Oxorhenium(V) complexes with bis-phosphinite chelating coligands (see abstract)

Article abstract of DOI:10.1016/S0277-5387(03)00334-6

The new ligand 1,2-bis(dicyclohexylphosphinite)ethane (L¹) was prepared by reaction of ethylenglycol with dicyclohexylphosphine in the presence of triethylamine. By treating this ligand with the arsine complex [ReOCl₃(AsPh₃)₂] and trituring the formed oil with methanol, the complex [ReOCl₂(OMe)L¹] (1) was isolated and its crystal structure was studied by X-ray diffractometry. The coordination sphere around the Re atom is a pseudo-octahedron. The crystal structure of the previously reported complex [ReOCl₃L²] (2) (L² = 1,2-bis[diphenylphosphinite]ethane) was solved by X-ray diffractometry. When Complex 2 was refluxed in EtOH, the oxo-alkoxide complex [ReOCl₂(EtO)L²] (3) was formed by a metathesis reaction. X-ray diffraction studies of Complex 3 show a pseudo-octahedral geometry around the Re atom with the oxo and ethoxy groups mutually trans. Finally, reaction of 2 with the monodentate phosphinite PPh₂(OEt) ligand yielded the paramagnetic Re(III) compound [ReCl₃L²{PPh₂(OEt)}] (previously reported) and the new unexpected Re(V) by-product [ReOCl₂(Ph₂POCH₂CH₂O) {PPh₂(OEt)}] (4). On the contrary, compounds 1 and 3 did not react with PPh₂(OEt) under the same conditions.

Full text of DOI:10.1016/S0277-5387(03)00334-6

Polyhedron 22 (2003) 1711Á1717
/
www.elsevier.com/locate/poly
Oxorhenium(V) complexes with bis-phosphinite chelating coligands.
The crystal structure of [ReOCl2(OMe)L1], [ReOCl3L2],
[ReOCl2(OEt)L2] and [ReOCl2{Ph2PO(CH2)2O}{PPh2(OEt)}]
[L1ꢀ
/
Cy2PO(CH2)2OPCy2, L2ꢀ
/
Ph2PO(CH2)2OPPh2]
Sandra Bolano, Jorge Bravo *, Rosa Carballo, Eduardo Freijanes *,
˜
Soledad Garc´ıa-Fonta´n, Pilar Rodr´ıguez-Seoane
Departamento de Qu´ımica Inorga´nica, Universidade de Vigo, E-36200 Vigo, Spain
Received 28 January 2003; accepted 5 May 2003
Abstract
The new ligand 1,2-bis(dicyclohexylphosphinite)ethane (L1) was prepared by reaction of ethylenglycol with dicyclohexylpho-
sphine in the presence of triethylamine. By treating this ligand with the arsine complex [ReOCl3(AsPh3)2] and trituring the formed
oil with methanol, the complex [ReOCl2(OMe)L1] (1) was isolated and its crystal structure was studied by X-ray diffractometry. The
coordination sphere around the Re atom is a pseudo-octahedron. The crystal structure of the previously reported complex
[ReOCl3L2] (2) (L2ꢀ
1,2-bis[diphenylphosphinite]ethane) was solved by X-ray diffractometry. When Complex 2 was refluxed in
/
EtOH, the oxo-alkoxide complex [ReOCl2(EtO)L2] (3) was formed by a metathesis reaction. X-ray diffraction studies of Complex 3
show a pseudo-octahedral geometry around the Re atom with the oxo and ethoxy groups mutually trans. Finally, reaction of 2 with
the monodentate phosphinite PPh2(OEt) ligand yielded the paramagnetic Re(III) compound [ReCl3L2{PPh2(OEt)}] (previously
reported) and the new unexpected Re(V) by-product [ReOCl2(Ph2POCH2CH2O){PPh2(OEt)}] (4). On the contrary, compounds 1
and 3 did not react with PPh2(OEt) under the same conditions.
# 2003 Elsevier Science Ltd. All rights reserved.
Keywords: Rhenium(V); Phosphinite ligands; Oxo-complexes; Alkoxo-complexes; Crystal structures
1. Introduction
are of current interest [8Á10], and there is an increasing
/
demand for a fundamental knowledge about the struc-
tural properties and redox and substitution ligand
reactivities to develop new, more sensitive Re pharma-
ceuticals.
