Strategies for the synthesis of lanthanum dialkyl complexes with monoanionic ancillary ligands

Article abstract of DOI:10.1021/om700919h

The synthesis of lanthanum dialkyl complexes with monoanionic ancillary ligands [L]^- is pursued by three different strategies: (a) in situ peralkylation of LaBr₃(THF)₄ with 3 equiv of LiCH ₂SiMe₃ followed by reaction with LH; (b) reaction of isolated La(CH₂Ph)₃(THF)₃with LH; (c) stepwise salt metathesis on LaBr₃(THF)₄. Methods (a) and (b) generally work well for triazacyclononane-amide and amidinate ligands, but are unsuitable for the sterically demanding β-diketiminate [HC(MeC-NAr) ₂]^- (Ar = 2,6-iPr₂C₆H₃) due to its high affinity for the Li cation and the sluggish reactivity of the diketimine. Nevertheless, the β-diketiminate lanthanum dibenzyl complex [HC(MeCNAr)₂]-La(CH₂Ph)₂(THF) could be obtained by first reacting LaBr₃(THF)₄ with K[HC(MeCNAr) ₂] to form [HC(MeCNAr)₂]LaBr₂(THF)₂ and subsequent reaction of this dibromide complex with 2 equiv of PhCH ₂K. When this reaction mixture is warmed, the product decomposes by H-abstraction from one of the diketiminate methyl groups and ligand redistribution, forming the coordination polymer {[μ-η²: η¹-ArNC(Me)CHC(CH₂)NAr]₂La[K(THF) ₄]}_∞.

Full text of DOI:10.1021/om700919h

704
Organometallics 2008, 27, 704–712
Strategies for the Synthesis of Lanthanum Dialkyl Complexes with
Monoanionic Ancillary Ligands
Sergio Bambirra, Francesca Perazzolo, Steven J. Boot, Timo J. J. Sciarone,
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 September 14, 2007
The synthesis of lanthanum dialkyl complexes with monoanionic ancillary ligands [L]- is pursued
by three different strategies: (a) in situ peralkylation of LaBr3(THF)4 with 3 equiv of LiCH2SiMe3
followed by reaction with LH; (b) reaction of isolated La(CH2Ph)3(THF)3 with LH; (c) stepwise salt
metathesis on LaBr3(THF)4. Methods (a) and (b) generally work well for triazacyclononane-amide
and amidinate ligands, but are unsuitable for the sterically demanding ꢀ-diketiminate [HC(MeC-
NAr)2]- (Ar ) 2,6-iPr2C6H3) due to its high affinity for the Li cation and the sluggish reactivity of
the diketimine. Nevertheless, the ꢀ-diketiminate lanthanum dibenzyl complex [HC(MeCNAr)2]-
La(CH2Ph)2(THF) could be obtained by first reacting LaBr3(THF)4 with K[HC(MeCNAr)2] to form
[HC(MeCNAr)2]LaBr2(THF)2 and subsequent reaction of this dibromide complex with 2 equiv of
PhCH2K. When this reaction mixture is warmed, the product decomposes by H-abstraction from
one of the diketiminate methyl groups and ligand redistribution, forming the coordination polymer
{[µ-η2:η1-ArNC(Me)CHC(CH2)NAr]2La[K(THF)4]}∞.
the tris(trimethylsilylmethyl) complexes have been extensively
used for alkane elimination reactions.8 These are only available
for the small and intermediate size metals (Ln ) Sc-Sm);
attempts to isolate Ln(CH2SiMe3)3(THF)x for the larger metals
(Ln ) Nd-La) have failed so far. Recently, we described an
in situ alkylation procedure for the larger metals Nd and La,9
as well as the synthesis of a well-defined tribenzyl complex for
the largest of the rare-earth metals, lanthanum, La(CH2Ph)3-
(THF)3.10 In this contribution we provide a comparison of
synthesis strategies for organometallics of lanthanum, showing
advantages and disadvantages of the various methods, using the
ligand systems HL shown in Chart 1.
Introduction
Nonmetallocene organo-rare-earth metal (Ln) complexes are
developing into an interesting class of catalysts for a variety of
transformations such as hydroamination and olefin polymeri-
zation.1 As the metal ionic radius is an important tunable
parameter for these metals (for the Ln3+ ions they vary from
0.74 Å for Sc to 1.03 Å for La, CN ) 6),2 versatile synthetic
procedures that can access related compounds over the full metal
size range are useful for finding the optimal ligand–metal ion
combination for catalysis. The use of classic salt metathesis
synthesis protocols for these metals can encounter several
problems, such as metal halide occlusion, the formation of ate-
complexes, and facile ligand redistribution.3 These problems
are especially severe for the larger metals in the series. One
way to avoid these difficulties is the alkane elimination route,
in which a homoleptic rare-earth metal alkyl LnR3(THF)x is
reacted with ligands that contain active protons (HL). Several
types of homoleptic rare-earth metal alkyl species are known,
such as [LnMe3]n (Ln ) Y, Lu)4 and Ln[CH(SiMe3)2]3,5
Ln(CH2-C6H4-NMe2-o)3,6 and Ln(CH2SiMe3)3(THF)2.7 Never-
theless, not all of these are suitable for this purpose, and only
Results and Discussion
In Situ Peralkylation. In the in situ peralkylation procedure,
LaBr3(THF)4 is reacted with 3 equiv of LiCH2SiMe3 in THF,
(7) (a) M(CH2SiMe3)3(THF)n: Lappert, M. F.; Pearce, R. J. Chem. Soc.,
Chem. Commun. 1973, 126. (b) Schumann, H.; Müller, J. J. Organomet.
Chem. 1978, 146, C5. (c) Schumann, H.; Müller, J. J. Organomet. Chem.
