Synthesis of Bis(NHC)-Based CNC-Pincer Rare-Earth-Metal Amido Complexes and Their Application for the Hydrophosphination of Heterocumulenes

Article abstract of DOI:10.1021/acs.organomet.5b00628

The bis(NHC) (NHC = N-heterocyclic carbene)-based CNC-pincer rare-earth-metal amido complexes LRE[N(SiMe₃)₂]₂ (L = 4-CH₃-2-{R-[N(CH)₂CN]}C₆H₃]₂N; L², R = CH

Full text of DOI:10.1021/acs.organomet.5b00628

Article
pubs.acs.org/Organometallics
Synthesis of Bis(NHC)-Based CNC-Pincer Rare-Earth-Metal Amido
Complexes and Their Application for the Hydrophosphination of
Heterocumulenes
Xiaoxia Gu,† Lijun Zhang,† Xiancui Zhu,† Shaowu Wang,*,†,‡ Shuangliu Zhou,† Yun Wei,†
Guangchao Zhang,† Xiaolong Mu,† Zeming Huang,† Dongjing Hong,† and Feng Zhang†
†Key Laboratory of Functional Molecular Solids, Ministry of Education, Anhui Laboratory of Molecule-Based Materials, College of
Chemistry and Materials Science, Anhui Normal University, Wuhu, Anhui 241000, People’s Republic of China
‡State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences,
Shanghai 200032, People’s Republic of China
S
* Supporting Information
ABSTRACT: The bis(NHC) (NHC = N-heterocyclic
carbene)-based CNC-pincer rare-earth-metal amido complexes
LRE[N(SiMe3)2]2 (L = 4-CH3-2-{R-[N(CH)2CN]}C6H3]2N;
L2, R = CH3; L3, R = CH(CH3)2) were synthesized and
characterized, and their catalytic activities toward hydro-
phosphination of heterocumulenes were developed. Reactions
of bis[2-(3-methylimidazolium)-4-methylphenyl]amine diio-
dide (H3L2I2) or bis[2-(3-isopropylimidazolium)-4-
methylphenyl]amine diiodide (H3L3I2) with 5 equiv of
NaN(SiMe3)2 followed by treatment with 1 equiv of RECl3
in THF at −78 °C afforded the bis(NHC)-based CNC-pincer rare-earth-metal amido complexes LRE[N(SiMe3)2]2 (L2 = [4-
CH3-2-{CH3-[N(CH)2CN]}C6H3]2N, RE = Y (1), Eu (2), Er (3); L3 = [4-CH3-2-{(CH3)2CH-[N(CH)2CN]}C6H3]2N, RE = Y
(4), Er (5), Yb (6)). Complexes 4−6 can also be prepared by stepwise reactions of H3L3I2 with n-BuLi in THF followed by
reactions with [(Me3Si)2N]3RE(μ-Cl)Li(THF)3. Stepwise reactions of H3L2I2 with n-BuLi in THF followed by treatment with
[(Me3Si)2N]3RE(μ-Cl)Li(THF)3 generated the bis(NHC)-based CNC-pincer rare-earth-metal amido complexes L2RE[N-
(SiMe3)2]2 (RE = Y (1), Er (3)) together with the fused-heterocyclic compound 3,8,9-trimethyl-8a,9-dihydro-8H-
benzo[4,5]imidazo[2′,1′:2,3]imidazo[1,2-a]imidazo[2,1-c]quinoxaline (7), which formed through carbene C−C and C−N
coupling. Attempts to prepare complexes of the type LRE[N(SiMe3)2]2 by reaction of H3L3I2 with [(Me3Si)2N]3Yb(μ-
Cl)Li(THF)3 in THF, however, afforded mixed complexes of the bis(NHC)-based CNC-pincer ytterbium complex
L3Yb[N(SiMe3)2]2 (6) and the unexpected bis(NHC)-based CNC-pincer monoamido ytterbium iodide L3YbI[N(SiMe3)2]
(8). Investigation of the catalytic activity of complexes 1−6 and 8 indicated that all complexes displayed high activity toward the
addition of the phosphine P−H bond to heterocumulenes, producing the corresponding phosphaguanidines, phosphaureas, and
phosphathioureas, which represents the first example of bis(NHC)-based CNC-pincer type rare-earth-metal amido complexes as
catalysts for the catalytic addition of the phosphine P−H bond to heterocumulenes with high efficiency in the presence of a low
catalyst loading at room temperature.
