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Sa n s , Es t h e r A l m a

REACTIONS OF HALOMETHYL TRISUBSTITUTEDSILANES WITH ALKOXIDES

The Ohio Slate University Ph.D. 1981

University Microfilms International 300 N. Zeeb Road, Ann Arbor, M I 48106 REACTIONS OP HALOMETHYLTRISUBSTITUTEDSILANES

WITH ALKOXIDES

DISSERTATION

Presented in Partial Fulfillment of the Requirements for

the Degree Doctor of Philosophy in the Graduate

School of The Ohio State University

By

Esther Alma Sans, B.A.

The Ohio State University

1981

Reading Committee:

Dr. Harold Shecter Dr. Andrew Wojcicki Dr. Matthew Platz Approved By

Adviser Department of Chemistry To my parents ACKNOWLEDGMENT S

I wish to thank Dr. Harold Shechter for his guidance throughout the course of this research and for his expert advice on the preparation of this manuscipt.

I would also like to express my gratitude to The

Ohio State University and the National Science Foundation for their financial support.

Finally, I would like to thank K. Takeuchi for his encouragement and useful discussions.

iii VITA

September 8 , 1953 Born, Kansas City, MO.

1975 ...... B.A., University of Pennsylvania, Philadelphia, Pennsylvania

1976-1978 ...... Teaching Assistant, Department of Chemistry, The Ohio State University, Columbus, Ohio 43210

1978-1981 ...... Research Associate, Department of Chemistry, The Ohio State University Columbus, Ohio 43210

iv TABLE OF CONTENTS Page

DEDICATION ...... ii

ACKNOWLEDGEMENTS...... iii

VITA ...... iv

LIST OF T A B L E S ...... vi

LIST OF GRAPHS ...... vii

STATEMENT OF PROBLEM ...... 1

HISTORICAL ...... 4

RESULTS AND DISCUSSION ...... 15

SUMMARY ...... 8 8

EXPERIMENTAL...... 91

REFERENCES ...... 127

V LIST OF TABLES

Reactions of (Chloromethyl)trimethylsilane (9) with Nucleophiles ...... 5

Reactions of (Chloromethyl)dimethylvinylsilane (1) with Sodium Methoxide, Isopropoxide and t-Butoxide...... 29

Carbon versus Silicon Attack by Methoxide in Methanol on Halomethylsi lanes 1, !2 and 9. . . 43

Rearrangement versus Cleavage Products in the Reactions of Halomethyl si lanes 1, 2, and 9^ with Methoxide...... ***. . 4 5

Reactions of (Chloromethyl)dimethylphenyl- silanes with Sodium Methoxide in Dioxane . . 62

Phenyl versus Methyl Migration in Reactions of Aryl(chloromethyl)dimethylsilanes with Sodium Methoxide ...... 64

Data Table for Graph 1 ...... 68

Data Table for Graph 2 ...... 70

Reactions of (Chloromethyl)dimethylphenyl- silane (3) with Methoxides in Methanol. . . . 81

Reactions of Halomethyltrimethylsilanes with Methoxides in Methanol ...... 83

Reactions of (Chloromethyl)dimethylphenyl- silane (3) with Methoxides in Bioxane .... 85

Reactions of (Chloromethyl)dimethylphenyl- silane (3) with Sodium Methoxide at Various Temperatures ...... 87

vi LIST OF GRAPHS Graph Page

1. Phenyl versus Methyl Migarion in Reactions of (Chloromethyl)dimethylphenylsilanes and Sodium Methoxide as Correlated with cr Values 67

2. Phenyl versus Methyl Migration in Reactions of (Chloromethyl)dimethylphenylsilanes and Sodium Methoxide as Correlated with cx° Values 69

vii STATEMENT OF PROBLEM

The present study involves investigation of nucleophilic attack on (chloromethyl)trisubstituted- silanes. When a (halomethyl)trialkylsilane is reacted with a nucleophile, a variety of products may result.

The nucleophile may attack on carbon to displace halide

ion, equation 1 .

SiR- ~

N ® | 3 -XG R_SiCH0X -----» N -C X ------► R~SiCH„N (1)

6 ® hA h ‘ 0

Alternately, attack on halogen may occur to yield a

trialkylsilylcarbanion, equation 2 .

N 0 ^ -NX Q R 3SiCH2X ----► R 3SiCH2-X + ► R 3SiCH2 (2)

The nucleophile may act as a base and remove a proton, equation 3.

H P

1 N G R-Si-CHX -----> RoSiCHX^ (3) J -NH

The anion thus formed may expel halide to generate a carbene or do chemistry directly. Finally, the

1 2

nucleophile may attach on the electropositive silicon center, equation 4. Two products can result from

N-SiR,

N ® - W CH_X

R 3 SiCH2X -----► N — Si-CH X (4) I ^ R R,

N-SiCH R this attack. Path a represents loss of the halomethyl anion. Path b illustrates migration of a substituent from silicon to carbon with expulsion of halide ion.

The nature of the nucleophile often determines the type of attack. Nucleophiles such as iodide, sulfur and phosphorus attack on carbon. In contrast, fluoride reacts directly on the silicon center. Alkoxides exhibit both forms of chemistry and will be used in the present study as they best reveal the scope of reactivity avail­ able to halomethylsilanes.

The primary goal of this investigation is to discover how silyl substituents affect the location and type of reaction with a nucleophile. To accomplish this, one silyl methyl group of (chloromethyl)trimethylsilane will be replaced by an unsaturated substituent and the compound subjected to reaction with alkoxide. 3

(Chloromethyl) dimethylvinylsilane (1) and allyl-

(chloromethyl) dimethylsilane (2 ) will be used to determine the influence of an olefinic unit. Electronic demands

will be explored by use of (chloromethyl)dimethy 1 -

(substitutedphenyl)silanes (3 through 8 ).

(CH3 )2 SiCH2Cl Z = H, E-CF3/ m-Cl, £-Cl, p-CH3, £-OCH 3

0-Z 3 4 5 6 7 8

The systems will be further characterized by varying temperature, cation and solvent. HISTORICAL

Since the preparation of the first organosilicon compound in 1863 by Friedel and Crafts, interest in the field has been growing.^ Such compounds have proven to be synthetically useful as well as mechanistically interest­ ing. More recently, attention has been focused on organofunctionalsilanes.

The chemistry of silanes is often remarkably different from that of their carbon analogs. Whitmore and Sommer prepared (chloromethyl)trimethylsilane (9) and found the halide much more susceptible to nucleophilic 2 attack than the analogous neopentylchloride. Various oxygen, nitrogen, carbon and sulfur nucleophiles among others can displace chloride ion leading to substitution on carbon, equation 5. Some examples are shown in Table 1.

N ©

(CH3) 3 SiCH2Cl g (CH3 ) 3 SiCH2N (5)

The low electronegativity of silicon makes it susceptible to nucleophilic attack, thus, halomethyl- silanes may react at the silyl center. Reaction of

(chloromethyl)trimethylsilane (9) with alcoholic sodium

4 TABLE 1

REACTIONS OF CHLOROMETHYLTRIMETHYLSILANE (9)

WITH NUCLEOPHILES N ©

(CH3 ) 3 SiCH2Cl O '4 (CH3) 3SiCH2N -Cl

Nucleophile Product Reference

Nal (CH3 ) 3 SiCH2I (2)

NaOCH, (CH3 ) 3 SiCH 2 OCH 3 (3)

k o 2 cch 3 (CH3 ) 3 SiCH 2 0 2 CCH 3 (4)

(CH_)-SiCH 0 NHCcH n .. (5) C6H 11NH2 O O Z D 11

NH (CH3 ) 3 SiCH2N (6)

(c h 3)3p (CH3) 3 SiCH2® P (CH3) 3 C 1 ® (7)

(CH3) 3 As (CH3) 3 SiCH 2 ^ks(CH3) 3 C I ® (7)

NaCH(C 0 2 C 2 H 5) 2 (CH3 ) 3 SiCH 2 CH 2 C 0 2 H a (6)

NaSC 4 H g-n (CH3 ) 3 SiCH 2 SC 4 H9-n (8)

KSCN (CH3 ) 3 SiCH2SCN (9)

aAfter treatment with KOH and HC1 alkoxides results in alkoxytrimethylsilanes (1 0 ) along 3 with (alkoxymethyl) trimethylsilanes (1 1 ,)/ equation 6 .

NaOR

(CH3) 3 SiCH2Cl ------► (CH3 ) 3 SiOR+ (CH3) 3 SiCH2OR (6 )

9 10 ii

R = CH 3 0% 75%

CH2CH3 11 70

(CH2)3CH3 31 19

The proposed mechanism for formation of 10 involves attack on silicon with expulsion of chloromethide ion, equation 7. The chloromethyl anion protonates and may

ft (CH3)3 ft ROU Ql -^CH-Cl

9 -----► RO -Si-CH 2 C1 ----- ► ROSi(CH 3 ) 3 (7)

10 undergo subsequent displacement. Methyl chloride has been isolated from the alkaline hydrolysis of (chloro­ methyl) siloxanes. Reasons for nucleophilic attack on silicon increasing with length of alkoxide were not defined.

Attack on silicon can lead to another type of product resulting from a unique rearrangement. Reaction

of (chloromethyl)dimethylsilane (1 2 ) with ethanolic 7

potassium hydroxide leads to trimethylsilanol (14), 12 equation 8 . Silane 14 reportedly forms via pentavalent

i (CH3) 2 SiCH2Cl -----¥ (CH3) 2 _Si-CH2-Cl ► (CH^SiC^

OH OH

12 13 14 (8 )

silicon complex (13) which collapses by hydrogen

rearrangement and chloride expulsion.

Migration of a trimethylsilyl group from silicon to

carbon has been reported in the reactions of (chloromethyl)- pentamethyldisilane (15) with sodium alkoxides in alcohol, Q 13,14 equation 9.

CH I J RO® I -Cl® I 6 *

(CH3) 3 SiSiCH2Cl -f RO-Si - CH 2 -C1 -----► ROSiCH2 Si(CH3 )3

(CH3)3Si CH3 15 16 17 (9)

R = CH3, C 2 H 5, iso-C 3 H 7, C 6 H 5

Alkoxydimethyl(trimethylsilylmethyl) silane (17) is claimed to result from decomposition of pentavalent 8

silane 1(5 by rearrangement of a trimetbylsilyl group with

loss of chloride.

(Chloromethyl)dimethylphenylsilane (8 ) has been

shown to react with ethanolic sodium ethoxide to produce 15 benzyldimethylethoxysilane (19), equation 10. Presumably

collapse of intermediate 1J3 with phenyl migration and

Q (CH3}2 « (CH3}2 y OC H \ -C1W I * * (CH_)„SiCH_Cl Z ■» HcC_0— Si-CH_-Cl ------» C oH cOSiCHo0 O Z | Z O Z | _ Z Z D Z 0 0

8 18 19 (10)

chloride expulsion is responsible for the formation of

19. Methyl migration is not observed. Other products

include those of substitution on carbon and reaction on

silicon with displacement of the chloromethyl group.

Reasons for the multiplicity of products and the factors

affecting their distribution are not clear.

Reaction of benzoyldime thy lphenylsilane (20) with

sodium ethoxide yields dimethyl(diphenylmethoxy)ethoxy- 16 silane (24) . Silane 2j4 is believed to form by two

subsequent rearrangmsnts as illustrated in equation 1 1 . Ethoxide attack on 20 initially forms pentavalent silane

21. Collapse of 21_ by phenyl migration from silicon to carbon results in 22. Rearrangement of 2J2 by migration of silicon from carbon to oxygen produces carbanion 23_ whose protonation yields 24. Only products explicable by phenyl migration are found.

Reactions of (chloromethyl)trimethylsilane (9) with strong bases and nucleophiles have been reported. Treat­ ment of 9 with n-butyllithium results in 1,2-bis(trimethyl- silyl) ethylene (27) and 1-n-butyl-l,2-bis(trimethylsilyl)- ethane (28). The authors propose a scheme involving intermediate trimethylsilylcarbene (26) as illustrated in 17 equation 12. Initial deprotonation of 9 forms tri- methylsilylchloromethyllithium (25) which could collapse 10

n-C.HQLi ^ -LiCl « • 9 ■» (CH3) 3SiCHCl + (CH3)3SiCH

25 26

1) n-C.H-Li

+ (CH3 ) 3 SiCH=CHSi(CH 3 ) 3

27 (12)

(CH3 ) 3 SiCH-CH 0 Si(CH 3 ) 3

28 by alpba elimination to carbene 26. Capture of 25^ by 2j5 with chloride elimination presumably produces 27.

Addition of n-butyllithium to olefin 27_ yields disilane

28. No intramolecular reaction of 2^6 was reported.

Trimethylsilylchloromethyllithium (25) can be generated from 9 and s-butyllithium in tetrahydrofuran/ tetramethylethylenediamine at -78°C. Anion 25_ has been developed as a synthetic reagent for converting aldehydes and ketones to a, |3-epoxy si lanes.

(Chloromethyl) trimethylsilane (9) and t-butyllithium 20 produce primarily tetramethylsilane (30), equation 13.

Silane 30_ reportedly results from attack of alkyllithium 11

(CH )_CLi (I) 9 ► (CH3) 3Si CH^ Li - — » (CH3 ) 3 SiCH 3 (13)

~ -(CH 3 ) 3 CC1 — B 29 30 directly on chloride followed by protonation of anion

29- Stereo specif ic trimethylsilylcyclopropanes can be

generated by reaction of 9^with lithium 2 , 2 ,6 ,6 -tetramethyl- 21 piperidide (LiTMP) in the presence of olefins, equation 14.

Apparently trimethylsilylcarbene (26) or carbenoid is involved. Further study of the carbenic character of the

LiTMP R\ 'R ------> H \”/ N H (14) _,R H V

H ^ C - C- H H' - S i ( C H 3 ) 3

22 system was made. Capture by both carbon-hydrogen and silicon-hydrogen bonds was used to confirm the presence of trimethylsilylcarbene (26). Reflux of 9 with LiTMP in cyclohexane yields (cyclohexylmethyl)trimethylsilane (32) along with high molecular weight compounds, equation 15.

(CH3 ) 3 SiCH 2 C 6Hll

LiTMP 32 9 > 26 (1 5 )

HSi3 (CH3)3SiCH2Si(C2H5)3 33 12

Carbene capture by triethylsilane proved to be a more efficient process producing trimethylsilylmethyltriethyl- silane (33) . Alpha elimination of 9_ by LiTMP was, thus, demonstrated, but the carbene capture was not high yielding.

Displacement reactions have also been reported on methyltrimethylsilanes substituted by bromide, iodide, and triflate rather than chloride. Reaction of (chloro­ methyl) trimethyl si lane (9) with sodium methoxide in dioxane produces dimethylethylmethoxysilane (37) as the 20 major product. Methoxytrimethylsilane (36) is also present in significant quantity, equation 16.

NaOCH 3

(CH3 ) 3 SiCH2X Dioxane (16)

(CH3 )3 SiCH 2 OCH 3 + (CH3 ) 3 SiOCH 3 + (CH3 )2 SiCH 2 CH 3

och 3

35 36 37

X = Cla 0% 14% 49%

Br 1 6 . 4 80 aMinor amounts of disilanes were present. 13

(Bromomethyl)trimethylsilane (34) reacts with methoxide 22 under the same conditions to form less 3j5 and more 2,1.

Evidently preference for methyl migration with halide loss over halomethyl cleavage increases with use of bromomethylsilane 34. Bromide expulsion is highly favored over bromomethide cleavage.

Reactions of (iodomethyl)trimethylsilane (38) and 9 with ammonia show 38 to be more reactive. (Chloromethyl)- silane 9 and ammonia produce mainly (aminomethyl) trimethyl­ silane (32.) while iodosilane 38_ reacts with ammonia to

5 6 yield only secondary amine 40, equation 17. ' Both

1) NH (CH ) ,SiCH Cl ------*-* (CH,) ,SiCH NH d Z 2) KOH 9 39 (17)

1) NH 2(CH,),SiCH0I ------[(CH,),SiCH ]„NH J J t 2j K0H •= ^ ^

38 40

reactions were conducted at high temperature and pressure for extended periods of time.

Reactions of trimethylsilylmethyltriflate (41) with nitrogen, sulfur and phosphorus nucleophiles have been 23 found to occur at room temperature, equation 18. 14

N

(CH3 ) 3 SiCH 2 0 3 SCF 3 (CH3) 3 SiCH 2 N ® (18)

cf 3 so3©

41 42

Triflate adducts (42) formed were used further to generate

ylids and were not usually isolated.

Halomethyltrimethylsilanes react with basic and

nucleophilic reagents in a surprising variety of ways.

The theory behind their behavior is not always well under­

stood. Systematic investigations of reactions are often

lacking. The goals of this research are to study the

influences of silyl substituents and external conditions

on the reactions of chloromethyltrisubstituted silanes with alkoxides. RESULTS AND DISCUSSION

PART I

Reactions of (Chloromethyl)dimethylvinylsilane (1) and

Allyl(chloromethyl)dimethylsilane (2) with Alkoxides.

