Further studies on formamidinate dirhenium(III) complexes of the type Re2(μ-form)2Cl4 and the isolation and characterization of the ferrocenyl ligand Fe[η5-C5H4C(NHCy)(NCy)]2

Article abstract of DOI:10.1016/S0020-1693(01)00454-6

The quadruply bonded dirhenium(III) complexes trans-Re₂(dpf)₂Cl₄·H₂O ·2THF (1) (dpf = N,N′-diphenylformamidinate) and Re₂(μ-RNCHO)₄Cl₂ (R = Ph (2) or Cy (3)) have been prepared i

Full text of DOI:10.1016/S0020-1693(01)00454-6

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Inorganica Chimica Acta 319 (2001) 224–228
Note
Further studies on formamidinate dirhenium(III) complexes of the
type Re2(m-form)2Cl4 and the isolation and characterization of the
ferrocenyl ligand Fe[h5-C5H4C(NHCy)(NCy)]2
N. Dastagiri Reddy, Phillip E. Fanwick, Richard A. Walton *
Department of Chemistry, Purdue Uni6ersity, 1393 Brown Building, West Lafayette, IN 47907-1393, USA
Received 28 February 2001; accepted 28 March 2001
Abstract
The quadruply bonded dirhenium(III) complexes trans-Re2(dpf)2Cl4·H2O·2THF (1) (dpf=N,N%-diphenylformamidinate) and
Re2(m-RNCHO)4Cl2 (R=Ph (2) or Cy (3)) have been prepared in good yield from the reactions of (n-Bu4N)2Re2Cl8 and
Re2(m-O2CCH3)4Cl2, respectively, with the appropriate molten ligands dpfH and RNHCHO. The ferrocenyl ligand
Fe[C5H4C(NHCy)(NCy)]2 (4) has been prepared but failed to yield dirhenium complexes that could be characterized. The
structures of 1, 2 and 4 have been established by single crystal X-ray crystallography. © 2001 Elsevier Science B.V. All rights
reserved.
Keywords: Crystal structures; Rhenium complexes; Formamidinate complexes; Metal–metal multiple bonds; Dinuclear complexes
1. Introduction
Re2(m-dpf)2Cl4 (dpf=N,N%-diphenylformamidinate) [7]
and have attempted to obtain other complexes of this
general type. Our findings are reported in the present
note.
Several recent studies have dealt with the synthesis
and structural characterization of multiply bonded
dirhenium(III) complexes that contain bridging amidate
[1–4] or amidinate [5,6] ligands. Only one of these
ligands, namely, N,N%-diphenylformamidinate ([Ph-
NC(H)NPh]−), forms the complete series of complexes
Re2(m-bridge)4Cl2, Re2(m-bridge)3Cl3 and Re2(m-
bridge)2Cl4 [6,7]. Because of our interest in the use of
2:4 complexes of the type Re2(m-bridge)2Cl4·nL
(bridge=acetate or 2-methyl-6-oxopyridinate; L=a
neutral monodentate axially bound ligand) [8,9] as syn-
thons in dirhenium chemistry, including their incorpo-
ration into coordination polymers [10], we have
examined further the previously reported complex
2. Experimental
2.1. Starting materials and reaction procedures
Standard literature procedures were used to prepare
(n-Bu4N)2Re2Cl8 [11], cis-Re2(m-O2CCH3)2Cl4(H2O)2
[8a] and Re2(m-O2CCH3)4Cl2 [12]. All other reagents
and organic solvents were purchased from commercial
sources. Solvents were deoxygenated by purging with
N2(g) prior to use and all reactions were carried out
under an atmosphere of N2. Spectroscopic and electro-
chemical measurements were carried out as described
previously [13]. Elemental microanalyses were per-
formed by Dr H.D. Lee of the Purdue University
Microanalytical Laboratory.
* Corresponding author. Tel.: +1-765-4945464; fax: +1-765-
4940239.
E-mail address: rawalton@purdue.edu (R.A. Walton).
