Elektronenreservoirkomplexe [FeICp(Aren)] als selektive Initiatoren für eine neue Elektrokatalysereaktion: Synthese fulvalenverbrückter homo‐ und heterozweikerniger Zwitterionen,
Abstract:Bei 20°C in nur fünf Minuten gelingt die intramolekulare Disproportionierung von Dimetallkomplexen 1 mit Fulvalenbrücke in Gegenwart von PMe3 oder P(OMe)3, wenn Elektronenreservoirkomplexe des Typs [Fe1Cp(Aren)] als Katalysatoren dienen. M1 = Mo, W, Fe, Ru; M2 = Mo, W; n = 2,3; m = 3; Aren = C6H6, C6Me6. Die Heterozweikernkomplexe reagieren dabei regioselektiv.magnified image
“…Obviously, similarities and differences were forecasted; in particular, the electronic delocalization through the fulvalenyl bridge between the two metal centers renders the bimetallic systems considerably richer and more versatile than the mononuclear ones. As a consequence, electron-transfer reactions have been extremely useful in fulvalenyldimetal chemistry, especially with first-row transition metals. − Stoichiometric electron transfer has provided redox recognition in heteronuclear chemistry, , and catalytic electron transfer (electron-transfer chain) − ,,,, has been responsible for spectacular reactivity. , In the present work, however, chain reactions are not efficient, and we are now comparing stoichiometric electron transfer with photolysis. ,, …”
Section: Introductionmentioning
confidence: 80%
“…As a consequence, electron-transfer reactions have been extremely useful in fulvalenyldimetal chemistry, especially with first-row transition metals. [41][42][43][44][45][46] Stoichiometric electron transfer has provided redox recognition in heteronuclear chemistry, 41,42 and catalytic electron transfer (electron-transfer chain) [33][34][35][36]46,47,50,51 has been responsible for spectacular reactivity. 43,44 In the present work, however, chain reactions are not efficient, and we are now comparing stoichiometric electron transfer with photolysis.…”
The bi-sandwich complex
[Fe2Fv(C6H6)2]2+(PF6
-)2
(1
2+; Fv =
μ2-η5:η5-fulvalenyl, unless
noted
otherwise) synthesized from biferrocene, was photolyzed with visible
light in acetonitrile in
the presence of 1,2-bis(diphenylphosphino)ethane (dppe) or
bis(diphenylphosphino)methane
(dppm) at −15 °C to give
[Fe2Fv(dppe)2(NCMe)2]2+(PF6
-)2
(2a
2+) or
[Fe2Fv(dppm)2(NCMe)2]2+(PF6
-)2
(2b
2+). The complexes
2a
2+ and 2b
2+ reacted
in refluxing 1,2-dichloroethane with CO to give
[Fe2Fv(dppe)2(CO)2]2+(PF6
-)2
(3a
2+) and
[Fe2Fv(dppm)2(CO)2]2+(PF6
-)2
(3b
2+), and 2a
2+
reacted similarly with PMe3 to give
[Fe2Fv(dppe)2(PMe3)]2+(PF6
-)2
(4
2+).
The direduced 38-electron (38e) complex 1 reacted at
−15 °C with 1 atm of CO to give [Fe2(μ2-η4:η4-Fv)(CO)6]
(7) and with PMe3 to give
[Fe2Fv(PMe3)4]
(9). When
Na+PF6
- was
present
in stoichiometric amounts in THF, these reactions followed a different
course and
Na+PF6
-
induced electron transfer (disproportionation) by irreversibly
dislocating ion pairs: the
reaction of 1 with 1 atm of CO gave
[Fe(η5-Fv)(η6-C6H6),
Na+PF6
-] (5),
and that with PMe3
gave
[Fe2Fv(PMe3)6]2+(PF6
-)2
(8
2+) and the known complex
[Fe(PMe3)4] (10). The
cyclic
voltammograms (CV) of 2a
2+ and
2b
2+ contain irreversible oxidation and
reduction waves,
but the CVs of 3a
2+ and
3b
2+ showed two close reversible
monoelectronic reduction waves
(no oxidation wave). The CVs of the hexaphosphine complexes
indicated partially or fully
irreversible reduction waves, respectively, but two reversible waves at
+0.71 and +0.95 V
for 4
2+ and +0.70 and +1.08 V for
8
2+ (vs SCE, Pt, DMF, 0.1 M
n-Bu4NBF4 −30 °C).
The
bielectronic reduction of 2a
2+ and the
bielectronic oxidation of 4
2+ and
8
2+ using redox
reagents led to decomposition, but the monoelectronic oxidation of
4
2+ and 8
2+ using
(p-Br-C6H4)3N+SbCl6
-
in CH2Cl2 gave the stable mixed-valence
trications 4
3+
and
8
3+
, for which
the Mössbauer spectra showed delocalized average valency on the
Mössbauer time scale.
