Molybdenum carbonyl complexes bearing PN ligands based on 2-aminopyridine

Article abstract of DOI:10.1002/ejic.200900535

Molybdenum complexes of the general formula Mo(PN)(CO)₄ containing both achiral and chiral phosphorus-nitrogen donor bidentate ligands based on 2-aminopyridine were prepared and characterized by their NMR and IR spectra. The oxidative addition

Full text of DOI:10.1002/ejic.200900535

FULL PAPER
DOI: 10.1002/ejic.200900535
Molybdenum Carbonyl Complexes Bearing PN Ligands Based on
2-Aminopyridine
Christina Maria Standfest-Hauser,[a] Georg Dazinger,[a] Julia Wiedermann,[a]
Kurt Mereiter,[b] and Karl Kirchner*[a]
Dedicated to Prof. Peter Stanetty on the occasion of his 65th birthday
Keywords: Molybdenum / Carbonyl complexes / Phosphanes / Amines / Oxidative addition / Allyl ligands / Density
functional calculations
Molybdenum complexes of the general formula Mo(PN)(CO)4
containing both achiral and chiral phosphorus-nitrogen do-
nor bidentate ligands based on 2-aminopyridine were pre-
pared and characterized by their NMR and IR spectra. The
oxidative addition of allyl bromide to Mo(PN)(CO)4 was
studied with PN = N-(diisopropylphosphanyl)-2-aminopyr-
idine (PN-iPr). X-ray structures of representative compounds
were determined. The mechanism of the oxidative addition
of allyl bromide to Mo(PN-iPr)(CO)4 was analyzed by DFT/
B3LYP calculations.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2009)
scribed.[4] In a preliminary study we have recently reported
on the synthesis of a series of square planar NiII and PdII
complexes featuring PN ligands.[2]
Introduction
Considering the comparative ease of phosphorus–nitro-
gen bond forming reactions compared to those in which
phosphorus–carbon bonds are formed, relatively few exam-
ples of pyridylphosphanes in which the donor atoms are
separated by amino groups are known. We have recently
described the synthesis of a series of tridentate (pincer)
PNP (I)[1] and bidentate PN ligands (II)[2] in which an
amine acts as spacer between the aromatic ring and the
phosphanes. In all these ligands, their electronic, steric, and
stereochemical properties can be easily varied in a modular
fashion by using different aryl and alkyl phosphanes as well
as different P–O bond containing achiral and chiral phos-
phane units. With PNP ligands, we thus far studied their
reactivity towards different transition metal fragments
which has been resulting in the preparation of a range of
new pincer complexes, including the first heptacoordinated
molybdenum pincer complexes,[1a] various iron complexes
acting as CO sensors,[1b,1d] and several pentacoordinate
nickel complexes.[3] Surprisingly, as PN complexes with li-
gands of the type II are concerned, in the literature only
few examples of transition metal complexes have been de-
Here we extend our studies on PN complexes based on
2-aminopyridine and report on the synthesis of a series of
molybdenum tetracarbonyl complexes of the general for-
mula Mo(PN)(CO)4. The oxidative addition of allyl bro-
mide to Mo(PN)(CO)4 is studied with PN = N-(diisopro-
pylphosphanyl)-2-aminopyridine (PN-iPr). Mechanistic as-
pects of this reaction will be supported by DFT/B3LYP cal-
culations.
Results and Discussion
Synthesis
Similarly to the known ligands PN-Ph,[5] PN-iPr, PN-
BIPOL, and PN-TARMe [2]
the new PN ligands PN-tBu,
,
PN-ETOL, and PN-BIPOL2tBu are prepared conveniently
in 68–85% yield by treatment of 2-aminopyridine with
1 equiv. of the respective chlorophosphane or chlorophos-
phite in the presence of a base (NEt3 and/or nBuLi)
(Scheme 1). All reactions were carried out in toluene at tem-
peratures between 25 to 90 °C for 15 h. The ligands were
[a] Institute of Applied Synthetic Chemistry, Vienna University of
Technology,
Getreidemarkt 9, 1060 Vienna, Austria
Fax: +43-1-58801-16399
E-mail: kkirch@mail.zserv.tuwien.ac.at
[b] Institute of Chemical Technologies and Analytics, Vienna Uni-
versity of Technology,
Getreidemarkt 9, 1060 Vienna, Austria
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K. Kirchner et al.
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Scheme 1.
isolated as air stable solids or oils and were characterized in the solid state and in solution for several days. Their
1
by 1H, 13C{1H}, and 31P{1H} NMR spectroscopy. Most di- identity was unequivocally established by H, 13C{1H} and
agnostic is the 31P{1H} NMR spectrum exhibiting a singlet 31P{1H} NMR, IR spectroscopy, and elemental analysis.
at 71.3, 140.0, and 151.0 ppm for PN-tBu, PN-ETOL, and
In the 31P{1H} NMR spectra, 1a–f exhibit singlets which
1
PN-BIPOL2tBu, respectively. In the H NMR spectrum the show the expected low-field shifts relative to the free unco-
NH proton gives rise to a slightly broadened singlet in the ordinated ligands [1a: 95.9 ppm (∆δ = 58.4 ppm), 1b:
range of 5.90 to 6.60 ppm. All other resonances are unre- 124.1 ppm (∆δ
= 64.0 ppm), 1c: 138.2 ppm (∆δ =
markable and are not discussed here. In addition, the solid- 66.9 ppm), 1d: 190.6 ppm (∆δ = 50.6 ppm), 1e: 196.5 ppm
state structure of PN-iPr was determined by X-ray crystal- (∆δ = 39.1 ppm), 1f: 194.2 ppm (∆δ = 43.2 ppm), 1f:
lography. A structural view is shown in Figure 1 with se- 202.9 ppm (∆δ = 52.8 ppm)]. In the 13C{1H} NMR spectra
lected bond lengths and angles given in the caption.
of 1a–f the carbon atoms of the four CO ligands give rise
to three characteristic low-field doublets. For instance, 1a
exhibits signals at 220.7 (JPC = 7.0 Hz), 216.1 (JPC
=
34.9 Hz), and 209.1 (JPC = 9.5 Hz) ppm. The two smaller
coupling constants are diagnostic for the phosphorus atom
in cis position with respect to the CO ligand.
