Rhenium(IV) and rhenium(V) complexes with 3,5-dimethylpyrazole

Article abstract of DOI:10.1007/s11172-006-0214-2

Mono- and dinuclear Re^IV and Re^V complexes with 3,5-dimethylpyrazole (Me₂pzH) were synthesized. The cis-[Re ₂O₃Cl₄(3,5-Me₂pzH)₄] complex (cis-1) was prepared by the reaction of NH₄ReO₄ with K[HB(Me₂pz)₃] in concentrated HCl or by refluxing of [ReCl₃(MeCN)(PPh₃)₂] with Me₂pzH in air. The bromide complex trans-[Re₂O₃Br ₄(3,5-Me₂pzH)₄] (trans-2) was synthesized by passing dry HBr through a solution of [Re₂O₃Br ₂(μ-3,5-Me₂pz)₂(3,5-Me₂pzH) ₂] (4) in chloroform. The pyrazolate-bridged complex [Re ₂O₃Cl₂(μ-3,5-Me₂pz) ₂(3,5-Me₂pzH)₂] (3) was prepared from (Et ₄N)₂[ReOCl₅] or Cs₂[ReOCl ₅] and Me₂pzH. The corresponding bromide and iodide complexes [Re₂O₃X₂(3,5-Me₂pz) ₂(3,5-Me₂pzH)₂] ? C₆H ₆ (X = Br (4) or I (5)) were synthesized by the reactions of (NH ₄)₂[ReBr₆] or K₂[ReI₆], respectively, with Me₂pzH. The [ReO(OMe)(3,5-Me₂pzH) ₄]Br₂ ? ? 3,5-Me₂pzH ? 4H ₂O complex (6) was obtained as a by-product in the synthesis of complex 4. The reaction of [ReNCl₂(PPh₃)₂] with Me₂pzH was accompanied by hydrolytic denitration giving rise to the mixed-ligand complex [Re₂O₃Cl₂(μ-3,5-Me ₂pz)₂(3,5-Me₂pzH)(PPh₃)] (7). The reaction of (NH₄)₂[ReBr₆] with a Me ₂pzH melt gave the trans-[ReBr₄(3,5-Me₂pzH) ₂] ? ? Me₂CO complex (8). The structures of complexes 2 and 4-8 were established by X-ray diffraction. All compounds were characterized by elemental analysis, electronic absorption spectroscopy, ¹H NMR and IR spectroscopy, mass spectrometry, and cyclic voltammetry.

Full text of DOI:10.1007/s11172-006-0214-2

Russian Chemical Bulletin, International Edition, Vol. 55, No. 1, pp. 53—61, January, 2006
53
Rhenium(IV) and rhenium(V) complexes with 3,5ꢀdimethylpyrazole
M. N. Sokolov,aꢀ N. E. Fedorova, N. V. Pervukhina, E. V. Peresypkina,
a,b
a
a
a
b
a
b
A. V. Virovets, R. Pätow, V. E. Fedorov, and D. Fenske
aA. V. Nikolaev Institute of Inorganic Chemistry, Siberian Branch of the Russian Academy of Sciences,
3
prosp. Akad. Lavrentieva, 630090 Novosibirsk, Russian Federation.
Fax: +7 (3832) 334 4489. Eꢀmail: caesar@che.nsk.su
b
Institute of Inorganic Chemistry, University of Karlsruhe, Engesser str. 30.45, 76128, Karlsruhe, Germany*
Monoꢀ and dinuclear ReIV and Re complexes with 3,5ꢀdimethylpyrazole (Me pzH) were
V
2
synthesized. The cisꢀ[Re O Cl (3,5ꢀMe pzH) ] complex (cisꢀ1) was prepared by the reaction
2
3
4
2
4
of NH ReO4 with K[HB(Me pz) ] in concentrated HCl or by refluxing of
4
2
3
[
ReCl (MeCN)(PPh ) ] with Me pzH in air. The bromide complex transꢀ[Re O Br (3,5ꢀ
3 3 2 2 2 3 4
Me pzH) ] (transꢀ2) was synthesized by passing dry HBr through a solution of
2
4
[
[
Re O Br (µꢀ3,5ꢀMe pz) (3,5ꢀMe pzH) ] (4) in chloroform. The pyrazolateꢀbridged complex
2 3 2 2 2 2 2
Re O Cl (µꢀ3,5ꢀMe pz) (3,5ꢀMe pzH) ] (3) was prepared from (Et N) [ReOCl ] or
2
3
2
2
2
2
2
4
2
5
Cs [ReOCl ] and Me pzH. The corresponding bromide and iodide complexes [Re O X (3,5ꢀ
2
5
2
2
3 2
Me pz) (3,5ꢀMe pzH) ]•C H (X = Br (4) or I (5)) were synthesized by the reactions of
2
2
2
2
6
6
(
NH ) [ReBr ] or K [ReI ], respectively, with Me pzH. The [ReO(OMe)(3,5ꢀMe pzH) ]Br •
4 2 6 2 6 2 2 4 2
•
3,5ꢀMe pzH•4H O complex (6) was obtained as a byꢀproduct in the synthesis of complex 4.
2 2
The reaction of [ReNCl (PPh ) ] with Me pzH was accompanied by hydrolytic denitration
2
3 2
2
giving rise to the mixedꢀligand complex [Re O Cl (µꢀ3,5ꢀMe pz) (3,5ꢀMe pzH)(PPh )] (7).
2
3
2
2
2
2
3
The reaction of (NH ) [ReBr ] with a Me pzH melt gave the transꢀ[ReBr (3,5ꢀMe pzH) ]•
4
2
6
2
4
2
2
•
Me CO complex (8). The structures of complexes 2 and 4—8 were established by Xꢀray
2
diffraction. All compounds were characterized by elemental analysis, electronic absorption
1
spectroscopy, H NMR and IR spectroscopy, mass spectrometry, and cyclic voltammetry.
Key words: rhenium; 3,5ꢀdimethylpyrazole; oxo complexes; structure.
Coordination chemistry of rhenium has been extenꢀ
sively developed in recent years due, to a large extent, to
Experimental
All reactions were carried out in air in organic solꢀ
vents, which were purified according to standard proceꢀ
dures. Commercial reagents were used without additional puriꢀ
fication.
