Syntheses of bimetallic lanthanide bis(amido) complexes stabilized by bridged bis(guanidinate) ligands and their catalytic activity toward the hydrophosphonylation reaction of aldehydes and ketones

Article abstract of DOI:10.1007/s11426-015-5407-9

A series of bimetallic lanthanide bis(amido) complexes stabilized by bridged bis(guanidinate) ligands {[(Me₃Si)₂N]₂Ln[(RN)₂-CN(CH₂)₂]}₂ [R= ⁱ Pr, Ln=Sm (1), Yb (2), Y

Full text of DOI:10.1007/s11426-015-5407-9

SCIENCE CHINA
Chemistry
• ARTICLES •
doi: 10.1007/s11426-015-5407-9
doi: 10.1007/s11426-015-5407-9
Syntheses of bimetallic lanthanide bis(amido) complexes
stabilized by bridged bis(guanidinate) ligands and their
catalytic activity toward the hydrophosphonylation
reaction of aldehydes and ketones
Kun Nie1,2*, Chengwei Liu2, Yong Zhang2 & Yingming Yao2*
1School of Chemistry and Chemical Engineering, Taishan University, Taian 271021, China
2Key Laboratory of Organic Synthesis of Jiangsu Province; College of Chemistry, Chemical Engineering and Materials Science,
Soochow University, Suzhou 215123, China
Received October 10, 2014; accepted November 13, 2014
A series of bimetallic lanthanide bis(amido) complexes stabilized by bridged bis(guanidinate) ligands {[(Me3Si)2N]2Ln[(RN)2-
CN(CH2)2]}2 [R=iPr, Ln=Sm (1), Yb (2), Y (3); R=cyclohexyl (Cy), Ln=Sm (4), and Yb (5)] were synthesized through the
metathesis reactions of {Ln(μ-Cl)[N(SiMe3)2]2(THF)}2 (Ln=Sm, Yb, Y) with lithium guanidinate {Li[(RN)2CN(CH2)2]}2
(R=iPr, Cy), the latter of which was generated in situ by the reaction of carbodiimides with lithium amides. Complexes 1–5
were well characterized by elemental analyses, IR spectra, and (for Complex 3) NMR spectroscopy. The solid-state molecular
structures of all of the complexes were determined by single-crystal X-ray analyses with the exception of Complex 3, which
showed similar unsolvated centrosymmetric dinuclear structures. Each of the lanthanide centers is four-coordinated with two
nitrogen atoms from a guanidinate ligand and two nitrogen atoms from two amido groups. The piperazidine rings adopt chair
conformations in all cases. These organolanthanide complexes were found to be efficient catalysts for the hydrophosphonyla-
tion reaction of various aldehydes and unactivated ketones and to afford -hydroxyphosphonates in high yields under low cat-
alyst loading (0.1 mol%) in a short reaction time.
bimetallic lanthanide complex, bridged bis(guanidinate) ligand, hydrophosphonylation reaction, aldehyde, ketone
plexes [7]. Furthermore, some lanthanide guanidinates have
1 Introduction
been shown to be efficient catalysts for the polymerization
of ethylene [2a], propylene [2a], styrene [3e], methyl meth-
acrylate [3f,4a], and lactones [3f,4a–4c,5]; the hydrosilyla-
tion of alkenes [3h]; the amidation of aldehydes with
amines [7a]; and the addition of amines to carbodiimides
[6,7b]. After the very recent introduction of bridged
bis-(guanidinate) ligands to lanthanide chemistry [8], they
were found to prevent ligand redistribution reactions as well
as to provide the metal center with a rigid framework and
more open coordination spheres, which are useful in homo-
geneous catalysis. However, no example of these ligands
being used to stabilize bimetallic lanthanide complexes has
been seen.
