Synthesis and reactivities of guanidinate dianion complexes of heterobimetallic lanthanide-lithium Cp2Ln[(CyN)2CNPh] Li(THF)3

Article abstract of DOI:10.1021/om9010615

The treatment of Cp3Ln with 1 equiv of N,N′-dicyclohexyl-N″- phenylguanidine followed by reacting with butyllithium yields a series of novel guanidinate dianion complexes of heterobimetallic lanthanide-lithium with formula Cp₂Ln[(CyN)₂CNPh]Li(THF)₃ (Ln = Yb (1a), Er (1b), Y (1c), Dy (1d)). Reactivities of these dianionic guanidinate complexes toward various electrophiles have been investigated. Reaction of 1 with Me₂RSiCl produced tetrasubstituted guanidinate monoanion complexes Cp₂Ln[(CyN)₂CN(Ph)SiRMe₂] ((R = Me, Ln = Yb (2a), Er (2b), Y (2c); R = 'Bu, Ln = Yb (3a), Er (3b)), indicating that the Li-N bond is preferred to couple with chlorosilanes. In contrast, the regioselective functionalization of the NCy group bonded to the lanthanide ion was achieved by reaction of 1a with Me₂SiCl₂ to produce Me₂Si(CyN)₂C=NPh (4) and Cp₂YbCl(THF) (5). Significantly, treatment of 1d with PhCOCl leads to the cleavage of one C-N bond of the dianionic guanidinate, giving the acylamino complex [Cp ₂Dy(OC(Ph)NCy)]₂ (6). These results have shown that the active site of the dianionic guanidinate ligand is tunable due to the derealization of the two negative charges on the three N atoms. All the compounds were characterized by elemental analysis and spectroscopic methods. The structures of compounds 1-6 are also determined through X-ray single-crystal diffraction analysis.

Full text of DOI:10.1021/om9010615

1284 Organometallics 2010, 29, 1284–1289
DOI: 10.1021/om9010615
Synthesis and Reactivities of Guanidinate Dianion Complexes of
Heterobimetallic Lanthanide-Lithium Cp2Ln[(CyN)2CNPh]Li(THF)3
Pengzhi Zheng,† Jianquan Hong,† Ruiting Liu,† Zhengxing Zhang,† Zhen Pang,†
Linhong Weng,† and Xigeng Zhou*,†,‡
†Department of Chemistry, Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials,
Fudan University, Shanghai 200433, People’s Republic of China, and ‡State Key Laboratory of
Organometallic Chemistry, Shanghai 200032, People’s Republic of China
Received December 11, 2009
The treatment of Cp3Ln with 1 equiv of N,N0-dicyclohexyl-N00-phenylguanidine followed by
reacting with butyllithium yields a series of novel guanidinate dianion complexes of heterobimetallic
lanthanide-lithium with formula Cp2Ln[(CyN)2CNPh]Li(THF)3 (Ln = Yb (1a), Er (1b), Y (1c), Dy
(1d)). Reactivities of these dianionic guanidinate complexes toward various electrophiles have been
investigated. Reaction of 1 with Me2RSiCl produced tetrasubstituted guanidinate monoanion
t
complexes Cp2Ln[(CyN)2CN(Ph)SiRMe2] ((R = Me, Ln = Yb (2a), Er (2b), Y (2c); R = Bu,
Ln = Yb (3a), Er (3b)), indicating that the Li-N bond is preferred to couple with chlorosilanes. In
contrast, the regioselective functionalization of the NCy group bonded to the lanthanide ion was
achieved by reaction of 1a with Me2SiCl2 to produce Me2Si(CyN)2CdNPh (4) and Cp2YbCl(THF)
(5). Significantly, treatment of 1d with PhCOCl leads to the cleavage of one C-N bond of the
dianionic guanidinate, giving the acylamino complex [Cp2Dy(OC(Ph)NCy)]2 (6). These results have
shown that the active site of the dianionic guanidinate ligand is tunable due to the delocalization of
the two negative charges on the three N atoms. All the compounds were characterized by elemental
analysis and spectroscopic methods. The structures of compounds 1-6 are also determined through
X-ray single-crystal diffraction analysis.
Introduction
and transamination,4 which highlight the value of such species.
There does not appear to be a large effort to expand upon this
class of compounds, which is probably due to the lack of
convenient synthetic methodologies to access these complexes.
Dianionic guanidinate complexes are rare and are mainly
prepared by the cycloaddition of transition-metal imido com-
plexes with carbodiimides.4,5 Only a few dianionic guanidinate
ligands are introduced by deprotonation of monoanionic
guanidinates using alkyl6 or amido7 metal reagents. Therefore,
it is highly desirable to develop new dianionic guanidinate
complexes and a new method for their construction.
Considerable recent interest has focused on the develop-
ment of guanidinate anions as sterically and electronically
flexible ligands for the design of new metal complexes.
Among them guanidinate monoanions are well established
as versatile ligands for a remarkably wide range of metals. A
major impetus for such studies can be traced to the well-
known applications of guanidinate metal complexes in
homogeneous catalysis1 and materials science.2 In contrast,
the guanidinate dianion complexes have received very lim-
ited attention as ligands in organometallic and coordination
chemistry. This is surprising, given the expectation that the
guanidinate dianion ligands should lead to novel coordina-
tion properties and may impart an enhanced reactivity to the
corresponding metal complexes due to the presence of an
added anionic nitrogen center and thus generating a unique,
conjugated π system. For example, transition-metal guani-
dinate dianion complexes have been implicated as reaction
intermediates in guanylation of amines with carbodiimides3
On the other hand, there is currently considerable interest
in studying the reactivities of the Ln-N bond of lanthanide
amides due to their applications in organic synthesis
and catalysis.8 Nonetheless, research efforts are primarily
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2612.
