Complexes derived from 4-(diphenylphosphino)benzoic acid and related ligands that contain mixed-metal assemblies of palladium(II) or gold(I) in combination with the multiply bonded dirhenium(II) unit

Article abstract of DOI:10.1016/S0020-1693(02)00983-0

The reactions of cis-Re₂(μ-O₂CCH₃)₂Cl ₂(μ-dppm)₂ (dppm=Ph₂PCH₂PPh₂) with substituted benzoic acids of the type 4-XC₆H₄CO₂H (X=Ph₂P, Ph₂P(O), Ph₂P(S) or Ph₂P(O)CH₂) and with quinoline-4-carboxylic acid afford the complexes cis-Re₂(μ-O₂CC₆H₄-4-X) ₂CI₂(μ-dppm)₂ (X=Ph₂P (1), Ph₂P(O) (2), Ph₂P(S) (3) or Ph₂P(O)CH₂ (4)) and cis-Re₂(μ-O₂CC₁₀H₆N) ₂Cl₂(μ-dppm)₂ (5). Similar reactions of trans-Re₂(μ-O₂CCH₃)₂Cl ₂(μ-dppE)₂ (dppE=Ph₂PC(=CH₂)PPh₂) with 4-Ph₂PC₆H₄CO₂H and quinoline-4-carboxylic acid give trans-Re₂(μ-O₂CC₆H₄-4-PPh ₂)₂Cl₂(μ-dppE)₂ (6) and trans-Re₂(μ-O₂CC₁₀H₆N) ₂Cl₂(μ-dppE)₂ (7), respectively. The ability of the unbound ligand functionality on the μ-carboxylate ligands in complexes 1-7 to be used to form mixed-metal complexes is demonstrated by the reactions of 1 and 6 with AuCl(tht) (tht=tetrahydrothiophene) to give cis-Re₂(μ-O₂CC₆H₄-4-PPh ₂)₂Cl₂(μ-dppm)₂(AuCl) ₂ (8) and trans-Re₂(μ-O₂CC₆H₄-4-PPh ₂)₂Cl₂(μ-dppE)₂(AuCl) ₂ (9). In addition, the reaction of 1 with PdCl₂(COD) affords the Re₂Pd₂ complex cis-Re₂(μ-O₂C₆H₄-4-PPh ₂)₂Cl₂(μ-dppm)₂(Pd ₂Cl₄) (10), in which the planar [(P)ClPd(μ-Cl)₂PdCl(P)] unit has the unusual cis planar structure. An alternative method for preparing mixed-metal Re₂Pd₂ assemblies is shown by the reaction of cis-Re₂(μ-O₂CCH₃)₂Cl ₂(μ-dppm)₂ with cis-PdCl₂[(Ph₂PCH₂)₂N-4-C ₆H₄CO₂H] to produce the complex cis-Re₂Cl₂(μ-dppm)₂[μ-O₂ CC₆H₄-4-N(CH₂PPh₂)₂ (PdCl₂)]₂ (11) in which the mononuclear cis-PdCl₂(P)₂ units are retained. The structures of 1, 7 and 10 have been established by X-ray crystallography.

Full text of DOI:10.1016/S0020-1693(02)00983-0

Inorganica Chimica Acta 338 (2002) 219Á227
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www.elsevier.com/locate/ica
Complexes derived from 4-(diphenylphosphino)benzoic acid and
related ligands that contain mixed-metal assemblies of palladium(II)
or gold(I) in combination with the multiply bonded dirhenium(II)
unit
Shan-Ming Kuang, Phillip E. Fanwick, Richard A. Walton *
Department of Chemistry, Purdue University, 1393 Brown Building, West Lafayette, IN 47907-1393, USA
Received 28 February 2002; accepted 8 April 2002
Abstract
The reactions of cis-Re2(m-O2CCH3)2Cl2(m-dppm)2 (dppmꢀ
XC6H4CO2H (XꢀPh2P, Ph2P(O), Ph2P(S) or Ph2P(O)CH2) and with quinolineÁ
O2CC6H4Ã4-X)2CI2(m-dppm)2 (XꢀPh2P (1), Ph2P(O) (2), Ph2P(S) (3) or Ph2P(O)CH2 (4)) and cis-Re2(m-O2CC10H6N)2Cl2(m-
dppm)2 (5). Similar reactions of trans-Re2(m-O2CCH3)2Cl2(m-dppE)2 (dppEꢀPh2PC(ÄCH2)PPh2) with 4-Ph2PC6H4CO2H and
quinolineÁ4-carboxylic acid give trans-Re2(m-O2CC6H4Ã4-PPh2)2Cl2(m-dppE)2 (6) and trans-Re2(m-O2CC10H6N)2Cl2(m-dppE)2 (7),
respectively. The ability of the unbound ligand functionality on the m-carboxylate ligands in complexes 1Á7 to be used to form
mixed-metal complexes is demonstrated by the reactions of 1 and 6 with AuCl(tht) (thtꢀtetrahydrothiophene) to give cis-Re2(m-
O2CC6H4Ã4-PPh2)2Cl2(m-dppm)2(AuCl)2 (8) and trans-Re2(m-O2CC6H4Ã4-PPh2)2Cl2(m-dppE)2(AuCl)2 (9). In addition, the
reaction of 1 with PdCl2(COD) affords the Re2Pd2 complex cis-Re2(m-O2C6H4Ã4-PPh2)2Cl2(m-dppm)2(Pd2Cl4) (10), in which the
planar [(P)ClPd(m-Cl)2PdCl(P)] unit has the unusual cis planar structure. An alternative method for preparing mixed-metal Re2Pd2
assemblies is shown by the reaction of cis-Re2(m-O2CCH3)2Cl2(m-dppm)2 with cis-PdCl2[(Ph2PCH2)2NÃ4-C6H4CO2H] to produce
the complex cis-Re2Cl2(m-dppm)2[m-O2CC6H4Ã4-N(CH2PPh2)2(PdCl2)]2 (11) in which the mononuclear cis-PdCl2(P)2 units are
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Ph2PCH2PPh2) with substituted benzoic acids of the type 4-
/
/
4-carboxylic acid afford the complexes cis-Re2(m-
/
/
/
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/
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/
/
/
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/
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retained. The structures of 1, 7 and 10 have been established by X-ray crystallography.
