Peripherally-metallated porphyrins: Preparations, spectroscopic properties and structural studies of trans-[PtBr(MDPP)(PPh3)2] (DPP = dianion of 5,15-diphenylporphyrin, M = MnCl, Co, Ni, Zn) and related meso-η1-organoplatinum porphyrins

Article abstract of DOI:10.1039/b205295b

A series of meso-η¹-platiniometalloporphyrins comprising DPP (= dianion of 5,15-diphenylporphyrin) and the first row transition metal ions Mn(III), Co(II), Ni(II) and Zn(II) has been prepared. The syntheses, spectroscopy and voltammetry as well as crystal structures of several of these derivatives are reported. The -PtBr(PPh₃)₂ moiety attached to the macrocycle at the meso position is a strong electron donor, as shown by its effects on spectra, oxidation potentials and reactivity. The crystal structures of trans-[PtBr(MDPP)(PPh₃)₂]·0.5CH₂Cl₂ , where M = Co (16), Ni (14) and Zn (17), and trans-[PtBr(NiDPPBr)(PPh₃)₂] were determined. The structures exhibit non-planar distortions of the macrocycle which are best described as hybrids of typical ruffled and saddled conformations.

Full text of DOI:10.1039/b205295b

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Peripherally-metallated porphyrins: preparations, spectroscopic
properties and structural studies of trans-[PtBr(MDPP)(PPh3)2]
(DPP ؍ dianion of 5,15-diphenylporphyrin, M ؍ MnCl, Co, Ni, Zn)
and related meso-ꢀ1-organoplatinum porphyrins†
Margaret J. Hodgson,a Peter C. Healy,*b Michael L. Williamsb and Dennis P. Arnold*a
a Centre for Instrumental and Developmental Chemistry, School of Physical and Chemical
Sciences, Queensland University of Technology, G.P.O. Box 2434, Brisbane 4001, Australia
b School of Science, Griffith University, Nathan 4111, Australia
Received 3rd May 2002, Accepted 1st October 2002
First published as an Advance Article on the web 4th November 2002
A series of meso-η1-platiniometalloporphyrins comprising DPP (= dianion of 5,15-diphenylporphyrin) and the first
row transition metal ions Mn(), Co(), Ni() and Zn() has been prepared. The syntheses, spectroscopy and
voltammetry as well as crystal structures of several of these derivatives are reported. The –PtBr(PPh3)2 moiety
attached to the macrocycle at the meso position is a strong electron donor, as shown by its effects on spectra,
oxidation potentials and reactivity. The crystal structures of trans-[PtBr(MDPP)(PPh3)2]ؒ0.5CH2Cl2, where M = Co
(16), Ni (14) and Zn (17), and trans-[PtBr(NiDPPBr)(PPh3)2] were determined. The structures exhibit non-planar
distortions of the macrocycle which are best described as hybrids of typical ruffled and saddled conformations.
(PPh3)2]ؒ0.25CH2Cl2 and cis-[PtBr(NiDPP)(PPh3)2].9 A com-
Introduction
mon feature revealed by crystal structures and NMR spectra is
the significant occlusion of the face of the porphyrin by at least
one of the phenyl groups of the phosphine ligand(s). This fact
suggested that these substituents may be useful as moieties for
the facile construction of molecules with a controllable degree
of steric encumbrance above and below the porphyrin plane. In
view of the apparent high stability of these compounds, they
may be useful as catalysts using the metal ion in the centre
of the porphyrin as a catalytically-active site, and the super-
structure provided by the phosphines as a shape-selective
region. By the use of chiral chelating diphosphines, the mole-
cules may also be useful for chiral recognition of ligands
coordinated to the metalloporphyrin. This requires us to be able
to vary the metal ion in the central cavity and include those
which are known to act as biomimetic oxidation and dehalo-
genation catalysts, e.g. Mn, Fe, Co etc. We have therefore
extended our range of organoplatinum derivatives to include
first row metal ions other than Ni(), namely Mn(), Co() and
Zn(). In this paper we report the results of our synthetic and
electrochemical work as well as crystal structures of a number
of these derivatives. These studies have allowed us to investigate
the electronic and steric effects of the –PtX(PPh3)2 moiety
attached to the DPP macrocycle, and will guide us in designing
new molecules based on this novel meso-metalloporphyrin
structural motif.
The chemistry of porphyrins directly bonded to a metal
ion through a peripheral carbon-to-metal σ-bond is very
undeveloped at present. Most representatives of “organo-
metallic” porphyrins comprise those with hydrocarbyl ligands
bound to a metal ion which is coordinated to the pyrrolic nitro-
gens. This field has been thoroughly reviewed recently.1 Of
other possible types of organometallic porphyrins, there exist
examples in which the metal is bonded in either σ or π fashion
to a peripheral aryl substituent2 or η5-bound to a pyrrole ring3
(or to the fused benzo ring of a phthalocyanine4), and there has
been much recent interest in the porphyrinoid macrocycles with
the N3C core—“inverted” or “N-confused” porphyrins5 and
carbaporphyrins6 and their complexes. This last class includes
examples in which the central metal ion is coordinated to three
pyrrole nitrogens and one carbon of the inverted ring (or
in one recent case, to two carbons of a doubly N-confused
macrocycle).
Our interest in η1-meso-metalloporphyrins arose from our
work on Pd-catalysed couplings involving meso-bromo-
porphyrins, especially derivatives of 5,15-diphenylporphyrin
(H2DPP, 1).7 We isolated and characterised by X-ray crystal-
lography the first example of a meso-η1-palladioporphyrin8 and
subsequently expanded this work to include a variety of meso-
palladio- and platinio-porphyrins.9 Amongst other examples of
peripherally-metallated porphyrins, there are the meso-
boronated DPP derivatives prepared by the Therien group,10
various phosphonium11 and arsonium salts,12 and the mercu-
ry() derivatives prepared by the Smith group.13
So far, we have reported a range of DPP complexes contain-
ing the fragments –PdBrL2 and –PtBrL2, where L = PPh3, and
–PdBr(L–L) where L–L = dppe, dppp and dppf.8,9 The X-ray
crystal structures of three of these complexes have been
reported, namely [PdBr(H2DPP)(dppe)],8 trans-[PtBr(H2DPP)-
Experimental
General
Instruments, solvents and general procedures were as described
in our previous publication.9 UV–visible spectra were recorded
1
in CH2Cl2. H NMR spectra were recorded at 300 MHz in
CDCl3, referenced to the solvent residual peak at 7.26 ppm, and
31P spectra at 121.4 MHz in CDCl3, referenced to external 85%
H3PO4. For the electrochemical measurements, a standard
three-electrode configuration was used, with Pt button work-
ing electrode and a Pt wire counter electrode. The reference
electrode comprised a silver wire coated with silver chloride
† Electronic supplementary information (ESI) available: linear displays
of the deviations of the macrocycle atoms from the C20N4 least-squares
plane for complexes 14, 16 and 17 (this work) and free base 12 (from
ref. 9). See http://www.rsc.org/suppdata/dt/b2/b205295b/
DOI: 10.1039/b205295b
J. Chem. Soc., Dalton Trans., 2002, 4497–4504
This journal is © The Royal Society of Chemistry 2002
4497

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Table 1 Correspondence of compound numbers and structures
removed to leave a dark green residue, which was recrystallised
from CH2Cl2–hexane to give a dark green–purple powder
(21 mg, 70%) (Found: C, 67.92; H, 3.86; N, 9.67. C32H20-
ClMnN4ؒ0.5CH2Cl2 requires C, 68.14; H, 3.64; N, 9.63%);
λmax/nm 347 (sh) (ε/103 dm3 molϪ1 cmϪ1 41.5), 367 (53.9), 392
(33.5), 442 (10.2), 470 (94.0), 518 (4.4), 568 (9.0), 599 (5.3), 679
(vbr) (0.7), 750 (0.8); δH Ϫ25 (4H, vbr, βH), Ϫ22 (4H, vbr, βH),
8.4 (vbr, overlapping signals for 5,15-Ph), 45 (vbr, meso-H);
m/z (FAB) 515.0 (MϪCl).
