Synthesis and structural analysis of mono-oxo Re(V) complexes with phosphino-carboxylato ligands

Article abstract of DOI:10.1016/S0020-1693(01)00374-7

[ⁿBu₄N][Re(O)Cl₄] or [Re(O)Cl₂(OEt)(PPh₃)₂] react with PCOOH (2-(diphenylphosphanyl)benzoic acid) in different stoichiometries leading to the mono-substituted complexes [ⁿBu

Full text of DOI:10.1016/S0020-1693(01)00374-7

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Inorganica Chimica Acta 315 (2001) 213–219
Synthesis and structural analysis of mono-oxo Re(V) complexes
with phosphino-carboxylato ligands
a
a
a,
b
.
Joa˜o D.G. Correia , Angela Domingos , Isabel Santos *, Cristina Bolzati ,
Fiorenzo Refosco c, Francesco Tisato c
a Departamento de Qu´ımica, Instituto Tecnolo´gico e Nuclear, Estrada Nacional 10, 2686-953 Saca6e´m Codex, Portugal
b Laboratorio di Medicina Nucleare, Dipartimento di Medicina Clinica e Sperimentale, Uni6ersita` di Ferrara, Via Borsari 46,
44100 Ferrara, Italy
c ICTIMA, CNR, Corso Stati Uniti, 4, 35127 Pado6a, Italy
Received 6 November 2000; accepted 31 January 2001
Abstract
[nBu4N][Re(O)Cl4] or [Re(O)Cl2(OEt)(PPh3)2] react with PCOOH (2-(diphenylphosphanyl)benzoic acid) in different stoi-
chiometries leading to the mono-substituted complexes [nBu4N][Re(O)Cl3(PCOO)] (2) and [Re(O)Cl2(PCOO)(PPh3)] (5), respec-
tively. In CH2Cl2–MeOH,
2
rearranges partially into the neutral [Re(O)Cl2(PCOO)(MeOH)] (3). The mixed
[Re(O)(OCH2CH2O)(PCOO)(MeOH)] (4) is obtained by reacting [nBu4N][Re(O)Cl4], ethylene glycol and PCOOH. The [PCOO]−
ligand is bidentate and the coordination geometry around rhenium is distorted octahedral, as shown by the X-ray structural
analysis of 2 and 3. In these complexes the phosphorus and the oxygen atoms of the phosphino-carboxylato ligand occupy an
equatorial and an axial position, respectively. © 2001 Elsevier Science B.V. All rights reserved.
Keywords: Oxo complexes; Phosphino-carboxylato complexes; Rhenium complexes; Crystal structures
1. Introduction
asymmetric positions in a distorted octahedral environ-
ment with mutual cis-P,P and cis-X,X configurations
(Scheme 2).
However, careful control of the ligand to metal ratio
allowed the isolation of a mono-substituted compound
[ReOCl3(PO)]− (1), in which the phosphino-phenolato
Previous investigations using some of the functional-
ized phosphines depicted in Scheme 1 have demon-
strated the efficacy of such chelate ligands towards both
reduction of the [MVIIO4]− salts (M=Tc, Re) and
coordination to the metal centers, producing complexes
of variable stoichiometry depending on the nature of
the functional group introduced in the tertiary phos-
phine framework [1–8].
Besides tris-substituted [MIII(PX)3] neutral com-
pounds (A) [1,3], various partially reduced oxo-MV
species have been prepared. When PNH2 and POH
ligands were utilized, the complexes were usually bis-
substituted with general formulae [MVO(PX)2Y] (B)
(Y=monodentate group such as halide) [2,5,7]. The
two phosphines act as bidentate ligands and occupy
Scheme 1.
* Corresponding author. Tel.: +351-21-994 6201; fax: +351-21-
994 1455.
E-mail address: isantos@itn1.itn.pt (I. Santos).
Scheme 2.
0020-1693/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0020-1693(01)00374-7

214
J.D.G. Correia et al. / Inorganica Chimica Acta 315 (2001) 213–219
fragment spans an equatorial position (P) and the
apical site (O) trans to the oxo group (Scheme 2),
thereby producing a quasi-linear OꢀRe–O stick [7].