Guanidinate anions [(RN)2CNR′2] have found wide appli-
cations as ancillary ligands in the field of organolanthanide
chemistry [1] because their steric and electronic properties
can be easily tailored by tuning the N-substituents and be-
cause their binding modes are variable due to the presence
of three nitrogen atoms. Various lanthanide guanidinate
derivatives have been synthesized, including lanthanide
hydride [2], alkylide [3], amide [4], alkoxide [5], and ar-
yloxide [4c,6], as well as trisguanidinate lanthanide com-
*Corresponding authors (email: nkniekun@163.com; yaoym@suda.edu.cn)
© Science China Press and Springer-Verlag Berlin Heidelberg 2015
chem.scichina.com link.springer.com

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Nie et al. Sci China Chem March (2015) Vol.58 No.3
Recently, we became interested in studying the synthesis
added dropwise into a THF solution of piperazine (0.17 g,
1.97 mmol) at 0 °C and immediately formed a white-yellow
powder. The mixture was stirred for 30 min at room tem-
perature, after which N,N′-diisopropylcarbodiimide (0.61
mL, 3.94 mmol) was added by syringe. After the reaction
mixture was stirred for 1 h at room temperature, a THF so-
lution of {Sm(μ-Cl)[N(SiMe3)2]2(THF)}2 (3.94 mmol) was
added. The precipitate then slowly disappeared. After the
mixture was stirred for 12 h, the solvent was removed under
vacuum and the solid residue was extracted with 30 mL of
toluene, removed by centrifugation, and concentrated under
reduced pressure. White yellow crystals were obtained from
the toluene solution at room temperature after several days
(1.50 g, 77%). Anal. calcd. for C42H108N10Si8Sm2 (1278.80):
C, 39.45; H, 8.51; N, 10.95; Sm, 23.52. Found: C, 39.25; H,
8.59; N, 10.72; Sm, 23.46%. IR (KBr pellet, cm1): 2963 (s),
2850 (m), 1625 (s), 1463 (w), 1388 (m), 1254 (s), 1163 (m),
933 (m), 841 (w).
and catalytic properties of bimetallic organometallic com-
plexes [9] because bimetallic complexes are anticipated to
exhibit a cooperative effect between two metal centers
and/or nuclearity effects in organic transformations and
polymerizations, in comparison with monomeric metal
complexes [10]. Controlled synthesis of stable bimetallic
organolanthanide complexes remains challenging, however,
because of their large ionic radii and the requirement of
high coordination numbers. Because the piperazidine ring is
flexible, its derivatives with chair conformations are favored
for stabilizing bimetallic organolanthanide complexes. Pi-
perazidine-bridged bis(phenolate) groups have been found
to stabilize some bimetallic lanthanide amides, a result that
is significantly influenced by reaction conditions, the size of
lanthanide metals, and the steric bulkiness of the ligands. To
develop a general ligand system to prepare bimetallic or-
ganolanthanide complexes, a bridged bis(guanidinate) lig-
and derived from an easily available piperazidine was syn-
thesized and was found to be applicable for synthesizing
bimetallic lanthanide bis(amido) complexes. These bimetal-
lic organolanthanide complexes are efficient catalysts for
the hydrophosphonylation reaction of aldehydes and ke-
tones with diethyl phosphate.
2.2.2 {[(Me3Si)2N]2Yb[(iPrN)2CN(CH2)2]}2 (2)
Complex 2 was prepared in analogy to Complex 1 from
{Yb(μ-Cl)[N(SiMe3)2]2(THF)}2; 3.94 mmol of this was
used instead of {Sm(μ-Cl)[N(SiMe3)2]2(THF)}2. Complex 2
was isolated as yellow crystals (2.09 g, 80%). Anal. calcd.
for C42H108N10Si8Yb2 (1324.18): C, 38.10; H, 8.22; N, 10.58;
Yb, 26.14. Found: C, 38.31; H, 8.33; N, 10.73; Yb, 26.39%.
IR (KBr pellet, cm1): 2963(s), 2851(m), 1625(s), 1464(w),
1388(m), 1254(s), 1164(m), 933(m), 842(w).
