Reactions of the complexes [Re2(CO)9(η 1-P-P)] (P-P = Ph2P(CH2)nPPh 2, n = 1-6) with Me3NO: Formation of close-bridged complexes [Re2(CO)8(μ-P-P)] and phosphine oxide complexes [Re2(CO)9{P-P(O)}]

Article abstract of DOI:10.1016/j.ica.2004.03.035

Reactions of [Re₂(CO)₁₀] with Me₃NO and diphosphines [Ph₂P(CH₂)_nPPh₂, n=1-6] yield mixtures of the monodentate-coordinated diphosphine complexes [Re ₂(CO)₉(η¹-P-P)] (P-P=Ph ₂P(CH₂)_nPPh₂, n=1-6) (yields 5-40%) and bridged dimers [{Re₂(CO)₉}₂(μ-P-P)] (5-50%). These complexes were isolated as either equatorial or axial isomers, or a mixture of two isomers. Reactions of the monodentate complexes with Me ₃NO yield close-bridged complexes [Re₂(CO) ₈(μ-P-P)] and phosphine oxide complexes [Re₂(CO) ₉{P-P(O)}]. The structures of the close-bridged complexes 1 (n=3) and 2 (n=4), were determined by X-ray crystallography. The Re-Re bond in the close-bridged complex with the longest phosphine chain (n=6) is readily cleaved in CDCl₃ to give the complex [{cis-ReCl(CO)₄} ₂(μ-dpph)] (3) as the product, the structure of which was also determined by X-ray crystallography.

Full text of DOI:10.1016/j.ica.2004.03.035

Inorganica Chimica Acta 357 (2004) 2441–2450
www.elsevier.com/locate/ica
Reactions of the complexes [Re2(CO)9(g1-P–P)]
(P–P ¼ Ph2P(CH2)nPPh2, n ¼ 1–6) with Me3NO: formation
of close-bridged complexes [Re2(CO)8(l-P–P)] and phosphine
oxide complexes [Re2(CO)9{P–P(O)}]
a
Wei Fan , Rui Zhang , Weng Kee Leong , Yaw Kai Yan
a
b
a,
*
a
Natural Sciences Academic Group, National Institute of Education, Nanyang Technological University, NIE Blk 7 Science,
1 Nanyang Walk, Singapore 637616, Republic of Singapore
b
Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543, Republic of Singapore
Received 7 July 2003; accepted 6 March 2004
Available online 30 April 2004
Abstract
Reactions of [Re2(CO)10] with Me3NO and diphosphines [Ph2P(CH2)nPPh2, n ¼ 1–6] yield mixtures of the monodentate–co-
ordinated diphosphine complexes [Re2(CO)9(g1-P–P)] (P–P ¼ Ph2P(CH2)nPPh2, n ¼ 1–6) (yields 5–40%) and bridged dimers
[{Re2(CO)9}2(l-P–P)] (5–50%). These complexes were isolated as either equatorial or axial isomers, or a mixture of two isomers.
Reactions of the monodentate complexes with Me3NO yield close-bridged complexes [Re2(CO)8(l-P–P)] and phosphine oxide
complexes [Re2(CO)9{P–P(O)}]. The structures of the close-bridged complexes 1 (n ¼ 3) and 2 (n ¼ 4), were determined by X-
ray crystallography. The Re–Re bond in the close-bridged complex with the longest phosphine chain (n ¼ 6) is readily cleaved in
CDCl3 to give the complex [{cis-ReCl(CO)4}2(l-dpph)] (3) as the product, the structure of which was also determined by X-ray
crystallography.
Ó 2004 Elsevier B.V. All rights reserved.
Keywords: Rhenium carbonyl; Diphosphine; Monodentate-coordinated; Close-bridged; Phosphorus-31 NMR; Phosphine oxide
1. Introduction
Me3NO-decarbonylation of [Re2(CO)10]) with excess
dppf [3]. It is noteworthy that Me3NO can, in principle,
also decarbonylate the monodentate–dppf complex and
cause the formation of the close-bridged complex
[Re2(CO)8(l-dppf)]. This octacarbonyl complex has not
been reported, however. Several [Re2(CO)8(l-P–P)]
complexes have been prepared by Brown and coworkers
[4], but no crystal structures or 31P NMR data were
reported.
Diphosphine ligands have played a major role in
modern coordination chemistry [1]. Their ability to form
chelate and bridged complexes is widely known. How-
ever, except for dppm complexes [2], few complexes
containing monodentate-coordinated diphosphines have
been reported, and these have not been systematically
studied.
The only known [Re2(CO)9(g1-P–P)] complex
(P–P ¼ diphosphine) is the dppf complex [dppf ¼
1,10-bis(diphenylphosphino)ferrocene], which was syn-
thesized by reaction of [Re2(CO)9(solvent)] (obtained by
In this paper, we report the synthesis of the com-
plexes [Re2(CO)9(g1-P–P)] (P–P ¼ Ph2P(CH2)nPPh2,
n ¼ 1–6) (Fig. 1) and their reactions with Me3NO to
yield the close-bridged complexes [Re2(CO)8(l-P–P)]
and the phosphine oxide complexes [Re2(CO)9{P–
P(O)}] (Fig. 2) as the major products. X-ray crystallo-
* Corresponding author. Tel.: +65-6790-3374; fax: +65-6896-9432.
E-mail address: ykyan@nie.edu.sg (Y.K. Yan).
graphic studies of the close-bridged complex 1
0020-1693/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2004.03.035

2442
W. Fan et al. / Inorganica Chimica Acta 357 (2004) 2441–2450
0.25 mm were purchased from Merck. Fourier trans-
CO
Re
OC
CO
CO
CO
form infrared spectra were recorded with a Perkin–El-
mer 1725X FT-IR Spectrometer. Phosphorus-31 NMR
spectra were recorded at room temperature on a Bruker
DRX400 spectrometer at 162 MHz. The phosphorus
chemical shifts are quoted from the proton-decoupled
spectra, and are reported in ppm to the higher frequency
of external 80% H3PO4. Elemental analyses were per-
formed using a LECO CHNS-932 instrument.
