Terphenyl Cyclooctatetraenyl Compounds of Samarium

Article abstract of DOI:10.1021/ic0301775

The syntheses and molecular structures of a number of terphenyl-based compounds of the lanthanide element samarium are reported. Reaction of 2 equiv of DppLi (Dpp = 2,6-diphenylphenyl) with 1 equiv of SmCl₃ in tetrahydrofuran at room temperature yields (Dpp)₂SmCl(μ -Cl)Li(THF)₃ (1). The one-pot reaction of 1 equiv of K ₂-COT (COT^2- = cyclooctatetraenyl dianion) with 1 equiv SmCl₃ in tetrahydrofuran at room temperature followed by addition of 1 equiv of terphenyllithium salt DppLi, DmpLi (Dmp = 2,6-dimesitylphenyl), or DanipLi (Danip = 2,6-di(o-anisol)phenyl) produces DppSmCOT(μ-Cl)Li(THF) ₃ (2), DmpSm(THF)COT (3), and DanipSm(THF)COT (4), respectively. In the case of the Danip-based compound 4 the order of addition of reagents can be reversed producing the same compound, however, in considerably lower yield. Compound 2 can also be prepared by reaction of 1 with 1 equiv of K ₂COT in tetrahydrofuran. The molecular structure of the bis(terphenyl) compound 1 exhibits a formally four-coordinate metal atom. The molecular structures of the terphenyl COT compounds 2-4 feature monomeric complexes which are obtained either as a lithium chloride adduct (2) or as tetrahydrofuran adducts (3, 4). In 4 the Danip ligand adopts the meso form.

Full text of DOI:10.1021/ic0301775

Inorg. Chem. 2003, 42, 7587−7592
Terphenyl Cyclooctatetraenyl Compounds of Samarium
,†
Gerd W. Rabe,* Mei Zhang-Presse,† Florian A. Riederer,† James A. Golen,‡
Christopher D. Incarvito,§ and Arnold L. Rheingold|
Technische UniVersita¨t Mu¨nchen, Anorganisch-chemisches Institut, Lichtenbergstrasse 4, 85747
Garching, Germany, Department of Chemistry, UniVersity of Massachusetts Dartmouth, North
Dartmouth, Massachusetts 02747, Department of Chemistry, Yale UniVersity, New HaVen,
Connecticut 06520, and Department of Chemistry and Biochemistry, UniVersity of California at
San Diego, La Jolla, California 92093
Received June 3, 2003
The syntheses and molecular structures of a number of terphenyl-based compounds of the lanthanide element
samarium are reported. Reaction of 2 equiv of DppLi (Dpp ) 2,6-diphenylphenyl) with 1 equiv of SmCl3 in
tetrahydrofuran at room temperature yields (Dpp)2SmCl(µ-Cl)Li(THF)3 (1). The one-pot reaction of 1 equiv of K -
2
COT (COT2- ) cyclooctatetraenyl dianion) with 1 equiv SmCl3 in tetrahydrofuran at room temperature followed by
addition of 1 equiv of terphenyllithium salt DppLi, DmpLi (Dmp ) 2,6-dimesitylphenyl), or DanipLi (Danip ) 2,6-
di(o-anisol)phenyl) produces DppSmCOT(µ-Cl)Li(THF)3 (2), DmpSm(THF)COT (3), and DanipSm(THF)COT (4),
respectively. In the case of the Danip-based compound 4 the order of addition of reagents can be reversed producing
the same compound, however, in considerably lower yield. Compound 2 can also be prepared by reaction of 1 with
1 equiv of K COT in tetrahydrofuran. The molecular structure of the bis(terphenyl) compound 1 exhibits a formally
2
four-coordinate metal atom. The molecular structures of the terphenyl COT compounds 2−4 feature monomeric
complexes which are obtained either as a lithium chloride adduct (2) or as tetrahydrofuran adducts (3, 4). In 4 the
Danip ligand adopts the meso form.
Introduction
the larger elements La-Nd. To date there are no published
reports on terphenylactinide compounds, an area which is
still to be developed.
During the past decade there have been research activities
in the field of terphenyl-based compounds, mostly involving
p block but also some s block as well as late d block elements
using a variety of different terphenyl ligand systems.1,2
Compared with a fairly large number of known terphenyl-
based compounds of the main group elements, the number
of complexes of group 3 and f block elements containing
terphenyl substituents as the only ancillary ligand is still
relatively small. Terphenyl-based compounds have been
reported for the group 3 elements scandium and yttrium as
well as the lanthanide elements Sm-Lu3-8 but not yet for
Our efforts to develop the area of terphenyllanthanide
compounds have demonstrated that a variety of monosub-
stituted compounds are accessible by salt metathesis reactions
using different sterically demanding terphenyls such as Dmp
[2,6-dimesitylphenyl]3,6,7 and Dnp [2,6-di(1-naphthyl)-
phenyl]4 or the donor-functionalized ligand Danip [2,6-di-
(o-anisol)phenyl].5,8 We have also been investigating the
reaction chemistry of Danip-based mono(terphenyl)lan-
thanide compounds, particularly the accessibility and struc-
tural characterization of further functionalized Danip-based
compounds of general composition DanipLnX2 employing
* To whom correspondence should be addressed. E-mail: g.rabe@
lrz.tum.de.