The coordination chemistry of rhenium is a matter of
considerable interest. In particular, the use of 186Re and
188Re as radionuclides for the development of radio-
pharmaceuticals with therapeutic potential is being
increased due to the continuous demand for more
specific probes for targeting diseased organs in nuclear
medicine. Thus many Re compounds have been recently
synthesized and studied for radiopharmaceutical and
Following previous work on rhenium phosphinite
complexes [11,12], and with the aim of analyzing the
influence of the nature of this ligands on the reactivity of
the complex, we describe in this report the synthesis and
characterization of the new ligand Cy2POCH2-
CH2OPCy2 (L1) as well as the synthesis, characteriza-
tion and crystal structure of the new complexes
therapeutic purposes [1Á/7]. Moreover, oxorhenium(V)
compounds containing halogen and phosphine ligands
[ReOCl2(OMe)L1], [ReOCl2(OEt)L2] (L2ꢀ
1,2-bis[di-
/
phenylphosphinite]ethane), and [ReOCl2(Ph2POCH2-
CH2O){PPh2(OEt)}]. The crystal structure of the
complex [ReOCl3L2], the synthesis of which has been
previously described [11], is also reported.
* Corresponding authors. Tel.: ꢁ
2313 (E.F.).
E-mail address: erivas@uvigo.es (E. Freijanes).
/
34-986-81-2275; fax: ꢁ34-986-81-
/
0277-5387/03/$ - see front matter # 2003 Elsevier Science Ltd. All rights reserved.
doi:10.1016/S0277-5387(03)00334-6

1712
S. Bolano et al. / Polyhedron 22 (2003) 1711Á
/
1717
˜
2. Experimental
Cy), 3.48 (s, 3H, OCH3), 4.22 (m, 2H, CH2), 4.37 (m,
2H, CH2). 13C{1H} NMR (CHCl3-d, 100 MHz): dꢀ
/
2.1. Materials and instrumentation
67.4 (s, Ã
26.3Á
27.8 (m, Cy). 31P{1H} NMR (CHCl3-d, 161
MHz): dꢀ126.1 (s). Anal. Found: C, 42.73; H, 6.78.
Calc. for C27H51Cl2O4P2Re (758.22): C, 42.74; H,
6.77%. MS: m/z (referred to the most abundant
/
(CH2)2Ã
/
), 59.0 (s, OCH3), 40.2Á
/
41.0 (m, Cy),
/
All synthetic operations were performed under dry
argon. A standard vacuum system and Schlenk type
glassware were used in handling metal complexes.
Solvents were pre-dried over sodium wire or calcium
chloride before reflux and subsequent distillation, under
argon, from a suitable drying agent [13]. Deuterated
solvents for NMR measurements (Aldrich) were dried
over molecular sieves. The complex [ReOCl3(AsPh3)2]
was prepared after Michos et al. [14]. All other
commercially available reagents were used as purchased.
The IR spectra of samples in KBr pellets were
recorded on a Bruker Vector IFS28 FT spectrophot-
ometer, and NMR spectra on a Bruker AMX 400
/
isotopes): 758, [M]; 727, [MÃ
/
OCH3]; 723, [MÃ
/
Cl]; 707,
[MÃOÃCl]; 692, [MÃClÃOCH3]. The isotope patterns
/
/
/
/
match those simulated. Single crystals were obtained by
slow evaporation of an MeOH/CH2Cl2 (10:2, v/v)
solution.
2.4. Crystallization of [ReOCl3L2] (2)
This complex was synthesized as previously reported
[11]: [ReOCl3(AsPh3)2] was reacted with L2 in THF. The
addition of methanol to the formed oil produced a violet
precipitate. After dissolving the solid in a Cl2CH2/EtOH
(10:2, v/v) mixture, X-ray suitable crystals were isolated.
1
spectrometer. H and 13C{1H} signals are referred to
internal TMS, and 31P{1H} chemical shifts to 85%
H3PO4, with downfield shifts considered positive.
Mass spectra were recorded in the LSIMS, Csꢁ mode
on a Micromass Autospec M instrument. Elemental
analyses were carried out on a Fisons EA-1108 appara-
tus.
2.5. Preparation of [ReOCl2(OEt)L2] (3)
Hundred milligram of [ReOCl3L2] suspended in
ethanol (20 ml) were refluxed under Ar. After 2Á3 h a
/
2.2. Synthesis of the ligand Cy2POCH2CH2OPCy2 (L1)
change of colour (from violet to pink) was observed.
