Ytterbium(III) Complexes Coordinated by Dianionic 1,4-Diazabutadiene Ligands

Article abstract of DOI:10.1021/om501121s

A series of new Yb(III) complexes XYb(DAD)^2-(L) (X = C₅Me₅, C₅Me₄H, N(SiMe₃)₂, ^tBuO; DAD = 2,6-R″₂C₆H₃N=C(R′)-C(R′)=NC₆H₃R″₂-2,6, R′ = H, Me, R″ = Me, ⁱPr; L = thf, dme) coordinated by redox-active diazabutadiene ligands in dianionic form were synthesized and characterized. The half-sandwich complexes Cp^#Yb(DAD)^2-(THF) (Cp^# = C₅Me₅, C₅Me₄H) were synthesized by the reactions of the ytterbocenes Cp^#₂Yb(THF)₂ with the corresponding DADs in a 1:1 molar ratio. These reactions are accompanied by oxidation of the Yb(II) to Yb(III), cleavage of one Cp^#-Yb bond, oxidation of cyclopentadienyl anion, and reduction of the diazabutadiene to dianionic form. It was found that the substituents by the DAD nitrogens (2,6-ⁱPr₂C₆H₃ vs 2,6-Me₂C₆H₃) and imino carbons (H vs Me) do not affect the reaction outcome and afford Cp^#Yb(DAD)^2-(thf). The amido and alkoxo derivatives XYb(DAD)^2-(dme) (X = N(SiMe₃)₂, ^tBuO) were obtained by the salt metathesis reactions of the in situ generated species [XYbCl₂(thf)_n] and Na₂(thf)_n[2,6-ⁱPr₂C₆H₃NC(Me)C(Me)NC₆H₃ⁱPr₂-2,6]. If the reaction was carried out in the presence of Li ions, it afforded an ate-complex {Li(thf)₃}{Yb[2,6-ⁱPr₂C₆H₃NC(Me)C(Me)NC₆H₃ⁱPr₂-2,6]^2-[N(SiMe₃)₂](μ-Cl)}. The X-ray studies of complexes XYb^III(DAD)^2-(L) revealed that they feature the 2σ:η²-type of coordination of dianionic DAD ligands. Introduction of Me-substituents by the imino carbons of DADs leads to some elongation of Yb-Cp^# bonds compared to the NCHCHN-analogues. The Yb-C_NCCN bonds and the dihedral YbNN-NCCN angles were found to be the most sensitive to replacing H by Me. Unlike the formerly reported complex Cp?Yb[2,6-ⁱPr₂C₆H₃NCHCHNC₆H₃ⁱPr₂-2,6]^2-(thf), the variable-temperature magnetic measurements (1.8-300 K) of complexes 3-5 and 7-9 did not reveal thermally induced redox isomeric transformations for these compounds. However, for complex (C₅Me₄H)Yb[2,6-ⁱPr₂C₆H₃NC(Me)C(Me)NC₆H₃ⁱPr₂-2,6](thf) at 9 K, the structural phase transition accompanied by changes of the coordination behavior of the DAD ligand was detected, which might hint for an onset of a temperature-induced redox isomerism. These results clearly indicate high sensitivity of redox isomeric transformations of XYb^III(DAD)^2-L to the smallest changes of the structural and electronic properties of the DAD ligands. (Chemical Equation Presented).

Full text of DOI:10.1021/om501121s

Article
pubs.acs.org/Organometallics
Ytterbium(III) Complexes Coordinated by Dianionic
1,4-Diazabutadiene Ligands
Boris G. Shestakov,† Tatyana V. Mahrova,† Joulia Larionova,‡ Jerome Long,‡ Anton V. Cherkasov,†
̂
Georgy K. Fukin,†,# Konstantin A. Lyssenko,§ Wolfgang Scherer,∥ Christoph Hauf,∥
Tatiana V. Magdesieva,⊥ Oleg A. Levitskiy,⊥ and Alexander A. Trifonov*,†,§,#
†G. A. Razuvaev Institute of Organometallic Chemistry of Russian Academy of Sciences, 49 Tropinina str., 603950, Nizhny Novgorod,
GSP-445, Russia
‡Institut Charles Gerhardt Montpellier, UMR 5253 CNRS-UM2-ENSCM-UM1, Chimie Molec
Universite Montpellier II, Place E. Bataillon, 34095 Montpellier cedex 5, France
́
ulaire et Organisation du Solide,
́
§A. N. Nesmeyanov Institute of Organoelement Compounds of Russian Academy of Sciences, 28 Vavilova str., 119991,
Moscow,GSP-1, Russia
∥Institute of Physics, University of Augsburg, 86135 Augsburg, Germany
⊥Moscow State University, GSP-1, Leninskie Gory, Moscow, 119991, Russia
#Nizhny Novgorod State University, 23 Gagarin av., 603950, Nizhny Novgorod, Russia
S
* Supporting Information
ABSTRACT: A series of new Yb(III) complexes XYb(DAD)2−(L)
t
(X = C5Me5, C5Me4H, N(SiMe3)2, BuO; DAD = 2,6-R″2C6H3N
C(R′)-C(R′)NC6H3R″2-2,6, R′ = H, Me, R″ = Me, iPr; L = thf, dme)
coordinated by redox-active diazabutadiene ligands in dianionic form
were synthesized and characterized. The half-sandwich complexes
Cp#Yb(DAD)2−(THF) (Cp# = C5Me5, C5Me4H) were synthesized by
the reactions of the ytterbocenes Cp# Yb(THF)2 with the correspond-
2
ing DADs in a 1:1 molar ratio. These reactions are accompanied by
oxidation of the Yb(II) to Yb(III), cleavage of one Cp#−Yb bond,
oxidation of cyclopentadienyl anion, and reduction of the diazabuta-
diene to dianionic form. It was found that the substituents by the DAD
nitrogens (2,6-iPr2C6H3 vs 2,6-Me2C6H3) and imino carbons (H vs Me) do not affect the reaction outcome and afford
t
Cp#Yb(DAD)2−(thf). The amido and alkoxo derivatives XYb(DAD)2−(dme) (X = N(SiMe3)2, BuO) were obtained by the
salt metathesis reactions of the in situ generated species [XYbCl2(thf)n] and Na2(thf)n[2,6-iPr2C6H3NC(Me)C(Me)-
i
NC6H3 Pr2-2,6]. If the reaction was carried out in the presence of Li ions, it afforded an ate-complex {Li(thf)3}{Yb-
i
[2,6-iPr2C6H3NC(Me)C(Me)NC6H3 Pr2-2,6]2−[N(SiMe3)2](μ-Cl)}. The X-ray studies of complexes XYbIII(DAD)2−(L)
revealed that they feature the 2σ:η2-type of coordination of dianionic DAD ligands. Introduction of Me-substituents by the
imino carbons of DADs leads to some elongation of Yb−Cp# bonds compared to the NCHCHN-analogues. The Yb−CNCCN
bonds and the dihedral YbNN−NCCN angles were found to be the most sensitive to replacing H by Me. Unlike the formerly
i
reported complex Cp*Yb[2,6-iPr2C6H3NCHCHNC6H3 Pr2-2,6]2−(thf), the variable-temperature magnetic measure-
ments (1.8−300 K) of complexes 3−5 and 7−9 did not reveal thermally induced redox isomeric transformations for these
compounds. However, for complex (C5Me4H)Yb[2,6-iPr2C6H3NC(Me)C(Me)NC6H3 Pr2-2,6](thf) at 9 K, the structural
i
phase transition accompanied by changes of the coordination behavior of the DAD ligand was detected, which might
hint for an onset of a temperature-induced redox isomerism. These results clearly indicate high sensitivity of redox
isomeric transformations of XYbIII(DAD)2−L to the smallest changes of the structural and electronic properties of the DAD
ligands.
