, as evidenced from the As(P)–Ccentr–Ccentr–As(P)
and Ccentr–Ccentr–As(P)–Cortho torsion angles. On the other
hand, the Re–P–Cipso–Cortho angles show that the phenyl
rings are oriented differently. Interestingly, for the two Re-
OCl3(dpae) molecules, three of the phenyl rings adopt sim-
ilarly orientations, whereas the remaining rings (type #2)
are 90ꢁ apart.
In ReOCl3(dppen) (Fig. 2) and ReOCl3(dpae) (Fig. 3),
the rhenium atom has a slightly distorted octahedral coor-
dination. The equatorial plane consists of the P (or As)
atoms of the bidentate ligand and two cis Cl atoms. A third
Cl ligand lies trans to the Re@O bond. The largest devia-
tion from octahedral coordination is the displacement of
the Re from the P(As)2Cl2 plane by 0.15–0.25 A on the
oxo side, which is typical of this type of compounds. Se-
lected distances and angles are listed in Table 3.
˚
In the equatorial plane, the Re–Cleq bond lengths
˚
(2.358–2.387 A) agree well with the expected values,
˚
whereas the Re–As distances (2.526–2.542 A) are normal,
˚
considering that As has a covalent radius ꢀ0.12 A greater
than P. Clearly, there is an anomaly in the Re@O and
Re–Cltrans bond lengths, which differ considerably from
those of the dppe complex and show large discrepancies be-
tween the two symmetry-independent molecules. This is an
artifact resulting from a subtle crystallographic disorder
affecting, to a different extent, both ReOCl3(dpae) mole-
cules: for some of the molecules, the O@Re–Cltrans segment
adopts the opposite direction in a random manner, without
affecting appreciably the remaining atoms in the molecule.
This problem is sometimes encountered when a complex
has its van der Waals envelope largely defined by one or
a few very bulky ligands, allowing small ligands (like Cl
or O here) to exchange positions without disturbing the
molecular structure and crystal packing [2,12,13]. Since
the weighted average position is obtained from the X-ray
data, the shorter bond appears longer than normal,
whereas the long bond seems to be too short. Originally,
these erratic bond lengths were mistakenly attributed to
Fig. 3. ORTEP drawing of one of the two independent ReOCl3(dpae)
molecules. The structure of the second molecule in the asymmetric unit is
very similar. Ellipsoids correspond to 30% probability. Hydrogens are
omitted for simplicity. In the phenyl ring numbering scheme, the last digit
corresponds to the position around the ring, starting with 1 for the ipso
position.

4494
O. Sigouin, A.L. Beauchamp / Inorganica Chimica Acta 358 (2005) 4489–4496
Table 3
˚
Distances (A) and angles (ꢁ) in ReOCl3(dppen) and ReOCl3(dpae) Æ CHCl3
ReOCl3(dppen) E = P
ReOCl3(dppe) E = P [21]
ReOCl3(dpae) Æ CHCl3 E = As
Re@O(1)
Re–E(1)
Re–E(2)
Re–Cl(1)
Re–Cl(2)
Re–Cl(3)
C(1)–C(2)
1.669(4)
2.437(2)
2.425(2)
2.419(2)
2.384(2)
1.680
2.429
2.463
2.445
2.377
2.380
1.537
1.812(10)
2.539(2)
2.526(2)
2.355(3)
2.387(4)
2.367(4)
1.48(2)
1.890(13)
2.530(2)
2.542(2)
2.196(6)
2.358(4)
2.387(4)
1.51(2)
2.385(2)
1.327(8)
O(1)@Re–Cl(1)
E(1)–Re–Cl(2)
E(2)–Re–Cl(3)
O(1)@Re–Cl(2)
O(1)@Re–Cl(3)
O(1)@Re–E(1)
O(1)@Re–E(2)
Cl(1)–Re–Cl(2)
Cl(1)–Re–Cl(3)
Cl(1)–Re–E(1)
Cl(1)–Re–E(2)
E(1)–Re–E(2)
164.1(2)
163.0
162.9(3)
175.9(1)
169.1(1)
96.5(3)
100.0(3)
87.5(3)
90.0(3)
95.60(13)
92.69(13)
80.37(10)
76.69(9)
163.4(4)
175.9(1)
169.0(1)
99.1(4)
99.6(4)
84.6(4)
90.2(4)
93.1(2)
92.0(2)
167.31(6)
168.39(6)
100.9(2)
102.9(2)
89.2(2)
90.4(2)
89.51(6)
89.53(7)
77.93(6)
173.2
164.5
101.4
103.9
84.3
91.4
91.5
87.7
82.2
82.91(19)
77.47(18)
82.83(6)
78.88(6)
82.01(6)
76.8
83.3
82.85(5)
Cl(3)–Re–E(1)
Cl(2)–Re-E(2)
Cl(2)–Re–Cl(3)
E(1)–C(1)–C(2)-E(2)
C(1)–C(2)–E(2)–C(31)
C(1)–C(2)–E(2)–C(41)
C(2)–C(1)–E(1)–C(11)
C(2)–C(1)–E(1)–C(21)
Re–E(1)–C(11)–Cortho
Re–E(1)–C(21)–Cortho
Re–E(2)–C(31)–Cortho
Re–E(2)–C(41)–Cortho
Reꢃ ꢃ ꢃE(1)E(2)Cl(1)Cl(2)
a
95.25(6)
93.74(7)
86.53(7)
95.9
92.9
86.3
93.21(13)
96.69(10)
86.5(2)
93.14(14)
95.31(12)
88.0(2)
ꢁ0.6(8)
ꢁ59.8a
163.7a
ꢁ81.8a
ꢁ76.4a
173.7a
28.9a
ꢁ74.2a
ꢁ54.2a
58.0a
ꢁ53.4(13)
167.9(10)
ꢁ85.1(11)
ꢁ86.2(13)
164.8(12)
64(1) [C12]
ꢁ40(2) [C22]
ꢁ30(2) [C32]
46(1) [C46]
0.153(2)
ꢁ53.9(12)a
171.8(11)a
ꢁ74.7(11)a
ꢁ81.1(13)a
163.3(11)a
68(2) [C56]a
51(2) [C62]a
ꢁ43(2) [C72]a
61(2)[C86]a
0.151(2)
109.4(5)
ꢁ136.9(5)
ꢁ108.8(5)
137.8(5)
72.6(6) [C16]
ꢁ66.5(6) [C26]
ꢁ56.2(5) [C36]
74.6(5) [C46]
0.250(1)
0.226
The torsion angles calculated from the coordinates reported in the paper correspond to the enantiomeric molecule. Their sign has been changed to
make comparisons easier.