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Evans, W. J.; Brady, J. C.; Ziller, J. W. J. Am. Chem. Soc. 2001, 123,
7711. (f) Arndt, S.; Spaniol, T. P.; Okuda, J. Chem. Commun. 2002, 896.
(g) Arndt, S.; Spaniol, T. P.; Okuda, J. Angew. Chem., Int. Ed. 2003, 42,
5075.
* Corresponding author. E-mail: B.Hessen@rug.nl.
(1) (a) Arndt, S.; Okuda, J. AdV. Synth. Catal. 2005, 347, 339. (b)
Zeimentz, P. M.; Arndt, S.; Elvidge, B. R.; Okuda, J. Chem. ReV. 2006,
106, 2404. (c) Hou, Z.; Luo, Y.; Li, X. J. Organomet. Chem. 2006, 691,
3114.
(8) (a) Alkane Elimination: 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) Bambirra, S.; van Leusen, D.; Meetsma, A.; Hessen, B.; Teuben,
J. H. Chem. Commun. 2001, 637. (f) Emslie, D. J. H.; Piers, W. E. ; Parvez,
M. Dalton Trans. 2003, 2615. (g) Bambirra, S.; van Leusen, D.; Meetsma,
A.; Hessen, B.; Teuben, J. H. Chem. Commun. 2003, 522. (h) Bambirra,
S.; Meetsma, A.; Hessen, B. Acta Crystallogr. 2006, E62, 314. (i) Bambirra,
S.; Otten, E.; van Leusen, D.; Meetsma, A.; Hessen, B. Z. Anorg. Allg.
Chem. 2006, 632, 1950.
(2) Shannon, R. D. Acta Crystallogr., Sect. A 1976, 32, 751.
(3) Piers, W. E.; Emslie, D. J. H. Coord. Chem. ReV. 2002, 233–234,
131.
(4) (a) Dietrich, H. M.; Raudaschl-Sieber, G.; Anwander, R. Angew.
Chem., Int. Ed. 2005, 44, 5303. (b) Dietrich, H. M.; Meermann, C. Törnroos,
K. W.; Anwander, R. Organometallics 2006, 25, 4316.
(5) (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)Y, Lu): Schaverien, C. J.; Orpen, A. G.
Inorg. Chem. 1991, 30, 4968.
(6) (a) Harder, S. Organometallics 2005, 24, 373. (b) Manzer, L. E.
J. Am. Chem. Soc. 1978, 100, 8068.
(9) (a) Hessen, B.; Bambirra, S. World Pat. WO0232909, 2002. (b)
Hessen, B.; Bambirra, S. World Pat. WO04000894, 2004.
10.1021/om700919h CCC: $40.75
2008 American Chemical Society
Publication on Web 01/17/2008

Synthesis of Lanthanum Dialkyl Complexes
Organometallics, Vol. 27, No. 4, 2008 705
Chart 1
Scheme 2
Scheme 1
gested the presence of two (L3a)La(alkyl) species, the main
product (80%) showing a ligand-to-alkyl ratio of 1:3,
suggesting the formation of [(L3a)La(CH2SiMe3)3] anion.
These results indicate that, although the in situ alkylation
procedure has given us a first opportunity to obtain
(L)Ln(CH2SiMe3)2 species for the largest rare-earth metals,
the formation of ionic species in the alkylation step results
in modest isolated yields of the desired neutral dialkyl
complexes.
Another limitation of the method was revealed in attempts
to extend this synthesis protocol to the ꢀ-diketimine H[HC-
(MeCNAr)2] (HL1, Ar ) 2,6-iPr2C6H3).14 This led only to the
isolation of the Li-diketiminate complex (L1)Li(THF)15 in high
yield (Scheme 1). Monitoring the reaction in THF-d8 by NMR
spectroscopy showed that this product is formed quantitatively.
This shows that the in situ alkylation procedure is unsuccessful
when the affinity of the ligand for lithium is particularly high.
Thus, for the synthesis of (L1)La(alkyl)2(THF)x species a
different strategy is required.
Use of La(CH2Ph)3(THF)3 as Precursor. Reaction of
La(CH2Ph)3(THF)3 (1) with the silylamino-substituted triaza-
cyclononane Me2TACN(SiMe2)NHtBu (HL2)16 led to the clean
formation of the monomeric, THF-free lanthanum dibenzyl
complex (L2)La(CH2Ph)2 (2, Scheme 2), which was isolated
in 65% yield after crystallization. Earlier attempts to generate
the analogous trimethylsilylmethyl complex (L2)La(CH2SiMe3)2
via the in situ alkylation approach mentioned above afforded
the dinuclear complex {[(µ-CH2)MeTACN(SiMe2)NtBu]La-
(CH2SiMe3)}2,16 which derives from intermolecular metalation
of one of the TACN methyl substituents. The benzyl groups in
2 thus appear to stabilize the compound toward ligand depro-
tonation. The molecular structure of 2 was determined by X-ray
diffraction (Figure 1, Table 1). When compared to typical
La-CH2-Si angles (126–142°) in (TACN-amide)La-CH2SiMe3
complexes,16,17 the La-C(22)-C(23) angle of 94.8(2)° and
followed by addition of a ligand with an active proton (HL)
and extraction with an apolar solvent to give
(L)La(CH2SiMe3)2(THF)n species (Scheme 1), albeit in rather
moderate isolated yield (33–48%).11The relatively low isolated
yields from this procedure might be related to the nature of
the species actually formed in the in situ alkylation. To
evaluate this, we monitored the reaction of LaBr3(THF)4 with
1
3, 4, and 5 equiv of LiCH2SiMe3 (LiR) in THF-d8 by H
NMR spectroscopy.12 Upon addition of 3 equiv of LiR, the
alkyl methylene protons show a rather broad resonance at δ
-0.93 ppm, considerably downfield from the δ -2.3 ppm
of LiR itself. Addition of a fourth equivalent of LiR leads to
a slight upfield shift (δ -1.0 ppm) and a sharpening of the
resonance, whereas addition of a fifth equivalent leads to
renewed broadening and a further upfield shift to δ -1.3
ppm. This suggests that (a) the system is highly dynamic,
with rapid interconversion of different alkyl species in
solution and (b) that the thermodynamically most favorable
species in the system probably has a La:R stoichiometry of
1:4. For smaller rare-earth metals, anionic [Ln(CH2SiMe3)4]-
species have been isolated.13 Reaction of LaBr3(THF)4 with
4 equiv of LiR in THF, followed by addition of the
benzamidine PhC(NAr)(NHAr) (Ar ) 2,6-iPr2C6H3, HL3a,
see Chart 1) and pentane extraction, afforded no pentane-
soluble products, whereas the corresponding reaction using
3 equiv of LiR afforded the benzamidinate complex (L3a)La-
11c
(CH2SiMe3)2(THF)2
in 33% isolated yield. A 1H NMR
spectrum of the pentane-insoluble material in THF-d8 sug-
(10) Bambirra, S.; Meetsma, A.; Hessen, B. Organometallics 2006, 25,
3454.
