2,5-bis{N-(2,6-diisopropylphenyl)iminomethyl}pyrrolyl complexes of the divalent lanthanides: Synthesis and structures

Article abstract of DOI:10.1021/om100539f

The reaction of potassium 2,5-bis{N-(2,6-diisopropylphenyl)iminomethyl} pyrrolyl, [(DIP₂pyr)K], with the anhydrous lanthanide diiodides resulted in the heteroleptic complexes [(DIP₂pyr)LnI(THF) ₃] (Ln = Sm, Eu, Yb). All complexes are monomeric in the solid state, which is remarkable, since samarium and europium complexes tend to form dimeric complexes bridged by iodine ions. The (DIP₂pyr)^- ligands are coordinated almost symmetrically in a κ³ N, N′, N″ mode to the metal center in the samarium and europium compounds. In contrast, for the ytterbium complex an asymmetric coordination mode was observed.

Full text of DOI:10.1021/om100539f

4410 Organometallics 2010, 29, 4410–4413
DOI: 10.1021/om100539f
2,5-Bis{N-(2,6-diisopropylphenyl)iminomethyl}pyrrolyl Complexes
of the Divalent Lanthanides: Synthesis and Structures
Jelena Jenter, Michael T. Gamer, and Peter W. Roesky*
Institut fu€r Anorganische Chemie, Karlsruher Institut fu€r Technologie (KIT ), Engesserstrasse 15,
76131 Karlsruhe, Germany
Received June 2, 2010
Scheme 1
Summary: The reaction of potassium 2,5-bis{N-(2,6-diisopro-
pylphenyl)iminomethyl}pyrrolyl, [(DIP2pyr)K], with the anhy-
drous lanthanide diiodides resulted in the heteroleptic complexes
[(DIP2pyr)LnI(THF)3] (Ln=Sm, Eu, Yb). All complexes are
monomeric in the solid state, which is remarkable, since samar-
ium and europium complexes tend to form dimeric complexes
bridged by iodine ions. The (DIP2pyr)- ligands are coordinated
almost symmetrically in a κ3 N, N0, N00 mode to the metal center in
the samarium and europium compounds. In contrast, for the
ytterbiumcomplex an asymmetric coordination mode was observed.
complexes11-14 ligated by 2,5-bis(N-aryliminomethyl)pyrrolyls
are known. The coordination mode of the resulting complexes
depends on the steric bulk of the aryl substituents of the ligand,
the number of ligands coordinated, the ionic radius of the metal
center, and the bulkiness of additional ligands coordinated to
the metal atom. In most of the reported compounds the ligand
binds in a tridentate fashion with the two Schiff base nitrogen
atoms and the pyrrolyl moiety onto the metal centers (Scheme 1A),
but in a few cases also a bidentate binding mode was observed
(Scheme 1B). Some of the reported complexes have been used
as catalysts for the polymerization of ethylene8,9,15,16 and the
oligomerization of ethylene and propylene to linear and
branched products.15
In 2001, Mashima et al. introduced 2,5-bis(N-arylimino-
methyl)pyrrolyl compounds into rare-earth-metal chemistry
by forming some yttrium complexes.11 These compounds
were obtained by amine elimination reactions from the
corresponding pyrroles with [Y{N(SiMe3)2}3]. The coordi-
nation mode and the number of the 2,5-bis(N-arylimino-
methyl)pyrrolyl ligands introduced to a metal center were
controlled by varying the bulkiness on the aryl group of the
ligands. We have been working now for some time with the
sterically very demanding 2,5-bis{N-(2,6-diisopropylphenyl)-
iminomethyl}pyrrolyl (DIP2pyr)- ligand in trivalent rare-
earth-metal chemistry.12-14 In this context a number of
chloride and borohydride complexes were synthesized, and
some of these compounds were used as Ziegler-Natta cata-
lysts for the polymerization of 1,3-butadiene to poly-cis-1,4-
butadiene.14
Recently we and other groups were attracted by 2,5-bis-
(N-aryliminomethyl)pyrrolyls, which can serve as unique
monoanionic nitrogen ligands in coordination chemistry. Some
actinide complexes in which the 2,5-bis(N-aryliminomethyl)-
pyrrole structural motif was part of a larger oligodentate macro-
cyclic ligand were published as the first examples in this area.1-3
Later some macrocyclic multinuclear nickel compounds were
reported.4,5 The first transition-metal complexes with the tri-
dentate 2,5-bis(N-aryliminomethyl)pyrrolyl ligands were re-
ported by Bochmann et al.6 Today alkali-metal,7,8 aluminum,9
group 4,6 iron,6 chromium,8 copper,10 and rare-earth-metal
*To whom correspondence should be addressed. E-mail: roesky@
kit.edu.