(5,15-Diphenylporphyrinato)cobalt(II) 5. To a solution of
H2DPP (23 mg, 0.05 mmol) in CHCl3 (20 mL) containing tri-
ethylamine (1 mL) was added a solution of Co(OAc)2ؒ4H2O
(187 mg, 0.75 mmol) in methanol (4 mL), and the mixture was
refluxed for 2.5 h. The solvents were removed by rotary evapor-
ation and the residue was dissolved in CH2Cl2, the solution was
washed with water to remove excess salt, then dried with
MgSO4 and concentrated to a dark red residue which was
recrystallised from CH2Cl2–hexane to give a fine orange–purple
powder. The preparation of this compound from Co(acac)2 was
previously reported by Shelnutt and co-workers.17 λmax/nm
401 (ε/103 dm3 molϪ1 cmϪ1 267), 516 (13.7), 543 (sh) (5.6);
δH 9.5 (2H, p-H of 5,15-Ph), 9.7 (4H, m-H of 5,15-Ph), 12.4
(4H, br, o-H of 5,15-Ph), 15.2, 17.2 (each 4H, br, βH), 24.1 (vbr,
meso-H); m/z (FAB) 519.1 (Mϩ).
Compound
M
X
Y
1
2
H2
H2
H2
H
H
Br
H
H
H
H
H
H
H
H
H
H
H
H
H
H
Br
Br
H
H
H
Br
Br
3
4
MnCl
Co
Ni
MnCl
Co
Ni
Zn
H2
H2
MnCl
Co
Ni
Ni
Zn
Ni
5
6
7
8
9
Br
Br
10
11
12
13
14
15
16
17
18
19
20
21
22
23
cis-PtBr(PPh3)2
trans-PtBr(PPh3)2
trans-PtBr(PPh3)2
trans-PtBr(PPh3)2
cis-PtBr(PPh3)2
trans-PtBr(PPh3)2
trans-PtBr(PPh3)2
Br
trans-PtBr(PPh3)2
trans-PtBr(PPh3)2
trans-PdBr(PPh3)2
trans-PdBr(PPh3)2
trans-PdBr(PPh3)2
Metallation of H2DPPBr
H
Br
Br
Chloro(5-bromo-10,20-diphenylporphyrinato)manganese(III)
7. This complex was prepared as described above for 4, from
H2DPPBr (27 mg, 0.05 mmol), yielding the product as fine dark
green–purple crystals (28 mg, 88%). (Found: C, 60.68; H, 3.10;
N, 8.89. C32H19BrClMnN4 requires C, 61.02; H, 3.04; N,
8.90%); λmax/nm 332 (sh) (ε/103 dm3 molϪ1 cmϪ1 32.9), 348
(49.5), 374 (62.5), 400 (50.6), 478 (113), 529 (5.4), 582 (9.7), 617
Ni
Ni
Ni
H2
trans-PtBr(PPh3)2
trans-PtBr(PPh3)2
H
H
Ni
1
(9.1), 693 (vbr) (0.5), 763 (0.5); H NMR data were unobtain-
separated from the working solution by two fritted jackets. The
internal chamber containing the wire was filled with 0.05 M
Bu4NCl–0.45 M Bu4NPF6, and the external chamber contact-
ing the working solution was filled with 0.5 M Bu4NPF6, all
in CH2Cl2. The working solution was pre-purged and sub-
sequently protected with N2. The voltammetry was carried out
at The Research School of Chemistry, The Australian National
University, in CH2Cl2 (freshly distilled from CaH2 under N2)
containing 0.5 M Bu4NPF6, using a PAR model 170 system
linked to an Apple Macintosh LC630 computer via a Maclab
interface controlled by EChem software (AD Instruments).
Electrode potentials are reported using ferrocene as internal
standard [E 0(ox) = ϩ0.55 V]. The stated E 0 values were oper-
ationally defined by the ac peak potentials (or the mean of the
forward and reverse ac peak potentials in some cases where
these were not precisely coincident).
able due to poor solubility and very broad peaks; m/z (FAB)
593.9 (MϪCl).
(5-Bromo-10,20-diphenylporphyrinato)cobalt(II) 8. This com-
plex was prepared as described above for 5, from H2DPPBr
(27 mg, 0.05 mmol), yielding the product as fine orange–purple
crystals (18 mg, 53%) (Found: C, 59.07; H, 3.24; N, 8.47.
C32H19BrCoN4ؒCH2Cl2 requires C, 58.73; H, 3.04; N, 8.06%);
λmax/nm 407 (ε/103 dm3 molϪ1 cmϪ1 247), 525 (13.7); δH 9.59 (2H,
p-H of 10,20-Ph), 9.77 (4H, m-H of 10,20-Ph), 12.6 (4H, br,
o-H of 10,20-Ph), 15.0, 15.6, 16.5, 17.1 (each 2H, br, βH), 27
(vbr, meso-H); m/z (FAB) 597.0 (Mϩ).