(11) (a) Bambirra, S.; Van Leusen, D.; Tazelaar; C, G. J.; Meetsma,
A.; Hessen, B. Organometallics 2007, 26, 1014. (b) Bambirra, S.; Meetsma,
A.; Hessen, B. Bruins, A. P. Organometallics 2006, 25, 3486. (c) Bambirra,
S. Bouwkamp, M. W.; Meetsma, A.; Hessen, B. J. Am. Chem. Soc. 2004,
126, 9182.
(14) Feldman, J.; McLain, S. J.; Parthasarathy, A.; Marshal, W. J.;
Calabrese, C. J.; Arthur, S. D. Organometallics 1997, 16, 1514.
(15) Stender, M.; Wright, R. J.; Eichler, B. E.; Prust, J.; Olmstead, M. M.;
Roesky, H. W.; Power, P. P. J. Chem. Soc., Dalton Trans. 2001, 3465.
(16) Tazelaar, C. G. J.; Bambirra, S.; Van Leusen, D.; Meetsma, A.;
Hessen, B.; Teuben, J. H. Organometallics 2004, 23, 936.
(17) Bambirra, S.; Meetsma, A.; Hessen, B. Bruins, A. P. Organome-
tallics 2006, 25, 3486.
1
(12) The corresponding H NMR spectra are shown in the Supporting
Information.
(13) (a) 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. (b) Evans, W. J.; Shreeve, J. L.; Broomhall-Dillard, R. N. R.;
Ziller, J. W. J. Organomet. Chem. 1995, 501, 7.

706 Organometallics, Vol. 27, No. 4, 2008
Bambirra et al.
solubility of the former. Performing the reaction on an NMR
tube scale in THF-d8 showed that the reaction proceeds
quantitatively. A crystal structure determination of 3b (Figure
2, Table 2) reveals that both benzyl groups are η2-bound to
lanthanum, with the La-C130-C131 angle of 85.01(19)°
noticeably smaller than the La-C137-C138 angle of 92.9(2)°.
This contrasts with the presence of one η3-benzyl and one η2-
benzyl group in 3a. The difference is possibly caused by the
steric demand of the tBu group on the ligand backbone, which
is reflected in the larger C-N-C(Ar) angles in 3b of 129.4(3)°
(C113-N11-C11) and 129.8(3)° (C113-N12-C118) versus
the equivalent angles of 128.3(4)° and 124.3(3)° in 3a.
The increased steric demand of L3b versus L3a is seen even
more clearly in the structure of the cationic monobenzyl
derivative [(L3b)La(CH2Ph)(THF)3][BPh4] (4), which was
obtained by reaction of 3b with [HNMe2Ph][BPh4] in THF. Its
structure (Figure 3, Table 3) shows the presence of three
coordinated THF molecules and an η1-bound benzyl group
(La-CH2-C ) 132(3)°). It can be readily compared with the
alkyl cation [(L3a)La(CH2SiMe3)(THF)4]+ (5) reported
previously.11c The latter carries four, instead of three, coordi-
nated THF molecules, revealing the increased steric demand of
the ligand L3b relative to L3a. A comparison of the key bond
angles within the [RC(NAr)2]La core of the neutral (3a, 3b)
and cationic (4, 5) complexes is shown in Figure 4.
Figure 1. Molecular structure of 2 (ellipsoid probability level at
50%).
Table 1. Selected Bond Lengths (Å) and Angles (deg) for
Complex 2
Bond Lengths
La-C15
La-C22
La-C23
La-N1
La-N2
La-N3
La-N4
2.699(4)
2.687(4)
3.150(4)
2.741(3)
2.744(3)
2.714(3)
2.384(3)
Despite the success of the tribenzyl complex 1 in the
synthesis of various derivatives, it still does not provide
access to the lanthanum dibenzyl complex of the ꢀ-diketimi-
nate ligand L1. The reaction of 1 with the diketimine HL1
in THF-d8 at ambient temperature is slow compared to the
reactions described above, which are essentially instanta-
neous. After 6 h (with agitation of the mixture, as 1 is
relatively poorly soluble) approximately 50% of HL1 is
consumed, as seen from the resonance of the acidic proton
at δ 12.07 ppm. New resonances are observed, partly
attributable to the expected (L1)La(CH2Ph)2(THF) species
(vide infra), but also arising from gradual decomposition of
this product. After full conversion of HL1 (after 12 h), the
1H NMR spectrum is complex, showing that this is an
inconvenient method for the synthesis of the ꢀ-diketiminate
dibenzyl species.
