The dehydrofluorination of primary amine-metalloid fluorides—IV The reaction of primary amines or alcohols with silicon tetrafluoride in the presence of tertiary amines

J. inorg, nucl. Chem., 1972, Vol. 34, pp. 75-87.

THE

Pergamon Press.

Printed in Great Britain

DEHYDROFLUORINATION OF PRIMARY AMINE-METALLOID FLUORIDES-IV

THE REACTION OF PRIMARY AMINES OR ALCOHOLS WITH SILICON TETRAFLUORIDE IN THE PRESENCE OF TERTIARY AMINES'* J A M E S J. H A R R I S and B. RUDNER Koppers Co., Inc., Monroeville, Pa. 15146 (Received 21 December 1970) Abstract-Aliphatic or aromatic primary amines are shown to react with silicon tetraltuoride in the presence of tertiary amines to give fluorosilazanes and trialkylammonium fluorosilicate salts. In a similar manner aliphatic or aromatic hydroxyl compounds react with silicon tetrafluoride in the presence of tertiary amines to give alkyl or aryl silicates and trialkylammonium fluorosilicate salts. Fluorosilicate anions such as SiFs-, Si2Fi-~, or Si3Fi-~ are formed, depending upon the amine and the reaction conditions. Reacting tertiary amines and fluorosilicic acid or silicon tetrafluoride gave a series of fluorosilicate salts containing SiF~-2, Si2Fi-~, or SiFs- anions again depending upon the amine and the reaction conditions. For the tertiary amines studied, the hexafluorosilicate salt was less stable than some salts of higher silicon tetrafluoride content; the hexafluorosilicate salt of trimethylamine could not be obtained free of water of hydration.

INTRODUCTION

PROCEDURES for the dehydrofluorination of primary amine adducts of boron trifluoride and phosphorus pentafluoride have been described by us in previous reports[la-c]. This manuscript describes the dehydrofluorination of primary amine-silicon tetrafluoride adducts. The same procedure is also applied to the preparation of organic silicates. Silicon tetrafluoride forms 1:2 adducts with primary amines [2] but the dehydrofluorination of these adducts to covalently bound silicon-nitrogen compounds has received little attention. In contrast to the reaction of silicon tetrachloride with primary amines which results in aminolysis of the silicon-chlorine bond [3], no product other than the adduct was detected from silicon tetrafluoride and primary amines[4]. Reported dehydrofluorination of adducts of primary amines and silicon tetrafluoride has been achieved under quite vigorous conditions [5, 6] by the action of metals, metal hydrides, or organometallic compounds *Presented in part at the 147th Meeting of the American Chemical Society, Philadelphia, Pa., April 1964, see Abstracts p. 25 I. 1. Part I: J. Am. chem. Soc. 90, 515 (1968). lb. Part II: J. Org. Chem. 33, 1352 (1968). lc. Part III: lnorg. Chem. 8, 1258 (1969). 2. V. Gutmann, P. Heilmayer and K. Utvary, Mh. Chem. 92,322 (1961). 3. H. H. Anderson, J. Am. chem. Soc. 73, 5802 (1951). 4. U. Wannagat and H. Burger, .4ngew. Chem. intern, edn. 3, 446 (1964). 5. B.J. Aylett and G. M. Burnett, U.S. Pat. 3,234,148 (Feb. 8 1966). 6. M. Allan, B.J. Aylett and I. A. Ellis, lnorg. Nucl. Chem. Lett. 2, 261 (1966). 75

