Dendronized scorpionate complexes of molybdenum in low and high oxidation states

Article abstract of DOI:10.1039/b710125b

Tridentate (L₃) and bidentate (L₂) poly(pyrazolyl)methane ligands (Gn-dend)OCH₂C(pz)₃ (1-4) and (Gn-dend)CH(3,5-Me₂pz)₂ (pz = pyrazol-1-yl) have been used to synthesize the molybdenum(0) complexes [Mo(CO)₃(L ₃)] (G0-G3, 5-8), [Mo(CO)₄(L₂)] (G0-G1, 13-14), and [Mo(CO)₃(NCMe)(L₂)] (G0, 15), and the molybdenum(vi) complexes [MoCl₂O₂(L₂)] (9-12). The G0-G3 prefixes represent the generation of poly(aryl ether) dendrons in which the metal complexes are embedded. The molecular structures of compounds 13 and 15 have been determined by X-ray diffraction studies and the hydrodynamic radii of tricarbonyl complexes 5-8 calculated by diffusion-ordered NMR spectroscopy (DOSY). Molybdenum(vi) compounds 9-12 have also been evaluated as catalysts for olefin epoxidation, showing comparable but inferior performances than ligand-free MoCl₂O₂, probably because of the labile coordination of L₂. The Royal Society of Chemistry.

Full text of DOI:10.1039/b710125b

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Dendronized scorpionate complexes of molybdenum in low and high
oxidation states†
Alberto Sa´nchez-Me´ndez, Alba M. Ortiz, Ernesto de Jesu´s,* Juan C. Flores* and Pilar Go´mez-Sal
Received 3rd July 2007, Accepted 18th September 2007
First published as an Advance Article on the web 4th October 2007
DOI: 10.1039/b710125b
Tridentate (L3) and bidentate (L2) poly(pyrazolyl)methane ligands (Gn-dend)OCH2C(pz)3 (1–4) and
(Gn-dend)CH(3,5-Me2pz)2 (pz = pyrazol-1-yl) have been used to synthesize the molybdenum(0)
complexes [Mo(CO)3(L3)] (G0–G3, 5–8), [Mo(CO)4(L2)] (G0–G1, 13–14), and [Mo(CO)3(NCMe)(L2)]
(G0, 15), and the molybdenum(VI) complexes [MoCl2O2(L2)] (9–12). The G0–G3 prefixes represent the
generation of poly(aryl ether) dendrons in which the metal complexes are embedded. The molecular
structures of compounds 13 and 15 have been determined by X-ray diffraction studies and the
hydrodynamic radii of tricarbonyl complexes 5–8 calculated by diffusion-ordered NMR spectroscopy
(DOSY). Molybdenum(VI) compounds 9–12 have also been evaluated as catalysts for olefin
epoxidation, showing comparable but inferior performances than ligand-free MoCl2O2, probably
because of the labile coordination of L2.
Despite this rapid development, poly(pyrazolyl) ligands have
Introduction
rarely been used in the chemistry of dendrimers or related
compounds. We initially incorporated scorpionate ligands into
metallodendrimers by taking advantage of the facile function-
alization of the bridging methine carbon atom in tris(pyrazol-
1-yl)methane,8 as first reported by Reger for the preparation of
related multitopic ligands and polynuclear compounds containing
tris(pyrazolyl)methane units.21 A different approach has also been
reported by Ciriano and Casado for the synthesis of carbosilane
dendrimers with peripheral bis- or tris(pyrazolyl)borate ligands
coordinated to rhodium.22 More recently, we have reported that
bis(pyrazol-1-yl)methane functionalized at the bridging methylene
group with poly(benzyl ether) dendritic wedges (Fre´chet dendrons)
forms monometallic nickel(II)9 and palladium(II) complexes.10
In a previous report,8 we showed that sterically demanding
substituents bonded directly to the methine bridging carbon of
tris(pyrazol-1-yl)methane ligands restrict the arrangement of the
pyrazolyl rings and can suppress the coordination capability of
these ligands. In order to relax the steric pressure caused by
dendritic substituents, we introduced an –OCH2– spacer between
the poly(benzyl ether) dendrons (Gn-dend) and the methine
carbon in the tris(pyrazol-1-yl)methane ligands reported here
(Chart 1). The coordination of bis(pyrazol-1-yl)methane ligands
is more flexible and Fre´chet’s dendrons can be linked directly to
their methylene bridges, as demonstrated elsewhere,9,10 even when
methyl substituents are introduced in the 3- and 5-positions of
the pyrazolyl rings. The synthesis and characterization of series of
Dendrimers functionalized with transition metals have aroused
great interest in catalysis, and a large variety of ligands have been
used for the fixation of metal complexes at the core, branches or
periphery of the dendritic macromolecules.1–3 We are interested
in the way in which the surrounding dendritic arms modulate
the properties of metal centers located at the core or focal
point of dendritic structures. With this aim, we have undertaken
studies on the functionalization of ligands with dendritic sub-
stituents [cyclopentadienido,4 siloxido,5 diketiminato,6 phosphine7
or poly(pyrazol-1-yl)methane8–10] and on the behavior of their
early and late transition metal complexes as catalysts (polymer-
ization and other carbon–carbon bond-formation reactions).4,6,7
These studies have been complemented with others to try to
understand the organization of the dendritic arms around the
metal centers in both the solid state and in solution.8,9
The work of Trofimenko in the field of scorpionate chemistry
meant that poly(pyrazolyl) ligands rapidly became a very impor-
tant class of nitrogen donors in modern coordination chemistry,11
and in the last few years the chemistry of poly(pyrazol-1-
yl)alkane complexes, the neutral and isoelectronic counterparts of
poly(pyrazol-1-yl)borates, has undergone significant progress.12,13
This renewed interest has been fuelled, in part, by advances in the
syntheses of the ligands themselves14 and also by their attractive
applications in catalysis,15 bioinorganic chemistry, inorganic and
organometallic syntheses, or crystal engineering.12–20 New metal
complexes with unusual structures have been prepared,16 and
major research fields such as heteroscorpionate metal chemistry
have grown.12,17–19
Departamento de Qu´ımica Inorga´nica, Universidad de Alcala´, Campus Uni-
versitario, 28871, Alcala´ de Henares (Madrid), Spain. E-mail: juanc.flores@
uah.es (J. C. F.), ernesto.dejesus@uah.es (E. de J.); Fax: +34 91 885 4683;
Tel: +34 91 885 4607
† CCDC reference numbers 652159 & 652160. For crystallographic data
in CIF or other electronic format see DOI: 10.1039/b710125b
Chart 1
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dioxidodichloridomolybdenum(VI) and molybdenum(0) carbonyl
complexes of both types of dendritic pyrazolyl ligands is described
in this work.
the IR spectra of these ligands is an absorption assigned to the
−1
=
asymmetric stretching of the C N bond at around 1520 cm ,
=
together with clearly visible bands assigned to the C C and C–
O–C vibrations (2–4). Peaks with isotope distributions that match
the calculated patterns for the molecular fragments plus sodium or
potassium cations were observed by ESI+-TOF mass spectrometry.
Results and discussion
Synthesis of dendronized tris(pyrazolyl)methane ligands 1–4
Synthesis of molybdenum complexes
Tridentate ligands (Gn-dend)OCH2C(pz)3 [Gn-dend = poly(benzyl
ether) dendron, pz = pyrazol-1-yl, 1–4] were synthesized by treat-
ing the bromoalkanes (Gn-dend)Br (G0–G3) with the alkoxide
NaOCH2C(pz)3 (Scheme 1) and isolated, after appropriate work-
up, as white or pale-yellow solids in good yields (>70%, see
Experimental for details). They are air-stable in the solid state and
in solution. Their solubility in alkanes or diethyl ether is poor and
decreases progressively as the generation number (n) increases. In
contrast, the solubility increases with generation in good solvents
such as acetone, THF, or aromatic and chlorinated solvents.
The carbonyl molybdenum(0) complexes [Mo(CO)3{(Gn-
dend)OCH2C(pz)3}] (5–8, Scheme 2, i) were isolated as yellowish
solids in good yields (> 83%) after treatment of one equivalent
6
of the tris(pyrazolyl)methane ligands 1–4 with [Mo(CO)3(g -
1,3,5-C6H3Me3)] in THF. The synthesis of the related com-
plexes [Mo(CO)3{HC(pz)3}] with tris(pyrazol-1-yl)methane or
tris(3,5-dimethylpyrazol-1-yl)methane ligands not substituted at
the bridging methine carbon was originally reported by Trofi-
menko starting from molybdenum hexacarbonyl.24,25 Complexes
5–8 are insoluble in alkanes or diethyl ether, partially soluble
in chlorinated or aromatic solvents, and soluble in acetone and
THF. Their solubility tends to increase with generation as a
consequence of the increase in the number of terminal groups at
the molecular surface of the dendritic wedge. They are relatively
stable to air in the solid state but decompose to brown materials
after several days.
Scheme 1 Synthesis of dendritic ligands 1–4. Reagents and conditions:
(a) 1 equiv. (Gn-dend)Br (n = 0, 1, 2, 3), THF, 0 ◦C; (b) room temperature,
overnight.
Scheme 2 Synthesis of molybdenum compounds with dendritic tris-
(pyrazolyl)methane ligands. Conditions: (i) 1 equiv. [Mo(CO)3(g -1,3,5-
6
C6H3Me3)], THF, room temperature, 5 h. (ii) 1 equiv. [MoCl2O2], THF,
room temperature, 1 h.
The three equivalent pyrazolyl rings of compounds 1–4 give rise
to three doublets of doublets at about d = 6.3 (H4), 7.4 (H5), and
7.6 ppm (H3) in the 1H NMR spectra and three singlets at about
Several oxidomolybdenum(VI) complexes have proven to be
useful catalysts for the epoxidation of olefins with hydroperoxides.
For example, Ku¨hn, Roma˜o and coworkers have synthesized
complexes of formula [MoXO2{HC(pz)3}]X (X = Cl, Br) starting
from [MoO2X2(THF)2].26 However, our attempts to isolate the
related complexes [MoClO2{(Gn-dend)OCH2C(pz)3}]Cl under
similar conditions failed to give pure products (Scheme 2, ii). Thus,
the treatment of ligands 1–4 with [MoCl2O2] or [MoCl2O2L2] (L =
THF or DMSO) in THF at room temperature resulted in the
precipitation of white, air-sensitive solids containing the expected
products spectroscopically almost pure (see Experimental for 1H
NMR data). These impure solids were found to be soluble in
chlorinated solvents and insoluble in diethyl ether, although all
attempts to obtain analytically pure samples failed or resulted in
decomposition.
