Aromatic and benzylic C-H bond activation in the system bis(dicarbonylrhodium(I))porphyrinate-hydrocarbon solvent

Article abstract of DOI:10.1021/ic0011112

Metalation of C₆H₆ has been known for a long time as a aside reaction occuring in refluxing benzene solutions of Rh₂(CO)₄(TPP) (TTP = tetraphenylporphyrin). Rather than representing the intrinsic reactivity of this complex, such hydrocarbon activation proceed via Rh^II(por) and Rh^III(por) derivatives resulting from oxidation can be extended to other aromatic substrates and represents an effecient synthetic route to certain organometallic Rh^III(TPP) derivatives.

Full text of DOI:10.1021/ic0011112

Inorg. Chem. 2001, 40, 2461-2464
2461
Therefore, it is not surprising that Rh2(CO)4(por) species
undergo relatively facile oxidative addition reactions with
various alkyl and aryl iodides, carboxylic acid anhydrides,
aldehydes, and methyl ketones.6 However, insertion into a strong
arene C-H bond is much more challenging, and only a limited
number of RhI complexes capable of such chemistry have been
discovered.7 Such presumed reactivity of Rh2(CO)4(por) could
conceivably be promoted by the synergetic effect of the two
metal centers. We are particularly interested in the different
reactivities of similar complexes containing one or several metal
centers because such information could assist in designing better
catalysts. In addition, since Rh2(CO)4(por) is a common starting
material for most other Rh(por) derivatives, a direct reaction
between a hydrocarbon and (por)Rh2(CO)4 can be an efficient
synthetic route to some organometallic RhIII(por) species. Such
complexes have attracted attention in part because they are
pertinent to the reactivity of cobalamine in vitamin B12.8
Aromatic and Benzylic C-H Bond Activation in
the System Bis(dicarbonylrhodium(I))-
porphyrinate-Hydrocarbon Solvent
James P. Collman* and Roman Boulatov
Department of Chemistry, Stanford University,
Stanford, California 94305
ReceiVed October 4, 2000
Introduction
Porphyrin complexes of both d6 RhIII and d7 RhII are known
to activate C-H bonds. Electrophilic aromatic metalation by
RhIII(OEP)+ 1 has been reported to show remarkable regiose-
lectivity, yielding exclusively para-metalated arenes, RhIII(OEP)-
(p-C6H4X) with ortho/para-directing substituents (X ) CH3,
OCH3, Cl). The meta isomers RhIII(OEP)(m-C6H4X) have been
observed in reactions with benzonitrile and methyl benzoate.2
Ortho metalation does not proceed for steric reasons. Using RhIII-
(OEP)+, catalytic derivatization of arenes has been achieved.
On the other hand, these species are not known to react with
aliphatic C-H bonds. In contrast, monomeric metalloradical
RhII-porphyrin complexes, RhII(por), readily react with methane
and benzylic C-H bonds, as well as Si-H and Sn-H bonds,
but are inert toward aromatic substrates.3 Both the d7 config-
uration of RhII and the steric restrictions of the porphyrin ligand
prohibit the oxidative-insertion mechanism. The reaction is
thought to proceed by concerted homolysis of the C-H bond
by two RhII(por) centers via a linear termolecular transition state
(TS). While the trigonal-bipyramidal geometry of the TS in the
case of an aliphatic substrate ensures sufficient separation
between the RhII(por) moieties, activation of non-sp3 C-H
bonds would require too close an approach of the two metal-
loporphyrins, destabilizing the corresponding TS. Such steric
factors are believed to be responsible for the inertness of RhII-
(por) toward aromatic C-H bonds.
Results and Discussion
Carefully purified samples of Rh2(CO)4(por) (por ) OEP or
TPP) fail to react with benzene or toluene after prolonged
heating at reflux under rigorously anaerobic and anhydrous
conditions. In the presence of at least 3 equiv of H2O under
N2, Rh2(CO)4(TPP) reacts slowly with toluene at 80 °C yielding
Rh(TPP)(CH2Ph). Arene metalation of toluene or activation of
benzene is not observed. The reactive species under these
conditions is undoubtedly RhII(TPP). Thus, if a solution of Rh2-
(CO)4(TPP) in CD3C6D5 containing three equiv of H2O is heated
in a sealed NMR tube at 80 °C for a few hours, two high-field
1H NMR resonances corresponding to Rh-bound hydrides
appear. The doublet at -40.23 ppm is that of the known species
Rh(TPP)H.9,11a The position (-36.76 ppm) and the large value
103
1
of the spin-coupling constant (J Rh- H ) 42 Hz) of the second
signal indicate a Rh(por)H unit, rather than a non-porphyrin
Rh hydride,10 while the slight deshielding of this signal relative
to that in Rh(TPP)H suggests the presence of a ligand trans to
the hydride, XRh(TPP)H.11 The nature of X is presently
unknown. A small amount of Rh2(TPP)2 is also observed.