(Chloromethyl)trimethylsilane (9) has been shown to 3 react with alcoholic sodium alkoxides Nonbulky

alkoxides attack primarily on carbon with chloride

displacement to give the corresponding alkyltrimethyl-

silylmethyl ethers (11) , equation 19. Reactions may also

occur on silicon with formation of chloromethide ion and

alkoxytrimethylsilanes (1 0 ), equation 2 0 .

Si(CH3) 3

* ROSi(CH 3 ) 3

CH (20) 3 10

Which of these reactions is predominant depends on the

alkoxide and the solvent (see Historical). 16

A major objective of the present research is to determine the effects of silyl substituents on reactions of (chloromethyl)trisubstitutedsilanes with alkoxides.

Olefinic substituents, vinyl and allyl, were chosen for initial investigation and comparison with their methyl counterparts. Study was thus begun of the behavior of

(chloromethyl)dimethylvinylsilane (1 ) and allyl(chloro­

methyl) dimethylsilane (2 ) with alkoxides.

Silane 1 was readily prepared as in equation 21 from vinylmagnesium bromide and chloro(chloromethyl)dimethyl- 24 silane (44). Dichloride 44 was obtained by photo- 25 chemical chlorination of trimethylsilylchloride (43) .

H C=CHMgBr ^ 2 (CH.)-SiCl --- *-* (CH_) 0 SiCH0Cl -s------«► 1 (2 1 ) 6 6 hv * A \ A THF Cl 43 44

Reaction of 1 was effected with 1.1 equivalents of sodium methoxide in methanol at 65°C. Three products were isolated by preparative gas chromatography, equation

22. Yields are based on consumed 1. Longer reaction times did not change the distribution of products. 17

CH=CH„ CH=CH- NaOCH I I ! (CH-.) oSiCH_0CH_ + (CH ) SiOCH-. + (CH.J-Si (OCHJ CH OH J ^ ^ 6 & -i - W 45 46 47 ~ ~ ( 22)

76% 1 2 % 1 2 %

By far the major reaction product is dimethyl (methoxy- methyl)vinylsilane (45). Ether 45 was identified by

spectral interpretation (NMR, IR, and MS) and presumably results from SN2 methoxide attack on carbon with chloride expulsion as in equation 23.

~ CH-=CHSi(CH_)_ CH=CH

CH O '0 2 I 3 2 - C l ® I 2 ! 3-- » CH-0 * • • C Cl ------► (CH_)-SiCH-OCH- 3 / \ 3223

© H H 6 U

6 45 (23)

Dimethylmethoxyvinylsilane (46) is a minor product of

reaction of 1 with methoxide and was identified by

comparison with authentic material as prepared from tri- methoxyvinylsilane and two equivalents of methylmagnesium bromide, equation 24.

CH=CH 2CH-MgBr I

CH2=CHSi (OCH3)------► (CH3 ) 2 SiOCH 3 (24)

46 18

Vinylsilane 46^ is assumed to result from methoxide attack

on silicon in 1 with loss of chloromethyl anion, equation

25. No efforts were made to detect methyl chloride or

CH=CH CH=CH_ NaOCH- I - CH-Cl I

1_ ------=-* CH30 -Si-CH 2 C1 ----- ► (CH3 )2 SiOCH 3 (25)

ch3oh ch 3 Vch 3

48 46

its expected displacement product, dimethyl ether, because

of their volatilities. Formation of 4j5 may be envisioned

as resulting from stepwise (as illustrated for 46) or

concerted displacement. Although formation of pentavalent

silicon intermediates such as 4*3 remains in dispute, the

concept will be invoked to describe the mechanisms 2 6 presumed in the present study.

Of particular mechanistic interest is that dimethyl-

dimethoxysilane (47) was formed in 1 2 % yield from reaction

of 1 with methanolic sodium methoxide. Silane 4^7 was

identified by comparison with an identical product prepared

by reaction of dichlorodimethylsilane with sodium methoxide 27 ( 2 equiv) in ethyl ether.

Formation of 47_ from 1 and sodium methoxide is of

mechanistic interest in that the overall process must 19 involve more than a single displacement reaction. One possible source of 47 is attack of methanolic sodium methoxide on 46, an initial displacement product, as in equation 26, in which ethylene is a coproduct. Such a

^H 3 NaOCH 3

CH 3 -SiCH=CH 2 /?-► (CH3) 2Si (OCH3) + C H 2 =CH 2

0CH3 £7 (26) 46 process may be ruled out because 46_ is not cleaved by sodium methoxide in methanol at 65°C. Apparently attack of methoxide ion on silicon in 4(S does not result in displacement of either the vinyl or methylcarbanions.

An additional logical route to 47 involves coordina­

tion of methoxide ion at silicon in 1 to give penta- coordinate intermediate 48 which collapses with chloride ion ejection and migration of its vinyl group to give allyldimethylmethoxysilane (49). Subsequent attack of methoxide on silicon in 49 with cleavage of the allyl carbanion and protolysis would yield 47 and propylene

(50), equation 27. Although 49_ was not isolated in reaction of 1 with methanolic methoxide, 49 was found 20

CH_ CH_ _ CH_

CH-.0© \3/ 3 f - C l ® I -- ► CH-O-Si _ CH_-C1 -----► CH_SiCH„CH=CH_ •0 Q | j t . 2 o | 2 2

CH=CH 2 OCH 3

48 49 (27)

CH3\ / CH3 H ©

CH 3 0-S1 - CH 2 CH=CH 2 ► (CH3) 2Si (OCH3) 2 + H 3 CCH=CH 2 © OCH 3

under similar conditions in dioxane as will be seen subsequently. Allylsilanes are known to cleave readily 28 under alkaline conditions. Such cleavage reactions presumably occur relatively easily because of the resonance 29 stabilization in the developing allyl carbanion.

Support for the mechanistic proposal involves detection of propylene as a reaction product.

Of mechanistic note is that vinyl rather than methyl migration occurs upon attack on silicon in 49. Rearrange­ ment is thought to occur by decomposition of an anionic pentavalent intermediate. In the collapse process electron density must travel with the migrating group from silicon to carbon, equation 28.

R ' 0 ° R s /R ^ - C l ° I 2 R~SiCH0Cl ---- > R'O— Si — CH-C1 ► R'O-SiCH-R (28) 3 2 | _ 2 2 R 21

Thus, a substituent with increased ability to attract

electrons should have enhanced migratory aptitude. A vinyl group can better accommodate a negative charge than 30 can a methyl group as revealed by their pkB values. On

this basis, migration of a vinyl substituent with its electron pair should be preferable to that of a methyl

substituent. Correlation of electron withdrawal with migratory aptitude will be further investigated by use of

(chloromethyl)dimethyl(substitutedphenyl)silanes (see

Part 2) .

In order to determine the effects of nucleophilic

bulk and solvent on the various reactions, 1 was treated with a series of alkoxides in aprotic environments. The bulk of an alkoxide can be changed simply by varying its

alkyl substituents. Methyl, isopropyl and t-butyl

alkoxides were thus used.

Reaction of 1 with sodium methoxide in dioxane

afforded three isolable products, equation 29. The ratio of 49 to 47_ was dependent upon the equivalents of methoxide used and the reaction time, silane 47 increasing with time and excess nucleophile. 22

NaOCH„

X ----- i*. (CH3)2SiCH2CH=CH2 + (CH3 ) 2 Si(OCH 3 ) 2 (29)

och 3

49_ 47

45% 19%

+ (CH3)2SiOCH3

ch=ch 2

46

9%

Allyldimethylmethoxysilane (49)/ the major product,

was not found in the reaction product from 1 with sodium methoxide in methanol and was identified by comparison with that prepared from dimethoxydimethylsilane and allyl- magnesium chloride, equation 30. Silane 49_ apparently

CH =CHCH9MgCl

(CH3) 2Si (OCH3) 2 ------► (CH3 ) 2 SiOCH 3 (30)

ch 2 ch=ch 2

49

results from methoxide attack on silicon in 1 possibly via pentavalent intermediate 48 which collapses with vinyl migration and chloride expulsion, equation 27. Once formed, allylsilane 49_ is susceptible to further reaction 23

and undergoes methoxide attach to lose allyl anion and

produce dimethoxydimethylsilane (47) and propylene. Allyl

cleavage was demonstrated by subjecting allyldimethyl- methoxysilane (49) to methoxide under the previous

reaction conditions where conversion to 4^7 occurs.

Dimethylmethoxyvinylsilane (46) was isolated in

relatively minor yield from reaction of 1 ^ with methoxide

in dioxane. Silane 4(5 is assumed to result from methoxide

attack on silicon with loss of chloromethide ion as in

equation 25.

Changing the solvent from methanol to dioxane causes

a shift from primarily methoxide displacement on carbon to

exclusively attack on silicon. This difference may be

explained by the lower nucleophilicity of methoxide in methanol due to hydrogen bonding. If attack on silicon

involves a higher activation energy than attack on carbon,

the former process should become more important in dioxane where methoxide is naked and thus a more potent nucleophile.

Further, methoxide is a donor solvent which in some cases 31 32 forms adducts with silanes. ' As a result, silicon may be partially blocked to nucleophilic attack by methanol, but remain more exposed in dioxane. Such effects could

account for the shift of reactivity from carbon to silicon with a change in solvent. 24

Silane 1 was reacted with sodium isopropoxide in tetrahydrofuran to evaluate the effects of nucleophilic bulk. The three silicon-containing products isolated are shown in equation 31.

NaOCH(CH )

1 *-4-* (CH ) SiCH 0CH(CH_)o + (CH.) 0 SiOCH(CH ) THF J j z

CH=CH 2 CH=CH 2

51 52

50% 30%

(31)

+ (CH3 ) 2 SiCH 2 CH=CH 2

och(ch3) 2

53

13%

The major product, dimethyl(isopropoxymethyl) vinyl- silane (51) was characterized by spectral interpretation

(IR, NMR, MS). Silane 5jL presumably results from alkoxide attack on carbon with chloride displacement, equation 32.

_ CH=CHSi(CH_) (CH_) CHO© ^ I J ^ -Cl®

1 ► (CH.) .CHO C -Cl ------> 6© / SH 6 © (32) (CH.).SiCH=CH_ 3 2 | 2

c h 2 och(ch3)

51 25

Dimethylisopropoxyvinylsilane (52J was obtained from

1 in 30% yield. Silane 52 was prepared independently

from vinylmagnesium bromide and diisopropoxydimethyl- 33 silane (540/ equation 33.

CH2=CHMgBr

(CH3 ) 2 SiOCH(CH3) (33)

ch=ch 2

54 52

Vinylsilane 52_ probably forms by isopropoxide attack on

silicon in 1 with expulsion of chloromethide ion.

The third product from reaction of 1 and sodium

isopropoxide is allyldimethylisopropoxysilane (53). The

structure of .53 was established by comparison with an

identical product prepared from diisopropoxydimethyl-

silane (54) and allylmagnesium chloride, equation 34.

CH 2 =CHCH2MgCl

(CH3) 2 Si[OCH(CH3) 2 12 ♦ (CH3 )2 SiOCH(CH3) 2

ch 2 ch=ch 2 (34) 54 53 26

Silane 53_ presumably forms by alkoxide attack on silicon

in 1 with vinyl migration and expulsion of chloride, equation 35.

®OCH(CH ) CH3n /CH3 f -Cl° ! (CH_) oCH0— Si — CH„Cl -----► — o A | ^ A

CH=CH 2 (35) 55

(CH3) 2 SiCH 2 CH=CH 2

OCH(CH3) 2

53

The investigation was continued by treatment of 1 with sodium t-butoxide in tetrahydrofuran at 65°C. Two products were isolated as shown in equation 36.

(CH3) 3CONa

♦ (CH3 ) 2 SiCH 2 OC(CH 3 ) 3 + (CH3 ) 2 Si[OC(CH 3 ) 3 12 THF CH=CH 56 57 (36)

58% 20%

The yields quoted are based on consumed 1. 27

The major product, dimethyl (t-butoxymethyl) vinyl-

silane (56), was identified by spectral methods. Formation of 5j5 can be envisioned as involving SN2 attack of

t-butoxide ion on carbon in 1 with expulsion of chloride, equation 37.

_ CH„=CHSi(CH-)0 CH=CH_ (CH_) _C0 z \ J z - C l © I z

3 3 + (CH3 )3 CO***C ---- Cl ------► (CH3) 2 SiCH 2 OC(CH^ 3

6 © H H fi©

^ (37)

The minor product, dimethyldi-t-butoxysilane (57), was assigned by comparison with identical material prepared from dichlorodimethylsilane and potassium t- 34 35 butoxide. ' Dialkoxysilane 57^ is assumed to arise from butoxide attack on allyldimethyl-t-butoxysilane (58) with

allyl displacement. Silane 5*3 is initially formed by

t-butoxide attack on silicon in 1 with vinyl migration

and chloride expulsion, equation 38. Allylsilane 58^ was not found in the reaction mixture. Apparently cleavage

of 58 occurs much faster than its formation from 1 . 28

(ch3) 3co° 1

58

(38) (ch3) 3 C 0 O

(ch3) 2si[ oc(ch3) 3 1 2

-CH 2 =CHCH2® 57

The effects of nucleophilic bulk in aprotic environ­ ment can be evaluated from the results for reactions of

1 with methoxide, isopropoxide and t-butoxide as shown in

Table 2. As the size of the alkoxide increases, displacement on carbon increases while attack on silicon diminishes. Perhaps formation of a pentavalent silicon intermediate with a large nucleophile beomces a higher energy process due to steric interference. As a result, displacement on carbon becomes the dominant reaction pathway.

Study was then made of various reactions of allyl-

(chloromethyl)dimethylsilane (2) with alkoxides. Silane

2 was prepared by coupling chloro(chloromethyl)dimethyl- 24 silane (44) and allylmagnesium chloride, equation 39. TABLE 2

REACTIONS OF CHLOROMETHYLDIMETHYLVINYLSILANE (1) WITH

SODIUM METHOXEDE, ISOPROPOXEDE AND t-BUTOXEDE

R O ®

1 ► (CH3 ) 2 SiCH 2 CH=CH 2 + (CH3)2SiOR + (CH3 )2 Si(OR ) 2 + (CH3 ) 2 SiCH2OR

OR CH=CH 2 CH=CH 2

R = CH 3 45% 9% 19%

CH(CH 3 ) 2 13 30 — 50%

C(CH3) 3 — — 20 58

to vo 30

CH 2 =CHCH2MgCl

(CH3) 2 SiCH2Cl --- ► (CH3) 2 SiCH2Cl (39)

ci c h 2c h =c h 2

44 2

Reaction of 2 with 1.5 equivalents of sodium methoxide in methanol at 65°C yielded three isolable products, equation 40.

NaOCH 2 (CH3) 2SiCH2OCH3 + (CH3) 2Si (OCH3) 2

CH30H OCH 3

59_ £7

33% 29%

(40)

+ (CH_)„SiOCH_ A t o

CH 2 CH 2 CH=CH 2

60

14%

The major product is dimethylmethoxy(methoxymethyl) - silane (59) as identified by comparison with an authentic sample prepared from chloro(chloromethyl)dimethylsilane

(44) and sodium methoxide, equation 41. 31

NaOCH

(CH3) 2®lCH2C 1 (CH3) 2 SiCH 2 OCH 3 (41) Cl o c h 3

44 59

Evidently 59^ results from more than a single displacement

reaction. Formation of 59_ may occur by methoxide attack

on carbon in 2 ^ with chloride expulsion leading to allyl-

dimethyl(methoxymethyl)silane (61) followed by cleavage of

allyl anion from 61 by methoxide attack on silicon.

Alternately, silane 59_ may result from initial methoxide

attack on silicon in 2 _ to form (chloromethyl) dimethyl-

methoxysilane (62) whose chloride is replaced by methoxide,

Scheme 1. Scheme 1

CH_CH=CH, (CH,)_SiCHo0CH OCH OCH 61 -CH„=CHCH -Cl (CH-)„SiCH_OCH, OCH OCH "icH„=CHCH„® OCH -Cl 59 2 (CH.)-SiCH.Cl 62 (CH3)2Si(OCH3)2 OCH * 47 —CH_=CHCH

49 The site of initial attack on 2_ is not known as neither

61 nor 6 j2 could be isolated.

Dimethoxydimethylsilane (47) is also a major product from reaction of 2_ and methoxide. Silane 47 was identified by comparison with an authentic sample.

Presumably/ 47^ is formed by methoxide attack on silicon leading to expulsion of both chloromethyl and allyl anions, Scheme 1. The order of the displacements is not known as neither allyldimethylmethoxysilane (49) nor

(chloromethyl)dimethylmethoxysilane (62) could be isolated.

The displacement reactions of 49 and 62 with methoxide are expected to be very rapid since an oxygen bound to silicon accelerates further alkoxide attack.

A minor product, 3-butenyldimethylmethoxysilane

(60) , was isolated from reaction of 2 _ and methoxide.

