Reactions of the dirhenium(in, iii) complex c/Y-Re2(n-O2CMe)2C14(H2O)2 that lead to the dirhenium(ni, ii) complexes Re2(u-O2CMe)Cl4(PR3)2 and tetrarheniumcyclodiyne clusters of the type Re4(u-O)4Cl4(PR3)4

Article abstract of DOI:10.1039/b005975g

The reaction of cw-Re2(u-O₂CMe)₂Cl4(H₂O)₂1 with P(C6H4OMe-/>)3 gives the tetranuclear complex Re4(u-O)4Cl4[P(C6H4OMe-p)3]414 along with the salt [(C6H4OMe-p)3PMe]₂Re2Cl815. Compound 14 is the first symmetrical, neutral, tetrarheniumcyclodiyne type cluster that contains phosphine ligands. Complexes of this same type with PPh3 (16) and PMe2Ph (17) have been prepared by alternative methods but have poor solubility properties. The paramagnetic complex Re2(u-O₂CMe)Cl4(PPh3)₂ 2, which is prepared from 1 by reaction with PPh3, undergoes phosphine substitution reactions when treated with dichloromethane solutions of other phosphines. Simple non-redox reactions can occur upon reaction of 2 with monodentate and bridging bidentate phosphines to afford complexes of the types Re2(u-O₂CMe)Cl4(PR3)₂ [PR3 = PBz3 3, P(C6H4OMe-/j)3 4 or PMePh2 5] and fra/w-Re2(u-O₂CMe)Cl4(u-PP)₂ [PP = dppm 9, Ph2PNHPPh210 or (Ph2P)₂C=CH₂11J. However, reactions that lead either to reduction to dirhenium(ii) complexes or Re-Re bond cleavage are encountered in the case of the reactions of 2 with PMePh2, PMe2Ph, PCy3 and dppe; these have led to the isolation of Re2Cl4(PMePh2)4 6, Re2Cl4(PMe2Ph)4 7, ;wi?/_/ra/u-ReOCl3(PCy3)₂ 8, a-Re2Cl4(dppe)₂12, and /ra/i.y-[ReO₂(dppe)₂]Cl 13. The structures of compounds 3, 8, 13, 14 and 15 have been determined by X-ray crystallography. ; The Royal Society of Chemistry 2000.

Full text of DOI:10.1039/b005975g

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Reactions of the dirhenium(III,III) complex cis-Re2(ꢀ-O2CMe)2-
Cl4(H2O)2 that lead to the dirhenium(III,II) complexes
Re2(ꢀ-O2CMe)Cl4(PR3)2 and tetrarheniumcyclodiyne clusters
of the type Re4(ꢀ-O)4Cl4(PR3)4
Jitendra K. Bera, Sophia S. Lau, Phillip E. Fanwick and Richard A. Walton*
Department of Chemistry, 1393 Brown Building, Purdue University, West Lafayette,
IN 47907-1393, USA. E-mail: rawalton@purdue.edu
Received 25th July 2000, Accepted 26th September 2000
First published as an Advance Article on the web 6th November 2000
The reaction of cis-Re2(µ-O2CMe)2Cl4(H2O)2 1 with P(C6H4OMe-p)3 gives the tetranuclear complex Re4(µ-O)4Cl4-
[P(C6H4OMe-p)3]4 14 along with the salt [(C6H4OMe-p)3PMe]2Re2Cl8 15. Compound 14 is the first symmetrical,
neutral, tetrarheniumcyclodiyne type cluster that contains phosphine ligands. Complexes of this same type with
PPh3 (16) and PMe2Ph (17) have been prepared by alternative methods but have poor solubility properties. The
paramagnetic complex Re2(µ-O2CMe)Cl4(PPh3)2 2, which is prepared from 1 by reaction with PPh3, undergoes
phosphine substitution reactions when treated with dichloromethane solutions of other phosphines. Simple
non-redox reactions can occur upon reaction of 2 with monodentate and bridging bidentate phosphines to
afford complexes of the types Re2(µ-O2CMe)Cl4(PR3)2 [PR3 = PBz3 3, P(C6H4OMe-p)3 4 or PMePh2 5] and
trans-Re (µ-O CMe)Cl (µ-PP) [PP = dppm 9, Ph PNHPPh 10 or (Ph P) C᎐CH 11]. However, reactions that
᎐
2
2
4
2
2
2
2
2
2
lead either to reduction to dirhenium() complexes or Re–Re bond cleavage are encountered in the case of the
reactions of 2 with PMePh2, PMe2Ph, PCy3 and dppe; these have led to the isolation of Re2Cl4(PMePh2)4 6,
Re2Cl4(PMe2Ph)4 7, mer-trans-ReOCl3(PCy3)2 8, α-Re2Cl4(dppe)2 12, and trans-[ReO2(dppe)2]Cl 13. The
structures of compounds 3, 8, 13, 14 and 15 have been determined by X-ray crystallography.
Introduction
Experimental
Several types of behavior have been encountered in the
Starting materials and general procedures
reactions of the dirhenium() carboxylate complex cis-Re2(µ-
O2CMe)2Cl4(H2O)2 with the tertiary phosphines PMe3,
Standard literature procedures were used to prepare the com-
plexes cis-Re2(µ-O2CMe)2Cl4(H2O)2 12b and Re2(µ-O2CMe)Cl4-
(PPh3)2 2.4 All phosphine ligands and common solvents were
used as received from commercial sources. Reactions were
performed under an atmosphere of dry dinitrogen, and solvents
were deoxygenated by purging with dinitrogen prior to use. IR
spectra, NMR spectra and cyclic voltammetric measurements
were determined as described previously.6 Elemental
microanalyses were performed by Dr H. D. Lee of the Purdue
University Microanalytical Laboratory.
1
PMe2Ph, PMePh2 and PPh3 in primary alcohol solvents.2,3
The first three phosphines afford the two-electron reduced
dirhenium() complexes of the type Re2Cl4(PR3)4, whereas
PPh3, which is the least basic of these phosphines, gives the
dirhenium(,) intramolecular disproportionation products
(RO)2Cl2ReReCl2(PPh3)2 (R = Me, Et or Prn).2,3 More recently,
we have examined the reactions of cis-Re2(µ-O2CMe)2
Cl4(H2O)2 towards an extensive range of triaryl phosphines
(PAr3) in methanol and isolated further examples of complexes
of the type (MeO)2Cl2ReReCl2(PAr3)2 [PAr3 = P(C6H4Me-p)3,
P(C6H4Me-m)3, P(C6H4Cl-p)3 or P(C6H4OMe-p].3 Variations
in the nature of the phosphine have led in several instances to
the formation of unexpected reaction products under these
same reaction conditions. Specifically, Re2(µ-O2CMe)Cl3-
(OMe)(PCyPh2)2 and Re2(µ-O2CMe)Cl4(PBz3)2 are the pre-
dominant products when PCyPh2 and PBz3 are used, while
Re4(µ-O)4Cl4[P(C6H4OMe-p)3]4 is a major product in the reac-
tion involving P(C6H4OMe-p)3.3 The paramagnetic complex
Re2(µ-O2CMe)Cl4(PBz3)2 is similar to compounds of this type
isolated previously with PPh3 and PPh2py.4
Synthesis
Re2(ꢀ-O2CMe)Cl4(PBz3)2 3. A mixture of Re2(µ-O2CMe)-
Cl4(PPh3)2 2 (127 mg, 0.116 mmol) and P(CH2Ph)3 (87 mg,
0.286 mmol) was stirred in dichloromethane (15 mL) for 6 h at
room temperature. The solvent was removed under reduced
pressure to leave an oily residue which was treated with diethyl
ether (ca. 10 mL) and the mixture stirred. A red solid was
filtered off, washed with diethyl ether (3 × 5 mL) and dried
under a vacuum; yield 119 mg (87%). Calc. for C44H45Cl4-
O2P2Re2: C, 44.71; H, 3.84. Found: C, 44.77; H, 3.88%.
