Synthesis and structure of samarium benzyl complex supported by bridged bis(guanidinate) ligand and its reactivity toward nitriles and phenyl isocyanate

Article abstract of DOI:10.1016/j.jorganchem.2012.06.004

Reaction of SmCl₃ with one equivalent of LLi₂ (L = iPr(Me₃Si)NC(NiPr)N(CH₂)₃NC(NiPr)N(SiMe ₃)iPr) in THF afforded monochloride complex LSmCl(THF)₂ (1) or LSmCl(DME) (2) upon crystallization from THF or DME. Treatment of 1 with KCH₂C₆H₅ yielded monobenzyl complex LSm(η¹-CH₂C₆H₅)(DME) (3). The reactivity of 3 has been further studied with MeCN, 4-MeOC₆H ₄CN and PhNCO. Complex 3 reacts with MeCN to produce [LSm(μ-(N,N′)-N(H)C(Me)C(H)CN)(THF)]₂ (4) via metalation of the methyl group of MeCN and followed by insertion of another MeCN into the new Sm-C bond and 1,3-H shift. Insertion into Sm-benzyl of 3 occurs with 4-MeOC ₆H₄CN to form a dimeric complex [LSm{μ-NH(C ₆H₅(p-OMe))CCC₆H₅}₂SmL] (5) with a new group NH(C₆H₅(p-OMe))CCC₆H ₅ in a η³-1-aza-allyl coordination mode via 1,3-H shift. Complex 3 reacts with PhNCO to yield a double insertion dinuclear complex [L′Sm{μ-OC(CH₂Ph)N(Ph)}₂SmL′] (6) (L′ = iPr(Me₃Si)NC(N iPr)N(CH₂) ₃(SiMe₃)C(NiPr)₂(CN(Ph)O)) via insertion reactions of PhNCO both into Sm-benzyl and into Sm-guanidinate of L followed by the rearrangement of the newly formed bridged ligand L′. Complexes 1-6 were fully characterized including X-ray structure analyses.

Full text of DOI:10.1016/j.jorganchem.2012.06.004

Journal of Organometallic Chemistry 716 (2012) 86e94
Contents lists available at SciVerse ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Synthesis and structure of samarium benzyl complex supported by bridged
bis(guanidinate) ligand and its reactivity toward nitriles and phenyl isocyanate
*
Xingmin Zhang, Chuanyong Wang, Mingqiang Xue, Yong Zhang, Yingming Yao, Qi Shen
College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou 215123, People’s Republic of China
a r t i c l e i n f o
a b s t r a c t
Article history:
Reaction of SmCl3 with one equivalent of LLi2 (L ¼ iPr(Me3Si)NC(NiPr)N(CH2)3NC(NiPr)N(SiMe3)iPr) in
THF afforded monochloride complex LSmCl(THF)2 (1) or LSmCl(DME) (2) upon crystallization from THF
Received 19 April 2012
Received in revised form
26 May 2012
or DME. Treatment of 1 with KCH2C6H5 yielded monobenzyl complex LSm(
reactivity of 3 has been further studied with MeCN, 4-MeOC6H4CN and PhNCO. Complex 3 reacts with
MeCN to produce [LSm(
-(N,N0)-N(H)C(Me)]C(H)C^N)(THF)]2 (4) via metalation of the methyl group of
MeCN and followed by insertion of another MeCN into the new SmeC bond and 1,3-H shift. Insertion into
Smebenzyl of 3 occurs with 4-MeOC6H4CN to form a dimeric complex [LSm{ -NH(C6H5(p-OMe))
C]CC6H5}2SmL] (5) with a new group NH(C6H5(p-OMe))C]CC6H5 in a
3-1-aza-allyl coordination mode
via 1,3-H shift. Complex 3 reacts with PhNCO to yield a double insertion dinuclear complex [L0Sm{
h
1-CH2C6H5)(DME) (3). The
Accepted 7 June 2012
m
Keywords:
m
Bridged bis(guanidinate) ligand
Monobenzyl complex
Insertion
Samarium
Lanthanide guanidinate
h
m
-
OC(CH2Ph)N(Ph)}2SmL0] (6) (L0 ¼ iPr(Me3Si)NC(N iPr)N(CH2)3(SiMe3)C(NiPr)2(CN(Ph)O)) via insertion
reactions of PhNCO both into Smebenzyl and into Smeguanidinate of L followed by the rearrangement
of the newly formed bridged ligand L0. Complexes 1e6 were fully characterized including X-ray structure
analyses.
Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction
for ring-open-polymerization of cyclic esters and the amide
complexes are active for catalytic addition of amines to nitriles
Guanidinate anions, as one of the alternatives to cyclo-
pentadienyl anions, have attracted increasing attention in organo-
lanthanide chemistry since they have the advantages of tunable
steric and electronic effects by variation of the substituents on the
nitrogen atoms and varied binding modes arisen from the third
nitrogen chelating ability [1e6]. A wide range of organolanthanide
derivatives stabilized by guanidinate ligands have been synthesized
and proven to be potential as efficient catalysts in homogenous
catalyzes [7e17], and as photoelectric materials [18] and the
precursors for ALD and MOCVD processes [19e22].
selectively to monosubstituted amidines [26]. Guanidinate and
amidinate groups possess similar coordination and chemical
properties. To expand our research on the lanthanide chemistry
with bridged noncyclopentadienyl ligands, we tried to synthesize
lanthanide benzyl complex bearing the bridged guanidinate L
(L ¼ iPr(Me3Si)NC(NiPr)N(CH2)3NC(NiPr)N(SiMe3)iPr). Here we
would like to report the detailed syntheses and molecular struc-
tures of samarium monochloride complexes LSmCl(THF)2 (1) and
LSmCl(DME) (2) and benzyl complex LSm(h
1-CH2C6H5)(DME) (3)
and the reactivity of 3 toward benzonitrile, acetonitrile and phenyl
In contrast, the application of bridged guanidinate ligands in
lanthanide chemistry still remains unexplored, although these
ligands can prevent ligand redistribution reactions and provide the
metal center with rigid framework and more open coordination
sphere, which are useful in homogeneous catalysis.
isocyanate.