discovery.9 Different types of NHC lanthanide complexes have
INTRODUCTION
■
been developed in the past decade.10 Advantages of the
Rare-earth-metal complexes have been successfully used as
bis(NHC)-incorporated tridentate pincer ligand with strongly
catalysts or precatalysts in a range of chemical transformations,
electron donating ylidene carbons and the precise tailoring of
including various types of polymerization and copolymeriza-
tion,1 hydroamination,2 hydrosilylation,3 hydroboration,4 hy-
the metal coordination sphere could provide viable complexes
droalkoxylation,5 hydrothiolation,5e,6 and hydrophosphinatio-
and enable the complexes to be used as homogeneous
catalysts.11 However, bis(NHC)-incorporated tridentate pincer
rare-earth-metal complexes have been less developed.10b,d,f
Recently, we reported the synthesis of a series of the CNC-
pincer diarylamido bis(NHC)-ligated rare-earth-metal com-
plexes under different reaction conditions which exhibited a
n.2a,7 Organolanthanide-catalyzed hydrophosphination was
focused on the area of intramolecular hydrophosphination/
cyclization of alkenes and alkynes and intermolecular hydro-
phosphination of alkenes and alkynes.2a,7 Rare-earth-metal
amido complex promoted intermolecular hydrophosphination
of heterocumulenes has still been poorly investigated.8
Functionalized N-heterocyclic carbene (NHC) ligands have
Received: July 21, 2015
undergone an upsurge in research interest since their first
© XXXX American Chemical Society
A
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high catalytic activity toward the addition of the terminal alkyne
C−H bond to carbodiimides.10b In order to offer more useful
information on the preparation of different types of bis(NHC)-
incorporated rare-earth-metal complexes, reactions of different
substituted imidazolium salts H3LI2 (L = [4-CH3-2-{(R-
[N(CH)2CN]}-C6H3]2N; L2, R = CH3; L3, R = CH(CH3)2)
with different bases followed by treatment with
[(Me3Si)2N]3RE(μ-Cl)Li(THF)3 or RECl3 under different
reaction conditions were examined.
Scheme 1. Synthetic Pathway for Preparation of
Diarylamido-Linked Bis(NHC) Rare-Earth-Metal Amides
On the other hand, catalytic addition of the phosphine P−H
bond to the heterocumulenes could provide a straightforward
and atom-economical route to valuable phosphorus analogues
of phosphaguanidines, phosphaureas, and phosphathioureas
which could be used as ligands for the metal complexes,12 in
medicine,13 in materials chemistry,14 and as synthons in organic
chemistry.15 Early investigations demonstrated that alkali-metal
and alkaline-earth-metal amides could serve as catalysts for the
hydrophosphination of carbodiimides.16 Recently, Hou et al.
reported that the half-sandwich rare-earth-metal
(trimethylsilyl)methyl alkyl complexes could catalyze the
addition of the phosphines P−H bond to carbodiimides,8a
but these reactions required an elevated temperature (80 °C).
Schmidt and co-workers showed that homoleptic α-metalated
dimethylbenzylamine lanthanide complexes could efficiently
catalyze the hydrophosphination of heterocumulenes; however,
these catalysts required a high loading (5 mol %), and 1.15
equiv of Ph2PH to offset the amount of consumed phosphine in
the process of activation of the precatalyst.8b Thus, catalysts
operating at room temperature exhibiting a high activity with
low catalyst loading and solvent compatibility for the catalytic
addition of the phosphine P−H bond to heterocumulenes are
highly required. Here, we wish to report the synthesis of
bis(NHC)-based CNC-pincer rare-earth-metal amido com-
plexes which displayed a high catalytic activity toward the
hydrophosphination of heterocumulenes in different solvents at
room temperature. To the best of our knowledge, this
represents the first example of bis(NHC)-based CNC-pincer
rare-earth-metal amido complexes used as catalysts for catalytic
addition of the phosphine P−H bonds to heterocumulenes,
producing phosphaguanidines, phosphaureas, and phospha-
thioureas with high efficiency.
the complexes L2RE[N(SiMe3)2]2 (RE = Y (1), Er (3)), not
the zwitterionic analogues, were isolated in moderate yields, but
the fused-heterocyclic compound 3,8,9-trimethyl-8a,9-dihydro-
8H-benzo[4,5]imidazo[2′,1′:2,3]imidazo[1,2-a]imidazo[2,1-c]-
quinoxaline (7) was also isolated as a byproduct (Scheme 2 and
Scheme 2. Stepwise Reactions of H3L2I2 or H3L3I2 with Base
Followed by Reaction with [(Me3Si)2N]3RE(μ-Cl)Li(THF)3
Figure 1). The fused-heterocyclic compound 7 was formed
through carbene C−C and C−N coupling. This result was
similar to that in our previous work in part.10b When the bis[2-
(3-methylimidazolium)-4-methylphenyl]amine diiodide
RESULTS AND DISCUSSION
■
Synthesis and Characterization of Bis(NHC)-Based
CNC-Pincer Rare-Earth-Metal Amido Complexes. The
bis(NHC)-based CNC-pincer rare-earth-metal amido com-
plexes L2RE[N(SiMe3)2]2 (L2 = [4-CH3-2-{CH3[N-
(CH)2CN]}C6H3]2N; RE = Y (1), Eu (2), Er (3)) were
prepared in moderate yields by treatment of bis[2-(3-
methylimidazolium)-4-methylphenyl]amine diiodide (H3L2I2)
with 5 equiv of NaN(SiMe3)2 followed by reaction with 1 equiv
of RECl3 in THF at −78 °C (Scheme 1). The bis(NHC)-based
CNC-pincer rare-earth-metal amido complexes L3RE[N-
(SiMe3)2]2 (L3 = [4-CH3-2-{(CH3)2CH[N(CH)2CN]}-
C6H3]2N; RE = Y (4), Er (5), Yb (6)) could be obtained
under similar conditions.
