Rhenium(I) methoxo carbonyl complexes containing tetraphosphine or triphosphine ligands; Facile separation and X-ray crystallographic studies of d/l- and meso-[{Re2(μ-OMe)2(CO)6} 2(μ,μ′-1,1,4,7,10,10-hexaphenyl-1,4,7,10-tetra- phosphadecane)]

Article abstract of DOI:10.1016/S0022-328X(99)00442-8

Reaction of the activated mixture of Re₂(CO)_10, Me₃NO and MeOH with a 1:1 mixture of rac (d/l)- and meso-1,1,4,7,10,10-hexaphenyl-1,4,7,10-tetraphosphadecane (hptpd) yields a mixture of (d/l)- and meso-[{Re₂(μ-OMe)₂(CO)₆} ₂(μ,μ′-hptpd)] 1. The diastereomers can be easily separated by selective dissolution of d/l-1 in benzene, and give clearly distinguishable ¹H- and ³¹P-NMR spectra. The fluxional behavior of d/l-1 in solution has been studied by variable-temperature ¹H- and ³¹P-{¹H}-NMR spectroscopy. The crystal structures of both d/l- and meso-1 have been determined. Both molecules consist of two {Re₂(μ-OMe)₂(CO)₆} moieties which are bridged by the two P-CH₂-CH₂-P moieties of the hptpd ligand. Whilst the molecules of meso-1 possess crystallographic i-symmetry, those of d/l-1 do not have any crystallographic symmetry. These diastereomers therefore give clearly distinguishable Raman spectra in the solid state. Reaction of tris[2-(diphenylphosphino)ethyl]phosphine (tdppep) with the activated mixture affords the complex [{Re₂(μ-OMe)₂(CO)₆}(μ,η ²-tdppep)] 2, and the analogous reaction involving bis[2-diphenylphospinoethyl)phenylphosphine (triphos) gives [{Re₂(μ-OMe)₂(CO) ₆}(μ,μ′,η³-triphos){Re ₂(CO)₉}] 3 and [{Re₂(μ-OMe)₂(CO)₆}(μ,η ²-triphos)] 4.

Full text of DOI:10.1016/S0022-328X(99)00442-8

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 590 (1999) 138–148
Rhenium(I) methoxo carbonyl complexes containing
tetraphosphine or triphosphine ligands; facile separation and X-ray
crystallographic studies of d/l- and meso-[{Re2(m-OMe)2-
(CO)6}2(m,m%-1,1,4,7,10,10-hexaphenyl-1,4,7,10-tetra-phosphadecane)]
Chenghua Jiang a, Yuh-Sheng Wen b, Ling-Kang Liu b, T.S. Andy Hor a,1,
Yaw Kai Yan c,*
a Department of Chemistry, Faculty of Science, National Uni6ersity of Singapore, Kent Ridge, Singapore 119260, Singapore
b Institute of Chemistry, Academia Sinica, Taipei 11529, Taiwan
c Di6ision of Chemistry, National Institute of Education, Nanyang Technological Uni6ersity, 469 Bukit Timah Road, Singapore 259756, Singapore
Received 22 June 1999; accepted 26 July 1999
Abstract
Reaction of the activated mixture of Re2(CO)10, Me3NO and MeOH with a 1:1 mixture of rac (d/l)- and meso-1,1,4,7,10,10-
hexaphenyl-1,4,7,10-tetraphosphadecane (hptpd) yields a mixture of (d/l)- and meso-[{Re2(m-OMe)2(CO)6}2(m,m%-hptpd)] 1. The
diastereomers can be easily separated by selective dissolution of d/l-1 in benzene, and give clearly distinguishable 1H- and
1
31P-NMR spectra. The fluxional behavior of d/l-1 in solution has been studied by variable-temperature H- and 31P-{1H}-NMR
spectroscopy. The crystal structures of both d/l- and meso-1 have been determined. Both molecules consist of two {Re2(m-
OMe)2(CO)6} moieties which are bridged by the two PꢀCH2ꢀCH2ꢀP moieties of the hptpd ligand. Whilst the molecules of meso-1
possess crystallographic i-symmetry, those of d/l-1 do not have any crystallographic symmetry. These diastereomers therefore give
clearly distinguishable Raman spectra in the solid state. Reaction of tris[2-(diphenylphosphino)ethyl]phosphine (tdppep) with the
activated mixture affords the complex [{Re2(m-OMe)2(CO)6}(m,h2-tdppep)] 2, and the analogous reaction involving bis[2-
diphenylphospinoethyl)phenylphosphine (triphos) gives [{Re2(m-OMe)2(CO)6}(m,m%,h3-triphos){Re2(CO)9}]
OMe)2(CO)6}(m,h2-triphos)] 4. © 1999 Elsevier Science S.A. All rights reserved.
3 and [{Re2(m-
Keywords: Rhenium carbonyl; Amine N-oxide; Carbonyl–methoxo complex; Triphosphine; Tetraphosphine; Multinuclear aggregates
[Re2(CO)9(solvent)] [3b]. The mono- and dinuclear
methoxo species have been trapped by coordination
with diphosphines (PP) [3b–e], and it appears that the
diphosphines are most adept at trapping and stabilizing
the {Re2(m-OMe)2} moiety, since [Re2(m-OMe)2(m-
PP)(CO)6] complexes are invariably the major phos-
phine-coordinated rhenium methoxo species formed in
the reaction of diphosphines with the activated mixture
of Re2(CO)10, Me3NO and MeOH [3c–e]. The yield of
the diphosphine-coordinated dirhenium methoxo com-
plexes [Re2(m-OMe)2(m-PP)(CO)6] decreases, however,
with increasing length of the hydrocarbon chain linking
the phosphino groups [3c].
