Dirhenium(II) complexes containing monodentate and polydentate nitrile ligands

Article abstract of DOI:10.1016/S0020-1693(00)00127-4

The complex Re₂Cl₄(μ-dppa)₂ (dppa = Ph₂PNHPPh₂) has been reacted with EtCN and PhCN to afford the complexes [Re₂Cl₃(μ-dppa)₂(NCR)₂]PF₆ (R = Et or Ph), [Re₂Cl₃(μ-HN₂C₂Et₂)(μ-dppa)₂(NCEt)]Cl and [Re₂Cl₃(μ-HN₂C₂Et₂)(μ-dppa)₂(NCEt)](PF₆)₂ which are derivatives of the [Re₂]⁴⁺, [Re₂]⁵⁺ and [Re₂]⁶⁺ cores, respectively. This behaviour is similar to the reactions of Re₂Cl₄(μ-dppm)₂ (dppm = Ph₂PCH₂PPh₂) with monodentate nitriles. The reactions of Re₂Cl₄(μ-dppm)₂ with the polydentate nitrile ligands 1,4-dicyanobenzene (1,4-DCB), 1,4-dicyanobut-2-ene (1,4-DCBE) and tris(2-cyanoethyl)phosphine (CEP) also give complexes of this same type in which the nitrile ligand utilizes only one of its CN groups. This is confirmed by an X-ray crystal structure determination of [Re₂Cl₃(μ-dppm)2(1,4-DCB)₂]PF₆, in which the Re≡Re bond is retained (Re-Re distance 2.2637(12) A?) and the 1,4-DCB ligands are monodentate. (C) 2000 Elsevier Science S.A.

Full text of DOI:10.1016/S0020-1693(00)00127-4

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Inorganica Chimica Acta 305 (2000) 215–220
Note
Dirhenium(II) complexes containing monodentate and polydentate
nitrile ligands
James Chantler, Phillip E. Fanwick, Richard A. Walton *
Department of Chemistry, Purdue Uni6ersity, 1393 Brown Building, West Lafayette, IN 47907-1393, USA
Received 13 March 2000; accepted 16 March 2000
Abstract
The complex Re2Cl4(m-dppa)2 (dppa=Ph2PNHPPh2) has been reacted with EtCN and PhCN to afford the complexes
[Re2Cl3(m-dppa)2(NCR)2]PF6 (R=Et or Ph), [Re2Cl3(m-HN2C2Et2)(m-dppa)2(NCEt)]Cl and [Re2Cl3(m-HN2C2Et2)(m-
dppa)2(NCEt)](PF6)2 which are derivatives of the [Re2]4+, [Re2]5+ and [Re2]6+ cores, respectively. This behaviour is similar to
the reactions of Re2Cl4(m-dppm)2 (dppm=Ph2PCH2PPh2) with monodentate nitriles. The reactions of Re2Cl4(m-dppm)2 with the
polydentate nitrile ligands 1,4-dicyanobenzene (1,4-DCB), 1,4-dicyanobut-2-ene (1,4-DCBE) and tris(2-cyanoethyl)phosphine
(CEP) also give complexes of this same type in which the nitrile ligand utilizes only one of its CN groups. This is confirmed by
an X-ray crystal structure determination of [Re2Cl3(m-dppm)2(1,4-DCB)2]PF6, in which the ReꢀRe bond is retained (Re–Re
,
distance 2.2637(12) A) and the 1,4-DCB ligands are monodentate. © 2000 Elsevier Science S.A. All rights reserved.
Keywords: Crystal structures; Rhenium complexes; Nitrile complexes; Dinuclear complexes
1. Introduction
these cations where RCN=EtCN, PhCN or 1,2-di-
cyanobenzene (1,2-DCB) have been determined [1–3].