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2003, 125, 8100. (b) Zuckerman, R. L.; Bergman, R. G. Organometallics
2001, 20, 1792. (c) Zuckerman, R. L.; Bergman, R. G. Organometallics
2000, 19, 4795. (d) Birdwhistell, K. R.; Lanza, J.; Pasos, J. J. Organomet.
Chem. 1999, 584, 200.
*Corresponding author. E-mail: xgzhou@fudan.edu.cn.
(1) (a) Edelmann, F. T. Chem. Soc. Rev. 2009, 38, 2253. (b) Edelmann,
F. T. Adv. Organomet. Chem. 2008, 57, 183.
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11405. (b) Milanov, A.; Bhakta, R.; Baunemann, A.; Becker, H. W.; Thomas,
R.; Ehrhart, P.; Winter, M.; Devi, A. Inorg. Chem. 2006, 45, 11008.
(3) Blake, A. J.; McInnes, J. M.; Mountford, P.; Nikonov, G. I.;
Swallow, D.; Watkin, D. J. J. Chem. Soc., Dalton Trans. 1999, 379.
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550, 213.
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J. Chem. Soc., Dalton Trans. 1999, 2947. (b) Tin, M. K. T.; Yap, G. P. A.;
Richeson, D. S. Inorg. Chem. 1999, 38, 998. (c) Bailey, P. J.; Gould, R. O.;
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r
pubs.acs.org/Organometallics
Published on Web 02/01/2010
2010 American Chemical Society

Article
Organometallics, Vol. 29, No. 5, 2010 1285
Scheme 1
focused on monoanionic amido lanthanide complexes.9 To
our knowledge, the selective reaction involving the dianionic
guanidinate ligands in organolanthanide chemistry has re-
mained unexplored to date, probably due to the lack of
suitable complexes. The scarcity of lanthanide complexes
supported with dianionic nitrogen-centered ligands warrants
exploration of guanidinate dianion ligands in this regard.
Recently, we have reported the synthesis of the first guani-
dinate dianion complexes of rare earth metals, which are
formed by the unexpected disproportionation of monoanio-
nic pyridyl-substituted guanidinate ligands.10 To elucidate
the structure-reactivity relationship of lanthanide guanidi-
nate dianion complexes, we are interested in developing new
targets and investigating the different reaction behavior of
mono- and dianionic guanidinates. In this contribution, we
describe our detailed studies into the synthesis of the first
heterobimetallic lanthanide-lithium complexes containing
the guanidinate dianion ligand and their reactivities with
chlorosilanes, dichlorosilane, and benzoyl chloride. In these
cases, the trisubstituted guanidinate dianion ligand under-
goes a coupling reaction, cyclization, and transamination, to
selectively transform into its tetrasubstituted monoanionic
form, neutral heterocycles, and the acylamino ligand, re-
spectively, which demonstrate the versatile reactivity of the
dianionic guanidinate ligand owing to the accessibility of
variable active sites. To our knowledge, the transformations
of dianionic guanidinate ligands into organic heterocycles
and acylamino groups have not been previously reported.
Figure 1. Thermal ellipsoid (30%) plot of Cp2Ln[(CyN)2C-
(NPh)]Li(THF)3 (Ln = Yb (1a), Er (1b), Y (1c), Dy (1d)).
Hydrogen atoms are omitted for clarity.
Table 1. Selected Bond Lengths and Angles for 1a, 1b, 1c, and 1d
1a
1b
1c
1d
˚
Bond Lengths (A)
Ln(1)-N(1)
Ln(1)-N(2)
N(1)-C(11)
N(2)-C(11)
N(3)-C(11)
N(3)-Li(1)
Li(1)-O(1)
Li(1)-O(2)
Li(1)-O(3)
2.247(7)
2.254(5)
2.272(5)
1.369(7)
1.356(7)
1.371(8)
2.03(1)
1.96(1)
1.97(1)
1.97(1)
2.278(4)
2.282(4)
1.349(7)
1.340(6)
1.375(7)
2.03(1)
1.98(1)
1.97(1)
1.96(1)
2.29(1)
2.29(1)
1.34(1)
1.35(1)
1.38(1)
2.03(2)
2.00(2)
2.00(2)
1.92(2)
2.267(7)
1.369(10)
1.347(11)
1.373(11)
2.02(2)
1.99(2)
1.97(2)
1.99(2)
Results and Discussion
Synthesis and Characterization of Dianionic Guanidinate
Lanthanide Complexes Cp2Ln[μ-η2:η1-(CyN)2CNPh]Li-
(THF)3. Reaction of Cp3Ln with 1 equiv of (CyHN)2CNPh
in THF followed by treatment with 1 equiv of LinBu gave the
expected dianionic guanidinate complexes Cp2Ln[μ-
η2:η1-(CyN)2CNPh]Li(THF)3 (Ln = Yb (1a), Er (1b), Y
(1c), Dy (1d)) in moderate to good yields. Presumably, the
formation of 1a-d may result from the protonation reaction
of Cp3Ln with neutral guanidine and subsequent deprotona-
tion, as shown in Scheme 1.
Bond Angles (deg)
N(1)-Ln(1)-N(2)
N(2)-C(11)-N(1)
N(2)-C(11)-N(3)
N(1)-C(11)-N(3)
C(11)-N(3)-Li(1)
59.4(2)
59.5(2)
58.5(2)
58.4(2)
110.9(8)
126.7(8)
122.1(8)
125.6(7)
111.0(5)
126.2(5)
122.7(5)
123.9(5)
111.9(5)
126.0(5)
122.0(5)
123.1(4)
112.0(7)
125.9(7)
122.0(7)
121.2(8)
Compounds 1a-d are sensitive to air and moisture and are
soluble in THF and toluene and slightly soluble in n-hexane.
