Mono- and heterodimetallic FeII and RuII complexes based on a novel heteroditopic 4′-{bis(phosphanyl)aryl}-2,2′: 6′,2″-terpyridine ligand

Article abstract of DOI:10.1002/ejic.200600928

In the search for a versatile building block that allows the preparation of heteroditopic tpy-pincer bridging ligands, the synthon {4′-[C ₆H₃(CH₂Br)₂-3,5]-2,2′: 6′,2″-terpyridine} was synthesized. Facile introdu

Full text of DOI:10.1002/ejic.200600928

FULL PAPER
DOI: 10.1002/ejic.200600928
Mono- and Heterodimetallic FeII and RuII Complexes Based on a Novel
Heteroditopic 4Ј-{Bis(phosphanyl)aryl}-2,2Ј:6Ј,2ЈЈ-terpyridine Ligand
[a]
[a]
[b]
[a]
ˇ
Marcella Gagliardo, Jolke Perelaer, Frantisek Hartl, Gerard P. M. van Klink, and
Gerard van Koten*[a]
Keywords: Ruthenium / Iron / Terpyridine ligands / Pincer ligands / Spectroelectrochemistry
In the search for a versatile building block that allows the
preparation of heteroditopic tpy-pincer bridging ligands, the
synthon {4Ј-[C6H3(CH2Br)2-3,5]-2,2Ј:6Ј,2ЈЈ-terpyridine} was
synthesized. Facile introduction of diphenylphosphanyl
groups in this synthon gave the ligand {4Ј-[C6H3(CH2-
properties of both complexes, investigated by cyclic and
square-wave voltammetries and UV/Vis spectroscopy, are
discussed and compared with those of [Fe(tpy)2](PF6)2 and
[Ru(PCP)(tpy)]Cl, which represent the mononuclear compo-
nents of the heterodinuclear species. An in situ UV/Vis spec-
PPh2)2-3,5]-2,2Ј:6Ј,2ЈЈ-terpyridine} ([tpyPC(H)P]). The asym- troelectrochemical study was performed in order to localize
metric mononuclear complex [Fe(tpy){tpyPC(H)P}](PF6)2,
prepared by selective coordination of [Fe(tpy)Cl3] to the tpy
moiety of [tpyPC(H)P], was used for the synthesis of the het-
erodimetallic complex [Fe(tpy)(tpyPCP)Ru(tpy)](PF6)3, which
applies the “complex as ligand” approach. Coordination of
the ruthenium centre at the PC(H)P-pincer moiety of
[Fe(tpy){tpyPC(H)P}](PF6)2 has been achieved by applying a
transcyclometallation procedure. The ground-state electronic
the oxidation and reduction steps and to gain information
about the FeII–RuII communication in the heterodimetallic
system [Fe(tpy)(tpyPCP)Ru(tpy)](PF6)3 mediated by the
bridging ligand [tpyPCP]. Both the voltammetric and spectro-
electrochemical results point to only very limited electronic
interaction between the metal centres in the ground state.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2007)
C6H3(CH2NMe2)2-3,5}-2,2Ј:6Ј,2ЈЈ-terpyridine [tpyNCNBr
(1)], which combines the properties of the tpy and NCNBr-
pincer {BrC6H3(CH2NMe2)-2,6} ligands.[6] It was shown
that selective metallation and coordination of the NCNBr
and tpy moieties, respectively, affords monometallic species
that can be further used as building blocks for the construc-
tion of heterodi- and trimetallic complexes containing co-
valently linked photosensitizing octahedral [Ru(tpy)2]2+ and
cyclometalated NCN–PdII domains.[6]
Introduction
In the past decades, much attention was devoted to the
field of coordination chemistry of substituted terpyridines.
Currently, a significant amount of research is devoted to
the preparation of mononuclear terpyridine complexes
bearing an externally oriented vacant binding site. A huge
potential is concealed in these compounds with tuneable
redox and photophysical properties, which can be used as
building blocks for the construction of molecular devices,[1]
metal-containing dendrimers[2] and one-dimensional poly-
mers.[3]
Only a few examples have been reported in which metal–
tpy and organometallic subunits are incorporated into a
single molecule.[4] Bridging ligands based on 2,2Ј:6Ј,2ЈЈ-ter-
pyridine (tpy) functionalized at the 4Ј-position with a cyclo-
metallating unit proved to have a high potential for linking
chromophoric Ru–tpy centres and robust organometallic
units containing a stable M–C σ-bond.[1b,5] Recently, we de-
scribed the synthesis of the heteroditopic ligand 4Ј-{4-Br-
Metallation of the NCNBr moiety in 1 can be performed
only by oxidative addition of the C–Br bond to transition-
metal salts.[7] For a broader application in template-directed
synthesis of multimetallic systems based on metal–tpy bind-
ing domains containing aryl pincer components, we ex-
tended our studies to the preparation of the versatile tpy-
pincer building block 4Ј-{C6H3(CH2Br)2-3,5}-2,2Ј:6Ј,2ЈЈ-
terpyridine (5). Interestingly, 5 can be used as a precursor
for several tpy-pincer ligand systems because the bromo
[a] Faculty of Science, Organic Chemistry and Catalysis, University
of Utrecht,
Padualaan 8, 3584 CH Utrecht, The Netherlands
Fax: +31-30-252-3615
E-mail: g.vankoten@chem.uu.nl
[b] Van’t Hoff Institute for Molecular Sciences, Homogeneous and
Supramolecular Catalysis, University of Amsterdam,
Nieuwe Achtergracht 166, 1018 WV Amsterdam, The Nether-
lands
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substituents at the benzylic arms can be easily converted PPh2)2-2,6]–)[14] to probe the degree of intramolecular elec-
into ER2 groups, where E = N, P, S, O and R = alkyl or tronic interaction between the metal centres in the novel
aryl.[8] In the pincer moiety, several parameters (e.g. nature dinuclear species mediated by the tpyPCP bridging ligand.
of the donor atoms, size and electron-withdrawing or releas-
ing character of the donor substituents) can readily be var-
Results and Discussion
ied. This allows for fine-tuning of the target ligand de-
pending on its envisaged application.[9] Moreover, incorpo-
ration of a wider range of transition metals into the pincer
moiety can at the same time be achieved through C–H acti-
Synthesis of the [tpyPC(H)P] Ligand
The starting point for the synthesis of the building
vation,[10] transmetallation[11] and transcyclometallation[12] block 4Ј-{C6H3(CH2Br)2-3,5}-2,2Ј:6Ј,2ЈЈ-terpyridine (5)
procedures.
