Rare-earth metal tris(trimethylsilylmethyl) anionic complexes bearing one 1-phenyl-2,3,4,5-tetrapropylcyclopentadienyl ligand: Synthesis, structural characterization, and application

Article abstract of DOI:10.1021/ic3018369

Synthesis and structural characterization of half-sandwich rare-earth metal tris(trimethylsilylmethyl) anionic complexes bearing one 1-phenyl-2,3,4,5- tetrapropylcyclopentadienyl ligand are achieved. These soluble anionic compounds show good reactivity in

Full text of DOI:10.1021/ic3018369

Article
pubs.acs.org/IC
Rare-Earth Metal Tris(trimethylsilylmethyl) Anionic Complexes
Bearing One 1‑Phenyl-2,3,4,5-tetrapropylcyclopentadienyl Ligand:
Synthesis, Structural Characterization, and Application
Ling Xu,† Zitao Wang,† Wen-Xiong Zhang,*,†,‡ and Zhenfeng Xi*,†
†Beijing National Laboratory for Molecular Sciences, Key Laboratory of Bioorganic Chemistry and Molecular Engineering of Ministry
of Education, College of Chemistry, Peking University, Beijing 100871, China
‡State Key Laboratory of Elemento-Organic Chemistry, Nankai University, Tianjin 300071, China
S
* Supporting Information
ABSTRACT: Synthesis and structural characterization of half-
sandwich rare-earth metal tris(trimethylsilylmethyl) anionic
complexes bearing one 1-phenyl-2,3,4,5-tetrapropylcyclopenta-
dienyl ligand are achieved. These soluble anionic compounds
show good reactivity in the stoichiometric reaction with
dibenzoylmethane (DBM) to give the salt-free half-sandwich
complex bearing two chelate DBM ligands. More importantly,
they can serve as excellent and general catalyst precursors for
the addition of different types of amines including primary
aromatic amines (ArNH2), acyclic (RR′NH, ArRNH, and ArAr′NH; R, R′ = Alkyl group, Ar, Ar′ = Aromatic group), or cyclic
secondary aliphatic amines to carbodiimides yielding efficiently guanidines. Acyclic secondary amines of the general formula
ArAr′NH and ArRNH cannot be achieved efficiently by the previous rare-earth catalysts because of their weak nucleophilicity
and steric hindrance. Our results show clearly the reactivities of anionic trialkyl precursors are comparable with the corresponding
neutral alkyl complex in the stoichimetric reaction but exhibit better catalytic activity than the known catalysts.
synthesis and application of the isolable and soluble anionic
alkyl complexes having one cyclopentadienyl ligand.
INTRODUCTION
■
Recent years have witnessed a significant growth in the
synthesis and catalytic application of neutral and cationic half-
sandwich rare-earth alkyl complexes bearing only one cyclo-
pentadienyl ancillary ligand.1 This is because these complexes
will provide a sterically and electronically more unsaturated
metal center and be expected to show unique reactivities
differing from those of the metallocenes.1 However, anionic
half-sandwich rare-earth alkyl complexes remain to be unex-
plored. This is mainly because it is generally known that anionic
alkyl complexes have the decreased reactivity due to the
additional electronic and steric saturation of the metal
environment.1c In addition, their sparing solubility in common
polar and nonpolar solvents hampers the isolation, purification,
and characterization as well as further application. However, the
formation of anionic rare-earth metal moieties is a commonly
observed process in the salt metathesis reaction when alkali
metal hydrocarbyl derivatives are utilized.2 The production of
anionic complexes is usually suppressed by carefully controlling
the amount of alkali metal hydrocarbyl derivatives and reaction
ratio. In some certain cases, it is an inevitable feature owing to
the concomitant and competitive process between neutral and
anionic complexes leading to the low-yield formation of the
desirable neutral complexes. It will be a promising field if the
reactivity of anionic half-sandwich rare-earth alkyl complexes is
much closer to or better than that of neutral complexes.
Therefore, it is of great interest and importance to explore the
The catalytic addition of amines to carbodiimides, also
known as guanylation reaction of amines or hydroamination of
carbodiimides, has received much current interest for the atom-
economical preparation of guanidines.3 Many catalysts
including transition metal, main group, and rare-earth metal
have been designed and tested for the guanylation reaction.4−7
We have also reported the guanylation reaction between amines
and carbodiimides by use of readily available Zn(OTf)2 and
AlMe3 to provide trisubstituted guanidines.4b,5d The guanyla-
tion reaction of primary aromatic amines (ArNH2), acyclic
(RR′NH), or cyclic secondary aliphatic amines has been
achieved by some catalysts.4−6 In comparsion, because of their
weak nucleophilicity and steric hindrance, the guanylation
reaction of ArAr′NH cannot be accomplished by the reported
rare-earth catalysts, but the guanylation reaction of secondary
amines of the general formula ArRNH cannot be achieved by
all reported catalysts. Thus, a general catalyst system perform-
ing the guanylation reaction of different types of amines is a
great challenge and is of great importance in academy and
pharmaceutical industry.
We report here the synthesis and characterization of rare-
earth metal tris(trimethylsilylmethyl) anionic complexes
Received: August 23, 2012
Published: October 24, 2012
© 2012 American Chemical Society
11941
dx.doi.org/10.1021/ic3018369 | Inorg. Chem. 2012, 51, 11941−11948

Inorganic Chemistry
Article
supported by one 1-phenyl-2,3,4,5-tetrapropylcyclopentadienyl
ligand (Cp4PrPh for short). The installation of four propyl
groups on the Cp ring ensures trialkyl anionic complexes highly
soluble in common solvents and makes them isolable. The
reaction of trialkyl anionic complex with dibenzoylmethane
(DBM) gave the salt-free half-sandwich complex. More
importantly, these anionic complexes act as general and highly
active catalysts for the guanylation reaction of various amines
including primary aromatic amines (ArNH2), acyclic (RR′NH,
ArRNH, and ArAr′NH), or cyclic secondary aliphatic amines.
anionic skeleton seems to be the three tripod piano. Each
lithium cation in 1-Lu is surrounded by three thf molecules and
one ether, which form a distorted tetrahedral coordination
sphere. The Li−O distances, which lie between 1.88(2) and
1.98(2) Å, agree with the range of 1.907(9) to 1.934(9) Å
found in [Li(thf)4]+[LuCl2{(C13H8)CPh2(C5H4)}]−.9 X-ray
analysis reveals that 1-Ho crystallizes in the orthorhombic
Pna2(1) space group. The holmium anionic skeleton in 1-Ho is
analogous to that of 1-Lu; however, lithium cation in 1-Ho is
surrounded by four thf molecules forming a distorted
tetrahedral environment.
RESULTS AND DISCUSSION
Reaction of 1-Lu with Dibenzoylmethane. The reaction
of 1-Lu with dibenzoylmethane (DBM) (see Scheme 2) gave
rise to the salt-free half-sandwich lutetium complex [Cp4PrPhLu-
(DBM)2(thf)], showing the reactivity of half-sandwich rare-
earth metal anionic trialkyl precursor is comparable with the
corresponding neutral dialkyl complex. An X-ray analysis
reveals that the space group of 2-Lu is P2(1)/c. The central
Lu atom was established as eight-coordinate and surrounded by
one η5-Cp4PrPh, one thf and two η2-dibenzoylmethane ligands.
