Rearrangements of alkyne and 1,3-diyne in transition metal center forming small ring complexes

Article abstract of DOI:10.1016/j.ica.2010.09.058

CC bond coupling of alkynes(s) and alkynyl(s) mediated by transition metal complexes have recently lead to isolations of the small organometallic ring constituted of unsaturated carbon atoms of the dimer ligand. The ring structures of four-membered 1-meta

Full text of DOI:10.1016/j.ica.2010.09.058

Inorganica Chimica Acta 366 (2011) 1–18
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Review
Rearrangements of alkyne and 1,3-diyne in transition metal center forming
small ring complexes
⇑
Shinsaku Yamazaki
Chemistry Laboratory, Kochi Gakuen College, 292 Asahi Tenjin-cho, Kochi 780-0955, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
CAC bond coupling of alkynes(s) and alkynyl(s) mediated by transition metal complexes have recently
lead to isolations of the small organometallic ring constituted of unsaturated carbon atoms of the dimer
ligand. The ring structures of four-membered 1-metallacyclo-2-butene and five-membered MCp com-
pounds reveal a diverse array of bond multiplicity that undergoes complexation. Some of these cyclomet-
allated alkynes(s) and 1,3-diyne(s) in solution undergo unusual isomerization, alkyne trimerization,
tetramerization, and also condensation, which may be included in an important intermediate of metal-
catalyzed organic syntheses of hetero- and carbocyclic molecules. This context is reviewed mainly along
syntheses and anomalous crystal structures of these metallacycles formed by the rearrangement of the
linear alkyne(s) and 1,3-diyne(s) in the metal center. Recently explored angular phenylene compounds
of cobaltacene, and metallapentalene are also described.
Received 16 June 2010
Received in revised form 28 September
2010
Accepted 30 September 2010
Available online 20 October 2010
Keywords:
Crystal structure
Rearrangement of alkyne
Metallacycle
Ó 2010 Published by Elsevier B.V.
Alkyne oligomerization
Shinsaku Yamazaki was on 7 September 1945. In 1969 he got his Bachelor of Engineering from the Nagoya Institute of Technology. In 1971 he was
awarded the master’s degree in Science and in 1975 Dr of Science both in Chemistry by the Faculty of Sciences, Osaka City University. In 1978 he
became Associate Professor of Kochi Gakuen College. From 1993 to 2000 he was Visiting Research Fellow of Chemistry Department, University College
London. Since 1998 he is working as Professor of Kochi Gakuen College.
Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2. Four-membered 1-metallacyclo-2-butene . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3. Metallacycles of alkynes in electron poor transition metal complexes of zirconocene and titanocene . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2
3
5
3.1. Five-membered metallacycle of 1,3-diyne that undergoes complexation and a succeeding cleavage of 1,3-diyne . . . . . . . . . . . . . . . . . . . . 5
3.2. Seven-membered metallacycle of alkynes in zirconocene . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.3. Titanocene interacting with saturated carbon atoms in sp3-hybrid. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
4. Five-membered metallacycles in electron rich transition metal clusters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
4.1. Cyclometallation through dimerization of alkynes and 1,3-diyne . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
4.2. Metallacycle through alkyne trimerization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
⇑
Tel.: +81 088 840 1121; fax: +81 088 840 1123.
E-mail address: yamazaki@kochi-gc.ac.jp
0020-1693/$ - see front matter Ó 2010 Published by Elsevier B.V.
doi:10.1016/j.ica.2010.09.058

2
S. Yamazaki / Inorganica Chimica Acta 366 (2011) 1–18
4.3. Cyclometallation through alkyne tetramerization. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
5. Phenylene and metallapentalene complexes formed by C–C bond coupling of alkynyls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
1. Introduction
versatilities to isomerize and further reactivities to carbon monox-
ide or metal-carbonyl to produce furans, lactone and cyclo-pentene
[5], like the Pauson–Khand reaction [6].
Oxidative coupling of alkynyl ligands may be one of the most
significant reactions studied more recently in the methodical syn-
theses of one-dimensional allotropes of the polyyne (–C„C–)n unit
with nonlinear optical properties [1]. 1,3-Diyne and polyyne func-
tion as a multi-electron supplier ligand whose nucleority enables
Small cyclic alkynes are unstable because of ring strain [7]. In
the electron poor transition metal complexes of titanocene and zir-
conoce, 1-metallacyclo-3-pentyne (Fig. 1.4.C) [8] has recently been
dramatically isolated by reacting zirconocene dichloride with
cumulenes having bulky substituents, (Z)-1,4-bis(trimethylsilyl)-
1,2,3-butatriene and (Z)-2,2,7,7-tetramethyl-3,4,5-octatriene, or
by a photoreaction of zirconocene dichloride in the presence of
1,4-dichloro-2-butyne and magnesium. 1-Metalla-2,3,4-pentatri-
to build up clusters by
r-,p-binding to be coupled with features
forming unusual frameworks [2] that may be included in signifi-
cant carbonylation reactions in the syntheses of carbocyclic and
heterocyclic molecules [1f]. Cyclometallation of alkynes in the
form of 1-metallacyclopenta-2,4-diene has been well known in
mono- and di-nuclear complexes [3]. Small ring complexes of cob-
alta- and rhodacycles with MC3-unit, as shown in Fig. 1(1), and
Fig. 1(2), have been prepared by the incorporation of nucleophile,
ene has been isolated by the sunlight treatment of bis(r-acety-
lide)zirconocene [9a]. The ring structures of these organometallic
compounds of 1,3-diyne have mostly been defined to be in the pla-
nar geometry exhibiting the diverse array of bond multiplicities
that further undergo complexation, isomerization, CAC bond
scission, and alkyne-oligomerization, indicating an important
isonitrile and diazoacetate, into the MAC bond of the
kynes [4,5a,5b]. These metallacyclic alkynes(s) in MC3-unit display
p-bonding al-
Fig. 1. Metallacyclic structures of alkyne(s) and 1,3-diyne(s).