(Scheme 1) is the preparation of the stannane pincer com-
In our previous work, we described a heterometallic sys- pound {C6H3(CH2OMe)2-3,5}-SnMe3 (3). Chemoselective
tem with weak electronic interactions between the RuII and lithiation of 3,5-bis(methoxymethyl)iodobenzene 2[15] at the
PdII centres mediated by tpy-pincer ligand 1.[6] However, C–I position was achieved by reaction of 2 with 2 equiv.
this study was hampered by the low redox activity of the of tBuLi in Et2O at –100 °C. Subsequent quenching with
PdII centre and by the instability of the NCN–Pd pincer Me3SnCl followed by slow warming of the reaction mixture
moiety upon electrochemical reduction.[6] Aimed at contin- to room temperature resulted in the formation of 3 in good
uing these physicochemical investigations and with synthon yield. Pd-catalyzed Stille cross-coupling[16] of 3 with 4Ј-tri-
5 in hand, we focused our attention on its derivatization flato-2,2Ј:6Ј,2ЈЈ-terpyridine[17] gave 4 in moderate yield after
to form the heteroditopic ligand 4Ј-{C6H3(CH2PPh2)2-3,5}- chromatographic purification.
2,2Ј:6Ј,2ЈЈ-terpyridine {[tpyPC(H)P] (7), see Scheme 1} con-
First attempts to replace the methoxy groups in 4 with
[18]
taining P-donor atoms. Facile attachment of redox active bromide substituents by using BF3·EtO2/AcBr in CH2Cl2
FeII and RuII centres to the tpy and PCP-pincer moieties of mainly resulted in the formation of unwanted side products
7, respectively, led to the formation of the heterodimetallic and only small amounts of 5. However, 5 was conveniently
complex [Fe(tpy)(tpyPCP)Ru(tpy)](PF6)3 (11). For the prepared by treatment of 4 with an excess amount of
purpose of comparison, the mononuclear complex HBr·AcOH in dichloromethane.
[Fe(tpy){tpyPC(H)P}](PF6)2 (9) was also prepared. Our
Subsequently, a two-step procedure was employed for the
main goal was to investigate the spectroelectrochemical be- preparation of 7. First, treatment of 5 with 2 equiv. of in
haviour of 11 and the known reference complexes [Fe- situ prepared LiPPh2·BH3 afforded 6. Deprotection of the
(tpy)2]2+[13] and [Ru(PCP)(tpy)]Cl (PCP = [C6H3(CH2- diphenylphopshine–BH3 moieties with Et2NH yielded 7 as
Scheme 1. Synthesis of [tpyPC(H)P] ligand 7. Reagents and conditions: i) (a) 2 equiv. tBuLi, Et2O, –100 °C, 0.5 h. (b) Me3SnCl, Et2O,
–100 °CǞ room temp., 15 h. ii) LiCl, [PdCl2(PPh3)2], toluene, reflux, 20 h. iii) (a) HBr·AcOH, CH2Cl2, room temp., 15 h. (b) aq. NaHCO3.
iv) HPPh2·BH3, nBuLi, THF, –78 °C Ǟ room temp., 20 h. v) (a) Et2NH, room temp., 2 h. (b) aq. NaHCO3.
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an air- and moisture-sensitive sticky white solid. Notably, large amount of free PPh3, are consistent with the incorpo-
both the tpy and PCP-pincer moieties of 7 proved to be ration of the ruthenium centre into the PCP-pincer unit by
stable both in acidic and basic media during the entire syn- TCM.[12a] However, the presence of a singlet at δ =
thetic procedure. All the intermediates and ligand 7 have 41.82 ppm indicated that an unwanted reaction concomi-
been fully characterized by analytical and spectroscopic tant to the TCM procedure occurred. The ruthenium centre
methods. The 1H and 13C NMR spectra of 7 show the char- of the {(PCP)RuCl(PPh3)} moiety partly reacted with the
acteristic coupling between the benzylic proton and carbon tpy site of another molecule of the bridging ligand, which
atoms, of the PPh2 groups, respectively. The 31P{1H} NMR produced an oligonuclear species containing the unit
spectrum exhibits a signal at δ = –8.5 ppm typical for the [(PCP)Ru(tpyPCP)RuCl(PPh3)]. The nature of this material
diphenylphosphanyl groups.
was not investigated in detail. However, fine-tuning of the
reaction conditions, as well as the introduction of solubiliz-
ing substituents at the phosphorus atoms, may give rise to
the formation of soluble redox- and photoactive organome-
tallic molecular wires. Because the synthesis of mononu-
Syntheses of Mono- and Heterodimetallic Complexes
Previous work carried out by Constable and co- clear complexes incorporating 7 failed as a result of the af-
workers[19] showed the high potential of the phosphane- finity of both PCP-pincer and tpy sites for ruthenium, we
functionalized terpyridine ligand 4Ј-(PPh2)-2,2Ј:6Ј,2ЈЈ-ter- decided to choose a different approach: to first coordinate
pyridine to link MII coordination centres (M = Fe, Ru) and an iron centre to the tpy unit in 7, and then to bind the
organometallic units through the N,N,N- and P-donor do- ruthenium centre at the PCP-site through a TCM reaction.
mains, respectively. Because it was demonstrated that reac-
The reaction of equivalent amounts of [Fe(tpy)Cl3][22]
tion of ruthenium(III) chloro complexes with this ligand and 7 in refluxing methanol resulted in the formation of an
leads to partial or complete oxidation of the PPh2 intensely purple-coloured solution, from which the cation
group,[19a] it was decided to employ different ruthenium [Fe{tpyPC(H)P}(tpy)]2+ could be isolated as the diamag-
starting materials to produce the (tpyPCP)Ru-containing netic PF6-salt 9 (Scheme 2). Similarly to what was found for
species. The use of [RuCl2(PPh3)3] gave a mixture of N,N,N- 7, complex 9 is highly air and moisture-sensitive and has to
and P-bound compounds. Confident that a selective and be handled under strictly anaerobic conditions. This sensi-
quantitative transfer of the RuClPPh3-moiey into the PCP- tivity hampered the removal of small amounts of tpy-con-
pincer unit of 7 could be achieved by a transcyclometalla- taining impurities by chromatography. Attempts to obtain
tion (TCM) procedure developed in our laboratories for the single-crystals suitable for X-ray diffraction analysis were,
synthesisofmulti(pincer–metal)complexes,[12,20]wereactedthe unfortunately, also unsuccessful. However, complex 9 was
ruthenium precursor [RuCl(NCN)(PPh3)][21] (NCN
=
sufficiently characterized by NMR spectroscopy and high-
[C6H3(CH2NMe2)2-2,6]–) (8, Scheme 2) with 7 in refluxing resolution ESI-MS analysis. In the ESI-MS spectrum of 9,
benzene. Resonances of free 7 or unreacted 8 (singlet at δ the highest mass peak at m/z = 497.20 corresponds to [M –
= 90.2 ppm) were subsequently not detected in the 31P{1H} 2 PF6]2+, which shows the correct isotopic pattern for this
NMR spectrum. The main signals present in the spectrum, formulation. The resonances in the aromatic region of the
a triplet at δ = 83.2 ppm (PPh3, 2JPP = 31.8 Hz) and a doub- 1H NMR spectrum could be unequivocally assigned to the
2
let at δ = 37.9 ppm (PCP, JPP = 31.8 Hz), together with a protons of the complexed tpy moieties. A single resonance
Scheme 2. Synthesis of 9 and heterodimetallic 11. Reagents and conditions: i) (a) 1 equiv. [Fe(tpy)Cl3], MeOH, reflux, 4 h. (b) Excess
NH4PF6. ii) 8, THF/MeCN, reflux, 2 d. iii) (a) tpy, MeOH. (b) Excess NH4PF6.