0020-1693/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0020-1693(01)00454-6

N. Dastagiri Reddy et al. / Inorganica Chimica Acta 319 (2001) 224–228
225
2.2. Synthesis of Re2(v-dpf)2Cl4 (1)
(dpf=N,N%-diphenylformamidinate)
and cis-Re2(m-O2CCH3)2Cl4(H2O)2 with PhNHCHO in
methanol, ethanol and other organic solvents. The only
compound we were able to isolate and identify was 2.
An alternative procedure involved reacting 1 with an
excess of molten PhNHCHO at 110°C for 12 h. The
cooled mixture was then treated with ethanol and
stirred for 10 min, filtered, and the solid recrystallized
from THF/hexane to afford crystals of composition
Re2(m-dpf)2Cl4·H2O·2THF (1·H2O·2THF) (see Section
2.6).
(a) A mixture of (n-Bu4N)2Re2Cl8 (0.50 g, 0.44
mmol) and dpfH (0.34 g, 1.73 mmol) was thoroughly
ground and sealed in a glass tube under N2(g). The tube
was kept in a vertical position for 15 h at 150°C, cooled
to room temperature, then broken open and the con-
tents washed with dichloromethane (25 ml) to leave
0.15 g of crystalline 1. The dichloromethane filtrate was
evaporated to dryness and the dark red residue washed
with hot ethanol (30 ml), and then re-dissolved in THF
(15 ml). The filtered THF extract was evaporated to
dryness and washed with diethyl ether (10 ml) to afford
a further quantity (0.05 g) of 1. Total yield 0.20 g
(50%).
2.4. Synthesis of Re2(v-CyNCHO)4Cl2 (3)
The reaction between (n-Bu4N)2Re2Cl8 (0.30 g, 0.26
mmol) and molten CyNHCHO (2.00 g, 15.87 mmol)
was carried out for 12 h at 180°C. The reaction mixture
was allowed to cool to room temperature, mixed with
30 ml of ethanol and stirred for 30 min. The yellow
crystalline solid was filtered off and washed with etha-
nol (20 ml) and diethyl ether (20 ml); yield 0.22 g (88%).
Anal. Found: C, 34.88; H, 5.12. Calc for
C28H48Cl2N4O4Re2: C, 35.47; H, 5.10%. IR spectrum
(KBr pellet, cm−1): 3005 (w), 2929 (s), 2854 (s), 1532
(s), 1450 (m), 1406 (m), 1358 (s), 1327 (s), 1300 (s), 1266
(m-w), 1190 (w), 1091 (m), 1071 (s), 1053 (m), 983 (w),
894 (m-w), 849 (w), 799 (w), 738 (m), 626 (m), 517
(m-s), 471 (s), 440 (m), 427 (m-s). Cyclic voltammogram
(0.1 M n-Bu4NPF6ꢀCH2Cl2): E1/2(red)= −1.15 V vs
(b) A mixture of (n-Bu4N)2Re2Cl8 (0.30 g, 0.26
mmol) and dpfH (0.114 g, 0.58 mmol) was dissolved in
1,2-dichlorobenzene (4 ml) and the solution refluxed for
24 h. The reaction mixture was cooled to room temper-
ature and 30 ml of diethyl ether added to precipitate a
quantity of 1 which was filtered off and washed with
hot ethanol (10 ml); yield 0.15 g (62%). Anal. Found: C,
34.81; H, 2.66; N, 5.90. Calc for C26H22Cl4N4Re2: C,
34.52; H, 2.45; N, 6.19%. IR spectrum (KBr pellet,
cm−1): 3055 (w), 1590 (m), 1489 (s), 1362 (w), 1300
(m-s), 1210 (s), 1029 (w), 942 (m), 760 (m-s), 696 (m-s),
550 (w), 456 (m). Cyclic voltammogram (0.1 M n-
Bu4NPF6ꢀCH2Cl2): E1/2 (red)= −0.69 V vs Ag/AgCl
1
Ag/AgCl (DEp=90 mV at w=200 mV s−1). H NMR
(DEp=80 mV at w=200 mV s−1). H NMR (CDCl3):
l=8.21 (s, 2H, CH), 7.45–7.30 (m, 20H, Ph).
