Bidentate ligands that contain pyrrole in place of pyridine

Article abstract of DOI:10.1021/ic990445s

A series of ligands are prepared that are analogues of benzo-fused derivatives of 2,2'-bipyridine (bpy), in which pyrrole has been substituted for a pyridine ring. These ligands include 2-(2'-pyridyl)-indole, 2-(2'-pyrrolyl)-quinoline, and pyrrolo[3,2-h]quinoline. A novel reductive cyclization approach to the latter species is presented. All these ligands react with [Ru(bpy-d₈)₂Cl₂], undergoing cyclometalation with concurrent deprotonation, to form complexes of the type [Ru(L)(bpy-d₈)₂]⁺ where L binds as a monoanionic ligand. The complexes are readily characterized by their ¹H NMR spectra. Changes in the redox potentials and the electronic absorption spectra of both the ligands and the complexes are interpreted in terms of charge delocalization on the ligand.

Full text of DOI:10.1021/ic990445s

584
Inorg. Chem. 2000, 39, 584-590
Bidentate Ligands That Contain Pyrrole in Place of Pyridine
Feiyue Wu, Charles M. Chamchoumis, and Randolph P. Thummel*
Department of Chemistry, University of Houston, Houston, Texas 77204-5641
ReceiVed April 23, 1999
A series of ligands are prepared that are analogues of benzo-fused derivatives of 2,2′-bipyridine (bpy), in which
pyrrole has been substituted for a pyridine ring. These ligands include 2-(2′-pyridyl)-indole, 2-(2′-pyrrolyl)-quinoline,
and pyrrolo[3,2-h]quinoline. A novel reductive cyclization approach to the latter species is presented. All these
ligands react with [Ru(bpy-d8)2Cl2], undergoing cyclometalation with concurrent deprotonation, to form complexes
of the type [Ru(L)(bpy-d8)2]+ where L binds as a monoanionic ligand. The complexes are readily characterized
by their 1H NMR spectra. Changes in the redox potentials and the electronic absorption spectra of both the ligands
and the complexes are interpreted in terms of charge delocalization on the ligand.
Introduction
electrons. As such, it is a good H-bond acceptor. Pyrrole or
indole, on the other hand, is π-excessive and exhibits increased
reactivity toward electrophiles. It is comparably nonbasic and
a good H-bond donor. The juxtaposition of these two nuclei in
a 1,4-relationship is particularly interesting in that the two
centers can potentially be interacting. It is noteworthy that the
indole nucleus, unlike its quinoline counterpart, fluoresces
strongly in the UV.
In earlier work, we have examined several cavity-shaped
molecules incorporating pyrrole and pyridine subunits arranged
so as to complement one another in forming hydrogen bonds
to appropriate guests.9-11 In particular, we found that urea could
form four well-organized hydrogen bonds with such hosts, using
both lone pairs of electrons on oxygen to bind to the pyrrole
N-H donors and two amide hydrogens that were accepted by
the host pyridine lone pairs.
Another feature of the juxtaposed pyridine and pyrrole nuclei,
found in 2-(2′-pyridyl)indole (4aH) and related systems, in-
volves photoinduced double proton transfer that occurs in
concert with an alcohol solvent molecule, leading to a bond-
shifted tautomer in the excited state.12,13 Ground-state analogues
have also been prepared and studied by methylation of systems
such as 4 and 5 followed by deprotonation.14
Two of the most important classes of ligands are the
polypyridines and the porphyrins. In the former class of ligand,
we may include 2,2′-bipyridine (bpy, 1), 2,2′;6′,2′′-terpyridine,
1,10-phenanthroline (phen), and a variety of other homologous
and benzo-fused derivatives.1-5 The latter class of ligands is
embodied by porphyrin (2), phthalocyanine, and a variety of
“tailor-made” analogues.6-8 The bipyridines are considered to
be ligands of the diimine-type, which is to say that in at least
one of their resonance forms, they possess the NdC-CdN
functionality which, when oriented in a cisoid fashion, is well
disposed to coordinate and thus form a five-membered chelate
ring with an appropriate metal. The porphyrin system, on the
other hand, consists of four pyrrole rings joined at their 2,5-
positions by methine units. Covalent resonance theory demands
that adjacent pyrrole rings have their bonds organized such that
one ring presents an N-H unit to the core of the molecule while
the other presents an imine CdN function. In the metallopor-
phyrins, the porphyrin core has lost two protons and thus binds
as a dinegative ligand. Although the pyrrole ring of porphyrins
has been replaced by pyridine, the converse exchange, the
replacement of a pyridine ring in bpy by a pyrrole to afford
2-(2′-pyridyl)pyrrole (3) has not been methodically examined.
This paper will initiate the examination of a series of ligands
related to 2-(2′-pyridyl)pyrrole (3). Being less readily pre-
pared,15-17 study of the parent 3 itself will not be undertaken
(5) Sammes, P. G.; Yahioglu, G. Chem. Soc. ReV. 1994, 327.
(6) The Porphyrin Handbook; Kadish, K. M., Smith, K. M., Guilard, R.,
Eds.; Academic Press: Burlington, 1999.
(7) The Porphyrins; Dolphin, D., Ed.; Academic Press: New York, 1978.
(8) Porphyrins and Metalloporphyrins; Smith, K. M., Ed.; Elsevier: New
York, 1975.
(9) Hung, C.-Y.; Ho¨pfner, T.; Thummel, R. P. J. Am. Chem. Soc. 1993,
115, 12601.
(10) Hegde, V.; Hung, C.-Y.; Madhukar, P.; Cunningham, R.; Ho¨pfner,
T.; Thummel, R. P. J. Am. Chem. Soc. 1993, 115, 872.
(11) Hegde, V.; Madhukar, P.; Madura, J.; Thummel, R. P. J. Am. Chem.
Soc. 1990, 112, 4549.
The fundamental properties of pyridine and pyrrole very
nicely compliment one another. Pyridine is π-deficient but
exhibits Lewis basicity because of its available lone-pair
* To whom correspondence should be addressed.
(1) Kalyanasundaram, K. Photochemistry of Polypyridine and Porphyrin
Complexes; Academic Press: San Diego, 1992.
(2) Juris, A.; Balzani, V.; Barigelletti, F.; Campagna, S.; Belser, P.; von
Zelewsky, A. Coord. Chem. ReV. 1988, 84, 85.
(3) Cargill Thompson, A. M. W. Coord. Chem. ReV. 1997, 160, 1.
(4) Constable, E. C. AdV. Inorg. Chem. Radiochem. 1986, 30, 69.
(12) Herbich, J.; Hung, C.-Y.; Thummel, R. P.; Waluk, J. J. Am. Chem.
Soc. 1996, 118, 3508.
(13) Herbich, J.; Dobkowski, J.; Thummel, R. P.; Hegde, V.; Waluk, J. J.
Phys. Chem. A 1997, 101, 5839.
(14) Wu, F.; Hardesty, J.; Thummel, R. P. J. Org. Chem. 1998, 63, 4055.
