Hetero trinuclear oxo-bridged complexes of ruthenium porphyrin and iron phthalocyanine

Article abstract of DOI:10.1139/v00-180

New diamagnetic hetero bi- and trinuclear oxo-bridged metal complexes of formula (L)(Pc)Fe-O-Ru(TPP′)(O) and (L)(Pc)Fe-O-Ru(TPP′)-O-Fe(Pc)(L) have been prepared from Ru(TPP′)(O)₂ and Fe(Pc)(L)₂ (TPP′ = tetrakis(4-methoxyphenyl)porphyrinate, Pc = phthalocyanate ion, L = monodentate ligand). The trinuclear complex binds a variety of ligands (4,4′-bipy, 4-MePy, P(OEt)₃, pip, NH₃, 1-MeIm, P(Me)₂Ph) trans to the oxo-bridge. ¹H NMR spectra are characterized by large ring current shifts (rcs) due to the TPP′ and Pc ions. The complexes show an unusually weak Pc Q band in their visible spectra at 700 nm and two CT bands in the near-IR region from 1000 to 1500 nm, which are sensitive to the trans ligand. The trinuclear complex can be reversibly oxidized to the +1 and +2 ions, formally Fe(IV)-O-Ru(IV)-O-Fe(III) and Fe(IV)-O-Ru(IV)-O-Fe(IV) at 0.4 and 0.76 V. The +1 ion is chemically obtained by reaction of the neutral species with (Cp)₂Fe⁺ for L = 4-MePy and this reaction is reversed upon addition of L′ = P(Me)₂Ph. Reductive cleavage by hydroquinone, phosphines and phosphites are the slowest of all RuTPP[O(FeN₄)]₂ systems studied to date (t_1/2 = 8 h at 40°C).

Full text of DOI:10.1139/v00-180

795
Hetero trinuclear oxo-bridged complexes of
ruthenium porphyrin and iron phthalocyanine
Fabio Zobi and Dennis V. Stynes
Abstract: New diamagnetic hetero bi- and trinuclear oxo-bridged metal complexes of formula (L)(Pc)Fe-O-
Ru(TPP′)(O) and (L)(Pc)Fe-O-Ru(TPP′)-O-Fe(Pc)(L) have been prepared from Ru(TPP′)(O)2 and Fe(Pc)(L)2 (TPP′ =
tetrakis(4-methoxyphenyl)porphyrinate, Pc = phthalocyanate ion, L = monodentate ligand). The trinuclear complex
1
binds a variety of ligands (4,4′-bipy, 4-MePy, P(OEt)3, pip, NH3, 1-MeIm, P(Me)2Ph) trans to the oxo-bridge. H NMR
spectra are characterized by large ring current shifts (rcs) due to the TPP′ and Pc ions. The complexes show an unusu-
ally weak Pc Q band in their visible spectra at 700 nm and two CT bands in the near-IR region from 1000 to
1500 nm, which are sensitive to the trans ligand. The trinuclear complex can be reversibly oxidized to the +1 and +2
ions, formally Fe(IV)-O-Ru(IV)-O-Fe(III) and Fe(IV)-O-Ru(IV)-O-Fe(IV) at 0.4 and 0.76 V. The +1 ion is chemically
obtained by reaction of the neutral species with (Cp)2Fe+ for L = 4-MePy and this reaction is reversed upon addition
of L′ = P(Me)2Ph. Reductive cleavage by hydroquinone, phosphines and phosphites are the slowest of all
RuTPP[O(FeN4)]2 systems studied to date (t1/2 = 8 h at 40°C).
Key words: ruthenium, iron, porphyrin, phthalocyanine, oxo.