Compounds 1a-d were characterized by elemental analysis
and spectroscopic methods. Their elemental analyses are in
good agreement with the suggested molecular formulas. The
-NCN- characteristic stretching frequency of the dianionic
guanidinate ligand was observed at ca. 1545 cm-1 6 and was
slightly red-shifted as compared with those of the mono-
anionic guanidinate ligands.11 Moreover, the medium bands
at about 1075 and 890 cm-1 could be defined for coordinated
THF molecules. The H NMR spectrum of 1c showed the
cyclopentadienyl, cyclohexyl, phenyl, and THF resonances
in the expected 2:2:1:3 ratio.
These heterobimetallic complexes were further confirmed
by the X-ray single-crystal structural determination. The
molecular structures are shown in Figure 1, and selected
bond distances and angles for each are given in Table 1.
Complexes 1a, 1b, 1c, and 1d are isostructural. Complex 1c is
1
(9) Collin, J.; Daran, J. C.; Jacquet, O.; Schulz, E.; Trifonov, A.
Chem.;Eur. J. 2005, 11, 3455.
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Z. X.; Weng, L. H.; Zhou, X. G. Organometallics 2007, 26, 1934. (b) Pi,
C. F.; Liu, R. T.; Zheng, P. Z.; Chen, Z. X.; Zhou, X. G. Inorg. Chem. 2007,
46, 5252. (c) Pi, C. F.; Zhu, Z. Y.; Weng, L. H.; Chen, Z. X.; Zhou, X. G.
Chem. Commun. 2007, 2190.
(11) Chang, C. C.; Hsiung, C. S.; Su, H. L.; Srinivas, B.; Chiang,
M. Y.; Lee, G. H.; Wang, Y. Organometallics 1998, 17, 1595.

1286 Organometallics, Vol. 29, No. 5, 2010
Zheng et al.
a heterodinuclear species possessing one bridging dianionic
guanidinate ligand, in which two of the nitrogen atoms, N(1)
and N(2), bond to the lanthanide center while the third N(3)
coordinates the Li center. The coordination geometry of the
Ln center can be described as a distorted tetrahedron. The
individual Ln center is in geometries reminiscent of the
previously reported monoanionic guanidinate lanthanide
complexes that have cyclopentadienyl ligands as the ancil-
lary ligands.12 The ligand spans axial equatorial sites with a
bite angle [N(1)-Y-N(2)] of 58.5(2)°. The central C atom of
the dianionic guanidinate CN3 core is planar. Furthermore,
three N atoms exhibit very similar geometric parameters. In
contrast to the observation that the dianionic guanidinate
ligand has localized C-N single and double bonds in mono-
nuclear complexes such as Pt[C(NPh)3](COD)13 and Ta-
(NMe2)3[(CyN)2C(NCy)],7a,14 the C(11)-N(1), C(11)-
N(2), and C(11)-N(3) distances of the dianionic guanidinate
group in 1c are approximately equivalent and significantly
shorter than the C-N single-bond distances, indicating that
the π electrons of the CdN double bond in the present
structure are delocalized over the CN3 unit.15 Consistent
with this observation, the Y-N(1) and Y-N(2) distances,
Scheme 2
Scheme 3
complexes Cp2Ln[(CyN)2CN(Ph)SiMe3] (Ln = Yb (2a), Er
˚
2.278(4) and 2.282(4) A, are between the values observed for
Scheme 4
the Y-N single-bond distance and the Y-N donor bond
distance16 and are comparable to the corresponding values
found in Cp2Ln[(iPrN)2CNiPr2] (Ln = Yb, Dy),12,17 when
the difference in the metal ionic radii is considered.18 The
cent-Ln-cent (cent = the center of cyclopentadienyl ring)
plane relative to the LnNCN plane is approximately perpen-
dicular. This disposition is likely the result of steric interac-
tions between bulky isopropyl groups and two cyclopenta-
dienyl ligands. The Li countercation is coordinated via three
THF molecules and an N(3) atom.
The geometry and the stereochemistry of 1a, 1b, and 1d are
not particularly different from those observed in 1c. In
particular, the bonding mode of the dianionic guanidinate
to metal ions is quite similar (Table 1).
Reactivity of Complexes 2 toward Chlorosilanes. Dianionic
guanidinate complexes are rare, and only a few are found to
lead to bridging structures.10 1a-d represent the first hetero-
bimetallic lanthanide-lithium complexes containing the
guanidinate dianion ligand. In order to obtain insight into
the properties of bridged guanidinate metal complexes, we
examine the reaction of Cp2Ln[μ-η2:η1-(CyN)2CNPh]Li-
(THF)3 with electrophiles. Treatment of 1a-c with 1 equiv
of chlorotrimethylsilane gave the monoanionic guanidinate
(2b), Y (2c)) in moderate to good yields (Scheme 2). Further-
t
more, reaction of 1a and 1b with 1 equiv of BuMe2SiCl
afforded the corresponding tetrasubstituted guanidinate
t
complexes Cp2Ln[(CyN)2CN(Ph)SiMe2 Bu] (Ln = Yb
(3a), Er (3b)). These results indicate that the Li-N bond is
preferentially attacked by the electrophiles rather than the
Ln-N bond in the present system. The solid-state structures
of 2 and 3 have been determined by X-ray analyses (Figures 2
and 3, Table 2).
As shown in Figure 2, complexes 2a-c are isostructural, in
which the newly formed silyl-substituted guanidinate anion
acts as a chelating bidentate ligand to coordinate to the
Cp2Ln unit. For each of these compounds the C(11)-N(1)
distance is comparable to the C(11)-N(2) length and shorter
than the value of C(11)-N(3). These features are consistent
with the negative charge of the ligand delocalized on the N(1)
and N(2) atoms, which are bonded to Ln3þ
.