# 2002 Elsevier Science B.V. All rights reserved.
Keywords: Crystal structures; Substituted benzoic acids; Palladium(II) complexes; Gold(I) complexes; Dirhenium(II) complexes; MetalÁmetal
/
multiple bonds
1. Introduction
ligands, as well as mixed-metal squares of the type
Re4Pt2 in which dirhenium pairs are linked to Pt(II)
units via isonicotinate ligands [3]. The use of [NCS]ꢁ,
[CN]ꢁ, [N(CN)2]ꢁ, [C(CN)3]ꢁ and [Ni(CN)4]2ꢁ
bridges has provided an entry to other types of
dirhenium dimers-of-dimers [4] and to mixed-metal
Re4Pd2, Re2Ag, Re2W, Re2Pt and Re2Rh assemblies [5].
While a few metal complexes of the 2-(diphenylphos-
The synthesis of homonuclear and heteronuclear
complexes that are derived by incorporating multiply
bonded dirhenium units into multi-metal assemblies, has
largely been focused on the use of carboxylic acids [1Á3],
/
and thiocyanate and cyanide-containing moieties [4,5] as
the linker ligands. By these means we have obtained
paramagnetic dimers-of-dimers [1,2], diamagnetic hy-
drogen-bonded chains of dimers-of-dimers [1], and
diamagnetic cyclic triangles [1] that are composed of
only dirhenium units linked through dicarboxylate
phino)benzoate ligand had been reported previously [6Á
/
10], multiply bonded dimetal complexes that contain
this ligand, and ones closely related to it, had not been
described until very recently when we reported several
dimolybdenum(II) complexes of the type Mo2(m-
* Corresponding author. Tel.: ꢂ
0239
E-mail address: rawalton@purdue.edu (R.A. Walton).
/
1-765-494 5464; fax: ꢂ1-765-494
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O2CC6H4X)4 where Xꢀ/4-Ph2P, 2-Ph2P, 4-Ph2P(O) or
4-Ph2P(S) [11]. Among the findings of note were: (1) that
0020-1693/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved.
PII: S 0 0 2 0 - 1 6 9 3 ( 0 2 ) 0 0 9 8 3 - 0

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Mo2(m-O2CC6H4Ã
/
4-P(O)Ph2)4 has a structure in which
88%. IR spectrum (cmꢁ1): n(COO) 1694(s) and 1294(s),
n(PÄS) 648 (mÁ
s). 31P{1H) NMR spectrum (in CDCl3):
dꢀ 44.2. The phosphine oxide ligand Ph2P(O)CH2Ã4-
C6H4CO2H was isolated as an oxidation product of
Ph2PCH2Ã4-C6H4CO2H from the reaction between
Ph2PLi (prepared from n-BuLi and Ph2PH) and 2-
ClCH2C6H4CO2Na in THF using the same procedure
and work-up as that we used to prepare 4-Ph2PC6H4-
CO2H; Yield: 32%. This oxide has also been prepared by
pairs of PÄO groups are coordinated to neighboring
/
/
/
dimolybdenum molecules in such a way so as to
generate a 2-dimensional polymeric array, and (2) that
the sets of uncoordinated phosphine groups in the 4-
Ph2P and 2-Ph2P complexes can be coordinated to AuCl
units to form mixed-metal Mo2Au4 assemblies. We now
report several triply bonded dirhenium(II) complexes
that contain the 4-(diphenylphosphino)benzoate ligand,
as well as related compounds derived from the 4-
Ph2P(O), 4-Ph2P(S) and 4-Ph2P(O)CH2 substituted
benzoic acids. In addition, we report a pair of dirhen-
/
ꢂ
/
/
/
the reaction between Ph2P(O)H, ClCH2Ã
and KOH [20]. IR spectrum (cmꢁ1): n(COO) 1685(s)
and 1290(mÁs), n(Pꢀ
O) 1195(m). 31P{1H} NMR
spectrum (in CDCl3): dꢀ 24.8. The reaction between
Ph2PH, (HCHO)n and 4-aminobenzoic acid afforded
(Ph2PCH2)2NÃ4-C6H4CO2H with the use of a proce-
/
4-C6H4CO2H
/
/
ium(II) complexes that contain the quinolineÁ
/
4-carbox-
/
ꢂ
/
ylate ligand and bear a close structural relationship to
the 4-(diphenylphosphino)benzoate complexes. The use
of several of these complexes to form mixed-metal
Re2Pd2 and Re2Au2 clusters is also described. Some of
these results have been the subject of a preliminary
communication [12].
/
dure similar to that described by Balch et al. [21] for
other ligands of this type; Yield: 62%. Anal. Found: C,
73.60; H, 5.38. Calc. for C33H29NO2P2: C, 74.29; H,
5.48%. IR spectrum (cmꢁ1): n(COO) 1672(s) and
1293(s). 31P{1H} NMR spectrum (in CDCl3): dꢀ
25.9. This phosphine was used to prepare
PdCl2[(Ph2PCH2)2NÃ4-C6H4CO2H] in the following
way. A mixture of (Ph2PCH2)2NÃ4-C6H4CO2H (106
mg, 0.20 mmol) and PdCl2(COD) (57 mg, 0.20 mmol) in
40 ml of dichloromethane was stirred at r.t. for 1 h and
the solvent evaporated slowly to leave a yellow micro-
crystalline product that was washed with diethyl ether
/
ꢁ
/
2. Experimental
/
/
2.1. Starting materials and reaction procedures
The dimetal complexes cis-Re2(m-O2CCH3)2Cl2(m-
dppm)2 (dppmꢀ
O2CCH3)2Cl2(m-dppE)2 (dppEꢀ
[14] were prepared by the published literature proce-
dures. The reagents AuCl(tht) (thtꢀtetrahydrothio-
phene) [15] and PdCl2(COD) (CODꢀ1,5-cycloocta-
/
Ph2PCH2PPh2) [13] and trans-Re2(m-
/
Ph2PC(ÄCH2)PPh2)
/
(4ꢃ
54.93; H, 4.41. Calc. for C33H29Cl2NO2P2Pd: C, 55.76;
H, 4.11%. IR spectrum (cmꢁ1): n(COO) 1677 (mÁ
s) and
1290(m), n(PdÃ
Cl) 311(s), 296(m) cmꢁ1 31P{1H} NMR
spectrum (in CDCl3): dꢀ 2.2.
/10 ml); Yield: 132 mg (94%). Anal. Found: C,
/
/
/
/
.
diene) [16] were obtained by the use of standard
methods.
