Preparation and characterization of oxorhenium(V) complexes with 2,2'-biimidazole: The strong affinity of coordinated biimidazole for chloride ions via N-H···Cl- hydrogen bonding

Article abstract of DOI:10.1021/ic000328t

N,N'-Dimethylbiimidazole and bipyridine (N-N) react with ReOCl₃(OPPh₃)(Me₂S) to give mer-ReOCl₃(N-N) compounds. Nonmethylated biimidazole forms a trans-O,O [ReOCl₂(OPPh₃)(biimH₂)]⁺ cation, which is tightly associated with the Cl^- counterion via N-H···Cl^- hydrogen bonding. Hydrolysis of ReOCl₃(biimMe₂) in wet acetone (5% water) leads to the linear oxo-bridged dinuclear species [{OReCl₂(biimMe₂)}₂(μ-O)] containing chelated biimMe₂. Acetone solutions containing only 1% water yield the bent oxo-bridged dinuclear species [{OReCl₂}₂(μ-O)(μ-biimMe₂)₂], where each Re center retains the ReO₂Cl₂N₂ coordination but the biimMe₂ ligands are bridging. The linear oxo-bridged [{OReCl₂(biimH₂)}₂(μ-O)] complex obtained with nonmethylated biimidazole includes two Cl^- ions held via N-H···Cl^- hydrogen bonds, leading to a dianionic [{OReCl₂(biimH₂···Cl)}₂(μ-O)]^2- unit in the crystals of the PPh₄⁺ salt. The compounds are characterized by IR and NMR spectroscopies, and the structures of [ReOCl₂(OPPh₃)(biimH₂)]Cl, [{OReCl₂(biimH₂)}₂(μ-O)](PPh₄Cl)₂·2H₂O, and [{OReCl₂}₂-(μ-O)(μ-biimMe₂)₂]·acetone are determined by X-ray diffraction.

Full text of DOI:10.1021/ic000328t

4886
Inorg. Chem. 2000, 39, 4886-4893
Preparation and Characterization of Oxorhenium(V) Complexes with 2,2′-Biimidazole: The
Strong Affinity of Coordinated Biimidazole for Chloride Ions via N-H‚‚‚Cl- Hydrogen
Bonding
Se´bastien Fortin and Andre´ L. Beauchamp*
De´partement de Chimie, Universite´ de Montre´al, C.P. 6128, Succ. Centre-ville,
Montre´al, Que´bec, Canada H3C 3J7
ReceiVed March 28, 2000
N,N′-Dimethylbiimidazole and bipyridine (N-N) react with ReOCl3(OPPh3)(Me2S) to give mer-ReOCl3(N-N)
compounds. Nonmethylated biimidazole forms a trans-O,O [ReOCl2(OPPh3)(biimH2)]+ cation, which is tightly
associated with the Cl- counterion via N-H‚‚‚Cl- hydrogen bonding. Hydrolysis of ReOCl3(biimMe2) in wet
acetone (5% water) leads to the linear oxo-bridged dinuclear species [{OReCl2(biimMe2)}2(µ-O)] containing
chelated biimMe2. Acetone solutions containing only 1% water yield the bent oxo-bridged dinuclear species
[{OReCl2}2(µ-O)(µ-biimMe2)2], where each Re center retains the ReO2Cl2N2 coordination but the biimMe2 ligands
are bridging. The linear oxo-bridged [{OReCl2(biimH2)}2(µ-O)] complex obtained with nonmethylated biimidazole
includes two Cl- ions held via N-H‚‚‚Cl- hydrogen bonds, leading to a dianionic [{OReCl2(biimH2‚‚‚Cl)}2(µ-
O)]2- unit in the crystals of the PPh4 salt. The compounds are characterized by IR and NMR spectroscopies,
+
and the structures of [ReOCl2(OPPh3)(biimH2)]Cl, [{OReCl2(biimH2)}2(µ-O)](PPh4Cl)2‚2H2O, and [{OReCl2}2-
(µ-O)(µ-biimMe2)2]‚acetone are determined by X-ray diffraction.
Introduction
Our interest in oxo-rhenium complexes with biimidazole
stemmed from previous studies on oxo-imidazole systems,7
whose optical properties were found to differ markedly from
those of the corresponding pyridine compounds.4 This work was
extended to biimidazole, whose ability to form chelate rings
should improve stability. Moreover, this potentially bridging
bis-bidentate ligand, when deprotonated, offers the possibility
of generating di- or polynuclear species with interesting
properties, since biimidazole is known to favor electron transfer
between metal centers20 and to promote catalytic activity in
various metal complexes.21,22
A number of new oxo-rhenium compounds have been
prepared during the past decade. Similarity with Tc imaging
agents used in nuclear medicine and potential applications of
rhenium compounds in radiotherapy1 have definitely contributed
to this increased activity. However, many other features of the
oxo-rhenium core have attracted attention, such as its spec-
troscopic properties,2-5 its basicity toward various Lewis acids,6,7
its influence on ligand distributions in coordination spheres,8-10
and its roles in oxygen transfer11-13 and catalytic processes.14-19
The present paper deals with the initial step of this study,
namely, the preparation of mononuclear and oxo-bridged
dinuclear complexes containing biimidazole (biimH2) and N,N′-
* Corresponding author. E-mail: beauchmp@chimie.umontreal.ca.
Fax: (514) 343-7586.
(1) Nicolini, M.; Mazzi, U. Technetium, Rhenium and Other Metals in
Chemistry and Nuclear Medicine 5; Servizi Grafici Editoriali: Padova,
Italy, 1999.
(2) Savoie, C.; Reber, C. J. Am. Chem. Soc. 2000, 122, 844 and references
therein.
(3) Oetliker, U.; Savoie, C.; Stanislas, S.; Reber, C.; Connac, F.;
Beauchamp, A. L.; Loiseau, F.; Dartiguenave, M. J. Chem. Soc., Chem.
Commun. 1998, 657 and references therein.
(4) Savoie, C.; Reber, C. Coord. Chem. ReV. 1998, 171, 387 and references
therein.
(5) Savoie, C.; Reber, C.; Be´langer, S.; Beauchamp, A. L. Inorg. Chem.
1995, 34, 3851.
(6) Doerrer, L. H.; Galsworthy, J. R.; Green, M. L.; Leech, M. A. J. Chem.
Soc., Dalton Trans. 1998, 2483.
dimethylbiimidazole (biimMe2), in which the ligand participates
(7) Be´langer, S.; Beauchamp, A. L. Inorg. Chem. 1996, 35, 7836; 1997,
36, 3640.
(16) Finlay, J.; McKervey, M. A.; Gunaratne, H. Q. N. Tetrahedron Lett.
1998, 39, 5651.
(17) Arterburn, J. B.; Perry, M. C.; Nelson, S. L.; Dible, B. R.; Holguin,
M. S. J. Am. Chem. Soc. 1997, 119, 9309.
(18) Arterburn, J. B.; Nelson, S. L. J. Org. Chem. 1996, 61, 2260.
(19) Jung, J.-H.; Albright, T. A.; Hoffmann, D. M.; Lee, T. R. J. Chem.
Soc., Dalton Trans. 1999, 4487.
(20) Carmona, D.; Ferrer, J.; Mendoza, A.; Lahoz, F. J.; Oro, L. A.; Viguri,
F.; Reyes, J. Organometallics 1995, 14, 2066 and references therein.
(21) Esteruelas, M. A.; Garcia, M. P.; Lopez, A. M.; Oro, L. A.
Organometallics 1991, 10, 127. Esteruelas, M. A.; Garcia, M. P.;
Lopez, A. M.; Oro, L. A. Organometallics 1992, 11, 702.
(22) Garcia, M. P.; Lopez, A. M.; Esteruelas, M. A.; Lahoz, F. J.; Oro, L.
