(Y = Cl, Br) and CX - American Chemical Society

Chapter 19 +

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Syntheses of the CFY (Y = Cl, Br) and C X (X = Cl, Br, OTeF ) Cations Employing the NobleGas Oxidant, XeOTeF Sb(OTeF ) 2

3

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Downloaded by UNIV OF CALIFORNIA SAN DIEGO on March 24, 2016 | http://pubs.acs.org Publication Date: July 7, 2007 | doi: 10.1021/bk-2007-0965.ch019

5

5

6

Hélène P. A. Mercier, Matthew D. Moran, and Gary J. Schrobilgen* The Department of Chemistry, McMaster University, Hamilton, Ontario L8S 4M1, Canada

The strong oxidant properties of the noble-gas salt, XeOTeF Sb(OTeF ) , have been exploited to synthesize Sb(OTeF ) salts of trihalomethyl cations by the low temperature oxidation of a halide ligand of the corresponding tetrahalomethane in S O C l F solvent. Among the trihalomethyl cations that have been synthesized are C C l , C B r , C F C l , and C F B r , as well as C(OTeF ) . The carbocations have been stabilized as salts of the preformed, oxidatively resistant and weakly coordinating Sb(OTeF ) anion, thus avoiding the use of more strongly coordinating anions derived from strong Lewis acid ligand acceptors such as SbF . The C F C l and CFBr cations are the only known persistent fluorinecontaining trihalomethyl cations, and appear to be the most electrophilic fluorine-containing cations synthesized to date. Evidence has been obtained for transient formation of C F C l , C F B r , and C F ) cations but, thus far, their high electrophilicities have precluded isolation. +

-

5

5

6

-

5

6

2

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3

+

+

+

3

2

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2

5

3

-

5

6

+

5

2

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2

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2

+

2

394

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3

© 2007 American Chemical Society

Laali; Recent Developments in Carbocation and Onium Ion Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 2007.

395 +

Earlier Studies of Long-Lived C X ) ( X = C l , B r , I) and C F A . / (X = CI, B r ; η = 0-3) Cations 3

+

Trihalomethyl cations, C X ( X = C l , Br, I), have been the subject of considerable interest. The C C 1 and C B r cations have been postulated as superelectrophilic intermediates that catalyze efficient cracking, isomerization, and oligimerization of alkanes and cycloalkanes, as well as facilitating the syntheses of carbocations via hydride abstraction by the C C 1 cation. The C C 1 cation, the first perhalomethyl cation to have been reported, was observed in the gas phase by mass spectrometry and by ion cyclotron resonance (ICR) mass spectrometry. The C C 1 cation has also been isolated in the solid state by ultraviolet or microwave irradiation of CHC1 and entrapment of the free cation in an argon matrix at 14 K , and by codeposition of CC1 and SbF on a C s l window at 77 Κ followed by warming to 150 Κ to produce C C l S b F C r in an SbF matrix. In all three cases, C C 1 was characterized by infrared spectroscopy. More recently, the C B r and C I cations have been generated in the gas phase and observed by ICR mass spectrometry. The C F cation has been observed by mass spectrometry and ICR mass spectrometry, and was first produced in the condensed state by photodecomposition of C F X (X = C l , Br, I, H) in argon matrices. The C F cation has also been obtained by photoionization and radiolysis of CF Br, by decomposition of an A r / F C N N C F mixture at 14 Κ that had been codeposited with a beam of microwave-excited neon atoms, and by codeposition of a Ne/CF mixture at 5 Κ with microwave-excited neon atoms. Matrix-isolated C F , generated in the aforementioned manners, was characterized by infrared spectroscopy, and the vibrational assignments for C F have been confirmed by ab initio calculations. The mixed, fluorine-containing halomethyl cations, C F C 1 , " C F C 1 , CFBr , and C F B r have been generated in the gas phase by various ionization methods and observed as short-lived cations. The ( C F C l | | C r ) i v ion pair has been generated as a transient species by pulse radiolysis of CFC1 in methylcyclohexane. Persistent C F C 1 and C F C 1 cations have been generated by matrix radiolysis and photoionization during co-condensation of CFC1 and CF C1 , respectively, with argon at 15 K . Both cations were characterized by infrared spectroscopy, but the assignments of the complex mixture of cationic and radical chlorofluorocarbon species were not corroborated by other means. In another matrix-isolation study, it has been claimed that the CFC1 —Cr ion pair was generated by irradiation of CFC1 at 77 Κ with γ-rays from a C o source, followed by irradiation with a xenon lamp using a cutoff of 900 nm. The proposed ion pair was characterized by UV-visible absorption spectrophotometry. Persistent C F B r has been generated by photoionization and radiolysis of C F B r and C F B r , whereas CF Br has been generated from C F B r and C F B r , during co-deposition with argon at 15 K . Both cations were characterized by infrared spectroscopy. 3

+

+

3

3

+

1

3

+

3


2

3

+

3

3

4 , 5

4

5

+

3

6

2

10

+

5

3

+

+

3

3

7

+

3

2

3

3

8

+

3

1 2 / I 3

9

3

3

3

10

4

11

+

3

+

3

12

+

13

16

2

+

1 3 , 1 5

+

2

+

14,15

2

1 3 , 1 5

2

+

2

s o

3

17

+

18

+

2

1 9

2

3

2

+

2

60

3

20

+

9

2

1 2 / 1 3

3

2

2

+

9

2

12/13

2

2

3


2

396 The first syntheses of long-lived perhalomethyl cations in solution were achieved by the reactions of C X (X = C l , Br, I) with SbF in S0 C1F solvent at -78 °C to give CX Sb F „X~ (X = CI, Br, I; > l ) . A l l three cations were characterized by C N M R spectroscopy. The C C 1 cation was also generated by reaction of CC1 C(0)C1, CC1 S0 C1, and CC1 C(0)F with SbF in S0 C1F at -78 ° C . Similar attempts to generate C F by reaction of SbF with C F , C F C ( 0 ) F , and C F S 0 C 1 in S0 C1F at -78 °C were unsuccessful and, in the cases of C F C ( 0 ) F and C F S 0 C 1 , yielded C F . The C I cation has been recently synthesized as CI A1(0C(CF ) ) " by the room temperature abstraction of iodide as A g i from C l in C H C 1 solution by use of Ag A1(0C(CF ) ) ~ and characterized by X-ray crystallography. 4

5

+

2

2 1

3

n

5

1 3

+

3

3

3

2

3

21,22

5

2

+

3

3

3

2

5

4

2

2 1 , 2 2

3

3

2

+

4

3

+

3

3

3

4


+

4

2

2

3

3

4

23

Although a considerable number of carbocations structures have been determined, " relatively few crystal structures are known for halogen- and oxygen-substituted carbocations. These include c-(F C-S-CF-S) , ( C H ) C F , ( w - C F C H ) ( C H ) C F , C H O C H F , (o-ClCôH.XQHsiCClV CICOV (p-CH C H )CO , CH CO , CH CH CO , (3,5-F-4-CH C H )CO , C1 C -NH , ClBrC -NH , CH 0CHC1 , C(OH) CH , ' HC(OH) , (p-CH C H )C(OH) , (C H )C(-OCH CH 0-)Y° and ( C H ) C ( - O C ( C H ) C ( C H ) 0 - ) , Until the work described in this Review, the C I and C ( O H ) cations were the only trihalo- and trioxy-substituted cations to have been characterized by X-ray crystallography. As a consequence of the relative paucity of solid state structural data for trihalomethyl cations, electronic structure calculations have been heavily relied upon for geometric data and have been used to account for the bonding and chemical properties of these cations. The relative stabilities of the trihalomethyl cations have been assessed in terms of relative degrees of σ and ρ(π) donation from the halogen atom to the carbon center. ' The σ effect, from the perspective of the halogen atoms of C X , has been found to be strongly withdrawing in the case of fluorine and weakly donating in the cases of chlorine, bromine and iodine (I > Br > CI). Conversely, ρ(π) back-donation is very weak for fluorine and stronger for the heavier halogens (I > Br > CI). Other properties have been computed for the C X series, including C chemical shifts, fluoride ion affinities (as measures of relative Lewis acidities), vibrational frequencies, and atomic charges. ' ' Recently electron pair affinities have been used to quantify Lewis acidities of the E X systems (E = B , C, A l , Si; X = F, C l , Br, I). Prior syntheses of long-lived perhalomethyl cations have been achieved by halide abstraction by use of either a strong Lewis acid (in superacidic or S0 C1F solvent media) or A g (vide supra), but no routes to such carbocations through oxidative removal of a halogen bound to carbon were known. The objectives of the current work have been to provide structural and spectroscopic data that, thus far, have been lacking for these systems, and to provide oxidative routes to 24

27

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28

2

+

3

29

+

2

3

6

4

6

2

+

3

+

6

3 3

6

+

3

6

4

+

3

2

3

3 3

2

3 5

3

+

33

+

3

2

39

2

+

3

+

2

+

2

1

3 3

3

+

2

38

3

3 0

3

+

3 4

2

+

5

33

4

+

2

29

6

5

2

2

41

2

+

3

3

23,42

29,32 43

+

3

+

1 3

44

3

23

12

22

23,29,32

43,45,46

0 / +

3

47

2

+


36

37

397

the perhalomethyl cations and related pentafluoroorthotellurate (OTeF ) substituted cations. A n oxidative route to carbocations using the strong oxidant salt, XeOTeF Sb(OTeF ) ", provides an interesting new application of noblegas compounds to chemical syntheses, " that has led to the solution characterization and isolation to several salts of the trihalomethyl cations and their (OTeF ) derivatives. 5

