Synthesis and crystal structures of [Rh(TTP)(CH3)]2(μ-CNpy) and [Rh(TTP)(C8H11)] (TTP = 5,10,15,20-tetra(p-tolyl)porphyrin dianion; CNpy = 4-cyanopyridine; C8H11 = (5-norbornen-2-yl)methyl)

Article abstract of DOI:10.1016/S0022-328X(00)00236-9

Interaction of [Rh(TTP)CH₃] (TTP = 5,10,15,20-tetra(p-tolyl)porphyrin dianion) with bidentate ligands L affords [Rh(TTP)CH₃]₂(μ-L) (L = 4-cyanopyridine (1) or 4,4′-bipyridine (2)). The structure of 1 has been established by X-ray crystallography. The average Rh-C, average Rh-N(pyrrole), and average Rh-N(CNpy) distances in 1 are 2.032(4), 2.032, and 2.273(4) A?, respectively. The reaction of Na[Rh(TTP)] with (5-norbornen-2-yl)methyl iodide (C₈H₁₁I) affords [Rh(TTP)(C₈H₁₁)] (5), which has been characterized by X-ray diffraction study. The Rh-C and average Rh-N distance in 5 are 2.052(6) and 2.022 A?, respectively.

Full text of DOI:10.1016/S0022-328X(00)00236-9

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 604 (2000) 197–201
Synthesis and crystal structures of [Rh(TTP)(CH )] (m-CNpy) and
3
2
[
Rh(TTP)(C H )] (TTP=5,10,15,20-tetra(p-tolyl)porphyrin
8
11
dianion; CNpy=4-cyanopyridine;
C H =(5-norbornen-2-yl)methyl)
8
11
1
Wa-Hung Leung *, Willetta Lai, Ian D. Williams
Department of Chemistry, Hong Kong Uni6ersity of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, PR China
Received 3 March 2000; accepted 16 April 2000
Abstract
Interaction of [Rh(TTP)CH3] (TTP=5,10,15,20-tetra(p-tolyl)porphyrin dianion) with bidentate ligands
L affords
[
Rh(TTP)CH ] (m-L) (L=4-cyanopyridine (1) or 4,4%-bipyridine (2)). The structure of 1 has been established by X-ray crystallog-
3
2
raphy. The average RhꢀC, average RhꢀN(pyrrole), and average RhꢀN(CNpy) distances in 1 are 2.032(4), 2.032, and 2.273(4) A
respectively. The reaction of Na[Rh(TTP)] with (5-norbornen-2-yl)methyl iodide (C H I) affords [Rh(TTP)(C H )] (5), which has
,
,
8
11
8
11
been characterized by X-ray diffraction study. The RhꢀC and average RhꢀN distance in 5 are 2.052(6) and 2.022 A
2000 Elsevier Science S.A. All rights reserved.
,
, respectively.
©
Keywords: Dinuclear; Rhodium porphyrin; Alkyl; Crystal structure
reactions of rhodium porphyrins with bidentate
pyridine ligands and (b) metathesis polymerization
rhodium porphyrins containing a norbornene function-
ality. In this paper, we report the synthesis and crystal
structure of a 4-cyanopyridine-bridged methylrho-
dium(III) porphyrin and a s-bonded (5-norbornen-2-
yl)methyl complex of rhodium porphyrin.
1
. Introduction
In recent years a variety of oligomeric metal por-
phyrins and phthalocyanines have been synthesized as
components of molecular devices, supramolecular as-
semblies [1–4], and light-harvesting systems [5]. Of
particular interest are a class of metalloporphyrin
oligomers based on square-planar [M(por)] (por=por-
phyrin dianion) cores and bidentate N-heterocycles
such as pyrazine and 4,4%-bipyridine. Well-defined one-
2
. Results and discussion
dimensional polymers of the type [M(por)(L)] (M=
n
Fe, Ru, Os) have been synthesized and shown to exhibit
interesting redox and optical properties [3]. There are,
however, relatively few examples of polymeric or
oligomeric rhodium porphyrins [6], which may find
applications in molecular recognition of amino acids [7]
and nucleobases [8]. In this connection, two approaches
to polynuclear rhodium porphyrins were attempted: (a)
2.1. Dimeric Rh(III) methyl complexes
Ogoshi and coworkers first studied the reactions
of amine ligands with methylrhodium(III) porphyrins
[9]. It was found that in solution the pyridine
adducts [Rh(OEP)CH (L)] (OEP=2,3,7,8,12,13,17,18-
3
octaethylporphyrin dianion; L=4-substituted pyridine)
characterized by NMR and UV–vis spectroscopy are
in equilibrium with [Rh(OEP)CH ]. In this work,
3
*
Corresponding author. Tel.: +852-2358-7360; fax: +852-2358-
594.