lanthanide atoms as neutral ligands3 withal; due to their elec-
INTRODUCTION
The application of redox-active 1,4-diaza-1,3-butadiene (DAD)1
■
tron affinity,4 they can oxidize electropositive Ln(II) species,5
transforming into radical anions3,6 or dianions7 by accepting
ligands has led to the development of rich coordination and
one or two electrons, respectively. An expansion of lanthanide
redox organolanthanide chemistry.2 The lone electron pairs at
nitrogen atoms and the π-electrons of the CN bonds allow
DAD molecules to act both as n- and π-electron donors, thus
Received: November 6, 2014
Published: April 1, 2015
providing a variety of coordination modes. DADs can coordinate
© 2015 American Chemical Society
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Article
chemistry due to DAD ligands allowed for finding new
phenomena in this field such as solvent-mediated redox tran-
formations6c,e,f and temperature-induced redox isomerism.7,8 In
our previous works, it was demonstrated that the redox reactions
of ytterbocenes with DADs are sterically and electronically
tunable. Depending on the extent of steric crowding of the
coordination sphere of metal atoms and the nature of metal−
ligand bonding, these reactions can occur with metal atom
oxidation,6 C−C bond formation,9 and C−H bond activation.9
Moreover, variation of steric saturation of the ytterbium
coordination sphere allows for switching the reductive capacity
of ytterbocenes in their reactions with DADs from one- to two-
electron reduction.7 The role of the steric demand of the
cyclopentadienyl ligands coordinated to Yb(II) in directing
redox reactions with DADs was elucidated to some extent,7,10
while the influence of steric and electronic properties of DAD
ligands still remains unclear. Hereafter, we report on the reac-
Scheme 1
Moreover, an ascertainment of possible interconnection of
the structural properties and redox behavior of complexes
Cp#YbIII(DAD2−)(thf) represents a special interest.
For quantitative estimation of redox ability of the DAD
ligands, as well as its dependence on the substituents at C and N
atoms, voltammetric investigation of four different diazabuta-
dienes was performed in DMF using a Pt disk electrode. Since the
reduction of DAD occurs within the NC-CN fragment, the
redox properties can be modulated by insertion of appropriate
substituents. For all ligands, one-electron reduction peaks were
detected (see the Supporting Information, Figure S1). The peak
potential values are given in Table 1. Electron affinities within the
tions of ytterbocenes Cp# Yb(THF)2 (Cp# = C5Me5, C5Me4H)
2
with the DADs having different steric and electronic properties,
2,6-R″2C6H3NC(R′)-C(R′)NC6H3R″2-2,6 (R′ = H, Me;
R″ = Me, iPr). Furthermore, in order to expand the series of the
Yb(III) complexes coordinated by dianionic DAD ligands
featuring temperature-induced redox isomeric transformations
[CpYbIII(DAD)2−(L)] ⇄ [CpYbII(DAD)− (L)]7 (L = neutral,
redox innocent ligand), we synthesized a series of new compounds
containing along with DAD2− electron-withdrawing (compared
to the electron-donating C5Me57) amido and alkoxy groups. The
structures and magnetic behavior in a wide temperature range of
complexes Cp*YbIII[R″2C6H3NC(R′)C(R′)NC6H3R″2](thf) (R′ =
H, Me; R″ = Me, iPr) and RYbIII[2,6-iPr2C6H3NC(Me)C(Me)-
c
a
Table 1. Direct (Ep ) and Reverse (Ep ) Peak Potential Values
Observed in the Reduction of DADs (DMF, Pt, 200 mV/s,
0.05 M Bu4NBF4, vs Ag/AgCl/KCl)
DAD
DAD4Me2H
1.59
DAD4iPr2H
1.62/1.54
DAD4Me2Me
1.98
DAD4iPr2Me
2.02/1.90
i
NC6H3 Pr2-2,6](dme) (R = N(SiMe3)2, OtBu) will be discussed
c
a
−Ep /Ep , V
also.
pairs DAD4Me2H, DAD4iPr2H and DAD4Me2Me, DAD4iPr2Me are
similar: the difference in the reduction potential values does not
exceed 30 mV. This means that redox properties of the ligand are
not sensitive to the type of alkyl substituent in the phenyl ring.
Unlike the small influence of the alkyl groups in the aromatic
moieties, the introduction of methyl groups at the imine carbon
atoms substantially influences the reduction potential values of
both DAD4Meand DAD4iPr. Thus, DAD4Me2H and DAD4iPr2H are
more readily reduced than their Me-substituted counterparts for
approximately 400 mV. This estimation is in agreement with the
literature data obtained for dimesityl substituted diazabutadienes
(DADMesH and DADMesMe).11 Electrochemical behavior of DADs
was investigated11 in acetonitrile and showed in all cases completely
irreversible peaks, indicating that electron transfer is followed by a
chemical follow-up step. Our results obtained in DMF showed that
this solvent sufficiently increases the stability of the reduced
monoanionic form of DAD, at least at the CV time scale.
Thus, for DAD4iPr2H, the reduction is quasi-reversible (the
current ratio Ic/Ia = 1 at scan rates in the range of 50−500 mV/s;
the peak separation ΔEp is equal to 80 mV at a scan rate of
200 mV/s) and diffusionally controlled (as follows from the
linear Ip − ν1/2 relationship, where ν is a scan rate). An insertion
of methyl groups at imine carbons decreases the stability of the
reduced form of DAD4iPr2Me even in DMF; the reverse-to-direct
peak current ratio decreases to 0.4 at a scan rate of 200 mV/s.
The reduction of DAD4Me is irreversible, despite the nature of the
substituent at the imine carbon (H or Me). Since the reduction
potential values for DAD4Me and DAD4iPr are similar, the relative
stability of the radical-anion in the latter case should be more
likely attributed to steric reasons.
RESULTS AND DISCUSSION
■
In our previous research, it was demonstrated that the outcome
of redox reactions of ytterbocenes with DADs is dependent
on the steric demand of cyclopentadienyl ligands coordinated
to Yb(II).7 Thus, ytterbocene (C5MeH4)2Yb(thf)2 reacts with
diazabutadiene 2,6-iPr2C6H3NCH-CHNC6H3 Pr2-2,6
i
(DAD4iPr2H) as a one-electron reductant to afford a bis-
(cyclopentadienyl) Yb(III) derivative containing a DAD radical
anion (C5MeH4)2YbIII(DAD−.). However, ytterbocenes
Cp# Yb(thf)2 coordinated by sterically demanding cyclopenta-
2
dienyl ligands act as two-electron reductants in their reactions
with DAD4iPr2H. These reactions occur by the abstraction
and oxidation of one Cp#-anion, and oxidation of Yb(II) to
Yb(III), and result in the formation of half-sandwich complexes
Cp#YbIII(DAD4iPr2H)2−(thf) (Cp# = C5Me5 (1), C5Me4H (2))7
coordinated by enediamido ligands. In order to evaluate the
limits of the above-mentioned synthetic approach and to
elucidate the effect of steric demand of the DAD ligand, the
reactions of ytterbocenes Cp# Yb(thf)2 (Cp = C5Me5, C5Me4H)
2
with less bulky1,4-diaza-1,3-butadiene 2,6-Me2C6H3N
CH-CHNC6H3Me2-2,6 (DAD4Me2H) were studied (Scheme 1).
The magnetic measurements for complex 17 in the wide range of
temperatures (2−300 K) were indicative of the existence of
thermally induced redox isomerism [CpYbIII(DAD)2−(L)] ⇄
[CpYbII(DAD)−·(L)] for this compound. To elucidate the
impact of the redox properties of DAD ligands on the feasibility
of redox isomeric transformation, less electron-withdrawing
diazabutadienes bearing by the imino carbons electron-donating
Me groups 2,6-R2C6H3NC(Me)-C(Me)NC6H3R2-2,6
i
(R = Me (DAD4Me2Me), Pr (DAD4iPr2Me)) were tested.