2.3. Synthesis of Re2(v-PhNCHO)4Cl2 (2)
(CD2Cl2): l=8.71 (s, 4H, CH), 4.10 (m, 4H, Cy),
2.3–0.8 (m, br, 40H, Cy).
1
2.5. Synthesis of Fe[p5-C5H4C(NHCy)(NCy)]2 (4)
A mixture of Re2(m-O2CCH3)4Cl2 (0.24 g, 0.35 mmol)
and PhNHCHO (1.00 g, 8.26 mmol) was heated
overnight at 110°C under N2(g). The mixture was then
allowed to cool to room temperature, 50 ml of diethyl
ether added with stirring, and the solid material was
filtered off. The solid was then extracted with 50 ml of
dichloromethane, the filtered extract slowly evaporated
to dryness, and the crystalline residue washed with
diethyl ether and dried under a vacuum; yield 0.15 g
(46%). Anal. Found: C, 36.40; H, 2.66. Calc. for
C28H24Cl2N4O4Re2: C, 36.40; H, 2.62%. IR spectrum
(KBr pellet, cm−1): 3048 (m-w), 1595 (m-w), 1516 (s),
1489 (s), 1454 (m-w), 1349 (m), 1324 (s), 1209 (s), 1076
(w), 1028 (m-w), 926 (m), 765 (m-s), 698 (s), 683 (s), 613
(m), 537 (w), 508 (w), 449 (s). Cyclic voltammogram
(0.1 M n-Bu4NPF6ꢀCH2Cl2): E1/2(red)= −0.81 V vs
A suspension of ferrocene (2.01 g, 10.81 mmol) in
hexane (150 ml) was treated with TMEDA (3.6 ml,
23.77 mmol) followed by the dropwise addition of
n-BuLi (10 ml of a 2.5 M solution in hexane). This
mixture was stirred at 25°C overnight and then cooled
to 0°C before being treated dropwise with a solution of
dicyclohexylcarbodiimide (CyNꢁCꢁNCy) (4.90 g, 23.75
mmol) in hexane (20 ml). Stirring was continued for
another 20 h at 25°C and the clear solution was care-
fully decanted from the solid precipitate. The latter was
treated with diethyl ether (150 ml) and then with the
dropwise addition of 10 ml of water. The resulting
mixture was stirred for 30 min. An additional quantity
of water was added (50 ml) and the diethyl ether layer
separated, the solvent evaporated, and the resulting
orange solid recrystallized from hot hexanes; yield 5.12
g (79%). Anal. Found: C, 72.43; H, 9.25. Calc for
C36H54FeN4: C, 72.22; H, 9.09%. IR spectrum (KBr
pellet, cm−1): 3447 (m-s), 3096 (m-w), 2928 (s), 2851
(s), 1624 (s), 1491 (s), 1450 (s), 1356 (m-w), 1350 (m),
1306 (w), 1301 (w), 1257 (m), 1192 (m), 1157 (m), 1102
(m), 1030 (m), 979 (w), 896 (m-s), 834 (s), 711 (m-w),
1
Ag/AgCl (ZEp=80 mV at w=200 mV s−1). H NMR
(CD2Cl2): l=8.96 (s, 4H, CH), 7.36 and 7.27 (m, 20H,
Ph).
A variety of unsuccessful attempts were made to
prepare the complex Re2(m-PhNCHO)2Cl4. These in-
cluded the stoichiometric reactions of (n-Bu4N)2Re2Cl8

226
N. Dastagiri Reddy et al. / Inorganica Chimica Acta 319 (2001) 224–228
676 (w), 566 (w), 528 (m-w), 478 (m-s). 1H NMR
(CDCl3): l=4.31 (s, 8H, C5H4), 3.80 (m, br, 2H, Cy),
3.14 (m, br, 2H, Cy), 2.1–1.2 (m, 40H, Cy).
atoms were located in succeeding difference Fourier
syntheses. Hydrogen atoms were placed in calculated
positions according to idealized geometries with
,
CꢀH=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 SHELXL-97 [16].
