Rhodium-Induced Reversible C?C Bond Cleavage: Transformations of Rhodium(III) 22-Alkyl-m-benziporphyrins

Article abstract of DOI:10.1002/chem.201704411

The structurally prearranged carbaporphyrins 22-methyl- and 22-ethyl-m-benziporphyrins provide the platform stabilizing aromatic rhodium(III) 22-(μ-methylene-m-benziporphyrin) and rhodium(III) 22-(μ-ethylidene-m-benziporphyrin). An intramolecular conversion facilitated by the m-phenylene reactivity and observed for both aromatic complexes efficiently leads to rhodium(III) 21-(μ-methylene)-21-carbaporphyrin and rhodium(III) 21-(μ-ethylidene)-21-carbaporphyrin. The distinctive macrocyclic environment of rhodium(III) 21-carbaporphyrin created an opportunity to trap unique organometallic transformations of inner core substituents affording the fulvene-like bond pattern or the rearrangement to 21-vinyl substituent. The one-electron reduction of the rhodium(III) carbaporphyrin anion π-radical with a (d_xy)²(d_xz)²(d_yz)²–(P^.?) electronic configuration is demonstrated. The further process of reduction of paramagnetic species triggers the ethyl migration from carbon(22) to rhodium(III), affording the diamagnetic rhodium(III) meta-benziporphyrin containing the apically coordinated σ-ethyl ligand providing an example of reversible C(sp²)?C(sp³) bond cleavage.

Full text of DOI:10.1002/chem.201704411

A Journal of
Accepted Article
Title: Rhodium-induced reversible C-C bond cleavage -
transformations of rhodium(III) 22-alkyl-m-benziporphyrins
Authors: Karolina Hurej, Milosz Pawlicki, and Lechoslaw Latos-
Grazynski
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Chem. Eur. J. 10.1002/chem.201704411
Link to VoR: http://dx.doi.org/10.1002/chem.201704411
Supported by

10.1002/chem.201704411
Chemistry - A European Journal
FULL PAPER
Rhodium-induced reversible C–C bond cleavage –
transformations of rhodium(III) 22-alkyl-m-benziporphyrins
Karolina Hurej,[a] Miłosz Pawlicki,[a] Lechosław Latos-Grażyński[a]*
porphyrinoids.
Abstract: The structurally prearranged carbaporphyrins: 22-methyl-
and 22-ethyl-m-benziporphyrins provided the platform stabilizing
aromatic rhodium(III) 22-(μ-methylene-m-benziporphyrin) and
rhodium(III) 22-(μ-ethylidene-m-benziporphyrin). An intramolecular
conversion facilitated by the m-phenylene reactivity and observed for
both aromatic complexes efficiently leads to rhodium(III) 21-(μ-
methylene)-21-carbaporphyrin and rhodium(III) 21-(μ-ethylidene)-21-
carbaporphyrin. The distinctive macrocyclic environment of
rhodium(III) 21-carbaporphyrin created an opportunity to trap unique
organometallic transformations of inner core substituents affording
the fulvene like bond pattern or the rearrangement to 21-vinyl
3
2
4
Ar
Ar
Ar
Ar
Ar
Ar
Ar
Ar
Ar
Ar
Ar
Ar
Ar
Ar
27
N
26
19
18
8
9
N
N
N
N
N
N
N
H
N
H
N
H
N
H
N
Ar
Ar
14 13
1
1-Me
2
1-Et
Scheme 1. m-Benziporphyrin 1, 22-methyl-m-benziporphyrin 1-Me, 22-ethyl-
m-benziporphyrin 1-Et and p-benziporphyrin 2.
substituent. The one electron reduction of the rhodium(III)
In contrast to C–C bond formation a C–C bond cleavage has
been for many years treated as a scientific curiosity, but recently
this type of reactivity has found its place and currently is an
important aspect of transition metal catalysis.[23-26] One of
reactions, where the cleavage of aromatic structure is of
fundamental importance, is transformation of benzene to
cyclopentadiene.[27-33] The coordination of metal cations to m-
benziporphyrin 1 and p-benziporphyrin 2 initiated contractions to
21-carbaporphyrin complexes, providing the illustrative
examples of such structural transformations.[2,15-19,34] For
(dxy)2(dxz)2(dyz)2
–
(P )
-
carbaporphyrin anion π-radical with
a
electronic configuration. The further process of reduction of
paramagnetic species triggers the ethyl migration from carbon(22) to
rhodium(III) affording the diamagnetic rhodium(III) meta-
benziporphyrin containing the apically coordinated σ-ethyl ligand
providing an example of reversible C(sp2)–C(sp3) bond cleavage.
Introduction
instance
a
rhodium(III) m-benziporphyrin
3
(Scheme 2)
underwent an unprecedented transformation of the built-in m-
phenylene in which a perimeter carbon atom is extruded from
the original six-membered ring to create five-membered
carbocycle, affording eventually three rhodium(III) 21-(μ-
acetaldehyde)-21-carbaporphyrins: a) non substituted 5 or b) β-
formyl substituted 5-1 and 5-2 (Scheme 2). [19] In course of the
detailed studies it has been demonstrated that the contraction of
rhodium(III) m-benziporphyrin was preceded by the
Carbaporphyrinoids – a specific class of macrocyclic ligands
provide a suitable platform for exploring unique aspects of
organometallic chemistry imposed by equatorial coordination,
leading to observation of unusual oxidation and electronic states
of incorporated metal cations.[1-4] Consequently, an encouraging
opportunity have been created to address fundamental issues,
investigated in such seemingly distant fields as: (a) the
aromaticity of molecules adopting the Möbius topology,[5-9] (b)
organometallic copper(II) compounds,[10-12] (c) the inclusion of a
d-electron subunit into a -electron conjugation[13,14] or (d) the
transformation
into
rhodium(III)
22-(μ-acetaldehyde)-m-
benziporphyrin 4, which incorporates the rhodacyclopropane
motif substituted with a formyl unit.
reactivity of built-in carbocyclic unit. [15-19] The close proximity of
[20,21]
C–H or C–C bonds of m-benziporphyrin 1,
22-methyl-m-
benziporphyrin 1-Me, [18] or p-benziporphyrin 2[15,17,20,22] (Scheme
1) to a metal ion enforces an unusual coordination geometry and
eventually prompts unique reactivity,[2] what, in broader definition
significantly distinguishes carbaporphyrinoids from the other
[a]
K. Hurej, Dr. M. Pawlicki, Prof. L. Latos-Grażyński*
Department of Chemistry,
Scheme 2. Transformations of rhodium(III) m-benziporphyrin 3.19
University of Wrocław
ul.14 F. Joliot-Curie,
50-383 Wrocław (Poland)
Fax:(+48)71-3282348
E-mail: lechoslaw.latos-grazynski@chem.uni.wroc.pl
Homepage:http://llg.chem.uni.wroc.pl/
Recently we have reported on synthesis of 22-methyl-m-
benziporphyrin 1-Me and its gold(III) coordination chemistry.
Significantly gold(III) 22-methyl-m-benziporphyrin undergoes the
facile m-benzene ring contraction yielding gold(III) 21-methyl-21-
carbaporphyrin with remarkably high yield.[18]
Supporting information for this article is given via a link at the end of the
document
In this contribution we have decided to explore the reactivity
of rhodium(III) 22-methyl-m-benziporphyrin 1-Me and 22-ethyl-
This article is protected by copyright. All rights reserved.