Preparation of trans-Pt(PPh3)2Br adducts
trans-[PtBr(MnClDPP)(PPh3)2] 13. (a) Toluene (5 mL) was
placed in a Schlenk flask and heated to 105 ЊC under a stream
of Ar. Pt(PPh3)3 (11.8 mg, 0.012 mmol) was added, followed by
MnCl(DPPBr) (6.3 mg, 0.01 mmol). The Mn porphyrin dis-
solved slowly over an hour. The reaction mixture was stirred
under Ar at 105 ЊC for 5 h, then cooled, and the solvent was
removed under vacuum. The residue was washed with hexane
(3 mL) and then recrystallised from CH2Cl2–hexane to give 13
as dark green crystals (8.6 mg, 64%) (Found: C, 60.05; H, 3.78;
N, 4.12. C68H49BrClMnN4P2Pt requires C, 60.52; H, 3.66; N,
4.15%); λmax/nm 345 (sh) (ε/103 dm3 molϪ1 cmϪ1 25.9), 361 (sh)
(29.7), 386 (35.0), 410 (34.0), 426 (30.8), 484 (71.0), 541 (4.5),
603 (7.0), 635 (10.0); δH Ϫ31 (4H, vbr, βH), Ϫ22 (2H, vbr, βH),
Ϫ17 (2H, vbr, βH), ca. 8.4 (vbr, overlapping signals for 10,20-
Ph), 3–15 (vbr, including peak at ca. 7, P-phenyl groups), 47
(vbr, meso-H); δP Ϫ26, 68 [pair of br d, 2J(PP) 420 Hz, 1J(PtP)
see text and Fig. 1]; m/z (FAB) 1349.1 (Mϩ, 13%), 1313.1
(MϪHCl, 100%). (b) This complex was also prepared as fol-
lows. To a solution of trans-[PtBr(H2DPP)(PPh3)2] (25 mg, 0.02
mmol) in CHCl3 (10 mL) were added 2,6-lutidine (2 drops) and
Porphyrin starting materials H2DPP 1,14 H2DPPBr 214,15 and
H2DPPBr2 314,15 and the complexes NiDPPBr 9, NiDPPBr2 187
and ZnDPPBr 1014 were prepared by literature procedures, as
was Pt(PPh3)3.16 The free-base organometallic porphyrin trans-
[PtBr(H2DPP)(PPh3)2] 12 was available from our previous
work.9 Metal salts were commercial analytical reagent quality.
Crystals for X-ray structure determinations were grown as thin
plates or needles by slow diffusion of hexane into a CH2Cl2
solution of the complex. A list of the complexes is given in
Table 1.
Metallation of H2DPP
Chloro(5,15-diphenylporphyrinato)manganese(III) 4. To
a
solution of H2DPP (23 mg, 0.05 mmol) in CHCl3 (10 mL)
were added 2,6-lutidine (2 drops) and MnCl2ؒ4H2O (158 mg,
0.8 mmol) in methanol (2 mL). After refluxing for 2.5 h, the
solution was washed with water to remove excess metal salt.
After drying the organic solution with MgSO4, the solvent was
4498
J. Chem. Soc., Dalton Trans., 2002, 4497–4504

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MnCl2ؒ4H2O (63 mg, 0.32 mmol) in methanol (2 mL). After
refluxing for 9 h, the solution was washed with water to remove
excess metal salt. After drying the organic solution with
MgSO4, the solvent was removed to leave a dark green residue,
which was recrystallised from CH2Cl2–hexane to give a dark
green crystalline material (17.5 mg, 65%).
added to a Schlenk flask and heated to 105 ЊC under a stream of
argon. Pt(PPh3)3 (98 mg, 0.10 mmol) was added, followed by
NiDPPBr2 18 (27 mg, 0.04 mmol). The mixture was heated at
105 ЊC for 4 h. At this point, TLC analysis showed that no
further change was occurring, so the solvent was removed
under vacuum, and the residue was subjected to column
chromatography on silica gel, eluting with CH2Cl2–hexane
70:30 (v/v). The mono-addition product 19 was eluted first,
followed by 20, and the complexes were recrystallised from
CH2Cl2–hexane as bright purple crystals and fine dark purple
needles, respectively. Data for 19: (21 mg, 37%) (Found: C,
58.48; H, 3.46; N, 3.98. C68H48Br2N4NiP2Pt requires C, 58.48;
H, 3.46; N, 4.01%); λmax/nm 432 (ε/103 dm3 molϪ1 cmϪ1 174), 545
(12.2), 579 (sh) (3.8); δH 6.55–6.75 (18H, m, PPh), 7.2–7.3 (m,
PPh), 7.64 (6H, m, m-, p-H of 10,20-Ph), 7.86 (4H, m, o-H of
10,20-Ph), 8.12, 8.57, 9.29, 9.40 (each 2H, d, βH); δP 23.1 [s,
1J(PtP) 2918 Hz]; m/z (FAB) 1396.0 (Mϩ). Data for 20: (27 mg,
32%) (Found: C, 58.44; H, 3.72; N, 2.64. C104H78Br2N4NiP4Pt2
requires C, 59.02; H, 3.71; N, 2.65%); λmax/nm 443 (ε/103 dm3
molϪ1 cmϪ1 283), 507 (13.3), 551 (23.3), 594 (16.1); δH 6.7 (36H,
m, PPh), 7.3 (m, PPh), 7.60 (6H, m, m-, p-H of 10,20-Ph), 7.85
(4H, m, o-H of 10,20-Ph), 8.07, 9.48 (each 4H, d, βH); δP 22.6
[s, 1J(PtP) 2971 Hz]; m/z (FAB) 2116.5 (Mϩ).
trans-[PtBr(CoDPP)(PPh3)2] 14. (a) Toluene (5 mL) was
placed in a Schlenk flask and heated to 105 ЊC under a stream
of Ar. Pt(PPh3)3 (11.8 mg, 0.012 mmol) was added, followed by
Co(DPPBr) (6 mg, 0.01 mmol). The mixture was stirred under
Ar at 105 ЊC for 6 h, after which it was cooled, and the solvent
was removed under vacuum. The residue was subjected to
chromatography through a short column of silica gel, eluting
with CH2Cl2–hexane–triethylamine 70:30:1 (v/v). Traces of
unreacted CoDPPBr eluted first, followed by the main product,
and then a weak band due to the corresponding cis isomer. The
trans isomer was recrystallised from CH2Cl2–hexane to give
dark purple crystals (8.3 mg, 63%) (Found: C, 60.73; H, 3.71; N,
4.06. C68H49BrCoN4P2Ptؒ0.5CH2Cl2 requires C, 60.65; H, 3.69;
N, 4.10%); λmax/nm 420 (ε/103 dm3 molϪ1 cmϪ1 214), 533 (12.4),
567 (sh) (4.2); δH Ϫ2.2 (vbr, PPh), 1.5 (vbr, PPh), 5.6 (br, PPh),
9.55 (2H, p-H of 10,20-Ph), 9.70 (4H, m-H of 10,20-Ph), 12.6
(4H, br, o-H of 10,20-Ph), 15.5, 15.8, 17.1, 17.9 (each 2H, br,
βH), 29.5 (vbr, meso-H); δP 24.1 [s, 1J(PtP) 2965 Hz]; m/z (FAB)
1317.1 (Mϩ). (b) This complex was also prepared as follows. To
a solution of trans-[PtBr(H2DPP)(PPh3)2] (25 mg, 0.02 mmol)
in CHCl3 (20 mL) containing triethylamine (1 mL) was added a
solution of Co(OAc)2ؒ4H2O (75 mg, 0.3 mmol) in methanol
(4 mL), and the mixture was refluxed for 27 h. The solvents
were removed by rotary evaporation and the residue was dis-
solved in CH2Cl2 and the solution was passed through a short
column of silica gel to remove excess salt. The eluate was con-
centrated to a dark red residue which was recrystallised from
CH2Cl2–hexane to give dark purple crystals (20 mg, 76%).
