Heteroleptic arene ruthenium complexes based on meso-substituted dipyrrins: Synthesis, structure, reactivity, and electrochemical studies

Article abstract of DOI:10.1021/ic9000957

First examples of heteroleptic arene ruthenium complexes containing dipyrrin ligands with the general formulations [(η⁶-arene)RuCI(L) ] [(arene = C₆H₆, C₁₀H₁₄; L = 5-(4-cyanophenyl)-dipyrromethene, cy

Full text of DOI:10.1021/ic9000957

Inorg. Chem. 2009, 48, 7593–7603 7593
DOI: 10.1021/ic9000957
Heteroleptic Arene Ruthenium Complexes Based on meso-Substituted Dipyrrins:
Synthesis, Structure, Reactivity, and Electrochemical Studies
Mahendra Yadav, Ashish Kumar Singh, Biswajit Maiti, and Daya Shankar Pandey*
Department of Chemistry, Faculty of Science, Banaras Hindu University, Varanasi - 221 005 (U.P.), India
Received January 17, 2009
First examples of heteroleptic arene ruthenium complexes containing dipyrrin ligands with the general formulations
[(η6-arene)RuCl(L)] [(arene = C6H6, C10H14; L = 5-(4-cyanophenyl)-dipyrromethene, cydpm; 5-(4-nitrophenyl)-
dipyrromethene, ndpm and 5-(4-benzyloxyphenyl)-dipyrromethene, bdpm] have been synthesized. The complexes
[(η6-C10H14)RuCl(L)] (L = ndpm and cydpm) reacted with NaN3 and NH4SCN to afford neutral mononuclear
complexes [(η6-C10H14)Ru(N3)(L)] and [(η6-C10H14)Ru(SCN)(L)]. Their reactions with EPh3 (E = P, As)
and exobidentate ditopic P-P and N-N donor ligands, namely, bis-(diphenylphosphino)methane (dppm) and
4,40-bipyridine (bpy) in the presence of AgSO3CF3 afforded cationic mono- and binuclear complexes [(η6-C10-
H14)Ru(L)(EPh3)]SO3CF3, [{(η6-C10H14)Ru(L)}2(μ-dppm)](SO3CF3)2, and [{(η6-C10H14)Ru(L)}2(μ-bpy)](SO3-
CF3)2, respectively. The reaction products have been characterized by analytical and spectral studies. Molecular
structures of the representative complexes [(η6-C10H14)RuCl(cydpm)], [(η6-C6H6)RuCl(cydpm)], [(η6-C10H14)RuCl-
(ndpm)], [(η6-C10H14)Ru(N3)(ndpm)], and [(η6-C10H14)Ru(PPh3)(ndpm)]SO3CF3 have been determined crystal-
lographically. Redox behavior of the complexes has been investigated by electrochemical studies. Emission spectral
studies at room temperature suggested that the complexes under study are non-emissive.
Introduction
porphyrin based biomimetic systems, diverse porphyrin
building blocks, and as intermediates in porphyrin transfor-
mations.1-5 Because of the presence of two nitrogen donor
atoms in the planar dipyrrin unit, it provides a versatile motif
for complexation to the metals and has emerged as a versatile
ligand in coordination chemistry.6 In this regard highly
conjugated meso-substituted dipyrrins have drawn consider-
able current attention.7,8 The ease of synthesis of meso-
substituted dipyrrins from aldehydes via condensation with
pyrrole followed by oxidation has made them very useful
in the synthesis of homo- and heteroleptic complexes.6,9,10
The extensive π-skeleton of the phenyl ring present as meso-
substituents and two of the conjugated rigid pyrrole rings in
dipyrrinsenable them tobehave as a better bidentate nitrogen
donor ligands like 2,20-bipyridine or 1,10-phenanthroline.
Dipyrromethenes have attracted sustained research inter-
est over past couple of decades owing to their potential use as
valuable precursor in the synthesis of dyes, porphyrins,
*To whom correspondence should be addressed. E-mail: dspbhu@
bhu.ac.in. Phone: þ 91 542 6702480. Fax: þ 91 542 2368174.
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Muthukumaran, K.; Hindin, E.; Kirmaier, C.; Diers, J. R.; Lindsey, J. S.; Hindine,
E.; Diers, J. R.; Bocian, D. F.; Holten, D. Inorg. Chem. 2003, 42, 6616–6628. (c)
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r
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Published on Web 07/17/2009
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7594 Inorganic Chemistry, Vol. 48, No. 16, 2009
Yadav et al.
Further, one can modulate properties of the dipyrrins by
incorporating electron withdrawing/donating substituents
which have a pronounced effect on electrochemical and
optical properties.11 In general electron-donating groups
increase electron density on the ligand and redox processes
take place at the more negative potential, while the opposite
effect occurs in the presence of electron withdrawing groups.
Numerous main group and transition metal homoleptic
complexes, their photoluminescence and other properties
along with MOF: metal-organic frameworks (MOFs) based
on meso-substituted dipyrrins are well documented.6a,9,10
While a number of heteroleptic dipyrrin complexes based
on Pd(II), Hg(II), Rh(I), Cr(III), Co(II), and Cu(II) are
reported in the literature, there is just one report dealing with
ruthenium dipyrrin complexes.9c Furthermore, ruthenium-
(II) complexes containing both the dipyrrin and η6-arene
ligands have not yet been reported.
including homogeneous catalysis, polymeric materials, na-
nocages and nanoparticle precursors.13 Arene ruthenium
complexes are also being explored for their medicinal proper-
ties as anticancer agents.14 The dimeric arene ruthenium
complexes [{(η6-arene)RuCl(μ-Cl)}2] (η6-arene = benzene,
p-cymene) undergo a rich variety of chemical transforma-
tions via intermediacy of the chloro bridge cleavage reactions
leading to the formation of a series of interesting neutral and
cationic mononuclear half-sandwich η6-arene ruthenium
complexes.15 Despite its extensive chemistry, reactivity of
the arene ruthenium complexes [{(η6-arene)RuCl(μ-Cl)}2]
with meso-substituted dipyrrins have not been explored.
Because of our interests inthis area we became interested in
developing the coordination chemistry of a new class of arene
ruthenium complexes based on meso-substituted dipyrrins.16
In this paper we report the reproducible synthesis, spectral
properties, structural characterization, and reactivity of some
heteroleptic arene ruthenium complexes [(η6-arene)RuCl(L)]
containing 5-(4-cyanophenyl)-dipyrromethene, 5-(4-nitro-
phenyl)-dipyrromethene, and 5-(4-benzyloxyphenyl)-dipyr-
romethene as co-ligands. Also, we present herein the
synthesis and characterization of some bis-(diphenylpho-
sphino)-methane (dppm), 4,40-bipyridine (bpy), and azido
bridged dinuclear complexes containing dipyrrin ligands.
Ruthenium(II) complexes possessing η6-cyclic hydrocar-
bon ligands are versatile and potentially valuable synthetic
intermediates that have seen applications in diverse areas of
organic syntheses.12 Air-stable, water-soluble cationic arene
ruthenium complexes find wide applications in many areas
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Experimental Section
Reagents. All the synthetic manipulations were performed
under nitrogen atmosphere in deaerated solvents. The solvents
were purified rigorously following standard procedures prior to
their use.17 Silver trifluoromethanesulfonate, triphenylphosphine,
triphenylarsine, bis-(diphenylphosphino)-methane, sodium
azide, potassium thiocyanate, 4,40-bipyridine, 1,3-cyclohexadiene,
R-phellandrene, 2,3-dicloro-5,6-dicyano-1,4-benzoquinone (DDQ),
4-cyanobenzaldehyde, 4-bezyloxybenzaldehyde, 4-nitrobenzal-
dehyde, pyrrole, tetrabutylammonium perchlorate, and ruthe-
nium(III) chloride hydrate (all Aldrich) were used as received
without further purifications. The precursor complexes [{(η6-
arene)RuCl(μ-Cl)}2] (arene=C6H6, C10H14)18 and ligands 5-(4-
cyanophenyl)-dipyrromethane, 5-(4-nitrophenyl)-dipyrromethane,
and 5-(4-benzyloxyphenyl)-dipyrromethane19 were prepared
and purified following literature procedures.
