Postmetalation ligand modification on the periphery of a diruthenium compound: Toward novel metallayne scaffoldings

Article abstract of DOI:10.1021/om049702d

A diruthenium compound bearing a peripheral iodo substituent cross-couples with acetylenes under Sonogashira conditions to yield a novel family of diruthenium compounds bearing a peripheral alkyne functionality, which can be further functionalized at the axial positions via a reaction with lithiated butadiynyl.

Full text of DOI:10.1021/om049702d

3766
Organometallics 2004, 23, 3766-3768
P ostm eta la tion Liga n d Mod ifica tion on th e P er ip h er y of
a Dir u th en iu m Com p ou n d : Tow a r d Novel Meta lla yn e
Sca ffold in gs
Wei-Zhong Chen and Tong Ren*
Department of Chemistry and Center for Supramolecular Science, University of Miami,
Coral Gables, Florida 33146
Received April 26, 2004
Summary: A diruthenium compound bearing a periph-
eral iodo substituent cross-couples with acetylenes under
Sonogashira conditions to yield a novel family of diru-
thenium compounds bearing a peripheral alkyne func-
tionality, which can be further functionalized at the axial
positions via a reaction with lithiated butadiynyl.
Boosted by the immense interest in carbon-rich
materials such as fullerenes and carbon nanotubes,
there have been growing efforts in recent years in both
the synthesis of new metallaynes1 and their material
applications as nonlinear optical chromophores2 and
active species in molecular electronic devices.3 Equally
exciting is the possibility of using metallaynes as
scaffoldings for 2-D and 3-D carbon-rich networks that
may rival fullerene in both the beauty and diversity of
material properties.4 Our laboratory has reported a host
of diruthenium compounds bearing axial σ-ethynyl/
polyynyl ligands5 and demonstrated the facile electron
delocalization along the conjugated backbone.6 Ru2
metallaynes are both intense visible-near-infrared
chromophores and excellent electrophores with multiple
reversible redox couples over a broad potential window.5
Clearly of great interest is whether Ru2 metallaynes can
be (i) incorporated in 2- and 3-D supramolecular as-
semblies and (ii) used as the reporter group in chemical
and biochemical sensors. To achieve these objectives,
Ru2 metallaynes need to be functionalized in the direc-
tion(s) orthogonal to the Ru2-σ-alkynyl vector, and our
initial exploratory efforts are described in this contribu-
tion.
F igu r e 1. ORTEP representation of molecule 1 at the 30%
probability level. Selected bond lengths (Å): Ru1-Ru2,
2.3220(7); Ru1-Cl, 2.405(2).
(OAc)Cl type compounds (LL
) N,N′-diarylform-
amidinate). Ru2(DmAniF)3(OAc)Cl (1; DmAniF is
N,N′-bis(m-methoxyphenyl)formamidinate) was obtained
in 87% yield using a modification of the recently
published procedures,7 and its molecular structure is
provided in Figure 1. As shown in Scheme 1, the ace-
tate in compound 1 can be readily displaced with
N,N′-dimethyl-4-iodobenzamidinate (I-DMBA) to yield
Ru2II,III(DmAniF)3(I-DMBA)Cl (2). The presence of the
iodo substituent gives access to a variety of Pd-catalyzed
cross-coupling reactions.8 Hence, treating 2 with the
terminal alkynes HCtCY (Y ) SiiPr3, Fc) under Sono-
gashira conditions furnished compounds 3a ,b. To our
knowledge, the conversion of 2 to 3 is the first example
of postmetalation modification of a bridging ligand in a
paddle-wheel species by design. Compounds 3a ,b re-
acted with 3 equiv of LiC4SiMe3 to yield trans-bis-
(butadiynyl) derivatives 4a ,b analogous to the estab-
lished alkynylation chemistry of diruthenium com-
pounds.5 We also sought an alternative route to 4:
treating 2 with 3 equiv of LiC4SiMe3 resulted in trans-
Ru2III,III(DmAniF)3(I-DMBA)(C4SiMe3)2 (5; 46%). How-
ever, the reaction between 5 and HC2Y under Sono-
gashira conditions yielded a mixture of Ru2 compounds
Critical to the orthogonal functionalization of
Ru2-metallayne is the accessibility of the Ru2II,III(LL)3-
* To whom correspondence should be addressed. E-mail: tren@
miami.edu. Tel: (305) 284-6617. Fax: (305) 284-1880.
(1) (a) Low, P. J .; Bruce, M. I. Adv. Organomet. Chem. 2001, 48, 71.
(b) Manna, J .; J ohn, K. D.; Hopkins, M. D. Adv. Organomet. Chem.
1995, 38, 79. (c) Special Issues on Carbon Rich Organometallics: J .
Organomet. Chem. 2003, 683. (d) Szafert, S.; Gladysz, J . A. Chem. Rev.
2003, 103, 4175. (e) Bruce, M. I.; Low, P. J . Adv. Organomet. Chem.
2004, 50, 179.
(2) (a) Whittall, I. R.; McDonagh, A. M.; Humphrey, M. G.; Samoc,
M. Adv. Organomet. Chem. 1998, 42, 291. (b) Ibid. 1999, 43, 349.
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(5) (a) Ren, T.; Xu, G.-L. Comments Inorg. Chem. 2002, 23, 355. (b)
Hurst, S. K.; Ren, T. J . Organomet. Chem. 2003, 670, 188.
(6) (a) Ren, T.; Zou, G.; Alvarez, J . C. Chem. Commun. 2000, 1197.
(b) Xu, G.-L.; Zou, G.; Ni, Y.-H.; DeRosa, M. C.; Crutchley, R. J .; Ren,
T. J . Am. Chem. Soc. 2003, 125, 10057. (c) Xu, G.-L.; DeRosa, M. C.;
Crutchley, R. J .; Ren, T. J . Am. Chem. Soc. 2004, 126, 3728.
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Murillo, C. A.; Villagra´n, D. Inorg. Chem. Commun. 2004, 7, 9. (b)
Barral, M. C.; Herrero, S.; J ime´nez-Aparicio, R.; Torres, M. R.;
Urbanos, F. A. Inorg. Chem. Commun. 2004, 7, 42. (c) Ren, T.; DeSilva,
V.; Zou, G.; Lin, C.; Daniels, L. M.; Campana, C. F.; Alvarez, J . C.
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(8) (a) Metal-catalyzed Cross-coupling Reactions; Diederich, F.,
Stang, P. J ., Eds.; Wiley-VCH: Weinheim, Germany, 1998. (b) Brands-
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10.1021/om049702d CCC: $27.50 © 2004 American Chemical Society
Publication on Web 07/02/2004

