Reactions of the dirhenium(II) complexes Re2X4(μ-dppm)2 (X = Cl, Br; dppm = Ph2PCH2PPh2) with isocyanides Part XX. Oxidation of the complexes Re2X4(μ-dppm)2(L) (X = Cl or Br; dppm = Ph2PCH2PPh2; L = t-BuNC, XylNC or CO)

Article abstract of DOI:10.1016/S0022-328X(99)00535-5

The reactions of the halogens X₂ (X = Cl or Br) with the diamagnetic dirhenium(II) complexes Re₂X₄(μ-dppm)₂(L), where dppm = Ph₂PCH₂PPh₂, X = Cl or Br, and L = XylNC (xylyl isocyanide), t-BuNC or CO, and with salts of the edge-sharing bioctahedral species [Re₂X₃(μ-dppm)₂(CO)(NCMe)₂] ⁺, provide convenient routes to the dirhenium(III) species [Re₂X₅(μ-dppm)₂(L)]⁺. These cations, where L = XylNC, t-BuNC or CO, have been isolated as their halide (Cl^- or Br₃^-), [PF₆]^- and [O₃SCF₃]^- salts. IR spectroscopy shows that terminal RNC and CO ligands are present, and a crystal structure determination of the complex [Re₂Cl₅(μ-dppm)₂(CO)]PF₆ confirms that the cation has the edge-sharing bioctahedral structure [Re₂(μ-Cl)₂(μ-dppm)₂Cl ₃(CO)]⁺ with a formal Re=Re bond (Re-Re distance = 2.6607(4) A?). ³¹P-NMR spectroscopy indicates that these salts are weakly paramagnetic, with their P resonances exhibiting unusually large upfield shifts.

Full text of DOI:10.1016/S0022-328X(99)00535-5

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 596 (2000) 27–35
Reactions of the dirhenium(II) complexes Re2X4(m-dppm)2 (X=Cl,
Br; dppm =Ph2PCH2PPh2) with isocyanides
Part XX 1. Oxidation of the complexes Re2X4(m-dppm)2(L) (X=Cl
or Br; dppm=Ph2PCH2PPh2; L=t-BuNC, XylNC or CO) to the
edge-sharing bioctahedral dirhenium(III) cations
[Re2(m-X)2(m-dppm)2X3(L)]+
James Chantler, David A. Kort, Phillip E. Fanwick, Richard A. Walton *
Department of Chemistry, Purdue Uni6ersity, 1393 Brown Building, West Lafayette, IN 47907-1393, USA
Received 1 July 1999
Dedicated to Professor F. Albert Cotton on the occasion of his 70th Birthday in recognition of his outstanding contributions as a mentor
and to the evolution of modern inorganic chemistry.
Abstract
The reactions of the halogens X2 (X=Cl or Br) with the diamagnetic dirhenium(II) complexes Re2X4(m-dppm)2(L), where
dppm=Ph2PCH2PPh2, X=Cl or Br, and L=XylNC (xylyl isocyanide), t-BuNC or CO, and with salts of the edge-sharing
bioctahedral species [Re2X3(m-dppm)2(CO)(NCMe)2]+, provide convenient routes to the dirhenium(III) species [Re2X5(m-
dppm)2(L)]+. These cations, where L=XylNC, t-BuNC or CO, have been isolated as their halide (Cl− or Br3−), [PF6]− and
[O3SCF3]− salts. IR spectroscopy shows that terminal RNC and CO ligands are present, and a crystal structure determination of
the complex [Re2Cl5(m-dppm)2(CO)]PF6 confirms that the cation has the edge-sharing bioctahedral structure [Re2(m-Cl)2(m-
dppm)2Cl3(CO)]+ with a formal ReꢀRe bond (ReꢁRe distance=2.6607(4) A). 31P-NMR spectroscopy indicates that these salts
,
are weakly paramagnetic, with their P resonances exhibiting unusually large upfield shifts. © 2000 Elsevier Science S.A. All rights
reserved.
Keywords: Carbonyl complexes; Crystal structure; Dirhenium(II) complexes; Dirhenium(III) complexes; Isocyanide complexes
1. Introduction
Previous studies on the monocarbonyl and monoiso-
cyanide complexes Re2X4(m-dppm)2(L), where X=Cl
or Br, dppm=Ph2PCH2PPh2 and L=CO, t-BuNC or
xylylNC (XylNC), have shown that the predominant
structural form in the solid state is that of the A-frame
isomer I (i.e. Re2(m-X)X3(m-dppm)2(L))[2–5].
A second isomeric form with an open structure, without
the bridging m-X ligand, has also been established [5].
These 1:1 adducts of Re2X4(m-dppm)2 with RNC and
CO are remarkably stable towards loss of the p-accep-
tor ligands. Furthermore, they show interesting reactiv-
ity when treated with further equivalents of RNC and
CO ligands [3,5–7] and with alkynes [8,9].
The triply bonded dirhenium(II) synthons Re2X4(m-
dppm)2 [10–12], which are the precursors to Re2X4(m-
dppm)2(L), are readily oxidized to the edge-sharing
bioctahedral dirhenium(III) complexes Re2(m-X)2X4(m-
* Corresponding author. Tel.: +1-765-494-5464; fax: +1-765-494-
0239.
E-mail address: rawalton@purdue.edu (R.A. Walton)
1 For Part XIX see Ref. [1].
0022-328X/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(99)00535-5

28
J. Chantler et al. / Journal of Organometallic Chemistry 596 (2000) 27–35
dppm)2 [13,14], in which there is a ReꢀRe bond
(s2p2d2d*2 configuration). In the present report, we
describe the nature of the products that are formed
upon the halogenation of the complexes Re2X4(m-
dppm)2(L), where X=Cl or Br when L=CO and
X=Cl when L=t-BuNC or XylNC.
with a Pt-bead electrode): E1/2(ox)= +1.52 and +0.85
V; E1/2(red)= −0.32 and −1.11 V vs. Ag ꢀ AgCl.
