Reactivity of ytterbium(II) hydride. Redox reactions: Ytterbium(II) vs hydrido ligand. Metathesis of the Yb-H bond

Article abstract of DOI:10.1021/om400015k

Oxidation reactions of the Yb(II) hydride [{tBuC(NC₆H ₃-2,6-iPr₂)₂}Yb(μ-H)]₂ (1) with CuCl (1:2 molar ratio) and (PhCH₂S)₂ (1:1 molar ratio) revealed that the hydrido anion in 1 is a stronger reductant than the Yb(II) cation. Both reactions occur with evolution of H₂ and afford the dimeric Yb(II) species [{tBuC(NC₆H₃-2,6-iPr ₂)₂}Yb(μ-X)]₂ (X = Cl (2), SCH₂Ph (3)) in which a κ¹-amido,η⁶-arene type of coordination of amidinate ligand is retained. Reaction of 1 with 2 equiv of (PhCH₂S)₂ results in oxidation of both Yb(II) and hydrido centers and leads to the formation of the Yb(III) complex [{tBuC(NC ₆H₃-2,6-iPr₂)₂}Yb(μ-SCH ₂Ph)₂]₂ (4). Complex 4 can be also synthesized by oxidation of 3 with an equimolar amount of (PhCH₂S)₂. It was demonstrated that oxidation of the ytterbium center to the trivalent state leads to switching of the coordination mode of amidinate ligand from κ¹-amido, η⁶-arene to classical κ¹,κ¹-N,N-chelating. Unlike Yb(III) bis(alkyl) species supported by bulky amidopyridinate ligands, the reaction of [{tBuC(NC₆H₃-2,6-iPr₂)₂}Yb(CH ₂SiMe₃)₂(THF)] (6) with PhSiH₃ (1:2 molar ratio) occurs with reduction of ytterbium to a divalent state and affords 1. Thus, reduction of Yb(III) to Yb(II) leads to a change of coordination mode from κ¹,κ¹-N,N to κ¹-N, η⁶-arene. Oxidation of 1 by 2,6-iPr₂C ₆H₃N=C(H)C(H)=NC₆H₃-2,6-iPr ₂ was found to result in oxidation of the hydrido ligand and ytterbium ion and formation of the mixed-valent ion-pair complex [{tBuC(NC ₆H₃-2,6-iPr₂)₂}Yb(DME) ₂]⁺[{2,6-iPr₂C₆H₃NC(H)= C(H)NC₆H₃-2,6-iPr₂}₂Yb]^- (5). The σ-bond metathesis reaction of 1 with Ph₂PH allowed for the synthesis of the first mixed-ligand hydrido-phosphido Yb(II) species [{tBuC(NC₆H₃-2,6-iPr₂)₂}Yb(μ-H) (μ-PPh₂)Yb{tBuC(NC₆H₃-2,6-iPr ₂)₂}] (7). The second hydrido ligand cannot be replaced by a phosphido ligand.

Full text of DOI:10.1021/om400015k

Article
pubs.acs.org/Organometallics
Reactivity of Ytterbium(II) Hydride. Redox Reactions: Ytterbium(II) vs
Hydrido Ligand. Metathesis of the Yb−H Bond
Ivan V. Basalov, Dmitry M. Lyubov, Georgy K. Fukin, Anton V. Cherkasov, 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: Oxidation reactions of the Yb(II) hydride [{tBuC-
(NC6H3-2,6-iPr2)2}Yb(μ-H)]2 (1) with CuCl (1:2 molar ratio) and
(PhCH2S)2 (1:1 molar ratio) revealed that the hydrido anion in 1 is a
stronger reductant than the Yb(II) cation. Both reactions occur with
evolution of H2 and afford the dimeric Yb(II) species [{tBuC-
(NC6H3-2,6-iPr2)2}Yb(μ-X)]2 (X = Cl (2), SCH2Ph (3)) in which a
κ1-amido,η6-arene type of coordination of amidinate ligand is
retained. Reaction of 1 with 2 equiv of (PhCH2S)2 results in
oxidation of both Yb(II) and hydrido centers and leads to the
formation of the Yb(III) complex [{tBuC(NC6H3-2,6-iPr2)2}Yb(μ-
SCH2Ph)2]2 (4). Complex 4 can be also synthesized by oxidation of
3 with an equimolar amount of (PhCH2S)2. It was demonstrated that
oxidation of the ytterbium center to the trivalent state leads to switching of the coordination mode of amidinate ligand from κ1-
amido, η6-arene to “classical” κ1,κ1-N,N-chelating. Unlike Yb(III) bis(alkyl) species supported by bulky amidopyridinate ligands,
the reaction of [{tBuC(NC6H3-2,6-iPr2)2}Yb(CH2SiMe3)2(THF)] (6) with PhSiH3 (1:2 molar ratio) occurs with reduction of
ytterbium to a divalent state and affords 1. Thus, reduction of Yb(III) to Yb(II) leads to a change of coordination mode from
κ1,κ1-N,N to κ1-N, η6-arene. Oxidation of 1 by 2,6-iPr2C6H3NC(H)C(H)NC6H3-2,6-iPr2 was found to result in oxidation of
the hydrido ligand and ytterbium ion and formation of the mixed-valent ion-pair complex [{tBuC(NC6H3-2,6-
iPr2)2}Yb(DME)2]+[{2,6-iPr2C6H3NC(H)C(H)NC6H3-2,6-iPr2}2Yb]− (5). The σ-bond metathesis reaction of 1 with
Ph2PH allowed for the synthesis of the first mixed-ligand hydrido−phosphido Yb(II) species [{tBuC(NC6H3-2,6-iPr2)2}Yb(μ-
H)(μ-PPh2)Yb{tBuC(NC6H3-2,6-iPr2)2}] (7). The second hydrido ligand cannot be replaced by a phosphido ligand.
Yb(II)−H− is a stronger reductant. The Yb−H bond can
INTRODUCTION
■
undergo insertions of multiple bonds as well as σ-bond
Hydrido complexes belong to the most interesting and
metathesis reactions with reagents containing acidic X−H
promising classes of organolanthanides. Their unique reactivity
bonds. The existence in the same molecule of Lewis acidic (Yb
in stoichiometric reactions1 and catalytic activity in a variety of
ion) and basic (M−H) sites can lead to rich coordination
olefinic transformations have stimulated intense development
chemistry. The synthesis of monomeric hydrido species1b,5 still
of this chemistry.2 Although the first reports on lanthanide
remains a challenge in organolanthanide chemistry, that is why
hydrides appeared in the 1980s,3 hydrido species of lanthanides
splitting of a dimeric Ln2H2 core under treatment with Lewis
in a divalent state still remain virtually unexplored.4 The first
base or acid seems to be an ongoing trend.
structurally defined Ln(II) hydrido complex supported by a
Recently we reported on the synthesis, structure, and
bulky hydrotris(pyrazolyl)borate ligand was published by
reactivity of the novel Yb(II) hydrido complex [{tBuC-
Takats et al. in 1999.4a Another example of a Yb(II) hydride
(NC6H3-2,6-iPr2)2}Yb(μ-H)]2 (1),4c supported by a bulky
involves a complex coordinated by a DIPP-nacnac ligand.4b
amidinate ligand. Complex 1 features a rather unusual κ1-
Despite the fact that some classes of stoichometric reactions of
amido, η6-arene type of coordination of amidinate ligand with a
4a
[(TptBu,Me)Yb(μ-H)]2 and the catalytic activity of [(DIPP-
surprisingly robust Yb(II)−η6-arene interaction. We found that
nacnac)YbH(thf)]2 in 1,1-diphenylethylene hydrosilylation4b
4b
despite the highly oxophilic nature of lanthanide metals arene
have been described, the reactivity of Ln(II) hydrido species
could not be replaced from the metal coordination sphere when
still remains poorly investigated. Indeed, Ln(II) hydrido
complexes containing two reaction centers which can provide
various types of reactivities present great interest for the
1 was treated with Lewis bases. Moreover, complex 1 exhibited
an ability for double addition to a CC bond, affording a
investigation of reactivity patterns. The presence of a low-valent
Special Issue: Recent Advances in Organo-f-Element Chemistry
Yb(II) ion and hydrido ligand possessing reductive properties
gives a basis for a rich redox chemistry of these complexes.