In our previous work, we found that the stepwise treatment
of bis[2-(3-benzylimidazolium)-4-methylphenyl]amine dichlor-
ide (H3L1Cl2) with n-BuLi in THF at −30 °C followed by
reactions with [(Me3Si)2N]3RE(μ-Cl)Li(THF)3 generated the
Figure 1. Structure of fused-heterocyclic compound 7. Hydrogen
atoms are omitted for clarity. Selected bond lengths (Å): C(1)−
C(18), 1.528(3); N(3)−C(18), 1.491(3); N(4)−C(18), 1.473(3);
N(5)−C(18), 1.456(3).
zwitterionic complexes [{L1 RE}{RECl[N(SiMe3)2]3}] (L1 =
2
[4-CH3-2-{(C6H4CH2-[N(CH)2CN]}C6H3]2N) and a fused-
heterocyclic compound.10b However, following this method,
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(H3L2I2) was changed to bis[2-(3-isopropylimidazolium)-4-
methylphenyl]amine diiodide (H3L3I2), only the bis(NHC)-
based CNC-pincer rare-earth-metal amido complexes L3RE[N-
(SiMe3)2]2 (RE = Y (4), Er (5), Yb (6)) were isolated under
the same conditions; neither the analogues of the fused-
heterocyclic compound 7 nor the zwitterionic complexes were
isolated. These results suggested that the substituents on the
imidazolium ring have a significant influence on the final
products.
Another method for the preparation of the bis(NHC)-based
CNC-pincer rare-earth-metal complexes was also tested by
reaction of [(Me3Si)2N]3Yb(μ-Cl)Li(THF)3 with 1 equiv of
bis[2-(3-isopropylimidazolium)-4-methylphenyl]amine diio-
dide (H3L3I2) in THF at room temperature, after workup,
producing the bis(NHC)-based CNC-pincer ytterbium amido
complex L3Yb[N(SiMe3)2]2 (6) and the unexpected bis-
(NHC)-based CNC-pincer monoamido ytterbium iodide
L3YbI[N(SiMe3)2] (16% yield) (8) (Scheme 3 and Figure 2).
The result is also different from that of the reaction of
[(Me3Si)2N]3Yb(μ-Cl)Li(THF)3 with H3L1Cl2, which only
afforded a fused-heterocyclic compound.10b
Figure 3. Molecular structure of complex 1. Hydrogen atoms are
omitted for clarity.
Scheme 3. Reactions of H3L3I2 with [(Me3Si)2N]3Yb(μ-
Cl)Li(THF)3
Figure 4. Molecular structure of complex 4. Hydrogen atoms are
omitted for clarity.
X-ray analyses revealed that complexes 1−6 adopt a similar
structure. The diarylamido-linked bis(NHC) ligand coordinates
to the central metal ion in a tridentate mode by the amido
nitrogen and the two carbene carbon atoms, forming a
distorted-trigonal-bipyramidal geometry with the two silylami-
do N″ groups and the amido group occupying the equatorial
positions having sums of the angles of N(3)−RE−N(6),
N(6)−RE−N(7), and N(7)−RE−N(3) of 359.34(9)° for 1,
359.30(11)° for 2, 359.5(2)° for 3, 359.91(14)° for 4,
359.91(11)° for 5, and 359.9(3)° for 6 and the two carbene
carbon atoms at the axial sites. The average RE−Ccarbene bond
lengths, 2.532(3) Å in 1, 2.579(4) Å in 2, 2.548(9) Å in 3,
2.547(4) Å in 4, 2.517(4) Å in 5, and 2.494(9) Å in 6, fall in the
range of the linkage of a lanthanide metal ion and an ylidene
carbon10f,17 and are quite consistent with the trend of ionic
radii of the corresponding lanthanide elements. These average
RE−Ccarbene bond lengths are comparable to the corresponding
RE−Ccarbene bond lengths found in previous reports.10b,f,h The
1H (or 13C) NMR spectra for 1 and 4 were also indicative of
the formation of the bis(NHC)-based CNC-pincer complexes.
The 1H NMR spectrum of the complex 1 showed the
disappearance of the proton resonances of NH, and NC(H)
Figure 2. Structure of complex 8. Hydrogen atoms are omitted for
clarity. Selected bond lengths (Å): Yb(1)−C(1), 2.420(8); Yb(1)−
C(18), 2.485(8); Yb−Cav, 2.453(8); Yb(1)−N(3), 2.228(6); Yb(1)−
N(6), 2.187(7); Yb(1)−I, 2.9506(9).
The molecular structures of complexes 1−6 and 8 were
determined by single-crystal X-ray analyses. The representative
structural diagrams of complexes 1 and 4 are shown in Figures
3 and 4, respectively. The important bond distances and angles
are summarized in Table 1.