X-Ray quality single crystals of 3 were obtained by the
diffusion of diethyl ether into a dichloromethane solution of
the complex.
In the present report we address two important points raised
by these earlier studies.2–4 First, we have examined the substi-
tutional lability of the PPh3 ligands in Re2(µ-O2CMe)Cl4(PPh3)2
as a possible strategy for accessing other derivatives of the
paramagnetic [Re2(µ-O2CMe)Cl4] core. Second, since the
tetranuclear complex Re4(µ-O)4Cl4[P(C6H4OMe-p)3] 4 is the first
example of a symmetrical tetrarhenium cyclodiyne type cluster
containing phosphine ligands,5 we have examined means by
which this novel cluster chemistry can be developed.
Re2(ꢀ-O2CMe)Cl4[P(C6H4OMe-p)3]2 4. A procedure similar
to that described for 3 afforded the title complex when 130 mg
(0.12 mmol) of 2 was reacted with 93 mg (0.26 mmol) of
P(C6H4OMe-p)3; yield 138 mg (90%). Calc. for C44H45Cl4O8-
P2Re2: C, 41.35; H, 3.55. Found: C, 41.28; H, 3.47%.
DOI: 10.1039/b005975g
J. Chem. Soc., Dalton Trans., 2000, 4277–4284
This journal is © The Royal Society of Chemistry 2000
4277

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Re2(ꢀ-O2CMe)Cl4(PMePh2)2 5 and Re2Cl4(PMePh2)4 6. A
dichloromethane solution (15 mL) of 2 (100 mg, 0.09 mmol)
was treated with 0.1 mL of PMePh2 and the mixture stirred for
8 h at room temperature. The reaction solvent was removed
under reduced pressure and the residue washed with pentane
(3 × 5 mL). The cyclic voltammogram showed the resulting
solid (96 mg) to be a mixture of products, so it was extracted
with benzene to leave an insoluble red paramagnetic solid
(49 mg, 56%), identified as 5 by cyclic voltammetry (see Results
and discussion), and a green benzene soluble product (44 mg,
37%) which was identified as 6 on the basis of its known
spectroscopic and electrochemical properties.7
0.169 mmol) was then added and the resulting mixture refluxed
for 3 days. The crop of red crystalline 14 was filtered off,
washed with a small volume of fresh methanol and diethyl ether
and dried; yield 67 mg (48%). Calc. for C86H92Cl4O18P4Re4
(i.e. 14ؒ2MeOH): C, 42.61; H, 3.83; Cl, 5.85. Found: C, 41.38;
H, 3.63; Cl, 6.35%. A suitable single crystal of composition
14ؒ2MeOH was selected from this batch for an X-ray structure
analysis.
The filtrate from the above reaction was collected and the
solvent removed under reduced pressure to afford an oily
residue. The addition of diethyl ether (10 mL) gave a green
solid which was filtered off, washed several times with this same
solvent, redissolved in dichloromethane (3 mL) and diethyl
ether allowed to diffuse slowly into this solution. After a period
of two weeks, X-ray quality crystals of 15 were obtained: yield
32 mg (41%). Calc. for C44H48Cl8O6P2Re2: C, 38.00; H, 3.48.
Found: C, 37.84; H, 3.42%. The identity of this product was
confirmed by X-ray crystallography.
An alternative synthesis of the tetrarhenium complex 14
involved the reaction between Re2(µ-O2CMe)Cl4[P(C6H4OMe-
p)3]2 4 (116 mg, 0.091 mmol) and LiOHؒ2H2O (10 mg, 0.24
mmol) in refluxing methanol (20 mL) for 2 days. The red micro-
crystalline product 14 was filtered off, washed with methanol
(3 × 5 mL) and diethyl ether (2 × 5 mL) and dried under a
vacuum; yield 28 mg (26%).
Re2Cl4(PMe2Ph)4 7. The same procedure that was used to
prepare 5, along with Re2Cl4(PMePh2)4 6, was carried out with
PMe2Ph in place of PMePh2. The product was exclusively
Re2Cl4(PMe2Ph)4 7, which was identified based upon a com-
parison of its properties with those reported in the literature.7,8
Yield: 90%.
mer-trans-ReOCl3(PCy3)2 8. The reaction between 2 (81 mg,
0.074 mmol) and 70 mg (0.25 mmol) of PCy3 in 15 mL of
dichloromethane was carried out for 8 h, the solvent removed
under reduced pressure, and diethyl ether (10 mL) added to
afford a green precipitate which was recrystallized from
dichloromethane–diethyl ether; yield 85 mg (70%). Calc. for
C36H66Cl3OP2Re: C, 49.73; H, 7.65. Found: C, 50.09; H, 7.67%.
Crystals suitable for an X-ray diffraction study were grown
by the slow diffusion of diethyl ether into a dichloromethane
solution of the complex.
Re4(ꢀ-O)4Cl4(PPh3)4 16. A procedure similar to the altern-
ative synthesis of 14 described above was used. The reaction
between Re2(µ-O2CMe)Cl4(PPh3)2 2 (130 mg, 0.12 mmol) and
LiOHؒ2H2O (12 mg, 0.28 mmol) afforded a small quantity of
16; yield 21 mg (18%). Calc. for C72H60Cl4O4P4Re4: C, 43.24; H,
3.02. Found: C, 41.87; H, 3.47%.
Re2(ꢀ-O2CMe)Cl4(ꢀ-dppm)2 9. A mixture of 2 (100 mg, 0.091
mmol) and bis(diphenylphosphino)methane (dppm) (85 mg,
0.22 mmol) was stirred in dichloromethane (15 mL) at room
temperature for 8 h. The solvent was removed under reduced
pressure and the oily residue treated with diethyl ether (10 mL)
and stirred to afford 9 as a yellow solid; yield 116 mg (92%).
The identity of this product was established by a comparison of
its spectroscopic and electrochemical properties with literature
data.9
Re4(ꢀ-O)4Cl4(PMe2Ph)4 17. A dichloromethane solution
(15 mL) of 14 (60 mg, 0.025 mmol) was treated with 0.1 mL of
PMe2Ph and the mixture stirred for 8 h at room temperature.
The orange solid was filtered off and washed with dichloro-
methane (2 × 5 mL); yield 29 mg (77%). The identity of 17 was
based upon its electrochemical and IR spectral properties. A
satisfactory microanalysis could not be obtained.
