Diruthenium phenylacetylide complexes bearing para -/ meta -amino phenyl substituents

Article abstract of DOI:10.1021/om100263c

Presented herein is the synthesis and characterization of four diruthenium(II,III) compounds of formulas Ru₂(Xap) ₄(C≡C-C₆H₄-4-NH₂) (Xap is 2-anilinopyridinate, 1a; and 2-(3,5-dimethoxy)anilinopyridinate, 1b) and Ru ₂(Xap)₄(C≡C-C₆H₄-3-NH ₂) (2a/2b). X-ray structural studies of compounds 1b and 2a revealed minimal changes in the coordination sphere of the Ru₂ core. Voltammetric measurements showed that compounds 1 exhibit three one-electron redox processes: a reversible reduction of Ru₂, a reversible oxidation of Ru₂, and a quasi-reversible oxidation of an amino group. Compounds 2 display the same Ru₂-based redox processes but not the -NH₂ oxidation. Compounds 1a/1b were successfully converted to the corresponding diazonium salts [Ru₂(Xap)₄-(C≡C-C ₆H₄-4-N₂)](BF₄) (3a/3b) via oxidation by nitrosonium tetrafluoroborate, which was generated in situ from t-BuONO and BF₃. However, the attempt to convert compounds 2 to the corresponding diazonium salts was unsuccessful. DFT calculations of model compounds were performed to rationalize some unusual structural and electrochemical characteristics observed for compounds 1/2.

Full text of DOI:10.1021/om100263c

Organometallics 2010, 29, 2783–2788 2783
DOI: 10.1021/om100263c
Diruthenium Phenylacetylide Complexes Bearing para-/meta-Amino
Phenyl Substituents
Steven P. Cummings, Zhi Cao, Carl W. Liskey, Alex R. Geanes, Phillip E. Fanwick,
Kerry M. Hassell, and Tong Ren*
Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47907
Received April 3, 2010
Presented herein is the synthesis and characterization of four diruthenium(II,III) compounds of
formulas Ru2(Xap)4(CtC-C6H4-4-NH2) (Xap is 2-anilinopyridinate, 1a; and 2-(3,5-dimethoxy)-
anilinopyridinate, 1b) and Ru2(Xap)4(CtC-C6H4-3-NH2) (2a/2b). X-ray structural studies of com-
pounds 1b and 2a revealed minimal changes in the coordination sphere of the Ru2 core. Voltammetric
measurements showed that compounds 1 exhibit three one-electron redox processes: a reversible
reduction of Ru2, a reversible oxidation of Ru2, and a quasi-reversible oxidation of an amino group.
Compounds 2 display the same Ru2-based redox processes but not the -NH2 oxidation. Compounds
1a/1b were successfully converted to the corresponding diazonium salts [Ru2(Xap)4-(CtC-C6H4-
4-N2)](BF4) (3a/3b) via oxidation by nitrosonium tetrafluoroborate, which was generated in situ from
t-BuONO and BF3. However, the attempt to convert compounds 2 to the corresponding diazonium
salts was unsuccessful. DFT calculations of model compounds were performed to rationalize some
unusual structural and electrochemical characteristics observed for compounds 1/2.
Introduction
of Tour and Paul succeeded in immobilizing polyoxo cluster
(Mo6)6 and Fe or Fe/Ru phenylacetylide complexes,7 respec-
tively, on p-type H-Si surfaces, demonstrating the feasibility
of functionalization with inorganic/organometallic species.
There has been a sustained interest in using metal alkynyl
compounds as molecular wires, active components of mole-
cular devices, or electro-optical materials from many labora-
tories around the world.8,9 Efforts from our laboratory focus
on diruthenium alkynyl compounds,10 and both wire charac-
teristics and conductance switching have been documented.11
The continuous scaling of Si-based CMOS transistors has
become increasingly challenging due to the materials limita-
tion such as the lack of effective dielectric materials at nano-
meter scale, and hybrid transistors based on the combination
of organic molecules and Si-based CMOS devices has been
speculated as a promising alternative.1 As an essential start-
ing point for molecule-CMOS hybrids, covalent attachment
of organic molecules to both flat and porous Si surfaces has
received intense interest from both chemists and engineers
during the last two decades.2-4 This is typically accom-
plished on the basis of a H-passivated Si surface that is
produced by etching of the native SiO2 layer with a solution
of HF or NH4F.3,4 Organic molecules with terminal func-
tional groups such as alkynes, alkenes, or diazonium can be
grafted onto a H-Si surface under thermal, photochemical,
or electrochemical conditions.3,5 Recently, the laboratories
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pet, L.; Ababou-Girard, S.; Sabbah, H.; Hapiot, P.; Fabre, B. Adv.