2.6. X-ray crystallography
Single crystals of composition 1·H2O·2THF that were
suitable for X-ray analysis were obtained by two proce-
dures. The first involved the recrystallization from
THF/hexanes of the solid obtained upon heating 1 with
molten PhNHCHO (1 fails to react under these condi-
tions — see Section 2.3). The second procedure used
was the recrystallization of the bulk samples of 1,
prepared as described in Section 2.2, from THF/hex-
anes. These procedures afforded different crystal forms,
3. Results and discussion
The procedure used previously to obtain the complex
trans-Re2(m-dpf)2Cl4 (1) utilized the reaction between
Re2(m-dpf)3Cl3 and 85% HBF4·Et2O in a mixture of
acetonitrile and dichloromethane [7]. The disadvantages
of this method are that 1 is obtained in low yield and
Re2(m-dpf)3Cl3 must itself be prepared from the reac-
tion between Re2Cl5(PMePh2)3 and dpfH [7]. The two
procedures we used for the synthesis of 1 involve the
reaction of the readily available starting material (n-
Bu4N)2Re2Cl8 [11] with either molten dpfH or a solu-
tion of this ligand in refluxing 1,2-dichlorobenzene.
Both methods give pure 1 in yields of at least 50%. We
found that neither Re2(m-dpf)4Cl2 nor Re2(m-dpf)3Cl3
are formed in significant quantities by our procedure.
The procedures we used to obtain single crystals of 1
involved recrystallization from THF/hexanes. This gave
crystals of composition 1·H2O·2THF, which we ob-
tained in both monoclinic and triclinic forms. Crystal
data for the C2/c monoclinic form (I) are given in
Table 1, while data for the P triclinic form (II) are
available as supplementary information (available from
R.A.W.). The structures are essentially the same, the
only difference being that the hydrogens of the coordi-
nated water molecule were not included in the refine-
ment of crystal II. The ORTEP [17] representation of the
structure of 1·H2O·2THF is shown in Fig. 1 and impor-
tant structural parameters are summarized in Table 2.
This structure resembles closely that of 1 reported
previously [7], with the exception of the presence of an
axially bound water molecule in 1·H2O·2THF, which is
in turn H-bonded to the oxygen atoms of the two THF
molecules. The ReꢀO(H2O) distances are 2.232(4) and
(
space groups C2/c and P1, respectively, with the same
structure. Crystals of 2 were harvested directly from the
preparative reaction mixture (Section 2.3), while those
of 4 were obtained by recrystallization at 0°C of a
concentrated solution of this complex in hexanes. Data
collections for 1, 2 and 4 were performed at 15091,
17391 and 15091 K, respectively, with graphite-
,
monochromated Mo Ka radiation (u=0.71073 A) on a
Nonius Kappa CCD diffractometer. Lorentz and polar-
ization corrections were applied to the data sets. The
crystallographic data for 1, 2 and 4 are given in Table
1.
The structures were solved using the structure solu-
tion program PATTY in DIRDIF92 [14]. The remaining
Table 1
Crystallographic
data
for
trans-Re2(m-dpf)2Cl4·H2O·2THF
(1·H2O·2THF), Re2(m-PhNCHO)4Cl2 (2) and Fe[C5H4C(NHCy)-
(NCy)]2 (4)
1·H2O·2THF
(I)
2
4
Chemical
formula
C34H40Cl4N4O3 C28H24Cl2N4O4
Re2
C
36H54FeN4
Re2
923.83
Formula
weight
1066.93
598.71
Space group
C2/c (no. 15)
P (no. 2)
P21/n (no. 14)
Unit cell dimensions
,
a (A)
15.3241(3)
13.0743(4)
18.5175(5)
90
101.8153(16)
90
3631.4(3)
4
1.951
6.4304(7)
9.9721(12)
12.3822(16)
101.802(6)
98.688(7)
106.251(8)
727.6(3)
1
14.3372(7)
7.7796(2)
14.3829(7)
90
92.9044(10)
90
,
b (A)
,
c (A)
h (°)
i (°)
k (°)
V (A )
,
2.258(4) A in crystals I and II, respectively. The H-
bonded interactions between the axially bound water
3
,
1602.2(2)
2
molecule and the lattice THF molecules are defined by
Z
,
an O· · ·O distance of 2.68 A for the two crystallograph-
zcalc (g cm−3
v(Mo Ka)
)
2.108
8.650
1.241
0.498
,
ically identical H-bonds in I, and distances of 2.71 A
7.089
(mm−1
)
for each of the crystallographically inequivalent H-
R (Fo) a
0.028
0.067
0.061
0.157
1.063
0.040
0.089
1.039
bonds present in crystal II. The ReꢀRe quadruple bond
wR (Fo2) b
,
distances of 2.2198(3) and 2.2174(3) A for I and II are
Goodness-of-fit 1.034
,
longer than that of 2.177(1) A in trans-Re2(dpf)2Cl4 [7],
a R=ꢀ ꢁꢁFoꢁ−ꢁFcꢁꢁ/ꢀ ꢁFoꢁ with Fo2\2|(Fo2).
