Direct proof for a lower reactivity of monomeric vs. dimeric oxidovanadium complexes in alcohol oxidation

Article abstract of DOI:10.1002/zaac.201300439

Previous attempts to synthesize and isolate (thiobisphenolate) vanadium(V) dioxido complexes had always provided their dimers containing [O=V(μ-O) ₂V=O]²⁺ cores, and these also dominate the solution reactivity. Hence, the behavior of their parent monomers, which represent the major species in solution, has remained uncertain. Herein we report the development of a synthetic route that allowed for the successful isolation, spectroscopic investigation, and structural characterization of the monomer PPh₄[^SLVO₂] (3) [^SL^2- = 2′2-thiobis(2, 4-di-tert-butylphenolate)]. For this purpose PPh ₄[^SLVOCl₂] (1) had to be accessed first in order to convert it to the ethoxido compound PPh₄[ ^SLVO(OEt)₂] (2), which is more prone to hydrolysis. Treatment of 2 with stoichiometric amounts of water followed by immediate cooling to -30°C led to crystals of 3. After its dissolution NMR spectra were recorded that were identical with those obtained after dissolution of its dimer, thus confirming the monomer/dimer equilibrium postulated previously. The molecular structure of 3 revealed the absence of a V···S interaction, which, however, stabilizes its dimer, and thus suggested the employment of a bisphenolate ligand lacking a bridging sulfur atom to obtain an analogue, which does not undergo dimerization in solution. In ^EtL^2- the sulfur atom is replaced by an ethylmethine unit and indeed the corresponding complex NBu₄[^EtLVO ₂] (4) proved to be stable as a monomer. Investigation of its potential as a catalyst for the oxidative dehydrogenation of 9-fluorenol confirmed a much lower reactivity in comparison to dimeric complexes, which is discussed. Copyright

Full text of DOI:10.1002/zaac.201300439

ARTICLE
DOI: 10.1002/zaac.201300439
Direct Proof for a Lower Reactivity of Monomeric vs. Dimeric
Oxidovanadium Complexes in Alcohol Oxidation
[a]
[a]
[a]
C. Gunnar Werncke, Christian Limberg,* and Ramona Metzinger
Dedicated to Professor Bernt Krebs on the Occasion of His 75th Birthday
Keywords: Dehydrogenation; Vanadium; Phenolates; Oxido complexes; Oxidation
Abstract. Previous attempts to synthesize and isolate (thiobisphenol-
mediate cooling to –30 °C led to crystals of 3. After its dissolution
ate) vanadium(V) dioxido complexes had always provided their dimers NMR spectra were recorded that were identical with those obtained
V=O]2+ cores, and these also dominate the
containing [O=V(μ-O)
2
after dissolution of its dimer, thus confirming the monomer/dimer
equilibrium postulated previously. The molecular structure of 3 re-
vealed the absence of a V···S interaction, which, however, stabilizes
its dimer, and thus suggested the employment of a bisphenolate ligand
solution reactivity. Hence, the behavior of their parent monomers,
which represent the major species in solution, has remained uncertain.
Herein we report the development of a synthetic route that allowed
for the successful isolation, spectroscopic investigation, and structural
lacking a bridging sulfur atom to obtain an analogue, which does not
Et 2–
undergo dimerization in solution. In
L
the sulfur atom is replaced
S
S 2–
characterization of the monomer PPh
4
[ LVO
2
] (3) [ L = 2Ј2-
[SLVOCl
1) had to be accessed first in order to convert it to the ethoxido com-
by an ethylmethine unit and indeed the corresponding complex
thiobis(2,4-di-tert-butylphenolate)]. For this purpose PPh
4
2
]
Et
4 2
NBu [ LVO ] (4) proved to be stable as a monomer. Investigation of
(
its potential as a catalyst for the oxidative dehydrogenation of 9-fluor-
enol confirmed a much lower reactivity in comparison to dimeric com-
S
4 2
pound PPh [ LVO(OEt) ] (2), which is more prone to hydrolysis.
Treatment of 2 with stoichiometric amounts of water followed by im- plexes, which is discussed.
