Mixed carbonyl-nitrile complexes of dirhenium(II). the structural characterization and reactivity of salts of the [Re2Cl3(μ-dPPm)2(CO)(NCMe)n] + cations (dppm = Ph2PCH2PPh2, n = 1 or 2)

Article abstract of DOI:10.1016/S0022-328X(00)00247-3

The monocarbonyl complexes Re₂X₄(μ-dppm)₂(CO) (X = Cl or Br) react with stoichiometric quantities of the nitriles RCN (R = Me or Ph) in the presence of TlY (Y = PF₆ or O₃SCF₃) to afford complexes of the type [Re₂X₃(μ-dppm)₂(CO)(NCR)]Y and [Re₂X₃(μ-dppm)₂(CO)(NCR)₂]Y in high yield. Crystal structure determinations on the salts [Re₂Cl₃(μ-dppm)₂(CO)(NCMe)]O ₃SCF₃ and [Re₂Cl₃(μ-dppm)₂(CO)(NCMe) ₂]ReO₄ have shown that the former has the unsymmetrical structure [(MeCN)(CO)ClRe(μ-dppm)₂ReCl₂]⁺ with a Re≡Re bond (Re-Re distance 2.2881(7) A?), while the bis-nitrile complex is the edge-sharing bioctahedron [(MeCN)ClRe(μ-Cl)(μ-CO)(μ-dppm)₂ReCl(NCMe)]⁺, with an all-cis arrangement of the μ-CO and two MeCN ligands and a Re=Re bond (Re-Re distance 2.5669(4) A?). The species [Re₂X₃(μ-dppm)₂(CO)(NCMe)]⁺ and [Re₂X₃(μ-dppm)₂(CO)(NCMe)₂] ⁺ readily interconvert upon the addition or loss of an acetonitrile ligand and, along with their benzonitrile analogues, they react with halide, XylNC and acetylene to afford Re₂X₄(μ-dppm)₂(CO), [Re₂X₃(μ-dppm)₂(CO)(CNXyl)₂]Y and [Re₂X₃(μ-dppm)₂(CO)(η²-C ₂H₂)]Y, respectively.

Full text of DOI:10.1016/S0022-328X(00)00247-3

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 604 (2000) 219–228
Mixed carbonyl–nitrile complexes of dirhenium(II). The structural
characterization and reactivity of salts of the
[Re2Cl3(m-dppm)2(CO)(NCMe)n]+ cations (dppm=Ph2PCH2PPh2,
n=1 or 2)
James Chantler, Phillip E. Fanwick, Richard A. Walton *
Department of Chemistry, Purdue Uni6ersity, 1393 Brown Building, West Lafayette, IN 47907-1393, USA
Received 4 February 2000; received in revised form 20 April 2000; accepted 24 April 2000
Abstract
The monocarbonyl complexes Re2X4(m-dppm)2(CO) (X=Cl or Br) react with stoichiometric quantities of the nitriles RCN
(R=Me or Ph) in the presence of TlY (Y=PF6 or O3SCF3) to afford complexes of the type [Re2X3(m-dppm)2(CO)(NCR)]Y and
[Re2X3(m-dppm)2(CO)(NCR)2]Y
in
high
yield.
Crystal
structure
determinations
on
the
salts
[Re2Cl3(m-
dppm)2(CO)(NCMe)]O3SCF3 and [Re2Cl3(m-dppm)2(CO)(NCMe)2]ReO4 have shown that the former has the unsymmetrical
structure [(MeCN)(CO)ClRe(m-dppm)2ReCl2]+ with a ReꢀRe bond (ReꢁRe distance 2.2881(7) A), while the bis-nitrile complex is
,
the edge-sharing bioctahedron [(MeCN)ClRe(m-Cl)(m-CO)(m-dppm)2ReCl(NCMe)]+, with an all-cis arrangement of the m-CO and
+
,
two MeCN ligands and a ReꢂRe bond (ReꢁRe distance 2.5669(4) A). The species [Re2X3(m-dppm)2(CO)(NCMe)] and
[Re2X3(m-dppm)2(CO)(NCMe)2]+ readily interconvert upon the addition or loss of an acetonitrile ligand and, along with their
benzonitrile analogues, they react with halide, XylNC and acetylene to afford Re2X4(m-dppm)2(CO), [Re2X3(m-
dppm)2(CO)(CNXyl)2]Y and [Re2X3(m-dppm)2(CO)(h2-C2H2)]Y, respectively. © 2000 Elsevier Science S.A. All rights reserved.
Keywords: Rhenium complexes; Carbonyl complexes; Nitrile complexes; Dirhenium(II) complexes; Crystal structures
1. Introduction
The coordination of organic nitriles to the [Re2(m-
dppm)2]4+ core has also been encountered in the case
of the mixed carbonyl–nitrile complexes [Re2Cl3(m-
dppm)2(CO)(NCR)2]PF6 (R=Me, Et or Ph) [5] and
[Re2Cl3(m-dppm)2(CO)2(NCR)]PF6 (R=Me, Et or Ph)
[6]. These complexes are most easily prepared from the
monocarbonyl and dicarbonyl precursors Re2Cl4(m-
dppm)2(CO) [5,7] and Re2Cl4(m-dppm)2(CO)2 [6,7],
respectively.
While the complex [Re2Cl3(m-dppm)2(CO)2(NCEt)]-
PF6 [6] has been structurally characterized (structure I),
the structure of the [Re2Cl3(m-dppm)2(CO)(NCR)2]+
cations has not been definitively established, although
based upon the spectroscopic and electrochemical prop-
erties of these complexes, structure II was favored [5] .
