Lanthanum tribenzyl complexes as convenient starting materials for organolanthanum chemistry

Article abstract of DOI:10.1021/om060262v

Simple tribenzyl complexes of lanthanum, [La(CH₂C ₆H₄-4-R)₃(THF)₃] (R = H (1a), Me (1b)), were prepared in a remarkably straightforward fashion from LaBr ₃(THF)₄ and potassium benzyl reagents. Single-crystal X-ray diffraction revealed a fac arrangement of the three THF ligands and η² binding of the benzyl groups. These compounds are convenient precursors to other organolanthanum complexes. Reaction of la with the amidine ArN=CPhNHAr (Ar = 2,6-Prⁱ₂C₆H₃) affords the corresponding mono(amidinate) dibenzyl derivative 2. Complex 1b reacts with LiCH₂C₆H₄-4-Me to give the THF-free anion [La(CH₂C₆H₄-4-Me)₄] ^- (3). Reactions of 1 with 1 or 2 equiv of [PhNMe₂H] [B(C₆X₅)₄] (X = H, F) generate the corresponding mono- and dicationic benzyl species [La(CH₂C ₆H₄-4-R)₂(THF)₄]⁺ (4) and [La(CH₂C₆H₄-4-R)(THF)₆] ²⁺ (5), which were structurally characterized. Scouting ethylene polymerization experiments indicate that these species are only modestly active catalysts but suggest that the monocationic dibenzyl species is more efficient. Both neutral and cationic lanthanum benzyl complexes effect the catalytic intramolecular hydroamination/cyclization of 2,2-dimethyl-4-pentenylamine. It was also observed that polycationic La species without ancillary ligands effectively catalyze the isomerization of the substrate to (E)-2,2-dimethyl-3- pentenylamine.

Full text of DOI:10.1021/om060262v

3454
Organometallics 2006, 25, 3454-3462
Lanthanum Tribenzyl Complexes as Convenient Starting Materials
for Organolanthanum Chemistry
Sergio Bambirra, Auke Meetsma, and Bart Hessen*
Center for Catalytic Olefin Polymerization, Stratingh Institute for Chemistry and Chemical Engineering,
UniVersity of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands
ReceiVed March 23, 2006
Simple tribenzyl complexes of lanthanum, [La(CH2C6H4-4-R)3(THF)3] (R ) H (1a), Me (1b)), were
prepared in a remarkably straightforward fashion from LaBr3(THF)4 and potassium benzyl reagents. Single-
crystal X-ray diffraction revealed a fac arrangement of the three THF ligands and η2 binding of the
benzyl groups. These compounds are convenient precursors to other organolanthanum complexes. Reaction
of 1a with the amidine ArNdCPhNHAr (Ar ) 2,6-Pri2C6H3) affords the corresponding mono(amidinate)
dibenzyl derivative 2. Complex 1b reacts with LiCH2C6H4-4-Me to give the THF-free anion [La(CH2C6H4-
4-Me)4]- (3). Reactions of 1 with 1 or 2 equiv of [PhNMe2H][B(C6X5)4] (X ) H, F) generate the
corresponding mono- and dicationic benzyl species [La(CH2C6H4-4-R)2(THF)4]+ (4) and [La(CH2C6H4-
4-R)(THF)6]2+ (5), which were structurally characterized. Scouting ethylene polymerization experiments
indicate that these species are only modestly active catalysts but suggest that the monocationic dibenzyl
species is more efficient. Both neutral and cationic lanthanum benzyl complexes effect the catalytic
intramolecular hydroamination/cyclization of 2,2-dimethyl-4-pentenylamine. It was also observed that
polycationic La species without ancillary ligands effectively catalyze the isomerization of the substrate
to (E)-2,2-dimethyl-3-pentenylamine.
followed by addition of LH.4 Nevertheless, readily accessible
yet reactive homoleptic trialkyl complexes of these metals would
be very useful.5 Early attempts to prepare homoleptic tribenzyl
complexes of Nd6 and La7 were reported but were inconclusive
as to the existence of these species. For the former, decomposi-
tion to the alkylidene [PhCH2NddCHPh] was proposed, whereas
for the latter decomposition to form [PhCH2La(H)OCHdCH2-
(THF)2] was suggested. Very recently, Harder reported the
synthesis of rare-earth tribenzyl complexes bearing intramo-
lecularly coordinating groups on the aryl moiety.8 Here we
describe a straightforward synthesis of the neutral, salt-free
lanthanum tribenzyl complexes La(CH2Ph)3(THF)3 and La(CH2-
Ph-4-Me)3(THF)3. With several examples, their use as precursors
to other neutral and cationic lanthanum benzyl complexes is
illustrated. Their catalytic performance in ethylene polymeri-
zation and intramolecular hydroamination/cyclization was also
briefly explored.
Introduction
Homoleptic trialkyl complexes of the type M(CH2SiMe3)3-
(THF)n (n ) 2, 3) of the group 3 metals and lanthanides1 are
valuable starting materials for organo-rare-earth-metal chem-
istry.2 They are readily prepared from the corresponding metal
trihalides and are sufficiently thermally stable to be handled
conveniently. Unfortunately, they are only available for the rare-
earth metals in the small to medium size range (Sc, Y, and Ln
) Lu-Dy). For the larger lanthanide metals, such as Nd and
La, salt-free neutral species of this type are only available for
very large alkyl groups, in particular CH(SiMe3)2,3 which
hamper further reactivity. Recently we showed that for these
metals various (L)Ln(CH2SiMe3)2 species (L ) monoanionic
ligand) can be obtained in moderate yield from in situ
procedures, reacting Ln trihalides with 3 equiv of Me3SiCH2Li
* To whom correspondence should be addressed. E-mail:
B.Hessen@rug.nl.
(1) M(CH2SiMe3)3(THF)n: (a) Lappert, M. F.; Pearce, R. J. Chem. Soc.,
Chem. Commun. 1973, 126. (b) Schumann, H.; Mu¨ller, J. J. Organomet.
Chem. 1978, 146, C5. (c) Schumann, H.; Mu¨ller, J. J. Organomet. Chem.
1979, 169, C1. (d) Atwood, J. L.; Hunter, W. E.; Rogers, R. D.; Holton, J.;
McMeeking, J.; Pearce, R.; Lappert, M. F. J. Chem. Soc., Chem. Commun.
1978, 140. (e) Niemeyer, M. Acta Crystallogr. 2001, E57, m553. (f) Evans,
W. J.; Brady, J. C.; Ziller, J. W. J. Am. Chem. Soc. 2001, 123, 7711. (g)
Arndt, S.; Spaniol, T. P.; Okuda, Chem. Commun. 2002, 896. (h) Schumann,
H.; Freckmann, D. M. M.; Dechert, S. Z. Anorg. Allg. Chem. 2002, 628,
2422. (i) Arndt, S.; Spaniol, T. P.; Okuda, J. Angew. Chem., Int. Ed. 2003,
42, 5075.
(2) (a) Booij, M. Kiers, N. H.; Heeres, H. J.; Teuben, J. H. J. Organomet.
Chem. 1989, 364, 79. (b) Deacon, G. B.; Forsyth, C. M.; Patalinghug, W.
C.; White, A. H.; Deitrich, A.; Schumann, H. Aust. J. Chem. 1992, 45,
567. (c) Mu, Y.; Piers, W. E.; MacQuarrie, D. C.; Zaworotko, M. J.; Young,
V. G., Jr. Organometallics 1996, 15, 2720. (d) Hultzsch, K. C.; Okuda, J.;
Voth, P.; Beckerle, K.; Spaniol, T. P. Organometallics 2000, 19, 228. (e)
Emslie, D. J. H.; Piers, W. E. Parvez, M. Dalton Trans. 2003, 2615.
(3) (a) Ln[CH(SiMe3)2]3 (Ln ) La, Sm): Hitchcock, P. B.; Lappert, M.
F.; Smith, R. G.; Bartlett, R. A.; Power, P. P. J. Chem. Soc. Chem. Commun.
1988, 1007. (b) Ln[CH(SiMe3)2]3 (Ln ) Y, Lu): Schaverien, C. J.; Orpen,
A. G. Inorg. Chem. 1991, 30, 4968.
Results and Discussion
Synthesis and Characterization of Tribenzyllanthanum
Complexes. Reaction of LaBr3(THF)4 with 3 equiv of the
potassium benzyls KCH2C6H4-4-R (R ) H, Me)9 in THF
solvent, followed by centrifugation and decantation (to remove
(4) (a) Tazelaar, C. G. J.; Bambirra, S.; Van Leusen, D.; Meetsma, A.;
Hessen, B.; Teuben, J. H. Organometallics 2004, 23, 936. (b) Bambirra,
S.; Bouwkamp, M. W.; Meetsma, A.; Hessen, B. J. Am. Chem. Soc. 2004,
126, 9183.
(5) For reactive homoleptic triallyl complexes see: (a) Sa´nchez-Barba,
L. F.; Hughes, D.; Simon, L.; Humphrey, M.; Bochmann, M. Organome-
tallics 2005, 24, 3792. (b) Taube, R.; Windisch, H.; Maiwald, S.; Hemling,
H.; Schumann, H. J. Orgamomet. Chem. 1996, 513, 49.
(6) Chigir, N. N.; Guzman, I. S.; Sharaev, O. K.; Tinyakova, E. I.;
Dolgoplosk, B. A. Dokl. Akad. Nauk SSSR 1982, 263, 375.
(7) Thiele, K.-H.; Unverhau, K.; Geitner, M.; Jakob, K. Z. Anorg. Allg.
Chem. 1987, 548, 175.
(8) Harder, S. Organometallics 2005, 24, 373.