Continued heating leads to further decrease in the intensity of
Finally, mononuclear d8 RhI(por)- species are not reactive
toward any type of C-H bonds. However, it has been known
since 1967 that heating solutions of a bimetallic RhI porphyrin
complex, (TPP)Rh2(CO)4, in benzene yields, as a side product,
a phenylrhodium(III) derivative.4 Details of this transformation
have not been studied. From crystallographic studies Rh2(CO)4-
(OEP) is known to contain two equivalent square-planar RhI
centers, residing on the opposite faces of the porphyrin and at
a separation of 3.04 Å.5 Each metal is coordinated to two CO
molecules and two adjacent nitrogens of the macrocyle.
(6) (a) Abeysekera, A. M.; Grigg, R.; Trocha-Grimshaw, J.; Viswanatha,
V. J. Chem. Soc., Perkin Trans. 1 1977 1395-1403. (b) Abeysekera,
A. M.; Grigg, R.; Trocha-Grimshaw, J.; Viswanatha, V. J. Chem. Soc.,
Perkin Trans. 1 1977, 36-44.
(7) (a) Chen, H.; Schlecht, S.; Semple, T. C.; Hartwig, J. F. Science 2000,
287, 1995-1997. (b) Wick, D. D.; Reynolds, K. A.; Jones, W. D. J.
Am. Chem. Soc. 1999, 121, 3974-3983 and references therein. (c)
McNamara, B. K.; Yeston, J. S.; Bergman, R. G.; Moore, C. B. J.
Am. Chem. Soc. 1999, 121, 6437-6443. (d) Bromberg, S. E.; Yang,
H.; Asplund, M. C.; Lian, T.; McNamara, B. K.; Kotz, K. T.; Yeston,
J. S.; Wilkens, M.; Frei, H.; Bergman, R. G.; Harris, C. B. Science
1997, 278, 260-263. (e) Arndtsen, B. A.; Bergman, R. G.; Mobley,
T. A.; Peterson, T. H. Acc. Chem. Res. 1995, 28, 154-162.
(8) For general references on chemistry and biomimetic studies of B12,
see: (a) Chemistry and Biochemistry of B12; Banerjee, R., Ed.;
Wiley: New York, 1999. (b) Murakami, Y.; Kikuchi, J.; Hisaeda,
Y.; Hayashida, O. Chem. ReV. 1996, 96, 721-758. For related work
on Rh porphyrins, see: (c) Wayland, B. B.; Van Voorhees, S. L.; Del
Rossi, K. J. J. Am. Chem. Soc. 1987, 109, 6513-6515.
(1) OEP ) octaethylporphyrin dianion, TPP ) meso-tetraphenylporphyrin
dianion; por ) any porphyrin dianion.
(2) (a) Aoyama, Y.; Yoshida, T.; Sakurai, K.; Ogoshi, H. Organometallics
1986, 5, 168-173. (b) Zhou, X.; Tse, M. K.; Wu, D.; Mak, T. C. W.;
Chan, K. S. J. Organomet. Chem. 2000, 598, 80-86. (c) Zhou, X.;
Li, Q.; Mak, T. C. W.; Chan, K. S. Inorg. Chim. Acta 1998, 270,
551-554.
(3) (a) Zhang, X.-X.; Wayland, B. B. J. Am. Chem. Soc. 1994, 116, 7897-
7898. (b) Wayland, B. B.; Ba, S.; Sherry, A. E. J. Am. Chem. Soc.
1991, 113, 5305-5311. (c) Del Rossi, K. J.; Wayland, B. B. J. Am.
Chem. Soc. 1985, 107, 7941-7944. (d) Mizutani, T.; Uesaka, T.;
Ogoshi, H. Organometallics 1995, 14, 341-346.