These properties are very similar to those of other
complexes of this type (see above).
All other reagents and solvents were obtained from
commercial sources and used as received. Syntheses
were performed under an atmosphere of dry nitrogen.
1
Routine IR spectra, H-, 31P-, 31P{1H}-NMR spectra
and cyclic voltammetric measurements were recorded as
previously described [5]. Temperature range 31P-NMR
spectra were recorded with the use of a Varian XL-
200A spectrometer and referenced to 85% H3PO4 as an
external standard. Elemental microanalyses were per-
formed by Dr H.D. Lee of the Purdue University
Microanalytical Laboratory.
2. Experimental
2.1. Starting materials and reaction procedures
The complexes Re2X4(m-dppm)2 (X=Cl or Br) [15],
Re2X4(m-dppa)2 (dppa=Ph2PNHPPh2; X=Cl or Br)
[13,16], Re2X4(m-dppm)2(CO) (X=Cl or Br) [2,3],
Re2Cl4(m-dppm)2(CNR) (R=t-Bu or Xyl) [4],
Re2Br4(m-dppm)2(CNXyl) [4] and [Re2Cl3(m-dppm)2
(CO)(NCMe)2]PF6 [3] were prepared according to liter-
ature procedures. Samples of [Re2Br3(m-dppm)2
(CO)(NCMe)2]PF6 were obtained by the use of a proce-
dure similar to that described for its chloro analog [3],
as were the triflate salts [Re2X3(m-dppm)2(CO)
(NCMe)2]O3SCF3 [17]. The compounds Re2Cl6(m-
dppm)2 and Re2Cl6(m-dppa)2 (dppa=Ph2PNHPPh2)
were prepared by the previously reported procedures
[13,14]. Samples of Re2Cl6(m-dppa)2 were also obtained
by the following alternative procedure. A sample of
Re2Cl4(m-dppa)2 [13,16] (0.100 g, 0.078 mmol) was
heated in 15 ml of 1,2-dichloroethane and the resulting
solution treated with 5 ml of dichloromethane which
had been saturated with Cl2 gas. The mixture was
stirred for ca. 5 min, the reaction volume was then
reduced to ca. 3 ml, and an excess of diethyl ether
added to precipitate the purple product. Yield 0.92 g
(87%). The cyclic voltammetric properties of this sam-
ple were identical to the literature data [13]. The bromo
complex Re2Br6(m-dppm)2 was prepared from the reac-
tion between Re2Br4(m-dppm)2 (0.200 g, 0.134 mmol) in
10 ml of dichloromethane and 4 ml of a solution of Br2
in 1,2-dichloroethane. The dark-purple solution was
stirred for ca. 10 min, reduced in volume to ca. 5 ml,
and treated with an excess of diethyl ether to produce
the desired complex. Yield 0.190 g (86%). Anal. Calc.
for C51H46Br6Cl2P4Re2 (i.e. Re2Br6(m-dppm)2·CH2Cl2):
C, 35.92; H, 2.71. Found: C, 36.16; H, 2.67%. The
presence of a molecule of lattice solvent CH2Cl2 was
confirmed by 1H-NMR spectroscopy. The cyclic
voltammetry (CV) of this product (recorded in 0.1 M
n-Bu4NPF6–CH2Cl2 with a Pt-bead electrode) was very
similar to that of Re2Cl6(m-dppm)2 [13], with processes
at E1/2(ox)= +1.53 and +0.85 V; E1/2(red)= −0.40
and −1.23 V vs. Ag ꢀ AgCl. A procedure similar to
that described for Re2Br6(m-dppm)2 was used to convert
Re2Br4(m-dppa)2 [16] to the green complex Re2Br6(m-
dppa)2. Yield 77%. This product was identified on the
basis of its CV (recorded in 0.1 M n-Bu4NPF6-CH2Cl2
2.2. Synthesis of complexes of the type
[Re2X5(v-dppm)2(L)]Y
2.2.1. [Re2Cl5(v-dppm)2(CO)]Cl (1)
A solution of Re2Cl4(m-dppm)2(CO) (0.200 g, 0.153
mmol) in dichloromethane (10 ml) was mixed with 5 ml
of a saturated solution of Cl2 in 1,2-dichloroethane and
then stirred for 2 min. The resulting purple solution
was reduced in volume to ca. 5 ml. An excess of diethyl
ether was added to precipitate a purple solid, which was
filtered off, washed with 3×15 ml of diethyl ether, and
dried under a vacuum. Yield 0.185 g (86%). A satisfac-
tory C and H microanalysis could not be obtained, but
the spectroscopic and cyclic voltammetric properties of
this product (see Section 3) agreed closely with those
for the analogous structurally characterized [PF6]− salt
(see Section 2.2.2). Attempts to convert [Re2Cl5(m-
dppm)2(CO)]Cl to [Re2Cl5(m-dppm)2(CO)]PF6 by reac-
tion with TlPF6 were unsuccessful due to the decom-
position of the chloride salt in solution.
2.2.2. [Re2Cl5(v-dppm)2(CO)]PF6 (2)
The mixed CO–acetonitrile complex [Re2Cl3(m-
dppm)2(CO)(NCMe)2]PF6 (0.200 g, 0.133 mmol) was
stirred in dichloromethane (10 ml) for 5 min and ca. 5
ml of a saturated solution of Cl2 gas in 1,2-dichlo-
roethane was added. The mixture was stirred for 2 min,
filtered, and the filtrate reduced in volume to ca. 5 ml.
The addition of an excess of diethyl ether afforded a
purple solid, which was filtered off and dried under
vacuum. Yield 0.165 g (83%). Anal. Calc. for C51H44
Cl5F6OP5Re2: C, 41.07; H, 2.97. Found: C, 40.10; H,
2.86%. The identity of this product was confirmed by
X-ray crystallography.