2. Results and discussion
2.1. Syntheses and characterization of LSmCl(THF)2 (1) and
Recently, we have reported that bis(amidinate) ligand can
LSmCl(DME) (2) (L ¼ iPr(Me3Si)NC(NiPr)N(CH2)3NC(NiPr)N(SiMe3)
provide
a suitable coordination environment for stabilizing
iPr)
lanthanide amides [23], alkoxides [24] and monoborohydrides [25].
All these complexes can serve as highly active single-site initiators
Reaction of anhydrous SmCl3 with one equivalent of lithium salt
LLi2, which was formed in situ by treatment of Li2(Me3
-
SiN(CH2)3NSiMe3) with two equivalents of N,N0-diisopropylcarbo-
diimide in THF at room temperature for 24 h, afforded the
monochloride complex LSmCl(THF)2 (1) upon crystallization from
* Corresponding author. Tel.: þ86 512 65880306; fax: þ86 512 65880305.
E-mail address: qshen@suda.edu.cn (Q. Shen).
0022-328X/$ e see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jorganchem.2012.06.004

X. Zhang et al. / Journal of Organometallic Chemistry 716 (2012) 86e94
87
a mixture of THF/hexane, or LSmCl(DME) (2) from DME solution
(Scheme 1).
a monomeric structure in which the coordination sphere around
the Sm atom is composed of four nitrogen atoms of the ligand L, one
carbon atom of the benzyl group and two oxygen atoms of the DME
Complexes 1 and 2 were fully characterized by elemental anal-
yses, IR and X-ray single-crystal structure determinations. Their
molecular structures are shown in Figs. 1 and 2, respectively, and
the selected bond lengths and angles are listed in Table 1.
Complexes 1 and 2 both adopt a monomeric structure in their
solid state. The central metal Sm in each complex is ligated by two
guanidinate moieties of one ligand L through four nitrogen atoms,
one chlorine atom, and two oxygen atoms to form a distorted
trigonal bipyramid, if the guanidinate ligands are considered to be
point donors located at the central carbon.
molecule. The benzyl ligand adopts an
bond angle of C(25)eC(24)eSm(1) is 136.8(7)ꢀ, which is compa-
rable with that in (C5Me5)2Sm(
1-CH2C6H5)(THF) [36] but much
h
1-coordination mode. The
h
larger than those found in the complexes with a h h
3- or a 2-benzyl
group: {(Me3Si)2NC(NCy)2}2Ln(
h
3-CH2C6H5) (Cy ¼ C6H11) [37] and
{HC-(MeCNAr)2}La(
h
2-CH2C6H5)2(THF) (Ar ¼ 2,6-iPr2C6H3) [38].
ꢀ
The distance of Sm(1)/C(25) is 3.687(8) A, indicative of no inter-
action between Sm(1) and C(25). The bond length of Sm(1)eC(24)
ꢀ
(2.510(12) A) is comparable with those found in the benzyl
The nearly identical CeN lengths within the chelating guanidi-
complexes reported previously [39]. The bond parameters in the
unit of LSm are comparable well with those in 1 and 2.
ꢀ
ꢀ
nate ligands (1.311(8) Ae1.325(8) A) suggest that the
p
-electrons
within the NCN fragments are delocalized. The average SmeN
distance for the guanidinate nitrogen atoms attached to the
bridge is about 0.10 A shorter than that for those attached to the
2.3. Reaction of 3 with acetonitrile (CH3CN)
ꢀ
eiPr groups. Whilst, almost the same average LneN distance for the
two guanidinate groups in the complexes bearing unbridged gua-
nidinate ligands were reported [27]. The only difference between 1
and 2 is that the two oxygen atoms are from the coordinated THF
molecules for 1 and from one DME molecule for 2.
The reactivity of lanthanide complexes toward nitriles is of
interest, as nitriles constitute another class of unsaturated
substrates. Two reaction pathways for the reaction of lanthanide
alkyl complexes with acetonitrile have been reported. One is the
insertion of acetonitrile into an Lnealkyl species affording the
azomethine insertion complexes [40]. The other one is the CeH
activation of an acetonitrile, followed by insertion reaction of the
second coordinated acetonitrile into the newly formed Lnealkyl
species [41,42].
2.2. Synthesis and characterization of LSm(h
1-CH2C6H5)(DME) (3)
With the monochloride 1 in hand the reaction of 1 with one
equivalent of KCH2C6H5 in THF was conducted at 0 ꢀC in an attempt
to synthesize the corresponding benzyl complex, as lanthanide
benzyl complexes can not only serve as catalysts for hydro-
amination/cyclization of aminoalkenes [28], dimerization of phe-
nylacetylenes [29] and activate unsaturated molecules [30,31], but
also serve as efficient initiators for polymerization of olefins
[32e35]. The reaction took place smoothly and the color of the
solution changed from light yellow to deep yellow. After workup,
To assess the chemical behavior of 3 with nitriles the reaction of
3 with acetonitrile was first tested. Treatment of 3 with two
equivalents of acetonitrile resulted in an instantaneous reaction.