1. Introduction
Low-valent transition metal alkoxo complexes con-
tinue to be the focus of much research [1], being
postulated as intermediates in many important metal-
catalyzed organic transformations [2]. The synthesis,
characterization and reactions of rhenium(I) carbonyl
alkoxo complexes is the subject of our current interest
[3]. Our studies indicated that the reaction of Re2(CO)10
with Me3NO and MeOH results in a complex mixture
of mono-, di- and trinuclear rhenium(I) methoxo spe-
cies, as well as the ReꢀRe bonded species
We have now extended the above studies to include
the triphosphines bis[2-diphenylphosphinoethyl)phenyl-
phosphine (triphos) and 1,1,1-tris(diphenylphosphi-
* Corresponding author. Fax: +65-469-8952.
E-mail address: ykyan@nie.edu.sg (Y.K. Yan)
1 Also corresponding author.
0022-328X/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(99)00442-8

C. Jiang et al. / Journal of Organometallic Chemistry 590 (1999) 138–148
139
nomethyl)ethane (tdppme), and the tetraphosphines
1,1,4,7,10,10 - hexaphenyl - 1,4,7,10 - tetraphosphadecane
(hptpd) and tris[2-(diphenylphosphino)ethyl]phosphine
(tdppep). These phosphines are versatile multidentate
ligands for transition metals in a variety of oxidation
states, and their complexes have been the subject of
studies of catalysis, structure–bonding relationships
and spectroscopy [4–6]. The linear tetraphosphine
hptpd is especially interesting since it can exist in three
stereoisomeric forms (d, l and meso) [6] (Scheme 1). It
is hoped that these multifunctional phosphines would
be able to scavenge for and trap novel rhenium
methoxo intermediates in the activated mixture, or
facilitate the formation of novel multinuclear aggre-
gates. It is also noteworthy that, amongst the numerous
transition metal polyphosphine complexes reported,
there are only a few polyphosphine complexes of rhe-
nium [5a,7].
In this paper, we report the formation of the
complexes (d/l)- and meso-[{Re2(m-OMe)2(CO)6}2-
(m,m%-hptpd)] 1, [{Re2(m-OMe)2(CO)6}(m,h2-tdppep)]
2, [{Re2(m-OMe)2(CO)6}(m,m%,h3-triphos){Re2(CO)9}] 3
and [{Re2(m-OMe)2(CO)6}(m,h2-triphos)] 4 in the reac-
tions of the respective polyphosphines with mixtures of
Re2(CO)10, Me3NO and MeOH (Scheme 2). We also
report the crystal structures of both d/l- and meso-1,
and the study of the fluxional behavior of d/l-1 by
variable-temperature 1H- and 31P-{1H}-NMR spec-
troscopy. The solid-state laser Raman spectra of d/l-
and meso-1 in the CO-stretching region are also
reported.
2. Results and discussion
2.1. Reaction of 1,1,4,7,10,10-hexaphenyl-1,4,7,10-
tetraphosphadecane (hptpd) with Re2(CO)10, Me3NO
and MeOH
2.1.1. Formation of d/l- and
meso-[{Re2(v-OMe)2(CO)6}2(v,v%-hptpd)] 1
The commercial hptpd used in this work is a roughly
1:1 mixture of meso- and rac-diastereomers, as shown
by 31P-{1H}-NMR spectroscopy. This isomeric mixture
was used directly for the reaction without pre-separa-
tion as described by Brown and Canning [8].
Reaction of hptpd with the mixture of Re2(CO)10,
Me3NO and MeOH gives the complexes d/l- and meso-
[{Re2(m-OMe)2(CO)6}2(m,m%-hptpd)] 1, with a total yield
of 18% (based on Re) and a meso:(d/l) ratio of ca. 3:2.
We were also able to synthesize 1 from the controlled
acidolysis [3a] of [Re2(m-OMe)3(CO)6]− in the presence
of hptpd, with an improved total yield of 41% and a
meso:(d/l) ratio of ca. 3:5. The different isomeric ratios
obtained by the different synthetic routes can be at-
tributed to the difference in reaction mechanisms [3a,
b]. Interestingly, although d/l- and meso-1 have very
similar Rf values and hence cannot be effectively sepa-
rated by TLC, they exhibit a great difference in solubil-
ity. While meso-1 is almost insoluble in benzene, d/l-1
Scheme 1.

140
C. Jiang et al. / Journal of Organometallic Chemistry 590 (1999) 138–148
Scheme 2.
,
The Re(1)···Re(2) distance of 3.3966(9) A in meso-1
is comparable to those in [Re2(m-OMe)2(m-dppf)(CO)6]
is readily soluble. This unusual property allows the two
diastereomers of 1 to be easily separated by benzene
extraction, hence obviating the need for pre-separation
of the diastereomers of the hptpd ligand, as described
in many reports of hptpd complexes [6]. The solubility
difference between meso- and d/l-1 is also consistent
with that between meso- and rac-hptpd–rac-hptpd is
more soluble than meso-hptpd in tetrahydrofuran [9].
,
[3.4042(6) A] [3e] and [Re2(m-OMe)2(m-dppm)(CO)6]
[3.3917(7) A] [3c]. However, the OꢀReꢀO angle [average
,
73.1(3)°] in meso-1 lies between those in [Re2(m-
OMe)2(m-dppf)(CO)6] [average 71.3(2)°] [3e] and [Re2(m-
OMe)2(m-dppm)(CO)6] [average 74.8(3)°] [3c]. These
features of meso-1 should be similar to those of [Re2(m-
OMe)2(m-dppe)(CO)6], which has not been structurally
characterized.