(1) Sessler, J. L.; Gorden, A. E. V.; Seidel, D.; Hannah, S.; Lynch, V.;
Gordon, P. L.; Donohoe, R. J.; Tait, C. D.; Keogh, D. W. Inorg. Chim.
Acta 2002, 341, 54–70.
(2) Sessler, J. L.; Mody, T. D.; Dulay, M. T.; Espinoza, R.; Lynch, V.
Inorg. Chim. Acta 1996, 246, 23–30.
(3) Sessler, J. L.; Mody, T. D.; Lynch, V. Inorg. Chem. 1992, 31,
529–31.
(4) Chernyadyev, A. Y.; Ustynyuk, Y. A.; Aleksandrov, G. G.;
Sidorov, A. A.; Novotortsev, V. M.; Ikorskii, V. N.; Nefedov, S. E.;
Eremenko, I. L.; Moiseev, I. I. Russ. Chem. Bull. 2001, 50, 1336–1338.
(5) Chernyadyev, A. Y.; Ustynyuk, Y. A.; Yazev, O. V.; Kataev,
E. A.; Reshetova, M. D.; Sidorov, A. A.; Aleksandrov, G. G.; Ikorskii,
V. N.; Novotortsev, V. M.; Nefedov, S. E.; Eremenko, I. L.; Moiseev,
I. I. Russ. Chem. Bull. 2001, 50, 2445–2450.
(6) Dawson, D. M.; Walker, D. A.; Thornton-Pett, M.; Bochmann,
Since the (DIP2pyr)- ligand was proven to show a rich
coordination chemistry for the trivalent rare-earth metals,
we are now interested in extending this chemistry to the
divalent lanthanides. Herein we report on the synthesis and
structure of the monomeric lanthanide iodo complexes
[(DIP2pyr)LnI(THF)3] (Ln = Sm, Eu, Yb).17
M. Dalton Trans. 2000, 459–466.
(7) Jenter, J.; Roesky, P. W. New J. Chem. 2009, 34, 1541–1543.
(8) Salisbury, B. A.; Young, J. F.; Yap, G. P. A.; Theopold, K. H.
Collect. Czech. Chem. Commun. 2007, 72, 637–648.
(9) Matsuo, Y.; Tsurugi, H.; Yamagata, T.; Tani, K.; Mashima, K.
Bull. Chem. Soc. Jpn. 2003, 76, 1965–1968.
(10) Wayland, B. B.; Charlton, J. A.; Ni, Y. Polym. Prepr. (Am.
Chem. Soc., Div. Polym. Chem.) 1999, 40, 307–308.
(11) Matsuo, Y.; Mashima, K.; Tani, K. Organometallics 2001, 20,
3510–3518.
(12) Meyer, N.; Jenter, J.; Roesky, P. W.; Eickerling, G.; Scherer, W.
Chem. Commun. 2009, 4693–4695.
(13) Meyer, N.; Kuzdrowska, M.; Roesky, P. W. Eur. J. Inorg. Chem.
2008, 1475–1479.
(14) Jenter, J.; Meyer, N.; Roesky, P. W.; Thiele, S. K.-H.; Eickerling,
(15) Dawson, D. M.; Walker, D. A.; Thornton-Pett, M.; Bochmann,
M. Dalton Trans. 2000, 459–466.
(16) Tsurugi, H.; Matsuo, Y.; Yamagata, T.; Mashima, K. Organo-
metallics 2004, 23, 2797–2805.
(17) Jenter, J. Dissertation, Karlsruher Institut f€ur Technologie (KIT),
2010.