The IR spectra of 1a–f show the typical pattern for cis-
[Mo(CO)4(L)(LЈ)] complexes [with local C2v symmetry, i.e.,
when only the symmetry of the Mo(CO)4 moiety of the
complexes is considered] in the carbonyl region. However,
in these and also related complexes[6] usually only three of
the four expected absorptions are observed. For instance,
while 1c exhibits four strong ν(C=O) absorptions at 2010,
1903, 1880, and 1812 cm–1, 1b gives rise to three absorp-
tions at 2019, 1879, and 1818 cm–1.
The solid-state structures of 1a–1d were determined by
X-ray crystallography. Structural views of 1b, 1c, and 1d are
shown in Figures 2, 3 and 4 with selected bond lengths and
angles given in Table 2. The coordination geometry around
the molybdenum center of the four complexes corresponds
to a modestly distorted octahedron with Mo–N 2.273 to
2.296 Å, Mo–P 2.409 (for 1d) to 2.560 Å (for 1c), and Mo–
C 1.963 to 2.064 Å. There is a clear trend that the Mo–
Figure 1. Molecular structure of PN-iPr showing 50% displace-
ment ellipsoids. Only N-bonded hydrogen is shown. Selected dis-
tances and angles (Å, deg): P1–N2 1.721(1), P1–C6 1.857(1), P1–
C9 1.856(1), N1–C1 1.339(1), N1–C5 1.346(1), N2–C1 1.382(1),
C1–C2 1.413(1), C2–C3 1.381(1), C3–C4 1.393(1), C4–C5 1.381(1);
P1···N1 2.999(1); P1–N2–C1–N1–17.9(1); hydrogen bond N2-
(H2n)···N1A 3.203(1).
Treatment of Mo(CO)6 with 1 equiv. of the respective PN C bonds trans to the pyridine N atom are short, trans to
ligands in toluene at 90 °C for 6 h afforded the tetra car- phosphorus are intermediate, and that the remaining are
bonyl complexes Mo(PN)(CO)4 (1a–g) in good isolated long. The bite angle N–Mo–P is near 76°. All other cis-
yields (74–91%) (Scheme 1). It has to be noted that the syn- bond angles about Mo are closer to 90°, varying between
thesis of 1a was already reported elsewhere.[5] All complexes 82 and 100°. All complexes deviate significantly from a pos-
are thermally robust yellow solids that are air stable both sible mirror symmetry for which Mo, P, pyridylamine, and
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Molybdenum Carbonyl Complexes Bearing PN Ligands
two CO groups would lie on a mirror plane. The r.m.s. 3.17 Å. In case of 1d this is a almost symmetrically
aplanarity of this moiety is in fact between 0.034 Å for 1d branched bifurcated hydrogen bond to O2 (N···O 3.10 Å)
(here the complex is closest to mirror symmetry) and and O3 (N···O 3.17 Å).
0.103 Å for 1c. It can be noted that the PN ligands cause a
systematic outward bending of the CO ligands off from the
PN ligand. This effect is due to the bulkiness of the PR2
moiety (PtBu2 Ͼ PiPr2 Ͼ ETOL ≈ PPh2) and is largest for
the tBu bearing complex 1c, which shows the longest Mo–
P bond length of 2.560 Å and the smallest C–Mo–C trans-
bond angle of 166.5° (all other corresponding angles lie be-
tween 172.5 and 174.4°). A typical feature of all four com-
plexes is the acidity of the NH group, which leads to inter-
molecular hydrogen bonding with the carbonyl oxygen
atom of a neighboring complex at N···O distances of 3.00–
Figure 4. Molecular structure of 1d. This complex approaches a
non-crystallographic Cs symmetry.
As part of our interest in the chemistry of molybdenum
PN complexes, we have begun to investigate the reactivity
of complexes 1 towards allyl bromide with the intention
to obtain η3-allyl complexes of the type Mo(PN)(η3-
CH2CHCH2)(CO)2Br. In the present study we have chosen
1b as model complex. Accordingly, the reaction of 1b with
1 equiv. of allyl bromide in toluene at 90 °C afforded, upon
workup, the seven coordinate η3-allyl complex Mo-
(PN-iPr)(η3-CH2CHCH2)(CO)2Br (2) as air-stable orange
solid in 82% yield (Scheme 2). Alternatively, however, 2 can
be also obtained under mild conditions (room temperature)
in 84% yield by treatment of Mo(η3-CH2CHCH2)(CO)2-
(CH3CN)2Br with 1 equiv. of PN-iPr in CH2Cl2. The ident-
ity of 2 was established by 1H, 13C{1H}, and 31P{1H}
NMR, IR spectroscopy, and elemental analysis.
Figure 2. Molecular structure of 1b showing 50% displacement el-
lipsoids. H atoms omitted for clarity.
1
The H NMR spectrum shows the expected resonances
for the allyl moiety giving rise to five signals. The central
allylic hydrogen atom exhibits a multiplet at δ = 4.30 ppm,
while the signals of the terminal allylic protons appear as
doublets or broad singlets at 4.10, 3.58, 1.81, and 1.70 ppm
(the latter being superimposed with the CH3 protons of the
iPr substituent). In the 13C{1H} NMR spectrum the allylic
carbon atoms appear at 120.6, 77.2, and 62.0 ppm. The
characteristic resonance of the magnetically inequivalent cis
carbonyl ligands give rise to resonances at δ = 226.3 and
223.1 ppm with coupling constants JCP of 13.2 and 8.0 Hz,
respectively, indicating that the CO ligands are both coordi-
nated cis with respect to the iPr2 moiety. The IR spectrum
displays the two expected peaks for a cis dicarbonyl struc-
ture at 1925 and 1835 cm–1.
Figure 3. Molecular structure of 1c (50% displacement ellipsoids,
H atoms omitted for clarity). The Figure emphasizes the steric ef-
fect of the bulky tBu groups on the two carbonyl groups C16–O3
und C17–O4. P1 deviates by –0.315(2) Å from the least-squares
plane of the pyridine ring, Mo1 by 0.152(2) Å. P1–N2–C1–N1
15.8(1)°.
Scheme 2.
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The molecular structure of 2 was unequivocally deter- substitution of the CH3CN ligands by PN-iPr is obviously
mined by X-ray crystallography. A structural view is shown accompanied by an isomerization step. The Mo–N, Mo–P,
in Figure 5 with selected bond lengths and angles given in and Mo–CCO bond lengths are close to those observed for
the caption. This molecule can be described as pseudo octa- complexes 1a through 1d (Table 2). The allyl group adopts
hedral with the assumption that the η3-allyl moiety occu- an orientation, which is fixed by intramolecular contacts
pies one coordination site. An equatorial plane can be de- between the allyl group and the pyridine ring, with the C5
fined to include the two carbonyls [C(15)–O(1) and C(16)– group of the pyridine ring intercalated between the allyl CH
O(2)], the halogen [Br(1)], and the nitrogen atom [N(1)] of group C13 and the allyl CH2 group C14. Different from
the PN-iPr ligand. The η3-allyl ligand and the phosphorus complexes 1a through 1d, the N–H group forms an inter-
atom of PN-iPr lie trans to one another in apical positions molecular hydrogen bond to Br rather than to O, N2···Br1
above and below the equatorial plane. This is in contrast to 3.465(2) Å.