From this suspension a pink solid was filtered off and
dried in vacuo (80% yield). The same complex was
The ligand was synthesized by the method previously
reported [12]: Cy2PCl (5 g, 21 mmol) was slowly added
obtained as follows:
a
suspension of [Re-
dropwise (ca. 30 min) to a cooled (ꢂ
/
80 8C) solution of
Cl3L2{PPh2(OEt)}] (100 mg) in ethanol (15 ml) was
stirred and air-ventilated for 4 h. The solid formed was
freshly distilled Et3N (2.93 ml, 21 mmol) and ethylene
glycol (0.59 ml, 10 mmol) in 56 ml of toluene. The
solution was stirred for 2 h and the formation of the
ligand was established by the presence of a unique signal
at 150.1 ppm in the 31P{1H} spectrum. The formed
solid, [Et3NH]Cl, was filtered off.
Attempts to isolate this product (by distillation and
column chromatography) were unsuccessful due to its
unstability, as shown by the disappearance of the
characteristic signal in the 31P{1H} spectrum. So that,
a ligand solution in toluene was used for the synthesis of
the complexes, this solution being stable at room
temperature for 1 week when stored under argon.
filtered off and dried under vacuum (70% yield). IR
1
O). H NMR (CHCl3-
(KBr pellets, cmꢂ1): 910s, n(ReÄ
/
d, 400 MHz): d (ppm)ꢀ
2.13 (q, 2H, CH2 Jꢀ7.0 Hz), 4.24Á
7.57Á
8.42 (m, 20H, Ph). 13C{1H} NMR (CHCl3-d, 100
MHz): d (ppm)ꢀ135.3 (t, Co,m Ph, Jꢀ6.0 Hz), 133.2
(s, Cp Ph), 131.9 (t, Co,m Ph, Jꢀ4.8 Hz), 131.8 (s, Cp
Ph), 129.2 (t, Co,m Ph, Jꢀ5.2 Hz), 128.3 (t, Co,m Ph,
Jꢀ5.6 Hz), 66.7 (s, CH2CH2), 64.6 (s, OCH2), 14.4 (s,
CH3). 31P{1H} NMR (CHCl3-d, 161 MHz): dꢀ
104.7
/
ꢂ
/
0.16 (t, 3H, CH3 Jꢀ
/
7.0 Hz),
/
/
4.46 (m, Ã(CH2)2Ã
/
/)
/
/
/
/
/
/
/
(s). Anal. Found: C, 45.02; H, 3.80. Calc. for
C28H29Cl2O4P2Re (748.04): C, 44.92; H, 3.88%. Single
crystals were obtained by slow evaporation of an EtOH/
CH2Cl2 (10:2, v/v) solution.
2.3. Synthesis of [ReOCl2(OMe)L1] (1)
A 0.12 M solution of L1 in toluene (9.2 ml) was added
to a solution of [ReOCl3(AsPh3)2] (1 g, 1 mmol) in
tetrahydrofuran (40 ml). The resulting mixture was
refluxed under argon for 1 h. After stirring for 3 h at
room temperature and concentrating in vacuo a dark oil
was formed. This oil was tritured with methanol,
resulting in a violet precipitate that was filtered off,
2.6. X-ray crystallography
Crystallographic data were collected on a Bruker
Smart CCD diffractometer at 293 K using graphite
˚
0.71073 A) and were
monochromated Mo Ka (lꢀ
/
corrected for Lorentz and polarization effects. The
frames were integrated with the Bruker SAINT [15]
software package and the data were corrected for
absorption using the program SADABS. The structures
were solved by direct methods using the program
washed with methanol and dried under vacuum (0.46 g,
1
O). H
56% yield). IR (KBr pellets, cmꢂ1): 945s, n(ReÄ
/
NMR (CHCl3-d, 400 MHz): dꢀ
/
1.14Á2.89 (m, 44H,
/

S. Bolano et al. / Polyhedron 22 (2003) 1711Á
/
1717
1713
˜
SHELXS-97 [16]. All non-hydrogen atoms were refined
with anisotropic thermal parameters by full-matrix
least-squares calculations on F2 using the program
SHELXL-97 [17]. Hydrogen atoms were inserted at
calculated positions and constrained with isotropic
thermal parameters. Complex 1 crystallizes in the chiral
space P21, and the analysis established its absolute
stereochemistry [Flack parameter 0.004(18)]. Neutral
atom scattering factors and anomalous dispersion
corrections were taken from International Tables for
X-ray Crystallography [18]. Drawings were produced
with PLATON [19]. Crystallographic data and structure
refinement parameters are listed in Table 1.
col with dicyclohexylphosphine chloride in the presence
of triethylamine following a previously reported method
[11]. This reaction (see Section 2) yielded a toluene
solution of the ligand that was used for ulterior
reactions since any attempt to isolate the compound
resulted in its decomposition. The solution remains
unaltered for a week when stored under Ar.
