Bis-adducts of substituted phenylethynyl on a Ru2(DMBA)4 core: Effect of donor/acceptor modifications

Article abstract of DOI:10.1021/om030401y

The reactions between arylethynes (either BuLi activated or Et₃N assisted) and Ru₂-(RDMBA)₄X₂, where RDMBA is either N,N′-dimethylbenzamidinate (R = H) or N,N′-dimethyl-m-methoxybenzamidinate (R = m-MeO) and X is either Cl^- or NO₃^-, resulted in the compounds Ru₂(RDMBA)₄(C≡CC₆H₄ Y)₂ (Y = H (1a,b), 4-NO₂ (2a,b), 4-CN (3a,b), 3-CN (4a,b), 4-NMe₂ (5a,b); R = H (a), m-MeO (b)). The single-crystal X-ray diffraction study of 1b and 2a revealed the linear alignment of the arylethynyl ligands along the Ru-Ru vector. All of the compounds display two Ru-based one-electron processes, an oxidation and a reduction, and their electrode potentials correlate linearly with the Hammett constants of substituent Y. Compounds 5a,b display an additional pair of one-electron processes attributed to the oxidation of 4-NMe₂ groups, on the basis of which an extensive electron delocalization along the metallayne backbone was inferred.

Full text of DOI:10.1021/om030401y

4118
Organometallics 2003, 22, 4118-4123
Bis-Ad d u cts of Su bstitu ted P h en yleth yn yl on a
Ru 2(DMBA)4 Cor e: Effect of Don or /Accep tor
Mod ifica tion s
Stephanie K. Hurst, Guo-Lin Xu, and Tong Ren*
Department of Chemistry, University of Miami, Coral Gables, Florida 33124
Received May 29, 2003
The reactions between arylethynes (either BuLi activated or Et3N assisted) and Ru2-
(RDMBA)4X2, where RDMBA is either N,N′-dimethylbenzamidinate (R ) H) or N,N′-
dimethyl-m-methoxybenzamidinate (R ) m-MeO) and X is either Cl- or NO3-, resulted in
the compounds Ru2(RDMBA)4(CtCC6H4Y)2 (Y ) H (1a ,b), 4-NO2 (2a ,b), 4-CN (3a ,b), 3-CN
(4a ,b), 4-NMe2 (5a ,b); R ) H (a ), m-MeO (b)). The single-crystal X-ray diffraction study of
1b and 2a revealed the linear alignment of the arylethynyl ligands along the Ru-Ru vector.
All of the compounds display two Ru-based one-electron processes, an oxidation and a
reduction, and their electrode potentials correlate linearly with the Hammett constants of
substituent Y. Compounds 5a ,b display an additional pair of one-electron processes attributed
to the oxidation of 4-NMe2 groups, on the basis of which an extensive electron delocalization
along the metallayne backbone was inferred.
In tr od u ction
between electrode potentials of metal-based redox pro-
cesses and the Hammett constants (σ) of the phenyl
substituent on DArF ligands, and both the optical and
structuralfeatures wereunaltered bythesubstituents.10-12
Similar results were found for the series of Rh2(DArF)4
compounds and Ru2(DArF)4 compounds bearing either
chloroor phenylethynylaxialligands in our laboratory,13-16
Re2(DArF)4Cl2 and Cr2(DArF)4 compounds in the labor-
atory of Eglin,17,18 and Ru2(X-ap)4Cl compounds (X-ap
) substituted 2-anilinopyridinates) in the laboratory of
Bear and Kadish.19 It was concluded that the phenyl
substitution of the bridging ligands imparts an inductive
effect on the dinuclear core.20 The significance of sub-
stituent effects in the chemistry of transition-metal
complexes of both alkynyl and other unsaturated carbon
ligands such as allenylidene and cumulenylidene is also
well documented.21,22 For example, the presence of
strong donor or acceptor groups has been a hallmark of
mononuclear complexes with enhanced nonlinear optical
properties.23
Dinuclear paddlewheel species continue to attract
significant attention, due to the diversity in both metal
centers and bridging ligands, as well as their interesting
electrochemical, magnetic, and other properties.1,2 Facile
electron delocalizations between dinuclear units linked
via a π-delocalized framework have been demonstrated
by the laboratories of Cotton,3 Bursten and Chisholm,4,5
and Ren,6,7 revealing the possibility of realizing molec-
ular electronic wires based on these paddlewheel spe-
cies.8,9 To achieve this goal, the ability to precisely
control the electronic properties of paddlewheel species
is crucial. Previously, substituent effects in paddlewheel
species were explored in our laboratory on a series of
M2(DArF)4 compounds with M ) Mo, Ni, Ru, Rh and
DArF ) diarylformamidinate.10-16 Initial studies of Mo2
and Ni2 series revealed that there is a linear correlation
* To whom correspondence should be addressed. E-mail: tren@
miami.edu. Tel: (305) 284-6617. Fax: (305) 284-1880.
(1) Cotton, F. A.; Walton, R. A. Multiple Bonds between Metal Atoms;
Oxford University Press: Oxford, U.K., 1993.
(2) Cotton, F. A.; Lin, C.; Murillo, C. A. Acc. Chem. Res. 2001, 34,
759 and references therein.