X-Ray crystallography
Data collection, structure solution and refinement. Unique
data sets were collected at 295 K for compounds 14, 16, 17 and
19 with a Rigaku AFC7R rotating anode diffractometer (ω–2θ
scan mode, monochromated Mo-Kα radiation λ = 0.7107 Å)
to 2θmax = 50Њ, yielding N independent reflections, No with
I > 2σ(I ) being considered ‘observed’. Empirical absorption
correction was applied based on ψ-scans. The structures were
solved by direct methods, expanded by using Fourier tech-
niques and refined by full-matrix least squares on |F| for
observed data using the teXsan for Windows crystallographic
software package, version 1.06, from the Molecular Structure
Corporation.18 Non-hydrogen atoms for all complexes except
16 were refined anisotropically. In 16, marginal crystal quality
yielded data sets that did not support anisotropic refinement of
all of the carbon and nitrogen atoms and these were refined
isotropically; (x,y,z,Uiso)H were included and constrained
at estimated values. Flack parameters for compounds 14
[0.0040(1)], 16 [0.0055(1)] and 17 [0.0002(1)] supported the
proposed absolute structures. Conventional residues, R, Rw
are quoted at convergence; weights derivative of w = 1/[σ2(F)]
were employed.
trans-[PtBr(NiDPP)(PPh3)2] 16. (a) The preparation of
this complex by oxidative addition of NiDPPBr to Pt(PPh3)3
was described previously.8,9 (b) A solution of trans-[PtBr-
(H2DPP)(PPh3)2] (12.6 mg, 0.01 mmol) and Ni(acac)2 (12.8 mg,
0.05 mmol) in 1,2-dichloroethane (50 mL) and triethylamine
(0.5 mL) was refluxed for 3.5 h. The volatiles were removed
under vacuum, the residue was dissolved in CH2Cl2 and passed
through a short column of silica gel, eluting with CH2Cl2. The
isolated complex was recrystallised from CH2Cl2–hexane to
give 16 as glistening purple plates (10 mg, 76%). Spectroscopic
data were as reported previously.8
Crystal data. 14. trans-[PtBr(CoDPP)(PPh3)2]ؒ0.5CH2Cl2,
C68.5H50BrClCoN4P2Pt, M = 1360.5, monoclinic, space group
trans-[PtBr(ZnDPP)(PPh3)2] 17. (a) This complex was pre-
pared by method (a) as described above for 14, and obtained as
bright purple crystals (7.0 mg, 53%) (Found: C, 60.68; H, 3.74;
N, 4.08. C68H49BrN4P2PtZnؒ0.5CH2Cl2 requires C, 60.35; H,
3.67; N, 4.08%); λmax/nm 369 (ε/103 dm3 molϪ1 cmϪ1 12.5), 430
(443), 482 (3.5), 518 (3.1), 555 (14.9), 599 (7.3); δH 6.35–6.50
(18H, m, PPh), 7.20–7.35 (m, PPh), 7.72 (6H, m, m-, p-H of
10,20-Ph), 8.13 (4H, m, o-H of 10,20-Ph), 8.50, 8.90, 9.19, 9.92
(each 2H, d, βH), 9.93 (1H, s, meso-H); δP 23.5 [s, 1J(PtP) 2989
Hz]; m/z (FAB) 1324.0 (Mϩ). (b) To a refluxing solution
of trans-[PtBr(H2DPP)(PPh3)2] (25 mg, 0.02 mmol) in CHCl3
(20 mL) containing triethylamine (1 mL) was added a solution
of Zn(OAc)2ؒ2H2O (22 mg, 0.1 mmol) in methanol (2 mL), and
the mixture was refluxed for 27 h. After treatment as described
above under 14 (b), the product was obtained as purple
crystals (20 mg, 75%). When the triethylamine was omitted, the
reaction was complete in less than 3 h, as shown by UV-visible
spectroscopy.
2
P21 (C2 , no. 4), a = 13.344(2), b = 29.730(6), c = 14.451(2) Å,
β = 91.10(1)Њ, V = 5732(2) Å3, Z = 4, Dc = 1.58 g cmϪ3, µ = 35.7
cmϪ1, crystal size: 0.50 × 0.35 × 0.10 mm; T min,max = 0.420,
0.703, N = 10316, No = 8123; R = 0.043 Rw = 0.040.
16. trans-[PtBr(NiDPP)(PPh3)2]ؒ0.5CH2Cl2, C68.5H50BrClN4-
NiP2Pt, M = 1360.3, monoclinic, space group P21, a =
13.333(6), b = 29.719(4), c = 14.441(7) Å, β = 91.14(4)Њ,
V = 5721(3) Å3, Z = 4, Dc = 1.58 g cmϪ3, µ = 36.1 cmϪ1, crystal
size: 0.45 × 0.25 × 0.12 mm; T min,max = 0.497, 0.652, N = 10343,
No = 7465; R = 0.064 Rw = 0.068.
17. trans-[PtBr(ZnDPP)(PPh3)2]ؒ0.5CH2Cl2, C68.5H50BrClN4-
P2PtZn, M = 1366.95, monoclinic, space group P21, a =
13.386(6), b = 29.890(7), c = 14.523(5) Å, β = 90.75(3)Њ,
V = 5810(3) Å3, Z = 4, Dc = 1.56 g cmϪ3, µ = 36.4 cmϪ1, crystal
size = 0.60 × 0.20 × 0.15 mm; T min,max = 0.491, 0.583, N = 10225,
No = 6730; R = 0.043 Rw = 0.042.
19. trans-[PtBr(NiDPPBr)(PPh3)2], C68H48Br2N4NiP2Pt,
1
¯
M = 1396.70, triclinic, space group P1(Ci , no. 2), a = 14.252(6),
{5-Bromo-15-[trans-PtBr(PPh3)2](NiDPPBr)} 19 and {5,15-
bis[trans-PtBr(PPh3)2](NiDPP)} 20. Toluene (10 mL) was
b = 15.381(6), c = 13.474(5) Å, α = 105.86(3), β = 91.20(3),
γ = 78.23(4)Њ, V = 2780(2) Å3, Z = 2, Dc = 1.67 g cmϪ3, µ = 43.9
J. Chem. Soc., Dalton Trans., 2002, 4497–4504
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cmϪ1, crystal size: 0.60 × 0.30 × 0.05 mm; T min,max = 0.365,
0.817, N = 9777, No = 7165; R = 0.033 Rw = 0.032.