The electron-rich triply bonded [Re2(m-dppm)2]4+
core (dppm=Ph2PCH2PPh2) has been found to accom-
modate two or four organic nitrile ligands in salts of
the cationic species [Re2Cl3(m-dppm)2(NCR)2]+ [1–3]
and [Re2Cl2(m-dppm)2(NCR)4]2+ [3]. Whereas the ni-
trile ligands in the former monocationic species are not
very labile [1], partial or complete displacement of the
nitrile ligands has been encountered in the reactions of
[Re2Cl2(m-dppm)2(NCR)4]2+ [3]. An interesting variant
in this chemistry is found in the case of the stable,
neutral dirhenium(II) complex Re2(m-dppm)2(NCBH3)4-
(H2O)2·THF [4], which contains four N-bound
[NCBH3]− ligands.
* Corresponding author. Tel.: +1-765-4945464; fax: +1-765-
4940239.
E-mail address: rawalton@purdue.edu (R.A. Walton).
0022-328X/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(00)00247-3

220
J. Chantler et al. / Journal of Organometallic Chemistry 604 (2000) 219–228
The absence of an unambiguous structure determination
of a salt of one of the [Re2Cl3(m-dppm)2(CO)(NCR)2]+
cations has hindered the development of the chemistry
of this group of complexes.
2.2.2. R=Ph (3b)
A quantity of benzonitrile (1.5 ml) was added to a
suspension of 1b (0.200 g, 0.134 mmol) and TlPF6 (0.055
g, 0.158 mmol) in acetone (5 ml). A yellow–brown
solution resulted after this reaction mixture was stirred
at r.t. for 24 h. A work-up procedure identical to that
described in Section 2.2.1 was utilized to afford a
yellow–brown solid. Yield 0.171 g (72%). Anal. Calc.
for C65H54Br3F6N2OP5Re2: C, 44.36; H, 3.09. Found: C,
44.03; H, 3.13%.
In the present report we provide details of the struc-
ture
determination
of
[Re2Cl3(m-dppm)2(CO)-
(NCMe)2]+, along with that of [Re2Cl3(m-dppm)2-
(CO)(NCMe)]+, and describe the reactions of salts of
these two cations, and other complexes of the same
type, with halide ion, xylyl isocyanide and acetylene.
2.3. Synthesis of [Re2Cl3(v-dppm)2(CO)(NCR)]O3SCF3
2. Experimental
2.3.1. R=Me (4a)
2.1. Starting materials and reaction procedures
A solution of acetonitrile (40 ml) in dichloromethane
(100 ml) was prepared and a 10.0 ml aliquot (containing
0.075 mmol of acetonitrile) was added to a mixture of
1a (0.100 g, 0.076 mmol) and TlO3SCF3 (0.030 g, 0.085
mmol). The resulting suspension was stirred at r.t. for
24 h. The reaction mixture was filtered to remove
insoluble thallium(I) salts and then reduced in volume
to ca. 2 ml. Subsequent addition of diethyl ether to the
green filtrate caused the precipitation of a green solid
which was filtered off, washed with diethyl ether and
dried in vacuo. Yield 0.102 g (91%). Anal. Calc. for
C54H47Cl3F3NO4P4Re2S: C, 44.25; H, 3.23. Found: C,
44.34; H, 3.58%.
The compounds Re2Cl4(m-dppm)2(CO) (1a) [7],
Re2Br4(m-dppm)2(CO) (1b) [5], [Re2Cl3(m-dppm)2-
(CO)(NCMe)2]PF6 (2a) [5], [Re2Cl3(m-dppm)2(CO)-
(NCPh)2]PF6 (2b) [5] and thallium(I) triflate [8] were
prepared according to the known literature procedures.
Xylyl isocyanide (2,6-dimethylphenylisocyanide, abbre-
viated XylNC) was purchased from Fluka Chemicals,
thallium(I) hexafluorophosphate from Strem Chemicals,
and acetylene from the Matheson Gas Products. All
other reagents were purchased from Aldrich Chemical.
Solvents were obtained from commercial sources and
thoroughly deoxygenated prior to use. Syntheses were
performed using standard Schlenk techniques under an
atmosphere of dry nitrogen.
2.3.2. R=Ph (4b)
IR spectra (Nujol mulls), 31P{1H}-NMR spectra and
single scan cyclic voltammetric (CV) measurements
(recorded in 0.1 M n-Bu4NPF6–CH2Cl2 with a scan rate
of 200 mV s−1 at a Pt-bead electrode) were determined
as previously described. [9]
A solution of benzonitrile (7.7 ml) in 5 ml of
dichloromethane was combined with 1a (0.100 g, 0.076
mmol) and TlO3SCF3 (0.030 g, 0.085 mmol), and the
mixture was stirred at r.t. for 24 h. A work-up proce-
dure similar to that described in Section 2.3.1 afforded
the green title complex. Yield 0.089 g (76%). This
compound was identified as [Re2Cl3(m-dppm)2-
(CO)(NCPh)]O3SCF3 based on the similarity of its spec-
troscopic properties to those of 4a.
2.2. Synthesis of [Re2Br3(v-dppm)2(CO)(NCR)2]PF6
2.2.1. R=Me (3a)
Acetonitrile (5 ml) was added to a mixture of 1b
(0.200 g, 0.134 mmol) and TlPF6 (0.055 g, 0.158 mmol)
in acetone (5 ml). The suspension was stirred for 24 h at
room temperature (r.t.). The resulting reaction mixture
was filtered to remove solid TlBr. This filtrate was
evaporated to dryness, extracted into dichloromethane
(10 ml) and filtered to remove further quantities of TlBr.
An excess of diethyl ether was then added to the extract,
resulting in the precipitation of a yellow solid which was
washed with an additional quantity of diethyl ether and
dried in vacuo. Yield 0.165 g (75%). This product was
identified based on a comparison of its electrochemical
and spectroscopic properties with the analogous chloro
complex [5]; a satisfactory C and H microanalysis was
not obtained due to partial loss of acetonitrile ligands
(see Section 3).
2.4. Synthesis of
[Re2Br3(v-dppm)2(CO)(NCMe)]O3SCF3 (5a)
A procedure similar to that described in Section 2.3.1
was used to convert 1b to the title complex 5a. Yield
85%. Anal. Calc. for C54H47Br3F3NO4P4Re2S: C, 40.56;
H, 2.96. Found: C, 40.45; H, 2.84%.