We reported recently the synthesis of Ru2(DMBA)4-
Cl2 and its reactions with lithiated alkynyls to yield Ru2-
(DMBA)4(C2R)2 (R ) H, SiMe3, C2SiMe3, C2H, Ph).24 The
(3) Cotton, F. A.; Donahue, J . P.; Murillo, C. A. J . Am. Chem. Soc.
2003, 125, 5436.
(4) Bursten, B. E.; Chisholm, M. H.; Clark, R. J . H.; Firth, S.; Hadad,
C. M.; MacIntosh, A. M.; Wilson, P. J .; Woodward, P. M.; Zaleski, J .
M. J . Am. Chem. Soc. 2002, 124, 3050.
(5) Bursten, B. E.; Chisholm, M. H.; Clark, R. J . H.; Firth, S.; Hadad,
C. M.; Wilson, P. J .; Woodward, P. M.; Zaleski, J . M. J . Am. Chem.
Soc. 2002, 124, 12244.
(14) Lin, C.; Ren, T.; Valente, E. J .; Zubkowski, J . D. J . Chem. Soc.,
Dalton Trans. 1998, 571.
(15) Lin, C.; Ren, T.; Valente, E. J .; Zubkowski, J . D. J . Organomet.
Chem. 1999, 579, 114.
(16) Ren, T.; Lin, C.; Valente, E. J .; Zubkowski, J . D. Inorg. Chim.
Acta 2000, 297, 283.
(6) Ren, T.; Zou, G.; Alvarez, J . C. Chem. Commun. 2000, 1197.
(7) Xu, G.-L.; Zou, G.; Ni, Y.-H.; DeRosa, M. C.; Crutchley, R. J .;
Ren, T. J . Am. Chem. Soc. 2003, 125, 10057.
(8) Paul, F.; Lapinte, C. Coord. Chem. Rev. 1998, 178-180, 431.
(9) Ren, T.; Xu, G.-L. Comments Inorg. Chem. 2002, 23, 355.
(10) Lin, C.; Protasiewicz, J . D.; Smith, E. T.; Ren, T. J . Chem. Soc.,
Chem. Commun. 1995, 2257.
(11) Lin, C.; Protasiewicz, J . D.; Ren, T. Inorg. Chem. 1996, 35, 7455.
(12) Lin, C.; Protasiewicz, J . D.; Smith, E. T.; Ren, T. Inorg. Chem.
1996, 35, 6422.
(13) Lin, C.; Ren, T.; Valente, E. J .; Zubkowski, J . D.; Smith, E. T.
Chem. Lett. 1997, 753.
(17) Carlson-Day, K. M.; Eglin, J . L.; Lin, C.; Smith, L. T.; Staples,
R. J .; Wipf, D. O. Polyhedron 1999, 18, 817.
(18) Eglin, J . L.; Lin, C.; Ren, T.; Smith, L.; Staples, R. J .; Wipf, D.
O. Eur. J . Inorg. Chem. 1999, 2095.
(19) Kadish, K. M.; Wang, L.-L.; Thuriere, A.; Caemelbecke, E. V.;
Bear, J . L. Inorg. Chem. 2003, 42, 834.
(20) Ren, T. Coord. Chem. Rev. 1998, 175, 43.
(21) Bruce, M. I. Chem. Rev. 1998, 98, 2797.
(22) Bruce, M. I. Coord. Chem. Rev. 1997, 166, 91.
(23) Whittall, I. R.; McDonagh, A. M.; Humphrey, M. G.; Samoc,
M. Adv. Organomet. Chem. 1999, 43, 349.
(24) Xu, G. L.; Campana, C.; Ren, T. Inorg. Chem. 2002, 41, 3521.
10.1021/om030401y CCC: $25.00 © 2003 American Chemical Society
Publication on Web 08/23/2003

Bis-Adducts of Phenylethyls on a Ru2(DMBA)4 Core
Organometallics, Vol. 22, No. 20, 2003 4119
Ch a r t 1. Str u ctu r e of Bis(p h en yleth yn yl) Ad d u cts
on th e Ru 2(DMBA)4 Cor e a n d Th eir Design a tion s
F igu r e 1. ORTEP plot of 1b with ellipsoids at the 30%
probability level.
ease of alkynyl adduct formation at the Ru2(DMBA)4
core prompts us to consider its utility as the platform
for the exploration of substituent electronic effects.
Reported herein are the synthesis and characterization
of the bis-adducts of substituted phenylethynyl (YC6-
H4CtC-) on both Ru2(DMBA)4 and its derivative Ru2-
(mMeODMBA)4 cores with their numerical designations
defined in Chart 1.
Resu lts a n d Discu ssion
Syn th esis a n d Ch a r a cter iza tion of σ-Alk yn yl
Com p lexes. Synthesis of compound 1a via the reaction
between Ru2(DMBA)4Cl2 and LiC2Ph was reported
previously.24 However, the utility of lithiated alkynyl
became less effective with phenylethynes bearing func-
tional groups such as -NO2 and -CN. For example, Pt2-
(µ-dppm)2(CtCC6H4-4-NO2)4 was prepared from Pt-
(P,P′-dppm)Cl2 and LiCtCC6H4-4-NO2 in only 21%
yield.25 We found that the newly reported complexes
Ru2(DMBA)4(NO3)2 and Ru2(DMBA)4(BF4)2 readily re-
acted with unactivated alkynes in the presence of Et3N
at room temperature to yield the desired alkynyl
derivatives:26
F igu r e 2. ORTEP plot of 2a with ellipsoids at the 30%
probability level.
current case, since the presence of four N-methyl groups
will likely block the formation of a η2-HCtCR adduct
on the Ru2 core. Instead, the reaction may proceed via
simple anion metathesis.