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in the 31P{1H} NMR spectrum (δ = –4.9 ppm in CD3CN) metal centres (oxidations) or the ligands (reductions).[23]
for the equivalent diphenylphosphanyl groups clearly indi- According to experimental results previously report-
cates that the iron centre is selectively coordinated to the ed,[13a,13b] oxidation of the FeII-tpy complexes can be as-
tpy moiety.
Ruthenation of the PCP-pincer unit of 9 was achieved by performed on the complexes [Fe(tpy)2]2+ and [Fe(B-
the TCM procedure: the reaction of 9 with an equivalent ptpy)2]2+ {B-ptpy
4Ј-(tert-butyl-phenyl)-2,2Ј:6Ј,2ЈЈ-
signed as metal-localized.[13c] However, DFT calculations
=
amount of 8 in refluxing THF/MeCN (8:3 v/v). Removal of terpyridine} showed that the highest molecular orbital
the volatiles gave intermediate species 10 (Scheme 2) that (HOMO) of these compounds is not solely iron-based.[13c]
was subsequently treated with tpy in refuxing methanol. In fact, the HOMO of the complex [Fe(tpy)2]2+ resides
Addition of aqueous NH4PF6 to the red–purple methanolic mainly on one of the tpy ligands and partly on the iron.
solution resulted in the precipitation of 11 as a wine-red Introduction of a substituted phenyl group at the 4Ј-posi-
solid.
tion of the terpyridine ligands in [Fe(B-ptpy)2]2+ signifi-
The presence of the PPh2 groups and three nonequiva- cantly changes the HOMO character relative to that of
lent tpy ligands results in a complicated 1H NMR spectrum [Fe(tpy)2]2+, which has a stronger metal dπ component,
in the aromatic region. Nevertheless, the resonances of 11 with a contribution from the phenyl π orbitals.[13c] The low-
could be assigned by comparison with the data obtained est unoccupied molecular orbital (LUMO) of [Fe(tpy)2]2+ is
1
for 9 and [Ru(PCP)(tpy)]Cl.[14] The H and 31P{1H} NMR localized on both tpy ligands, whereas the LUMO of [Fe(B-
spectra reveal a high degree of symmetry for the {(PCP)- ptpy)2]2+ is mainly localized on only one of the B-ptpy li-
Ru(tpy)} unit in 11, with the geometry in solution probably gands and partly on the metal.[13c]
very close to that of [Ru(PCP)(tpy)]Cl. The aliphatic region
The redox potentials determined for 9 and 11 are close
1
of the H NMR spectrum shows a singlet resonance for to those reported for other FeII–tpy complexes (Table 1).
the equivalent benzylic hydrogens, which is indicative of a This indicates that the oxidation and reduction of these spe-
molecular mirror plane containing the benzylic carbon cies involve frontier orbitals having comparable energy and
atoms. These data, together with the peak at δ = 41.82 ppm probably also similar character to those calculated for
in the 31P{1H} NMR spectrum for the equivalent phospho- [Fe(B-ptpy)2]2+. Thus, the reversible anodic wave at E1/2
=
rus nuclei, suggest an octahedral geometry of the ruthenium 0.74 V (∆Ep = 0.60 mV) in the cyclic voltammogram of 9
coordination sphere, with both the PCP-pincer and tpy li- corresponds to a one-electron oxidation of the FeII–tpy
gands coordinated in a meridional fashion. The ESI-MS moiety. In the cathodic region, two reversible one-electron
spectrum of 11 displays [M – 3PF6]3+ (m/z = 442.75) and waves at –1.59 V (∆Ep = 0.58 mV) and –1.69 V (∆Ep
=
[M – 2PF6]2+ (m/z = 736.67) for the heterodinuclear com- 0.54 mV) belong to the sequential reduction of the tpy li-
plex with good isotopic matching to the simulated spec- gands. By comparison with [Fe(tpy)2]2+ [13b]
we assign the
first and second reduction steps in 9 to the pincer-substi-
,
trum.
tuted and terminal tpy ligands, respectively. The electron-
withdrawing character of the phenyl moiety renders the
substituted tpy less electron rich, thereby decreasing its re-
duction potential. The anodic potential region of the hetero-
dimetallic complex 11 exhibits two reversible, one-electron
anodic waves due to the RuII centre at E1/2 = 0.16 V (∆Ep
= 0.56 mV) and the FeII–tpy moiety at E1/2 = 0.71 V, respec-
tively. These values are nearly identical with the electrode
potentials of the FeII–tpy and RuII-based oxidations of
complex 9 and [Ru(PCP)(tpy)Cl], respectively. Apparently,
the electronic communication between the metal centres is
very limited. In the cathodic region, complex 11 undergoes
three ligand-centred reduction processes. The first two cath-
odic waves lie at –1.62 V and –1.77 V. The initial reduction
is fully reversible (∆Ep = 0.54 mV). The second cathodic
step, however, is characterized by slower electron transfer
as indicated by decreased peak currents in both voltam-
metric (CV and SWV) records. More information about
this behaviour has been obtained from the corresponding
spectroelectrochemical experiments (see below). According
to the reference data in Table 1, these reductions are local-
ized at the terminal and substituted tpy ligands that are
coordinated to the iron centre, respectively. The third cath-
odic step at –1.92 V (∆Ep = 0.60 mV), which is fully revers-
Redox Behaviour and Electronic Absorption Spectra
The electrochemical and spectroscopic properties of the
prepared compounds were studied with the aim to estimate
the extent of the FeII–RuII interactions within 11, mediated
by bridging ligand 7. The redox behaviour of 9 and 11 was
investigated by cyclic and square-wave voltammetries (CV
and SWV) in MeCN at room temperature. Pertinent elec-
trochemical data are collected in Table 1. Literature data
[13]
for [Fe(tpy)2](PF6)2
and [Ru(PCP)(tpy)]Cl[14] have been
included for reference purposes.