After workup, pale yellow crystals were isolated in 64% yield. The
crystals were fully characterized including an X-ray crystal struc-
ture analysis proven to be the crotononitrileamido complex
[LSm(m
-(N,N0)-N(H)C(Me)]C(H)C^N) (THF)]2 (4) (Scheme 3).
The IR spectrum shows the strong absorption at 3415 and
2187 cmꢁ1 which can be assigned to NeH and C^N stretching
vibrations, respectively.
the DME-solvated benzyl complex LSm(h
1-CH2C6H5)(DME) (3) was
isolated as yellow crystals in 58% yield (Scheme 2).
Complex 3 is very sensitive to air and moisture. It is well soluble
in THF and toluene and moderately soluble in hexane. Elemental
analysis of 3 is consistent with its formula. The structure of 3 was
further confirmed by an X-ray crystal structure analysis.
Complex 3 crystallizes in a triclinic system with space group P1.
The molecular structure of 3 is shown in Fig. 3 and the selected
bond lengths and angles are listed in Table 2. Complex 3 adopts
The molecular structure of 4 is shown in Fig. 4, and selected
bond distances and angles are given in Table 3. Complex 4 crys-
tallizes in a triclinic system with space group P1.
Complex 4 has a centrosymmetric dimeric structure in which the
two units of LSm connected together by two crotononitrileamido
fragments
displays a distorted pentagonal bipyramid formed by the ligand L,
m
-(N,N0)-N(H)C(Me)]C(H)C^N. Each samarium atom
Scheme 1. Syntheses of complexes 1 and 2.

88
X. Zhang et al. / Journal of Organometallic Chemistry 716 (2012) 86e94
Fig. 1. ORTEP diagram of the molecular structure of complex 1. Thermal ellipsoids are drawn at the 30% probability level. Hydrogen atoms and the free THF molecules are omitted
for clarity. Symmetry transformations used to generate equivalent atoms: #1 ꢁ x þ 1, y, ꢁz þ 1/2.
two nitrogen atoms from the newly formed crotononitrileamido
ligand and one oxygen atom of a THF molecule. The four nitrogen
atoms (N(1), N(2), N(3) and N(4)) from the ligand L and N(7A) atom
from the nitrile (C^N) group occupy equatorial positions, while
oxygen atom O(1) and N(8) site at axial positions with the O(1)e
Sm(1)eN(8) angle of 158.7(3)ꢀ.
afforded the intermediate [LSm(m-(C,N)-CH2C^N)]2; The interme-
diate further reacted with another acetonitrile molecule to give 4
via insertion of acetonitrile followed by a 1,3-H shift.
2.4. Reaction of 3 with 4-methoxybenzonitrile (4-MeOC6H4C^N)
The average SmeN distance for the guanidinate nitrogen atoms
Two examples concerning the reactivity of lanthanide alkyl
complexes to benzonitriles have been found in the literature till
now. The reaction of (C5Me5)ScMe with two equivalents of 4-
ꢀ
attached to the bridge is about 0.13 A shorter than those attached to
ꢀ
the iPr groups. The bond length of C(27)eN(7) is 1.155(11) A, in the
range of the C^N triple bond, and which is comparable with that
MeOC6H4C^N afforded a b-diketiminate complex via an attack-
found in [{Me2Si(NCMe3)(OCMe3)}2Y(
m
-(N,N0)-N(H)C(Me)]C(H)
ing of the second coordinated nitrile and a second 1,3-H shift [43].
Whilst, the reaction of (C5Me5)YCH2(3,5-Me2C6H3) with 2,6-
ꢀ
C^N)]2 [41]. The shorter N(8)eC(25) (1.301(12) A) and C(26)eC(27)
Me2C6H3C^N yielded the complex (h h
5-C5Me5)2Y[ 2-C{CH2(3,5-
ꢀ
ꢀ
(1.378(13) A) distances and the longer C(25)eC(26) (1.388(14) A)
bond indicate considerable charge delocalization within the cro-
tononitrileamido fragment. The same situation was also found in
Me2C6H3)}]N(2,6-Me2C6H3)](THF) formed via the insertion of
2,6-Me2C6H3C^N into the YeC bond [31].
Thus, the reaction of 3 with 4-MeOC6H4C^N was then con-
ducted. Addition of one equivalent of 4-MeOC6H4C^N into
a n-hexane solution of 3 at room temperature led to the formation
[{Me2Si(NCMe3)(OCMe3)}2Y(
[41].
m
-(N,N0)-N(H)C(Me)]C(H)C^N)]2
It is likely that 4 was formed via the following steps as proposed
previously [41]. The CeH bond activation of acetonitrile by 3
of the new samarium complex [LSm{m-NH(C6H5(p-OMe))
C]C(C6H5)}2SmL] (5) in 59% yield upon crystallization from hexane
solution (Scheme 4).
The elemental analysis and IR spectroscopy of complex 5 are in
good agreement with the proposed structure. The IR spectrum
Table 1
ꢀ
ꢀ
Selected bond lengths (A) and angles ( ) for complexes 1 and 2.