2 Experimental
2.1 General information
2.2.3 {[(Me3Si)2N]2Y[(iPrN)2CN(CH2)2]}2 (3)
All manipulations were performed in a purified argon at-
mosphere using standard Schlenk techniques. The solvents
were degassed and distilled from sodium benzophenone
ketyl under argon prior to use. {Ln(μ-Cl)[N(SiMe3)2]2-
(THF)}2 (Ln=Sm, Yb, Y) [11] and {Li[(RN)2CN(CH2)2]}2
(R=iPr, Cy) [12] were prepared by slightly modified litera-
ture methods. Solid aldehydes and ketones were used as
received; liquid aldehydes and ketones were distilled before
use. Lanthanide analyses were performed by EDTA titration
with a xylenol orange indicator and a hexamine buffer [13].
Carbon, hydrogen, and nitrogen analyses were performed
by direct combustion with a Carlo-Erba EA-1110 instru-
ment (Thermo Scientific, USA). The IR spectra were rec-
orded with a Nicolet-550 FTIR (Thermo Scientific, USA)
spectrometer using KBr pellets. The 1H and 13C NMR spec-
tra were recorded in C6D6 for Complex 3 and in CDCl3 for
organic compounds with a Unity Varian spectrometer (Uni-
ty Inova, USA). Because of their paramagnetism, no re-
solvable NMR spectra for other lanthanide complexes were
obtained.
Complex 3 was prepared in analogy to Complex 1 from
{Y(μ-Cl)[N(SiMe3)2]2(THF)}2; 3.94 mmol of this was used
instead of {Sm(μ-Cl)[N(SiMe3)2]2(THF)}2. Complex 3 was
obtained as colorless crystals (1.50 g, 81%). Anal. calcd. for
C42H108N10Si8Y2 (1155.89): C, 43.64; H, 9.42; N, 12.12; Y,
15.38. Found: C, 43.61; H, 9.77; N, 12.03; Y, 15.41%. IR
(KBr pellet, cm1): 2963(s), 2851(m), 1625(s), 1464(w),
1389(m), 1254(s), 1164(m), 933(m), 842(w). 1H NMR (400
MHz, C6D6, 25 °C): δ 3.43 (m, 4H, NCH(CH3)2), 2.80 (d,
8H, J=1.21 Hz, NC2H4NC2H4), 1.19 (24H, NCH(CH3)2),
0.38 (72H, SiMe3). 13C{1H} NMR (101 MHz, C6D6, 25 °C):
 169.88 ((iPrN)2C), 48.73 (NCH(CH3)2), 46.70 (NC2H4-
NC2H4), 26.40 (NCH(CH3)2), 5.03 (SiMe3).
2.2.4 {[(Me3Si)2N]2Sm[(CyN)2CN(CH2)2]}2 (4)
The synthesis of Complex 4 was carried out in analogy to
Complex 1 from N,N′-dicyclohexylcarbodiimide (0.82 g,
3.94 mmol) was used instead N,N′-diisopropylcarbodiimide.
Yellow crystals were obtained from a toluene solution at
room temperature after several days (2.13 g, 75%). Anal.
calcd. for C54H124N10Si8Sm2 (1439.06): C, 45.07; H, 8.69; N,
9.73; Sm, 20.90. Found: C, 45.24; H, 8.78; N, 9.69; Sm,
20.78%. IR (KBr pellet, cm1): 2927(s), 2851(m), 1635(s),
1450(m), 1390(w), 1256(m), 1143(m), 996(m), 933(m),
889(w), 844(m).
2.2 Synthesis of lanthanide bis(amido) complexes
2.2.1 {[(Me3Si)2N]2Sm[(RN)2CN(CH2)2]}2 (1)
A hexane solution of n-BuLi (1.42 mL, 3.94 mmol) was

Nie et al. Sci China Chem March (2015) Vol.58 No.3
3
2.2.5 {[(Me3Si)2N]2Yb[(CyN)2CN(CH2)2]}2 (5)
final products were further purified by washing with hexane
(for those from aldehydes) or by column chromatography
(for those from ketones).
Following the procedure described for preparing Complex 1,
reaction of {Yb(μ-Cl)[N(SiMe3)2]2(THF)}2 (3.94 mmol)
with the corresponding lithium guanidinate {Li[iPr2NCN-
(CH2)2]}2 (1.97 mmol) gave Complex 5 as yellow crystals
(2.25 g, 77%). Anal. calcd. for C54H124N10Si8Yb2 (1484.44):
C, 43.69; H, 8.42; N, 9.44; Yb, 23.32. Found: C, 43.55; H,
8.21; N, 9.60; Yb, 23.43%. IR (KBr pellet, cm1): 2928(s),
2852(m), 1636(s), 1450(m), 1386(w), 1255(m), 1144(m),
996(m), 933(m), 890(w), 844(m).