2.1.2. Crystal structures of meso- and
The crystals of d/l-1 (small elongated plates) dif-
fracted rather weakly and gave diffraction data with a
rather high Rint value (0.061 based on F2). Conse-
quently, the structural parameters determined have rel-
atively high estimated S.D. Specifics of the bonding
within the molecule are therefore not discussed; these
are expected to be similar to those observed in meso-1.
The essential features of the structure, however, have
been established and hence an overall analysis of the
gross features of the molecule is still considered
valid.
In contrast to the structure of meso-1, the molecule
of d/l-1 has a distorted C2 symmetry, resulting in all the
phosphorus atoms and all the methoxo groups being
non-equivalent. As in the meso isomer, however, the
PꢀRe bonds in the different {Re2(m-OMe)2(PP)} frag-
ments of d/l-1 point in approximately opposite direc-
tions, probably to minimize steric repulsion between the
two {Re2(m-OMe)2(PP)} fragments. The stereochemical
d/l-[{Re2(v-OMe)2(CO)6}2(v,v%-hptpd)] 1
The molecules of both meso-1 (Fig. 1) and d/l-1 (Fig.
2) consist of two {Re2(m-OMe)2(CO)6} moieties which
are bridged by the two PꢀCH2ꢀCH2ꢀP moieties of the
hptpd ligand. Thus, the complexes can be thought of as
‘dimers’ of the dppe complex [Re2(m-OMe)2(m-
dppe)(CO)6] [3c]. This clearly illustrates the ability of
short-chain diphosphines to stabilize the {Re2(m-
OMe)2} moiety.
Although the molecule of meso-1 possesses crystallo-
graphic i-symmetry, so that only one-half of the
molecule (consisting of one {Re2(m-OMe)2(CO)6} frag-
ment and half of the hptpd ligand) is unique, the
asymmetrical substitution of P(1) and P(1a) results in
the two m-OMe groups of each {Re2(m-OMe)2(CO)6}
fragment being non-equivalent. Consequently, the solu-
1
tion H-NMR spectrum of meso-1 shows two separate
peaks for the m-OMe groups.

C. Jiang et al. / Journal of Organometallic Chemistry 590 (1999) 138–148
141
configurations at P(2) and P(3) and the requirement for
the trans disposition of the two {Re2(m-OMe)2(PP)}
fragments force the backbone of the hptpd ligand in
d/l-1 into a U-shape, as shown in Fig. 2. This is in
contrast to the molecule of meso-1, which adopts a
linear configuration.
further split into doublets. This is attributed to the
coupling between the two internal phosphorus atoms
(3JPꢀP ca. 17 Hz).
1
The two H peaks of the m-OMe groups at 300 K
(4.35 and 4.17 ppm) are also split into four at 190 K,
although these four peaks are still very broad (Fig. 4).
The peak at 4.35 ppm broadens more quickly as tem-
perature is lowered, and is split into two broad signals
4.54 and 4.08 ppm) at 200 K. The 4.17 ppm signal at
300 K, on the other hand, is only barely resolved into
two peaks (4.18 and 4.16 ppm) at 190 K. From the
structure of d/l-1 (Fig. 2), it is apparent that two of the
methoxo ligands [C(2) and C(3)] point inwards and the
other two [C(1) and C(4)] point outwards. The signals
at 4.54 and 4.08 ppm are assigned to the internal
methoxo protons, which are expected to have a larger
difference in chemical shifts due to the larger difference
in their chemical environments.
2.1.3. Variable-temperature 1H- and 31P-{1H}-NMR
spectra of d/l-1
The 1H- and 31P-{1H}-NMR spectra of meso-1 at
ambient temperature show two 1H peaks due to the
methoxo ligands and two 31P peaks, respectively. This is
consistent with the crystal structure of meso-1. The
1
room-temperature H- and 31P-{1H}-NMR spectra of
d/l-1 also show two 1H resonances for the methoxo
ligands and two 31P signals. This is, however, inconsis-
tent with the crystal structure of d/l-1, and warrants a
study of the variable-temperature 1H- and 31P-{1H}-
NMR spectra of the complex.
The fluxional motion of the molecule most probably
results in the exchange of chemical environments be-
tween the two internal methoxo groups and that be-
tween the two external methoxo groups, in terms of
their spatial relationships with the phenyl rings. The
same process probably causes the exchange of environ-
ments between the internal phosphorus atoms and that
between the terminal phosphorus atoms, since the tem-
perature-dependent behaviors of the 31P and methoxo
proton signals are very similar.
An exchange mechanism that is consistent with the
above observations involves the twisting of the two
terminal CH2–CH2 axes in the hptpd backbone. It is
apparent from Fig. 2 that one of the terminal
{PCH2CH2P} segments [P(1)ꢀP(2)] adopts a l gauche
conformation, while the other [P(3)ꢀP(4)] adopts a u
At 300 K the 31P-{1H}-NMR spectrum of d/l-1 (Fig.
3) consists of two sharp singlets at 16.7 and 7.9 ppm,
which are assigned to the terminal and internal phos-
phorus atoms, respectively, of the hptpd ligand. At 240
K, the peak at 7.9 ppm broadens and moves slightly
upfield, eventually splitting into two peaks at 220 K.
