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The Structure Of Tas⁺ CF₃C(O)NS(CF₃)NS(CF₃)NC(O)CF₃^-, A Salt With A Bis(Sulfinyl) Amide Anion

Lork, E.¹; Müller, M.¹; Mews, R.¹

¹Institute of Inorganic and Physical Chemistry University of Bremen, PO Box 330440 D-28334 Bremen, Germany Fax:+49-421-218 4267; e-mail: mews@chemie.uni-bremen.de

Received March 10, 2004. In Final Form April 12, 2004
Dedicated to Professor Dr. Pedro J. Aymonino on the occasion of his 75^th birthday.

Abstract
The title compound TAS ⁺ CF₃C(O)N S(CF₃)NS(CF₃) NC(O)CF₃^- (3) was isolated as a minor product from the reaction of TAS-fluoride with CF₃C(O)NS(CF₃)F. The X-ray structure of 3 is reported and the bonding situation in the anion is discussed.

Resumen
Como producto secundario de la reacción entre TAS-fluoruro con CF₃C(O)NS(CF₃)F se pudo aislar el compuesto TAS⁺ CF₃C(O)NS(CF₃)NS(CF₃) NC(O)CF₃^- (3) cuya estructura de rayos X se reporta aqui. Se discuten las caracteristicas de enlace del anión.

Introduction

     Acyl-sulfur(IV)imides RN=SR'R" (R= ClC(O), FC(O), CF₃C(O); R'=R"=Cl, F, CF₃, R'=R"=F, Cl, CF₃) are an extraordinary interesting class of compounds, not only because of spectroscopic reasons but also from a synthetic point of view. Investigations of the structures and conformations of FC(O)NSF₂ [1], CF₃C(O)NSF₂ [2], and FC(O)NSCl₂ [3] by gas phase electron diffraction, IR- and  Raman-spectroscopy have been reported. In both the gas and in the liquid phase dominantly a syn-syn conformation (the acyl group syn-periplanar with respect to the SF₂ bisector and the oxygen directed towards the sulfur ) is observed. If one of the sulfur bonded fluorines is exchanged by a CF₃-group, as e.g. in FC(O)N=S(CF₃)F [4] and CF₃C(O)NS(CF₃)F [5] unexpectedly the anti-syn conformer (acyl group in an anti-position) is dominant. Besides these structural differences due to the F/CF₃ exchange also remarkable differences in the reactivity result from this exchange. While the C-N- bond in sulfur difluoride imides RC(O)NSF₂ (R=F, CF₃) is readily cleaved by fluoride ions to give salts with the sulfur difluoride imide anion (e.g. Cs⁺NSF₂^- [6,7] Hg(NSF₂)₂ [6-8] TAS⁺NSF₂ [9]), with RC(O)NS(CF₃)F no formation of the corresponding NS(CF₃)F^--salts is observed. Stable salts with the RC(O)NS(CF₃)F₂^- anion were isolated [9].

Experimental, X-Ray Crystallography

     The starting materials  TASF [10] and CF₃C(O)NS(CF₃)F [11] were prepared according to the literature, both compounds were reacted as described in our earlier paper [9]. Onto the frozen CH₃CN solution of 3 an equal volume of diethyl ether was condensed at –196°C on a vacuum line. The reaction vessel was warmed to –30°C and kept at this temperature for several days.
     By slow diffusion of the ether into the CH₃CN solution single crystals of 3 were formed. From the cold solution they were transferred to cooled KEL-F oil, single crystals were selected at the same temperature under a microscope in an atmosphere of dry nitrogen. The single crystals were mounted on a thin glass fibre.
     The single-crystal X-ray structure determination (Table 1) was carried out on a Siemens P4 diffractometer using Mo(Ka) radiation (0.71073 Å) with a graphite monochromator. Refinement based on F²; R1 = åççF_oç - çF_cçç/åçF_oç; wR2 = {å[w(F_o² – F_c²)²/å[w(F_o²)²]}^1/2. Programs used: SHELX-97 [12] and DIAMOND [13]
     The structures were solved by direct methods (SHELXS [12]). Subsequent least-squares refinements (SHELXL-97-2 [12]) located the positions of the remaining atoms in the electron density maps. All non-H atoms were refined anisotropically.
     CCDC-232900 (3) contains the supplementary crystallographic data for this paper. These data can be obtained free of charge at www.ccdc.cam.ac.uk/conts/retrieving.html [or from the Cambridge Crystallographic Data Centre, 12, Union Road, Cambridge CB2 1EZ, UK;  fax: +44-1223/336-033; E-mail: deposit@ccdc.cam.ac.uk.