Résumé : En faisant réagir du Ru(TPP′)(O)2 et du Fe(Pc)(L)2 (TPP′ = tétrakis(4-méthoxyphényl)porphyrinate, Pc = ion
phtalocyanate, L = ligand monodentate), on a préparé de nouveaux complexes métalliques diamagnétiques, hétéro-bi et
-trinucléaires, à ponts oxo, de formules (L)(Pc)Fe-O-Ru(TPP′)(O) et (L)(Pc)Fe-O-Ru(TPP′)-O-Fe(Pc)(L). Le complexe
trinucléaire se fixe à une variété de ligands (4,4′-bipy, 4-MePy, P(OEt)3, pip, NH3, 1-MeIm, P(Me)2Ph), de façon trans
1
par rapport au pont oxo. Les spectres de RMN du H sont caractérisés par d’importants déplacements de courant de
cycle causés par les ions TPP′ et Pc. Dans leurs spectres dans le visible, ces complexes comportent une bande Q anor-
malement faible pour le Pc, à 700 nm, et deux bandes CT dans la région du proche infrarouge, entre 1000 et 1500 nm,
qui sont sensibles au ligand trans. À des valeurs de 0,4 et 0,76 V suivant le cas, le complexe trinucléaire peut être
oxydé de façon réversible vers les ions +1 et +2 qui sont formellement le Fe(IV)-O-Ru(IV)-O-Fe(III) et le Fe(IV)-O-
Ru(IV)-O-Fe(IV). On peut obtenir l’ion +1 de façon chimique par réaction de l’espèce neutre avec (Cp)2Fe+, pour L =
4-MePy, et cette réaction est renversée par l’addition de L′ = P(Me)2Ph. De tous les clivages réducteurs par
l’hydroquinone, les phosphines et les phosphites observés à date avec des systèmes RuTPP[O(FeN4)]2, ce sont les plus
lents (t1/2 = 8 h, à 40°C).
Mots clés : ruthénium, fer, porphyrine, phtalocyanine, oxo.
[Traduit par la Rédaction] 801
Introduction
Zobi and Stynes study we extend this reaction to a new class of oxo-bridged
heterotrinuclear complexes containing the iron
The study of oxo-bridged multinuclear metal complexes
has continued to attract interest both for their biological rele-
vance (1) and as the most common example of single atom
bridged systems (2). Oxo-bridged metal complexes have
been prepared by hydrolytic processes (3), by one-electron
redox reactions in which a high valent metal-oxo compound
is reacted with a lower valent metal complex (4), and by
autoxidation (5). We and others have employed a RuVI(O)2
porphyrin as a route to µ-oxo trinuclear species (6, 7) In this
phthalocyanine (FePc) moiety.
Experimental
Materials
Common ligands were obtained from standard sources
and were used as received. Solvents were distilled and kept
over molecular sieves (3 Å). CDCl3 was dried over activated
molecular sieves (3 Å) and freed of acid by filtering through
vacuum
porphyrin
dried
(H2TPP′),
Al(OH)3.
Tetrakis(4-methoxyphenyl)
and
Received August 31, 2000. Published on the NRC Research
Press Web at http://canjchem.nrc.ca site on June 30, 2001.
Ru(TPP′)(CO)(C2H5OH),
Ru(TPP′)(O)2 were prepared by literature methods (8–10).
Dedicated to Professor Brian James on the occasion of his
65th birthday.
Physical measurements
F. Zobi and D.V. Stynes.1 Department of Chemistry York
University, Toronto, ON M3J 1P3, Canada.
Visible spectra were recorded on a HP-8451 Diode array
UV–vis spectrometer in 1 cm glass cuvettes thermostated at
1
1Corresponding author (telephone: (416) 736-2100, ext.
22308; e-mail: stynes@yorku.ca).
25°C. H NMR spectra were obtained on a Bruker ARX
400 MHz spectrometer at 300 K using CDCl3 as the solvent
Can. J. Chem. 79: 795–801 (2001)
© 2001 NRC Canada
DOI: 10.1139/cjc-79-5/6-795

796
Can. J. Chem. Vol. 79, 2001
Fig. 1. Experimental (a) and simulated (b) MS spectra of 2. Shown is the isotopic distribution of the peak at m/z 2002, assigned to the
[(Pc)FeO]2Ru(TPP′) skeleton.