76

J . J . H A R R I S and B. R U D N E R

at 300°C or with metal amides [7a]. The pyrolysis of secondary amine-silicon tetrafluoride adducts has been shown[7b] to cause dehydrofluorination in good yields; poor yields were obtained from primary amine-silicon tetrafluoride adducts unless the amine was sterically hindered. Phenyl[8-10] and alkyl[11] silicon fluorides have been reported to react with primary amines to give aminolysis of the Si-F bond. Primary amine adducts of silicon tetrafluoride cleave cyclosilazanes to give fluorosilazanes [12]. With alcohols, silicon tetrafluoride forms a weak adduct [ 13a] which dissociates reversibly; no alcoholysis of the Si-F bond was reported. A more recent report [ 13 b] indicates that methanol causes methanolysis of one of the Si-F bonds in SiF4 giving CH3OSiF3. Further methanolysis was slow. Complete alcoholysis of SiF4 in the presence of ammonia has been claimed [ 14] in the patent literature. Equilibria involving the pentafluorosilicate anion, perhaps anticipated by an earlier finding that fluorosilicic acid solutions add an equimolar quantity of SiF4 [15], have been reported by many observers [ 16-18]. Several salts of SiFs- have been reported [1, 19-23]. Several salts of the similarly pentacoordinated RSiF4-anion have also been reported[20, 24, 25]. Polymeric anions of the formula o,n~5.+1 ¢; r~c.+l)have not been reported; polymeric anions formed by fluorine bridging have been reported for arsenic and antimony pentafluoride [26-28] and for niobium pentafluoride[28]. It has been suggested that silicon tetrachloride adducts form polymeric anions by chlorine bridging between silicon atoms [29]. 7a. U. Wannagat, H. Burger and F. Hoefler, Mh. Chem. 99, 1198 (1968). 7b. B.J. Aylett, I. A. Ellis and C. J. Porritt, Chem. and Ind. 489 (1970). 8. V. Chugunov, Zh. obshch. Khim. 23, 777 (1953). 9. L. Tansjo, Acta chem. scand. 18, 465 (1964). 10. N. Ishikano and K. Kurada, J. chem. Soc. Japan 89, 421 (1968). 11. L. Tansjo, Acta chem. scand. 18, 456 (1964). 12. U. Wannagat, F. Hoefler and H. Burger, Mh. Chem. 99, 1186 (1968). 13a. J. P. Guertin and M. Onyszchuk, Can.J. Chem. 41, 1477 (1963). 13b. J. L. Margrave, K. G. Sharp and P. W. Wilson, lnorg. Nucl. Chem. Lett. 5, 995 (1969). 14. K. Scheel and H. W. Schmidt, U.S. Pat. 2,814,635 (Nov. 26, 1957) to Kali-Chem. Akt. 15. S. M. Thomsen, J . A m . chem. Soc. 72, 2798 (1950). 16. K. Kleboth, Mh. Chem. 99, 1177 (1968). 17. L. N. Arkhipova, S. Ya Shpunt, Tr. Nauchn. Inst. po Udabr L. Insektofung 208, 69 (1965). 18. Ya A. Buslaev, N. S. Nikolaev, and M. P. Gustyakova, lsvest. Sibir del Akad., Nauk S S S R 10, 57 (1968). 19. K. Kuroda and N. Ishikawa, J. chem. Soc. Japan 91, 77 (1970). 20. F. Klanberg and E. L. Muetterties, lnorg. Chem. 7, 155 (1968). 21. H. C. Clark, P. W. R. Corfield, K. R. Dixon and J. A. Ibers, J. Am. chem. Soc. 89, 3360 (1967); H. C. Clark and K. R. Dixon, Chem. Comm. 717 (1967); H. C. Clark, K. R. Dixon and J. G. Nicolson, lnorg. Chem. 8, 450 (1969). 22. K. Kleboth, Mh. Chem. 101,357 (1970). 23. E. Heckel, Ger. Pat. 1,230,025 (Dec. 8 1966), to Deutsch Geld und Sflber Scheideanstalt vorn Roessler. 24. R. Mueller and C. Dathe, Z. anorg, allg. Chem. 343, 150 (1966). 25. R. Mueller, Z. Chem. 5, 220 (1965). 26. J. Bacon, P. A. W. Dean and R. J. Gillespie, Can. J. Chem. 47, 1655 (1969). 27. P.A.W. Dean and R. J. Gillespie, J. Am. chem. Soc. 91, 7264 (1969). 28. A.J. Edwards and (3. R. Jones, J. chem. Soc. A, 1491 (1970). 29. H.J. Campbell-Ferguson and E. A. V. Ebsworth, J. chem. Soc. A, 708 (1967).