+

5

5

6

48

59

5

+

The X e L (L = F, OSeF , OTeF ) Cations and M(OTeF ) " (M = As, Sb, Bi) Anions; General Background The electronegativity of the OTeF group is comparable to that of fluorine in its ability to stabilize a variety of noble-gas species. Derivatives of the OTeF group are known for the +2, +4, and +6 oxidation states of xenon, " as well as for the +2 oxidation state of krypton. The OTeF analogue of the wellknown X e F cation, X e O T e F , was first obtained as the A s F " salt by reaction of FXeOTeF with A s F . The X e O T e F s ^ F u " salt was subsequently synthesized from X e O T e F A s F " by A s F displacement in liquid SbF , and the X e O T e F cation has been characterized in solution by F , Te, and Xe N M R spectroscopy in SbF solvent, and in the solid state by Raman spectroscopy of X e O T e F A s F and XeOTeFs^bzFn". The X-ray crystal structure of X e O T e F A s F " shows that the incomplete primary coordination sphere of XeOTeF , like that of X e F , renders it a Lewis acid that interacts with the A s F " anion by means of a fluorine bridge. The Xe—F cationanion distance (2.24(3) Â ) is significantly less than the sum of xenon and fluorine van der Waals radii (3.63 A ) and is similar to that in X e F A s F " (2.208(3) A ) and X e O S e F A s F - (2.31(4) A ) . Until recently, no solid state structural data currently exists for salts of the X e F or X e O T e F cations in which either X e F or XeOTeF , or any other noble-gas cation, may be regarded as "devoid" of interactions with their counter anions. Likely candidates for anions that may prove to be weakly coordinating with respect to X e F and X e O T e F are members of the oxidatively resistant M(OTeF ) " ( M = As, Sb, Bi) anion series. The latter anions effectively disperse a single negative charge over 30 fluorine atoms rather than over six fluorine atoms as in their M F " analogues. In addition to their low basicities, the high effective group electronegativity of the OTeF ligands and their steric requirements in these hexa-coordinate anions may be expected to make the electron lone pairs of the linking oxygen atoms less accessible to attack by strong electrophiles. The Sb(OTeF ) " anion has been shown to resist attack by the strong oxidant cations S b C l and S b B r / , leading to the X-ray crystal structure determinations of their Sb(OTeF ) ~ salts. The generation of main-group cations by use of xenon cations as oxidants has been limited to salts of the X e F and C F X e cations and has focused on the oxidation of the central element rather than on the oxidation of a ligand.


5

5

5

6

5

60,61

62

69

5

70

5

+

+

5

6

64

5

5

+

8

5

6

5

5

+

1 9

125

129

5

69

5

+

6 4 , 6 5 , 6 8

5

69

6

+

5

6

+

+

5

6

6 8

7 1

+

6

7 2

+

6 8

5

+

6

+

+

+

5

5

+

+

5

73

5

6

6

5

5

6

+

74

4

5

6

+ 4 9 , 5 6

+ 5 8

6

5


398 +

Synthesis of X e O T e F S b ( O T e F ) ~ The salt, XeOTeE Sb(OTeF ) ", provides an example of a synthetically useful low-temperature noble-gas oxidant in which the noble-gas cation is not coordinated to its counter ion (see X-ray Crystal Structure of XeOTeF Sb(OTeF ) ~S0 ClF). The ability of the neutral precursor, Xe(OTeF ) , to oxidatively introduce two OTeF groups has been previously exploited in the syntheses of NR4 Sb(OTeF ) " salts (R = C H or C H C H ) from NR4 Sb(OTeF ) ". The XeOTeF Sb(OTeF ) " salt was first observed in an attempt to synthesize Sb(OTeF ) by reaction of equimolar amounts of Xe(OTeF ) and Sb(OTeF ) . A 2:1 molar ratio of Xe(OTeF ) (eq 1) and Sb(OTeF ) (eq 2) [< 1% molar excess of Xe(OTeF ) ] react in S0 C1F solvent at -20 °C in near quantitative yield to form bright yellow to yellow-orange solutions of XeOTeF Sb(OTeF )6~ (eq 3). Unlike its fluorine analogue, 5

s

6

+

5

5

6

+

5

5

5

6

2

2

5

+

5

+

73

5

3

3

2

+

4

5

5


6

5

6

5

75

5

5

2

5

3

5

3

5

2

2

2

+

5

5

3 X e F + 2 B(OTeF ) -> 3 Xe(OTeF ) + 2 B F 2

5

SbF + B(OTeF ) 3

5

3

5

-> Sb(OTeF ) + B F

3

5

2

5

3

(1)

3

(2)

3

+

2 Xe(OTeF ) + Sb(OTeF ) -> 5

2

XeOTeF Sb(OTeF ) " + X e

3

5

5

(3)

6

+

XeF SbF ~, which is insoluble in S0 C1F at room temperature, the solubility of XeOTeF Sb(OTeF ) " in S0 C1F at -78 °C is high, exceeding 2 M . The solid salt, isolated as the pale yellow solvate, X e O T e F S b ( O T e F ) 6 ~ S 0 C l F at -78 to 0 °C, is stable to pumping at 0 °C for at least 4-5 h. The solid decomposes above 10 °C after 4-6 h, in marked contrast with X e O T e F A s F " and XeF SbF ", which are stable at room temperature. Solutions of XeOTeF Sb(OTeF ) " in S0 C1F show significant decomposition after 30 min to 1 h a t - 1 0 ° C . 6

2

+

5

5

6

2

+

5

5

2

+

5

+

6 4 , 6 5 6 8

6

76

6

+

5

5

6

2

+

Structural Studies of X e O T e F S b ( O T e F ) " (a) M u l t i - N M R Spectroscopy. The 0 , F , S b , T e and Xe N M R spectra of XeOTeF Sb(OTeF ) C C l S b ( O T e F ) - + C10TeF + X e

4

3

5

6

(4)

5

+

-78 °C gives colorless, crystalline CCl Sb(OTeE ) ". The C N M R spectrum (S0 C1F solvent, -80 °C) of the products resulting from eq 4 give rise to a sharp singlet (237.1 ppm) assigned to CCl Sb(OTeF ) ", which is in agreement with the previously reported value (236.3 ppm). The C chemical shift of C C 1 is significantly deshielded relative to CC1 [5( C), 96.4 ppm; S0 C1F, -80 °C], which is consistent with carbocation formation. The F N M R spectrum shows the very strongly coupled A B pattern that typifies the Sb(OTeF ) " anion and a well-resolved A B pattern for C10TeF (Table 2). The reaction of stoichiometric amounts of C B r with XeOTeF Sb(OTeF ) ~ in S0 C1F is initially rapid at -78 °C, giving a deep red-brown solution which lightens to red-orange over a period of several hours at ca -50 °C (eq 5). The color change corresponds to the further reaction of the C B r cation with BrOTeF to produce B r and the mixed carbocations, C B r ( O T e F ) , C B r ( O T e F ) and, ultimately, C ( O T e F ) according to eq 6-8, with the overall reaction being represented by eq 9. The C B r S b ( O T e F ) ~ S 0 C l F and 3

5

6

1 3

2

+

3

5

21

+

6

1 3

,3

3

4

19

2

4

73

5

83

6

4

5

+

4

5

5

6

2

+

3

+

5

2

2

+

5

5

+

2

5

3

+

3

+

5

6

2

+

XeOTeF Sb(OTeF ) " + C B r -> CBr Sb(OTeF ) ~ + BrOTeF + Xe 5

5

6

4

3

+

CBr Sb(OTeF ) " + BrOTeF 3

5

6

5

6

(5)

5

+

5

-> CBr (OTeF ) Sb(OTeF ) " + B r 2

5

5

6

2

(6)

+

CBr (OTeF ) Sb(OTeF ) " + BrOTeF -> CBr(OTeF ) Sb(OTeF ) " + B r 2

5

5

6

5

+

5

2

5

6

2

(7)

+

CBr(OTeF ) Sb(OTeF )6" + BrOTeF -> C(OTeF ) Sb(OTeF ) ~ + B r 5

2

5

5

+

5

+

3 XeOTeF Sb(OTeF ) " + 3 C B r 5

5

6

3

5

6

(8)

2

+

4

-> 2 CBr Sb(OTeF ) " + C(OTeF ) Sb(OTeF ) " + 3 B r + 3 Xe 3

5

6

+

5

3

5

6

2

+

(9)

C(OTeF ) Sb(OTeF ) ~3S0 ClF salts have been characterized by single-crystal X-ray diffraction (vide infra). 5

3

5

6

2



3

CBr

5

4

3

5

r

6

2

5

2

+

c

25

" Te)

i a / u s

Te)

5

6

-A2.6

c

123

b

73563

73852

A

178

^19.2

-54.0

180

^17.0

-53.8

B

73474

73419

(3350)/(4047)

3324/4013

164

-58.2

-24.4

3140/3786

3029/3653

180

3120/3758

64

-49.9

—41.5

7(4075)

A

115.8

l 9

'j( F -

74012

74099

123

3337/4025

c

B

164

f

19

'j( F -

-57.6

FB)

-31.6

2

, 9

156

FA-

168.8

, 9

3343/4029

^(

162

2

-59.3

d

Te)

-24.4 69

V( C-

+

187.6

A

3

coupling constants, H z

4

5

+c

F

4

w

e

Nuclear magnetic resonance spectra were obtained for S0 C1F solutions at -80 °C. The symbols, F and F , denote axial and equatorial fluorine atoms, respectively. The anion parameters apply to all carbocation salts and to the Br(OTeF ) salt of Sb(OTeF ) "; also see ref 73. Predicted from pairwise additivity parameters as described in the Chemical Shifts and Coupling Constant Trends section. See ref 84 and 8 5 . The T e satellites were not observed.

