Heteroleptic rhodium complexes containing both the dipyrrin/cyclooctadiene ligands and application of [(η4-C8H12)Rh(4-pyrdpm)] in the construction of homo-/hetero-bimetallic complexes

Article abstract of DOI:10.1016/j.poly.2009.10.028

Heteroleptic rhodium(I) complexes with the general formulations [(η⁴-C₈H₁₂)Rh(L)] [η⁴-C₈H₁₂ = 1,5-cyclooctadiene; L = 5-(4-cyanophenyl)dipyrromethene, cydpm; 5-(4-nitrophenyl)dipyrromethene, ndpm; and 5-(4-benzyloxyphenyl)dipyrromethene, bdpm; 5-(4-pyridyl)dipyrromethene, 4-pyrdpm; 5-(3-pyridyl)dipyrromethene, 3-pyrdpm] have been synthesized. The complex [(η⁴-C₈H₁₂)Rh(4-pyrdpm)] have been used as a synthon in the construction of homo-bimetallic complex [(η⁴-C₈H₁₂)Rh(μ-4-pyrdpm)Rh(η⁵-C₅Me₅)Cl₂] and hetero-bimetallic complexes [(η⁴-C₈H₁₂)Rh(μ-4-pyrdpm)Ir(η⁵-C₅Me₅)Cl₂], [(η⁴-C₈H₁₂)Rh(μ-4-pyrdpm)Ru(η⁶-C₁₀H₁₄)Cl₂] and [(η⁴-C₈H₁₂)Rh(μ-4-pyrdpm)Ru(η⁶-C₆H₆)Cl₂]. Resulting complexes have been characterized by elemental analyses and spectral studies. Molecular structures of the representative mononuclear complexes [(η⁴-C₈H₁₂)Rh(ndpm)] and [(η⁴-C₈H₁₂)Rh(4-pyrdpm)] have been authenticated crystallographically.

Full text of DOI:10.1016/j.poly.2009.10.028

Polyhedron 29 (2010) 791–800
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Heteroleptic rhodium complexes containing both the dipyrrin/cyclooctadiene
ligands and application of [(g
4-C8H12)Rh(4-pyrdpm)] in the construction
of homo-/hetero-bimetallic complexes
*
Mahendra Yadav, Prashant Kumar, Daya Shankar Pandey
Department of Chemistry, Faculty of Science, Banaras Hindu University, Varanasi 221 005, UP, India
a r t i c l e i n f o
a b s t r a c t
Heteroleptic rhodium(I) complexes with the general formulations [(g g
4-C8H12)Rh(L)] [ 4-C8H12 = 1,5-
cyclooctadiene; L = 5-(4-cyanophenyl)dipyrromethene, cydpm; 5-(4-nitrophenyl)dipyrromethene,
Article history:
Received 7 October 2009
Accepted 29 October 2009
Available online 15 November 2009
ndpm; and 5-(4-benzyloxyphenyl)dipyrromethene, bdpm; 5-(4-pyridyl)dipyrromethene, 4-pyrdpm; 5-
(3-pyridyl)dipyrromethene, 3-pyrdpm] have been synthesized. The complex [(
have been used as a synthon in the construction of homo-bimetallic complex [(
dpm)Rh( -4-pyrdpm)Ir(
5-C5Me5)Cl2] and hetero-bimetallic complexes [( 4-C8H12)Rh(
[( -4-pyrdpm)Ru( -4-pyrdpm)Ru(
4-C8H12)Rh( 6-C10H14)Cl2] and [( 4-C8H12)Rh( 6-C6H6)Cl2]. Result-
ing complexes have been characterized by elemental analyses and spectral studies. Molecular structures
g
4-C8H12)Rh(4-pyrdpm)]
4-C8H12)Rh(
-4-pyr-
5-C5Me5)Cl2],
g
l
Keywords:
Rhodium
Heteroleptic
Dipyrrins
g
g
l
g
g
l
g
g
l
g
of the representative mononuclear complexes [(
g
g
4-C8H12)Rh(ndpm)] and [( 4-C8H12)Rh(4-pyrdpm)]
Homo-/hetero-bimetallic complexes
have been authenticated crystallographically.
Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction
rhodium(I) complexes have been widely investigated by various
research groups during recent past [20,21]. Furthermore, hetero-
leptic dipyrrin complexes based on Fe(II), Zn(II), Pd(II), Hg(II),
Rh(I), Cr(III), Co(III), and Cu(II) metal centers are well documented
in the literature [4,6–10,22,23]. However, rhodium(I) complexes
containing both the dipyrrin and cyclooctadiene group have not
yet been reported.
Immense current interest has arisen in the chemistry of dipyrrin
compounds owing to their rich optical properties [1–3]. In this re-
gard meso-substituted dipyrrins have drawn special attention [4].
Synthesis of the meso-substituted dipyrrins can be easily achieved
by condensation of the aldehydes with pyrrole followed by oxida-
tion using DDQ or p-chloranil [5]. Extensive
p
-skeleton of the
With an objective of expanding the chemistry of heteroleptic
dipyrrin complexes we have synthesized cyclooctadiene rho-
dium(I) complexes imparting meso-substituted dipyrrins. These
represent the first examples of rhodium(I) complexes containing
both the dipyrrin and cyclooctadiene ligands. In this paper we re-
port reproducible syntheses, spectral and structural characteriza-
tion of some neutral heteroleptic rhodium(I) complexes based on
substituted phenyl ring as the meso-substituent and two conju-
gated rigid pyrrole rings in dipyrrins represents a versatile and fas-
cinating class of ligands. Although, there are a number of reports
dealing with the dipyrrin complexes with boron, main group met-
als or first row transition metals and multimetallic complexes
based on 5-(4-pyridyl)dipyrromethene [1–4,6–10], there are only
a few reports dealing with the ruthenium, rhodium and iridium
dipyrrin complexes [11–14].