(12) Zhang, J.; Cai, R. F.; Weng, L. H.; Zhou, X. G. Organometallics
2004, 23, 3303.
(13) Dinger, M. B.; Henderson, W.; Nicholson, B. K. J. Organomet.
Chem. 1998, 556, 75.
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37, 6728.
As shown in Figure 3, compounds 3a and 3b are also
isostructural, and the lanthanide atom is coordinated by two
η5-C5H5 groups and one chelating η2-(CyN)2CN(Ph)-
t
SiMe2 Bu ligand, and its coordination number is 8. The
geometry and the stereochemistry of 3 are not particularly
different from those observed in 2, and the bonding mode of
the guanidinate to the metal ion is quite similar (Table 2).
The C(11)-N(3)-Si(1) angle is slightly larger than the
corresponding value in 2, due to the greater hindrance of
(15) (a) Thirupathi, N.; Yap, G. P. A.; Richeson, D. S. Chem.
Commun. 1999, 2483. (b) Rodriguez, G.; Sperry, C. K.; Bazan, G. C.
J. Mol. Catal. A: Chem. 1998, 128, 5. (c) Foley, S. R.; Yap, G. P. A.;
Richeson, D. S. Inorg. Chem. 2002, 41, 4149.
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Doedens, R. J.; Bott, S. G.; Zhang, H. M.; Atwood, J. L. J. Am. Chem.
Soc. 1988, 110, 4983. (b) Zhou, X. G.; Huang, Z. E.; Cai, R. F.; Zhang, L. X.;
Hou, X. F.; Feng, X. J.; Huang, X. Y. J. Organomet. Chem. 1998, 563, 101.
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X. Y. Organometallics 1999, 18, 4128. (d) Wang, Y. R.; Shen, Q.; Xue, F.;
Yu, K. B. J. Organomet. Chem. 2000, 598, 359.
t
the SiMe2 Bu compared with SiMe3 substituent.
Reactivity of Complexes 1 toward Dichlorosilanes. Con-
trolling the metal coordination environment and reactivity
through modification of supporting ligation is an important
strategy in organometallic chemistry. Considerable interest
has focused on the tailoring of two independent monoanion
ligands to a defining and constraining linked dianion ligand
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1976, 32, 751.

Article
Organometallics, Vol. 29, No. 5, 2010 1287
Figure 4. Thermal ellipsoid (30%) plot of Me2Si(CyN)2CdNPh
(4). Hydrogen atoms are omitted for clarity. Selected bond lengths
˚
Figure 2. Thermal ellipsoid (30%) plot of Cp2Ln[(CyN)2CN-
(Ph)SiMe3] (Ln = Yb (2a), Er (2b), Y (2c)). Hydrogen atoms are
omitted for clarity.
(A) and angles (deg): Si(1)-N(2) 1.721(3), Si(1)-N(1) 1.749(3),
N(1)-C(1) 1.420(5), N(2)-C(1) 1.410(4), N(3)-C(1) 1.257(4),
N(2)-Si(1)-N(1) 76.3(2), N(2)-C(1)-N(1) 98.4(4), C(1)-
N(3)-C(16) 121.3(4).
aryloxides,20 amidinates,21 amides, and imides.22 However,
there are few reports employing linked diguanidinate di-
anion analogues.10b Encouraged by the above result, we were
interested in establishing whether two of these dianionic
guanidinate ligands could be linked together by reaction
with dichlorosilane. In contrast to Me3SiCl and tBuMe2SiCl,
reaction of 1a with 1 equiv of Me2SiCl2 in THF yielded
Cp2YbCl(THF) (5) as the main lanthanide-containing pro-
duct without the formation of the expected linked diguani-
dinate complex, even with only 0.5 equiv or less of Me2SiCl2
used. The results indicate that Me2SiCl2 is preferably
coupled to one guanidinate dianion ligand through the two
nitrogen atoms of the NCy groups rather than the NPh to
form the silicon-containing heterocycle 4. These features are
consistent with negative charges of the guanidinate dianion
ligand of 1 delocalized on the three N atoms and, thus,
demonstrate that the active site of the ligand is tunable.
Complex 5 was characterized by X-ray diffraction.23 Single
crystals of the resulting organic heterocycle Me2Si(CyN)2C-
(NPh) (4) (Figure 4) were also obtained by extraction of the
reaction mixture with toluene.
Figure 3. Thermal ellipsoid (30%) plot of Cp2Ln[(CyN)2CN-
t
(Ph)SiMe2 Bu] (Ln = Yb (3a), Er (3b)). Hydrogen atoms are
omitted for clarity.
Table 2. Selected Bond Lengths and Angles for 2a, 2b, 2c, 3a,
and 3b
Figure 4 confirms clearly that the Me2SiCl2 is coupled to
the two nitrogen atoms of the NCy groups rather than the
anticipated nitrogen of the NPh group, and the selectivity is
different from that observed in reaction of 1a with Me3SiCl.
The short N(3)-C(1) distance (1.257(4) A) and the planar
geometry of the C(1) (sum of angles 360°) are consistent
with a localized double bond between these two atoms.
2a
2b
2c
3a
3b
˚
Bond Lengths (A)
Ln(1)-N(1)
Ln(1)-N(2)
N(1)-C(11)
N(2)-C(11)
N(3)-C(11)
Si(1)-N(3)
2.296(8) 2.299(4) 2.334(6) 2.299(5) 2.307(4)
2.312(7) 2.316(4) 2.343(6) 2.280(5) 2.299(4)
1.340(10) 1.322(6) 1.342(8) 1.324(7) 1.336(5)
1.298(11) 1.329(6) 1.315(8) 1.337(7) 1.337(5)
1.431(11) 1.455(6) 1.453(9) 1.456(7) 1.445(5)
1.765(7) 1.756(4) 1.737(6) 1.757(5) 1.770(3)
˚
(20) Evans, W. J.; Greci, M. A.; Ziller, J. W. J. Chem. Soc., Dalton
Trans. 1997, 3035.