This geometry allows delocalization of the electron
density of the oxo oxygen and the generation of a
substitution-inert [Re(O)(h2-PO)] moiety. On the other
hand, the halide groups in 1 are substitution-labile and
they can be readily replaced by incoming ligands of
superior denticity. Hence, a class of oxo-Re(V) mixed
ligand complexes of general formula [Re(O)(h2-
PO)(SNS)] (SNS=tridentate aminedithiolato), have
been synthesized [9,10]. Attempts to transfer this
‘mixed-ligand’ approach at ‘non-carrier added’ level
utilizing the 99mTc isomer have met severe obstacles so
far owing to the difficulty to isolate mono-substituted
P, O species. In fact, the excess of ligand utilized during
these nanomolar preparations always promotes the for-
mation of bis-substituted 99mTcV and homoleptic tris-
substituted 99mTcIII species [8]. On going from five-
membered chelate rings typical of the phosphino-phe-
nolato fragment to six-membered chelate rings arising
from the coordination of the phosphino-carboxylato
ligand (PCOOH) we have observed an increasing ten-
dency to form mono-substituted compounds. Aiming at
the elucidation of this behavior we have investigated in
detail the reactivity of labile oxo-rhenium(V) precursors
with the potentially bidentate (2-diphenylphos-
phanyl)benzoic acid ligand (PCOOH). A series of
mono-substituted oxo-rhenium(V) 2–5 have been pre-
pared and characterized by means of the usual physico-
chemical techniques including X-ray crystal structure
analysis of the representative anionic [Re(O)Cl3-
(PCOO)]− (2) and neutral [ReOCl2(PCOO)(MeOH)] (3)
complexes.
2.2. Preparation of the rhenium complexes
2.2.1. [nBu4N][Re(O)Cl3(PCOO)] (2)
Solid PCOOH (0.050 g, 0.16 mmol) was added under
stirring at room temperature (r.t.) to a pale-green solu-
tion of [nBu4N][Re(O)Cl4] (0.081 g, 0.14 mmol) in
EtOH (20 cm3). The mixture turned blue and after 15
min deposited a turquoise solid, which was filtered off,
washed with ethanol (1 cm3), ether (10 cm3) and dried
under vacuum. The product is soluble in CH2Cl2,
CHCl3, Me2CO, insoluble in alcohols and Et2O. Green
crystals, suitable for X-ray diffraction analysis were
obtained by recrystallization from dichloromethane–
methanol. Yield 0.110
g (93%). Anal. Calc. for
C35H50Cl3NO3PRe: C, 49.1; H, 5.9; N, 1.4. Found: C,
49.6; H, 5.9; N, 1.5%. IR (cm−1): 2962, 2874, w(C–
Haliphatic); 1651, w(CꢀO); 983, w(ReꢀO). 1H NMR
(CDCl3): l 0.87 (t, 12H), 1.26 (q, 8H), 1.56 (m, 8H) and
3.16 (m, 8H) [CH3–CH2–CH2–CH2]4–N; 6.92 (m,
1H), 7.36–7.66 (12H) 8.19 (m, 1H), [(C6H5)2–P–
C6H4–COO]. 31P{1H} NMR (CDCl3): l −22.8 (s).
2.2.2. [Re(O)Cl2(PCOO)(MeOH)] (3)
During recrystallization of complex 2, a small
amount of light blue crystals corresponding to complex
3 were obtained. The complex was only characterized
by X-ray diffraction analysis.
2.2.3. [Re(O)(eg)(PCOO)(MeOH)] (4)
To a MeOH (20 cm3) solution of [nBu4N][Re(O)Cl4]
(0.140 g, 0.24 mmol) are added ethylene glycol (eg)
(0.054 cm3, 0.96 mmol) and 1 M sodium acetate in
MeOH (0.96 cm3, 0.96 mmol). Solid PCOOH (0.073 g,
0.24 mmol) is added to the brown colored solution,
which quickly turns violet. After stirring for 1 h, during
which the color remained unchanged, the mixture was
taken to dryness under a gentle stream of nitrogen. To
the resulting violet oil, water is added (4×3 cm3
aliquots), and the resulting precipitate is dried under
P2O5. The compound is soluble in MeOH, EtOH,
MeCN, CH2Cl2, CHCl3, insoluble in Et2O and hydro-
carbons. Recrystallization by slow evaporation in
MeOH gave, after 1 day, a violet crystalline powder.