Re2(ꢀ-O2CMe)Cl4(ꢀ-dppa)2 10. This complex was prepared
by the reaction of 2 with Ph2PNHPPh2 (dppa) with the use of
a procedure similar to that described above for its dppm
analogue; yield 90%. The identity of 10 was based upon its
spectroscopic and electrochemical properties.10
X-Ray crystallography
Crystals of the complexes Re2(µ-O2CMe)Cl4(PBz)2 3, mer-
trans-ReOCl3(PCy3)2 8, trans-[ReO2(dppe)2]Clؒ3CH2Cl2 13,
Re4(µ-O)4Cl4[P(C6H4OMe-p)3]4ؒ2MeOH 14 and [(C6H4OMe-
p)3PMe]2Re2Cl8 15 were obtained as described in the appropri-
ate sections detailing their syntheses.
Re2(ꢀ-O2CMe)Cl4(ꢀ-dppE)2 11. A procedure similar to that
described for 9 was used to prepare the title complex which
The data were collected at 173 ( 1) K for the crystals of 3, 13
and 15, 193 ( 1) K for 8, and 296 ( 1) K for 14. All measure-
ments were carried out on a Nonius KappaCCD diffractometer
with graphite-monochromated Mo-Kα radiation (λ = 0.71073
Å). Crystal data and the relevant experimental details on data
collection and refinement are given in Table 1. Lorentz and
polarization corrections were applied to the data sets. The
structures of 3, 8, 13 and 15 were solved using the structure
solution program PATTY in DIRDIF9212 while the structure
of 14 was solved by direct methods using SIR97.13 The remain-
ing atoms were located in succeeding difference Fourier
syntheses. Hydrogen atoms were placed in calculated positions
according to idealized geometries with U(H) = 1.3Ueq(C). An
empirical absorption correction using SCALEPACK14 was
applied in all cases except 3 and 14 for which DELABS in
PLATON15 was used. The final refinements were performed by
the use of the program SHELXL-97.16 All non-hydrogen atoms
were refined with anisotropic thermal parameters with the
exception of atom O(1) of 8.
contained the ligand (Ph P) C᎐CH (dppE); yield 90%. Calc.
᎐
2
2
2
for C54H47Cl O2P4Re2: C, 47.48; H, 3.47. Found: C, 47.21; H,
4
3.58%.
ꢁ-Re2Cl4(dppe)2 12 and trans-[ReO2(dppe)2]Cl 13. A pro-
cedure similar to that described for the preparation of 9,
employing 130 mg (0.12 mmol) of 2 and 104 mg (0.26 mmol) of
Ph2P(CH2)2PPh2 (dppe), afforded a green solid that was shown
by cyclic voltammetry to be a mixture of products. The reaction
residue was dissolved in dichloromethane and diethyl ether
allowed to slowly diffuse into this solution; this gave a separable
mixture of green and yellow crystals. The green product
(103 mg) was shown to be α-Re2Cl4(dppe)2 12 on the basis of its
spectroscopic and electrochemical properties,11 while the yellow
crystals (35 mg) were found to be trans-[ReO2(dppe)2]Cl 13 by a
single crystal X-ray structure determination.
Re4(ꢀ-O)4Cl4[P(C6H4OMe-p)3]4 14and[(C6H4OMe-p)3PMe]2-
Re2Cl8 15. A sample of P(C6H4OMe-p)3 (184 mg, 0.522 mmol)
was heated in methanol (20 mL) until it had completely dis-
solved. A quantity of cis-Re2(µ-O2CMe)2Cl4(H2O)2 1 (113 mg,
In the crystal structure of 8, the molecule sits on an inversion
center and like its analogue mer-trans-ReOCl3(PMe3)2 shows
an orientational disorder involving the sets of trans O and Cl
17
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J. Chem. Soc., Dalton Trans., 2000, 4277–4284

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Table 1 Crystallographic data for Re2(µ-O2CMe)Cl4(PBz3)2 3, mer-trans-ReOCl3(PCy3)2 8, trans-[ReO2(dppe)2]Clؒ3CH2Cl2 13, Re4(µ-O)4-
Cl4[P(C6H4OMe-p)3]4ؒ2MeOH 14 and [(C6H4OMe-p)3PMe]2Re2Cl8 15
3
8
13
14
15
Formula
Formula weight
Crystal system
Space group
a/Å
b/Å
c/Å
α/Њ
C44H45Cl4O2P2Re2
1182.01
C36H66Cl3OP2Re
869.43
C55H54Cl7O2P4Re
1305.31
C86H92Cl4O18P4Re4
2424.19
Monoclinic
P21/c (no. 14)
13.9995(7)
23.5126(7)
14.3633(7)
90.00
114.1998(16)
90.00
2
4312.4(6)
5.93
35082
C44H48Cl8O6P2Re2
1390.86
Monoclinic
P21/c (no. 14)
16.5256(3)
18.6675(4)
33.0129(4)
90.00
100.5122(11)
90.00
8
10013.3(6)
5.436
75534
Triclinic
Triclinic
Triclinic
¯
¯
¯
P1 (no. 2)
P1 (no. 2)
P1 (no. 2)
9.8942(5)
13.5625(9)
18.4975(12)
69.437(3)
76.902(4)
69.586(3)
2
2162.7(3)
6.027
17466
9088
6436
489
0.041
9.9534(5)
10.2535(5)
10.9010(5)
114.311(3)
107.608(3)
93.089(3)
1
945.76(19)
3.579
7186
3917
3881
201
0.043
9.4968(3)
12.9135(5)
24.8886(10)
97.9692(19)
91.753(2)
110.195(2)
2
2826.8(4)
2.662
19987
11859
7006
625
0.061
β/Њ
γ/Њ
Z
V/Å3
µ(Mo-Kα)/mmϪ1
Reflections collected
independent
observed [I > 2σ(I)]
No. of variables
R(Fo)a
10854
7175
550
0.062
15630
8019
1171
0.053
2
Rw(Fo )b
0.099
0.114
0.123
0.104
0.122
GOF
0.998
1.102
1.090
1.138
0.946
2
2
2 2
a R = Σ||Fo| Ϫ |Fc||/Σ|Fo| with Fo2 > 2σ(Fo ). b Rw = [Σw(|Fo | Ϫ |Fc2|)2/Σw|Fo | ]1/2
.
half atoms [i.e. O(1), Cl(1) and O(1)Ј, Cl(1)Ј]; these atoms are
resolved in the refinement. In the refinement of 13, the asym-
metric unit was found to contain two independent Re cations
located at inversion centers each at 0.5 occupancy, and three
full molecules of lattice CH2Cl2. During the course of the
refinement of the tetrarhenium complex 14, the Re–Re units of
the rectangular cluster were found to be disordered such that
there are two incompletely occupied, approximately orthogonal
sets, which to a first approximation share the same set of ligand
atoms. The multiplicities of the major and minor forms are
0.949 and 0.051, respectively. This result is similar to that found
(PPh3)2 are formed.2,3 In the present study we have established
that the coordinatively unsaturated complex 2 can be used
as a convenient precursor to complexes of the types Re2(µ-O2-
CMe)Cl4(PR3)2 (PR3 = monodentate tertiary phosphine) and
Re2(µ-O2CMe)Cl4(PP)2 (PP = bridging bidentate phosphine).