100
90
80
(a)
(b)
70
60
50
40
30
20
10
0
1991.0
2000.8
2010.6
with TMS as an internal standard. Near-IR spectra were re-
corded on a Cary 2400 UV–vis – near-IR spectrometer at
25°C. Electrochemical data were collected with a computer-
controlled Electroanalytical Cypress System model CS-
1090. Cyclic voltammetry experiments were performed un-
der a nitrogen atmosphere in a CH2Cl2 solution containing
0.1 M (TBA)PF6 and ~5 × 10–3 M complex at –42°C. A
platinum disk sealed in glass was used as a working elec-
trode. Graphite was used as a counter electrode and
AgCl/Ag was used as the reference electrode. Ferrocene was
used as an internal reference (Fc+/Fc = 0.46 V in CH2Cl2 vs.
SCE). Mass spectra were collected with a Perseptive
Biosystems MALDI spectrometer, model Voyager-DE STR
operating in the positive-ion mode.
an insoluble precipitate both in solution (within minutes)
and in the solid state even when stored in vacuo at –20°C.
[(4-MePy)Fe(Pc)O]2Ru(TPP′) (2)
Freshly made Ru(TPP′)(O)2 (100 mg, 0.116 mmol) and
Fe(Pc)(4-MePy)2 (200 mg, 0.265 mmol) were mixed as sol-
ids and dissolved in a CH2Cl2–CHCl3 solution (3:1, 18 mL).
After 40 min hexane (50 mL) was slowly added depositing
223 mg of a black crude precipitate. The product was found
to be contaminated by unreacted Fe(Pc)(4-MePy)2 and
[Ru(TPP′)(OH)]2O, which were subsequently removed by
recrystallizing the complex from a hexane–CHCl3 solution.
Yield: 199 mg, 79%. MALDI-MS (CHCl3) m/z: 2188 ([M]+).
Other relevant peaks are at 2002 ([(PcFeO)2Ru(TPP′)]+)
(Fig. 1), 1418 ([(Pc)FeORu(TPP′)]+), 850 ([Ru(TPP′)(O)]+),
662 ([Fe(Pc)(4-MePy)]+), 569 ([Fe(Pc)]+). Anal. calcd for
C124H82N22O6Fe2Ru: C 68.04, H 3.78, N 14.08; found:
C 68.39, H 3.76, N 13.91. This complex is sensitive to trace
acid normally present in CDCl3, therefore, its 1H NMR spec-
trum must be taken in acid free solvents. Various ligated de-
rivatives of 2 were generated in situ in a NMR tube by
addition of excess ligand L (L = 4,4′-bipy, pip, NH3, 1-MeIm,
P(CH3)2Ph) to the 4-MePy-ligated derivative in a chloroform
solution. Solid samples were obtained in quantitative yields
by precipitation with hexane (typically 1–3 mg).
Fe(Pc)(L)2 (L = 4-MePy, 1-MeIm)
Fe(Pc) (Pc = phthalocyanate ion) (Aldrich) (1 g,
1.76 mmol) was dissolved in a CHCl3 solution (25 mL) con-
taining 4-MePy (5 mL, 51.4 mmol). After stirring the solu-
tion for 10 h at room temperature a purple crystalline
precipitate was collected by filtration through paper. The
product was then washed with hexane and dried in vacuo.
Yield: 579 mg, 44%. Fe(Pc)(1-MeIm)2 was prepared by a
similar procedure. Yield: 697 mg, 54%.
[(1-MeIm)Fe(Pc)O]Ru(TPP′)(O) (1)
Kinetic measurements
Freshly made Ru(TPP′)(O)2 (5 mg, 5.8 × 10–3 mmol) and
Fe(Pc)(1-MeIm)2 (10 mg, 1.36 × 10–2 mmol) were dissolved
in a N2 purged CDCl3 solution (5 mL) and the reaction fol-
lowed by NMR. When all Ru(TPP′)(O)2 had reacted (indi-
cated by the disappearance of the Hβ peak at 9.11 ppm) the
reaction was quenched by slowly adding hexane (10 mL).