The IR spectra (4000—400 cm–1) were measured on a Bruker
IFSꢀ85 Fourierꢀtransform spectrometer in KBr pellets. The
NMR spectra were recorded on a Bruker AC 250 spectrometer
(250.13 MHz for H and 101.26 MHz for P) with the use of
Me Si and 85% H PO as the external standard. The electronic
absorption spectra were measured on a Shimadzu UV 2101 PC
instrument. The FAB mass spectra were obtained on a Finnigan
MS 8230 instrument. Cyclic voltammetry experiments were
the fact that shortꢀlived rhenium isotopes hold promise as
βꢀemitters in radiotherapy.1
—3
Rhenium complexes with
amines and derivatives of pyridine and imidazole are used
for studying electron transfer, oxygen atom transfer,
electrocatalysis, luminescence, and fluorescence.4—8
Complexes with nitroimidazoles and nitropyrazoles have
found application as markers for hypoxic tumor cells.9,10
These aspects of the chemistry of rhenium complexes
with pyridine and imidazole derivatives have been studied
1
31
4
3
4
in depth.1
1—20
Coordination compounds of rhenium with
other heterocyclic ligands, such as pyrazoles and triazoles,
carried out on
EG&G INSTRUMENTS) instrument with the use of the
Ag/AgCl electrode and 0.1 M Bu NClO as the supporting elecꢀ
a Potentiostat/Galvanostat Model 263
have received attention only recently.2
1—28
Rhenium comꢀ
(
plexes with poly(pyrazolyl)borates were studied in deꢀ
4
4
2
9
tail. The first structurally characterized rhenium comꢀ
plex with the pyrazole ligand, [Re O Cl (3,5ꢀMe pzH) ]•
trolyte. Under these conditions, the potential of the standard
Fc /Fc pair is 0.44 V. Thermogravimetric analysis was perꢀ
+
2
3
4
2
4
V
•
(CH ) CO, was isolated in attempting to synthesize Re
complexes with [HB(3,5ꢀMe pz) ] . The aim of the
present study was to investigate the reactions of Re , Re ,
and Re complexes with 3,5ꢀdimethylpyrazole.
formed on a TA 7000 instrument. Elemental analyses were
carried out in the Laboratory of Microanalysis of the
N. N. Vorozhtsov Institute of Organic Chemistry of the Siberian
Branch of the Russian Academy of Sciences (Novosibirsk).
The starting compounds [ReCl (CH CN)(PPh ) ],
3
2
–
10
2
3
V
IV
III
3
3
3 2
*
Institüt für Anorganishe Chemie, Universität Karlsruhe,
(Et N) [ReOCl ],
Cs [ReOCl ],
[ReNCl (PPh ) ],
4
2
5
2
5
2 3 2
Engesserstraße Geb. 30.45, 76128 Karlsruhe, Germany.
(NH ) ReBr , and K ReI were synthesized according to
4
2
6
2
6
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 52—59, January, 2006.
066ꢀ5285/06/5501ꢀ0053 © 2006 Springer Science+Business Media, Inc.
1

54
Russ.Chem.Bull., Int.Ed., Vol. 55, No. 1, January, 2006
Sokolov et al.
known procedures. 3,5ꢀDimethylpyrazole (3,5ꢀMe pzH) and
(Re—O—Re), 480 m, 444 m. FABꢀMS: m/z (I (%)): 874
2
rel
+
+
+
K[HB(3,5ꢀMe pz) ] were purchased from Aldrich.
(28) [M] , 840 (29) [M – Cl] , 774 (14) [M – 3,5ꢀMe pzH] ,
2
2
3
+
1
Xꢀray diffraction study. Xꢀray diffraction data sets were colꢀ
lected on Stoe IPDS1 (for 4), Stoe IPDS2 (for transꢀ2, 7, and 8),
and Nonius CADꢀ4 (for 5) diffractometers (MoKα radiation,
λ = 0.71073 Å). The structures were solved by direct methods
and refined anisotropically by the fullꢀmatrix leastꢀsquares
method against |F |2 using the SHELXTL program package.45
The positions of the hydrogen atoms were calculated geometriꢀ
cally. For compounds transꢀ2, 4, 7, and 8, empirical absorption
corrections were applied. The absorption correction for comꢀ
pound 5 was applied by the ψꢀscan method. The crystallographic
data were deposited with the Cambridge Structural Database
682 (40) [M – 2 (3,5ꢀMe pzH)] . H NMR (CDCl ), δ: 2.19,
2
3
2.43, 2.73, and 2.83 (all s, 6 H each, CH ); 5.83 and 6.03
3
(both s, 2 H each, CH).
Bis(3,5ꢀdimethylpyrazole)bis(µ-dimethylpyrazolato)trioxoꢀ
dibromodirhenium(V) benzene monosolvate, Re O Br (µꢀ3,5ꢀ
2
3
2
Me pz) (3,5ꢀMe pzH) •C H (4). A mixture of (NH ) ReBr
2
2
2
2
6
6
4 2
6
(200 mg, 0.29 mmol) and 3,5ꢀdimethylpyrazole (240 mg,
2.5 mmol) (or K[HB(Me pz) ] (98 mg, 0.29 mmol)) in methaꢀ
2
3
nol (30 mL) was refluxed for 4 h. The brown solution was filꢀ
tered and slowly concentrated. After several days, the green
crystals of complex 4 that formed were filtered off, washed with
ethanol, and dried in air. The yield was 46 mg (34%). Crystals
suitable for Xꢀray diffraction were prepared by recrystallization
from a benzene—nꢀhexane mixture. Found (%): C, 24.93;
H, 3.12; N, 11.86; Br, 16.26. C20H30Br N O Re . Calcuꢀ
(
CCDC 265471ꢀ265474).
cisꢀTetrakis(3,5ꢀdimethylpyrazole)trioxotetrachlorodiꢀ
rhenium(V), Re O Cl (3,5ꢀMe pzH) (cisꢀ1). A mixture of
2
3
4
2
4
[
ReCl (CH CN)(PPh ) ] (200 mg, 0.23 mmol) and 3,5ꢀdiꢀ
3 3 3 2
2
8
3
2
–
1
methylpyrazole (45 mg, 0.46 mmol) was refluxed in a
CHCl —(CH ) CO mixture (1 : 1, v/v) for 1 h. The solvent was
lated (%): C, 24.95; H, 3.14; N, 11.64; Br, 16.60. IR (ν/cm ):
3320 sh, 3288 s, 2980 m, 2933 m, 2857 m, 1570 s, 1535 s, 1475 w,
1420 s, 1384 m, 1350 m, 1288 m, 1180 sh, 1150 m, 1120 m,
1058 s, 968 s (Re=O), 825 m, 814 m, 788 m, 750 w, 670 sh, 638 s
(Re—O—Re), 600 m, 580 m, 500 m, 480 w, 449 w. EAS
3
3 2
evaporated, the precipitate was dissolved in chloroform, and the
solution was stirred at ∼ 20 °C for 4 h. Then the solution was
filtered, the darkꢀyellow filtrate was concentrated, and the resiꢀ
due was dissolved in acetonitrile. An orange precipitate, which,
most likely, has the structure [ReCl (Me pzH)(PPh ) ], was
(CHCl ), λ /nm (ε/L mol– cm ): 714 (328). H NMR
1
–1
1
3
max
(CDCl ), δ: 2.29, 2.47, 2.80, and 2.82 (all s, 6 H each, CH ); 5.84
3
2
3 2
3
3
obtained by diethyl ether vapor diffusion into the solution, after
which the solution gradually turned green, and crystals of comꢀ
plex cisꢀ1 precipitated. The yield was 16 mg (15%). IR (ν/cm– ):
and 6.05 (both s, 2 H each, CH); 9.96 (s, 2 H, NH). FABꢀMS:
+
+
m/z (Irel (%)): 962 (100) [M] , 867 (18) [M – 3,5ꢀMe pzH] ,
2
1
+
785 (26) [M – 3,5ꢀMe pzH – Br] .
