Merging of inner and outer ruthenium organometallic coordination motifs within an azuliporphyrin framework

Article abstract of DOI:10.1039/c4cc04271a

The insertion of ruthenium(ii) into an azuliporphyrin (TPAP) has yielded carbonyl ruthenium(ii) azuliporphyrin [Ru(TPAP)(CO)] featuring an equatorial CNNN set of donors. Its azulene moiety serves as the π-coordination platform to accommodate the Ru₄(CO)₉ cluster. This chemistry proved to be general giving rise to a series of bimetallic complexes [M(TPAP){Ru ₄(CO)₉}] (M = Ru(CO), Ni, Pd, Pt).

Full text of DOI:10.1039/c4cc04271a

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Merging of inner and outer ruthenium
organometallic coordination motifs within an
azuliporphyrin framework†
Cite this: Chem. Commun., 2014,
50, 9270
Received 4th June 2014,
Accepted 28th June 2014
Michał J. Białek and Lechosław Latos-Grazynski*
´
˙
DOI: 10.1039/c4cc04271a
www.rsc.org/chemcomm
The insertion of ruthenium(II) into an azuliporphyrin (TPAP) has yielded
carbonyl ruthenium(II) azuliporphyrin [Ru(TPAP)(CO)] featuring an
equatorial CNNN set of donors. Its azulene moiety serves as the
p-coordination platform to accommodate the Ru4(CO)9 cluster. This
chemistry proved to be general giving rise to a series of bimetallic
complexes [M(TPAP){Ru4(CO)9}] (M = Ru(CO), Ni, Pd, Pt).
Scheme 1 Reaction of ruthenium dodecacarbonyl with an azuliporphyrin.
The dynamic development of synthetic routes for carbaporphyrinoids
allows for the exploration of porphyrin-like or porphyrin-unlike
coordination chemistry.1–3 The scope of possible coordination modes
includes metal–carbon (sp2) and metal–carbon (sp3) s-bonds, an detected.2,10–12 This study aims to explore the diversity of
agostic side-on interaction between the inner C–H and a metal centre, ruthenium toward azuliporphyrin coordination modes.
and an intramolecular metal(II)–Z2–CC interaction inside a
A ruthenium(II) ion has been readily inserted into azuliporphyrin
porphyrinoid frame. A unique p-coordination was identified in 1, following the procedure reported previously for ruthenium(II)
metalloceneporphyrinoids.4 More intricate organometallic structures regular porphyrins, to give the corresponding complexes 2 and 3
have been reported which include the tripalladium sandwich in which the azuliporphyrin acts as a dianionic organometallic
complex consisting of two dianionic palladium(II) dicarbaporphyrin ligand (Scheme 1).
units surrounding a palladium(IV) cation,5 and a gable-porphyrin-
type organization where two N-confused porphyrins are bridged by reacted with a sub- or equimolar amount of [Ru3(CO)12]. In the
the rhodium Rh4(CO)4 cluster.6
presence of a ruthenium source in excess, only the cluster complex 3
The regular complex 2 can be detected and isolated when 1 is
Unconventional coordination motifs can be foreseen presuming is obtained (see ESI†). This step reveals the unique coordination
that the p-surface of carbaporphyrinoids provides several potential reactivity of the azulene unit, merging two (inner and perimeter)
metal binding sites by analogy to the p-complexes reported for coordination motifs. Namely, the ruthenium(II) azuliporphyrin binds
tetrapyrrolic ligands where the external coordination involves the Ru4(CO)9 cluster taking advantage of the azulene p-surface.
pyrrole fragments.7
Observations of reactivity of compound 3 show essentially
Facile introduction of an azulene fragment instead of one three kinds of such toward some nucleophilic agents (deactivated
pyrrolic unit gives an azuliporphyrin8,9 – a highly attractive alumina, pyridine, acetonitrile), i.e. contraction of a seven-membered
candidate for exploration of organometallic chemistry inside a ring leading to demetalated benzocarbaporphyrins, secondary
carbaporphyrinoid core.1 Until now, meso-tetraaryl and b-alkylated cluster reactivity connected with its stepwise substitution and
azuliporphyrins have formed organometallic compounds where a complete cluster removal forming 2.