CCDC reference numbers 186868–186871.
See http://www.rsc.org/suppdata/dt/b2/b205295b/ for crystal-
lographic data in CIF or other electronic format.
of the bromo starting material.9 Purification of trans-[PtBr-
(CoDPP)(PPh3)2] 14 and trans-[PtBr(ZnDPP)(PPh3)2] 17 was
achieved by column chromatography, but the analogous MnCl
complex 13 was immobile on silica gel in weakly polar solvents,
presumably due to binding of active sites to the axial position,
so recrystallisation was used for purification.
For the alternative route to the complexes containing the
trans-PtBr(PPh3)2 moiety, namely metallation of the free-base
trans-[PtBr(H2DPP)(PPh3)2], the same metallation methods as
for MDPPBr were employed. We took the precaution in these
reactions of adding excess triethylamine as an acid scavenger in
the case the Pt–C bond was labile under metallation conditions.
The metallations of this unusual porphyrin free base are
unexpectedly rather slow under these conditions. In fact, com-
pletion of Zn() insertion required over 24 h, a very long time
for such a reaction. Insertion of Zn() into octaalkylporphyrins
takes only seconds, although diarylporphyrins require longer.
By omitting the base, insertion was complete in less than 3 h,
and there was no evidence of acid cleavage of the Pt fragment,
so addition of the base would appear to be unwarranted in
future. In conclusion, the oxidative addition to form the free-
base organoplatinum porphyrin followed by metallation is the
favoured route for these first-row metal ions, and the C–Pt bond
is robust enough to survive the metallations. This may not be
true for more difficult metal ion insertions, such as those for
second-row metals, but the alternative route via the DPPBr
complexes should be appropriate.
Results and discussion
Syntheses
We used the two strategies shown in Scheme 1 to obtain the
In the interests of preparing more crowded organoplatinum
porphyrins, we treated NiDPPBr2 18 with excess PtL3. How-
ever, the maximum yield of bis Pt adduct {5,15-bis[trans-
PtBr(PPh3)2](NiDPP)} 20 was 32%, after chromatographic
separation from the intermediate mono-adduct {5-bromo-15-
[trans-PtBr(PPh3)2](NiDPP)} 19. We report here the crystal
structure of 19, but so far we have not obtained X-ray quality
crystals of 20. The latter was characterised both spectro-
scopically and electrochemically (see next section). We reported
19 previously as an intermediate in the synthesis of the unsym-
metrical bis-metallo complex 21, which possesses PdBr(PPh3)2
and PtBr(PPh3)2 moieties on opposite meso carbons.9 The
ability to achieve this selective two-step conversion is conferred
by the strong deactivating effect of the PtBrL2 substituent. We
discuss this in more detail below.
Scheme 1
series of complexes trans-[PtBr(MDPP)(PPh3)2]. The sequence
H2DPPBr
MDPPBr
trans-[PtBr(MDPP)(PPh3)2] involves
metallation followed by oxidative addition to Pt(0), while the
alternative involves the opposite order of reactions. It is by far
preferable to use the latter sequence, since the complexes of
DPPBr are rather insoluble (especially that of MnCl), and so
are more difficult to handle than the common intermediate Pt
free-base trans-[PtBr(H2DPP)(PPh3)2] 12. However, for the
purposes of spectroscopic comparisons and completeness, we
carried out both sequences on all four metal ions Mn(),
Co(), Ni() and Zn(). In addition, to assist in assigning the
1H NMR spectra of the complexes of the paramagnetic Mn
and Co ions, we also prepared their complexes with H2DPP,
namely 4 and 5, respectively. To our knowledge, the complexes
MnCl(DPP) 4 and MnCl(DPPBr) 7 have not been previously
reported. We used the method of Borovkov et al. to insert
Mn(),19 using MnCl2 in the presence of 2,6-lutidine as base,
but as for all complexes of the DPP ligand, metal insertion is
much slower than for octaalkylporphyrins. CoDPP 5 was
reported by Shelnutt and co-workers,17 but CoDPPBr 8 is new,
and the electronic spectral data for 5 have not previously been
reported. The analogous Ni complex 9 and Zn complex 10 were
first reported by ourselves7 and Therien and co-workers,
respectively.14
Conversion of the MDPPBr metalloporphyrins into the
respective trans-[PtBr(MDPP)(PPh3)2] complexes was achieved
by oxidative addition to the Pt(0) precursor Pt(PPh3)3 under our
standard conditions of heating in near-boiling toluene. The
reactions were continued long enough for the initially-formed
cis adducts to be converted to the trans complexes (ca. 6 h). In
our previous work, we showed how the cis adducts [PtBr-
(H2DPP)(PPh3)2] 11 and [PtBr(NiDPP)(PPh3)2] 15 could be
isolated by interrupting the reaction after partial conversion
Spectroscopy and electrochemistry
The 1H and 31P NMR spectra of the diamagnetic complexes are
typical of this class of compound. As expected, the trans-
bis(phosphine)Pt unit exhibits a singlet 31P resonance with 195Pt
satellites, and 1J(PtP) ca. 2950 Hz, a value typical for P trans to
P. The substituent effect of the Pt fragment can be assessed by
considering the chemical shifts of the porphyrin peripheral pro-
tons, most easily at the opposite meso position. In all cases,
there is an upfield shift of this resonance with respect to the
position for the precursor bromoporphyrin. The meso-proton
chemical shifts for the bromoporphyrins are likewise upfield of
those in the respective unsubstituted porphyrins. These shifts
could be due to either or both of the following factors: (i) the
group –PtBr(PPh3)2 is an electron donor; (ii) the bulky substitu-
ent causes out-of-plane distortions of the aromatic macrocycle,
resulting in reduced ring current. The latter is certainly expected
to apply, especially for the Ni() complexes (see X-ray section
below). In all cases, there is also a red-shift of the electronic
absorption bands upon substitution of the porphyrin by Br or
the Pt fragment, and again this is probably due to a convolution
of electronic effects on the porphyrin frontier π orbitals and
non-planar distortions.
In order to assign the 1H NMR spectrum of [PtBr-
(CoDPP)(PPh3)2] 14 we used comparisons with the precursors 8
and 5. Porphyrin complexes of d7 Co() give reasonably sharp
1H resonances, exhibiting widths-at-half-heights of the meso
4500
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Table 2 Electrochemical data for peripherally-metallated porphyrins
and precursors (in Bu4NPF6–CH2Cl2 vs. Ag/AgCl, 293 K)
proton signal of ca. 200 Hz. The spectrum of CoDPP 5 is easily
assigned by integration and linewidth considerations, as the
lines narrow rapidly as the distance from the metal increases.