meso-substituted dipyrrins with the general formulations [(g4
-
C8H12)Rh(L)] and L = cydpm, ndpm, bdpm, 3-pyrdpm or 4-pyr-
dpm). Also, we describe herein the syntheses and characterization
of some homo- and hetero-bimetallic complexes employing the
Further, the dimeric chloro-bridged rhodium complex di-
chlorobis[(1,2,5,6-
4)-1,5-cyclooctdiene] dirhodium [{( 4-C8H12
Rh( -Cl)}2] have proved to be a good starting material in the orga-
l-
g
g
)
l
complex [(g
4-C8H12)Rh(4-pyrdpm)] as a synthon.
nometallic chemistry [15,16]. The complex undergoes rich variety
of chemistry via intermediacy of the chloro bridge cleavage reac-
tions leading to the formation of a number of interesting neutral
and cationic mononuclear complexes [17–19]. Because of their
2. Experimental
potential applications in many areas,
g
4-cyclooctadienyl
2.1. Materials and physical measurements
All the synthetic manipulations were performed under nitrogen
atmosphere. The solvents were purified rigorously by standard
procedures prior to their use [24]. Hydrated rhodium(III) chloride,
* Corresponding author. Tel.: +91 542 6702480; fax: +91 542 2368174.
E-mail address: dspbhu@bhu.ac.in (D.S. Pandey).
0277-5387/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2009.10.028

792
M. Yadav et al. / Polyhedron 29 (2010) 791–800
cyclooctadiene, 2,3-dicloro-5,6-dicyano-1,4-benzoquinone (DDQ),
4-cyanobenzaldehyde, 4-benzyloxybenzaldehyde, 4-nitrobenzal-
dehyde, 4-pyridylcarboxaldehyde, 3-pyridylcarboxaldehyde and
pyrrole (all Aldrich) were used as received without further purifi-
cations. The precursor complexes [{(
6-arene)Ru( 6-arene) = p-cymene,
[{( -Cl)Cl}2]; [(
[26,27] and [{( l-Cl)Cl}2] [28–30] (M = Rh or Ir)
5-C5Me5)M(
g
4-C8H12)Rh(
l-Cl)}2] [25],
g
l
g
benzene]
g
and the ligands 5-(4-cyanophenyl)dipyrromethane [31], 5-(4-
nitrophenyl)dipyrromethane [32], 5-(4-benzyloxyphenyl)dipyr-
romethane [33], 5-(4-pyridyl)dipyrromethane [34] and 5-(3-pyri-
dyl)dipyrromethane [34] were prepared and purified by the
literature procedures. Elemental analyses for C, H and N were
performed on an Exeter Analytical Inc. Model CE-440 Elemental
Analyzer. IR spectra in the region 4000–400 cmꢀ1 in KBr discs were
acquired on a Varian 3300 FT-IR spectrometer. Electronic and
emission spectra were recorded on a Shimadzu UV-1700 series
and LS-45 (Perkin–Elmer) luminescence spectrophotometers,
respectively. 1H NMR spectra were acquired on a JEOL AL 300 FT-
NMR spectrometer at r.t. using CDCl3 as a solvent and TMS as an
internal reference. FAB mass spectra were recorded on a JEOL SX
102/Da-600 Mass Spectrometer.
2.2. Syntheses
2.2.1. Synthesis of [(
2,3-Dichloro-5,6-dicyano-1,4-benzoquinone
g
4-C8H12)Rh(cydpm)] 1
(0.320 g,
1.40
mmol) dissolved in benzene (100 mL) was added dropwise to a
stirred solution of 5-(4-cyanophenyl)dipyrromethane (0.346 g,
1.40 mmol) in 150 mL of CHCl3 cooled in an ice bath (4ꢀC). After
the completion of addition, the reaction mixture was concentrated
to half of it’s volume and rhodium complex [{(g l-
4-C8H12)Rh(
Cl)}2] (0.247 g, 0.50 mmol) dissolved in MeOH (50 mL) was added
to this solution. The mixture was stirred for an additional
10 min. The dark red solution thus obtained was concentrated to
dryness, and resulting product was purified by column chromatog-
raphy (SiO2; CHCl3 with 10% hexane) to afford a dichroic red/green
solid. Yield: 42%, (0.191 g). Anal. Calc. for C24H22N3Rh: C, 63.30; H,
4.87; N, 9.23. Found: C, 63.61; H, 4.99: N, 9.03%. IR (KBr pellet,
cmꢀ1): 2225, 1557, 1480, 1379, 1338, 1237, 1175, 1032, 989,
Fig. 1. The aromatic region of the 1H NMR spectrums of complexes 1–3 in CDCl3..
Cl
Ar
Rh
Rh
Cl
N
N
+
DCM/MeOH
TEA, r.t.
Rh
Ar
NH
N
Ar =
CN
;(1)42%
NO2 ;(2)44%
O
Ph ;(3)40%
N
;(4)40%
N
;(5)36%
Scheme 1. Scheme showing the synthesis of mononuclear complexes 1–5.

M. Yadav et al. / Polyhedron 29 (2010) 791–800
793
811, 770, 723, 532, 474. 1H NMR (300 MHz, CDCl3, d ppm): 2.03 (d,
4H, J = 8.1 Hz), 2.56 (bs, 4H), 4.60 (bs, 4H), 6.23 (d, 2H, J = 3.9 Hz),
6.28 (d, 2H, J = 3.9 Hz), 7.12 (s, 2H), 7.48 (d, 2H, J = 8.1 Hz), 7.67
66.85; H, 5.31: N, 5.33%. IR (KBr pellet, cmꢀ1): 1603, 1550, 1504,
1379, 1336, 1284, 1238, 1171, 1030, 991, 891, 809, 772, 725,
d ppm): 2.01 (d, 4H,
J = 8.1 Hz), 2.54 (bs, 4H), 4.60 (bs, 4H), 5.11 (s, 2H), 6.27 (d, 2H
J = 3.3 Hz), 6.45 (d, 2H, J = 3.6 Hz), 6.97 (d, 2H, J = 8.4 Hz), 7.10 (s,
643, 461. 1H NMR (300 MHz, CDCl3,
(d, 2H, J = 8.1 Hz) UV–Vis. (CH2Cl2, kmax nm,
e
): 513 (2.18 ꢁ 104),
427 (1.30 ꢁ 104), 307 (1.16 ꢁ 104), 270 (1.76 ꢁ 104), 238
(3.06 ꢁ 104).