The new compounds (1b and 2-5) were characterized
by combustion analysis, FAB mass spectrometry, 1H
NMR, visible-near-infrared (vis-near-IR), and IR spec-
troscopic techniques. The IR spectra generally display
characteristic ν(CtC) bands around 2070 cm-1, ac-
companied by a ν(CtN) band between 2217 and 2226
cm-1 in compounds 3 and 4. The vis-near-IR spectra
feature two intense absorption bands around ca. 515 and
883 nm, which are similar to the spectra reported for
the series of Ru2(DMBA)4(CtCR)2 compounds with R
) SiMe3, C2SiMe3.24 All the compounds reported herein
are diamagnetic, with well-resolved 1H NMR spectra,
and the protons of the arylethynyl ligands can be
unambiguously assigned in most cases.
Molecular structures of both compounds 1b and 2a
determined via X-ray diffraction studies are shown in
Figures 1 and 2, respectively, and the selected bond
lengths and angles are collected in Table 1. Both
molecules adopt the paddlewheel motif, and their gen-
eral features are very similar to those reported earlier
for Ru2(DMBA)4(C2R)2 with R ) SiMe3, C2H.24 The
coordination spheres of the Ru centers can be described
as pseudo-octahedral with four N centers from DMBA
occupying the equatorial positions and the other Ru
center and the alkynyl assuming two axial positions.
The Ru-Ru bond length in 1b (2.448(1) Å) is clearly
Ru2(DMBA)4(NO3)2 + 2HC2R Et N, THF, room temp8
3
-(Et3NH)NO3
Ru2(DMBA)4(C2R)2
Under these conditions, compounds 1-4 formed in
quantitative yields (monitored by thin-layer-chroma-
tography), and workups were fairly straightforward.
However, compounds 5a ,b could not be obtained simi-
larly. Instead, they were prepared using the appropriate
lithiated alkynyl. Alkynylation of a mononuclear Ru
complex by 1-alkyne under weakly basic conditions is a
well-established reaction, and the mechanism may
involve the formation of a Ru-(η2-HCtCR) intermedi-
ate and its subsequent conversion to a Ru-vinylidene
moiety.27 This mechanism may not be operative in the
(25) Yam, V. W. W.; Hui, C. K.; Wong, K. M. C.; Zhu, N. Y.; Cheung,
K. K. Organometallics 2002, 21, 4326.
(26) Xu, G.-L.; J ablonski, C. G.; Ren, T. Inorg. Chim. Acta 2003,
343, 387.
(27) Bruce, M. I. Chem. Rev. 1991, 91, 197.

4120 Organometallics, Vol. 22, No. 20, 2003
Hurst et al.
Ta ble 1. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for Molecu les 1b a n d 2a
1b
2a
Ru-Ru′
2.4478(9)
2.058(5)
2.036(5)
2.023(5)
2.052(5)
1.996(7)
1.20(1)
Ru-Ru′
2.459(1)
1.980(5)
2.028(5)
2.137(5)
2.015(5)
1.982(7)
1.190(9)
Ru-N(1)
Ru-N(2)
Ru-N(3)
Ru-N(4)
Ru-C(1)
C(1)-C(2)
Ru-N(2)
Ru-N(3)
Ru-N(4)
Ru-N(5)
Ru-C(1)
C(1)-C(2)
N(1)-Ru-Ru
N(2)-Ru-Ru
N(3)-Ru-Ru
N(4)-Ru-Ru
C(1)-Ru-Ru′
C(2)-C(1)-Ru
84.6(1)
88.6(1)
88.8(1)
84.9(1)
175.1(2)
177.5(6)
N(2)-Ru-Ru′
N(3)-Ru-Ru′
N(4)-Ru-Ru
N(5)-Ru-Ru′
C(1)-Ru-Ru′
C(2)-C(1)-Ru
94.7(2)
86.8(1)
78.5(1)
86.5(1)
165.5(2)
176.3(7)
Ta ble 2. Electr od e P oten tia ls a n d Rela ted Da ta
Deter m in ed u sin g CV for Com p ou n d s 1-5
a
compd
σY
E
1/ 2(A)/V, ∆E/V, ib/ifb
E
1/ 2(B)/V, ∆E/V, ib/ifb
1a c
1b
2a
2b
3a
3b
4a
4b
5a
5b
0
0
0.52, 0.058, 0.89
0.51, 0.058, 0.93
0.69, 0.069, 0.99
0.70, 0.067, 0.93
0.65, 0.065, 0.89
0.66, 0.065, 0.87
0.62, 0.063, 0.89
0.63, 0.066, 0.91
0.31, 0.066, 0.95
0.29, 0.069, 0.88
-1.10, 0.057, 0.79
-1.10, 0.062, 0.80
-0.87, 0.073, 0.92
-0.86, 0.074, 0.68
-0.92, 0.060, 0.93
-0.94, 0.062, 0.98
-0.98, 0.064, 0.93
-0.98, 0.068, 0.99
-1.17d
0.81
0.81
0.70
0.70
0.62
0.62
-0.83
-0.83
F igu r e 3. Cyclic voltammograms of complexes n a (n )
2-5) recorded in a 0.20 M THF solution of Bu4NPF6 at a
scan rate of 100 mV/s.