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Scheme 2
The reactions of Cp# Yb(thf)2 with equimolar amounts of
X-ray Crystal Structures. Crystals of 3−5 suitable for single-
crystal X-ray diffraction studies were obtained by continuous
cooling their hexane solutions at −5 °C. The crystal structures of
complexes 3, 4, and 7 were determined at 100(2) K and of 8, 9 at
150(2) K. Moreover, the crystal structure of complex 5 was
determined at 100(2) K and at 9(2) K; they are denoted as
5HT and 5LT, respectively. The molecular structures of 3−5
and 7−9 determined at 100(2) K are depicted in Figures 1−6,
2
DADs (DAD4Me2H, DAD4Me2Me, DAD4iPr2Me) were carried out in
toluene at 50 °C (Scheme 1).
It was found that, for all tested 1,4-diaza-1,3-butadienes
DAD4Me2H, DAD4Me2Me, and DAD4iPr2Me, the reactions occur
similarly and afford mixed-ligand Yb(III) complexes
Cp#YbIII(DAD2−)(thf) 3−5 (Scheme 1)) in moderate yields
(49, 57, and 35%, respectively). In the case of the reaction of
(C5Me4H)2Yb(thf)2 with DAD4iPr2Me, the second ytterbium
containing product (C5Me4H)3Yb (6) was isolated from the
reaction mixture in 10% yield (for the structure of (C5Me4H)3Yb,
see Figure S2 and Table S1, Supporting Information). The
formation of complex 6 apparently results from the oxidation of
(C5Me4H)2Yb(thf)2 by a C5Me4H· radical, which appears in the
reaction mixture due to oxidation of the C5Me4H− anion by
DAD4iPr2Me. Tedious separation of complexes 5 and 6 by frac-
tional crystallization results in decrease of their yields. In all the
attempts to detect in the reaction mixtures the [Cp#]2 dimers, the
expected products of transformation of the related radicals,
failed. However, the GC and GC-MS methods give evidence for
the presence of Cp#H. The formation of Cp#H obviously results
from the hydrogen abstraction by cyclopentadienyl radicals.
The reaction solvent seems to be the most plausible source of
hydrogen.
Yellowish green complexes 3, 4, and 5 are highly air- and
moisture-sensitive, soluble in toluene, and less soluble in hexane.
Another goal of the present work was to expand the family of
Yb(III) complexes coordinated by dianionic DAD ligands
prospective objects for investigation of thermally induced redox
isomerism. The idea was to combine in the Yb(III) coordination
sphere DAD2− ligands with electron-withdrawing (compared
to electron-donating Cp#) groups (N(SiMe3)2 and OtBu).
Although this task turned out rather difficult to realize, we
succeeded to develop a synthetic approach which allowed for
the synthesis of complexes RYbIII(DAD4iPr2Me)(dme) (R =
N(SiMe3)2 (7), OtBu (8)) (Scheme 2). The treatment of YbCl3
Figure 1. Molecular structure of complex 3. Thermal ellipsoids drawn at
the 30% probability level. Carbon atoms of THF molecule and hydrogen
atoms are omitted for clarity.
respectively, the selected bond lengths and angles are compiled
in Table 2, and crystal and structural refinement data are listed in
Table S1 (see the Supporting Information).
The X-ray crystal structure determinations of 3−5 revealed
that these complexes have structures similar to those of pre-
viously published for 1 and 2. The coordination environment of
the Yb(III) ion in complexes 3−5 is set up by an η5-coordinated
Cp# ligand, 2σ:η2-coordinated dianion of diazabutadiene, and
one THF molecule (Figures1−3).
t
with equimolar amounts of (Me3Si)2NNa or BuOK in THF
(60 °C, 72 h) and subsequent addition of the solution of
Na2(THF)x(DAD4iPr2Me) in THF (1:1 molar ratio) afforded
complexes 7 and 8 after extraction of the reaction products with
toluene and recrystallization from DME/hexane mixtures in 44
and 58% yields, respectively. When(Me3Si)2NLi(Et2O) was used
instead of (Me3Si)2NNa, the reaction afforded the ate-complex
{Li(thf)3}{Yb[2,6-iPr2C6H3NC(Me)C(Me)NC6H3iPr2-2,6]2−[N-
(SiMe3)2](μ-Cl)} (9) (42%) (Scheme 2). Complexes 7 (blue
green), 8 (blue green), and 9 (blue green) are highly air- and
moisture-sensitive, soluble in toluene, and less soluble in hexane.
The Yb−C(Cp#) distances in 3-5HT vary in the range of
2.586(2)−2.623(2) (3), 2.585(2)−2.637(2) (4), and 2.551(3)−
2.679(3) Å (5HT). The average Yb−C(Cp#) bond lengths in
complex 3-5HT (2.60, 2.61, and 2.62 Å, respectively) are much
shorter than the corresponding values in the parent Yb(II)
complexes (for comparison, see: Cp*2Yb(py)2, 2.74 Å)12 and
clearly indicate oxidation of ytterbium during the reactions.
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Figure 2. Molecular structure of complex 4. Thermal ellipsoids drawn at
the 30% probability level. Carbon atoms of THF molecule and hydrogen
atoms are omitted for clarity.
These distances are somewhat longer compared to those in
1 and 2 (2.59 Å).7 The Yb−N distances in 3-5HT (2.151(2),
2.151(2) Å in 3; 2.132(1), 2.152(1) Å in 4; 2.139(2), 2.151(2) Å
in 5HT) are similar to those measured for 1 and 2 and are
noticeably shorter compared to the coordination bonds in
the related eight-coordinate Yb(III) complexes (2.193(1)−
2.286(7) Å).13 The lengths of N−C (1.418(3), 1.408(3) Å in 3;
1.418(2), 1.429(2) Å in 4; 1.424(4), 1.433(4) Å in 5HT) and
C−C (1.356(4) Å in 3; 1.365(2) Å in 4; 1.368(4) Å in 5HT)
bonds within the planar N-CC-N fragments are consistent with
the dianionic character of the diazabutadiene ligands.14 The CC
bond of a doubly reduced ene-diamido N-CC-N moiety also
contributes in metal−ligand bonding: η2-coordination of the
ene-diamido moiety to the Yb(III) ion results in the short Yb−C
contacts (2.622(3), 2.623(2) Å in 3; 2.710(2), 2.717(2) Å in 4;
2.813(3), 2.824(3) Å in 5HT).
Complexes 2 and 5 coordinated by 2,6-iPr2C6H3NC(R)C-
i
(R)NC6H3 Pr2-2,6 (R = H, Me) ligands turned out to be sensitive
to the substituent by the imino carbons: the comparison of their
geometric parameters indicates some elongation of Yb−Cp#
bonds (Yb−Caver: 2.59 (2), 2.62 Å (5HT)), while the Yb−N
distances remain unchanged. The Yb−CNCCN bonds undergo the
most noticeable elongation when replacing H by Me (2.629(5),
2.622(4) Å in 2 vs 2.813(3), 2.824(3) Å in 5HT). At the same
time, the dihedral YbNN−NCCN angle increases from 132.4°
(2) to 145.4° (5HT).
To explore the possibility of a structural phase transition as a
consequence of a redox isomerism, the low temperature struc-
ture of complex 5 has been studied at 9 K by single-crystal
X-ray diffraction (5LT). Upon cooling, a subtle disorder−
order transition occurs in the case of complex 5LT, which is
accompanied by a space group change from Pbca to P21/c at 9 K.
