Construction of multiporphyrin arrays using ruthenium and rhodium coordination to phosphines

Article abstract of DOI:10.1021/ic034699w

The synthesis of linear multiporphyrin arrays with mono- and bisphosphine-substituted porphyrins as ligand donors and ruthenium(II) or rhodium(III) porphyrins as ligand acceptors is described. With appropriate amounts of the building blocks mixed, linear dimeric and trimeric arrays have been synthesized and analyzed by ¹H NMR and ³¹P NMR spectroscopy. The Ru/Rh acceptor porphyrins can be located either at the periphery or in the center of the array. Likewise, the monophosphine porphyrins can be positioned at the periphery, thus allowing a high degree of freedom in the overall composition of the arrays. This way, both donor and acceptor porphyrins can act as chain extenders or terminators. One of the trimeric complexes with two nickel and one ruthenium porphyrin has also been analyzed by X-ray crystallography. Attempts have also been made to synthesize higher order arrays by mixing appropriate amounts of the porphyrins; however, from the NMR data it cannot be concluded if monodisperse five, seven, or nine porphyrin arrays are present or if the solutions are composed of a statistical mixture of smaller and larger arrays.

Full text of DOI:10.1021/ic034699w

Inorg. Chem. 2003, 42, 6564−6574
Construction of Multiporphyrin Arrays Using Ruthenium and Rhodium
Coordination to Phosphines
Eugen Stulz,*,†,‡ Sonya M. Scott,† Yiu-Fai Ng,† Andrew D. Bond,†,§ Simon J. Teat,| Scott L. Darling,†
,†
Neil Feeder,† and Jeremy K. M. Sanders*
UniVersity Chemical Laboratory, UniVersity of Cambridge, Lensfield Road,
Cambridge, CB2 1EW, United Kingdom, and CLRC Daresbury Laboratory,
Warrington, Cheshire, WA44AD, United Kingdom
Received June 19, 2003
The synthesis of linear multiporphyrin arrays with mono- and bisphosphine-substituted porphyrins as ligand donors
and ruthenium(II) or rhodium(III) porphyrins as ligand acceptors is described. With appropriate amounts of the
building blocks mixed, linear dimeric and trimeric arrays have been synthesized and analyzed by 1H NMR and 31P
NMR spectroscopy. The Ru/Rh acceptor porphyrins can be located either at the periphery or in the center of the
array. Likewise, the monophosphine porphyrins can be positioned at the periphery, thus allowing a high degree of
freedom in the overall composition of the arrays. This way, both donor and acceptor porphyrins can act as chain
extenders or terminators. One of the trimeric complexes with two nickel and one ruthenium porphyrin has also
been analyzed by X-ray crystallography. Attempts have also been made to synthesize higher order arrays by
mixing appropriate amounts of the porphyrins; however, from the NMR data it cannot be concluded if monodisperse
five, seven, or nine porphyrin arrays are present or if the solutions are composed of a statistical mixture of smaller
and larger arrays.
Introduction
semblies. Despite the overall diversity of these assemblies,
the individual constructs usually are homoporphyrinic in
nature. Our concept of using simultaneous orthogonal metal-
ligand coordination to synthesize mixed metallo-porphyrin
arrays, first realized by the construction of a tin(IV)-
zinc(II)-ruthenium(II) trimer,13 has led to the synthesis of
a heterometallic porphyrin undecamer combining Sn(IV)-
oxygen and Rh(III)-nitrogen coordination and incorporating
porphyrins in four different metalation states.14 Recently, we
have added the Ru(II)-phosphorus coordination linkage and
demonstrated the utility of phosphine-substituted porphyrins
to assemble linear dimeric and trimeric arrays.15 With
Ru(II) and Rh(III) porphyrins, cyclic tetraporphyrin arrays
The construction of multiporphyrin arrays, where the
connectivity of the individual porphyrins is realized through
central-metal coordination, has led to a number of linear,1-3
branched,4-6 cyclic,7,8 dendritic,9,10 and polymeric11,12 as-
* Authors to whom correspondence should be addressed. E-mail:
eugen.stulz@unibas.ch (E.S.); jkms@cam.ac.uk (J.K.M.S.).
† University of Cambridge.
‡ Present address: Department of Chemistry, University of Basel, St.
Johanns-Ring 19, 4056 Basel, Switzerland.
§ Present address: Syddansk Universitet, Kemisk Institut, Campusvej
55, 5230 Odense M, Denmark.
| CLRC Daresbury Laboratory.
(1) Funatsu, K.; Kimura, A.; Imamura, T.; Ichimura, A.; Sasaki, Y. Inorg.
Chem. 1997, 36, 1625-1635.
(2) Maiya, B. G.; Bampos, N.; Kumar, A. A.; Feeder, N.; Sanders, J. K.
M. New J. Chem. 2001, 25, 797-800.
(3) Mak, C. C.; Bampos, N.; Darling, S. L.; Montalti, M.; Prodi, L.;
Sanders, J. K. M. J. Org. Chem. 2001, 66, 4476-4486.
(4) Mak, C. C.; Bampos, N.; Sanders, J. K. M. Chem. Commun. 1999,
1085-1086.
(5) Susumu, K.; Tanaka, K.; Shimidzu, T.; Takeuchi, Y.; Segawa, H. J.
Chem. Soc., Perkin Trans. 2 1999, 1521-1529.
(6) Giribabu, L.; Rao, T. A.; Maiya, B. G. Inorg. Chem. 1999, 38, 4971-
4980.
(9) Prodi, A.; Indelli, M. T.; Kleverlaan, C. J.; Scandola, F.; Alessio, E.;
Gianferrara, T.; Marzilli, L. G. Chem.-Eur. J. 1999, 5, 2668-2679.