The peak at 16.7 ppm is however only slightly broad-
ened at 220 K. At 200 K, the signals due to the internal
phosphorus atoms become sharp and clear at 13.8 and
−0.9 ppm, and the peak at 16.7 ppm is split into two
sharp signals at 17.0 and 16.1 ppm. Thus, at 200 K
there are four 31P signals corresponding to the four
non-equivalent phosphorus atoms in the crystal struc-
ture of d/l-1. At 190 K, the lowest temperature achiev-
able for CD2Cl2, the two peaks at 13.8 and −0.9 ppm
Fig. 1. Crystal structure of meso-[{Re2(m-OMe)2(CO)6}2(m,m%-hptpd)] 1 (hydrogen atoms omitted for clarity).

142
C. Jiang et al. / Journal of Organometallic Chemistry 590 (1999) 138–148
Fig. 2. Crystal structure of d/l-[{Re2(m-OMe)2(CO)6}2(m,m%-hptpd)] 1 (hydrogen atoms omitted for clarity).
2.2. Reactions of other multidentate phosphines with
Re2(CO)10, Me3NO and MeOH
conformation. The twisting of the CH2–CH2 axes most
probably results in the interchange of the molecular
conformation between {l[P(1)ꢀP(2)], u[P(3)ꢀP(4)]} and
{u[P(1)ꢀP(2)], l[P(3)ꢀP(4)]}. This twisting motion is
probably correlated with the rotation of the phenyl
rings. The anti conformation of the central {PCH2-
CH2P} segment is probably maintained throughout,
since that minimizes the steric interaction between the
two bulky {Re2(m-OMe)2(PP)} fragments.
2.2.1. Tris[2-(diphenylphosphino)ethyl]phosphine (tdppep)
The reaction of the tetraphosphine tdppep with the
mixture of Re2(CO)10, Me3NO and MeOH affords the
complex [{Re2(m-OMe)2(CO)6}(m,h2-tdppep)] 2 as the
main product (21% based on Re). Only two of the
phosphorus atoms of the tdppep ligand are coordinated
to the {Re2(m-OMe)2(CO)6} fragment, the other two
remaining free. There is no evidence for the formation
of any quadridentate coordinated tdppep-mono-rhe-
nium species that are analogous to the other tdppep
complexes reported [11].
It is interesting to note that the {Re2(m-OMe)2} core
is bonded to the central phosphino group and one
terminal phosphino group of the ligand, rather than to
two terminal phosphino groups, i.e. [ReꢀP(CH2)2PꢀRe]
and not [ReꢀP(CH2)2P(CH2)2PꢀRe]. This again illus-
trates the preference of the {Re2(m-OMe)2(CO)6} frag-
ment for short-chain diphosphines [3c].
2.1.4. Raman spectra of meso- and d/l-1
The X-ray crystallographic studies on d/l- and meso-
1 have shown that while the molecules of the former do
not possess any symmetry elements, molecules of the
latter possess both molecular and crystallographic i-
symmetry. The solid-state Raman spectrum of meso-1
is thus expected to contain fewer CO stretching peaks
than that of the d/l isomers. The CO stretching absorp-
tions in the IR spectra of both d/l- and meso-1 are very
intense and poorly resolved, resulting in broad wCO
envelopes instead of sharp peaks. The wCO intensities in
the Raman spectra, on the other hand, should be much
weaker, and should give well-resolved peaks.
The Raman spectra of meso- and d/l-1 in the wCO
region are shown in Fig. 5. It is evident that the
diastereomers give distinctive spectra and that there are
fewer peaks in the spectrum of the meso isomer. Raman
spectroscopic studies of rhenium carbonyl complexes
are uncommon [10]; especially the use of Raman spec-
troscopy to differentiate diastereomeric carbonyl
complexes.
2.2.2. Bis[2-(diphenylphosphino)ethyl]phenylphosphine
(triphos)
The reaction of triphos with the mixture of
Re2(CO)10, Me3NO and MeOH affords the complexes
[{Re2(m-OMe)2(CO)6}(m,m%,h3-triphos){Re2(CO)9}]
3
and [{Re2(m-OMe)2(CO)6}(m,h2-triphos)] 4, with yields
of 10 and 9%, respectively. As in complexes 1 and 2, the
{Re2(m-OMe)2} moieties in 3 and 4 are bonded to the
[PꢀCH2ꢀCH2ꢀP] fragment of the triphos ligand. Whilst
the third phosphino group in 4 is uncoordinated, that
in 3 is coordinated to an [Re2(CO)9] fragment. It can

C. Jiang et al. / Journal of Organometallic Chemistry 590 (1999) 138–148
143
thus be deduced that Re2(CO)9(L) and rhenium
methoxo carbonyl species are co-existent in the mixture
of Re2(CO)10, Me3NO and MeOH. No tridentate coor-
dinated mono-rhenium complexes of triphos similar to
those reported [12] were isolated from the reaction
mixture.
Fig. 4. Variable-temperature 1H-NMR spectra of d/l-[{Re2(m-
OMe)2(CO)6}2(m,m%-hptpd)] 1 in CD2Cl2 (121.5 MHz, 300–190 K).
2.2.3. 1,1,1-Tris(diphenylphosphinomethyl)ethane
(tdppme)
The reaction of the triphosphine tdppme with the
mixture of Re2(CO)10, Me3NO and MeOH gave oily
products which could not be crystallized, even after
isolation by TLC. The major product gave FT-IR and
31P-{1H}-NMR spectra that are consistent with the
formulation [Re2(CO)9(tdppme)], with a unidentate-co-
ordinated tdppme ligand. There is no evidence for the
formation of species containing the {Re2(m-
OMe)2(CO)6} fragment or that of tridentate coordi-
nated mono-rhenium–tdppme species analogous to
those reported [13].