Silane 60^ was identified by comparison with an authentic sample prepared from dimethoxydimethylsilane and bromo-3- butenylmagnesium, equation 42. Formation of 6(3 presumably

CH 2CHCH CH MgBr

(CH3) 2 Si(OCH3) 2 ------^-- *-----> (CH3 ) 2 SiOCH 3 (42) occurs by methoxide attack on silicon in 2 ^ with subsequent migration of the allyl substituent to carbon from which chloride is expelled, equation 43.

ch 3 ch 3 ® OCH \3/ 3 ^ _cie 3 2 ♦ CHo0-Si - CH 0 C1 ♦ CH 3 OSiCH 2 CH 2 CH=CH 2 (43)

3 2

c h 2 ch=ch 2 60 63

Of mechanistic significance is that allyl rather

than methyl migration occurs from methoxide attack on 2 .

The ability of an allyl group to effectively stabilize excess charge by resonance is believed to be responsible for its preferential migration.

Allyl (chloromethyl) dimethylsilane (2) was then investigated with various alkoxides in aprotic media.

Reaction of 12 with sodium methoxide in tetrahydrofuran at

65°C led to a single silyl product, 3-butenyldimethyl- methoxysilane (60), equation 44.

NaOCH

2 2-4 (CH3) 2 SiCH 2 CH 2 CH=CH 2 (44) THF Butenylsilane 60 clearly results from methoxide attack on silicon with allyl migration and chloride expulsion, as illustrated in equation 43.

As has been described earlier (see equation 40),

reaction of 2 ^ with methoxide in methanol yielded products of allyl displacement and allyl migration. The experiment in tetrahydrofuran showed only allyl migration. Evidently, in the aprotic solvent allyl movement from silicon to carbon from which chloride is ejected is more facile than allyl displacement. Possible mechanisms for this efficient rearrangement deserve consideration.

Migration might be presumed to take place by decomposition of a pentacoordinate intermediate (63) formed from methoxide attack on silicon in 2. Collapse to product (60) could then proceed by cyclic and/or noncyclic displacement mechanisms. The noncyclic pathway is illustrated in equation 45, in which chloride is lost and the allyl group moves to adj acent carbon by a

1 , 2 -migration process while maintaining the location of its double bond. Alternately, the allyl group could 35

migrate to carbon by a cyclic process, a Claisen-like rearrangement, involving shift of the double bond, equation 46. Both mechanisms yield 3-butenyldimethyl- methoxysilane (60), but the terminal butenyl carbons are in reverse order.

C^3 CH3 (CH ) \ / /* -cie I 3 2 CH30— Si— CH2-C1 ----- » CH3OSiCH2CH2CH=CH2 (46)

V C H , 321 1 2 \ ^ O T V 3 2 2 60 63

Cyclic five-center intramolecular rearrangement mechanisms have been previously invoked to explain formation of silyl products. Thus, (acetoxymethyl)penta- methyldisilane (64) rearranges on heating to acetoxydi- methyl(trimethylsilylmethyl)silane (65), possibly as in 37 equation 47.

(CH,),Si 3 I N A

(CH3) 2Si - CH > (CH ) 2 SiCH2Si (CH3) 3 (47)

OCCH- y } n J C - CH 3 o

64 65 36

Cyclic rearrangements of dipolar intermediates have also been proposed in the reactions of allyl methyl 38 ethers with dimethyl si lylene, as shown in equation 48.

Thus, dimethylsilylene (6 6 )/ generated by photolysis of dodecamethylcyclohexasilane, is presumed to be captured

by oxygen in methyl 1 -(3-methyl-2-butenyl) ether whereupon

cyclic rearrangement leads to dimethyl(1 ,1 -dimethyl- 2 - propenyl)methoxysilane (67) .

CH CH3 /CH3 /H V < -

C=C + [ (CH_) 0 Si : ] > ji. x © S i ( C H _ ) 0 (48) / N C \ 7 ' 3' 2 ch 3 ch 2 och 3 h Y _ £ © \ 66 CH2 w n CH3

?H 3 -*■ CH_ = CHC - Si (CH_) _ A | y o A

CH 3 OCH 3 67

Differentiation between cyclic and noncyclic

mechanisms in the reaction of 2 _ with sodium methoxide may be accomplished by making the allyl group unsymmetrical and subjecting this compound to displacement. The structure of the unsymmetrical substituent in the product would reveal the process occurring. 37

(Chloromethyl) dimethyl-l-methyl-2-propenylsilane

(6 8 ) was chosen for investigation. The methyl group on

the one position of the allyl group would serve as a marker with minimal steric interference to cyclic

rearrangement. After reaction with methoxide/ the

location of the methyl group in the products would show the mechanism.

Preparation of 6S3 was accomplished by coupling

chloro(chloromethyl)dimethylsilane (44) with the Grignard

reagent formed from 3-chloro-l-butene. Because of the

allylic character of the Grignard reagent, three compounds were formed, equation 49.

(CH3 ) 2 SiCH2Cl © MgCl

(CH_) _SiCH_Cl + CH.CH© - CH 0 ( 49) 2. I 2 - j ■* y * f 2

44 (CH3 ) 2 SiCH2Cl

CH 2 CH=CH-CH 3

cis and trans

69 70

The product mixture contained 52% (chloromethyl)dimethyl-

(1-methyl-2-propenyl) silane (6!3) and 48% cis and trans-

(chloromethyl) dimethyl (2-butenyl) silanes (69^ and 70) as 38

established by NMR integration. Separation of silane 6 8 from 69^ and 70 could not be accomplished by distillation.

Preparative gas chromatography allowed isolation of a mixture of cis and trans-butenyl si lanes 69_ and 70.

Silane 6 8 / however, could not be totally freed from 69^ and 70.

Silanes 6 8 , 69, and 70_ were identified by spectral methods. (Chloromethyl) dimethyl (l-methyl-2-propenyl) -

silane (6 8 ) showed the following NMR spectrum: 6 0.09

(s, 6 H, Si-CH3), 1.09(d, 3H, C-CH3), 1.59(m, 1H, C-H),

2.8 6 (s, 2H, CH 2 C1), 4.73(m, 1H, -CH=C), 5.84(m, 2H, C=CH2) .

The isolated doublet at 1.09 6 allowed determination by

integration of the percentage 6 8 in admixture with 69 and

70. Cis and trans-(chloromethyl)dimethyl(2-butenyl)silanes

(69 and 70) have the following NMR spectra: 6 0.1(s, 6 H,

Si_CH3), 1.60(m, 5H, Si-CH 2 C=CCH3) , 2.79(s, 2H, CH 2 C1),

5.47(m, 2H, CH=CH). The ratio of cis (69) to trans (70) isomers could not be distinguished. Comparison with'the

spectra of (l-methyl- 2 -propenyl)trimethylsilane and cis

and trans- 2 -butenyltrimethylsilanes reported in the literature corroborated the assignments of 68-70.^ ^

A mixture containing 52% silane 6 8 _ and 48% silanes

69 and 70^ was reacted with sodium methoxide in tetrahydro- furan at 65°C. Two fractions were isolated by preparative 39

gas chromatography. The more volatile product was

assigned as dimethylmethoxy( 2 -methyl-3-butenyl)silane

(71) on the basis of its NMR spectrum: 6 0.13(s, 6 H,

Si-CH3), 0. 72 (d, 2H, Si-CH2), 1.06(d, 3H, C-CH3) , 2.29

(m, 1H, HC-C=C), 3.34(S/ 3H, 0CH3), 4.92(m, 2H, C=CH2),

5.82(m, 1H, CH=C). The second fraction was determined to be cis and trans-dimethylmethoxy(3-pentenyl)silanes (72

and 7 3) based on the following NMR spectrum: 6 0.12(s,

6 H, 31-0112), 0. (m, 2H, Si-CH2), 1.65(m, 3H, C-CH3),

2.Km, 2H, C-CH 2 -C) , 3.48(3, 3H, 0CH3) , 5.46(m, 2H, CH=CH)

The assignments of 7JL, 72, and 73_ are consistent with those reported for 2,4-dimethyl-3-butenyltrimethylsilane 24 and 3-pentenyltrimethylsilane.

The overall reactions of 68-70 with sodium methoxide

are illustrated in equation 5 0 .

(CH3)2SiCH2Cl + (CH3)2SiCH2Cl (50) CH,CHCH=CH CH_CH=CHCH, J 1 2 3 2 1 22 3 J cis and trans 68 69 70 ratio 1

NaOCH3, THF

CH3I 3 (CH3)2SiCH2CHCH=CH2 + (CH3)2SiCH2CH2CH=CHCH3 Il234 Il234 h 3co h 3co 71 cis and trans 72 73 r a t i o 1 : l 40

Silanes 71, 12, and 7j3 are apparently formed by methoxide attach on silicon with meth-allyl and cis and trans-crotyl migrations and chloride expulsion. Of mechanistic

significance is that the ratio of 1 -methyl (6 8 ) to

3-methylallylsilanes (69_ and 70) in the starting material is the same as that of 2-methyl (71) to 4-methylsilanes

(72 and 73) in the product. This result seems to indicate one operational mechanism.

In order to determine whether the displacement reaction involves cyclic or noncyclic mechanisms, a different ratio of starting silanes was desired.

Extensive preparative gas chromatography allowed enrich­ ment of the mixture to 73% silane 6£3 and 27% silanes 6^9 and 70. This mixture was then reacted with sodium methoxide in tetrahydrofuran at 65°C. The products were the same as those in equation 54, the the ratio of 71 to

72 and 7J3 was 2.7. Thus, the ratio of 2-methyl (71) to

4-methyl si lanes (7j2 and 73) in the product is the same as

that of 1-methyl (6 8 ) to 3-methyl si lanes (69^ and 70) in the starting mixture.

The maintenance of ratio from reactant to product implies that silane 7_1 is formed from 6J3 and silanes 72^ and from 69_ and 70. The methyl groups in the products, 41

then, have the same locations relative to the double bonds

as the starting silanes. This result thus indicates that

a noncyclic mechanism is responsible for allylic migration,

not a cyclic Claisen-like rearrangement.

The effect of nucleophilic bulk on reaction of

allylchloromethyldimethylsilane (2) was then explored with sodium isopropoxide in tetrahydrofuran at 65°C. Only

one silyl product, 3-butenyldimethylisopropoxylsilane (74), was isolable, equation 51. Silane 74 presumably results

NaOCH(CH-) (CH-)0SiCH Cl ------(CHJ SiCH CH CH=CH (51) 6 A THF I

CH 2 CH=CH 2 O C H (CH 3 ) 2

2 JA 81%

from methoxide attack on silicon in 2 ^ with allyl migration

and chloride expulsion. The behavior of 2 with sodium

isopropoxide is thus similar to that with sodium methoxide.

A bulkier nucleophile, sodium t-butoxide, was then

found to react with 2_ in tetrahydrofuran at 65°C to yield one isolable silyl derivative, 3-butenyl-t-butoxydimethyl-

silane (75), equation 52. 42

NaOC (CH.,) ,

(CH_) 0 SiCH0Cl ------(CH_) SiCH CH 0 CH=CH 0 (52) o Z j THF I c h 2c h =c h 2 o c (c h 3)3

2 75

64%

Silane 7J5 is identical with the product from reaction of

t-butyl alcohol and 3-butenyldimethylsilane (? 6 ) which was prepared by coupling chlorodimethylsilane and bromo-

3-butenylmagnesium, equation 5 3.

(CH3) 2^lCH2CH2CH=CH2 ---- ^ (CH_) SiCH CH CH=CH ' KOC(CH_) _ J Z 7fi OC(CH ) (53) — DCH 18-crown-6 75

Silane 7J5 is presumably formed by t-butoxide attack on

silicon in 2 with subsequent allyl migration and chloride expulsion.

The results of reactions of 2_ with sodium alkoxides in aprotic media show that alkoxide attacks exclusively on silicon and only allyl migrates. Evidently the silicon center remains susceptible to attack even with bulky nucleophiles.

The effects of silyl substituents can be evaluated by comparing the results of the reactions of 43

(chloromethyl) dimethylvinylsilane (1), allyl (chloromethyl) - dimethylsilane (2), and (chloromethyl) trimethylsilane (9).

In alcoholic alkoxide two major types of products are produced/ those resulting from alkoxide displacement from carbon and from direct alkoxide attack on silicon, see equations 19 and 20. The ratio of these processes is influenced by the silyl substituents as summarized in

Table 3.

TABLE 3

CARBON VERSUS SILICON ATTACK BY METHOXIDE IN

METHANOL ON HALOMETHYLSILANES 1, 2, AND 9

NaOCH (CH3)2SiCH2Cl ------— Carbon Silicon CH3OH Attack Attack R

R = CH3 ~ 100% trace

CH=CH2 76 24

CH2CH=CH2 44 56

Replacing a methyl group in (chloromethyl)trimethylsilane

(9) by vinyl or allyl substituents results in less methoxide attack on carbon and increased reaction on silicon. 44

A number of explanations for these results are possible. Silicon-carbon bonds are polarized due to carbon being more electronegative. Vinyl and allyl substituents should increase the polarization as compared 39 to methyl on the basis of inductive effects. A vinyl group should inductively withdraw more electron density from silicon than an allyl group.^ Since such effects do not conform with the present experimental results with alkoxides, other factors must be operational.

A vinyl group is generally accepted to be able to 41 participate in (p-d) tt bonding with silicon. Such bonding causes a decrease of electron density in the

carbon-carbon 71 system and an increase into silicon, equation 54.“^

R_Si_CH=CH ---- * R_Si = CH - C H (54) 2 e ©

The ability of the vinyl group to (p-d) 71 bond may thus be in part responsible for decreased attack on silicon in 1 as compared with 2.

Further, the ability of an allyl group to delocalize electrons during migration makes it an excellent leaving group. Displacement of the allyl anionic moiety from 45

silicon might thus require less energy than corresponding cleavage of methyl or vinyl counterparts.

The effects of allyl, vinyl and methyl groups on the reactions of halomethylsilanes with alkoxides in aprotic media can also be evaluated. In an aprotic solvent, two processes occur involving alkoxide attack on silicon: displacement of chloromethide ion and migration from silicon to carbon with chloride expuslion, see equations 7 and 9. The ratio of these processes is dependent on the silyl substituents. The percentages of rearrangement versus cleavage processes are summarized in

Table 4.

TABLE 4

REARRANGEMENT VERSUS CLEAVAGE PRODUCTS IN THE REACTIONS

OF HALOMETHYLSILANES 1, 2, AND 9 WITH METHOXIDE

Rearrangement Cleavage NaOCH3 (CH.)0SiCH0Cl (CH_)_SiCH_R (CH3)2SiOCH3 6 z. | Z 6 Z | Z THF or R o c h 3 R Dioxane

R = CH 78% 22% 3 CH=CH 88 12 2 c h 2c h =c h 2 100 46

Vinyl and allyl silanes 1 and 2 show increased rearrange­ ment at the expense of cleavage. Since both types of processes are believed to involve anionic pentavalent silyl intermediates, rearrangement rather than cleavage of the vinyl and allyl groups must reflect their enhanced migrating abilities. RESULTS AND DISCUSSION

PART 2

Reactions of (Chloromethyl)dimethylphenylsilanes with

Sodium Methoxide in Dioxane

Alkoxide attack on the silicon center of a

(chloromethyl)trisubstituted silane presumably leads to an anionic pentavalent intermediate. One path to product is by migration of a substituent from silicon to adjacent carbon with chloride expulsion, equation 55. Since the intermediate possesses an anionic silyl center, the

R 2 R '0° \ / R 3SiCH2Cl + R 10-Si-CH_-Cl + R'0SiCH2R (55) © I-* 2 R migrating group must travel from silicon to carbon with a negative charge. It thus might be presumed that the migratory ability of a substituent will correlate with its capacity to stabilize that charge. On the other hand, since the carbon atom undergoing displacement becomes electron deficient because of loss of chloride ion, the migrating group might stabilize the developing cationic center by donating electron density, Scheme 2. In such a

47 48

*2 6© 6© R 'O - Si - C H „ Cl Scheme 2 ©\ 2 R case, electron donation by a substituent would enhance its migratory ability.

The objective of this portion of research is to determine whether anionic or cationic stabilization is a controlling feature in the migration process. The distinction can be made by investigating a system whose electronic effects are well defined. The behavior of meta and para-substituted phenyl groups in various systems has been used extensively to determine the electrical 43 requirements for reaction processes which occur. Thus, reactions of methoxide with (chloromethyl)dimethylphenyl­ si lanes 3^ through 8 were chosen for the present study.

Increased or decreased phenyl migration caused by the substituents should reveal the electronic demands of the reaction.

(CH3)2SiCH2Cl Z = H, p-CF3, m-Cl, p-Cl, p-CH3, p-OCH3

0 3 4 5 6 7 8

Phenylsilanes 3, 4, 5, 6, 7, and 8 were prepared by reactions of chloro(chloromethyl)dimethylsilane (44) with 49

appropriately substituted phenylmagnesium bromides in 15 tetrahydrofuran, equation 56. New compounds were

(CH_)0SiCH0Cl + Z-0-MgBr > (CH_)„SiCH0Cl (56) 6 *\ Z THF J A \ A Cl 0 Z assigned from analytical data and by spectral methods.

The investigation was begun by treatment of (chloro­ methyl) dimethylphenylsilane (3) with two equivalents of sodium methoxide in dioxane at 60°C which led to isolation of four silicon-containing products, equation 57.

Prolonged heating or conducting the reaction at 100°C caused disappearance of silane 7^7 and an increased yield of 47. Toluene was also found as a reaction product in a yield equal to 47.