Introduction
I is a dinuclear compound in the solid state but upon dissol-
D
ution is present in an equilibrium between the dimeric form I
Supported vanadium oxide catalysts are among the most ef-
ficient systems for the oxidative dehydrogenation (ODH) of
alkanes and alcohols.[ For several years we have been inter-
ested in the elucidation of the reaction mechanisms of these
M
(
as in the solid state) and a monomeric form (I ). The results
D
of kinetic investigations suggested that only dimer I is the
1]
catalytically active species in the ODH of alcohols.[ In the
10]
D
first and rate-determining step of the catalytic cycle I oxidizes
catalysts, by mimicking their postulated active sites on a mo-
one equivalent of alcohol (exemplified for 9-fluorenol) to give
the corresponding ketone as well as the vanadium(IV) interme-
lecular level,[
2–10]
that is, we used molecular model com-
pounds capable of simulating either the structural and the spec-
troscopic properties or the reactivity of corresponding vana-
dium oxide surface species. In order to simulate the oxidic
environments that oxidovanadium moieties experience on the
surfaces of oxidic support materials we have successfully em-
ployed three different types of ligands: The deprotonated
diate II, that could be isolated. In the following step O reoxi-
2
dizes II, which leads to the formation of starting material I as
well as to the generation of a vanadium peroxide (III). The
peroxide III is able to oxidize a second equivalent of alcohol
but also mediates the internal sulfoxidation of the thioether
function of the employed thiobisphenolate ligand. The latter
process leads to a doubly S-oxidized derivative of I as the
actual catalytically active species for which the shown catalytic
cycle stays valid.[ All the dimeric as well as peroxidic spe-
cies occurring were isolated and/or their reactivity was exam-
[2–4]
forms of incompletely condensed silsesquioxanes,
calixar-
enes,[
5–8]
and thiacalixarenes, and very recently, of thiobis-
which represent a section of a thiacalixar-
As part of these studies, the results of a detailed
[9,10]
phenols,
10]
ene.[10,20]
mechanistic work on the thiobisphenolate based oxidovana-
dium model system I (Scheme 1) with respect to the ODH of ined directly. While this mechanism is thus plausible, the low
alcohols were reported. The insights obtained regarding the reactivity of the mononuclear dioxidovanadium complexes
catalytic cycle are summarized in Scheme 1.[
10]
within the system has been inferred only indirectly. Against the
background that the relevance either of monomeric, dimeric, or
polymeric vanadium sites on the surface of supported vana-
*
Prof. Dr. C. Limberg
Fax: +49-30-2093-6966
[1]
dium oxide catalysts is still intensely debated, a more quanti-
tative comparison of the reactivities of I vs. ID appeared
valuable. Hence, we were interested to take a closer look at
properties and behavior of the monomeric dioxidovanadium
E-Mail: christian.limberg@chemie.hu-berlin.de
M
[
a] Institut für Chemie
Humboldt-Universität zu Berlin
Brook-Taylor Str. 2
12489 Berlin
2
426
© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2013, 639, (14), 2426–2432

Monomeric Oxidovanadium Complexes
Scheme 1. Catalytic cycle for the oxidative dehydrogenation of alcohols (exemplified by 9-fluorenol) with I as the catalyst.
species of system I. A deeper understanding on the possible
origin of the reactivity difference in the ODH activity between
monomeric and dimeric oxidovanadium units was envisaged.
Results and Discussion
S
M
Synthesis, Structure and Properties of PPh [ LVO ] (I )
4
2
Attempts to crystallize I from solutions always led to the
D [9]
isolation of the thermodynamically stable dimeric form I .
M
Therefore, for the selective isolation of the monomer I a dif-
ferent approach had to be pursued. We started off with the
S
S 2–
preparation of PPh [ LVOCl ] (1) [ L = 2Ј2-thiobis(2,4-di-
4
2
tert-butylphenolate], which was anticipated to be a mononu-
clear compound, both in solution and in the solid state: A solu-
S
tion of LH2 dissolved in acetonitrile was treated with
PPh [VO Cl ] (Scheme 2), and subsequent workup led to the
4
2
2
isolation of 1 in form of dark violet single crystals, which were
investigated by X-ray diffraction analysis. The molecular
structure of the anion is shown in Figure 1.
Within the anion the vanadium atom exhibits a distorted oc-
tahedral coordination arrangement, which consists of a ter-
minal oxido function, two chloride ligands, and the tridentate
Scheme 2. Synthetic approach for the direct isolation of 3, alias the
monomer I .
M
2Ј2-thiobis(2,4-di-tert-butylphenolate) ligand. The latter binds
in a facial fashion, whereas its thioether unit is positioned trans
to the terminal oxido ligand. The vanadium atom is situated [172.91(15)°]. The overall structure of the anion exhibits Cs
approximately 0.3 Å above the mean plane defined by Cl1, symmetry with the mirror plane lying between O2 and O1 as
Cl2, O1, and O2, and the O3–V1–S1 unit is nearly linear well as Cl1 and Cl2. In solution the anion retains its C sym-
s
Z. Anorg. Allg. Chem. 2013, 2426–2432
© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
2427

C. G. Werncke, C. Limberg, R. Metzinger
ARTICLE
atoms and the vanadium atom amounts to 1.8333(11) Å (O1–
V) and 1.8635(11) Å (O2–V), respectively, which is approxi-
D
mately 0.1 Å shorter than corresponding bonds in 1 or I . The
distance between the vanadium atom and the sulfur atom [V–
S1 3.1121(5) Å] is only slightly shorter than the sum of the
van der Waals radii of vanadium and sulfur (3.19 Å), which
implies only weak interactions between those two atoms. The
bond angles between the vanadium atom and the surrounding
oxygen atoms lie between 104° and 113°, so that the coordina-
tion sphere of the vanadium ion can be described best – ne-
glecting the weak V–S interactions – as distorted tetrahedral.