E-mail address: chleung@ust.hk (W.-H. Leung).
we found that when [Rh(TTP)CH ] was treated
3
1
with one equivalent of 4-cyanopyridine (CNpy) a
1
To whom crystallographic inquires should be addressed.
mixture
of
[Rh(TTP)CH ] (m-CNpy)
(1)
and
3
2
0022-328X/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(00)00236-9

198
W.-H. Leung et al. / Journal of Organometallic Chemistry 604 (2000) 197–201
Table 2
Selected bond lengths (A
[
Rh(TTP)(CH )(CNpy)] (2) were formed. Complexes 1
3
,
) and angles (°) for[Rh(TTP)CH ] (m-CNpy)
3
2
and 2 could be separated by fractional recrystallization
and were isolated as crystalline solids (see Section 3).
The dimer 1 was isolated in good yield when 0.5
equivalents of CNpy were used. The wCN for 1 was
(
1)
Bond lengths
Rh(1)ꢀN(1)
Rh(1)ꢀN(3)
Rh(1)ꢀN(5)
2.038(3)
2.029(4)
2.273(4)
Rh(1)ꢀN(2)
Rh(1)ꢀN(4)
Rh(1)ꢀC(7)
2.028(3)
2.032(3)
2.032(4)
Bond angles
N(1)ꢀRh(1)ꢀN(2) 89.94(14)
N(1)ꢀRh(1)ꢀN(4) 179.19(14)
N(1)ꢀRh(1)ꢀC(7) 90.4(2)
N(2)ꢀRh(1)ꢀN(4) 90.03(14)
N(2)ꢀRh(1)ꢀC(7) 89.4(2)
N(3)ꢀRh(1)ꢀN(5) 89.15(13)
N(4)ꢀRh(1)ꢀN(5) 87.29(13)
N(5)ꢀRh(1)ꢀC(7) 177.7(2)
N(1)ꢀRh(1)ꢀN(3) 89.97(14)
N(1)ꢀRh(1)ꢀN(5) 91.89(13)
N(2)ꢀRh(1)ꢀN(3) 179.9(2)
N(2)ꢀRh(1)ꢀN(5) 90.79(13)
N(3)ꢀRh(1)ꢀN(4) 90.06(14)
N(3)ꢀRh(1)ꢀC(7) 90.7(2)
N(4)ꢀRh(1)ꢀC(7) 90.4(2)
−
1
located at 1907 cm , which is lower than for free wCN
−
1
(
2200 cm ), due to Rh-to-CN backbonding. On the
other hand, the wCN for 2 was found at the same
−
1
frequency as that for free CNpy (ca. 2200 cm ),
indicating that the CNpy in 2 binds to Rh via pyridyl
1
nitrogen. The H-NMR spectrum of complex 1 in
2
CDCl shows a doublet at l −6.14 with JRhH=2.7
3
Hz, assignable to the axial methyl protons. The obser-
vation of only one methyl resonant signal for 1 suggests
that in solution there exists a rapid exchange equi-
Fig. 1. Crystal structure of [Rh(TTP)(CH )] (m-CNpy) (1).