1
d = 106 (C4), 131 (C5), and 141 ppm (C3) in the 13C{ H} NMR
spectra (See Chart 1 for the numbering scheme of the pyrazolyl
rings). The methine carbon [C(pz)3] is found at d = 90 ppm and
the protons attached to the neighboring methylene group appear
as a singlet at around d = 5.1 ppm. The protons of the dendritic
moieties give sets of resonances in the three regions characteristic
for this type of poly(benzyl ether) dendrons,9,10,23 namely multiplets
at d = 7.2–7.4 ppm for the terminal phenyl groups (Ph), a doublet
and a triplet at d = 6.4–6.6 ppm for each layer of internal aryl
groups (Ar), and a singlet at d = 4.5–4.9 ppm for each generation
1
of –CH2O– groups. The 13C{ H} NMR spectra of compounds
1–4 also show a set of resonances for each layer, the relative
intensities of which increase on going from the focal point to
the periphery of the dendron. The most significant band found in
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As an alternative to the preceding cationic molybdenum(VI)
complexes, neutral dioxido compounds of general formula
[MoCl2O2(L2)] can be prepared with bidentate instead of tridentate
pyrazolylmethane ligands.26 Thus, complexes 9–12 were isolated
as yellowish solids in good yields (77–89%) by treatment of
the dendritic bis(pyrazolyl)methane ligands (Gn-dend)CH(3,5-
Me2pz)2 (3,5-Me2pz = 3,5-dimethylpyrazol-1-yl)9 with [MoCl2O2]
in THF (Scheme 3, i). Complexes 9–12 are rather unstable to
air and moisture in both the solid state and in solution. They
are insoluble in alkanes or diethyl ether, partially soluble in
chlorinated or aromatic solvents, and soluble in THF.
in a matter of hours at room temperature (Scheme 3, iii). This
reaction led to pure [Mo(CO)3(NCMe){PhCH2CH(3,5-Me2pz)2}]
(15) in good yields (80%) thanks to the precipitation of the
complex from the reaction solution. However, treatment of
6
PhCH2CH(3,5-Me2pz)2 with [Mo(CO)3(NCMe)3], [Mo(CO)3(g -
1,3,5-C6H3Me3)], or [Mo(CO)6] in acetonitrile or in other polar
solvents such as THF or acetone in the presence of added
acetonitrile led to product mixtures containing varying amounts
of 13, 15, and the free ligand. Compounds 13–15 are insoluble in
alkanes, diethyl ether, aromatic solvents, and soluble in acetone or
acetonitrile; they decompose quickly in THF solution. They are
unstable to air and moisture in the solid state and in solution.
Moreover, solutions of pure compound 15 in [D6]acetone or
[D3]acetonitrile change over time to give mixtures of 15, 13, and
free ligand with relative compositions 6 : 2 : 1 (acetone) or 4 :
1 : 1 (acetonitrile) after 10 min, stabilizing after about 16 h at 2 :
3 : 1 (acetone) or 4 : 3 : 1 (acetonitrile) ratios. These solutions
were found to contain only 13 and free ligand [and probably
Mo(CO)6] after bubbling CO gas through them briefly. The initial
composition could be slowly recovered after replacing the CO
with an argon atmosphere. Similarly, solutions of compound
13 were transformed into the same mixture in [D3]acetonitrile
or in [D6]acetone and MeCN. It appears that compound 13
is more stable than 15 and that the CO/MeCN scrambling
process, which is promoted by polar solvents,29 facilitates the
equilibrium process, with concomitant formation of unidentified
Mo species and free ligand. It has been suggested that the
moderate stability of the bis(pyrazolyl)methane coordination in
[M(CO)4{CH2(pz)2}] (M = Cr, Mo, and W) complexes is partly
a consequence of the differences in the conformational energy
between the coordinated and free ligand.27a The steric repulsion
between the Gn-dend and pz-Me5 groups increases the rigidity of
the metallacycle in the complexes described here (see NMR and
X-ray discussion) and probably makes the coordination of the (Gn-
dend)CH(3,5-Me2pz)2 ligands even more unstable than that of the
unsubstituted CH2(pz)2 ligand. Shiu has shown that prolonged
thermolysis of [Mo(CO)4{(C6H5)CH(3,5-Me2pz)2}] in DME gives
[Mo(CO)3{(g2-C6H5)CH(3,5-Me2pz)2}] by decarbonylation and
Scheme
3
Synthesis of molybdenum compounds with dendritic
bis(pyrazolyl)methane ligands. Conditions: (i) 1 equiv. [MoCl2O2], THF,
room temperature, 1 h. (ii) 1 equiv. [Mo(CO)6], toluene, 55 ◦C, 4 (13) or
7 (14) days. (iii) 1 equiv. [Mo(CO)3(NCMe)3], toluene, room temperature,
4 h.
2
weak intramolecular g -binding of the phenyl group to the metal
Bis(pyrazolyl)methane ligands form molybdenum(0) carbonyl
complexes of general formula [M(CO)n{RRꢀC(pz)2}] (n = 3
or 4).27,28 Such compounds are usually prepared by heating a
solution of the free ligands and Mo(CO)6 for several hours
at temperatures higher than 70–80 ◦C in solvents such as
toluene, DME, or acetonitrile. The preparation of the dendritic
complexes [Mo(CO)n{(Gn-dend)CH(3,5-Me2pz)2}] was, however,
not that straightforward. Direct combination of Mo(CO)6 with
the respective (Gn-dend)CH(3,5-Me2pz)2 ligands in warm toluene
afforded compounds 13 (G0) and 14 (G1) in approximately 75%
yields (Scheme 3, ii), whereas almost complete decomposition
was observed in DME or THF. The reaction in toluene had to
be conducted at 55 ◦C because of the poor thermal stability of
the reaction mixtures, which gradually became dark at higher
center.28b A simple Cochrane molecular model suggests that such
2
an g -binding is even more favorable for the benzyl group of
complex 13. All attempts to promote a similar transformation
in 13 at reflux or by warming samples of the complex in a
sealed ampoule under vacuum in DME, THF, acetone, or toluene
resulted, however in mixtures of decomposition products and
unreacted 13.
All the reported complexes were characterized by 1H and
1
13C{ H} NMR and IR spectroscopy, elemental analysis, and mass
spectrometry. Coordination of the ligands to the molybdenum
atom only produces significant shifts in the proton and carbon-
13 resonances of the nuclei close to the metal center, especially
those in the 3-position of the pyrazolyl ring (Dd = +0.8, +0.7,
and +0.5 ppm for H3 and +5, +10, and +8 ppm for C3 in 5–8,
9–12, and 13–15, respectively).‡ The chemical shifts of most of
◦
temperatures (≥ 70 C). The reaction proceeded more slowly at
these lower temperatures and required several days for completion.
Periodic removal of the CO evolved under vacuum also proved
necessary to avoid its recoordination. In contrast, two of the
three acetonitrile ligands of [Mo(CO)3(NCMe)3] were replaced
by the G0 ligand PhCH2CH(3,5-Me2pz)2} in toluene or benzene
‡ Ligand (G0-dend)CH(3,5-Me2pz)2: 1H NMR (C6D6): d 1.97 (s, 6 H, pz-
Me3), 2.19 (s, 6 H, pz-Me5), 3.96 (d, JH,H = 7.2 Hz, 2 H, CH2), 5.57 (s, 2 H,
1
pz-H4), 6.38 (t, JH,H = 7.2 Hz, 1 H, CH), 6.9–7.0 ppm (m, 5 H, Ph). H
NMR ([D6]acetone): d 2.08 (s, 6 H, pz-Me3), 2.10 (s, 6 H, pz-Me5), 3.87 (d,
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the nuclei located at the core of dendrons are shifted progressively
upfield with increasing generation, from G0 to G3, in the metal
complexes described here. For example, the chemical shift of the
CH2C(pz)3 protons in 5–8 moves from d = 5.87 ppm in 5 to d =
5.82, 5.80, and 5.77 ppm in 6–8, respectively, the chemical shift of
H4 moves from d = 6.47 ppm in 5 to d = 6.45, 6.42 and 6.40 ppm
in 6–8, respectively, and that of H3 moves from d = 8.42 ppm in 5
to d = 8.38, 8.36, and 8.32 ppm in 6–8, respectively. Likewise, on
going from 9 to 11 the chemical shift of Me5 follows the sequence
d = 2.10, 2.05, and 2.01 ppm, that of Me3 the sequence d = 2.74,
2.73, and 2.71 ppm, that of pz-H4 the sequence d = 6.47, 6.45,
and 6.42 ppm, and that of CH(3,5-Me2pz)2 the sequence d = 6.09,
6.00, and 5.98 ppm. This small but consistent effect might be due
to an increased shielding at the focal point caused by the presence
of an increasing number of aryl groups.
The IR spectra were recorded for all the new complexes in KBr
=
pellets and show a mas(C N) absorption at around 1520 (5–8) or
1560 cm−1 (9–15). The number of IR bands in the region of the CO
stretching vibrations is in agreement with the proposed structures,
namely two absorptions for the tricarbonyl compounds 5–8 or 15
of approximate C3v symmetry (A1 + E) and four absorptions for
the tetracarbonyl complexes 13 and 14 of local C2v symmetry (2
A1, B1, and B2 modes). Two strong absorptions are observed in the
=
m(Mo O) region for complexes 9–12 at about 950 (asymmetric)
and 920 cm−1 (symmetric), in agreement with a cis-[MoO2]2+
geometry.
The molecular ions of complexes 5–9 were detected in the
ESI+-TOF mass spectra with the expected isotopic distributions,
although often with hydrogen or alkali-metal cations incorpo-
rated. The bis(pyrazolyl)methane complexes 9, 10, and 12 only
gave peaks corresponding to the free ligands, whereas fragments
derived from the molecular ions by the loss of one or more CO
groups (or acetonitrile for 15) were observed in the mass spectra
of the carbonyl compounds 13–15.
We recently published several studies dealing with the confor-
mational disposition of poly(benzyl ether) dendrons around the
metal center in bis(pyrazolyl)methane complexes of nickel(II)9
and palladium(II).10 These studies are relevant on account of
the role that dendrimers can play in the confinement of active
centers in catalytic processes.3 Our studies were based on solid-
state structures determined by single-crystal X-ray diffraction and
on nuclear longitudinal relaxation rates obtained in solution for
molecules with paramagnetic metal centers. In addition to its
conventional role of providing detailed information about the local
environment of active nuclei, NMR spectroscopy is also a powerful
tool for the study of overall molecular properties. Translational
motion can be studied in a practical way by diffusion NMR
spectroscopy.31 The hydrodynamic radii, RH, can be calculated
from the diffusion coefficient of a certain molecular species using
the Stokes–Einstein equation (eqn (1)), where kB is the Boltzmann
constant, T the absolute temperature, and g the viscosity of the
solution.