Bond Angles (deg)
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(b) Hagadorn, J. R.; McNevin, M. J.; Wiedenfeld, G.; Shoemaker, R.
Organometallics 2003, 22, 4818. (c) Hagadorn, J. R.; McNevin, M. J.
Organometallics 2003, 22, 609. (d) Grundy, J.; Coles, M. P.; Hitchcock,
P. B. J. Organomet. Chem. 2002, 662, 178. (e) Clare, B.; Sarker, N.;
Shoemaker, R.; Hagadorn, J. R. Inorg. Chem. 2004, 43, 1159. (f) Chen,
C. T.; Huang, C. A.; Tzeng, Y. R.; Huang, B. H. Dalton Trans. 2003, 2585.
(22) (a) Zhao, B.; Li, H. H.; Shen, Q.; Zhang, Y.; Yao, Y. M.; Lu, C.
R. Organometallics 2006, 25, 1824. (b) Hogarth, G.; Humphrey, D. G.;
Kaltsoyannis, N.; Kim, W. S.; Lee, M. Y.; Norman, T.; Redmond, S. P.
J. Chem. Soc., Dalton Trans. 1999, 2705. (c) Dorado, I.; Garces, A.;
Lopez-Mardomingo, C.; Fajardo, M.; Rodriguez, A.; Antinolo, A.; Otero, A.
J. Chem. Soc., Dalton Trans. 2000, 2375. (d) Antinolo, A.; Dorado, I.;
Fajardo, M.; Garces, A.; Lopez-Solera, I.; Lopez-Mardomingo, C.; Kubicki,
M. M.; Otero, A.; Prashar, S. Eur. J. Inorg. Chem. 2004, 1299.
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2001, 627, 1659.
N(1)-Ln(1)-N(2) 58.4(3)
57.89(15) 57.5(2) 58.6(2) 58.27(12)
N(2)-C(11)-N(1) 116.9(8) 114.8(5) 115.8(7) 114.9(6) 114.1(4)
N(2)-C(11)-N(3) 122.3(8) 122.0(5) 123.2(8) 120.5(6) 121.5(4)
N(1)-C(11)-N(3) 120.8(8) 123.2(5) 121.0(7) 124.6(6) 124.4(4)
C(11)-N(3)-Si(1) 120.3(5) 120.6(3) 119.0(5) 122.8(4) 122.1(3)
for further perfecting the versatility of these ligands. Such
concepts have been elegantly applied to ansa-metallocene
complexes19 and other anionic functionalities including
(19) (a) Qian, C. T.; Nie, W. L.; Sun, J. J. Organomet. Chem. 2001,
626, 171. (b) Qian, C. T.; Nie, W. L.; Chen, Y. F.; Sun, J. J. Organomet.
Chem. 2002, 645, 82. (c) Nie, W. L.; Qian, C. T.; Chen, Y. F.; Jie, S.
J. Organomet. Chem. 2002, 647, 114.

1288 Organometallics, Vol. 29, No. 5, 2010
Zheng et al.
through one nitrogen atom and one bridging oxygen to yield
a planar four-membered cycle of sp2-hybridized N and C
centers with a bite angle of 117.0(8)°. The bond distances
˚
within the OCN moiety (N(1)-C(1) 1.26 A, O(1)-C(1)
˚
1.31 A) are in agreement with a delocalized π interaction.
Conclusions
In summary, we have synthesized the first heterobimetallic
lanthanide-lithium complexes containing the guanidinate
dianion ligand. Furthermore, some novel reactivity features
of dianionic guanidinate ligands, such as the coupled cycli-
zation with dichlorosilane and the acylation/decarbodiimi-
nation with benzoyl chloride, have also been established.
These results have shown that deprotonation of monoanio-
nic guanidinate ligands is a convenient and applicable
methodology for synthesis of guanidinate dianion complexes
of rare earth elements. On the basis of the reactions with
Me3SiCl, Me2SiCl2, and PhCOCl it would appear that the
active site of the dianionic guanidinate ligand is tunable due
to the delocalization of the two negative charges on the three
N atoms. The dianionic cooperative effect not only tends to
increase the coordination and reactivity availability in the
guanidinate ligand but delicately induces some unusual
tandem reactions.
Figure 5. Thermal ellipsoid (30%) plot of [Cp2Dy(OC(Ph)NCy)]2
(6). Hydrogen atoms are omitted for clarity. Selected bond lengths
(A) and angles (deg): Dy1-O1A 2.327(3), Dy1-O1 2.422(3),
Dy1-N1 2.490(4), N1-C1 1.268(5), O1-C1 1.312(5),
O1A-Dy1-O1 67.6(1), O1A-Dy1-N1 120.3(1), O1-Dy1-N1
53.2(1), C1-N1-Dy1 94.0(3), C1-O1-Dy1A 150.9(3),
C1-O1-Dy1 95.9(2), Dy1A-O1-Dy1 112.4(1), N1-C1-O1
116.9(4), N1-C1-Dy1 59.9(2), O1-C1-Dy1 57.0(2).