8

2

+c

+c

Sb(OTeF ) "

ClOTeFs

BrOTeFs

5

Br(OTeF )

5

C(OTeF )

5

C(OTeF )

3

, 9

125

6

4

-61.3

F ΓΒ ,3

5

5

-19.9

9

8

201.1"

,

b

+

+c

209.7

C

+ c

, 3

237.1

CBr(OTeF )

2

5

chem shifts (δ), ppm

, 9

+ C

CBr (OTeF )

3

CC1

Species

1 3

Table 2. The C and F N M R Parameters for C(OTeF ) and CBr (OTeF ) -„ (n = 0-3), and Products Resulting from the Reaction of XeOTeF Sb(OTeF ) " with CC1 and C B r


404 l 3

+

The C N M R spectrum of CBr Sb(OTeF ) ~ in S0 C1F at -80 °C is a singlet (209.7 ppm), in good agreement with the previously reported value (207 ppm). A s in the case of C C 1 , the C resonance of C B r is significantly deshielded with respect to that of its parent molecule, C B r [5( C), -29.7 ppm; S0 C1F, -80 °C], and is again characteristic of carbocation formation. The F N M R spectrum shows a very strongly coupled A B pattern corresponding to the Sb(OTeF ) " anion (Table 2), similar to that obtained for C C l S b ( O T e F ) " The F N M R spectrum of pure BrOTeF dissolved in S0 C1F at -80 °C (Table 2) was also obtained and demonstrated that BrOTeF formed in eq 5 was not present. The absence of BrOTeF is consistent with the formation of mixed Br/OTeF -substituted methyl cations and the oxidation of BrOTeF by XeOTeF Sb(OTeF ) " to give the new Br(OTeF ) cation (eq 10). The 3

21

5

+

6

2

1 3

+

3

3

13

4

1 9

2

4

+

5

6

3

5

6

,9

5

2


5

5

5

5

+

+

5

5

6

5

2

+

+

XeOTeF Sb(OTeF ) "+ BrOTeF -> Br(OTeF ) Sb(OTeF )6~ + X e 5

5

6

5

5

2

5

(10)

+

formation of Br(OTeF ) was confirmed, in a separate experiment, by the reaction of BrOTeF with XeOTeF Sb(OTeF ) " in S0 C1F at-78 ° C . The formation of the CBr (OTeF ) . (n = 0-2) cations and their N M R assignments were confirmed by addition of BrOTeF at -20 °C to the reaction products of eq 9, in a 3:1 molar ratio relative to the initial amounts of XeOTeF Sb(OTeF ) ~ and C B r . This resulted in increased amounts of the OTeF -containing carbocations and B r as outlined in eq 6-8 (Table 2). The C N M R spectrum indicated that a small quantity of CBr Sb(OTeF ) " remained unreacted (7% based on integration of all C resonances), with C(OTeF ) Sb(OTeF ) " as the major product (70%; 6( C), 168.8 ppm). O f the mixed CBr„(OTeF ) _„ (n = 1,2) cations, only C B r ( O T e F ) was detected by C N M R spectroscopy [10%; 5( C), 187.6 ppm], whereas the C chemical shift of C B r ( O T e F ) was predicted by use of empirical (pairwise additivity) trends [5( C), 201.1 ppm]. * A singlet was also observed [13%; 5( C), 124.7 ppm] that is tentatively assigned to 0=C(OTeF ) based on the similarity of its d chemical shift to that of 0 = C E (134.2 ppm), and may arise from the formal loss of the TeF) cation from d(OTeF )) according to eq 11. 5

2

+

5

86

5

5

6

2

+

w

5

3

w

5

+

5

5

6

4

1 3

5

2

+

3

5

6

1 3

+

5

13

3

5

6

+

5

3

5

13

2

13

1 3

+

2

5

13

8

88

13

5

t3

2

89

2

5

+

+

C(OTeF ) Sb(OTeF ) " - » 0=C(OTeF ) + [TeF Sb(OTeF ) "] 5

3

5

6

5

2

5

5

(11)

6

Alternatively, 0=C(OTeF ) may prove to be unstable, decomposing to C 0 [6( C), 124.2 ppm] and 0 ( T e F ) [5( F ), -41.4 ppm; F was not observed because of overlap with F of C(OTeF ) ; V ( F A - F ) , 164 Hz] according to eq 12. The T e F cation presumably is not observed because of its high 5

13

2

2

90

19

5

2

B

+

A

5

3

A

1 9

I 9

b

+

5

0=C(OTeF ) -> C 0 + 0 ( T e F ) 5

2

2

5

(12)

2

electrophilicity, which leads to OTeF " abstraction from Sb(OTeF ) ", forming 0 ( T e F ) according to eq 13 and/or F~ abstraction to form T e F [6( F), -52.6 5

5

6

19

5

2

6


405 +

[TeF Sb(OTeF ) -] -> 0(TeF ) + Sb(OTeF ) 5

5

l 9

ppm; ' j ( F -

l 2 5

6

5

2

5

l9

(13)

5

l23

T e ) , 3747 Hz; ' . / ( F - T e ) , 3095 Hz] according to eq 14. The

+

[TeF Sb(OTeF ) ~] -> TeF + F TeOSb(OTeF ) 5

5

6

6

4

5

(14)

5

7

91

proposed Sb(V) species, Sb(OTeF ) , which is known to be unstable, *' and F TeOSb(OTeF )s have not been further investigated. The formation of the C(OTeF ) cation was confirmed by the presence of a satellite doublets in the C N M R spectrum that arise from spin-spin coupling of C to natural abundance T e (0.87%) and Te (6.99%) [V( C- Te), 69 H z ] . Separate integrations of T e and T e satellites were not possible as a result of their relatively broad line widths (v « 5 Hz), thus, the T e satellites only appear as shoulders. Because T e and T e are low abundance, sp'm-Vi nuclei, only a superposition of subspectra arising from the most abundant isotopomers, C ( 0 ° T e F ) (singlet) and C ( O T e F ) ( O T e F ) (doublet) (where °Te represents all spin-inactive isotopes of tellurium) are observed. Taking into account the natural isotopic abundances, multiplicities, and statistical distributions of tellurium isotopes among three sites, the experimental combined T e integrated satellite peak/central peak area ratios of 0.111 : 1.000 : 0.123 in the C N M R spectrum were used to confirm coupling to three equivalent tellurium atoms when compared with the calculated relative intensity ratios (0.000 : 0.0054 : 0.1268 : 1.0000 : 0.1268 : 0.0054 : 0.0001). Tellurium satellites could not be observed for CBr(OTeF ) owing to the low concentration of this species (10%). In order to compare the N M R parameters of C(OTeF ) with those of the unknown neutral parent, C(OTeF ) , C B r was allowed to react with a stoichiometric amount of BrOTeF at -78 °C according to eq 15. The C N M R 5

4

5

5

+

5

3


1 3

13

,23

125

92

123

13

125

,25

123

1/2

123

13

125

+

5

13

123/125

0

3

+

5

5

2

123/125

1 3

+

5

2

+

5

5

4

3

4

1 3

5

C B r + 4 BrOTeF -> C(OTeF ) + 4 B r 4

5

5

4

(15)

2

resonance of C(OTeF ) is a singlet at 115.8 ppm, accompanied by tellurium satellites. As expected, the C chemical shift of C(OTeF ) in S0 C1F solvent is significantly shielded with respect to that of the C(OTeF ) cation. As in the case of C(OTeF ) , the formation of C(OTeF ) was confirmed by the relative intensities of the overlapping T e satellites [ J ( C - T e ) , 64 Hz] in its C N M R spectrum. 5

4

1 3

5

4

2

+

5

3

+

5

3

5

4

l 2 3 / , 2 5

2

13

125

1 3

93

+

+

X-ray Crystal Structures of C C l S b ( O T e F ) " , C B r S b ( O T e F ) " S 0 C 1 F , and C ( O T e F ) S b ( O T e F ) - 3 S 0 C 1 F Key bond lengths and bond angles for the CC1 , C B r , and C(OTeF ) cations and secondary contacts to Sb(OTeF ) ~ and S0 C1F are provided in Figures 2-4. 3

5

6

3

5

6

2

+

5

3

5

6

2

+

+

3

5

6

3

2


+

5

3


406

+

+

Figure 2. (a) Crystal structure ofCCl Sb(OTeF )i. (b) A view of the CCl cation, with key bond lengths and bond angles, showing the two-fold positional disorder around the crystallographic inversion center. 3

5

3

82



407

Figure 3. (a) Crystal structure ofCBr Sb(OTeF ) S0 ClF. (b) A view of the CBr cation with key bond lengths and bond angles. 3

5 6

2

82

3



408

Figure 4. (a) Crystal structure ofC(OTeF ) Sb(OTeF ) -3S0 ClF. The key geometric parameters for C(OTeF ) are: C-O, 1.258(15) -1.313(16) Â; Ζ O-C-O, 119(1) -121(1)°; Ζ C-O-Te, 125.5(7) -132.7(9)°. (b) A view of the C(OTeF ){ cation, showing the contacts between the carbon atom and an oxygen atom from each of two S0 CIF molecules in the crystal lattice. 5 3