/
ꢂ
/
Solvents were deoxygenated by purging with dinitro-
gen prior to use and all reactions were performed under
an atmosphere of dinitrogen.
The synthesis of 4-(diphenylphosphino)benzoic acid
was accomplished by a modification of the procedure
for the synthesis of 2-(diphenylphosphino)benzoic acid
described by Hoots et al. [17]. Our method involved the
reaction between a THF solution of 4-ClC6H4CO2Na
and a solution of Ph2PLi that was generated from the
reaction between Ph2PH and n-BuLi. Work-up by the
literature method [17] afforded colorless crystals of 4-
Ph2PC6H4CO2H in 58% yield. This method is different
from that used previously to obtain this acid which
involved the reaction between (4-lithiophenyl)-diphenyl-
phosphine and carbon dioxide [18]. IR spectrum
(cmꢁ1): n(COO) 1690(s) and 1296(s). 31P{1H} NMR
2.2. Synthesis of cis-Re2(m-O2CC6H4Ã
/
4-PPh2)Cl2(m-
dppm)2 (1)
A mixture of cis-Re2(m-O2CCH3)2Cl2(m-dppm)2 (133
mg, 0.10 mmol) and 4-Ph2PC6H4CO2H (80 mg, 0.26
mmol) was refluxed in 50 ml of ethanol for 3 days. The
reaction mixture was cooled to r.t., filtered and the
insoluble red crystals washed with ethanol (2ꢃ
and diethyl ether (2ꢃ5 ml); Yield: 170 mg (92%). Anal.
Found: C, 56.43; H, 4.12. Calc. for C92H84Cl2O6P6Re2
(i.e. 1×2EtOH): C, 57.71; H, 4.42%. The identity of these
crystals was confirmed by X-ray crystallography.
Complexes 2Á4 were prepared by the same procedure
used to obtain 1.
/5 ml)
/
spectrum (in CDCl3): dꢀ
Ph2P(X)C6H4CO2H, where Xꢀ
/
ꢁ
/
4.1. Samples of 4-
/
/O or S, were obtained
by the reactions of 4-Ph2PC6H4CO2H with H2O2, in
dichloromethane at room temperature (r.t.), and with
S8, in refluxing toluene, respectively, using the proce-
dures described by Auscott et al. [19] for similar
phosphine ligands. For 4-Ph2P(O)C6H4CO2H; Yield:
92%. IR spectrum (cmꢁ1): n(COO) 1707(s) and 1255(s)
/
2.3. Synthesis of cis-Re2(m-O2CC6H4Ã
/
4-
P(O)Ph2)2Cl2(m-dppm)2 (2)
cmꢁ1, n(PÄ
/
O) 1160(s). 31P{1H} NMR spectrum (in
30.4. For 4-Ph2P(S)C6H4CO2H; Yield:
Yield: 79%. Recrystallization from CH2Cl2Á
/Et2O
CDCl3): dꢀ
/
ꢂ
/
gave orange microcrystals. Anal. Found: C, 54.74; H,

S.-M. Kuang et al. / Inorganica Chimica Acta 338 (2002) 219Á
/227
221
4.19. Calc. for C89H74Cl4O6P6Re2 (2×
/CH2Cl2): C, 55.11;
2.9. Synthesis of cis-Re2(m-O2CC6H4Ã
/
4-PPh2)2Cl2(m-
H, 3.85%.
dppm)2(AuCl)2 (8)
A solution of 1 (91 mg, 0.05 mmol) and AuCl(tht) (32
mg, 0.10 mmol) in 45 ml of dichloromethane was stirred
at 25 8C for 2 h, the solvent evaporated slowly, and the
red microcrystals of 8 were washed with diethyl ether
2.4. Synthesis of cis-Re2(m-O2CC6H4Ã
/
4-
P(S)Ph2)2Cl2(m-dppm)2 (3)
Yield: 79%. Anal. Found: C, 55.29; H, 3.88. Calc. for
C88H72Cl2O4P6Re2S2: C, 56,02; H, 3.85%.
(2ꢃ5 ml); Yield: 100 mg (88%). Anal. Found: C, 46.50;
H, 3.25; Cl, 6.44. Calc. for C89H74Au2Cl4O4P6Re2: C,
46.21; H, 3.17; Cl, 6.20%.
/
2.5. Synthesis of cis-Re2(m-O2CC6H4Ã
/
4-
2.10. Synthesis of trans-Re2(m-O2CC6H4Ã
/
4-
CH2P(O)PPh2)2Cl2(m-dppm)2 (4)
PPh2)2Cl2(m-dppE)2(AuCl)2 (9)
Yield: 67%. Recrystallization from CH2Cl2Á
gave orange microcrystals. Anal. Found: C, 55.44; H,
4.40. Calc. for C91H78Cl4O6P6Re2 (i.e. 4×CH2Cl2): C,
55.55; H, 4.00%.
/
Et2O
This complex was obtained with the use of a
procedure similar to that described in Section 2.9 from
the reaction between 5 and AuCl(tht): Yield: 85%. Anal.
Found: C, 44.47; H, 3.26. Calc. for C91H74Au2-
/
Cl6O4P6Re2 (i.e. 9×/CH2Cl2): C, 45.61; H, 3.11%.
2.6. Synthesis of cis-Re2(m-O2CC10H6N)2Cl2(m-dppm)2
(5)
2.11. Synthesis of cis-Re2(m-O2CC6H4Ã
/
4-PPh2)2Cl2(m-
dppm)2(PdCl2)2 (10)
A mixture of cis-Re2(m-O2CCH3)2Cl2(m-dppm)2 (100
A solution of Pd(COD)Cl2 (16.0 mg, 0.056 mmol) in 5
ml of dichloromethane was added to a solution of 1
(45.5 mg, 0.025 mmol) in 30 ml of acetonitrile. The clear
mixed solution was left undisturbed for 3 days to
produce orange crystals of 10. These were filtered off
mg, 0.075 mmol) and quinolineÁ4-carboxylic acid (85
/
mg, 0.50 mmol) was refluxed in 60 ml of ethanol for 4
days and the reaction mixture then allowed to cool
before being filtered. The insoluble red crystals were
washed with ethanol (2ꢃ
/
5 ml) and diethyl ether (2ꢃ
/
5
and washed with dichloromethane (2ꢃ10 ml); Yield: 26
/
ml); Yield: 81 mg (70%). Anal. Found: C, 53.73; H, 3.63.