librium among 1, 2, and [Rh(TTP)(CH )] on the NMR
3
2
3
timescale. It seems likely that the major species at
Table 1
Crystal data and structure refinement details for [Rh(TTP)CH ] (m-
equilibrium are [Rh(TTP)CH )] and 2, thus explaining
3
3
2
why the ligand chemical shifts for 1 and 2 are more or
less identical. Consistent with the rapid exchange pro-
cess, broad singlets instead of sharp doublets were
found for the pyridyl protons in 1 and 2. It should be
noted that pyridine ligand dissociation for
CNpy) (1) and [Rh(TTP)(C H )]·C H (5·C H14)
8
11
6
14
6
1
5·C H
6 14
Empirical formula
Formula weight
Color
C52H41N Rh
838.81
Red
C62H61N Rh
934.99
Red
5
4
[
Rh(OEP)CH (CNpy)] in solution has been previously
3
Habit
Plate
Plate
reported by Ogoshi and coworkers [9]. The solid-state
structure of dinuclear 1 has been established by X-ray
crystallography. Fig. 1 shows a perspective view of the
molecule; selected bond lengths and angles are listed in
Table 2. The CNpy ligand in 1 was found to be 50:50
disordered, resulting in pseudo twofold symmetry of the
crystal structure. The average RhꢀC, average
RhꢀN(pyrrole), and average RhꢀN(CNpy) distances in
a (A
,
)
)
)
11.238(3)
12.167(2)
17.827(4)
108.11(1)
99.23(1)
100.97(1)
2210.6(9)
2
13.225(3)
13.834(2)
16.729(3)
72.820(1)
88.82(2)
63.55(2)
2595.9(8)
2
b (A
,
c (A
,
h (°)
i (°)
k (°)
V (A
,
3)
Z
Crystal system
Space group
Dcalc (g cm−3)
T (K)
Triclinic
Triclinic
(
P1 (no. 2)
1.235
1
are 2.032(2), 2.032, and 2.273(4) A
,
, respectively. The
P1
1.26
(
(no. 2)
RhꢀC distance is similar to that for [Rh(OEP)CH ]
3
293
293
(2.031(6) A) [10]. Similarly, treatment of [Rh(TTP)CH3]
,
u (A
Scan type
,
)
0.71073
ꢀ–2q
0.426
7639
5446
0.71073
ꢀ–2q
0.369
7922
5076
(I\2.0|(I))
0.1161
0.1865
976
with 0.5 equivalents of 4,4%-bpy afforded the 4,4%-bpy-
1
bridged dimer [Rh(TTP)CH ] (m-4,4%-bpy) (3). The H-
−
1
3 2
v (mm
)
NMR spectrum of 3 shows two signals at l 2.86 and
4.99 ppm assignable to the ortho and meta protons of
the 4,4%-bpy ligand, consistent with the symmetric
bridging mode of 4,4%-bpy. The cyclic voltammogram
for 3 in CH Cl features two reversible oxidation cou-
No. of reflections measured
No. of reflections observed
(
I\2.0|(I))
R (F2)
wR2
F(000)
0.0827
0.01109
866
2
2
2
ples at 0.42 and 0.75 V versus the ferrocenium–ferro-
Goodness of fit (F )
1.040
1.059
cene couple, which are tentatively assigned as the

W.-H. Leung et al. / Journal of Organometallic Chemistry 604 (2000) 197–201
199
porphyrin ring oxidation and Rh(IV/III) couple, re-
spectively. Similar oxidation potentials were found for
lysts, notably [Ru(ꢁCHPh)(PCy ) Cl ] or the Grubbs’
3
2
2
catalyst, to give poly(norbornene)s [11]. To this end an
attempt was made to prepare a s-bonded (5-norbor-
nen-2-yl)methyl complex of rhodium porphyrin, which
may be used as a precursor to rhodium-containing
poly(norbornene)s. (5-Norbornen-2-yl)methyl iodide
[
Rh(TTP)CH ] under the same conditions. The ob-
3
served DEp values of ca. 100 mV for the oxidation
couples for 3 are consistent with single electron transfer
processes.
