Page 26 - Nomenclature of Inorganic Chemistry (IUPAC Recommendations 2005)

IR-10.2 O R G A N O M E T A L L I C C O M P O U N D S

Organic l igands with the ability to form more than one bond to a m etal centre may
be chelating (if bonding to a s ingle metal), bridging ( if bonding to more than one metal),
or sometimes even both chelating and bridging. The bridging b onding mode is indicated by
the Greek letter m (mu) prefixing the ligand name ( Section IR-9.2.5.2). This convention is
further exemplified for organometallic compounds in Sections IR-10.2.3.1 and IR-10.2.3.4.

IR-10.2.1.4 Oxidation n umber and net charge
The concept of oxidation number or state (see also Sections IR-4.6.1, IR-5.4.2.2 and
IR-9.1.2.8) is sometimes difficult to apply t o o rganometallic compounds. This is especially
true when i t c annot be determined whether c omplexation by a l igand is better regarded
as a L ewis-acid or Lewis-base association or as an oxidative addition. Thus, for nomen-
clature purposes it is only the net c harge on the coordination entity that is important, a nd
formal oxidation numbers will not be assigned to the central atoms of the organometallic
complexes in the following sections. The reader is referred to standard textbooks o n
organometallic chemistry f or discussion of the assignment of oxidation number in such
compounds.

IR-10.2.2 Compounds with one metal–carbon single bond

In naming organometallic compounds the usual rules for naming ligands in coordination
entities a re applied if the ligand coordinates via an atom other t han carbon (Section IR-

9.2.2.3). T hus, the ligand MeCOO is named acetato, Me 2 As is named dimethylarsanido,
and PPh 3 is named triphenylphosphane.
If an organic ligand coordinating via one carbon atom is regarded as an anion formed by
the removal of one hydron from that atom, the ligand name i s f ormed by replacing the
ending ‘ide’ of the anion name by ‘ido’.

Examples:
methanido
1. CH 3

2. CH 3 CH 2 ethanido
3. (CH 2 ¼CHCH 2 ) prop-2-en-1-ido

4. C 6 H 5 benzenido
5. (C 5 H 5 ) cyclopentadienido

Although strictly speaking ambiguous, the anion n ame c yclopentadienide is acceptable
as a s hort form of cyclopenta-2,4-dien-1-ide (and consequently the ligand name
cyclopentadienido).
The compound [TiCl 3 Me] would be called t richlorido(methanido)titanium using t he
above type of ligand name.
The alternative for naming an organic ligand attached via a s ingle carbon atom is to
regard it as a s ubstituent g roup, its name b eing d erived from a p arent hydride from which
one hydrogen atom has been removed. T his designation is somewhat arbitrary a s s uch
ligands in organometallic chemistry are generally treated as anions when d educing oxidation
states, although the bonding in reality may be highly covalent. H owever, it has a l ong

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