(10) Darling, S. L.; Mak, C. C.; Bampos, N.; Feeder, N.; Teat, S. J.; Sanders,
J. K. M. New J. Chem. 1999, 23, 359-364.
(11) Michelsen, U.; Hunter, C. A. Angew. Chem., Int. Ed. 2000, 39, 764+.
(12) Imamura, T.; Fukushima, K. Coord. Chem. ReV. 2000, 198, 133-
156.
(13) Kim, H. J.; Bampos, N.; Sanders, J. K. M. J. Am. Chem. Soc. 1999,
121, 8120-8121.
(7) Ambroise, A.; Li, J. Z.; Yu, L. H.; Lindsey, J. S. Org. Lett. 2000, 2,
2563-2566.
(8) Haycock, R. A.; Hunter, C. A.; James, D. A.; Michelsen, U.; Sutton,
L. R. Org. Lett. 2000, 2, 2435-2438.
(14) Redman, J. E.; Feeder, N.; Teat, S. J.; Sanders, J. K. M. Inorg. Chem.
2001, 40, 2486-2499.
(15) Darling, S. L.; Stulz, E.; Feeder, N.; Bampos, N.; Sanders, J. K. M.
New J. Chem. 2000, 24, 261-264.
6564 Inorganic Chemistry, Vol. 42, No. 20, 2003
10.1021/ic034699w CCC: $25.00 © 2003 American Chemical Society
Published on Web 09/11/2003

Construction of Multiporphyrin Arrays
a
Scheme 1
a Reagents and conditions: (a) NaOH, PhMe-nBuOH, reflux, 5 h, 95%; (b) LiHMDS, CdCl2 ClPPh2, THF, -78 °C to RT, 60%; and (c) Zn(OAc)2 or
Ni(OAc)2, CHCl3-MeOH, reflux; quantitative. R ) C6H13.
ligands for both ruthenium and rhodium porphyrins.19-21
Chart 1
Since they are sterically much less demanding than their
triaryl counterparts, their complexes with acceptor porphyrins
show enhanced stability. Our previous investigations on the
properties of ruthenium complexes with a series of phenyl
acetylene phosphines and phosphonites as model complexes
for the arrays discussed below have shown that the electronic
properties of the acceptor porphyrins are largely unaffected
by the substitution pattern on the acetylene phosphorus
ligand.19,20 Thus, we have focused on the diphenyl substitu-
tion pattern on the phosphine, which conveniently is also
the most straightforward derivative to synthesize (Scheme
1).
Monophosphine complexes of the form P-Ru(CO)(por)
(por ) porphyrin) are stable in solution, but partial decar-
bonylation occurs upon isolation of the complexes, leading
to the bisphosphine ruthenium complexes P2-Ru(por).19,20
Isolation of arrays containing monocoordinated ruthenium-
(II) porphyrins is therefore not expected. Rhodium(III)
porphyrins also provide access to the bisphosphine complexes
P2-Rh(por),21 since the iodide on the rhodium is readily
displaced in solution (in P-Ru(CO)(por), complete removal
of the carbonyl ligand must be achieved by repeated
evaporating-dissolving cycles). In contrast, the σ-bonded
methyl group in Rh(Me)(por) is inert to displacement by
DPAP, giving easy access to monophosphine rhodium
complexes P-Rh(Me)(por) with essentially the same elec-
tronic properties as for P2-Rh(por) complexes.
have been selected and amplified virtually completely from
a biased dynamic combinatorial library using 4,4′-bipyridine
as scaffold, the cyclic complex being stabilized by orthogonal
Ru(II)- or Rh(III)-phosphorus and Zn(II)-nitrogen coor-
dination.16 Here, we report on the use of mono- and
bisphosphine-substituted porphyrins m-1, p-1, and m-2
(Scheme 1) as ligand donors (D) and their coordination
behavior toward a variety of Ru(II) and Rh(III) porphyrins
(Chart 1) as ligand acceptors (A). The approach used here
to construct arrays incorporating porphyrins displaying a
large diversity in substitution pattern and central metal
expands the diversity in previously synthesized arrays.
The synthesis of acetylenic phosphines is well docu-
mented,17,18 and they provide easily accessible and versatile
(19) Stulz, E.; Maue, M.; Feeder, N.; Teat, S. J.; Ng, Y. F.; Bond, A. D.;
Darling, S.; Sanders, J. K. M. Inorg. Chem. 2002, 41, 5255-5268.
(20) Stulz, E.; Sanders, J. K. M.; Montalti, M.; Prodi, L.; Zaccheroni, N.;
de Biani, F.; Grigiotti, E.; Zanello, P. Inorg. Chem. 2002, 41, 5269-
5275.
(21) Stulz, E.; Scott, S. M.; Bond, A. D.; Otto, S.; Sanders, J. K. M. Inorg.
Chem. 2003, 42, 3086-3096.
(16) Stulz, E.; Ng, Y. F.; Scott, S. M.; Sanders, J. K. M. Chem. Commun.
2002, 524-525.
(17) Carty, A. J.; Hota, N. K.; Ng, T. W.; Patel, H. A.; O’Connor, T. J.
Can. J. Chem. 1971, 49, 2706-2711.
(18) Hengefeld, A.; Kopf, J.; Rehder, D. Organometallics 1983, 2, 114-
121.
Inorganic Chemistry, Vol. 42, No. 20, 2003 6565

Stulz et al.
Figure 1. Molecular units of m-Fb-1, m-Ni-1, and m-Zn-1, showing atomic displacement ellipsoids drawn at the 50% probability level. Hydrogen atoms
and the hexyl side chains (except for the first carbon atom) have been omitted for clarity.
