38 Silicon Compounds
Broadly speaking, molecular structures containing both carbon and silicon are known as organic silicon compounds. When at least one organic group is attached directly to silicon through a carbon atom, the more specific term organosilicon compound is applicable. As might be expected, the nomenclature of silicon hydrides closely parallels that of hydrocarbons, and in general the naming of functional and nonfunctional derivatives is analogous to that of the corresponding organic structures. Recommended Nomenclature Practice The compound SiH is called silane; its acyclic homologs, H S i (SiH )n SiH , are called disilane, trisilane, tetrasilane, etc., according to the number of silicon atoms present. As with hydrocarbons, cyclic nonaromatic structures are designated by the prefix cyclo. The class name silanes includes both open-chain and cyclic systems. 4
2
3
3
CH SiH SiH2SiH CH CH 2
3
2
CH 0-SiH—SiH 3
2
2
I SiH -SiH-OCH 2
3
l-Ethyl-3-methyltrisilane
1,3 -Dimethoxy cy clotetrasilane 3
SiH^ SiH
| ^"SiHj SiH
2
2
SiH,
Bicyclo [2.2.1] heptasilane
SiH? ^SiH
When, as often occurs, a chain or ring system is composed entirely of alternating silicon and oxygen atoms, the stem name siloxane is used, with a multiplying prefix denoting the number of silicon atoms present. H SiOSiH 3
3
Disiloxane 293
294
N O M E N C L A T U R E O F ORGANIC C O M P O U N D S
H SiOSiH OSiH OSiH3 3
2
Tetrasiloxane
2
sm
siH
I
^
2
SiH
2
Cyclotrisiloxanc
2
Analogous structures containing sulfur and nitrogen are named by using the stem names silatbiane and silazane, respectively. Examples are included in Table 38.1. Organic heterocyclic and hetero-acyclic systems containing silicon are named by using the prefixes stia, disila, trisila, etc. to designate replacement of carbon, as described in Chapters 6 and 7.
l-Oxa-4-silacyclohexane
o
CH CH SiH CH CH SiH CH CH SiH CH CH 3,6,9-Trisilaundccane 3
2
2
2
2
2
2
2
2
2
3
Simple open-chain structures that do not qualify for replacement nomenclature (see Chapter 7) are named as silane derivatives by the principles recommended in other chapters for various organic functional classes. H SiSiH OCH CH CH 3
2
2
2
CH SSiH SiH SiH SCH 3
2
2
H SiNHCH C H 3
2
6
2
2
5
2
l,3-Bis(methylthio)trisilanc
2-Methyldisilanccarboxylic acid
2
C H CH CH SiH(OH) 6
3
N-(Phenylmethy Dsilanamine
5
CH SiH SiH COOH 3
Propoxydisilane
3
2
2
(2-Phcnylcthyl)sUanediol
Functional derivatives of siloxanes, silathianes, and silazanes are treated in the same manner. HSSiH OSiH SH 2
Cl SiNHSiH NHSiH 3
1,3-Disiloxanedithiol
2
2
3
1,1,1-Trichlorotrisilazane
38.
Silicon Compounds
295
Compounds having the structures (RO) Si, (RO) SiOH, (RO) Si(OH) and ROSi(OH) are named as esters of orthosilicic acid, Si(OH) . 4
2
3
2
3
4
(CH CH 0) Si 3
2
Tetraethyl orthosilicate
4
(C H 0) Si(OH) 6
5
2
Diphenyl dihydrogen orthosilicate
2
Prefix names for silicon-containing groups are formed analogously to those for the corresponding carbon-containing groups by using the endings yl, ylene, ylidene, ylidyne, triyl, tetrayl, etc., as described in Chapter 2, or, preferably, by simply attaching the suffixes yl, diyl, triyl, etc. to the name of the appropriate silicon chain or ring system. For H Si—, the shortened form silyl, rather than silanyl, is used (see Discussion section). 3
4-(Tribromosilyl)cyclohexanecarboxamide
CH SiH SiH OCH CH OH 3
2
2
2
H SiOSiH
2- [ (2-Methyldisilanyl)oxy lethanol
2
CH COCH CH
3
2
2
3
1 -(4-Disiloxany lpheny l)-2-bu tanone