Bond lengths
1
2
Bond angles
1
2
Sm(1)eN(1)
2.385 (5) 2.484 O(1)eSm(1)eO(1A) 171.2 (2)
e
(15)
Sm(1)eN(2)
Sm(1)eC(1)
Sm(1)eO(1)
2.480 (6) 2.355 N(2)eSm(1)eN(2A) 179.3 (2)
e
(15)
2.878 (5) 2.846 N(2)eSm(1)eN(1)
54.1 (7)
54.5 (5)
(18)
2.447 (5) 2.514 N(1)eSm(1)eN(3)
e
172.5 (6)
160.1 (4)
(13)
Sm(1)eCl(1) 2.722 (3) 2.653 O(2)eSm(1)eCl(1)
e
(5)
N(1)eC(1)
N(2)eC(1)
1.325 (8)
1.311 (8)
1.32 N(2)eC(1)eN(1)
(3)
1.31
(2)
114.4 (5) 114.9 (17)
Fig. 2. ORTEP diagram of the molecular structure of complex 2. Thermal ellipsoids are
drawn at the 30% probability level. Hydrogen atoms are omitted for clarity.

X. Zhang et al. / Journal of Organometallic Chemistry 716 (2012) 86e94
89
Scheme 2. Synthesis of complex 3.
Fig. 3. ORTEP diagram of the molecular structure of complex 3. Thermal ellipsoids are drawn at the 30% probability level. Hydrogen atoms are omitted for clarity.
shows a strong absorption at 3415 cmꢁ1 indicative of the presence
of NeH bond, which should be formed via 1,3-H shift.
mode by 1,3-H shift as confirmed by the bond parameters. The
ꢀ
bond lengths of C(54)eC(47) (1.379(19) A) and C(62)eC(69)
ꢀ
The confirmation of 5 was further made by an X-ray structure
analysis. The molecular structure of 5 is shown in Fig. 5 and the
selected bond lengths and angles were listed in Table 4. Complex 5
is an unsolvated dimeric structure, in which the two monomers
LSmNH(C6H5(p-OMe))C]C(C6H5) were linked by two nitrogen
bridges (N(13) and N(14)).
(1.366(19) A) are longer than the corresponding C]C double
ꢀ
bond and the bond lengths of N(13)eC(54) (1.390(15) A) and
ꢀ
N(14)eC(69) (1.402(18) A) are shorter than that for the NeC single
bond. The bond angles of N(13)eSm(1)eC(47) and N(14)eSm(2)e
C(62) are 50.8(4)ꢀ and 50.0(4)ꢀ, respectively. The bond lengths of
ꢀꢀ
ꢀꢀ
Sm(1)eC(47) (2.943(13) A), Sm(2)eC(54) (2.863(14) A), Sm(2)e
ꢀꢀ
ꢀꢀ
The most interesting structure feature of 5 is that the group
C(62) (2.954(17) A) and Sm(2)eC(69) (2.904(17) A) also indicate
the presence of the interactions between Sm atoms and these
carbon atoms.
NH(C6H5(p-OMe))C]C(C6H5) adopts a
h
3-1-azaallyl coordination
The bond lengths of Sm(1)eN(13) and Sm(1)eN(14) are
Table 2
ꢀꢀ
ꢀꢀ
ꢀ
ꢀ
Selected bond lengths (A) and angles ( ) for complex 3.
2.485(12) A and 2.554(10) A, respectively, which indicate the two
nitrogen atoms unsymmetrically coordinated to the samarium atom.
Two samarium atoms (Sm(1) and Sm(2)) and two nitrogen atoms
(N(13) and N(14)) are nearly coplanar with the sum angles of 360.1(6)ꢀ
(N(13)eSm(1)eN(14) 74.4(4)ꢀ, Sm(1)eN(13)eSm(2) 106.2(4)ꢀ,
N(13)eSm(2)eN(14) 105.1(4) and N(13)eSm(1)eN(14) 74.3(4)ꢀ).
The average bond length in the two guanidinate units of the
ligand L are well comparable with each other, which is different
from that found in complexes 1e3. The difference in bond param-
eters among them may be attributed to the steric demanding
resulted from the presence of the bulky NH(C6H5(p-OMe)C]
CC6H5) group in 5.
ꢀ
Bond distances (A)
Sm(1)eN(1)
Sm(1)eN(3)
Sm(1)eC(1)
Sm(1)eC(24)
N(1)eC(1)
N(3)eC(2)
Bond angles (ꢀ)
N(1)eSm(1)eN(2)
N(1)eSm(1)eC(24)
N(1)eSm(1)eN(3)
N(1)eC(1)eN(2)
2.501 (8)
2.527 (8)
2.868 (9)
2.510 (12)
1.309 (13)
1.304 (11)
Sm(1)eN(2)
Sm(1)eN(4)
Sm(1)eC(2)
Sm(1)$$$C(25)
N(2)eC(1)
2.384 (8)
2.370 (7)
2.905 (8)
3.687 (8)
1.319 (12)
1.335 (12)
N(4)eC(2)
53.9(3)
96.5(4)
171.4(3)
114.9(9)
N(3)eSm(1)eN(4)
O(2)eSm(1)eC(24)
C(25)eC(24)eSm(1)
53.5(3)
161.2(9)
136.8(7)

90
X. Zhang et al. / Journal of Organometallic Chemistry 716 (2012) 86e94
Scheme 3. Reaction of 3 with acetonitrile.
