Dissymmetrical trans-ethynyl-butadiynyl adducts on a diruthenium core: Synthesis, characterization, and selective deprotection

Article abstract of DOI:10.1021/om0109004

Reactions between the ethynyl complexes (4,0)-[Ru₂(ap)₄](C₂SiR₃) (ap is 2-anilinopyridinate, R = ⁱPr (1a) and CH₃ (1b)) and LiC₄SiMe₃ result in the formation of dissymmetrical ethynylbutadiynyl adducts trans-(4,0)-(Me₃SiC₄)[Ru₂(ap)₄](C ₂SiR₃) (R = ⁱPr (2a) and CH₃ (2b)). Treating 2b with K₂CO₃ in MeOH/THF leads to trans-(HC₄)[Ru₂(ap)₄](C₂SiMe₃ ) (3b) and trans-(HC₄)[Ru₂(ap)₄](C₂H) (4) in 86% and ca. 10% yields, respectively, and the former can be quantitatively converted to 4 using NaOH. Treating 2a with NaOH in MeOH/THF yields trans-(HC₄)[Ru₂(ap)₄](C₂Siⁱ Pr₃) (3a) only. Single-crystal structural analysis of 2a and 3b revealed that the Ru - Ru unit and the axial alkynyl ligands are approximately collinear in both molecules. Rich redox chemistry was revealed for all the compounds through voltammetric study: compound 1 exhibits reversible one-electron oxidation and reduction, and compounds 2-4 exhibit one one-electron oxidation and two one-electron reductions. All the ethynyl-butadiynyl adducts (2-4) exhibit an intense charge-transfer absorption of λ_max around 1035 nm, revealing a HOMO - LUMO gap of 1.20 eV.

Full text of DOI:10.1021/om0109004

732
Organometallics 2002, 21, 732-738
Dissym m etr ica l tr a n s-Eth yn yl-Bu ta d iyn yl Ad d u cts on a
Dir u th en iu m Cor e: Syn th esis, Ch a r a cter iza tion , a n d
Selective Dep r otection
Tong Ren*
Department of Chemistry and Center for Supramolecular Science, University of Miami,
Coral Gables, Florida 33124
Received October 15, 2001
Reactions between the ethynyl complexes (4,0)-[Ru2(ap)4](C2SiR3) (ap is 2-anilinopyridinate,
R ) iPr (1a ) and CH3 (1b)) and LiC4SiMe3 result in the formation of dissymmetrical ethynyl-
i
butadiynyl adducts trans-(4,0)-(Me3SiC4)[Ru2(ap)4](C2SiR3) (R ) Pr (2a ) and CH3 (2b)).
Treating 2b with K2CO3 in MeOH/THF leads to trans-(HC4)[Ru2(ap)4](C2SiMe3) (3b) and
trans-(HC4)[Ru2(ap)4](C2H) (4) in 86% and ca. 10% yields, respectively, and the former can
be quantitatively converted to 4 using NaOH. Treating 2a with NaOH in MeOH/THF yields
trans-(HC4)[Ru2(ap)4](C2SiiPr3) (3a ) only. Single-crystal structural analysis of 2a and 3b
revealed that the Ru-Ru unit and the axial alkynyl ligands are approximately collinear in
both molecules. Rich redox chemistry was revealed for all the compounds through voltam-
metric study: compound 1 exhibits reversible one-electron oxidation and reduction, and
compounds 2-4 exhibit one one-electron oxidation and two one-electron reductions. All the
ethynyl-butadiynyl adducts (2-4) exhibit an intense charge-transfer absorption of λmax around
1035 nm, revealing a HOMO-LUMO gap of 1.20 eV.
Sch em e 1. Retr osyn th eses of Both Sim p le Rod
w ith [Ru 2] Ter m in u s (A) a n d Oligom eta lla yn e Rod
(B) fr om Syn th on s C a n d D; [Ru 2] ) [Ru 2(a p)4]
In tr od u ction
Synthesis of monodisperse conjugated oligomers has
attracted much attention recently due to the ubiquitous
role of monodisperse conjugated oligomers in both
electronic and optoelectronic applications.1 Among syn-
thetic strategies explored, the divergent-convergent
approach has been elegantly demonstrated in the syn-
thesis of hydrocarbon oligomers,2 where an orthogonal
synthon is the key. Based on the orthogonal synthon
p-diethylazaphenylacetylene, monodisperse oligo(p-phen-
ylene ethynylene) up to 16mer have been prepared by
Tour et al.3,4 Using m-dialkylazaphenylacetylene and
related building blocks, Moore and co-workers have
realized shape-persistent phenylene ethynylene den-
drimers, which further self-assemble into well-defined
nano-architectures.5
Recently, we succeeded in synthesizing a simple rigid
rod (A in Scheme 1) by capping the polyyne-diyl chain
(C2 and C4) with [Ru2(ap)4] termini (ap ) 2-anilinopy-
ridinate) and demonstrated the existence of a significant
electronic delocalization between two Ru2-termini medi-
ated by the polyyne-diyl chain.6 Type A rigid rods with
short carbyne bridge (k ) 1/2 and 1) were obtained
through a metathesis reaction between [Ru2(ap)4]Cl and
Li(CC)2kLi.6 Analogous rods with 2k g 4 can be obtained
by homocoupling of [Ru2(ap)4](C2kH) (C in Scheme 1), a
monofunctional building block established in our labo-
ratory,7,8 under either Hay or Eglington conditions.9,10
To extend our scope into the monodisperse oligomer (B,
Scheme 1), difunctional building block D (Scheme 1) is
necessitated from structural considerations. Examples
of this type of building block, trans-[Ru2(ap)4](C4SiMe3)2
and trans-[Ru2(DmAniF)4](C4SiMe3)2 (DmAniF is di(m-
methoxyphenylformamidinate)), have also been estab-
lished in our8,11 and Lehn’s laboratories.12 Reported
herein are the synthesis and characterization of a family
* Tel: (305) 284-6617. Fax: (305) 284-1880. E-mail: tren@miami.edu.