Benzyldimethylmethoxysilane (77), the major product was identified by comparison with an identical sample prepared as in equation 58.

Et _0 (CH3) 2Si (OCH3) 2 + 0CH2MgCl --- =-* (CH3) 2SiOCH3 (58)

c h 20

77

Formation of silane 77_ from 3^ is explicable by methoxide attack on silicon in 3^ with phenyl migration to carbon o in

%9

6l

eHDOTS2 (eHD) I 0

%93 8Z 0 £ 1 £ U5) HOOTS HD £ Z 1 HO HO

°/oTS _ TL 0 HO Q — Z (CHDO)TSZ eHO) «-=------eHOOTS3 (£HO) HOO 7 I o 0 HO 51

from which chloride is expelled, equation 57, path a.

As shown in equation 57, dimethoxydimethylsilane

(47) is a product of reaction of .3 and methoxide. Silane

47 presumably results from methoxide attack on 77. with

cleavage of benzyl anion whose protonolysis yields toluene.

Alkaline cleavage of silyl benzyl groups has been previously reported and is accelerated by electron-with- drawing groups.^ Ethylmethoxymethylphenylsilane (78) was isolated in 26% yield from reaction of 3^ and methoxide.

Preparation of an authentic sample was accomplished by reaction of ethyltrichlorosilane and three equivalents of

sodium methoxide to yield ethyltrimethoxysilane (80) which was then treated with methyl magnesium bromide to 45 46 give dimethoxyethylmethylsilane (81). ' Finally, reaction of 8^L and phenylmagnesium bromide led to 78, equation 59. Silane 7J3 is presumably formed by methoxide

CH3MgBr CH3CH2Si(0CH3)3 * CH3C H 2Si(0CH3)2

80 81 (59) 0MgBr CH_,CH„SiOCH

78 52

attack on silicon in .3 with methyl migration and chloride expulsion. This is apparently the first example of methyl migration from silicon to carbon in a halomethylsilane

containing a phenyl group capable of rearrangement. Phenyl migration appears to be five times as efficient as methyl

rearrangement.

A further product of reaction of 3 and methoxide is dimethylmethoxyphenylsilane (79). Silane 79_ was prepared

independently from dimethoxydimethylsilane and phenyl magnesium bromide, equation 60, and is believed to form

(CH3)2Si(0CH3)2 + 0MgBr -----* (CH3)2SiOCH3 (60)

47 79

in reaction of methoxide with 3_ by attack on silicon and

loss of chloromethide ion.

Reaction of sodium methoxide with (chloromethyl)di­ methyl (4-trifluoromethylphenyl)silane (4) was then studied

at 60°C in dioxane, equation 61. By far the major product

is dimethoxydimethylsilane (47) . Silane 47^ presumably

results from methoxide attack on dimethylmethoxy(4-

trifluoromethylbenzyl)silane (82) initially formed by rO in %T t8

eHDOTS3 (eHD) F 1

%9 10 HO © E8

£ .JO-3 - 0 £^0 - ^ - 0 e^0 -3 - 0 £ I e Z ^ ® £ (19) HOOTS HO TO- HO-TS-O HO «- TOSHOTSZ (eH0) 'HOO o £ z ^ £ ^ © HO HO HO HO

°/cZQ

It 28 e^O-^-0-2HOQ-

2foo)rss (ch o ) eHOOTS2 (£H0) 'HOO I JO-^"0 HO 54 phenyl migration and chloride loss. Benzylsilane 82 was not detected in the reaction product, but the presence of p-trifluoromethyltoluene lends support to the proposed mechanism. Ethylmethoxymethyl(4-trifluoromethylphenyl)- silane (83) is a product of attack of methoxide on silicon with methyl migration. Silane 8J3 was identified upon synthesis from dimethoxyethylmethylsilane and

4-trifluoromethylphenylmagnesium bromide. Dimethyl- methoxy(4-trifluoromethylphenyl)silane (84), found in only 1% yield, apparently results from methoxide attack on silicon in 4 with expulsion of chloromethide ion. The cleavage product was prepared independently from dimethoxydimethylsilane and 4-trifluoromethylphenyl­ magnesium bromide.

The results of reaction of (chloromethyl)(3-chloro- phenyl)dimethylsilane (5) with sodium methoxide are summarized in equation 62. Dimethoxydimethylsilane (47) , the major reaction product, presumably arises by methoxide cleavage of (3-chlorobenzyl)dimethylmethoxysilane (85) initially produced by phenyl migration. It was not possible to isolate silane 85, but detection of 3-chloro- toluene as a product supports this mechanistic proposal.

(3-Chlorophenyl)ethylmethoxymethylsilane (86) is formed HOOTS (HD) I T O - r n - 0 TO HO %8

9 8

TO-ui-0 TO-ui-0

£ HOOTS 1 £HO TO HO-TS-O HO TO^HOTS2 (£HO) o 'HOO £ Z ^ © HO HO HO HO

- 2 5 8 13- u i - 0 H O q - 4- €h o o t s z (£h o ) ^'HOOp 56 from 5 and methoxide in low yield. The product is that derived from nucleophilic attack on silicon, chloride displacement and methyl migration. Identification of 86 by synthesis from dimethoxyethylmethylsilane and

3-chlorophenylmagnesium bromide was straightforward.

(3-Chlorophenyl)dimethylmethoxysilane (87), a very minor product of chloromethide displacement, was prepared from dimethoxydimethylsilane and 3-chlorophenylmagnesium bromide.

(Chloromethyl)(4-chlorophenyl)dimethylsilane (6) and sodium methoxide in dioxane at 60°C gave the products and yields shown in equation 63. Dimethoxydimethylsilane

(47), by far the major product, presumably arises from methoxide attack on silicon with p-chlorophenyl migration and then p-chlorobenzyl cleavage. Isolation of 4-chloro- toluene supports the reaction mechanism proposed.

(4-Chlorophenyl)ethylmethoxymethylsilane (89), formed in only 8% yield, is a product of methyl migration. Upon collapse of a pentacovalent silyl intermediate. The rearrangement product was synthesized from dimethoxy­ ethylmethylsilane and 4-chlorophenylmagnesium bromide. A minor amount of (4-chlorophenyl)dimethylmethoxysilane

(90) was isolated from reaction of 6 and methoxide and t" in

%Z

~06

eHOOTS3 (eH0) I0-3-0

%8 TO HO

68

XO-^-0 10- £ I £ (£9) HOOTS HD TO H0-TS"0 HO * 10 HOTS (HO) HOO £ ? ^ £ HO HD HO HO

%SL %T 88 I f T O - 3 - 0 2H O q - 2 (£HDO)TS3(eHD) <— £ eHOOTS2 (eHD) H 0 0 q 7 1 10-3-0°HO 58

presumably is a product of chloromethide dissociation.

An authentic sample of 9(3 was prepared from dimethoxy­ dimethylsilane and 4-chlorophenylmagnesium bromide.

(4-Chlorobenzyl)dimethylmethoxysilane (88), found in 1% yield, apparently forms by p-chlorophenyl migration and is identical with a sample prepared from dimethoxydi­ methylsilane and 4-chlorobenzylmagnesium chloride.

Study of substituent effects on the reactions of aryl(chloromethyl)silanes was extended to (chloromethyl)- dimethyl(4-methylphenyl)silane (7). Reaction of methoxide and resulted in the products and yields depicted in equation 64. Para-xylene is also a product in a yield equal to silane 47.

Dimethylmethoxy(4-methylbenzyl)silane (91), the major product, was readily identified by synthesis from dimethoxy­ dimethylsilane and p-methylbenzylmagnesium chloride and appears to form from methoxide attack on silicon with phenyl migration and chloride expulsion. Ethylmethoxy­ methyl ( 4-methylphenyl) silane (92), prepared independently from dimethoxyethylmethylsilane and p-methy1pheny1 magnesium bromide, must result from attack on silicon with methyl migration and chloride ejection. Dimethyl­ methoxy ( 4-methylphenyl) silane (93), synthesized by m %f

£6

£HOOTSZ (£H0)

£HD-^-0 %0T

Z 6

£HO-3-0 HO-^-0 TO f 1 £ (P9) HOOTS" HO) TO HO-TS-O HO TO^HOTS2 (£h o ) 'HOO £ Z ^ © HO HO HOHO

% 6 %TS I f Y6 £HO-3'-0-£HO- z (£hoo) ts°(ch3,3/£t <- 'HOOTS£ (£h o ) 'HOO ° £HO-3-0SHO 60

coupling of dimethoxydimethylsilane and p-methylphenyl- magnesium bromide/ forms by attack on silicon with displacement of chloromethide ion. Finally, dimethoxy­ dimethylsilane (47) results from methoxide attack on 91 with benzyl cleavage. Isolation of p-xylene supports this mechanism.

(Chloromethyl)dimethyl(4-methoxyphenyl)silane (8) reacted with methoxide to produce four silyl products, shown in equation 65, and p-methylanisole. Dimethyl- methoxy(4-methoxybenzyl)silane (94) results from methoxide attack on silicon with anisyl migration and chloride expulsion and was identified by spectral methods. The product of methyl migration, ethylmethoxy(4-methoxyphenyl)- methylsilane (95), was compared with an identical sample prepared from dimethoxyethylmethylsilane and p-methoxy- phenylmagnesium bromide. Dimethylmethoxy(4-methoxyphenyl)- silane (96), produced by chloromethide expulsion was synthesized by reaction of dimethoxydimethylsilane and p-methoxyphenylmagnesium bromide. Dimethoxysilane 47 apparently forms by methoxide attack on 94 with p-methyl- anisyl displacement.

The reactions of phenylsilanes 3_, 4, !5, 6, 7, and 8 with sodium methoxide in dioxane at 60°C are summarized c h 20-e -o c h 3 © b OCH. (CH3)2 SiOCH3 -> (CH3) 2Si(OCH3) 2 -@ c h 2-0-e -o c h 3 94 £L

58% 4% -Cl

CH CH CH„CH © OCH. (65) (CH3)2SiCH2Cl - CH-.0-Si-CHoCl -Cl 0-E -OCH3 0-2-OCH 0-2-OCH

8 95

CH„C1 14%

0-jd-OCH

(CH3)2SiOCH3

96

4% TABLE 5

REACTIONS OF (CHLOROMETHYL)DIMETHYLPHENYLSILANES WITH

SODIUM METHOXIDE IN DIOXANE AT 60°C

CH CH NaOCH I 2 13 (CH.).SiCHCl ------— » (CH_).SiOCH. + CH.SiOCH. + (CH.) .SiOCH., + (CHJ _Si (OCH.) . 3 2I 2 Dioxane 32| 3 3I 3 32| 3 32 32 0-Z 0-Z 0-Z CH20-Z

Z = E-CF3 1 % 6 % — 82%

m-Cl 1.5 8 — 83

E-Cl 2 8 1% 75

E-CH a 4 10 51 9 3 a E -OCH3“ 4 14 58 4

H 6 26 51 16

a Based on consumed starting material.

cn to 63

in Table 5. Methoxide attack on silicon results in phenyl and methyl migrations and chloromethyl displacement.

Dimethoxydimethylsilane (47) is also a product of phenyl migration since it results from cleavage of the benzyl- silanes formed. Evidently phenyl substitution in 3 affects product distribution. Phenyl rearrangement is favored by electron-withdrawing substituents in 3^. Methyl migration and chloromethyl cleavage increase with electron donation to phenyl in 3_ but are highest in the parent silane.

The electrical effects are further illustrated by comparing the extent of phenyl and methyl migration. A comparison was made from the sum of the yields of benzyl- silane and dimethoxydimethylsilane devided by one half that for ethylsilane. The value for the ethylsilane was thus statistically corrected for the two methyl groups in each parent aryl(chloromethyl)dimethylsilane. The results obtained are tabulated in Table 6 along with the o value of each phenyl substituent. Qualitative examination of

Table 6 shows (with the exception when z = H) that electron withdrawal from phenyl enhances its migration. 64

TABLE 6

PHENYL VERSUS METHYL MIGRATION IN REACTIONS OF

ARYL(CHLOROMETHYL)DIMETHYLSILANES WITH SODIUM METHOXIDE

z r r 0/CH3

0.54 26 £-cf3 m-Cl 0.37 21 i—i 0 01 1

0.23 19

P-c h 3 -0.17 11

e -o c h 3 -0.27 8

H 0 5

Linear free energy correlations of substituent effects in aromatic systems have contributed enormously to understanding of reaction mechanisms. Of particular importance has been the Hammett equation, equation 66, for correlating the effects of meta and para substituents 43 on the acidities of benzoic acids. The cr constants,

KS log --- = pa (66) 65 experimentally obtained, provide a quantitative measure of a substituent's ability to withdraw or donate electrons.

The p value is a constant that measures the extent to which a reaction depends on cr values. If a series of substituted phenyl compounds shows rates,which logarithmi­ cally correlate linearly with cr values, a mechanistic consistency within the series is highly likely.

The rates of base-catalyzed hydrolysis of substituted dimethylphenylsilanes and triphenylsilanes to their corresponding silanols and hydrogen, equation 67, have

Rp R 2 I 2 HO | 2 Z-0-SiH --- — ■------> Z-0-SiOH + H„ (67) H 0 @ or piperidine

R = CH3, 0, 0-Z

Z = m-CF^, p-Cl, p-CHg, p-OCH^, H

been previously investigated. The rate constants were 48 initially correlated with c values, but improvement resulted upon introduction and use of values, equation 49 68. Subsequently it was demonstrated that cr

(68) 66

offered no advantage over c r ° constants compiled by

Taft.50'51

In the present system attempts have been made to

correlate the ratios of methyl to phenyl migration (Tables

7 and 8) with o and c r ° values. Graph 1 shows that the

logarithm of the ratios of migration plots linearly

against cr values with a standard deviation of 0.798.

Graph 2 uses c r ° constants and leads to a linear correlation with a deviation of 0.826. Standard deviation has been

recommended as a measure of goodness of fit of data 52 points to a line. The correlations in Graphs 1 and 2 53 can thus be termed poor.

A significant feature in both Graphs 1 and 2 is that

unsubstituted phenyl migration in silane 3^ is too small

and thus does not appear to be on the lines established by the other points. Graph 1, which includes error bars,

reveals that the deviation is greater than acceptable

for experimental error. If the value for silane 3^ is

dropped, the standard deviations in Graphs 1 and 2 are

0.987 and 0.970 and are thus satisfactory.

There has been a previous observation that unsubstituted phenyl migrates less readily from silicon

than do either electronegatively- or electropositively-

substituted phenyl groups. Thus, Eaborn and coworkers LOG t0 /CH CO O O o «— 4 O C\J O o ZP ■t 'I CD CD O CD CD D CO CO CD D Graph 1. Phenyl versus methyl migration in reactions of reactions in migration methyl versus Phenyl 1. Graph b = including including = b a = excluding cr 0 = excluding = a 2-OCH - 0.200 methoxide as correlated with cr with values. correlated as methoxide clrmty)iehlhnliae ad sodium and (chloromethyl)dimethylphenylsilanes E-CH 0 a . 0 = 0 0 000 a

0 . 200 E-Cl m-Cl 0 . 430 jd -CF 67 . 600

TABLE 7

DATA TABLE FOR GRAPH 1

Z = X Y Error Calculation cr log (0/CH3) log (0 + 5%/CH3-5°/o) log(0-5%/CH3 + 5%)

E- c f 3 0.54 1.41 1.46 1.38 m-Cl 0.37 1.32 1.34 1.26

E-Cl 0.23 1.28 1.33 1.25 e -c h 3 -0.17 1.04 1.10 1.01

£-OCH3 -0.27 0.903 0.976 0.888

H 0 0.699 0.756 0.668

o\ CD LOG ( 0/CH m to o O Z? CD CD \ 2-C1 r\j CD o o o CD CO CD CD CD CO CD CD ^— rp . hnlvru ehlmgaini ratos of reactions in migration methyl versus Phenyl 2. Graph £-OCH : c - P excluding excluding including including methoxide as correlated with cro with values correlated as methoxide clrmty)dmtypeyslns n sodium and dimethylphenylsilanes (chloromethyl) 0. 000 -0.200 ct cr m-Cl £-CF 69 0.600

70

TABLE 8 DATA TABLE FOR GRAPH 2

z = XY CT°51 log (0/CH3)

e -c f 3 0.54 1.41 m-Cl 0.37 1.32 i—i u CM 1 0.27 1.28 as u CM 1 on -0.15 1.04

£-OCH3 -0.15 0.903

H 0 0.699 71

have found for (chloromethyl)dimethylphenylsilanes possessing p-chloro, p-methyl and p-methoxy substituents that in reaction with sodium ethoxide in ethanol the rates of phenyl rearrangement decrease in the order p-Cl > H > p-CH3 > p-OCH^, whereas the proportion of 15 rearrangement is in the order p-Cl > p-CH^ > p-OCH^ > H.

No explanation for the deviation of the rates from the product distribution was offered.