Fig. 4. ORTEP diagram of the molecular structure of complex 4. Thermal ellipsoids are drawn at the 30% probability level. Hydrogen atoms and free hexanes molecules in the lattice
are omitted for clarity (Symmetry transformations used to generate equivalent atoms: #1 ꢁ x þ 1, y, ꢁz þ 1/2. #1 ꢁ x þ 2, ꢁy þ 1, ꢁz #2 ꢁ x þ 1, ꢁy þ 1, ꢁz þ 1).
2.5. Reaction of 3 with phenyl isocyanate (PhNCO)
amide complexes with PhNCO afforded the monoinsertion or
diinsertion products depending on the amide complexes used
[49e55]. The reactions of (MeC5H4)2Ln(nBu) and (C5Me5)3Ln with
PhNCO afforded the monoinsertion and diinsertion complexes,
respectively [45,46]. In 2009, Zhou’s group reported the insertion
The reactive chemistry of organolanthanide complexes with
isocyanates is of interest as isocyanates are not only the useful
reagents in organic synthesis, but also important monomers in
polymerization chemistry [44e48]. The reaction of lanthanide
reaction of PhNCO into the LneN bond of a
h
1-guanidinate group in
complex [(C5H5)2Y(
m
- :h
h1 3-N]C(NMe2)2)]2 [56]. Thus, the reac-
tivity of 3 with PhNCO should be of interest, as the potential two
active groups of Lnebenzyl and Lneguanidinate are existent in 3. To
see whether the two active species both can react with PhNCO
molecules, the reaction of 3 with two equivalents of PhNCO was
tested in hexane at room temperature. The reaction went smoothly.
After workup, colorless crystals were obtained in 61% yield
(Scheme 5). Elemental analysis of the crystals is consistent with the
formula of a double insertion product, and IR spectrum showed the
Table 3
ꢀ
ꢀ
Selected bond lengths (A) and angles ( ) for complex 4.
ꢀ
Bond distances (A)
Sm(1)eN(1)
Sm(1)eN(2)
Sm(1)eN(3)
Sm(1)eN(4)
Sm(1)-N(7A)
N(7)-Sm(1A)
Sm(1)eN(8)
2.495 (8)
2.373 (7)
2.501 (8)
2.383 (7)
2.576 (8)
2.576 (8)
2.428 (8)
1.378 (13)
Sm(1)eC(1)
Sm(1)eC(2)
N(1)eC(1)
N(2)eC(1)
N(3)eC(2)
N(4)eC(2)
N(8)eC(25)
C(25)eC(26)
2.869 (9)
2.885 (8)
1.312 (12)
1.321 (12)
1.316 (11)
1.315 (11)
1.301 (12)
1.388 (14)
presence of O
tals showed they are the double insertion complex [L0Sm{
OC(CH2Ph)N(Ph)}2SmL0] (6) (L0
iPr(Me3Si)NC(NiPr)N(CH2)3
C
N groups. X-ray structural analysis of the crys-
m
-
C(26)eC(27)
¼
Bond angles (ꢀ)
N(2)eSm(1)eN(4)
N(2)eSm(1)eN(8)
N(4)eSm(1)eO(1)
N(8)eSm(1)eO(1)
N(1)eC(1)eN(2)
(SiMe3)C(NiPr)2(CN(Ph)O)). Clearly, complex 6 is formed via inser-
tion reaction of PhNCO into the SmeC bond and the insertion of the
another PhNCO molecule into the Smeguanidinate group followed
by the 1,3-migration of a SiMe3 group and the rearrangement of the
newly formed bridged ligand L0. The occurrence of the ligand
73.0 (2)
105.2 (3)
91.4 (3)
158.7 (3)
115.1 (8)
N(2)eSm(1)eN(1)
N(4)eSm(1)eN(1)
O(1)eSm(1)eN(1)
N(1)eSm(1)eN(3)
N(4)eC(2)eN(3)
54.2 (2)
126.8 (3)
84.5 (3)
169.0 (3)
114.7 (7)

X. Zhang et al. / Journal of Organometallic Chemistry 716 (2012) 86e94
91
Scheme 4. Reaction of 3 with 4-methoxybenzonitrile.
ꢀ
ꢀ
rearrangement should be attributed to the overcrowded coordi-
nation environment around the Sm atoms in the original state.
The molecular structure of 6 is shown in Fig. 6 and the selected
bond lengths and angles are given in Table 5. Complex 6 is
a solvent-free dinuclear complex containing two newly bridged
ligand L0 and two O C(CH2Ph) N(Ph) ligands.
observed Sm(1)eN(7A) (2.485(6) A) and Sm(1)eN(8) (2.541(5) A)
bond lengths are comparable well to those in complexes
[(MeC5H4)2Ln(m,h
3-(OC(SPh)NPh))]2 [57] and {(MeC5H4)2Ln(THF)
[O CN(iPr)2 NPh]} [49].
The bond angles around C(2) atom is 360ꢀ, which is consistent
with sp2 hybridization. The three CeN bond lengths of guanidine
group (C(2)eN(6) 1.279(8) A, C(2)eN(3) 1.433(8) A and C(2)eN(4)
ꢀ
ꢀ
Each central metal is coordinated by one guanidinate and two
ꢀ
O
C(CH2Ph) N(Ph) ligands in bidentate fashion. The coordina-
1.392(8) A) indicate that the p electron of C]N double bond is
tion geometry around each Sm atom can be viewed as a capped
octahedron. The two oxygen atoms are unsymmetrically coordi-
nated to the samarium atom with the bond lengths of SmeO being
2.482(4) A for Sm(1)eO(2) and 2.387(4) A for Sm(1)eO(2A) A. The
bond lengths of N(7)eC(24), O(1)eC(24), N(8)eC(31) and O(2)e
not delocalized within the NCN unit.