The ppt was filtered through paper and dried in vacuo. Yield:
6.9 mg, 80%. The complex was very reactive and it formed
Neat phosphines, phosphites, or a dichloromethane solu-
tion of hydroquinone were injected via syringe into a therm-
ostated (40°C) CHCl3 solution of the complex (1 × 10–5 M)
and the subsequent reaction followed by visible spectros-
copy. Pseudo-first-order rate constants were obtained by
monitoring the growth of the Soret band of the Ru(TPP′)L2
complex. Spectra were typically scanned between 380 and
820 nm under anaerobic conditions.
© 2001 NRC Canada

Zobi and Stynes
797
Fig. 2. Reaction sequence in the formation of [(4-MePy)Fe(Pc)O]2Ru(TPP′) (2). The intermediate binuclear species is indicated by 1.
O
CH3
O
N
O
N
Ru
O
N
N
N
O
N
O
N
O
Ru
O
N
N
N
Fe
N
N
N
O
O
N
N
O
N
N
N
N
N
O
Ru
O
O
N
O
CH3
N
O
N
N
N
N
Fe
N
O
N
N
N
N
N
O
N
N
N
N
Fe
N
N
N
N
N
N
N
Fe
N
N
N
N
CH3
N
N
CH3
CH3
( )
1
( )
2
The binuclear complex is formally FeIV-O-RuIV and is the
Fig. 3. Eclipsed (a) and staggered (b) conformations of stacked
TPP and Pc rings. A staggered conformation leads to prohibited
contacts between Pc benzopyrrole rings and TPP phenyls.
first example of a Ru porphyrin complex containing both a
terminal and a bridging oxo ligand. The presence of the re-
active terminal oxygen is inferred from the observation that
the binuclear species reacts with a second Fe(Pc) unit to
form the trinuclear compound and undergoes rapid reactions
on mixing with hydroquinone, DMSO, or dimethylphenyl-
phosphine. The oxidation products quinone, DMSO2, and
dimethylphenylphosphine oxide, respectively, were identi-
fied in the NMR spectrum.
1H NMR spectra
Both 1 and 2 are diamagnetic as expected for linear spe-
1
cies with axial dπ4 and dπ8 configurations (6). H NMR pro-
(a)
(b)
vides definitive characterization of the different ligated bi-
and trinuclear µ-oxo species. All spectra are characterized
by large ring current shifts (rcs) due to the TPP′ and Pc ions.
Observed shifts are consistent with rcs calculations carried
out on the basis of Abraham 12-loop model (12). An
eclipsed conformation of the macrocycles is most consistent
with the NMR data as this places the porphyrin Hβ protons
directly over the benzopyrrole rings. A staggered conforma-
tion would lead to prohibited contacts with the TPP′ phenyls
(Fig. 3). An eclipsed structure is rare for X-bridged dimers
and trimers (X = C, N, O). The only other known examples
are [(THF)(TPP)Fe-N-Fe(Pc)(H2O)](I5) (13), [(Pc)Al]2O
(14), and [Fe(OEP)]2O (15). Complex 2 is the first example
of a fully eclipsed macrocyclic trinuclear.2
1H NMR spectra of the bi- and trinuclear complexes are
shown in Figs. 4a and b, respectively. The binuclear species
is identified on the basis of differentiated TPP′ phenyls pro-
tons. Phenyl protons directed toward the Fe(Pc) face project
into the deshielding region of the Pc ring and experience a
downfield shift, while those directed to the open face (de-
noted Ho′ and Hm′ in Fig. 4a) experience a small upfield shift.
In the centrosymmetric trinuclear species a single set of
ortho and meta phenyl resonances is observed (Ho and Hm in
Fig. 4b). The porphyrin Hβ protons are shifted upfield (rela-
Results and discussion
Synthesis
Formation of 2, the trinuclear complex, proceeds through
the initial formation of a reactive binuclear species 1
(Fig. 2). Both steps involve an inner-sphere oxidation of the
FeII metal center by the dioxo Ru-porphyrin. Attempts to
isolate the 4-MePy derivative of 1 proved unsuccessful as 1-
(4-MePy) is extremely reactive.