Upon dissolving the yellow crystals of 3 in CD CN a violet
3
solution was obtained (as observed for I), and NMR spectro-
scopic studies showed the typical features of I with its mono-
mer/dimer equilibrium.
Figure 1. Structure of 1·MeCN within the single crystal. All hydrogen
+
atoms, the PPh
4
cation and co-crystallized acetonitrile solvent mole-
cules are omitted for clarity. Selected bond lengths /Å and angles /°:
V1–O1 1.882(4), V1–O2 1.865(4), V1–O3 1.599(4), V1–Cl1 2.364(2),
V1–Cl2 2.364 (2), V1–S1 2.7362(19), V1–(Cl1, Cl2, O1, O2)
0.3157(12), O3–V1–Cl1 97.44(16), O3–V1–Cl2 100.87(15), O3–V1–
O1 98.90(19), O3–V1–O2 97.7(2), O3–V1–S1 172.91(15).
1
metry as confirmed by H NMR spectroscopic investigations.
5
1
The V NMR spectrum of 1 dissolved in CD Cl reveals a
2
2
sharp singlet signal at δ = –253 ppm.
The reaction of a solution of 1 with two equivalents of thal-
lium(I) ethoxide gave a rapid color change from violet to red
Figure 2. Structure of 3·Et
2
O within the single crystal. All hydrogen
+
atoms, the PPh
4
cation, and the co-crystallized diethyl ether solvent
brown accompanied by the precipitation of a white solid [pre- molecule are omitted for clarity. Selected bond lengths /Å and angles
/
°: O1–V1 1.8333(11), O2–V1 1.8635(11), O3–V1 1.6275(12),
sumably thallium(I) chloride]. Work-up led to the isolation of
S
O4–V1 1.6162(12), S1–V1 3.1121(5), O1–V1–O2 113.20(5), O1–V1–
O3 115.17(6), O1–V1–O4 104.38(6), O2–V1–O3 110.96(6), O2–V1–
O4 105.04(6), O3–V1–O4 107.15(7).
PPh [ LVO(OEt) ] (2), and its identity was confirmed inter
4
2
5
1
alia with the aid of NMR techniques. The V NMR spectrum
of 2 in CD Cl shows a singlet signal at δ = –428 ppm. This
2
2
up-field shift of the signal of 2 compared to the one of 1 is in
line with observations made for other vanadium(V) com-
pounds on exchanging chloride functions by alkoxide li-
gands.[
Synthesis of a Strictly Monomeric Dioxidovanadium
Complex
11]
The treatment of a solution of 2 in deuterated acetonitrile
Although through the isolation of 3 the existence of the mo-
M
with stoichiometric amounts of H O at room temperature in- nomeric form I and its spectroscopic and structural properties
2
stantaneously led to a complete conversion to I as confirmed as well as its solution behavior were confirmed, the following
5
1
by V NMR spectroscopy. However, after hydrolysis of a red direct examination of its ODH reactivity was not possible due
brown solution of 2 in Et O at –30 °C immediate storage at the to the inherent monomer/dimer equilibrium of I in solution,
2
same temperature led to the growth of yellow single crystals of the ODH reactivity of which was ascribed mainly to the dimer
S
M
D [10]
PPh [ LVO ] (3) (Scheme 2, 3 corresponds to I in Scheme 1) I .
To circumvent this problem we decided to synthesize a
4
2
within 1 d, which were investigated by X-ray diffraction analy- similar monomeric bisphenolate based tetrahedral dioxidova-
sis. The molecular structure of the anion of 3 is shown in Fig- nadium compound, which does not tend to dimerization. From
D
M
ure 2. The vanadium ion is coordinated by the two phenolate comparison of the solid-state structures of I and 3 (I ) it
oxygen atoms of the thiobisphenolate ligand as well as by two became obvious that the coordinative properties of the bridging
terminal oxido ligands. The V=O bond lengths [1.6275(12) Å sulfur atom inherent to the thiobisphenolate ligand are advan-
D
(
O3–V1), 1.6162(12) Å (O4–V1)] are approximately 0.2 Å tageous for stabilizing the dimeric form I , whereas they seem
D
M
longer than the corresponding ones within compound 1 and I , to have no influence in the monomer I (see the large V–S
Et
respectively. Such elongation of the V=O bonds in dioxidova- bond length in 3). Therefore we set out using LH as the
2
nadium compounds, compared to monooxidovanadium com- ligand precursor, whose bridging unit has no relevant coordina-
Et
plexes, is a known phenomenon and originates in the competi- tive features. Reacting LH with NBu VO in acetonitrile as
2
4
3
tion of both oxido ligands for the same d orbitals of the cen- the solvent led, after work-up, to the isolation of
π
tral metal atom.[ The distance between the phenolate oxygen NBu [ LVO ] (4) (Scheme 3).
