Metalloporphyrin as a ligand in organometallic complexes: Synthesis and characterization of a nickel(II) porphyrin complex of 1,5- cyclooctadienedichlororuthenium(II)

Article abstract of DOI:10.1016/j.jorganchem.2005.07.030

A method for the synthesis of dinuclear metal complexes has been developed which utilizes the multichelating porphyrin ligand, α,α-5,15-bis(o- nicotinoylphenyl)-2,8,12,18-tetraethyl-3,7,13,17-tetramethylporphyrin, H ₂[DPE]-(py)₂ (di[o-nicotinoylphenyl]etioporphyrin). In addition to the porphyrin site, the two terminal pyridyl groups of the ligand serve as an additional chelate. The two metal binding sites are chemically different and can be used to bind different metal centers. The versatility of this ligand is demonstrated by fabricating a heterobimetallic complex, [Ni(DPE)-(py₂)]Ru(COD)Cl₂, composed of a porphyrin coordination complex linked to an organometallic fragment.

Full text of DOI:10.1016/j.jorganchem.2005.07.030

Journal of Organometallic Chemistry 690 (2005) 4978–4981
www.elsevier.com/locate/jorganchem
Note
Metalloporphyrin as a ligand in organometallic complexes:
Synthesis and characterization of a nickel(II) porphyrin complex
of 1,5-cyclooctadienedichlororuthenium(II)
a
b,
*
Mannar R. Maurya , L. Keith Woo
a
Indian Institute of Technology Roorkee, Roorkee 247 667, India
Departments of Chemistry, Iowa State University, Gilman Hall, Ames, IA 50011-3111, USA
b
Received 25 May 2005; received in revised form 6 July 2005; accepted 8 July 2005
Available online 22 August 2005
Abstract
A method for the synthesis of dinuclear metal complexes has been developed which utilizes the multichelating porphyrin ligand,
a,a-5,15-bis(o-nicotinoylphenyl)-2,8,12,18-tetraethyl-3,7,13,17-tetramethylporphyrin, H2[DPE]-(py)2 (di[o-nicotinoylphenyl]etiopor-
phyrin). In addition to the porphyrin site, the two terminal pyridyl groups of the ligand serve as an additional chelate. The two metal
binding sites are chemically different and can be used to bind different metal centers. The versatility of this ligand is demonstrated by
fabricating a heterobimetallic complex, [Ni(DPE)-(py2)]Ru(COD)Cl2, composed of a porphyrin coordination complex linked to an
organometallic fragment.
Ó 2005 Elsevier B.V. All rights reserved.
Keywords: Ruthenium; Nickel; Metalloporphyrin; Heterobinuclear; Diene
1. Introduction
generating new properties or reactivities that cannot be
produced by the individual metal complexes alone.
These include opportunities for unusual electronic, mag-
netic, catalytic and redox properties and providing new
models for charge transfer, electron transport, etc.
Fabrication of discrete multinuclear complexes relies
heavily on ligand design. In addressing this issue, we
developed difunctionalized porphyrin macrocycles that
are capable of chelating more than one metal. These ver-
satile ligands are useful for preparing a variety of di- and
trinuclear coordination complexes [5] as well as for
forming monolayers at gold [6]. The framework of our
ligand is based upon a,a-bis(o-aminophenyl)-2,8,12,18-
tetraethyl-3,7,13,17-tetramethylporphyrin or di[o-ami-
nophenyl]etioporphyrin (H2[DPE]) that was originally
prepared by Young and Chang [7]. In extending our
work, we have used a difunctionalized porphyrin ligand
to link a coordination complex with an organometallic
fragment. The results of this work are reported here.
Multinuclear transition metal complexes are widely
studied as biomimetic models for enzyme active sites
[1]. Examples that contain a porphyrin fragment are
particularly relevant to the class of enzymes known as
cytochrome c oxidases [2]. These are the terminal en-
zymes in the electron transfer cascade, mediating the
four-electron reduction of O2 to water. By employing
dinuclear metal complexes containing multichelating
porphyrin ligands, considerable progress has been made
in understanding structure–function relationships in en-
zyme active sites [3]. Moreover, multimetal complexes
have strong prospects for generating unusual character-
istics [4]. Particularly intriguing is the possibility of
*
Corresponding author. Tel.: +1 515 294 5854; fax: +1 515 294
9623.
E-mail address: kwoo@iastate.edu (L.K. Woo).
0022-328X/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2005.07.030

