Synthesis and crystal structure of one carbon-atom bridged lutetium complex [Ph2C(Flu)(Cp)]LuN(TMS)2 and catalytic activity for polymerization of polar monomers

Article abstract of DOI:10.1016/S0022-328X(01)01317-1

The one-carbon atom bridged amide complex [Ph₂C(Flu)(Cp)]LuN(TMS)₂ (2) (Flu = C₁₃H₈, Cp = C₅H₄, TMS = SiMe₃) has been synthesized by reaction of its chloride precursor with LiN(T

Full text of DOI:10.1016/S0022-328X(01)01317-1

Journal of Organometallic Chemistry 645 (2002) 82–86
www.elsevier.com/locate/jorganchem
Synthesis and crystal structure of one carbon-atom bridged
lutetium complex [Ph2C(Flu)(Cp)]LuN(TMS)2 and catalytic activity
for polymerization of polar monomers
Changtao Qian *, Wanli Nie, Yaofeng Chen, Jie Sun
State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 354 Fenglin Lu,
Shanghai 200032, China
Received 2 July 2001; received in revised form 7 September 2001; accepted 10 September 2001
Abstract
The one-carbon atom bridged amide complex [Ph2C(Flu)(Cp)]LuN(TMS)2 (2) (Flu=C13H8, Cp=C5H4, TMS=SiMe3) has
been synthesized by reaction of its chloride precursor with LiN(TMS)2 in toluene. An X-ray structure of the amide complex 2
exhibits apparently intramolecular bSiꢀC agostic interaction with Lu. Polymerization of methyl methacrylate (MMA) and lactones
with this complex has also been investigated. © 2002 Elsevier Science B.V. All rights reserved.
Keywords: Ansa-Lanthanoidocene; Lutetium; Crystal structure; Poly(MMA); Poly(lactone)
generally with less stereospecificity; syndiotactic
polypropylene has been produced using essentially a
1. Introduction
single type of Cs symmetric ansa-metallocene catalyst
[2]. However, the chemistry of ansa-lanthanocene has
Since the discovery of the first stereorigid chiral
ansa-metallocene complex [1] and their application as
been very limited, especially when compared with that
homogeneous catalysts in stereospecific polymerization
of the Group 4 metallocenes. Since the metallocenes of
of a-olefins to polymers with stereoregular microstruc-
tures, a wide variety of metallocene catalysts from
the rare earth elements are isoelectronic structure with
Group
4
cationic alkyl metallocene complexes
Group 3 and 4 have now been prepared. The tactility of
polypropylene varies predictably with the structure of
the ansa-metallocene catalysts: C2 symmetric metal-
locenes produce highly isotactic polypropylene; C1
metallocenes also produce isotactic polypropylene, but
Cp2MR+ d0 (CpꢁC5H5), they are single-component cat-
alysts for olefin polymerization. This fact facilitates
significantly the study of olefin polymerization mecha-
nism and the influence of the metal ligation environ-
ment on the structure and properties of the resultant
polymer for that the intermediates can be isolated more
easily than in the case of the Group 4 matallocenes
[3,4]. They can also catalyze polymerization of polar
monomers [4–8] and block copolymerization of olefins
with polar monomers [4,9,10].
Until now most of the work reported was on com-
pounds stabilized by bis(pentamethylcyclopoentadienyl)
or closely related ligand systems [4,6,10,11]. Most of the
works for study of one-atom bridged lanthanoidocenes
are using silicon as the bridging atom. In connection
with our previous investigation on a series study of the
synthesis and structural characterization of one-atom
(Si and C) bridged fluorenyl cyclopentadienyl lan-
Scheme 1.
* Corresponding author. Tel.: +86-21-64163300; fax: +86-21-
64166128.
E-mail address: qianct@pub.sioc.ac.cn (C. Qian).
0022-328X/02/$ - see front matter © 2002 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(01)01317-1

C. Qian et al. / Journal of Organometallic Chemistry 645 (2002) 82–86
83
Table 1
toluene, we isolated the monomeric salt-free and sol-
vent-free amide complex [Ph2C(C5H4)(C13H8)]LuN-
(TMS)2 (2) (Scheme 1). Compound 2 can also be made
by one-pot synthesis procedure that is by reaction of
anhydrous LuCl3 with dilithium salt of the diphenyl-
methylene-bridged ligand in ether, followed by the
treatment with the KN(TMS)2 in toluene. The amide
complex 2 is very soluble in toluene and benzene, and
sparingly soluble in hexane. It has also been further
characterized by Elemental Analysis, MS, FT-Raman,
and X-ray diffraction analysis.