˚
The distances of the N(1)-C(1) and N(2)-C(1) bonds are in
the typical C-N single-bond range. The average Si-N
distance of 1.735(3) A is comparable to the values found in
Experimental Section
˚
General Remarks. All operations involving air- and moisture-
sensitive compounds were carried out under an inert atmosphere
of purified nitrogen gas using standard Schlenk techniques. The
solvents THF, toluene, and n-hexane were refluxed and distilled
over sodium benzophenone ketyl under nitrogen gas prior to
use. Elemental analyses for C, H, and N were carried out on a
Vario EL III elemental analyzer (Analysensysteme GmbH,
Germany). Infrared spectra were recorded on a Nicolet
Avatar-360 FT-IR spectrometer with samples prepared in Nujol
mulls. 1H NMR and 13C NMR spectra were recorded on a JEOL
[{Ln(η2-C3N2HMe2-3,5)(μ-η1:η2-OSiMe2C3N2HMe2-3,5)-
(η-C5H4Me)}2] (Ln = Yb, Dy), 1.792(6) A,24 but is signifi-
˚
cantly shorter than the Si-N donor bond distances.25
Reactivity of Complexes 1 toward Benzoyl Chloride. To
further reveal the reactivity of 1, we attempted to introduce
an acyl substituent on the nitrogen atom of the guanidinate
dianion ligands with benzoyl chloride. We anticipated that
this would allow a straightforward avenue for future mod-
ifications. However, treatment of 1d with PhCOCl led to the
disruptive acylation of the dianionic guanidinate ligand, to
afford the corresponding acylamino complex [Cp2Dy(OC-
(Ph)NCy)]2 (6), indicating that the dianionic guanidinate
ligand underwent a tandem acylation/elimination of cyclo-
hexylphenylcarbodiimide moiety. Although the details of the
reaction mechanism are not yet clear, the reaction system
described here is the first example in which the coordinated
guanidinate dianion is converted into acylamido.
1
ECA400 NMR spectrometer (FT, 400 MHz for H; 100 MHz
for 13C). The chemical shifts are reported in ppm referenced to
tetramethylsilane. The starting materials Cp3Ln27 and neutral
guanidines were prepared according to the literature methods.28
All amines and carbodiimides used were purchased from com-
mercial sources and were used without further purification.
Preparation of Cp2Yb[(CyN)2C(NPh)]Li(THF)3 (1a). A 1:1
mixture of Cp3Yb (0.482 g, 1.31 mmol) and N,N0-dicyclohexyl-
N00-phenylguanidine (0.392 g, 1.31 mmol) was dissolved in
30 mL of THF and was stirred at 50 °C for 2 h. After the volatile
materials were removed under vacuum, the residue was dis-
solved in 30 mL of THF. To the above solution was added
dropwise n-butyllithium (2.5 M in hexane, 0.52 mL, 1.31 mmol)
at -78 °C. After stirring at low temperature for 30 min, the
reaction mixture was slowly warmed to room temperature and
stirred for another 12 h. Then, the solution was concentrated to
ca. 2 mL and was stored at -15 °C. 1a was obtained as dark red
crystals. Yield: 0.87 g (81%). Anal. Calcd for C41H61LiN3O3Yb:
C, 59.77; H, 7.46; N, 5.10. Found: C, 59.67; H, 7.49; N, 5.08. IR
(Nujol): 3087 w, 3062 w, 3042 w, 1594 m, 1534 m, 1460 s, 1378 s,
1308 m, 1215 m, 1176 m, 1073 m, 1049 m, 1011 m, 890 m, 766 m,
Complex 6 was characterized by elemental analysis and
spectroscopic properties, which were in good agreement with
the proposed structures. In the IR spectral data, the O-C-N
stretching vibration of the coordinated acylamino groups is
observed at 1606 cm-1 26
Direct confirmation of the struc-
.
tural features of 6 was obtained through a single-crystal
X-ray study. The results are summarized in Figure 5.
Examination of Figure 5 shows that the pseudo-trigonal-
bipyramal coordination geometry of the Dy center is defined
by a bidentate acylamino anion and two Cp ligands, with one
coordination site occupied by an oxygen atom from another
acylamino ligand. The acylamino ligand is bonded to Dy
693 m, cm-1
.
Preparation of Cp2Er[(CyN)2C(NPh)]Li(THF)3 (1b). Follo-
wing the method described for 1a, using Cp3Er (0.359 g,
0.99 mmol), N,N0-dicyclohexyl-N00-phenylguanidine (0.296 g,
(24) (a) Zhou, X. G.; Ma, H. Z.; Huang, X. Y.; You, X. Z. J. Chem.
Soc., Chem. Commun. 1995, 2483. (b) Zhou, X. G.; Ma, W. W.; Huang, Z.
E.; Cai, R. F.; You, X. Z.; Huang, X. Y. J. Organomet. Chem. 1997, 545, 309.
(25) Maaranen, J.; Andell, O. S.; Vanne, T.; Mutikainen, I.
J. Organomet. Chem. 2006, 691, 240.
(27) Birmingham, J. M.; Wilkinson, G. J. Am. Chem. Soc. 1956, 78,
42.
(28) Li, Q. H.; Wang, S. W.; Zhou, S. L.; Yang, G. S.; Zhu, X. C.; Liu,
(26) Zhou, X. G.; Zhang, L. B.; Zhu, M.; Cai, R. F.; Weng, L. H.;
Huang, Z. X.; Wu, Q. J. Organometallics 2001, 20, 5700.
Y. Y. J. Org. Chem. 2007, 72, 6763.

Article
Organometallics, Vol. 29, No. 5, 2010 1289
0.99 mmol), and n-butyllithium (2.5 M in hexane, 0.40 mL,
1.00 mmol) afforded 1b as pink crystals. Yield: 0.70 g (87%).
Anal. Calcd for C41H61ErLiN3O3: C, 60.19; H, 7.52; N, 5.14.