The series of acceptor porphyrins (Chart 1) has been
chosen with the aim of incorporating a large structural
diversity into the arrays, varying both in the central metal
and in the substitution pattern. The latter is based on an
increasing number of meso-phenyl substituents on the
porphyrin, ranging from none in Ru/Rh-3 (octaethyl por-
phyrin, OEP) to two in Ru/Rh-4 (5,15-diphenyl porphyrin,
DEDPP) and four in Ru/Rh-5 (tetraphenyl porphyrin, TPP).
In this respect, Ru/Rh-4 may be considered as a structural
hybrid between TPP and OEP. The 3′,5′-di-tBu derivatives
tbRu-4 and Ru/Rh-6 were chosen to probe the steric
influence on the stability of the arrays, and Rh-5Me should
be useful to form selective monophosphine complexes with
a rhodium porphyrin. From our studies with DPAP,19-21 we
can expect that the association constants in solution of the
phosphine-substituted porphyrins to the acceptor porphyrins
to be within the range of 106 M-1 for mono- and bisphos-
phine complexes with ruthenium porphyrins, 104 M-1 for
bisphosphine complexes with rhodium porphyrins, and 104
M-1 in the case of complexes with Rh-5Me.
rins Zn-7 and Zn-8, respectively. Attachment of the diphenyl
phosphine group via a cadmium(II) Grignard-type reaction
yields the diphenyl phosphine porphyrins p-1, m-1, and m-2.
The synthesis and characterization of the porphyrins m-1 and
p-1 have been described earlier,15 but the data for m-2 and
the porphyrins 7 and 8 are given for the first time. The
1
characteristic H NMR chemical shifts of the meso protons
of the porphyrins are independent of the substitution pattern
on the meso-phenyl substituents. The 31P{1H} NMR spectra
show the typical resonance for the acetylene phosphine at
δ(31P) ) -32 ppm, which is independent both of the
metalation state and of the substitution pattern of the
porphyrin and is isochronous with the resonance of the model
ligand DPAP. These data indicate that there is no electronic
communication between the phosphine substituents and the
porphyrin core.
The synthesis, workup, and purification of the porphyrins
must be carried out with strict exclusion of oxygen, since
the phosphines are highly susceptible to oxidation. The
formation of the phosphine oxide can be followed by 31P
NMR spectroscopy, showing a characteristic resonance at δ
9 ppm for all mono- and diphosphine oxides. In the case of
p-Zn-1, formation of the phosphine oxide has also been
confirmed by single-crystal X-ray diffraction analysis.22 In
contrast to the synthesis of the building block m-2, the
formation of the para-substituted diphosphine porphyrin was
not clean due to the low solubility of the intermediate
dilithiated bisacetylene and the increased sensitivity of the
para isomer to oxidation. We therefore did not pursue the
p-diphosphine building blocks any further.
Crystal Structures of the m-Monophosphine Porphy-
rins. We have reported previously the crystal structure of
p-Zn-1.15 In this paper, we present the single-crystal
structures of the m-monophosphines m-Fb-1, m-Zn-1, and
m-Ni-1 (Figure 1). Selected geometrical data are compiled
in Table 1. The crystallographic data are given in the
electronic SI. Crystals of m-Fb-1 were small and weakly
diffracting, and a synchrotron radiation source was utilized
to collect diffraction data for this compound.23 In all three
structures, several of the hexyl substituents were found to
be disordered and these were modeled in two orientations
with restrained geometries. A single isotropic displacement
parameter was refined for each hexyl chain, scaled along
Here we demonstrate that the phosphine porphyrin building
blocks m-1, p-1, and m-2 either can be used to form
homopolymeric supramolecular structures in the solid state
or can be incorporated into discrete linear dimeric, trimeric,
pentameric, heptameric, and nonameric heteroporphyrinic
arrays. The arrays, which are thermodynamically stable at
ambient temperature and millimolar concentration, were
1
characterized by H, 31P{1H}, and 2D-NMR spectroscopy.
In the linear arrays, m-2 and Ru/Rh-3-6 act as chain
extenders, whereas m/p-1, Ru(CO)(por), and Rh-5Me can
be used to terminate the chain. The ratio of extender vs
terminator determines the length of the chain obtained.
Results and Discussion
Synthesis and Characterization of the Phosphine-
Substituted Porphyrins. The synthetic route to acetylenic
diphenyl phosphine substituted porphyrins is outlined in
Scheme 1 (full experimental details are available as electronic
Supporting Information (SI)). The tertiary hydroxy protecting
group for the acetylene substituent has a major advantage
over the use of the TMS protecting group in the mixed
porphyrin synthesis in that the products can be separated with
greater ease by column chromatography due to their dis-
tinctively different polarity. Deprotection of the acetylene
by base is best performed on the zinc(II)-metalated porphy-
(22) Darling, S. L.; Sanders, J. K. M.; Feeder, N. Private communication
to the CCDC, 1999. CSD Refcode: HOJCOY.
6566 Inorganic Chemistry, Vol. 42, No. 20, 2003

Construction of Multiporphyrin Arrays
Table 1. Selected Geometrical Data for m-Fb-1, m-Zn-1, and m-Ni-1
m-Fb-1
m-Zn-1
2.062(5)
m-Ni-1
1.937(9)
Zn/Ni-N1/Å
Zn/Ni-N2/Å
Zn/Ni-N3/Å
Zn/Ni-N4/Å
σ/Å
2.051(4)
2.080(5)
2.051(5)
0.107
1.923(9)
1.948(9)
1.955(8)
0.270
0.177
δ/°a
80.3(1) (C5-Ph) 80.5(1) (C5-Ph) 81.4(2) (C5-Ph)
75.8(1) (C15-Ph) 87.8(2) (C15-Ph) 83.8(3) (C15-Ph)
Figure 2. Stereo representation of part of the crystal packing in m-Ni-1.
d/Å
0.192(5) (C5)
0.201(5) (C5)
0.283(10) (C5)
Hydrogen atoms are omitted for clarity.
