MoF6 and WF6: Nonrigid molecules?

Article abstract of DOI:10.1002/chem.200400095

Calculations reveal that the octahedral-trigonal prismatic-octahedral rearrangement has particularly low-energy barriers for MoF₆, WF ₆, and (hypothetical) CrF₆. Experimental evidence is obtained from the dynamic ¹⁹

Full text of DOI:10.1002/chem.200400095

FULL PAPER
MoF and WF : Nonrigid Molecules?
6
6
[
a]
[b]
[a]
Gustavo Santiso Quiæones, Gerhard Hägele, and Konrad Seppelt*
Abstract: Calculations reveal that the
octahedral–trigonal prismatic–octahe-
dral rearrangement has particularly
low-energy barriers for MoF , WF ,
WF5, C F ꢀOꢀMoF , C F ꢀOꢀWF ,
tahedral; at elevated temperatures the
nonequivalent metal-bound fluorine
atoms undergo an intramolecular ex-
change. The exchange mechanism
could be a 3+3 or a 2+4 twist; calcula-
tions favor the 3+3 twist.
6
5
5
6
5
5
and (CF ) CꢀOꢀWF . The ground-state
3
3
5
structure of all these compounds is oc-
6
6
and (hypothetical) CrF . Experimental
19
6
Keywords: F NMR spectroscopy ·
evidence is obtained from the dynamic
fluorides · fluxionality · molybde-
num · nonrigid structures · tungsten
19
F NMR spectra of the derivatives
CF ꢀCH ꢀOꢀMoF , C ꢀC HF ꢀOꢀ
3
2
5
3
2
Introduction
count on molybdenum above 12, and at the latest at 18-va-
lence electrons the octahedron will prevail.
The octahedron represents the principal structure for the
vast majority of six-coordinate complex molecules. Recently
this paradigm has been questioned, since stoichiometrically
simple compounds like Mo(CH ) , W(CH ) , or Re(CH )
are distorted or regular trigonal prismatic. There exist a
fairly large number of binary hexafluorides, including main
group (S, Se, Te, Xe), transition-metal (Mo, Tc, Ru, Rh, W,
While there is no doubt that MoF and WF are octahe-
6
6
[2,3]
dral, also for derivatives such as W(OCH3)6
or
[4]
W(NR ) , which carry nonbonding electron pairs on the li-
2
6
gands, the question raised here is how close in energy a
trigonal-prismatic structure would be. If it is close to
3
6
3
[
6
1]
3
6
ꢀ
1
10 kcalmol , then it can be assumed that the molecules
would show fluxionality at ambient or slightly elevated tem-
peratures, so that they could be called nonrigid. This is diffi-
cult to prove by experiment, since all fluorine atoms in
MoF and WF remain equal before and after the rearrange-
Re, Os, Ir, Pt), and actinide elements (U Np, Pa), that are
,
all octahedral (with the single but now well-understood ex-
ception of XeF ); although Mo(CH ) and MoF , W(CH ) ,
6
3
6
6
3
6
6
6
and WF , Re(CH ) and ReF are isoelectronic. If one ac-
ment. We therefore decided to answer this question by a
typical chemical approach, namely by replacing one fluorine
atom with a ligand that displays similar chemical behavior.
The auxiliary ligands CF ꢀCH ꢀOꢀ, C F ꢀOꢀ, and (CF ) Cꢀ
6
3
6
6
cepts the distorted trigonal prismatic structure, for example,
for the 12-electron Mo(CH3)6 system as ground state, as
theory demands, then the octahedral structure of, for exam-
3
2
6
5
3 3
ple, MoF can be explained by one or both of the following
Oꢀ have been chosen because they are fairly easy to intro-
duce, and the resulting compounds are at least in part stable
enough for subsequent high-temperature NMR investiga-
tions.
6
effects: 1) The fairly high partial negative charge on the fluo-
rine ligands results in a strong repulsion effect, which favors
the octahedron as the geometry with the least ligand repul-
sion of all possible six-coordinate structures. 2) In contrast
to Mo(CH ) , there exists in MoF a considerable ligand-to-
3
6
6
central-atom electron back donation. This raises the electron
Results
[
a] M. Sc. G. Santiso Quiæones, Prof. Dr. K. Seppelt
Freie Universität Berlin
Institut für Chemie, Anorganische und Analytische Chemie
Fabeckstrasse 34–36, 14195 Berlin (Germany)
Fax : (+030)838-53310
Theoretical predictions for MoF , WF , CF ꢀCH ꢀOꢀMoF ,
6
6
3
2
5
CF ꢀCH ꢀOꢀWF ,
C F ꢀOꢀMoF ,
C F ꢀOꢀWF ,
3
2
5
6
5
5
6
5
5
(
CF ) CꢀOꢀMoF , and (CF ) CꢀOꢀWF : All calculations
3
3
5
3
3
5
were done on the density functional level of theory, Becke
3 LYP method. For details see the Experimental Section.
The octahedral–trigonal-prismatic rearrangement barrier
E-mail: seppelt@chemie.fu-berlin.de
[
b] Prof. Dr. G. Hägele
Institut für Anorg. Chemie und Strukturchemie I
Universität Düsseldorf
Universitätsstrasse 1, 40225 Düsseldorf (Germany)
Fax (+49)221-8113085
[1]
has been calculated before, for present calculations see
Table 1. As expected, the ground state for MoF and WF ,
6
6
ꢀ
+
+
as well for CrF , NbF , TcF6 , and ReF6 , is octahedral.
6
6
E-mail: haegele@uni-duesseldorf.de
The calculated MꢀF bond lengths are about 4 pm longer
Chem. Eur. J. 2004, 10, 4755 – 4762
DOI: 10.1002/chem.200400095
ꢀ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
4755

FULL PAPER
Table 1. DFT calculations on selected molecular, anionic, and cationic hexafluorides: energies, bond lengths,
and lowest vibrational frequency.
cies like PF , for which a 2+2
5
exchange mechanism (Berry
pseudorotation) can be differ-
entiated from a 3+2 exchange
mechanism (Turnstile rota-
ꢀ
1
[a]
ꢀ1
Energy + zero point energy [a.u.]
rMꢀF [pm]
n [cm
]
DE [kcalmol ]
CrF
MoF
WF
6
O
h
ꢀ686.172442
ꢀ686.152051
ꢀ667.592595
ꢀ667.582059
ꢀ666.564772
ꢀ666.547373
ꢀ656.667833
ꢀ656.651896
ꢀ679.601872
ꢀ679.594678
ꢀ677.203127
ꢀ677.188196
174.0
174.8
186.6(182.0(3)
186.9
187.5 (183.2(3)
188.0
193.9
194.2
182.6
183.1
129.9
97.5i
91.2 (116)
49.0i
111.5 (127)
75.5i
99.3
74.5i
76.5
39.0i
0.0
12.7
0.0
6.6
0.0
10.9
0.0
10.0
0.0
4.4
0.0
D
D
D
D
D
D
3h
[
b]
[c]
[c]
6
O
h
)
tion). In MoF , the aesthetical-
6
3h
[
d]
ly more pleasing exchange
mechanism would be of a 3+3
type (see Figure 1a), which is
6
O
h
)
3h
6ꢀ
h
NbF
O
3h
sometimes called
a
Bailar
+
TcF
6
O
h
twist, named after J. CBailar,
Jr. who first mentioned it in
3h
+
ReF
6
O
h
183.4
184.1
109.1
72.0i
[12]
3h
9.4
the literature in 1958.
