Bidentate phosphinophenol ligands. Preparation and electrochemistry of the RE(III) complexes of 2-(diphenylphosphinomethyl)-4-methylphenol (P1-OH) and 2-diphenylphosphinophenol (P2-OH). Crystal and molecular structure of mer-Re[P1-O]3

Article abstract of DOI:10.1016/S0020-1693(00)00156-0

The reaction of 2-(diphenylphosphinomethyl)-4-methylphenol (P₁-OH) and 2-diphenylphosphinophenol (P₂-OH) on ReCl₃(MeCN)(PPh₃)₂ in a 3:1 ratio leads to the formation of the homoleptic Re(III) complexes Re(P₁-O)₃ (1) and Re(P₂-O)₃ (2) in high yield. 1 is reasonably stable in air in the solid state and in solution, which is not the case for 2. Orange-red crystals of 1 contain distorted octahedral Re entities in which the metal is coordinated to three bidentate phosphinophenolato ligands in the mer configuration. Cyclic voltammetry of 1 and 2 shows two well defined monoelectronic quasi-reversible redox waves, one reductive attributed to the Re(III)/Re(II) couple and one oxidative due to the Re(III)/Re(IV) one. A second oxidative wave, attributed to the Re(IV)/Re(V) couple, is reversible only for 1, indicating the lower stability of 2 toward oxidation. In agreement with this, 2 gives, in air, the Re(V)-oxo species ReO(O-P₂=O)(P₂-O)₂ (3) quantitatively, whose structure is confirmed by X-ray diffraction. (C) 2000 Elsevier Science S.A.

Full text of DOI:10.1016/S0020-1693(00)00156-0

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Inorganica Chimica Acta 306 (2000) 94–100
Bidentate phosphinophenol ligands. Preparation and
electrochemistry of the Re(III) complexes of
2-(diphenylphosphinomethyl)-4-methylphenol (P1ꢀOH) and
2-diphenylphosphinophenol (P2ꢀOH). Crystal and molecular
structure of mer-Re[P1ꢀO]3
Fre´de´rique Loiseau a, Fabienne Connac a, Yolande Lucchese a,
Miche`le Dartiguenave a,*, Se´bastien Fortin b, Andre´ L. Beauchamp b, Yvon Coulais c
a Laboratoire de Chimie Inorganique, Uni6ersite´ Paul Sabatier, 118 Route de Narbonne, F-31062 Toulouse Cedex, France
b De´partement de Chimie, Uni6ersite´ de Montre´al, C.P. 6128, Succ. Centre-Ville, Montre´al, Que., Canada, H3C 3J7
c Laboratoire d’Imagerie Me´dicale, Morphologique et Fonctionnelle, Hoˆpital Purpan, Uni6ersite´ Paul Sabatier, Place du Dr. Baylac,
F-31059 Toulouse, France
Received 27 January 2000; accepted 4 April 2000
Abstract
The reaction of 2-(diphenylphosphinomethyl)-4-methylphenol (P1ꢀOH) and 2-diphenylphosphinophenol (P2ꢀOH) on
ReCl3(MeCN)(PPh3)2 in a 3:1 ratio leads to the formation of the homoleptic Re(III) complexes Re(P1ꢀO)3 (1) and Re(P2ꢀO)3 (2)
in high yield. 1 is reasonably stable in air in the solid state and in solution, which is not the case for 2. Orange–red crystals of
1 contain distorted octahedral Re entities in which the metal is coordinated to three bidentate phosphinophenolato ligands in the
mer configuration. Cyclic voltammetry of 1 and 2 shows two well defined monoelectronic quasi-reversible redox waves, one
reductive attributed to the Re(III)/Re(II) couple and one oxidative due to the Re(III)/Re(IV) one. A second oxidative wave,
attributed to the Re(IV)/Re(V) couple, is reversible only for 1, indicating the lower stability of 2 toward oxidation. In agreement
with this, 2 gives, in air, the Re(V)-oxo species ReO(OꢀP2ꢁO)(P2ꢀO)2 (3) quantitatively, whose structure is confirmed by X-ray
diffraction. © 2000 Elsevier Science S.A. All rights reserved.