Bond Angles
La-C15-C16
La-C22-C23
N1-Si-N4
N4-La-C15
N4-La-C22
98.6(3)
94.8(2)
99.43(15)
88.06(13)
110.5(1)
La-C(15)-C(16) angle of 98.6(3)° suggest additional η2-like
interaction of the benzyl group with the metal center in 2. This
may be the reason for the enhanced thermal stability of 2 over
the trimethylsilylmethyl analogue. The structure of 2 shows a
distorted octahedral geometry, with the three nitrogen atoms of
the TACN moiety coordinated in a facial arrangement to
lanthanum, with average La-N distances of 2.74 Å. The
compound in the solid state is asymmetric, as seen in the
difference between the two N(4)-La-CH2 angles of 88.06(13)°
for C15 and 110.5(1)° for C22. This asymmetry is similar to
that of the related trimethylsilymethyl derivatives of rare-earth
metals. Nevertheless, the NMR (THF-d8) spectra of 2 are
consistent with an average Cs symmetry, even down to -60
Salt Metathesis. The problems observed above in the
synthesis of ꢀ-diketiminate La dialkyl compounds are reminis-
cent of reported unsuccessful attempts to prepare (L1)yttrium
dialkyl complexes via alkane and amine elimination as well as
salt metathesis starting from YCl3.19 However, reaction of
20
YI3(THF)3.5 with KL1 afforded (L1)YI2(THF),19,21 which
1
served to generate the dialkyl complex (L1)Y(CH2-
SiMe3)2(THF).19 Thus we pursued the synthesis of
(L1)La(CH2Ph)2(THF) via sequential salt metathesis. Reaction
of LaBr3(THF)4 with KL1 in THF afforded (L1)LaBr2(THF)2
(6) as yellow crystals in 76% isolated yield. A single-crystal
X-ray structure determination of 6 (Figure 5 and Table 4) shows
the complex to be monomeric with a distorted octahedral
geometry around the metal center. The ligand nitrogen and the
THF oxygen atoms N(1), N(1a), O(1), and O(1a) occupy the
equatorial positions and Br(1) and Br(2) the axial sites. A
crystallographic mirror plane is present through C(15), La, Br(1),
and Br(2). The structure of 6 is related to that of [HC-
°C, with a broad H LaCH2 resonance at δ 1.96 ppm and its
13C resonance at δ 66.8 (1JCH ) 133.6 Hz). Thus 2 appears to
be more flexible in its geometry than related trimethylsilylmethyl
derivatives.11a
We showed earlier that La(CH2Ph)3(THF)3 (1) reacts smoothly
with the sterically demanding benzamidine H[PhC(NAr)2]
(HL3a, Ar ) 2,6-iPr-C6H3) to afford (L3a)La(CH2Ph)2(THF)
(3a).10 The more sterically hindered amidine H[tBuC(NAr)2]
(HL3b), with a tert-butyl substituent on the backbone,18 also
leads to the corresponding amidinate dibenzyl complex
(L3b)La(CH2Ph)2(THF) (3b) with concomitant elimination of
1 equiv of toluene. The isolated yield of 3b from crystallization
of 60% is somewhat lower than for 3a (70%) due to the higher
(19) Hayes, P. G. Ph.D. Dissertation, University of Calgary, Canada,
2004.
(18) (a) Coles, M. P.; Swenson, D. C.; Jordan, R. F.; Young, V. G., Jr
Organometallics 1997, 16, 5183. (b) Coles, M. P.; Swenson, D. C.; Jordan,
R. F.; Young, V. G., Jr Organometallics 1998, 17, 4042.
(20) Izod, K.; Liddle, S. T.; Clegg, W. Inorg. Chem. 2004, 43, 214.
(21) Liddle, S. T.; Arnold, P. L. Dalton Trans. 2007, 3305.

Synthesis of Lanthanum Dialkyl Complexes
Organometallics, Vol. 27, No. 4, 2008 707
Figure 2. Molecular structure of 3b (left) and 3a (right) (ellipsoid probability level at 50%).
Table 2. Selected Bond Lengths (Å) and Angles (deg) for Complex
3b in Comparison to 3a
3b
Bond Lengths
3a
La(1)-C(130)
La(1)-C(131)
La(1)-C(136)
La(1)-C(137)
La(1)-C(138)
La(1)-C(139)
La(1)-N(11)
La(1)-N(12)
La(1)-O(1)
2.595(3)
2.850(3)
3.267(3)
2.585(3)
3.029(3)
3.421(3)
2.540(2)
2.507(3)
2.610(2)
2.590(5)
2.897(5)
3.030(3)
2.632(3)
2.847(5)
3.401(5)
2.497(3)
2.581(3)
2.557(3)
Bond Angles
La(1)-C(130)-C(131)
La(1)-C(137)-C(138)
C(11)-N(11)-C(113)
C(118)-N(12)-C(113)
85.01(19)
92.9(2)
129.4(3)
129.8(3)
87.0(3)
83.3(2)
128.3(4)
124.3(3)
(MeCNPh)2]GdBr2(THF)2,22 which has sterically less demand-
ing substituents on the diketiminate nitrogen atoms. In the latter
compound, the gadolinium is located in the plane defined by
the NCCCN ligand backbone. In 6 the lanthanum center is
located out of plane by 0.7347(3) Å. This puckered geometry
is similar to that of scandium and yttrium complexes with
ꢀ-diketiminates containing the 2,6-diisopropylphenyl substitu-
ents.23 The steric demand of the ligand L1 is illustrated by the
comparison of six-coordinate 6 with lanthanum dibromide
complexes of N,N-bidentate amidinate and aminopyrimidinato
ligands,24 which are seven-coordinate due to the presence of
an additional THF ligand.
