q
MASS SPECTRAL STUDY OF TRIMETHYLSILYLMETHYL-
SUBSTITUTED CHLOROSILANES
THESIS
Presented to the Graduate Council of the
North Texas State University in Partial
Fulfillment of the Requirements
For the Degree of
MASTER OF SCIENCE
By
Keith Randal Pope, B.S.
Denton, Texas
December, 1982 Pope, Keith Randal, Mass Spectral Study of Trimethylsilyl- methyl substituted Chlorosilanes. Master of Science (Chemistry),
December, 1982, 47, pp., 5 tables, bibliography, 22 titles.
The mass spectra of the compounds [Me 3 SiCH2 nSiCl 4 n (n=1-3) were studied in detail. MIKES and CID spectra were used in conjunction with the observance of metastable processes to develop consistent fragmentation schemes. Particular attention is drawn to the formation of charged and neutral species containing the silicon-carbon double bond, including
2-silaallene, under conditions of electron impact. TABLE OF CONTENTS
Page
LIST OF TABLES...... ii
LIST OF ILLUSTRATIONS...... iii
Chapter
I. INTRODUCTION.o...... 1
II. RESULTS AND DISCUSSION ...... 9
III. EXPERIMENTAL ...... 39
APPENDIX...... 45
BIBLIOGRAPHY,*...... 46
i LIST OF TABLES
Table Page
I, [Me 3 SiCH2 InSiCl 4 -n ...... 9
II. Mass Spectrum of Trimethylsilyl- methyltrichlorosilane (I)...... 11
III. Metastable Peaks Observed in the Mass Spectra of Compounds I-III...... 13
IV. Mass Spectrum of Bis(trimethylsilylmethyl)- dichlorosilane (II)...... 16
V. Mass Spectrum of Tris(trimethylsilylmethyl)- chlorosilane (III) ...... 27
ii LIST OF ILLUSTRATIONS
Figure Page
1 Inverse Nier-Johnson Geometry with field-free regions A,B,C...... 5
2 Mass Spectrum of Trimethylsilylmethyl- trichlorosilane (I)...... 12
3 Mass Spectrum of Bis(trimethylsilylmethyl)- dichlorosilane (II),...... 17
4 Unimolecular MIKES Spectrum of m/e 257.0. . .0 20
5 CID Spectrum of m/e 257...... 21
6 Unimolecular MIKES Spectrum of m/e 149. . . .0 22
7 CID Spectrum of m/e 149...... 23
8 CID Spectrum of m/e 93....0...... 25
9 Unimolecular MIKES Spectrum of m/e 93 . .0. .0 26
10 Mass Spectrum of Tris(trimethylsilylmethyl)- chlorosilane (III) ...... 28
11 Unimolecular MIKES Spectrum of m/e 309. .0.0.0 30
12 CIDSpectrum of m/e 309*...... 0 .. 31
13 Unimolecular MIKES Spectrum of m/e 201. .0.0.0 32
14 CID Spectrum of m/e 201..0 ...... 33
iii CHAPTER I
INTRODUCTION
The synthesis and reactivity of chemical species containing the silicon-carbon double bond, silenes, have been the subject of great interest for nearly a decade.1
Silenes are accessible under a wide variety of conditions including thermal decomposition of substituted monosilacyclo- butanes, 2 photochemical decomposition of polyorganosilanes, 3 and elimination of metal halides from a-lithiohalosilanes.4
Evidence also exists for the generation of silenes by electron impact, presently the most common method of ioni- zation in mass spectrometers. One such case is the mass spectra of substituted monosilacyclobutanes, reported by
Auner and Grobe,5 in which prominent peaks in the spectra may be ascribed to ions containing the silicon-carbon double bond. These investigators have used mass spectral fragmen- tation patterns to characterize condensate from the pyrolysis of 1,3-disilacyclobutane under high vacuum at 6000C and again propose the formation of silenes under conditions of electron
impact.6 A subsequent paper suggested the formation of
silenes in the mass spectral decomposition of methylcyclo- pentadienyl silacyclobutane. Fragmentation patterns have
also provided evidence for the formation of neutral species
1 2
incorporating double bonds between silicon and the chalcogens
(O,S,Se,Te)8 and charged species containing double bonds between silicon and oxygen.9
Of particular interest is the possibility of correlating mass spectral fragmentation patterns with mechanisms involved in the high energy generation of silenes. The method of generating silenes by electron impact would seem to be a good method for studying the energetics of this highly reactive moiety if the genetic relationships between the observed fragments could be determined unambiguously.
Indeed, typical mass spectra are obtained using 50-70 ev electrons, whereas the energies necessary to ionize most 10 organic compounds are in the neighborhood of 10 ev0. Under typical conditions, then, the ions produced initially in a mass spectrometer are in a highly excited state. This results in a large number of daughter fragments from the parent ion, but rarely are recombinations observed in mass spectrometry.
Thus, most processes occurring under these conditions are unimolecular decompositions.