Mo(η3-CH2CHCH2)(CO)2(CH3CN)2Br where the bromide
ligand is coordinated trans to the η3-allyl moiety. Thus, the
Mechanistic Aspects of the Oxidative Addition of Allyl
Bromide
In the absence of detectable intermediates on the way
from 1b (A in the calculations) to the η3-allyl complex 2
(G1 in the calculations) we performed DFT (B3LYP) calcu-
lations using Gaussian03. Along these lines several path-
ways and key intermediates can be proposed and these are
depicted in Figures 6, 7, and 8 (free energies in kcal/mol).
The reliability of the computational method (Details in Ex-
perimental Section) is supported by the excellent agreement
between the calculated geometries of 1b and 2 and their X-
ray structures.
The reaction is most likely initiated by CO loss from A
creating a vacant coordination site for an incoming sub-
strate. For comparison, it has to be mentioned that in re-
lated complexes such as Mo(CO)5(pyridine) and Mo(CO)5-
(piperidine) first bond dissociation energies have been ex-
perimentally determined to be 29.7 and 43.7 kcal/mol,
respectively.[7] For Mo(CO)6 first bond dissociation energies
were found to be in the range of about 35 to 40 kcal/mol.[8]
Figure 5. Molecular structure of 2 (50% displacement ellipsoids, H
atoms omitted for clarity). Selected bond lengths and angles (Å,
deg): Mo1–C16 1.935(2), Mo1–C15 1.957(2), Mo1–C13–2.223(2),
Mo1–C12–2.328(2), Mo1–N1 2.329(2), Mo1–C14 2.351(2), Mo1–
P1–2.5215(5), Mo1–Br1–2.6863(3) Å; N1–Mo1–P1 75.20(4), P1–
Mo1–C13 163.46(5).
Figure 6. Profile of the B3LYP potential energy surfaces (free energies in kcal/mol) for the formation and interconversion of tricarbonyl
complexes B1 and B2 and addition of allyl bromide via (a) an initial η2 π complex and via (b) a direct Br attack to give C1 and C2,
respectively.
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Molybdenum Carbonyl Complexes Bearing PN Ligands
Figure 7. Profile of the B3LYP potential energy surfaces (free energies in kcal/mol) for the conversion of C1 to the final η3-allyl complex
G1.
ticularly B3 is unlikely. However, B1 is able to isomerize to
B2 via TSBB with an energy barrier of 22.0 kcal/mol (Fig-
ure 6). As it turns out, B2 is the crucial intermediate on
the pathway to the final η3-allyl complex G1. The oxidative
addition of allyl bromide leads to the formation of the pre-
liminary η2-π complex C1 where the terminal C=C double
bond interacts with the metal center (pathway a). In an al-
ternative pathway, the oxidative addition can follow a dif-
ferent mechanism where the bromine atom directly attacks
the molybdenum center to give intermediate C2 (pathway
b). Similar pathways have been established recently by DFT
calculations for the oxidative addition of allyl bromide to
Ni(CO)4.[9] Both intermediates are formed without any bar-
rier lying 14.8 and 9.3 kcal/mol, respectively, lower in en-
ergy than B2 + free allyl bromide. The octahedral interme-
diates C1 and C2 contain trans CO ligands which is an es-
Figure 8. Profile of the B3LYP potential energy surfaces (free ener-
sential prerequisite for rendering the subsequent CO disso-
ciation step feasible. Accordingly, the calculated free energy
required to form D1 and D2 of 22.5 and 24.8 kcal/mol,
respectively, is experimentally accessible (Figures 7 and 8)
and is associated with the cleavage of a Mo–C bond. D1
reacts via TSDE to afford E1 where the allyl ligand is coor-
dinated in an η3-C,C,Br fashion. This is essentially a rota-
tion about the C–C single bond by about 180° thereby
forming a new Mo–Br bond. E1 is an unstable intermediate
which undergoes facile C–Br bond cleavage with a barrier
of merely 0.5 kcal/mol to form the η3-allyl complex F1.
Counter-clockwise rotation of the η3-allyl moiety by
roughly 80° leads to the final product G1.
gies in kcal/mol) for the conversion of C2 to the intermediate η3-
allyl complex E2.
Since CO has a higher trans influence and trans effect
than phosphanes and pyridine, dissociation of one of the
two CO ligands which are coordinated trans to one another
is strongly favored. This is also in line with DFT calcula-
tions showing that the formation of square pyramidal inter-
mediate B1 is strongly favored over B2 and B3 (Scheme 3).
The free energy of formation for B1 is 26.9 kcal/mol,
whereas B2 and B3 require free energies of formation of
35.4 and 45.1 kcal/mol, respectively. It has to be noted how-
ever that experimentally this is not an equilibrium situation
In the case of the second pathway, the conversion of D2
since CO will at least partially escape from solution and A to F1 involves migration of the η1-Br allyl ligand trans to a
will not be reformed completely. We therefore have chosen CO ligand with concomitant coordination of the terminal
B1 arbitrarily as zero energy point. Due to the high free C=C double bond and C–Br bond cleavage as shown in
energies of formation the direct formation of B2 and par- Figure 8. The free activation energy for this process is
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Scheme 3.
1
sieves. H, 13C{1H}, and 31P{1H} NMR spectra were recorded on
a Bruker AVANCE-250 spectrometer and were referenced to SiMe4
and H3PO4 (85%), respectively.
5.7 kcal/mol. It has to be noted that in contrast to the oxi-
[9]
dative addition of allyl bromide to Ni(CO)4 an η1-allyl
intermediate as a result of an oxidative addition via a SN2
type mechanism is not a stable entity in this particular sys-
tem and no stationary point could be located. This may
largely be attributed to steric reasons.