12]
Et
4
2
2
428
www.zaac.wiley-vch.de
© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2013, 2426–2432

Monomeric Oxidovanadium Complexes
By comparison of the initial ODH rates of the systems I and
4
the difference in catalytic activity becomes more obvious:
The aerobic catalytic oxidation of 9-fluorenol gave an ob-
served reaction rate approximately 18-fold larger in the case
of system I (Figure 4). Additionally, it has to be stressed that
D
only a fraction of employed I (the active species I ) is effec-
tive during the catalytic process – due to the monomer/dimer
4 2
Scheme 3. Synthesis of NBu [EtLVO ] (4).
equilibrium of I – so it has to be concluded that the dimeric
D
form I is even more superior.
The molecular structure of the anion of single-crystalline 4
is shown in Figure 3. The vanadium oxygen bond lengths in 4
are very similar to those in 3 and comparable to other, structur-
–
[2,4,13]
ally similar [VO (OR) ] -systems.
bridging unit of the
In contrast to 3, the
2
2
Et 2–
L
ligand in 4 points away from the
dioxidovanadium center, which can be considered as the result
of a lack of coordinative ability of the bridging CH(Et) group.
51
A
V NMR spectrum of a solution of 4 in CD CN showed
3
only a single signal at δ = –504 ppm, whose shift is nearly
M
identical to the one determined for the monomer I (δ =
–
502 ppm). An IR spectrum of 4 shows inter alia a strong
–
1
absorption band at 938 cm
exhibiting a shoulder at
Figure 4. Reaction rates observed for the catalytic ODH of 9-fluorenol
–
1
9
22 cm . Such bands are typically caused by the symmetric with 1 mol% of I and 4, respectively.
and antisymmetric vibrational stretching modes of [VO ]-units
2
Comparably low hydrogen atom abstraction rates (and thus
–1
and resemble those observed in the case of 3 (937 cm and
+
ODH reactivity) of ligated [VO ] systems have been reported
–
1
2
9
20 cm ).
[
4]
for the cases of tetrahedral silsesquioxane based compounds
and the octahedral dioxidovanadium bipyridyl complex
BF [(bipy) VO ] (IV) (Scheme 4), respectively. In the latter
[14]
4
2
2
case Mayer et al. demonstrated that the low HAT (hydrogen
atom transfer) reactivity of IV, leading to the formation of the
respective vanadium(IV) compound IVa, is due to a large in-
trinsic reorganization barrier. This barrier originates from the
electronic and structural changes occurring during the transfor-
mation of II and is reflected in relatively large changes in bond
order and lengths of the involved V–O-bonds (Scheme 4). The
same is conceivable for the monomeric dioxidovanadium com-
pounds 3 and 4 described in this paper.
Figure 3. Structure of 4·½Et
2
O within the crystal. All hydrogen atoms,
cation and the co-crystallized diethyl ether solvent molecule
are omitted for clarity. Selected bond lengths /Å and angles /°: O1–V1
.8586(8), O4–V1 1.8408(7), O5–V1 1.6223(7), O7–V1 1.6168(8),
+
the NBu
4
1
O1–V1–O4 109.62(3), O1–V1–O5 110.52(4), O1–V1–O7 107.26(4),
O4–V1–O5 111.75(4), O4–V1–O7 107.61(4), O5–V1–O7 109.94(4).
Given the tremendous spectroscopic and structural similarity
M
of the dioxidovanadium cores of 4 and 3 (respectively I ) the
ODH reactivity of 4 towards 9-fluorenol was examined: Re-
acting 4 with stoichiometric amounts of 9-fluorenol did not
lead to a significant oxidation of the alcohol within the course
of 1 h (ϽϽ 5%). After 24 h a mere 23% conversion of the
substrate was detected. In contrast, previous examinations on
the system I had shown a complete turnover of the substrate
under similar conditions within 1 h.[10]
Scheme 4. Change of the bond situation around the vanadium atom in
+
the dioxidovanadium compound [(bipy)
2
VO
2
] . The bond lengths were
[8]
theoretically calculated.
Z. Anorg. Allg. Chem. 2013, 2426–2432
© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
2429

C. G. Werncke, C. Limberg, R. Metzinger
ARTICLE
Applying these principles on the dimeric form of 3, namely Microanalyses were performed with a Leco CHNS-932 or HEKAtech
D
Euro EA 3000 elemental analyzer. Infrared (IR) spectra were recorded
I , it becomes obvious that the structural and electronic
changes due to the HAT in case of I are less pronounced:
D
using samples prepared as KBr pellets with a Shimadzu FTIR 8400S
FT IR spectrometer. The high resolution mass spectra were recorded
with an Agilent Technologies 1200 Series mass spectrometer with a
The V–μ-O bond elongates only by approx. 0.15 Å (ca. 0.1 Å
less than in case of the monomeric dioxidovanadium system
IV) and the length of the V=O bond, which is not directly
involved, remains almost unchanged (Scheme 5A). Also, there
is formally no change in the bond orders of these V–O-moie-
time of flight analyzer. Solvents were dried using a Braun Solvent
Et
Purification System. LH
2
, thallium(I) ethoxide, and 9-fluorenol were
S
[15]
[16]
obtained commercially and used as received. LH
2
, NBu
4
[VO
3
]
,
[17]
[9]
4 2 2
PPh [VO Cl ]
and I were prepared according to literature pro-
ties as the electrons accepted during the HAT occupy non- cedures.
bonding d orbitals of the vanadium atoms (Scheme 5B).