(15) Kruse, C. G.; Bouw, J. P.; van Hes, R.; van de Kuilen, A.; den Hertog,
J. A. J. Heterocycles 1987, 26, 3141.
10.1021/ic990445s CCC: $19.00 © 2000 American Chemical Society
Published on Web 02/07/2000

Bidentate Ligands That Contain Pyrrole
Inorganic Chemistry, Vol. 39, No. 3, 2000 585
Table 1. Electronic Absorption Dataa for Pyrrolo[3,2-h]quinolines,
Salts, and Tautomers
at this time; rather, we will investigate a series of benzo-fused
derivatives 4-6. The fusion of a benzo-ring at the 4,5-position
on the pyrrole moiety of 3 provides the 2-(2′-pyridyl)indole
(4aH). Benzo fusion at the 5,6-position of the pyridine ring of
3 provides the 2-(2′-pyrrolyl)quinoline (5aH). Benzo-fusion to
the central bond of 3 provides pyrrolo[3,2-h]quinoline (6aH),
which is an analogue of 1,10-phenanthroline.
compound
λmax (nm)
6aH
6bH
6cH
6dH
9
324 (3.72), 262 (4.90), 211 (4.72)
315 (4.54), 287 (4.71), 205 (4.73)
318 (4.47), 286 (4.63), 209 (4.28)
324 (4.38), 290 (4.47), 256 (4.07)
375 (4.10), 277 (4.73), 246 (4.62)
10
448 (4.02), 298 (4.44), 254 (4.44)
326 (4.35), 296 (4.40), 247 (4.40), 209 (4.51)
390 (4.52), 306 (4.10), 248 (4.48)
14aH
14bH
15
460 (4.27), 393 (4.39), 307 (4.02), 279 (4.00), 248 (4.21)
a 10-5 M in CH3CN, log ꢀ in parentheses.
pyridyl nitrogen would provide such a tautomer. The consequent
loss of aromatic stabilization makes such a process somewhat
unfavorable. By methylating the pyridyl nitrogen, however, we
can cause deprotonation of the indole to become irreversible
and thus stabilize the tautomer. Thus, 6aH may be methylated
with iodomethane and then treated with base to provide the
bridged diaza[13]annulene 10. This species possesses a 14π
periphery, is quite stable, and is apparently diatropic by NMR.
From the point of view of ligand design, 10 is not useful
because the lone pair electrons on the pyridyl nitrogen are now
part of the delocalized π-system. This problem may be
circumvented by inducing tautomerization into an appropriately
appended pyridinium ring. Thus, methylation of the 4-pyridyl
derivative 6dH occurs exclusively at the less hindered 4-pyridyl
group, providing the salt 14bH, which then deprotonates to give
the diazafulvalene derivative 15A. This species now possesses
the diimine functionality needed to act as a neutral chelating
ligand. Methylation of the analogous 3-pyridyl derivative 6cH
provides 14aH which, as expected, does not afford a tautomer
upon deprotonation.
Synthesis and Properties of the Ligands
The synthesis of 4a,b and 5a,b has been presented in earlier
work.14 A three-step preparation of the parent pyrrolo[3,2-h]-
quinoline (6a) starting from 8-hydrazinoquinoline has been
reported.18,19 We have developed a simple alternative approach
starting from readily available 8-nitro-7-methylquinoline (7).20-22
Treatment of 7 with dimethylformamide dimethylacetal (DMF-
DMA) affords an almost quantitative yield of the N,N-
dimethylaminoethene derivative 8 which undergoes reduction
and ring closure to afford 6aH in good yield.
The 2-substituted derivatives 6b-dH can be prepared via the
8-quinolinehydrazone of the appropriate acetyl aromatic, which
then undergoes Fisher cyclization upon heating with polyphos-
phoric acid (PPA).23
All the species 4-6, as well as their corresponding salts and
tautomers, could be readily characterized by high-field NMR.
When necessary, 2D-COSY techniques were used to establish
proton connectivities.
A useful way to analyze the electronic character of these
species is by inspection of their absorption spectra (Table 1).
The pyrroloquinolines 6aH and 14aH exhibit a long wavelength
π-π* band at 315-326 nm. The 4-pyridyl system 14bH is
capable of more extended delocalization and thus absorbs at
lower energy (390 nm). Conversion of 6aH to its salt 9 induces
a bathochromic shift of 51 nm, whereas the corresponding
tautomer 10 appears red, absorbing at 448 nm.
The electronic spectra of the series 6aH, 14a,bH, and 15
reflect the degree of conjugative interaction. Due to the absence
of effective delocalization in 14aH, the absorption spectrum of
this species resembles its precursor 6cH with a bathochromic
tail. The 4′-pyridyl analogue behaves quite differently (Figure
1). Compared with its precursor, the salt 14bH exhibits a 66-
One of the interesting features of molecules such as 4aH and
6aH is their potential to exist in a tautomeric form. Intramo-
lecular hydrogen transfer from the acidic N-H to the basic
(16) Savoia, D.; Concialini, V.; Roffia, S.; Tarai, L. J. Org. Chem. 1991,
56, 1822.
(17) Seki, K.; Ohkura, K.; Terashima, M.; Kanaoka, Y. Heterocycles 1984,
22, 2347.
(18) Sergeeva, Zh. F.; Akhvlediani, R. N.; Shabunova, V. P.; Korolev, B.
A.; Vasil′ev, A. M.; Babushkina, T. N.; Suvorov, N. N. Khim.
Geterotsik. Soedin. (Engl. Transl.) 1975, 12, 1402.
(19) Krasnokutskii, S. N.; Kurkovskaya, L. N.; Shibanova, T. A.; Shabuno-
va, V. P. Zh. Struct. Khim. (Engl. Transl.) 1991, 32, 106.
(20) Kozikowski, A. P.; Ishida, H.; Chen, Y. Y. J. Org. Chem. 1980, 45,
3350.
(21) Batcho, A. D.; Leimgruber, W. Org. Synth. 1985, 63, 214.
(22) Ponticello, G. S.; Baldwin, J. J. J. Org. Chem. 1979, 44, 4003.
(23) Robinson, B. The Fischer Indole Synthesis; John Wiley and Sons:
New York, 1982.

586 Inorganic Chemistry, Vol. 39, No. 3, 2000
Wu et al.
Figure 2. Molecular mechanics simulation of [Ru(L)(bpy)2]2+ (left)
and [Ru(6b)(bpy)2]+ (right) where L ) 2-phenyl-1,10-phenanthroline.
charge density of the ligand as well as changes in shielding
and deshielding effects due to the local environment in the
complex. The most dramatic shift occurs for H7 of 4a,b, which
moves upfield 2.11-2.13 ppm upon complexation. This proton
points toward the face of an auxiliary bpy-d8, which accounts
for some of the shielding.
For comparison, we can consider [Ru(5a)(bpy-d8)2]+ or [Ru-
(16)(bpy-d8)2]2+. For both of these complexes, H8 should point
even more toward the orthogonal bpy-d8, and complexation
induced upfield shifts of +0.82 and +0.48 ppm are observed,
respectively, suggesting that the major part of the shift for ligand
4 is due to the increased negative charge on the indole nucleus.
In fact, all the proton resonances for the pyrrole containing
ligands experience a similar upfield shift due to this increase
of negative charge on the coordinated ligand.27,28 The sole
exceptions are H3 and H3′, which are held in a more deshielded
environment due to the planar cisoid conformation required for
chelation.
Figure 1. Electronic absorption spectra of 6dH (______), 14bH (- - -),
and 15 (........) in CH3CN (10-5 M) at 25 °C.
nm bathochromic shift, indicating a strong conjugative interac-
tion of the pyridinium ring with the parent pyrrolo[3,2-
h]quinoline. Interestingly, the tautomer 15 shows strong bands
at 460 and 393 nm, suggesting that both polar (15B) and
nonpolar (15A) resonance forms make significant contributions
to the hybrid.