Here
0
0
the reaction coordinate is the
twist angle between the two
sets of triangular positioned li-
gands with a = 608 for the oc-
[
a] Lowest calculated vibrational frequencies, T2u in O
h
1
, imaginary frequencies A in D3h. [b] Experimental
value, see ref [5]. [c] Experimental value, see ref [6,7]. [d] Experimental value, see ref. [5,8].
than those for which experimental values are known. In all
cases, the trigonal-prismatic structure is a transition state, as
is evidenced by one imaginary frequency. The MꢀF bond
tahedron and a = 08 for the trigonal prism. Interestingly, a
2+4 ligand twist (with b = 08 for the octahedron, see Fig-
ure 1b) would result also in a regular trigonal prism with b
[13]
19
lengths in the transition state are marginally longer than in
the octahedral ground state, reflecting the small loss of
energy. It is evident that in MoF this O –D barrier is even
= 458.
Simulated dynamic F NMR spectra for RꢀOꢀ
MF molecules show no difference between these two mech-
5
anisms, so they are experimentally undistinguishable. The ar-
gument favoring the 3+3 mechanism (Figure 1a) is derived
by calculation: All calculated trigonal-prismatic structures
have one imaginary frequency for all the compounds dis-
cussed here, and the vector of this vibration is identical to
the reaction coordinate of the 3+3 mechanism.
6
h
3h
lower than in CrF and WF . That the barrier in MoF is
6
6
6
lower than that in CrF can be explained by the increased
6
size of the MoF molecule, which results in lower interligand
6
repulsion, making the trigonal-prismatic structure more fa-
vorable. The higher barrier in WF is explained by the influ-
6
ence of the strongly increased relativistic effect: The WꢀF
bond lengths are only slightly longer than the MoꢀF bond
lengths, but the polarity of the bond is increased.
The DFT calculations of the monosubstituted derivatives
RꢀOꢀMoF and RꢀOꢀWF are summarized in Table 3.
5
5
Again the major difference is that experimental MoꢀF bond
lengths (see below) are a few pm shorter than calculated.
The energy difference between the octahedral ground state
ꢀ
+
In the series NbF6 , MoF , and TcF , the decreasing
6
6
bond polarity favors the trigonal-prismatic structure, so that
+
for the unknown TcF6 ion the octahedral structure is no
longer guaranteed if the errors of the DFT calculations are
taken somewhat generously.
Looking at all known hexafluorides (except XeF ) clearly
6
reveals the exceptional case of MoF . The n (T ) vibration
6
6
2u
(
both IR and Raman forbidden) of these octahedral mole-
cules has the lowest value for MoF (Table 2). This is be-
6
cause this vibration contributes to the octahedral–trigonal-
prismatic rearrangement (see Figure 1; for simplification the
1
4
structures of the d -d hexafluorides ReF –PtF , and TcF –
6
6
6
RhF6 are considered to be octahedral, although some of
[9–11]
them may exhibit very small Jahn–Teller distortions
).
The exact mechanism of the ligand exchange in MoF is
6
difficult to prove, in contrast to that in five-coordinate spe-
ꢀ
1
Table 2. Experimental values [cm ] for the Raman- and IR-forbidden n
6
[
6]
(T2u) vibration of molecular octahedral hexafluorides.
SF
47
SeF
6
3
6
2
TeF
6
197
64
Figure 1. a) The 3+3 octahedral–trigonal-prismatic rearrangement reac-
tion coordinate is the twist angle between the two trigonal sets of ligands.
b) The 2+4 octahedral–trigonal-prismatic rearrangement. The reaction
coordinate is the twist angle between two cis-oriented ligands relative to
MoF
16
WF
27
UF
6
TcF
6
RuF
186
6
RhF
192
6
1
145
ReF
193
NpF
164
6
6
OsF
205
6
IrF
206
6
PtF
211
6
1
6
the other four. c) The Raman- and IR-forbidden n (T2u) vibration of the
octahedron, which is a component of both the 3+3 and 4+2 rearrange-
ments.
6
6
PuF
173
6
1
42
4756
ꢀ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
Chem. Eur. J. 2004, 10, 4755 – 4762

Fluxionality of Mo and W Fluorides
4755 – 4762
Table 3. Results of DFT calculations on CF
3
ꢀCH
2
ꢀOꢀMF
5
, C
6
F
5
ꢀOꢀMF
DE [kcalmol ]
5
, (C F
3
)
3
CꢀOꢀMF
5
; M = Mo, W.
LiO(CF3)3 gave just the
tungsten derivative, it does not
ꢀ
1
Energy + zero point energy [a.u]
ꢀ1019.983954
Bond lengths [pm]
CF3ꢀCH ꢀOꢀMoF (O )
0
MoꢀO
185.2
187.2
187.2–190.2
140.3
188.2
187.0–187.8
189.2
141.6
186.0
188.4
188.1–190.3
140.5
188.8
188.1–188.8
190.1
141.9
188.4
186.8
187.4–189.9
132.3
193.6
react with MoF . Under suit-
6
2
5
h
MoꢀFax
MoꢀFeq
CꢀO
able conditions only single sub-
stitution is observed. Four of
these compounds are liquids at
CF
CF
CF
3
ꢀCH
2
ꢀOꢀMoF
5
(D3h
)
ꢀ1019.967650
ꢀ1018.951387
ꢀ1018.928884
ꢀ1370.901500
ꢀ1370.88428
ꢀ1369.867201
ꢀ1369.842479
ꢀ1694.214825
ꢀ1694.194078
ꢀ1693.184774
ꢀ1693.158812
10.23
0
MoꢀO
MoꢀF1,2,3
MoꢀF4,5
CꢀO
room temperature, and C F ꢀ
6
5
OꢀMoF is a solid. All these
5
compounds are characterized
by NMR and vibrational spec-
tra and elemental analyses; a
single-crystal structure deter-
mination was carried out for
C F ꢀOꢀMoF . The structure
ꢀCH
ꢀOꢀWF
h
(O )
Wꢀ0
3
2
5
5
WꢀFax
WꢀFeq
C
ꢀ
O
ꢀCH
ꢀOꢀWF
(D3h
)
14.12
0
WꢀO
3
2
WꢀF1,2,3
WꢀF4,5
CꢀO
6
5
5
around the metal center in all
five compounds is octahedral,
C
C
C
C
6
6
6
6
F
F
F
F
5
ꢀOꢀMoF
5
5
(O
h
)
MoꢀO
MoꢀFax
MoꢀFeq
CꢀO
as is evidenced by the AB pat-
4
1
9
terns in the F NMR spectra
at room temperature or below.