The 1-MeIm derivative was isolated but survives only
long enough to obtain an NMR and observe its reactions
with reductants. Oxidation of the FeII metal center by
Ru(TPP′)(O)2 requires a vacant coordination site on Fe(Pc).
Ligand dissociation in Fe(Pc)(1-MeIm)2 is about 50 times
slower than Fe(Pc)(4-MePy)2 (11) and this allows for a
better control over the reaction. Slow dissociation of 1-
MeIm in the binuclear complex may also retard polymeriza-
tion of 1. While 1-(4-MePy) is generated in situ by reacting
Ru(TPP′)(O)2 with Fe(Pc)(4-MePy)2 in a 1:1 ratio, an ex-
cess of Fe(Pc)(1-MeIm)2 was used in the slower formation
of 1-(1-MeIm) to avoid formation of the [Ru(TPP′)(OH)]2O
dimer.
2 The [Mo3O4(TPP)3]+ ion shows partial eclipse of two Mo(TPP) moieties (16).
© 2001 NRC Canada

798
Can. J. Chem. Vol. 79, 2001
1
Fig. 4. Aromatic region of H NMR spectra of (a) binuclear 1-(1-MeIm); and (b) trinuclear 2-(4-MePy)2 species in CDCl3 (* indicates
solvent peak).
tive to Ru(TPP′)(O)2) in both 1 and 2. Axial ligand reso-
nances are also shifted upfield as a result of the cumulative
effect of Pc and TPP′ rcs. Hydrogen atoms at the ortho posi-
tion in 4-MePy, for example, suffer a 8.5 ppm upfield shift
in 1 and over 9 ppm upfield shift in 2 when compared to the
free ligand. Spectral data are collected in Table 1.
500 nm and is well-resolved in the IR. The same is true for
CT1 (see Tables 3 and 4). Both CT bands undergo a
bathochromic shift with increasing π-acceptor strength and
(or) increasing basicity of the axial ligand. A typical change
is shown in Fig. 6.
Ligation
The Fe(Pc) based heterotrinuclear complexes are substan-
tially more stable in solution than borylated dioxime and
paramagnetic heme or Fe(Schiff base)-derived Fe-O-Ru-O-
Fe systems (6, 7). Ligand displacement at the FeIII center
can be followed at room temperature by both NMR and
near-IR spectroscopy. 4-MePy in 2 is easily displaced by
stonger σ-donors such as NH3 and 1-MeIm, by π-acid lig-
ands including P(Me)2Ph, and by ligands capable of promot-
ing chain elongation like 4,4′-bipy (eq. [1]). These
substitution reactions are over on mixing at ambient temper-
Electronic spectra
The visible spectrum of 2 is given in Fig. 5. It shows a
typical porphyrin Soret band at 410 nm in contrast to a red-
shifted Soret band at about 435 nm in DMG and DPG
trinuclears (6). A weak bathochromic shifted phthalocyanine
Q band at about 700 nm is present in the visible spectrum of
2. An unusually weak Pc Q band is also reported for the µ-
nitrido (TPP)Mn-N-Fe(Pc) (17) and the µ-oxo (TPP)Cr-O-
Fe(Pc) (18) complexes. This feature may be characteristic of
X-bridged metal atoms containing face-to-face Pc and
porphyrin rings. Additionally, two low energy charge trans-
fer bands (CT1 and CT2) appear in the near-IR region at
1050 and 1330 nm (see Fig. 6 and Table 2).
The CT bands show significant shifts as a function of the
axial ligand suggesting that MO’s with substantial iron char-
acter are involved. The two bands are tentatively assigned to
an oxo-to-metal (CT1) and to an intervalence metal-to-metal
charge transfer (CT2). A similar assignment was made in
DMG based systems (6). The lower oxidation potential of 2
translates in a smaller HOMO–LUMO gap and less energy
is required for this transition. Consequently CT2 in 2 shifts
1
ature but are in the slow exchange limit in the H NMR.
