η3-Edge-bridging versus η3-face-capping coordination of a conjugated ynenyl ligand on a triruthenium cluster core

Article abstract of DOI:10.1021/om049524o

The reaction of the cluster complex [Ru₃(μ-H) (μ₃-η²-apyr)(CO)₉] (1; Hapyr = 2-aminopyrimidine) with 1,6-diphenoxy-2,4-hexadiyne in refluxing THF gives the trinuclear derivative [Ru₃(μ₃-η²-apyr) (μ-η³-PhOCH₂CH=CC≡CCH₂OPh)(μ- CO)₂(CO)₆] (2), which contains an edgebridging ynenyl ligand. Heating 2 in refluxing toluene leads to an equilibrium mixture of compounds 2 and [Ru₃(μ₃η²-apyr) (μ₃-η³-PhOCH₂CH=CC≡CCH ₂OPh)(CO)₈] (3), in which the ynenyl ligand is in a face-capping position. A mechanistic proposal that accounts for the interconversion of 2 and 3 has been obtained from DFT calculations, which have also revealed that isomer 2 is slightly more stable than 3 (3.5 kcal/mol). The bonding of the ynenyl ligands of 2 and 3 to their corresponding triruthenium frameworks has been studied by MO calculations.

Full text of DOI:10.1021/om049524o

Organometallics 2004, 23, 5849-5855
5849
η3-Edge-Bridging versus η3-Face-Capping Coordination
of a Conjugated Ynenyl Ligand on a Triruthenium
Cluster Core
Javier A. Cabeza,*,† Ignacio del R´ıo,† Santiago Garc´ıa-Granda,‡ Marta Moreno,†
Enrique Pe´rez-Carren˜o,‡ and Marta Sua´rez†
Departamento de Quı´mica Orga´nica e Inorga´nica, Instituto de Qu´ımica Organometa´lica
“Enrique Moles”, Universidad de Oviedo-CSIC, E-33071 Oviedo, Spain, and Departamento de
Quı´mica Fı´sica y Analı´tica, Universidad de Oviedo, E-33071 Oviedo, Spain
Received June 30, 2004
The reaction of the cluster complex [Ru3(µ-Η)(µ3-η2-apyr)(CO)9] (1; Hapyr ) 2-aminopy-
rimidine) with 1,6-diphenoxy-2,4-hexadiyne in refluxing THF gives the trinuclear derivative
[Ru3(µ3-η2-apyr)(µ-η3-PhOCH2CHdCCtCCH2OPh)(µ-CO)2(CO)6] (2), which contains an edge-
bridging ynenyl ligand. Heating 2 in refluxing toluene leads to an equilibrium mixture of
compounds 2 and [Ru3(µ3-η2-apyr)(µ3-η3-PhOCH2CHdCCtCCH2OPh)(CO)8] (3), in which the
ynenyl ligand is in a face-capping position. A mechanistic proposal that accounts for the
interconversion of 2 and 3 has been obtained from DFT calculations, which have also revealed
that isomer 2 is slightly more stable than 3 (3.5 kcal/mol). The bonding of the ynenyl ligands
of 2 and 3 to their corresponding triruthenium frameworks has been studied by MO
calculations.
Introduction
Previous studies have shown that amidopyridine-
bridged hydridotriruthenium carbonyl complexes11,12 are
ideal candidates for the activation of alkynes, rendering
alkenyl derivatives of the type [Ru3(µ3-η2-apy)(µ-η2-
alkenyl)(µ-CO)2(CO)6] (apy ) 2-amidopyridine-type
ligand).12,13 The face-capping apy ligands help maintain
the cluster integrity while still providing reaction
pathways of low activation energy.14
Diynes have attracted the attention of organometallic
cluster chemists1-9 because they are more reactive and
generally lead to a richer, though more complicated,
derivative chemistry than monoalkynes.10
* To whom correspondence should be addressed. E-mail: jac@fq.
uniovi.es. Fax: +34-985103446.
† Departamento de Qu´ımica Orga´nica e Inorga´nica.
‡ Departamento de Qu´ımica F´ısica y Anal´ıtica.
The natural evolution of these investigations led us
to study the reactivity of apy-bridged hydridotriruthe-
nium complexes with diynes. In this field, we have
already reported that the complex [Ru3(µ-Η)(µ3-η2-
ampy)(CO)9] (Hampy ) 2-amino-6-methylpyridine) re-
acts with diphenylbutadiyne,9 1,6-diphenoxy-2,4-hexa-
diyne,9 and 2,4-hexadiyne15 to give edge-bridging ynenyl
(1) (a) Corrigan, J. F.; Doherty, S.; Taylor, N. J.; Carty, A. J.
Organometallics 1992, 11, 3160. (b) Corrigan, J. F.; Doherty, S.; Taylor,
N. J.; Carty, A. J. J. Chem. Soc., Chem. Commun. 1991, 1511. (c)
Corrigan, J. F.; Doherty, S.; Taylor, N. J.; Carty, A. J. Organometallics
1993, 12, 1365.
(2) (a)Adams, R. D.; Qu, B. Organometallics 2000, 19, 2411. (b)
Adams, R. D.; Qu, B. Organometallics 2000, 19, 4090. (c) Adams, R.
D.; Qu, B. J. Organomet. Chem. 2001, 619, 271. (d) Adams, R. D.; Qu,
B. J. Organomet. Chem. 2001, 620, 303.
(3) (a) Bruce, M. I.; Low, P. J.; Werth, A.; Skelton, B. W.; White, A.
H. J. Chem. Soc., Dalton Trans. 1996, 1551. (b) Bruce, M. I.; Zaitseva,
N. N.; Skelton, B. W.; White, A. H. Inorg. Chim. Acta 1996, 250, 129.
(c) Bruce, M. I.; Zaitseva, N. N.; Skelton, B. W.; White, A. H. J.