-1.21d
0.90 V, respectively, which are clearly due to the
sequential oxidations of two 4-NMe2 groups.31
Taken from ref 32. ib/if ) ibackward/iforward
Epc, irreversible process.
.
c Taken from ref 24.
a
b
d
It is clear from Figure 3 that the electrode potentials
for both the oxidation (A) and reduction couples (B) shift
cathodically as the electron-withdrawing power of phen-
ylethyne substituents decreases (NO2 > CN > H >
NMe2). This trend can be further quantified by fitting
the plot of electrode potentials versus the Hammett
constant of substituent Y (σY) according to the following
shorter than that in 2a (2.459(1) Å), while the Ru-C
distance in 1b is slightly longer than that in 2a . As
discussed previously,9 the lengthening of the Ru-Ru
bond in bis-alkynyl adducts is generally attributed to
the formation of a strong σ(Ru-C) bond, which polarizes
equation:32
E1/2(Y) ) E1/2(H) + F(2σY), where F is the
2
the dz orbital toward the C center. The strong acceptor
reactivity constant. Both the plot and fit for compounds
n a (n ) 1-5) are shown in Figure 4, and the reactivity
constants are 110 and 86 mV for the oxidation (F(A))
and reduction (F(B)) processes, respectively. While the
linear fit of oxidation potentials yields an excellent
correlation coefficient (R ) 99.5%), the linear fit of
reduction potentials is of marginal quality (R ) 95%),
which is mainly due to the irreversibility of the reduc-
tion couple of compound 5a . Similar reactivity constants
(F(A) ) 121 mV and F(B) ) 97 mV) were obtained for
compounds n b (n ) 1-5), and the least-squares plots
are provided in the Supporting Information (Figure S2).
Comparison of both the F and electrode potentials in
Table 2 between n a and n b series reveals that the redox
processes associated with the Ru2 core are relatively
insensitive to the presence of substituents on the phenyl
ring of DMBA ligands. Such a substituent independence,
although surprising, can be explained by the fact that
the phenyl group of the DMBA ligand is always far from
being coplanar with the amidine group, due to the
nature of 4-NO2 groups in 2a further enhances this
effect. The ligand arrangement around the Ru2 core in
2a deviates significantly from the idealized D4 sym-
metry, an effect commonly observed for trans-Ru2(L)4-
(C2Y)2 complexes and attributed to second-order J ahn-
Teller distortion.14 Interestingly, the deviation is negligi-
ble in 1b.
Electr och em ica l Stu d ies. The results of cyclic vol-
tammetric (CV) measurements of the ruthenium alkynyl
compounds 1-5 are summarized in Table 2. Previous
work with diruthenium metallaynes revealed rich redox
characteristics,9 and the compounds described here are
no exception. Compounds 1-5 generally feature two
one-electron Ru2-based couples: an oxidation (A), and
a reduction (B), as shown by both the CVs of compounds
n a (n ) 2-5) in Figure 3 and those of n b provided in
the Supporting Information. Both the oxidation and
reduction couples are (quasi)reversible in compounds
1-4, as evidenced by both small ∆E values and a near-
unity ibackward/iforward ratio. The reduction couples in
compounds 5a ,b are irreversible, and the irreversibility
is indicative of alkynyl dissociation upon reduction.24
Compounds 2a ,b also feature a second reduction around
-1.29 V (C in the CV of 2a ), which is attributed to the
reduction of the 4-NO2 group on the basis of comparison
with previous work.28-30 Compounds 5a ,b, on the other
hand, feature two additional oxidations at ca. 0.70 and
(28) Hurst, S. K.; Cifuentes, M. P.; Morrall, J . P. L.; Lucas, N. T.;
Whittall, I. R.; Humphrey, M. G.; Asselberghs, I.; Persoons, A.; Samoc,
M.; Luther-Davies, B.; Willis, A. C. Organometallics 2001, 20, 4664.
(29) Yam, V. W. W.; Fung, W. K. M.; Cheung, K. K. Organometallics
1998, 17, 3293.
(30) Wu, I. Y.; Lin, J . T.; Luo, J .; Li, C. S.; Tsai, C.; Wen, Y. S.; Hsu,
C. C.; Yeh, F. F.; Liou, S. Organometallics 1998, 17, 2188.
(31) Denis, R.; Toupet, L.; Paul, F.; Lapinte, C. Organometallics
2000, 19, 4240.
(32) Hansch, C.; Leo, A.; Taft, R. W. Chem. Rev. 1991, 91, 165.

Bis-Adducts of Phenylethyls on a Ru2(DMBA)4 Core
Organometallics, Vol. 22, No. 20, 2003 4121
the differential pulse voltammogram of 5a (Figure 5)
as 0.20 V. Considering the fact that two NMe2 groups
are separated by over 20.0 Å (estimated from the
structural data of 2a ), such a coupling strength is
remarkable. In comparison, a ∆E value of 60 mV was
reported for a bis(triarylamine) bridged by an organic
linker over a distance of 19.3 Å.35 The large ∆E value
determined for 5a reveals the exceptional ability of the
Ru2 metallayne in mediating electron delocalization.
Unfortunately, the instabilities of the oxidized species
preclude probing the intervalence charge-transfer tran-
sition to provide more insight into the electron delocal-
ization in the mixed-valence species.