H. Ruthenium Catalysis and Fine Chemistry; Springer: Berlin, 2004; pp 45-79.
::
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General Methods. Elemental analyses for C, H, and N were
performed on Exeter Analytical Inc. Model CE-440 CHN
analyzer. Infrared spectra in KBr pellets were acquired on a
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recorded on a JEOL AL 300 MHz spectrometer at room
temperature (RT) using CDCl3 as solvent and TMS as an
internal reference. Electronic and emission spectral data were
acquired on a Shimadzu UV-1700 series and LS-45 Lumines-
cence spectrophotometers, respectively. FAB mass spectra were
obtained on a JEOL SX 102/Da-600 Mass Spectrometer. Cyclic
voltammetric and spectroelectrochemical measurements were
performed on a CHI 620c electrochemical analyzer. A glassy
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11427–11440.

Article
Inorganic Chemistry, Vol. 48, No. 16, 2009 7595
carbon working electrode, platinum wire auxiliary electrode, and
Ag/Agþ reference electrode were used in a standard three-electrode
configuration. Tetrabutylammonium perchlorate (TBAP) was
used as a supporting electrolyte, and the solution concentration
was about 10-3 M. A platinum gauze working electrode was used
in the spectroelectrochemical experiments. Spectroelectrochemical
studies were performed in acetonitrile/0.1 M Bu4NClO4 at 298 K
using Oceanoptics Spectrasuite.
1145, 1034, 995, 893, 821, 786, 736, and 478. 1H NMR (δ, ppm):
5.69 (s, 6H), 6.47 (d, 2H, J=4.5 Hz), 6.52 (d, 2H, J=3.6 Hz), 7.60
(d, 2H, J=8.4 Hz), 8.16 (s, 2H), 8.27 (d, 2H, J=8.4 Hz). UV-vis.
(CH2Cl2, λmax nm, ε): 497 (2.52 ꢀ 104), 441 (1.18 ꢀ 104), 301
(1.31 ꢀ 104), 273 (1.71 ꢀ 104), 228 (1.51 ꢀ 104).
Synthesis of [(η6-C10H14)RuCl(bdpm)] (5). This complex was
prepared following the above procedure for 1 except that 5-(4-
benzyloxyphenyl)-dipyrromethane was used in place of 5-(4-
cyanophenyl)-dipyrromethane (0.328 g, 1.0 mmol). Yield: 50%
(0.298 g). Anal. Calcd for C32H31ClN2ORu: C, 64.47; H, 5.24;
N, 4.70%. Found: C, 64.35; H, 5.30; N, 4.68%. IR (cm-1): 1708,
1603, 1547, 1460, 1380, 1342, 1244, 1171, 997, 796, 733, 699, and
472. 1H NMR (δ, ppm): 1.09 (d, 6H, J=6.9 Hz), 2.22 (s, 3H),
2.45 (m, 1H), 5.27 (dd, 4H), 5.12 (s, 2H), 6.47 (d, 2H, J=3.9 Hz),
6.64 (d, 2H, J=4.5 Hz), 6.99 (d, 2H, J=8.1 Hz), 7.32-7.48 (m,
7H), 7.99 (s, 2H). 13C NMR (75.45 MHz, δ, ppm): 18.57 (C-
CH3), 22.07 {CH(CH3)2}, 30.54 {CH(CH3)2}, 70.09 (-CH2-
Ph), 84.68 (C6H4), 100.17 (C-CH3), 102.00 (C-CHMe2), 113.51,
118.14, 127.54, 128.07, 128.63, 130.83, 131.80, 135.37, 136.75,
146.40, 154.55, 159.05 (dipyrrin). UV-vis. (CH2Cl2, λmax nm, ε):
493 (2.52 ꢀ 104), 440 (1.72 ꢀ 104), 350 (1.17 ꢀ 104), 271 (1.19 ꢀ
104), 233 (3.05 ꢀ 104).
Synthesis of [(η6-C10H14)RuCl(cydpm)] (1). DDQ (0.228 g,
1.0 mmol) dissolved in benzene (150 mL) was added slowly (over
an hour) to a stirring solution of 5-(4-cyanophenyl)-dipyrro-
methane (0.247 g, 1.0 mmol) in CHCl3 (150 mL) cooled in an ice
bath. After thin-layer chromatography (TLC) examination
revealed complete consumption of the starting material, the
solvent was evaporated, and the resulting dark residue was
dissolved in CHCl3/MeOH (75 mL; 1:1 v/v). Triethylamine
(0.75 mL) and [{(η6-C10H14)RuCl(μ-Cl)}2] (0.306 g, 0.50 mmol)
dissolved in dichloromethane (5 mL) were added to this solu-
tion. The dark reaction mixture thus obtained was refluxed
overnight. After cooling to RT it was concentrated to dryness
under reduced pressure to afford a black solid. The crude
product was charged on a flash column (20ꢀ3 cm, SiO2; CH2-
Cl2/hexane). Second, a bright orange band was collected and
concentrated to dryness to afford [(η6-C10H14)RuCl(cydpm)].
Yield: 52% (0.268 g) Anal. Calcd for C26H24ClN3Ru: C, 60.64;
H, 4.70; N, 8.16%. Found: C, 60.62; H, 4.74: N, 8.12%. IR (cm-1):
2227, 1948, 1720, 1557, 1447, 1376, 1343, 1249, 1206, 992, 891,
Synthesis of [(η6-C10H14)Ru(N3)(cydpm)] (6). Complex 1
(0.515 g, 1.0 mmol) in dry acetone (20 mL) was treated with
sodium azide NaN3 (0.065 g, 1.0 mmol), and the suspension was
stirred at RT for 3 h. It was concentrated to dryness under
reduced pressure, extracted with dichloromethane (10 mL) and
filtered to remove solid sodium chloride. The filtrate was con-
centrated to ∼2 mL, and an excess of hexane was added to it.
The orange colored microcrystalline compound thus obtained
was filtered, washed with diethyl ether, and dried under vacuum.
Yield: 79% (0.412 g). Anal. Calcd for C26H24N6Ru: C, 59.87; H,
4.64; N, 16.11%. Found: C, 59.70; H, 4.56; N, 16.15%. IR (cm-1):
2226, 2025, 1707, 1555, 1460, 1378, 1342, 1246, 1031, 993, 893, 812,
769, 720, and 474. 1H NMR (δ, ppm): 1.06 (d, 6H, J=6.6 Hz), 2.17
(s, 3H), 2.38 (m, 1H), 5.27 (d, 2H, J=6.3 Hz), 5.42 (d, 2H, J=6.6
Hz), 6.44 (d, 2H, J=3.9 Hz), 6.50 (d, 2H, J=3.6 Hz), 7.49 (d, 2H,
J = 8.1 Hz), 7.71 (d, 2H, J = 8.1 Hz), 8.04 (s, 2H). UV-vis.
(CH2Cl2, λmax nm, ε): 490 (2.40 ꢀ 104), 300 (1.21 ꢀ 104), 265
(1.50 ꢀ 104), 236 (3.01 ꢀ 104).
1
814, 766, 717, and 474. H NMR (δ, ppm): 1.10 (d, 6H, J =
6.9 Hz), 2.24 (s, 3H), 2.40 (m, 1H), 5.30 (dd, 4H), 6.45 (d, 2H, J=
4.8 Hz), 6.49 (d, 2H, J=4.8 Hz), 7.50 (d, 2H, J=6.6 Hz), 7.71 (d,
2H, J=8.1 Hz), 8.03 (s, 2H). 13C NMR (75.45 MHz, δ, ppm):
18.60 (C-CH3), 22.05 {CH(CH3)2}, 30.60 {CH(CH3)2}, 84.70
(C6H4), 100.49 (C-CH3), 102.16 (C-CHMe2), 112.28 (CꢁN),
118.51, 119.00, 130.50-131.30, 134.22, 142.67, 143.44, 155.51
(dipyrrin). UV-vis. (CH2Cl2, λmax nm, ε): 495 (2.41 ꢀ 104), 440
(2.29 ꢀ 104), 301 (1.09 ꢀ 104), 267 (1.22 ꢀ 104), 237 (2.77 ꢀ 104).
Synthesis of [(η6-C6H6)RuCl(cydpm)] (2). Complex 2 was
prepared following the above procedure for 1 except that
[{(η6-C6H6)RuCl(μ-Cl)}2] was used in place of [{(η6-C10H14)-
RuCl(μ-Cl)}2]. Yield 54% (0.248 g). Anal. Calcd for C22H16-
ClN3Ru: C, 57.58; H, 3.51; N, 9.16%. Found: C, 57.54; H, 3.39:
N, 9.12%. IR (cm-1): 2227, 1648, 1556, 1460, 1378, 1341, 1245,
Synthesis of [(η6-C10H14)Ru(SCN)(cydpm)] (7). This complex
was prepared following the above procedure for 6 using
NH4SCN in place of NaN3. Yield: 75% (0.403 g). Anal. Calcd
for C27H24N4SRu: C, 60.32; H, 4.50; N, 10.42%. Found: C,
60.28; H, 4.48; N, 10.37%. IR (cm-1): 2227, 2100, 1708, 1553,
1459, 1378, 1342, 1246, 1229, 992, 893, 813, 769, 719, and 471.