Organomet. Chem. 1997, 536-537, 93. (d) Adams, C. J.; Bruce, M. I.;
Skelton, B. W.; White, A. H. J. Organomet. Chem. 1999, 589, 213. (e)
Bruce, M. I.; Zaitseva, N. N.; Skelton, B. W.; White, A. H. Russ. Chem.
Bull. 1998, 47, 983. (f) Bruce, M. I.; Zaitseva, N. N.; Skelton, B. W.;
White, A. H. Aust. J. Chem. 1998, 51, 165. (g) Bruce, M. I.; Skelton,
B. W.; White, A. H.; Zaitseva, N. N. J. Organomet. Chem. 1998, 558,
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Inorg. Chem. Commun. 1998, 1, 134. (i) Adams, C. J.; Bruce, M. I.;
Skelton, B. W.; White, A. H. J. Chem. Soc., Dalton Trans. 1999, 1283.
(j) Bruce, M. I.; Zaitseva, N. N.; Skelton, B. W.; White, A. H. Dalton
2002, 1678. (k) Bruce, M. I.; Skelton, B. W.; White, A. H.; Zaitseva, N.
N. J. Organomet. Chem. 2002, 650, 188.
(7) Unpublished results cited in: (a) Lavigne, G.; Bonneval, B. In
Catalysis by Di- and Polynuclear Metal Cluster Complexes; Adams, R.
D., Cotton. F. A., Eds.; Wiley-VCH: New York, 1998; p 39. (b) Lavigne,
G. Eur. J. Inorg. Chem. 1999, 917. (c) Nombel, P. Ph.D. Thesis,
Universite´ Paul Sabatier, Toulouse, France, 1996.
(8) Cabeza, J. A.; Moreno, M.; Riera, V.; Rosales, M. J. Inorg. Chem.
Commun. 2001, 4, 57.
(9) Cabeza, J. A.; del R´ıo, I.; Garc´ıa-Granda, S.; Lavigne, G.; Lugan,
N.; Moreno, M.; Nombel, P.; Pe´rez-Priede, M.; Riera, V.; Rodr´ıguez,
A.; Sua´rez, M.; van der Maelen, J. F. Chem. Eur. J. 2001, 7, 2370.
(10) For a recent review on the reactivity of conjugated diynes with
metal complexes, see: Low, P. J.; Bruce, M. I. Adv. Organomet. Chem.
2002, 48, 72.
(11) (a) Cabeza, J. A.; Oro, L. A.; Tiripicchio, A.; Tiripicchio-
Camellini, M. J. Chem. Soc., Dalton Trans. 1988, 1437. (b) Andreu, P.
L.; Cabeza, J. A.; Riera, V.; Jeannin, Y.; Miguel, D. J. Chem. Soc.,
Dalton Trans. 1990, 2201. (c) Lugan, N.; Laurent, F.; Lavigne, G.;
Newcomb, T. P.; Liimata, E. W.; Bonnet, J. J. Organometallics 1992,
11, 1351.
(12) Lugan, N.; Laurent, F.; Lavigne, G.; Newcomb, T. P.; Liimata,
E. W.; Bonnet, J. J. J. Am. Chem. Soc. 1990, 112, 8607.
(13) (a) Cabeza, J. A.; Ferna´ndez-Colinas, J. M.; Llamazares, A.;
Riera, V. J. Mol. Catal. 1992, 71, L7. (b) Cabeza, J. A.; Ferna´ndez-
Colinas, J. M.; Llamazares, A.; Riera, V.; Garc´ıa-Granda, S.; van der
Maelen, J. F. Organometallics 1994, 13, 4352 and references therein.
(14) Shen, J. K.; Basolo, F.; Nombel, P.; Lugan, N.; Lavigne, G. Inorg.
Chem. 1996, 35, 755.
(4) (a) Clarke, L. P.; Davies, J. E.; Raithby, P. R.; Rennie, M. A.;
Shields, G. P.; Sparr, E. J. Organomet. Chem. 2000, 609, 169. (b) Lau,
C. S. W.; Wong, W. T. J. Chem. Soc., Dalton Trans. 1999, 2511.
(5) (a) Tunik, S. P.; Grachova, E. V.; Denisov, V. R.; Starova, G. L.;
Nikol’skii, A. B.; Dolgushin, F. M.; Yanovsky, A. I.; Struchkov, Y. T.
J. Organomet. Chem. 1997, 536-537, 339. (b) Karpov, M. G.; Tunik,
S. P.; Denisov, V. R.; Starova, G. L.; Nikol’skii, A. B.; Dolgushin, F.
M.; Yanovsky, A. I.; Struchkov, Y. T. J. Organomet. Chem. 1995, 485,
219. (c) Tunik, S. P.; Khripun, V. D.; Balova, I. A.; Nordlander, E.;
Raithby, P. R. Organometallics 2001, 20, 3854.
(6) Cabeza, J. A.; Grepioni, F.; Moreno, M.; Riera, V. Organometallics
2000, 19, 5424.
10.1021/om049524o CCC: $27.50 © 2004 American Chemical Society
Publication on Web 10/23/2004

5850 Organometallics, Vol. 23, No. 24, 2004
Cabeza et al.