Behavior as Ligands
As described earlier, the parent systems in this study, 4aH,
5aH, and 6aH, are benzo-fused analogues of 2-(2′-pyridyl)-
pyrrole. The pyridine analogues which may be used for
comparison are 2-(2′-pyridyl)quinoline (16) and 1,10-phenan-
throline (17). The pyrrole containing ligands will be compared
with 16 and 17 with respect to both geometric and electronic
influences on the properties of their complexes with Ru(II).
From a geometric viewpoint, the pyrrole containing ligands
are more “open,” which is to say that the nitrogens are further
separated, than their pyridine counterparts. Thus, we expect a
larger N-Ru-N angle and, when coordinated to Ru(II), the
benzo ring of 4a will be further from the metal center than the
benzo ring of 16.
This situation is perhaps best illustrated for the 2-phenyl
derivative 6b as compared with the analogous 2-phenyl-1,10-
phenanthroline. Figure 2 depicts a molecular mechanics simula-
tion for the mixed ligand Ru(II) complexes of both ligands.29
In the phenanthroline case, the 2-phenyl substituent is nearly
orthogonal to the parent ring and thus parallel to the pyridine
ring of an auxiliary bpy. The steric crowding in this system is
somewhat compensated by a favorable phenylpyridyl π-stacking
interaction. From the NMR spectrum of this complex, we find
that rotation about the 2,2′-bond is restricted at room temper-
ature. Similar systems have been analyzed by variable temper-
ature NMR to detect conformational mobility of a pendant
aromatic substituent.30-32 For the mixed ligand complex of
2-phenylphen (Figure 2), raising the temperature to +65 °C
effects coalescence of the ortho and meta phenyl protons and
reveals a rotational energy barrier of 16.3 kcal/mol.
To effectively coordinate in a bidentate fashion, the pyrrole
containing ligands must deprotonate and, as such, then act as
monoanionic ligands. This deprotonation and cyclometalation
process has previously been examined for 4a complexation with
Pd(II).24 During the reaction of the ligand with [Ru(bpy)2Cl2],
the deprotonation step occurs spontaneously, so that after the
initial coordination with the pyridyl nitrogen, oxidative addition
of Ru(II) to the N-H occurs. The complexes were generally
formed in moderate yields (40-80%). For 5a,b, where the fused
benzo or pyrido ring is more encumbering than for 4a,b, the
yields were lower. For 6d, the pendant 4-pyridyl ring is the
most nucleophilic site. Its interference with the chelation process
lowers the yield of desired material to only 5%.
Since the pyrrole containing ligands are unsymmetrical, the
resulting [Ru(bpy)2L]+ complexes lack a symmetry axis, causing
the 16 proton resonances for the two auxiliary bpys to be
nonequivalent. To remove these signals, and thus greatly
simplify the NMR spectrum, we prepared the complexes
employing bpy-d8 as the auxiliary ligand, so that only peaks
For the pyrrole analogue [Ru(6b)(bpy-d8)2]+, the phenyl ring
points further away from the site of complexation, and free
(27) Constable, E. C.; Hannon, M. J. Inorg. Chim. Acta 1993, 211, 101.
(28) Constable, E. C.; Holmes, J. M. J. Organomet. Chem. 1986, 301, 203.
(29) Calculations performed using PC MODEL from Serena Software,
Bloomington, IN.
(30) Kelly, J. M.; Long, C.; O’Connell, C. M.; Vos, J. G.; Tinnemans, A.
H. A. Inorg. Chem. 1983, 22, 2818.
1
from the ligand of interest appear in the H NMR.25,26
Shifts in the proton resonances of the ligands occur as a result
of complexation with Ru(II). These shifts reflect changes in
(24) Thummel, R. P.; Hegde, V. J. Org. Chem. 1989, 54, 1720.
(25) Chirayil, S.; Thummel, R. P. Inorg. Chem. 1989, 28, 812.
(26) Keyes, T. E.; Weldon, F.; Mu¨ller, E.; Pechy, P.; Gra¨tzel, M.; Vos, J.
G. J. Chem. Soc., Dalton Trans. 1995, 2705.
(31) Dieck, H.; Kollvitz, W.; Kleinwa¨chter, I. K. Inorg. Chem. 1984, 23,
2685.
(32) Bolger, J. A.; Ferguson, G.; James, J. P.; Long, C.; McArdle, P.; Vos,
J. G. J. Chem. Soc., Dalton Trans. 1993, 1577.

Bidentate Ligands That Contain Pyrrole
Inorganic Chemistry, Vol. 39, No. 3, 2000 587
Table 2. 1H NMR Data for Systems Related to
2-(4′-Pyridyl)-pyrrolo[3,2-h]quinolinea
these eight ligands, the narrowness of the absorption range
suggests that the pyrrole containing ligands are not involved in
the MLCT transition, which rather involves the bpy-d8 ligands
that are common to all the complexes. Stabilization of the
photooxidized excited state by the anionic ligands would account
for the bathochromic shift over the expected value of about 450
nm, as evidenced by the model complexes [Ru(16)(bpy-d8)2]2+
and [Ru(17)(bpy-d8)2]2+
.
The second longest wavelength band appears to be reasonably
consistent with MLCT to the pyrrole containing ligand, which
would be a poorer acceptor due to its anionic character. Ligands
4a,b and 5a should have similar electronegativities, and for their
complexes, this band comes at 358-385 nm. Ligand 5b is more
electronegative, and the band is shifted to 472 nm. For the
complexes of 6a-d and 14a, the 2-substituents, being nearly
orthogonal, have relatively little electronic influence on the
coordinated pyrroloquinoline ring, and this band is observed in
the range of 445-467 nm. The increased energy of the
2-substituted derivatives as compared to 6a (467 nm) may be
more due to steric disruption of the ligand field.
The complex of 15 involves a formally neutral but quite
dipolar ligand. Of the two long-wavelength absorption bands,
one can assign the band at 386 nm to MLCT involving 15,
whereas the band at 457 nm appears more like a normal bpy-
centered transition without the stabilizing effect of an anionic
ligand.
ligand/complex
H2′/H6′
H3′/H5′
H3
6dHb
8.59
7.98
8.87
8.38
7.80
7.58
6.82
8.65
8.23
7.35
7.18
6.74
7.87
7.40
7.15
[Ru(6d)(bpy-d8)2]+c
14bHd
15d
[Ru(15)(bpy-d8)2]+c
a Reported in ppm downfield from Me4Si. b CDCl3. c CD3CN. d DM-
SO-d6.
rotation about the 2,2′-bond is possible at room temperature.
The unfortunate coincidence of the phenyl ring signals for this
complex does not allow an estimate of the rotational barrier by
lowering the temperature.
Ligand 15 is interesting in that it can function as a neutral
chelating diimine species. The complex [Ru(15)(bpy-d8)2]2+ may
be prepared either directly from 15 or from 14bH, which
deprotonates to 15 upon complexation. The proton resonances
of the pendant pyridinium ring, as well as the pyrrole H3, are
good indicators of electronic changes that occur upon quater-
nization or complexation, and these data are summarized in
Table 2. As expected, quaternization of the pendant pyridine
creates a deshielding effect and causes a downfield shift of all
five protons. This shift is less pronounced for H2′/H6′, which
were already deshielded in 6dH due to the proximal nitrogen.
When 6dH is complexed with Ru(II), the ligand becomes
anionic, and this increased negative charge causes an upfield
shift of 0.44-0.76 ppm. Some of this shielding effect in the
pyridine moiety may also be due to π-stacking with an
orthogonal bpy-d8. When the quaternized species 14bH is
deprotonated, deshielding is diminished, and upfield shifts of
0.42-0.49 ppm are evidenced. Complexation of 15 again leads
to increased shielding, and the shifts are consistent with what
was observed for 6d, with H3′/H5′ showing the strongest effect
(0.88 ppm) and H3 showing the weakest (0.25 ppm). It is
noteworthy that for 15 and its complex, the major resonance
contributor appears to be 15B, because free rotation about the
4,2′-bond is demonstrated by the equivalency of H2′ and H6′
as well as H3′ and H5′.