1H NMR (δ, ppm): 1.08 (d, 6H, J=6.6 Hz), 2.17 (s, 3H), 2.37 (m,
1H), 5.34 (d, 2H, J=6.0 Hz), 5.40 (d, 2H, J=6.0 Hz), 6.47 (dd,
4H), 7.49 (d, 2H, 8.4 Hz), 7.72 (d, 2H, J=8.1 Hz), 7.94 (s, 2H) .
UV-vis. (CH2Cl2, λmax nm, ε): 486 (2.40 ꢀ 104), 300 (1.26 ꢀ
104), 266 (1.53 ꢀ 104), 237 (2.98 ꢀ 104).
1
1195, 1033, 993, 889, 807, 722, 670, 528, and 473. H NMR
(δ, ppm); 5.68 (s, 6H), 6.46 (d, 2H, J=3.9 Hz), 6.51 (d, 2H, J=
3.3 Hz), 7.51 (d, 2H, J=6.6 Hz), 7.70 (d, 2H, J=8.1 Hz), 8.15 (s,
2H) .UV-vis. (CH2Cl2, λmax nm, ε): 495 (2.50 ꢀ 104), 442
(1.34 ꢀ 104), 302 (1.01 ꢀ 104), 268 (1.22 ꢀ 104), 236 (2.85 ꢀ 104).
Synthesis of [(η6-C10H14)RuCl(ndpm)] (3). It was prepared
following the method for 1 except that 5-(4-nitrophenyl) dipyr-
romethane (0.267 g, 1.0 mmol) was used in place of 5-(4-cyano-
phenyl)-dipyrromethane. Yield: 54% (0.289 g). Anal. Calcd for
C25H24ClN3O2Ru: C, 56.13; H, 4.52: N, 7.85%. Found: C,
56.09; H, 4.48; N, 7.79%. IR (cm-1): 1555, 1519, 1471, 1376,
Synthesis of [(η6-C10H14)Ru(PPh3)(cydpm)]SO3CF3 (8).
Complex 1 (0.515 g, 1.0 mmol) in dry acetone (30 mL) was
treated with AgSO3CF3 (0.257 g, 1 mmol) and stirred for 2 h at
RT. It was filtered through Celite to remove silver chloride.
Triphenylphosphine (0.262 g, 1 mmol) was added to the filtrate
and stirred at RT for 4 h. The solvent was removed under
reduced pressure and residue extracted with dichloromethane
(5 mL) and filtered. An excess of hexane was added to the filtrate
to afford a yellow colored precipitate. It was separated by
filtration, washed with diethyl ether, and dried under vacuum.
Yield: 68%(0.606 g). Anal. Calcd for C45H39N3O3F3PSRu: C,
60.67; H, 4.41; N, 4.72%. Found: C, 60.49; H, 4.53; N, 4.68%.
IR (cm-1): 2223, 1558, 1473, 1437, 1382, 1345, 1253, 1156, 1092,
1030, 993, 892, 812, 752, 698, 635, 569, and 517. 1H NMR
(δ, ppm): 0.92 (d, 6H, J=6.6 Hz), 1.68 (s, 3H), 2.18 (m, 1H), 5.90
(d, 2H, J=5.7 Hz), 6.01 (d, 2H, J=6.3 Hz), 6.29 (d, 2H, J=
3.9 Hz), 6.38 (d, 2H, J=3.9 Hz), 7.43-7.02 (m, 17H), 7.70 (d,
2H, J = 8.1 Hz), 7.96 (s, 2H). 31P{1H} NMR (121.50 MHz,
1
1344, 1247, 1102, 1027, 992, 893, 822, 720, and 477. H NMR
(δ, ppm): 1.10 (d, 6H, J=6.9 Hz), 2.25 (s, 3H), 2.46 (m, 1H), 5.31
(dd, 4H), 6.45 (d, 2H, J=3.9 Hz), 6.49 (d, 2H, J=4.2 Hz), 7.55
(d, 2H, J=8.4 Hz), 8.04 (s, 2H), 8.27 (d, 2H, J=8.7 Hz). 13C
NMR (75.45 MHz, δ, ppm): 18.62 (C-CH3), 22.07 {CH(CH3)2},
30.63 {CH(CH3)2}, 84.73 (C6H4), 100.51 (C-CH3), 102.25 (C-
CHMe2), 119.10, 122.55, 130.61, 131.63, 134.16, 143.02, 144.57,
147.85, 155.62 (dipyrrin). UV-vis. (CH2Cl2, λmax nm, ε): 498
(2.37 ꢀ 104), 446 (1.61 ꢀ 104), 303 (1.41 ꢀ 104), 272 (1.86 ꢀ 104),
237 (1.63 ꢀ 104).
Synthesis of [(η6-C6H6)RuCl(ndpm)] (4). Complex 4 was
synthesized following the method employed for 1 using 5-(4-
nitrophenyl) dipyrromethane (0.267 g, 1.0 mmol) and [{(η6-
C6H6)RuCl(μ-Cl)}2]. Yield: 53% (0.254 g). Anal. Calcd for
C21H16ClN3O2Ru: C, 52.67; H, 3.37; N, 8.77%. Found: C,
52.62; H, 3.31: N, 8.73%. IR (cm-1): 1555, 1378, 1343, 1246,

7596 Inorganic Chemistry, Vol. 48, No. 16, 2009
Yadav et al.
δ, ppm): 40.38 (P, PPh3). UV-vis. (CH2Cl2, λmax nm, ε): 498
(2.42 ꢀ 104), 438 (0.83 ꢀ 104), 309 (1.12 ꢀ 104), 242 (2.51 ꢀ 104).
Synthesis of [(η6-C10H14)Ru(ndpm)N3] (9). This complex was
prepared following the procedure adopted for 6 using complex 3
(0.535 g, 1.0 mmol) in place of 1. Yield: 84% (0.454 g). Anal.
Calcd for C25H24N6O2Ru: C, 55.44; H, 4.47; N, 15.52%. Found:
C, 55.00; H, 4.39; N, 15.55%. IR (cm-1): 2025, 1556, 1502, 1464,
2.36 (m, 2H), 5.30 (s, 8H), 5.85 (d, 2H, J=6.0 Hz), 5.94 (d, 2H,
J=5.7 Hz), 6.46 (d, 4H, J=3.9 Hz), 6.68 (d, 4H, J=4.2 Hz), 7.45
(d, 2H, J=6.0 Hz), 7.60 (bs, 2H), 7.72 (d, 4H, J=6.0 Hz), 8.20 (d,
2H, J=3.9 Hz), 8.41 (d, 2H, J=4.2 Hz), 8.48 (bs, 2H), 8.52 (d,
2H, J=6.6 Hz). UV-vis. (CH2Cl2, λmax nm, ε): 496 (2.49 ꢀ 104),
424 (1.48 ꢀ 104), 302 (1.97 ꢀ 104), 266 (2.32 ꢀ 104).
Synthesis of [{(η6-C10H14)Ru(cydpm)}2(μ-N3)]Cl (15). To a
suspension of complex 1 (0.515 g, 1.0 mmol) in dry acetone
(15 mL) sodium azide NaN3 (0.033 g, 0.5 mmol) was added and
stirred for 3 h at RT. The solvent was removed under reduced
pressure, and residue extracted with dichloromethane (10 mL)
and filtered to remove solid sodium chloride. The filtrate was
concentrated to ∼2 mL and an excess of hexane was added to it.
An orange colored complex separated which was filtered,
washed with diethyl ether, and dried under vacuum. Yield
79% (0.425 g). Anal. Calcd for C50H48ClN9O4Ru2: C, 55.78;
H, 4.49; N, 11.78%. Found: C, 55.72; H, 4.46; N, 11.71%. IR
(cm-1): 2226, 2026, 1705, 1555, 1462, 1379, 1342, 1247, 1031,
1
1378, 1341, 1246, 1099, 1031, 994, 897, 822, 725, and 477. H
NMR (δ, ppm): 1.05 (d, 6H, J=6.6 Hz), 2.28 (s, 3H), 2.44 (m,
1H), 5.27 (d, 2H, J=5.1 Hz), 5.37 (d, 2H, J=5.1 Hz), 6.48 (d, 2H,
J=4.2 Hz), 6.53 (d, 2H, J=4.5 Hz), 7.55 (d, 2H, J=8.4 Hz), 8.02 (s,
2H), 8.26(d, 2H, J=8.7 Hz). UV-vis. (CH2Cl2, λmax nm, ε): 489
(2.36 ꢀ 104), 305 (2.18 ꢀ 104), 273 (2.31 ꢀ 104), 232 (2.51 ꢀ 104).