Scheme 1
Scheme 2
derivatives which are prone to react further with
alkynes and diynes to give interesting coupling prod-
ucts, such as η5-cyclopentadienyl,9 η5-ruthenacyclopen-
tadienyl,9 and diynedienyl15 derivatives. The complex
[Ru3(µ-Η)(µ3-η2-apyr)(CO)9] (1; Hapyr ) 2-aminopyri-
midine) also reacts with 2,4-hexadiyne16 and diphenylb-
utadiyne17 to give ynenyl derivatives that are capable
of incorporating two additional diyne molecules, render-
ing products that contain large unsaturated hydrocar-
bon ligands. For example, we have recently described
the formation of a highly functionalized azulene ligand
by metal cluster mediated coupling of three conjugated
diynes.17
We now report (a) that the study of the reactivity of
the 2-amidopyrimidine-bridged complex 1 with 1,6-
diphenoxy-2,4-hexadiyne has led us to observe a change
of the coordination mode of an ynenyl ligand from edge
bridging to face capping on a triruthenium cluster, (b)
that a possible mechanism for such an isomerization
process has been envisaged with the help of DFT
calculations, and (c) that for both coordination modes,
simple MO calculations have shed light on the nature
of the orbital interactions between the ynenyl ligand and
the corresponding triruthenium fragments.
been determined by X-ray diffraction methods.9 In that
article, a mechanistic proposal accounting for the for-
mation of compounds similar to 2 from hydrido tri-
nuclear clusters and conjugated diynes is also reported.9
Apart from the compounds mentioned in the Intro-
duction, only a few more ynenyl derivatives have so far
been reported as products of reactions of ruthenium
carbonyl clusters with diynes. They are the complexes
[Ru2(µ-NdCPh2)(µ-η2-CH2dCCH2CtCSiMe3)(CO)6],6[Ru3-
(µ3-η2-pyNMe)(µ-η3-PhCHdCCtCPh)(µ-CO)2(CO)6],7 and
[Ru4(µ-η2-dmpz)(µ4-η4-MeCHdCCtCMe)(µ-CO)(CO)10]
(Hdmpz ) 3,5-dimethylpyrazole),8 which arise from the
insertion of conjugated diynes into a metal-hydride
bond of trinuclear cluster precursors. An additional
ruthenium cluster complex containing an ynenyl ligand
has been reported, [Ru3{µ-NS(O)MePh}(µ3-η3-PhCHd
CCtCPh)(CO)9].18 As it contains a face-capping ynenyl
ligand, additional comments on this cluster complex are
given below.
In an attempt to shorten the reaction time for the
synthesis of compound 2, we performed the reaction of
complex 1 with 1,6-diphenoxy-2,4-hexadiyne in refluxing
toluene. This time, two reaction products were observed:
i.e., 2 and a new complex which was subsequently
identified as [Ru3(µ3-η2-apyr)(µ3-η3-PhOCH2CHdCCt
CCH2OPh)(CO)8] (3). The thermolysis of complex 2 in
refluxing toluene for 20 min also led to a ca. 50%
mixture of 2 and 3 (1H NMR integration of the crude
reaction mixture). Longer reaction times did not change
the 2:3 ratio but only increased the amount of intrac-
table decomposition products. Heating 3 in refluxing
toluene for 20 min also led to a ca. 50% mixture of 2
and 3 (1H NMR integration of the crude reaction
mixture). Therefore, both compounds interconvert into
each other under these reaction conditions to give ca.
50% of each complex in the equilibrium (Scheme 2).
The molecular structure of compound 3 was deter-
mined by X-ray diffraction methods (Figure 1). The
ruthenium atoms define an isosceles triangle with an
edge, Ru(2)-Ru(3), ca. 0.35 Å longer than the other two.
The apyr ligand caps a face of the metal triangle in the
same way as that previously found in other 2-amidopy-
ridine-capped trinuclear clusters.9,11-15 The ynenyl ligand
caps the opposite face of the metal triangle through only
three carbon atoms, C(20), C(21), and C(22), in such a
way that the alkenyl fragment is σ-bonded to Ru(1)
through C(22), and the CtC fragment is attached to the
three metal atoms in a perpendicular fashion:19 i.e., the
C(20)-C(21) vector is perpendicular to the Ru(2)-Ru-
(3) vector. The carbon-carbon double bond of the
alkenyl fragment, C(22)-C(23), is not coordinated. All
Results and Discussion
Synthesis and Structural Characterization of 2
and 3. The treatment of compound 1 with 1.5 equiv of
1,6-diphenoxy-2,4-hexadiyne (refluxing THF, 30 min)
allowed the isolation of the trinuclear derivative [Ru3-
(µ3-η2-apyr)(µ-η3-PhOCH2CHdCCtCCH2OPh)(µ-CO)2-
(CO)6] (2) in 72% yield (Scheme 1).
Compound 2 was characterized by analytical and
spectroscopic techniques. Its trinuclear nature was
indicated by its microanalysis and mass spectrum,
which shows the molecular ion. Its IR spectrum shows
1
the presence of two bridging CO ligands. The H NMR
spectrum also confirms the transfer of a hydrogen atom
(the hydride ligand of 1) to the original diyne to give an
ynenyl ligand. The multiplicity of the signal of this
hydrogen atom (triplet, J ) 6.7 Hz) indicates that it is
adjacent to a methylene group. The structure depicted
for compound 2 in Scheme 1, which shows an edge-
bridging three-electron-donor 1,6-diphenoxyhex-2-yn-4-
en-4-yl ligand, is also supported by the similarity of its
spectroscopic data with those reported for the com-
pounds [Ru3(µ3-η2-ampy)(µ-η3-RCHdCCtCR)(µ-CO)2-
(CO)6] (R ) Ph, CH2OPh), the structures of which have
(15) Cabeza, J. A.; del R´ıo, I.; Garc´ıa-Granda, S.; Moreno, M.; Riera,
V. Organometallics 2001, 20, 4993.
(16) Cabeza, J. A.; del R´ıo, I.; Moreno, M.; Garc´ıa-Granda, S.; Pe´rez-
Priede, M.; Riera, V. Eur. J. Inorg. Chem. 2002, 3204.
(17) Cabeza, J. A.; del R´ıo, I.; Garc´ıa-Granda, S.; Mart´ınez-Me´ndez,
L.; Moreno, M.; Riera, V. Organometallics 2003, 22, 1164.
(18) Ferrand, V.; Gambs, C.; Derrien, N.; Bolm, C.; Stoeckli-Evans,
H.; Su¨ss-Fink, G. J. Organomet. Chem. 1997, 549, 275.