-0.192(6) (C10) -0.062(6) (C10) -0.498(11) (C10)
0.205(5) (C15) 0.118(5) (C15) 0.526(11) (C15)
-0.138(5) (C20) -0.208(5) (C20) -0.433(12) (C20)
coplanar arrangements with a perpendicular separation of
3.55(1) Å between least-squares planes. The lateral offset
between adjacent porphyrins is large (centroid-centroid
separation 8.00(2) Å), however, so that the interaction does
not constitute significant π-π stacking. Adjacent dimers also
associate in coplanar arrangements but with a somewhat
larger interplanar separation (3.86(1) Å) and a centroid-
centroid separation of 8.96(2) Å. Thus, offset stacks are
formed with alternate large and small interporphyrin separa-
tions. Between these stacks, hexyl chains interlock and the
phosphine substituents associate such that the edge of the
meso-phenyl group bearing the phosphine fits into the
concave surface formed by the two phenyl rings of an
adjacent phosphine group. The lone pair of the phosphorus
atom is directed toward a hydrogen atom of the meso-phenyl
group in the 10-position of an adjacent porphyrin, with an
H‚‚‚P separation of 3.28 Å and a C-H‚‚‚P angle of 138.0
Å, and does not appear to have any significant structure-
directing role.
In the crystal structure of m-Ni-1 (space group P21/c),
porphyrins adopt offset π-π stacking arrangements with a
separation of 3.73(1) Å between the least-squares planes of
adjacent porphyrins and a Ni‚‚‚Ni offset distance of
6.554(1) Å. Alternate porphyrins within a single stack are
rotated by ca. 120° with respect to each other, facilitating
effective matching of the distorted porphyrin cores (Figure
2). The stacks may be considered to form layers parallel to
the crystallographic bc plane, with the alkyl and tert-
butylphenyl substituents interlocking between adjacent stacks
within each layer. The layers expose predominantly alkyl
and tert-butylphenyl substituents on one side and alkyne
phosphine substituents on the other side, which associate like-
to-like; the phenyl groups of the alkyne phosphine substit-
uents associate in mutual edge-face arrangements across
centers of symmetry (forming a quadruple “phenyl em-
brace”),24 and the alkyl and tert-butylphenyl substituents
interlock on the opposite side of the layers, leading to an
overall bilayer-type arrangement.
a C5 is substituted with the phenyl ring bearing the acetylene phosphine
group.
the length of the chain, such that the first carbon atom has
Uiso ) 1 × free variable, the second carbon atom has Uiso
)
1.15 × free variable, etc. All porphyrins adopt a ruffle
distortion, in which the meso carbons around the core are
displaced alternately upward and downward with respect to
the mean porphyrin plane (expressed by the deviation (d)
perpendicular to the porphyrin plane in Table 1). The
absolute deviation from planarity (measured by the average
perpendicular deviation from the least-squares plane through
all 24 porphyrin core atoms, denoted σ in Table 1) is specific
to the metalation state; the average deviations in m-Fb-1 (σ
) 0.177 Å) and m-Zn-1 (σ ) 0.107 Å) are similar and are
much smaller than those in m-Ni-1 (σ ) 0.270 Å). The large
distortion in the latter stems from the relatively small size
of the nickel(II) ion (reflected by the relatively short Ni-N
bond distances) and its tendency to drive the ideal square-
planar geometry of the porphyrin toward the preferred
tetrahedral geometry; the geometry in m-Ni-1 is not unusual
for electronically unperturbed nickel(II) porphyrins. In all
three structures, the meso-phenyl substituent to which the
phosphine group is attached is rotated with respect to the
porphyrin plane by an angle in the range 75-88° (expressed
as the dihedral angle δ between the least-squares planes of
the phenyl ring and the porphyrin core, Table 1). The phenyl
groups of the phosphine point inward toward the porphyrin,
such that the lone pair of the phosphorus points away from
the porphyrin. Slight variations in the relative orientation of
the phosphine group are observed in the three structures,
consistent with observed rotational freedom around the
acetylene spacer (indicated by the equivalency of the
corresponding phenyl protons in the solution 1H NMR
spectra). The exact conformational preference of the phos-
phine group in the three structures is likely to be influenced
by secondary intermolecular interactions.
m-Fb-1 crystallizes in space group P21/n as monomeric
units that associate across centers of symmetry, adopting
Clearly, there is no intermolecular coordination between
the phosphine and the Ni centers of adjacent porphyrins in
m-Ni-1. By contrast, intermolecular coordination of the
phosphine to the zinc atom is observed in the crystal structure
of m-Zn-1. This is consistent with the solution NMR
spectrum of m-Zn-1 (and also p-Zn-1), which displays a
broadened 31P{1H} NMR resonance, which sharpens upon
cooling the sample to -20° or upon addition of pyridine.15
(23) In the refined structure of m-Fb-1, residual electron density of ca. 3.0
e Å-3 was observed at the center of the porphyrin cavity. This result
was repeated for several different crystals and was interpreted therefore
as a partial zinc atom, present in ca. 8% of the porphyrin molecules,
probably as a result of incomplete demetalation during acidic workup
in this particular sample. It should be noted that the structure of m-Fb-1
differs dramatically from that of m-Zn-1 (reported herein), and we
conclude therefore that the gross structure is that of the free-base form.
Literal interpretation of the X-ray results would suggest that the crystals
analyzed actually comprise solid solutions of ca. 8% m-Zn-1 in a lattice
of m-Fb-1.
(24) Dance, I.; Scudder, M. J. Chem. Soc., Chem. Commun. 1995, 1039-
1040.