Figure 3. Molecular structure of 4 (ellipsoid probability level at
50%, anion is omitted).
described above and elsewhere19). Nevertheless, reaction of 6
with methyl magnesium chloride in THF also led to quantitative
ligand transfer from lanthanum to magnesium to generate the
known compound (L1)MgMe(THF).25 In contrast, reaction of
the dibromide 6 with 2 equiv of PhCH2K in THF resulted in
formation of the desired complex (L1)La(CH2Ph)2(THF) (7,
Scheme 3), which was isolated as analytically pure material by
crystallization from a 3:1 hexane/THF mixture in 46% yield.
Although crystals of sufficient quality for an X-ray structure
determination could not be obtained, the NMR spectroscopic
features of 7 are consistent with its formulation. The resonances
of the ligand methyne group are found at δ 5.25 ppm (1H) and
δ 96.6 ppm (13C; d, JCH ) 154 Hz) and those of the La-CH2
groups at δ 1.35 ppm (1H) and δ 70.3 ppm (13C; t, JCH ) 131
Hz). The dibenzyl complex 7 reacts in THF-d8 with the Brønsted
acid [HPhNMe2][BPh4] under liberation of toluene and the
formation of the ionic monobenzyl species [(L1)La(CH2Ph)(THF-
d8)x][BPh4], as seen by NMR spectroscopy. The La-CH2
The lanthanum dibromide 6 was then used in subsequent
alkylation reactions. Lithium alkyl reagents were avoided in
view of the high affinity of L1 anion to the lithium cation (as
(22) Drees, D.; Magull, J. Z. Anorg. Allg. Chem. 1994, 620, 814.
(23) (a) Conroy, K. D.; Hayes, P. G.; L, K.; Piers, W. E.; Parvez, M.
Organometallics 2007, 26, 4464. (b) P, G.; Piers, W. E.; Parvez, M. J. Am.
Chem. Soc. 2003, 125, 5622. (c) Hayes, P. G.; Piers, W. E.; McDonald, R.
J. Am. Chem. Soc. 2002, 124, 2132. (d) Hayes, P. G.; Lee, L. W. M.; Knight,
L. K.; Piers, W. E.; Parvez, M.; Elsegood, M. R. J.; Clegg, W.; MacDonald,
R. Organometallics 2001, 20, 2533. (e) Lee, L. W. M.; Piers, W. E.;
Elsegood, M. R. J.; Clegg, W.; Parvez, M. Organometallics 1999, 18, 2947.
(24) Kretschmer, W. P.; Meetsma, A.; Hessen, B.; Scottb, N. M.;
Qayyumb, S.; Kempe, R. Z. Anorg. Allg. Chem. 2006, 1936.
(25) Bailey, P. J.; Dick, C. M. E.; Fabre, S.; Parsons, S. J. Chem. Soc.,
Dalton Trans. 2000, 1655.

708 Organometallics, Vol. 27, No. 4, 2008
Bambirra et al.
Table 3. Selected Bond Lengths (Å) and Angles (deg) for
Complex 4
Table 4. Selected Bond Lengths (Å) and Angles (deg) for
Complex 6
Bond Lengths
Bond Lengths
La(1)-C(130)
La(1)-N(11)
La(1)-N(12)
La(1)-O(11)
La(1)-O(12)
La(1)-O(13)
2.503(5)
2.492(3)
2.563(3)
2.582(3)
2.564(3)
2.559(3)
La-N(1)
La-Br(1)
La-Br(2)
La-O(1)
2.470(3)
2.8592(9)
2.9025(9)
2.592(3)
Bond Angles
Br(1)-La-Br(2)
O(1)-La-O(1)′
N(1)-La-Br(1)
N(1)-La-Br(2)
149.89(2)
91.25(10)
93.50(7)
Bond Angles
La(1)-C(130)-C(131)
C(11)-N(11)-C(113)
C(118)-N(12)-C(113)
132.0(3)
129.2(3)
130.0(3)
110.39(7)
respectively, suggests that one of the ligand backbone methyl
groups has been deprotonated. From a 0.2 mmol scale
reaction, performed at 80 °C, crystalline material was
obtained that allowed X-ray diffraction. Although the crystal
quality was poor, the composition and connectivity of the
product was unequivocally established. It can be formulated
as [(L1-H)2La][K(THF)4] (8, Figure 6), and its structure in
the solid state is a coordination polymer of the type {[µ-η2:
η1-ArNC(Me)CHC(CH2)NAr]2La[K(THF)4]}∞, in which [(L1-
H)2La] anions are bridged via the methylene groups of the
deprotonated ligands to [K(THF)4] cations in which the K
ions are distorted octahedrons with the ligand methylene
groups in the axial positions. The decomposition reaction thus
involves deprotonation of the diketimine methyl group and
a ligand redistribution. Very recently such a combination of
ligand deprotonation and ligand redistribution was described
for the reaction of (L1)YI2(DME) with
2 equiv of
Figure 4. Schematic representation of the core structures of the
neutral (3a, 3b) and cationic (4, 5) compounds.
KCH2SiMe3 to yield {[µ-η5:η1-ArNC(Me)CHC(CH2)NAr]2-
Y[K(DME)2]}.21 This product differs from 8 in its solid state
structure in that it is monomeric, with the K ion interacting
with the arene groups of the ligand rather than with the
deprotonated methyl group.
Conclusions
We have applied three different synthesis routes to the
preparation of lanthanum dialkyl complexes of three types of
monoanionic ancillary ligand. The in situ alkylation procedure
of LaBr3(THF)4 with 3 equiv of trimethylsilylmethyl lithium
works well for triazacyclononane-amide and sterically demand-
ing amidinate ligands, although isolated yields are moderate (at
best up to 50%). This may be due to the predominant formation
of [LaR4]- species in the alkylation, although the alkyl groups
appear to redistribute readily in this highly dynamic reaction
mixture. The method fails when ligands with a very high affinity
for Li+ are used (in casu a sterically demanding ꢀ-diketiminate).