A. J. Chem. Soc., Chem. Commun. 1988, 793.
(8) van Bommel, K. J. C.; Verboom, W.; Kooijman, H.; Spek, A. L.;
Reinhoudt, D. N. Inorg. Chem. 1998, 37, 4197.
(9) Hahn, F. E.; Imhof, L.; Lu¨gger, T. Inorg. Chim. Acta 1998, 269, 347.
(10) Fortin, S.; Beauchamp, A. L. Inorg. Chim. Acta 1998, 279, 159.
(11) Conry, R. R.; Mayer, J. M. Inorg. Chem. 1990, 29, 4862.
(12) Bryan, J. C.; Stenkamp, R. E.; Tulip, T. H.; Mayer, J. M. Inorg. Chem.
1987, 26, 2283.
(13) Seymore, S. B.; Brown, S. N. Inorg. Chem. 2000, 39, 325.
(14) Ku¨hn, F. E.; Rauch, M. U.; Lobmaier, G. M.; Artus, G. R. J.;
Herrmann, W. A. Chem. Ber. 1997, 130, 1427.
(15) Gunaratne, H. Q. N.; McKervey, M. A.; Feutren, S.; Finlay, J.; Boyd,
J. Tetrahedron Lett. 1998, 39, 5655.
10.1021/ic000328t CCC: $19.00 © 2000 American Chemical Society
Published on Web 09/29/2000

Oxorhenium(V) Complexes with 2,2′-Biimidazole
Inorganic Chemistry, Vol. 39, No. 21, 2000 4887
IR (CH2Cl2 solution; sample between NaCl plates; cm-1): 982, ν(Red
O). All attempts to remove the Bu4NCl produced and to separate the
isomers failed.
in a single bidentate interaction. Compounds with pyridine have
been known for some time,10,23,24 but systems with imidazole
and its derivatives have been described only recently.25-28
The chemistry described here reveals interesting ligating
features of the biimidazole framework. First, it can either behave
as a chelating agent or adopt a syn-bridging role in oxo-bridged
dinuclear compounds. Second, N-methylation of biimidazole
introduces drastic changes in reactivity because halide ion
association with coordinated biimidazole by hydrogen bonding
via the N-H groups is a significant stabilizing factor.
In one case, moist PPh4Cl was added to the residue dissolved in
CH2Cl2 solution to favor precipitation. No precipitate formed spontane-
ously, but vapor diffusion of diethyl ether into this solution produced
a small amount of blue crystals (4). An X-ray diffraction study of a
specimen from this crystallographically homogeneous sample showed
the composition to be [{OReCl2(biimH2)}2O](PPh4Cl)2‚2H2O.
[ReOCl2(OPPh3)(biimH2)]Cl (5). A suspension of 1 (496 mg; 0.76
mmol) in CHCl3 was heated to reflux, and biimidazole (15 mg, 1.14
mmol) was added in small portions. A grass-green solution was rapidly
obtained, and a small amount of solid remained. The mixture was
refluxed for 10 min, cooled in an ice bath, and filtered to remove a
small amount of brown solid. The filtrate was evaporated to dryness,
the oily residue was dissolved in a minimum amount of acetone, and
diethyl ether was added dropwise until the solution became slightly
cloudy. A drop of acetone was added to obtain a clear solution, which
was allowed to stand while a pale green solid slowly appeared. After
a few hours, the mixture was filtered, and the solid was washed with
small portions of a 1:4 acetone:diethyl ether mixture. Yield: 208 mg
Experimental Section
Reactants and Methods. Reagent grade KReO4, 2,2′-bipyridine
(Aldrich), solvents, and other chemicals were used as received.
Deuterated solvents were purchased from CDN Isotopes. 1H NMR
spectra were recorded at 300 MHz on a Bruker AMX-300 spectrometer
or at 400 MHz on a Bruker ARX-400 instrument. 13C{1H} and 31P-
{1H} NMR spectra were recorded on the latter instrument at 101 and
162 MHz, respectively. Residual solvent signals were used as internal
1
references,29 and the chemical shifts are reported vs Me4Si for the H
1
and 13C spectra. H3PO4 was used as the external standard (δ ) 0) for
the 31P spectra. Solid-state CP-MAS 13C NMR spectra were recorded
at 75.5 MHz on a Bruker Avance DSX-300 instrument, glycine being
used as the external standard (δ(carboxyl) ) 176.0 ppm). IR spectra
were generally recorded for samples in KBr pellets on a Perkin-Elmer
1750 FTIR spectrophotometer. Elemental analyses were performed at
the Laboratoire d’analyse e´le´mentaire de l’Universite´ de Montre´al.
Preparative Work. Biimidazole was prepared according to Fie-
selmann et al.30 and recrystallized in boiling aqueous NaOH (0.25 M).
N,N′-Dimethylbiimidazole was prepared according to Melloni et al.31
The starting materials ReOCl3(OPPh3)(Me2S) (1) and (Bu4N)[ReOCl4]
(2) were prepared by following published procedures.32,33
(38%). H NMR (CDCl3; ppm): δ 14.76 (s, 2H, N-H), 7.80 (s, 2H,
3
3
H4 or H5), 7.61 (t, 3H, JHH ) 7.4 Hz, PPh3 para), 7.44 (td, 6H, JHH
4
) 7.8 Hz, JHP ) 3.4 Hz, PPh3 meta), 7.30 (s, 2H, H5 or H4), 7.21
(dd, 6H, 3JHH ) 8.0 Hz, 3JHP ) 13.1 Hz, PPh3 ortho). 13C NMR (CDCl3;
4
ppm): δ 147.3 (s, C2), 134.0 (d, JCP ) 3.1 Hz, PPh3 para), 132.5 (s,
3
3
C4 or C5), 132.3 (d, JCP ) 11.5 Hz, PPh3 ortho), 129.2 (d, JCP
)
13.4 Hz, PPh3 meta), 125.6 (d, 1JCP ) 110.7 Hz, PPh3 ipso), 120.0 (s,
C5 or C4). 31P NMR (CDCl3; ppm): δ 46.1. IR (KBr; cm-1): 1000,
ν(RedO). Anal. Calcd for C24H21Cl3N4O2PRe: C, 39.98; N, 7.77; H,
2.94. Found: C, 39.91; N, 7.87; H, 2.92.
mer-ReOCl3(biimMe2) (6). biimMe2 (52 mg; 0.31 mmol) and 1 (200
mg; 0.31 mmol) were suspended in THF under argon, and the mixture
was stirred for 1 h at room temperature. The color changed rapidly
from light green to yellow-green. The yellow-green solid was filtered
off and washed successively with THF and diethyl ether. Yield: 111
ReOCl3(bpy). A pure yellow-green sample of the mer isomer was
obtained from 1 by the method of Bryan et al.12 1H NMR (DMSO-d6;
ppm): δ 9.08 (d, 1H, J ) 8 Hz), 8.69 (d, 1H, J ) 8 Hz), 8.57 (d, 1H,
J ) 6 Hz), 8.35 (t, 1H, J ) 8 Hz), 8.28 (d, 1H, J ) 6 Hz), 8.01(t, 1H,
J ) 6 Hz), 7.87 (t, 1H, J ) 8 Hz), 7.58 (t, 1H, J ) 6 Hz).