2.4 X-ray diffraction analysis
Suitable single crystals of complexes 1, 2, 4, and 5 were
sealed in a thin-walled glass capillary for determination of
their solid-state structures. Intensity data were collected
with a Rigaku Mercury CCD area detector (Rigaku, Japan)
in ω scan mode using Mo-Kα radiation (λ=0.71070 Å). The
diffracted intensities were corrected for Lorentz/polarization
effects and empirical absorption corrections. Details of
the intensity data collection and crystal data are given in
Table 1.
2.3
General procedures for hydrophosphonylation
reactions
A 30.0 mL Schlenk tube under dry argon was charged with
the lanthanide amido Complex 1 (12.8 mg, 0.01 mmol),
diethyl phosphite (1.66 g, 12 mmol), after which an alde-
hyde (10.0 mmol) or a ketone (10 mmol) was added to the
mixture. The resulting mixture was allowed to stir at room
temperature for 5 min (for aldehyde) or 20 min (for ketone).
After the reaction was completed, the reaction mixture was
hydrolyzed by water (3.0 mL), extracted with ethyl acetate
(3×10.0 mL), dried over anhydrous Na2SO4, and filtered.
After the solvent was removed under reduced pressure, the
The structures were solved by direct methods and refined
by full-matrix least-squares procedures based on |F|2. The
hydrogen atoms in these complexes were generated geo-
metrically, assigned appropriate isotropic thermal parame-
ters, and allowed to ride on their parent carbon atoms. All of
the hydrogen atoms were held stationary and included in the
structure-factor calculation in the final stage of full-matrix
least-squares refinement. The structures were solved and
refined using SHELEXL-97 programs (University of Göt-
tingen, Germany).
Table 1 Crystallographic data for complexes 1, 2, 4, and 5
Compound
Formula
fw
1·2Toluene
C56H124N10Si8Sm2
1463.07
223(2)
2·2Toluene
C56H124N10Si8Yb2
1508.45
223(2)
4·Toluene
C61H132N10Si8Sm2
1531.19
5·Toluene
C61H132N10Si8Yb2
1576.57
T (K)
223(2)
293(2)
Crystal system
Crystal size (mm)
Space group
a (Å)
triclinic
0.60×0.25×0.18
P-1
triclinic
0.60×0.55×0.40
P-1
monoclinic
0.80×0.40×0.40
P21/n
monoclinic
0.70×0.40×0.20
P21/n
11.7327(9)
12.2703(8)
14.5591(10)
79.367(4)
77.788(4)
84.166(5)
2009.1(2)
1
11.6583(11)
12.1953(11)
14.5133(13)
80.292(5)
77.622(5)
84.085(6)
1981.8(3)
1
9.677(2)
9.783(2)
b (Å)
23.520(5)
23.285(5)
18.763(5)
c (Å)
18.869(5)
α (°)
β (°)
103.860(6)
102.700(7)
γ (°)
V (Å3)
4169.5(16)
2
4169.5(18)
2
Z
Dcalcd (g/cm3)
μ (mm1)
F(000)
1.209
1.264
1.220
1.232
1.603
2.503
1.547
2.381
766
782
1608
1580
25.50
25.50
25.50
25.35
max (°)
Collected
16308
15986
20983
7690
38197
7618
Unique reflns
7423
7308
Obsd reflns [I>2.0σ(I)]
6370
6607
5927
6221
No. of variables
285
285
329
329
GOF
1.056
1.096
1.084
1.226
R
0.0478
0.0420
0.0562
0.1591
0.0403
1.001, 1.181
0.0980
0.2194
0.0792
1.191, 1.187
wR
0.1170
0.1010
Rint
0.0359
0.0372
Largest diff. peak, hole (e/Å3)
1.454, 0.744
0.857, 0.778

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Nie et al. Sci China Chem March (2015) Vol.58 No.3
nate. The IR spectra of these complexes exhibit strong ab-
3 Results and discussion
sorptions in the range 1625–1636 cm1, consistent with a
partial C=N double-bond character and supporting that the 
electrons are delocalized within the N–C–N linkage.