The distance of Lu1−Cp(centroid) 2.338(11) Å in this
compound is slightly larger than that of the analogue
Cp4MeEtLu(acac)2 (acac = acetylacetonate, 2.276(2) Å),10
whereas all of the four Li−O(DBM anion) bond lengths in
2-Lu are consistent with those of Cp4MeEtLu(acac)2. The
centroid of Cp ring,Lu atom and the O atom of thf are almost
collinear with the bond angle of 177.4(3)°. The bond angles of
O1−Lu1−O2 and O3−Lu1−O4 are smaller than those of O1−
Lu1−O4 and O2−Lu1−O3 probably owning to the strain of
the six-membered [LuO2C3] ring.
Catalytic Application in Addition of Amines to
Carbodiimides. a). Addition of Primary Aromatic Amines
to Carbodiimides. No reaction was observed when the mixture
of aniline and N,N′-diisopropylcarbodiimide (iPrNCNiPr)
was heated to 140 °C for 24 h in C6D5Cl (Table 2, entry 1). In
contrast, when 1 mol % 1-Y was involved, the guanylation
between aniline and N,N′-diisopropylcarbodiimide proceeded
even at room temperature (Table 2, entries 2 and 3). Increased
temperatures could accelerate this reaction, as it rose up to 50
or 80 °C, the yields of 3a arrived up to 86% or 99%,
respectively (Table 2, entries 4 and 5). This guanylation
process also worked in toluene or THF, whereas the yields
were slightly lower than in benzene (Table 2, entries 6 and 7).
Other analogous complexes, 1-Ho, 1-Er, 1-Tm, and 1-Lu, also
showed similar catalytic reactivity to 1-Y. These slightly lower
yields are possibly owing to the minor radii (Table 2, entries 8−
11).
■
Synthesis and Structure of Rare-Earth Metal Tris-
(trimethylsilylmethyl) Anionic Complexes Bearing One
1-Phenyl-2,3,4,5-tetrapropylcyclopentadienyl Ligand.
HCp4PrPh ligand was prepared by Lewis acid mediated reaction
of tetrapropyl zirconacyclopentadiene with benzaldehyde.8
Initially, we expected to synthesize salt-free rare-earth metal
bis(trimethylsilylmethyl) complexes having one Cp4PrPh ligand
by acid−base reaction between the rare-earth tris-
(trimethylsilylmethyl) complexes Ln(CH2SiMe3)3(thf)2 (Ln =
Y, Ho, Er, Tm, and Lu) and a ligand HCp4PrPh. The target
dialkyl complexes were not observed at room temperature or
even at higher temperatures because of the weak acidity of
HCp4PrPh. Then the salt metathesis reaction among LiCp4PrPh
,
LnCl3(thf)3 and two Me3SiCH2Li was attempted; however, a
mixture of neutral dialkyl and anionic trialkyl complexes was
observed. So we turned our attention to the synthesis and
isolation of anionic trialkyl complexes. Thus, after LiCp4PrPh
which was generated from HCp4PrPh and n-BuLi was first
treated with LuCl3(thf)3 at room temperature for 12 h, then
reacted with three equiv of Me3SiCH2Li at room temperature
for 0.5 h in THF/OEt2, the anionic trialkyl complex
[Cp4PrPhLu(CH2SiMe3)3][Li(thf)3(OEt2)] (1-Lu) was obtained
in 74% isolated yield. Similar to the synthesis of 1-Lu, the
analogous [Cp4PrPhLn(CH2SiMe3)3][Li(thf)n(OEt2)4‑n] 1-Ln
(Y, Er and Tm: n = 3, Ho: n = 4) were easily prepared in
high yields. Rare-earth metal anionic complexes 1-Ln (Ln = Y,
Ho, Er, Tm, and Lu) are soluble in benzene, toluene, and many
polar solvents (Scheme 1).
Scheme 1. Preparation of Half-Sandwich Rare-Earth Metal
Tris(trimethylsilylmethyl) Anionic Complexes
Complex 1-Y was chosen as the catalyst for the guanylation
process between various substituted anilines and carbodiimides.
Representative results were shown in Table 3. For most
anilines, the process could afford excellent yields whatever the
position of functional group and whether electron-donating or
electron-withdrawing substituents were installed on benzene
ring. The reaction of an aniline with the bulkier N,N′-di-tert-
butylcarbodiimide provided relatively low yield of guanidine 3d
probably owing to its steric hindrance. Aromatic C−F (3e and
3f), C−Cl (3g and 3h), C−Br (3i), and C−I (3j) bonds as well
as CN group (3n) could tolerate the reaction conditions. In
addition, 5-methylthiazol-2-amine was tested to be a good
substrate in this reaction as a representative of heterocyclo-
substituted amines (3o).
All of these anionic complexes 1-Ln were structurally
characterized by X-ray diffraction analyses. Their selected
bond lengths and angles are summarized in Table 1, and only
the ORTEP drawings of 1-Lu and 1-Ho are shown in Figures 1
and 2, respectively. X-ray analyses reveal that 1-Ln (Ln = Y, Er,
Tm, and Lu) are isostructural and isomorphous, which
crystallize in the monoclinic P2(1)/n space group. The solid
state structure of 1-Lu reveals a solvent separated ion pair. The
lutetium atom in the anionic unit is surrounded by one Cp4PrPh
ligand and three tris(methylsilylmethyl) ligands. The lutetium
b). Addition of Secondary Amines to Carbodiimides.
Generally, secondary amines are not as reactive as primary
11942
dx.doi.org/10.1021/ic3018369 | Inorg. Chem. 2012, 51, 11941−11948

Inorganic Chemistry
Article
Table 1. Selected Bond Lengths (Å) and Angles (deg) for 1-Ln (Ln: Y, Ho, Er, Tm, and Lu)
1-Y
1-Ho
1-Er
1-Tm
1-Lu
Ln−C(CH2TMS)
2.424(5)
2.430(5)
2.437(4)
2.425(5)
2.711(5)
1.91 (3)
2.392(10)
2.427(10)
2.428(10)
2.396(10)
2.685(10)
1.90(4)
2.392(7)
2.400(7)
2.404(7)
2.396(7)
2.684(7)
1.93 (3)
112.9(2)
113.2(2)
113.6(3)
104.4(3)
105.6(3)
106.4(3)
2.373(7)
2.375(7)
2.411(7)
2.403(7)
2.690(7)
1.924(16)
112.1(2)
115.6(2)
114.0(2)
103.1(3)
104.2(2)
106.9(3)
2.367(9)
2.373(8)
2.375(8)
2.366(8)
2.657(8)
1.93(2)
Ln−Cp(centroid)
Ln−Cp(av)
Li−O(av)
∠ C(CH2TMS)−Ln−Cp(centroid)
112.5(2)
113.0(2)
114.5(2)
104.53(18)
106.30(17)
106.33(18)
113.2(4)
117.2(4)
115.5(3)
102.3(4)
103.0(4)
103.8(4)
112.8(3)
113.6(3)
114.4(3)
104.5(4)
104.6(4)
105.9(3)
∠ C(CH2TMS)−Ln−C(CH2TMS)
Figure 1. ORTEP drawing of 1-Lu with 20% thermal ellipsoids.