S
Synthesis of 1: LH
2
(884 mg, 2.00 mmol, 1 equiv.) was dissolved in
[VO Cl ] (984 mg, 2.00 mmol,
equiv.) the color of the reaction mixture immediately turned to dark
MeCN (40 mL). Upon addition of PPh
1
4
2
2
violet. After 16 h of stirring the violet solution was filtered, the filtrate
reduced to approximately half of its volume and stored at –30 °C. After
1
d the solution was removed by filtration and drying of the remaining
violet crystalline solid afforded 1.04 g of 1·½MeCN (1.09 mmol,
4%). Reduction of the mother liquor to half its volume and storage
at –30 °C gave another crop of 1·½MeCN (250 mg, 0.26 mmol, 13%).
5
1
3
H NMR (400 MHz, CD CN, room temp., ppm): δ = 7.91 (m, 4 H,
+
+
+
PPh
4
), 7.70 (m, 8 H, PPh
4 4
), 7.63 (m, 8 H, PPh ), 7.40 [d, 2 H,
4
4
J(H,H) = 2.4 Hz, ArH], 7.20 [d, 2 H, J(H,H) = 2.4 Hz, ArH], 1.38
para
ortho
51
1
[s, 18 H,
(100 MHz, CD
(MeCN, neg): m/z = 577.1224 (100%, calcd. for [ LVOCl
C(CH
3
)
3
], 1.26 [s, 18 H,
3 3
C(CH ) ]. V{ H} NMR
2
Cl
2
, room temp., ppm): δ = –253 (s, br). HR-ESI
S
–
2
]
5
1
1
8
77.1547). IR (KBr): ν˜ = 2953 (s), 2903 (w), 2865 (w), 1585 (w),
483 (w), 1441 (s), 1436 (s), 1425 (m), 1398 (w), 1360 (w), 1279 (w),
256 (m), 1135 (w), 1108 (vs), 1099 (w), 996 (w), 977 (vs), 915 (w),
39 (m), 760 (w), 748 (w), 723 (s), 689 (m), 635 (w), 551 (m), 526
Scheme 5. A: Change in the bond situation of the oxidovanadium core
in I due to the twofold HAT occurring during the alcohol oxidation.
B: qualitative representation of the frontier orbitals of the vanadium
D
–
1
(
vs), 488 (s) cm . Elemental analysis for C52
2 3 3
H60Cl O PSV·0.5CH CN
(
938.4): calcd. C 67.76, H 6.59, N 0.78, S 3.24, Cl 7.72%; found:
atom in an idealized pseudo octahedral surrounding (C4V symmetry).
[
9,10]
C 67.83, H 6.61, N 0.75, S 3.41, Cl 7.56%.
Bond lengths were taken from the respective solid-state structures.
Synthesis of 2: 1·½MeCN (938 mg, 1.00 mmol, 1 equiv.) was dis-
solved in a mixture of THF (20 mL) and MeCN (10 mL). After ad-
dition of thallium(I) ethoxide (500 mg, 2.00 mmol, 2 equiv.) the dark
violet solution turned to reddish brown with concomitant precipitation
of a colorless solid [presumably thallium(I) chloride]. After 16 h of
stirring the red brown reaction mixture was filtered and the filtrate was
Conclusions
The postulated monomeric dioxidovanadium species IM of
the formerly published system I was now isolated (3) after
development of a selective synthetic procedure, and thus its reduced to dryness. The remaining solid was extracted with CH Cl
2
2
spectroscopic and structural features could be studied. The un- (10 mL) and layered with hexane (30 mL). After 3 d the removal of
ambiguous examination of the ODH activity of 3 in solution the solvents by filtration afforded a red brown oily solid. The removal
of remaining volatiles under reduced pressure gave 850 mg of 2
was hampered by the equilibrium with its more reactive di-
meric form I . This problem was circumvented by the use of
1
D
(0.90 mmol, 90%) as a red brown solid. H NMR (400 MHz, CD
3
CN,
+
room temp., ppm): δ = 7.91 (m, 4 H, PPh
4
4
), 7.70–7.65 (m, 8 H,
a modified bisphenolate ligand, which led to the synthesis of
the strictly monomeric dioxidovanadium compound 4, which
very much resembles 3 in its spectroscopic and structural be-
havior. Compound 4 showed a vastly lower ODH reactivity
compared to system I. This could be rationalized by a higher
+
+
PPh
4
), 7.63 (m, 8 H, PPh
4
), 7.24 [d, 2 H, J(H,H) = 2.4 Hz, ArH],
4
7.04 [d, 2 H, J(H,H) = 2.4 Hz, ArH], 4.87–4.66 (m, 4 H, O–CH –
2
para
ortho
CH
3
), 1.39 [s, 18 H,
C(CH
3
)
3
], 1.20 [s, 18 H,
C(CH
]. V{ H} NMR (100 MHz,
2
Cl , room temp., ppm): δ = –428 (s). IR (KBr): ν˜ = 3055 (w),
3 3
) ], 1.13
3
51
1
[
t, 6 H, J(H,H), = 6.8 Hz, O–CH
2
–CH
3
CD
2
intrinsic reorganization barrier for a HAT onto monomeric di- 2957 (s), 2903(m), 2864 (m), 1464 (m), 1435 (s), 1359 (w), 1312 (m),
oxidovanadium systems than on dimeric ones, where bridging 1294 (m), 1256 (m), 1108 (vs), 1052 (m), 997 (w), 964 (m), 930 (w),
–
1
oxido ligands are the reactive sites.