(
C H I) (4) was synthesized by tosylation of commer-
8
11
2.2. Rh(III) (5-norbornen-2-yl)methyl complex
cially available 5-norbornene-2-methanol with tosyl
chloride in the presence of Et N, and subsequent reac-
tion with NaI in acetone. Treatment of Na[Rh(TTP)],
which was prepared in situ from [Rh(TTP)I] and
3
Norbornene and its derivatives are known to un-
dergo facile ring-opening metathesis polymerization
ROMP) in the presence of ruthenium carbene cata-
(
NaBH [10], with 4 afforded the rhodium (5-norbornen-
4
2
-yl)methyl complex [Rh(TTP)(C H )] (5), isolated as
8
11
an air-stable solid (Scheme 1).
1
The H-NMR spectrum of 5 is complex apparently
due to the presence of both exo and endo forms of the
5
-norbornene-2-methyl ligand. The resonant signals for
the axial norbornene protons for 5 are in general more
upfield than those for 4 due to the porphyrin ring
current. The multiplets in l −4.72 to −5.11 and l
4
.80 to 6.26 are tentatively assigned to the axial
methylene and the olefinic protons, respectively. The
FAB mass spectrum shows the signal for a molecular
+
ion at m/z 878 corresponding to [Rh(TTP)(C H )] .
8
11
The UV–vis spectrum of 5 in CH Cl shows a soret
Scheme 1.
2
2
band at 413 nm, which is close to that for
Rh(TTP)CH ]. The identity of 5 was unambiguously
[
3
confirmed by X-ray crystallography. To our knowledge,
this is the first example of the Rh s-norbornenylmethyl
complex. Fig. 2 shows a perspective view of 5; selected
bond lengths and angles are listed in Table 3. The
geometry around Rh is distorted square pyramidal. The
RhꢀC (2.052(6) A
tances are comparable to those for 1. A preliminary
study showed that the reaction of with
) and average RhꢀN (2.022 A) dis-
, ,
5
[
Ru(ꢁCHPh)(PCy ) Cl ] [11] led to isolation of a purple
3
2
2
solid, presumably an oligomer of 5. However, the
molecular weight of this purple material is rather low
(
M :5600 according to gel permeation chromatogra-
w
phy). High-molecular-weight oligomers were not ob-
tained, possibly due to steric hindrance of the bulky
porphyrin ring in monomer 5. The steric repulsion
among the porphyrin monomers may be relieved if a
longer spacer between the norbornene functionality and
Rh, e.g. a hexylene instead of methylene group, is used.
The synthesis of this kind of norbornenylalkyl rhodium
porphyrins is underway.
In summary, we have demonstrated that substitution-
ally inert alkylrhodium porphyrins may serve as build-
ing blocks for rhodium porphyrin oligomers. The
alkylrhodium porphyrin monomers may be linked to-
gether via either coordination bonding with bidentate
pyridine ligands or polymerization of the axial alkyl
group.
Fig. 2. Crystal structure of [Rh(TTP)(C H11)] (5).
8
Table 3
Selected bond lengths (A) and angles (°) for [Rh(TTP)(C H11)] (5)
,
8
Bond lengths
Rh(1)ꢀN(1)
Rh(1)ꢀN(3)
Rh(1)ꢀC(1)
2.028(4)
2.017(4)
2.052(6)
Rh(1)ꢀN(2)
Rh(1)ꢀN(4)
2.023(4)
2.020(4)
Bond angles
N(1)ꢀRh(1)ꢀN(2)
N(1)ꢀRh(1)ꢀN(4)
N(2)ꢀRh(1)ꢀN(3)
N(2)ꢀRh(1)ꢀC(1)
N(4)ꢀRh(1)ꢀC(1)
90.0(2)
179.9(2)
173.9(2)
99.6(2)
N(1)ꢀRh(1)ꢀN(3)
N(1)ꢀRh(1)ꢀC(1)
N(2)ꢀRh(1)ꢀN(4)
N(3)ꢀRh(1)ꢀN(4)
90.1(2)
89.2(2)
90.0(2)
90.0(2)
90.8(2)

200
W.-H. Leung et al. / Journal of Organometallic Chemistry 604 (2000) 197–201
NMR spectroscopy. When the mixture in CH Cl –hex-
2
2
ane was left to stand at r.t. overnight, purple crystals
identified as 1 were formed and were collected. Addi-
tion of hexane and slow evaporation led to formation
of a microcrystalline solid characterized as 2, which
was found to be contaminated with a small amount
1
of 1. Characterization data for 2: H-NMR (CDCl ): l
3
2
−
6.42 (d, J
=2.40 Hz, 3H, RhCH ), 2.69 (s, 12H,
RhH 3
p-CH ), 3.40 (s br, 2H, H of CNpy), 5.92 (d, 2H, H
3
o
m
of CNpy), 7.52 (d, 8H, H ), 8.02 (d, 8H, H ), 8.77 (s,
8H, Hb).