Primary amine-metalloid fluorides- IV

77

RESULTS

Several amines in benzene were treated with SiF4 at 25°C. As shown in Table 1 all reacted except for tetraaminobiphenyl (which did react in the presence of a tertiary amine) and o-aminobenzenethiol. The reaction mixtures were usually very viscous and difficult to filter. The adducts were more stable after isolation than in benzene. For example, the aniline adduct dissociated if refluxed in benzene but sublimed at 80-100°C with only partial loss of SiF4. The reversibility of adduct formation with SiF4 and primary amines is in marked contrast to the primary amine adducts of phosphorus pentafluoride [lb] (which disproportionate at 80°-100°C) and of boron trifluoride [1 c] which disproportionate in some instances at 200°C but do not dissociate. In no instance was there evidence for rearrangement of the amine-SiF4 adducts to any aminolysis products. The weakness of the amine-SiF4 adducts is illustrated by the attempted dehydrofluorination of aniline-silicon tetrafluoride with diisopropylethylamineboron trifluoride [ 1c]. Only trianilinoborane and diisopropylethylammonium tetrafluoroborate were found. The SiF4 was lost as its aniline adduct served only as a source of aniline. Fluorosilazanes were readily synthesized by reacting either primary amines or their silicon tetrafluoride adducts with a tertiary amine in the presence of silicon tetrafluoride, according to the stoichiometry of Equations (1) and (2) depending upon the tertiary amine, as explained later. RNH2 + 2R3N + 3SiF4 ~- I(RNSiF2)n + 2R3NH+SiFs -

RNHe+2R3N+(m+ 1)SiF4 ~

(RNSiF2),+ ~ + 1

(1)

+ • -(m+l) (2) (RzNH)m+lSlmFsra+l

Equation (2) represents the formation of species such as the Si2F~- anion. In contrast to the corresponding reactions [ lb, 1c] of boron trifluoride and phosphorus pentafluoride, Equations (1) and (2) were reversible in refluxing benzene since refluxing the completed reactions under N2 caused complete loss of silicon tetrafluoride and recovery of the free amines. Filtration of the soluble fluorosilazanes from the insoluble fluorosilicate salt was often difficult because of the viscous nature of the solutions. The systems were very moisture sensitive and could not be handled in the atmosphere. Methylamine, aniline, and 2-amino-4-chlorotoluene gave mixtures of silazanes indicated by molecular weight measurement to be between trimeric and pentameric. The absence of N - H i.r. absorptions and an approximate 1 : 1 nitrogensilicon ratio indicated the products were cyclic. The fluorosilazanes sublimed at reduced pressure when heated, Polymers of the composition (CHzNSiF2)n have been said[5] to be stable at 500°C, and inert to water and other nucleophilic reagents. The product which we obtained from methylamine did not polymerize to a polymer stable to heat and water, when pyrolyzed. The results obtained from the dehydrofluorination experiments using primary amines are summarized in Table 2. The silicon tetrafluoride addition products of multi-functional amines such as

78

J . J . H A R R I S and B. R U D N E R

•

~

r ~ ,_.~

0

o e~ o

~1"4

.-~

o

7 ~

¢.I o

,.d

0

o o

~6 e~

z z,.%

z ~

o

~

=

z

i

~'~

"~ "

79

Primary amine-metalloid fluorides- IV Table 2. Reaction of primary amines, tertiary m i n e s , and silicon tetrafluoride Primary amine

Tertiary amine

Aniline 10.2g,0.11m 10-2 g, 0.11 m 10.2 g, 0.11 m

SiF4

Solvent

Conditions

Pyridine 17.4g,0.22m 17.4 g, 0.22 m 17.4 g, 0.22 m

excess excess excess

benzene benzene benzene

4hr, 25 ° 4 hr, 80 ° 4 hr, 80 °

10.2g,0.11m

17.4g,0.22m

excess

Aniline 15.4 g,0.16 m

(C2H~)3N 33.4 g, 0.33 m

Aniline 10.2 g,0.11 m

(CH3)~N 13-5 g, 0.22 m

excess

benzene

8 hr, 25 °

10.2 g, 0.11 m

(i-C3HT)~C2HsN 28.5 g, 0-22 m

excess

benzene

1 hr, 25 °

CHaNH2 67g, 2.16m

(CH3)aN 246g, 4.17m

380 g 3.64m

benzene

4 hr, 50 °

(CH3)zN

excess

benzene

15 hr, 25 °

(i-CaH7)2C2HsN- none

benzene

2-Amino4-chlorotoluene 28.3 g, 0.2 m aniline-

SiF4 19.7 g

Tetrahy- 4hr, 80 ° drofuran excess benzene 1 hr, 25 °

26.6 g, 45 m

BF3 38.4 g, 0.22 m

4 hr, 25 °

Products

(C6HsNH2)2SiF4; (C5H~N)2SiF4 As above, if refluxed under SiF4 Aniline, pyridine when refluxed under N2 (CoHsNH2)2SiF4; (CsHsN)~SiF4 A benzene-immiscible oil con