(1) Mullen, K.; Wegner, G. Electronic Materials: the Oligomer
Approach; Wiley-VCH: Weinheim, 1998.
(2) Geerts, Y.; Klarner, G.; Mullen, K. In Electronic Materials: the
Oligomer Approach; Mullen, K., Wegner, G., Eds.; Wiley-VCH: Wein-
heim, 1998.
(7) Zou, G.; Alvarez, J . C.; Ren, T. J . Organomet. Chem. 2000, 596,
152.
(8) Xu, G.; Ren, T. Organometallics 2001, 20, 2400.
(9) Ni, Y.; Ren, T. Angew. Chem., Int. Ed., manuscript in prepara-
tion.
(3) Schumm, J . S.; Pearson, D. L.; Tour, J . M. Angew. Chem., Int.
Ed. Engl. 1994, 33, 1360.
(4) Tour, J . M. Chem. Rev. 1996, 96, 537.
(5) Moore, J . S. Acc. Chem. Res. 1997, 30, 402.
(6) Ren, T.; Zou, G.; Alvarez, J . C. Chem. Commun. 2000, 1197.
(10) Siemsen, P.; Livingston, R. C.; Diederich, F. Angew. Chem., Int.
Ed. 2000, 39, 2632.
(11) Xu, G.; Ren, T. Inorg. Chem. 2001, 40, 2925.
(12) Wong, K.-T.; Lehn, J .-M.; Peng, S.-M.; Lee, G.-H. Chem.
Commun. 2000, 2259.
10.1021/om0109004 CCC: $22.00 © 2002 American Chemical Society
Publication on Web 01/19/2002

Dissymmetrical trans-Ethynyl-Butadiynyl Adducts
Organometallics, Vol. 21, No. 4, 2002 733
Sch em e 2. Eth yn yl a n d Eth yn yl-Bu ta d in yl
Ad d u cts on th e [Ru 2(a p)4] Cor e
F igu r e 1. ORTEP plot of molecule 2a at 30% probability
level. All non-acetylenic carbons are shown as isotropic
atoms.
adduct may be expected if the monoethynyl adduct is
treated with a longer poly-ynyl ligand such as butadi-
ynyl.
Similar to the synthesis of [Ru2(ap)4]C2SiMe3 (1b),7
[Ru2(ap)4]C2SiiPr3 (1a ) was prepared by treating [Ru2-
(ap)4]Cl with 1 equiv of LiC2SiiPr3 and the yield was
quantitative. When 1a was treated with 6 equiv of LiC4-
SiMe3 under inert atmosphere, the initially green solu-
tion gradually changed to dark red, a color likely
attributed to {trans-(R′C4)[Ru2(ap)4](C2R)}-1. The ali-
quot of reaction mixture turned to dark blue instantly
upon exposure to air, and TLC analysis revealed the
formation of a dominant blue product and the presence
of 1a . After ca. 3 h, the ratio between the blue product
and 1a became constant on TLC plate, and the reaction
was terminated by bubbling O2 through the reaction
mixture, which led to a royal blue solution in minutes.
Compound 2a was isolated in satisfactory yield (76%)
after the chromatography purification of reaction mix-
ture. Starting with 1b, compound 2b was prepared
similarly in good yield (77%).
Sch em e 3. Step w ise F or m a tion of Mon o- a n d
Bis-bu ta d iyn yl a d d u cts on [Ru 2(a p)4]
The Me3Si group in compound 2a can be readily
removed with the weak base K2CO3 to yield 3a in 24 h,
and the process is shortened to 30 min by using the
strong base NaOH. In either case, there was no evidence
of the removal of the SiiPr3 group. When treated with
K2CO3, the Me3Si group of the butadiynyl ligand in 2b
was completely removed in 48 h, and partial removal
of the second Me3Si group to yield compound 4 was
noticed. Removal of both Me3Si groups in 2b was
accomplished by using the strong base NaOH, where
the conversion of 2b to 3b completed within 30 min, and
the subsequent conversion of 3b to 4 finished in 24 h.
The sequential deprotection of Me3Si groups in 2b
clearly indicates that they are electronically differenti-
ated. A plausible explanation is that the carbon ends of
the C4-Ru2-C2 backbone are electronically communi-
cating due to full conjugation.
of dissymmetric ethynyl-butadiynyl adducts on the [Ru2-
(ap)4] core, illustrated in Scheme 2, which not only
satisfy the structural requirement for a type D building
block but also exhibit selective desilylation chemistry
to yield two compounds (3a /3b) that are amenable to
the divergent-convergent synthesis.
