Meso-η1-Metalloporphyrins: Preparation of palladio- And platinioporphyrins and the crystal structure of 5-[bromo-1,2-bis(diphenylphosphino)-ethanepalladio(II)]-10,20-diphenylporphyrin

Article abstract of DOI:10.1039/a806769d

meso-η¹-Palladio- and platinioporphyrins have been isolated for the first time by means of oxidative addition of bromoporphyrins to Pd(0) and Pt(0) complexes; the X-ray crystal structure of the title complex was determined.

Full text of DOI:10.1039/a806769d

1
meso-h -Metalloporphyrins: preparation of palladio- and platinioporphyrins
and the crystal structure of 5-[bromo-1,2-bis(diphenylphosphino)-
ethanepalladio(II)]-10,20-diphenylporphyrin
Dennis P. Arnold,*a Yoshiteru Sakata,b Ken-ichi Sugiurab and Elizabeth I. Worthingtona
a Centre for Instrumental and Developmental Chemistry, Queensland University of Technology, G.P.O. Box 2434,
Brisbane, Australia 4001. E mail: d.arnold@qut.edu.au
b The Institute of Scientific and Industrial Research, Osaka University, Mihogaoka 8-1, Ibaraki, Osaka 567-0047,
Japan
Received (in Cambridge, UK) 1st September 1998, Accepted 21st September 1998
1
meso-h -Palladio- and platinioporphyrins have been iso-
lated for the first time by means of oxidative addition of
bromoporphyrins to Pd(0) and Pt(0) complexes; the X-ray
crystal structure of the title complex was determined.
[Pd(PPh3)4 or Pd2dba3† + PPh3, AsPh3, or dppe] to 5-bro-
moDPP or 5,15-dibromoDPP or the corresponding nickel(II
)
complexes, in argon-purged toluene at 105 °C. The mono-
adducts with the monodentate Group 15 ligands were formed
quantitatively within a few minutes, while the double addition
to form 4 required 40 minutes heating, and the dppe complex 5
required 8 hours heating. The complexes were readily isolated
in high yield by evaporation of the toluene and trituration with
ether. The palladioporphyrins are air-stable solids which
undergo some Br/Cl exchange when dissolved in chlorinated
solvents. We have also extended this chemistry to the analogous
meso-platinioporphyrins. The addition of Pt(PPh3)3 to either
5-bromoDPPNi or 5-bromoDPP free-base in refluxing toluene
initially leads within about 20 minutes to the cis adducts 6 and
8, respectively, as shown by the characteristic 1J(PtP) coupling
constants in the 31P NMR spectra [e.g. for 6, J trans to
porphyrin = 1790 Hz, J trans to Br = 4250 Hz, 2J(PP) = 17
Hz]. These initial adducts isomerise over a period of 6 hours to
the respective trans isomers 7 and 9. The complexes were
Palladium-catalysed coupling reactions have been employed by
a number of research groups to prepare novel porphyrins.
Mercuration/palladation was used by Smith and co-workers to
introduce unsaturated substituents into mono-porphyrins,1 and
one of us first applied palladium/phosphine catalysis to the
formation of bis(porphyrins).2 Numerous coupling reactions of
the Heck, Suzuki, Sonogashira, and Stille types have since been
used to prepare substituted porphyrins and multi-porphyrin
arrays linked by alkenes and alkynes, with or without
accompanying aryl linkers.3,4 The most direct entry to this
chemistry is via meso-haloporphyrins,4 which are readily
prepared in the case of b-unsubstituted porphyrins of the