Con clu sion s
Alkynylation under weak base conditions adds a new
dimension to the research of dinuclear alkynyl com-
pounds and can be a powerful method to introduce other
functionalized alkynes. Both the linear E1/2-σY correla-
tion and large reactivity constants for the Ru2-based
processes revealed the feasibility of achieving significant
modulation of electronic structures of metallaynes
through the substitution on axial phenylethynyls. We
are currently investigating the synthesis of polar
DC6H4CtC-Ru2-CtCC6H4A type compounds (D and
A are donor and acceptor substituents, respectively),
which are similar to the molecular diode proposed by
Ratner and Aviram.36
F igu r e 4. Hammett plot of E1/2 vs 2σ. The crosses (×) are
the measured values of E1/2(B), circles (O) are the measured
values of E1/2(A), and the solid lines are the least-squares
fit.
Exp er im en ta l Section
Gen er a l Con d ition s, Rea gen ts, a n d In str u m en ts. n-
BuLi was purchased from Aldrich, PhCtCH from Acros, and
silica gel from Merck. Ru2(DMBA)4Cl2,24 Ru2(m-MeODMBA)4-
Cl2,37 Ru2(DMBA)4(NO3)2 and Ru2(m-MeODMBA)4(NO3)2,26 and
4-NO2-C6H4CtCH and 3-/4-CN-C6H4CtCH38 were prepared
as previously described. 4-Me2NC6H4I was prepared via the
method of Fabbrini et al.39 and converted to 4-Me2NC6H4Ct
CH by the standard method. THF and hexanes were distilled
over Na/benzophenone under a N2 atmosphere prior to use.
Infrared spectra were recorded on a Perkin-Elmer 2000 FT-
IR spectrometer using KBr disks. Absorption spectra were
obtained with a Perkin-Elmer Lambda-900 UV-vis-near-IR
F igu r e 5. Differential pulse voltammogram of compound
5a in the anodic region recorded in a 0.20 M THF solution
of Bu4NPF6 at a scan rate of 4 mV/s.
presence of N-methyl groups, which effectively elimi-
nates the propagation of electronic effect through con-
jugation.
The reactivity constants obtained for compounds 1-5
are comparable to the largest obtained for the M2-
(DArF)4 series,20 which is truly remarkable, considering
that the substituted phenyl is only two bonds away from
the M2 center in the latter but three bonds away from
the Ru2 center in compounds 1-5. The enhanced
response to the substituent in compounds 1-5 indicates
that the π-conjugation along the Ph-CtC-Ru2 back-
bone is extensive. Lapinte et al. reported the study of a
comprehensive series of Cp*Fe(dppe)(C2C6H4-4-Y) com-
pounds with Y ) NO2, CN, CF3, F, Br, H, Me, tBu, OMe,
spectrophotometer. 1H NMR spectra were recorded on
a
Bruker AVANCE 300 NMR spectrometer with chemical shifts
(δ) referenced to the residual CHCl3. Cyclic and differential
pulse voltammograms were recorded in 0.2 M [NBu4]PF6
solution (THF, N2-degassed) on a CHI620A voltammetric
analyzer with a glassy-carbon working electrode (diameter 2
mm), a Pt-wire auxiliary electrode, and a Ag/AgCl reference
electrode. The concentration of diruthenium species was
always 1.0 mM. The ferrocenium/ferrocene couple was ob-
served at 0.595 V (vs Ag/AgCl) under these experimental
conditions. Elemental analysis was performed by Atlantic
Microlab, Norcross, Georgia.
NH2, NMe2.31,33,34 While a large range in E°(Fe3+/Fe2+
)
was observed, the electrode potentials do not correlate
with σY at all, and the lack of correlation was attributed
to the coexistence of several canonical structures.
The stepwise appearance of 4-NMe2 oxidation waves
(D and E) in 5a indicates that the mixed-valence species
generated by the second oxidation (D) is delocalized.
Although the separation between D and E could not be
determined from the CV, it is readily determined from
[Ru 2(m-MeODMBA)4(CtCP h )2] (1b). Ru2(m-MeODMBA)4-
(NO3)2 (134 mg, 0.129 mmol) was suspended in 20 mL of THF,
to which were added HCtCPh (104 mg, 1.02 mmol) and NEt3
(5 mL). After the mixture was stirred for 20 h under argon,
the solvent was removed under reduced pressure. The residue
(35) Lambert, C.; No¨ll, G. J . Am. Chem. Soc. 1999, 121, 8434.
(36) Aviram, A.; Ratner, M. A. Chem. Phys. Lett. 1974, 29, 277.
(37) Xu, G.-L.; J ablonski, C. G.; Ren, T. J . Organomet. Chem., in
press.
(33) Paul, F.; Mevellec, J .-Y.; Lapinte, C. J . Chem. Soc., Dalton
Trans. 2002, 1783.
(34) Paul, F.; Costuas, K.; Ledoux, I.; Deveau, S.; Zyss, J .; Halet,
J .-F.; Lapinte, C. Organometallics 2002, 21, 5229.
(38) Takahashi, S.; Kuriyama, Y.; Sonogashira, K.; Hagihara, N.
Synthesis 1980, 627.
(39) Fabbrini, M.; Galli, C.; Gentili, P.; Macchitella, D.; Petride, H.