Moreover, to date it is not clear which partner in the couple
Received: January 10, 2013
Published: February 14, 2013
© 2013 American Chemical Society
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Scheme 1
dimeric complex with a 1,2-dianionic bibenzyl ligand.
Preliminary studies on the oxidation of 1 revealed that both
Yb(II) and hydrido centers are oxidized under the reaction
conditions. Herein we report on the selective competitive
oxidation of Yb(II) ion and hydrido ligand and metathesis of
the Yb−H bond with Ph2PH.
atoms in the molecule; however, the poor quality of the crystals
does not allow us to discuss the geometric parameters of 2. The
X-ray study revealed that complex 2 adopts a dimeric structure
similar to that observed for the parent hydride 1. The ytterbium
centers are connected by two μ-bridging chloro ligands, and the
κ1-N, η6-arene coordination mode of amidinate ligands is
retained. The molecular structure of 2 is depicted in Figure 1.
RESULT AND DISCUSSION
■
In order to estimate the comparative reductive capacities of the
hydrido ligand and Yb(II) ion in our previous work, a series of
reactions of 1 with one-electron oxidants (I2, AgBF4, AgBPh4,
N,N′-dimethylthiuram disulfide) was carried out.4c The
reactions of 1 with I2, AgBF4, and AgBPh4 turned out to be
not selective and resulted in oxidation of both the Yb(II) ion
and hydrido ligand. These reactions lead to hydrogen evolution
(resulting from oxidation of the hydrido anion) and the
formation of intractable mixtures of products containing both
Yb(II) and Yb(III) species.4c The reaction with the milder
oxidant N,N′-dimethylthiuram disulfide occurred without H2
evolution, but regardless of the reagent ratio the bis-
(dithiocarbamato)amidinato Yb(III) complex [{tBuC(NC6H3-
2,6-iPr2)2}Yb(S2CNMe2)2] was isolated from the reaction
mixture.
Finally we succeeded in choosing selective one-electron
oxidants which allowed us to identify a stronger reductant
within the Yb(II)−hydrido anion couple. Thus, the reaction of
complex 1 with 2 molar equiv of copper(I) chloride occurs
selectively in toluene solution at −60 °C and results in
evolution of H2 along with precipitation of metallic copper.
From the reaction mixture the ytterbium(II) chloro complex
[{tBuC(NC6H3-2,6-iPr2)2}Yb(μ-Cl)]2 (2) (Scheme 1) was
isolated in 84% yield.
Figure 1. Ball-and-stick plot of [{tBuC(NC6H3-2,6-iPr2)2}Yb(μ-Cl)]2
(2).
Selective oxidation of the hydrido ligand was also performed
in the reaction of 1 with an equimolar amount of a mild one-
electron oxidantdibenzyl disulfide (PhCH2S)2 (toluene, −60
°C). The reaction occurred with H2 evolution and afforded the
related benzyl sulfide Yb(II) complex [{tBuC(NC6H3-2,6-
iPr2)2}Yb(μ-SCH2Ph)]2 (3), which was isolated in 90% yield
(Scheme 2). When the reaction of 1 was carried out with 2
equiv of (PhCH2S)2 or when 3 was treated with (PhCH2S)2
(1:1 molar ratio), oxidation of Yb(II) took place; both reactions
resulted in the formation of the bis(benzyl sulfide) Yb(III)
complex [{tBuC(NC6H3-2,6-iPr2)2}Yb(μ-SCH2Ph)2]2 (4)
(Scheme 2). The yields of 4 in these reactions were 92 and
76%, respectively. The magnetic measurements of complex 4
revealed that the value of the effective magnetic moment at
room temperature is 4.3 μB, which is indicative of a trivalent
oxidation state of the ytterbium atom.6 Successive oxidation of
hydrido and Yb(II) centers in 1 by (PhCH2S)2 unambiguously
demonstrated that in this compound the hydrido ligand is a
stronger reductant than the Yb(II) ion.
Complex 2 was isolated as dark red-brownish moisture- and
air-sensitive crystals. 2 is well soluble in THF, moderately
soluble in toluene or benzene, and poorly soluble in hexane.
According to the NMR spectra and magnetic measurements
complex 2 is diamagnetic. This indicates a divalent state of the
1
ytterbium metal in 2. The H and 13C{1H} NMR spectra
recorded for 2 in C6D6 solution at room temperature exhibit
the set of signals expected for an amidinate ligand. The methyl
and methyne protons of isopropyl groups appear as two
complex multiplets at 1.22−1.37 and 3.19−3.45 ppm,
respectively; a singlet at 1.44 ppm is assigned to the protons
of the tBu group. The aromatic protons of 2,6-diisopropyl-
phenyl groups give rise to a multiplet at 7.01−7.11 ppm. The
presence of signals with characteristic satellites due to coupling
to 171Yb attributed to quaternary tBu carbons (41.8 ppm, s,
171Yb satellites 3JYbC = 25.7 Hz) and NCN (171.5 ppm, s, 171Yb
2
satellites JYbC = 50.1 Hz, NCN) in the 13C{1H} NMR
spectrum of 2 gives evidence for the coordination of the
amidinate ligand to ytterbium.
Crystals of 2 suitable for X-ray analysis were obtained by
slow concentration of a toluene solution at room temperature.
The X-ray study established the order of connectivity of the
Complex 3 is well soluble in aromatic solvents and
moderately soluble in hexane. According to NMR spectroscopy
and magnetic measurements complex 3 is diamagnetic. The 1H
NMR spectrum of 3 in C6D6 exhibits a singlet at 0.89 ppm due
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Scheme 2
Figure 2. Molecular structure of [{tBuC(NC6H3-2,6-iPr2)2}Yb(μ-
SCH2Ph)]2 (3). Thermal ellipsoids are drawn at the 30% probability
level. Hydrogen atoms and isopropyl carbons are omitted for clarity.
