Synthesis, reactivity, and structural characterization of sodium and ytterbium complexes containing new imidazolidine-bridged bis(phenolato) ligands

Article abstract of DOI:10.1021/ic0701054

A new imidazolidine-bridged bis(phenol) [ONNO]H₂ ([ONNO]H ₂ = 1,4-bis(2-hydroxy-3,5-di-tert-butyl-benzyl)-imidazolidine) was prepared in relatively high yield by Mannish reaction of 2,4-di-tert- butylphenol, formaldehyde, and ethylenediamine in a 2:3:1 molar ratio. Reaction of the bis(phenol) with NaH in THF, after workup, afforded the sodium bis(phenolate) {[ONNO]Na₂(THF)₂}₂·2THF (1) as a dimeric tetranuclear complex in an almost quantitative yield. Reaction of YbCl₃ with complex 1 in a 2:1 molar ratio in THF, in the presence of HMPA, produced the desired bis(phenolate) ytterbium dichloride as bimetallic complex [ONNO]{YbCl₂(HMPA)}₂·2.5C₇H ₈ (2). Complex 2 can be used as a precursor for the synthesis of ytterbium derivatives by salt metathesis reactions. Reaction of complex 2 with NaOⁱPr in a 1:2 molar ratio in THF led to the formation of bimetallic alkoxide [ONNO]{Yb(μ-Oⁱ-Pr)CI(HMPA)}₂·THF (3). However, the residual chlorine atoms in complex 3 are inactive for the further substituted reaction. Further study revealed that the bulkiness of the reagent has profound effect on the outcome of the reaction. Complex 2 reacted with bulky NaOAr (ArO = 2,6-di-tert-butyl-4-methylphenoxo) or NaNPh₂ in a 1:2 molar ratio under the same reaction conditions, after workup, to give the ligand redistributed products, (ArO)₂YbCl-(HMPA)₂ (4) and [ONNO]YbCI(HMPA)₂ (5) for the former and complexes 5 and (Ph ₂N)₂YbCl(HMPA)₂ (6) for the latter. If the molar ratio of complex 2 to NaNPh₂ decreased to 1:4, the expected ligand redistributed products [ONNO]YbNPh₂(HMPA) (7) and (Ph ₂N)₃Yb(HMPA)₂·C₇H ₈ (8) can be isolated in high yields. All of the complexes were well characterized, and the definitive molecular structures of complexes 1-4, 7, and 8 were provided by single-crystal X-ray analysis.

Full text of DOI:10.1021/ic0701054

Inorg. Chem. 2007, 46, 3743−3751
Synthesis, Reactivity, and Structural Characterization of Sodium and
Ytterbium Complexes Containing New Imidazolidine-Bridged
Bis(phenolato) Ligands
Xiaoping Xu, Yingming Yao,* Yong Zhang, and Qi Shen*
Key Laboratory of Organic Synthesis of Jiangsu ProVince, Department of Chemistry and Chemical
Engineering, Dushu Lake Campus, Suzhou UniVersity, Suzhou 215123, P. R. China
Received January 21, 2007
A
new imidazolidine-bridged bis(phenol) [ONNO]H2 ([ONNO]H2 ) 1,4-bis(2-hydroxy-3,5-di-tert-butyl-benzyl)-
imidazolidine) was prepared in relatively high yield by Mannish reaction of 2,4-di-tert-butylphenol, formaldehyde,
and ethylenediamine in a 2:3:1 molar ratio. Reaction of the bis(phenol) with NaH in THF, after workup, afforded the
sodium bis(phenolate)
yield. Reaction of YbCl3 with complex 1 in a 2:1 molar ratio in THF, in the presence of HMPA, produced the
desired bis(phenolate) ytterbium dichloride as bimetallic complex [ONNO] YbCl2(HMPA)}2‚2.5C7H8 (2). Complex 2
can be used as a precursor for the synthesis of ytterbium derivatives by salt metathesis reactions. Reaction of
complex 2 with NaOiPr in a 1:2 molar ratio in THF led to the formation of bimetallic alkoxide [ONNO] -Oi-
Yb(
{[ONNO]Na2(THF)2}2‚2THF (1) as a dimeric tetranuclear complex in an almost quantitative
{
{
µ
Pr)Cl(HMPA)}2‚THF (3). However, the residual chlorine atoms in complex 3 are inactive for the further substituted
reaction. Further study revealed that the bulkiness of the reagent has profound effect on the outcome of the
reaction. Complex 2 reacted with bulky NaOAr (ArO
) 2,6-di-tert-butyl-4-methylphenoxo) or NaNPh2 in a 1:2 molar
ratio under the same reaction conditions, after workup, to give the ligand redistributed products, (ArO)2YbCl-
(HMPA)2 (4) and [ONNO]YbCl(HMPA)2 (5) for the former and complexes 5 and (Ph2N)2YbCl(HMPA)2 (6) for the
latter. If the molar ratio of complex 2 to NaNPh2 decreased to 1:4, the expected ligand redistributed products
[ONNO]YbNPh2(HMPA) (7) and (Ph2N)3Yb(HMPA)2‚C7H8 (8) can be isolated in high yields. All of the complexes
were well characterized, and the definitive molecular structures of complexes 1−4, 7, and 8 were provided by
single-crystal X-ray analysis.
Introduction
(phenolate) lanthanide alkoxides can polymerize ꢀ-capro-
lactone in a controllable manner,2b,e and the divalent ytter-
bium complex stabilized by amine bis(phenolate) ligands,
In recent years, bridged bis(phenolate) ligands have
received considerable attention in organolanthanide chemistry
because they are easily available, tunable, and even poten-
tially recyclable, which thus allows for the systematic
variation of the steric and electronic properties of the
bisphenolic portion.1-3 In particular, some of these bridged
bis(phenolate) lanthanide complexes exhibit exciting reactiv-
ity. For example, the amine bis(phenolate) group 3 and
lanthanide metal complexes are highly active initiators for
the synthesis of poly(ꢀ-caprolactone) and poly(lactide),
respectively,1c,e,h,j and syndiospecific poly(â-butyrolactone)
from racemic â-butyrolactone.1i The carbon-bridged bis-
(1) For recent examples of amine bis(phenolate) lanthanide complexes:
(a) Skinner, M. E. G.; Tyrell, B. R.; Ward, B. D.; Mountford, P. J.
Organomet. Chem. 2002, 647, 145. (b) Cai, C. X.; Toupet, L.;
Lehmann, C. W.; Carpentier, J.-F. J. Organomet. Chem. 2003, 683,
131. (c) Cai, C. X.; Amgoune, A.; Lehmann, C. W.; Carpentier, J. F.
Chem. Commun. 2004, 330. (d) Kerton, F. M.; Whitwood, A. C.;
Willans, C. E. Dalton Trans. 2004, 2237. (e) Yao, Y. M.; Ma, M. T.;
Xu, X. P.; Zhang, Y.; Shen, Q.; Wong, W. T. Organometallics 2005,
24, 4014. (f) Boyd, C. L.; Toupance, T.; Tyrrell, B. R.; Ward, B. D.;
Wilson, C. R.; Cowley, A. R.; Mountford, P. Organometallics 2005,
24, 309. (g) Ma, M. T.; Xu, X. P.; Yao, Y. M.; Zhang, Y.; Shen, Q.
