G. A. Ardizzoia, G. La Monica, A. Maspero, N. Masciocchi, M. Moret
FULL PAPER
tained by slow diffusion of n-hexane into dichloromethane solu-
tions of the complex.
nals, three doublets (6 H, in a 1:1:1 ratio) centered at δ ϭ
7.77 (J ϭ 1.92 Hz), δ ϭ 7.53 (J ϭ 1.75 Hz), and δ ϭ 7.43
(J ϭ 1.75 Hz), respectively, along with two triplets (3 H, in
a 1:2 ratio) centered at δ ϭ 6.25 and δ ϭ 6.21, respectively.
On lowering the temperature, the second doublet and the
downfield triplet broaden and disappear, and finally, at
Ϫ40°C, only three signals remain. Further lowering of the
temperature leads to a drastic change in the spectrum with
the appearance of new, partially overlapped signals. Pre-
sently, we are unable to give a complete explanation of this
behaviour. This effect might be a manifestation of exchange
processes similar to those observed for 2b, but the non-
equivalence of the ReϪ[NϪN]2ϪAu fragments further in-
creases the complexity of the spectrum.
{(CO)3Re(µ-pz)3[Ag(CyNC)]2} (2b): To
a solution of [(CO)3-
Re(Hpz)2(pz)] (100 mg, 0.21 mmol) in acetonitrile (4 mL), was ad-
ded a solution of AgNO3 (94 mg, 0.55 mmol) in water (ca. 2 mL).
Triethylamine (0.5 mL) was then added dropwise to the colorless
solution, resulting in the sudden deposition of a white solid. The
suspension was stirred for a further 15 min, and then the solid
was collected by filtration, washed with water, and dried in vacuo
(compound 1b). 1b was suspended in CH2Cl2 (ca. 2 mL) and cyclo-
hexyl isocyanide (60 µL) was added to the white suspension, giving
a colorless solution. The solvent was then evaporated in vacuo and
the residue was treated with Et2O, filtered, and dried in vacuo (108
mg, 57% yield). Ϫ C26H31Ag2N8O3Re (905.53): calcd. C 34.51, H
3.46, N 12.39; found C 34.83, H 3.54, N 12.35. Ϫ Crystals suitable
for X-ray structure analysis were obtained by slow diffusion of
n-hexane into dichloromethane solutions of the complex.
{(CO)3Re(µ-pz)3[Au(CyNC)]2} (2c): To a stirred solution of [(CO)3-
Re(Hpz)2(pz)] (200 mg, 0.422 mmol) in acetonitrile (ca. 6 mL) at
0°C under nitrogen, was added [Au(tht)Cl][15] (tht: tetrahydrothio-
phene) (269 mg, 0.883 mmol). Tributylamine (0.5 mL) was then ad-
ded dropwise. After a few minutes, a white solid separated from
the colorless solution. The suspension was kept at 0°C and stirred
for a further 3 h. The white solid was then collected by filtration
and dried in vacuo (compound 1c). Cyclohexyl isocyanide (60 µL)
was added to a suspension of 1c in CH2Cl2 (ca. 3 mL), giving a
colorless solution. This solution was then concentrated to dryness
and the residue was treated with ethanol. The white solid obtained
was filtered off, washed with ethanol, and dried in vacuo (261 mg,
57% yield). Ϫ C26H31Au2N8O3Re (1083.72): calcd. C 28.78, H 2.88,
N 10.33; found C 28.81, H 2.80, N 10.26. Ϫ Crystals suitable for
X-ray structure analysis were obtained by slow diffusion of n-hex-
ane into dichloromethane solutions of the complex, with protection
from light.
Crystallography:[16] Crystals of 2a؊c were studied by conventional
single-crystal X-ray methods; an overview of the methodology used
can be found in ref.[11b] Owing to disorder involving the cyclohexyl
moieties in 2b and 2c, special procedures were adopted during the
structure refinement. For 2b, the cyclohexyl rings were each de-
scribed by two models having 62/38% and 52/48% occupancy fac-
tors, respectively. In 2c, only one cyclohexyl ring was found to be
disordered (with a 54/46% ratio) but required, in order to achieve
least-squares stability, a common (isotropic) atomic displacement
parameter. Hydrogen atoms of the disordered groups were omitted
from the structure factor calculations. A list of crystal data, refine-
ment parameters, and final agreement factors is presented in
Table 3.