Keywords: Rhenium complexes; Phosphinophenol complexes; Crystal structures; Electrochemistry
1. Introduction
been known for a while, the related Re(III) species,
Re(P2ꢀO)3 has not been synthesized yet. This is not the
case for the phosphinothiophenol ligand, for which
both the Tc(III) and Re(III) complexes are known [3,6].
We wish to report here the synthesis of the two
homoleptic Re(P1ꢀO)3 (1) and Re(P2ꢀO)3 (2) complexes.
Surprisingly, we observed that using Ph2PCH2C6H3-
(CH3)OH (P1ꢀOH), which introduces more flexibility in
the bonding because of the presence of an sp3 carbon
atom in the metallacycle, increases the stability of the
complex. Complex 1 was characterized by X-ray dif-
fraction. The air sensitive Re(P2ꢀO)3 complex (2) gives
the Re(V) complex ReO(OꢀP2ꢁO)(P2ꢀO)2 (3) as an
oxidation product, quantitatively in air, which was
characterized by X-ray diffraction. These differ-
The reaction of mono- and polydentate phos-
phinophenol ligands on rhenium and technetium cen-
ters has been investigated thoroughly in relation with
their applications as radiopharmaceuticals. There are
several examples of rhenium(V) oxo, imido and nitrido
complexes with Ph2PC6H4OH (P2ꢀOH) [1–4] and
Ph2PCH2C6H3(CH3)OH (P1ꢀOH) [5]. However, al-
though the technetium(III) complex, Tc(P2ꢀO)3 [2] has
* Corresponding author. Tel.: +33-5-6155 6121; fax: +33-5-6155
6118.
E-mail address: dartigue@iris.ups-tlse.fr (M. Dartiguenave).
0020-1693/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0020-1693(00)00156-0

F. Loiseau et al. / Inorganica Chimica Acta 306 (2000) 94–100
95
2.2.2. Synthesis of Re(P2ꢀO)3 (2)
ences are also apparent on the cyclic voltammograms of
these two complexes.
Same method as 1, using 0.308 g (0.36 mmol) of
ReCl3(MeCN)(PPh3)2, 0.30 g (1.08 mmol) of P2ꢀOH
and 0.109 g (1.08 mmol) of NEt3 in 25 ml of ethanol.
The dark red precipitate was filtered off, washed with
cold ethanol and diethyl ether, and dried in vacuo.
Yield: 65%. The product was soluble in common or-
ganic solvents. Anal. Calc. (Found) for C54H42O3P3Re:
C, 63.71 (63.47); H, 4.16 (4.13); O, 4.71 (4.90%). MS
(FAB+): m/z=1018 [M]+. veff (r.t., solid state): 1.5
BM.
2. Experimental
2.1. Reactants and physical measurements
ReCl3(MeCN)(PPh3)2 [7], 2-(diphenylphosphino-
methyl)-4-methylphenol (P1ꢀOH) [8] and diphenylphos-
phinophenol (P2ꢀOH) [9] were synthesized by the pro-
cedures described in the literature. The reactions were
carried out in an atmosphere of nitrogen using standard
Schlenk techniques. Ether was dried over sodium ben-
zophenone ketyl and distilled prior to use. CH2Cl2 and
ethanol were distilled freshly over molecular sieves (3
2.2.3. Synthesis of ReO(OꢀP2ꢁO)(P2ꢀO)2 (3)
A red solution of Re(P2ꢀO)3 (2) (0.20 g, 0.20 mmol)
in 15 ml of diethyl ether was stirred in air for 2 h,
during which time it turned green. Slow concentration
of the solution precipitated a green crystalline com-
pound, which was filtered off, washed with cold diethyl
ether, and dried in vacuo. Yield: 80%. Anal. Calc.
(Found) for C54H42O5P3Re: C, 61.77 (60.21); H, 4.03
(4.33%). IR (CsI, cm−1): 957, w(ReꢁO); 1175, w(PꢁO).