Coordination of a Conjugated Ynenyl Ligand
Organometallics, Vol. 23, No. 24, 2004 5851
Figure 2. Energy profile for the interconversion of 2′ and
3′.
have been recently reported. In these cases, the butyne-
nyl ligands are derived from bis(ferrocenyl)butadiyne.2b
Mechanism of Interconversion of Complexes 2
and 3. As noted above, complexes 2 and 3 interconvert
in toluene at reflux temperature. Since the intercon-
version of edge-bridging and face-capping ynenyl ligands
on a trimetal core had no precedents, we decided to
undertake a theoretical mechanistic study of this pro-
cess by DFT calculations.
To simplify the calculations without losing chemical
information, compounds 2 and 3 were modeled by
changing their 1,6-diphenoxyhex-2-yn-4-en-4-yl ligand
to a pent-2-yn-4-en-4-yl ligand. Hereafter, these model
compounds will be named 2′ and 3′.
Figure 1. Molecular structure of compound 3. Selected
interatomic distances (Å): Ru(1)-Ru(2) ) 2.848(2), Ru(1)-
Ru(3) ) 2.881(2), Ru(2)-Ru(3) ) 3.218(2), Ru(1)-N(3) )
2.221(3), Ru(1)-C(21) ) 2.171(4), Ru(1)-C(22) ) 2.033(4),
Ru(2)-N(1) ) 2.180(3), Ru(2)-C(20) ) 2.179(3), Ru(2)-
C(21) ) 2.283(4), Ru(3)-N(1) ) 2.177(3), Ru(3)-C(20) )
2.207(3), Ru(3)-C(21) ) 2.242(4), C(19)-C(20) ) 1.480(5),
C(20)-C(21) ) 1.350(5), C(21)-C(22) ) 1.416(5), C(22)-
C(23) ) 1.325(5), C(23)-C(24) ) 1.496(7). Selected inter-
atomic angles (deg): C(19)-C(20)-C(21) ) 129.2(3), C(20)-
C(21)-C(22) ) 158.2(3), C(21)-C(22)-C(23) ) 135.6(4),
C(22)-C(23)-C(24) ) 121.9(4).
We first optimized the structures of the model com-
plexes 2′ and 3′. The input data were based on the X-ray
structural data of the complexes [Ru3(µ3-η2-ampy)(µ-η3-
PhCHdCCtCPh)(µ-CO)2(CO)6]9 and 3, which were
conveniently modified by replacing some atoms in order
to transform them into 2′ and 3′, respectively. The
calculated structures of 2′ and 3′ are in reasonable
agreement with the experimental X-ray structures of
[Ru3(µ3-η2-ampy)(µ-η3-PhCHdCCtCPh)(µ-CO)2(CO)6]9
and 3, the greatest divergences corresponding to the
Ru-Ru distances, which are 0.06-0.10 Å longer in the
model compounds than in the real complexes. The
overestimation of the optimized Ru-Ru distances is
expected at the GGA level. As far as energy is concerned,
the models 2′ and 3′ differ by only 3.5 kcal/mol, the
former being more stable. This explains why, once the
interconversion equilibrium was reached, 2 and 3 were
obtained as ca. 50% mixtures.
The search for transition states and intermediate
species on the potential energy surface was very tedious
and time-consuming. This was due to the large number
of atoms involved (including three transition-metal
atoms) and the complicated nature of the resulting
mechanism, for which seven transition states (hereafter
labeled as TS1-TS7) and six intermediate species
(hereafter labeled as I1-I6) were found to connect 2′
and 3′ (Figures 2 and 3, Table 1).
six carbon atoms of the hexynenyl moiety and the atoms
of the apyr ligand are coplanar, and this plane is
perpendicular to the metal triangle. The cluster shell
is completed with eight terminal carbonyl ligands.
Therefore, the cluster can be considered as a 50-electron
species with only two Ru-Ru bonds, the ynenyl ligand
behaving as a 5-electron donor.
The 1H NMR spectrum of 3 shows that both H atoms
of each methylene group are equivalent. Therefore, in
solution, the complex displays Cs symmetry, probably
due to free rotation about the C(23)-C(24) and C(19)-
C(20) single bonds. Accordingly, the alkenyl proton is
observed as a triplet, due to coupling with the protons
of the adjacent methylene group.
As noted above, the complex [Ru3{µ-NS(O)MePh}(µ3-
η3-PhCHdCCtCPh)(CO)9] is, to our knowledge, the
only precedent in ruthenium chemistry of a cluster
complex containing an ynenyl ligand coordinated in a
way similar to that found in 3. Curiously, the butynenyl
ligand of [Ru3{µ-NS(O)MePh}(µ3-η3-PhCHdCCtCPh)-
(CO)9] does not arise from a diyne but from an alkynyl-
vinylidene coupling and the N-donor sulfoximido ligand
is not face capping but edge bridging.18 In the related
complex [Ru3{µ3-NS(O)MePh}(µ3-η3-PhCHdCdCdCPh)-
(µ-CO)(CO)7], the bridging hydrocarbyl ligand is best
described as a buta-1,2,3-trien-1-yl fragment, rather
than as a but-1-yn-3-en-4-yl fragment.18 A few trios-
mium carbonyl clusters containing butynenyl ligands
that asymmetrically cap a face of the metal triangle
Transition state TS1 is 28.3 kcal/mol less stable than
2′ and 9.0 kcal/mol less stable than I1. In the transfor-
mation of 2′ into I1, the lengthening of the Ru(1)-Ru-
(3) distance (from 3.031 Å in 2′ to 3.777 Å in TS1 and
4.529 Å in I1) is accompanied by the conversion of the
two bridging CO ligands into terminal ones, the folding
of the ynenyl fragment (from 179.0° in 2′ to 144.0° in
I1), and its slippage from its initial situation to a new
one that involves the lengthening of the C(21)-Ru(1)
(19) Complexes containing alkyne ligands coordinated to three
ruthenium atoms in a perpendicular fashion are scarce. See, for
example: (a) Ferrand, V.; Merzweiler, K.; Rheinwald, G.; Stoeckli-
Evans, H.; Su¨ss-Fink, G. J. Organomet. Chem. 1997, 549, 263. (b)
Rivomanana, S.; Lavigne, G.; Lugan, N.; Bonnet, J. J. Inorg. Chem.
