π-conjugated α,ω-diphenylpolyene complexes of RuClCp* fragment(s) in η4-S-cis conformation

Article abstract of DOI:10.1002/ejic.200600620

π-Conjugated polyene complexes of the general formula (RuClCp*)_n(polyene) [2: n = 1, polyene = 1,4-diphenylbuta-1,3- diene; 3: n = 1, polyene = 1,6-diphenylhexa-1,3,5-triene; 4: n = 2, polyene = 1,8-diphenylocta-1,3,5,7-tetraene; 5: n = 2, poly

Full text of DOI:10.1002/ejic.200600620

FULL PAPER
DOI: 10.1002/ejic.200600620
π-Conjugated α,ω-Diphenylpolyene Complexes of RuClCp* Fragment(s) in
η4-s-cis Conformation
Hiroki Fukumoto[a] and Kazushi Mashima*[b]
Keywords: π-Conjugated polyenes / Coordination modes / Fluxionality / Multinuclear complexes / Ruthenium
π-Conjugated polyene complexes of the general formula
(RuClCp*)n(polyene) [2: n = 1, polyene = 1,4-diphenylbuta-
1,3-diene; 3: n = 1, polyene = 1,6-diphenylhexa-1,3,5-triene;
4: n = 2, polyene = 1,8-diphenylocta-1,3,5,7-tetraene; 5: n =
2, polyene = 1,10-diphenyldeca-1,3,5,7,9-pentaene; 6: n = 3,
and chlorido ligands, were prepared by treating [Ru(µ3-Cl)-
Cp*]4 (1) with the corresponding α,ω-diphenylpolyenes. All
diene units of the complexes were fully metalated by the co-
ordination of “RuClCp*” fragments in an η4-s-cis conforma-
tion.
polyene
=
1,12-diphenyldodeca-1,3,5,7,9,11-hexaene], in
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2006)
which each ruthenium(II) atom has Cp* (Cp* = η5-C5Me5)
extension of our continuing interest in this area, we have
investigated the complexation of the “RuClCp*” fragment
with longer polyenes. Here, we report the synthesis of a
series of α,ω-diphenylpolyene complexes (polyene = di-, tri-,
tetra-, penta-, and hexaene) bearing RuClCp* fragments
and their structural features.
Introduction
One-dimensional π-conjugated polyenes are excellent
supporting ligands to which plural transition metals can co-
ordinate, and their metal complexes are expected to show
unique properties on the basis of an extended pπ–dπ conju-
gated organometallic system.[1] Their physical properties are
thus controlled by not only the number of transition metals
bound to the polyene ligand but also their coordination fea-
tures such as nuclearity (mono-,[2,3] di-,[4] or polynuclear[5]),
stereochemistry (syn and anti for polynuclear complexes),
and fluxionality[6,7] (metal migration on a polyene). More-
over, ancillary ligands on a metal center also play an impor-
tant role in controlling the structure and properties of π-
conjugated polyene complexes. We have recently reported
the systematic preparation of α,ω-diphenylpolyene com-
plexes bearing Ru(acac)2 (acac = acetylacetonato) frag-
ments, which coordinate to all diene units of the polyene in
an η4-s-trans fashion,[8a] resulting in the full metalation of
all diene units of the polyenes. In contrast, ruthenium frag-
ments with Cp* (Cp* = C5Me5) and chlorido ligands prefer
to coordinate to a diene moiety of diene and tetraene in
an η4-s-cis fashion revealed by our previous work.[8b] The
selectivity of coordination mode originating from the differ-
ence of ancillary ligands on a ruthenium center has at-
tracted interest. Furthermore, “RuClCp*” fragments as
well as “Ru(acac)2”[8a] and “Fe(CO)3”[7] fragments are also
expected to move on a π-conjugated polyene with an odd
number of olefinic parts such as triene and pentaene. As an
Results and Discussion
The reaction of α,ω-diphenylpolyenes with [Ru(µ3-Cl)-
Cp*]4 (1)[2g] in THF or dichloromethane at room tempera-
ture gave the corresponding chlorido(η5-pentamethylcyclo-
pentadienyl)ruthenium(II) complexes of the general for-
mula (RuClCp*)n(polyene) [2: n = 1, polyene = 1,4-di-
phenylbuta-1,3-diene; 3: n = 1, polyene = 1,6-diphenylhexa-
1,3,5-triene; 4: n = 2, polyene = 1,8-diphenylocta-1,3,5,7-
tetraene; 5: n = 2, polyene = 1,10-diphenyldeca-1,3,5,7,9-
pentaene; 6: n = 3, polyene = 1,12-diphenyldodeca-
1,3,5,7,9,11-hexaene] in modest yields [Equation (1)].