Further proof comes from the
single-crystal structure deter-
mination of C F ꢀOꢀMoF ,
ꢀOꢀMoF
(D3h
)
10.81
0
MoꢀO
MoꢀF1,2,3
5
186.6–187.6
189.0–189.1
133.4
Mo
ꢀ
F
4,5
CꢀO
6
5
5
ꢀOꢀWF
(O
)
WꢀO
187.4
187.9
188.4–189.2
133.2
191.8
188.0–188.6
189.5
135.0
5
5
5
h
which delivers structural de-
tails (Table 4 and Figure 2). It
WꢀFax
WꢀFeq
CꢀO
may be of interest that C F ꢀ
6
5
ꢀOꢀWF
(D3h
)
15.51
0
WꢀO
OꢀMoF is deeply colored in
5
5
WꢀF1,2,3
WꢀF4,5
CꢀO
the condensed phase. In the
crystal structure, there is an in-
termolecular interaction be-
tween the C F ring of one
(
(
(
(
CF
CF
CF
CF
3
3
3
3
)
3
)
3
)
3
)
CꢀOꢀMoF
CꢀOꢀMoF
5
5
(O
h
)
MoꢀO
186.5
Mo ax
MoꢀFeq
CꢀO
ꢀ
F
186.6
6
5
187.4–187.7
137.9
186.5
187.4–187.7
187.5, 186.6
137.9
187.2
187.6
188.3–188.4
138.1
188.7
molecule and the MoF group
5
of another molecule, which re-
sults in a charge-transfer inter-
action in which the aromatic
ring is clearly the donor and
(D3h
)
13.02
0
MoꢀO
MoꢀF1,2,3
MoꢀF4,5
CꢀO
CꢀOꢀWF
(O
)
WꢀO
the OꢀMoF group the accep-
5
h
5
WꢀFax
WꢀFeq
CꢀO
tor. Aside from this finding,
the structure is completely as
expected. Reaction between
3CꢀOꢀWF (D )
16.29
WꢀO
5
3h
WꢀF1,2,3
WꢀF4,5
CꢀO
188.3–189.7
188.7, 188.8
138.4
MoF6
and
CF ꢀCH ꢀOꢀ
3
2
Si(CH3)3 does not produce
solely CF ꢀCH ꢀOꢀMoF . At
3
2
5
longer reaction times and espe-
cially if CF ꢀCH ꢀOꢀSi(CH )
3
2
3 3
and the trigonal-prismatic excited state is calculated to be
is applied in excess, cis-[(CF CH O) MoF ] is detectable as a
3 2 2 4
ꢀ
1
around 10 kcalmol for the three molybdenum compounds
by-product. This is indicated by the A B spectrum of the
2 2
ꢀ1
and around 15 kcalmol for the three tungsten compounds.
molybdenum-bound fluorine atoms. This compound crystal-
lizes spontaneously from the reaction mixture, and geomet-
rical data from the single-crystal structure determination are
Preparation of CF ꢀCH ꢀOꢀMoF , CF ꢀCH ꢀOꢀWF ,
3
2
5
3
2
5
C F ꢀOꢀMoF , C F ꢀOꢀWF , and (CF ) CꢀOꢀWF , struc-
collected in Table 4. The cis orientation of the two CF ꢀ
6
5
5
6
5
5
3
3
5
3
tural determinations: These monosubstituted derivatives of
CH ꢀO groups within the octahedral molybdenum environ-
2
MoF and WF are readily prepared by variations of litera-
ment is confirmed.
6
6
ture procedures [Eq. (1) and (2)].
1
9
Dynamic F NMR spectra of CF ꢀCH ꢀOꢀMoF , CF ꢀ
3
2
5
3
CH ꢀOꢀWF , C F ꢀOꢀMoF , C F ꢀOꢀWF , and (CF ) -
2
5
6
5
5
6
5
5
3 3
MF þ RꢀOꢀSiðCH Þ ! RꢀOꢀMF þ ðCH Þ SiF
6
3
3
5
3 3
ð1Þ
ð2Þ
CꢀOꢀWF : All five compounds under investigation exhibit
5
M ¼ Mo, W; R ¼ CF ꢀCH ꢀ, C F ꢀ
19
3
2
6
5
strongly temperature-dependent F NMR spectra for the
1
9
metal-bound fluorine atoms, while the typical F NMR (and
WF þ LiOCðCF Þ ! ðCF Þ CꢀOꢀWF þ LiF
1
ꢀ
ꢀ
6
3
3
3
3
5
H NMR) spectra of the CF CH O , C F O , and (CF ) -
3 2 6 5 3 3
Chem. Eur. J. 2004, 10, 4755 – 4762
www.chemeurj.org
ꢀ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
4757

K. Seppelt et al.
FULL PAPER
Figure 2. Crystal structure of
C
6
F
5
ꢀOꢀMoF
5
(50% probability plot).
Shown is a pair of molecules that have a mutual charge-transfer interac-
tion that results in a deep color. The second molecule is generated by the
inversion center.
Figure 3. Experimental (left) and simulated (right) temperature-depend-
1
9
ent F NMR (376 MHz) spectra of C
6
F
5
ꢀOꢀWF
5
.
Table 4. Experimental bond lengths [pm] and selected bond angles [8] of C
MoF ].
