Monomeric and linear polymeric samarium(II) complexes of the 2-(N-Arylimino)pyrrolide ligand

Article abstract of DOI:10.1021/om9001236

The synthesis and structural characterization of monomeric and linear polymeric divalent samarium complexes as well as their related trivalent species supported by an (imino)pyrrolide ligand are described. The divalent samarium 2-(N-arylamino)pyrrolide co

Full text of DOI:10.1021/om9001236

3100
Organometallics 2009, 28, 3100–3104
Monomeric and Linear Polymeric Samarium(II) Complexes of the
2-(N-Arylimino)pyrrolide Ligand
Jingjun Hao, Haibin Song, and Chunming Cui*
State Key Laboratory of Elemento-organic Chemistry, Nankai UniVersity, Tianjin, 300071,
People’s Republic of China
ReceiVed February 17, 2009
The synthesis and structural characterization of monomeric and linear polymeric divalent samarium
complexes as well as their related trivalent species supported by an (imino)pyrrolide ligand are described.
The divalent samarium 2-(N-arylamino)pyrrolide complex [NN]2Sm(THF)2 (1) was prepared by the reaction
of SmI2(THF)2 with 2 equiv of [NN]K ([NN] ) [2-(2,6-iPr2C6H3NdCH)-5-tBuC4H2N]-) in THF. Upon
treatment of 1 with dry oxygen, the oxo-bridged dimer [NN]2Sm(µ-O)Sm[NN]2 (2) was generated. Reaction
of [NN]2SmCH2SiMe3 (3) with 3 equiv of AlEt3 in n-hexane gave the samarium aluminate [NN]2Sm(µ-
Et)2AlEt2 (4). Reduction of 4 with potassium in toluene yielded the linear polymeric species
{[NN]2SmAlEt4K(C7H8)}n (5). Compounds 1, 2, 4, and 5 have been characterized by X-ray single-crystal
analysis. 5 features a linear polymeric structure, in which the potassium ion links the neighboring
monomeric samarium moieties via η2 and η5 coordination to the pyrrolide rings in the two different
units, with one toluene molecule and one of the ethyl groups of the [AlEt4] anion being also η2 coordinated
to the potassium to complete its coordination sphere.
metal catalysis.5 So far, the most extensive studied pyrrolide
ligands include methylene (dimethyl and diphenylmethylene)
Introduction
Since (C5Me5)2Sm(THF)2 was reported in 1981, the organo-
metallic chemistry of Sm(II) has seen remarkable growth and
development.1 Recent developments in organolanthanide chem-
istry have focused on the use of non-cyclopentadienyl ancillary
ligands,2 with much of the interest in the synthesis and
characterization of lanthanide complexes with unusual reactivity
and bonding using nitrogen-based ligand systems.3 In this
context, we are interested in exploring bulky 2-(N-arylimino)py-
rrolide ligands in divalent samarium chemistry. It has been
reported by Gambarotta and co-workers that multiple dentate
pyrrolide ligands display either a η1 or η5 bonding mode and
could support interesting polynuclear Sm(II) species capable
of activation of small molecules.4 Recent studies on pyrrolide
transition metal complexes have shown that this family of
ligands are promising versatile supporting ligands in transition
bridged polypyrrolide and 2-(imino)pyrrolide imine systems. The
later has been used to prepare a variety of metal complexes
including trivalent lanthanide complexes.6 However, very little
has been carried out to prepare Sm(II) complexes with the
(imino)pyrrolide system since the imine moiety could be reduced
by Sm(II) in most cases.7 We reasoned that it is possible to
suppress the reduction of the imino group by Sm(II) atoms by
employing bulky substituents on the nitrogen atom of the imino
group and introducing a bulky group on the 5-position of the
(4) (a) Jubb, J.; Gambarotta, S. J. Am. Chem. Soc. 1994, 116, 4417. (b)
Song, J.; Gambarotta, S. Angew. Chem., Int. Ed. 1995, 34, 2141. (c) Dube′,
T.; Conoci, S.; Gambarotta, S.; Yap, G. P. A.; Vasapollo, G. Angew. Chem.,
Int. Ed. 1999, 38, 3657. (d) Dube´, T.; Ganesan, M.; Conoci, S.; Gambarotta,
S.; Yap, G. P. A. Organometallics 2000, 19, 3716. (e) Guan, J.; Dube´, T.;
Gambarotta, S.; Yap, G. P. A. Organometallics 2000, 19, 4820. (f) Ganesan,
M.; Gambarotta, S.; Yap, G. P. A. Angew. Chem., Int. Ed. 2001, 40, 766.
(g) Ganesan, M.; Lalonde, M. P.; Gambarotta, S.; Yap, G. P. A.