J. Mol. Struct. 2005, 740, 69. (h) Bonnet, F.; Cowley, A. R.;
Mountford, P. Inorg. Chem. 2005, 44, 9046. (i) Amgoune, A.; Thomas,
C. M.; Ilinca, S.; Roisnel, T.; Carpentier, J.-F. Angew. Chem., Int.
Ed. 2006, 45, 2782. (j) Amgoune, A.; Thomas, C. M.; Roisnel, T.;
Carpentier, J. F. Chem.sEur. J. 2006, 12, 169. (k) Delbridge, E. E.;
Dugah, D. T.; Nelson, C. R.; Skelton, B. W.; White, A. H. Dalton
Trans. 2007, 143. (l) Zhou, H.; Guo, H. D.; Yao, Y. M.; Zhang, Y.;
Shen, Q. Inorg. Chem. 2007, 46, 958.
* To whom correspondence should be addressed. E-mail: yaoym@
suda.edu.cn (Y.Y.), qshen@suda.edu.cn (Q.S.). Phone: (86)512-65882806
(Y.Y.). Fax: (86)512-65880305 (Y.Y.).
10.1021/ic0701054 CCC: $37.00
Published on Web 04/03/2007
© 2007 American Chemical Society
Inorganic Chemistry, Vol. 46, No. 9, 2007 3743

Xu et al.
as a single electron-transfer reagent, can activate some small
molecules, such as PhNCO and PhCtCH, etc.1l
(phenolate) ligands and X ) a monoanionic active group,
were synthesized by reaction of the appropriate trivalent
homoleptic lanthanide amide or alkyl with an equivalent LH2
ligand via a protolytic ligand exchange reaction.1b-d,i,j,3 In
addition to ligand exchange pathways, we recently reported
the successful synthesis of neutral ytterbium (III) amine bis-
(phenolate) complexes by direct metathesis reaction.1e It is
interesting to know whether this is a special case. Therefore,
we intend to expand this synthetic method to other bis-
(phenolate) ligand systems. In this paper, a new imidazoli-
dine-bridged bis(phenol) was prepared, and a series of
lanthanide derivatives supported by this ligand system were
synthesized by direct salt metathesis reaction. Here we report
these results.
The presence of a heteroatom on the bridged bis(phenolate)
ligands seems to have significant effect on the reactivity of
the corresponding metal complexes. The titanium complexes
containing sulfur- or tellurium-bridged bis(phenolate) ligands
were reported to show distinctively high activity for the
polymerization of ethylene and propylene upon activation
with methylaluminoxane (MAO) in comparison with those
of the corresponding methylene-bridged bis(phenolate) and
the similar 2,2′-diphenolate titanium complexes.4 A theoreti-
cal study revealed that the coordination of the sulfur or
tellurium atom was essential to reduce the activation energy
for olefin insertion into a metal-carbon bond.5 Our previous
studies also revealed that the lanthanide complexes supported
by the amine bis(phenolate) ligands showed higher catalytic
activities for ꢀ-caprolactone polymerization than the meth-
ylene-linked ones.1e,2b This encouraged us to systematically
investigate the effect of heteroatoms of the ancillary ligands
on the reactivity of the corresponding lanthanide complexes.
In general, the metathesis reaction of bis(cyclopentadienyl)
lanthanide halides with lithium alkyls or amides is a
convenient method for the synthesis of the lanthanocene
derivatives.6 However, this general rule is problematic for
the synthesis of non-cyclopentadienyl lanthanide complexes,
due to the formation of salt inclusion lanthanide complexes.1k
To date, most of the lanthanide complexes which have the
general formula LLnX, where L ) dianionic bridged bis-
Experimental Section
All reagents are reagent grade and commercially available and
used as received unless otherwise noted. All manipulations were
performed under argon, using the standard Schlenk techniques.
THF, toluene, and hexane were distilled from sodium benzophenone
ketyl before use. HMPA was dried over CaH2 for 4 days and
distilled under reduced pressure. (Caution! HMPA is a cancer
suspect agent and should be handled with discretion.) Isopropanol
was dried with a small amount of sodium and distilled before use.
Lanthanide metal analysis was performed by EDTA titration with
an xylenol orange indicator and a hexamine buffer,7 and chloride
analysis was carried out using the Volhard method. Carbon,
hydrogen, and nitrogen analyses were performed by direct combus-
tion with a Carlo-Erba EA-1110 instrument. The IR spectra were
recorded with a Nicolet-550 FTIR spectrometer as KBr pellets. 1H
NMR spectra were obtained on an INOVA-400 MHz apparatus.
The uncorrected melting points of crystalline samples in sealed
capillaries (under argon) are reported as ranges.
(2) For recent examples of carbon-bridged bis(phenolate) lanthanide
complexes: (a) Deng, M. Y.; Yao, Y. M.; Shen, Q.; Zhang, Y.; Sun,
J. Dalton Trans. 2004, 944. (b) Yao, Y. M.; Xu, X. P.; Liu, B.; Zhang,
Y.; Shen, Q. Inorg. Chem. 2005, 44, 5133. (c) Xu, X. P.; Ma, M. T.;
Yao, Y. M.; Zhang, Y.; Shen, Q. Eur. J. Inorg. Chem. 2005, 676. (d)
Xu, X. P.; Ma, M. T.; Yao, Y. M.; Zhang, Y.; Shen, Q. J. Mol. Struct.
2005, 743, 163. (e) Xu, X. P.; Yao, Y. M.; Hu, M. Y.; Zhang, Y.;
Shen, Q. J. Polym. Sci., Part A: Polym. Chem. 2006, 44, 4409.
(3) For recent examples of sulfur-bridged bis(phenolate) and biphenolate
lanthanide complexes: (a) Arnold, P. L.; Natrajan, L. S.; Hall, J. J.;
Bird, S. J.; Wilson, C. J. Organomet. Chem. 2002, 647, 205. (b) Ma,
H. Y.; Spaniol, T. P.; Okuda, J. J. Chem. Soc., Dalton Trans. 2003,
4470. (c) Ma, H. Y.; Okuda, J. Macromolecules 2005, 38, 2665. (d)
Schaverien, C. J.; Meijboom, N.; Orpen, A. G. J. Chem. Soc., Chem.
Commun. 1992, 124. (e) Gribkov, D. V.; Hultzsch, K. C.; Hampel, F.
Chem.sEur. J. 2003, 9, 4796. (f) Gribkov, D. V.; Hampel, F.;
Hultzsch, K. C. Eur. J. Inorg. Chem. 2004, 4091.
(4) (a) Miyatake, T.; Mizunuma, K.; Seki, Y.; Kakugo, M. Makromol.
Chem., Rapid Commun. 1989, 10, 349. (b) van der Linden, A.;
Schaverien, C. J.; Meijboom, N.; Ganter, C.; Orpen, A. G. J. Am.
Chem. Soc. 1995, 117, 3008. (c) Nakayama, Y.; Watanabe, K.;
Ueyama, N.; Nakamura, A.; Harada, A.; Okuda, J. Organometallics
2000, 19, 1498. (d) Takashima, Y.; Nakayama, Y.; Hirao, T.; Yasuda,
H.; Harada, A. J. Organomet. Chem. 2004, 689, 612.