OC
OC
Re
P
P
OC
CO
=
Ph2P(CH2) PPh2
n
P
P
n
1
2
3
4
5
6
Name
Abbreviation
2.2. Synthesis of the complexes [Re2(CO)9(g1-P–P)]
(P–P ¼ Ph2P(CH2)nPPh2, n ¼ 1–6)
bis(diphenylphosphino)methane
1,2–bis(diphenylphosphino)ethane
1,3–bis(diphenylphosphino)propane
1,4–bis(diphenylphosphino)butane
1,5–bis(diphenylphosphino)pentane
1,6–bis(diphenylphosphino)hexane
dppm
dppe
dppp
dppb
dpppe
dpph
Solid Me3NO ꢀ 2H2O (0.0511 g, 0.46 mmol) was ad-
ded to a continuously stirred solution of [Re2(CO)10]
(0.3132 g, 0.48 mmol) in 50 ml of THF at room tem-
perature. The yellow reaction mixture so formed was
stirred under reduced pressure. After all the
Me3NO ꢀ 2H2O solid had dissolved, stirring was con-
tinued for another 30 min, and half of the solvent was
removed under reduced pressure. The remaining solu-
tion was stirred for a further 15 min before it was
slowly transferred to a stirred solution of the diphos-
phine (P–P) (0.44 mmol) in 24 ml of THF via a PTFE
transfer tube. The resultant yellow solution was stirred
under nitrogen for about 1 h. Half of the solvent was
then removed and stirring was continued for another 50
min, after which the solution was evaporated to dryness
to give a yellow residue.
Fig. 1. General structure of the monodentate-coordinated complexes
[Re2(CO)9(g1-P–P)].
(P–P ¼ dppp) and 2 (P–P ¼ dppb) show that the ac-
commodation of diphosphine chains between two
mutually bonded Re atoms creates significant strain on
the molecules. Due to the immense steric strain on the
molecule, the Re–Re bond of [Re2(CO)8(l-dpph)]
readily cleaves to give [{cis-ReCl(CO)4}2(l-dpph)] (3)
the structure of which was determined by X-ray crys-
tallography. For the first time, the 31P chemical shifts of
the close-bridged complexes are analyzed for the ring
contributions.
2.2.1. Workup procedure for the complexes [Re2(CO)9-
(g1-P–P)] [P–P ¼ Ph2P(CH2)nPPh2, n ¼ 1, 3–6]
The yellow residue was redissolved in a minimum
quantity of CH2Cl2 and chromatographed on silica TLC
plates. A diethyl ether–hexane (1:3) mixture eluted two
closely-spaced yellow bands. A very light yellow solid was
recovered from each of the two bands by recrystallization
from CH2Cl2–MeOH mixture. The first band (that of the
higher Rf value, typically ca. 0.70) yielded the monoden-
tate-coordinated complex [Re2(CO)9(g1-P–P)] and the
second band (Rf typically ca. 0.60) yielded the ‘‘dimer’’
complex [{Re2(CO)9}2(l-P–P)] (Fig. 3). The yields of
both products, except for the dppm complexes, are very
sensitive to experimental conditions, and when the yield
of the monodentate complex was low, there was always a
corresponding increase in the yield of the dimer. The
2. Experimental
2.1. General
All reactions were routinely performed under pure
dry nitrogen using standard Schlenk techniques [5,6]. All
solvents for the reactions were also vacuum degassed
before use. The solvents were of reagent grade and were
freshly purified and dried by published procedures [7].
Chemical reagents, unless otherwise stated, were com-
mercial products and were used without further purifi-
cation. Pre-coated silica TLC plates of layer thickness
P
CO
P
CO
OC
CO
CO
CO
OC
OC
Re
CO
Re
OC CO
CO
OC
OC
Re
Re
P
P
O
OC
CO
CO
close-bridged complex
Phosphine oxide complex
Fig. 2. General structures of the close-bridged [Re2(CO)8(l-P–P)] and phosphine oxide [Re2(CO)9{P–P(O)}] complexes.

W. Fan et al. / Inorganica Chimica Acta 357 (2004) 2441–2450
2443
2.2.2. Workup Procedure for the complex [Re2(CO)9-
(g1-dppe)]
CO
Re
CO
Re
OC CO
CO
OC CO
P Re
CO
CO
About 3 ml of CH2Cl2 was added to the yellow res-
idue. A suspension was obtained, which was centrifuged
to yield the light yellow [{Re2(CO)9}2(l-dppe)] solid and
a yellow supernatant. The yellow supernatant was
chromatographed on silica TLC plates. Elution with
CH2Cl2–hexane (1:3) followed by further recrystalliza-
tion from CH2Cl2–MeOH mixture yielded the pure
complex [Re2(CO)9(g1-dppe)]. The yields, elemental
analysis data and spectroscopic data are given in Tables
1–3.
OC
OC
Re
P
OC
OC CO
OC CO
CO
CO
Fig. 3. General structure of the dimer complexes [{Re2(CO)9}2(l-P–P)].
yields and elemental analysis data are given in Table 1,
and IR and 31P NMR data are given in Tables 2 and 3,
respectively.
Table 1
Yields and analytical data for [Re2(CO)9(g1-P–P)] and [{Re2(CO)9}2(l-P–P)] complexes
[Re2(CO)9(g1-P–P)]
[{Re2(CO)9}2(l-P–P)]
P–P
Yield (%)
Ca
Ha
Yield (%)
Ca
Ha
dppm
dppe
40
40.6 (40.5)
40.6 (41.1)
42.2 (41.7)
42.5 (42.3)
43.0 (42.9)
43.7 (43.5)
2.0 (2.2)
2.7 (2.4)
2.5 (2.5)
2.9 (2.7)
2.9 (2.8)
2.9 (3.0)
10
31.2 (31.6)
31.9 (32.1)
32.5 (32.5)
32.8 (33.0)
32.9 (33.4)
34.1 (33.8)
1.4 (1.4)
1.9 (1.5)
1.6 (1.6)
1.7 (1.7)
1.7 (1.8)
1.9 (1.9)
5–20
15–25
6–18
14–30
14–20
15–50
5–10
15–20
9–15
6–10
dppp
dppb
dpppe
dpph
a Observed value; calculated value in brackets.
Table 2
Solution (CH2Cl2) IR absorptions for [Re2(CO)9(g1-P–P)] and [{Re2(CO)9}2(l-P–P)] complexes in the carbonyl stretching region (cmꢁ1
)
P–P
[Re2(CO)9(g1-P–P)]
[{Re2(CO)9}2(l-P–P)]
dppm
eq, 2103(m), 2034(m), 1991(s), 1960(m), 1931(m)
ax, 2104(m), 2034(m), 1994(s), 1960(m), 1936(m)
ax–ax, 2105(m), 2035(m), 1998(s), 1963(m), 1938(m)
dppe
dppp
ax, 2104(m), 2034(m), 1994(s), 1962(m), 1934(m)
ax, 2105(m), 2033(m), 1995(m), 1958(m), 1936(m)
ax–ax, 2105(m), 2035(m), 1996(s), 1964(m), 1936(m)a
ax–ax, 2105(m), 2034(m), 1996(s), 1960(m), 1936(m)
dppb
eq, 2103(m), 2034(m), 1992(s), 1961(m), 1930(m)
ax, 2104(m), 2033(m), 1994(s), 1960(m), 1935(m)
eq–eq, 2103(m), 2034(m), 1993(s), 1961(m), 1930(m)
ax–ax, 2105(m), 2035(m), 1995(s), 1961(m), 1935(m)
dpppe
dpph
ax, 2105(m), 2033(m), 1994(s), 1959(m), 1935(m)
ax, 2105(m), 2033(m), 1994(s), 1959(m), 1935(m)
ax–ax, 2105(m), 2033(m), 1995(s), 1960(m), 1935(m)
ax–ax, 2105(m), 2033(m), 1994(s), 1960(m), 1935(m)
a Recorded in toluene.
