Organometallic complexes with terminal imidazolato ligands and their use as metalloligands

Article abstract of DOI:10.1021/ic1012395

Compounds [Re(bipy)(CO)₃(HIm)]OTf (1) and [Mo(η³- C₃H₄-R-2)(CO)₂(HIm)(phen)]BAr′ ₄ [R = Me (2a), H (2b); Ar′ = 3,5-bis(trifluoromethyl)phenyl; HIm = 1H-imidazole] were prepared from 1H-imid

Full text of DOI:10.1021/ic1012395

Inorg. Chem. 2010, 49, 9527–9534 9527
DOI: 10.1021/ic1012395
Organometallic Complexes with Terminal Imidazolato Ligands
and Their Use as Metalloligands
†
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,‡
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´
Eva Gomez, Miguel A. Huertos, Julio Perez,* Lucıa Riera,* and Amador Menendez-Velazquez
†
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Departamento de Quımica Organica e Inorganica, IUQOEM, Universidad de Oviedo, CSIC,
‡
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C/Julian Claverıa 8, 33006 Oviedo, Spain, Instituto de Ciencia de Materiales de Aragon (ICMA),
Universidad de Zaragoza, CSIC, C/Pedro Cerbuna 12, 50009 Zaragoza, Spain, and
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Centro de Investigacion en Nanomateriales y Nanotecnologıa, Instituto Tecnologico de Materiales de Asturias,
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Parque Tecnologico de Asturias, E-33428 Llanera, Asturias
Received June 21, 2010
Compounds [Re(bipy)(CO)3(HIm)]OTf (1) and [Mo(η3-C3H4-R-2)(CO)2(HIm)(phen)]BAr04 [R = Me (2a), H (2b); Ar0 =
3,5-bis(trifluoromethyl)phenyl; HIm = 1H-imidazole] were prepared from 1H-imidazole and either [Re(OTf)(bipy)-
(CO)3] or [MoCl(η3-C3H4-R-2)(CO)2(phen)]. Compounds 1, 2a, and 2b were deprotonated to afford the terminal κ-N-
imidazolate complexes [Re(bipy)(CO)3(Im)] (3) and [Mo(η3-C3H4-R-2)(CO)2(Im)(phen)] [R = Me (4a), H (4b)],
which were fully characterized, including an X-ray structural determination of 3. The topological analysis of the electron
density (obtained from the X-ray diffraction study) and its Laplacian were used to characterize the differences in the
electron density at the five-membered ring ligand between the imidazole and imidazolate complexes 1 and 3. The
reaction of complexes 3, 4a, and 4b with the appropriate organometallic complexes afforded the bimetallic imidazolate-
bridged compounds [{Re(bipy)(CO)3}2(μ-Im)]OTf (5), [{Mo(η3-C4H7)(CO)2(phen)}2(μ-Im)]OTf (6), and [{Mo(η3-
C3H5)(CO)2(phen)}(μ-Im){Re(phen)(CO)3}]OTf (7). The reaction of [Mo(η3-C4H7)(CO)2(Im)(phen)] (4a) with
SnClPh3 led to the formation of the trinuclear complex [{Mo(η3-C4H7)(CO)2(phen)(μ-Im)}2{SnPh3}]BAr04 (8).
Introduction
analogues of N,N0-dialkylimidazolium cations, i.e., com-
plexes in which an (anionic) imidazolate ligand would bridge
two cationic metal fragments, so that the overall dinuclear
complex would be cationic.
N,N0-Dialkylimidazolium salts serve as ionic liquids,1 as
hydrogen-bond donors in supramolecular hosts,2 and as
precursors for the synthesis of N-heterocyclic carbenes.3 Cat-
ionic metal complexes with N-alkylimidazole ligands can be
regarded as N-metalated analogues of N,N0-dialkylimidazo-
lium cations.4 We have investigated the ability of the C2-H
groups of N-alkylimidazole ligands in cationic metal com-
plexes to act as hydrogen-bond donors,5 as well as the un-
precedented reactivity patterns resulting from deprotonation
of these groups.6 Aiming to extend these works, we decided to
investigate the possibility of preparing N,N0-dimetalated
In our previous studies with imidazole complexes, we have
employed allylmolybdenum(II) dicarbonyl and -rhenium(I)
tricarbonyl fragments because of their stability (CO-substitu-
tion reactions in complexes of this type do not occur easily),
ease of preparation, and presence of CO groups, which could
serve as a spectroscopic (IR) handle. 2,20-Bipyridine (bipy)
and 1,10-phenanthroline (phen) are stable chelates. There-
fore, their presence as ancillary ligands, blocking two co-
ordination sites, would help to prevent the direct formation
of dinuclear compounds upon deprotonation (see below).
Also, the redox stability of allylmolybdenum(II) dicarbonyl
and -rhenium(I) tricarbonyl complexes would ensure that
deprotonation of cationic complexes would afford neutral
products rather than trigger electron transfer. Therefore, the
imidazolato complexes of {Mo(allyl)(CO)2(phen)} and {Re-
(CO)3(bipy)} fragments were targeted.
*To whom correspondence should be addressed. E-mail: riera@unizar.es
(L.R.), japm@uniovi.es (J.P.).
(1) Dullius, J. E. L.; Suarez, P. A. Z.; Einloft, S.; de Souza, R. F.; Dupont,
J.; Fischer, J.; De Cian, A. Organometallics 1998, 17, 815.
(2) (a) Yoon, J.; Kim, S. K.; Singh, N. J.; Kim, K. S. Chem. Soc. Rev. 2006,
35, 355. (b) Amendola, V.; Boiocchi, M.; Colasson, B.; Fabbrizzi, L.; Douton,
M.-J. R.; Ugozzoli, F. Angew. Chem., Int. Ed. 2006, 45, 6920.
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29, 554.
Imidazoles form stable complexes with a variety of metal
fragments, which, in most cases, are easily prepared through
substitution reactions. We therefore thought that the most
general route to the synthesis of cationic imidazolate-bridged
dinuclear compounds would be deprotonation of a cationic
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(5) Perez, J.; Riera, L.; Ion, L.; Riera, V.; Anderson, K. M.; Steed, J. W.;
Miguel, D. Dalton Trans. 2008, 878.
(6) (a) Huertos, M. A.; Perez, J.; Riera, L. J. Am. Chem. Soc. 2008, 130,
5662. (b) Huertos, M. A.; Perez, J.; Riera, L.; Menendez-Velazquez, A. J. Am.
Chem. Soc. 2008, 130, 13530.
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2010 American Chemical Society
Published on Web 09/17/2010
pubs.acs.org/IC

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Gomez et al.