Communications
Organometallics, Vol. 23, No. 16, 2004 3767
Sch em e 1a
a
i
Legend: (i) 2 equiv of N,N′-dimethyl-4-iodobenzamidine, LiCl, Et3N; 79%; (ii) HC2Y, trans-Pd(PPh3)2Cl2, CuI, Pr2NH, THF,
room temperature, yield 41% (3a ), 49% (3b); (iii) Bu4NF, THF; quantitative; (iv) 3 equiv of LiC4TMS, THF, yield 43% (4a ), 37%
(4b).
F igu r e 2. Cyclic voltammograms of compounds 1, 4a , and
5 recorded in a 0.20 M THF solution of Bu4NPF6 at a scan
rate of 0.10 V/s.
free of axial alkynyl ligands instead of 4. Clearly, the
axial Ru-butadiynyl bonds are unstable under Sono-
gashira conditions.
Similar to other Ru2(LL)3(OAc)Cl type compounds,7
F igu r e 3. ORTEP representation of molecule 4a at the
20% probability level. Selected bond lengths (Å): Ru1-Ru2,
2.5467(7); Ru1-C1, 1.976(6); Ru2-C8, 1.988(7); Ru-N(av-
eraged), 2.051[6].
compound 1 is purple. Compounds 2 and 3a ,b are green,
which is typical for Ru2(DArF)4Cl type compounds.9
Compounds 1-3 are paramagnetic, with effective mag-
netic moments corresponding to an S ) 3/2 ground state.
On the other hand, compounds 4a ,b and 5 are diamag-
netic and deep red, both being characteristics of trans-
Ru2(DArF)4(C2R)2 species (DArF is diarylformamidi-
nate).10 All compounds display at least three redox
couples (cyclic voltammograms of compounds 1-5 are
provided in the Supporting Information). As typified by
the CV of 1 in Figure 2, compounds of Ru2II,III(LL)3(LL′)-
Cl type (1-3; LL′ is either OAc or I-DMBA) exhibit a
one-electron oxidation (B) and two one-electron reduc-
tions (C and D). The first reduction of 1 is irreversible,
due to the fast dissociation of the axial Cl- ligand, and
the resultant Ru2(LL)3(LL′) species is reoxidized at a
Compounds 1-5 are generally crystalline, and the
molecular structures of 1, 4a , and 5 have been deter-
mined through X-ray diffraction studies.11 The struc-
tural plots of 4a and 5 are presented in Figures 3 and
4, respectively, along with some selected geometric
parameters. While the Ru-Ru bond is short in the
parent compound 1 (2.3220(7) Å), bis(butadiynyl) de-
rivatives 4a and 5 have significantly elongated Ru-Ru
(11) X-ray single-crystal data for crystals of 1, 4a , and 5 were
collected on a Bruker SMART1000 CCD diffractometer using Mo KR
radiation at 300 K. Crystal data for 1‚H2O: C47H48N6O9Ru2Cl, fw )
1078.50, triclinic, P1h, a ) 13.173(1) Å, b ) 15.358(1) Å, c ) 16.802(1)
Å, R ) 116.426(1)°, â ) 107.284(1)°, γ ) 96.207(1)°, V ) 2789.2(4) Å3,
Z ) 2, Dcalcd ) 1.284 g cm-3. Of 14 739 reflections measured, 9687 were
unique (Rint ) 0.040). Least-squares refinement based on 5913 reflec-
tions with I g 2σ(I) and 586 parameters led to convergence with final
R1 ) 0.065 and wR2 ) 0.189. Crystal Data for 4a : C79H93N8O6Ru2-
Si3, fw ) 1537.0, triclinic, P1h, a ) 15.375(2) Å, b ) 17.521(2) Å, c )
18.281(3) Å, R ) 80.35(1)°, â ) 82.95(1)°, γ ) 66.348(9)°, V ) 4439(1)
Å3, Z ) 2, Dcalcd ) 1.150 g cm-3. Of 28 565 reflections measured, 19 986
were unique (Rint ) 0.062). Least-squares refinement based on 7921
reflections with I g 2σ(I) and 876 parameters led to convergence with
final R1 ) 0.067 and wR2 ) 0.182. Crystal Data for 5: C68H73N8O6-
Ru2Si2I, fw ) 1483.6, monoclinic, P21/n, a ) 21.260(1) Å, b ) 10.406-
(1) Å, c ) 33.170(1) Å, â ) 107.811(1)°, V ) 6986.2(4) Å3, Z ) 4, Dcalcd
) 1.411 g cm-3. Of 44 520 reflections measured, 16 601 were unique
(Rint ) 0.071). Least-squares refinement based on 8316 reflections with
I g 2σ(I) and 784 parameters led to convergence with final R1 ) 0.053
and wR2 ) 0.078.
more positive potential (E).9b Similar to the previously
III,III
studied bis(alkynyl) Ru2
compounds,10 compounds
4 and 5 exhibit one irreversible oxidation (A) and
two reversible one-electron reductions (B and C), and
the latter reflect the robustness of Ru-C bonds upon
reduction.
(9) (a) Cotton, F. A.; Ren, T. Inorg. Chem. 1995, 34, 3190. (b) Lin,
C.; Ren, T.; Valente, E. J .; Zubkowski, J . D.; Smith, E. T. Chem. Lett.
1997, 753.
(10) (a) Xu, G.-L.; Ren, T. Inorg. Chem. 2001, 40, 2925. (b) Lin, C.;
Ren, T.; Valente, E. J .; Zubkowski, J . D. J . Chem. Soc., Dalton Trans.
1998, 571. (c) Bear, J . L.; Han, B.; Huang, S.; Kadish, K. M. Inorg.
Chem. 1996, 35, 3012. (d) Bear, J . L.; Han, B.; Huang, S. J . Am. Chem.
Soc. 1993, 115, 1175.

