Assemblies of multiply bonded [Re2]n+ cores possessing bond orders of 3 or 3.5 that are linked by dicarboxylate bridges

Article abstract of DOI:10.1039/b200561c

An earlier study describing the exchange of the μ-acetato ligands of Re₂(μ-O₂CCH₃)Cl₄(μ-dppm) ₂ (1) and cis-Re₂(μ-O₂CCH₃)₂Cl ₂(μ-dppm)₂ (2) by dicarboxylic acids has been expanded to include reactions with the monocarboxylic acid isonicotinic acid, and the dicarboxylic acids adipic acid, 4,4′-biphenyldicarboxylic acid, fumaric acid, trans-1,4-cyclohexanedicarboxylic acid and 1,1′-ferrocenedicarboxylic acid. Further examples of complexes that are "dimers-of-dimers" and triangular supramolecular assemblies involving retention of the basic electronic and molecular structures of the dirhenium units present in 1 and 2 have been obtained. In addition, the dirhenium complexes Re₂(μ-O₂CC₆H₄N)Cl₄ (μ-dppm)₂ (7) and cis-Re₂(μ-O₂C₆H₁₀CO ₂Et)₂Cl₂(μ-dppm)₂ (11) have been isolated, as well as the trimetallic complex cis-Re₂Cl₂(μ-dppm)₂[(μ-O₂ CC₅H₄)₂Fe] (14) that is formed from the reaction of 2 with (C₅H₄CO₂H)₂Fe. The crystal structures of 7, 11 and 14 are reported.

Full text of DOI:10.1039/b200561c

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n؉
Assemblies of multiply bonded [Re ] cores possessing bond
2
orders of 3 or 3.5 that are linked by dicarboxylate bridges
a
b
a
a
Jitendra K. Bera, Rodolphe Clérac, Phillip E. Fanwick and Richard A. Walton*
a
Department of Chemistry, Purdue University, 1393 Brown Building, West Lafayette,
Indiana 47907-1393, USA. E-mail: rawalton@purdue.edu
Centre de Recherche Paul Pascal, CNRS UPR 8461, Avenue du Dr. Schweitzer, 33600 Pessac,
France
b
Received 9th January 2002, Accepted 15th March 2002
First published as an Advance Article on the web 18th April 2002
An earlier study describing the exchange of the µ-acetato ligands of Re (µ-O CCH )Cl (µ-dppm) (1) and
2
2
3
4
2
cis-Re (µ-O CCH ) Cl (µ-dppm) (2) by dicarboxylic acids has been expanded to include reactions with the
2
2
3
2
2
2
monocarboxylic acid isonicotinic acid, and the dicarboxylic acids adipic acid, 4,4Ј-biphenyldicarboxylic acid,
fumaric acid, trans-1,4-cyclohexanedicarboxylic acid and 1,1Ј-ferrocenedicarboxylic acid. Further examples of
complexes that are “dimers-of-dimers” and triangular supramolecular assemblies involving retention of the basic
electronic and molecular structures of the dirhenium units present in 1 and 2 have been obtained. In addition, the
dirhenium complexes Re (µ-O CC H N)Cl (µ-dppm) (7) and cis-Re (µ-O C H CO Et) Cl (µ-dppm) (11) have
2
2
6
4
4
2
2
2
6
10
2
2
2
2
been isolated, as well as the trimetallic complex cis-Re Cl (µ-dppm) [(µ-O CC H ) Fe] (14) that is formed from
2
2
2
2
5
4 2
the reaction of 2 with (C H CO H) Fe. The crystal structures of 7, 11 and 14 are reported.
5
4
2
2
Introduction
and 9 over the temperature range 1.8 to 300 K and at 300 K for
1, and were corrected for the sample holder, paramagnetic
impurities (S = 1/2, 1% of Curie Law for 4) and for the
1
1
We have shown that the multiply bonded dirhenium(,) and
dirhenium(,) complexes Re (µ-O CCH )Cl (µ-dppm) (1)
2
2
2
3
4
2
experimental diamagnetic contribution calculated from Pascal
2
,3
and cis-Re (µ-O CCH ) Cl (µ-dppm) (2), where dppm =
6
2
2
3
2
2
2
constants. The electrospray ionization (ESI) mass analyses
Ph PCH PPh , which contain labile µ-O CCH ligands in
2
2
2
2
3
were recorded by Dr. Karl V. Wood with use of a Finnigan
MAT LCQ (Thermoquest Corp. San Jose, CA) mass spec-
trometer system. Measurements were carried out on CH Cl /
combination with substitutionally inert dppm and Cl ligands,
react with the dicarboxylic acids terephthalic acid and trans-
2
2
1
,4-cyclohexanedicarboxylic acid to afford “dimers-of-dimers”,
CH CN or 1,2-C H Cl solutions. Elemental microanalyses
3
2
4
2
hydrogen-bonded chains of “dimers-of-dimers”, and supra-
molecular triangles that contain three dirhenium pairs. In the
present report we examine further the substitutional lability
of the acetate groups present in 1 and 2 with the object
of expanding the supramolecular chemistry involving the
incorporation of dirhenium species into assemblies that contain
two or more such units.
were carried out by Dr. H. D. Lee of the Purdue University
Microanalytical Laboratory.