2.5. Reactions of [Re2Cl3(v-dppm)2(CO)(NCR)2]PF6
with halide
2.5.1. R=Me (2a) with chloride
A
solution of 2a (0.050 g, 0.033 mmol) in
dichloromethane (10 ml) was treated with a stoichio-

J. Chantler et al. / Journal of Organometallic Chemistry 604 (2000) 219–228
221
metric quantity of [Ph4As]Cl (0.014 g, 0.033 mmol). The
color of the solution immediately changed from yellow
to orange–brown. After 30 min, the mixture was
filtered and the filtrate evaporated to leave a brown
solid which was identified by IR and NMR spec-
troscopy to be pure Re2Cl4(m-dppm)2(CO) (1a) [7].
Yield 0.041 g (94%). The reaction course was the same
when an excess of [Ph4As]Cl was used.
ml) was stirred at r.t. for 6 h. The resulting yellow
precipitate was filtered off, washed with diethyl ether to
remove any excess XylNC, and dried in vacuo. Yield
0.048 g (86%). This complex was identified as one of the
known structural isomers of [Re2Cl3(m-dppm)2-
(CO)(CNXyl)2]PF6, based on its IR spectrum which
was identical to that previously reported [10].
A repetition of the above reaction but with the use of
refluxing 1,2-dichloroethane as the solvent and a large
excess of XylNC yielded the same product. Yield 82%.
2.5.2. R=Ph (2b) with chloride
Compound 1a was formed in essentially quantitative
yield through the use of this same procedure (see Sec-
tion 2.5.1). Yield 95%.
2.9.2. X=Cl, R=Ph (2b)
The reaction between 2b (0.050 g, 0.031 mmol) and
XylNC (0.0085 g, 0.065 mmol) in
5
ml of
dichloromethane yielded this same XylNC product fol-
lowing the usual work-up. Yield 0.043 g (82%).
2.5.3. R=Me (2a) with iodide
The reaction of 2a with one equivalent of [n-Bu4N]I
gave a product which 31P{1H}-NMR spectroscopy
showed was a mixture of species of the type Re2Cl4−
nIn(m-dppm)2(CO); each component of the mixture dis-
played a characteristic AA%BB% pattern [7]. Attempts to
separate the individual components were unsuccessful.
2.9.3. X=Br, R=Me (3a)
A quantity of 3a (0.050 g, 0.031 mmol) was com-
bined with XylNC (0.0085 g, 0.065 mmol) and
dichloromethane (5 ml) and the mixture was stirred at
r.t. for 2 days. The brown solution was reduced in
volume to ca. 2 ml and added to ca. 25 ml of diethyl
ether which led to the precipitation of a yellow–brown
solid. The solid was filtered off, washed with diethyl
ether and dried in vacuo. Yield 0.049 g (88%). IR
spectroscopy showed the product to be the same iso-
meric form of [Re2Br3(m-dppm)2(CO)(CNXyl)2]PF6
[10,11] as that of the analogous chloro complex which
was prepared in Section 2.9.1.
2.6. Reaction of [Re2Br3(v-dppm)2(CO)(NCMe)2]PF6
(3a) with bromide
Compound 3a converted to Re2Br4(m-dppm)2(CO)
(1b) upon reaction with one equivalent of [n-Bu4N]Br.
Yield 96%. The identity of the product was based upon
its spectroscopic properties [5].
2.7. Reactions of [Re2Cl3(v-dppm)2(CO)(NCR)]O3SCF3
2.10. Reactions of
with chloride
[Re2Cl3(v-dppm)2(CO)(NCMe)]O3SCF3 (4a) with
XylNC
2.7.1. R=Me (4a)
Compound 1a was formed upon reacting 4a and
[Ph4As]Cl with use of the procedure described in Sec-
tion 2.5.1. Yield 89%.
A solution that contained 4a (0.050 g, 0.034 mmol),
XylNC (0.009 g, 0.069 mmol) and dichloromethane (5
ml) was stirred for 1 min at r.t. A large quantity of
diethyl ether was then added to the solution, quenching
the reaction and precipitating a green solid. This solid
was filtered off and washed with diethyl ether and dried
in vacuo. Yield 0.048 g (90%). The IR spectrum showed
the green product to be a mixture of two compounds;
the starting complex 4a (the minority species), and
[Re2Cl3(m-dppm)2(CO)(CNXyl)]O3SCF3 which was
identified based on a comparison of its properties with
those obtained in a previous study [12].
2.7.2. R=Ph (4b)
A similar reaction afforded 1a following use of the
above procedure. Yield 93%.
2.8. Reaction of
[Re2Br3(v-dppm)2(CO)(NCMe)]O3SCF3 (5a) with
bromide
The product formed from the reaction of 5a with one
equivalent of [n-Bu4N]Br in dichloromethane was
Re2Br4(m-dppm)2(CO) (1b). Yield 93%.
When this same reaction was carried out for 2 days
the yellow product which precipitated was shown to be
the same structural isomer of [Re2Cl3(m-dppm)2-
(CO)(CNXyl)2]O3SCF3 as that formed in the reactions
described in Sections 2.9.1 and 2.9.2 which afford the
analogous [PF6]− salt. Yield 89%. This result is consis-
tent with a previous study [10] which showed that
[Re2Cl3(m-dppm)2(CO)(CNXyl)]O3SCF3 is the precur-
sor to this isomeric form of [Re2Cl3(m-dppm)2-
(CO)(CNXyl)2]O3SCF3.
2.9. Reactions of [Re2X3(v-dppm)2(CO)(NCR)2]PF6
with XylNC
2.9.1. X=Cl, R=Me (2a)
A solution containing 2a (0.050 g, 0.033 mmol) and
XylNC (0.009 g, 0.069 mmol) in dichloromethane (5

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J. Chantler et al. / Journal of Organometallic Chemistry 604 (2000) 219–228
2.11. Reactions of [Re2X3(v-dppm)2(CO)(NCR)2]PF6
with C2H2
of a procedure similar to that described in Section
2.11.1. Yield 61%. This complex was identified as a
close structural analogue of the related chloro complex
on the basis of its spectroscopic and electrochemical
properties [13].