X-ray diffraction data collection parameters for complex 2
Empirical formula
Formula weight
Crystal system
Color
C37H40LuNSi2
729.87
Triclinic
red
,
a (A)
15.777(3)
17.147(6)
14.434(5)
110.10(3)
93.46(2)
91.39(2)
3656(1)
1472.00
27.89
,
b (A)
,
c (A)
h (°)
i (°)
k (°)
3
,
V (A )
F(000)
v (cm−1
Z
2.2. Molecular structure
)
2
(
Space group
Dcalc (g cm−3
Reflections
P1
1.326
X-ray diffraction quality crystal was grown from
toluene solution. Detail of the crystal data and refine-
ments for complex 2 is shown in Table 1, and selected
bond lengths and internal angles are given in Table 2.
The X-ray structure of 2 is shown in Fig. 1.
)
10369
7747
0.057; 0.073
1.64; −1.98
Observations
a
Final R, wR
peak, hole (e A
−3
,
)
The first aspect is involved with the bonding modes
of the two five-membered ring fragments to Lu when
compared with its chloride precursor. This neutral
structure of complex 2 is very different from that of the
‘ate’ complex 1. As can be seen from the bond distance
data in Table 2, the distances of five LuꢀC(ring) range
2 0.5
a R=SꢀꢀFoꢀ−ꢀFcꢀꢀ/SꢀF0ꢀ, Rw=[Sw(ꢀFoꢀ−ꢀFcꢀ)2/SꢀF0ꢀ ]
.
Table 2
,
Selected bond lengths (A) and internal angles (°) for complex 2
Bond lengths
LuꢀC(32)
LuꢀN
LuꢀSi(1)
Si(2)ꢀN
Si(1)ꢀN
Si(1)ꢀC(32)
Si(2)ꢀC(37)
LuꢀC(1)
2.74(1)
2.167(8)
3.020(3)
1.722(9)
1.687(10)
1.89(1)
1.87(2)
2.731(10)
2.621(9)
2.50
LuꢀC(7)
LuꢀC(8)
2.558(9)
2.568(10)
2.741(9)
2.541(10)
2.533(9)
2.59(1)
2.58(1)
2.588(9)
0.97
,
from 2.558(9) to 2.741(9) A for fluorenyl fragment and
,
2.533(9)–2.59(1) A for cyclopentadienyl ligand are
LuꢀC(13)
LuꢀC(15)
LuꢀC(16)
LuꢀC(17)
LuꢀC(18)
LuꢀC(19)
C(32)ꢀH(23)
C(32)ꢀH(24)
C(32)ꢀH(25)
shorter when compared with those of 2.570(6)–2.841(5)
,
and 2.561(5)–2.626(5) A in complex 1, showing the
typical pattern of normal p5-bonding fashion instead of
the p3-bonding mode in 1. This difference might be due
to the steric decreasing around the rare-earth center
when one of the amide group N(TMS)2 takes place of
the two chloride ligands coordinated on it in the ate
complex 1. The smaller angle of 101.1(7)° among the
two CbridgeheadꢀCPh2ꢀCbridgehead bonds and the acute
dihedral angle of 74.38° between two p-ring plans com-
pared with those (102.4(3), 96.98°) observed in complex
1 also indicate the reduced steric effect around the
central metal atom.
LuꢀC(6)
LuꢀH(23)
LuꢀH(24)
LuꢀH(25)
Bond angles
LuꢀNꢀSi(1)
LuꢀNꢀSi(2)
Si(2)ꢀNꢀSi(1)
0.96
0.94
2.50
3.50
102.5
131.9(5)
125.6(5)
C(20)ꢀC(14)ꢀC(26) 103.2(8)
C(17)ꢀLuꢀN
C(18)ꢀLuꢀN
93.3(4)
103.1(4)
C(7)ꢀC(14)ꢀC(15) 101.1(7)
Dihedral angles
Plan (1) and (5)
74.38
Although the bite angle of 2 is smaller than that in
the corresponding ate chloride 1, it is still larger when
compared with that of the dimethylsilyl-bridged
fluorenyl cyclopentadienyl lanthanide amides such as in
[Me2Si(C5H4)(C13H8)]DyN(TMS)2 [12], the bite angle
is 99.7(3)°; [Me2Si(C5H4)(C13H8)]ErN(TMS)2 [12],
99.5(2)°, and [Me2Si(C5Me4)(C13H8)]YN(TMS)2 [14],
100.4(9)°. Remarkably, such large bite angle is assumed
to facilitate the agostic approach of the bis(trimethylsi-
lyl)amide moiety to the Lewis acidic metal ion. Com-
thanocenes [12,13]. We wish to report here the synthesis
and structure of a new diphenylmethene bridged
fluorenyl cyclopentadienyl lutetium amide [Ph2C(C13-
H8)(C5H4)]LuN(SiMe3)2 and their application of cata-
lyst to polar monomer polymerization.