G.; Scherer, W. Chem. Eur. J. 2009, 16, 5472–5480.
r
pubs.acs.org/Organometallics
Published on Web 09/07/2010
2010 American Chemical Society

Note
Organometallics, Vol. 29, No. 19, 2010 4411
Scheme 2
Results and Discussion
As reported earlier, 2,5-bis{N-(2,6-diisopropylphenyl)-
iminomethyl}pyrrole, (DIP2pyr)H, can be deprotonated
with KH to give the corresponding potassium salt [(DIP2-
pyr)K].13 Reaction of [(DIP2pyr)K] with anhydrous lantha-
nide diiodides in THF at elevated temperature resulted in the
heteroleptic complexes [(DIP2pyr)LnI(THF)3] (Ln = Sm
(1), Eu (2), Yb (3)) in good yields (Scheme 2).
Figure 1. Perspective ORTEP view of the molecular structure of 1.
Thermal ellipsoids are drawn to encompass 50% probability. Hydro-
˚
gen atoms are omitted for clarity. Selected distances (A) and angles
(deg) are given for 1 and the isostructural complex 2. Complex 1:
Sm-N1=2.928(7),Sm-N2=2.474(7),Sm-N3=2.934(7),Sm-O1=
2.600(6), Sm-O2=2.596(6), Sm-O3=2.580(6), Sm-I=3.2233(9);
N1-Sm-N2=61.3(2), N1-Sm-N3=121.9(2), N2-Sm-N3=
60.7(2), N1-Sm-O1 = 89.3(2), N1-Sm-O2 = 75.7(2), N1-
Sm-O3 = 151.3(2), N2-Sm-O1 = 81.8(2), N2-Sm-O2 =
135.9(2), N2-Sm-O3 = 143.3(2), N3-Sm-O1 = 79.1(2), N3-
Sm-O2=158.1(2), N3-Sm-O3=83.7(2), N1-Sm-I=98.91(14),
N2-Sm-I = 104.8(2), N3-Sm-I = 98.85(13), O1-Sm-I =
171.25(14), O2-Sm-I = 90.40(14), O3-Sm-I = 88.47(13),
O1-Sm-O2 = 88.7(2), O1-Sm-O3 = 82.9(2), O2-Sm-O3 =
76.7(2). Complex 2: Eu-N1=2.934(8), Eu-N2=2.464(8), Eu-
N3=2.969(8), Eu-O1=2.472(9), Eu-O2=2.598(8), Eu-O3=
2.595(8), Eu-I=3.2088(11); N1-Eu-N2=61.6(3), N1-Eu-N3=
122.3(2), N2-Eu-N3 = 60.9(3), N1-Eu-O1 = 90.5(3), N1-
Eu-O2=76.0(3), N1-Eu-O3=152.7(3), N2-Eu-O1=84.2(3),
N2-Eu-O2=136.7(3), N2-Eu-O3=142.4(3), N3-Eu-O1=
80.9(3), N3-Eu-O2 = 158.3(3), N3-Eu-O3 = 82.5(3), N1-
Eu-I = 98.3(2), N2-Eu-I = 104.6(2), N3-Eu-I = 98.5(2),
O1-Eu-I=169.8(2), O2-Eu-I=89.0(2), O3-Eu-I=87.7(2),O1-
Eu-O2=88.1(3), O1-Eu-O3=82.1(3), O2-Eu-O3=77.5(3).
The new complexes were characterized by standard ana-
lytical/spectroscopic techniques, and the solid-state struc-
tures were established by single-crystal X-ray diffraction.
The diamagnetic compound 3 was also investigated by NMR
techniques. The NMR spectra show the expected set of
signals for the (DIP2pyr)- ligand and point to a symmetrical
coordination of the ligand in solution. This is in contrast to
the solid-state structure and indicates a dynamic behavior of
the ligand in solution. In the 1H NMR spectrum, one doublet
(δ 1.25 ppm) and one septet (δ 3.25 ppm) were observed for
the isopropyl groups, indicating that the 2,6-diisopropylani-
line moieties of the ligand can freely rotate in solution. The
13C{1H} NMR data are consistent with these observations.