The unambiguous mapping of mass spectral fragmentation patterns is not, however, a trivial matter. Although it is often possible to narrow the possibilities for ion genisis based upon structural arguments, it is difficult to absolutely prove that two fragments are related by a one-step process, as illustrated in Scheme 1.11 3
M0 M+ -- > + +
Scheme 1
In principle, the ion Mt may be the parent molecular ion or any ion which results from some sequence of fragmen- tations of the parent ion, and the dissociation of M+l to + 0 anywhere produce M2 and the neutral species M3 may occur along the path of the ion beam from source to detector. If the ion M+ is long-lived, then fragmentation may occur after
it has been accelerated by an electric potential towards
the magnetic focusing sector; in particular, this may
happen in a field-free region (FFR). The product M2 may 12 then give rise to a so-called "metastable peak."12 These
peaks are readily identifiable because they are broader
than normal peaks, much less intense, and need not occur at
13 integral mass values. The maximum intensity of the meta-
stable peak corresponds to a mass M dependent upon the
masses of the parent and daughter ions according to the well-
known formula,
* 2 M = M2/M
A magnetic sector is necessary to observe such metastable
peaks. 14 Although the presence of such a peak is consistent
with the process in Scheme 1, it does not define the masses
M and M2 independently. 4
A detailed analysis of mass spectral fragmentation patterns is facilitated by the recently developed techniques of mass analyzed ion kinetic energy spectrometry (MIKES) and collision induced decomposition (CID).15,16 The MIKES technique is performed on a double focusing mass spectrometer with inverse Nier-Johnson geometry as shown in Figure 1.17
The relevant features of this configuration are the presence of a magnetic sector followed by an electric sector with three interposing field-freE regions. The field strength of the magnetic sector can be varied to allow ions of a particular mass to pass intc the second FFR. The electric focusing sector can then be decoupled and tuned to obtain a spectrum of fragmentations Occurring in the second FFR. The important result is that the origin of the daughter ions analyzed by the electric sector is clear.
In practice, the number of fragmentations occurring in region B of Figure 1 will be small in relation to the number occurring in the ion source. Thus MIKES spectra will detect only a few fragmentations. To overcome this difficulty,
ions entering region B can be collisionally activated. If
a slight pressure of some inert gas is present in region B
of the spectrometer, enteri-n-g ions will collide with the gas
molecules and may dissociate. Helium is usually preferred
as a target gas because of its inertness, and because small
target particles tend to fayor excitation of the incident
ions to a dissociative electronic state.18 Most importantly, 5
MAGNETIC SECTOR ELECTRIC SECTOR
- - ~------B------~ N / / I I
I I I I I I
I A C
ION SOURCE DETECTOR
Figure 1: Inverse Nier-Johnson Geometry with field-free regions A,B,C. 6 ions which have added stability can be induced to dissociate through collisional activation. Therefore, the CID technique, in conjunction with a MIKES scan, can be used to probe frag- mentation pathways to a greater extent than would be possible with conventional mass spectrometry. The major disadvantage in using this method appears to be a decreased resolving power due to the scattering effects of collisional processes. If a high resolution mass spectrum is available to compare with the MIKES and CID data, poor resolution is not a great barrier to the illucidation of fragmentation pathways. In general, the MIKES and CID techniques provide information which is necessary for the detailed analysis of mass spectral fragmentation patterns. 7
REFERENCES
1. Bush, R. D.j Golino, C. M. and Sommer, L. H., J. Amer.
Chem. Soc. 1, 96, 7105 (1974).
2. Barton, T. J., Kilgour, J. A. and Marquardt, G.,' J.
Organometal. Chem., 85, 317 (1975).
3. Ishikawa, M., Pure Ap. Chem., 50(1), 11 (1978).
4. Jones, P. R. and Lim, T. F. 0., J. Amer. Chemi. Soc.,
99(6), 2013 (1977).
5. Auner, N. and Grobe, J., J. Organometal. Chem., 188(1),
25 (1980).
6. Auner, N. and Grobe, J.., Zeit. Anorg. Allg. Chem., 459,
15 (1979).
7. Auner, N. and Grobe, J., J. Organometal. Chem., 190(2),
129 (1980).
8. Drake, J. E., Glavincevski, B. M. and Wong, C., J. Inorg.
Nucl. Chem., 42, 175 (1980).
9. Larsen, *G. L., Oliva, A. and Tsai, R. S.-C.,, Org. Mass
Spectrom. , 14, 364 (1979).
10. Schlunegger, U. P., Advanced Mass Spectrometry, New York,
Pergamon Press, 1980.
11. Bowen, R. D., Howe, I. and Williams, D. H., Mass
Spectronmetry, 2 ed., New York, McGraw-Hill, 1981.
12. Beynon, J. H. and Cooks, R. G., Res./Dev, 22, 26 (1971) .
13. Reference 11, p. 56. 8
14. Reference 11, p. 54.
15. Reference 10, p. 13.
16. Reference 12, p. 26.
17. Reference 10, p. 32.
18. Dong, P., Durup, J. and Yamaoka, H., Chem. Phys. , 51,
3465 (1969). CHAPTER II
RESULTS AND DISCUSSION
Reports published as early as 1968 suggested that a silene might be generated by reacting an organohalosilane with tert-butyllithium at low temperatures in the presence of a chelating amine.1 To investigate this possibility more thoroughly, the compounds [Me3 SiCH2 InSiC4-n were prepared by a method similar to that of Sommer and Murch. 2
The mass spectra for the compounds I-III (Table I) were obtained initially to confirm the molecular weights of the products. However, the data suggested very interesting fragmentation patterns which warranted a more detailed study.