The pyrazolyl rings of complexes 5–15 give rise to a unique
set of proton and carbon-13 resonances at room temperature.
This is indicative of apparent C3v (5–8) or Cs (9–15) symmetry in
solution and is also in accordance with the single 13C resonances
observed for the carbonyl groups in complexes 5–8 (d = 230 ppm).
1
In contrast, the 1H and 13C{ H} NMR spectra of complexes
[MoClO2{(Gn-dend)OCH2C(pz)3}]Cl show the existence of two
different pyrazolyl groups in a 2 : 1 ratio assigned, respectively,
to the rings trans to the oxido and trans to the chlorido
ligands of a rigidly coordinated tris(pyrazolyl)methane ligand (see
Scheme 2).
The carbonyl groups of complexes 13 and 14 give rise to
three 13C resonances at d = 220, 208, and 207 ppm, respectively.
Because carbonyl groups are p-acceptors, the low-field signal was
assigned to the carbonyl groups located trans to the pyrazolyl
groups and the two higher field resonances to the mutually trans
CO ligands. The chemical inequivalence of the latter is coherent
with the predominance in solution of a boat conformation for
the bis(pyrazolyl) metallacycle, similar to that found in the solid
state, with no boat-to-boat conformational exchange (see below
and Fig. 1).8–10,28c,30 The number of CO resonances reduces to
two for 15 (d = 228, 207 ppm), as expected, as the coordinated
acetonitrile replaces one of the two mutually trans carbonyl groups
in 13.
kBT
6pgD
RH
=
(1)
We measured the self-diffusion coefficients of dendrimers 5–8
in deuterated acetone at 25 ◦C using high-resolution diffusion-
ordered spectroscopy (DOSY, see Experimental for details).32 The
values obtained were 13.4 × 10−10 (G0), 11.3 × 10−10 (G1), 9.1 ×
10−10 (G2), and 6.5 × 10−10 m2 s−1 (G3), respectively. The hydro-
dynamic radii of complexes 5–8 were calculated to be 5.0 (G0),
˚
5.9 (G1), 7.4 (G2), and 10.2 A (G3) from these measurements.
Eqn (1) assumes that sample molecules are spherical and much
larger than the solvent, therefore the calculated radii should be
considered as estimates. Riley et al.33 have reported RH values
for similar poly(benzyl ether) dendrons with pyrene units at their
focal point in good solvents, where the dendritic structures tend
to be extended, and in bad solvents, which favor the collapse
of the structure. Taking into account the larger size of the
tris(pyrazolyl)molybdenum tricarbonyl complex, the radii of 5–
8 in deuterated acetone are in good agreement with those reported
for the pyrene compounds in a good solvent such as THF (3.7
Fig. 1 ORTEP diagram of the structure of compound 13 with thermal
ellipsoids at 50% probability.
JH,H = 7.2 Hz, 2 H, CH2), 5.72 (s, 2 H, pz-H4), 6.42 (t, JH,H = 7.2 Hz, 1 H,
˚
CH), 7.15–7.25 ppm (m, 5 H, Ph).
(G0), 4.9 (G1), 6.2 (G2), and 10 A (G3)].
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99.9(1)◦ for those in cis positions, with the exception of the
Structures of [Mo(CO)4{PhCH2CH(3,5-Me2pz)2] (13) and
[Mo(CO)3(NCMe){PhCH2CH(3,5-Me2pz)2}] (15)
acute angle defined by the pyrazolyl nitrogen atoms [79.2(1)◦].
˚
˚
The average Mo–N [2.314(2) A] and Mo–C [2.004(3) A] bond
distances fall in the usual range,28,34 with slightly longer distances
to the carbonyl carbons that are mutually trans, as would be
expected. These carbonyl groups are somewhat tilted toward the
axis bisecting the Mo–CO(cis) bonds: the angle C(21)–Mo–C(22)
is 166.5(1)◦, while the dihedral angle defined by the N(1)–Mo–
N(3) and C(21)–Mo–C(22) planes is almost a right angle [89.7(1)◦].
This distortion is most likely due to the steric repulsions between
the trans carbonyl groups and the bis(pyrazolyl)methane ligand.
The metallacycle adopts a boat conformation, as typically found
in related complexes,28,34 and the benzyl group attached to the
methine carbon C(11) occupies the axial position. The same
arrangement has been found in palladium(II),8,10,30 nickel(II),9 and
molybdenum(0)28c complexes with RCH(3,5-Me2pz)2 ligands (R =
phenyl, benzyl, pyridyl, or dendrons) and has been ascribed to
the steric hindrance that would arise in the equatorial location
with the adjacent methyl groups at the 5-position of the pyrazolyl
rings. This steric repulsion between the R and pz-Me5 groups
confers rigidity on the metallacycle and explains the absence of
a boat-to-boat conformational exchange in solution (see NMR
discussion). The boat conformation is less pronounced on the side
of the metal centre than on that of the carbon bridge, and the
pyrazolyl rings show a saddlebag-type disposition with a dihedral
angle of 48.6(1)◦. The benzyl group is orientated asymmetrically
towards the hemi-space that contains the N(1)–N(2) pyrazolyl
ring, with a dihedral angle defined by the C(12)–C(13) bond and
the Mo · · · C(11) molecular axis of 137.4◦.
Fig. 1 and 2 show ORTEP representations of the molecular
structure of compounds 13 and 15, respectively, as determined
in the solid state by single-crystal X-ray diffraction studies; the
relevant structural data are given in Table 1.
The molecular structure of 13 (Fig. 1) shows a six-coordinate
central molybdenum atom in a distorted octahedral geometry with
the bis(pyrazolyl)methane group acting as a bidentate chelating
ligand. The bond angles around the metal centre are in the range
166.5(1)–177.0(1)◦ for atoms located trans each other and 84.0(1)–
Complex 15 was crystallized from C6D6. The asymmetric part
of the unit cell consists of two enantiomers (a and b) with similar
bond parameters—they differ only in the relative orientation of
the benzyl group—and two crystallization benzene molecules.
Fig. 2 and Table 1 concern the enantiomer adduct 15a·C6D6.
The molecular structure of 15 resembles that of 13 but with
the CO group situated anti to the phenyl ring replaced by
an acetonitrile ligand. Similar distortions are observed in the
octahedral geometry around the metal center, with bond angles
ranging from 177.6(3)◦ to 174.8(3)◦ for the atoms located trans
or from 101.7(3)◦ to 81.46(3)◦ for those located cis, and an N(1)–
Fig. 2 ORTEP diagram of the structure of compound 15·C6D6 (enan-
tiomer a) with thermal ellipsoids at 50% probability.
◦
˚
Table 1 Bond lengths [A] and angles [ ] for compounds 13 and 15
13
15 (enantiomer a)
Mo–C(21)
Mo–C(24)
Mo–C(23)
Mo–C(22)
Mo–N(1)
Mo–N(3)
2.044(3)
1.954(3)
1.963(3)
2.056(0)
2.320(2)
2.308(2)
Mo–C(21)
Mo–C(22)
Mo–C(23)
Mo–N(5)
Mo–N(1)
Mo–N(3)
1.967(9)
1.934(7)
1.916(8)
2.278(7)
2.328(6)
2.327(6)
◦
˚
Mo–N(3) angle of 78.6(2) . The Mo–N(pz) [2.328(6) A] and Mo–
˚
CO(mean) [1.939(8) A] bond distances are slightly longer and
shorter, respectively, than those found in 13, and the distances
to the carbonyl carbons trans to the chelate ligand are again
slightly shorter. The acetonitrile ligand is coordinated in a rather
linear mode [Mo–N(5)–C(24) = 173.6(6)◦, N(5)–C(24)–C(25) =
C(21)–Mo–C(23)
C(21)–Mo–C(24)
C(21)–Mo–C(22)
C(21)–Mo–N(1)
C(21)–Mo–N(3)
C(24)–Mo–N(1)
C(24)–M–N(3)
C(23)–Mo–C(24)
C(23)–Mo–N(1)
C(23)–Mo–N(3)
C(22)–Mo–C(23)
C(22)–Mo–C(24)
C(22)–Mo–N(1)
C(22)–Mo–N(3)
N(1)–Mo–N(3)
Mo–C(21)–O(1)
Mo–C(22)–O(2)
Mo–C(23)–O(3)
Mo–C(24)–O(4)
84.35(11)
83.95(11)
166.53(10)
97.70(9)
98.65(9)
175.37(9)
96.24(9)
84.51(11)
99.94(9)
176.96(9)
85.33(11)
86.47(11)
92.58(9)
91.77(9)
79.25(7)
170.4(2)
171.2(2)
175.8(2)
177.6(2)
C(21)–Mo–C(23)
C(21)–Mo–C(22)
C(21)–Mo–N(5)
C(21)–Mo–N(1)
C(21)–Mo–N(3)
C(22)–Mo–N(1)
C(22)–Mo–N(3)
C(23)–Mo–C(22)
C(23)–Mo–N(1)
C(23)–Mo–N(3)
N(5)–Mo–C(23)
N(5)–Mo–C(22)
N(5)–Mo–N(1)
N(5)–Mo–N(3)
N(1)–Mo–N(3)
Mo–C(21)–O(1)
Mo–N(5)–C(24)
Mo–C(23)–O(3)
Mo–C(22)–O(2)
N(5)–C(24)–C(25)
83.0(3)
81.6(3)
174.8(3)
99.6(2)
101.7(3)
177.6(3)
99.1(3)
83.3(3)
98.9(3)
175.0(3)
92.0(0)
96.4(3)
82.6(2)
83.4(2)
78.6(2)
171.2(6)
173.6(6)
177.1(6)
174.7(7)
178.0(9)
◦
˚
178.0(9) ] with an Mo–N(5) distance of 2.278(7) A. The carbonyl
group trans to acetonitrile is the most affected by the steric
repulsion between the ligands, being tilted toward the other
carbonyl ligands. The metallacycle in 15 adopts a similar boat
conformation to that described for 13. The dihedral angle between
the pyrazolyl rings is 50.2(3)◦, and the asymmetric positioning of
the benzyl group is defined by the dihedral angle C(13)–C(12)–
C(11) · · · Mo of 110.9◦.