1
mg (76%). H NMR (DMSO-d6; ppm): δ 7.69 (d, 1H, J ≈ 1.4 Hz),
7.25 (d, 1H, J ≈ 1.4 Hz), 7.19 (d, 1H, J ≈ 1.4 Hz), 6.99 (d, 1H, J ≈
1.4 Hz), 4.61 (s, 3H), 4.41 (s, 3H). 13C NMR (DMSO-d6; ppm): δ
136.9 and 133.9 (C2, C2′), 128.5, 128.4, 128.0, and 127.8 (C4, C4′,
C5, C5′), 37.3 and 37.1 (N-CH3). 13C CP-MAS (ppm): δ 138.9 and
135.4 (C2, C2′), 129.4 (br, C4, C4′, C5, C5′), 40.8 (N-CH3). IR (KBr;
cm-1): 985 (vs), ν(RedO). Anal. Calcd for C8H10Cl3N4ORe: C, 20.41;
N, 11.90; H, 2.14. Found: C, 20.56; N, 11.46; H, 2.08. The 1H NMR
spectrum indicated that the sample contained a small amount (<5%)
of the fac isomer, which could be responsible for a weak ν(RedO) IR
band at 970 cm-1. Recrystallizing the crude product in boiling acetone
reduced the amount of the fac isomer to <3%.
The method of Chakravorti34 gave a 3:2 fac:mer mixture. 1H NMR
signals of the fac isomer (DMSO-d6; ppm): δ 9.22 (d, 2H, J ) 7.6
Hz), 8.90 (d, 2H, J ) 7.6 Hz), 8.55 (dt, 2H, J ) 6 and 1.5 Hz), ∼8.0
(2H, overlapping with a signal of the mer isomer).
ReOCl3(biimH2) (3). Biimidazole (20 mg; 0.15 mmol) was slowly
added to a yellow solution of 2 (57 mg; 0.10 mmol) in CH2Cl2 (15
mL), and the resulting mixture became bright yellow-green. After 10
min, the reaction was stopped, the mixture was filtered, and the solvent
was evaporated to near dryness, but no precipitate appeared. Complete
1
removal of the solvent afforded a green oily residue whose H NMR
spectrum indicated a 3:2 mixture of the mer and fac isomers. 1H NMR
(CDCl3; ppm): δ 14.67 (s, N-H, fac), 13.89 and 13.58 (s, N-H, mer),
7.86 and 7.47 (s, C-H, fac), 7.22, 7.05, 6.99, and 6.74 (s, C-H, mer).
[{OReCl2(biimMe2)}2(µ-O)] (7). Compound 6 (250 mg; 0.53 mmol)
was stirred in 50 mL of acetone containing 5% water for 17 h at room
temperature. The green solid was filtered off and washed successively
with acetone and diethyl ether. Yield: 18 mg (77%). IR (KBr; cm-1):
980 (m), ν(RedO); 700-740 (br, vs), ν(Re-O-Re); 1700 (m), ν(Cd
O) (acetone). 13C CP-MAS (ppm): δ 144.4 (C2, C2′), 136.0, 134.2,
and 128.5 (C4, C4′, C5, C5′), 37.4 (N-CH3), 211.5 and 33.0 (acetone).
Solution spectra could not be obtained because of the very low solubility
of 7 in common organic solvents. Anal. Calcd for C16H20Cl4N8O3Re2‚
0.5C3H6O: C, 22.96; N, 12.24; H, 2.53. Found: C, 22.78; N, 12.30;
H, 2.45.
(23) Johnson, N. P.; Taha, F. I. M.; Wilkinson, G. J. Chem. Soc. 1964,
2614.
(24) Chakravorti, M. C. J. Indian. Chem. Soc. 1970, 47, 844.
(25) Pearson, C.; Beauchamp, A. L. Acta Crystallogr. 1994, C50, 42.
(26) Alessio, E.; Hansen, L.; Iwamoto, M.; Marzilli, L. G. J. Am. Chem.
Soc. 1996, 118, 7593.
(27) Hansen, L.; Alessio, E.; Iwamoto, M.; Marzilli, P. A.; Marzilli, L. G.
Inorg. Chim. Acta 1995, 240, 413.
(28) Alessio, E.; Zangrando, E.; Iengo, E.; Macchi, M.; Marzilli, P. A.;
Marzilli, L. G. Inorg. Chem. 2000, 39, 294.
(29) Gottlieb, H. E.; Kotlyar, V.; Nudelman, A. J. Org. Chem. 1997, 62,
7512.
(30) Fieselmann, B. F.; Hendrickson, D. N.; Stucky, G. D. Inorg. Chem.
1978, 17, 2078.
(31) Melloni, P.; Dradi, E.; Logemann, W.; de Carneri, I. D.; Trane, F. J.
Med. Chem. 1972, 15, 926.
(32) Grove, D. E.; Wilkinson, G. J. Chem. Soc. A 1966, 1224.
(33) Alberto, R.; Schibli, R.; Egli, A.; Schubiger, P. A.; Herrmann, W. A.;
Artus, G.; Abram, U.; Kaden, T. A. J. Organomet. Chem. 1995, 462,
217.
[{OReCl2}2(µ-O)(µ-biimMe2)2] (8). 6 (52 mg; 0.11 mmol) was
refluxed for 17 h in 10 mL of acetone containing 1% water. A light-
blue solid was filtered off and washed successively with acetone and
diethyl ether. Yield: 30 mg (62%). IR (KBr; cm-1): 972 (w), ν(Red
O); 1700 (s), ν(CdO) (acetone). 13C CP-MAS (ppm): δ 136.0 (C2,
C2′), 132.0, 128.7, 126.4, 125.5, and 124.1 (C4, C4′, C5, C5′), 38.6
and 34.8 (N-CH3), 211.5 and 33.0 (acetone). Anal. Calcd for C16H20-
Cl4N8O3Re2‚C3H6O: C, 24.16; N, 11.86; H, 2.77. Found: C, 23.89;
N, 11.88; H, 2.64. Overnight pumping did not remove lattice acetone.
The same compound was obtained in lower yield when the reaction
was run at room temperature for 5 days.
(34) Chakravorti, M. C. J. Inorg. Nucl. Chem. 1975, 37, 1991.

4888 Inorganic Chemistry, Vol. 39, No. 21, 2000
Fortin and Beauchamp
Table 1. Crystallographic Data
5
4
8‚acetone
formula
fw
a, Å
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
Z
C24H21Cl3N4O2PRe
720.98
9.370(3)
9.573(3)
16.394(5)
86.46(2)
80.57(2)
68.69(3)
1351.5(7)
2
C60H56Cl6N8O5P2Re2
1616.23
10.323(3)
11.794(3)
13.548(4)
86.22(2)
83.63(2)
71.64(2)
1555.0(8)
1
C19H26Cl4N8O4Re2
944.70
9.802(3)
10.022(3)
15.188(4)
72.56(2)
82.77(2)
89.47(2)
1411.5(7)
2
space group
temp, °C
λ, Å
P1h (No. 2)
P1h (No. 2)
P1h (No. 2)
20
20
20
1.540 56 (Cu KR)
1.772
1.540 56 (Cu KR)
1.726
1.540 56 (Cu KR)
2.223
F
calcd, g cm-3
crystal size, mm
0.51 × 0.38 × 0.08
0.41 × 0.22 × 0.20
0.31 × 0.08 × 0.07
µ, mm-1
12.09
10.57
19.77
transm coeff
0.455-0.044
-10 e h e 11
-11 e k e 11
-19 e l e 19
0.0293
0.0816
1.121
0.292-0.102
-12 e h e 12
-14 e k e 14
-16 e l e 16
0.0554
0.1547
1.080
0.373-0.121
-11 e h 11
-12 e k e 0
-18 e l e 18
0.0370
0.0942
1.088
ranges of h, k, and l
R1a (I > 2σ(I))
wR2b (I > 2σ(I))
Sc
a R1 ) ∑(||Fo| - |Fc||/∑(|Fo|). b wR2 ) [∑w(Fo - Fc2)2/∑w(Fo )2]1/2
.
c S ) [∑w(Fo - Fc2)2]/(Nreflns - Nparams).
2
2
2
Upon refluxing in methanol for 24 h, 7 partially converted to 8.