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*To whom correspondence should be addressed. E-mail: tren@
purdue.edu.
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2010 American Chemical Society
Published on Web 06/01/2010
pubs.acs.org/Organometallics

2784 Organometallics, Vol. 29, No. 12, 2010
Scheme 1. Preparation of Compounds 1-3
Cummings et al.
Figure 1. Structural plot of compound 1b. Hydrogen atoms
˚
Among several types of diruthenium alkyl compounds attain-
able, those based on Ru2(ap)4 (ap is 2-anilinopyridinate) are
particularly attractive due to their rich and robust redox
properties, the choice between mono- and bis-alkynylation,
and possibility of ligand engineering.12-17 Previously, we rea-
lized the synthesis of Ru2(ap)4-alkynyls with the thiol (-SH)
alligator clip,18 which were used in the said device work through
the formation of the Au-S bond.11 Described in this contribu-
tion are the preparation of Ru2(Xap)4 phenylacetylide com-
pounds containing either a 4- or 3-NH2 phenyl substituent and
the conversion of 4-NH2 compounds to the corresponding
diazonium salts, which can function as an “alligator clip” for
the Si surface.
were omitted for clarity. Selected bond lengths (A): Ru1-Ru2,
2.329(10); Ru1-C1, 2.097(10); Ru1-Nav, 2.093[7]; Ru2-Nav,
2.022[7]; C1-C2, 1.178(14); C2-C3, 1.470(16). Bond angles
(deg): Ru2-Ru1-C1, 178.9(2); Ru1-C1-C2, 168.4(8); C1-
C2-C3, 176.5(11).
Results and Discussion
Similar to the earlier studies of other Ru2(ap)4 monoalk-
ynyl compounds,13,16 compounds 1 and 2 were prepared via
anion metathesis reactions between Ru2(Xap)4Cl and LiCt
CC6H4-NH2 (in slight excess) as outlined in Scheme 1. Puri-
fication via silica column using CH2Cl2-hexanes resulted in
compounds 1 and 2 as dark purple and green microcrystal-
line solids, respectively, in yields of 60-85%. Both com-
pounds 1 and 2 are paramagnetic with effective magnetic
moments between 3.5 and 3.9 μB, which are consistent with a
ground state of S = 3/2.
The diazonium derivatives 3 were prepared using a proce-
dure modified from that of Doyle and Bryker:19 to a THF
solution containing 1 was added boron trifluoride diethyl
etherate, followed by tert-butyl nitrite, which resulted in the
precipitation of diazonium salts 3.
Figure 2. Structural plot of compound 2a. Hydrogen atoms
˚
were omitted for clarity. Selected bond lengths (A): Ru1-Ru2,
2.3420(5); Ru1-C45, 2.094(6); Ru1-Nav, 2.105[5]; Ru2-Nav,
2.037[4]; C45-C46, 1.217(8). Bond angles (deg): Ru2-Ru1-
C45, 178.58(16); Ru1-C45-C46, 174.2(5); C45-C46-C47,
178.9(7).
The molecular structures of both compounds 1b and 2a
were determined using X-ray single-crystal diffraction, and
their structural plots are presented in Figures 1 and 2,
respectively. Both compounds were crystallized in the space
group P1, and the asymmetric unit contains one independent
molecule in the case of 1b and two in the case of 2a. Both
independent molecules in 2a exhibit very similar geometric
parameters, and only one is shown in Figure 2.
(12) Chakravarty, A. R.; Cotton, F. A. Inorg. Chim. Acta 1986, 113,
19.
(13) Zou, G.; Alvarez, J. C.; Ren, T. J. Organomet. Chem. 2000, 596,
152.
It is clear from Figures 1 and 2 that the coordination
geometry around the Ru2 core in both 1b and 2a is very
similar to those determined earlier for related Ru2(ap)4-
(CtCR) compounds.10,20 In particular, the Ru-Ru
(14) Ren, T.; Zou, G.; Alvarez, J. C. Chem. Commun. 2000, 1197. Ren,
T. Organometallics 2002, 21, 732. Xu, G.-L.; Zou, G.; Ni, Y.-H.; DeRosa,
M. C.; Crutchley, R. J.; Ren, T. J. Am. Chem. Soc. 2003, 125, 10057. Shi, Y.;
Yee, G. T.; Wang, G.; Ren, T. J. Am. Chem. Soc. 2004, 126, 10552. Bear,
J. L.; Li, Y.; Han, B.; Caemelbecke, E. V.; Kadish, K. M. Inorg. Chem. 1997,
36, 5449. Kadish, K. M.; Phan, T. D.; Wang, L.-L.; Giribabu, L.; Thuriere, A.;
Wellhoff, J.; Huang, S.; Caemelbecke, E. V.; Bear, J. L. Inorg. Chem. 2004,
43, 4825. Nguyen, M.; Phan, T.; Caemelbecke, E. V.; Kajonkijya, W.; Bear,
J. L.; Kadish, K. M. Inorg. Chem. 2008, 47, 7775.
(15) Xu, G.-L.; Ren, T. Organometallics 2001, 20, 2400.