J . Chem. Soc., Perkin Trans. 2 2001, 1516.

4122 Organometallics, Vol. 22, No. 20, 2003
Hurst et al.
was loaded onto a silica gel column deactivated by 10% Et3N
in hexanes and eluted with ethyl acetate-hexanes-Et3N (30/
70/5, v/v), giving pure 1b as a deep red material. Yield: 103
mg (72% based on Ru). Data for 1b are as follows. Rf 0.41 (ethyl
acetate-hexanes-Et3N, 20/70/10, v/v; the same combination
is also used for the determination of other Rf’s). Anal. Found
(calcd) for C56H62N8O4Ru2: C, 60.65 (60.42); H, 5.49 (5.61); N,
10.07 (9.98). MS-FAB (m/e, based on 101Ru): 1114 [MH+]. UV-
vis (λmax, nm (ꢀ, M-1 cm-1)): 874 (1500), 500 (9500). IR (cm-1):
H, 5.01 (5.02); N, 12.98 (13.43). MS-FAB (m/e, based on
101Ru): 1046 [(MH)+]. UV-vis (λmax, nm (ꢀ, M-1 cm-1)): 860
(2600), 502 (13 700). IR (cm-1): ν(CtC), 2073 (m); ν(CtN),
2226 (w). Electrochemistry (E1/2, V; ∆Ep, V; ibackward/iforward): A,
0.63, 0.063, 0.89; B, -0.98, 0.064, 0.93. 1H NMR (CDCl3):
7.80-6.90 (28H, C6H4 + Ph), 3.25 (24H, NMe).
[Ru 2(m -MeODMBA)4(CtC-3-C6H4CN)2] (4b). The syn-
thesis is similar to that of 1b, with PhCtCH being replaced
by 3-CN-C6H4CtCH. Yield: 64%. Data for 4b are as follows.
Rf 0.26. Anal. Found (calcd) for C58H60N10O4Ru2‚CH2Cl2 (4b‚CH2-
Cl2): C, 56.68 (56.73); H, 5.03 (4.97); N, 11.03 (11.22). MS-
FAB (m/e, based on 101Ru): 1165 [(MH)+]. UV-vis (λmax, nm
(ꢀ, M-1 cm-1)): 857 (2600), 500 (14 100). IR (cm-1): ν(CtC),
2071 (m); ν(CtN), 2226 (w). Electrochemistry (E1/2, V; ∆Ep,
V; ibackward/iforward): A, 0.63, 0.066, 0.91; B, -0.98, 0.068, 0.99.
1H NMR (CDCl3, δ): 7.40-6.45 (4H, C6H4 + Ph), 3.80 (12H,
OMe), 3.26 (24H, NMe).
ν(CtC), 2071 (w). Electrochemistry (E1/2, V; ∆Ep, V; ibackward
i
/
forward): A, 0.51, 0.058, 0.93; B, -1.10, 0.062, 0.80. 1H NMR
(CDCl3, δ): 7.80-6.40 (26H, Ph), 3.81 (12H, OMe), 3.25 (24H,
NMe).
[Ru 2(DMBA)4(CtC-4-C6H4NO2)2] (2a ). Ru2(DMBA)4(NO3)2
(81.3 mg, 0.089 mmol) was suspended in 20 mL of THF, to
which were added HCtC-4-C6H4NO2 (52.5 mg, 0.357 mmol)
and NEt3 (5 mL). The solution changed from dark green to
red immediately upon the addition of the alkyne. After the
mixture was stirred overnight under argon, the solution was
filtered through a plug of deactivated silica, which was rinsed
with CH2Cl2. The solvent was removed under reduced pres-
sure, and the resulting solid was triturated with hexanes to
yield pure 2a as a deep red material. Yield: 91 mg (94% based
on Ru). Data for 2a are as follows. Rf 0.65. Anal. Found (calcd)
for C52H52N10O4Ru2‚C6H14‚0.5CH2Cl2: C, 58.22 (57.98); H, 5.53
(5.57); N, 11.40 (11.56). MS-FAB (m/e, based on 101Ru): 1084
[MH+]. UV-vis (λmax, nm (ꢀ, M-1 cm-1)): 859 (1820), 528
[Ru 2(DMBA)4(CtC-4-C6H4NMe2)2] (5a ). Ru2(DMBA)4Cl2
(101 mg, 0.117 mmol) was dissolved in 20 mL of THF, to which
was added LiCtC-4-C6H4NMe2 (0.45 mmol) prepared in situ
from HCtC-4-C6H4NMe2 and n-BuLi. The solution changed
from brown to dark red immediately upon the addition of the
lithiated alkyne. After the mixture was stirred overnight under
argon, the solvent was removed under reduced pressure. The
residue was placed on a sintered funnel and washed with cold
hexanes to give pure 5a as a purple material. Yield: 40 mg
(32%). Data for 5a are as follows. Rf 0.66. Anal. Found (calcd)
for C56H64N10Ru2‚2CH2Cl2‚H2O (5a ‚2CH2Cl2‚H2O): C, 54.55
(54.93); H, 5.25 (5.52); N, 10.87 (11.05). MS-FAB (m/e, based
on 101Ru): 1080 [MH+]. UV-vis (λmax, nm (ꢀ, M-1 cm-1)): 890
(2100), 511 (12 700). IR (cm-1): ν(CtC), 2078 (m). Electro-
chemistry (E1/2, V; ∆Ep, V; ibackward/iforward): A, 0.31, 0.066, 0.95;
B, -1.17, 0.070, 0.41. 1H NMR (CDCl3, δ): 7.45-7.33 (12H,
Ph), 7.00-6.95 (12H, C6H4 + Ph), 6.59 (J HH ) 9 Hz, 4H, C6H4),
3.28 (24H, NMe), 2.88 (12H, NMe2).