This structural transition mainly affects the orientation of the
coordinated THF molecules and the Cp* ligands and finally
emerges in a space group change and the observation of two
crystallographically independent molecules of complex 5LT
(Figure 3b,c).
Figure 3. (a) Molecular structure of complex 5HT. Thermal ellipsoids
drawn at the 30% probability level. Carbon atoms of THF molecule and
hydrogen atoms are omitted for clarity. (b, c) Molecular structures of
complex 5LT at 9 K showing the orientation of the THF ligands in both
crystallographically independent molecules of the low-temperature
modification. Thermal ellipsoids drawn at the 30% probability level.
Hydrogen atoms are omitted for clarity.
We note that the structural phase transition is accompanied by
subtle changes of the coordination behavior of the DAD4iPr2Me
ligands in 5. These minute structural changes during the phase
transition reflect some systematic trends which might hint for an
onset of a temperature-induced redox isomerism. Indeed, the low
temperature phase of 5LT differs from its high temperature
analogue 5HT by (i) a shortening of the N−C bonds of the
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Figure 6. Molecular structure of complex 9. Thermal ellipsoids drawn at
the 30% probability level. Carbon atoms of THF and ether molecules
and hydrogen atoms are omitted for clarity.
Figure 4. Molecular structure of complex 7. Thermal ellipsoids drawn
at the 30% probability level. Carbon atoms of DME molecules and
hydrogen atoms are omitted for clarity.
and 5HT (1.368(4) Å). This is caused by the cancellation of two
reverse effects: (i) shortening of the C−CNCCN bond distances
due to reduced interactions between Yb and the ene-diamido
moiety in 5LT and (ii) elongation of the C−C bond distances
in 5LT due to the diminished double bond character in the
partially radical-anionic form of the DAD ligand relative to 5HT
(dianionic form of the DAD ligand). Numerous trials to detect
by X-ray crystallography a structural phase transition for complex
1 whose variable-temperature magnetic properties clearly
indicated the existence of redox isomerism7 have been done.
Unfortunately, all the trials failed because of the crystal
destruction during cooling to 9 K.
The monocrystalline samples of complexes 7, 8 suitable for
X-ray analysis were obtained by recrystallization from DME−
hexane mixtures, while complex 9 was crystallized from a THF−
hexane mixture at ambient temperature. The structures of
complexes 7−9 were also established by the X-ray diffraction
studies. The molecular structures of 7−9 are depicted in Figures 4−6,
selected bond lengths and angles are given in Table 2, and
crystal and structural refinement data are listed in Table S1. In
neutral complexes 7 and 8, the ytterbium ions are coordinated by
two nitrogens and two carbons of the DAD4iPr2Me ligand, two
oxygens of the DME molecule, and a covalently bonded R-group
(R = N(SiMe3)2 (7), OtBu (8)). In ate-complex 9, the co-
ordination sphere of ytterbium is composed by two nitrogen and
two carbon atoms of the DAD4iPr2Me ligand and N(SiMe3)2
amido nitrogen, but instead of a bidentate DME molecule, there
is a chloro ligand μ-bridging the Yb and Li ions. The X-ray analysis
revealed that, similarly to 3−5, complexes 7−9 feature 2σ:η2-
coordination of DAD4iPr2Me ligands; however, the Yb−CNCCN
distances detected in complex 7 are essentially longer compared to
those of other related complexes (Yb−N bond lengths: 2.169(1),
2.201(1) Å in 7; 2.152(2), 2.175(2) Å in 8; 2.139(2), 2.145(2) Å
in 9. Yb−C distances: 2.961(2), 2.975(2) Å in 7; 2.642(3),
2.644(3) Å in 8; 2.620(2), 2.624(2) Å in 9). The geometric
parameters of DAD4iPr2Me ligands (C−N bond lengths: 1.432(2),
1.426(2) Å in 7; 1.424(4), 1.433(4) Å in 8; 1.415(3), 1.438(3) Å
in 9. CC bond lengths: 1.356(2) Å in 7; 1.370(4) Å in 8,
1.383(4) Å in 9) are indicative of their dianionic character.
Figure 5. Molecular structure of complex 8. Thermal ellipsoids drawn at
the 30% probability level. Carbon atoms of DME molecule and
hydrogen atoms are omitted for clarity.
DAD4iPr2Me ligand (N−C = 1.424(4)−1.433(4) Å for 5HT and
N−C = 1.405(8)−1.419(8) Å for 5LT) and (ii) an increase of the
Yb−CNCCN bonds (Yb−C = 2.813(3)−2.824(3) Å for 5HT and
Yb−C = 2.825(5)−2.881(6) Å for 5LT). This observation
reveals a slightly increased NC double bond character of the
DAD ligands in 5LT vs 5HT and might thus suggest an onset of
a redox isomerism which renders 5 from its dianionic form
(5HT) into the radical-anionic form (5LT). This process is also
supported by the second structural trend (increase of the
Yb−CNCCN distances in 5LT), which reflects the reduced
Yb ← σ(CC) donor and Yb → π*(CC) back-donation
capabilities of the ene-diamido moiety in 5LT as a consequence
of the starting redox isomerization. Unfortunately, this trend
cannot be verified by inspection of the C−CNCCN distances,
which remain rather invariant in 5LT (1.364(8)−1.372(8) Å)
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Table 2. Selected Bond Lengths (Å) and Angles (deg) for Complexes 1−9
Yb−C(Cp)
Yb−N
Yb−C
C−C
complex
average
Yb−CpCenter or Yb−E (E = N,O)
(NCCN)
(NCCN)
N−C
(NCCN)
dihedral angle NYbN−NCCN
1
2.59
2.59
2.60
2.61
2.62
2.61
2.29
2.136(3)
2.145(3)
2.141(3)
2.148(3)
2.151(2)
2.151(2)
2.132(1)
2.152(1)
2.139(2)
2.151(2)
2.150(6)
2.150(5)
2.169(1)
2.201(1)
2.152(2)
2.175(2)
2.139(2)
2.145(2)
2.628(5)
2.618(4)
2.629(5)
2.622(4)
2.622(3)
2.623(2)
2.710(2)
2.717(2)
2.813(3)
2.824(3)
2.881(6)
2.866(5)
2.961(2)
2.975(2)
2.642(3)
2.644(3)
2.620(2)
2.624(2)
1.409(5)
1.387(6)
1.411(6)
1.406(5)
1.418(3)
1.408(3)
1.418(2)
1.429(2)
1.424(4)
1.433(4)
1.417(8)
1.415(8)
1.432(2)
1.426(2)
1.431(4)
1.426(4)
1.415(3)
1.438(3)
1.348(7)
1.360(6)
1.356(4)
1.365(2)
1.368(4)
1.372(8)
1.356(2)
1.370(4)
1.383(4)
142.2
2
2.29
134.4
132.4
137.6
145.4
150.4
159.5
128.3
126.2
3
2.31
4
2.32
5HT
5LT
7
2.32
2.32
2.227(1)
2.037(2)
2.220(2)
8
9
The Yb−N, Yb−O, and Yb−Cl bond lengths in complexes
7−9 are in line with the trivalent oxidation state of ytterbium
atoms in these compounds.15 It is noteworthy that, in the series
of the related compounds Cp#YbIII(DAD)2−(thf) (3−5), the
values of the dihedral angle NYbN−NCCN vary in the range of
131.2−145.4° depending on the steric demand of both DAD and
Cp* ligands. However, for complexes 7−9, the range of variation
of this angle is significantly larger: thus, for six-coordinate com-
plex 9, it is 126.2°, while for seven-coordinate 7 containing the
same N(SiMe3)2 group, this value increases up to 159.5°. The
geometry changes appear also in lengthening of Yb−CNCCN
distances from 2.620(2) and 2.624(2) Å in 9 to 2.961(2) and
2.975(2) Å in 7, reflecting weakening of η2-interaction between
Yb and the CC fragment.