Catalytic oxidation using molybdenum(VI) complexes 9–12
We tested these compounds as catalyst precursors for the epoxi-
dation of cis-cyclooctene with tert-butyl hydroperoxide under the
5662 | Dalton Trans., 2007, 5658–5669
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conditions described by Roma˜o and coworkers.26 The reactions
proved to be highly exothermic under these conditions, with
conversions of the olefin to the corresponding epoxide of more
than 90% in 10 min. Complete conversion were reached in less
than 30 min without significant differences between the four
dendritic complexes. [MoCl2O2] showed the same performance
as the bis(pyrazolyl) complexes in the absence of ligands.
We then reduced the Mo loading from 1 mol% to 0.05 mol% and
monitored the reaction under these milder conditions by GC (see
Experimental for further details). The catalytic profile was again
almost independent of the dendritic generation of the catalyst
(Fig. 3), and only the G0 compound 9 showed a slightly inferior
initial turnover frequency (5760 h−1 compared with approx.
11 000 h−1 for 10–12 in the first 5 min of reaction). Surprisingly,
ligand-free MoCl2O2 proved to be more active (14 640 h−1) than
any of the bis(pyrazolyl) complexes and afforded 100% conversion
after 5 h (compared with 92–96% for 9–12).
eration. The presence of an –OCH2– spacer between the dendritic
wedge and the C(pz)3 moiety permits the tridentate coordination
of the tris(pyrazolyl) ligands, as demonstrated by the straightfor-
ward preparation of their molybdenum(0) tricarbonyl complexes.
While the products resulting from the reaction of [Mo2Cl2O2]
with the tridentate ligands could not be isolated in a pure form,
the synthesis of the bis(pyrazolyl)methane complexes worked
well. Furthermore, compounds [Mo(CO)4{Gn-(dend)CH(3,5-
Me2pz)2}] [Gn
= G0 (13), G1 (14)] and [Mo(CO)3{G0-
(dend)CH(3,5-Me2pz)2}MeCN] (15) were isolated in good yields
as substances that are fairly unstable in solution. The character-
ization of these bidentate metal complexes in solution by NMR
spectroscopy and of 13 and 15 in the solid state by X-ray diffraction
is consistent with the conformational rigidity of the coordinated
bis(pyrazolyl)methane ligands, which could explain the tendency
of some of them to dissociate. The catalytic behavior of complexes
9–12 found in the epoxidation of cis-cyclooctene with tert-butyl
hydroperoxide is almost independent of the dendron-generation,
being slightly inferior in activity than the ligand-free MoCl2O2
parent compound.
Experimental
General remarks
All operations were performed under argon using Schlenk
or dry-box techniques. Unless otherwise stated, reagents were
obtained from commercial sources and used as received. The
6
compounds NaOCH2C(pz)3,8 [Mo(CO)3(g -1,3,5-C6H3Me3)],37
[Mo(CO)3(NCMe)3],38 (Gn-dend)Br (G1–G3),23 and (Gn-dend)-
CH(3,5-Me2pz)2 (G0–G3)9 were prepared according to literature
procedures. Solvents were previously dried and distilled under
argon as described elsewhere.39 NMR spectra were recorded with
Varian Unity 500+, VR-300, or 200 spectrometers. Chemical shifts
(d) are reported in ppm relative to SiMe4, and were referenced
Fig. 3 Catalytic profile in the oxidation of cis-cyclooctene for 9–12, and
the reference compound MoCl2O2.
1
with respect to 13C and residual H resonances of the deuterated
solvents. Coupling constants (J) are given in Hz. The following
abbreviations/notations are used: Ph refers to aromatic ring of
terminal benzyl groups, Ar to internal rings of benzyl ethers,
and ipso refers to the first ring-position on going from the di-
or tridentate pyrazolyl ligand. The numbering scheme for the
pyrazolyl ring atoms is given in Chart 1. IR spectra were recorded
with a Perkin-Elmer FT-IR Spectrum-2000 spectrophotometer.
The Microanalytical Laboratories of the University of Alcala´
performed the elemental analyses with a Heraeus CHN–O-Rapid
microanalyzer and the mass spectra with a Thermoquest-Finnigan
Automass Multi or an AGILENT 6210 LC/MS TOF Multi (ESI)
mass spectrometer. The products of catalysis were analyzed with a
CHROMPACK CP 9001 gas chromatograph using a fused silica
HP-INNOWax capillary column (15 m, 0.25 mm i.d., 0.25 lm df)
under the following conditions: injector and detector temperature:
250 ◦C; oven temperature program: 140 ◦C isotherm.
We have shown above that bidentate (Gn-dend)CH(3,5-Me2pz)2
ligands are more prone to dissociate from the metal center
due to steric conformational restraints. We can speculate that,
under catalytic conditions, the ligand dissociates quickly to afford
more active species, therefore the less congested G0 ligand is
initially less active and the ligand-free MoO2Cl2 precursor has
a higher initial TOF, although the differences are small. Colbran
and coworkers have recently studied alkene epoxidation using a
dioxo(pentaarylcyclopentadienido)molybdenum(VI) complex and
postulated that, in spite of the stability of the cyclopenta-
dienido coordination, decomposition to a much more active
non-cyclopentadienido-containing catalyst occurs as the reaction
proceeds.35 The low binding constants of bis(pyrazolyl)methane
ligands has been argued previously by Jordan to explain the per-
formance of bis(pyrazolyl)methanepalladium(II) compounds in
ethylene polymerization,36 and also explains the behavior observed
by us for nickel(II) complexes containing similar dendritic ligands.9
General procedure for the preparation of (Gn-dend)OCH2C(pz)3
(1–4). The corresponding benzyl wedge (Gn-dend)Br (n = 0,
1, 2, 3) and NaOCH2C(pz)3 were combined in THF (15 mL) at
0 ◦C. The temperature was subsequently allowed to rise to room
temperature and stirring was continued overnight. The resulting
reaction mixture was filtered through Celite using a cannula-filter,
the solvent was removed in vacuo, and the crude residue treated as
Conclusions
We have reported the synthesis of molybdenum(0) and molybde-
num(VI) complexes with bis- and tris(pyrazolyl)methane ligands
embedded in poly(benzyl ether) dendrons of up to the third gen-
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described individually below to give the title compounds as white
Ar), 141.3 (pz-C3), 159.9 (G0-m-Ar), 160.1 ppm (G1-m-Ar). IR
=
=
(1–3) or pale-yellow (4) solids.
(KBr pellet): m 1517 (m, C N), 1595 and 1451 (vs, C C), 1296
(s, C–O–Cas), 1146 and 1037 cm−1 (s, C–O–Cs). MS (ESI+-TOF
in CH2Cl2/MeOH/NH4HCOO 5 mM): m/z 1804.78 [(M − pz −
H)2]+, 1010.22 [M + K]+, 992.40 [M + Na – H]+, 767.30 [M − 3
pz − 2H]+.
(G0-dend)OCH2C(pz)3 (1). PhCH2Br (0.30 mL, 2.5 mmol)
and NaOCH2C(pz)3 (544 mg, 2.04 mmol). Recrystallized from
pentane. Yield: 616 mg (90%). Anal. Calc. for C18H18N6O (334.38):
C, 64.66; H, 5.43; N, 25.13%. Found: C, 64.12; H, 5.43; N,
1
(G3-dend)OCH2C(pz)3 (4). (G3-dend)Br (993 mg, 0.60 mmol)
and NaOCH2C(pz)3 (160 mg, 0.60 mmol). The resulting yellow
oil was triturated repeatedly with diethyl ether to give a solid.
Yield: 895 mg (82%). Anal. Calc. for C116H102N6O15 (1820.12): C,
76.55; H, 5.65; N, 4.62%. Found: C, 76.25; H, 5.59; N, 4.58%. 1H
NMR (CDCl3): d 4.42 (s, 2 H, G0–ArCH2O), 4.88 (s, 4 H, G1–
ArCH2O), 4.94 (s, 8 H, G2–ArCH2O), 4.99 (s, 16 H, PhCH2O),
5.09 [s, 2 H, CH2C(pz)3], 6.27 (dd, JH,H = 1.6, 2.5 Hz, 3 H, pz-H4),
24.71%. H NMR (CDCl3): d 4.50 (s, 2 H, PhCH2O), 5.12 [s,
2 H, CH2C(pz)3], 6.32 (dd, JH,H = 1.5, 2.5 Hz, 3 H, pz-H4), 7.14–
7.20 (m, 2 H, Ph), 7.25–7.34 (m, 3 H, Ph), 7.42 (d, JH,H = 2.5 Hz,
3 H, pz-H5), 7.64 ppm (d, JH,H = 1.5 Hz, 3 H, pz-H3). H NMR
1
([D6]acetone): d 4.55 (s, 2 H, PhCH2O), 5.11 [s, 2 H, CH2C(pz)3],
6.34 (dd, JH,H = 1.5, 2.5 Hz, 3 H, pz-H4), 7.20–7.35 (m, 5 H, Ph),
7.49 (d, JH,H = 2.5 Hz, 3 H, pz-H5), 7.59 (d, JH,H = 1.5 Hz, 3 H,
1
pz-H3). 13C{ H} NMR (CDCl3): d 73.4 and 74.1 (CH2OCH2), 89.8
4
4
[C(pz)3], 106.5 (pz-C4), 127.9 (p-Ph), 127.7 and 128.4 (o- and m-
6.41 (d, JH,H = 1.8 Hz, 2 H, G0-o-Ar), 6.50 (t, JH,H = 1.7 Hz,
4
Ph), 130.9 (pz-C5), 137.0 (ipso-Ph), 141.4 ppm (pz-C3). 13C{ H}
1
1 H, G0-p-Ar), 6.52 (t, JH,H = 2.0 Hz, 2 H, G1-p-Ar), 6.54 (t,
4JH,H = 2.2 Hz, 4 H, G2-p-Ar), 6.62 (d, JH,H = 2.0 Hz, 4 H,
4
NMR ([D6]acetone): d 73.9 and 74.3 (-CH2OCH2-), 90.6 [C(pz)3],
106.8 (pz-C4), 128.6 (p-Ph), 128.5 and 129.1 (o- and m-Ph), 131.7
(pz-C5), 138.5 (ipso-Ph), 141.5 ppm (pz-C3). IR (KBr pellet): m 1519
4
G1-o-Ar), 6.65 (d, JH,H = 2.2 Hz, 8 H, G2-o-Ar), 7.26–7.40 (m,
43 H, Ph and pz-H5 overlapping), 7.62 ppm (d, JH,H = 1.6 Hz, 3 H,
pz-H3). 13C{ H} NMR (CDCl3): d 70.0 (G1-ArCH2O), 70.1 (G2-
1
−1
+
=
=
=
(s, C N), 1620 (m, C C), 1451 cm (s, C C). MS (ESI -TOF
in CH2Cl2/MeOH/NH4HCOO 5 mM): m/z 357.14 [M + Na]+,
267.31 [M − pz]+, 199.23 [M − 2 pz − H]+.