838 (m), 723 (s), 689 (s), 668 (m), 526 (vs) cm . Elemental analysis
for C56 PSV (937.1): calcd. C 71.77, H 7.53, S 3.42%; found:
70 5
H O
C 71.56, H 7.09, S 3.81%.
Experimental Section
2
Synthesis of 3: 2 (95 mg, 0.1 mmol, 1 equiv.) was dissolved in Et O
All manipulations were carried out in a glove-box, or else by means
of Schlenk-type techniques involving the use of a dry argon atmo-
(15 mL), cooled to –30 °C and the red brown solution was treated with
O (3.2 μL, 0.2 mmol, 2 equiv.). After stirring for half a minute the
H
2
sphere. The NMR spectra were recorded with a Bruker AV-400 NMR reaction mixture was stored at –30 °C immediately. Removal of the
1
51
1
1
(
for H and V) or DPX-300 spectrometer ( H). The H NMR spectra then bright violet solution after 1 d by filtration and drying of the
were calibrated against the residual proton of the deuterated solvent
and the 51V NMR spectra against VOCl
as an external standard.
remaining yellow crystalline solid gave 75 mg of 3 (0.85 mmol, 85%).
IR (KBr): ν˜ = 3056 (w), 2957 (vs), 2903 (s), 2866 (m), 1586 (w),
3
2
430
www.zaac.wiley-vch.de
© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2013, 2426–2432

Monomeric Oxidovanadium Complexes
476 (m), 1462 (s), 1433 (vs), 1396 (w), 1385 (w), 1359 (m), 1296
–
1
1
0.406 mm ; 17815 reflections measured, 9416 unique (Rint = 0.0640);
Final R indices [I Ͼ 2σ(I)] R = 0.0830, wR = 0.2338.
(
(
s), 1283 (s), 1254 (s), 1226 (w), 1198 (m), 1108 (vs), 1025 (w), 996
m), 937 (vs), 920 (vs), 881 (w), 863 (w), 843 (s), 772 (w), 756 (s),
2 70 5 r
Crystal Data for 3·Et O: C56H O PSV, M = 927.09, T = 100(2)
K, λ = 0.71073 Å, triclinic, space group P1, a = 10.6544(4) Å, b =
13.3254(4) Å, c = 19.9298(7) Å, α = 94.303(3)°, β = 94.127(3)°, γ =
7
23 (vs), 689 (vs), 628 (w), 567 (m), 526 (vs), 495 (w), 451 (w)
¯
–1
cm . Elemental analysis for C52
.01, S 3.72%; found C 72.82, H 6.92, S 3.97%. The H and
NMR spectroscopic features of 3 dissolved in CD CN are identical
60 4
H O PSV (863.1): cacld. C 72.37, H
1
51
7
V
3
–3
1
12.562(3)°, V = 2589.95(15) Å , Z = 2, ρcalcd. = 1.202 Mg·m , μ =
3
–
1
[
10]
0.308 mm ; 29569 reflections measured, 10177 unique (Rint
.0606); Final R indices [I Ͼ 2σ(I)] R = 0.0353, wR = 0.0996.
=
with those found for I.