The reaction of L1 with the arsine complex [ReO-
Cl3(AsPh3)2] afforded the oxo-alkoxide complex [ReO-
Cl2(OMe)L1] (1) as a result of the replacement of two
arsine ligands with the bidentate L1 ligand and of one Cl
atom with the methoxy group coming from the metha-
nol used in the breaking of the oil produced in the
reaction. This behaviour is markedly different from that
observed in a previously reported reaction [11], in which
the similar ligand 1,2-bis(diphenylphosphinite)ethane
(L2) had been used instead of L1. There, the reaction
of that ligand with the arsine complex had yielded the
oxo complex [ReOCl3L2] (2), the conversion of which
into the corresponding oxo-alkoxy complex [ReO-
Cl2(OEt)L2] (3) (see Scheme 1) required much more
3. Results and discussion
3.1. Synthesis and general properties
A new bidentate ligand, 1,2-bis(dicyclohexylphosphi-
nite)ethane (L1), was synthesized by reacting ethylengly-
Table 1
Crystal data and structure refinement parameters for the complexes 1Á4
/
1
2
3
4
Empirical formula
Formula weight
Temperature (K)
C27H51Cl2O4P2Re
758.72
293(2)
C52H48Cl6O6P4Re2
1477.88
293(2)
C28H29Cl2O4P2Re
748.55
293(2)
C28H29Cl2O4P2Re
748.55
293(2)
˚
Wavelength (A)
0.71073
monoclinic
P21
0.71073
monoclinic
P21/a
0.71073
monoclinic
P21/n
0.71073
triclinic
Crystal system
Space group
Unit cell dimensions
¯
P1
/
˚
a (A)
9.25(7)
14.25(11)
11.36(9)
90
16.9015(2)
15.559
9.650
9.724(2)
11.962(3)
13.452(4)
96.85(2)
108.268(18)
98.19(2)
1448.1(7)
2
˚
b (A)
14.0477(3)
21.8875(4)
90.0450(10)
91.8875(11)
90.0124(9)
2965.40(8)
4
˚
c (A)
22.24090(10)
90.1564(6)
110.9851(6)
89.8356(4)
5460.67(7)
4
a (8)
b (8)
g (8)
90.00(17)
90
3
˚
V (A )
1497(21)
2
Z
Dcalc (Mg mꢂ3
Absorption coefficient (mmꢂ1
F(0 0 0)
)
1.683
4.374
768
1.798
4.888
2880
1.677
4.417
1472
1.717
4.523
736
)
Crystal size (mm)
0.03ꢃ/0.05ꢃ/0.09
0.40ꢃ/0.20ꢃ/0.15
0.35ꢃ/0.20ꢃ/0.10
0.30ꢃ
/
0.10ꢃ0.05
/
u Range for data collection (8) 1.79Á
/
30.88
0.98Á28.31
/
1.72Á28.27
/
1.62Á28.28
/
Index ranges
ꢂ
/
125h 5
195k 5
125l 514
9831
/
/
12,
ꢂ
/
215h 5
205k 5
295l 528
37 097
/
/
22,
ꢂ
/
65h 512,
185k 518,
295l 529
19 878
/
/
ꢂ
/
125h 5
155k 5
175l 511
9738
/
/
12,
ꢂ
/
/
/
17,
ꢂ
/
/
/
18,
ꢂ
/
/
/
ꢂ
/
/
/
15,
ꢂ/
/
/
ꢂ/
/
/
ꢂ/
/
/
ꢂ/
/
/
Reflections collected
Independent reflections
Absorption correction
Max. and min. transmission
Refinement method
5997 [Rint
ꢀ
/
0.0824]
13 459 [Rint
ꢀ
/
0.0509]
7326 [Rint
ꢀ
/
0.0376]
6935 [Rint
ꢀ0.0350]
/
SADABS
SADABS
SADABS
SADABS
1.0000 and 0.6741
full-matrix least-squares
on F2
1.0000 and 0.4057