Yield 0.130 g (89%). Anal. Found: C, 44.3; H, 3.8. Calc.
for C22H22O6PRe: C, 44.1; H, 3.7%. IR (cm−1): 2914,
2. Experimental
2.1. General
All chemicals were of reagent grade. 2-
(Diphenylphosphanyl)benzoic acid and the complexes
[nBu4N][Re(O)Cl4] and [Re(O)Cl2(EtO)(PPh3)2] were
prepared as reported in the literature [11–13]. The
1
reactions were run in air unless otherwise indicated. H
and 31P NMR spectra were recorded on a Varian Unity
2818, w(C–Haliphatic); 1634, w(CꢀO); 946, w(ReꢀO). H
1
1
300 MHz spectrometer; H chemical shifts were refer-
NMR (CDCl3): l 2.69 (s, 3H; CH3OH), 4.43 (m, 2H)
and 4.85 (m, 2H) [O–CH2–CH2–O], 7.31–7.75 (14 H)
[(C6H5)2–P–C6H4–COO]. 31P{1H} NMR (CDCl3): l
−1.3 (s).
enced with the residual solvent resonance relative to
tetramethylsilane and the 31P chemical shifts were mea-
sured with external 85% H3PO4 solution as reference.
Chemical shifts are given in ppm. The NMR samples
were prepared in CDCl3. Infrared (IR) spectra were
recorded in the range 4000–400 cm−1 on a Perkin–
Elmer 577 spectrometer using KBr pellets. Elemental
analyses were performed on a Fisons EA1108 elemental
analyzer.
2.2.4. [Re(O)Cl2(PCOO)(PPh3)] (5)
To a suspension of [Re(O)Cl2(EtO)(PPh3)2] (0.102 g,
0.12 mmol) in EtOH (15 cm3) solid PCOOH (0.037 g,
0.12 mmol) is added. The mixture is refluxed for 2 h
during which the color of the suspended solid changes

J.D.G. Correia et al. / Inorganica Chimica Acta 315 (2001) 213–219
215
Table 1
2.3. X-ray structural determination
Crystallographic data for 2 and 3
A green crystal of 2 and a blue crystal of 3 were
mounted in thin-walled glass capillaries. The crystals
were mounted in nujol and fixed inside the capillaries in
solvent atmosphere to avoid loss of crystallinity, mainly
for 2. The relevant crystal data and structural parame-
ters of the two complexes are summarized in Tables
1–3. Data were collected at r.t. on an Enraf–Nonius
CAD4-diffractometer with graphite-monochromatized
Mo Ka radiation, using a ꢀ–2q scan mode. Unit cell
dimensions were obtained by least-squares refinement
of the setting angles of 25 reflections with 15.8B2qB
23.8° for 2 and 15.0B2qB19.2° for 3. Data were
corrected [14] for Lorentz and polarization effects, for
linear decay (for 2) and for absorption by empirical
corrections based on c scans. The heavy atom posi-
tions were located by Patterson methods using SHELXS-
86 [15]. The remaining atoms were located by sucessive
difference Fourier maps and refined by least-squares
refinements on F2 using SHELXL-93 [16]. One methanol
and an half-methanol disordered molecules of crystal-
lization were also located in the Fourier difference map
for 2 and 3, respectively. All the non-hydrogen atoms
(except the solvent methanol atoms in 3) were refined
with anisotropic thermal motion parameters and the
contribution of the hydrogen atoms were included in
calculated positions (except those of the solvent in 2
and of the OH groups in the methanol molecules in 3).