The UV−visible spectra of complexes 3−5 and 7−9 in THF
similarly to K+ [2,6-R″2C6H3NC(R′)C(R′)NC6H3R″2-2,6]2−
2
i
(R′ = H, Me; R″ = Me, Pr) show strong absorptions in the
region λ = 280−290 nm characteristic for dianionic diazabuta-
diene ligands (see Figures S10−13, Supporting Information).
The 1H NMR spectra of complexes 3−5 and 7−9 (C6D6, 20 °C)
exhibit the signals in the range from −130 to 130 ppm and are
indicative of a trivalent oxidation state of ytterbium in these
compounds (see Figures S10−13). Thereby, the spectroscopic
data of complexes 3−5 and 7−9 are consistent with the Yb(III)
derivatives coordinated by dianionic diazabutadiene ligands.
Magnetic Measurements. Magnetic measurements of crys-
talline samples 3−5 and 7−9 have been carried out by using an
MPMS-XL SQUID magnetometer in the temperature range of
1.8−300 K with an applied magnetic field of 1000 Oe. The tem-
perature dependences of the χT product (or magnetic moment)
for all of these samples present a relatively simlar shape and
characteristic of the presence of paramagnetic Yb(III) and
diamagnetic ligands (Figure 7a,b).
Figure 7. (a) χT vs T curves performed at an applied magnetic field of
□
■
●
○
1000 Oe for 3 (▶), 4 ( ), 5 ( ), 7 ( ), 8 ( ), 9 (Δ). (b) Magnetic
moment vs T curves performed at an applied magnetic field of 1000 Oe
□
■
●
○
for 3 (▶), 4 ( ), 5 ( ), 7 ( ), 8 ( ), 9 (Δ).
observed χT values for all compounds are in the range 2.38−
2.56 cm3 K mol−1 or 4.36−4.52 μB (3: 2.48 cm3 K mol−1
(4.45 μB); 4: 2.51 cm3 K mol−1 (4.48 μB); 5: 2.49 cm3 K mol−1
(4.46 μB); 7: 2.38 cm3 K mol−1 (4.36 μB); 8: 2.56 cm3 K mol−1
(4.52 μB)); 9: 2.49 cm3 K mol−1 (4.47 μB)), which is close to the
expected value for paramagnetic Yb(III). Therefore, this
confirms that the ligand is diamagnetic.
As the temperature decreases, χT for all curves decreases, and
at 1.8 K, it reaches the values comprised in the range of 0.93−
1.44 cm3 K mol−1 (2.72−3.39 μB). Such a decrease can be
explained by the depopulation of the Stark levels of Yb(III)
2
Indeed, the Yb(III) ion has a F7/2 ground state with a first-
order orbital momentum.16 In the low symmetry site, as it may be
expected for all described compounds, this state is split into Stark
components by the crystal field, each of them being a Kramers
doublet. At room temperature, the excited states of the 2F7/2 of
Yb(III) ion are populated and the theoretical Yb(III) free-ion
value of χT is equal to 2.49 cm3 K mol−1(4.46 μB). At 300 K, the
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ground state: at room temperature, the excited states of Yb(III)
ion are populated, but as the temperature decreases, there is the
progressive depopulation of the excited Kramers doublets, and at
low temperature, only the ground Kramers doublet is populated.
The lower χT value observed for sample 9 may be explained by
slightly different symmetry of this complex, which induces the
difference in the thermal depopulation phenomenon.
EXPERIMENTAL SECTION
■
General Considerations and Materials Characterization. All
experiments were performed in evacuated tubes, using standard
Schlenk-tube and glovebox techniques, with rigorous exclusion of traces
of moisture and air. After drying over KOH, THF was purified by
distillation from sodium/benzophenone ketyl and hexane and toluene
by distillation from sodium/triglyme benzophenone ketyl prior to use.
(C5Me5)2Yb(thf)2,17 (C5Me4H)2Yb(thf)2,18 anhydrous YbCl3 and
19
Formerly, we reported on unusual magnetic behavior of
1 indicative of the existence of thermally induced redox
isomerism for this compound. Thus, the value of magnetic
moment at T = 300 K is 4.41 μB, which is close to the calculated
2,6-R″2C6H3NC(R′)-C(R′)NC6H3R″2-2,6 (R′ = H, Me; R″ = Me,
iPr)20 and (Me3Si)2NLi(Et2O)21 were prepared according to literature
procedures. tBuOK and (Me3Si)2NNa were purchased from Acros and
were used without further purification. All other commercially available
chemicals were used after the appropriate purification. IR spectra were
recorded as Nujol mulls on a Bruker-Vertex 70 spectrophotometer. A
“Polaris Q GC/MS” spectrometer was used for GS/MS analysis. NMR
spectra were recorded with Bruker Avance DRX-400 and Bruker DRX-
200 spectrometers in C6D6 at 20 °C, unless otherwise stated. Chemical
2
free Yb(III) ion value for a F7/2 multiplet and corresponds to
the [Cp*YbIII(DAD)2−(thf)] form. The value of the magnetic
moment of 1 at T = 2 K of 2.03 μB is too low for Yb(III) and is
more compatible with the magnetic moments observed for
organic radical anions with spin S = 1/2 (1.73 μB) consistent with
[Cp*YbII(DAD)−(thf)] isomer. Surprisingly the related Yb(III)
complexes 3−5, 7−9 coordinated by dianionic diazabutadiene
ligands and having the similar structures do not feature the
similar magnetic behavior in the broad temperature interval: with
temperature decrease, their magnetic moments do not drop to
such a low value and remain within the range characteristic for
Yb(III) species and behave as isolated paramagnets.
1
shifts for H and 13C NMR spectra were referenced internally to the
residual solvent resonances and are reported relative to TMS. The C, H,
N elemental analysis was carried out in the microanalytical laboratory of
IOMC. Lanthanide metal analyses were carried out by complexometric
titration.22
Synthesis of (C5Me4H)Yb(4Me2HDAD)(thf) (3). A solution of
4Me2HDAD (0.30 g,1.14 mmol) in thf (5 mL) was added to a solution of
(C5Me4H)2Yb(thf)2 (0.64 g, 1.14 mmol) in thf (10 mL). The reaction
mixture was stirred for 0.5 h at 40 °C. After removal of thf in vacuum,
toluene (15 mL) was added and the solution was heated at 60 °C for 5 h.
The volatiles were evaporated in vacuum (80 °C) and collected.
Recrystallization of the solid residue from hexane (−5 °C) gave 3 as
yellowish green crystals (0.36 g, 49%). The crystals were washed with
cold hexane and dried in vacuum at room temperature for 15 min. In the
condensate, 0.10 g (78%) of C5Me4H2 was detected by GC. 1H NMR
(400 MHz, C6D6, 293 K): δ −48.58 (s, 2H, NCHCHN), −21.83 (s, 2H,
CH Ar), −12.09 (s, 6H, (CH3)2Ar), −8.34 (s, 2H, CH Ar), −4.93 (s,
6H, C5(CH3)4H), 1.28 (s, 1H, C5(CH3)4H), 4.39 (s, 6H, C5(CH3)4H),
6.93 (s, 2H, CH Ar), 34.84 (s, 4H, C4H8O), 40.62 (s, 6H, (CH3)2Ar),
93.13 (s, 4H, C4H8O). IR (Nujol, KBr, cm−1): 1589 (m), 1273 (s), 1197
(s), 1123(m), 1093(s), 1011(m), 858(m), 763 (m), 577 (m). Anal.