2.11.1. X=Cl, R=Me (2a)
A sample of 2a (0.150 g, 0.100 mmol) was dissolved
in dichloromethane (15 ml) and the solution was then
treated with a stream of C2H2 gas for 2 h, during which
time the volume of the mixture was reduced to ca. 5 ml.
The reaction mixture was then stirred at r.t. for 3 days
under an atmosphere of acetylene. The resulting tan
colored precipitate of [Re2Cl3(m-dppm)2(CO)(h2-
HCCH)]PF6 was filtered off, washed with diethyl ether
and dried in vacuo. Yield 0.110 g (76%). Anal. Calc. for
C53H46Cl3F6OP5Re2: C, 44.01; H, 3.21. Found: C,
43.57; H, 3.15%. IR and NMR spectroscopic data
showed that both nitrile ligands had been lost and that
the product was identical to that of this same stoi-
chiometry which had been prepared previously from
the reaction between Re2Cl4(m-dppm)2(CO), TlPF6 and
acetylene [13].
2.12. Reactions of
[Re2X3(v-dppm)2(CO)(NCMe)]O3SCF3 (X=Cl or Br)
The use of the monoacetonitrile complexes 4a (X=
Cl) and 5a (X=Br) in place of [Re2X3(m-
dppm)2(CO)(NCR)2]PF6 (see Section 2.11) afforded the
complexes [Re2X3(m-dppm)2(CO)(h2-HCCH)]O3SCF3
in yields of ca. 70%. The identity of these tan colored
products was established on the basis of their spectro-
scopic and electrochemical properties (see Section 3).
2.13. X-ray crystallography
Suitable single crystals of 2a (brown) and 4a (olive-
green) were obtained by the slow evaporation of a
solution of 2a in acetonitrile–toluene and the diffusion
of diethyl ether into a dichloromethane solution of 4a,
respectively.
The data collections were performed at 29491 K
with graphite-monochromated MoꢁKa radiation 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.
2.11.2. X=Cl, R=Ph (2b)
The same acetylene complex as described in Section
2.11.1 was prepared by the reaction of the benzonitrile
complex 2b with acetylene in dichloromethane. Yield
70%.
2.11.3. X=Br, R=Me (3a)
The
analogous
bromo
complex
[Re2Br3(m-
dppm)2(CO)(h2-HCCH)]PF6 was prepared by the use
The structures were solved using the structure solu-
tions program PATTY in DIRDIF [14]. The remaining
atoms were located in succeeding difference Fourier
syntheses. Hydrogen atoms were placed in calculated
positions according to idealized geometries with
Table 1
Crystallographic data for the complexes [Re2Cl3(m-dppm)2(CO)-
(NCMe)2]ReO4·MeCN (2a%) and [Re2Cl3(m-dppm)2(CO)(NCMe)]-
O3SCF3 (4a)
,
2a%
4a
CꢁH=0.95 A and U(H)=1.3 Ueq(C). They were in-
cluded in the refinement but constrained to ride on the
atom to which they are bonded. An empirical absorp-
tion correction using SCALEPACK [15] was applied. The
final refinements were performed by the use of the
program SHELX-97 [16].
Chemical formula
Re3Cl3P4O5N3- Re2Cl3SP4F3O4-
C57H53
1648.93
NC54H47
1465.70
C2/c (no. 15)
26.6998(15)
12.2824(6)
16.8438(10)
90
93.457(3)
90
5513.7(9)
4
Formula weight
Space group
a (A)
b (A)
c (A)
(
P1 (no. 2)
13.0124(5)
14.5980(5)
17.1187(7)
75.573(3)
75.7886(18)
73.467(2)
2965.2(3)
2
The crystal obtained from the recrystallization of
[Re2Cl3(m-dppm)2(CO)(NCMe)2]PF6 (2a) that was se-
lected for the X-ray structure analysis was found to be
that of the [ReO4]− salt (subsequently designated 2a%),
with disorder of the anion being observed in which
there were two positions for the Re atom. The forma-
tion of [ReO4]− is due to the degradation of a small
quantity of the dirhenium complex, presumably due to
its reaction with O2 which diffuses into the system
during the crystal growing process. This type of behav-
ior has been observed previously during such crystal
growing procedures [11,17]. The refinement gave occu-
pancies of 0.696 and 0.304 for these two positions. This
crystal was also found to contain a molecule of lattice
acetonitrile.
h (°)
i (°)
k (°)
3
,
V (A )
Z
Dcalc (g cm−3
)
1.847
1.766
v (MoꢁKa) (mm−1
)
6.483
4.799
Transmission factors
0.16/0.38
0.37/0.58
(min./max.)
b
R
a/Rw
0.062/0.140
0.049/0.116
Largest shift/estimated S.D. 0.08
in final cycle
GOF
0.00
1.006
0.998
a R=SꢀꢀFoꢀ−ꢀFcꢀꢀ/SꢀFoꢀ with Fo2\2|(F2o).
b Rw=[Sw(ꢀFo2ꢀ−ꢀFc2ꢀ)2/SwꢀF2oꢀ2]1/2
.

J. Chantler et al. / Journal of Organometallic Chemistry 604 (2000) 219–228
223
(CO)(NCR)2]PF6 (R=Me (3a) or Ph (3b)) are prepared
by a very similar procedure through the use of
Re2Br4(m-dppm)2(CO) and TlPF6. The important spec-
troscopic and cyclic voltammetric properties of the
complexes 3a and 3b, which are summarized in Table 2,
are very similar to those of their chloro analogues
(R=Me (2a), Et or Ph (2b)) which were previously
reported [5]. These complexes show a bridging w(CO)
mode in their IR spectra, a singlet in their 31P{1H}-
NMR spectra, and a one-electron oxidation and two
one-electron reductions in their cyclic voltammograms.
