Double cleavage of sp2 C-H and sp3 C-H bonds on one metal center: DMF-appended cyclometalated platinum(II) and -(IV) porphyrins

Article abstract of DOI:10.1021/ic8019149

DMF-appended cyclometalated platinum(II) and -(IV) porphyrins were synthesized via the double cleavage of sp² C - H and sp³ C - H bonds on one platinum center.

Full text of DOI:10.1021/ic8019149

Inorg. Chem. 2009, 48, 795-797
Double Cleavage of sp2 C-H and sp3 C-H Bonds on One Metal
Center: DMF-Appended Cyclometalated Platinum(II) and -(IV) Porphyrins
Shigeru Yamaguchi, Hiroshi Shinokubo,†,* and Atsuhiro Osuka*
Department of Chemistry, Graduate School of Science, Kyoto UniVersity, Sakyo-Ku, Kyoto
606-8502, Japan
Received October 8, 2008
Scheme 1. Isolation of DMF-Appended Platinum(IV) Porphyrin 3Nia
DMF-appended cyclometalated platinum(II) and -(IV) porphyrins
were synthesized via the double cleavage of sp2 C-H and sp3
C-H bonds on one platinum center.
Porphyrins generally accommodate a variety of metals in
the central cavity, and the research on peripherally metalated
porphyrins is a relatively new area.1 In particular, porphyrins
with a peripheral carbon-transition metal (M-C) σ bond
are still rare.2-4 The pioneering work of such porphyrins
was reported by Arnold et al., who synthesized η1-meso-
palladium or platinum porphyrins by the oxidative addition
of Pt0 or Pd0 species to meso-haloporphyrins.2a Recently, we
have introduced cyclometalation strategy to access these
types of porphyrins by use of coordinating substituents such
as pyridyl groups.3 Matano and co-workers reported the
ꢀ-M-C σ-bond-linked dimers of meso-phosphanylporphyrins
(M ) PdII or PtII).4 Metallacycles on benzene rings have
been extensively investigated in terms of their reactivity,
catalytic activity, and photophysical property.5 However, the
chemistry of peripherally cyclometalated porphyrins is still
in their infancy. Here we report the serendipitous isolation
of novel porphyrin metallacycles constituted by ꢀ-(2-
a Reagents and conditions: (a) 2-iodopyridine, Pd2(dba)3, PPh3, Cs2CO3,
CsF, toluene/DMF/H2O, 100 °C; (b) K2PtCl4, toluene/DMF, 100 °C. Ar )
3,5-di-tert-butylphenyl, Bpin ) 3,3,4,4-tetramethyl-2,5-dioxaboranyl.
pyridyl)porphyrins and N,N-dimethylformamide (DMF) via
the double cleavage of sp3 C-H and sp2 C-H bonds on
one platinum center. The transition-metal complex resulting
from a double-cleaVage eVent of sp2 C-H and sp3 C-H
bonds on one metal center is unprecedented, despite recent
enthusiastic efforts to deVelop a C-H bond functionalization
strategy.6,7
The synthesis of DMF-appended platinum(IV) porphyrin
3Ni is shown in Scheme 1. ꢀ-(2-Pyridyl)porphyrin 2Ni was
prepared by the Suzuki-Miyaura cross-coupling reaction of
ꢀ-borylated porphyrin 1Ni8 with 2-iodopyridine. The reaction
* To whom correspondence should be addressed. E-mail: hshino@
apchem.nagoya-u.ac.jp (H.S.), osuka@kuchem.kyoto-u.ac.jp (A.O.). Fax:
+81-52-789-5113 (H.S.), +81-75-753-3970 (A.O.).
†
Present address: Department of Applied Chemistry, Graduate School
of Engineering, Nagoya University, Nagoya 464-8603, Japan.
(1) Klein Gebank, R. J. M.; Suijkerbuijk, B. M. J. M. Angew. Chem., Int.
Ed. 2008, 47, 7396.
(2) (a) Arnold, D. P.; Sakata, Y.; Sugiura, K.; Worthington, E. I. Chem.