2
3
2
1
6
553 s, 3474 s, 3416 s (NH), 3929 s, 3150 s (CH of the ring),
Bis(3,5ꢀdimethylpyrazole)bis(µ-dimethylpyrazolato)trioxoꢀ
diiododirhenium(V) benzene monosolvate, Re O I (µꢀ3,5ꢀ
934 w (CH ), 1617 m, 1574 s, 1473 w, 1408 s, 1278 m, 1178 m,
3
2
3 2
055 s, 969 m (Re=O), 904 s, 796 s, 756 s, 705 s (Re—O—Re),
Me pz) (3,5ꢀMe pzH) •C H (5). Complex 5 was synthesized
2 2 2 2 6 6
+
16 m, 472 w. FABꢀMS: m/z (Irel (%)): 946 (10) [M] , 850 (100)
in 26% yield analogously to complex 4 (see above) with the use
+
+
[
(
M – 3,5ꢀMe pzH] , 719 (88) [M – 3,5ꢀMe pzH – Cl] . EAS
of K [ReI ] as a source of rhenium. Crystals suitable for Xꢀray
2
2
2
6
CHCl ), λ /nm (ε/L mol–1 cm ): 684 (394). H NMR
–1
1
diffraction were prepared by recrystallization from a benꢀ
zene—nꢀhexane mixture. Found (%): C, 27.19; H, 2.84;
N, 9.76; I, 23.30. C H I N O Re . Calculated (%): C, 27.52;
3
max
(
CDCl ), δ: 1.79, 2.28, 2.80, and 2.86 (all s, 6 H each, CH );
3
3
5
2
.85 and 5.96 (both s, 2 H each, CH); 10.87 and 11.72 (both s,
H each, NH).
transꢀTetrakis(3,5ꢀdimethylpyrazole)trioxotetrabromodiꢀ
2
6
36 2
8
3
2
–
1
H, 3.20; N, 9.87; I, 22.37. IR (ν/cm ): 3286 s, 2920 m, 2853 w,
1567 s, 1530 m, 1474 w, 1413 s, 1380 m, 1340 m, 1281 m,
1148 m, 1049 s, 960 s (Re=O), 913 s, 784 m, 666 sh, 624 s
rhenium(V), Re O Br (3,5ꢀMe pzH) (transꢀ2). Dry HBr was
2
3
4
2
4
passed through a boiling solution of complex 4 (30 mg) in chloꢀ
roform (30 mL) for 1 h. The resulting green solution was conꢀ
centrated to a minimum volume. The crystals were grown by
diethyl ether vapor diffusion into the solution. The yield was
(Re—O—Re), 487 w, 443 w. EAS (CHCl ), λmax/nm
3
(ε/L mol– cm–1): 726 (277). H NMR (CDCl ), δ: 2.29, 2.53,
1
1
3
2.80, and 2.84 (all s, 6 H each, CH ); 5.84 and 6.05 (both s,
3
2 H each, CH); 10.05 (s, 2 H, NH). FABꢀMS: m/z (I (%)):
rel
+
+
3
2 mg (90%). Found (%): C, 22.61; H, 2.89; N, 9.63; Br, 30.50.
1056 (100) [M] , 833 (18) [M – 3,5ꢀMe pzH – I] , 739 (26)
2
+
C H Br N O Re . Calculated (%): C, 21.36; H, 2.87; N, 9.96;
[M – (3,5ꢀMe pzH) – I] , 610 (23) [M – 2 (3,5ꢀMe pzH) –
2
0
32
4
8
3
2
2
2
–
1
+
+
Br, 28.42. IR (ν/cm ): 3227 s, 3130 sh, 1617 m, 1570 s, 1475 w,
402 s, 1380 sh, 1300 m, 1180 m, 1150 w, 1062 s, 1030 w, 975 m
2 I] , 425 (79) [Re O ] .
2 3
1
Tetrakis(3,5ꢀdimethylpyrazole)oxo(methoxo)rhenium(V) diꢀ
bromide 3,5ꢀdimethylpyrazole tetrahydrate, [ReO(OMe)(3,5ꢀ
Me pzH) ]Br •3,5ꢀMe pzH•4H O (6). The filtrate obtained
(
1
Re=O), 800 s, 780 s, 750 s, 680 s (Re—O—Re), 650 m, 600 m.
H NMR (CDCl ), δ: 2.48 and 2.91 (both s, 12 H each, CH );
3
3
2
4
2
2
2
5
.91 and 11.34 (both s, 4 H each, NH).
after separation of the green crystals of compound 4, was conꢀ
centrated to dryness, and the residue was extracted with water.
Slow evaporation of the filtrate in air afforded violet crystals of
complex 6. The yield was 17 mg (7%). Found (%): C, 32.98;
H, 4.80; N, 14.13; Br, 16.80. C20H30Cl N O Re . Calcuꢀ
lated (%): C, 32.16; H, 5.51; N, 15.00; Br, 17.11. IR (ν/cm ):
3400 m, 3132 s, 2926 s, 2360 m, 2337 m, 1699 w, 1649 m, 1573 s,
1503 m, 1418 m, 1294 m, 1151 m, 1120 m, 1062 m, 1027 m,
Bis(3,5ꢀdimethylpyrazole)bis(µ-dimethylpyrazolato)trioxodiꢀ
chlorodirhenium(V), Re O Cl (µꢀ3,5ꢀMe pz) (3,5ꢀMe pzH) (3).
A solution of the (Et N) [ReOCl ] complex (200 mg, 0.31 mmol)
and 3,5ꢀdimethylpyrazole (60 mg, 0.62 mmol) in ethanol (30 mL)
was refluxed for 6.5 h, cooled to room temperature, and filtered.
The green precipitate of complex 3 that formed was rapidly
washed with ethanol and diethyl ether and dried in air. The yield
was 120 mg (80%). Found (%): C, 28.68; H, 2.98; N, 10.23;
Cl, 8.25. C H Cl N O Re . Calculated (%): C, 27.49; H, 3.46;
2
3
2
2
2
2
2
4
2
5
2
8
3
2
–
1
948 m, 908 s (Re=O), 813 m, 712 w. EAS (H O), λmax/nm
2
(ε/L mol– cm ): 543 (605). H NMR (CDCl ), δ: 1.75 (s,
1
–1
1
2
0
30
2
8
3
2
3
–
1
N, 12.82; Cl, 8.11. IR (ν/cm ): 3424 m, 2926 w, 2831 w,
12 H, CH ); 2.26 (s, 6 H, CH ); 2.36 (12 H, CH ); 3.74 (s, 3 H,
3
3
3
1
1
605 s, 1569 sh, 1532 s, 1487 m, 1451 s, 1416 s, 1365 s, 1214 m,
148 m, 1053 m, 962 s (Re=O), 760 s, 688 sh, 661 sh, 631 s
OCH ); 5.84 (s, 1 H, CH); 6.18 (s, 4 H, CH); 11.2 (s, 4 H, NH).