10.1021/om060262v CCC: $33.50 © 2006 American Chemical Society
Publication on Web 06/09/2006

Lanthanum Tribenzyl Complexes
Scheme 1
Organometallics, Vol. 25, No. 14, 2006 3455
Figure 2. Top view of the molecular structure of [La(CH2C6H4-
4-Me)3(THF)3] (1b), with 50% probability ellipsoids. Selected
interatomic distances (Å) and angles (deg): La-C(1) ) 2.6163(19),
La-C(2) ) 2.961(2), La-C(9) ) 2.627(2), La-C(10) ) 2.989-
(2), La-C(17) ) 2.634(2), La-C(18) ) 2.960(2), La-O(1) )
2.7067(14), La-O(2) ) 2.6971(16), La-O(3) ) 2.6732(16); La-
C(1)-C(2) ) 88.76(12), La-C(8)-C(9) ) 89.57(12), La-C(17)-
C(18) ) 87.96(11), O(1)-La-O(2) ) 74.97(4), O(1)-La-O(3)
) 71.96(4), O(2)-La-O(3) ) 75.27(5).
the amidine ArNdCPhNHAr (Ar ) 2,6-Pri2C6H3)11 in THF
solvent generates cleanly the monoamidinate dibenzyl com-
plexes [PhC(NAr)2]La(CH2C6H4-R)2(THF)n (R ) H, Me) with
elimination of 1 equiv of toluene or p-xylene, respectively
(Scheme 2). A preparative-scale reaction of 1a with ArNd
CPhNHAr, followed by crystallization from hexane/THF, af-
forded [PhC(NAr)2]La(CH2C6H5)2(THF) (2) in 70% isolated
yield. A crystal structure determination of 2 (Figure 3; crystal
data and collection parameters are given in Table 4) shows that
in this complex one of the two remaining benzyl groups is again
η2-bound to the metal, with a La-C(39)-C(40) angle of
83.3(1)°. The other, with a La-C(32)-C(33) angle of 87.0(3)°,
has a phenyl group that is significantly tilted, suggesting an
η3-like bonding, with a short La-Co distance (La-C(34)) of
3.030(3) Å. Such an η3 coordination mode has been observed
before in lanthanide metallocene benzyl complexes.12 Probably
in response to the ηn bonding of the benzyl groups, complex 2
only contains a single coordinated THF molecule, whereas two
were found in the related bis((trimethylsilyl)methyl) complex
[PhC(NAr)2]La(CH2SiMe3)2(THF)2.4b The room-temperature
13C NMR spectrum of 2 in C6D6 shows a single resonance for
the La-CH2 groups at δ 69.5 ppm (1JCH ) 136 Hz). In THF-
Figure 1. Molecular structure of [La(CH2Ph)3(THF)3] (1a), with
50% probability ellipsoids. Selected interatomic distances (Å) and
angles (deg): La-C(1) ) 2.648(2), La-C(2) ) 2.968(2), La-
C(8) ) 2.649(2), La-C(9) ) 2.972(2), La-C(15) ) 2.639(2), La-
C(16) ) 2.994(2), La-O(1) ) 2.6779(16), La-O(2) ) 2.6630(15),
La-O(3) ) 2.6497(16); La-C(1)-C(2) ) 88.05(13), La-C(8)-
C(9) ) 88.09(13), La-C(15)-C(16) ) 89.53(14), O(1)-La-O(2)
) 72.90(5), O(1)-La-O(3) ) 74.59(5), O(2)-La-O(3) ) 74.06(5).
the KBr) and subsequent crystallization from THF/hexane,
afforded La(CH2Ph)3(THF)3 (1a) and [La(CH2C6H4-4-Me)3-
(THF)3] (1b) as analytically pure orange-yellow crystals in 57%
and 45% isolated yields, respectively (Scheme 1). A crystal
structure determination of 1a (Figure 1; crystal data and
collection parameters are given in Table 4) revealed that the
metal center is bound to three η2-benzyl groups, with La-CH2-
Cipso angles of 88.0-89.5(1)°, and three THF molecules. The
latter are located in a facial arrangement on one side of the
molecule, with O-La-O angles of 72.90-74.59(5)°. The
p-tolyl derivative 1b is essentially isostructural with 1a, with
comparable bond lengths and angles around the lanthanum
center (Figure 2). Due to the η2 coordination of the benzyl
ligands to lanthanum, the structures of 1a,b deviate from the
octahedral geometry observed for [Y(CH2SiMe3)3(THF)3].1f The
latter readily loses one THF molecule to adopt the trigonal-
bipyramidal geometry more common for the small- to medium-
sized group 3 and lanthanide members.10
d8 solvent, this resonance is observed at δ 71.1 ppm (JCH
)
131 Hz). The slight, but significant, reduction of the latter 1JCH
coupling constant relative to that in benzene may indicate
(reversible) binding of an additional THF molecule in this
solvent.
Reaction of the tribenzyl complex 1b with 1 equiv of
LiCH2C6H4-4-Me in THF generates the ionic compound [La-
(CH2C6H4-4-Me)4][Li(THF)4] (3) (Scheme 2), obtained by
crystallization from THF/hexane as red-orange crystals in 52%
yield. The room-temperature solution NMR spectra of 3 are
Complexes 1a,b are rather poorly soluble in hydrocarbon
solvents but quite soluble in THF. In THF-d8, both compounds
show one singlet 1H NMR resonance for the benzyl methylene
protons, suggesting an averaged structure in solution of at least
C
3V symmetry. The benzyl methylene 13C NMR resonances are
(11) Ogata, S.; Mochizuki, A.; Kakimoto, M.-A.; Imai, Y. Bull. Chem.
Soc. Jpn. 1986, 59, 2171. (b) Boere´, R. T.; Klassen, V.; Wolmersha¨user,
G. J. Chem. Soc., Dalton Trans. 1998, 4147. (c) Bambirra, S.; van Leusen,
D.; Meetsma, A.; Hessen, B.; Teuben, J. H. Chem. Commun. 2003, 522.
(12) For η3-bound benzyls to Ln see: (a) Booij, M.; Meetsma, A. Teuben,
J. H. Organometallics 1991, 10, 3246. (b) Evans, W. J.; Perotti, J. M.;
Ziller, J. W. J. Am. Chem. Soc. 2005, 127, 3894. For η1-bound benzyls to
Ln see: (c) Mandel, A.; Magull, J. Z. Anorg. Allg. Chem. 1996, 622, 1913.
(d) Mandel, A.; Magull, J. Z. Anog. Allg. Chem. 1997, 623, 1542. (e) Hayes,
P. G.; Piers, W. E.; Lee, L. W. M.; Knight, L. K.; Parvez, M.; Elsegood,
M. R. J.; Clegg, W. Organometallics 2001, 20, 2533.
found at δ 67.2 ppm (1JCH ) 133 Hz; 1a) and δ 66.0 ppm (1JCH
) 131 Hz; 1b).
Reactivity with an Amidine and a Lithium Benzyl Re-
agent. NMR tube reactions of the tribenzyl complexes 1a,b with
(9) Prepared according to the procedure described by: Schlosser, M.;
Hartmann, J. Angew. Chem., Int. Ed. Engl. 1973, 12, 508.
(10) Emslie, D. J. H.; Piers, W. E. Parvez, M. Organometallics 2002,
21, 4226.

3456 Organometallics, Vol. 25, No. 14, 2006
Bambirra et al.
Scheme 2
Figure 4. Molecular structure of [La(CH2C6H4-4-Me)4][Li(THF)4]
(3), with 50% probability ellipsoids. The cation is omitted for clarity.
Selected interatomic distances (Å) and angles (deg): La(1)-C(11)
) 2.616(3), La(1)-C(12) ) 3.004(3), La(1)-C(19) ) 2.635(2),
La(1)-C(110) ) 2.835(2), La(1)-C(117) ) 2.658(3), La(1)-
C(118) ) 2.871(2), La(1)-C(125) ) 2.658(3), La(1)-C(126) )
2.839(2); La(1)-C(11)-C(12) ) 90.80(14), La(1)-C(19)-C(110)
) 82.78(13), La(1)-C(117)-C(118) ) 83.36(15), La(1)-C(125)-
C(126) ) 81.97(14).
Figure 3. Molecular structure of [PhC(NAr)2]La(CH2Ph)2(THF)
(2), with 50% probability ellipsoids. Selected interatomic distances
(Å) and angles (deg): La-C(32) ) 2.590(5), La-C(33) ) 2.897(5),
La-C(34) ) 3.030(3), La-C(38) ) 3.813(2), La-C(39) )
2.632(3), La-C(40) ) 2.847(5), La-C(45) ) 3.401(5), La-N(1)
) 2.497(3), La-N(2) ) 2.581(3), La-O(1) ) 2.557(3); La-
C(32)-C(33) ) 87.0(3), La-C(39)-C(40) ) 83.3(2).
simple, indicative of a symmetrically averaged structure of the
La-tetrabenzyl anion. In a comparison of the spectra of 1b and
tribenzyl complexes 1a and 1b with 1 or 2 equiv of the the
Brønsted acid [PhNMe2H][B(C6F5)4] in THF-d8 solvent generate
cleanly (as seen by NMR spectroscopy) the ionic species [La-
(CH2C6H4-R)2(THF-d8)n][B(C6F5)4] (R ) H (4a), Me (4b)) and
[La(CH2C6H4-R)(THF-d8)m][B(C6F5)4]2 (R ) H (5a), Me (5b)),
respectively, accompanied by liberation of toluene or p-xylene
and free PhNMe2.