in accord with the trans weakening influence of the
axially bound water molecule. The ReꢀO bond dis-
b wR=[ꢀ w(ꢁFo2ꢁ−ꢁFc2ꢁ)2/ꢀ wꢁFo2ꢁ2]1/2
.

N. Dastagiri Reddy et al. / Inorganica Chimica Acta 319 (2001) 224–228
227
inversion center, is very similar to those of various
amidate and amidinate complexes of rhenium(III) that
are of this same Re2(m-bridge)4Cl2 type [1–6]. The
ReꢀRe and ReꢀCl bond distances in 2 are 2.249(5) and
,
2.506(2) A, respectively.
A further aspect of our study involved the synthesis
of the ferrocenyl ligand Fe[h5-C5H4C(NHCy)(NCy)]2
(4) and a preliminary study of its reactions with a
variety of dirhenium(III) and dirhenium(II) synthons.
A structure determination of 4 (Fig. 3) shows the two
formamidine moieties to be in a trans arrangement to
one another in the solid state. The important structural
parameters are given in Table 4. The CꢀN distances
C(10)ꢀN(10) and C(10)ꢀN(20) are 1.284(2) and 1.369(2)
,
A, respectively, in accord with N(20) being the amido
Fig. 1. ORTEP [17] representation of the structure of trans-Re2(m-
dpf)2Cl4·H2O·2THF (1·H2O·2THF) with the important atoms la-
beled. The thermal ellipsoids are drawn at the 50% probability level.
Table 2
,
Important bond lengths (A) and bond angles (°) for the complex
trans-Re2(m-dpf)2Cl4·H2O·2THF (1·H2O·2THF) (I)
Bond lengths
Re(1)ꢀRe(2)
Re(1)ꢀCl(1)
Re(1)ꢀO(1)
Re(1)ꢀN(3)
2.2198(3)
2.3704(10) Re(2)ꢀN(1)
2.232(4)
2.069(3)
Re(2)ꢀCl(2)
2.3169(9)
2.055(3)
1.318(5)
1.327(5)
N(3)ꢀC(2)
N(1)ꢀC(2)
Bond angles
N(3)ꢀRe(1)ꢀN(3)%
N(3)ꢀRe(1)ꢀRe(2)
N(3)ꢀRe(1)ꢀO(1)
Re(2)ꢀRe(1)ꢀO(1)
N(3)ꢀRe(1)ꢀCl(1)
N(3)ꢀRe(1)ꢀCl(1)%
178.85(16) Cl(1)ꢀRe(1)ꢀCl(1)% 159.64(5)
90.57(8)
89.43(8)
180.00(8)
N(1)ꢀRe(2)ꢀN(1)%
N(1)ꢀRe(2)ꢀRe(1)
N(1)ꢀRe(2)ꢀCl(2)
177.05(16)
91.48(8)
87.62(10)
91.46(10)
91.61(10) N(1)ꢀRe(2)ꢀCl(2)%
88.19(10) Re(1)ꢀRe(2)ꢀCl(2) 108.17(2)
Cl(2)ꢀRe(2)ꢀCl(2)% 143.66(5)
Fig. 2. ORTEP [17] representation of the structure of Re2(m-PhN-
CHO)4Cl2 (2) with the important atoms labeled. The thermal ellip-
soids are drawn at the 50% probability level.