2-Amino-N-(di-tert-butylphosphanyl)pyridine (PN-tBu): A solution
of 2-aminopyridine (0.50 g, 5.31 mmol) and NEt3 (0.81 mL,
5.844 mmol) in 10 mL of anhydrous toluene was cooled to 0 °C
and treated with nBuLi (5.31 mmol, 2.3 mL of a 2.3  solution in
n-hexane). After 15 min of stirring at this temperature ClPtBu2
(1.01 mL, 5.31 mmol) was slowly added and the solution was
heated to 90 °C and stirred for 15 h. The solution was then filtered
and the solvent was removed under vacuum; yield 0.86 g (68%).
C13H23N2P (238.31): calcd. C 65.52, H 9.73, N 11.76; found C
The overall reaction sequence A + allyl bromide Ǟ G1
+ 2CO in the gas phase is endergonic by 14.9 kcal/mol. The
rate-determining step is the dissociation of CO. Note-
worthy, solvation effects were evaluated with the polarized
continuum model (PCM) method leading to similar results
with only 2–3 kcal/mol differences. Under experimental
conditions, however, one can expect that once CO has dis-
sociated from the metal complexes, it will at least partially
escape from solution with minimal chances for recombina-
tion with the metal complex to reform A. Accordingly, the
equilibrium will be shifted towards the formation of the η3-
allyl complex G1 Moreover, the increase of entropy in this
particular case appears to be underestimated by DFT calcu-
lations.[10]
1
65.12, H 9.77, N 11.80. H NMR (CDCl3, 20 °C): δ = 8.03 (d, J =
4.1 Hz, 1 H, py6), 7.43 (vt, J = 7.9 Hz, 1 H, py4), 7.13 (d, J =
8.4 Hz, 1 H, py3), 6.62 (vt, J = 5.9 Hz, 1 H, py5), 5.02 (d, J =
9.6 Hz, 1 H, NH), 1.16 and 1.11 [2s, 9H each, C(CH3)3] ppm.
13C{1H} NMR (CDCl3, 20 °C): δ = 160.9 (d, JCP = 18.2 Hz, py2),
147.9 (d, JCP = 0.8 Hz, py6), 137.6 (d, JCP = 1.5 Hz, py4), 114.2 (d,
JCP = 0.8 Hz, py5), 109.0 (d, JCP = 18.4 Hz, py3), 34.2 and 33.9 [2s,
C(CH3)3], 28.2 and 27.9 [2s, C(CH3)3] ppm. 31P{1H} NMR
(CDCl3, 20 °C): δ = 71.3 ppm.
2-Amino-N-(1,3,2-dioxaphospholane-1-yl)pyridine (PN-ETOL):
A
solution of 2-aminopyridine (0.50 g, 5.31 mmol) in 15 mL of anhy-
drous toluene was treated with NEt3 (0.81 mL, 5.84 mmol) and co-
Conclusion
oled to 0 °C.
A solution of 2-chloro-1,3,2-dioxaphospholane
(0.48 mL, 5.31 mmol) in toluene (5 mL) was added dropwise and
the mixture was allowed to reach room temperature and stirred for
15 h. The solution was then filtered and the solvent removed under
vacuum; yield 0.83 g (85%). C7H9N2O2P (184.13): calcd. C 45.66,
H 4.93, N 15.21; found C 45.76, H 4.80, N 15.12. 1H NMR
(CDCl3, 20 °C): δ = 8.03 (d, J = 4.1 Hz, 1 H, py6), 7.43 (td, J =
7.7, J = 1.5 Hz, 1 H, py4), 6.79–6.74 (m, 2 H, py3,5), 6.06 (s, 1 H,
NH), 4.22–4.10 (m, 2 H, CH2), 4.03–3.94 (m, 2 H, CH2) ppm.
13C{1H} NMR (CDCl3, 20 °C): δ = 155.9 (d, JCP = 13.8 Hz, py2),
148.1 (d, JCP = 1.2 Hz, py6), 137.9 (d, JCP = 1.5 Hz, py4), 116.1 (s,
py5), 109.7 (d, JCP = 10.7 Hz, py3), 63.6 (d, JCP = 1.3 Hz, CH2)
ppm. 31P{1H} NMR (CDCl3, 20 °C): δ = 140.0 ppm.
Tetracarbonyl complexes of the type Mo(PN)(CO)4 are
readily available upon treatment of Mo(CO)6 with several
phosphanylamine ligands based on 2-aminopyridine at ele-
vated temperatures. In the case of Mo(PN-iPr)(CO)4 we
have studied the oxidative addition of allyl bromide to give
the η3-allyl complex Mo(PN-iPr)(η3-CH2CHCH2)(CO)2Br.
Two reasonable reaction pathways for this process have
been established by means of DFT calculations proceeding
via a preliminary η2-π complex where the terminal C=C
double bond interacts with the metal center and where the
bromine directly attacks the molybdenum atom.
2-Amino-N-(3,5,8,10-tetra-tert-butyldibenzo[d,f]-1,3,2-dioxaphos-
phepine-1-yl)pyridine (PN-BIPOL2tBu): To a solution of 2-amino-
pyridine (0.80 mg, 8.4 mmol) in 20 mL of toluene NEt3 (1.2 mL,
8.4 mmol) and 4,6,9,11-tetra-tert-butyl-2-chlorodibenzo[d,f]-1,3,2-
dioxaphosphepine (4.0 g, 8.4 mmol) were added at 0 °C. The reac-
tion mixture was allowed to reach room temperature and heated at
90 °C for 15 h. The solution was then filtered and the solvent re-
moved under vacuum; yield 0.99 g (88%). C33H45N2O2P (532.70):
Experimental Section
General: All manipulations were performed under an inert atmo-
sphere of argon by using Schlenk techniques. The solvents were
purified according to standard procedures.[11] The ligands 2-(di-
phenylphosphanylamino)pyridine (PN-Ph),[4e,5] 2-amino-N-(di-
isopropylphosphanyl)pyridine (PN-iPr),[2] 2-[(2-pyridyl)amino]di-
benzo[d,f][1,2,3]dioxaphosphepine (PN-BIPOL),[2] and dimethyl
(4S,5S)-2-[(2-pyridyl)amino]-1,3,2-dioxaphospholane-4,5-dicarbox-
1
calcd. C 74.41, H 8.51, N 5.26; found C 74.50, H 8.65, N 5.60. H
NMR (CDCl3, 20 °C): δ = 8.17 (d, J = 4.0 Hz, 1 H, py6), 7.93 (d,
J = 4.7 Hz, py4), 7.43 (d, J = 2.4 Hz, 2 H, Ph), 6.89 (d, J = 8.2 Hz,
1 H, py3), 6.78 (dd, J = 6.8, J = 5.4 Hz, 1 H, py5), 6.62 (vt, J =
6.5 Hz, 1 H, Ph), 6.55 (d, J = 8.4 Hz, 1 H, Ph), 6.15 (s, 1 H, NH),
1.37–1.19 [m, 36 H, C(CH3)3] ppm. 13C{1H} NMR (CDCl3, 20 °C):
ylate (PN-TARMe [2] and Mo(η3-CH2CHCH2)(CO)2(CH3CN)2-
)
Br[12] were prepared according to the literature. The deuterated sol-
vents were purchased from Aldrich and dried with 4-Å molecular
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Molybdenum Carbonyl Complexes Bearing PN Ligands
δ = 156.3 (Ph), 155.7 (d, JCP = 17.2 Hz, py2), 148.3 (py6), 146.6 110.9 (d, JCP = 5.7 Hz, py3), 65.5 (d, JCP = 7.5 Hz, CH2) ppm.