2. Results and discussion
,
plex 2 features a LuꢀN bond length of 2.167(8) A,
which is shorter than in the dimethylsilyl-bridged
fluorenyl cyclopentadienyl lanthanocene amides (for
example, in [Me2Si(C5H4)(C13H8)]DyN(TMS)2 (Dyꢀ
2.1. Synthesis
By reaction of the chloride compound [Ph2C(C13H8)-
(C5H4)Lu(Cl)2][Li(THF)4] [13a] (1) with LiN(TMS)2 in
,
N=2.207(5) A), [Me2Si(C5H4)(C13H8)]ErN(TMS)2

84
C. Qian et al. / Journal of Organometallic Chemistry 645 (2002) 82–86
,
(ErꢀN=2.194(4) A) and [Me2Si(C5Me4)(C13H8)]-
Si-bridged amide complexes, for example, in our previ-
,
YN(TMS)2 (YꢀN=2.243(11)A)) and five-coordinate
ous reported Si-bridged amides the LnꢀC distances are
,
,
amide precursor (2.184(3)–2.238(3) A) [15]. The short-
equal to 2.834–2.901 A [12]. The longer distances of the
est LnꢀN bond reported so far was observed in the
central metal atom Lu to the two hydrogens H (23, 24)
,
complex: rac-Me2Si(2-MeꢀInd)2LuN(TMS)2 (2.159(4)
on the k-methyl group (equal to 2.50 A) further demon-
strate that there is the SiꢀMeꢀmetal agostic interaction
i
,
A) [16], in which both of the SiꢀH moieties approach
the Lu(III) center in an agostic manner.
not the (kC)Hꢀmetal interaction [20]. The 1H-NMR
data of 2 show only one signal of the methyls of TMS
groups at l 0.00. This is inconsistent with the agostic
structure shown in the X-ray structure, implying the
fluxionality of 2 in THF solution.
The second interesting structural feature in complex
2 is the possible presence of an agostic interaction
between the SiꢀC bond and the central metal atom. In
b
this amide complex, one of the trimethylsilyl substituent
approaches the Ln3+ center at an acute ÚLnꢀChꢀ
Sib(1). In this one carbon atom bridged complex 2 (Fig.
1), one of the LuꢀNꢀSi angles is 102.5°, the other is
131.9(5)°. This multicenter LnꢀMeꢀSi interaction has
been observed in numerous organolanthanide amide
complexes, for example (C5Me5)2LnN(TMS)2 [17],
(S)ꢀ[Me2Si(C5Me4)((+)−neomenthylCp)]LnN(TMS)2
[18], (S)ꢀ[Me2Si(C5Me4)((−)menthylCp)]LnN(TMS)2
[19], [Me2Si(C5Me4)(C13H8)]YN(TMS)2 [14] with the
two ÚLnꢀNꢀSib angles ranging from 103.6(6) to
109.4(3)° for ÚLnꢀNꢀSib(1) and from 121.5(5) to
132.0(7)° for ÚLnꢀNꢀSib(2). The larger C(7)ꢀ
C(14)ꢀC(15) angle of 101.1(7)° and the dihedral angles
of 74.38°, compared to that of the Si-bridged ligands,
makes the metal center more open and induces the
2.3. Polymerization of MMA and lactones
To investigate the catalytic ability of compound 2
toward polar monomers, polymerization of methyl
methacrylate (MMA) and lactones has been examined.
Polymerization of MMA and lactones was performed
in toluene and after a fixed time was quenched with
acidic methanol, the polymers were isolated as colorless
solids and characterized by GPC in THF using stan-
dard polystyrene. Triad microstructures analysis of the
1
PMMA was carried out using H-NMR spectra. The
results of polymerization are summarized in Table 3.