FABꢀMS: m/z (Irel (%)): 617 (100%) [M – H] .
3
+

V
IV
Re and Re complexes with 3,5ꢀdimethylpyrazole Russ.Chem.Bull., Int.Ed., Vol. 55, No. 1, January, 2006
55
(
3,5ꢀDimethylpyrazole)(triphenylphosphine)bis(µ-diꢀ
viz., cisꢀ[Re O Br (3,5ꢀMe pzH) ] (cisꢀ2), was syntheꢀ
2 3 4 2 4
methylpyrazolato)trioxodichlorodirhenium(V), Re O Cl (µꢀ3,5ꢀ
24
2
3
2
sized from [ReOBr (OAsPh )(AsPh )] and 3,5ꢀMe pzH
3 3 3 2
Me pz) (3,5ꢀMe pzH)(PPh ) (7).
A
mixture of the
2
2
2
3
in 40% yield along with a small amount of the comꢀ
plex with the deprotonated bridging pyrazolate ligand,
[
ReNCl (PPh ) ] complex (200 mg, 0.025 mmol) and 3,5ꢀdiꢀ
2
3 2
methylpyrazole (97 mg, 0.1 mmol) in methanol (30 mL) was
refluxed for 3 h. Then methylene chloride (20 mL) was added
and the mixture was refluxed for 16 h. The hot solution was
filtered and slowly evaporated in air. After three days, the green
crystals of complex 7 that formed were filtered off, washed with
acetone, and dried in air. The yield was 15 mg (12%). Found (%):
C, 37.95; H, 3.32; N, 8.02; Cl, 6.70. C H Cl N PO Re . Calꢀ
[
Re O Br (µꢀ3,5ꢀMe pz) (3,5ꢀMe pzH) ] (4). Attempts
2 3 2 2 2 2 2
to efficiently separate the mixture of these compounds
failed. The corresponding chloride complex [Re O Cl (µꢀ
2
3
2
3,5ꢀMe2pz)2(3,5ꢀMe2pzH)2] (3) was prepared by the reꢀ
action of (Et N) [ReOCl ] or Cs [ReOCl ] with 3,5ꢀdiꢀ
4
2
5
2
5
3
3
37
2
6
3
2
methylpyrazole in 80% and 10% yields, respectively. In
the reaction with Cs [ReOCl ], K[HB(3,5ꢀMe pzH) ] can
–
1
culated (%): C, 38.11; H, 3.59; N, 8.08; Cl, 6.82. IR (ν/cm ):
2
5
2
3
3
1
7
5
300 m, 1560 w, 1525 w, 1480 w, 1433 sh, 1408 m, 1343 m,
280 w, 1158 w, 1100 w, 1050 m, 960 s (Re=O), 820 w, 780 w,
53 m, 747 w, 695 m, 664 m, 635 s (Re—O—Re), 590 m, 533 w,
10 w, 480 w. P{ H} NMR (CDCl ), δ: 7.07 (s). EAS, λmax/nm
ε/L mol cm–1): 704 (304).
serve as a source of dimethylpyrazole (the yield of comꢀ
plex 3 was 9%). The yield is low because of very poor
2
1
solubility of Cs [ReOCl ]. Earlier, this complex has
31
1
2
5
3
–
1
been structurally characterized as the [Re O Cl (µꢀ3,5ꢀ
(
2 3 2
Me pz) (3,5ꢀMe pzH) ]•2[3,5ꢀMe pzH ]Cl compound
transꢀBis(3,5ꢀdimethylpyrazole)tetrabromorhenium(IV) acꢀ
2
2
2
2
2
2
etone monosolvate, ReBr (3,5ꢀMe pzH) •Me CO (8). The salt
(3a). We found that both complex 4 and its previously
unknown iodide analog 5 can be selectively prepared
in satisfactory yields by the reaction of (NH ) [ReBr ]
4
2
2
2
(
NH ) ReBr (62 mg, 0.09 mmol) was melted with a sixfold
4 2 6
molar excess of 3,5ꢀdimethylpyrazole (51 mg, 0.53 mmol). The
reaction mixture was kept at 100 °C for 3 days and then at
4
2
6
or K [ReI ] with 3,5ꢀdimethylpyrazole. These comꢀ
2
6
2
00 °C for 2 days. The solidified melt was extracted with acetone
plexes crystallize as benzene solvates [Re O X (µꢀ3,5ꢀ
2
3 2
and the solution was filtered. Large red crystals of complex 8
suitable for Xꢀray diffraction were grown by slow evaporation of
the filtrate in air. The yield was 8 mg (13%). FABꢀMS,
Me pz) (3,5ꢀMe pzH) ]•C H . In these reactions,
2
2
2
2
6
6
IV
V
Re is oxidized to Re . In the reaction with the broꢀ
mide, the purple [Re(O)(OCH )(3,5ꢀMe pzH) ]Br •
+
+
m/z (Irel (%)): 699 (39) [M] , 506.5 (22) [ReBr ] , 442 (47)
3
2
4
2
4
+
–1
–1
•[3,5ꢀMe pzH]•4H O complex was isolated in 7%
2 2
[
M – 2 Br – (3,5ꢀMe pzH)] . EAS, λmax/nm (ε/L mol cm ):
2
2
2
5
24 (107).
yield. The coordinated methoxy group is formed as a
result of the nucleophilic attack of methanol on the rheꢀ
nium atom. It should be emphasized that earlier all known
Results and Discussion
2
+
[
ReO(OCH )L ] complexes (L are pyridines or imidꢀ
3 4
azoles) have been synthesized by the reaction of the dioxo
Syntheses and interconversions of complexes
2
+
43,46
complexes [ReO L ] with methyl triflate.
2
4
The treatment of complex 4 with dry HBr in CHCl3
led to cleavage of the pyrazolate bridges due to protonaꢀ
tion of the ligand with the resulting selective formation of
the trans isomer (transꢀ2).
The green cisꢀ[Re O Cl (3,5ꢀMe pzH) ] complex
cisꢀ1) was prepared in low yield by the reaction of
2
3
4
2
4
(
NH ReO with K[HB(Me pz) ] in concentrated HCl or
4
4
2
3
by refluxing of [ReCl (MeCN)(PPh ) ] with 3,5ꢀMe pzH
3
3 2
2
in air. The latter procedure afforded also another product
as an orange precipitate. According to elemental analysis,
the composition of the latter is [ReCl (Me pzH)(PPh ) ].