2.2.3. [Re2Cl5(v-dppm)2(CO)]O3SCF3 (3)
The complex [Re2Cl3(m-dppm)2(CO)(NCMe)2]O3
SCF3 was converted to the title complex by the use of
a procedure similar to that described in Section 2.2.2
but with a reaction time of 2 h. Yield 85%. Anal. Calc.
for C52H44Cl3F3O4P4Re2S: C, 41.76; H, 2.97. Found: C,

J. Chantler et al. / Journal of Organometallic Chemistry 596 (2000) 27–35
29
42.16; H, 3.01%. The identity of this product was also
based upon the close similarity of its properties to those
of the analogous [PF6]− salt.
2.2.8. [Re2Cl5(v-dppm)2(CN-t-Bu)]Cl (8)
A procedure similar to that described in Section 2.2.7
was used to convert Re2Cl4(m-dppm)2(CN-t-Bu) to
[Re2Cl5(m-dppm)2(CN-t-Bu)]Cl, but this product was
contaminated with Re2Cl6(m-dppm)2 as a result of par-
tial decomposition of the starting material during the
chlorination process. However, this product can be
‘purified’ by anion exchange (see below).
2.2.4. [Re2Br5(v-dppm)2(CO)]Br3 (4)
A solution of Re2Br4(m-dppm)2(CO) (0.352 g, 0.236
mmol) in 20 ml of dichloromethane was stirred for 5
min. and then treated with ca. 0.1 ml of liquid Br2 (0.31
g, 1.94 mmol). The brown solution, which darkened
immediately upon the addition of Br2, was allowed to
stand for 8 h during which time black crystals de-
posited. The reaction mixture was then filtered and the
crystals washed with 2×15 ml portions of diethyl ether
and dried under a vacuum. Yield 0.398 g (92%). Anal.
Calc. for C51H44Br8OP4Re2: C, 33.87; H, 2.45. Found:
C, 33.88; H, 2.41%. The presence of the tribromide ion
was confirmed by X-ray crystallography, which also
revealed an edge-sharing bioctahedral geometry for the
2.2.9. [Re2Cl5(v-dppm)2(CNXyl)]O3SCF3 (9)
A mixture of [Re2Cl5(m-dppm)2(CNXyl)]Cl (0.160 g,
0.107 mmol) and TlO3SCF3 (0.039 g, 0.110 mmol) in
dichloromethane (15 ml) was stirred at room tempera-
ture for 24 h. The white precipitate of TlCl was filtered
off, and the purple filtrate reduced in volume to ca. 5
ml. This solution was layered with diethyl ether (40 ml)
to induce precipitation of a product, which was filtered
off, washed with diethyl ether (2×10 ml) and dried
under a vacuum. Yield 0.149 g (87%). Anal. Calc. for
C60H53Cl5F3NO3P4Re2S: C, 45.07; H, 3.34; Cl, 11.09.
Found: C, 45.05; H, 3.53; Cl, 11.29%.
,
dirhenium cation (ReꢁRe distance 2.76 A). Unfortu-
nately, a disorder problem precluded the location and
refinement of the CO ligand. Consequently, the struc-
ture refinement was abandoned, but there is no doubt
that this compound has a structure closely similar to
that of the chloro complex [Re2Cl5(m-dppm)2(CO)]PF6
(see Section 3).
2.2.10. [Re2Cl5(v-dppm)2(CN-t-Bu)]O3SCF3 (10)
A procedure similar to that described in Section 2.2.9
was used to convert impure [Re2Cl5(m-dppm)2(CN-t-
Bu)]Cl to the title complex. Yield 88%. Anal. Calc. for
C56H53Cl5F3NO3P4Re2S: C, 43.38; H, 3.45; Cl, 11.47.
Found: C, 43.48; H, 3.58; Cl, 11.30%.
2.2.5. [Re2Br5(v-dppm)2(CO)]PF6 (5)
This dark-green complex was prepared from
[Re2Br3(m-dppm)2(CO)(NCMe)2]PF6 (0.200 g, 0.122
mmol) by the use of a procedure similar to that de-
scribed in Section 2.2.2 for the chloro analog. Yield
0.170 g (81%). Anal. Calc. for C51H44Br5F6OP5Re2; C,
35.75; H, 2.59. Found: C, 33.95; H, 2.70%.
2.2.11. [Re2Cl5(v-dppm)2(CNXyl)]PF6 (11)
The reaction between [Re2Cl5(m-dppm)2(CNXyl)]Cl
(0.100 g, 0.07 mmol) and TlPF6 (0.024 g, 0.07 mmol) in
dichloromethane (15 ml) was carried out as described in
Section 2.2.9. Yield 0.085 g (78%).
2.2.6. [Re2Br5(v-dppm)2(CO)]O3SCF3 (6)
This complex was prepared upon mixing a dichlo-
2.2.12. [Re2Cl5(v-dppm)2(CN-t-Bu)]PF6 (12)
A procedure similar to that described in Section 2.2.9
was used to convert [Re2Cl5(m-dppm)2(CN-t-Bu)]Cl to
the title complex. Yield 76%.
romethane
solution
of
[Re2Br3(m-dppm)2(CO)
(NCMe)2]O3SCF3 with a 1,2-dichloroethane solution of
Br2 with use of a procedure similar to that described in
Section 2.2.2. Yield 90%. Anal. Calc. for C52H44Br5
F3O4P4Re2S: C, 36.36; H, 2.58. Found: C, 35.70; H,
2.44%.
2.2.13. [Re2Br5(v-dppm)2(CNXyl)]Br3 (13)
A quantity of Re2Br4(m-dppm)2(CNXyl) (0.100 g,
0.063 mmol) in 5 ml of dichloromethane was treated
with a 2 ml solution of liquid Br2 in 1,2-dichloroethane
and then stirred for ca. 10 min. The dark-green solution
was reduced in volume to ca. 2 ml and an excess of
diethyl ether added. A green solid precipitated upon
cooling this mixture to 0°C. Yield 0.091 g (73%). Anal.