These
properties
imply
that
the
[Re2X3(m-
dppm)2(CO)(NCR)2]+ cations possess a symmetric
structure. This has been confirmed by an X-ray struc-
ture determination of a crystal obtained from a solution
of 2a in acetonitrile–toluene. The crystal proved to be
that of the perrhenate salt 2a% of composition
[Re2Cl3(m-dppm)2(CO)(NCMe)2]ReO4·MeCN (see Sec-
tion 2 for further details). To further confirm the
Fig. 1. ORTEP [18] representation of the structure of the dirhenium
cation [Re2Cl3(m-dppm)2(CO)(NCMe)2]+ as present in 2a%. The ther-
mal ellipsoids are drawn at the 50% probability level except for the
phenyl group atoms of the dppm ligands which are circles of arbitrary
radius.
identity of this crystal,
a sample of [Re2Cl3(m-
dppm)2(CO)(NCMe)2]ReO4 was prepared by the reac-
tion shown in Eq. (1) but with the use of TlReO4 in
place of TlPF6. Its properties were the same as those of
2a%, with w(CO) and w(ReO4) bands at 1688(s) and
906(vs) cm−1, respectively, in the IR spectrum, a singlet
at l −17.3 in the 31P{1H}-NMR spectrum (recorded in
CDCl3), and a CV essentially identical to that of the
analogous [PF6]− salt 2a [5]. An ORTEP [18] representa-
tion of the structure of the dirhenium cation present in
2a% is given in Fig. 1 and key structural parameters are
listed in Table 3. The presence of an edge-sharing
bioctahedral geometry, with an all-cis arrangement of
the m-CO and two acetonitrile ligands is confirmed. The
The structure refinement of [Re2Cl3(m-dppm)2(CO)-
(NCMe)]O3SCF3 (4a) revealed that the molecule exhib-
ited two types of disorder. The triflate anion was found
at an inversion center, thereby resulting in disorder
between the F3C and SO3 fragments. In the dirhenium
cation, the two rhenium atoms and a chlorine atom
were found to lie on a two-fold crystallographic rota-
tion axis. The presence of this axis imposed a chair
conformation on the Re2(m-dppm)2 unit and led to a
disorder between the CO and acetonitrile ligands.
The structures were refined in full-matrix least-
2
squares where the function minimized was Sw(ꢀFoꢀ −
,
ReꢁRe distance of 2.5669(4) A is typical for a dirhe-
ꢀFcꢀ ) , where w=1/[|2(Fo)2+(AP)2] with A=0.0877
2 2
nium complex of this type which possess a ReꢁRe
double bond. For example, the complex cation
[Re2Cl3(m-dppm)2(CO)(CNXyl)2]+, which possesses the
same structure as that of the cation in 2a%, has a ReꢁRe
for 2a% and 0.0760 for 4a and P=(F2o+2Fc2)/3 for both
structures. The highest peaks observed in the final
−3
,
difference Fouriers had heights of 1.95 and 3.51 e A
for 2a% and 4a, respectively.
,
distance of 2.576(1) A [19], while in the isostructural
tricarbonyl complex cation [Re2Cl3(m-dppm)2(CO)3]+
,
this double bond length is 2.582(1) A [20]. The eight-
3. Results and discussion
membered ring formed by the Re atoms and the two
bridging dppm ligands adopts a boat conformation in
both the nitrile (2a%) and XylNC [19] structures with the
CH2 bridges of both dppm ligands directed towards
that side of the molecule which contains the nitrile (or
isocyanide) ligands. Although the XylNC ligand usually
acts as a p-acceptor, while acetonitrile is a s-donor
with no significant p-accepting ability, the structures of
the cation of 2a% and [Re2Cl3(m-CO)(m-dppm)2-
(CNXyl)2]+ [19] are remarkably similar, and possess
essentially identical ReꢁP, ReꢁCl and ReꢁC bond dis-
tances. The bond angles associated with each cation are
also closely matched. This same type of structure was
also shown to be present in crystals of [Re2Br3(m-
dppm)2(CO)(NCPh)2]PF6 (3b) that had been grown
3.1. Synthesis and structural characterization of
complexes of the type
[Re2X3(v-dppm)2(CO)(NCR)2]PF6
In an earlier report [5] we had established that com-
plexes of the type [Re2Cl3(m-dppm)2(CO)(NCR)2]PF6
(R=Me, Et or Ph) can be prepared by the procedure
shown in Eq. (1).
Re2Cl4(m-dppm)2(CO)+2RCN+TIPF6
“[Re2Cl3(m-dppm)2(CO)(NCR)2]PF6+TlCl
(1)
In the present study we have shown that the
analogous bromo complexes [Re2Br3(m-dppm)2-

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J. Chantler et al. / Journal of Organometallic Chemistry 604 (2000) 219–228
225
3.2. Synthesis and structural characterization of
complexes of the type [Re2X3(v-dppm)2(CO)-
(NCR)]O3SCF3
from a solution of this complex in di-isopropyl ether–
1,2-dichloroethane. However, the quality of the data
did not merit full refinement of the structure. The
,
ReꢁRe bond distance of 2.567 A was essentially identi-
As mentioned in the preceding section, the bis-ace-
tonitrile complexes 2a and 3a lose acetonitrile in the
solid state and solution to afford, amongst other prod-
ucts, the mononitrile species [Re2X3(m-dppm)2(CO)-
(NCMe)]+. The triflate salts of these complexes and
their benzonitrile analogs were prepared in high yield
by use of the procedure shown in Eq. (2).
cal to that of 2a%.
During our attempts to grow single crystals of the
bis-acetonitrile complex 2a, we observed that it decom-
posed with loss of acetonitrile. Accordingly, crystals
were grown in the presence of excess acetonitrile (see
Section 2). Decomposition of samples 2a and its bromo
analog 3a also occurred in the solid state; IR spectral
measurements showed that the species [Re2X3(m-
dppm)2(CO)(NCMe)]+ (see Section 3.2) and Re2X4(m-
dppm)2(CO) were among the products of these
decompositions. In contrast, the benzonitrile analogs 2b
and 3b are much more stable to loss of the nitrile
ligands.