Fig. 3. Variable-temperature 31P-{1H}-NMR spectra of d/l-[{Re2(m-
OMe)2(CO)6}2(m,m%-hptpd)] 1 in CD2Cl2 (121.5 MHz, 300–190 K).

144
C. Jiang et al. / Journal of Organometallic Chemistry 590 (1999) 138–148
Fig. 5. Solid-state laser Raman spectra of meso and d/l-[{Re2(m-OMe)2(CO)6}2(m,m%-hptpd)] 1 in the wCO region.
probably involves the twisting of the two terminal
CH2–CH2 axes in the hptpd backbone, which is corre-
lated with the rotation of the phenyl rings.
3. Summary and conclusions
Reactions of the mixture of Re2(CO)10, Me3NO and
MeOH with tetra- and tridentate phosphines afford
novel polyphosphine-coordinated rhenium methoxo
carbonyl complexes. The tetraphosphine hptpd gives a
diastereomeric mixture of meso- and d/l-[{Re2(m-
OMe)2(CO)6}2(m,m%-hptpd)] 1, which can be easily sepa-
rated by extraction with benzene. Reactions with the
tetraphosphine tdppep and triphosphine triphos yield
the complexes [{Re2(m-OMe)2(CO)6}(m,h2-tdppep)] 2,
4. Experimental
All reactions were performed under pure dry argon
using standard Schlenk techniques. Solvents used were
of reagent grade and were dried by published proce-
dures and freshly distilled under argon before use. All
other reagents were of AR grade and were obtained
from commercial sources unless stated otherwise. All
the polyphosphines were purchased from Aldrich and
used as supplied. Precoated silica plates of layer thick-
ness 0.25 mm were obtained from Merck. 1H- and
31P-{1H}-NMR spectra were recorded at ca. 300 K at
operating frequencies of 300.0 and 121.5 MHz, respec-
[{Re2(m-OMe)2(CO)6}(m,m%,h3-triphos){Re2(CO)9}]
3
and [{Re2(m-OMe)2(CO)6}(m,h2-triphos)] 4, respectively.
The formation of complexes 1–4 confirms the affinity
of the {Re2(m-OMe)2(CO)6} fragment for a bridging
{PCH2CH2P} unit, since all the available {PCH2CH2P}
units in each of the polyphosphines used are bonded to
{Re2(m-OMe)2(CO)6} fragments. Any remaining phos-
phino groups not coordinated to {Re2(m-OMe)2(CO)6}
units are either left uncoordinated or are terminally
bonded to {Re2(CO)9} fragments. The complex d/l-1 is
fluxional at room temperature; the fluxional motion
1
tively. H and 31P chemical shifts are quoted in ppm
downfield of tetramethylsilane and external 80% H3PO4,
respectively. Infrared spectra were recorded on a
Perkin–Elmer 1600 FT-IR Spectrometer or a Bio-Rad

C. Jiang et al. / Journal of Organometallic Chemistry 590 (1999) 138–148
145
FT-IR Spectrometer. Laser Raman spectra were run
using a Renishaw Raman Spectrometer with a 782 nm
laser and a scan range of 150–3000 cm−1. The Raman
samples in microcrystalline form were loaded on a
platinum plate and covered with thin silica glass.
Elemental analyses were performed by the Micro-
analytical Laboratory, Department of Chemistry,
National University of Singapore.
30H, Ph), 4.46 (s, 6H, m-OCH3), 4.28 (s, 6H, m-OCH3),
2.55 (m, br, 4H, CH2), 2.08 (br, 4H, CH2), 1.68 (br, 4H,
CH2). Solubility in solvents: CH2Cl2, CHCl3\ben-
zeneꢀhexane. The ratio of yields of meso and d/l-1
was ca. 3:2.
4.2. Synthesis of meso- and d/l-[{Re2(v-OMe)2(CO)6}2-
(v,v%-hptpd)] 1 6ia controlled acidolysis of [Re2-
(v-OMe)3(CO)6]− in the presence of hptpd
4.1. Reaction of the mixture of Re2(CO)10, Me3NO and
MeOH with 1,1,4,7,10,10-hexaphenyl-1,4,7,10,-
tetraphosphadecane (hptpd)
A solution of p-toluenesulfonic acid monohydrate
(0.038 g, 0.20 mmol) in 10 cm3 of CHCl3 and 10 cm3
MeOH was transferred into a stirred solution of
[Et4N][Re2(m-OMe)3(CO)6] (0.152 g, 0.20 mmol) and
hptpd (0.067 g, 0.10 mmol) in 10 cm3 of CHCl3. The
resultant mixture was stirred under argon for 2 h. The
solvent was then removed under reduced pressure. The
residue obtained was redissolved in a minimum amount
of CH2Cl2 and chromatographed on silica TLC plates
(2:3 CH2Cl2–hexane). The mixture of complexes meso-
and d/l-[{Re2(m-OMe)2(CO)6}2(m,m%-hptpd)] 1 was iso-
lated from the main band (Rf 0.23) and resolved as
described above. Yield of meso-1, 0.028 g (15%). Yield
of d/l-1, 0.048 g (26%).