(CeHsNSiF2)n, 15'2 g, 88%t [(CHa)sNH+]sSizFT?, 27'4 g, 84%~t (C6HsNSiF2),, 10"7 g, 61%t (i-CzH7)~C2HsNH+SiF5 -, 37'5 g, 67% (CHsNSiF2)n, 82"4 g, 40%§ 610 g benzene-insoluble fluoro silicate salt~ 34.8 g aromatic product H 52 g trimethylammonium fluorosilicate, see text (C~HsNH)aB 11 "5 g, 0"04 m, 75% (i-C3HT)2C2HsNH+BF4 35.8 g,0-165 m

0.08m

*The i.r. spectra of the oil indicated it contained triethylammonium fluorosilicate salt and dehydrofluorination products of aniline-silicon tetrafluoride. Refluxing under N2 caused the oil to decompose to aniline and triethylamine. tAnal. Calc. for CsHsNSiF2, %N, 8.91; %Si, 17.86; %F, 24.17 Found; %N, 8-41; %Si, 17.15; %F, 23"57 ~The composition of the fluorosilicate formed varied from Si2F~3 to one approximating SiFs-, as discussed in the text. ~Both completely and partially dehydrofluorinated products were obtained. Fractionation with benzene and petroleum ether (35-50*) gave products with and without N - H single i.r. absorptions. The N - H band free product had ebuUioscopic (benzene molecular weight of 718, between a trimer (615) and tetramer (820). §The N-methylfluorosilazane sublimed at 80°C at 1 mm and melted at 108-112 °. Ebullioscopic molecular weight (benzene) was 495; the molecular weight of CH~NSiF~ units is 95.1. Pyrolysis at 350°C gave a non-volatile paste which was less air-sensitive than the starting material, indicating some polymerization had occurred. Analysis: Calc. for CHsNSiF2, %C, 12.63; %N, 14.73; %Si, 29.53; %F, 39.94 Found; %C, 12.59, %N, 14'36; %Si, 30.10; %F, 39.15

80

J.J. HARRIS and B. RUDNER

o-phenylenediamine, o-aminophenol, and 3,3',4,4'-tetraaminobiphenyl were readily dehydrofluorinated by triethylamine in the presence of silicon tetrafluoride. The reaction products combined with the by-product triethylammonium fluorosilicate salt to give a benzene-insoluble oil. Removal of the benzene left solids which were not separable by various solvents. Dissolving the fluorosilicate salt in water caused some decomposition of the fluorosilizane; consequently separation with water was not practical. Surprisingly, 3,3',4,4'-tetraaminobiphenyl which did not react with silicon tetrafluoride alone, did so in the presence of triethylamine. Alcohols (or phenol) and silicon tetrafluoride reacted in the presence of tertiary amines to give alkyl or aryl silicates, according to Equations (3) and (4): 4 R O H + 4R3N + 5SiF4 . ~ ( R O ) 4 S i + 4 R 3 N H + S i F 5 -

4ROH + 4 R 3 N + ~ +

1SiF, ~

(3)