S. Yamazaki / Inorganica Chimica Acta 366 (2011) 1–18
3
intermediate of the organic syntheses of hetero- and carbo-cyclic
organic molecules [10]. The electronic density calculations of
1-metallacyclo-3-pentyne and 1-metallacyclopenta-2,3,4-triene
have recently been studied and the ring structures may be better
described by the resonance hybrid, and the differencies are only
in the electronic configurations [11]. However, by reacting these
toward the application to use as a single source precursor of orga-
nometallic chemical vapour desorption (OMCVD) of thin ceramic
film [13]. Another intriguing complex isolated by the rearrange-
ment of alkynes in the transition metal center may be the ruthe-
na-cyclopentatriene featured as
a bis(carbene) functionality
(Fig. 1.4.D), which undergoes an extraoridinary ring opening to
transform into an allyl-carbene complex.
two MCp compounds with the metallocene sources, (
and (
5-Cp)Zr, two distinct products have been isolated, respec-
tively: 1-metallacyclopenta-2,3,4-triene transforming into a
g
5-Cp)Ti
g
Recently, 1,3-diyne and polyyne in transition metal complexes
have been extensively reviewed [14a,14b]. In this context, how-
ever, small ring metallacycles given by the rearrangement of the
linear alkynes and 1,3-diynes in the transition metal center, and
subsequent condensation forming unprecedented metallapenta-
lene complexes (Fig. 1.8 and 1.9) are focused and reviewed along
their syntheses and anomalous crystal structures. The methodical
syntheses of the angular cobaltaphenylene complexes are also
described.
l
-
trans butadiyne with the hybrid structure contributed of a bridging
butynediyl and a bridging butatriene (Fig. 1.4.B1), while 1-metalla-
3-pentyne an analogous but a -cis-butene having a bridging but-
l
enediyl structure with (l– :g
g1 1)-bond, (Fig. 1.4.C2). Most re-
cently, in the electron rich transition metal complexes, an
unprecedented manganacyclic compound of 1,3-diyne, with a
Mn2C4 unit (Fig. 1.6), has been derived by using Pt(II) diacetylies
and manganese-carbonyl [12]. All ring carbon atoms underwent
complexation, and the ring structure with 1-manganacyclo-3-pen-
tyne has been proposed of a hybrid structure largely contributed of
1-metallacyclopenta-2,3,4-triene. The mixed metal complexes
thus derived from MCp compounds are currently in direction
2. Four-membered 1-metallacyclo-2-butene
The first four-membered MC3 ring of 1-cobaltacyclo-2-butene,
CpCo(CR1@CR2–C(@NR3)(PPh3) 2 was derived by the incorporation
of nucleophile, isocyanide R3NC (R3 = p-MeC6H4, 2,6-Me2C6H3, Ph),
into
p-alkyne complex (g g 1 [4], as
5-Cp)Co( 2-R1CCR2)(PPh3)
shown in Scheme 1. 2 have been notified as an important interme-
diate of the metal-catalyzed alkyne oligomerization.
On heating 2 in toluene, the metallacycle is unstable and frag-
mentation into an acetylene derivative and isocyanide took place,
as shown in Scheme 2. In addition, interestingly, four-membered
metallacycle with R = p-MeC6H4 undergoes isomerization reaction
to give its regioisomer 4, and the reaction proceeds quantitatively
when excess PPh3 was added in benzene at 95°. The reaction has,
Scheme 1.
Scheme 2.
Scheme 3.

4
S. Yamazaki / Inorganica Chimica Acta 366 (2011) 1–18
Scheme 4.
Scheme 5.
therefore, been suggested to proceed via an intermediate of
plex 3.
p
-com-
(g g
5-Cp)Co ( 2-Me3SiC„CSO2Ph)(PPh3) 5 [5a], and 7 was obtained
in 43% yield, when reaction has been carried in benzene for 18 h at
Another noticeable four-membered 1-cobaltacyclo-2-butene
compound is shown in Scheme 3. [(
5-Cp)Co{CH(CO2Et)-C(Me3-
Si)C@C(SO2Ph)}(PPh3)] 7, was obtained by an incorporation of
CH(CO2Et)-fragment from diazoacetate into MAC bond of -alkyne
room temperature (Scheme 3). For 7, 1H NMR doublet resonance at
g
1.48 with JP,H = 7.2 Hz is assigned to a hydrogen atom on a-carbon
atom in the metallacycle. An analogous PMe3-complex 8 was iso-
lated from solution of a (1:1) mixture of diastereomers by reacting
p