Compounds 1 and 2, which are isostructural in the solid
state, crystallize in the monoclinic space group P21/c with
four molecules of the corresponding complex and eight THF
molecules in the unit cell (Figure 1). Data collection para-
meters and selected bond lengths and angles are given in
Table S1 (Supporting Information) and in the caption of
Figure 1. The coordination polyhedron of the lanthanide
atoms in both compounds is formed by the (DIP2pyr)-
ligand, the iodine atom, and three THF molecules and shows
a distorted-pentagonal-bipyramidal geometry. The apexes
of each bipyramid are formed by the iodine atom and one
THF molecule with an almost linear setup (O1-Sm-I =
171.25(14)° (1) and O1-Eu-I = 169.8(2)° (2)). The nearly
planar arrangement of the LnN3O2 fragments is confirmed
by the sums of the corresponding five valence angles (358.1° (1)
and 358.5° (2)). The (DIP2pyr)- ligands are coordinated almost
symmetrically in a κ3 N, N0, N00 mode to the metal center
two n-pentane molecules in the unit cell (Figure 2). Due to
twinning problems, the quality of the structure is low. As
observed for compounds 1 and 2, the coordination polyhe-
dron of complex 3 consists of a distorted pentagonal bipyr-
amid in the solid state. In contrast to 1 and 2, the apexes of
the bipyramid are formed by two THF molecules, which are
arranged almost linearly (O1-Yb-O3 = 170.8(5)°). The
sum of the corresponding five valence angles shows a nearly
planar arrangement of the YbN3OI fragment (360.1°). As a
result of the smaller ion radius of Yb, the (DIP2pyr)- ligand
in 3 is coordinated asymmetrically to the metal center, which
is in contrast to the case for compounds 1 and 2. In complex 3
one Schiff-base function (N1) shows an Yb-N bond dis-
˚
˚
(Sm-N1 = 2.928(7) A, Sm-N2 = 2.474(7) A, Sm-N3 =
˚
˚
˚
2.934(7) A (1) andEu-N1 = 2.934(8) A,Eu-N2 = 2.464(8) A,
Eu-N3 = 2.969(8) A (2)). The Ln-I bond distances Sm-I =
˚
˚
˚
3.2233(9) A and Eu-I = 3.2088(11) A are in the expected
range.18,19 The iodine atoms are in the apex of the pentagonal
bipyramid (N1-Sm-I = 98.91(14)°, N2-Sm-I = 104.8(2)°,
N3-Sm-I = 98.85(13)° (1) and N1-Eu-I = 98.3(2)°,
N2-Eu-I = 104.6(2)°, N3-Eu-I = 98.5(2)° (2)).
˚
tance of 2.757(12) A, while the other function exhibits a long
˚
interaction to the metal center (Yb-N1 = 3.1997(6) A).
Obviously the asymmetrical coordination of the (DIP2pyr)-
ligand is caused by the smaller ionic radius of the metal center
in 3 compared with those of 1 and 2. Additionally, crystal
packing may also be considered. The Yb-I bond distance
Compound 3 crystallizes as green plates in the monoclinic
space group P21/c with four molecules of the complex and
˚
(3.100(2) A) of 3 is within the same range observed for other
monomeric ytterbium(II) iodo complexes.20-22
(18) Maudez, W.; Meuwly, M.; Fromm, K. M. Chem. Eur. J. 2007,
13, 8302–8316.
(19) Giesbrecht, G. R.; Cui, C.; Shafir, A.; Schmidt, J. A. R.; Arnold,
(20) Panda, T. K.; Zulys, A.; Gamer, M. T.; Roesky, P. W.
J. Organomet. Chem. 2005, 690, 5078–5089.
J. Organometallics 2002, 21, 3841–3844.

4412 Organometallics, Vol. 29, No. 19, 2010
Jenter et al.
ring to the samarium(II) center. Consequently, the coordina-
tion sphere is already saturated and a monomer is formed. This
complex cannot be compared with our compounds, because
the (DIP2pyr)- ligand is less sterically demanding and the
coordination spheres of compounds 1 and 2 are satisfied by
three solvent molecules. The other example is the samarium(II)
compound [Sm(LPh,tBu)I(THF)4] (LPh,tBu = {N(C(Ph)dN)2-
C(tBu)Ph}-), which coordinates four THF molecules to satu-
rate the coordination sphere instead of forming a dimer.31 In
addition, the nitrogen atom of the monodentate (LPh,tBu -
)
ligand and the iodine atom exhibit a relatively small angle
(N1-Sm-I = 100.25(9)°) instead of building a nearly linear
N-Sm-I unit. This arrangement was also observed for 1
and 2, as described above. The reason for the formation of the
cisoid isomers is unclear. The crystal structures of the diodides
of samarium(II) and europium(II) coordinated by different
solvents have been comprehensively described in the literature,
and transoid as well as cisoid isomers were observed.32-37 No
doubt a subtle interplay of crystal packing and steric effects are
the dominant factors for the differences.
