Synthesis and characterization of tin tetrafluoride adducts with fluoroalkyl phosphoryl ligands

Article abstract of DOI:10.1016/j.jfluchem.2012.12.012

The reaction of SnF₄ with (R₂N)_nP(O) (OCH₂CF₃)_3-n (n = 0-2) produces a series of new octahedral complexes of SnF₄L₂ type (L = (R ₂N)₂P(O)OCH₂CF₃; R = Me (1); Et (2), L = R₂NP(O)(OCH₂CF₃)₂; R = Me (3); Et (4) or L = P(O)(OCH₂CF₃)₃ (5)). The adducts have been characterized by multinuclear (¹⁹F, ³¹P and ¹¹⁹Sn) NMR, IR spectroscopy and elemental analyses. The NMR data particularly the ¹⁹F NMR spectra show the existence of complexes as mixtures of cis and trans isomers. The variable temperature NMR study in CH ₂Cl₂ solutions in the presence of excess ligand indicated that the ligand exchange at room temperature is slow for 1-4 and fast only for 5. The results were compared with those of SnCl₄ analogues and show the formation of higher trans ratios for the studied complexes.

Full text of DOI:10.1016/j.jfluchem.2012.12.012

Journal of Fluorine Chemistry 146 (2013) 15–18
Contents lists available at SciVerse ScienceDirect
Journal of Fluorine Chemistry
journal homepage: www.elsevier.com/locate/fluor
Synthesis and characterization of tin tetrafluoride adducts with fluoroalkyl
phosphoryl ligands
*
Med Abderrahmane Sanhoury , Med Taieb Ben Dhia, Med Rachid Khaddar
Laboratory of Coordination Chemistry, Department of Chemistry, Faculty of Sciences of Tunis, University of Tunis El Manar, 2092 Tunis, Tunisia
A R T I C L E I N F O
A B S T R A C T
Article history:
The reaction of SnF4 with (R2N)nP(O)(OCH2CF3)3Àn (n = 0–2) produces a series of new octahedral
complexes of SnF4L2 type (L = (R2N)2P(O)OCH2CF3; R = Me (1); Et (2), L = R2NP(O)(OCH2CF3)2; R = Me (3);
Et (4) or L = P(O)(OCH2CF3)3 (5)). The adducts have been characterized by multinuclear (19F, 31P and
119Sn) NMR, IR spectroscopy and elemental analyses. The NMR data particularly the 19F NMR spectra
show the existence of complexes as mixtures of cis and trans isomers. The variable temperature NMR
study in CH2Cl2 solutions in the presence of excess ligand indicated that the ligand exchange at room
temperature is slow for 1–4 and fast only for 5. The results were compared with those of SnCl4 analogues
and show the formation of higher trans ratios for the studied complexes.
Received 17 November 2012
Received in revised form 23 December 2012
Accepted 28 December 2012
Available online 7 January 2013
Keywords:
Fluoroalkyl phosphoryl ligands
Tin tetrafluoride
ß 2013 Elsevier B.V. All rights reserved.
NMR spectroscopy
cis/trans isomers
1. Introduction
2. Results and discussion
Octahedral tin(IV) complexes of the general formula SnX4L2
(X = halide and L is the phosphoryl ligand), readily accessible via
reaction between SnX4 and various neutral donor ligands, have
attracted much interest [1–4]. For instance, an extensive coordi-
nation chemistry has been devoted to tin(IV) chloride and bromide
[5–11]. Although it was reported that the Lewis acidity of the four
SnX4 is greatest for SnF4 [12], and despite the very different
electronic properties conferred on the metal by the hard, small
electronegative fluoride, the coordination chemistry of SnF4 is still
much less studied compared to the other tin halides (X = Cl, Br or I)
[12–15].
In a previous work, we reported a systematic study of the
complexes of SnCl4 with the ligands (R2N)nP(O)(OCH2CF3)3Àn and
found that the trans isomer dominates the chemistry [16–18].
More recently, we have shown that the use of complexes of the
harder SnF4 Lewis acid with (R2N)nP(O)F3Àn led to higher formation
rates of the trans complex even with the weaker Lewis bases
R2NP(O)F2 [19] compared to corresponding SnCl4 analogues
[16,17]. Herein, we report the synthesis and spectroscopic
2.1. Synthesis
Anhydrous SnF4 has a polymeric sheet structure [20] and is
therefore unreactive towards neutral ligands.