Table 3
31P NMR data, dp (ppm), for [Re2(CO)9(g1-P–P)] and [{Re2(CO)9}2(l-P–P)] recorded in CDCl3
P–P
[Re2(CO)9(g1-P–P)]b
[{Re2(CO)9}2(l-P–P)]
ax–ax, 5.9(s)
dppm
eq, )10.3(d), )25.7(d), Jpꢁp ¼ 48 Hz
ax, 6.3(d), )23.5(d), Jpꢁp ¼ 104 Hz
dppe
dppp
ax, 9.6(d), )11.5(d), Jpꢁp ¼ 39:5 Hz
ax, 5.6(s), )16.9(s)
ax–ax, 8.1(s)a
ax–ax, 5.5(s)
dppb
eq, )11.5(s), )16.2(s)
ax, 5.6(s), )16.9(s)
eq–eq, )11.6(s)
ax–ax, 5.5(s)
dpppe
dpph
ax, 6.1(s), )14.6(s)
ax, 6.0(s), )14.7(s)
ax–ax, 6.3(s)
ax–ax, 5.9(s)
a Recorded in deuterated toluene.
b The higher field signal was assigned to the phosphorus atom of the free phosphino end and the lower field signal was assigned to the equatorial or
axial coordinated phosphorus atom.

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W. Fan et al. / Inorganica Chimica Acta 357 (2004) 2441–2450
2.2.3. Isomerization reactions of eq-[Re2(CO)9(g1-P–P)]
and eq,eq-[{Re2(CO)9}2(l-P–P)] (P–P ¼ dppm, dppb)
complexes [Re2(CO)8(l-P–P)] (typical Rf 0.43) and
[Re2(CO)9{P–P(O)}] (typical Rf 0.32). The yields, ele-
mental analysis, IR and 31P NMR spectroscopic data
are given in Tables 4–6. In the reaction of [Re2(CO)9(g1-
P–P)] (P–P ¼ dppb, dpppe and dpph), mixtures of eq–eq,
ax–eq or ax–ax [Re2(CO)8(l-P–P)] products were iso-
lated first, which then isomerized to the eq–eq isomers
after leaving the solution at room temperature for 2–3
days.
A
sample of either [Re2(CO)9(g1-P–P)] or
[{Re2(CO)9}2(l-P–P)] (equatorial isomers, about 10 mg)
was placed in a small Schlenk tube with a stirring bar,
and toluene (about 2 ml) was added. The solution was
vacuum-degassed, and the tube was refilled with nitro-
gen. A slow flow of nitrogen was maintained through
the tube via an outlet needle inserted through the rubber
septum. The solution was magnetically stirred, and he-
ated to boiling with a heat gun. After 10 min of boiling,
the solvent was removed under reduced pressure to yield
a solid residue of the axial isomer. The IR and 31P
NMR spectroscopic data are given in Tables 2 and 3
respectively.
2.4. Crystallography
Single crystals of both complexes 1 and 2 were grown
by slow evaporation of solutions in CH2Cl2–hexane
mixtures at ca. 5 °C. Those of complex 3 were similarly
grown from solutions in CDCl3–hexane mixtures.
Crystals were mounted on quartz fibres (1, 2) or sealed
in a glass capillary (3). X-ray data were collected on a
Siemens SMART CCD system, using Mo Ka radiation,
at ambient temperatures [295(2) K], with 6s (1) or 10s (2
and 3) exposures. Data were corrected for Lorentz and
polarisation effects with the SMART suite of programs
[8], and for absorption effects with SADABS [9]. Struc-
tural solution and refinement were carried out with the
SHELXTL suite of programs [10].
Final unit cell parameters were determined from
5874, 6628 and 9371 reflections, for 1, 2 and 3, respec-
tively. The structures were solved by either direct
methods, or by a Patterson map to locate the heavy
atoms, followed by difference maps for the light, non-
hydrogen atoms. H atoms were placed in calculated
2.3. Reactions of the complexes [Re2(CO)9(g1-P–P)]
(P–P ¼ Ph2P(CH2)nPPh2, n ¼ 1–6) with Me3NO
In a typical experiment, [Re2(CO)9(g1-P–P)] (0.036
mmol) was dissolved in 5 ml of freshly distilled and
degassed THF. A 0.012 M solution of Me3NO ꢀ 2H2O in
THF–MeOH (49:1) mixture (3 ml, 0.036 mmol of
Me3NO) was then added dropwise under nitrogen. The
resultant solution was degassed again and stirred under
nitrogen for 4 h at room temperature. The solution was
then evaporated to dryness and the yellow residue was
redissolved in a minimum quantity of CH2Cl2 and
chromatographed on silica TLC plates. Elution with
acetone–hexane (1:3) mixture followed by further re-
crystallization from CH2Cl2–hexane mixture yielded the
Table 4
Yields and analytical data for [Re2(CO)8(l-P–P)] and [Re2(CO)9{P–P(O)}] complexes
Starting material [Re2(CO)9(g1-P–P)] P–P:
[Re2(CO)8(l-P–P)]
[Re2(CO)9{P–P(O)}]
Yield (%)
Ca
Ha
Yield (%)
Ca
Ha
eq, dppm
ax, dppm
ax, dppe
ax, dppp
eq, dppb
ax, dppb
ax, dpppe
ax, dpph
76
42
32
17
42
14
14
11
40.2 (40.4)
40.0 (40.4)
40.8 (41.0)
41.9 (41.7)
42.2 (42.3)
42.1 (42.3)
42.7 (42.8)
43.0 (43.4)
2.3 (2.3)
2.2 (2.3)
2.3 (2.4)
2.8 (2.6)
2.9 (2.8)
2.9 (2.8)
2.9 (2.9)
3.1 (3.0)
5
–
39.5 (39.8)
–
2.2 (2.1)
–
9
40.8 (40.5)
40.9 (41.1)
41.4 (41.6)
41.7 (41.6)
41.9 (42.2)
42.7 (42.8)
2.5 (2.3)
2.7 (2.5)
2.7 (2.6)
2.6 (2.6)
3.0 (2.8)
3.0 (2.9)
17
11
8
17
8
a Observed value; calculated value in brackets.