(RO)4Si+m-~(R,NH+)m+1(SimFsm+,)'(4)m+"-

Alkoxysilicon fluorides were also formed. Preparation of alkoxysilicon fluorides by the proper reagent stoichiometry should be possible, but was not studied. The difunctional catechol, like the difunctional amines, combined with the fluorosilicate salt to form an oil from which the product could not be separated. The results are shown in Table 3. The choice of tertiary amine is critical in the dehydrofluorination reaction. Pyridine, despite the fact that it forms a stable fluorosilicate salt[30], and its silicon tetrafluoride adduct is sufficiently weak that it decomposes in refluxing benzene, did not cause dehydrofluorination, perhaps reflecting the weakly basic nature of pyridine to hydrogen ions. Trimethyl-, triethyl-, and diisopropylethylamine which are more basic to the hydrogen ion than pyridine, and which form highly dissociated adducts with silicon tetrafluoride [31 ], readily caused dehydrofluorination. The type of fluorosilicate anion formed depends upon the tertiary amine used. Triethylamine or diisopropylethylamine gave their SiF5- salts. With triethylamine the by-product SiF5- salt, an oil, dissolved the product, hindering its recovery, Trimethylamine gave either its Si2F,1-3 salt, or a strongly fuming product having a somewhat variable composition near that required for the SiF5salt. The i.r. spectrum of the product had absorptions characteristic of the SiF5anion[20, 21], but lacked the absorption at 720 cm -1 shown by SiF6-2, Si2Fl1-3 or other fluorosilicate anions (discussed later). This salt of trimethylamine was found only when the reaction mixture contained at least some excess (CH3)3NSiF4, perhaps accounting for its variable composition. Systems of tertiary amine fluorosilicate salts, amines, fluorosilicic acid, and SiF4 (the latter in aprotic systems) were studied to obtain further insight into the tertiary amine fluorosilicate salts formed during the dehydrofluorination procedures. A series of salts shown in Table 4 was formed. 30. E. Sehnell, Mh. Chem. 93, 67 (1962). 31. C.J. Wilkins and D. K. Grant, J. chem. Soc. 927 (1953). Only the SiF4 adduct of trimethylamine is considered in this reference. However the adducts of triethyl- and diisopropylethylamine a r e certainly even more dissociated because of their greater steric requirements.

Primary amine-metalloid fluorides- IV

o

O

81

¢..}

E "~ 0

~ 0 ~

E 0

0 ~

a ~

o ~

i

oaO

0 0 N

.~

¢-

p.

0 'N

..~ 0 t"l

e.,

0 ~D

d b.

z~

C'4

2~

~o

°

87

J . J . HARRIS and B. R U D N E R

~do~

!g,

o

o

- ' Z o°

.~ "~ ~ ..,9,

i

iZ

"

0

~ ~.~

.,= . ~ . ~ ' , ,

• ~ ~

~ ~..~~.

zz z ~ z - ~ z . ~

~~."z.,.'z..

,

0

Primary amine-metaUoid fluorides- IV

83

The most stable salt of either trimethylamine or triethylamine was that of the Si2Fl1-3 anion. This composition was obtained from either of these amines by: (1) (2) (3) (4) (5)

sublimation of the hexafluorosilicate salt sublimation of salts of higher SiF4 content reacting the amine with fluorosilicic acid to a pH of 5 treating the pentafluorosilicate salt with aqueous amine treating the hexafluorosilicate salt with fluorosilicic acid

For trimethylamine the Si2FH3- salt was also obtained by either saturating the SiFt 2- salt in benzene with SiF4 or by removing volatiles from a solution of the SiFs- salt in acetonitrile. The Si2FI? salt of diisopropyle thylamine was obtained from the sublimation of the SiF02- salt. Compositions corresponding to the Si3F46- salt were obtained for tfiethylamine by placing its SiFs- salt under reduced pressure at 25°C, and for diisopropylethylamine by neutralizing the amine with fluorosilicic acid to a pH of 5. This composition for the latter amine sublimed unchanged. The SiFs- salts oftrimethyl-, triethyl-, and diisopropylethylamine were formed by adding SiF4 to any of the lower salts in acetonitrile, or in benzene for the latter two amines. This synthesis should be a general means of preparing the SiFssalts, providing the lower salt used has at least a slight solubility in aprotic media. Previously reported syntheses have used silica, hydrofluoric acid, and the chloride salt [21], or the fluoride salt and silicon tetrafluoride [20]. The stability of the trialkylammonium pentafluorosilicate salts increased as the amine size in.creased, in agreement with results reported [21] by others for the quaternary nitrogen salts. The bulky diisopropylethylamine gave a stable SiFssalt. The smaller triethylamine gave a SiFs- salt which was stable in benzene, as well as acetonitrile, but which lost SiF4 and gave the Si3F4~ salt upon removal of solvent. With the smaller trimethylamine, solvent free solids having analyses near, and the infrared spectra of the SiFs- ion were obtained as a by-product in the dehydrofluorination procedures, providing excess trimethylamine adduct of silicon tetra.fluoride was present. The salt was at best an unstable fuming species. A composition corresponding to the SiFs- salt of trimethylamine was stable in acetonitrile, but not in benzene. All attempts to recover the salt from acetonitrile by crystallization at low temperatures with or without non-solvent were unsuccessful; only the Si2F2~- salt was recovered. Surprisingly, the SiF62- salts were more difficult to prepare than salts of higher silicon fluoride content. The SiF62- salt of trimethylamine could not be obtained anhydrous since attempts to remove the last traces of water caused loss of trimethylamine. The anhydrous product recovered nearest in composition to the SiF62- salt had the composition NSio.54F3.26. The salt isolated having the mole ratio required for the SiF62- salt analysed for the dihydrate. The procedure of Clark et al. [21] for preparing tetramethylammonium hexafluorosilicate gave the SizF~- salt when applied to trimethylamine. The SiF6- salt of triethylamine was obtained by treating the Si2F~- salt in methanol with excess amine foll0wed by drying at 100°C at 1 mm. The SiF6 2- salt of diisopropylethylamine was obtained by neutralizing the amine to a pH of 7 with fluorosilicic acid. The solids remaining after devolatization at 1 mm at 60 ° were extracted with chloroform to give the