Hydrogen atoms are omitted for clarity.
Figure 3. ORTEP drawing of 2-Lu with 30% thermal ellipsoids.
Hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and
angles (deg): Lu1−O1 2.188(6), Lu1−O2 2.186(7), Lu1−O3
2.207(7), Lu1−O4 2.214(8), Lu1−Cp(centroid) 2.338(11); O1−
Lu1−O2 77.4(2), O3−Lu1−O4 78.6(3), O2−Lu1−O3 89.0(2), O1−
Lu1−O4 99.7(3), O1−Lu1−Cp(centroid) 104.8(3), O2−Lu1−Cp-
(centroid) 106.8 (3), O3−Lu1−Cp(centroid) 105.2(3), O4−Lu1−
Cp(centroid) 103.1(3), O5−Lu1−Cp(centroid) 177.4(3).
Table 2. Rare-Earth Trialkyl Anionic Complexes Catalyzed
a
Addition of an Aniline to N,N′-Diisopropylcarbodiimide
Figure 2. ORTEP drawing of 1-Ho with 20% thermal ellipsoids.
Hydrogen atoms are omitted for clarity.
b
Scheme 2. Reaction of 1-Lu with Dibenzoylmethane
entry catalyst (mol %)
solvent
C6D5Cl
temp (°C) time (h) yield (%)
1
0
140
r.t.
r.t.
50
80
80
80
80
80
80
80
24
1
0
2
1-Y
1-Y
1-Y
1-Y
1-Y
1-Y
1-Ho
1-Er
1-Tm
1-Lu
C6D6
37
81
86
>99
96
93
95
96
95
95
3
C6D6
24
1
4
C6D6
5
C6D6
1
6
[D8]toluene
[D8]THF
C6D6
1
7
1
8
1
9
C6D6
1
amines in the addition reaction toward carbodiimides.
However, 1-Y could also catalyze various cyclic and acyclic
secondary amines to furnish guanidines with the loading of 1
mol % in toluene at 130 °C (Table 4). Interestingly, in the
presence of 1-Y, the addition of N-methylaniline to a
carbodiimide can smoothly provide the corresponding
10
11
C6D6
1
C6D6
1
a
Conditions: aniline, 0.51 mmol; N,N′-diisopropylcarbodiimide, 0.50
b
1
mmol. Yields were determined by H NMR.
11943
dx.doi.org/10.1021/ic3018369 | Inorg. Chem. 2012, 51, 11941−11948

Inorganic Chemistry
Article
Table 3. Catalytic Addition of Various Primary Amines to
Carbodiimides
Table 4. Catalytic Addition of Secondary Amines to
Carbodiimides
ab
,
a
a
Conditions: amines, 0.51 mmol; carbodiimides, 0.50 mmol; 1-Y,
b
c
0.005 mmol; benzene, 0.5 mL. NMR yield (%). Condition: 34 h.
d
e
f
g
Isolated yield. Condition: 6 h. Condition: 2 h. Condition: 4 h.
guanidine 5d in 81% yield. This result showed obviously better
catalytic activity than the well-investigated 4-Y compound
(Table 4, entries 4−5). Similarly, the addition reaction of
diphenylamine or N-methylaniline having a substituent on the
phenyl ring also showed better catalytic activity using 1-Y than
4-Y(Table 4, entries 6−9). Although the guanylation reaction
of acyclic (RR′NH) or cyclic secondary aliphatic amines have
been achieved in good yields by those reported catalysts,4−6 as
far as we are aware, the complex 1-Y is found to be the first
catalyst to effect efficiently the guanylation reaction of
secondary amines of the general formula ArRNH.
c). Mechanism. A possible mechanism of the catalytic cycle
for the addition of amines into carbodiimides was proposed
(Scheme 3). The precursor 1-Y underwent an acid−base
reaction with amine to give the active intermediate A. Then a
nucleophilic addition of A to carbodiimide led to the formation
of the guanidinate species B. The next step of the cycle was
determined by the type of amines. If secondary amines were
involved here, B would be protonated straightforwardly by
another molecule of amine to give the final product 5 with the
regeneration of A. However, when primary aromatic amines
were involved, B could rearrange to the unsymmetrical
guanidinate C as a more stable intermediate. The following
a
Conditions: amines, 0.51 mmol; carbodiimides, 0.50 mmol; 1-Y,
b
c
0.005 mmol; toluene 0.5 mL. NMR yield. Determined by 13C NMR
(inverse gated decoupling). Isolated yield.
d
steps were similar to that of secondary amines, C would react
with another molecule of primary amine to give the guanidine
D with the regeneration of species A. Intramolecular 1,3-
hydrogen shift of D then afforded more stable guanidine 3
owing to the conjugation effect between the aromatic ring and
CN bond.
CONCLUSION
■
In summary, we report here the first synthesis of rare-earth
metal tris(trimethylsilylmethyl) anionic complexes bearing one
1-phenyl-2,3,4,5-tetrapropylcyclopentadienyl ligand, whose
structures are fully characterized. These soluble anionic
compounds show similar reactivity to the neutral half-sandwich
rare-earth metal dialkyl compounds in the stoichiometric
reaction with dibenzoylmethane. For 1-Y, it can catalyze the
guanylation process between various amines and carbodiimides
in good to excellent yields. For aromatic secondary amines, 1-Y
shows much better catalytic activity in the guanylation than the
11944
dx.doi.org/10.1021/ic3018369 | Inorg. Chem. 2012, 51, 11941−11948

Inorganic Chemistry
Article
J = 7.3 Hz, 6H; CH2CH2CH3), 1.11 (t, J = 7.0 Hz, 6H; O(CH2CH3)2),
1.26−1.42 (m, 4H; CH2CH2CH3), 1.49−1.57 (m, 4H; CH2CH2CH3),
1.75−1.79 (m, 12H; β-CH2, THF), 2.37−2.47 (m, 4H; CH2CH2CH3),
2.49−2.56 (m, 4H; CH2CH2CH3), 3.38 (q, J = 7.0 Hz, 4H;
O(CH2CH3)2), 3.60−3.63 (m, 12H; α-CH2, THF), 6.97−7.00 (m,
1H; p-C6H5), 7.13−7.16 (m, 2H; m-C6H5), 7.31−7.33 (m, 2H; o-
C6H5) ppm; 13C NMR (75 MHz, [D8]THF, Me4Si): δ = 5.3, 15.2,
15.5, 26.4, 26.9, 27.7, 31.0, 31.1, 38.1, 68.3, 119.3, 120.1, 122.7, 124.5,
127.7, 132.1, 141.7 ppm.
Scheme 3. Possible Mechanism of Catalytic Addition of
Amines to Carbodiimides
[Cp4PrPhHo(CH2SiMe3)3][Li(thf)4] (1-Ho). Starting from HoCl3
(136 mg, 0.50 mmol), complex 1-Ho was obtained as an orange
powder (398 mg, 0.38 mmol, 77% yield) in a manner analogous to
that described for the preparation of 1-Y. Single crystals of 1-Ho
suitable for X-ray analysis could be grown from Et2O/hexane for 2
days at −20 °C.