Selected distances (Å) and angles (deg): Yb(1)−N(1) = 2.386(4),
Yb(1)−S(1) = 2.7599(12), Yb(1)−S(2) = 2.7694(12), Yb(2)−N(3) =
2.408(4), Yb(2)−S(1) = 2.7622(13), Yb(2)−S(2) = 2.8116(12),
Yb(1)−CArene = 2.723(5)−2.862(5), Yb(1)−AreneCentroid = 2.432,
Yb(2)−CArene = 2.729(5)−2.853(5), Yb(2)−AreneCentroid = 2.440,
Yb(1)−Yb(2) = 4.101(4); Yb(1)−S(1)−Yb(2) = 95.91(4), Yb(1)−
S(2)−Yb(2) = 94.57(4), S(1)−Yb(1)−S(2) = 79.13(4), S(1)−
Yb(2)−S(2) = 78.38(4), N(1)−C(1)−N(2) = 120.6(4), N(3)−
C(30)−N(4) = 121.8(4), AreneCentroid−Yb(1)−N(1) = 91.9, Are-
neCentroid−Yb(2)−N(3) = 91.5.
to the protons of the tBu group. The broad singlet at 0.51 ppm
and a complex multiplet in the region 1.21−1.34 ppm are
assigned to the CH3 protons of isopropyl groups. The
methylene protons of SCH2Ph fragments along with the
methyne protons of isopropyl groups of the amidinate ligand
give rise to a complex multiplet in the region 3.04−3.54 ppm.
The aromatic protons of iPr2C6H3 and SCH2Ph groups appear
in the 1H NMR spectrum as a multiplet in the region 6.90−7.05
ppm. In the 13C{1H} NMR spectrum of 3 the quaternary
carbons of NCN and tBu groups exhibit signals with satellites
3
due to coupling to 171Yb (45.7 ppm, s, JYbC = 45.1 Hz, CMe3;
2
173.9 ppm, s, JYbC = 22.5 Hz, NCN).
Single-crystal samples of 3 suitable for X-ray analysis were
obtained by slow cooling of a concentrated solution in toluene
from 60 °C to room temperature. Complex 3 crystallizes as a
toluene solvate. The molecular structure of 3 is depicted in
Figure 2; the crystal and structure refinement data are given in
Table 1. The X-ray study revealed that 3 adopts a dimeric
structure where two {tBuC(NC6H3-2,6-iPr2)2}Yb fragments are
connected by two μ2-benzyl sulfide groups. It is noteworthy
that the amidinate ligand in 3 retains the κ1-N, η6-arene
coordination mode similar to that in the parent complex 1. The
Yb−N (2.386(4), 2.408(4) Å) and Yb−AreneCentroid (2.432(5),
2.440(5) Å) distances in 3 are slightly longer than those in 1
(Yb−N = 2.329(3) Å; Yb−AreneCentroid = 2.420(4) Å). This
fact obviously reflects the greater steric demand of benzyl
sulfide groups in comparison to hydrido ligands. The Yb−S
distances in 3 fall into the region 2.7599(12)−2.8116(12) Å,
which correspond to the related distances previously reported
for the dimeric Yb(II) thiolate complex [(C4Me4P)Yb(μ-
SPh)(THF)2]2 (Yb−S = 2.789(4)−2.834(4) Å).7 In complex 3,
unlike in [(C4Me4P)Yb(μ-SPh)(THF)2]2, the four-membered
Yb2S2 core is not planar; the value of the dihedral angle
between the planes S(1)−Yb(1)−S(2) and S(1)−Yb(2)−S(2)
is 145.8°. The Yb(1)−Yb(2) distance (4.101(4) Å) in 3 is
substantially shorter in comparison to that in [(C4Me4P)Yb(μ-
SPh)(THF)2]2 (4.596(4) [4.669(4)] Å), where the Yb2S2 core
is planar.
Figure 3. Molecular structure of [{tBuC(NC6H3-2,6-iPr2)2}Yb(μ-
SCH2Ph)2]2 (4). Thermal ellipsoids are drawn at the 30% probability
level. Symmetry transformations used to generate equivalent A atoms:
−x, −y, −z + 1. Hydrogen atoms and 2,6-iPr2C6H3-groups are omitted
for clarity. Selected distances (Å) and angles (deg): Yb(1)−N(1) =
2.291(3), Yb(1)−N(2) = 2.294(3), Yb(1)−S(1) = 2.6998(11),
Yb(1)−S(1a) = 2.7603(10), Yb(1)−S(2) = 2.7716(9), Yb(1)−S(2a)
= 2.7877(9), Yb(1)−Yb(1a) = 3.2862(4), N(1)−C(1) = 1.349(4),
N(2)−C(1) = 1.341(5); N(1)−Yb(1)−N(2) = 57.17(11), S(1)−
Yb(1)−S(1a) = 106.01(3), S(2)−Yb(1)−S(2a) = 107.53(2), S(1)−
Yb(1)−S(2) = 68.65(3), N(1)−C(1)−N(2) = 109.2(3).
a dimeric structure where two {tBuC(NC6H3-2,6-iPr2)2}Yb
moieties are linked by four μ2-benzyl sulfide fragments. The
most important structural feature of 4 is the coordination mode
of the amidinate ligand. In contrast to the κ1-N, η6-arene
coordination mode detected in Yb(II) species 1−3, oxidation of
the ytterbium center to a trivalent state leads to switching to the
“classical” κ1,κ1-N,N-chelating mode characteristic of Ln(III)
Single-crystal samples of 4 suitable for X-ray analysis were
obtained by slow cooling of a concentrated solution in toluene
from 60 °C to room temperature. The molecular structure of 4
is depicted in Figure 3; the crystal and structure refinement
data are given in Table 1. According to the X-ray study 4 adopts
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Scheme 3
amidinates.8 The Yb−N (2.291(3), 2.294(3) Å) and C−N
(1.349(4), 1.341(5) Å) bonds within the YbNCN fragment are
equivalent, indicating a symmetric coordination to the metal
ion with delocalization of the negative charge within the
conjugated amidinate ligand. The Yb−N distances in 4 are
slightly shorter in comparison to the related values measured
for six-coordinated amidinate Yb(III) compounds (2.290(4)−
2.385(4) Å).9 Formerly it was shown that κ1-N, η6-arene
coordination of amidinate and guanidinate ligands bearing
bulky aryl groups by nitrogen atoms is characteristic of Yb(II)
derivatives,4c,10 and the interconversion of κ1-N, η6-arene and
κ1,κ1-N,N coordination modes can be driven by modification of
steric and coordination saturation of the metal. Herein we have
demonstrated that a change of oxidation state of Yb(II) to
Yb(III) leads to switching of the coordination mode of
amidinate ligand from κ1-N, η6-arene to κ1,κ1-N,N. This can
originate from a decrease of ytterbium ion size caused by its
oxidation from Yb(II) to Yb(III)11 as well as from a change of
electronic structure of the Yb ion. The fore-membered cores
Yb(1)S(1)(S1a)Yb(1a) and Yb(1)S(2)S(2a)Yb(1a) in 4 are
planar and adopt a nearly orthogonal orientation (the dihedral
angle between the Yb(1)S(1)(S1a)Yb(1a) and Yb(1)S(2)S-
(2a)Yb(1a) planes is 88.8°). Due to the difference in ionic radii
of Yb(II) and Yb(III) ions in 3 and 4, the Yb−S and Yb−Yb
distances in Yb(III) complex 4 (Yb−S = 2.6998(11)−
2.7877(9) Å; Yb−Yb = 3.2862(4) Å) are shorter in comparison
to the related distances in the Yb(II) complex 3 (Yb−S =
2.7599(12)−2.8116(12) Å; Yb−Yb = 4.101(4) Å).