Commun. 1998, 2331. (b) Hartnell, R. D.; Arnold, D. P. Organome-
tallics 2004, 23, 391. (c) Hartnell, R. D.; Arnold, D. P. Eur. J. Inorg.
Chem. 2004, 1262. (d) Hodgson, M. J.; Healy, P. C.; Williams, M. L.;
Arnold, D. P. J. Chem. Soc., Dalton Trans. 2002, 4497. (e) Arnold,
D. P.; Healy, P. C.; Hodgson, M. J.; Williams, M. L. J. Organomet.
Chem. 2000, 607, 41. (f) Atefi, F.; Arnold, D. P. J. Porphyrins
Phthalocyanines 2008, 12, 801.
(3) (a) Yamaguchi, S.; Katoh, T.; Shinokubo, H.; Osuka, A. J. Am. Chem.
Soc. 2007, 129, 6392. (b) Yamaguchi, S.; Katoh, T.; Shinokubo, H.;
Osuka, A. J. Am. Chem. Soc. 2008, 130, 14440.
(4) Matano, Y.; Matsumoto, K.; Nakano, Y.; Uno, H.; Sakaki, S.; Imahori,
H. J. Am. Chem. Soc. 2008, 130, 4588.
(6) (a) Stuart, D. R.; Fagnou, K. Science 2007, 316, 1172. (b) Hull, K. L.;
Sanford, M. S. J. Am. Chem. Soc. 2007, 129, 11904. (c) Xia, J.-B.;
You, S.-L. Organometallics 2007, 26, 4869. (d) Dwight, T. A.; Rue,
N. R.; Charyk, R.; Josselyn, R.; DeBoef, B. Org. Lett. 2007, 9, 3137.
(e) Li, R.; Jiang, L.; Lu, W. Organometallics 2006, 25, 5973.
(7) sp2 C-H and sp3 C-H dehydrogenated cross-coupling reaction has
been reported. In the literature, the authors suggest that the coupling
occurs via the Friedel-Crafts-type reaction mechanism. (a) Li, Z.;
Li, C.-H. J. Am. Chem. Soc. 2005, 127, 6968. For related reactions,
see: (b) Li, Z.; Li, C.-H. J. Am. Chem. Soc. 2005, 127, 3672. (c) Li,
Z.; Li, C.-H. J. Am. Chem. Soc. 2004, 126, 11810. (d) Murahashi,
S.-I.; Komiya, N.; Terai, H. Angew. Chem., Int. Ed. 2005, 44, 6931.
(8) Hata, H.; Shinokubo, H.; Osuka, A. J. Am. Chem. Soc. 2005, 127,
8264.
(5) (a) Albrecht, M.; van Koten, G. Angew. Chem., Int. Ed. 2001, 40,
3750. (b) Dupont, J.; Consorti, C. S.; Spencer, J. Chem. ReV. 2005,
105, 2527. (c) van der Boom, M. E.; Milstein, D. Chem. ReV. 2003,
103, 1759. (d) Singleton, J. T. Tetrahedron 2003, 59, 1837.
10.1021/ic8019149 CCC: $40.75  2009 American Chemical Society
Inorganic Chemistry, Vol. 48, No. 3, 2009 795
Published on Web 01/06/2009

COMMUNICATION
Figure 1. X-ray crystal structure of DMF-appended platinum porphyrins:
(a) top view of 5Ni; (b) side view of 5Ni; (c) top view of 3Ni; (d) side
view of 3Ni. The thermal ellipsoids are scaled to 50% probability level.
meso-Aryl substituents are omitted for clarity.