Found: C, 60.15; H, 7.50; N, 5.13. IR (Nujol): 3088 w, 3063 w,
3042 w, 1593 m, 1547 m, 1460 s, 1378 s, 1308 m, 1213 m, 1176 m,
2839 s, 1642 m, 1599 s, 1578 s, 1546 m, 1461 s, 1379 s, 1355 s,
1307 m, 1253 s, 1195 s, 1141 s, 1089 m, 1075 m, 1046 m, 1034 m,
1009 m, 980 m, 929 m, 900 m, 888 m, 840 m, 767 m, 733 m, 696 m,
674 m, 644 m, 616 m, cm-1
.
t
Preparation of Cp2Yb[(CyN)2CN(Ph)SiMe2 Bu] (3a). Follow-
ing the method described for 2a, reaction of 1a (1.15 mmol) with
tert-butyldimethylchlorosilane (0.91 mL, 1.15 mmol) gave 3a as
brown-yellow crystals. Yield: 0.72 g (88%). Anal. Calcd for
C35H52N3SiYb: C, 58.72; H, 7.32; N, 5.87. Found: C, 58.69; H,
7.32; N, 5.89. IR (Nujol): 3095 w, 2854 s, 1638 m, 1596 m, 1576
m, 1461 s, 1378 s, 1343 m, 1306 m, 1257 m, 1227 m, 1195 m, 1139
s, 1073 m, 1048 w, 1031 w, 1010 m, 978 m, 937 w, 919 m, 890 m,
1072 m, 1049 m, 1011 m, 889 m, 765 m, 693 m, cm-1
.
Preparation of Cp2Y[{(CyN)2C(NPh)}Li(THF)3] (1c). Fol-
lowing the method described for 1a, using Cp3Y (0.617 g,
2.17 mmol), N,N0-dicyclohexyl-N00-phenylguanidine (0.649 g,
2.17 mmol), and n-butyllithium (2.5 M in hexane, 0.87 mL,
2.17 mmol) afforded 1c as colorless crystals. Yield: 1.28 g (79%).
Anal. Calcd for C41H61LiN3O3Y: C, 66.56; H, 8.31; N, 5.68.
Found: C, 66.51; H, 8.34; N, 5.65. 1H NMR (C6D6, 7.16): δ 7.97
(m, 2H, C6H5), 7.84 (m, 1H, C6H5), 7.40 (m, 2H, C6H5), 7.17 (s,
5H, C5H5), 7.15 (s, 5H, C5H5), 4.20 (m, 12H, THF), 3.83 (m, 2H,
C6H11), 2.76 (m, 8H, C6H11), 2.40 (m, 4H, C6H11), 2.06 (m, 12H,
THF), 1.87 (m, 8H, C6H11). 13C NMR (THF-d8): δ 171.4, 156.8,
127.8, 123.7, 114.4, 109.7, 67.2, 53.5, 37.3, 26.3, 26.1, 25.4. IR
(Nujol): 3087 w, 3062 w, 3042 w, 1593 m, 1546 m, 1460 s, 1377 s,
1307 m, 1211 m, 1176 m, 1073 m, 1049 m, 1011 m, 888 m, 764 m,
836 m, 811 m, 802 m, 770 s, 733 m, 695 m, 674 m, 611 m, cm-1
.
t
Preparation of Cp2Er[(CyN)2CN(Ph)SiMe2 Bu] (3b). Follow-
ing the method described for 2a, reaction of 1b (1.34 mmol) with
tert-butyldimethylchlorosilane (1.06 mL, 1.34 mmol) afforded
3b as pink crystals. Yield: 0.89 g (94%). Anal. Calcd for
C35H52ErN3Si: C, 59.20; H, 7.38; N, 5.92. Found: C, 59.27; H,
7.35; N, 5.91. IR (Nujol): 3093 w, 3074 w, 3091 w, 2859 s, 1648 w,
1597 s, 1577 m, 1465 s, 1378 s, 1325 m, 1306 m, 1265 m, 1216 s,
1190 m, 1141 m, 1088 m, 1056 s, 1033 m, 1011 s, 970 m, 942 m,
919 m, 878 m, 834 m, 819 m, 807 m, 768 s, 725 m, 699 m, 675 m,
693 m, cm-1
.
Preparation of Cp2Dy[{(CyN)2C(NPh)}Li THF3] (1d). Fol-
3
lowing the method described for 1a, using Cp3Dy (0.479 g, 1.34
mmol), N,N0-dicyclohexyl-N00-phenylguanidine (0.400 g, 1.34
mmol), and n-butyllithium (2.5 M in hexane, 0.54 mL, 1.35
mmol) afforded colorless crystals of 1d. Yield: 0.94 g (86%).
Anal. Calcd for C41H61DyLiN3O3: C, 60.54; H, 7.56; N, 5.17.
Found: C, 60.48; H, 7.54; N, 5.18. IR (Nujol): 3087 w, 3062 w,
3042 w, 1593 m, 1546 m, 1460 s, 1377 s, 1307 m, 1211 m, 1176 m,
614 m, cm-1
.