1991, 30, 4110. (c) Rivomanana, S.; Mongin, C.; Lavigne, G. Organo-
metallics 1996, 15, 1195.

5852 Organometallics, Vol. 23, No. 24, 2004
Cabeza et al.
Figure 3. DFT-calculated structures of the intermediates (I) and transition states (TS) involved in the interconversion
of 2′ and 3′. In all structures, the apyr ligand is behind the metallic triangle.
Table 1. Structural Parameters for the Intermediates (I) and Transition States (TS) Involved in the
Interconversion of Compounds 2′ and 3′
2′
TS1
I1
TS2
I2
TS3
I3
TS4
I4
TS5
I5
TS6
I6
TS7
3′
Relative Energy (kcal/mol)
28.28 19.26 24.47 18.23 39.02 18.82 23.76 18.28 26.61 15.46 25.46 15.47
Distances (Å)
0.00
16.95
3.49
Ru(1)-Ru(2)
Ru(1)-Ru(3)
Ru(2)-Ru(3)
C(20)-Ru(2)
C(20)-Ru(3)
C(21)-Ru(3)
C(21)-Ru(2)
C(21)-Ru(1)
C(22)-Ru(1)
N(3)-Ru(1)
N(1)-Ru(2)
N(1)-Ru(3)
2.849 2.898 2.721 2.772 2.784 2.780 2.941 2.854 2.837 2.880 2.857 2.934 2.842
3.031 3.777 4.529 4.639 4.585 4.594 4.795 4.647 4.376 4.273 3.992 4.080 4.121
2.753 2.762 2.731 2.781 2.745 2.657 2.794 2.834 3.112 2.883 3.161 3.149 3.307
4.593 4.510 3.547 3.008 2.835 3.131 2.363 2.330 2.265 2.081 2.093 2.331 2.274
2.184 2.323 2.141 2.036 2.074 2.271 2.382 2.369 2.200 2.210 2.143 2.133 2.144
2.638 2.352 2.326 2.681 3.005 3.230 3.213 2.783 2.172 2.177 2.125 2.138 2.147
4.462 3.977 2.626 2.117 2.346 3.057 2.246 2.502 2.550 2.289 2.703 2.807 2.429
2.588 2.986 2.966 2.532 2.232 2.859 2.723 2.830 2.811 2.611 2.412 2.487 2.630
2.112 2.150 2.136 2.139 2.136 2.224 2.120 2.127 2.137 2.099 2.239 2.094 2.066
2.206 2.234 2.282 2.266 2.245 2.227 2.235 2.236 2.253 2.251 2.232 2.216 2.238
2.206 2.153 2.144 2.165 2.154 2.133 2.183 2.154 2.152 2.152 2.179 2.165 2.186
2.226 2.238 2.310 2.295 2.224 2.323 2.246 2.250 2.287 2.321 2.315 2.314 2.294
2.862
3.773
3.300
2.254
2.144
2.176
2.379
2.440
2.050
2.306
2.206
2.277
2.950
2.950
3.283
2.231
2.232
2.336
2.337
2.232
2.043
2.301
2.228
2.228
Angles (deg)
C(20)-C(21)-C(22)
C(21)-C(22)-C(23)
Ru(1)-Ru(2)-Ru(3)
179.0 168.5 144.0 123.9 128.7 179.7 173.1 168.5 148.0 147.1 146.6 145.4 149.5
132.6 120.4 121.3 136.6 148.3 130.5 126.3 123.3 126.5 131.3 147.6 138.0 133.4
147.2
136.5
75.1
160.6
136.2
56.2
65.5
83.7
26.8
112.3 113.4 112.1 115.3 113.4 109.4 94.6
-17.8 -33.3 -39.4 -43.2 -71.3 -78.2 -86.4 -87.0 -82.9 -76.0 -100.7 -105.9 -111.9
95.7
82.9
84.2
83.8
C(20)-Ru(3)-Ru(2)- 27.4
Ru(1)
distance (from 2.588 Å in 2′ to 2.966 Å in I1) and the
approximation of C(21) to Ru(2) (4.462 Å in 2′ and 2.626
Å in I1).
bends toward Ru(2), allowing the coordination of C(20)
and C(21) to this metal atom (I3). One of the CO ligands
attached to Ru(3) in I2 moves from a terminal to a
bridging position between Ru(2) and Ru(3), and the
bridging CO ligand of I2 moves to a terminal position
on the Ru(1) atom of I3. The high coordinative unsat-
uration of TS3 (only two Ru-Ru bonds and only two
Ru-Cynenyl bonds) accounts for the high energy of this
transition state (39.0 kcal/mol above 2′).
From I3 to I4, the shortening of the Ru(1)-Ru(3)
distance (from 4.795 Å in I3 to 4.376 Å in I4) induces
the coordination of C(21) to Ru(3). This is accompanied
by a lengthening of the Ru(2)-Ru(3) distance to 3.112
Å and by a movement of the bridging CO ligand of I3
to a terminal position on the Ru(3) atom of I4.
From I1 to I2, the C(21) atom continues its approach
to Ru(2) (2.346 Å in I2) at the same time that it moves
away from Ru(3) (3.005 Å in I2) and again gets close to
Ru(1) (2.232 Å in I2). These movement of the ynenyl
fragment implies an important bending of the C(20)-
C(21)-C(22) angle (128.7° in I2). The three carbonyl
ligands on Ru(3) undergo a tripodal rotation that is
accompanied by a movement of a CO ligand from a
terminal position on Ru(1) to a bridging position be-
tween Ru(1) and Ru(2).