[1]
[(4-MePy)Fe(Pc)O]2Ru(TPP′) + 2L′ →
[(L′)Fe(Pc)O]2Ru(TPP′) + 2(4-MePy)
The relative binding strength of the different ligands was
obtained from spectrochemical titrations in the near-IR and
follows the order:
4,4′-bipy < 4-MePy ~ P(OEt)3 < pip < NH3 <
1-MeIm < P(CH3)2Ph
© 2001 NRC Canada

Zobi and Stynes
799
1
Table 1. H NMR data (δ, ppm) in CDCl3.
Complex
Hβ
Ho
Hm
OCH3 Ha
Hb
Ligand
L
L
2-(4-MePy)2
2-(1-MeIm)2
2-[P(Me2Ph)]2
2-(NH3)2
2-[P(OEt)3]2
2-(4-MePy)
[P(OEt)3]
6.89 10.18 8.00
6.88 10.15 7.97
6.81 10.00 7.92
6.78 10.00 7.92
6.84 10.10 7.93
6.86 10.15, 7.93, 4.57
10.10 7.91
6.92 10.18 8.00
4.59
4.58
4.54
4.53
4.55
8.82
7.80
7.77
7.70
7.78
7.69
LHo –0.90, Hm 3.59, CH3 0.30
H2 –1.05, H4 –0.61, H5 3.31, CH3 0.88
Hα 2.60, Hβ 5.30, Hγ 6.00, CH3 –4.12
NH3 –9.00
8.80
8.67
8.76
8.76
8.85,
8.46
8.84
9.37
CH3 –1.29, CH2 –0.36
L
L
P
P
7.81, LHo –0.90, Hm 3.59, CH3 0.30, CH3 –1.29, CH2 –0.36
7.68
7.82
8.16
2-(4,4′-bipy)2
1-(4-MePy)
4.60
Hα –0.64, Hβ 3.90, Hγ 5.51, Hδ 7.72
L
L
7.89 10.59, 8.09, 4.30
7.35 7.07
LHo –0.15, Hm 4.09, CH3 0.61
1-(1-MeIm)
7.88 10.57, 8.09, 4.30
7.37 7.07
9.35
8.15
H2 –0.38, H4 0.89, H5 3.82, CH3 1.37
Ru(TPP′)(O)2
9.11
8.26 7.36
4.14
Fe(Pc)(4-MePy)2
Fe(Pc)[P(Me2Ph)]2
Fe(Pc)[P(OEt)3]2
3-(1-MeIm)a
9.30
9.07
9.26
1.56 (DMG
CH3)
7.95
7.87
7.91
Ho 1.98, Hm 4.81, CH3 1.07
Hα 4.36, Hβ 6.24, Hγ 6.66, CH3 –2.11
CH3 –0.20, CH2 1.27
9.20
8.77 7.46
4.15
H2 4.87, H4 4.49, H5 5.71, CH3 2.83
a3 = [Fe((DMG)BF2)2O]2Ru(TPP′), ref. 6.
Fig. 6. Spectral changes in the near-IR region during the oxida-
tion and subsequent reduction of 2. (a) 2-(4-MePy)2; (b) [2-(4-
MePy)2]+, obtained upon addition of 1 equiv. of [(η5-
Cp)2Fe](PF6); and (c) 2-[(PMe2Ph)]2 obtained by addition of neat
P(Me)2Ph to the +1 ion.
Fig. 5. Visible spectrum of 2 in CHCl3. Insert shows the growth
of the Pc Q band during the reductive cleavage of the oxo-
bridge.