Preparation of Me2Si(CyN)2CdNPh (4). To a THF (30 mL)
solution of 1a (1.10 mmol) held at -50 °C was added dropwise
dimethyldichlorosilane (0.065 mL, 0.55 mmol). After stirring
for 24 h, the solvent was evaporated under vacuum, and the oily
residue was extracted with toluene (30 mL). The clear solution
was concentrated by reduced pressure to ca. 2 mL. The pre-
cipitate was redissolved with several drops of THF. The result-
ing solution was stored at -15 °C. 4 was obtained as colorless
crystals. Yield: 0.17 g (86%). Anal. Calcd for C21H33N3Si: C,
70.93; H, 9.35; N, 11.82. Found: C, 70.87; H, 9.32; N, 11.85. 1H
NMR (C6D6): δ 7.24 (m, 2H, C6H5), 7.20 (m, 1H, C6H5), 6.92
(m, 2H, C6H5), 3.86 (m, 2H, C6H11), 1.49 (m, 8H, C6H11), 1.00
(m, 4H, C6H11), 0.87 (m, 8H, C6H11), 0.28 (s, 6H, CH3). 13C
NMR (CDCl3): δ 129.1, 128.2, 123.0, 121.9, 120.9, 50.7, 34.6,
25.8, 25.3, 2.0. IR (Nujol): 3055 w, 2856 s, 1638 m, 1588 m, 1463
s, 1376 s, 1347 m, 1304 m, 1254 m, 1147 m, 982 m, 764 m, 697 m,
1073 m, 1047 m, 1010 m, 887 m, 761 m, 693 m, cm-1
.
Preparation of Cp2Yb[(CyN)2CN(Ph)SiMe3] (2a). To a THF
(30 mL) solution of 1a (0.88 mmol) held at -50 °C was added
dropwise chlorotrimethylsilane (0.11 mL, 0.88 mmol). The
reaction mixture was slowly warmed to room temperature and
stirred for 24 h. The solvent was evaporated under vacuum. The
oily residue was extracted with toluene (30 mL), and the
precipitate was removed by centrifugation. The solution was
concentrated by reduced pressure to about 1 mL, and a white
solid precipitated. The precipitate was resolved by addition of
several drops of THF, and red crystals of 2a were obtained upon
cooling at -15 °C. Yield: 0.50 g (84%). Anal. Calcd for
C32H46N3SiYb: C, 57.04; H, 6.88; N, 6.24. Found: C, 57.08;
H, 6.86; N, 6.23. IR (Nujol): 3087 m, 3074 m, 2840 s, 1642 m,
1599 s, 1578 s, 1551 m, 1455 s, 1378 s, 1360 s, 1308 m, 1255 s,
1197 s, 1141 s, 1076 m, 1046 m, 1034 m, 1009 m, 981 m, 928 m,
cm-1
.
Preparation of [Cp2Dy(PhCONCy)]2 (6). To a toluene (30 mL)
solution of 1d (1.27 mmol) held at -30 °C was added dropwise
benzoyl chloride (0.147 mL, 1.27 mmol), and the reaction solution
was slowly warmed to room temperature and stirred for another
24 h. The precipitate was removed by centrifugation. The clear
solution was concentrated by reduced pressure to about 2 mL.
Cooling the solution at -15 °C gave 6 as orange-red crystals.
Yield: 0.64 g (51%). Anal. Calcd for C46H52Dy2N2O2:C, 55.81;H,
5.29; N, 2.83. Found: C, 55.78; H, 5.30; N, 2.82. IR (Nujol):
2955s,2924s, 2853s, 1606m, 1573s,1460s,1377s, 1342s, 1087m,
900 m, 889 m, 838 m, 767 m, 695 m, 674 m, 644 m, 616 m, cm-1
.
Preparation of Cp2Er[(CyN)2CN(Ph)SiMe3] (2b). Following
the method described for 2a, reaction of 1b (0.95 mmol) with
chlorotrimethylsilane (0.12 mL, 0.95 mmol) afforded 2b as pink
crystals. Yield: 0.52 g (81%). Anal. Calcd for C32H46ErN3Si: C,
57.53; H, 6.94; N, 6.29. Found: C, 57.51; H, 6.96; N, 6.28. IR
(Nujol): 3090 m, 3076 m, 2842 s, 1644 m, 1599 m, 1578 m, 1557
m, 1444 s, 1380 s, 1360 s, 1307 m, 1254 s, 1189 s, 1141 s, 1075 m,
1046 m, 1034 m, 1008 m, 979 m, 928 m, 900 m, 889 m, 840 m,
1010 m, 769 m, cm-1
.
Crystallographic parameters for compounds 1a-d, 2a-c, 3a,
3b, 4, and 6 along with details of the data collection and
refinement are included in the Supporting Information.
727 m, 694 m, 674 m, 644 m, 616 m, cm-1
.
Preparation of Cp2Y[(CyN)2CN(Ph)SiMe3] (2c). Following
the method described for 2a, reaction of 1c (1.34 mmol) with
chlorotrimethylsilane (0.17 mL, 1.34 mmol) afforded 2c as pale
Acknowledgment. We thank the National Natural Science
Foundation of China, 973 program (2009CB825300),
Shanghai Science and Technology Committee, the Re-
search Fund for the Doctoral Program of Higher Education
of China, and Shanghai Leading Academic Discipline
Project (B108) for financial support.
yellow crystals. Yield: 0.53
g (67%). Anal. Calcd for
C32H46N3SiY: C, 65.17; H, 7.86; N, 7.13. Found: C, 65.19; H,
7.83; N, 7.11. 1H NMR (C6D6, 7.16): δ 7.14 (m, 2H, C6H5), 7.02
(m, 1H, C6H5), 6.74 (m, 2H, C6H5), 6.39 (s, 5H, C5H5), 6.30 (s,
5H, C5H5), 3.06 (m, 2H, C6H11), 1.64 (m, 8H, C6H11), 1.45 (m,
4H, C6H11), 0.98 (m, 8H, C6H11), 0.39 (s, 9H, CH3). 13C NMR
(THF-d8): δ 158.1, 145.7, 128.6, 118.3, 115.5, 110.7, 55.2, 37.4,
37.2, 25.8, 25.7, 25.6, 0.3. IR (Nujol): 3090 m, 3076 m, 3022 m,
Supporting Information Available: Tables of atomic coordi-
nates and thermal parameters are available free of charge via the
Internet at http://pubs.acs.org.