Table 5
Solution (CH2Cl2) IR absorptions of [Re2(CO)8(l-P–P)] and [Re2(CO)9{P–P(O)}] in the carbonyl stretching region (cmꢁ1
)
P–P
[Re2(CO)8(l-P–P)]
[Re2(CO)9{P–P(O)}]
dppm
dppe
2072(m), 2019(m), 1978(s), 1956(w), 1940(w), 1914(m)
2070(m), 2016(m), 1978(s), 1944(m), 1911(m)
2068(m), 2014(m), 1976(s), 1938(m), 1910(m)
2066(m), 2009(m), 1975(s, sh), 1937(m), 1910(m)
2065(m), 2009(m), 1977(s, sh), 1934(m), 1907(m)
2067(m), 2006(w), 1966(s), 1918(m, sh)
eq, 2105(w), 2036(m), 1994(s), 1962(m), 1938(m)
ax, 2106(w), 2034(m), 1996(s), 1959(m), 1937(m)
ax, 2105(w), 2033(m), 1995(s), 1960(m), 1936(m)
ax, 2104(w), 2034(m), 1994(s), 1962(m), 1934(m)
ax, 2105(w), 2033(m), 1994(s), 1958(m), 1935(m)
ax, 2105(w), 2033(m), 1994(s), 1960(m), 1935(m)
dppp
dppb
dpppe
dpph
eq or ax: equatorial or axial isomer.

W. Fan et al. / Inorganica Chimica Acta 357 (2004) 2441–2450
2445
Table 6
31P NMR data, dp(ppm), of [Re2(CO)8(l-P–P)] and [Re2(CO)9{P–P(O)}], recorded in CDCl3
Starting material [Re2(CO)9(g1-P–P)] P–P:
[Re2(CO)8(l-P–P)]
[Re2(CO)9{P–P(O)}]
eq, dppm
ax, dppe
ax, dppp
eq, dppb
ax, dppb
ax, dpppe
ax, dpph
0.3 (s)
4.2 (s)
eq, 22.4 (d), )3.7 (d), J
ax, 31.7 (d), 9.0 (d), J
ax, 32.8 (s), 6.0 (s)
¼ 7 Hz
ðP;PÞ
¼ 51 Hz
ðP;PÞ
)17.5 (s)
)1.0 (s)a, )9.3 (s)
ax, 32.4 (s), 4.9 (s)
ax, 32.1 (s), 5.0 (s)
ax, 32.3 (s), 4.8 (s)
)1.0 (s)a, )8.3 (s)
11.7 (s), )1.0 (s)a, )14.5 (s)
a After completing the isomerization to the eq–eq isomer, only this signal was observed.
Table 7
Crystallographic data for [Re2(CO)8(l-dppp)] (1)
Table 8
Selected bond lengths (A) and angles (°) for [Re2(CO)8(l-dppp)] (1)
ꢀ
Empirical formula
Formula weight
Temperature (K)
C35H26O8P2Re2
1008.90
293(2)
Re(1)–Re(1a)
Re(1)–C(11)
Re(1)–C(13)
Re(1)–C(14)
Re(1)–C(12)
Re(1)–P(1)
3.1075(3) P(1)–C(1)
1.839(4)
1.142(5)
1.132(5)
1.137(4)
1.143(5)
1.519(5)
1.913(4)
1.954(4)
1.978(5)
1.984(5)
O(11)–C(11)
O(12)–C(12)
O(13)–C(13)
O(14)–C(14)
ꢀ
Wavelength (A)
0.71073
orthorhombic
Pnna
Crystal system
Space group
2.4811(9) C(1)–C(2)
Unit cell dimensions
ꢀ
C(11)–Re(1)–C(13) 91.6(2)
C(11)–Re(1)–C(14) 96.1(2)
C(13)–Re(1)–C(14) 86.9(2)
C(11)–Re(1)–C(12) 93.4(2)
C(13)–Re(1)–C(12) 90.9(2)
C(14)–Re(1)–C(12) 170.4(2)
C(12)–Re(1)–P(1)
C(11)–Re(1)–Re(1a)
C(13)–Re(1)–Re(1a)
C(14)–Re(1)–Re(1a)
C(12)–Re(1)–Re(1a)
P(1)–Re(1)–Re(1a)
C(1)–P(1)–Re(1)
86.1(1)
174.3(1)
83.6(1)
86.6(1)
83.8(1)
96.9(2)
122.2(1)
116.3(2)
116.6(4)
a (A)
14:6848ð2Þ
23:1878ð5Þ
10:3998ð2Þ
3541.2(1)
ꢀ
b (A)
ꢀ
c (A)
3
ꢀ
V (A )
Z
4
1.892
D
(Mg/m3)
C(11)–Re(1)–P(1)
C(13)–Re(1)–P(1)
C(14)–Re(1)–P(1)
87.8(1)
176.9(1)
96.1(1)
ðcalcÞ
Absorption coefficient (mmꢁ1
F ð000Þ
)
6.969
1920
C(2)–C(1)–P(1)
C(1)–C(2)–C(1a)
Crystal size (mm3)
0.325 ꢂ 0.250 ꢂ 0.200
2.15–29.32
ꢁ19 6 19; ꢁ31 6 k 6 21;
ꢁ13 6 l 6 9
21 422
h range for data collection (°)
Index ranges
3. Results and discussion
Reflections collected
Independent reflections [Rint
Completeness to h ¼ 29:32°
Absorption correction
Maximum and minimum
transmission
]
4530 [0.0321]
93.3%
3.1. Synthesis of the complexes [Re2(CO)9(g1-P–P)]
(P–P ¼ Ph2P(CH2)nPPh2, n ¼ 1–6)
SADABS
0.341697 and 0.212105
full-matrix least-squares on F2
4530/0/214
1.121
The reactions of [Re2(CO)10] with the diphosphines
(P–P) and Me3NO invariably yielded a mixture of
[Re2(CO)9(g1-P–P)] (monodentate complex, Fig. 1) and
[{Re2(CO)9}2(l-P–P)] (dimer complex, Fig. 3). The
presence of Me3NO leads to oxidative decarbonylation
of [Re2(CO)10], which results in the formation of an
intermediate species [Re2(CO)9(solvent)]. Reaction of
this intermediate with the diphosphine results in the
formation of the monodentate complex. Further reac-
tion of the monodentate complex with another molar
equivalent of the solvent-stabilized intermediate would
produce the dimer. The isolation of dimer reflects the
high reactivity of the monodentate complex with
[Re2(CO)9(solvent)].