2
3
Empirical formula
C
35H50Cl3NO3-
C20H18Cl2O4PRe·
0.5CH3OH
626.43
triclinic
P1
PRe·CH3OH
888.32
monoclinic
P21/n
Formula weight
Crystal system
Space group
(
Unit cell dimensions
,
a (A)
9.727(1)
26.741(3)
17.784(2)
9.835(2)
11.840(2)
19.540(3)
83.25(1)
82.81(1)
81.18(2)
2219.5(7)
4
,
b (A)
,
c (A)
h (°)
i (°)
k (°)
97.829(9)
3
,
V (A )
Z
4582.8(8)
4
1.288
Dcalc (g cm−3
)
1.875
Crystal size (mm)
v (mm−1
2q Range (°)
0.52×0.20×0.16 0.45×0.23×0.18
2.893
3.0–52.0
)
5.814
3.0–56.0
10 930
No. of measured reflections 7372
No. of independent 6936 (0.0692)
reflections (Rint
No. of observed [I\2|(I)] 3683
10622 (0.0337)
)
7378
526
0.0560
0.1153
1.055
No. of parameters
405
aR1
0.0762
0.1567
1.065
bwR2
Goodness-of-fit
a R1=ꢀꢁꢁFoꢁꢁ−ꢁFcꢁꢁ/ꢀꢁFoꢁ.
b wR2=[ꢀ(w(Fo2−Fc2)2)/ꢀ(w(Fo2)2)]1/2
;
w=1/[|2(Fo2)+(aP)2+
bP], where P=(Fo2+2Fc2)/3.
Table 2
Table 3
,
Selected bond lengths (A) and angles (°) for 2
,
Selected bond lengths (A) and angles (°) for 3
Re–O(1)
Re–O(2)
Re–P
1.64(1)
2.03(1)
2.421(4)
1.32(2)
Re–Cl(1)
Re–Cl(2)
Re–Cl(3)
C(1)–O(3)
2.377(4)
2.364(5)
2.379(5)
1.21(2)
Molecule 1
Molecule 2
Re(1)–O(1)
Re(1)–O(2)
Re(1)–O(4)
Re(1)–Cl(1)
Re(1)–Cl(2)
Re(1)–P(1)
O(2)–C(2)
C(2)–O(3)
1.670(6)
2.035(6)
2.098(7)
2.381(3)
2.348(3)
2.400(2)
1.31(1)
Re(2)–O(1A)
Re(2)–O(2A)
Re(2)–O(4A)
Re(2)–Cl(3)
Re(2)–Cl(4)
Re(2)–P(2)
1.654(7)
2.048(6)
2.088(6)
2.363(3)
2.364(3)
2.403(2)
1.28(1)
O(2)–C(1)
O(1)–Re–O(2)
O(1)–Re–Cl(1)
O(1)–ReCl(2)
O(1)–Re–Cl(3)
O(1)–Re–P
O(2)–Re–Cl(1)
O(2)–Re–Cl(2)
O(2)–Re–Cl(3)
167.0(5)
94.9(4)
96.7(4)
103.7(4)
91.2(4)
86.4(3)
83.4(3)
89.4(3)
O(2)–Re–P
75.8(3)
167.4(2)
85.6(2)
89.9(1)
86.8(2)
94.8(2)
164.7(2)
Cl(1)–Re–Cl(2)
Cl(1)–Re–Cl(3)
Cl(1)–Re–P
Cl(2)–Re–Cl(3)
Cl(2)–Re–P
O(2A)–C(2A)
C(2A)–O(3A)
1.24(1)
1.23(1)
Cl(3)–Re–P
O(1)–Re(1)–O(2)
O(1)–Re(1)–O(4)
O(1)–Re(1)–Cl(1)
O(1)–Re(1)–Cl(2)
O(1)–Re(1)–P(1)
O(2)–Re(1)–O(4)
O(2)–Re(1)–Cl(1)
O(2)–Re(1)–Cl(2)
O(2)–Re(1)–P(1)
O(4)–Re(1)–Cl(1)
O(4)–Re(1)–Cl(2)
O(4)–Re(1)–P(1)
168.2(3)
102.5(3)
94.8(3)
98.2(3)
91.1(3)
89.2(3)
84.4(2)
83.9(2)
77.2(2)
89.8(2)
82.1(2)
166.3(2)
O(1A)–Re(2)–O(2A)
O(1A)–Re(2)–O(4A)
O(1A)–Re(2)–Cl(3)
O(1A)–Re(2)–Cl(4)
O(1A)–Re(2)–P(2)
O(2A)–Re(2)–O(4A)
O(2A)–Re(2)–Cl(3)
O(2A)–Re(2)–Cl(4)
O(2A)–Re(2)–P(2)
O(4A)–Re(2)–Cl(3)
O(4A)–Re(2)–Cl(4)
O(4A)–Re(2)–P(2)
Cl(3)–Re(2)–Cl(4)
Cl(3)–Re(2)–P(2)
168.0(3)
104.9(3)
97.2(3)
97.0(3)
91.6(3)
87.0(3)
84.7(2)