(Ph), 137.7 (py4), 133.2 (d, JCP = 18.2 Hz, Ph), 126.3 (Ph), 124.3
31P{1H} NMR (CD Cl , 20 °C): δ = 190.6 ppm. IR (ATR): ν =
˜
2 2
(Ph), 112.1 (py5), 112.1 (Ph), 110.1 (d, JCP = 14.4 Hz, py3), 35.5 2025 (s, νC=O), 1920 (s, νC=O), 1887 (s, νC=O), 1850 (s, νC=O) cm–1.
[C(CH3)3], 34.7 [C(CH3)3], 31.6 [C(CH3)3], 31.3 [C(CH3)3] ppm.
Mo(PN-BIPOL)(CO)4 (1e): This compound was prepared analo-
31P{1H} NMR (CDCl3, 20 °C): δ = 151.0 ppm.
gously to 1a with PN-BIPOL (0.76 g, 2.45 mmol) and Mo(CO)6
Mo(PN-Ph)(CO)4 (1a): A mixture of PN-Ph (0.50 g, 1.80 mmol) (0.65 g, 2.45 mmol) as the starting materials; yield 1.03 g (81%).
and Mo(CO)6 (0.46 g, 1.80 mmol) was stirred in toluene at 90 °C C21H13MoN2O6P (516.26): calcd. C 48.86, H 2.54, N 5.43; found
1
for 6 h. After that time the solvent was removed under reduced
pressure and the crude product was purified by flash chromatog-
raphy (neutral Al2O3, eluent CH2Cl2); yield 0.59 g (68%).
C 48.79, H 2.52, N 5.38. H NMR (δ = , CD2Cl2, 20 °C): 8.52 (d,
J = 4.7 Hz, 1 H, py6), 7.64–7.08 (m, 9 H, py4 and Ph), 6.82–6.79
(m, 2 H, py3, and py5), 6.60–6.52 (m, 1 H, NH) ppm. 13C{1H}
C21H15MoN2O4P (486.27): calcd. C 51.87, H 3.11, N 5.76; found NMR (CD2Cl2, 20 °C): δ = 218.5 (d, JCP = 10.9 Hz, CO), 214.4
1
C 51.99, H 3.02, N 5.61. H NMR (δ = , CD2Cl2, 20 °C): 8.51 (d,
(d, JCP = 55.7 Hz, CO), 206.2 (d, JCP = 13.8 Hz, CO), 157.8 (d,
J = 5.4 Hz, 1 H, py6), 7.66–7.50 (m, 11 H, py4, and Ph), 6.91 (d, J
JCP = 20.7 Hz, py2), 153.9 (d, JCP = 4.6 Hz, py6), 148.8 (d, JCP
=
= 8.4 Hz, 1 H, py3), 6.69 (t, J = 6.6 Hz, 1 H, py5), 6.18 (d, J = 9.2 Hz, Ph), 139.4 (py4), 130.3 (d, JCP = 2.3 Hz, Ph), 129.9 (d, JCP
5.8 Hz, 1 H, NH) ppm. 13C{1H} NMR (CD2Cl2, 20 °C): δ = 220.7 = 1.7 Hz, Ph), 129.8 (d, JCP = 1.7 Hz, Ph), 126.2 (d, JCP = 1.7 Hz,
(d, JCP = 7.0 Hz, CO), 216.1 (d, JCP = 34.9 Hz, CO), 208.1 (d, JCP Ph), 121.9 (d, JCP = 2.9 Hz, Ph), 116.8 (py5), 111.2 (d, JCP = 6.9 Hz,
= 9.5 Hz, CO), 160.0 (d, JCP = 15.5 Hz, py2), 153.6 (d, JCP
=
py3) ppm. 31P{1H} NMR (CD2Cl2, 20 °C): δ = 196.5 ppm. IR
4.5 Hz, py6), 139.0 (py4), 137.7 (d, JCP = 39.4 Hz, Ph), 130.6 (d, (ATR): ν = 2022 (s, νC=O), 1944 (s, νC=O), 1885 (s, νC=O), 1860 (s,
˜
JCP = 15.5 Hz, Ph), 130.6 (d, JCP = 2.0 Hz, Ph), 128.7 (d, JCP
=
νC=O) cm–1.
10.0 Hz, Ph), 115.7 (py5), 111.2 (d, JCP = 6.0 Hz, py3) ppm.
Mo(PN-BIPOL2tBu)(CO)4 (1f): This compound was prepared anal-
ogously to 1a with PN-BIPOL2tBu (0.381 g, 0.728 mmol) and
Mo(CO)6 (0.192 g, 0.728 mmol) as the starting materials; yield
0.352 g (65%). C37H45MoN2O6P (740.69): calcd. C 60.00, H 6.12,
31P{1H} NMR (CD Cl , 20 °C): δ = 95.9 ppm. IR (ATR): ν = 2075
˜
2
2
(s, νC=O), 1895 (s, νC=O), 1807 (s, νC=O) cm–1.
Mo(PN-iPr)(CO)4 (1b): This compound was prepared analogously
to 1a with PN-iPr (0.50 g, 2.39 mmol) and Mo(CO)6 (0.63 g,
2.39 mmol) as the starting materials; yield 0.66 g (66%).
1
N 3.78; found C 59.89, H 6.08, N 3.81. H NMR (CD2Cl2, 20 °C):
δ = 8.52 (s, 1 H, py6), 7.55–7.12 (m, 5 H, py4, and Ph), 6.74–6.59
C15H19MoN2O4P (418.24): calcd. C 43.08, H 4.58, N 6.70; found (m, 3 H, py3, py5, and NH), 1.54–1.24 [m, 36 H, C(CH3)3] ppm.