These studies have opened the route to a variety of mono- and
diiron fulvalenyl organometallic compounds, confirming the great importance of the presence of
Na+PF6
-. This
salt
can change reaction pathways and, in particular, induce
electron-transfer reactions,
underlining the extraordinary electronic flexibility of the fulvalenyl
ligand and its ability to
transfer the electron flow between two metal centers.
“…Obviously, similarities and differences were forecasted; in particular, the electronic delocalization through the fulvalenyl bridge between the two metal centers renders the bimetallic systems considerably richer and more versatile than the mononuclear ones. As a consequence, electron-transfer reactions have been extremely useful in fulvalenyldimetal chemistry, especially with first-row transition metals. − Stoichiometric electron transfer has provided redox recognition in heteronuclear chemistry, , and catalytic electron transfer (electron-transfer chain) − ,,,, has been responsible for spectacular reactivity. , In the present work, however, chain reactions are not efficient, and we are now comparing stoichiometric electron transfer with photolysis. ,, …”
Section: Introductionmentioning
confidence: 80%
“…As a consequence, electron-transfer reactions have been extremely useful in fulvalenyldimetal chemistry, especially with first-row transition metals. [41][42][43][44][45][46] Stoichiometric electron transfer has provided redox recognition in heteronuclear chemistry, 41,42 and catalytic electron transfer (electron-transfer chain) [33][34][35][36]46,47,50,51 has been responsible for spectacular reactivity. 43,44 In the present work, however, chain reactions are not efficient, and we are now comparing stoichiometric electron transfer with photolysis.…”
The bi-sandwich complex
[Fe2Fv(C6H6)2]2+(PF6
-)2
(1
2+; Fv =
μ2-η5:η5-fulvalenyl, unless
noted
otherwise) synthesized from biferrocene, was photolyzed with visible
light in acetonitrile in
the presence of 1,2-bis(diphenylphosphino)ethane (dppe) or
bis(diphenylphosphino)methane
(dppm) at −15 °C to give
[Fe2Fv(dppe)2(NCMe)2]2+(PF6
-)2
(2a
2+) or
[Fe2Fv(dppm)2(NCMe)2]2+(PF6
-)2
(2b
2+). The complexes
2a
2+ and 2b
2+ reacted
in refluxing 1,2-dichloroethane with CO to give
[Fe2Fv(dppe)2(CO)2]2+(PF6
-)2
(3a
2+) and
[Fe2Fv(dppm)2(CO)2]2+(PF6
-)2
(3b
2+), and 2a
2+
reacted similarly with PMe3 to give
[Fe2Fv(dppe)2(PMe3)]2+(PF6
-)2
(4
2+).
The direduced 38-electron (38e) complex 1 reacted at
−15 °C with 1 atm of CO to give [Fe2(μ2-η4:η4-Fv)(CO)6]
(7) and with PMe3 to give
[Fe2Fv(PMe3)4]
(9). When
Na+PF6
- was
present
in stoichiometric amounts in THF, these reactions followed a different
course and
Na+PF6
-
induced electron transfer (disproportionation) by irreversibly
dislocating ion pairs: the
reaction of 1 with 1 atm of CO gave
[Fe(η5-Fv)(η6-C6H6),
Na+PF6
-] (5),
and that with PMe3
gave
[Fe2Fv(PMe3)6]2+(PF6
-)2
(8
2+) and the known complex
[Fe(PMe3)4] (10). The
cyclic
voltammograms (CV) of 2a
2+ and
2b
2+ contain irreversible oxidation and
reduction waves,
but the CVs of 3a
2+ and
3b
2+ showed two close reversible
monoelectronic reduction waves
(no oxidation wave). The CVs of the hexaphosphine complexes
indicated partially or fully
irreversible reduction waves, respectively, but two reversible waves at
+0.71 and +0.95 V
for 4
2+ and +0.70 and +1.08 V for
8
2+ (vs SCE, Pt, DMF, 0.1 M
n-Bu4NBF4 −30 °C).
The
bielectronic reduction of 2a
2+ and the
bielectronic oxidation of 4
2+ and
8
2+ using redox
reagents led to decomposition, but the monoelectronic oxidation of
4
2+ and 8
2+ using
(p-Br-C6H4)3N+SbCl6
-
in CH2Cl2 gave the stable mixed-valence
trications 4
3+
and
8
3+
, for which
the Mössbauer spectra showed delocalized average valency on the
Mössbauer time scale.
These studies have opened the route to a variety of mono- and
diiron fulvalenyl organometallic compounds, confirming the great importance of the presence of
Na+PF6
-. This
salt
can change reaction pathways and, in particular, induce
electron-transfer reactions,
underlining the extraordinary electronic flexibility of the fulvalenyl
ligand and its ability to
transfer the electron flow between two metal centers.