The spectrum of 5 was reported for toluene solution by Shel-
nutt and co-workers,17 and closely resembles our spectrum
recorded in CDCl3. The spectrum of 8 was more difficult to
obtain because of the poor solubility, but the change of sym-
metry to C2v was clear because of the split of the β-pyrrole
signals into four lines. For the assignment of the trans-
[PtBr(CoDPP)(PPh3)2] complex 14, it only remained to locate
the P-phenyl signals, and these were found as broad resonances
at ca Ϫ2.2, 1.5 and 5.6 ppm. The isotropic shifts due to the
Compound
E 0 (red1)/V
E 0 (ox1)/V
1
2
Ϫ1.05
Ϫ0.93
Ϫ1.32
Ϫ1.24a
Ϫ1.13
Ϫ1.02
Ϫ1.44
Ϫ1.66
Ϫ1.37a
ϩ1.16
ϩ1.19
ϩ0.83
ϩ0.89
ϩ1.17
ϩ1.20
ϩ0.90
ϩ0.61
ϩ0.95
12
22
6
9
16
20
23
2
unpaired electron in the dz orbital of Co() are usually positive
a Irreversible with loss of –PdBr(PPh3)2 moiety.
for protons near the plane of the porphyrin ring,20 so these
negative paramagnetically-induced shifts are to be expected for
the protons of the phenyl rings on the PPh3 ligands. In the
diamagnetic trans-PtBr(PPh3)2 adducts, the m- and p-protons
of the P-phenyl groups experience an upfield shift to the region
of 6–6.5 ppm, because of the proportion of time they spend in
the shielding zone of the magnetically anisotropic porphyrin
ring. So for the Co() complex, this effect will be magnified by
the upfield isotropic shift. The 31P resonance for 14 is almost as
sharp as those for the diamagnetic analogues, and occurs also at
a very similar shift.
the square-pyramidal metalloporphyrin, apparently greatly
amplified by the effects of the paramagnetism. The two 31P
resonances appear at 68 and Ϫ26 ppm, as a pair of doublets
with a P–P coupling constant of ca. 420 Hz, a value consistent
with a pair of non-equivalent trans-disposed phosphines. Inter-
estingly, the average of these shifts is 21 ppm, placing it near the
typical position for the complexes of Co, Ni and Zn. The sig-
nals are considerably broader than those for the other com-
plexes, and the 195Pt satellites appear as broad humps around
the bases of the central lines. The two phosphines exchange
environments by a rotation of the porphyrin meso carbon–
platinum bond, so it is only the very large chemical shift differ-
ence brought about by the paramagnetism that enables us to
see this separation. To investigate this point, 31P spectra were
recorded at temperatures up to 115 ЊC in C2D2Cl4 solution, and
although the two chemical shifts began to converge, it is
clear that the coalescence temperature would be near 600 K.
Attempts to investigate the solid-state structure of 13 were frus-
trated by the poor quality and twinning of the crystals, but the
connectivity of the molecule was confirmed.
The effects of the Pt moiety on the redox properties of the
porphyrin ring were studied for the free base and the nickel()
complex by cyclic and ac voltammetry. For comparison, the
unsubstituted DPP compounds 1 and 6 and the mono-bromo
compounds 2 and 9 were also measured. The first reduction and
oxidation potentials are summarized in Table 2. Experiments
were conducted in CH2Cl2 with Bu4NPF6 as supporting electro-
lyte, and because of solubility constraints, the porphyrin con-
centrations were 7.5 × 10Ϫ4 M or less, which produced a
relatively high background current. This meant that ac vol-
tammetry generally gave better results than conventional cyclic
voltammetry. The Pt-containing species gave good reversible or
quasi-reversible waves, and the cyclic and ac voltammograms
for [PtBr(H2DPP)(PPh3)2] (12) are shown in Fig. 2. The
voltammetric data, particularly the first oxidation potential,
The situation for the chloro Mn() complexes, in which the
1
2
4
1
1
1
metal ion is square-pyramidal d , with the (dxy) (dyz) (dxy) (dz )
configuration, is more complex. The spectrum of MnCl(DPP)
4, prepared to assist in the assignments, could be interpreted by
comparison with that of the analogous chloromanganese com-
plex of meso-tetraphenylporphyrin (TPP).21 The former
exhibits upfield isotropic shifts of the β-pyrrole protons to ca.
Ϫ25 ppm, and a large downfield shift of the meso proton to 45
ppm. The β-protons of MnCl(TPP) appear at Ϫ22.3 ppm.21
The protons of the 5,15-phenyl groups of 4 appear as a broad
unsymmetrical resonance peaking at ca. 8.4 ppm, and this
apparently represents all three sets of phenyl protons. Why
these do not split more clearly into ortho, meta and para sets is
obscure, but again this is quite similar to what is found for the
TPP analogue.21 We could not obtain a spectrum of the
bromoDPP complex 7 because of its low solubility. The signals
for the Pt complex [PtBr(MnClDPP)(PPh3)2] (13) could be
located by comparison with the spectrum of 4, the β-pyrrole
protons appearing in a 2:2:4 pattern at ca. Ϫ17, Ϫ22 and
Ϫ31 ppm, and the meso-proton appeared as a very broad signal
at ca. 47 ppm. The 10,20-phenyl group protons were observed
in similar positions to those in 4, and overlap a very broad
unsymmetrical envelope spanning the region 3–15 ppm, which
can only be due to the P-phenyl protons. One sharper signal
protrudes at 7.0 ppm.
The 31P spectrum of 13 is remarkably different from any of
the others in the series. The spectrum is shown in Fig. 1, and
one can see immediately the effects of the facial asymmetry of
Fig. 2 Cyclic (200 mV sϪ1, solid line) and ac (50 mV sϪ1, dotted line)
voltammograms of trans-PtBr(H2DPP)(PPh3)2 12 in CH2Cl2–Bu4NPF6
at 293 K.
Fig. 1 31P NMR spectrum of trans-PtBr(MnClDPP)(PPh3)2 13 in
CDCl3 at 293 K.