A. Reactions of Re (ꢀ-O CCH )Cl (ꢀ-dppm) (1)
2
2
3
4
2
(i) Synthesis of Re
(ꢀ-O
CC
H
N)Cl
(ꢀ-dppm) (7). A mixture
2
2
2
5
4
4
of 1 (0.111 g, 0.08 mmol) and isonicotinic acid (0.065 g, 0.53
mmol) was refluxed in ethanol for one day. A mixture of
Re Cl (µ-dppm) (3) and the carboxylate-exchanged product
2
4
2
Experimental
The dirhenium complexes Re (µ-O CCH )Cl (µ-dppm) (1),
Re (µ-O CC H N)Cl (µ-dppm) (7) was obtained as shown by
2
2
5
4
4
2
2
cyclic voltammetry. The products were separated by hand.
Yield of 7: 0.053 g (47%). Calc. for C56 NO Re : C,
47.87; H, 3.44. Found: C, 47.31; H, 3.47%. MS (ESI): m/z 1404
2
2
3
4
2
2,3
cis-Re (µ-O CCH ) Cl (µ-dppm) (2)
and Re Cl (µ-dppm)
H48Cl
4
2
P
4
2
2
2
3
2
2
2
2
4
3
4
(
(
(
(
3), and the dicarboxylate-bridged complexes [Re Cl -
2 4
1
ϩ
µ-dppm) ] (µ-O CC H CO )
(4),
µ-O CC H CO )] (5) and [cis-Re (µ-O CC H CO H)Cl -
[cis-Re Cl (µ-dppm) -
for [M] (
where [M] represents the parent molecule).
(ii) Synthesis of [Re Cl (ꢀ-dppm) (ꢀ-O C(CH ) CO ) (8).
2 4 2
2
2
2
6
4
1
2
2
2
2
2
6
4
2
3
2
2
6
10
2
2
1
µ-dppm) ] (µ-O CC H CO ) (6) were prepared by the
2
4
2
]
2
2
2
2
2
6
10
2
literature methods. All carboxylic acids and other reagents
were obtained from Aldrich Chemical Co., and used as
received. Solvents were purchased from commercial sources
and were dried and degassed by standard methods and distilled
prior to use. All reactions were carried out under an atmosphere
of dry dinitrogen.
Routine IR spectra, NMR spectra and cyclic voltammetric5
measurements were determined as described previously.
Differential pulsed voltammetric (DPV) measurements and
magnetic data were recorded in the laboratory of Professor
Kim R. Dunbar at Texas A & M University. The magnetic
susceptibility measurements were obtained with the use of a
Quantum Design SQUID magnetometer MPMS-XL and data
were collected for complexes 4, 8, 9 and 11 at 1000 G on finely
divided polycrystalline samples. Data were obtained for 4, 8
The reaction of 1 (0.107 g, 0.08 mmol) with adipic acid (0.075 g,
0.51 mmol) in refluxing ethanol for 26 h afforded a yellow solid
that was filtered off and washed with fresh ethanol (3 × 5 mL)
and diethyl ether (3 × 5 mL). The crude product was extracted
with hot 1,2-dichloroethane (20 mL), and the extract con-
centrated and kept at 4 ЊC to obtain complex 8 as yellow micro-
crystals; yield 0.077 g (71%). Calc. for C106H96Cl O P Re : C,
8 4 8 4
46.97; H, 3.57; Cl, 10.33. Found: C, 45.96; H, 3.56, Cl 10.19%.
(iii) Synthesis of [Re Cl (ꢀ-dppm) ] (ꢀ-O CC H C H CO )
2
4
2
2
2
6
4
6
4
2
(9). A mixture of 1 (0.103 g, 0.08 mmol) and 4,4Ј-biphenyl-
dicarboxylic acid (0.151 g, 0.62 mmol) was refluxed in ethanol
for 2 days, the insoluble product filtered off and washed with
ethanol (2 × 5 mL) and diethyl ether (2 × 5 mL) and then
recrystallized from dichloromethane/benzene; yield 0.171 g
2
168
J. Chem. Soc., Dalton Trans., 2002, 2168–2172
This journal is © The Royal Society of Chemistry 2002
DOI: 10.1039/b200561c

View Article Online
(
76%). Calc. for C114H Cl O P Re : C, 48.78; H, 3.45; Cl,
matrices were determined by least-squares refinement of the
96
8
4
8
4
1
0.11. Found: C, 48.01; H, 3.47; Cl, 10.57%.
appropriate number of reflections in the range of 4 < θ < 27Њ.
Space groups were determined by use of the program ABSEN.