Inorganic Chemistry, Vol. 42, No. 20, 2003 6567

Stulz et al.
part of each helix is largely occupied by the phenyl
substituents on the phosphorus, which show mutual edge-
face interactions. Between helices, porphyrins adopt offset
π-π stacking arrangements, with a distance of 3.63(1) Å
between the least-squares planes of adjacent porphyrins and
a Zn‚‚‚Zn offset separation of 5.170(1) Å. This arrangement
of helices leaves apparent tubular channels, which are filled
by (disordered) hexyl side chains. Two hexyl side chains
that are part of the same unsubstituted dipyrromethane moiety
(i.e., at the 7- and 13-positions of the macrocycle core)
interlock within the channels, while the other two wrap
partially around the helices to form an apparent hydrophobic
surface (Figure 3 and Figure 4).
Figure 3. Stereo representation of the helical structure in the crystal of
m-Zn-1. In the lower part, the hexyl side chains on the porphyrins and the
tBu groups on the meso-phenyl substituents have been omitted to allow
better view of the interior of the helix.
Two-Porphyrin Arrays. In a previous report, we have
shown that m-1 and p-1 readily form two-porphyrin dimeric
arrays with tbRu-4 both in solution and in the gas phase,
the latter being analyzed by matrix-assisted laser desorption
ionization time-of-flight mass spectrometry.15 This can be
generalized to all ruthenium porphyrins investigated here,
including the sterically hindered Ru-6. In Figure 5, the low-
This behavior is indicative of weak binding of the phosphine
to the zinc porphyrin and is not observed in the free-base or
nickel analogues. The zinc-phosphorus bond distance of
2.792(2) Å in m-Zn-1 is relatively long compared with the
metal-phosphorus bond distances of 2.3-2.4 Å found in
ruthenium or rhodium porphyrin complexes and suggests that
the interaction is rather weak not only in solution but also
in the solid state.
Compared with p-Zn-1, which forms a dimeric methanol
complex in the solid state,15 the shift of the acetylene
substituent from the para to the meta position has a dramatic
impact on the intermolecular association. In m-Zn-1, Zn-P
coordination leads to formation of a C3-symmetrical helix,
with a helical repeat distance of ca. 18 Å (the lattice
parameter c, Figure 3). In the crystal, the helices are arranged
into a hexagonal superstructure in which right-handed and
left-handed helices are always adjacent to each other (render-
ing the overall crystal structure achiral, Figure 4).The internal
1
field region of the H NMR spectra of the OEP-complexes
[m-Fb-1/Ru-3] and [p-Fb-1/Ru-3] and of the complexes with
the bulky TPP-derivative [p-Fb-1/Ru-6] and [m-Fb-1/Ru-
6] are shown. The dimeric complexes show two sets of
1
signals of nonequal integral values in the H NMR spectra
for both porphyrins, one set consisting of sharp resonances
(Hx in Figure 5) and the other consisting of slightly broadened
resonances (Hx′ in Figure 5). This aspect is most predominant
for the meso- and â-pyrrole protons of the porphyrins
(δ 8.5-10.5, denoted Hm(1), Hb and Hm(3) in Figure 5) and
for the ortho protons of the phenyl substituent of the bound
phosphine (δ ∼ 4.5 ppm, denoted Ho). This feature also
extends to the signals of the pyrrole nitrogen protons at
Figure 4. Crystal packing diagram in m-Zn-1, viewing along the crystallographic c-axis. The hexyl side chains on the porphyrins and the hydrogens have
been omitted.
6568 Inorganic Chemistry, Vol. 42, No. 20, 2003

Construction of Multiporphyrin Arrays
1
Figure 5. Low-field region of the H NMR spectra of (A) [p-Fb-1/Ru-6], (B) [m-Fb-1/Ru-6], (C) [p-Fb-1/Ru-3], and (D) [m-Fb-1/Ru-3].
1
δ ∼ -2.5 ppm (not shown). In the H NMR spectrum of
[m-Fb-1/Ru-6], an additional very weak signal at δ 4.70 ppm
(Ho′′) could be identified and assigned to a third conformation
sion of the different conformations. The relative ratio of the
two different conformations is 1:0.5 in [p-Fb-1/Ru-3], 1:0.3
in [p-Fb-1/Ru-6], 1:0.2 in [m-Fb-1/Ru-3], and 1:0.1 in
[m-Fb-1/Ru-6]. The smaller integral values always cor-
respond to the broadened set of resonances. The resonances
Hb′ and Hm(3)′ become smaller, broader, and more downfield
shifted when the ligand is changed from p-Fb-1 to m-Fb-1,
which could indicate reduced stability of the conformation
associated with these signals. At present, the exact geometries
of the two conformations are not clear. It seems that two
major conformations are present but probably more could
be possible in the case of [m-Fb-1/Ru-6]. In the analogous
complexes with the model ligand DPAP, only one averaged
spectrum per ruthenium complex could be observed.19,20
As expected,21 dimeric complexes with the iodo rhodium
porphyrins were not formed cleanly, except with Rh-5Me,
as shown in Figure 7 for the [m-Fb-1/Rh-5Me] complex.