An important property of Ru(II) polypyridine complexes is
the nature of the excited state as reflected in the electronic
absorption and emission spectra. The longest wavelength band
characterizes the lowest energy excited state, which is generally
associated with the promotion of an electron from a metal based
d-orbital to the π*-orbital of the most electronegative ligand,
the so-called metal-to-ligand charge transfer (MLCT) state.33
In this excited state, the metal becomes photooxidized (RuII to
RuIII) so that good electron donating ligands will stabilize the
state and lower its energy. At the same time, such good donor
ligands will be poor MLCT acceptors.
The complexes were nonemissive at room temperature but
did emit at 77 K. These emission bands fall into three groups.
The highest energy bands belong to the complexes of 4a,b,
whereas the lowest energy bands are associated with complexes
of 5a,b. The complexes of 6a-d fall between the highest and
lowest energy bands with a fairly monotonic increase in energy
along the series.
The electrochemical properties of the complexes are sum-
marized in Table 4 and are consistent with the photochemical
model. The oxidation potentials for the Ru(II) complexes of
ligands 4-6 range from 0.58 to 0.94 V, indicating that oxidation
is considerably facilitated as compared with the model com-
plexes of 16 and 17, which appear at 1.26 and 1.23 V,
respectively. If one considers that the anionic ligand assists in
stabilizing the Ru(III) state, this potential should be a direct
measure of that stabilizing or donor ability. The indole systems
4 are the best donors, showing the lowest potentials. The effect
of the 2-substituent for ligands 6b-d appears to be minimal,
with the oxidation potential for all four pyrrolo[3,2-h]quinoline
complexes falling in the narrow range of 0.74-0.80 V.
The reduction process for Ru(II) polypyridine complexes is
normally ligand-based and involves the addition of an electron
to the most electronegative ligand. The complexes of 4-6 all
involve formally anionic ligands, and thus reduction would be
expected to occur on the auxiliary bpy-d8 species. The first and
second reductions for [Ru(bpy)3]2+ occur at -1.33 and -1.52
V, respectively,35 and correlate well with the corresponding
value ranges of -1.19 to -1.44 and -1.42 to -1.72 V observed
for the complexes of 4-6.
The complexes of 14a and 15 both exhibit an irreversible
wave at -1.02 and -1.37 V, respectively. This reduction is
attributed to the pendant pyridinium ring. The more facile
reduction of 14a is consistent with a higher concentration of
positive charge resulting from less conjugative interaction of
the pyridinium ring with the parent pyrrolo[3,2-h]quinoline
Table 3 lists the electronic absorption and emission data for
the complexes under consideration. For all complexes of 4, 5,
and 6, we observe a long-wavelength band in the range of 490-
508 nm. Considering the pronounced structural variations among
(34) Elfring, W. H., Jr.; Crosby, G. A. J. Am. Chem. Soc. 1981, 103, 2683.
(35) Thummel, R. P.; Lefoulon, F.; Korp, J. D. Inorg. Chem. 1987, 26,
2370.
(33) Roundhill, D. M. Photochemistry and Photophysics of Metal com-
plexes; Plenum: New York, 1994; p. 165.

588 Inorganic Chemistry, Vol. 39, No. 3, 2000
Wu et al.
Table 3. Electronic Absorption and Emission Dataa for RuII(L)(bpy-d8)2 Complexes
ligand L
absorption (298 K) λmax (nm)
emission (77 K) λmax (nm)
4a
4b
5a
5b
6a
6b
6c
6d
14a
15
16
17
493 (3.98), 358 (4.36), 335 (4.36), 291 (4.71)
493 (3.92), 361 (4.23), 332 (4.25), 291 (4.60)
508 (4.07), 385 (4.31), 331 (4.37), 291 (4.82)
507 (4.25), 472 (4.28), 406 (4.44), 338 (4.44), 292 (4.92)
503 (3.92), 467 (3.86), 350 (3.98), 289 (4.69)
495 (4.04), 458 (4.03), 291 (4.88)
654
660
732
721
707
686
676
666
670
649
660
575b
496 (3.81), 449 (3.79), 291 (4.69)
490 (3.96), 458 (3.94), 323 (4.37), 291 (4.74)
481 (3.89), 445 (3.89), 339 (4.10), 290 (4.62)
457 (4.14), 386 (4.46), 290 (4.74)
484 (3.96), 444 (4.04), 286 (4.75)
448 (4.31), 285 (4.91)
a 10-5 M in CH3CN, log ꢀ in parentheses. b Reported for the corresponding protio complex, ref 34.
Table 4. Half-Wave Redox Potentials for RuII(L)(bpy-d8)2
The reaction mixture was filtered through Celite, and the filtrate was
evaporated to provide a viscous oil, which was purified by chroma-
tography on alumina (25 g), eluting with EtOAc/CH2Cl2 (1:1), to give
6aH as a brown solid (0.91 g, 77%), which was recrystallized from
hexanes: mp 97-98 °C (lit.7a mp 99.5-100.5 °C); 1H NMR (CDCl3)
δ 11.47 (bs, 1H, NH), 8.87 (dd, 1H, J ) 4.5 Hz, 1.5 Hz, H8), 8.31 (dd,
1H, J ) 8.4 Hz, 1.5 Hz, H6), 7.84 (d, 1H, J ) 8.7 Hz, H5 or H4), 7.48
(d, 1H, J ) 8.4 Hz, H4 or H5), 7.44 (q, 1H, H7), 7.42 (t, 1H, J ) 2.4
Hz, H3), 6.75 (t, 1H, J ) 2.4 Hz, H2).
Complexesa,b
ligand L
E1/2(ox)
E1/2(red)
4a
4b
5a
5b
6a
6b
6c
6d
14a
15
16
17e
0.58c,d
0.64c,d
0.94c,d
0.73c,d
0.80c
-1.22 (90)
-1.26 (150)
-1.19 (120)
-1.44 (120)
-1.37 (90)
-1.32 (120)
-1.43 (110)
-1.37 (70)
-1.17 (70)
-1.54 (70)
-1.19 (30)
-1.51 (125)
-1.48 (100)
-1.52 (130)
-1.42 (140)
-1.72 (110)
-1.62 (120)
-1.60 (150)
-1.68 (130)
-1.63 (100)
-1.47 (100)
-1.84 (130)
-1.57 (100)
-1.67 (200)
0.78c
0.74c
9-Methylpyrrolo[3,2-h]quinolinium iodide (9). A mixture of
pyrrolo[3,2-h]quinoline (0.46 g, 2.7 mmol) and CH3I (1.42 g, 10.0
mmol) in CH3CN (20 mL) was refluxed for 24 h to provide 9 as a
yellow solid (0.59 g, 70%), which was washed with a small amount of
cold acetone and was further purified by recrystallization from H2O:
0.79c
1.08c
-1.02c
-1.37c
0.83c,d
1.26 (90)
1.19 (150)
1
mp 187-189 °C; H NMR (DMSO-d6) δ 12.53 (s, 1H, NH), 9.23 (d,
a Potentials are in volts vs. SSCE, difference between anodic and
cathodic peaks (mV) is given in parentheses. b Solutions are in 0.1 M
TBAP; the solvent was CH3CN; T ) 25 ( 1 °C. c Irreversible.
d Becomes quasi-reversible at higher sweep rates. e For protio-bpy
complex.