Among them, the diene and tetraene complexes 2 and 4
had previously been prepared and characterized.[8b] Both
complexes are stable to air and moisture in the solid state,
but are not stable in solution. Complexes 3, 5, and 6 are
soluble in dichloromethane and chloroform, and are
slightly soluble in THF. The treatment of 1 with longer
polyenes such as 1,14-diphenyltetradeca-1,3,5,7,9,11,13-
heptaene and 1,16-diphenylhexadeca-1,3,5,7,9,11,13,15-oc-
taene did not yield any products because of the low solubil-
ity of heptaene and octaene ligands in any common organic
solvent.
[a] Chemical Resources Laboratory, Tokyo Institute of Technology,
4259, Nagatsuta, Midori-ku, Yokohama 226-8503, Japan
[b] Department of Chemistry, Graduate School of Engineering Sci-
ence, Osaka University,
In the obtained complexes, RuClCp* fragments coordi-
nated in an η4-s-cis fashion to all diene units of the poly-
enes. The 1H NMR spectra of all complexes (except 2)
showed signals of the outer protons of coordinated diene
Toyonaka, Osaka 560-8531, Japan
Fax: +81-6-6850-6296
E-mail: mashima@chem.es.osaka-u.ac.jp
5006
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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π-Conjugated Polyene Complexes of RuClCp* Fragment(s) in η4-s-cis Conformation
FULL PAPER
have almost the same absorption maxima because their π-
conjugation systems are separated into individual diene
units due to the structural deformation of ruthenium-coor-
dinated diene units. These UV/Vis data also suggest that
ancillary ligands (Cp* or acac) on a ruthenium center can
control not only their structural shape, such as the metal
coordination mode (s-cis or s-trans for diene complexation),
but also the planarity of the polyene backbone.
(1)
units in the range of δ = 2.5–4.0 ppm. Siganls of the inner
protons of the s-cis diene moieties are observed at δ ≈
5 ppm, with a smaller coupling constant (3J = 5.9 Hz),[2] in
sharp contrast to those (3J = 7–8 Hz) observed for η4-s-
trans-diene[3] complexes of Ru(acac)2 fragments.
Table 1. UV/Vis spectroscopic data of (polyene)ruthenium com-
plexes, [Ru](α,ω-diphenylpolyene) in CH2Cl2.
λmax/nm (ε/cm–1)
Diphenylpolyene
[Ru] = RuClCp*
[Ru] = Ru(acac)2
Butadiene
Hexatriene
Octatetraene
Decapentaene
Dodecahexaene
481 (5900) (2)
492 (6800) (3)
518 (11400) (4)
525 (16500) (5)
525 (–) (6)[c]
325 (1300)[a]
340 (21000)[b]
340 (2600)[a]
343 (35000)[b]
340 (43000)[b]
The conformation of a diene moiety around a ruthenium
center can be explained by the electron influence of
ancillary ligands.[1b] Some (diene)ruthenium complexes,
Ru(acac)2(η4-1,3-diene),[3f] TpRuCl(η4-1,3-diene),[3h] and
[Ru(NH3)4(η4-1,3-diene)]2+ [3i]
prefer the s-trans mode, pre-
,
[a] Ref.[8b] [b] Ref.[8a] [c] Because of the low solubility of 6, we could
not estimate the ε value.