TABLE I
(Me3 SiCH 2] nSiCl4-n
n Compound M.W. (g./mole)
1 I 220.5 2 II 273.0 2 III 324.5
In addition to the conventional high resolution mass spectra obtained for the three compounds, CID and uni- molecular MIKES spectra were obtained for compounds II and III
9 10 to clarify ion genetic relationships in the development of a consistent fragmentation scheme.
The high resolution mass spectrum of trimethylsilyl- methylchlorosilane (I) is summarized in Table II. The prominent features of the spectrum are presented graphically in Figure 2, and the metastable peaks which were observed are listed in Table III. The proposed fragmentation pattern is shown in Scheme 2.
The parent molecular ion of I is not observed, but the loss of methyl would account for appearance of the peak at m/e 205. Metastable peaks observed at m/e 139.3, 42.2, and 86.3 support three pathways of decomposition for this ion giving rise to peaks at 169, 93, and 133, respectively.
The fact that there are several metastable peaks associated with the decomposition processes suggests that the ion at
205 has some added stability.
The fragmentation behavior of methoxydisilanes has
similar features, and has been explained in terms of direct
conjugation or bridging structures involving a highly electronegative atom adjacent to silicon as shown in
Scheme 3. 3
* + Me Me3SiSiMe2(OCH)K- L Me3SiSiMe(OCH3) or Me2Si SiMe 3 2 3 3 3 2 ie2
Scheme 3
Bridging structures such as that shown for the ion at m/e 205 11
TABLE II
Mass Spectrum of Trimethylsilylmethyltrichlorosilane (I) m/ea Parent-x % of base peakb FormulaC
211 P-9 6.4 210 P-10 6.4 209 P-l 36.2 208 P-12 14.2 207 P-13 100.0 206 P-14 14.9 205 P-15 92.2 C3H9 Si2C1 3 171 P-49 9.7 C 3H 9Si 2 23 10.8 C H Si Cl + 169 P-51 37'2 2 145 P-75 10.6 8.5 135 P-85 + 133 P-87 8.5 C1Si 115 P-105 7.1 113 P-107 7.4 95 P-125 14.9 93 P-127 29.1 C 2 H6 SiC1+ 92 P-128 8.5 91 P-129 7.1 81 P-139 7.8 79 P-141 14.5 CH 4 SiC1+ 78 P-142 8.5 71 P-149 9.2 67 P-153 6.0 65 P-155 36.2 64 P-156 5.7 63 P-157 64.5 12.1 59 P-161 + 58 P-162 7.8 C2H6 57 P-163 11.3 256 55 P-165 20.9 53 P-167 7.8 46 P-174 5.7 45 P-175 40.4 CH5S 44 P-176 31.2 43 P-177 74.5 CH 3 Si+ 42 P-178 14.2
(a) masses less than 42 m/e were not reported (b) intensities less than 5% were not reported (c) isotopic ratios for the p:p+2:p+4 peaks are consistent with these formulas 12
AN E
0 c\J
LOO q-4H 0 0*-' 0 ~cr0
0o H
tOH ct)
3~1 G)I-
-PU
(1) 4
______( - 13
TABLE III
Metastable Peaks as Observed in the Mass
Spectra of Compounds I-III
Compound Metastable Peaks (Parent-Dau9hter)
I 27.7(73-49) 42.2(205-93) 45.1(72-57) 46.7(72-58) 65.4(93-78) 67.1(93-79) 86.3(205-133) 139.3(205-169)
II 58 (149-93) 86.4(257-149) 45.4(93-65) 98.3(149-121) 59.7(121-85)
III 26. 5(201-73) 71.8(293-145) 95.1(221-145) 158.1 (309-221) 166.7(293-221) 277.8(309-293) 147,,3(129-113) 83.0(201-129) 14
--CH2SiC13-c2H -H Me SiCH SiC 2- - - Me Si+ 3 2 3 3 MeSiH 2 2 MeSi+ 220 (0) ,C 73 (79) 45 (40) 43 (74) SC3
3 Me CH C:1 - -SiCI x% 7 2 y - HC1 + Me Si=CH2 ---- %) Me SiCHSiC1 2 2 3 Si + Si 2 2 Me Cl 72 (18) 169 (12) 205 (100)
-CH -CH
- Me2Si=CF 12 3 2 - CH2 SiC2
MeSiCH + Me2 Si+ SiCi Me2 2 3 57 (11) 58 (8) 133 (8) 93 (29)
k- C H J CH - CH 2 6 33 2 SiC1+ MeSiCl+ MeHSi=Cl 63 (64) 78 (8) 79 (14)
Scheme 2
solid lines indicate metastable supported processes 15 in Scheme 2 are consistent with these findings and will be used where applicable.
The ion observed at m/3 72 might arise from the loss of trichlorosilyl radical from m/e 205. However, no meta- stable peak was observed that would support this. Subsequent losses of both methyl and methylene are supported by meta- stable peaks at 45.1 and 46.7, respectively. Similar processes are proposed for the decomposition of the ion at m/e 93 giving rise to peaks at 78 and 79. The trimethylsilyl ion at m/e 73 is a well-known feature of the mass spectra of methyl-substituted silicon compounds. In this case, the possible sources are limited to the parent ion. Subsequent loss of ethylene and hydrogen are processes which have been previously studied.