(16) Xu, G.-L.; Cordova, A.; Ren, T. J. Cluster Sci. 2004, 15, 413.
(17) Xi, B.; Xu, G.-L.; Ying, J.-W.; Han, H.-L.; Cordova, A.; Ren, T.
J. Organomet. Chem. 2008, 693, 1656.
˚
(2.329(10)/2.3420(5) A for 1b/2a) and Ru-C (2.097(10)/
˚
2.094(6) A for 1b/2a) bond lengths are the same as those
reported for Ru2(ap)4(CtCPh) within experimental error.12
The average Ru1-N(pyridyl) and Ru2-N(anilino) bond
lengths for both 1b and 2a are comparable to those tabulated
for other related Ru2(ap)4(CtCR) compounds.10
A curious feature about 1b is the significant deviation
of the Ru1-C1-C2 linkage from linearity, which results
in an apparent bend of the 4-NH2C6H4 ring from the
(18) Ren, T.; Parish, D. A.; Xu, G.-L.; Moore, M. H.; Deschamps,
J. R.; Ying, J.-W.; Pollack, S. K.; Schull, T. L.; Shashidhar, R. J.
Organomet. Chem. 2005, 690, 4734.
(19) Doyle, M. P.; Bryker, W. J. J. Org. Chem. 1979, 44, 1572.
(20) Ren, T.; Xu, G.-L. Comments Inorg. Chem. 2002, 23, 355.

Article
Organometallics, Vol. 29, No. 12, 2010 2785
Figure 4. CV of compound 3a recorded in MeCN at a scan rate
of 0.10 V/s. The cathodic region was scanned continuously.
reduction.10 For compounds 1a/b, there is an additional quasi-
reversible oxidation around 0.88 V that is attributed to the
4-NH2 group. The corresponding peak, however, was not
observed for compounds 2 within the potential window allowed
by THF. Voltammetric measurements conducted in CH2Cl2,
which allows for a more positive potential window, did not reveal
a NH2 oxidation either. It is obvious from Figure 3 that the CVs
of 1a and 1b are nearly identical, and the same is true about those
of 2a and 2b. This is consistent with the fact that the substitution
on the anilino ring causes very minimal change in the electronic
properties of Ru2(Xap)4 species.16,17 Examination of E1/2 data
also reveals that the peaks attributed to Ru2 in 2 are generally
20-40 mV more positive than those in 1, which is due to the
weaker electron-donating ability of 3-NH2 (Hammett constant
σ(3-NH2) = -0.09) than that of 4-NH2 (σ(4-NH2) = -0.30).
Diazonium salts are generally prone to quick degradation
when subjected to demanding techniques such as MS and
elemental analysis. An ESI-MS study of 3a led to the
observation of only fragments (see the Experimental Section
below). Hence, diazonium salts are often characterized with
Figure 3. CVs of compounds 1 and 2 recorded in THF at a scan
rate of 0.10 V/s.
Ru2-Ru1-C1 axis (Figure 1). In contrast, the Ru1-
C45-C46 angle in 2a (174.2(5)°) is more in line with typical
Ru-CR-Cβ (175° or higher) angles found for other Ru2-
(ap)4(CtCR) compounds.10,20 Inspection of the packing
diagram of 1b did not reveal any significant intermolecular
interaction involving the 4-NH2C6H4 ring, hinting that the
bend may have an electronic origin. Structural examples of
metal-σ-arylacetylides containing -NH2 aryl substituent
are sparse, and entries found in the CSD include those of the
4-NH2 substituent with M as Pt,21 Au,9,22 Fe,23,24 and Ru25 and
those of the 2-NH2 substituent with M as Pt26 and Re.27 There is
no reported structure for the [M]-CtC-C6H4-3-NH2 type. In
most of the cases, the nonlinearity of M-CR-Cβ linkage is
small but noticeable from the structural plots and typically went
unnoticed by the authors. Exceptions to this are the detailed and
thorough studies of the MII-CtC-C6H4-4-X series (M = Fe
and Ru) by Paul and Lapinte,23,25 where a significant bend in
the M-CR-Cβ linkage was noticed for compounds with both
the electron donor (NH2) and acceptor (NO2) substituents.