Further studies by Eaborn et al. of alkaline cleavage of (phenylethynyl)trimethylsilanes to trimethyl- silanol and phenylacetylenes, equation 69, show the rates of reaction to be accelerated in part by electron-with- 54 drawing phenyl substituents. Overall correlation of the rate constants with the Hammett equation is, however,

® o h /c h 3o h Z-0-CS C-Si(CH3)3 » (CH3)3SiOH+ Z-0C= CH (69) poor. Pertinent to the present research is that the rates decrease in the order m-Br > p-CH3 > p-OCH3 > H; that is, the unsubstituted (ethynylphenyl)trimethylsilane reacts slowest of the series. Cleavage of silicon-aryl bonds often show aberrant orderings of reactivity.

Hammett correlation is more applicable to substituted aryl-

silanes in reactions in which the silicon-aryl bonds . . . 4 1 remain intact. 72

The lack of correlation of reaction rates or equilibria with the Hammett equation may result from changes in mechanism within a series of compounds.

Sommer has proposed two mechanisms for substitution 55 reactions at silicon. Reactions proceeding with retention of stereochemical configuration at silicon are thought to involve a transition state with the leaving group at a 90° angle to the nucleophile and are termed SNi-Si processes. The departure of the leaving group may be from the apical or basal positions of penta- coordinate intermediates as in Scheme 3. Reactions

S cheme 3 Nu A I — Si - or Nu— Si — C / \ A B /L / x B taking place with inversion of configuration are believed to occur via a transition state resembling the SN2 mechanism with the leaving group at a 180° angle from the nucleophile and are termed SN2-Si displacements,

Scheme 4. This latter mechanism involves large charge

S cheme 4 A I ^ N u — Si — L /\ B C 73

separation and is consequently favored by good leaving

groups, solvents of high dielectric constant and by

nucleophiles which are stable anions.

The mechanistic dependence on a leaving group is

dramatically illustrated by the reactions of optically

active naphthylmethylphenylsilanes, R.jR2R 3Si*X with 55 organolithium reagents, equation 70.

R 1 Li R1R2R3Si*X ------* R1R2R3Si*Rl + LiX (70)

When X = Cl, all displacements proceed with inversion of

configuration regardless of R', consistent with the idea

that chloride is a good leaving group. However, when

X = F, 0CH3 or H, reactions with organolithium compounds which gradually increase in stabilities as carbanions

result in a change of stereochemistry from retention to

inversion at a certain point for each leaving group.

Similar stereochemical crossovers have been demonstrated 56 57 by changes in solvent or the cation. ' In order to

explain the stereochemistry of displacement on silicon,

initial attack of a nucleophile or silicon is presumed

to result in a pentacoordinate trigonal bipyramidal 58 intermediate. Apical positions are favored by 74 electronegative groups while bulky substituents prefer basal locations. Thus, the stabilities of pentacoordinate silyl intermediates are important in determining their contributions to displacement mechanisms.

In the system presently investigated, an electron- withdrawing aryl substituent should increase the leaving group ability of a phenyl group and, thus, its migratory aptitude. Perhaps the p-Cl, m-Cl and p-CF^ substituted phenylsilanes 4, !5, and 6 undergo dominent SN2-Si reactions, as shown in equation 71, where methoxide and

_ CH.. CH (CH ) CH,0® N3 / 3 -Cl© | 3 2 2—* CH-0— Si— 0- Z ► CH~OSiCHo0-Z (71) 3 | Qj 3 2 CH0 I 2 /Cl

Z = p-Cl, m-Cl, p-CF^ phenyl occupy apical positions due to their electro­ negativities and the chloromethyl group is basal because of its bulk or by default. Migration of such phenyls then occurs with a 180° angle relative to methoxide.

Such intermediates would result in highly predominant phenyl migration as is found experimentally for silanes

4, 5, and 6. 75

For unsubstituted phenylsilane 3^ or those containing electron-donating substituents on phenyl, 7 and 8, the migrating abilities of the phenyl groups should be diminished as compared with 4, 5, and 5.

Perhaps then the mechanisms shift in part to SN2-Si. If methoxide is maintained in the apical position and chloromethyl remains basal/ two pentacoordinate inter­ mediates are possible. Scheme 5.

Scheme 5

CH., 0 C H 0 CH- \3/ \3 / 3 CH.,0 Si CH., CH-0— S i 0 .3 j -j 6 | CH„ CH I I Cl Cl

A B

In the SN2-Si mechanism the migrating group leaves at a

90° angle from the coordinated nucleophile. Thus, intermediate A can lead to methyl and to phenyl migration, whereas B can give only methyl migration. Since more electronegative groups are generally in apical positions, perhaps phenyl groups with electron-donating substituents prefer to be basal as in intermediate A. Thus, if unsubstituted phenylsilane 3_ develops a higher population 76 of intermediate B than do silanes 2_ and 8 with p-CH^ and p-OCH^ substituents, more substituted-phenyl migration should occur in the latter two cases. Indeed, parent silane 3 gives the least phenyl migration.

There are alternative mechanisms to that proposed for explaining the unusual electronic effects on the migratory aptitudes of substituted phenyl groups in the above reactions. One interesting possibility is based on the idea that the pentacoordinate intermediate is anionic, but in rearrangement the reaction also reflects the cationic character of carbon from which chloride is being displaced, as shown in Scheme 6.

Scheme 6

6 ©^ Cl

z

Thus, the observed electronic effects could be a combination of electron-withdrawing phenyl substituents helping to dissipate the negative charge on silicon during rearrangement and electron-donating phenyl substituents participating at the developing cationic 77 center. It might then be possible that phenyl groups with electron-withdrawing or electron-donating substituents will migrate better than the unsubstituted phenyl groups in reactions of (chloromethyl)dimethylphenylsilanes with alkoxides.

Whatever the mechanistic reasons for the above electronic effects, this problem is worth investigating in much greater depth. Other monosubstituted aryl-

(chloromethyl)dimethylsilanes should be studied. In particular the effects of other electron-donor para-phenyl

substituents are of interest. Further, the migratory aptitudes of a wide variety of meta-substituted phenyl groups might be highly informative.

Further interesting extensions would be reactions of nucleophiles with (chloromethyl)triphenylsilanes having one phenyl group substituted, Z-0 02SiCH2Cl. Leaving group effects (Br, I, sulfonate ester, etc) might also be revealing. Lack of any effect would imply minimal

significance to participation at the cationic center in the transition state.

The hypothesis of changes in stereochemistry resulting from varying phenyl substitution could be

studied with chiral halomethyl phenylsilanes, 78

ZH^Rj^SiCH^X. If electron-withdrawing substituents react largely by the SN2-Si pathway inversion should result. Electron-donating substituents should give retention if the SNi-Si mechanism is followed. The stereochemistry of rearrangement reactions of optically active chloromethylsilanes with other nucleophiles (F®, hard and soft, RS®, etc) may prove interesting. Hard nucleophiles have been previously found to effect displacement on silicon with retention whereas soft 58 nucleophiles react with inversion. RESULTS AND DISCUSSION

PART 3

Reactions of (ChloromethylJdimethylphenylsilane (3_) with

Methoxides under Various Conditions

Previously, solvent was shown to play an important role in determining product distribution in the reactions of chloromethylsilanes and alkoxides (see Part 1). Thus, it was of interest to study the behavior of (chloro­ methyl) dimet hylphenylsi lane (3) with sodium methoxide in methanol. Reaction of 3_ with 1.8 equivalents of sodium methoxide in methanol at 65°C was thus found to give the products in equation 72 in the yields indicated.

Dimethyl(methoxymethyl)phenylsilane (97) is the major product and presumably forms by methoxide attack on carbon with chloride expulsion. Dimethylmethoxy- phenylsilane (79) results from methoxide attack on silicon with chloromethide displacement. Dimethoxydi- methylsilane (47) evidently forms by cleavage of benzyldimethylmethoxysilane (77) initially produced from methoxide attack on silicon in .3 with phenyl migration and chloride ejection. Toluene was also a reaction product. The overall behavior of 3 with sodium

79 0 (CH3)2SiCH2OCH3

97 (CH3)2 Si0 79% CH30 • c * ■ Cl / \ 6© 6© H H NaOCH 3 CH CH_ 0 (72) \ / I CH_0 Si — CH„Cl -*■ (CH3) 2SiOCH3 © ° c h 2c i 0 79 5% OCH. -Cl© © OCH (CH3)2SiCH20 3— * (CH3)2Si(OCH3)2 - ® C H 20 £7 00 6% o 81

methoxide in methanol is thus similar to that of

(chloromethyl)dimethylvinylsilane (1) under similar

conditions.

It was then of interest to determine whether

different cations affect the behavior of 3^ with methoxide.

The reactions of (chloromethyl)dimethylphenylsilane (3)

with potassium and cesium methoxides in methanol and

with sodium methoxide in the crown ether, 18-crown-6,

are summarized in Table 9.

TABLE 9

REACTIONS OF (CHLOROMETHYL) DIMETHYLPHENYLSI LANE

(3) WITH METHOXIDES IN METHANOL

3 ------> (CH3)2SiCH2OCH3 + (CH3)2SiOCH3 + (CH3)2Si(OCH3)2 0 0 92 79 47

NaOCH3 79% 5% 6%

+18-crown-6 60 11 26

K0CH3 28 14 46

C sOCH3 8 20 66 82

The distribution of products depends upon the cation.

The percentage of methoxymethylsilane 97^ decreases as the cation is changed from sodium to cesium while those of 79_ and 47_ increase. This shows a shift from mostly reaction on carbon to predominately attack on silicon.

This change in reaction pathway must result from the various cations. Cesium is the biggest and most 59 ionic of the cations. Thus, cesium methoxide should be the most ionic and most reactive of the methoxides.

This is supported by the observation that reaction of 3^ with cesium methoxide is much faster than with either sodium or potassium methoxide. Evidently methoxide, when activated by association with a large very ionic cation, prefers attack on silicon.

Addition of a crown ether caused an increase in both reaction rate and attack on silicon. The crown ether, 18-crown-6, is known to complex sodium cations thus increasing the activity of the anion.60'6'*'

Methoxide, thus, activated behaved in a fashion similar to cesium and potassium methoxides showing more reaction on silicon.

The behavior of sodium and potassium methoxides with (chloromethyl)trimethylsilane (9) and with 83

(bromomethyl) trimethylsilane (34) was then studied

(Table id) . Of note is that 9 and 34 undergo little

reaction on silicon with either methoxide in methanol.

Displacement of halide from carbon therefore is also the major or exclusive process with potassium methoxide.

Thus, the activation energy difference for attack on

silicon and on carbon appears to be larger for

trimethylsilanes 9 and j34 than for phenylsilane 3^ as the product distribution is influenced by the cation only in

the latter case.

TABLE 10

REACTIONS OF HALOMETHYLTRIMETHYLSILANES

WITH METHOXIDES IN METHANOL

(CH3)3SiCH2X h "q h-» (CH3) 3SiCH2OCH3 + (CH3) 3SiOCH3

X = Cl NaOCH3 97% trace k o c h 3 91 trace

X = Br NaOCH 3 - 100% KOCH ~ 100% 3 84

Since cationic effects with 2_ were so pronounced in methanol, a logical extension was to investigate the systems in an aprotic solvent. Thus, (chloromethyl)- dimethylphenylsilane (3) was reacted with a series of methoxides in dioxane. The products and yields are shown in Table 11.

Lithium, calcium and magnesium methoxides do not react with 3^ on prolonged heating. Even addition of a lithium-specific crown ether, 12-crown-4, does not 6 2 induce reaction. Evidently these methoxides are too covalently bonded to react.

Sodium, potassium and cesium methoxides react readily in dioxane, the rates of reaction increasing in the order Na < K < CS. All products result from methoxide attack on silicon. As the size and ionic stability of the cation increase, somewhat more 79, the product of chloromethyl cleavage, is produced. Methyl and phenyl migration remain fairly constant except for the low value (2%) for methyl migration with cesium methoxide.

The origins of this deviation would appear to lie in the diminished covalent character of pentavalent silyl intermediates when the counter ion is cesium. TABLE 11

REACTIONS OF (CHLOROMETHYL)DIMETHYLPHENYLSILANE (3)

WITH METHOXIDES IN DIOXANE

0 (CH ) CH CH 1 M -OCH-* | | ^ J (CH3) SiCH Cl ------^ 0SiOCH3 + CH3SiOCH3 + (CH3) 2SiCH20 + (CH3) Si (OCH3) 2 Dioxane 0 OCH-, o„ 3 30WC 79 78 77 47

NaOCH3 3% 14% 76% 3%

NaOCH3/ 18-crown-6 12 11 75

KOCH3 10 14 — 76

KOCH3/ 18-crown-6 26 11 — 60

C sOCH3 13 2 — 78

LiOCH3/ 100°C NR LiOCH3/ 12-crown-4/ 100°C NR Ca(OCH3)2, 100°c NR Mg(OCH3)2/ 100UC NR

00 cn 86

Inclusion of the crown ether, 18-crown-6, in

reactions of 3 with potassium or sodium methoxides,

increased the percentages of chloromethyl displacement

significantly, largely at the expense of phenyl

migration. Although chloromethide expulsion seems a

high energy process because of the poor leaving group

ability of the carbanion, it gains in importance the more reactive the nucleophile.

The effects of temperature on the reactions of

(chloromethyl)dimethylphenylsilane (3) with sodium

methoxide were then determined in dioxane. From the

results at 30°, 60°, and 100°C, listed in Table 12, it

is obvious that the product distribution is temperature

dependent.

Exclusive reaction on silicon occurs at all three

temperatures. The percentages of 79, the chloromethide

expulsion product and those of 78, the product of methyl

migration increase with temperature while those of 77

and 47, resulting from phenyl migration decrease.

Reaction of 7^7 with methoxide to form 47^ and toluene

becomes more predominant at a higher temperature. 87

TABLE 12

REACTIONS OF (CHLOROMETHYL)DIMETHYLPHENYLSILANE (3)

WITH SODIUM METHOXIDE AT VARIOUS TEMPERATURES

NaOCH, 3 ------» Dioxane CH CH I 2 3 (CH3)2SiOCH3 + CH3SiOCH3 + (CH3)2SiCH20 + (CH3)2Si(OCH3)2

0 0 OCH3

79 78 77 47

30° 3% 14% 76% 3%

60° 6 26 51 16

100° 12 32 — 44 SUMMARY

A study has been made of the reactions of (chloro­ methyl) tri substituted silanes with alkoxides. (Chloro­ methyl) dimethylvinylsi lane (1) reacts with methanolic

sodium methoxide primarily on carbon with chloride expulsion to give dimethyl(methoxymethyl)vinylsilane (45) .

In dioxane reaction on silicon is the exclusive process yielding dimethylmethoxyvinylsilane (46) by chloromethide displacement and allyldimethylmethoxysilane (490 by vinyl group migration from silicon to carbon with loss of chloride. Allylsilane 4£ is cleaved to dimethoxydimethyl-

silane (47) and propylene under the reaction conditions.

Attack on carbon in 1 is enhanced by sodium isopropoxide

and sodium t-butoxide.

Allyl(chloromethyl)dimethylsilane (2) reacts with

sodium methoxide in methanol to yield dimethylmethoxy-

(methoxymethyl) silane (59,)/ dimethoxydimethylsilane (£7)

and 3-butenyldimethylmethoxysilane (60). In aprotic

solvents sodium methoxide, sodium isopropoxide or sodium

t-butoxide and 2 produce only alkoxy-3-butenyldimethyl-

silanes by allyl group migration. Allylic rearrangement

could occur via a 1,2-shift from silicon to carbon or by a

88 89

cyclic Claisen-type mechanism involving shift of the double bond. To determine the mechanism a methallylsilane,

(chloromethyl)dimethyl(1-methyl-2-propenyl)silane (68), was reacted with methoxide. One product, dimethylmethoxy-

(2-methyl-3-butenyl)silane (71), is apparently formed from

68 with its methyl group in the same location relative to the double bond as the starting silane. Thus, allylic rearrangement is non-cyclic.

The electronic demands of reactions of chloromethyl- silanes with sodium methoxide in dioxane were studied with

(chloromethyl)dimethyl(substitutedphenyl)silanes. The products obtained result from chloromethide cleavage and from methyl and from phenyl migrations. The phenyl migration products react with methoxide to yield dimethoxy- dimethylsilane and substituted toluenes. Aryl rearrange­ ment for the substituted phenyl groups decreases in the order: jd-CF^ > m-Cl > £-Cl > jd-CH^ > £-OCH3 > H.

Presumably electron-withdrawal from phenyl aids its migration due to stabilization of the charge put on silicon by methoxide attach. Electron-donating substituents may assist phenyl migration by participation with the develop­ ing cationic center resulting from chloride loss. 90

Studies of cationic effects on reactions of methoxides in methanol with (chloromethyl) dimethylphenylsilane show increased reaction on silicon by potassium and cesium methoxides compared to sodium methoxide. In dioxane the former two methoxides result in more chloromethide cleavage at the expense of phenyl rearrangement. Generally, the addition of a crown ether to the reaction has the same effect as the use of a more ionic methoxide.

The various reactions of (chloromethyl)dimethylphenyl­ silane with methoxide are temperature dependent. Methyl migration and chloromethide expulsion increase at high temperature.

In conclusion, replacement of a silyl methyl group by a vinyl, allyl, or phenyl substituent leads to increased alkoxide reaction on silicon probably resulting from increased electron attraction by the unsaturated groups.

