Pentafluoropyridine as a fluorinating reagent for preparing a hydrocarbon soluble β-diketiminatolead(ii) monofluoride

Article abstract of DOI:10.1039/c1cc11310k

A well-designed method for the preparation of a β-diketiminatolead(ii) monofluoride has been developed using LPbNMe₂ (L = [CH{C(Me)(2,6-iPr₂C₆H₃N)}₂]) and pentafluoropyridine (C₅F₅

Full text of DOI:10.1039/c1cc11310k

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Pentafluoropyridine as a fluorinating reagent for preparing a
hydrocarbon soluble b-diketiminatolead(II) monofluoridewz
Anukul Jana, Sankaranarayana Pillai Sarish, Herbert W. Roesky,* Dirk Leusser,
Ina Objartel and Dietmar Stalke*
Received 6th March 2011, Accepted 21st March 2011
DOI: 10.1039/c1cc11310k
A well-designed method for the preparation of a b-diketiminato
lead(II) monofluoride has been developed using LPbNMe2
(L = [CH{C(Me)(2,6-iPr2C6H3N)}2]) and pentafluoropyridine
(C5F5N). The resulting LPbF was used for the synthesis of
amidinatosilicon(II) monofluoride. Moreover the activation of a
ketone was observed when the LPbF was treated with
PhCOCF3.
compared with other silicon halides, probably due to the lack
of convenient synthetic routes to the fluoro compounds.8
This encouraged us to synthesize lead (II) and silicon (II)
monofluoride. Herein we report on the synthesis of hydro-
carbon soluble b-diketiminatolead(II) and amidinatosilicon(II)
monofluorides and the reactivity of the former with 2,2,2-
trifluoro acetophenone.
For the preparation of silicon(II) and lead(II) monofluorides
initially we followed the routes which are already applied for
the synthesis of germanium(II) and tin(II) monofluorides.3b,4b
However we were not able to obtain the expected product
following this protocol. Recently, we reported on the synthesis
of lead(II) amide,7c e.g. LPbNMe2 (1) and its reaction with
ketones, where the dimethylamino group acts as a nucleophile.7c
Moreover, we demonstrated that the para fluorine atom of the
pentafluoropyridine is easily activated by silylenes.9
Organometallic fluorides of group 14 elements are important
due to their application in synthetic methodology as well in the
laboratory as in industry.1 In the literature, the known group
14 fluoro compounds are preferentially in the +4 oxidation
state.2 Only few examples of organogermanium(II) and tin(II)
monofluorides are known.3,4 In contrast, the chemistry of
Pb(II) tends to be dominated by compounds with inorganic
ligands. Organometallic compounds with two valent lead are
relatively rare and their chemistry is poorly explored.5,6
Recently, we reported on a variety of lead complexes which
can be used as precursors for new lead derivatives.7 However a
fluoride derivate of lead like its lighter congener is still elusive.
The difficulties with lead-based chemistry are its tendency to
form insoluble precipitates besides its susceptibility to undergo
redox chemistry to form metallic lead. We anticipated that the
introduction of sufficiently large substituents is necessary for
kinetic stabilization of such reactive species. Such a complex
even as a monomer can be obtained by exploiting the unique
property of the b-diketiminate ligand L (L = [CH{C(Me)
(2,6-iPr2C6H3N)}2] that coordinates tightly to the lead atom,
and is also capable of providing enough steric bulk to prevent
the formation of oligomers. Moreover, the Pb–F bond
strength is the weakest within the element(II) fluorides of group
14, due to the large Pb2+ radius. However at the same
time relatively little is known about silicon(II) monofluorides
Consequently, we treated LPbNMe2 (1) in a 1 : 1 ratio with
pentafluoropyridine (C5F5N) in diethyl ether or THF at room
temperature (Scheme 1). After 12 hours it resulted in the
formation of the b-diketiminatolead(II) monofluoride,
LPbF (2) together with 4-dimethylaminotetrafluoropyridine
(4-NMe2C5F4N) (3). The 1H NMR spectrum of the crude
reaction mixture indicates the complete disappearance of the
resonances for NMe2 (d 3.80 ppm) of 1, and the formation of a
new signal at d 2.60 ppm for 3. This reaction is comparable
with the synthesis of 4-dimethylaminotetrafluoro-pyridine (3)
from dimethyl amine or trimethylsilyl-dimethylamine
(Me3SiNMe2) and C5F5N.10 The energy required to cleave the
C–F bond is compensated by the formation of a C–N bond.
