Construction of polymeric and oligomeric lanthanide(III) thiolates from preformed complexes [(TMS)2N]3Ln(μ-Cl)Li(THF) 3 (Ln = Pr, Nd, Sm; (TMS)2N = Bis(trimethylsilyl)amide)

Article abstract of DOI:10.1021/ja043415j

The complex [{(TMS)₂N}₄(μ₄-Cl)Sm₄(μ-SPh)₄(μ₃-Cl)Li(THF)] has been formed by protonolysis of [(Me₃Si)₂N]₃Sm(μ-Cl)Li(THF)₃ with 1 equiv of HSPh, which contains a square array of Sm(III) ions connected by a central μ₄-Cl ligand. The edges of the square Sm₄ array are bridged by four μ₃-Cl and four μ-SPh ligands. The four Sm atoms and Li atom are connected by four μ₃-Cl ligands. Copyright

Full text of DOI:10.1021/ja043415j

Published on Web 01/08/2005
Construction of Polymeric and Oligomeric Lanthanide(III) Thiolates from
Preformed Complexes [(TMS)2N]3Ln(µ-Cl)Li(THF)3 (Ln ) Pr, Nd, Sm; (TMS)2N
) Bis(trimethylsilyl)amide)
Hong-Xi Li,† Zhi-Gang Ren,† Yong Zhang,† Wen-Hua Zhang,† Jian-Ping Lang,*,†,‡ and Qi Shen†
School of Chemistry and Chemical Engineering, Suzhou UniVersity, 1 Shizi Street, Suzhou 215006, Jiangsu, China,
and State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry,
Chinese Academy of Sciences, Shanghai 200032, China
Received November 1, 2004; E-mail: jplang@suda.edu.cn
As in past decades, much interest in lanthanide thiolates continues
to be motivated by their chemistry1 and their potential applications
in advanced materials2 and catalysis.3 Several synthetic approaches
to lanthanide thiolates, including metathesis of a lanthanide halide
with an alkali metal thiolate,4 oxidative addition of organic disulfide
RSSR to lanthanide(II) complexes5 or lanthanide metals under the
presence of catalyst,6 and the reactions of lanthanide thiolates with
elemental sulfur,7 have been developed. However, an additional
approach, protonolysis of preformed lanthanide complexes with
Figure 1. Perspective view of a section of the polymeric chain of 4 with
labeling scheme and 50% probability. All hydrogen atoms are omitted for
clarity.
thiols,8 has been less explored for synthesizing polymeric or
oligomeric lanthanide thiolate complexes. Lanthanide tri(dimethyl-
silyl)amide complexes, [Ln(N(TMS)2)3], could serve as suitable
precursors for such a protonolysis since thiol has an acidity stronger
than that of HN(TMS)2 and may protonate and remove the
(TMS)2N- anion ligated on Ln centers.8 For example, the rare earth
Si)2N)2Pr(µ′-Cl)Li(THF)3}(µ-Cl)]2 (7), in 11% yield. The similar
reaction of 2 with equimolar HSPh, followed by a similar workup,
gave rise to an anionic tetranuclear cluster, 5‚C6H6 (39% yield),
mixed with the unreacted precursor 2. Intriguingly, the analogous
reaction of 3 with equimolar HSPh generated a neutral tetranuclear
cluster 6 in 30% yield coupled with a side-product, [{((TMS)2N)2Sm-
(µ′-Cl)Li(THF)2}(µ3-Cl)]2 (8) (9% yield)11 (see Supporting Informa-
complex [Yb(N(TMS)2)2] can be acidified with 2 equiv of HSC6H2-
But3-2,4,6 to form [Yb(SC6H2But3-2,4,6)2].8b Intriguingly, treatment
of [Ln(N(TMS)2)3] with high concentrations of ButSH (3 equiv)
led to the rapid formation of insoluble lanthanide thiolate polymeric
material.8d Previously, the ways to tackle this problem were to use
a low concentration of ButSH (1 equiv) at lower temperature,4a to
dissolve the insoluble material into strong donor solvents,8d to
directly use very bulky thiol (e.g., HSC6H2But3-2,4,68b or HESi-
(TMS)3 (E ) Se, Te)),9a,b or to use slightly excess thiol plus
noncoordinating tertiary amine in aprotic solvents.9c
tion). As discussed below in this paper, the Li+ and/or Cl- were
incorporated into the polymeric backbone or cluster frameworks,
which guarantee the formation of the soluble compounds 4-6.
However, when 1-3 were treated with 2 equiv of HSPh, the
unidentified oily materials were always observed. Attempts to
synthesize late lanthanide (e.g., Yb) thiolate complexes from the
[{(TMS)2N}3Yb(µ-Cl)Li(THF)3]/HSPh reaction system always led
to the formation of an unidentified red oily material, which may
be due to the smaller ionic radii of Yb3+. Fortunately, 4-6 were
successfully characterized by elemental, IR, and X-ray single-crystal
analysis.
During the process of the construction of oligomeric and
polymeric metal sulfide compounds from preformed metal clusters,
we found that added lithium chloride may play a critical role in
the construction of aggregated clusters.10 The incorporation of Li+
or Cl- ions into the resulting compound may change its charge
