Reversible switching of coordination mode of ansa bis(Amidinate) ligand in ytterbium complexes driven by oxidation state of the metal atom

Article abstract of DOI:10.1021/ic402530w

Reaction of bisamidine C₆H₄-1,2-{NC(t-Bu)NH(2,6- Me₂C₆H₃)}₂ (1) and [(Me ₃Si)₂N]₂Yb(THF)₂ (THF = tetrahydrofuran) (toluene; room temperature) in a 1:1 molar ratio afforded a bis(amidinate) Yb^II complex [C₆H₄-1,2-{NC(t-Bu) N(2,6-Me₂C₆H₃)}₂]Yb(THF) (2) in 65% yield. Complex 2 features unusual κ¹amide, η⁶- arene coordination of both amidinate fragments to the ytterbium ion, resulting in the formation of a bent bis(arene) structure. Oxidation of 2 by Ph ₃SnCl (1:1 molar ratio) or (PhCH₂S)₂ (1:0.5) leads to the Yb^III species [C₆H₄-1,2-{NC(t-Bu) N(2,6-Me₂C₆H₃)}₂]YbCl(1,2- dimethoxyethane) (3) and {[C₆H₄-1,2-{NC(t-Bu)N(2,6-Me ₂C₆H₃)}₂]Yb(μ-SCH ₂Ph)}₂ (4), performing classic κ²N,N′-chelating coordination mode of ansa bis(amidinate) ligand. By the reduction of 3 with equimolar amount of sodium naphthalide [C₁₀H₈^?-][Na⁺] in THF, complex 2 can be recovered and restored to a bent bis(arene) structure. Complex 3 was also synthesized by the salt metathesis reaction of equimolar amounts of YbCl₃ and the dilithium derivative of 1 in THF.

Full text of DOI:10.1021/ic402530w

Article
pubs.acs.org/IC
Reversible Switching of Coordination Mode of ansa bis(Amidinate)
Ligand in Ytterbium Complexes Driven by Oxidation State of the
Metal Atom
Aleksei O. Tolpygin, Anton V. Cherkasov, Georgii K. Fukin, and Alexander A. Trifonov*
G. A. Razuvaev Institute of Organometallic Chemistry of Russian Academy of Sciences, Tropinina 49, GSP-445, 603950 Nizhny
Novgorod, Russia
*
S Supporting Information
ABSTRACT: Reaction of bisamidine C H -1,2-{NC(t-Bu)-
6
4
NH(2,6-Me C H )} (1) and [(Me Si) N] Yb(THF) (THF
2
6
3
2
3
2
2
2
=
tetrahydrofuran) (toluene; room temperature) in a 1:1
II
molar ratio afforded a bis(amidinate) Yb complex [C H -1,2-
6
4
{
NC(t-Bu)N(2,6-Me C H )} ]Yb(THF) (2) in 65% yield.
2 6 3 2
1
6
Complex 2 features unusual κ amide, η -arene coordination of
both amidinate fragments to the ytterbium ion, resulting in the
formation of a bent bis(arene) structure. Oxidation of 2 by
Ph SnCl (1:1 molar ratio) or (PhCH S) (1:0.5) leads to the
3
2
2
III
Yb species [C H -1,2-{NC(t-Bu)N(2,6-Me C H )} ]YbCl-
6
4
2
6
3
2
2
(
1,2-dimethoxyethane) (3) and {[C H -1,2-{NC(t-Bu)N(2,6-Me C H )} ]Yb(μ-SCH Ph)} (4), performing “classic” κ N,N′-
6
4
2
6
3
2
2
2
chelating coordination mode of ansa bis(amidinate) ligand. By the reduction of 3 with equimolar amount of sodium naphthalide
C H ][Na ] in THF, complex 2 can be recovered and restored to a bent bis(arene) structure. Complex 3 was also
•−
+
[
10 8
synthesized by the salt metathesis reaction of equimolar amounts of YbCl and the dilithium derivative of 1 in THF.
3
III
INTRODUCTION
divalent ytterbium species, while in the Yb complexes the
■
2
5
same ligand adopts κ N,N′-chelating coordination mode. To
get deeper insight into the factors determining the realization of
κ N, η -arene or κ N,N′-coordination type, a complex of
divalent ytterbium coordinated by ansa bis(amidinate) ligand
was synthesized, and its redox chemistry was investigated.
Organic derivatives of lanthanides containing neutral π-bonded
arene ligands are of considerable interest as promising objects
for investigation of the nature of f-metal−ligand bonding. By
virtue of the electropositivity of lanthanides, the metal−ligand
1
6
2
1
2
bonding in their organic derivatives is assumed to have
predominantly ionic character, and ligands capable of forming3
stable anions were traditionally used in this field of chemistry.
On the other hand an insignificant contribution of the covalent
component to lanthanide−ligand interactions removes re-
strictions associated with the compatibility of the orbitals in
symmetry, and this can give rise to novel types of compounds
whose reactivity differs from that of d-element derivatives.