Calcd for C31H41N2OYb: C, 59.04; H, 6.54; N, 4.44; Yb, 27.43. Found:
C, 58.52; H, 6.11; N, 4.02; Yb, 27.77.
SUMMARY AND CONCLUSIONS
■
The electrochemical measurements performed for a series of
bulky DADs demonstrated that the alkyl groups in the aromatic
substituents by the nitrogens have negligible influence on the
reduction potential values, while the introduction of methyl
groups at the imine carbon atoms substantially modifies these
values. Thus, DAD4Me2H and DAD4iPr2H are more readily reduced
than their Me-substituted analogues for approximately 400 mV.
It was found that the reactions of Cp# Yb(THF)2 (Cp# = C5Me5,
2
C5Me4H) with diazabutadienes 2,6-R″2C6H3NC(R′)-
C(R′)NC6H3R″2-2,6 (R′ = H, Me; R″ = Me, iPr) afford com-
plexes Cp#YbIII(DAD)2−(thf) regardless of the different steric
bulk of the substituents by the nitrogens (2,6-iPr2C6H3− and
2,6-Me2C6H3). The variation of redox properties of the DAD
ligands due to the change of the substituents by the imino
carbons (Me vs H) also does not affect the reactions outcome.
The X-ray studies of complexes 3−5 and 7−9 revealed that they
feature the 2σ:η2-type of coordination of dianionic DAD ligands.
The Me-substituents by the imino carbons of DADs lead to some
elongation of Yb−Cp# bonds. The Yb−CNCCN bonds and the
dihedral YbNN−NCCN angles were found to be the most
sensitive to replacing H by Me. A synthetic approach to the
amido and alkoxo Yb(III) complexes supported by the dianionic
Synthesis of (C5Me5)Yb(4Me2MeDAD)(thf) (4). A solution
of 4Me2MeDAD (0.40 g, 1.37 mmol) in thf (5 mL) was added to a
solution of (C5Me5)2Yb(THF)2 (0.80 g, 1.36 mmol) in thf (20 mL).
The reaction mixture was stirred for 0.5 h at 40 °C. After removal of thf
in vacuum, toluene (15 mL) was added and the solution was heated at
60 °C for 5 h. The volatiles were evaporated in vacuum (80 °C) and
collected. Recrystallization of the solid residue from hexane (−5 °C)
gave 4 as yellowish green crystals (0.52 g, 57%). The crystals were
washed with cold hexane and dried in vacuum at room temperature for
15 min. In the condensate, 0.10 g (52%) of C5Me5H was detected by
1
GC. H NMR (400 MHz, C6D6, 293 K): −59.87 (s, 6H, NC(CH3)-
i
C(CH3)N), −16.43 (s, 2H, CH Ar), −11.47 (s, 6H, (CH3)2Ar), −5.26
(s, 2H, CH Ar), −4.43 (s, 6H, (CH3)2Ar), −0.43 (s, 2H, CH Ar), 6.10 (s,
15H, C5(CH3)5), 7.03 (s, 4H, C4H8O), 57.18 (s, 4H, C4H8O). IR
(Nujol, KBr, cm−1): 1588 (s), 1269 (s), 1199 (m), 1148 (m), 1096(m),
1008 (m), 857 (m), 805 (m), 761 (m), 577 (m). Anal. Calcd for
C34H47N2OYb: C, 60.70; H, 7.03; N, 4.16; Yb, 25.72. Found: C, 60.24;
H, 6.79; N, 4.00; Yb, 25.99.
[2,6-iPr2C6H3NC(Me)C(Me)NC6H3 Pr2-2,6]2− ligand was de-
veloped. For complex 5 at 9 K, the structural phase transition
accompanied by subtle changes of the coordination behavior of
the DAD4iPr2Me ligand was detected. These structural changes
during the phase transition reflect some systematic trends
which might hint for an onset of a temperature-induced redox
isomerism. Thermally induced redox isomeric transformations in
Yb(III) complexes coordinated by the dianionic diazabutadiene
ligand were demonstrated to be very subtle processes highly
sensitive to the changes in steric and redox properties of the DAD
ligand and those of the redox innocent ligand coordinated to the
Yb(III) center.
Synthesis of (C5Me4H)Yb(4iPr2MeDAD)(thf) (5) and
(C5Me4H)3Yb (6). A solution of 4iPr2MeDAD (0.36 g, 0.89 mmol) in
THF (5 mL) was added to a solution of (C5Me4H)2Yb(thf)2 (0.54 g,
0.96 mmol) in thf (10 mL). The reaction mixture was stirred for 0.5 h at
40 °C. After removal of thf in vacuum, toluene (15 mL) was added and
the solution was heated at 60 °C for 4 h. The volatiles were evaporated in
vacuum (80 °C) and collected. Recrystallization of the solid residue
from hexane (−5 °C) gave the mixture of yellow and dark maroon
crystals. Fractional crystallization afforded yellowish green crystals of
5 (0.26 g, 35%) and dark maroon crystals (0.05 g, 10%) of 6. In the
condensate, 0.07 g (64%) of C5Me4H2 was detected by GC. 5: 1H NMR
The further studies on the synthesis of Yb(III) and Yb(II)
complexes containing various N,N redox active ligands and
investigation of their structural and magnetic properties are
pursued in our groups.
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(400 MHz, C6D6, 293 K): −108.23 (s, 2H, CH(CH3)2); −43.6 (s, 6H,
NC(CH3)), −18.44 (s, 2H, CH Ar), −14.00 (s, 6H, CH(CH3)2), −8.53
(s, 2H, CH(CH3)2), −8.09 (s, 6H, CH(CH3)2), −6.94 (s, 2H, CH Ar),
−2.27 (s, 6H, C5(CH3)4H), −0.63 (s, 2H, CH Ar), 1.36 (s, 6H,
C5(CH3)4H), 7.02 (s, 1H, C5(CH3)4H), 20.43 (s, 6H, CH(CH3)2),
36.10 (s, 6H, CH(CH3)2), 58.63 (s, 4H, C4H8O), 125.48 (s, 4H,
C4H8O). IR (Nujol, KBr, cm−1): 1591 (s), 1267 (s), 1183 (m), 1122 (s),
1043 (m), 937 (m), 765 (m), 523 (m). Anal. Calcd for C41H61N2OYb:
C, 63.82; H, 7.96; N 3.63; Yb, 22.44. Found: C, 63.41; H, 7.80; N, 3.23;
Yb 22.59. 6: IR (Nujol, KBr, cm−1) 1326 (m), 1149 (s), 1019 (m), 969
(m), 608 (m). Anal. Calcd for C29H37Yb: C, 64.85; H, 6.90; Yb, 27.43.
Found: C, 64.49; H, 7.15; Yb, 27.59.
auxiliary electrode, and a saturated silver chloride electrode was used as
the reference electrode. The potential of the Fc/Fc+ redox couple in our
experimental conditions is +0.53 V.
Crystal Structure Determination of 3−9. X-ray diffraction
intensity data for compounds 3−9 were collected on Bruker Smart
APEX-II (3) and Bruker Smart APEX (4, 5HT, 6−9) diffractometers
with graphite monochromated Mo−Kα radiation (λ = 0.71073 Å) using
ω scans. The structures were solved by direct methods and were refined
on F2 using the SHELXTL package.23 All non-hydrogen atoms were
found from Fourier syntheses of electron density and were refined
anisotropically. All hydrogen atoms were placed in calculated positions
and were refined in the riding model with Uiso(H) = 1.2 Ueq (Uiso(H) =
1.5 Ueq for the hydrogen atoms in CH3 groups) of their parent atoms.
SADABS24 was used to perform area-detector scaling and absorption
corrections.