These complexes are implicated as intermediates in the
reductive coupling of nitriles by Re2Cl4(m-dppm)2 [4],
which is a consequence of the reducing ability of the
electron-rich dirhenium(II) core [5,6]. The products of
these reductive coupling reactions are the paramagnetic
species [Re2Cl3(m-HN2C2R2)(m-dppm)2(NCR)]+ (struc-
ture II, with dppm ligands omitted), which are in turn
easily oxidized to their diamagnetic dirhenium(III) con-
geners [Re2Cl3(m-HN2C2R2)(m-dppm)2(NCR)]2+ [4].
In the present report, we have extended these nitrile
reactivity studies in order to establish whether other
dirhenium(II) starting materials behave in a like man-
ner. For this purpose, we have chosen the complex
Re2Cl4(m-dppa)2, where dppa=Ph2PNHPPh2 [6–8],
whose reactivity has not previously been studied. In
addition, we have examined the reactivity of Re2Cl4(m-
dppm)2 towards polydentate nitriles with the objective
The dirhenium(II) complex Re2Cl4(m-dppm)2, where
dppm=Ph2PCH2PPh2, has been shown to react with
organic nitrile ligands to afford complexes of the type
[Re2Cl3(m-dppm)2(NCR)2]+ which have the structure
represented in I (dppm ligands omitted) [1].
In addition, several complexes that are derived from
Re2Cl4(m-dppm)2, and which retain the [Re2(m-dppm)2]
unit, have also been found to form these bis-nitrile
complexes [2,3]. The X-ray crystal structures of salts of
of generating polymeric {[ReꢀRe]4+
}
compounds
ꢀ
* Corresponding author. Tel.: +1-765-494 5464; fax: +1-765-494
0239.
E-mail address: rawalton@purdue.edu (R.A. Walton).
whose redox chemistry would be of interest in view of
the possibility of forming paramagnetic chains.
0020-1693/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0020-1693(00)00127-4

216
J. Chantler et al. / Inorganica Chimica Acta 305 (2000) 215–220
(heptet, [PF6]−). CV: E1/2(ox)= +0.56 V (DEp=70
2. Experimental
mV), E1/2(red)= −1.28 V (DEp=90 mV) versus Ag/
AgCl. Conductivity (1.0×10−3 M solution in acetone):
2.1. Starting materials and reaction procedures
97 V−1 cm2 mol−1
.
The standard literature procedure was used to pre-
pare Re2Cl4(m-dppm)2 (1) [9] and Re2Cl4(P-n-Pr3)4 [10].
A new higher yield synthesis of Re2Cl4(m-dppa)2 (2)
[6,7] was developed. A mixture of Re2Cl4(P-n-Pr3)4
[10] (0.200 g, 0.173 mmol) and dppa (0.200 g, 0.519
mmol) in 6 ml of toluene was heated at reflux for 16 h
in a flask that contained a pine boiling stick. The
resulting purple crystals were filtered off, washed with
toluene, and dried under a vacuum; yield 0.198 g (89%).
The product was identified as 2 on the basis of a
comparison of its electrochemical and spectroscopic
properties with the literature data for this compound
[6,7].
2.2.2. Synthesis of [Re2Cl3(v-dppa)2(NCPh)2]PF6 (3b)
A procedure similar to that described in Section 2.2.1
afforded 3b, which was identified on the basis of its
spectroscopic properties; yield 74%. IR (Nujol mull):
w(CN)=2253(vw) cm−1, w(P–F) of [PF6]−=842(vs)
1
cm−1. H NMR (recorded in CDCl3): l +7.9 to +6.9
(m, 50H, C6H5). 31P{1H} NMR (recorded in CDCl3):
AA%BB% pattern with multiplets at l +51.8 and l
+43.2, l ca. −144 (heptet, [PF6]−).
