Superimposed saddle and ruffled distortions of the porphyrin in iodo-(pyridine-N) (5,10,15,20-tetraphenyl-porphyrinato-κ4 N) rhodium(III) toluene solvate

Article abstract of DOI:10.1107/S0108270101001536

In the title compound, [RhI(C₄₄H₂₈N₄)(C₅H ₅N)]·C₇H₈, the porphyrin ring experiences significant distortion from planarity (a saddle conformation with a superimposed ruffling), as a result of steric interactions with the 2,6-H atoms of the axial pyridine ligand. This also leads to a slight lengthening of the Rh-pyridine bond [Rh-N 2.102 (7) A] relative to those seen in other pyridine adducts of six-coordinate Rh^III. The metric parameters of the porphyrin core are comparable with those of related metalloporphyrin derivatives. No significant intermolecular interactions are observed between the metalloporphyrin and disordered solvate species.

Full text of DOI:10.1107/S0108270101001536

metal-organic compounds
Acta Crystallographica Section C
Crystal Structure
Communications
catalytic site of the enzyme under study. It thus becomes useful
to know the type and degree of the distortion that a
metalloporphyrin undergoes upon coordination of a hetero-
cyclic base to the metal centre. Since, for synthetic reasons,
derivatives of the meso-tetraphenylporphyrin dianion (TPP)
are usually used in such biomimetic studies, we have chosen to
investigate the molecular structure of the toluene solvate of
the title [Rh(TPP)I] adduct with pyridine, i.e. [Rh(TPP)I-
(py)]ÁC7H8, (I). Another interesting issue that such studies can
address is whether the signi®cantly lower af®nity of the RhIII
centre in a porphyrin environment for pyridine compared with
phosphines (Collman & Boulatov, 2000) correlates with the
different degree of steric perturbation of the macrocycle in the
corresponding adducts.
ISSN 0108-2701
Superimposed saddle and ruffled
distortions of the porphyrin in iodo-
(pyridine-N)(5,10,15,20-tetraphenyl-
porphyrinato-j4N)rhodium(III)
toluene solvate
Geoffrey B. Jameson,a* James P. Collmanb and Roman
Boulatovb
aCentre for Structural Biology, Institute of Fundamental Sciences, Massey University,
Palmerston North, New Zealand, and bDepartment of Chemistry, Stanford
University, Stanford, CA 95495-5080, USA
Correspondence e-mail: g.b.jameson@massey.ac.nz
Received 24 November 2000
Accepted 22 January 2001
The molecular structure of (I) is shown in Fig. 1, and
selected interatomic distances and angles are presented in
Table 1. The most conspicuous feature of the structure is the
signi®cant distortion of the TPP core from planarity. The
`ruf¯ing' of the core is superimposed on a `saddle' deforma-
tion, resulting in a decrease in the overall symmetry of the
core to C1 (Fig. 2). As expected for a ruf¯ed porphyrin, the
meso-C atoms are displaced alternately above and below the
least-squares plane of the 24-atom porphyrin core. The
maximum displacement of an atom of the porphyrin core from
In the title compound, [RhI(C44H28N4)(C5H5N)]ÁC7H8, the
porphyrin ring experiences signi®cant distortion from
planarity (a saddle conformation with a superimposed
ruf¯ing), as a result of steric interactions with the 2,6-H atoms
of the axial pyridine ligand. This also leads to a slight
Ê
lengthening of the Rh±pyridine bond [RhÐN 2.102 (7) A]
relative to those seen in other pyridine adducts of six-
coordinate RhIII. The metric parameters of the porphyrin core
are comparable with those of related metalloporphyrin
derivatives. No signi®cant intermolecular interactions are
observed between the metalloporphyrin and disordered
solvate species.
Ê
Ê
its least-squares plane is 0.356 (8) A (r.m.s. deviation 0.199 A).