sumably because the electronic deficiency around the ruthe-
nium center of each fragment, as compared with the
“RuClCp*” fragment, is compensated for by electron do-
nation from the s-trans-diene ligand. In addition, the overall
1
The H NMR spectra of 2, 4, and 6 displayed no peaks
stereochemistry at a ruthenium center may influence the assignable to the uncoordinated olefinic protons in the
conformation mode. The above s-trans-diene complexes range of δ = 6–7 ppm, indicating that polyenes with an even
have a hexacoordinate octahedral structure when the s- number of olefinic parts are fully metalated.[8] For 4, we
trans-diene moiety is regarded as a bidentate chelating li- attempted to carry out the reaction of a tetraene ligand
gand. In the case of RuClCp*(η4-1,3-diene), the regular oc- with 1 equiv. of 1 to obtain a mononuclear complex; how-
tahedral structure of the RuII complex is deviated by a ever, no partly metalated olefinic parts with one ruthenium
bulky tridentate Cp* ligand. Thus, the diene moiety of the fragment was observed, and a mixture of 4 and a free
polyene complexes prefers the s-cis coordination.
tetraene was detected by NMR analysis. Likewise, the reac-
UV/Vis spectroscopic data of 2–6 together with those of tion of 1 with a hexaene gave 6, without any complexes,
η4-s-trans-polyene complexes with Ru(acac)2 fragments[8a] having one or two ruthenium fragments. For the multinu-
are summarized in Table 1. The absorption maxima of 2–6 clear complexes 4 and 6, there are several possible syn and
shift to a longer wavelength as the number of diene units anti isomers owing to the relative face selection of sequen-
of the polyene ligand increases, indicating that the π-conju- tial metal coordination across the polyene ligand. For the
gated system along the polyene chain is kept even after the tetraene complex 4, an anti structure of two RuClCp* frag-
dπ orbital of the RuClCp* fragment is incorporated in the ments coordinated to a tetraene has been revealed by X-ray
1
pπ orbital of the polyene, consistent with the results of the analysis.[8b] The H NMR spectrum of the trinuclear hexa-
X-ray analysis of 4.[8b] In contrast, we observed that η4-s- ene complex 6 in CDCl3 showed only one set of six olefinic
trans-polyene complexes containing Ru(acac)2 fragments protons together with two methyl protons (1:2 ratio) of Cp*
Scheme 1.
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H. Fukumoto, K. Mashima
FULL PAPER
ligands, suggesting that 6 may have a C2 axis or a mirror
plane passing through the central ruthenium atom and the
center of the hexaene ligand. For 6, four isomers are pos-
sible, which are categorized into three types: syn/syn-,
anti/anti-, and anti/syn- (= syn/anti-) -6, as depicted in
1
Scheme 1. On the basis of the H NMR spectrum of 6, the
structurally unsymmetrical isomer anti/syn-6 is excluded.
Furthermore, syn/syn-6 is also ruled out because of steric
repulsion among the three bulky RuClCp* fragments. Thus,
The dinuclear pentaene complex 5 was isolated as a mix-
it is reasonably conceivable that 6 has an anti/anti structure. ture of two isomers: 5a (major, 90%) and 5b (minor, 10%).
1
In contrast to those of 4 and 6, the H NMR spectrum In the 2D COSY and NOESY spectra of 5 (Figures 1 and
of the triene complex 3 exhibited six signals of magnetically 2), 10 signals of magnetically nonequivalent nuclei assign-
nonequivalent nuclei: four peaks in the range of δ = 3.3– able to the major isomer 5a revealed that two ruthenium
5.4 ppm were from olefinic protons of the diene part bound fragments coordinated to two neighboring diene moieties
to a ruthenium atom and the other two signals observed (1,2,3,4-η4 and 5,6,7,8-η4 coordination); five peaks due to
at δ ≈ 6.5 ppm were assignable to noncoordinating olefin the minor isomer 5b indicated that two ruthenium frag-
protons. The RuClCp* fragment coordinated in an s-cis ments coordinated at separated positions (1,2,3,4-η4 and
fashion to a diene part of the triene, as judged from a typi- 7,8,9,10-η4 coordination).
cal coupling constant (3J = 5.9 Hz) between the inner pro-
There are four (= 22) possible structures of complex 5:
tons H2 and H3 (signals observed at δ = 5.28 and 4.90 two syn and two anti isomers are schematically depicted in
ppm).[2] The coupling constants J4,5 (10.3 Hz) and J5,6 Scheme 2. When the pentaene ligand reacted with 1, it is
(15.6 Hz) further indicated that the C(3)–C(4)–C(5)–C(6) assumed that there were two partly metalated intermediates
sequence is s-trans.