Calc. for C70H56Cl2N2O4P4Re2: C, 54.02; H, 3.63,
Found: C, 53.73; H, 3.63%.
mg (48%). This complex, the identity of which was
established by X-ray crystallography, was insoluble in
polar and non-polar organic solvents. We were unable
to obtain satisfactory elemental microanalyses for 10.
2.7. Synthesis of trans-Re2(m-O2CC6H4Ã
/4-
2.12. Synthesis of cis-Re2Cl2(m-dppm)2[m-O2CC6H4Ã
/4-
PPh2)2Cl2(m-dppE)2 (6)
N(CH2PPh2)2(PdCl2)]2 (11)
A similar procedure to that described in Section 2.2
was used to react trans-Re2(m-O2CCH3)2Cl2(m-dppE)2
with 4-Ph2PC6H4CO2H. Brown microcrystals were ob-
A mixture of cis-Re2(m-O2CCH3)2Cl2(dppm)2 (66 mg,
4-C6H4CO2H]
(71 mg, 0.10 mmol) was refluxed in 50 ml of EtOH for
4 days. The cooled reaction mixture was filtered and the
0.05 mmol) and PdCl2[(Ph2PCH2)2NÃ
/
tained by recrystallization of the product from CH2Cl2Á
Et2O; Yield: 55%. Anal. Found: C, 56.72; H, 3.87. Calc.
for C91H74Cl4O4P6Re2 (i.e. 5×CH2Cl2): C, 56.58; H,
3.86%.
/
insoluble yellow powder washed with ethanol (2ꢃ
and diethyl ether (2ꢃ5 ml). Yellow microcrystals were
obtained by recrystallization from dichloromethaneÁ
/
5 ml)
/
/
/
diethyl ether; Yield: 97 mg (74%). Anal. Found: C,
51.16; H, 3.90. Calc. for C117H102Cl8N2O4P8Pd2Re2 (i.e.
2.8. Synthesis of trans-Re2(m-O2CC10H6N)2Cl2(m-
dppE)2 (7)
11×/CH2Cl2); C, 51.73; H, 3.78%.
2.13. X-ray crystallography
A procedure similar to that described in Section 2.7
was used to react trans-Re2(m-O2CCH3)2Cl2(m-dppE)2
Single crystals of 1, 7, and 10 were obtained directly
from the reaction mixtures. Subsequent structure ana-
lysis showed that the crystals of 1 contained ethanol
with quinolineÁ4-carboxylic acid to produce brown
/
crystals of 7; Yield: 77%. Anal. Found: C, 53.98; H,
3.86. Calc. for C72H56Cl2N2O4P4Re2: C, 54.72; H,
3.57%. The identity of this product was confirmed by
X-ray crystallography.
solvent molecules and were of composition 1×
/2EtOH.
The crystals were mounted on glass fibers in random
orientations. The data collections for 1 and 7 were

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S.-M. Kuang et al. / Inorganica Chimica Acta 338 (2002) 219Á227
/
carried out at 150(9
/
1) K and for 10 at 170(9
/
1) K with
The most important bond distances and bond angles
for 1, 7 and 10 are given in Tables 2, 4 and 5 while the
ORTEP [27] representation of the structures are shown in
graphite-monochromated Mo Ka radiation (lꢀ
/
˚
0.71073 A) on a Nonius Kappa CCD diffractometer.
Figures Figs. 1Á3.
/
Lp corrections were applied to the data sets. The key
crystallographic data are given in Table 1.
The structure of 1 was solved using the structure
solution program PATTY in DIRDIF92 [22] while for 7
and 10 DIRDIF99 was used [23]. The remaining non-
hydrogen atoms were located in succeeding difference
Fourier syntheses. Hydrogen atoms bound to carbon
2.14. Physical measurements
Infrared spectra were recorded in the region 4000Á400
/
cmꢁ1 as KBr pellets and from 700 to 150 cmꢁ1 as Nujol
1
were placed in calculated positions according to idea-
˚
mulls on a PerkinÁ/Elmer 2000 FT IR spectrometer. H
and 31P{1H} NMR spectra were obtained on a Varian
INOVA 300 spectrometer. Proton resonances were
referenced internally to the residual protons in the
incompletely deuterated solvent. The 31P{1H} NMR
spectra were recorded at 121.6 MHz, with 85% H3PO4
as an external standard. Cyclic voltammetric measure-
ments were carried out with the use of a BAS Inc. Model
CV-27 instrument in conjunction with a BAS Model
RXY recorder and were recorded on dichloromethane
solutions that contained 0.1 M tetra-n-butylammonium
hexafluorophosphate (TBAH) as supporting electrolyte.
lized geometries with CÃ
/
Hꢀ
/
0.95 A and U(H)ꢀ
/
1.31Ueq(C). They were included in the refinement but
constrained to ride on the atom to which they are
bonded. An empirical absorption correction using
SCALEPACK [24] was applied. The final refinements
were performed by the use of the program SHELXL-97
[25]. The highest peak in the final difference Fouriers of
ꢁ3
˚
1, 7, and 10 had a height of 1.27, 2.04 and 1.59 e A
respectively.
,
The structure solutions and refinements of all three
compounds proceeded without significant problems.
The C and O atoms of the ethanol solvent molecules
present in the structure of 1 was refined with anisotropic
thermal parameters although one of these molecules was
disordered; specifically the O atom and one of the C
atoms occupied two half positions. An unidentified and
disordered solvent molecule was present in the crystal of
17 but the disorder could not be adequately modeled.
Accordingly, the molecule was removed with squeeze
option in PLATON [26].