The monodentate complexes and dimers were iso-
lated as either equatorial or axial isomers, or a mixture
of two isomers (Fig. 4). Distinction between axial and
equatorial complexes was mainly based on 31P NMR
spectra, as the resonance for the axial isomer occurs 10–
20 ppm downfield of that for the equatorial isomer [11].
Refinement method
Data/restraints/parameters
Goodness-of-fit on F 2
Final R indices [I > 2rðIÞ]
R indices (all data)
R1 ¼ 0:0258, wR2 ¼ 0:0470
R1 ¼ 0:0439, wR2 ¼ 0:0532
0.00122(4)
Extinction coefficient
Largest differential peak and
0.684 and )0.856
ꢁ3
ꢀ
hole (e A
)
positions and given isotropic thermal parameters at 1.2
times that of the C atoms to which they are attached. All
non-hydrogen atoms were given anisotropic thermal
parameters in the final model. An extinction parameter
was also refined for 1. A half molecule of CH2Cl2 was
found in 2. This was refined with isotropic thermal pa-
rameters and with the C–Cl bond lengths restrained to
be equal. A molecule of CDCl3 was found in 3, and this
was refined fully. Crystallographic data for 1, 2 and 3
are summarized in Tables 7, 9 and 11, respectively. Se-
lected bond lengths and angles for the complexes are
given in Tables 8, 10 and 12 respectively.
In addition, the coordination shift (Dd ¼ dcoord ꢁ dfree
)

2446
W. Fan et al. / Inorganica Chimica Acta 357 (2004) 2441–2450
Table 9
Crystallographic data for [Re2(CO)8(l-dppb)] (2)
Table 10
ꢀ
Selected bond lengths (A) and angles (°) for [Re2(CO)8(l-dppb)] (2)
Empirical formula
Formula weight
Temperature (K)
Wavelength
C
36:5H29ClO8P2Re2
Re(1)–Re(2)
Re(1)–C(14)
Re(1)–C(12)
Re(1)–C(13)
Re(1)–C(11)
Re(1)–P(1)
Re(2)–C(24)
Re(2)–C(22)
Re(2)–C(21)
Re(2)–C(23)
Re(2)–P(2)
P(2)–C(4)
3.1791(2) P(1)–C(1)
1.855(4)
1.134(5)
1.146(6)
1.150(5)
1.155(5)
1.152(6)
1.148(5)
1.139(6)
1.150(5)
1.535(7)
1.519(7)
1.540(6)
1065.39
293(2)
1.913(5)
1.952(5)
1.991(5)
2.001(5)
2.513(1)
1.929(5)
1.960(5)
1.980(5)
2.001(5)
2.502(1)
1.838(5)
O(11)–C(11)
O(12)–C(12)
O(13)–C(13)
O(14)–C(14)
O(21)–C(21)
O(22)–C(22)
O(23)–C(23)
O(24)–C(24)
C(1)–C(2)
0.71073
monoclinic
P21=n
Crystal system
Space group
Unit cell dimensions
ꢀ
a (A)
12.8610
17.4869(2) A
ꢀ
17.8955(1) A
ꢀ
ꢀ
b (A)
ꢀ
c (A)
C(2)–C(3)
C(3)–C(4)
b (°)
V (A )
107.85(1)
3830.92(6)
3
ꢀ
Z
4
1.847
C(14)–Re(1)–C(12)
C(14)–Re(1)–C(13)
C(12)–Re(1)–C(13)
C(14)–Re(1)–C(11)
C(12)–Re(1)–C(11)
C(13)–Re(1)–C(11)
C(14)–Re(1)–P(1)
C(12)–Re(1)–P(1)
C(13)–Re(1)–P(1)
C(11)–Re(1)–P(1)
C(14)–Re(1)–Re(2)
C(12)–Re(1)–Re(2)
C(13)–Re(1)–Re(2)
C(11)–Re(1)–Re(2)
P(1)–Re(1)–Re(2)
C(24)–Re(1)–C(22)
C(24)–Re(2)–C(21)
C(22)–Re(2)–C(21)
89.3(2)
97.0(2)
87.0(2)
94.4(2)
89.9(2)
168.2(2)
84.8(1)
172.8(2)
97.7(1)
86.5(1)
171.5(1)
82.4(2)
84.7(1)
83.7(1)
103.3(3)
88.6(2)
96.1(2)
90.6(2)
C(24)–Re(2)–C(23)
C(22)–Re(2)–C(23)
C(21)–Re(2)–C(23)
C(24)–Re(2)–P(2)
C(22)–Re(2)–P(2)
C(21)–Re(2)–P(2)
C(23)–Re(2)–P(2)
C(24)–Re(2)–Re(1)
C(22)–Re(2)–Re(1)
C(21)–Re(2)–Re(1)
C(23)–Re(2)–Re(1)
P(2)–Re(2)–Re(1)
C(4)–P(2)–Re(2)
C(1)–P(1)–Re(1)
C(2)–C(1)–P(1)
98.1(2)
89.1(2)
165.8(2)
86.0(1)
174.4(1)
91.6(1)
90.1(1)
167.3(1)
78.8(1)
82.8(1)
83.2(1)
106.6(3)
121.0(2)
126.9(2)
114.0(3)
113.9(4)
112.7(4)
119.2(3)
D
(Mg/m3)
ðcalcÞ
Absorption coefficient (mmꢁ1
F ð000Þ
)
6.515
2036
Crystal size (mm3)
0.400 ꢂ 0.300 ꢂ 0.140
h range for data collection (°) 2.03–29.27
Index ranges
ꢁ17 6 h 6 15; 0 6 k 6 23; 0 6 l 6 23
Reflections collected
Independent reflections [Rint
Completeness to h ¼ 29:27°
Absorption correction
Maximum and minimum
transmission
24 732
9463 [0.0283]
90.6%
]
SADABS
0.368256 and 0.191728
Refinement method
full-matrix least-squares on F 2
9463/1/446
1.165
Data/restraints/parameters
Goodness-of-fit on F 2
Final R indices [I > 2rðIÞ]
R indices (all data)
C(3)–C(2)–C(1)
C(2)–C(3)–C(4)
C(3)–C(4)–P(2)
R1 ¼ 0:0307, wR2 ¼ 0:0613
R1 ¼ 0:0430, wR2 ¼ 0:0667
0.662 and )0.747
Largest differential peak and
ꢁ3
ꢀ
hole (e A
)
always accompanied by a relatively high yield of the
dimer complex, and vice versa.