82.8(2)
76.7(2)
87.6(2)
82.1(3)
163.3(3)
164.2(1)
87.57(9)
98.92(9)
from green–brown to light-green. The precipitate is
filtered off and washed with EtOH (4×1 cm3 aliquots)
and dried under vacuum. The product is soluble in
CH2Cl2, CHCl3, insoluble in MeOH, EtOH, MeCN,
Et2O and hydrocarbons. Yield 0.096 g (95%). Anal.
Found: C, 53.2; H, 3.4. Calc. for C37H29O3P2Cl2Re: C,
52.9; H, 3.5%. IR (cm−1): 1667, w(CꢀO); 977, w(ReꢀO).
1H NMR (CDCl3): l 7.15–8.26 [(C6H5)2–P–C6H4–
COO]. 31P{1H} NMR (CDCl3): l 2.2 (d) and −17.6
Cl(1)–Re(1)–Cl(2) 165.9(1)
Cl(1)–Re(1)–P(1)
Cl(2)–Re(1)–P(1)
90.58(9)
94.55(9)
Cl(4)–Re(2)–P(2)
2
(d), JPP=332 Hz.

216
J.D.G. Correia et al. / Inorganica Chimica Acta 315 (2001) 213–219
Scheme 3. (i) EtOH, r.t.; (ii) NaOAc, MeOH, ethylene glycol, r.t.; (iii) CH2Cl2–MeOH.
The final difference-Fourier synthesis was featureless
diethyl ether and hydrocarbons. Complexes 2–5 are air
for 2, and revealed residual electron densities between
and moisture stable.
−3
,
2.57 and −2.05 e A
for 3, near the heavy atoms.
Atomic scattering factors and anomalous dispersion
terms were taken as in Ref. [16]. The drawings were
made with ORTEPII [17] and all the calculations were
performed on a DEC a 3000 computer.
3.2. Characterization
The characterization of 2, 4 and 5 has been done by
elemental analysis, IR, H and 31P NMR spectroscopy,
1
and by X-ray crystallographic analysis in the case of 2.
Complex 3 was only characterized by X-ray diffraction
analysis.
3. Results and discussion
The IR spectra of compounds 2, 4 and 5 display the
characteristic bands of PCOOH, namely the C–H and
C–C out-of-plane bending vibrations in mono-substi-
tuted benzene rings (in the 690–750 cm−1 region) and
the w(CꢀO) stretching vibrations of the carboxylato
group (2, 1651 cm−1; 4, 1634 cm−1; 5, 1667 cm−1).
The w(CꢀO) vibrations are significantly shifted and
lower in energy, with respect to the free ligand (1690
cm−1), indicating co-ordination of the chelate. The
values found for w(CꢀO) in 2, 4 and 5 compare well
with the value found for the same vibration in the
complex [Re(O)(h3-PNO)(h2-PCOO)] and [Tc(h2-
PCOO)3] [3,19]. The IR spectra of 2, 4 and 5 exhibit
also characteristic w(ReꢀO) stretching bands at 983, 946
and 977 cm−1, respectively, which are in the range
reported for similar mono-oxorhenium complexes
(945–1067 cm−1) [18].