S. Yamazaki / Inorganica Chimica Acta 366 (2011) 1–18
5
7 with PMe3 at 353 K. X-ray structure of 8 reveals that the geom-
etry of CoC3-ring is flat with C–Co–C angle constrained to 66.7°,
and the ester substituent is located anti to PMe3 ligand. Four-mem-
with 1,2-heterodimetalla-3-petene-5-one structure, and the reac-
tion indicates a significant intermediate of alkyne-carbonylation
reactions [6b], like the Pauson–Khand reaction. 15 may be formed
bered rhodacyclic compound, (
g
5:Cp)Rh{C(@NMe)C(Ph)@C(Ph)}
5-Cp)
from 16 electron species of
PhC„CAC„CPh)] (dppe) 14 by a subsequent incorporation of
Fe(CO)4-group into M-C2 -bond. While, 16 with 1,2-heterodime-
p -
-1,3-diyne compound, Pt(g2
(SbiPr3) 11 (Scheme 4), was isolated from reaction of (
g
Rh(g
2-PhCCPh)(SbiPr3) 9 with isonitrile CH3NC, followed with
p
SbiPr3 [5b]. The formation reaction of the rhodacyclobutene ring
talla-3-petene-5-one structure may be given by the incorporation
was also suggested not via a simple insertion of CH3NC into the
of Fe(CO)3-group into VꢀC1 bond.
p-alkyne, but rather via an intermediate of isonitrile compound
10, since reaction of the
p-alkyne compound with twice molar
3. Metallacycles of alkynes in electron poor transition metal
complexes of zirconocene and titanocene
amount of SbiPr3 and CH3NC facilitates a formation of metallacyc-
lobutene complex 11. An excess of methylisocyanide reacts with
p
-alkyne compound 9 or metallacyclobutene compound 11 to
3.1. Five-membered metallacycle of 1,3-diyne that undergoes
complexation and a succeeding cleavage of 1,3-diyne
afford metallacyclopentene 12 in 90% yield. Interestingly, its crystal
structure reveals that C4Rh-ring is not in planar, but considerably
tilt with a long-short-long sequence of the CAC single and C@C
double bond lengths.
Another intriguing four-membered metallacycle may be a
cyclone compound 15 (Scheme 5), which has been derived by
homocoupling of acetylides in cis-Pt(–C„CTp)2(dppe), being
induced by Fe(CO)5 [15]. The reaction gave another product 16
In addition of alkyne-carbonylation and oxometallation of alkyne
[16], CAC bond coupling reactions of alkynes in the electron poor
metallocene compounds have lead to isolations of five-membered
metallacycles constituted of 1,3-diyne. 1-Metallacyclo-2,4-diene
(A in Fig. 2) and an unprecedented 1-metallacyclopenta-2,3,4-
triene (B) have recently been isolated in titanocene and zirconocene
complexes [17]. X-ray analyses of these, in addition of 1-metalla-
cyclo-3-pentyne (Fig. 2C), reveal that the geometries of the
Fig. 2. Ring structures of MCp compounds.
Scheme 7.
Fig. 3. Five-membered TiCp compound and seven-membered zirconacycle formed
by CAC bond coupling of 1,3-diyne.
Scheme 8.
Scheme 6.

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S. Yamazaki / Inorganica Chimica Acta 366 (2011) 1–18
Table 1
Structure data of 1-metallacyclo-2,3,4-pentatriene.
Bond length (Å) (C@C)
Bond angles (°)
a
a0
M = Ti, L = Cp, R = tBu
C2@C3
C3@C4
C4@C5
1.243
1.339
1.276
150.0
147.8
M = Zr, L = Cp, R = tBu
C2@C3
C3@C4
C4@C5
1.28
1.31
1.29
150.0
147.2
Scheme 11.
bulky substituents, (Z)-1,4-bis(trimethylsilyl)-1,2,3-butatriene and
(Z)-2,2,7,7-tetramethyl-3,4,5-octatriene, or by photo reaction of
zirconocene dichloride in the presence of 1,4-dichloro-2-butyne
and magnesium [8]. 1-Zircona cyclo-2,3,4-triene compound B
was obtained by the intra-molecular CAC bond coupling of the
Scheme 9.
bis(
Cp2Zr(L) (
r
-acetylide) by the sunlight treatment [19]. Reaction of
g
2-Me3SiCCSiMe3) (L = THF, pyridine) with 1,3-diyne
and polyyne affords a coupling product of the two diyne entities
at the core complex newly forming a seven-membered ring
(Fig. 3.B), while the corresponding reaction of titanocene using
two equiv. amount of the diyne undergoes the regioselective cou-
pling of the diynes transforming into a titanacyclopentadiene
(Fig. 3.A), by which one alkynyl-group bond to the metal in the
a- and another one in the b-carbon, respectively [19].
If 2 equiv. of metallocene reacts with the diynes, the reactions
depend on the substituents of the diyne, and for M = Ti with
t
R = Ph or Bu, a dimetal complex 18 with zig-zag coordination of
tetradehydrobutadiene by (l– :g
g1 1)-bridge is formed (Scheme 6)
[9b]. While for M = Ti, Zr with the diyne having trimethylsilyl sub-
stituents, the coupling transforms to an unusual cleavage reaction
depositing a dimetal 17 bridged by the alkynyls (Scheme 6).
Another intriguing five-membered titana- and zirconacycle is
metallacyclocumulene with the planar geometry 19 (Scheme 7).
Permethylziroconacyclocumulene 20 has also been prepared by
Scheme 10.
the sunlight treatment of the bis(r-acetylide). 20 was also ob-
metallacyclic rings are mostly flat but exhibit bond multiplicity
that undergoes complexation [18] (Fig. 2). The resulting mixed
metal compound having Ni(0) is known to undergo an extraordinary
CAC bond cleavage of 1,3-diyne.
The first 1-zirconacyclo-3-pentyne was obtained by treating
zirconocene dichloride with Bu–Li, followed with cumulenes with
tained by treating zirconocene dichloride with the diyne and mag-
nesium (Scheme 8).
The crystal structure data of 20 (selected bond lengths and an-
gles) are shown in Table 1. In the ring structure with three CAC
double bonds, the central one is elongated that may be ascribed
to an intra molecular p-interaction of this bond to the metal center.