Compounds 4 and 5 are related to the mono- and dicationic
alkyl species [Ln(CH2SiMe3)2(THF)n]+ and [Ln(CH2SiMe3)-
(THF)m]2+ of the smaller rare-earth metals (Ln ) Sc, Y, Tb-
Lu) reported by Okuda et al.1g,h The 13C NMR spectrum of 4a
shows a single resonance for the La-CH2 groups at δ 71.3 ppm
(JCH ) 134 Hz). In the dication 5a, the corresponding resonance
is found at δ 78.9 ppm (JCH ) 130 Hz).
1
3, the benzyl methylene H and 13C NMR resonances in 3 are
shifted upfield (δ 1.11 and 62.0 ppm, respectively, vs δ 1.36
1
and 66.0 ppm in 1b). The JCH coupling constant in 3 of 139
Hz is significantly larger than the 131 Hz for 1b. Single-crystal
X-ray diffraction of 3 (Figure 4; crystal data and collection
parameters are given in Table 4) shows the four benzyl ligands
in the anion to be η2-bound to the metal. A similar complex,
but with a Me3Si substituent on the 2-position of the benzyl
group, [La(CH2C6H4-2-SiMe3)4][Li(THF)4], was recently re-
ported by Harder.8 The average La-CH2 and La‚‚‚Cipso distances
in 3 of 2.64 and 2.88 Å, respectively, are somewhat shorter
than those in the more sterically congested o-SiMe3 analogue
(2.69 and 2.94 Å).
Generation and Structure of Cationic Lanthanum Benzyl
Complexes. Complexes 1a and 1b can be used as precursors
to cationic lanthanum benzyl complexes. Reactions of the
The couple 4b/5b follows the same trend in chemical shift
for the benzyl methylene groups. The La-CH2 13C NMR
resonances move downfield from 70.6 ppm (JCH ) 134 Hz) in

Lanthanum Tribenzyl Complexes
Organometallics, Vol. 25, No. 14, 2006 3457
Scheme 3
the monocation 4b to 78.0 ppm (JCH ) 130 Hz) for the dication
1
5b. This trend is also observed in the respective H NMR
spectra. The triad from the neutral 1a over the monocation 4a
to the dication 5a displays the La-CH2 resonances at δ 1.41,
1.74, and 1.85 ppm, respectively, in response to the increased
positive charge at the metal center. For the p-tolyl species these
chemical shifts are observed from the neutral complex 1b (1.36
ppm) via the monocation 4b (1.63 ppm) to the dication 5b (1.79
ppm). Reaction of 1a or 1b with 3 equiv of [PhNMe2H]-
[B(C6F5)4] in THF-d8 appears to generate the alkyl-free species
[La(THF)x]3+[B(C6F5)4]3-. This is based on the disappearance
of all resonances of lanthanum-bound benzyl groups and the
emergence of 3 equiv of either toluene or p-xylene, as seen by
1H NMR spectroscopy. Reaction of the dibenzyl complex 2 with
[PhNMe2H][B(C6F5)4] in THF-d8 solvent cleanly generates the
ionic species {[PhC(NAr)2]La(CH2Ph)(THF-d8)n}[B(C6F5)4] (6).
Its 13C NMR spectrum shows the remaining benzyl methylene
resonance at δ 78.2 ppm (JCH ) 130 Hz).
To facilitate the crystallization of the ionic lanthanum benzyl
species to allow single-crystal structure determinations, the
corresponding tetraphenylborate salts were prepared using the
Brønsted acid [HNMe2Ph][BPh4]. Reactions of the tribenzyl
complexes 1a,b with 1 equiv of [HNMe2Ph][BPh4] in THF
solvent at ambient temperature produce clear solutions. Cooling
these solutions to -30 °C afforded the ion pairs [La(CH2C6H4-
4-R)2(THF)4][B(C6H5)4] (R ) H (4a′), Me (4b′)) in about 70%
yield as plate-shaped crystals. Similarly, reaction of 1b with 2
equiv of [HNMe2Ph][BPh4] in THF, followed by cooling to -30
°C, afforded crystals of 5b′ in 61% yield (Scheme 3). The
corresponding parent benzyl dication 5a′ appears to be much
less soluble and precipitates as an oil that gradually solidified
upon rinsing with hexanes.
Figure 5. Molecular structure of [La(CH2Ph)2(THF)4][B(C6H5)4]
(4a′), with 50% probability ellipsoids. Selected interatomic distances
(Å) and angles (deg): La(1)-C(18) ) 2.649(4), La(1)-C(19) )
2.936(3), La(1)-C(110) ) 3.052(2), La(1)-C(11) ) 2.592(2), La-
(1)-C(12) ) 2.959(2), La(1)-C(17) ) 3.057(2), La(1)-O(11) )
2.589(2), La(1)-O(12) ) 2.584(2), La(1)-O(13) ) 2.579(2), La-
(1)-O(14) ) 2.554(2); La(1)-C(11)-C(12) ) 89.8(2), La(1)-
C(18)-C(19) ) 86.7(2), O(11)-La(1)-O(12) ) 74.78(7), O(11)-
La(1)-O(13) ) 74.63(7), O(12)-La(1)-O(13) ) 79.57(7).
1a (average La-O ) 2.664 Å). The fourth THF molecule is
located at the other side of the cation and essentially replaces
the abstracted benzyl group. The remaining two benzyl ligands
are tilted to suggest an η3 bonding mode. The two short La‚‚
‚Cortho distances are 3.057(2) and 3.052(2) Å for C(17) and
C(110), respectively. The La-CH2 bond distances in 4a′ of
2.649(4) and 2.592(2) Å are somewhat longer than those in the
seven-coordinate complexes [[P(C6H4-2-H2NMe2){CH(SiMe3)-
(SiMe2CH2)}]La(THF)4][BPh4]13 and [{PhC(NAr)2}La(CH2-
SiMe3)(THF)4][BPh4],4b where the La-CH2 bond distances are
2.485(9) and 2.510(4) Å, respectively. The multihapto bonding
The molecular structure of the cation of 4a′, [La(CH2Ph)2-
(THF)4]+, is shown in Figure 5 (crystal data and collection
parameters are given in Table 4). Three THF molecules (O11-
O13) coordinate to the lanthanum center in a facial arrangement
with La-O distances of 2.579(2)-2.589(2) Å. These La-O
bond lengths are much shorter than those in the neutral precursor
(13) Izod, K.; Liddle, S. T.; Clegg, W. Chem. Commun. 2004, 1748.

3458 Organometallics, Vol. 25, No. 14, 2006
Bambirra et al.
Table 1. Catalytic Ethylene Polymerization Experimentsa
precursor
yield (g)
activityd
10-3Mw
Mw/Mn
1b/TiBAOb
0
0
0.79
0.45
0.74
none
none
63
36
59
2/TiBAOb
1b/TiBAOb/Bc
1b/TiBAOb/2B
2/TiBAOb/Bc
338.4
367.9
89.5
9.8
9.3
14.6
a Conditions: toluene solvent (30 mL), 50 °C, 10 µmol of La, 5 bar of
ethylene pressure, 15 min run time. b 100 µmol of Al. c B ) 10 µmol of
[HNMe2Ph][B(C6F5)4]. d In units of kg of PE (mol of La)-1 h-1 bar-1
.
more soluble than 1a) with 1 or 2 equiv of the Brønsted acid
[PhNMe2H][B(C6F5)4]. Similarly, the cationic amidinate benzyl
species was generated from 2 and 1 equiv of [PhNMe2H]-
[B(C6F5)4]. All experiments were performed in the presence of
TiBAO (isobutylalumoxane, La/Al ) 1/10) at 50 °C in toluene
solvent. The results are given in Table 1. The neutral complexes
1b and 2, under the given conditions, were themselves inactive
for ethene polymerization.
Figure 6. Molecular structure of [La(CH2Ph-4Me)(THF)6]-
[B(C6H5)4]2 (5b′), with 50% probability ellipsoids. Selected inter-
atomic distances (Å) and angles (deg): La(1)-C(11) ) 2.534(3),
La(1)-C(12) ) 2.968(3), La(1)-C(17) ) 3.136(3), La(1)-O(11)
) 2.6835(19), La(1)-O(12) ) 2.588(2), La(1)-O(13) ) 2.5954(19),
La(1)-O(14) ) 2.5632(19), La(1)-O(15) ) 2.5754(19), La(1)-
O(16) ) 2.5127(19); La(1)-C(11)-C(12) ) 92.27(17), O(11)-
La(1)-O(12) ) 69.17(6), O(11)-La(1)-O(16) ) 71.58(6), O(12)-
La(1)-O(13) ) 77.39(6), O(13)-La(1)-O(15) ) 73.90(6), O(15)-
La(1)-O(16) ) 73.66(6), O(14)-La(1)-C(11) ) 150.84(8),
O(14)-La(1)-C(12) ) 163.45(8).
The cationic species derived from 1b show low activites, but
the monocationic species is clearly the more active of the two.16
The activity of the cationic amidinate benzyl species is higher
than that observed previously with the cation generated from
[PhC(NAr)2]La(CH2SiMe3)2(THF)2,4b which may be associated
with the coordination of an additional THF molecule in the latter.
The polydispersities of the polymers obtained are broad, an
indication that the ethylene polymerization behavior of these
catalysts with very large metal centers is not straightforward.