Discussion The recommendations made here follow closely those developed by the IUPAC Organic Commission in 1949 and subsequently officially adopted by the American Chemical Society (i), taking into account certain changes expected to be made by IUPAC in an updated version of its silicon rules. As can be seen, the nomenclature of organic silicon compounds is well systematized. The stem name silathiane is now preferred to the previously recommended silthiane for compounds having the generic structure H Si(SSiH )„SSiH . Names for chain and ring systems incorporating the stems siloxane, silathiane, and silazane are used in the same way as silane, disilane, etc. in parent names of functional and nonfunctional derivatives. When there is a choice between two parent polysilicon chains having the same number of silicon atoms, the preference is in the decreasing order listed above, with the silanes coming last. 3
2
3
296
NOMENCLATURE OF ORGANIC COMPOUNDS
By using the shortened form silyl for the substituting group H Si— rather than silanyl, the need for bis, tris, etc. as multiplying prefixes is eliminated. Thus, disilanyl denotes the group H SiSiH —, and disilyl denotes two H Si— groups; otherwise, this distinction would have to be made by using bis(sUanyl) or bissilanyl. An additional simplification is achieved by using siloxy for H SiO— rather than silyloxy; the latter, though properly formed, is a two-part prefix name requiring bis, tris, etc. whereas with siloxy, di, tri, etc. can be used. Names of other siliconcontaining substituting groups connected through oxygen should not be shortened in this manner although such abbreviations were permitted by the 1949 IUPAC Rules. 3
3
2
3
3
The officially approved name for Si(OH) is orthosilicic acid, but in common practice the prefix ortho is often omitted. Since the 1970 IUPAC Inorganic Rules do not recognize the term silicic acid, retention of the prefix is recommended here. Structures in which halogen or nitrogen may be regarded as having replaced one or more OH groups in orthosilicic acid are named as silane derivatives—e.g., chlorosilanetriol for ClSi(OH) , not "chlorosilicic" acid. 4
3
Table 38.1.
CH
SiH
3
Examples of Acceptable Usage
3
1.
2-Methyl-4-silylpentasilane H SiSiHSiH SiHSiH 3
2
SiH
3
2
1,3,5-Trichlorocyclohexasilane
2. SiH
SiH
2
2
CI H SiOSiHOSiH 3
3.
3
OCH
3-Methoxytrisiloxane
3
H SiSSiH SSiHSSiH 3
4.
2
3
OSiH
3-Siloxytetrasilathiane 3
38.
297
Silicon Compounds
5.
H SiSiH OSiH SiH 3
2
2
CH
1,3 -Disily ldisiloxane Bis(disilanyl) ether
3
3
1,2, 3-Trimethyldisilazane CH SiH NSiH CH 3
2
CH
2
CH
3
3
CH
3
CH SiCH SiCH SiCH 3
2
I
CH
2
I I
CH
3
3
3
2,2,4,4,6,6-Hexamethy 1-2,4,6trisilaheptane
3
CH
3
9H-9-Silafluorene
Si-CH
3
3,7
Tetramethyltricy clo [3.3.1.1 ]tetrasiloxane
0 1 ^Si I
CH
3
CH ^H CJ:H 3
10.
3
3
CH SiO-SiO-SiCH 3
1 OH
I I OH OH
H SiN(CH )
12.
C H NHSiH SiH NHC H
13.
3
1,1,3,5,5 -Pentamethy 1-1,3,5 -tr isiloxanetriol
N, AT-Dimethylsilanamine
11.
3
3
2
5
N,N'-Diphenyl-l,2-disilanediamine
(CH CH CH ) Si(COOH)
2
Dipropylsilanedicarboxylic acid
14.
(ClCH CH 0) SiCl
Chlorotris(2-chloroethoxy)silane
15.
(C H CH 0) Si
Tetrakis(phenylmethyl) orthosilicate Tetrabenzyl orthosilicate
16.
CH CH CH CH OSi(OH)
6
5
2
3
2
2
2
6
5
3
6
2
2
2
2
2
3
4
2
2
3
Butyl trihydrogen orthosilicate
298
NOMENCLATURE OF ORGANIC COMPOUNDS
17.
(CH CH=CHCOO) SiNH
18.
(ClCH COO) Si
3
3
2
4
2
Aminosilanetriyl tri-2-butenoate Tris(2-butenoyloxy)silan amine Chloroethanoic orthosilicic tetraanhydride Chloroacetic orthosilicic tetraanhydride
19. V-
HO—/
SiH — 2
OH
4,4'-Silanediyldibenzenol 4,4'-Silylenediphenol 20.
(C H ) SiLi
21.
(CH CH CH ) SiSNa
6
5
3
(Triphenylsilyl)lithium
3
2
2
3
Sodium trip ropy lsilanethiolate
Literature Cited 1. "Silicon Compounds", Cbem. Eng. News (1952) 30, 4517. 2. "Nomenclature of Inorganic Chemistry. Definitive Rules," IUPAC, 1970, Butter worths, London, 1971; Pure Appl. Chem. (1971) 28, 1-110.