84

J.J. HARRIS and B. RUDNER

SiF62- salt. The hexafluorosilicate salts of triethylamine and diisopropylethylamine were very hygroscopic, unlike the salts of higher silicon fluoride content which had moderate to low hygroscopicity. The Si2F~- and Si3F~6 salts do not appear to be either fortuitious mixtures of the SiF62- and SiFs- salts or double salts similar to the well-known[32] double salt of ammonium fluoride and ammonium hexafluorosilicate. The Si2F~- salt of trimethylamine and triethylamine and the Si3F4~ salt of triethylamine cannot be mixtures containing the SiF5- salt since the latter salt for these amines is not stable in the absence of solvent. Also the Si2F~- salt of these amines sublimed unchanged and is formed by subliming mixtures containing amine in excess of this composition by loss of amine, or SiF4 in excess of this composition by loss of SiF4. The Si2F~salt of diisopropylethylamine which might be a mixture of the SiFe 2- and SiFssalts was shown by X-ray powder patterns to be a distinct product. The composition corresponding to the Si3F~ salt of diisopropylethylamine sublimes unchanged, possibly indicating it to be a separate species. The compositions corresponding to the Si2F~- and Si3F14~salts have a stoichiometry consistent with their formation by fluorine bridging at corners of siliconfluorine octahedra. Compositions formed by the sharing of fluorine at the edges of silicon-fluorine octahedra were not detected, except for SiFs- which might be a dimer formed by the addition of SiF4 to the edge of SiF62-. If this addition occurred further addition of SiF4 to the anion might be expected; none was detected in the systems studied. Fluorosilicate solutions have been reported [ 16] to consist of an equilibrium of SiF4, SiFs-, and SiF62- species. Salts containing anions such as Si2Flal would then be formed by addition of SiFs- to SiF62- in the presence of a cation giving a stable salt. The particular anion in the salt isolated will depend on the ratio of SiFs- to SiF62- in the equilibrium and the stabilizing effect of the cation on the fluorosilicate salt. Large cations stabilize the SiFs- salt perhaps because their smaller charge to radius ratio results in less interaction with, and consequently less distortion of the SiF5- anion. A smaller cation might induce asymmetry into the SiFs- anion increasing its Lewis acidity and causing it to be more susceptible to attack by donor molecules such as the SiF62- anion (which might be a fluorine bridge donor) to give intermediate fluorosilicate salts, or to F- to give SiF6 2-. Similarly the SiFs- salts were more stable in acetonitrile because the basic solvent solvated the anion preferentially, preventing attack of the SiFs- anion by SiFe2- or F-. I.R. spectra The i.r. absorptions of the fluorosilicate salts (Nujol mulls), and the CHaCN solutions of the trimethyl- and triethylamine salts of SiFs- are shown in Table 5 for the N H and SiF regions. The CHoCN solutions of the SiFs- salt of trimethyland triethylamine absorbed at 880, and 788 cm -1 and 882 and 789 cm -1 respectively, about identical to the reported absorptions of (875 and 790 cm -1) [20] and (874 and 785 cm -1) [22] for the SiFs- anion. The metastable dehydrofluorination product from trimethylamine absorbed at 878 and 778 cm -1 again close to the reported values for the SiFs- anion. The absorptions of the SiFn- salt of diisopropylethylamine which were at 890 and 756 cm -~ differed somewhat from these values. The intermediate fluorosilicate salts which we postulate contain bridged