Diversity of types of metal−ligand bonding and ability of arene
ligands to stabilize unusual oxidation states enhance the
fundamental significance of lanthanide complexes containing
RESULTS AND DISCUSSION
■
An amine elimination reaction of equimolar amounts of C H -
6
4
6
1
,2-{NC(t-Bu)NH(2,6-Me C H )} (1) and [(Me Si) N] Yb-
2 6 3 2 3 2 2
7
(
THF)2 (THF = tetrahydrofuran) was carried out in toluene
at ambient temperature (12 h). Evaporation of the volatiles and
subsequent recrystallization of the solid residue from a THF−
hexane mixture (∼1:1) allowed for the isolation of red-brown
crystals of complex 2 (Scheme 1) in 65% yield.
Complex 2 is highly air- and moisture-sensitive; it is well-
soluble in THF, toluene, and hexane. H NMR monitoring of
4
II
III
π-bonded neutral aromatic ligands. Two types of Ln and Ln
complexes coordinated by π-bonded neutral aromatic ligands
are known to date. The arene-halogenoaluminates (η -arene)-
1
6
the reaction indicated the quantitative formation of 2 and
(Me Si) NH. Lowering of the isolated yield obviously is
6
3 2
Ln[(μ-X) (AlX )] (X = Cl, Br, I) and (η -arene)Eu(AlCl )
2
2
3
4 2
4a
associated with high solubility of 2 in organic solvents.
Monocrystalline samples of 2 suitable for X-ray analysis were
obtained by slow concentration of a THF−hexane solution at
ambient temperature. The molecular structure of 2 is depicted
in Figure 1; the crystal and structural refinement data are
summarized in Table 1. Complex 2 has four crystallographically
constitute the first type, which appeared in the mid-1980s.
The second type is presented by σ-bonded aryloxides, thiolates,
and terphenyl derivatives featuring π-bonding between Ln ions
and pendant aryl groups. The bonding mode of arene
fragments to lanthanide ion can vary from η to η .
Recently we reported on unusual κ N, η -arene coordination
2
6
4a
1
6
II
of bulky amidinate ligand in Yb hydride, which can be assigned
to the second group of lanthanide arene complexes. This
coordination mode was proved to be characteristic only for
Received: October 7, 2013
Published: January 21, 2014
©
2014 American Chemical Society
1537
dx.doi.org/10.1021/ic402530w | Inorg. Chem. 2014, 53, 1537−1543

Inorganic Chemistry
Article
Scheme 1
ligand bonding since the Yb−N distances exceed the sum of
covalent radii of these elements (R(Yb) = 1.70, R(N) = 0.75
10
Å). The Yb−C distances fall into a rather large region
2.820(6)−3.657(6) Å) wherein one phenyl ring is located
closer to the ytterbium ion than the second one (Yb−C
(
:
average
2
.91(1) and 3.30(1) Å; Yb-Ph
: 2.55(1) and 3.01(1) Å).
centroid
Bent bis(arene) structures resembling that of complex 2 were
described for Yb ionic complexes containing BPh4− anion
II
1
1
[
[
Yb(t-Bu pz)(THF)BPh ], [Yb{N(SiMe ) }BPh ], and
2 4 3 2 4
12
Cp*YbBPh4]. However despite the similar coordination
numbers of the central atoms in 2 and [Yb(t-Bu pz)(THF)-
2
BPh ], [Cp*YbBPh ] displays noticeably longer Yb−C
4
4
distances (compare, [Yb(t-Bu pz)(THF)BPh ]: Yb−C =
2
4
2
2
.799(2)−2.945(2), Yb−C
.860(2)−3.050(2), Yb−C
= 2.88(1); Yb−C =
average
11
= 2.95(1); [Cp*YbBPh ]:
average
4
12
Yb−C = 2.884(5)−3.128(5), Yb−C
= 2.970(4) Å). The
average
average Yb−C bond lengths (2.96(1), 2.98(1) Å) in eight-
II
6
coordinated Yb thiolate complex [Yb{SC H -2-(η -C H i-
6
3
6
2
6
Pr )-6-(C H i-Pr )} ] featuring additional Yb-η -arene inter-
3
6
2
3
2
Figure 1. Molecular structure of complex [C H -1,2-{NC(t-Bu)N(2,6-
6
4
actions with coplanar orientation of C H i-Pr rings are also
6
2
3
Me C H )} ]Yb(THF) (2). Thermal ellipsoids drawn at the 30%
13
2
6
3
2
shorter than those in 2. Apparently elongation of the Yb−C
probability level. C atoms of THF molecule and all hydrogen atoms
are omitted for clarity. Bond lengths, Å: Yb(1)−N(2) 2.373(7),
Yb(1)−N(3) 2.406(6), Yb(1)−O(1) 2.383(6), N(1)−C(9) 1.30(1),
N(2)−C(9) 1.39(1), N(3)−C(20) 1.358(9), N(4)−C(20) 1.321(9);
bond angles, deg: N(2)−Yb(1)−N(3) 69.0(2), N(1)−C(9)−N(2)
II
bonds in 2 as compared with the above-mentioned related Yb
−
arene complexes is due to connectivity of amidinate moieties
with rigid ortho-phenylene linker. The value of the dihedral
angle between the planes of two phenyl rings is 63.9(1)°. The
N−C bonds within the NCN fragments are nonequivalent.