A convenient
method for the synthesis of its complexes is provided by
SnF4(MeCN)2 made from SnF2, I2 and MeCN as described by
Tudela and co-workers [21,22]. Treatment of SnF4(MeCN)2 in
anhydrous dichloromethane solution with (R2N)2P(O)OCH2CF3,
R2NP(O)(OCH2CF3)2 (R = Me or Et), or (CF3CH2O)3PO gives white
solids with the composition SnF4L2 (L = phosphoryl ligand) in
moderate to good yields. The solids are moderately soluble in
dichloromethane and chloroform with (CF3CH2O)3P(O) adduct
being poorly soluble. They are, in general, much less soluble in
these solvents than their SnCl4 analogues.
2.2. Spectroscopic studies
The strong bands observed in the infrared spectra within the
range 1200–1210 cmÀ1 for 1 and 2 and 1240–1260 cmÀ1 for 3–5
characterization of
a
new series of SnF4 complexes with
are assigned to n(P55O) stretching vibrations. These are shifted
(R2N)2P(O)OCH2CF3, R2NP(O)(OCH2CF3)2, and (CF3CH2O)3PO and
show again the importance of using 19F NMR spectroscopy to easily
assign the trans and cis isomers of such complexes even at room
temperature.
towards lower wave numbers compared to those of the free
ligands. The coordination shift is consistent with phosphoryl
coordination to the tin atom. This shift is 32, 78 and 85 cmÀ1 for 5, 1
and SnF4[(Me2N)3PO]2 [19], respectively, reflecting a difference in
the basicity strength between the ligands in these complexes. This
is most probably due to the nature of the substituents on the
phosphorus atom in these ligands (i.e. due to difference in the
electronegativities of nitrogen and oxygen atoms linked directly to
* Corresponding author. Tel.: +216 98269495; fax: +216 71885008.
E-mail address: senhourry@yahoo.com (M.A. Sanhoury).
0022-1139/$ – see front matter ß 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jfluchem.2012.12.012

16
M.A. Sanhoury et al. / Journal of Fluorine Chemistry 146 (2013) 15–18
Table 1
NMR data (
d
/ppm and J/Hz) for the complexes [SnF4L2] in CD2Cl2.
31P
20.39
Ligand (L)
19F
119Sn
1JSn–F
2JSn–P
2JF–F
(Me2N)2P(O)OCH2CF3
(Et2N)2P(O)OCH2CF3
Me2NP(O)(OCH2CF3)2
Et2NP(O)(OCH2CF3)2
cis
À75.6(t), À151(t), À162(t)
À75.7(t), À154(t)
À648
À652
–
16.8
36.3
53.6
–
trans
19.18
1711
cis
16.70
15.84
À76.2(t), À150(t),À159(t)
À76.3(t), À153(t)
À652
À659
–
26.8
50.3
53.6
–
trans
1700
cis
5.95
6.40
À76.07(t), À151(t),À163(t)
À76.04(t), À153(s)
À647
À650
1965
1754
–
–
56.5
–
trans
cis
5.06
4.68
À76.4(t), À151(t), À163(t)
À76.5(t), À153(s)
À648
À651
1965
1754
–
55.0
–
trans
43.1
a
P(O)(OCH2CF3)3
cis
À5.27
À4.98
À76.2(t),À149(t), À164(t)
À77.8(d), À151(s)
À649
À652
2016
1790
–
–
57.9
–
trans
a
At 218 K.
the phosphorus atom of the ligand). A strong absorption band at
570–590 cmÀ1 with two to three much weaker bands in the region
575–615 cmÀ1 are also observed in the IR spectra of these
complexes in the solid state and correspond to the stretching
vibration of the Sn–F bond. In chloroform solution, the intensity of
the bands at 575–615 cmÀ1 is relatively raised but remains weak
when compared to that at 570–590 cmÀ1. In addition, the latter
band becomes broad and two bands may coalesce within a wider
envelope especially for complex 5. Such a behaviour could be
attributable to a mixture of the cis isomer, which would be
expected to show two to four bands in the tin–halogen stretching
region, and the trans isomer, which should show only one [23] with
the latter form predominating. This is in good agreement with our
solution NMR data shown below.
spectra also show, in the region of the ligand fluorine atoms, two
triplets for the cis and trans isomers due to 3J(H–F) couplings.