M.R. Maurya, L.K. Woo / Journal of Organometallic Chemistry 690 (2005) 4978–4981
4979
2. Results and discussion
region [8]. IR and NMR spectral data strongly support
the coordination of pyridine nitrogens to ruthenium of
1
The structure and schematic representation of the
binucleating porphyrin [H2(DPE)]-(py)2 is shown below
(Fig. 1). Metallation of this porphyrin with Ni(II) was
achieved by treatment with nickel acetate as described
previously [5a]. This mononuclear complex behaves as
a bidentate ligand. Thus, treatment of Ru(g4-C8H12)-
Cl2(CH3CN)2 with equimolar amounts of [Ni(DPE)]-
(py)2 in refluxing CHCl3 led to the formation of the
organometallic binuclear species [Ni(DPE)]-(py)2Ru-
(g4-C8H12)Cl2. The complex [H2(DPE)]-(py)2Ru-
(g4-C8H12)Cl2 was also isolated in a manner identical
to that for the binuclear complex by substituting
[H2(DPE)]-(py)2 for [Ni(DPE)]-(py)2. Systematic
formation of these complexes is presented in Scheme 1.
While dinuclear complex 2 can also be obtained by
treating complex 1 with nickel acetate, synthesis via
[Ni(DPE)]-(py)2 resulted in purer product with better
yields. Complex 2 is robust as a solid and in solution.
the Ru(g4-C8H12)Cl2 group, while the UV–vis and H
NMR spectra indicate that complex 1 contains an
unmetallated porphyrin. For example, the upfield pro-
ton singlet at ꢀ2.13 ppm is diagnostic of the internal
N–H protons of the porphyrin. Thus, no insertion of
ruthenium into the N4–porphyrin chelate occurs despite
the presence of labile ligands on Ru(g4-C8H12)Cl2. This
is not unusual as Ru(II) is d6, low spin and insertion into
the porphyrin binding site typically requires reaction
temperatures above 80 °C [9].
The far-IR spectrum of the dinuclear complex 2
shows two peaks at 638 and 466 cmꢀ1 assignable to
in-plane and out-of-plane pyridine ring deformations
[8]. These bands are shifted to higher frequencies than
for those of free pyridines and reflect the metal coordi-
nation of these ligands. Complex 2 exhibits only a single
band in CH2Cl2 solution as well as in mulls at 346 cmꢀ1
,
consistent with Ru–Cl stretches due to a trans-geometry.
1
However,
[H2DPE]-(py)2Ru(g4-C8H12)Cl2
slowly
The H NMR spectrum of the dinuclear complex 2
decomposed in solution to free porphyrin and unidenti-
fied paramagnetic products.
shows distinctive changes in its proton resonances rela-
tive to those of the mononuclear Ru(g4-C8H12)Cl2-
(CH3CN)2 [10] and [Ni(DPE)]-(py)2 species [11]. The
absence of signals due to bound CH3CN in 2 indicate
the replacement of the coordinated acetonitriles by pyr-
idine nitrogens of the binucleating ligand. The mononu-
clear complex Ru(g4-C8H12)Cl2(CH3CN)2 exhibits three
proton resonances at 4.27, 2.40 and 2.03 ppm due to ole-
finic hydrogens and exo and endo methylene protons of
COD, respectively. The general up-field shift of the
COD proton signals to 3.81, 2.99, and 1.84 ppm in com-
plex 2 reflect the position of the Ru fragment above the
porphyrin, within the cone of deshielding due to the ring
current. The pyridyl proton resonances also reveal con-
formational changes of the chelate appendages upon
binding to Ru. For example, in [Ni(DPE)]-(py)2, the
The UV–vis spectrum of mononuclear complex 1
exhibits a soret band at 410 nm and four visible bands
at 510, 542, 576, and 628 nm, identical to that of the free
base porphyrin. The presence of three resonances at
3.86, 2.67, and 2.01 ppm in the 1H NMR spectrum indi-
cates g4-coordination of COD. The appearance of only
a single band in the far-IR spectrum at 338 cmꢀ1 dem-
onstrates the trans-chloride configuration at Ru. In
addition, bands at 634 and 468 cmꢀ1 lie in the coordi-
nated pyridyl in-plane and out-of-plane deformation
H6'
N
N
H2'
O
H5'
0
0
H4 and H5 protons (see Fig. 1) resonate at 6.83 and
6.59 ppm. In complex 2, these signals shift down field
to 7.10 and 6.89 ppm, respectively. Thus, prior to bind-
ing to Ru, the pyridyl groups are generally positioned
with the N atom facing away from the porphyrin nor-
H4'
O
NH
HN
N
HN
NH
N
0
0
mal, placing H4 and H5 over the ring current. On che-
lation to Ru (Fig. 2), the pyridyl groups must rotate to
Fig. 1. Structural representation of the ligand [H2(DPE)]-(py)2 with
numbering convention for pyridyl hydrogens.
O
[Ni(DPE)]-(py)2
(ii)
(i)
O
NH
N
NH
N
[H2(DPE)]-(py)2
N
N
N
N
N
N
Ru(COD)Cl2
N
Ni
(iv)
Ru(COD)Cl2
N
Ni
(iii)
N
N
[H2DPE]-(py)2Ru(η4-C8H12)Cl2
NH
1
O
NH
2
O
Scheme 1. (i) and (iv) Ni(CH3COO)2; (ii) and (iii) Ru(g4-C8H12)Cl2
(CH3CN)2.
Fig. 2. Structural representation of [Ni(DPE)]-(py)2Ru(COD)Cl2.