1
C 43.12, H 4.62, N 6.61. H NMR (CD2Cl2, 20 °C): δ = 8.41 (d, J 13C{1H} NMR (CD2Cl2, 20 °C): δ = 219.2 (d, JCP = 10.9 Hz, CO),
= 4.9 Hz, 1 H, py6), 7.49 (vt, J = 7.3 Hz, 1 H, py4), 6.75 (d, J = 215.2 (d, JCP = 56.9 Hz, CO), 206.7 (d, JCP = 12.1 Hz, CO), 157.5
8.2 Hz, 1 H, py3), 6.58 (vt, J = 6.2 Hz, 1 H, py5), 5.45 (d, J =
4.4 Hz, 1 H, NH), 2.44–2.23 [m, 2 H, CH(CH3)2], 1.34–1.20 [m, 12
(d, JCP = 19.5 Hz, py2), 153.7 (d, JCP = 4.6 Hz, py6), 147.6 (Ph),
145.7 (d, JCP = 10.9 Hz, Ph), 140.6 (d, JCP = 3.4 Hz, Ph), 139.4 (d,
H, CH(CH3)2] ppm. 13C{1H} NMR (CD2Cl2, 20 °C): δ = 221.5 (d, JCP = 3.4 Hz, py4), 131.6 (d, JCP = 2.9 Hz, Ph), 127.2 (Ph), 124.9
JCP = 7.0 Hz, CO), 215.7 (d, JCP = 33.4 Hz, CO), 209.6 (d, JCP
=
(Ph), 116.4 (py5), 111.0 (d, JCP = 6.3 Hz, py3), 35.4 [C(CH3)3], 34.6
9.5 Hz, CO), 161.0 (d, JCP = 12.0 Hz, py2), 153.4 (d, JCP = 4.5 Hz, [C(CH3)3], 31.2 [C(CH3)3], 30.9 [C(CH3)3] ppm. 31P{1H} NMR
py6), 138.8 (py4), 114.8 (py5), 110.6 (d, JCP = 5.0 Hz, py3), 30.6 and
30.3 [2s, CH(CH3)2], 18.2 and 18.1 [2s, CH(CH3)2] ppm. 31P{1H}
(CD Cl , 20 °C): δ = 194.2 ppm. IR (ATR): ν = 2028 (s, νC=O),
˜
2 2
1959 (s, νC=O), 1915 (s, νC=O), 1877 (s, νC=O) cm–1.
NMR (CD Cl , 20 °C): δ = 124.1 ppm. IR (ATR): ν = 2019 (s,
˜
2
2
Mo(PN-TARMe)(CO)4 (1g): This compound was prepared analo-
gously to 1a with PN-TARMe (0.40 g, 1.33 mmol) and Mo(CO)6
(0.35 g, 1.33 mmol) as the starting materials; yield 0.51 g (75%).
νC=O), 1879 (s, νC=O), 1818 (s, νC=O) cm–1.
Mo(PN-tBu)(CO)4 (1c): This compound was prepared analogously
to 1a with PN-tBu (0.41 g, 1.74 mmol) and Mo(CO)6 (0.46 g, C15H13MoN2O10P (508.19): calcd. C 35.45, H 2.58, N 5.51; found
1
1.74 mmol) as the starting materials; yield 0.57 g (74%).
C 35.38, H 2.53, N 5.60. H NMR (CD2Cl2, 20 °C): δ = 8.44 (br.
C17H23MoN2O4P (446.29): calcd. C 45.75, H 5.19, N 6.28; found s, 1 H, py6), 7.59 (br. s, 2 H, py4 and py3), 6.84–6.74 (m, 2 H, py5
1
C 45.69, H 5.02, N 6.39. H NMR (CD2Cl2, 20 °C): δ = 8.39 (d, J and NH), 5.33–5.10 (m, 2 H, CH), 3.93 (s, 3 H, COOCH3), 3.90
= 5.4 Hz, 1 H, py6), 7.49 (vt, J = 7.6 Hz, 1 H, py4), 6.87 (d, J = (s, 3 H, COOCH3) ppm. 13C{1H} NMR (CD2Cl2, 20 °C): δ = 218.5
8.2 Hz, 1 H, py3), 6.59 (vt, J = 6.3 Hz, 1 H, py5), 5.54 (d, J =
3.9 Hz, 1 H, NH), 1.42 and 1.36 [s, 9H each, C(CH3)3] ppm.
(d, JCP = 11.5 Hz, CO), 214.8 (d, JCP = 55.7 Hz, CO), 205.8 (d,
JCP = 13.8 Hz, CO), 205.6 (d, JCP = 13.8 Hz, CO), 170.9 (s,
13C{1H} NMR (CD2Cl2, 20 °C): δ = 222.2 (d, JCP = 6.9 Hz, CO), COOCH3), 168.3 (d, JCP = 2.3 Hz, COOCH3), 157.4 (d, JCP
=
216.4 (d, JCP = 34.9 Hz, CO), 211.4 (d, JCP = 8.3 Hz, CO), 161.5 20.1 Hz, py2), 153.3 (d, JCP = 5.2 Hz, py6), 139.2 (py4), 116.6 (py5),
(d, JCP = 10.6 Hz, py2), 153.2 (d, JCP = 4.6 Hz, py6), 138.9 (py4), 111.4 (d, JCP = 6.3 Hz, py3), 78.1 (d, JCP = 8.0 Hz, CH), 76.7 (d,
115.0 (py5), 111.1 (d, JCP = 4.6 Hz, py3), 37.7 [d, JCP = 9.2 Hz,
C(CH3)3], 28.8 and 28.7 [s, C(CH3)3] ppm. 31P{1H} NMR (CD2Cl2,
JCP = 10.3 Hz, CH), 53.8 (s, COOCH3), 53.7 (s, COOCH3) ppm.
31P{1H} NMR (CD Cl , 20 °C): δ = 202.9 ppm. IR (ATR): ν =
˜
2
2
20 °C): δ = 138.2 ppm. IR (ATR): ν = 2010 (s, νC=O), 1903 (s,
2030 (s, νC=O), 1900 (s, νC=O), 1857 (s, νC=O) cm–1.
˜
νC=O), 1880 (s, νC=O), 1812 (s, νC=O) cm–1.
Mo(PN-iPr)(η3-allyl)(CO)2Br (2). Method 1: A solution of 1b
(0.23 g, 0.54 mmol) in 10 mL of anhydrous toluene was treated with
a slight excess of allyl bromide (51 µL, 0.60 mmol) and heated at
90 °C for 15 h. After removal of the solvent under reduced pressure
the product was washed twice with n-pentane and dried under vac-
Mo(PN-ETOL)(CO)4 (1d): This compound was prepared analo-
gously to 1a with PN-ETOL (0.37 g, 2.02 mmol) and Mo(CO)6
(0.53 g, 2.02 mmol) as the starting materials; yield 0.63 g (80%).