E1/2 values, determined as (EpaꢂEpc)/2, were referenced
to the silver/silver chloride (Ag/AgCl) electrode at 25 8C
and were uncorrected for junction potentials. Under our
/
Table 2
˚
Important bond lengths (A) and bond angles (8) for cis-Re2(m-
a
O2CC6H4Ã4-PPh2)2Cl2(m-dppm)2×2EtOH(1)
Bond lengths
Re(1)ÃRe(2)
Re(1)ÃO(1)
Re(1)ÃO(3)
Re(1)ÃP(5)
Re(1)ÃP(7)
Re(1)ÃCl(1)
Re(2)ÃO(2)
Re(2)ÃO(4)
2.3040(2)
2.144(3)
2.150(3)
Re(2)ÃP(8)
Re(2)ÃP(6)
Re(2)ÃCl(2)
2.3868(11)
2.4025(12)
2.5347(11)
1.272(5)
Table 1
Crystallographic data for cis-Re2(m-O2CC6H4Ã4-PPh2)2Cl2(m-dppm)2
2EtOH (1×2EtOH), trans-Re2(m-O2CC10H6N)2Cl2(m-dppE)2 (7), and
cis-Re2(m-O2CC6H4Ã4-PPh2)2Cl2(m-dppm)2(PdCl2)2 (10)
2.3926(12) O(1)ÃC(10)
2.4031(11) O(2)ÃC(10)
2.5562(11) O(3)ÃC(30)
1.263(5)
1.264(5)
1.272(5)
1×2EtOH
7
10
2.129(3)
O(4)ÃC(30)
2.141(3)
Empirical formula
C
92H84Cl2O6- C72H56Cl2N2- C88H72Cl6O4P6-
P6Re2
1914.84
P21/n (No. 14) C2/c (No. 15) C2/c (No. 15)
O4P4Re2
1580.46
Pd2Re2
2177.31
Bond angles
Formula weight
Space group
O(1)ÃRe(1)ÃO(3)
O(1)ÃRe(1)ÃRe(2)
O(3)ÃRe(1)ÃRe(2)
O(1)ÃRe(1)ÃP(5)
O(3)ÃRe(1)ÃP(5)
Re(2)ÃRe(1)ÃP(5)
O(1)ÃRe(1)ÃP(7)
O(3)ÃRe(1)ÃP(7)
Re(2)ÃRe(1)ÃP(7)
P(5)ÃRe(1)ÃP(7)
O(1)ÃRe(1)ÃCl(1)
O(3)ÃRe(1)ÃCl(1)
80.04(11) O(2)ÃRe(2)ÃRe(1)
88.96(8)
86.76(8)
95.24(8)
170.45(8)
100.38(3)
170.25(9)
92.65(9)
94.50(3)
93.10(4)
82.31(9)
82.57(8)
87.22(8)
89.10(8)
170.61(8)
94.09(8)
100.10(3)
91.30(8)
170.76(9)
93.75(3)
94.06(4)
81.88(8)
82.17(8)
O(4)ÃRe(2)ÃRe(1)
O(2)ÃRe(2)ÃP(8)
O(4)ÃRe(2)ÃP(8)
Re(1)ÃRe(2)ÃP(8)
O(2)ÃRe(2)ÃP(6)
O(4)ÃRe(2)ÃP(6)
Re(1)ÃRe(2)ÃP(6)
P(8)ÃRe(2)ÃP(6)
O(2)ÃRe(2)ÃCl(2)
O(4)ÃRe(2)ÃCl(2)
˚
a (A)
17.8968(2)
31.8530(4)
18.6342(2)
90
14.9241(5)
19.4965(8)
22.8248(10)
90
19.0226(4)
17.4693(4)
25.2040(7)
90
˚
b (A)
˚
c (A)
a (8)
b (8)
g (8)
V (A )
Z
Dcalc (g cmꢁ3
97.5326(8)
90
107.3107(19) 109.5935(10)
90
90
7890.6(6)
4
3
˚
10531.1 (4)
4
1.208
6340.5(8)
4
)
1.656
4.10
1.833
3.92
m (Mo Ka)
2.51
Re(1)ÃRe(2)ÃCl(2) 167.37(3)
(mmꢁ1
)
a
Re(2)ÃRe(1)ÃCl(1) 167.05(3)
P(8)ÃRe(2)ÃCl(2)
P(6)ÃRe(2)ÃCl(2)
O(2)ÃC(10)ÃO(1)
89.53(4)
92.73(4)
123.7(4)
124.1(4)
R(Fo)
Rw(Fo
0.043
0.096
0.953
0.050
0.110
1.021
0.049
0.116
1.025
P(5)ÃRe(1)ÃCl(1)
P(7)ÃRe(1)ÃCl(1)
O(2)ÃRe(2)ÃO(4)
90.10(4)
93.47(4)
2
b
)
Goodness-of-fit
78.43(11) O(3)ÃC(30)ÃO(4)
a
RꢀajjFojꢁjFcjj/ajFoj with Fo2ꢀ2s(Fo2).
a
Numbers in parentheses are estimated standard deviations in the
least significant digits.
b
2
2
2 2 1/2
Rwꢀ[aw(jFo jꢁjFc j)2/awjFo j ]
.

S.-M. Kuang et al. / Inorganica Chimica Acta 338 (2002) 219Á
/227
223
3. Results and discussion
3.1. Carboxylate exchange reactions of complexes of the
types cis- and trans-Re2(m-O2CCH3)2Cl2(m-PP)2
(PPꢀ/dppm or dppE) with 4-substituted benzoic acids
and quinolineÁ/4-carboxylic acid
The lability of the cis pair of m-acetato ligands in cis-
Re2(m-O2CCH3)2Cl2(m-dppm)2 towards 4-Ph2PC6H4-
CO2H, 4-Ph2P(O)C6H4CO2H, 4-Ph2P(S)C6H4CO2H
and 4-Ph2P(O)CH2C6H4CO2H in refluxing ethanol
solutions of these reagents provides a high yield route
to compounds of the type cis-Re2(m-O2CC6H4Ã
/
4-
X)2Cl2(m-dppm)2 (XꢀPh2P (1), Ph2P(O)(2), Ph2P(S)(3)
/
or Ph2P(O)CH2(4)) in which the basic structure of the
starting material is retained. This is shown by a single
crystal X-ray structure determination of compound 1.
An ORTEP [27] representation of this structure is shown
in Fig. 1, while the important bond distances and angles
Fig. 1. ORTEP [27] representation of the structure of the cis-Re2(m-
O2CC6H4Ã4-PPh2)2Cl2(m-dppm)2 molecule present in the crystals of 1×
2EtOH with the important atoms labeled. The thermal ellipsoids are
drawn at the 50% probability level except for the carbon atoms which
are circles of arbitrary radius.
/
/
are listed in Table 2. The ReÃ
/
Re triple bond distance in
˚
˚
1 of 2.3040(2)A is very similar to that of 2.3151(7)A for
the bisÁacetato complex [13]. The CIÃReÃReÃCl unit is
non-linear with ReÃReÃCl angles of 167.05(3) and
167.37(3)8, while the pairs of cis OÃReÃO and PÃReÃ
P angles average to 79.2 and 93.68, respectively.