The conventional mass spectrum also provides information by way of the isotopic ratios for each fragment. The relative abundance of 35Cl:37lC is 3:1 in nature. Therefore, one would predict that for an ion of the formula C 3H 8 SiCl+, the p:p+2:p+4 ratio would be 3:3:1. Indeed, this is the case
for the ion at m/e 205 if allowances are made for the presence of silicon.
The high resolution mass spectrum of bis(trimethylsilyl- methyl)dichlorosilane (II) is summarized in Table IV. The prominent features are presented graphically in Figure 3, and
the proposed fragmentation pattern is shown in Scheme 3.
The primary fragmentation for II is, once again, loss 16
TABLE IV
Mass Spectrum of bis (trimethylsilylmethyl) dichlorosilane (II)
m/ea Parent-x % of base peakb Formula f .. 'WOMAM.. "
262 P-10 5.3 261 P-li 20.1 260 P-12 18.9 259 P-13 76.9 258 P-14 24.3 P-15 100.0 257 Cc7 H,19H Si3i3 Cl22 243 P-29 6.5 152 P-120 5.6 151 P-121 36.7 150 P-122 16.0 149 P-123 91.7 C4 H 1 0 S 2 Cl 135 P-137 7.1 133 P-139 7.1 C3H 6 Si 2C1 129 P-143 19.8 127 P-145 7.1 123 P-149 5.3 122 P-150 14.8 121 P-151 18 .3 C 2H6 Si 2C14 12.4 95 P-177 C2 H 6 SiC2 93 P-179 28.4 C H SiCl+ 85 P-187 8.9 C 2H 5Si 2+ 79 P-193 5.3 CH 4 SiCl+ 75 P-197 10.7 74 P-1 9R 241 9 73 P-199 59.5 C3 H 9 Si 72 P-200 5.6 71 P-201 8.9 65 P-207 5.3 H2SiC1 59 P-213 21.9 2 55 P-217 6.2 45 P-227 20.1 44 P-228 6.5 43 P-229 14.2 CH3 +Si
(a) masses less than 43 m/e were not reported (b) intensities less than 5% were not reported (c) peak intensity ratios are consistent with these formulas 17
C\%
H
00 4& 00
4 )
)) -
0.H
Cj prH
4 4J -y -P
N O 0)0
(em to
0-' 18
ii
00 C.1
(N C) C.) C.) 1 .(NOII 00 /I ii C.)
(N
N U) .) /
'H C.) -I -. %4 0 Z vI0) uC) m C.) C.)+C) O( D -H -i + v-i
-0 (N(D C/N c?) 04)
ci) 0 ]I 10
u I)>U).) 'H o 4 10 1 tIi - r .4)-) u 4-)
Q) 04W 4-) ED04 U) u o r
>1 >1 (N
'H 0 C.) 'H o S + -" ( 4-) 4J)c
O LO e rO$ 0 0 -CI OH 04 14 (N O.U - -- 10- H4 Q04 0 :: U) U) ca N U+C1)+10 19 of methyl giving rise to the base peak at m/e 257. The subsequent loss of trimethylchlorosilane could produce the ion at 149 and is supported by a metastable peak observed at 86.4. The unimolecular MIKES spectrum of the ion at 257
(Figure 4) shows this to be the most prominent fragmentation pathway. However, the CID scan (Figure 5) shows that an ion observed at 241, which may be ascribed to the loss of methane from 257, becomes an important feature at higher energy.
The CID scan also indicates four other prominent ions at m/e 226, 205, 184 and 164, none of which are detected at greater than 5 percent of the base peak intensity in the conventional mass spectrum.
A most interesting feature of the fragmentation scheme proposed for compound II is the parent-daughter relationship between the ions at m/e 149 and 93. Such a relationship implies the loss of a neutral fragment with a mass of 56 and is supported both by a metastable peak at 58.0 and by a peak at
93 in the MIKES and CID scans for m/e 149 (Figures 6 and 7).
This particular decomposition could be ascribed to the loss of 2-silaallene.
Other decomposition pathways available to the ion at
149 include the predicted losses of HC1,CH4 and C2H4 . Although these losses are prominent features of the CID spectrum, only the loss of ethylene is detected in the conventional mass spectrum at a relative abundance of greater than 5 percent. The p:p+2 intensity ratios for 149 and 93 also indicate the presence of one chlorine. 20
.women.sme.------CD
C) -) N
C)
LI) CNI 0 ~LO -t r N4 4J 0D CD CD Lt CD C) -D- Z 2 4 Q : C1 C) F-C) C/D .NJ 0-)C\; CD C) Lli CD 2: H c- --
C/I C/) W. rz 'C C wI CD\] C\. CD H CM0 M2 1.J C C 4 (" WI- > n
LL DVCD
I" LU CD-oo 79CC ~IDf 4 7) OH f 0 21
-)
0D
LO -'~Z2c~
-.p..im,...a...... sem m.wse-,-
CN "C) cj0
O 0\ CD LC
0
c/O
D 0 04 C\i mCr Q 0 Lij - -pD LL CD U OCM <~ C\j - U)m Oci co LO) LL I U--
LO" <. Ci) ri CIT <) U LL) -H C oT ______~ * _ 22
C) LO)
it F
C)
0
H
N CC) 4 C-) -- o U) CD 0: O.N )C) CU)
C C\ H LC LO) C) * Ck CD - 7- z
C) Cm C' o -- CD * f 0C D LC) (p & -r- C)~ ci ' -- 0 f\-V-C DD L -
C) (Ni' . L - - 0-1 Z~cio D2 7. Ox C C-. ) 23
. - .-...... C) "w$rsaM'''m''"#'e-"I'*Iia-hs-.m.mmF.- -L()
"N _ __Ji oV G-) C) "CD 0 N C) 4-4
]C 0
c-) C) C LL.CD )) N H- C\jcc C c N U "N (CI r() C Zc\ L-> H u LdL 00cC)
0 0
c91 Z (a
c L-. LCQo
a - 10 24
The observance of a metastable peak at m/e 45.4 supports the loss of ethylene from 93, the product ion being observed at 65. This particular fragmentation is very prominent in the CID and unimolecular MIKES spectra of m/e 93 (Figures 8 and 9). Other pathways for the decomposition of this ion
include the losses of C2H6 and CH3 , previously noted features of ions of tl is type.