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Table 1. Selected Bond Distances (Å) and Angles (deg) for Complexes 1−6
RE
Y (1)
Eu (2)
Er (3)
Y (4)
Er (5)
Yb (6)
RE(1)−N(3)
RE(1)−N(6)
RE(1)−N(7)
RE(1)−C(1)
RE(1)−C(18)
RE−Cav
N(3)−RE(1)−N(6)
N(3)−RE(1)−N(7)
N(6)−RE(1)−N(7)
C(1)−RE(1)−C(18)
2.322(2)
2.300(2)
2.260(3)
2.505(3)
2.559(3)
2.532(3)
139.53(9)
101.88(9)
117.93(9)
131.25(11)
2.364(3)
2.329(6)
2.293(6)
2.244(7)
2.489(7)
2.608(9)
2.548(9)
139.6(2)
102.5(2)
117.4(2)
130.8(2)
2.321(3)
2.305(3)
2.279(8)
2.265(8)
2.267(8)
2.493(9)
2.495(9)
2.494(9)
137.4(3)
101.5(3)
121.0(3)
142.8(3)
2.342(3)
2.313(4)
2.299(3)
2.303(3)
2.272(4)
2.262(3)
2.606(4)
2.553(4)
2.513(4)
2.552(4)
2.542(4)
2.521(4)
2.579(4)
2.547(4)
2.517(4)
137.65(11)
102.64(11)
119.01(11)
128.17(13)
135.96(13)
101.85(13)
122.10(14)
140.56(15)
136.46(11)
101.82(11)
121.63(11)
141.47(12)
N at 5.30 and 9.55 ppm assigned to the free ligand H3L2I2. The
13C NMR spectrum of complex 1 showed a doublet carbene
carbon resonances at about 192.0 ppm (1JY−C = 38 Hz),
suggesting that the carbene carbons were bound to the metal
center. Similarly, the formation of complex 4 can also be proved
by the NMR results.
Table 2. Optimization of the Conditions for the Catalytic
Addition of the Diphenylphosphine P−H Bond to
a
Diisopropylcarbodiimide
The above results indicated that the substituents on the
bis(imidazolium) salts had a significant influence on controlling
the reaction pathway and the final complexes. The fact that a
low-temperature reaction could prevent the in situ formed
bis(NHC) from coupling is noted. The results provided useful
information for the preparation of different types of NHC-
ligated rare-earth-metal complexes.
c
b
entry
cat. (amt (mol %))
solvent
yield (%)
1
1 (1)
THF
THF
THF
toluene
hexane
THF
THF
THF
THF
THF
THF
100
99
47
98
96
99
98
99
98
96
94
2
1 (0.5)
1 (0.25)
1 (0.5)
1 (0.5)
2 (0.5)
3 (0.5)
4 (0.5)
5 (0.5)
6 (0.5)
8 (0.5)
3
4
5
Catalytic Activity toward Addition of the Phosphine
P−H Bond to Heterocumulenes. Catalytic hydrophosphi-
nation of heterocumulenes could be a straightforward and
atom-economical route to the phosphorus analogues of
guanidines, ureas, thioureas, and amidines. Previously devel-
oped rare-earth-metal complexes as catalysts for the catalytic
addition of the phosphine P−H bond to the carbodiimides and
heterocumulenes required harsh conditions such as elevated
reaction temperatures of 80 °C,8a were only active in polar
solvents, and required a high catalyst loading (5 mol %).8b The
fact that the carbene ligands have a strongly electron donating
property which affects the catalytic activity of the complexes has
been established;10b with the above bis(NHC)-based CNC-
pincer rare-earth-metal amido complexes in hand, the catalytic
activities of these complexes toward the hydrophosphination of
heterocumulenes were examined. The catalytic reaction of
diphenylphosphine (Ph2PH) with N,N′-diiospropylcarbodii-
mide (iPrNCNiPr) was examined under various con-
ditions (Table 2).
The catalytic reaction of diphenylphosphine (Ph2PH) with
N,N′-diisopropylcarbodiimide (iPrNCNiPr) was first
examined in the presence of a 1 mol % loading of complex 1
in THF; the reaction was completed in 0.5 h with a quantitative
conversion of the substrate to the final product. Decreasing the
catalyst loading to 0.5 mol % also afforded the product in
almost quantitative yield. Different solvents such as toluene and
n-hexane only slightly affected the yields of the reaction,
indicating the solvent compatibility of the catalysts. Different
catalysts 2−6 and 8 also exhibited an excellent catalytic activity
for the reaction. These results indicated that the bis(NHC)-
based CNC-pincer type rare-earth-metal amido complexes have
the advantages of high activity, solvent compatibility, and high
efficiency.
6
7
8
9
10
11
a
Reaction conditions: diisopropylcarbodiimide (2.0 mmol), diphenyl-
phosphine (2.0 mmol), solvent (5 mL), room temperature, 0.5 h.
b
c
Isolated yields. cat.: L2RE[N(SiMe3)2]2 (RE = Y (1), Eu (2), Er
(3)); L3RE[N(SiMe3)2]2 (RE = Y (4), Er (5), Yb (6)); L3YbI[N-
(SiMe3)2] (8).
mol % loading of catalyst 1, room-temperature reaction in
THF). It is found that both Ph2PH and (4-MeC6H4)2PH
worked well with N,N′-diisopropylcarbodiimide and N,N′-
dicyclohexylcarbodiimide, producing the corresponding final
products in almost quantitative yields. However, the sterically
bulky N,N′-di-tert-butylcarbodiimide is inactive in the reaction,
probably due to steric effects. This result is parallel to that
previously reported (Table 3, entry 3).16b The hydro-
phosphination reaction also worked well with the isothiocya-
nates; the reaction was tolerant of both electron-donating
groups such as CH3O− and CH3− and electron-withdrawing
groups such as F− and Br−, producing the corresponding
phosphathioureas in very good to quantitative yields. However,
isothiocyanates with electron-withdrawing substituted groups
such as F− and Br− afforded better results than isothiocyanates
with electron-donationg groups such as CH3O− and CH3− on
the phenyl ring (Table 3, entries 7−10); these results can be
attributed to the electron-withdrawing groups making the
carbons more electron deficient favorable following addition of
the diphenylphosphinyl group (RE−PPh2) to the carbon.