An alternative could be the use of alkylpotassium reagents in
the in situ alkylation process, this still needs to be investigated.
The use of the preformed trialkyl La(CH2Ph)3(THF)3 in
combination with ligands with active protons HL affords very
smooth and clean reactions, provided the HL species is
sufficiently reactive. For the sterically demanding ꢀ-diketiminate
ligand, the best option is stepwise salt metathesis (first introduc-
ing the ligand on the metal, then the alkyl groups), using
potassium reagents exclusively. The observations made in this
study can be useful for the identification of successful synthesis
protocols for new organometallic compounds of the larger rare-
earth metals.
Figure 5. Molecular structure of 6 (ellipsoid probability level at
50%).
resonances in the cation at δ 1.61 ppm (1H) and δ 77.2 ppm
(13C; t, JCH ) 134 Hz) show typical downfield shifts, relative
to the precursor 7, associated with the formation of a cation.10,11
When monitoring the reaction of 6 with 2 equiv of KCH2Ph
in THF-d8 by NMR spectroscopy, it was observed that initial
precipitation of KBr and formation of 7 is followed by a
slow decomposition reaction in which toluene is released and
a new compound is formed with a complex 1H NMR
spectrum. Four inequivalent ligand iPr groups appear to be
present (four methyne septets and eight methyl doublets),
but only a single ligand backbone methyne resonance (δ 5.19
ppm). The presence of three resonances in a 3:1:1 ratio, at δ
1.67 ppm (s), 2.78 and 2.07 ppm (both d, J ) 2.4 Hz)
Experimental Section
General Considerations. All experiments were carried out under
an inert atmosphere of purified N2 using standard Schlenk and

Synthesis of Lanthanum Dialkyl Complexes
Organometallics, Vol. 27, No. 4, 2008 709
Scheme 3
3
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. H[HC(MeCNAr)2] (Ar ) 2,6-
iPr2C6H3, HL1),14 Me2TACNSiMe2NHtBu (HL2),8e Me3SiCH2Li,26
LaBr3(THF)4,27 KCH2Ph,28 H[RC(N-2,6-iPr-C6H3)2] (R ) Ph,8g
HL3a; tBu,29 HL3b), and La(CH2Ph)3(THF)310 (1) were prepared
according to published procedures. [PhNMe2H][B(C6F5)4] (Strem)
was used as purchased. NMR spectra were recorded on Varian
Unity 500, VXR 300, and Gemini 200 spectrometers. Elemental
analyses were performed at the Microanalytical Department of H.
Kolbe (Mülheim an der Ruhr).
(d, JHH ) 6.5 Hz, 12 H, CHMe2), -0.18 (s, 27 H, CH2SiMe3),
-1.15 (s, 6 H, CH2SiMe3).
Reaction of LaBr3(THF)4/3 LiCH2SiMe3 with HL1. Solid
LiCH2SiMe3 (280 mg, 3.00 mmol) was added to a suspension of
LaBr3(THF)4 (0.66 g, 1.00 mmol) in THF (10 mL, ambient
temperature). Within 5 min a colorless solution had formed. The
solution was stirred for 30 min, after which HL1 (0.42 g, 1.00
mmol) was added. The resulting yellowish solution was stirred for
18 h, after which the volatiles were removed under vacuum. The
mixture was extracted with a pentane/toluene mixture (1:1, 50 mL).
The obtained extract was evaporated to dryness, yielding
(L1)Li(THF),15 identified by NMR spectroscopy, as light yellowish
crystals (350 mg, 0.7 mmol, 70.5%).
Synthesis of [Me2TACNSiMe2NtBu]La(CH2Ph)2 (2). Solid 1
(125.0 mg, 0.2 mmol) was reacted with a solution of HL2 (57.0
mg, 200 µmol) in benzene (2 mL). The resulting red-brown solution
was left to stand overnight, after which yellow crystals of 2 had
deposited (70 mg, 0.11 mmol, 58%). H NMR (500 MHz, THF-
d8, 20 °C): δ 6.83 (t, JHH ) 6.6 Hz, 2 H, m-Ph), 6.57 (d, JHH
In Situ Alkylation of LaBr3(THF)4. A mixture of LaBr3(THF)4
(66 mg, 0.1 mmol) and 3 equiv of LiCH2SiMe3 (28 mg, 300 µmol)
1
1
was dissolved in THF-d8 at ambient temperature. H NMR (500
3
3
MHz, THF-d8, 20 °C): δ -0.21 (s, 27H, SiMe3), -0.93 (s br, 6H,
CH2Si). 13C{1H} NMR (125.8 MHz, THF-d8, 20 °C): δ 49.0 (br,
CH2Si), 5.69 (SiMe3). In similar fashion, samples with La:Li ratios
)
3
6.6 Hz, 4 H, o-Ph), 6.26 (t, JHH ) 6.6 Hz, 2 H, m-Ph), 3.17 (m,
2 H, NCH2), 2.70 (m, 6 H, NCH2), 2.61 (m, 2 H, NCH2), 2.46 (m,
2 H, NCH2), 2.40 (s, 6H, NMe), 1.96 (br s, 4 H, LaCH2), 1.31 (s,
9 H, tBu), 0.24 (s, 6 H, SiMe2). 13C NMR (125.7 MHz, THF-d8,
1
1:4 and 1:5 were made. Their H NMR spectra are shown in the
Supporting Information.