Organometallics 2001, 20, 2443. (h) Christian, D.; Yazdanbakhsh, M.;
Gambarotta, S.; Yap, G. P. A. Organometallic 2003, 22, 3742. (i) Evans,
W. J.; Lee, D.; Rego, D. B.; Perotti, J. M.; Kozimor, S. A.; Moore, E. K.;
Ziller, J. W. J. Am. Chem. Soc. 2004, 126, 14574. (j) Guillemot, G.;
Castellano, B.; Prange´, T.; Solari, E.; Floriani, C. Inorg. Chem. 2007, 46,
5152.
* Corresponding author. E-mail: cmcui@nankai.edu.cn.
(1) (a) Evans, W. J.; Bloom, I.; Hunter, W. E.; Atwood, J. L. J. Am.
Chem. Soc. 1981, 103, 6507. (b) Evans, W. J. J. Organomet. Chem. 2002,
647, 2. (c) Evans, W. J. J. Organomet. Chem. 2002, 652, 61. (d) Evans,
W. J.; Allen, N. T.; Ziller, J. W. Angew. Chem., Int. Ed. 2002, 41, 359. (e)
Meyer, G. Angew. Chem., Int. Ed. 2008, 47, 4962.
(2) (a) Edelmann, F. T.; Freckmann, D. M. M.; Schumann, H. Chem.
ReV. 2002, 102, 1851. (b) Piers, W. E.; Emslie, D. J. H. Coord. Chem.
ReV. 2002, 233, 131. (c) Gibson, V. C.; Spitzmesser, S. K. Chem. ReV.
2003, 103, 283. (d) Mishra, S. Coord. Chem. ReV. 2008, 252, 1996. (e)
Scott, J.; Basuli, F.; Fout, A. R.; Huffman, J. C.; Mindiola, D. J. Angew.
Chem., Int. Ed. 2008, 47, 8502. (f) Masuda, J. D.; Jantunen, K. C.; Ozerov,
O. V.; Noonan, K. J. T.; Gates, D. P.; Scott, B. L.; Kiplinger, J. L. J. Am.
Chem. Soc. 2008, 130, 2408.
(3) (a) Gountchev, T. I.; Tilley, T. D. Organometallics 1999, 18, 5661.
(b) Roesky, P. W. Z. Anorg. Allg. Chem. 2003, 629, 1881. (c) Bambirra,
S.; Bouwkamp, M. W.; Meetsma, A.; Hessen, B. J. Am. Chem. Soc. 2004,
126, 9182. (d) Bambirra, S.; Boot, S. J.; Leusen, D. v.; Meetsma, A.; Hessen,
B. Organometallics 2004, 23, 1891. (e) Gamer, M. T.; Roesky, P. W.;
Palard, I.; Hellaye, M. L.; Guillaume, S. M. Organometallics 2007, 26,
651. (f) Zimmermann, M.; To¨rnroos, K. W.; Anwander, R. Angew. Chem.,
Int. Ed. 2007, 46, 3126. (g) Li, S.; Miao, W.; Tang, T.; Dong, W.; Zhang,
X.; Cui, D. Organometallics 2008, 27, 718. (h) Do¨ring, C.; Kempe, R. Eur.
J. Inorg. Chem. 2009, 412.
(5) For examples, see: (a) Iverson, C. N.; Carter, C. A. G.; Baker, R. T.;
Scollard, J. D.; Labinger, J. A.; Bercaw, J. E. J. Am. Chem. Soc. 2003,
125, 12674. (b) Vanka, K.; Xu, Z.; Ziegler, T. Organometallics 2004, 23,
2900. (c) Yoshida, Y.; Mohri, J.; Ishii, S.; Mitani, M.; Saito, J.; Matsui, S.;
Makio, H.; Nakano, T.; Tanaka, H.; Onda, M.; Yamamoto, Y.; Mizuno,
A.; Fujita, T. J. Am. Chem. Soc. 2004, 126, 12023. (d) Chen, Y.; Lin, C.;
Li, C.; Huang, J.; Chang, L.; Lee, T. Chem.sEur. J. 2008, 14, 9747.
(6) (a) Matsuo, Y.; Mashima, K.; Tani, K. Organometallics 2001, 20,
3510. (b) Yang, Y.; Li, S.; Cui, D.; Chen, X.; Jing, X. Organometallics
2007, 26, 671. (c) Yang, Y.; Liu, B.; Lv, K.; Gao, W.; Cui, D.; Chen, X.;
Jing, X. Organometallics 2007, 26, 4575. (d) Xiang, L.; Wang, Q.; Song,
H.; Zi, G. Organometallics 2007, 26, 5323. (e) Wang, Q.; Xiang, L.; Song,
H.; Zi, G. Inorg. Chem. 2008, 47, 4319. (f) Chen, J.; Lin, C.; Chen, J.; Chi,
Y.; Chiu, Y.; Chou, P.; Lai, C.; Lee, G.; Carty, A. J. Inorg. Chem. 2008,
47, 5154. (g) Zi, G.; Li, X.; Song, H. Organometallics 2008, 27, 1242.
(7) (a) Berube, C. D.; Gambarotta, S.; Yap, G. P. A.; Cozzi, P. G.