Again, it is found that the (4-MeC6H4)2PH worked well with
the isothiocyanates, producing the corresponding products in
good to quantitative yields. Electronic effects for the substrates
Next, different substrates of phosphines and heterocumu-
lenes were tested under the above optimized conditions (0.5
D
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a
Table 3. Catalytic Addition of Various Phosphines to Heterocumulenes by Catalyst 1
b
entry
R2PH
Ph2PH
R′/X
iPr/NiPr
product R/R′/X
Ph/iPr/NiPr
yield (%)
1
9a (99)
9b (99)
2
Ph2PH
Cy/NCy
Ph/Cy/NCy
3
Ph2PH
tBu/NtBu
iPr/NiPr
no product
4
(4-MeC6H4)2PH
(4-MeC6H4)2PH
Ph2PH
4-MeC6H4/iPr/NiPr
4-MeC6H4/Cy/NCy
Ph/Ph/S
9c (99)
9d (98)
9e (100)
9f (100)
9g (100)
9h (94)
9i (86)
5
Cy/NCy
6
Ph/S
7
Ph2PH
4-FC6H4/S
4-BrC6H4/S
4-MeC6H4/S
4-MeOC6H4/S
Ph/S
Ph/4-FC6H4/S
8
Ph2PH
Ph/4-BrC6H4/S
Ph/4-MeC6H4/S
Ph/4-MeOC6H4/S
4-MeC6H4/Ph/S
4-MeC6H4/4-FC6H4/S
4-MeC6H4/4-BrC6H4/S
4-MeC6H4/4-MeC6H4/S
4-MeC6H4/4-MeOC6H4/S
Ph/Cy/O
9
Ph2PH
10
11
12
13
14
15
16
17
Ph2PH
(4-MeC6H4)2PH
(4-MeC6H4)2PH
(4-MeC6H4)2PH
(4-MeC6H4)2PH
(4-MeC6H4)2PH
Ph2PH
9j (99)
4-FC6H4/S
4-BrC6H4/S
4-MeC6H4/S
4-MeOC6H4/S
Cy/O
9k (99)
9l (96)
9m (90)
9n (81)
9o (97)
c
Ph2PH
4-FC6H4/O
-
10a
a
b
c
Reaction conditions: heterocumulenes (2.0 mmol), phosphine (2.0 mmol), catalyst (0.01 mmol), THF (5 mL). Isolated yields. The trimerized
isocyanate product 10a.
2400 Series II macro-elemental analyzer. 1H NMR, 13C NMR, and 31
P
of the isothiocyanates similar to those of the reactions of
Ph2PH with isothiocyanates were found (Table 3, entries 12−
15). However, when the isocyanates were used for the reaction,
only an aliphatic substrate such as CyNCO worked well,
producing the phosphaurea in very high yield (Table 3, entry
16). The aromatic isocyanates all produced the cyclotrimeriza-
tion products; no phosphaureas could be isolated (Table 3,
entry 17). These results were different from previous
observations.8b
NMR spectra for analyses of compounds were recorded on a Bruker
1
300 or 500 NMR spectrometer (300 MHz for H; 75 MHz for 13C;
500 MHz for 1H; 125 MHz for 13C; 121 MHz for 31P), and all
chemical shift values refer to TMS (δ 0.00 ppm), CDCl3 (δ(1H), 7.26
ppm; δ(13C), 77.16 ppm), C6D6 (δ(1H), 7.15 ppm; δ(13C), 128.06
ppm), or C4D8O (δ(1H), 1.72, 3.58 ppm; δ(13C), 25.31, 67.21 ppm). J
values are reported in Hz. Phosphorus chemical shifts were measured
relative to an external 85% aqueous solution of H3PO4. IR spectra
were recorded on a Shimadzu Model FTIR-8400s spectrometer (KBr
pellet). Mass spectra were performed on an Agilent Model 6220
Micromass GCT-MS spectrometer. Crystallographic X-ray data were
collected on a SMART 1000 CCD area detector diffractometer.
Preparation of [L2Y{[N(SiMe3)2]2}] (1). To a suspension of bis[2-
(3-methylimidazolium)-4-methylphenyl]amine diiodide H3L2I2 (920
mg, 1.50 mmol) in THF (20 mL) was added a solution of 2 M
NaN(SiMe3)2 in THF (3.75 mL, 7.50 mmol)) dropwise with stirring
for 8 h at −78 °C, and then a THF suspension of YCl3 (293 mg, 1.50
mmol) was added to the mixture. The mixture was slowly warmed to
room temperature overnight. The solvent was removed under reduced
pressure to afford a yellow solid, which was recrystallized from hexane
to give yellow crystals of 1 in 38% yield (437 mg) for X-ray analysis.