7
(
iv) Synthesis of [Re Cl (ꢀ-dppm) ] (ꢀ-O CCH᎐CHCO ) (10).
Crystal data and the relevant experimental details on data
collections and refinements are given in Table 1. Lorentz and
polarization corrections were applied to the data sets.
2
4
2
2
2
᎐
2
A mixture of 1 (0.111 g, 0.08 mmol) and fumaric acid (0.059 g,
.51 mmol) was refluxed in ethanol for 8–10 h, the reaction
0
mixture filtered, and the red colored filtrate evaporated to low
volume and kept at 4 ЊC for 12 h. The insoluble product was
filtered off and washed with ethanol (2 × 5 mL) and diethyl
ether (2 × 5 mL); yield 0.099 g (46%). Cyclic voltammetry
showed that 10 was contaminated by small amounts of
Re Cl (µ-dppm) (3), the proportion of which increased with
The structures were solved using the structure solution
program PATTY in DIRDIF92. The remaining atoms were
8
located in succeeding difference Fourier syntheses. Hydrogen
atoms were placed in calculated positions according to ideal-
ized geometries with U(H) = 1.3 Ueq (C). They were included in
the refinement but constrained to ride on the atom to which
they are bonded. An empirical absorption correction using
2
4
2
increasing reaction time.
v) Synthesis of cis-Re (ꢀ-O CC H CO Et) Cl (ꢀ-dppm)
2
9
SCALEPACꢀ was applied in all cases. The final refinements
10
(
were performed by the use of the program SHELXL-97.
2
2
6
10
2
2
2
(
11). A mixture of 1 (0.119 g, 0.09 mmol) and trans-1,4-
All non-hydrogen atoms were refined with anisotropic
cyclohexanedicarboxylic acid (0.144 g, 0.84 mmol) was refluxed
in ethanol for 3 days. Red crystals of composition 11ؒ2EtOH
were filtered off and washed with fresh ethanol (3 × 5 mL) and
diethyl ether (3 × 5 mL); yield: 0.113 g (74%). Calc. for
C H Cl O P Re (i.e. 11ؒ2EtOH): C, 52.20; H, 5.09. Found:
C, 51.85; H, 5.16%. MS (ESI): m/z 1575 for [M Ϫ Cl] . H
NMR spectrum (δ in CD Cl ): 7.6–6.9 (m, 40H, Ph), 6.40 and
4
thermal parameters unless indicated otherwise. Crystallo-
11
graphic drawings were done using the program ORTEP.
The structure solutions and refinements of all three com-
pounds proceeded without significant problem. The crystals of
11 and 14 contained solvent molecules, the non-hydrogen atoms
of which were refined with anisotropic thermal parameters in
the case of 11 but isotropically for 14. The two independent
molecules of lattice ethanol present in the crystals of 14 refined
to occupancies of 0.730 and 0.703.
7
4
86
2
10
4
2
ϩ
1
2
2
.95 (m, 4H, CH of dppm), 4.18 (q, 8H, CH of EtOH and
2
2
–
CO Et), 2.38, 2.10, 1.93 and 1.70–1.43 (m, 20H, C H ), 1.34
2
6
10
31
1
(
t, 12H, CH of EtOH and –CO Et). P{ H} NMR spectrum
CCDC reference numbers 178305–178307.
3
2
(
δ in CD Cl ): Ϫ9.32.
See http://www.rsc.org/suppdata/dt/b2/b200561c/ for crystal-
lographic data in CIF or other electronic format.
2
2
B. Reactions of cis-Re (ꢀ-O CCH ) Cl (ꢀ-dppm) (2)
2
2
3
2
2
2
(
i) Synthesis of [cis-Re Cl (ꢀ-dppm) (ꢀ-O CC H CO )] (12).
Results and discussion
2
2
2
2
6
10
2
3
A mixture of 2 (0.119 g, 0.09 mmol) and trans-1,4-cyclo-
hexanedicarboxylic acid (0.016 g, 0.09 mmol) was refluxed in
ethanol for 2 days and the yellow product filtered off and washed
with ethanol (3 × 5 mL) and diethyl ether (3 × 5 mL); yield 0.113
g (91%). Calc. for C174H162Cl O P Re : C, 50.40; H, 3.94.
(
a) Reactions of Re (ꢀ-O CCH )Cl (ꢀ-dppm) (1) with
2 2 3 4 2
carboxylic acids
The lability of the acetate ligand of compound 1 is shown by its
reaction with isonicotinic acid in refluxing ethanol to afford the
dirhenium(,) complex Re (µ-O CC H N)Cl (µ-dppm) (7).
6
12 12
6
Found: C, 51.06; H, 4.16%. MS (ESI): m/z 3727 for [M Ϫ Cl Ϫ
dppm] . H NMR spectrum (δ in CD Cl ): 7.8–6.8 (m, 150H,
2
2
5
4
4
2
ϩ
1
This product was contaminated with a small amount of
2
2
Ph of dppm), 6.42 and 4.91 (m, 12H, CH of dppm), 2.42–1.43
Re Cl (µ-dppm) (3) which is formed from the competing
thermal reduction of 1 in refluxing ethanol.