Organometallics 2003, 22, 434. (b) Dub, T.; Gambarotta, S.; Yap, G. P. A.
Organometallics 1998, 17, 3967.
10.1021/om9001236 CCC: $40.75
2009 American Chemical Society
Publication on Web 04/30/2009

Polymeric Samarium(II) Complexes
Organometallics, Vol. 28, No. 10, 2009 3101
1272, 1234, 1202, 1180, 1124, 1101, 1047, 999, 933, 858, 821,
801, 778. 749, 730, 704, 654, 592, 569. Anal. Calcd for
C84H116N8OSm2 (1556.77): C, 64.90; H, 7.52; N, 7.21. Found: C,
64.28; H, 7.62; N, 6.88.
pyrrolide ring. Previous studies have shown that the bulky
(imino)pyrrolide ligand [NN] ([NN] ) [2-(2,6-iPr2C6H3NdCH)-
5-tBuC4H2N]-) could support rigid C1 symmetric samarium and
yttrium alkyls, which promote polymerization of methyl meth-
acrylate to generate highly isotactic polymers.8 Herein, we report
on the synthesis and structures of stable monomeric and linear
polymeric samarium(II) complexes with this bulky (imino)py-
rrolide ligand along with the related trivalent species. Interest-
ingly, the polymeric samarium species features an unusual
assembly linked by the potassium atom surrounded by two
different pyrrolide ligands in the neighboring units in η2 and η5
fashions, respectively, and one η2 toluene molecule as well as
an agostic interaction with one ethyl group in the [AlEt4] anion.
Synthesis of [NN]2Sm(AlEt4) (4). To a solution of 3 (4.65 g,
5.0 mmol) in n-hexane (60 mL) was added AlEt3 (1.71 g, 15.0
mmol) in n-hexane (20 mL). The mixture was stirred at room
temperature for 4 h. All volatiles were removed, and the remaining
solid was extracted with toluene (10 mL). After filtration, n-hexane
(15 mL) was carefully added to the filtrate. The solution was stored
at -40 °C for 3 days to give orange crystals of 4 (2.93 g, 64%).
Mp: 168 °C (dec). 1H NMR (C6D6): δ -4.13 (s, 18H, CMe3), -0.56
(d, 6H, J ) 8.0 Hz, CHMe2), 0.80 (d, 6H, J ) 8.0 Hz, CHMe2),
1.36 (d, 6H, J ) 8.0 Hz, CHMe2), 1.43 (d, 6H, J ) 8.0 Hz, CHMe2),
2.14 (m, 2H, CHMe2), 2.51 (m, 18H, CH2CH3), 3.38 (m, 2H,
CHMe2), 5.46 (m, 2H, Ar-H), 5.93-6.06 (m, 4H, Ar-H), 6.53 (d,
2H, J ) 4.8 Hz, pyrrole-H), 8.90 (d, 2H, J ) 4.8 Hz, pyrrole-H),
9.17 (s, 2H, CH ) N), 18.63 (m, br, 2H, CH2CH3). 13C NMR (C6D6,
300 MHz): δ 14.3, 20.8, 21.5, 23.0, 26.5, 26.7, 27.1, 27.6, 29.3,
30.5, 31.9, 109.7, 122.3, 122.6, 124.6, 129.1, 138.3, 139.6, 142.9,
149.8, 165.3, 175.3. IR: 3060, 2960, 2866, 1919, 1861, 1796, 1624,
1588, 1560, 1495, 1460, 1437, 1382, 1364, 1318, 1271, 1253, 1233,
1201, 1179, 1124, 1101, 1046, 1004, 980, 955, 932, 885, 858, 777,
746, 703, 655. Satisfactory elemental analysis were not obtained
for the aluminates 4 and 5 due to the easy loss of the ethyl groups
upon the exposure to air.
Synthesis of [NN]2SmAlEt4K(C7H8) (5). Toluene (50 mL) was
condensed into the mixture of L2SmAlEt4 (0.46 g, 0.5 mmol) and
K (0.23 g, 0.6 mmol) at room temperature. The mixture was stirred
at room temperature for 2 days, and the color turned from orange
to black. It was filtered, and the filtrate was concentrated (ca. 20
mL) and then stored at -40 °C for 2 days to yield dark brown
crystals of 5 (0.44 g, 84%). Mp: 197-199 °C. IR: 3060, 2960,
2865, 1625, 1581, 1560, 1496, 1460, 1438, 1382, 1363, 1319, 1275,
1255, 1234, 1201, 1179, 1123, 1101, 1045, 997, 983, 932, 857,
777, 746, 653. µeff ) 3.77 µB.
Experimental Section
All operations were carried out under an atmosphere of dry argon
or nitrogen by using modified Schlenk line and glovebox techniques.