1H, J ) 6.0 Hz, H8), 9.20 (d, 1H, J ) 8.1 Hz, H6), 8.22 (d, 1H, J )
8.7 Hz, H4 or H5), 8.01-7.97 (m, overlapping, 2H, H3 and H7), 7.93
(d, 1H, J ) 8.7 Hz, H5 or H4), 7.06 (t, 1H, J ) 1.8 Hz, H2), 4.90 (s,
3H, CH3); 13C NMR (DMSO-d6) δ 146.2, 145.4, 133.0, 131.0, 130.0,
127.1, 124.9, 121.2, 120.7, 118.7, 105.1, 48.5. Anal. Calcd for
C12H11N2I: C, 46.45; H, 3.55; N, 9.03. Found: C, 46.06; H, 3.37; N,
8.79; MS m/z 183 (M+).
nucleus. The free ligand 14a shows a similar irreversible
reduction at -1.36 V. The subsequent reduction waves observed
for 14a appear consistent with reduction of the auxiliary ligand,
whereas in the case of 15 this assignment is less clear.
1-Methyl-3,3′-ethenyl-2-(2′-pyrrolenylidene)-1,2-dihydropyri-
dine (10). A solution of 9-methylpyrrolo[3,2-h]quinolinium iodide (150
mg, 0.5 mmol) in water (20 mL) was stirred with NH4OH (20 mL) for
10 min and then extracted with CH2Cl2 (2 × 60 mL). The CH2Cl2
layers were washed with NH4OH (20 mL) and dried over anhydrous
MgSO4. The solvent was evaporated to provide 10 as a brown yellow
Experimental Section
Nuclear magnetic resonance spectra were recorded on a General
Electric QE-300 spectrometer at 300 MHz for 1H NMR and 75 MHz
for 13C NMR. Chemical shifts are reported in parts per million
downfield from Me4Si. The proton numbering scheme for 6a-dH is
given in Table 2. Electronic spectra were obtained on a Perkin-Elmer
330 spectrophotometer. Emission spectra were measured on a Perkin-
Elmer LS-5 spectrophotometer. Elemental analyses were performed by
National Chemical Consulting, Inc., Tenafly, NJ. Mass spectra were
obtained on a Hewlett-Packard 5989B mass spectrometer (59987A
Electrospray) using the Atmospheric Pressure Ionization (API) method
at a temperature of 160 °C for the complexes and Atmospheric Pressure
Chemical Ionization (APCI) at 300 °C for the ligands; M denotes the
positive ion. Cyclic voltammograms were recorded using a BAS CV-
27 voltammograph and a Houston Instruments model 100 X-Y recorder
according to a procedure which has been described previously.36 All
solvents were freshly distilled reagent grade, and all melting points
are uncorrected.
1
solid (62 mg, 70%): mp 156-158 °C; H NMR (DMSO-d6) δ 8.70
(d, 1H, J ) 5.4 Hz, H8), 8.68 (d, 1H, J ) 7.5 Hz, H6), 7.93 (d, 1H, J
) 8.4 Hz, H4 or H5), 7.85 (d, 1H, J ) 1.2 Hz, H3), 7.44 (dd, 1H, H7),
7.31 (d, 1H, J ) 8.4 Hz, H5 or H4), 6.71 (d, 1H, J ) 1.5 Hz, H2), 5.04
(s, 3H, CH3); 13C NMR (DMSO-d6) δ 142.9, 142.1, 141.3, 134.8, 132.8,
132.6, 126.4, 124.8, 114.6, 113.4, 103.7, 48.8; MS m/z 183 (M + 1).
8-Quinolinylhydrazone of acetophenone (13b). A mixture of
acetophenone (0.51 g, 4.30 mmol) and 8-hydrazinoquinoline (0.65 g,
4.30 mmol) in absolute EtOH (10 mL) was refluxed for 2 h to provide
1
13b (1.0 g, 89%): mp 135-136 °C; H NMR (CDCl3) δ 9.56 (broad
s, 1 H, NH), 8.77 (dd, 1 H, J ) 4.2, 1.4 Hz, H2′), 8.12 (d, 1 H, J ) 8.0
Hz, H4′), 7.9 (dd, 1 H, J ) 7.4, 1.4 Hz, H2), 7.75 (d, 1 H, J ) 7.6 Hz,
H5′), 7.52 (t, 1 H, J ) 7.8 Hz, H6′), 7.44-7.33 (m, 3 H), 7.26 (t, J )
7.8 Hz, H7′), 2.40 (s, -CH3); IR (KBr) 3295 (NH), 3020, 2960, 1665,
1530, 1460, 1420, 1335, 1105, 800 cm-1
.
2-Phenylpyrrolo[3,2-h]quinoline (6bH). The hydrazone 13b (0.56
g, 2.14 mmol) was mixed with PPA (12 g) and heated at 120 °C for 4
h to give 0.42 g of crude product. This material was purified by column
chromatography (20 g of SiO2, 1:4 EtOAc/CH2Cl2) to provide 6bH
The preparations of ligands 4a,b and 5a,b have been described.14
Literature procedures were followed for the preparation of 8-hydrazi-
noquinoline,10 7-(â-trans-N,N-dimethylaminoethenyl)-8-nitroquinoline,37
and [Ru(bpy-d8)2Cl2].25
1
(0.38 g, 73%): mp 156-157 °C; H NMR (CDCl3) δ 10.42 (broad s,
1 H, NH), 8.79 (dd, 1 H, J ) 4.4, 1.3 Hz, H8), 8.25 (d, 1 H, J ) 8.1
Hz, H6), 7.81-7.77 (m, 3 H), 7.48-7.43 (m, 3 H), 7.37 (dd, 1 H, J )
8.1, 4.4 Hz, H7), 7.35-7.26 (m, 1 H), 7.01 (d, 1 H, J ) 2.3 Hz, H3);
13C NMR (CDCl3) δ 147.2, 138.3, 137.3, 132.0, 130.8, 129.1, 128.5,
127.8, 125.3, 125.2, 122.0, 120.0, 119.1, 101.4, 96.1; IR (KBr) 3420
Pyrrolo[3,2-h]quinoline (6aH). A mixture of 7-(â-trans-N,N-
dimethylaminoethenyl)-8-nitroquinoline (1.70 g, 7.0 mmol) and 5%
Pd/C (0.40 g) in EtOAc (150 mL) was hydrogenated (40 atm) for 2 h.
(36) Goulle, V.; Thummel, R. P. Inorg. Chem. 1990, 29, 1767.
(37) Riesgo, E. C.; Jin, X.; Thummel, R. P. J. Org. Chem. 1996, 61, 3017.
(NH), 3040, 2985, 1580, 1520, 1460, 1360, 1300, 830 cm-1
.

Bidentate Ligands That Contain Pyrrole
Inorganic Chemistry, Vol. 39, No. 3, 2000 589
8-Quinolylhydrazone of 3-acetylpyridine (13c). Following the
procedure described for 13b, a mixture of 3-acetylpyridine (0.60 g, 5
mmol) and 8-hydrazinoquinoline (0.80 g, 5 mmol) in absolute EtOH
(20 mL) was heated at reflux for 2 h to provide 13c as a yellow solid
The organic layer was washed with ammonium hydroxide and dried
over anhydrous Na2CO3. The solvent was evaporated to provide 15 as
a brown-red solid (62 mg, 61%): mp 224-227 °C; 1H NMR (DMSO-
d6) δ 8.65 (d, 1H, J ) 4.2 Hz, H8), 8.38 (d, 2H, J ) 6.0 Hz, H2′ and
H6′), 8.23 (d, 2H, J ) 6.0 Hz, H3′ and H5′), 8.05 (d, 1H, J ) 8.1 Hz,
H6), 7.55 (d, 1H, J ) 8.4 Hz, H4 or H5) 7.40 (s, 1H, H3), 7.26 (m, 1H,
H7), 7.03 (d, 1H, J ) 8.1 Hz, H4 or H5), 4.03 (s, 3H, CH3). Anal.