Interestingly, the corresponding 119Sn NMR spectra show also
the presence of both cis and trans isomers. This was observed at
ambient temperatures for 1–4 as a symmetrical quintet of triplets
for the trans isomer and a multiplet (t,t,t) for the cis isomer (Fig. 2)
with coupling constants consistent with those deduced from the
19F{1H} and 31P{1H} spectra. These data are in good agreement with
those obtained for related complexes [12]. For complex 5, the 119Sn
resonances are broad and ill-defined at ambient temperatures but
on cooling the samples at 218 K, the resonances sharpen and split
giving defined features with predominance of the multiplet related
to the cis isomer. However, the quality of the 119Sn NMR spectrum
of 5 was lower than those of 1–4 due to poor solubility of this
complex. The above results are in good agreement with our
previously reported data on corresponding (R2N)nP(O)F3Àn com-
plexes [19].
We have previously shown that SnCl4 complexes with
(R2N)nP(O)(OCH2CF3)3Àn are labile in solution with a fast ligand
exchange at room temperature; cooling the samples was necessary
to observe sharp resonances and resolved couplings [18]. This was
compared with the solution behaviour of the corresponding SnF4
analogues, 1–5, in the presence of an excess of ligand. The 31P and
19F NMR spectra of these solutions display for complexes 1–4
separate signals for free, cis and trans ligands, showing that no
ligand exchange is occurring at room temperature in these
complexes (Fig. 3). However, the solution spectra of 5 show at
room temperature average signals which broaden and split on
cooling and give at 218 K separate signals for free, cis and trans
The NMR spectra of the complexes were recorded in
dichloromethane solutions and the data show the presence of
both cis and trans isomers (Table 1). The approximate isomer ratio
was determined from the 19F{1H} NMR spectra. Whilst the trans
isomer predominates in complexes 1–4, the cis form is the major
isomer in complex 5. Despite the fact that resonances were
observed at ambient temperatures in the 31P, 19F and 119Sn NMR
spectra of complexes 1–4, the corresponding spectra of complex 5
showed broad and poorly resolved features and the solutions were
cooled to 218 K to improve resolution.
The 31P NMR spectra display a singlet resonance for each isomer
with similar chemical shifts and weak 117/119Sn satellites. The 19
F
NMR spectra are more useful and show, in the SnF4 region, singlet
resonances for the trans isomers and two triplets for the cis with
clearly resolved 1J(119Sn–19F) and 1J(117Sn–19F) (Fig. 1). The 19F
Fig. 1. SnF4 region of the 19F-{1H} NMR spectrum of 1 in CD2Cl2 at 298 K (*: 119/117Sn satellites in the trans isomer).

M.A. Sanhoury et al. / Journal of Fluorine Chemistry 146 (2013) 15–18
17
Fig. 2. 119Sn NMR spectrum of 2 in CD2Cl2 at 298 K (8: cis and +: trans multiplets).
Fig. 3. 31P-{1H} NMR spectrum of 2 in the presence of excess ligand in CD2Cl2 at 298 K (LF, Lcis and Ltrans indicate the ligand in the free, cis and trans positions, respectively; *: 119/
117Sn satellites).
ligands. This indicates that ligand exchange at room temperature is
slow on the NMR time scale for 1–4 and only fast for complex 5, in
contrast to SnF4 complexes with (R2N)2P(O)F and R2NP(O)F2 which
all show fast ligand exchange at room temperature [19].
Comparison of cis and trans ratios with those obtained for
SnF4[(Me2N)3PO]2 [19], SnF4(Me3PO)2 and SnF4(Ph3PO)2 [12]
suggests that the donor power of the ligands Me3PO and
(Me2N)3PO are similar to that of (Me2N)2P(O)OCH2CF3, while
the ligands Ph3PO and Me2NP(O)(OCH2CF3)2 form similar cis:trans
ratios showing nearly identical donor power (Table 2).
SnCl4, bothcis and transadductsareobtained withSnF4 (seeTable 2).
Our solution NMR data suggest therefore that the weaker the Lewis
basicityoftheligandand/ortheacidityofthemetalthemoreitforms
higher cis ratios and the more the complex is labile, indicating a
decrease in (the Lewis basicity of the ligand) complex stability in the
Table 2
Comparison of the approximate cis isomer ratios in the complexes [SnX4L2] in
dichloromethane.