S. Yamazaki / Inorganica Chimica Acta 366 (2011) 1–18
7
Five-membered 1-titanacyclo-2, 5-diphenyl-2,3,4-pentatriene
in solution has been suggested to attain an equilibrium of g2
titanacyclopropene 21 with
4-complex(titanacyclocumulene)
Bis(trimethylsilyl)octatetrayne also reacts with twice molar
-
amount of metallocene to afford a dimetal complex 30 of the tetra-
g
yne bridged by a (l– :g
g1 1)-bond with the zig-zag coordination of
22, as shown in Scheme 9. Interestingly, both of the equilibrium
mixtures react even with each other. 22 reacts with acetone and
water to afford unsymmetrical compounds of oxo-titanacycle 23
and an oxo-bridging dinuclear titanocene compound 24
(Scheme 9). While, 1-titanacyclopenta-2,3,4-triene underwent an
extraordinal annealation transforming to two dinuclear com-
pounds, 25 and 26 (Scheme 10), for which carbon atoms at 2,3-
positions of 1-titanacyclo-2,3,4-pentatriene underwent the inter-
molecular coupling reactions. The metallacycle in the cumulene
structure reacts with Ni(0) compound to give two products: one,
five-membered metallacyclobutadiene that underwent complexa-
tion to Ni(0): 27; the other, an interesting bond cleavage of the
cumulene transforming to 28 and 29 (Scheme 11) [18].
a tetradehydrobutadiene-form (Scheme 12).
While, four-equivalent of metallocene reacts with the octa-
tetrayne to undergo an unusual cleavage of the tetrayne giving
two products, 31 and 32.
An analogous reaction of 1,3,5-tris(tert-butylbutadiynyl)ben-
zene with the metallocenes gave 34 and 35, each with six metallo-
cenes, as attributed Scheme 13.
Five-membered titanacycles, 36–41 in Fig. 4, have been pre-
pared by reacting (
(CH2)nAC„CR [20].
is displaced by the
g g
5-Cp)2Ti( 2-Me3SiCCSiMe3) with RC„CA
P
-Bonding alkyne in Cp2Ti(Me3SiCCSiMe3)
a,x
-diynes with substituent R, RC„
CA(CH2)nAC„CR B, and subsequent intramolecular cyclization af-
fords bicyclic titanametallacycles, 38–41, as attributed in Fig. 4. In
Scheme 12.
Scheme 13.

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S. Yamazaki / Inorganica Chimica Acta 366 (2011) 1–18
Fig. 4. Five-membered titanacycles attained by the substitution of Me3SiC„CSiMe3 in Cp2Ti(Me3SiC„CSiMe3) with RC„CA(CH2)nAC„CR.
Fig. 5. Crystal structure of seven-membered zirconacycle formed by CAC bond
coupling between
butatriene.
p-(SiMe3AC„CCH3) and (Z)-1,4-bis(trimethylsilyl)-1,2,3-
Fig. 6. Crystal structure of a titanacycle having Ti–C interactions with the saturated
carbon atoms in sp3-hybrid.
case of a,x-diynes with n = 2, the metallacycle formation reaction
was carried in hexane at 195 K to precipitate 36 in 71% yield for
R = Me and in 51% yields for R = Bu, respectively. By an analogous
procedure, 37 with R = Et was prepared in 80% yield. While, 39
was obtained from 37 by allowing to stand the solution at room
yield from a mixture with its trans-isomer (19%), as affirmed by
NMR. Crystal structure of 42 is in Fig. 5. The bond length C2AC3
1.239(3) Å is short enough to be regarded as the triple bond, and
the alkyne moiety is bent toward the metal, and the bond lengths
temperature for 24 h, or by reacting (
with B with n = 4, in 75% yield. 38 with n = 5 was prepared by
reacting (
5-Cp)2Ti(Me3SiCCSiMe3) and B in hexane at room tem-
g
5-Cp)2Ti(Me3SiCCSiMe3)
ZrAC2 2.417(2) Å and ZrAC3 2.425(2) Å are consistent with
p-
g
bond.
perature in 63% yield.
3.2. Seven-membered metallacycle of alkynes in zirconocene
3.3. Titanocene interacting with saturated carbon atoms in sp3-hybrid
Seven-membered metallacycle of triyne 42 (Fig. 5) was first
achieved by treating
bis(trimethylsilyl)-1,2,3-butatriene in THF at 193 K for 1 h [21].
The zirconacyclic product 42 in cis-form was thus isolated in 62%
In contrast to the metallacycles containing unsaturated carbon
atoms, a titanocene compound that unusually interacts with satu-
rated carbon atoms in sp3-hybrid has recently been isolated [22]. A
(g
5-Cp)2Zr(Me3SiC„CMe) with (Z)-1,4-
reaction of the enyl compound, (g
5-Cp)Ti(C8H11)(PEt3), with three