85

P r i m a r y a m i n e - m e t a l l o i d f l u o r i d e s - IV Table 5. Principle i.r. absorption bands* of amine fluorosilicate salts N H str [ (CH3)zNH+]2SiF6 ~-.2 H 2 0 [ (CH3)3NH+]3Si2F~i (CH~)3NH+SiF5 - (in acetonitrile) Dehydrofluorination product:~ [ (C~Hs)3NH+],,SiF~ 2[ (C2Hs)3NH÷]3Si2F~ [ (C2Hs)3NH+]4Si3F14g (C2Hs)3NH+SiF5 - (in acetonitrile) [ (i-C3Hr)~C2HsNH+]2SiF62[ (i-C:~HT)2C2HsNH+]3Si2F~ [ (i-C.~H~)zC2HsNH+]4SiaF?6(i-C3H7),~C2HsNH+SiFs-

3050 m+ 3050 m 3150 m 3150 m 3030 m 3050 m 3075 m 3075 m 3020 m 3010 m 3030 m 3100 m

SiF A b s o r p t i o n s

877 880 878 808 887 878 882

s s s m s s s

878 s 878 s 890 vs

720 vs 720 vs

790 s 788 s 778 s

720 vs 720 vs 719 vs

788 s 788 s 789 s 787 m 788 s 788 s 756 vs

719 vs 717 vs 720 vs 706 m

* G i v e n in wave n u m b e r s . ~Other b a n d s typical of bonded amine salts were p r e s e n t from 2 5 0 0 - 2 9 0 0 c m -1. CThe product referred to is the by-product fluorosilicate salt obtained w h e n trimethylamine, in slight e x c e s s was used in the dehydrofluorination procedure. T h e mulls were made up and placed on the salt plates in a dry-box. E v e n slight exposure of the mull to air changed the spectra to that of a mixture of hydrated silica and the Si~F~i- salt.

fluorosilicate octahedra had the strong absorption near 720 cm -1 characteristic of the SiF62- anion[30, 33, 34], as well as the absorptions reported for the SiFsanion. The N H stretching vibration had a small tendency to shift to higher frequencies as the SiF4 content of the salt increased, indicating decreasing hydrogen bonding to the anion. The i.r. spectra of the primary amine silicon tetrafluoride adducts shown in Table 6 contain several broad but well-defined absorptions from 700-900 cm -1. Previously reported[2] spectra of primary amine silicon tetrafluoride adducts Table 6. I.r. absorptions of silicon tetrafluoride adducts* Analine 1079 m 862 s 800 s

730 s, sh 715s

o-Phenylenediamine

872 s 838 s 795 s 770 s 7 6 0 - 7 4 6 s, br 725 s

4-Chloro-2-aminotoluene 1045 848 811

o-Aminophenol 1038 m m 800 s

770

748

7 1 5 - 7 0 0 br

728

* G i v e n in wave n u m b e r s . T h e samples were run as Nujol mulls. Only the absorptions in the silicon fluorine region are given. 32. J. F. H o a r d and M. W. Williams, J. Am. chem. Soc. 64, 633 (1942). 33. D. H. Brown, K. R. Dixon, C. M. Livingston, R. H. Nuttal and D. W. A. Sharp, J. chem. Soc. A, 100(1967). 34. R. B. Badachappe, G. H u n t e r , L. D. M c C o r y a n d J . L. Margrave, lnorg. Chem. 5, 929 (1966).