Similar to the established Ru2(ap)4(CtCR) compounds,
compounds 1 and 2 display rich redox chemistry with three
one-electron waves attributed to the Ru2 center: a reversible
oxidation (A, Ru2(II,III) to Ru2(III,III)), a reversible reduc-
tion (B, Ru2(II,III) to Ru2(II,II)), and subsequent irrever-
sible reduction (C, Ru2(II,II) to Ru2(II,I)), as shown in
Figure 3. The irreversibility of couple C is due to the
dissociation of the axial acetylide ligand upon the second
1
IR and H NMR.6 Although the paramagnetic nature of 3
prevents a meaningful NMR study, FT-IR of 3 revealed the
characteristic NdN stretch at 2228 cm-1. Voltammetric
measurement of 3, shown in Figure 4 for 3a, also offers some
insight and indirect proof of the presence of diazonium. For
the diazonium salt 3a, its open circuit potential (OCP) is
shifted by þ0.37 V from that of 1a. The anodic region
features a reversible oxidation and a quasi-reversible oxida-
tion. The initial scan of the cathodic region revealed four
quasi-reversible reductions, labeled as B1, B2, C1, and C2.
Interestingly, the first three waves gradually diminished
when the CV was scanned continuously (Figure 4), while
C2 remains throughout. This type of behavior is expected for
a diazonium species: waves B1, B2, and C1 originate from 3a
and disappear as 3a degrades under electrolytic conditions;
wave C2 is likely due to a degradation product that deposits
on the glassy carbon working electrode.
(21) Deeming, A. J.; Hogarth, G.; Lee, M.-y. V.; Saha, M.; Redmond,
S. P.; Phetmung, H. T.; Orpen, A. G. Inorg. Chim. Acta 2000, 309, 109.
ꢀ
ꢀ
(22) Hogarth, G.; Alvarez-Falcon, M. M. Inorg. Chim. Acta 2005,
358, 1386.
(23) Costuas, K.; Paul, F.; Toupet, L.; Halet, J.-F.; Lapinte, C.
Both compounds 1 and 2 exhibit two intense peaks with
peak maxima at 480-488 and 744-770 nm, as shown in
Figure 5, and this feature is consistent with the prior studies
of related Ru2(ap)4(CtCR)-type compounds.10,13,15,17,28
Organometallics 2004, 23, 2053.
(24) Paul, F.; Toupet, L.; Thepot, J. Y.; Costuas, K.; Halet, J. F.;
Lapinte, C. Organometallics 2005, 24, 5464.
(25) Paul, F.; Ellis, B. G.; Bruce, M. I.; Toupet, L.; Roisnel, T.;
Costuas, K.; Halet, J.-F.; Lapinte, C. Organometallics 2006, 25, 649.
(26) Fratoddi, I.; Delfini, M.; Sciubba, F.; Hursthouse, M. B.;
Ogilvie, H. R.; Russo, M. V. J. Organomet. Chem. 2006, 691, 5920.
(27) Liddle, B. J.; Lindeman, S. V.; Reger, D. L.; Gardinier, J. R.
Inorg. Chem. 2007, 46, 8484.
(28) Zhang, L.; Xi, B.; Liu, I. P. C.; Choudhuri, M. M. R.; Crutchley,
R. J.; Updegraff, J. B.; Protasiewicz, J. D.; Ren, T. Inorg. Chem. 2009,
48, 5187.

2786 Organometallics, Vol. 29, No. 12, 2010
Cummings et al.
our prior DFT study of a related model compound,28 spin-
unrestricted DFT calculations for model 1, model10, and model
2 all converged to the same configuration with HOMO,
HOMO-1, and HOMO-2 being energetically close and singly
occupied. The computed molecular orbital diagrams for the
three model compounds are shown in Figure 6.
It is clear from Figure 6 that the HOMO of model 1 is
predominantly the δ*(Ru-Ru) orbital with an additional
contribution from the π*(py). The HOMO-1 is primarily
made of the antibonding combination of π*(Ru-Ru) and
π(CtC) orbitals, while the HOMO-2 is a even mix between
the antibonding combination of π*(Ru-Ru) and π(CtC)
orbitals and the π* orbitals of both pyridinyl and anilino
rings. Clearly, the π-interactions between the Ru2 core and
axial acetylide are dominated by the filled-filled type first
proposed by Lichtenberger.29 The DFT results of model 1
unambiguously confirm the ground-state configuration of
σ2π4δ2π*2δ*1 for the Ru2(II,III) core.10,30 The LUMO of
model 1 is largely a combination of the π* orbitals of four
pyridinyl rings and the dx2-y2 orbital of Ru(py), while an
early study resulted in a LUMO of σ*(Ru-Ru) nature.28 The
discrepancy is likely due to the oversimplification in the early
calculation, where all anilino rings were replaced by methyl
groups and arylacetylide was replaced by simple acetylide
(-CtCH). The DFT calculation of model 10 yielded results,
both the make up and energies of the frontier MOs, nearly
identical to those of model 1. The only subtle difference is
that the energy of HOMO-1 in model 10 is 0.03 eV higher
than that in model 1.