A solution of Me3NO·2H2O (0.062 g, 0.56 mmol) in
THF–MeOH(1:1, 20 cm3) was transferred into a
Schlenk flask containing a stirred solution of Re2(CO)10
(0.151 g, 0.23 mmol) in THF(10 cm3) at room tempera-
ture (r.t.). The resultant yellow solution was stirred in
vacuo for 4 h at r.t. This intermediate solution was
clear green–yellow. Solid Ph2P(CH2)2P(Ph)(CH2)2-
P(Ph)(CH2)2PPh2, hptpd (0.077 g, 0.115 mmol) was
then introduced and the light-yellow solution so formed
was stirred in vacuo for 1 h. The solution was stirred
for another 3 h under argon. The solution became
colorless and solvent was removed under reduced pres-
sure. The resultant white residue was redissolved in a
minimum amount of CH2Cl2 and chromatographed on
silica TLC plates (2:3 CH2Cl2–hexane).
4.3. Reaction of the mixture of Re2(CO)10, Me3NO
and MeOH with tris[2-(diphenylphosphino)-
ethyl]phosphine (tdppep)
The mixture of meso- and d/l-[{Re2(m-OMe)2-
(CO)6}2(m,m%-hptpd)] 1 was extracted with CH2Cl2 from
the main band (Rf 0.23). Layering of the CH2Cl2 solu-
tion with hexane gave a mixture of meso- and d/l-1 as
a white powder, total yield 0.039 g (18% based on Re).
C58H54O16P4Re4 ( fw 1875.5) requires: C, 37.1; H, 2.9; P,
6.6; Re, 39.7%. Found: C, 37.3; H, 3.0; P, 6.7; Re,
39.7%. The powder was stirred with benzene (20 cm3) at
r.t. for 30 min, during which time d/l-1 dissolved. The
insoluble meso-1 was separated by filtration and recrys-
tallized by slow evaporation of its solution in CH2Cl2–
hexane to give colorless prismatic crystals. w˜max/cm−1
(CH2Cl2) 2026s, 2009m, 1924m, 1899s(sh), 1890s (CO);
w˜max/cm−1 (THF) 2025s, 2009m, 1924m, 1900s(sh),
1894s (CO). lP(CD2Cl2) 15.5(s), 11.3(s); lH(CD2Cl2)
7.57–7.18 (m, 30H, Ph), 4.12 (s, 6H, m-OCH3), 4.06 (s,
6H, m-OCH3), 2.60 (br, 4H, CH2), 2.11 (br, 4H, CH2),
1.3 (s, 4H, CH2).
The reaction was carried out in a similar manner to
that described above except that hptpd was replaced by
(Ph2PCH2CH2)3P, tdppep (0.077 g, 0.115 mmol). The
residue obtained after evaporation of the reaction mix-
ture was redissolved in a minimum amount of CH2Cl2
for TLC (2:3 CH2Cl2–hexane). The complex [{Re2(m-
OMe)2(CO)6}(m,h2-tdppep)] 2 was isolated from main
band at Rf=0.35, and fine colorless crystals of 3 were
obtained from CH2Cl2–hexane. Yield 0.064 g (21%).
C50H48O8P4Re2 ( fw 1273) requires C, 47.1; H, 3.8; P,
9.7%. Found C, 46.6; H, 3.9; P, 9.9%. w˜max/cm−1
(CH2Cl2) 2024s, 2007m, 1921m, 1896s(sh), 1889vs
(CO); w˜max/cm−1 (CHCl3) 2025s, 2008m, 1922m,
1897s(sh), 1890vs (CO). lP(CDCl3): 15.6 (s, 1P, coord.
PPh2), 10.8 (t, 1P, P(CH2)3, JPꢀP=30 Hz), −12.6 (d,
2P, uncoord. PPh2, JPꢀP=30 Hz); lH(CDCl3): 7.5–7.3
(m, 30H, Ph), 4.08 (s, 6H, v-OCH3), 2.44–2.39 (m, 2H,
CH2), 2.0–1.9 (m, 8H, CH2), 1.8–1.7 (m, 2H, CH2).
Colourless plate-like crystals of d/l-1 were obtained
by layering the benzene solution with hexane. w˜max
/
cm−1 (CH2Cl2) 2026s, 2009m, 1924m, 1900s, 1888s
(CO); w˜max/cm−1 (THF) 2026s, 2009m, 1923m,
1900s(sh), 1880vs (CO); w˜max/cm−1 (C6H6) 2028s,
2012m, 1927m, 1907s, 1897s 1881s(sh) (CO).
lP(CD2Cl2) 16.7(s), 7.9(s); lH (CD2Cl2) 7.57–7.18 (m,
30H, Ph), 4.34 (s, 6H, m-OCH3), 4.15 (s, 6H, m-OCH3),
2.8 (m, br, 4H, CH2), 2.2 (br, 4H, CH2), 1.9 (br, 4H,
CH2). lP(C6D6) 16.9(s), 8.4(s); lH(C6D6) 7.58–6.93 (m,
4.4. Reaction of the mixture of Re2(CO)10, Me3NO
and MeOH with bis(2-diphenylphosphinoethyl)-
phenylphosphine (triphos)
The reaction was carried out as described for the
reaction with hptpd except that hptpd was replaced by
PhP[CH2CH2PPh2]2, triphos (0.082 g, 0.154 mmol). The
resultant residue was treated similarly by TLC (2:3

146
C. Jiang et al. / Journal of Organometallic Chemistry 590 (1999) 138–148
Table 1
CH2Cl2–hexane). The complexes [{Re2(m-OMe)2-
Crystallographic data for meso and d/l-[{Re2(m-OMe)2(CO)6}2(m,m%-
(CO)6}(m,m%,h3-triphos){Re2(CO)9}]
3
and [{Re2(m-
hptpd)] 1 a
OMe)2(CO)6}(m,h2-triphos)] 4 were isolated from main
bands at Rf=0.47 and 0.40, respectively.