Calc. for C59H53Br8NP4Re2: C, 37.07; H, 2.79. Found:
C, 38.09; H, 2.96%.
2.2.7. [Re2Cl5(v-dppm)2(CNXyl)]Cl (7)
In
a typical reaction, Re2Cl4(m-dppm)2(CNXyl)
(0.100 g, 0.071 mmol) was added to 5 ml of dichlo-
romethane, the solution stirred for 10 min, and 2 ml of
1,2-dichloroethane, which had been saturated with Cl2
gas, was then added. The mixture was stirred (2 min)
and the volume of the reaction solution reduced to ca.
2 ml. The addition of an excess of diethyl ether af-
forded a purple solid which was filtered off, washed
with diethyl ether and dried under vacuum. Yield 0.087
g (83%). Anal. Calc. for C60H55Cl8NP4Re2 (i.e. [Re2Cl5
(dppm)2(CNXyl)]Cl·CH2Cl2): C, 45.90; H, 3.53. Found:
C, 46.15; H, 3.64%.
2.3. Redox chemistry of the complexes
[Re2Cl5(v-dppm)2(L)]Y
2.3.1. Synthesis of Re2Cl5(v-dppm)2(CNXyl)
A mixture of [Re2Cl5(m-dppm)2(CNXyl)]Cl (7) (0.100
g, 0.07 mmol) and (h5-C5H5)2Co (0.017 g, 0.09 mmol)

30
J. Chantler et al. / Journal of Organometallic Chemistry 596 (2000) 27–35
in 6 ml of acetone was stirred at room temperature for
2 h, and the insoluble green product filtered off, washed
with acetone (2×10 ml) and diethyl ether (2×10 ml),
and dried under a vacuum. Yield 0.065 g (67%). The
product was recrystallized from a 1:1 mixture of
dichloromethane and di-isopropyl ether. Anal. Calc. for
C60H55Cl7NP4Re2 (i.e. Re2Cl5(dppm)2(CNXyl)·CH2Cl2:
C, 46.96; H, 3.61. Found: C, 47.29; H, 3.63%. The use
of 1H-NMR spectroscopy confirmed the presence of
lattice solvent CH2Cl2. This same complex can be pro-
duced through the use of the triflate salt 9 in place of 7.
2.4. X-ray crystallography
Suitable single crystals of [Re2Cl5(m-dppm)2(CO)]PF6
(2) were obtained by the slow diffusion of di-isopropyl
ether into a solution of the complex in 1,2-dichloro-
ethane.
The data collection was performed at 29391 K on a
Nonius Kappa CCD diffractometer. Lorentz and polar-
ization corrections were applied to the data. The crys-
tallographic data are presented in Table 1.
The structure was solved using the structure solution
program PATTY in DIRDIF92 [18]. The remaining atoms
were located in succeeding difference Fourier syntheses.
Hydrogen atoms were placed in calculated positions
2.3.2. Synthesis of Re2Cl5(v-dppm)2(CN-t-Bu)
The reaction between [Re2Cl5(m-dppm)2(CN-t-Bu)]Cl
(8) (0.100 g, 0.06 mmol) and (h5-C5H5)2Co (0.017 g,
0.09 mmol) in acetone, followed by work-up as de-
scribed in Section 2.3.1, afforded the title complex.
Yield 0.059 g(60%). The use of the triflate salt 10 in
place of 8 afforded the same product, which was iden-
tified on the basis of its electrochemical and spectro-
scopic properties.
,
according to idealized geometries with CꢁH=0.95 A
and 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 correc-
tion using SCALEPACK [19] was applied. The final refin-
ements were performed by the use of the program
SHELXL-97 [20].
During the course of the structural analysis of
[Re2Cl5(m-dppm)2(CO)]PF6 the dirhenium unit was
found to be located about an inversion center so that
each of the four terminal sites in the equatorial plane
was (CO)0.25/Cl0.75. However, these CO and Cl ligands
were resolved in the disorder. The structure was satis-
factorily modeled in this way. The structure of 1 was
refined in full-matrix least squares where the function
2.3.3. Attempted synthesis of Re2Cl5(v-dppm)2(CO)
Various attempts were made to reduce [Re2Cl5(m-
dppm)2(CO)]PF6 (2) to the one-electron reduction
product Re2Cl5(m-dppm)2(CO). Reactions between 2
and different stoichiometric quantities of (h5-C5H5)2Co
or (h5-C5Me5)2Fe in dichloromethane at room tempera-
ture or −78°C were carried out for periods of up to 30
min. In all instances, a dark-green product was isolated,
which proved to be Re2Cl4(m-dppm)2(CO), based upon
its CV properties and IR spectrum [2], along with
evidence for a small amount of another product (possi-
bly Re2Cl5(m-dppm)2(CO)), which was identified by a
2
2 2
minimized was Sw(ꢀFoꢀ −ꢀFcꢀ ) , where w=1/
[|2(Fo)2+(0.0392P)2+10.1274P] and P=(Fo2 +2F2c)/
3. The highest peak/hole in the final difference Fourier
−3
,
had heights of 1.27/−2.43 e A
.
The important intramolecular bond distances and
w(CO) band at 2000 cm−1
.
angles for the structure of 1 are given in Table 2.
Table 1
Crystallographic data for the complex [Re2Cl5(m-dppm)2(CO)]PF6 (2)
3. Results and discussion
Chemical formula
Formula weight
Space group
C
51H44Cl5F6OP5Re2
3.1. Synthetic procedures and preliminary
characterization
1491.44
P1 (No. 2)
(
,
a (A)
11.2645(3)
12.6994(3)
13.5212(4)
88.4142(16)
66.2077(14)
64.1305(16)
1566.44(9)
1
1.581
4.304
0.33/0.47
0.035/0.102
0.00
,
b (A)
The 1:1 adducts of the triply bonded dirhenium(II)
complexes Re2X4(m-dppm)2 (X=Cl or Br) with CO,
t-BuNC and XylNC react with the appropriate halogen
X2 to afford the dirhenium(III) complexes [Re2X5(m-
dppm)2(L)]X (Eq. (1)).