In this case, splitting of the proton resonances was not
observed, but the 31P NMR spectrum showed a slightly
from the H-1H nuclear Overhauser effect spectrometry
1
(NOESY) spectrum (dash-dotted lines in Figure 6). Since
the 31P NMR spectra showed only bound phosphine (δ -12
ppm, singlet resonance), there is no equilibrium between free
and bound species, and the splitting of the signals must arise
from two distinct conformations, which are stable on the
chemical-shift time scale. Studies with CPK models suggest
that rotation around the acetylene group could result in two
different conformations, and cross-peaks in the 1H-1H
NOESY spectra between the two sets of signals indicate that
these are slowly interchanging at room temperature. Figure
6 shows part of the H-1H NOESY spectrum of [m-Fb-1/
1
Ru-6]. NOE connectivities between Hb and the hexyl side
chain of m-Fb-1 and between Ha and Hc prove the integrity
of the complex, and the cross-peaks between the resonances
of the bound ligand Ho, Ho′, and Ho′′ show the interconver-
Inorganic Chemistry, Vol. 42, No. 20, 2003 6569

Stulz et al.
proton resonances are highlighted; the singlets at δ 10.26
ppm (meso proton of m-Fb-1) and 8.69 ppm (â-pyrrole
proton of Rh-5Me) confirm the 1:1 stoichiometry, the upfield
shifted resonances of the phenyl substituents of the phosphine
at δ 6.93 ppm (para), 6.70 ppm (meta), and 4.72 ppm (ortho)
confirm binding of the phosphine in the shielding region of
Rh-5Me, and the resonance at the very low value of δ -6.27
ppm (σ-bonded methyl group on Rh-5Me) is consistent with
monomeric binding of phosphine to rhodium.
Complexes with the various donor and acceptor porphyrins
are possible in all combinations (except for rhodium) by
mixing equimolar amounts of the donor and acceptor
porphyrins, leading to stable dimeric arrays of the form A-D.
In the ruthenium(II) arrays, different conformers could be
1
detected by H NMR spectroscopy. On the other hand, the
rhodium(III) arrays having an association constant that is
about 100 times smaller than those in the Ru(II) complexes,
the larger off-rate leads to a shorter lifetime of one particular
conformer; hence only an averaged proton NMR spectrum
is observed. The crystal structures of the model complexes
with DPAP reveal that the complex with Rh-5Me has a
Rh-P bond distance (2.512(3) Å) significantly longer than
the typical Ru-P bond distance (ca. 2.36 Å), and the binding
constant is also lower by a factor of about 103. These
properties might allow for several possible conformations
of the rhodium complex to interconvert rapidly on the NMR
time scale.
Figure 6. Part of the NOESY spectrum of [m-Fb-1/Ru-6].
Three-Porphyrin Arrays. Three-porphyrin arrays are
readily available from 2:1 mixtures of donor-acceptor
porphyrins.15 All of the ruthenium porphyrins investigated
broadened resonance at δ -28 ppm for the bound phosphine,
analogous to the DPAP-Rh-5Me complex. The diagnostic
1
Figure 7. (A) H NMR and (B) 31P NMR spectra of [m-Fb-1/Rh-5Me].
6570 Inorganic Chemistry, Vol. 42, No. 20, 2003

Construction of Multiporphyrin Arrays
moiety are tilted further from orthogonality in [p-Ni-1/tbRu-
4/p-Ni-1] (69.9° and 66.4°) than those in m-Ni-1 (81.4° and
83.8°). The geometrical parameters of the ruthenium coor-
dination sphere (Table 2) match well with those of the model
complex (DPAP)2tbRu-4; the Ru-P bond distance of
2.343(2) Å and the angle of the Ru-P bond to the porphyrin
planeR86.2°differonlyslightlyfromthosein(DPAP)2tbRu-4
(2.3623(10) Å, 89.5°).19 Thus, attachment of the nickel
porphyrin on the phosphine ligand does not significantly alter
the coordination behavior of the phosphorus. The overall
conformation of the complex is such that the two nickel(II)
porphyrins are twisted in opposite directions with respect to
the tbRu-4 moiety, forming dihedral angles of 79.8° between
the least-squares planes of the porphyrins. This conformation
might be related to one of the conformations observed in
Figure 8. X-ray structure of [p-Ni-1/tbRu-4/p-Ni-1]. Hydrogen atoms and
the hexyl side chains (except for the first carbon atom) have been omitted
for clarity.
Table 2. Selected Geometrical Parameters for [p-Ni-1/tbRu-4/p-Ni-1]
p-Ni-1 residue
tbRu-4 residue
Ni/Ru-N1/Å
Ni/Ru-N2/Å
Ni/Ru-N3/Å
Ni/Ru-N4/Å
σ /Å
1.915(8)
1.924(8)
1.920(8)
1.939(8)
2.067(6)
2.075(6)
1
the H NMR spectra.
0.470
0.046
85.8(2) (C5/15-Ph)
In the case of the rhodium porphyrins, the iodide is readily
displaced upon mixing 2 equiv of the donor porphyrins with
the acceptor porphyrin. The arrays adopt several geometries
in solution that can be detected in the 1H NMR spectra. For
the â-pyrrole protons of Rh-6, three singlets at δ 9.01, 9.00,
and 8.87 ppm could be found; also, the phosphine-phenyl
proton resonances appear as two distinctively different sets
of signals. For all rhodium-containing arrays, the 31P NMR
spectra only showed the characteristic doublet resonances
δ/° a
69.9(2) (C5-Ph)
66.4(2) (C15-Ph)
0.473(9) (C5)
-0.482(11) (C10)
0.497(10) (C15)
-0.504(12) (C20)
2.343(2)
d/Å
0.083(8) (C5)
-0.011(7) (C10)
Ru-P/Å
R/° b
86.2(1)
a C5 is substituted with the phenyl ring bearing the acetylene phosphine
group. b R denotes the angle between the ruthenium-phosphorus bond and
the least-squares plane of the porphyrin core of tbRu-4.
1
(δ ∼ -10 ppm, JRh-P ∼ 90 Hz) for the bisphosphine
complexes with rhodium and no indication of the presence
of various geometries, as in the ruthenium porphyrin arrays.