Calcd for C17H13N3‚CH2Cl2: C, 62.79; H, 4.36; N, 12.20. Found: C,
63.27; H, 4.76; N, 12.39.
[Ru(4a)(bpy-d8)2](PF6). A mixture of [Ru(bpy-d8)2Cl2] (54 mg, 0.1
mmol) and 2-(2′-pyridyl)-indole (4aH, 19 mg, 0.1 mmol) in EtOH/
H2O (3:1, 20 mL) was heated at reflux for 30 h under Ar. After the hot
reaction mixture was filtered, a solution of NH4PF6 (50 mg, 0.3 mmol)
in EtOH/H2O (3:1, 5 mL) was added to the filtrate. The solvent was
evaporated to produce a brown solid. The residue was purified by
chromatography on alumina (15 g). After unreacted 4aH was eluted
with CH2Cl2/hexanes (2:1), a following fraction, eluted with CH2Cl2,
was evaporated to produce the complex as a brown red solid (45 mg,
49%): 1H NMR (CD3CN) δ 8.00 (d, 1H, J ) 7.8 Hz, H3′), 7.69 (t, 1H,
J ) 7.8 Hz, H4′), 7.45 (d, 1H, J ) 8.1 Hz, H4), 7.33 (d, 1H, J ) 5.4
Hz, H6′), 7.18 (s 1H, H3), 6.88 (t, 1H, J ) 6.6 Hz, H5′), 6.67 (t, 1H, J
) 7.5 Hz, H5), 6.45 (t, 1H, J ) 7.5 Hz, H6), 5.36 (d, 1H, J ) 8.4 Hz,
H7); MS m/z 626 (M + 4+).
[Ru(4b)(bpy-d8)2](PF6). Following the procedure described for [Ru-
(4a)(bpy-d8)2](PF6), a mixture of 3-methyl-2-(2′-pyridyl)-indole (4bH,
32 mg, 0.15 mmol) and [Ru(bpy-d8)2Cl2] (80 mg, 0.15 mmol) in EtOH/
H2O (3:1, 20 mL) was heated at reflux for 15 h to afford the complex
as a brown red solid (51 mg, 43%): 1H NMR (CD3CN) δ 8.06 (d, 1H,
J ) 7.8 Hz, H3′), 7.72 (t, 1H, J ) 7.5 Hz, H4′), 7.44 (d, 1H, J ) 8.1
Hz, H4), 7.40 (d, 1H, J ) 5.4 Hz, H6′), 6.86 (t, 1H, J ) 6.9 Hz, H5′),
6.63 (t, 1H, J ) 7.5 Hz, H5), 6.44 (t, 1H, J ) 7.5 Hz, H6), 5.32 (d, 1H,
J ) 8.4 Hz, H7), 2.70 (s, 3H, CH3); MS m/z 640 (M + 4+).
[Ru(5a)(bpy-d8)](PF6). Following the procedure described for [Ru-
(4a)(bpy-d8)2](PF6), a mixture of 2-(2′-pyrrolyl)-quinoline (5aH, 39 mg,
0.2 mmol) and [Ru(bpy-d8)2Cl2] (107 mg, 0.2 mmol) in EtOH/H2O
(3:1, 20 mL) was heated at reflux for 24 h to afford the complex as a
brown red solid (29 mg, 19%): 1H NMR (CD3CN) δ 7.96 (d, 1H, J )
8.7 Hz, H4), 7.79 (d, 1H, J ) 8.7 Hz, H3), 7.65 (d, 1H, J ) 7.8 Hz,
H5), 7.19 (t, 1H, J ) 7.2 Hz, H6), 7.11-7.09 (m, overlapping, 2H, H8
and H3′), 7.01 (t, 1H, J ) 7.5 Hz, H7), 6.21 (m, 1H, H4′), 5.89 (s, 1H,
H5′); MS m/z 626 (M + 4+).
[Ru(5b)(bpy-d8)2](PF6). Following the procedure described for [Ru-
(4a)(bpy-d8)2](PF6), a mixture of 2-(2′-pyrrolyl)-[1,8]-naphthyridine
(5bH, 59 mg, 0.3 mmol) and [Ru(bpy-d8)2Cl2] (161 mg, 0.3 mmol) in
EtOH/H2O (3:1, 20 mL) was heated at reflux for 24 h to afford the
complex as a brown red solid (20 mg, 13%): 1H NMR (CD3CN) δ
7.96 (dd, 1H, J ) 8.7 Hz, 1.8 Hz, H5), 7.91 (d, 1H, J ) 8.7 Hz, H4),
7.80 (dd, 1H, J ) 4.5 Hz, 1.8 Hz, H7), 7.77 (d, 1H, J ) 8.7 Hz, H3),
7.13 (dd, 1H, J ) 3.9 Hz, 0.9 Hz, H3′), 7.08 (q, 1H, H6), 6.23 (q, 1H,
H4′), 6.02 (q, 1H, H5′).
1
(1.14 g, 87%): mp 135-137 °C; H NMR (CDCl3) δ 9.66 (s, 1H,
NH), 9.07 (d, 1H, J ) 2.1 Hz, H2′), 8.75 (dd, 1H, J ) 3.9 Hz, 1.2 Hz,
H6′ or H2), 8.54 (dd, 1H, J ) 5.1 Hz, 1.2 Hz, H2 or H6′), 8.19 (dd, 1H,
J ) 8.1 Hz, 1.5 Hz, H4 or H4′), 8.11 (dd, 1H, J ) 8.1 Hz, 0.9 Hz, H4′
or H4), 7.72 (d, 1H, J ) 7.5 Hz, H5), 7.51 (t, 1H, J ) 8.1 Hz, H6), 7.40
(dd, 1H, H5′ or H3), 7.32 (dd, 1H, H3 or H5′), 7.27 (d, 1H, J ) 8.1 Hz,
H7), 2.42 (s, 3H, CH3).
2-(3′-Pyridyl)-pyrrolo[3,2-h]quinoline (6cH). Following the pro-
cedure described for 6bH, the hydrazone 13c (1.02 g, 3.9 mmol) was
treated with PPA (10 g) at 120-130 °C for 2 h to provide 6cH as an
1
off-white solid (0.82 g, 86%): mp 181-183 °C; H NMR (CDCl3) δ
11.10 (s, 1H, NH), 9.06 (s, 1H, H2′), 8.74 (d, 1H, J ) 4.2 Hz, H8),
8.54 (d, 1H, J ) 4.2 Hz, H6′), 8.26 (d, 1H, J ) 8.1 Hz, H6), 7.98 (d,
1H, J ) 7.2 Hz, H4′), 7.81 (d, 1H, J ) 8.4 Hz, H4 or H5), 7.48 (d, 1H,
J ) 8.7 Hz, H5 or H4), 7.36 (dd, 1H, H7), 7.29 (dd, 1H, H5′), 7.06 (s,
1H, H3). Anal. Calcd for C16H11N3‚0.5H2O: C, 75.59; H, 4.72; N, 16.54.
