Page 50 - 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

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To avoid t his ambiguity, the name bis(Z -cyclopentadienyl)iron(1þ), for example, is
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þ
strongly p referred to ferrocenium(1þ) f or [Fe(Z -C 5 H 5 ) 2 ] . T he same comment applies to
substituted derivatives.

Examples:
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14. [Co(Z -C 5 H 5 ) 2 ][PF 6 ]
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bis(Z -cyclopentadienyl)cobalt(1þ) h exafluoridophosphate
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15. [Co(Z -C 5 H 5 )(Z -C 5 H 4 COMe)][BF 4 ]
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(acetyl-Z -cyclopentadienyl)(Z -cyclopentadienyl)cobalt(1þ)
tetrafluoridoborate
The oxidized f orm of osmocene is dinuclear in the solid state, with a l ong Os–Os bond,
so should not in any case be named using the ‘ocenium’ nomenclature. However,
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[Os(Z -C 5 Me 5 ) 2 ] þ has a m ononuclear sandwich structure and may be described as the
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decamethylosmocenium(1þ) i on, a lthough b is(pentamethyl-Z -cyclopentadienyl)osmium(1þ)
is strongly p referred.
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In strong protic acid media, ferrocene is hydronated to [Fe(Z -C 5 H 5 ) 2 H] . þ T o
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avoid ambiguities, this should b e n amed by the additive procedure, i.e. bis(Z -
cyclopentadienyl)hydridoiron(1þ).
Transition element complexes derived from ligands with additional rings fused to the
cyclopentadienyl rings are also k nown. The names of these c omplexes are derived from the
retained common or semisystematic names of the hydrocarbon ligands, e.g. 1H-inden-1-yl
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(C 9 H 7 ), fluoren-9-yl (C 13 H 9 ), and azulene (C 10 H 8 ). Thus, [Fe(Z -C 9 H 7 ) 2 ] i s n amed
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bis(Z -indenyl)iron or, more specifically, bis[(1–3,3a,7a-Z)-1H-inden-1-yl]iron. To avoid
possible a mbiguities, the use of fusion nomenclature, such as ‘benzoferrocene’, is strongly
discouraged.
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Many compounds have ligands in addition to two Z -cyclopentadienyl rings. They
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are often referred to as metallocene di(ligand) species, e.g. [Ti(Z -C 5 H 5 ) 2 Cl 2 ] i s
frequently named ‘titanocene dichloride’. This practice is discouraged since metallocene
nomenclature applies only to compounds in which the two rings are parallel. Thus,
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[Ti(Z -C 5 H 5 ) 2 Cl 2 ] i s n amed dichloridobis(Z -cyclopentadienyl)titanium, and [W(Z -
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C 5 H 5 ) 2 H 2 ], [Ti(CO) 2 (Z -C 5 H 5 ) 2 ] a nd [Zr(Z -C 5 H 5 ) 2 Me 2 ] s hould be named bis(Z -
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cyclopentadienyl)dihydridotungsten, dicarbonylbis(Z -cyclopentadienyl)titanium and
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bis(Z -cyclopentadienyl)dimethylzirconium, respectively.
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The bis(cyclooctatetraene) compound [U(Z -C 8 H 8 ) 2 ] h as sometimes been described as
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‘uranocene’. Related species are obtained from zirconium, [ Zr(Z -C 8 H 8 ) 2 ], and the
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lanthanoids, e.g. [Ce(Z -C 8 H 8 ) 2 ] . I n s uch complexes, the carbocyclic rings are parallel
and there are certain s imilarities to ferrocene in the molecular orbital descriptions of their
bonding. However, some lanthanoids also form metal(II) cyclopentadienyl complexes, such
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as [Sm(Z -C 5 Me 5 ) 2 ]. Extension of the ‘ocene’ nomenclature to [U(Z -C 8 H 8 ) 2 ] a nd similar
compounds c an therefore lead to confusion and is strongly d iscouraged.
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Furthermore, the cyclooctatetraene ring can also function as an Z -ligand, as in [Ti(Z -
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C 8 H 8 )(Z -C 8 H 8 )]. Compounds of cyclooctatetraene should therefore be named using
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standard o rganometallic nomenclature, e.g. bis(Z -cyclooctatetraene)uranium and [(1–4-Z)-
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cyclooctatetraene](Z -cyclooctatetraene)titanium. The ligand C 8 H 8 is occasionally
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