(24 100). IR (cm-1): ν(CtC), 2060 (m). Electrochemistry (E1/2
V; ∆Ep, V; ibackward/iforward): A, 0.69, 0.069, 0.99; B, -0.83, 0.073,
,
1
0.92, C, -1.29, 0.116, 0.79. H NMR (CDCl3, δ): 8.03 (J HH
)
9 Hz, 4H, C6H4), 7.48-7.38 (12H, Ph), 7.12 (J HH ) 9 Hz, 4H,
C6H4), 7.01-6.94 (8H, Ph), 3.24 (24H, NMe).
[Ru 2(m -MeODMBA)4(CtC-4-C6H4NO2)2] (2b). The syn-
thesis is similar to that of 2a , with Ru2(DMBA)4(NO3)2 being
replaced by Ru2(MeO-m-DMBA)4(NO3)2. Yield: 74%. Data for
2b are as follows. Rf 0.30. Anal. Found (calcd) for C56H60N10O8-
Ru2: C, 55.65 (55.90); H, 5.22 (5.03); N, 11.13 (11.64). MS-
FAB (m/e, based on 101Ru): 1204 [MH+]. UV-vis (λmax, nm (ꢀ,
M-1 cm-1)): 855 (2500), 523 (34 600). IR (cm-1): ν(tCH), 2062
(m). Electrochemistry (E1/2, V; ∆Ep, V; ibackward/iforward): A, 0.70,
0.067, 0.93; B, -0.86, 0.074, 0.68, C, -1.29, 0.124, 0.64. 1H
NMR (CDCl3, δ): 8.03 (J HH ) 9 Hz, 4H, C6H4), 7.80-7.20 (4H,
Ph), 7.12 (J HH ) 9 Hz, 4H, C6H4), 7.00-6.40 (12H, Ph), 3.81
(12H, OMe), 3.26 (24H, NMe).
[Ru 2(DMBA)4(CtC-4-C6H4CN)2] (3a ). The synthesis is
similar to that of 2a , with 4-NO2-C6H4CtCH being replaced
by 4-CN-C6H4CtCH. Yield: 83%. Data for 3a are as follows.
Rf 0.61. Anal. Found (calcd) for C54H52N10Ru2: C, 61.09 (61.18);
H, 5.05 (5.36); N, 12.16 (12.41). MS-FAB (m/e, based on
101Ru): 1044 [MH+]. UV-vis (λmax, nm (ꢀ, M-1 cm-1)): 869
(2900), 504 (18 800). IR (cm-1): ν(CtC), 2070 (m). Electro-
chemistry (E1/2, V; ∆Ep, V; ibackward/iforward): A, 0.65, 0.065, 0.89;
B, -0.92, 0.060, 0.93. 1H NMR (CDCl3, δ): 7.50-7.35 (16H,
C6H4 + Ph), 7.10 (J HH ) 8 Hz, 4H, C6H4), 7.00-6.95 (8H, Ph),
3.25 (24H, NMe).
[R u 2(m -MeODMBA)4(CtC-4-C6H 4NMe2)2] (5b ). Ru2(m-
MeODMBA)4Cl2 (208 mg, 0.212 mmol) was dissolved in 25 mL
of THF, to which was added LiCtC-4-C6H4NMe2 (0.854 mmol)
prepared in situ from HCtC-4-C6H4NMe2 and n-BuLi. The
solution changed from brown to dark red immediately upon
the addition of the lithiated alkyne. After the mixture was
stirred for 1 h under argon, the solvent was removed under
reduced pressure. The residue was loaded onto a silica gel
column deactivated by 10% Et3N in hexanes and eluted with
ethyl acetate-hexanes-Et3N (30/70/5, v/v), giving pure 5b as
a deep red material. Yield: 86 mg (34%). The reduced yield is
due to slow decomposition of 5b on silica. Data for 5b are as
follows. Rf 0.15. Anal. Found (calcd) for C66.5H87N10O4ClRu2
(5b‚C6H14‚1/2CH2Cl2): C, 61.07 (60.14); H, 6.74 (6.60); N, 10.07
(10.55). MS-FAB (m/e, based on 101Ru): 1200 [MH+]. UV-vis
(λmax, nm (ꢀ, M-1 cm-1)): 851 (1800), 504 (9800). IR (cm-1):
ν(CtC), 2075 (w). Electrochemistry (E1/2, V; ∆Ep, V; ibackward
i
/
forward): A, 0.29, 0.069, 0.88; B, -1.21, 0.00, 0.41. 1H NMR
(CDCl3, δ): 7.41 (J HH ) 8 Hz, 4H, C6H4), 7.40-7.30 (4H, Ph),
7.05 (J HH ) 8 Hz, 4H, C6H4), 7.00-6.40 (12H, Ph), 3.79 (12H,
OMe), 3.28 (24H, NMe), 2.86 (12H, NMe2).