S. Yamazaki / Inorganica Chimica Acta 366 (2011) 1–18
9
Scheme 14.
Scheme 15.
Scheme 16.

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S. Yamazaki / Inorganica Chimica Acta 366 (2011) 1–18
equiv of Me3ASiC„CPh has lead to the isolation of an air-sensitive
product 43, as shown in Fig. 6. X-ray structure reveals that one al-
kyne couples with the dienyl ends (C1 and C9), while the other two
alkynes are coupled and bond to phenyl-substituted ends to two of
the remaining three dienyl positions, C(2,7). The bond distances
TiAC2 and TiAC7 are 2.579(7) and 2.293(7) Å, respectively, the lat-
ter of which are shorter than those for the bound C(4,5) or even any
of the C5H5 carbon.
above Fe1, C3, C2 plane. The dihedral angle between Fe1–C1–C2
and F1–C3–C2 planes is 302.5 K. 45 reacts with Fe2(CO)9 in hexane
at 313 K to yield dark green three-iron cluster 48 and four-iron
cluster 49, as attributed in Scheme 15. 48 is a Fe3C4 closo pentag-
onal bipyramid with an open cluster Fe3(CO)8-moiety. The Fe1, C1,
C2, C4, and C3 atoms form a perfect plane. In 49, the dangling triple
bond in 45 now transformed into a (l3–g
2)-bonding ligand with a
link to Fe1, Fe3, and Fe4 atoms.
Recently, an intriguing cyclodimerization of two alkynes has
been achieved in media of substitutionally labile pseudo 14 VE
4. Five-membered metallacycles in electron rich transition
metal clusters
complex of
(
g
5-Cp)RuBr(COD), cationic complexes
(
g
g
5-Cp)
5-C5
Ru(CH3CN)2L+ (L: Brꢀ: CO, PR3, SbR3, and CH3CN) and Ru(
H4CH2CH2-k1-PPh2). These compounds display diversified variety
of rearrangements within and between alkynes and transition
metal center as an intermediate of ruthena-cyclopentatriene 51
featured as a bis(carbene) functionality, as shown in Scheme 16
[24].
4.1. Cyclometallation through dimerization of alkynes and 1,3-diyne
The first ferracyclopentadiene 45 [23] was prepared by reacting
a dinuclear dicarbene complex 44 with 1,4-diphenyl-1,3-butadiyne
in refluxing hexane, as shown in Scheme 14. 45 is formed by CAC
bond coupling of the ynamine and 1,3-diyne. The crystal structure
of 45 shows that metallacycle is not in planar, but folded around an
axis through C1 and C3, with Fe1 located 0.368 Å above butadiene
plane, while Fe1(CO)3-moiety is linked to Fe2(CO)3-group
{2.4997(9) Å}. X-ray crystal structure of another product 47 reveals
that the bond lengths of Fe1AFe2 2.548(1) Å and Fe1AC1
1.980(7) Å are close to those of the carbene bond of 44, indicating
that 1,3-diyne in 47 may be inserted into one FeAC bond of the
bridging carbene.
While, for cationic compound [(g
5-Cp)Ru(CH3CN)2(PR3)]+ 53,
CAC bond coupling of terminal alkynes first takes place selectively
in the head-to-tail coupling rather than in the head-to-head cou-
pling, affording metallacyclopentatriene 54, which undergoes a
phosphine coligand migrate from ruthenium to carbon atom, gen-
erating complex 55 with an allyl and carbene bonds, as attributed
in Scheme 17.
A six-membered diplatinacycle of alkynes has been derived by
reacting triplatinum compound [Pt3(tBuNC)6] 56 with alkynes
(R = Ph, C6H4Me-4, or C6F4OMe-4; R1 = CO2Me, R2 = Me) in toluene
at 373 K [25]. Platinacyclopenta-2,4-diene, [PtC4R4](tBuNC)2] 57
(R = C6H5, C6H4Me-4), and 1,4-diplatinacyclohexa-2,5-diene,
C1AN bond length 1.328(9) Å in 47 is significantly shorter than
in 45, and close to carbon–nitrogen double bond. The Fe1C4-ring is
not planar and has a half-chair conformation with C1 atom 0.465 Å
Scheme 17.
Scheme 18.