The relatively high and constant yield of the dppm
monodentate complex may be attributed to the reluc-
tance of this metalloligand complex to coordinate to
another [Re2(CO)9] fragment, which in turn can be at-
tributed to the unfavourable steric interactions that
would occur between the two [Re2(CO)9(PPh2)] frag-
ments held in close proximity by the methylene bridge
[13–15].
for an axial phosphorus atom can be expected to
be around +24 ppm by comparison with
ax-[Re2(CO)9(PPh3)] (Dd ¼ þ23:9 ppm) [12] and ax-
[Re2(CO)9(g1-dppf)] (Dd ¼ þ22:9 ppm) [3]. The equa-
torial isomers can be converted to the axial isomers by
refluxing in toluene for 10 min. At room temperature,
isomerization is complete within a week. Unlike the
monophosphine complexes [Re2(CO)9(PR3)] [PR3 ¼
PMe2Ph, PMePh2, P(O-o-tol)3, PPh3, P(CH2Ph)3] [11],
where complete isomerization is not always observed,
complete isomerization is always obtained in the
monodentate diphosphine complexes.
3.2. Reactions of the complexes [Re2(CO)9(g1-P–P)]
(P–P ¼ Ph2P(CH2)nPPh2, n ¼ 1–6) with Me3NO
Generally, reactions of [Re2(CO)9(g1-P–P)] with
Me3NO proceeded readily at room temperature. Two
major products, the close-bridged complex 1,2-dieq-
[Re2(CO)8(l-P–P)] and the phosphine oxide complex
[Re2(CO)9{P–P(O)}], were isolated by TLC using an
eluant of acetone–hexane (1:3) mixture. The formation
of phosphine oxide complexes is unexpected and the
mechanism for their formation will be discussed in an-
other paper. Suffice it to say here that the phosphine
oxide complexes result from the reaction of Me3NO
with [Re2(CO)9(g1-P–P)], and that this reaction was not
In general, yields of the monodentate complexes were
relatively low and very dependent on the exact reaction
conditions, except for the dppm complex, the yield of
which was consistently reproducible (Table 1). The low
yield may be attributed to the fact that the monodentate
complexes have a tendency to be irreversibly adsorbed
on the silica TLC plates. The variation of the yield may
reflect the high reactivity of the monodentate complexes
with the [Re2(CO)9(solvent)] intermediate to form the
dimer complexes. This is supported by the observation
that a relatively low yield of the monodentate complex is

W. Fan et al. / Inorganica Chimica Acta 357 (2004) 2441–2450
2447
Table 11
Crystallographic data for [{cis-ReCl(CO)4}2(l-dpph)] (3)
eq
eq
eq
eq
eq
eq
Empirical formula
Formula weight
Temperature (K)
C20H17Cl4O4PRe
680.31
293(2)
ax
eq
ax
Re
eq
Re
ꢀ
Wavelength (A)
0.71073
triclinic
Crystal system
Space group
ꢁ
P1
Fig. 4. Equatorial and axial positions of dirhenium carbonyl
complexes.
Unit cell dimensions
ꢀ
a (A)
8.9488(3)
ꢀ
b (A)
11.6877(4)
12.9457(5)
98.043(1)
ꢀ
c (A)
a (°)
b (°)
c (°)
In principle, the oxidative decarbonylation of the
[Re2(CO)9(g1-P–P)] complexes by Me3NO can give rise
to either chelate [(CO)5Re–Re(CO)3(g2-P–P)] or close-
bridged [Re2(CO)8(l-P–P)] complexes. The presence of
only one signal in the 31P NMR spectra could reflect
either a 1,2-diequatorial (closed-bridge) or 1,1-diequa-
torial (chelate) coordination mode of the diphosphine.
One major evidence for the formation of only close-
bridged products and not chelate products comes from
the expected difference in IR spectra of the two types of
products in the carbonyl stretching region. The major
difference between their m(CO) spectra relates to the
highest-frequency absorptions of the [Re(CO)5] and
[Re(CO)4] units. The [Re(CO)5] unit would show the
highest absorption band at around 2105 cmꢁ1 while the
[Re(CO)4] unit would exhibit the highest absorption
peak in the range of 2065–2072 cmꢁ1 [16,17]. All the
[Re2(CO)8(P–P)] complexes isolated have their highest
m(CO) peak occurring within the latter range, confirming
the absence of [Re(CO)5] units.
Site selectivity studies on substitution reactions of
[Re2(CO)9L] by Ingham and Coville [16] showed that
when L ¼ P(O-o-tol)3 or P(CH2Ph)3, reaction of
[Re2(CO)9L] with Me3NO and a second ligand L0
(L0 ¼ RCN) only yields products in which the two sub-
stituents are coordinated to different Re atoms. The
authors argued that the initially attached P-donor ligand
plays a major role in the Me3NO reaction, directing
reactivity to only the second metal center. The forma-
tion of close-bridged complexes here further confirms
their results.