Resu lts a n d Discu ssion
It was demonstrated previously that monoethynyl
adduct [Ru2(ap)4](C2R) was the only product isolated
when treating Ru2(ap)4Cl with either 1 equiv or excess
lithiated ethynyl ligand (LiC2R).7,8,13 However, replacing
the ethynyl ligand with a longer butadiynyl ligand
enabled the isolation of the bis-adduct trans-[Ru2(ap)4]-
(C4R)2 (R ) SiMe3) in addition to the monoadduct when
excess LiC4R was used.8 Evidently, the addition of
butadiynyl ligands to [Ru2(ap)4] core proceeds stepwise,
as described in Scheme 3.
Compound 1a has a room-temperature effective mag-
netic moment of 4.11, indicating a S ) 3/2 ground state
that was observed for 1b as well.7 Compounds 2, 3, and
1
4 are diamagnetic, as reflected by the well-resolved H
NMR spectra.
Molecular structures determined via X-ray diffraction
studies are shown in Figures 1 and 2 for 2a and 3b,
respectively, and the selected metric parameters are
presented in Table 1. Clearly, the ap bridging ligands
in both structures retain the (4,0)-arrangement common
to all [Ru2(ap)4]-based alkynyl compounds:7,8,13 all py-
In the case of ethynyl ligands, the second addition
step is prohibited by the steric repulsion between the R
and anilino groups. On the other hand, a dissymmetrical
(13) Chakravarty, A. R.; Cotton, F. A. Inorg. Chim. Acta 1986, 113,
19.

734 Organometallics, Vol. 21, No. 4, 2002
Ren
F igu r e 2. ORTEP plot of molecule 3b at 30% probability
level. All non-acetylenic carbons are shown as isotropic
atoms.
Ta ble 1. Selected Bon d Len gth s a n d An gles for
Molecu les 2a a n d 3b
2a
3b
Ru(1)-Ru(2)
Ru(1)-N(2)
Ru(1)-N(4)
Ru(1)-N(6)
Ru(1)-N(8)
Ru(2)-N(1)
Ru(2)-N(3)
Ru(2)-N(5)
Ru(2)-N(7)
Ru(2)-C(1)
C(1)-C(2)
2.4584(6)
2.038(3)
2.075(4)
2.036(3)
2.039(4)
2.060(4)
2.049(4)
2.082(4)
2.101(4)
1.969(5)
1.193(6)
1.833(6)
1.963(6)
1.202(7)
1.399(8)
1.200(7)
1.794(6)
2.4662(3)
2.142(2)
2.025(2)
1.968(2)
2.035(2)
1.999(2)
2.080(2)
2.156(2)
2.044(2)
1.972(3)
1.214(4)
1.812(3)
1.966(3)
1.206(4)
1.370(4)
1.175(5)
NA
F igu r e 3. Space-filling plots of molecules 2a (a) and 3b
(b).
Ru(1)-N(2) bond (2.142(2) Å) is 0.1 Å longer than the
mean of Ru(1)-N bonds (2.043 Å), while the bond trans
to it, Ru(1)-N(6), is only 1.968(2) Å long. Similar
distortions occur on the Ru(2) center: elongation of the
Ru(2)-N(5) bond and compression of the Ru(2)-N(1)
bond. In comparison, the distortion of Ru-N bonds in
2a is relatively subtle, with the largest deviation from
the mean (2.06 Å) in Ru(2)-N(7) (2.101(4) Å). Variation
in the degree of distortion is also apparent in bond
angles: the Ru-Ru-CR angles in 2a (175.12(15)° and
177.74(17)°) are very close to 180°, but those in 3b
(165.31(9)° and 164.84(8)°) are ca. 15° away from
linearity. Inspection of the space-filling plots of both 2a
and 3b (Figure 3) reveals that the SiiPr3 group fully
occupies the space around the acetylenic bond and
leaves little space for the Ru-CR bond to bend, while
the same steric restraint is unavailable from the SiMe3
group in 3b. It is plausible that the bulkiness of the
SiiPr3 group suppresses the second-order J ahn-Teller
effect in 2b.
Si(1)-C(2)
Ru(1)-C(3)
C(3)-C(4)
C(4)-C(5)
C(5)-C(6)
Si(2)-C(6)
N(2)-Ru(1)-Ru(2)
N(4)-Ru(1)-Ru(2)
N(6)-Ru(1)-Ru(2)
N(8)-Ru(1)-Ru(2)
N(1)-Ru(2)-Ru(1)
N(3)-Ru(2)-Ru(1)
N(5)-Ru(2)-Ru(1)
N(7)-Ru(2)-Ru(1)
C(1)-Ru(2)-Ru(1)
C(2)-C(1)-Ru(2)
C(3)-Ru(1)-Ru(2)
C(4)-C(3)-Ru(1)
C(3)-C(4)-C(5)
85.89(10)
83.55(10)
87.19(10)
88.84(10)
87.99(11)
89.68(11)
86.74(10)
84.68(10)
175.12(15)
177.1(5)
78.02(6)
86.60(6)
93.51(6)
85.55(6)
94.71(7)
86.05(6)
78.89(6)
87.33(6)
165.31(9)
175.2(3)
164.84(8)
173.1(3)
172.7(3)
177.2(4)
177.74(17)
172.6(5)
172.7(6)
C(6)-C(5)-C(4)
176.9(8)
ridine N-centers coordinate to Ru(2), while all anilino
N-centers coordinate to Ru(1). The Ru-Ru bond lengths
in 2a (2.4584(6) Å) and 3b (2.4662(3) Å) are consistent
with a formal Ru-Ru single bond. Four chemically
distinct Ru-CR distances in molecules 2a and 3b are
identical within experimental error and a mean of 1.968-
[4] Å. The C-C bond lengths of ethynyl-butadiynyl
ligands in 2a and 3b are comparable, and those of
butadiynyls generally conform to the alternating single
and triple bond formalism.