One pair of bonds (N(1)−C(9) 1.30(1), N(4)−C(20)
120.1(8), N(4)−C(20)−N(3) 119.9(7).
1
.321(9) Å) is somewhat shorter compared to the second
independent molecules in an asymmetric unit. However since
all of them have similar geometric parameters, only one
molecule will be discussed. The X-ray study revealed that,
one (N(2)−C(9) 1.39(1), N(3)−C(20) 1.358(9) Å).
1
In the H NMR spectrum of diamagnetic complex 2 (C D ,
6
6
2
0 °C) the bis(amidinate) ligand gives a single set of signals: a
III
6,8
unlike previously reported Ln complexes featuring “classic”
sharp singlet at 1.78 ppm due to the t-Bu protons, the Me
2
κ N,N′-chelating coordination mode of ansa bis(amidinate)
protons of Me C H groups appear as two singlets at 2.00 and
II
2
6
3
ligand, in 2, both amidinate groups chelate the Yb ion by
2
.22 ppm, while the aromatic protons of Me C H and o-C H
1
6
2 6 3 6 4
κ amide and η -arene interactions. The most interesting feature
of 2 is the formation of bent bis(arene) structure due to η -
coordination of two 2,6-Me C H -units to the Yb center. The
κ N, η -arene chelating coordination mode is rather rare and
was previously documented for the Yb complexes with the
bulky guanidinate and amidinate ligands. Besides two
nitrogen atoms and two η -coordinated 2,6-Me C H rings,
fragments give rise to a multiplet in the low-field region (6.28−
6.65 ppm). Two broadened singlets (at 1.03 and 2.53 ppm)
correspond to the methylene protons of a coordinated THF
6
II
2
6
3
1
6
1
13
II
molecule. The variable temperature (−60−50 °C) H and
C
5
,9
NMR spectra of complex 2 in C D and THF-d were recorded,
however did not give prove for retention of η -arene
coordination in solution.
7 8 8
6
6
2
6
3
the ytterbium ion in 2 is coordinated by one oxygen atom of
THF molecule, giving a formal coordination number of nine.
The Yb−N bonds in 2 (2.406(6) and 2.373(7) Å) are
It is worth noting that despite its apparent similarity with
lanthanide arene-haloaluminates, σ,π-bonded alyloxides and
6
II
thiolates, complex 2 features stronger Ln−η interaction. Thus
somewhat longer compared to those in the Yb amidinate-
arene-haloaluminates dissociate to the starting materials LnX
hydrido complex [{t-BuC(NC H -2,6-i-Pr ) }Yb(μ-H)]
3
6
3
2
2
2
5
a
and AlX3 when treated with THF. π-Bonded ligands in
alyloxides and thiolates easily undergo displacement from the
metal coordination sphere by coordinating donor solvents
(2.329(3) Å) and guanidinate-iodido [{[Cy NC(NC H -2,6-
2 6 3
9
i-Pr ) ]Yb(μ-I)} ] (2.360(3) Å) complexes performing the
2
2
2
same type of coordination of the NCN ligands. This fact can
II
originate from higher coordination number of Yb in 2. Two
(THF, 1,2-dimethoxyethane (DME), and NH ) upon dis-
3
other nitrogen atoms are remote from the ytterbium atom
solution, while the bent bis(arene) structure of 2 remains after
crystallization from THF−hexane mixture.