4
6
F
5
ꢀOꢀMoF
5
and cis-[(CF
O) MoF
3
CH
2
O)2-
For the molybdenum atoms
this method is not available,
since the satellites from the
C
6
F
5
ꢀOꢀMoF
5
cis-[(CF
3
CH
2
2
4
]
MoꢀO
182.7(2)
184.4(2)
182.7(2)–184.7(2)
133.0(3)
178.5(4)–179.2(4)
only NMR-active isotopes of
Mo ax
ꢀ
F
95/97
Mo ( Mo, I
= 5/2, 15.9,
MoꢀFeq
MoꢀF
147.8(9)–150.9(9)
184.0(4)–185.3(4)
140.5(6)–142.1(6)
9
.6% natural abundance) are
CꢀO
not observed except in highly
symmetric molecules such as
MoF . In the case of C F ꢀOꢀ
CꢀC137.1(4)–139.8(4)
CꢀF
132.1(3)–133.0(3)
170.8(1)
85.8(1)–97.1(1)
126.2(9)–133.5(8)
98.2(2), 98.3(2)
83.8(2)–89.1(2), 171.8(2), 171.7(2)
F
axꢀMoꢀO
OꢀMoꢀO
FꢀMoꢀF
6
6
5
F
eqꢀMoꢀO
MoF , temperature-dependent
5
MoꢀOꢀC149.8(2)
144.1(4), 144.7(4)
19
F NMR spectra at different
concentrations in different sol-
vents (C D Cl and CD Cl )
2
2
4
2
2
CꢀOꢀ groups are less sensitive towards temperature and
hence insignificant for this study. The numerical data for
these groups are given in the Experimental Section and will
not be discussed any further.
did not show concentration dependence. There is yet anoth-
er argument against intermolecular exchange: If one as-
sumes that upon heating the metal-bound fluorine atoms
could move from one metal atom to another, the OR
groups could as well. This would result in a scrambling of F
and OR groups and therefore in the formation of some or
The typical AB spectra (approximately doublet + quin-
4
tet) of the ꢀOMF groups are best resolved at room temper-
5
ature or below. Upon warming, line broadening takes place.
all members of (RO) MF
compounds. This is indeed ob-
6ꢀn
n
The A and B parts exhibit intrinsic shifts upfield with in-
4
creasing temperature, and the apical fluorine is more sensi-
tive than the four equatorial fluorine atoms. Consequently,
the second-order character of the underlying AB spectrum
4
increases since D = d ꢀd decreases with increasing tem-
d
B4
A
perature. At higher temperatures coalescence is observed
and further heating results in a sharpening of the remaining
single line (Figure 3). The high-temperature limit of the
spectra could only be obtained in the case of C F ꢀOꢀWF ,
6
5
5
since our spectrometers have an upper temperature limit of
1858Cfor the 90 MHz and 150 8Cfor the 400 MHz instru-
ment. The molybdenum compounds start to decompose at
these temperatures.
It is clear that fluorine exchange of the metal-bound fluo-
rine atoms is occurring. Is this exchange intra- or intermo-
lecular? In the case of C F ꢀOꢀWF we can give definite
6
5
5
proof that the exchange is intramolecular. The tungsten-
1
83
bound fluorine atoms have side bands from W (I = 1/2,
4% natural abundance). These side bands are still visible
at the high temperature limit (Figure 4), which shows that
the five fluorine atoms remain bound to the tungsten atom.
1
19
Figure 4. The low- (308C) and high-temperature (1848C) limit F NMR
(
6 5 5
84.25 MHz) spectra of C F O WF at high resolution, showing the
ꢀ ꢀ
1
83
19
W– F satellite lines, marked by *, arbitrary scales.
4758
ꢀ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
Chem. Eur. J. 2004, 10, 4755 – 4762

Fluxionality of Mo and W Fluorides
4755 – 4762
served, but only at temperatures above 1008Cand at a very
slow rate, so that no coalescence of this type is seen.
19
The F NMR spectra were successfully simulated (see
Figure 3) by using the program gNMR. Spin enumeration
and permutational operators used for gNMR, assuming the
aforementioned 3+3 or 2+4 torsional mechanisms, are de-
fined in Figure 5.
k
T
1000
T
Figure 6. Eyring plot ln( ) versus
for rate constants obtained by NMR
simulation.
imentally determined activation energies can only be
guessed. Slight variation of some of the parameters change
ꢀ
1
the energy values by about 0.5 kcalmol .
Conclusion and Outlook
Figure 5. Definition of permutation operators used to describe the 3+3
MꢀOR (R =
Octahedral MoF , WF , and their derivatives RꢀOꢀMoF
(
ꢀ
a) and 2+4 (b) exchange for compounds of the type F
CH ꢀCF , ꢀC F , for M = Mo, W; R = ꢀC(CF ) for M = W).
5
6
6
5
2
3
6
5
3 3
and RꢀOꢀWF are at the edge of structural stability. More
5
exact numbers for the activation energies could be obtained
if compounds were to become available that fulfil three re-
quirements: Stable to 2008C, intrinsically small line width
for the metal-bound fluorine atoms, and nonaggressivity (at
least towards quartz), so that Teflon inserts in the NMR
A series of meticulous simulations yielded rate constants
for specific temperatures (Table 5). Using the standard line-
k
T
DH
RT
*
kkB
DS
*
arized Eyring equation ln( ) =
+ln( h
+
), activation
R
energies were estimated as shown in Figure 6. Clearly an
agreeable linear behavior is achieved by experiment. The
following data were found: CF ꢀCH ꢀOꢀMoF 12.6, C F ꢀ
tubes are no longer required. If one were out to find a hexa-
+
fluoride that is even less rigid, then TcF
would be the best
6
choice. However, attempts to isolate this compound have so
3
2
5
6
5
[14]
OꢀMoF 12.3, CF ꢀCH ꢀOꢀWF 13.0, C F ꢀOꢀWF 13.4,
far been unsuccessful.
5
3
2
5
6
5
5
ꢀ
1
and (CF ) CꢀOꢀWF 15.9 kcalmol , which correspond to
3
3
5
DH* for the octahedral–trigonal-prismatic interchange de-
scribed above as the 3+3 mechanism. These values can be
compared with calculated energies (Table 3). Calculated and
experimental energy barriers agree fairly well. We must
keep in mind that simulations of these dynamic F NMR
spectra are not trivial, mainly because there is a strong tem-
perature dependence of both chemical shifts, especially of
the apical fluorine atom, and because of the high second-
Experimental Section
General: All reactions were carried out under a dry argon atmosphere
1
9
(for example, by handling in a dry box with H
than 1 ppm). Solvents were dried by standard methods. Commercially
available chemicals (MoF , WF , C OH, (CH SiCl, (CF COH, and
2 2
O and O content lower
6
6
6
F
5
3
)
3
3 3
)
nBuLi) were used as received. The 2,2,2-trifluoroethanol was distilled
twice before use. NMR spectra were recorded by using a JEOL JNM-LA
1
13
19
order character of the AB systems. The errors of the exper-
400 spectrometer ( H at 399.65 MHz, Cat 100.40 MHz, and
F at
4
ꢀ
1
Table 5. Rate constants k [s ] at different temperatures [K] for CF
lations using the 3+3 exchange mode.