meso-1
d/l-1
Fine off-white crystals of complex 3 were obtained by
the slow evaporation of a CH2Cl2–hexane solution of
the complex over 1 week. Yield 0.021 g (10% based on
Re). C51H39O17P3Re4 ( fw 1761) requires C, 34.8; H, 2.2;
P, 5.3%. Found C, 34.1; H, 2.3; P, 5.4%. w˜max/cm−1
(CH2Cl2) 2106w, 2033w(sh), 2026m, 2007m(sh), 1996vs,
1963m, 1937m(sh), 1925s, 1897s(sh), 1890s (CO) (un-
derlined absorption maxima are assigned to the [Re2(m-
OMe)2(CO)6] fragment, the others are assigned to the
[Re2(CO)9] fragment). lP(CD2Cl2): 16.3 (d, Ph2P-
Crystal system Monoclinic
Triclinic
(
Space group
P21/n
P1
Unit cell dimensions
,
a (A)
13.001(1)
18.990(2)
13.267(3)
90
94.76(1)
90
12.963(8)
13.994(12)
20.09(2)
79.32(6)
75.06(5)
68.34(5)
3256(5)
7.57
,
b (A)
,
c (A)
h (°)
i (°)
k (°)
3
,
V (A )
3264.1(9)
7.65
v (mm−1
)
ReOMe, JPꢀP=6.5 Hz), 9.6 (dd, PPhꢀReOMe, JPꢀP
=
Absorption
corrections
Min/max
transmission
Diffractometer Nonius
„-scans
Face-indexed numerical
27 Hz, J%PꢀP=6.5 Hz), 8.4 [d, PPh2ꢀRe2(CO)9, JPꢀP=27
Hz]. lH (CD2Cl2): 7.71–6.90 (m, 25H, Ph), 4.14(s, 3H,
m-OCH3), 4.06 (s, 3H, m-OCH3), 2.8–2.2 (m, br, 8H,
CH2).
0.687, 0.999
0.488, 0.736
Siemens P4
50.0
−1 to 15, −15 to 16,
−23 to 23
13120
Max. 2q (°)
hkl range
49.8
Complex 4 was obtained as a white powder by the
slow evaporation of a CH2Cl2–hexane solution of the
complex over 1 week. Yield 0.023 g (9% based on Re).
C42H39O8P3Re2 ( fw 1137) requires C, 44.3; H, 3.4; P,
8.2%. Found. C, 43.8; H, 3.5; P, 8.1%. w˜max/cm−1
(CH2Cl2) 2024s, 2008m, 1922m, 1897s(sh), 1890vs
(CO). lH(CD2Cl2) 7.6–7.2 (m, 25H, Ph), 4.17 (s, 3H,
m-OCH3), 4.09 (s, 3H, m-OCH3), 2.7–1.8 (m, 8H, CH2);
lP(CD2Cl2): 15.7 (d, coord. Ph2P, JPꢀP=6 Hz), 10.8
(dd, coord. PhP, JPꢀP=29 Hz, J%PꢀP=6 Hz), −12.9 (d,
free Ph2P, JPꢀP=29 Hz).
−15 to 15,
0 to 22, 0 to 15
6009
Reflections
measured
Unique
5742
11460
reflections (Rint
)
(0.015, based on F) (0.061, based on F2)
0.028, 0.029 (Rw) d 0.070, 0.135
c
R1, b wR
[I\2|(I)]
a Details in common: chemical formula C58H54O16P4Re4; M,
1875.7; Z, 2; temperature of 29792 K; graphite-monochromated
Mo–Ka radiation; q−2q scan mode.
b R1=S ꢀꢀFoꢀ−ꢀFcꢀꢀ/ S ꢀFoꢀ.
c wR=[S w(Fo2−Fc2)2/ S w(F2o)2]1/2
.
.
d Rw=[S w(ꢀFoꢀ−ꢀFcꢀ)2/ S wꢀFoꢀ ]
2 1/2
4.5. Reaction of the mixture of Re2(CO)10, Me3NO
and MeOH with 1,1,1-tris(diphenyl-phosphinomethyl)-
ethane (tdppme)
CH2Cl2–hexane at r.t. The number of data used for
structure solution and refinement was 3807 [I\
2.0|(I)]. The structure was solved by direct methods
The reaction was carried out as described for the
reaction with hptpd except that hptpd was replaced by
CH3C[CH2PPh2]3, tdppme (0.096 g, 0.154 mmol). The
resultant residue was treated similarly by TLC (2:3
CH2Cl2–hexane). The product extracted by CH2Cl2
from the main band (Rf 0.73) was oily and could not be
crystallized. From its FT-IR and 31P-NMR spectra, the
product was tentatively identified as [Re2(CO)9-
(tdppme)]. w˜max/cm−1 (CH2Cl2) 2103w, 2032w, 1993vs,
1960m, 1933m (CO). lP(CD2Cl2): −4.6 (s, 1P, coord.
Ph2P), −7.1 (s, 2P, free Ph2P).
(MULTAN [14]). Refinement (on F) was carried out by
the full-matrix least-squares method with all non-hy-
drogen atoms being allowed anisotropic motion. All
hydrogen atoms were held fixed in the final cycles of
least-squares refinement. The last least-squares cycle
was calculated with 370 parameters and 3807 reflec-
tions. The weighting function used was w−1=|2(Fo)+
0.000100F2o. The maximum shift/| ratio was less than
0.001. In the last difference map the deepest hole was
−3
−3
,
,
−0.760 e A , and the highest peak was 0.550 e A
Computations were carried out on a Microvax 3600
computer with the NRCVAX system [15].