9528 Inorganic Chemistry, Vol. 49, No. 20, 2010
Scheme 1. General Reaction Scheme of the Results Included in This
Article
the synthesis of zeolitic metal-organic fragments that show
potential for gas (H2 and CO2) storage.11
The isolation of monomeric imidazolato (Im) complexes
has proven to be difficult because of the bidentate nature of
Im, which frequently led to oligomeric or polymeric species.12
As far as we know, just a few terminal imidazolato metal
complexes have been reported (fully characterized examples,
including the X-ray structure, are very scarce13), and none of
them is an organometallic complex.14
Herein we report the synthesis of a complete series of
complexes of rhenium(I) and molybdenum(II), including the
parent imidazole species (type I, Scheme 1), the monomeric
κ-N-imidazolate derivatives (type II, Scheme 1), and the use
of the latter as metalloligands to afford homo- or hetero-
polymetallic complexes containing μ-κ-N:κ-N0-imidazolate
units (type III, Scheme 1).
mononuclear complex of a parent imidazole. The product
would be a neutral complex with a terminal imidazolate
ligand. Next this product would be allowed to react with a
cationic complex containing a labile ligand, which could be
displaced by the uncoordinated nitrogen of the imidazolate
ligand (Scheme 1).
Imidazolato-bridged transition-metal complexes have
been known since the early 1960s7 and have attracted con-
siderable interest because the X-ray crystal structure of the
enzyme bovine erythrocyte superoxide dismutase showed
that the active site consisted of a Zn-Cu bimetallic pair
bridged by the imidazolato group of a deprotonated histidine
residue.8 An imidazolato (histidine) bridge has also been
proposed to exist between copper and iron in cytochrome
c oxidase.9 Therefore, numerous studies have been focused
on the synthesis of binuclear imidazolato-bridged complexes
to mimic active sites in metalloproteins [the more widely
employed metals have been copper(II), zinc(II), nickel(II),
and iron(III)].10 Imidazolato bridges have also been used in
Experimental Section
General Procedures. All manipulations were carried out
under a nitrogen atmosphere using Schlenk techniques. Solvents
were distilled from sodium (hexanes), sodium/benzophenone
(tetrahydrofuran, THF), and CaH2 (CH2Cl2). Compounds [Re-
(OTf)(bipy)(CO)3],15 [MoCl(η3-C3H4-2-R)(CO)2(phen)] (R =
H, Me),16 and NaBAr0417 were prepared as previously reported.
Deuterated dichloromethane (Cambridge Isotope Labora-
tories, Inc.) was stored under nitrogen in a Young tube and
used without further purification. 1H and 13C NMR spectra
were recorded on a Bruker Advance 300, DPX-300, or Advance
400 spectrometer. NMR spectra are referred to the internal
1
residual solvent peak for H and 13C{1H} NMR. IR solution
spectra were obtained in a Perkin-Elmer FT 1720-X spectro-
meter using 0.2 mm CaF2 cells. NMR samples were prepared
under nitrogen using Kontes manifolds purchased from Aldrich.
Crystal Structure Determination. General Description. For
Compounds 3, 5, and 8. Data collection was performed at 293(2) K
(compounds 3 and 5) and 150 (2) K (compound 8) on a Nonius
Kappa CCD single-crystal diffractometer, using Mo KR radiation
(λ = 0.710 73 A). Images were collected up to 2θ = 140° at a 29 mm
fixed crystal-detector distance, using the oscillation method. The
data collection strategy was calculated with the program Collect.18
Data reduction and cell refinement were performed with the pro-
grams HKL Denzo and Scalepack.19 A semiempirical absorption
correction was applied using the program SORTAV.20 For Com-
pounds 1 and 7. Data collection was performed at 150(2) K
(compound 1) and 293(2) K (compound 7) on an Oxford Diffrac-
tion Xcalibur Nova single-crystal diffractometer, using Cu KR
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Chim. Acta 1993, 206, 117. (o) Pierre, J.-L.; Chautemps, P.; Refaif, S.; Beguin,
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1995, 117, 1965. (p) Mao, Z.-W.; Chen, M.-Q.; Tan, X.-S.; Liu, J.; Tang, W.-X.
Inorg. Chem. 1995, 34, 2889. (q) Rettig, S. J.; Storr, A.; Summers, D. A.;
Thompson, R. C.; Trotter, J. J. Am. Chem. Soc. 1997, 119, 8675. (r) Colacio, E.;
(12) For example, see: (a) Masciocchi, N.; Ardizzoia, G. A.; LaMonica,
G.; Maspero, A.; Galli, S.; Sironi, A. Inorg. Chem. 2001, 40, 6983. (b) Glaser,
T.; Heidemeier, M.; Hahn, F. E.; Pape, T.; L€ugger, T. Z. Naturforsch. 2003, 505.
(c) Zhang, J.-P.; Chen, X.-M. Chem. Commun. 2006, 1689. (d) Zhang, J.; Cai, R.;
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R.; Strouse, C. E.; Valentine, J. S. Inorg. Chem. 1983, 22, 3934. (c) Mandon, D.;
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(14) Selectedexamplesofκ1-imidazolate complexes: (a) Veltheer, J. E.; Burger,
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K.; Tanabe, Y.; Nagano, H. J. Inorg. Biochem. 1998, 69, 9. (c) Sunatsuki, Y.;
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Article
Inorganic Chemistry, Vol. 49, No. 20, 2010 9529
radiation (λ = 1.5418 A) for compound 1 and Mo KR radiation
(λ = 0.710 73 A) for compound 7. Images were collected at a 65 mm
fixed crystal-detector distance, using the oscillation method, with 1°
oscillation and variable exposure time per image (4-16 s). The data
collection strategy was calculated with the program CrysAlis CCD.21
Data reduction and cell refinement were performed with the pro-
gram CrysAlis RED.21 An empirical absorption correction was
applied using the SCALE3 ABSPACK algorithm, as implemented
in the program CrysAlis RED.21 Structure Solution and Refine-
ment (All). The structures were solved by direct methods with
SHELXTL.22 All non-hydrogen atoms were refined anisotropically.
Hydrogen atoms were set in calculated positions and refined as
riding atoms, with a common thermal parameter. Calculations were
made with SHELXTL and PARST.23
1955vs, 1873s (νCO). 1H NMR (CD2Cl2): δ 9.85 [s, br, 1H, NH],
9.27 [m, 2H, H1 phen], 8.58 [m, 2H, H3 phen], 7.99 [s, 2H, H4 phen],
7.94 [m, 2H, H2 phen], 7.74 [m, 8H, Ho BAr04], 7.56 [m, 4H, Hp
BAr04], 7.49 [s, 1H, HC HIm], 6.73 [s, 1H, HA HIm], 5.84 [s, 1H, HB
HIm], 3.24 [s, 2H, Hsyn], 1.78 [s, 2H, Hanti], 0.67 [s, 3H, CH3]. 13
C
NMR (CD2Cl2): δ 224.8 [CO], 162.2 [q (1JCB = 49.8 Hz), Ci
BAr04], 152.7, 144.8, 139.5, 130.9, 128.3, 126.1 [phen], 135.2 [Co
BAr04], 129.3 [q (2JCF = 31.5 Hz), Cm BAr04], 124.9 [q (1JCF
=
272.5 Hz), CF3, BAr04], 144.8, 127.3, 121.7 [HIm], 117.8 [Cp BAr04],
84.0 [C2 η3-C4H7], 56.6 [C1 and C3 η3-C4H7], 18.5 [CH3 η3-C4H7].