MS (FAB+): m/z=1050 [M]+. 31P{1H} NMR
A). Infrared spectra (400–4000 cm−1) were recorded as
,
CsI pellets on a Bruker VICTOR spectrophotometer.
The 31P{1H} NMR spectrum of 3 was recorded in
CD2Cl2 at room temperature (r.t.) on a Bruker ARX
400 instrument. Magnetic moments were determined in
the solid state at 25°C by the Faraday method, using a
Cahn microbalance coupled with a Drusch electromag-
net. HgCo(NCS)4 was used as standard (Xg=
16.44.10−6 cgs emu) and corrections were applied for
the diamagnetism of the ligands [10]. Mass determina-
tions were made with a NERMAG-R 1010 spectrome-
ter (FAB+). Electrochemical measurements were
carried out at room temperature with a locally made
potentiostat controlled by a personal computer. A con-
ventional three-electrode electrochemical cell (10 ml)
was used: Pt working electrode (disk of 2 mm diameter,
EDI Tacussel 1 mm diameter for cyclic voltammetry
experiments); platinum wire counter electrode; double-
junction saturated calomel reference electrode. The ex-
periments were run in 0.1 M NBu4ClO4–DMF or
NBu4PF6–CH2Cl2 (Aldrich Electrochemical Grade),
which were used without further purification. Elemental
analyses were carried out at the Laboratoire de Chimie
de Coordination du CNRS, Toulouse.
2
(CD2Cl2, 161.98 MHz, ppm): 3.6, 7.7 (dd, JPP=6.7
Hz), 28.5 (s). Recrystallization in acetonitrile gave crys-
tals suitable for X-ray work.
2.3. X-ray diffraction studies
In both cases, the crystal was mounted on a glass
fiber and transferred to an Enraf–Nonius CAD-4 dif-
fractometer, where the data were collected at room
temperature with the graphite-monochromatized Cu
Ka radiation. The reduced cells were obtained from
rotation photographs [11]. Space group was determined
from the Laue symmetry and systematic absences
checked in the final data set. Intensity data were cor-
rected for absorption (Gaussian integration based on
crystal faces, NRCVAX package [12]) and averaged.
Crystal data and conditions for data collection are
summarized in Table 1.
2.3.1. Structure resolution for Re(P1ꢀO)3 (1)
2.2. Synthetic work
Suitable crystals were obtained by recrystallization
from CH2Cl2–ether at 4°C. The structure was solved by
the direct-methods of SHELXS-86 [13] and DF syntheses
using SHELXL-93 [14]. All non-hydrogen atoms were
refined anisotropically. Hydrogens were placed initially
at idealized positions and moved after each run using a
riding model, the fixed CꢀH distances being 0.93 (CH),
2.2.1. Synthesis of Re(P1ꢀO)3 (1)
A
solution of 0.31
g
(0.35 mmol) of
ReCl3(MeCN)(PPh3)2, 0.32 g (1.1 mmol) of P1ꢀOH and
0.11 g (1.1 mmol) of NEt3 in ethanol (40 ml) was
refluxed for 17 h under stirring. An orange–red solid
deposited on cooling, which was filtered, washed with
alcohol and dried in vacuo. Yield: 70%. Recrystalliza-
tion from CH2Cl2–ether (1/1) at 4°C gave orange–red
crystals suitable for X-ray work. Anal. Calc. (Found)
for C60H54O3P3Re: C, 65.38 (65.07); H, 4.94 (4.93%).
MS (FAB+): m/z=1102 [M]+. veff (r.t., solid state):
0.7 BM.
,
0.97 (CH2) or 0.96 A (CH3). The isotropic displacement
factors Uiso were adjusted to 50 (CH3) or 20% (others)
higher than that of the bonded carbon atom. The
CH2Cl2 solvent molecule was found to be disordered
over two positions with populations of 0.45 and 0.55,
respectively. Constraints were imposed for the refine-
ment of the two sets of individual positions, as ex-

96
F. Loiseau et al. / Inorganica Chimica Acta 306 (2000) 94–100
plained in the supplementary material. Refinement con-
verged normally to R=0.039.
verged to R=0.037. The highest residuals were +1.15
−3
,
and −1.41 e A
ground was below 90.8 e A
(near Re) and the general back-
−3
,
.