m
o
Scheme 2.
3. Experimental
3.3. Preparation of [Rh(TTP)CH ] (v-4,4%-bpy) (3)
3
2
3
.1. General information
This was prepared similarly as for 1 using 4,4%-bpy
1
instead of CNpy. Yield: 75% (based on 4,4%-bpy). H-
2
Solvents were purified and distilled prior to use.
NMR (CDCl ): l −6.42 (d, JRhH=2.4 Hz, 6H,
3
NMR spectra were recorded on a Bruker ALX 300
RhCH ), 2.65 (s, 24H, p-Me), 2.86 (s br, 4H, H of
3
o
spectrometer. Chemical shifts (l, ppm) were reported
4,4%-bpy), 4.99 (s br, 4H, Hm of 4,4%-bpy), 7.45 (d,
J=7.9 Hz, 16H, H ), 7.90 (d, J=8.0 Hz, 16H, H ),
with reference to SiMe . Infrared spectra (Nujol) were
4
m
o
recorded on a Perkin–Elmer 16 PC FT-IR spectropho-
tometer. Mass spectra were obtained on a Finnigan
TSQ-7000 spectrometer. Cyclic voltammetry was per-
formed with a Princeton Applied Research (PAR)
Model 273A potentiostat. The working and reference
8.58 (s, 16H, Hb).
3.4. Preparation of (5-norbornen-2-yl)methyl iodide (4)
A mixture of 5-norbornene-2-methanol (0.5 g, 4.03
mmol), 4-toluenesulfonyl chloride (1 g, 5.25 mmol),
Et N (5 ml) in CH Cl (25 ml) was stirred under
electrodes are glassy carbon and Ag ꢀ AgNO (0.1 M in
3
acetonitrile) electrodes, respectively. Potentials were re-
ported with reference to the ferrocenium–ferrocene
couple. Elemental analyses were performed by Medac
Ltd, Surrey, UK.
3
2
2
nitrogen at r.t. for 5 h. Then NaI (1 g, 6.67 mmol) in
N,N-dimethylformamide (10 ml) was added and the
mixture was stirred for 3 h. The resulting mixture was
diluted with ethyl acetate (150 ml), and washed five
times with water (10 ml). The organic fraction was
[
Rh(TPP)I] and [Rh(TTP)CH ] were prepared ac-
3
cording to a literature method [12]. 5-Norbornene-1-
methanol (as a mixture of exo and endo isomers) was
obtained from Aldrich Ltd and used as received. Hy-
drogen atom labeling schemes for TTP and (5-norbor-
nen-2-yl)methyl (C H ) are shown in Scheme 2.
dried with anhydrous MgSO and subjected to column
chromatography (silica) using hexane as eluent. The
4
product was isolated as a colorless oil. Yield 50%.
1
8
11
H-NMR (CDCl ): l 0.56–0.62 (m, 2H), 1.50–1.54 (m,
3
1
H), 1.93–2.01 (m, 1H), 2.49–2.60 (m, 1H), 2.85–3.02
3
.2. Preparation of [Rh(TTP)CH ] (v-CNpy) (1)
(m, 4H), 5.99–6.25 (m, 2H). MS (CI): m/z 233 [M−
3
2
+
1
] .
To a solution of [Rh(TTP)CH ] (50 mg, 0.08 mmol)
3
in CH Cl (10 ml) was added 0.5 equivalents of CNpy.