(
3.647(6) and 3.667(6) Å) and are not involved in the metal−
1
538
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Inorganic Chemistry
Article
Table 1. Crystallographic Data and Structure Refinement Details for Complexes 2−4
2
3
4
formula
Mr
C H N OYb
C39.5H56.5ClN O2.5Yb
C H N S Yb
2
3
6
48
4
4
78 94
8
2
725.82
835.88
1553.81
crystal size, mm
crystal system
space group
a, Å
0.27 × 0.23 × 0.09
orthorhombic
P2(1)2(1)2(1)
15.4041(4)
26.9046(7)
32.7428(8)
90
0.16 × 0.10 × 0.08
triclinic
0.17 × 0.13 × 0.10
triclinic
P1
̅
P1
̅
12.3731(7)
15.9925(9)
19.727(1)
86.857(1)
78.881(1)
82.954(1)
3799.3(4)
4
12.0273(5)
12.6115(6)
13.6486(6)
110.180(1)
108.300(1)
94.120(1)
1806.8(1)
1
b, Å
c, Å
α, deg
β, deg
90
γ, deg
90
cell volume, Å
Z
13570.0(6)
16
3
dcalc, g/cm
1.421
1.461
1.428
μ, mm−
1
2.789
2.572
2.677
F000
5920
1714
790
2θ range, deg
52
52
52
index ranges
−18 ≤ h ≤ 19
−15 ≤ h ≤ 14
−19 ≤ k ≤ 15
−24 ≤ l ≤ 24
23 019
−14 ≤ h ≤ 14
−15 ≤ k ≤ 15
−16 ≤ l ≤ 16
15 786
−
−
33 ≤ k ≤ 33
40 ≤ l ≤ 39
reflns collected
independent reflns
Rint
117 198
26 604
14 838
7082
0.0733
0.0292
0.0112
completeness to θ
data/restraints/parameters
GOF
99.8
99.2
99.6
26 604/20/1547
1.021
14 838/54/890
0.968
7082/0/416
1.063
R1 (I > 2σ(I))
0.0460
0.0374
0.0159
wR (all data)
2
0.0990
0.0873
0.0409
max. and min. transmission
0.7874/0.5197
1.782/−0.727
0.8207/0.6837
1.707/−1.019
0.7756/0.6589
1.287/−0.616
3
largest diff. peak and hole, e/Å
Scheme 2
Recently, with the example of Yb(II) hydrido complex [{t-
BuC(NC H -2,6-i-Pr )2}Yb(μ-H)] , we have demonstrated
The reaction of 2 with Ph SnCl in THF in 1:1 molar ratio
3
6
3
2
2
was carried out at ambient temperature (12 h) and afforded
Yb(III) bis(amidinate) chloro complex and Ph Sn−SnPh
1
6
that the κ N, η -arene chelating coordination of bulky
3
3
II
amidinate ligand is realized only in Yb complexes, while
(
Scheme 2). Recrystallization of the reaction product from
III
oxidation of the ytterbium center to Yb results in a change of
DME−THF−hexane mixture allowed for isolation of orange
crystals of 3 in 75% yield. Magnetic mesurements indicated
2
5b
coordination fashion to a κ N,N′-chelating one. To get a
deeper insight into the nature of bonding between ytterbium
ion and ansa bis(amidinate) ligand and to explore the factors
that govern the type of coordination, a series of oxidation
reactions of 2 by mild one-electron oxidants was performed.
The possibility of retention of a bent bis(arene) structure by
14
trivalent state of ytterbium in 3 (μeff = 4.7 μB, T = 293 K).
Complex 3 was also synthesized by the salt metathesis reaction
of equimolar amounts of YbCl and the dilithium derivative of
3
1 in THF (Scheme 2). This synthetic approach afforded 3 in
81% yield.
III
Yb species was the focus of our interest.
1
539
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Inorganic Chemistry
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The molecular structure of complex 3 was established by X-
ray analysis and is depicted in Figure 2; the crystal and
coordination environment of the metal atoms in 3 adopts
geometry of distorted pentagonal bipyramid. Four nitrogen
atoms, the metal atom, and one oxygen atom are disposed in
the equatorial plane (maximum deviation of atoms from plane
is 0.14(2) Å), while the chloro ligand and the second oxygen
occupy the apical positions. The dihedral angle between two
NMN planes in complex 3 has the value of 170.7(1)° and is
slightly narrower compared to that in the lutetium analogue
6
(
176.3(1)°). The MNCN fragments have different geometries:
one is close to being planar (the value of dihedral angle
between MNN and NCN planes is 179.7(2)°), while the
second one is noticeably curved (the dihedral angle between
the planes MNM and NCN is 148.6(2)°). The average Yb−N
bond length in 3 (2.33(1) Å) is similar to the related values
reported for the seven-coordinated ytterbium complexes
coordinated by ansa bis(amidinate) ligands ([{(CH ) {NCN-
2
3
(
[
SiMe )i-PrN(i-Pr)} }Yb(μ-Cl)(THF)] (2.34(1) Å),
3 2 2
(CH ) {NCN(SiMe )i-PrN(i-Pr)} ]YbCl(DME) (2.34(1)
2
3
3
2
1
5
Å), [{(CH ) {NC(Ph)NSiMe } ]Yb(μ-Cl)(THF) (2.34(1)
2
3
3
2
2
16
Å) ). The distances from Yb to “internal” nitrogens are
significantly shorter (Yb(1)−N(2) 2.257(3), Yb(1)−N(3)
2
.278(3) Å) than those to “external” nitrogens (Yb(1)−N(1)
.382(2), Yb(1)−N(4) 2.390(3) Å). The lengths of amidinate
2
N−C bonds in complex 3 have similar values, indicating the
negative charge delocalization within the NCN fragments
Figure 2. Molecular structure of complex [C H -1,2-{NC(t-Bu)N(2,6-
6
4
Me C H )} ]YbCl(DME) (3). Thermal ellipsoids drawn at the 30%
2
6
3
2
(
(
1.317(4)−1.357(4) Å). The Yb−Cl bond length in 3
probability level. C-atoms of DME molecule and all hydrogen atoms
are omitted for clarity. Bond lengths, Å: Yb(1)−N(1) 2.382(2),
Yb(1)−N(2) 2.257(3), Yb(1)−N(3) 2.278(3), Yb(1)−N(4)
2.544(1) Å) has a value close to that in [(CH ) {NCN-
2 3
15
(SiMe )i-PrN(i-Pr)} ]YbCl(DME) (2.559(4) Å).