Figure 2. Perspective ORTEP view of the molecular structure
of 3. Thermal ellipsoids are drawn to encompass 30% prob-
ability. Hydrogen atoms are omitted for clarity. Selected dis-
˚
tances (A)] and angles (deg): Yb-N1 = 2.757(12), Yb-N2 =
2.387(13), Yb-N3=3.1997(6), Yb-O1=2.431(11), Yb-O2=
2.439(12), Yb-O3=2.415(14), Yb-I=3.100(2); N1-Yb-N2=
65.0(4), N1-Yb-N3 = 123.08(4), N2-Yb-N3 = 58.13(4),
N1-Yb-O1 = 92.2(4), N1-Yb-O2 = 168.0(5), N1-Yb-
O3=94.5(4), N2-Yb-O1=87.8(4), N2-Yb-O2=127.0(5),
N2-Yb-O3=89.4(5), N3-Yb-O1=84.55(4), N3-Yb-O2=
68.63(4), N3-Yb-O3 = 86.50(4), N1-Yb-I = 83.9(3), N2-
Yb-I=148.8(3), N3-Yb-I=152.96(3), O1-Yb-I=92.8(3),
O2-Yb-I = 84.4(3), O3-Yb-I = 94.2(3), O1-Yb-
O2=86.1(4), O1-Yb-O3=170.8(5), O2-Yb-O3=89.4(5).
Experimental Section
General Considerations. All manipulations of air-sensitive
materials were performed with the rigorous exclusion of oxygen
and moisture in flame-dried Schlenk-type glassware either on a
dual manifold Schlenk line, interfaced to a high-vacuum (10-3
Torr) line, or in an argon-filled MBraun glovebox. THF was
distilled under nitrogen from potassium benzophenone ketyl
prior to use. Hydrocarbon solvents (toluene and n-pentane)
were dried using an MBraun solvent purification system (SPS-
800). All solvents for vacuum line manipulations were stored in
vacuo over LiAlH4 in resealable flasks. Deuterated solvents
were obtained from Aldrich (99 atom % D). NMR spectra were
recorded on a Bruker Avance 400 MHz NMR spectrometer.
Chemical shifts are referenced to internal solvent resonances and are
reported relative to tetramethylsilane. IR spectra were obtained on a
Bruker IFS 113v FTIR spectrometer. Mass spectra were recorded
at 70 eV on a Varian Mat SM 11 instrument. Elemental analyses
were carried out with an Elementar Vario EL apparatus. LnCl3,38
LnI2,39-41 (DIP2pyr)H,42,43 and [(DIP2pyr)K]13,44 were prepared ac-
cording to literature procedures.
Interestingly, complexes 1-3 are all monomeric in the
solid state, which is remarkable, since samarium and euro-
pium with larger ionic radii tend to form dimeric complexes
bridged by iodine ions:20,23-30 e.g., [{(Me3SiNPPh2)2CH}-
Ln(μ-I)(THF)]2 (Ln = Eu, Sm)20,23 and [{(Me3Si)2N}Sm(μ-I)-
(DME)(THF)]2.30 To the best of our knowledge, only a few
monomeric heteroleptic iodo complexes of divalent samarium
and europium have been reported in the literature. For divalent
europium there has also been only one structurally characterized
monomeric heteroleptic iodo complex reported, which is the
cluster [IEu(OtBu)4{Li(THF)}4(OH)].18 This compound is sta-
bilized by a bulky alkali-metal cage on one side and thus cannot
be compared with our complexes.
There are two examples for structurally characterized
monomeric samarium(II) iodo complexes in the literature.