These phosphine substitution reactions proceed in high yield
when carried out in dichloromethane at room temperature.
The monodentate phosphines PBz3 (Bz = CH2Ph) and P(C6H4-
OMe-p)3 produced Re2(µ-O2CMe)Cl4(PBz3)2 3 and Re2(µ-
O2CMe)Cl4[P(C6H4OMe-p)3]2 4, respectively [Scheme 1(a)].
during the solution of the structure of (Bun N)2[Re4Cl8(µ-O)2-
4
(µ-OMe)2]18 in which a disordered structure of this same
type was encountered; in this instance the multiplicities were
0.96 and 0.04, respectively. Two molecules of methanol per
tetrarhenium unit were found in the lattice. The refinement of
the structure of 15 showed the presence of two pairs of
independent cations and anions in the asymmetric unit. For
each of the [Re2Cl8]2Ϫ anions, two sets of fractional Re–Re units
were found to be present such that within each anion these units
were perpendicular to one another and shared the same set of
Cl ligands. These pairs refined satisfactorily to occupancies for
Re(1A)/Re(2A) and Re(1B)/Re(2B) of 0.473 and 0.027, respect-
ively, and for Re(3A)/Re(4A) and Re(3B)/Re(4B) of 0.432
and 0.068, respectively. This type of disorder is commonly
encountered for dimetal complexes which contain a metal–
metal multiple bond and an eclipsed M2L8 geometry.19
CCDC reference number 186/2199.
See http://www.rsc.org/suppdata/dt/b0/b005975g/ for crystal-
lographic files in .cif format.
Results and discussion
The products from the reactions of cis-Re2(µ-O2CMe)2Cl4-
(H2O)2 1 with phosphines are both phosphine and solvent
dependent. Thus, with PPh3 in acetone the paramagnetic
dirhenium(,) complex Re2(µ-O2CMe)Cl4(PPh3)2 2 is pro-
duced4 whereas in alcohol solvents (MeOH, EtOH or PrnOH)
the quadruply bonded dirhenium(,) alkoxides Re2Cl4(OR)2-
Scheme 1 Products from the reactions of Re2(µ-O2CMe)Cl4(PPh3)2
with monodentate phosphines.
Interestingly, 3 had been reported previously as the product
when cis-Re2(µ-O2CMe)2Cl4(H2O)2 1 is reacted with PBz3 in
refluxing methanol,3 while the use of methanol as the solvent in
the reaction of 1 with P(C6H4OMe-p)3 affords the tetranuclear
complex 14 (vide infra). The properties of 3 isolated herein and
those of samples reported previously are the same.3 A single
crystal X-ray structure determination of 3 confirms its close
J. Chem. Soc., Dalton Trans., 2000, 4277–4284
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Fig.
2
ORTEP20 representation of the structure of mer-trans-
Fig. 1 ORTEP20 representation of the structure of the dirhenium(,)
complex Re2(µ-O2CMe)Cl4(PBz3)2 3. Thermal ellipsoids are drawn at
the 50% probability level.
ReOCl3(PCy3)2 8. Only one-half of the orientational disorder involving
the trans O and Cl ligands [O(1) and Cl(1)] is shown. Thermal ellipsoids
are drawn at the 50% probability level.
Table 2 Important bond distances (Å) and angles (Њ) for Re2(µ-O2-
CMe)Cl4(PBz3)2 3a
Table 3 Important bond distances (Å) and angles (Њ) for mer-trans-
ReOCl3(PCy3)2 8a
Re(1)–Re(2)
Re(1)–O(1)
Re(1)–Cl(11)
Re(1)–Cl(12)
Re(1)–P(1)
2.2166(4)
2.076(5)
2.3462(18) Re(2)–Cl(22)
2.3730(19) Re(2)–P(2)
2.428(2)
Re(2)–O(2)
Re(2)–Cl(21)
2.106(5)
Re–O(1)
Re–Cl(1)
1.699(14)
2.282(4)
Re–Cl(2)
Re–P(1)
2.3822(16)
2.5322(14)
2.3508(18)
2.3666(19)
2.4036(19)
O(1)–Re–Cl(1)
O(1)–Re–Cl(2)
O(1)–Re–Cl(2)
Cl(1)–Re–Cl(2)
179.6(5)
91.0(5)
89.0(5)
Cl(1)–Re–Cl(2)
P(1)–Re–Cl(1)
P(1)–Re–O(1)
P(1)–Re–Cl(2)
90.76(12)
88.03(9)
91.7(5)
O(1)–Re(1)–Re(2)
O(1)–Re(1)–Cl(11)
Re(2)–Re(1)–Cl(11)
O(1)–Re(1)–Cl(12)
Re(2)–Re(1)–Cl(12)
Cl(11)–Re(1)–Cl(12)
O(1)–Re(1)–P(1)
Re(2)–Re(1)–P(1)
Cl(11)–Re(1)–P(1)
Cl(12)–Re(1)–P(1)
90.61(15) O(2)–Re(2)–Re(1)
162.80(16) O(2)–Re(2)–Cl(21)
106.53(5)
86.87(15) O(2)–Re(2)–Cl(22)
114.60(5)
87.21(7)
89.70(16)
165.74(16)
104.54(5)
84.91(16)
117.28(5)
87.79(7)
94.41(15)
96.12(5)
84.97(7)
89.24(12)
90.68(5)
a Numbers in parentheses are estimated standard deviations in the least
significant digits.
Re(1)–Re(2)–Cl(21)
Re(1)–Re(2)–Cl(22)
Cl(21)–Re(2)–Cl(22)
complex 5 in 0.1 M Bun NPF6–CH2Cl2 showed reversible pro-
91.77(15) O(2)–Re(2)–P(2)
4
94.57(5)
85.58(7)
150.80(7)
Re(1)–Re(2)–P(2)
Cl(21)–Re(2)–P(2)
Cl(22)–Re(2)–P(2)
cesses at E1/2(ox) = ϩ0.48 V and E1/2(red) = Ϫ0.65 V vs. Ag–
AgCl in the CV, with ∆Ep values of 70 mV at ν = 200 mV sϪ1
.
146.56(7)
These characteristics are similar to those displayed in the
CVs of 3 and 4 (vide supra). The dirhenium() complex 6 is a
known compound that has been characterized previously.7 The
addition of an excess of PMePh2 to a dichloromethane solution
of 5 led to mixtures of 5 and 6 as monitored by CV. Accord-
ingly, it is reasonable to conclude that 5 is the intermediate
in the conversion of 2 to 6. For the reaction of 2 with the
phosphine PMe2Ph, which is more basic than PMePh2 and has
a significantly smaller cone angle, the dirhenium(,) inter-
mediate Re2(µ-O2CMe)Cl4(PMe2Ph)2 could not be isolated;
instead, the dirhenium() complex Re2Cl4(PMe2Ph)4 7 was
obtained in almost quantitative yield [Scheme 1(c)]. This
behavior reflects the greater propensity of the [Re2]5ϩ core to be
reduced to [Re2]4ϩ in the presence of PMe2Ph, a phosphine
which is also less sterically demanding than the phosphines
which afford stable Re2(µ-O2CMe)Cl4(PR3)2 compounds.
a Numbers in parentheses are estimated standard deviations in the least
significant digits.
structural relationship to the analogous PPh3 complex 2.4 An
ORTEP20 representation of the structure of 3 is shown in Fig. 1
and important structural parameters are given in Table 2.