5 6

2

5 3

5

82

2


409 +

+

(a) CCl Sb(OTeF )6 and CBr Sb(OTeF )6~S0 ClF. The trigonal planar C C 1 cation in CCl Sb(OTeF ) " is positionally two-fold disordered about the crystallographic inversion center (Figure 2), but its geometry is unaffected by the disorder. In contrast, the C B r cation in CBr Sb(OTeF ) " S0 C1F is not disordered (Figure 3). In both cases, the three halogen atoms are crystallographically independent and carbocation planarity is not imposed by symmetry. The C - X bond lengths of each cation are all equal within ±3σ and the X - C - X angles are all equal to the ideal trigonal planar value within ±3σ, giving the expected D symmetry. The C - C l and C - B r bond lengths are found to be shorter than in CC1 [1.751(13) A], CFC1 [1.75(1) A ] and C B r (1.91(4) A ) by ca. 0.15 A, 0.13 A, and 0.10 A, respectively, as expected for positively charged species [also see calculated Charge and Bonding in CF„X _„ (X = CI, Br; η = 0-3) and C(OTeF ) ]. In both the C C 1 and C B r salts, one short cation-anion C - F contact [2.962(9) A and 3.09(2) A, respectively; cf. the sum of the carbon and fluorine van der Waals radii, 3.10, 3.30 A] occurs and approaches the carbon at angles of 3° (CC1 ) and 8° (CBr ) with respect to the C symmetry axis. Additionally, longer C - F contacts [CC1 , 3.464(9), 3.574(11) and 3.574(11) A; C B r , 3.39(2) A] approach above and below the CX -plane at angles of 4, 13 and 37° (CC1 ) and 8° (CBr ), respectively/The bond length and bond angle trends are consistent with the previously noted trend of decreasing contact angle with decreasing contact distance in a number of carbocation structures. The structures indicate that the Sb(OTeF ) " anions are very weakly coordinated to the carbon centers. The occurrence of cation-anion contacts is a common feature, and the C - F contact distances are comparable to those observed in CI A1(0C(CF ) ) " (the shortest is 3.26 A) and in (wC F C H ) ( C H ) C F A s F f [3.01(2) and 3.07(2) A]. The chlorine and bromine atoms also interact with the fluorine atoms of the anion and, in the case of the C B r salt, with the oxygen atoms of S0 C1F [ C l - F : 2.833(5) - 3.022(5) A; B r - F : 2.977(9) - 3.301(11) A; B r - O : 2.778(13), 2.839(12) A] (Figure 5). These interactions are shorter than or are at the limit of the sum of the halogenfluorine (oxygen) van der Waals radii ( C l - F , 3.15, 3.22 A; B r - O , 335, 337 A; B r - F , 3.30, 3.32 A) and are apparently a consequence of the positive charges on the halogen atoms [also see calculated charge Distributions in C C 1 \ C B r , and C ( O T e F ) and Correlations with Their Solid State coordination]. The Br—O contacts, which occur with the oxygen atoms of two S0 C1F solvent molecules, are shorter than the secondary C - F cation-anion contacts in the C C 1 and C B r salts and are likely responsible for the absence of disorder in theCBr structure. 3

5

+

3

5

2

+

3

3

5

6

+

+

3

3

5

6

2

3h


94

95

4

96

3

4

+

3

+

5

+

3

+

3

3

97

71

+

+

3

3

+

3

3

+

3

+

3

+

3

3

24

5

+

2 3

3

3

3

4

29

+

3

6

4

6

6

5

2

1

+

3

2

97

71

97

+

3

71

97

71

+

3

5

3

2

+

+

3

3

+

3

+

(b) C(OTeF ) Sb(OTeF ) "\3S0 ClF. The crystal structure of C(OTeF ) Sb(OTeF ) ~3S0 ClF consists of Sb(OTeF ) " anions that are well separated from the cations and the solvent molecules, while two of the three S0 C1F solvent molecules are oxygen coordinated to the carbon atom of the cation (Figure 4). There are no noticeable differences between the geometric 5

3

5

6

2

+

5

3

5

6

2

5

6

2



410

Figure 5. Diagrams showing the halogen-fluorine/oxygen and carbonfluorine/oxygen contacts for the X-ray crystal structures of (a) CCl{ in CCWSb(OTeFs) - and β) CBri inCBr Sb(OTeF ) SO£lF. +

6

3

47

5 6


411 parameters of the two coordinated and one non-coordinated S0 C1F molecule in the C(0TeF ) Sb(0TeF ) ~ 3S0 C1F structure. The C ( O T e F ) cation is isoelectronic and isostructural with the known B(OTeF ) molecule. The C(OTeF ) cation is only the second example of a trioxy-substituted carbocation to have been isolated and characterized in the solid state by X-ray crystallography, the first being the AsF ~ salt of the trigonal planar acidium ion of carbonic acid, C ( O H ) . The O - C - 0 angles of the C ( O T e F ) cation are equal, within ±3σ, to the ideal 120° angle expected for a trigonal planar arrangement. Unlike B(OTeF ) and C ( O H ) , which have B 0 and C 0 arrangements that are planar by symmetry ( C point symmetry), the planarity of the C 0 moiety of C(OTeF ) is not forced by symmetry, and the three OTeF groups bonded to the central carbon atom are crystallographically independent. Despite the low local crystallographic symmetry of C ( O T e F ) (CO, the conformational geometry of the cation is very close to the optimized Czh gas-phase geometry of this cation and the known solid state and calculated gas-phase geometries of B ( O T e F ) . The tellurium and axial fluorine atoms are slightly out of plane and lie to one side of the C 0 plane by 0.087 and 0.149 Â, respectively. The C - 0 bond lengths are similar to those in C ( O H ) [1.231(4) A], C H C ( O H ) [1.265(6), 1.272(6) A ; 1.261(7), 1.273(7) A ), and H C ( O H ) (1.239(6), 1.255(5) A]. As expected for a positively charged isoelectronic species, the C - 0 bond lengths are shorter than the B - 0 bond lengths of B(OTeF ) [1.358(6) A ] and the C - O - T e bond angles, which range from 125.7(7) to 132.4(9)°, are similar to those in B(OTeF ) [132.3(4)°]. The bond lengths and bond angles in the OTeF groups are in good agreement with those observed for the OTeF groups of the Sb(OTeF ) " anion and other OTeF derivatives. 2

+

5

3

5

6

2

+

5

3

98

5

+

3

5

3

6

+

42

3

+

5

3

+


5

3

3

3

3

3/l

+

3

5

3

5

+

5

3

98

82

5

3

3

+

3

42

36

+

3

37

2

38

+

2

98

5

3

98

5

3

5

5

5

6

5

73,74

The C ( O T e F ) cation has two C - 0 contacts [2.690(17) and 2.738(18) A] with two S0 C1F solvent molecules (Figure 4), which are both nearly perpendicular to the trigonal C 0 plane, approaching the carbon atoms at angles of 1 and 3° with respect to the pseudo three-fold symmetry axis of the cation. The contact distances are shorter than the sum of carbon and oxygen van der Waals radii (3.15, 3.20 A) and the C - F contacts in CCl Sb(OTeF ) " and C B r S b ( O T e F ) ~ S 0 C l F ; but are similar to the C - F contacts observed in ( C H ) C F A s F - [2.66(1), 2.78(1) A] and in ( w - C F C H ) ( C H ) C F A s F [2.78(1), 2.79(1) A]. These interactions with the weak Lewis base, S0 C1F, reflect the high positive charge borne by the carbon atom and its substantial electrophilicity. (c) Calculated Charge Distributions in C C 1 , C B r , and C(OTeF ) and Correlations with Their Solid State Coordination Environments. In the X ray crystal structures of CCl Sb(OTeF ) " and C B r S b ( O T e F ) ~ S 0 C l F , t h e chlorine and bromine atoms of the C C 1 and C B r cations interact with the fluorine atoms of the anion and, in the case of the C B r salt, with the oxygen atoms of S0 C1F as shown in Figures 2, 3, and 5. These interactions are shorter than or are at the limit of the sum of the accepted halogen-fluorine/oxygen van +