† Technische Universita¨t Mu¨nchen.
(4) Rabe, G. W.; Be´rube´, C. D.; Yap, G. P. A. Inorg. Chem. 2001, 40,
2682.
(5) Rabe, G. W.; Be´rube´, C. D.; Yap, G. P. A. Inorg. Chem. 2001, 40,
4780.
‡ University of Massachusetts Dartmouth.
§ Yale University.
| University of California at San Diego.
(1) Twamley, B.; Haubrich, S. T.; Power, P. P. AdV. Organomet. Chem.
(6) Rabe, G. W.; Be´rube´, C. D.; Yap, G. P. A.; Lam, K.-C.; Concolino,
T. E.; Rheingold, A. L. Inorg. Chem. 2002, 41, 1446.
(7) Rabe, G. W.; Rhatigan, B.; Golen, J. A.; Rheingold, A. L. Acta
Crystallogr. 2003, E59, m99.
1999, 44, 1 and references therein.
(2) Clyburne, J. A. C.; McMullen, N. Coord. Chem. ReV. 2000, 210, 73
and references therein.
(3) Rabe, G. W.; Strissel, C. S.; Liable-Sands, L. M.; Concolino, T. E.;
Rheingold, A. L. Inorg. Chem. 1999, 38, 3446.
(8) Rabe, G. W.; Zhang-Presse, M.; Riederer, F. A.; Yap, G. P. A. Inorg.
Chem. 2003, 42, 3527.
10.1021/ic0301775 CCC: $25.00 © 2003 American Chemical Society
Published on Web 10/18/2003
Inorganic Chemistry, Vol. 42, No. 23, 2003 7587

Rabe et al.
purified prior to use by drying over molecular sieves followed by
three freeze-pump-thaw cycles and, finally, vacuum transfer.
DppLi,20 DmpLi,21 DanipLi,5,22 and K2COT23,24 were prepared
according to the literature. K2COT was not isolated but used in
situ. SmCl3 was purchased from Aldrich (packaged under argon in
ampules) and was used as received. NMR spectra were recorded
on a JMN-GX 400 instrument. 13C NMR spectra were referenced
to the solvent signals (benzene-d6, 128.0 ppm; THF-d8, 67.4 and
25.2 ppm, respectively).
both sterically encumbering mono anionic amides and
alkoxides.8
Additionally, there are reports by Niemeyer et al. on the
synthesis and structural characterization of both mono- and
bis(terphenyl)lanthanide complexes of divalent ytterbium and
europium containing the smallest terphenyl ligand Dpp [Dpp
) 2,6-diphenylphenyl] as a supporting ligand.9,10 Those
compounds were prepared directly from the metal and Dpp
iodide in tetrahydrofuran solution.
(Dpp)2SmCl(µ-Cl)Li(THF)3 (1). In the glovebox, a colorless
suspension of SmCl3 (257 mg, 1.0 mmol) in 5 mL of tetrahydro-
furan was stirred overnight. Addition of a freshly prepared solution
of (2,6-diphenylphenyl)lithium (472 mg, 2.0 mmol) in 5 mL of
tetrahydrofuran gave a bright yellow solution. The reaction mixture
was stirred for 30 min and was centrifuged. All volatiles were
removed, and the residues were washed with hexanes. A couple of
milliliters of toluene were added to the residues first, followed by
stepwise addition of small amounts of tetrahydrofuran (upon
stirring) until the residues were dissolved. The obtained solution
was centrifuged, layered with a small portion of hexanes, and cooled
to -30 °C. Repeated layering with additional small portions of
hexanes over a period of several days resulted in almost quantitative
crystallization of 1. Removal of the mother liquor followed by
drying under vacuum gave bright yellow 1 as a crystalline material
(542 mg, 60%). Analytically pure 1 is insoluble in hexanes and
only sparingly soluble in aromatic solvents but well soluble in
tetrahydrofuran. Solutions of 1 in toluene or tetrahydrofuran at room
temperature decompose slowly but appear to be unchanged over
longer time periods if stored at -25 °C.
We here report our continued systematic investigations in
this area of chemistry exploring the accessibility of terphenyl
based lanthanide compounds vis-a-vis a dianionic ligand
system, i.e. the cyclooctatetraenyl dianion, thereby providing
more details on the reaction chemistry as well as structural
aspects of terphenyl lanthanide compounds. We also report
on the synthesis of a first example of a bis(terphenyl)
compound of a trivalent lanthanide element.