Synthesis of Ligand [ONNO]H2. 2,4-Di-tert-butylphenol (4.12
g, 20.0 mmol) was dissolved in 50 mL methanol, and to this solution
was added aqueous formaldehyde solution (4.11 mL, 50.0 mmol)
and ethylenediamine (0.67 mL, 10.0 mmol). The mixture was stirred
overnight and refluxed in methanol, and a white precipitate appeared
during this period. After the reaction mixture was cooled to room
temperature, the product was collected by filtration and finally
recrystallized from hot petroleum ether (3.31 g, 65%). Mp: 184.1-
184.5 °C. Anal. Calcd for C33H52N2O2: C, 77.90; H, 10.30; N,
5.50%. Found: C, 78.06; H, 10.44; N, 5.38%. IR (KBr, cm-1):
3167 (br, m), 2955 (s), 2905 (s), 2866 (s), 2827 (s), 1770 (w), 1608
(m), 1481 (s), 1389 (s), 1362 (s), 1304 (s), 1234 (s), 1087 (m), 880
(m). 1H NMR (400 Hz, CDCl3): 10.73 (br, 2H, OH), 7.22 (s, 2H,
Ph), 6.83 (s, 2H, Ph), 3.89 (s, 4H, CH2), 3.52 (s, 2H, imidazolidine
ring), 2.99 (br, 4H, imidazolidine ring), 1.42 (s, 18H, tBu), 1.28 (s,
t
18H, Bu). HRMS, m/z: 508.3871 (M+).
(5) (a) Froese, R. D. J.; Musaev, D. G.; Matsubara, T.; Morokuma, K. J.
Am. Chem. Soc. 1997, 119, 7190. (b) Froese, R. D. J.; Musaev, D.
G.; Morokuma, K. Organometallics 1999, 18, 373.
Synthesis of {[ONNO]Na2(THF)2}2‚2THF (1). To a stirred
suspension of NaH (1.5 equiv) in THF, the solution of [ONNO]H2
(5.08 g, 10.0 mmol) in THF was added dropwise. The mixture was
continuously stirred at room temperature overnight and then
centrifuged. The precipitate was washed with hot THF twice, and
the decantate was combined and concentrated. Colorless crystals
were obtained from the concentrated THF solution (7.61 g, 99%).
Mp: 219-221 °C. Anal. Calcd for C90H148N4Na4O10: C, 70.28;
H, 9.70; N, 3.64%. Found: C, 70.16; H, 9.57; N, 3.48%. IR (KBr,
cm-1): 2956 (s), 2871 (s), 1775 (w), 1652 (w), 1605 (m), 1459
(s), 1389 (m), 1358 (m), 1297 (w), 1235 (m), 1165 (w), 880 (m).
1H NMR (400 Hz, CDCl3): 7.21 (s, 2H, Ph), 6.82 (s, 2H, Ph),
(6) Schumann, H.; Meese-Marktscheffel, J. A.; Esser, L. Chem. ReV. 1995,
95, 865.
(7) Atwood, J. L.; Hunter, W. E.; Wayda, A. L.; Evans, W. J. Inorg. Chem.
1981, 20, 4115.
(8) Burke, W. J.; Glennie, E. L. M.; Weatherbee, C. J. Org. Chem. 1964,
29, 909.
(9) Tshuva, E. Y.; Gendeziuk, N.; Kol, M. Tetrahedron Lett. 2001, 42,
6405.
(10) Xu, X. P.; Yao, Y. M.; Zhao, Y. P.; Zhang, Y.; Shen, Q. Chin. J.
Chem. Res. Appl. 2005, 17, 384.
(11) (a) Caulton, K. G.; Hubert-Pfalzgraf, L. G. Chem. ReV. 1990, 90, 969.
(b) Chissholm, M. H.; Rothwell, I. P. In ComprehensiVe Coordination
Chemistry; Wilkinson, G., Ed.; Pergamon Press: Oxford, U.K., 1987;
Vol. 2.
3744 Inorganic Chemistry, Vol. 46, No. 9, 2007

Sodium and Ytterbium Complexes
Table 1. Crystallographic Data for Complexes 1-4, 7, and 8
compd
1
2
3
4
7
8
formula
fw
T(K)
C
90H148N4Na4O10
C62.50H106Cl4N8O4P2Yb2
1583.37
193(2)
C55H108Cl2N8O7P2Yb2
1472.41
173(2)
C42H82ClN6O4P2Yb
1005.57
193(2)
C51H78N6O3PYb
1027.20
153(2)
C55H74N9O2P2Yb
1128.21
173(2)
1538.08
193(2)
cryst syst
space group
a (Å)
b (Å)
c (Å)
triclinic
P1h
Monoclinic
P21/c
15.9447(17)
24.683(3)
monoclinic
P21/n
17.4291(11)
17.1060(11)
23.4174(16)
orthorhombic
Pbcn
32.547(2)
18.1550(8)
16.7632(10)
orthorhombic
Pbca
14.1000(5)
27.5165(11)
54.844(2)
monoclinic
P21/c
16.5515(13)
16.2383(12)
20.9858(17)
10.4123(18)
15.5300(18)
15.9655(19)
66.699(11)
85.856(16)
78.656(15)
2324.7(6)
1
18.6684(19)
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
94.481(3)
91.022(2)
102.783(2)
7324.7(13)
4
1.436
2.774
3228
6980.6(8)
4
1.401
2.834
3016
9905.3(10)
8
1.349
2.050
21278.6(14)
16
1.283
1.832
8560
5500.5(7)
4
1.806
2.774
D
calcd (g cm-3
)
1.099
0.086
840
µ (mm-1
F(000)
)
4200
2332
cryst size (mm)
max (deg)
0.40 × 0.28 × 0.22
0.30 × 0.23 × 0.14
0.50 × 0.44 × 0.30
0.32 × 0.30 × 0.29
0.50 × 0.30 × 0.12
0.48 × 0.30 × 0.29
θ
25.3
25.35
25.35
25.35
25.35
25.35
collected reflns
unique reflections
observed reflns
[I > 2.0σ (I)]
no. of variables
GOF
23344
8467
5875
69167
13390
11062
65653
12742
11616
89927
9052
7971
113177
19127
15937
52864
10051
8589
500
759
640
532
1154
636
1.103
0.0817
0.2042
1.178
0.0723
0.1732
1.135
0.0596
0.1382
1.225
0.0424
0.0792
1.141
0.0621
0.1226
1.080
0.0664
0.1732
R
wR
3.87 (s, 4H, CH2), 3.72 (br, 12H, THF), 3.50 (s, 2H, imidazolidine
ring), 2.98 (br, 4H, imidazolidine ring), 1.84 (br, 12H, THF), 1.40
(s, 18H, Bu), 1.28 (s, 18H, Bu).
was added to the stirred THF solution of complex 2 (4.20 g, 2.65
mmol). The color of the mixture turned from orange to yellow,
and a gel-like precipitate was formed immediately. The reaction
mixture was stirred at room temperature overnight, and the
precipitate was removed by centrifugation. To the solution was
added HMPA (0.90 mL), and the mixture was stirred for about an
hour. The solvent was evaporated in vacuum, and hot toluene (25
mL) was added. Yellow star-like crystals of complex 4 were
obtained in 4 days in 37% yield (1.00 g). Mp: 108-110 °C. Anal.