Table 1. Electrochemical data for complexes 9 and 11, and refer-
ence compounds.[a]
Complex
E1/2 [V]
(oxidation)
E1/2 [V]
(reduction)
[b]
[Fe(tpy)2](PF6)2
0.74
0.17
0.74
0.16
0.71
–1.64, –1.82
–1.95
–1.59; –1.69
–1.93
[Ru(PCP)(tpy)]Cl[c]
[Fe(tpy){tpyPC(H)P}](PF6)2 (9)
[Fe(tpy)(tpyPCP)Ru(tpy)](PF6)3 (11)
–1.62; –1.77
[a] Measured in MeCN containing 10–1  TBAH at 298 K. Elec-
trode potentials are given in Volt versus Fc/Fc+. Scan rate =
100 mVs–1. [b] Ref.[13] [c] Ref.[14]
It is well known that redox processes for common RuII– ible, can be readily assigned to the reduction of the terminal
polypyridine complexes are mainly localized either on the tpy ligand bound to the ruthenium centre. The reduction
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FULL PAPER
potential is only slightly less negative than that of the tpy
For the ruthenium centre in [Ru(PCP)(tpy)]Cl, it is ex-
ligand in [Ru(PCP)(tpy)]Cl (Table 1). These observations pected that the lowest MLCT excited state involves the co-
are consistent with a negligible electronic communication ordinated tpy ligands rather than the strongly donating cy-
between the Ru(tpy) and the doubly reduced (tpy)Fe- clometallated PCP-pincer ligand.[14] The Ru-to-tpy CT
(tpyPCP) moieties.
band of complex 11 at 489 nm is only slightly shifted to a
The electronic absorption spectra of 9 and 11 were re- lower energy relative to the mononuclear [Ru(PCP)(tpy)]Cl
corded in MeCN solution at room temperature. Absorption (Table 2). This shift, although small, is in agreement with
maxima (λmax) and molar absorption coefficients (εmax) for the less positive oxidation and less negative reduction po-
both compounds are listed in Table 2, together with the ref- tentials of the Ru(tpy) moiety in the latter complex
erence data for [Fe(tpy)2](PF6)2[13] and [Ru(PCP)(tpy)]Cl.[14] (Table 1), that is, with a slightly larger HOMO – LUMO
The UV/Vis spectra of 9 and 11 show features typical for gap: ∆E = 0.03 eV. These results again reveal that the elec-
other FeII– and RuII–tpy compounds,[13,23] in particular in- tronic communication between the tpyPCP-bridged Ru(tpy)
tense πǞπ* intraligand (IL) transitions in the UV region, and Fe(tpy) moieties in complex 11 is very limited. A large
320 and 280 nm for 9, and at 308, 319 and 275 nm for 11. dihedral angle between the tpy and the PCP-pincer units of
In the visible spectral region, complexes 9 and 11 exhibit the bridging ligand is the most likely reason for the lack of
moderately intense visible absorption bands (Figure 1) that electronic coupling between the two motifs.[24]
are tentatively attributed to electronic transitions having a
However, it cannot be excluded that stabilization of the
mixed π(tpy)Ǟπ*(tpy) IL and dπ(Ru)Ǟπ*(ph) MLCT ruthenium orbitals by π-back donation to the PPh2 moieties
character by comparison with literature data on the basis to some extent contributes to a decrease in the mixing be-
of the TD-DFT calculations performed on the complexes tween the dπ(Ru)- and the bridging ligand-based orbitals,
[Fe(tpy)2]2+ and [Fe(B-ptpy)2]2+ (B-ptpy
= 4Ј-(n-bu- and thus, the metal-coupling in the studied heterodimetallic
tylphenyl)-2,2Ј:6Ј,2ЈЈ-terpyridine) (vide supra).[13c,23] The complex.
small shift in the lowest absorption of 9 and 11 (Figure 1)
to a lower energy relative to [Fe(tpy)2](PF6)2 is consistent
UV/Vis Spectroelectrochemistry
with the electrochemical results. The lowest transition of 9
is only slightly affected by the incorporation of the ruthe-
nium centre into the PCP-pincer unit (Table 2).
UV/Vis spectroelectrochemical studies of heterodimetal-
lic complex 11 were performed in MeCN at room tempera-
ture within an optically-transparent thin-layer electrochemi-
cal (OTTLE)[25] cell. These investigations were mainly
aimed at gaining more information about the degree of the
FeII–RuII interaction mediated by the twisted bridging li-
gand [tpy(PCP)]. In addition, the spectral changes recorded
during the oxidation and reduction steps help to more accu-
rately appoint their assignment in the preceding section.
Electrochemical oxidation of 11 to 11+ at 0.16 V caused
flattening of the band at 500 nm (Figure 2), consistent with
Table 2. UV/Vis absorption maxima (λmax) and molar absorption
coefficients (εmax) of complexes 9 and 11, and reference com-
pounds.[a]
Compound
λmax [nm] (εmax 10–4 [–1 cm–1])
[b]
[Fe(tpy)2](PF6)2
548 (1.4)
275 (3.7), 305 (3.9), 479 (0.8)
280 (5.9), 320 (5.6), 563 (1.0)
[Ru(PCP)(tpy)]Cl[c]
[Fe(tpy){(tpyPC(H)P})](PF6)2 (9)
[Fe(tpy)(tpyPCP)Ru(tpy)](PF6)3 (11) 275 (5.1), 308 (4.1), 319 (4.0),
489 (0.8), 563 (1.0)
[a] Measured at 298 K in MeCN. [b] Ref.[13] [c] Ref.[14]
Figure 1. Visible region of the absorption spectra of complexes
Figure 2. UV/Vis spectra recorded during one-electron oxidation of
[Ru(PCP)(tpy)]Cl (– – –), 9 (–––), and 11 (-----) recorded in MeCN the RuII centre in complex 11. Conditions: OTTLE cell, MeCN/
at 298 K.
10–1  TBAH, 293 K.
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its assignment to the MLCT transition in the {Ru(tpy)}
moiety. Further oxidation of 11+ to 112+ at 0.70 V then re-
sulted in disappearance of the composed absorption band
at 565 nm (Figure 3), which agrees with the oxidation of
the Fe(tpy) moiety. The formation of 11+ and 112+ is also
accompanied by stepwise disappearance of the πǞπ* ab-
sorption bands at 308 and 319 nm, respectively. Accord-
ingly, they can be attributed to intraligand Ru(tpy) and
Fe(tpy) transitions, respectively. This assignment, supported
also by the reference data ([Ru(PCP)(tpy)]Cl and complex
9 in Table 2), is also important for the discussion of the
cathodic steps (see below). Reduction of 112+ at 0.16 V led
to full recovery of the electronic absorption spectrum of 11.
Figure 4. UV/Vis spectral changes accompanying reduction of
complex 11 (a) to 11– (b) and 112– (c) in two tpy(Fe)-localized steps.
Conditions: OTTLE cell, MeCN/10–1  TBAH, 293 K.
Importantly, the Ru-to-tpy CT and πǞπ* Ru(tpy) bands
also do not change during the second cathodic step, which
indicates that this step is localized on the substituted tpy
part of the bridging [tpyPCP] ligand. These findings again
reveal only a weak communication between the two metal
centres through the tpyPCP bridge. The qualitatively dif-
ferent changes in the visible spectral region upon the forma-
tion of 112– compared with the doubly reduced reference
[Fe(tpy)2][13b] may reflect some involvement of the phenyl
ring of the pincer part of the bridging ligand in the occu-
pied π* system, possibly due to some variation in the cen-
tral twist angle caused by the second reduction. This obser-
vation may explain the slower voltammetric response to the
second electron transfer than the first, electrochemically re-
versible cathodic step of 11. The third one-electron re-
duction producing 113– caused flattening of the Ru-to-tpy
CT band. The πǞπ* Ru(tpy) absorption band at 308 nm
Figure 3. UV/Vis spectra recorded during one-electron oxidation of
complex 11+, which is probably localized at the Fe(tpy) moiety.[13c]
The preceding anodic step is depicted in Figure 2. Conditions:
OTTLE cell, MeCN/10–1  TBAH, 293 K.