(9) Wayland, B. B.; Van Voorhees, S. L.; Wilker, C. Inorg. Chem. 1986,
25, 4039-4024.
(10) Hydride resonances of Rh-H moieties in non-porphyrin complexes
appear at ca. -10 to -30 ppm with J(103Rh-1H) values of 0-10 Hz:
(a) Bergman, R. G. J. Organomet. Chem. 1990, 400, 273-282. (b)
Sheridan, P. S. In ComprehensiVe Coordination Chemistry; Wilkinson,
G., Gillard, R. D., McCleverty, J. A., Eds.; Pergamon Press: Oxford,
1987; pp 920-925, 1017-1027.
(4) Fleischer, E. B.; Lavallee, D. J. Am. Chem. Soc. 1967, 89, 7132-
7133.
(5) Takenaka, A.; Sasada, Y.; Ogoshi, H.; Omura, T.; Yoshida, Z. Acta
Crystallogr. 1975, B31, 1-6.
10.1021/ic0011112 CCC: $20.00 © 2001 American Chemical Society
Published on Web 04/12/2001

2462 Inorganic Chemistry, Vol. 40, No. 10, 2001
Notes
Table 1. Product Distribution and Yields of Organometallic Rh(por) Derivatives under Various Experimental Conditionsa
reactn
time, h
isolated organometallic species
(molar ratio)
total isolated
yield, %
solvent
reactn T, °C
Rh2(CO)4(TPP)
C6H6
80 (reflux)
80 or 110
80
12
12
12
24
Rh(TPP)Ph
80-90b
75-90b
85
C6H5CH3
C6H5OCH3
C6H5Cl
Rh(TPP)CH2Ph
Rh(TPP)CH2OPh
Rh(TPP)(m-C6H4Cl),
Rh(TPP)(p-C6H4Cl) (2:1)
none
none
Rh(TPP)CH3
Rh(TPP)(m-C6H5CH3),
Rh(TPP)(p-C6H5CH3) (2:1)
Rh(TPP)(m-C6H5CH3),
Rh(TPP)(p-C6H5CH3),
Rh(TPP)Ph (3:2:6)
110
15
C6H5F
85 (reflux)
102 (reflux)
150
24
24
24
12
-
-
5
C6H5CF3
C6H5CN
c
C6H5CH3
80
65
C6H6-C6H5CH3
80
12
65
(1:1)c
Rh2(CO)4(OEP)
12
12
C6H6
C6H5CH3
80 (reflux)
80
Rh(OEP)Ph
15-30b
20
Rh(OEP)(m-C6H5CH3),
Rh(OEP)(p-C6H5CH3),
Rh(OEP)(CH2Ph),
Rh(OEP)Ph, Rh(OEP)Me
(4:2:3:0.5: 0.5)
RhIII(OEP)(PF6)
2
d
C6H5CH3
80
Rh(OEP)(m-C6H5CH3),
Rh(OEP)(p-C6H5CH3) (1.6:1)
100 by
NMR
a In the presence of traces of H2O and O2 unless noted otherwise. b Range of yields observed in three repeats. c Anhydrous solvent. d Anhydrous
and anaerobic conditions.
Figure 1. Proposed reaction sequence leading to activation of aromatic and benzylic C-H bonds in the system Rh2(CO)4(TPP)-aromatic hydrocarbon.
1
The starting material and the final products are in bold; the intermediates in italics have been observed by H NMR.
the 1H NMR signals corresponding to Rh2(CO)4(TPP) and
appearance of those corresponding to Rh(TPP)(CD2C6D5).