5,15-diaryl type, such as 5,15-diphenylporphyrin, DPP.5 For
example, 5-bromoDPP and 5-iodoDPP [as the nickel(II) or
zinc(II) complexes], couple easily with terminal alkynes,
organotin or organozinc compounds, in the presence of Pd(II) or
Pd(0) phosphine complexes.4,6 An essential process in these
catalytic cycles appears to be the oxidative addition of the meso-
carbon-to-halogen bond to a zerovalent palladium precursor.
However, until now there were no examples of isolated and
1
characterised by H and 31P NMR, electronic absorption, and
FAB-mass spectra,‡ and in the case of the diphosphine
derivative 5, by X-ray crystallography.§ For all the Pd
complexes except 5, the 31P NMR spectra showed that the Pd(II
centres have the trans geometry.
)
The crystal structure of 5 comprises two independent
molecules in the asymmetric unit. Molecules A and B both
display slightly distorted square-planar coordination about the
1
characterised meso-h -palladioporphyrins. Here we report the
stoichiometric (rather than catalytic) preparations of a number
of such novel organometallic porphyrins, and the single crystal
X-ray structure of one example.
1
Pd(II) atom, which is h -bonded to the meso-carbon of a weakly-
ruffled porphyrin core (maximum deviation from the 24-atom
mean plane = 0.28 Å in molecule A). Molecules A and B differ
most markedly in the dihedral angles between the mean planes
of the porphyrin and the 10,20-phenyl groups. In molecule A,
these angles are 88 and 58°, and in molecule B, 56 and 59°.
There is no obvious reason for the unique orthogonality of the
phenyl ring in molecule A. Fig. 1 shows the coordination plane
of the Pd atom for molecule A. The view from above the
porphyrin ring, shown in space-filling form in Fig. 2, indicates
how the phenyl groups of the diphosphine ligand shield the face
of the porphyrin. This suggests immediately a use for this
methodology in the engineering of cavities with tailored shape
and hydrophobicity above and below a porphyrin ring, without
the typically difficult and tedious synthetic work associated
with ‘capping’ and ‘strapping’ opposite sides of a porphyrin.
Moreover, the use of a chiral diphosphine may offer the
intriguing possibility of generating chiral catalytic metal-
loporphyrins based on the present structural class.
Ph
N
N
N
N
X
M
Y
Ph
M
X
Y
1
2
3
4
5
6
7
8
9
Ni
H
H
H
Pd(PPh3)2Br
Pd(PPh3)2Br
Pd(AsPh3)2Br
H2
H2
Ni
Pd(PPh3)2Br Pd(PPh3)2Br
H2
Ni
H
H
H
H
H
Pd(dppe)Br
The second insertion of the Pt(0) fragment into 5,15-di-
bromoDPPNi is so slow that the interesting compound 10
(containing all three members of the nickel triad) could be
prepared by addition of Pt(PPh3)3, heating for 3 hours, followed
by addition of Pd2dba3/PPh3, and a further 3 hours heating. A
similar but weaker deactivating effect of the Pt(II) fragment was
noted by Stang and co-workers in their work on simpler arylene-
bridged dipalladium and diplatinum organometallics, examples
of which have also recently been reported by Kim et al.7
cis-Pt(PPh3)2Br
trans-Pt(PPh3)2Br
cis-Pt(PPh3)2Br
trans-Pt(PPh3)2Br
Ni
H2
H2
10 Ni
Pd(PPh3)2Br trans-Pt(PPh3)2Br
The palladioporphyrins 1–5 were prepared by addition of the
appropriate stoichiometric amount of palladium(0) precursor
Chem. Commun., 1998, 2331–2332
2331