2.3.2. Structure resolution for ReO(OꢀP2ꢁO)(P2ꢀO)2
(3)
Final atomic coordinates and complete crystallo-
graphic results for 1 and 3 are available as supplemen-
tary material.
Single crystals were obtained by recrystallization
from acetonitrile. The Re atom located from a Patter-
son map was used as the starting model. All other
non-hydrogen atoms in the complex were found from
successive DF maps. The non-hydrogen atoms were
handled as above. Refinement converged to a conven-
tional R factor of 0.041. The DF map phased on the
complex showed a series of weak residuals around (0, 0,
0) and (1/2, 1/2, 1/2), likely due to acetonitrile solvent
molecules. However, because of severe disorder, these
residuals could not be assembled into discrete orienta-
tions. Therefore, this part of the structure was modeled
by using the SQUEEZE procedure of the PLATON soft-
3. Results and discussion
The reaction of 3 equiv. of (PꢀOH) ligand on
ReCl3(MeCN)(PPh3)2 for 17 h in refluxing ethanol, in
presence of 3 equiv. of NEt3 as a proton quencher,
leads to the formation of Re(PꢀO)3 (1 and 2), which
precipitate as orange–red powders in good yield.
1 was recrystallized from CH2Cl2–ether (1/1) at 4°C
giving orange–red crystals suitable for X-ray work.
They can be handled in air and in solution without
noticeable decomposition. This is in contrast with the
behavior of Re(P2ꢀO)3 (2), which in air leads irre-
versibly to the Re(V)-oxo complex ReO(P2ꢀO)2-
(OꢀP2ꢁO) (3) (vide infra).
ware [15], which indicated that each of the two symme-
3
,
try-equivalent pockets had a void volume of 245 A and
contained ꢀ26 electrons. Thus, each pocket included
one acetonitrile molecule, which corresponds to one-
half acetonitrile per complex. This composition was
used to calculate the derived quantities in Table 1. The
contribution of the disordered solvent was calculated
with the Bypass procedure of van der Sluis and Spek
[16], and a new hkl/Fo2 list bypassing the solvent contri-
bution was generated. The final model consisting of the
ordered part only, without the disordered solvent con-
tribution, was refined against this new data list, which
is the one provided in the CIF file. Refinement con-
The elemental analysis and mass spectrometry
(FAB+ technique), which shows the molecular peaks at
[M]+=1102 (1) and 1018 (2), confirm the molecular
structure. The magnetic moment of the solids, veff=0.7
B.M for 1 and 1.5 B.M for 2, is temperature indepen-
dent between 300 and 90 K. This value lies in the wide
range reported for d4 low-spin octahedral Re(III) com-
plexes (3T1g ground state) [17–24]. This paramagnetism
precludes the obtention of a 31P NMR spectrum, but
1
the H NMR spectrum gives many sharp signals in the
0–20 ppm range, that we have not been able to inter-
pret yet.
Table 1
Crystal data and details of the structure determination for Re(P1ꢀO)3
(1) and ReO(OꢀP2ꢁO)(P2ꢀO)2 (3)
3.1. Crystal structure of 1
Formula
C60H54O3P3Re, C53H42O5P3Re,
CH2Cl2
1187.08
monoclinic
P21/n
13.466(5)
22.390(9)
18.314(6)
103.56(3)
5368(3)
4
1/2CH3CN
1070.6
monoclinic
P21/n
14.756(5)
18.691(5)
17.840(5)
102.18(2)
4810(2)
4
1.478
6.10
Cu Ka
293(2)
33 354
9096
An ORTEP view is shown in Fig. 1. Selected bond
distances and angles are given in Table 2.