5

3

2

3

97

71

+

3

5

6

+

3

5

6

2

+

3

+

2

6

3

6

4

6

5

6

32

2

+

+

3

+

3

+

3

5

+

5

6

3

82

3

+

3

5

6

2

+

3

+

3

2


412 der Waals radii ( C l - F , 3.15, 3.22 A; B r - O , 335, 337 A; B r - F , 3.30, 3.32 A; I - F , 3.50, 3.45 A). These contacts are consistent with the positive charges that have been allocated to the halogen atoms of these cations in computational studies. The I - F contacts in CI A1(0C(CF ) ) ~ range from 3.29 to 3.58 A and suggest less cation-anion interaction through the halogen ligands despite the net positive charges allocated to the iodine atoms may, in part, be a consequence of the diffuse nature of the positive charges on the larger iodine ligands. The Sb(OTeF ) ~ salts also exhibit long contacts between the carbon atoms of C C 1 [2.962(9)^3.574(11) A] and C B r [3.09(2), 3.39(2) A ] and the fluorine atoms of the anions which are at the limit of or longer than the sum of the carbon and fluorine van der Waals radii (3.10, 3.30 A). The long C - F contacts of these structures are comparable to those observed in C I A l ( O C ( C F ) ) " (3.26, 3.69, 3.76 A) and are consistent with the negative charges that have been allocated to the carbon centers of all three trihalomethyl cations. [also see calculated charge Distributions and Bonding in CF„X _„ (X = C l , Br; η = 0-3) and C t O T e F s ) ^ ] . With the exception of the shortest C - F contact distance in CI A1(0C(CF ) ) ~, no other C - F contacts approach the carbocation center of C I along the pseudo three-fold axis of its vacant ρ orbital. The coordination behaviors of the C X (X = C l , Br, I) cations in their presently known salts contrast with the C—F contact distances and contact angles in (m'CF C H )(C H )CF As Fn [3.01(2), 3.07(2) A], (mC F C H ) ( C H ) C F A s F - (2.78(1), 2.79(1) A), and ( C H ) C F A s F - [2.66(1), 2.78(1) A]. A l l three salts exhibit carbocation environments in which the trigonal planar cation interacts with fluorine ligands of neighboring AsF ~ or A s F " anions along the trajectory of the vacant ρ orbital of carbon to give trigonal bipyramidal coordination at the carbocation center. Moreover, the C - F contact distances are significantly shorter than the sum of the carbon and fluorine van der Waals radii (vide supra). The study notes that the coordination behaviors of these monofluorinated carbocations are consistent with positive charges at the carbocation center. The substantial positive charge on carbon was confirmed by calculations for ( C H ) C F at the MP2/cc-pVTZ level of theory, which also provided geometric parameters that are in good agreement with those of the experimental structure. The experimental geometric parameters for ( C H ) C F are taken from ref 29 and the calculated values are given in square brackets: C - C , 1.413(13), 1.450(13) A [1.431 A]; C - F , 1.285(11) A [1.319 A]; Z C - C - C , 126.1(8)° [130.3°]; Z F - C - C , 116.5(8), 117.3(8)° [114.8°]. N B O natural charges; methyl C (-0.740), central C (0.922), F (-0.192). Valencies; methyl C (3.956), central C (4.000), F (1.836). Ionic bond orders: C - C (0.127), C - F (1.131). The coordination behaviors of the C X ( X = C l , Br, I) cations also contrast with that of the C ( O T e F ) cation in the crystal structure of C(OTeF ) Sb(OTeF )6~3S0 ClF (Figure 4). In this instance, the carbon atom 97

71

97

71

97

71

47

+

2 3

3


5

97

71

3

3

4

6

+

82

+

3

3

97

+

71

2 3

3

3

3

4

47

+

3

+

3

3

3

4

+

3

+

3

+

3

6

4

6

5

2

+

3

6

4

6

+

5

6

3

2

6

29

6

2

n

47

+

3

2

+

3

47

2

+

3

+

5

+

5

3

3

82

5

2


413 is coordinated to two oxygen ligands of two S0 C1F molecules which again results in trigonal bipyramidal coordination around the central carbon atom, with C O contacts [2.69(2), 2.74(2) À] that are significantly less than the van der Waals radii sums for the oxygen and carbon atoms (3.15, 3.20 Â). The C—Ο contact distances and coordination around carbon are again consistent with the calculated positive charge on carbon (1.30) at the HF/(SDB)-cc-pVTZ level of theory. Moreover, this charge is similar to those predicted for C F (1.57), B F (1.56) and B(OTeF ) (1.45) at the HF/(SDB-)cc-pVTZ level of theory. It is worth noting that the homologous series of H .„C(ChH)„ (Ch = O, S, Se, Te) cations has been investigated by quantum mechanical calculations (natural population analysis calculations at the MP2(full)/LANLlDZ + P' level). The carbon atom is positively charged for C(OH) (1.212), whereas the charges on carbon for the remaining members of the series are all negative, with the negative charge increasing upon descending group 16. This trend agrees well with that determined for the C X ( X = F, C l , Br, I) series. 2

97

71

+

3

3

82

5

3

+


3

99

+

3

+

47

3

Fluorine-Containing Trihalomethyl Cations Preliminary studies have revealed that the chlorofluorocarbons (CFCs) CFC1 (Freon-11) and CF C1 (Freon-12) are oxidized, albeit more slowly, by XeOTeF Sb(OTeF ) " in S0 C1F at -78 °C but that CF C1 (Freon-13) and COC1F are not oxidized at temperatures approaching room temperature. Thus far, the C F C 1 cation has been synthesized (eq 16) and characterized by C 3

2

2

+

5

5

6

2

3

+

1 3

2

+

+

CFC1 + XeOTeF Sb(OTeF ) " -> CFCl Sb(OTeF ) - + C10TeF + Xe 3

5

5

6

2

1 9

5

19

6

(16)

5

1 3

and F N M R spectroscopy. The F (168.6 ppm) and C (214.3 ppm) chemical shifts are significantly deshielded with respect to those of its parent, CFC1 [6( F), -1.1 ppm; 5( C), 117.1 ppm; J ( F - C ) , 335 Hz; S0 C1F solvent at -80 °C]. The large increase in J ( F - C ) coupling in going from CFC1 (335 Hz) to CFC1) (429 Hz) is consistent with the increase in s-character in going from sp -hybridization to sp -hybridization at the carbon center. The C F C 1 cation is unambiguously established by observation of the secondary isotope shift on the F resonance arising from C1 and C1, which gives three peaks in the correct intensity ratios corresponding to the isotopomers F C C 1 , FC C1 C1 , and F C C 1 (Figure 6). It was shown by C and F N M R spectroscopy that the C F C 1 cation undergoes ligand exchange with CFC1 at -50 °C over a period of several hours to give CCl Sb(OTeF ) " and CF C1 (eq 17). Furthermore, the highly electrophilic C F C 1 cation and C10TeF react, with redox elimination of chlorine, to give the CFCl(OTeF ) cation (eq 18) which has also been 3

19

13

!

I9

13

2

!

, 9

1 3

3

3

2

+

2

19

35

37

35

+

2

35

37

+

37

+

2

1 3

19

+

2

3

+

3

5

6

2

2

+

2

5

+

5

+

+

CFC1 + CFCl Sb(OTeF ) - -> CCl Sb(OTeF ) - + CF C1 3

2

5

6

3

5

6

2

2


(17)

414

35

CF CI

+ 2

10 Hz I

1 35

37


CF CI CI

4

3 7

CF CI;

168.3

168.1

168.2

5i9p(ppm, from C F C I ) 3

δ, ppm 1 9

13

F

J, Hz

X

19

C

Isotope Shift, ppm 2

13

F- C

A

, 9

F

(

3 7 / 3 5

C

CFCL

-1.1

117.1

334.6

-0.0079

CFCI/

168.2

213.2

429.3

-0.0137

19

19

|

)

13

Figure 6. The F NMR spectrum (470.665 MHz) and F and C (125.770 MHz) NMR parameters for CFCl generated by the reaction of CFiCl^with XeOTeF Sb(OTeF ) ~ and recorded at -78 °C in SOÎF solvent. +

2

+

5

86

5 t


415 +

+

C F C l S b ( O T e F ) - + C10TeF - » CFCl(OTeF ) Sb(OTeF ) ~ + C l 2

5

6

5

5

, 3

5

6

19

(18)

2

13

unambiguously characterized by C and F N M R spectroscopy [6( C) doublet, 175.4 ppm, \ / ( C - F ) = 399.3 Hz; 6( F) quintet, 90.0 ppm, for fluorine bonded to carbon, V ( F - F ) = 9.7 Hz; the quintet pattern arising from coupling to the equatorial fluorines, F , of the OTeF group shows a secondary isotope shift, A F( C1) = -0.0099 ppm, arising from one chlorine atom bound to carbon]. Evidence for the existence of the CFC1 cation in the solid state has been obtained from Raman spectroscopy. The Raman spectrum of CFCl Sb(OTeF ) ", synthesized in S0 C1F solvent at -78 °C according to eq 16 and isolated as a white solid, was obtained at -160 °C. The study provided the vibrational frequencies for C F C 1 (C ) [vÂO, not observed; v (B ), 1224 cm* ] v (A,), 649 cm' ; v (B,), 618 cm" ; v (B ), 448 cm" ; v (A,), 337 cm" ] which were assigned with the aid of electronic structure calculations and are in good agreement with the calculated values [MP2/cc-pVTZ; vÂj), 1409; v (B ), 1191 cm' ; v (A,), 678 cm' ; v (B,), 618 cm' ; v (B ), 455 c m ; v ( A 0 , 338 cm' ]. The reaction of C F C 1 and XeOTeF Sb(OTeF ) " at -78 °C in S0 C1F has also been studied by N M R spectroscopy (eq 19). It is proposed that the l 3

1 9

19

19

l9

e

e

2

5

37/35


+

2

86

+

2

5

6

2

+

2

1

2v

5

1

1

2

2

1

4

6

1

2

3

5

1

1

1

2

2

1

4

6

2

3

1

+

2

2

5

+

5

6

2

+

C F C 1 + X e O T e F S b ( O T e F y -> [CF Cl ]Sb(OTeF ) "" + C10TeF + X e (19) 2

2

5

5

2

5

6

5

+

CF C1 cation is generated, but is not observed because it rapidly undergoes halogen exchange reactions to generate C F C 1 , CC1 , CFC1 , and CF C1 according to eq 20-22. This result is not unexpected as CF C1 is destabilized 2

+

2

+

3

3

3

+

2

+

(20)

+

[CF C1 ] + C F C l - > [CFC1 ] + CF C1 2

2

2

2

+

3

(21)

+

[CFC1 ] + C F C 1 -> [CF C1 ] + CFC1 2

2

2

2

+

3

(22)

+

[CF C1 ] + CFC1 -> C C 1 + CF C1 2

3

3

3

+

with respect to C F C 1 and CC1 * by virtue of the greater inductive effect of fluorine [see calculated charge Distributions and Bonding in C F X . / ( X = CI, Br; η = 0-3) and C(OTeF ) ]. Nuclear magnetic resonance spectroscopy has also been used to study the formation of the mixed bromofluoromethyl cation C F B r . Generation of this cation has proven more difficult than CFC1 because halogen exchange is more facile in the case 5f bromine, and because the product, BrOTeF , is more reactive towards the C F B r cation with respect to redox elimination of B r . Thus, it is proposed that the reaction of C F B r with XeOTeE Sb(OTeF ) ~ in 2