direct M–C s-bond [M = Ni(II), Pd(II), Pt(II), Ir(III)] has been solely
The effects of p-coordination are highly pronounced in
spectroscopy as well as in the solid state. The H NMR spectra
1
of the tripyrrolic unit, which is common for structures 2 and 3
(Fig. 1), resemble the basic pattern of the azuliporphyrin
consistent with its borderline aromaticity.8,9 The typical spectrum
of 2 affords an AB spin system at d = 7.70, H(7,18), and d 7.62 ppm,
H(8,17), with a coupling constant (3J = 4.9 Hz) typical for a pyrrole
ring in porphyrinoids, which is accompanied by a singlet at
Department of Chemistry, University of Wrocław, F. Joliot-Curie 14,
50-383 Wrocław, Poland. E-mail: lechoslaw.latos-grazynski@chem.uni.wroc.pl
† Electronic supplementary information (ESI) available: Synthetic procedures,
figures of spectra (1H, 13C NMR; HRMS; UV-Vis), detailed crystallographic
description and data. CCDC 1006123–1006129. For ESI and crystallographic data
in CIF or other electronic format see DOI: 10.1039/c4cc04271a
9270 | Chem. Commun., 2014, 50, 9270--9272
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Fig. 1 1H NMR spectra of (a) [Ru(TPAP)(CO)(Py-d5)] (2) 600 MHz, CDCl3,
270 K; (b) [Ru(TPAP)(CO){Ru4(CO)9}] (3) 600 MHz, CD2Cl2, 250 K.
Fig. 2 Presentation of the geometry of the complexes: (a) 2-1, (b) 2-2,
(c) 3, (d) 4. Displacement ellipsoids drawn at 30% probability.
d = 7.69 ppm from H(12,13) of the central pyrrole unit. The
NMR resonances of an azulene unit have been assigned to 2,
namely: 1H NMR – 6.80 H(21,31), 6.38 H(22,32), 6.64 H(23) ppm;
13C NMR – 131.5 C(21,31), 136.9 C(22,32), 135.1 C(23) ppm.
The remarkable relocations of 1H and 13C azulene resonances of
3 (1H NMR: 3.74 H(21,31), 4.84 H(22,32), 1.84 H(23) ppm; 13C NMR:
63.2 C(21,31), 66.7 C(22,32), 32.3 C(23) ppm) reflect a cluster attach-
ment. Actually, the change in the azuliporphyrin coordination
mode determined for 3 can be readily appreciated by an analysis
of coordination shifts defined here as 1H or 13C chemical shift
differences between 2 and 3 at chosen positions (Fig. 1). These
values: 1H NMR – 3.06 H(21,31), 1.54 H(22,32), 4.80 H(23) ppm; 13
C
Fig. 3 Ball-and-stick representations for fragments of 2-1, 2-2, 3 showing
peculiar azulene flexibility.
NMR – 68.3 C(21,31), 70.2 C(22,32), 102.5 C(23) ppm, clearly point
toward the azulene moiety acting as a coordinating unit. Analogous
1
coordination shifts were previously detected in the H NMR and
13C NMR spectra of the ruthenium cluster – regular azulene the seven-membered ring into strong C–HÁÁÁp interactions as
complexes.13,14 Coupling constants for azulene protons have also revealed by analysis of the Hirshfeld surface (Fig. S26, ESI†) as
decreased from about 10 Hz, typical for azulene derivatives, to a well as the higher deformation of the CNNN coordination centre
range of 6–8 Hz.
(Table S2, ESI†). The discussed angle is even higher for structure 3
Further investigation of metal(II) azuliporphyrin coordina- since it amounts to 43.3(3)1. This is the result of cluster-azulene
tion abilities against ruthenium has led to a series of bimetallic interactions (Fig. 2c).
complexes with the general formula [M(TPAP){Ru4(CO)9}],
Compound 3 features an interesting metallic skeleton that can
where M = Ni (4), Pd (5), Pt (6). Chemical shift patterns of be described as a distorted tetrahedron (Ru2, Ru3, Ru4, Ru5) with
these complexes resemble those of 3 (Fig. S3, ESI†), and the close contact to the ruthenium(II) cation (Ru1) (Fig. 4a). Three out of
azulene unit proved to be an unambiguous spectroscopic probe
which could be used to identify the perimeter binding.
The structure of azulene-uncoordinated regular complex 2
has been determined for two forms that differ in the sixth axial
ligand: 4-(N,N-dimethylamine)pyridine – DMAP (2-1) or acetonitrile
(2-2) (Fig. 2a and b). These two structures show the specific
flexibility of the azulene fragment (Fig. 3). Thus, the azulene moiety
is notably prone to conformational changes enforced by external
stimuli. To describe the situation quantitatively, the value of the
angle between the planes generated by the coordination centre
(RuCNNN) and the tropylium ring of azulene can be compared. The
deflection of azulene from the macrocyclic plane is significant and
equals 15.73(13)1 for 2-1 and 28.0(3)1 for 2-2. This much higher
deformation for structure 2-2 is consistent with the involvement of
Fig. 4 Cluster geometry and porphyrin conformations for (a) 3 and (b) 4.