Ligand (L)
% cisa
Inaddition,examinationofTable2shows, foreachtinhalide, that
higher cis ratios are obtained as the substituents on the phosphorus
atom become more electronegative, consistent with reduced Lewis
basicity of the ligand. The same trend is observed, for each ligand,
when going from SnF4 to SnCl4 complexes, in agreement with the
stronger Lewis acidity of SnF4 which gives more stable complexes
and higher trans ratios when compared to corresponding SnCl4
complexes. This could also explain the fact that while the weakest
ligands R2NP(O)F2 and (CF3CH2)3PO only form a cis isomer with
SnCl4
SnF4
(Me2N)3P(O)
50b
80c
25b
45b
85c
32b
42b
55e
(Me2N)2P(O)F
Me2NP(O)F2
100d
40b
(Me2N)2P(O)OCH2CF3
Me2NP(O)(OCH2CF3)2
P(O)(OCH2CF3)3
65b
100e
a
Measured at slow exchange (b: at 298 K; c: 258 K; d: 198 K; e: 218 K) from 119Sn
(for SnCl4) and 19F (for SnF4) NMR signals.

18
M.A. Sanhoury et al. / Journal of Fluorine Chemistry 146 (2013) 15–18
order:
(Me2N)3P(O) > (Me2N)2P(O)OCH2CF3 > Me2NP(O)(OCH2
22.85; H, 3.29; N, 3.22. IR (KBr): IR (KBr): nP5O (3: 1245 cmÀ1, 4:
1242 cmÀ1); nSn–F (570–585 cmÀ1).
CF3)2 > (Me2N)2P(O)F > P(O)(OCH2CF3)3 > Me2NP(O)F2.
3. Conclusions
4.3. SnF4[P(O)(OCH2CF3)3]2
New fluoroalkyl phosphoryl complexes with SnF4 have been
described and studied in solution by NMR spectroscopy. Our
results show higher formation rates of the trans isomers in these
complexes when compared to their corresponding SnCl4 analo-
gues. The latter were found to be more labile in solution than the
former complexes. It has also been shown that while the weakest
ligand, (CF3CH2O)3PO, forms only a cis adduct with SnCl4 both
isomers are formed between this ligand and SnF4, presumably due
to the greater Lewis acidity of the SnF4 compared to SnCl4. The
lability of complex 5 compared to 1–4 is likely due to the lack of
electron donating ability of dialkylamino groups and the presence
of more electron withdrawing character of fluoroalkoxy groups in
the ligand (CF3CH2O)3PO.
This compound has been prepared similarly from SnF4(MeCN)2
(0.28 g, 1.0 mmol) and P(O)(OCH2CF3)3 (2.1 mmol) and stirred for
24 h. Yield 0.47 g, 54%. Anal. Calcd. for C14H18F22O8P2Sn (5): C,
16.33; H, 1.37. Found: C, 15.81; H, 1.15. IR (KBr): n
P5O (1256 cmÀ1);
nSn–F (586 cmÀ1).
Acknowledgements
We are grateful to the Tunisian Ministry of High Education and
Scientific Research for financial support (LR99ES14) of this
research and to Emeritus Professor A. Baklouti for his valuable
help and continuous support.
References
4. Experimental
[1] D. Fa`rsaiu, R. Leu, P.J. Ream, J. Chem. Soc. Perkin Trans. 2 (2001) 427–431.
[2] S.E. Dann, A.R.J. Genge, W. Levason, G. Reid, J. Chem. Soc., Dalton Trans. (1997)
2207–2213.
[3] C.H. Yoder, L.A. Margolis, J.M. Horne, J. Organomet. Chem. 633 (2001) 33–38, and
refs. therein.
[4] H.R. Hays, D.J. Peterson, in: G.M. Kosolopoff, L. Mair (Eds.), Organic Phosphorus
Compounds, vol. 3, Wiley, New York, 1972.
[5] E. Le Coz, J.E. Guerchais, Bull. Soc. Chim. Fr. (1971) 80–87.
[6] S.J. Ruzicka, A.E. Merbach, Inorg. Chim. Acta 20 (1976) 221–229.
[7] L.A. Aslanov, V.M. Ionov, V.M. Attiya, A.B. Permin, V.S. Petrosyan, Zhur. Strukt.
Khim. 18 (1977) 1103–1112.
All preparations were carried out under a nitrogen atmosphere
in solvents dried by standard techniques [24] and stored over
molecular sieves. SnF2 was obtained from Aldrich and used as
received. The ligands (R2N)2P(O)OCH2CF3 [25], R2NP(O)(OCH2CF3)2
[25] and P(O)(OCH2CF3)3 [26] were prepared as described in the
literature. NMR spectra were recorded on a Bruker AV-300
instrument in CD2Cl2 as solvent; 31P at 121 MHz (85% H3PO4),
19F at 282 MHz (CFCl3) and 119Sn at 111.8 MHz (SnCl4). IR spectra
were recorded on a Perkin Elmer Paragon 1000 PC spectrometer.