“…Since the zwitterion 6 was the first one obtained in the series, suitable crystals were grown by slow cooling of a saturated acetonitrile solution and the X-ray diffraction study was carried out by Boese. The results were reported in a preliminary communication, and the ORTEP drawing is shown in Figure . The X-ray structure confirmed the proposed formulation of the product and showed a trans orientation of the metal centers with respect to the fulvalene ligand, an arrangement which is always observed in bimetallic complexes lacking a metal−metal bond. 1 Crystal structure of 6 .…”
Section: Resultsmentioning
confidence: 91%
“…In former papers, we have detailed the electrochemistry and stoichiometric electron-transfer chemistry of heterodinuclear fulvalene complexes [WMFv(CO) 5 ] (Fv = fulvalene; M = Fe, Ru). Along this line, we now report electrocatalytic reactions of these complexes as well as those of the homodimers [M 2 Fv(CO) 6 ] (M = Mo, W) with PMe 3 and P(OMe) 3 , including the synthetic and analytical aspects . In synthetic-scale reactions, we use three electron-reservoir [Fe I Cp(arene)] complexes as electrocatalysts and will show their selectivity depending on their redox potential values.…”
The electron-reservoir complexes
[FeICp(C6H6)],
[FeICp(C6Me6)],
and
[FeICp*(C6Me6)]
(Cp
= η5-C5H5; Cp* =
η5-C5Me5) have been used as
initiators in THF for the electron-transfer-chain-catalyzed (electrocatalyzed) synthesis of the homobimetallic
zwitterions
[(CO)3M-FvM+(CO)2(PR3)2]
(M = Mo, W; Fv = μ2-η10-fulvalene; R
= Me, OMe) from [M2Fv(CO)6] and PR3 and of the heterobimetallic
zwitterions
[(CO)3MIFvM2(CO)(PR3)2]
(M1 = Mo,
W; M2 = Fe, Ru) from
[M1M2Fv(CO)5] and
PR3. Cyclic voltammetry (CV) experiments
(DMF,
0.1 M n-Bu4NBF4, Pt, 0.400 V
s-1) show that the CV's of the homobimetallic starting
materials
are unchanged in the presence of PR3 (R = Me, OMe)
whereas those of the heterobimetallic
complexes in the presence of PMe3 show only the CV's of the
zwitterions. This indicates
that the electrocatalytic process of the homobimetallic complexes is
slow on the electrochemical time scale whereas that of the heterobimetallic complexes with
PMe3 is fast on the same
time scale. This dichotomy is taken into account in terms of the
very low concentration of
the primary radical anion responsible for the reactivity with
PR3 in the case of the
homodinuclear systems due to an intrinsically high disproportionation
constant (K
disp); with
heterodinuclear complexes, the dissymmetry is responsible for a
relatively good thermodynamic stability and, thus, a higher concentration of the primary radical
anion
[(CO)3M1
-FvM2(CO)2
•],
which reacts with PR3. The effect of the
PMe3 concentration is also
important, consistent with second-order kinetics. Subsequently,
the K
disp values are
qualitatively found in the following order, which is opposite to that
of the electrocatalytic
reactivity: RuRu (unreactive) ≫ WW > MoMo > 1 > RuMo, RuW >
FeW. In THF, initiation
with
[FeICp(C6Me6)] of
the reaction of
[(CO)3WFvRu(CO2)] with
PR3 yields the monophosphine
zwitterionic adduct
[(CO)3W-FvRu+(CO)2(PMe3)],
whose formation is partially driven by its
insolubility. On the other hand, with
[FeCp*(C6Me6)] as the initiator,
the bis(phosphine)
zwitterion
[(CO)3W-FvRu+(CO)(PMe3)2]
is formed as a result of the stronger driving force
in the initiation electron-transfer step. The synergistic roles of
the insolubility of the
monophosphine intermediate and of the driving force provided by the
electron-reservoir
initiator are confirmed for electrocatalytic experiments in solvents of
high dielectric constants
(synthesis in MeCN or electrochemistry in DMF) in which the
monophosphine zwitterion is
neither formed nor detected. In conclusion, initiation of
electrocatalytic reactions by the
electron-reservoir [FeICp(arene)] complexes is
very useful (cobaltocene is inefficient in many
cases), highly efficient (no side reactions), and highly selective (as
a function of the number
of Me groups on the ligands providing a wide range of redox
potentials).
“…3) Initiator reagents for electron‐transfer‐chain (electrocatalytic) reactions,30 such as arene exchange by phosphines in sandwich complexes,20 CO substitution by phosphines in dinuclear metal–carbonyl complexes and clusters31, 32 or alkyne polymerization co‐catalyzed by W species 33. 34…”
Section: Electron‐transfer Functions Of the Electron‐reservoir [Cpfe(mentioning
In this review, which is mostly focused on the concepts and work developed in the author's laboratory, the access and properties of electron-reservoir (redox-robust) transition-metal complexes with sufficiently negative redox potentials and their branching to the tethers of dendrimers and other related nanodevices are highlighted, with the idea of designing dendritic molecular batteries.
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