2
2
4
2
31
1
2
(
m, 30H, C H ). P{ H} NMR spectrum (δ in CD Cl ): Ϫ9.87.
6
10
2
2
(
ii) Synthesis of [cis-Re Cl (ꢀ-dppm) (ꢀ-O C(CH ) CO )]
2 2 2 2 2 4 2 n
(
13). Complex 2 (0.105 g, 0.08 mmol) was reacted with adipic
acid (0.015 g, 0.10 mmol) in refluxing ethanol as described in
section B(i); yield 0.097 g (90%). Calc. for C H Cl O P Re :
56
52
2
4
4
2
C, 49.59; H, 3.86; Cl, 5.23. Found: C, 48.93; H, 3.79; Cl, 5.30%.
This product had very poor solubility in common organic
solvents.
The crystal structure of 7 (Fig. 1) showed it to be similar
(
iii) Synthesis of cis-Re Cl (ꢀ-dppm) [(ꢀ-O CC H ) Fe] (14).
2 2 2 2 5 4 2
2
to that of 1. The Re–Re bond distance of 2.3055(3)Å in 7 is
Red crystals of 14 were obtained by the reaction of 2 (0.104 g,
.08 mmol) with 1,1Ј-ferrocenedicarboxylic acid (0.033 g, 0.12
mmol) in refluxing ethanol following the procedure described in
section B(i); yield 0.112 g (94%). Calc. for C H Cl FeO P Re :
C, 50.17; H, 3.53; Cl, 4.78. Found: C, 49.61; H, 3.77; Cl, 4.84%.
2
essentially the same as that of 2.2998(4)Å reported for 1. The
0
identity of 7 is further supported by its ESI mass spectrum
which shows the parent molecule ion at m/z = 1404 with the
correct isotopic splitting pattern. Cyclic voltammetric (CV)
measurements on solutions of 7 in 0.1 M n-Bu NPF (TBAH)–
62
52
2
4
4
2
ϩ
1
4
6
MS (ESI): m/z 1484 for [M] . H NMR spectrum (δ in CD Cl ):
2
2
CH Cl2 showed a reversible process at E1/2 = ϩ0.57 V vs.
2
7
5
.8–6.9 (m, 40H, Ph), 6.41 and 5.00 (m, 4H, CH of dppm),
2
31 1
Ag/AgCl, with ∆E = 60 mV, that corresponds to a one-electron
p
.41 and 4.59 (m, 8H, C H ). P{ H} NMR spectrum (δ in
5 4
oxidation of the bulk complex, and an irreversible reduction at
Ep,c = Ϫ0.53 V vs. Ag/AgCl; additional irreversible processes
at Ep,a = ϩ1.65 V and Ep,c = Ϫ1.60 V are attributable to the
isonicotinate ligand. The CV of 7 resembles that of 1 which has
CD Cl ): Ϫ9.13.
2
2
X-Ray crystal structure determinations
2
Single crystals of composition Re (µ-O CC H N)Cl (µ-dppm)
E (ox) = ϩ0.52V and E = Ϫ0.60 V.
2
2
5
4
4
2
1/2
p,c
(
2
(
7), cis-Re (µ-O CC H CO Et) Cl (µ-dppm) ؒ2EtOH (11ؒ
The substitutional lability of the acetate ligand of 1 towards
dicarboxylic acids was first established in its reaction with
terephthalic acid that produces the centrosymmetric µ-
terephthalate complex [(µ-dppm) Cl Re ](µ-O CC H CO )-
2
2
6
10
2
2
2
2
EtOH), and cis-Re Cl (µ-dppm) [(µ-O CC H ) Fe]ؒ1.43EtOH
2 2 2 2 5 4 2
14ؒ1.43EtOH) were obtained as described in the individual
synthetic procedures outlined previously.