ArCH2O and PhCH2O overlapping), 73.4 and 73.9 (-CH2OCH2-),
89.8 [C(pz)3], 101.5 (G0-p-Ar, G1-p-Ar and G2-p-Ar overlapping),
106.3 (G1-o-Ar, G2-o-Ar overlapping), 106.4(G0-o-Ar), 106.5(pz-
C4), 127.9 (p-Ph), 127.5 and 128.5 (o- and m-Ph), 130.8 (pz-C5),
136.7 (ipso-Ph), 139.1 (G1-ipso-Ar and G2-ipso-Ar overlapping),
139.5 (G0-ipso-Ar), 141.2 (pz-C3), 159.9 (G0-m-Ar), 160.0 (G1-m-
(G1-dend)OCH2C(pz)3 (2). (G1-dend)Br (766 mg, 2.00 mmol)
and NaOCH2C(pz)3 (532 mg, 2.00 mmol). Recrystallized by
dissolving the crude reaction mixture in the minimum volume of
diethyl ether, adding hexane, and stirring for several hours. Yield:
787 mg (72%). Anal. Calc. for C32H30N6O3 (546.63): C, 70.31; H,
5.53; N, 15.37%. Found: C, 70.31; H, 5.34; N, 15.07%. 1H NMR
(CDCl3): d 4.44 (s, 2 H, ArCH2O), 4.97 (s, 4 H, PhCH2O), 5.11
[s, 2 H, CH2C(pz)3], 6.31 (dd, JH,H = 1.5, 2.4 Hz, 3 H, pz-H4),
=
Ar), 160.1 ppm (G2-m-Ar). IR (KBr pellet): m 1516 (w, C N), 1595
and 1451 (vs, C C), 1295 (s, C–O–Cas), 1155 and 1047 cm (vs,
C–O–Cs). MS (ESI+-TOF in CH2Cl2/MeOH/NH4HCOO 5 mM):
m/z 1842.73 [M + Na]+, 1797.47 [M − pz + HCOO]+, 242.28
[OCH2C(pz)3 − H]+.
General procedure for the preparation of [Mo(CO)3{(Gn-dend)-
OCH2C(pz)3}] (5–8). Molybdenum compounds 5–8 were pre-
pared by combining the corresponding ligand 1–4 and
−1
=
4
4
6.43 (d, JH,H = 2.1 Hz, 2 H, o-Ar), 6.51 (t, JH,H = 2.1 Hz, 1 H,
p-Ar), 7.30–7.38 (m, 10 H, Ph), 7.40 (d, JH,H = 2.4 Hz, 3 H, pz-H5),
7.63 ppm (d, JH,H = 1.5 Hz, 3 H, pz-H3). 13C{ H} NMR (CDCl3):
1
d 70.1 (PhCH2O), 73.4 and 74.0 (-CH2OCH2-), 89.8 [C(pz)3], 101.6
(p-Ar), 106.5 (pz-C4), 106.6 (o-Ar), 128.0 (p-Ph), 127.5 and 128.6
(o- and m-Ph), 130.9 (pz-C5), 136.7 (ipso-Ph), 139.5 (ipso-Ar),
141.3 (pz-C3), 160.0 ppm (m-Ar). IR (KBr pellet): m 1515 (m,
6
[Mo(CO)3(g -1,3,5-C6H3Me3)] in THF (30 mL) in a Schlenk tube
at room temperature and stirring for 4–5 h. The solvent was
removed under reduced pressure and the residue washed with
pentane or diethyl ether to give 5–8 as yellow solids.
=
=
C N), 1595 and 1452 (s, C C), 1297 (s, C–O–Cas), 1165 and
1028 cm−1 (s, C–O–Cs). MS (ESI+-TOF in CH2Cl2/MeOH/
NH4HCOO 5 mM): m/z 1115.47 [M2 + Na]+, 569.23 [M + Na]+,
411.18 [M − 2 pz − H]+.
[Mo(CO)3{(G0-dend)OCH2C(pz)3}]
(5). (G0-dend)OCH2-
6
C(pz)3 (1; 100 mg, 0.30 mmol) and [Mo(CO)3(g -1,3,5-C6H3Me3)]
(88 mg, 0.29 mmol). Yield: 133 mg (86%). Anal. Calcd. for
C21H18MoN6O4 (514.35): C, 49.04; H, 3.53; N, 16.34%. Found:
(G2-dend)OCH2C(pz)3 (3). (G2-dend)Br (500 mg, 0.62 mmol)
and NaOCH2C(pz)3 (165 mg, 0.62 mmol). The resulting yellow
oil was triturated with diethyl ether to give a solid. Yield: 518 mg
(86%). Anal. Calc. for C60H54N6O7 (971.12): C, 74.21; H, 5.60; N,
1
C, 48.62; H, 3.69; N, 16.53%. H NMR ([D6]acetone): d 5.20 (s,
2 H, PhCH2O), 5.87 [s, 2 H, CH2C(pz)3], 6.47 (dd, JH,H = 1.5,
2.5 Hz, 3 H, pz-H4), 7.35–7.45 (m, 3 H, Ph), 7.50–7.55 (m, 2 H,
Ph), 8.02 (d, JH,H = 2.5 Hz, 3 H, pz-H5), 8.42 ppm (d, JH,H
=
1
8.65%. Found: C, 74.00; H, 5.73; N, 8.14%. H NMR (CDCl3):
1
1.5 Hz, 3 H, pz-H3). 13C{ H} NMR ([D6]acetone): d 68.7 and
74.3 (-CH2OCH2-), 85.2 [C(pz)3], 107.6 (pz-C4), 129.2, 129.3
and 129.5 (Ph), 133.9 (pz-C5), 137.0 (ipso-Ph), 146.3 (pz-C3),
d 4.43 (s, 2 H, G0-ArCH2O), 4.89 (s, 4 H, G1-ArCH2O), 5.01 (s,
8 H, PhCH2O), 5.11 [s, 2 H, CH2C(pz)3], 6.29 (dd, JH,H = 1.5,
2.0 Hz, 3 H, pz-H4), 6.40 (d, 4JH,H = 1.8 Hz, 2 H, G0-o-Ar), 6.48
229.9 ppm (CO). IR (KBr pellet): m 1906 and 1795 (vs, CO), 1517
(m, C N). MS (ESI -TOF in THF/MeOH/NH4HCOO 5 mM):
m/z 1028.70 [M2]+, 515.36 [M + H]+, 486.34 [M − CO]+, 458.33
[M− 2 CO]+, 430.32 [M − 3 CO]+, 357.37 [1 + Na]+, 335,39 [1 +
H]+, 199.23 [1 − 2 pz − H]+.
4
4
(t, JH,H = 1.8 Hz, 1 H, G0-p-Ar), 6.55 (t, JH,H = 2.1 Hz, 2 H,
+
=
4
G1-p-Ar), 6.64 (d, JH,H = 2.1 Hz, 4 H, G1-o-Ar), 7.26–7.40 (m,
23 H, Ph and pz-H5 overlapping), 7.62 ppm (d, JH,H = 1.5 Hz,
1
3 H, pz-H3). 13C{ H} NMR (CDCl3): d 69.9 (G1-ArCH2O), 70.1
(PhCH2O), 73.4 and 74.0 (-CH2OCH2-), 89.8 [C(pz)3], 101.5 (G0-
p-Ar and G1-p-Ar overlapping), 106.3 (G1-o-Ar), 106.4 (G0-o-
Ar), 106.5 (pz-C4), 128.0 (p-Ph), 127.5 and 128.6 (o- and m-Ph),
130.9 (pz-C5), 136.7 (ipso-Ph), 139.2 (G1-ipso-Ar), 139.5 (G0-ipso-
[Mo(CO)3{(G1-dend)OCH2C(pz)3}]
(6). (G1-dend)OCH2-
6
C(pz)3 (2; 109 mg, 0.20 mmol) and [Mo(CO)3(g -1,3,5-C6H3Me3)]
(60 mg, 0.20 mmol). Yield: 123 mg (85%). Anal. Calc. for
5664 | Dalton Trans., 2007, 5658–5669
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C35H30MoN6O6 (726.60): C, 57.86; H, 4.16; N, 11.57%. Found: C,
57.28; H, 3.96; N, 11.76%. 1H NMR ([D6]acetone): d 5.10 (s, 6 H,
ArCH2O and PhCH2O overlapping), 5.82 [s, 2 H, CH2C(pz)3],
6.45 (m, 3 H, pz-H4), 6.69 (t, 4JH,H = 2.0 Hz, 1 H, p-Ar), 6.78 (d,
4JH,H = 2.0 Hz, 2 H, o-Ar), 7.30–7.45 (m, 10 H, Ph), 8.02 (m, 3 H,
C–O–Cs). MS (ESI+-TOF in THF/MeOH/NH4HCOO 5 mM):
m/z 2001.10 [M + H]+.
General procedure for the preparation of [MoCl2O2{(Gn-dend)-
CH(3,5-Me2pz)2}] (9–12). [MoCl2O2] was weighed into
a
Schlenk tube in a dry-box and THF (15 mL) added. A THF
(15 mL) solution of one equivalent (see below) of the corre-
sponding chelating ligand (Gn-dend)CH(3,5-Me2pz)2 (n = 0–3)
was added, and the resulting yellow solution was stirred for 1 h at
room temperature. The solvent was then removed under vacuum
and the residue either washed with diethyl ether or recrystallized
from a mixture of toluene and hexane to give compounds 9–12 as
white or pale-yellow solids.
1
pz-H5), 8.38 ppm (m, 3 H, pz-H3). 13C{ H} NMR ([D6]acetone): d
70.5 (PhCH2O), 68.6 and 74.2 (-CH2OCH2-), 85.2 [C(pz)3], 102.6
(p-Ar), 107.7 (pz-C4), 108.2 (o-Ar), 128.7 (p-Ph), 128.4 and 129.3
(o- and m-Ph), 133.8 (pz-C5), 138.1 (ipso-Ph), 139.1 (ipso-Ar),
146.3 (pz-C3), 161.1 (m-Ar), 229.9 ppm (CO). IR (KBr pellet):
=
m 1900 and 1774 (vs, CO), 1519 (m, C N), 1598 and 1448 (s,
−1
=
C C), 1297 (s, C–O–Cas), 1160 and 1061 cm (s, C–O–Cs). MS
(ESI+-TOF in THF/MeOH/NH4HCOO 5 mM): m/z 1454.20
[M2]+, 1189.20 [M2 − Mo(CO)6]+, 1116.25 [(2)2Na]+, 727.61 [M +
H]+, 569.23 [2 + Na]+, 411.18 [2 − 2 pz − H]+.