Re2X4(m-dppm)2(CO)+RCN+TlO3SCF3
“[Re2X3(m-dppm)2(CO)(NCR)]O3SCF3+TlX
(X=Cl or Br; R=Me or Ph)
(2)
To maximize the yield of the complexes 4a (X=Cl,
R=Me), 4b (X=Cl, R=Ph) and 5a (X=Br, R=
Me), it was necessary to ensure that the mole ratio of
reagents was close to 1:1:1. These complexes were sta-
ble to loss of nitrile, and when the acetonitrile com-
plexes 4a and 5a were exposed to an excess of
acetonitrile they converted quantitatively to the bis-ace-
tonitrile complexes [Re2X3(m-dppm)2(CO)(NCMe)2]-
O3SCF3 (as confirmed by IR spectroscopy).
The important spectroscopic and cyclic voltammetric
properties of 4a, 4b and 5a are summarized in Table 2.
Each complex shows a strong band at ca. 2000 cm−1 in
its IR spectrum due to a terminal w(CO) mode, and an
AA%BB% pattern in the 31P{1H}-NMR spectrum, which
accords with an unsymmetrical structure for the dirhe-
nium(II) cations. Conductivity measurements on 1.0×
10−3 M solutions of 4a and 5a in acetone showed the
expected behavior for 1:1 electrolytes, with \m values of
92 and 95 V−1 cm2 mol−1, respectively. These proper-
ties are consistent with the results of a single-crystal
Table 3
,
Important bond distances (A) and angles (°) for the complex
[Re2Cl3(m-dppm)2(CO)(NCMe)2]ReO4·MeCN (2a%) a
Bond distances
Re(1)ꢁRe(2)
Re(1)ꢁC(1)
Re(1)ꢁN(11)
Re(1)ꢁCl(12)
Re(1)ꢁCl(1)
Re(1)ꢁP(3)
Re(1)ꢁP(1)
Re(2)ꢁC(1)
Re(2)ꢁN(21)
2.5669(4)
2.028(8)
2.049(7)
2.427(2)
2.448(2)
2.465(2)
2.491(2)
2.026(8)
2.060(7)
Re(2)ꢁCl(2)
Re(2)ꢁCl(12)
Re(2)ꢁP(2)
Re(2)ꢁP(4)
C(1)ꢁO(1)
N(11)ꢁC(12)
N(21)ꢁC(22)
C(12)ꢁC(13)
C(22)ꢁC(23)
2.443(2)
2.4436(19)
2.466(2)
2.470(2)
1.204(10)
1.107(11)
1.107(11)
1.465(14)
1.465(14)
Bond angles
C(1)ꢁRe(1)ꢁN(11)
C(1)ꢁRe(1)ꢁCl(12)
76.9(3)
109.2(2)
Cl(2)ꢁRe(2)ꢁCl(12)
C(1)ꢁRe(2)ꢁP(2)
N(11)ꢁRe(1)ꢁCl(12) 173.08(19) N(21)ꢁRe(2)ꢁP(2)
89.19(7)
93.2(2)
85.61(19)
85.93(7)
94.14(7)
91.0(2)
83.51(19)
86.29(7)
96.07(7)
167.07(7)
50.7(2)
C(1)ꢁRe(1)ꢁCl(1)
N(11)ꢁRe(1)ꢁCl(1)
Cl(12)ꢁRe(1)ꢁCl(1)
C(1)ꢁRe(1)ꢁP(3)
N(11)ꢁRe(1)ꢁP(3)
Cl(12)ꢁRe(1)ꢁP(3)
Cl(1)ꢁRe(1)ꢁP(3)
C(1)ꢁRe(1)ꢁP(1)
N(11)ꢁRe(1)ꢁP(1)
Cl(12)ꢁRe(1)ꢁP(1)
Cl(1)ꢁRe(1)ꢁP(1)
P(3)ꢁRe(1)ꢁP(1)
C(1)ꢁRe(1)ꢁRe(2)
158.8(2)
82.7(2)
91.54(8)
90.1(2)
Cl(2)ꢁRe(2)ꢁP(2)
Cl(12)ꢁRe(2)ꢁP(2)
C(1)ꢁRe(2)ꢁP(4)
N(21)ꢁRe(2)ꢁP(4)
X-ray
structure
determination
of
[Re2Cl3(m-
dppm)2(CO)(NCMe)]O3SCF3 (4a). The ORTEP [18] rep-
resentation of the structure of the dirhenium cation
present in 4a is shown in Fig. 2 and the important
structural parameters are listed in Table 4.