Synthesis of [(η6-C10H14)Ru(SCN)(ndpm)] (10). This complex
was prepared from [(η6-C10H14)RuCl(ndpm)] (0.535 g, 1.0
mmol) and NH4SCN (0.076 g, 1.0 mmol) following the method
employed for 7. Yield: 84% (0.467 g). Anal. Calcd for C26H24-
N4O2SRu: C, 56.00; H, 4.34; N, 10.05% Found: C, 56.08; H,
4.30 ; N, 10.08%. IR (cm-1): 2100, 1552, 1521, 1377, 1344, 1246,
1096, 1030, 993, 893, 822, 719, and 476. 1H NMR (δ, ppm): 1.12
(d, 6H, J=6.9 Hz), 2.21 (s, 3H), 2.38 (m, 1H), 5.38 (dd, 4H), 6.50
(s, 4H), 7.56 (bs, 2H), 7.88 (s, 1H), 7.95 (s, 1H), 8.29 (s, 2H).
UV-vis. (CH2Cl2, λmax nm, ε): 495 (2.35 ꢀ 104), 444 (1.45 ꢀ
104), 304 (1.53 ꢀ 104), 267 (2.20 ꢀ 104), 231 (2.57 ꢀ 104).
Synthesis of [(η6-C10H14)Ru(PPh3)(ndpm)]SO3CF3 (11). It
was prepared following the method employed for 8 using the
complex [(η6-C10H14)RuCl(ndpm)] (0.535 g, 1.0 mmol). Yield:
70% (0.637 g). Anal. Calcd for C44H39N3O5F3PSRu: C, 58.02;
H, 4.32; N, 4.61%. Found: C, 58.04; H, 4.28; N, 4.58%. IR (cm-1):
1597, 1556, 1521, 1477, 1437, 1382, 1348, 1262, 1159, 1093,
1033, 994, 892, 824, 748, 700, 637, and 530. 1H NMR (δ, ppm):
0.95 (d, 6H, J=6.6 Hz), 1.69 (s, 3H), 2.26 (m, 1H), 5.90 (d, 4H,
J=6.0 Hz), 6.02 (d, 2H, J=6.3 Hz), 6.31 (d, 2H, J=3.9 Hz), 6.34
(d, 2H, J=4.5 Hz), 7.11-7.46 (m, 17H), 7.98 (s, 2H), 8.25 (d, 2H,
J = 8.7 Hz). 31P{1H} NMR (121.50 MHz, δ, ppm): 41.68
(P, PPh3) UV-vis. (CH2Cl2, λmax nm, ε): 495 (2.39 ꢀ 104), 436
(0.74 ꢀ 104), 308 (1.00 ꢀ 104), 258 (2.51 ꢀ 104), 232 (2.54 ꢀ 104).
Synthesis of [(η6-C10H14)Ru(AsPh3)(ndpm)]SO3CF3 (12). It
was prepared following the above procedure using [(η6-C10-
H14)RuCl(ndpm)] (0.535 g, 1.0 mmol) and AsPh3 (0.109 g,
1.0 mmol). Yield: 68% (0.649 g). Anal. Calcd for C44H39N3O5-
F3AsSRu: C, 55.35; H, 4.12; N, 4.40%. Found: C, 55.32; H,
4.09; N, 4.37%. IR (cm-1): 1555, 1383, 1346, 1260, 1154, 1031,
995, 826, 742, 635, and 474. 1H NMR (δ, ppm): 0.94 (d, 6H, J=
6.9 Hz), 1.85 (s, 3H), 2.29 (m, 1H), 6.00 (d, 2H, J=6.0 Hz), 6.07
(d, 2H, J=6.0 Hz), 6.28 (d, 2H, J=4.5 Hz), 6.45 (d, 2H, J=
3.9 Hz), 7.19-7.45 (m, 17H), 8.12 (s, 2H), 8.22 (t, 2H, J =
6.0 Hz). UV-vis. (CH2Cl2, λmax nm, ε): 495 (2.39 ꢀ 104), 438
(0.76 ꢀ 104), 306 (1.19 ꢀ 104), 262 (2.52 ꢀ 104), 231 (2.55 ꢀ 104).
Synthesis of [{(η6-C10H14)Ru(ndpm)}2(μ-dppm)](SO3CF3)2
(13). Complex 13 was prepared following the above procedure
using [(η6-C10H14)RuCl(ndpm)] (0.535 g, 1.0 mmol) and dppm
(0.192 g, 0.50 mmol). Yield: 62% (0.521 g). Anal. Calcd for
C77H70N6O10F6P2S2Ru2: C, 55.00; H, 4.20; N, 5.00%. Found:
C, 54.97; H, 4.16; N, 5.04%. IR (cm-1): 1556, 1436, 1382, 1347,
1259, 1157, 1102, 1031, 993, 827, 742, 704, 637, 512, and 478. 1H
NMR (δ, ppm): 0.93 (d, 12H, J=4.2 Hz), 2.18 (s, 6H), 2.32 (m,
2H), 3.18 (s, 2H), 5.88-5.71 (m, 8H), 6.52-6.48 (m, 8H), 6.90-
7.65 (m, 24H), 8.09 (s, 4H), 8.32 (dd, 4H). UV-vis. (CH2Cl2,
1
993, 893, 812, 770, 721, and 474. H NMR (δ, ppm): 1.05 (d,
12H, J=6.9 Hz), 2.24 (s, 6H), 2.43 (m, 2H), 5.26 (d, 4H, J=
6.0 Hz), 5.36 (d, 4H, J=6.3 Hz), 6.46 (d, 4H, J=3.6 Hz), 6.52 (d,
4H, J=4.2 Hz), 7.50 (d, 4H, J=8.4 Hz), 7.70 (d, 4H, J=8.1 Hz),
8.01 (s, 4H). UV-vis. (CH2Cl2, λmax nm, ε): 486 (2.41 ꢀ 104), 302
(1.19 ꢀ 104), 268 (1.50 ꢀ 104), 234 (3.13 ꢀ 104).
X-ray Structure Determinations. Crystals suitable for single
crystal X-ray diffraction analyses for 1, 2, 3, 9, and 11 were
grown by slow diffusion of hexane in dichloromethane solution
of the respective compounds. Preliminary data on the space
group and unit cell dimensions as well as intensity data for 2, 9,
and 11 were collected on Oxford Diffraction Xcalibur-S and on
a Bruker Smart Apex diffractometer for 1 and 3 using graphite
monochromatized Mo KR radiation. The structures were solved
by direct methods and refined by using SHELX-97.20 Non-
hydrogen atoms were refined with anisotropic thermal para-
meters. All the hydrogen atoms were geometrically fixed and
allowed to refine using a riding model. PLATON was used for
analyzing the interaction and stacking distances.20
Results and Discussion
Syntheses of the Ligands and Complexes 1-5. One pot
reaction of aldehyde with an excess of pyrrole at RT offers
a suitable route for the synthesis of meso-substituted
dipyrromethanes.7 In our systematic studies on the pos-
sibility of binding of the dipyrrinato ligands to metal
centers we have prepared and characterized various Ru-
(II) complexes. In a typical reaction, dipyrromethanes
were oxidized to the corresponding dipyrrin by reaction
of the respective dipyrromethane with DDQ in a chloro-
form/benzene solution. The dipyrrin ligands were not
isolated, rather these were used in situ to generate the
desired complexes.6d,8a,10c,21,22 Neutral heteroleptic
complexes with the formulations [(η6-arene)Ru(L)Cl]
were obtained by treatment of the dipyrrins with arene
ruthenium complexes [{(η6-arene)RuCl(μ-Cl)}2] (arene=
C6H6, C10H14) in the presence of triethylamine under
refluxing conditions. A simple scheme showing synthesis
of the complexes 1-5 is depicted in Scheme 1. These are
λ
max nm, ε): 491 (2.37 ꢀ 104), 434 (1.08 ꢀ 104), 304 (0.92 ꢀ 104),
258 (1.93 ꢀ 104), 248 (2.01 ꢀ 104).
Synthesis of [{(η6-C10H14)Ru(ndpm)}2(μ-bpy)](SO3CF3)2
(14). Complex 14 was prepared following the above procedure
using [(η6-C10H14)RuCl(ndpm)] (0.535 g, 1.0 mmol) and 4,40-
bpy (0.078 g, 0.50 mmol). Yield: 65% (0.472 g). Anal. Calcd for
C62H56N8O10F6S2Ru2: C, 51.24; H, 3.88; N, 7.71%. Found: C,
51.16; H, 3.81; N, 7.76%. IR (cm-1): 1556, 1436, 1382, 1347,
1259, 1157, 1102, 1031, 993, 827, 742, 704, 637, 512, and 478.