2.2.3. Synthesis of [Re2Cl3(v-HN2C2Et2)-
(v-dppa)2(NCEt)]Cl (4)
Tris(2-cyanoethyl)phosphine (CEP) and NOPF6 were
purchased from Strem Chemicals Inc., while 1,4-di-
cyanobenzene (1,4-DCB) and 1,4-dicyanobut-2-ene
(1,4-DCBE) were obtained from the Aldrich Chemical
Co. These reagents were used without further purifica-
tion. Solvents were obtained from commercial sources
and thoroughly deoxygenated prior to use. Reactions
were carried out under an atmosphere of N2. IR spec-
tra, 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 described previously [11].
Elemental microanalyses were performed by Dr. H.D.
Lee of the Purdue University Microanalytical
Laboratory.
A sample of 2 (0.070 g, 0.054 mmol) in propionitrile
(5 ml) was heated at reflux for 4 h. The resulting green
reaction solution was filtered and the filtrate treated
with 50 ml of diethyl ether. The precipitate of 4 was
filtered off, washed with diethyl ether and dried under a
vacuum; yield 0.067
g
(85%). Anal. Calc. for
C66H52Cl3F6N4P5Re2: C, 47.18; H, 4.03; N, 4.83.
Found: C, 47.12; H, 3.81; N, 4.51%. IR (Nujol mull):
w(NH) of HN2C2Et2=3358(w) cm−1
,
w(CN) of
EtCN=2273(vw) cm−1
.
CV: E1/2(ox)= +0.28V
(DEp=70 mV), E1/2(red)= −0.66 V (DEp=60 mV)
versus Ag/AgCl.
2.2.4. Synthesis of [Re2Cl3(v-HN2C2Et2)(v-dppa)2-
(NCEt)](PF6)2 (5)
A mixture of 4 (0.04 g, 0.028 mmol) and NOPF6
(0.015 g, 0.087 mmol) in 5 ml of dichloromethane was
stirred for 1 h at r.t. The title compound was isolated as
a red solid by use of a work-up procedure similar
to that described in Section 2.2.1; yield 0.039 g
2.2. Reactions of Re2Cl4(v-dppa)2 (2) with propionitrile
2.2.1. Synthesis of [Re2Cl3(v-dppa)2(NCEt)2]PF6 (3a)
A sample of 2 (0.100 g, 0.078 mmol) was mixed with
KPF6 (0.20 g, 1.08 mmol) in 10 ml of acetone and 0.5
ml of propionitrile. The reaction mixture was stirred at
room temperature (r.t.) for 30 min, then reduced to
about one-half volume by vacuum evaporation, the
mixture filtered, and the filtrate added to ca. 40 ml of
diethyl ether and stirred for 30 min. The resulting beige
coloured solid was filtered off, extracted into approxi-
mately 10 ml of dichloromethane and the extract again
reduced in volume (approximately 5 ml). An excess of
diethyl ether was added to re-precipitate the title com-
pound 3a; yield 0.097 g (83%). Anal. Calc. for
C54H52Cl3F6N4P5Re2: C, 43.11; H, 3.48. Found: C,
42.91; H, 3.56%. IR (Nujol mull): w(CN)=2273(vw)
(81%). Anal. Calc. for
C57.5H59Cl4F12N5P6Re2
(i.e. 5 · 0.5CH2Cl2): C, 39.50; H, 3.40; N, 4.00. Found:
C, 39.45; H, 3.69; N, 3.60%. The presence of a small
1
amount of lattice CH2Cl2 was confirmed by a H NMR
spectrum recorded in CDCl3. IR (Nujol mull): w(NH)
of HN2C2Et2=3338(w) cm−1, w(CN) of EtCN=
1
2287(vw) cm−1, w(P–F) of [PF6]−=845(vs) cm−1. H
NMR (recorded in CD2Cl2): l +7.8 to +7.1 (m, 40H,
Ph), l +4.73(q, 2H, CH2¦), l +4.15(q, 2H, CH2%), l
+2.25(q, 2H, CH2), l +1.55 (t, 3H, CH3¦), l +0.58 (t,
3H, CH3), l −0.05 (t, 3H, CH3%). 31P{1H} NMR
(recorded in CD2Cl2): AA%BB% pattern with multiplets
at l +34.6 and l +28.0, l ca. −144 (heptet, [PF6]−).