2
4
2
2
6
4
2
1
The data were collected at 173(±1) ꢀ for 7, 11 and 14. All
measurements were carried out on a Nonius ꢀappaCCD
diffractometer with graphite-monochromated Mo ꢀα radiation
[Re Cl (µ-dppm) ] (4). In the present study we show that adipic
2 4 2
acid, 4,4Ј-biphenyldicarboxylic acid and fumaric acid form
the yellow–red colored complexes [Re Cl (µ-dppm) ] (µ-
2
4
2 2
(
λ = 0.71073 Å). Accurate unit cell parameters and orientation
O C(CH ) CO ) (8), [Re Cl (µ-dppm) ] (µ-O CC H C H CO )
2
2
4
2
2
4
2 2
2
6
4
6
4
2
J. Chem. Soc., Dalton Trans., 2002, 2168–2172
2169

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Table 1 Crystallographic data for the dirhenium complexes of composition Re (µ-O CC H N)Cl (µ-dppm) (7), cis-Re (µ-O CC H CO Et) Cl (µ-
2
2
5
4
4
2
2
2
6
10
2
2
2
dppm) ؒ2EtOH (11ؒ2EtOH), and cis-Re Cl (µ-dppm) [(µ-O CC H ) Fe]ؒ1.43EtOH (14ؒ1.43EtOH)
2
2
2
2
2
5
4 2
7
11
14
C64.87H60.60Cl FeO P Re
2
Formula
Formula weight
Crystal system
C H Cl NO P Re
C H Cl O P Re
5
6
48
4
2
4
2
74 86
2
10
4
2
2
5.43
4
1405.12
Monoclinic
1702.71
Monoclinic
1550.17
Monoclinic
Space group
P2 /n (No. 14)
C2/c (No. 15)
22.1984(10)
12.4860(4)
25.8565(12)
90
P2 /c (No. 14)
1
1
a/Å
b/Å
c/Å
α/Њ
17.8053(5)
14.4632(2)
21.1278(5)
90
12.4009(2)
17.7630(3)
27.8096(6)
90
β/Њ
γ/Њ
105.9273(9)
90
99.5236(18)
90
96.7556(12)
90
Z
V/Å
D /g cm
µ(Mo-ꢀ )/mm
4
4
4
3
5232.0(4)
1.784
5.056
7067.9(9)
1.600
3.690
6127.4(3)
1.680
4.468
Ϫ3
c
Ϫ1
α
Reflections
collected
independent
42362
12282
9566
622
0.052
0.036
0.080
1.022
22575
14030
4885
418
0.080
0.046
0.082
0.936
54835
15590
10599
705
0.066
0.046
0.098
1.021
observed [I > 2σ(I )]
No. of variables
Rint
a
R(Fo)
w
2
b
R (F )
o
GOF
a
2
2
b
2
2
c
2
2 2 1/2
o
R = Σ||F | Ϫ |F ||/Σ|F | with F > 2σ(F ). R = [Σw(|F | Ϫ |F |) /Σw|F | ]
.
o
c
o
o
o
w
o
and perfect Curie Law behavior is observed. This result is in
accord with long non-conjugated organic linkers in these two
complexes that do not facilitate magnetic interactions between
the dirhenium units. In contrast, temperature range measure-
ments (down to 2 ꢀ) show an antiferromagnetic interaction to
Ϫ1
be present in 4, estimated to be Ϫ5.8 cm (2J) by fitting the
1
experimental data to a dimer model of S = 1/2 (H = Ϫ2JS ؒS ).
1
2
The differences in magnetic behavior between 4, and 8 and 9,
are paralleled by differences in the CV and differential pulsed
voltammetric (DPV) properties of solutions of 4 and 9 in 0.1 M
TBAH–CH Cl . CV and DPV measurements on 4 show
2
2
evidence for electronic coupling between the one-electron
5ϩ
6ϩ
oxidation [Re2]
[Re2] that characterizes each of the
component dirhenium units. These two reversible one-electron
processes have E1/2 values of ϩ0.59 V and ϩ0.49 V vs. Ag/AgCl,
while there are additional coupled reductions at E ∼ Ϫ0.45 V
p,c
−
1
and Ϫ0.53 V vs. Ag/AgCl. It is convenient to represent the
magnitude of the electronic coupling in a molecule such as 4 in
terms of a comproportionation constant K for the equilibrium
represented in eqn. (1).
1
1
c
Fig. 1 ORTEP representation of the structure of the dirhenium
complex Re (µ-O CC H N)Cl (µ-dppm) (7). Thermal ellipsoids are
12–15
2
2
5
4
4
2
drawn at the 40% probability level. The P atoms are unlabeled; P(1) and
P(3) are bound to Re(1), and P(2) and P(4) to Re(2). Selected bond
distances (Å) and bond angles (Њ) are as follows: Re(1)–Re(2) 2.3055(3),
Re(1)–O(1) 2.071(3), Re(1)–Cl(11) 2.3511(12), Re(1)–Cl(12) 2.5829(12),
Re(2)–O(2) 2.092(3), Re(2)–Cl(21) 2.3653(11), Re(2)–Cl(22) 2.5743(12),
O(1)–C(10) 1.268(6), O(2)–C(10) 1.275(5); O(1)–Re(1)–Re(2) 88.55(9),
O(1)–Re(1)–Cl(11) 165.81(9), Re(2)–Re(1)–Cl(11) 103.03(3), O(1)–
Re(1)–Cl(12) 79.71(9), Re(2)–Re(1)–Cl(12) 163.47(3), Cl(11)–Re(1)–
Cl(12) 90.43(4), O(1)–C(10)–O(2) 122.0(4). The torsional angles
(
1)
The greater the degree of delocalization in the monocation
Re ---Re ] , the larger is the value of ∆E and hence the
larger is K . In the case of 4, ∆E = 100 mV and thus K = 49, a
value that is characteristic of a weakly coupled valence trapped
system, for which a value for K of less than 100 is expected.