,
c (A)
h (°)
i (°)
k (°)
3
,
V (A )
Z
Dcalc. (g cm−3
)
Re2X4(m-dppm)2(L)+X2“[Re2X5(m-dppm)2(L)]X (1)
v (MoꢁKa) (mm−1
)
In the case of X=Br and L=CO, the isolated complex
contains the [Br3]− anion rather than Br−. The course
of these reactions resembles the oxidations of Re2X4(m-
dppm)2 to Re2X6(m-dppm)2 (X=Cl or Br) and of
Re2X4(m-dppa)2 to Re2X6(m-dppa)2 (X=Cl or Br) (see
Refs. [13,14] and Section 2.1).
Transmission factors (min/max)
b
R
a/Rw
Largest shift/estimated S.D. in final cycle
GOF
1.110
a R=SꢀFoꢀ−ꢀFcꢀ/SꢀFoꢀ with Fo2\2|(F2o).
b Rw=[Sw(ꢀFo2ꢀ−ꢀFc2ꢀ)2/SwꢀF2oꢀ2]1/2
.

J. Chantler et al. / Journal of Organometallic Chemistry 596 (2000) 27–35
31
Table 2
The complexes that were prepared in the present
study, along with the compound numbering scheme
and their IR spectra and CV properties are given in
Table 3. Conductivity measurements on acetone solu-
tions of several of the complexes confirmed their behav-
ior as 1:1 electrolytes. Each compound displays an
intense w(CN)t or w(CO)t mode in its Nujol mull IR
spectrum, although in a few instances this band is split.
The similarity of the CV properties of all the complexes
implies a close structural similarity; each exhibits a
reversible one-electron oxidation and two reversible
one-electron reductions which are shifted by ca. 0.2 V
to more negative potentials in the case of compounds
7–13, in accordance with the greater s-donor ability of
the RNC ligands compared to CO. In all cases, these
three processes for the chloro complexes are shifted by
at least 0.40 V to more positive potentials compared to
the corresponding oxidation and two reductions seen in
the CV of Re2Cl6(m-dppm)2 [13].
,
Important bond distances (A) and angles (°) for the complex
[Re2Cl5(m-dppm)2(CO)]PF6 (2) a
Bond lengths
ReꢁRe%
ReꢁC(1)
ReꢁC(2)
ReꢁCl(1)
ReꢁCl(2)
ReꢁCl
2.6607(4) Re%ꢁCl
2.3934(14)
2.4906(15)
2.4908(15)
1.18(5)
1.93(5)
2.10(3)
ReꢁP(2)
ReꢁP(1)
O(1)ꢁC(1)
O(2)ꢁC(2)
2.356(3)
2.357(3)
2.3904(13)
0.97(4)
b
Bond angles
Cl(1)ꢁReꢁCl(2)
C(1)ꢁReꢁCl
C(2)ꢁReꢁCl
Cl(1)ꢁReꢁCl
Cl(2)ꢁReꢁCl
ClꢁReꢁCl
C(1)ꢁReꢁP(2)
C(2)ꢁReꢁP(2)
Cl(1)ꢁReꢁP(2)
77.87(11)
74.5(13)
173.4(8)
85.36(8)
161.93(9)
112.41(4)
84.3(12)
90.9(7)
Cl(2)ꢁReꢁP(2)
ClꢁReꢁP(2)
C(1)ꢁReꢁP(1)
C(2)ꢁReꢁP(1)
Cl(1)ꢁReꢁP(1)
Cl(2)ꢁReꢁP(1)
ClꢁReꢁP(1)
84.90(8)
88.17(5)
90.0(12)
84.8(7)
84.47(7)
89.76(7)
95.30(5)
172.27(5)
67.59(4)
P(2)ꢁReꢁP(1)
ReꢁClꢁRe%
88.94(7)
Successful attempts were made to access the one-elec-
tron reduction at E1/2 ca. +0.05 V in the case of the
isocyanide complexes 7–10, through the use of the
one-electron reductant cobaltocene. The dark-green
paramagnetic products Re2Cl5(m-dppm)2(CNXyl) (14)
and Re2Cl5(m-dppm)2(CN-t-Bu) (15) were isolated in
yields of 60% or greater. The two products dissolved in
acetone to produce solutions which were essentially
non-conducting (\m valuesB10 V−1 cm2 mol−1). The
Nujol mull IR spectra of 14 and 15 show sharp, intense
w(CN) bands at 2130 and 2144 cm−1, respectively;
these frequencies are shifted by ca. −50 cm−1 com-
pared to the salts of the parent cations, in accord with
the lower oxidation state of the dimetal core in 14 and
15 and an increase in Re“CNR(p*) back bonding.
The CV properties of 14 and 15 are essentially identical
to those of the complexes 7–12 (Table 3) with the
exception that the processes labeled as E1/2(red)(1) cor-
respond to oxidations of the bulk complexes in the case
of 14 and 15. These two compounds possess broad,
a Numbers in parentheses are estimated S.D. in the least significant
digits.
b The label Re% is used for the unlabeled Re atom in Fig. 1; this
atom and all other unlabeled non-phenyl group atoms in this Figure
are related to the labeled atoms by a crystallographic inversion
center. The atoms labeled as C(1), O(1) and Cl(2) that are not shown
in Fig. 1, are the other CO and Cl ligand atoms that arise from the
other half of the disorder in the asymmetric unit involving the
terminal CO and Cl ligands.
Anion exchange of X− by [PF6]− and [O3SCF3]− can
be accomplished through the use of the TlPF6 and
TlO3SCF3 reagents in the case of the t-BuNC and
XylNC complexes, but with the monocarbonyls
[Re2X5(m-dppm)2(CO)]Y (Y=PF6 or O3SCF3) a pre-
ferred strategy involved the reactions of X2 with the
all-cis dirhenium(II) complexes [Re2X3(m-dppm)2(CO)-
(NCMe)2]Y(II) [3,17] according to Eq. (2).