10.1002/chem.201704411
Chemistry - A European Journal
FULL PAPER
benziporphyrin and 22-methyl-m-benziporphyrin.[18,37] After
chromatographic workup 5,20-diphenyl-10,15-ditolyl-22-ethyl-m-
benziporphyrin 1-Et was obtained in 19% yield.
m-benziporphyrin 1-Et aiming firstly to establish an efficient
route
carbaporphyrins (Rh-CH2–C(21)) and 21-(μ-ethylidene)-21-
carbaporphyrins (Rh–CH(CH3)–C(21)) in each case the
to
create
rhodium(III)
21-(μ-methylene)-21-
-
As expected the electronic spectra of 1-Et and its dication 1-
2+
formula of the bridging unit given in the parentheses. As the
access to the crucial 22-alkyl-m-benziporphyrin macrocycles is
straightforward, the synthesis of rhodium(III) 21-(μ-methylene)-
21-carbapophyrins via the novel route is expected to be more
Et-H2 resemble the relevant spectra of 5,20-diphenyl-10,15-
ditolyl-22-methyl-m-benziporphyrin 1-Me (see the SI, Figure
1
S60).[18] The H NMR spectrum of 1-Et (Figure 1, Trace A)
presents a similar pattern as that reported for methylated
efficient once compared to the previously reported contraction of
derivative 1-Me 18
.
The characteristic set of 22-Et
[17]
rhodium(III) p-benziporphyrin.
The several aspects of the
resonances is located at 2.35 (q, CH2) and 0.70 ppm and (t,
CH3).
explored inner core reactivity of originally incorporated 22-ethyl
group have been found to be particularly intriguing including its
reversible migration to the rhodium(III) centre affording σ-ethyl
rhodium(III) m-benziporphyrin.
Results and Discussion
22-alkylated m-benziporphyrin syntheses. 5,20-diphenyl-
10,15-ditolyl-22-methyl-m-benziporphyrin 1-Me has been
synthesized in a condensation of pyrrole, benzaldehyde and (2-
methyl-1,3-phenylene)bis-(phenylmethanol) with 22% yield as
previously reported.[18] A key step in the synthesis of 5,20-
diphenyl-10,15-ditolyl-22-ethyl-m-benziporphyrin 1-Et is the
construction
of
suitable
synthon
(2-ethyl-1,3-
phenylene)bis(phenyl-methanol) 10 to be used for introducing
the 2-ethyl-1,3-phenylene unit into a porphyrin-like frame.
2-Ethylisophthalonitrile
commercially available isophthalonitrile
ethylation at the C(2) position (yield 85%).[35] The reduction of
nitrile substituents ( ) followed by a hydrolysis yielded 2-
ethylisophthalaldehyde
reduction step has been followed by reaction of 2-
ethylisophthalaldehyde with phenylmagnesium bromide to
7
was obtained from the
6
via the direct
Figure 1. 1H NMR spectra of A) 1-Et, B) 11, C) 12 (600 MHz, CDCl3, 300 K).
Resonance assignments follow the typical numbering of 22-alkyl-m-
benziporphyrin shown in Scheme 1.
8
]
9
as shown in Scheme 3.[36 The
9
produce 10 (2-ethyl-1,3-phenylene)bis(phenylmethanol) with
yield of 80%.
Insertion of Rhodium(III) into 22-Alkyl-m-benziporphyrins.
Reaction of di-μ-chloro-tetracarbonyl-dirhodium(I) [RhCl(CO)2]2
with 22-methyl-m-benziporphyrin 1-Me in benzene (1 h, reflux)
results in practically quantitative formation of the rhodium(III) 22-
(μ-methylene)-m-benziporphyrin 11. The analogous procedure
has been applied to obtain rhodium(III) 22-(μ-ethylene)-m-
benziporphyrin 12 starting from 22-ethyl-m-benziporphyrin 1-Et
(Scheme 4).
Scheme 3. Synthesis of 22-ethyl-m-benziporphyrin 1-Et (a) LDA,CH3CH2I,
THF, 4 h, 193 K; (b) DIBAH, 4 h, 193 K, (c) H2O, H+ (d) PhMgBr, 1 h, 293 K,
.
(e) BF3 Et2O, pyrrole, ArCHO, CHCl3, (f) DDQ, 1 h.
Scheme 4. Insertion of rhodium(III) into 5,20-diphenyl-10,15-ditolyl-22-alkyl-m-
benziporphyrins 1-Me and 1-Et.
The condensation procedure (Scheme 3) follows the stochastic
methodology previously utilized for the synthesis of regular m-
This article is protected by copyright. All rights reserved.

10.1002/chem.201704411
Chemistry - A European Journal
FULL PAPER
The composition of 11 was unambiguously confirmed by
high-resolution mass spectrometry (m/z calcd. for C49H35N3Rh
[M-Cl]+: 768.1886; found: 768.1868) reflecting the preservation
of a six-membered ring. The pattern of the 1H NMR spectrum of
11 (Figure 1, Trace B) is consistent with the effective Cs
symmetry and confirms the formation of methylene bridge
between the rhodium(III) center and the C(22) carbon atom of
the benzene ring as presented in Scheme 4. This the most
notable feature of 11 has been inferred from the identification of
the upfield located signal (δ = −0.80 ppm) in the 1H NMR
spectrum (Figure 1, Trace B).
The six membered ring protons H(2,4) 8.32, H(3) 8.62 ppm
and β-pyrrolic resonances H(8,19) 7.93, H(9,18) 7.65, H(13,14)
7.89 ppm (for systematic numbering see Scheme 1) are
markedly downfield relocated in comparison to the free base.
The fundamental spectroscopic features of 12 resemble those of
11 showing the resonance lines assigned to the macrocyclic
perimeter significantly downfield relocated (H(2) 8.33, H(3) 8.58
H(4) 8.64 ppm and β-pyrrolic resonances H(18) 7.97 ppm, H(9)
7.88 ppm, H(8) 7.87 ppm, H(19) 7.78 ppm and H(13,14) 7.66
ppm) and preserving the aromatic characteristics (Figure 1,
Trace C).[1] Nevertheless the 1H NMR spectrum of 12 reveals an
increased multiplicity of carbaporphyrin resonances, as
compared to the Cs-symmetric 11 homologue, consistently with
decreased symmetry (C1), previously reported and discussed in
detail for analogous rhodium(III) 22-(μ-acetaldehyde)-m-
benziporphyrin 4. [1,19] In addition the 1H NMR spectrum shows
the evidently upfield relocated signals assigned to the μ-
ethylidene bridge. The quartet from H(26) is found at −0.51 ppm,
while the methyl doublet (H(27)) at −2.17 ppm.
In general the DFT optimized structure of 12 resembles the
one reported previously for rhodium(III) 22-(μ-acetaldehyde)-m-
benziporphyrin 4 (Figure 2).[19]
The carbon atom C(22) displays the essential degree of
pyramidal distortion from the planar geometry expected for sp2
hybridized carbon as reflected by the sum of respective bond
angles
[Σ= C(1)-C(22)-C(5) + C(1)-C(22)-C(26) + C(5)-C(22)-
C(26)] equaling 359.3°. Considering solely the diatropic
properties of 12 one could refer to the analogous properties of
previously reported examples of aromatic rhodium(III) 22-(μ-
acetaldehyde)-m-benziporphyrin 4 and gold(III) 22-methyl-m-
benziporphyrin.[18,19] The DFT optimized structure of 12 reveals
that the environment of the coordinated carbon C(22) was
modestly distorted from planarity still sufficiently to limit the
[6]annulene aromaticity and to prefer the macrocyclic 18 π-
electron one as reflected by experimental and calculated
chemical shifts (see the SI, Figure S62). Thus, the aromaticity
observed for 12 does result from the strong coordination of the
rhodium(III) ion as documented by the remarkable relocation of
C(22) resonance (δ22 = 57.9 ppm) comparing to 1-Et
(δ22 = 114.6 ppm) which is quite typical for substituted carbon
donors in carbaporphyrinoid complexes.[15,19,38,39]
Scheme 5. Contraction of rhodium(III) 22-(μ-methylene)-m-benziporphyrin 11.
In course of these investigations in order to gain some
insight into the molecular electronic structure of the novel
rhodium(III) carbaporphyrinoids, all structures were subjected to
DFT optimization at the B3LYP level of theory with the LANL2DZ
pseudopotential applied for rhodium center and 6-31G(d,p) for
other atoms. The selected results are systematically reported
corroborating with the respective NMR analysis including the
geometrical constrains reflected by NOE connectivity and the
characteristic values of the chemical shifts.
Conditions a) basic Al2O3 (GIII), CH2Cl2.
Contraction of rhodium(III) 22-alkyl-m-benziporphyrin. The
profound but, to some extent predictable structural modifications,
resembling
one
observed
for
gold(III)
22-
methylbenziporphyrin,[18] were observed when 11 has been
placed on a basic alumina or has been treated with selected
basic reagent in solution (triethylamine, 2,4,6-trimethylpyridine).
In such conditions 11 immediately converts into a mixture of
reddish brown compounds of rhodium(III) 21-(μ-methylene)-21-
carbaporphyrin
13
and
2-formyl-21-(μ-methylene)-21-
carbaporphyrin 14 (Scheme 5), typically in 1:1 molar ratio as
determined by 1H NMR, once the reaction has been directly
followed by 1H NMR (300 K, CDCl3). One can appreciate the
remarkable total yield of transformation equalling 60-65% which
in previously reported examples has never exceeded 10% for
rhodium(III) benziporphyrins. [17,19] Finally the target compound
13 has been separated from the reaction mixture by column
chromatography on silica gel with the practical yield of the
synthesis 33% with respect to 11. Evidently the contraction of 11
is the procedure of choice to generate 13 via an intramolecular
conversion of m-phenylene.
Figure 2. DFT-optimized molecular structure of 12. A) a perspective view, B) a
side view with aryl groups omitted for clarity, and C) the geometry of the
rhodacyclopropane in the fragment, which resembles a spiro[2.5]octa-4,6-
diene. Selected distances: Rh–C(22) 2.388 Å, C(22)–C(26) 1.491 Å, C(26)–
C(27) 1.519 Å, Rh–C(26) 2.105 Å, Rh···C(27) 3.317 Å.
The 1H NMR spectrum of 13 has been previously analysed in
detail as this compound has been already generated by the
independent
route
starting
from
rhodium(III)
p-
benziporphyrins.[17] Subsequently the resonances of 14 in the
This article is protected by copyright. All rights reserved.