3

29

W

3

+

5

3

+

2

+

2

5

+

2

2

+

2

2

5


5

6

416 +

S0 C1F at -78 °C initially yields C F B r , which rapidly undergoes halogen exchange with C F B r t o give C F B r , C B r , and C F B r (eq 23-25). Although 2

2

+

2

2

+

2

3

3

+

+

C F B r + XeOTeF Sb(OTeF ) - -> [CF Br ]Sb(OTeF ) ~ + BrOTeF + Xe 2

2

5

5

+

[CF Br ] + C F B r 2

2


CFBr

+

+ CF,Br

2

-> C F B r

2

-> C B r

2

6

+

2

+

5

6

5

(23)

+ CF Br

2

(24)

3

+ CF Br

3

(25)

3

+

the reactivity of C E B r has precluded its direct detection by N M R spectroscopy, the C F B r cation persists for several hours at -80 °C. As with CFC1 , the F (207.9 ppm) and the C (208.4 ppm) chemical shifts are significantly deshielded with respect to those of its parent, C F B r [5( F), 7 ppm; 5( C), 45.9 ppm; ' y ( F - C ) , 372 H z ] , with a ^ F - C ) coupling (471 Hz) that is again indicative of an sp -hybridized carbon center. The F N M R spectrum also showed that BrOTeF was not present in solution, but reacted with both C F B r and C F B r to generate F C O T e F and F B r C O T e F . While the former is known, the latter is the first example of a mixed bromofluoro-teflate of carbon. Attempts to grow crystals of CFBr Sb(OTeF ) " at -50 °C over several hours yielded SbBr Sb(OTeF ) ~ instead by the following proposed reaction pathway (eq 26-29): 2

+

2

+

19

1 3

2

I9

3

13

,9

,3

100

l 9

, 3

2

19

5

3

2

2

3

5

101

2

5

+

2

5

6

+

4

5

6

C F B r + Sb(OTeF ) ~ -> F BrCOTeF + [Sb(OTeF ) ]

(26)

[Sb(OTeF ) ] - » Sb(OTeF ) + 0 ( T e F )

(27)

2

5

5

CFBr

+ 2

6

2

5

5

5

3

5

2

+ BrOTeF -> B r F C O T e F 5

5

+ 5

5

2

+ Br

(28)

2

+

2 Sb(OTeF ) + 2 B r -> SbBr Sb(OTeF ) ~ 5

3

2

4

5

(29)

6

+

The SbBr Sb(OTeF ) ~ S0 C1F was characterized by single crystal X-ray diffraction, and the parameters determined for the cation and anion proved to be in excellent agreement with those obtained from the crystal structure of SbBr Sb(OTeF ) ". Attempts to generate persistent C F in solution failed, likely because of the high electrophilicity of C F \ The reaction between C F B r and XeOTeF Sb(OTeF ) ~ presumably generates insipient [CF ]Sb(OTeF ) ~, which then abstracts F or OTeF " to give C F and F C O T e F , respectively (eq 30 and 31). The resulting neutral antimony species are, themselves, unstable (see 4

5

+

6

2

74

4

5

6

+

3

3

3

+

+

5

5

6

3

5

4

3

+

[CF ]Sb(OTeF ) " -> C F + [Sb(OTeF ) (OTeF ] 3

5

6

4

5

5

5

6

5

4


(30)

417 +

[CF ]Sb(OTeF ) ~ - » F C O T e F 3

5

6

3

5

+ [Sb(OTeF ) ] 5

(31)

5

eq 12 and 13). +

Indirect evidence for C F as a reactive intermediate is also indicated by the formation of the F C B r O T e F cation (eq 32) which has been 3

+

3

5

+

[CF ]Sb(OTeF ) ~ + BrOTeF 3

5

6

, 3

+

- » F CBrOTeF Sb(OTeF ) "

5

3

5

19

5

(32)

6

19

19

characterized by C and F N M R spectroscopy [5( F), -12.0 ppm; ô ( F ) , -44.6 ppm; 5( F), -48.1 ppm; J ( C - F ) , 323 Hz; V ( F F ) , 177 Hz; V ( F - % ) , 4.3 Hz]. eq


19

!

I3

I9

19

19

eq

ax

1 9

+

Gas-Phase Thermodynamics of Reactions of XeOTeF with CF X4.„ (X = Cl, Br; #i = 0-3) The calculated standard gas-phase enthalpies (AH ) and Gibbs free energies (AG ) corresponding to eq 33 are given in Scheme 1. The spontaneity 5

n

0

0

+

C F A - * + X e O T e F S b ( O T e F y -> C F X . / S b ( O T e F ) " + X O T e F + Xe 5

5

w

3

5

6

5

(33)

with which CF C1 . and CF Br4.„ (n = 0-3) are oxidized decreases dramatically with each successive addition of a fluorine ligand. This trend is in agreement with the experimental findings. For example, CF C1 and XeOTeF Sb(OTeF ) ~, are unreactive at temperatures as high as 0 °C in S0 C1F solvent, with AH = -5.41 and AG = -34.06 kJ mol" indicating that the reaction is only slightly favored in the gas phase at 298.15 K . In contrast, the corresponding reaction with CC1 occurs rapidly at -78 °C in S0 C1F solvent, with AH = -158.4 and AG = -191.9 kJ mol" . Standard heats of reaction leading to the formation of the CF„Br - cations are 55-65 kJ mol' more favorable than their CF C1 _„ analogues, in accord with the anticipated relative ease of oxidation of a bromine ligand versus a chlorine ligand. W

4

M

n

+

3

5

5

86

6

0

2

0

1

82

4

0

0

2

1

+

3

1

+

M

W

+

3

Calculated Charge Distributions and Bonding in CF„X . (X = CI, Br; #1 = 0-3) and C(OTeF ) Several prior studies have assessed the bonding and relative stabilities of the C X ( X = F, CI, Br, and I) cations in terms of relative degrees of σ and ρ(π) donation from the halogen atom to the carbon center. ' ' The Natural Bond Orbital (NBO) analyses have shown that the σ effect is strongly withdrawing in the case of fluorine and weakly donating in the cases of chlorine, bromine, and iodine (I > Br > CI), with the ρ(π) back-donation trend following the order I > Br > C l > F, and are mirrored N B O charge analyses (Figure 7). Figure 8 provides analogous assessments of charge distributions and σ and ρ(π) donation for the mixed fluoro-chloro and fluoro-bromo trihalomethyl 3

n

+

5

3

+

3

29 32 43



5

+

5

+

2

+

+

+

2

3

5

+

5

5

+

+

-

-

-

-

CCI 3

+

>

>.

>

+

CF 3

2

2

+

+

+

0

5

1

+ BrOTeF + Xe

5

5

+ BrOTeF + Xe

5

+ ClOTeFs + Xe

CF Br + BrOTeF + Xe

CFBr

3

+

CBr + BrOTeF + Xe

3

>

4

+

+ ClOTeFs + Xe

CF

2

+

CF CI + ClOTeFs + Xe

2

+ ClOTeFg + Xe

>

•

>· CFCI

*•

-61.1

-140.1

-188.3

-223.2

-5.4

-73.3

-121.3

-158.4

Scheme 1. Gas-phase values of Aff and AG (U mot ) for the reactions ofXeOTeF/ CF„K .„(X=Cl, Br; η = 0-3) (MP2/cc-pVTZ).

CF Br + XeOTeF

2

CF Br + XeOTeF

3

5

5

CFBr + XeOTeF

4

5

+ XeOTeF

CBr + XeOTeF

CF3CI

2

CF CI + XeOTeF

CFCb + XeOTeF

4

CCI + XeOTeF

Ahf


0

with

-89.6

-173.2

-220.1

-263.3

-34.1

-106.5

-153.0

-191.9

AG


Figure 7. Calculated geometries and natural (NBO) charges for CXf (X CI, Br; MP2/cc-pVTZ//MP2/cc-pVTZ) andCI [MP2/(SDB-)ccp VTZ//MP2/(SDB-)cc-p VTZJ. }



420

T

Figure 8a. Calculated geometries for CFJT .„ (X = Cl, Br; 3

MP2/cc-pVTZ).



421

Figure 8b. Calculated natural (NBO) charges for CF„X . MP2/cc-p VTZ//MP2/CC-P VTZ).