This value is signi®cantly larger than the maximum displace-
ment observed in most other Rh±porphyrin derivatives
containing either ®ve- or six-coordinate Rh, for example,
Ê
0.18 A in [Rh(OEP)(m-C6H4CN)] (OEP is the 2,3,7,8,12,13,-
17,18-octaethylporphyrin dianion; Zhou et al., 1998) and
Comment
Ê
0.11 A in [(PhCH2NC)Rh(TPP){ C(NHCH2Ph)2}] (Boschi
et al., 1989), but is appreciably smaller than the maximum
Ê
displacement of 0.484 (4) A observed in the highly distorted
While the molecular structures of several Co±porphyrin
adducts with nitrogenous heterocyclic axial ligands have been
determined, the Rh analogues remain crystallographically
uncharacterized (Senge, 2000). Since the imidazole residue of
histidine is a common axial ligand in heme-based proteins,
metalloporphyrin complexes of this and related heterocycles,
such as pyridine, pyrazole and their derivatives, are used
extensively in biomimetic studies (Collman & Wang, 1999).
Although, in bioinorganic chemistry, Co±porphyrins are by far
the most popular group IX metalloporphyrin derivatives, the
high af®nity of Rh±porphyrin species for O2 and the kinetic
stability of the resulting adducts make the Rh analogues very
interesting candidates for biomimetic work on respiratory
chain enzymes, such as cytochrome c oxidase (Collman &
Boulatov, 2000). The success of such studies relies on the
ability of the synthetic chemist to construct a porphyrin ligand
that provides a coordination environment similar to that at the
porphyrin core of [Rh(TPP)(CH2Cl)] (Collman & Boulatov,
2001a). Ruf¯ed cores have been observed in other metal-
loporphyrin±pyridine adducts, such as [Co(TPP)Cl(py)]
(Sakurai et al., 1975) and [Co(TPP)(3,5-lutidine)] (Scheidt &
Ramanuja, 1975). The distortion of the macrocycle is a result
of unfavourable steric interactions between the 2,6-H atoms of
the aromatic six-membered cyclic ligand and the porphyrin
core. Orientation of the pyridine plane relative to the MÐ
Nporphyrin vectors is also determined by the drive to decrease
steric interactions. Thus, the N1ÐRhÐN5ÐC61 dihedral
angle in (I) is 41.0 (7)ꢁ, with 45ꢁ representing the minimum
steric interaction. Despite these structural changes, the closest
Ê
HpyÁ Á ÁNporphyrin contact of 2.66 A is still signi®cantly shorter
Ê
than the normal packing distance of 2.90 A (Scheidt, 2000).
ꢀ
406 # 2001 International Union of Crystallography
Printed in Great Britain ± all rights reserved
Acta Cryst. (2001). C57, 406±408

metal-organic compounds
Ê
bond lengths of 2.666 (8) and 2.659 (8) A occur for the trans
Interestingly, only the `saddle' deformation of the macrocycle
is observed in a structurally closely related complex,
IÐRhÐI unit in mer-[RhI3(py)(CO)(COMe)] (Adams et al.,
Ê
[Rh(TPP)(phenyl)],
HligandÁ Á ÁNporphyrin contact of 2.74 A, despite having the
which
possesses
Ê
a
closest
1988), and lengths of 2.685 (1) and 2.661 (1) A occur in
[Rh(9S3)(PPh3)I2]+ (9S3 is 1,4,7-trithiacyclononane; Kim et
al., 1995).
Ê
shorter Rh±axial-ligand distance [RhÐC of 1.985 (6) A, cf.
Ê
RhÐNpy of 2.102 (7) A in (I); Collman & Boulatov, 2001b].
This arises because of the substantial displacement of the Rh
atom from the porphyrin plane towards the phenyl ligand. In
contrast, Rh±porphyrin adducts with axial ligands bound
through an sp3 donor atom, such as [Rh(OEP)Cl(PPh3)]
(Thackray et al., 1986) and [Rh(por)(NMe2H)2]+ [por is TPP
(Fleisher et al., 1973) or etioporphyrin I (Hanson et al., 1973)],
manifest signi®cantly more planar cores, as do organometallic
derivatives with compact alkyls, such as [Rh(OEP)(CH3)]
(Whang & Kim, 1991).