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linear optical properties on this new class of organometallic
compound. We will be exploring their potential applications in
this field, as well as in catalysis and for the construction of
multi-porphyrin supramolecular arrays.8
We thank Q.U.T. for a Special Small Grant, and the Centre
for Instrumental and Developmental Chemistry for financial
support.
Notes and references
† dba = dibenzylideneacetone (1,5-diphenylpenta-1,4-dien-3-one).
‡ Spectroscopic data for 7: NMR (CDCl3) dH 9.52 (s, meso-H), 9.51, 8.92,
8.66, 8.21 (all d, b-H), 7.9, 7.65 (m, 10,20-Ph), 7.25, 6.65 (m, PPh); dP (vs.
ext. 85% H3PO4) 28.5 [s with 195Pt satellites, J(PtP) 2940 Hz]; UV–VIS
(CH2Cl2) lmax/nm (log e) 415 (5.36), 488 sh (3.57), 523 (4.20), 555 sh
(3.67); FAB-MS maximum of cluster calc. for C68H49BrN4NiP2Pt 1318.16,
found 1318.1.
Fig. 1 Molecular structure of 5 (molecule A), showing the Pd coordination
plane. Selected bond lengths and angles: Pd(1)–Br(1) 2.469(3), Pd(1)–P(1)
2.240(6), Pd(1)–P(2) 2.327(6), Pd(1)–C(5) 2.05(2) Å; P(1)–Pd(1)–P(2)
85.2(2), Br(1)–Pd(1)–P(2) 96.2(2), Br(1)–Pd(1)–C(5) 91.9(5), P(1)–Pd(1)–
C(5) 87.2(6)°.
§ Crystal data for 5: C58H45N4BrPdP2, Mr = 1046.27, monoclinic, space
group P21/c, a = 17.006(6), b = 27.248(8), c = 22.13(1) Å, b = 91.18(5)°,
V = 10254(6) Å3, Z = 8, m(Mo-Ka) = 12.47 cm21, Dc = 1.355 g cm23
,
T = 232(1) K, R = 0.075, Rw = 0.098 for 7246 reflections with I > 3s(I).
CCDC 182/1024.
1 I. K. Morris, K. M. Snow, N. W. Smith and K. M. Smith, J. Org. Chem.,
1990, 55, 1231.
2 D. P. Arnold and L. J. Nitschinsk, Tetrahedron Lett., 1993, 34, 693.
3 See, for example R. Gauler and N. Risch, Eur. J. Org. Chem., 1998,
1193; J.-P. Strachan, S. Gentemann, J. Seth, W. A. Kalsbeck, J. S.
Lindsey, D. Holten and D. C. Bocian, Inorg. Chem., 1998, 37, 1191;
R. W. Wagner, T. E. Johnson, F. Li and J. S. Lindsey, J. Org. Chem.,
1995, 60, 5266; K. S. Chan, X. Zhou, M. T. Au and C. Y. Tam,
Tetrahedron, 1995, 51, 3129; D. P. Arnold and D. A. James, J. Org.
Chem., 1997, 62, 3460.
4 S. G. DiMagno, V. S.-Y. Lin and M. J. Therien, J. Am. Chem. Soc.,
1993, 115, 2513; V. S.-Y. Lin, S. G. DiMagno and M. J. Therien,
Science, 1994, 264, 1105; S. G. DiMagno, V. S.-Y. Lin and M. J.
Therien, J. Org. Chem., 1993, 58, 5983.
5 J. S. Manka and D. S. Lawrence, Tetrahedron Lett., 1989, 30, 6989.
6 R. W. Boyle, C. K. Johnson and D. Dolphin, J. Chem. Soc., Chem.
Commun., 1995, 527; D. P. Arnold, R. C. Bott, H. Eldridge, F. Elms, G.
Smith and M. Zojaji, Aust. J. Chem., 1997, 50, 495.
7 J. Manna, C. J. Kuehl, J. A. Whiteford and P. J. Stang, Organometallics,
1997, 16, 1897; Y.-J. Kim, S.-W. Song, S.-C. Lee, S.-W. Lee, K.
Osakada and T. Yamamoto, J. Chem. Soc., Dalton Trans., 1998,
1775.
Fig. 2 Space-filling version of the molecular structure of 5, viewed from
normal to the porphyrin plane.
8 Sanders and co-workers reported a cyclic trimer comprised of
organoplatinum porphyrins in which the platinum atom is linked to the
porphyrin meso positions by meta-ethynylphenyl units, rather than
directly as in our compounds: L. G. Mackay, H. L. Anderson and
J. K. M. Sanders, J. Chem. Soc., Perkin Trans. 1, 1995, 2269.
The electronic absorption spectra of our compounds are
unexceptional, and the bromobis(phosphine/arsine)metallo
moiety exerts a bathochromic effect of similar magnitude to that
of a simple bromo substituent. The high polarizability of the
heavy metal atoms(s) in direct communication with the
porphyrin p-electrons may confer interesting third-order non-
Communication 8/06769D
2332
Chem Commun., 1998