Close examination of structures of 2a and 3b reveals
that neither molecule has a perfectly linear C4-Ru2-
C2 backbone. The deviation of the Ru-Ru-C angles
from linearity is largely attributed to a second-order
J ahn-Teller distortion that is common to trans-bis-
(alkynyl) adducts on a Ru2(III,III) core.14 This effect is
very pronounced in 3b, as indicated by the great
disparity in Ru-N bond lengths. More specifically, the
Similar to compound 1b reported earlier,7 compound
1a exhibits two reversible one-electron processes in its
cyclic voltammogram (CV) shown in Figure 4: an
oxidation at 0.455 V and a reduction at -0.877 V. Cyclic
voltammograms recorded at the scan rate of 0.100 V/s
for bis-alkynyl adducts, compounds 2a /b, 3a /b, and 4
are also shown in Figure 4, and they appear more
complicated in comparison with that of 1a . The main
features of the CVs of 2a /b consist of three one-electron
couples: an oxidation (ca. 0.830 V, A), the first reduction
(-0.365 V, B), and the second reduction (-1.480 V, C).
These couples have been respectively shifted by ca.
-0.06, -0.08, and -0.12 V from that of trans-[Ru2(ap)4]-
(C4SiMe3)2,8 which are attributed to the slight electron-
richness of both 2a and 2b in comparison with trans-
(14) Lin, C.; Ren, T.; Valente, E. J .; Zubkowski, J . D. J . Chem. Soc.,
Dalton Trans. 1998, 571.

Dissymmetrical trans-Ethynyl-Butadiynyl Adducts
Organometallics, Vol. 21, No. 4, 2002 735
F igu r e 5. Cyclic voltammograms of compound 3a recorded
in 0.20 M THF solution of Bu4NPF6 at scan rates of 0.10,
0.40, and 1.60 V/s (see legend). A silver wire was used as
a pseudo-reference electrode, and ferrocene was added as
the internal reference.
(marked as E in the CV of 3b), which indicates the
partial dissociation of the butadiynyl anion upon the
formation of monoanion. The irreversibility of the oxida-
tion couple (A) is associated with the desilylation of
butadiynyl, as evidenced by the contrast between the
CVs of 2a /b and 3a /3b. However, the fate of the cation
remains unclear presently.
It was noted for compounds 3a /3b and 4 that the
reversibility of both A and C couples improves upon the
increase in scan rate from 0.10 V/s. Due to the instabil-
ity of the Ag/AgCl reference electrode (Cypress) at
higher scan rates, a silver wire pseudo-reference elec-
trode was used and the potential was calibrated with
ferrocene as the internal standard. The dependence of
reversibility on scan rate is typified by the CVs of 3a
shown in Figure 5, where the oxidation couple (A)
becomes reversible and the second reduction couple (C)
becomes quasi-reversible with scan rate higher than 1
V/s. Similar results were obtained for compounds 3b and
4, and all the rate-dependent results are provided as
Supporting Information (Tables S9-S11).
Compounds 1-4 display rich features in their vis-
NIR (visible-near-infrared) spectra, as shown in Figure
6. Compound 1a has two intense peaks centered at 471
and 745 nm, respectively, which are similar to these
observed for both Ru2(ap)4Cl15 and Ru2(ap)4(CCR) (R )
H, Ph, CH2OCH3).7,13 The low-energy absorption can be
attributed to the π(Ru-N) to π*/δ*(Ru2) charge-transfer
band, while the high-energy band is likely associated
with π(CCR) to π*/δ*(Ru2).13,16 It is interesting to note
that the HOMO-LUMO gap (∆E) of solvated 1a is
estimated to be 1.332 eV from voltammetric data
(∆E ) e{E1/2(+1/0) - E1/2(0/-1)})17,18 and 1.664 eV from
F igu r e 4. Cyclic voltammograms of compounds 1-4
recorded in 0.20 M THF solution of Bu4NPF6 at a scan rate
of 0.10 V/s.
[Ru2(ap)4](C4SiMe3)2. While the first two couples of 2
are reversible, the latter has an ibackward/iforward ratio
equal or less than 0.70 and, hence, is quasi-reversible.
Both compounds 2a /b also display a small but signifi-
cant wave around -0.820 V (D) during the backward
sweeping of cathodic scan.
For both partially and fully desilylated compounds,
i.e., 3a /b and 4, their CVs also feature three couples,
an irreversible oxidation (A), a reversible reduction (B),
and an irreversible reduction (C). Clearly, the redox
stability of bis-alkynyl adducts is reduced significantly
upon desilylation. Coupled with the disappearance of
the anodic wave of couple C, the wave at ca. -0.820 V
(D) becomes very pronounced. On the other hand, the
backward sweep of the anodic scan reveals the super-
position of many featureless small waves.