As shown in Figure 6, the frontier orbitals of model 2 are
similar to those of model 1 in both energies and general
composition, and the occupancy conforms to a π*2δ*1
configuration. Nevertheless, there exists a significant con-
trast in both the HOMO-1 and HOMO-2 orbitals between
the two models. In model 1, the lone pair of 4-NH2 con-
tributes significantly to both orbitals through the mixing
with the aryl π orbitals. On the other hand, contributions
from both the lone pair of 3-NH2 and the aryl π orbitals are
hardly noticeable in the HOMO-1 and HOMO-2 orbitals of
model 2. Instead, the π* orbitals from both pyridyls and
anilino rings make up a significant portion of HOMO-1 and
HOMO-2. The absence of -NH2 contribution indicates
that the lone pair of the 3-NH2 group is deeply buried,
making its oxidation energetically challenging.
Figure 5. Vis-NIR spectra of compounds 1 and 2 recorded in
THF.
On the basis of our recent TD-DFT study of a model com-
pound,28 the higher energy peak is assigned to the transition
to the δ*(Ru-Ru) orbital from both the π(Ru-Ru) and
π(Ru-N) orbitals, while the lower energy peak is primarily
the π(CtC) to δ*(Ru-Ru) transition. Both compounds 1a and
1b also exhibit a broad shoulder trailing off the high-energy
band, which is absent in the spectra of both compounds 2 and
other Ru2(ap)4(CtCR)-type compounds studied earlier. This
feature perhaps accounts for the purple color of 1 in THF, which
is distinctly different from the brown color of other Ru2(ap)4-
(CtCR)-type compounds including 2. The appearance of this
shoulder is likely due to the lone pair of p-NH2, although the
exact nature of the transition remains unclear. The visible region
of the absorption spectrum of 3a (Supporting Information)
features a single peak at 676 nm. The contrast between the
spectral features of compounds 1 and 3 reflects a significant
stabilization of both the π(Ru-Ru) and π(CtC) orbitals by
the diazonium group, which blue-shifts the band from around
750 nm in 1 to 676 nm in 3, and the high-energy peak around
480 nm in 1 into the UV region.
Because of the interest in using compounds 1 and 2 as the
precursors for molecule-CMOS hybrid devices, we are
particularly interested in their electronic structures. Seeking
the possible electronic origins of several peculiar experimen-
tal observations, such as the bend of the -CCC6H4-4-NH2
fragment and the difficulty in oxidizing the 3-NH2 deriva-
tive, DFT calculations were performed on the models for
compounds 1 and 2, namely, model 1, model 10, and model 2.
The geometries of model 1 and model 2 were optimized from
the crystal structures of 1b and 2a, respectively, with the only
simplification being the replacement of anilino methoxy
substituents with H atoms in the former. The bond lengths
and angles around the Ru2 core in the optimized geometries
match well with those from the crystal structures, and they
are given in the Supporting Information. The geometry of
model 10 was idealized from that of model 1 by restricting
both Ru-Ru-CR and Ru-CR-Cβ to 180°.
In the course of investigating many [MII]-CtC-C6H4-4-X
(M = Fe and Ru) type compounds, Lapinte and co-workers
proposed that the quinoidal resonance structure (analogous
to B in Scheme 2) may contribute significantly to the
electronic properties of metal-acetylide species in addition
to the traditional arylacetylide structure (A in Scheme 2) with
X = NH2.23-25,31 This classical valence bond (VB) descrip-
tion is clearly applicable to our compounds 1a/1b, as corro-
borated by the N-lone pair contribution to both the
HOMO-1 and HOMO-2 from the model 1 calculation.
The classical VB theory also suggests that a significant
contribution by the 3-NH2 lone pair would invoke a higher
(29) Lichtenberger, D. L.; Renshaw, S. K.; Bullock, R. M. J. Am.
Chem. Soc. 1993, 115, 3276. Lichtenberger, D. L.; Renshaw, S. K.; Wong,
A.; Tagge, C. D. Organometallics 1993, 12, 3522.
(30) Angaridis, P. In Multiple Bonds between Metal Atoms; Cotton,
F. A.; Murillo, C. A.; Walton, R. A., Eds.; Springer Science and Business
Media, Inc.: New York, 2005.
It is well established on the basis of the room-temperature
effective magnetic moment that the Ru2(ap)4(CtCR)-type
compounds have an S = 3/2 ground state.10 Consistent with
(31) Denis, R.; Toupet, L.; Paul, F.; Lapinte, C. Organometallics
2000, 19, 4240.