1
poorly-defined signals in their H-NMR spectra and no
resonances are observed in the 31P{1H}-NMR spectra.
The X-band ESR spectrum of 14, recorded as a 1:1
CH2Cl2–toluene glass at 110 K, exhibits two broad
signals with gÞ and gꢀ values of ca. 2.6 and 2.2, respec-
tively. Similar attempts were made to reduce the mono-
carbonyl complex 2 to its neutral Re2Cl5(m-dppm)2(CO)
form by the use of cobaltocene and (h5-C5Me5)2Fe
as one-electron reductants to access the process at
E1/2(red)= +0.35 V. Under our experimental condi-
tions, this neutral dirhenium(III,II) carbonyl complex
was found to be unstable and the dirhenium(II) complex
Re2Cl4(m-dppm)2(CO) was identified as the predominant
product (by the use of CV and IR spectroscopy),
although a w(CO) band of medium intensity at 2000
cm−1 in the IR spectrum of the resulting reaction
mixture could be due to small quantities of Re2Cl5-
[Re2X3(m-dppm)2(CO)(NCMe)2]Y+X2
“[Re2X5(m-dppm)2(CO)]Y+2MeCN
(Y=[PF6]− or [O3SCF3]−)
(2)
The chloride salts [Re2Cl5(m-dppm)2(CO)]Cl and
[Re2Cl5(m-dppm)2(CN-t-Bu)]Cl were not particularly
stable in solution, whereas the analogous [PF6]− and
[O3SCF3]− salts were much more stable. Solutions of
[Re2Cl5(m-dppm)2(CO)]Cl decompose to give mixtures
in which the majority species is the monocarbonyl
precursor Re2Cl4(m-dppm)2(CO).

Table 3
IR spectra and cyclic voltammetric properties of [Re2X5(m-dppm)2(L)]Y (X=Cl or Br; L=CO, t-Bu or Xyl; Y=Cl, Br3, PF6 or O3SCF3)
a
Complex
Compound no.
IR spectra (cm−1
)
CV half-wave potentials (V) b
Conductivity (\m) c
w(CO) or w(CN)
w(SO)
w(PF6)
839(vs)
840(vs)
E1/2(ox)
E1/2(red)(1)
E1/2(red)(2)
/
[Re2Cl5(m-dppm)2(CO)]Cl
1
2
3
4
5
6
7
8
9
10
11
12
13
2048(s)
2061(s), 2047(s)
2067(s)
2032(s)
2028(s)
2037(s), 2030(s)
2180(s)
2192(s), 2161(sh)
2188(s)
2196(s)
2180(s)
+1.43(70)
+1.43(60)
+1.43(70)
+1.35(70) d
+1.35(80)
+0.35(60)
+0.35(60)
+0.35(60)
+0.36(60)
+0.37(70)
−0.57(70)
−0.56(70)
−0.55(70)
−0.59(70)
−0.49(60)
89
83
[Re2Cl5(m-dppm)2(CO)]PF6
[Re2Cl5(m-dppm)2(CO)]O3SCF3
[Re2Br5(m-dppm)2(CO)]Br3
[Re2Br5(m-dppm)2(CO)]PF6
1258(vs)
1262(vs)
[Re2Br5(m-dppm)2(CO)]O3SCF3
[Re2Cl5(m-dppm)2(CNXyl)]Cl
[Re2Cl5(m-dppm)2(CN-t-Bu)]Cl
[Re2Cl5(m-dppm)2(CNXyl)]O3SCF3
[Re2Cl5(m-dppm)2(CN-t-Bu)]O3SCF3
[Re2Cl5(m-dppm)2(CNXyl)]PF6
[Re2Cl5(m-dppm)2(CN-t-Bu)]PF6
[Re2Br5(m-dppm)2(CNXyl)]Br3
+1.26(70)
+1.21(90)
+1.24(70)
+1.20(70)
+1.25(70)
+1.19(70)
+1.22(60) d
+0.07(60)
+0.03(70)
+0.07(60)
+0.03(60)
+0.08(60)
+0.03(60)
+0.15(70)
−0.83(60)
−0.89(80)
−0.84(60)
−0.89(60)
−0.80(60)
−0.90(70)
−0.69(60)
102
95
91
96
89
95
1264(vs)
1264(vs)
840(vs)
838(vs)
2190(s)
2169(s)
596
a Recorded as Nujol mulls.
(
b Measurements carried out on 0.1 M n-Bu4NPF6–CH2Cl2 solutions and referenced to the Ag ꢀ AgCl electrode with a scan rate of 200 mV s−1
at a Pt-bead electrode. Under these experimental conditions, E1/2=+0.47 V vs. Ag ꢀ AgCl for the ferrocenium/ferrocene couple. DEp(Ep,a−Ep,c
values are given in parentheses.
)
2
c Molar conductivity, V−1 cm2 mol−1. Recorded on 1×10−3 M solutions of the compounds in acetone.
d This compound also displays irreversible processes at Ep,a ca. +1.0 and +0.8 V vs. Ag ꢀ AgCl in its CV due to the [Br3]− anion.

J. Chantler et al. / Journal of Organometallic Chemistry 596 (2000) 27–35
33
Scheme 1. Possible fluxional process for compounds of the type
[Re2Cl5(m-dppm)2(CNR)]Cl (R=XylNC (7) or t-BuNC (8)).
,
[Re2Cl5(m-dppm)2(CO)]PF6 and, therefore, only 0.045 A
longer than the ReꢁRe distance in Re2Cl6(m-dppm)2 [13].