1H NMR (500 MHz, C6D6/d8-THF 3/1 v/v): δ 6.92−6.91 (d, J = 5.0
Hz, 2H, imi-H), 6.87−6.86 (d, J = 5.0 Hz, 2H, imi-H), 6.69−6.68 (d, J
= 5.0 Hz, 1H, Ar-H), 6.67−6.66 (d, J = 5.0 Hz, 1H, Ar-H), 6.61 (s, 1H,
Ar-H), 6.59 (s, 1H, Ar-H), 6.26−6.26 (d, J = 1.7 Hz, 2H, Ar-H), 3.70
(s, 6H, Ar-CH3), 2.07 (s, 6H, N-CH3), 0.25 (s, 18H, Si(CH3)3), −0.20
(s, 18H, Si(CH3)3). 13C NMR (125 MHz, C6D6/d8-THF 3/1 v/v): δ
CONCLUSION
■
In summary, we have demonstrated that a variety of bis(NHC)-
based CNC-pincer rare-earth-metal amido complexes can be
synthesized and characterized. The results indicated that the
reaction conditions and substituents of imidazolium salts both
play important roles in the formation of final products. This
work offers useful information for the preparation of different
types of bis(NHC)-based rare-earth-metal complexes. The
bis(NHC)-based CNC-pincer rare-earth-metal amides dis-
played a high catalytic activity toward the addition of the
phosphine P−H bond to heterocumulenes, producing the
corresponding phosphaguanidines, phosphaureas, and phos-
phathioureas with low catalyst loading at room temperature.
Further studies on the reactivity and catalytic activities of these
kinds of complexes are in progress.
1
192.0 (NCN, d, JY−C(carbene) = 38 Hz), 146.9, 132.4, 129.0, 127.0,
EXPERIMENTAL SECTION
123.3 (Ar-C), 121.2, 120.1 (imi-C), 38.2 (NCH3), 20.4 (ArCH3), 6.7
(Si(CH3)3), 4.5 (Si(CH3)3). Anal. Calcd for C34H58N7Si4Y: C, 53.30;
H, 7.63; N, 12.80. Found: C, 53.03; H, 7.67; N, 12.44. Mp: 162−164
°C. IR (KBr pellets, cm−1): ν 2951 (s), 1663 (w), 1605 (w), 1585 (m),
1516 (s), 1485 (m), 1381 (m), 1310 (m), 1076 (m), 934 (s), 837 (m),
746 (s), 667 (m).
■
General Procedure. All manipulations were carried out under a
dry oxygen-free argon atmosphere using standard Schlenk techniques
or in a glovebox unless otherwise stated. All solvents (hexane, THF,
diethyl ether) were refluxed and distilled over sodium benzophenone
ketyl under argon prior to use unless otherwise noted. RECl3,18
[(Me3Si)2N]3RE(μ-Cl)Li(THF)3 (RE = Y, Eu, Er, Yb),19 bis[2-(3-
methylimidazolium)-4-methylphenyl]amine diiodide (H3L2I2),20 and
bis[2-(3-isopropylimidazolium)-4-methylphenyl]amine diiodide
(H3L3I2)20 were prepared according to the literature methods.
Elemental analysis data were obtained on a PerkinElmer Model
Preparation of [L2Eu{[N(SiMe3)2]2}] (2). This complex was
prepared as purple crystals in 35% yield (435 mg) following the
procedures similar to those described for the preparation of 1 by
treatment of a THF suspension of H3L2I2 (920 mg, 1.50 mmol) with a
solution of 2 M NaN(SiMe3)2 in THF (3.75 mL, 7.50 mmol),
E
DOI: 10.1021/acs.organomet.5b00628
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
followed by reaction with a THF suspension of EuCl3 (387 mg, 1.50
mmol). Anal. Calcd for C34H58N7Si4Eu·C6H14 (2·C6H14): C, 52.49; H,
7.93; N, 10.71. Found: C, 52.74; H, 7.62; N, 10.77. Mp: 167−169 °C.
IR (KBr pellets, cm−1): ν 2963 (s), 1670 (m), 1577 (w), 1516 (m),
1400 (m), 1312 (w), 1251 (s), 1096 (m), 1031 (m), 939 (s), 918 (s),
843 (m), 802 (s), 700 (m).
C6D6, ppm): δ 7.30 (d, J = 7.3 Hz, 1H, Ar-H), 7.12 (d, J = 8.0 Hz, 1H,
Ar-H), 6.71−6.62 (m, 3H, Ar-H), 6.45 (s, 1H, Ar-H), 5.87 (d, J = 2.6
Hz, 1H, NCHCHN), 5.58 (d, J = 2.4 Hz, 1H, NCHCHN), 5.37 (d, J =
2.6 Hz, 1H, NCHCHN), 5.31 (d, J = 2.4 Hz, 1H, NCHCHN), 4.30 (s,
1H, NCHN), 2.56 (s, 3H, N-CH3), 2.44 (s, 3H, N−CH3), 2.24 (s, 3H,
Ar-CH3), 2.19 (s, 3H, Ar-CH3). 13C NMR (125 MHz, C6D6): δ 138.3,
135.8, 129.9, 128.2, 127.1, 123.2, 121.1, 120.5, 118.2, 116.0, 112.9 (Ar-
C), 108.8, 108.7, 105.0, 104.9 (NCHCHN), 94.9 (NCN), 80.3
(NCHN), 37.7, 31.6 (N-CH3), 18.8, 18.5 (Ar-CH3). HRMS (ESI):
calcd for C22H24N5 ([M + 1]+) m/z 358.2026 ([M + 1]+), found
358.2025. Anal. Calcd for C22H23N5: C, 73.92; H, 6.49; N, 19.59.
Found: C, 73.65; H, 6.40; N, 19.55. Mp: 97−99 °C. IR (KBr pellets,
cm−1): ν 2940 (w), 2886 (w), 1618 (m), 1605 (m), 1570 (m), 1520
(m), 1489 (s), 1464 (m), 1445 (m), 1333 (m), 1300 (s), 1242 (w),
1184 (w), 1173 (m), 1053 (w), 1016 (m), 999 (m), 943 (w), 843 (m),
791 (m), 764 (m), 735 (m), 656 (m).