All solvents were freshly distilled from Na and degassed im-
mediately prior to use. Elemental analyses were carried out on an
Elemental Vario EL analyzer. The 1H and 13C NMR spectroscopic
data were recorded on Bruker AV300 and AV400 spectrometers.
Infrared spectra were recorded on a Bio-Rad FTS 6000 spectro-
photometer. Magnetic susceptibility of the solid sample was
measured using a SQUID MPMS XL-7 magnetometer at 300 K
and was corrected for diamagnetism by the tabulated Pascal’s
constants. Effective magnetic moment was calculated by the
equation µeff ) 2.828(ꢀmT)1/2, where ꢀm is the magnetic susceptibility
per formula unit. [NN]2SmCH2SiMe3(THF) was synthesized ac-
cording to the published procedure.8
Synthesis of [NN]2Sm(THF)2 (1). THF (150 mL) was condensed
to a mixture of [NN]H (3.1 g, 10.0 mmol) and KH (0.40 g, 10.0
mmol) at 0 °C. The mixture was warmed to room temperature and
stirred overnight. It was then transferred into the solution of
SmI2(THF)2 (2.74 g, 5.0 mmol) in THF. After the mixture was
stirred at room temperature for 10 h, the solvents were removed
and the remaining solid was extracted with toluene (100 mL) at 50
°C. It was filtered and the filtrate was concentrated and stored at
-40 °C for 2 days to give black crystals of 1 (6.6 g, 72%). Mp:
190-192 °C. 1H NMR (C6D6, 300 MHz): δ -18.67 (m, 2H), -8.3
(s, 2H), -4.3 (s, 4H), -1.65 (s, 18H, CMe3), 0.29 (s, 2H), 0.96 (s,
2H), 1.21 (s, 2H), 1.35 (m, 4H), 1.90 (s, 8H, THF), 3.68 (br s, 8H,
THF), 4.59 (br s, 6H), 7.02 (m, 6H), 9.64 (br s, 4H), 9.79 (s, 4H),
31.6 (m, 2H). 13C NMR: δ 21.4, 23.9, 26.8, 27.8, 28.3, 30.0, 53.7,
92.7, 116.7, 120.6, 123.4, 125.6, 125.7, 128.5, 129.3, 137.9, 208.4.
IR: 3061, 2961, 2868, 1629, 1588, 1559, 1497, 1460, 1437, 1364,
1254, 1201, 1124, 1101, 1044, 932, 858, 777, 746, 704, 667, 576,
530. µeff ) 2.53 µB. Anal. Calcd for C50H74N4O2Sm (913.51): C,
65.74; H, 8.16; N, 6.13. Found: C, 65.69; H, 7.60; N, 5.67.
Synthesis of [NN]2Sm(µ-O)Sm[NN]2 (2). A solution of
[NN]2Sm(THF)2 (0.92 g, 1.0 mmol) in toluene (30 mL) was stirred
under an atmosphere of purified dioxygen. The color of the solution
turned from black to yellow immediately, then the solution was
concentrated and stored at -40 °C overnight to give yellow crystals
of 2 (0.53 g, 68%). Mp: 262-264 °C. 1H NMR (C6D6, 400 MHz):
δ -5.89 (m, 4H, CHMe2), -3.18 (d, J ) 4.4 Hz, 12H, CHMe2),
-1.81 (s, 36H, CMe3), -0.42 (d, J ) 4.4 Hz, 12H, CHMe2), 3.07
(t, J ) 6.4 Hz, 24H, CHMe2), 4.52 (d, J ) 7.2 Hz, 4H, Ar-H),
5.98 (t, J ) 7.2 Hz, 4H, Ar-H), 6.83 (d, J ) 7.2 Hz, 4H, Ar-H),
7.33 (s, 4H, NdCH), 7.83 (s, 4H, pyrrole-H), 8.94 (s, 4H, pyrrole-
H), 11.91 (m, 4H, CHMe2). 13C NMR (C6D6): δ 21.2, 22.6, 23.82,
24.3, 29.2, 30.1, 33.8, 34.1, 110.7, 121.6, 122.8, 123.8, 128.8, 135.0,
141.3, 141.7, 149.9, 169.0 (NdCH), 171.3 (NdCH). IR: 3060,
2960, 2868, 1623, 1595, 1577, 1491, 1460, 1440, 1386, 1362, 1320,
X-ray Structural Determination. All intensity data were
collected with a Bruker SMART CCD diffractometer using
graphite-monochromated Mo KR radiation (λ ) 0.71073 Å). The
structures were resolved by direct methods and refined by full-
matrix least-squares on F2. Hydrogen atoms were considered in
calculated positions. All non-hydrogen atoms were refined aniso-
tropically. Crystals of 1 suitable for X-ray analysis were grown
from THF at room temperature, and 2, 4, and 5 were obtained from
toluene at room temperature.