2H), 7.29–7.48 (m, 7H). UV–Vis. (CH2Cl2, kmax nm,
e): 496
(2.18 ꢁ 104), 426 (1.26 ꢁ 104), 363 (1.38 ꢁ 104), 264 (1.61 ꢁ 104),
236 (3.36 ꢁ 104).
2.2.2. Synthesis of [(g
4-C8H12)Rh(ndpm)] 2
It was prepared following the above procedure employed for 1
using 5-(4-nitrophenyl)dipyrromethane in place of 5-(4-cyano-
phenyl)dipyrromethane. Yield: 44%, (0.209 g). Anal. Calc. for
C23H22N3O2Rh: C, 58.12; H, 4.66; N, 8.84. Found: C, 57.85; H,
4.73: N, 8.72%. IR (KBr pellet, cmꢀ1): 1558, 1517, 1381, 1340,
1239, 1174, 1101, 1035, 993, 894, 823, 771, 721, 478. 1H NMR
(300 MHz, CDCl3, d ppm): 2.04 (d, 4H, J = 7.8 Hz), 2.57 (bs, 4H),
4.61 (bs, 4H), 6.25 (d, 2H, J = 3.6 Hz), 6.30 (d, 2H, J = 3.6 Hz), 7.14
(s, 2H), 7.55 (d, 2H, J = 8.4 Hz), 8.25 (d, 2H, J = 8.4 Hz). UV–Vis.
2.2.4. Synthesis of [(g
4-C8H12)Rh(4-pyrdpm)] 4
It was prepared by the same procedure as employed for 1 using
5-(4-pyridyl)dipyrromethane in place of 5-(4-cyanophenyl)dipyr-
romethane. Yield: 40% (0.172 g). Anal. Calc. for C22H22N3Rh: C,
61.26; H, 5.14; N, 9.74. Found: C, 60.94; H, 5.00: N, 9.86%. IR (KBr
pellet, cmꢀ1): 1616, 1560, 1474, 1381, 1339, 1240, 1175, 1034,
992, 891, 808, 772, 725, 473. 1H NMR (300 MHz, CDCl3, d ppm):
2.03 (d, 4H, J = 8.4 Hz), 2.54 (m, 4H), 4.60 (bs, 4H), 6.28 (bs, 4H)
7.12 (s, 2H), 7.32 (d, 2H, J = 5.4 Hz) 8.66 (d, 2H, J = 5.1 Hz). UV–
(CH2Cl2, kmax nm,
e
): 506 (2.17 ꢁ 104), 427 (1.35 ꢁ 104), 307
(1.74 ꢁ 104), 273 (2.85 ꢁ 104), 223 (2.63 ꢁ 104).
Vis. (CH2Cl2, kmax nm,
e
): 513 (2.10), 426 (1.28 ꢁ 104), 283
(1.45 ꢁ 104), 250 (1.77 ꢁ 104), 231 (2.28 ꢁ 104).
2.2.3. Synthesis of [(g
4-C8H12)Rh(bodpm)] 3
This complex was prepared following the same procedure used
for 1 except that, 5-(4-benzyloxy)dipyrromethane was used in
place of 5-(4-cyanophenyl)dipyrromethane. Yield: 40% (0.215 g).
Anal. Calc. for C30H29N2ORh: C, 67.17; H, 5.45; N, 5.22. Found: C,
2.2.5. Synthesis of [(g
4-C8H12)Rh(3-pyrdpm)] 5
It was synthesized following the procedure adopted for 1 start-
ing from 5-(3-pyridyl)dipyrromethane in place of 5-(4-cyano-
phenyl)dipyrromethane. Yield: 36% (0.155 g). Anal. Calc. for
Fig. 2. Space-filling representations of [(g g
4-C8H12)Rh(ndpm)] 2 (left) and [( 4-C8H12) Rh(4-pyrdpm)] 4 (right).
Fig. 3. UV-Vis. spectra of complexes 1–5 in dichloromethane.

794
M. Yadav et al. / Polyhedron 29 (2010) 791–800
C22H22N3Rh: C, 61.26; H, 5.14; N, 9.74. Found: C, 60.90; H, 5.02: N,
9.82%. IR (KBr pellet, cmꢀ1): 1615, 1560, 1475, 1381, 1340, 1239,
1174, 1034, 992, 893, 808, 771, 724, 475. 1H NMR (300 MHz, CDCl3,
d ppm): 2.03 (d, 4H, J = 8.1 Hz), 2.55 (bs, 4H), 4.61 (s, 4H), 6.31 (bs,
4H) 7.14 (s, 2H), 7.35 (t, 1H) 7.69 (d, 1H, J = 7.5 Hz), 8.61 (d, 1H,
place of [{(g l-Cl)Cl}2]. Yield: 80%, (0.662 g). Anal. Calc.