C11H9MoN2O6P (392.12): calcd. C 33.69, H 2.31, N 7.14; found C
33.58, H 2.22, N 7.12. H NMR (δ = , CD2Cl2, 20 °C): 8.42 (d, J uum; yield 0.22 g (82%). Method 2: A solution of Mo(η3-allyl)-
= 4.7 Hz, 1 H, py6), 7.56 (vt, J = 7.5 Hz, 1 H, py4), 6.75–6.69 (m, (CO)2(CH3CN)2Br (0.300 g, 0.845 mmol) was treated with PN-iPr
(0.178 g, 0.845 mmol) in 10 mL of CH2Cl2. The deep red solution
(CD2Cl2, 20 °C): δ = 219.1 (d, JCP = 11.5 Hz, CO), 214.8 (d, JCP was stirred for 2 h. After removal of the solvent, the product was
1
3 H, py3,5, NH), 4.35–4.30 (m, 4 H, CH2) ppm. 13C{1H} NMR
= 53.4 Hz, CO), 206.1 (d, JCP = 13.2 Hz, CO), 157.8 (d, JCP
=
dried under vacuum; yield 0.342 g (83.8%). C16H24BrMoN2O2P
(483.20): calcd. C 39.77, H 5.01, N 5.80; found C 39.70, H 5.06, N
19.0 Hz, py2), 153.4 (d, JCP = 5.2 Hz, py6), 139.1 (py4), 116.3 (py5),
Eur. J. Inorg. Chem. 2009, 4085–4093
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
4091

K. Kirchner et al.
FULL PAPER
Table 1. Details for the crystal structure determinations of compounds PN-iPr, 1a·CH2Cl2, 1b, 1c, 1d, and 2.
PN-iPr
1a·CH2Cl2
1b
1c
1d
2
Formula
Fw
C11H19N2P
210.25
C21H15MoN2O4P·CH2Cl2 C15H19MoN2O4P
C17H23MoN2O4P
446.28
C11H9MoN2O6P
392.11
C16H24BrMoN2O2P
483.19
571.19
418.23
Crystal size [mm] 0.35ϫ0.30ϫ0.12
0.65ϫ0.45ϫ0.40
yellow oval
triclinic
0.54ϫ0.40ϫ0.38
yellow oval
monoclinic
C2/c (no. 15)
20.9340(3)
10.3981(2)
16.8091(3)
90
99.173(1)
90
3612.11(11)
100(2)
0.58ϫ0.55ϫ0.53
yellow oval
orthorhombic
P212121 (no. 19)
9.0235(2)
13.3324(2)
16.0575(3)
90
0.59ϫ0.12ϫ0.11
yellow prism
monoclinic
P21/c (no. 14)
8.7014(6)
12.4996(8)
13.2883(9)
90
92.385(1)
90
1444.0(2)
100(2)
0.56ϫ0.24ϫ0.22
orange prism
monoclinic
C2/c (no. 15)
33.2832(16)
8.5131(4)
13.7154(7)
90
101.252(2)
90
3811.5(3)
100(2)
Color, shape
Crystal system
Space group
a [Å]
b [Å]
c [Å]
colorless plate
monoclinic
P21/c (no. 14)
16.6403(15)
7.7974(7)
9.2521(9)
90
¯
P1(no. 2)
8.8999(2)
11.4108(2)
13.3360(2)
108.005(1)
94.390(1)
109.668(1)
1187.96(4)
100(2)
α [°]
β [°]
93.968(1)
90
1197.6(2)
100(2)
90
90
γ [°]
V [Å3]
1931.80(6)
100(2)
T [K]
Z
4
2
8
4
4
8
ρcalc [gcm–3]
µ [mm–1]
(Mo-Kα)
F(000)
1.166
1.597
1.538
1.534
1.804
1.684
0.196
456
0.875
572
0.834
1696
0.785
912
1.046
776
2.878
1936
Number of
reflections
measured
Rint
16297
0.031
24509
0.018
23511
0.017
24308
0.021
19512
0.023
26966
0.028
Number of
reflections unique 3471
Number of
reflections
6884
6529
5266
5087
5613
5582
4187
3738
5533
4979
IϾ2σ(I)
3211
Number of
parameters
131
266
215
235
190
217
R1 [IϾ2σ(I)][a]
R1 (all data)
wR2 [IϾ2σ(I)]
wR2 (all data)
Min./max. resid.
electron density
[eÅ–3]
0.0301
0.0323
0.0826
0.0854
0.0227
0.0237
0.0608
0.0615
0.0185
0.0193
0.0485
0.0489
0.0144
0.0146
0.0386
0.0388
0.0267
0.0314
0.0641
0.0674
0.0232
0.0272
0.0576
0.0590
–0.40/0.45
–0.40/0.66
–0.32/0.56
–0.41/0.26
–0.97/1.14
–0.58/0.69
[a] R1 = Σ||Fo| – |Fc||/Σ||Fo|; wR2 = {Σ[w(Fo – Fc ) ]/Σ[w(Fo2)2]}1/2
.
2
2 2
5.76. 1H NMR (CD2Cl2, 20 °C): δ = 7.96 (d, J = 5.2 Hz, 1 H, py6), non-H atoms were refined anisotropically. H atoms were placed in
7.49 (vt, J = 7.5 Hz, 1 H, py4), 6.83–6.76 (m, 2 H, py3, and py5), calculated positions and thereafter treated as riding. The disor-
5.70 (d, J = 5.4 Hz, 1 H, NH), 4.37–4.24 (m, 1 H, CH), 4.10 (br.
s, 1 H, CH), 3.58 (br. s, 1 H, CH), 3.14–2.98 [m, 1 H, CH(CH3)2],
2.88–2.72 [m, 1 H, CH(CH3)2], 1.81 (d, J = 9.5 Hz, 1 H, CH), 1.70–
1.61 (m, 4 H, CH and CH3), 1.49–1.33 (m, 9 H, CH3) ppm.