When the turquoise solid mixture of 7 and 8 obtained by filtration was
stirred in DMSO, 8 dissolved (more readily than the above acetone
Results and Discussion
Monooxo Compounds with Bipyridine. To define prepara-
tive strategies for biimidazole compounds, methods used for
the related ligand bipyridine were tested first. Bryan et al.12
reported that bipyridine reacts cleanly with ReOCl3(OPPh3)-
(SMe2) (1) to give high yields of a ReOCl3(bpy) compound.
However, the stereochemistry was not specified. We repeated
this experiment and isolated the expected yellow-green com-
1
solvate) and insoluble 7 was removed by filtration. H and 13C NMR
spectra of 8 were recorded on DMSO-d6 solutions so obtained. 1H NMR
(DMSO-d6; ppm): δ 7.82 (s, 2H), 7.69 (s, 2H), 7.48 (s, 2H), 7.17 (s,
2H), 3.70 (s, 6H), 3.66 (s, 6H). 13C NMR (DMSO-d6; ppm): δ 136.8
(C2), 135.5 (C2′ and C4/C4′), 132.4 (C4′/C4), 124.2 and 123.2 (C5,
C5′), 35.2 and 34.4 (N-CH3).
Crystallographic Measurements and Structure Determinations.
Bright-green crystals of 5 suitable for X-ray diffraction work were
obtained from an acetone-diethyl ether mixture. Blue crystals of 4
were grown as described above. Blue crystals of 8 were obtained when
6 dissolved in acetone was left in a freezer (-15 °C) for 2 weeks. The
crystals were glued onto glass fibers and mounted on an Enraf-Nonius
CAD-4 diffractometer. In each case, low-angle spots in an axial
photograph led to a reduced triclinic cell,35 for which no higher
symmetry was detected. A half-sphere of data were collected for 8,
and whole spheres were collected for 4 and 5. These data were corrected
for absorption and averaged36 to provide basic four-octant data sets.
The structures were solved by direct methods using SHELXS-8637
and ∆F syntheses of NRCVAX38 and SHELXL-93.39 They refined
normally in the centric space group P1h. All non-hydrogen atoms were
refined anisotropically. Hydrogen atoms were placed at idealized
positions and refined as riding atoms with the following distances: C-H
0.93 (sp2 C) or 0.96 Å (methyl), N-H 0.86 Å, O-H 0.83 Å (H2O).
Their isotropic temperature factors were adjusted to 20% (sp2 C and
N) or 50% (methyl and water) above the value for the supporting atom.
The VOID routine of the PLATON software40 was used to check that
no holes large enough to contain solvent molecules remained in the
structure. Crystal data for the three compounds are collected in Table
1.
1
pound. The presence of a single species was indicated by H
NMR spectroscopy. Eight signals of equal intensity were
observed, indicating that the two rings of bipyridine are
inequivalent and the complex must be the mer isomer (A). This
was further confirmed by preliminary X-ray diffraction results.
The crystals41 were all twinned and the R factor could not be
reduced below 15%, but these results unambiguously established
that the composition and ligand arrangement about the Re center
correspond to mer-ReOCl3(bpy). Thus, since the starting
ReOCl3(OPPh3)(SMe2) complex is the trans-O,O isomer,42 the
reaction can be regarded as a simple displacement of the good
leaving ligands SMe2 and OPPh3 without rearrangement. In the
recently described [ReOMe2(bpy)]BF4 and ReOClMe2(bpy)
complexes,22 bipyridine is also coordinated with an N donor
trans to the oxo group.
(35) CAD-4 Software, Version 5.0; Enraf-Nonius: Delft, The Netherlands,
1989.
(36) Ahmed, F. R.; Hall, S. R.; Pippy, M. E.; Huber, C. P. NRC
Crystallographic Computer Programs for the IBM/360: Accession Nos.
133-147. J. Appl. Crystallogr. 1973, 6, 309.
(37) Sheldrick, G. M. SHELXS-86: Program for the Solution of Crystal
Structures; University of Go¨ttingen: Go¨ttingen, Germany, 1990.
(38) Gabe, E. J.; LePage, Y.; Charland, J. P.; Lee, F. L.; White, P. S. J.
Appl. Crystallogr. 1989, 22, 384.
Chakravorti34 isolated a ReOCl3(bpy) material when a mixture
of Re2O7 and bipyridine in HCl-ethanol was reduced with H3-
PO2. We obtained a yellow-green solid by this method starting
1
with HReO4 or KReO4. The H NMR spectra included the
(39) Sheldrick, G. M. SHELXL-93: Program for the Refinement of Crystal
Structures (Beta Test 03); University of Go¨ttingen: Go¨ttingen,
Germany, 1993.
(40) Spek, A. L. PLATON: Molecular Geometry Program; University of
Utrecht: Utrecht, The Netherlands, July 1995.
(41) Crystal data for the green crystals isolated from the reaction of ReOCl3-
(OPPh3)(SMe2) and bpy in boiling acetonitrile: orthorhombic, Fdd2;
a ) 12.627(4), b ) 21.300(7), c ) 28.927(15) Å.
(42) Abu-Omar, M. M.; Khan, S. I. Inorg. Chem. 1998, 37, 4979.

Oxorhenium(V) Complexes with 2,2′-Biimidazole
Inorganic Chemistry, Vol. 39, No. 21, 2000 4889
Scheme 1
signals of the mer isomer (40%), together with another set of
four signals (60%) for a species in which the two rings of
bipyridine are equivalent. By adding bipyridine to the NMR
tube, we verified that these signals were not due to the free
ligand. This new species is undoubtedly the fac isomer (B). All
attempts to separate these two isomers by fractional crystal-
lization failed, and chromatographic methods were ruled out
by poor solubility. When a solution of this mixture in DMSO
was left at room temperature, decomposition occurred (faster
for the fac isomer) and the free ligand appeared.
Wilkinson’s group reported the preparation of a brown
bipyridine compound from ReOCl3(PPh3)(OPPh3),43 but in our
hands, this method yielded a black material that was not further
investigated.
Monooxo Compounds with Biimidazoles. Since the pro-
cedure of Bryan et al.12 yielded the pure mer-ReOCl3(bpy)
isomer, it was used for the reactions with the biimidazole
ligands, and it gave satisfactory results.
resonances is present: a broad N-H singlet at 14.76 ppm and
sharp singlets at 7.80 and 7.30 ppm for the C-H protons. Ring
equivalence is also indicated by the 13C NMR spectrum. The
OPPh3 carbons were unambiguously assigned from 1H-13C 2D
and DEPT experiments. The ipso carbon exhibits a very strong
13C-31P coupling (1JCP ) 111 Hz), whereas ortho, meta, and
para carbons also couple to 31P with constants of 11.4, 13.5,
and 3.1 Hz, respectively.
X-ray work (see below) shows that the crystal contains the
[ReOCl2(OPPh3)(biimH2)]+ cation (C, Scheme 1), in which the
OPPh3 ligand remains trans to the RedO bond, whereas biimH2
has displaced an adjacent Cl atom and the SMe2 ligand. The
Cl- counterion is not independent of the complex cation, since
it is strongly hydrogen-bonded to the two N-H groups. Thus,
SMe2 is displaced first, as noted by Hansen et al.,27 producing
an intermediate with biimidazole coordinated in a monodentate
manner (Scheme 1). In the case of biimMe2, the following step
would be the displacement of the next best leaving group,
namely, OPPh3, to give the neutral mer complex (A). In contrast,
the monodentate intermediate with biimH2 is likely stabilized
by an intramolecular N-H‚‚‚Cl hydrogen bond, which appar-
ently enhances the capability of the Cl ligand to leave the
coordination sphere.