[Cp4PrPhEr(CH2SiMe3)3][Li(thf)3(OEt2)] (1-Er). Starting from ErCl3
(137 mg, 0.50 mmol), complex 1-Er was obtained as a pink powder
(423 mg, 0.41 mmol, 82% yield) in a manner analogous to that
described for the preparation of 1-Y. Single crystals of 1-Er suitable for
X-ray analysis could be grown from Et2O/hexane for 2 days at −20 °C.
When 1-Er was dried up under reduced pressure, the solvents
coordinated to Li center were released to give pink powder. Anal.
Calcd for C35H66ErLiSi3: C, 56.40; H, 8.93; Found: C, 56.54; H, 8.91.
[Cp4PrPhTm(CH2SiMe3)3][Li(thf)3(OEt2)] (1-Tm). Starting from
TmCl3 (138 mg, 0.50 mmol), complex 1-Tm was obtained as a
colorless powder (451 mg, 0.44 mmol, 87% yield) in a manner
analogous to that described for the preparation of 1-Y. Single crystals
of 1-Tm suitable for X-ray analysis could be grown from Et2O/hexane
for 2 days at −20 °C.
corresponding well-investigated rare-earth alkyl compound
bearing CGC (constrained geometry compound) ligand.
These results on the application of half-sandwich rare-earth
metal anionic trialkyl complexes show clearly the reactivity of
anionic trialkyl precursor is comparable with the corresponding
neutral dialkyl complex and, even in some cases, show better
catalytic activity than the known catalysts.
[Cp4PrPhLu(CH2SiMe3)3][Li(thf)3(OEt2)] (1-Lu). Starting from
LuCl3 (281 mg, 1.00 mmol), complex 1-Lu was obtained as a
colorless powder (768 mg, 0.74 mmol, 74% yield) in a manner
analogous to that described for the preparation of 1-Y. Single crystals
of 1-Lu suitable for X-ray analysis could be grown from Et2O/hexane
EXPERIMENTAL SECTION
■
General Methods. All reactions were conducted under a slightly
positive pressure of dry nitrogen using standard Schlenk line
techniques or under a nitrogen atmosphere in a Vigor (SG 1200/
750TS-F) glovebox. The nitrogen in the glovebox was constantly
circulated through a copper/molecular sieves catalyst unit. The oxygen
and moisture concentrations in the glovebox atmosphere were
monitored by an O2/H2O Combi-Analyzer to ensure both were
always below 1 ppm. Unless otherwise noted, all starting materials
were commercially available and were used without further
purification. Solvents were purified by an Mbraun SPS-800 Solvent
Purification System and dried over fresh Na chips in the glovebox. n-
BuLi was obtained from J&K. Organometallic samples for NMR
spectroscopic measurements were prepared in the glovebox by use of
J. Young valve NMR tubes (Wilmad 528-JY). 1H and 13C NMR
1
for 2 days at −20 °C. H NMR (500 MHz, [D8]THF, Me4Si): δ =
−1.29 (s, 6H; CH2SiMe3), −0.05 (s, 27H; Me3Si), 0.83 (t, J = 7.3 Hz,
6H; CH2CH2CH3), 1.05 (t, J = 7.3 Hz, 6H; CH2CH2CH3), 1.18 (t, J =
7.0 Hz, 6H; O(CH2CH3)2), 1.32−1.47 (m, 4H; CH2CH2CH3), 1.55−
1.62 (m, 4H; CH2CH2CH3), 1.82−1.87 (m, 12H; β-CH2, THF),
2.42−2.63 (m, 8H; CH2CH2CH3), 3.45 (q, J = 7.0 Hz, 4H;
O(CH2CH3)2), 3.67−3.70 (m, 12H; α-CH2, THF), 7.05 (t, J = 7.3
Hz, 1H; p-C6H5), 7.20 (t, J = 7.5 Hz, 2H; m-C6H5), 7.39 (d, J = 7.8
Hz; 2H; o-C6H5) ppm; 13C NMR (75 MHz, [D8]THF, Me4Si): δ =
5.3, 15.2, 15.5, 26.4, 26.9, 27.7, 31.0, 31.1, 38.1, 68.3, 119.3, 120.1,
122.7, 124.5, 127.7, 132.1, 141.7 ppm.
[Cp4PrPhLu(DBM)2(thf)] (2-Lu). A solution of dibenzoylmethane
(149 mg, 0.663 mmol) was added to the solution of 1-Lu (230 mg,
0.221 mmol) in benzene (5 mL). The reaction mixture was stirred at
room temperature for 1 h. After removal of the solvent under reduced
pressure, the residue was extracted with hexane, and the insoluble light
yellow powder was removed. After 24 h, 2-Lu was given as orange
crystals (202 mg, 0.201 mmol, 91% yield). Single crystals of 2-Lu
suitable for X-ray analysis could be grown from benzene/hexane for 2
1
spectra were recorded on a Bruker-500 (FT, 500 MHz for H; 125
MHz for 13C), Bruker-400 spectrometer (FT, 400 MHz for H; 100
1
MHz for 13C), or a JEOL-AL300 spectrometer (FT, 300 MHz for 1H;
75 MHz for 13C) at room temperature, unless otherwise noted.
Infrared spectra (IR) were recorded on a Thermo Nicolet Avatar 330
FT-IR spectrometer. High-resolution mass spectra (HRMS) were
recorded on a Bruker Apex IV FTMS mass spectrometer using ESI
(electrospray ionization).
1
days at room temperature. H NMR (500 MHz, [D8]THF, Me4Si): δ
Preparation of [Cp4PrPhY(CH2SiMe3)3][Li(thf)3(OEt2)] (1-Y). A
solution of Cp4PrPhLi (316 mg, 1.00 mmol) in THF (5 mL), which was
prepared by reaction n-BuLi with one equivalent of Cp4PrPhH in Et2O/
hexane (1:1 V/V), was added to suspension of YCl3 (195 mg, 1.00
mmol) in THF (15 mL). The reaction mixture was stirred for 12 h at
room temperature. Then a solution of Me3SiCH2Li (282 mg, 3.00
mmol) in THF (5 mL) was added to the reaction mixture at room
temperature. After having been stirred for 0.5 h at room temperature,
the solvent was removed under reduced pressure. The residue was
extracted with toluene. Evaporation of toluene gave dark oil. The
colorless powder of 1-Y could be given by mixing the dark oil in the
mixed solvents of Et2O and hexane at −20 °C (784 mg, 0.82 mmol,
82% yield). Single crystals of 1-Y suitable for X-ray analysis could be
grown from Et2O/hexane for 2 days at −20 °C. 1H NMR (500 MHz,
[D8]THF, Me4Si): δ = −1.19 (d, J(Y,H) = 3.0 Hz, 6H; CH2SiMe3),
−0.13 (s, 27H; Me3Si), 0.76 (t, J = 7.4 Hz, 6H; CH2CH2CH3), 0.98 (t,
= 0.61 (t, J = 7.3 Hz, 6H; CH2CH2CH3), 0.89 (t, J = 7.3 Hz, 6H;
CH2CH2CH3), 1.26−1.34 (m, 4H; CH2CH2CH3), 1.44−1.60 (m, 4H;
CH2CH2CH3), 1.72−1.78 (m, 4H; β-CH2, THF), 2.27−2.61 (m, 8H;
CH2CH2CH3), 3.57−3.62 (m, 4H; α-CH2, THF), 6.85 (s, 2H;
C(O)CHC(O)), 7.16 (t, J = 7.4 Hz, 1H; p-C6H5, Cp), 7.32 (t, J = 7.6
Hz, 2H; m-C6H5, Cp), 7.38 (t, J = 7.3 Hz, 8H; m-C6H5, DBM), 7.43
(t, J = 7.3 Hz, 4H; p-C6H5, DBM), 7.73 (d, J = 7.5 Hz, 2H; o-C6H5,
Cp), 7.98 (d, J = 7.3 Hz, 8H; o-C6H5, DBM) ppm; 13C NMR (125
MHz, [D8]THF, Me4Si): δ = 15.0, 15.4, 26.1, 26.4, 26.9, 29.5, 30.7,
68.2, 95.3, 122.9, 130.10, 130.11, 124.8, 128.2, 128.3, 129.0, 131.5,
131.8, 140.9, 141.0, 185.3 ppm.