Calcd for C42H82ClN6O4P2Yb (4): C, 50.17; H, 8.22; N, 8.35; Cl,
3.53; Yb, 17.21%. Found: C, 49.96; H, 8.06; N, 8.18; Cl, 3.37;
Yb, 17.06%. IR (KBr, cm-1): 2955 (s), 2913 (w), 2871 (w), 1731
(w), 1603 (s), 1430 (s), 1389 (m), 1367 (m), 1232 (s), 1153 (s),
1121 (w), 866 (s), 772 (s). After toluene was removed from the
mother liquor, hot hexane (30 mL) was added to extract another
product. A pale yellow crystalline solid of complex 5 was obtained
in 2 days in 18% yield (0.49 g). Mp: 187-189 °C. Anal. Calcd
for C45H86ClN8O4P2Yb (5): C, 50.34; H, 8.07; N, 10.44; Cl, 3.30;
Yb, 16.12%. Found: C, 50.06; H, 7.84; N, 10.28; Cl, 3.13; Yb,
15.98%. IR (KBr, cm-1): 2951 (s), 2919 (s), 2857 (s), 1743 (w),
1652 (w), 1611 (m), 1453 (s), 1389 (m), 1357 (m), 1285 (w), 1233
(m), 1158 (w), 854 (m).
t
t
Synthesis of [ONNO]{YbCl2(HMPA)}2‚2.5C7H8 (2). To a
slurry of anhydrous YbCl3 (1.40 g, 5.0 mmol) in THF was added
a hot solution of complex 1 (1.92 g, 1.25 mmol) in THF. The
mixture was stirred at 50 °C for about 8 h, and a red precipitate
formed gradually. After the reaction mixture was cooled to room
temperature, 0.87 mL of HMPA was added dropwise to the stirred
suspension. The color of the system turned slowly yellow, and a
colorless gel-like matter appeared at the same time. The system
was continuously stirred at room temperature for another 2 h, and
the precipitate was removed from the reaction mixture by centrifu-
gation. THF was completely evaporated in vacuum, and toluene
was added. Yellow crystals were obtained from the concentrated
toluene solution at -10 °C in a few days (2.65 g, 67%). Mp: 245-
247 °C. Anal. Calcd for C62.50H106Cl4N8O4P2Yb2: C, 47.41; H, 6.75;
N, 7.07; Cl, 8.96; Yb, 21.86%. Found: C, 47.16; H, 6.54; N, 6.88;
Cl, 8.74; Yb, 21.69%. IR (KBr, cm-1): 2953 (s), 2921 (s), 2856
(s), 1743 (w), 1650 (w), 1604 (m), 1463 (s), 1369 (m), 1356 (m),
1287 (w), 1235 (m), 1165 (w), 850 (m).
Synthesis of [ONNO]{Yb(µ-OiPr)Cl(HMPA)}2‚THF (3). The
crystalline solid of complex 2 (3.65 g, 2.31 mmol) was dissolved
in THF, and the hot THF solution of NaOiPr (0.38 g, 4.61 mmol)
was added. The color of the reaction mixture turned lemon-yellow,
and the gel-like precipitate formed immediately. The reaction
mixture was stirred overnight at room temperature, and the
precipitate was removed by centrifugation. The solution was
concentrated to about 8 mL, and a colorless crystal-like solid formed
Synthesis of (Ph2N)2YbCl(HMPA)2 (6). The synthesis of
complex 6 was carried out as described for complex 4, but NaNPh2
(5.68 mL, 4.86 mmol) was used in place of NaOAr. After workup,
complex 6 was obtained from the toluene solution in 32% yield
(0.71 g). Mp: 211-213 °C. Anal. Calcd for C36H56ClN8P2O2Yb:
C, 47.87; H, 6.25; N, 12.40; Cl, 3.92; Yb, 19.16%. Found: C, 48.06;
H, 6.26; N, 11.98; Cl, 3.63; Yb, 18.87%. IR (KBr, cm-1): 3036
(w), 2952 (s), 2903 (s), 2863 (s), 1734 (w), 1597 (s), 1522 (s),
1491 (s), 1459 (s), 1332 (s), 1244 (w), 1172 (m), 1087 (w), 880
(m), 702 (m), 690 (s). Complex 5 was also isolated from the hexane
solution in 23% yield (0.62 g).
in 2 days (2.82 g, 83%). Mp: 223-225 °C. Anal. Calcd for C55H108
-
Cl2N8O7P2Yb2: C, 44.87; H, 7.39; N, 7.61; Cl, 4.82; Yb, 23.50%.
Found: C, 44.57; H, 7.14; N, 7.38; Cl, 4.65; Yb, 23.22%. IR (KBr,
cm-1): 2951 (s), 2920 (s), 2855 (s), 2812 (m), 1736 (w), 1604
(m), 1481 (s), 1442 (s), 1361 (s), 1304 (s), 1238 (s), 1192 (m),
1149 (s), 1068 (m), 991 (s), 841 (m), 756 (s). Crystals suitable for
X-ray structure analysis were obtained by the slow cooling of a
hot THF solution.
Synthesis of [ONNO]YbNPh2(HMPA) (7) and (Ph2N)3Yb-
(HMPA)2‚C7H8 (8). The synthesis of complexes 7 and 8 was
carried out similarly as described for complexes 5 and 6, but the
molar ratio of complex 2 (3.80 g, 2.40 mmol) to NaNPh2 was 1:4.
After the NaCl was removed from the reaction mixture, the system
was dried in vacuum, and hot hexane (35 mL) was added. Complex
Synthesis of (ArO)2YbCl(HMPA)2 (4) and [ONNO]YbCl-
(HMPA)2 (5). A THF solution of NaOAr (6.0 mL, 5.30 mmol)
Inorganic Chemistry, Vol. 46, No. 9, 2007 3745

Xu et al.
Scheme 1
1
8 was precipitated immediately as a deep red crystalline solid in
36% yield (0.97 g). Mp: 185-187 °C, Anal. Calcd for C55H74N9O2P2-
Yb: C, 58.55; H, 6.61; N, 11.17; Yb, 15.34%. Found: C, 55.26;
H, 6.35; N, 10.84; Yb, 15.17%. IR (KBr, cm-1): 3035 (w), 2951
(s), 2903 (s), 2862 (s), 1734 (w), 1595 (s), 1523 (s), 1491 (s), 1457
(s), 1332 (s), 1244 (w), 1170 (m), 1087 (w), 881 (m), 702 (m),
691 (s). Complex 7 was obtained as a yellow powder from the
concentrated hexane solution in 22% yield (0.54 g). Mp: 257-
259 °C. Anal. Calcd for C51H78N6O3PYb: C, 59.63; H, 7.65; N,
8.18; Yb, 16.85%. Found: C, 59.32; H, 7.36; N, 7.87; Yb, 16.63%.
IR (KBr, cm-1): 2958 (s), 2904 (s), 2866 (s), 1739 (w), 1602 (s),
1525 (m), 1472 (s), 1410 (m), 1389 (m), 1362 (m), 1303 (s), 1238
(m), 1029 (m), 879 (m), 748 (s). Crystals suitable for an X-ray
crystal structure study were obtained by cooling the hot toluene
(for complex 8) or the hot hexane solution (for complex 7) in about
2 weeks.
X-ray Crystallography. Suitable single crystals of complexes
1-4, 7, and 8 were sealed in a thin-walled glass capillary for
determining the single-crystal structure. Intensity data were collected
with a Rigaku Mercury CCD area detector in ω scan mode using
Mo KR radiation (λ ) 0.710 70 Å). The diffracted intensities were
corrected for Lorentz polarization effects and empirical absorption
corrections. Details of the intensity data collection and crystal data
are given in Table 1.
compound is fully characterized by elemental analysis, H
NMR, IR, and HRMS.
Reaction of [ONNO]H2 with NaH in THF, after workup,
afforded sodium bis(phenolate) {[ONNO]Na2(THF)2}2 (1)
in an almost quantitative yield. Complex 1 is well character-
ized by elemental analysis, IR, and 1H NMR, and the
definitive molecular structure was confirmed by X-ray
diffraction to be a dimeric complex. Complex 1 was slightly
soluble in THF and toluene and soluble in hot THF.