This one-carbon atom bridged ansa-complex initiates
MMA polymerization to yield PMMA with rich-syn-
diotacticity (rr 59%; mm 18%; mr 23%). Its activity is
,
LuꢀC(32) of 2.71(1) A much shorter than that of
Fig. 1. ORTEP diagram of [(C13H8)CPh2(C5H4)LuN(TMS)2] (2) with the adopted atom numbering (only one of the two molecules of the unit cell
is shown).
Table 3
Data for the polymerization reactions
Entry
Mon.
[mon]/[cat]
Tp ( °C)
Y (%)
Mw (×10−4
)
Mn (×10−4
)
Mw/Mn
1
2
3
4
MMA
MMA
CL
200
200
600
600
0
−78
25
12.3
0
53
17
5.44
–
8.15
3.90
2.40
–
4.38
2.32
2.27
–
1.85
1.68
VL
25
Reaction conditions: time, 2 h; solv/[M0]=2 vol/vol; solvent, toluene.

C. Qian et al. / Journal of Organometallic Chemistry 645 (2002) 82–86
85
less than those of [Ln(C5Me5)2H]2 and [Ln-
(C5Me5)2Me]2 [5]. The low activity of 2 is mainly due to
the slow initial 1,4-addition of the LnꢀN(TMS)2 func-
tionality to MMA compared with those of LnꢀR (R=
H, Me) functionality[6]. In connection with the slow
initial 1,4-addition, the polymer formed by 2 shows
broader polydisperisity than those obtained by
[Ln(C5Me5)2H]2 and [Ln(C5Me5)2Me]2. The activity of 2
is also less than those of our previously reported one-
silylcane bridged fluorenyl cyclopentadienyl lan-
thanocene derivatives [12]. The stereoselectivity of 2 is
less than those of [Ln(C5Me5)2H]2 and [Ln(C5Me5)2-
Me]2. The complex 2 also initiate ring opening polymer-
ization of o-Caprolactone (CL) and d-Valerolactone
(VL). In the case of CL polymerization, the activity of
this complex is higher than that of [Yb(C5Me5)2Me]2,
and its activity can compare with that of
[Sm(C5Me5)2Me]2 considering the reaction time [7]. The
PCL and PVL formed are of moderate polydisperisities
(Mw/Mn=1.85, 1.68).
slightly to 30 ml, and then cooled overnight at −20 °C
for crystallization. Orange crystal 92 mg (12.6%) was
formed, which is suitable for X-ray analysis. Anal.
Calc. for C37H40LuNSi2 (2): C, 60.91; H, 5.49; N, 1.92.
Found: C, 62.64; H, 5.63; N, 2.09%. 1H-NMR (300
MHz; [2H8]THF, 25 °C): l (J /Hz) 8.45 (d, 2H, J=8.2
Hz, CH(Ar)), 8.34 (d, 2H, J=6.5 Hz, CH(Ar)), 8.20 (d,
2H, J=8.1 Hz, CH(Ar)), 7.2–7.7 (m, CH(Ar)), 6.31
(m, 2H,CH(Cp)), 6.50 (m, 2H, CH(Cp)), 0.00 (s, 18H,
CH3(Si)). EI mass spectrum (70 eV, 50–400 °C): m/z
730 (19.14, [M]+), 654 (21.91, [M−Ph]+), 146 (65.71,
[N(SiMe3)2]+). FT-Raman (cm−1): 3056 (m), 2898 (m),
1528 (m), 1435 (m), 1327 (vs), 1003 (s), 741 (m), 667
(m), 618 (m), 522 (w), 440 (m), 285 (m).
3.3. Polymerization of MMA
A solution of preweighted catalyst (0.5 mmol) in
C6H5CH3 was adjusted to a constant temperature using
an external bath. Into the well-stirred solution was
syringed 100 mmol of methyl methacrylate, and the
reaction was continuously stirred for an appropriate
period at that temperature. Polymerization was stopped
by addition of the acidic MeOH. The resulting precipi-
tated PMMA was collected, washed with MeOH sev-
eral times, and dried in vacuum at 50 °C for 12 h.