[MoCl2O2{(G0-dend)CH(3,5-Me2pz)2}] (9). (G0-dend)CH(3,5-
Me2pz)2 (79 mg, 0.27 mmol) and [MoCl2O2] (50 mg, 0.25 mmol).
Yield: 110 mg (89%). Anal. Calcd for C18H22Cl2MoN4O2 (493.24):
C, 43.83; H, 4.50; N, 11.36. Found: C, 43.6; H, 4.05; N, 11.55. 1H
NMR (CDCl3): d 2.10 (s, 6H, pz-Me5), 2.74 (s, 6H, pz-Me3), 3.63
[Mo(CO)3{(G2-dend)OCH2C(pz)3}]
(7). (G2-dend)OCH2-
6
C(pz)3 (3; 110 mg, 0.11 mmol) and [Mo(CO)3(g -1,3,5-C6H3Me3)]
(32 mg, 0.11 mmol). Yield: 105 mg (83%). Anal. Calc. for
C63H54MoN6O10 (1151.10): C, 65.74; H, 4.73; N, 7.30%. Found: C,
65.35; H, 4.64; N, 7.19%. 1H NMR ([D6]acetone): d 5.06 (s, 4 H,
(d, JH,H = 7.5 Hz, 2 H, CH2), 5.98 (s, 2 H, pz-H4), 6.09 (t, JH,H
=
7.5 Hz, 1 H, CH), 6.81–6.84 (m, 2 H, Ph), 7.14–7.22 ppm (m,
1
3 H, Ph). 13C{ H} NMR (CDCl3): d 11.6 (pz-Me5), 15.6 (pz-Me3),
G1-ArCH2O), 5.08 (s, 8 H, PhCH2O), 5.10 (s, 2 H, G0-ArCH2O),
43.0 (CH2), 69.8 (CH), 109.7 (pz-C4), 128.9 (p-Ph), 128.8 and
4
5.80 [s, 2 H, CH2C(pz)3], 6.42 (m, 3 H, pz-H4), 6.64 (t, JH,H
=
129.1 (o- and m-Ph), 134.4 (ipso-Ph), 144.2 (pz-C5), 157.8 ppm
4
3
=
=
2.1 Hz, 2 H, G1-p-Ar), 6.68 (t, JH,H = 2.1 Hz, 1 H, G0-p-Ar),
(pz-C ). IR (KBr pellet): m 1562 (s, C N), 1620 (w, C C), 1459
4
4
−1
+
=
=
=
6.72 (d, JH,H = 2.1 Hz, 4 H, G1-o-Ar), 6.81 (d, JH,H = 2.1 Hz,
(s, C C), 950 (s, Mo Oas), 914 cm (s, Mo Os). MS (ESI -
TOF in THF/MeOH/NH4HCOO 5 mM): m/z 611.79 [(L)2Na]+,
317.39 [L + Na]+, 294.40 [L]+, 199.28 [L − Me2pz]+; L = (G0-
dend)CH(3,5-Me2pz)2.
2 H, G0-o-Ar), 7.26–7.45 (m, 20 H, Ph), 7.98 (m, 3 H, pz-H5),
8.36 ppm (m, 3 H, pz-H3). 13C{ H} NMR ([D6]acetone): d 70.3
1
(G1-ArCH2O), 70.5 (PhCH2O), 68.5 and 74.4 (–CH2OCH2–),
85.1 [C(pz)3], 101.9 (G1-p-Ar), 102.7 (G0-p-Ar), 107.2 (G1-o-Ar),
107.6 (pz-C4), 108.6 (G0-o-Ar), 128.6 (p-Ph), 128.5 and 129.3 (o-
and m-Ph), 133.8 (pz-C5), 138.1 (ipso-Ph), 139.0 (G0-ipso-Ar),
140.5 (G1-ipso-Ar), 146.1 (pz-C3), 161.0 (G1-m-Ar), 161.1
(G0-m-Ar), 229.9 ppm (CO). IR (KBr pellet): m 1904 and 1785
[MoCl2O2{(G1-dend)CH(3,5-Me2pz)2}] (10). (G1-dend)CH-
(3,5-Me2pz)2 (127 mg, 0.25 mmol) and [MoCl2O2] (48 mg,
0.24 mmol). Yield: 146 mg (86%). Anal. Calc. for C32H34Cl2-
MoN4O4 (705.49): C, 54.48; H, 4.86; N, 7.94%. Found: C, 54.44;
H, 4.71; N, 8.32%. 1H NMR (CDCl3): d 2.05 (s, 6 H, pz-Me5), 2.73
(s, 6 H, pz-Me3), 3.53 (d, JH,H = 7.5 Hz, 2 H, CH2), 4.90 (s, 4 H,
PhCH2O), 5.97 (s, 2 H, pz-H4), 6.00 (t, JH,H = 7.5 Hz, 1 H, CH
partially overlapped), 6.04 (d, 4JH,H = 2.2 Hz, 2 H, o-Ar), 6.46 (t,
=
=
(vs, CO), 1517 (m, C N), 1594 and 1451 (vs, C C), 1295 (s,
C–O–Cas), 1155 and 1053 cm−1 (s, C–O–Cs). MS (ESI+-TOF in
THF/MeOH/NH4HCOO 5 mM): m/z 1152.10 [M + H]+, 994.11
[3 + Na]+, 768.91 [3–3 pz − H]+.
1
4JH,H = 2.2 Hz, 1 H, p-Ar), 7.30–7.40 ppm (m, 10 H, Ph). 13C{ H}
NMR (CDCl3): d 11.6 (pz-Me5), 16.6 (pz-Me3), 43.0 (CH2), 69.6
(CH), 69.9 (PhCH2O), 101.7 (p-Ar), 107.9 (pz-C4), 108.0 (o-Ar),
127.4 and 128.7 (o- and m-Ph), 128.1 (p-Ph), 136.5 (ipso-Ar), 136.6
(ipso-Ph), 144.3 (pz-C5), 157.7 (pz-C3), 159.9 ppm (m-Ar). IR (KBr
[Mo(CO)3{(G3-dend)OCH2C(pz)3}]
(8). (G2-dend)OCH2-
6
C(pz)3 (4; 114 mg, 0.06 mmol) and [Mo(CO)3(g -1,3,5-C6H3Me3)]
(18 mg, 0.06 mmol). Yield: 102 mg (85%). Anal. Calc. for
C119H102MoN6O18 (2000.09): C, 71.46; H, 5.14; N, 4.20%. Found:
C, 71.21; H, 4.93; N, 3.85%. 1H NMR ([D6]acetone): d 5.00 (s, 8 H,
G2-ArCH2O), 5.02 (s, 4 H, G1-ArCH2O), 5.06 (s, 18 H, PhCH2O
and G0-ArCH2O overlapping), 5.77 [s, 2 H, CH2C(pz)3], 6.40
(m, 3 H, pz-H4), 6.61 (m, 7 H, G0-p-Ar, G1-p-Ar and G2-p-Ar
=
=
pellet): m 1561 (s, C N), 1595 and 1460 (s, C C), 1295 (vs, C–
−1
=
O–Cas), 1151 and 1030 (s, C–O–Cs), 956 (s, Mo Oas), 920 cm
+
=
(s, Mo Os). MS (ESI -TOF in THF/MeOH/NH4HCOO 5 mM):
m/z = 1036.29 [(L)2Na]+, 529.64 [L + Na]+, 507.66 [L + H]+, 411.52
[L − Me2pz]+, 316.40 [L − 2 Me2pz]+; L = (G1-dend)CH(3,5-
Me2pz)2.
4
overlapping), 6.68 (d, JH,H = 2.2 Hz, 4 H, G1-o-Ar), 6.71 (d,
4JH,H = 2.2 Hz, 8 H, G2-o-Ar), 6.78 (d, 4JH,H = 2.2 Hz, 2 H, G0-o-
Ar), 7.26–7.45 (m, 40 H, Ph), 7.97 (m, 3 H, pz-H5), 8.32 ppm (m,
[MoCl2O2{(G2-dend)CH(3,5-Me2pz)2}] (11). (G2-dend)CH-
(3,5-Me2pz)2 (140 mg, 0.15 mmol) and [MoCl2O2] (30 mg,
0.15 mmol). Yield: 140 mg (87%). Anal. Calc. for
C60H58Cl2MoN4O8 (1129.99): C, 63.78; H, 5.17; N, 4.96%. Found:
1
3 H, pz-H3). 13C{ H} NMR ([D6]acetone): d 70.4 (G1-ArCH2O),
70.5 (G2-ArCH2O and PhCH2O overlapping), 68.6 and 74.4
(-CH2OCH2-), 85.1 [C(pz)3], 102.0 (G2-p-Ar and G1-p-Ar
overlapping), 102.8 (G0-p-Ar), 107.3 (G2-o-Ar), 107.4 (G1-o-Ar),
107.7 (pz-C4), 108.6 (G0-o-Ar), 128.6 (p-Ph), 128.5 and 129.3 (o-
and m-Ph), 133.7 (pz-C5), 138.1 (ipso-Ph), 139.0 (G0-ipso-Ar),
140.5 (G1-ipso-Ar), 140.6 (G2-ipso-Ar), 146.3 (pz-C3), 161.0
(G1-m-Ar), 161.1 (G2-m-Ar), 161.2 (G0-m-Ar), 230.0 ppm (CO).