Figure 2. UV-vis absorption spectra of 2Ni (red), 3Ni (blue), and 5Ni
(green) in CH2Cl2.
of ligand 2Ni with K2PtCl4 at 100 °C for 24 h in a toluene/
DMF solution afforded 3Ni in 8% yield as an air- and
moisture-stable green solid after separation by silica gel
column chromatography.9,10 The parent mass ion peak was
observed at m/z 1345.4783 (calcd for (C70H80N6NiOPtCl2)+
) m/z1345.4762 [(M)+]) in its high-resolution electrospray
ionization time-of-flight (HR ESI-TOF) mass spectrum. In
the 1H NMR spectrum, no meso proton was observed,
suggesting metalation at the meso position. The peak due to
the CHO proton is observed as a singlet at 7.85 ppm, which
has a correlation in the CH-hetero COSY with the peak
observed at 168.0 ppm in the 13C NMR spectrum. The signal
due to the methyl protons of the DMF group is observed as
a singlet at 3.07 ppm. The methylene protons of the DMF
group attached to the Pt atom are not observed at room
temperature but appear as mutually coupled doublet peaks
at 5.49 and 3.59 ppm at -50 °C because of different
circumstances of the two protons. Finally, X-ray diffraction
analysis unambiguously elucidated the structure bearing sp2
C-Pt and sp3 C-Pt bonds in a cis configuration with an
octahedral PtIV center (Figure 1c,d).
Scheme 2. Synthesis of DMF-Appended Platinum(II) Porphyrin 5M
and the Oxidation Reaction of 5Ma
a Reagents and conditions: (a) K2PtCl4, NaOAc, toluene/DMF, 100 °C;
(b) FeCl3 ·6H2O, CH2Cl2/MeOH, rt. Ar ) 3,5-di-tert-butylphenyl.
was carried out in the presence of NaOAc as a proton
scavenger. The reaction proceeded via simultaneous C-H
bond double cleavage to provide DMF-appended platinum(II)
porphyrin 5Ni instead of 3Ni in 64% yield as an air- and
moisture-stable green solid (Scheme 2). The parent mass ion
peak was observed at m/z 1274.5446 (calcd for
(C70H80N6NiOPt)+ ) m/z 1274.5396 [(M)+]) in its HR ESI-
1
TOF mass spectrum. In the H NMR spectrum, no signal
From the reaction mixture, a CO complex 4 was also
isolated in 29% yield (Scheme 1). The CO complex 4 was
characterized by IR [ν(CO) ) 2103 cm-1], mass (HR-ESI:
observed ) m/z 1266.4635 (calcd for (C68H75N5NiPtOCl)
) m/z 1266.4655 [(M + H)+]), 1H NMR and X-ray
diffraction analyses.11 To prevent the generation of CO,
which is probably caused by the decomposition of DMF by
acid generated from the C-H bond cleavage, the reaction
due to a meso proton was observed. Doublet peaks at 4.17
and 2.84 ppm and a singlet peak at 2.99 ppm are assigned
as methylene and methyl protons of the DMF group. In the
13C NMR spectrum, a peak due to the carbonyl carbon of
the DMF group appeared at 168.8 ppm, which has a
correlation in the CH-hetero COSY spectrum with the CHO
1
signal (δ ) 8.13) in the H NMR spectrum.
This procedure works nicely for the synthesis of 5M (M
) Zn, Cu, H2). 2H2 was synthesized from 1H2 as a similar
procedure of the synthesis of 2Ni. 2Zn and 2Cu were
obtained by metalation of 2H2 with the corresponding metal
salts. C-H bond double cleavages between 2M (M ) Zn,
Cu, H2) and DMF also occurred smoothly to provide 5M
(M ) Zn, Cu, H2) in 49%, 39%, and 45% yield, respectively.
The divalent platinum centers of 5M are susceptible to
oxidation reaction: treatment of 5Ni with an excess amount
of FeCl3 · 6H2O in a CH2Cl2/MeOH solution provided plati-
num(IV) complex 3Ni in 73% yield. 3M (M ) Cu, Zn, H2)
was also synthesized by the same procedure in 30%, 36%,
(9) The PtII atom was oxidized to PtIV probably by air in the course of
the reaction. The reaction under an inert atmosphere did not afford
4Ni. For an oxidant-promoted C-H bond activation reaction, see:
Newman, C. P.; Casey-Green, K.; Clarkson, G. J.; Cave, G. W. V.;
Errington, W.; Rourke, J. P. Dalton Trans. 2007, 3170.