3. Experimental
3.1. General procedure
All operation involving organometallic was carried
out under an inert atmosphere of Ar using standard
schlenk techniques. Toluene and C6H14 were distilled
from Naꢀbenzophenone Ketyl. [Ph2C(C13H8)(C5H4)Lu-
(Cl)2]Li(THF)4 (1) was synthesized using the method
described in literature [13a]. Methyl methacrylate was
purified by distillation from CaH2 followed by storage
over activated molecular sieves (3A) and then vacuum
transferred using a high-vacuum line prior to use. o-
Caprolactone (CL) was dried over CaH2 for 10 days,
distilled in vacuo, and stored over molecular sieves.
d-Valerolactone (VL) was distilled in vacuo and stored
over molecular sieves. Mass spectra were recorded on a
Hp 5989A spectrometer (T=50–400 °C, 1.3 KV). The
solvents C6D6 was degassed and dried over a Na–K
3.4. Polymerization of Lactones
To a solution of the catalyst (0.5 mmol) in C6H5CH3
was added lactone using a syringe at r.t. with vigorous
stirring. After 120 min, the polymerization was
quenched by addition of MeOH and the solvent was
removed. The polymer was redissolved in CHCl3 (5 ml)
and precipitated with MeOH (50 ml). The polymer was
filtered and dried under vacuum.
3.5. X-ray structure determination
Single crystals were sealed in thin-walled glass capil-
laries under an atmosphere of Ar. X-ray diffraction
data were collected at a r.t. using the w-2q scan tech-
nique to a maximum 2q value of 21.5°. The intensities
of three representative reflections were measured after
every 200 reflections. Over the course of data collection,
the standards decreased by 0.9%. A linear correction
factor was applied to the data to account for this
phenomenon. The data were corrected for Lorentz po-
larization effects. The structure was solved by heavy-
atom Patterson methods and expanded using Fourier
techniques. The non-hydrogen atoms were refined an-
isotropically. All calculations were performed using the
TEXSAN crystallographic software package of Molecu-
lar Structure Corporation [21].
1
alloy. H-NMR on IX-90Q (300 MHz) spectrometer.
Elemental analyses were performed by the Analytical
Laboratory of the Shanghai Institute of Organic Chem-
istry.
3.2. Synthesis of [Ph2C(C5H4)(C13H8)]LuN(TMS)2 (2)
A solution of 230 mg (1.15 mmol) KN(TMS)2 was
added dropwise to a stirred suspension of 770 mg (1.27
mmol) of 1 in 50 ml C6H5CH3 at −78 °C under Ar.
The reaction mixture was then slowly warmed to room
temperature (r.t.) and stirred for 1 day, and then
warmed to 60 °C and stirred for 1 day. The precipitate
was filtered off. The solvent was decanted, concentrated

86
C. Qian et al. / Journal of Organometallic Chemistry 645 (2002) 82–86
(c) G. Jeske, L.E. Schock, P.N. Swepstone, H. Schumann, T.J.
4. Conclusion
Marks, J. Am. Chem. Soc. 107 (1985) 8103;
(d) P.J. Shapiro, W.D. Cotter, W.P. Schaefer, J.A. Labinger, J.E.
Bercaw, J. Am. Chem. Soc. 116 (1994) 4623;
(e) E.B. Coughlin, J.E. Bercaw, J. Am. Chem. Soc. 114 (1992)
7606.
In summary, we have successfully synthesized one
new carbon-bridged fluorenyl cyclopentadienyl trivalent
lutetium amide complex with Cs-symmetry, and charac-
terized its structural features by X-ray diffraction stud-
ies. This complex initiates polymerization of polar
monomers.
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[6] M.A. Giardello, Y. Yamamoto, L. Brard, T.J. Marks, J. Am.
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[7] M. Yamashita, E. Ihara, H. Yasuda, Macromolecules 29 (1996)
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[8] K.C. Hultzsch, T.P. Spaniol, J. Okuda, Organometallics 16
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5. Supplementary material
Crystallographic data for the structure analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC no. 171166 for compound 2.
Copies of this information may be obtained free of
charge from The Director, CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK (Fax: +44-1223-336033;
e-mail: deposit@ccdc.cam.ac.uk or www: http://
www.ccdc.cam.ac.uk).
(b) G. Desurmont, T. Tokimitsu, H. Yasuda, Macromolecules 33
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(b) P.W. Roesky, U. Denninger, C.L. Stern, T.J. Marks,
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Acknowledgements
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[12] C. Qian, W. Nie, J. Sun, Organometallics 19 (2000) 4134.
[13] (a) C. Qian, W. Nie, J. Sun, J. Chem. Soc. Dalton Trans. (1999)
3283;
The authors are grateful to the National Engineer
Research Center of New Rubble and Plastic Materials
and the National Nature Science Foundation of China
for their financial support.
(b) C. Qian, W. Nie, J. Sun, J. Organomet. Chem. 626 (2001)
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