[8] S.J. Ruzicka, A.E. Merbach, Inorg. Chim. Acta 22 (1977) 191–200.
[9] S.E. Denmark, X. Su, Tetrahedron 55 (1999) 8727–8738.
`
[10] D. Tudela, V. Fernandez, J.D. Tornero, J. Chem. Soc., Dalton Trans. (1985)
4.1. SnF4[(R2N)2P(O)OCH2CF3]2
91281–1284.
[11] J. Rupp-Bensadon, E.A.C. Lucken, J. Chem. Soc., Dalton Trans. (1983) 495–497.
[12] M.F. Davis, W. Levason, G. Reid, M. Webster, Polyhedron 25 (2006) 930–936, and
refs. therein.
[13] M.F. Davis, M. Clarke, W. Levason, G. Reid, M. Webster, Eur. J. Inorg. Chem. (2006)
2773–2782.
[14] M.F. Davis, W. Levason, G. Reid, M. Webster, W. Zhang, Dalton Trans. (2008)
533–538.
[15] T. Bo¨ttcher, B.S. Bassil, G.-V. Ro¨schenthaler, Inorg. Chem. 51 (2012) 763–765.
[16] M.A.M. Khouna, M.T. Ben Dhia, M.R. Khaddar, Phosphorus Sulfur Silicon 180
(2005) 1673–1682.
[17] M.A.M. Khouna Sanhoury, M.T. Ben Dhia, K. Essalah, M.R. Khaddar, Polyhedron 25
(2006) 3299–3304.
[18] M.A.K. Sanhoury, M.T. Ben Dhia, M.R. Khaddar, Inorg. Chim. Acta 362 (2009)
3763–3768.
[19] M.A. Sanhoury, M.T. Ben Dhia, M.R. Khaddar, J. Fluorine Chem. 132 (2011)
865–869.
A solution of (R2N)2P(O)OCH2CF3 (2.1 mmol) in CH2Cl2 (5 mL)
was added to a suspension of SnF4(MeCN)2 (0.28 g, 1.0 mmol) in
CH2Cl2 (20 mL) and the mixture stirred at room temperature for
2 h. The white precipitate was filtered off and dried in vacuo.
(Yields R = Me (1): 0.47 g, 72% R = Et (2): 0.59 g, 77%.) Anal. Calcd.
for C14H34F10N4O4P2Sn (1): C, 21.74; H, 4.26; N, 8.45. Found: C,
21.50; H, 4.33; N, 8.24. Anal. Calcd. for C22H50F10N4O4P2Sn (2): C,
30.99; H, 5.72; N, 7.23. Found: C, 30.85; H, 5.68; N, 6.89. IR (KBr):
nP5O (1: 1208 cmÀ1 2: 1205 cmÀ1); nSn–F (1: 579 cmÀ1
, , 2:
577 cmÀ1).
4.2. SnF4[R2NP(O)(OCH2CF3)2]2
[20] M. Bork, R. Hoppe, Z. Anorg. Allg. Chem. 622 (1996) 1557–1563.
[21] D. Tudela, F. Rey, Z. Anorg. Allg. Chem. 575 (1989) 202–208.
[22] D. Tudela, J.A. Patron, Inorg. Synth. 31 (1997) 92–93.
[23] P.G. Harrison, B.C. Lane, J.J. Zuckerman, Inorg. Chem. 11 (1972) 1537–1543.
[24] W.L.F. Armarego, D.D. Perrin, Purification of Laboratory Chemicals, 14th ed.,
Butterworth-Heinemann, Oxford, 1996.
[25] C.M. Timperley, M. Bird, J.F. Broderick, I. Holden, I.J. Morton, M.J. Waters, J.
Fluorine Chem. 104 (2000) 215–223.
[26] C.M. Timperley, I. Holden, I.J. Morton, M.J. Waters, J. Fluorine Chem. 106 (2000)
153–161.
These compounds have been prepared similarly on mixing
SnF4(MeCN)2 (0.28 g, 1.0 mmol) with R2NP(O)(OCH2CF3)2
(2.1 mmol) and stirring for 8 h. (Yields R = Me (3): 0.47 g, 61%
R = Et (4): 0.58 g, 70%.) Anal. Calcd. for C14H26F16N2O6P2Sn (3): C,
18.65; H, 2.61; N, 3.62. Found: C, 18.10; H, 2.84; N, 3.12. Anal. Calcd.
for C18H34F16N2O6P2Sn (4): C, 23.18; H, 3.40; N, 3.38. Found: C,