Results and Discussion
The samarium(II) complex [NN]2Sm(THF)2 (1, [NN] )
[2-(2,6-iPr2C6H3NCH)-5-tBuC4H2N]-) was prepared by salt
elimination reaction of SmI2(THF)2 with 2 equiv of K[NN] in
THF. 1 is inert to CO and N2 under normal conditions. Attempts
to prepare the THF-free [NN]2Sm by sublimation were unsuc-
cessful. Addition of AlEt3 (2, 3, and 4 equiv) to 1 in toluene
resulted in the formation of the corresponding aluminate
[NN]2Sm(µ-Et)2AlEt2 (4) in low yield. Alternatively, 4 can be
prepared reproducibly in good yield by the reaction of
[NN]2SmCH2SiMe3(THF) (3) with 3 equiv of AlEt3 in n-hexane.
Reduction of 4 with 1.1 equiv of K in toluene furnished the
linear polymeric species {[NN]2SmAlEt4K(C7H8)}n (5) in high
yield. Reduction of 4 with K in cyclohexane presumably also
yielded polymeric Sm(II) species. Unfortunately, direct crystal-
lization of the product from cyclohexane under different
conditions failed. However, crystallization of the solid from
toluene after removal of cyclohexane also yielded 5, indicating
that toluene seems to be essential for the formation of the linear
polymeric chain.
(8) Cui, C.; Shafir, A.; Reeder, C. L.; Arnold, J. Organometallics 2003,
22, 3357.

3102 Organometallics, Vol. 28, No. 10, 2009
Hao et al.
successful isolation of monomeric 1 with the bulky 2-(imino)py-
rrolide ligand [NN] prompts us to study its interaction with
dioxygen, in the hopes of generating novel species. Upon exposure
of a solution of 1 in toluene to one atmosphere of dry dioxygen,
a yellow solution was obtained immediately, indicating the rapid
oxidation process. The oxidation product was isolated as yellow
crystals after crystallization from toluene. Its structure was identified
as the oxo-bridged dimer [NN]2Sm(µ-O)Sm[NN]2 (2) by 1H NMR,
13C NMR, and IR spectroscopy, elemental analysis, and X-ray
single-crystal analysis. The structure of 2 is shown in Figure 2
alone with a list of relevant bond lengths and angles. The molecule
resides on a C2 axis in the space group P-421c, resulting in the
disorder of the oxygen atom by occupying two positions (O1-O1A
) 1.29(3) Å). The short O1-O1A contact, significantly shorter
than a single O-O bond (1.46 Å) and those of lanthanide peroxo
complexes (1.46-1.65 Å),12 excludes the possibility of a peroxo
complex. The Sm1-O1 and Sm1A-O1 bond lengths (2.222(15)
and 2.269(16) Å) are significantly longer than those found in the
linear or almost linear Sm-O-Sm species [(C5Me5)2Sm]2(µ-
O) (2.094(1) Å),13 [(C5Me4iPr)2Sm]2(µ-O) (2.116(3) Å), and
[(C5Me5)2Sm(NC5H5)]2(µ-O) (2.151(2) Å),14 in which the short
Sm-O bond lengths are explained by possible multiple bonding
between the samarium atom and the oxygen atom. The
Sm1-O1-Sm1A angle (138.4(7)°) is significantly deviated
from linearity, like those observed in the reported Sm-O-Sm
species mentioned above. The complete cleavage of the dioxy-
gen double bond by 1 along with the formation of 2 is
unexpected. A few reported complexes containing a Sm-O-Sm
unit were not generated by dioxygen reactions but prepared by
reactions of Sm (II) or Sm(III) species with nitroarenes,
epoxybutane, pyridine N-oxide, and Ph3PO.13-15 The formation
of 2 may involve the peroxo intermediate [NN]2Sm(µ-
O2)Sm[NN]2, which was immediately trapped by the highly
reactive 1. However, we were unable to monitor the rapid
reaction by spectroscopic methods and isolate the intermediate.
Complex 4 was initially obtained by the reaction of 1 with
AlEt3. The reaction proved to be unpractical due to its low yield.
It can be prepared in good yield by reaction of the trivalent
alkyl 3 with AlEt3. Single crystals of 4 amenable for X-ray
diffraction analysis were obtained from toluene. The ORTEP
diagram of 4 is shown in Figure 3, and the crystallographic
data are summarized in Table 1. The C2 symmetric structure of
4 is monomeric with the Et4Al anion coordinated to the
samarium atom via two bridging methylene carbon atoms. This
coordination mode has been previously observed in
(C5Me5)2SmA1Et4.16 The Sm-C(µ-CH2) distances (2.781(5) Å)
in 4 are longer than those observed in (C5Me5)2SmA1Et4
(2.662(4) Å) and L2SmMe(THF) (2.625(2) Å).8 The Al-C(µ-
CH2) distance (2.099(7) Å) is only marginally longer than the
Al-C (CH2) terminal distances (2.063(12) Å), and these Al-C
distances are in the range of those found in (C5Me5)2SmA1Et4
(Al-C(µ-CH2) ) 2.106(5) and Al-C(CH2) ) 2.032(6) Å). The
long Sm-C distances and almost average Al-C distances in 4
indicate the relatively weak bonding of the Et4Al anion to the
Figure 1. Molecular structure of 1. Hydrogen atoms are omitted
for clarity. Selected bond lengths (Å) and angles (deg): Sm1-N1
2.7218(19),Sm1-N22.5224(18),Sm1-O12.6624(15);N2-Sm1-N2A
145.92(8), N2-Sm1-O1 83.45(5), N2A-Sm1-O1 125.01(5),
O1-Sm1-O1A 76.69(7), N2-Sm1-N1 66.51(6).