Anal. Calcd for C53H31BF24MoN4O2: C, 48.28; H, 2.37; N, 54.25.
Found: C, 48.42; H, 2.01; N, 4.09.
[Mo(η3-C3H5)(CO)2(HIm)(phen)]BAr04 (2b). Compound 2b
was prepared as described above for compound 2a, starting
from [MoCl(η3-C3H5)(CO)2(phen)] (0.060 g, 0.147 mmol),
NaBAr04 (0.130 g, 0.147 mmol), and HIm (0.010 g, 0.147 mmol).
Compound 2b was obtained as a garnet solid. Yield: 0.154 g
(80%). IR (CH2Cl2): 1957vs, 1872s (νCO). 1H NMR (CD2Cl2):
δ 9.61 [s, br, 1H, NH], 9.24 [m, 2H, H1 phen], 8.59 [m, 2H, H3
phen], 8.01 [s, 2H, H4 phen], 7.93 [m, 2H, H2 phen], 7.74 [m, 8H,
Ho BAr04], 7.56 [m, 4H, Hp BAr04], 7.63 [s, 1H, HC HIm], 6.74 [s,
1H, HA HIm], 5.80 [s, 1H, HB HIm], 3.47 [d (J = 6.4 Hz), 2H,
For topological analysis of the electron densities, the MOL-
FINDER procedure was used.24
1
The labeling schemes for H and 13C NMR spectra are as
follows:
H
syn], 2.94 [m, 1H, Hc], 1.83 [d (J = 9.5 Hz), 2H, Hanti]. Anal.
Calcd for C52H29BF24MoN4O2: C, 47.88; H, 2.24; N, 4.29.
Found: C, 48.03; H, 2.41; N, 4.12.
[Re(bipy)(CO)3(Im)] (3). To a solution of 1(0.050 g, 0.078 mmol)
in THF at -78 °C was added KN(SiMe3)2 (0.170 mL of a 0.5 M
solution in toluene, 0.085 mmol), and the color of the solution
changed immediately from yellow to light green. The mixture was
allowed to reach room temperature, and the solvent was evaporated
under vacuum. The residue was extracted with CH2Cl2 (30 mL),
filtered via a cannula, and evaporated to dryness. The slow diffusion
of hexane (20 mL) into a concentrated solution of compound 3 in
THF (5-7 mL) at -20 °C afforded pale-green crystals, one of
which was used for X-ray analysis. Yield: 0.031 g (80%). IR (THF):
2017vs, 1911s, 1904s (νCO). 1H NMR (CD2Cl2): δ 9.15 [m, 2H, H1
bipy], 8.20 [m, 2H, H4 bipy], 8.14 [s, 2H, H2 bipy], 7.61 [m, 2H, H3
bipy], 6.72 [s, 1H, HC HIm], 6.64 [s, 1H, HA HIm], 6.35 [s, 1H, HB
HIm]. 13CNMR(CD2Cl2):δ197.6 [2CO], 193.4 [CO], 155.6, 153.1,
139.8, 139.6, 127.7 [bipy], 125.7, 123.4, 123.3 [Im]. Anal. Calcd for
C16H11N4O3Re: C, 38.94; H, 2.25; N, 11.35. Found: C, 38.71; H,
2.39; N, 10.96.
[Mo(η3-C4H7)(CO)2(Im)(phen)] (4a). KN(SiMe3)2 (0.130 mL
of a 0.5 M solution in toluene, 0.065 mmol) was added to a
solution of 2a (0.080 g, 0.060 mmol) in THF (20 mL), previously
cooled to -78 °C. The reaction mixture was allowed to reach
room temperature and then was evaporated to dryness. The
dark-red residue was extracted with CH2Cl2 (30 mL), filtered via
a cannula, and concentrated under reduced pressure to a volume
of 5 mL. The addition of hexane (20 mL) caused precipitation of
a dark-red solid that was washed with hexane (2 ꢀ 20 mL).
Yield: 0.022 g (80%). IR (CH2Cl2): 1947vs, 1863s (νCO). 1H
NMR (CD2Cl2): δ 9.13 [m, 2H, H1 phen], 8.52 [m, 2H, H3 phen],
7.98 [s, 2H, H4 phen], 7.84 [m, 2H, H2 phen], 7.20 [s, 1H, HIm],
6.35 [s, 1H, HIm], 5.43 [s, 1H, HIm], 3.08 [s, 2H, Hsyn], 1.65 [s,
2H, Hanti], 0.63 [s, 3H, CH3]. 13C NMR (CD2Cl2): δ 225.9 [CO],
152.5, 145.1, 138.9, 130.5, 128.0, 125.7 [phen], 137.7, 127.4,
124.0 [HIm], 83.0 [C2 η3-C4H7], 55.3 [C1 and C3 η3-C4H7], 18.3
[CH3 η3-C4H7]. Anal. Calcd for C21H18MoN4O2: C, 55.52; H,
3.99; N, 12.33. Found: C, 55.61; H, 4.09; N, 12.01.
[Re(bipy)(CO)3(HIm)]OTf (1). 1H-Imidazole (HIm; 0.006 g,
0.088 mmol) was added to a solution of [Re(OTf)(bipy)(CO)3]
(0.050 g, 0.087 mmol) in CH2Cl2 (20 mL), and the mixture was
stirred overnight at room temperature. The resulting yellow
solution was concentrated under reduced pressure to a volume
of 10 mL, and the addition of hexane (20 mL) caused precipita-
tion of a yellow solid, which was washed with hexane (2 ꢀ 20 mL)
and diethyl ether (2 ꢀ 20 mL). The slow diffusion of hexane into
a concentrated solution of compound 1 in CH2Cl2 at -20 °C
afforded yellow crystals, one of which was used for the X-ray
structure determination. Yield: 0.053 g (96%). IR (CH2Cl2):
2032vs, 1926s (νCO). 1H NMR (CD2Cl2): δ 11.85 [s, br, 1H, NH],
9.11 [m, 2H, H1 bipy], 8.33 [m, 2H, H4 bipy], 8.24 [m, 2H, H2
bipy], 7.71 [m, 2H, H3 bipy], 7.12 [s, 1H, HC HIm], 6.94 [s, 1H,
HA HIm], 6.71 [s, 1H, HB HIm]. 13C NMR (CD2Cl2): δ 196.3
[2CO], 191.2 [CO], 155.9, 153.6, 141.1, 129.3, 124.7 [bipy], 137.9,
128.8, 119.1 [HIm]. Anal. Calcd for C17H12F3N4O6ReS: C,
31.73; H, 1.88; N, 8.71. Found: C, 31.61; H, 2.02; N, 8.60.