3
ꢀCH
2
ꢀOꢀMF
5
, C
6
F
5
ꢀOꢀMF
5
, M = W, Mo, and (CF
CF
ꢀCH ꢀOꢀMoF
3
)
3
CꢀOꢀWF
5
obtained by simu-
ꢀOꢀMoF
CF
3
ꢀCH
2
ꢀOꢀWF
5
C
6
F
5
ꢀOꢀWF
5
(CF
3
)
3
CꢀOꢀWF
5
3
2
5
C
6
F
5
5
5
9
1
3
5
1
4
.3
.4
6.8
3.2
8.9
313
323
333
343
353
373
393
5.1
20.5
80.5
250.0
645.0
1615.0
303
324
344
363
383
403
0.10
0.29
0.71
293
303
313
323
333
343
353
363
35.6
71.6
273
278
283
288
293
298
303
135.1
196.9
299.2
444.0
656.4
303
313
333
353
363
373
138.0
256.0
460.1
796.1
1340.2
3.80
14.26
27.57
45.62
70.1
40.8
926.6
1332.0
2702.7
5405.4
9459.5
3
3
3
13
23
33
Chem. Eur. J. 2004, 10, 4755 – 4762
www.chemeurj.org
ꢀ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
4759

K. Seppelt et al.
FULL PAPER
1
3
1
3
76.00 MHz). NMR spectra for C
6
F
5
ꢀOꢀWF
5
at 208Cand 184 8Cwere
8.66 Hz, 2H; ꢀCH
2
ꢀ), 0.1 ppm (s, 9H; ꢀCH
3
); C{ H} NMR (CDCl
3
): d
C,F = 35.7 Hz, 1C;
): d = ꢀ77.4 ppm (t,
1
9
1
2
recorded by using a JEOL F 90 Q instrument ( F at 84.25 MHz). Chemi-
= 124.3 (q,
J
C,F = 278.6 Hz, 1C; ꢀCF
3
), 61.2 (q, J
); F NMR (CDCl
1
13
19
cal shift values are reported with respect to TMS ( H, C) and CCl
F). Deuterated solvents were used as received. NMR spectra were re-
3
F
ꢀCH
2
ꢀ), ꢀ0.9 ppm (s, 3C; ꢀCH
3
3
1
9
3
J
F,H = 7.7 Hz, 3F;
ꢀ
CF ).
3
(
1
9
corded at room temperature unless otherwise stated. The F NMR dy-
namic spectra were measured by using C Cl as solvent, occasionally
CD Cl was used. Raman spectra were recorded on a Bruker RFS 100
(Pentafluorophenoxy)trimethylsilane (C F ꢀOꢀSi(CH ) ): (Pentafluoro-
6
5
3 3
2
D
2
4
phenoxy)trimethylsilane was prepared in a similar manner to the proce-
dure described above, as the reaction between pentafluorophenol and
chlorotrimethylsilane reported in the literature proved to be unreli-
2
2
FT-Raman spectrometer. Elemental analyses were performed by Beller
Co., Göttingen, Germany.
[
19]
able. Pentafluorophenol (30.0 g, 0.163 mol) was added to a previously
dried three-neck flask equipped with a reflux condenser. [(CH Si] NH
18 mL, 84.7 mmol) was added dropwise slowly into the flask followed by
stirring as soon as there was enough liquid. The reaction mixture was re-
fluxed for 4 h. After distillation, the mixture contained 85% C
ꢀOꢀ
Si(CH and 15% bis(trimethylsilyl)amine. Vacuum distillation from
3
)
3
2
Single crystals were handled in a special device, cut to an appropriate
size, and mounted on a Bruker SMART CCD 1000 TU diffractometer,
using MoKa irradiation, a graphite monochromator, a scan width of 0.38
in w, and a measurement time of 20 s per frame. After semiempirical ab-
sorption corrections (SADABS) by equalizing symmetry-equivalent re-
(
6
F
5
3 3
)
[
15]
ꢀ308Cinto a ꢀ1968Ctrap gave the pure compound (25.05 g; 60% yield)
flections, the SHELX programs were used for solution and refinement.
1
as a colorless liquid. H NMR (CDCl
3
): d = 0.1 ppm (s, 9H; ꢀCH
3
);
All atoms except hydrogen were refined anisotropically. Hydrogen atoms
were located by difference Fourier maps and refined independently from
other atomic positions but with a single isotropic displacement parameter
for all hydrogen atoms. Experimental details are laid down in Table 6, re-
sults in Table 4, see also Figure 2. CCDC-218240 (C
CCDC-218241 ((CF CH O) MoF ) contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of charge via
www.ccdc.can.ac.uk/conts/retrieving.html (or from the Cambridge Crys-
tallographic Center, 12 Union Road, Cambridge CB21EZ, UK; Fax:
1
3
19
C{ F} NMR (CDCl
33.7 (s, 1C; ꢀC
3
): d = 138.6 (s, 1C; C2,6), 135.640 (s, 1C; ꢀC3,5),
1
1
4
), 128.1 (s, 1C; ꢀC
1
), ꢀ1.6 ppm (q, JC,H = 119.5 Hz, 3C;
1
9
3
ꢀ
CH ); F NMR (CDCl ): d = ꢀ159.7 (d,
J
F,F
= 18.4 Hz, 2F; -o),
3
3
3
3
ꢀ
165.8 (t, JF,F = 21.3 Hz, 2F; -m), ꢀ168.2 ppm (t, JF,F = 21.3 Hz, 1F; -
6
F
5
ꢀOꢀMoF
5
) and
p).
3
2
2
4
3 3
Lithium perfluoro(tert-butoxide) (LiOC(CF ) ): Lithium perfluoro(tert-
[20]
butoxide) was prepared in a similar manner to a literature procedure.
Perfluoro(tert-butyl aclohol) (1.5 mL, 10.74 mmol) was added under
argon pressure to a previously dried three-neck flask equipped with a
reflux condenser. With the aid of a syringe, nBuLi (1.6m in hexane,
(
+44)1223-336033; or deposit@ccdc.cam.ac.uk).
6
.7 mL, 10.72 mmol) was added dropwise while the mixture was stirred at
Table 6. Crystallographic data.
room temperature. After the reaction mixture was refluxed for 4 h, the
flask was cooled down and kept at 08Cwhile all volatile materials were
pumped off over a period of 6 h. A yellowish oily material remained in
Compounds
C
6
F
5
ꢀOꢀMoF
5
3 2 2 4
cis-[(CF CH O) MoF ]
M
374.00
370.01
ꢀ3
the flask. After the material was sublimed (48 h/1508C/10 mbar), a
T [8C]
space group
a [pm]
b [pm]
c [pm]
a [8]
ꢀ100
ꢀ100
white crystalline material identified as LiOC(CF
3
)
3
(0.51 g; 19.6% yield)
): d = 122.1 (s, 3C; ꢀCF
),
O/CDCl
): d = ꢀ77.3 ppm (s, 9F;
¯
13
19
P2
1
/n
P1
was recovered. C{ F} NMR (Et
2
O/CDCl
3
3
647.6(1)
1256.7(3)
1123.1(2)
90
1008.6(1)
1041.3(1)
1085.9(1)
73.499(2)
74.614(2)
89.603(2)
1051.5
4
1.38
30.6
13084
6340
308
1.1 ppm (s, 1C; ꢀOC); F NMR (Et
19
8
2
3
ꢀCF ).