CV: E1/2(red)= +0.26 V (DEp=60 mV), E1/2(red)=
−0.68 V (DEp=60 mV) versus Ag/AgCl. Conductivity
(1.0×10−3 M solution in acetone): 175 V−1 cm2
cm−1, w(P–F) of [PF6]−=840(vs) cm−1 1H NMR
.
(recorded in CD2Cl2): l +7.9 to +7.2 (m, 40H,
C6H5), l +1.58 (q, 4H, CH2), l +0.48 (t, 6H, CH3).
31P{1H} NMR (recorded in CD2Cl2): AA%BB% pattern
with multiplets at l +53.2 and l +44.2, l ca. −144
mol−1
.

J. Chantler et al. / Inorganica Chimica Acta 305 (2000) 215–220
217
2.3. Reactions of Re2Cl4(v-dppm)2 (1) with polydentate
nitrile ligands
yield 0.052 g (80%). Its identity was based primarily on
its electrochemical and conductivity properties (see Sec-
tion 3).
2.3.1. Synthesis of [Re2Cl3(v-dppm)2(1,4-DCB)2]PF6 (6)
A mixture of 1 (0.200 g, 0.156 mmol), KPF6 (0.40 g,
2.17 mmol) and 1,4-dicyanobenzene (0.50 g, 3.90 mmol)
in 20 ml of acetone was stirred at r.t. for 2 h. A
work-up procedure similar to that described in Section
2.2.1 afforded the orange–brown title complex 6; yield
0.208 g (81%). Anal. Calc. for C66H52Cl3F6N4P5Re2: C,
48.07; H, 3.18; Cl, 6.45. Found: C, 48.03; H, 3.25; Cl,
6.58%.
2.4. X-ray crystallography
Suitable single crystals of [Re2Cl3(m-dppm)2(1,4-
DCB)2]PF6 (6) were obtained as orange plates by layer-
ing a solution of this complex in dichloromethane with
n-pentane, followed sequentially by layers of n-hexane
and n-heptane. The data collection was carried out at
296(91) K on an Enraf–Nonius CAD 4 diffractome-
ter equipped with a graphite monochromator. Lorentz
and polarization corrections were applied to the data
set. The crystallographic data for 6 are given in Table 1.
The structure was solved by use of the structure
solution program PATTY in DIRDIF92 [12]. The remain-
ing atoms were located in succeeding difference Fourier
syntheses. Hydrogen atoms were placed in calculated
positions according to idealized geometries with C–
2.3.2. Synthesis of [Re2Cl3(v-dppm)2(1,4-DCBE)2]PF6
(7)
A mixture of 1 (0.100 g, 0.078 mmol), KPF6 (0.20 g,
1.14 mmol) and 1,4-dicyanobut-2-ene (0.5 ml, 3.8
mmol) in 10 ml of acetone was reacted and worked-up
following the procedure described in Section 2.3.1; yield
0.114 g (91%). Anal. Calc. for C62H56Cl3F6N4P5Re2: C,
46.40; H, 3.52. Found: C, 46.04; H, 3.52%.
,
H=0.95 A and U(H)=1.3Ueq(C). They were included
in the refinement but constrained to ride on the atom to
which they are bonded. An empirical absorption correc-
tion [13] was applied. The final refinements were per-
formed by the use of the program SHELXL-97 [14]. The
structure was refined in full-matrix least-squares where
the function minimized was ꢀw(ꢁFoꢁ −ꢁFcꢁ ) , where w
is the weighting factor defined as w=1/[|2(Fo)2+
(0.0814P)2+26.7660P] where P=(Fo2+2Fc2)/3. The
2.3.3. Synthesis of [Re2Cl3(v-dppm)2(CEP)2]PF6 (8)
The reaction of 1 (0.100 g, 0.078 mmol), KPF6 (0.20
g, 1.14 mmol), CEP (0.50 g, 2.59 mmol) in 10 ml of
acetone afforded 8 when the procedure described in
Section 2.3.1 was used; yield 0.110 g (79%). Anal. Calc.
for C68H68Cl3F6N6P7Re2: C, 45.91; H, 3.85; Cl, 5.98.