It is worth noting that attempts to synthesize monometal-
lic lanthanide amido complex supported by the aforemen-
tioned bis(guanidinate) ligands failed. Theoretically, a pi-
perazidine ring may also adopt a boat conformation, which
may favor monometallic complexes. However, only bime-
tallic lanthanide amido complexes were isolated even when
the lithium bis(guanidinate) was treated with one equivalent
of {Ln(μ-Cl)[N(SiMe3)2]2(THF)}2. This result is quite dif-
ferent from that of the piperazidine-bridged bis(phenolate)
system [9a,9c], in which monometallic complexes formed
under suitable reaction conditions.
3.1 Synthesis of bimetallic lanthanide bis(amido) com-
plexes stabilized by bridged bis(guanidinate) ligands
Generally, organolanthanide guanidinate complexes are
prepared from the metathesis reaction of lanthanide guani-
dinate chlorides or the insertion reaction of lanthanide am-
ides with carbodiimides. In this study, lanthanide amido
chlorides {Ln(μ-Cl)[N(SiMe3)2]2(THF)}2 were found to be
useful precursors for the synthesis of lanthanide guanidinato
amides via salt metathesis reaction. One equivalent of lith-
ium guanidinate {Li[(RN)2CN(CH2)2]}2 (R=iPr, Cy), which
was generated in situ from the reaction of carbodiimide and
lithium salt of piperazine, reacted with two equivalents of
{Ln(μ-Cl)[N(SiMe3)2]2(THF)}2 (Ln=Sm, Yb, Y) in THF at
room temperature. Five bimetallic lanthanide bis(amido)
complexes stabilized by bridged bis(guanidinate) ligands
{[(Me3Si)2N]2Ln[(RN)2CN(CH2)2]}2 [R=iPr, Ln=Sm (1),
Yb (2), Y (3); R=Cy, Cy=cyclohexyl, Sm (4), Yb (5)] were
isolated in good to high yields (Scheme 1).
Complexes 1–5 are sensitive to air and moisture. The
crystals decompose in a few minutes when they are exposed
to air. However, both the crystals and the solution are rather
stable when stored under argon. They are well soluble in
THF and toluene, but insoluble in hexane.
All complexes were characterized by elemental analysis,
IR spectroscopy, and (for Complex 3) NMR spectroscopy.
Elemental analysis revealed that each of these complexes
consists of one bis(guanidinate) group, four amido groups,
and two lanthanide ions. The 1H NMR spectrum shows one
set of signals for four isopropyl units and a single resonance
for TMS protons in the high-field region (δ 0.38 ppm),
which indicates that the chemical environments of all four
amido groups in Complex 3 are the same; this result is con-
sistent with a flexible bimetallic structure in solution. No
3.2 Crystal structures
To provide complete structural information for these new
bimetallic lanthanide guanidinato species, single-crystal
X-ray structural analyses were carried out for complexes 1,
2, 4, and 5. Single crystals suitable for X-ray structure de-
termination were obtained from toluene solution at room
temperature. X-ray diffraction analyses revealed that these
complexes have analogous centrosymmetric dinuclear
structures. Complexes 1 and 2 as well as 4 and 5 are iso-
morphous; only the ORTEP diagrams of complexes 1 and 4
are shown, respectively, in Figures 1 and 2. The selected
bond lengths and angles for these molecules are provided in
Table 2.
1
signal for THF was observed in the H NMR spectrum,
which revealed that Complex 3 is unsolvated. The 13C NMR
spectrum is consistent with the proposed structures, includ-
ing a diagnostic signal resonating at δ 169.88 ppm for the
central carbon atom of a κ2 monoanionic chelating guanidi-
Scheme 1 Synthesis of complexes 1–5.

Nie et al. Sci China Chem March (2015) Vol.58 No.3
5
Figure 1 ORTEP diagram of Complex 1 showing an atom-numbering scheme. Thermal ellipsoids are drawn at the 30% probability level. Hydrogen atoms
are omitted for clarity. Complex 2 is isomorphous with Complex 1.