5-C5Me5)Rh(
for C32H37Cl2N3IrRh: C, 46.32; H, 4.49; N, 5.06. Found: C, 46.66; H,
4.38: N, 5.00%. IR (KBr pellet, cmꢀ1): 1626, 1559, 1473, 1378, 1337,
1237, 1171, 1032, 989, 796, 675, 476. 1H NMR (300 MHz, CDCl3, d
ppm): 1.56 (s, 15H), 2.03 (d, 4H, J = 7.8 Hz), 2.54 (bs, 4H), 4.59 (s,
4H), 6.20 (d, 2H, J = 4.2 Hz), 6.31 (d, 2H, J = 3.6 Hz), 7.14 (s, 2H),
7.37 (d, 2H, J = 5.4 Hz), 9.02 (d, 2H, J = 6.0 Hz). UV–Vis. (CH2Cl2,
J = 1.8 Hz), 8.66 (d, 1H, J = 3.3 Hz). UV–Vis. (CH2Cl2, kmax nm, e):
512 (2.09 ꢁ 104), 426 (1.26 ꢁ 104), 283 (1.43 ꢁ 104), 264
(1.40 ꢁ 104), 232 (1.84 ꢁ 104).
kmax nm,
e
): 513 (2.12 ꢁ 104), 434 (1.51 ꢁ 104), 279 (2.38 ꢁ 104),
234 (4.12 ꢁ 104).
2.2.6. Synthesis of [(
A solution of [(
dichloromethane (25 mL) was treated with [{(
g
g
4-C8H12)Rh(
4-C8H12)Rh(4-pyrdpm)] (0.431 g, 1.0 mmol) in
5-C5Me5)Rh(
l-
l-4-pyrdpm)Rh(g
5-C5Me5)Cl2] 6
2.2.8. Synthesis of [(g l-4-pyrdpm)Ru[(g
4-C8H12)Rh( 6-C10H14)Cl2] 8
g
This complex was prepared following the procedure for 6 ex-
cept that, [{( -Cl)Cl}2] (0.306 g, 0.5 mmol) was used
6-C10H14)Ru(
in place of [{( -Cl)Cl}2]. Yield: 75%, (0.553 g). Anal.
5-C5Me5)Rh(
Cl)Cl}2] (0.308 g, 0.5 mmol) and the resulting solution was stirred
at room temperature for 4 h. After filtration the solution was con-
centrated to dryness under reduced pressure. Resulting solid thus
obtained was re-dissolved in dichloromethane and precipitated
by addition of hexane and separated by filtration. Yield: 78%
(0.578 g). Anal. Calc. for C32H37Cl2N3Rh2: C, 51.91; H, 5.04; N,
5.68. Found: C, 51.60; H, 5.14: N, 5.59%. IR (KBr pellet, cmꢀ1):
1625, 1557, 1473, 1379, 1337, 1236, 1170, 1032, 991, 796, 674,
478. 1H NMR (300 MHz, CDCl3, d ppm): 1.63 (s, 15H), 2.03 (d, 4H,
J = 8.4 Hz), 2.54 (bs, 4H), 4.59 (s, 4H), 6.18 (d, 2H, J = 3.6 Hz), 6.30
(d, 2H, J = 3.6 Hz), 7.13 (s, 2H), 7.39 (d, 2H, J = 5.7 Hz), 9.05 (d,
2H, J = 6.0 Hz). MS (FAB): (M)+ 741 (740.38). UV–Vis. (CH2Cl2, kmax
g
l
g
l
Calc. for C32H36Cl2N3RhRu: C, 52.11; H, 4.92; N, 5.70. Found: C,
52.44; H, 5.02: N, 5.63%. IR (KBr pellet, cmꢀ1): 1618, 1557,, 1381,
1380, 1341, 1243, 1030, 993, 891, 808, 721, 475. 1H NMR
(300 MHz, CDCl3, d ppm): 1.34 (d, 6H, J = 6.6 Hz), 2.03 (d, 4H,
J = 7.8 Hz), 2.13 (s, 3H), 2.56 (bs, 4H), 3.04 (m, 1H), 4.59 (s, 4H),
5.29 (d, 2H, J = 6.6 Hz), 5.50 (d, 2H, J = 6.0 Hz), 6.23 (d, 2H,
J = 3.6 Hz), 6.30 (d, 2H, J = 3.3 Hz), 7.13 (s, 2H), 7.34 (d, 2H,
J = 6.0 Hz), 9.08 (d, 2H, J = 5.7 Hz). MS (FAB): (M)+ 739 (737.54).
UV–Vis. (CH2Cl2, kmax nm,
e
): 512 (2.10 ꢁ 104), 429 (1.54 ꢁ 104),
280 (2.23 ꢁ 104), 232 (4.01 ꢁ 104).
nm,
e
): 514 (2.11 ꢁ 104), 420 (1.71 ꢁ 104), 279 (2.39 ꢁ 104), 240
(3.20 ꢁ 104).
2.2.9. Synthesis of [(
It was prepared by the method employed for 6 starting from
6-C6H6)Ru( -Cl)Cl}2] (0.250 g, 0.5 mmol) in place of [{(g5
g l-4-pyrdpm)Ru[(g
4-C8H12)Rh( 6-C6H6)Cl2] 9
2.2.7. Synthesis of [(g l-4-pyrdpm)Ir(g
4-C8H12)Rh( 5-C5Me5)Cl2] 7
[{(g
l
-
It was prepared following the procedure employed for 6 except
C5Me5)Rh(l-Cl)Cl}2]. Yield: 77%, (0.525 g). Anal. Calc. for
that, [{(
g
5-C5Me5)Ir(
l-Cl)Cl}2] (0.398 g, 0.5 mmol) was used in
R
Cl
Cl
Cl
Cl
Cl
Ru
Ru
M
R
M
Cl
Cl
+
Cl
+
Ar-R = p-cymene, benzene
M = Rh(III), Ir(III)
N
N
N
N
Rh
Rh
N
N
4
4
DCM
r.t.
DCM
r.t.
R
N
N
Rh
Rh
N
Ru
Cl
N
M
Cl
Cl
N
N
Cl
M = Rh(III) (6)78%
Ir(III) (7)80%
Ar-R = p-cymene (8)75%
benzene (9)77%
Scheme 2. Scheme showing the synthesis of binuclear complexes 6–7.
Scheme 3. Scheme showing the synthesis of binuclear complexes 8–9.