The most important structural change from I2 to I3
is that C(20), which is attached to Ru(3) in I2, spans
the Ru(2)-Ru(3) edge in I3. This situation will be
maintained all the way to 3′. To reach this situation,
the C(21) carbon atom is released from Ru(2) to give a
nearly linear ynenyl fragment (TS3) that subsequently
From I4 to I5, the Ru(1) and Ru(3) atoms get closer
(3.992 Å in I5). This provokes the approach of C(21) to
Ru(1) (2.412 Å in I5) and the lengthening of the C(21)-
Ru(2) distance (from 2.550 Å in I4 to 2.703 Å in I5).

Coordination of a Conjugated Ynenyl Ligand
Organometallics, Vol. 23, No. 24, 2004 5853
From I5 to I6, the ynenyl ligand moves toward its
final position in 3′ and the Ru(2)-Ru(3) distance
lengthens (3.307 Å in I6). This causes the lengthening
of the C(21)-Ru(1) distance (2.630 Å in I6) and the
shortening of the C(21)-Ru(2) distance (2.429 Å in I6).
A CO ligand, originally attached to Ru(1), is transferred
to Ru(2).
From I6 to 3′, the ynenyl ligand moves to its final
position and the Ru(1)-Ru(3) edge shortens to a bonding
distance (from 4.121 Å to 2.950 Å). This step has a very
low activation energy (1.5 kcal/mol) and results in a
considerable stabilization of the system, because the
coordinative unsaturation of I6 is eliminated in 3′ (the
latter is 12.02 kcal/mol more stable than I6).
The activation energy of the whole interconversion
process is associated with the energy of the least stable
transition state, TS3. The relatively high value of this
energy, 39.0 kcal/mol above 2′ and 35.5 kcal/mol above
3′, implies that the interconversion of 2′ and 3′ should
take place only at high temperatures. This matches the
experimental observation that the interconversion of 2
and 3 takes place in refluxing toluene, but it is not
observed in refluxing THF. The low energy of 2′ and 3′
(as compared with those of all intermediate species I1-
I6) and the low energy of the transition states TS1, TS2,
and TS4-TS7 (as compared with that of TS3) also
explain the fact that no intermediate species have been
observed during the interconversion of 2′ and 3′. All
these facts support the proposed mechanism. Although
an alternative mechanism involving CO dissociation and
reassociation steps (2 and 3 have the same number of
CO ligands) cannot be completely ruled out, we think
it would be less likely than the proposed mechanism,
because CO would rapidly escape from the reacting
solution at the working temperature and this would lead
to extensive decomposition.
Orbital Interactions between the Ynenyl Ligands
and the Trimetallic Fragments of 2 and 3. A simple
fragment molecular orbital (FMO) approach, at the
extended Hu¨ckel level, allowed us to identify the FMOs
that are responsible for the bonding between the ynenyl
and triruthenium fragments of 2 and 3. The character-
istics of the bonding between these fragments were
elucidated by analyzing the overlaps between their
FMOs. Again, the simplified model compounds 2′ and
3′ were used for the calculations.
For 2′, three interactions between FMOs of the ynenyl
fragment and FMOs of the trimetallic fragment account
for 91.5% of the bonding between these two fragments
(Figure 4). Many other minor interactions are respon-
sible for the remaining 8.5%. The ynenyl fragment
behaves as a σ-donor-π-acceptor ligand, the σ-donor
component being mainly due to the bonding interactions
of the filled FMO11 and FMO13 orbitals of the ynenyl
ligand (its LUMO is FMO14, not represented in Figure
4) with the empty FMO71 and FMO70 orbitals, respec-
tively, of the metallic fragment (its LUMO is FMO70).
The interaction of the HOMO of the metallic fragment
(FMO69) with the empty orbital FMO15 of the ynenyl
fragment is the major orbital interaction responsible for
the retrodonation of electron density from the metal
atoms to the ynenyl ligand (π-acception).
Figure 4. The most important overlaps between orbitals
of the ynenyl (left) and triruthenium (right) fragments of
2′. The arrows connect the overlapping filled (start) and
empty (end) orbitals. The percentages represent the con-
tribution of each overlap to the bonding between the two
fragments. For clarity, CO ligands have been omitted.
trimetallic fragments that individually account for more
than 12% of the bonding. They all represent 71.1% of
the bonding between these two fragments. As in 2′, the
ynenyl fragment of 3′ is a σ-donor-π-acceptor ligand,
the principal σ-donor contributions being the bonding
interactions of the filled FMO11 and FMO13 orbitals
of the ynenyl ligand with the empty FMO71 and FMO70
orbitals, respectively, of the metallic fragment, while the
most important π-accepting contributions are the in-
teractions of the filled metallic orbitals FMO68 and
FMO69 with the empty orbitals FMO14 and FMO15,
respectively, of the ynenyl fragment.
An analysis of the individual overlap populations
between the carbon atoms C(20), C(21), and C(22) and
the three metal atoms of 2′ indicates that, while strong
overlaps are observed between C(20) and C(22) with
Ru(3) and Ru(1), respectively, the orbitals of C(21)
overlap very little with those of Ru(1) and Ru(3). This
bonding situation is due to the fact that the interaction
of the triple bond of the ynenyl ligand with the Ru(3)
metal atom is very asymmetric. In fact, in the DFT-
optimized molecule 2′, the distances that separate C(20)
and C(21) from Ru(3) are 2.180 and 2.638 Å, respec-
tively, the latter being very similar to the separation
between C(21) and Ru(1), 2.588 Å.