These groups, also, migrate from silicon to carbon better than methyl substituents presumably because they can more effectively accept excess charge from silicon. EXPERIMENTAL

General Procedures

Reactions were generally conducted under dry

nitrogen in flame dried glassware. Yields were usually

determined by gas chromatography (GC) using internal

standard techniques and are corrected for detector

response. Yields determined by these methods are 63 accurate to approximately + 5% of the absolute value.

Products were identified by isolation and comparison with authentic samples or, in some cases, by detailed

spectral analysis.

Gas Chromatography

Gas chromatography (GC) was performed using a

Wilkins Aerograph Model A-90-P3 instrument with a

thermal conductivity detector. Frequently used columns were: column A, 10 ft x % in, 15% SE 30 on 60/80

Chromosorb P and column B, 10 ft x in, 10% GE XF-1150

on 60/80 Chromsorb P. Helium was used as the carrier

gas generally at a flow rate of 40 ml/min.

91 92

Infrared Spectra

Infrared spectra were obtained on a Perkin-Elmer

Model 457 spectrophotometer. Spectra of liquids were obtained from neat films on NaCl plates. All spectra were calibrated against a polystyrene absorption peak at

1601 cm-1.

H Nuclear Magnetic Resonance Spectra

■^H nuclear magnetic resonance spectra were obtained using Varian Associates Models 360L and 390L. All spectra were measured in deuteriochloroform using chloroform or cyclohexane as internal standards.

Mass Spectra

Mass spectra were determined on a MS-9 mass spectrometer by Mr. C. Weisenberger.

Elemental Analyses

Elemental analyses were performed by Galbraith

Laboratories, Inc., Knoxville, Tennessee.

Reaction of (Chloromethyl)dimethylvinylsilane (1) with

Sodium Methoxide in Methanol 24 A mixture of (chloromethyl)dimethylvinylsilane

(1, 3.20 g, 24 mmol), sodium methoxide (1.40 g, 26 mmol) 93

and methanol (5 mL) was refluxed for 12 hr. Analysis by GC on column A at 100°C using m-xylene as the internal standard revealed the presence of (1) (chloromethyl)di­ methylvinylsilane (1, 1.6 g, 12 mmol, 50%), (2) dimethyl-

(methoxymethyl)vinylsilane (45, 1.21 g, 9 mmol, 38%); exact mass: calcd. 130.08139, found, 130.08171; NMR 6 0.15

(s,6H,Si-CH3), 2.16(s,2H,CH2-0), 3.34(s,3H,OCH3), 6.02(m,

3H, CH=CH2); IR 1596 cm-1 (CH=CH2), 1110 cm-1 (C-0-C).

Anal. Calcd for C^H, „0Si: C, 55.38, H, 10.77. ------b 14 Found: C, 55.46, H, 10.58.

(3) dimethylmethoxyvinylsilane (46, 0.16 g, 1.4 mmol,

6%); exact mass: calcd, 116.06574, found 116.06548;

NMR 6 0.09(s,6H Si-CH3), 3.34(s,3H, 0CH3), 5.95(m, 3H,

CH=CH2); IR 2840 cm-1 (Si-OCH3), 1596 cm-1 (CH=CH2).

Anal. Calcd for C5H 12OSi: C, 51.72, H, 10.34.

Found: C, 51.68, H, 10.36.

27 and (4) dimethyldimethoxysilane (47, 0.17 g, 1.4 mmol,

6%). An authentic sample of 47 was prepared from sodium methoxide and dichlorodimethylsilane in ether. 94

Preparation of Dimethylmethoxyvinylsilane (46) .

Methylmagnesium bromide (0.34 mol) in ethyl ether

(700 mL) was added dropwise to a stirring solution of 64 trimethoxyvinylsilane (25.0 g, 0.17 mol) in ethyl ether (300 mL) at 30°C. The mixture was refluxed 14 hr and then distilled through a column packed with stainless steel staples. Dimethylmethoxyvinylsilane (6.1 g, 31%) was collected at 78°C.

Reaction of (Chloromethyl)dimethylvinylsilane (1) with

Sodium Methoxide in Dioxane.

Sodium methoxide was generated by addition of methanol (0.36 g, 11.4 mmol) to sodium hydride (50% oil dispersion, 0.55 g, 11.4 mmol). After liberation of hydrogen ceased, dioxane (4 mL) was added followed by

(chloromethyl)dimethylvinylsilane (1, 0.95 g, 7.1 mmol).

The mixture was heated at 100°C for 12 hr. Analysis by

GC on column A at 80° using m-xylene as the internal standard showed the presence of (1) allyldimethylmethoxy- 6 5 silane (49, 0.42 g, 3.2 mmol, 45%); exact mass: calcd

130.08139, found 130.08088; NMR 6 -0.10(s, 6H, Si_CH3),

1.42(d, 2H, Si-CH2-C=C), 3.27(s, 3H, Si-0CH3), 4.69(m,

2H, H2C=CH), 5.65(m, 1H, H2C=CH); IR 2840 cm"1 (Si-OCH3),

1640 cm"1 (CH2CH=CH2). 95

Anal. Calcd for C^H^OSi: C, 55.38, H, 10.77.

Found: C, 55.13, H, 11.02.

(2) dimethyldimethoxysilane (47, 0.16 g, 1.3 mmol, 19%) and (3) dimethylmethoxyvinylsilane (46, 0.073 g, 0.63 mmol, 9%) . Compounds 46, 47, and 49^ were identified by comparison with authentic samples.

Preparation of Allyldimethylmethoxysilane (4S0 .

Allylmagnesium chloride, from allylchloride (9.8 g,

0.13 mol) and magnesium (2.4 g, 0.1 mol) in ethyl ether

(100 mL) , was added dropwise to a stirring solution of dimethyldimethoxysilane (47 12.0 g, 0.10 mol) in ethyl ether (100 mL). After the mixture had been refluxed 12 hr, distillation yielded allyl dimethylmethoxysilane which was purified by preparative gas chromatography.

Reaction of Allyldimethylmethoxysilane (49) with Sodium

Methoxide in Dioxane.

To a mixture of sodium methoxide (0.10 g, 1.8 mmol) in dioxane (1 mL) was added allyldimethylmethoxysilane

(49, 0.20 g, 1.5 mmol). The reaction was held at 100°C while aliquots were intermitently removed and analyzed.

After 4 hr allyldimethylmethoxysilane (49) was converted effectively to dimethyldimethoxysilane (47). 96

Reaction of (Chloromethyl)dimethylvinylsilane (1) with

Sodium Isopropoxide in Tetrahvdrofuran..

Isopropyl alcohol (0.49* g, 8.1 mmol) was slowly added to sodium hydride (50% oil dispersion/ 0.39 g, 8.1 mmol). After reaction ceased, tetrahydrofuran (2.5 mL) was added followed by £hloromethyl)dimethylvinylsilane (1,

0.70 g, 5.2 mmol). The solution was heated at 68°C overnight. Analysis on column A at 100°C using, octane as an internal standard showed the presence of (1) dimethyl-

(isopropoxymethyl)vinylsilane (51, 0.42 g, 2.7 mmol, 51%); exact mass: calcd for C^H^gOSi, M+-CH3, 143.08921, found

143.08886; NMR 6 0.1(s, 6H, Si-CH3), l.l(d, 6H, C(CH^)2),

3.l(s, 2H, Si-CH2-0), 3.41 (m, 1H, CH(CH3)2), 6.0(m, 3H,

CH=CH2); IR 1596 cm-1 (CH=CH2), (2) dimethylisopropoxy- vinylsilane (52, 0.23 g, 1.6 mmol, 30%); exact mass: calcd 144.09704, found 144.09658; NMR 6 0.15(s, 6H, Si-

CH3), 1.14(d, 6H, CH(CH3)2), 3.96(m, 1H, CH(CH3)2), 5.96

(m, 3H, CH=CH2); IR 1596 cm-1 (CH=CH2);

Anal. Calcd for C^H^OSi: C, 58.33, H, 11.11.

Found: C, 57.97, H, 10.96. and (3) allyldimethylisopropoxysilane (53, 0.11 g, 0.68 mmol, 13%); exact mass: calcd for C^H^^OSi, M -CH3,

143.08921, found 143.08872; NMR 6 0.17(s, 6H, Si-CH3), 97

1.13(3, 6H, CH(CH3)2), 1.82(111, 2H, Si-CH2 CH=CH2) , 4.1(m,

1H, CH(CH3)2), 6.1(m, 3H, CH=CH2); IR 1612 cm-1

(c h 2c h =c h 2) .

Preparation of Dimethylisopropoxyvinylsilane (52).

To a stirring solution of diisopropoxydimethylsilane

(17.0 g, 0.10 mol) in tetrahydrofuran (100 mL) was added vinylmagnesium bromide prepared from vinyl bromide (14.0 g, 0.13 mol) and magnesium (2.4 g, 0.1 mol) in tetra- hydrofuran (100 mL). The mixture was refluxed for 14 hr.

Distillation yielded a fraction boiling at 105°C

consisting primarily of dimethylisopropoxyvinylsilane.

Preparation of Allyldimethylisopropoxysilane (53).

Allylmagnesium chloride (7.6 g, 0.10 mol) in tetrahydrofuran (100 mL) was added to a stirring solution 33 of diisopropoxydimethylsilane (13.0 g, 0.074 mol) in tetrahydrofuran (150 mL). The solution was held at reflux for 14 hr and distilled. Allyldimethylisopropoxy­

silane (53) was inseparable from the starting silane which always remained in some quantity.

Reaction of (Chloromethyl)dimethylvinylsilane (1) with

Sodium t-Butoxide in Tetrahydrofuran.

After preparation of sodium t-butoxide from sodium

(0.21 g, 9 mmol) and t-butyl alcohol (0.67 g, 9 mmol), 98 tetrahydrofuran (4 mL) and (chloromethyl)dimethylvinyl­ silane (1) were added. The mixture was refluxed 96 hr after which GC analysis on column A at 100°C using methyl- cyclohexane as the internal standard revealed: (1) starting silane (1, 0.40 g, 3 mmol/ 50%), (2) dimethyl(t-butoxy- methyl)vinylsilane (56, 0.31 g, 1.8 mmol, 29%), exact mass: calcd for CgH^OSi, M+-CHg, 157.10486, found

157.10527; NMR 6 0.01(s, 6H, Si-CHg) , 1.05(s, 9H, C (CH3) 3) ,

2.88(s, 2H, CH2-0), 5.97(m, 3H, CH=CH2); IR 1596 cm-1

(CH=CH2), 1055 cm-1 (C-0-C);

Anal. Calcd for CgH 2QOSi: C, 62.79, H, 11.63.

Found: C, 62.61, H, 11.48. and (3) dimethyldi-t-butoxysilane^' (57, 0.12 g, 0.60 mmol, 10%) . An authentic sample of silane 57_ was prepared from dichlorodimethylsilane, and potassium t-butoxide in ethyl ether.

Reaction of Allyl(chloromethyl)dimethylsilane (2) with

Sodium Methoxide in Methanol.

Sodium methoxide was prepared from methanol (5 mL) and sodium (0.33 g, 1.4 mmol) and then allyl(chloro- 24 methyl)dimethylsilane (2, 1.33 g, 9 mmol) was added.

This solution was refluxed 20 hr. Analysis by GC at 78°C 99

using octane as the internal standard revealed the presence of (1) dimethyl(methoxymethyl)methoxysilane (59, 0.40 g,

3 mmol, 33%); exact mass: calcd 134.07630, found

134.07674; NMR 6 0.13(s, 6H, Si_CH3), 3.1(s, 2H, Si-CH2~0),

3.45(s, 3H, 0-CH3); IR 3840 cm-1 (Si-0CH3);

Anal. Calcd for C^H^C^Si: C, 44.77, H, 10.45.

Pound: C, 45.04, H, 10.84.

(2) dimethyldimethoxysilane (£7, 0.31 g, 2.6 mmol, 29%), and (3) 3-butenyldimethylmethoxysilane (60, 0.18 g, 1.3 mmol, 14%); exact mass: calcd for C^H^OSi, M+-CH3

129.07356, found 129.07408; NMR 6 0.09(s, 6H, SiCH3), 0.7

(m, 2H, SiCH2CH2), 2.05(m, 2H, CH2CH=CH2), 3.4(s, 3H,

0CH3), 4.98(m, 2H, HC=CH2), 5.9(m, 1H, CH=CH2); IR

3840 cm-1 (Si-0CH3), 1620 cm-1(CH=CH2);

Anal. Calcd for C^H^gOSi: C, 58.33, H, 11.11.

Found: C, 58.43, H, 11.21.

Products 47, 59 and 6(3 were identified by comparison with

authentic samples. 100

Preparation of Dimethyl (methoxymethyl) methoxysilane (59).

Dried sodium methoxide formed from sodium (3.14 g,

0.14 mol) and methanol was slurried in ethyl ether (200 mL). Chloro(chloromethyl)dimethylsilane (16.0 g, 0.11 mol) in ethyl ether (100 mL) was dripped in at a rate slow enough to maintain gentle reflux. After 1 hr at reflux sodium methoxide (7.5 g, 0.14 mol) in methanol

(100 mL) was added and the mixture refluxed for an additional 12 hr. Fractional distillation yielded a fraction boiling at 110°-111°C containing only dimethyl-

(methoxymethyl)methoxysilane (1.73 g, 13 mmol, 12%).

Preparation of 3-Butenyldimethylmethoxysilane (60).

Bromo-3-butenylmagnesium was prepared by adding

3-bromobutene (16.0 g, 0.12 mol) in ethyl ether (100 mL) to magnesium (3.6 g, 0.15 mol). This solution was slowly added to dimethoxydimethylsilane (12.0 g, 0.10 mol) in ethyl ether (100 mL). After 12 hr reflux, distillation yielded 3-butenyldimethylmethoxysilane (60, 8.87 g,

0.061 mol, 61%). 101

Reaction of Allyl(chloromethyl)dimethylsilane (2) with

Sodium Methoxide in Tetrahydrofuran

Methanol (3 mL) and sodium (0.28 g, 0.012 mol)

resulted in sodium methoxide which was subsequently dried. Tetrahydrofuran (5 mL) and allyl(chloromethyl)- dimethylsilane (2, 1.18 g, 7.9 mmol) were added. The mixture was refluxed 14 hr. Analysis on GC column A at

80°C using octane as the internal standard revealed only

3-butenyldimethylmethoxysilane (6(3, 1.07 g, 7.4 mmol,

94%) as compared with an authentic sample.

Preparation of (Chloromethyl)dimethyl(1-methyl-2-propenyl)-

silane (68).

Tetrahydrofuran (100 mL) containing 3-bromobutene

(27.0 g, 0.3 mol) was dripped onto magnesium turnings

(7.5 g, 0.3 mol) in tetrahydrofuran (200 mL) at such a rate to maintain reflux. After 1 hr at reflux, chloro-

(chloromethyl)dimethylsilane (35.5 g, 0.25 mol) in tetrahydrofuran (125 mL) was added. The mixture was refluxed further for 10 hr. Saturated ammonium chloride solution was used to quench reaction. The salts were extracted with ethyl ether. The combined organic liquids were dried over MgSO^ and then distilled. A fraction 102 collected at 47°C at 12 mm Hg contained (1) (Chloro­

methyl) dimethyl (l-methyl-2-propenyl) silane (68)7 exact mass: calcd 162.06315, found 163.06371; NMR 6 0.09(s,

6H, Si-CH3), 1.09(d, 3H, HC-CH3), 1.59(m, 1H, SiCHCH3),

2.86(s, 2H, CH 2C1), 4.73(m, 1H, -CH=C), 5.84(m, 2H,

C=CH2); IR 1630 cm-1 (C=C), 895 cm"1 (CH=CH2);

Anal. Calcd C^H^^ClSi: C, 51.86, H, 9.26.

Found: C, 51.79, H, 9.18. and (2) cis and trans-2-butenyl(chloromethyl)dimethyl- silanes (69 and 70); NMR 6 0.1(s, 6H, Si-CH3) , 1.60(m,

5H, SiCH2CH=CHCH3), 2.79(s, 2H, CH2C1), 5.47(m, 2H,

CH=CH); IR 1640 cm"1 (C=C).

Reaction of (Chloromethyl)dimethyl(l-methyl-2-propenyl)- silane (68) with Sodium Methoxide in Tetrahydrofuran.

A 2.7 to one mixture of (chloromethyl)dimethyl(1- methyl-2-propenyl)silane (68) and 2-butenyl(chloromethyl)- dimethylsilanes (69^ and 70) (0.26 g, 1.6 mmol) was added to a solution of sodium methoxide in tetrahydrofuran

(2 mL) which had been prepared by the addition of methanol

(0.1 g, 3.0 mmol) to sodium (0.07 g, 3.0 mmol) in tetra­ hydrofuran. Analysis of the reaction mixture was performed after 12 hr reflux. 103

Use of column A at 80°C with m-xylene as an internal standard revealed (1) dimethyl(2-methyl)-3- butenyl)methoxysilane (71, 0.11 g, 7.2 mmol, 47%); exact mass: calcd 158.11269, found, 158.11312; NMR 6 0.13(s,

6H, Si-CH3), 0.72(d, 2H, Si-CH2), 1.06(d, 3H, CH-CH3),

2.29(m, 1H, HC-HC=CH2), 3 . 3 4 (s , 3H, 0CH3), 4.92(m, 2H,

HC=CH2), 5.82(m, 1H, CH=CH2); IR 2839 cm-1 (Si-0CH3),

1620 cm-1 (CH=CH2) ;

Anal. Calcd for CQH 180Si: C, 60.76, H, 11.39.