3
2
2.390(3), Yb(1)−Cl(1) 2.544(1), Yb(1)−O(1) 2.373(2), Yb(1)−
One-electron oxidation of complex 2 by (PhCH S) in 1:0.5
2 2
O(2) 2.378(3), N(1)−C(9) 1.317(4), N(2)−C(9) 1.356(4), N(4)−
C(20) 1.332(4), N(3)−C(20) 1.357(4); bond angles, deg: N(1)−
Yb(1)−N(4) 170.9(1), N(2)−Yb(1)−N(3) 68.9(1), N(1)−C(9)−
N(2) 109.4(3), N(4)−C(20)−N(3) 109.5(3).
molar ratio was carried out in THF at 20 °C (6 h). The
reaction resulted in the formation of Yb bis(amidinate)
III
sulfido complex 4 (Scheme 3), which was isolated after
recrystallization from a THF−hexane mixture in 63% yield.
Single-crystal samples of 4 suitable for X-ray analysis were
obtained by slow concentration of a solution in THF−hexane
mixture at room temperature. The molecular structure of 4 is
depicted in Figure 3; the crystal and structural refinement data
are listed in Table 1. The X-ray study revealed that 4 adopts a
structural refinement data are summarized in Table 1. Complex
3
crystallizes with two crystallographically independent
molecules in the asymmetric unit. It crystallizes as a solvate
3
·(THF) (C H14)0.25. The X-ray study revealed that in
0.5 6
complex 3 unlike 2 the ansa bis(amidinate) ligand is
dimeric structure where two [C
6 4
H -1,2-{NC(t-Bu)N(2,6-
2
2
coordinated to ytterbium in κ N,N′-chelating fashion. Similarly
Me )} ]Yb units are connected by two μ -bridging
2
C
6
H
3
2
to the previously described lutetium derivative [C H -1,2-
benzylsulfide groups. The most important structural feature
of 4 is the coordination mode of the amidinate ligand. In
6
4
6
{
NC(t-Bu)N(2,6-Me C H )} ]LuCl(THF) , complex 3
2 6 3 2 2
1
6
adopts a monomeric structure. The ytterbium atom is
coordinated by four nitrogen atoms of the bis(amidinate)
ligand, terminal chloro ligand, and two oxygen atoms of DME
molecule, thus resulting in coordination number of seven. The
contrast to the κ N, η -arene coordination mode detected in
the parent complex 2, oxidation of the ytterbium center to the
1
1
trivalent state led to switching to the classical κ ,κ N,N-
III
6
chelating fashion that is characteristic for Ln amidinates. The
Scheme 3
1
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Inorganic Chemistry
Article
Figure 3. Molecular structure of complex {[C H -1,2-{NC(t-Bu)N(2,6-Me C H )} ]Yb(μ-SCH Ph)} (4). Thermal ellipsoids drawn at the 30%
6
4
2
6
3
2
2
2
probability level. Hydrogen atoms, t-Bu−, and 2,6-i-Pr C H − fragments are omitted for clarity. Bond lengths, Å: Yb(1)−Yb(1A) 4.2834(2), Yb(1)−
2
6
3
S(1) 2.6604(5), Yb(1)−S(1A) 2.7484(5), Yb(1)−N(1) 2.337(2), Yb(1)−N(2) 2.296(2), Yb(1)−N(3) 2.329(2), Yb(1)−N(4) 2.281(2); bond
angles, deg: N(4)−Yb(1)−N(1) 123.98(5), N(2)−Yb(1)−N(3) 67.26(5), Yb(1)−S(1)−Yb(1A) 104.72(2), S(1)−Yb(1)−S(1A) 75.28(2).
1
6
Yb−N (Yb(1)−N(1) 2.337(2), Yb(1)−N(2) 2.296(2), Yb(1)−
N(3) 2.329(2), Yb(1)−N(4) 2.281(2) Å) and C−N (N(1)−
C(9) 1.339(2), N(2)−C(9) 1.340(2), N(3)−C(20) 1.328(2),
N(4)−C(20) 1.358(2) Å) bonds within the YbNCN fragment
are equivalent, indicating a symmetric coordination to the metal
ion with delocalization of a negative charge within the
conjugated amidinate ligand. The Yb−N distances in 4 (Yb−
The X-ray study proved κ N, η -arene type of coordination of
ansa bis(amidinate) ligand to ytterbium in the isolated complex.