Formation of Rh(TPP)D is also evident. A similar reaction is
observed with a sample of Rh(TPP)H in CD3C6D5/H2O mixtures
at 80-110 °C. The presence of H2O is essential, as anhydrous
Rh(TPP)H does not undergo homolysis of the Rh-H bond under
theseconditionsandisthereforeunreactivetowardhydrocarbons.11a
These data suggest that neither RhI nor RhII states are the active
species in the arene metalation which is a side reaction in
refluxing benzene solutions of Rh2(CO)4(por). Such a transfor-
mation most likely proceeds by an SEAr mechanism via an
electrophilic RhIII(por) derivative, apparently arising from a
relatively facile oxidation of the starting material, Rh2(CO)4-
(por), by adventitious O2.12 Thus, heating at 80 °C under N2 a
solution of anhydrous Rh2(CO)4(TPP) in anhydrous toluene,
which was saturated with dry air and briefly degassed prior to
dissolving Rh2(CO)4(TPP), yielded a statistical mixture of meta-
and para-metalated tolyls, Rh(TPP)(m-C6H4CH3) and Rh(TPP)-
(p-C6H4CH3). In a similar experiment using a 1:1 benzene-
toluene solvent, a mixture of the tolyl and phenyl complexes,
enriched in the former, was isolated (Table 1). In a control
experiment, which was run under identical conditions, with the
exception that water-saturated toluene was used as a solvent,
Rh(TPP)(CH2Ph) was cleanly produced. These observations
suggest that apparent activation of aromatic and benzylic C-H
bonds in solutions of Rh2(CO)4(por) in aromatic hydrocarbon
solvents at elevated temperatures arises from RhII(por) and RhIII-
(por) derivatives, rather than representing the intrinsic reactivity
of Rh2(CO)4(por).
(11) Deshielding of the hydride in Rh(por)H upon coordination of an axial
ligand has been observed before: (a) Collman, J. P.; Boulatov, R. J.
Am. Chem. Soc. 2000, 122, 11812-11821. (b) Collman, J. P.; Ha,
Y.; Guilard, R.; Lopez, M.-A. Inorg. Chem. 1993, 32, 1788-1794.
(c) Wayland, B. B.; Balkus, K. J.; Farnos, M. D. Organometallics
1989, 8, 950-955. (d) Coffin, V. L.; Brennen, W.; Wayland, B. B. J.
Am. Chem. Soc. 1988, 110, 6063-6069.
(12) (a) Grodowski, J.; Neta, P.; Hambright, P. J. Phys. Chem. 1995, 99,
6019-6023. (b) Wayland, B. B.; Newman, A. R. Inorg. Chem. 1981,
20, 3093-3097. (c) James, R. R.; Stynes, D. V. J. Am. Chem. Soc.
1972, 94, 6225-6226.

Notes
In order to test this hypothesis further we have examined the
Inorganic Chemistry, Vol. 40, No. 10, 2001 2463
reactions of RhIII(OEP)(PF6) and RhIII(TPP)(O2) with toluene
at elevated temperatures. Electrophilic metalation of arenes with
RhIII(OEP)+ was reported to yield p-aryls irrespectively of the
reaction temperature.2a However, we have found that, at 80 °C,
RhIII(OEP)(PF6) reacts with anhydrous toluene under N2 yielding
a mixture of m- and p-tolyls. The product distribution is
comparable to that observed in the Rh2(CO)4(TPP)-anhydrous
toluene system (Table 1). Oxidation of Rh2(CO)4(TPP) with O2
produces a relatively stable superoxido derivative, Rh(TPP)-
(O2), rather than the more reactive “naked” RhIII(por)+ elec-
trophile. Nonetheless, heating a toluene solution of Rh(TPP)(O2)
at reflux overnight produces a mixture of the m- and p-tolyl
complexes. No reaction was observed with C6H5F.
A plausible set of reactions which accounts for production
of Rh(por) alkyl complexes upon heating solutions of Rh2(CO)4-
(por) in an aromatic hydrocarbon under various experimental
conditions is shown in Figure 1. In the presence of traces of
H2O, Rh(TPP)H is produced,13,14 which is converted to RhII-
(TPP) either via the Rh-H bond homolysis or by reaction with
adventitious O2.15 The monomeric RhII(por) species reacts with
substrates that possess activated CH3 groups (toluene and
anisole, vide infra), generating the observed organometallic
products, Rh(TPP)(CH2Ph) and Rh(TPP)(CH2OPh), and Rh-
(TPP)H. During the course of the reaction, significant amounts
of the intermediate, Rh(TPP)H, were detected by 1H NMR. The
active RhII(TPP) is regenerated via a reaction of Rh(TPP)H with
O2 or the thermal homolysis of the Rh-H bond.16 The former
reaction also scavenges traces of O2, suppressing further
oxidation to electrophilic RhIII(TPP) species. In contrast, in a
solvent that does not react with RhII(TPP) (such as benzene),
RhIII(TPP) species are more readily produced, ultimately result-
ing in arene activation. The same outcome is obtained in
anhydrous toluene, probably because a sufficient concentration
of Rh(TPP)H does not build up in the absence of H2O.