3.1. Synthesis
The new mono-anionic trichlorooxorhenium(V) com-
plex 2 was obtained in high yield by reaction of
[nBu4N][Re(O)Cl4] with (2-diphenylphosphanyl) benzoic
acid (PCOOH) in ethanol at r.t. The same mono-substi-
tuted complex 2 is obtained by using a threefold molar
excess of PCOOH ligand and/or refluxing the reaction
mixture for hours. This compound is soluble in chlori-
nated solvents and insoluble in alcohols. Complex 2
was recrystallized from a mixture of CH2Cl2–MeOH,
yielding green crystals suitable for X-ray crystallo-
graphic analysis. During recrystallization of 2 some
blue crystals appeared, which were identified by X-ray
as the neutral mono-oxo complex 3 (Scheme 3). The
formation of 3 results from the replacement of a chlo-
ride atom by a methanol molecule, with formation of
[nBu4N]Cl. The ‘mixed ligand’ oxocomplex 4 is ob-
tained in high yield by reacting [nBu4N][Re(O)Cl4] with
PCOOH and ethylene glycol (1:1:4 molar ratio) in the
presence of a base (NaOAc) (Scheme 3). Complex 4 is
a violet crystalline solid soluble in chlorinated solvents
and in alcohols but insoluble in diethyl ether and
hydrocarbons.
The 31P NMR spectra of complexes 2 and 4 show
one singlet at l −22.8 and −1.3, respectively. The 31P
NMR spectrum of 5 presents two doublets at l 2.2 and
2
−17.6 ppm, with a JPP coupling constant of 332 Hz,
which indicates the magnetic unequivalence of the two
The neutral mono-oxo complex 5 was obtained as a
light-green solid in high yield by refluxing
[Re(O)Cl2(EtO)(PPh3)2] with PCOOH in EtOH, at a 1:1
molar ratio (Scheme 4). Complex 5 is soluble in chlori-
nated solvents and insoluble in alcohols, acetonitrile,
Scheme 4. (i) EtOH, reflux.

J.D.G. Correia et al. / Inorganica Chimica Acta 315 (2001) 213–219
217
of the anchor function inserted in the phosphine
chelate. As sketched in Scheme 5, phenolato- and car-
boxylato-oxygen are located trans to the oxo group in
complexes 5 and 6, whereas the phosphine-amido nitro-
gen prefers an equatorial site [21], cis-oriented with
respect to the oxo group in complex 7. Also, the mutual
phosphine phosphorus donors, which invariably occupy
an equatorial site, show different orientations. As indi-
Scheme 5.
2
cated by the magnitude of the JPP coupling constant,
the magnetically unequivalent P are trans-positioned
only in the phosphino-carboxylato complex 5, whereas
they assume a cis-orientation in phosphino-phenolato
and phosphino-amido complexes 6 and 7.
While the coordination of the phosphine anchor
groups appear to be governed primarily by electronic
factors through the formation of strong [OꢀRe–O] (in 5
and 6) and [P–Re–N] (in 7) sticks, steric factors seem
to play a determining role for the mutual phosphine
phosphorus orientation. In fact, when five-membered
chelate rings are involved in coordination (complexes 6
and 7), a cis-P configuration warrants an additional
stabilization resulting from the p-stacking interaction of
two facing phenyl rings [22]. Such stabilization is not
active when the chelate ring increases from five- to
six-membered, thereby favoring the more common
trans-P configuration.
Fig. 1. An ORTEP view of the anionic complex 2, with thermal
ellipsoids drawn at the 35% probability level. Hydrogen atoms are
omitted for clarity.
trans-positioned phosphorus atoms (Scheme 4) [20].
The resonances at −17.6 and 2.2 ppm were assigned to
the phosphorus atom of the [h2-PCOO]− ligand and of
the PPh3, respectively, by comparison with the spec-
trum of 2. The 31P signal of the phosphino-carboxylato
in 2 and 5 is significantly high field shifted (Z=18.8
ppm, 2; 13.6 ppm, 5) compared with the value found
for this resonance in the free PCOOH (−4.0 ppm).