Lithium and sodium aryloxides are common starting
materials for the synthesis of transition metal and lanthanide
aryloxides via a transmetalation reaction.11 In general, these
alkali metal aryloxides have polymeric or polynuclear
structure, and the steric bulk and electron-donation ability
of the ortho-substituent groups have profound effect on their
solid-state structures.12 The molecular structures of alkali
metal complexes bearing monoaryloxides have been widely
reported,13 but that of bridged bis(phenolate), especially for
sodium, is rather scant.14 Crystals of complex 1 suitable for
X-ray structure determination were obtained from a concen-
trated THF solution. The selected bond lengths and angles
are listed in Table 2. An ORTEP of complex 1 is depicted
in Figure 1. Complex 1 has a dimeric tetranuclear structure:
two inner sodium atoms are coordinated by two nitrogen
atoms from the imidazolidine rings and two oxygen atoms
from the aryloxo groups, respectively, whereas two outer
sodium atoms are coordinated by two oxygen atoms from
the aryloxo groups and two oxygen atoms from two THF
molecules. The coordination environment of each of the outer
sodium atoms is similar to those in [(THF)nLn(MBMP)2Na-
(THF)2] (Ln ) Nd, Yb; MBMP ) 2,2′-methylene-bis(6-tert-
butyl-4-methyl-phenoxo)).2c The coordination number of the
sodium atoms is 4, and the coordination geometry of each
sodium atom can be best described as a distorted tetrahedron.
This coordination geometry is similar to that in [(4-F-C6H4-
ONa)6(THF)8]13a but different from that in [NaOC6H2-(CH2-
The structures were solved by direct methods and refined by
2
full-matrix least-squares procedures based on |F| . All the non-
hydrogen atoms were refined anisotropically. All the H atoms were
held stationary and included in the structure factor calculation in
the final stage of full-matrix least-squares refinement. The structures
were solved and refined using SHELEXL-97 programs.
Results and Discussion
Synthesis and Characterization of the Ligand and Its
Sodium Salt. Mannich reaction is a convenient method to
synthesize amine bridged bis(phenol). However, the product
of the reaction of phenol, aldehyde, and diamine will be
affected by the reagent and the reaction temperature.8 Kol
and co-workers once reported the synthesis of ethylenedi-
amine bridged bis(phenol) by refluxing corresponding re-
agents in methanol,9 but our attempts to repeat this reaction
failed. A bridged benzoxazine can be obtained in very high
yield when the reaction proceeded at about 85 °C (oil bath).10
Further study revealed that the reaction temperature is a key
for the reaction pathway. A new imidazolidine bridged bis-
(phenol) [ONNO]H2 ([ONNO]H2 ) 1,4-bis(2-hydroxy-3,5-
di-tert-butyl-benzyl)imidazolidine) can be isolated as the
major product in about 65% yield when the reaction
proceeded at about 66 °C (oil bath) (Scheme 1). This
(12) (a) van der Schaaf, P. A.; Jastrzebski, J. T. B. H.; Hogerheide, M. P.;
Smeets, W. J. J.; Spek, A. L.; van Koten, G. Inorg. Chem. 1993, 32,
4111. (b) Hogerheide, M. P.; Ringelberg, S. N.; Janssen, M. D.;
Boersma, J.; Spek, A. L.; van Koten, G. Inorg. Chem. 1996, 35, 1195.
(13) (a) Evans, W. J.; Golden, R. E.; Ziller, J. W. Inorg. Chem. 1993, 32,
3041. (b) Kunert, M.; Dinjus, E.; Nauck, M.; Sieler, J. Chem. Ber.
1997, 130, 1461. (c) MacDougall, D. J.; Morris, J. J.; Noll, B. C.;
Henderson, K. W. Chem. Commun. 2004, 456. (d) MacDougall, D.
J.; Noll, B. C.; Henderson, K. W. Inorg. Chem. 2005, 44, 1181.
(14) (a) Ko, B. T.; Lin, C. C. J. Am. Chem. Soc. 2001, 123, 7973. (b)
Huang, B.-H.; Ko, B. T.; Athar, T.; Lin, C. C. Inorg. Chem. 2006,
45, 7348.
3746 Inorganic Chemistry, Vol. 46, No. 9, 2007

Sodium and Ytterbium Complexes
Table 2. Selected Bond Lengths (Å) and Bond Angles (deg) in
Complex 1
Na(1)-O(2A)
Na(1)-O(1)
2.226(2)
2.247(3)
2.481(3)
2.496(3)
3.069(3)
3.077(3)
Na(2)-O(1)
Na(2)-O(2A)
Na(2)-O(3)
Na(2)-O(4)
Na(1)-Na(2)
Na(1)-Na(1A)
2.183(2)
2.213(3)
2.282(3)
2.304(4)
3.114(2)
4.035(2)
Na(1)-N(1)
Na(1)-N(2A)
Na(1)-C(17A)
Na(1)-C(16)
O(2A)-Na(1)-O(1)
O(1)-Na(1)-N(1)
89.55(9) Na(2)-O(1)-Na(1)
89.34(9)
87.60(9) Na(2A)-O(2)-Na(1A) 89.11(9)
O(2A)-Na(1)-N(2A) 86.49(8) O(1)-Na(2)-O(3)
105.50(11)
105.44(12)
99.08(16)
N(1)-Na(1)-N(2A)
O(1)-Na(2)-O(2A)
138.63(9) O(2A)-Na(2)-O(4)
91.54(9) O(3)-Na(2)-O(4)
NMe2)2-2,6-Me-4]4,12b in which the sodium atoms are
surrounded by three bridging aryloxide oxygen atoms and
two nitrogen atoms from two amino groups.
The Na-O(Ar) bond lengths range from 2.183(2) to 2.247-
(3) Å, giving an average of 2.217(3) Å, which is close to
those Na-O(Ar) bond lengths reported for other sodium
aryloxides.12,13 The Na-N bond lengths of 2.481(3) and
2.496(3) Å are comparable with those in [NaOC6H4-(CH2-
NMe2)-2]6.12a There are remote π interactions between the
sodium atom and the carbon atoms connecting the aryl rings
and the imidazolidine rings. The bond lengths of Na(1)-
C(16) and Na(1)-C(17A) are 3.077(3) and 3.069(3) Å,
respectively, which are comparable with that reported in
(THF)La(OC6H3-iPr2-2,6)2(µ-OC6H3-iPr2-2,6)2Na(THF)2
(3.085(9) Å)15 but slightly longer than those observed in
(TMEDA)NaC(SiMe3)2(SiMe2Ph) (3.026(5) Å).16
Synthesis and Reactivity of Ytterbium Complexes.