The spectroscopic changes observed during one-electron
reduction of the heterodinuclear complex 11 to 11– were
very similar to those observed in the UV/Vis spectra of the
singly and doubly reduced complex [Fe(tpy)2]2+ [13b]
Re-
.
duction of 11 at –1.73 V led to the disappearance of the
mixed IL/MLCT band at 565 nm (Figure 4). New low-lying
absorption bands due to π*Ǟπ*(tpy·–) transitions[13b] arose
at 641, 736 and 905 nm (Figure 4). The persisting Ru-to-tpy
CT transition of 11– at 498 nm, as well as the unaffected
intraligand Ru(tpy) transition at 308 nm also prove that the
first reduction step is localized on the terminal tpy ligand
coordinated at the iron(II) centre. The slightly decreased
intensity of the band at 498 nm in the UV/Vis spectrum of
11– is most probably caused by the disappearance of the
underlying shoulder of the composed IL/MLCT
Fe(tpy)-band (Figure 1).[13c] Unlike that reported for
[Fe(tpy)2]2+ [13b]
the addition of the second electron did not
,
result in a shift of the π*Ǟπ*(tpy·–) transitions to lower
energies. Instead, the formation of 112– resulted in the in-
creasing intensity of the broad π*Ǟπ* absorption between
550–900 nm, with the main absorption maximum at 732 nm
(Figure 4).
Figure 5. UV/Vis spectrum of 113– (b) formed from 112– (a) in the
third, tpy(Ru)-localized cathodic step. Conditions: OTTLE cell,
MeCN/10–1  TBAH, 293 K.
2116
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© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2007, 2111–2120

Mono- and Heterodimetallic FeII and RuII Complexes
FULL PAPER
also became affected (Figure 5). Importantly,
a
new passing from the mononuclear FeII to the heterodimetallic
π*Ǟπ*(tpy·–) absorption appeared around 550 nm.
FeII–RuII complex. UV/Vis spectroelectrochemical studies
Similar spectral changes are characteristic for the one- of the heterodimetallic complex confirm the voltammetric
electron reduction of the reference complex [Ru(PCP)- results. The spectral changes allow the stepwise RuII– and
(tpy)]Cl (Figure 6), which confirms that the third reduction FeII–tpy oxidations to be distinguished. The first and sec-
step of complex 11 involves occupation of the lowest π* ond reduction steps are localized at the terminal and
orbital that is essentially localized on the Ru-bound ter- pincer-substituted tpy ligands coordinated at the iron cen-
minal terpyridine ligand, tpy(Ru).
tre, respectively. The third reduction resides at the tpy li-
gand coordinated at the ruthenium centre.
Apparently, despite the relatively moderate internuclear
separation, only a very weak electronic interaction exists
between the {Fe(tpy)2} and {(PCP)Ru(tpy)} fragments.
This can be rationalized in terms of the very limited ability
of the nonplanar (twisted) [tpyPCP] bridging ligand to me-
diate electronic communication between the metal centres.
However, stabilization of the dπ(Ru) orbitals as a result of
the π-accepting properties of the PPh2 moieties may also
cause a decrease in the Fe–Ru coupling by limiting the over-
lap between the ruthenium orbitals and the bridging ligand
orbitals. Connection of the {Fe(tpy)2} and {(PCP)Ru(tpy)}
fragments through a bridge capable of achieving a more
effective aromatic conjugation would be highly desirable.[26]
Figure 6. UV/Vis spectral changes accompanying the tpy-localized
one-electron reduction of the reference complex [Ru(PCP)(tpy)]Cl.
Conditions: OTTLE cell, MeCN/10–1  TBAH, 293 K.
Experimental Section
General: All experiments were carried out under a dry nitrogen
atmosphere by using standard Schlenk techniques. Benzene, tolu-
ene, pentane, hexane and diethyl ether (Et2O) were distilled from
sodium/benzophenone. Dichloromethane and methanol were dried
with CaH2 and magnesium, respectively. All solvents were freshly
distilled under a nitrogen atmosphere prior to use. 1D NMR spec-
tra were recorded with a Varian Inova 300 MHz spectrometer.
Chemical shifts are given in ppm relative to the residual solvent
signal (1H and 13C NMR spectra) or 85% H3PO4 external reference
(31P{1H} NMR spectra). EtOAc and all reagents were purchased
from Acros or Aldrich and used as received. Compounds 2,[15]
4Ј-trifluoromethylsulfonato-2,2Ј:6Ј,2ЈЈ-terpyridine,[17] 8[21] and
[Fe(tpy)Cl3][22] were synthesized according to literature procedures.
Elemental analyses were performed by Dornis und Kolbe, Mikro-
analytisches Laboratorium, Mülheim a. d. Ruhr, Germany. Elec-
Reoxidation of all three one-electron-reduced species,
11n– (n = 1, 2, 3), fully regenerated the UV/Vis spectrum of
parent 11. It is clear that the reduction steps are largely
tpy-localized. The stability of the Ru–C σ-bond during the
second and third cathodic steps is remarkable and is a con-
sequence of this localization. In fact, significant delocaliza-
tion of the added electron density over the PCP-pincer moi-
ety would most likely break the Ru–C σ-bond.[6]
Conclusions
In this work, the synthesis of novel building block 4Ј-
{C6H3(CH2Br)2-3,5}-2,2Ј:6Ј,2ЈЈ-terpyridine is presented,
which can be used as a precursor for bridging ligands con- tron spray ionization (ESI) mass spectra were recorded with a
Micromass LC-TOF mass spectrometer by the Department of
Biomolecular Mass Spectrometry, Utrecht University.
taining an N,N,N-domain and an E,C,E-coordination (E
= N, P, S, O) motive. Heteroditopic tpy-pincer ligands are
interesting from different viewpoints. In particular, elec-
Electrochemical Measurements: Cyclic and square-wave voltam-
tronic and steric properties of the pincer moiety, in which metric scans were performed with a gas-tight single compartment
cell under a dry nitrogen atmosphere. The cell was equipped with
a Pt microdisk working electrode (apparent surface area of
0.42 mm2), Pt wire auxiliary electrode and a Ag wire pseudorefer-
ence electrode. The working electrode was carefully polished with
a 0.25 µm-grain diamond paste between scans. The potential con-
trol was achieved with a PAR Model 283 potentiostat. All redox
potentials are reported against the ferrocene–ferrocenium (Fc/Fc+)
redox couple used as an internal standard[27] (E1/2 = +0.63 V versus
NHE[28]). All electrochemical samples were 5ϫ10–4  in the studies
complexes and 10–1  in Bu4NPF6 used as the supporting electro-
several transition metals can be incorporated by applying
various metallation procedures, can easily be tuned.