3.5. Preparation of [Rh(TTP)(C H )]
2
2
8
11
The mixture was stirred at room temperature (r.t.) for
0 min and half of the solvent was removed in vacuo.
[C H =(5-norbornen-2-yl)methyl] (5)
8
11
3
Addition of hexane (ca. 20 ml) and cooling at −10°C
led to isolation of a purple solid, which was collected
and washed with methanol. Recrystallization from
CH Cl –hexane afforded red crystals (Yield: ca. 50%
To a solution of [Rh(TTP)I] (0.06 g, 0.067 mmol) in
EtOH (10 ml) was added NaBH (4 mg) in 0.5 M
4
NaOH(aq) (2 ml) and the mixture was stirred under
nitrogen at r.t. The red mixture turned to orange in ca.
30 min, indicating the formation of Na[Rh(TTP)], and
was stirred for a further 30 min. Then one equivalent of
4 was added under nitrogen and the mixture was stirred
for 1 h. The solvent was pumped off and the residue
was extracted with CH Cl , washed with water (2×15
2
2
based on CNpy). Anal. Calc. For C104H N Rh : C,
82
10
2
7
4.5; N, 4.9; N, 8.4. Found: C, 74.0; H, 5.2; N, 8.1%.
1
2
H-NMR (CDCl ): l −6.14 (d, JRhH=2.4 Hz, 6H,
3
RhCH ), 2.69 (s, 24H, p-CH ), 3.40 (s br, 2H, H of
3
3
o
CNpy), 5.92 (s br, 2H, Hm of CNpy), 7.52 (d, J=8.0
Hz, 16H, H ), 8.02 (d, J=8.0 Hz, 16H, H ), 8.77 (s,
2
2
ml), and dried with anhydrous MgSO . The filtrate was
m
o
4
−
1
1
6H, H ). IR (cm ): 2000 wCN. If excess CNpy was
concentrated and chromatographed on alumina. The
product was eluted as a red band by CH Cl . Recrystal-
b
used
a
mixture of
1
and the monomer
2
2
[
Rh(TTP)(CH )(CNpy)] (2) was formed, as indicated by
lization from CH Cl –hexane afforded red crystals,
2 2
3

W.-H. Leung et al. / Journal of Organometallic Chemistry 604 (2000) 197–201
201
which were suitable for X-ray diffraction study. Yield:
0 mg (50%, based on [Rh(TTP)I]). Anal. Calc. For
C H N Rh: C, 76.53; N, 5.4; N, 6.4. Found: C, 76.4;
References
3
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5
6
47
4
1
H, 5.3; N, 5.3%. H-NMR (CDCl ): l −4.72 to −5.11
3
3
(
m, 2H, RhCH ), −3.15 to −3.39 (m, 1H, H ), −0.20
to −1.18 (m, 2H, H and H ), 1.57–1.32 (m, 4H, H
and H ), 2.73 (s, 12H, p-Me), 4.80–6.26 (m, 2H, H
and H ), 7.57 (d, J=9.0 Hz, 8H, H ), 8.07 (m, 8H,
2
1
4
2
5
7
6
m
+
H ), 8.78 (m, 8H, pyrrolic H). FABMS: m/z 878 [M ].
o
4. X-ray crystallography
[
3] (a) H. Schultz, H. Lehmann, M. Rein, M. Hanack, Struct.
Bonding 74 (1990) 41. (b) M. Hanack, in: P. Wisian-Neilson,
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Weinheim, 1989 (Chapter 2).
A summary of crystallographic data and experimen-
tal details for 1 and 5·C H are given in Table 1. All
6
14
data were collected on a Siemens P4 diffractometer.
Both structures were solved by direct methods and
2
refined on F by full-matrix least-squares analyses. Ab-
[
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3
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6
14
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6
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Acknowledgements
We thank The Hong Kong Research Grants Council
(
project no. HKUST 6152/97P) for financial support.
[
The interpretation of NMR spectral data for the
methylrhodium porphyrins provided by a referee is
gratefully acknowledged.
5
305.
[13] G.M. Sheldrick, SHELXL, Siemens Analytical Instruments,
Madison, WI, 1993.
.