The possible mechanism for the formation of 6 is presented in
Scheme 6. The insertion of PhNCO into Ln-benzyl affords the
monoinsertion intermediate A. The coordination of the second
PhNCO molecule to Sm atom in A results in the change of the
ꢀ
ꢀ
ꢀ
C(31) are 1.319(8) A, 1.295(7) A, 1.289(9) A and 1.317(7) A, respec-
tively, which are intermediate between a corresponding double-
bonding mode of one guanidinate ligand from
h h
3 to 1 fashion (B).
ꢀ
ꢀ
ꢀ
ꢀ
The insertion of the second coordinated PhNCO into the Sm-h1
-
ꢀ
ꢀ
bond distance (N]C, 1.26 A; C]O, 1.20e1.22 A) and a single-
bond distance (NeC, 1.51 A; CeO, 1.43 A), indicative of electron
delocalization within the newly formed OeCeN units. The
guandinate bond followed by the 1,3-migration of SiMe3 group and
the rearrangement of the L ligand leads to the formation of 6.
ꢀ
ꢀ
3. Experimental section
3.1. General considerations
All manipulations were performed under purified argon or
nitrogen atmosphere using standard Schlenk techniques and
Table 4
ꢀ
ꢀ
Selected bond distances (A) and angles ( ) for complex 5.
ꢀ
Bond distances (A)
Sm(1)eN(1)
Sm(1)eN(2)
Sm(1)eN(3)
Sm(1)eN(4)
Sm(2)eN(7)
Sm(2)eN(8)
Sm(2)eN(9)
Sm(2)eN(10)
Sm(1)eC(1)
2.412 (11)
2.430 (11)
2.415 (14)
2.364 (12)
2.448 (12)
2.358 (11)
2.409 (14)
2.440 (11)
2.837 (15)
2.838 (16)
2.850 (13)
2.820 (16)
2.485 (12)
2.554 (10)
2.538 (10)
2.507 (12)
2.943 (13)
2.860 (14)
2.954 (17)
N(3)eC(2)
N(4)eC(2)
N(5)eC(1)
N(6)eC(2)
N(7)eC(24)
N(8)eC(24)
N(9)eC(25)
Sm(2)eC(69)
N(1)eC(1)
1.344 (18)
1.314 (19)
1.458 (18)
1.461 (19)
1.334 (18)
1.331 (17)
1.331 (17)
2.904 (17)
1.304 (18)
1.335 (18)
1.31 (2)
1.402 (18)
1.390 (15)
1.366 (19)
1.379 (19)
1.482 (18)
1.507 (19)
1.48 (2)
Sm(1)eC(2)
N(2)eC(1)
Sm(2)eC(24)
Sm(2)eC(25)
Sm(1)eN(13)
Sm(1)eN(14)
Sm(2)eN(13)
Sm(2)eN(14)
Sm(1)eC(47)
Sm(1)eC(54)
Sm(2)eC(62)
Bond angles (ꢀ)
N(1)eSm(1)eN(2)
N(4)eSm(1)eN(3)
N(8)eSm(2)eN(7)
N(9)eSm(2)eN(10)
N(1)eSm(1)eN(3)
N(13)eSm(1)eC(47)
N(10)eC(25)
N(14)eC(69)
N(13)eC(54)
C(62)eC(69)
C(47)eC(54)
C(47)eC(48)
C(54)eC(55)
C(62)eC(63)
C(69)eC(70)
1.49 (2)
54.9 (4)
55.2 (4)
55.3 (4)
54.9 (4)
112.1 (5)
50.8 (4)
N(14)eSm(2)eN(13)
N(13)eSm(1)eN(14)
Sm(2)eN(14)eSm(1)
Sm(1)eN(13)eSm(2)
N(9)eSm(2)eN(7)
74.3 (4)
74.4 (4)
105.1 (4)
106.2 (4)
108.4 (5)
50.0 (4)
Fig. 5. ORTEP diagram of the molecular structure of complex 5. Thermal ellipsoids are
drawn at the 30% probability level. The SiMe3 and iPr fragments at N(5), N(6), N(11)
and N(12) are omitted for clarity. Hydrogen atoms of carbon atoms and free THF
molecule in the lattice are omitted.
N(14)eSm(2)eC(62)

92
X. Zhang et al. / Journal of Organometallic Chemistry 716 (2012) 86e94
Scheme 5. Reaction of 3 with phenyl isocyanate.
a glovebox. Tetrahydrofuran, toluene, DME and n-hexane were
dried and distilled from sodium benzophenone ketal under argon
prior to use. The other reagents were purchased from Acros
Chemical and used as received without further purification.
Me3Si(H)N(CH2)3N(H)SiMe3 was prepared according to the litera-
ture method [58]. Elemental analyses were performed by direct
combustion using a Carlo-Erba EA 1110 instrument. Lanthanide
analyses were performed by ethylenediaminetetraacetic acid
(EDTA) titration with a xylenol orange indicator and a hexamine
buffer [59]. The IR spectra were recorded on a Magna-IR 550
spectrometer as KBr pellets.
0 ꢀC, then stirred for 2 h. The resulting solution was slowly warmed
to room temperature. The THF solvent was removed in vacuo. The
remaining crystalline solid was washed with hexane three times
and dried to give 11.1 g (95% yield) of the title compound LLi2(THF).