biimMe2 reacts with ReOCl3(OPPh3)(SMe2), giving a yellow-
green material whose microanalysis corresponds to ReOCl3-
(biimMe2). The presence of a RedO group is evidenced by the
strong IR band at 985 cm-1, in the normal range.34,44 The
featureless 31P NMR spectrum indicates that OPPh3 has been
1
Attempts to obtain ReOCl3(biimH2) from ReOCl3(OPPh3)-
(SMe2) by using higher temperatures or longer reaction times
invariably led to decomposition with precipitation of the
insoluble biimH2 ligand. Therefore, [ReOCl4]- (D) was tried
totally displaced. In the H NMR spectrum of the species in
DMSO-d6, four doublets in the aromatic region (7.0-7.7 ppm)
and two methyl singlets of triple intensity at 4.4-4.6 ppm show
that the two rings are inequivalent. This same conclusion is
reached from the 13C spectra. Thus, biimMe2 reacts according
to the same pattern as bipyridine, giving the same mer isomer
(A). However, in this case, the crude product contains a small
amount (<5%) of another species (1H NMR signals at 8.11 and
8.05 ppm for ring protons and at 4.44 ppm for the methyl group),
probably the fac isomer (B), in which the two imidazole rings
are equivalent. Besides the strong ν(RedO) band at 985 cm-1
,
as a starting species, since an empty coordination site is already
available and a single chlorine atom has to be substituted. When
the Bu4N+ salt of [ReOCl4]- was used, an oily material was
the IR spectrum shows a weak signal at 970 cm-1 assigned to
the fac isomer. Recrystallization leads to the essentially pure
mer isomer.
1
obtained and shown by H NMR to contain both the mer and
Reacting biimH2 and ReOCl3(OPPh3)(SMe2) for a few
minutes in hot CHCl3 leads to a light-green solid showing a
31P NMR signal at 46 ppm for coordinated OPPh3 and a strong
IR band for the RedO group at 1000 cm-1, a frequency ∼20
cm-1 higher than those found for other compounds containing
the OdRe-OPPh3 moiety.32,43 1H NMR signals are found for
biimH2 and OPPh3 between 7 and 8 ppm. A set of three signals
(1:2:2 intensity ratio) is assigned to the aromatic protons of
OPPh3, couplings to 31P being identified by 31P decoupling. The
ortho protons appear as a doublet of doublets, due to coupling
with 31P (13.1 Hz) and the meta protons (8.0 Hz), whereas the
meta protons show couplings with both the ortho and para
protons (7.8 Hz) and with 31P (3.4 Hz). The weaker triplet at
7.61 ppm (7.4 Hz) originates from the para protons. The two
rings of coordinated biimH2 are equivalent since a single set of
the fac isomers (3:2 ratio), despite the fact that initial attack at
the empty site across the RedO bond was hoped to favor the
mer isomer. The ν(RedO) band at 982 cm-1 is broader than
usual because both isomers are present. It proved to be
impossible to separate the two isomers and to remove the Bu4-
NCl salt produced. This may be related to the tendency of Cl-
to strongly associate with N-H groups in the [ReOCl2(OPPh3)-
(biimH2)]Cl compound mentioned above and in an oxo-bridged
dinuclear compound to be described below. Since such ion
pairing was recently shown to survive in halogenated solvents
for related Re(III)-biimH2 complexes,45 high solubility of
ReOCl3(biimH2) may be ascribed to the formation of a
[ReOCl3(biimH2)‚‚‚Cl]- adduct that cannot be precipitated with
Bu4N+. This association probably accounts for the slow
exchange of the N-H protons, which give clear signals at 14.67
ppm (fac) and at 13.89 and 13.58 ppm (mer). Dry PPh4Cl was
(43) Rouschias, G.; Wilkinson, G. J. Chem. Soc. A 1967, 993.
(44) Jezowska-Trzebiatowska, B.; Hanuza, J.; Baluka, M. Spectrochim. Acta
1971, 27A, 1753.
(45) Fortin, S.; Beauchamp, A. L. Inorg. Chem., submitted for publication.

4890 Inorganic Chemistry, Vol. 39, No. 21, 2000
Fortin and Beauchamp
space for the other equatorial ligands and leads to cis angles
greater than those in the benzimidazole complex. The OdRe-O
moiety does not deviate greatly from linearity (175.7(1)°), but
the phosphine oxide is tilted away from this direction (Re-
O-P ) 163.4(2)°). This angle is within the range 160-
165° 27,42,47,48 reported for related compounds. In the present
case, the ligand is so oriented that the C(101)-C(106) phenyl
ring is approximately parallel to biimidazole (dihedral angle )
8.6(4)°) and participates in π-stacking interactions with the
N(21)-C(25) ring (inter-ring distance ∼ 3.7 Å).
The RedO distance (1.640(3) Å) lies at the short end of the
range found for monooxo complexes (1.63-1.71 Å)49 and is
consistent with a triple-bond character.50 The Re-Cl and Re-N
distances are normal, whereas the Re-O(P) distance (2.105(3)
Å) is at the upper limit of the range (2.07-2.10 Å) reported
for other OdRe-OPPh3 complexes.27,42,47,48
The biimH2 ligand undergoes severe distortion upon chelation,
since ring closure requires that the N donors move together.
The geometry of the individual rings is not appreciably
affected,51,52 but strain develops at ring junction: the intra-ring
N3-C2-C2′ angles (117°) are reduced by 8°, whereas the
external N1-C2-C2′ angles increase (133°). Furthermore, the
metal is not coordinated exactly along the lone-pair direction:
the Re-N3-C2 angles in the chelate ring (114°) differ
considerably from the Re-N3-C4 angles outside (139°).
Although the two independent imidazole rings remain individu-
ally planar, the molecule is bent slightly about the C2-C2′ bond,
leading to a dihedral angle of 6.7(4)° between these rings. The
metal atom lies within 0.05 Å from the imidazole planes.
The Cl- counterion forms strong hydrogen bonds with the
two N-H groups of coordinated biimH2. The Cl‚‚‚N distances
(N(11)-Cl(3) ) 3.067(5), N(21)-Cl(3) ) 3.112(5) Å) are in
the accepted range (2.91-3.53 Å),53 and the hydrogen bonds
do not deviate much from linearity (N-H-Cl ∼ 151°). The
rest of the environment of Cl- consists of weaker normal van
der Waals contacts. Therefore, the structure is best described
as a tight [ReOCl2(OPPh3)(biimH2)]+‚‚‚Cl- ion pair, and
considering the high solubility of this ionic compound in CHCl3,
CH2Cl2, and acetone, this ion pair probably survives in solution,
as recently observed for related biimH2 compounds.45
Figure 1. ORTEP drawing of [ReOCl2(OPPh3)(biimH2)]Cl (5). El-
lipsoids correspond to 40% probability. Dashed lines represent hydrogen
bonds with the chloride ion.
Table 2. Selected Bond Lengths (Å) and Angles (deg) for
Compound 5
Re-O(1)
Re-N(23)
Re-Cl(1)
P-O(2)
1.640(3)
2.084(3)
2.3478(13)
1.509(3)
3.112(5)
Re-O(2)
2.105(3)
2.107(3)
2.3518(12)
3.067(5)
Re-N(13)
Re-Cl(2)
N(11)-Cl(3)
N(21)-Cl(3)
O(1)-Re-O(2)
O(1)-Re-N(13)
O(1)-Re-N(23)
O(1)-Re-Cl(1)
O(1)-Re-Cl(2)
O(2)-Re-N(23)
O(2)-Re-N(13)
O(2)-Re-Cl(1)
Re-N(13)-C(12)
Re-N(13)-C(14)
175.74(14) O(2)-Re-Cl(2)
85.73(8)
93.30(10)
164.28(10)
78.42(14)
165.12(10)
92.49(10)
92.60(5)
163.4(2)
114.3(3)
138.5(3)
96.0(2)
95.0(2)
N(13)-Re-Cl(1)
N(13)-Re-Cl(2)
98.18(14) N(13)-Re-N(23)
97.55(13) N(23)-Re-Cl(1)
82.09(13) N(23)-Re-Cl(2)
80.38(12) Cl(1)-Re-Cl(2)
84.35(9) Re-O(2)-P
113.5(3)
139.8(4)
Re-N(23)-C(22)
Re-N(23)-C(24)
N(21)-C(22)-C(12) 132.7(4)
N(23)-C(22)-C(12) 116.8(4)
N(21)-H(21)-Cl(3) 151
N(11)-C(12)-C(22) 132.4(4)
N(13)-C(12)-C(22) 116.8(4)
N(11)-H(11)-Cl(3) 153
added to induce crystallization, and a solid was isolated. The
N-H protons appear at the same positions as above for the
two isomers of ReOCl3(biimH2). The C-H resonances are
partially masked by the strong peaks of PPh4+, whose integra-
tions indicate that free PPh4Cl has coprecipitated.