The 10 π aromatic cyclooctatetraenyl dianion ()COT2-)
is the second most important ligand in organolanthanide
chemistry, next to the cyclopentadienyl and the pentameth-
ylcyclopentadienyl anion, which clearly dominate the area
of organolanthanide chemistry.11-13 The first report on a rare-
earth element containing the COT2- ligand was in 1969 by
Hayes and Thomas.14 The reaction of COT with metallic
europium or ytterbium in liquid ammonia was described to
produce mono-COT lanthanide complexes of composition
(COTLn)x. Other reports followed on COT compounds of
the lighter and middle rare-earth elements of composition
COTLnCl(THF)x (x ) 1 or 2) and COT2LnK, which were
synthesized by reaction of 1 or 2 equiv of K2COT with the
corresponding lanthanide trichloride.15-18 Mono-COT lan-
thanide(III) complexes represent the largest and most thor-
oughly studied group of rare-earth COT compounds.11-13 We
note that there is a report on a lanthanide aryl COT
compound of the element lutetium using the internally
chelating [(dimethylamino)methyl]phenyl ligand.19 However,
there are so far no reports on terphenyl COT compounds of
the lanthanides.
Anal. Calcd for C48H50Cl2LiO3Sm: C, 63.84; H, 5.58. Found:
1
C, 63.62; H, 5.43. Mp: 84-86 °C (dec). H NMR (C4D8O, 400
MHz, 25 °C): δ 5.00 (br s, 4H), 5.35 (br s, 2H), 7.24 (br s, 2H),
7.56 (br s, 1H), 8.28 (br s, 4H). We failed to detect any signals in
the 13C NMR spectrum in tetrahydrofuran-d8 solution. We note that
1 is not sufficiently stable in THF solution at ambient temperature
to allow for long time runs.
DppSmCOT(µ-Cl)Li(THF)3 (2). In the glovebox, a colorless
suspension of SmCl3 (257 mg, 1.0 mmol) in 5 mL of tetrahydro-
furan was stirred overnight. A freshly prepared solution of K2COT
(1.0 mmol) in 5 mL of tetrahydrofuran was added to the suspension.
The reaction mixture was stirred for 30 min yielding a purple
suspension. A freshly prepared solution of DppLi (236 mg, 1.0
mmol) in tetrahydrofuran was slowly added via syringe. After being
stirred for 10 min, the obtained red suspension was centrifuged
and the mother liquor was removed. Washing of the residues with
hexanes followed by extraction with toluene in the presence of a
couple of drops tetrahydrofuran, centrifugation of the obtained red
solution, and cooling to -25 °C resulted in crystallization of 2.
Removal of the mother liquor and drying under vacuum gave dark
red 2 as microcrystalline material (447 mg, 60%). Analytically pure
2 is insoluble in hexanes, only sparingly soluble in aromatic
solvents, but well soluble in tetrahydrofuran.
Experimental Section
The compounds described below were handled under nitrogen
using Schlenk double-manifold, high-vacuum, and glovebox (MBraun,
Labmaster 130) techniques. Solvents were dried and physical
measurements were obtained by following typical laboratory
procedures. Cyclooctatetraen was purchased from Aldrich and
(9) Heckmann, G.; Niemeyer, M. J. Am. Chem. Soc. 2000, 122, 4227.
(10) Niemeyer, M. Acta Crystallogr. 2001, E57, m578.
(11) Edelmann, F. T. New. J. Chem. 1995, 19, 535.
(12) Edelmann, F. T.; Freckmann, D. M. M.; Schumann, H. Chem. ReV.
2002, 102, 1851.
(13) Edelmann, F. T. In ComprehensiVe Organometallic Chemistry II; Abel,
E. W., Stone, F. G. A., Wilkinson, G., Eds.; Pergamon Press: Oxford,
U.K., 1995; Vol. 4, p 11.
Anal. Calcd for C38H45ClLiO3Sm: C, 61.47; H, 6.11. Found:
C, 61.25; H, 6.04. Mp: 119-120 °C (dec). 1H NMR (C4D8O, 400
MHz, 25 °C): δ 5.89 (d, JH-H ) 7 Hz, 4H), 6.00-6.05 (m, 6H),
(14) Hayes, R. G.; Thomas, J. L. J. Am. Chem. Soc. 1969, 91, 6876.
(15) Mares, F.; Hodgson, K. O.; Streitwieser, A., Jr. J. Organomet. Chem.
1970, 24, C68.
(16) Mares, F.; Hodgson, K. O.; Streitwieser, A., Jr. J. Organomet. Chem.
1971, 28, C24.
(17) Hodgson, K. O.; Mares, F.; Starks, D. F.; Streitwieser, A., Jr. J. Am.
Chem. Soc. 1973, 95, 8650.
(20) Rabe, G. W.; Sommer, R. D.; Rheingold, A. L. Organometallics 2000,
19, 5537.
(21) Ruhlandt-Senge, K.; Ellison, J. J.; Wehmschulte, R. J.; Pauer, F.;
Power, P. P. J. Am. Chem. Soc. 1993, 115, 11353.
(22) Rabe, G. W.; Zhang-Presse, M.; Yap, G. P. A. Acta Crystallogr. 2002,
E58, m434.