This result accords with the earlier conclusion of Chisholm
and co-workers that terephthalate is a poor linker ligand for
electronic coupling. While the poor solubility properties of 8
prevented us from obtaining satisfactory electrochemical data
for this complex, DPV measurements on its 4,4Ј-biphenyl-
dicarboxylate bridged analogue (9) showed coupled processes
ϩ
[
2
2
1
/
2
c
1/2
c
Cl(11)–Re(1)–Re(2)–Cl(21),
Re(2)–P(4) and O(1)–Re(1)–Re(2)–O(2) are 16.04(4)Њ, 11.55(4)Њ,
3.09(4)Њ and 4.79(12)Њ, respectively.
P(1)–Re(1)–Re(2)–P(2),
P(3)–Re(1)–
c
1
12
(
9) and [Re Cl (µ-dppm) ] (µ-O CCH᎐CHCO ) (10) that are
2 4 2 2 2 2
᎐
1
probable close structural analogues of 4.
In order to probe the influence of the organic spacers in
transmitting magnetic interactions between the individual
paramagnetic dirhenium units in complexes of the type [(µ-
dppm) Cl Re ](µ-O CRCO )[Re Cl (µ-dppm) ], we carried out
E (ox) = ϩ0.48 V and ϩ0.44 V vs. Ag/AgCl, and E =
1/2
p,c
Ϫ0.50 V and Ϫ0.55 V vs. Ag/AgCl. For the coupled oxidations
∆E1/2 = 40 mV, a value that implies the absence of any signif-
icant coupling between the two dirhenium units.
2
4
2
2
2
2
4
2
magnetic susceptibility measurements on 4, 8 and 9 over the
temperature range 2 to 300 ꢀ. These complexes have magnetic
moments at 300 ꢀ of 2.45 µ , 2.51 µ and 2.49 µ , respectively,
Although 1 reacts with fumaric acid to give what we believe
B
B
B
that correspond to g values slightly higher than 2. The effective
moment is constant down to 2 ꢀ in the case of both 8 and 9,
is the expected “dimers-of-dimers” product [Re Cl (µ-dppm) ] -
2
4
2 2
(µ-O CCH᎐CHCO ) (10), the analogous reaction with acetyl-
2
2
2
170
J. Chem. Soc., Dalton Trans., 2002, 2168–2172

View Article Online
2
17
enedicarboxylic acid gave the paramagnetic µ-η -acetylene
Cl (µ-dppa) , where dppa = Ph PNHPPh (2.3067(5) Å).
2 2 2 2
complex Re Cl (µ-HCCH)(µ-dppm) , resulting from the decarb-
The CV of 11 (recorded in 0.1 M TBAH–CH Cl ) shows two
2
5
2
2 2
oxylation of the acetylenedicarboxylic acid. Details of the latter
reversible one-electron oxidations at E1/2 = ϩ0.32 V and ϩ1.39
16
reaction have been communicated previously. The identity of
paramagnetic 10 was based primarily upon its CV and DPV
properties since it was difficult to isolate it free of small
amounts of diamagnetic 3, which is formed by the competitive
reductive decarboxylation of 1. The electrochemical properties
of 10 resemble those of 4 that were discussed previously; there
are two coupled one-electron processes at E1/2 = ϩ0.56 V
and ϩ0.43 V vs. Ag/AgCl, as well as irreversible reductions at
Ep,c = Ϫ0.50 V and Ϫ0.59 V vs. Ag/AgCl. Since the magnitude
of ∆E1/2 is greater for 10 than for 4 (130 mV vs. 100 mV), the
V vs. Ag/AgCl, behavior which resembles that of cis-Re -
2
2
(µ-O CCH ) Cl (µ-dppm) .
2
3
2
2
2
(b) Reactions of cis-Re
(ꢀ-O CCH ) Cl (ꢀ-dppm) (2) with
2 3 2 2 2
2
carboxylic acids
We had anticipated that the reactions of dicarboxylic acids with
, a complex that contains a pair of exchangeable cis µ-acetato
2
ligands, might afford compounds in which there were a square
arrangement of dirhenium() units.
comproportionation constant K is larger (158 vs. 49), thereby
c
signifying the presence of a stronger electronic coupling in 10.
31
The absence of resonances in the P NMR spectrum of 10, and
1
the presence of broad poorly defined resonances in its H NMR
spectrum, accord with the paramagnetism of this complex.