89.32(19) Cl(2)ꢁRe(2)ꢁP(4)
93.87(7)
83.83(7)
95.1(2)
Cl(12)ꢁRe(2)ꢁP(4)
P(2)ꢁRe(2)ꢁP(4)
C(1)ꢁRe(2)ꢁRe(1)
The structure of 4a closely resembles those of struc-
turally characterized salts of the cations [Re2Br3(m-
dppm)2(CO)(CNXyl)]+ [9] and [Re2Cl3(m-dppm)2-
(NCR)2]+ (R=Et, Ph, 1,2-DCB or 1,4-DCB, where
DCB=dicyanobenzene) [1–3,21]. Formally, the dirhe-
nium cation present in the structure of 4a contains a
ReꢁRe triple bond; this is supported by the observed
85.03(19) N(21)ꢁRe(2)ꢁRe(1) 127.3(2)
91.06(7)
88.87(7)
171.29(7)
50.7(2)
Cl(2)ꢁRe(2)ꢁRe(1)
Cl(12)ꢁRe(2)ꢁRe(1)
P(2)ꢁRe(2)ꢁRe(1)
P(4)ꢁRe(2)ꢁRe(1)
147.09(6)
57.89(5)
95.63(5)
96.52(5)
63.60(5)
N(11)ꢁRe(1)ꢁRe(2) 127.44(19) Re(1)ꢁCl(12)ꢁRe(2)
Cl(12)ꢁRe(1)ꢁRe(2)
Cl(1)ꢁRe(1)ꢁRe(2)
C(1)ꢁRe(2)ꢁN(21)
C(1)ꢁRe(2)ꢁCl(2)
N(21)ꢁRe(2)ꢁCl(2)
C(1)ꢁRe(2)ꢁCl(12)
58.51(5)
149.82(6)
76.6(3)
162.2(2)
85.6(2)
C(12)ꢁN(11)ꢁRe(1) 173.9(7)
C(22)ꢁN(21)ꢁRe(2) 177.2(7)
O(1)ꢁC(1)ꢁRe(2)
O(1)ꢁC(1)ꢁRe(1)
Re(2)ꢁC(1)ꢁRe(1)
N(11)ꢁC(12)ꢁC(13) 177.7(11)
N(21)ꢁC(22)ꢁC(23) 179.0(12)
,
ReꢁRe distance of 2.2881(7) A, which is very similar to
141.3(7)
140.0(6)
78.6(3)
,
the ReꢁRe distance of 2.289(1) A present in the
analogous XylNC-containing cation [Re2Br3(m-
dppm)2(CO)(CNXyl)]+ [9], and compares closely with
108.6(2)
N(21)ꢁRe(2)ꢁCl(12) 174.8(2)
,
the ReꢁRe bond distances in the range 2.264–2.270 A
a Numbers in parentheses are estimated S.D. values to the least
significant decimal point.
which have been found for the [Re2Cl3(m-dppm)2-
(NCR)2]+ complexes [1–3,21].

226
J. Chantler et al. / Journal of Organometallic Chemistry 604 (2000) 219–228
trans lengthening effect. Similar differences between
these two types of ReꢁCl bond lengths are found in the
structures of [Re2Cl3(m-dppm)2(NCR)2]+ [1–3,21]. The
torsional
angles
P(1)ꢁRe(1)ꢁRe(2)ꢁP(2)
and
N(1)ꢁRe(1)ꢁRe(2)ꢁCl(2) have values of 27.7 and 28.6°,
respectively, which reflects the presence of a partially
staggered rotational geometry. This accords with simi-
lar behavior in the case of [Re2Br3(m-dppm)2-
(CO)(CNXyl)]O3SCF3 [9] and salts of the [Re2Cl3(m-
dppm)2(NCR)2]+ cations [1–3,21].
A comparison of the spectroscopic and electrochemi-
cal properties of 4a (Table 2) with those of [Re2Cl3(m-
dppm)2(CO)(CNXyl)]O3SCF3 [22], which presumably
has the same structure as its bromo analog [9], show
striking similarities, implying that these chloro com-
plexes are structurally very similar. The difference be-
tween the s-donor/p-acceptor properties of MeCN and
XylNC, leads to the w(CO) mode being shifted by
about 30 cm−1 to higher frequency in the case of the
XylNC complex in which the degree of Re“p*(CO)
back-bonding is decreased (relative to that in 4a). The
CV of 4a, which shows processes at E1/2(ox)= +0.90 V
and Ep,c= −0.97 V vs. Ag/AgCl, compares closely
with that for [Re2Cl3(m-dppm)2)(CO)(CNXyl)]O3SCF3
[22], which has E1/2(ox)= +0.96 V and Ep,c= −0.89
V vs. Ag/AgCl. For the bis-nitrile complexes [Re2Cl3(m-
dppm)2(NCR)2]+, the E1/2 values for these two pro-
cesses are ca. +0.6 and −1.3 V, respectively [1–3,21].
This shift of ca. +0.3 V to more negative potentials
reflects the absence of a strongly p-back bonding CO
ligand and therefore a decrease in the relative positive
charge at the dirhenium core.
Fig. 2. ORTEP [18] representation of the structure of the dirhenium
cation [Re2Cl3(m-dppm)2(CO)(NCMe)]+ as present in 4a. This repre-
sentation is of one half the disorder involving the CO and MeCN
ligands which are related by two-fold rotation axis coincident with
Re(2)ꢁRe(1)ꢁCl(1). The thermal ellipsoids are drawn at the 50%
probability level except for the phenyl group atoms of the dppm
ligands which are circles of arbitrary radius.
Table 4
,
Important bond distances (A) and angles (°) for the complex
[Re2Cl3(m-dppm)2(CO)(NCMe)]O3SCF3 (4a) a
b
Bond distances
Re(1)ꢁRe(2)
Re(1)ꢁN(1)/C(1)
Re(1)ꢁP(1)
2.2881(7) Re(2)ꢁCl(2)
1.994(10) Re(2)ꢁP(2)
2.354(2)
2.441(3)
2.490(3)
2.508(3)
N(1)/C(1)ꢁC(2)/O(2) 1.146
C(2)ꢁC(3)
Re(1)ꢁCl(1)
1.53(2)
b
Bond angles
N(1)ꢁRe(1)ꢁC(1)
N(1)/C(1)ꢁRe(1)ꢁRe(2) 91.9(2)
176.3(4)
Re(1)ꢁRe(2)ꢁCl(2)
Cl(2)ꢁRe(2)ꢁCl(2)
Re(1)ꢁRe(2)ꢁP(2)
108.72(6)
142.56(13)
95.82(6)
84.54(9)
91.72(9)
168.36(12)
175.21
3.3. Reacti6ities of the complexes
[Re2X3(v-dppm)2(CO)(NCR)2]PF6 and
[Re2X3(v-dppm)2(CO)(NCR)]O3SCF3 (X=Cl or Br;
R=Me or Ph)
N(1)/C(1)ꢁRe(1)ꢁP(1)
Re(2)ꢁRe(1)ꢁP(1)
N(1)/C(1)ꢁRe(1)ꢁP(1)
P(1)ꢁRe(1)ꢁP(1)
Re(2)ꢁRe(1)ꢁCl(1)
P(1)ꢁRe(1)ꢁCl(1)
87.0(3)
95.50(5) Cl(2)ꢁRe(2)ꢁP(2)
92.7(3) Cl(2)ꢁRe(2)ꢁP(2)
169.01(11) P(2)ꢁRe(2)ꢁP(2)
180.0(2) Re(1)ꢁN(1)/C(1)ꢁ
84.50(5) C(2)/O(2)
N(1)ꢁC(2)ꢁC(3)
We described in Sections 3.1 and 3.2 that the bis-ace-
tonitrile complexes 2a and 3a readily lose an acetoni-
trile ligand to afford 4a and 5a, respectively, and that
the latter react with an excess of acetonitrile to regener-
ate 2a and 3a (Eq. (3)).