full-matrix least-squares
on F2
1.0000 and 0.6317
full-matrix least-squares
on F2
1.0000 and 0.5809
full-matrix least-squares
on F2
Data/restraints/parameters
Goodness-of-fit on F2
5997/1/326
0.847
13 459/0/631
0.976
7326/0/334
1.041
6935/0/334
1.022
Final R indices [I ꢀ
R indices (all data)
Largest difference peak and hole 2.098 and ꢂ
/
2s(I)]
R1ꢀ
/
0.0723, wR2ꢀ
0.1282, wR2ꢀ
1.706
/
0.1360 R1ꢀ
0.1538 R1ꢀ
1.242 and ꢂ
/
0.0361, wR2ꢀ
0.0632, wR2ꢀ
1.816
/
0.0744 R1ꢀ
0.0849 R1ꢀ
0.884 and ꢂ
/
0.0332, wR2ꢀ
0.0566, wR2ꢀ
0.702
/
0.0595 R1ꢀ
0.0667 R1ꢀ
1.862 and ꢂ
/
0.0497, wR2ꢀ
0.0754, wR2ꢀ
3.137
/
0.1046
R1ꢀ
/
/
/
/
/
/
/
/0.1164
/
/
/
/
ꢂ3
˚
(e A
)

1714
S. Bolano et al. / Polyhedron 22 (2003) 1711Á1717
/
˜
Scheme 3.
Scheme 1.
Table 2
Selected bond lengths (A) and angles (8) for the prepared complexes
˚
drastic conditions (i.e. reflux in the alcohol for several
hours).
1
2
3
4
The same Complex 3 was obtained when a suspension
of [ReCl3L2{PPh2(OEt)}] in ethanol was air-stirred at
room temperature (Scheme 2). The pink solid was
filtered off and vacuum dried. If the suspension is
stirred under inert atmosphere no reaction is observed.
Finally, it is noteworthy to point out the serendipitous
Bond lengths
Re(1)Ã
Re(1)Ã
Re(1)Ã
Re(1)Ã
Re(1)Ã
Re(1)Ã
Re(1)Ã
Re(2)Ã
Re(2)Ã
Re(2)Ã
Re(2)Ã
Re(2)Ã
Re(2)Ã
/
O(1)
1.569(14) 1.686(3)
1.717(3)
1.700(5)
/
Cl(1)
Cl(2)
Cl(3)
P(1)
2.459(16) 2.3793(12) 2.4458(10) 2.416(2)
2.518(13) 2.3872(12) 2.4619(10) 2.4455(18)
2.3835(11)
/
/
/
2.495(17) 2.4353(11) 2.4214(10) 2.438(2)
2.504(14) 2.4586(11) 2.4319(10) 2.4100(18)
isolation of the new oxoÁalkoxo complex [ReOCl2(Ph2-
/
/P(2)
/O(2)
1.722(14)
1.853(3)
1.894(4)
POCH2CH2O){PPh2(OEt)}] (4). After reducting [Re-
OCl3L2] (Complex 2) with PPh2(OEt) to yield
[ReCl3L2{PPh2(OEt)}] as reported in a previous paper
[11], from the mother liquor the unexpected Re(V)
complex was obtained as a crystal solid suitable for X-
ray diffraction (see Scheme 3). In the new P,O-donor
/
O(11)
Cl(12)
Cl(13)
Cl(11)
P(12)
P(11)
1.696(3)
/
2.3703(12)
2.3739(12)
2.3984(12)
2.4411(12)
2.4593(11)
/
/
/
/
ligand resulted from the breakage of a PÃ
/
O bond in L2,
Bond angles
O(1)ÃRe(1)Ã
O(1)ÃRe(1)Ã
Cl(1)ÃRe(1)Ã
O(1)ÃRe(1)ÃCl(3)
Cl(1)ÃRe(1)Ã
Cl(2)ÃRe(1)Ã
O(1)ÃRe(1)Ã
Cl(1)ÃRe(1)Ã
Cl(2)ÃRe(1)Ã
Cl(3)ÃRe(1)Ã
O(1)ÃRe(1)Ã
Cl(1)ÃRe(1)Ã
Cl(2)ÃRe(1)Ã
Cl(3)ÃRe(1)Ã
P(1)ÃRe(1)Ã
O(1)Ã
O(2)Ã
O(2)Ã
O(2)Ã
O(2)Ã
/
/
Cl(1)
96.3(6)
95.2(7)
94.6(5)
101.67(11) 93.53(9)
102.70(11) 94.38(9)
99.5(2)
97.57(18)
86.50(8)
a ‘pseudo-alkoxy’ character could be regarded.