4980
M.R. Maurya, L.K. Woo / Journal of Organometallic Chemistry 690 (2005) 4978–4981
0
0
allow the N-donors to bind to Ru, placing H4 and H5
COD), 2.67 (m, 4H, exo-CH2, COD), 2.52 (s, 12H,
CH3), 2.01 (m, 4H, endo-CH2), 1.76 (t, 12H, CH2CH3),
ꢀ2.13 (s, 2H, pyrrole-NH). IR (CH2Cl2): m(NH), 3395;
further away from the shielding cone of the porphyrin
ring current.
m(CO), 1685; d(Ru–py), 634, 468; m(Ru–Cl), 338 cmꢀ1
4.2. [Ni(DPE)]-(py)2Ru(g4-C8H12)Cl2 (2)
.
3. Conclusion
A solution of Ru(g4-C8H12)Cl2(CH3CN)2 (42 mg,
0.11 mmol) in 5 mL CHCl3 was added to a stirred solu-
tion of Ni(DPE)-(py)2 (93 mg, 0.10 mmol) in 10 mL
CHCl3. The reaction mixture was heated at reflux for
8 h. After concentrating the solvent to 2 mL, 10 mL of
hexanes was added and the mixture was cooled to
ꢀ10 °C for 18 h. A dark-red crystalline solid was
filtered, washed with hexanes and dried in vacuo at
100 ° C for 5 h. Yield: 92 mg (75%). UV–vis (CHCl3):
The [H2(DPE)]-py2 ligand is a versatile chelate with
two unique metal binding sites. Heterobinuclear com-
plexes can be prepared in a designed fashion by metal-
lating each site selectively and sequentially. By using
chemical control, we have prepared a novel binuclear
complex that consists of a coordination complex linked
to an organometallic compound. With labile ligands
bound to the organometallic fragment, it should be pos-
sible to elicit metal mediated processes in which a single
substrate can interact simultaneously with both metals
of the heterobimetallic complex.
1
410 (soret), 530, 566 nm. H NMR (CDCl3): 9.48 (s,
2H, meso-H), 9.21 (d, 2H, aryl), 8.75 (d, 2H, 20-py),
8.29 (d, 2H, 60-py), 7.79 (m, 4H, aryl), 7.69 (s, 2H,
NH), 7.61 (m, 2H, aryl), 7.10 (s, 2H, 40-py), 6.89 (t,
2H, 50-py), 3.81 (m, 4H, @CH, COD), 3.64 (m, 8H,
CH2CH3), 2.99 (m, 4H, exo-CH2, COD), 2.30 (s, 12H,
CH3), 1.84 (m, 4H, endo-CH2 COD), 1.63 (t, 12H,
CH2CH3). IR (mull): m(NH), 3379; m(CO), 1688, d(Ru–
py), 638, 466; m(Ru–Cl), 346 cmꢀ1. Anal. Calc. for
C66H64N8O2Cl2NiRu Æ H2O: C, 62.71; H, 5.39; N,
9.14%. Found: C, 62.89; H, 5.18; N, 9.04%.
4. Experimental
All commercial chemicals were used without further
purification. CHCl3 was dried over molecular sieves for
several days and degassed before use. All reactions were
carried out under an atmosphere of purified nitrogen.
Synthesis of a,a-5,15-bis(o-nicotinamidophenyl)2,8,12,
18-tetraethyl-3,7,13,17-tetramethylporphyrin, [H2(DPE)]-
(py)2, and its Ni(II) complex were accomplished by the
literature procedures [5c]. The method of Albers et al.
[12] was used to prepare Ru(g4-C8H12)Cl2(CH3CN)2.
IR spectra were recorded as nujol mulls or in CH2Cl2
on an IBM IR-98 Fourier transform infrared spectrom-
eter. Visible spectra were obtained in CHCl3 at ambient
temperature on a HP 8452A diode array spectropho-
Acknowledgments
We thank the National Science Foundation for par-
tial support of this work.
1
References
tometer. H NMR spectra were recorded in CDCl3 on
a Nicolet NIC 300 spectrometer and chemical shifts
(in ppm) are reported relative to residual proton impuri-
ties in CDCl3 (7.24 ppm).
[1] L. Que, A.E. True, Prog. Inorg. Chem. 90 (1990) 97.
[2] T.P. Thrash, L.J. Wilson, Inorg. Chem. 40 (2001) 4556.
[3] J.P. Collman, R. Boulatov, C.J. Sunderland, in: K.M. Kadish,
R.M. Smith, R. Guilard (Eds.), The Porphyrin Handbook, Wiley,
New York, 2003, p. 279 (Chapter 46).
[4] L.F. Lindoy, Adv. Inorg. Chem. 45 (1998) 75.
[5] (a) L.K. Woo, M.R. Maurya, C.J. Tolppi, R.A. Jacobson, S.
Yang, E. Rose, Inorg. Chim. Acta 182 (1991) 41;
4.1. [H2(DPE)]-(py)2Ru(g4-C8H12)Cl2 (1)
A mixture of Ru(g4-C8H12)Cl2(CH3CN)2 (42 mg,
0.11 mmol) and [H2(DPE)]-(py)2 (87 mg, 0.10 mmol) in
15 mL CHCl3 was heated at reflux for 8 h while stirring.
After evaporating the solvent to dryness, 2 mL CHCl3
and 8 mL hexanes were added and the mixture was
cooled to ꢀ10 °C for 5 h. The precipitated brown solid
was filtered, washed with hexanes and dried in vacuo
at 80 °C. Yield: 60 mg (51%). UV–vis (CHCl3): 410
(soret), 510, 542, 576, 628 nm. 1H NMR (CDCl3):
10.16 (s, 2H, meso-H), 9.03 (d, 2H, aryl), 8.81 (d, 2H,
20-py), 8.54 (d, 2H, 40-py), 7.87 (m, 6H, aryl and NH),
7.70 (t, 2H, aryl), 6.81 (m, 2H, 60-py), 6.66 (s, 2H, 50-
py), 4.08 (m, 12H, CH2CH3), 3.88 (m, 4H, @CH,
(b) L.K. Woo, M.R. Maurya, Inorg. Chem. 30 (1991) 4671;
(c) L.K. Woo, M.R. Maurya, R.A. Jacobson, S. Yang, S.L.
Ringrose, Inorg. Chem. 31 (1992) 913;
(d) L.K. Woo, M.R. Maurya, R.A. Jacobson, S. Yang, S.L.
Ringrose, Inorg. Chim. Acta 193 (1992) 143.
[6] J. Zak, H. Yuan, M.-K. Ho, L.K. Woo, M.D. Porter, Langmuir
9 (1993) 2772.
[7] R. Young, C.K. Chang, J. Am. Chem. Soc. 107 (1985) 898.
[8] (a) K. Nakamoto, Infrared and Raman Spectra of Inorganic and
Coordination Compounds, fifth ed., Wiley, New York, 1997, Part
B, p. 24;
(b) R.J.H. Clark, C.S. Williams, Inorg. Chem. 4 (1965) 350.
[9] (a) J.W. Buchler, in: D. Dolphin (Ed.), The Porphyrins, vol. 1,
Academic Press, New York, 1978, p. 406 (Chapter 10);