Contrasting behavior was shown by complex 4, which
presents a 31P resonance low field shifted (Z=2.7 ppm)
relatively to the free phosphino-carboxylic ligand.
These results seem to indicate that [h2-PCOO]− is a
better donor in 4 than in 2 and 5, where it seems to
behave as a better acceptor. This trend agrees with the
shift observed for the w(CꢀO) vibration which presents
a higher decrease in energy for 4 (Z=56 cm−1) than
for 2 (Z=39 cm−1) and 5 (Z=23 cm−1). The
w(ReꢀO) stretching vibration in 4 is also significantly
lower in energy than the values observed for 2 (Z=37
cm−1) and 5 (Z=31 cm−1), and the value found is
typical of compounds with alkoxo groups coordinated
trans to the oxo moiety [2]. All these data indicate that
the acidity of the [ReꢀO]3+ moiety in 2 and 5 is higher
than in 4 and also that in this complex there is a higher
electron density along the ReꢀO axis. The spectroscopic
data obtained for all the compounds as well as the
X-ray structural analysis of 2 and 3 were the basis for
the stereochemistry proposed for 4 and 5 and are
depicted in Schemes 3 and 4.
3.2.1. Crystal structures of
[nBu4N][Re(O)Cl3(p2-PCOO)] (2) and
[Re(O)Cl2(p2-PCOO)(MeOH)] (3)
The structure of 2 consists of discrete monomeric
[N(nBu)4] cations and [Re(O)Cl3(h2-PCOO)] anions.
Complex 3 crystallizes from a mixture of CH2Cl2–
MeOH as monomers with two independent molecules
in the asymmetric unit. ORTEP views of the anion of 2
and of molecule 1 of complex 3 are shown in Figs. 1
and 2, respectively.
Tables 2 and 3 present the selected bond distances
and angles, respectively, for 2 and for molecules 1 and
2 of 3. For both compounds the coordination geometry
around the six-co-ordinate ReV atom is distorted octa-
hedral. The axial positions in 2 and 3 are occupied by
the oxo group and by one oxygen atom of the carboxy-
late group of the [h2-PCOO]− ligand. The equatorial
positions are defined by the phosphorus and the three
chloride atoms in 2 and by the phosphorus, two chlo-
ride atoms and a methanol molecule in 3.
In 2 the distortion from the regular octahedral is
mainly seen by the value found for the angles O(2)–
Re–P (75.8(3)°) and O(1)–Re–O(2) (167.0(5)°). The Re
,
atom in 2 is 0.27 A deviated from the mean least-
squares equatorial plane, [P–Cl(1)–Cl(2)–Cl(3)], to-
wards the axial O(1) atom. For molecules 1 and 2 of 3
the distortion from the regular octahedral geometry is
comparable: O(2)–Re(1)–P(1) and O(2A)–Re(2)–P(2)
angles of 77.2(2) and 76.7(2)°; the bent axial O(1)–
It is interesting to note the different stereochemistry
exhibited by 5-type complexes, depending on the nature

218
J.D.G. Correia et al. / Inorganica Chimica Acta 315 (2001) 213–219
,
The Re–Ooxo bond distances in 2 (1.64(1) A) and 3
Re(1)–O(2) and O(1A)–Re(2)–O(2A) angles of
168.2(3) and 168.0(3)° for molecules 1 and 2, respec-
tively; the Re(1) and the Re(2) atoms are, respectively,
,
(average, 1.662(6) A) are comparable and are at the
,
range (1.65–1.70 A) so far observed for other six-coor-
dinated oxocompounds [18]. However, the value found
for the anionic compound 2 is at the lower end of this
range, and is slightly shorter than the corresponding
,
0.26 and 0.30 A out of the mean equatorial plane
towards the axial O(1) and O(1A) atoms. The previ-
ously described [NBu4][ReOCl3(PO)], in which the
phosphino-phenolato ligand also adopts a meridional
configuration and forms a five-membered chelate ring,
presents a distortion from the regular polyhedron com-
,
value 1.669(6)
A
found in the analogous
[Re(O)Cl3(PO)]− [PO=(phosphino-phenolate]. This
difference is certainly related to the nature of the phos-
phino-carboxylate ligand, that acting as a weaker
