Page 24 - 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

An organometallic compound is defined as any compound c ontaining at least one bond
between a metal atom and a c arbon atom. The names of organometallic compounds should
therefore accord with the rules of both organic and coordination chemistry nomenclature
(even though t hese have tended to evolve separately).
The major part of this Chapter presents a s ystem of nomenclature for transition element
organometallic compounds, b ased on the additive nomenclature system introduced in
Chapter I R-7 and applied to coordination compounds in Chapter IR-9 but incorporating, as
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far as possible, the rules for naming organic ligands. Most importantly, further rules are
formulated which unambiguously designate the special modes o f b onding often found in
organometallic compounds.
The later part of this Chapter briefly describes aspects of the naming of main group
organometallic compounds, where the substitutive system of nomenclature (introduced i n
Chapter I R-6) is applied by substituting the appropriate parent hydrides of the elements of
groups 13–16. The names of organometallic compounds o f g roup 1 a nd 2 e lements are, on
the other hand, based on the additive nomenclature system.
It should b e e mphasized that the nomenclature described in this Chapter is confined to
the precise description of the composition of a c ompound and the connectivity of atoms
within a m olecule or ion; it is often also important to specify the spatial r elationships
between t he structural components of the molecule or ion (see Section IR-9.3). It is
particularly true of organometallic chemistry that nomenclature should n ot attempt to
convey details about the polarity of bonds, patterns of reactivity or methods of synthesis.

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

IR-10.2.1 Concepts and conventions

The (additive) n omenclature of coordination complexes, the general definitions and rules of
which are given i n S ections IR-9.1 and IR-9.2, p rovides the basis for the system presented
here for naming organometallic compounds of the transition elements. The general concepts
of coordination chemistry can be applied to organometallic compounds but n eed to be
expanded to deal with the additional modes of connectivity afforded by the interaction of
metals with, for example, organic ligands containing unsaturated groupings, such as alkenes,
alkynes and aromatic compounds. This section e xamines relevant c oncepts and conventions
from coordination chemistry as they are applied to organometallic compounds, and indicates
what new conventions need to be introduced in order to designate unambiguously the special
bonding modes o f o rganometallic compounds.

IR-10.2.1.1 Coordination number

The definition of coordination number as being equal to the number of s-bonds between t he
ligands and the central atom (Section IR-9.1.2.6) also applies to ligands such as CN , C O,

N 2 and PPh 3 , w here the bonding of a s ingle ligating atom to a m etal may involve a
combination of s- a nd p-components. The p-bond components are not considered in
determining the coordination number, and so [Ir(CO)Cl(PPh 3 ) 2 ], [RhI 2 (Me)(PPh 3 ) 2 ] a nd
[W(CO) 6 ] h ave coordination numbers of four, fi ve and six, respectively.

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