J. Chem. Soc., Dalton Trans., 2002, 4497–4504
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Table 3 Selected geometric data (bond lengths, bond angles, phenyl group dihedral angles and displacements from macrocyclic mean planes) for
trans-PtBr(MDPP)(PPh3)2 and trans-PtBr(NiDPPBr)(PPh3)2
Bond lengths (Å)
H2DPP 12 (ref. 9)
CoDPP 14
NiDPP 16
ZnDPP 17
mol. A
mol. B
mol. A
mol. B
mol. A
mol. B
mol. A
mol. B
NiDPPBr 19
Pt–Br
Pt–P1
Pt–P2
Pt–C5
M–N1
M–N2
M–N3
M–N4
2.518(1)
2.323(3)
2.307(3)
2.05(1)
2.511(1)
2.309(3)
2.325(3)
1.95(1)
2.527(2)
2.367(4)
2.268(4)
1.95(1)
1.96(1)
1.97(1)
1.97(1)
1.95(1)
2.501(2)
2.248(4)
2.374(4)
2.06(2)
1.94(1)
1.94(1)
1.97(1)
1.96(1)
2.504(3)
2.232(7)
2.389(7)
2.02(2)
1.94(2)
1.91(2)
1.96(2)
1.94(2)
2.535(3)
2.375(7)
2.264(7)
1.97(2)
1.99(2)
1.96(2)
1.93(2)
1.93(2)
2.521(2)
2.302(5)
2.328(5)
1.98(2)
2.04(2)
2.00(2)
2.06(2)
2.02(2)
2.521(2)
2.327(5)
2.316(5)
2.02(2)
2.03(2)
2.05(2)
2.05(2)
2.04(2)
2.517(1)
2.329(2)
2.305(2)
2.011(5)
1.930(4)
1.919(4)
1.939(5)
1.933(5)
Bond angles (Њ)
Br–Pt–P1
Br–Pt–P2
Br–Pt–C5
P1–Pt–P2
P1–Pt–C5
P2–Pt–C5
Pt–C5–C4
Pt–C5–C6
89.52(8)
88.88(8)
175.0(3)
176.2(1)
92.6(3)
89.2(3)
116.2(8)
118.3(8)
91.80(9)
91.12(9)
177.2(3)
176.8(1)
89.9(3)
87.3(3)
121.7(8)
118.4(8)
90.2(1)
89.3(1)
178.1(5)
177.5(2)
90.1(5)
90.4(5)
119(1)
91.4(1)
90.2(1)
175.9(4)
178.1(2)
92.7(4)
85.7(4)
122(1)
92.7(2)
89.7(2)
176.6(7)
177.4(2)
90.7(7)
86.9(7)
121(2)
89.3(2)
89.3(2)
177.5(7)
178.3(2)
89.0(7)
92.4(7)
119(2)
91.3(1)
89.9(1)
177.9(5)
178.4(2)
90.2(5)
88.5(5)
117(1)
90.4(1)
89.7(1)
178.0(5)
179.1(2)
91.6(5)
88.4(5)
120(2)
89.38(6)
91.32(6)
177.6(2)
176.2(6)
88.4(2)
90.9(2)
119.0(4)
120.6(4)
122(1)
120(1)
123(2)
123(2)
123(1)
116(2)
Dihedral angles of the 10,20 phenyl substituents to the macrocyclic mean plane (Њ)
10–Ph
20–Ph
56.8
71.2
66.3
93.2
128.5
79.9
113.8
114.5
129.3
79.5
113.9
113.1
126.4
80.2
113.5
114.9
50.2
81.7
Distances of selected atoms from the macrocyclic mean plane (Å)
C5
C10
C15
C20
M
Pt
Br
ϩ0.13
Ϫ0.11
ϩ0.05
Ϫ0.07
Ϫ0.10
ϩ0.03
Ϫ0.06
ϩ0.04
Ϫ0.17
ϩ0.32
Ϫ0.30
ϩ0.29
ϩ0.03
Ϫ0.11
Ϫ0.03
ϩ0.08
Ϫ0.19
ϩ0.13
Ϫ0.10
ϩ0.02
ϩ0.07
Ϫ0.12
Ϫ0.28
ϩ0.30
Ϫ0.40
ϩ0.32
Ϫ0.05
Ϫ0.31
Ϫ0.20
ϩ0.14
Ϫ0.22
ϩ0.19
Ϫ0.10
Ϫ0.03
Ϫ0.06
Ϫ0.23
Ϫ0.16
ϩ0.21
Ϫ0.24
ϩ0.24
ϩ0.01
Ϫ0.15
Ϫ0.06
ϩ0.03
Ϫ0.18
ϩ0.06
Ϫ0.07
Ϫ0.04
Ϫ0.02
Ϫ0.16
ϩ0.31
Ϫ0.46
ϩ0.48
Ϫ0.46
Ϫ0.01
ϩ0.37
ϩ0.34
ϩ0.19
ϩ0.20
Ϫ0.52
Ϫ1.13
clearly confirm the proposal that the –Pt(PPh3)2Br group is a
strong electron donor. This is manifest in a cathodic shift of
about 300 mV, for both the free base 12 and the corresponding
Ni() complex 16. Moreover, the effect of a second Pt substitu-
ent is essentially additive, and the first oxidation potential of
{5,15-bis[trans-PtBr(PPh3)2](NiDPP)} 20 is remarkably low for
a Ni() porphyrin, namely ϩ0.61 V (Fc/Fcϩ at ϩ0.55 V) . The
fact that both the free base and the Ni() complexes exhibit very
similar effects is good evidence that (i) oxidation occurs at the
porphyrin ring, not at the Ni() centre and (ii) the changes in
spectra and electrode potentials due to the Pt substituent are
electronic in origin, and not related to out-of-plane distortions
in the Ni() complexes. Similar effects are noted for the corre-
sponding compounds 22 and 23 containing the palladium
bis(phosphine) fragment, although the shifts in redox potentials
are not quite as large (Table 2), and the first reduction is
irreversible, with loss of the Pd substituent. Literature search-
ing reveals no comparable electrochemical data for simple aryls,
e.g. phenyl-platinum() or -palladium() organometallics, but
there have been several studies of the substituent effects of
nickel(), palladium() and platinum() on aromatic rings
C–Br bond and inhibiting the insertion of the Pt(0) moiety.
Stang and co-workers noted in their work on double Pt(PPh3)2
addition to 4,4Ј-diiodobiphenyl, a similar but apparently
weaker electron-donating effect.23
Crystal structures
An objective of this work was to compare the coordination
chemistry of late first-row transition metal ions with the new
organoplatinum porphyrin ligands and to study the structures
of both the ligands and complexes by single-crystal X-ray
crystallography wherever possible. We have previously reported
the structure of trans-[PtBr(H2DPP)(PPh3)2].9 In this present
study, we have extended the structural analysis of this system,
completing structure determinations for trans-[PtBr(MDPP)-
(PPh3)2]ؒ0.5CH2Cl2 for M = Ni (16), Co (14) and Zn (17),
and trans-[PtBr(NiDPPBr)(PPh3)2] 19, the preparation and
spectroscopic characterisation of 16 having been reported
previously.9
trans-[PtBr(NiDPPBr)(PPh3)2] (19). This complex crystal-
1
using H, 19F or 13C NMR data.23,24 The last piece of evidence
lizes in the triclinic space group P1 with one molecule compris-
¯
for a strong electron-donating substituent effect is the remark-
able decrease in reactivity towards the second oxidative addi-
tion in the attempted conversion of NiDPPBr2 to 20. Clearly
the Pt substituent is decreasing the polarity of the opposite
ing the asymmetric unit. A representative view of the structure
of the molecule is shown in Fig. 3. Relevant geometric param-
eters are listed in Table 3. The trans PPh3 ligands adopt three-
fold propeller conformations of opposite chirality and are
4502
J. Chem. Soc., Dalton Trans., 2002, 4497–4504

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Fig.