M. Yadav et al. / Polyhedron 29 (2010) 791–800
795
C28H28Cl2N3RhRu: C, 49.35; H, 4.14; N, 6.17. Found: C, 49.63; H,
2.3. Crystallographic studies
4.25: N, 6.23%. IR (KBr pellet, cmꢀ1): 1557, 1381, 1337, 1235,
1175, 1035, 991, 890, 796, 728, 675, 474. 1H NMR (300 MHz, CDCl3,
d ppm): 2.03 (d, 4H, J = 8.1 Hz), 2.56 (bs, 4H), 4.59 (s, 4H), 5.72 (s,
6H), 6.26 (d, 2H, J = 4.2 Hz), 6.31 (d, 2H, J = 3.0 Hz), 7.14 (s, 2H),
7.36 (d, 2H, J = 6.0 Hz), 9.13 (d, 2H, J = 6.0 Hz). UV–Vis. (CH2Cl2,
Crystals suitable for single crystal X-ray diffraction analyses for
2 and 4 were obtained by slow diffusion of diethyl ether in dichlo-
romethane solution of the respective complexes at room tempera-
ture. Preliminary data on space group and unit cell dimensions as
well as intensity data for 2 were collected on OXFORD DIFFRAC-
TION X CAUBER-S while, for 4 on a BRUKER SMART APEX diffrac-
kmax nm,
e
): 512 (2.10 ꢁ 104), 425 (1.54 ꢁ 104), 276 (2.24 ꢁ 104),
235 (3.86 ꢁ 104).
Fig. 4. FAB mass spectra of complex 8.
Fig. 5. 1H NMR spectra of complex 8 in CDCl3.

796
M. Yadav et al. / Polyhedron 29 (2010) 791–800
tometer using graphite monochromatized Mo K
a
radiation. Struc-
[{(g
4-C8H12)Rh(
l-Cl)}2]
[g
4-C8H12 = 1,5-cyclooctadiene] with
tures were solved by direct methods and refined using SHELX 97
[35–37]. The non-hydrogen atoms were refined with anisotropic
thermal parameters. H-atoms attached to the carbon were in-
cluded as a fixed contribution and were geometrically calculated
and refined using SHELX riding model.
meso-substituted dipyrrins; cydpm, ndpm, bdpm, 4-pyrdpm and
3-pyrdpm in dichloromethane/methanol (1:1) at room tempera-
ture in the presence of triethylamine under stirring conditions.
The dipyrrins employed in these reactions were obtained by oxida-
tion of the corresponding dipyrromethanes using 2,3-dichloro-5,6-
dicyano-1,4-benzoquinone (DDQ) in a chloroform/benzene solu-
tion. The dipyrrin ligands were not isolated but were used in situ
to generate the desired metal complexes (Scheme 1) [38–41].
Resulting complexes were purified by column chromatography
(silica).
These were isolated as bright orange–red compounds that gen-
erally became dark red upon loss of the solvent. Complexes 1–5 are
air-stable solids and do not show any signs of decomposition in
solution upon exposure to air. The solids readily dissolve in com-
mon organic solvents such as benzene, chloroform, dichlorometh-
ane and acetone and are insoluble in diethyl ether, petroleum
ether. These were characterized by elemental analyses; IR, NMR
electronic spectral and emission spectral studies and crystal struc-
tures of the complexes 2 and 4 have been determined by X-ray
crystallographic analyses.
2.3.1. Selected crystallographic data for 2
ꢁ
Formula = C23H22N3O2Rh, Mr = 475.35, Triclinic space group P1,
a
(Å) = 9.8901(5),
(°) = 110.649(5), b (°) = 108.207(4),
954.21(8), Z = 2, Dc (Mg mꢀ3) = 1.654,
(K) = 150(2), (Å) = 0.71073, (all) = 0.0589,
0.0540, wR2 = 0.1400, wR2 [I > 2 (I)] = 0.1366, GOF = 1.134.
b
(Å) = 10.7254(5),
(°) = 103.221(4), V (Å3) =
(mmꢀ1) = 0.921,
(I > 2 (I)) =
c
(Å) = 10.9466(5), a
c
l
T
k
R
R
r
r
2.3.2. Selected crystallographic data for 4
Formula = C22H22N3Rh, Mr = 431.34, Monoclinic space group
P21/n, a (Å) = 6.6233(4), b (Å) = 15.2997(10), c (Å) = 17.5899(11),
a
(°) = 90.00, b (°) = 97.7020(10),
38(19), Z = 4, Dc (Mg mꢀ3) = 1.622,
100(2), k (Å) = 0.71073, R (all) = 0.0369, R (I > 2
wR2 = 0.1023, wR2 [I > 2 (I)] = 0.0927, GOF = 0.921.
c
(°) = 90.00, V (Å3) = 1766.
l
(mmꢀ1) = 0.977, T (K) =
(I)) = 0.0347,
r
1H NMR spectral data of the complexes (summarized in the Sec-
tion 2) corroborated well to their respective formulations. To facil-
itate assignment of the various resonances, comparative studies
were performed and resulting 1H NMR spectra of 1–3 is depicted
in Fig. 1. It was observed that upon complexation with the metal
center dipyrrin protons exhibited an appreciable downfield shift
as compared to that in the respective dipyrrin ligands. In general,
r
3. Results and discussion
3.1. Synthesis and characterization of the heteroleptic complexes 1–5
a
-pyrrolic protons displayed
a
significant deshielding (ꢂd
Synthesis of the neutral heteroleptic dipyrrin complexes 1–5
was achieved by treatment of the dimeric rhodium complex
7.14 ppm) which may be attributed to the steric interaction be-
Fig. 6. ORTEP diagrams of 2 (a) and 4 (b) at 30% thermal ellipsoid probability (H-atoms omitted for clarity).