Crystal Structure of 5. The unit cell contains the structural
unit shown in Figure 1, which consists of a distorted octahedral
[ReOCl2(OPPh3)(biimH2)]+ cation and a Cl- counterion hydrogen-
bonded to the N-H groups of biimH2. The OPPh3 ligand lies
trans to the oxo ligand along the axial direction, whereas the
chelating bidentate biimH2 ligand and two cis Cl atoms occupy
the equatorial plane. Selected distances and angles are listed in
Table 2.
Oxo-Bridged Dinuclear Compounds. Wilkinson et al.23 first
prepared Re2O3Cl4(bpy)2 from ReCl5 and bpy in acetone. Guest
and Lock54 obtained the same material by refluxing ReOCl3-
(bpy) in ethanol. The stereochemistry was postulated to be that
of the Re2O3Cl4(py)4 analogue, that is, to consist of a linear
OdRe-O-RedO backbone with perpendicular cis-dichloro-
bipyridine planes (E). In our hands, hydrolysis of ReOCl3(bpy)
As often observed in monooxo systems, the equatorial ligands
are displaced away from the RedO group: the L-Re-O(P)
angles are in the 80-86° range and the OdRe-L angles lie
between 95 and 98°, the chlorines being slightly more displaced
than the nitrogen donors, as noted for ReOCl3(OPPh3)(Me3-
benzimidazole).27 The small bite angle (78.4(1)°) of biimH2,
similar to those found in other Re compounds,45,46 leaves more
in wet acetone afforded a green solid, whose 1H NMR spectrum
showed a single set of bpy signals, consistent with the above
assumption.
(46) Be´langer, S.; Beauchamp, A. L. Acta Crystallogr. 1999, C55, 517.
(47) Bryan, J. C.; Perry, M. C.; Arterburn, J. B. Acta Crystallogr. 1998,
C54, 1607.
(48) Rose, D. J.; Maresca, K. P.; Kettler, P. B.; Chang, Y. D.; Soghomo-
mian, V.; Chen, Q.; Abrams, M. J.; Larsen, S. K.; Zubieta, J. Inorg.
Chem. 1996, 35, 3548.
(49) Mayer, J. M.; Thorn, D. L.; Tulip, T. H. J. Am. Chem. Soc. 1985,
107, 7454.
(50) Nugent, W. A.; Mayer, J. M. Metal-ligand Multiple Bonds; John Wiley
& Sons: New York, 1987.
(51) Cromer, D. T.; Ryan, R. R.; Storm, C. B. Acta Crystallogr. 1987,
C43, 1435.

Oxorhenium(V) Complexes with 2,2′-Biimidazole
Inorganic Chemistry, Vol. 39, No. 21, 2000 4891
Hydrolysis of ReOCl3(biimMe2) is not so simple. Refluxing
in acetone containing 5% water yields a green material (7),
which likely corresponds to the oxo-bridged bipyridine analogue.
Its IR spectrum is typical of such oxo-bridged dimers:10
a
medium absorption at ∼975 cm-1 attributed to the terminal oxo
stretch and a very strong and broad band at ∼700 cm-1 for the
Re-O-Re stretch. Our frequency is slightly higher, but the
shape is identical with the one described by Cotton et al.55 for
cis,cis-Re2O3Cl4(py)4. Lattice acetone gives rise to a medium
CdO stretching band at 1700 cm-1. Solution NMR spectra
could not be obtained because of the poor solubility of 7 in all
common solvents, but the simplicity of the 13C CP-MAS
spectrum is consistent with the relatively high symmetry
expected for a [{OReCl2(biimMe2)}2(µ-O)] species.
When ReOCl3(biimMe2) is refluxed in acetone containing less
water (1%), a different light-blue compound (8) is obtained,
whose microanalysis corresponds to the same stoichiometry as
above. Besides the absorptions due to biimMe2, this material
shows a RedO band, weaker than above, at 972 cm-1, but no
Re-O-Re absorption in the 700-740 cm-1 range. The intensity
of the acetone band at 1700 cm-1 is approximately twice as
high as that for 7, in agreement with elemental analysis. In
DMSO-d6, four 1H NMR signals are observed for C-H protons
and two for the methyl groups of biimMe2. Coupling constants
(3JHH) of 1.6 Hz are found for the aromatic signals. These data
are consistent with two types of imidazole rings. The 13C results
lead to the same conclusion.
Figure 2. ORTEP drawing of the [{OReCl2(biimH2‚‚‚Cl)}2O]2- units
in 4. The bridging O(2) atom lies on a crystallographic inversion center.
The PPh4 ions and lattice water molecules are not shown. Ellipsoids
correspond to 40% probability. Dashed lines represent hydrogen bonds
with the chloride ions.
+
Table 3. Selected Bond Lengths (Å) and Angles (deg) for
Compound 4
Re(1)-O(1)
Re(1)-N(13)
Re(1)-Cl(1)
1.693(5)
2.109(6)
2.408(2)
Re(1)-O(2)
Re(1)-N(23)
Re(1)-Cl(2)
1.9047(6)
2.138(6)
2.386(2)
O(1)-Re(1)-O(2)
O(1)-Re(1)-N(13)
O(1)-Re(1)-N(23)
O(1)-Re(1)-Cl(1)
O(1)-Re(1)-Cl(2)
O(2)-Re(1)-N(13)
O(2)-Re(1)-N(23)
O(2)-Re(1)-Cl(1)
Re-N(13)-C(12)
Re-N(13)-C(14)
173.6(2) O(2)-Re(1)-Cl(2)
89.21(5)
92.1(3) N(13)-Re(1)-N(23) 77.2(2)
91.1(3) N(13)-Re(1)-Cl(1) 170.1(2)
95.2(2) N(13)-Re(1)-Cl(2)
95.7(2) N(23)-Re(1)-Cl(1)
83.2(2) N(23)-Re(1)-Cl(2) 170.5(2)
83.5(2) Cl(2)-Re(1)-Cl(1)
88.93(5) Re(1)-O(2)-Re(2)
115.0(5) Re-N(23)-C(22)
139.0(5) Re-N(23)-C(24)
96.0(2)
96.1(2)
The crystallographic work described hereafter shows that the
latter compound contains the OdRe-O-RedO backbone and
cis-ReCl2N2 planes perpendicular to this direction, but this time,
the biimidazole ligands are bridging the two Re centers (F).
89.86(7)
180.0
113.1(5)
139.6(5)
N(13)-C(12)-C(22) 116.7(6) N(23)-C(22)-C(12) 117.5(6)
N(11)-C(12)-C(22) 131.6(7) N(21)-C(22)-C(12) 131.4(7)
taining chelating biimH2, which was isolated as the bisadduct
(PPh4)2[{OReCl2(biimH2)‚‚‚Cl}2(µ-O)]‚2H2O.