Figure 2 ORTEP diagram of Complex 4 showing an atom-numbering scheme. Thermal ellipsoids are drawn at the 10% probability level. Hydrogen atoms
are omitted for clarity. Complex 5 is isomorphous with Complex 4.
All of the complexes have unsolvated dinuclear struc-
tures in solid state, and their piperazidine rings adopt chair
conformations. Each of the lanthanide ions in these com-
plexes is four-coordinated by two nitrogen atoms from the
chelating guanidinate ligand and two nitrogen atoms from
two amido groups, which proves that the combination of a
guanidinate ligand and two amido groups is sufficient to
meet the requirement of coordination saturation of lantha-
nide ions in this system. The coordination geometry around
the metal center can be described as a distorted tetrahedron.
The four-membered LnNCN rings in these complexes are
essentially planar. The two C–N bonds within a chelating
guanidinate ligand, which are equal in length, are shorter
than C–N single bonds (1.47 Å) but significantly longer
than C=N double bonds (1.29 Å), which reveals a -elec-
tron delocalization around the guanidinate ligand. The av-
erage lengths of Ln-N(Guan) bonds, which are 2.381(4) Å
(for 1), 2.371(5) Å (for 4), 2.281(3) Å (for 2), and 2.261(10)
Å (for 5), reflect the influence of lanthanide contraction.
Similar sequences following the decreasing order of the
Ln3+ ionic radii are also observed from the Ln–N(amide)
bond lengths in these complexes. The Ln–N(Guan) and
Ln–N(amide) bond lengths of 1 and 2 are slightly longer
than those of 4 and 5. However, the angles of C2–N1–Sm1
(136.7(3)°) and C5–N2–Sm1 (136.0(3)°) in 1 are larger than
the corresponding angles in 4 (133.6(13)° and 134.8(13)°,
respectively). These differences probably resulted from the
change of the substituent group from isopropyl to cyclohex-
yl on the guanidinate ligand.

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Nie et al. Sci China Chem March (2015) Vol.58 No.3
Table 2 Selected bond lengths and bond angles for Complexes 1, 2, 4, and 5
1
2
4
5
Bond
Bond lengths (Å)
Ln1–N1
Ln1–N2
Ln1–N4
Ln1–N5
N1–C1
N2–C1
N3–C1
2.370(4)
2.391(4)
2.296(4)
2.292(4)
1.334(6)
1.331(6)
1.394(6)
2.273(3)
2.288(4)
2.205(4)
2.190(4)
1.338(6)
1.341(6)
1.398(5)
2.374(5)
2.367(5)
2.287(5)
2.290(5)
1.329(9)
1.341(10)
1.431(11)
2.252(10)
2.269(10)
2.180(9)
2.185(8)
1.388(18)
1.294(17)
1.40(2)
Bond angles (°)
N1–Ln1–N2
N1–Ln1–N4
N1–Ln1–N5
N2–Ln1–N4
N2–Ln1–N5
N4–Ln1–N5
N1–C1–N2
56.43(13)
105.41(15)
126.06(14)
129.13(14)
106.38(14)
119.64(15)
115.3(4)
59.52(13)
105.46(14)
125.35(15)
127.52(15)
106.29(14)
119.98(14)
115.3(4)
56.8(2)
126.07(19)
107.20(17)
107.58(19)
122.40(19)
121.27(18)
115.2(6)
60.1(4)
125.2(4)
106.0(4)
107.6(4)
123.6(3)
120.9(4)
115.1(10)
132.4(14)
112.0(15)
136(2)
N1–C1–N3
121.1(4)
121.2(4)
134.6(7)
N2–C1–N3
123.6(4)
123.4(4)
109.4(7)
C2–N1–Ln1
C5(C8)–N2–Ln1
136.7(3)
137.8(3)
133.6(13)
134.8(10)
136.0(3)
137.1(3)
136(2)
Table 3 Optimizations of hydrophosphonylation of benzaldehyde cata-
lyzed by Complexes 1–5 a)
3.3 Catalytic hydrophosphonylation of aldehydes and
ketones
The synthesis of -hydroxyphosphonates has received con-
siderable recent attention because they possess interesting
biological activities and are widely used in the pharmaceu-
tical industry for a variety of potential drugs [14]. The cata-
lytic addition reaction of dialkyl phosphites to aldehydes or