3
Tungsten pentafluoride (2,2,2-trifluoroethoxide) (CF
mixture of CF (1.590 g, 9.23 mmol) with a few drops
ꢀCH ꢀOꢀSi(CH
of 2,2,2-trifluoroethanol was added to a previously dried PFA tube equip-
ped with a magnetic stirrer. An excess of WF (7.41 g, 24.91 mmol) was
3
ꢀCH
2
ꢀOꢀWF
5
): A
3
2
3 3
)
b [8]
g [8]
V [10 pm ]
Z
91.400(4)
90
913.8
4
6
3
6
condensed into this mixture. The reaction vessel was kept at ꢀ908Cover
a period of 3 h. The temperature was allowed to rise up to ꢀ308Cwhile
the mixture was being stirred. At this point a light pink solution was ob-
served. The mixture was kept at ꢀ308Cand stirred for a further 1 h. The
PFA tube was kept between ꢀ408Cand ꢀ308Cwhile it was evacuated
for 5 h, a transparent liquid (3.313 g; 95% yield), highly sensitive to
moisture and slightly volatile at room temperature, remained inside the
ꢀ
1
m [mm
]
1.58
q
max [8]
30.6
reflections collected
reflections, independent
refined parameters
R
11435
2802
163
0.029
0.068
0.068
0.206
13
1
1
tube. M.p. ꢀ55.58C; C{ H} NMR (CDCl
3 C,F
ext.): d = 121.4 (q, J =
wR
2
2
19
2
78.9 Hz, 1C; ꢀCF
3
), 76.7 ppm (q,
J
C,F = 40.2 Hz, 1C; ꢀCH
2
ꢀ);
F
2
2
NMR (CDCl
3
ext.): d = 129.2 (d, JF,F = 64.0 Hz, 4F; Feq.), 107.5 (q, JF,F
); Raman spectroscopy: n˜ =
=
66.3 Hz, 1F; Fax.), ꢀ75.6 ppm (s, 3F; ꢀCF
3
The program gNMR was used for the simulation of the dynamic NMR
3
1
3
6
022(4), 2971(14), 2864(1), 2772(1), 1437(12), 1395(5), 1279(15),
145(38), 950(7), 841(41), 732(100), 638(16), 618(41), 528(29), 360(28),
[
16]
spectra. DFT calculations were performed with the program GAUSSI-
[
17]
AN revision A7, 1998,
method Becke 3 LYP, as implemented in the
ꢀ1
06(59), 247(12), 187(9), 123(33) cm ; elemental analysis calcd (%): C
.36, H 0.53; found: C6.93, H 0.65.
program. Basis sets: 6–311G(d,p) for C, H, O, and F. The relativistically
corrected pseudopotentials and basis sets for Cr, Mo, W, Nb, Tc, and Re
were obtained from the Institut für Theoretische Chemie, Universität
Stuttgart. Cr: 10 core electrons; Nb, Mo, Tc: 28 core electrons; W, Re: 60
core electrons, 8s 7p 6d valency basis for each metal.
Molybdenum pentafluoride (2,2,2-trifluoroethoxide) (CF
MoF ): In a dry box, a mixture of CF (0.901 g, 5.23 mmol)
ꢀCH ꢀOꢀSiR
with a few drops of 2,2,2-trifluoroethanol was placed in a previously
dried PFA tube equipped with a magnetic stirrer. An excess of MoF
3
ꢀCH ꢀOꢀ
2
5
3
2
3
6
(
2,2,2-Trifluoroethoxy)trimethylsilane (CF
3
ꢀCH
2
ꢀOꢀSi(CH
3 3
) ): (2,2,2-
(
2.779 g, 13.24 mmol) was condensed into this mixture. At ꢀ788C, vari-
Trifluoroethoxy)trimethylsilane was prepared by using a literature proce-
ous colors (yellow, light brown, light green) were observed at the contact
surface between the two reactants. The mixture was maintained and stir-
red at ꢀ508Cfor 2 h. The PFA tube with the dark brown mixture was
evacuated between ꢀ758Cand ꢀ608Cfor 3 h. Three more hours at
[
18]
dure.
Bis(trimethylsilyl)amine (45 mL, 0.212 mol) and two drops of
chlorotrimethylsilane were added under argon pressure to a previously
dried three-neck flask equipped with a reflux condenser. With the aid of
a syringe, 2,2,2-trifluoroethanol (30 mL, 0.417 mol) was added dropwise
while the mixture was stirred slowly. After the mixture had been refluxed
for three hours, the liquid was distilled at atmospheric pressure to give a
ꢀ308Cof evacuation were needed to pump off all unreacted MoF . A
6
light yellow liquid (1.432 g; 94.4% yield), very reactive to moisture and
slightly volatile at room temperature, remained inside the tube. M.p.
1
3
1
1
mixture of CF
3
ꢀCH
2
ꢀOꢀSi(CH
3
)
2
and [(CH
3
)
3
Si]
2
NH (84% and 16%, re-
ꢀ31.08C; C{ H} NMR (CDCl ext.): d = 122.9 (q,
J
= 280.13 Hz,
3
C,F
19
1
2
spectively, as shown by the H NMR integrals). The mixture was evacuat-
1C; ꢀCF ), 84.8 ppm (q, J = 39.98 Hz, 1C; ꢀCH ꢀ); F NMR (CDCl
3
C,F
2
3
2
2
ed at ꢀ308Cand with the aid of a double cold trap ( ꢀ608C/ꢀ1968C)
ext.): d = 234.8 (d,
J
F,F eq.
= 82.4 Hz, 4F; F ), 207.5 (q, JF,F = 87.7 Hz,
CF
3
ꢀCH
2
ꢀOꢀSi(CH
3
)
3
(59.58 g; 83% yield) was collected as a colorless
1F; Fax.), ꢀ71.1 ppm (s, 3F; ꢀCF ); Raman spectroscopy: n˜ = 30.10(6),
3
1
3
liquid in the ꢀ1968Ctrap.