10.1002/chem.201704411
Chemistry - A European Journal
FULL PAPER
spectrum of the 13 and 14 mixture were distinguished by default.
The 1H NMR spectrum of 14 demonstrated the key similarities to
the 13 features reflecting clearly the symmetry lowering (seven
β-H resonances), the formyl functionality (9.16 ppm) and the
presence of two stereocenters (at C(21) and C(25)) gives a raise
to two diastereomers 16 and 17 readily differentiated from 15 by
their 1H NMR spectra.
most characteristic signature, i.e. the AB patter of bridging
2
methylene (

A = −3.85 ppm, B = −3.98 ppm, JAB = 10.2 Hz). In
analogous conditions as described above for 11, the rhodium(III)
22-(μ-ethylidene)-m-benziporphyin 12 converts to rhodium(III)
21-(μ-ethylidene)-21-carbaporphyrin
15,
and
to
two
diastereomers of rhodium(III) 2-formyl-21-(μ-ethylidene)-21-
carbaporphyrin 16 and 17 (Scheme 6).
Figure 4.1H NMR spectrum (600 MHz, chloroform-d, 300 K) of A) 15, B) 19.
Scheme 6. Contraction of rhodium(III) 22-(μ-ethylidene)-m-benziporphyrin 12.
Core reactivity – Oxidation. In the aerobic condition an
addition of hydrochloride to rhodium(III) 21-(μ-ethylidene)-21-
carbaporphyrin 15 or its β-formylated congeners has been
followed by H NMR. Presumably the initial protonation centred
at C(25) carbon atom affords transient rhodium(III) 21-ethyl-21-
Conditions a) basic Al2O3 (GIII), CH2Cl2
.
The final separation via column chromatography on silica gel
(elution with dichloromethane) yielded two fractions containing
15 (reddish brown) and the mixture of 16 and 17 (pinkish brown).
Any further attempt of chromatographic separation of 16 and 17
failed as in chromatographic conditions these two species seem
to be mutually convertible in the presence of silica gel or alumina.
Eventually we have realized that under typical conditions 15,
16 and 17 exhibited a limited stability both in solution and in the
solid state. Their identification was made solely in solution using
NMR spectroscopy. To account for the determined properties of
15, 16 and 17 which incorporate the rhodacyclopropane motif
substituted with methyl (Scheme 6) the DFT optimized structure
(Figure 3) has been considered.
1
carbaporphyrin 15-H (Scheme 7).
Scheme 7. Transformation of 15 or 16/17.
The protonation triggers two electron oxidation accompanied by
removal of a proton transforming 15 into rhodium(III) 21-
ethylidene-21-carbaporphyrin 18, which formally incorporates
the 6-methylfulvene motive (5-ethylidenecyclopenta-1,3-diene)
into the 21-carbaporphyrin frame (Scheme 7, Figure 5).
Figure 3. DFT-optimized molecular structure of 15. A) perspective view, B)
side view with aryl groups omitted for clarity, C) the geometry of the
rhodacyclopropane motif. Selected distances: Rh–C(21) 2.138 Å, C(21)–C(25)
1.463 Å, C(25)–C(26) 1.510 Å, Rh–C(25) 2.051 Å, Rh···C(26) 3.101 Å.
The 1H NMR spectrum of 15 (Figure 4, Trace A) resembles
closely the features recorded previously for 5 (Scheme 2). [19]
The characteristic AX3 pattern of the μ-ethylidene unit (−3.12
3
3
Figure 5. DFT-optimized molecular structure of 18: A) perspective view, B)
side view with aryl groups omitted for clarity, C) the geometry of the
rhodium(III) methylfulvene interaction. Selected distances: Rh–C(21) 2.189 Å,
C(21)-C(25). 1.435 Å, C(25)-C(26) 1.500 Å, Rh···C(25) 2.051 Å, Rh···C(26)
3.101 Å.
ppm (q, J = 6.7 Hz; 25-H); −3.60 ppm (d, J= 6.7 Hz; 26–H)) is
consistent with formation of rhodacyclopropane unit substituted
with the single methyl group. 1H NMR features of 16 and 17 (see
the SI) are readily related to those of 15. Nevertheless the
This article is protected by copyright. All rights reserved.

10.1002/chem.201704411
Chemistry - A European Journal
FULL PAPER
The most characteristic NMR features of 18 (Figure 7A) reflect
the chemical shifts related to the fulvene like bond pattern of the
C(21)=C(25)H-C(26)H3 unit (1H NMR: C(25)H: −0.01 ppm,
C(26)H3: −1.52 ppm; 13C NMR: C(21): 82.5 ppm, C(25): 111.8
ppm, C(26): 14.6 ppm). The composition of 18 and its 2-CHO or
3-CHO derivatives 18-CHO was unambiguously confirmed by
high-resolution mass spectrometry (18 m/z calcd. for
C49H35N3Rh [M]+: 768.1886; found: 768.1890; 18-CHO: m/z
calcd. for C50H35N3ORh [M]+: 796.1835; found: 796.1837). The
subsequent isomerization of 18 facilitated by the added nitrogen
base (e.g. Et3N) converts the 21-ethylidene unit into the 21-vinyl
one (ca. 72 h) encompassed in rhodium(III) 21-vinyl-21-
carbaporphyrin 19 (Scheme 7, Figure 6).
The reaction of the vinyl derivative 19 with hydrochloric acid led
to the formation of rhodium(III) 21-(3-chloroethylidene)-21-
carbaporphyrin 20, which formally incorporates the 6-
(chloromethyl)fulvene motive (5-(2-chloroethylidene)cyclopenta-
1,3-diene) instead of the single pyrrole (Scheme 8).
The most characteristic features of 20 (Figure 7B) reflect the
fulvene like bond pattern at the C(21)=C(25)H-C(26)H2Cl (1H
NMR: C(26)HA: 1.06, C(25)HX: −0.22 ppm, C(26)HM: −1.52 ppm,
2
3JAX = 10.7 Hz, JBX = 5.2 Hz, JAB = 10.7 Hz; 13C NMR: C(21):
80.0 ppm, C(25): 97.0 ppm, C(26): 37.8 ppm) with the
characteristic values of coupling constants which is consistent
with the 3-chloroprop-1-ene structure built into 20. One can
readily notice that 19 and 20 are formed as racemic mixtures.
The specific coordination of 21-vinyl in 19 or the asymmetric
substitution of fulvene in 20 induces their planar chirality
identified previously in appropriately substituted regular
metalloporphyrins. [42-46] Consistently the strong differentiation of
chemicals shifts of resonances assigned the geminal CH2
hydrogen atoms of chloromethyl group exposes the
diasterotopic effect imposed by the intrinsic planar chirality of 20
.
Figure 6. DFT-optimized molecular structure of 19: A) perspective view, B)
side view with aryl groups omitted for clarity, C) the geometry of the geometry
of the rhodium(III) …21-vinylcyclopentadiene interaction. Selected distances:
Rh–C(21) 2.166 Å, C(21)–C(25) 1.458 Å, C(25)–C(26) 1.381 Å, Rh···C(25)
2.200 Å, Rh···C(26) 2.416 Å.
The 1H NMR spectrum of 19 contains the finger print like
signature, i.e. the AMX spin system, assigned to C(25)H and
C(26)H2 (Figure 4B) of the vinyl unit (25-Hx: –1.99 ppm, 26-HA: –
Figure 7. 1H NMR spectrum (600 MHz, chloroform-d, 300 K) of A) 18, B) 20.
3
2
0.84 ppm, 26-HM: –3.75 ppm, JAX = 8.9 Hz, JBX = 14.3 Hz, JAB
<1 Hz) with the characteristic order of coupling constants (Jtrans
>
DFT Studies – oxidized species. Complexes 15, 18, 19 and 20
were subjected to DFT optimizations (Figure 3,5,6, Figure S82).
In fact Rh…η2-C2 coordination already suggested for 19 is well
illustrated at the comparison of DFT optimized structures
including. In particular the Rh-C(25) and Rh-C(26) distances of
1
Jcis>> Jgeminal). Significantly, the overall H NMR spectral pattern
demonstrates intrinsic asymmetry of 19 as reflected by the AB
system identified for the scalar coupled H(2)-H(3) hydrogens
3
(H(2) 9.27 ppm, H(3) 9.47 ppm, J = 4.6 Hz). Consistently the
19 are within the limits (2.050–2.787 Å) of Rh-η2-CC bonding
rotational freedom with respect to the formally single C(21)–
C(25) bond is restricted. Such a structure accounts for the
relatively small 13C chemical shifts (C(25): 96.8 ppm, C(26) 63.0
ppm) in comparison to the regular vinyl unit, but consistent with
the upfield contribution of the coordination shifts seen in
[17,47-50]
interactions (Figure 6, Table S2).
The rhodium(III)
approaches the carbon atoms at distances much shorter than
that expected for van der Waals contact (4.21 Å). [51] In addition
the reduction of the C(25)–C(26) bond length in comparison to
15, 18 or 20 reflects the double bond character. Importantly, the
satisfactory agreements between the experimental and
calculated 1H and 13C chemical shifts have been found for 15, 18,
19 and 20 (see the SI, Table S1).
analogous
situations
of
η2-alkene-to-rhodium
coordination.[17,40,41]
Reactivity of 12 with DCl. Titration studies in which aliquots of
deuterochloric acid in D2O (37%) were added to an initial sample
of 12 in CDCl3 (300 K) demonstrated that 12 reacts rapidly to
yield a new species with broadened resonances tentatively
assigned to 24-D (α-CHD (CH2) at 1.99 ppm, β-CH3 at 0.07
ppm). After the evaporation of solvent 24-D converts to mixture
of 12 and 12-D (Scheme 9). The peculiar 12 → 12-CHDCH3 →
12-D conversion involving
a
regioselective α-methine
Scheme 8. Transformation of 19.
This article is protected by copyright. All rights reserved.