M.R. Maurya, L.K. Woo / Journal of Organometallic Chemistry 690 (2005) 4978–4981
4981
(b) J.K.M. Sanders, N. Bampos, Z. Clyde-Watson, S.L. Darling,
J.C. Hawley, C.C. Mak, S.J. Webb, in: K.M. Kadish, R.M.
Smith, R. Guilard (Eds.), The Porphyrin Handbook, vol. 3,
Wiley, New York, 2000, p. 19 (Chapter 15).
[11] H NMR of Ni(DPE)-(py)2 (CDCl3): 9.48 (s, 2H, meso), 8.91 (d,
2H, 20-py), 8.24 (s, 2H, NH), 8.20 (m, 2H, aryl), 8.14 (d, 2H, 60-
py), 7.81 (m, 2H, aryl), 7.39 (m, 4H, aryl), 6.83 (m, 2H, 40-py),
6.59 (m, 2H, 50-py), 3.66 (m, 8H, CH2CH3), 2.31 (s, 12H, CH3),
1.55 (t, 12H, CH2CH3).
[10] 1H NMR of [Ru(g4-C8H12)Cl2(CH3CN)2] in CDCl3: 4.27 (m, 4H,
@CH, COD), 2.61 (s, 6H, CH3CN), 2.40 (m, 4H, exo-CH2, COD),
2.03 (pseudo q, 4H, endo-CH2, COD).
[12] M.O. Albers, T.V. Ashworth, H.E. Oosthuizen, E. Singleton,
Inorg. Synth. 26 (1989) 68.