A crystal of 5LT was glued under an inert gas atmosphere on a
MiTeGenMicroMount, mounted on a Huber 4-circle diffractometer
equipped with a 4K-Displex closed-cycle helium cryostat and was cooled
to 9(1) K. Preliminary examination and final data collection were carried
out with graphite-monochromated Mo Kα radiation (λ = 0.71073 Å)
generated from a Bruker FR 591 rotating anode running at 50 kV and
60 mA. Intensity data were collected employing a MAR345 IP Detector
and 1° φ-scans with a detector-to-sample distance of 160 mm.
The systematic pseudo-merohedrically twining of the crystals of
5LT afforded an empirical absorption correction using the program
TWINABS25 (Tmin = 0.3195, Tmax = 0.4305) for a total of 58 914
reflections and 15 169 unique reflections (Rint = 0.0214). For the
refinements, a HKLF5 formatted data file with 29 621 reflections was
used. Subsequent full-matrix least-squares refinements against F2 were
carried out using the SHELXL97 program.26 All non-hydrogen atoms
were found from Fourier syntheses of electron density and were refined
anisotropically. All hydrogen atoms were placed in geometrically idealized
positions and treated as riding with Uiso(H) = 1.2 Ueq (Uiso(H) = 1.5 Ueq
for the hydrogen atoms in CH3 groups) of their parent atoms. Due to
strong correlation between the parameters of the two crystallographically
independent molecules in the unit cell, it was necessary to restrain the
displacement parameters of seven atoms to be isotropic. A batch scaling
factor was introduced to describe the twin volume fractions, resulting in a
0.6813/0.3187 ratio for the volume of domains 1 and 2, respectively. Low
values of completeness (90.8% for θ = 26° and 85.6% for θ = 25°) are
explained by poor quality of the crystal specimen.
Crystal data and details of data collection and structure refinement
for the different compounds are given in Table S1 (Supporting
Information). Main crystallographic data (excluding structure factors)
are available as Supporting Information, as CIF files. CCDC-1024539
(3), 1024540 (4), 1024541 (5LT), 1024542 (5HT), 1031761 (6),
1024543 (7), 1024544 (8), and 1024545 (9) contain the supplementary
crystallographic data for this paper; crystallographic data for 1 and 2
were previously published7 as CCDC-607546 (1) and 607547 (2).
These data can be obtained free of charge via ccdc.cam.ac.uk/community/
requestastructure.
Magnetic Measurements. Magnetic susceptibility data were
collected with a Quantum Design MPMS-XL SQUID magnetometer
working between 1.8 and 350.0 K with the magnetic field up to 7 T.
The samples were prepared in a glow box and kept in an anaerobic
atmosphere. The magnetic data were corrected for the sample holder,
and the diamagnetic contributions were calculated from the Pascal’s
constants.27
Synthesis of (Me3Si)2Yb(DAD4iPr2Me)(dme) (7). A solution of
DAD4iPr2Me (0.80 g, 1.98 mmol) in thf (20 mL) was added to Na
shavings (0.09 g, 3.96 mmol), and the reaction mixture was stirred at
room temperature for 3 days until complete dissolution of the metal.
The resulting dark-red solution was filtered and added slowly to a
solution of (1.98 mmol) ((Me3Si)2N)YbCl2(THF)n, which was
obtained in situ from YbCl3 (0.55 g, 1.98 mmol) and NaN(SiMe3)2
(0.36 g, 1.98 mmol) in thf (15 mL) (60 °C, 72 h). The reaction mixture
was stirred at room temperature for 2 days (20 °C). The resulting
brownish-green solution was filtered, the volatiles were evaporated in
vacuum, the resulting solid residue was extracted with toluene (25 mL),
and the extracts were filtered. Toluene was then evaporated in vacuum.
Recrystallization of the solid residue from a DME−hexane (1:3) mixture
(20 °C) afforded 7 as blue green crystals (0.72 g, 44%). IR (Nujol,
KBr, cm−1): 1583 (s), 1252 (s), 1202 (s), 1120 (m), 1091 (m), 1043
(m), 826 (m), 763 (m), 670 (m). Anal. Calcd for C38H68N3O2Si2Yb: C,
55.06; H, 8.21; N, 5.07; Yb, 20.89; found: C, 55.83; H, 8.01; N, 5.99; Yb,
21.07.
Synthesis of (tBuO)Yb(DAD4iPr2Me)(dme) (8). A solution of
DAD4iPr2Me (0.88 g, 2.18 mmol) in THF (20 mL) was added to an
excess of Na shavings (0.10 g, 4.36 mmol), and the reaction mixture was
stirred at room temperature for 3 days until complete dissolution of the
metal. The resulting dark-red solution was filtered and added slowly to
a solution of (2.18 mmol) (tBuO)YbCl2(THF)n, which was obtained
in situ from YbCl3 (0.61 g, 2.18 mmol) and tBuOK (0.24 g, 2.18 mmol)
in THF (15 mL) (60 °C, 72 h). The reaction mixture was stirred at room
temperature for 2 days (20 °C). The resulting brownish-green solution
was filtered, the solvent was evaporated in vacuum, the resulting solid
residue was extracted with toluene (25 mL), and the extracts were
filtered. Toluene was then evaporated in vacuum. Recrystallization of
the solid residue from a DME−hexane (1:4) mixture (20 °C) afforded 8
as blue green crystals (0.93 g, 58%). IR (Nujol, KBr, cm−1):1589 (s),
1269 (s), 1210 (s), 1197 (m), 1148 (m), 1088 (s), 1029 (m), 825 (m),
793 (m), 752 (m), 696 (m), 553 (m). Anal. Calcd for C36H59N2O3Yb:
C, 58.31; H, 7.96; N, 3.78; Yb, 23.36; found: C, 57.95; H, 8.09; N, 3.99;
Yb 23.83.
Synthesis of {Li(thf)3}{Yb[4iPr2MeDAD][N(SiMe3)2](μ-Cl)} (9). A
solution of 4iPr2MeDAD (0.57 g, 1.41 mmol) in THF (20 mL) was added
to Li shavings (0.02 g, 2.82 mmol), and the reaction mixture was stirred
at room temperature for 3 days until complete dissolution of the metal.
The resulting dark-red solution was filtered and added slowly to a
solution of (1.41 mmol) [(Me3Si)2N]YbCl2(THF)n, which was obtained
in situ from YbCl3 (0.39 g, 1.41 mmol) and LiN(SiMe3)2(Et2O) (0.34 g,
1.41 mmol) in THF (15 mL) (60 °C, 72 h). The reaction mixture was
stirred at room temperature for 2 days. The solvent was evaporated in
vacuum, and the resulting solid residue was extracted with toluene
(25 mL). Recrystallization from a THF−hexane mixture afforded 9 as
blue green crystals (0.59 g, 42%). IR (Nujol, KBr, cm−1):1586 (s),
1249(s), 1115(s), 1038(s), 937 (m), 887 (m), 773 (m), 728 (m), 561
(s), 527 (s). Anal. Calcd for C46H83ClLiN3O3Si2Yb: C, 55.32; H, 8.32;
N, 4.21; Yb, 17.34; found: C, 55.00; H, 8.13; N, 3.99; Yb 18.07.
Electrochemical Studies. Electrochemical studies were carried out
using an IPC-Win digital potentiostat/galvanostat connected to a PC.
Voltammograms were recorded by cyclic voltammetry (CV) at a
stationary Pt disk electrode (d = 3.2 mm) at different potential scan rates
in DMF using a 0.05 M n-Bu4NBF4 solution as the supporting elec-
trolyte at 20 °C in a 10 mL electrochemical cell. Oxygen was removed
from the cell by purging with dry argon. Platinum wire served as the
ASSOCIATED CONTENT
■
S
* Supporting Information
CV curves, molecular structure, table of crystallographic data and
structure refinement details, IR spectra, UV/vis spectra, and 1H
NMR spectra. This material is available free of charge via the
Internet at http://pubs.acs.org.