[Re O Br (µꢀ3,5ꢀMe pz) (3,5ꢀMe pzH) ] + 2 HBr =
2
3
2
2
2
2
2
4
3
2
3 2
=
[Re O Br (3,5ꢀMe pzH) ]
(1)
2
3
4
2
4
The IR spectrum of this complex shows bands of both PPh3
transꢀ2
and 3,5ꢀMe pzH. However, the FABꢀmass spectrum has
2
+
+
only the ion peaks [PPh ] (100%), [Me pzH] (100%),
ReCl (Me pzH)] (1.5%), and [ReCl (Me pzH) ]
3 2 4 2 2
1.8%). Single crystals of this complex suitable for Xꢀray
Our attempts to perform the reverse reaction by
deprotonation of [Re O X (3,5ꢀMe pzH) ] (X = Cl or Br)
3
2
+
+
[
(
2
3
4
2
4
with such bases as pyridine (pK 5.20) or 3,5ꢀdimethylꢀ
a
diffraction were not obtained because of low solubility of
this product in most organic solvents. Recently, the redꢀ
orange [ReCl (Me pzH) (PPh )] complex has been synꢀ
pyrazole (pK 4.38) failed. The reaction (1) should lead to
a
cleavage of the Re—N bond in the trans position with
respect to the Re—Br bond because this bond is the longꢀ
est one (Xꢀray diffraction data). It is the selective cleavage
of this bond that gives rise to the trans isomer.
3
2
2
3
thesized2 in 85% yield under similar conditions with the
5
only exception that the Re : 3,5ꢀMe pzH molar ratio of
2
1
: 6.6 has been used in the cited study, whereas we used
The reaction of [ReNCl (PPh ) ] with 3,5ꢀdimethylꢀ
2
3 2
the 1 : 2 ratio. Apparently, oxo complex 1 was formed as
pyrazole unexpectedly led to hydrolytic denitration giving
a result of hydrolysis and oxidation of the intermediꢀ
rise to the mixedꢀligand complex [Re O Cl (µꢀ3,5ꢀ
2
3
2
III
ate Re complex with 3,5ꢀMe pzH. The reaction of
Me pz) (3,5ꢀMe pzH)(PPh )] (7) in 12% yield as one
2
2 2 2 3
[
ReOCl (OAsPh )(AsPh )] with 3,5ꢀMe pzH afforded
of products. This compound and its bromide analogs
were prepared in good yields (40%) by the reactions of
3
3
3
2
2
4
complex 1 in higher yield (42%). Its bromide analog,

56
Russ.Chem.Bull., Int.Ed., Vol. 55, No. 1, January, 2006
Sokolov et al.
2
4
[
ReO(OEt)X (PPh ) ] with the ligand in ethanol. The
Crystal structures
2
3 2
symmetric [Re O X (µꢀ3,5ꢀMe pz) (PPh ) ] complexes
2
3
2
2
2
3 2
(
X = Cl or Br) can be prepared by performing the reaction
The characteristics of Xꢀray diffraction study are sumꢀ
marized in Table 1. The geometric parameters of the
cisꢀ[Re O Cl (3,5ꢀMe pzH) ] molecule (cisꢀ1) deterꢀ
2
4
of [ReOX (PPh ) ] with a larger amount of the ligand.
We failed to replace dimethylpyrazole in [Re O Cl (µꢀ
3
3
3 2
2
3
2
2
3
4
2
4
1
0,21,24
,5ꢀMe pz) (3,5ꢀMe pzH) ] with PPh even after proꢀ
mined in three independent studies
agree well with
2
2
2
2
3
31
longed refluxing in chloroform ( P NMR monitoring).
each other and are not discussed in the present study. The
Red crystals of transꢀ[ReBr (3,5ꢀMe pzH) ]•Me CO
molecular structure of transꢀ[Re O Br (3,5ꢀMe pzH) ]
4
2
2
2
2
3
4
2
4
(
8) were isolated in 13% yield from the solution, which
(transꢀ2) is shown in Fig. 1. Selected distances and bond
angles are given in Table 2. In both complexes, the rheꢀ
nium atom is in a distorted octahedral environment, two
oxygen atoms are in trans positions with respect to each
other, and the Re=O and Re—O bond lengths have stanꢀ
dard values. The cis and trans isomers differ in the mutual
orientation of the halide and pyrazole ligands. The cenꢀ
tral Re—O—Re fragment is almost linear in cisꢀ2 (angle
is 178.7° (2)) and is strictly linear in transꢀ2. In the latter
complex, the geometry is strictly linear because the molꢀ
ecules have the crystallographic symmetry C2.
was obtained in the reaction of (NH ) [ReBr ] with 3,5ꢀdiꢀ
4
2
6
methylpyrazole performed in the absence of a solvent by
melting with a large excess of the ligand (200 °C, 2 days)
followed by extraction of the solidified melt with acetone.
IV
This is the only known Re complex with a pyrazoleꢀtype
ligand. The formation of the trans isomer can easily be
attributed to the steric requirements of the bulky ligand.
The reaction can proceed either as the direct attack of the
ligand on [ReBr6] or through the initial elimination of
ammonia to form (3,5ꢀMe pzH ) [ReBr ]. The latter unꢀ
dergoes the Anderson rearrangement to give complex 8. It
is noteworthy that Re is only partially reduced to Re
under these drastic conditions. In turn, the Re comꢀ
plexes [ReCl (pzH) (PPh )] and [ReCl (pzH) ] can easꢀ
2
–
2
2 2
6
4
+
Numerous complexes containing the linear Re O
2 3
IV
III
fragment were described in the literature: [Re O Cl (py) ]
2 3 4 4
III
11,12
(both cis and trans isomers are known),
cisꢀ[Re O Cl (C H N ) ] (C H N is pyrazine),
1
7
3
2
3
3
3
2
3
4
4
4
2 4
4
4
2
ily be prepared from [ReOCl (PPh ) ] by prolonged reꢀ
fluxing with an excess of the ligand. Apparently, these
transꢀ[Re O Cl (1ꢀMeIm) ] (1ꢀMeIm is 1ꢀmethylꢀ
2 3 4 4
imidazole), cisꢀ[Re O Cl (Me Bzm) ] (Me Bzm is
2 3 4 3 4 3
3
3 2
3
0
reactions occur due to the presence of PPh , which can
1,5,6ꢀtrimethylbenzimidazole), symm,cisꢀ[Re O Cl ꢀ
2 3 4
3
act as an oxygen acceptor.2
5,27
(Me Bzm) (py) ],
13,31
and cisꢀ[Re O Cl (Haza) ] (Haza
2 3 4 4
3
2
2
Table 1. Crystallographic parameters for complexes 2, 4, 5, and 8
Parameter
2
4
5
8
Molecular formula
C20H32Br N O Re
C26H Br N O Re
C26H I N O Re
C H Br N ORe
13 22 4 4
4
8
3
2
36
2
8
3
2
36 2
8
3
2
Molecular weight
T/K
Space group
a/Å
b/Å
c/Å
1124.58
203(2)
Pccn
11.322(2)
12.507(3)
21.651(4)
90
1040.85
203(2)
C2/c
27.573(6)
15.521(3)
15.486(3)
90
1040.85
293(2)
C2/c
27.718(4)
15.786(2)
15.860(2)
90
814.26
100(2)
P2 /c
1
13.366(3)
9.285(2)
19.346(4)
90
α/deg
β/deg
90
90
94.67(3)
90
6605(2)
8
2.093
9.783
94.33(1)
90
6919.8(2)
8
2.179
8.814
93.79(3)
90
2395.7(8)
4
2.252
11.762
γ/deg
3
V/Å
3065.9(11)
4
2.436
Z
–
3
dcalc/g cm
µ/mm
–
1
13.139
Number of reflections
measured
independent
GOOF
22088
3400
1.149
8412
5120
1.069
5057
4946
0.977
14453
4960
1.175
R factors
for reflections with I > 2σ(I ):
R1
wR2
0.0666
0.1777
0.0468
0.1237
0.0375
0.1207
0.0372
0.0997
for all reflections:
R
wR2
0.0779
0.1891
0.0504
0.1302
0.0604
0.1260
0.0380
0.1004

V
IV
Re and Re complexes with 3,5ꢀdimethylpyrazole Russ.Chem.Bull., Int.Ed., Vol. 55, No. 1, January, 2006
57
complexes (in which L is a monodentate ligand) were
prepared as cis isomers. The only exceptions are the
[
Re O Cl py ] complex, for which both isomers were synꢀ
2 3 4 4
thesized (trans isomer was prepared 34 years later than the
1
1,12
cis isomer!),
and the [Re O Cl (MeIm) ] complex,
2 3 4 4
30
which exists only as the trans isomer. A comprehensive
analysis of the possible conformations and nonbonded
contacts in the [Re O Cl py ] complex did not provide
N(3)#1
N(1)
2
3
4
4
Br(2)#1
an explanation for this seemingly preferential formation
Br(1)#1
11,12
of the cis isomer.