Compound 1 was isolated as black crystals and represents a rare
example of a stable Sm(II) complex with an imino functionality.
Gambarotta and co-workers have investigated the reactions of
pyrrole-based and salen-type tetradentate Schiff base ligands with
Sm[N(SiMe3)2]2(THF)2 and SmI2(THF)5. Only in one case was a
samarium(II) species isolated as a dimer linked by two Sm-pyrrole
π interactions. The structure of 1 determined by X-ray single-crystal
analysis (Figure 1) showed that 1 is a monomer with the two [NN]
ligands and two THF molecules being coordinated to the samarium
ion. The molecule has a crystallographic C2 axis. The two
(imino)pyrrolide ligands adopt an η2 coordination with acute
N-Sm-N angles (66.51(6)°). The largest angles around the
samarium atom observed in 1 are those of O1-Sm1-N1A and
O1A-Sm1-N1 (158.08(6)°). The Sm-N bond lengths (2.5224(18)
and 2.7218(19) Å) are longer than those found in the tri-
valent samarium compound [NN]2SmCH2SiMe3(THF) (average
Sm-Npyrrolide ) 2.46 and Sm-Nimino ) 2.60 Å),8 in accordance
with relatively large Sm(II) ionic radius. The Sm-O distance
(2.6624(15) Å) is longer than those found in the six-coordi-
nate (C12H8N)2Sm(THF)4 (2.560-2.602 Å)9 and even marginally
longer than those found in the formally eight-coordinated samarium
species (C5Me5)2Sm(THF)2 (2.62 and 2.64 Å)10 probably due to
the bulkiness of the (imino)pyrrolide ligand.
The interaction of divalent lanthanide complexes with dioxygen
has been less investigated in comparison with that of late transition
metal complexes. Takats and co-workers reported the first lan-
thanide superoxo complex (TpMe2)2Sm(η2-O2) (TpMe2 ) HB(3,5-
Me2pz)3) via the reaction of (TpMe2)2Sm with O2.11 Following
this work, several other lanthanide superoxo and peroxo complexes
were obtained by reactions of divalent lanthanide complexes with
O2.12 This work demonstrated that suitable ligand sets are essential
for the stabilization of these activated dioxygen complexes. The
(12) (a) Niemeyer, M. Z. Anorg. Allg. Chem. 2002, 628, 647. (b) Cui,
D.; Tang, T.; Cheng, J.; Hu, N.; Chen, W.; Huang, B. J. Organomet. Chem.
2002, 650, 84. (c) Deng, D.; Zhang, Y.; Dai, C.; Zeng, H.; Ye, C.; Hage,
R. Inorg. Chim. Acta 2000, 310, 51.
(13) Evans, W. J.; Grate, J. W.; Bloom, I.; Hunter, W. E.; Atwood, J. L.
J. Am. Chem. Soc. 1985, 107, 405.
(9) Evans, W. J.; Rabe, G. W.; Ziller, J. W. Organometallics 1994, 13,
1641.
(10) Evans, W. J.; Grate, J. W.; Choi, H. W.; Bloom, I.; Hunter, W. E.;
Atwood, J. L. J. Am. Chem. Soc. 1985, 107, 941.
(11) Zhang, X.; Loppnow, G. R.; McDonald, R.; Takats, J. J. Am. Chem.
Soc. 1995, 117, 7828.
(14) Evans, W. J.; Davis, B. L.; Nyce, G. W.; Perotti, J. M.; Ziller,
J. W. J. Organomet. Chem. 2003, 677, 89.
(15) Evans, W. J.; Forrestal, K. J.; Ziller, J. W. J. Am. Chem. Soc. 1998,
120, 9273.
(16) Evans, W. J.; Chamberlain, L. R.; Ziller, J. W. J. Am. Chem. Soc.
1987, 109, 7209.