(10) The reaction of 1Ni with a platinum(IV) salt in toluene/AcOH provided
a platinum(IV)-bridged cofacial diporphyrin. See ref 3b. However,
none of such diporphyrins was detected in the reaction in toluene/
DMF.
(11) Crystallographic data for 4: C68H74ClN5NiOPt·3CCl4, Mw ) 1728.00,
j
triclinic, space group P1 (No. 2), a ) 11.841(5) Å, b ) 16.521(5) Å,
c ) 19.620(5) Å, R ) 99.387(5)°, ꢀ ) 103.850(5)°, γ ) 93.508(5)°,
V ) 3656(2) Å3, Z ) 2, Dcalc ) 1.569 Mg/cm3, R ) 0.0807 [I >
2.0σ(I)], Rw ) 0.2353 (all data), GOF ) 1.006 [I > 2.0σ(I)].
796 Inorganic Chemistry, Vol. 48, No. 3, 2009

COMMUNICATION
Table 1. Selected Bond Lengths (Å) of 3Ni, 3H2, 5Ni, and 5Zn
of 3M are slightly longer than those of 5M. This fact
indicates repulsion between the Cl ion and π orbitals of the
ligand.
3Ni
3H2
5Ni
5Zn
C20-Pt
C69-Pt
N5-Pt
O-Pt
2.021(4)
2.017(5)
2.116(4)
2.138(3)
2.028(3)
2.042(4)
2.124(3)
2.141(3)
1.960(4)
2.019(4)
2.084(4)
2.129(3)
1.988(5)
2.032(6)
2.074(4)
2.134(4)
The UV-vis absorption spectra of 2Ni, 3Ni, and 5Ni in
CH2Cl2 are shown in Figure 2. The spectrum of 5Ni exhibits
a substantial red shift as compared to that of 2Ni (∆λ ) 64
nm for the Q bands), which is mainly due to expansion of
conjugation by the forced coplanarity of the pyridyl group
and the porphyrin core. Although the absorption spectrum
of 3Ni also exhibits a red shift as compared to that of 2Ni,
the spectrum is substantially more blue-shifted than that of
5Ni (∆λ ) 20 nm for the Q bands). The same tendency is
also observed between 3M and 5M (M ) Cu, Zn, H2; see
the Supporting Information). The result can be accounted
for by the difference in the electron density between PtII and
PtIV atoms. The electron-rich PtII atom raises the highest
occupied molecular orbital (HOMO) energy of the porphyrin
macrocycles to a higher level than the less electron-rich PtIV
atom, while the energy levels of π* orbitals are similar. Thus,
the optical energy gaps of 5M are narrower than those of
3M. In fact, the difference of the lowest unoccupied
molecular orbital energy between 3Ni and 5Ni obtained by
density functional theory calculations is smaller (0.25 eV)
than that of the HOMO energy (0.39 eV) (see the Supporting
Information).
and 53% yield, respectively. 3M or 5M (M ) Zn, H2)
displayed similar spectral features in the 1H NMR as 3Ni or
5Ni.
The crystal structures of 3Ni, 3Zn, 5Ni, and 5H2 were
determined by X-ray diffraction analyses (Figure 1 and the
Supporting Information).12 In all of the complexes, the DMF
group is out of the plane of the porphyrin core because of
the repulsion between methylene protons of DMF and ꢀ
protons of the porphyrin. Because of the repulsion, the Pt
atom is also out of the plane. Thus, deviations of the meso-C
attached to the Pt atom are slightly large. Displacements of
the meso-C from the plane of 24 atoms are 0.784 Å for 3Ni,
0.403 Å for 3H2, 0.852 Å for 5Ni, and 0.395 Å for 5Zn.
The mean plane deviations of porphyrins from the 4N plane
are 0.386 Å for 3Ni, 0.158 Å for 3H2, 0.333 Å for 5Ni, and
0.180 Å for 5Zn. In 3Ni and 5Ni, the macrocycle takes a
ruffled conformation, as is often seen in nickel porphyrins.