On the whole, the geometric paꢀ
O(2)
O(3)
Re(2)
Re(1)
rameters of the complexes transꢀ2, transꢀ[Re O X py ],
2
3
4
4
and transꢀ[Re O Cl (1ꢀMeIm) ] are very similar. The
2
3
4
4
O(1)
conformations of all three molecules can be described as
intermediate between eclipsed and staggered because both
ReX L planes are twisted about the Re—O—Re axis
Br(1)
Br(2)
2
2
N(3)
N(1)#1
by 29.5° (transꢀ2), 27.5° (transꢀ[Re O X py ]), and 28.5°
2 3 4 4
(
transꢀ[Re O Cl (1ꢀMeIm) ]) (0° corresponds to the
2 3 4 4
completely eclipsed conformation). The planes of the hetꢀ
erocycles are inclined with respect to the ReX N planes
2
2
by 50.0° (transꢀ2), 40.9° (transꢀ[Re O X py ]), and 37.1°
2
3
4
4
(
transꢀ[Re O Cl (1ꢀMeIm) ]), as is evident from the
2 3 4 4
O=Re—N—Cortho torsion angles. This conformation can
be considered as a compromise between the necessity to
avoid too close contacts between the substituents in the
ring and the cisꢀligands (which do not allow the rings to
lie in a single plane), between two rings in the eclipsed
configuration (resulting in the twist of the ReN X planes
Fig. 1. Molecular structure of transꢀ2. The atoms are repreꢀ
sented by anisotropic displacement ellipsoids drawn at the 50%
probability level. The hydrogen atoms are omitted.
2
2
is 7ꢀazaindole).32,33 Bidentate 2,2´ꢀbis(1Hꢀimidazole)
about the O=Re—O—Re=O axis), and the tendency to
(
[
biimH2)
forms
the
[Re O Cl (biimH ) ],
retain stabilizing stacking interactions between the π orꢀ
2
3
4
2 2
1
2
Re O Cl (biimH ) ]Cl , and [Re O (biimH) ] comꢀ
bitals of the heterocycles.
In the [ReOBr (OAsPh )(pzH)] complex with unsubꢀ
2
3
3
4
2 4
4
2
3
4
4,35
plexes.
The [Re O Cl (2,2´ꢀbipy) ] complex was
2 3 4 2
3
38
3
3
6
characterized in the study. 4,6ꢀDimethylpyrimidineꢀ
(1H )ꢀthione (Me pymSH) forms the neutral
stituted pyrazole, the Re—N distance is 2.09(2) Å and
the Re—Br distances are 2.496(2) and 2.542(2) Å.
2
2
37
4+
cisꢀ[Re O (Me pymS) ] complex. As can be seen from
In complexes 3a, 4 (Fig. 2), and 5, the central Re O
2
3
2
4
2
3
the aboveꢀmentioned examples, almost all [Re O X L ]
fragment is nonlinear due to the contracting effect of two
2
3 4 4
Table 2. Bond lengths (d) and bond angles (ω) in complex transꢀ2
Bond
d/Å
Angle
ω/deg
Angle
ω/deg
Re(1)—O(2)
Re(1)—O(1)
Re(1)—N(1)
Re(1)—N(1)
Re(1)—Br(1)
Re(1)—Br(1)
Re(2)—O(3)
Re(2)—O(1)
Re(2)—N(3)
1.689(14)
1.929(9)
Re(1)—O(1)—Re(2)
O(2)—Re(1)—O(1)
O(2)—Re(1)—N(1)
O(1)—Re(1)—N(1)
O(2)—Re(1)—N(1)#
180.0
180.000(1)
94.0(3)
86.0(3)
94.0(3)
O(3)—Re(2)—O(1)
O(3)—Re(2)—N(3)
180.000(2)
94.2(3)
85.8(3)
94.2(3)
85.8(3)
171.5(5)
92.87(3)
87.13(3)
91.6(3)
#
1
2.111(10)
2.111(10)
2.5504(13)
2.5504(13)
1.698(14)
1.944(9)
2.114(11)
2.114(11)
2.5520(13)
2.5520(13)
O(1)—Re(2)—N(3)#1
O(3)—Re(2)—N(3)
O(1)—Re(2)—N(3)
#
1
1
#
1
#1
#1
O(1)—Re(1)—N(1)
86.0(3)
N(3) —Re(2)—N(3)
N(1)—Re(1)—N(1)#1
O(2)—Re(1)—Br(1)
O(1)—Re(1)—Br(1)
N(1)—Re(1)—Br(1)
N(1)#1—Re(1)—Br(1)
O(2)—Re(1)—Br(1)#1
O(1)—Re(1)—Br(1)#1
N(1)—Re(1)—Br(1)#1
Br(1)—Re(1)—Br(1)#1
172.1(5)
92.54(3)
87.46(3)
88.6(3)
O(3)—Re(2)—Br(2)
O(1)—Re(2)—Br(2)
#
1
N(3) —Re(2)—Br(2)
N(3)—Re(2)—Br(2)
O(3)—Re(2)—Br(2)#
#
1
Re(2)—N(3)
Re(2)—Br(2)
Re(2)—Br(2)
91.6(3)
1
88.6(3)
92.87(3)
87.13(3)
91.6(3)
#
1
#1
92.54(3)
87.46(3)
87.46(3)
174.93(6)
O(1)—Re(2)—Br(2)
N(3)—Re(2)—Br(2)
Br(2)—Re(2)—Br(2)#1
#
1
174.25(6)
Note. The symmetry code: #1 –x + 1/2, –y + 1/2, z.