Rationales for the observed redox characteristics are
summarized in Scheme 4. Electrochemically generated
dianions are relatively unstable and dissociate the
butadiynyl anion on the electrochemical time scale to
yield the monoalkynyl complex anion, which was oxi-
dized to yield wave D. This assignment is readily
verified by noticing that Epa(D) is about the same as
the Epa of the reduction couple of 1a . Dissociation upon
reduction is not limited to the dianion: a small but
significant iforward has been observed at the potential
corresponding to Epc(0/-1) of 1a for both 3b and 4
Sch em e 4. Assign m en t of Red ox Cou p les a n d Rela ted Ch em ica l Step s

736 Organometallics, Vol. 21, No. 4, 2002
Ren
Ta ble 2. Electr och em ica l a n d Sp ectr oscop ic Da ta for Com p ou n d s 1-4
1b 2a 2b 3a 3b
0.455 0.835 0.827
0.843a 0.834a
4
E(+1/0)/V
0.830a
(∆Ep/V, iback/iforward
E(0/-1)/V
)
)
)
(0.103, 0.99)
-0.877
(0.102, 0.88)
-0.370
(0.099, 0.90)
-0.362
-0.380
-0.378
-0.390
(∆Ep/V, iback/iforward
E(-1/-2)/V
(0.109, 0.96)
NA
(0.100, 1.00)
-1.493
(0.104, 0.86)
-1.476
(0.101, 1.01)
(0.100, 1.15)
(0.102, 1.12)
-1.539a
-1.514a
-1.527a
(∆Ep/V, iback/iforward
(0.098, 0.72)
440 (sh)
480 (5300)
656 (7500)
1040 (4600)
1.206
(0.102, 0.61)
440 (sh)
480 (9600)
655 (13 700)
1040 (8450)
1.209
λ
max/nm (ꢀ, cm-1M-1
)
471 (8000)
745 (5700)
437 (3870)
476 (4650)
644 (6500)
1035 (3970)
1.223
435 (6140)
477 (6430)
645 (10 700)
1035 (6580)
1.212
435 (8530)
477 (9050)
644 (14 950)
1029 (9090)
1.220
{E(+1/0) - E(0/-1)}/V
1.332
1.66
E
op, eVb
1.19
1.19
1.20
1.20
1.21
a
These couples are irreversible at the scan rate of 0.10 V/s; E1/2 values listed were averaged from those obtained at higher scan rates.
Eop ) 107/(8065.5λmax).
b
The most noteworthy feature of compounds 2-4 is the
small HOMO-LUMO gap, which is around 1.20 eV
from both electrochemical and optical data (see Table
2). The value of 1.20 eV is remarkably small for
organometallic species that are stable toward both air
and moisture. Since the reduction of the HOMO-LUMO
gap has been the primary goal of band gap engineering
of the conjugated oligomer/polymer,19,20 it is very im-
portant to understand the electronic nature of com-
pounds 2-4 on the basis of first-principles calculations,
which are being carried out in our group.
Con clu sion s
Several dissymmetric ethynyl-butadiynyl adducts on
[Ru2(ap)4] core have been synthesized, and they display
rich redox chemistry and spectroscopic features. Most
significantly, the monodesilylated compounds 3a /b can
be readily synthesized due to the electronic asymmetry.
With these orthogonally protected building blocks, one
can envision the divergent-convergent synthesis of
monodisperse oligomers outlined in Scheme 5, which is
being vigorously pursued in our laboratory.
F igu r e 6. Vis-NIR absorption spectra of compounds 1-4
recorded in THF.
Sch em e 5. Diver gen t-Con ver gen t Cou p lin g of
Ru 2-m eta lla -yn e
the λmax (745 nm). The discrepancy is perhaps related
to the open-shell nature of 1a .
As shown in Figure 6, bis-alkynyl species 2-4 exhibit
more intense peaks, which are generally shifted to
longer wavelengths in comparison with those of 1a . The
lowest energy charge-transfer bands appear around
1035 nm, which is assigned as the π(Ru-N) to
π*/δ*(Ru2) charge-transfer band. The dramatic red-shift
from that of 1 can be attributed to the decrease in the
energies of π*/δ*(Ru2) orbitals upon the increase in
formal oxidation state (Ru2(III,III) in 2-4 versus Ru2-
(II,III) in 1). The intense peaks at ca. 650 and 480 nm,
which were also observed for trans-[Ru2(ap)4](C4SiMe3)2,8
are tentatively assigned as π(CCR) to π*/δ*(Ru2) transi-
tions. Compounds 2-4 also exhibit an additional peak/
shoulder around 440 nm that is likely due to the
dissymmetric nature of 2-4 since such a peak was
absent in trans-[Ru2(ap)4](C4SiMe3)2.