M. Yadav et al. / Polyhedron 29 (2010) 791–800
797
tween the
a
-pyrrolic protons of the dipyrrins and cyclooctadiene
elemental analyses. Information about composition of the binu-
clear complexes 6 and 8 were also obtained from FAB-MS spectral
studies and resulting spectrum for 8 with the assignments is
shown in Fig. 4. Fragmentation pattern in these complexes pro-
vided valuable information about relative stability of the various
moieties and bonding of the Rh(III)/Ru(II) to the Rh(I). Complex 8
in its FAB-Mass spectrum, displayed peaks at m/z 739 (737.54),
703 (702.09), 665 (666.63) and 432 (431.36), assignable to [M+],
[M+ꢀCl], [MꢀCl2], [Rh(COD)(4-pyrdpm)], respectively. Complex 6
exhibited prominent peaks at m/z 741 (740.38), 668 (669.40),
431 (431.34). The presence of molecular ion peaks at m/z 739
(737.54) and 741 (740.38) in the FAB-MS of 8 and 6, respectively
strongly supported formation of the binuclear complexes.
protons (Fig. 2) [38]. The b-protons in 1 and 2, where meso-susb-
stituents are electron withdrawing groups (–CN, or NO2), appeared
as closely spaced doublets. On the other hand, in complexes 4 and
5 where meso-susbstituents are pyridyl group these appeared as a
broad singlet. However, in complex 3, possessing an electron
releasing group as the meso-susbstituent (–OCH2Ph) two well re-
solved doublets were observed. Comparative results demonstrated
that b-protons are magnetically different but resonances associ-
ated with these appear as a doublet of doublets at NMR time scale.
Electron withdrawing or donating nature of the phenyl substitu-
ents exhibited pronounced effect on the position of the resonances
corresponding to various protons of the coordinated dipyrrins. For
example, 1H NMR spectrum of complex 2 exhibited resonances at
6.25 (d, 2H, J = 3.6 Hz), 6.30 (d, 2H, J = 3.6 Hz), 7.14 (s, 2H), 7.55
(d, 2H, J = 8.4 Hz), 8.25 (d, 2H, J = 8.4 Hz) ppm assignable to pyrrolic
and phenyl protons of the dipyrrin (ndpm). This region of spectrum
integrated for ten protons as expected for the coordinated ndpm.
The protons due to cyclooctadiene group resonated at d 2.04 (d,
4H, J = 7.8 Hz), 2.57 (bs, 4H), 4.61 (bs, 4H). The position and inte-
grated intensity of various signals conformed well to the proposed
formulation of the complexes. Similar trends have been observed
in the 1H NMR spectra of other complexes.
Electronic spectra of the mononuclear complexes 1–5 in dichlo-
romethane (Fig. 3) exhibited moderately intense bands in the re-
gion ꢂ506, 427, 307, 273, and 223 nm (see experimental
section). By analogy with the earlier reports intense low-energy
bands (506/427 nm) have been assigned to highly conjugated
dipyrrin-based S0 ? S1
with the metal–dipyrrin charge transfer transitions in the visible
region [11–14,38,41,43]. In complex 3, the bands at 363 nm exhib-
ited a red shift in comparison to the complexes 1, 2, 4, and 5
(ꢂ307 nm). This shift may be attributed to the presence of benzyl-
oxy chromophore. Emission experiments on the complexes were
carried out in DCM with 1.0 mM solutions at r.t. Upon excitation
at their respective lowest energy bands these complexes did not
exhibit any emission.
Table 1
Important geometrical parameters of the complexes 2 and 4 (length (Å) and angle in
(°)).
Complex 2
Rh1–N1
Rh1–N2
Rh1–Cav(COD)
N3–O1
N3–O2
N3–C21
2.082(5)
2.090(5)
2.131
1.215(7)
1.223(7)
1.475(7)
N1–Rh1–N2
N1–Rh1–C5
N2–Rh1–C5
N1–Rh1–C1
N2–Rh1–C1
C5–Rh1–C1
N1–Rh1–C6
N2–Rh1–C6
C5–Rh1–C6
C1–Rh1–C6
N1–Rh1–C2
N2–Rh1–C2
C5–Rh1–C2
C1–Rh1–C2
C6–Rh1–C2
87.92(18)
160.4(2)
92.4(2)
90.6(2)
154.0(2)
97.5(2)
161.5(2)
92.2(2)
38.1(2)
81.2(2)
94.4(2)
168.0(2)
81.4(2)
37.9(2)
89.2(2)
*
(p
?
p
) transitions [11–14,42–43] along
C21–N3–O1
C21–N3–O2
O1–N1–O2
118.0(5)
124.0(5)
124.0(5)
3.2. Synthesis and characterization of the dinuclear complexes 6–9
Complex 4 is highly stable, soluble in many organic solvents
and possesses 4-pyridyl group as the meso-substituent. Due to
the presence of pendant 4-pyridyl group it may behave as a metal-
lo-ligand in the synthesis of homo-/hetero-binuclear complexes. In
order to exploit its applicability as a synthon in the synthesis
homo-/hetero-bimetallic complexes, its reactivity was examined
N2–Rh1–N1–C12
N1–Rh1–N2–C14
C12–C13–C18–C19
C20–C21–N3–O1(NO2)
ꢀ14.1(5)
18.2(5)
67.8(7)
ꢀ7.5(8)
Complex 4
Rh1–N1
Rh1–N2
Rh1–Cav(COD)
N3–C12
N3–C13
2.082(2)
2.084(2)
2.139
1.339(4)
1.350(4)
with the chloro-bridged complexes [{(
(M = Rh, Ir) and structurally analogous ruthenium complexes
[{( -Cl)Cl}2] (
6-arene)Ru( 6-arene = C6H6 and C10H14). Synthesis
g l-Cl)Cl}2]
5-C5Me5)M(
g
l
g
N1–Rh1–N2
87.94(8)
163.01(9)
93.02(9)
of the various neutral homo-/hetero-bimetallic complexes is de-
picted in Scheme 2 and 3.