It is interesting to note that in the reactions of the
dppm, dppe and dppp monodentate complexes, the
phosphorus atoms of the close-bridged products are
both coordinated equatorially, while in the reactions of
the dppb, dpppe and dpph monodentate complexes, the
31P NMR data suggest that ax–eq or even ax–ax
products were isolated first, which then isomerized to
the eq–eq products. This difference may be due to the
different lengths of the carbon chains of the diphos-
phines. In the dppm, dppe and dppp complexes, the
carbon chains are too short to allow the P atoms to
coordinate in the ax–eq or ax–ax fashion. In the dppb
and dpppe complexes, however, the carbon chains
are long enough for one P atom to be coordinated
102.155(1)
103.28(1)
3
ꢀ
V (A )
1262.79(8)
2
1.789
Z
D
(Mg/m3)
ðcalcÞ
Absorption coefficient (mmꢁ1
F ð000Þ
)
5.320
654
Crystal size (mm3)
0.56 ꢂ 0.48 ꢂ 0.26
2.20–29.29
ꢁ12 6 h 6 11; ꢁ16 6 k 6 15;
0 6 l 6 17
9371
h range for data collection (°)
Index ranges
Reflections collected
Independent reflections (Rint
Completeness to h ¼ 29:29°
Absorption correction
Maximum and minimum
transmission
)
5868 [0.0289]
85.1%
SADABS
0.189197 and 0.030441
Refinement method
full-matrix least-squares on
F 2
5868/0/271
Data/restraints/parameters
Goodness-of-fit on F 2
Final R indices [I > 2rðIÞ]
R indices (all data)
1.065
R1 ¼ 0:0365, wR2 ¼ 0:0922
R1 ¼ 0:0405, wR2 0:0973
¼
Largest differentꢁia3l peak
1.287 and )1.494
ꢀ
and hole (e A
)
Table 12
ꢀ
Selected bond lengths (A) and angles (°) for [{cis-ReCl(CO)4}2(l-
dpph)] (3)
Re(1)–C(13)
Re(1)–C(11)
Re(1)–C(14)
Re(1)–C(12)
Re(1)–P(1)
1.911(6)
1.981(7)
1.998(6)
2.015(6)
2.476(1)
Re(1)–Cl(1)
P(1)–C(1)
C(1)–C(2)
C(2)–C(3)
C(3)–C(3a)
2.480(2)
1.833(5)
1.529(7)
1.514(7)
1.57(1)
C(13)–Re(1)–C(11)
C(13)–Re(1)–C(14)
C(11)–Re(1)–C(14)
C(13)–Re(1)–C(12)
C(11)–Re(1)–C(12)
C(14)–Re(1)–C(12)
C(13)–Re(1)–P(1)
C(11)–Re(1)–P(1)
C(14)–Re(1)–P(1)
C(12)–Re(1)–P(1)
C(13)–Re(1)–Cl(1)
C(11)–Re(1)–Cl(1)
90.6(3)
92.3(2)
89.0(3)
91.5(3)
91.9(3)
176.1(2)
91.5(2)
177.5(2)
89.6(2)
89.4(2)
176.3(2)
88.8(2)
C(14)–Re(1)–Cl(1)
C(12)–Re(1)–Cl(1)
P(1)–Re(1)–Cl(1)
91.4(2)
84.8(2)
89.2(5)
C(121)–P(1)–C(111) 102.1(2)
C(121)–P(1)–C(1)
C(111)–P(1)–C(1)
C(121)–P(1)–Re(1)
C(111)–P(1)–Re(1)
C(1)–P(1)–Re(1)
C(2)–C(1)–P(1)
104.6(2)
104.2(3)
111.3(2)
117.3(2)
115.8(2)
113.9(4)
110.5(4)
112.5(6)
C(3)–C(2)–C(1)
C(2)–C(3)–C(3a)
observed in the synthesis of [Re2(CO)9(g1-P–P)] since in
the latter Me3NO was reacted with [Re2(CO)10] prior to
the addition of the diphosphines.

2448
W. Fan et al. / Inorganica Chimica Acta 357 (2004) 2441–2450
equatorially to one Re atom and the other coordinated
axially to the other Re atom. Lastly, the carbon chain in
the dpph complex is so long that even the ax–ax product
can be formed.
by 40.1° from the C(13)–C(13a) eclipsed position and
exhibiting a P–Re–Re–P torsional angle of 46.2°. The
P. . .P axis makes a projection of 26.4° onto the Re–Re
ꢀ
bond, and the P. . .P distance (4.176 A) is much larger
ꢀ
than the Re–Re bond length of 3.1075(3) A.
The effect of increase in the length of the carbon chain
between the two phosphorus atoms on the formation of
close-bridged complexes is also reflected in the yields
(Table 4). The yields decrease with the increase in the
length of the carbon chain. This is consistent with the
increase in steric strain that accompanies the increase in
length of the diphosphine chain that needs to be ac-
commodated between two mutually-bonded Re atoms.
It is also observed that, for the monodentate com-
plexes which can be isolated in both equatorial and axial
forms, the yields of [Re2(CO)8(l-P–P)] complexes from
equatorial isomers are always higher than those from
the axial isomers. Unreacted axial monodentate com-
plexes were also isolated at the end of the reactions of
these complexes with Me3NO. This suggests that the ax-
[Re2(CO)9(g1-P–P)] complexes are less reactive than
their equatorial isomers towards Me3NO.
The accommodation of the dppp chain between two
mutually bonded Re atoms creates significant strain on
the molecule, as shown by the obtuse P–Re–Re angle
[96.87(2)°] and an elongation of the Re–Re bond com-
ꢀ
pared to that in [Re2(CO)10] [3.041(1) A] [18]. The strain
is also evident from the very large C(1)–P(1)–Re(1),
C(2)–C(1)–P(1) and C(1)–C(2)–C(1a) bond angles in-
volving the dppp bridge.
The two Re octahedra in the molecule of 2 (Fig. 6)
are also staggered, being rotated by 47.2° from the
C(12)–C(22) eclipsed position, and exhibiting a P–Re–
Re–P torsional angle of 53.1°. These angles are much
larger than the corresponding angles in complex 1, re-
flecting the larger steric demand of the dppb ligand
compared to dppp. Although the P. . .P distance
ꢀ
(4.968 A) is much longer than that in the dppp analogue,
The length of the carbon chain of the diphosphine
also appears to affect the yield of the phosphine oxide
complexes. The formation of the phosphine oxide
complex is apparently inhibited when the carbon chain
is either too short (dppm) or too long (dpph) (Table 4).
the projection of the P. . .P axis makes a similar angle of
26.0° with the Re–Re bond in 2. The molecule of 2 also
shows much distortion due to the presence of the long
dppb bridge. For example, the P–Re–Re angles [average
ꢀ
104.93(3)°] and the Re–Re bond distance [3.1791(2) A]
are much larger than those of 1 [96.87(2)° and
3.1075(3) A]. The elongated Re–P bond distances [av-
ꢀ
erage 2.508(1) A] and decreased Re–Re–C(axial) bond
ꢀ
3.3. Crystal structures of [Re2(CO)8(l-dppp)] (1) and
[Re2(CO)8(l-dppb)] (2)
angles [average 169.4(1)°] compared to those of 1
ꢀ
In view of the lack of structural data for close-bridged
complexes, X-ray crystallographic analyses for com-
plexes 1 and 2 were carried out.
The molecule of 1 (Fig. 5) possesses a crystallo-
graphic C2 axis which joins C(2) of the propylene group
and the middle of the Re–Re bond. The geometry about
each rhenium is best described as distorted octahedral,
and the two Re octahedra are staggered, being rotated
[2.4811(9) A and 174.3(1)°] are also indicative of the
increased steric strain when dppp is replaced by dppb.
Within the dppb backbone, the strain is reflected in the
large bond angles, especially the C(3)–C(4)–P(2) angle
[119.2(3)°].
3.4. Formation and crystal structure of [{cis-ReCl-
(CO)4}2(l-dpph)] (3)
Several attempts were made to grow single crystals of
[Re2(CO)8(l-dpph)] by slow evaporation of CH2Cl2–
O13
C13
O12
C11
O12_4
O11
Re1
O14
P1
C114
C121
C1
C2
Fig. 5. Crystal structure of [Re2(CO)8(l-dppp)] (1).