Crystal Structure of 4. This compound contains the oxo-
bridged dinuclear species [{OReCl2(biimH2)}2(µ-O)] with a
linear OdRe-O-RedO backbone (Figure 2) similar to those
of the [{OReCl2(py)2}2(µ-O)] compound studied by Lock and
Turner56 and related systems. The unit cell also contains two
This [{OReCl2}2(µ-O)(µ-biimMe2)2] species possesses a 2-fold
axis through the bridging oxo ligand, making the two biimMe2
ligands equivalent, in agreement with the NMR data.
Compound 8 seems to be the thermodynamic compound,
since refluxing the chelate complex 7 in methanol leads to 8
instead of the expected oxo-methoxo compound ReO(OMe)-
Cl2(N-N).10
+
Cl- and two PPh4 ions per dinuclear molecule. As observed
above, a Cl- ion is hydrogen-bonded to the N-H groups of
each biimH2 ligand. Therefore, the structure is best described
+
as the bis-PPh4 salt of the tightly associated [{OReCl2-
(biimH2‚‚‚Cl)}2(µ-O)]2- unit. Selected distances and angles are
listed in Table 3.
Hydrolysis experiments were not run on the nonmethylated
complex ReOCl3(biimH2) because it had been obtained only as
an oily mixture of the mer and fac isomers. However, an oxo-
bridged species was isolated when recrystallization of the
ReOCl3(biimH2) mixture was attempted in the presence of moist
PPh4Cl. Since the structure of 5 indicated a high affinity of Cl-
for the N-H groups of coordinated biimH2, we hoped a
[ReOCl3(biimH2)‚‚‚Cl]- adduct could form and precipitate as
Deviation from linearity in the OdRe-O-RedO backbone
is small. The halves of the molecule are related by a crystal-
lographic inversion center. Therefore, the Re-O-Re angle is
exactly 180° and the two O-RedO angles are equal (173.6-
(2)°). As usual, the donor atoms in the ReCl2N2 plane are
repelled by the RedO group, but the deviation from 90° is ∼3°
less here than in the monomeric complex 5. The RedO and
Re-O distances of 1.693(5) and 1.905(1) Å are typical of this
backbone.10,25,56
The particularities of chelated biimidazole mentioned above
are observed here as well: bite angle of 77.2(2)°, strain at ring
junction (intra-ring N3-C2-C2′ angles ∼15° greater than
external N1-C2-C2′ angles), and coordination off the lone-
pair direction (Re-N3-C2 angles in the chelate ring ∼15°
+
the PPh4 salt. Chloride association with N-H groups indeed
occurred, but the water introduced with PPh4Cl converted
ReOCl3(biimH2) to an oxo-bridged dinuclear compound con-
(52) Therrien, B.; Beauchamp, A. L. Acta Crystallogr. 1999, C55,
IUC9900054.
(53) Stout, G. H.; Jensen, L. H. X-ray Structure Determination: A Practical
Guide; Macmillan: New York, 1968.
(54) Guest, A.; Lock, C. J. L. Can. J. Chem. 1971, 49, 603.
(55) Cotton, F. A.; Robinson, W. R.; Walton, R. A. Inorg. Chem. 1967, 6,
223.
(56) Lock, C. J. L.; Turner, G. Can. J. Chem. 1978, 56, 179.

4892 Inorganic Chemistry, Vol. 39, No. 21, 2000
Fortin and Beauchamp
Table 4. Selected Bond Lengths (Å), Bond Angles (deg), and
Torsion Angles (deg) for Compound 8
Re(1)-O(1)
Re(1)-O(2)
Re(1)-N(13)
Re(1)-N(23)
Re(1)-Cl(1)
Re(1)-Cl(2)
1.685(5)
1.894(5)
2.144(7)
2.127(6)
2.373(2)
2.389(2)
Re(2)-O(3)
Re(2)-O(2)
Re(2)-N(33)
Re(2)-N(43)
Re(2)-Cl(3)
Re(2)-Cl(4)
1.681(6)
1.897(5)
2.131(6)
2.170(6)
2.370(2)
2.372(2)
O(1)-Re(1)-O(2)
O(1)-Re(1)-N(13)
O(1)-Re(1)-N(23)
O(1)-Re(1)-Cl(1)
O(1)-Re(1)-Cl(2)
O(2)-Re(1)-N(13)
O(2)-Re(1)-N(23)
O(2)-Re(1)-Cl(1)
O(2)-Re(1)-Cl(2)
N(23)-Re(1)-N(13)
N(23)-Re(1)-Cl(1)
N(13)-Re(1)-Cl(2)
Cl(1)-Re(1)-Cl(2)
Cl(1)-Re(1)-N(13)
Cl(2)-Re(1)-N(23)
Re(1)-O(2)-Re(2)
Re-N(13)-C(12)
Re-N(13)-C(14)
Re-N(23)-C(22)
Re-N(23)-C(24)
168.2(2)
90.0(3)
87.5(2)
98.3(2)
96.8(2)
81.1(2)
84.7(2)
90.5(2)
91.1(2)
90.3(2)
88.8(2)
90.0(2)
O(3)-Re(2)-O(2)
O(3)-Re(2)-N(33)
O(3)-Re(2)-N(43)
O(3)-Re(2)-Cl(3)
O(3)-Re(2)-Cl(4)
O(2)-Re(2)-N(33)
O(2)-Re(2)-N(43)
O(2)-Re(2)-Cl(3)
O(2)-Re(2)-Cl(4)
N(33)-Re(2)-N(43)
N(33)-Re(2)-Cl(4)
N(43)-Re(2)-Cl(3)
166.0(2)
86.3(3)
90.0(3)
97.4(2)
98.9(2)
83.9(2)
80.3(2)
92.6(2)
90.8(2)
91.5(2)
88.7(2)
89.3(2)
89.98(8)
176.3(2)
171.0(2)
Figure 3. ORTEP drawing of the [{OReCl2}2(µ-O)(µ-biimMe2)2]
molecule (8) in the acetone solvate. Ellipsoids correspond to 40%
probability. Hydrogens are omitted for clarity.
90.36(8) Cl(3)-Re(2)-Cl(4)
171.6(2)
175.7(2)
162.6(3)
128.5(5)
126.0(5)
129.6(5)
123.5(5)
Cl(3)-Re(2)-N(33)
Cl(4)-Re(2)-N(43)
greater than the Re-N3-C4 angles outside). The two imidazole
rings show a dihedral angle of 6.8°, and the Re atom is only
0.104 and 0.039 Å out of the imidazole planes.