Generally, the lanthanide halides bearing suitable ancillary
ligands are considered to be useful precursors for the
synthesis of miscellaneous lanthanide derivatives. Therefore,
the ytterbium chloride supported by the new imidazolidine-
bridged bis(phenolate) ligands was prepared by the normal
salt metathesis reaction. Taking into account the bulkiness
and the rigidity of the [ONNO] ligand, we intend to
synthesize a dinuclear ytterbium dichloride stabilized by this
ligand system. Anhydrous YbCl3 reacted with complex 1 in
THF in a 4:1 molar ratio at 50 °C for 8 h to give a red
precipitate. The red precipitate has sparing solubility even
in THF, and the attempts to obtain its crystals suitable for
structure determination failed. Because no NaCl precipitated
from this reaction system, it is reasonable to postulate that
the NaCl is still connected with the ytterbium center. In order
to dissociate the NaCl from the precipitate, some chelating
solvents such as DME and TMEDA were used, but these
attempts were unsuccessful. It was found that the addition
of HMPA can solve this problem. After addition of HMPA
to the THF suspension of the precipitate, the red precipitate
disappeared gradually, and the color of the solution turned
yellow. Meanwhile, NaCl precipitated from the reaction
system. After workup, complex 2 was isolated from the
concentrated toluene solution as yellow crystals in a good
yield. Elemental analysis results of complex 2 agree with
Figure 1. ORTEP diagram of complex 1 showing the atom-numbering
scheme. Thermal ellipsoids are drawn at the 20% probability level. Hydrogen
atoms are omitted for clarity.
that of a dinuclear structure with only one-half of the
[ONNO] ligand per ytterbium with a formula corresponding
to [ONNO]{YbCl2(HMPA)}2, which was confirmed by
X-ray structure determination as shown in Scheme 2.
Complex 2 has good solubility in THF and toluene and is
sensitive to air and moisture.
Few examples are available of bridged bis(phenolate)
lanthanide systems where salt metathesis routes are successful
in the synthesis of lanthanide derivatives from halides.
Mountford and co-workers previously reported that the
yttrium and scandium chlorides supported by the tetradentate
t
t
diamino-bis(phenolate) ligands O2 BuNN′ [O2 BuNN′ ) (2-
t
C5H4N)CH2N{CH2-(2-OC6H2 Bu2-3,5)2}] were inactive for
many halide substitution reactions.1f We had found that the
ytterbium chloride bearing amine bis(phenolate) ligands is
a useful precursor for the synthesis of ytterbium alkyls and
amides by general metathesis reactions.1g In order to elucidate
the reactivity of the Yb-Cl bonds in complex 2, the chloride
substituted reactions were employed. Complex 2 reacted with
sodium isopropoxide in a 2:1 molar ratio in THF, after
workup, to give complex 3 as colorless crystals. Elemental
analysis results are consistent with that of a dinuclear
structure. The definitive molecular structure was determined
to be [ONNO]{Yb(µ-OiPr)Cl(HMPA)}2 by X-ray diffraction
as shown in Scheme 2. Attempts to substitute the residual
chlorine atoms by other organic groups were unsuccessful.
A total of 2 equiv of NaOiPr was added to the THF solution
of complex 3, and no reaction was detected. Furthermore,
complex 2 reacted even with 4 equiv of NaOiPr in THF,
and in a few days, after workup, the isolated product was
identified still to be complex 3. These results indicated that
the terminal Yb-Cl bonds in complex 3 were almost inert
for substituted reactions. This might be attributed to the
ytterbium atoms in complex 3 being blocked by the bulky
bis(phenolate) ligands and HMPA molecules, which hindered
the interaction of NaOiPr with the metal atoms.
(15) Clark, D. L.; Hollis, R. V.; Scott, B. L.; Watkin, J. G. Inorg. Chem.
1996, 35, 667.
(16) Eaborn, C.; Clegg, W.; Hitchcock, P. B.; Hopman, M.; Izod, K.;
O’Shaughnessy, P. N.; Smith, J. D. Organometallics 1997, 16, 4728.
Since the terminal chlorine atoms are inert for the
substituted reaction, we wonder whether the terminal chlorine
Inorganic Chemistry, Vol. 46, No. 9, 2007 3747

Xu et al.
Scheme 2
atoms in complex 2 can be substituted first and the bridged
ones be retained. Maybe the bridged chlorine atoms are more
active and the further chloride substituted reaction can
proceed smoothly. Thus, a bulky aryloxo group, 2,6-di-tert-
butyl-4-methylphenoxo (ArO), was chosen because this
ligand was usually coordinated to the lanthanide atom as a
terminal group.17 However, it was found that an unexpected
ligand redistribution reaction occurred, and the dinuclear
backbone was broken. Complex 2 reacted with ArONa in a
1:2 molar ratio in THF, after workup, to give two mono-
nuclear complexes (ArO)2YbCl(HMPA)2 (4) and [ONNO]-
YbCl(HMPA)2 (5) in moderate isolated yields as shown in
Scheme 2, which were separated according to the difference
in solubility. Complex 4 was well characterized by elemental
analysis and IR, and its definitive structure was determined
by X-ray diffraction. The composition of complex 5 was
confirmed by elemental analysis. Due to its paramagnetism,
no resolvable NMR spectrum was obtained. Attempts to
obtain the definitive structure failed, due to solvent loss and
the deterioration in crystal quality. The occurrence of the
ligand redistribution reaction might be attributed to the
bulkiness of the aryloxo group. The coordination of the bulky
aryloxo group to the ytterbium atom brings about the steric
overcongestion around the metal atom, which induces the
redistribution reaction in this system.
In order to further elucidate the effect of the bulkiness of
the reagent on the outcome of the reaction, the reaction of
complex 2 with another bulky reagent, sodium diphenyl
amide, was explored. Complex 2 reacted with sodium
diphenyl amide in a 1:2 molar ratio in THF, after workup,
and the expected two ligand redistributed products 5 and 6
were isolated as microcrystals as shown in Scheme 2. The
elemental analysis results of complexes 5 and 6 were
consistent with the formulas of “[ONNO]YbCl(HMPA)2”
and “(Ph2N)2YbCl(HMPA)2”. Attempts to obtain high-
quality crystals to determine their definitive structures
were unsuccessful. Due to the presence of Yb-Cl bonds in
complexes 5 and 6, the complexes (ONNO)Yb(NPh2)-
(HMPA) (7) and Yb(NPh2)3(HMPA)2 (8) should be iso-
lated as the final products by the reaction of complex 2 with
4 equiv of NaNPh2, if these Yb-Cl bonds are active for
substitution reaction. Indeed, the expected complexes 7
and 8, after workup, were obtained in good isolated
yields from the reaction mentioned above as shown in
Scheme 2. Complexes 7 and 8 were well characterized
by elemental analyses and X-ray diffraction structure
determination.
(17) (a) Mehrotra, R. C.; Singh, A.; Tripathi, U. M. Chem. ReV. 1991, 91,
1287. (b) Qi, Q. Z.; Lin, Y. H.; Hu, J. Y.; Shen, Q. Polyhedron 1995,
14, 413. (c) Hou, Z. M.; Fujita, A.; Yoshimura, T.; Jesorka, A.; Zhang,
Y. G.; Yamazaki, H.; Wakatsuki, Y. Inorg. Chem. 1996, 35, 7190.
(d) Zhang, L. L.; Yao, Y. M.; Luo, Y. J.; Shen, Q.; Sun, J. Polyhedron
2000, 19, 2243.
3748 Inorganic Chemistry, Vol. 46, No. 9, 2007

Sodium and Ytterbium Complexes
Figure 4. ORTEP diagram of complex 4 showing the atom-numbering
scheme. Thermal ellipsoids are drawn at the 20% probability level. Hydrogen
atoms are omitted for clarity.
Figure 2. ORTEP diagram of complex 2 showing the atom-numbering
scheme. Thermal ellipsoids are drawn at the 20% probability level. Hydrogen
atoms are omitted for clarity.
Figure 5. ORTEP diagram of complex 7 showing the atom-numbering
scheme. Thermal ellipsoids are drawn at the 20% probability level. Hydrogen
atoms are omitted for clarity.
similar to that of complex 2, except that two isopropoxy
groups are the bridges instead of the two bridging chlorine
atoms and are coordinated to the two ytterbium atoms.