[Ru 2(m -MeODMBA)4(CtC-4-C6H4CN)2] (3b). The syn-
thesis is similar to that of 2b, with PhCtCH being replaced
by 4-CN-C6H4CtCH. Yield: 54%. Data for 3b are as follows.
Rf 0.25. Anal. Found (calcd) for C58H60N10O4Ru2‚CH2Cl2 (3b‚CH2-
Cl2): C, 56.98 (56.73); H, 5.01 (4.97); N, 11.12 (11.22). MS-
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
1b and 2a were grown via slow evaporation of the fractions
from column purification. The X-ray intensity data were
measured at 300 K on a Bruker SMART1000 CCD-based X-ray
diffractometer system using Mo KR radiation (λ ) 0.710 73
Å). Crystals of dimension 0.58 × 0.46 × 0.23 mm3 (1b) and
0.39 × 0.13 × 0.06 mm3 (2a ) were cemented onto a quartz fiber
with epoxy glue for X-ray crystallographic analysis. Data were
FAB (m/e, based on 101Ru): 1162 [(M - H)+]. UV-vis (λmax
nm (ꢀ, M-1 cm-1)): 860 (2600), 479 (17 700). IR (cm-1): ν(Ct
C), 2066 (w). Electrochemistry (E1/2, V; ∆Ep, V; ibackward
forward): A, 0.66, 0.065, 0.87; B, -0.94, 0.062, 0.98. 1H NMR
,
/
i
(CDCl3, δ): 7.41 (J HH ) 8 Hz, 4H, C6H4), 7.40-7.30 (4H, Ph),
7.05 (J HH ) 8 Hz, 4H, C6H4), 7.00-6.45 (12H, Ph), 3.81 (12H,
OMe), 3.25 (24H, NMe).
measured using ω 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
[Ru 2(DMBA)4(CtC-3-C6H4CN)2] (4a ). The synthesis is
similar to that of 2a with 4-NO2-C6H4CtCH being replaced
by 3-CN-C6H4CtCH. Yield: 64%. Data for 4a are as follows.
Rf 0.63. Anal. Found (calcd) for C52H52N10Ru2: C, 61.53 (62.17);

Bis-Adducts of Phenylethyls on a Ru2(DMBA)4 Core
Organometallics, Vol. 22, No. 20, 2003 4123
narrow-frame integration algorithm,40 which also corrects for
the Lorentz and polarization effects. Absorption corrections
were applied using SADABS, supplied by George Sheldrick.
The structures of both 1b and 2a were solved and refined
using the Bruker SHELXTL (version 5.1) software package
in the space group C2/c.41-43 Positions of all non-hydrogen
atoms of diruthenium moieties were revealed by direct meth-
ods. In each case, the asymmetric unit contains half of the
diruthenium molecule, which is related to the other half via a
crystallographic 2-fold axis orthogonal to and bisecting the
Ru-Ru′ vector. One of the phenyl rings of the DMBA ligand
in 1b was severely disordered and consequently refined as a
rigid hexagon. With all non-hydrogen atoms being anisotropic
and all hydrogen atoms in calculated position and riding mode,
both structures were refined to convergence by least-squares
methods on F2, SHELXL-93, incorporated in SHELXTL.PC
version 5.03. Relevant information on the data collection and
the figures of merit of final refinement are listed in Table 3.
Ta ble 3. Cr ysta l Da ta for Com p ou n d s 1b a n d 2a
1b
2a ‚2CH2Cl2
formula
fw
C
56H62N8O4Ru2
C
54H56Cl4N10O4Ru2
1113.3
1253.0
space group
a, Å
b, Å
C2/c
C2/c
19.845(2)
15.222(2)
19.967(2)
116.806(3)
5383.6(9)
4
1.374
0.613
27
21.366(3)
18.020(3)
16.741(3)
115.581(2)
5814(2)
4
1.432
0.755
27
c, Å
â, deg
V, Å3
Z
F
calcd, g cm-3
µ, mm-1
T, °C
no. of rflns collected
no. of indep rflns
13 691
21 507
4740 (R(int) )
0.0763)
R1 ) 0.065,
wR2 ) 0.186
5107 (R(int) )
0.1162)
R1 ) 0.064,
wR2 ) 0.1372
final R indices
(I > 2σ(I))
No. CHE 0242623) for financial support. G.-L.X. thanks
the University of Miami for a Maytag Graduate Fel-
lowship.
Ack n ow led gm en t. We thank both the University
of Miami and the National Science Foundation (Grant
(40) SAINT V 6.035 Software for the CCD Detector System; Bruker-
AXS Inc., 1999.
(41) SHELXTL 5.03 (Windows NT Version), Program Library for
Structure Solution and Molecular Graphics; Bruker-AXS Inc., 1998.
(42) Sheldrick, G. M. SHELXS-90, Program for the Solution of
Crystal Structures; University of Go¨ttingen, Go¨ttingen, Germany,
1990.
(43) Sheldrick, G. M. SHELXL-93, Program for the Refinement of
Crystal Structures; University of Go¨ttingen, Go¨ttingen, Germany,
1993.
Su p p or tin g In for m a tion Ava ila ble: Tables of X-ray
crystallographic data and figures giving additional ORTEP
views for the structure determination of compounds 1b and
2a ; X-ray data are also available as electronic CIF files. This
material is available free of charge via the Internet at
http://pubs.acs.org.
OM030401Y