The properties of 1Á4 are very similar thereby
/
/
/
/
/
/
experimental conditions E1/2
ꢀ
/
ꢂ0.47 V versus Ag/AgCl
/
/
/
/
/
for the ferrocenium/ferrocene couple.
Elemental microanalyses were performed by Dr. H.D.
Lee of the Purdue University Microanalytical Labora-
tory.
/
confirming the close structural relationship of this set
of complexes. The 31P{1H} NMR spectrum (recorded in
Fig. 2. ORTEP [27] representation of the structure of trans-Re2(m-O2CC10H6N)2Cl2(m-dppE)2 (7) with the important atoms labeled. The Cl(1)Ã
Re(1)ÃRe(2)ÃCl(2) unit is coincident with a crystallographic twofold rotation axis. The thermal ellipsoids are drawn at the 50% probability level
except for the phenyl group atoms of the dppE ligands which are circles of arbitrary radius.
/
/
/

224
S.-M. Kuang et al. / Inorganica Chimica Acta 338 (2002) 219Á227
/
Fig. 3. ORTEP [27] representation of the structure of the Re2Pd2 complex cis-Re2(m-O2CC6H4Ã
contains a crystallographic twofold rotation axis that contains atoms Cl(12) and Cl(13) and bisects the ReÃ
the 50% probability level except for the phenyl group atoms of the dppm ligands and diphenylphosphino groups which are circles of arbitrary radius.
/
4-PPh2)2Cl2(m-dppm)2(Pd2Cl4) (10). This molecule
/Re bond. Thermal ellipsoids are drawn at
CDCl3) of each complex shows two singlets, one due to
the coordinated P atoms of the m-dppm ligands (d ꢁ
10.0, ꢁ9.3, ꢁ9.4 and ꢁ9.7 for 1Á4, respectively) and
the other assigned to the atoms of the uncoordinated
Ph2P, Ph2P(ÄO) or Ph2P(ÄS) groups at the 4-position
on the phenyl ring (d ꢁ4.6, ꢂ30.4, ꢂ44.1 and ꢂ
29.71
for 1Á4, respectively. While the corresponding phos-
phorus resonance is at d ꢁ8.9 in the spectrum of the
Table 3
Cyclic voltammetric potentials for dirhenium(II) complexes
a
/
/
/
/
/
Compound
El/2(ox)(1) (V) E1/2(ox)(2) (V)
b
1
ꢂ0.33(80)
ꢂ0.39(60)
ꢂ0.39(60)
ꢂ0.34(80)
ꢂ0.49(90)
ꢁ0.23(80)
ꢁ0.12(90)
ꢂ0.40(60)
ꢁ0.15(60)
ꢂ0.31(60)
ꢂ1.40
ꢂ1.48
ꢂ1.45
ꢂ1.41
/
/
b
b
b
2
/
/
/
/
3
/
4
c
/
5
6
ꢂ1.05(60)
ꢂ1.13(80)
ꢂ1.44
ꢂ1.06(60)
ꢂ1.25(70)
ꢂ1.34
acetate complex cis-Re2(m-O2CCH3)2Cl2(m-dppm)2 (re-
corded in CDCl3)2, the free acids 4-Ph2PC6H4CO2H, 4-
Ph2P(O)C6H,CO2H, 4-Ph2P(S)C6H4CO2H and 4-
7
b
8
9
11
Ph2P(O)CH2C6H4Ã
30.4, ꢂ44.2 and ꢂ
these observations we note that the IR spectra of 2, 3
and 4 (recorded at KBr pellets) show n(PÄO) or n(PÄS)
modes at 1190(s), 657(mÁs) and 1185(mÁ
s), cmꢁ1
/
CO2H have resonances at d ꢁ
/
4.1,
d
d
ꢂ
/
/
/
24.8, respectively. In support of
cis-Re2(m-O2CCH3)2Cl2(m-dppm)2
trans-Re2(m-O2CCH3)2Cl2(m-dppE)2 ꢁ0.27
ꢂ0.28
e
e
ꢂ0.97
/
/
a
Data (in V) are based upon single scan cyclic voltammograms
CH2Cl2 solutions and referenced to the
Ag/AgCl electrode with a scan rate (v) of 200 mV sꢁ1 at a Pt-bead
electrode. The E1/2 values are for one-electron processes with ipaꢀipc
/
/
,
measured on 0.1 M TBAHÁ
/
respectively, very similar to the corresponding vibra-
tional frequencies for the free benzoic acids themselves
.
Values of DEp i.e. EpaꢁEpc, for the individual processes are given in
parentheses.
which are 1160(s), 648(mÁ
tively.
The cyclic voltammetric (CV) properties of solutions
of 1Á4, recorded in 0.1 M n-Bu4NPF6ÃCH2Cl2, are very
/
s) and 1195(m) cmꢁ1, respec-
b
Epa value given for a one-electron process for which ipaꢀipc
.
c
d
e
Second oxidation ꢀꢂ1.55 V.
Data taken from ref. [13].
Data taken from ref. [14].
/
/
similar to one another and to the CV of cis-Re2(m-
O2CCH3)2Cl2(m-dppm)2 [13], each showing two one-
electron oxidations (see Table 3) at ꢁ
/
ꢂ
/
0.35 and ꢁ
/
ꢂ
/
The lability of the pair of acetate ligands in cis-Re2(m-
O2CCH3)2Cl2(m-dppm)2 towards other carboxylic acids
1.4 V.
is shown by its reaction with quinolineÁ4-carboxylic
/
1
acid to afford cis-Re2(m-O2CC10H5N)2Cl2(m-dppm)2 (5).
A closely related study has recently led [3] to the
This spectrum was recorded in CD2Cl2.
2
The resonance is at d ꢁ10.2 in CD2Cl2 ÁCH2Cl2 (see ref. [13]).