Found: C, 45.83; H, 3.92; Cl, 6.04%.
2
2 2
highest peak in the final difference Fourier had a height
−3
,
2.3.4. Synthesis of [Re2Cl3(v-dppm)2(CEP)2](PF6)2 (9)
The oxidation of a sample of 8 (0.060 g, 0.034 mmol)
of 0.93 e A
.
by NOPF6 (0.007 g, 0.040 mmol) in
5 ml of
dichloromethane was carried out at r.t. for 30 min, the
reaction mixture filtered, and the filtrate reduced in
volume to approximately 2 ml. The addition of an
excess of diethyl ether afforded 9 as a purple powder;
3. Results and discussion
The reactions of Re2Cl4(m-dppa)2 (2) with EtCN and
PhCN in the presence of KPF6 proceed as described
previously for the complex Re2Cl4(m-dppm)2 (1) [1],
namely, the formation of the unsymmetrical bis-nitrile
complexes [(RCN)2ClRe(m-dppa)2ReCl2]PF6 (R=Et
(3a) or Ph (3b)) with a structure as shown in I.
The spectroscopic and electrochemical properties of
3a and 3b are given in Section 2 and are very similar
to those of their dppm analogues [1]. Furthermore,
the use of more forcing reaction conditions in the case
of the EtCN reaction (4 h reflux in neat proprioni-
trile in the absence of KPF6) converted 2 to the para-
magnetic [Re2]5+ complex [Re2Cl3(m-HN2C2Et2)(m-
dppa)2)(NCEt)]Cl (4) in which the m-HN2C2Et2 ligand
has resulted from the reductive coupling of two EtCN
molecules. This same reaction course occurs when 1 is
reacted with nitriles under similar conditions [4]. When
4 is reacted with NOPF6 in dichloromethane it is oxi-
dized to the diamagnetic [Re2]6+ congener of 4, i.e.
[Re2Cl3(m-HN2C2Et2)(m-dppa)2(NCEt)](PF6)2 (5). The
properties of 4 and 5 (see Section 2) resemble closely
Table 1
Crystallographic data for [Re2Cl3(m-dppm)2(1,4-DCB)2]PF6 (6)
Chemical formula
Formula weight
Space group
Re2Cl3P5F6N4C66H52
1648.80
Pbca (no. 61)
15.930(7)
25.758(8)
34.848(15)
14 298(17)
8
1.528
3.697
0.18/0.74
0.052
0.181
,
a (A)
,
b (A)
,
c (A)
3
,
V (A )
Z
zcalc (g cm−3
)
v(Mo Ka)(mm−1
)
Transmission factors: min./max.
R(Fo) a
Rw(Fo2) b
GoF
0.999
a R=ꢀꢁꢁFoꢁ−ꢁFcꢁꢁ/ꢀꢁFoꢁ for Fo2\2|(Fo2).
b Rw=[ꢀw(ꢁFo2ꢁ−ꢁFc2ꢁ)2/ꢀwꢁFo2ꢁ2]1/2
.

218
J. Chantler et al. / Inorganica Chimica Acta 305 (2000) 215–220
It had been our hope that complexes 6 and 7 could
be used as precursors to polymeric dirhenium(II) com-
plexes of the type represented in structure III (dppm
ligands omitted).
However, it appears that either the weak s-donor
ability of the unbound CN group in 6 and 7 or the
presence of unfavourable steric interactions between the
phenyl groups of neighbouring dppm ligands in adja-
cent dirhenium units prevented the formation of such
species. Note that 1,4-DCB has been used to link
Rh2(m-O2CCH3)4 units in polymeric chains through ax-
ial Rh–N coordination [16]. Our unsuccessful synthetic
strategies included, (i) the reaction of 1 with one or
fewer equivalents of 1,4-DCB or 1,4-DCBE, (ii) the
reaction of 1 with an equivalent of 6 or 7 under a
variety of reaction conditions. Future studies will in-
volve the reactions of 6 and 7 with other substitution-
ally labile dirhenium species, which are less sterically
crowded.