Exp er im en ta l Section
Tri(isopropyl)silylacetylene, 1,4-bistrimethylsilyl-1,3-buta-
diyne, 2-anilinopyridine, and n-BuLi were purchased from
Aldrich, and silica gel was purchased from Merck. Both
Ru2(ap)4Cl and Ru2(ap)4(CCSiMe3) (1b) were prepared as
previously described.7 THF was distilled over Na/benzophe-
none under an N2 atmosphere prior to use. H and 13C NMR
1
spectra were recorded in CDCl3 (except 4) on a Bruker
AVANCE300 NMR spectrometer, and chemical shifts (δ) were
respectively referenced to the residual CHCl3 and the solvent
CDCl3. Infrared spectra were recorded on a Perkin-Elmer 2000
FT-IR spectrometer using KBr disks. UV-vis spectra in THF
were obtained with a Perkin-Elmer Lambda-900 UV-vis
spectrophotometer. Magnetic susceptibility was measured at
293 K with a J ohnson Matthey Mark-I Magnetic Susceptibility
(15) Chakravarty, A. R.; Cotton, F. A.; Tocher, D. A. Inorg. Chem.
1985, 24, 172.
(16) Miskowski, V. M.; Hopkins, M. D.; Winkler, J . R.; Gray, H. B.
In Inorganic Electronic Structure and Spectroscopy; Solomon, E. I.,
Lever, A. B. P., Eds.; Wiley: New York, 1999; Vol. 2.
(17) Ren, T. Coord. Chem. Rev. 1998, 175, 43.
(19) Roncali, J . Chem. Rev. 1997, 97, 173.
(20) van Mullekom, H. A. M.; Vekemans, J .; Havinga, E. E.; Meijer,
E. W. Mater. Sci. Eng. R-Rep. 2001, 32, 1.
(18) Loutfy, R. O.; Loutfy, R. O. Can. J . Chem. 1976, 54, 1454.

Dissymmetrical trans-Ethynyl-Butadiynyl Adducts
Organometallics, Vol. 21, No. 4, 2002 737
Balance. Cyclic voltammograms (CV) were recorded in 0.20
M (n-Bu)4NPF6 solution (THF, N2-degassed) on a CHI620A
voltammetric analyzer with a glassy carbon working electrode
(i ) 3 mm), a Pt wire auxiliary electrode, and a concentration
of diruthenium species about 1.0 mM. For the CV shown in
Figure 4 (all with a scan rate of 0.10 V/s), a Ag/AgCl reference
electrode for nonaqueous solution (Cypress) was used and the
ferrocenium/ferrocene couple was observed at 0.576 V under
the experimental conditions. However, responses of the Ag/
AgCl reference electrode became sluggish at higher scan rate.
Hence, a Ag wire pseudo-reference electrode was used for the
scan-rate dependence study of compounds 3 and 4, and the
potentials reported were calibrated with ferrocene as the
internal standard.
P r ep a r a tion of Ru 2(a p )4(C2SiiP r 3) (1a ). To a 20 mL THF
solution containing 1.2 mmol of iPr3SiC2H was added 0.80 mL
of BuLi (1.6 M in hexanes) at -80 °C. The mixture was slowly
warmed to room temperature and stirred for another hour to
yield a light yellow solution. All the solution was transferred
to a flask containing a THF solution (100 mL) of Ru2(ap)4Cl
(0.98 g, 1.05 mmol). The solution color changed from dark
green to yellow-green gradually, and the reaction mixture was
stirred for an hour. Removal of the solvents in vacuo yielded
a green residue, which was rinsed with a copious amount of
warm methanol and filtered. A light green flaky crystalline
solid was obtained after drying in a vacuum and identified as
pure 1a . Yield: 1.07 g (96%). Data for 1a : Rf, 0.88 (Et3N/ethyl
acetate/hexanes, 1/1/10, v/v, and the same solvent combination
was used for all the Rf values thereafter). Anal. for C55H57N8-
SiRu2, found (calcd): C, 62.13 (62.30); H, 5.53 (5.42); N, 10.39
(10.57). MS-FAB (m/e, based on 101Ru): 1061 [MH+]. IR: ν(C
t C)/cm-1, 1993(w). Magnetic (293 K): ømol(corr): 7.20 × 10-3
esu‚mol-1. µeff: 4.11 µB.
SiRu2, found (calcd): C, 63.60 (63.88); H, 5.60(5.27); N, 9.81-
(10.10). MS-FAB (m/e, based on 101Ru): 1110 [MH+]. 1H
NMR: 9.34 (q, 4H, aromatic), 7.01-7.11 (m, 16H, aromatic),
6.43 (d, 4H, aromatic), 6.32 (dd, 4H, aromatic), 5.76 (d, 8H,
aromatic), 1.22 (br, 21H), 1.09 (s, 1H, C4H). 13C NMR (CtC,
all singlet): 109.5, 104.6, 74.2, 73.9, 73.7, 73.3. IR: ν(C t C)/
cm-1, 1989(s) and 2133(s).
P r ep a r a tion of tr a n s-(MeSi3C4)Ru 2(a p)4(C2SiMe3) (2b).
Similar to the preparation of 2a , Ru2(ap)4(C2SiMe3)7 (1b, 0.40
g, 0.41 mmol) was treated with 2.45 mmol of LiC4SiMe3 in
THF. After a similar workup, 2b was isolated as a blue
crystalline powder (0.35 g, 77% based 1b). Data for 2b: Rf,
0.81. Anal. for C56H54N8Si2Ru2, found (calcd): C, 60.99 (61.29);
H, 4.92 (4.96); N, 10.29 (10.21). MS-FAB (m/e, based on
101Ru): 1098 [MH+]. 1H NMR: 9.26 (q, 4H, aromatic), 7.11 (m,
4H, aromatic), 7.03 (m, 12H, aromatic), 6.35-6.46 (m, 8H, a
romatic), 5.77 (s, 8H, aromatic), 0.37 (s, 9H, CH3), 0.18 (s, 9H,
CH3). 13C NMR (CtC, all singlet): 109.7, 104.8, 74.2, 73.9,
73.7, 73.3. IR: ν(C t C)/cm-1, 1998(s), 2117(s), and 2180(w).