10.1002/chem.201704411
Chemistry - A European Journal
FULL PAPER
deuteration can be considered as an intriguing example of
selective and reversible aliphatic (i.e. benzylic-like) C-H bond
activation. [52]
during reaction can be monitored by the solution color change
from the greyish brown of 12 to green one observed for 21. The
spectacular changes, consistent with the one-electron reduction
1
yielding 21 were detected in H NMR spectrum (Figure 8). Thus
the formation of 21 has been manifested by the raise of
characteristic set of 1H NMR signals located in the range of
−150 - 200 ppm.
The spectrum pattern including the paramagnetic shifts did not
depend on the choice of the reducing reagent. Noticeably, the
reduction of rhodium(III) 22-(μ-ethylidene)-m-benziporphyrin 12
occurs preferentially at the carbaporphyrinoid ring. There are
two alternative electronic structures for the one-electron
reduction of rhodium(III) 22-carbaporphyrinod: metal-centered
with formation of rhodium(II) regular 22-carbaporphyrinod
(P)Rh(II) or one-electron reduction of the 21-carbaporphyrinoid
Scheme 9. Deuteration of 12.
ring to give
electronic structure can be described by two main resonance
contributors [(P-)Rh(III)
(P)Rh(II)] combining the
a
π-anion radical (P-)Rh(III). Eventually the
Redox processes of 12. Cyclic voltammetry (Supporting
Information, Figure S86) demonstrates that 12 undergoes two
consecutive, reversible one-electron reductions with semi-
reversible half-wave potentials at −1.414 V and −0.794 V
(dichloromethane, tetrabutylammonium perchlorate (TBAP),
relative to the ferrocene/ferrocenium (Fc/Fc+) couple). The first
potential is relatively high, which accounts for the easy
accessibility of an one-electron reduced form in chemical
reduction. The appropriate oxidation potentials equal: E1/2(1) =
0.42 V, E1/2(2) = 0.68 V, E1/2(3) = 0.82 V.

spectroscopic feature of two limiting electronic structures. The
1H NMR spectroscopy is well known to be a uniquely definitive
method for detecting and characterizing paramagnetic
metalloporphyrinoids.[53-55]
The chemical reduction of 12 was followed using two specific 1H
NMR windows. The first region (−150 to 200 ppm) considers an
assumption that formed forms can be paramagnetic. In the case
of feasible diamagnetic species, the spectroscopic analysis has
been mainly focused on the extremely useful and analytically
effective −6 – 1 ppm range. The 22-μ-ethylidene of 12 and the
relevant transformed moieties (22-ethyl of 21, σ-ethyl of 23) are
expected to reveal the appropriate set of resonances at this
particular range due to the shielding effect consistent with
Figure 8. 1H NMR spectrum of 21 (C6D6, 325 K).
The hyperfine shift patterns are sensitive to the oxidation and
spin states as well as the ligation types which allows to address
fine details of the electronic structure. Unfortunately the
1
characteristic H NMR shifts for representative and analytically
diatropicity of the appropriate equatorial macrocycle
.
useful examples of one electron reduced paramagnetic
rhodium(III) porphyrins are in fact limited to the single example
due to their intrinsic reactivity. Thus the relevant rhodium(II)
meso-tetramesitylporphyrin is characterized by low-spin (d7)
metal electronic ground state (dxy)2(dxz)2(dyz)2(dz2)1 which is
consistent with location of paramagnetically shifted 1H NMR
resonances (296 K) at the relatively narrow spectroscopic
window: 18.3 ppm (β-pyrroles, 3.35 ppm (o-CH3), 8. 87 ppm (m-
CH3) and 3.51 (p-CH3). [56] Accordingly the spectacularly different
spectroscopic pattern encountered for 21 implies fundamentally
different electron structure initially described by two main
resonance contributors [(P-)Rh(III)  (P)Rh(II)] but with a
dominant participation of one-electron ligand centred reduction
(P-)Rh(III) (vide infra). A continuation of reduction transforms
the paramagnetic form 21 into the diamagnetic rhodium(III)
meta- benziporphyrin 23 containing the apically coordinated σ-
ethyl ligand. 23 demonstrates a distinctive set of upfield signals
assigned to the σ-ethyl ligand (α-CH2 0.73 ppm, quartet of
doublets 3JHH = 7.3 Hz, 2JRhH =2.2 Hz; β-CH3 −0.74 ppm, triplet of
Scheme 10. Reactivity of 12.
Initially the reduction of 12 has been conducted under strictly
anaerobic, glove box conditions using as a reducing agent zinc
amalgam or triethylamine (Scheme 10). The profound changes
3
3
doublets, JHH = 7.3 Hz, JRhH = 2.2 Hz (Figure 9A). The
additional splitting seen simultaneously for α-CH2 and β-CH3
This article is protected by copyright. All rights reserved.

10.1002/chem.201704411
Chemistry - A European Journal
FULL PAPER
course of DFT studies on organic radicals or paramagnetic
metalloporphyrins can be compared with experimental values –
isotropic hyperfine coupling constants aN and contact shifts
obtained from EPR and NMR spectroscopic measurements. [54]
The spin density on carbon or hydrogen atoms (Figure 10, Table
S3) can be converted into the isotropic shifts of attached protons
(Figure 11). The detailed discussion of the methodology was
given previously. [63-65]
reflects the scalar Rh-H coupling encountered previously for
[57]
ethylrhodoximes.
In fact 23 has been generated via an
independent route in a typical reaction of rhodium(III) m-
benziporphyrin 3 with the ethyl Grignard reagent perfectly
reproducing the characteristic σ-ethyl pattern encountered
already for 23.
Figure 9. 1H NMR spectrum (600 MHz, C6D6, 300 K) of A) 23 formed in
reaction of 3 with EtMgBr, B) presents the upfield part of spectrum produced in
transformation of 12 in reductive conditions (Scheme 10).
Thus the two-electron reduction of 12 eventually coupled with
the heterolytic cleavage of C(26)–Rh bond and protonation
afforded the 22-ethyl unit of transient 22. Interestingly, the
rhodium(I) 22-ethyl-m-benziporphyrin 22 is prone to undergo an
ethyl group migration via a clean oxidative addition to form the
σ-ethyl rhodium(III) m-benziporphyrin 23. Such a reactivity is
unprecedented for metallocarbaporphyrinoids. [2] However it was
previously reported that the formation of palladium(II) 21-
methylbenzocarbaporphyrin via insertion of palladium(II) into 22-
N-methylbenzocarbaporphyrin requires a peculiar inner core
N(22) - C(21) methyl migration.[38]
Figure 10. Distribution of spin-density for 21-Cl (A) and 21 (B) with isovalues =
0.0004 e/a.u.3
The comparison of experimental and theoretical spectra was
schematically presented in Figure 11. The largest atomic spin
density was determined at m-phenylene and some pyrrole
positions. Relevantly, the small atomic spin density at the
rhodium ion is consistent with the rhodium(III) d6 π-anion radical
description.
In the presence of dioxygen σ-ethyl rhodium(III) m-
benziporphyrin 23 placed on silicagel column undergoes the fast
conversion to 12. One can suggest that 23 undergoes a
reductive elimination to generate the rhodium(I) 22-ethyl-m-
benziporphyrin 24 (Scheme 10). The subsequent oxidative
addition of α-CH (α-methylene group of 22-ethyl) causes
transformation into original complex 25. Presumably in the same
time the created hydride reacts with the acidic proton in the
solution affording 12 readily identified by the characteristic 1H
NMR pattern. The unique 12 → 23 → 12 conversion can be
considered as an intriguing example of reversible C(sp2)-C(sp3)
bond cleavage in carbaporphyrin environment resembling
chemistry reported for rhodium pincer ligand complexes.[58-62] To
confirm the analysis the σ-ethyl rhodium(III) m-benziporphyrin 23,
generated on the NMR scale by addition of etylmagnesium
bromide to 3 (Scheme10) has been exposed to dioxygen
affording 12.
Figure 11. Schematic representation of A) experimental data for 21, B)
calculated contact shift patterns for 21, C) calculated contact shift patterns for
21-Cl, D) literature data for complex of rhodium(II). [56] Used color code: red –
pyrroles, orange – meta-phenylene, green – ethyl ligand, grey – meso-aryls.
Electronic structure of 21. To assess the electronic structure
of 21, the density functional theory (DFT) calculations were
performed. The electronic structures of 21 and 21-Cl correspond
to the classical description expected for rhodium(III) 22-ethyl-m-
benziporphyrin π-anion radical structure with a (dxy)2(dxz)2(dyz)2 –
P- electronic configuration. Spin densities determined in the
The spin density on carbon atoms can be transformed into the
isotropic shifts of attached protons, connected with these carbon
atoms. A comparison of the theoretical and experimental values
is presented at Figure 11.
This article is protected by copyright. All rights reserved.

