Page 36 - 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

IR-10.2.4 Compounds with metal–carbon multiple bonds
Ligands regarded as forming metal–carbon double o r t riple b onds may also be given
substituent p refix names derived from the parent hydrides, t he ligand names ending with
‘ylidene’ for a d ouble bond and with ‘ylidyne’ for a t riple bond. These suffixes are used
according to two methods (see Section P-29 of Ref. 3).

(a) The suffix ‘ylidene’ or ‘ylidyne’ replaces the ending ‘ane’ of the parent hydride name.
If the parent hydride is a c hain, the atom with the free valencies is understood to terminate
the chain. This atom has, in all cases, the locant ‘1’ (which is omitted from the name). This
method is used only for saturated acyclic a nd monocyclic hydrocarbon substituent g roups
and for the mononuclear parent hydrides of silicon, germanium, t in and lead. N ote that the
suffix ‘ylene’ should o nly be used in conjunction with m to designate b ridging CH 2
(methylene) or C 6 H 4 (phenylene) (see Section IR-10.2.3.1).

(b) In a m ore general method, the suffix ‘ylidene’ or ‘ylidyne’ is added to the name of the
parent hydride with elision of the teminal ‘e’, if present. The atom with the free v alence is
given a n umber as low as is consistent with the established numbering of the parent hydride.
For ligand names with the suffix ‘ylidene’, this locant must always be cited, except if it is the
only locant in the name and there is no ambiguity.

Example:
1. EtCH¼ propylidene [method (a)]
Me 2 C¼ propan-2-ylidene [method (b)]

Note that in numbering a l igand that has several points of attachment, the longest chain o f
carbon atoms is chosen as the parent chain b efore assigning the lowest possible locant to the
atom with the free valence. In a m etallacycle, the direction of numbering is chosen s o a s t o
give the lowest possible locants to side chains or substituents. Once again, special numbering
schemes apply to heterocyclic and polycyclic systems ( see Sections P-25 and P-29 of Ref. 3).
If a l igand forms one or more metal–carbon single bonds a s w ell as metal–carbon
multiple b onds, the order of endings is ‘yl’, ‘ylidene’, ‘ylidyne’. Method (b) should t hen be
used to give the lowest possible s et of locants for the free valencies. If a c hoice remains,
lower numbers are selected for the ‘yl’ p ositions before the ‘ylidene’ positions and then for
any side chains or substituents.

Example:
2.
CH 3 CH 2 C propan-1-yl-1-ylidene

Typical ligands forming a m etal–carbon double o r t riple b ond are listed in Table IR-10.3, and
this is followed by examples illustrating the naming of compounds containing one or more
metal–carbon multiple bonds. The Z term in Example 5 i s e xplained in Section IR-10.2.5.1.
Note that the anion names given i n T able IR-10.2 ( methanediido, ethane-1,1-diido, etc.)
may also b e u sed for these ligands, b ut it is then not possible t o c ommunicate the concept of
the carbon–metal bond as being a double or triple b ond.

213