13C{1H} NMR (CD2Cl2, 20 °C): δ = 226.3 (d, JCP = 13.2 Hz, CO),
223.1 (d, JCP = 8.0 Hz, CO), 160.7 (d, JCP = 10.9 Hz, py2), 147.9
(py6), 138.7 (py4), 120.6 (CH), 115.7 (py5), 111.5 (d, JCP = 5.7 Hz,
py3), 77.2 (CH2), 62.0 (CH2), 29.3 [d, JCP = 20.1 Hz, CH(CH3)2],
27.9 [d, JCP = 22.4 Hz, CH(CH3)2], 19.3 [d, JCP = 8.0 Hz, CH-
(CH3)2], 17.3 [d, JCP = 4.3 Hz, CH(CH3)2] ppm. 31P{1H} NMR
dered solvent in 1a·CH2Cl2 was squeezed with program
PLATON.[15] The bromine Br1 of compound 2 was modestly disor-
dered by interchanging position with the trans-located carbonyl
Table 2. Selected geometric data (Å and °) of compounds
1a·CH2Cl2, 1b, 1c, and 1d.
1a·CH2Cl2 1b
1c
1d
Mo–N1
2.282(1)
2.4803(3)
1.968(1)
1.982(1)
2.026(1)
2.064(1)
75.89(3)
173.41(4)
94.83(4)
89.43(5)
94.98(4)
170.01(4)
174.19(5)
2.296(1)
2.4912(3) 2.5596(3)
1.963(1)
1.995(1)
2.035(1)
2.051(1)
76.31(2)
2.287(1)
2.273(2)
2.4092(6)
1.965(2)
1.997(2)
2.031(2)
2.050(2)
76.64(6)
175.18(9)
94.18(8)
92.70(8)
92.60(7)
170.81(6)
174.43(8)
Mo–P
6
Mo–CI[a]
1.979(1)
1.967(1)
2.028(1)
2.057(1)
75.22(2)
([D ]acetone, 20 °C): δ = 106.6 ppm. IR (ATR): ν = 1925 (s, νC=O),
˜
1835 (s, νC=O) cm–1.
Mo–CII
Mo–CIII
Mo–CIV
N1–Mo–P
N1–Mo–CI
N1–Mo–CII
N1–Mo–CIII
N1–Mo–CIv
P–Mo–Cii
CIII–Mo–CIV
X-ray Structure Determination for PN-iPr, 1a–d, and 2: X-ray data
of the ligand PN-iPr and the complexes 1a (as the solvate
1a·CH2Cl2), 1b, 1c, 1d, and 2 were collected at T = 100 K on a
Bruker Smart APEX CCD diffractometer using graphite-mono-
chromated Mo-Kα radiation (λ = 0.71073 Å) and 0.3° ω-scan
frames covering complete spheres of the reciprocal space with θmax
= 30°. After data integration with program SAINT+ corrections
for absorption, λ/2 effects, and crystal decay were applied with pro-
gram SADABS.[13] The structures were solved by direct methods
(SHELXS97) and refined on F2 with program SHELXL97.[14] All
176.38(4) 172.33(4)
94.53(4)
92.42(4)
94.55(4)
170.46(4) 170.35(3)
172.52(4) 166.49(5)
95.25(4)
90.97(4)
98.00(4)
[a] CI through CIV are the four carbonyl C atoms, with CI trans to
N1, CII trans to P1, and CIII and CIV cis to N1 and P1.
4092
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© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2009, 4085–4093

Molybdenum Carbonyl Complexes Bearing PN Ligands
[7] H. Daamen, H. Van der Poel, D. J. Stufkens, A. Oskam,
Thermochim. Acta 1979, 34, 69.
[8] a) J. A. Ganske, R. N. Rosenfeld, J. Phys. Chem. 1990, 94,
4315; b) K. E. Lewis, D. M. Golden, G. P. Smith, J. Am. Chem.
Soc. 1984, 106, 3905.
[9] a) A. Bottoni, G. P. Miscione, J. J. Novoa, X. Prat-Resina, J.
Am. Chem. Soc. 2003, 125, 878; b) A. Bottoni, G. P. Miscione,
M. A. Carvajal, J. J. Novoa, J. Organomet. Chem. 2006, 691,
4498.
[10] For problems with entropy effects in DFT calculations see:
A. A. C. Braga, G. Ujaque, F. Maseras, Organometallics 2006,
25, 3647.
group at a level of ca. 7%, whereas the allyl group – usually prone
to orientation disorder – was fully ordered. Crystal data and experi-
mental details are given in Table 1. Selected geometric data of 1a
through 1d are presented in Table 2, while for PN-iPr and 2 they
are reported in the Figure captions.
CCDC-735385 (for PN-iPr), -735386 (for 1a·CH2Cl2), -735387 (for
1b), -735388 (for 1c), -735389 (for 1d), -735390 (for 2) contain the
supplementary crystallographic data for this paper. These data can
be obtained free of charge from The Cambridge Crystallographic
Data Centre via http://www.ccdc.cam.ac.uk/data_request/cif.
[11] D. D. Perrin, W. L. F. Armarego, Purification of Laboratory
Chemicals, 3rd ed., Pergamon, New York, 1988.
[12] T. Dieck, H. Friedel, J. Organomet. Chem. 1968, 14, 375.
[13] Bruker programs: SMART, v. 5.629; SAINT, v. 6.45; SADABS,
v. 2.10; XPREP, v. 6.1; SHELXTL, v. 6.14 Bruker AXS Inc.,
Madison, WI, 2003.
[14] G. M. Sheldrick, Acta Crystallogr., Sect. A: Found. Crystallogr.
2008, 64, 112.
[15] A. L. Spek, J. Appl. Crystallogr. 2003, 36, 7.
Computational Details: All calculations were performed using the
Gaussian03 software package on the Phoenix Linux Cluster of the
Vienna University of Technology.[16] The geometry and energy of
the model complexes and the transition states were optimized at
the B3LYP level[17] with the Stuttgart/Dresden ECP (SDD) basis
set[18] to describe the electrons of the molybdenum atom. For all
other atoms atoms the 6-31g** basis set was employed.[19] Transi-
tion state optimizations were performed with the Synchronous
Transit-Guided Quasi-Newton Method (STQN) developed by
Schlegel and co-workers.[20] Frequency calculations were performed
to confirm the nature of the stationary points, yielding one imagi-
nary frequency for the transition states and none for the minima.
Each transition state was further confirmed by following its vi-
brational mode downhill on both sides, and obtaining the minima
presented on the reaction energy profile. All geometries were opti-
mized without symmetry constraints. Solvation effects were evalu-
ated with the polarized continuum model (PCM) method.[21]
[16] M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
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Received: June 15, 2009
Published Online: August 12, 2009
Eur. J. Inorg. Chem. 2009, 4085–4093
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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