S. Yamazaki / Inorganica Chimica Acta 366 (2011) 1–18
11
Scheme 19.
Scheme 20.
[Pt2(R1C„CR2)2(tBuNC)4] (58 with R1@R2@CO2Me; 59 with
R1 = Me, R2 = CO2Me), was proposed by elemental analyses, IR,
and NMR spectroscopies (Scheme 18).
in refluxing hexane in 40% yield, with the other product of four-
Ru butterfly cluster 63 in 40% yield (Scheme 20) [27]. While,
reaction of Ru4(l3-PPh)(CO)12 with three times molar quantity
For the metallacyclic ring with MC4-unit, an unusual metal
atom exchange reaction has recently been observed [26]. The cob-
altacycle in CpCo(R1C@CR2ACR3@CR4)(PPh3) 60, on reaction with
Fe2(CO)9, is cleaved and extraordinarily displaced by a newly
formed ferracyclic compound 61, as shown in Scheme 19. The ring
carbon atoms of the ferracycle are bound to cobalt atom by four
of the triyne produces 64 in a high yield, in which 4-Ru cluster
nuclei are unusually bound by trimer of the triyne. 64 consists of
an open-triangular array of Ru2, Ru3, and Ru4 metal atoms,
capped by a
tal atoms of which also cap onto a cyclobutadiene ring and ruth-
enacyclopentadiene ring by
4-bond fashions, respectively. Ru2
l
3-phosphinidene (31P NMR d 427.28), the end me-
g
CoAC
p
-bonds.
atom in the formation of metallacyclopentadiene ring is signifi-
cantly displaced out of the plane defined by the other metal
atoms.
Five-membered ruthenacyclic compound 62 was recently ob-
tained by reacting Ru3(CO)12 with bis(trimethylsilyl)-1,3-5-triyne

12
S. Yamazaki / Inorganica Chimica Acta 366 (2011) 1–18
Scheme 21.
Recently, a novel type of 1-ruthenacyclopenta-2,4-diene 66 [28]
was derived by homo-coupling of alkynyls in cis-Pt(
1-C„CPh)2
(dppe) 65, being induced by Ru3(CO)11(CH3CN) (Scheme 21).
69 with dppe was, in fact, obtained by treating 68 with Ru3
(CO)9(PPh3)3. 69 with P = PPh3, on reaction with Fe(CO)5, affords
heterobimetallic compound 71 quantitatively, indicating that an
g
RuCp-ring in 66 is in 1-metallacyclopenta-2,4-diene, whose ring
incorporation of Fe(CO)4-group may first occurs at MAC1
p-bond
carbon atoms of 1,3-diyne cross-link to Pt-Ru3-nuclei by (
l
4–4
r
:
in 69. It should be noticed that 1,3-diyne in 69 remains intact as
a dangling triple bond [15e] which indicates an active site for the
metal attachment. The reaction of 69 (P = PPh3) with metal-car-
bonyls, Fe(CO)5 and Ru3(CO)12 gave a heteronuclear triangular
cluster 72 in considerable yields [14f]. 69, on the other hand, reacts
2p)-bond. The head-to-head CAC bond coupling reaction of the
alkynyls also gave a diastereomer 67 with a bridging dppe. In
both of 66 and 67, the metal atom Ru3 is occupied at the apex of
pentagonal pyramid and bound to carbon atoms of the RuC4 ring
by 4
p-bonds, resulting in an elongation of bond lengths C1AC3
with (
the formation of a butterfly cluster, (
2-C4Ph2) 73 in 26% yield [14f]. Interestingly, 1,3-diyne of both
g
5-Cp)2Fe2(CO)6 to undergo 1,3-diyne transfer resulting in
5-Cp)4Fe4(
3–CO)(l4
and C2AC4 from the pure carbon–carbon double bond.
g
l
– : :
g1 g1
An analogous head-to-head coupling of alkynyls in cis-
Pt(C„CPh)2(dppe) was also induced by Mn2(CO)9(CH3CN), and
the reaction afforded an unprecedented 1-manganacyclo-3-pen-
tyne compound 68 in 38% yield (Scheme 22), in which two manga-
g2
:g
72 and 73 still remains intact as the dangling triple bond. The
structure of 73 consists of an iron four butterfly structure overbrid-
ged by 1,3-diyne, as shown in Scheme 23. Carbon atoms in one
alkyne group of 1,3-diyne bond to the wing-tip iron atom by
nese atoms with four MnAC
r-bonds are equivalently arranged
through a plane of C1, C2, C3, and C4 atoms [14a]. The ring carbon
atoms may bond to platinum and two Mn atoms by totally 6 MAC
(
g
2:2
p
)-bonds, and also to the hinge iron atoms by (
The dihedral angle of the two Fe3-triangles is 108.65(4)°, which is
almost intermediate between 119° of [( 2-H)Fe4(CO)12(COCH3)]
and 104° of anionic [(
2-H)CFe4(CO)12]ꢀ, both being shown by a
large flap motion of the Fe4-butterfly [14h]. Interestingly, 73 can-
g r)-bonds.
1:2
p-bonds, which may enforce a large elongation of bond length
l
C1AC2 1.45(3) Å longer than 1.398(18)–1.440(20) Å of the CAC
double bond and unusually close to the corresponding single bond
1.450(20)–1.465(18) Å of PtRu3(C4Ph2)(CO)10(dppe) (Scheme 22).
The ring structure of 70 may, therefore, be viewed largely
contributed of 1-metallacyclopenta-2,3,4-triene structure. 70 has
been asserted to proceed via a preliminal intermediate of a 16
electron species 69 given by a reductive elimination of acetylides
in 68.
l
not be obtained by reacting (
1,3-butadiyne.
g
5-Cp)Fe2(CO)4 with 1,4-diphenyl-
By reacting Ru3(CO)12 with 4-methylpent-2-yne in refluxing
heptane for 30 min, the tail-to-tail coupling of alkyne and dehydro-
genation processes forms an open cluster of 1,3-diyne having a
ruthenacyclopentadiene 74 in 20% yield [29a] (Fig. 7).