(b) Intramolecular Hydroamination/Cyclization. Another
reaction that can be efficiently catalyzed by organolanthanide
catalysts is the intramolecular hydroamination/cyclization of
aminoalkenes.17-19 Although for catalytic olefin polymerization
it has been well established that cationic catalysts generally show
higher activities than related neutral species, this situation is
not as clear-cut for the intramolecular hydroamination/cycliza-
tion reaction. The few comparative studies that have been carried
out suggest that the relative reactivity of cationic catalysts
relative to their neutral congeners is highly dependent on the
ancillary ligand system.20,21 We have compared the activities
of the various lanthanum benzyl species reported here in the
hydroamination/cyclization of the commonly used standard
substrate 2,2-dimethyl-4-pentenylamine to give 2-methyl-4,4-
dimethylpyrrolidine. The results are given in Table 2. All
cationic species were generated in situ from the listed com-
pounds by reaction with [PhNMe2H][B(C6F5)4].
of the benzyl groups in 4a′ distorts the overall geometry of the
cation relative to that in the six-coordinate yttrium dialkyl
species [Y(CH2SiMe3)2(THF)4]+, which is closer to a regular
octahedron.1h
Whereas the overall geometry of the cation in 4a′ is still
closely related to that in the parent tribenzyl 1a, this is no longer
the case for the dication in 5b′. The molecular structure of this
cation is shown in Figure 6 (crystal data and collection
parameters are given in Table 4) and can be described as a
capped pentagonal bipyramid. The structure of 5b′ is related to
that of the dicationic yttrium complex [YMe(THF)6][BPh4]2
reported by Okuda et al.,1h where the alkyl group is located in
the apical position of the pentagonal bipyramid. The ipso carbon
atom C(12) of the benzyl group and O(14) occupy the axial
positions and the benzyl methylene carbon atom C(12) then caps
the edge of two trigonal planes defined by C(12)-O(12)-O(13)
and C(12)-O(13)-O(15). The benzyl ligand is bound es-
sentially in an η2 fashion to the lanthanum center; the shortest
distance to one of the aromatic ortho carbon atoms is 3.136(8)
Å. The lanthanum-methylene carbon bond distance of 2.534-
(3) Å is the shortest La-C bond length in the series studied
here. As in the structure of 4a′, there are no obvious interactions
between the dicationic lanthanum center and the two tetraphe-
nylborate anions in the lattice.
Catalysis Studies of Neutral and Cationic Lanthanum
Benzyl Complexes. (a) Ethylene Polymerization. While
cationic alkyl complexes of the transition metals have long been
known as highly active catalysts for olefin polymerization,
related species of the rare-earth metals have only recently
become available.14 In the few comparative studies on olefin
polymerization catalysis by cationic lanthanide species that
include lanthanum derivatives, these showed very poor activities
compared to the intermediate size metals.4b,15 We have examined
the new lanthanum benzyl compounds for their activity in
ethylene polymerization. Cationic and dicationic catalysts were
generated in toluene solvent by reacting complex 1b (which is
A comparison of the neutral vs cationic amidinate lanthanum
benzyl species shows that both reactions are zeroth order in
substrate (characteristic of rate-determining intramolecular alk-
(15) (a) Hessen, B.; Bambirra, S. World Pat. WO0232909, 2002. (b)
Hessen, B.; Bambirra, S. World Pat. WO04000894, 2004.
(16) (a) For enhanced catalytic activity of dicationic Ln alkyls over the
parent monocationic species see: Ward, B. D.; Bellemin-Laponnaz, S.;
Gade, L. H. Angew. Chem., Int. Ed. 2005, 44, 1668. (b) Reference 1i.
(17) (a) Gagne´, M. R.; Marks, T. J. J. Am. Chem. Soc. 1989, 111, 4108.
(b) Gagne´, M. R.; Stern, C. L.; Marks, T. J. J. Am. Chem. Soc. 1992, 114,
275. (c) Li, Y.; Marks, T. J. J. Am. Chem. Soc. 1996, 118, 9295. (d) Li, Y.;
Marks, T. J. J. Am. Chem. Soc. 1998, 120, 1757.
(18) (a) Bu¨rgstein, M. R.; Berberich, H.; Roesky, P. W. Chem. Eur. J.
2001, 7, 3078. (b) Kim, Y. K.; Livinghouse, T. Angew. Chem., Int. Ed.
2002, 41, 3645. (c) Kim, Y. K.; Livinghouse, T.; Horino, Y. J. Am. Chem.
Soc. 2003, 125, 9560. (d) Hultzsch, K. C.; Hampel, F.; Wagner, T.
Organometallics 2004, 23, 2601.
(19) (a) Gribkov, D. V.; Hultzsch, K. C.; Hampel, F. Chem. Eur. J. 2003,
9, 4796. (b) Gribkov, D. V.; Hultzsch, K. C.; Hampel, F. J. Am. Chem.
Soc. 2006, 128, 3748.
(20) Lauterwasser, F.; Hayes, P. G.; Bra¨se, S.; Piers, W. E.; Schafer, L.
L. Organometallics 2004, 23, 2234.
(21) Bambirra, S.; Tsurugi, H.; van Leusen, D.; Hessen, B. Dalton Trans.
2006, 1157.
(14) For recent reviews see: (a) Arndt, S.; Okuda, J. AdV. Synth. Catal.
2005, 347, 339. (b) Gromada, J., Carpentier, J.-F.; Mortreux, A. Coord.
Chem. ReV. 2004, 248, 397.

Lanthanum Tribenzyl Complexes
Organometallics, Vol. 25, No. 14, 2006 3459
Table 2. Catalytic Hydroamination/Cyclization of
2,2-Dimethyl-4-pentenylamine by Neutral and Cationic
Lanthanum Benzyl Complexesa
first order in substrate and proceeds, under the chosen condi-
tions, essentially to completion in 2 h (Table 3). Isomerization
of this and related aminoalkene substrates was observed
previously as a side reaction in the nBuLi-catalyzed hydroami-
nation/cyclization and attributed to allylic deprotonation/repro-
tonation.23 In case of the La polycationic species, the strong
Lewis acidity of the metal center and the presence of amines
(substrate, product, and PhNMe2) in the reaction mixture may
combine in promoting this isomerization.
catalyst
time/h
conversnb/%
k/s-1 c
1b
10
45
99
99
99
50
35
31
e
1b/B
1b/2B
2d
0.7
1.4
0.8
23
12
10
6.21 × 10-2
3.43 × 10-2
3.85 × 10-2
5.10 × 10-4
1.88 × 10-3
e
2/Bd
3
3/1B
a Conditions: C6D5Br solvent (total volume 0.5 mL), 50 °C, 10 µmol of
catalyst and [PhNMe2H][B(C6F5)4] (B) activator where appropriate, 1.0
mmol of substrate. b Determined by 1H NMR. c Over the first 50%
conversion. d In C6D6 solvent. e Not determined, due to the poor solubility
of the catalyst.
Conclusions
The lanthanum tribenzyl complexes 1 provide easily prepared
neutral and salt-free homoleptic trialkyl complexes that are
sufficiently reactive to serve as convenient starting materials
for organolanthanum chemistry. Reactions with organic mol-
ecules containing active protons can provide derivatives with
anionic ancillary ligands, and solvated cationic benzyl deriva-
tives can be obtained by reaction with ammonium salts. These
lanthanum benzyl species are active for some of the best known
reactions catalyzed by rare-earth-metal compounds (ethene
polymerization, hydroamination/cyclization).
Scheme 4
As the synthesis of salt-free rare-earth organometallics is
usually most problematic for the largest metal, lanthanum, it is
likely that related tribenzyl species will also be readily available
for the smaller sized rare-earth metals. They should provide a
convenient starting point for studies addressing the effect of
rare-earth-metal ionic radius on reactivity.
Experimental Section
ene insertion into the metal-amide bond; Scheme 4). The
cationic species is nearly 2 orders of magnitude slower than
the neutral catalyst. This observation is similar to that made by
us on the related amidinate ((trimethylsilyl)methyl)yttrium
system.21 Nevertheless, although the Y and La neutral catalysts
display similar activities, the cationic La catalyst is 3 times faster
than its analogue with the smaller metal Y.
Although the activity of the neutral tribenzyl 1b was difficult
to quantify due to its poor solubility,22 the mono- and dicationic
derivatives showed good activities (comparable to that of the
neutral amidinate catalyst). The monocationic system is nearly
twice as active as the dicationic derivative.
As the tribenzyl complex 1b contains three coordinated THF
molecules, we attempted to use the anionic tetrabenzyl complex
3 to generate unsolvated lanthanum benzyl cations by reaction
with the appropriate amounts of [PhNMe2H][B(C6F5)4]. Com-
pound 3 itself is moderately active, and the intrinsic activity of
the derived neutral species, like that of 1b, was difficult to
determine due to poor solubility. Interestingly, the combination
of 3 with 2 equiv of [PhNMe2H][B(C6F5)4] resulted in relatively
rapid conversion of the substrate, but yielded a 1:2 mixture of
2-methyl-4,4-dimethylpyrrolidine and (E)-2,2-dimethyl-3-pen-
tenylamine, the product of double-bond isomerization of the
substrate.
General Considerations. All experiments were carried out under
an inert atmosphere of purified N2 using standard Schlenk and
glovebox techniques, unless mentioned otherwise. Toluene, pentane,
diethyl ether, and THF were distilled from Na or Na/K alloy before
use or purified by percolation under a nitrogen atmosphere over
columns of alumina, molecular sieves, and supported copper oxygen
scavenger (BASF R3-11). Benzene-d6 and THF-d8 were dried over
Na/K alloy and vacuum-transferred before use. Bromobenzene-d5
was degassed and dried over CaH2. KCH2Ph-4-R (R ) H, Me)9
and [PhC(N-2,6-Pri2C6H3)2]H24 were prepared according to pub-
lished procedures. [PhNMe2H][B(C6F5)4] (Strem) was used as
purchased. TIBAO was prepared by careful partial hydrolysis of
Bui3Al (Witco) in toluene.25 For the polymerization experiments,
the toluene solvent (Aldrich anhydrous, 99.5%) as well as the ethene
(AGA, polymer grade) were passed over columns of oxygen
scavenger (BASF R3-11) and molecular sieves (4 Å) before being
passed to the reactor. NMR spectra were recorded on Varian Unity
500, VXR 300, and Gemini 200 spectrometers. Gel permeation
chromatography (GPC) analysis of the polyethylene was carried
out by A. Jekel (University of Groningen) on a Polymer Labora-
tories Ltd. (PL-GPC210) chromatograph using 1,2,4-trichloroben-
zene (TCB) as the mobile phase at 150 °C. Elemental analyses
were performed at the Microanalytical Department of H. Kolbe
(Mu¨lheim an der Ruhr).