3
Molecular structure of trans-PtBr(NiDPPBr)(PPh3)2 19
(hydrogen atoms omitted for clarity).
related by a pseudo-mirror plane of symmetry. Ring 1 on each
ligand overhangs the porphyrin macrocycle in face-to-face
contact with the second pyrrole ring. The porphyrin ring is
symmetrically coordinated to the platinum through the C5
meso carbon with Pt–C5–C(4,6) angles of 120.6(4) and
119.0(4)Њ, respectively. The coordination geometry about the
platinum atom (Table 3) is very similar to that found in the
analogous H2DPP complex,9 showing that insertion of metal
atoms into the macrocyclic ring and substitution of a bromine
atom at C15 exerts only minimal influence on this geometry.
The coordinated nickel lies in the macrocyclic mean plane
(C20N4) and adopts the expected square planar geometry with
Ni–N bond lengths ranging from 1.919(4)–1.939(5) Å. The
porphyrin macrocycle is not flat, but rather adopts a distorted
shape with C10 and C20 respectively 0.46, 0.45 Å below and C5
and C15 respectively 0.31, 0.48 Å above the macrocyclic plane
(see below). The Pt atom and its coordinated Br atom lie
respectively 0.37 and 0.34 Å above this plane while the bromine
bonded to C15 lies 1.03 Å above the plane. The substituent
phenyl groups at C10 and C20 are twisted by 31.5Њ with respect
to each other and lie at dihedral angles of 81.7 and 50.2Њ to the
macrocyclic mean plane.
Fig. 4 Molecular structure of trans-PtBr(CoDPP)(PPh3)2 14 (hydro-
gen atoms omitted for clarity; molecule 1, top; molecule 2, bottom).
series and correlation effects between the two molecules may be
the cause of the observed range of values.
trans-[PtBr(MDPP)(PPh3)2]ؒ0.5CH2Cl2, M ؍ Co (14), Ni
(16), Zn (17). The structures of these three compounds are
isomorphous, crystallizing in space group P21 with a ∼13.4,
b ∼ 29.7, c ∼ 14.4 Å, and β ∼ 91Њ. The asymmetric unit consists
of two independent molecules of the complex with a co-
crystallized molecule of dichloromethane (modelled with 50%
occupancy) located in the vicinity of the PPh3 phenyl substitu-
ents. As a representative of the set, the molecules of the cobalt
complex 14 are shown in Fig. 4. Relevant geometric parameters
are listed in Table 3. The conformational structures of the two
molecules are very similar with the exception of the relative
orientations of the phenyl substituents on C10 and C20 of the
porphyrin ring. For molecule A, these two rings are twisted by
approximately 45Њ with respect to other while for molecule B,
the two rings are essentially parallel. As for the other trans
complexes in this series, the PPh3 ligands adopt three-fold pro-
peller conformations and are related by a pseudo-mirror plane
of symmetry with ring 1 on each ligand overhanging the mac-
rocycle in face-to-face contact with the second pyrrole ring. The
coordination geometry about the platinum atom shows a con-
siderable dispersion of values across the three complexes with
Pt–Br in the range 2.501(2)–2.535(3) Å with an average value of
2.51(1) Å, Pt–P in the range 2.264(4)–2.389(7) Å with an aver-
age value of 2.32(5) Å and Pt–C in the range 1.95(1)–2.06(2)
with an average value of. 2.00(4) Å. These average values are
consistent with those observed for the other members of the
Non-planar distortions of the porphyrin rings
Given the novelty of our –PtBrL2 substituent, and the fact that
we now have crystal structures for the free base and several
metallo derivatives, it is worthwhile to examine the steric con-
sequences of platinum attachment on the planarity of the por-
phyrin macrocycle. As is common for many Ni() porphyrin
structures,17,24,25 the porphyrin ring in complexes 16 and 19 is
not planar, but rather adopts a distorted shape due to the short
Ni–N bond distances (average of all over the two complexes
1.94 Å). The details of the non-planar distortions for 19 are
displayed in linear form in Fig. 5 as the vertical displacement of
the atom from the C20N4 plane. Similar plots for the complexes
14, 16 and 17 as well as the free base 129 are provided in the
ESI.† The metal–nitrogen bond distances are quite typical for
these divalent four-coordinate metals in porphyrin complexes,
resulting in the order Zn–N > Co–N > Ni–N. This order is
reflected in the typical pattern of out-of-plane distortions (Zn <
Co < Ni) in response to the contraction of the MN4 core.25 The
most typical distorted conformations for four-coordinate
metalloporphyrins are “ruffled” and “saddled”. In the former,
the meso carbons are alternately up and down with respect to
the macrocycle plane, while in the latter, it is the pairs of pyrrole
β carbons which lie alternately out of the plane. In our struc-
tures, the free base is virtually planar, but the four metallo
J. Chem. Soc., Dalton Trans., 2002, 4497–4504
4503

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of Chemistry, The Australian National University, for Visiting
Fellowships. We also thank Dr Alison Edwards, Research
School of Chemistry, The Australian National University, for
the confirmatory structure determination of 13.
References
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rotated to lie between normal ruffling and saddling axes. This
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Conclusion
The ease of preparation of these platinio-porphyrins and their
chemical robustness makes them promising candidates as
porphyrin building blocks from which supramolecular arrays
may be derived. The fact that the phosphine ligands, the lateral
aryl groups on the porphyrin, and the centrally-coordinated
metal ion can all be varied, allows the synthesis of a wide
variety of structures. The strong electron-donating influence
of the –PtBrL2 unit may be useful in tailoring the properties
of porphyrins. This moiety provides an inert substituent
which causes a strong cathodic shift of the redox potentials.
However, the lowered oxidation potentials may force us to
rethink our original proposal that the phosphine ligand
superstructure could provide selective cavities for biomimetic
metalloporphyrin-catalysed oxidations. Experiments to investi-
gate this point, and to use the Pt substituents as scaffolds for
multiporphyrin supramolecules are planned for the near future.
Acknowledgements
We thank the Australian Research council for a Small Grant to
D. P. A. and for financial support for the purchase of the dif-
fractometer, and the Faculty of Science, Q.U.T. for a post-
graduate scholarship for M. J. H. D. P. A. thanks Prof. J. Jiang
(Shandong University, Jinan, China) and the Research School
24 J. A. Shelnutt, X.-Z. Song, J.-G. Ma, S.-L. Jia, W. Jentzen and
C. J. Medforth, Chem. Soc. Rev., 1998, 27, 31.
25 W. R. Scheidt, in The Porphyrin Handbook, ed. K. M. Kadish,
K. M. Smith and R. Guilard, Academic Press, San Diego, CA, 2000,
vol. 3, ch. 16, pp. 49–112.
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J. Chem. Soc., Dalton Trans., 2002, 4497–4504