[Mo(η3-C4H7)(CO)2(HIm)(phen)]BAr04 (2a). NaBAr04 (0.126 g,
0.140 mmol) was added to a solution of [MoCl(η3-C4H7)(CO)2-
(phen)] (0.060 g, 0.140 mmol) in CH2Cl2 (20 mL), and it was
allowed to stir at room temperature for 15 min. The red solution
was filtered from the white solid (NaCl) via a cannula, and HIm
(0.010 g, 0.150 mmol) was added. After 1 h, the solution was
concentrated under reduced pressure to a volume of 5 mL, and the
addition of hexane caused precipitation of a red solid, which was
washed with hexane (2 ꢀ 20 mL). Compound 2a was obtained as a
red microcrystalline solid. Yield: 0.146 g (79%). IR (CH2Cl2):
[Mo(η3-C3H5)(CO)2(Im)(phen)] (4b). Compound 4 was pre-
pared as described above for complex 3 starting from 2b (0.080 g,
0.061 mmol) and KN(SiMe3)2 (0.130 mL of a 0.5 M solution in
toluene, 0.065 mmol). Compound 4 was obtained as a dark-red
microcrystalline solid. Yield: 0.021 g (78%). IR (CH2Cl2):
1946vs, 1863s (νCO). 1H NMR (CD2Cl2): δ 9.15 [m, 2H, H1
phen], 8.57 [m, 2H, H3 phen], 8.06 [s, 2H, H4 phen], 7.84 [m, 2H,
H2 phen], 6.54 [s, br, 2H, HIm], 6.22 [s, 1H, HIm], 3.29 [d (J =
6.3 Hz), 2H, Hsyn], 2.79 [m, 1H, Hc], 1.63 [d (J = 9.4 Hz), 2H,
(21) CrysAlispro CCD and CrysAlispro RED; Oxford Diffraction Ltd.:
Abingdon, Oxfordshire, U.K., 2009.
(22) Sheldrick, G. M. SHELXTL, An integrated system for solving,
refining, and displaying crystal structures from diffraction data, version 5.1;
Bruker AXS, Inc.: Madison, WI, 1998.
(23) (a) Nardelli, M. Comput. Chem. 1983, 7, 95. (b) Nardelli, M. J. Appl.
Crytallogr. 1995, 28, 659.
ꢀ
ꢀ
(24) Menendez-Velazquez, A.; Garcı
´
a-Granda, S. Appl. Crystallogr.
2003, 36, 193.

ꢀ
Gomez et al.
9530 Inorganic Chemistry, Vol. 49, No. 20, 2010
Hanti]. Anal. Calcd for C20H16MoN4O2: C, 54.56; H, 3.66; N,
12.72. Found: C, 54.91; H, 3.29; N, 12.50.
vacuum, and the brown residue was extracted with CH2Cl2 (30 mL)
and filtered via a cannula. The resulting solution was concen-
trated under reduced pressure to a volume of 10 mL, and the
addition of hexane (20 mL) caused precipitation of a red solid,
which was washed with hexane (2 ꢀ 20 mL) and diethyl ether
(2 ꢀ 20 mL). The slow diffusion of hexane into a concentrated
solution of compound 7 in CH2Cl2 at -20 °C afforded poor-
quality crystals. Yield: 0.051 g (80%). Anal. Calcd for C36H24-
F3MoN6O8ReS: C, 41.58; H, 2.33; N, 8.08. Found: C, 41.26; H,
2.66; N, 8.29. Method B: Compound 7 was prepared following
the procedure described as method A starting from [Re(CO)3-
(HIm)(phen)]OTf (0.050 g, 0.075 mmol), KN(SiMe3)2 (0.150 mL
of a 0.5 M solution in toluene, 0.075 mmol), and [Mo(OTf)(η3-
C3H5)(CO)2(phen)] (0.039 g, 0.075 mmol). Yield: 0.59 g (76%).
[{Re(bipy)(CO)3}2(μ-Im)}OTf (5). Method A: KN(SiMe3)2
(0.125 mL of a 0.5 M solution in toluene, 0.062 mmol) was added
to a solution of HIm (0.004 g, 0.052 mmol) in THF (10 mL)
cooled to -78 °C. After 5 min at low temperature, the mixture
was allowed to reach room temperature and was transferred into
a solution of [Re(OTf)(bipy)(CO)3] (0.060 g, 0.104 mmol) in
THF (15 mL) previously cooled to -78 °C. The reaction mixture
was allowed to warm to room temperature and then was stirred
for 1 h. The solvent was evaporated to dryness and the residue
extracted with CH2Cl2 (30 mL) and filtered through Celite to
afford an orange solution, which was concentrated under
reduced pressure to a volume of 10 mL. The addition of hexane
(20 mL) caused precipitation of an orange solid, which was washed
with hexane (2 ꢀ 20 mL). The slow diffusion of hexane into a
concentrated solution of compound 5 in CH2Cl2 (7-10 mL) at
-20 °C afforded orange crystals, one of which was used for the
X-ray structure determination. Yield: 0.042 g (79%). Anal.
Calcd for C30H19F3N6O9Re2S: C, 40.82; H, 2.17; N, 9.52.
Found: C, 40.58; H, 2.29; N, 9.43. Method B: To a solution of
1 (0.050 g, 0.078 mmol) in THF at -78 °C was added KN-
(SiMe3)2 (0.170 mL of a 0.5 M solution in toluene, 0.085 mmol).
The mixture was allowed to reach room temperature and then
was transferred via a cannula into a solution of [Re(OTf)(bipy)-
(CO)3] (0.045 g, 0.078 mmol) in THF (20 mL). The reaction
mixture was stirred for 1 h and then was evaporated to dryness.
The residue was extracted with CH2Cl2 (20 mL), filtered through
Celite, and concentrated under vacuum to a volume of 10 mL.
The addition of hexane (20 mL) caused precipitation of an
orange solid, which was washed with hexane (2 ꢀ 20 mL). Yield:
0.035 g (52%). IR (CH2Cl2): 2024vs, 1918s (νCO). 1H NMR
(CD2Cl2): δ 8.88 [m, 4H, H1 bipy], 8.50 [m, 4H, H4 bipy], 8.25
[m, 4H, H2 bipy], 7.58 [m, 4H, H3 bipy], 6.30 [s, 2H, HA and HB
HIm], 5.84 [s, 1H, HC HIm]. 13C NMR (CD2Cl2): δ 197.2 [4CO],
192.7 [2CO], 156.0, 153.4, 144.5, 141.1, 128.2 [bipy], 139.4, 127.8
[HIm]. Anal. Calcd for C30H19F3N6O9Re2S: C, 40.82; H, 2.17;
N, 9.52. Found: C, 40.61; H, 2.35; N, 9.35.