Disubstituted 1,4-diazabutadienes established a reputation of
mild one- and two-electron oxidants in organolanthanide
chemistry capable of oxidizing Yb(II) to Yb(III).12 This
prompted us to attempt oxidation of the Yb(II) hydrido
complex 1 with [2,6-iPr2C6H3NC(H)C(H)NC6H3-2,6-
iPr2] (DAD). One should mention that the reactivity of
diazabutadienes toward lanthanide hydrides remains unex-
plored. In the case of the Yb(II) hydrido complex one can
conjecture two reaction pathways. The first pathway is
oxidation of the hydrido ligand or of Yb(II), and the second
is addition of the Yb−H bond to the CN bonds of 1,4-
diazabutadiene.
isolation of the mixed-valent ion-pair complex [{tBuC(NC6H3-
2,6-iPr2)2}Yb(DME)2]+[{2,6-iPr2C6H3NC(H)C(H)NC6H3-
2,6-iPr2}2Yb]− (5) (Scheme 3), as shown by X-ray crystallog-
raphy, as brownish green crystals in 23% yield.
C o m p o u n d
5
c r y s t a l l i z e s a s t h e s o l v a t e
5·0.167C6H6·0.167C6H14·0.167C4H8O. The asymmetric unit
of 5 contains three crystallographically independent molecules.
The molecular structures of the cationic and anionic parts of 5
are depicted in Figures 4 and 5 respectively; the crystal and
Figure 4. Molecular structure of the cationic part of [{tBuC(NC6H3-
2,6-iPr2)2}Yb(DME)2]+[{2,6-iPr2C6H3NC(H)C(H)NC6H3-2,6-
iPr2}2Yb]− (5). Thermal ellipsoids are drawn at the 30% probability
level. Hydrogen atoms and isopropyl carbons are omitted for clarity.
Selected distances (Å) and angles (deg): Yb(1D)−N(2D) =
2.349(10), Yb(1D)−N(1D) = 2.417(11), Yb(1D)−O(1D) =
2.406(9), Yb(1D)−O(2D) = 2.450(11), Yb(1D)−O(3D) =
2.468(8), Yb(1D)−O(4D) = 2.526(9), N(1D)−C(1D) = 1.268(16),
N(2D)−C(1D) = 1.47(2); N(1D)−Yb(1D)−N(2D) = 57.0(4),
O(1D)−Yb(1D)−O(2D) = 68.5(3), O(3D)−Yb(1D)−O(4D) =
67.6(3), N(1D)−C(1D)−N(2D) = 112.1(12).
structure refinement data are given in Table 1. The cationic part
of 5 consists of a Yb(II) ion coordinated by one monoanionic
amidinate ligand and two DME molecules. The coordination
mode of the amidinato ligand is κ1,κ1-N,N, similar to that
previously reported for the Yb(II) amidinate complexes
[{tBuC(NC6H3-2,6-iPr2)2}Yb{N(SiMe3)2}(THF)] and
[{tBuC(NC6H3-2,6-iPr2)2}2Yb].4c The main structural distinc-
tion of the cationic part of 5 is a rather unsymmetrical
The reaction of complex 1 with 2 equiv of DAD was carried
out in toluene solution. At 20 °C no reaction was detected in
∼24 h; the starting compounds were recovered from the
reaction mixture. At 50 °C the reaction took place. Removal of
the solvent under vacuum, treatment of the solid residue with
DME, and further recrystallization of the reaction products
from a THF/benzene/hexane (1/1/1) mixture allowed the
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The anionic part of 5 contains an Yb(III) ion coordinated by
two dianionic diazabutadiene ligands. The Yb−N bond
distances (2.174(9)−2.232(7) Å) are comparable with the
related distances found in the Yb(III) complexes with dianionic
enediamido ligands [{2,6-iPr2C6H3NC(H)C(H)NC6H3-2,6-
iPr2}Yb(μ-Cl)(THF)2]2 (2.235(5), 2.209(5) Å)14 and
[(C5Me4R)Yb{2,6-iPr2C6H3NC(R)C(R)NC6H3-2,6-iPr2}]
(R = Me, 2.136(3) and 2.145(3) Å; R = H, 2.141(4) and
2.148(3) Å)15 and are indicative of the trivalent state of
ytterbium. The dianionic diazabutadiene ligands are coordi-
nated to ytterbium in an η4 fashion. Along with two covalent
Yb−N bonds (2.174(9)−2.232(7) Å),16 short Yb−C contacts
(2.635(10)−2.684(9) Å) are also found in 5. The geometry of
the planar NCCN fragments (deviation from the plane −0.028
Å) in 5 is consistent with the dianionic character of the
diazabutadiene ligand. The N−C bonds in the diazabutadiene
dianion of 5 (1.412(12), 1.440(14) Å and 1.390(12), 1.447(12)
Å) are substantially elongated, whereas the C−C bonds
(1.337(15) and 1.363(15) Å) are shortened, relative to the
NC (1.266(3) Å) and C−C bond lengths (1.467(5) Å) in
the free diazabutadiene molecule.17 The C−C bond lengths are
close to the values of CC double-bond lengths.13 The CC
bond of the doubly reduced ene-diamido moiety NCCN also
participates in metal−ligand bonding. η2 coordination of the
ene-diamido moiety to the Yb atom results in short Yb−C
contacts (2.669(10), 2.672(8) Å and 2.684(9), 2.635(10) Å).
Unfortunately our attempts to isolate other reaction products
failed. The formation of 5 obviously results from the oxidation
of both hydride and Yb(II) ions and a ligand redistribution
reaction.
Recently we reported on the synthesis, structure, and
reactivity of trinuclear alkyl hydrido and cationic hydrido
clusters supported by bulky amidopyridinate ligands (Ap*)
which turned out to be efficient catalysts for ethylene
polymerization.18 We found that the reaction of [Ap*Yb-
(CH2SiMe3)2(THF)] with 2 equiv of PhSiH3 afforded
[(Ap*Yb)3(μ2-H)3(μ3-H)2(CH2SiMe3)(THF)2].18a In order
to enlarge the series of alkyl hydrido or polyhydrido clusters,
we attempted the reaction of the ytterbium(III) bis(alkyl)
complex supported by a bulky amidinate ligand [{tBuC-
(NC6H3-2,6-iPr2)2}Yb(CH2SiMe3)2(THF)] (6) with PhSiH3
(1:2 molar ratio). Complex 6 was prepared by the reaction of
[(Me3SiCH2)3Yb(THF)2] with the amidine [tBuC(NHC6H3-
2,6-iPr2)(NC6H3-2,6-iPr2)] in THF at 0 °C and was isolated in
76% yield (Scheme 4).
Figure 5. Molecular structure of the anionic part of [{tBuC(NC6H3-
2,6-iPr2)2}Yb(DME)2]+[{2,6-iPr2C6H3NC(H)C(H)NC6H3-2,6-
iPr2}2Yb]− (5). Thermal ellipsoids are drawn at the 30% probability
level. Hydrogen atoms of diisopropylphenyl fragments and isopropyl
carbons are omitted for clarity. Selected distances (Å) and angles
(deg): Yb(1A)−N(1A) = 2.197(8), Yb(1A)−N(2A) = 2.232(7),
Yb(1A)−N(3A) = 2.188(7), Yb(1A)−N(4A) = 2.174(9), Yb(1A)−
C(1A) = 2.669(10), Yb(1A)−C(2A) = 2.672(8), Yb(1A)−C(27A) =
2.684(9), Yb(1A)−C(28A) = 2.635(10), N(1A)−C(1A) = 1.412(12),
N(2A)−C(2A) = 1.440(14), N(3A)−C(27A) = 1.390(12), N(4A)−
C(28A) = 1.447(12), C(1A)−C(2A) = 1.337(15), C(27A)−C(28A)
= 1.363(15); N(1A)−Yb(1A)−N(2A) = 83.8(3), N(4A)−Yb(1A)−
N(3A) = 86.1(3).
coordination mode of the amidinate ligand. Thus, one Yb−N
bond (2.349(10) Å) is noticeably shorter in comparison to the
second bond (2.417(11) Å). For comparison the Yb−N bond
distances in related amidinate Yb(II) complexes are as follows:
[{tBuC(NC6H3-2,6-iPr2)2}Yb{N(SiMe3)2}(THF)], 2.377(3)
and 2.378(3) Å; [{tBuC(NC6H3-2,6-iPr2)2}2Yb], 2.363(4)−
2.398(4) Å. Nevertheless, the Yb−N distances in the cationic
part of 5 give evidence for the divalent state of the ytterbium
atom. On the other hand, the bonding situation within the
NCN fragment in 5 is rather unusual for an amidinate ligand.