Formula weight
Crystal system
Space group
The structure consists of a discrete distorted octahe-
dral Re(III) monomer, the rhenium atom being bonded
to three PꢀO anionic ligands in a mer configuration,
with two trans P and two trans O atoms. If electronic
effects were predominant, a fac configuration would be
generated, that is, three s-donor oxygen atoms would
be located trans to the p-acceptor phosphorus atoms.
This is not the case and the mer configuration results
probably from the important steric effect due to the
presence of nine phenyl rings in the molecule. It must
be noticed that the mer arrangement is the only one
reported so far for homoleptic Re(III) and Tc(III)
complexes of this type, namely M(Ph2PC6H4S)3 (M=
Tc, Re) [6], Tc(2-Ph2PCH2CH2CO2)3, 2Me2SO [25] and
even ReCl3(PEt2Ph)3 [26].
,
a (A)
,
b (A)
,
c (A)
i (°)
3
,
V (A )
Z
Dcalc (g cm−3
)
1.469
6.41
v (mm−1
)
,
Radiation (u, A)
T (K)
Cu Ka
293(2)
37 936
10 160
6727
Reflections measured
Unique reflections
Reflections with
7639
[Inet\2.0|(Inet)]
Rf (significant reflections) a
Rw (significant reflections) b
0.0391
0.0782
0.0373
0.1009
a Rf=ꢀꢁꢁFoꢁ−ꢁFcꢁꢁ/ꢀꢁFoꢁ.
The distortion of the octahedron is illustrated in the
bond distance and angle values. One P1ꢀO1 ligand
b Rw=[ꢀ[w(Fo2−Fc2)2]/ꢀ[w(Fo2)2]]1/2
.

F. Loiseau et al. / Inorganica Chimica Acta 306 (2000) 94–100
97
phosphorus, the angle values range from 96.9(2)° for
C211ꢀP2ꢀC221 to 126.2(2)° for C111ꢀP1ꢀRe, while
those at the carbon atoms are 106.1(3)° for
P1ꢀC10ꢀC11, 116.6(4)° for P2ꢀC20ꢀC21 and 117.1(4)°
for P3ꢀC30ꢀC31. The increase of the ReꢀOꢀC angle
from 120.6(3)° (ReꢀO1ꢀC12) to 128.9(3)° (ReꢀO2ꢀC22)
and 135.3(3)° (ReꢀO3ꢀC32) could result from a modifi-
cation of the original sp3 hybridization of the phenolic
oxygen atom due to an increasing contribution of the
oxygen p electrons to the bonding. However, since
,
short ReꢀO bond distances (ꢀ1.95 A) have also been
reported for monodentate phenolate ligands coordi-
nated with ReꢀOꢀC angles of ꢀ126° [27], change in
hybridization is probably not the only factor involved,
intramolecular inter-ligand non-bonded contacts and
distortion in the coordination polyhedron undoubtedly
making contributions as well.
The structure of 1 is quite similar to that of the
phosphinothiol complex Re(P2ꢀS)3, for which a dis-
torted octahedral geometry with a mer configuration
was also observed [6]. Although in this case the ligand
generates three planar five-membered metallacycles, dis-
tortion of the octahedron is less severe than in 1,
Fig. 1. ORTEP drawing of Re(P1ꢀO)3 (1). Ring atoms are assigned
symbols Cij, where j corresponds to the position around the ring
starting with j=1 for the ipso carbon, and i is the (one- or two-digit)
ring number. Hydrogens are omitted for clarity. Ellipsoids corre-
spond to 50% probability.
Table 2
,
Selected interatomic distances (A) and bond angles (°) in Re(P1ꢀO)3
(1)
ReꢀP1
ReꢀP2
ReꢀP3
2.462(2)
2.412(2)
2.405(2)
ReꢀO1
ReꢀO2
ReꢀO3
2.080(3)
1.993(3)
1.992(4)
,
because of the presence of ReꢀS bonds (2.349(5) A av.)
that are significantly longer than ReꢀO bonds (2.022(4)
,
A av.).