S. Yamazaki / Inorganica Chimica Acta 366 (2011) 1–18
13
Scheme 22.
Scheme 23.
4.2. Metallacycle through alkyne trimerization
an alkyne donor reagent to ruthenium clusters, Ru3(CO)12 or
t
t
Ru3H(CO)9(C2 Bt). Reaction of Ru3(CO)12 or Ru3H(CO)9(C2 Bu) with
t
1-Ruthenacyclopenta-2,4-diene constructed by alkyne trimer-
3,3-dimethyl-1-butyne gave Ru3(CO)8(HC2 Bu)3 75 (Fig. 8) in only
ization reaction was achieved by using (
g
5-Cp)2Ni2(HCCBut) as
1% yield [29b]. However, by using (g
5-Cp)2Ni2(HCCBut) {green

14
S. Yamazaki / Inorganica Chimica Acta 366 (2011) 1–18
Fig. 8. Crystal structure of the open cluster with a ruthenacyclopentadiene formed
by alkyne trimerization.
Fig. 7. Crystal structure of the ruthenium open cluster having a ruthenacycle of iso-
propenylbutyne dimer.
sessing Ru@Ru double bond also binds an alkyne in a lateral
bridging mode in the complex Ru2(l-CO)(l-RC2R)(g
5-C5H5)2
solution in-situ prepared by reacting
(g
5-Cp)2Ni2(CO)2 with
HCCtBu} instead of HC„CtBu, the yield of the alkyne trimerized
compound 73 was raised up to 10% when the reaction was carried
under reflux in heptane for 3 h. The crystal structure reveals that
trimerization underwent by two head-to-head and one tail-to-
head couplings of alkynes via a hydrogen shift. One ruthenium
atom in an open cluster forms 1-ruthenacyclo-2,4-pentadiene,
while the other two ruthenium atoms are bound to the ring car-
bons by totally eight. The bond distance C5AC6 1.29(2) Å is consis-
tent with the carbon–carbon double bond.
(R = Ph, CF3) 76, as shown in Scheme 24. The unsaturated com-
pound reacts slowly with alkynes, R0C„CR0 (R0 = CO2Me or CF3)
under reflux in heptane or xylen to give [Ru2(CO)(l -
-C4R2R02)(g5
C5H5)2] 77 with a metalla cyclo pentadiene in 50–90% yield. On
UV irradiation, reactions of 77 having 1,3-diyne with R = Ph and
R0 = CO2Me produce an alkyne trimerized complex 78 in 35% yield,
while an analogous thermal reaction yields 78 slowly. 78 rapidly
converts to an alkyne tetramerized complex 79. Both crystal struc-
tures of 79 with R = CF3 and 79 with R = CF3, R0 = CO2Me are alkyne
oligomerized products with single RuARu bond. Ruthenacyclo-
pentadiene unit of 77 is puckered with fold angle 23.1°, and the
metallacycle also bond to the other ruthenium nucleus by
4.3. Cyclometallation through alkyne tetramerization
g
4-bond. While, 79 is an alkyne tetramerized product forming a
six-membered ring with a tail alkyne-group and X-ray crystal
Cyclotetramerization of alkyne was achieved at the bis(cyclo-
pentadienyl)diruthenium center [30]. The diruthenium center pos-
Scheme 24.