Synthesis of K(CH2Ph-4-Me). To a suspension of potassium
tert-butoxide (5.6 g, 50 mmol) in xylene (100 mL) and hexanes
(100 mL) was added dropwise n-butyllithium (20 mL, 2.5 M
solution in hexanes). The reaction mixture turned orange. The
It turns out that the cationic Lewis acidic species generated
by the full protonation of either solvated 1b or nonsolvated 3
can effectively isomerize 2,2-dimethyl-4-pentenylamine to 2,2-
dimethyl-3-pentenylamine (eq 1). The reaction appears to be
(23) Ates, A.; Quinet, C. Eur. J. Org. Chem. 2003, 1623.
(24) Bambirra, S.; van Leusen, D.; Meetsma, A.; Hessen, B.; Teuben. J.
H. Chem. Commun. 2003, 522.
(25) van Baar, J. F.; Schut, P. A.; Horton, A. D.; Dall’occo, T.; van
Kessel, G. M. M. World Pat. WO 00/35974, 2000.
(22) Tsurugi, H.; Bambirra, S.; Hessen, B. Unpublished results. When
[Y(CH2SiMe3)3(THF)2] was exposed to solutions of the substrate 2,2-
dimethyl-4-pentenylamine in C6D6, cloudy suspensions were obtained, which
(remarkably) give clear solutions when [PhNMe2H][B(C6F5)4] was added.

3460 Organometallics, Vol. 25, No. 14, 2006
Bambirra et al.
d8, 20 °C): δ 6.92 (m, 2 H, Ar H), 6.87 (m, 5 H, Ph), 6.84 (t, 3JHH
) 7.5 Hz, 4 H, Bz m-H), 6.81 (m, 4 H, Ar H), 6.41 (d, 3JHH ) 7.5
Hz, 4 H, Bz o-H), 6.32 (t, 3JHH ) 7.5 Hz, 2 H, Bz p-H), 3.41 (sept,
Table 3. Catalytic Isomerization of
2,2-Dimethyl-4-pentenylamine to
(E)-2,2-Dimethyl-3-pentenylamine by
Cationic Lanthanum Speciesa
3
3JHH ) 6.6 Hz, 4 H, CHMe2), 1.76 (s, 4 H, LaCH2), 1.19 (d, JHH
3
) 6.6 Hz, 12 H, Pri Me), 0.85 (d, JHH ) 6.6 Hz, 12 H, Pri Me).
catalyst
time/h
conversnb/%
k/L mol-1 s-1
13C NMR (125.7 MHz, THF-d8, 20 °C): δ 174.7 (NCN), 153.0
(Bz Cipso), 146.7 (Ph Cipso), 141.5 (Ar Cipso), 134.7 (Ar C), 131.9
(d, 1JCH ) 160.0 Hz, Bz CH), 130.6 (d, 1JCH ) 156.2 Hz, Ar CH),
129.8 (d, 1JCH ) 158.8 Hz, Ph CH), 128.3 (d, 1JCH ) 161.5 Hz, Ph
1b/3B
3/4B
1.5
2
95
96
3.99 × 10-2
3.43 × 10-2
a Conditions: C6D5Br solvent (total volume 0.5 mL), 50 °C, 10 µmol of
catalyst, B ) 10 µmol of [PhNMe2H][B(C6F5)4] activator, 1.0 mmol of
1
1
substrate. b Determined by H NMR.
1
CH), 125.2 (d, JCH ) 158.7 Hz, Ph CH), 125.1 (d, JCH ) 153.6
Hz, Ar CH), 122.8 (d, 1JCH ) 152.8 Hz, Bz CH), 117.6 (d, 1JCH
)
157.8 Hz, Bz CH), 71.1 (t, 1JCH ) 130.6 Hz, LaCH2), 30.2 (d, 1JCH
reaction mixture was stirred for 4 h at room temperature. After
filtration, the orange solid was washed by continuous extraction
with hot hexanes (LiOtBu removal) and dried under vacuum,
yielding 6.5 g (46 mmol, 93%) of KCH2Ph-4-Me as a red,
pyrophoric solid. 1H NMR (300 MHz, THF-d8, 20 °C): δ 5.97 (d,
3JHH ) 7.5 Hz, 2H, Ar m-H), 5.62 (d, 3JHH ) 7.5 Hz, 2H, Ar o-H),
1.94 (s, 2H, KCH2), 1.78 (s, 3 H, Me). 13C NMR (75.4 MHz, THF-
d8, 20 °C): δ 154.5 (Ar Cipso), 132.0 (d, 1JCH ) 145.8 Hz, Ar CH),
112.6 (d, 1JCH ) 149.6 Hz, Ar CH), 105.7 (Ar CMe), 46.9 (t, 1JCH
) 126.6 Hz, Pri CH), 26.8 (q, JCH ) 125.0 Hz, Pri Me), 24.7 (q,
1
1JCH ) 124.8 Hz, Pri Me).
(b) Preparative Scale. Solid 1a (0.31 g, 0.50 mmol) and [PhC-
(N-2,6-Pri2C6H3)2]H (0.22 g, 0.50 mmol) were mixed and dissolved
in THF (30 mL). The solution was stirred at ambient temperature
for 1 h, after which the volatiles were removed in vacuo. The residue
was dissolved in hexanes (5 mL) with some added THF (ca. 1.0
mL). Cooling to -30 °C afforded the crystalline title compound
1
) 149.2 Hz, KCH2), 21.7 (q, JCH ) 125.3 Hz, Me).
1
(0.29 g, 0.35 mmol, 70%). H NMR (300 MHz, C6D6, 20 °C): δ
Synthesis of Li(CH2Ph-4-Me). Solid KCH2Ph-4-Me (650 mg,
5.0 mmol) and LiBr (435 mg, 5 mmol) were mixed, and 50 mL of
diethyl ether was added with stirring. The color of the suspension
changed from red to yellow, and the mixture was stirred for 3 h.
The solvent was removed in vacuo, and the solids were extracted
with toluene (50 mL). The filtrate was evaporated to dryness under
reduced pressure, leaving the title compound as a yellow pyrophoric
3
7.19-7.15 (m, 2 H, Ar H), 7.03 (m, 5 H, Ph), 6.96 (t, JHH ) 7.2
Hz, 4 H, Bz m-H), 6.69-6.66 (m, 4 H, Ar H), 6.53 (d, 3JHH ) 6.9
Hz, 4 H, Bz o-H), 6.42 (t, 3JHH ) 6.9 Hz, 2 H, Bz p-H), 3.62 (sept,
3JHH ) 6.7 Hz, 4 H, CHMe2), 3.06 (m, 4 H R-THF), 2.34 (s, 4 H,
3
LaCH2), 1.32 (d, JHH ) 6.7 Hz, 12 H, Pri Me), 1.12 (m, 4 H
3
â-THF), 1.03 (d, JHH ) 6.7 Hz, 12 H, Pri Me). 13C NMR (75.4
MHz, C6D6, 20 °C): δ 173.2 (NCN), 150.2 (Bz Cipso), 144.8 (Ph
1
powder (400 mg, 3.5 mmol, 71%). H NMR (300 MHz, THF-d8,
1
Cipso), 141.5 (Ar Cipso), 132.9 (Ar C), 131.9 (d, JCH ) 156.2 Hz,
3
3
20 °C): δ 6.80 (d, JHH ) 7.7 Hz, 2H, Ar m-H), 6.70 (d, JHH
)
1
1
Bz CH), 130.6 (d, JCH ) 160.3 Hz, Ar CH), 128.9 (d, JCH
)
7.7 Hz, 2H, Ar o-H), 2.32 (s, 3 H, Me), 1.90 (s, 2H, LiCH2). 13C
NMR (75.4 MHz, THF-d8, 20 °C): δ 159.4 (Ar Cipso), 130.4 (d,
1
154.1 Hz, Ph CH), 127.0 (d, JCH ) 152.1 Hz, Ph CH), 124.1 (d,
1JCH ) 160.4 Hz, Ph CH), 123.8 (d, JCH ) 156.2 Hz, Ar CH),
1
1
1JCH ) 156.0 Hz, Ar CH), 119.3 (d, JCH ) 150.6 Hz, Ar CH),
121.0 (d, 1JCH ) 152.1 Hz, Bz CH), 116.2 (d, 1JCH ) 160.3 Hz, Bz
CH), 69.4 (t, 1JCH ) 135.8 Hz, LaCH2), 68.7 (t, 1JCH ) 147.6 Hz,
R-THF), 28.8 (d, 1JCH ) 125.8 Hz, Pri CH), 25.5 (q, 1JCH ) 125.2
1
1
115.6 (Ar CMe), 34.4 (t, JCH ) 126.1 Hz, LiCH2), 22.3 (q, JCH
) 123.3 Hz, Me). Anal. Calcd for C8H9BLi (mol wt 112.10): C,
85.72; H, 8.09; Li, 6.19. Found: C, 85.65; H, 8.93; Li, 6.08.