(18) Boussie, T. R.; Eisenberg, D. C.; Rigsbee, J.; Streitwieser, A., Jr.;
Zalkin, A. Organometallics 1991, 10, 1922.
(19) Wayda, A. L.; Rogers, R. D. Organometallics 1985, 4, 1440.
(23) Katz, T. J. J. Am. Chem. Soc. 1960, 82, 3784.
(24) Wayda, A. L. In Inorganic Synthesis; Ginsberg, A. P., Ed.; Wiley:
New York, 1990; Vol. 27, p 150.
7588 Inorganic Chemistry, Vol. 42, No. 23, 2003

Terphenyl Cyclooctatetraenyl Compounds of Samarium
Table 1. Crystallographic Data for (Dpp)2SmCl(µ-Cl)Li(THF)3 (1), DppSmCOT(µ-Cl)Li(THF)3 (2), DmpSm(THF)COT (3), and DanipSm(THF)COT
(4)a
param
formula
1
2
3
4
C48H50Cl2LiO3Sm
903.07
C38H45ClLiO3Sm
742.48
C36H41OSm
640.04
C32H33O3Sm
615.93
fw
space group
a, Å
b, Å
P21/c
P21/n
Pbca
Pbca
12.055(3)
19.984(5)
18.316(4)
103.154(4)
4296.6(17)
4
12.7753(8)
16.8698(10)
16.9344(11)
103.4950(10)
3548.9(4)
4
14.1920(9)
14.9607(9)
28.2053(18)
8.3673(11)
19.780(3)
32.181(4)
c, Å
â, deg
V, Å3
Z
5988.6(6)
8
1.420
5326.1(12)
8
1.536
D
calcd, g cm-3
1.396
1.390
temp, °C
-50(2)
-126(2)
Mo KR (0.710 73)
17.63
-55(2)
Mo KR (0.710 73)
19.87
-123(2)
Mo KR (0.710 73)
22.36
radiation (λ, Å)
Mo KR (0.710 73)
15.30
µ
MoKR, cm-1
GOF
1.049
1.042
1.186
1.055
R1, % (obsd)
wR2, % (all data)
3.48
9.28
3.44
8.72
6.66
15.00
2.85
7.47
2
2
2
2
a The quantity minimized was wR2 ) Σ[w(Fo - Fc )2]/Σ[(wFo )2]1/2; R1 ) Σ∆/Σ(Fo), ∆ ) |(Fo - Fc)|, w ) 1/[σ2(Fo ) + (aP)2 + bP], P ) [2Fc2 +
max(Fo, 0]/3.
7.48 (d, JH-H ) 7 Hz, 2H), 8.03 (t, JH-H ) 7 Hz, 1H), 9.51 (s,
COT, 8H). 13C NMR (C4D8O, 100.4 MHz, 25 °C): δ 78.6 (COT),
115.2, 123.8, 125.0, 126.7, 127.6, 145.3, 157.7. The signal
corresponding to the ipso carbon atom could not be located,
presumably due to the direct neighborhood of the paramagnetic
samarium atom.
methoxy functions is concentration dependent. A 13C-solution NMR
spectrum of 4 could not be obtained because of the limited solubility
of analytically pure 4 in benzene solution and limited stability in
THF solution.
General Aspects of X-ray Data Collection, Structure Deter-
mination, and Refinement for Complexes 1-4. Crystal, data
collection, and refinement parameters are given in Table 1. Data
were collected on a Bruker AXS CCD system or a modified
Siemens-Bruker Apex AXS CCD system. The systematic absences
in the diffraction data are uniquely consistent for the reported space
groups. All crystals were mounted on glass fibers with Paratone-N
oil and cooled to indicated temperatures. The structures were solved
using direct methods, completed by subsequent difference Fourier
syntheses, and refined by full-matrix, least-squares procedures.
SADABS absorption corrections were applied to all data sets. All
non-hydrogen atoms except those exhibiting disorder were refined
with anisotropic displacement coefficients. All hydrogen atoms were
treated as idealized contributions. In 1, carbon atoms C(37) and
C(38) of one tetrahydrofuran ligand were disordered over two
positions at 0.51 occupancy and carbon atom C(41) of another
tetrahydrofuran molecule at 0.41 occupancy. These atoms were
refined isotropically. Carbon atom C(40) exhibited a high thermal
parameter, but its disorder could not be modeled. In 2, the carbon
atom pairs C(29), C(30) and C(31), C(33) and C(37), C(38) of the
tetrahydrofuran ligands were disordered with occupancy 0.53, 0.56,
and 0.40, respectively. These atoms were refined isotropically.
Residual electron density for 1-3 were less than 1 e/A3 and were
within 1 Å of the samarium atoms. In 4, residual electron density
of 1.11 and 1.05 e/A3 were found at 0.86 and 0.84 Å from the
samarium atom.