1
IR (CH2Cl2): 2026vs, 1948 m, 1919s, 1864 m (νCO). H NMR
(CD2Cl2): δ 9.14, 8.87, 8.78, 8.70 [m, 2H each, phen], 8.19, 8.18
[s, 2H each, phen], 7.95, 7.83 [m, 2H each, phen], 5.97, 5.86, 5.71
[s, 1H each, HIm], 3.22 [d (J = 6.4 Hz), 2H, Hsyn], 2.75 [m, 1H,
Hc], 1.54 [d (J = 9.5 Hz), 2H, Hanti]. 13C NMR (CD2Cl2): δ 225.4
[2CO, Mo-CO], 196.5 [2CO, Re-CO], 192.3 [CO, Re-CO],
152.8, 152.3, 144.3, 144.1, 139.1, 139.0, 130.9, 130.1, 128.1,
127.8, 126.5, 125.5 [2phen], 146.4, 127.7, 127.3 [HIm], 73.5 [C2
η3-C3H5], 57.5 [C1 and C3 η3-C3H5]. Anal. Calcd for C36H24-
F3MoN6O8ReS: C, 41.58; H, 2.33; N, 8.08. Found: C, 41.63; H,
2.61; N, 7.95.
[{Mo(η3-C4H7)(CO)2(phen)(μ-Im)}2{SnPh3}]BAr04 (8). To a
solution of 2a (0.080 g, 0.060 mmol) in THF (20 mL) at -78 °C
was added KN(SiMe3)2 (0.120 mL of a 0.5 M solution in
toluene, 0.060 mmol), and the mixture was stirred at low tem-
perature for 5 min. A solution of SnClPh3 (0.012 g, 0.030 mmol)
in THF (10 mL) was then transferred over the solution described
above, and the reaction mixture was allowed to reach room tem-
perature. After 15 min, the solvent was evaporated under vac-
uum, and the purple residue was extracted with CH2Cl2 (30 mL)
and filtered via a cannula. The resulting solution was concen-
trated under reduced pressure to a volume of 10 mL, and the
addition of hexane (20 mL) caused precipitation of a solid, which
was washed with hexane (2 ꢀ 20 mL). The slow diffusion of
hexane into a concentrated solution of compound 8 in CH2Cl2
at -20 °C afforded purple crystals. Yield: 0.025 g (83%). IR
(CH2Cl2): 1947vs, 1867 m (νCO). 1H NMR (CD2Cl2): δ 8.97 [m,
4H, H1 phen], 8.41 [m, 4H, H3 phen], 7.89 [s, 4H, H4 phen], 7.73
[m, 12H, H2 phen and Ho BAr04], 7.59 [m, 4H, Hp BAr04], 7.13
[m, 15H, Ph], 6.20 [s, 2H, HC HIm], 5.96, 5.58 [s, 2H each, HA
and HB HIm], 3.04 [s, 4H, Hsyn], 1.60 [s, 4H, Hanti], 0.58 [s, 6H,
CH3]. Anal. Calcd for C92H63BF24Mo2N8O4Sn: C, 52.08; H,
2.99; N, 5.28. Found: C, 52.21; H, 3.12; N, 5.01.
[{Mo(η3-C4H7)(CO)2(phen)}2(μ-Im)]OTf (6). Method A: Com-
pound 6 was prepared following method A as described above for
compound 5, starting from [Mo(OTf)(η3-C4H7)(CO)2(phen)]
(0.090 g, 0.170 mmol), HIm (0.006 g, 0.088 mmol), and KN-
(SiMe3)2 (0.200 mL of a 0.5 M solution in toluene, 0.100 mmol).
The slow diffusion of hexane into a concentrated solution of 6 in
CH2Cl2 at -20 °C afforded red crystals. Yield: 0.061 g (70%).
Anal. Calcd for C40H33F3Mo2N6O7S: C, 48.50; H, 3.38; N, 8.48.
Found: C, 48.22; H, 3.45; N, 8.16. Method B: Compound 6 was
prepared following method B as described above for compound 5,
starting from 2a (0.050 g, 0.038 mmol), KN(SiMe3)2 (0.080 mL of
a 0.5 M solution in toluene, 0.040 mmol), and [Mo(OTf)(η3-
C4H7)(CO)2(phen)] (0.020 g, 0.038 mmol). Compound 6 was
obtained as a red microcrystalline solid. Yield: 0.020 g (53%).
IR (CH2Cl2): 1949vs, 1865s (νCO). 1H NMR (CD2Cl2): δ 8.90 [m,
4H, H1 phen], 8.64 [m, 4H, H3 phen], 8.10 [s, 4H, H4 phen], 7.86
[m, 4H, H2 phen], 5.93 [s, 1H, HC HIm], 5.54 [s, 2H, HA and HB
Results and Discussion
The addition of a slight excess of HIm to a solution of
[Re(OTf)(bipy)(CO)3] (bipy = 2,20-bipyridine)15 in CH2Cl2
led, in 8 h at room temperature, to the formation of complex
1, by a simple substitution of the labile triflato ligand by the
imidazole (see Scheme 2a).
HIm], 2.98 [s, 4H, Hsyn], 1.48 [s, 4H, Hanti], 0.56 [s, 6H, CH3]. 13
C
Compound 1 was obtained as a single product of the
reaction in 96% yield and was fully characterized in solution
by IR and NMR and in the solid state by X-ray diffraction.
The IR νCO bands of 1, indicative of a fac-{Re(CO)3}
geometry, occur at wavenumber values that are almost
identical to those of the triflato precursor, despite the fact
that the reaction transforms a neutral complex into a cationic
one, reflecting the large σ-donor ability of the HIm ligand.
The incorporation of the HIm moiety into the complex is
NMR (CD2Cl2): δ 225.6 [CO], 151.9, 144.4, 138.4, 130.3, 127.7,
125.6 [phen], 145.2, 126.8 [HIm], 83.0 [C2 η3-C4H7], 55.3 [C1 and
C3 η3-C4H7], 18.3 [CH3 η3-C4H7]. Anal. Calcd for C40H33F3Mo2-
N6O7S: C, 48.50; H, 3.38; N, 8.48. Found: C, 48.91; H, 3.67; N,
8.74.
[{Mo(η3-C3H5)(CO)2(phen)}(μ-Im) {Re(phen)(CO)3]OTf (7).
Method A: KN(SiMe3)2 (0.130 mL of a 0.5 M solution in tolu-
ene, 0.065 mmol) was added to a cooled (to -78 °C) solution of
2b (0.080 g, 0.061 mmol) in THF (20 mL). The reaction mixture
was allowed to stir at low temperature for 5 min, and then it was
transferred via a cannula into a solution of [Re(OTf)(CO)3-
(phen)] (0.037 g, 0.061 mmol) in THF (15 mL). After 1 h of
stirring at room temperature, the solvent was evaporated under
1
evidenced by the observation in the H NMR spectrum of
three signals at 7.12, 6.94, and 6.71 ppm, assigned to the
three C-H groups of the azole ring, and a characteristically
broad singlet at 11.85 ppm, attributable to the N-H group.