CONCLUSIONS
■
The results of oxidation of 2 and reduction of 3 unambiguously
prove that the coordination fashion of [C H -1,2-{NC(t-
6
4
2−
Bu)N(2,6-Me C H )} ] ligand to ytterbium ion can be
2
6
3
2
N
= 2.311(2) Å) are similar to the related values measured
1
6
2
average
reversibly switched from κ N, η -arene to κ N,N′ by changing
the oxidation state and consequently the ionic radius of the
ytterbium ion. Reversible reconstruction of the bent bis(arene)
III
for six-coordinated amidinate Yb compounds (2.290(4)−
.385(4) Å). In complex 4 the four-membered Yb S core is
1
7
2
2 2
II
absolutely planar, with the values of bond angles of YbSYb and
SYbS of 104.72(2) and 75.28(2)°, respectively. The distance
Yb(1)−Yb(1A) is 4.2834(2) Å. The Yb−S bond lengths in 4
are slightly different (2.6604(5) and 2.7484(5) Å), and their
values are noticeably shorter, compared to those measured in
the related amidinate bis(sulfide) complex of six-coordinated
ytterbium ([{t-BuC(NC H -2,6-i-Pr ) }Yb(μ-SCH Ph) ] )
structure of the Yb complex is the most exciting issue in this
redox chemistry. To be able to distinguish which factor,
electronic (electronic structure of the metal atom) or steric (ion
size), plays the predominant role in the realization of either
1
6
2
κ N, η -arene or κ N,N′ coordination, currently we are working
III
II
on the synthesis and structural characterization of La and Ca
2
−
complexes coordinated by {NC(t-Bu)N(2,6-Me
C H )} ]
6 3 2
6
3
2
2
2
2 2
2
5
b
ligand.
(
Yb−S
= 2.7548(9) Å). The MNCN fragments have
average
slightly different geometries. The N(1)C(9)N(2)Yb(1) unit is
nearly planar (the value of dihedral angle between the
N(1)C(9)N(2) and N(1)Yb(1)N(2) planes is 177.4(1)°),
while the N(3)C(20)N(4)Yb(1) fragment is noticeably
distorted (the value of dihedral angle between the N(3)C(20)-
N(4) and N(3)Yb(1)N(4) is 146.2(1)°).
EXPERIMENTAL SECTION
■
All experiments were performed in evacuated tubes by using standard
Schlenk techniques, with rigorous exclusion of traces of moisture and
air. After being dried over KOH, THF and DME were purified by
distillation from sodium/benzophenone ketyl; hexane and toluene
were dried by distillation from sodium/triglyme and benzophenone
ketyl prior to use. C D was dried with sodium and condensed in
Thereby it was proved that oxidation of ytterbium center
results in transformation of coordination mode of the amidinate
6
6
vacuo into NMR tubes prior to use. Ph SnCl, (PhCH S) , and n-BuLi
3
2
2
1
6
1 1
fragments from κ N, η -arene to κ ,κ N,N.
18
were purchased from Acros. Anhydrous YbCl , Yb[N(SiMe ) ]
3
3 2 2-
7
8
To explore reversibility of change of coordination mode of
the linked bis(amidinate) ligand system in the course of redox
(THF)2, and [C H -1,2-{NC(t-Bu)NH(2,6-Me C H )} ] were
6 4 2 6 3 2
prepared according to literature procedures. NMR spectra were
recorded with Bruker Avance DRX-400 and Bruker DRX-200
spectrometers in C D at 25 °C, unless otherwise stated. Chemical
•−
+
reactions, reduction of complex 3 by [C H ][Na ] (1:1
1
0
8
6
6
molar ratio) was carried out in THF at ambient temperature
Scheme 2). The reaction occurs with NaCl precipitation,
1
13
shifts for H and C NMR spectra were referenced internally to the
residual solvent resonances and are reported relative to TMS. Infrared
(
III
II
reduction of Yb to Yb , and results in the formation of
(
IR) spectra were recorded as Nujol mulls with a Bruker-Vertex 70
complex 2 in 71% yield. Complex 2 was authenticated by the X-
instrument. Lanthanide metal analyses were carried out by
1
13
19
ray analysis, H and C NMR-spectroscopy, and microanalysis.
complexometric titration. The C, H, and N elemental analyses
1
541
dx.doi.org/10.1021/ic402530w | Inorg. Chem. 2014, 53, 1537−1543

Inorganic Chemistry
Article
were performed in the microanalytical laboratory of the G. A.