10.1002/chem.201704411
Chemistry - A European Journal
FULL PAPER
pseudopotential applied for Rh centers and solvation (PCM=CHCl3).
Harmonic vibrational frequencies were calculated using analytical second
derivatives as a verification of local minimum achievement with no
negative frequencies observed. The structures were found to have
converged to a minimum on the potential energy. Proton and carbon
chemical shifts were calculated using the GIAO method and referenced
to the absolute shielding of tetramethylsilane calculated at the same level
of theory. The structure models reflect consistently the constrains
imposed by the appropriate NOE experiments.
The analysis leads to a fundamental conclusion that the
density distribution of 21 is sufficiently consistent with the
proposed π-anion radical structure. The detailed analysis of the
electronic structure requires unambiguous assignment of the
resonance lines, however fundamental features of the isotropic
shift – it means such a wide range of 1H NMR spectrum and
signs alternation were superbly recreated by models of
rhodium(III) d6 π-anion radical structures (P-)Rh(III).
Solvents and reagents: All solvents (MeOH, Ethyl Acetate, CHCl3,
Petroleum Ether (40-60), toluene) if not indicated differently were used
without purification. CH2Cl2 was distilled over CaH2. THF was dried by
passing through a silica column with MBraun drying system. Chloroform-
d was prepared directly before using by passing through a basic alumina
column. 6,11,16,21-tetraaryl-meta-benziporphyrin and 6,11,16,21-
tetraaryl-22-methyl-m-benziporphyrin were obtained as previously
described.[18]
22-ethyl-m-benziporphyrin 1-Et: (2-ethyl-1,3-phenylene)bis(phenylme-
thanol) (290 mg, 1 mmol), pyrrole (208 μL, 3 mmol), and p-tolualdehyde
(204 μL, 2 mmol) were added to dry CH2Cl2 (900 ml) under nitrogen.
BF3·Et2O (100 μL) was then added and the reaction mixture was
protected from light and stirred for 1 h. 2,3-dichloro-5,6-dicyano-1,4-
benzoquinone (DDQ; 750 mg, 3 mmol) was subsequently added and the
mixture evaporated under reduced pressure. The residue was subjected
to chromatography (grade II, neutral alumina, CH2Cl2). The final
compound was eluted with 10% ethyl acetate. Yield: 19%.
Conclusions
The incorporation of the 22-alkyl substituents facilitated the
specific m-benzene ring contraction yielding respectively
rhodium(III)
21-(μ-methylene)-21-carbaporphyrin
13
and
rhodium(III) 21-(μ-ethylidene)-21-carbaporphyrin 15. The
peculiar examples of unique inner-core transformation of 21-(μ-
ethylidene)-unit into 21-vinyl one both confined 21-
carbaporphyrin structure provide the illustrative and encouraging
examples of such explorations. Moreover the intramolecular
migration of the ethyl group was detected. It is an intriguing
example of selective and reversible carbon-carbon bond
activation. Potentially it provides a general path to generate a
variety of aromatic rhodium(III) 22-alkyl-m-benziporphyrin
starting from σ-ethyl rhodium(III) m-benziporphyrins. Thus
1H NMR (500 MHz, CDCl3, 300 K): δ = 9.29 (s; NH); 7.61 (d; 3J = 7.5; o-
Ph); 7.49–7.44 (m; m,p-Ph); 7.39 (d; 3J = 4.8; 8,19-H); 7.32 (d; 3J = 7.9;
o-Tol); 7.21 (d; 3J = 7.9; m-Tol); 7.08 (t; 3J = 7.4; 3-H); 6.96 (d; 3J = 7.4;
2,4-H); 6.71 (s; 13,14-H); 6.57 (d; 3J = 4.8; 9,18-H); 2.43 (s; p-Tol); 2.32
(q, 3J = 7,3; 26-H); 0.82 (t, 3J = 7.3; 27-H). 13C NMR (151 MHz, CDCl3,
300 K): δ = 170.1; 156.5; 147.8; 145.6; 142.3; 139.8; 137.0; 137.0; 134.8;
133.1(2x); 132.3(2x); 131.4; 130.0; 128.6; 128.5(2x); 128.4; 127.8(2x);
126.3; 116.0; 114.6; 22.8; 21.3; 15.8. HRMS (ESI) m/z calcd for C50H40N3
organometallic
chemistry
of
rhodium(III)
22-alkyl-m-
benziporphyrins provided conditions for pursuing the intriguing
research possibilities at the crossroads of organic,
[M+H]+: 682.3222, found: 682.3231. UV-Vis (CH2Cl2, 298 K,
417(4.51), 653(3.86), 701(3.95).
, log ):
2-Ethylisophthalonitrile 7: 7 was obtained in the modified procedure
organometallic and inorganic chemistry aimed to trap
fundamental reactive transient species relevant
organometallic transformations
a
for
applied previously to synthesize 2,6-dicyanotoluene but using iodoethane
as the alkylating agent.[35] To
a solution of 40 ml of lithium
diisopropylamide (1.0 M in THF/hexanes) in 150 mL of THF cooled to
183 K and a solution of isophthalonitrile 6 (1.5 g, 11.7 mmol) and
N,N,N,N-tetramethylethylenediamine (750 μl, 5 mmol) in 20 ml of THF
was added dropwise. The mixture was stirred for 2 hr (183 K). The
resulting solution was quenched with large excess of iodoethane (8 ml,
100 mmol) and stirred for 2 hr (300 K). Ice (50 g) was then added, and
the organic layer was extracted with ether. After the solvent removal
under reduced pressure the residual brown oil was chromatographed
over silica gel by using dichloromethane yielding 2-ethylisophthalonitrile 7,
yield: 85%. 1H NMR (600 MHz, CDCl3, 300 K): δ = 7.82 (d; 3J = 7.8; 2,4-
H); 7.42 (t; 3J = 7.8; 3-H); 3.10 (q; 3J = 7.7; CH2); 1.35 (t; 3J = 7.7; CH3).
13C NMR (151 MHz, CDCl3, 300 K): δ = 151.9; 136.8; 127.3; 116.2;
114.1; 27.3; 15.0.
Experimental Section
NMR Spectroscopy. 1H NMR spectra were recorded on a high-field
spectrometers (1H 600.15 MHz and 500 MHz, 13C 151 MHz), equipped
with a broadband inverse gradient probehead. Spectra were referenced
to the residual solvent signals. A typical spectrum for paramagnetic
species was collected over a 400 ppm spectral window with 64K data
points with 5000 transients for the experiment and a 50 ms prepulse
delay. The free induction decay (FID) was apodized using exponential
multiplication depending on the natural line width.
2-ethylisophthalaldehyde
9:
The
conversion
of
2-
ethylisophthalonitrile
7
to 2-ethylisophthalaldehyde
9
followed the
procedure described in literature. [36] 1H NMR (600 MHz, CDCl3, 300 K): δ
= 10.41 (s, CHO); 8.07 (d; 3J = 7.4; 2,4-H); 7.52 (t; 3J = 7.4; 3-H); 3.50 (q;
3J = 7.3; CH2); 1.33 (t; 3J = 7.3; CH3). 13C NMR (151 MHz, CDCl3, 300 K):
δ = 191.4; 136.4; 126.9; 131.5; 125.2; 29.8; 17.3.
Mass Spectrometry. High resolution and accurate mass spectra were
recorded on a Bruker apex ultra FTMS and a Bruker microTOF-Q
spectrometers using the electrospray technique.
(2-ethyl-1,3-phenylene)bis(phenylmethanol)
10:
2-
UV-Vis Spectroscopy. Electronic spectra were recorded on a Varian
Carry-50 Bio spectrophotometer.
ethylisophthalaldehyde (1 g, 6.76 mmol) was dissolved in dry degassed
THF (100 mL). PhMgBr (3 mL of a 3M solution in Et2O, 9 mmol) was
added and the mixture was stirred for 1 h. The reaction product was
hydrolyzed with aqueous ammonium chloride and extracted with CH2Cl2.
The extracts were washed twice with water and the solvent was removed
under reduced pressure. Yield: 84%. 1H NMR (500 MHz, CDCl3, 300 K,
mixture of stereomers): 7.41, 7.38 (2t; 3J = 7.5; 2,3,4-H); 7.34–7.30 (m;
Ar); 6.12 (s; CH-OH); 2.15 (s; OH); 1.85 (q; 3J = 7.1; CH3); 1.00 (t; 3J =
7.1; CH2).
Electrochemical measurements (CH2Cl2, 0.03M TBAP) were
performed on PGStat 100 (Autolab) using a glassy-carbon working
electrode, platinum wire as the auxiliary electrode, and Ag/AgCl as a
reference electrode. The voltammograms were referenced against the
halfwave potential of Fc/Fc+ (internal standard).
Theoretical calculations. Geometry optimizations were carried out with
the Gaussian 09 software package[66] within unconstrained C1 symmetry,
with starting coordinates derived from molecular mechanics or X-ray
analysis. Becke's three-parameter exchange functionals with the gradient
corrected correlation formula of Lee, Yang and Parr (DFT-B3LYP)[67, 68]
were used with the 6-31G(d,p) basis set with the LANL2DZ
Rhodium(III) 22-(μ-methylene)-m-benziporphyrin: 1-Me[18] (20 mg,
0,032 mmol, 1 equiv) and [Rh(CO)2Cl]2 (12 mg, 0,032 mmol, 1 equiv)
were added to benzene (30 mL) and the mixture was refluxed for 1 h
under nitrogen. Products were subjected to chromatography (silica gel,
mesh 70-230; CH2Cl2). The final compound was eluted with 50% ethyl
This article is protected by copyright. All rights reserved.