 Table 1. Crystal data and structure refinement for TAS⁺CF₃C(O)NS(CF₃)NS(CF₃)C(O)CF₃^- (3).

Empirical Formula	C12H18F12N6O2S3
M	602.50
T/K	173(2)
Wave length/ pm	71.073
Crystal system	triclinic
Space group	P-1
a/pm	932.0(2)
b/pm	1095.5(2)
c/pm	1199.5(2)
a/°	92.560(10)
b/°	100.600(10)
Γ/°	93.840(10)
U/nm3	1.1991(4)
Z	2
Dc/Mg m-3	1.669
m (MoKa) mm-1	0.425
F(000)	608
Crystal size /mm3	0.8 x 0.7 x 0.6
q range/ °	2.55 to 27.50
Indexrange	–12£h£12, –14£k£14, –15£1£15
Reflections collected	11078
Independent  Reflections	5489 [R(int) = 0.0248]
Completeness to theta= 27.50°	99.9%
Refinement	Full-matrix least-squares on F2
Data/Restraints/Parameter	5489/0/324
Goodness-of-fit on F2	1.021
R1, wR2  [I > 2s(I)]	0.0358,  0.0933
R1, wR2 (all Data)	0.0438,  0.0982
Extinction coefficient	0.0173(15)
Largest difference peak, hole/eÅ-3	0.369 / –0.327 e. Å-3

Results And Discussion

     Recently we reported the reactions of FC(O)NS(CF₃)F with TAS-fluoride ((Me₂N)₃S⁺Me₃SiF₂^- (Tris(dimethylamino)sulfonium difluorotrimethylsilicate) [9]:

1 was characterized by NMR spectroscopy and X-ray crystallography, 2 was also isolated in almost quantitative yield and unequivocally characterised by ¹⁹F-NMR spectroscopy. Compound 2 seemed to the stable in solution, cleavage of the CN-bond was not observed. Therefore it was rather surprising that from our present attempt to crystallize 2 from CH₃CN/diethylether at –30 °C. single crystals of 3 were isolated. The formation of 3 is rationalised by the equation.

TASF  +  3 CF₃C(O)NS(CF₃)F    →     TAS⁺ CF₃C(O)NS(CF₃)NS(CF₃)NC(O)CF₃^-
                                                                                             3
                                                                                 + Me₃SiF { + CF₃C(O)F    +  CF₃SF₃}

The bridging nitrogen between the two acylsulfurimide moieties probably results from the decomposition of the primarily formed anion of salt 2. CN bond cleavage might be the next step, followed by attack of the resulting nucleophile at CF₃C(O)NS(CF₃)F. In a further step SC-bond cleavage should have occurred. Until now these speculations could not be confirmed by spectroscopic investigations. 

X-ray structure of TAS⁺CF₃C(O)NS(CF₃)NS(CF₃)C(O)CF₃^- (3)

     3 crystallizes in the triclinic space group P-1 with 2 molecules in the asymmetric unit. The structure of the anion of 3 is presented in Figure 1, details of the structure determination of 3 are given in Table 1, Table 2 lists selected bond lengths and bond angles.
     The unique anion of 3 is an imino derivative of a hitherto unknown class of compounds, of the bis(sulfinyl)amides (RS(O))₂N^-. The corresponding bis(sulfonyl)amides (RS(O)₂)₂N^- with various counterions (R=F, perfluoroalkyl) have been previously reported and are presently investigated in many laboratories for their application as electrolytes in batteries and fuel cells [14]. A mixed fluorosulfinyl – fluorosulfonyl-amide, TAS⁺ FS(O)₂NS(O)F^- was prepared in our laboratory from FS(O)₂NSO and TASF [15]. In a similar way bis(sulfinyl)amides should be available from N-sulfinyl sulfinamides, e. g. CF₃S(O)NSO [16], and TASF.
     According to the bond distances determined the amide is best described as superposition of the two resonance structures B and B', by C, because all SN distances are almost of equal length (163.2 (2)–164.0(2) pm). Compared to CF₃-C(=O)-N=S(CF₃)F (SN = 155.4(8) pm) the SN-bonds are significantly lengthened, while the CN bonds in 3 are shortened by approximately 5 pm, the CO distances are stretched by 2.5–2.9 pm. The negative charge is delocalised over 9 bonds.