As a result of the ruf¯ed core, two of the peripheral phenyl
groups of (I) are tilted signi®cantly towards the iodide. The
RhÐNporphyrin bonds are quite similar and are comparable
with those found in other Rh±porphyrin complexes (Scheidt,
2000). The plane of the pyridine ligand forms an angle of
88.7 (2)ꢁ with the least-squares plane of the porphyrin core,
while the RhÐI vector is tilted at 4.0ꢁ to the latter. Among the
crystallographically studied species containing the trans pyÐ
RhÐI unit, [Rh(dH)2I(py)] (dH is the dimethylglyoxime
monoanion) is most closely related, both structurally and
electronically, to (I). The rhodoxime derivative manifests a
Figure 2
The conformation of the porphyrin in (I), showing the displacements of
the core atoms and of Rh from the 24-atom least-squares plane of the
porphyrin core (in pm; negative values correspond to displacement
towards the iodide ligand). Absolute values of the angles (ꢁ) between the
pyrrole rings and the least-squares plane of the 24-atom porphyrin core
are shown in bold, and absolute values of the angles (ꢁ) between the least-
squares planes of the phenyl substituents and the 24-atom least-squares
plane are shown in italics. The relative orientation of the pyridine ligand
is depicted by bold lines.
Ê
somewhat shorter RhÐNpy bond length [2.079 (3) A], but a
Ê
Finally, no signi®cant intermolecular interactions are
observed in the crystal lattice of (I). The closest porphyrin±
porphyrin contact occurs between the phenyl substituents and
slightly longer RhÐI bond [2.6423 (4) A; Geremia et al.,
1994]. Other RhIII±py complexes with trans ligands which are
comparable to iodide in their trans in¯uence also demonstrate
Ê
shorter RhÐNpy bonds, viz. 2.046 (1) A in [Rh(dH)2Cl(py)]
Ê
(Geremia et al., 1994), 2.083 (9) and 2.041 (9) A in the trans
NpyÐRhÐNpy unit of mer-[Rh(py)3Cl2(CH2Cl)] (Bradd et al.,
Ê
is longer than 3.5 A. Because of the axial ligands, the closest
Ê
RhÁ Á ÁRh distance is longer than 8 A, which precludes ꢀ±ꢀ
interactions.
Ê
1999), and 2.069 (2) A in trans-[RhBr2(py)4] (Muir et al.,
1987). The lengthening of the RhÐNpy bond in (I) is most
likely due to steric destabilization from the porphyrin core. In
contrast, the respective RhÐI bond is slightly shorter than
such bonds in comparable RhIII±iodo complexes; for example,
Experimental
[Rh(TPP)I] was synthesized as described previously by Collman &
Boulatov (2000). Crystals of (I) suitable for crystallographic studies
were obtained as the toluene solvate at room temperature by layering
a toluene solution of [Rh(TPP)I] containing 5 equivalents of pyridine
with 5 volumes of pentane under anhydrous conditions. NMR and
UV±visible spectra were taken on UnityInova-500 and Hewlett±
Packard 8453 spectrometers, respectively. Spectroscopic analysis:
1H NMR (C6D6, 500 MHz, ꢁ, p.p.m.): 9.00 (s, ꢂ-pyrrolic, 8H), 8.15 (dt,
J = 7.9 and 2.3 Hz, o-Ph, 4H), 8.06 (d, J = 7.9 Hz, o0-Ph, 4H), 7.42 (m,
m-Ph and m0-Ph, 8H), 7.34 (m, p-Ph, 4H), 7.12±6.98 (m, toluene, 5H),
4.78 (tt, J = 7.6 and 1.7 Hz, p-py, 1H), 4.08 (t, J = 7.2 Hz, m-py, 2H),
2.09 (s, CH3-toluene, 3H), 1.33 (d, J = 6.5 Hz, o-py, 2H); UV±vis
(toluene, ꢃmax, nm): 431, 541, 576.
Crystal data
3
[RhI(C44H28N4)(C5H5N)]ÁC7H8
Dx = 1.503 Mg m
Mo Kꢄ radiation
Cell parameters from 5069
re¯ections
Mr = 1013.75
Monoclinic, P21/n
Ê
Ê
a = 13.3463 (3) A
b = 23.4600 (1) A
ꢅ = 1.43±24.70ꢁ
ꢆ = 1.115 mm
T = 173 (1) K
1
Ê
c = 14.5584 (3) A
Figure 1
ꢂ = 100.560 (1)ꢁ
Ê
V = 4481.1 (2) A
Z = 4
The structure of (I), showing the atomic labelling scheme and 40%
probability displacement ellipsoids. H atoms are drawn as small spheres
of arbitrary radii and the toluene solvate molecule has been omitted.