Found: C, 60.67, H, 11.28. and cis and trans-dimethylmethoxy-3-pentenylsilanes (72 and 73, 0.045 g, 0.28 mmol, 17%); exact mass: calcd

158.11269, found, 158.11233; NMR 6 0.12(s, 6H, Si-CH3),

0.07(m, 2H, Si-CH2), 1.65(m, 3H, CH-CH3), 2.1(m, 2H,

H_C-CH -CH), 3.48(s, 3H, OCH^), 5.46(m, 2H, CH=CH); IR

2839 cm-1 (Si-0CH3);

Anal. Calcd for CgH^OSi: C, 60.76, H, 11.39.

Found: C, 60.52, H, 11.58. 104

Reaction of Allyl(chloromethyl)dimethylsilane (2) with

Sodium Isopropoxide in Tetrahydrofuran

Generation of sodium isopropoxide was accomplished

by addition of isopropyl alcohol (0.57 g, 9.5 mmol) to

sodium (0.22 g, 9.5 mmol) in tetrahydrofuran (4 mL)

followed by heating. Upon addition of allyl(chloromethyl)-

dimethylsilane (2, 0.94 g, 6.4 mmol), the mixture was

refluxed 14 hr. GC analysis on column A at 80°C with octane as the internal standard yielded one compound,

3-butenyldimethylisopropoxysilane (74, 0.89 g, 5.2 mmol,

81%). mass spectral: 157, 118, 104, 100; NMR 6 0.11 (s,

6H, Si-CH ), 1.2(d, 6H, CH(CH3)2), 0.70(m, 2H, Si-CH2-CH2),

2.05(m, 2H, CH2-CH=CH2), 4.0(m, 1H, CH(CH3)2), 4.98(m,

2H, HC=CH2), 5.9(m, 1H, CH=CH2); IR 1621 cm"1 (CH=CH2).

Anal. Calcd for C gH 2C)0Si: C, 62.79, H, 11.63.

Found: C, 62.61, H, 11.86.

Reaction of Allyl(chloromethyl)dimethylsilane (2) with

Sodium t-Butoxide in Tetrahydrofuran

Sodium t-butoxide was prepared by reaction of

sodium hydride (0.60 g, 12.5 mmol) and t-butyl alcohol

(0.92 g, 12.5 mmol). After hydrogen evolution ceased, 105

allyl(chloromethyl)dimethylsilane (2, 0.87 g, 5.8 mmol) was added. After the mixture had been heated at 65°C for

48 hr, analysis by GC on column A revealed the presence of

allyl (chloromethyl) dimethylsilane (2, 0.39 g, 002.6 mmol,

45%) and 3-butenyldimethyl t-butoxysilane (75, 0.39 g,

2.1 mmol, 35%). Exact mass: calcd 186.14398, found

186.14457? NMR 6 0.08(s, 6H, Si-CH3), 0.6(m, 2H, Si-CH2),

1.22 (s, 9H, C(CH3)3), 2.0 (m, 2H, CH 2-CH2-CH) , 4.91(m, 2H,

HC=CH2) , 5.91(m, 1H, CH=CH2); IR 1610 cm-1 (CH=CH2) .

Anal. Calcd for C^H^OSi: C, 64.52, H, 11.83.

Found: C, 64.38, H, 11.89.

Preparation of 3-Butenyl-t-butoxydimethylsilane (75).

Chlorodimethylsilane was treated with bromo-3- 66 butenylmagnesium to give 3-butenyldimethylsilane.

3-Butenyldimethylsilane (1.56 g, 1.4 mmol) was then

added to a solution of potassium t-butoxide in t-butanol.

According to GC analysis, no reaction took place until

dicyclohexyl 18-crown-6 was added in small amount (0.20 g). whereupon reaction was immediate. The mixture was

distilled and the product isolated by preparative GC. 106

Preparation of (Chloromethyl)dimethylphenylsilanes

3, 4, 5, 6, 7, and 8.

(Chloromethyl)dimethylphenylsilanes 3, 4, 5, 6, 7

and 8 were prepared from chloro(chloromethyl)dimethyl­

silane and the appropriate arylmagnesium bromide in 15 67 ethyl ether. ' Silanes 4 and 5, not previously

reported, showed the following properties: (chloromethyl)-

dimethyl(4-trifluoromethylphenyl)silane (4), exact mass:

calcd for CgH^F^i, M+-CH2C1 203.05038, found 203.05105;

NMR 6 0.41(s, 6H, Si-CH3), 2.95 (s, 2H, CH2C1), 7.62(m,

4H, aromatic); IR cm-1 1611, 1397, 1260. Silane 4

contained small amounts of impurities, possibly resulting

from halide exchange at the chloromethyl carbon, making

proper analysis impossible. (Chloromethyl)(3-chloro-

phenyl)dimethylsilane (5), exact mass: calcd 218.00853,

found 218.00791; NMR 6 0.43(s, 6H, Si-CH3), 2.94(s, 2H,

CH2-C1), 7.49(m, 4H, aromatic); IR cm-1 1560, 1397, 1260;

Anal. Calcd for CgH 12Cl2Si: C, 49.54, H, 5.50.

Found: C, 49.47, H, 5.46. 107

Preparation of Dimethylmethoxyphenylsilanes 79, 84, 87,

90, 9J3, and 96.

Dimethylmethoxyphenylsilanes 79, 84, ET7, 90, 93, and 9j5 were prepared from dimethoxydimethylsilane and the appropriately substituted phenylmagnesium bromide as described for dimethylmethoxyphenylsilane (79). Ethyl ether (100 mL) containing bromobenzene (8.1 g, 0.052 mol) was added dropwise to magnesium (1.44 g, 0.06 mol) at

such a rate to cause reflux. Excess magnesium was filtered off and the resultant solution dripped into dimethoxydimethylsilane (6.0 g, 0.05 mol) in ethyl ether

(100 mL). After the solution was kept at reflux for 12 hr, fractional distillation yielded dimethylmethoxyphenyl­ silane (79, 5.5 g, 67%). Substituted dimethylmethoxy­ phenylsilanes were obtained in the yields indicated: dimethylmethoxy(4-trifluoromethylphenyl)silane (84, 62%),

(3-chlorophenyl)dimethylmethoxysilane (87, 79%), (4- chlorophenyl)dimethylmethoxysilane (90, 59%), dimethyl­ methoxy (4-methylphenyl) silane (93, 61%), dimethylmethoxy-

(4-methoxyphenyl)silane (96, 66%). 108

Preparation of Ethylmethoxymethylphenylsilanes 78/ 83/

86/ 89. 92 and 95.

The preparation of the title compounds was

initiated by reaction of ethyltrichlorosilane with sodium methoxide in ethyl ether to yield ethyltrimethoxysilane which was then treated with methylmagnesium bromide to 45 46 give dimethoxyethylmethylsilane. ' Reaction of

dimethoxyethylmethylsilane with an appropriately sub­

stituted phenylmagnesium bromide yielded ethylmethoxy- methylphenylsi lanes 78, 83, 86, 89 , 92 and 95_ as

illustrated for ethylmethoxymethylphenylsilc.na (78) .

Phenylmagnesium bromide, as prepared from bromobenzene

(11.7 g, 0.075 mol) and magnesium (2.4 g, 0.1 mol), in ethyl ether (100 mL) was filtered and then added to a

solution of dimethoxyethylmethylsilane (9.78 g, 0.073 mol) in ethyl ether (100 mL). After 12 hr at reflux the

solution was distilled yielding ethylmethoxymethylphenyl- silane (78, 8.4 g, 64%). Substituted phenylsilanes were obtained in the following yeilds: ethylmethoxymethyl(4- trif luoromethylphenyl) silane (83^, 66%), (3-chlorophenyl)- ethylmethoxymethylsilane (8(5, 72%), (4-chlorophenyl)- ethylmethoxymethylphenylsilane (89, 55%), ethylmethoxy­ methyl (4-methylphenyl) silane (92, 71%), ethylmethoxy(4- methoxyphenyl)methylsilane (95, 69%). 109

Preparation of Benzyldimethylmethoxysilanes 77, 88 and 91.

Preparation of benzylsilanes T7, 88 and 91 was

accomplished by the addition of a substituted benzyl- magnesium chloride to dimethoxydimethylsilane as

described for benzyldimethylmethoxysilane (77). Ethyl

ether (100 mL) containing benzylmagnesium chloride,

prepared from benzylchloride (16.4 g, 0.13 mol) and magnesium (2.4 g, 0.10 mol), was added to a mixture of

dimethoxydimethylsilane (12.0 g, 0.10 mol) and ethyl

ether (100 mL). Distillation after 12 hr reflux gave

benzyldimethylmethoxysi lane (7J7, 11.7, g, 65%). (4-

Chlorobenzyl)dimethylmethoxysilane (88) and dimethyl­ methoxy (4-methylbenzyl)silane (91) were obtained in 69%

and 55%.

Reaction of (Chloromethyl)dimethylphenylsilane (3) with

Sodium Methoxide in Dioxane at 60°C.

Sodium methoxide was generated by the addition of methanol (5 mL) to freshly cut sodium (0.29 g, 0.013 mol)

followed by evaporation of the excess solvent. Dioxane

(2 mL) and (chloromethyl)dimethylphenylsilane (3, 1.15 g,

6.2 mmol) were added. The mixture was kept at 60°C for

108 hr. Analysis by GC on columns A and B at 80°C and 110

150°C using octane and mesilylene as the internal standards revealed the presence of (1) benzyldimethyl- methoxysilane (77, 0.50 g, 2.8 mmol, 45%), exact mass: calcd 180.09704, found 180.09730; NMR 6 0.09(s, 6H,

Si-CH3), 2.19(s, 2H, Si-CH2), 3.31(s, 3H, OCH3), 7.18(m,

5H, aromatic) ; IR 2839 cm- '*' (Si-OCH3) ;

Anal. Calcd for C ^ H ^ O S i : C, 66.6, H, 8.88.

Found: C, 66.54, H, 8.92.

(2) ethylmethoxymethylphenylsilane (78, 0.25 g, 1.4 mmol,

22%), exact mass: calcd 180.09704, found 180.09646;

NMR 6 0.31(s, 3H, Si-CH3), 0.82 (m, 5H, Si-CH2CH3), 3.39

(s, 3H, 0CH3) , 7.41(m, 5H, aromatic), IR 2839 cm-'*'

(Si-0CH3);

Anal. Calcd for C^gH^gOSi: C, 66.67, H, 8.89.

Found: C, 66.56, H, 8.88.

(3) dimethoxydimethylsilane (47, 0.10 g, 0.87 mmol, 14%),

(4) chloromethyldimethylphenylsilane (3, 0.14 g, 0.77 mol,

12%), and (5) dimethylmethoxyphenylsilane^® (79, 0.052 g,

0.3 mmol, 5%), exact mass: calcd for CgH^OSi 166.08139, found 166.08097. All products compared satisfactorily with authentic samples independently prepared. Ill

Reaction of (Chloromethyl)dimethyl(4-trifluoromethylphenyl) silane (4) with Sodium Methoxide in Dioxane at 60°C...... ~ r ...... — - __ ■...... , — — ___

Dioxane (3 mL) and (chloromethyl) dimethyl(4- trifluoromethylphenyl)silane (4, 0.39 g, 15.5 mmol) were added to dried sodium methoxide prepared from sodium

(0.09 g, 0.0039 mol) and methanol. The solution was kept at 60°C for 5 hr. Analysis by GC on column A using mesitylene and xylene as internal standards revealed the presence of: (1) dimethoxydimethylsilane (47, 0.15 g,

13 mmol, 82%); (2) ethylmethoxymethyl(4-trifluoromethyl­ phenyl) silane (83, 0.025 g, 0.10 mmol, 7%); exact mass: calcd 248.08442, found 248.08531; NMR 6 0.39(s, 3H,

Si-CH3), 0.96(m, 5H, Si-CH2CH3), 3.41(s, 3H, 0CH3), 7.68

(m, 4H, aromatic); IR cm-1 2840 (Si-0CH3)y

Anal. Calcd for C^H^,-0F3S i : C, 53.22, H, 6.05.

Found: C, 53.24, H, 6.09.

(3) (chloromethyl)dimethyl(4-trifluoromethylphenyl)silane

(4, 0.0093 g, 0.04 mmol, 2.5%), and (4) dimethylmethoxy-

(4-trifluoromethylphenyl)silane (84, 0.0047 g, 0.02 mol,

1.5%); exact mass: calcd 234.06877, found 234.06935; NMR

6 0.42(s, 6H, Si-CH3), 3.50(s, 3H, 0CH3), 7.71(m, 4H, aromatic); IR cm- '*' 2840 (Si-0CH3). 112

Anal. Calcd for C-^qH-^OSIF^ C, 51.28/ H, 5.55.

Found: C, 50.97, H, 5.70.

All compounds were identified by comparison with independently prepared samples.

Reaction of (Chloromethyl)(3-chlorophenyl)dimethylsilane

(5) with Sodium Methoxide in Dioxane at 60°C.

Sodium methoxide was prepared from methanol and sodium (0.22 g, 0.0096 mol) and evaporating the excess solvent. After addition of dioxane (3 mL) and (chloro­ methyl) - (3-chlorophenyl) dimethylsilane (5, 0.99 g, 4.5 mmol), the mixture was heated at 60°C for 10 hr. Analysis by GC using trans-decalin and octane as the internal standards indicated the following compounds were formed:

(1) dimethoxydimethylsilane (47/ 0.46 g, 3.8 mmol, 83%),

(2) (3-chlorophenyl)ethylmethoxymethylsilane (86, 0.082 g,

0.38 mmol, 8%); exact mass: calcd 214.05807, found

214.05881; NMR 6 0.35(s, 3H, Si-CH3), 0.85(m, 5H,

Si-CI^CH^) , 3.42(s, 3H, Si-OCH^) , 7.37(m, 4H, aromatic);

IR cm”1 2840 (Si_0CH3);

Anal. Calcd for C.JH,„ClOSi: C, 56.07, H, 7.01. ------1U lb Found: C, 56.09, H, 6.97. 113 and (3) (3-chlorophenyl)dimethylmethoxysilane (87, 0.013 g, 0.065 mmol, 1.5%); exact mass: calcd 200.04247, found

200.04305; NMR 6 0.38(s, 6H, Si-CH3), 3.48(s, 3H,

Si-OCH3)/ 7.43(m, 4H, aromatic); IR cm"1 2840 (Si-OCH3).

Anal. Calcd for CgH 13ClOSi: C, 54.00, H, 6.50.

Found: C, 53.95, H, 6.39.

The products compared satisfactorily with independently prepared samples.

Reaction of (Chloromethyl)(4-chlorophenyl)dimethylsilane

(6) with Sodium Methoxide in Dioxane at 60°C.

Addition of methanol (3.5 mL) to sodium (0.29 g,

0.013 mol) and subsequent evaporation of the alcohol led to dry sodium methoxide. Dioxane (1 mL) and (chloro­ methyl) ( 4-chlorophenyl) dimethylsilane (6, 0.99 g, 4.5 mmol) were added and the mixture was maintained at 60°C for 12 hr. Analysis on column A at 185°C and 80°C using trans-decalin and octane as the internal standards revealed the following products: (1) dimethoxydimethyl­ silane (47, 0.41 g, 3.4 mmol, 75%), (2) (4-chlorophenyl)- ethylmethoxymethylsilane (89, 0.077 g, 0.36 mmol, 8%), exact mass: calcd 214.05807, found 214.05865; NMR 6 0.32

(s, 3H, Si-CH3), 0.92(m, 5H, Si-CH2CH3), 3.34(s, 3H, 0CH3),

7.44(m, 4H, aromatic); IR 2839 cm"1 (Si-0CH3); 114

Anal. Calcd for C10H 15ClOSi: C, 56.07, H, 7.01.

Found: C, 55.88, H, 6.98.

(3) (4-chlorphenyl) dimethylmethoxysi lane (90, 0.014 g,

0.069 mmol, 2%); exact mass: calcd 200.04242, found

200.04288; NMR 6 0.35(s, 6H, Si-CH3>, 3.39(s, 3H, OCH^),

7.38(m, 4H, aromatic); IR 2839 cm-^ (Si-OCH^);

Anal. Calcd for CgH-^ClOSi: C, 54.00, H, 6.50.

Found: C, 53.96, H, 6.39. and (4) (4-chlorobenzyl)dimethylmethoxysilane (88,

0.0097 g, 0.045 mmol, 1%); exact mass: calcd 214.05807, found 214.05881; NMR 6 0.09(s, 6H, Si-CH3), 2.11(s, 2H,

Si-CI^), 3.40(s, 3H, OCH3), 7.05 (m, 4H, aromatic); IR

2839 cm-1 (Si-0CH3);

Anal. Calcd for C^qH^^CIOSI: C, 56.07, H, 7.01.