Typical Procedures for the Catalytic Reaction between
Primary Aromatic Amines and Aarbodiimides. i). NMR Tube
Reaction. In the glovebox, a J. Young valve NMR tube was charged
with 1-Y (4.8 mg, 0.005 mmol), C6D6 (0.5 mL), aniline (48 mg, 0.51
mmol), and N,N′-diisopropylcarbodiimide (63 mg, 0.50 mmol). The
11945
dx.doi.org/10.1021/ic3018369 | Inorg. Chem. 2012, 51, 11941−11948

Inorganic Chemistry
Article
Table 5. Crystallographic Data and Structure Refinement Details for 1-Ln (Ln = Y, Ho, Er, Tm, and Lu) and 2-Lu
1-Y
1-Ho
1-Er
1-Tm
1-Lu
2-Lu
formula
Mw
C51H100YLiO4Si3
957.43
C51H98HoLiO4Si3
1031.43
orthorhombic
Pna2(1)
24.927(5)
12.716(3)
19.096(4)
90
C51H100ErLiO4Si3
1035.78
monoclinic
P2(1)/n
13.102(3)
22.346(5)
20.541(4)
101.08(3)
5902(2)
4
C51H100TmLiO4Si3
1037.45
C51H100LuLiO4Si3
1043.49
monoclinic
P2(1)/n
13.362(3)
21.979(5)
20.520(5)
99.219(3)
5949(2)
4
C57H63LuO5
1003.04
monoclinic
P2(1)/c
13.627(3)
16.234(3)
23.257(5)
105.18(3)
4965.4(17)
4
crystal system
space group
a (Å)
monoclinic
P2(1)/n
13.149(3)
22.409(5)
20.587(4)
100.99(3)
5955(2)
4
monoclinic
P2(1)/n
13.444(3)
24.242(5)
18.393(4)
100.10(3)
5902(2)
4
b (Å)
c (Å)
β (°)
V (Å3)
6053(2)
4
Z
ρcalcd (g cm−3
)
1.068
1.132
1.166
1.168
1.165
1.342
μ (mm−1
)
1.076
1.402
1.519
1.600
1.756
2.035
F(000)
2088
2192
2204
2208
2216
2064
θ range (°)
no of reflns
collected
1.82 to 25.00
31742
1.80 to 27.50
40718
1.83 to 27.48
25947
1.40 to 27.48
25922
1.80 to 25.01
39299
1.55 to 27.48
11360
no of indep reflns 10168 [R(int) =
13276 [R(int) =
0.1463]
13395 [R(int) =
0.0612]
13482 [R(int) =
0.0580]
10379 [R(int) =
0.0570]
11360 [R(int) =
0.0955]
0.0828]
no of variables
GOF
717
507
638
557
469
573
1.155
0.0896
0.1417
0.871
0.0691
0.1579
1.144
0.0817
0.1678
1.004
0.0428
0.1024
1.180
0.0778
0.1802
1.001
0.0406
0.0918
R [I > 2σ (I)]
Rw
tube was taken out of the glovebox and then heated at 80 °C in an oil
bath for 1 h. Formation of 3 was monitored by 1H NMR spectroscopy.
The NMR data of 3a-e and 3g-o were consistent with those
reported.4b,5c,g,6l,j
gel column chromatography using CH2Cl2 and EtOAc as eluent to
give a colorless oil (350 mg, 1.50 mmol) in 75% yield.
Broad peaks in 13C NMR spectrum in 5d−g are observed, and the
integration of broad peaks is determined using inverse gated
decoupling technique.
ii). Preparative Scale Reaction. In the glovebox, the mixture of
benzene solution (1 mL) of 1-Y (4.8 mg, 0.005 mmol) and benzene
solution (2 mL) of 2,6-difluoroaniline (65 mg, 0.505 mmol) was added
to a Schlenk tube. Then N,N′-diisopropylcarbodiimide (63 mg, 0.5
mmol) was added to the above reaction mixture. The Schlenk tube
was taken outside the glovebox, and the mixture was stirred at 80 °C
for 1 h. After the solvent and N,N′-diisopropylcarbodiimide were
removed under vacuum, the white solid was extracted with Et2O and
then filtered to give colorless solution. After removal of Et2O under
reduced pressure, colorless solid (115 mg, 0.45 mmol) was given in
90% yield.
2-(2,6-Difluorophenyl)-1,3-diisopropylguanidine (3f). Color-
less solid, 90% isolated yield. 1H NMR (300 MHz, C6D6, Me4Si): δ =
0.93 (d, J = 6.3 Hz, 12H; CH(CH3)2), 3.58 (br, 2H; NH), 3.65−3.73
(m, 2H; CH(CH3)2), 6.45−6.53 (m, 1H; p-C6H3), 6.71−6.77 (m, 2H;
m-C6H3) ppm; 13C NMR (100 MHz, CDCl3, Me4Si): δ = 23.2, 43.4,
2,3-Diisopropyl-1-methyl-1-phenylguanidine (5d). Colorless
1
oil, 75% isolated yield. H NMR (400 MHz, C6D6, Me4Si): δ = 1.08
(br, 12H; CH(CH3)2), 2.70 (s, 3H; NCH3), 3.02 (br, 1H; NH), 3.78
(br, 2H; CH(CH3)2), 6.71−6.81 (m, 3H; C6H5), 7.18−7.20 (m, 2H;
C6H5) ppm; 13C NMR (100 MHz, C6D6, Me4Si): δ = 24.0 (br, 4C),
36.2, 44.0 (br), 47.3 (br), 112.7, 118.3, 129.4, 146.6, 148.3 ppm. IR
(film): ν = 1650 (CN) cm−1; HRMS: m/z calcd for C14H24N3:
234.1965 [M + H]+; found: 234.1964.