DmpSm(THF)COT (3) and DanipSm(THF)COT (4). In the
glovebox, a colorless suspension of SmCl3 (257 mg, 1.0 mmol) in
5 mL of tetrahydrofuran was stirred overnight. A freshly prepared
solution of K2COT (1.0 mmol) in 5 mL of tetrahydrofuran was
added to the suspension. The reaction mixture was stirred for 30
min yielding a purple suspension. A freshly prepared solution of
DmpLi (320 mg, 1.0 mmol) or DanipLi (296 mg, 1.0 mmol),
respectively, in tetrahydrofuran was slowly added via syringe. After
being stirred for 15 min, the obtained red suspension was
centrifuged and the mother liquor was removed. Washing of the
residues with hexanes followed by extraction with toluene, cen-
trifugation of the obtained red solution, and cooling to -25 °C
resulted in crystallization of 3 and 4, respectively. Removal of the
mother liquor and drying under vacuum gave red 3 and 4,
respectively, as microcrystalline material (3, 384 mg, 60%; 4, 370
mg, 60%). Analytically pure 3 and 4 are insoluble in hexanes but
soluble in aromatic solvents and quite soluble in tetrahydrofuran.
3. Anal. Calcd for C36H41OSm: C, 67.56; H, 6.46. Found: C,
67.35; H, 6.27. Mp: 130-140 °C (dec). 1H NMR (C6D6, 400 MHz,
25 °C): δ 1.92 (br, THF, 4H), 2.16 (s, p-Me, 6H), 2.21 (s, o-Me,
12H), 4,51 (br, THF, 4H), 6.29 (s, 4H), 6.50 (d, JH-H ) 7 Hz,
2H), 7.58 (t, JH-H ) 7 Hz, 1H), 9.28 (s, COT, 8H). 13C NMR (C6D6,
100.4 MHz, 25 °C): δ 22.2 (o-Me), 25.9 (p-Me), 29.9 (THF), 75.3
(THF), 83.9 (COT), 117.9, 134.8, 135.9, 150.9. We failed to detect
in the 13C NMR spectrum all aromatic signals of the terphenyl
moiety which is probably due to overlap of the solvent signal with
some of the signals. Also, the signal corresponding to the ipso
carbon atom could not be located, presumably due to the direct
neighborhood of the paramagnetic samarium atom.
All software and sources of the scattering factors are contained
in SHELXTL (5.10) program library (G. M. Sheldrick, Siemens
XRD, Madison, WI).
Results and Discussion
4. Anal. Calcd for C32H33O3Sm: C, 62.40; H, 5.40. Found: C,
62.23; H, 5.28. Mp: 180-185 °C (dec). 1H NMR (C6D6, 400 MHz,
25 °C): δ 0.69 (br s, OMe, 6H), 1.46 (s, THF, 4H), 3.67 (s, THF,
4H), 9.07 (s, COT, 8H) plus sets of signals in the aromatic region
ranging from 6.31 to 8.03 ppm (11H). 1H NMR (C4D8O, 400 MHz,
25 °C): δ -1.38 (br s, OMe, 6H), 10.37 (s, COT, 8H) plus sets of
signals in the aromatic region ranging from 6.94 to 7.55 ppm (11H).
We note that the chemical shift of the signal corresponding to the
(Dpp)2SmCl(µ-Cl)Li(THF)3 (1). Reaction of 2 equiv of
DppLi with 1 equiv of SmCl3 in tetrahydrofuran solution at
ambient temperature produces a heterobimetallic bis(ter-
phenyl) compound of composition (Dpp)2SmCl(µ-Cl)Li-
(THF)3 (1). It is noteworthy that 1 is also obtained using a
1:1 stoichiometry of reagents, leaving 0.5 equiv of unreacted
SmCl3 as a side product. The crude product of compound 1
Inorganic Chemistry, Vol. 42, No. 23, 2003 7589

Rabe et al.
an Sm(1)-Cl(1)-Li(1) angle of 134.07(17)° while atom
Cl(2) is a terminal chloride ligand. The bridging Sm-Cl
distance [2.6673(9) Å] is only slightly longer than the
terminal one [2.6174(9) Å]. The lithium atom in 1 is four-
coordinate with a Li...Cl distance of 2.329(6) Å and Li-O
distances ranging from 1.913(7) to 1.947(7) Å. Further
interatomic distances and angles of 1 can be derived from
Table 2.
DppSmCOT(µ-Cl)Li(THF)3 (2). The one-pot reaction of
1 equiv of K2COT and 1 equiv of SmCl3 in tetrahydrofuran
at room temperature followed by addition of 1 equiv of
DppLi yields tetrahydrofuran-soluble DppSmCOT(µ-Cl)Li-
(THF)3 (2). The dark red compound 2 can also be prepared
by an alternative route, i.e. reaction of (Dpp)2SmCl(µ-Cl)-
Li(THF)3 and 1 equiv of K2COT in tetrahydrofuran. Interest-
ingly, the tris(tetrahydrofuran)lithium chloride moiety of 1
is retained in the course of the reaction, while 1 equiv of
KCl and 1 equiv of “KDpp” are eliminated. We note that
previous studies by Power et al. have shown that terphenyl
compounds of the heavier alkali metals sodium and potas-
sium are very reactive and undergo C-H activation by
metalation of solvents yielding the protonated terphenyl.25
The first route appears to be the method of choice because
compound 2 is obtained in higher yield. Furthermore, no
purification of the intermediate 1 is necessary. As a side
product, varying amounts of the known bis-COT sandwich
compound [Li(THF)3{µ-(η2:η8-COT)}Sm(η8-COT)]26 are
obtained in both cases, which is tetrahydrofuran soluble and
is formed by a ligand redistribution reaction in which the
terphenyllithium salt solely functions as the lithium source.