/
/

S.-M. Kuang et al. / Inorganica Chimica Acta 338 (2002) 219Á
/227
225
isolation and structural characterization of the isonico-
tinate complex cis-Re2(m-O2CC5H4N)2Cl2(m-dppm)2,
which can be used to prepare molecular squares that
incorporate monometal units such as Pt(II). The spec-
troscopic and electrochemical properties of 5 confirm its
structure. A singlet is observed in its 31P{1H} NMR
Table 4
˚
Important bond lengths (A) and bond angles (8) for trans-Re2(m-
O2CC10H6N)2Cl2(m-dppE)2 (7)
a
Bond lengths
Re(1)ÃRe(2)
Re(1)ÃO(1)
Re(1)ÃP(1)
Re(1)ÃCl(1)
Re(2)ÃO(2)
2.2808(4)
2.119(5)
Re(2)ÃP(2)
Re(2)ÃCl(2)
2.4230(16)
2.5772(19)
1.261(7)
2.4367(17) O(1)ÃC(10)
2.590(2)
2.132(4)
spectrum (recorded in CDCl3) at d ꢁ
value of d ꢁ9.4 (in CD2Cl2) for the related isonicotinate
complex [3]. Its CV shows a reversible one-electron
oxidation with an E1/2 value of ꢂ0.49 V (see Table 3); a
second oxidation is beyond the range of our measure-
ments (i.e. ꢀ 1.5 V). The first oxidation is very similar
to that for cis-Re2(m-O2CC5H4N)2Cl2(m-dppm)2
(E1/2(ox)ꢀ 0.45 V vs. Ag/AgCl) [3], and clearly
/
9.6, similar to a
O(2)ÃC(10)
1.283(7)
/
Bond angles
/
O(1)ÃRe(1)ÃO(1a)
O(1)ÃRe(1)ÃRe(2)
O(1)ÃRe(1)ÃP(1)
O(1a)ÃRe(1)ÃP(1)
Re(2)ÃRe(1)ÃP(1)
P(1)ÃRe(1)ÃP(1a)
O(1)ÃRe(1)ÃCl(1)
Re(2)ÃRe(1)ÃCl(1) 180.00(10) P(2)ÃRe(2)ÃCl(2)
P(1)ÃRe(1)ÃCl(1)
O(2)ÃRe(2)ÃO(2a)
178.5(2)
O(2)ÃRe(2)ÃRe(1)
88.54(11)
91.99(12)
88.46(13)
98.77(4)
89.23(10) O(2)ÃRe(2)ÃP(2)
86.01(13) O(2a)ÃRe(2)ÃP(2)
94.19(12) Re(1)ÃRe(2)ÃP(2)
/
ꢂ
/
97.29(4)
P(2)ÃRe(2)ÃP(2a)
O(2)ÃRe(2)ÃCl(2)
162.45(8)
91.46(11)
/
ꢂ
/
165.42(8)
distinguishes it from the potentials observed for com-
plexes of the type trans-Re2(m-O2CR)2Cl2(m-dppE)2 that
are given in Table 3.
90.77(10) Re(1)ÃRe(2)ÃCl(2) 180.00(11)
81.23(4)
123.9(6)
82.71(4)
177.1(2)
O(1)ÃC(10)ÃO(2)
The lability of the acetato ligands in trans-Re2(m-
O2CCH3)2Cl2(m-dppE)2 (dppEꢀ
/
Ph2PC(Ä/CH2)PPh2) is
a
Numbers in parentheses are estimated standard deviations in the
least significant digits.
shown by the reactions of this complex with 4-
Ph2PC6H4CO2H and quinolineÁ4-carboxylic acid to
afford the brown crystalline complexes trans-Re2(m-
/
ined the reactions of cis-Re2(m-O2CC6H4Ã
Cl2(m-dppm)2 (1) and trans-Re2(m-O2CC6H4Ã
/
4-PPh2)2-
4-PPh2)2-
O2CC6H4Ã4-PPh2)2Cl2(m-dppE)2 (6) and trans-Re2((m-
/
/
O2CC10H6N)2Cl2(m-dppE)2 (7), respectively. The
Cl2(m-dppE)2 (7) with AuCl(tht) which afford in high
yield the Re2Au2 complexes cis-Re2(m-O2CC6H4Ã4-
PPh2)2Cl2(m-dppm)2(AuCl)2 (8) and trans-Re2(m-
O2CCgH4Ã4-PPh2)2Cl2(m-dppE)2(AuCl)2 (9), respec-
tively. The coordination of the free phosphine groups
of 1 by AuCl was confirmed by the 31P{1H} NMR
spectrum of 8 (recorded in CDCl3) which shows a pair
31P{1H} NMR spectra of 6 and 7 were recorded in
/
CDCl3. The former complex has singlets at d ꢂ
/
29.9 and
d ꢁ3.7 that are assigned to m-dppE ligands and
/
/
uncomplexed Ph2P groups, respectively; the precursor
complex trans-Re2(m-O2CCH3)2Cl2(m-dppE)2 shows a
resonance at d ꢂ
d ꢁ9.5. The CV properties of solutions of 6 and 7 in 0.1
M n-Bu4NPF6ÃCH2Cl2 show two reversible one-elec-
tron oxidations at potentials approximately 0.5 V more
negative than those for the cis complexes 1Á4 (Table 3)
/22.1 [14]. Complex 7 has a singlet at
/
of singlets at d ꢂ
Au(I)) and d ꢁ9.9 (4P, dppm ligands). The correspond-
ing 31P{1H} NMR spectrum of 9 (recorded in CDCl3)
displayed singlets at d ꢂ34.2 (2P, PPh2 groups coordi-
nated to Au(I)) and d ꢂ33.9 (4P, dppE ligands). The cis
stereochemistry of 8 and trans stereochemistry of 9 were
confirmed by CV measurements (Table 3) which gave
redox potentials that resemble closely those observed for
/
33.5 (2P, PPh2 groups coordinated to
/
/
/
/
and similar to the data reported previously for trans-
Re2(m-O2CCH3)2Cl2(m-dppm)2 [13,28] and trans-Re2(m-
O2CCH3)2Cl2(m-dppE)2 [14]. The implication that the
trans structure is present in 6 and 7 is confirmed by a
single crystal X-ray determination of 7, an ORTEP [27]
representation of which is shown in Fig. 2. The
important bond distances and angles for 7 are given in
Table 4. The dirhenium molecule in the asymmetric unit
possesses a twofold axis of rotation coincident with the
/
other complexes that have cis (compounds 1Á
/
5) or trans
(compounds 6 and 7) sterochemistries.
In the case of compound 1, we also examined its
reaction with PdCl2(COD). Orange crystals of the
Re2Pd2 complex cis-Re2(m-O2CC6H4Ã4-PPh2)2Cl2(m-
/
ClÃ
/
ReÃ
/
ReÃ
/
Cl unit which is, therefore, linear. The ReÃ
/
dppm)2(PdCl2)2 (10) was obtained but these proved to
be insoluble in common polar and non-polar solvents,
thereby preventing its characterization in solution.