The pyridyl groups are rather coplanar (ca. 1-11°) to the
adjacent pyrrole units in the porphyrin core. The coordination
mode of the platinum centers of 5M is square planar and
that of 3M is octahedral. The bond lengths around the Pt
atom are listed in Table 1. Although C69-Pt bond lengths
of 3M and 5M are almost the same, C20-Pt bond lengths
In conclusion, the synthesis of DMF-appended cyclom-
etalated platinum(II) and -(IV) porphyrins was achieved. This
is the first example of double cleavage of sp2 C-H and sp3
C-H bonds on one metal center. The synthesis of other types
of peripherally cyclometalated porphyrins toward reaction
catalysts or functional materials is currently underway in our
laboratory.
(12) Crystallographic data for 3Ni: C70H80Cl2N6NiOPt·3C6H5Cl, Mw
)
j
1683.75, triclinic, space group P1 (No. 2), a ) 14.277(4) Å, b )
16.450(5) Å, c ) 17.619(4) Å, R ) 89.353(12)°, ꢀ ) 78.992(11)°, γ
) 85.740(12)°, V ) 4051(2) Å3, Z ) 2, Dcalc ) 1.380 Mg/cm3, T )
90 K, R ) 0.0521 [I > 2.0σ(I)], Rw ) 0.1396 (all data), GOF ) 1.047
[I > 2.0σ(I)]. Crystallographic data for 3H2: C70H82Cl2N6OPt ·4C6H5Cl,
Acknowledgment. This work was supported by Grant-
in-Aid for Scientific Research on Priority Areas (No.
20037034, “Chemistry of Concerto Catalysis”) from MEXT,
Japan. S.Y. appreciates the JSPS Research Fellowships for
Young Scientists.
j
Mw ) 1739.61, triclinic, space group P1 (No. 2), a ) 9.117(5) Å, b
) 16.014(5) Å, c ) 31.276(5) Å, R ) 78.593(5)°, ꢀ ) 89.631(5)°, γ
) 74.974(5)°, V ) 4318(5) Å3, Z ) 2, Dcalc ) 1.338 Mg/cm3, R )
0.0465 [I > 2.0σ(I)], Rw ) 0.1335 (all data), GOF ) 1.147 [I >
2.0σ(I)]. Crystallographic data for 5Ni: C70H80N6NiOPt·1.5C4H8O2,
j
Mw ) 1407.36, triclinic, space group P1 (No. 2), a ) 11.816(5) Å, b
) 17.236(5) Å, c ) 19.442(5) Å, R ) 115.141(5)°, ꢀ ) 100.801(5)°,
γ ) 93.685(5)°, V ) 3475(2) Å3, Z ) 2, Dcalc ) 1.345 Mg/cm3, R )
0.0453 [I > 2.0σ(I)], Rw ) 0.1094 (all data), GOF ) 1.027 [I >
2.0σ(I)]. Crystallographic data for 5Zn: C73H87N6O2PtZn ·
Supporting Information Available: General procedures, spec-
tral data for compounds, absorption spectra, and CIF files for the
X-ray analysis of 3Ni, 3H, 4, 5Ni, and 5Zn. This material is
available free of charge via the Internet at http://pubs.acs.org.
j
C3H8O·2CHCl3, Mw ) 1639.78, triclinic, space group P1 (No. 2), a
) 11.446(4) Å, b ) 14.031(4) Å, c ) 25.134(6) Å, R ) 82.391(9)°,
ꢀ ) 81.968(11)°, γ ) 78.623(12)°, V ) 3895(2) Å3, Z ) 2, Dcalc
)
1.398 Mg/cm3, R ) 0.0544 [I > 2.0σ(I)], Rw ) 0.1505 (all data),
GOF ) 1.048 [I > 2.0σ(I)].
IC8019149
Inorganic Chemistry, Vol. 48, No. 3, 2009 797