ketones is undoubtedly the most straightforward and atom-
economical pathway for the synthesis of -hydroxyphos-
phonates [15,16]. In 2010, the tetracoordinated lanthanide
amides [(Me3Si)2N]3Ln(μ-Cl)Li(THF)3 were found to be
highly efficient catalysts for the hydrophosphonylation of
aromatic aldehydes under mild reaction conditions [17], a
discovery that provided new insights for the development of
new and efficient organolanthaide-based catalysts for such
transformations. Very recently, some organolanthanide am-
ido complexes respectively supported by pyrrolyl, bridged
bis(indolyl), bridged bis(-diketiminato), and anilido lig-
ands were reported to be highly efficient catalysts for the
hydrophosphonylation of diethyl phosphite with aldehydes
and unactivated ketones [18,19]. To explore the application
of these bimetallic organolanthanide bis(amido) complexes
as catalysts in homogeneous catalysis, the catalytic behavior
of complexes 1–5 toward the hydrophosphonylation of al-
dehydes and ketones with diethyl phosphite were studied.
The addition reaction of diethyl phosphite to benzalde-
hyde to afford diethyl [hydroxy(phenyl)methyl]phosphonate
was selected as the model reaction in our initial screening of
reaction conditions; representative results are summarized
in Table 3. We found that all of the complexes catalyzed
this reaction with high efficiency, and obtained nearly quan-
Entry
Cat. (mol%)
1 (0.1%)
2 (0.1%)
3 (0.1%)
4 (0.1%)
5 (0.1%)
1 (0.05%)
1 (0.1%)
1 (0.1%)
Solvent
solvent-free
solvent-free
solvent-free
solvent-free
solvent-free
solvent-free
THF
Yield (%) b)
1
97
83
91
92
80
90
74
83
2
3
4
5
6
7 c)
8 c)
toluene
a) Reaction conditions: benzaldehyde (10.0 mmol), diethyl phosphite
(12.0 mmol), solvent (2.0 mL) or solvent-free, ambient temperature, 5 min;
b) isolated yields; c) 10 min.
titative yields at ambient temperatures under solvent-free
conditions when the catalyst loading was 0.1 mol%. High
yield (90%) was obtained even when the catalyst loading
was decreased to 0.05 mol% under otherwise same reaction
conditions (Table 3, Entry 6). The ionic radii of the catalysts
had some effect on the reaction. Using the samarium com-
plex (1) as the catalyst, the yield was as high as 97% (Entry
1) but dropped to 83% when the ytterbium complex (2) was
used as the catalyst under the same reaction conditions (En-
try 2). Changing the substituent of the guanidinate ligand
from the isopropyl to the cyclohexyl group slightly influ-
enced the reaction (Entries 1 vs. 4). The reaction went much

Nie et al. Sci China Chem March (2015) Vol.58 No.3
7
Table 4 Hydrophosphonylation of aldehydes catalyzed by Complex 1
faster under solvent-free conditions than under THF or tol-
uene (Entries 7 and 8).
Under optimized reaction conditions, the scope of the
hydrophosphonylation reaction catalyzed by Complex 1 was
investigated; results are summarized in Table 4. Reactions
of both aromatic and aliphatic aldehydes proceeded
smoothly to give corresponding -hydroxyphosphonates in
81%–99% yields. The electronic properties of the aromatic
aldehydes had no obvious influence on the yield. All of the
aromatic aldehydes bearing substituents at para- or meta-
positions, which are either electron-donating groups such as
CH3– (8c), CH3O– (8e and 8f) and (CH3)2N– (8g), or elec-
tron-withdrawing groups such as F– (8h), Cl– (8j and 8k),
Br– (8l) and NO2– (8m and 8n), gave good isolated yields.