In complex 2, the Yb-O(Ar) bond lengths are 2.046(6)
and 2.078(7) Å, giving an average of 2.062(6) Å, which is
slightly shorter than that in (ArO)YbCl2(THF)3.20 The
averaged bridged Yb-Cl bond length of 2.688(3) Å is
comparable with that observed in [{CH(PPh2NSiMe3)2}-
LnCl2]2 (2.660(3) Å)19 and {[(DIPPh)2nacnac]YbCl(µ-Cl)3Yb-
[(DIPPh)2nacnac](THF)} (2.708(2) Å) ((DIPPh)2nacnac )
N,N-diisopropylphenyl-2,4-pentanediimine anion)21 but is
apparently longer than those in [(C5Me5)Yb(Ph2nacnac)(µ-
Cl)]2 (Ph2nacnac ) N,N-diphenyl-2,4-pentanediimine anion)
(2.571(3) Å).22 The averaged terminal Yb-Cl bond length
of 2.530(3) Å is comparable with those observed in (Me2-
Figure 3. ORTEP diagram of complex 3 showing the atom-numbering
scheme. Thermal ellipsoids are drawn at the 20% probability level. Hydrogen
atoms are omitted for clarity.
Crystal Structures of Ytterbium Complexes. The mo-
lecular structures of complexes 2-4, 7, and 8 are shown in
Figures 2-6, and selected bond lengths are given in Tables
3 and 4. Complex 2 has a dinuclear structure in which two
YbCl fragments are linked by two chlorine atoms and one
bridging [ONNO] ligand. Each ytterbium atom is six-
coordinated by one oxygen atom and one nitrogen atom from
the [ONNO] ligand, three chlorine atoms, and one oxygen
atom from the HMPA molecule to form a distorted-
octahedral geometry. Rare examples reported so far have the
dinuclear structure linked by one multidentate ligand.18 The
coordination mode of chlorine atoms to ytterbium atom in
complex 2 is the same as that in [{CH(PPh2NSiMe3)2}-
LnCl2]2.19 The overall molecular structure of complex 3 is
t
NCH2CH2N{CH2-(2-O-C6H2-Bu2-3,5)}2)YbCl(THF)(2.5363(10)
Å)1e and (ArO)YbCl2(THF)3 (2.555(2) Å)20 but is slightly
longer than that in (ArO)2YbCl(THF)2 (2.477(9) Å).23 In
(20) Yao, Y. M.; Shen, Q.; Sun, J. Polyhedron 1998, 17, 519.
(21) Yao, Y. M.; Zhang, Y.; Shen, Q.; Yu, K. B. Organometallics 2002,
21, 819.
(22) Yao, Y. M.; Xue, M. Q.; Luo, Y. J.; Zhang, Z. Q.; Jiao, R.; Zhang,
Y.; Shen, Q.; Wong, W. T.; Yu, K. B.; Sun, J. J. Organomet. Chem.
2003, 678, 108.
(23) Yao, Y. M.; Shen, Q.; Zhang, Y.; Xue, M. Q.; Sun, J. Polyhedron
2001, 20, 3201.
(18) Okuda, J.; Fokken, S.; Kleinhenn, T.; Spaniol, T. P. Eur. J. Inorg.
Chem. 2000, 1321.
(19) Gamer, M. T.; Dehnen, S.; Roesky, P. W. Organometallics 2001, 20,
4230.
Inorganic Chemistry, Vol. 46, No. 9, 2007 3749

Xu et al.
Table 4. Selected Bond Lengths (Å) in Complexes 4, 7, and 8
4
7a
7b
8
Yb(1)-O(1)
Yb(1)-O(2)
Yb(1)-O(3)
Yb(1)-O(4)
Yb(1)-Cl(1)
Yb(1)-N(1)
Yb(1)-N(2)
Yb(1)-N(3)
Yb(1)-N(6)
Yb(1)-C(14)
Yb(1)-C(40)
2.110(3)
2.110(3)
2.214(3)
2.217(3)
2.541(10)
2.153(4)
2.102(4)
2.220(4)
2.144(4)
2.094(4)
2.219(4)
2.198(19)
2.212(2)
2.504(4)
2.497(5)
2.497(5)
2.570(5)
2.305(2)
2.268(2)
2.288(2)
2.298(5)
2.825(6)
3.138(5)
2.310(5)
3.201(6)
2.871(6)
geometry. Complex 7 crystallizes with two crystallographi-
cally independent but chemically similar molecules (7a, 7b)
in the unit cell. Like those found in other amine or
N-heterocycle bridged bis(phenolate) metal complexes,26 two
nitrogen atoms from the imidazolidine ring were found to
bind to the metal center in the solid state. In addition, one
carbon atom (C(14)) of the imidazolidine ring is also
coordinated to the ytterbium atom. Thus, the imidazolidine
ring is η3-coordinated to the ytterbium atom, and the
ytterbium atom is seven-coordinated by two oxygen atoms,
two nitrogen atoms and one carbon atom from the bis-
(phenolate) ligands, one nitrogen atom from the amido group,
and one oxygen atom from the HMPA molecule. The
coordination geometry at the central metal can be best
described as a distorted trigonal bipyramid if the η3-
coordinated imidazolidine ring is considered to occupy one
coordination site, in which O(1), O(2), and N(6) are
considered to occupy the equatorial plane.
Figure 6. ORTEP diagram of complex 8 showing the atom-numbering
scheme. Thermal ellipsoids are drawn at the 20% probability level. Hydrogen
atoms are omitted for clarity.
Table 3. Selected Bond Lengths (Å) in Complexes 2 and 3
2
3
2
3
Yb(1)-O(1) 2.046(6) 2.117(5) Yb(2)-O(2) 2.078(7) 2.121(5)
Yb(1)-O(3) 2.159(6) 2.201(5) Yb(2)-O(4) 2.138(7) 2.272(5)
Yb(1)-O(5)
2.240(5) Yb(2)-O(6)
2.275(5) Yb(2)-O(3)
2.235(5)
2.203(5)
Yb(1)-O(4)
Yb(1)-Cl(3) 2.531(3)
Yb(1)-N(1) 2.548(8) 2.532(6) Yb(2)-N(2) 2.543(8) 2.528(6)
Yb(1)-Cl(1) 2.665(2) 2.560(2) Yb(2)-Cl(2) 2.684(3) 2.561(2)
Yb(1)-Cl(2) 2.701(3)
Yb(2)-C(17) 3.207(9)
Yb(2)-C(34)
Yb(2)-Cl(4) 2.528(3)
Yb(2)-Cl(1) 2.700(2)
Yb(2)-C(7) 3.179(10)
3.137(13) Yb(2)-C(37)
3.149(15)
addition, remote π interactions of C(17) and C(7) with Yb-
(2) were observed in complex 2. The bond lengths of Yb-
(2)-C(17) and Yb(2)-C(7) are 3.207(9) and 3.179(10) Å,
respectively, which are comparable to those of 2.986(6) and
3.180(9) Å for bridging η2-C5H5 bonding in (C5Me5)2Sm-
(µ-C5H5)Sm(C5Me5)2,24 and 2.814(4)-3.148(6) Å for chelat-
ing η6-,η1-Ph-Yb bonding in [Yb(Odpp)3]2 (Odpp ) 2,6-
diphenylphenolate).25
In complex 4, The Yb-O(Ar) bond length of 2.110(3) Å
compares well with the corresponding value in (ArO)2YbCl-
(THF)2 (2.080(1) Å),23 but the Yb-O(HMPA) bond lengths
are relatively larger than the Yb-O(THF) bond lengths,
while the Yb-Cl bond length in complex 4 is relatively
smaller.