58
Russ.Chem.Bull., Int.Ed., Vol. 55, No. 1, January, 2006
Sokolov et al.
Table 3. Bond lengths (d) and bond angles (ω) in molecules 4
and 5 (X = Br or I)
Parameter
4 (X = Br)
5 (X = I)
N(4)
Bond
d/Å
Br(1)
Re(1)—O(2)
Re(1)—O(1)
Re(1)—N(1)
Re(1)—N(5)
Re(1)—N(7)
Re(1)—X(1)
Re(2)—O(3)
Re(2)—O(1)
Re(2)—N(3)
Re(2)—N(6)
Re(2)—N(8)
Re(2)—X(2)
1.682(5)
1.935(4)
2.127(8)
2.137(5)
2.079(6)
2.5411(10)
1.700(5)
1.931(4)
2.124(7)
2.090(6)
2.147(6)
2.5397(10)
1.688(12)
1.915(10)
2.130(14)
2.118(14)
2.085(14)
2.7442(15)
1.654(12)
1.896(10)
2.091(15)
2.081(14)
2.103(14)
2.7302(15)
N(8)
N(3)
N(7)
Re(2)
Re(1)
N(1)
O(1)
N(2)
N(5)
O(2)
O(3)
Br(2)
N(6)
Angle
ω/deg
Re(1)—O(1)—Re(2)
O(2)—Re(1)—O(1)
O(2)—Re(1)—N(7)
O(1)—Re(1)—N(7)
O(2)—Re(1)—N(1)
O(1)—Re(1)—N(1)
N(7)—Re(1)—N(1)
O(2)—Re(1)—N(5)
O(1)—Re(1)—N(5)
N(7)—Re(1)—N(5)
N(1)—Re(1)—N(5)
O(2)—Re(1)—Br(1)
O(1)—Re(1)—Br(1)
N(7)—Re(1)—Br(1)
N(1)—Re(1)—Br(1)
N(5)—Re(1)—Br(1)
O(3)—Re(2)—O(1)
O(3)—Re(2)—N(6)
O(1)—Re(2)—N(6)
O(3)—Re(2)—N(3)
O(1)—Re(2)—N(3)
N(6)—Re(2)—N(3)
O(3)—Re(2)—N(8)
O(1)—Re(2)—N(8)
N(6)—Re(2)—N(8)
N(3)—Re(2)—N(8)
O(3)—Re(2)—Br(2)
O(1)—Re(2)—Br(2)
N(6)—Re(2)—Br(2)
N(3)—Re(2)—Br(2)
N(8)—Re(2)—Br(2)
122.7(3)
169.4(2)
97.4(3)
80.3(2)
99.4(3)
83.0(2)
163.1(2)
89.8(3)
80.0(2)
90.6(2)
125.6(6)
168.7(6)
96.6(6)
80.1(5)
98.8(6)
84.2(5)
164.3(6)
90.8(6)
78.5(5)
90.4(5)
86.6(6)
100.2(5)
90.5(3)
88.8(4)
91.1(4)
169.0(4)
168.7(5)
96.6(6)
79.5(5)
97.7(6)
86.1(5)
165.6(6)
91.1(6)
78.5(5)
91.3(5)
86.8(5)
100.9(5)
89.7(3)
88.8(4)
90.2(4)
168.0(4)
Fig. 2. Molecular structure of the [Re O Br (µꢀ3,5ꢀMe pz) (3,5ꢀ
2
3
2
2
2
Me pzH) ] complex in the crystals of 4. The atoms are repreꢀ
2
2
sented by anisotropic displacement ellipsoids drawn at the 50%
probability level. The hydrogen atoms are omitted.
bridging pyrazolate ligands. These fragments are addiꢀ
tionally coordinated by two neutral pyrazole molecules
and two halogen atoms. The structure of 3a has been
88.2(3)
30
discussed in detail in the study. Complexes 4 and 5
crystallize as isostructural benzene solvates. The strucꢀ
tural data for complexes 4 and 5 are given in Table 3. The
Re—O—Re angles are only slightly different (122.7° in 3a
and 4 and 125.6° in 5). The Re=O and Re—O bond
100.9(2)
89.31(14)
87.81(16)
90.3(2)
169.26(16)
168.9(3)
96.0(3)
81.1(2)
98.9(3)
83.9(2)
165.0(2)
90.0(3)
79.3(2)
89.5(2)
88.5(2)
102.1(2)
88.59(14)
88.97(18)
89.84(18)
167.92(16)
4
+
lengths in the linear Re O3 group differ insignificantly
2
from those in the nonlinear fragment. However, the terꢀ
minal Re=O bond in complex 5 is one of the shortest
4
+
bonds found in compounds containing the Re O
fragꢀ
2
3
ment.3 The Re—N bonds in trans positions with respect
to the coordinated halogen atoms are slightly longer than
those in cis positions. Apparently, this is responsible for
the formation of complex transꢀ2 in the reaction of comꢀ
plex 4 with dry HBr. The µꢀbenzotriazolate complexes
9
[
Re O X (µꢀC H N ) (Ph P) ] (X = Cl or Br) prepared
2 3 4 6 4 3 2 3 2
from [ReOX (PPh ) ] and benzotriazole are the closest
3
3 2
structural analogs of the bridged pyrazolate complexes.
The Re—O—Re angles in these complexes have very simiꢀ
lar values (125—126°). The Re—N distances in both types
2
6
2
of complexes are virtually equal. The [ReO{η ꢀBpz }(ηꢀ
4
pz)] (µꢀO) and [Re O Cl (µꢀMe biimz) ] complexes also
contains the nonlinear central fragment.
the [Ru (NO) (µꢀO)(µꢀ3,5ꢀMe pzH) (3,5ꢀMe pzH) Cl ]
2 2 2 2 2 2 2
2
2
3
4
2
2
3
4,35,39
complex, which is an analog of complex 3. The
4
+
4+
Let us note the interesting common features of
the chemistry of pyrazole and pyrazolate complexes
{(NO)Ru—O—Ru(NO)} and Re O
groups can be
2
3
considered as isoelectronic if the terminal oxygen atoms
in the rhenium complex are considered as donors of four
3
+
3+
of ReO
and Ru(NO) . The transꢀ[Ru (NO) (µꢀ
2 2
4
0
O)Cl (3,5ꢀMe pzH) ] complex has the linear
electrons.