2,3-Diisopropyl-1-methyl-1-(p-tolyl)guanidine (5e). Colorless
oil, 64% yield. 1H NMR (400 MHz, C6D6, Me4Si): δ = 1.10 (br, 12H;
CH(CH3)2), 2.17 (s, 3H; p-C6H4−CH3), 2.72 (s, 3H; NCH3), 3.21
(br, 1H; NH), 3.84 (br, 2H; CH(CH3)2), 6.69 (br, 2H; C6H4), 7.01
(d, J = 7.3 Hz, 2H; C6H4) ppm; 13C NMR (100 MHz, C6D6, Me4Si): δ
= 20.5, 23.9 (br, 4C), 36.3, 44.4 (br), 47.4 (br), 113.0, 127.2, 130.0,
144.6, 148.8 ppm. IR (film): ν =1649 (CN) cm−1; HRMS: m/z
calcd for C15H26N3: 248.2121 [M + H]+; found: 248.2119.
2,3-Diisopropyl-1,1-diphenylguanidine (5f). Colorless oil, 88%
isolated yield. 1H NMR (400 MHz, C6D6, Me4Si): δ = 1.02 (br, 12H;
CH(CH3)2), 3.31 (br, 1H; NH), 4.01 (br, 2H; CH(CH3)2), 6.84 (t, J
= 7.3 Hz, 2H; p-C6H5), 7.04−7.12 (m, 4H; m-C6H5), 7.15−7.21 (m,
4H; o-C6H5) ppm; 13C NMR (100 MHz, C6D6, Me4Si): δ = 22.7 (br),
24.5 (br), 43.7 (br), 47.8 (br), 121.1, 123.7, 129.5, 145.0, 146.0 ppm.
IR (film): ν = 1654 (CN) cm−1; HRMS: m/z calcd for C19H26N3:
296.2121 [M + H]+; found: 296.2121.
2,3-Dicyclohexyl-1,1-diphenylguanidine (5g). Colorless oil,
66% isolated yield. 1H NMR (400 MHz, C6D6, Me4Si): δ = 0.84−1.95
(m, 20H; CH2, Cy), 3.42 (br, 1H; NH), 3.63−3.84 (m, 2H; CH, Cy),
6.84 (t, J = 7.3 Hz, 2H; p-C6H5), 7.10 (t, J = 7.9 Hz, 4H; m-C6H5),
7.21 (d, J = 7.7 Hz, 4H; o-C6H5) ppm; 13C NMR (100 MHz, C6D6,
Me4Si): δ = 25.3 (4C), 26.3 (2C), 32.9, 35.1 (br), 50.6 (br), 56.5 (br),
121.2, 122.7, 129.5, 145.1, 146.0 ppm. IR (film): ν = 1653 (CN)
cm−1; HRMS: m/z calcd for C25H34N3: 376.2747 [M + H]+; found:
376.2750.
111.5 (dd, J(C,CF), (C,CCCF) = 17.0, 7.4 Hz), 120.8 (t, J(C,CCF) = 9.6 Hz),
127.0 (t, J(C,CF) = 16.6 Hz), 151.3, 156.9 (dd, J(C, F), (C,CCF) = 243.8, 6.8
Hz) ppm. IR (film): ν =1617 (CN) cm−1; HRMS: m/z calcd for
C13H20F2N3: 256.1620 [M + H]+; found: 256.1613.
Typical Procedures for the Catalytic Reaction between
Secondary Amines and Carbodiimides. i). NMR Tube Reaction.
In the glovebox, a J. Young valve NMR tube was charged with 1-Y (4.8
mg, 0.005 mmol), [D8]toluene (0.5 mL), tetrahydropyrrole (36 mg,
0.51 mmol), and N,N′-diisopropylcarbodiimide (63 mg, 0.50 mmol).
The tube was taken out of the glovebox and then heated at 130 °C in
1
an oil bath for 1 h. Formation of 3 was monitored by H NMR and
13C NMR spectroscopy. The NMR data of 5a-c were consistent with
those reported.6j
ii). Preparative Scale Reaction. In the glovebox, a mixture of
toluene solution (2 mL) of 1-Y (19.1 mg, 0.02 mmol) and toluene
solution (4 mL) of N-methylaniline (217 mg, 2.02 mmol) was added
to a Schlenk tube. Then N,N′-diisopropylcarbodiimide (252 mg, 2.00
mmol) was added to the above reaction mixture. The Schlenk tube
was taken outside the glovebox, and the mixture was stirred at 130 °C
for 1 h. After the solvent and N,N′-diisopropylcarbodiimide were
removed under vacuum, the light yellow residue was purified by silica-
X-ray Crystallographic Studies. The single crystals of 1-Y, 1-Ho,
1-Er, 1-Tm, 1-Lu, and 2-Lu suitable for X-ray analysis were grown as
shown in the Experimental Section. The crystals of 1-Y, 1-Ho, 1-Er, 1-
Tm, 1-Lu, and 2-Lu were manipulated under a nitrogen atmosphere
11946
dx.doi.org/10.1021/ic3018369 | Inorg. Chem. 2012, 51, 11941−11948

Inorganic Chemistry
Article
and were sealed in a thin-walled glass capillary. Data collections for 1-
Y, 1-Lu, and 1-Er was performed at −100 °C on a RIGAKU CCD
SATURN 724 diffractometer, using graphite-monochromated Mo Kα
radiation (λ = 0.71073 Å). 1-Ho, 1-Tm, and 2-Lu were performed at
−150 °C on a Rigaku RAXIS RAPID IP diffractometer, using graphite-
monochromated Mo Kα radiation (λ = 0.71073 Å). The
determination of crystal class and unit cell parameters was carried
out by the CrystalClear (Rigaku Inc., 2007) for 1-Y, 1-Lu, and 1-Er or
Rapid-AUTO (Rigaku 2000) program package for 1-Ho, 1-Tm, and 2-
Lu. The raw frame data were processed using Crystal Structure
(Rigaku/MSC 2000) for 1-Ho, 1-Tm, and 2-Lu or CrystalClear
(Rigaku Inc., 2007) for 1-Y, 1-Lu, and 1-Er to yield the reflection data
file. The structures of 1-Y, 1-Ho, 1-Er, 1-Tm, 1-Lu, and 2-Lu were
solved by use of the SHELXTL program.11 Refinement was performed
on F2 anisotropically for all the non-hydrogen atoms by the full-matrix
least-squares method. The hydrogen atoms were placed at the
calculated positions and were included in the structure calculation
without further refinement of the parameters. Crystal data, data
collection, and processing parameters for the rare-earth complexes 1-Y,
1-Ho, 1-Er, 1-Tm, 1-Lu, and 2-Lu are summarized in Table 5.
Crystallographic data (excluding structure factors) have been
deposited with the Cambridge Crystallographic Data Centre as
supplementary publication nos. CCDC-886169 (1-Y), CCDC-
886166 (1-Ho), CCDC-886165 (1-Er), CCDC-886168 (1-Tm),
CCDC-886167 (1-Lu), and CCDC-886170 (2-Lu). Copies of these
data can be obtained free of charge from the Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
(t) Piers, W. E.; Emslie, D. J. H. Coord. Chem. Rev. 2002, 233−234,
131.