Re(2)ꢀRe(1)ꢀCl(1) 100.18(2)
O(1)ꢀRe(1)ꢀCl(1) 79.82(2)
Numbers in parentheses are estimated standard deviations in the least
significant digits.
Table 3
,
Important bond lengths (A) and bond angles (°) for the complex
Re2(m-PhNCHO)4Cl2 (2) a
tances can be compared with those of 2.50(2) and
Bond lengths
ReꢀRe%
ReꢀO(10)
ReꢀO(20)
ReꢀN(20)
ReꢀN(10)
,
2.51(2) A that were reported in an early structure
2.2491(5)
2.024(7)
2.052(6)
2.066(7)
2.081(8)
ReꢀCl
2.506(2)
determination of the complex cis-Re2(m-O2CCH3)2-
C(10)ꢀO(10)
C(20)ꢀO(20)
C(10)ꢀN(10)
C(20)ꢀN(20)
1.276(11)
1.266(10)
1.327(12)
1.314(12)
,
Cl4(H2O)2, for which the ReꢀRe distance is 2.224(5) A
[18]. The compound trans-Re2(m-O2CCH3)2Cl4, which
contains no axially bound ligand molecules but is
linked through weak intermolecular ReꢀCl· · ·Re
bridges, has a much shorter ReꢀRe distance of
Bond angles
O(10)ꢀReꢀO(20)
O(10)ꢀReꢀN(20)
O(20)ꢀReꢀN(20)
O(10)ꢀReꢀN(10)
O(20)ꢀReꢀN(10)
N(20)ꢀReꢀN(10)
O(10)ꢀReꢀRe%
O(20)ꢀReꢀRe%
90.3(3)
87.7(3)
177.9(2)
179.25(19)
90.1(3)
91.9(3)
91.30(18)
90.02(19)
N(20)ꢀReꢀRe%
N(10)ꢀReꢀRe%
O(10)ꢀReꢀCl
O(20)ꢀReꢀCl
N(20)ꢀReꢀCl
N(10)ꢀReꢀCl
Re%ꢀReꢀCl
90.5(2)
89.3(2)
84.82(19)
83.3(2)
96.0(2)
94.6(2)
,
2.2084(3) A [19].
Our attempts to prepare complexes that were
analogous to 1 and contained the [PhNCHO]− and
[CyNCHO]− ligands were unsuccessful. The only pure
complexes that were isolated had the compositions
Re2(m-PhNCHO)4Cl2 (2) and Re2(m-CyNCHO)4Cl2 (3).
Their structural identity was confirmed by a single
crystal X-ray structure determination of 2 (Fig. 2 and
Table 3). This structure, which has a crystallographic
172.23(6)
a Numbers in parentheses are estimated standard deviations in the
least significant digits. Re% is used for the unlabeled Re atom in Fig.
2.

228
N. Dastagiri Reddy et al. / Inorganica Chimica Acta 319 (2001) 224–228
identifiable products, studies involving the reactivity of
4 are continuing.
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 compounds 1·H2O·2THF, 2 and 4 are
available on request from the author (R.A.W.).
Acknowledgements
Fig. 3. ORTEP [17] representation of the structure of Fe[h5-
C5H4(NHCy)(NCy)]2 (4) with the important atoms labeled. The
thermal ellipsoids are drawn at the 50% probability level.
We thank the John A. Leighty Endowment Fund for
support of this work.
Table 4
,
Important bond lengths (A) and bond angles (°) for the complex
Fe[C5H4C(NHCy)(NCy)]2 (4)
References
Bond lengths
FeꢀC(1)
FeꢀC(2)
FeꢀC(3)
FeꢀC(4)
FeꢀC(5)
C(10)ꢀN(10)
C(11)ꢀN(10)
C(10)ꢀN(20)
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Staples, J. Chem. Soc., Dalton Trans. (1998) 2813.
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[6] J.L. Eglin, C. Lin, T. Ren, L. Smith, R.J. Staples, D.O. Wipf,
Eur. J. Inorg. Chem. (1999) 2095.