Reaction of LaBr3(THF)4/4 LiCH2SiMe3 with HL3a. Solid
LiCH2SiMe3 (188 mg, 2.00 mmol) was added to a suspension of
LaBr3(THF)4 (335 mg, 0.50 mmol) in THF (20 mL) at ambient
temperature. The colorless solution was stirred for 2 h, after which
[PhC(N-2,6-iPr2C6H3)2]H (HL3a, 220 mg, 0.50 mmol) was added.
The resulting yellowish solution was stirred for 2 h, after which
the volatiles were removed under vacuum. Residual THF was
removed from the solids by stirring with pentane (10 mL), which
was subsequently removed under vacuum. Attempts to extract the
mixture with pentane (2 × 50 mL) did not afford any soluble
1
20 °C): δ 155.3 (Ph Cipso), 130.8 (d, JCH ) 154.8 Hz, Ph CH),
123.3 (d, 1JCH ) 151.9 Hz, Ph CH), 116.2 (d, 1JCH ) 157.8 Hz, Ph
CH), 66.8 (t, 1JCH ) 133.6 Hz, LaCH2), 58.5 (t, 1JCH ) 134.0 Hz,
NCH2), 56.1 (t, 1JCH ) 134.3 Hz, NCH2), 55.0 (s, tBu C), 48.4 (q,
1JCH ) 134.8 Hz, NCH2), 47.8 (t, JCH ) 132.7 Hz, NCH2), 36.4
1
1
1
(q, JCH ) 123.9 Hz, NMe), 5.0 (q, JCH ) 117.0 Hz, Me). Anal.
Calcd for C31H50N4SiLa(C6H6)0.3: C 56.95; H 7.81; N 8.85. Found:
C, 56.90; H, 7.74; N, 8.63.
Synthesis of [tBuC(NAr)2]La(CH2Ph)2(THF) (3b). Solid
La(CH2Ph)3(THF)3 (1, 410 mg, 0.50 mmol) and [tBuC(N-2,6-
iPr2C6H3)2]H (HL3b, 0.21 g, 0.50 mmol) were mixed and dissolved
in THF (10 mL). The solution was stirred at ambient temperature for
1 h, after which the volatiles were removed under vacuum. The residue
was dissolved in hexanes (3 mL) with some added THF (ca. 1.0 mL).
Cooling to -30 °C afforded crystalline 3b (250 mg, 0.30 mmol, 60%).
1H NMR (500 MHz, C6D6, 20 °C): δ 7.07 (d, 3JHH ) 7.3 Hz, 4 H, Ar
H), 7.01 (d, 3JHH ) 7.3 Hz, 2 H, Ar H), 6.96 (t, 3JHH ) 7.1 Hz, 4 H,
Bz m-H), 6.61 (d, 3JHH ) 7.1 Hz, 4 H, Bz o-H), 6.43 (t, 3JHH ) 7.1
Hz, 2 H, Bz p-H), 3.71 (sept, 3JHH ) 6.6 Hz, 4 H, CHMe2), 2.52 (m,
4 H R-THF), 2.23 (s, 4 H, LaCH2), 1.38 (d, 3JHH ) 6.6 Hz, 12 H, iPr
Me), 1.31 (d, 3JHH ) 6.7 Hz, 12 H, iPr Me), 1.05 (s, 9 H, tBu), 0.98
(m, 4 H ꢀ-THF). 13C NMR (75.4 MHz, C6D6, 20 °C): δ 178.8 (NCN),
150.0 (Bz Cipso), 145.4 (Ar Cipso), 141.8 (Ar C), 131.2 (d, 1JCH ) 153.7
1
product. Analysis of the residue by H NMR in THF-d8 showed
the presence of two compounds in a 4:1 ratio, as evidenced by two
sets of signals attributable to the amidinate resonances. The major
product appears to be an ionic species containing the {[PhC(N-
2,6-iPr2C6H3)2]La(CH2SiMe3)3} anion. 1H NMR (300 MHz, THF-
3
d8) major product: δ 6.80 (d, JHH ) 7.2 Hz, 2 H, C6H3), 6.6 (m,
3
3
5 H, Ph), 6.55 (d, JHH ) 7.2 Hz, 4 H, C6H3), 3.41 (sept, JHH
)
6.5 Hz, 4 H, CHMe2), 1.09 (d, 3JHH ) 6.5 Hz, 12 H, CHMe2), 0.68
(26) Lewis, H. L.; Brown, T. L. J. Am. Chem. Soc. 1970, 92, 4664.
(27) (a) LaBr3: Taylor, M. D.; Carter, C. P. J. Inorg. Nucl. Chem. 1962,
24, 387. (b) LaBr3(THF)4: Herzog, S.; Gustav, K.; Krüger, E.; Oberender,
H.; Schuster, R. Z. Chem. 1963, 3, 428.
(28) Prepared according to the procedure described by: Schlosser, M.;
Hartmann, J. Angew. Chem., Int. Ed. Engl. 1973, 85, 544.
(29) Xia, A.; El-Kaderi, H. M.; Jane Heeg, M.; Winter, C. H. J.
Organomet. Chem. 2003, 682, 224.
1
1
Hz, Bz CH), 128.5 (d, JCH ) 157.5 Hz, Ar CH), 123.8 (d, JCH
156.2 Hz, Ar CH), 122.0 (d, JCH ) 155.1 Hz, Bz CH), 116.8 (d,
)
1

710 Organometallics, Vol. 27, No. 4, 2008
Bambirra et al.
Figure 6. Solid state structure of 8. Chain of the polymeric structure (top) and view of the repeating unit (bottom) (ellipsoid probability
level at 50%).