+

3 n

(X = CI, Br;


422 +

+

cations with C F , C C 1 \ and C B r included for comparison. The individual σand π- components are relatively constant throughout the series. The C - F σcontribution is withdrawing but opposite to the C - F ρ(π) contribution which, like all C - X contributions, are donating with respect to carbon. In all cases the π-donation, which increases along the series F < C l < Br < I, serves to stabilize the positive carbon center and dominates the σ-contribution, which also increases in the same direction for CI, Br, and I. With the exception of negative charges on the fluorine ligands, the halogen ligands are always positively charged (see Calculated charge Distributions in CC1 , C B r , and C ( O T e F ) and correlations with Their Solid State coordination Environments) and the charge on carbon becomes significantly more positive with each additional fluorine ligand that is added. Based on calculated carbon charges, the C F C 1 and CFBr cations are, thus far, the most electrophilic trihalomethyl cations that have been shown to persist. While rapid halogen exchange involving the more electrophilic C F C 1 and C F B r cations may preclude their isolation, the isolation and characterization of a stable salt of the S0 ClF-solvated C ( O T e F ) cation, which has a carbon charge and σ- and π-components, in the absence of solvation, that are similar to those of C F , suggests that C F may still be attainable as a persistent entity. 3

3

3

+

+


3

+

3

5

3

+

2

+

2

+

+

2

2

+

2

5

+

3

+

3

3

Conclusions and Outlook The present studies provide a new oxidative route to carbocations and the first solid state characterization of the previously reported C C 1 and C B r cations as well as the novel C(OTeF ) cation. The cations have been stabilized as salts of the preformed oxidatively resistant and weakly coordinating Sb(OTeF ) " anion, which avoids the use of more strongly coordinating anions derived from strong Lewis acid ligand acceptors, such as SbF . Despite the anticipated high electrophilicity of their cations, these salts are stable up to at least -20 °C, with CCl Sb(OTeF ) " being stable at room temperature for indefinite periods of time. In addition, the CBr(OTeF ) and Br(OTeF ) cations, and the neutral precursor to C(OTeF ) , C(OTeF ) , have been characterized by C and F N M R spectroscopy. X-ray crystallographic studies show, in all cases, that the carbocation center is planar in the absence of symmetry constraints imposed by the crystal lattice. Despite the strong Lewis acidities predicted for perhalomethyl cations, the C C 1 and C B r cations are well isolated in their respective crystal lattices and possess only long secondary C - F contacts to fluorine atoms of the Sb(OTeF ) " anion that do not significantly exceed the sum of the van der Waals radii of carbon and fluorine. Secondary X—F and Χ · · Ό (X = CI, Br) contacts that are close to the sums of the van der Waals radii of the halogen and an oxygen atom of cocrystallized S0 C1F or a fluorine atom of the anion exist for C C 1 and C B r that are in accord with the calculated positive charges on the halogen atoms of both cations. +

+

3

3

+

5

5

3

6

5

+

3

5

6

+

5

+

2

5

2

+

5

, 3

3

5

4

19

+

3

+

3

5

6

+

2

3


+

3

423 Computational studies reproduce the experimental geometric parameters of CC1 , C B r and C(OTeF ) , and the vibrational frequencies of C C 1 and C B r , and have been extended to their OTeF derivatives. Contrasting with the C C 1 and C B r cations, the C(OTeF ) cation possesses two short C - 0 contacts to the oxygen atoms of two weakly basic, co-crystallized S0 C1F molecules, which is consistent with the high positive charge on carbon predicted by electron structure calculations and which approximates that of the highly electrophilic C F cation. Nuclear magnetic resonance spectroscopy has also been used to great advantage to establish the existence of CC1 , C B r , CFC1 , C F B r and C(OTeF ) " as persistent cations in S0 C1F at low temperatures, as well as to monitor carbocation formation, ligand substitution by means of redox elimination, and decomposition pathways in these systems and in on-going studies. Attempts to obtain evidence for persistent CF C1 , C F B r , and C F have met with limited success. The study has presently been limited by the Sb(OTeF ) ~ anion and the OTeF ligand, which provide sufficiently strong nucleophilic sites that can be attacked by these extremely strong electrophiles. While the use of XeOTeF Sb(OTeF ) " has proven successful in providing an oxidative routes to CC1 , C B r , and C(OTeF ) in the solid state and solution, the only examples of persistent mixed chlorofluoro- and bromofluoro-cations that have been characterized in the course of these studies are the monofluorinated CFC1 and C F B r cations. Although both cations are sufficiently long-lived to permit their low temperature characterization in solution by N M R spectroscopy, the only fluorine-containing trihalomethyl cation to have been isolated in the solid state is the CFC1 which, thus far, has been characterized by low-temperature Raman spectroscopy. Prospects for stabilizing CF C1 , C F B r , and C F will hinge upon the use of a more weaklycoordinating, less nucleophilic, anion that is resistant to oxidative attack by the noble-gas cation, as well as to electrophilic attack by the fluoro-carbocation, and the formation of other reaction products that are not susceptible to electrophilic attack by the fluoro-carbocation. +

+

3

+

3

5

+

3

3

+

82

3

5

+

+

3

+

3

5

3

2

+

3


+

+

3

5

6

+

3

2

2

+

+

2

5

+

2

6

2

+

3

5

+

5

5

+

6

+

3

+

3

5

+

3

+

2

2

+

2

+

2

+

2

+

3

Acknowledgement We thank the donors of the Petroleum Research Fund, administered by the American Chemical Society, for support of this work under ACS-PRF No. 40959-AC3.

References 1.

Olah, G . Α.; Rasul, G.; Yudin, A . K . ; Burrichter, Α.; Prakash, G. K . S.; Chistyakov, A . L . ; Stankevich, I. V . ; Akhrem, I. S.; Gambaryan, N . P.; Vol'pin, M . E. J. Am. Chem. Soc. 1996, 118, 1446-1451 and references therein.


424 2. 3. 4. 5. 6.


7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29.

Martin, R. H . ; Lampe, F. W.; Taft, R. W. J. Am. Chem. Soc. 1966, 88, 1353-1357. Lias, S. G.; Eyler, J. R.; Ausloos, P. Int. J. Mass Spectrom. Ion Phys. 1976, 19, 219-239. Jacox, M . E.; Milligan, D. E. J. Chem. Phys. 1971, 54, 3935-3950. Jacox,M.E.;Chem. Phys. 1976, 12, 51-63. Vančik, H . ; Percač, K . ; Sunko, D. E. J. Am. Chem. Soc. 1990, 112, 74187419. Abboud, J.-L. M.; Castano, O.; Herreros, M.; Elguero, J.; Jagerovic, N.; Notario, R.; Sak, K . Int. J. Mass Spectrom. Ion Processes 1998, 175, 35-40. Prochaska, F. T.; Andrews, L. J. Am. Chem. Soc. 1978, 100, 2102-2108. Prochaska, F. T.; Andrews, L. J. Phys. Chem. 1978, 82, 1731-1742. Jacox, M. E. Chem. Phys. 1984, 83, 171-180. Forney, D.; Jacox, M. E.; Irikura, K . K . J. Chem. Phys. 1994, 101, 82908295. Maclagan, R. G . A . R. J. Mol. Struc. (Theochem) 1991, 235, 21-24. Langford, M. L.; Harris, F. M. Int. J. Mass Spectrom. Ion Processes 1990, 96, 111-113. Sheng, L . ; Q i , F.; Gao, H . ; Zhang, Y . ; Y u , S.; Li, W . - K . Int. J. Mass Spectrom. Ion Processes 1997, 161, 151-159. Seccombe, D. P.; Tuckett, R. P.; Fisher, Β. Ο. J. Chem. Phys. 2001, 114, 4074-4088. Lee, M. S.; Park, M.; Chung, Y. J. Korean Phys. Soc. 2003, 42, 493-498. Domazou, A . S.; Quadir, M. Α.; Buehler, R. E. J. Phys. Chem. 1994, 98, 2877-2822. Prochaska, F. T.; Andrews, L. J. Chem. Phys. 1978, 68, 5568-5576. Prochaska, F. T.; Andrews, L . J. Chem. Phys. 1978, 68, 5577-5586. Truszkowski, S.; Ichikawa, T. J. Phys. Chem. 1989; 93, 4522-4526. Olah, G. Α.; Heiliger, L . ; Prakash, G . K . S. J. Am. Chem. Soc. 1989, 111, 8020-8021. Olah, G. Α.; Rasul, G.; Heiliger, L . ; Prakash, G. K . S. J. Am. Chem. Soc. 1996, 118, 3580-3583. Krossing, I.; Bihlmeier, Α.; Raabe, I.; Trapp, N. Angew. Chem., Int. Ed. Engl. 2003, 42, 1531-1534. Laube, T. Chem. Rev. 1998, 98, 1277-1312. Müller, T.; Juhasz, M . ; Reed, C. A . Angew. Chem., Int. Ed. Engl. 2004, 43, 1543-1546. Kato, T.; Reed, C. A . Angew. Chem., Int. Ed. Engl. 2004, 43, 2908-2911. Kato, T.; Stoyanov, E. S.; Geier, J.; Grützmacher, H . ; Reed, C. A . J. Am. Chem. Soc. 2004, 126, 12451-12457. Antel, J.; Klaus, H.; Jones, P. G.; Mews, R.; Sheldrick, G . M.; Waterfeld, A . Chem. Ber. 1985, 118, 5006-5008. Christe, K . O.; Zhang, X . ; Bau, R.; Hegge, J.; Olah, G. Α.; Prakash, G. K . S.; Sheehy, J. A. J. Am. Chem. Soc. 2000, 122, 481-487.