S. Yamazaki / Inorganica Chimica Acta 366 (2011) 1–18
15
(4) using (
employing (
30% to 51%. An intermediate of (
g
g
5-Cp)Co(CO)2, was replaced by a two-step method
5-Cp)Co(C2H4)2, which raised the yield of A from
5-Cp)Co-compound was also iso-
g
lated by using the trapping reagent, 1,3-cyclohexadiene, which was
eliminated from the intermediate and affirmed as 83 (Scheme 26).
Thin needle crystal of A was analysed by synchrotron radiation X-
ray, and its crystal structure is shown in Scheme 27. The geometry
of A is unusually flat and the internal benzene ring have the signif-
icant bond alternate, which may be consistent with a more cyclo-
*
hexatriene environment. 82, a Cp analog to 81, was also isolated
and its structure is shown in Scheme 25. Bond lengths CoAC
2.042 and 2.039 Å are larger in comparison with the other alkyne–
cobalt complexes, suggesting that 82 is in a weak cobalt–alkyne
bond. On irradiation with the slide projector lamp, 81 undergoes
a reductive elimination affording a cyclobutadiene complex 84
(Scheme 26).
Fig. 9. Crystal structure of rhenacyclopentadiene formed by alkyne tetramerization.
An anomalous iridapentalene 86 was obtained quantitatively by
reacting iridacyclopentadiene-carbene complex 85 with propiolic
acid at 323 K in CDCl3, as shown in Scheme 28. The crystal struc-
ture shows that a C2H2 fragment from propiolic acid, accompany-
ing a loss of 2(CO), newly incorporated into the original iridium
complex [33]. Crystal structure of 86 also exhibits the presence
of iridium at the bridging head position of a [3.3.0] fused ring sys-
tem of metallapentalene with a pronounced distortion from the
ideal octahedral geometry about iridium: the bond angle
C1AIrAC8 166.6(9)°, C8AIrAC15 95.8(10)°, and C1AIrAC15
97.4(10)°. In both metallacyclic rings, the bond angle CAIrAC is
ca. 83°. The bond distances C2AO1 1.520(33) Å and C1AO1
1.157(31) Å indicate the presence of methylated acyl oxygen. The
bond distance IrAC1 2.019(25) Å is not unreasonable with a reso-
nate structure 86B, but the chemical shift arising from C1 was ob-
served at d 230, which is typical of an acyl carbon than a carbene
carbon. 86 was deprotonated by methylamine to afford a neutral
metallabicycloctatrienone complex 87 (Scheme 29). 87 is in more
structure reveals that the ring carbon atoms bond to ruthenium
nuclei by
ment forms
g g
3- and 2-bond, respectively, while the tail alkyne frag-
r
-bond to Ru1 and g
2-bond to Ru2.
Reaction of (CO)5Re(C„CPh) with ethynylbenzene in refluxing
toluene undergoes an unusual CAC bond coupling of the alkynyls
to afford
a binuclear compound of an alkynyl-tetramer Re2
(CO)7(C2Ph)4 80 with ReARe bond (bond length ReARe 2.895 Å)
[31]. Its crystal structure (Fig. 9) reveals 1-metallacyclopenta-2,4-
diene framework as found for Ru2{C12(SiMe3)4}(CO)6 62
(Scheme 20) and PtRu3(C4Ph2)(CO)10(dppe) 66 (Scheme 21).
5. Phenylene and metallapentalene complexes formed by C–C
bond coupling of alkynyls
Recently explored angular phenylene compound of cobaltacene
was synthesized in nine steps from 1-bromo-2-iodo benzene
(Scheme 25) [32]. The final step of cyclotrimerization of triyne
Scheme 25.

16
S. Yamazaki / Inorganica Chimica Acta 366 (2011) 1–18
Scheme 26.
distorted octahedral geometry with an angle C1–Ir–C8 154.6° than
86. The C4–O2 distance 1.206(17) Å is shortened in 87, and methyl
carboxylate group bonded to C6 has rotated out of plane of the
metallacycle, indicating that the proton which bridged to O2
and O3 is no longer present. For both 86 and 87, the metallacycle
ring through Ir, C5, C6, C7, and C8 atoms is folded through an
axis C5, C8.
Most recently, by a reaction of Pt(C„CTp)2(dppe), with Ru3
(CO)11(CH3CN) under reflux in toluene for 45 min, an unprece-
dented 1,4-heterodimetalla[5,6-b] thieno pentalene complex of
Ru3–Pt system, PtRu3(C4Tp2)2(CO)8(dppe) 88, was isolated in 54%
Scheme 27.
Scheme 28.

S. Yamazaki / Inorganica Chimica Acta 366 (2011) 1–18
17
Scheme 29.
Fig. 10. Structure framework of heterodimetallapentalene derived by CAC bond coupling of alkynyls having thiophene substituents.
(e) R. D’Amato, I. Fratoddi, A. Cappotto, P. Altamura, M. Delfini, C. Bianchetti, A.
Bolasco, G. Polzonetti, M.L. Russo, Organomtallics 23 (2004) 2860;
(f) T. Takahashi, M. Ishikawa, S. Huo, J. Am. Chem. Soc. 124 (2002) 388.
[2] (a) M.I. Bruce, N.N. Zaitseva, B.W. Skelton, A.H. White, Inorg. Chim. Acta 250
(1996) 129;
yield [15a]. Its crystal structure (Fig. 10) shows that a dimerization
of alkynyls simultaneously accompanies a hydrogen shift, resulting
in a formation of PtC4 and RuC4 rings, both with 1-metallacyclo-
2,4-pentadiene structure. The Ru3(l-CO)2(CO)6 moiety conforms
to an open cluster, and its centralruthenium atom forms a RuCp
(b) L. Liu, K. Chang, Y. Wen, J. Chin. Chem. Soc. 250 (1996) 33;
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(1998) 9135.
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