The Sm-C(ipso) distance in 2 [2.509(3) Å; Figure 2] is
only slightly longer than the two Sm-C(ipso) distances in
1 [2.476(3) and 2.489(3) Å, respectively]. As was found in
1, besides the Sm-C(ipso) distance there are secondary
Sm-C(terphenyl) interactions with two ortho carbon atoms
of phenyl rings in the 2,6-position, namely atom C(16)
[3.211(3) Å] and atom C(26) [3.223(3) Å]. The dihedral
angles between the central phenyl ring of the Dpp ligand
and the aryl rings in the 2,6-position are 42.9° (C(15-20))
and 36.4° (C(21-26)). The Sm-C(COT) distances (aver-
age: 2.62 Å) are within the expected range.26 The Sm-Cl-
Li angle in 2 of 134.40(17)° can favorably be compared with
the corresponding angle in 1, while the bridging Sm-Cl
distance of 2.7414(9) Å is slightly longer than the value
found in 1 [2.6673(9) Å]. Further interatomic distances and
angles of 2 can be derived from Table 2.
Figure 1. ORTEP diagram of (Dpp)2SmCl((µ-Cl)Li(THF)3 (1), showing
the atom labeling scheme. Thermal ellipsoids are at the 30% level.
Disordered carbon atoms as well as hydrogen atoms were omitted for clarity.
slowly dissolves in toluene after dropwise addition of small
amounts of tetrahydrofuran. Cooling of a toluene/tetra-
hydrofuran solution to -30 °C and repeated layering with
small portions of hexanes (over several days) results in
almost complete crystallization of yellow 1. Analytically pure
1 is only sparingly soluble in toluene but quite soluble in
tetrahydrofuran. Solutions of 1 in toluene or tetrahydrofuran
at ambient temperature decompose slowly forming a colorless
precipitate (presumably lithium chloride). We note that we
failed to isolate any characterizable material from the
remaining mother liquor. On the other hand, solutions of
compound 1 show no visible signs of decomposition in both
solvents at -30 °C, even over prolonged time periods.
The molecular structure of 1 (Figure 1) shows a samarium
atom surrounded by two σ-bonded Dpp ligands and two
chlorine atoms. In contrast to 1 all previously structurally
characterized samarium terphenyl compounds were mono-
substituted.5,7,8 The Sm-C(ipso) distances [Sm-C(1) )
2.476(3) Å; Sm-C(19) ) 2.489(3) Å] are somewhat shorter
than the value found in the six-coordinate mono(terphenyl)
compound DmpSmCl2(N-MeIm)2THF [2.536(7) Å],7 as one
would expect in light of the lower coordination number at
the metal atom in 1. The coordination geometry about the
metal atom can best be described as a distorted tetrahedron
with interligand angles ranging from 99.00(3)° [Cl(1)-Sm-
(1)-Cl(2)] to 124.45(7)° [C(19)-Sm(1)-Cl(1)]. Besides the
two Sm-C(ipso) distances the next closest Sm-C distances
are to two ortho carbon atoms of phenyl rings in the 2,6-
position belonging to different terphenyl moieties, namely
atom C(36) [3.127(3) Å] and atom C(14) [3.151(3) Å]. As
a consequence, both Dpp ligands are slightly tilted, as can
be seen by inspecting the Sm(1)-C(ipso)-C(ortho) angles
[124.9(2) and 116.7(2)° for the Dpp ligand containing atom
C(1), 123.46(18)° and 118.14(19)° for the other]. The
C(ipso)-C(ortho)-C(ipso′) angles are 119.2(3) and
117.9(2)° for the Dpp ligand containing atom C(1)
[118.5(2) and 116.9(2)° for the other Dpp moiety]. The four
dihedral angles between the central phenyl rings of the two
Dpp ligands and the aryl rings in the 2,6-position are within
a narrow range [40.8° (C(7-12)) and 42.6° (C(13-18)) for
the Dpp ligand containing atom C(1), 39.3° (C(25-30)) and
42.5° (C(31-36)) for the other]. Atom Cl(1) is bridging with
DmpSm(THF)COT (3) and DanipSm(THF)COT (4).