The length of one of C−N bond (1.268(16) Å) is indicative of
its double-bond character, while the second bond is much
longer (1.47(2) Å) and can be considered as a single bond.13
Thereby no negative charge delocalization takes place in the
NCN fragment and it can be classified as an amido-imino
ligand.
Bis(alkyl) complex 6 is extremely air and moisture sensitive
but can be stored under vacuum in a crystalline state or in
solution for several weeks without any traces of decomposition.
6 is well soluble in toluene and THF and moderately soluble in
hexane. The X-ray crystal study revealed that complex 6 is
monomeric. The molecular structure of 6 is depicted in Figure
Scheme 4
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6; the crystal and structure refinement data are given in Table 1.
The coordination environment of the ytterbium atom is made
which affords Yb(II) species [(TpMe2)2Yb]. Thus, one can
conclude that the balance of redox properties in the couple
Yb(III/II)−hydrido ligand is very subtle and can be influenced
by the ancillary ligand environment.
In order to evaluate the basicity/acidity of the Yb(II)−H
bond, the reaction of 1 with an equimolar amount of Ph2PH
was carried out.22 The reaction occurs in toluene solution at 0
°C with H2 evolution and formation of a dimeric complex in
which only one hydrogen ligand is substituted by phosphido
group, [{tBuC(NC6H3-2,6-iPr2)2}Yb(μ-H)(μ-PPh2)Yb{tBuC-
(NC6H3-2,6-iPr2)2}] (7) (Scheme 5). Complex 7 does not
react with another 1 equiv of Ph2PH, even at 50 °C.
Scheme 5
Figure 6. Molecular structure of [{tBuC(NC6H3-2,6-iPr2)2}Yb-
(CH2SiMe3)2(THF)] (6). Thermal ellipsoids are drawn at the 30%
probability level. Hydrogen atoms are omitted for clarity. Selected
distances (Å) and angles (deg): Yb(1)−N(1) = 2.3145(19), Yb(1)−
N(2) = 2.3295(19), Yb(1)−C(30) = 2.331(3), Yb(1)−C(34) =
2.332(2), Yb(1)−O(1) = 2.3134(17), N(1)−C(1) = 1.345(3), N(2)−
C(1) = 1.333(3); N(1)−Yb(1)−N(2) = 56.45(7), C(30)−Yb(1)−
C(34) = 108.53(10), N(2)−C(1)−N(1) = 110.2(2).
Complex 7 is well soluble in aromatics and moderately
soluble in hexane. The single-crystal samples of 7 suitable for X-
ray analysis were obtained by slow concentration of a hexane
solution at room temperature. The molecular structure of 7 is
depicted in Figure 7; the crystal and structure refinement data
up of two nitrogen atoms of the chelating amidinato ligand, by
two carbon atoms of alkyl groups, and by the oxygen atom of
the coordinated THF molecule. The amidinate ligand in 6 is
coordinated to the ytterbium atom in a κ1,κ1-N,N fashion
common for lanthanide(III) complexes. The Yb−N bonds have
similar values (2.3145(19), 2.3295(19) Å), reflecting the
symmetric coordination of the amidinate ligand. The C−N
bond lengths (1.345(3), 1.333(3) Å) within the NCN fragment
are equivalent. The Yb−C bond lengths in 6 (2.331(3) and
2.332(2) Å) are very close to the values in previously reported
Yb(III) bis(alkyl) species [(C5 Me4 SiMe3 )Yb-
(CH2SiMe3)2(THF)] (2.336(4), 2.345(4) Å),19a [{2-(2,6-
Me2C6H3N)-C6H4PPh2}Yb(CH2SiMe3)2(THF)] (2.357(3),
2.328(3) Å),19b and [(TpMe2)Yb(CH2SiMe3)2(THF)]
(2.373(2), 2.377(2) Å).19c
To our great surprise we found that, unlike [Ap*Yb-
(CH2SiMe3)2(THF)], the reaction of 6 with 2 equiv of
PhSiH3 (toluene, 0 °C) does not afford the desired Yb(III)
polyhydrido cluster supported by an amidinate ligand but
occurs with reduction of the ytterbium atom to a divalent state
and evolution of H2, resulting in the formation of complex 1
(Scheme 4). Complex 1 was isolated in 84% yield. Formation
of 1 can only be rationalized by the intramolecular reduction of
the Yb(III) ion by hydrido ligand to Yb(II).20 The reaction of
equimolar amounts of 6 and PhSiH3 under similar conditions
does not allow for the synthesis of an alkyl hydrido Yb(III)
complex coordinated by an amidinate ligand but results in a
mixture of starting bis(alkyl) complex 6 and Yb(II) hydride 1,
which were isolated in 35 and 40% yields, respectively.
Figure 7. Molecular structure of [{tBuC(NC6H3-2,6-iPr2)2}Yb(μ-
H)(μ-PPh2)Yb{tBuC(NC6H3-2,6-iPr2)2}] (7). Thermal ellipsoids are
drawn at the 30% probability level. Symmetry transformations used to
3
generate equivalent A atoms: −x, y, −z + /2. Hydrogen atoms of
amidinate and diphenylphosphine ligand and isopropyl carbons are
omitted for clarity. Selected distances (Å) and angles (deg): Yb(1)−
N(1) = 2.3838(19), Yb(1)−P(1) = 2.8981(7), Yb(1)−H(1) =
2.22(4), Yb(1)−Yb(1A) = 3.7695(2), Yb(1)−CArene = 2.709(2)−
2.874(3), Yb(1)−AreneCentroid = 2.438, N(1)−C(1) = 1.358(3),
N(2)−C(1) = 1.316(3); Yb(1)−P(1)−Yb(1A) = 81.13(3), Yb(1)−
H(1)−Yb(1A) = 116.5(4), P(1)−Yb(1)−H(1) = 81.2(4), N(2)−
C(1)−N(1) = 120.1(2), AreneCentroid−Yb(1)−N(1) = 92.7.
are given in Table 1. According to the X-ray analysis complex 7
is dimeric, where two {tBuC(NC6H3-2,6-iPr2)2}Yb moieties are
linked by one μ-hydrido and one μ-diphenylphosphido ligand.
The four-membered fragment Yb−H−Yb−P is planar, similar
to that in the parent hydrido complex 1. The Yb−Yb distance
in 7 is 3.7695(2) Å and is expectedly longer in comparison to
that in 1 (3.3553(4) Å). The bulkier μ-diphenylphosphido
ligand affects a reciprocal orientation of the {tBuC(NC6H3-2,6-
To date only three Yb(III) polyhydrido complexes supported
by bulky amidopyridinate ([(Ap*Yb)3(μ2-H)3(μ3-
H)2(CH2SiMe3)(THF)2]18b) or tris(pyrazolyl)borate ligands
([(TpH2)Yb(μ-H)2]6,21 [(TpMe2)Yb(μ-H)2]421) are known.