Compound 2 is a yellow solid soluble in benzene, THF, and
toluene. It shows no decomposition on exposure to dry air. 2
1
was characterized by H, 13C, 19F, and 207Pb NMR spectro-
scopy, EI mass spectrometry, elemental analysis, and X-ray
structural analysis. We recorded the low temperature (ꢀ80 1C)
19F and 207Pb NMR sprectra. The 19F NMR spectrum of 2
exhibits a resonance at d ꢀ102.7 ppm, which is accompanied
Institut fur Anorganische Chemie, Universitat Gottingen,
¨
¨
¨
¨
Tammannstrasse 4, 37077 Gottingen, Germany.
E-mail: hroesky@gwdg.de, dstalke@chemie.uni-goettingen.de;
Fax: +49 551-39-3373
w Electronic supplementary information (ESI) available: Synthetic
and spectral details. CCDC 808034 (2) and 808035 (6). For ESI and
crystallographic data in CIF or other electronic format see DOI:
10.1039/c1cc11310k
z Dedicated to Professor Reinhart Ahlrichs on the occasion of his 70th
birthday.
Scheme 1 Synthesis of b-diketiminatolead (II) monofluoride 2.
c
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Scheme 2 Synthesis of a organosilicon(II) monofluoride 5.
protons appears as a singlet (d 1.0 ppm) in the 1H NMR
spectrum. The 19F NMR spectrum of the reaction mixture
exhibits the consumption of lead(II) monofluoride and indicates
the formation of a new 19F resonance at d ꢀ121.59 ppm, which
is accompanied by 29Si satellite signals (J = 438.17 Hz). The
29Si NMR spectrum shows a doublet of quartets (d 23.63 ppm
and J(29Si–11B) = 66.78 Hz) indicative for one silicon–boron
and silicon–fluorine bond. The 11B NMR spectrum is also
consistent with the presence of one BH3 group. No molecular
ion peak was found in the EI mass spectrum of 5, but the most
intense peak corresponds to [M+–BH3]. Therefore we conclude
the preparation of silicon(II) monofluoride, L1SiF(BH3) (5), was
successful.
Fig. 1 Solid state structure of 2. The anisotropic displacement
parameters are depicted at the 50% probability level. All hydrogen
atoms and the second disordered part of the molecule are omitted for
clarity. The whole molecule is disordered (ratio 0.56 : 0.44). Selected
averaged bond lengths (A) and angles (1): Pb1–N1 2.317(36), Pb1–N2
2.296(34), Pb1–F1 2.088(17); N1–Pb1–N2 82(3), N1–Pb1–F1 90(4),
N2–Pb1–F1 91(3).
by two 207Pb satellites (d ꢀ106.4 and ꢀ99.0 ppm). The 207Pb
NMR spectrum shows a doublet at d 787.4 ppm, with a
coupling constant of J(19F–207Pb) = 2792 Hz, which is upfield
shifted when compared with that of 1 (d 1674 ppm).7c The
satellite resonances and coupling constants of the 19F and
207Pb NMR spectra are not observed, when the measurements
are carried out at room temperature. This suggests that the
Pb–F bond is kinetically labile on the NMR time scale at room
temperature. Dissolving 2 in hot n-hexane and keeping it for
two days at ꢀ32 1C resulted in yellow single crystals suitable
for X-ray structural analysis.w 2 crystallizes in the monoclinic
space group P21/n, with one molecule in the asymmetric unit
(Fig. 1).y Compound 2 exists as a monomer in the solid
state with a terminal bound fluorine atom, which has the
potential to be used as a fluorinating agent. The coordination
polyhedron around the lead atom comprises two nitrogen
atoms from the supporting ligand, one fluorine atom, and
one lone pair featuring a distorted tetrahedral geometry. The
Pb–F bond length is 2.088(17) A, obviously longer when
compared with those of Ge–F (1.805(17) A) in LGeF3b and
Sn–F (1.988(2) A) in LSnF.4b The average Pb–N bond lengths
are 2.317(36) and 2.296(34) A, and slightly longer than the
Pb–N bond lengths in 1 (2.155(10) A).