For complex 3′, an analogous analysis shows that the
highest overlap population corresponds to that between
C(22) and Ru(1), followed by those of C(20) with Ru(2)
and Ru(3). The orbitals of the C(21) carbon atom clearly
overlap with those of the three metal atoms, the C(21)-
Ru(1) overlap population being slightly greater than
those of C(21)-Ru(2) and C(21)-Ru(3). This bonding
situation is that expected for a face-capping ynenyl
ligand interacting with the three metal atoms through
both carbon atoms of its CtC triple bond (in a perpen-
dicular fashion19), being additionally bonded to one
metal atom through the carbon atom of its CdC frag-
For complex 3′, Figure 5 represents the four orbital
interactions between the FMOs of the ynenyl and the

5854 Organometallics, Vol. 23, No. 24, 2004
Cabeza et al.
both the edge-bridged and face-capped ynenyl complexes
have been identified. A study of the overlaps between
these orbitals has shown that the ynenyl fragment
behaves as a σ-donor-π-acceptor ligand in both com-
plexes.
Experimental Section
General Data. Solvents were dried over sodium diphenyl
ketyl (THF, hydrocarbons) or CaH2 (dichloromethane) and
distilled under nitrogen prior to use. The reactions were
carried out under nitrogen, using Schlenk and vacuum line
techniques, and were routinely monitored by solution IR
spectroscopy (carbonyl stretching region) and spot TLC. Com-
pound 1 was prepared as described previously.16 IR spectra
were recorded in solution on a Perkin-Elmer Paragon 1000
FT spectrophotometer. NMR spectra were run at room tem-
perature on a Bruker DPX-300 instrument, using the dichlo-
romethane solvent resonance (δ 5.33) as internal standard.
Microanalyses were obtained from the University of Oviedo
Analytical Service. Positive FAB-MS measurements were
obtained from the University of Santiago de Compostela Mass
Spectrometric Service; data given refer to the most abundant
molecular ion isotopomer.
[Ru3(µ3-η2-apyr)(µ-η3-PhOCH2CHdCCtCCH2OPh)(µ-
CO)2(CO)6] (2). 1,6-Diphenoxy-2,4-hexadiyne (170 mg, 0.648
mmol) was added to a solution of compound 1 (275 mg, 0.423
mmol) in THF (20 mL). The solution was heated at reflux
temperature until the IR spectrum showed the complete
disappearance of the starting complex (ca. 30 min, IR monitor-
ing). The color changed from yellow to dark red. The solvent
was removed under reduced pressure, the residue was dis-
solved in 2 mL of dichloromethane, and the resulting solution
was placed on a column of neutral alumina (2 × 5 cm, activity
IV) packed in hexane. After the column was washed with
hexane, hexane-dichloromethane (1:1) eluted a yellow band,
which afforded compound 2 upon solvent removal (270 mg,
72%). Anal. Calcd for C30H19N3O10Ru3 (Mr ) 884.69): C, 40.72;
H, 2.16; N, 4.74. Found: C, 40.73; H, 2.07; N, 4.68. FAB MS:
m/z 886 [M+]. IR (THF): νCO 2069 (s), 2031 (vs), 2001 (s), 1977
(sh), 1878 (w), 1829 (m) cm-1. 1H NMR (CDCl3): δ 7.95 (dd, J
) 4.8, 2.6 Hz, 1 H, Hapyr), 7.81 (dd, J ) 5.7, 2.6 Hz, 1 H, Hapyr),
7.2-6.9 (m, 8 H, Ph), 6.90 (dd, J ) 6.7, 2.3 Hz, 1 H, CHH),
6.82 (d, J ) 8.6 Hz, 1 H, Ph), 6.68 (t, J ) 6.7 Hz, 1 H, dCH),
6.54 (d, J ) 8.5 Hz, 1 H, Ph), 6.35 (dd, J ) 5.7, 4.8 Hz, 1 H,
Figure 5. The most important overlaps between orbitals
of the ynenyl (left) and triruthenium (right) fragments of
3′. The arrows connect the overlapping filled (start) and
empty (end) orbitals. The percentages represent the con-
tribution of each overlap to the bonding between the two
fragments. For clarity, CO ligands have been omitted.
Hapyr), 5.80 (d, J ) 15.9 Hz, 1 H, CHH), 5.38 (d, J ) 15.9 Hz,
1 H, CHH), 4.99 (dd, J ) 6.7, 2.3 Hz, 1 H, CHH), 2.73 (s, br,
1H, NHapyr).
ment that is attached to one of the carbon atoms
involved in the CtC triple bond.
[Ru3(µ3-η2-apyr)(µ3-η3-PhOCH2CHdCCtCCH2OPh)-
(CO)8] (3). A solution of compound 2 (150 mg, 0.169 mmol) in
toluene (20 mL) was heated at reflux temperature for 20 min.
The color changed from yellow to brown. The solvent was
partially removed under reduced pressure, and the resulting
solution (ca. 1 mL) was placed on a column of neutral alumina
(2 × 8 cm, activity IV) packed in hexane. After the column
was washed with hexane, a broad yellow band was eluted with
hexane-dichloromethane (1:1). The head of this band con-
tained pure complex 3, which was isolated as a yellow solid
after solvent removal (19 mg, 13%). The remaining portion of
the band contained a mixture of compounds 2 and 3, for which
no subsequent separation was attempted. Anal. Calcd for
C30H19N3O10Ru3 (Mr ) 884.69): C, 40.72; H, 2.16; N, 4.74.
Found: C, 40.80; H, 2.23; N, 4.62. FAB MS: m/z 886 [M+]. IR
(CH2Cl2): νCO 2085 (w), 2068 (vs), 2016 (s), 1995 (sh), 1944
It is interesting to note that, for 2′, the sum of the
overlap populations found between the carbon atoms
C(20), C(21), and C(22) with the three metal atoms is
ca. 45% smaller than that found for complex 3′. This is
in reasonable agreement with the assignment of the
ynenyl ligand as a three-electron donor in complex 2′
and as a five-electron donor in complex 3′.
Concluding Remarks
The present work describes the synthesis of two
isomeric triruthenium carbonyl complexes that contain
edge-bridging (2) and face-capping (3) ynenyl ligands.