P1ꢀReꢀP2
P1ꢀReꢀP3
P1ꢀReꢀO1
P1ꢀReꢀO2
P1ꢀReꢀO3
O1ꢀReꢀO2
O1ꢀReꢀO3
O2ꢀReꢀO3
96.72(5)
166.71(5)
85.51(10)
82.71(11)
91.88(11)
94.11(14)
87.39(15)
174.24(14)
P2ꢀReꢀP3
P2ꢀReꢀO1
P2ꢀReꢀO2
P2ꢀReꢀO3
P3ꢀReꢀO1
P3ꢀReꢀO2
P3ꢀReꢀO3
96.27(5)
177.41(10)
87.51(11)
91.21(11)
81.58(10)
95.05(11)
90.66(11)
3.2. Voltammetric study
The redox properties of 1 and 2 were studied by
cyclic voltammetry at a platinum wire electrode in
DMF solution containing Bu4NClO4 under an atmo-
sphere of nitrogen. The cyclic voltammograms are
shown in Figs. 2 and 3, and the data in Table 3. Both
complexes display two well-defined monoelectronic
quasi-reversible redox waves, one reductive and one
oxidative, by comparison of the anodic and cathodic
currents with the ferrocenium/ferrocene couple as the
internal standard. They conform to the conventional
criteria for Nernstian diffusion-controlled one-electron
reversible electron transfer. The reductive waves are
consistent with the Re(III)/Re(II) couple and the oxida-
tion wave with the Re(III)/Re(IV) one. The second
oxidative couple corresponds to the Re(IV)/Re(V) pro-
Fig. 2. Cyclic voltammogram of Re(P1ꢀO)3 (1) 10−3
NBu4ClO4–DMF at a platinum electrode, scan rate: 0.1 V s−1
M in
.
shows ReꢀP and ReꢀO bond distances significantly
,
longer (by 0.05 and 0.08 A, respectively) than the other
two. As a consequence, the corresponding O1ꢀReꢀP1
bite angle value (85.5(1)°) is smaller. The importance of
steric effects is also emphasized by the large angular
distortions observed at the phosphorus atoms,
methylene carbons and phenolic oxygens. In the case of
Fig. 3. Cyclic voltammogram of Re(P2ꢀO)3 (2) 10−3
NBu4ClO4–DMF at a platinum electrode, scan rate: 0.1 V s−1
M in
.

98
F. Loiseau et al. / Inorganica Chimica Acta 306 (2000) 94–100
Table 3
Cyclic voltammetry data (E°1/2) for the phosphinophenol rhenium complexes
Compound
E°
(V)
1/2
Re(II)/Re(III)
Re(III)/Re(IV)
Re(IV)/Re(V)
Re(V)/Re(VI)
Re(P1ꢀO)3 (1)
−1.231
−1.078
−0.043
0.151
0.885
0.972
−1.196
−1.053
0.976
Re(P2ꢀO)3 (2) a
ReO(OꢀP2ꢁO)(P2ꢀO)2(3) a
ReOCl(P2ꢀO)2
Re(Ph2PC6H4S)3
1.100
b
c
−1.025
0.201
a In 0.1 M NBu4ClO4–DMF, platinum disk electrode, 6=0.1 V s−1
.
b In NBu4PF6–CH2Cl2, platinum disk electrode; 6=81.3 V s−1
c From [6]. E°1/2=1/2(Epa+ Epr).
.
cess that is a quasi-reversible monoelectronic process
for 1 only. In 2, it is not associated with an anodic
response, indicating that the Re(V) homoleptic complex
is unstable on the cyclic-voltammetry time scale.
Such a variety of available oxidation states was ob-
served for the related M(PꢀS)3 (M=Tc, Re) complexes
[6] (Table 3). It appears that 1 is slightly harder to
reduce and easier to oxidize than 2, which could result
from the presence in 1 of non-planar six-membered
metallacycles less favorable to electron delocalization
from the metal than the planar five-membered metalla-
cycles present in the other complex. Differences in the
flexibility of the metallacycles is probably also the
factor responsible for the different reversibilities of the
Re(IV)/Re(V) couples, the P1ꢀO ligand being more able
to accommodate the shortening of the bond distances
in the Re(V) species.