0
Synthesis of 4: EtLH
MeCN (30 mL). After addition of NBu
equiv.) the colorless solution turned yellow immediately. After stir-
ring for 2 h the solvent was evaporated under reduced pressure, and
the yellow residue was extracted with 2ϫ5 mL Et O. The filtrate was
stripped of all its volatiles and the remaining solid washed with hexane
10 mL). The removal of all volatiles gave 1.04 g (1.34 mmol, 67%)
(876 mg, 2.00 mmol, 1 equiv.) was dissolved in
[VO ] (682 mg, 2.00 mmol,
2
Crystal Data for 4·½Et
O: C96
H
N
O
V
, M
= 1598.22, T =
2
170
2
9
2
r
4
3
100(2) K, λ = 0.71073 Å, triclinic, space group P1, a = 12.8993(4) Å,
¯
1
b = 18.3014(5) Å, c = 21.7120(6) Å, α = 87.524°, β = 86.518(2)°, γ =
3
–3
7
0
0
7.125(2)°, V = 4985.3(2) Å , Z = 2, ρcalcd. = 1.081 Mg·m , μ =
.239 mm ; 36962 reflections measured, 19583 unique (Rint
.0566); Final R indices [I Ͼ 2σ(I)] R = 0.0566, wR = 0.1222.
–1
2
=
(
1
4
3
as a yellow powder. H NMR (400 MHz, CD CN, room temp.,
4
4
ppm): δ = 7.44 [d, J(H,H) = 2.4 Hz, 2 H, ArH], 7.09 [d, J(H,H) = Acknowledgements
2
3
.4 Hz, 2 H, ArH], 5.35 [q, J(H,H) = 7.6 Hz, 1 H, Ph
2
3
CHCH ], 3.09
+
4 4
+
3
We are grateful to the Deutsche Forschungsgemeinschaft, the CRC546,
the Fonds der Chemischen Industrie, and the Bundesministerium für
Bildung und Forschung for the financial support.
(m, 8 H, NBu ), 1.60 (m, 8 H, NBu ), 1.49 [d, J(H,H) = 7.6 Hz, 3
+
H, Ph
3
2
–CH–CH
3
], 1.35 (m, 8 H, NBu
4
), 1.30 (s, 36 H, tBu), 0.97 [t,
+
51
1
4 3
J(H,H) = 7.2 Hz, 12 H, NBu ]. V{ H} NMR (100 MHz, CD CN,
room temp., ppm): δ = –504 (s). HR-ESI (MeCN, neg): m/z =
Et
–
5
19.2820 (100%, calcd. for [ LVO
2
] 519.2711). IR (KBr): ν˜ = 2960
References
(
1
8
vs), 2904 (m), 2873 (m), 1474 (w), 1466 (m), 1459 (m), 1438 (s),
360 (w), 1238 (m), 1158 (vw), 1136 (vw), 1115 (vw), 938 (vs, br), [1] a) A. Comite, A. Sorrentino, G. Capannelli, M. Di Serio, R.
–1
77 (vw), 838 (w), 803 (vw), 778 (vw), 583 (w) cm . Elemental
Tesser, E. Santacesaria, J. Mol. Catal. A 2003, 198, 151–165; b)
analysis for C46H80NO
4
found C 72.80, H 10.85, N 1.58%. Crystals which were suitable for
X-ray diffraction analysis were obtained by cooling a saturated solu-
V (762.1): calcd. C 72.50, H 10.58, N 1.84%;
R. Zhou, Y. Cao, S. Yan, J. Deng, Y. Liao, B. Hong, Catal. Lett.
2001, 75, 107–112; c) T. Blasco, A. Galli, J. Lopez Nieto, F. Tri-
fido, J. Catal. 1997, 169, 203–211; d) M. A. Chaar, D. Patel,
H. H. Kung, J. Catal. 1988, 109, 463–467; e) A. Corma, J. M.
Lopez Nieto, N. Paredes, J. Catal. 1993, 144, 425–438; f) F. D.
Hardcastle, I.-E. Wachs, J. Mol. Catal. 1988, 46, 173–186; g) G.
Deo, I.-E. Wachs, J. Haber, Crit. Rev. Surf. Chem. 1994, 4, 141–
2
tion of 4 in Et O to –30 °C for several days.
Crystal Structure Determinations: Data collections were performed
either with a Stoe IPDS 1 diffractometer at 180 K (1·MeCN) or on a
187; h) I.-E. Wachs, B. M. Weckhuysen, Appl. Catal. A 1997,
Stoe IPDS 2T diffractometer at 100 K (3·Et
Mo-K radiation (λ = 0.71073 Å) from a sealed tube generator with
graphite monochromator. Numerical absorption corrections
applied for 1·MeCN. The structures were solved by direct methods
2
O and 4·Et
2
O) both using
157, 67–90; i) J. G. Eon, R. Olier, J. C. Volta, J. Catal. 1994, 145,
318–326; j) T. Balsko, J. M. Lopez Nieto, Appl. Catal. A 1997,
157, 117–142; k) A. Khodakov, B. Olthof, A. T. Bell, E. Iglesia,
J. Catal. 1999, 181, 205–216; l) A. Khodakov, J. Yang, S. Su, E.
Iglesia, A. T. Bell, J. Catal. 1998, 177, 343–351; m) E. V. Kond-
ratenko, M. Baerns, Appl. Catal. A 2001, 222, 133–143; n) M. D.