Attempts to prepare other examples of “dimers-of-dimers”
from the reactions of 1 with tetrafluoroterephthalic acid and
1
,1Ј-ferrocenedicarboxylic acid afforded the known dirheniu-
m() complex 3. It is clear that in these instances, reductive
decarboxylation of 1 proceeds more rapidly than does carb-
oxylate ligand exchange. The analogous reaction of 1 with
trans-1,4-cyclohexanedicarboxylic acid unexpectedly gave
the dirhenium() complex cis-Re (µ-O CC H CO Et) Cl (µ-
When 2 was reacted with terephthalic acid, trans-1,4-cyclo-
hexanedicarboxylic acid or adipic acid in refluxing ethanol the
red insoluble products [cis-Re Cl (µ-dppm) (µ-dicarboxylate)]
n
2
2
2
were obtained. In the cases of the terephthalate (5) and trans-
2
2
6
10
2
2
2
1,4-cyclohexanedicarboxylate (12) complexes, n = 3 as shown
1
dppm) (11) rather than [Re Cl (µ-dppm) ] (µ-O CC H CO ).
previously by an X-ray crystal structure of 5, and in the present
2
2
4
2 2
2
6
10
2
With the use of shorter reaction times we found no evidence for
the intermediacy of the latter coupled product. The formation
study in the case of 12 by an ESI mass spectrum (see Experi-
mental). Note that a strict adherence to 1 : 1 proportions of
reagents is necessary to produce 12, since if more than 1.5
equivalents of the acid are used the reaction favors the complex
[cis-Re (µ-O CC H CO H)Cl (µ-dppm) ] (µ-O CC H CO )
(6); the latter complex is an infinite polymer in which “dimers-
of-dimers” are linked through intermolecular hydrogen-bonds
involving the “free” carboxylic acid groups to generate zig-zag
chains (see Scheme 1). The adipate complex 13 was too insol-
5
ϩ
of 11 involves three processes; reduction of the [Re ] core of 1
2
4ϩ
to [Re ] , substitution of the acetate group and two Re–Cl
2
bonds of 1, and esterification of one of the acid groups of
trans-1,4-cyclohexanedicarboxylic acid by the ethanol solvent.
However, this reaction does not proceed via 3, since the latter
complex does not react with trans-1,4-cyclohexanedicarboxylic
acid in refluxing ethanol.
2
2
6
10
2
2
2 2
2
6
10
2
1
The structure of 11 was established by X-ray crystallography
(
Fig. 2) and shown to be closely related to that of cis-Re -
2
2
(
µ-O CCH ) Cl (µ-dppm) . The Re–Re triple bond distance of
2
3
2
2
2
2
.3120(5) Å is similar to those determined for the analogous
2
acetate complex (2.3151(7) Å) and for cis-Re (µ-O CCH ) -
2
2
3 2
Scheme 1
uble in suitable solvents for us to grow X-ray quality crystals or
obtain electrochemical data or a satisfactory mass spectrum.
However, the value of n is probably 3 since the adipate spacer is
capable of spanning distances between the adjacent Re units
2
that are similar to those in the analogous terephthalate and
trans-1,4-cyclohexanedicarboxylate bridged complexes.
We attribute the stability of the triangular structures of 5 and
1
2, relative to a square assembly, to the unfavorable intra-
molecular phenyl–phenyl interactions between adjacent
Re Cl (µ-dppm) ] units that would arise in the square complex
[
2
2
2
as the angle between cis carboxylate ligands opens up upon
going from a triangular arrangement to a square. With shorter
spacers such as oxalate or acetylenedicarboxylate, we failed to
isolate any coupled dirhenium complexes when the appropriate
acids were reacted with 2. In the case of acetylenedicarboxylic
acid, this is probably a consequence of decarboxylation of the
ligand occurring under the reflux conditions that we used since
a similar reaction pathway ensues when 1 is reacted with this
1
1
Fig. 2 ORTEP representation of the structure of the dirhenium
complex cis-Re (µ-O CC H CO Et) Cl (µ-dppm) (11). The thermal
2
2
6
10
2
2
2
2
ellipsoids are drawn at the 40% probability level. The molecule contains
a crystallographic two-fold axis of symmetry. The unlabeled Re atom is
ReЈ and the unlabeled P atoms are P(1) and P(2). Selected bond
distances (Å) and bond angles (Њ) are as follows: Re–ReЈ 2.3120(5), Re–
O(11) 2.163(4), Re–O(12) 2.114(4), Re–Cl 2.5362(16), O(11)–C(10)
.262(7), O(12)–C(10) 1.277(7); O(12)–Re–O(11) 80.44(15), O(12)–Re–
ReЈ 88.55(11), P(1)–Re–P(2) 93.30(5), ReЈ–Re–Cl 166.50(4), O(11)–
C(10)–O(12) 123.0(5).
16
acid.