1.0
a
c
0.8
c
0.6
a
b
b
0.4
0.2
0.0
800
1000
1200
1400
1600
Wavelength (nm)
Shifts in the near-IR as a function of axial ligand are simi-
lar to those previously described for Fe(DMG) systems (6).
chemical oxidation is reversible upon changing the axial
ligand to P(CH3)2Ph. Figure 6 shows the change in the near-
IR spectrum caused by the oxidation and subsequent reduc-
tion of the 4-MePy derivative. No reduction wave for 2 was
detected up to –2.0 V. In related systems reduction normally
results in irreversible oxo-bridge cleavage as electrons are
added to antibonding orbitals (21).
Electrochemistry and redox reactions
Cyclic voltammetry experiments were carried out for 2 in
CH2Cl2 containing 0.1 M (TBA)PF6. Four reversible one-
electron oxidation waves are observed for the 4-MePy
adduct at –42°C and these occur at E1/2 = 0.4, 0.76, 1.04,
and 1.32 V (Fig. 7). The two lower oxidation waves are as-
signed to successive FeIII/IV oxidations in agreement with
what previously reported for (PcFe)2O (19). The third and
fourth waves (1.04 and 1.32 V) are tentatively ascribed to
successive oxidations of the Pc rings (20). Complex 2 shows
a lower oxidation potential than the borylated dioxime-
derived heterotrinuclear of Vernik (6) (Table 3).
Kinetics of reductive cleavage of oxo-bridge
The trinuclear complex undergoes slow reductive cleavage
of the oxo-bridge with hydroquinones (H2Q), phosphines, or
phosphites. The kinetics of the reactions were studied at
40°C under anaerobic conditions and all changes were moni-
tored by visible spectroscopy. Products were identified on
The complex may be chemically oxidized to the +1 cation
by using [(η5-Cp)2Fe](PF6) (E1/2 = 0.46 V in CH2Cl2). This
the basis of distinctive visible–IR and H NMR spectra and
1
© 2001 NRC Canada

800
Can. J. Chem. Vol. 79, 2001
Table 2. Visible and near-IR data for trinuclear [(L)FeN4O]2Ru(TPP′) oxo-bridged complexes
(λmax, nm).
N4
Ligand
Soret
α
β
Q
CT1
CT2
a
Pc
Pc
Pc
Pc
Pc
Pc
Pc
Pc
4-MePy2
1-MeIm
410
410
410
412
410
412
412
410
435
435
433
530
528
536
526
538
532
530
530
541
538
542
576
566
572
572
570
572
574
568
576
572
577
702
702
700
702
698
702
700
702
1050
1071
1096
1056
1130
1040
1088
1007
703
1332
1325
1404
1312
1380
1340
1341
1300
857
P(Me2Ph)
NH3
CN–
4,4′-bipy
pip
CH3CN
1-MeIm
1-MeIm
1-MeIm
b
((DMG)BF2)2
((DMG)BPh2)2
((DPG)BF2)2
b
732
714
890
836
b
aExtinction coefficient for 2-(4-MePy)2 log (ε): 4.70, 4.18, 4.15, 4.33, 4.17, 4.03 for Soret, α, β, Q, CT1, and
CT2, respectively. Other derivatives of 2 give comparable values.
bRef. 6.
Table 3. Electrochemical data for trinuclear
[(L)FeN4O]2Ru(TPP′) oxo-bridged complexes.
Fig. 8. Possible pathways of oxo-bridge reductive cleavage in
trinuclear complexes. (a) Dissociative path; occurs in
[(L)Fe(N4)O]2Ru(TPP′) complexes where N4 is the Pc ring. The
rate-determining step is the dissociation of a Fe(Pc) unit. (b)
Bent µ-oxo path; occurs in [(L)Fe(N4)O]2Ru(TPP′) complexes
where N4 is the DMG or the DPG ring. The rate-determining
step involves oxo-transfer from the trinuclear to S; S = reducing
substrate (H2Q, P(Me2Ph), or P(OEt)3).