Preparation of [L2Er{[N(SiMe3)2]2}] (3). This complex was
prepared as yellow crystals in 30% yield (380 mg) following
procedures similar to those described for the preparation of 1 by
treatment of a THF suspension of H3L2I2 (920 mg, 1.50 mmol) with a
solution of 2 M NaN(SiMe3)2 in THF (3.75 mL, 7.50 mmol),
followed by reaction with a THF suspension of ErCl3 (410 mg, 1.50
mmol). Anal. Calcd for C34H58N7Si4Er·1.5C6H14 (3·1.5C6H14): C,
53.04; H, 8.18; N, 10.07. Found: C, 53.04,; H, 7.84; N, 10.38. Mp:
161−163 °C. IR (KBr pellets, cm−1): ν 2951 (m), 1681 (w), 1572
(m), 1512 (s), 1491 (s), 1302 (m), 1240 (m), 1177 (m), 1138 (m),
1064 (m), 1016 (w), 945 (s), 837 (m), 793 (s), 669 (m).
Preparation of [L3YbI{N(SiMe3)2}] (8). To a THF solution of
[(Me3Si)2N]3Yb(μ-Cl)Li(THF)3 (1.369 g, 1.50 mmol) was added
H3L3Cl2 (1.004 g, 1.50 mmol) suspended in THF (30 mL), the
mixture was stirred for 12 h at room temperature. The solvent was
removed under reduced pressure to afford a yellow solid which was
recrystallized from hexane, giving red crystals of 8 (209 mg, 16%
yield), and yellow crystals of 6 (258 mg, 19% yield). Anal. Calcd for
C32H48N6ISi2Yb: C, 44.03; H, 5.54; N, 9.63. Found: C, 44.02; H, 5.70;
N, 9.31. Mp: 149−150 °C. IR (KBr pellets, cm−1): ν 2955 (s), 1663
(m), 1605 (m),1547 (m), 1508 (s), 1483 (m), 1466 (w), 1375 (m),
1312 (m), 1259 (s), 1180 (s), 1136 (m), 1065 (w), 982 (w), 883 (m),
839 (s), 748 (m), 683 (m), 658 (m).
General Procedures for the Hydrophosphination of Hetero-
cumulenes.8b Method A. In the glovebox, a Schlenk tube was
charged with complex 1 (8 mg, 0.01 mmol), diphenylphosphine (252
mg, 2.0 mmol), and THF (5 mL). Then the carbodiimide (2.0 mmol)
was added to the mixture. The mixture was stirred at room
temperature for 0.5 h. After the solvent was removed under reduced
pressure, the residue was triturated with hexane (2 mL), extracted with
hexane, filtered, concentrated, and recrystallized from hexane at −20
°C to afford the related phosphaguanidines 9a−d.
Preparation of [L3Y{[N(SiMe3)2]2}] (4). This complex was
prepared as yellow crystals in 36% yield (453 mg) following the
procedures similar to those described for the preparation of 1 by
treatment of a THF suspension of H3L3I2 (1.004 g, 1.50 mmol) with a
solution of 2 M NaN(SiMe3)2 in THF (3.75 mL, 7.50 mmol),
followed by reaction with a THF suspension of YCl3 (293 mg, 1.50
1
mmol). H NMR (500 MHz, C6D6/d8-THF, 1/5 v/v): δ 7.64 (d, J =
1.8 Hz, 2H, imi-H), 7.51 (d, J = 1.4 Hz, 2H, imi-H), 7.15 (s, 2H, Ar-
H), 6.73 (dd, J = 8.3, 1.7 Hz, 2H, Ar-H), 6.43 (d, J = 8.3 Hz, 2H, Ar-
H), 5.23 (dt, J = 13.2, 6.6 Hz, 2H, CH(CH3)2), 2.24 (s, 6H, CH3),
1.60 (d, J = 6.5 Hz, 6H, CH(CH3)2), 1.53 (d, J = 6.6 Hz, 6H,
CH(CH3)2), 0.09 (s, 18H, Si(CH3)3), −0.38 (s, 18H, Si(CH3)3). 13C
NMR (125 MHz, C6D6/d8-THF, 1/5 v/v): δ 190.3 (NCN, d,
1JY−C(carbene) = 38 Hz), 147.1, 132.8, 128.5, 128.4, 128.3, 125.9, 123.6
(Ar-C), 121.6, 116.8 (imi-C), 51.6 (CH(CH3)3), 20.0 (ArCH3), 6.7
(CH(CH3)3), 4.6 (Si(CH3)3), 2.1 (Si(CH3)3). Anal. Calcd for
C38H66N7Si4Y·C6H14 (4·C6H14): C, 58.18; H, 8.88; N, 10.79. Found:
C, 58.44; H, 8.65; N, 10.83. Mp: 145−147 °C. IR (KBr pellets, cm−1):
ν 2955 (s), 1663 (s), 1603 (m), 1512 (s), 1368 (m), 1250 (m), 1180
(m), 1138 (m), 1074 (w), 1005 (w), 934 (s), 883 (m), 839 (s), 750
(m), 683 (m), 660 (m).