425 30. Minkwitz, R.; Reinemann, S.; Blecher, Ο.; Hartl, Η.; Brüdgam, I. Inorg. Chem. 1999, 38, 844-847. 31. Laube, T.; Bannwart, E.; Hollenstein, S. J. Am. Chem. Soc. 1993, 115, 1731-1733. 32. Christe, K . O.; Hoge, B.; Boatz, J. Α.; Prakash, G . K . S.; Olah, G . Α.; Sheehy, J. A . Inorg. Chem. 1999, 38, 3132-3142. 33. Davlieva, M. G.; Lindeman, S. V.; Neretin, I. S.; Kochi, J. K . J. Org. Chem. 2005, 70, 4013-4021. 34. Minkwitz, R.; Meckstroth, W.; Preut, Η. Z. Anorg. Allg. Chem. 1992, 617, 136-142. 35. Minkwitz, R.; Meckstroth, W.; Preut, Η. Ζ. Natuforsch., B: Chem. Sci. 1992, 48, 19-22. 36. Jönsson, P.-G.; Olovsson, I. Acta. Crystallogr. 1968, B24, 559-564. 37. Kvick, Α.; Jönsson, P.-G.; Olovsson, 1. Inorg. Chem. 1969, 8, 2775-2780. 38. Minkwitz, R.; Schneider, S.; Seifert, Μ. Ζ. Anorg. Allg. Chem. 1996, 622, 1404-1410. 39. Lindeman, S. V . ; Neretin, I. S.; Davlieva, M . G.; Kochi, J. K. J. Org. Chem. 2005, 70, 3263-3266. 40. Caira, M. R.; De Wet, J. F. Acta. Crystallogr. 1981, B37, 709-711. 41. Paulsen, H.; Dammeyer, R. Chem. Ber. 1973, 106, 2324. 42. Minkwitz, R.; Schneider, S. Angew. Chem., Int. Ed. Engl. 1999, 38, 714715. 43. Frenking, G.; Fan, S.; Marchand, C. M.; Grützmacher, H. J. Am. Chem. Soc. 1997, 119, 6648-6655. 44. Kaupp, M.; Malkina, O. L.; Malkin, V . G. Chem. Phys. Lett. 1997, 265, 5 5 59. 45. Robinson, Ε. Α.; Johnson, S. Α.; Tang, T.-H.; Gillespie, R. J. Inorg. Chem. 1997, 36, 3022-3030. 46. Robinson, Ε. Α.; Heard, G. L . ; Gillespie, R. J. J. Mol. Struct. 1999, 485486, 305-319. 47. Mercier, Η. P. Α.; Moran, M . D.; Schrobilgen, G. J.; Suontamo, R. J. J. Fluorine Chem. 2004, 125, 1563-1578. 48. Lehmann, J. F.; Mercier, H. P. Α.; Schrobilgen, G. J. Coord. Chem. Rev. 2002, 233-234, 1-39. 49. Minkwitz, R.; Bäck, B. In Inorganic Fluorine Chemistry, Toward the 21st Century, Thrasher, J. S., Strauss, S. H . , Eds.; A C S Symposium Series 555; Washington, DC, 1994; Chapter 6, pp 90-103. 50. Minkwitz, R.; Nowicki, G . Angew. Chem., Int. Ed. Engl. 1990, 29, 688689. 51. Minkwitz, R.; Molsbeck, W. Ζ. Anorg. Allg. Chem. 1992, 607, 175-176. 52. Minkwitz, R.; Bernstein, D.; Preut, H . ; Sartori, P. Inorg. Chem. 1991, 30, 2157-2161. 53. Hartl, H.; Nowicki, J.; Minkwitz, R. Angew: Chem., Int. Ed. Engl. 1991, 30, 328-329.



426 54. Clegg, M. J.; Downs, A . J. J. Fluorine Chem. 1989, 45, 13. 55. Stein, L. J. Fluorine Chem. 1982, 20, 65-74. 56. Brown, D. R.; Clegg, M . J.; Downs, A . J.; Fowler, R. C.; Minihan, A . R.; Norris, J. R.; Stein, L . Inorg. Chem. 1992, 31, 5041-5052. 57. Drews, T.; Seppelt, K. Angew. Chem., Int. Ed. Engl. 1997, 36, 273-274. 58. Frohn, H.-J.; Klose, Α.; Henkel, G. GIT Fachz. Lab. 1993, 37, 752-755. 59. Frohn, H.-J.; Klose, Α.; Henkel, G . In 11th Winter Fluorine Conference; St. Petersburg, F L , January 1993; Paper 58. 60. Lentz, D.; Seppelt, K . Angew. Chem., Int. Ed. Engl. 1978, 17, 355-356. 61. Birchall, T.; Myers, R. D.; de Waard, H . ; Schrobilgen, G . J. Inorg. Chem. 1982, 21, 1068-1073. 62. Sladky, F. O. Monatsh. Chem. 1970, 101, 1559-1570. 63. Sladky, F. O. Monatsh. Chem. 1970, 101, 1571-1577. 64. Sladky, F. O. Monatsh. Chem. 1970, 101, 1578-1582. 65. Sladky, F. O. Angew. Chem., Int. Ed. Engl. 1970, 9, 375-376. 66. Lentz, D.; Seppelt, K. Angew. Chem., Int. Ed. Engl. 1978, 17, 356-361. 67. Lentz, D.; Seppelt, K. Angew. Chem., Int. Ed. Engl. 1979, 18, 66-67. 68. Fir, Β. Α.; Mercier, Η. P. Α.; Sanders, J. C. P.; Dixon, D. Α.; Schrobilgen, G. J. J. Fluorine Chem. 2001, 110, 89-107. 69. Keller, N.; Schrobilgen, G . J. Inorg Chem. 1981, 20, 2118-2129. 70. Sanders, J. C. P.; Schrobilgen, G . J. J. Chem. Soc., Chem. Commun. 1989, 1576-1578. 71. Bondi, A . J. Phys. Chem. 1964, 68, 441-451. 72. Elliott, H . S. Α.; Lehmann, J. F.; Schrobilgen, G . J., unpublished results. 73. Mercier, Η. P. Α.; Sanders, J. C. P.; Schrobilgen, G . J. J. Am. Chem. Soc. 1994, 116, 2921-2937. 74. Casteel, W. J.; Kolb, P.; LeBlond, N.; Mercier, Η. P. Α.; Schrobilgen, G . J. Inorg. Chem. 1996, 35, 929-942. 75. Syvret, R. G . ; Mitchell, Κ. M.; Sanders, J. C. P.; Schrobilgen, G . J. Inorg. Chem. 1992, 31, 3381-3385. 76. Selig, H.; Holloway, J. H., In Topics in Current Chemistry-, Boschke, F. L . , Ed.; Springer-Verlag: Berlin, 1984; Vol. 124, pp 33-90. 77. Brownstein, M.; Gillespie, R. J. J. Am. Chem. Soc. 1970, 92, 2718-2721. 78. Dean, P. A . W.; Gillespie, R. J. J. Am. Chem. Soc. 1969, 91, 7260-7264. 79. Mercier, Η. P. Α.; Moran, M . D.; Sanders, J. C. P.; Schrobilgen, G . J.; Suontamo, R. J. Inorg. Chem. 2005, 44, 49-60. 80. Holloway, J. H . ; Hope, E. G. Adv. Inorg. Chem. 1998, 46, 51-100. 81. Drews, T.; Seppelt, Κ. Ζ. Anorg. Allg. Chem. 1991, 606, 201-207. 82. Mercier, Η. P. Α.; Moran, M . D.; Schrobilgen, G. J.; Steinberg, C.; Suontamo, R. J. J. Am. Chem. Soc. 2004, 126, 5533-5548. 83. Seppelt, Κ. Ζ. Anorg. Allg. Chem. 1973, 399, 65-72. 84. Seppelt, K . Chem. Ber. 1973, 106, 1920-1926. 85. Gerken, M.; Kolb, P.; Wegner, Α.; Mercier, Η. P. Α.; Borrmann, Η.; Dixon, D. Α.; Schrobilgen, G. J. Inorg. Chem. 2000, 39, 2813-2824.


427 86. 87. 88. 89. 90.

Mercier, H. P. Α.; Moran, M. D.; Schrobilgen, G . J., unpublished results. Vladimiroff, T.; Malinowski, E. R. J. Chem. Phys. 1967, 46, 1830-1841. Hartman, J. S.; Schrobilgen, G . J. Inorg. Chem. 1972, 11, 940-951. Gombler, W. Spectrochim. Acta., Part A 1981, 37, 57-61. Timoshkin, A . Y.; Suvorov, Α. V . ; Bettinger, H . F.; Schaefer, H . F. I. J. Am. Chem. Soc. 1999, 121, 5687-5699. 91. Lentz, D.; Seppelt, Κ. Ζ. Anorg. Allg. Chem. 1983, 502, 83-88. 92. The J ( C - T e ) coupling of 57 Hz was calculated using the relationship J = ( γ J / γ ) , where A = Te Β = C, and γ and γ , are the gyromagnetic ratios of Te and Te, respectively. 93. The calculated value of J ( C - T e ) is 53 Hz (see ref 92). 94. Cohen, S.; Powers, R.; Rudman, R. Acta. Crystallogr. 1979, B35, 16701674. 95. Cockcroft, J. K.; Fitch, Α. Ν. Z. Kristallogr. 1994, 209, 488-490. 96. More, M.; Baert, F.; Lefebvre, J. Acta. Crystallogr. 1977, B33, 36813684. 97. Pauling, L., The Nature of the Chemical Bond. 3rd ed.; Cornell University Press: Ithaca, New York, 1960, ρ 260. 98. Sawyer, J. F.; Schrobilgen, G . J. Acta. Crystallogr. 1982, B38, 15611563. 99. Ohlmann, D.; Marchand, C. M.; Grutzmacher, H . ; Chen, G. S.; Farmer, D.; Glaser, R.; Currao, Α.; Nesper, R.; Pritzkow, H . Angew. Chem., Int. Ed. Engl. 1996, 35, 300-303. 100. Muller, N.; Carr, D. T. J. Phys. Chem. 1963, 67, 112-115. 101. Schack, C. J.; Christe, K . O. J. Fluorine Chem. 1990, 47, 79-87. 2

13

123

n

n

AB

A

123

A'B

A'


13

Α

123

2

A

125

13

123


(Y = Cl, Br) and CX - American Chemical Society

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