(1,2,3,4-η4-7 and 3,4,5,6-η4-7). For the latter intermediate,
Figure 1. The 2D COSY spectrum of 5 in CDCl3 at 30 °C. Peaks marked with * are due to solvent impurities.
5008 Eur. J. Inorg. Chem. 2006, 5006–5011
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π-Conjugated Polyene Complexes of RuClCp* Fragment(s) in η4-s-cis Conformation
FULL PAPER
Figure 2. The 2D NOESY spectrum of 5 in CDCl3 at 30 °C. Peaks marked with * are due to solvent impurities.
Scheme 2.
Eur. J. Inorg. Chem. 2006, 5006–5011
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H. Fukumoto, K. Mashima
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one diene part [C(7)–C(8)–C(9)–C(10)] remained intact and vealed by UV/Vis spectroscopy. We also discussed the struc-
was applicable to the coordination of another RuClCp* tures of pentaene and hexaene complexes on the basis of
fragment, giving anti-5a and syn-5a. On the other hand, the the bulkiness of RuClCp* moieties: the hexaene complex 6
former one has a triene part, to which the coordination of was assumed to have anti/anti geometry. The pentaene com-
another ruthenium fragment affords four possible isomers plex 5 was isolated as a mixture of two isomers: 5a (major)
(anti-5a, syn-5a, anti-5b, and syn-5b). Among these isomers, and 5b (minor). The RuClCp* fragment of one minor iso-
syn-5a was ruled out because of steric repulsion between mer, anti-5b, suprafacially moved over the pentaene back-
the two Cp* rings. Thus, the structure of the major isomer bone to afford the major isomer anti-5a, and the other iso-
1
5a was concluded to be anti-5a. In contrast, from the H mer, syn-5b, remained as the minor product. This supports
NMR spectrum of 5b, the stereochemistry of the minor our previous conclusion that ancillary ligands (Cp* or acac)
product 5b could not be determined because two possible on a ruthenium center play an important role in controlling
isomers (anti-5b and syn-5b) displayed the same signals their structural shape, such as the metal coordination mode
(magnetically equivalent nuclei) due to the inversion at the (s-cis or s-trans for diene complexation) and planarity of
center of C(5)–C(6) in the pentaene ligand for anti-5b, and the polyene backbone.
the C2 axis passing through the center of the pentaene
backbone for syn-5b.[8a]
The minor product 5b remained even at elevated tem-
peratures; the percentage of 5b did not change on heating
the chloroform solution of 5, indicating that either syn-5b
or anti-5b is thermodynamically stable. As shown in
Experimental Section
General Procedure: All manipulations involving air- and moisture-
sensitive organometallic compounds were carried out using stan-
dard Schlenk techniques under argon. THF, hexane, toluene, and
diethyl ether were dried and deoxygenated by distillation from so-
Scheme 2, the major isomer anti-5a was also produced by
the migration of an RuClCp* fragment of anti-5b via the
η2-intermediate anti-8, based on the assumption that a ru-
thenium fragment suprafacially moved over the pentaene
ligand. On the other hand, the suprafacial migration of a
ruthenium fragment on syn-5b did not proceed via syn-8,
because of the steric congestion between two RuClCp*
fragments of syn-5a. Thus, syn-5b was observed as the
minor product and its percentage did not change. Scheme 3
depicts an example of metal migration on a polyene ligand
for a trienal complex of the iron compound Fe(CO)3(7-
phenyl-2,4,6-heptatrienal). An isomer with an iron frag-
ment at neighboring positions of a phenyl group has been
isomerized to another isomer with an iron fragment at
neighboring positions of an electron-withdrawing formyl
group through the migration of a tricarbonyliron fragment
over a trienal ligand.[7b] Accordingly, it is concluded that
the treatment of 1 with a pentaene ligand finally gives anti-
5a and syn-5b as major and minor products, respectively.