Polymeric Samarium(II) Complexes
Organometallics, Vol. 28, No. 10, 2009 3103
Figure 2. Molecular structure of 2. The oxygen atom is disordered in two positions related by a C2 axis; the other half and hydrogen atoms
are omitted for clarity. Selected bond distances (Å) and angles (deg): Sm1-O1 2.222(15), Sm1A-O1 2.269(16), Sm1-N2 2.493(9), Sm1-N4
2.498(10), Sm1-N3 2.521(9), Sm1-N1 2.562(11), O1-Sm1-N2 87.3(4), O1-Sm1-N2A 120.1(5), O1-Sm1-N4A 86.0(5), O1-Sm1-N4
118.9(4), N2-Sm1-N4 153.8(3), O1-Sm1-N3A 107.6(5), O1-Sm1-N3 121.1(6), N2-Sm1-N3 97.3(3), N4-Sm1-N3 70.7(3),
O1-Sm1-N1 143.6(6), O1-Sm1-N1A 131.0(6), N2-Sm1-N1 70.4(3), N4-Sm1-N1 89.8(3).
Table 1. Crystallographic Data for 1, 2, 4, and 5
1
2
4
5
formula
fw
T (K)
C50H74N4O2Sm C84H116N8OSm2 C50H76AlN4Sm C57H85AlKN4Sm
913.48
113(2)
1554.59
113(2)
P-421c
18.045(3)
18.045(3)
26.868(5)
90.00
909.38
113(2)
Cc
13.485(3)
27.386(5)
15.247(3)
90.00
1042.72
113(2)
P21/n
11.576(2)
35.840(7)
13.549(3)
90.00
space group C2/c
a (Å)
b (Å)
c (Å)
R (deg)
ꢁ (deg)
γ (deg)
V (Å3)
Z
13.591(3)
20.265(4)
18.043(4)
90.00
90.00(3)
90.00
90.00
90.00
99.66(3)
90.00
99.62(3)
90.00
4969.4(18)
4
8748(3)
8
5550.9(19)
4
5542.2(19)
4
dcalcd (g/cm3) 1.221
1.183
1.088
1.250
F(000)
1920
3248
1888
2196
GOF
1.094
1.074
1.058
1.066
R1, wR2
0.0241, 0.0611 0.0823, 0.2355 0.0587, 0.1573 0.0372, 0.0841
(I > 2σ(I))
R1, wR2
(all data)
0.0254, 0.0618 0.0993, 0.2544 0.0628, 0.1605 0.0464, 0.0881
to those in K[Nd(OC6H3iPr2-2,6)4] (3.097(10)-3.473(11) Å) and
KBPh4 (3.191(5) Å).17 Additional K-C short contacts (3.486(5)
and 3.421(5) Å) are found in 5 involving the η2 agostic interaction
with one of the ethyl groups coordinated to the samarium in the
[AlEt4]-, leading to the lengthening of the Sm-C distance (2.982(4)
Å) compared to the other Sm-C distance (2.904(4) Å). The K-N
distance (3.044(3) Å) and the short K-C distances (3.062(3)-
3.172(4) Å) observed in the K(η5-pyrrolide) fragment are compa-
rable to those found in other transition metal pyrrolide ate
complexes.18 In each of the monomeric samarium units, the
samarium atom is six-coordinated and the coordination geometry
resembles that of 4. However, the bond distances around the
samarium are quite distinct from those found in 4 due to the
interactions of the two pyrrolide rings with the two different
potassium atoms and the different oxidation states of the samarium
atoms in 4 and 5. Especially, Sm1-N3A (to the nitrogen atom of
Figure 3. Molecular structure of 4. Hydrogen atoms are omitted
for clarity. Selected bond distances (Å) and angles (deg): Sm1-N2
2.425(3), Sm1-N1 2.544(3), Sm1-C22 2.781(5), Al1-C22 2.099(7),
Al1-C24 2.063(12), N2-Sm1-N2A 140.72(16), N2-Sm1-N1A
86.25(11), N2-Sm1-N1 70.39(11), N1-Sm1-N1A 106.74(14),
N2-Sm1-C22129.76(17),N2-Sm1-C22A83.13(17),N1-Sm1-C22
154.90(17), N1-Sm1-C22A 91.00(16), C22-Sm1-C22A 78.7(3),
C22-Al1-C22A 114.2(3).
samarium atom and the partial ion pair structure. In 4, the
Sm1-N1 and Sm1-N2 bond lengths (2.544(3) and 2.425(3)
Å) and the N-Sm-N angles in the bidentate ligand (70.39(11)°)
are comparable to those found in [NN]2SmCH2SiMe3(THF).
The crystal structure of 5 is shown in Figure 4 along with
selected bond parameters. The most striking feature of 5 is that
each unit is linked by a potassium atom to form a linear polymeric
structure, in which each of the potassium ions is surrounded by
one η2-coordinated pyrrolide ring in one unit and the other pyrrolide
ring in the neighboring unit in η5 fashion and one toluene mole-
cule and one ethyl group of the [AlEt4]- moiety in η2 modes. The
K-Carene distances range from 3.026(3) to 3.263(4) Å, comparable
(17) (a) Clark, D. L.; Watkin, J. G.; Huffman, J. C. Inorg. Chem. 1992,
31, 1554. (b) Hoffmann, K.; Weiss, E. J. Organomet. Chem. 1974, 67, 221.