.
4.6. X-ray crystallography
The crystallographic data for meso- and d/l-1 are
summarized in Table 1, and selected bond lengths and
angles for meso-1 are given in Table 2.
4.6.2. d/l-[{Re2(v-OMe)2(CO)6}2(v,v%-hptpd)] 1
Single colorless crystals of d/l-1 were grown by layer-
ing a solution of the compound in benzene with hexane.
The number of data used for structure solution and
refinement was 5980 [I\2.0|(I)]. The structure was
solved by the heavy-atom method. All non-hydrogen
atoms were refined anisotropically by the full-matrix
4.6.1. meso-[{Re2(v-OMe)2(CO)6}2(v,v%-hptpd)] 1
Single colorless crystals of meso-1 were grown by
slow evaporation of a solution of the complex in

C. Jiang et al. / Journal of Organometallic Chemistry 590 (1999) 138–148
147
Table 2
acknowledged. C.H.J. is grateful to NUS for a scholar-
ship award.
,
Selected bond lengths (A) and angles (°) for complex meso-[{Re2-
(m-OMe)2(CO)6}2(m,m%-hptpd)] 1
Bond lengths
Re(1)···Re(2)
Re(1)ꢀC(1)
Re(1)ꢀC(3)
Re(1)ꢀO(8)
Re(2)ꢀC(4)
Re(2)ꢀC(6)
Re(2)ꢀO(8)
3.3966(9) Re(1)ꢀP(1)
1.889(9) Re(1)ꢀC(2)
1.894(10) Re(1)ꢀO(7)
2.140(5) Re(2)ꢀP(2)
1.916(10) Re(2)ꢀC(5)
1.896(9) Re(2)ꢀO(7)
2.148(5)
2.485(2)
1.939(10)
2.146(5)
2.478(2)
1.932(9)
2.161(5)
References
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Bond angles
P(1)ꢀRe(1)ꢀC(1)
P(1)ꢀRe(1)ꢀC(3)
P(1)ꢀRe(1)ꢀO(8)
O(7)ꢀRe(1)ꢀC(3)
C(1)ꢀRe(1)ꢀC(3)
P(2)ꢀRe(2)ꢀC(5)
P(2)ꢀRe(2)ꢀO(7)
O(7)ꢀRe(2)ꢀO(8)
O(8)ꢀRe(2)ꢀC(5)
88.5(3)
93.7(3)
83.7(1)
97.8(3)
87.5(4)
174.7(2)
89.0(1)
72.8(2)
97.8(3)
P(1)ꢀRe(1)ꢀC(2)
174.5(3)
P(1)ꢀRe(1)ꢀO(7)
O(7)ꢀRe(1)ꢀO(8)
O(8)ꢀRe(1)ꢀC(3)
P(2)ꢀRe(2)ꢀC(4)
P(2)ꢀRe(2)ꢀC(6)
P(2)ꢀRe(2)ꢀO(8)
O(7)ꢀRe(2)ꢀC(5)
C(4)ꢀRe(2)ꢀC(6)
90.1(1)
73.3(2)
170.7(3)
90.8(3)
88.4(3)
86.2(1)
95.5(3)
87.5(4)
Re(1)ꢀO(7)ꢀRe(2) 104.2(2)
Re(1)ꢀP(1)ꢀC(9)
P(1)ꢀC(9)ꢀC(10)
Re(1)ꢀO(8)ꢀRe(2) 104.8(2)
Re(2)ꢀP(2)ꢀC(10) 116.9(2)
P(2)ꢀC(10)ꢀC(9)
120.4(2)
115.6(5)
113.8(5)
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least-squares method (on F2). Hydrogen atoms were
introduced in calculated positions and refined isotropi-
cally (riding model) in the final cycles of least-squares
refinement. The last least-squares cycle was calculated
with 721 parameters and 11 401 data (all of the unique
reflections except very negative ones). The weighting
function used was w−1=|2(F2o)+(0.0600P)2, where
P=(F2o+2F2c)/3. The maximum shift/| ratio was
0.008. In the last difference map the deepest hole was
−3
−3
,
,
−2.467 e A , and the highest peak was 2.352 e A
,
[within 1 A from Re(2)]. Computations were carried
out on a Pentium PC using the SHELXTL PLUS software
package [16].
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5. Crystallographic data
Crystallographic data for the structural analysis has
been deposited with the Cambridge Crystallographic
Data Centre, CCDC nos. 127345 for meso-1, 121769
for d/l-1.
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Acknowledgements
We thank the National University of Singapore
(NUS) (RP 950695), the National Institute of Educa-
tion, Nanyang Technological University (RP 15/95
YYK), and the Academia Sinica, Taipei, for financial
support. Technical assistance from the staff of the
NMR Laboratory, Department of Chemistry, NUS is

148
C. Jiang et al. / Journal of Organometallic Chemistry 590 (1999) 138–148
[14] P. Main, S.E. Fiske, S.L. Hull, G. Germaine, J.P. Declerq, M.H.
Woolfson, MULTAN, A System of Computer Programs for Crys-
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versity of York and Louvain, Belgium, 1980.
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Appl. Cryst. 22 (1989) 384.
[16] G.M. Sheldrick, SHELXTL PC, Version 5.03, Siemens Analytical
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.