H NMR (CDCl
3
): d
=
3.9 (q,
J
F,H
=
2953(21), 2838(1), 2747(1), 1424(14), 1382(14), 1267(19), 1098(82),
4760
ꢀ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
Chem. Eur. J. 2004, 10, 4755 – 4762

Fluxionality of Mo and W Fluorides
4755 – 4762
ꢀ1
9
3
44(8), 840(44), 701(100), 641(41), 608(65), 530(45), 383(41), 357(22),
24(66), 302(56), 246(21), 172(18), 122(56) cm ; elemental analysis calcd
208(15), 196(16), 178(17), 156(12), 111(16) cm ; elemental analysis calcd
(%): C19.27; found: C18.34.
ꢀ1
(
%): C8.28, H 0.69; found: C8.73, H 0.76.
Molybdenum bis (2,2,2 trifluoroethoxide) tetrafluoride (cis-[(CF
MoF ]): In an attempt to synthesize CF as described in
ꢀCH ꢀOꢀMoF
the literature, a mixture of compounds with the molecular formula
CF
ꢀCH ꢀO)
ꢀ ꢀ
Tungsten pentafluoride (tert(perfluoro)butoxide) ((CF
LiOC(CF
6
tube equipped with a magnetic stirrer. An excess of WF (1.83 g,
3 3 5
) C O WF ):
3
CH
2
O)
2
-
3 3
) (0.326 g, 1.496 mmol) was added to a previously dried PFA
4
3
2
5
[
21,22]
6.144 mmol) was condensed into the tube. After the reaction mixture had
been stirred at room temperature for 4.5 days, an F NMR spectrum of
1
9
19
(
3
2
n
MF6ꢀn, n = 1, 2, and 3 (as shown by the F NMR spec-
troscopy) was obtained. After letting the sample stand for a few days at
room temperature, some yellow crystals were observed on the walls of
the reaction flask. The crystals were suitable for X-ray diffraction (see
Table 6). The structure obtained was cis-[(CF
tempts to crystallize the trans derivative or the other higher members of
the solution showed F
5
WꢀOꢀC(CF
3 3
) as the only main product. The PFA
tube was cooled to ꢀ508Cand warmed up gradually to 0 8Cover a
period of 18 h, while all volatile materials were pumped off into two
traps (ꢀ788C/ꢀ1968C). A colorless liquid (0.47 g, 61.1% yield) identified
ꢀCH
ꢀOꢀ)
2 4
MoF ]. At-
3
2
as F
5
WꢀOꢀC(CF
3
)
3
was recovered in the ꢀ788Ctrap. M.p. ꢀ598C;
1
3
19
the series from this mixture failed, and no other substance could be iso-
C{ F} (08C , C
2
Cl DCDCl
2
): d = 118.2 (s, 3C; ꢀCF
3
), 85.8 (s, 1C; ꢀOC);
1
9
2
19
2
lated. F NMR {CDCl
3
ext): d=171.3 (t,
F,F = 91.5 Hz, 2F), ꢀ74.6 ppm (s, 3F).
Tungsten pentafluoride pentafluorophenoxide (C
to synthesize a pure sample according to reported procedures
all unsuccessful. Even modifications on the procedure, such as the use of
a solvent (CH Cl , C C lF ), higher reaction temperatures, and longer reac-
tion times, gave either unreacted WF and C or a mixture
ꢀOꢀSi(CH
of compounds with the molecular formula (C O) WF6ꢀn, n = 1, 2, 3 as
J
F,F = 91.5 Hz, 2F), 151.9 (t,
F NMR (08C , C
2
Cl DCDCl
2
): d = 150.0 (d,
J
F,F = 64.8 Hz, 4F; Feq.),
). Raman
2
2
J
157.5 (q,
J
F,F = 65.18 Hz, 1F; Fax.), ꢀ74.8 ppm (s, 9F; ꢀCF
3
specrtroscopy: n˜ =1316(10), 1273(10), 1229(5), 1177(23), 986(2), 859(12),
F
5
ꢀOꢀWF
5
): Attempts
[23, 24]
6
761(88), 735(100), 674(10), 659(14), 539(16), 426(4), 333(49), 305(67),
were
ꢀ
1
2
84(55), 241(19), 134(39), 113(24) cm .
1
9
F NMR input parameters for the simulations in gNMR: CF
3
ꢀCH
65.80 Hz,
W,Feq = 39.57 Hz; line width (Hz; A part, B part) :
14, 16; temperature (K)/chemical shift (ppm; A part, B part): 313/
108.982, 129.777; 323/109.671, 130.12; 333/111.226, 131.123; 343/111.900,
2
ꢀOꢀ
2
2
3
2
F
5
3
)
3
5 2 2 4 Fax,Feq
WF : Sample concentration: 1.52m (in C D Cl ); J =
1
6
6
1
F
5
n
J
W,Fa = 44.20 Hz,
J
4
6
1
9
shown by the F NMR spectra. No possible purification of the desired
compound was achieved.
4
1
31.365; 353/112.458, 131.438; 373/113.770, 131.928; 393/115.275, 470.
A
(
solution of
0.099 g, 0.54 mmol) was placed in a previously dried PFA tube equipped
with a stainless steel valve. An excess of WF (12.119 g, 40.69 mmol) was
C
6
F
5
ꢀOꢀSi(CH
3 3 6 5
) (3.610 g, 14.09 mmol) and C F OH
2
C
6
F
5
ꢀOꢀWF
5
: Sample concentration: 1.035m (in C
2
D
2
Cl
4
);
J
Fax,Feq
=
1
1
66.00 Hz,
B
J
W,Fa = 61.20 Hz,
J
W,Feq = 35.90 Hz; line width (Hz; A part,
part):
6
condensed into the tube. The reaction mixture was stirred at ꢀ58Cfor
seven days. The reaction vessel was evacuated at ꢀ458Cfor 4 h. Two
more hours of evacuation at ꢀ308Cwere needed to pump off all unreact-
4
part): 15, 12; temperature (K)/chemical shift (ppm; A part, B
4
303/143.948, 147.229; 324/144.925, 147.588; 344/145.755, 147.926; 363/
146.380, 148.222; 383/147.135, 148.535; 403/147.939, 148.794.
ed WF
ꢀ
6
. A red-orange solid (6.44 g) remained inside the tube. CCl
3
F at
ꢀ ꢀ
2
(
CF
3
)
3
C
O WF
5
: Sample concentration: 0.526m (in C
2
D
2
Cl
4
); JFax,Feq
=
308Cwas added to the reaction vessel with a Teflon tube; most of the
1
1
6
B
2
1
1
5.30 Hz,
J
W,Fa = 65.18 Hz,
J
W,Feq = 34.90 Hz; line width (Hz; A part,
material was insoluble at this temperature, but at ꢀ158Calmost every-
part): 3.6, 6.2; temperature (K)/chemical shift (ppm; A part, B part):
4 4
93/158.073, 150.332; 303/158.327, 150.441; 313/158.576, 150.552; 333/
59.059, 150.778; 353/159.528, 151.014; 363/159.750, 151.130; 373/159.946,
thing dissolved. By means of a Teflon tube, the solution was transferred
1
9
13
at ꢀ158Cto a new PFA tube; F and CNMR spectra of the sample
were obtained at the same temperature, and revealed signals for only
51.252.
one kind of C
6
F
5
ꢀOꢀ compound. The PFA tube was evacuated at ꢀ158C
2
CF
=
3
ꢀCH
89.68 Hz; line width (Hz; A part, B
part): 303/215.947, 233.646; 313/217.053,
33.934; 323/218.110, 234.200; 333/219.200, 234.472; 343/220.150, 234.750;
53/221.100, 235.030; 363/222.800, 235.280.