Here it is worth mentioning that Jutzi et al. reported the
formation of unstable Cp*SiF (where Cp* indicates 1,2,3,4,5-
pentamethylcyclopentadienyl), which is highly reactive and
dimerizes to the unstable disilene Cp*(F)SiQSi(F)Cp*, which
further reacts to the isolable cyclotetrasilane by a [2 + 2]
cycloaddition.14
After the successful reaction of 2 with 4, we turned our
attention to the activated ketone, 2,2,2-trifluoro-acetophenone.
The reaction of 2 with PhCOCF3 leads to the formation of
homoleptic Pb(II) compound, L02Pb [L0 = CH(CPhCF3O)-
(C(Me)(Q2,6-iPr2C6H3N))2] (6) in good yield (Scheme 3).
This reaction is quite different when compared with those of
LGeH or LSnH and PhCOCF3.15 In the latter case the
nucleophilic addition reactions occurred under formation of
germanium(II) or tin(II) alkoxide, respectively.
Single crystals suitable for X-ray structural analysisw were
obtained when a concentrated solution of 6 in a mixture of
THF and n-pentane was stored at ꢀ5 1C. 6 crystallizes in the
monoclinic space group P21/c with one molecule in the asym-
metric unit.y The structure of 6 (Fig. 2) reveals the homoleptic
nature of the complex and contains two six-membered
OC3NPb rings, that are connected by the common lead atom.
Thus, the Pb atom is four-coordinate and adopts a distorted
trigonal bipyramidal geometry with two nitrogen atoms of the
b-diketiminate ligand occupying the axial positions, two
oxygen atoms, and the lone pair residing in the equatorial
positions. As expected, the average Pb–N (2.620av A) bond
length is longer than those of the corresponding bonds in 2
(2.307av A). The average Pb–O bond distance (2.169av A) is
longer than that in LPbOiPr (2.135(3) A) and LPbOtBu
(2.126(3) A).16
After the isolation of lead(II) monofluoride, we focused on
the synthesis of silicon(II) monofluoride. The stable LPbF
contains a terminal fluorine atom, which can serve as a
nucleophilic reagent. However, the reaction of silicon(II)
chloride L1SiCl [L1 = PhC(NtBu)2]11 with Me3SnF, LGeF,
LSnF, and LPbF, respectively, as a fluorinating reagent
12
mostly resulted in the formation of L1SiF3 and some
unidentified products. Finally we used L1SiCl(BH3) (4)13
instead of L1SiCl, and treated this compound with LPbF.
The 1 : 1 reaction of L1SiCl(BH3) with LPbF in toluene at
ꢀ30 1C leads to the formation of L1SiF(BH3) (5) and LPbCl
(Scheme 2). Compound 5 is a white solid soluble in benzene,
toluene, and THF and shows no decomposition on exposure
to dry air. It was characterized by 1H, 11B, 13C, 19F, and
29Si NMR spectroscopy, EI mass spectrometry, and elemental
analysis. The resonance corresponding to the tert-butyl
Scheme 3 Synthesis of a homoleptic lead(II) complex 6.
Chem. Commun., 2011, 47, 5434–5436 5435
c
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CCDC 808034, 808035 contain the supplementary crystallographic
data for 2 and 6.
1 E. F. Murphy, R. Murugavel and H. W. Roesky, Chem. Rev.,
1997, 97, 3425–3468.
2 See examples of fluorides in +4 oxidation state of group 14:
(a) G. V. Odabashyan, V. A. Ponomarenko and A. D. Petrov,
Russ. Chem. Rev., 1961, 30, 407–426; (b) A. P. Kostikov,
¨ ¨
L. Iovkova, J. Chin, E. Schirrmacher, B. Wangler, C. Wangler,
K. Jurkschat, G. Cosa and R. Schirrmacher, J. Fluorine Chem.,
2011, 132, 27–34; (c) K. Junold, C. Burschka, R. Bertermann and
R. Tacke, Dalton Trans., 2010, 39, 9401–9413; (d) M. Mehring,
I. Vrasidas, D. Horn, M. Schurmann and K. Jurkschat, Organo-
¨
metallics, 2001, 20, 4647–4653; (e) W.-P. Leung, W.-H. Kwok,
Z.-Y. Zhou and T. C. W. Mak, Organometallics, 2003, 22,
1751–1755; (f) R. A. Varga, K. Jurkschat and C. Silvestru, Eur.