Synthesis of [La(CH2Ph)3(THF)3] (1a). A solution of KCH2-
Ph (1.56 g, 12.0 mmol) in 10 mL of THF was added to a suspension
of LaBr3(THF)4 (2.70 g, 4.0 mmol) in THF (100 mL) at 0 °C. The
resulting yellow suspension was stirred for 2 h at 0 °C, after which
the mixture was centrifuged and decanted from the KBr precipitate.
The solution was concentrated under reduced pressure to about 10
mL, during which a crystalline solid formed. Pentane was layered
onto the mixture, and cooling to -30 °C afforded the title compound
as yellow-orange crystals (1.45 g, 2.3 mmol, 57%). 1H NMR (300
Hz, Pri Me), 25.4 (t, JCH ) 132.2 Hz, â-THF), 23.5 (q, JCH
)
1
1
125.2 Hz, Pri Me). Anal. Calcd for C49H61LaN2O (mol wt 832.94):
C, 70.66; H, 7.38; N, 3.36. Found: C, 70.48; H, 7.32; N, 3.24.
Reaction of 1b with ArNdCPhNHAr. Solid 1b (67.0 mg, 100.0
µmol) and [PhC(N-2,6-Pri2C6H3)2]H (44.0 mg, 100.0 µmol) were
mixed together and dissolved in 0.6 mL of THF-d8. NMR
spectroscopy showed clean conversion to {[PhC(NAr)2]La(CH2-
1
Ph-4-Me)2(THF)x} and 1 equiv of p-xylene. H NMR (300 MHz,
THF-d8, 20 °C): δ 6.94 (m, 2 H, Ar H), 6.90 (m, 5 H, Ph), 6.83
3
(m, 4 H, Ar H), 6.75 (d, JHH ) 7.5 Hz, 4 H, Bz m-H), 6.30 (d,
3
MHz, THF-d8, 20 °C): δ 6.78 (t, 6H, JHH ) 7.5 Hz, Ph m-H),
3
3JHH ) 7.5 Hz, 4 H, Bz o-H), 3.42 (sept, JHH ) 6.6 Hz, 4 H,
3
3
6.22 (t, JHH ) 7.2 Hz, 3H, Ph p-H), 6.14 (d, JHH ) 7.5 Hz, 6H,
Ph o-H), 1.41 (s, 6H, CH2Ph). 13C NMR (300 MHz, THF-d8, 20
°C): δ 153.0 (Ph Cipso), 131.4 (d, 1JCH ) 152.9 Hz, Ph CH), 122.7
(d, 1JCH ) 153.0 Hz, Ph CH), 116.1 (d, 1JCH ) 158.5 Hz, Ph CH),
3
CHMe2), 1.79 (s, 4 H, LaCH2), 1.18 (d, JHH ) 6.6 Hz, 12 H, Pri
Me), 0.85 (d, 3JHH ) 6.6 Hz, 12 H, Pri Me). 13C NMR (125.7 MHz,
THF-d8, 20 °C): δ 174.4 (NCN), 149.5 (Bz Cipso), 146.7 (Ph Cipso),
143.2 (Ar Cipso), 134.7 (Ar C), 132.9 (d, 1JCH ) 160.0 Hz, Bz CH),
130.3 (d, 1JCH ) 156.2 Hz, Ar CH), 128.3 (d, 1JCH ) 158.2 Hz, Ph
1
67.2 (t, JCH ) 133.0 Hz, LaCH2). Anal. Calcd for C33H45LaO3
(mol wt 628.62): C, 63.05; H, 7.22. Found: C, 62.85; H, 7.13.
Synthesis of [La(CH2Ph-4-Me)3(THF)3] (1b). A reaction on
the same scale and under the same conditions, but using KCH2-
Ph-4-Me (1.7 g, 12.0 mmol) as benzylating agent, afforded the title
compound as yellow-orange crystals (1.20 g, 1.8 mmol, 45%). 1H
1
1
CH), 126.3 (d, JCH ) 157.5 Hz, Ph CH), 125.0 (d, JCH ) 158.7
Hz, Ph CH), 125.1 (d, 1JCH ) 151.4 Hz, Ar CH), 123.0 (d, 1JCH
)
152.8 Hz, Bz CH), 69.8 (t, 1JCH ) 130.5 Hz, LaCH2), 30.1 (d, 1JCH
) 126.6 Hz, Pri CH), 26.6 (q, JCH ) 125.0 Hz, Pri Me), 24.8 (q,
1
1
3
1JCH ) 124.8 Hz, Pri Me), 21.6 (q, JCH ) 126.8 Hz, BzMe).
NMR (300 MHz, THF-d8, 20 °C): δ 6.65 (d, JHH ) 7.6 Hz, 6H,
m-H), 6.07 (d, 3JHH ) 7.6 Hz, 6H, o-H), 2.08 (s, 9 H, Me), 1.36 (s,
6H, LaCH2). 13C NMR (75.4 MHz, THF-d8, 20 °C): δ 150.0 (Ar
Synthesis of [La(CH2Ph-4-Me)4][Li(THF)4] (3). Solid 1b (670
mg, 1.0 mmol) and LiCH2Ph-4-Me (112 mg, 1.0 mmol) were
mixed, and THF (5 mL) was added with stirring. The red solution
was stirred for 1 h, after which the solution was layered with
hexanes (30 mL). Cooling to -30 °C yielded the title compound
C
ipso), 132.0 (d, 1JCH ) 153.3 Hz, Ar CH), 125.0 (Ar CMe), 123.1
1
1
(d, JCH ) 150.0 Hz, Ar CH), 66.0 (t, JCH ) 131.2 Hz, LaCH2),
1
21.7 (q, JCH ) 125.9 Hz, Me). Anal. Calcd for C36H51LaO3 (mol
1
as red-orange crystals (450 mg, 52%). H NMR (300 MHz, THF-
wt 670.70): C, 64.47; H, 7.66. Found: C, 64.36; H, 7.64.
Synthesis of [PhC(NAr)2]La(CH2Ph)2(THF) (2). (a) NMR-
Tube Scale. Solid 1a (63.0 mg, 100.0 µmol) and [PhC(N-2,6-
Pri2C6H3)2]H (44.0 mg, 100.0 µmol) were mixed together and
dissolved in 0.6 mL of THF-d8. NMR spectroscopy showed clean
conversion to 2 and 1 equiv of toluene. 1H NMR (500 MHz, THF-
3
3
d8, 20 °C): δ 6.51 (d, 8H, JHH ) 7.9 Hz, Ar m-H), 5.70 (d, JHH
) 7.9 Hz, 8H, Ar o-H), 2.06 (s, 12 H, Me), 1.11 (s, 8H, LaCH2).
13C NMR (75.4 MHz, THF-d8, 20 °C): δ 150.0 (Ar Cipso), 132.7
(d, 1JCH ) 152.0 Hz, Ar CH), 121.9 (Ar C), 120.7 (d, 1JCH ) 153.0
1
1
Hz, Ar CH), 62.0 (t, JCH ) 139.6 Hz, LaCH2), 21.8 (q, JCH
)

Lanthanum Tribenzyl Complexes
Organometallics, Vol. 25, No. 14, 2006 3461
Table 4. Crystal Data and Collection Parameters of Complexes 1a,b, 2, 3, 4a′, and 5b′
1a
1b
2
3
4a′
5b′
formula
C36H51LaO3
C36H45LaO3
C49H61LaN2O
[C32H36La]-
[C16H32LiO4]+‚
C4H8O
[C30H64LaO4]+
[C24H20B]-
[C32H57LaO6]2+
[C24H20B]-2‚C4H8O
fw
628.62
yellow
664.66
orange
832.94
orange
927.02
orange
928.83
yellow
1387.28
yellow
cryst color
cryst size (mm)
0.51 × 0.42 ×
0.53 × 0.41 ×
0.31 × 0.11 ×
0.37 × 0.31 ×
0.41 × 0.34 ×
0.49 × 0.27 ×
0.37
0.33
0.07
0.26
0.10
0.25
cryst syst
space group (No.)
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
monoclinic
P21/c (14)
14.092(1)
10.443(1)
20.773(2)
triclinic
P1h (2)
orthorhombic
Pbca (61)
19.961(2)
15.566(1)
26.987(2)
triclinic
P1h (2)
orthorhombic
Pbca (61)
18.3872(9)
18.3346(9)
27.242(1)
triclinic
P1h (2)
10.5672(8)
13.420(1)
15.033(1)
64.923(1)
73.314(1)
73.363(1)
1816.0(2)
2
13.599(1)
13.605(1)
15.016(1)
71.147(1)
89.847(1)
67.519(1)
2406.0(3)
2
13.9488(8)
15.7315(9)
17.528(1)
106.521(1)
96.670(1)
98.939(1)
3590.1(4)
2
100.879(2)
3002.1(5)
4
1.391
14.53
1296
8385.2(12)
8
1.320
10.56
3472
9183.9(7)
8
1.343
9.76
3872
Z
F
calcd, g cm-3
1.215
12.05
684
1.280
9.32
976
1.280
6.5
1456
µ(Mo KRj), cm-1
F(000), e
θ range (deg)
3.33, 28.28
0.0290
0.0716
3.63, 28.28
0.0236
0.0664
(14, (17,
-19 to +20
100(1)
2.54, 26.02
0.0423
0.1077
(24, (19,
-31 to +33
100(1)
2.56, 28.28
0.0320
0.0790
-18 to +17, (18,
-19 to +20
100(1)
2.48, 26.37
0.0365
0.0859
(22, (22,
-34 to +29
100(1)
1.016
2.46, 28.28
0.0425
0.1085
(18, -19 to +20,
-22 to +23
200
R1
wR2 (all data)
index ranges (hkl)
(18, (13, (27
T (K)
GOF
100(1)
1.043
1.116
1.025
1.025
1.521
3
125.5 Hz, Ar Me). Anal. Calcd for C60H78BLaO5 (mol wt 854.91):
C, 67.44; H, 8.02; La, 16.25; Li, 0.81. Found: C, 67.28; H, 7.88;
La, 16.11; Li, 0.84.