In complex 7, the averaged Yb-O(Ar) and Yb-N(ring)
bond lengths of 2.127(4) and 2.500(5) Å, respectively, are
comparable with the corresponding values observed in
complexes 2 and 3 and other amine bridged bis(phenolate)
lanthanide complexes.1 The Ln-N(Ph) bond length of 2.298-
(5) Å lies within the range of the corresponding bond lengths
that have been reported for (CH3C5H4)2YbNPh2(THF), (C5-
Me5)2YbNPh2,27 [(DIPPh)2nacnac]Yb(NPh2)Cl(THF),28 and
[Me2NCH2CH2N{CH2-(2-O-C6H2-tBu2-3,5)}2]Yb(NPh2)-
(THF)1e when the effect of coordination number on the
effective ionic radius is considered. It is worth noting that
there is a strong π interaction of one carbon atom of the
imidazolidine ring with the ytterbium atom. The Yb-C(14)
bond length of 2.825(6) Å is apparently lower than the Ln-C
In complex 3, two isopropoxy groups are unsymmetrically
coordinated to two ytterbium atoms with the deviation of
0.07 Å. The averaged Yb-O(iPr) bond length is 2.238(6)
Å, which is consistent with that in [(MBMP)Yb(µ-OiPr)-
(THF)2].2b The averaged Yb-N bond length compares well
with the terminal ones in complex 2. The averaged Yb-
O(Ar) and Yb-O(HMPA) bond lengths of 2.119(5) and
2.237(5) Å, respectively, are larger than the corresponding
values in complex 2 (2.062(6) and 2.148(7) Å); meanwhile,
the averaged Yb-Cl bond length of 2.560(2) Å is apparently
smaller than that in complex 2 (2.674(3) Å). These bond
parameters indicated that the chlorine atoms in complex 3
might be shielded by bulky aryloxides and HMPA molecules,
which caused the inert to substituted reaction.
Complexes 4, 7, and 8 have monomeric structure. The
coordination geometries around the ytterbium atoms in
complexes 4 and 8 are similar, and each ytterbium atom is
five-coordinate to form a distorted trigonal bipyramid
(26) (a) Halfen, J. A.; Jazdzewski, B. A.; Mahapatra, S.; Berreau, L. M.;
Wilkinson, E. C.; Que, L.; Tolman, W. B. J. Am. Chem. Soc. 1997,
119, 8217. (b) Baldamus, J.; Hecht, E. Z. Anorg. Allg. Chem. 2003,
629, 188. (c) Mukhopadhyay, S.; Mandal, D.; Chatterjee, P. B.;
Desplanches, C.; Sutter, J. P.; Butcher, R. J.; Chaudhury, M. Inorg.
Chem. 2004, 43, 8501.
(27) Wang, Y. R.; Shen, Q.; Xue, F.; Yu, K. B. J. Organomet. Chem. 2000,
598, 359.
(28) Yao, Y. M.; Zhang, Z. Q.; Peng, H. M.; Zhang, Y.; Shen, Q.; Lin, J.
Inorg. Chem. 2006, 45, 2175.
(24) Evans, W. J.; Ulibarri, T. A. J. Am. Chem. Soc. 1987, 109, 4292.
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J. Chem. 1990, 43, 1245.
3750 Inorganic Chemistry, Vol. 46, No. 9, 2007

Sodium and Ytterbium Complexes
contacts observed in complex 2 and the other known
examples of Ln-C agostic interactions mentioned above.
The Yb-C(14) bond length compares well with that
observed in the neutral arene ytterbium complex Yb(η6-
HMB)(AlCl4)3 (HMB ) hexamethylbenzene) (2.865(39) Å),
in which the Yb-C π interaction was considered to exist
unambiguously.29 Additionally, there is a remote π interaction
between the R carbon atom of the diphenylamido group with
the central metal atom. The Yb-C(40) bond length of 3.138-
(5) Å is in accordance with the values in [Yb(Odpp)3]2 (from
2.814(4) to 3.148(6) Å). Variations in the Ln-N(Ph)-C
angles are associated with the existence of π interactions in
this complex. The angle that is associated with the nearby
carbon atom (Yb(1)-N(6)-C(40)) is 113.8(4)°, and the other
angle (Yb(1)-N(6)-C(46)) is 127.3(4)°.
In complex 8, the Yb-N bond lengths range from 2.268-
(2) to 2.305(2) Å, giving an average of 2.287(2) Å, which
is apparently larger than that in Yb(NPh2)3(THF)2 (2.219(6)
Å)30 and accords well with the Yb-N bond lengths in
complexes [Yb(NPh2)4][Li(THF)4] (2.212(9) Å)31 and Yb-
[N(SiMe3)2]3 (2.158(13) Å)32 when the effect of coordination
number on the effective ionic radius is considered.33 It is
reasonable to ascribe the difference in bond parameters to
the increased steric congestion in complexes 8 and Yb-
(NPh2)3(THF)2 that results from the replacement of the THF
molecules by two bulky HMPA molecules.
Conclusion
A new imidazolidine-bridged bis(phenol) was prepared by
a simple Mannich reaction. This compound can be used as
an ancillary ligand for a series of sodium and ytterbium
complexes. The bis(phenol) reacted with NaH to give sodium
bis(phenolate) as a dimeric tetranuclear complex, which
reacted with anhydrous YbCl3 to produce a novel bimetallic
ytterbium dichloride. It was found that this ytterbium
dichloride can be used as a useful precursor to prepare a
series of ytterbium derivatives by direct salt metathesis
reactions, and the bulkiness of the reagents has profound
effect on the outcome of these reactions. For the less bulky
reagent, such as sodium isopropoxide, the bimetallic back-
bone remained, whereas for the more bulky reagents, such
as sodium aryloxide and sodium diphenyl amide, the ligand
redistribution reaction occurred, and the mononuclear com-
plexes were isolated. Further studies on the synthesis and
reactivity of lanthanide derivatives supported by the het-
eroatom-bridged bis(phenolate) ligands are in progress in our
laboratory.
Acknowledgment. Financial support from the National
Natural Science Foundation of China (Grants 20472063 and
20632040), State Key Laboratory of Polymer Physics and
Chemistry, Innovation Project of Graduate Education of
Jiangsu Province, and the Key Laboratory of Organic
Synthesis of Jiangsu Province is gratefully acknowledged.
(29) Liang, H. Z.; Shen, Q.; Lin, Y. H. J. Organomet. Chem. 1994, 474,
113.
(30) Yao, Y. M.; Mao, L. S.; Lu, X. H.; Shen, Q.; Sun, J. J. Rare Earths
2002, 20, 592.
(31) Wang, W. K.; Zhang, L. L.; Xue, F.; Mak, T. C. W. Polyhedron 1997,
16, 345.
(32) Eller, P. G.; Bradley, D. C.; Hursthouse, M. B.; Meek, D. W. Coord.
Chem. ReV. 1977, 24, 1.
(33) Shannon, R. D. Acta Crystallogr., Sect. A 1976, 32, 751.
Supporting Information Available: Crystallographic data for
complexes 1-4, 7, and 8 in CIF format. This material is available
free of charge via the Internet at http://pubs.acs.org.
IC0701054
Inorganic Chemistry, Vol. 46, No. 9, 2007 3751