The structure of
3 resembles closely that of Re2(µ-
O2CMe)Cl4(PPh3)2. The Re–Re bond distance of 2.2166(4) Å is
identical to that of 2.2165(7) Å in its PPh3 analogue, while the
Re–Cl, Re–O and Re–P distances fall in very similar ranges for
these two complexes. The rotational geometry is close to being
fully eclipsed, with values for the torsional angles O(1)–Re(1)–
Re(2)–O(2), Cl(11)–Re(1)–Re(2)–Cl(21), P(1)–Re(1)–Re(2)–
Cl(22) and Cl(12)–Re(1)–Re(2)–P(2) of 3.8(2), 3.2(1), 11.5(1)
and 11.4(1)Њ, respectively.
The properties of 3 and 4 are very similar. The cyclic volt-
The reaction of 2 with PCy3, which is the most basic of the
phosphines we studied and also possesses the largest cone angle
(170Њ), resulted in the substitution of the PPh3 ligands and also
the cleavage of the Re–Re multiple bond. This led to the prod-
uct mer-trans-ReOCl3(PCy3)2 8 (ca. 70% yield) along with some
unidentified Re-containing species [Scheme 1(d)]. The source of
oxygen is presumably small amounts of adventitious O2 and/or
H O. Complex 8 possesses a ν(Re᎐O) mode in its IR spectrum
ammograms of solutions of 4 in 0.1 M Bun NPF6–CH2Cl2
4
reveal a one-electron oxidation at E1/2 = ϩ0.47 V and a one-
electron reduction at E1/2 = Ϫ0.67 V vs. Ag–AgCl; these
processes have ∆Ep values (Ep,a Ϫ Ep,c) of 60–65 mV at ν = 200
mV sϪ1. This behavior resembles closely the CVs of 33 and its
PPh3 and PPh2py analogues.4 Like these paramagnetic [Re2]5ϩ
complexes, 4 shows only very broadened peaks in its 1H NMR
spectrum and no resonances in its 31P NMR spectrum.
᎐
2
(KBr disc) at 971 cmϪ1 and a singlet in its 31P{1H} NMR
When 2 is reacted with phosphines that are less sterically
demanding than PBz3 and P(C6H4OMe-p)3, we observed
behavior different than just substitution of the PPh3 ligands of
2. With PMePh2, which has a similar basicity to P(C6H4-
OMe-p)3 but possesses a smaller cone angle (136 vs. 145Њ), a
spectrum (recorded in CDCl3) at δ Ϫ26.0. The CV of 8 recorded
on a solution in 0.1 M Bun NPF6–CH2Cl2 shows irreversible
4
processes at Ep,c = ϩ1.39 V and Ep,a = Ϫ0.97 vs. Ag–AgCl with
ν = 200 mV sϪ1. The identity of this green complex was con-
firmed by a single crystal X-ray structure determination. The
ORTEP20 representation of 8 is shown in Fig. 2 and important
structural parameters are listed in Table 3.
separable mixture of Re2(µ-O2CMe)Cl4(PMePh2)2
5 and
Re2Cl4(PMePh2)4 was obtained {both complexes were
6
unambiguously identified by their cyclic voltammetric proper-
ties) [Scheme 1(b)]}. Solutions of the red paramagnetic
As described in the Experimental section, the mer-trans-
ReOCl3(PCy3)2 molecule shows an orientational disorder in the
4280
J. Chem. Soc., Dalton Trans., 2000, 4277–4284

View Article Online
crystal similar to that found in mer-trans-ReOCl3(PMe3)2,17 so
that there are two sets of trans O and Cl half atoms; only one of
these sets is shown in Fig. 2. In spite of this disorder the pairs of
disordered atoms O(1)/Cl(1) can be resolved; the Re–O distance
in 8 [1.699(14) Å] is similar to that observed in mer-trans-
ReOCl3(PPh3)221 and mer-trans-ReOCl3(PEt2Ph)2.22
The substitutional lability of the PPh3 ligands of 2 towards
bridging bidentate ligands is illustrated by the high yield con-
version of 2 (у 90% yield) to trans-Re2(µ-O2CMe)Cl4(µ-PP)2,
where PP = dppm (9), dppa (10) or dppE (11). Compounds 9
and 10 have been prepared previously,9,10 but the dppE ana-
logue 11 is new. The CV of a solution of 11 in 0.1 M Bun -
4
NPF6–CH2Cl2 shows processes with E1/2(ox) = ϩ0.45
V
(∆Ep = 60 mV) and Ep,c = Ϫ0.54 V vs. Ag–AgCl, which are very
similar to the CVs reported for 9 and 10.9,10 An alternative
synthesis of 11, utilizing the reaction between cis-Re2(µ-
O2CMe)2Cl4(H2O)2 1 and dppE, was unsuccessful since this
afforded Re2Cl4(µ-dppE)2.23 However, an analogous strategy
works well for the preparation of 9 and 10.9,10
The conformational requirements of two bridging Ph2P-
CH2CH2PPh2 (dppe) ligands in a [Re(µ-dppe)2Re] unit favors a
staggered rotational geometry,24 thereby destabilizing a com-
plex such as Re2(µ-O2CMe)Cl4(µ-dppe)2, in which the acetate-
containing [Re(µ-O2CMe)Re] unit should be approximately
planar. Accordingly, in the reaction between 2 and dppe,
although both PPh 3 ligands are displaced, the reaction is quite
complicated and a mixture of the triply bonded dirhenium()
complex α-Re2Cl4(dppe)2 12, which contains chelating dppe
ligands,11 and trans-[ReO2(dppe)2]Cl 13 was obtained. The
formation of 12 derives formally from the reductive elimination
Fig. 3 ORTEP20 representation of the structure of the tetranuclear
cluster Re4(µ-O)4Cl4[P(C6H4OMe-p)3]4 in crystals of 14ؒ2MeOH.
Thermal ellipsoids are drawn at the 50% probability level except for the
phenyl group atoms of the phosphine ligands which are circles of arbi-
trary radii. Unlabeled atoms are related to the labeled atoms by an
inversion center. The four Re atoms shown are those of the primary
form of a disorder in which a secondary and very minor form, sharing
the same ligand atoms, is in a plane orthogonal to the primary form.
ؒ
of MeCO2 from the unstable intermediate {Re2(µ-O2CMe)Cl4-
(µ-dppe)2}. Compound 13 probably arises from a competing
disruption of the Re–Re multiple bond and the reaction of a
coordinatively unsaturated intermediate with adventitious O2.