2.0706(16) C(21)ꢀN(20)
2.0560(17) C(1)ꢀC(2)
2.0566(18) C(1)ꢀC(5)
2.0563(17) C(1)ꢀC(10)
2.0654(17) C(2)ꢀC(3)
1.456(2)
1.433(2)
1.424(2)
1.499(2)
1.429(3)
1.416(3)
1.417(2)
1.284(2)
1.465(2)
1.369(2)
C(3)ꢀC(4)
C(4)ꢀC(5)
Bond angles
C(1)ꢀFeꢀC(2)
C(10)ꢀC(1)ꢀFe
[7] F.A. Cotton, L.M. Daniels, S.C. Haefner, Inorg. Chim. Acta 285
(1999) 149.
[8] (a) A.R. Chakravarty, F.A. Cotton, A.R. Cutler, R.A. Walton,
Inorg. Chem. 25 (1986) 3619;
40.63(7)
C(10)ꢀN(20)ꢀC(21) 123.89(16)
129.65(12) N(10)ꢀC(10)ꢀN(20) 119.97(10)
C(10)ꢀN(10)ꢀC(11) 120.23(15)
(b) S.S. Lau, P.E. Fanwick, R.A. Walton, Inorg. Chim. Acta 308
(2000) 8;
(c) J.K. Bera, S.S. Lau, P.E. Fanwick, R.A. Walton, J. Chem.
Soc., Dalton Trans. (2000) 4277.
Numbers in parentheses are estimated standard deviations in the least
significant digits.
[9] A.R. Cutler, S.M.V. Esjornson, P.E. Fanwick, R.A. Walton,
Inorg. Chem. 27 (1988) 287.
[10] Y. Ding, S.S. Lau, P.E. Fanwick, R.A. Walton, Inorg. Chim.
Acta 300–302 (2000) 505.
nitrogen; this was confirmed by the location and refine-
ment of the hydrogen atom H(20), with the distance
,
N(20)ꢀH(20) being 0.84(2) A. The torsional angles
C(11)ꢀN(10)ꢀC(10)ꢀC(1) and C(21)ꢀN(20)ꢀC(10)ꢀ
N(10) are 6.6(3) and −8.0(3)°, respectively, while
C(2)ꢀC(1)ꢀC(10)ꢀN(10) and C(5)ꢀC(1)ꢀC(10)ꢀN(10)
are −114.2(2) and 61.2(2)°, respectively. In accord
with the non-planarity of the formamidine ligand units
with respect to the C5H4 rings, and the trans disposition
of the amine NꢀH and imido lone pair in each for-
mamidine unit, we failed to isolate complexes in which
the deprotonated ligand bridged pairs of dirhenium
units. Reactions of 4 that were attempted included
those with (n-Bu4N)2Re2Cl8, Re2Cl4(PMe3)4, Re2(m-
[11] (a) T.J. Barder, R.A. Walton, Inorg. Chem. 21 (1982) 2510;
(b) T.J. Barder, R.A. Walton, Inorg. Synth. 23 (1985) 116.
[12] F.A. Cotton, C. Oldham, W.R. Robinson, Inorg. Chem. 5 (1966)
1798.
[13] W. Wu, P.E. Fanwick, R.A. Walton, Inorg. Chem. 34 (1995)
5810.
[14] 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.
[15] Z. Otwinowski, W. Minor, Methods Enzymol. 276 (1996) 307.
[16] G.M. Sheldrick, SHELXL-97, A Program for Crystal Structure
Refinement, University of Go¨ttingen, Germany, 1997.
[17] C.K. Johnson, ORTEPII, Rep. ORNL-5138, Oak Ridge National
Laboratory, TN, 1976.
O2CCH3)4Cl2,
cis-Re2(m-O2CCH3)2Cl4(H2O)2,
cis-
Re2(m-O2CCH3)2Cl4(py)2 and cis-Re2(m-O2CCH3)2Cl2-
(m-dppm)2 (dppm=Ph2PCH2PPh2), which were carried
out under reflux conditions in a variety of organic
solvents. While we have not yet isolated any pure
[18] P.A. Koz’min, M.D. Surazhskaya, V.G. Kuznetsov, Zh. Strukt.
Khim. 11 (1970) 313.
[19] S.M.V. Esjornson, P.E. Fanwick, R.A. Walton, Inorg. Chim.
Acta 162 (1989) 165.