Found: C, 75.89; H, 4.76; N, 16.48; MS m/z 245 (M+).
2-[3′-(1-Methylpyridyl)]-pyrrolo[3,2-h]quinolinium iodide (14aH).
The 2-(3′-pyridyl)-pyrrolo[3,2-h]quinoline (0.30 g, 1.2 mmol) was
dissolved in CH3CN (20 mL) with heating. Excess CH3I (1.5 g, 10.6
mmol) was added, and the mixture was heated at reflux for 30 min.
After cooling, 14aH was obtained as a yellow solid (0.33 g, 70%):
1
mp 220-223 °C; H NMR (DMSO-d6) δ 13.10 (s, 1H, NH), 9.70 (s,
1H, H2′), 9.14 (d, 1H, J ) 8.4 Hz, H4′), 8.92 (d, 1H, J ) 4.2 Hz, H8),
8.83 (d, 1H, J ) 6.0 Hz, H6′), 8.42 (d, 1H, J ) 8.4 Hz, H6), 8.17 (dd,
1H, H5′), 7.84 (d, 1H, J ) 8.7 Hz, H4 or H5), 7.57 (d, 1H, J ) 8.7 Hz,
H5 or H4), 7.57-7.54 (m, overlapping, 2H, H3 and H7), 4.39 (s, 3H,
CH3). Anal. Calcd for C17H14N3I: C, 52.71; H, 3.62; N, 10.85. Found:
C, 52.33; H, 3.62; N, 10.60; MS m/z 259 (M-1+).
8-Quinolylhydrazone of 4-acetylpyridine (13d). Following the
procedure described for 13b, a mixture of 8-hydrazinoquinoline (0.80
g, 5 mmol), 4-acetylpyridine (0.60 g, 0.5 mmol), and HOAc (2 drops)
in EtOH (25 mL) was heated at reflux for 4 h to provide 13d as a
1
yellow solid (1.22 g, 93%): mp 151-152 °C; H NMR (CDCl3) δ
9.81 (s, 1H, NH), 8.78 (dd, 1H, J ) 3.6 Hz, 0.9 Hz, H2), 8.61 (d, 2H,
J ) 6.0 Hz, H2′ and H6′ ), 8.14 (d, 1H, J ) 8.4 Hz, H5 or H4), 7.77 (m,
overlapping, 3H, H3′, H5′ and H4 or H5), 7.54 (t, 1H, J ) 7.8 Hz, H6),
7.43 (t, 1H, H3), 7.33 (d, 1H, J ) 8.1 Hz, H7), 2.41 (s, 3H, CH3).
2-(4′-Pyridyl)-pyrrolo[3,2-h]quinoline (6dH). Following the pro-
cedure described for 6bH, the hydrazone 13d (0.66 g, 2.5 mmol) was
treated with PPA (10 g) at 120 °C for 2 h to afford 6dH as a brown-
gray solid (0.55 g, 90%): mp 218-219 °C; 1H NMR (CDCl3) δ 11.19
(s, 1H, NH), 8.75 (dd, 1H, J ) 4.2 Hz, 1.2 Hz, H8), 8.59 (d, 2H, J )
5.7 Hz, H2′ and H6′), 8.26 (dd, 1H, J ) 8.1 Hz, 1.2 Hz, H6), 7.80 (d,
1H, J ) 8.4 Hz, H5 or H4), 7.58 (d, 2H, J ) 6.0 Hz, H3′ and H5′), 7.48
(d, 1H, J ) 8.7 Hz, H4 or H5), 7.39 (dd, 1H, H7), 7.18 (s, 1H, H3); 13
C
NMR (CDCl3) δ 150.4, 148.1, 139.2, 137.9, 136.8, 134.6, 132.4, 127.8,
[Ru(16)(bpy-d8)2](PF6)2. Following the procedure described for [Ru-
(4a)(bpy-d8)2](PF6), a mixture of 2-(2′-pyridyl)-quinoline (16, 21 mg,
0.1 mmol) and [Ru(bpy-d8)2Cl2] (54 mg, 0.1 mmol) in EtOH/H2O (3:
1, 20 mL) was heated at reflux for 24 h to afford the complex38,39 as
a brown red solid (20 mg, 22%): 1H NMR (CD3CN) δ 8.70 (d, 1H, J
) 8.1 Hz, H3′), 8.54 (AB quartet, 2H, H3 and H4), 8.13 (t, 1H, J ) 7.8
Hz, H4′), 8.00 (d, 1H, J ) 8.1 Hz, H5), 7.62 (d, 1H, J ) 5.7 Hz, H6′),
7.59 (t, 1H, J ) 7.8 Hz, H6), 7.43 (d, 1H, J ) 7.5 Hz, H8), 7.40 (t, 1H,
J ) 7.2 Hz, H5′), 7.26 (t, 1H, J ) 7.8 Hz, H7); MS m/z 317 (M - 1+).
[Ru(6a)(bpy-d8)2](PF6). A mixture of pyrrolo[3,2-h]quinoline (6aH,
51 mg, 0.3 mmol), [Ru(bpy-d8)2Cl2] (161 mg, 0.3 mmol), and Et3N (2
drops) in EtOH/H2O (4:1, 25 mL) was heated at reflux for 20 h under
Ar. After cooling, a solution of NH4PF6 (326 mg, 2 mmol) in H2O (5
mL) was added. H2O (50 mL) was added, and a precipitate formed.
The brown solid was collected by filtration and purified by chroma-
tography on alumina (25 mg). The first fraction eluted with CH2Cl2
provided unreacted ligand. The second fraction eluted with CH2Cl2/
125.8, 121.8, 120.4, 119.9, 119.1, 103.8; MS m/z 245 (M+).
2-[4′-(1′-Methylpyridyl)]-pyrrolo[3,2-h]quinolinium iodide (14bH).
A mixture of 2-(4′-pyridyl)-pyrrolo[3,2-h]quinoline (0.20 g, 0.8 mmol)
and CH3I (1.00 g, 7.0 mmol) in CH3CN was stirred for 10 min at 45
°C. The salt 14bH was obtained as a yellow solid (0.20 g, 65%): mp
1
> 300 °C; H NMR (DMSO-d6) δ 13.36 (s, 1H, NH), 8.94 (d, 1H, J
) 3.3 Hz, H8), 8.87 (d, 2H, J ) 6.6 Hz, H2′ and H6′), 8.65 (d, 2H, J )
6.9 Hz, H3′ and H5′), 8.43 (d, 1H, J ) 7.5 Hz, H6), 7.87 (s, 1H, H3),
7.83 (d, 1H, J ) 8.7 Hz, H4 or H5), 7.61 (dd, 1H, H7), 7.59 (d, 1H, J
) 9.0 Hz, H5 or H4), 4.23 (s, 3H, CH3); 13C NMR (DMSO-d6) δ 148.7,
145.6, 145.0, 138.0, 136.6, 135.3, 131.5, 127.1, 126.4, 121.7, 121.3,
121.2, 121.1, 109.9, 46.7. Anal. Calcd for C17H14N3I‚H2O: C, 50.37;
H, 3.95; N, 10.37. Found: C, 50.01; H, 3.70; N, 10.05; MS m/z 259
(M-1+).
2-[4′-(1′-Methylpyridinylidene)]-2H-pyrrolo[3,2-h]quinoline (15).
A mixture of 2-[4′-(1′-methylpyridyl)]-pyrrolo[3,2-h]quinolinium iodide
(150 mg, 0.4 mmol) and sodium acetate (2.0 g) in water (40 mL) was
heated until it dissolved completely. After cooling to room temperature,
ammonium hydroxide (20 mL) was added, and the solution was stirred
for 10 min. The solution was then extracted with CH2Cl2 (3 × 50 mL).