Accordingly, it is reasonable to conclude that a ReꢀRe
bond is present in 2, and in other compounds of this type,
albeit one that is weakened (relative to Re2Cl6(m-dppm)2)
through some degree of Re“CO (or RNC) p* back
bonding. The ReꢁClb bonds are longer than the terminal
,
bonds ReꢁClt in 2 by ca. 0.03 A, although this compari-
Fig. 1. ORTEP representation [21] of the structure of the [Re2(m-Cl)2(m-
dppm)2Cl3(CO)]+ cation as present in 2. This representation shows
one-quarter of the disorder involving the terminal CO and Cl ligands.
son is complicated by the disorder between the terminal
CO and Cl ligands as described in more detail in Section
2.4. The ReꢁClb and ReꢁClt bonds in Re2Cl6(m-dppm)2
[13] are essentially identical, in accord with a shorter
ReꢁRe bond distance and more tightly bound bridging
chlorides. The ReꢁP distances for 2 are identical (2.491
Each terminal site in the equatorial plane is (CO)0.25/Cl0.75
.
(mdppm)2(CO). The frequency for this w(CO) mode is
shifted by about −60 cm−1 relative to the spectrum of
[Re2Cl5(m-dppm)2(CO)]PF6; this shift is comparable to
that for the IR-active w(CN) mode of [Re2Cl5(m-
dppm)2(CNXyl)]PF6 when this compound is reduced to
Re2Cl5(m-dppm)2(CNXyl).
,
A) and slightly longer than those present in the symmet-
rical complex Re2Cl6(m-dppm)2 (2.478 and 2.471 A) [13]
and, like the latter compound, complex 2 possesses a
chair conformation for the [Re2P4C2] ring. The [PF6]−
anion refined satisfactorily and showed no evidence of
disorder.
,
3.2. Crystal structure of [Re2Cl5(v-dppm)2(CO)]PF6
Another property of complexes 1–13 which shows a
close comparison to the behavior of Re2Cl6(m-dppm)2, is
the unusual upfield shifts of the 31P-NMR resonances. As
was discussed previously [13], a consequence of the weak
paramagnetism of Re2Cl6(m-dppm)2 is a broad resonance
at l −140.6 in its room temperature 31P-NMR spectrum
(recorded in 1:1 CH2Cl2–CDCl3); this resonance is
shifted ca. 118 ppm upfield of the free ligand resonance.
In the present study, we have remeasured this spectrum
over the temperature range 20–50°C (in CDCl3) and find
that the resonance shifts upfield from l −138 to l
−147. These same measurements on the isostructural
complex Re2Cl6(m-dppa)2 (dppa=Ph2PNHPPh2) show
very similar behavior to that of Re2Cl6(m-dppm)2, with
the resonance shifting from l −155 at +20°C to l
−170 at +50°C. The bromo analog Re2Br6(m-dppm)2
was not soluble enough for us to obtain satisfactory
NMR spectral data, but the isostructural compound
Re2Br6(m-dppa)2 was sparingly soluble and its 31P-NMR
spectrum recorded in CDCl3 at room temperature exhib-
ited a broad resonance at l −316.
and other structural considerations
The structures of the dirhenium compounds of the type
[Re2X5(m-dppm)2(L)]Y were confirmed as being di-m-
halo bridged bioctahedral species (see III) by a single-
crystal X-ray structural analysis of the complex
[Re2Cl5(m-dppm)2(CO)]PF6 (2). An ORTEP representa-
tion [21] of the structure is given in Fig. 1 and key
structural parameters are listed in Table 2.
Formally, this structure is derived from that of Re2Cl6(m-
dppm)2 [13] by the replacement of a terminal chloride
ligand by CO or RNC and the generation of a
monocation2. This substitution process need not result in
a change in the ReꢁRe bond order, which is two in the
case of Re2Cl6(m-dppm)2 (i.e. a s2p2d2d*2 configuration)
,
[13]. Indeed, the ReꢁRe bond length is 2.6607(4) A in
The CO-containing chloro compounds 1, 2 and 3 each
show a single resonance at l ca. −97 (spectra recorded
in CDCl3 or CD2Cl2). These upfield shifts are again
consistent with weak paramagnetic behavior. The
2 Note that the reactions of Re2Cl6(m-dppm)2 with CO or XylNC in
the presence of Tl+ failed to produce [Re2Cl5(m-dppm)2(L)]+
.

34
J. Chantler et al. / Journal of Organometallic Chemistry 596 (2000) 27–35
31P-NMR spectrum of [Re2Cl5(m-dppm)2(CO)]Cl (1)
was recorded over the temperature range +76°C to
−80°C, using CD2Cl2 as the solvent below +20°C and
1,2-C2H4Cl2 above this temperature. A single resonance
is observed at l −115 at the high-temperature limit
and this shifts progressively downfield as the tempera-
ture is lowered to −40°C (Dl/DT ca. 0.28 ppm/°C).
Coalescence is observed at ca. −50°C and by −80°C
the spectrum has the appearance of a broad closely
spaced AA%BB% pattern (resonances at l −81.5 and
−82.5). We attribute this behavior to a fluxional spe-
cies which is weakly paramagnetic through thermal
population of triplet states (such as s2p2d2d*1p*1) at
higher temperatures. This fluxionality may involve a
‘merry-go-round’ process of the type we have discussed
previously for closely related edge-sharing bioctahedral
species [22]. The corresponding CO-containing bromo
complex 5 exhibits a broad resonance at l −207 in its
31P-NMR spectrum (recorded at 20°C in 1,2-C2H4Cl2).
This upfield shift is far greater than that observed for
the chloro analogs 1–3 but resembles the very large
upfield shift exhibited by the complex Re2Br6(m-dppa)2
compared to its chloro analog.