(18) (a) Nikiforov, G. B.; Crewdson, P.; Gambarotta, S.; Korobkov, I.;
Budzelaar, P. H. M. Organometallics 2007, 26, 48. (b) Gao, G.; Korobkov,
I.; Gambarotta, S. Inorg. Chem. 2004, 43, 1108. (c) Scott, J.; Gambarotta,
S.; Yap, G.; Rancourt, P. G. Organometallics 2003, 22, 2325.

3104 Organometallics, Vol. 28, No. 10, 2009
Hao et al.
Figure 4. Extended structure of 5. Hydrogen atoms are omitted for clarity. Selected bond distances (Å) and angles (deg): Sm1-N1 2.586(3),
Sm1-N3A 2.630(3), Sm1-N2A 2.664(3), Sm1-N4A 2.731(3), Sm1-C43 2.904(4), Sm1-C45 2.982(4), Al1-C47 1.993(4), Al1-C43
2.024(4), Al1-C45 2.030(4), Al1-C49 2.042(5), K1-C2 3.219(4), K1-C3 3.263(4), K1-N3 3.044(3), K1-C22 3.102(3), K1-C23 3.172(4),
K1-C24 3.170(4), K1-C25 3.062(3), K1-C55, 3.233(4), K1-C56 3.156(4), K1-C45A 3.486(5), K1-C46A 3.421(5), N1- Sm1-N3
143.01(9), N1-Sm1-N2 67.49(8), N3-Sm1-N2 91.55(8), N1-Sm1-N4 92.55(8), N3-Sm1-N4 66.45(8), N2-Sm1-N4 111.88(9),
C56-K1-C55 24.62(10), C2-K1-C3 24.88(9), C46-K1-C45 25.92(9).
the K(η5-pyrrolide), 2.630(3) Å) is longer by ca. 0.1 Å than those
Scheme 1. Synthesis and Reaction of 1
found in the divalent species 1, but Sm1-N4A (to the imino
nitrogen, 2.731(3) Å) is comparable to those observed in 1. The
samarium atom to the other ligand nitrogen atom distances
(Sm1-N1A ) 2.586(3) and Sm1-N2A ) 2.664(3) Å) are slightly
different from the corresponding distances found in 1: the former
is longer and the latter is shorter than those in 1, probably resulting
from the relatively strong conjugation of the imino group with the
pyrrolide ring due to the η2-coordinated potassium atom. Thus,
Scheme 2. Synthesis of the Linear Polymeric 5
the overall samarium coordination can be viewed as one neutral
potassium (imino)pyrrolide and one monoanionic (imino)pyrrolide
ligand as well as one [AlEt4] anion. The divalent nature of the
samarium atom is indicated by its black color and significantly
shifted and very broad proton NMR resonances. The high stability
of the (imino)pyrrolide ligand [NN] in the presence of potassium
is noteworthy since imino groups could be easily reduced by alkali
metals, resulting in reductive C-C coupling. The stability may be
attributed to the strong conjugation of the imino group with the
aromatic pyrrole ring in the presence of bulky substituents. A few
examples of linear polymeric divalent samarium species linked by
an alkali ion with arene π interactions are known.4g,19 Compound
5 is unique in that both the η2- and η5-bonded pyrrolides to the
potassium ion and only the N-coordination to samarium ion are
observed; especially the η2-bonded pyrrolide ring to the potassium
ion has no precedent.
Conclusion
Novel stable divalent samarium complexes 1 and 5 with the
bulky 2-(N-arylimino)pyrrolide ligand [NN] ([NN] ) [2-(2,6-
iPr2C6H3NdCH)-5-tBuC4H2N]-) have been synthesized and
structurally characterized. These compounds do not undergo
intramolecular electron transfer reactions between the divalent
samarium and the imino group under normal conditions. The
results indicate that the bulky (imino)pyrrolide ligand [NN] may
be used for the preparation of other divalent lanthanide
complexes. Further investigations of the reactivity and properties
of 1 and 5 as well as the synthesis of other divalent lanthanide
derivatives with this ligand are currently in progress.
Acknowledgment. We are grateful to the National Science
Foundation of China (20572050 and 20725205), Tianjin
Natural Science Foundation (05YFJMJC00500), and 111
plan for the support of this work.
Supporting Information Available: CIF files giving X-ray
structural information on 1, 2, 4, and 5. This material is available
free of charge via the Internet at http://pubs.acs.org.
(19) (a) Evans, W. J.; Anwander, R.; Ansari, M. A.; Ziller, J. W. Inorg.
Chem. 1995, 34, 5. (b) Hou, Z.; Zhang, Y.; Tezuka, H.; Xie, P.; Tardif, O.;
Kozumi, T.; Yamazaki, H.; Wakatsuki, Y. J. Am. Chem. Soc. 2000, 122,
10533. (c) Hou, Z.; Zhang, Y.; Tardif, O.; Wakatsuki, Y. J. Am. Chem.
Soc. 2001, 123, 9216.
OM9001236