It has been shown that these two complexes interconvert
at high temperature (refluxing toluene). A plausible
mechanism for this interconversion has been elucidated
with the help of DFT calculations. The fragment mo-
lecular orbitals that are responsible for the bonding
between the ynenyl and the triruthenium fragments of
1
(m) cm-1. H NMR (CDCl3): δ 8.73 (dd, J ) 5.3, 2.3 Hz, 1 H,
H
apyr), 8.02 (dd, J ) 4.8, 2.3 Hz, 1 H, Hapyr), 7.9-6.5 (m, 12 H),
5.67 (t, J ) 6.5 Hz, 1 H, dCH), 5.21 (s, 2 H, CH2), 4.42 (d, J
) 6.5 Hz, 2 H, CH2).
X-ray Structure of 3. The crystal was selected from a batch
obtained by slow diffusion of a layer of pentane into a solution

Coordination of a Conjugated Ynenyl Ligand
Organometallics, Vol. 23, No. 24, 2004 5855
of 3 in toluene. Details of crystal and refinement data are given
in ref 20. X-ray diffraction data were collected on a Nonius
CAD-4 diffractometer, using graphite-monochromated Mo KR
radiation and the ω-2θ scan technique. An empirical absorp-
tion correction was applied using DIFABS,21 with transmission
factors in the range 0.762-0.338. The structure was solved
by Patterson interpretation using the program DIRDIF-96.22
Isotropic and full-matrix anisotropic least-squares refinements
were carried out using SHELXL-97.23 All non H-atoms were
refined anisotropically. All H atoms were located on Fourier
difference maps and were refined freely with isotropic thermal
parameters. The molecular plot was made with PLATON.24
All operations were performed within the WinGX program
system.25 The CCDC deposition number is 249358.
Computational Details. Density functional theory calcu-
lations were performed using Becke’s three-parameter hybrid
exchange-correlation functional (DFT/Hartree-Fock)26 con-
taining the nonlocal gradient correction of Lee, Yang, and Parr
(B3LYP).27 The basis set used for Ru was the LanL2DZ of Hay
and Wadt with the associated double-ú valence basis func-
tions.28 The standard 6-31G basis set, with addition of (d,p)-
polarization, was used for the remaining atoms. Transition
states were found using the QST2/QST3 method. All stationary
points were confirmed as minima or as transition states by
calculation of analytical frequencies. To verify that the transi-
tion states found were correct saddle points connecting the
proposed minima, the structure of each transition state was
first distorted forward and back along the unique imaginary
eigenvector and then it was allowed to relax to the correspond-
ing minimum (reactant or product) in subsequent structure
optimizations. All these calculations were performed using the
GAUSSIAN98 software package.29
EHMO calculations and orbital diagrams were performed
with the CACAO software package.30
Acknowledgment. This work has been supported
by the MCYT grants BQU2002-2623 (to J.A.C.) and
BQU2003-5093 to (S.G.-G.). M.M. thanks the MECD for
a predoctoral fellowship (FPI program).
Supporting Information Available: Tables giving crys-
tallographic data for 3 and atomic coordinates for the DFT-
calculated structures of 2′, 3′, and all the intermediates and
transition states involved in the interconversion of 2′ and 3′.
This material is available free of charge via the Internet at
http://pubs.acs.org.
(20) Crystal and selected refinement data for 3: C30H19N3O10Ru3;
fw ) 884.69; crystal size 0.40 × 0.33 × 0.33 mm; crystal system
triclinic; space group P1h; a ) 9.209(5) Å; b ) 11.477(7) Å; c ) 16.107(2)
Å; R ) 96.44(4)°; â ) 98.92(4)°; γ ) 99.33(7); V ) 1643(1) Å3; Z ) 2;
Fcalcd ) 1.788 g/cm3; λ ) 0.710 73 Å; µ ) 1.419 mm-1; F(000) ) 864;
index range 0 e h e 11, -14 e k e 13, -19 e l e 19; θ range 1.82-
25.97°; T ) 293(2) K; collected reflections 6838; unique reflections 6421;
Rint ) 0.0252; reflections with I < 2σ(I) 5480; variables 491; weighting
scheme w ) 1/[σ2Fo2 + (0.0453P)2 + 1.5071P], P ) (Fo2 + 2Fc2)/3; GOF
OM049524O
(28) (a) Hay, P. J.; Wadt, W. R. J. Chem. Phys. 1995, 82, 270. (b)
Wadt, W. R.; Hay, P. J. J. Chem. Phys. 1995, 82, 284. (c) Hay, P. J.;
Wadt, W. R. J. Chem. Phys. 1995, 82, 299.
) 1.063; final R12σ(I) ) 0.0292; final wR2all
difference peak and hole 0.754 and -0.783 e/Åd3a.ta
) 0.0827; largest
(29) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Zakrzewski, V. G.; Montgomery, J. A.;
Stratmann, E.; Burant, J. C.; Dapprich, S.; Millam, J. M.; Daniels, A.
D.; Kudin, K. N.; Strain, M. C.; Farkas, O.; Tomasi, J.; Barone, V.;
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S.; Ochterski, J.; Petersson, G. A.; Ayala, P. Y.; Cui, Q.; Morokuma,
K.; Malick, D. K.; Rabuk, A. D.; Raghavachari, K.; Foresman, J. B.;
Cioslowski, J.; Ortiz, J. V.; Baboul, A. G.; Stefanov, B. B.; Liu, G.;
Liashenko, A.; Piskorz, P.; Komaromi, I.; Gomperts, R.; Martin, R. L.;
Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.;
Gonza´lez, C.; Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.;
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(21) Walker, N.; Stuart, D. Acta Crystallogr. 1983, A39, 158.
(22) (a) Beurskens, P. T.; Beurskens, G.; Bosman, W. P.; de Gelder,
R.; Garc´ıa-Granda, S.; Gould, R. O.; Israe¨l, R.; Smits, J. M. M. The
DIRDIF-96 Program System; Crystallography Laboratory, University
of Nijmegen, Nijmegen, The Netherlands, 1996.
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