Article
Inorganic Chemistry, Vol. 49, No. 20, 2010 9531
Scheme 2. Synthesis of Cationic Imidazole Complexes 1, 2a, and 2b
from the solution spectroscopic data (see above) and similar
to the phen analogue previously reported.29
The addition of an equimolar amount of the strong base
KN(SiMe3)2 to a solution of the imidazole compounds 1, 2a,
and 2b in THF at low temperature caused deprotonation of
the N-H group, to afford the terminal imidazolate com-
plexes 3, 4a, and 4b, respectively. The transformation was
evidenced by a noticeable shift to lower wavenumbers of the
ν
CO bands in their IR spectra (from 2032 and 1926 cm-1 to
2017 and 1911 cm-1 for 1 and from 1955 and 1873 cm-1 to
1946 and 1863 cm-1 for 2a), consistent with the formation of
neutral products. The most characteristic feature of the H
1
NMR spectra of the new compounds is the absence of the
signal of the N-H group, while a pattern similar to that
found for the cationic precursors is encountered for the
remaining signals. The solid-state structure of the complex
3 was determined by single-crystal X-ray diffraction, and the
results are shown in Figure 1b.30 The rhenium atom is in an
approximately octahedral coordination geometry, and the
three carbonyl ligands are in a facial disposition. The imida-
zolate ligand is κ-N-coordinated and features a noncoordi-
nated nitrogen atom (N3).
The metallic fragments present in 1 and 3 differ only in one
hydrogen atom, the one at the N3 nitrogen atom in 1.31 The
most significant structural consequence of this difference is
the shortening of the Re1-N1 distance as a result of deproto-
nation of the imidazole ligand [from 2.193(3) A in 1 to
2.157(3) A in 3], reflecting the stronger σ-donor character of
imidazolate compared with the imidazole ligand. The C2-
N3-C5 angle is slightly more acute in 3 than in 1 [103.0(3)° vs
106.3(4)°], andtheN1-C2-N3 angle is broader in 3[114.9(3)°]
than in 1 [108.4(4)°]. These differences can be explained
considering that the nonbonding electron pair at N3 in
compound 3 is sterically more demanding than the one at
the N-H bond in 1 (Table 1).
The 13C NMR spectrum shows three signals at 137.9, 128.8,
and 119.1 ppm for the HIm ligand.25
In a similar way, complexes 2a and 2b were prepared by
substitution of the chloride ligand by HIm in the presence of
the salt NaBAr04 [Ar0 = 3,5-bis(trifluoromethyl)phenyl; see
Scheme 2b].26 The 1H and 13C NMR spectra of the new com-
pounds 2a and 2b agree with the proposed formulation,
showing the existence of a mirror plane in the complex and
the incorporation of one HIm ligand per metal center. The
observation of three imidazole C-H signals for the rhenium
and molybdenum complexes indicates that no fast dissociation-
recoordination of imidazole is taking place. Such a fast dis-
sociation would allow the concomitant exchange of the posi-
tions of hydrogen and metal (prototropy and metallotropy),
giving rise to the observation of only two CH ring signals in
the NMR spectra.27
Admittedly, these differences in distances and angles are
small. The topological analysis of the experimental electron
density, as obtained from Fourier maps in the X-ray diffrac-
tion experiment, can be used as an assessment of bonding
beyond the metrical parameters: the bonding properties of
the molecular structure are characterized in terms of the
charge density at (3, -1) or bond critical points, Fb.24,32 In 1
and 3, all bonds to the rhenium atom have a relatively low
value of Fb, ranging from 0.3 to 0.6 e A-3, diagnostic of the
metal-ligand bonds between closed-shell fragments. The
values of Fb at the Re1-N1 bonds are 0.361 and 0.475 e
The slow diffusion of hexane into a concentrated solution
of 1 in CH2Cl2 at -20 °C afforded yellow crystals, one of which
was used for the X-ray structure determination (Figure 1a).28
The solid-state structure is in agreement with the one deduced
(25) (a) Manganese imidazole complexes closely related to 1 have been
studied by Carlos et al.: Aguiar, I. de; Inglez, S. D.; Lima, F. C. A.; Daniel,
J. F. S.; McGarvey, B. R.; Tedesco, A. C.; Carlos, R. M.; et al. Inorg. Chem.
2008, 47, 11519. (b) Rhenium tricarbonylimidazole complexes have been
synthesized by Herrick, Ziegler, and co-workers: Franklin, B. R.; Herrick,
R. S.; Ziegler, C. J.; Cetin, A.; Barone, N.; Condon, L. R. Inorg. Chem. 2008,
47, 5902. (c) The behavior of [Re(CO)3(phen)(His)]þ species was studied by
Crane, Vlcek, Gray, and co-workers: Blanco-Rodríguez, A. M.; Busby, M.;
Gradinaru, C.; Crane, B. R.; Di Bilio, A. J.; Matousek, P.; Towrie, M.; Leigh, B. S.;
Richards, J. H.; Vlek, A., Jr.; Gray, H. B. J. Am. Chem. Soc. 2006, 128, 4365.
(26) The use of η3-allyl or η3-methallyl does not imply a substantial difference
in the chemical behavior of the compounds, although in some cases, it may be
crucial for crystallization. The choice of the allyl or methallyl ligand has been done
trying to obtain better crystallinity.
(27) Federov, L. A.; Kravtsov, D. N.; Peregudov, A. S. Russ. Chem. Rev.
1981, 50, 682.
(28) Selected crystallographic data for 1: C14H12F3N4O6ReS, M = 643.57,
monoclinic, P21/c, a = 11.8608(1) A, b = 6.8182(1) A, c = 25.4623(3) A,
R = 90.0°, β = 102.233(1)°, γ = 90.0°, 293(2) K, V = 2012.36(4) A3, Z = 4,
9474 reflections measured, 3834 independent (Rint = 0.0331), R1 = 0.0345,
wR2 = 0.0646 (all data).
A
-3 in 1 and 3, respectively, indicating that imidazolate is a
stronger σ donor than the imidazole ligand.33
The electron pairs, either bonding or nonbonding, can be
located using the topology of the Laplacian of the charge
(30) Selected crystallographic data for 3: C16H11N4O3Re, M = 493.49,
triclinic, P1, a = 7.7800 A, b = 7.9400 A, c = 12.6460 A, R = 91.411°, β =
100.554°, γ = 91.310°, 293(2) K, V = 767.4 A3, Z = 2, 12 228 reflections
measured, 4938 independent (Rint = 0.0409), R1 = 0.0405, wR2 = 0.0614
(all data).