Article
Organometallics, Vol. 29, No. 12, 2010 2787
Figure 6. Molecular orbital diagrams for model 1, model 10, and model 2 obtained from DFT calculations.
Scheme 2. Resonance Structures Available to Compounds 1
3 using tert-butyl nitrite as the oxidant. The 3-NH2 analogues
cannot be converted similarly. The contrast between two
compounds was rationalized based on DFT studies. Currently,
the grafting of 3 onto H-Si surfaces is being explored in our
laboratory.
Experimental Section
General Procedures. Trimethylsilylacetylene (TMS-acetylene)
was purchased from GFS Chemicals; BF3 etherate, tert-butyl
3
nitrite, and n-BuLi (2.5 M in hexanes) were purchased from
Aldrich. THF was distilled over Na/benzophenone under an N2
atmosphere. Ru2(ap)4Cl,13 Ru2(DiMeOap)4Cl,17 1-amino-4-tri-
methylsilylethynylbenzene,33 and 1-amino-3-trimethylsilylethy-
nylbenzene34 were prepared according to literature procedures.
1-Amino-4-trimethylsilylethynylbenzene and 1-amino-3-trimethyl-
silylethynylbenzene were deprotected via K2CO3 in MeOH-THF.
All reactions were done using Schlenk techniques under nitrogen
and monitored by TLC with EtOAc-hexanes (v/v, 3:7) . UV-
vis-NIR spectra were obtained with a JASCO V-670 UV-vis-
NIR spectrophotometer. Infrared spectra were obtained on a
JASCO FT-IR 6300 spectrometer via ATR on a ZnSe crystal.
Magnetic susceptibility data were measured at 293 K with a Johnson
Matthey Mark-1 magnetic susceptibility balance. Elemental analysis
was performed by Atlantic Microlab, Norcross, GA. Cyclic vol-
tammograms were recorded in 0.2 M n-Bu4NPF6 and a 1.0 mM
diruthenium species solution (THF, N2 degassed) on a CHI620A
voltammetric analyzer with a glassy carbon working electrode
(diameter = 2 mm), a Pt-wire counter electrode, and an Ag/AgCl
reference electrode with ferrocene used as an internal reference
(0.620 V).
32
energy non-Kekule-type resonance structure, and hence is
ꢀ
energetically unfavorable. This is again confirmed by the
absence of the N-lone pair contribution to either the HOMO-1
and HOMO-2 from the model 2 calculation. The other
possible quinoidal structure, C, is less likely for neutral 1, but
contributes to the stabilization of the cation upon -NH2
oxidation. The unavailability of such a resonance structure
for the 3-NH2 species (2) may explain the difficulty in oxidizing
3-NH2.
Conclusion
Several diruthenium arylacetylide compounds with 4-/3-NH2
substituents have been prepared and characterized. The 4-NH2
species can be readily converted to the corresponding diazonium
(33) Takahashi, S.; Kuroyama, Y.; Sonogashira, K.; Hagihara, N.
Synthesis 1980, 627.
(34) Lavastre, O.; Cabioch, S.; Dixneuf, P. H.; Vohlidal, J. Tetra-
(32) Borden, W. T.; Iwamura, H.; Berson, J. A. Acc. Chem. Res. 1994,
27, 109.
hedron 1997, 53, 7595.

2788 Organometallics, Vol. 29, No. 12, 2010
Cummings et al.
Preparation of Ru2(ap)4-(C2C6H4-4-NH2) (1a). Ru2(ap)4Cl
(196 mg, 0.213 mmol), dried under vacuum for 30 h at 80 °C,
was dissolved in 25 mL of THF. To the Schlenk flask containing
4-ethynylaniline (50 mg, 0.42 mmol) dissolved in 5 mL of THF
was added 200 μL of 2.5 M n-BuLi in hexanes (0.50 mmol)
at -70 °C. Upon warming to ambient temperature, the lithiated
ligand was transferred via cannula to the Ru2(ap)4Cl solution.
The reaction mixture turned black and was allowed to stir
overnight. The reaction mixture was filtered through a silica
plug deactivated by 10% v/v TEA-hexanes and purified on a
silica column with CH2Cl2-hexanes (v/v, 1:10 to 1:2) to yield
169 mg of 1a as a purple crystalline solid (80% based on Ru).
Data for 1a: Rf = 0.22; ESI-MS, [M]þ, 996.16; visible spectra,
(96.9%).Datafor3a: ESI-MS, 878.7 [M - CC - Ph - N2þBF4-]þ,
903.0 [M - Ph - N2þBF4-]þ, 1007.9 [M - BF4-]þ; visible spectra,
λ
max (nm, ε (M-1 cm-1)) 668(16 000); IR (cm-1) NdN 2228 (m),
CtC 2131 (m). Cyclic voltammogram in MeCN, Epa/V: 1.145,
0.940, Epc/V: 0.140, -0.120, -1.158, 1.313, -1.81 (E1/2(Fcþ/Fc):
0.430 V; open circuit potential 0.37 V).
Preparation of [Ru2(diMeOap)4-(C2-C6H4-4-N2)]BF4 (3b).