Fig. 1. ORTEP [15] representation of the structure of the dirhenium
unit present in the structure of [Re2Cl3(m-dppm)2(1,4-DCB)2]PF6 (6).
The thermal ellipsoids are drawn at the 50% probability level except
for the phenyl group carbon atoms which are circles of arbitrary
radius. The unlabeled C and N atoms of the second 1,4-DCB ligand
are N(20), C(20), C(27) and N(27), with atom N(20) being coordi-
nated to Re(2).
those of their dppm analogues [4] so that they must be
close structural analogues. These results clearly estab-
lish the close relationship between 1 and 2 in their
reactivity towards nitrile ligands.
The second part of this study involved the reactivity
of 1 towards polydentate nitrile ligands. We had previ-
ously shown that 1,2-dicyanobenzene (1,2-DCB) reacts
with 1 in the presence of KPF6 to afford [Re2Cl3(m-
dppm)2(1,2-DCB)2]PF6, possessing structure I, in which
each 1,2-DCB ligand possesses one coordinated and
one uncoordinated CN group. With the use of 1,4-di-
cyanobenzene (1,4-DCB) or 1,4-dicyanobut-2-ene (1,4-
DCBE) in place of 1,2-DCB, similar bis-nitrile
complexes were obtained. The important spectroscopic
and electrochemical properties of 6 and 7 are summa-
rized in Table 3. Note in particular the close similarity
between the CVs of 6 and 7 and those of other com-
plexes of these types [1,3]. A single crystal X-ray struc-
Table 2
,
Important bond distances (A) and angles (°) for the complex
[Re2Cl3(m-dppm)2(1,4-DCB)2]PF6 (6) a
Distances
Re(1)–Re(2)
Re(1)–Cl(2)
Re(1)–Cl(1)
Re(1)–P(1)
Re(1)–P(3)
Re(2)–N(20)
Re(2)–N(10)
Re(2)–P(4)
Re(2)–P(2)
2.2637(12) Re(2)–Cl(3)
2.536(4)
1.13(2)
1.16(3)
1.13(2)
1.13(2)
1.48(3)
1.39(3)
1.47(3)
1.44(3)
2.364(5)
2.364(5)
2.434(4)
2.438(5)
2.015(5)
N(10)–C(10)
N(17)–C(17)
N(20)–C(20)
N(27)–C(27)
C(10)–C(11)
2.029(16) C(14)–C(17)
2.478(5)
2.481(4)
C(20)–C(21)
C(24)–C(27)
Angles
Re(2)–Re(1)–Cl(2)
Re(2)–Re(1)–Cl(1)
Cl(2)–Re(1)–Cl(1)
Re(2)–Re(1)–P(1)
Cl(2)–Re(1)–P(1)
Cl(1)–Re(1)–P(1)
Re(2)–Re(1)–P(3)
Cl(2)–Re(1)–P(3)
Cl(1)–Re(1)–P(3)
P(1)–Re(1)–P(3)
106.18(13) N(20)–Re(2)–P(2)
107.46(13) N(10)–Re(2)–P(2)
146.34(18) Re(1)–Re(2)–P(2)
96.05(11) P(4)–Re(2)–P(2)
93.28(16) N(20)–Re(2)–Cl(3)
84.55(15) N(10)–Re(2)–Cl(3)
98.78(12) Re(1)–Re(2)–Cl(3)
83.85(16) P(4)–Re(2)–Cl(3)
89.76(16) P(2)–Re(2)–Cl(3)
96.0(4)
85.8(4)
94.64(11)
170.42(17)
84.1(4)
ture determination of the 1,4-DCB complex
6
confirmed the close relationship of these complexes to
others with this stoichiometry [1–3]. An ORTEP [15]
representation of the structure of the dirhenium cation
present in the structure of 6 is shown in Fig. 1 and
important bond distances and angles are listed in Table
87.5(4)
178.20(11)
85.68(16)
85.11(15)
,
2. The Re–Re distance of 2.2637(12) A is similar to
165.12(16) C(10)–N(10)–Re(2) 176.1(16)
,