10.1002/chem.201704411
Chemistry - A European Journal
FULL PAPER
acetate (solution in CH2Cl2) as a brown, slow moving fraction. Yield: 93%.
3J = 7.0; o-Ph); 8.69 (d; 3J = 5.3; 8-H); 8.66 (d; 3J = 4.9; 17-H); 8.64 (d; 3J
= 4.7; 13-H); 8.59 (d; 3J = 4.7; 12-H); 8.56 (d; 3J = 4.9; 18-H); 8.49 (d; 3J
= 5.3; 7-H); 8.30–8.27 (m; o-Ph); 8.26 (d; 3J = 7.3; o-Tol); 8.14 (d; 3J =
7.3; o-Tol); 8.00–7.99 (m; o-Ph); 7.97 (d; 3J = 7.3; o-Tol); 7.89–7.86 (m;
o-Ph, o-Tol); 7.81–7.57 (m; m,p-Ph); 7.66–7.63 (m; m,p-Ph); 7.60 (d; 3J =
7.7; m-Tol); 7.60 (d; 3J = 7.7; m-Tol); 7.57 (d; 3J = 7.7; m-Tol); 7.52 (d; 3J
= 7.8; m-Tol); 7.47 (d; 3J = 7.5; m-Tol); 2.67 (s; CH3); 2.65 (s; CH3); −0.84
1H NMR (500 MHz, CDCl3, 300 K): δ = 8.62 (t; 3J = 7.7; 3-H); 8.32 (d; 3J
3
= 7.7; 2,4-H); 7.93 (d; J = 5.3; 8,19-H); 7.89 (s; 13,14-H); 7.88–7.77 (m;
o-Ph); 7.82 (d; 3J = 7.1; o-Tol); 7.71–7.64 (m; m,p-Ph); 7.65 (d; 3J = 5.3;
9,18-H); 7.45–7.39 (m; m-Tol); 2.55 (s; Tol-CH3); −0.74 (s. 26-H). 13C
NMR (151 MHz, CDCl3, 300 K): δ = 159.4; 156.9; 152.5; 150.9; 146.9;
145.4; 142.5; 140.6; 139.8; 138.4 (2x); 137.0; 136.7(2x); 135.8(2x);
134.7; 134.5; 134.0; 129.2; 128.6; 128.2; 127.8; 124.7; 54.8; 44.3; 21.8.
HRMS (ESI) m/z calcd for C49H35N3Rh [M+H]+: 768.1886, found:
768.1868.
3
3
3
(d; JAX = 8.9; 26-H); −1.99 (dd; JAX = 8.9; JBX = 14.0; 25-H); −3.75 (d;
3JBX = 14.0; 26-H). 13C NMR – partial data based on HSQC and HMBC
spectrum – δ = 143.4; 137.5; 135.9; 135.1; 134.9; 134.7; 134.2; 134.1;
134.0; 133.9; 133.8(2x); 133.6(2x); 133.5; 133.4; 132.7; 132.6(2x);
132.4(2x); 131.8(2x); 131.2(2x); 130.8; 128.7; 128.0(2x); 127.8(2x);
127.7(2x); 127.5; 127.2(2x); 127.1; 96.8; 63.0; 56.5. HRMS (ESI) m/z
calcd for C49H35N3Rh [M]•+: 768.1886, found: 768.1890.UV-Vis (CH2Cl2,
298 K, λ, log ε): 428(4,57), 492(4,36). 568(3.75).
Rhodium(III) 22(μ-ethylidene)-m-benziporphyrin 12: 1-Et (20 mg,
0,032 mmol, 1 eq) and [Rh(CO)2Cl]2 (12 mg, 0,032 mmol, 1 eq) were
added to benzene and the mixture was refluxed for 1 hour under nitrogen.
The only fraction from column chromatography (silica gel, mesh 70-230;
CH2Cl2/ethyl acetate (10:1)) contains 12. Yield: 91%.
Alternative route: 23 was chromatographed using the SilicaGel (mesh 70-
230, CH2Cl2) column. The green 23 converted to greyish brown 12. The
final product was eluted with 15% ethyl acetate. Yield: 50 %.
19-CHO1 and 19-CHO2: 1H NMR (600 MHz, CDCl3, 300 K): δ = 9,70 (s;
31-H); 9.52 (s; 32-H); 9.41 (s; 22-H); 9.34 (s; 21-H); 8.70–8.51 (m;
7,8,12,13,17,19-H, o-Ph); 8.27–7.81 (m, o-Ph, o-Tol); 7.68–7.42 (m, m,p-
Ph, m-Tol); 2.64 (s; CH3); 2.63 (s; CH3); 2.62 (s; CH3); 2.61 (s; CH3);
1H NMR (500 MHz, CDCl3, 300 K): δ = 8.69 (d; 3J = 7.6; 4-H); 8.65 (t; 3J
= 7.6; 3-H); 8.00 (d; 3J = 7.6; 2-H); 7.97 (d; 3J = 5.3; 18-H); 7.88 (d; 3J =
5.4; 9-H); 7.94–7.92 (m, o-Ph); 7.87 (d; 3J = 5.4; 8-H); 7.83 (d; 3J = 7.1;
o-Tol); 7.80-7.79 (m, o-Ph); 7.78 (d; 3J = 5.3; 19-H); 7.69–7.64 (m, m,p–
Ph, 13,14-H) 7.45–7.38 (m, m-Tol); 2.55 (s; p-Tol); 2.54 (s; p-Tol); −0.41
(q, 3J = 7.0; 26-H); −2.11 (d, 3J = 7.0; 27-H). 13C NMR (151 MHz, CDCl3,
300 K): δ= 178.4; 177.8; 159.1; 159.0; 158.9; 157.9; 157.5; 157.3; 157.0;
155.6; 155.3; 152.3; 151.9; 150.9; 150.3; 149.9; 142.8; 142.7; 141.4(2x);
140.9; 140.8(2x); 139.8; 138.2; 137.6; 137.0; 136.5; 136.1; 135.7; 134.8;
134.7; 133.2; 131.0; 128.9; 128.6; 128.5; 128.4; 127.9; 127.8; 127.6;
127.5; 125.1; 125.0; 57.9; 21.3(2x); 16.4. HRMS (ESI) m/z calcd for
C50H37N3Rh [M+H]+: 782.2043, found: 782.1987.
Rhodium(III) 21-(μ-methylene)-21-carbaporphyrin 13: 11 was stirred
with a base (trimethylamine or 2,4,6-trimethylpyridine) for 1 hour. After
that the product was subjected to chromatography (silica gel, mesh 70-
230; CH2Cl2). The final compound was eluted as a second, pinkish-brown
fraction (solution in CH2Cl2). Yield: 33%.1H NMR (500 MHz, CDCl3, 300
K): δ = 9.35 (s; 3-H); 9.16 (s; 2-CHO); 8.45–8.31 (m; 7,8,12,13,17,18-H);
8.13–8.05 (m; o-Ph, o-Tol); 7.88–7.79 (m; m,p-Ph, m-Tol); 2.61 (s; p-Tol);
−3.95 (dd; 2J = 10.2; 25-H). HRMS (ESI) m/z calcd for C49H35N3ORh
[M+H]+: 784.1835, found: 784.1800.
−0.74 (d, 3JAX = 9.4; 261-H); −0.76 (d, 3JAX = 9.3; 262-H); −1.89 (dd, 3JAX
=
9.4; 3JBX = 14.5; 251-H); −2.04 (dd, 3JAX =9.3; 3JBX = 14.1; 252-H); −3.69 (d,
3
3JBX = 14.5; 261-H); −3.81 (d, JBX = 14.1; 261-H);HRMS (ESI) m/z calcd
for C50H35N3ORh [M]•+ : 796.1835, found: 796.1846.
Rhodium(III) (σ-ethyl)-m-benziporphyrin 23: 3 was stirred with
EtMgBr (1 μl) in anaerobic conditions in the 1H NMR tube. The