X-ray analysis (vide infra) confirms the structure of this
green compound formed according to Scheme 1. This
diamagnetic complex contains a Re(V) center. This
agrees with its cyclic voltammogram, that shows a
reversible Re(V)/Re(IV) reduction wave at −1.196 V, a
value that compares well with that of the related
ReOCl(P2ꢀO)2, complex. Thus, comparing the Re(V)/
Re(IV) redox couples for 1 (0.967 V) and 3 (−1.196 V)
confirms that the ReꢁO core stabilizes considerably the
+5 oxidation state. The irreversible oxidation peak,
observed for 3 at 1.1 V, should probably correspond to
the Re(V)/Re(VI) process, the Re(VI) species being
chemically unstable [30]. It was checked that no redox
reaction involving the ligand lies in this potential range.
A
Re(III) complex Re(PPh2(CH2)2S)2(S(CH2)2-
Ph2PꢁO) with a pendant PꢁO unit was described previ-
ously [31]. It did not result from air oxidation of the
five-coordinate Re(PꢀS)2(SꢀP) molecule, where SꢀP is a
S-bonded monodentate phosphinethiolate ligand, but
from the reaction of a mixture of PꢀSH and OꢁPꢀSH
ligands on ReCl3(MeCN)(PPh3)2. It was noticed that
exposure of the Re(PꢀS)2(SꢀP) solution to air during the
synthesis generated no oxidation of the pendant phos-
phine, but that oxidation took place at the rhenium
center giving ReOCl(PꢀS)2. In the present system, oxi-
dation does not occur under strictly anaerobic condi-
tions, but conversion of 2 is complete in air at room
temperature. A concerted oxidation mechanism is tenta-
tively proposed (Scheme 2), involving simultaneous oxi-
dation of the Re center and the phosphine, in a
transition state where a ReꢀP bond is broken and the
molecule adopts the five-coordinate, trigonal-bipyrami-
dal, structure observed for Re(PꢀS)2(SꢀP) [16]. The
stereo-non-rigidity of this coordination could explain
the formation of the cis-P,P twisted structure of 3, via
O2/P2 interchange by a twist mechanism [32] (Scheme 2).
Compound 1 is stable in the solid state and in
solution. In contrast, when the red diethylether solution
of 2 is exposed to air, it turns green. By reducing the
volume, a green powder precipitates, and green single
crystals of ReO(OꢀP2ꢁO)(P2ꢀO)2 (3) are obtained by
crystallization from acetonitrile.
Besides the main absorptions of the P2ꢀO ligand, the
IR spectrum of 3 includes two strong absorptions at
1157 and 957 cm−1, characteristic of the w(PꢁO) [27]
and w(ReꢁO) [28] vibrations, respectively. These results,
together with the microanalysis and the FAB+ mass
spectrum (parent peak [M+]=1050), confirm the for-
mation of an oxo-rhenium(V) species. The 31P{1H}
NMR spectrum exhibits a singlet at 28.5 ppm, consis-
tent with a phosphine oxide [29], as well as an AX spin
2
system (doublets at 3.6 and 7.7 ppm, JPP=6.7 Hz),
typical of a cis-P,P twisted octahedral structure. An
3.3. Crystal structure of ReO(OꢀP2ꢁO)(P2ꢀO)2 (3)
Crystals of 3 contain the neutral, six-coordinate,
rhenium(V) monomer shown in Fig. 4. Selected bond
lengths and angles are listed in Table 4.
Scheme 1.

F. Loiseau et al. / Inorganica Chimica Acta 306 (2000) 94–100
99
Scheme 2.
The compound presents two bidentate PꢀO ligands
and adopts the cis-P,P twisted arrangement with the
trans OꢁReꢀO linkage reported for ReOCl(P2ꢀO)2 [4].
The sixth site is occupied by the phenolate group of a
monodentate phosphinophenol ligand whose P atom
has oxidized to phosphine oxide.