Argyle, K. Chen, E. Iglesia, A. T. Bell, J. Catal. 2002, 208, 139–
α
[
18]
were
[
19]
(
SHELXS-97)
and refined by full-matrix least-squares procedures
2
[19]
based on F with all measured reflections (SHELXL-97).
All non-
hydrogen atoms were refined anisotropically. Hydrogen atoms were
introduced in their idealized positions and refined by using a riding
model.
1
49; o) L. Owens, H. H. Kung, J. Catal. 1993, 144, 202–213; p)
O. R. Evans, A. T. Bell, T. D. Tilley, J. Catal. 2004, 226, 292–
00.
3
[
[
2] C. Ohde, M. Brandt, C. Limberg, J. Döbler, B. Ziemer, J. Sauer,
Dalton Trans. 2008, 326–331; C. Ohde, C. Limberg, D. Schmidt,
M. Enders, S. Demeshko, C. Knispel, Z. Anorg. Allg. Chem. 2010,
Crystallographic data (excluding structure factors) for the structures in
this paper have been deposited with the Cambridge Crystallographic
Data Centre, CCDC, 12 Union Road, Cambridge CB21EZ, UK. Copies
of the data can be obtained free of charge on quoting the depository
6
36, 2315–2322.
3] C. Ohde, C. Limberg, R. Stösser, S. Demeshko, Inorg. Chem.
010, 49, 2479–2485.
2
numbers CCDC-957922 (1·MeCN), CCDC-957923 (3·Et
CCDC-957924 (4·½Et O) (Fax: +44-1223-336-033; E-Mail:
deposit@ccdc.cam.ac.uk, http://www.ccdc.cam.ac.uk).
2
O) and
[4] C. Ohde, C. Limberg, Chem. Eur. J. 2010, 16, 6892–6899.
5] E. Hoppe, C. Limberg, B. Ziemer, Inorg. Chem. 2006, 45, 8308–
2
[
8317.
[
6] E. Hoppe, C. Limberg, B. Ziemer, C. Mügge, J. Mol. Catal. A
2006, 251, 34–40.
Due to beginning loss of co-crystallized ethyl ether solvent molecules
in case of complex 4·½Et O, remaining fragments, which must proba-
bly belong to the solvent of crystallization were squeezed out. In the [8] C. Limberg, Eur. J. Inorg. Chem. 2007, 3303–3314.
2
[7] E. Hoppe, C. Limberg, Chem. Eur. J. 2007, 13, 7006–7016.
[
[
[
[
9] C. G. Werncke, C. Limberg, C. Knispel, R. Metzinger, B. Braun,
Chem. Eur. J. 2011, 17, 2931–2938.
10] C. G. Werncke, C. Limberg, C. Knispel, S. Mebs, Chem. Eur. J.
011, 17, 12129–12135.
11] D. Rehder, T. Polenova, M. Bühl, Annu. Rep. NMR Spectrosc.
007, 62, 49–114.
12] J. M. Mayer, Inorg. Chem. 1988, 27, 3899–3903.
unit cell there are two molecules of 4 with minimal structural differ-
ences, of which one was chosen as representative structure for dis-
cussion.
2
Crystal Data for 1·MeCN: C54
80(2) K, λ = 0.71073 Å, triclinic, space group P1, a = 9.699(3) Å,
b = 10.715(3) Å, c = 25.838(10) Å, α = 92.77(4)°, β = 99.42(4)°, γ =
2 3 r
H63Cl NO PSV, M = 958.92, T =
2
¯
1
[13] M. Vennat, P. Herson, J.-M. Brégeault, G. B. Shulpin, Eur. J. In-
org. Chem. 2003, 5, 908–917.
3
–3
1
00.18(4)°, V = 2599.0(15) Å , Z = 2, ρcalcd. = 1.225 Mg·m , μ =
Z. Anorg. Allg. Chem. 2013, 2426–2432
© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
2431

C. G. Werncke, C. Limberg, R. Metzinger
ARTICLE
[
14] C. R. Waidmann, X. Zhou, E. A. Tsai, W. Kaminsky, D. A. Hro-
[17] V. W. Day, W. G. Klemperer, A. Yagasakl, Chem. Lett. 1990,
vat, W. T. Borden, J. M. Mayer, J. Am. Chem. Soc. 2009, 131,
1267–1270.
[
[
[
18] A. L. Spek, J. Appl. Crystallogr. 2003, 36, 7–13.
4729–4743.
19] G. M. Sheldrick, Acta Crystallogr., Sect. A 2008, 64, 112–122.
20] R. Metzinger, C. Limberg, Z. Anorg. Allg. Chem. 2012, 638,
[15] G. Brauer (Ed.) Handbook of Preparative Inorganic Chemistry,
Academic Press, New York, 1963;.
16] E. Ahlborn, E. Diemann, A. Müller, Z. Anorg. Allg. Chem. 1972,
2225–2234.
[
394, 1–7.
Received: August 29, 2013
Published Online: September 23, 2013
2
432
www.zaac.wiley-vch.de
© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2013, 2426–2432