One of these is a complex with the very bulky ligand {C5Me4-
SiMe2(iPr2-tacn)}- (tacn =1,4-diisopropyl-1,4,7-triazacyclo-
nonane).19 This ligand coordinates via the cyclopentadienyl
moiety and the three nitrogen atoms of the triazacyclononane
[(DIP2pyr)LnI(THF)3] (1-3). General Procedure. THF
(20 mL) was condensed at -78 °C onto a mixture of LnI2(THF)n
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Note
Organometallics, Vol. 29, No. 19, 2010 4413
(Ln = Sm, Eu, Yb) and [(DIP2pyr)K], and the resulting reaction
mixture was stirred for 16 h at 60 °C. The deeply colored solution
was filtered off and concentrated until a precipitate appeared. The
mixture was heated carefully until the solution became clear. For
Ln = Yb the solution was layered with n-pentane. The products
were obtained at room temperature overnight as deeply colored
crystals.
[(DIP2pyr)SmI(THF)3] (1). SmI2(THF)2.5 (643 mg, 1.10
mmol), [(DIP2pyr)K] (480 mg, 1.00 mmol). Black crystals from
hot THF; yield 706 mg, 0.76 mmol, 76% IR (KBr, ν/cm-1): 731
(m), 766 (m), 800 (m), 860 (m), 1039 (m), 1093 (m), 1155 (s), 1254
(w), 1315 (m), 1360 (w), 1437 (m), 1574 (m), 1616 (s), 1714 (w),
2046 (w), 2181 (w), 2864 (w), 2927 (w), 2963 (m), 3450 (m). Anal.
(m), 3450 (m). Anal. Calcd for C42H62N3O3IEu (2; 935.83): C,
53.90; H, 6.68; N, 4.49. Found: C, 53.58; H, 6.70; N, 4.21.
[(DIP2pyr)YbI(THF)3] (3). YbI2(THF)2 (286 mg, 0.50 mmol),
[(DIP2pyr)K] (240 mg, 0.50 mmol). Green crystals from THF/
1
n-pentane; yield 200 mg, 0.21 mmol, 42% (single crystals). H
NMR (THF-d8, 400 MHz, 25 °C): δ 1.25 (d, 24 H, CH(CH3),
JH,H = 6.9 Hz), 3.25 (sept, 4 H, CH(CH3), JH,H = 6.9 Hz), 6.75
(s, 2 H, 3,4-pyr), 7.07-7.12 (m, 2 H, p-Ph), 7.17-7.19 (m, 4 H,
Ph), 8.21 (s, 2 H, NdCH) ppm. 13C{1H} NMR (THF-d8, 100.4
MHz, 25 °C): δ 28.2 (CH(CH3)2), 34.8 (CH(CH3)2), 118.0 (3,4-pyr),
123.1 (Ph), 124.4 (Ph), 139.7 (Ph), 143.8 (2,5-pyr), 151.4 (Ph), 161.5
(NdCH) ppm. Anal. Calcd for C42H62N3O3IYb (3; 956.90): C,
52.72; H, 6.53; N, 4.39. Found: C, 52.86; H, 6.63; N, 4.23.
Calcd for C40H58N3O2.5ISm (1 0.5THF; 935.83): C, 53.49; H,
6.51; N, 4.68. Found: C, 53.33; H, 6.63; N, 4.26.
3
Acknowledgment. This work was supported by the
Deutsche Forschungsgemeinschaft (Grant No. SPP 1166).
[(DIP2pyr)EuI(THF)3] (2). EuI2(THF)2 (412 mg, 0.75 mmol),
[(DIP2pyr)K] (360 mg, 0.75 mmol). Red crystals from hot THF;
yield 360 mg, 0.39 mmol, 51% (single crystals). IR (KBr,
ν/cm-1): 735 (m), 769 (m), 796 (m), 860 (m), 1039 (m), 1097
(m), 1155 (s), 1230 (w), 1319 (m), 1360 (w), 1437 (m), 1574 (m),
1616 (s), 1710 (w), 2046 (w), 2181 (w), 2868 (w), 2924 (w), 2962
Supporting Information Available: CIF files and a table giving
X-ray crystallographic data for the structure determinations of
1-3. This material is available free of charge via the Internet at
http://pubs.acs.org.