conversion was almost quantitative (~95%) after 15 minutes. 1H
NMR (600 MHz, CDCl3, 300 K): δ = 7.69 (d; 3J = 7.6; 2,4-H); 7.66–
7.57 (m; o,m-Ph, o-Tol); 7.54–7.53 (m, p-Ph, o,m-Tol); 7.37 (s;
3
3
13,14-3J = 5.1; 8,19-H); 7.11 J = 5.1; 9,18-H); 6.80 (d; J = 7.6; 3-
H); 2.23 (s; p-Tol); 0.70 (q; 3J = 7.3; JRhH = 2.2; 26-H); −0.73 (t; 3J =
7.3; JRhH = 2.2; 27-H).
Acknowledgements
Financial support from the National Science Centre, Poland
(2012/04/A/ST5/00593) is kindly acknowledged. The Wrocław
Supercomputer Centre (KDM WCSS) is kindly acknowledged for
sharing computation resources necessary for DFT calculations
General procedure for 15, 16 and 17:
12 was applied to the column with Al2O3 (basic, grade III). The first brown
fraction was collected and subjected to another chromatography (silica
gel, mesh 70-230; CH2Cl2). The first and second fractions were collected
giving 15 (reddish-brown) and mixture of 16 and 17 (pinkish-brown)
respectively. Yield: 15 – 23%, 16 and 17 – 21%.
Keywords: carbaporphyrinoid • C-C bond activation • reversible
bond cleavage • migration • rhodium
Rhodium(III) 21-(μ-ethylidene)-21-carbaporphyrin 15: 1H NMR (500
MHz, CDCl3, 300 K): δ = 9.28 (d; 3J = 4.3; 3-H); 8.98 (d; 3J = 4.3; 2-H);
8.46 (d; 3J = 4.8; 7-H); 8.44–8.43 (m; o-Ph); 8.42 (d; 3J = 4.3; 18-H); 8.41
(d; 3J = 4.3; 17-H); 8.40 (d; 3J = 7.4; o-Ph); 8.39 (d; 3J = 4.8; 13-H); 8.36
(d; 3J = 4.8; 8-H); 8.17 (d; 3J = 7.6; o-Tol); 8.10 (d; 3J = 7.6; o-Tol); 7.89–
7.85 (m; o-Ph); 7.84 (d; 3J = 7.4; o-Tol); 7.80 (d; 3J = 7.4; o-Tol); 7.79–
7.77 (m; o,m-Ph); 7.72–7.66 (m; m,p-Ph); 7.52 (d; 3J = 7.7; m-Tol); 7.49
(d; 3J = 7.7; m-Tol); 7.49 (d; 3J = 7.2; m-Tol); 7.42 (d; 3J = 7.2; m-Tol);
2.64 (s; CH3); −3.12 (q, 3J = 6.7; 25-H); −3.60 (d, 3J = 6.7; 26-H). 13C
NMR – partial data based on HSQC and HMBC spectrum – δ = 151.2;
149.0. 148.6; 147.4; 147.2; 144.5; 143.9; 143.7; 141.0; 139.0; 138.6;
138.2; 138.0; 137.5; 137.0(2x); 136.1; 135.5; 134.7; 134.0; 133.5;
133.7(3x); 132.5; 131.9; 131.1(2x); 127.3; 127.2(2x); 127.0; 124.1; 56.4;
49.5; 21.4; 13.1. UV-Vis (CH2Cl2, 298 K, λ, log ε): 339(3.87), 447(4.00),
573(3.19).
Reference List
[1]
M. Pawlicki, L. Latos-Grażyński, in Handbook of Porphyrin Science:
with Applications to Chemistry, Physics, Materials Science,
Engineering, Biology and Medicine ,Vol. 2, (Eds.: K. M. Kadish, K. M.
Smith, R. Guilard), World Scientific Publishing, Singapore 2010, pp.
104-192.
[2]
[3]
B. Szyszko, L. Latos-Grażyński, Chem.Soc.Rev. 2015, 44, 3588-3616.
M. Toganoh, H. Furuta, in Handbook of Porphyrin Science: with
Applications to Chemistry, Physics, Materials Science, Engineering,
Biology and Medicine, Vol. 2, (Eds.: K. M. Kadish, K. M. Smith, R.
Guilard), World Scientific Publishing, Singapore 2010, pp. 295-367.
T. D. Lash, Chem.Rev., 2017, 117, 2313-2446.
Rhodium(III) (2- or 3-formyl)-21-(μ-ethylidene)-21-carbaporphyrin 16
and 17: 1H NMR (600 MHz, CDCl3, 300 K): δ = 9.35 (s; 31-H); 9.34 (s; 32-
H); 9.24 (s; 22-H); 9.05 (s; 21-H); 8.42–8.27 (m; 7,8,12,13,17,19-H, o-Ph);
8.15–8.02 (m, o-Tol); 7.79–7.62 (m, m,p-Ph); 7.48–7.38 (m, m-Tol); 2.59
(s; CH3); 2.58 (s; CH3); −2.80 (q, 3J = 6.8; 251-H); −2.74 (q, 3J = 6.8; 252-
H); −3.19 (d, 3J = 6.8; 261-H); −3.26 (d, 3J = 6.8; 262-H).
[4]
[5]
M. Stępień, L. Latos-Grażyński, N. Sprutta, P. Chwalisz, L.
Szterenberg, Angew.Chem.Int.Ed. 2007, 46, 7869-7874.
M. Stępień, N. Sprutta, L. Latos-Grażyński, Angew.Chem.Int.Ed. 2011,
50, 4288-4340.
[6]
[7]
In the air, both in solution and in solid, 15 (16 and 17) converts to 19 (19-
CHO1 and 19-CHO2) (the complete transformation in a few hours).
Alternative route: 15 or 16/17 was stirred in the NMR tube (CD2Cl2) with
HCl (1 μl). 18 or 18-CHO has been detected after 24 hr. The
isomerization of 18 or 18-CHO facilitated by the added base (2 μl, e.g.
Et3N) converts the 21-ethylidene unit into the 21-vinyl one (complete
transformation - ca. 72 h).
Y. Tanaka, S. Saito, S. Mori, N. Aratani, H. Shinokubo, N. Shibata, Y.
Higuchi, Z. S. Yoon, K. S. Kim, S. B. Noh, J. K. Park, D. Kim, A. Osuka,
Angew.Chem.Int.Ed. 2008, 47, 681-684.
[8]
[9]
T. Tanaka, A. Osuka, Chem.Rev. 2017, 2584-2640.
M. Pawlicki, L. Latos-Grażyński, Chem.Asian J. 2015, 10, 1438-1451.
Rhodium(III) 21-vinyl-21-carbaporphyrin 19: 1H NMR (500 MHz,
CDCl3, 300 K): δ = 9.47 (d; 3J = 4.6; 3-H); 9.27 (d; 3J = 4.6; 2-H); 8.75 (d;
[10] H. Furuta, H. Maeda, A. Osuka, Org.Lett. 2002, 4, 181-184.
This article is protected by copyright. All rights reserved.