Fig. 2 Solid state structure of 6. The anisotropic displacement
parameters are depicted at the 50% probability level. All hydrogen
atoms, the phenyl groups (Ph), and the 2,6-diisopropylphenyl moieties
(dipp) are omitted for clarity. Selected bond lengths (A) and angles (1):
Pb1–N1 2.6075(16), Pb1–N3 2.6319(16), Pb1–O1 2.1679(13), Pb1–O2
2.1707(14); N1–Pb1–O1 77.37(5), N3–Pb1–O1 93.24(5), N3–Pb1–N1
166.23(5), O1–Pb1–O2 85.09(5).
J. Inorg. Chem., 2008, 708–716; (g) D. J. Brauer, H. Burger and
¨
R. Eujen, Angew. Chem., 1980, 92, 859–860 (Angew. Chem., Int.
Ed. Engl., 1980, 19, 836–837); (h) E. Lukevics, S. Belyakov,
P. Arsenyan and J. Popelis, J. Organomet. Chem., 1997, 549,
163–165.
3 (a) P. Riviere, J. Satge, A. Castel and H. Normant, C. R. Acad.
´
Sci. Paris, 1976, 282, 971–974; (b) Y. Ding, H. Hao, H. W. Roesky,
M. Noltemeyer and H.-G. Schmidt, Organometallics, 2001, 20,
4806–4811.
4 (a) R. W. Chorley, D. Ellis, P. B. Hitchcock and M. F. Lappert,
Bull. Soc. Chim. Fr., 1992, 129, 599–604; (b) A. Jana,
H. W. Roesky, C. Schulzke, A. Doring, T. Beck, A. Pal and
¨
R. Herbst-Irmer, Inorg. Chem., 2009, 48, 193–197; (c) A. Jana,
H. W. Roesky, C. Schulzke and P. P. Samuel, Organometallics,
2010, 29, 4837–4841.
6 has been also characterized by spectroscopic and analytic
measurements in addition to the X-ray structural analysis. The
1H NMR spectrum of 6 agrees with the solid state structure.
Two singlet resonances were observed for the methyl (d 2.96
and d 1.86 ppm) and the CH protons also appear as another
singlet at d 5.19 ppm. In the 19F NMR spectrum of 6 the C–F
resonance appears as a sharp singlet at d ꢀ76.2 ppm. This
shows an upfield shift compared to that of the ketone,
PhCOCF3 (d ꢀ71.6). The 207Pb NMR spectrum of 6 exhibits
a singlet which is shifted downfield (d 853.9 ppm), when
compared with 2 (d 787.4 ppm). Compound 6 is found to be
sensitive towards moisture and air and it is soluble in benzene,
THF, toluene, and diethyl ether.
5 Review: (a) M. Driess and H. Grutzmacher, Angew. Chem., 1996,
¨
108, 900–929 (Angew. Chem., Int. Ed. Engl., 1996, 35, 828–856);
(b) P. J. Davidson, D. H. Harris and M. F. Lappert, J. Chem. Soc.,
Dalton Trans., 1976, 2268–2274; (c) S. Wingerter, H. Gornitzka,
R. Bertermann, S. K. Pandey, J. Rocha and D. Stalke, Organo-
metallics, 2000, 19, 3890–3894.
6 (a) M. Kaupp and P. v. R. Schleyer, J. Am. Chem. Soc., 1993, 115,
1061–1073; (b) K. Jurkschat, K. Peveling and M. Schurmann, Eur.
¨
J. Inorg. Chem., 2003, 3563–3571 and references therein.
7 (a) A. Murso, M. Straka, M. Kaupp, R. Bertermann and
D. Stalke, Organometallics, 2005, 24, 3576–3578; (b) A. Jana,
S. P. Sarish, H. W. Roesky, C. Schulzke, A. Doring and
¨
M. John, Organometallics, 2009, 28, 2563–2567; (c) A. Jana,
In conclusion, after the successful syntheses of amidinato-
silicon(II) and b-diketiminatolead(II) monofluorides, the series
of fluorides with the heavier low valent group 14 elements has
been completed, although the corresponding stable fluoride of
low valent carbon remains still elusive. The reaction of lead(II)
monofluoride with PhCOCF3 results in a homoleptic lead
compound in which the ketone is incorporated. Currently we
are investigating the reactivity of this lead(II) monofluoride as
fluorinating reagent.