This fact denotes a remarkable difference in the
reactivity of the oxo Complex 2 when compared with
/
/Cl(2)
/
/
Cl(2)
86.83(5)
163.08(11)
90.46(5)
87.63(4)
/
/
the oxoÁalkoxo complexes 1 and 3. In effect, whereas
/
/
/
Cl(3)
Cl(3)
the reduction of Re(V) oxo-chloride complexes by an
excess of phosphonite or phosphinite PPhn(OR)(3ꢂn)
/
/
89.58(5)
/
/P(1)
86.6(6)
87.98(10) 87.49(9)
85.07(19)
/
/
P(1)
P(1)
P(1)
171.22(17) 169.54(5) 178.18(4) 174.89(6)
90.79(4)
(nꢀ1, 2) ligands to form the corresponding Re(III)
/
/
/
76.9(4)
87.10(4)
80.98(4)
90.59(7)
paramagnetic complexes is well documented [11,20],
compounds 1 and 3 do not seem to react with PPh2(OEt)
under the same conditions. (All attempts lead to the
starting material.)
/
/
/
/P(2)
88.2(7)
83.0(4)
88.60(11) 95.33(9)
86.90(4) 86.33(4)
93.30(18)
87.78(7)
/
/
P(2)
P(2)
P(2)
/
/
176.02(17) 167.99(5) 168.86(4) 168.42(7)
80.24(4)
/
/
/
/
P(2)
105.4(4)
176.9(6)
87.4(7)
89.1(7)
95.6(6)
81.9(6)
97.48(4)
95.08(3) 94.34(7)
175.62(12) 167.3(2)
3.2. Crystal structures
/
ReÃ
ReÃ
ReÃ
ReÃ
ReÃ
/
O(2)
Cl(2)
P(2)
/
/
85.25(9)
85.49(9)
88.16(9)
90.81(9)
88.19(14)
/
/
81.96(14)
83.59(16)
92.12(16)
3.2.1. [ReOCl3L2] (2)
/
/
P(1)
Table 2 lists selected bond distances and angles for the
four complexes, and Fig. 1 shows a PLATON drawing of
Complex 2 with the atom numbering scheme. The
asymmetric unit consists of two [ReOCl3L2] pseudo-
octahedral entities with small structural differences
/
/
Cl(1)
and it is noteworthy that in both cases there is no
difference among the ReÃCl bond lengths despite the
trans influence of the oxo ligand. In fact, the ReÃCl
O [2.3835(11), 2.3739(12) A] are
roughly equal to ReÃClcis [2.3793(12), 2.3872(12);
/
between them. The bond lengths around both metal
˚
Cl (avg.)ꢀ2.3833 A, 2.3809
/
atoms are very similar: ReÃ
/
/
˚
bonds trans to ReÃ
/
˚
˚
A; ReÃ
2.4586(11) A; Re(2)Ã
Re(1) and Re(2), respectively. The ReÃ
the ranges reported by several authors for similar
/
Oꢀ
/
1.686(3), 1.696(3) A; Re(1)Ã
/
Pꢀ
2.4593(11), 2.4411(12) A for
Cl distances lie in
/
2.4353(11),
/
˚
˚
/
Pꢀ
/
˚
2.3703(12), 2.3984(12) A], even though the oxo group
has been reported to lengthen the opposite ReÃCl bond
in related compounds [24]. The ReÃO distances, on the
other hand, are in keeping with that expected for Re(V)
monooxo complexes showing a triple bond character,
since attempts to rationalize the bond orders [25,26]
/
/
/
˚
˚
systems (ca. 2.31Á
/
2.39 A [21Á
/
23], 2.37Á2.44 A [9,24]),
/
assign to ReÃ
/
O single, double and triple bonds the
˚
theoretical values of 2.04, 1.86 and 1.75 (or less) A,
Scheme 2.