1H NMR (δ, ppm): 1.01 (d, 12H, J = 6.6 Hz), 1.83 (s, 6H),
(20) (a) Mackay, S.; Dong, W.; Edwards, C.; Henderson, A.; Gilmox, C.;
Stewart, N.; Shankland, K.; Donald, A. MAXUS; University of Glasgow:
Scotland, 1999. (b) Sheldrick, G. M. SHELX-97, Programme for refinement of
crystal structures; University of Gottingen: Gottingen, Germany, 1997. (c)
PLATON; Spek, A. L. Acta Crystallogr. A 1990, 46, C31.
(21) Halper, S. R.; Cohen, S. M. Chem.;Eur. J. 2003, 9, 4661–4669.
(22) Yu, L. H.; Muthukumaran, K.; Sazanovich, I. V.; Kirmaier, C.;
Hindin, E.; Diers, J. R.; Boyle, P. D.; Bocian, D. F.; Holten, D.; Lindsey, J. S.
Inorg. Chem. 2003, 42, 6629–6647.

Article
Inorganic Chemistry, Vol. 48, No. 16, 2009 7597
˚
1.675 (1), 1.682 (2), and 1.678 (3) A. These separations
Scheme 1
are shorter than those reported in other arene ruthe-
nium complexes.16,24 and may be attributed to enhanced
back-bonding. The pyrrole rings of dipyrrin are not copla-
nar and meso-phenyl rings are twisted out of the methene
plane by 113.3(4) (1), 91.0(4) (2), and 70.3(7)° (3), and
consequently there are major differences in crystal pack-
ing. The Ru1 to dpm nitrogen bond lengths Ru1-N1 and
˚
Ru1-N2 are 2.077(3) and 2.075(3) A in 1, 2.081(2) and
25
˚
˚
2.081(2) A in 2, and 2.075(4) and 2.070(4) A in 3. The
Ru-Cl distances are 2.4226(8), 2.4194(8), and 2.3982(15)
A in 1, 2, and 3, respectively. These are consistent with the
˚
values reported in other related complexes.15,16,24
Weak interaction studies on the complex [(η6-C6H6)-
RuCl(cydpm)] 2 revealed an interesting structural
features. In the crystal packing two molecules of [(η6-
C6H6)RuCl(cydpm)] are involved in π-π stacking,
resulting in a dimeric structure with centroid-centroid
˚
separation of 3.649 A. Observed distances are consis-
tent with the theoretical value calculated for π-πstacking.26
The C-H Cl and C-H O [Supporting Information,
3 3 3
3 3 3
Table S1] interactions in 2 and 3 lead to various structural
motifs shown in the Supporting Information, Figures S10-
S12, S14. It is well established that these types of interactions
play an important role in the construction of huge supra-
molecular architectures.15,27
Syntheses and Characterization of Substituted Deriva-
tives of 1 and 3. Space-filling representations of [(η6-
C10H14)RuCl(cydpm)] 1 and [(η6-C10H14)RuCl(ndpm)]
3 (Figure 1) indicated that the coordination geometry
about metal center ruthenium provides an open face for
facile replacement of the chloro group by other ligands. It
prompted us to examine the reactivity of the complexes 1
and 3 with some nitrogen and phosphorus donor ligands.
It was observed that reactions of the complexes 1 and 3
with anionic ligands like N3- or SCN- in acetone led in
the formation of neutral complexes [(η6-C10H14)Ru-
(cydpm)N3] 6, [(η6-C10H14)Ru(cydpm)SCN] 7, [(η6-C10-
H14)Ru(ndpm)N3] 9, and [(η6-C10H14)Ru(ndpm)SCN]
10. On the other hand, reactions with neutral ligands like
EPh3 (P, As) or exobidantate ligands dppm or 4,40-bpy in
the presence of AgSO3CF3 afforded cationic mononuc-
lear complexes [(η6-C10H14)Ru(PPh3)(cydpm)]SO3CF3 8,
[(η6-C10H14)Ru(PPh3)(ndpm)SO3CF3 11, [(η6-C10H14)Ru-
(AsPh3)(ndpm)]SO3CF3 12, and binuclearcomplexes [{(η6-
C10H14)Ru(ndpm)}2(μ-dppm](SO3-
bright orange-red compounds that generally appear lus-
trous green upon removal of the solvent and are stable
toward air and moisture. The complexes readily dissolve
in common organic solvents such as chloroform, dichlor-
omethane, acetone, acetonitrile, dimethylformamide,
and dimethylsulfoxide.
Crystallographic Studies. Molecular structures of the
complexes 1-3 have been determined crystallographically.
Crystallographic data and selected geometrical parameters
for 1-3 are summarized in Table 1 and 2. Oak Ridge
Thermal Ellipsoid Plot (ORTEP) views with the atom-
numbering scheme (30% probability) are shown in Figure 2.
The dipyrrin ligands in these complexes are coordinated to
metal center in an analogous manner as observed in other
dipyrrinato complexes.6f,8a,21,23 Coordination geometry
about the metal center ruthenium in 1-3 is typical “piano-
stool” geometry with two positions occupied by dipyrrin
nitrogen, one chloro group and arene rings (arene=C10H14,
1 and 3; C6H6, 2) bonded in η6-manner.
CF3)2 13, [{(η6-C10H14)Ru(ndpm)}2(μ-bpy)](SO3CF3)2 14.
Further, it was observed that reaction of 1 with NaN3 under
controlled conditions afforded a binuclear complex with
the formulation [{(η6-C10H14)Ru(cydpm)}2(μ-N3)]Cl 15.
A simple scheme showing synthesis of the derivatives of
1 and 3 is depicted in Scheme 2.
The piano-stool arrangement about ruthenium center is
further reflected by small bite angles of dpm [N(1)-
Ru(1)-N(2) 84.86(12)° (1), N(1)-Ru(1)-N(2) 86.79(9)°
(2), and N(1)-Ru(1)-N(2) 85.70(17)° (3)].23 Arene rings
in these complexes are normal with an average Ru-C
IR spectra of the complexes 6 and 7 exhibited an
insignificant shift in the position of bands associated
with ν(CꢁN) at ∼2227 cm-1 and the appearance of
additional bands at ∼2025 and ∼2100 cm-1, respectively,
˚
distances of 2.194 (1), 2.179 (2), and 2.196 A (3), respec-
tively. The metal to arene ring centroid separations are
(23) (a) Gill, H. S.; Finger, I.; Bozidarevic, I.; Szydlo, F.; Scott, M. J. New
J. Chem. 2005, 29, 68–71. (b) Do, L.; Halper, S. R.; Cohen, S. M. Chem.
Commun. 2004, 2662–2663.
(24) (a) Singh, A.; Chandra, M.; Sahay, A. N.; Pandey, D. S.; Pandey, K.
K.; Mobin, S. M.; Puerta, M. C.; Valerga, P. J. Organomet. Chem. 2004, 68,
1821–1834. (b) Clear, J. M.; O'Connell, C. M.; Vos, J. G.; Cardin, C. J.; Edwards,
A. J. J. Chem. Soc., Chem. Commun. 1980, 750–751.
(25) Thoi, V. S.; Stork, J. R.; Magde, D.; Cohen, S. M. Inorg. Chem. 2006,
45, 10688–10697.
(26) (a) Scaccianoce, L.; Braga, D.; Calhorda, M. J.; Grepioni, F.;
Johnson, B. F. G. Organometallics 2000, 19, 790–797. (b) Tsuzuki, S.; Honda,
K.; Uchimura, T.; Mikami, M.; Tanabe, K. J. Am. Chem. Soc. 2004, 124, 104–
112.
(27) Severin, K. Chem. Commun. 2006, 3859–3867.

7598 Inorganic Chemistry, Vol. 48, No. 16, 2009
Yadav et al.