1
C, 63.81; H, 5.46; N, 5.01%. H NMR (CDCl3): d 2.01 (s, 6 H,
pz-Me5), 2.71 (s, 6 H, pz-Me3), 3.52 (d, JH,H = 7.3 Hz, 2 H, CH2),
4.84 (s, 4 H, ArCH2O), 5.01 (s, 8 H, PhCH2O), 5.95 (s, 2 H, pz-
H4), 5.98 (t, JH,H = 7.3 Hz, 1 H, CH partially overlapped), 6.01
4
4
(d, JH,H = 2.2 Hz, 2 H, G0-o-Ar), 6.48 (t, JH,H = 2.2 Hz, 1 H,
IR (KBr pellet): m 1905 and 1787 (vs, CO), 1518 (w, C N), 1595
G0-p-Ar), 6.55 (t, 4JH,H = 2.2 Hz, 2 H, G1-p-Ar), 6.66 (d, 4JH,H
=
=
−1
1
=
and 1449 (vs, C C), 1294 (s, C–O–Cas), 1152 and 1051 cm (vs,
2.2 Hz, 4 H, G1-o-Ar), 7.30–7.44 ppm (m, 20 H, Ph). H NMR
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(C6D6): d 1.32 (s, 6 H, pz-Me5), 2.75 (s, 6 H, pz-Me3), 3.57 (d,
JH,H = 7.5 Hz, 2 H, CH2), 4.75 (s, 12 H, ArCH2O and PhCH2O
overlapping), 5.36 (s, 2 H, pz-H4), 5.65 (t, JH,H = 7.3 Hz, 1 H,
N, 11.27%. 1H NMR ([D6]acetone): d 2.16 (s, 6 H, pz-Me5), 2.55
(s, 6 H, pz-Me3), 4.11 (d, JH,H = 7.8 Hz, 2 H, CH2), 6.08 (s, 2 H,
pz-H4), 6.45 (t, JH,H = 7.8 Hz, 1 H, CH), 7.02–7.10 (m, 2 H,
4
4
1
CH), 6.13 (d, JH,H = 2.0 Hz, 2 H, G0-o-Ar), 6.60 (t, JH,H
=
Ph), 7.22–7.30 ppm (m, 3 H, Ph). 13C{ H} NMR ([D6]acetone):
4
2.0 Hz, 2 H, G1-p-Ar), 6.64 (t, JH,H = 2.0 Hz, 1 H, G0-p-Ar),
6.69 (d, 4JH,H = 2.2 Hz, 4 H, G1-o-Ar), 7.05–7.30 ppm (m, 20 H,
d 11.2 (pz-Me5), 16.7 (pz-Me3), 40.1 (CH2), 69.6 (CH), 108.4 (pz-
C4), 128.4 (p-Ph), 129.5 and 130.2 (o- and m-Ph), 135.5 (ipso-
Ph), 144.3 (pz-C5), 155.5 (pz-C3), 206.5 and 208.0 (CO cis to pz),
1
Ph). 13C{ H} NMR (C6D6): d 11.0 (pz-Me5), 16.7 (pz-Me3), 43.1
(CH2), 69.8 (CH and ArCH2O overlapping), 70.1 (PhCH2O), 101.7
(G1-p-Ar), 102.3 (G0-p-Ar), 106.5 (G1-o-Ar), 108.2 (pz-C4), 109.5
(G0-o-Ar), 127.9 and 128.7 (o- and m-Ph), 128.1 (p-Ph), 137.2
(ipso-Ph), 137.3 (G0-ipso-Ar), 139.8 (G1-ipso-Ar), 144.2 (pz-C5),
157.7 (pz-C3), 160.6 (G0-m-Ar), 160.8 ppm (G1-m-Ar). IR (KBr
221.1 ppm (CO trans to pz). IR (KBr pellet): m 2012, 1890, 1868
−1
=
=
and 1809 (vs, CO), 1565 (s, C N), 1495 cm (s, C C). MS (ESI+
in THF/MeOH/NH4HCOO 5 mM): m/z 894.74 [(M − 2 CO +
H)2]+, 475.38 [M–CO + H]+, 451.40 [M – 3 CO + MeOH +H]+,
447.37 [M − 2 CO + H]+, 419.36 [M − 3 CO + H]+, 391.34 [M − 4
CO + H]+, 317.39 [L + Na]+, 199.28 [L − Me2pz]+; L = (G0-dend)-
CH(3,5-Me2pz)2.
=
=
pellet): m 1562 (s, C N), 1595 and 1452 (vs, C C), 1291 (vs, C–O–
−1
=
Cas), 1159 and 1046 (vs, C–O–Cs), 959 (s, Mo Oas), 923 cm (s,
+
=
Mo Os). MS (ESI -TOF in toluene/MeOH/NH4HCOO 5 mM):
[Mo(CO)4{(G1-dend)CH(3,5-Me2pz)2}] (14). (G1-dend)CH-
(3,5-Me2pz)2 (106 mg, 0.21 mmol) and [Mo(CO)6] (66 mg,
0.25 mmol). Yield: 115 mg (77%). Anal. Calc. for C36H34MoN4O6
(714.63): C, 60.51; H, 4.80; N, 7.84%. Found: C, 60.25; H, 4.45;
m/z 1885.28 [(L)2Na]+,1169.09 [M + K]+, 1152.98 [M + Na]+,
954.13 [L + Na]+, 932.15 [L + H]+, 836.01 [L − 2Me2pz]+; L =
(G2-dend)CH(3,5-Me2pz)2.
1
N, 7.32%. H NMR ([D6]acetone): d 2.13 (s, 6 H, pz-Me5), 2.56
[MoCl2O2{(G3-dend)CH(3,5-Me2pz)2}] (12). (G3-dend)CH-
(3,5-Me2pz)2 (150 mg, 0.08 mmol) and [MoCl2O2] (16 mg,
0.08 mmol). Yield: 0.122 g (77%). Anal. Calc. for C116H106Cl2-
MoN4O16 (1978.98): C, 70.40; H, 5.40; N, 2.83%. Found: C, 69.85;
(s, 6 H, pz-Me3), 4.00 (d, JH,H = 7.7 Hz, 2 H, CH2), 5.02 (s, 4 H,
PhCH2O), 6.11 (s, 2 H, pz-H4), 6.30 (d, 4JH,H = 2.2 Hz, 2 H, o-Ar),
6.37 (t, JH,H = 7.5 Hz, 1 H, CH), 6.56 (t, 4JH,H = 2.2 Hz, 1 H, p-Ar),
1
7.30–7.50 ppm (m, 10 H, Ph). 13C{ H} NMR ([D6]acetone): d 11.4
1
H, 5.62; N, 2.93%. H NMR (C6D6): d 1.34 (s, 6 H, pz-Me5),
(pz-Me5), 16.8 (pz-Me3), 40.3 (CH2), 69.4 (CH), 70.3 (PhCH2O),
102.7 (p-Ar), 108.6 (pz-C4), 109.1 (o-Ar), 128.3 and 129.3 (o-
and m-Ph), 128.7 (p-Ph), 137.6 (ipso-Ph), 138.1 (ipso-Ar), 144.6
(pz-C5), 155.6 (pz-C3), 161.1 (m-Ar), 206.4 and 207.9 (CO cis to
pz), 221.8 ppm (CO trans to pz). IR (KBr pellet): m 2012, 1883,
2.75 (s, 6 H, pz-Me3), 3.53 (d, JH,H = 8.1 Hz, 2 H, CH2), 4.68
(s, 4 H, G1-ArCH2O), 4.72 (s, 16 H, PhCH2O), 4.76 (s, 8 H, G2-
ArCH2O), 5.37 (s, 2 H, pz-H4), 5.64 (t, JH,H = 8.1 Hz, 1 H, CH),
6.12 (broad d, 2 H, G0-o-Ar), 6.64 (broad t, 5 H, G0-p-Ar and
G2-p-Ar overlapping), 6.70 (broad t, 2 H, G1-p-Ar), 6.73 (broad
d, 4 H, G1-o-Ar), 6.76 (broad d, 8 H, G2-o-Ar), 7.00–7.30 ppm
=
=
1869 and 1832 (vs, CO), 1562 (s, C N), 1593 and 1459 (s, C C),
1290 (s, C–O–Cas), 1150 and 1029 cm−1 (s, C–O–Cs). MS (ESI+ in
THF/MeOH/NH4HCOO 5 mM): m/z 1036.28 [(L)2Na]+, 687.63
[M–CO + H]+, 529.64 [L + Na]+, 507.27 [L + H]+, 411.52 [L −
Me2pz]+; L = (G1-dend)CH(3,5-Me2pz)2.
1
(m, 40 H, Ph). 13C{ H} NMR (C6D6): d 11.0 (pz-Me5), 16.8 (pz-
Me3), 43.0 (CH2), 69.7 (CH), 70.1 (G1-ArCH2O, G2-ArCH2O and
PhCH2O overlapping), 101.8 (G1-p-Ar), 101.9, (G2-p-Ar), 102.4
(G0-p-Ar), 106.6 (G1-o-Ar), 106.7 (G2-o-Ar), 108.3 (pz-C4), 109.6
(G0-o-Ar), 127.8 and 128.7 (o- and m-Ph), 127.9 (p-Ph), 137.3
(G0-ipso-Ar), 137.4 (ipso-Ph), 139.8 (G2-ipso-Ar), 139.9 (G1-ipso-
Ar), 144.4 (pz-C5), 157.7 (pz-C3), 160.3 (G0-m-Ar), 160.7 (G1-m-
[Mo(CO)3(NCMe){(G0-dend)CH(3,5-Me2pz)2}] (15). (G0-
dend)CH(3,5-Me2pz)2 (85 mg, 0.29 mmol) and [Mo(CO)3-
(NCMe)3] (88 mg, 0.29 mmol). Yield: 120 mg (80%). Anal. Calc.
for C23H25MoN5O3 (515.42): C, 53.60; H, 4.89; N, 13.59%. Found:
=
Ar), 161.1 ppm (G2-m-Ar). IR (KBr pellet): m 1560 (s, C N),
=
1598 and 1447 (vs, C C), 1294 (vs, C–O–Cas), 1163 and 1047
1
C, 53.82; H, 4.85; N, 13.69%. H NMR ([D6]acetone): d 2.05 (s,
−1
=
=
(vs, C–O–Cs), 954 (s, Mo Oas), 919 cm (s, Mo Os). MS (ESI+
in toluene/MeOH/NH4HCOO 5 mM): m/z 1803.13 [L + Na]+,
1780.14 [L + H]+; L = (G0-dend)CH(3,5-Me2pz)2.
3 H, CH3CN), 2.15 (s, 6H, pz-Me5), 2.43 (s, 6H, pz-Me3), 4.38
(d, JH,H = 8.0 Hz, 2 H, CH2), 5.96 (s, 2 H, pz-H4), 6.45 (t, JH,H
=
8.0 Hz, 1 H, CH), 7.15–7.20 (m, 2 H, Ph), 7.22–7.30 ppm (m, 3 H,
1
Ph). 13C{ H} NMR ([D6]acetone): d 11.2 (pz-Me5), 16.1 (pz-Me3),
General procedure for the preparation of [Mo(CO)3L{(Gn-dend)-
CH(3,5-Me2pz)2}] [L = CO (13, 14) and NCMe (15)]. The molyb-
40.0 (CH2), 69.8 (CH), 107.8 (pz-C4), 128.1 (p-Ph), 129.3 and
130.6 (o- and m-Ph), 136.4 (ipso-Ph), 142.7 (pz-C5), 154.2 (pz-C3),
6
denum precursor ([Mo(CO)6], [Mo(CO)3(g -1,3,5-C6H3Me3)], or
206.7 (CO cis to pz), 227.6 ppm (CO trans to pz). IR (KBr pellet):
[Mo(CO)3(NCMe)3]) was placed in an ampoule equipped with
a PTFE valve together with the appropriate amount of the
corresponding ligand (Gn-dend)CH(3,5-Me2pz)2 (n = 0, 1, see
below) and toluene (20 mL). The tube was sealed and the mixture
stirred at room temperature for 4 h (15) or warmed at 55 ◦C for four
(13) or seven days (14), applying vacuum briefly and periodically
through the PTFE valve. Compounds 13–15 precipitated out of the
reaction mixture as off-white to brown solids, which were filtered
and washed with hexane and diethyl ether.