86

J . J . HARRIS and B. R U D N E R

which had been run as KBr pellets gave broad, featureless absorptions from 750-700 cm -1 typical of the SiF62- anion[30, 33, 34] indicating some hydrolysis may have occurred. The spectra of the adducts reported here had medium to strong absorptions near the bands at 760, 800, and 1065 cm -1 previously assigned to the Si-F bonds in the SiF4 adducts of pyridine and isoquinoline[29, 30, 35]. The adducts contained several other bands in this region which may also be associated with Si-F vibrations, but some of which belong to the aromatic substitution vibrations. The fluorosilazanes reported here had several very strong absorptions between 1100 and 600 cm -1 in regions which have been assigned to silicon-nitrogen and silicon-fluorine vibrations, as shown in Table 7. The silicon-nitrogen bond in cyclic silazane trimers and tetramers has been reported[36, 37] to absorb at 1168-1183 cm -1 and at 924-976 cm -~. The silicon-nitrogen bond in linear fluorosilazanes has been reported [7, 12] to absorb at 917-979 cm -1. Table 7. I.r. absorptions of silazanes

(CH~NSiFz)

(CrHsNSiF2)

1055 vs 1010 vs 925s 908s 895s

1087 vs 1022 m 937 920s 853s

~NSiF~) CH3 / 1060 vs 997 m 948 vs 890s 808s

*Given in wave numbers. The samples were run as Nujol mulls. Only the absorptions in the siliconnitrogen and the silicon-fluorine region are given.

The silicon-fluorine bond has been reported[38, 39] to absorb at 950-1031 cm -~ for the asymmetric stretching vibration and at 800-900 cm -~ for the symmetric stretching vibration, with the asymmetric absorption being more intense [40]. In a number of linear fluorosilazanes the silicon-fluorine absorption has been reported[7, 12] to occur at 870-895 cm -1. Both the silicon-nitrogen and silicon-fluorine absorptions are relatively intense because of the bond polarity. The absorptions shown in Table 7 above 1050 cm -~ are probably due to the silicon-nitrogen bond, but the absorptions below this frequency cannot be assigned because both bonds absorb in the same regions and coupling of the vibrations may be expected. 35. I. R. Beattie and M. Webster, J. chem. Soc. 3672 (1965). 36. H. Kriegsmann, Z. anorg, allg. Chem. 298, 223 (1959). 37. G. V. Tsitsishvili, G. D. Bagratishviki, K. A. Andrianov, L. M. Khananashviki and M. L. Kantariya, Bull. Acad. Sci. USSR, Div. Chem. Sci., Eng. Tran. 1123 (1962). 38. U. Wannagat, F. H. Hofler and H. Burger, Mh. Chem. 99, 1185 (1968). 39. (3. J. (3anz and Y. Mikawa, Bull. chem. Soc. Japan 34, 1495 (1961). 40. A. L. Smith, Spectrochim. A cta 16, 87 (1960).

Primary amine-metalloid fluorides- IV

87

EXPERIMENTAL Solvents and amines were obtained from laboratory supply houses. Gaseous amines were used as supplied, while volatile ones were refluxed over Call2, then distilled from, and stored over Call,. Nonvolatile amines, e.g. tetraaminobiphenyl were dried by azeotroping with benzene. Silicon tetrafluoride, from Matheson, was used as received as was fluorosilicic acid from Ozark-Mahoning Co. With the exception of a few autoclave runs, as indicated in the text, all reactions were run in standard laboratory glassware. In a typical reaction, aniline and trimethylamine were added to benzene in a stirred 500 ml flask in which the benzene had been azeotroped 'in situ'. The exit neck of the flask was fitted with a dry-ice cold-finger condenser which discharged to an inert atmosphere through a bubbler to indicate gas flow. Silicon tetrafluoride was added to the flask, whose contents were cooled to 0 °, until its absorption was completed, then the flask was warmed to room temperature in an atmosphere of silicon tetrafluoride. After the reaction was completed the flask was placed under reduced pressure, briefly, to remove excess silicon tetrafluoride from the system. The mixture was then filtered in an inert system, usually in a N2-pressure funnel, but occasionally in a dry-box.

Acknowledgements-Analyses were run in these laboratories, by Galbralth Laboratories or by Schwaxzkopf Microanalytical Laboratory. The X-ray diffraction data were obtained by Dr. Ed Kiffer and the i.r. spectral data were obtained by the author at these laboratories.