Preparation of [L3Er{[N(SiMe3)2]2}] (5). This complex was
prepared as yellow crystals in 32% yield (432 mg) following
procedures similar to those described for the preparation of 1 by
treatment of a THF suspension of H3L3I2 (1.004 g, 1.50 mmol) with a
solution of 2 M NaN(SiMe3)2 in THF (3.75 mL, 7.50 mmol),
followed by reaction with a THF suspension of ErCl3 (410 mg, 1.50
mmol). Anal. Calcd for C38H66N7Si4Er: C, 50.68; H, 7.39; N, 10.89.
Found: C, 50.33; H, 7.47; N, 10.74. Mp: 139−141 °C. IR (KBr pellets,
cm−1): ν 2955 (s), 1655 (s), 1605 (w), 1560 (w), 1545 (m), 1510 (s),
1481 (m), 1369 (m), 1314 (w), 1250 (m), 1180 (m), 1136 (m), 1074
(w), 1007 (w), 934 (m), 883 (m), 837 (s), 748 (m), 683 (m), 660
(w).
Method B. In the glovebox, the Schlenk tube was charged with
complex 1 (8 mg, 0.01 mmol), diphenylphosphine (252 mg, 2.0
mmol), and THF (5 mL). Then the heterocumulene (2.0 mmol) was
added to the mixture. The mixture was stirred at room temperature for
0.5 h. After the solvent was removed under reduced pressure, the
residue was triturated with hexane (2 mL), washed with hexane,
filtered, and dried under vacuum, yielding the corresponding
phosphathioureas 9e−n or phosphaurea 9o.
Crystal Structure Determination. Suitable crystals of complexes
1−6 and 8, fused-heterocyclic compound 7, and the trimerized
isocyanate 10a were each mounted on a sealed capillary. Diffraction
was performed on a SMART CCD area detector diffractometer using
graphite-monochromated Mo Kα radiation (λ = 0.71073 Å). An
empirical absorption correction was applied using the SADABS
program.21 All structures were solved by direct methods, completed by
subsequent difference Fourier syntheses, and refined anisotropically for
all non-hydrogen atoms by full-matrix least-squares calculations on F2
using SHELXTL-97.22 All hydrogen atoms were refined using a riding
model. Crystal and refinement data can be found in the Supporting
Information.
Preparation of [L3Yb{[N(SiMe3)2]2}] (6). This complex was
prepared as yellow crystals in 31% yield (421 mg) following
procedures similar to those described for the preparation of 1 by
treatment of a THF suspension of H3L3I2 (1.004 g, 1.50 mmol) with a
solution of 2 M NaN(SiMe3)2 in THF (3.75 mL, 7.50 mmol),
followed by reaction with a THF suspension of YbCl3 (419 mg, 1.50
mmol). Anal. Calcd for C38H66N7Si4Yb·0.6C6H14 (6·0.6C6H14): C,
52.15; H, 7.83; N, 10.23. Found: C, 52.51; H, 7.57; N, 10.63. Mp:
150−152 °C. IR (KBr pellets, cm−1): ν 2949 (s), 1662 (s), 1605
(w),1553 (w), 1514 (s), 1499 (m), 1427 (w), 1381 (m), 1238 (s),
1194 (s), 1140 (m), 1074 (w), 983 (m), 883 (m), 804 (s), 689 (m),
663 (w), 615 (w).
ASSOCIATED CONTENT
■
S
* Supporting Information
Complexes 1 and 3−6 can also be prepared in 32%, 38%, 46%, 40%,
and 33% yields, respectively, by the stepwise treatment of H3L2I2
(H3L3I2) with n-BuLi (2 equiv) in THF at −30 °C for 4 h followed by
reaction with [(Me3Si)2N]3RE(μ-Cl)Li(THF)3.
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.5b00628.
The fused-heterocyclic compound 3,8,9-trimethyl-8a,9-dihydro-8H-
benzo[4,5]imidazo[2′,1′:2,3]imidazo[1,2-a]imidazo[2,1-c]quinoxaline
(C22H23N5, 7) was isolated in 22% and 25% yields, respectively, in the
Characterization data and spectra for compounds and
crystallographic data and structure refinement details for
1−8 and 10a (PDF)
1
preparation of 1 and 3 following this method. H NMR (300 MHz,
F
DOI: 10.1021/acs.organomet.5b00628
Organometallics XXXX, XXX, XXX−XXX

Organometallics
X-ray crystallographic files for structure determinations
Article
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AUTHOR INFORMATION
Corresponding Author
*E-mail for S.W.: swwang@mail.ahnu.edu.cn.
■
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Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was cosupported by the National Natural Science
Foundation of China (Grant Nos. 21372010, 21172003, and
21432001), the National Basic Research Program of China
(2012CB821600), and the Special and Excellent Research Fund
of Anhui Normal University.
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DOI: 10.1021/acs.organomet.5b00628
Organometallics XXXX, XXX, XXX−XXX