The synthesis followed the same procedure as that for 3a using
72.3 mg of 1b in 5 mL of THF. The diazonium salt was obtained
in quantitative yield. Data for 3b: visible spectra, λmax (nm,
ε (M-1 cm-1)) 681(11 000); IR (cm-1) NdN 2228 (m), CtC
2111 (m). Cyclic voltammogram in MeCN: Epa/V 1.128, 0.976,
Epc/V 0.117; -0.083; -1.101; -1.289 (E1/2(Fcþ/Fc): 0.414 V;
open circuit potential 0.30 V).
Computational Methods. The full geometry optimizations of
structures 1b and 2a were based on obtained crystal structures,
with 1b treated as 1a by removal of the methoxy substituents and
using the density functional theory (DFT) method, and were
based on the hybrid B3LYP density functional model,35 con-
sisting of the Slater local exchange,36 the nonlocal exchange
of Becke,37 the local correlation functional of Vosco-Wilk-
Nusair,38 and the nonlocal correlation functional of Lee-
Yang-Parr.39 The basis set used for all atoms was the LanL2DZ
by considering the involvement of metals. All calculations were
carried out with the Gaussian 03 suite of programs.40 No
negative frequency observed in the vibrational frequency analy-
sis indicates that these aniline-substituted diruthenium com-
plexes are metastable equilibrium structures.
λmax (nm, ε (M-1 cm-1)) 484(7200), 744(5200); IR (cm-1
)
NH2 3377(m), CtC 2033(m). Anal. Calcd for Ru2C52H42N9O3
(1a 2THF 1H2O) (found): C, 62.27 (62.50); H, 5.23 (5.18); N,
3
3
10.89 (10.56). Cyclic voltammogram [E1/2/V, ΔEp/V, ibackward
/
iforward]: Epa(-NH2), 0.882; A, 0.389, 0.031, 0.80; B, -0.931,
0.033, 0.81; Epc(C), -2.082. μeff: 3.57 μB.
Preparation of Ru2(ap)4-(C2C6H4-3-NH2) (2a). The synthesis
of 2a followed the procedure for 1a using 1.38 g of Ru2(ap)4Cl
(1.51 mmol), 295 mg (2.52 mmol) of m-ethynylaniline, and
1.0 mL of 2.5 M n-BuLi. After filtering through a silica pad
the residue was loaded onto deactivated silica gel and eluted via
hexanes-EtOAc-Et3N beginning with 20:1:0.1 and slowly
increasing EtOAc to 2:1:0.01, yielding 940 mg (63%) of brown
material. Data for 2a: Rf = 0.20; ESI-MS, [M]þ, 996.16; visible
spectra, λmax (nm, ε(M-1 cm-1)) 480(12 900), 748(8700); IR (cm-1
)
NH2 3367(m), CtC 2047(w). Anal. Calcd for Ru2C52H42N9
(found): C, 62.76 (62.95); H, 4.25 (4.15); N, 12.67 (12.64). Cyclic
voltammogram [E1/2/V, ΔEp/V, ibackward/iforward]: Epa(-NH2),
1.132; A, 0.433, 0.027, 0.84; B, -0.884, 0.028, 0.84; Epc(C),
-2.036. μeff: 3.73 μB.
Preparation of Ru2(diMeOap)4-(C2C6H4-4-NH2) (1b). The
synthesis and purification of 1b followed the procedure for
1a using 580 mg (0.501 mmol) of Ru2(diMeOap)4Cl, 139 mg
(1.19 mmol) of p-ethynylaniline, and 500 μL (1.25 mmol) of
2.5 M n-BuLi to yield 400 mg (65%) of a purple solid. Data
for 1b: Rf = 0.08; ESI-MS, [M]þ, 1235.30; visible spectra, λmax
(nm, ε (M-1 cm-1)) 488(8400), 767(5800); IR (cm-1) NH2
3371(m), CtC 2033(m). Anal. Calcd for Ru2C68H80N9O13
(found): C, 58.34 (57.91); H, 4.73 (4.69); N, 10.20 (9.90). Cyclic
voltammogram [E1/2/V, ΔEp/V, ibackward/iforward]: Epa(-NH2),
0.878; A, 0.393, 0.026, 0.73; B, -0.907, 0.030, 0.94; Epc(C),
-2.067. μeff: 3.79 μB.