(38) Thummel, R. P.; Decloitre, Y. Inorg. Chim. Acta 1987, 128, 245.
(39) Anderson, S.; Seddon, K. R.; Wright, R. D.; Cocks, A. T. Chem. Phys.
Lett. 1980, 71, 220.

590 Inorganic Chemistry, Vol. 39, No. 3, 2000
Wu et al.
CH3CN (4:1) provided the complex as a violet solid (175 mg, 79%):
1H NMR (CD3CN) δ 8.15 (d, 1H, J ) 7.8 Hz, H6), 7.78 (d, 1H, J )
8.4 Hz, H4 or H5), 7.40 (d, 1H, J ) 5.1 Hz, H8), 7.25 (d, 1H, J ) 8.4
Hz, H5 or H4), 7.08 (dd, 1H, H7), 6.72 (d, 1H, J ) 1.8 Hz, H3), 6.52
(d, 1H, J ) 1.8 Hz, H2); MS m/z 596 (M+).
and 2-[3′-(1-methylpyridyl)]-pyrrolo[3,2-h]quinolinium iodide (14aH,
77 mg, 0.2 mmol) in EtOH/H2O (3:1, 20 mL) was heated at reflux for
24 h to provide the complex as a violet solid (175 mg, 49%): 1H NMR
(CD3CN) δ 8.46 (s, 1H, H2′), 8.25 (d, 1H, J ) 8.1 Hz, H6), 8.08 (d,
1H, J ) 6.0 Hz, H6′), 7.86 (d, 1H, J ) 8.7 Hz, H4 or H5), 7.54 (d, 1H,
J ) 8.4 Hz, H4′), 7.42-7.39 (m, overlapping, 2H, H8 and H4 or H5),
7.19-7.15 (m, overlapping, 2H, H5′ and H7), 6.83 (s, 1H, H3), 4.15 (s,
3H, CH3); MS m/z 343 (M - 1+).
[Ru(15)(bpy-d8)2](PF6)2. Method A: Following the procedure
described for [Ru(6a)(bpy-d8)2](PF6), a mixture of [Ru(bpy-d8)2Cl2] (107
mg, 0.2 mmol) and 2-[4′-(1′-methylpyridyl)]-pyrrolo[3,2-h]quinolinium
iodide (14bH, 77 mg, 0.2 mmol) in EtOH/H2O (3:1, 20 mL) was heated
at reflux for 24 h to provide the complex as a violet solid (150 mg,
77%): 1H NMR (CD3CN) δ 8.26 (d, 1H, J ) 8.1 Hz, H6), 7.82 (d, 1H,
J ) 8.4 Hz, H5 or H4), 7.80 (d, 2H, J ) 6.6 Hz, H2′ and H6′ ), 7.40 (d,
1H, J ) 8.7 Hz, H5 or H4), 7.41 (d, 1H, J ) 4.8 Hz, H8), 7.35 (d, 2H,
J ) 6.6 Hz, H3′ and H5′), 7.22 (dd, 1H, H7), 7.15 (s, 1H, H3), 3.94 (s,
3H, CH3); MS m/z 343 (M - 1+).
[Ru(6b)(bpy-d8)2](PF6). Following the procedure described for [Ru-
(6a)(bpy-d8)2](PF6), a mixture of 2-phenylpyrrolo[3,2-h]quinoline (6bH,
49 mg, 0.2 mmol), [Ru(bpy-d8)2Cl2] (107 mg, 0.2 mmol), and Et3N (2
drops) in EtOH/H2O (3:1, 25 mL) was heated at reflux under Ar for
36 h to provide the complex as a violet solid (104 mg, 64%): 1H NMR
(CD3CN) δ 8.16 (d, 1H, J ) 8.1 Hz, H6), 7.80 (d, 1H, J ) 8.7 Hz, H4
or H5), 7.32-7.29 (m, overlapping, 2H, H5 or H4 and H8), 7.04 (dd,
1H, H7), 6.85 (m, 5H, Ar), 6.58 (s, 1H, H3); MS m/z 675 (M + 3+).
[Ru(6c)(bpy-d8)2](PF6). Following the procedure described for [Ru-
(6a)(bpy-d8)2](PF6), a mixture of [Ru(bpy-d8)2Cl2] (161 mg, 0.3 mmol)
and 2-(3′-pyridyl)-pyrrolo[3,2-h]quinoline (6cH, 74 mg, 0.3 mmol) in
EtOH/H2O (3:1, 20 mL) was heated at reflux for 24 h to provide the
complex as a violet solid (103 mg, 42%): 1H NMR (CD3CN) δ 8.20
(d, 1H, J ) 8.1 Hz, H6), 8.15 (d, 1H, J ) 1.8 Hz, H2′), 8.07 (dd, 1H,
J ) 4.2 Hz, 0.9 Hz, H6′), 7.82 (d, 1H, J ) 8.4 Hz, H4 or H5), 7.35 (d,
1H, J ) 3.9 Hz, H8), 7.33 (d, 1H, J ) 8.4 Hz, H5 or H4), 7.13-7.06
(m, overlapping, 2H, J ) 8.1 Hz, H4′ and H7), 6.74 (dd, 1H, H5′), 6.63
(s, 1H, H3); MS m/z 675 (M + 2+).
[Ru(6d)(bpy-d8)2](PF6). Following the procedure described for [Ru-
(6a)(bpy-d8)2](PF6), a mixture of [Ru(bpy-d8)2Cl2] (107 mg, 0.2 mmol)
and 2-(4′-pyridyl)-pyrrolo[3,2-h]quinoline (6dH, 49 mg, 0.2 mmol) in
EtOH/H2O (3:1, 20 mL) was heated at reflux for 24 h to provide the
complex as a violet solid (8 mg, 5%): 1H NMR (CD3CN) δ 8.20 (dd,
1H, J ) 8.1 Hz, 0.9 Hz, H6), 7.98 (d, 2H, J ) 5.7 Hz, H2′ and H6′ ),
7.82 (d, 1H, J ) 8.4 Hz, H5 or H4), 7.35 (d, 1H, J ) 4.8 Hz, H8), 7.34
(d, 1H, J ) 8.4 Hz, H5 or H4), 7.10 (dd, 1H, H7), 6.82 (d, 2H, J ) 5.7
Hz, H3′ and H5′), 6.74 (s, 1H, H3); MS m/z 675 (M + 2+).
Method B: Following the procedure described for [Ru(6a)(bpy-
d8)2](PF6), a mixture of [Ru(bpy-d8)2Cl2] (80 mg, 0.15 mmol) and 2-[4′-
(1′-methylpyridinylidene)]-2H-pyrro[3,2-h]quinoline (15, 39 mg, 0.15
mmol) in EtOH/H2O (3:1, 20 mL) was heated at reflux for 24 h to
1
provide a violet solid (110 mg, 75%) having an H NMR and MS
identical with the material described under Method A.
Acknowledgment. We would like to thank the Robert A.
Welch Foundation (E-621), the National Science Foundation
(CHE-9714998), and the Petroleum Research Fund of the
American Chemical Society for financial support of this work.
We would also like to thank Dr. C.-Y. Hung for the preparation
of 6bH.
[Ru(14a)(bpy-d8)2](PF6). Following the procedure described for [Ru-
(6a)(bpy-d8)2](PF6), a mixture of [Ru(bpy-d8)2Cl2] (107 mg, 0.2 mmol)
IC990445S