and thus enhance its solubility in solution. Therefore, it may produce
new soluble lanthanide thiolate compounds if LiCl is also introduced
into [Ln(N(TMS)2)3]. In this context, we deliberately chose the
known lanthanide amide complexes containing a bridging Cl- and
a [Li(THF)3]+ unit, [(TMS)2N]3Ln(µ-Cl)Li(THF)3 (Ln ) Pr (1),
Nd (2), and Sm (3)) for their protonolysis via thiol. When 1-3
were treated with equimolar benzenthiol, three different soluble Ln-
thiolate complexes, [{(TMS)2N}2(µ-SPh)Pr(µ-SPh)Li(THF)2]∞ (4),
Li[{(TMS)2N}4(µ4-Cl)Nd4(µ-SPh)8]‚C6H6 (5‚C6H6), and [{(TMS)2N}4-
(µ4-Cl)Sm4(µ-SPh)4(µ3-Cl)4Li(THF)] (6), were successfully isolated.
In this communication, we report their synthesis, characterization,
and catalytic property for the ring-opening polymerization (ROP)
of ꢀ-caprolactone.
An X-ray analysis11a revealed that 4 has an interesting 1D
wavelike chain structure in which the two ((TMS)2N)2Pr+ and Li-
+
(THF)2 units are alternatively bridged by SPh groups along the
crystallographic a axis (Figure 1). There are no other apparent
interactions between the chains. In the structure of 4, each Pr atom
is tetrahedrally coordinated by two S and two N atoms, while Li
ions also show a normal tetrahedral coordination geometry with
two µ-SPh and two THF molecules. On the other hand, the structure
of the cluster anion of 5 can be viewed as a cyclic tetramer of a
square array of Nd(III) ions with a Cl- ligand capping slightly above
the Nd4 plane (Figure 2).11b Alternatively, the anion is composed
of a starlike {((TMS)N)2Nd}4(µ-Cl) unit connected by four pairs
of bridging SPh groups, forming a “four-flier pinwheel” structure
with an approximate S4 symmetry. Each Nd atom in 5 is coordinated
by one Cl atom, one N atom, and four S atoms, forming a distorted
octahedral coordination geometry. The structure of the square Nd4
array resembles that of (THF)6Yb4I2(µ-η2:η2-S2)4(µ4-S),7a which
contains a square array of seven coordinate Yb(III) ions connected
Treatment of 1 in THF with equimolar HSPh in n-hexane resulted
in a clear solution, from which a standard workup produced
colorless crystals of 4 in 23% yield along with a byproduct, [{((Me3-
† Suzhou University.
‡ Chinese Academy of Sciences.
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C O M M U N I C A T I O N S
three unprecedented Ln-thiolate compounds (4-6) when treated
with a low concentration of benzenthiol. It is anticipated that the
synthetic methodology may be applied to other Ln-amide com-
pounds to yield previously unknown species with better catalytic
activities. Studies on these respects are underway in our laboratory.
Acknowledgment. This research was supported by the NNSF
of China (No. 20271036), the NSF of Jiangsu Province (No.
BK2004205), and the State Key Laboratory of Organometallic
Chemistry of SIOC (No. 04-31).
Supporting Information Available: Crystallographic data for 4-8
(CIF); synthesis and polymerization details (PDF). This material is
available free of charge via the Internet at http:// pubs.acs.org.
Figure 2. Perspective view of the anion of 5 with labeling scheme and
50% probability. All hydrogen atoms are omitted for clarity.
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Figure 3. Molecular structure of 6 with labeling scheme and 50%
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As shown in Figure 3, 6 may be viewed as having a wine-cup-
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(11) Crystal data for 4: triclinic, space group P1h, a ) 8.693(2) Å, b ) 11.595-
(3) Å, c ) 22.719(6) Å, R ) 103.694(6)°, â ) 95.940(6)°, γ ) 90.653-
(5)°, V ) 2211.4(10) Å3, Z ) 2, Fcalcd ) 1.248 g/cm3, µ(Mo KR) ) 1.331
cm-1, T ) 193 K, R ) 0.065, Rw ) 0.078, GOF ) 1.007. (b) Crystal
data for 5: monoclinic, space group C2/c, a ) 18.305(2) Å, b ) 24.227-
(2) Å, c ) 24.326(3) Å, â ) 98.520(3)°, V ) 10669.3(19) Å3, Z ) 4,
Fcalcd )1.337 g/cm3, µ(Mo KR) ) 2.221 cm-1, T ) 193 K, R ) 0.052,
Rw ) 0.056, GOF ) 1.003. (c) Crystal data for 6: triclinic, space group
P1h, a ) 13.7062(11) Å, b ) 17.0964(13) Å, c ) 19.882(2) Å, R ) 75.817-
(4)°, â ) 83.698(5)°, γ ) 77.496(4)°, V ) 4401.8(6) Å3, Z ) 2, Fcalcd
1.461 g/cm3, µ(Mo KR) ) 3.016 cm-1, T ) 193 K, R ) 0.050, Rw
0.065, GOF ) 1.055.
)
)
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In conclusion, the present work demonstrates that the introduction
of Li+ and Cl- ions into lanthanide amide complexes (1-3) afforded
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