d8, 20 °C): δ 7.26 (br, 8H, BPh4 o-H), 7.03 (t, JHH ) 7.5 Hz, 4
H, Ph m-H), 6.85 (t, 7.3 Hz, 8H, BPh4 m-H), 6.72 (t, 7.1 Hz, 4H,
3
3
BPh4 p-H), 6.50 (t, JHH ) 7.5 Hz, 2 H, Ph p-H), 6.26 (d, JHH
)
7.6 Hz, 4 H, Ph o-H), 1.69 (s, 4H, LaCH2). 13C NMR (75.4 MHz,
Reaction of 1a with 1 Equiv of [HNMe2Ph][B(C6F5)4]. Solid
[La(CH2Ph)3(THF)3] (31 mg, 50.0 µmol) and [HNMe2Ph][B(C6F5)4]
(40 mg, 50.0 µmol) were mixed, and THF-d8 (0.6 mL) was added.
The obtained solution was transferred to an NMR tube and analyzed
by NMR spectroscopy, which showed full conversion to the ionic
species [La(CH2Ph)2(THF-d8)n][B(C6F5)4] (4a), 1 equiv of toluene,
1
20 °C, THF-d8): δ 165.8 (q, JCB ) 49.6 Hz, BPh4 Cipso), 150.5
1
(Ph Cipso), 137.9 (dt, JCH ) 153.6, 7.3 Hz, BPh4 o-H), 132.7 (dd,
1JCH ) 156.6, 7.7 Hz, Ph CH), 126.7 (d, 152.5 Hz, BPh4 m-H),
123.7 (dt, 1JCH ) 152.0, 7.2 Hz, Ph CH), 122.7 (dt, 155.5, 8.2, 7.3
1
Hz, BPh4 p-H), 119.4 (dt, JCH ) 162.0, 7.4 Hz, Ph CH), 71.1 (t,
1JCH ) 133.5 Hz, LaCH2). Anal. Calcd for C54H66LaBO4 (mol wt
928.83): C, 69.83; H, 7.16. Found: C, 69.58; H, 6.83.
1
and free PhNMe2. H NMR (300 MHz, THF-d8, 20 °C): 4a, δ
7.09 (t, 3JHH ) 7.6 Hz, 4 H, Ph m-H), 6.50 (t, 3JHH ) 7.6 Hz, 2 H,
Ph p-H), 6.33 (d, 3JHH ) 7.6 Hz, 4 H, Ph o-H), 1.74 (s, 4 H, LaCH2);
Synthesis of [La(CH2Ph)(THF)6][B(C6H5)4]2 (5a′). THF (0.5
mL) was added to a mixture of 63 mg (100 µmol) of 1a and 88
mg (200 µmol) of [HNMe2Ph][BPh4]. From the resulting yellow
solution an oil precipitated. The supernatant was decanted off, and
the oil was rinsed with hexanes. Drying of the residue in vacuo
gave yellow microcrystalline 5a′ (69 mg, 75%). H NMR (300
MHz, room temperature, THF-d8, 20 °C): δ 7.11 (t, JHH ) 7.4
Hz, 4 H, Ph m-H), 6.80 (t, JHH ) 7.4 Hz, 2 H, Ph p-H), 6.60 (d,
PhNMe2, δ 7.12 (t, 3JHH ) 7.8 Hz, 2 H, Ph m-H), 6.63 (d, 3JHH
)
7.8 Hz, 2 H, Ph o-H), 6.54 (t, 3JHH ) 7.00 Hz, 1 H, Ph p-H), 2.82
3
(s, 6H, Me); C7H8, δ 7.18 (t, JHH ) 7.2 Hz, 2 H, Ph m-H), 7.11
3
3
(t, JHH ) 7.2 Hz, 2 H, Ph o-H), 7.07 (t, JHH ) 7.2 Hz, 2 H, Ph
p-H), 2.24 (s, 3 H, Me). 13C NMR (75.4 MHz, THF-d8, 20 °C):
4a, δ 150.5 (Ph Cipso), 149.9 (d, 1JCF ) 242.6 Hz, C6F5), 140.0 (d,
1
3
1JCF ) 245.2 Hz, C6F5), 138.5 (d, JCF ) 243.6 Hz, C6F5), 132.8
1
3
(d, 1JCH ) 155.6 Hz, Ph CH), 123.8 (d, 1JCH ) 156.1 Hz, Ph CH),
3JHH ) 7.4 Hz, 4 H, Ph o-H), 1.84 (s, 2H, LaCH2). For resonances
of the anion, see the data for 4a′. Anal. Calcd for C79H95LaB2O6
(mol wt 1301.15): C, 72.93; H, 7.36. Found: C, 72.42; H, 6.95.
Reaction of 1b with 1 Equiv of [HNMe2Ph][B(C6F5)4]. Solid
1b (34 mg, 50.0 µmol) and [HNMe2Ph][B(C6F5)4] (40 mg, 50.0
µmol) were mixed, and THF-d8 (0.6 mL) was added. The obtained
solution was transferred to an NMR tube and analyzed by NMR
spectroscopy, which showed full conversion to the ionic species
[La(CH2Ph-4-Me)2(THF-d8)n][B(C6F5)4] (4b), 1 equiv of p-xylene,
1
1
119.6 (d, JCH ) 162.0 Hz, Ph CH), 71.3 (t, JCH ) 133.7 Hz,
1
LaCH2); PhNMe2, δ 152.4 (Ph Cipso), 130.2 (d, JCH ) 161.0 Hz,
Ph m-CH), 117.7 (d, 1JCH ) 161.0 Hz, Ph p-CH), 114.0 (d, 1JCH
154.6 Hz, Ph o-CH), 41.2 (s, Me).
)
Reaction of 1a with 2 Equiv of [HNMe2Ph][B(C6F5)4]. Solid
1a (31.0 mg, 50.0 µmol) and [HNMe2Ph][B(C6F5)4] (80.0 mg, 100.0
µmol) were mixed, and THF-d8 (0.6 mL) was added. The obtained
solution was transferred to an NMR tube and analyzed by NMR
spectroscopy, which showed full conversion to the ionic species
[La(CH2Ph)(THF-d8)n][B(C6F5)4]2 (5a), 2 equiv of toluene, and free
1
and free PhNMe2. H NMR (300 MHz, THF-d8, 20 °C): 4b, δ
3
3
6.72 (d, JHH ) 7.7 Hz, 4 H, Ar m-H), 6.12 (d, JHH ) 7.7 Hz, 2
H, Ar o-H), 2.09 (s, 6 H, Me), 1.63 (s, 4 H, LaCH2); p-C8H10, δ
6.93 (s, 4 H, Ar H), 2.18 (s, 6 H, Me). 13C NMR (75.4 MHz, THF-
PhNMe2. 1H NMR (300 MHz, THF-d8, 20 °C): δ 7.29 (t, 3JHH
)
3
7.5 Hz, 2 H, Ph m-H), 6.82 (t, JHH ) 7.5 Hz, 1 H, Ph p-H), 6.65
3
1
(d, JHH ) 7.2 Hz, 2 H, Ph o-H), 1.85 (s, 2 H, LaCH2). 13C NMR
d8, 20 °C): 4b, δ 149.2 (Ar Cipso), 132.4 (d, JCH ) 151.3 Hz, Ar
1
1
(75.4 MHz, THF-d8, 20 °C): δ 148.0 (Ph Cipso), 133.6 (d, JCH
)
m-CH), 129.2 (Ar C-Me), 123.5 (d, JCH ) 152.7 Hz, Ar o-CH),
1
157.5 Hz, Ph CH), 125.4 (d, JCH ) 154.1 Hz, Ph CH), 122.8 (d,
70.6 (t, 1JCH ) 134.0 Hz, LaCH2), 21.5 (q, 1JCH ) 125.0 Hz, Me);
1
1
1JCH ) 160.5 Hz, Ph CH), 78.9 (t, JCH ) 130.0 Hz, LaCH2).
p-C8H10, 136.2 (Ar C), 130.6 (d, JCH ) 155.5 Hz, Ar CH), 22.1
1
(q, JCH ) 125.7 Hz, Me).
Synthesis of [La(CH2Ph)2(THF)4][B(C6H5)4] (4a′). THF (0.5
mL) was added to a mixture of 63 mg (100 µmol) of 1a and 44
mg (100 µmol) of [HNMe2Ph][BPh4]. The resulting yellow solution
was cooled to -30 °C for 3 days, producing yellow crystals of the
title compound (69 mg, 69 µmol, 75%). 1H NMR (300 MHz, THF-
Reaction of 1b with 2 Equiv of [HNMe2Ph][B(C6F5)4]. Solid
1b (34.0 mg, 50.0 µmol) and [HNMe2Ph][B(C6F5)4] (80.0 mg, 100.0
µmol) were mixed, and THF-d8 (0.6 mL) was added. The obtained
solution was transferred to an NMR tube and analyzed by NMR

3462 Organometallics, Vol. 25, No. 14, 2006
Bambirra et al.
spectroscopy, which showed full conversion to the ionic species
in a vacuum oven for at least 2 h. In a drybox, the miniclave was
charged with 1b or 2 (10 µmol), [HNMe2Ph][B(C6F5)4] (where
appropriate 10 µmol or 20 µmol), 30 mL of toluene, and TiBAO
(100 µmol of Al). The reactor was taken out of the drybox, heated
at 50 °C in an oil bath, and pressurized with 5 bar of ethylene. The
pressure was kept constant during the reaction by replenishing the
flow. The reaction mixture was stirred for 15 min and then vented.