Conclusions
We have demonstrated herein that the organometallic
complex [(CO)3Re(Hpz)2(pz)], once deprotonated, can act
as a multidentate ligand towards a variety of metal atoms.
The analogy with the tris(pyrazolyl)borate anion is, how-
ever, partially obscured by the fact that “tripod-like” coor-
dination of Group-11 metal atoms was not observed, prob-
ably because of the specific electronic/steric requirements of
the present systems, which favour low coordination num-
bers. Preliminary studies of ReϪMn derivatives have re-
vealed that triply bridged [(CO)3Re(µ-pz)3MnLn] systems
can indeed be prepared, but these will be reported in a
forthcoming paper.
Additionally, variable-temperature NMR analyses have
clearly revealed the nonrigidity of the isolated species and
have indicated that fluxionality can be attributed to simul-
taneous scrambling of monodentate pyrazolato ligands and
ring-opening/closure equilibria, leading to a rather complex
“argentotropic” behaviour.[12]
Experimental Section
General: Solvents were dried and purified by standard methods.
Pyrazole (Aldrich Chemical Co.) was used as supplied. Ϫ Infrared
1
spectra were recorded with a Bio Rad FT-IR 7 instrument. Ϫ H-
NMR spectra were acquired with a Bruker AC-300 FT spec-
trometer operating at 300.13 MHz. Ϫ Elemental analyses were per-
formed at the Microanalytical Laboratory of this university (C, H,
N). Ϫ All reactions were carried out under dry nitrogen using
standard Schlenk techniques.
Acknowledgments
{(CO)3Re(µ-pz)3[Cu(CyNC)]2}
(2a):
[(CO)3Re(Hpz)2(pz)][4]
`
This work was supported by the Ministero dellЈUniversita e della
(150 mg, 0.317 mmol) was dissolved in acetonitrile (10 mL) and
solid [Cu(CH3CN)4](BF4)[14] (210 mg, 0.668 mmol) was added un-
der stirring. Triethylamine (0.5 mL) was then added and the yellow
solution was stirred for a further 15 min. A solution of cyclohexyl
isocyanide (90 µL) in degassed CH2Cl2 (ca. 2 mL) was then added,
leading to a colorless solution. After stirring for 30 min, the solvent
was completely evaporated, the residue was treated with ethanol,
and the white solid was collected by filtration, washed with ethanol,
and dried in vacuo (155 mg, 60% yield). Ϫ C26H31Cu2N8O3Re
(816.87): calcd. C 38.23, H 3.83, N 13.73; found C 38.06, H 3.78,
N 13.38. Ϫ Crystals suitable for X-ray structure analysis were ob-
Ricerca Scientifica e Tecnologica (MURST) and by the Italian
Consiglio Nazionale delle Ricerche (CNR). The technical support
of Mr. Gianni Mezza is also acknowledged.
[1] [1a]
[1b]
R. Poilblanc, Inorg. Chim. Acta 1982, 62, 75Ϫ89. Ϫ
C.
´
´
Tejel, J. M. Villoro, M. A. Ciriano, J. A. Lopez, E. Eguizabal,
F. J. Lahoz, V. I. Bakhmutov, L. A. Oro, Organometallics 1996,
15, 2967Ϫ2978.
[2]
[2a] S. Trofimenko, Chem. Rev. 1972, 72, 497Ϫ509. Ϫ [2b] S. Trof-
[2c]
imenko, Prog. Inorg. Chem. 1986, 34, 115Ϫ210. Ϫ
G. La
Monica, G. A. Ardizzoia, Prog. Inorg. Chem. 1997, 46,
151Ϫ238.
1306
Eur. J. Inorg. Chem. 1999, 1301Ϫ1307