10.1002/chem.201704411
Chemistry - A European Journal
FULL PAPER
[11] P. J. Chmielewski, L. Latos-Grażyński, I. Schmidt, Inorg.Chem. 2000,
39, 5475-5482.
[44] P. J. Chmielewski, L. Szterenberg, M. Siczek, Chem.Eur.J. 2011, 17,
1009-1020.
[12] M. Pawlicki, I. Kańska, L. Latos-Grażyński, Inorg.Chem. 2007, 46,
6575-6584.
[45] A. C. Gehrold, T. Bruhn, H. Schneider, U. Radius, G. Bringmann,
J.Org.Chem. 2015, 80, 12359-12378.
[13] I. Grocka, L. Latos-Grażyński, M. Stępień, Angew.Chem.Int.Ed. 2013,
52, 1044-1048.
[46] A. C. Gehrold, T. Bruhn, H. Schneider, U. Radius, G. Bringmann, Org.
Lett. 2015, 17, 210-213.
[14] I. Simkowa, L. Latos-Grażyński, M. Stępień, Angew.Chem.Int.Ed. 2010,
49, 7665-7669.
[47] A. Vigalok, L. J. W. Shimon, D. Milstein, Chem.Commun. 1996, 1673-
1674.
[15] B. Szyszko, L. Latos-Grażyński, L. Szterenberg, Angew.Chem.Int.Ed.
2011, 50, 6587-6591.
[48] F. A. Cotton, E. V. Dikarev, M. A. Petrukhina, S. E. Stiriba,
Organometallics 2000, 19, 1402-1405.
[16] B. Szyszko, K. Kupietz, L. Szterenberg, L. Latos-Grażyński,
Chem.Eur.J. 2014, 20, 1376-1382.
[49] C. L. Higgitt, A. H. Klahn, M. H. Moore, B. Oelckers, M. G. Partridge, R.
N. Perutz, J.Chem.Soc., Dalton Trans. 1997, 1269-1280.
[50] F. A. Cotton, E. V. Dikarev, M. A. Petrukhina, M. Schmitz, P. J. Stang,
Inorg.Chem. 2002, 41, 2903-2908.
[17] A. Idec, L. Szterenberg, L. Latos-Grażyński, Chem.Eur.J. 2015, 21,
12481-12487.
[18] K. Hurej, M. Pawlicki, L. Latos-Grażyński, Chem.Eur.J. 2017, 23, 2059-
2066.
[51] S. Alvarez, Dalton Trans. 2013, 42, 8617-8636.
[52] B. Rybtchinski, L. Konstantinovsky, L. J. W. Shimon, A. Vigalok, D.
Milstein, Chem.Eur.J. 2000, 6, 3287-3292.
[19] K. Hurej, M. Pawlicki, L. Szterenberg, L. Latos-Grażyński,
Angew.Chem.Int.Ed. 2016, 55, 1427-1431.
[53] F. A. Walker, in Handbook of Porphyrin Science: with Applications to
Chemistry, Physics, Materials Science, Engineering, Biology and
Medicine ,Vol. 2, (Eds.: K. M. Kadish, K. M. Smith, R. Guilard), World
Scientific Publishing, Singapore 2010, pp. 11-304.
[20] M. Stępień, L. Latos-Grażyński, L. Szterenberg, J. Panek, Z. Latajka,
J.Am.Chem.Soc. 2004, 126, 4566-4580.
[21] C. H. Hung, F. C. Chang, C. Y. Lin, K. Rachlewicz, M. Stępień, L.
Latos-Grażyński, G. H. Lee, S. M. Peng, Inorg.Chem. 2004, 43, 4118-
4120.
[54] F. A. Walker, in The Porphyrin Handbook ,Vol. 5, (Eds.: K. M. Kadish,
K. M. Smith, R. Guilard), Academic Press, San Diego, CA 2000, pp.
81-183.
[22] M. Stępień, L. Latos-Grażyński, J.Am.Chem.Soc. 2002, 124, 3838-
3839.
[55] S. Nardis, D. O. Cicero, S. Licoccia, G. Pomarico, B. B. Berna, M.
Sette, G. Ricciardi, A. Rosa, F. R. Fronczek, K. M. Smith, R. Paolesse,
Inorg.Chem. 2014, 53, 4215-4227.
[23] M. Murakami, T. Matsuda, Chem.Commun. 2011, 47, 1100-1105.
[24] F. Chen, T. Wang, N. Jiao, Chem. Rev. 2014, 114, 8613-8661.
[25] K. Ruhland, Eur.J.Org.Chem. 2012, 2683-2706.
[26] K. J. Jonasson, A. V. Polukeev, R. Marcos, M. S. G. Ahlquist, O. F.
Wendt, Angew.Chem. Int.Ed. 2015, 54, 9372-9375.
[27] D. Ellis, D. McKay, S. A. Macgregor, G. M. Rosair, A. J. Welch,
Angew.Chem.Int.Ed. 2010, 49, 4943-4945.
[56] B. B. Wayland, A. E. Sherry, G. Poszmik, A. G. Bunn, J.Am.Chem.Soc.
1992, 114, 1673-1681.
[57] F. Asaro, G. Costa, R. Dreos, G. Pellizer, W. von Philipsborn,
J.Organomet.Chem. 1996, 513, 193-200.
[58] C. M. Frech, L. J. Shimon, D. Milstein, Chem.Eur.J. 2007, 13, 7501-
7509.
[28] L. Kaplan, L. A. Wendling, K. E. Wilzbach, J.Am.Chem.Soc. 1971, 93,
3819-3820.
[59] C. M. Frech, D. Milstein, J.Am.Chem.Soc. 2006, 128, 12434-12435.
[60] M. Gandelman, L. Konstantinovski, H. Rozenberg, D. Milstein,
Chem.Eur.J. 2003, 9, 2595-2602.
[29] C. Krempner, H. Reinke, R. Wustrack, Inorg.Chem.Comm. 2007, 10,
239-242.
[30] R. M. Pope, S. L. VanOrden, B. T. Cooper, S. W. Buckner,
Organometallics 1992, 11, 2001-2003.
[61] M. E. van der Boom, D. Milstein, Chem.Rev. 2003, 103, 1759-1792.
[62] A. Vigalok, B. Rybtchinski, L. J. W. Shimon, Y. Ben-David, D. Milstein,
Organometallics 1999, 18, 895-905.
[31] A. Sattler, G. Parkin, Nature 2009, 463, 523-526.
[32] S. Hu, T. Shima, Z. Hou, Nature 2014, 512, 413-415.
[33] D. Kvaskoff, H. Lueerssen, P. Bednarek, C. Wentrup, J.Am.Chem.Soc.,
2014, 136, 15203-15214.
[63] N. V. Shokhirev, F. A. Walker, J.Phys.Chem. 1995, 99, 17795-17804.
[64] L. Szterenberg, L. Latos-Grażyński, J. Wojaczyński, ChemPhysChem
2002, 3, 575-583.
[34] B. Szyszko, L. Latos-Grażyński, Organometallics, 2011, 30, 4354-4363.
[35] Y. Mao, V. Boekelheide, J.Org.Chem. 1980, 45, 2746-2749.
[36] T. Toyoshima, S. Yoshida, S. Watanabe, Tetrahedron 2013, 69, 1904-
1911.
[65] L. Szterenberg, L. Latos-Grażyński, J. Wojaczyński, ChemPhysChem
2003, 4, 691-698.
[66] G. W. T. J. Frisch, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R.
Cheeseman, G. Scalmani, V. Barone, B. Mennucci, G. A. Petersson, H.
Nakatsuji, M. Caricato, X. Li, H. P. Hratchian, A. F. Izmaylov, J. Bloino,
G. Zheng, J. L. Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda,
J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T.
Vreven, J. A. Montgomery, Jr., J. E. Peralta, F. Ogliaro, M. Bearpark, J.
J. Heyd, E. Brothers, K. N. Kudin, V. N. Staroverov, R. Kobayashi, J.
Normand, K. Raghavachari, A. Rendell, J. C. Burant, S. S. Iyengar, J.
Tomasi, M. Cossi, N. Rega, J. M. Millam, M. Klene, J. E. Knox, J. B.
Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E.
Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W.
Ochterski, R. L. Martin, K. Morokuma, V. G. Zakrzewski, G. A. Voth, P.
Salvador, J. J. Dannenberg, S. Dapprich, A. D. Daniels, Ö. Farkas, J.
B. Foresman, J. V. Ortiz, J. Cioslowski, D. J. Fox, Gaussian 09,
Revision E.01, Wallingford CT, 2009.
[37] M. Stępień, L. Latos-Grażyński, Chem.Eur.J. 2001, 7, 5113-5117.
[38] T. D. Lash, Org.Lett. 2011, 13, 4632-4635.
[39] M. Stępień, L. Latos-Grażyński, T. D. Lash, L. Szterenberg,
Inorg.Chem. 2001, 40, 6892-6900.
[40] O. V. Zenkina, E. C. Keske, R. Wang, C. M. Crudden, Organometallics
2011, 30, 6423-6432.
[41] A. Angelini, M. Aresta, A. Dibenedetto, C. Pastore, E. Quaranta, M. R.
Chierotti, R. Gobetto, I. Papai, C. Graiff, A. Tiripicchio, Dalton Trans.
2009, 7924-7933.
[42] H. Kubo, T. Aida, S. Inoue, Y. Okamoto, J.Chem.Soc.Chem.Commun.
1988, 1015-1017.
[67] C. T. Lee, W. T. Yang and R. G. Parr, Phys. Rev. B, 1988, 37, 785-789.
[68] A. D. Becke, Phys. Rev. A, 1988, 38, 3098-3100.
[43] K. Konishi, Y. Takahata, T. Aida, S. Inoue, R. Kuroda, J.Am.Chem.Soc.
1993, 115, 1169-1170.
This article is protected by copyright. All rights reserved.

10.1002/chem.201704411
Chemistry - A European Journal
FULL PAPER
Entry for the Table of Contents (Please choose one layout)
Layout 1:
FULL PAPER
The distinctive macrocyclic
environment of rhodium(III)
carbaporphyrinoids created an
opportunity to detect a contraction
of 22-alkylated m-phenylene to
cyclopentadiene via a perimeter
extrusion of carbon atom and to
trap unique organometallic
transformations of inner core
substituents. In particular the
intramolecular migration of ethyl
from the coordinating carbon atom
to rhodium(III) documented a unique
reversible C(sp2)–C(sp3) bond
cleavage.
K. Hurej, M. Pawlicki, L. Latos-
Grażyński*
Page No. – Page No.
Rhodium-induced reversible C–C
bond cleavage – transformations of
rhodium(III) 22-alkyl-m-
benziporphyrins
Layout 2:
FULL PAPER
Author(s), Corresponding Author(s)*
((Insert TOC Graphic here; max. width: 11.5 cm; max. height: 2.5 cm))
Page No. – Page No.
Title
Text for Table of Contents
This article is protected by copyright. All rights reserved.