However, an alternative oxygen source, such as the acetate
ligands, cannot be ruled out. Compound 12 does not convert to
13 under our experimental conditions. The structure of the
[ReO2(dppe)2]ϩ cation present in 13 was confirmed by X-ray
crystallography, but since this structure is essentially identical
to that present in the previously characterized [ReO4]Ϫ, [I]Ϫ and
[PF6]Ϫ salts of this cation,25,26 further discussion of the structure
is unnecessary (see supplementary material for further details).
In addition to the phosphine ligand substitution reactions of
2 that lead to complexes of the types Re2(µ-O2CMe)Cl4(PR3)2
and Re2(µ-O2CMe)Cl4(PP)2 (vide supra), and reactions (with
PCy3 and dppe) which can result in disruption of the Re–Re
multiple bond, a third type of reaction was encountered in the
present study. This involved non-redox transformations of the
type [Re2]6ϩ → [Re4]12ϩ
.
Fig. 4 ORTEP20 representation of the structure of the [Re2Cl8]2Ϫ
anion present in the crystals of 15 showing one of the two crystallo-
graphically independent anions with a two-fold orientational disorder
of the Re–Re unit [Re(1a)/Re(2a) and Re(1b)/Re(2b)]. Thermal ellips-
oids are drawn at the 50% probability level.
We had described previously how the [Re2]5ϩ core complex
Re2(µ-O2CMe)Cl4(PBz3)2 3 can be prepared both through the
reduction of cis-Re2(O2CMe)2Cl4(H2O)2 1 by PBz3 (see ref. 3)
and the non-redox substitution reaction of 2 with PBz3
(this work). While P(C6H4OMe-p)3 reacts with 2 to give
Re2(µ-O2CMe)Cl4[P(C6H4OMe-p)3]2 4, which is structurally
analogous to 3, the reaction of this phosphine with 1 in
refluxing methanol affords the novel tetranuclear complex
Re4(µ-O)4Cl4[P(C6H4OMe-p)3]4 14. This reaction course not
only differs from that between 1 and PBz3 (vide supra) but also
from those involving the triaryl phosphines PAr3 (Ar = Ph,
C6H4Me-p, C6H4Me-m and C6H4Cl-p) all of which produce the
quadruply bonded ‘mixed-valence’ dirhenium (,) complexes
Cl2(MeO)2ReReCl2(PAr3)2 under these same conditions.2,3 For
reasons that are not entirely clear, the phosphine P(C6H4O-
Me-p)3 is unique in affording this unusual tetranuclear rhenium
cluster by this procedure. Complex 14 is the first symmetrical
tetrarheniumcyclodiyne type cluster containing phosphine
ligands. While the dimerization of quadruply bonded dimetal
complexes is well established in Mo and W chemistry,27,28 it has
rarely been encountered in Re chemistry.19,29
Compound 14 could be reproducibly obtained in yields
that approached 50%, so that a considerable quantity of Re
was originally not accounted for.5 However, work-up of the
reaction filtrate yielded the phosphonium salt [(C6H4OMe-p)3-
PMe]2Re2Cl8 15 in isolated yields exceeding 40%, thereby
accounting for most of the Re. Accordingly, it is reasonable
to propose the following reaction stoichiometry (where
Ar = C6H4OMe-p):
3 cis-Re2(µ-O2CMe)2Cl4(H2O)2 ϩ 6 PAr3 ϩ 4MeOH
1
→ Re4(µ-O)4Cl4(PAr3)4 ϩ (Ar3PMe)2Re2Cl8 ϩ
14
15
2MeCO2Me ϩ 8H2O
J. Chem. Soc., Dalton Trans., 2000, 4277–4284
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The origin of the oxygen that is incorporated into the tetra-
nuclear cluster 14 is most likely the methanol solvent, based on
the observations by Cotton and co-workers18,29 who isolated the
mixed oxide/methoxide species [Re4(µ-O)2(µ-OMe)2Cl8]2Ϫ and
[Re4(µ-O)2(µ-OMe)(µ-Cl)Cl8]2Ϫ
.
The structures of 14 and 15 were confirmed by X-ray crystal-
lography. The ORTEP20 representations of the Re containing
species are given in Figs. 3 and 4, and a representation of the
structure of the cation that is present in 15 is shown in Fig. 5.
Important bond distances and angles are listed in Tables 4 and
5. The structure of the tetranuclear complex 14 (Fig. 3) consists
᎐
of a rectangular cluster of metal atoms with two Re᎐Re bonds
᎐
linked by two Re–Re single bonds, each of which is bridged by a
pair of O2Ϫ ligands. The bare Re4 cluster arises formally from
᎐
᎐
the [2 ϩ 2] cycloaddition of two Re᎐Re units (originating from
᎐
Fig. 5 ORTEP20 representation of one of the two crystallographically
independent [(C6H4OMe-p)3PMe]ϩ cations present in the crystals of
15. Thermal ellipsoids are drawn at the 50% probability level.
two molecules of 1) by loss of their δ components. The cluster
possesses a crystallographic inversion center and Re᎐Re and
᎐
᎐
Re–Re bond distances of 2.2726(5) and 2.5388(5) Å (Table 4),
respectively, which are very similar in magnitude to the analo-
gous distances encountered in salts of the [Re4(µ-O)2(µ-
OMe)2Cl 8]2Ϫ, [Re4(µ-O)2(µ-OMe)(µ-Cl)Cl8]2Ϫ and [Re4(µ-O)2(µ-
Cl)2Cl8]2Ϫ anions that have been reported previously by Cotton
and co-workers.18,29 The structural identification of 14 is note-
worthy in that it is the first neutral tetrarheniumcyclodiyne type
cluster possessing the [Re4(µ-O)4]4ϩ core, and the first to contain
phosphine ligands. This cluster represents an extreme in the
chemistry of metal rectangles that range from those in which
there are four separate ligand-bridged metal centers32 to those
with pairs of ligand-bridged multiply bonded M2 units which
may or may not be linked by M–M bonds within the rect-
angular cluster.33
Table 4 Important bond distances (Å) and bond angles (Њ) for Re4-
(µ-O)4Cl4[P(C6H4OMe-p)3]4ؒ2MeOH 14a,b
Re(1)–Re(2)
Re(1)–Re(2)Ј
Re(1)–Cl(1)
Re(2)–Cl(2)
Re(1)–P(1)
2.2726(5)
2.5388(5)
2.350(2)
2.359(2)
2.521(2)
Re(2)–P(2)
Re(1)–O(1)
Re(1)–O(2)
Re(2)–O(1)
Re(2)–O(2)
2.524(2)
1.943(5)
1.995(5)
1.960(5)
1.988(5)
Re(1)–Re(2)–Re(1)Ј
Re(2)Ј–Re(1)–Re(2)
Re(2)–Re(1)–O(1)
Re(2)–Re(1)–O(2)
O(1)–Re(1)–Cl(1)
O(2)–Re(1)–Cl(1)
O(1)–Re(1)–P(1)
O(2)–Re(1)–P(1)
Cl(1)–Re(1)–P(1)
90.099(16) O(1)–Re(2)–Cl(2)
89.901(16) O(2)–Re(2)–Cl(2)
146.77(17)
87.30(15)
77.66(15)
152.26(18)
84.41(7)
96.0(2)
95.7(2)
81.15(19)
79.19(19)
99.50(17)
101.77(17)
146.48(17)
87.12(16)
77.08(15)
151.08(18)
84.16(7)
O(1)–Re(2)–P(2)
O(2)–Re(2)–P(2)
Cl(2)–Re(2)–P(2)
O(1)–Re(1)–O(2)
O(1)–Re(2)–O(2)
Re(1)–O(1)–Re(2)Ј
Re(1)–O(2)–Re(2)Ј
For 15, the presence of the [(C6H 4OMe-p)3PMe]ϩ cation was
confirmed, and the [Re2Cl8]2Ϫ anion was found to have a two-
fold orientational disorder of the Re–Re unit within the cube of
eight Cl ligands. Two sets of crystallographically independent
cations and anions were present so that the complete set of four
Re2 units, labeled Re(1a)/Re(2a), Re(1b)/Re(2b), Re(3a)/Re(4a)
and Re(3b)/Re(4b), have occupancies of 47.3, 2.7, 43.2 and
6.8%, respectively. The Re–Re distances for the two major pairs
[Re(1a)/Re(2a) and Re(3a)/Re(4a)] are 2.2231(6) and 2.2157(7)
Å respectively; these values are typical for the quadruply
bonded [Re2Cl8]2Ϫ anion,30 and are similar to those
encountered in other salts possessing this type of crystallo-
a Numbers in parentheses are estimated standard deviations in the least
significant digits. b The four Re atoms shown in Fig. 4 are those of the
primary form of a disorder in which a secondary form [atoms Re(3) and
Re(4)] appears to share the same ligand atoms and is in a plane
approximately orthogonal to the primary form. The distances Re(3)–
Re(4) and Re(3)–Re(4)Ј are 2.275(8) and 2.528(8) Å, respectively, and
the major and minor forms of this disorder have occupancies of 94.9
and 5.1%, respectively.