Structure Determination. Single crystals of compounds 1b and
2a were grown by slow cooling in a 1:3 mixture of THF-hexanes
and vapor-vapor diffusion of pentane into a CH2Cl2 solution,
respectively. X-ray diffraction data were collected on a Rigaku
Rapid II image plate diffractometer using Cu KR radiation (λ =
˚
1.54184 A) at 150 K, and the structures were solved using the
structure solution program PATTY in DIRDIF9941 and refined
using SHELX-07.42 Crystal data for 1b: C60H58N9O8Ru2
3
˚
3(C4H8O), fw = 1451.6, triclinic, P1, a = 13.2318(13) A, b =
˚
˚
13.9353(13) A, c = 21.626(2) A, R = 105.296(6)°, β = 90.477(8)°,
o
3
γ = 97.294(8) , V = 3811.6(6) A , Z = 2, Dcalc = 1.265 g cm-1
,
˚
R1 = 0.087, wR2 = 0.259. Crystal data for 2a: C52H42N9Ru2
˚
CH2Cl2, fw = 1080.05, triclinic, P1, a = 10.0003(5) A, b =
3
˚
˚
20.0034(8) A, c = 25.6160(9) A, R = 74.969(3)°, β = 81.982(4)°,
γ = 79.121(4) , V = 4837.8(4) A , Z = 4, Dcalc = 1.483 g cm-1
R1 = 0.059, wR2 = 0.179.
,
o
3
˚
Preparation of Ru2(diMeOap)4-(C2C6H4-3-NH2) (2b). The
synthesis and purification of 2b followed the procedure for 1a
using 150 mg (0.132 mmol) of Ru2(diMeOap)4Cl, 22 mg (0.188
mmol) of m-ethynylaniline, and 90 μL (0.225 mmol) of 2.5 M
n-BuLi to yield 120 mg (75%) of a brown solid. Data for 2b:
Rf = 0.12; ESI-MS, [M]þ, 1235.30; visible spectra, λmax (nm,
ε (M-1 cm-1)) 485(10 100), 770(6300); IR (cm-1) NH2 3371(m),
CtC 2048(w). Anal. Calcd for Ru2C60H58N9O8 (found): C,
58.34 (57.91); H, 4.73 (4.69); N, 10.20 (9.90). Cyclic voltammo-
gram [E1/2/V, ΔEp/V, ibackward/iforward]: A, 0.424, 0.031, 0.96;
B, -0.872, 0.033, 0.87; Epc(C), -2.026. μeff: 3.81 μB.
Acknowledgment. We thank the National Science
Foundation (Grant No. CHE 0715404) for support.
Supporting Information Available: DFT calculation details
for model 1, model 10, and model 2, voltammograms and vis
spectra of compounds 3, and X-ray crystallographic details
(CIF) of 1b and 2a. This material is available free of charge
via the Internet at http://pubs.acs.org.
(35) Becke, A. D. J. Chem. Phys. 1993, 98, 5648. Stephens, P. J.; Devlin,
F. J.; Chabalowski, C. F.; Frisch, M. J. J. Phys. Chem. 1994, 98, 11623.
(36) Slater, J. C. The Self-consistent Field for Molecules and Solids, in
Quantum Theory of Molecules and Solids; McGraw Hill: New York, 1974.
(37) Becke, A. D. Phys. Rev. A 1988, 38, 3098.
(38) Vosko, S. H.; Wilk, L.; Nusair, M. Can. J. Phys. 1980, 58, 1200.
(39) Lee, C. T.; Yang, W. T.; Parr, R. G. Phys. Rev. B 1988, 37, 785.
(40) Frisch, M. J.; et al. et al. Gaussian 03, Revision D.02; Gaussian,
Inc.: Wallingford, CT, 2003.
(41) Beurskens, P. T.; Beurskens, G.; deGelder, R.; Garcia-Granda,
S.; Gould, R. O.; Smits, J. M. M. The DIRDIF2008 Program System;
Crystallography Laboratory, University of Nijmegen: The Netherlands,
2008.
Preparation of [Ru2(ap)4-(C2-C6H4-4-N2)]BF4 (3a). In a three-
neck flask 100 mg (0.100 mmol) of compound 1a was dissolved
in 6 mL of THF and placed in a dry ice-acetone bath. In
a Schlenk tube 350 μL (3.22 mmol) of BF3 Et2O was diluted in
3
10 mL of Et2O and cooled in a dry ice-acetone bath, then
transferred to the three-neck flask via cannula. The mixture was
stirred for 45 min, turning brown. The three-neck flask was then
placed at room temperature, and 325 μL (2.06 mmol) of
t-BuNO2 was added and stirred until a precipitate formed.
The mixture was filtered through a double male frit and the solid
placed on high vacuum to yield 107 mg of a dark green solid
(42) Sheldrick, G. M. Acta Crystallogr. A 2008, 64, 112.