Generation of both Rh(TPP)(m-C6H4CH3) and Rh(TPP)(p-C6H4-
CH3) under the latter conditions apparently reflects the reversible
formation of Wheland complexes,17 since these isomers do not
interconvert even after prolonged heating in toluene.
Figure 2. ORTEP drawing of Rh(TPP)Ph (50% probability thermal
ellipsoids) showing the atom number scheme. Hydrogen atoms are
omitted for clarity.
Table 2. Crystallographic Data for Rh(TPP)Ph
empirical formula
fw
cryst dimens (mm)
lattice params
C56H47N4Rh
878.92
0.26 × 0.17 × 0.10
a ) 12.1483(3) Å
b ) 12.5044(3) Å
c ) 16.7334(4) Å
R ) 91.356(1)°
â ) 110.979(1)°
γ ) 114.425(1)°
V ) 2116.5(1) Å3
P1h (No. 2)
space group
Z value
2
Dcalc
1.38 g/cm3
R1 (wR2)a
GOF indicator
0.086 (0.135)
1.86
aR1 ) ∑||Fo| - |Fc||/∑|Fo|; wR2 ) [∑(w(Fo2 - Fc2)2)/∑w(Fo )2]1/2
.
2
RhIII(por) derivatives. Since various degrees of decomposition
have been observed during careful purification of Rh2(CO)4-
(por) (por ) OEP or TPP, see Experimental Section), the
synthetic utility of this reaction was studied using crude samples.
Likewise, to find the simplest synthetic protocols, we used
solvents “as received” which were briefly degassed.18 Finally,
the experiments intended to probe relatiVe reactivities of Rh2-
(CO)4(por) toward different hydrocarbons were carried out under
as uniform conditions as were experimentally achievable (see
Experimental Section).
The aromatic C-H bond activation was observed in benzene
solutions of Rh2(CO)4(TPP), but metalation of both toluene and
anisole proceeded exclusively at the methyl group (Table 1).
Arenes bearing electron-withdrawing substituents yielded Rh-
aryls either in poor yields (C6H5Cl) or not at all (C6H5F, C6H5-
CF3, C6H5CN). Analogous reactions of Rh2(CO)4(OEP) were
qualitatively similar, but displayed poorer regioselectivity, yields,
and reproducibility, compared with the TPP analogue. For
example, toluene underwent activation of both aromatic and
benzylic C-H bonds, as well as an apparent Cphenyl-Cmethyl bond
cleavage (Table 1).19-20 The different reactivity of Rh2(CO)4-
(OEP) reflects both its higher susceptibility to oxidation, as a
result of stronger σ-donor properties of the OEP ligand, and
more facile homolysis of the (OEP)Rh-H bond. This leads to
competition between the two reaction pathways (A and B, Figure
1) and observation of both aromatic and aliphatic metalation in
the same reaction.
While the above data indicate that the long-known benzene
activation observed in solutions of Rh2(CO)4(por) does not
reflect the intrinsic reactivity of the RhI species, such transfor-
mations can provide a suitable synthetic route to organometallic
(13) Rh2(CO)4(TPP) was also reported to undergo a photoinduced intramo-
lecular redox reaction producing RhII(por) and metallic Rh.14
(14) (a) Yamamoto, S.; Hoshino, M.; Yasufuki, K.; Imamura, M. Inorg.
Chem. 1984, 23, 195-198. (b) Hoshino, M.; Yasufuku, K. Inorg.
Chem. 1985, 24, 4408-4410. (c) Hoshino, M.; Yasufuku, K.; Konishi,
S.; Imamura, M. Inorg. Chem. 1984, 23, 1982-1984.
(15) This reaction has occasionally been used for preparative purposes of
converting Rh(por)H into the corresponding dimer, Rh2(por)2: Refer-
ence 11b. Ogoshi, H.; Setsune, J.; Yoshida, Z. J. Am. Chem. Soc. 1977,
99, 3869-3870.
(16) It has been reported that conversion of Rh(por)H into RhII(por) is
promoted by metallic Rh;3b in the reactions studied deposits of metallic
Rh appear only at late stages of the transformation and this Rh-assisted
decomposition of Rh(por)H is probably not a dominant pathway for
RhII(por) regeneration.
(17) Reversible formation of Wheland-type complexes has been proposed
to account for generation of para/meta isomers in metalation of toluene
with Pt(IV) species: (a) Shilov, A. E.; Shul’pin, G. B. Chem. ReV.