(2) Selected examples of rare-earth-metal anionic complexes:
(a) Aillaud, I.; Olier, C.; Chapurina, Y.; Collin, J.; Schulz, E.;
Guillot, R.; Hannedouche, J.; Trifonov, A. Organometallics 2011, 30,
3378. (b) Xu, B.; Huang, L.; Yang, Z.; Yao, Y.; Zhang, Y.; Shen, Q.
Organometallics 2011, 30, 3588. (c) Chapurina, Y.; Hannedouche, J.;
Collin, J.; Guillot, R.; Schulz, E.; Trifonov, A. Chem. Commun. 2010,
46, 6918. (d) Yao, H.; Zhang, Y.; Sun, H.; Shen, Q. Eur. J. Inorg. Chem.
2009, 1920. (e) Meyer, N.; Roesky, P. W.; Bambirra, S.; Meetsma, A.;
Hessen, B.; Saliu, K.; Takats, J. Organometallics 2008, 27, 1501.
(f) Schumann, H.; Freckmann, D. M. M.; Dechert, S. Z. Anorg. Allg.
Chem. 2008, 634, 2199. (g) Natrajan, L. S.; Blake, A. J.; Wilson, C.;
Weinstein, J. A.; Arnold, P. L. Dalton Trans. 2006, 4465. (h) Harder, S.
Organometallics 2005, 24, 373. (i) Collin, J.; Daran, J.-C.; Jacquet, O.;
Schulz, E.; Trifonov, A. Chem.−Eur. J. 2005, 11, 3455. (j) Evans, W. J.;
Broomhall-Dillard, R. N. R.; Ziller, J. W. Organometallics 1996, 15,
1351. (k) Evans, W. J.; Shreeve, J. L.; Broomhall-Dillard, R. N. R.;
Ziller, J. W. J. Organomet. Chem. 1995, 501, 7. (l) Schaverien, C. J.; van
Mechelen, J. B. Organometallics 1991, 10, 1704. (m) Hitchcock, P. B.;
Lappert, M. F.; Smith, R. G. J. Chem. Soc., Chem. Commun. 1989, 369.
(n) Atwood, J. L.; Lappert, M. F.; Smith, R. G.; Zhang, H. J. Chem.
Soc., Chem. Commun. 1988, 1308. (o) Schumann, H.; Muller, J.;
̈
Bruncks, N.; Lauke, H.; Pickardt, J.; Schwarz, H.; Eckart, K.
Organometallics 1984, 3, 69. (p) Atwood, J. L.; Hunter, W. E.;
Rogers, R. D.; Holton, J.; McMeeking, J.; Pearce, R.; Lappert, M. F. J.
Chem. Soc., Chem. Commun. 1978, 140.
(3) Selected reviews: (a) Nishiura, M.; Hou, Z. Bull. Chem. Soc. Jpn.
2010, 83, 595. (b) Suzuki, T.; Zhang, W.-X.; Nishiura, M.; Hou, Z. J.
Synth. Org. Chem., Jpn. 2009, 67, 451. (c) Shen, H.; Xie, Z. J.
Organomet. Chem. 2009, 694, 1652. (d) Zhang, W.-X.; Hou, Z. Org.
Biomol. Chem. 2008, 16, 1720. (e) Williams, A.; Ibrahim, I. T. Chem.
Rev. 1981, 81, 589.
(4) Selected examples of guanylation reaction catalyzed by transition
metals: (a) Shen, H.; Wang, Y.; Xie, Z. Org. Lett. 2011, 13, 4562.
(b) Li, D.; Guang, J.; Zhang, W.-X.; Wang, Y.; Xi, Z. Org. Biomol.
ASSOCIATED CONTENT
■
S
* Supporting Information
Additional NMR data, copies of H NMR and 13C NMR
1
spectra of all new compounds, crystallographic tables, and X-ray
crystallographic data in CIF format. This material is available
free of charge via the Internet at http://pubs.acs.org
AUTHOR INFORMATION
Corresponding Author
*E-mail: wx_zhang@pku.edu.cn (W.-X.Z.), zfxi@pku.edu.cn
(Z.X.).
■
Chem. 2010, 8, 1816. (c) Romero-Fernan
́
dez, J.; Carrillo-Hermosilla,
ez-Solera,
F.; Antinolo, A.; Alonso-Moreno, C.; Rodríguez, A. M.; Lop
́
̃
I.; Otero, A. Dalton Trans. 2010, 39, 6419. (d) Shen, H.; Chan, H.-S.;
Xie, Z. Organometallics 2006, 25, 5515. (e) Montilla, F.; del Río, D.;
Pastor, A.; Galindo, A. Organometallics 2006, 25, 4996. (f) Ong, T.-G.;
Yap, G. P. A.; Richeson, D. S. J. Am. Chem. Soc. 2003, 125, 8100.
(5) Selected examples of guanylation reaction catalyzed by main
group metals: (a) Zhao, F.; Wang, Y.; Zhang, W.-X.; Xi, Z. Org.
Biomol. Chem. 2012, 10, 6266. (b) Alonso-Moreno, C.; Carrillo-
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by the Natural Science Foundation of
China and the “973” program from National Basic Research
Program of China (2012CB821600).
Hermosilla, F.; Garces
́
, A.; Otero, A.; Lop
́
ez-Solera, I.; Rodríguez, A.
M.; Antinolo, A. Organometallics 2010, 29, 2789. (c) Koller, J.;
̃
Bergman, R. G. Organometallics 2010, 29, 5946. (d) Zhang, W.-X.; Li,
D.; Wang, Z.; Xi, Z. Organometallics 2009, 28, 882. (e) Crimmin, M.
R.; Barrett, A. G. M.; Hill, M. S.; Hitchcock, P. B.; Procopiou, P. A.
Organometallics 2008, 27, 497. (f) Lachs, J. R.; Barrett, A. G. M.;
REFERENCES
■
(1) Selected reviews: (a) Nishiura, M.; Hou, Z. Nat. Chem. 2010, 2,
257. (b) Zimmermann, M.; Anwander, R. Chem. Rev. 2010, 110, 6194.
(c) Zi, G. Dalton Trans. 2009, 9101. (d) Amin, S. B.; Marks, T. J.
Crimmin, M. R.; Kociok-Kohn, G.; Hill, M. S.; Mahon, M. F.;
̈
Procopiou, P. A. Eur. J. Inorg. Chem. 2008, 26, 4173. (g) Rowley, C.
N.; Ong, T.; Priem, J.; Woo, T. K.; Richeson, D. S. Inorg. Chem. 2008,
47, 9660. (h) Ong, T.; O’Brien, J. S.; Korobkov, I.; Richeson, D. S.
Organometallics 2006, 25, 4728.
Angew. Chem., Int. Ed. 2008, 47, 2006. (e) Muller, T. E.; Hultzsch, K.