The octahedron is severely distorted, as evidenced
from the trans angles varying from 161 to 163° (Table
4). Geometry is controlled to a large extent by the bite
of the PꢀO ligand, which imposes intra-ring PꢀReꢀO
angles of 78–80°, and by the size of the cis PPh2 units,
which opens the PꢀReꢀP angles to 101.27(4)°. The
ligands do not experience the repulsive effect of the oxo
group to the same extent. The Re atom lies at 0.275(2)
,
A from the OꢀPꢀPꢀO plane and the OꢁReꢀL angles are
Fig. 4. ORTEP drawing of ReO (P2ꢀO)2(OꢀP2ꢁO) (3). Ellipsoids
large for the negatively O donors (101.0(1) and
112.0(1)°), but close to 90° for the phosphines (92.2(1)
and 86.6(1)°). Steric crowding is also indicated by the
significant departures of the Re atom from the
OꢀCꢀCꢀP plane in the chelate rings (0.269 and 0.120
correspond to 50% probability. Hydrogens are omitted for clarity.
The monodentate phenolate group is part of a phos-
phine oxide molecule. It behaves as a simple phenolate
unit [34] by coordinating with a ReꢀO72ꢀC72 angle of
,
A), which may reflect the greater steric demand of the
,
phosphine oxide ligand.
123.2(3)°. However, the ReꢀO72 bond (2.020(3) A)
,
The ReꢁO distance of 1.679(3) A is typical of mono-
remains similar to those in the chelate rings and much
,
oxo compounds [33]. The ReꢀO12 bond (2.027(3) A),
longer than observed for a simple phenolate (ꢀ1.95
,
trans to ReꢁO, is longer than the cis ReꢀO42 bond
A). The PꢁO bond points away from the metal and
,
(1.990(3) A). This difference cannot be safely related to
does not participate in particular interactions with the
,
the trans influence of ReꢁO, because of the presence of
an highly distorted octahedron and bulky substituents
on phosphorus.
rest of the structure. The PꢁO distance (1.496(3) A) is
normal [35]. There is a small, but significant, difference
between the mean values of the O7ꢀP7ꢀC (111.0°) and
CꢀP7ꢀC angles (108.0°), and those of free OPPh3 (112.5
and 106.4°, respectively), which reflects greater crowd-
ing in the complex.
Table 4
,
Selected interatomic distances (A) and bond angles (°) in
ReO(OꢀP2ꢁO)ꢀ(P2ꢀO)2 (3)
4. Supplementary material
ReꢀP1
ReꢀP4
ReꢀO1
2.434(1)
2.460(1)
1.679(3)
ReꢀO12
ReꢀO42
ReꢀO72
2.027(3)
1.990(3)
2.020(3)
Crystallographic data (excluding structure factors)
for the structures in this paper have been deposited
with the Cambridge Crystallographic Data Centre as
supplementary publication Nos. CCDC142218 (1) and
CCDC142219 (3). Copies of the data can be obtained,
free of charge, on application to The Director, CCDC,
12 Union Road, Cambridge CB2 1EZ, UK (fax: +44-
1223-336033; e-mail: deposit@ccdc.cam.ac.uk or
www:hhttp://www.ccdc.cam.ac.uk).
P1ꢀReꢀO42
P4ꢀReꢀO72
O12ꢀReꢀO1
P1ꢀReꢀO1
P1ꢀReꢀP4
P1ꢀReꢀO12
P1ꢀReꢀO72
O1ꢀReꢀO72
161.35(10)
161.87(9)
163.01(13)
86.56(11)
101.27(4)
78.09(9)
P4ꢀReꢀO1
92.19(10)
83.80(9)
80.42(9)
83.67(12)
86.96(13)
112.02(14)
83.09(12)
P4ꢀReꢀO12
P4ꢀReꢀO42
O12ꢀReꢀO42
O12ꢀReꢀO72
O42ꢀReꢀO1
O42ꢀReꢀO72
92.00(9)
100.97(13)

100
F. Loiseau et al. / Inorganica Chimica Acta 306 (2000) 94–100
[15] A.L. Spek, PLATON, Molecular Geometry Program, University
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