N4
Pc
Ligand
E1/2 (V)a
CT1
CT2
4-MePy
0.40, 0.76,
1.04, 1.32
0.80, 1.20
0.60, 1.06
0.51, 1.04
1.00
1050
1332
b
((DMG)BF2)2
((DMG)BPh2)2
CH3CN
CH3CN
NH3
691
709
716
686
812
839
850
799
b
b
((DPG)BF2)2
CH3CN
Ru
Fe
Fe
L
O
O
L
aHalf-wave potentials for reversible oxidation.
bRef. 6.
- L
+ L
Table 4. Kinetic data for the reductive µ-oxo cleavage of
trinuclear [(L)FeN4O]2Ru(TPP′) complexes.
Slow
Fe
L
L
N4
Reductant
Kobs (1 × 10–4) (s–1)
L
L
Pca
P(Me2Ph)
P(OEt)3
H2Qb
0.074
0.078
0.069
453
Fe
O
Pca
Fe
O
Pca
(a)
(b)
((DMG)BF2)2
((DPG)BF2)2
H2Qc
Ru
O
H2Qc
1340
Ru
O
a[2-(4-MePy)2] = 1.0 × 10–5 M. Reaction carried out in CHCl3 at 40°C.
bIn the presence of 4-MePy (1.0 × 10–3 M).
Fe
cReaction carried out in CH2Cl2 at 25°C in the presence of 1 M
CH3CN. Ref. 6.
S
Fig. 7. Cyclovoltammogramm of 2 in CH2Cl2 at –42°C (Ag/Ag+
used as the reference electrode).
2Sox
90.8
Ru
Fe
L
L
+
2 L
L
27.3
–36.1
+ 0.40 V
+ 0.76 V
+ 1.06 V
the overall stoichiometry shown in eqs. [2] and [3] was con-
firmed by NMR.
+ 1.32 V
1144
–99.6
–163.1
[2]
2-(4-MePy)2 + 8PX3 → 2Fe(Pc)(PX3)2 +
Ru(TPP′)(PX3)2 + 2(O=PX3)
1441
846
550
253
–44
Potential (mV)
© 2001 NRC Canada

Zobi and Stynes
801
Inorg. Chem. 20, 761 (1981); (c) C. Ercolani, M. Gardini, F.
Monacelli, G. Pennesi, and G. Rossi. Inorg. Chem. 22, 2584
(1983); (d) C. Ercolani, G. Rossi, and F. Monacelli. Inorg.
Chem. Acta, 44, L215 (1980).
[3]
2-(L)2 + 4L + 2H2Q → 2Fe(Pc)(L)2 +
Ru(TPP′)(L)2 + 2Q (where L = 4-MePy)
The rate constant for the reduction of 2 (7 × 10–6 s–1) was
found to be independent of the concentration or nature of the
reductant used and it is at least four orders of magnitude
slower than that of µ-oxo borylated dioxime systems (6) (see
Table 4). The reaction proceeds cleanly (isosbestic point at
688 nm) with no binuclear or other intermediates detected.
Mechanism A in Fig. 8 is proposed in which the rate deter-
mining step is the dissociation of a Fe(Pc) unit to generate a
binuclear species, which is subsequently reduced to the
monomeric RuII(TPP′) and FeII(Pc) complexes. In contrast,
mechanism B was proposed in DMG systems where reduc-
tion was found to show an inverse first-order dependence on
the axial ligand concentration implying a loss of one ligand
prior to the rate determining µ-oxo cleavage (6, 22). A fold-
ing back of the pentacoordinate FeN4 fragment in a bent ge-
ometry permits direct attack at the oxo site in these systems.
Mechanism B may be much more difficult in FePc-based
trinuclears as the Pc ring lacks the flexibility of the DMG
macrocycles. Thus, only a [L] independent dissociative path
is observed in the FePc systems.
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Acknowledgments
Financial support from NSERC (Canada) is gratefully ac-
knowledged. The authors are also thankful to Christos
Alexiou for his assistance in CV data collection, and Gianni
Manno of the Department of Mathematics at the King’s Col-
lege, London, U.K. for his suggestions regarding rcs calcula-
tions.
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© 2001 NRC Canada