Razuvaev Institute of Organometallic Chemistry.
recrystallized from THF/hexane mixture. Complex 4 was obtained
−1
in 63% yield (0.34 g). IR (Nujol, KBr; υ (cm )) 491 (s), 501 (s), 551
(s), 601 (s), 640 (m), 675 (s), 698 (m), 707 (w), 745 (s), 766 (s), 797
(w), 818 (m), 827 (w), 840 (w), 864 (w), 916 (w), 946 (s), 955 (s),
978 (s), 1029 (s), 1041 (m), 1092 (s), 1139 (s), 1167 (s), 1195 (m),
1209 (s), 1253 (w), 1273 (s), 1299 (s), 1402 (s), 1424 (s), 1445 (s),
1512 (s), 1578 (s), 1594 (s), 1656 (s), 1776 (m), 1849 (m), 1915 (m)
Synthesis of [C H -1,2-{NC(t-Bu)N(2,6-Me C H )} ]Yb(THF)
6
4
2
6
3 2
(
2). Method A. A solution of compound 1 (0.45 g, 0.93 mmol) in
3
0 mL of toluene was added to a solution of Yb(NSiMe ) (THF)
3 2 2
(0.59 g, 0.93 mmol) in toluene (30 mL), and the reaction mixture was
stirred overnight. Evaporation of the volatiles under vacuum and
recrystallization of the resulting solid from THF/hexane (1:1) mixture
−
1
cm ; Anal. Calcd for C H N S Yb (1553.87): C, 60.29; H, 6.10; N,
78
94
8
2
2
1
afforded 2 as red-brownish crystals in 65% yield (0.44 g). H NMR:
7.21; Yb, 22.27. Found C, 60.13; H, 6.17; N, 7.28; Yb, 22.31%.
X-ray Crystallography. The X-ray data for 2−4 were collected on
a Smart Apex diffractometer (graphite-monochromated, Mo Kα
radiation, ω-scan technique, λ = 0.71073 Å, T = 100(2) K). The
(
1
400 MHz, C D , 25 °C, TMS) δ 1.03 (br. s, 4H, β-THF), 1.78 (s,
6 6
8H, C(CH ) ), 2.00, 2.22 (s, 6H, (C H (CH ) )), 2.53 (br. s, 4H, α-
3 3 6 3 3 2
3
3
THF), 6.28 (t, J = 7.01 Hz, 2H, 2,6-Me C H ), 6.51 (d, J =
H,H
2
6
3
H,H
2
7
.01 Hz, 2H, 2,6-Me C H ), 6.65 (m, 2H, C H ), 6.84 (m, 4H, 2,6-
structures were solved by direct methods and were refined on F , using
2
6
3
6
4
13
1
20
Me C H , C H ); C{ H} NMR (100 MHz, C D , 25 °C, TMS) δ
1
SHELXTL package. All non-hydrogen atoms were found from
2
6
3
6
4
6
6
7.6, 18.5 (C H (CH ) ), 24.7 (β-THF), 32.3 (C(CH ) ), 40.3
Fourier syntheses of electron density and were refined anisotropically.
6
3
3
2
3 3
(
1
C(CH ) ), 68.8 (α-THF), 118.2, 118.3, 123.1, 128.8, 129.1, 130.0,
All hydrogen atoms were placed in calculated positions and were
3
3
2
1
30.7, 142.3, 159.4 (2,6-Me C H , C H ), 172.5 (NCN); IR (Nujol,
refined in the riding model. The SADABS program was used to
perform area-detector scaling and absorption corrections. Compound
2 is a racemic twin with Flack parameter of x = 0.51(1). The details of
crystallographic, collection, and refinement data are shown in Table 1,
and corresponding cif files are available in the Supporting Information.
CCDC-963778 (2), 963779 (3), 963780 (4) contain the supple-
mentary crystallographic data for this Paper. These data can be
obtained free of charge from The Cambridge Crystallographic Data
Centre via ccdc.cam.ac.uk/products/csd/request.
2
6
3
6
4
−1
KBr; υ (cm )) 493 (s), 502 (m), 548 (s), 561 (s), 632 (m), 647 (s),
6
9
1
94 (s), 742 (s), 777 (s), 792 (s), 809 (s), 875 (s), 920 (s), 962 (w),
82 (m), 1022 (s), 1039 (s), 1089 (s), 1217 (m), 1238 (s), 1256 (m),
274 (s), 1360 (s), 1389 (s), 1511 (s), 1550 (s), 1581 (s), 1654 (s)
−1
cm ; Anal. Calcd for C H N OYb (725.85): C, 59.57; H, 6.67; N,
7
36
48
4
.72; Yb, 23.84; Found: C, 59.89; H, 6.93; N, 7.59; Yb, 23.75%.