Table 1. Crystal Data and Structure Refinement Parameters for 1, 2, 3, 9, and 11
1
2
3
9
11
empirical formula
crystal system
space group
C26H24N3ClRu
triclinic
P1
C22H16N3ClRu
monoclinic
P21/n
13.1357(3)
7.3731(1)
19.0071(5)
90.00
101.851(2)
90.00
1801.62(7), 4
0.71073
orange, plates
120(2)
14673
3177/0/244
1.692
1.030
C25H24N3O2ClRu
triclinic
P1
C25H24N6O2Ru
triclinic
P1
C44H39N3PO5SRu
monoclinic
P21/c
20.2148(4)
12.6772(2)
16.3008(3)
90.00
101.722(2)
90.00
4090.24(13), 4
0.71073
brown, blocks
150(2)
25504
7173/0/526
1.479
0.537
˚
a (A)
9.6577(6)
10.4759(6)
11.9408(7)
73.9480(10)
77.9880(10)
83.9790(10)
1134.12(12), 2
0.71073
red-green, blocks
293(2)
5891
3922/0/283
1.508
0.827
14.860(3)
16.732(3)
17.731(3)
108.592(3)
101.479(3)
109.477(3)
3702.4(12), 2
0.71073
red, blocks
293(2)
32947
12990/0/874
1.440
0.769
9.9452(4)
9.9780(3)
11.5966(3)
104.577(2)
91.193(3)
92.054(3)
1112.48(6), 2
0.71073
red, blocks
150(2)
10057
3906/0/310
1.617
0.742
˚
b (A)
˚
c (A)
R (deg)
β (deg)
γ(deg)
3
˚
V (A ), Z
˚
λ (A)
color and habit
T (K)
reflns collected
reflns/restraint/params
Dcalcd (Mg m-3
)
μ (mm-1
GOF on F2
)
1.094
0.927
1.054
1.043
0.930
final R indices I > 2σ(I)a
R1=0.0387
wR2=0.0994
R1=0.0424
wR2=0.1030
R1= 0.0260
wR2= 0.0510
R1= 0.0466
wR2= 0.0541
R1= 0.0563
wR2= 0.1684
R1=0.0758
wR2= 0.1840
R1= 0.0200
wR2= 0.0489
R1= 0.0241
wR2= 0.0497
R1= 0.0278
wR2= 0.0591
R1= 0.0449
wR2= 0.0621
R indices(all data)a
P
P
P
P
a R1 = ||Fo| - |Fc||/ |Fo|; R2 = { [w(Fo2 - Fc2)2]/ [wFo4]}1/2
.
Table 2. Important Geometrical Parameters of Complexes 1-3, 9, and 11
1
2
3
9
11
Ru-N1
2.077(3)
2.075(3)
2.194
2.081(2)
2.081(2)
2.179
2.075(4)
2.070(4)
2.196
2.3982(15)
1.179(10)
1.220(10)
2.0788(15)
2.0766(16)
2.203
2.1185(17)
1.234(3)
1.216(2)
2.0783(17)
2.0797(19)
2.246(2)
2.0797(19)
1.227(3)
1.226(3)
Ru-N2
Ru1-Cav(arene)
Ru1-Cl1/N3/P1
N1-O1
N1-O2
CdN
2.4226(8)
2.4194(8)
1.142(5)
1.130(4)
N2-Ru1-N1
84.86(12)
87.83(9)
86.72(9)
175.8(4)
86.79(9)
84.68(7)
83.87(7)
85.70(17)
85.91(13)
87.14(13)
117.0(8)
123.2(8)
86.45(6)
85.07(7)
86.63(6)
118.99(19)
123.13(18)
86.85(7)
88.04(5)
86.62(5)
118.1(2)
124.0(2)
N2-Ru1-Cl1/N3/P1
N1-Ru1-Cl1/N3/P1
C13-N3-O2/O1
O1-N1-O2
C13/19-C14/20-N3
175.8(4)
174.4(5)
N2-Ru1-N1-C6/C4
23.3(3)
-27.6(3)
113.3(4)
-9.6(2)
7.4(2)
91.0(4)
13.4(4)
-15.0(5)
70.3(7)
-13.28(17)
10.55(17)
91.5(2)
-14.11(18)
16.93(19)
67.6(3)
N1-Ru1-N2-C4/C6
C4/C6-C5-C10-C11(phenyl)
C14-C13-N3/N6-O1/O2(NO2)
C15-C13-C14-N3 (CdN)
-5.5(14)
1.5(3)
14.7(3)
174.62
158.01
corresponding to ν(N3) and ν(SCN). It suggested linkage of
N3- and SCN- to the metal center which has further been
established by structural studies. Analogous trends have
been observed in the IR spectra of 9 and 10. The complexes
containing PPh3, AsPh3, dppm, and 4,40-bipyridine (8, 11,
12, 13 and 14) in its IR spectra also exhibited characteristic
Crystallographic Studies on Derivatives of the Arene
Ruthenium Dipyrrinato Complexes. Molecular structures
of the complexes 9 and 11 have been determined crystal-
lographically. Details about data collection, refinement,
and structure solution are summarized in Table 1, and
selected geometrical parameters are recorded in Table 2.
ORTEP views at 30% thermal ellipsoid probability are
depicted in Figure 2. The asymmetric unit of 9 contains
one ruthenium bonded to nitrogen atoms of the dipyrrin,
nitrogen from azide and p-cymene ring in η6-manner
resulting in piano stool geometry about the metal center.
The Ru(1)-N(1) and Ru(1)-N(2) (dipyrrin) distances
bands associated with the respective ligands and counter-
anion SO3CF3
-
.
˚
are 2.0788(15) and 2.0766(16) A, respectively, which vary
˚
by 0.006 A from the precursor complex 3. The Ru(1)-
N(3) distance (azide) is 2.118 A, and is comparable to the
˚
Ru-N distances reported in the literature.15a,15f The aver-
˚
Figure 1. Space-filling representations of [(η6-C10H14)RuCl(ndpm)] 3
(left) and [(η6-C10H14)RuCl(cydpm)] 1 (right).
age Ru-C(arene) distance is 2.203 A, which is slightly longer
(0.007 A) compared to that in the precursor complex 3.
˚

Article
Inorganic Chemistry, Vol. 48, No. 16, 2009 7599
Scheme 2. Synthesis of Mono-/Bi-Nuclear Complexes (i) NaN3/Acetone, (ii) NH4SCN/Acetone, (iii) AgSO3CF3/PPh3/Acetone, (iv) AgSO3CF3/L-L/
Acetone, and (v) NaN3/Acetone
1
Lengthening of this distance may result from replacement of
NMR Spectral Studies. H NMR spectral data of the
complexes are summarized in the Experimental Section. To
facilitate assignments 1H-1H COSY experiments were per-
formed, and the resulting spectra for 1 and 3 are depicted in
the Supporting Information, Figures S14-17. The electron
withdrawing or donating nature of the phenyl substituents
exhibited a pronounced effect on the position of the reso-
nances corresponding to various protons of the coordinated
dipyrrins. The R-pyrrolic protons of the dipyrrins in the
complexes exhibited significant deshielding (∼δ8.03 ppm) as
compared to that in the respective dipyrrins, while β-protons
appeared as doublets of doublets in the complexes having
electron withdrawing substituents (-CN, -NO2) and as
two well resolved doublets (see in Supporting Information,
Figure S18) in the complexes containing the electron releas-
ing group -OCH2Ph. Comparative results demonstrate
that, although β-protons are magnetically different, reso-
nances associated with them appear as doublets of doublets
on the NMR time scale. The combined effect of the co-
ordination of pyrrolic nitrogen to ruthenium and the nature
of the meso-substituent (electron withdrawing or releasing)
of dipyrrins determines the position of doublets correspond-
ing to β-protons. Further, space filling models of 1 and 3
show that steric interaction between R-pyrrolic protons and
η6-aromatic ring current and the additional electron with-
drawing effect imposed by ruthenium on adjacent nitrogen
leads to greater deshielding of R-relativetoβ-protons.10c For
example in the 1H NMR spectrum of 1, signals associated
with the cydpm protons resonated at δ 6.45 (d, 2H, J =
4.8 Hz, β-H py), 6.49 (d, 2H, J=4.8 Hz, β-H py), 7.50 (d, 2H,
J=6.6 Hz, phenyl), 7.71 (d, 2H, J=8.1 Hz, phenyl), 8.03 (s,
2H, R-H py) ppm. An analogous pattern of the resonances
have been observed in the spectrum of 2. The resonances
associated with meso-substituted phenyl protons of the
-
Cl- by the bulkier N3 group. The separation between
˚
ruthenium to the centroid of the p-cymene ring is 1.684 A
and is comparable to that in the precursor complex 3 (1.678
˚
A). The N-Ru-N angle is 86.45(6)° which is slightly larger
than in the complex 3 (85.70(17)° and smaller than that in
most of the other dipyrrin complexes based on 3d metals.6,28
The phenyl ring is perpendicular to the methene plane with a
dihedral angle of 91.5(2)°.