Among these complexes only the last one demonstrated a
tendency to undergo a reductive ligand redistribution reaction
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iPr2)2}Yb fragments. Thus, in 1 the η6-coordinated aromatic
rings are coplanar and two {tBuC(NC6H3-2,6-iPr2)2}Yb are
oriented trans relative to the Yb2H2 core, while in 7 the value of
the dihedral angle between the planes of the η6-coordinated
aromatic rings is 32.3°. The Yb−P bond lengths in 7
(2.8981(7) Å) are comparable with the values previously
published for Yb(II) phosphido complexes: [{Me2Si(C5Me4)-
(PC6H2-2,4,6-tBu3)}Yb(THF)3] (2.851(4) Å),23a [Yb{(μ-
PtBu2)2Li(THF)2}2] (2.948(1)−2.985(1) Å).23b
oxidation of both Yb(II) and hydrido centers and the formation
of the Yb(III) complex [{[tBuC(NC6H3-2,6-iPr2)2]Yb(μ-
SCH2Ph)2}2] (4). Complex 4 can be also synthesized by
oxidation of 3 with an equimolar amount of (SCH2Ph)2. We
found that the κ1-amido, η6-arene coordination mode of the
amidinate ligand is typical only for Yb(II) species, while
oxidation of the metal center results in switching to “classical”
κ1,κ1-N,N-chelating coordination. Comparison of the results of
the reactions of [LYb(CH2SiMe3)2(THF)] (L = Ap*, {tBuC-
(NC6H3-2,6-iPr2)2}) with PhSiH3 (1:2 molar ratio) drove us to
a conclusion that the balance of reductive properties in the
Yb(II/III)−hydrido anion couple is flexible and can be
influenced by tuning the nature of the ancillary ligand bound
to ytterbium. Reaction of 1 with [2,6-iPr2C6H3NC(H)C-
(H)NC6H3-2,6-iPr2] was found to result in oxidation of the
hydrido ligand and ytterbium ion and to afford the mixed-valent
ion-pair complex [{tBuC(NC6H3-2,6-iPr2)2}Yb(DME)2]+[{2,6-
iPr2C6H3NC(H)C(H)NC6H3-2,6-iPr2}2Yb]− (5). It was
found that the σ-bond metathesis reaction of 1 with Ph2PH,
regardless of the reagent ratio, occurs via substitution of one
hydrido ligand. The reaction afforded the first mixed-ligand
hydrido phosphido Yb(II) species, [{tBuC(NC6H3-2,6-iPr2)2}-
Yb(μ-H)(μ-PPh2)Yb{tBuC(NC6H3-2,6-iPr2)2}] (7).
In the 1H NMR spectrum of 7 recorded in benzene-d6 at 293
K the hydrido ligand appears as a doublet at 8.25 ppm due to
2
coupling with 31P nuclei (d, JPH = 52 Hz) (Figure 8). This
EXPERIMENTAL SECTION
■
All experiments were performed in evacuated tubes, using standard
Schlenk-tube or glovebox techniques, with rigorous exclusion of traces
of moisture and air. After drying over KOH, THF and DME were
purified by distillation from sodium/benzophenone ketyl and hexane,
benzene, and toluene by distillation from sodium/triglyme benzophe-
none ketyl prior to use. C6D6 was dried with sodium/benzophenone
ketyl and condensed under vacuum prior to use. [tBuC(NHC6H3-2,6-
iPr2)(NC6H3-2,6-iPr2)],26 [2,6-iPr2C6H3NC(H)C(H)NC6H3-
2,6-iPr2] (DAD),17 and [(Me3SiCH2)3Yb(THF)2]27 were prepared
according to literature procedures. PhSiH3 was purchased from
Aldrich, stored over CaH2, and condensed under vacuum prior to use.
CuCl and (PhCH2S)2 were purchased from Aldrich and were used
without any additional purification. NMR spectra were recorded on a
1
1
Figure 8. (A) H NMR spectrum of 7 (C6D6, 293 K), (B) H{171Yb}
NMR spectrum of 7 (C6D6, 293 K), and (C) 1H{31P} NMR spectrum
of 7 (C6D6, 293 K).
signal also has characteristic satellites reflected in the coupling
of the hydrido ligand with 171Yb nuclei (1JYbH = 486 Hz)
(compare the following: 1, 1JYbH = 460 Hz;4c [(TptBu,Me)YbH]2,
1
Bruker Avance-II 400 MHz spectrometer. Chemical shifts for H and
13C spectra were referenced internally using the residual solvent
resonances and are reported relative to TMS. The 171Yb chemical shift
was referenced internally and is reported relative to (C5Me5)2Yb-
(THF)2 (1 M solution in THF). Lanthanide metal analysis was carried
out by complexometric titration. The C, H, N elemental analysis was
carried out in the microanalytical laboratory of the IOMC.
1JYbH = 369 Hz;4a [(DIPPnacnac)YbH(THF)]2, JYbH = 398
1
Hz4b). The chemical shift of the signal for the hydrido ligand
for 7 is shifted to low field in comparison to that for 1 (7.74
ppm)4c but shifted upfield in comparison to those for the
related Yb(II) hydrides in an N,N-coordination environment:
[{(TptBu,Me)YbH}2] (10.5 ppm)4a and [{(DIPPnacnac) YbH-
Synthesis of [{tBuC(NC6H3-2,6-iPr2)2}Yb(μ-Cl)]2 (2). A suspen-
sion of CuCl (0.046 g, 0.466 mmol) in 5 mL of toluene was added to a
solution of 1 (0.277 g, 0.233 mmol) in toluene (25 mL) at −60 °C
with stirring. The reaction mixture was warmed to room temperature
and was stirred for an additional 12 h. The Cu precipitate was removed
by filtration. Slow concentration of a toluene solution at room
temperature afforded crystals of 2 (0.246 g, 84% yield). 1H NMR (400
MHz, C6D6, 293 K): 1.22−1.37 (complex m, 48H, CH3 iPr), 1.44 (s,
(THF)}2] (9.92 ppm).4b The H NMR spectrum of 7 gives
1
evidence that a dimeric structure is retained in benzene-d6
solution (Figure 8). The 31P{1H} NMR spectrum of 7 presents
a singlet at 30.9 ppm with satellites due to coupling to 171Yb
(1JYbP = 810 Hz),24 while in the 171Yb{1H} NMR spectrum a
doublet at 1149 ppm (d, JYbP = 810 Hz) is observed.25
1
t
18H, CH3 tBu), 3.19−3.45 (complex m, 8H, CH iPr), 6.94 (d, 3JHH
=
Surprisingly, complex 1 does not react with BuCCH in
toluene, even at 50 °C (72 h).
