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Hexamethyldisilazane (HMDS, $\ce{(SiMe3)2NH}$) and its conjugate base hexamethyldisilazide (as the Li/Na/K salt) find wide use in organic chemistry.

In my quest to only use preferred IUPAC names in my thesis1 I have come across a problem with this compound. According to P-21.2.3.1 of the Blue Book the name disilazane for the parent hydride $\ce{H3Si-NH-SiH3}$ is no longer preferred because

When nitrogen atoms are present, amine names (see P-62) are preferred because of the higher functionality of amines. This concept does not extend to other elements.

and the name given is N-silylsilanamine.2 Just going off this, I would guess that the PIN of the hexamethyl compound is something along the lines of "trimethyl-N-(trimethylsilyl)silanamine".

However, I'm also not sure whether the addition of the methyl groups makes the choice of parent hydride different, as per P-21.2.3.2 (for example). The frequently used name bis(trimethylsilyl)amine is also a possibility, although I've personally not seen a rule suggesting that it could be a PIN.

What is the PIN of this amine?


  1. I'm just kidding; writing "4-methylbenzene-1-sulfonyl" multiple times is quite silly. But I’m still curious about this PIN.

  2. The original publication has this written as N-silylsilan-1-amine but this has since been corrected in the errata, which are published online.

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  • $\begingroup$ Why not name it just bis(trimethylsilyl)amine? $\endgroup$ – Mithoron Dec 30 '17 at 23:38
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    $\begingroup$ I would suggest not using IUPAC names for every compound. HDMS is a widely-recognized name in both fully written and abbreviated forms. You want your committee and anyone else who reads your thesis to focus on what work you have done, not get distracted by why you chose an obscure name for a common reactant. $\endgroup$ – buckminst Dec 31 '17 at 0:08
  • $\begingroup$ @buckminst Thanks for the comment, I definitely agree. It was a joke, although I admit didn’t make it very clear. Using PINs everywhere means using ethoxyethane instead of diethyl ether, etc. I’m not planning to go down that route, not least because it’s a huge waste of time for me to search the Blue Book for every compound, and as you said it simply leads to needless confusion. $\endgroup$ – orthocresol Dec 31 '17 at 1:20
  • $\begingroup$ @buckminst I think it's still a good idea to be aware of it, just in case if someone asks a passionate/spiteful question. (Of course, depending on how much the thesis has to do with this particular compound.) Anyhow, the question on its own still stands, even if it is not required in the original context. $\endgroup$ – Linear Christmas Dec 31 '17 at 13:28
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    $\begingroup$ @LinearChristmas LiHMDS and KHMDS are only mentioned essentially in passing; for the real important compounds in my thesis, nobody will be able to tell whether I found the PINs or whether I just used ChemDraw's auto name generator... $\endgroup$ – orthocresol Dec 31 '17 at 14:13
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According to the current version of Nomenclature of Organic Chemistry – IUPAC Recommendations and Preferred Names 2013 (Blue Book), as already mentioned in the question, the name ‘disilazane’ is no longer recommended for $\ce{H3Si-NH-SiH3}$. Such structures are now named as amines. (Also note that the name ‘hexamethyldisilazane’ is ambiguous and therefore never was in accordance with IUPAC nomenclature.)

P-21.2.3.1 Heterogeneous parent hydrides composed of alternating heteroatoms, i.e., [a(ba)n hydrides], excluding carbon atoms and the halogen atoms.
Compounds containing an unbranched chain of alternating atoms terminated by two identical atoms of the element coming later in the seniority order O > S > Se > Te > N > P > As > Sb > Bi > Si > Ge > Sn > Pb > B > Al > Ga > In > Tl may be named by citing successively a multiplying prefix denoting the number of atoms of the terminal element followed by the ‘a’ term for that element, then the ‘a’ term of the other element in the chain and the ending ‘ane’. The terminal letter ‘a’ of an ‘a’ term is elided when followed by a vowel; the terminal vowel of a numerical prefix is not elided even when the ‘a’ term begins with the same vowel. When nitrogen atoms are present, amine names (see P-62) are preferred because of the higher functionality of amines. This concept does not extend to other elements. These parent hydrides are preselected parent hydrides (see P-12.2) and have priority to receive preferred IUPAC names, as long as they are used to name compounds containing carbon.

Symmetrical secondary amines are named according to Subsection P-62.2.2.1, which describes three different methods.

P-62.2.2.1 Symmetrical and unsymmetrical secondary and tertiary amines are named only by the same methods described in P-62.2.1.2.

(1) substitutively using the retained name ‘aniline’ or the suffix ‘amine’ and the name of a parent hydride with further N-substitution;

(2) substitutively, by prefixing, in alphabetical order when required, the name(s) of the substituent group(s) R, R' or R" to the parent hydride name ‘azane’. In order to avoid ambiguity, the second prefix in a secondary amine, and the second and the third prefixes in a tertiary amines must be enclosed in parentheses when these prefixes denote simple substituents.

(3) substitutively, by prefixing, in alphabetical order when required, the name(s) of the substituent group(s) R, R' or R" to the parent hydride name ‘amine’. In order to avoid ambiguity, the second prefix in a secondary amine, and the second and the third prefixes in a tertiary amines must be enclosed in parentheses when these prefixes denote simple substituents.

Method (1) generates preferred IUPAC names. Functional parent names like diethylamine and triethylamine are deprecated. The prefixes in names of such secondary and tertiary amines formed by method (2)[sic: read (3)] are set off by parentheses to distinguish them from these deprecated names.

The corresponding names for $\ce{H3Si-NH-SiH3}$ are actually given as examples in the Blue Book:

(1) N-silylsilanamine
(2) disilylazane
(3) disilylamine
(not disilazane; see P-21.2.3.1)

Note that, since $\ce{H3Si-NH-SiH3}$ does not contain any carbon, no preferred IUPAC name (PIN) is indicated in the Blue Book for this compound.

The corresponding names for the complete compound that is given in the question are:

(1) 1,1,1-trimethyl-N-(trimethylsilyl)silanamine
(2) bis(trimethylsilyl)azane
(3) bis(trimethylsilyl)amine

Since P-62.2.2.1 explicitly states that Method (1) generates preferred IUPAC names even for symmetrical amines, the preferred name for the complete compound that is given in the question is 1,1,1-trimethyl-N-(trimethylsilyl)silanamine.

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  • $\begingroup$ New abbreviation: LTTSA $\endgroup$ – Jan Jan 1 '18 at 11:36

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