Similar to the preparation of 2, the toluene-soluble Dmp-
based compound 3 can be prepared from the one-pot reaction
of K2COT, SmCl3, and DmpLi in tetrahydrofuran at ambient
temperature. An alkali halide-free, neutral compound is
obtained with the samarium atom being complexed by one
molecule of tetrahydrofuran. We note that our attempts to
reverse the order of addition of reagents resulted in exclusive
formation of the known bis-COT sandwich compound
(25) Niemeyer, M.; Power, P. P. Organometallics 1997, 16, 3258.
(26) Wetzel, T. G.; Dehnen, S.; Roesky, P. W. Organometallics 1999, 18,
3835.
7590 Inorganic Chemistry, Vol. 42, No. 23, 2003

Terphenyl Cyclooctatetraenyl Compounds of Samarium
Table 2. Comparison of Selected Interatomic Separations (Å) and Angles (deg) of 1-4a
param
1
2
3
4
Sm-C(ipso)
2.476(3) [C(1)]
2.489(3) [C(19)]
2.509(3)
2.529(7)
2.543(3)
Sm-C(COT)
2.597(4) [C(6)]
2.602(4) [C(5)]
2.603(4) [C(3)]
2.611(4) [C(2)]
2.616(4) [C(7)]
2.616(4) [C(4)]
2.661(4) [C(1)]
2.663(4) [C(8)]
1.889(7)
2.570(10) [C(8)]
2.585(9) [C(7)]
2.604(9) [C(5)]
2.606(10) [C(1)]
2.609(9) [C(6)]
2.610(10) [C(4)]
2.636(11) [C(2)]
2.673(10) [C(3)]
1.885(10)
2.631(3) [C(6)]
2.641(3) [C(5)]
2.641(3) [C(4)]
2.660(3) [C(7)]
2.672(3) [C(3)]
2.703(3) [C(8)]
2.721(3) [C(2)]
2.759(3) [C(1)]
1.948(7)
Sm-Cnt
Sm-Cl
2.6174(9) [Cl(2)]
2.6673(9) [Cl(1)]
2.7414(9)
Sm-O
2.444(5)
2.535(2) [O(3)]
2.5436(19) [O(2)]
2.576(2) [O(1)]
Li-Cl
Li-O
2.329(6)
2.327(7)
1.913(7) [O(3)]
1.923(7) [O(2)]
1.947(7) [O(1)]
1.904(7) [O(1)]
1.916(7) [O(3)]
1.921(7) [O(2)]
Sm-Cipso-Cortho
Cipso-Cortho-Cipso
116.7(2) [C(6)]
124.9(2) [C(2)]
118.14(19) [C(24)]
123.46(18) [C(20)]
117.9(2) [C(13)]
119.2(3) [C(7)]
116.9(2) [C(31)]
118.5(2) [C(25)]
119.2(2) [C(14)]
121.3(2) [C(10)]
108.7(5) [C(10)]
136.0(6) [C(14)]
122.30(19) [C(10)]
123.13(19) [C(14)]
117.0(3) [C(15)]
117.8(3) [C(21)]
116.0(6) [C(24)]
119.1(6) [C(15)]
119.8(3) [C(15)]
120.5(3) [C(22)]
Cnt-Sm-C(ipso)
Cnt-Sm-O
132.2(2)
141.6(4)
122.4(4)
124.2(4)
115.6(2) [O(3)]
127.0(2) [O(1)]
129.3(2) [O(2)]
a Cnt ) centroid.
that toluene solutions of 4 show a pronounced tendency at
room temperature to decompose forming the above-
mentioned anionic COT sandwich compound, which pre-
cipitates as an orange-brown powder. Additionally, it needs
to be mentioned that our previous attempts to synthesize a
mixed terphenyl COT compound using lanthanide ions
smaller than samarium failed. In all cases an anionic bis-
COT sandwich compounds was obtained as the only isolable
product.27,28
The molecular structures of both 3 and 4 (Figures 3 and
4) are comprised of one η8-bonded COT ligand and one
σ-bonded terphenyl moiety, as well as a tetrahydrofuran
ligand. While in all compounds reported in this paper the
terphenyl moieties are not or only slightly tilted, the Dmp
ligand in 3 is considerably tilted with Sm-C(ipso)-C(ortho)
angles of 108.7(5)° [C(10)] and 136.0(6)° [C(14)]. In
addition, besides the Sm-C(ipso) distance of 2.529(7) Å the
next closest Sm...C(terphenyl) distances are to three phenyl
carbon atoms of one mesityl ring, namely 3.071(7) Å [C(24)],
3.243(7) Å [C(25)], and 3.269(7) Å [C(10)], which docu-
ments the presence of a weak allyl-like electrostatic interac-
tion between the samarium atom, one of the ortho carbon
atoms of the central phenyl ring, and the ipso and one of
the ortho carbon atoms of one of the mesityl rings. A similar
asymmetric but still different arrangement of the Dmp ligand
was previously observed in the molecular structure of Cp2-
Figure 2. ORTEP diagram of DppSmCOT(µ-Cl)Li(THF)3 (2), showing
the atom labeling scheme. Thermal ellipsoids are at the 30% level.
Disordered carbon atoms as well as hydrogen atoms were omitted for clarity.