C27H60Li2N6OSi2 (554.86) calcd.: C, 58.45; H, 10.90; N, 15.15. Found:
C, 58.85; H, 11.03; N, 14.79. IR (KBr, cmꢁ1): 2971 (s), 2875 (m), 1625
(s), 1528 (m), 1384 (s), 1131 (m), 1016 (m), 843 (w), 593 (w). 1H NMR
(400 MHz, C6D6):
THF), 3.41 (m, 6 H, eCH(CH3)2 and eNCH2), 1.85 (m, 2 H,
eCH2CH2CH2e), 1.40 (m, 4 H, -CH2, THF), 1.34e1.12 (m, 24 H,
eCH3), 0.28 (m, 18 H, Si(CH3)3). 13C NMR (101 MHz, C6D6)
¼ 170.36
(C]N), 67.90 -CH2, THF), 49.48 (eCH2CH2CH2e), 48.60
(eCH2CH2CH2e), 46.20 (eCH(CH3)2), 35.00 (eCH2CH2CH2e), 25.60,
-CH2, THF), 24.47 (eCH3), 3.04 (eSi(CH3)3).
d
¼ 3.87 (m, 2 H, CH(CH3)2), 3.57 (m, 4 H,
a-CH2,
b
d
(a
3.2. Synthesis of LLi2(THF)
(b
A solution of Me3Si(H)N(CH2)3N(H)SiMe3 (4.6 g, 21.1 mmol in
40 mL THF) was cooled at 0 ꢀC, n-BuLi (17.6 mL, 42.2 mmol, 2.40 M
in hexane) was added dropwise, and stirred for 2 h then slowly
warmed to room temperature. To this solution was added N,N0-
diisopropylcarbodiimide (iPrN]C]NiPr) (6.6 mL, 42.2 mmol) at
3.3. Synthesis of LSmCl(THF)2 (1)
A stirred pale yellow suspension of SmCl3 (1.10 g, 4.3 mmol) in
20 mL THF was added to a freshly prepared THF solution of LLi2
(40 mL, 4.3 mmol). The reaction mixture was stirred for 24 h at
room temperature, and then the solvent was removed in vacuum.
The residue was extracted with hot toluene to remove the LiCl by
centrifugation led to a yellow solution. Removing the toluene
solvent, washing the residues with hexane, and crystallization from
a mixture of THF/hexane at 0 ꢀC gave the product 1 as yellow
crystals (2.7 g, 79%). C31H68ClN6SmO2Si2 (798.89) calcd.: C, 46.61;
Table 5
ꢀ
ꢀ
Selected bond lengths (A) and angles ( ) for complex 6.
ꢀ
Bond distances(A)
Sm(1)eO(2)
Sm(1)eO(1A)
Sm(1)eO(2A)
Sm(1)eN(1)
Sm(1)eN(2)
Sm(1)eN(7A)
Sm(1)eN(8)
Sm(1)eC(24A)
Sm(1)eC(1)
2.482 (4)
2.366 (4)
2.387 (4)
2.418 (5)
2.415 (5)
2.485 (6)
2.541 (5)
2.834 (6)
2.864 (6)
2.942 (7)
N(3)eC(2)
N(4)eC(2)
N(6)eC(2)
O(1)eSm(1A)
O(2)eSm(1A)
N(1)eC(1)
O(1)eC(24)
N(7)eC(24)
N(8)eC(31)
O(2)eC(31)
1.433 (8)
1.392 (8)
1.279 (8)
2.366 (4)
2.387 (4)
1.322 (8)
1.295 (7)
1.319 (8)
1.289 (9)
1.317 (7)
Sm(1)eC(31)
Bond angles (ꢀ)
O(1A)eSm(1)eO(2A)
O(1A)eSm(1)eN(2)
O(2A)eSm(1)eN(2)
N(2)eSm(1)eN(1)
N(2)eSm(1)eN(7A)
N(1)eC(1)eN(2)
N(4)eC(2)eN(3)
82.25 (15)
135.51 (18)
88.52 (17)
55.00 (18)
145.25 (18)
114.3 (6)
O(1A)eSm(1)eO(2)
O(2A)eSm(1)eO(2)
N(2)eSm(1)eO(2)
O(2A)eSm(1)eN(7A)
N(1)eSm(1)eN(7A)
C(2)eN(4)eC(5)
115.89 (15)
66.82 (16)
99.61 (17)
125.35 (16)
93.64 (18)
120.4 (5)
Fig. 6. ORTEP diagram of the molecular structure of complex 6. Thermal ellipsoids are
drawn at the 30% probability level. Hydrogen atoms and methyl groups of SiMe3 are
omitted for clarity. Symmetry transformations used to generate equivalent atoms:
#1 ꢁ x, ꢁy þ 2, ꢁz þ 1.
116.1 (6)
N(6)eC(2)eN(3)
126.8 (6)

X. Zhang et al. / Journal of Organometallic Chemistry 716 (2012) 86e94
93
Scheme 6. The possible mechanism for the formation of complex 6.