N(1)/C(1)ꢁRe(1)ꢁCl(1) 88.1(2)
173.20
a Numbers in parentheses are estimated S.D. values to the least
significant decimal point.
b As a consequence of the disorder between the terminal CO and
MeCN ligands, the atoms labeled N(1) and C(2) occupy equivalent
positions to those labeled C(1) and O(2), respectively. Accordingly
these atoms are labeled as N(1)/C(1) and C(2)/O(2) in this table.
[Re2X3(m-dppm)2(CO)(NCMe)]+
+MeCN ? [Re2X3(m-dppm)2(CO)(NCMe)2]+
(3)
When any of these 1:2 and 1:1 acetonitrile complexes
(2a–5a), or their benzonitrile analogues 2b, 3b or 4b,
are treated with one equivalent of [Ph4As]Cl or [n-
Bu4N]Br, the neutral monocarbonyl starting materials
Re2X4(m-dppm)2(CO) (X=Cl (1a) or Br(1b)) are
formed in essentially quantitative yield. This clearly
demonstrates the lability of the nitrile ligands in these
complexes and, therefore, their potential use as precur-
sors to other dirhenium(II) complexes.
,
The ReꢁCl bond distance Re(1)ꢁCl(1) is 2.508(3) A
,
and ca. 0.15 A longer than the identical pair of equato-
,
rial ReꢁCl bonds (Re(2)ꢁCl(2)=2.354(2) A). This dif-
ference reflects both the difference in coordination
numbers at the two Re centers (Re(2) is the ligand
deficient center), and the fact that Re(1)ꢁCl(1) is colin-
ear with the ReꢀRe bond and therefore subject to a

J. Chantler et al. / Journal of Organometallic Chemistry 604 (2000) 219–228
227
In accord with the preceding observations, the reac-
tions of [Re2X3(m-dppm)2(CO)(NCR)2]PF6, where R=
Me when X=Cl or Br and R=Ph when X=Cl, with
xylyl isocyanide (XylNC) in dichloromethane were
found to afford complexes of the type [Re2X3(m-
dppm)2(CO)(CNXyl)2]PF6 in which the dirhenium
cation was shown to have the edge-sharing bioctahedral
structure III [10,11].
or addition of a RCN ligand. In contrast to the lack of
ligand lability in the case of complexes of the type
[Re2X3(m-dppm)2(NCR)2]Y [1–3], these mixed CO–ni-
trile complexes show reactivity towards halide ion,
XylNC and acetylene to afford the complexes Re2X4(m-
dppm)2(CO), [Re2X3(m-dppm)2(CO)(CNXyl)2]Y and
[Re2X3(m-dppm)2(CO)(h2-C2H2)]Y, respectively, with
complete loss of nitrile. Similar instances of nitrile
lability have been encountered previously in the case of
salts of dirhenium cations of the types [Re2X3(m-
dppm)2(CO)(CNR)(NCR)]+ [22–24] and [Re2Cl(m-
dppm)2(CO)(CNXyl)3(NCMe)]+ [25] towards CO and
RNC ligands. Further studies of the reactivities of
[Re2X3(m-dppm)2(CO)(NCR)2]Y
and
[Re2X3(m-
dppm)2(CO)(NCR)]Y are underway.
This is one of several isomeric forms known for these
cations [23]. A similar reaction course ensued when the
monoacetonitrile complex 4a was reacted with two
equivalents of XylNC over a period of two days. How-
ever, in this case, the formation of [Re2Cl3(m-
dppm)2(CO)(CNXyl)2]O3SCF3, in which the cation also
possessed structure III, proceeded through the interme-
diacy of [Re2Cl3(m-dppm)2(CO)(CNXyl)]O3SCF3. The
dirhenium cation in this complex has the same structure
(IV), as that of the acetonitrile complex 4a from which
it is derived (Fig. 2).
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 2a% and 4a have been deposited with the Cambridge
Crystallographic Data Center (deposit numbers 145479
and 145480). Copies of this information may be ob-
tained free of charge from: The Director, CCDC, 12
Union Road, Cambridge, CB2 1EZ, UK (Fax: +44-
1223-336033; e-mail: deposit@ccdc.cam.ac.uk or www:
http://www.ccdc.cam.ac.uk).
This XylNC-containing cation, and its bromo ana-
logue, have been isolated and characterized previously
[9,22], and are known [10] to be intermediates in the
formation of the isomer of [Re2X3(m-dppm)2(CO)-
(CNXyl)2]+ which has structure III. The high yields
(\80%) achieved in the present reactions from conve-
nient starting materials offer advantages over the previ-
ous synthetic procedure [9,22].
Another illustration of the usefulness of these mixed
CO–nitrile complexes as synthons are the conversions
of 2a, 2b, 3a, 4a and 5a to [Re2X3(m-dppm)2(CO)(h2-
C2H2)]Y (Y=PF6 or O3SCF3) in high yields when these
complexes are reacted with acetylene. This procedure
provides an alternative route to that in which Re2X4(m-
dppm)2(CO) (X=Cl or Br) are reacted with C2H2 in
the presence of TlY [13].
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