The three porphyrin arrays of the composition D-A-D
can also be synthesized.19,21 The arrays are stable in solution,
judged from the 1H and 31P NMR spectra, and the phosphines
are fully coordinated to the acceptor porphyrin in the
millimolar concentration range. The rhodium arrays generally
are easier to synthesize and show a better solubility in CHCl3
than the ruthenium arrays. However, solubility is also greatly
influenced by the nature of the acceptor porphyrin, which is
enhanced for Ru/Rh-4 and Ru/Rh-6 but rather low for Ru-3
and Ru-5.
here form bisphosphine complexes in the same way. Thus,
the diphenyl porphyrin-acetylene substitution pattern on the
ligand does not interfere with the coordination abilities of
the phosphine, and formation of stable trimeric arrays is
unaffected by employing sterically hindered ruthenium
porphyrins such as Ru-6. The 31P{1H} NMR spectra show
singlet resonances in the range of δ -1 ppm (Ru-3) to +3
ppm (Ru-6), consistent with the chemical shift of bisphos-
1
phine ruthenium porphyrin complexes.19 In the H NMR
spectra, further splitting of the signals is observed as
compared to the dimeric arrays. For example, in [m-Fb-1/
Ru-6/m-Fb-1], the â-pyrrole protons of Ru-6 appear as three
singlets at δ 8.24, 8.17, and 8.15 ppm in a ratio of 0.1:1:0.8
(the spectra of all the arrays discussed here can be found in
the electronic SI). The extension of the array from two to
three porphyrins thus also increases the complexity of the
constructs in solution.
The trimeric array [p-Ni-1/tbRu-4/p-Ni-1] was crystallized
from a chloroform solution layered with methanol, giving
small, weakly diffracting single crystals that were examined
using a synchrotron radiation source. The molecular unit of
the array is shown in Figure 8, and selected geometrical
parameters are given in Table 2. The complex crystallizes
as a dichloroform solvate in space group P1h, with the
ruthenium atom sited on a center of symmetry. The nickel-
porphyrin units show a ruffle distortion similar to that in
m-Ni-1 but deviating much further from planarity (σ 0.470
Å). This is also expressed in the larger deviation of the meso
carbons (d) perpendicular to the porphyrin plane (Table 2).
The ruthenium porphyrin is essentially planar (σ 0.046 Å).
In addition, the meso-phenyl substituents on the p-Ni-1
The building blocks m-2 allow us to build three porphyrin
arrays where the acceptor porphyrins are located at the
periphery. The order of the porphyrins is reversed, giving
arrays of the form A-D-A. In Figure 9, the NMR spectra
of the arrays [Ru-4/m-Fb-2/Ru-4] and [Rh-5Me/m-Zn-2/
Rh-5Me] are displayed as representative examples. In the
case of the ruthenium-containing arrays, three different
species could be detected, which is best seen in the spectrum
of [Ru-4/m-Fb-2/Ru-4]. The relative ratio of the signals at
δ 8.96, 8.88, and 8.82 ppm is 0.2:1:0.8, an almost identical
distribution to that in the array [m-Fb-1/Ru-6/m-Fb-1]. A
1
close inspection of the H NMR spectrum shows that for
the meso protons of the Ru-4 residue three large singlets
and several small peaks can be observed; the meso protons
of the m-Fb-1 residue display at least four signals, and the
signal for the pyrrole NH’s at δ -2.43 ppm shows a much
more complex pattern with several overlapped and broadened
peaks (inset in Figure 9). This suggests that there could be
an even larger diversity in conformations than expected. The
31P NMR spectra show the phosphine resonances in the
Inorganic Chemistry, Vol. 42, No. 20, 2003 6571

Stulz et al.
Figure 9. 1H NMR spectra of (A) [Rh-5Me/m-Zn-2/Rh-5Me] (A-X ) Rh-Me, D ) Zn) and (B) [Ru-4/m-Fb-2/Ru-4] (A-X ) Ru-CO, D ) 2H). The
inset in A shows the resonance of the rhodium bound methylide, and the inset in B displays the resonances of the pyrrole N-H’s.
expected regions for monophosphine complexes. In the case
of the ruthenium-porphyrin arrays, the 31P NMR spectrum
shows two signals, e.g., for [Ru-6/m-Fb-2/Ru-6] at δ -10.6
and -10.7 ppm. This was not observed for the D-A-D
arrays. For the [Rh-5Me/m-Zn-2/Rh-5Me] complex, the
phosphorus resonance is broadened and appears at a slightly
lower field than the free phosphine, which is consistent with
the observations made with DPAP and Rh-5Me.21 No free
phosphine could be detected in any case.
In summary, both mono- and disubstituted porphyrins
m/p-1 and m-2 form stable complexes with both ruthenium
and rhodium porphyrins. The composition of the arrays,
D-A, D-A-D, or A-D-A, can be chosen by mixing the
appropriate amounts of the building blocks in solution. The
substitution pattern or the metalation state has no influence
on the coordination ability of the phosphine, and in m-2,
both phosphines are available for complexation. It should
therefore be possible to form larger arrays, incorporating
different porphyrins in the center and on the periphery. The
arrays are not kinetically inert, judged from our studies with
the model ligand DPAP;19,21 this feature is in fact exploited
to form dynamic combinatorial libraries.16 For the trimeric
arrays, this does however prevent the formation of arrays
with different building blocks A and A′ (or D and D′).
Synthesizing mixed arrays of the form A-D-A′ would result
in scrambling and in the formation of a statistical mixture,
composed of the three complexes A-D-A, A′-D-A′, and
A-D-A′. No attempts were thus made to construct such
mixed arrays. As we will show below, mixing different
building blocks is still possible to a certain extent in larger
arrays.