•−
+
Method B. A solution of [C H ][Na ] in situ obtained from
10
8
C H (0.0845 g, 0.66 mmol) and Na (0.0152 g, 0.66 mmol) in THF
10
8
(
10 mL) was added to a solution of 3 (0.55 g, 0.66 mmol) in 20 mL of
THF. The resulting dark-red solution was stirred for 12 h at room
temperature. After NaCl was separated by filtration and THF was
removed under vacuum, the solid residue was extracted with toluene
ASSOCIATED CONTENT
Supporting Information
■
*
S
Figures giving NMR and IR spectra; CIF files giving
crystallographic data for the structures determined in this
Paper. This material is available free of charge via the Internet
at http://pubs.acs.org. CCDC-963778 (2), 963779 (3), 963780
(4) contain the supplementary crystallographic data for this
Paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via ccdc.cam.ac.uk/
products/csd/request.
(
30 mL). Toluene was removed, and the remaining solid was
recrystallized from THF/Hexane mixture. Red-brownish crystals of 2
1
were isolated in 71% yield (0.34 g). H NMR: (400 MHz, C D , 25
6
6
°
C, TMS) δ 1.03 (br. s, 4H, β-THF), 1.78 (s, 18H, C(CH ) ), 2.00,
3 3
3
2
.22 (s, 6H, (C H (CH ) )), 2.53 (br. s, 4H, α-THF), 6.28 (t, J
=
H,H
6
3
3
2
3
7
.01 Hz, 2H, 2,6-Me C H ), 6.51 (d, JH,H = 7.01 Hz, 2H, 2,6-
2
6
3
Me C H ), 6.65 (m, 2H, C H ), 6.84 (m, 4H, 2,6-Me C H , C H ).
2
6
3
6
4
2
6
3
6
4
Synthesis of [C H -1,2-{NC(t-Bu)N(2,6-Me C H )} ]YbCl(DME)
6
4
2 6 3 2
(
3). Method A. To a solution of compound 1 (0.48 g, 0.99 mmol) in
Et O (10 mL) (Et = ethyl) a solution of n-BuLi (0.96 M, 2.1 mL, 2.00
2
AUTHOR INFORMATION
Corresponding Author
*E-mail: trif@iomc.ras.ru. Fax: (+7)8314621497.
Notes
■
mmol) in hexane was added at 0 °C, and the reaction mixture was
stirred for 1 h. The volatiles were removed under vacuum, and the
resulting solid residue was dissolved in 10 mL of THF. The solution
formed was added to a suspension of YbCl (0.28 g, 1.00 mmol) in
3
THF (20 mL), and the reaction mixture was stirred at room
temperature for 12 h. The reaction mixture was filtered, and the
solvent was removed under vacuum. The remaining solid was
extracted with toluene (50 mL), and the toluene extracts were filtered.
The solvent was removed under vacuum, and the solid residue was
recrystallized from DME/hexane mixture. Orange crystals of 3 were
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
The work was supported by the Russian Foundation for Basic
Research (Grant 12-03-3300113; 12-03-31865), the Ministry of
Education and Science of Russian Federation (Project No.
445), Program of the Presidium of the Russian Academy of
Science (RAS), and RAS Chemistry and Material Science
Division.
−1
isolated in 81% yield (0.63 g). IR (Nujol, KBr; υ
(
(
̃
(cm )) 494 (s), 554
s), 566 (w), 602 (s), 674 (m), 695 (s), 745 (s), 765 (s), 821 (s), 861
s), 919 (s), 940 (m), 962 (s), 988 (s), 1004 (s), 1045 (s), 1095 (s),
8
1
1
102 (s), 1162 (s), 1210 (s), 1249 (s), 1276 (s), 1361 (s), 1369 (s),
415 (s), 1571 (s), 1589 (s), 1643 (s), 1774 (m), 1847 (m), 1907 (s)
−1
cm ; Anal. Calcd for C H Cl N O Yb (779.31): C, 55.48; H, 6.47;
36
50
4
2
REFERENCES
N, 7.19; Yb, 22.21; Found: C, 55.03; H, 6.12; N, 7.00; Yb 22.28%.
■
Method B. A solution of Ph SnCl (0.15 g, 0.39 mmol) in THF (10
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(
50 mL). After filtration of the toluene extracts the solvent was
removed, and the solid residue was recrystallized from THF/DME/
hexane mixture. Orange crystals of 3 were obtained in 75% yield (0.23
g). Ph Sn−SnPh was isolated from the mother liquor as colorless
3
3
crystals in 100% yield (0.13 g).
Synthesis of {[C H -1,2-{NC(t-Bu)N(2,6-Me C H )} ]Yb(μ-
6
4
2
6
3 2
SCH Ph)} (4). A solution of (PhCH S) (0.086 g, 0.35 mmol) in
2
2
2
2
THF (20 mL) was added to a solution of 2 (0.34 g, 0.70 mmol) in
THF (20 mL), and the reaction mixture was stirred for 6 h. The
solvent was evaporated in vacuo, and the solid residue was
̈ ̈
L. N.; Dietrich, H. M.; Maichle-Mossmer, C.; Tornroos, K. W.;
1
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Inorganic Chemistry
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