dium/benzophenone ketyl under argon. Dichloromethane was puri-
fied by distillation after drying with CaH2. 1,6-Diphenyl-1,3,5-
hexatriene was purchased from Aldrich Chemical Co., Inc.; [Ru(µ3-
Cl)Cp*]4,[2g] 1,10-diphenyl-1,3,5,7,9-decapentaene,[9] and 1,12-di-
phenyl-1,3,5,7,9,11-dodecahexaene[9] were prepared according to
literature procedures. The preparation of 2 and 4 has already been
reported.[8b] NMR [1H (400 MHz)] spectra were measured using a
JEOL JNM-GSK400 spectrometer. The assignments of the 1H
NMR peaks of some complexes were aided by 2D COSY and
NOESY spectra. Other spectra were recorded using the following
instruments: IR: Jasco FTIR-120 and Hitachi 295; low- and high-
resolution MS: JEOL SX-102. UV/Vis: Jasco Ubest-30 and Shim-
adzu UV-265FS. Elemental analyses were performed with a Per-
kin–Elmer 2400 instrument at the Faculty of Engineering Science,
Osaka University. All melting points were measured in sealed tubes
and are not corrected.
Synthetic Procedures
Complex 3: 1,6-Diphenyl-1,3,5-hexatriene (0.092 g, 0.40 mmol) was
added to a solution of [Ru(µ3-Cl)Cp*]4 (1) (0.120 g, 0.11 mmol) in
THF (50 mL) at 25 °C. The color of the reaction mixture turned
bright red, and then red solids precipitated. After the reaction mix-
ture was stirred for 3 h, the red precipitates were collected and
washed with hexane (5 mL). Recrystallization from dichlorometh-
ane afforded 3 (0.12 g, 60% yield) as red microcrystals, m.p. 220–
1
Scheme 3.
230 °C (dec.). H NMR (CDCl3, 30 °C): δ = 7.17–7.52 (m, 10 H,
C6H5), 6.82 (d, J5,6 = 15.6 Hz, 1 H, H6), 6.44 (dd, J4,5 = 10.3 Hz,
1 H, H5), 5.28 (dd, J1,2 = 10.7 and J2,3 = 5.9 Hz, 1 H, H2), 4.90
(dd, J3,4 = 10.7 Hz, 1 H, H3), 3.68 (d, 1 H, H1), 3.40 (dd, 1 H, H4),
1.36 (s, 15 H, C5Me5) ppm. UV/Vis (CH2Cl2): λmax (ε) = 492 nm
(6800 Lmol–1 cm–1). MS (FAB): m/z = 504 [M+]. C28H31ClRu
(504.07): calcd. C 66.72, H 6.20; found C 66.43, H 6.30.