N1–Rh1–C19
N2–Rh1–C19
N1–Rh1–C16
N2–Rh1–C16
C19–Rh1–C16
N1–Rh1–C20
N2–Rh1–C20
C19–Rh1–C20
C16–Rh1–C20
N1–Rh1–C15
N2–Rh1–C15
C19–Rh1–C15
C16–Rh1–C15
C20–Rh1–C15
It was observed that the complex 4 upon treatment with chloro-
91.11(9)
bridged dimeric rhodium/iridium complexes [{(g l-
5-C5Me5)M(
156.46(9)
81.26(10)
158.71(9)
91.75(9)
38.27(10)
97.44(10)
93.97(9)
165.22(10)
89.41(10)
38.27(10)
81.17(10)
Cl)Cl}2] (M = Rh, Ir) in 2:1 molar ratio in dichloromethane under
stirring conditions at room temparature afforded homo- and het-
ero-bimetallic complexes 6 and 7. While its reaction with arene
ruthenium
complexes
[{(g
6-arene)Ru(
l-Cl)Cl}2]
[(g
6-are-
ne = C10H14, C6H6) under analogous conditions gave hetero-bime-
tallic complexes 8 and 9 in appreciably good yields. These are
readily soluble in common organic solvents such as chloroform,
dichloromethane and acetone.
The binuclear complexes 6–9 are crystalline solids but all the
attempts to obtain single crystals suitable for X-ray diffraction
analyses failed at our hands. However, elemental analyses, 1H
NMR and FAB-mass spectral studies strongly supported formation
of the binuclear complexes. All the complexes gave satisfactory
C12–N3–C13
115.7(2)
N2–Rh1–N1–C4
N1–Rh1–N2–C6
C6–C5–C10–C11
8.5
ꢀ7.25
111.4

798
M. Yadav et al. / Polyhedron 29 (2010) 791–800
1H NMR spectral data of 6–9 are mentioned in the experimental
gle crystal X-ray diffraction analyses. ORTEP views of the com-
plexes at 30% probability with atom numbering scheme is
depicted in Fig. 6 and important geometrical parameters are
gathered in Table 1. Coordination geometry about the metal cen-
ter rhodium in both the complexes is distorted square planar
with two coordination sites occupied by dipyrin ligand and other
two by the cyaclooctadiene in g4-manner. Considering cyaclooct-
adiene ring as occupying two sites overall coordination geometry
about the metal center rhodium is square planar which is re-
flected by C1-Rh-C6/C2-Rh-C5 cis angles of 81.2(2)/81.4(2)° in 2
and C20–Rh–C15/C19–Rh–C16 cis angles of 81.17(10)/81.26(10)°
in the complex 4. These are comparable to the values reported
in other rhodium complexes [15]. The cyclooctadiene ring
adopted a twisted boat configuration in the both the complexes
2 and 4. Average Rh–N bond distances in 2 and 4 are 2.086
and 2.083 Å, respectively. The N–Rh–N angle is 87.92° in 2 and
87.94(18)° in 4. The bond lengths and angles are in good agree-
ment with other heteroleptic complexes reported in the litera-
ture [6–10,42–43]. The Rh–C bond distances are almost equal
with an average distance of 2.131 in 2 and 2.139 Å in 4. As ex-
pected, the meso-phenyl substituents are twisted out of plane
section and representative spectrum for complex 8 with the
assignments is depicted in Fig. 5. The position and integrated
intensity of the various signals corroborated well to a system
involving coordination of the complex 4 through pyridyl nitrogen
of dipyrrin to another metal center. Notably, protons associated
with cyclooctadiene of the metallo-ligand 4 did not exhibit any
appreciable shift in the position of resonances upon coordination
to another metal center through 4-pyridyl nitrogen resulting in
the formation of in 6–9. It may be attributed to the rather long dis-
tance to the ligating site. However, a significant deshielding of the
pyridyl proton C1 (Fig. 5) was observed upon complexation to an-
other metal center, while pyridyl proton C2 displayed a small shift.
The pyridyl proton C1 resonated at 9.05 (d, 2H, J = 6.0 Hz), 9.02 (d,
2H, J = 6.0 Hz), 9.08 (d, 2H, J = 5.7 Hz), 9.13 (d, 2H, J = 6.0 Hz), and
C2 at 7.39 (d, 2H, J = 5.7 Hz), 7.37 (d, 2H, J = 5.4 Hz), 7.34 (d, 2H,
J = 6.0 Hz), 7.36 (d, 2H, J = 6.0 Hz) ppm, in the complexes 6, 7, 8,
and 9, respectively. The b-pyrrolic protons of dipyrrin in the pre-
cursor complex 4 resonated as a singlet at 6.28 (bs, 4H) ppm but,
after linkage of the second metal center two separate doublets
were observed at [6.18 (d, 2H, J = 3.6 Hz), 6.30 (d, 2H, J = 3.6 Hz)],
[6.20 (d, 2H, J = 4.2 Hz), 6.31 (d, 2H, J = 3.6 Hz)], [6.23 (d, 2H,
J = 3.6 Hz), 6.30 (d, 2H, J = 3.3 Hz)] and [6.26 (d, 2H, J = 4.2 Hz),
6.31 (d, 2H, J = 3.0 Hz)] ppm in the complexes 6–9, respectively.
from the dipyrrin
The weak interaction study on complexes 2 and 4 shows differ-
ent interactions like C–H. . . and C–H. . .N/O leading to formation
p-system by ꢂ67.8° in 2 and ꢂ111.4° in 4.
p
However,
a
-protons of the dipyrrin ligands did not exhibit any sig-
of interesting motifs (Figs. 7 and 8). Matrices of weak interac-
nificant shift. The methyl protons of cyclopetadiene resonated at
1.63 (s, 15H) ppm in the rhodium complex 6 which are more
deshielded than in the iridium complex 7 [1.56(s, 15H)] ppm. In
the p-cymene complex methyl protons in 8 resonated at 1.34 (d,
6H, CH–(CH3)2), 2.13 (s, 3H, C–CH3) and as a multiplet at 3.04 (m,
1H, CH–(CH3)2) ppm. In addition to this, phenyl (C6H4) protons of
the p-cymene displayed two separate doublets at 5.29 (d, 2H)
and 5.50(d, 2H) ppm, which are slightly deshielded than those in
the p-cymene precursor. The benzene protons of complex 9 reso-
nated as a singlet at 5.72 (s, 6H, C6H6) ppm.
tions studies are given Table 2.