 

Figure 1. X-ray Structure of TAS⁺ CF₃C(O)NS(CF₃)NS(CF₃)NC(O)CF₃^- (3)

 

Table 2 Selected bond distances and bond angles in 3

N(1)-S(1)	163.29(15)
N(1)-S(2)	164.01(15)
S(1)-N(2)	163.64(15)
S(1)-C(3)	183.7(2)
N(2)-C(1)	134.5(2)
C(1)-O(1)	122.9(2)
C(1)-C(4)	153.2(3)
S(2)-N(3)	163.18(16)
S(2)-C(5)	183.8(2)
N(3)-C(2)	133.7(2)
C(2)-O(2)	122.6(2)
C(2)-C(6)	153.7(3)
S(3)-N(5)	160.42(16)
S(3)-N(6)	161.70(16)
S(3)-N(4)	168.37(15)
S(1)-N(1)-S(2)	108.05(9)
N(1)-S(1)-N(2)	109.58(8)
N(1)-S(1)-C(3)	98.29(9)
N(2)-S(1)-C(3)	94.68(8)
C(1)-N(2)-S(1)	107.82(13)
O(1)-C(1)-N(2)	128.58(19)
O(1)-C(1)-C(4)	119.44(17)
N(2)-C(1)-C(4)	111.97(16)
N(3)-S(2)-N(1)	110.38(9)
N(3)-S(2)-C(5)	94.82(8)
N(1)-S(2)-C(5)	98.04(9)
C(2)-N(3)-S(2)	109.62(13)
O(2)-C(2)-N(3)	130.00(18)
O(2)-C(2)-C(6)	118.81(17)
N(3)-C(2)-C(6)	111.19(16)
N(5)-S(3)-N(6)	115.26(9)
N(5)-S(3)-N(4)	100.64(8)
N(6)-S(3)-N(4)	98.83(8)

As mentioned in the introduction, of special interest is the conformation of the RC(O)-groups with respect to the –N=SRR’-group. The structure of the anion of 3 corresponds to the structure of CF₃C(O)N=S(CF₃)F [5], two CF₃C(O)NSCF₃-units are connected by N1. As observed for CF₃C(O)NS(CF₃)F both CF₃C(O)-units adopt the anti- syn conformation: the CO-group is in an anti-position to the NSC bisector, the oxygen points towards the sulfur (Figure 2). The atoms CSNCO are coplanar (Figure 3), the distances S1O1 (268.1 pm) and S2O2 (274.5 pm) are considerably shorter than the sum of the v.d. Waals radii of sulfur and oxygen (330 pm) [17]. These distances are slightly shorter than in the neutral CF₃C(O)NS(CF₃)F, probably due to increased electrostatic interaction between O and S in the anion. This electrostatic interaction might be the reason for the unexpected conformation in acyl–S^_trifluoromethyl sulphurimides. In both structures sulphur adopts nearly a ψ-trigonal bipyramidal coordination with the O^..S^_C atoms in axial positions. The angles O1^..S1^_C3 and  O2^..S2^_C5 in 3 are 151.6° and 153.8°, respectively.

Figure 2. Conformation of the CF₃C(O)NS(CF₃)NS(CF₃)NC(O)CF₃^- -anion (for clarity the F-atoms of the CF₃-groups are omitted)

Figure 3.   View showing the coplanarity of the atoms CSNCO and C and the ψ-trigonal bipyramidal environment of the sulphur atoms

Conclusions

     From the reaction of TASF with CF₃C(O)NS(CF₃)F, unexpectedly TAS⁺CF₃C(O)NS(CF₃)NS
     (CF₃)NC(O)CF₃^- (3) was isolated and characterized by X-ray crystallography. The anion of 3 is the first member of a hitherto unknown class of compounds, of the bis(sulfinyl)amides [RS(NR’)]₂N- and [RS(O)]₂N-, respectively. Possible direct pathways to these compounds, the reactions of RS(NR)F or RS(O)F with LiN(SiMe₃)₂ or related amides or the addition of “naked” anions (nucleophiles) [18] to RS(O)NSO will be followed in the future.

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