S. Bolano et al. / Polyhedron 22 (2003) 1711Á
/
1717
1715
˜
Fig. 1. A PLATON drawing of Complex 2 with the atom numbering scheme. Ellipsoids at 30% probability.
respectively [22,27Á
/
32]. This Re-oxide bond lengths are
atom in Complex 2 by an ethoxy group results in this
new compound, which also shows a pseudo-octahedral
arrangement around the Re atom but with some
significant irregularities (see Table 2), the most remark-
comparable to that observed in many other Re mono-
oxo compounds, whereas in dioxide species they are
usually longer (close to the double bond values) which
has been regarded as a consequence of a competition in
able of which affecting the two ReÃ
markedly different as a consequence of their bond
character. In fact, the rheniumÁoxide distance
/O bond lengths,
the ReÃ
/
O p-bonding [33]. On the contrary, the ReÃ
/P
bond lengths are in our case slightly shorter than found
in other six-co-ordinated oxorhenium(V) complexes,
˚
/
˚
[1.717(3) A] denotes a certain triple bond character,
and is longer than in Complex 2 due to the competition
usually in the range 2.46Á
/
2.52 A [33Á/35]. Nevertheless,
this small difference can be related with steric con-
straints imposed by the bidentate ligand rather than
with electronic factors.
for the ReÃ
/
O p-bonding established between the oxo
O(ethoxy)
distance, 1.853(3) A, corresponds to a double bond.
On the other hand, the values of O(1)ÃReÃO(2)
P(1) [87.49(9)8] and O(1)ÃReÃ
and the alkoxy groups, whereas the ReÃ
/
˚
Regarding the bond angles, the major deviation from
/
/
a regular geometry lies in the value of the O(1)Ã
Cl(3) angle [163.08(11)8], as well as in that of both O(1)Ã
Re(1)ÃP angles [87.98(10)8 and 88.60(11)8 for P(1) and
/
Re(1)Ã
/
[175.62(12)8], O(1)Ã
P(2) [95.33(9)8] angles indicate that the oxo ligand [O(1)]
is bent towards P(1), making Cl(2) come near the ethoxy
group [O(2)Ã
ligand approaches the plane containing the P(1), P(2)
and Re atoms: O(2)ÃReÃP(1): 88.16(9)8, O(2)ÃReÃ
P(2): 85.49(9)8.
/
ReÃ
/
/
/
/
/
P(2), respectively], which confirm that the oxo ligand (in
both units) is bent towards the bidentate ligand as
occurs in other diphosphine oxocomplexes of Re(V)
[29].
/
ReÃ
/
Cl(2)ꢀ85.25(9)8]. Finally, this EtO
/
/
/
/
/
3.2.2. [ReOCl2(OEt)L2] (3)
The PLATON representation of the structure of Com-
plex 3 is shown in Fig. 2. The substitution of one Cl
3.2.3. [ReOCl2(OMe)L1] (1)
Fig. 3 shows the PLATON representation of the
molecular structure of Complex 1. The structural
parameters of this compound, when compared with
those discussed above, provide some suggestions about
the reasons why any attempt to synthesize an L1 adduct
similar to Complex 2 was unsuccessful. In fact, the
presence of Cy instead of Ph makes this phosphinite
ligand less p-acceptor and lowers the multiple character
/
in the ReÃ
/
P bond. This causes an increase in the metalÁ
ligand bond lengths [2.495(17), 2.504(14) vs. 2.4214(10),
˚
2.4319(10) A] and, therefore, a strengthening of the
internal (P-substituent) bonds in the ligand [i.e. (PÃ
/
˚
1.558(14), 1.552(15) vs. 1.609(3), 1.613(3) A].
O)ꢀ
Consequently, the Re atom in Complex 1 bears electro-
nic charge enough to result in a shortening of ReÃ
distances and a weakening of the rheniumÁchloride
/
/
O
/
bonds, so that one of the Cl is easily exchanged by an
alkoxy group, being the remaining chloro ligands more
distant from Re than in Complex 2 [2.459(16), 2.518(13)
Fig. 2. Structure of Complex 3, showing the atom-labeling scheme.
Ellipsoids at 30% probability.