In this study we wished to explore dipyrrin chemistry of the
organometallic compounds. In this direction, we have prepared
various meso-substituted dipyrromethene ligands possessing both
the electron withdrawing and releasing meso-substituents and uti-
lized them in the synthesis of heteroleptic Rh(I) complexes 1, 2,
and 3. Many metallo-ligands have been employed as a building
block in the synthesis of homo-/hetero- bi-/tri-/tetra-metallic coor-
dination solids. These synthetic manipulations need: (1) designing
multi-dentate ligands for the synthesis of metallo-ligands (2) isola-
tion of stable metallo-ligands (3) ligating ability towards targeted
metal center. This peculiar feature is seldom found in dipyrrin li-
3.3. Molecular structures
gands having multi-dentate sites. In the complexes [Rh(g4
COD)(4-pyrdpm)] 4 and [Rh(
4-COD)(3-pyrdpm)] 5, the Rh center
is coordinated to dipyrrolic moiety of the dipyrrin and 4-pyridyl/3-
-
g
4-C8H12)Rh(ndpm)] (2)
g
Crystal structures of the complexes [(
and [(
4-C8H12)Rh(4-pyrdpm)] (4) have been determined by sin-
g
Fig. 7. Linear channel like structural motif results by C–H. . .O and C–H. . .p weak interactions along ‘a’axis in complex 2.

M. Yadav et al. / Polyhedron 29 (2010) 791–800
799
Fig. 8. Zig-zag structural motif results by C–H. . .N and C–H. . .
p
weak interactions along ‘c’axis in complex 4.
Table 2
Data of weak interaction study.
C–H–Cg
H–Cg (Å)
H–(ring plane) (Å)
C–Cg (Å)
C–H–Cg (°)
c (°)
Complex 2
C(7)–H(7A)ꢃꢃꢃCg(Rh1N1C12C13C14N2)a
C(8)-H(8B)ꢃꢃꢃCg(Rh1N1C12C13C14N2)a
C(23)-H(23)ꢃꢃꢃCg(Rh1N1C12C13C14N2)b
3.00
2.86
2.73
2.849
2.510
2.717
3.6853
3.4782
3.6143
128
122
155
18.04
28.51
5.93
Complex 4
C(18)-H(18B)ꢃꢃꢃCg(N2C6C7C8C9)c
2.97
2.55
2.835
2.469
3.8713
3.4786
152
156
17.09
14.47
C(21)H(21A)ꢃꢃꢃCg(Rh1N1C4C5C6N2)d
a = 1 ꢀ X, ꢀY, ꢀZ. b = 1 ꢀ X, 1ꢀY, 1ꢀZ. c = 1 ꢀ X, ꢀY, ꢀZ. d = 1 + X, Y, Z
D–HꢃꢃꢃA
D (D–H)
0.99
d (HꢃꢃꢃA)
2.50
d (DꢃꢃꢃA)
3.4598
3.4903
\ðDHAÞ
164
Complex 2(Å and °)
C(4)–H(4B)ꢃꢃꢃO(2)a
Complex 4 (Å and °)
C(7)–H(7)ꢃꢃꢃN(3)b
0.95
2.56
167
a = 1 ꢀ x, 1 ꢀ y, 1 ꢀ z. b = ꢀx, 1 ꢀ y, ꢀz
pyridyl group is present as a pendant donor group. The presence of
unccordinated sites in the form of 4-pyridyl/3-pyridyl group pro-
vides them a unique opportunity to behave as metallo-ligands in
the synthesis of homo-/hetero-bimetallic complexes. Homo-/het-
ero-bimetallic complexes can be prepared using these complexes
following a stepwise synthetic approach. Our synthetic strategy
(Scheme 1–3), can be summarized as follows: (1) preparation of
the relatively simple metallo-ligand by ligation of 5-(4-pyri-
dyl)dipyrrins with the chloro-bridged Rh(I) precursors (2) exploita-
tion of these metallo-ligands in the construction of homo-/hetero-
bimetallic complexes. In complex 6, two rhodium centers Rh(I) and
Supplementary data
CCDC 743122 and 743123 contain the supplementary crystallo-
graphic data for complexes 2 and 4, respectively. These data can be
obtained free of charge via http://www.ccdc.cam.ac.uk/conts/
retrieving.html, or from the Cambridge Crystallographic Data Cen-
tre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-
033; or e-mail: deposit@ccdc.cam.ac.uk.
Acknowledgments
Rh(III) are linked through pyridyl nitrogen of [Rh(g
4-COD)(4-pyr-
Thanks are due to the Council of Scientific and Industrial Re-
search, New Delhi, India for providing financial assistance through
the scheme (HRDG 01(2074)/06/EMR-II). We also thank the Head,
SAIF, Central Drug Research Institute, Lucknow, for providing spec-
tral facilities, and National Single Crystal X-ray Diffraction Labora-
tory, Indian Institute of Technology, Powai, Mumbai, for X-Ray
facilities.
dpm)]. Analogous structural features have been observed for the
complex 7, except that, the other metal center is Ir(III). In com-
plexes 8–9 ruthenium(II) is bonded through pyridyl nitrogen of
the complex 4.
In summary, through this work first examples of heteroleptic
rhodium(I) dipyrrin complexes have been synthesized and charac-
terized by various physicochemical techniques. The complex
[Rh(g
4-COD)(4-pyrdpm)] possessing uncoordinated nitrogen do-
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