̈
C.; Yus, M.; Foubelo, F.; Tada, M. Chem. Rev. 2008, 108, 3795. (f) Yu,
N.; Hou, Z.; Xi, Z. Prog. Chem. 2008, 20, 1515. (g) Hou, Z.; Nishiura,
M.; Shima, T. Eur. J. Inorg. Chem. 2007, 2535. (h) Gottfriedsen, J.;
Edelmann, F. T. Coord. Chem. Rev. 2007, 251, 142. (i) Hou, Z.; Luo,
Y.; Li, X. J. Orgnomet. Chem. 2006, 691, 3114. (j) Edelmann, F. T. In
Comprehensive Organometallic Chemistry III; Crabtree, R. H., Mingos,
D. M. P., Eds.; Elsevier: Oxford, 2006; Vol. 4.01, pp 1−199.
(k) Zeimentz, P. M.; Arndt, S.; Elvidge, B. R.; Okuda, J. Chem. Rev.
2006, 106, 2404. (l) Arndt, S.; Okuda, J. Adv. Synth. Catal. 2005, 347,
339. (m) Hong, S.; Marks, T. J. Acc. Chem. Res. 2004, 37, 673.
(n) Nishiura, M.; Hou, Z. J. Mol. Catal. A: Chem. 2004, 213, 101.
(o) Hou, Z. Bull. Chem. Soc. Jpn. 2003, 76, 2253. (p) Okuda, J. Dalton
Trans. 2003, 2367. (q) Arndt, S.; Okuda, J. Chem. Rev. 2002, 102,
1953. (r) Hou, Z.; Wakatsuki, Y. J. Organomet. Chem. 2002, 647, 61.
(s) Molander, G. A.; Romero, J. A. C. Chem. Rev. 2002, 102, 2161.
(6) Selected examples of guanylation reaction catalyzed by rare-earth-
metals: (a) Zhang, X.; Wang, C.; Qian, C.; Han, F.; Xu, F.; Shen, Q.
Tetrahedron 2011, 67, 8790. (b) Han, F.; Teng, Q.; Zhang, Y.; Wang,
Y.; Shen, Q. Inorg. Chem. 2011, 50, 2634. (c) Cao, Y.; Du, Z.; Li, W.;
Li, J.; Zhang, Y.; Xu, F.; Shen, Q. Inorg. Chem. 2011, 50, 3729. (d) Liu,
C.; Zhou, S.; Wang, S.; Zhang, L.; Yang, G. Dalton Trans. 2010, 39,
8994. (e) Jiao, R.; Xue, M.; Shen, X.; Zhang, Y.; Yao, Y.; Shen, Q. Eur.
J. Inorg. Chem. 2010, 17, 2523. (f) Zhu, X.; Xu, F.; Shen, Q. Chin. J.
Chem. 2009, 27, 19. (g) Wu, Y.; Wang, S.; Zhang, L.; Yang, G.; Zhu,
X.; Liu, C.; Yin, C.; Rong, J. Inorg. Chim. Acta 2009, 362, 2814.
(h) Du, Z.; Li, W.; Zhu, X.; Xu, F.; Shen, Q. J. Org. Chem. 2008, 73,
8966. (i) Li, Q.; Wang, S.; Zhou, S.; Yang, G.; Zhu, X.; Liu, Y. J. Org.
Chem. 2007, 72, 6763. (j) Zhu, X.; Du, Z.; Xu, F.; Shen, Q. J. Org.
11947
dx.doi.org/10.1021/ic3018369 | Inorg. Chem. 2012, 51, 11941−11948

Inorganic Chemistry
Article
Chem. 2009, 74, 6347. (k) Zhou, S.; Wang, S.; Yang, G.; Li, Q.; Zhang,
L.; Yao, Z.; Zhou, Z.; Song, H. Organometallics 2007, 26, 3755.
(l) Zhang, W.-X.; Nishiura, M.; Hou, Z. Chem.−Eur. J. 2007, 13, 4037.
(m) Zhang, W.-X.; Nishiura, M.; Hou, Z. Synlett 2006, 1213.
(n) Zhang, X.; Wang, C.; Qian, C.; Han, F.; Xu, F.; Shen, Q.
Tetrahedron 2011, 67, 8790.
(7) Selected examples of addition of nucleophiles to carbodiimides:
(a) Wang, Y.; Chi, Y.; Zhang, W.-X.; Xi, Z. J. Am. Chem. Soc. 2012,
134, 2926. (b) Wang, Y.; Luo, Y.; Chen, J.; Xue, H.; Liang, H. New J.
Chem. 2012, 36, 933. (c) Wang, Y.; Zhang, W.-X.; Wang, Z.; Xi, Z.
Angew. Chem., Int. Ed. 2011, 50, 8122. (d) Li, D.; Wang, Y.; Zhang, W.-
X.; Zhang, S.; Guang, J.; Xi, Z. Organometallics 2011, 30, 5278.
(e) Yuan, Y.; Wang, X.; Li, Y.; Fan, L.; Xu, X.; Chen, Y.; Li, G.; Xia, W.
Organometallics 2011, 30, 4330. (f) Casely, I. J.; Ziller, J. W.; Evans, W.
J. Organometallics 2011, 30, 4873. (g) Zhang, J.; Zhou, X. Dalton
Trans. 2011, 40, 9637. (h) Zhang, J.; Zhou, X. C. R. Chim. 2010, 13,
633. (i) Wang, Z.; Wang, Y.; Zhang, W.-X.; Hou, Z.; Xi, Z. J. Am.
Chem. Soc. 2009, 131, 15108. (j) Zhang, W.-X.; Nishiura, M.; Mashiko,
T.; Hou, Z. Chem.−Eur. J. 2008, 14, 2167. (k) Cui, P.; Chen, Y.; Li, G.;
Xia, W. Angew. Chem., Int. Ed. 2008, 47, 9944. (l) Xu, X.; Gao, J.;
Cheng, D.; Li, J.; Qiang, G.; Guo, H. Adv. Synth. Catal. 2008, 350, 61.
(m) Liu, B.; Yang, Y.; Cui, D.; Tang, T.; Chen, X.; Jing, X. Dalton
Trans. 2007, 4252. (n) Zhang, W.-X.; Nishiura, M.; Hou, Z. Chem.
Commun. 2006, 3812. (o) Arliguie, T.; Doux, M.; Mez
́
ailles, N.;
Thuery, P.; Floch, P. L.; Ephritikhine, M. Inorg. Chem. 2006, 45, 9907.
́
(p) Zhang, W.-X.; Nishiura, M.; Hou, Z. J. Am. Chem. Soc. 2005, 127,
16788.
(8) (a) Fang, H.; Zhao, C.; Li, G.; Xi, Z. Tetrahedron 2003, 59, 3779.
(b) Zhao, C.; Li, P.; Cao, X.; Xi, Z. Chem. −Eur. J. 2002, 8, 4292.
(c) Xi, Z.; Li, P. Angew. Chem., Int. Ed. 2000, 39, 2950.
(9) Qian, C.; Nie, W.; Sun, J. J. Chem. Soc., Dalton Trans. 1999, 3283.
(10) Schumann, H.; Winterfeld, J.; Glanz, M.; Kohn, R. D.; Hemling,
̈
H. J. Organomet. Chem. 1994, 481, 275.
(11) Sheldrick, G. M. SHELXTL 5.10 for Windows NT: Structure
Determination Software Programs; Bruker Analytical X-ray Systems,
Inc.: Madison, WI, 1997.
11948
dx.doi.org/10.1021/ic3018369 | Inorg. Chem. 2012, 51, 11941−11948