P r epar ation of tr a n s-(HC4)Ru 2(a p)4(C2SiMe3) (3b). Com-
pound 2b (150 mg) was stirred with 7 g of K2CO3 in 50 mL of
THF/MeOH (2/1) solution for 48 h when TLC analysis indi-
cated the complete disappearance of 2b. The solution was
filtered, and the filtrate was loaded onto silica and eluted with
Et3N/ethyl acetate/hexanes (1/10/90, v/v). Compound 3b was
isolated as a blue crystalline solid (120 mg, 86%). A Trace
amount of 4 (<10%) was also present. Data for 3b: Rf, 0.65.
Anal. for C53H46N8SiRu2, found (calcd): C, 62.12 (62.09); H,
4.58 (4.52); N, 10.65 (10.93). MS-FAB (m/e, based on 101Ru):
1
1026 [MH+]. H NMR: 9.20 (q, 4H, aromatic), 7.00-7.10 (m,
16H, aromatic), 6.42 (d, 4H), 6.39 (t, 4H, aromatic), 5.75 (d,
8H, aromatic), 1.09 (s, 1H, C4H), 0.31 (s, 9H, Si(CH3)3). 13C
NMR (CtC, all singlet): 109.6, 104.9, 74.2, 73.9, 73.7, 73.3.
IR: ν(C t C)/cm-1, 1996(s) and 2129(s).
P r epar ation of tr a n s-(4,0)-(Me3SiC4)[Ru 2(ap)4](C2SiiP r 3)
(2a ). To a 30 mL THF solution containing 3.0 mmol of Me3-
SiC4SiMe3 was added 1.9 mL of n-BuLi (1.6 M in hexanes) at
-80 °C. The mixture was slowly warmed to room temperature
and stirred for 2 h to yield a light yellow solution. The solution
was transferred to a flask containing a THF solution (35 mL)
of Ru2(ap)4(C2SiiPr3) (0.53 g, 0.50 mmol). The solution color
changed from dark green to reddish purple over a period of
an hour, and the reaction mixture was stirred for an additional
2 h. The reaction was terminated by bubbling dry O2 through
the solution, which turned dark blue immediately. TLC
analysis (Et3N/ethyl acetate/hexanes, 1/1/10, v/v) revealed the
presence of starting material 1 (<10%), 2a (dominant), and
3a (trace). After the solvent removal, the dark residue was
loaded onto a silica gel column deactivated by 1% Et3N in
hexanes and eluted with a linear gradient of Et3N/ethyl
acetate/hexanes (1/0/100 to 1/10/100, v/v). Removal of solvents
in the blue fraction resulted in 2a as a dark blue polycrystal-
line solid (450 mg, 76% based on Ru). Data for 2a : Rf 0.81.
Anal. for C62H66N8Si2Ru2, found (calcd): C, 63.34 (63.02); H,
5.84 (5.63); N, 9.27 (9.48). MS-FAB (m/e, based on 101Ru): 1182
[M+]. 1H NMR: 9.33 (q, 4H, aromatic), 7.04 (m, 4H, aromatic),
6.98 (m, 12H, aromatic), 6.39 (d, 4H, aromatic), 6.29 (t, 4H,
aromatic), 5.72 (s, 8H, aromatic), 1.23 (br, 21H, i-Pr) 0.12 (s,
9H, Si(CH3)3). 13C NMR (CtC, all singlet): 109.6, 104.6, 74.1,
73.9, 73.7, 73.3, IR: ν(C t C)/cm-1, 1999(s), 2110(s), and
2173(w).
P r ep a r a t ion of tr a n s-(4,0)-(H C4)[R u 2(a p )4](C2SiiP r 3)
(3a ). 2a (0.40 g) was dissolved in 150 mL of THF/MeOH (2/1
v/v) to which was added 4.0 g of NaOH. The mixture was
stirred vigorously, and 2a was cleanly converted to 3a in 30
min (monitored by TLC). After removal of solvent, compound
3a was extracted using CH2Cl2 and the extract was rinsed
thoroughly with water. The residue after solvent removal was
recrystallized from hexanes/CH2Cl2 to yield blue crystalline
3a (0.35 g, 93%). Treating 2a with K2CO3 under similar
conditions also produced 3a in good yield, but the reaction time
was longer (24 h). Data for 3a : Rf 0.67. Anal. for C59H58N8-
P r ep a r a tion of tr a n s-(HC4)Ru 2(a p )4(C2H) (4). Com-
pound 2b (120 mg) was dissolved in 40 mL of THF to which
was added 6.0 g of NaOH and 20 mL of MeOH. Starting
material was completely converted to 3b and 4 within 30 min,
and the remaining 3b was converted to 4 after 24 h vigorous
stirring. Some purple polar materials also appeared toward
the end of the reaction, which have not been identified yet.
After solvent removal, the dark blue jelly residue was dissolved
in CH2Cl2 and washed with a copious amount of water until
the washing became neutral. The CH2Cl2 solution was loaded
onto silica and eluted with Et3N/ethyl acetate/hexanes (1/10/
100 to 1/40/40), yielding pure 4 as blue microcrystalline solids.