A similar treatment of the data obtained for tris
(trimethylsi ylmethyl) chlorosilane (III) provides a consistent picture of the overall decomposition pathway for these
compounds. The mass spectrum of III has been reported, 6 although not in detail. The predicted loss of methyl from
the parent i n produces a peak at m/e 309 (Table V, Figure 10,
Scheme 4).
The ori in of the ion at m/e 221 (19 percent of the
base peak) would seem to be twofold. Either a loss of
tetramethyls4lane from 309 or a loss of methane followed by a
loss of dimejhylsilene could be envisioned. Interestingly, all
three fragmentations are supported by the presence of meta-
stable peaks, The presence of an ion at m/e 293 is implied
by this pathway, and is confirmed by the unimolecular MIKES
and CID spectra of m/e 309 (Figures 11 and 12).
The ion at m/e 121, as depicted in Scheme 4, is
structurally analogous to the ion at m/e 149 in Scheme 3,
proposed in he fragmentation of compound II. If similar
structures undergo similar decomposition processes, a loss 25
0CF ~N
0 (N
r--4 m/ Cf 04-
C ~ 0) CD L. J
CPC r4)
LcR
L CL 0. 26
CY 00 LOi
4-4 LUC) U-)
C) Ccci c
Of Cf) -0 C C CD CD ci? (lC\JflC\F-0 C\j o LUC)o0ZOD)Gc O C \,("k- 0CO~ c00 XI C) C\jUC/{ Cf)h C).- 1 o t- co 2: 0
LL- C) '- LU
LU > 0C o D CC00F- 27
TABLE V
Mass Spectrum of Tris (trimethylsilylmethyl) chlorosilane (III) m/ea Parent-x % of base peak Formula
312 P-12 5.6 311 P-13 17.3 310 P-14 11. 1 309 P-15 35.2 C 1 1 H 3 0Si 4 C+ 223 P-101 10.5 222 P-102 4.9 221 P-103 19.1 C H Si Cl 7 18 3 203 P-121 18.5 202 P-122 25.3 201 P-123 100.0 C8 H21s 3 187 P-137 4.9 185 P-139 12.3 167 P-157 19.8 166 P-158 8.0 165 P-159 45.1 C5Hc5 H14 4Si2C1+ i2 c 147 P-177 4.9 146 P-178 6.8 145 P-179 39.5 C6 H 1 7 Si2 131 P-193 6.2 130 P-194 4.9 29.0 Si 129 P-195 C 5.13H 2 115 P-209 5.6 s 2+ 113 P-211 11.1 c 4H 84 P-240 5.6 73 P-251 33.3 59 P-265 18.5 42 P-282 10.5
a) masses less than 42 m/e were not reported b) intensities less than 5% were not reported c) peak intensity ratios are consistent with these formulas 28
CMj (Y)
wo> 0
H H A0) H *E E C- C\j Cj 4-)-r a4 4 H 0 H
CD 4J 5 CMj to r-4
4-A (1) to a w C\i o0D iH CDH
(9) CMj
rdN
0 r4 0 a. -L4. 0 I-- --w a K 29
3-S0CH0 CHi-CH CH
p - - - -) Me2Si..+2 Si (CH2SiMe3)2 -HC=Si +-2 Si(CH2SiMe
22C S1 ( 2S3 )2 324 (0) M C. C MC + 309 (36) -Sime4 293 (<5)
MC - Me3SiC - CH2=SiMe2 O~o CH CH i Sie oCHCH M 2e S -- C5H12- 2M+ ,CH N /CH SiMe 2 Si 2 3 m2 + Si=CHme2 ) si H2C=Si + HMC32 CH Cl Me 2 73 (33) 221 (19) SiMe3 201 (100) - HCSiC1 - H2C=Si=CH I 2 2 MC - CH 2=SiMe2
H2C=SiCH2SiMe3 Me SiCH2SiV/e3 +CI=Si M 2 Si 3
129 (29) 145 (40) 165 (45)
CH 4
H 2C=SiCH2Si=CH2 MeI + 113 (11)
Scheme 4
solid lines indicate nMetastable supported processes supported by MIKE spectrum:M supported by CID spectrum: C 30
-CD C)
C-) LO
C)~-- 0 0
r- L-03
0 C) C -0
0C C) m C) o o 0 0 C~ 0-)
*: 0 LtN~C) Hq
01-1C)D C -C) t . ~ ) 0 H -T7o
L . co 31
~C)
0- -0
27- C
cr
CC)4 0 0
(7) cc,
N - CD 4 7 C- - Lii) Q)
L: ci) ciz N) 000 C", t-- LO U)
CN
c CC 32
j7O CC) c c> CCD
H
U-))
-f) HC
Q~UD0
N C (NC L0CM C-) W LQ) CD Cf) Cf)M "
C) C\i - CD 0 0z
0 -i mi- CD > C CD i 0 m iH CM CDO CD -
t~L- - O r. 33
LC)
-J
CN C)C)fNJ Je -- 0 4
LL Q)o C- (\C)::D UN C 4-)
(2-.C) 00 Q U)ZC) N CD LtU LUI L
(1 :C\
co!