1184
DOI: 10.1021/om501121s
Organometallics 2015, 34, 1177−1185

Organometallics
Article
(14) For standard C−C and C−N bond lengths, see: Allen, A.;
Konnard, O.; Watson, D. G.; Brammer, L.; Orpen, G.; Taylor, R. J.
Chem. Soc., Perkin Trans. 1987, 1−19.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: trif@iomc.ras.ru. Fax: (+7)8314621497 (A.A.T.).
(15) For comparison, see: (a) Deacon, G. B.; Forsyth, C. M.; Scott, N.
M. Dalton Trans. 2003, 3216−3229. (b) Hou, Z.; Koizumi, T.; Nishiura,
M.; Wakatsuki, Y. Organometallics 2001, 20, 3323−3328. (c) Hao, J.;
Song, H.; Cui, C. Organometallics 2001, 20, 3323−3328.
(16) Carlin, R. L. Magnetochemistry; Springer-Verlag: Berlin, 1986.
(17) Watson, P. L. J. Chem. Soc., Chem. Commun. 1980, 652−653.
(18) Zinnen, H. A.; Pluth, J. J.; Evans, W. J. J. Chem. Soc.,
Chem.Commun. 1980, 810−812.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by the Russian Foundation for Basic
Research grants 13-03-97027 and 14-03-31281 mol_a, by the
grant of The Ministry of Education and Science of the
Russian Federation (the agreement of August 27, 2013 No.
02.B.49.21.0003 between The Ministry of Education and Science
of the Russian Federation and Lobachevsky State University
of Nizhni Novgorod). We thank Synor Ltd. and personally
Dr. A. Tatarnikov for donation of C5Me5H and C5Me4H2.
(19) Taylor, M. D.; Carter, C. P. J. Inorg. Nucl. Chem. 1962, 24, 387−
391.
(20) Svoboda, M.; Dieck, H. T. J. Organomet. Chem. 1980, 191, 321−
327.
(21) Manzer, L. E. Inorg. Chem. 1978, 17, 1552−1558.
(22) Lyle, S. J.; Rahman, M. M. Talanta 1953, 10, 1177−1182.
(23) Sheldrick, G. M. SHELXTL v.6.12: Structure Determination
Software Suite; Bruker AXS: Madison, WI, 2000.
(24) Sheldrick, G. M. SADABS v.2.01: Bruker/Siemens Area Detector
Absorption Correction Program; Bruker AXS: Madison, WI, 1998.
(25) Sheldrick, G. M. TWINABS; Bruker AXS: Madison, WI, 2001.
(26) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112−122.
(27) Boudreaux, E. A.; Mulay, L.; Sons, L. J. W. Theory and Applications
of Molecular Paramagnetism; Wiley: New York, 1976.
REFERENCES
■
(1) van Koten, G.; Vrieze, K. Adv. Organomet. Chem. 1982, 21, 151−
239.
(2) Trifonov, A. A. Eur. J. Inorg. Chem. 2007, 3151−3167.
(3) (a) Moore, J. A.; Cowley, A. H.; Gordon, J. C. Organometallics
2006, 25, 5207−5209. (b) Vasudevan, K.; Cowley, A. H. Chem.
Commun. 2007, 3464−3466.
(4) (a) tom Dieck, H.; Renk, I. W. Chem. Ber. 1971, 104, 110−130.
(b) tom Dieck, H.; Franz, K.-D.; Hoffmann, F. Chem. Ber. 1975, 108,
163−173. (c) Reinhold, J.; Benedix, R.; Birner, P.; Hennig, H. Inorg.
Chim. Acta 1979, 33, 209−213.
(5) (a) Morss, L. R. Chem. Rev. 1976, 76, 827−841. (b) Finke, R. G.;
Keenan, S. R.; Shirardi, D. A.; Watson, P. L. Organometallics 1986, 5,
598−601. (c) Bond, A. M.; Deacon, G. B.; Newnham, R. H.
Organometallics 1986, 5, 2312−2316.
(6) (a) Trifonov, A. A.; Kirillov, E. N.; Bochkarev, M. N.; Schumann,
H.; Muehle, S. Russ. Chem. Bull. 1999, 48, 382−384. (b) Trifonov, A. A.;
Kurskii, Yu. A.; Bochkarev, M. N.; Muehle, S.; Dechert, S.; Schumann,
H. Russ. Chem. Bull. 2003, 52, 601−606. (c) Trifonov, A. A.; Fedorova,
E. A.; Ikorskii, V. N.; Dechert, S.; Schumann, H.; Bochkarev, M. N. Eur. J.
Inorg. Chem. 2005, 2812−2818. (d) Trifonov, A. A.; Fedorova, E. A.;
Fukin, G. K.; Ikorskii, V. N.; Kurskii, Yu. A.; Dechert, S.; Schumann, H.;
Bochkarev, M. N. Russ. Chem. Bull. 2004, 53, 2736−2743. (e) Wang, J.;
Amos, R. I. J.; Frey, A. S. P.; Gardiner, M. G. Organometallics 2005, 24,
2259−2261. (f) Cui, P.; Chen, Y.; Wang, G.; Li, G.; Xia, W.
Organometallics 2008, 27, 4013−4016. (g) Walter, M. D.; Berg, D. J.;
Andersen, R. A. Organometallics 2007, 26, 2296−2307. (h) Booth, C. H.;
Walter, M. D.; Kazhdan, D.; Hu, Y.-J.; Lukens, W. W.; Bauer, E. D.;
Maron, L.; Eisenstein, O.; Andersen, R. A. J. Am. Chem. Soc. 2009, 131,
6480−6491.
(7) Trifonov, A. A.; Borovkov, I. A.; Fedorova, E. A.; Fukin, G. K.;
Larionova, J.; Druzhkov, N. O.; Cherkasov, V. K. Chem.Eur. J. 2007,
13, 4981−4987.
(8) Fedushkin, I. L.; Maslova, O. V.; Morozov, A. G.; Dechert, S.;
Demeshko, S.; Meyer, F. Angew. Chem., Int. Ed. 2012, 51, 10584−10587.
(9) (a) Trifonov, A. A.; Fedorova, E. A.; Fukin, G. K.; Druzhkov, N. O.;
Bochkarev, M. N. Angew. Chem., Int. Ed. 2004, 5045−5048. (b) Trifonov,
A. A.; Fedorova, E. A.; Fukin, G. K.; Baranov, E. V.; Druzhkov, N. O.;
Bochkarev, M. N. Chem.Eur. J. 2006, 12, 2752−2757.
(10) Trifonov, A. A.; Shestakov, B. G.; Lyssenko, K. A.; Larionova, J.;
Fukin, G. K.; Cherkasov, A. V. Organometallics 2011, 30, 4882−4889.
(11) Allan, C. J.; Cooper, B. F. T.; Cowley, H. J.; Rawson, J. M.;
Macdonald, C. L. B. Chem.Eur. J. 2013, 19, 14470−14483.
(12) Tilley, D.; Andersen, R. A.; Spencer, B.; Zalkin, A. Inorg. Chem.
1982, 21, 2647−2649.
(13) (a) Pi, C.; Zhu, Z.; Weng, L.; Chen, Z.; Zhou, X. Chem. Commun.
2007, 2190−2192. (b) Mao, L.; Shen, Q.; Jin, S. Polyhedron 1994, 13,
1023−1025. (c) Wang, Y.; Shen, Q.; Xue, F.; Yu, K. J. Organomet. Chem.
2000, 598, 359−364.
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DOI: 10.1021/om501121s
Organometallics 2015, 34, 1177−1185