(31) Hu, C.; Sulok, C. D.; Paulat, F.; Lehnert, N.; Twigg, A. I.; Hendrich,
M. P.; Schulz, C. E.; Scheidt, W. R. J. Am. Chem. Soc. 2010, 132, 3737.
(32) (a) Bader, R. F. W. In Atoms in Molecules;A Quantum Theory;
Oxford University Press: Oxford, U.K., 1990. (b) Bader, R. F. W. Chem. Rev.
1991, 91, 893.
(33) All other bonds are characterized by values of the electron density at
the bond critical point from 1.5 to 2.7 e A-3, indicating a shared interaction
consistent with covalent bonds. The Fb values in both azole rings (in the range
1.6-1.9 e A-3) indicate a bond character intermediate between single and
double, consistent with the bonds of highly delocalized, aromatic rings.
(29) Connick, W. B.; Di Bilio, A. J.; Hill, M. G.; Winkler, J. R.; Gray,
H. B. Inorg. Chim. Acta 1995, 240, 169.

ꢀ
Gomez et al.
9532 Inorganic Chemistry, Vol. 49, No. 20, 2010
Figure 1. (a) Molecular structure of the cation of compound 1. (b) Molecular structure of complex 3.
Table 1. Selected Bond Distances (A) and Angles (deg) for Compounds 1 and 3
bond distances (A) bond angles (deg)
Scheme 3. Synthesis of the Homobinuclear Compounds 5 and 6
1
3
1
3
Re1-N1 2.193(3)
2.157(3) N1-C2-N3 108.3(4) 114.9(3)
1.355(5) C2-N3-C5 106.4(5) 103.0(3)
1.330(5) N3-C5-C4 108.2(4) 110.5(3)
1.384(5) C5-C4-N1 110.7(4) 107.6(4)
1.360(6) C4-N1-C2 106.4(4) 104.0(3)
1.383(5)
N1-C2
C2-N3
N3-C5
C4-C5
C4-N1
1.374(6)
1.366(7)
1.357(7)
1.330(6)
1.322(6)
distribution: the maxima correspond in number, location,
and size to the localized pairs of electrons of a Lewis de-
scription.34 In complex 3, the imidazolate uncoordinated N3
nitrogen atom exhibits two large nonbonded electron pairs,
2
in the plane of the nuclei (r F = -10.1 e A-5) and per-
2
pendicular to that plane (r F = -10.3 e A-5), corresponding
to the two nonbonding electron pairs. In contrast, in the
imidazole complex of compound 1, the N3 nitrogen atom
2
shows a maximum perpendicular to the ring plane (r F =
2
-10.2 e A-5) and, in the plane, a less intense one (r F =
-5.1 e A-5), indicating nonbonded (the lone pair) and
bonded (the N-H bond) charge concentrations, respectively.
With the monomeric imidazolate complexes 3, 4a, and 4b
in hand, we aimed at the preparation of homo- and hetero-
bimetallic complexes. The addition of compound 3 to a
solution of [Re(OTf)(bipy)(CO)3] afforded, in about 1 h at
room temperature, the homobinuclear compound 5. The
homobinuclear molybdenum compound 6 was prepared in
a similar way (see Scheme 3a). Complexes 5 and 6 can be pre-
pared in an alternative, straightforward manner by the re-
action of the triflato complexes with in situ generated potas-
sium imidazolate in a 2:1 stoichiometry (see Scheme 3b).
The binuclear complexes 5 and 6 are symmetric, as evi-
1
denced by their spectroscopic data in solution. Hence, H
Figure 2. Molecular structure of the cation present in 5. Selected bond
distances (A) and angles (deg): Re1-N1 2.174(7), Re2-N3 2.165(8),
N1-C2 1.32(1), C2-N3 1.34(1), N3-C5 1.37(2), C5-C5 134(2), C4-N1
1.37(2); N1-C2-N3 115.4(9), C2-N3-C5 102.1(8), C4-N1-C2
103.8(9).
NMR spectra show only four sets of signals for the bipy (5) or
phen (6) ligands. The signals corresponding to the μ-κ-N:κ-
N0-imidazolate ligands are two singlets, one for the NC(H)N
group, and one for the two equivalent C-H groups. For
compound 6, the spectrum shows also the typical set of
signals of a η3-methallyl group in a complex with a mirror
plane (equivalent CH2 termini), integrating as two methallyl
groups for each Im unit. The 13C NMR spectra are also
consistent with the formation of symmetric binuclear com-
pounds. The slow diffusion of hexane into a concentrated
solution of compound 5 in CH2Cl2 at -20 °C afforded yellow
(34) (a) Bader, R. F. W.; Gillespie, R. J.; McDougall, P. J. J. Am. Chem.
Soc. 1988, 110, 7329. (b) Bader, P. J. In The Lagrangian Approach to
Chemistry, in Quantum Theory of Atoms in Molecules: From Solid State to
DNA and Drug Design; Matta, C. F., Boyd, R., Eds.; Wiley-VCH: Weinheim,
Germany, 2007; pp 37-59.

Article
Inorganic Chemistry, Vol. 49, No. 20, 2010 9533
Scheme 4. Synthesis of the Trimetallic Compound 8
Figure 3. Molecular structure of the cation of compound 8. Selected bond distances (A) and angles (deg): Mo1-N1 2.224(4), Mo2-N21 2.214(4),
Sn1-N3 2.299(4), Sn1-N23 2.296(4); N3-Sn1-N23 177.3(1), N1-C2-N3 113.1(4), N23-C22-N21 113.4(5).
crystals, one of which was used for the X-ray structure deter-
mination.35 Compound 5 is a (triflate) salt with a dirhenium
cation, shown in Figure 2. The two virtually identical {Re-
(CO)3(bipy)} fragments are linked by a μ-κ-N:κ-N0-imidazo-
late group. The Re-N(imidazolate) bond distances [Re1-N1
2.174(7) A and Re2-N3 2.165(8) A] are intermediate be-
tween that of the terminal imidazolate 3 [2.157(3) A] and the
one found in the imidazole complex 1 [2.193(3) A], reflect-
ing that the anionic character of the bridging ligand is, in
compound 5, shared by two {Re(bipy)(CO)3} fragments, and
therefore each one undergoes less electron donation than the
one in the terminal imidazolate complex 3. The bond dis-
tances and angles of the five-membered ring are also inter-
mediate between those in the imidazole (as in 1) and those in
the terminal imidazolate (as in 3).
complexes). Thus, the reaction of compound [Re(CO)3(Im)-
(phen)], the phen analogues of 3, with an equimolar amount
of [Mo(OTf)(η3-C3H5)(CO)2(phen)] led to the formation of 7.