8.1 Hz, 2H, CH Ar), 7.01−7.11 (complex m, 10H, CH Ar), 7.23 (d,
3JHH = 7.4 Hz, 2H, CH Ar) ppm. 13C{1H} NMR (100 MHz, C6D6, 293
K): 20.0 (br s, CH3 iPr), 21.2 (br s, CH3 iPr), 23.4 (br s, CH3 iPr),
25.7 (s, CH3 iPr), 28.3 (br s, CH iPr), 29.7 (s, CH iPr), 31.2 (s, CH3
tBu), 41.8 (s, CMe3, with 171Yb satellites 3JYbC = 25.7 Hz), 123.0 (br s,
CH Ar), 123.8 (br s, CH Ar), 124.7 (br s, CH Ar), 142.5 (br s, C Ar),
143.4 (br s, C Ar), 144.3 (br s, C Ar), 147.6 (br s, C Ar), 171.5 (s, with
CONCLUSIONS
■
CuCl and (PhCH2S)2 turned out to be reagents which allow for
selective competitive oxidation of one of two redox-active
centers in the Yb(II) hydride [{tBuC(NC6H3-2,6-iPr2)2}Yb(μ-
H)]2. Our studies on the oxidation of 1 with CuCl and
(PhCH2S) (1:1 molar ratio) elucidated that the hydrido anion
in 1 is a stronger reductant than Yb(II). The reactions result in
evolution of H2 and afford the dimeric Yb(II) species
[{tBuC(NC6H3-2,6-iPr2)2}Yb(μ-X)]2 (X = Cl (2), SCH2Ph
(3)). Reaction of 1 with 2 equiv of (PhCH2S)2 leads to
2
171Yb satellites JYbC = 50.1 Hz, NCN) ppm. Anal. Calcd for
C58H86Cl2N4Yb2 (1256.34 g/mol): C, 55.45; H, 6.90; N, 4.46; Yb,
27.55. Found: C, 55.50; H, 7.00; N, 4.36; Yb, 27.42.
Synthesis of [{tBuC(NC6H3-2,6-iPr2)2}Yb(μ-SCH2Ph)]2 (3). A
toluene solution (5 mL) of (PhCH2S)2 (0.040 g, 0.163 mmol) was
added to a solution of 1 (0.194 g, 0.163 mmol) in toluene (25 mL) at
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Table 1. Main Crystallographic Data and Structure Refinement Details for 3−7
3
4
5
6
7
formula
C72H100N4S2Yb2·C7H8)
C86H114N4S4Yb2
(C52H72N4Yb),
C41H73N2OSi2Yb
C70H97N4PYb2
(C37H63N2O4Yb)·1/6C6H6·1/6C6H14·1/6C4H8O
Mr
1523.89
1678.13
1738.51
839.23
1371.57
cryst size, mm3
0.2 × 0.2 × 0.1
100(2)
0.2 × 0.2 × 0.04 0.17 × 0.16 × 0.03
100(2)
0.35 × 0.30 × 0.15 0.2 × 0.1 × 0.05
100(2)
T, K
100(2)
triclinic
100(2)
cryst syst
space group
a, Å
triclinic
monoclinic
P21/n
monoclinic
P21/c
monoclinic
C2/c
P1
̅
P1
̅
12.7391(3)
14.3319(3)
21.0538(6)
75.308(2)
82.800(2)
89.461(2)
3687.90(17)
2
15.4161(4)
17.4607(4)
15.9777(4)
90
20.671(2)
26.709(3)
29.791(3)
111.023(2)
106.486(3)
97.723(3)
14200(3)
6
11.9708(7)
13.2488(7)
27.7865(16)
90
15.2958(2)
21.1987(3)
19.8807(3)
90
b, Å
c, Å
α, deg
β, deg
γ, deg
114.938(3)
90
93.5430(10)
90
90.602(1)
90
cell vol, Å3
3899.81(19)
2
4398.5(4)
4
6446.00(16)
4
Z
D
calcd, g/cm3
1.372
1.429
1.220
1.267
1.413
μ, mm−1
2.620
2.537
2.011
2.211
2.951
F000
1564
1724
5430
1756
2800
2θ range, deg
index ranges
2.94−26.00
−15 ≤ h ≤ 15
−17 ≤ k ≤ 17
−25 ≤ l ≤ 25
55204
3.04−30.00
−21 ≤ h ≤ 21
−24 ≤ k ≤ 24
−22 ≤ l ≤ 22
79002
1.34−25.97
−23 ≤ h ≤ 25
−28 ≤ k ≤ 32
−36 ≤ l ≤ 31
84342
2.13−26.00
−14 ≤ h ≤ 14
−16 ≤ k ≤ 16
−34 ≤ l ≤ 34
37006
3.18−30.00
−21 ≤ h ≤ 21
−29 ≤ k ≤ 29
−27 ≤ l ≤ 27
65032
no. of rflns collected
no. of indep rflns
Rint
14080
11337
54635
8623
9396
0.0722
0.1436
0.2078
0.0307
0.0958
completeness to θ, %
97.1
99.6
98.1
99.8
99.9
no. of data/restraints/
params
14080/160/796
11337/0/444
54635/1083/2530
8623/26/496
9396/0/360
GOF
1.039
0.945
0.823
1.058
1.037
final R indices (I >
2σ(I))
R1 = 0.0575
R1 = 0.0500
R1 = 0.1105
R1 = 0.0294
R1 = 0.0409
wR2 = 0.1216
R1 = 0.0759
wR2 = 0.1281
wR2 = 0.0667
R1 = 0.0910
wR2 = 0.0742
1.695/−1.847
wR2 = 0.1754
R1 = 0.3462
wR2 = 0.2314
1.552/−1.523
wR2 = 0.0672
R1 = 0.0384
wR2 = 0.0702
1.499/−0.855
wR2 = 0.0572
R1 = 0.0682
wR2 = 0.0613
1.087/−1.142
R indices (all data)
largest diff peak/hole, e 4.079/−1.503
Å3
−60 °C. The reaction mixture was stirred for 2 h at −60 °C and then
was warmed to room temperature and stirred for an additional 2 h.
After removal of toluene, the solid residue was dissolved in hexane.
Slow concentration of the resulting solution at room temperature
Method B. A toluene solution (5 mL) of (PhCH2S)2 (0.031 g,
0.124 mmol) was added to a solution of 3 (0.178 g, 0.124 mmol) in
toluene (10 mL) at room temperature. The reaction mixture was
stirred for 3 h. Slow concentration of the resulting solution at room
temperature afforded bright yellow crystals of 4 (0.159 g, 76% yield).
Reaction of 1 with [2,6-iPr2C6H3NC(H)C(H)NC6H3-2,6-iPr2].
Synthesis of [{tBuC(NC6H3-2,6-iPr2)2}Yb(DME)2]+[{2,6-
iPr2C6H3NC(H)C(H)NC6H3-2,6-iPr2}2Yb]− (5). A solution of
DAD (0.167 g, 0.443 mmol) in toluene (5 mL) was added to a
solution of 1 (0.263 g, 0.221 mmol) in toluene (25 mL) at room
temperature. The reaction mixture was heated to 50 °C and was stirred
for 12 h. The solvent was removed under vacuum, and the solid
residue was treated with DME (5 mL). The resultant solution was
warmed to 50 °C for 1 h, the solvent was removed under vacuum, and
the solid residue was dissolved in a THF/benzene/hexane (1/1/1)
mixture (15 mL). Slow concentration of the resulting solution at room
temperature afforded 5 (0.086 g, 23% yield). Anal. Calcd for
C89H135N6O4Yb2 (1697.63 g/mol): C, 62.91; H, 8.01; N, 4.95; Yb,
20.37. Found: C, 63.29; H, 8.53; N, 4.71; Yb, 19.94.
Synthesis of [{tBuC(NC6H3-2,6-iPr2)2}Yb(CH2SiMe3)2(THF)] (6).