Incorporation of diphenylphosphanyl groups gave the 4Ј-
{C6H3(CH2PPh2)2-3,5}-2,2Ј:6Ј,2ЈЈ-terpyridine [tpyPC(H)P]
ligand. The asymmetric complex [Fe(tpy){tpyPC(H)P}]-
(PF6)2, prepared by reaction of [tpyPC(H)P] with 1 equiv.
of [Fe(tpy)Cl3], was used for the construction of the hetero-
dimetallic complex [Fe(tpy)(tpyPCP)Ru(tpy)](PF6)3, which
follows the “complex as ligand” approach.
For both complexes, the oxidation and reduction pro- lyte.
cesses have been assigned by comparison with literature
Electronic Spectroscopic Measurements: UV/Vis absorption spectra
were obtained with a Varian Cary 1 spectrophotometer by using
matched 1 cm cells and operating with a 0.5 nm spectral resolution.
data reported for related FeII–tpy compounds and with
[Ru(PCP)(tpy)]Cl, which was extensively studied in this
work. The redox potentials do not significantly change on Peak positions are given within 0.5 nm accuracy.
Eur. J. Inorg. Chem. 2007, 2111–2120
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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2117

M. Gagliardo, J. Perelaer, F. Hartl, G. P. M. van Klink, G. van Koten
FULL PAPER
1
UV/Vis Spectroelectrochemical Measurements: All the experiments
were performed with an optically transparent thin-layer electro-
chemical (OTTLE)[25] cell, equipped with a Pt minigrid working
electrode and quartz optical windows. The controlled-potential
electrolyses were carried out with a PA4 potentiostat (EKOM,
Polná, Czech Republic). All electrochemical samples were
5ϫ10–4  in the studied complex and 10–1  in Bu4NPF6. UV/Vis
spectra were recorded with a Hewlett Packard 8453 diode-array
spectrophotometer.
vacuo. Yield: 0.31 g, 64%. H NMR (300 MHz, CDCl3): δ = 8.75
[d, JH,H = 4.8 Hz, 2 H, tpyH(6, 6ЈЈ)], 8.73 [s, 2 H, tpy(3Ј, 5Ј)], 8.69
[d, JH,H = 8.1 Hz, 2 H, tpy(3, 3ЈЈ)], 7.90 [td, JH,H = 7.80, 1.60 Hz,
2 H, tpy(4, 4ЈЈ)], 7.85 (s, 2 H, ArH), 7.53 (s, 1 H, Ar), 7.38 [t, JHH
= 6.13 Hz, 2 H, tpy(5, 5ЈЈ)], 4.58 (s, 4 H, CH2) ppm. 13C NMR
(75 MHz, CDCl3): δ = 156.3, 156.1, 149.3, 149.2, 139.9, 139.5,
137.2, 130.5, 128.1, 124.2, 121.7, 118.9, 32.7 (CH2) ppm. Because
of its toxicity, elemental and ESI analyses were not carried out.
Caution: Substituted benzyl bromides can be powerful lachrymators
and should be used with adequate ventilation and precaution against
skin contact or ingestion.
[C6H3(CH2OMe)2-3,5]-SnMe3 (3): A solution of tBuLi (13.0 mL,
1.5  in pentane, 19.52 mmol) was added dropwise to a solution of
2 (3.00 g, 10.27 mmol) in Et2O (75 mL) at –100 °C with vigorous
stirring. After 0.5 h, a solution of Me3SnCl (3.07 g, 15.41 mmol) in
Et2O (35 mL) was slowly added. The resulting pale yellow coloured
suspension was warmed to room temperature and stirring was con-
tinued for another 15 h. Subsequently, water was added, and the
obtained mixture was treated with a NaOH solution (0.1 ,
2ϫ50 mL). The Et2O layer was separated, and the water layer was
washed with Et2O (2ϫ50 mL). The organic layers were combined,
washed with brine, dried with MgSO4, filtered and concentrated to
afford 3 as a colourless oil. Yield: 2.95 g, 85%. 1H NMR
(300 MHz, CDCl3): δ = 7.37 (s, 2 H, Ar), 7.26 (s, 2JSn,H = 21.7 Hz,
4Ј-{C6H3{CH2P(BH3)Ph2}2-3,5}-2,2Ј:6Ј,2ЈЈ-terpyridine ([tpyPC(H)P]·
2BH3, 6): nBuLi (0.8 mL, 1.34 mmol) was added to HPPh2·BH3
(0.27 g, 1.34 mmol) in dry THF (30 mL) at –78 °C. The tempera-
ture was allowed to rise to room temperature and stirring was con-
tinued overnight. A solution of 5 (0.32 g, 0.67 mmol) in dry THF
(20 mL) was then added at –78 °C. The mixture was warmed to
room temperature and stirred for ca. 20 h. All volatiles were then
removed in vacuo, and the obtained residue was dissolved in
CH2Cl2. The organic layer was washed with water and brine and
dried with MgSO4. Product 6 was obtained after evaporation of
CH2Cl2 as a white solid that was washed with hot EtOH and hex-
2
1
1 H, Ar), 4.43 (s, 4 H, OCH2), 3.34 (s, 6 H, OCH3), 0.29 [s, JSn,H
ane and dried in vacuo. Yield: 0.63 g, 64%. H NMR (300 MHz,
= 27.0 Hz, 9 H, Sn(CH3)3] ppm. 13C NMR (75 MHz, CDCl3): δ =
CDCl3): δ = 8.77 [d, JH,H = 4.0 Hz, 2 H, tpyH(6, 6ЈЈ)], 8.60 [d,
142.9 (1JSn,C = 228.3 and 451 Hz), 137.9 (2JSn,C = 18.3 Hz), 134.7 JH,H = 7.8 Hz, 2 H, tpyH(3, 3ЈЈ)], 8.19 [s, 2 H, PyrH(3Ј, 5Ј)], 7.86
(2JSn,C = 22.3 Hz, ArH), 127.5, 75.0 (OCH3), 58.4 [CH2, Sn- [td, JH,H = 7.8, 1.6 Hz, 2 H, tpyH(4, 4ЈЈ)], 7.63 (m, 8 H, meta-H
(CH3)3], –9.3 [1JSn,C = 171.5 Hz, Sn(CH3)3] ppm. ESI-MS: m/z
PAr), 7.47 (m, 12 H, ortho- and para-H PAr), 7.35 [t, JH,H =
331.05 [M – H]+. C13H22O2Sn (329.02): calcd. C 47.46, H 6.74; 6.13 Hz, 2 H, tpyH(5, 5ЈЈ)], 7.15 (s, 2 H, ArH), 6.95 (s, 1 H, Ar),
2
found C 47.55, H 6.62.
3.58 (d, JH,P = 11.0 Hz, 4 H, CH2), 0.90 (br. m, 6 H, BH3) ppm.