In complex 11 the metal center ruthenium is bonded with
the dipyrrin nitrogen N(1) and N(2), P(1) from PPh3 and
p-cymene ring in η6-manner. Considering the p-cymene ring
as a single coordination site, the overall geometry about the
ruthenium center might be described as piano-stool geome-
try. The p-cymene ring in this complex is almost planar, and
ruthenium is displaced from the centroid of the p-cymene
˚
ring by 1.749 A. It is longer than that in the precursor
˚
complex 3(1.678 A). TheangleN(1)-Ru(1)-N(2) is 86.85°,
which is almost the same [86.45(6)°] as that in complex
9 (Table 2). However, the Ru-N bond distances in 11
˚
(2.077-2.079 A) are comparable to those in the complexes
3 and 9. Substitution of the Cl- by bulky ligands PPh3 (9)
and N3 (11) leads to lengthening of the Ru-p-cymene
-
separations [Ru-C(average), Ru-centroid; 2.203, 1.684 (9)
and 2.246, 1.749 A (11)] in comparison to that in the
˚
˚
precursor complex 3 (2.196, 1.678 A). Like other complexes,
pyrrole rings within the dipyrrin moiety are not coplanar,
rather the mean planes of the two rings intersect at an angle
of 21.25(27)° in complex 11. The C-H N, C-H
O
3 3 3
3 3 3
interactions [Supporting Information, Table S1] in 9 and 11
lead to various structural motifs shown in the Supporting
Information, Figures S13,15-16.
(28) Heinze, K.; Reinhart, A. Inorg. Chem. 2006, 45, 2695–2703.

7600 Inorganic Chemistry, Vol. 48, No. 16, 2009
Yadav et al.
Figure 2. ORTEP diagrams of 1(a), 2(b), 3(c), 9(d), and 11(e) at 30% thermal ellipsoid probability (H-atoms omitted for clarity).
dipyrrin (ndpm) in 3 and 4 were relatively deshielded. It may
be attributed to the strong electron withdrawing nature of
that two types of phenyl protons are interacting with each
other. Protons associated with dipyrrin (bdpm) in 5 were
displayed in the range δ 5.12-7.99 ppm. Further, protons
1
the nitro group. The H-1H COSY experiments showed

Article
Inorganic Chemistry, Vol. 48, No. 16, 2009 7601
observation at this stage. The possibility for deactivation of
the excited state via some other non-radiative energy transfer
pathway can not be ruled out. However, these results are
consistent with the observations made by Lindsey and co-
workers on some other systems.30,31
Mass Spectrometry. The FAB-Mass spectra of the
complexes 4, 5, 8, 12, 13, and 15 provided valuable infor-
mation about relative stability of various moieties and
supported formation of the respective complexes. The
FAB-Mass spectrum of 4 displayed peaks at m/z
478(478.9), 443(443.4), 365(365.3), and 265(264.2) as-
signable to [Mþ], [Mþ - Cl], [Mþ - (Cl þ benzene)], and
[Lþ], respectively, while, that of 5 exhibited peaks at m/z
595(596.1), 560(560.7), 426(426.5), and 468(469.5) as-
signable to [Mþ], [Mþ - Cl], [Mþ - (Cl þ p-cymene)],
[Mþ - (Cl þ CH2-Ph)], respectively. The overall frag-
mentation pattern and relative abundance of the various
peaks in the FAB-MS spectra of 4 and 5 indicated that
the arene ligand is loosely bonded to the ruthenium
center in comparison to the dpm ligands. Ionic com-
plexes 8 and 12 in their FAB-mass spectra displayed
molecular ion peaks (resulting from loss of the counter-
ion SO3CF3-) at m/z 741(741.8) and 805 (805.8), respec-
tively. The loss of the coordinated PPh3 or AsPh3 in the
next step is supported by the presence of the peaks at m/z
479(479.6) and 499(499.5), respectively. This step is
followed by loss of the arene ligand p-cymene, which is
further supported by the presence of the peaks at m/z
345(345.4) and 365(365.3). Formations of the binuclear
complexes were also strongly supported by the FAB-MS
spectral studies. Peaks observed at 1532(1532.5),
1113(1115.1), 883(883.9), 749(749.7), and 499(499.5) in
the spectrum of 13 conformed well to its dinuclear
formulation. The fragmentation pattern of 15
(Figure 4), which displayed peaks at m/z 999(999.1),
479(479.6), 345(345.4), 244(244.2) also, corresponded
well to its dinuclear formulation.
Electrochemical Studies. Redox properties of the com-
plexes 1, 3, 5, 9, 11, and 14 have been followed by cyclic
voltammetry. Theresultingdataissummarizedin Table3,
and a representative voltammogram for 1 is depicted in
Figure 5. The potential of the Fc/Fcþ couple under the
experimental conditions was 0.10 V (80 mv) vs Ag/Agþ.
Neutral and cationic species exhibited one electron oxida-
tion corresponding to the Ru(II)/Ru(III) redox couple
(Table 2) in the potential range of 0.80-0.98 and 0.96-
1.26 V vs Ag/Agþ.16a,32 Data on the complexes 1, 3, and 5
suggested that the oxidation potentials are affected by the
electron withdrawing/donating ability of meso-substitu-
ents of the dipyrrin ligands. Electron-donating groups
(benzyloxy, 5) increases electron density on the ligand and
also the ruthenium center, which in turn leads the redox
Figure 3. Electronic spectra of 1-5 in dichloromethane.
associated with the coordinated p-cymene (1, 3, 5) and ben-
zene (2, 4) resonated at δ1.10(d, 6H, CH(CH3)2, J=6.9 Hz),
2.24 (s, 3H, C-CH3),2.40(m,1H, CH(CH3)2),5.30(dd, 4H,
C6H4), and 5.68 (s, 6H, C6H6) ppm, respectively.16 Signals
associated with the arene protons exhibited an insignificant
shift in these complexes. Substitution of the Cl- by various
ligands from precursor complexes 1 and 3 causes splitting
and deshielding of the various signals associated with dipyr-
rin and arene protons. It may be attributed to the change in
electron density on the metal center because of the linkage of
the displacing ligands.
Electronic Spectroscopy. UV-vis spectra of the com-
plexes were recorded in dichloromethane, and the resulting
data is summarized in the Experimental Section. The elec-
tronic spectra of 1-5(Figure 3) exhibited moderately intense
bands at ∼ 400-500, 301, 267, and 237 nm. Highly con-
jugated dipyrrin complexes usually display intense bands in
the range of 400-500 nm corresponding to dipyrrin-based
S0fS1 (πfπ*) transitions6e,9c,10c along with metal-dipyrrin
charge transfer transitions in the visible region.10c,21,29 High
energy transitions have been tentatively assigned to intrali-
gand transitions associated with the dipyrrins.6e,8a,19c,21,23 In
complex 5, bands at 350 nm exhibited a red shift in compar-
ison to the complexes 1-4 (∼305 nm). This shift may be
attributed to the presence of the benzyloxy chromophore. It
was further observed that substitution of the Cl- in com-
-
plexes 1 and 3 by neutral or anionic ligands (PPh3, N3
,
SCN-) resulted in a small blue shift in the position of the
absorption bands. The electronic spectra of the binuclear
complexes did not show any appreciable shift in the position
of the lowest energy transition bands.
Emission Spectroscopy. Emission experiments on the
complexes were carried out in DCM with 1.0 mM solutions
at RT Upon excitation at their respective lowest energy
bands these complexes did not exhibit any emission (detec-
tion limit=0.1%). Most of the complexes containing dpm
reported in the literature exhibit strong fluorescence.6a
Quenching of the fluorescence in the complexes under study
is a matter of discussion. The absence of the fluorescence
may be attributed to non-rigidity of the meso-phenyl rings of
dipyrrins, which may lead to deactivation of the excited
state.9b We do not have any strong evidence to suppot the
(30) Sazanovich, I. V.; Kirmaier, C.; Hindin, E.; Yu, L.; Bocian, D. F.;
Lindsey, J. S.; Holten, D. J. Am. Chem. Soc. 2004, 126, 2664–2665.
(31) Sutton, J. M.; Rogerson, E.; Wilson, C. J.; Sparke, A. E.; Archibald,
S. J.; Boyle, R. W. Chem. Commun. 2004, 1328–1329.
(32) (a) Lever, A. B. P. Inorg. Chem. 1990, 29, 1271–1285. (b) Lever, A. B.