Table 5 Important bond distances (Å) and bond angles (Њ) for [(C6H4OMe-p)3PMe]2Re2Cl8 15a,b
Re(1A)–Re(2A)
Re(1A)–Cl(11)
Re(1A)–Cl(12)
Re(1A)–Cl(14)
Re(1A)–Cl(13)
Re(2A)–Cl(21)
Re(2A)–Cl(23)
2.2231(6) Re(2A)–Cl(22)
2.326(3)
2.330(3)
2.207(11) Re(2B)–Cl(23)
2.314(9)
2.332(7)
2.388(7)
2.397(8)
Re(2B)–Cl(11)
Re(2B)–Cl(14)
2.339(8)
2.345(8)
2.351(8)
2.383(9)
1.784(12) P(2)–C(231)
1.784(11) P(2)–C(241)
P(1)–C(131)
P(1)–C(141)
P(2)–C(211)
P(2)–C(221)
1.800(11)
1.808(10)c
1.770(11)
1.778(13)
1.783(12)
1.783(10)c
2.319(3)
2.320(3)
2.325(3)
2.339(3)
2.324(3)
2.326(3)
Re(2A)–Cl(24)
Re(1B)–Re(2B)
Re(1B)–Cl(12)
Re(1B)–Cl(24)
Re(1B)–Cl(13)
Re(1B)–Cl(21)
Re(2B)–Cl(22)
P(1)–C(121)
P(1)–C(111)
Re(2A)–Re(1A)–Cl(11) 104.17(8) Cl(23)–Re(2A)–Cl(22)
Re(2A)–Re(1A)–Cl(12) 103.62(7) Re(1A)–Re(2A)–Cl(24) 102.33(7) Re(1B)–Re(2B)–Cl(14) 101.6(3)
Cl(11)–Re(1A)–Cl(12) 87.69(11) Cl(21)–Re(2A)–Cl(24) 86.79(10) Cl(11)–Re(2B)–Cl(14) 86.1(3)
Re(2A)–Re(1A)–Cl(14) 102.65(7) Cl(23)–Re(2A)–Cl(24) 86.73(10) Re(1B)–Re(2B)–Cl(23) 101.7(4)
86.74(11) Re(1B)–Re(2B)–Cl(11) 101.4(4)
Re(2A)–Cl(22)–Re(2B) 39.3(2)
Re(2A)–Cl(23)–Re(2B) 39.56(19)
Re(2A)–Cl(24)–Re(1B) 39.3(2)
C(121)–P(1)–C(111)
C(121)–P(1)–C(131)
C(111)–P(1)–C(131)
C(121)–P(1)–C(141)
C(111)–P(1)–C(141)
C(131)–P(1)–C(141)
C(211)–P(2)–C(221)
C(211)–P(2)–C(231)
111.7(5)
107.9(5)
108.6(5)
108.1(6)
110.3(5)
110.3(5)
109.6(5)
112.9(6)
107.2(5)
108.5(5)
109.8(6)
108.9(5)
Cl(11)–Re(1A)–Cl(14)
Cl(12)–Re(1A)–Cl(14) 153.71(10) Re(2B)–Re(1B)–Cl(12) 103.6(4)
Re(2A)–Re(1A)–Cl(13) 104.18(7) Re(2B)–Re(1B)–Cl(24) 102.7(4)
Cl(11)–Re(1A)–Cl(13) 151.64(10) Cl(12)–Re(1B)–Cl(24)
Cl(12)–Re(1A)–Cl(13)
Cl(14)–Re(1A)–Cl(13)
87.04(10) Cl(22)–Re(2A)–Cl(24) 153.50(10) Cl(11)–Re(2B)–Cl(23)
91.2(3)
Cl(14)–Re(2B)–Cl(23) 156.7(4)
Re(1B)–Re(2B)–Cl(22) 101.8(4)
Cl(11)–Re(2B)–Cl(22) 156.8(4)
89.4(3)
85.87(11) Re(2B)–Re(1B)–Cl(13) 102.6(4)
86.64(10) Cl(12)–Re(1B)–Cl(13) 84.9(3)
Cl(14)–Re(2B)–Cl(22)
Cl(23)–Re(2B)–Cl(22)
88.6(3)
84.9(3)
Re(1A)–Re(2A)–Cl(21) 104.20(7) Cl(24)–Re(1B)–Cl(13) 154.6(4)
Re(1A)–Re(2A)–Cl(23) 103.90(7) Re(2B)–Re(1B)–Cl(21) 102.2(4)
Cl(21)–Re(2A)–Cl(23) 151.89(10) Cl(12)–Re(1B)–Cl(21) 154.2(4)
Re(1A)–Cl(11)–Re(2B) 39.5(2)
Re(1B)–Cl(12)–Re(1A) 38.86(19) C(221)–P(2)–C(231)
Re(1A)–Cl(13)–Re(1B) 38.05(19) C(211)–P(2)–C(241)
Re(1A)–Cl(14)–Re(2B) 39.4(2)
Re(2A)–Cl(21)–Re(1B) 38.73(19) C(231)–P(2)–C(241)
Re(1A)–Re(2A)–Cl(22) 104.17(7) Cl(24)–Re(1B)–Cl(21)
Cl(21)–Re(2A)–Cl(22) 86.97(10) Cl(13)–Re(1B)–Cl(21)
85.1(3)
89.4(3)
C(221)–P(2)–C(241)
a Numbers in parentheses are estimated standard deviations in the least significant digits. b Data are given for one of the two crystallographically
independent molecules of 15. The pairs Re(1A)/Re(2A) and Re(1B)/Re(2B) are the two disordered Re2 units represented in Fig. 5. Full data are
available as supplementary material. c Distance involving the methyl carbon atom of the phosphonium cation.