Re-N(33)-C(32)
Re-N(33)-C(34)
Re-N(43)-C(42)
Re-N(43)-C(44)
N(31)-C(32)-C(12) 122.1(7)
N(33)-C(32)-C(12) 128.0(7)
N(41)-C(42)-C(22) 122.1(7)
N(43)-C(42)-C(22) 128.4(7)
131.1(5)
123.7(5)
129.3(5)
123.7(5)
In contrast to the case of [{OReCl2(py)2}2(µ-O)]10,56 and
related systems with monodentate N ligands,25,28 the biimH2
ligand must be perpendicular to the backbone. The halves of
the molecule being related by a crystallographic inversion center
at the central µ-oxo ligand, the two biimidazole ligands are on
opposite sides and show no stacking interactions. The distances
of the Cl atoms of one unit to the biimidazole plane in the other
unit are 3.70 (Cl(1)) and 3.64 Å (Cl(2)), that is, roughly equal
to the sum of the van der Waals radii.57
N(11)-C(12)-C(32) 120.3(7)
N(13)-C(12)-C(32) 129.4(7)
N(21)-C(22)-C(42) 122.7(7)
N(23)-C(22)-C(42) 128.6(6)
N(11)-C(12)-C(32)-N(31)
N(13)-C(12)-C(32)-N(33)
N(23)-C(22)-C(42)-N(43)
N(21)-C(22)-C(42)-N(41)
56.2(11)
65.3(12)
64.3(12)
60.9(10)
The strong affinity of the Cl- anion for the N-H groups of
coordinated biimH2 has been noted above and elsewhere.45,46
The chloride ion is attached to biimidazole through two
moderately strong hydrogen bonds: N(11)‚‚‚Cl(5) ) 3.216(8)
Å; N(21)‚‚‚Cl(5) ) 3.040(7) Å; N-H-Cl angle ∼153°. The
lattice also includes one water molecule per Cl- ion, which is
hydrogen-bonded to this anion (O(4)‚‚‚Cl(5) ) 3.149(8) Å;
O-H-Cl ) 169°) and to a coordinated Cl atom (O(4)‚‚‚Cl(1)
Re-Lcis angles are, on average, ∼6° greater than the corre-
sponding Lcis-Re-O angles. Thus, by trading a chelating for
a bridging role, the biimidazole units introduce some strain in
the dimer, especially in the backbone. However, from the
standpoint of the biimidazole moiety, coordination takes place
more “naturally”: the Re-N-C angles inside and outside the
chelate ring now differ by only ∼4°, and they are close to those
observed for imidazole or benzimidazole dioxo complexes.4,58
Similarly, strain at the ring junction is reduced: the internal
and external angles at C2 differ by only ∼6.3°. However, less
energy-costly distortions appear elsewhere. The two imidazole
rings in the ligands are not coplanar: rotation about the C2-
C2′ bonds generates a dihedral angle of ∼62°. The two ReCl2N2
units are rotated by ∼50° from the eclipsed conformation, which
allows the bridging biimidazoles to interact by π stacking via
rings N(21)-C(25) and N(31)-C(35): these planes are almost
parallel (dihedral angle ) 11.3(5)°), and the distance between
the ring centers is 3.3 Å.
Structural Differences between the biimH2 and bpy
Ligands. Although ReOCl3(N-N) and [{OReCl2(N-N)}2(µ-
O)] compounds are formed by both biimidazole and bipyridine,
these two ligands exhibit major structural differences due to
the sizes of their respective aromatic rings. In idealized
bipyridine, the lone-pair directions meet at ∼2.8 Å from the N
donors, which is not drastically greater than a normal Re-N
distance (∼2.10 Å). A chelate ring can form with minimal
distortion: the C-C-N angles at the ring junction remain close
to 120° (θ ∼ 116°, θ′ ∼ 124°), and the metal lies only 3-4°
off the lone-pair direction (φ ∼ 116°, φ′ ∼ 124°), whereas the
small bite angle â (∼75°) is accommodated readily in an
+
) 3.279(9) Å; O-H-Cl ) 179°). PPh4 simply acts as a
counterion without particular interactions with the rest of the
structure.
Crystal Structure of 8. The molecule (Figure 3) contains
an OdRe-O-RedO backbone, and an equatorial set of Cl2N2
donors is found about each Re atom. In contrast with 4, the
two biimMe2 ligands are bridging and the OdRe-O-RedO
unit is bent at the center. Selected distances and angles are given
in Table 4.
The rhenium-oxygen bonds do not differ greatly from those
found in 4, but the Re-Cl bonds are, on average, ∼0.020 Å
shorter, whereas the Re-N bonds are ∼0.020 Å longer.
Departure from linearity in the OdRe-O-RedO backbone is
unusually large: the central Re-O-Re unit is bent to 162.6-
(3)° and the OdRe-O angles average 167.1°. On the other
hand, the cis angles in the ReCl2N2 planes are close to ideality
(88.7-91.5°): the N-Re-N angle, which was imposed (77°)
by the chelate ring in 4 and 5, has now returned to the normal
∼91° value, without introducing appreciable changes in the Cl-
Re-Cl angles (∼90.2°). A general displacement of the cis
ligands away from the RedO bond is noted, as usual: the Od
(57) Huheey, J. E.; Keiter, R. L.; Keiter, E. A. Inorganic Chemistry:
Principles of Structure and ReactiVity, 4th ed.; HarperCollins: New
York, 1993; p 292.
(58) Be´langer, S.; Fortin, S.; Beauchamp, A. L. Can. J. Chem. 1997, 75,
37.

Oxorhenium(V) Complexes with 2,2′-Biimidazole
Inorganic Chemistry, Vol. 39, No. 21, 2000 4893
is bridging: the differences between the angles inside and
outside the chelate rings are now only 5° at N3 and 6° at C2.
In bridging biimMe2, the rings are no longer coplanar, which
suggests that breaking the resonance between the two aromatic
systems is not energy costly.
Concluding Remarks
Synthetic work with nonmethylated biimidazole (biimH2) is
hampered by the very low solubility of this ligand, which can
be ascribed to extended stacking interactions and efficient
N-H‚‚‚N hydrogen bonding in the crystal.51 Unreacted ligand
is difficult to remove; compounds initially formed tend to
decompose when the reaction is pursued or redissolution is
attempted for purification. On the other hand, short reaction
times lead to [ReOCl2(OPPh3)(biimH2)]Cl, in which strong ion
pairing is observed to take place via N-H‚‚‚Cl- hydrogen
bonding. Chloride association also allows isolation of the oxo-
bridged complex [{OReCl2(biimH2)}2(µ-O)] as the bis-PPh4Cl
octahedral environment.59 For an idealized biimidazole unit, the
lone-pair directions converge at a much greater distance (4.9
Å), so that severe distortion is required to close the ring. In the
structures above and that of [{ORe(biimH2)2}2(µ-O)]Cl4,46 the
intra-ring angles θ at the connecting C2-C2′ bonds have
reduced from 125 to 117° to bring the N donors closer.
Furthermore, the Re-N vector deviates by 13° from the lone-
pair direction (φ ∼ 115°, φ′ ∼ 140°). However, in the case of
methylated biimidazole, which normally exists as the anti
conformer52 but is forced into a syn arrangement in the chelate,
distortion moves the methyl groups apart, thereby reducing steric
hindrance.
+
adduct, which is best described as the PPh4 salt of the
[{OReCl2(biimH2‚‚‚Cl)}2(µ-O)]2- unit. This type of interaction
seems to exist whenever halide ions are present45,46,60 and
apparently has an important, although yet unpredictable, role.
We believe the solubility of ReOCl3(biimH2), much higher than
thatofReOCl3(biimMe2),isduetoanassociated[ReOCl3(biimH2‚‚‚Cl)]-
species that cannot be precipitated by Bu4N+. Therefore, the
strong tendency of coordinated biimH2 to form hydrogen bonds
should be taken into account in devising strategies for preparing
clean materials.
In contrast to bipyridine, biimMe2 forms two isomeric oxo-
bridged dinuclear compounds: the standard single-bridge
[{OReCl2(biimMe2)}2(µ-O)] molecule (E), containing chelated
biimMe2, and the triple-bridge [{OReCl2}2(µ-O)(µ-biimMe2)2]
species (F), in which both biimMe2 ligands are bridging. The
latter is apparently the more stable, since it forms instead of
the expected alkoxo compound ReO(OMe)Cl2(biimMe2) when
the single-bridge complex is refluxed in methanol. By comparing
structures 4 and 8, we note that the distortions pointed out earlier
for chelated biimidazole are appreciably reduced when the ligand
Acknowledgment. We thank J. Labelle for the preparation
of biimMe2 and F. Be´langer-Garie´py, S. Be´langer, and M.
Simard for assistance with the X-ray diffraction studies.
Financial support from the Natural Sciences and Engineering
Research Council of Canada is also gratefully acknowledged.
Supporting Information Available: X-ray crystallographic files
in CIF format for 4, 5, and 8. This material is available free of charge
via the Internet at http://pubs.acs.org.
(59) Based on nine crystal structures of Re-bipyridine compounds.
Cambridge Structural Database, Version 5.18; Cambridge Univer-
sity: Cambridge, England (accessed Oct 1999).
(60) Be´langer, S.; Beauchamp, A. L. Acta Crystallogr. 1996, C52, 2588.
IC000328T