Compound 7 could also be prepared by the inverse route,
i.e., the reaction of the molybdenum imidazolate complex 4b
and [Re(OTf)(phen)(CO)3]. The IR spectrum of 7 shows, in
the CO region, the bands corresponding to the fac-{Re(CO)3}
and cis-{Mo(CO)2} fragments. The 1H and 13C NMR spectra
are in concordance with the proposed formulation and show
the signals of two different phen ligands (each Cs-symmetric),
three different sets of signals for the three C-H groups of the
imidazolate bridge, and the signals of a symmetric, static (not
undergoing η3-η1 interconversions), η3-allyl. The slow diffu-
sion of hexane into a concentrated solution of 7 in CH2Cl2
afforded poor-quality crystals (see the Supporting Informa-
tion). The results of the X-ray structure determination are
hence of low quality, but the connectivity in the heterobime-
tallic cation present in 7, as derived from a topological
analysis of the experimental electron density, is unambiguous
and in agreement with the structure deduced from the
spectroscopic data in solution.
The synthesis of polynuclear compounds using a terminal
imidazolato complex as a ligand toward a second metal center
is not limited to transition metals. Thus, the imidazole com-
pound 2a was deprotonated in situ in THF, and the resulting
solution was treated with a hemimolar amount of SnClPh3,
affording the trinuclear complex 8 (Scheme 4). When the re-
action was carried out in a 1:1 stoichiometry, a mixture of 8
and unreacted SnClPh3 was obtained instead of the expected
Mo-Sn binuclear product, reflecting the tendency of the
Lewis acidic tin center to achieve pentacoordination. A similar
formation of 2:1 products in the reaction of tin compounds
For compound 5, the Laplacian of the electron density at
the N1 and N3 nitrogen atoms exhibit two pairs of maxima:
2
one perpendicular to the plane (r F = -10.0 e A-5 in N1
2
2
and r F = -10.1 e A-5 in N3) and one in the plane (r F =
5.7 e A-5 in N1 and r F = 5.5 e A-5 in N3). These values are
2
characteristic of nonbonded and closed-shell-bonded (metal-
ligand bond) charge concentrations, respectively.
Using a route like the one depicted in Scheme 3a, heterobi-
nuclear imidazolate-bridged complexes can be prepared (while
homobinuclear complexes could be prepared via the route
shown in Scheme 3b without isolation of mononuclear com-
plexes, route 3a allows the preparation of heterobinuclear
(35) Selected crystallographic data for 5: C30H19F3N6O9Re2S, M =
1068.97, orthorhombic, PC21n, a = 18.978 A, b = 10.373 A, c = 16.684 A,
R = 90.0°, β = 90.0°, γ = 90.0°, 293(2) K, V = 3284.4 A3, Z = 4, 23 194
reflections measured, 9828 independent (Rint = 0.0396), R1 = 0.0534, wR2 =
0.0660 (all data).

ꢀ
Gomez et al.
9534 Inorganic Chemistry, Vol. 49, No. 20, 2010
and simple (metal-free) imidazoles has been observed pre-
viously, and it was attributed to the formation of hydrogen
bonds between the imidazole N-H (a parent imidazole was
used) and halide ligands.36
scopic data in solution are in agreement with the structure
found in the solid state. The IR spectrum shows the expected
1
νCO pattern for a cis-{MoII(CO)2} fragment, and the H
NMR spectrum show the signals corresponding to two
equivalent {Mo(η3-methallyl)(CO)2(Im)(phen)} fragments per
bridging {SnPh3} group.
Compound 8 was fully characterized, including an X-ray
structure determination (see Figure 3).37 The cationic com-
plex consists of two {Mo(η3-methallyl)(CO)2(Im)(phen)} frag-
ments linked by a {SnPh3} unit. The Mo-N(imidazolate)
distances [2.224(4) A and 2.214(4) A] are intermediate
between the Mo-N(amine) [2.303(3) A] and Mo-N(amide)
[2.105(4) A] bond distances found for the corresponding
complexes of the analogous {Mo(η3-methallyl)(bipy)(CO)2}
fragment.38 The tin atom is pentacoordinated with a fairly
regular trigonal-bipyramidal configuration, with the three
phenyl groups occupying the equatorial positions and an
angle N3-Sn1-N23=177.3(2)°. The Sn-N(imidazolate)
distances are almost identical [2.299(4) A and 2.296(4) A] and
slightly shorter than the mean value (2.347 A) found for the
Sn-N bond distance for other tin(IV) imidazole adducts
(without taking into account their coordination numbers and
chemical nature).39 The bond distances and angles within the
imidazolate rings are very similar to each other and to those
found in the structure of 5 (see above), showing the slight
opening on the N-C-N angle as a consequence of the
bridging coordination mode of these ligands. The spectro-
Conclusions
In summary, we have synthesized the first organometallic
complexes with terminal imidazolato ligands by deprotona-
tion of stable, easily prepared, cationic imidazole complexes.
Topological analysis of the experimental electron density and
its Laplacian were used to provide information about the
differences in the electron density between the imidazolato
complexes and their imidazole precursors. The imidazolato
complexes serve as metalloligands in the rational synthesis of
homo- and heteronuclear compounds.
ꢀ
Acknowledgment. We thank the Ministerio de Educacion
y Ciencia (Ramon y Cajal contract to L.R. and Grant
ꢀ
CTQ2006-07036/BQU) and the Principado de Asturias
(FICYT, Grant IB08-104) for financial support.
Supporting Information Available: X-ray crystallographic
data for compounds 1, 3, 5, and 8 in CIF format, molecular
structures and crystallographic data for compounds 1, 3, 5, 7,
and 8, and IR and NMR spectra of compounds 1, 2a, 3, and
5-8. This material is available free of charge via the Internet at
http://pubs.acs.org. The atomic coordinates for these structures
have been deposited with the Cambridge Crystallographic Data
Centre. The coordinates (CCDC 735954, 735955, 735956, and
735957 for compounds 1, 3, 5, and 8, respectively) can be
obtained, upon request, from the Director, Cambridge Crystal-
lographic Data Centre, 12 Union Road, Cambridge CB2 1EZ,
U.K.
(36) (a) Pettinari, C.; Marchetti, F.; Pellei, M.; Cingolani, A.; Barba, L.;
Cassetta, A. J. Organomet. Chem. 1996, 515, 119. (b) Pettinari, C.; Pellei, M.;
Miliani, M.; Cingolani, A.; Cassetta, A.; Barba, L.; Pifferi, A.; Rivarola, E.
J. Organomet. Chem. 1998, 553, 345.
(37) Selected crystallographic data for 8: C92H63BF24Mo2N8O4Sn, M =
2140.88, monoclinic, P21/c, a = 13.685(5) A, b = 19.135(5) A, c = 35.816(5)
A, R = 90.0°, β = 108.895(5)°, γ = 90.0°, 293(2) K, V = 8915(4) A3, Z = 4,
16 798 reflections measured, 16 259 independent, R1=0.0807, wR2=0.1675
(all data).
ꢀ
(38) Morales, D.; Perez, J.; Riera, L.; Riera, V.; Miguel, D.; Mosquera,
M. E. G.; Garcıa-Granda, S. Chem.;Eur. J. 2003, 9, 4132.
(39) See ref 36 and references cited therein.
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