[Li(THF)3{µ-(η2:η8-COT)}Sm(η8-COT)],26 as was observed
in the case of compound 2.
The Danip-based compound 4 is prepared as well in a one-
pot synthesis. As was found in the case of compound 3, a
toluene-soluble neutral tetrahydrofuran solvate and not an
anionic “ate” complex is obtained. We were able to
demonstrate that in the case of the synthesis of compound 4
the order of addition of reagents can actually be reversed. 4
can be separated from small amounts of tetrahydrofuran-
soluble side-product [Li(THF)3{µ-(η2:η8-COT)}Sm(η8-COT)]
by extraction of the crude product with toluene. We note
(27) Rabe, G. W.; Zhang-Presse, M.; Yap, G. P. A. Inorg. Chim. Acta 2003,
348, 245.
(28) Rabe, G. W.; Zhang-Presse, M.; Golen, J. A.; Rheingold, A. L. Acta
Crystallogr. 2003, E59, m255.
Inorganic Chemistry, Vol. 42, No. 23, 2003 7591

Rabe et al.
29)), respectively. Further interatomic distances and angles
of 3 can be derived from Table 2.
In the molecular structure of compound 4 for the first time
the Danip ligand is seen to adopt the meso form, presumably
as a result of steric crowding at the metal atom, while in all
previously reported Danip-based terphenyllanthanide com-
pounds the Danip ligand adopts the chiral (racemic) d,l
form.5,8 This view is further supported by the observation
of both Sm-C(ipso)-C(ortho) angles being larger than 120°
[122.30(19) and 123.13(19)°, respectively]. The dihedral
angles between the central phenyl ring and the two aryl rings
in the 2,6-position of 50.2° [C(15-20)] and 48.7° [C(22-
27)], respectively, are considerably larger than the corre-
sponding angles in complexes 1-3. Both the Sm-C(ipso)
[2.543(3) Å] and the Sm-Cnt distance [1.948(7) Å] are
noticeably longer than the same distances in 2 and 3 (see
Table 2). Also, the Sm-O(THF) distance in Danip-based 4
[2.535(2) Å] is considerably longer than the same distance
in the Dmp-based complex 3 [2.444(5) Å]. An observation
that can be explained by the higher coordination number at
the metal atom in 4. Further interatomic distances and angles
of 4 can be derived from Table 2.
Figure 3. ORTEP diagram of DmpSm(THF)COT (3), showing the atom
labeling scheme. Thermal ellipsoids are at the 30% level. Hydrogen atoms
were omitted for clarity.
Conclusions
Our work demonstrates that a number of novel terphenyl-
based lanthanide COT compounds of the element samarium
are accessible by simple straightforward salt metathesis
reaction starting from K2COT, SmCl3, and the corresponding
terphenyllithium salt. The compounds are obtained either as
anionic “ate” complexes (1 and 2) or as neutral tetrahydro-
furan solvates (3 and 4). In 4 the Danip ligand adopts the
meso form, while all previously reported Danip-based
lanthanide compounds show the chiral (racemic) d,l confor-
mation. Also, the synthesis and structural characterization
of the first bis(terphenyl) compound of a trivalent lanthanide
element is reported. Our work gives more insight into
structural aspects as well as the reactivity of terphenyl-based
lanthanide compounds. Further reactivity studies with these
compounds are currently being undertaken.
Figure 4. ORTEP diagram of DanipSm(THF)COT (4), showing the atom
labeling scheme. Thermal ellipsoids are at the 30% level. Hydrogen atoms
were omitted for clarity.
SmDmp, which shows Sm-C(ipso) distances of 2.560(8)
and 2.536(9) Å for both independent molecules.29 However,
other than in the molecular structure of 3, in the case of the
molecular structure of Cp2SmDmp the allyl-type arrangement
is between the samarium atom and the ipso carbon atom and
the two ortho carbon atoms of one of the mesityl rings.29
Other than in the molecular structures of 1 and 2, in 3 the
central phenyl ring of the terphenyl moiety and the two
mesityl rings are arranged in an almost rectangular fashion
with dihedral angles of 86.5° (C(15-20)) and 79.5° (C(24-
Acknowledgment. The authors are thankful for financial
support from the Deutsche Forschungsgemeinschaft and the
Fonds der Chemischen Industrie. G.W.R. thanks the Deut-
sche Forschungsgemeinschaft for the award of a Heisenberg
stipend.
Supporting Information Available: X-ray crystallographic files
in CIF format for the structures of (Dpp)2SmCl(µ-Cl)Li(THF)3 (1),
DppSmCOT(µ-Cl)Li(THF)3 (2), DmpSm(THF)COT (3), and Da-
nipSm(THF)COT (4). This material is available free of charge via
the Internet at http://pubs.acs.org.
(29) Niemeyer, M.; Hauber, S.-O. Z. Anorg. Allg. Chem. 1999, 625, 137.
IC0301775
7592 Inorganic Chemistry, Vol. 42, No. 23, 2003