4
2
4
4
+
{
(NO)Ru—O—Ru(NO)} fragment, whereas the nonꢀ
linear {(NO)Ru—O—Ru(NO)} fragment is present in
The crystal structure of the solvate [ReBr (3,5ꢀ
4
4
+
Me pzH) ]•Me CO (8) contains two crystallographically
2
2
2

V
IV
Re and Re complexes with 3,5ꢀdimethylpyrazole Russ.Chem.Bull., Int.Ed., Vol. 55, No. 1, January, 2006
59
cyclic voltammetry experiments. Generally, only one
quasireversible peak in the region from 2.0 to –1.0 V is
Br(2)
Br(1)#1
N(1)
V
observed. This peak corresponds to oxidation of Re
VI
to Re . The potentials E
(in CHCl , relative to
1
/2
3
Ag/AgCl) are 1.357 V for chloride cisꢀ1 and 1.373 V for
bromide transꢀ2. For comparison, two oneꢀelectron oxiꢀ
dation peaks and two oneꢀelectron reduction peaks are
observed for the pyridine complexes [Re O Cl (Rpy) ]
N(1)#1
Re(1)
2
3
4
4
4
2
(
Rpy are different pyridine derivatives). The pyrazolateꢀ
Br(2)#1
bridged complexes are characterized by substantially lower
potentials. For complex 4, E1/2 = 1.082 V. For triꢀ
phenylphosphine complex 7 (E1/2 = 1.095 V), an addiꢀ
tional irreversible oxidation peak is observed at 1.4 V,
which is apparently associated with oxidation of the coorꢀ
Br(1)
Fig. 3. Molecular structure of the [ReBr (3,5ꢀMe pzH) ] comꢀ
4
2
2
plex in the crystals of 8. The atoms are represented by anisotroꢀ
pic displacement ellipsoids drawn at the 50% probability level.
The hydrogen atoms are omitted.
dinated PPh ligand to form oxide. The mononuclear oxo
3
methoxo complex 6 has one pronounced reversible reꢀ
duction peak (E1/2 = –0.785 V) in the region from 1.0
independent transꢀ[ReBr (3,5ꢀMe pzH) ] molecules
4
2
2
V
IV
to –1.2 V corresponding to the reversible Re /Re pair.
(
Fig. 3) characterized by very similar geometric paramꢀ
4
3
It is known that the analogous complexes with pyridine,
eters (Table 4). The rhenium atoms are in a slightly disꢀ
torted octahedral environment (angles at the rhenium atꢀ
oms are 88—92°) formed by four bromine atoms (Re—Br,
2
+
[
Re(O)(OMe)(Rpy)4] , can undergo oneꢀelectron reꢀ
duction at similar potentials. Tetrabromo complex 8 can
undergo quasireversible reduction at moderately negative
potentials (E = –0.20 V, E = –0.11 V). This indicates
2
.4826(5)—2.5024(8) Å) and two nitrogen atoms of the
pyrazolate ligands in trans positions with respect to each
other (Re—N, 2.118(3)—2.130(3) Å). The Re—Br disꢀ
c
a
that the corresponding rhenium(III) complex [ReBr (3,5ꢀ
4
–
4
1
MepzH)2] can be isolated taking into account that the
tances are similar to those observed in the salt K [ReBr ]
2
6
–
44
transꢀ[ReBr (py) ] complex was synthesized.
(
2.49(4) Å). The Re—N—Re angle is 180°, and the rheꢀ
4
2
nium atoms lie on inversion centers. Both pyrazole rings
in complex 8 are in a single plane. However, the crystalloꢀ
graphically independent molecules differ slightly in the
orientation of the heterocyclic rings. The angles between
these rings and the ReBr N plane in two molecules are
Vibrational and electronic spectra
The IR spectra show characteristic ν(Re=O) bands
–1
2
2
at 970—950 cm
and ν(Re—O—Re) bands at
4
4.42(2)° and 48.26(2)°.
–1
4+
6
00—700 cm belonging to the Re O
fragments. In
2
3
the spectra of cisꢀ1 and transꢀ2, vibrations involving the
bridging oxygen atom are observed at 705 and 680 cm–
1
,
Electrochemistry
respectively, whereas these bands in the spectra of comꢀ
All dinuclear rhenium complexes synthesized in the
present study can undergo oxidation under conditions of
plexes 3—5 are observed at lower frequencies in the
600—630 cm region. The IR spectrum of complex 6
–
1
Table 4. Bond lengths (d) and bond angles (ω) in molecule 8*
Bond
d/Å
Angle
ω/deg
180
89.25(8)
90.75(8)
89.25(8)
Angle
ω/deg
180
88.62(9)
91.38(9)
91.38(9)
Re(1)—N(1)
Re(1)—N(1)#
Re(1)—Br(1)
Re(1)—Br(2)
Re(1)—Br(1)
Re(1)—Br(2)#
Re(2)—N(3)
Re(2)—N(3)#
Re(2)—Br(3)
Re(2)—Br(3)#
Re(2)—Br(4)#
Re(2)—Br(4)
2.119(3)
2.119(3)
2.4946(6)
2.4925(8)
2.4946(6)
2.4925(8)
2.131(3)
2.131(3)
2.4825(5)
2.4825(5)
2.5024(8)
2.5024(8)
N(1)#1—Re(1)—N(1)
N(3)—Re(2)—N(3)#2
N(3)—Re(2)—Br(3)
1
#1
N(1) —Re(1)—Br(2)
#
2
N(1)—Re(1)—Br(2)
N(1)—Re(1)—Br(2)#1
Br(2)—Re(1)—Br(2)
N(3) —Re(2)—Br(3)
#2
N(3)—Re(2)—Br(3)
Br(3)—Re(2)—Br(3)
N(3)—Re(2)—Br(4)
Br(3)—Re(2)—Br(4)
#
1
#1
#2
180
180
1
#1
#2
N(1)—Re(1)—Br(1)
91.75(9)
91.94(2)
91.75(9)
88.25(9)
88.06(2)
91.94(2)
91.18(8)
88.36(2)
88.82(8)
91.18(8)
91.64(2)
88.36(2)
#
1
#2
Br(2)—Re(1)—Br(1)
2
#1
N(1) —Re(1)—Br(1)
N(1)—Re(1)—Br(1)
Br(2)—Re(1)—Br(1)
N(3)—Re(2)—Br(4)
#
2
N(3) —Re(2)—Br(4)
Br(3)—Re(2)—Br(4)
2
2
#1
#2
Br(2) —Re(1)—Br(1)
Br(3) —Re(2)—Br(4)
#
1
#2
Br(1) —Re(1)—Br(1)
180
Br(4) —Re(2)—Br(4)
180
*
The symmetry codes: #1 –x + 1, –y + 1, –z + 1; #2 –x + 2, –y + 2, –z + 1.

60
Russ.Chem.Bull., Int.Ed., Vol. 55, No. 1, January, 2006
Sokolov et al.
shows ν(Re—OCH ) (712 cm–1), ν(Re=O) (948 cm–1),
and the Russian Science Support Foundation (Program
"Young Doctors of Science," the personal grant for M. N.
Sokolov).
3
–
1
and ν(ReO—CH ) (1120 cm ) bands. The bands correꢀ
3
sponding to the C=C and C=N bonds are shifted to lower
–
1
–1
frequencies by ∼ 70 cm (cf. 1663 and 1595 cm for free
,5ꢀdimethylpyrazole). The N—H bonds in the coordiꢀ
nated ligand are responsible for the appearance of intense
3
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This study was financially supported by the Russian
Foundation for Basic Research (Project No. 04ꢀ03ꢀ32159)

V
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Received September 1, 2005;
in revised form January 10, 2006