A THF solution (10 mL) of [tBuC(NHC6H3-2,6-iPr2)(NC6H3-2,6-
iPr2)] (0.498 g, 1.183 mmol) was added to a solution of
(Me3SiCH2)3Yb(THF)2 (0.685 g, 1.183 mmol) in THF (10 mL) at
0 °C. The reaction mixture was stirred for 2 h and then was warmed to
room temperature and stirred for 12 h. THF was removed under
vacuum, and the solid residue was dissolved in hexane (25 mL). Slow
concentration of the resulting solution at room temperature afforded
1
afforded red-purple crystals of 3 (0.211 g, 90% yield). H NMR (400
MHz, C6D6, 293 K): 0.51 (br s, 12H, CH3 iPr), 0.89 (s, 18H, CH3
tBu), 1.21−1.34 (complex m, 36H, CH3 iPr), 3.04−3.54 (complex m,
12H, CH iPr and SCH2), 6.90−7.05 (complex m, 22H, CH Ar) ppm.
13C{1H} NMR (100 MHz, C6D6, 293 K): 21.5 (br s, CH3 iPr), 21.6
(br s, CH3 iPr), 25.1 (br s, CH3 iPr), 26.4 (br s, CH3 iPr), 28.3 (br s,
CH iPr), 28.4 (br s, CH iPr), 30.2 (s, CH3 tBu), 34.6 (s, SCH2), 45.7
3
(s, with 171Yb satellites JYbC = 45.1 Hz, CMe3), 122.5 (s, CH Ar),
122.8 (s, CH Ar), 125.8 (s, CH Ar), 128.2 (s, CH Ar), 128.4 (s, CH
Ar), 129.0 (s, CH Ar), 140.1 (br s, C Ar), 140.5 (br s, C Ar), 141.7 (s,
2
C Ar), 145.8 (s, C Ar), 173.9 (s, with 171Yb satellites JYbC = 22.5 Hz,
NCN) ppm. Anal. Calcd for C72H100N4S2Yb2 (1431.83 g/mol): C,
60.40; H, 7.04; N, 3.91; Yb, 24.17. Found: C, 59.73; H, 6.89; N, 3.86;
Yb, 24.12.
Synthesis of [{tBuC(NC6H3-2,6-iPr2)2}Yb(μ-SCH2Ph)2]2 (4).
Method A. A toluene solution (5 mL) of (PhCH2S)2 (0.102 g,
0.413 mmol) was added to a solution of 1 (0.245 g, 0.206 mmol) in
toluene (25 mL) at −60 °C. The reaction mixture was stirred for 2 h at
−60 °C and then warmed to room temperature and stirred for an
additional 2 h. Slow concentration of the resulting solution at room
temperature afforded bright yellow crystals of 4 (0.319 g, 92% yield).
Anal. Calcd for C86H114N4S4Yb2 (1678.22 g/mol): C, 61.55; H, 6.85;
N, 3.34; Yb, 20.62. Found: C, 61.68; H, 6.97; N, 3.14; Yb, 20.51.
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Organometallics
Article
orange-yellow crystals of 6 (0.754 g, 76% yield). Anal. Calcd for
C41H73N2OSi2Yb (839.26 g/mol): C, 58.68; H, 8.77; N, 3.34; Yb,
20.62. Found: C, 59.29; H, 8.93; N, 3.27; Yb, 20.44.
(CrysAlis Pro)29 (3, 4, and 7) were used to perform area-detector
scaling and absorption corrections. Crystallographic data and
collection and refinement details are shown in Table 1, and the
corresponding CIF files are available as Supporting Information.
CCDC-918719 (3), CCDC-918720 (4), CCDC-918721 (5), CCDC-
918722 (6), and CCDC-918723 (7) also contain 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/.
Reaction of 6 with PhSiH3 (1:2 Molar Ratio). PhSiH3 (0.109 g,
1.003 mmol) was added to a solution of 6 (0.428 g, 0.501 mmol) in
toluene (20 mL) at 0 °C. The reaction mixture was stirred for 2 h and
then was warmed to room temperature and stirred for 12 h. Toluene
was removed under vacuum, and the solid residue was washed with
hexane (10 mL). Further recrystallization of the solid residue from
toluene by slow concentration at 50 °C resulted in formation of black
crystals of 1 (0.250 g, 84%). 1H NMR (400 MHz, C6D6, 293 K): 0.91
(s, 18H, CH3 tBu), 1.22−1.37 (complex m, 48H, CH3 iPr), 3.24−3.55
(complex m, 8H, CH iPr), 6.93−7.10 (complex m, 12H, CH Ar), 7.74
ASSOCIATED CONTENT
■
S
* Supporting Information
1
(s, 2H, with 171Yb satellites, JYbH = 460 Hz) ppm. Anal. Calcd for
Figures giving NMR spectra and CIF files giving crystallo-
graphic data for the structures determined in this paper. This
material is available free of charge via the Internet at http://
pubs.acs.org.
C58H88N4Yb2 (1187.45 g mol−1): C, 58.67; H, 7.47; N, 4.72; Yb, 29.15.
Found: C, 59.05; H, 7.72; N, 4.46; Yb, 28.95.
Reaction of 6 with PhSiH3 (1:1 Molar Ratio). PhSiH3 (0.065 g,
0.599 mmol) was added to a solution of 6 (0.503 g, 0.599 mmol) in
toluene (20 mL) at 0 °C. The reaction mixture was stirred for 2 h and
then was warmed to room temperature and stirred for 12 h. Toluene
was removed under vacuum, and the solid residue was extracted with
hexane (15 mL). The solution was separated from the solid residue by
decantation. Slow concentration of the resulting hexane solution at
room temperature afforded orange-yellow crystals of 6 (0.176 g, 35%
yield). Complex 6 was identified by microanalysis. Recrystallization of
the solid residue from toluene by slow concentration at 50 °C afforded
1 (0.142 g, 40% yield). Complex 1 was identified by its spectral
characteristics and microanalysis.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: trif@iomc.ras.ru.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by the Russian Foundation for Basic
Research (Grant No 12-03-31865) and Ministry of Science and
Innovations of N. Novgorod region (Grant No 11-03-97030-
p), Grant of President of Russian Federation for young
scientists (Grant No MK-4908.2012.3, DML), The Ministry of
education and science of Russian Federation (project No.
8445).
Synthesis of [{tBuC(NC6H3-2,6-iPr2)2}Yb(μ-H)(μ-PPh2)Yb-
{tBuC(NC6H3-2,6-iPr2)2}] (7). A solution of Ph2PH (0.100 g, 0.542
mmol) in toluene (5 mL) was slowly added to a solution of 1 (0.322 g,
0.271 mmol) in toluene (25 mL) at 0 °C. The reaction mixture was
stirred at this temperature for 1 h and then warmed to room
temperature and stirred for 1 h. Recrystallization of the solid residue
from a toluene/hexane (1/1) mixture by slow concentration at room
1
temperature resulted in the formation of 7 (0.180 g, 82% yield). H
NMR (400 MHz, C6D6, 293 K): 1.21−1.34 (complex m, 48H, CH3
iPr), 1.50 (s, 18H, CH3 tBu), 3.23−3.36 (complex m, 8H, CH iPr),
6.57 (t, 3JHH = 7.6 Hz, 2H, p-CH PPh), 6.65 (t, 3JHH = 7.6 Hz, 4H, o-
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