Yield: 0.090 g (81%). Data for 4: Rf, 0.40. Anal. for C50H41N8O1.5
-
Ru2 (4‚1.5H2O), found (calcd): C, 61.60 (61.38); H, 4.30 (4.22);
N, 11.17 (11.43). MS-FAB (m/e, based on 101Ru): 954 [MH+].
1H NMR((CD3)2CO): 9.20 (d, 4H, aromatic), 7.00-7.10, (m,
16H), 6.36-6.44 (m, 8H), 5.75 (d, 8H, aromatic), 5.27 (s, 1H),
and 2.91 (s, 1H). 13C NMR (C6D6; CtC, all singlet): 109.8,
104.9, 64.0, 61.8, 60.4. IR: ν(CtC)/cm-1, 1943(w) and 2121(s).
X-r a y Da ta Collection , P r ocessin g, a n d Str u ctu r e
An a lysis a n d Refin em en t. Single crystals of both compounds
2a and 3b were grown via slow evaporation of the fractions of
column purification. The X-ray intensity data were measured
at 300 K on a Bruker SMART1000 CCD-based X-ray diffrac-
tometer system using Mo KR radiation (λ ) 0.71073 Å).
Crystals used for X-ray crystallographic analysis were ce-
mented onto a quartz fiber with epoxy glue. Data were
measured using omega scans of 0.3° per frame such that a
hemisphere (1271 frames) was collected. No decay was indi-
cated for either data set by the re-collection of the first 50
frames at the end of each data collection. The frames were
integrated with the Bruker SAINT software package using a
narrow-frame integration algorithm,21 which also corrects for
the Lorentz and polarization effects. Absorption corrections
were applied using SADABS supplied by George Sheldrick.
(21) SAINT V 6.035 Software for the CCD Detector System; Bruker-
AXS Inc., 1999.

738 Organometallics, Vol. 21, No. 4, 2002
Ren
Ta ble 3. Cr ysta l Da ta for Com p ou n d s 2a a n d 3b
revealed by direct methods. In both cases, the asymmetric unit
contains one diruthenium molecule. The methyl carbon atoms
of the SiMe3 group in 2a are disordered over two positions and
were refined with occupancy and distance constraints. The H6
atom in 3b, the terminal hydrogen of the butadiynyl ligand,
was located from the difference map and refined freely, while
the positions of all other hydrogen atoms were calculated. Both
structures were refined to convergence by least-squares method
on F2, SHELXL-93, incorporated in SHELXTL.PC V 5.03.
Relevant information on the data collection and the figures of
merit of final refinement are listed in Table 3.
2a
3b
formula
fw
space group
a, Å
b, Å
c, Å
C
62H66N8Si2Ru2
C53H46N8SiRu2
1025.2
P21/c (No. 14)
14.203(1)
14.954(1)
22.605(1)
90
93.576(1)
90
4791.6(5)
4
1181.6
P1h (No. 2)
10.533(1)
16.089(2)
19.641(2)
69.229(2)
88.810(2)
72.410(2)
2952.5(6)
2
1.329
0.597
0.71073
27
R, deg
â, deg
γ, deg
V, Å3
Z
Ack n ow led gm en t. The generous support from both
the University of Miami (start-up fund and the funding
for the CCD-diffractometer) and the Petroleum Re-
search Fund/ACS(36595-AC3) is gratefully acknowl-
edged. The author thanks Mr. G.-L. Xu for recording
NMR and IR spectra and Professor A. Kaifer for
insightful discussions about electrochemistry. Interest
in dissymmetric alkynyl adducts was stimulated by the
comment from an anonymous reviewer of our earlier
manuscript (ref 8).
F
calc., g cm-3
1.421
0.700
0.71073
27
µ, mm-1
λ(Mo KR), Å
T, °C
no. of reflns
collected
15 686
25 242
no. of ind reflns
10 270 [R(int) )
0.0246]
8428 [R(int) )
0.0238]
final R indices
[I>2σ(I)]
R1 ) 0.0481,
wR2 ) 0.0969
R1 ) 0.0282,
wR2 ) 0.0594
The structures were solved and refined using the Bruker
SHELXTL (Version 5.1) software package in the space groups
P1h and P21/c for crystals 2a and 3b, respectively.22-24 Positions
of all non-hydrogen atoms of diruthenium moieties were
Su p p or tin g In for m a tion Ava ila ble: Tables of all atomic
positional and equivalent isotropic displacement parameters,
anisotropic displacement parameters, all bond distances and
bond angles, and torsion angles of compounds 2a and 3b, and
tables of scan-rate dependence of voltammetric data of com-
pounds 3a /b and 4. This material is available free of charge
via the Internet at http://pubs.acs.org.
(22) SHELXTL 5.03 (WINDOW-NT Version), Program library for
Structure Solution and Molecular Graphics; Bruker-AXS Inc., 1998.
(23) Sheldrick, G. M. SHELXS-90, Program for the Solution of
Crystal Structures; University of Go¨ttigen: Germany, 1990.
(24) Sheldrick, G. M. SHELXL-93, Program for the Refinement of
Crystal Structures; University of Go¨ttigen: Germany, 1993.
OM0109004