10
‘‘bond-stretch isomerism’’, but the situation was straight-
ened out in a classic paper by Yoon, Parkin and Reinghold
[12]. The normal Re@O and Re–Cltrans bond lengths in
˚
molecules of this type are 1.68 and 2.44 A, respectively.
˚
The apparently long Re@O (1.812 A) and short Re–Cl
˚
bonds (2.355 A) suggest that a sizable fraction of the mol-
ecules adopt the other orientation, but the proportion does
5
not reach 50%, since the distances would become equal.
For the other ReOCl3(dpae) molecule, the distances
˚
(1.890 and 2.196 A) indicate that the proportion is closer,
but still different from, 50%.
The overall connectivity and structure are definitely
established unambiguously by our X-ray study. However,
the distances and angles should be used with caution, even
0
those between non-disordered atoms, since disorder proba-
bly has a small local effect on the positions of atoms that
appear not to be disordered.
10000
15000
(cm-1
20000
ν
)
Fig. 4. UV–visible spectra of ReOCl3(dppen) in DMSO (full line). Dashed
lines correspond to the two components obtained by deconvolution.
3.3. UV–visible spectroscopy
The typical spectrum of ReOCl3(dppen) is shown in
Fig. 4. The ground state (S) and the two lowest-energy sin-
glet states (S* and S**) for this type of systems are schemat-
ically represented in Fig. 5. As noted previously for the
dppe compounds [2], only two components can be identified
in the spectrum, which are assigned to the spin-allowed

O. Sigouin, A.L. Beauchamp / Inorganica Chimica Acta 358 (2005) 4489–4496
4495
compounds, since they adopt the fac-trichloro and trans-
oxo-ethoxo arrangements, respectively. The visible spectra
of the dppen and dpae compounds are similar to those of
related dppe compounds. Replacing the central –CH2–
CH2– section by a more rigid –C(H)@C(H)– unit does
not produce drastic changes on the HOMO–LUMO gap.
Although the replacement of P by softer As donors pro-
duces a small shift to the transition to lower energies, this
change is rather modest.
E
LUMO's
dxz
dyz
HOMO
dxy
S
S*
S**
Fig. 5. Low-energy singlet electron configurations for the oxo-Re(V) d2
systems.
Acknowledgements
´
We wish to thank Dr. M. Simard and F. Belanger-
´
Gariepy for assistance in the interpretation of the X-ray
Table 4
diffraction data, and the Natural Sciences and Engineering
Research Council of Canada for financial support.
Observed transition energies (cmꢁ1 · 103) [e] (L molꢁ1 cmꢁ1
)
[S ! S*]
[S ! S**]
ReOCl3(dppe)a
ReOCl3(dppen)
ReOCl3(dppf)
ReOCl3(dpae)
ReOCl2(OEt)(dppe)a
ReOCl2(OEt)(dppen)
ReOCl2(OEt)(dppf)
12.0 [13]
12.6 [4]
12.2 [15]
11.3 [22]
16.4 [12]
18.4 [18]
N/Ob
16.4 [25]
16.8 [7]
16.5 [52]
16.0 [41]
20.0 [21]
19.3 [52]
N/Ob
Appendix A. Supporting information
Crystallographic data for ReOCl3(dpae) and ReOCl3-
(dppen) have been deposited with the Cambridge Crystal-
lographic Data Center, CCDC nos. 267886 and 267887,
respectively. Copies of these information may be obtained
free of charge on application to CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK (fax: +44 1223 336033; e-mail:
deposit@ccdc.cam.ac.uk or http://www.cam.ac.uk).
a
In DMSO, Ref. [2].
Masked by a strong absorption of the dppf ligand.
b
transitions of an electron to the two LUMO orbitals,
respectively. These bands may be used to make compari-
sons with the dppe systems. The data are given in Table
4. ReOCl2(OEt)(dppf) cannot be included, since the d–d
transitions are masked by the strong ligand band at
22700 cmꢁ1, located in the ferrocene moiety. The trend
noted earlier for an alkoxo group to increase the transition
energy is obeyed here, the first transition of dppen moving
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from 12600 to 18400 cmꢁ1
.
With respect to ReOCl3(dppe), substitution by another
diphosphine induces a small displacement to higher energy,
but the change is not spectacular. On the other hand, intro-
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