0 -11r7~) rC
1~~~~ 34 of 2-silaallene might be predicted and would explain the ion observed at m/e 165, although no corresponding metastable peak was detected. From the high resolution mass spectrum of III, one is tempted to assign the ions at m/e 145 and 165 as daughters of the ion at m/e 201. Production of 145 from
201 would again imply a loss of 2-silaallene. However, the unimolecular MIKES and CID spectra (Figures 13 and 14) clearly show that this is not the case. On the other hand, careful inspection of the conventional mass spectrum of III revealed a broad metastable peak at m/e 95.1 and supports the parent-daughter relationship between 221 and 145.
Metastable peaks observed at m/e 83.0 and 147.3 indicate a loss of dimethylsilene to form the ion at 129 followed by a loss of-methane to produce the peak detected at 113. A metastable peak observed at m/e 26.5 indicates that the ion at 201 is a likely precursor to the trimethylsilyl ion at 73.
The loss of trimethylchlorosilane is a prominent feature in the fragmentation patterns of compounds II and III.
This process is structurally precluded in the case of compound I. Metastable peaks corresponding to this loss indicate that the precursor ion has unusual stability ascribable to the effect of the chlorine substituents on silicon. In at least one case, the loss of 2-silaallene is strongly implied by the presence of a metastable peak and by a corroborating CID spectrum. One previous report suggests the loss of allene from a structurally analogous ion, as shown in Scheme 5. 35
S Si Me2 ArSiOH Ar CH> Ar 0 tCH ) + + 12 2 .2 CH 2 =C=CH2
Scheme 5
Previous studies have demonstrated the facile generation of silenes under conditions of electron impact from mono- and disilacyclobutanes.8 In these cases the ring cleavage reactions were similar to the proposed mechanism for thermal generation of silenes.
The most prominent fragmentation processes for compounds
II and III appear to be loss of methyl followed by a loss of trimethylchlorosilane. The associated energy barrier for the latter is apparently rather low despite the formation of a silicon-carbon double bond. When the ions at m/e 257
(Scheme 3) and 309 (Scheme 4) decompose following collisional activation, the additional internal energy allows other processes to become more competitive. In the case of II, an increase in the intensity of the peak at 241 relative to
149 in the CID spectrum of 257 indicates that a loss of methane is actually more favorable at higher energies.
The proposed loss of 2-silaallene from the ion at m/e 149 in the spectrum of compound II dominates all other fragmen- tation pathways when observed at electron energies of 60 ev on a single focusing instrument. The ion appearing at m/e 221 in the fragmentation scheme for compound III is similar in 36 structure to the ion at m/e 149 from compound II. This similarity in structure suggests that 165 is a likely daughter of 221, especially since the CID scan shows that
165 can not be a daughter of 201. Higher internal energies favor other processes, i.e. the losses of HCl, C2 H4 , C2 H6 and CH4 , from the ion at m/e 149 in Scheme 3.
Fragmentation of the ion at m/e 205 from compound I may occur by either of three metastable supported processes. The loss of dichlorosilene apparently has a lower activation energy than either loss of HCl or dimethylsilene. In the fragmentation pattern for all three compounds, stabilization of a siliconium ion by the lone pair of electrons on chlorine would seem to be an important factor. Ions which do not contain chlorine as a silicon substituent, such as the ion at m/e 201 in Scheme 4, give rise to daughter ions at much less relative intensity.
These results show that unimolecular decomposition processes for these silicon compounds invariably involve the formation of fragments, both neutral and charged, which incorporate doubly-bonded silicon. It is not expected that the thermal decomposition of these compounds will exactly parallel the strictly unimolecular pathways observed in mass spectroscopy because of the lower internal energies and collisional phenomena. However, other studies indicate precedence for formation of these highly reactive species by both electron impact and thermal decomposition pathways 37 and these data suggest that a study of the thermal decompo- sition of highly branched chloro-substituted organosilanes may be of interest in the further study of silenes. 38
REFERENCES
1. Gornowicz, G. A. and West, R. C., J. Amer. Chem. 'Soc.,
90(16) , 4478 (1968) .
2. Mitch, F. A., Murch, R. M. and Sommer, L. H., J. Amer.
Chem. Soc., 76, 1619 (1954).
3. Kira, M., Kobayashi, T., Nakadaira, Y. and Sakurai, H.,
J. Organometal. Chem., 113, 24 9 (1976).
4. Bursey, M. M., Groenwald, G. S., Gross, M. L. and Jones,
P. R., J. Organometal. Chem., in press.
5. Reference 4.
6. Homer, G. D. and Sommer, L. H., J. Amer. Chem. Soc.,
95(3)., 7700 (1973).