Found: C, 56.02, H, 6.96.

All compounds were compared with authentic samples obtained by independent synthesis.

Reaction of (Chloromethyl)dimethyl(4-methylphenyl)silane

(7) with Sodium Methoxide in Dioxane at 60°C.

(Chloromethyl) dimethyl (4-methylphenyl) silane (7_,

0.88 g, 4.4 mmol) was added to a slurry of dry sodium 115 methoxide, prepared from methanol and sodium (0.24 g,

0.01 mol), in dioxane (4 mL). The mixture was kept at

60°C for 36 hr. Analysis by GC on column A at 160°C and

S0°C using mesitylene and octane as internal standards revealed: (1) dimethylmethoxy(4-methylbenzyl) silane (91

0.36 g, 1.8 mmol, 42%), exact mass: calcd 194.11269, found

194.11222; NMR 6 0.03 (s, 6H, Si-CH3), 2.10(s, 2H, CH2~Si)

2.28(s, 3H, 0-CH3), 3 . 4 1 (s , 3H, OCH3), 6.97(m, 4H, aromatic) ; IR 2839 cm- '*' (Si-OCH3) ;

Anal. Calcd for C^ H ^ O S i : C, 68.04, H, 9.28.

Found: C, 67.82, H, 9.20.

(2) ethylmethylmethoxy(4-methylphenyl)silane (92, 0.10 g,

0.53 mmol, 12%); exact mass: calcd 194.11269, found

194.11222; NMR 6 0.36(s, 3H, Si_CH3), 0.91(m, 5H,

Si_CH2CH3), 2.31(s, 3H, 0-CHg), 3.41(s, 3H, 0CH3), 7.32

(m, 4H, aromatic) ; IR cm- "*- 2839 (Si-0CH3) ;

Anal. Calcd for C^H^gOSi: C, 68.04, H, 9.28.

Found: C, 67.77, H, 9.23.

(3) (chloromethyl)dimethyl(4-methylphenyl)silane (7,

0.082 g, 0.41 mmol, 9%)), (4) dimethoxydimethylsilane

(47, 0.042 g, 0.35 mmol, 8%), and (5) dimethylmethoxy-

(4-methylphenyl)silane (93, 0.031 g, 0.17 mmol, 4%), 116 exact mass: calcd 180.09704, found 180.09747; NMR 6 0.33

(s, 6H, Si-CH3), 2.30 (s, 3H, 0-CH3) , 3.39 (s, 3H, OCH^) ,

7.30(m, 4H, aromatic); IR 2839 cm-1 (Si-0CH3);

Anal. Calcd for C ^ H ^ O S i : C, 66.66, H, 8.88.

Found : C, 66.42, H, 8.98.

All compounds were compared with authentic samples.

Reaction of (Chloromethyl)dimethyl(4-methoxyphenyl)silane

(8_) with Sodium Methoxide in Dioxane at 60°C.

To sodium methoxide, prepared by reaction of sodium

(0.30 g, 0.013 mol) and methanol followed by evaporation of the solvent, was added dioxane (3 mL) and (chloromethyl)- dimethyl(4-methoxyphenyl)silane (8, 0.86 g, 4.0 mmol).

The mixture was kept at 60°C for 48 hr. Analysis by GC using column A and trans-decalin and octane as internal standards showed the following compounds were present:

(1) dimethylmethoxy(4-methoxybenzyl)silane (94, 0.42 g,

2.0 mmol, 49%); exact mass: calcd 210.10760, found 210.

210.10701; NMR 6 0.05(s, 6H, Si-CH3), 2.09(s, 2H, Si-CH2),

3.39(s, 3H, Si_0CH3), 3.70(s, 3H, 0-OCH3) , 6.86(m, 4H, aromatic) ; IR cm- '*' 2840 (Si-OCH3) ;

Anal. Calcd for cu Hi8°2S:i': C/ H' 8*57. Found: C, 62.97, H, 8.63. 117

(2) (chloromethyl) dimethyl (4-methoxyphenyl) silane (8,

0.13 g, 0.61 mmol, 15%); (3) ethylmethoxy(4-methoxy­ phenyl) methylsilane (95, 0.10 g, 0.48 mmol, 12%); exact mass: calcd 210.10760, found 210.10701; NMR 6 0.31(s, 3H,

Si-CH3), 0.90(m, 5H, Si-CH2CH3), 3.40(s, 3H, Si-0CH3),

3.80(s, 3H, 0-OCH3), 7.25(m, 4H, aromatic); IR 2840 cm-1

(Si-0CH3);

Anal. Calcd for cn H i8°2S:'': C/ 62.86, H ' 8.57. Found: C, 62.63, H, 8.49.

(4) dimethylmethoxy(4-methoxyphenyl)silane (96, 0.025 g,

0.13 mmol, 3%); exact mass: calcd 196.09195, found

196.09243; NMR 6 0.41 (s, 6H, Si-CH3), 3.43(s, 3H,

Si-0CH3), 3.80(s, 3H, 0-OCH3), 7.23(m, 4H, aromatic); IR

2840 cm-1 (Si-0CH3);

Anal. Calcd for C^ H ^ C ^ S i : C, 61.22, H, 8.16.

Found: C, 61.01, H, 7.98.

and (5) dimethoxydimethylsilane (47, 0.13 g, 0.11 mmol,

3%) .

Reaction of (Chloromethyl)dimethylphenylsilane (3) with

Sodium Methoxide in Methanol.

(Chloromethyl)dimethylphenylsilane (8, 0.38 g, 2.1

mmol) was added to sodium methoxide prepared from sodium 118

(0.09 g, 3.9 mmol) and methanol (1.5 m L ) . After the mixture had been refluxed for 12 hr, analysis by GC on

column A at 80°C using octane as an internal standard

revealed the presence of dimethoxydimethylsilane (47,

0.014 g, 0.012 mmol/ 5%). Further analysis at a column

temperature of 145°C using mesitylene as internal

standard led to isolation of (1) dimethyl(methoxymethyl)- 15 phenylsilane (97/ 0.25 g, 1.4 mmol/ 66%), exact mass:

calcd 180.097037, found, 180.097469.

Anal. Calcd for C^H^OSi: C, 66.66, H, 8.89.

Found: C, 66.50, H, 8.89.

(2) starting silane (3, 0.065 g, 0.35 mol, 17%) and

(3) dimethylmethoxyphenylsilane (79, 0.017 g, 0.001 mmol,

5%) exact mass: calcd for C^H^OSi, 166.081388, found

166.080971. Compounds were characterized by spectal

analysis.

Reaction of (Chloromethyl)dimethylphenylsilane (3) with

Sodium Methoxide in Methanol and 18-Crown-6.

Addition of sodium (0.12 g, 0.0052 mol) to methanol

(5 mL) was followed by 18-crown-6 (10 mg) and (chloro­ methyl) dimethylphenylsilane (3, 0.45 g, 2.4 mmol). The 119 mixture was held at 65°C for 16 hr. GC analysis revealed formation of dimethyl(methoxymethyl)phenylsilane (97,

0.26 g, 1.5 mmol, 60%), dimethoxydimethylsilane (47/

0.076 g, 0.63 mmol/ 26%) and dimethylmethoxyphenylsilane

(79/ 0.043 g, 0.26 mmol, 11%).

Reaction of (Chloromethyl) dimethylphenylsilane (3) with

Potassium Methoxide in Methanol. .

Methanol (3 mL) was added to potassium (0.54 g,

1.4 mmol). After introduction of, (chloromethyl)dimethyl­ phenylsilane (3, 1.14 g, 6.2 mmol), the mixture was stirred at 65°C for 12 hr. By GC analysis on column A at

80°C and then at 150°C using octane and mesitylene as internal standards, the following silyl compounds were identified: (1) dimethoxydimethylsilane (4?, 0.34 g,

0.28 mmol, 46%), (2) dimethylmethoxyphenylsilane (79, 0.15 g, 0.088 mmol, 14%) and (3) dimethyl(methoxymethyl)phenyl­ silane (97, 0.31 g, 0.17 mmol, 28%). Benzyldimethyl- methoxysilane (77) and ethylmethoxymethylphenylsilane (78) were also present in trace amounts.

Reaction of (Chloromethyl)dimethylphenylsilane (3) with

Cesium Methoxide in Methanol.

Cesium (5 g, 0.037 mol) was added to methanol (50 mL) in an inert atmosphere glovebox. An aliquot (10 mL) 120

(1.0 g, 0.0075 mol Cs) of the resultant solution was used for reaction with (chloromethyl)dimethylphenylsilane

(3, 0.55 g, 3.0 mmol) in methanol. The mixture was heated at 68°C for 2 hr and then analyzed by GC using column A. Mesitylene and octane were used as internal standards. The compounds detected were: dimethoxy­ dimethylsilane (47/ 0.24 g, 2.0 mmol/ 66%), dimethyl­ methoxyphenylsilane (79, 0.098 g, 0.59 mmol, 20%) and dimethyl(methoxymethyl)phenylsilane (97, 0.044 g, 0.25 mmol, 8%) .

Reaction of (Chloromethyl)trimethylsilane (9) with

Potassium Methoxide in Methanol.

(Chloromethyl)trimethylsilane (9, 1.2 g, 10.0 mmol) was added to a solution of potassium (0.52 g, 0.013 mol) in methanol (2.5 mL) and the mixture was refluxed 18 hr.

The presence of (methoxymethyl)trimethylsilane (11, 0.95 g,

8 mmol, 11%), starting silane (9, 0.19 g, 1.5 mmol, 15%) and a trace of methoxytrimethylsilane (10) was revealed by GC analysis on column A at 70° with toluene as internal standard. The compounds were compared with authentic . 20 samples. 121

Reaction of (Bromomethyl)trimethylsilane (34) with — ■ — ------Potassium Methoxide in Methanol.

Addition of methanol (2.5 mL) to potassium (0.60 g,

15 mmol) resulted in methanolic potassium methoxide.

(Bromomethyl) trimethylsilane (3j4, 1.7 g, 10 mmol) was added. Upon refluxing the mixture 12 hr and analyzing the product by GC on column A at 70°C using toluene as the internal standard, (methoxymethyl)trimethylsilane (11,

1.18 g, 10 mmol) was found to be produced quantitatively.

Reaction of (Chloromethyl) dimethylphenylsilane {3) with

Lithium Methoxide in Dioxane

Lithium methoxide was prepared from methanol (5 mL) and n-butyllithium in hexane (1.6 M, 7 mL, 11.2 mmol) and evaporation of solvents. Addition of dioxane (2 mL) and

(chloromethyl)dimethylphenylsilane (3, 1.0 g, 5.5 mmol), refluxing the mixture 120 hr and GC analysis revealed that !3 had not reacted.

Reaction of (Chloromethyl) dimethylphenylsilane (3) with

Lithium Methoxide in Dioxane with 12-Crown-4.

Methanol (4 mL) was added to n-butyllithium (1.6 M in hexane, 7 mL, 11.2 mmol) and the solvents were evaporated. Upon addition of dioxane (1.5 mL), 122

(chloromethyl) dimethylphenylsilane (3_, 0.61 g, 3.3 mmol)/ and 12-crown-4 (0.25 mL), the mixture was heated at 100°C for 24 hr. No reaction occurred as evidenced by GC analysis.

Reaction of (Chloromethyl) dimethylphenylsilane (3) with

Magnesium Methoxide in Dioxane

Magnesium methoxide was prepared from magnesium

(0.08 g, 3.3 mol) and methanol (3 m L ) . The methanol was evaporated, dioxane (1 mL) and (chloromethyl)dimethyl­ phenylsilane (3, 0.29 g, 1.5 mmol) were added, and the mixture was heated at 100°C for 84 hr. Analysis by GC showed that no reaction of 3^ had occurred.

Reaction of (Chloromethyl) dimethylphenylsilane (3^) with

Calcium Methoxide in Dioxane.

Calcium methoxide was generated by the addition of methanol (4 mL) to calcium hydride (0.40 g, 9.5 mmol).

After removal of the solvent, dioxane (2 mL) and (chloro­ methyl) dimethylphenylsilane (3, 0.49 g, 2.7 mmol) were added. The reaction was heated at 100°C for 168 hr. GC analysis showed no evidence for product formation. 123

Reaction of (Chloromethyl)dimethylphenylsilane (3) with

Sodium Methoxide in Dioxane at 30°C.

(Chloromethyl)dimethylphenylsilane (3, 1.02 g, 5.5 mmol) and dioxane (4 mL) were added to sodium methoxide prepared by reaction of sodium (0.31 g, 0.013 mol) and methanol. The reaction was stirred at 30°C for 168 hr.

Analysis on column A at 80°C and 150°C and column B at

100°C using octane and mesitylene as internal standards revealed: (1) dimethoxydimethylsilane (47, 0.015 g,

0.012 mmol, 2%), (2) dimethylmethoxyphenylsilane (79,

0.016 g, 0.01 mmol, 2%), (3) ethylmethoxymethylphenyl- silane (78, 0.09 g, 0.05 mmol, 9%), (4) benzyldimethyl- methoxysilane (77, 0.45 g, 0.25 mmol) and (5) (chloro­ methyl) dimethylphenylsilane (3, 0.41 g, 0.22 mmol, 40%).

Reaction of (Chloromethyl) dimethylphenylsilane (3) with

Sodium Methoxide and 18-Crown-6 in Dioxane

To sodium methoxide, produced by addition of methanol to sodium (0.17 g, 0.0074 mol) and evaporation of solvent, were added dioxane (5 mL), 18-crown-6 (10 mg) and (chloromethyl)dimethylphenylsilane (3, 0.55 g, 3.0 mmol). The reaction was stirred for 18 hr. GC analysis showed the presence of: (1) dimethoxydimethylsilane (47, 124

0.27 g, 2.3 mmol, 75%), (2) dimethylmethoxyphenylsilane

(79, 0.059 g, 0.36 mmol, 12%), and (3) ethylmethoxymethyl- phenylsilane (7j3, 0.060 g, 0.33 mmol, 11%).

Reaction of (Chloromethyl)dimethylphenylsilane (3) with

Potassium Methoxide in Dioxane at 30°C.

Dry potassium methoxide was formed by addition of methanol (2 mL) to potassium (0.16 g, 4.1 g mol) and removal of solvent. Dioxane (2 mL) and (chloromethyl)- dimethylphenylsilane (3, 0.37 g, 2.0 mmol) were added.

After 10 hr at 30°C, GC analysis on column A at 80°C using octane as internal standard showed the presence of dimethoxydimethylsilane (47, 0.18 g, 1.5 mmol, 76%).

Further, analysis at 145°C revealed: (1) dimethylmethoxy­ phenylsilane (79, 0.033 g, 0.02 mmol, 10%) and (2) ethyl- methoxymethylphenylsilane (78, 0.051 g, 0.03 mmol, 14%).

Reaction of (Chloromethyl)dimethylphenylsilane (3) with

Potassium Methoxide and 18-Crown-6 in Dioxane

Dioxane (5 mL), 18-crown-6 (10 mg) and (chloromethyl)- dimethylphenylsilane (3, 0.49 g, 2.6 mmol) were added to potassium methoxide prepared by reaction of potassium

(0.30 g, 0.0077 mol) and methanol. GC analysis, after

18 hr at 30°C, showed the formation of: 125

(1) dimethoxydimethylsilane (47, 0.19 g, 1.6 mmol, 60%),

(2) dimethylmethoxyphenylsilane (79, 0.12 g, 0.70 mmol,

26%), and (3) ethylmethoxymethylphenylsilane (78, 0.054 g,

0.30 mmol, 11%).

Reaction of (Chloromethyl)dimethylphenylsilane (3) with

Cesium Methoxide in Dioxane at 30°C.

An aliquot (15 mL) of the previously prepared methanolic cesium methoxide solution was evaporated to

dryness. Dioxane (4 mL) and (chloromethyl)dimethylphenyl­

silane (3, 0.87 g, 4.7 mmol) were added. The solution was m-mm

stirred at 30°C for 14 hr and then analyzed by GC using

column A with octane and mesitylene as internal standards.

The compounds present were determined to be: (1) dimethoxy­

dimethylsilane (47^ 0.44 g, 3.7 mmol, 78%), (2) dimethyl­ methoxyphenylsilane (79, 0.10 g, 0.6 mmol, 13%) and

(3) ethylmethoxymethylphenylsilane (78, 0.018 g, 0.10 mmol, 2%) .

Reaction of (Chloromethyl)dimethylphenylsilane (3) with

Sodium Methoxide in Dioxane at 100°C.

Methanol (2 mL) was added to sodium (0.12 g, 0.0052 mol) and the solvent evaporated. Dioxane (1,5 mL) and 126

(chloromethyl)dimethylphenylsilane (!3, 0.56 g, 3.0 mmol) were added. After heating at 100°C for 12 hr GC analysis on column A revealed the presence of: (1) dimethoxy­ dimethylsilane (47, 0.16 g, 1.3 mmol, 44%), (2) ethyl­ methoxymethylphenylsilane (78, 0.17 g, 0.97 mmol, 32%), and (3) dimethylmethoxyphenylsilane (79, 0.060 g, 0.36 mmol, 12%). REFERENCES

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