An almost quantitative yield was achieved for o-methyl-
benzaldehyde (8b). However, the presence of a coordinating
heteroatom at the ortho-position is disadvantageous for this
transformation. When the o-methoxybenzdehyde and
2-furaldehyde were used as the substrates, obviously low
yields (87% for 8d, and 81% for 8p) were obtained. It is
reasonable to attribute this drop in activity to the coordina-
tion of the heteroatom with lanthanide metal, which shuts
down the catalytic cycle. The reaction proceeded smoothly
with 1-naphthaldehyde to produce the desired product 8o in
a high yield. Pentanal and 3-methylbutanal were also re-
spectively converted to the corresponding hydroxyphos-
phonates 8q (95% yield) and 8r (89% yield).
To further understand the scope of hydrophosphonylation
reactions catalyzed by these bimetallic lanthanide bis(amido)
complexes, unactivated ketones catalyzed by Complex 1
were tested. It was found that the hydrophosphonylation of
acetophenone afforded the desired product 10a in satisfac-
tory yields of up to 78% with 0.1 mol% of Complex 1 as the
catalyst at ambient temperature within a short time of 20
min (Table 5, Entry 4). As the reaction temperature dropped
slightly to 10 °C, a higher yield (83%) was obtained (Table
2, Entry 5). Reactions of various ketones were then studied
employing 0.1 mol% of Complex 1 as the catalyst at 10 °C
for 20 min (results are summarized in Table 6). The elec-
tronic properties of the ketones significantly influenced this
transformation. The presence of an electron-withdrawing
substituent on the phenyl ring is advantageous for the addi-
tion reaction, whereas the presence of an electron-donating
group is disadvantageous. For instance, ketones bearing a
NO2– or Cl– substituent at the para-position of the phenyl
ring gave products in high isolated yields (10d, 94%; 10e,
97%), whereas the p-methylacetophenone produced the
final product 10f in an obviously lower yield (75%). It was
found that this catalytic system is sensitive to the steric hin-
drance of ketones. The presence of substitutions at the
ortho-positions of the aromatic ketones resulted in a dra-
matic decrease in the yield (41% for 10b and 58% for 10c).
For the diphenyl ketone, the product of -hydroxy diaryl
phosphonate 10h was obtained in an excellent yield. Com-
plex 1 worked well for heterocyclic aromatic ketones such
a) Reaction conditions: aldehyde (10 mmol), diethyl phosphite (12
mmol), solvent-free, ambient temperature, isolated yield.
Table 5 Optimizations of hydrophosphonylation of acetophenone cata-
lyzed by Complex 1 a)
Entry
Cat. (mol%)
1 (0.1%)
1 (0.05%)
1 (0.1%)
1 (0.1%)
1 (0.1%)
Time
5 min
Yield (%) b)
1
70
56
78
76
83
2
5 min
3
20 min
60 min
20 min
4
5 c)
a) Reaction conditions: acetophenone (10 mmol), diethyl phosphite (12
mmol), ambient temperature; b) isolated yield; c) 10 °C.
as 3-acetylpyridine and cyclic aliphatic ketone to give the
corresponding products in high yields.

8
Nie et al. Sci China Chem March (2015) Vol.58 No.3
Table 6 Hydrophosphonylation of ketones catalyzed by Complex 1 a)
submitted, without typesetting or editing. The responsibility for scientific
accuracy and content remains entirely with the authors.
This work was supported by the National Natural Science Foundation of
China (21132002, 21372172, 21402138), the Major Research Project of
the Natural Science Foundation of the Jiangsu Higher Education
Institutions (14KJA150007), and the Qing Lan Project.
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4 Conclusions
A series of bimetallic lanthanide bis(amido) complexes
supported by bridged bis(guanidinate) ligands were synthe-
sized from the general metathesis reaction and their struc-
tural features were determined by X-ray diffraction study.
The piperazidine-bridged bis(guanidinato) group proved to
be a suitable ligand system to synthesize bimetallic com-
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lic lanthanide complexes, which were efficient catalysts for
the hydrophosphonylations of aldehydes and unactivated
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aromatic substrates bearing substituents with different steric
and electronic properties, were smoothly transformed into
the final products. Further study is ongoing in our laborato-
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