H. W. Roesky, C. Schulzke, P. P. Samuel and A. Doring, Inorg.
Chem., 2010, 49, 5554–5559.
¨
8 (a) P. L. Timms, Inorg. Chem., 1968, 7, 387–389; (b) P. L. Timms,
R. A. Kent, T. C. Ehlert and J. L. Margrave, J. Am. Chem. Soc.,
1965, 87, 2824–2828.
9 A. Jana, P. P. Samuel, G. Tavcar, H. W. Roesky and C. Schulzke,
J. Am. Chem. Soc., 2010, 132, 10164–10170.
10 (a) R. E. Banks, J. E. Burgessw, M. Cheng and R. N. Haszeldine,
J. Chem. Soc., 1965, 575–581; (b) L. I. Goryunov,
V. D. Shteingarts, J. Grobe, B. Krebs and M. U. Triller, Z. Anorg.
Allg. Chem., 2002, 628, 1770–1779.
11 (a) C.-W. So, H. W. Roesky, J. Magull and R. B. Oswald, Angew.
Chem., 2006, 118, 4052–4054 (Angew. Chem., Int. Ed., 2006, 45,
3948–3950); (b) S. S. Sen, H. W Roesky, D. Stern, J. Henn and
D. Stalke, J. Am. Chem. Soc., 2010, 132, 1123–1126.
Support of the Deutsche Forschungsgemeinschaft and the
DNRF funded Center of Materials Crystallography is highly
acknowledged.
Notes and references
y Crystal data for 2: C29H41FN2Pb, Mr = 643.84, 0.05 ꢁ 0.1 ꢁ 0.1 mm,
a = 11.7697(16), b = 20.465(3), c = 11.7727(16) A, b = 95.906(2),
V = 2820.6(7) A3, Z = 4, rcalcd = 1.516 Mg mꢀ3, m(Mo Ka) =
6.066 mmꢀ1, 2ymax = 611, 90 262 reflections measured, 8667 inde-
pendent (Rint = 0.039), R1 = 0.021 (I 4 2s(I)), wR2 = 0.0503
(all data), res. density peaks: 3.12 to ꢀ1.41 e Aꢀ3; crystal data for 6:
C74H92F6N4O2Pb, Mr = 1390.71, 0.15 ꢁ 0.15 ꢁ 0.1 mm, a =
15.7060(15), b = 18.9000(18), c = 26.336(3) A, b = 107.0930(10),
V = 7472.3(12) A3, Z = 4, rcalcd = 1.236 Mg mꢀ3, m (Mo Ka) =
2.316 mmꢀ1, 2ymax = 521, 1 666 483 reflections measured, 14 728
12 R. S. Ghadwal, K. Propper, B. Dittrich, P. G. Jones and
¨
H. W. Roesky, Inorg. Chem., 2011, 50, 358–364.
13 A. Jana, D. Leusser, I. Objartel, H. W. Roesky and D. Stalke,
Dalton Trans., 2011, DOI: 10.1039/c0dt01675f.
14 P. Jutzi, U. Holtmann, H. Bogge and A. Muller, J. Chem. Soc.,
¨
Chem. Commun., 1988, 305–306.
¨
15 (a) A. Jana, H. W. Roesky and C. Schulzke, Dalton Trans., 2010,
39, 132–138; (b) A. Jana, H. W. Roesky, C. Schulzke and
A. Doring, Angew. Chem., 2009, 121, 1126–1129 (Angew. Chem.,
¨
Int. Ed., 2009, 48, 1106–1109).
independent (Rint = 0.0387), R1 = 0.0208 (I 4 2s(I)), wR2
=
16 E. C. Y. Tam, N. C. Johnstone, L. Ferro, P. B. Hitchcock and
J. R. Fulton, Inorg. Chem., 2010, 49, 5554–5559.
0.0543 (all data), res. density peaks: 0.717 to –1.197
e .
Aꢀ3
c
5436 Chem. Commun., 2011, 47, 5434–5436
This journal is The Royal Society of Chemistry 2011