3768 Organometallics, Vol. 23, No. 16, 2004
Communications
outlined in Scheme 1 demonstrated the facile synthesis
of a series of novel Ru2 compounds 3-5, which may
provide a viable alternative in constructing supramol-
ecules. One can easily envision the formation of a linked
dimer through either the homocoupling of 3c under
Glaser conditions or cross-coupling between 2 and 3c
under Sonogashira conditions. Furthermore, the pres-
ence of the peripheral iodo substituent in compound 2
should enable both the functionalization of biological
macromolecules such as proteins and nucleic acids with
the diruthenium unit and incorporation of the diruthe-
nium unit into a dendrimer. These interesting aspects
are being vigorously pursued in our laboratory.
Ack n ow led gm en t. We are grateful to the National
Science Foundation (Grant No. CHE0242623), the Office
of Naval Research (Contract No. N00014-03-1-0531),
and the University of Miami (CCD-diffractometer fund)
for providing financial support.
F igu r e 4. ORTEP representation of molecule 5 at the 30%
probability level. Selected bond lengths (Å): Ru1-Ru2,
2.5581(5); Ru1-C1, 1.949(5); Ru2-C8, 1.954(5); Ru-N(av-
eraged), 2.050[4].
Su p p or tin g In for m a tion Ava ila ble: Text giving details
of syntheses and characterizations of compounds 1-5 and
X-ray crystallographic files in CIF format for compounds 1,
4a , and 5. This material is available free of charge via the
Internet at http://pubs.acs.org.
bonds, reflecting the loss of σ(Ru-Ru) upon the forma-
tion of two σ(Ru-C) bonds (Ru1-C1 and Ru2-C8). The
coordination geometries around the diruthenium core
in compounds 4a and 5 are very similar to those
previously reported for the Ru2(DArF)4(C2R)2 type com-
pounds,10 which indicates a minimal impact on the
electronic properties of Ru2 metallaynes upon the
covalent modification of the N,N ′-bidentate bridging
ligand.
Recent years have witnessed significant progress in
supramolecular chemistry based on linking dimetallic
units at the equatorial positions,12 where the ditopic
linkers are typically preformed. Our preliminary studies
OM049702D
(12) (a) Cotton, F. A.; Lin, C.; Murillo, C. A. Acc. Chem. Res. 2001,
34, 759. (b) Cotton, F. A.; Lin, C.; Murillo, C. A. Proc. Nat. Acad. Sci.
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