P. In Comprehensive Coordination Chemistry II, Lever, A. B. P., Ed.; Elsevier
Science: Oxford, U.K., 2004; Vol. 2, Chapter 2.19, pp 251-268 and references
therein. (c) Pombeiro, A. J. L. In Encyclopedia of Electrochemistry; Scholz, F.,
Pickett, C. J., Eds.; Wiley-VCH: New York, 2006; Vol. 7A, Chapter 6, pp 77-108
and references therein. (d) Reisner, E.; Arion, V. B.; Eichinger, A.; Kandler, N.;
Geister, G.; Pombeiro, A. J. L.; Keppler, B. K. Inorg. Chem. 2005, 44, 6704–
6716.
(29) Halper, S. R.; Stork, J. R.; Cohen, S. M. Dalton Trans. 2007, 1067–
1074.

7602 Inorganic Chemistry, Vol. 48, No. 16, 2009
Yadav et al.
Figure 4. FAB mass spectra of 15.
In contrast, substitution of Cl- by PPh3 to form 11 is
expected to result in a measurable anodic shift in the oxida-
tion potential, but a measurable shift was not observed.
However, replacement of Cl- by 4,40-bpy to form 14 (from
þ 0.98 to þ1.26 V).33 leads to an appreciable potential shift.
The presence of a single oxidation wave (at Ep,a 1.26 V)
corresponding to Ru(II)/Ru(III) in the binuclear complex
14 suggested lack of electronic communication between the
two ruthenium centers through the bridging ligand.32,34 All
the complexes exhibited an additional oxidation wave with
lower current intensity at a potential of about 0.65-0.85 V.
This may be attributed to the oxidation of dipyrrin which
falls within the range for the dipyrrin complexes.6a,22,35,36
Reduction of the complexes shows two well resolved quasi-
reversible peaks (some complexes shows reversible peaks) in
the potential range 0.00 to -2.00 V; this is expected because
of the reduction of dipyrrins.6a,22,35,37
Table 3. Cyclic Voltammetric Data for Arene Ruthenium(II)-dpm Complexes
complexes E°ox, V (ΔE, mV)
E°ox, V (ΔE, mV)
Fc
1
3
0.10(80)
0.82(89), 0.71
0.98(110), 0.83
0.80(94), 0.67
-0.25, -1.44, -1.52(73)
-0.18, -0.99, 1.11b, -1.26b
-0.09, -0.27, -1.10, -1.23(62), -1.55,
-1.61(68)
5
9
11
14
0.88(78), 0.65
-0.36a, -1.17, -1.38(26)
0.96(115), 0.75, 0.54 -0.26, -1.28b
1.26a, 0.85, 0.27a
-0.42, -1.16(94), -1.25b
a = peak potentials, Ep,a for irreversible processes. b = quasi-rever-
sible processes.
Spectroelectrochemistry. The UV/vis spectra and redox
potentials of 1, 3, and 5 do not differ much; therefore, com-
plex 3 and its derivative 11 along with one of the binuclear
complexes 14 were chosen for spectroelectrochemical stu-
dies. The studies were performed in acetonitrile solution
(33) (a) Sullivan, B. P.; Salmon, D. J.; Meyer, T. J. Inorg. Chem. 1978, 17,
5239. (b) Kaim, W.; Reinhardt, R.; Sieger, M. Inorg. Chem. 1994, 33, 4453–
4459.
::
(34) Broring, M.; Brandt, C. D.; Bley-Escrich, J.; Gisselbrecht, J. P. Eur.
J. Inorg. Chem. 2002, 910–917.
(35) (a) Gill, H. S.; Finger, I.; Bozidarevic, I.; Szydlo, F.; Scott, M. J. New
J. Chem. 2005, 29, 68–71. (b) Cui, A.; Peng, X.; Fan, J.; Chen, X.; Wu, Y.; Guo,
B. J. Photochem. Photobiol. A: Chem. 2007, 186, 85–92. (c) Goze, C.; Ulrich,
Figure 5. Cyclic voltammogram of 1.
process to occur at more negative potentials, while the
opposite effect occurs when electron withdrawing groups
are employed. The value of the Ru(II)/Ru(III) oxidation
potential in the complexes under study reflects the electron-
donor behavior of the ligands as follows: Replacement of
chloride in complex 3 by azide to form 9 results in a
measurable shift (although rather small) in the cathodic
potential (from þ 0.98 to þ 0.88 V), which is in keeping with
slightly better electron donor properties of the latter.32a
G.; Ziessel, R. J. Org. Chem. 2007, 72, 313–322.
::
(36) (a) Broring, M.; Brandt, C. D.; Lex, J.; Humpf, H. U.; Bley-Escrich,
J.; Gisselbrecht, J. P. Eur. J. Inorg. Chem. 2001, 2549–2556. (b) Rawling, T.;
Xiao, H.; Lee, S. T.; Colbran, S. B.; McDonagh, A. M. Inorg. Chem. 2007, 46,
ꢁ
2805–2813. (c) Kadish, K. M.; Shao, J.; Ou, Z.; Fremond, L.; Zhan, R.; Burdet, F.;
Barbe, J.-M; Gros, C. P.; Guilard, R. Inorg. Chem. 2005, 44, 6744–6754.
(37) (a) Tabba, H. D.; Cavaleiro, J. A. S.; Jeyakumar, D.; Graca, M.;
::
Neves, P. M. S.; Smith, K. M. J. Org. Chem. 1989, 54, 1943–1948. (b) Broring,
M.; Brandt, C. D.; Bley-Escrich, J.; Gisselbrecht, J. P. Eur. J. Inorg. Chem. 2002,
910–917. (c) Falk, H.; Leodolter, A.; Schade, G. Monatsh. Chem. 1978, 109,
183–192.

Article
Inorganic Chemistry, Vol. 48, No. 16, 2009 7603
significantly and a shoulder appeared in the lower energy
region. This behavior may be attributed to the metal-dipyr-
rin centered redox reactions. The peaks below 301 nm
exhibiting only a slight increase in the intensity of transition
bands have been assigned to the dpm based transitions.
Appearance of a shoulder at 542 (3) and 537 nm (14) upon
oxidation was slightly blue-shifted and attains some intensity
upon generation of the Ru(III) species.
Conclusions
In summary, in this work we have reported syntheses and
characterizations of a series of heteroleptic ruthenium com-
plexes containing both the dipyrrin and the arene ligands.
New series of piano-stool complexes with the general for-
mulations [(η6-arene)RuCl(dpm)] (η6-arene=C6H6, C10H14)
represent first examples of complexes imparting both the
dipyrrin and the arene ligands. The reactivity of the resul-
ting complexes have been examined with various bases to
afford substitution products [(η6-arene)Ru(dpm)X] (X =
N3-, SCN-) and [(η6-arene)Ru(dpm)(EPh3)]þ (E=P, As).
Chelation of the dipyrrin ligands through pyrrolic nitrogen
have been authenticated crystallographically. In addition,
some bimetallic complexes have also been synthesized and
characterized by analytical and spectral studies.
Figure 6. Electronic spectra of 3 in acetonitrile upon applying oxidizing
potential.
Table 4. Electronic Transition Data on Applying Potential
complexes
peak positions (oxidized species)
3
11
14
240, 263, 301, 423, 493, 542(sh)
253, 310, 444, 496-486
263, 294, 424-416, 496-487, 537(sh)
atRT. A representative spectrum for 3is depictedinFigure6,
while those of 11 and 14 are shown in the Supporting
Information, Figures S8-9, and the resulting data are
summarized in Table 4. Oxidative spectroelectrochemistry
was performed with an applied potential of 1.20 V for (3, 11)
and 1.40 V for 14. After oxidation, regenerated radical
cations of the respective complexes were followed by a shift
in the position of bands and the appearance of a shoulder in
the optical spectra. Electrogenerated species exhibited broad
absorption bands with low absorbance. The UV/vis spectra
of complexes 11 and 14 also, displayed changes upon
oxidation, and electrogenerated species displayed analogous
trends within the series (Supporting Information, Figures
S8-9). Broadening of the absorption bands were observed
during oxidation. Further, the lowest energy band weakened
Acknowledgment. Thanks are due to the Council of
Scientific and Industrial Research, New Delhi, India for
providing financial assistance through the schemes
[HRDG 01(2074)/06/EMR-II] and [HRDG 01(2097)/
07/EMR-II] (partial assistance). We also thank the Head,
SAIF, Central Drug Research Institute, Lucknow for
extending FAB mass spectral data and Prof. P. Mathur,
In-charge, National Single Crystal X-ray Diffraction
Laboratory, Indian Institute of Technology, Powai,
Mumbai, for X-ray facilities.
Supporting Information Available: Figures S1-S21, full
crystallographic data in CIF format for the structure determi-
nations of 1, 2, 3, 9, and 11 and Table S1. This material is
available free of charge via the Internet at http://pubs.acs.org.