that in [Re2Cl3(m-dppm)2(1,2-DCB)2]PF6 (2.265(1) A)
N(20)–Re(2)–N(10) 171.2(6)
C(20)–N(20)–Re(2) 172.1(16)
N(10)–C(10)–C(11) 178(2)
N(17)–C(17)–C(14) 168(3)
N(20)–C(20)–C(21) 174.9(19)
N(27)–C(27)–C(24) 176(3)
[3]; all other bond distances and angles are normal
[1–3]. The torsional angles Cl(1)–Re(1)–Re(2)–N(10),
N(20)–Re(2)–Re(1)
N(10)–Re(2)–Re(1)
N(20)–Re(2)–P(4)
N(10)–Re(2)–P(4)
Re(1)–Re(2)–P(4)
94.2(4)
94.3(4)
85.7(4)
91.2(4)
94.65(12)
Cl(2)–Re(1)–Re(2)–N(20),
P(1)–Re(1)–Re(2)–P(2)
and P(3)–Re(1)–Re(2)–P(4) are 25.8°, 24.7°, 25.8° and
24.8°, respectively, which shows the presence of a par-
tially staggered rotational conformation in this Re–Re
triply bonded complex.
a Numbers in parentheses are e.s.d. values in the least significant
digits.

J. Chantler et al. / Inorganica Chimica Acta 305 (2000) 215–220
219
As an alternative strategy to obtaining polymeric
dirhenium complexes we looked at the potential for
2-cyanoethylphosphine (CEP) to act as a multidentate
donor. The complex [Re2Cl3(m-dppm)2(CEP)2]PF6 (8)
was isolated and characterized by IR and NMR spec-
troscopy and cyclic voltammetry (Table 3). The CV of
8 is very similar to that of other nitrile bound com-
plexes of this type. Interestingly, this complex can be
oxidized to the paramagnetic complex [Re2Cl3(m-
dppm)2(CEP)2](PF6)2 (9) through the use of NOPF6;
complex 9 has the same CV as that of 8 (Table 3) and
behaves as a 1:2 electrolyte in acetone (Lm=164 V−1
cm2 mol−1 for a 1×10−3 M solution). The 31P{1H}
NMR spectrum of 8 shows an AA%BB% pattern with the
most intense peaks of the component multiplets at l
−5.5 and l −6.0. An additional singlet at l −21.5 is
due to the unbound phosphorus atoms of the two CEP
ligands; the 31P{1H} NMR spectrum of free CEP shows
1
a singlet at l −20.8. The H NMR spectrum of free
CEP shows resonances for the methylene protons at l
+2.62 (m, 6H) and l +1.93 (m, 6H). The resonance at
l +2.62 represents the CH2 protons bound to the P
atom of CEP, while the other set of CH2 protons are
for those bound to CN. In spite of the inequivalence of
the –CH2CH2CN units once one of them is bound to
Re in complex 8, the resonance at l ꢁ +1.7 is not
resolved into two sets of multiplets (ratio 1:2) but
appears as an unresolved single broad resonance.
We note that although 8 contains uncoordinated P
and CN groups, it did not react with Re2Cl4(m-dppm)2
(1). This may simply reflect unfavourable steric effects
and the conformational requirements of the dangling
CEP ligands.
4. Supplementary material
Tables giving full details for the crystal data and data
collection parameters, atomic positional parameters,
anisotropic thermal parameters, bond distances and
bond angles for 6 are available on request from author
R.A.W.
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