˚
vs. 2.4458(10), 2.4619(10) A]. Finally, the trans influence

1716
S. Bolano et al. / Polyhedron 22 (2003) 1711Á1717
/
˜
Fig. 3. Structure of Complex 1 with the atom numbering scheme. Ellipsoids at 30% probability.
caused by the oxo ligand decides which one of the three
Cl atoms is the leaving ligand.
thought to play some role in the losing of the trans-
chloro ligand; and the new compound could be con-
sidered as arisen from Complex 3 by replacing one P
atom of the bidentate ligand and the ethoxy group by
the monodentate PPh2(OEt) ligand and the O terminal
(regarded as a ‘pseudo-alkoxy’ group) of the new P,O-
donor ligand, respectively. The major differences be-
tween both pseudo-octahedral co-ordination spheres lie
3.2.4. [ReOCl2(Ph2POCH2CH2O){PPh2(OEt)}] (4)
Reaction of 2 with the monodentate PPh2(OEt) ligand
yielded the paramagnetic Re(III) compound [Re-
Cl3L1{PPh2(OEt)}] (previously reported) and the new
unexpected Re(V) complex [ReOCl2(Ph2POCH2-
CH2O){PPh2(OEt)}] (Complex 4), which molecular
structure is shown in Fig. 4. In this complex, around
the Re atom coexist (besides one oxo and two Cl
ligands) the monodentate PPh2(OEt) ligand and a
bidentate P,O-donor ligand arised from the breakage
in the O(1)Ã
/
ReÃ
/
O(2) [167.3(2)8], O(2)Ã
/
ReÃ
/
Cl(1)
[92.12(16)8] and O(2)Ã
/
ReÃCl(2) [88.19(14)8] bond an-
/
gles as a result of the bite of the bidentate ligand [O(2)Ã
/
ReÃ
3.3. Spectroscopic studies
The IR spectra of the complexes show the ReÅ
/
P(1), 83.59(16)8].
of a PÃ
/
O bond in L2. The Re atom is six-co-ordinated,
with the two O atoms mutually in trans in competition
for the p-interaction with the metal. Consequently, the
/O
stretching band at frequencies similar to other oxorhe-
ReÃ
/
O(1) bond is weaker than in 2 [1.700(5) vs. 1.686(3)
nium(V) compounds, that is, in the range 1000Á900
/
˚
A] but considerably stronger than the ReÃ
/O(2) bond
cmꢂ1 [10,33]. This band lies at higher wave number for
Complex 1 (945 cmꢂ1) than for Complex 3 (910 cmꢂ1),
˚
[1.894(4) A]. As commented above, the oxo group is
in keeping with the different ReÃ
/
O bond lengths in both
compounds showed by the X-ray diffractometric stu-
dies.
1
Regarding the H NMR spectra, the signals of the
ethyl and methyl hydrogens of the alkoxo groups are
found at high field as occurs in other similar systems
[33], whereas the signals of the other hydrogens are
unremarkable. The 13C{1H} NMR spectra are similar to
that found previously in other rhenium(V) alkoxo
complexes. The 31P{1H} NMR spectrum of Complex 3
shows a singlet at higher field (104.7 ppm) than that of 1
(126.1 ppm). This fact is a consequence of the greater
electronic density on the P atom in the first case, as a
result of the more intense back-donor behaviour of the
Re atom (due to the Ph substituents on the L2 ligand),
that causes a stronger ReÃ
/
P bond as confirmed by the
Fig. 4. PLATON view of Complex 4 with the atom-labeling scheme.
Ellipsoids at 30% probability.
difference in the bond lengths.

S. Bolano et al. / Polyhedron 22 (2003) 1711Á
/
1717
1717
˜
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[14] D. Michos, X.-L. Luo, J.A.K. Howard, R.H. Crabtree, Inorg.
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4. Supplementary material
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC Nos. 201163 (1), 201164 (2),
201165 (3) and 201166 (4). Copies of this information
may be obtained free of charge from The Director,
CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK
[15] SMART (control) and SAINT (integration) Software. Bruker
Analytical X-ray Systems, Madison, WI, 1994.
[16] G.M. Sheldrick, SHELXS97. Program for the Solution of Crystal
Structures from X-ray Data, University of Gottingen, Germany,
¨
1997.
[17] G.M. Sheldrick, SHELXL97. Program for the Refinement of
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¨
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/
Germany, 1997.
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Financial support from Xunta de Galicia (Project
PGIDT-PX130102PR) is gratefully acknowledged. We
thank the CACTI NMR and X-ray diffraction services
(Universidade de Vigo) for recording NMR spectra and
collecting X-ray data.
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