7. Larson, G. L., Oliva, A. and Tsai, R. S.-C., Org. Mass
Spectrom., 14, 364 (1979).
8. Auner, N. and Grobe, J., J. Organometal. Chem., 222,
33 (1981). CHAPTER III
EXPERIMENTAL
High resolution mass spectra were obtained for all compounds using an Hitachi Perkin-Elmer RMU-6E Mass Spectrometer which contains a 900 magnetic sector. The ionization energy used was 60 ev and the source temperature was set at 100 0C.
MIKE and CID spectra were obtained on a KRATOS MS-50 triple analyzer which is located at the Midwest Center for Mass
Spectrometry at the University of Nebraska in Lincoln,
Nebraska. The ionization energy used was 70 ev and the source temperature was 2500C. The accelerating potential used was 8 kv. Collisional activation was achieved by bleeding helium gas into the third field-free region of the spectrometer until the intensity of the main beam was decreased by fifty percent.
A Perkin-Elmer Sigma 3 gas chromatograph with a flame ionization detector was used to determine yields and retention times for all products of reactions. A six-foot by one-eighth-inch stainless steel column packed with
3 percent OV-17 on 80/100 Supelcoport was used. Yields were determined using tert-butylbenzene as an internal standard.
For the analysis of compounds I-III, the analytical chroma- tograms were obtained by programming the oven from 100-2000C at 200 per minute with a carrier gas flow rate of 20 mililiters
39 40 per minute. A Varian Aerograph Series 1800 gas chromo- tograph was used to collect analytically pure samples for spectroscopic characterization. A twenty-foot by three- eighths-inch stainless steel column packed with 10 percent
SE-30 on chromosorb-W was used. The chromatograph oven was programmed from 230 to 280 0 C at 100 per minute with a helium gas flow rate of 190 mililiters per minute. Proton magnetic resonance spectra were obtained on an Hitachi Perkin-Elmer
R-24B 60 MHZ NMR spectrometer. Chloroform was used as an internal standard with carbon tetrachloride as a solvent. l3C magnetic resonance spectra were obtained on JEOL FX-90Q fourier transform spectrometer using D2 0 as an external lock solvent.
All glassware was assembled and then flame-dried with a rapid purge of argon gas. All reactions and distillations were carried out under argon gas. The hexanes used in the reactions were distilled from a sodium/potassium alloy under nitrogen atmosphere. Tetrahydrofuran and diethylether were distilled from lithium aluminum hydride under nitrogen.
Chloromethyltrimethylsilane and tetrachlorosilane were obtained from Petrarch Systems, Inc., in Levittown,
Pennsylvania. Lithium wire was obtained from Alpha Products in Danvers, Massachusetts.
1. Preparation of trimethylsilylmethyltrichlorosilane from
a Grignard reagent. 2
A 250 ml three-neck round-bottomed flask, fitted with a 41
250 ml addition funnel and magnetic stirring bar, was charges with 1.19 g (0.0490 mole) magnesium turnings. To this was added 150 ml dry diethylether. From the addition funnel was added, over a period of one hour, 5.0 g (0.0408 mole) chloromethyltrimethylsilane dissolved in 100 ml ether, Three drops of methyliodide were added to initiate the reaction.
The reaction was subsequently refluxed for a day. The reagent appeared as a gray suspension in ether.
The freshly prepared Grignard reagent was transferred via a double-ended needle to an additional funnel attached
to a previously dried 500 ml round-bottomed, three-neck
flask. This flask was then charged with 2.33 ml (3.47 g,
0.0204 mole) silicon tetrachloride in 150 ml dry ether.
The Grignard reagent was then added over a period of an
hour to the stirring solution of chlorosilane. An exothermic
reaction and refluxing of the solvent was observed. After
the addition was complete, the reaction mixture was
refluxed an additional 24 hours. The reaction mixture was
then filtered through a coarse sintered glass funnel and
fractionally distilled. Product was collected in the fraction
boiling at 470C at 1.5 torr.
Yield: (based on Me 3 SiCH2Cl) was 2.89% of trimethylsilyl-
methyltrichlorosilane (I) from gas chromatography.
NMR -- 1: 0.82 ppm (broad singlet)
This product was characterized by mass spectrometry. 42
2. Preparation of trimethylsilylmethyllithium.3
A one-liter Morton flask was charged with about 500 ml paraffin oil, previously dried with activated 4 5 molecular
sieve. To this was added about 5 g. lithium wire. The flask was then heated to 2000C with occasional stirring. When the
lithium was completely melted, 4 drops of oleic acid was
added to prevent coalesence of the metal. The flask was
then shaken vigorously for several minutes. As a result, the
lithium had divided into small round pieces with diameters
ranging between 0.5 and 2.0 mm. The mixture was then stirred
until it cooled and the metal was filtered off and washed
with two 50 ml portions of dry hexanes.