Conclusions
We demonstrated that the ruthenium fragment RuClCp*
coordinates in an s-cis fashion to α,ω-diphenylpolyenes to
afford the corresponding polyene complexes 2–6, in sharp
contrast to the case of η4-s-trans-polyene complexes with
Ru(acac)2 fragments. All diene units were fully metalated
with RuClCp* fragments. We also found that the coordina-
tion of RuClCp* fragments maintains a long π-conjugation
system along the polyene chain in comparison with η4-s-
Complex 5: 1,10-Diphenyl-1,3,5,7,9-decapentaene (0.170 g,
0.60 mmol) was added to a dichloromethane (50 mL) solution of 1
(0.350 g, 0.32 mmol), and the reaction mixture was stirred at room
temperature for 3 h. After removing insoluble impurities by centri-
fugation, the resulting red solution was concentrated to approxi-
mately 5 mL and kept at –20 °C, affording 5 (0.26 g, 52% yield) as
red microcrystals, m.p. 190–200 °C (dec.). Major isomer (anti-5a):
trans-polyene complexes with Ru(acac)2 fragments, as re- 1H NMR (CDCl3, 30 °C): δ = 7.10–7.50 (m, 10 H, C6H5), 6.74 (d,
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π-Conjugated Polyene Complexes of RuClCp* Fragment(s) in η4-s-cis Conformation
FULL PAPER
J9,10 = 15.6 Hz, 1 H, H10), 6.38 (dd, J8,9 = 10.3 Hz, 1 H, H9), 5.15
(dd, J1,2 = 10.3 and J2,3 = 5.9 Hz, 1 H, H2), 5.14 (dd, J3,4 = 9.3 Hz,
[1]
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1 H, H3), 5.10 (dd, J6,7 = 5.9 and J5,6 = 9.3 Hz, 1 H, H6), 4.75 (dd,
J7,8 = 10.3 Hz, 1 H, H7), 3.52 (d, 1 H, H1), 3.15 (t, 1 H, H8), 2.85
(dd, J4,5 = 10.3 Hz, 1 H, H4), 2.81 (dd, 1 H, H5), 1.53 (s, 15 H,
C5Me5), 1.31 (s, 15 H, C5Me5) ppm. Minor isomer (syn-5b): 1H
NMR (CDCl3, 30 °C): δ = 7.10–7.50 (m, 10 H, C6H5), 6.12 (m, 2
H, H5 and H6), 5.21 (dd, J2,3 and J8,9 = 5.9, J1,2 and J9,10 = 10.7 Hz,
2 H, H2 and H9), 4.89 (dd, J3,4 and J7,8 = 10.3 Hz, 2 H, H3 and
H8), 3.62 (d, 2 H, H1 and H10), 3.15 (m, 2 H, H4 and H7), 1.32 (s,
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30 H, C5Me5) ppm. UV/Vis (CH2Cl2): λmax (ε)
= 525 nm
(16000 Lmol–1 cm–1). MS (FAB): m/z = 556 [M+ – RuCp*Cl].
C42H50Cl2Ru2 (827.89): calcd. C 60.92, H 6.09; found: C 60.44, H
5.90.
[3]
Complex 6: A reaction mixture of 1 (0.0820 g, 0.075 mmol) and
1,12-diphenyl-1,3,5,7,9,11-dodecahexaene (0.0310 g, 0.10 mmol) in
CH2Cl2 (30 mL) was stirred at 25 °C for 3 h to give a red precipi-
tate. The precipitate was filtered and then washed with hexane
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(5 mL). Recrystallization from dichloromethane afforded
6
(0.043 g, 38% yield) as red microcrystals, m.p. 195–200 °C (dec.).
1H NMR (CDCl3, 30 °C): δ = 7.12–7.46 (m, 10 H, C6H5), 5.15 (dd,
2 H, H2 and H11), 5.09 (dd, J2,3 and J10,11 = 5.9 Hz, 2 H, H3 and
H10), 5.01 (dd, J6,7 = 4.4 and J5,6 and J7,8 = 9.3 Hz, 2 H, H6 and
H7), 3.53 (d, J1,2 and J11,12 = 10.7 Hz, 2 H, H1 and H12), 2.91 (dd,
J3,4 and J9,10 = 10.3 and J4,5 and J8,9 = 9.8 Hz, 2 H, H4 and H9),
2.69 (dd, 2 H, H5 and H8), 1.52 (s, 15 H, C5Me5), 1.32 (s, 30 H,
C5Me5) ppm. UV/Vis (CH2Cl2): λmax = 525 nm. MS (FAB): m/z =
547 [M+ – 2 Cp*RuCl – Cl]. The low solubilities of both the com-
plex and 1,12-diphenyl-1,3,5,7,9,11-dodecahexaene prevented the
separation of the polyene by repeated crystallizations, and an ele-
mental analysis of the complexes could not be performed.
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Received: June 30, 2006
Acknowledgments
This research was supported by a Grant-in-Aid for Scientific Re-
search from the Ministry of Education, Culture, Sports, Science
and Technology, Japan.
Published Online: October 31, 2006
Eur. J. Inorg. Chem. 2006, 5006–5011
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
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