donor, transfers less electron density to the metal than
the phosphino-phenolate. The Re–Ocarboxylate bond dis-
,
parable to what we observed for 2 and 3 (Re is 0.25 A
out of the mean equatorial plane; non-linear Ooxo–Re–
O axis, 163.6(3); O–Re–P, 76.1(2)) [7]. Apparently, the
presence of six-membered chelate rings in 2 and 3 does
not affect significantly the bond angles around the
metal center as well as the displacement of the metal
from the equatorial plane, showing wider Re–O–C and
Re–P–C ring angles than in the above mentioned
[ReOCl3(PO)] anion, much likely due the greater flexi-
bility of the chelate rings. In 2 the PC3O chelate ring
show significant deviations from planarity (atomic devi-
,
,
tances in 2 (2.04(1) A) and 3 (average, 2.042(6) A) are
comparable but are longer and shorter than the Re–
,
,
Ophenolate (2.016(6) A) and Re–Ocarboxylate (2.100(4) A)
bond distances found in [Re(O)Cl3(PO)]− and
[Re(O)(h3-PNO)(h2-PCOO)]−,
respectively
[7,19].
These differences are due to the nature of the coordi-
nating group and to the presence of co-ligands with
different electronic and steric properties.
,
The Re–P bond length in 2 (2.421(4) A) compares
,
ations in the range −0.113 to 0.118 A) as well as the
well with the value found in the anionic
corresponding RePC3O ring. For 3, the six-membered
rings are non-planar in both molecules. The P(1)C3O
ring of one of the two independent molecules is planar
[Re(O)Cl3(PO)]− (2.422(2) A) but is longer than the
,
,
Re–P bond length in 3 (average, 2.402(2) A). The
shorter distance in 3 is related to the lower trans effect
of MeOH relatively to chloride. This effect compares
with what was observed for the homoleptic [Tc(h2-
PCOO)3], in which the Tc–P bond trans to oxygen
atoms is shorter than the Tc–P bonds trans to other p
accepting ligands [3]. The Re–Cl bond distances in 2
,
(atomic deviations B0.007 A), which leads to a folding
of the corresponding Re(1)PC3O ring about the
O(2)···P(1) axis of 39.9°. This difference between the
two independent molecules is more likely a result of the
packing of the molecules in the lattice. In the related
[Re(O)Cl3(PO)]−, the ligand P–C–C–O is planar and
the Re–P–C–C–O ring displays an envelope
configuration.
,
,
(average, 2.373(5) A) and 3 (average, 2.364(3) A) are
comparable with those in the related [Re(O)Cl3(PO)]−
,
[average, 2.380(3) A].
A comparison of bond lengths and angles is difficult
since only a few related compounds are available:
[Re(O)Cl3(PO)]−, [Re(O)(h3-PNO)(h2-PCOO)]− and
the homoleptic [Tc(h2-PCOO)3], in which the metal is
in a lower oxidation state [3,7,19].
4. Concluding remarks
In this work we have described novel and stable
monosubstituted oxorhenium complexes 2–5, which are
the only species formed even when an excess of the
phosphino-carboxylato ligand (PCOOH) is used. The
tendency to form this type of compound is different
from what has been observed with the phosphino-phe-
nolato and can be related to the presence of the six-
membered chelate ring, arising from the coordination
of the phosphino-carboxylato ligand. These results are
promising for further studies at the ‘non-carrier added
level’, where an excess of ligand is normally used.
5. Supplementary material
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC Nos. 155580 for complex 2 and
155581 for complex 3. Copies of this information may
Fig. 2. An ORTEP drawing of molecule 1 of complex 3, with thermal
ellipsoids at the 35% probability level. Hydrogen atoms are omitted
for clarity.

J.D.G. Correia et al. / Inorganica Chimica Acta 315 (2001) 213–219
219
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