A 500 ml Morton flask equipped with mechanical stirrer,
addition funnel, reflux condenser, and argon inlet was charged
with 200 ml dry hexanes followed by an excess (5 g.) of the
previously prepared lithium shot. A small amount of sodium
metal and several pieces of broken glass were added. The
lithium shot was then stirred vigorously overnight to clean
the metal surface. The next day the addition funnel was
charged with 5.0 g. (0.0408 mole) of chloromethyltrimethyl-
silane in 50 ml dry hexanes. Initially, about 5 ml of this
solution was added to the stirring metal with three drops
of methyl iodide. The silane was then added over a period
of 10 hours followed by refluxing overnight. The resulting
mixture was a milky lavender color. The Gilman test I4
showed the presence of active organometallic compounds. 43
The titration of the mixture with diphenylacetic acid in
THF5 showed the yield to be 70.9 percent, based upon starting silane.
3. Preparation of bis (trimethylsilylmethyl) dishlorosilane
(II) and tris (trimethylsilylmethyl) chlorosilane (III). 6
The freshly prepared lithium reagent was transferred to a one-liter addition funel attached to a three-liter round- bottomed flask. This vessel was charged with 16.6 ml (0.145 mole) silicon tetrachloride in 750 ml tetrahydrofuran. The addition of the lithium reagent was carried out over the course of two days. The reaction mixture was refluxed vigorously during this time. Subsequently, the reaction mixture was filtered and fractionally distilled at reduced pressure. The fraction boiling between 80 and 90 0C at
0.375 torr. gave 31.9 percent (Me3SiCH 2 )3 SiCl (III) and
5.24 percent (Me3SiCH2 2 (II) based upon Me3SiCH2Cl.
H NMR--(Me3SiCH2 2 2 (II): 0.19 ppm (broad singlet).
(Me3SiCH2)2Si 1 (III): 0.30 ppm (broad singlet).
13C NMR--(MeSiCH2 )2Si 12 (II): 12.55 ppm(t), 1.04 ppm(t).
(MeSiCH2)3 Si 1 (III): 9.88 ppm(t) , 1.49 ppm(q) .
Letters in parentheses indicate peak multiplicities in off- resonance decoupled spectra. Both products were also charac- terized by mass spectrometry. 44
REFERENCES
1. These data were obtained from the Midwest Center for
Mass Spectrometry which is a National Science
Foundation regional instrumentation facility.
A 2. Kumada, M. and Shiina, K., Kogyo Kagaku Zasshi, 60,
1395 (1957).
3. Mitch, F.A., Murch, R.M. and Sommer, L.H., J. Amer.
Chem. Soc., 76, 1619 (1954).
4. Wakefield, B.J., The Chemistry of Organalithium Compounds,
New York, Pergamon Press, 1974.
5. Kofron, W., J. Org. Chem., 41, 1879 (1976).
6. Reference 3, p. 1619. APPENDIX
CROSS-REFERENCE TABLE OF COMPOUND
NUMBER TO NOTEBOOK NUMBER
Compound Number Notebook Number
IKRP-64 II IKRP-Q100A III IKRP-100B
45 BIBLIOGRAPHY
Books
Bowen, R. D., Howe, I. and Williams, D. H., Mass Spectrometry, 2 ed., New York, McGraw-Hill, 1981.
Schlunegger, U. P., Advanced Mass Spectrometry, New York, Pergamon Press, 1980.
Wakefield, B. J., The Chemistry of Organolithium Compounds, New York, Pergamon Press, 1974.
Articles
Auner, N. and Grobe, J., J. Organometal. Chem., 188 (l), 25 (1980).
Auner, N. and Grobe, J., J. Organometal. Chem., 190(2), 129 (1980).
Auner, N. and Grobe, J., J. Organometal. Chem., 222, 33 (1981).
Auner, N. and Grobe, J., Zeit. Anorg. Allg. Chem., 459, 15 (1979).
Barton, T. J., Kilgour, J. A. and Marquardt, G., J. Amer. Chem. Soc., 96, 7105 (1974).
Beynon, J. H. and Cooks, R. G., Res./Dev., 22, 26 (1971).
Bursey, M. M., Groenwald, G. S., Gross, M. L. and Jones, P. R., J. Organometal. Chem., in press.
Bush, R. D., Golino, C. M. and Sommer, L. H., J. Amer. Chem. Soc., 96, 7105 (1974).
Dong, P., Durap, J. and Yamaoka, H., Chem. y 51, 3465 (1969).
Drake, J. E., Glavincevski, B. M. and Wong, C., J. Inorg. Nucl. Chem., 42, 175 (1980).
Gornowicz, G. A. and West, R. C., J. Amer. Chem. Soc., 90(16), 4478 (1968).
46 47
Homer, G. D. and Sommer, L. H., J. Amer. Chem. Soc., 95 (3), 7700 (1973) .
Ishilawa, M., Pure Ap . Chem. , 50(1), 11 (1978),
Jones, P. R. and Lim, T. F. 0., J. 'Amer. Chem. Soc., 99(6), 2013 (1977)1.
Kira, M., Kobayashi, T., Nakadaira, Y. and Sakurai, H., J. Organometal. Chem., 113, 249 (1976),
Kofron, W., J. Org. Chem., 41, 1879 (1976).
Kumada, M. and Shiina, K., Kogo Kagaku Zasshi, 60, 1395 (1957).
Larsen, G. L., Oliva, A. and Tsai, R. S.-C., Org. Mass Spectrom., 14, 364 (1979).
Mitch, F. A., Murch, R. M. and Sommer, L. H., J. Amer. Chem. Soc., 76, 1619 (1954).