13C NMR (75 MHz, CDCl3): δ = 156.3, 155.9, 149.8, 149.0, 138.3,
4Ј-{C6H3(CH2OMe)2-3,5}-2,2Ј:6Ј,2ЈЈ-terpyridine (4): 4Ј-Trifluoro-
methylsulfonato-2,2Ј:6Ј,2ЈЈ-terpyridine (2.66 g, 6.99 mmol),
1
137.2, 133.3, 132.9 (d, JC,P = 8.5 Hz, Cquat., PAr), 131.7, 129.0 (d,
3
2JC,P = 9.2 Hz, PAr), 128.2, 128.0, 124.0, 121.7, 119.2, 34.2 (d, 1JC,P
= 31.7 Hz, CH2) ppm. 31P{1H} NMR: δ = (121.4 MHz, CDCl3): δ
= 19.3 (br. m) ppm. C35H33B2N3P (548.25): calcd. C 76.97, H 5.91,
N 5.73, B 2.95, P 8.45; found C 76.78, H 6.10, N 5.59, B 3.01, P
8.50.
(2.315 g, 6.99 mmol), [PdCl2(PPh3)2] (0.41 g, 0.58 mmol) and dried
LiCl (1.72 g, 40.6 mmol) were heated at reflux in dry toluene
(100 mL) for 20 h in a 100-mL round-bottomed flask under a nitro-
gen atmosphere. Subsequently, the solvent was removed in vacuo,
and the residue was redissolved in CH2Cl2. The CH2Cl2 solution
was washed with water, filtered through Celite and dried with
MgSO4. The crude product was obtained as a light yellow oil after
removal of the solvent as purified by silica gel column chromatog-
raphy (EtOAc/MeOH 8:1). The fractions containing 4 were col-
lected, concentrated and cooled to –30 °C. Product 4 precipitated
as a white crystalline solid and was collected and dried in vacuo.
Yield: 1.02, g, 40%. 1H NMR (300 MHz, CDCl3): δ = 8.75 [s, 2 H,
4Ј-{C6H3(CH2PPh2)2-3,5}-2,2Ј:6Ј,2ЈЈ-terpyridine ([tpyPC(H)P], 7):
Freshly distilled Et2NH (5 mL) was added to a solution of 6 in
CH2Cl2. The mixture was stirred at reflux for 4 h. All the volatiles
were removed in vacuo, and the obtained white solid was redis-
solved in dry CH2Cl2 (10 mL). The organic layer was collected,
washed with degassed water and brine and dried with MgSO4. Af-
ter evaporation of the CH2Cl2 in vacuo, product 7 was obtained as
tpy(3Ј, 5Ј)], 8.73 [d, JH,H = 4.3 Hz, 2 H, tpyH(6, 6ЈЈ)], 8.67 [d, JH,H an extremely air- and moisture-sensitive white sticky solid. This
= 9.0 Hz, 2 H, tpyH(3, 3ЈЈ)], 7.88 [td, JH,H = 7.89, 1.61 Hz, 2 H,
tpyH(4, 4ЈЈ)], 7.80 (s, 2 H, ArH), 7.43 (s, 1 H, Ar), 7.35 [m, 2 H,
product was used without further purification. Yield: 0.54 g, 88%.
1H NMR (300 MHz, CDCl3): δ = 8.76 [d, JH,H = 3.0 Hz, 2 H,
tpyH(5, 5ЈЈ)], 4.57 (s, 4 H, CH2), 3.44 (s, 12 H, OCH3) ppm. 13C tpyH(6, 6ЈЈ)], 8.75 [d, JH,H = 3.0 Hz, 2 H, tpyH(3, 3ЈЈ)], 8.38 [s, 2
NMR (75 MHz, CDCl3): δ = 156.4, 156.0, 150.4, 149.2, 139.6,
H, tpyH(3Ј, 5Ј)], 7.86 [td, JH,H = 7.5, 1.6 Hz, 2 H, tpyH(4, 4ЈЈ)],
139.0, 137.3, 127.8, 126.2, 124.0, 121.7, 119.3, 74.6 (OCH3), 58.5 7.37 [m, 2 H, tpyH(5, 5ЈЈ) and PAr], 7.18 (s, 2 H, ArH), 6.93 (s, 1
(CH2) ppm. C25H23N3O2 (397.47): calcd. C 75.54, H 5.83, N 10.57; H, Ar), 3.39 (s, 4 H, CH2) ppm. 13C NMR (75 MHz, CDCl3): δ =
1
found C 75.63, H 5.88, N 10.62.
156.6, 155.9, 150.6, 149.2, 138.3, 138.2, 136.9, 133.2 (d, JC,P
=
2
18.0 Hz, Cquat., PAr), 131.2, 129.0, 128.6 (d, JC,P = 6.0 Hz, PAr),
126.4, 123.9, 121.6, 119.2, 36.2 (d, JC,P = 16.0 Hz, CH2) ppm.
4Ј-{C6H3(CH2Br)2-3,5}-2,2Ј:6Ј,2ЈЈ-tpy (5): Compound 4 (0.25 g,
0.7 mmol) was dissolved in dry CH2Cl2 (20 mL) under a nitrogen
atmosphere. The temperature of the solution was lowered with an
ice bath and excess HBr·AcOH (110 mL, 33%) was slowly added.
The mixture was then stirred at room temperature for 15 h and
then cooled to 0 °C. Subsequently, aqueous 6  K2CO3 was slowly
added until the solution reached a pH of 8. The organic layer was
then collected, washed with water and brine, dried with MgSO4,
filtered and concentrated to ca. 5 mL. Addition of hexane caused
the precipitation of 5 as a white crystalline material. The crystals
were collected by filtration, washed with cold hexane and dried in
1
31P{1H} NMR (121.4 MHz, CDCl3): δ = –8.5 (s) ppm.
[Fe(tpy){tpyPC(H)P}](PF6)2 (9): Ligand 7 (0.17 g, 0.25 mmol) and
[Fe(tpy)Cl3] (0.095 g, 0.25 mmol) were heated at reflux in dry
MeOH for 4 h. The yellow mixture rapidly turned purple upon
heating. The solution was then cooled down to room temperature,
filtered and excess NH4PF6 in degassed water was added. The
formed deep purple precipitate was filtered off, washed with de-
gassed water and dried in vacuo. Yield: 0.10 g, 40%. Removal of a
small amount of a tpy-containing impurity by chromatography
2118
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© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2007, 2111–2120

Mono- and Heterodimetallic FeII and RuII Complexes
FULL PAPER
Hofmeier, A. El-Ghayoury, A. P. H. J. Schenning, U. S. Schu-
bert, Chem. Commun. 2004, 3, 318–319.
V. W.-W. Yam, W. W. Lee, K. K. Cheung, Organometallics
1997, 16, 2833–2841.
E. A. Medlycott, G. S. Hannan, Chem. Soc. Rev. 2005, 34, 133–
142.