Assembly of Larger Arrays. The diphosphine-substituted
porphyrin m-2 and the bisphosphine complexes (P)Ru(P) or
(P)Rh(P) can be regarded as chain extenders and the
monophosphines m/p-1, (P)Ru(CO), and (P)Rh-5Me as
chain terminators. Larger porphyrin arrays thus seem to be
accessible by mixing appropriate equivalents of chain
extender and chain terminator. The composition of these
arrays would be either of the form A-D-(A′-D)n-A or
of the form D-A-(D′-A)n-D. We therefore attempted to
assemble larger arrays from different building blocks,
incorporating structurally very different porphyrins into the
complexes. For example, a 2:2:1 (A-D-A′ or D-A-D′)
mixture of m-Fb-1, Rh-5, and m-Zn-2 or of Ru-3, m-Fb-2,
and Rh-5 should form arrays of the composition [m-Fb-1/
Rh-5/m-Zn-2/Rh-5/m-Fb-1] or [Ru-3/m-Fb-2/Rh-5/m-Fb-
2/Ru-3], respectively. The complexities of both the 31P NMR
1
and H NMR spectra increase as expected. The 31P NMR
spectrum of the latter mixture shows the two types of
phosphine complexes: two doublets at δ ∼ -10 ppm for
the rhodium bisphosphine in the center, and the broadened
singlet at δ -15 ppm of the ruthenium monophosphine
complex at the periphery of the array (see electronic SI for
NMR spectroscopic details).
Changing the stoichiometry of the building blocks to 2:3:2
would yield seven porphyrin arrays of the composition
D-A-D′-A-D′-A-D, e.g., [m-Fb-1/Rh-5/m-Fb-2/Rh-
5/m-Fb-2/Rh-5/m-Fb-1] and [p-Fb-1/Rh-4/m-Zn-2/Rh-4/
m-Zn-2/Rh-4/p-Fb-1]. The 31P NMR spectrum showed
several doublets at δ ∼ -9 ppm (1JRh-P ) 89 Hz), consistent
with the formation of bisphosphine complexes. Multiple
singlets for the meso- and â-pyrrole protons show again an
6572 Inorganic Chemistry, Vol. 42, No. 20, 2003

Construction of Multiporphyrin Arrays
Figure 10. 1H NMR spectrum of a 2:4:3 mixture of m-Fb-1, Rh-5, and m-Zn-2. The inset displays part of the 31P NMR spectrum.
Scheme 2
increased number of different complexes present. The 2:4:3
mixture of m-Fb-1, Rh-5, and m-Zn-2 could yield a nine-
porphyrin array [m-Fb-1/Rh-5/m-Zn-2/Rh-5/m-Zn-2/Rh-5/
rated as predetermined by the structure of the building blocks
and by the relative stoichiometries in the mixtures.
Conclusions
1
m-Zn-2/Rh-5/m-Fb-1], of which both H NMR and 31P
We have demonstrated that phosphine-substituted porphy-
rins are versatile building blocks for the construction of
supramolecular arrays. Arrays have been made incorporating
three different porphyrins, as outlined in Scheme 2. The
substitution pattern (meta or para) and the metalation state
(free-base, zinc, nickel) has no influence on the affinity of
the phosphine toward a variety of ruthenium and rhodium
porphyrins. As for the acceptor porphyrins, variations in the
porphyrin substituents, on both the meso- and â-pyrrole
position, have no influence on the coordination as well. Even
the bulky porphyrin 6 forms stable arrays with all phosphine
porphyrins. The arrays are easily accessible simply by mixing
appropriate amounts of the building blocks in solution.
However, care has to be taken by choosing the correct
acceptor porphyrins, i.e., if a rhodium porphyrin is intended
to be located at the periphery. Also, if monophosphine
ruthenium complexes are prepared, they cannot be isolated
due to the lability of the bound carbonyl on ruthenium, which
would be lost and result in scrambling of the array. By the
introduction of a variety of different metalation states and
substitution patterns, it should thus be possible to create
arrays with well-defined electronic gradients, which could
NMR spectra are displayed in Figure 10. No free phosphine
is detectable in the 31P NMR spectrum at δ -32 ppm; thus
all the binding sites on rhodium are occupied by phosphine
ligands.
One has to be cautious when analyzing higher-order
architectures such as those described here because the kinetic
lability leads to a weighted distribution of dimeric, trimeric,
and higher-order assemblies, as can be observed in self-
assembled supramolecular structures in solution.25,26 The
kinetic lability of the systems16 unfortunately prohibits
analysis of a molecular weight distribution using chromato-
graphic methods, such as gel permeation chromatography
or using mass spectrometry,27 and the determination of the
mole fractions of the individual complexes is not possible
from the NMR spectroscopic data. Therefore, the complex
mixtures described here may not contain the anticipated array
as a major component. Nevertheless, any array formed will
have the desired peripheral and central porphyrins incorpo-
(25) Ercolani, G. Chem. Commun. 2001, 1416-1417.
(26) Ercolani, G. J. Phys. Chem. B 2003, 107, 5052-5057.
(27) Stulz, E.; Mak, C. C.; Sanders, J. K. M. J. Chem. Soc., Dalton Trans.
2001, 604.
Inorganic Chemistry, Vol. 42, No. 20, 2003 6573

Stulz et al.
be used to transmit energy from either the periphery to the
center, or vice versa. These interactions could be controlled
by careful choice of the chain extenders and terminators.
gratefully acknowledged. We thank a referee for helpful
comments on the composition of the higher-order complexes.
Supporting Information Available: Full experimental details
and analytical data of the building blocks, of the discussed arrays,
and X-ray crystallographic files for m-Fb-1, m-Zn-1, m-Ni-1, and
[p-Ni-1/tbRu-4/p-Ni-1] in PDF and CIF formats. This material is
available free of charge via the Internet at http://pubs.acs.org.
Acknowledgment. We thank Brian Crysell, Duncan
Howe, and Andrew Mason for help and support in running
the NMR spectrometers. Financial support from the Swiss
National Science Foundation (E.S.) and from the EPSRC is
IC034699W
6574 Inorganic Chemistry, Vol. 42, No. 20, 2003