Fig. 6. Crystal structure of [Re2(CO)8(l-dppb)] (2).

W. Fan et al. / Inorganica Chimica Acta 357 (2004) 2441–2450
2449
ꢀ
hexane solutions of the complex. These attempts re-
sulted in either powdery solids or polycrystalline mate-
rial. Good crystals were obtained when CH2Cl2 was
replaced by CDCl3, but the crystals were of the complex
[{cis-ReCl(CO)4}2(l-dpph)] (3) and not [Re2(CO)8-
(l-dpph)]. Complex 3 probably resulted from the
oxidative chlorination of [Re2(CO)8(l-dpph)] by chlo-
roform in the presence of light. A possible reason for the
easy oxidation may be that the breaking of the Re–
Re bond results in a substantial relief of the immense
steric strain originating from the accommodation of
the long dpph chain between two mutually-bonded Re
atoms.
The 31P NMR spectrum of 3 shows only one signal at
0.7 ppm. This reflects the symmetrical bridging mode of
dpph. The solution IR spectrum of 3 (in CH2Cl2)
exhibits a different m(CO) pattern from those of the
[Re2(CO)8(l-P–P)] complexes. Four bands [2110w,
2020s(sh), 2005s, 1943m] were observed in the carbonyl-
stretching region. This (3A0 + A00) pattern is similar to
those of other octahedral cis-[ReX(CO)4L] complexes
(L ¼ neutral donor, X ¼ halide) [17,19].
other Re–C bonds [1.981(7), 1.998(6) and 2.015(6) A].
This phenomenon is also observed in the complex cis-
[ReCl(CO)4(PPh2H)] [19].
3.5. Trends in 31P chemical shifts of [Re2(CO)8(l-P–P)]
complexes
Compounds of phosphorus with transition metals
have been intensively studied by 31P NMR spectroscopy
[20–24]. Generally, the dp values for metal complexes
with alkylphosphine or arylphosphine ligands can be
approximately predicted using empirical relationships of
the type indicated in Eq. (1), which states that the co-
ordination shift Dd is a linear function of the dp value of
the free ligand [24].
Dd ¼ dpðcomplexÞ ꢁ dpðfree ligandÞ
¼ A½dpðfree ligandÞꢃ þ B:
The constants A and B depend on the metal, the type of
ð1Þ
complex and the other ligands present.
For complexes with chelating ligands, the expression
for the coordination shift should be modified by adding
a ring contribution DR [24]. The ring contribution is the
difference between the coordination shifts for complexes
with chelating ligands (e.g., dppe) and those in which the
bidentate ligand is replaced by two similar, but
monodentate ligands (e.g., PMePh2). Although the
theoretical explanations of DR are not well-developed,
the knowledge of its contribution to the dp value is
The molecule of 3 (Fig. 7) consists of two octahedral
rhenium centers singly-bridged by a dpph ligand. Each
rhenium atom is coordinated to four carbonyl ligands,
one chloro ligand, and one phosphino group which is cis
to the chloro ligand. The dpph chain is fully extended
and not coiled, thus maximising the distance between
the [ReCl(CO)4] units. Interestingly, the C(1)–C(2) bond
is anti to the phenyl group C(121)–C(126) rather than
the apparently more sterically demanding [ReCl(CO)4]
group. The molecule possesses a crystallographic in-
version center at the midpoint of the C(3)–C(3a) bond of
the hexylene bridge. Thus only one half of the molecule
is crystallographically unique.
useful for structure determination and assignment of 31
resonances.
P
There is no study, to our knowledge, reported for ring
contributions of close-bridged transition metal com-
plexes with diphosphines. The 31P data for the close-
bridged dirhenium complexes with Ph2P(CH2)nPPh2
(n ¼ 1–6) are therefore inspected to see if any note-
worthy features are observed. The dP values for the
close-bridged complexes are compared with those for
the free phosphines in Table 13, and a plot of Dd against
dP (free) is given in Fig. 8. It can be seen that the Dd
value for the dppp complex is much smaller than those
The strongest Re–CO linkage occurs in the carbonyl
group trans to the p-donating chloro ligand, the Re–
ꢀ
C(13) bond [1.911(6) A] being much shorter than the
Table 13
31P NMR data for 1,2-dieq-[Re2(CO)8(l-P–P)] and free phosphines
P–P
dp(free)a
[Re2(CO)8(l-P–P)]
b
dp
Dd
dppm
dppe
)25.0
)14.7
)17.8c
)17.8
)18.3
)18.2
0.3
4.2
+25.3
+18.9
+0.3
dppp
dppb
dpppe
dpph
)17.5
)1.0
)1.0
)1.0
+16.8
+17.3
+17.2
a In THF.
b In CDCl3.
c In toluene.
Fig. 7. Crystal structure of [{cis-ReCl(CO)4}2(l-dpph)] (3).

2450
W. Fan et al. / Inorganica Chimica Acta 357 (2004) 2441–2450
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Fig. 8. Plot of Dd against dP(free) for [Re2(CO)8(l-P–P)] complexes
(P–P ¼ Ph2P(CH2)nPPh2, n ¼ 1–6).
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of the other diphosphine complexes, suggesting the
presence of a ring contribution. It would be of interest to
extend this study to other close-bridged [Re2(CO)8-
(l-P–P)] complexes with diphosphines containing pro-
pylene backbones, to see if they also exhibit small Dd
values.
[8] SMART Software Reference Manual, Version 4.0, Siemens
Energy & Automation, Inc., Analytical Instrumentation, Madi-
son, WI, 1996.
4. Supplementary material
[9] G.M. Sheldrick, SADABS, a Software for Empirical Absorption
€
Correction, University of Gottingen, 1996.
Crystallographic data (excluding structure factors)
for the structures reported in this paper have been de-
posited with the Cambridge Crystallographic Data
Centre as supplementary publications nos. CCDC
214442 (for 1), 214443 (for 2), and 214444 (for 3).
Copies of the data can be obtained free of charge on
application to CCDC, 12 Union Road, Cambridge CB2
1EZ, UK (fax: +44-1223-336-033; e-mail: de-
posit@ccdc.cam ac.uk or http://www.ccdc.cam.ac.uk).
[10] SHELXTL Reference Manual, Version 5.03, Siemens Energy &
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1996.
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Acknowledgements
We acknowledge the financial support (Grant No. RP
15/95 YYK) of the National Institute of Education,
Nanyang Technological University (NTU). Wei Fan and
Rui Zhang are grateful to NTU for scholarship awards.
[18] M.R. Churchill, K.N. Amoh, H.J. Wasserman, Inorg. Chem. 20
(1981) 1609.
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NMR Spectroscopy in Stereochemical Analysis, Methods in
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