1997, 97, 2879-2932. (b) Shul’pin, G. B.; Nizova, G. V.; Nikitaev,
A. T. J. Organomet. Chem. 1984, 276, 115-153. The ratio of tolyl to
phenyl derivatives observed for a reaction in a 1:1 benzene-toluene
mixture was higher than expected from statistical arguments, which
suggests either that the reaction is not completely under thermodynamic
control or that the Wheland-type complex derived from benzene is
thermodynamically less stable than the corresponding toluene deriva-
tive.
(18) Reactions in thoroughly degassed solvents were much slower and
manifested poor yields.

2464 Inorganic Chemistry, Vol. 40, No. 10, 2001
Notes
atoms of the TPP and a C atom of the phenyl group make up
a slightly distorted square-pyramidal coordination around Rh.
The Rh-C bond at 1.984(6) Å is within the range of values
observed in other organometallic Rh(por) derivatives (1.896-
2.078 Å). The axial phenyl group is almost perpendicular to
the least-squares plane of the porphyrin core (the corresponding
angle is 88.5°) and is oriented away from the N atoms (the N3-
Rh-C45-C50 angle of 40.5°) (Figure 3). This relative orienta-
tion of aromatic axial ligands (such as phenyl or pyridine) and
the M-N vectors decreases steric interactions between the ortho
hydrogens and the porphyrin core.21 A rather significant “saddle”
distortion of the TPP core in Rh(TPP)Ph (Figure 4) is most
likely caused by the same forces. As is often the case, this
distortion is accompanied by shortening of the Rh-N bonds
(average Rh-N distance of 2.024 Å). Interestingly, while the
macrocycle undergoes a relatively large distortion, the displace-
ment of Rh from the least-squares plane of the chelating
nitrogens is only 0.03 Å.
Acknowledgment. We thank the NSF (Grant CHE-9612725)
and acknowledge a Stanford Graduate Fellowship (R.B.) for
financial support. X-ray data were collected by Dr. F. Hollander
(UCsBerkeley).
Figure 3. ORTEP view of Rh(TPP)Ph (50% probability thermal
ellipsoids) along the Rh-C axis.
Supporting Information Available: Details of experimental
procedures, crystallographic data in the CIF format, and least-squares
planes and deviations therefrom. This material is available free of charge
via the Internet at http://pubs.acs.org
IC0011112
(19) Metal-assisted cleavage of C-C bonds both on metal surfaces20a and
by metal complexes in solution20b is known. The latter, however, is
limited to special substrates.20b The generation of Rh(OEP)Ph and Rh-
(OEP)Me in the Rh2(CO)4(OEP)-toluene system may provide an
interesting lead in search for metal complexes capable of C-C bond
activation in relatively unreactive substrates. However, at this time
any conclusions regarding the mechanistic aspects of the observed
C-C bond cleavage in the above system are precluded by the
complexity of the Rh2(CO)4(OEP)-toluene reaction mixture. The
possibility of heterogeneous C-C bond activation on metallic Rh16 is
less likely, since in such a case C-C bond cleavage should not be
limited to the OEP derivatives. However, which of the three speciess
(RhI)2(CO)4(OEP), RhII(OEP), or RhIII(OEP)X, present in the reaction
mixture in significant relative amountssis responsible for the C-C
bond activation is not obvious.
(20) (a) See, for example: Hagedorn, C. J.; Weiss, M. J.; Kim, T. W.;
Weinberg, W. H. J. Am. Chem. Soc. 2001, 123, 929-940 and
references therein. (b) For a comprehensive review, see: Rybtchinski,
B.; Milstein, D. Angew. Chem., Int. Ed. 1999, 38, 870-883.
(21) Scheidt, W. R. In The Porphyrin Handbook; Kadish, K. M., Smith,
K. M., Guilard, R., Eds.; Academic Press: New York, 2000; Vol. 3,
pp 49-112.
Figure 4. Displacement (in pm) of the atoms of the porphyrin core
and Rh from the 24-atom least-squares plane. Positive values correspond
to displacement toward the phenyl axial ligand. Relative orientation of
the phenyl axial ligand is shown in bold lines.
Finally, Rh(TPP)Ph, generated in one such reaction was
studied crystallographically (Figure 2, Table 2). The four N