However, its structural identity was established by X-
ray crystallography. An ORTEP [27] representation of the
structure is given in Fig. 3 and important bond distances
˚
Re triple bond distance of 2.2808(4) A is very similar to
this distance in the complexes trans-Re2(m-O2CCH3)2-
˚
Cl2(m-dppm)2 (2.2763(7)A) [28] and trans-Re2(m-
˚
O2CCH3)2Cl2(m-dppE)2 (2.2861(6)A) [14].
3.2. Mixed-metal assemblies that contain Re2Au2 and
Re2Pd2 units
and angles are listed in Table 5. The ReÃRe bond
˚
distance of 2.3295(6)A is slightly longer than that in the
/
˚
structure of the precursor complex 1 (2.3040(2) A). The
structures of the cis-Re2(m-O2CC6H4Ã4-PPh2)2Cl2(m-
dppm)2 units in 1 and 10 are very similar, including
the non-linearity of the ClÃReÃReÃCl units; the ReÃ
The use of the uncoordinated donor groups asso-
/
ciated with the m-carboxylato ligands of compounds 1Á
/
7
to complex other metal centers provides an entry to
mixed-metal assemblies. In the present study, we exam-
/
/
/
/

226
S.-M. Kuang et al. / Inorganica Chimica Acta 338 (2002) 219Á227
/
Table 5
values of 311(s) and 296(m) cmꢁ1 in the related
spectrum of cis-PdCl2[(Ph2PCH2)2NÃ 4-C6H4CO2H]
and of 330(s) and 297(vs) for cis-PdCl2(COD). The
˚
Important bond lengths (A) and bond angles (8) for cis-Re2(m-
O2CC6H4Ã4-PPh2)2Cl2(m-dppm)2(PdCI2)2 (10)
/
a
dirhenium(II) precursor cis-Re2(m-O2CCH3)2Cl2(m-
Bond lengths
dppm)2 has n(ReÃ
/
Cl) at 213(mÁ .
s) and 196(m) cmꢁ1
/
ReÃRe(a)
ReÃO(31)
ReÃO(32)
ReÃP(1)
ReÃP(2)
ReÃCl(1)
2.3295(6)
2.134(5)
2.167(5)
2.392(2)
2.412(2)
2.517(2)
PdÃP(3)
2.212(2)
2.268(2)
2.332(2)
2.365(3)
1.272(9)
1.250(9)
PdÃCl(11)
PdÃCl(13)
PdÃCl(12)
O(31)ÃC(30)
O(32)ÃC(30)
4. Supplementary material
Bond angles
Tables giving full details for the crystal data and data
collection parameters, atomic positional parameters,
anisotropic thermal parameters, bond distances and
bond angles for compounds 1, 7 and 10 are available
on request from the author (R.A.W.).
O(31)ÃReÃO(32)
O(31)ÃReÃRe(a)
O(32)ÃReÃRe(a)
O(31)ÃReÃP(1)
O(32)ÃReÃP(1)
Re(a)ÃReÃP(1)
O(31)ÃReÃP(2)
O(32)ÃReÃP(2)
Re(a)ÃReÃP(2)
P(1)ÃReÃP(2)
75.2(2)
Re(a)ÃReÃCl(1)
166.54(6)
91.78(8)
90.04(8)
86.65(9)
96.15(8)
177.19(9)
172.75(7)
90.30(10)
86.88(9)
92.29(14)
93.94(12)
90.59(14) P(1)ÃReÃCl(1)
85.74(13) P(2)ÃReÃCl(1)
95.01(16) P(3)ÃPdÃCl(11)
168.43(15) P(3)ÃPdÃCl(13)
100.71(5)
Cl(11)ÃPdÃCl(13)
169.54(15) P(3)ÃPdÃCl(12)
95.87(15) Cl(11)ÃPdÃCl(12)
94.20(5)
93.23(7)
Acknowledgements
Cl(13)ÃPdÃCl(12)
PdÃCl(12)ÃPd(a)
O(31)ÃReÃCl(1)
O(32)ÃReÃCl(1)
83.28(15) PdÃCl(13)ÃPd(a)
81.12(14)
We thank the John A. Leighty Endowment Fund for
support of this work.
a
Numbers in parentheses are estimated standard deviations in the
least significant digits.
References
ReÃ
/
Cl angles are in the range 166.5Á167.48 (Tables 2
/
and 5). The structure of 10 is especially noteworthy
because 1 behaves as a chelating phosphine in assem-
bling the dipalladium(II) unit to form a moiety of the
type cis-(R3P)ClPd(m-Cl)2PdCl(PR3). Only the trans
isomers of Pd2(m-Cl)2Cl2(PR3)2 have previously been
structurally characterized when PR3 is a tertiary phos-
phine [29] or phosphite [30] ligand.
[1] (a) J.K. Bera, P. Angaridis, F.A. Cotton, M.A. Petrukhina, P.E.
Fanwick, R.A. Walton, J. Am. Chem. Soc. 123 (2001) 1515;
(b) J.K. Bera, R. Cle´rac, P.E. Fanwick, R.A. Walton, J. Chem.
Soc., Dalton Trans., in press.
[2] (a) S.M. Kuang, P.E. Fanwick, R.A. Walton, Inorg. Chem.
Commun. 4 (2001) 745;
(b) S.M. Kuang, P.E. Fanwick, R.A. Walton, Inorg. Chem. 41
(2002) 405.
[3] J.K. Bera, B.W. Smucker, K.R. Dunbar, R.A. Walton, Chem.
Commun. (2001) 2562.
As an alternative strategy for synthesizing Re2Pd2
clusters we reacted cis-Re2(m-O2CCH3)2Cl2(m-dppm)2
with the palladium(II) complex cis-PdCl2[(Ph2CH2)2-
[4] S.M. Kuang, P.E. Fanwick, R.A. Walton, Inorg. Chem. 41 (2002)
147.
NÃ
/
4-C6H4CO2H] in which the chelating phosphine
[5] (a) S.M. Kuang, P.E. Fanwick, R.A. Walton, Inorg. Chem. 39
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crystalline cis-Re2Cl2(m-dppm)2[m-O2C6H4Ã
/4-N(CH2-
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structurally from 10 in containing two uncoupled
mononuclear cis-PdCl2(PR3)2 units in contrast to the
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d ꢂ
11.5 (4P, dppm ligands), while its low frequency IR
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