In contrast to the behavior of the monocarbonyl
complexes, the isocyanide analogues [Re2Cl5(m-
dppm)2(CNXyl)]Cl (7) and [Re2Cl5(m-dppm)2(CN-t-
Bu)]Cl (8) show an AA%BB% pattern in their 31P-NMR
spectra (recorded in CD2Cl2), with the multiplets being
centered at l −90 and −261, and l −84 and −251,
respectively. A temperature range study of the spectrum
of 7 was carried out from +20 to −70°C. The pattern
does not change over this range although these two
multiplets shift progressively downfield; at the low tem-
perature limit they are observed at l −73 and −211,
respectively. These data indicate that 7 and 8 do not
exhibit the same type of fluxional process as their
carbonyl analogues 1–3; the AA%BB% pattern signifies
the preservation of an unsymmetrical structure over
this temperature range. However, a more limited type
of fluxionality is not precluded, namely, that illustrated
in Scheme 1 in which the isocyanide ligand remains
bound to one Re atom. In support of this possibility we
note that the solution IR spectra of 7 and 8 (recorded
in CH2Cl2) display two w(CN) modes (2183 and 2150
cm−1 for 7, 2192 and 2164 cm−1 for 8), which could
correspond to the two structures shown in Scheme 1.
um(II) complexes Re2X4(m-dppm)2(L) (X=Cl or Br;
L=XylNC, t-BuNC or CO) and [Re2X3(m-
dppm)2(CO)(NCMe)2]+ (X=Cl or Br) with the appro-
priate halogen (X2). The complexes of the type
[Re2X5(m-dppm)2(L)]Y constitute the first multiply
bonded [Re2]6+ compounds that contain these p-accep-
tor ligands, which have been structurally characterized
in the solid state. Their stability is sufficient to enable
their complete characterization. This paucity of higher
oxidation state multiply bonded dirhenium complexes
that contain p-acceptor ligands contrasts with the
plethora of dirhenium(II) complexes which have RNC
or CO ligands bound to the [Re2(m-dppm)2] unit, in
combination with chloride or bromide ligands [2–7,22].
5. Supplementary material
Full details for the crystal data and data collection
parameters, atomic positional parameters, anisotropic
thermal parameters, bond distances and bond angles
for 2 have been deposited with the Cambridge Crystal-
lographic Data Center (deposit number 134045). Copies
of this information may be obtained free of charge
from: The Director, CCDC, 12 Union Road, Cam-
bridge, CB2 1EZ, UK (Fax: +44-1223-336033; email:
deposit@ccdc.cam.ac.uk or www: http://www.ccdc.
cam.ac.uk).
References
[1] Y. Ding, P.E. Fanwick, R.A. Walton, Inorg. Chem. 38 (1999)
5165.
[2] F.A. Cotton, L.M. Daniels, K.R. Dunbar, L.R. Falvello, S.M.
Tetrick, R.A. Walton, J. Am. Chem. Soc. 107 (1985) 3524.
[3] F.A. Cotton, K.R. Dunbar, A.C. Price, W. Schwotzer, R.A.
Walton, J. Am. Chem. Soc. 108 (1986) 4843.
[4] L.B. Anderson, T.J. Barder, D. Esjornson, R.A. Walton, B.E.
Bursten, J. Chem. Soc. Dalton Trans. 34 (1986) 2607.
[5] W. Wu, P.E. Fanwick, R.A. Walton, Inorg. Chem. 34 (1995)
5810.
[6] W. Wu, P.E. Fanwick, R.A. Walton, Inorg. Chim. Acta 242
(1996) 81.
[7] Y. Ding, W. Wu, P.E. Fanwick, R.A. Walton, Inorg. Chem. 38
(1999) 1918.
[8] K.-Y. Shih, P.E. Fanwick, R.A. Walton, Organometallics 12
(1993) 347.
[9] D.A. Kort, W. Wu, P.E. Fanwick, R.A. Walton, Trans. Met.
Chem. 20 (1995) 625.
4. Conclusions
[10] A.C. Price, R.A. Walton, Polyhedron 6 (1987) 729.
[11] R.A. Walton, Polyhedron 8 (1989) 1689.
[12] F.A. Cotton, R.A. Walton, Multiple Bonds Between Metal
Atoms, second ed., Oxford University Press, Oxford, UK, 1993.
[13] T.J. Barder, F.A. Cotton, D. Lewis, W. Schwotzer, S.M. Tetrick,
R.A. Walton, J. Am. Chem. Soc. 106 (1984) 2882.
[14] S.M.V. Esjornson, Ph.D. Thesis, Purdue University, 1989.
[15] A.R. Cutler, D.R. Derringer, P.E. Fanwick, R.A. Walton, J.
Am. Chem. Soc. 110 (1988) 5024.
Although the edge-sharing bioctahedral complex
Re2Cl6(m-dppm)2 fails to react with the organic iso-
cyanide ligands XylNC and t-BuNC and with carbon
monoxide to produce species of the type [Re2Cl5(m-
dppm)2(L)]+, salts of these cations and their bromo
analogues can be generated by reactions of the dirheni-

J. Chantler et al. / Journal of Organometallic Chemistry 596 (2000) 27–35
35
[16] D.R. Derringer, P.E. Fanwick, J. Moran, R.A. Walton, Inorg.
Chem. 28 (1989) 1384.
[19] Z. Otwinowski, W. Minor, Methods Enzymol. 276 (1996) 307.
[20] G.M. Sheldrick, SHELXL-97. A Program for Crystal Structure
Refinement. University of Go¨ttingen, Germany, 1997.
[21] C.K. Johnson, ORTEP II, Rep. ORNL-5138, Oak Ridge National
Laboratory, TN, 1976.
[17] J. Chantler, R.A. Walton, unpublished results.
[18] P.T. Beurskens, G. Admirall, G. Beurskens, W.P. Bosman, S.
Garcia-Granda, R.O. Gould, J.M.M. Smits, C. Smykalla, The
DIRDIF92 Program System, Technical Report, Crystallography
Laboratory, University of Nijmegen, Netherlands, 1992.
[22] Y. Ding, D.A. Kort, W. Wu, P.E. Fanwick, R.A. Walton, J.
Organomet. Chem. 573 (1999) 87.
.
.