H, 8.58; N, 10.52; Sm, 18.82. Found: 46.92; H, 8.73; N, 10.19; Sm,
18.47. IR (KBr, cmꢁ1): 2971 (s), 2875 (m), 1620 (s), 1520 (m), 1469
(m), 1216 (m), 1164 (m), 891 (w), 841 (m), 624 (w).
concentrated, pale yellow crystals of 4 (0.59 g, yield 64%) were
isolated at 0 ꢀC. C62H130N16O2Si4Sm2 (1544.86) calcd.: C, 48.20; H,
8.48; N, 14.51; Sm, 19.47. found: C, 48.68; H, 8.31; N, 14.77; Sm,
19.22. IR (KBr, cmꢁ1): 3414 (s), 2972 (s), 2187(s), 1617 (s), 1524 (m),
1468 (m), 1384 (m), 1170 (w), 839 (w).
3.4. Synthesis of LSmCl(DME) (2)
Complex 1 (1.28 g, 1.6 mmol) was dissolved in DME (15 mL).
Removing the DME solvent, washing the residues with hexane, and
crystallization from a mixture of THF and hexane at 0 ꢀC gave the
product 2 as yellow crystals (0.95 g, 80%). C27H62ClN6O2Si2Sm
(744.80) calcd.: C, 43.54; H, 8.39; N, 11.28; Sm, 20.19. Found: C,
43.09; H, 8.18; N,11.51; Sm, 20.57. IR (KBr, cmꢁ1): 2974 (s), 2871 (m),
1618 (s), 1385 (m), 1164 (m), 605 (m).
3.7. Reaction of 3 with 4-MeOC6H4CN to afford complex 5
To a hexane solution (20 mL) of 3 (0.66 g, 0.82 mmol) was added
4-MeOC6H4CN (0.11 g, 0.82 mmol, dissolved in 2 mL THF). The
resulting solution was stirred overnight at room temperature. After
the clear solution was concentrated, pale yellow crystals of 5
(0.41 g, yield 59%) were isolated at 0 ꢀC. C76H132N14O2Si4Sm2
(1687.01) calcd.: C, 54.11; H, 7.89; N, 11.62; Sm, 17.83. found: C,
54.68; H, 8.03; N, 11.36; Sm, 18.19. IR (KBr, cmꢁ1): 3415 (s), 2970 (s),
1618 (s), 1508 (w), 1384 (s), 1171 (w), 839 (w).
3.5. Synthesis of LSm(h
1-CH2C6H5)(DME) (3)
To a THF solution (20 mL) of 1 (2.0 g, 2.5 mmol) was added
KCH2C6H5 (0.325 g, 2.5 mmol) at 0 ꢀC. The mixture was allowed to
slowly warm to room temperature and stirred for 12 h. The KCl
precipitation was removed by centrifugation led to a yellow solu-
tion. Removing the THF solvent, washing the residues with hexane,
and crystallization from a mixture of DME and hexane at 0 ꢀC gave
the product 3 as yellow crystals (1.16 g, 58%). C34H69N6O2Si2Sm
(800.48) calcd: C, 51.01; H, 8.69; N, 10.50; Sm, 18.78. Found: C,
50.34; H, 8.41; N, 10.77; Sm, 19.12. IR (KBr, cmꢁ1): 2965 (s), 1628 (s),
1468 (s), 1368 (m), 1160 (m), 842 (m).
3.8. Reaction of 3 with phenyl PhNCO to afford complex 6
To a hexane (20 mL) solution of 3 (0.80 g, 1.0 mmol) was added
PhNCO (2.0 mL, 1 M in THF). The resulting solution was stirred
overnight at room temperature. After the clear solution was
concentrated, pale yellow crystals of 6 (0.58 g, yield 61%) were
isolated. C88H138N16O4Si4Sm2 (1897.20) calcd.: C, 55.71; H, 7.33; N,
11.81; Sm, 15.85. Found: C, 56.32; H, 7.60; N, 11.45; Sm, 15.98. IR
(KBr, cmꢁ1): 2968 (s), 1620 (s), 1531 (m), 1498 (m), 1442 (m), 1384
(m), 1168 (w), 843 (w).
3.6. Reaction of 3 with CH3CN to afford complex 4
4. Conclusion
To a toluene solution (20 mL) of 3 (0.96 g, 1.2 mmol) was added
acetonitrile (2.4 mL, 1 M in THF). The resulting solution was stirred
overnight at room temperature. After the clear solution was
This investigation shows that bridged guanidinates ligand can
be used to stabilize a variety of SmeX (X ¼ Cl, C, and heteroatom)

94
X. Zhang et al. / Journal of Organometallic Chemistry 716 (2012) 86e94
bonds in the form of complexes LSmX. The reaction of LSm(h1
-
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CH2C6H5)(DME) (3) with MeCN proceeds rapidly to provide the
complex via metalation of methyl group of an acetonitrile, followed
by insertion reaction of the second coordinated acetonitrile into the
newly formed Lnealkyl species. This reaction is very similar to that
of [Me2Si(NCMe3)(OCMe3)]2YCH(SiMe3)2 [41]. However, the reac-
tion of 3 with 4-MeOC6H4CN affords the insertion product with 1,3-
H shift. A double insertion reaction with a ligand rearrangement is
observed during the reaction of 3 with PhNCO. This result clearly
demonstrates the limited suitability of bridged guanidinates ligand
to be applied as inert spectator ligands, as the fluxionality of gua-
nidinate group in binding fashion.
Acknowledgments
We are grateful for financial support from the National Natural
Science Foundation of China (Grant NO. 20972107, 21132002) and
a Project Funded by the Priority Academic Program Development of
Jiangsu Higher Education Institutions.
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Appendix A. Supplementary material
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complexes 1e6. These data can be obtained free of charge from The
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