4282
J. Chem. Soc., Dalton Trans., 2000, 4277–4284

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graphic disorder.30,31 The spectroscopic and electrochemical
properties of 15 confirmed the purity of the bulk product. The
1H NMR spectral resonances for the [(C6H4OMe-p)3PMe]ϩ
cation (recorded in CD2Cl2) are at δ ϩ7.7–7.5(m) and δ ϩ7.2–
7.1(m) (12H, C6H4), δ ϩ3.92(s) (9H, OMe) and δ ϩ2.75(d)
(3H, Me), while a singlet at δ ϩ19.1 is observed in the 31P{1H}
NMR spectrum (recorded in CD2Cl2). The cyclic voltammetric
P(C6H4OMe-p)3, PMePh2, Ph2PCH2PPh2, Ph2PNHPPh2 and
Ph PC(᎐CH )PPh ; these reactions afford complexes of the
᎐
2
2
2
types Re2(µ-O2CMe)Cl4(PR3)2 [PR3 = PBz3, P(C6H4OMe-p)3
or PMePh2] and trans-Re2(µ-O2CMe)Cl4(µ-PP)2 (PP = bridging
bidentate phosphine), generally in very high yield. The reaction
of 2 with PMePh2 is complicated by a redox reaction which
produces a considerable quantity of the dirhenium() complex
Re2Cl4(PMePh2)4, while the more basic and least sterically
demanding phosphine PMe2Ph gives exclusively Re2Cl4(P-
Me2Ph)4. With the use of certain phosphines, specifically PCy3
and Ph2PCH 2CH2Ph2, which are either very sterically demand-
ing or prefer a chelating coordination mode to Re, the Re–Re
multiple bond is cleaved to produce mononuclear species. For
PCy3, the complex mer-trans-ReOCl3(PCy3)2 is formed, whereas
properties of a solution of 15 in 0.1 M Bun NPF6–CH2Cl2
4
(recorded with a scan rate of 200 mV sϪ1 at a Pt-bead electrode)
show reversible one-electron processes at E1/2(ox) = ϩ1.21 V
and E1/2(red) = Ϫ0.87 V vs. Ag–AgCl that are characteristic of
the [Re2Cl8] 2Ϫ anion.19
While the tetrarhenium complex 14 was the only tetranuclear
cluster we isolated from the reactions of cis-Re2(µ-O2CMe)2-
Cl4(H2O)2 with triaryl phosphines in methanol, two other
derivatives of the type Re4(µ-O)4Cl4(PR3)4 were obtained by the
use of other methods. The triphenylphosphine complex Re4-
(µ-O)4Cl4(PPh3)4 16 was obtained in low yield (ca. 20%) upon
heating Re2(µ-O2CMe)Cl4(PPh3)2 2 in methanol in the presence
of LiOHؒ2H2O but the absence of added phosphine. The use
of LiOH as a source of O2Ϫ is known in the literature as,
for example, in the synthesis of tetrahedral [M4(µ4-O)]nϩ
clusters.34 A similar procedure with the use of 4 {i.e. Re2-
(µ-O2CMe)Cl4[P(C6H4OMe-p)3]2} in place of 2 provided an
alternative means of obtaining 14 but in a lower yield (26%).
The substitutional lability of the P(C6H4OMe-p)3 ligands of
14 was established by the conversion of this complex to
Re4(µ-O)4Cl4(PMe2Ph)4 17 upon its treatment with an excess of
PMe2Ph.
Ph2PCH2CH2PPh2 gives a mixture of dinuclear α-Re2Cl4(dppe)2
᎐
(chelating phosphine, Re᎐Re bond) and trans-[ReO (dppe) ]Cl.
᎐
2
2
Future studies are now being directed at examining the
carboxylate substitution chemistry of Re2(µ-O2CMe)Cl4(PR3)2,
trans-Re2(µ-O2CMe)Cl4(µ-dppm)2 and cis-Re2(µ-O2CMe)2Cl2-
(µ-dppm)2,9 a strategy which we have found can be used to
synthesize [Re 2]n (n = 2, 3 or 4) clusters.
Acknowledgements
We are grateful to the John A. Leighty Endowment Fund for
support of this work.
References
The identities of 16 and 17 were established through a com-
parison of their electrochemical properties and far-IR spectra,
but their poor solubility properties limited their full character-
ization. Furthermore, our inability to recrystallize these prod-
ucts is probably a factor in the poor C and H microanalytical
data that were obtained. The crystallographically characterized
complex 14 shows well defined NMR spectral properties
(recorded in CD2Cl2), with multiplets at δ ϩ8.15, ϩ7.58, ϩ6.90,
ϩ6.80, ϩ6.33 and ϩ6.22 for the C6H4 rings of the phosphine
ligands, singlets at δ ϩ3.87, ϩ3.84 and ϩ3.58 for the OMe sub-
stituents, and δ ϩ3.42(s) for the lattice methanol. The 31P{1H}
NMR spectrum of 14 consists of a singlet at δ ϩ13.6. The
compounds 16 and 17 were not soluble enough to obtain satis-
factory NMR spectra. However, the single scan CVs of dilute
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4
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Concluding remarks
While PPh3 is known to react with the dirhenium() synthon
cis-Re2(µ-O2CMe)2Cl4(H2O)2 1 to afford the paramagnetic
dirhenium(,) complex Re2(µ-O2CMe)Cl4(PPh3)2 2,4 the
reaction of 1 with the triarylphosphine P(C6H4OMe-p)3 in
methanol affords the novel tetranuclear complex Re4(µ-O)4-
Cl4[P(C6H4OMe-p)3]4 14, along with the dirhenium() salt
[(C6H4OMe-p)3PMe]2Re2Cl8. While no other phosphine-
containing tetranuclear complexes of this type can be
synthesized by this particular route,3 the clusters Re4(µ-O)4-
Cl4(PPh3)4 15 and Re4(µ-O)4Cl4(PMe2Ph)4 16 have been
obtained by the alternative methods of reacting 2 with LiOH,
and the substitution of the phosphine ligands in 14 by PMe2Ph.
The non-redox substitutional lability of the PPh3 ligands of
Re2(µ-O2CMe)Cl4(PPh3)2 2 towards both monodentate and
bidentate phosphines has been demonstrated for PBz3,
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33 F. A. Cotton, L. M. Daniels, I. Guimet, R. W. Henning, G. T.
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28 Ref. 19, pp 554–558 and references cited therein.
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34 F. A. Cotton, C. A. Murillo and J. Pascual, Inorg. Chem., 1999, 38,
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4284
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