The CV of the dirhenium() complex cis-Re (µ-O CCH ) -
2
2
3 2
1
Cl (µ-dppm) (2) shows one-electron oxidations at E = ϩ0.28
2
2
1/2
2
V and ϩ1.34 V vs. Ag/AgCl. For the terephthalate-bridged
J. Chem. Soc., Dalton Trans., 2002, 2168–2172 2171

View Article Online
complex 5, the measurement of its CV and DPV properties
reveals the presence of sequential coupled oxidation processes
exceptions, such as the coupling of a pair of Re Cl (µ-dppm)
2 4 2
units through the agency of the bridging 7,7,8,8,-tetracyano-
23
with E1/2 values of ca. ϩ0.40 V and ϩ0.33 V vs. Ag/AgCl, along
p-quinodimethane ligand (TCNQ), designed syntheses of
general utility are lacking. We have addressed this deficiency
1
with an irreversible oxidation at Ep,c = ϩ1.47 V. The ∆E value
1/2
1
of 70 mV accords with a very small comproportionation con-
in both our initial report and in the present study, and show
stant (K ∼ 15 from eqn. (1)), and therefore with the presence
of at most a very weak electronic coupling between the Re2
that the acetate ligand labilities of Re (µ-O CCH )Cl (µ-dppm)
(1) and cis-Re (µ-O CCH ) Cl (µ-dppm) (2) can be used to
2 2 3 2 2 2
c
2
2
3
4
2
units present in 5. The CV of 12 shows broad processes at E1/2
=
synthesize dicarboxylate-bridged dirhenium species that
include “dimers-of-dimers”, triangular assemblies and mixed-
metal trimetallic species.
ϩ0.35 V and E1/2 = ϩ1.40 V vs. Ag/AgCl. As might be expected,
although 12 is structurally related to 5, the saturated nature of
the organic spacer is not conducive to electronic communic-
ation between the dirhenium units.
Compound 2 is of special note because it is the thermo-
2,3
dynamically stable isomer of a cis/trans pair. With other
bridging phosphine ligands, it is the trans isomer that is the
thermodynamically stable form (e.g. trans-Re (µ-O CCH ) -
A final reaction between 2 and a dicarboxylic acid that we
investigated involved 1,1Ј-ferrocenedicarboxylic acid, a reagent
2
2
3 2
4
ϩ
24
that has been used previously to couple [Mo ] units into
“
Cl (µ-dppE) , where dppE = Ph PC(᎐CH )PPh ) and the trans
2
2
2
2
2
2
18
13b
dimers-of-dimers” or supramolecular squares. In these
isomer can be easily oxidized to its paramagnetic monocationic
congener. We are now investigating the acetate ligand lability in
cases, the two carboxylate groups on each [(O CC H ) Fe]
2
5
4 2
0
,ϩ
moiety are anti to one another and can therefore effect the
coupling of dimetal units. To our surprise, the reaction of 2
with this diacid afforded exclusively the trimetallic compound
cis-Re Cl (µ-dppm) [(µ-O CC H ) Fe] (14) in almost quantit-
compounds of the type [trans-Re (µ-O CCH ) Cl (µ-PP) ]
2 2 3 2 2 2
0,ϩ
with a view to incorporating the [trans-Re Cl (µ-PP) ] unit
2
2
2
into long chain polymers.
2
2
2
2
5
4 2
ative yield, the structure of which is shown in Fig. 3. This com-
Acknowledgements
R.A.W. thanks the John A. Leighty Endowment Fund for
support of this work.
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Re(1)–Re(2) 91.30(10), O(11)–Re(1)–Re(2) 86.15(10), O(12)–Re(2)–
Re(1) 91.40(10), O(22)–Re(2)–Re(1) 86.20(9), P(3)–Re(1)–P(1) 96.31(5),
P(4)–Re(2)–P(2) 94.20(5), Re(2)–Re(1)–Cl(1) 166.27(4), Re(1)–Re(2)–
Cl(2) 167.68(3), O(12)–C(10)–O(11) 124.1(5), O(22)–C(20)–O(21)
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2
2
2
2
2
1
7 D. R. Derringer, P. E. Fanwick, J. Moran and R. A. Walton, Inorg.
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redox processes (both oxidations) in its CV (recorded in 0.1 M
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18 F. A. Cotton, J. P. Donahue, C. Lin and C. A. Murillo, Inorg. Chem.,
2001, 40, 1234.
1
2
2
1/2
These processes, which are reversible (with ip,a = ip,c and ∆E =
p
9 (a) J. D. Chen and F. A. Cotton, J. Am. Chem. Soc., 1991, 113, 5857;
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6
0 mV), are accompanied by a reversible process at E1/2 = ϩ1.12
(
V (∆E = 60 mV) vs. Ag/AgCl that is associated with oxidation
p
2
0 F. A. Cotton, J. Lu and Y. Huang, Inorg. Chem., 1996, 35, 1839.
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2
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R. A. Walton, J. Chem. Soc., Dalton Trans., 2000, 4277.
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More often than not, compounds in which pairs of multiply-
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2
2
3 S. L. Bartley and ꢀ. R. Dunbar, Angew. Chem.,Int. Ed. Engl., 1991,
3
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4 S.-M. ꢀuang, P. E. Fanwick and R. A. Walton, Inorg. Chim. Acta,
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19–22
discovered more by chance than design.
While there are
2
172 J. Chem. Soc., Dalton Trans., 2002, 2168–2172