−1
=
=
m = 1906 and 1764 (vs, CO), 1562 (s, C N), 1494 cm (s, C C).
MS (ESI+-TOF in THF/MeOH/NH4HCOO 5 mM): m/z 611.79
[(L)2Na]+, 519.46 [M–CO + MeOH]+, 475.38 [M–MeCN + H]+,
451.40 [M − 2 CO–MeCN + MeOH + H]+, 317.39 L + Na]+,
199.28 [L − Me2pz]+; L = (G0-dend)CH(3,5-Me2pz)2.
Spectroscopic characterization of
[MoClO2{Gn-(dend)OCH2C(pz)3}]Cl
[Mo(CO)4{(G0-dend)CH(3,5-Me2pz)2}] (13). (G0-dend)CH-
(3,5-Me2pz)2 (100 mg, 0.34 mmol) and [Mo(CO)6] (90 mg,
0.34 mmol). Yield: 130 mg (76%). Anal. Calc. for C22H22MoN4O4
(502.38): C, 52.60; H, 4.41; N, 11.15%. Found: C, 52.58; H, 3.90;
G0. 1H NMR (CDCl3): d 4.26 (s, 2 H, PhCH2O), 4.67 [s, 2 H,
CH2C(pz)3], 6.55 (dd, JH,H = 1.5, 2.8 Hz, 2 H, pz-H4), 6.63 (dd,
JH,H = 1.5, 2.8 Hz, 1 H, pz-H4), 6.86 (d, JH,H = 2.8 Hz, 2 H,
pz-H5), 7.10–7.15 (m, 2 H, Ph), 7.25–7.30 (m, 3 H, Ph), 7.94 (d,
5666 | Dalton Trans., 2007, 5658–5669
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JH,H = 1.5 Hz, 1 H, pz-H3), 7.99 (d, JH,H = 2.8 Hz, 1 H, pz-H5),
8.93 ppm (d, JH,H = 1.5 Hz, 2 H, pz-H3).
DOSY experiments
The diffusion coefficients were measured at 25 ◦C by using the
Dbppste (DOSY Bipolar Pulse Simulated Echo) pulse sequence in
a Varian NMR System 500 equipped with a high accuracy variable
G1. 1H NMR (CDCl3): d 4.16 (s, 2 H, ArCH2O), 4.62 [s, 2 H,
CH2C(pz)3], 4.98 (s, 4 H, PhCH2O), 6.37 (d, 4JH,H = 2.2 Hz, 2 H,
◦
temperature unit ( 0.1 C), a Performa IV PFG amplifier, and
o-Ar), 6.55 (m, 3 H, pz-H4 and p-Ar overlapping), 6.63 (dd, JH,H
=
a Z-PFG Triple Resonance 5-mm probe. Fine calibration of the
PFG strength (DAC to G unit) was performed with an H2O/HDO
(2 Hz) sample as standard supplied by Varian (D = 19.04 ×
10−10 m2 s−1 at 25 ◦C). The diffusion NMR data (Fig. 4) were
acquired over 64 scans, with settings pw90, an acquisition time of
3 s, a relaxation delay of 2 s, in each one of the 15 steps of the
gradient level array between 1 and 50 G cm−1 (50 ms of diffusion
delay and 2 ms of total defocusing time). The experimental data
(32 K × 1 K) was treated with the “DOSY” software from
VNMRJ2.1B.
1.8, 2.6 Hz, 1 H, pz-H4), 6.81 (d, JH,H = 2.6 Hz, 2 H, pz-H5), 7.30–
7.38 (m, 10 H, Ph), 7.95 (2 broad d, 1 + 1 H, pz-H3 and pz-H5,
overlapping), 8.91 ppm (d, JH,H = 1.8 Hz, 2 H, pz-H3).
G2. 1H NMR (CDCl3): d 4.17 (s, 2 H, G0-ArCH2O), 4.64
[s, 2 H, CH2C(pz)3], 4.94 (s, 4 H, G1-ArCH2O), 5.03 (s, 8 H,
4
PhCH2O), 6.37 (d, JH,H = 1.9 Hz, 2 H, G0-o-Ar), 6.50 (t,
4JH,H = 2.3 Hz, 2 H, G1-p-Ar), 6.57 (m, 3 H, pz-H4 and G0-p-
4
Ar, overlapping), 6.62 (m, 1 H, pz-H4), 6.65 (d, JH,H = 2.3 Hz,
4 H, G1-o-Ar), 6.82 (d, JH,H = 2.4 Hz, 2 H, pz-H5), 7.30–7.40 (m,
20 H, Ph), 7.92 (d, JH,H = 1.5 Hz, 1 H, pz-H3), 7.95 (d, JH,H
2.4 Hz, 1 H pz-H5), 8.91 ppm (d, JH,H = 1.5 Hz, 2 H, pz-H3).
=
X-Ray crystallographic studies
Single crystals of 13 and 15 suitable for X-ray diffraction studies
were obtained from their corresponding reaction mixtures in
C6D6 in NMR tubes. A summary of the crystal data, data
collection, and refinement parameters for the structural analysis
of each compound is given in Table 2. Suitable crystals were
covered with mineral oil and mounted in the N2 stream of a
Bruker-Nonius Kappa-CCD diffractometer equipped with an
area detector and an Oxford Cryostream 700 unit; data were
collected using graphite-monochromated Mo-Ka radiation (k =
G3. 1H NMR (CDCl3): d 4.13 (s, 2 H, G0-ArCH2O), 4.59
[s, 2 H, CH2C(pz)3], 4.91 (s, 4 H, G1-ArCH2O), 4.94 (s, 8 H,
4
G2-ArCH2O), 5.00 (s, 16 H, PhCH2O), 6.36 (d, JH,H = 2.0 Hz,
4
2 H, G0-o-Ar), 6.44 (t, JH,H = 2.2 Hz, 2 H, G1-p-Ar), 6.52 (t,
4JH,H = 2.2 Hz, 4 H, G2-p-Ar), 6.55 (m, 3 H, pz-H4 and G0-p-Ar,
overlapping), 6.61 (d, 4JH,H = 2.2 Hz, 4 H, G1-o-Ar), 6.62 (m, 1 H,
4
pz-H4), 6.65 (d, JH,H = 2.2 Hz, 8 H, G2-o-Ar), 6.78 (d, JH,H
=
=
2.4 Hz, 2 H, pz-H5), 7.25–7.40 (m, 40 H, Ph), 7.86 (d, JH,H
1.5 Hz, 1 H, pz-H3), 7.91 (broad d, 1 H, pz-H5), 8.86 ppm (d,
0.71069 A) at 200 K, with an exposure time of 10 s per frame (5
˚
JH,H = 1.5 Hz, 2 H, pz-H3).
sets; 266 frames; phi and omega scan 2◦ scan-width) for compound
Table 2 Crystal data and structure refinement for compounds 13 and 15
13
15·C6H6
Empirical formula
Formula weight
Color
C22H22MoN4O4
502.938
Yellow
200.0(2)
0.71069
C29H31MoN5O3
593.537
Yellow
Temperature/K
200.0(2) K
˚
˚
Wavelength (k)/A
0.71069 A
Crystal system, space group
Unit cell dimensions:
Monoclinic, P21/n
Triclinic, P-1
˚
a/A
12.651(5)
12.999(5)
13.437(5)
12.280(5)
12.284(5)
19.122(5)
83.470(5)
89.970(5)
89.760(5)
2865.8(1.8)
4, 1.376
˚
b/A
˚
c/A
a/◦
b/◦
c /◦
96.271(5)
3
˚
Volume/A
2196.5(1.5)
4, 1.519
0.633
1024
Z, Calculated density/g cm−3
Absorption coefficient/mm−1
F(000)
0.495
1224
Crystal size/mm
0.40 × 0.40 × 0.3
0.50 × 0.23 × 0.23
h ranges/◦
3.05 to 27.51
3.05 to 27.50
Limiting indices
−16 ≤ h ≤ 16, −16 ≤ k ≤ 16, −17 ≤ l ≤ 17
42259/5053 [Rint = 0.1094]
4008 [I > 2r (I)]
−15 ≤ h ≤ 15, −15 ≤ k ≤ 15, −24 ≤ l ≤ 23
25236/13133 [Rint = 0.13120]
5790 [I > 2r (I)]
Reflections collected/unique
Reflections observed
Completeness to h (%)
Refinement method
Data/restraints/parameters
Goodness of fit on F2
Final R indices [I > 2r(I)]a
99.8
99.8
Full-matrix least-squares on F2
5053/0/368
1.131
R1 = 0.0358, wR2 = 0.0814
Full-matrix least-squares on F2
13133/0/707
1.035
R1 = 0.0755, wR2 = 0.1729
2
1/2
a R1 = RꢁFo| − |Fcꢁ/R|Fo|; wR2 = {[Rx(Fo − Fc2)]/[Rx(Fo2)2]}
.
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The Royal Society of Chemistry 2007
Dalton Trans., 2007, 5658–5669 | 5667
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Dr M. V. Galakhov (NMR centre of the University of Alcala´) for
performing the DOSY experiments.
Notes and references
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Fig. 4 2D diffusion spectrum for compound 6.
13, and an exposure time of 36 s per frame (11 sets; 526 frames;
phi and omega scans 1.8◦ scan-width) for compound 15. Raw data
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The structure was solved by direct methods, completed by
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CCDC reference numbers 652159 & 652160.
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Acknowledgements
This work was financially supported by the Ministerio de
Educacio´n y Ciencia (project CTQ2005–00795/BQU), the Co-
munidad de Madrid (project S-0505/PPQ/0328–03), and the
Universidad de Alcala´ (FPI grant to A. S.-M. and Research
Initiation grant for A. O. A.). P. G.-S. is also indebted to the
“Factoria de Cristalizacio´n” (Consolider-Ingenio 2010). We thank
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The Royal Society of Chemistry 2007
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©