Phenyl rings removed to preserve clarity of the figure.
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the four ruthenium atoms (Ru2, Ru3, Ru4), which construct the distances considered for Ru–Ru bonding interactions detected in
tetrahedron skeleton, are directly coordinated to the azulene moiety ruthenium clusters. The Ru2 atom definitely approaches the Ru1
and also bonded to two terminal carbonyl ligands.
cation at a distance much shorter than that expected for van der
The fourth ruthenium atom (Ru5) is linked to three basal Waals contact. The Ru1–Ru2 distance of 3 can be compared with
ruthenium atoms and its coordination sphere is completed by the longest bonding Ru–Ru contact detected in the first
three terminal carbonyl groups. To enable efficient facial bis(metallabenzene) sandwich complex (bis(Z6-3,5-dimethyl-1-
coordination to the base of the tetrahedron the azulene moiety tricarbonyl-ruthenabenzene)ruthenium) comprising two ruthena-
is strongly bent as described above.
benzene ligands whereas the Ru–Ru distance between the
In fact two modes of cluster coordination have been recognized. ruthenabenzene rings equals 3.38 Å.16 In terms of metal–metal
The five-membered ring of azulene prefers Z5-coordination to one bonded metalloporphyrins the structure of 3 provides an unpre-
Ru2 atom in the standard half-sandwich fashion. The Ru4CO9 cedented structural motif as the sixth position is occupied by the
cluster coordinates all seven carbon atoms of the tropylium moiety ruthenium of the cluster, feasibly involved in a weak Ru1–Ru2
(Fig. 2 and Fig. S28, ESI†). The five carbon atoms are bound to the interaction. A distinct feature of the structure is the very pro-
other two ruthenium atoms in a Z4-coordination mode, with the nounced bending of the Ru1–Ru2 axis from the perfect axial
central carbon atom C(23) bonded to two ruthenium atoms. The position (ca. 451) as a consequence of strain induced by the
fundamental features of the azulene–Ru4(CO)9 unit encompassed incorporation of Ru2 into a Ru4(CO)9 scaffold.
in 3 are reminiscent of the structure seen for the Ru4(CO)9 adduct
The azulene moiety in the ruthenium(II) azuliporphyrin pro-
to 1,3-bis(3-methylthienyl)azulene used as the fundamental vides the suitable p-surface to bind the Ru4(CO)9 cluster. Two
building block in studies on post-coordination of multinuclear conceptually different organometallic motifs are merged in a
transition metal clusters to azulene-based polymers.15
unique three-dimensional architecture. We proved that these
In bimetallic complexes [Ni(TPAP){Ru4(CO)9}] 4, [Pd(TPAP){Ru4- unique coordination abilities of azulene introduced into a
(CO)9}] 5, and [Pt(TPAP){Ru4(CO)9}] 6, the azulene moiety reveals carbaporphyrinoid frame are preserved in other suitable systems
the same coordination mode (Fig. S22–S24, ESI†). The deflection producing a series of bimetallic complexes [M(TPAP){Ru4(CO)9}],
angle between the coordination core and the tropylium ring where M = Ni, Pd, Pt.
is 36.19(9)1 and 32.8(2)1, for 4 and 5, respectively, and less
We thank Professor Tadeusz Lis for valuable discussions.
pronounced for 6 – 24.69(15)1 (Table S3, ESI†). The changes Financial support from the NCN (Grant 2012/04/A/ST5/00593) is
are significant in comparison to geometry of [Pt(TPAP)] (7) where kindly acknowledged.
this angle is 21.8(3)1 and the azulene fragment is twisted in
respect to a macrocyclic frame.
Azulene p-coordination results in the folding of a tripyrrolic
brace (Fig. 2d and 4b). This can be expressed by the Cmeso–M–Cmeso
Notes and references
´
1 M. Pawlicki and L. Latos-Gra˙zynski, in Handbook of Porphyrin
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The highest degree of folding can be noticed for 4, which results in
C5–Ni1–C15 and C10–Ni1–C20 angles equal to 167.28(8)1 and
168.24(9)1, respectively. This can be compared to the nearly planar
[Pt(TPAP)] (7) (Fig. S25, ESI†), where the analogous angles are close
to 1801 (178.4(3)1 and 178.4(2)1, respectively).
Within the tetrahedron of ruthenium atoms the Ru–Ru
distances fall distinctly into two groups (Table S2, ESI†). In
the first set Ru2–Ru4, Ru2–Ru5, Ru2–Ru3, Ru3–Ru4 distances
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atom of the cluster and the azuliporphyrinic metal(II) cation.
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9272 | Chem. Commun., 2014, 50, 9270--9272
This journal is ©The Royal Society of Chemistry 2014