The polymer was repeatedly rinsed with acidified methanol and
dried in a vacuum oven.
[La(CH2Ph-4-Me)(THF-d8)n][B(C6F5)4]2 (5b), 2 equiv of p-xylene,
1
and free PhNMe2. H NMR (300 MHz, THF-d8, 20 °C): δ 7.14
(d, 3JHH ) 7.5 Hz, 2 H, Ar m-H), 6.57 (d, 3JHH ) 7.5 Hz, 2 H, Ar
o-H), 2.20 (s, 3 H, Ar p-H), 1.79 (s, 4 H, LaCH2). 13C NMR (75.4
MHz, THF-d8, 20 °C): δ 149.2 (Ar Cipso), 134.3 (d, 1JCH ) 151.4
1
Hz, Ar m-CH), 125.6 (d, JCH ) 151.3 Hz, Ar o-CH), 132.8 (Ar
1
1
C-Me), 78.0 (t, JCH ) 129.7 Hz, LaCH2), 21.1 (q, JCH ) 126.6
Hz, Me).
Synthesis of [La(CH2Ph-4-Me)2(THF)4][B(C6H5)4]‚THF (4b′).
THF (0.5 mL) was added to a mixture of 67 mg (100 µmol) of 1b
and 44 mg (100 µmol) of [HNMe2Ph][BPh4]. The resulting light
yellow solution was cooled to -30 °C for 3 days, producing
yellowish crystals of 4b′ (74 mg, 72%). 1H NMR (300 MHz, THF-
d8, 20 °C): δ 6.87 (d, 3JHH ) 7.5 Hz, 4 H, Ar m-H), 6.18 (d, 3JHH
) 7.7 Hz, 2 H, Ar o-H), 2.14 (s, 6 H, Me), 1.59 (s, 4 H, LaCH2).
Procedure for Intramolecular Hydroamination/Cyclization.
All samples for the hydroamination/cyclization reactions were
prepared in a N2-filled glovebox. Typically, an NMR tube equipped
with a Teflon (Young) valve was charged with the (pre)catalyst
(10 µmol), the activator [PhNMe2H][B(C6F5)4] (10 µmol, where
appropriate), ferrocene (as internal standard, 100 µmol), and the
aminoalkene substrate 2,2-dimethyl-4-pentenylamine (1000 µmol)
dissolved in C6D6 or C6D5Br (total volume 0.5 mL). The reactions
were followed in time, either directly in the NMR spectrometer
(thermostated at 50 °C unless mentioned otherwise; measurements
taken in an array of regular intervals) or warmed in an electric
oven at 50 °C and transferred to the spectrometer periodically.
Conversions were determined by 1H NMR following the decrease
of the olefinic resonances of the substrate relative to the ferrocene
internal standard (single-pulse spectra). The product 2-methyl-4,4-
1
13C NMR (75.4 MHz, THF-d8, 20 °C): δ 166.1 (q, JCB ) 48.7
1
Hz, BPh4 Cipso), 148.5 (Ar Cipso), 133.5 (d, JCH ) 155.2 Hz, Ar
1
m-CH), 128.9 (Ar C-Me), 124.0 (d, JCH ) 153.0 Hz, Ar o-CH),
70.4 (t, 1JCH ) 131.0 Hz, LaCH2), 21.6 (q, 1JCH ) 125.0 Hz, Me).
Anal. Calcd for C60H78BLaO5 (mol wt 1028.99): C, 70.04; H, 7.64.
Found: C, 69.87; H, 7.54.
Synthesis of [La(CH2Ph-4-Me)(THF)6][B(C6H5)4]2 (5b′). THF
(0.5 mL) was added to a mixture of 67 mg (100 µmol) of 1b and
88 mg (200 µmol) of [HNMe2Ph][BPh4]. The resulting light yellow
solution was cooled to -30 °C for 3 days, producing yellowish
1
dimethylpyrrolidine was identified by H NMR and GC-MS in
comparison with literature data.
1
crystals of 5b′ (80 mg, 61%). H NMR (300 MHz, THF-d8, 20
Procedure for the Isomerization of 2,2-Dimethyl-4-pentenyl-
amine. Samples were prepared and examined as described above
for the hydroamination/cyclization procedure. Conversions were
determined by 1H NMR following the decrease of the olefinic
resonances of the substrate. The product was characterized as (E)-
2,2-dimethyl-3-pentylamine by 1H and 13C NMR and GC-MS. Data
°C): δ 76.90 (d, 3JHH ) 7.3 Hz, 2 H, Ar m-H), 6.47 (d, 3JHH ) 7.3
Hz, 2 H, Ar o-H), 2.09 (s, 6 H, Me), 1.77 (s, 2H, LaCH2). Anal.
Calcd for C80H97B2LaO6 (mol wt 1315.17): C, 73.06; H, 7.43.
Found: C, 73.00; H, 7.48.
Reaction of 2 with [HNMe2Ph][B(C6F5)4]. A solution of 2 (42
mg, 50.0 µmol) in THF-d8 (0.6 mL) was added to solid [HNMe2-
Ph][B(C6F5)4] (40 mg, 50.0 µmol). The obtained solution was
transferred to an NMR tube and analyzed by NMR spectroscopy,
which showed full conversion to the ionic species {[PhC(N-2,6-
Pri2C6H3)2]La(CH2Ph)(THF-d8)n}[B(C6F5)4] (6), 1 equiv of toluene,
1
for (E)-2,2-dimethyl-3-pentylamine are as follows. H NMR (500
3
3
MHz, C6D5Br, 20 °C): δ 5.49 (dq, 1 H, JHH ) 6.1 Hz, JHH
)
3
15.4 Hz, MeCHdCH), 5.43 (d, 1 H, JHH ) 15.4 Hz, MeCHd
CH), 2.28 (s, 2 H, CH2NH2), 1.56 (d, 3JHH ) 6.1 Hz, 3 H, MeCHd
CH), 0.85 (s, 6 H, CMe2), 0.73 (s, 2 H, NH2). 13C NMR (125.7
1
1
and free PhNMe2. H NMR (500 MHz, THF-d8, 20 °C): δ 7.13
MHz, C6D5Br, 20 °C): δ 135.6 (d, JCH ) 148.2 Hz, MeCHd
(m, 2 H, Ar H), 7.00 (m, 5 H, Ph), 6.94 (m, 4 H, Ar H), 6.84 (t,
CH), 118.7 (d, 1JCH ) 151.0 Hz, MeCHdCH), 49.9 (t, 1JCH ) 130.7
3
1
3JHH ) 7.5 Hz, 4 H, Bz m-H), 6.65 (d, JHH ) 7.5 Hz, 4 H, Bz
Hz, CH2NH2), 34.2 (s, CMe2) 21.2 (q, JCH ) 124.6 Hz, CMe2),
o-H), 6.55 (t, 3JHH ) 7.5 Hz, 2 H, Bz p-H), 3.25 (sept, 3JHH ) 6.7
14.7 (d, JCH ) 125.0 Hz, MeCHdCH). GC-MS: m/z 113 [M+].
1
3
Hz, 4 H, CHMe2), 1.90 (s, 4 H, LaCH2), 1.22 (d, JHH ) 6.7 Hz,
3
Acknowledgment. This investigation was financially sup-
ported by The Netherlands Research School Combination
Catalysis (NRSC-C). We thank A. Jekel for GPC and GC-MS
analysis.
12 H, Pri Me), 0.81 (d, JHH ) 6.7 Hz, 12 H, Pri Me). 13C NMR
(125.7 MHz, THF-d8, 20 °C): δ 176.8 (NCN), 151.2 (Bz Cipso),
1
146.0 (Ph Cipso), 142.7 (Ar Cipso), 133.1 (Ar C), 131.9 (d, JCH
)
1
160.5 Hz, Bz CH), 131.4 (d, JCH ) 156.5 Hz, Ar CH), 128.7 (d,
1JCH ) 160.0 Hz, Ph CH), 127.0 (d, JCH ) 160.5 Hz, Ph CH),
1
Supporting Information Available: CIF files giving crystal-
lographic data for 1a,b, 2, 3, 4a′, and 5b′, including atomic
coordinates, full bond distances, and bond angles as well as
anisotropic thermal parameters, and figures giving fits used for
determination of rate constants and 1H NMR spectra of neutral and
cationic lanthanum complexes. This material is available free of
charge via the Internet at http://pubs.acs.org.
126.5 (d, 1JCH ) 158.8 Hz, Ph CH), 125.7 (d, 1JCH ) 154.1 Hz, Ar
1
1
CH), 124.2 (d, JCH ) 152.3 Hz, Bz CH), 120.5 (d, JCH ) 160.7
1
1
Hz, Bz CH), 78.3 (t, JCH ) 130.0 Hz, LaCH2), 30.5 (d, JCH
)
123.9 Hz, CHMe2), 26.2 (q, JCH ) 125.6 Hz, Pri Me), 24.8 (q,
1
1JCH ) 125.6 Hz, Pri Me).
Procedure for Ethylene Polymerization. Polymerizations were
performed in a 50 mL glass miniclave (Bu¨chi AG, Switzerland)
with a magnetic stirrer. Before use, the reactor was dried at 80 °C
OM060262V