2
ꢀOꢀMoF
5
: Sample concentration 1.249m (in C
2
D
2
Cl
4
); JFax,Feq
for 6 h. A red solid material (6.081 g; 89.9% yield), extremely reactive
4
part): 38, 30. Temperature (K)/
1
3
19
towards moisture, remained in the tube. M.p. ꢀ1.58C; C{ F} NMR
CDCl
chemical shift (ppm; A part, B
2
3
4
(
ꢀ
3
ext.): d = 143.2 (s, 1C; ꢀC
4
), 142.4 (s, 2C; ꢀC2,6), 137.0 (s, 2C;
1
9
C3,5), 134.2 ppm (s, 1C; ꢀC ); F NMR (376 MHz, 208C, CDCl ext.):
1
3
2
2
1
d = 144.3 (d,
J
F,F = 64.3,
5.6 Hz, 1F; Fax.), ꢀ150.6 (t,
J
W,F = 40 Hz, 4F; Feq.), 136.6 (q,
J
F,F
=
=
2
ꢀ
OꢀMoF : Sample concentration 0.259m (in C D Cl ); JFax,Feq
=
3
3
C
6
F
5
5
2
2
4
6
1
(
4
1
1
4
2
J
F,F = 18.5 Hz, 1F; ꢀp), ꢀ151.7 (d, JF,F
3
1
9
91.50 Hz; line width (Hz; A part, B
ical shift (ppm; A part, B part): 273/243.251, 249.189; 278/243.774,
49.295; 283/244.290, 249.405; 288/244.802, 249.518; 293/245.305, 249.629;
4
part): 25, 29; temperature (K)/chem-
2 Hz, 2F; ꢀo), ꢀ160.7 ppm (t,
J
=
17.0 Hz, 2F; ꢀm); F NMR
F,F
1
4
84.25 MHz, 1848C, 1.04m, C C
2
DlCCl
2
D): d = 145.7 ppm (s,
J
W,F
=
2
2
2
0 Hz, 5F); Raman spectroscopy: n˜
= 1641(15), 1535(3), 1517(3),
98/245.804, 249.741; 303/246.290, 249.858; 313/247.232, 250.090; 323/
48.328, 250.328; 333/249.187, 250.558.
466(100), 1325(33), 1263(3), 118(31), 1160(4), 1051(18), 1041(22),
018(5), 787(6), 765(33), 720(18), 714(27), 653(4), 641(6), 583(5), 501(15),
52(7), 423(13), 406(6), 377(9), 336(10), 307(9), 297(8), 280(20), 262(12),
ꢀ1
24(6), 201(6), 185(6), 155(11), 120(8) cm ; elemental analysis calcd
%): C15.60; found: C16.46.
Molybdenum pentafluoride pentafluorophenoxide (C
MoF (1.830 g, 8.72 mmol) and CH Cl (1.160 g, 13.82 mmol) were con-
densed into a previously dried PFA tube equipped with a magnetic stir-
rer. A solution of C (1.311 g, 5.12 mmol) and C OH
ꢀOꢀSi(CH
0.069 g, 0.37 mmol) was added dropwise with a syringe, while the reac-
tion mixture was stirred and kept at ꢀ208C. Additional CH Cl (1.32 g,
5.73 mmol) was added to wash down the inner walls of the tube. After
(
6
F
5
ꢀOꢀMoF
5
):
Acknowledgement
6
2
2
The authors are indebted to the Deutsche Forschungsgemeinschaft and
the Fonds der Chemischen Industrie for financial support. Thanks are
also due to Dr. P. Budzelaar for some introduction into gNMR.
6
F
5
3
)
3
6 5
F
(
2
2
1
the dark purple solution was stirred for 2 weeks at ꢀ208C, a black precip-
itate was observed. The PFA tube was evacuated first at ꢀ508Cfor 1 h
and then at ꢀ208Cfor 5 h. A black solid crystalline material 1.69 g,
[1] For reviews on this subject see: K. Seppelt, Acc. Chem. Res. 2003,
36, 147–153; M. Kaupp, Angew. Chem. 2001, 113, 3642–3677;
Angew. Chem. Int. Ed. 2001, 40, 3534–3565.
[2] G. A. Seisenbaeva, L. Kloo, P. Werndrup, V. G. Kessler, Inorg.
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8
2.5% yield), extremely reactive to moisture, remained in the tube. Crys-
tals suitable for X-ray diffraction were taken from this sample (Table 6).
1
3
19
M.p. 57.3–588C; C{ F} NMR (ꢀ208C, 0.35m, C
2
lCDCDCl
2
): d = 147.2
1
9
(
(
s, 1C; ꢀC ), 145.2 (s, 2C; ꢀC2,6), 136.8 ppm (s, 2C; ꢀC3,5); F NMR
4
2
ꢀ208C, 0.35m, C
2
lCDCDCl
2
): d = 254.5 (d,
J
J
F,F = 82.0 Hz, 4F; Feq.),
2
3
2
50.2 (q,
J
F,F = 88.5 Hz, 1F; Fax.), ꢀ134.9 (t,
F,F = 20.0 Hz, 1F; ꢀp),
3
3
ꢀ
140.8 (d,
J
F,F = 15 Hz, 2F; ꢀo), ꢀ154.9 (t,
J
F,F = 18.5 Hz, 2F; ꢀm);
Raman spectroscopy: n˜
= 1636(25), 1507(6), 1424(45), 1397(49),
1
6
4
380(15), 1320(77), 1183(57), 1039(75), 1017(21), 789(9), 732(100),
97(45), 669(60), 640(12), 622(10), 604(23), 580(40), 496(84), 447(12),
05(11), 384(23), 366(25), 353(20), 306(53), 290(48), 252(13), 226(14),
Chem. Eur. J. 2004, 10, 4755 – 4762
www.chemeurj.org
ꢀ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
4761

K. Seppelt et al.
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Received: January 30, 2004
Published online: August 13, 2004
4762
ꢀ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
Chem. Eur. J. 2004, 10, 4755 – 4762