M. Gagliardo, G. Rodríguez, H. H. Dam, M. Lutz, A. L. Spek,
R. W. A. Havenith, P. Coppo, L. De Cola, F. Hartl, G. P. M.
van Klink, G. van Koten, Inorg. Chem. 2006, 45, 2143–2155.
a) B. R. Steele, K. Vrieze, Transition Met. Chem. 1977, 2, 140–
144; b) D. M. Grove, G. van Koten, H. J. C. Ubbels, R. Zoet,
A. L. Spek, Organometallics 1984, 3, 1003–1009; c) J. A. M.
van Beek, G. van Koten, M. J. Ramp, N. C. Coenjaarts, D. M.
Grove, K. Goublitz, M. C. Zoutberg, C. H. Stam, W. J. J.
Smeets, A. L. Spek, Inorg. Chem. 1991, 30, 3059–3068; d) A. J.
Canty, J. Patel, B. W. Skelton, A. H. White, J. Organomet.
Chem. 2000, 607, 194–202; e) G. Rodríguez, M. Albrecht, J.
Schoenmaker, A. Ford, M. Lutz, A. L. Spek, G. van Koten, J.
Am. Chem. Soc. 2002, 124, 5127–5138.
could not be carried out because of the high sensitivity to air and
moisture of the PPh2 moieties. Complex 9 was used in the next
reaction without further purification. 1H NMR (300 MHz,
CD3CN): δ = 8.96 [d, JH,H = 7.8 Hz, 2 H, tpyA(3Ј, 5Ј)], 8.70 [t,
JH,H = 8.1 Hz, 1 H, tpyA(4Ј)], 8.51 [d, JH,H = 8.4 Hz, 4 H, tpyA(3,
3ЈЈ) + tpyA(3, 3ЈЈ)], 7.98 [s, 2 H, tpyB(3Ј, 5Ј)], 7.91–7.86 [m, 4 H,
tpyA(4, 4ЈЈ) + tpyA(4, 4ЈЈ)], 7.71 [d, JHH = 7.8 Hz, 2 H, tpyA(6,
6ЈЈ)], 7.61 [d, JH,H = 8.0 Hz, 2 H, tpyB(6, 6ЈЈ)], 7.43–7.39 (m, 12
H, para-H + meta-H PAr), 7.34–7.28 [m, 6 H, Ar + tpyA(5, 5ЈЈ) +
tpyA(5, 5ЈЈ)], 7.09 (m, 9 H, Ar + ortho-H PAr), 2.7 (s, 4 H, CH2)
ppm. 31P{1H} NMR (121.4 MHz, CD3CN): δ = –4.9 (s, 2 P),
[4]
[5]
[6]
[7]
1
–143.28 (sept, JP,F = 705 Hz, [PF6]–) ppm. ESI-MS: m/z = 497.20
[M – 2 PF6]2+
.
[Fe(tpy)(tpyPCP)Ru(tpy)](PF6)3 (11): Compounds
8
(0.10 g,
0.08 mmol) and 9 (0.05 g, 0.08 mmol) were dissolved in THF/
MeCN (2:1, 30 mL). The solution was stirred at reflux for 10 h.
The solvent was evaporated in vacuo. The deep purple residue was
washed several times with hexane until no more free bis(amino)-
[8]
[9]
H. P. Dijkstra, P. Steenwinkel, D. M. Grove, M. Lutz, A. L.
Spek, G. van Koten, Angew. Chem. Int. Ed. 1999, 38, 2186–
2188.
1
arene (NCN) ligand could be detected by H NMR spectroscopy,
and then dried in vacuo. The obtained deep purple solid (10), char-
acterized only by NMR spectroscopy, was added to 2,2Ј:6Ј,2ЈЈ-ter-
pyridine (0.02 g, 0.08 mmol) dissolved in dry MeOH (25 mL). The
mixture was heated at reflux for 2 d. Subsequently, the methanolic
solution was cooled to room temperature, filtered, and concen-
trated until a small residual amount remained. Addition of aque-
ous NH4PF6 resulted in the precipitation of 11 as an air-stable red–
purple solid that was collected by filtration, washed with water,
hexane and dried in vacuo. The crude product was purified by col-
umn chromatography on silica gel (MeCN/water/saturated NaNO3
solution 70:25:5). The major fraction was dried to afford 11 as a
red-purple solid. Yield: 0.07 g, 52%. 1H NMR (300 MHz,
CD3COCD3): δ = 9.07 [d, JH,H = 8.1 Hz, 2 H, tpyC(3Ј, 5Ј)], 8.86
[d, JH,H = 8.1 Hz, 2 H, tpyA(3Ј, 5Ј)], 8.82–8.70 [m, 3 H, tpyA(4Ј)
+ tpyC(3, 3ЈЈ)], 8.58 [t, JH,H = 8.5 Hz, 1 H, tpyC(4Ј)], 8.48 [d, JH,H
= 8.1 Hz, 4 H, tpyA(3, 3ЈЈ) + tpyB(3, 3ЈЈ)], 8.09 [s, 2 H, tpyB(3Ј,
5Ј)], 8.06–8.00 [m, 8 H, Ar + tpyA(4, 4ЈЈ) + tpyB(4, 4ЈЈ) + tpyC(4,
Representative examples of aryl pincer complexes applied as
liquid crystalline materials, optical and electro-optical devices,
sensors and catalysts: a) B. Donnio, D. W. Bruce in Structure
and Bonding (Liquid Crystals II) (Ed.: D. M. P. Mingos),
Springer, 1999; b) M. Ghedini, G. Pucci, A. Crispini, I. Aiello,
F. Barigelletti, A. Gessi, O. Francescangeli, Appl. Organomet.
Chem. 1999, 13, 565–581; c) P. Espinet, E. Garcìa-Orodea, J. A.
Miguel, Inorg. Chem. 2000, 39, 3645–3651; d) L. Omnes, B. A.
Timini, T. Gelbrich, M. B. Hursthouse, G. R. Luckhurst, D. W.
Bruce, Chem. Commun. 2001, 2248–2249; e) M. Albrecht, G.
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4ЈЈ)], 7.69 [d, JH,H = 5.4 Hz, 2 H, tpyC(6, 6ЈЈ)], 7.42 [d, JH,H
=
[10]
5.1 Hz, 4 H, tpyA(6, 6ЈЈ) + tpyA(6, 6ЈЈ)], 7.64–7.53 [m, 6 H, tpyA(5,
5ЈЈ) + tpyB(5, 5ЈЈ) + tpyC(5, 5ЈЈ)], 7.35–6.77 (m, 20 H, PAr) ppm.
31P{1H} NMR (121.4 MHz, CD3CN): δ = 41.82 (s, 2 P), –142.92
1
(sept, JP,F = 705 Hz, [PF6]–) ppm. ESI-MS: m/z = 442.75 [M – 3
PF6]3+, 736.67 [M – 2 PF6]2+
.
Acknowledgments
This work was financially supported by the Council for Chemical
Sciences of the Netherlands Organization of Scientific Research
(CW-NWO).
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Received: October 2, 2006
Published Online: February 14, 2007
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