3
Plate, brown±red
0.20 Â 0.11 Â 0.07 mm
ꢀ
Acta Cryst. (2001). C57, 406±408
Geoffrey B. Jameson et al.
[RhI(C44H28N4)(C5H5N)]ÁC7H8 407

metal-organic compounds
Data collection
Data collection: SMART (Siemens, 1995b); cell re®nement:
SMART; data reduction: SAINT (Siemens, 1995b); program(s) used
to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to
re®ne structure: SHELXL97 (Sheldrick, 1997); molecular graphics:
SHELXTL (Siemens, 1995a); software used to prepare material for
publication: SHELXL97.
Siemens SMART CCD area-
detector diffractometer
! scans
Absorption correction: empirical
[SADABS (Sheldrick, 1996) and
XPREP in SHELXTL (Siemens,
1995a)]
20 724 measured re¯ections
7556 independent re¯ections
4849 re¯ections with I > 2ꢇ(I)
Rint = 0.099
ꢅ
max = 24.70ꢁ
h = 15 ! 15
k = 20 ! 27
l = 17 ! 17
This work was supported ®nancially by the NSF (grant
CHE-9612725 to JPC) and by a Stanford Graduate Fellowship
(to RB). The X-ray data were collected by Dr F. Hollander
(University of California±Berkeley).
Tmin = 0.82, Tmax = 0.97
Re®nement
Re®nement on F2
R(F) = 0.070
w = 1/[ꢇ2(Fo2) + (0.0107P)2
+ 27.4982P]
wR(F2) = 0.126
S = 1.130
where P = (Fo2 + 2Fc2)/3
(Á/ꢇ)max = 0.001
Supplementary data for this paper are available from the IUCr electronic
archives (Reference: FG1606). Services for accessing these data are
described at the back of the journal.
3
Ê
7556 re¯ections
560 parameters
H-atom parameters constrained
Áꢈmax = 0.64 e A
3
Ê
0.76 e A
Áꢈmin
=
References
Table 1
Selected geometric parameters (A, ).
ꢁ
Ê
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RhÐN3
RhÐN2
2.6335 (9)
2.022 (6)
2.032 (6)
RhÐN4
RhÐN1
RhÐN5
2.032 (6)
2.035 (6)
2.102 (7)
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N3ÐRhÐN2
N3ÐRhÐN4
N2ÐRhÐN4
N3ÐRhÐN1
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N4ÐRhÐN1
N3ÐRhÐN5
N2ÐRhÐN5
89.7 (2)
90.2 (2)
179.5 (3)
179.1 (3)
90.3 (3)
89.8 (2)
89.5 (3)
89.9 (3)
N4ÐRhÐN5
N1ÐRhÐN5
N3ÐRhÐI1
N2ÐRhÐI1
N4ÐRhÐI1
N1ÐRhÐI1
N5ÐRhÐI1
90.6 (2)
89.5 (3)
88.89 (18)
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92.02 (18)
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The toluene solvate species in (I) is disordered about two inde-
pendent inversion centres. Re®nements with an overall Uiso and
occupancy parameter assigned to each solvate species established
half-occupancy at each site, leading to a total of four toluene mol-
ecules per unit cell. Because some atoms are nearly overlapped at
each site, the geometry of the toluene solvate species was tightly
restrained to standard values, and atomic displacement parameters of
pairs of atoms were constrained to be equal (C84 and C86, C73 and
C77, and C74 and C76). In addition, the proximity of the two solvate
sites leads to correlated occupancy of the sites. Representing the two
solvate sites as A and B, and their centrosymmetrically related mates
as A0 and B0, leads to the spatial arrangement A0AÁ Á ÁBB0 where
species A and B are unacceptably close. Thus, the pairs A0B and AB0
are stochastically dispersed throughout the crystal. H atoms were
È
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Ê
included at their calculated positions (CÐH = 0.93 and 0.96 A) and in
least-squares re®nements were allowed to ride with an equivalent
isotropic atomic displacement parameter 1.2 times (1.5 times for
methyl-H atoms) that of the C atom to which they were attached.
ꢀ
408 Geoffrey B. Jameson et al.
[RhI(C44H28N4)(C5H5N)]ÁC7H8
Acta Cryst. (2001). C57, 406±408