Table 5. Crystal Data and Collection Parameters of Complexes 2, 3b, 4, 6, and 8
2
3b
4
6
8
formula
2[C28H47LaN4Si] · [C6H6] C47H65LaN2O
[C48H74LaN2O3]+
·
[C37H57Br2LaN2O2] · [C58H80LaN4]-.[(C4H8O)4K]+
·
[C24H20B]- · [C4H8O]
1257.37
[C4H8O]
0.5(C4H8O) · 0.5(C6H14)
1378.87
fw
1291.51
812.95
932.70
cryst color, habit
cryst size (mm)
cryst syst
space group
a (Å)
orange, needle
0.41 × 0.13 × 0.10
monoclinic
Pc, 7
17.277(1)
9.7710(6)
yellow, block
0.43 × 0.29 × 0.14
monoclinic
P21/c, 14
12.0223(9)
38.554(3)
yellow, block
0.35 × 0.24 × 0.19
monoclinic
P21/c, 14
21.148(1)
yellow, block
0.45 × 0.41 × 0.36
monoclinic
P21/m, 11
10.045(2)
20.093(4)
colorless, block
0.53 × 0.23 × 0.19
monoclinic
C2/c, 15
21.519(3)
b (Å)
17.242(1)
14.637(2)
c (Å)
18.618(1)
18.699(1)
18.497(1)
10.410(2)
48.082(7)
R (deg)
ꢀ (deg)
γ (deg)
V (Å3)
94.561(1)
102.521(1)
92.309(1)
91.951(3)
96.458(2)
3133.0(3)
2
1.369
14.27
1340
2.57, 27.51
0.0283
0.0650
8461.(1)
8
1.276
10.45
3408
2.43, 28.28
0.0481
0.0991
6739.2(6)
4
1.239
6.83
2664
2.26, 26.37
0.0575
0.1341
2099.9(7)
2
1.475
29.57
952
2.82, 26.73
0.0464
0.1271
15049(4)
8
1.207
6.73
5808
2.32, 28.28
0.0911
0.1753
Z
F
calcd, g cm3
µ, cm-1
F(000), electrons
θ range (deg)
R1
wR2(all data)
index ranges (h,k,l) (22, -11f12, ( 24
(16, ( 51, -11f24 (26, ( 21, ( 23
(12, ( 25, -11f13 (28, ( 19, -63f64
T (K)
100
100
100
100
100
GOF
0.972
1.120
1.147
1.037
1.255
1JCH ) 157.4 Hz, Bz CH), 70.0 (t, 1JCH ) 134.1 Hz, LaCH2), 68.7 (t,
1JCH ) 149.4 Hz, R-THF), 45.4 (s, tBu C), 31.0 (d, 1JCH ) 127.8 Hz,
iPr CH), 28.8 (q, 1JCH ) 125.2 Hz, iPr Me), 25.2 (t, 1JCH ) 133.9 Hz,
ꢀ-THF), 25.2 (q, JCH ) 125.2 Hz, iPr Me), 23.6 (q, JCH ) 129.4
Hz, tBu C). Anal. Calcd for C47H65LaN2O [812.94]: C, 69.44; H, 8.06;
N, 3.45. Found: C, 69.70; H, 8.26; N, 3.38.
(4). THF (1 mL) was added to a mixture of 3b (81.0 mg, 100.0
µmol) and [HNMe2Ph][B(C6H5)4] (44.0 mg, 0.1 mmol). The
resulting yellowish solution was layered with 2 mL of hexanes.
Upon standing overnight at ambient temperature, yellow crystals
formed (80 mg, 64%). 1H NMR (500 MHz, THF-d8, 20 °C): δ
1
1
3
7.15–7.08 (m, 6 H, Ar H), 7.00 (t, JHH ) 7.3 Hz, 2 H, Bz m-H),
Synthesis of {[tBuC(NAr)2]La(CH2Ph)(THF)3}[BPh4] · THF
6.67 (d, 3JHH ) 7.3 Hz, 2 H, Bz o-H), 6.57 (t, 3JHH ) 7.3 Hz, 1 H,

Synthesis of Lanthanum Dialkyl Complexes
Organometallics, Vol. 27, No. 4, 2008 711
3
Bz p-H), 3.30 (sept, JHH ) 6.7 Hz, 4 H, CHMe2), 1.70 (s, 4 H,
γ-CH), 3.03 (sept, 3JHH ) 6.8 Hz, 4H, CHMe2), 1.80 (s, 6H, Me),
3
3
3
LaCH2), 1.35 (d, JHH ) 6.7 Hz, 12 H, iPr Me), 1.18 (d, JHH
)
1.35 (s, 4H, LaCH2), 1.12 (d, JHH ) 6.8 Hz, 12H, CHMe2), 1.10
6.7 Hz, 12 H, iPr Me), 0.95 (s, 9 H, tBu). 13C NMR (75.4 MHz,
3
(d, JHH ) 6.8 Hz, 12H, CHMe2). 13C NMR (500 MHz, THF-d8,
1
THF-d8, 20 °C): δ 182.7 (NCN), 166.1 (q, JCB ) 49.6 Hz, BPh4
20 °C): δ 166.5 (C-N), 152.3 (ipso, Ph), 147.3 (ipso, Ar, C-N),
1
C
ipso), 151.6 (Bz Cipso), 145.0 (Ar Cipso), 143.5 (Ar C), 137.9 (dt,
144.4 (ipso, Ar, C-iPr), 131.4 (d, JCH ) 152.9 Hz, Ph-m), 127.2
1JCH ) 153.6, 7.3 Hz, BPh4 o-H), 131.9 (d, JCH ) 156.2 Hz, Bz
1
1
1
(d, JCH ) 160.9 Hz, Ar), 125.8 (d, JCH ) 155.6 Hz, Ar), 122.8
1
1
1
1
CH), 131.6 (d, JCH ) 160.3 Hz, Ar CH), 126.7 (d, JCH ) 152.5
(d, JCH ) 150.2 Hz, Ph-o), 117.7 (d, JCH ) 158.2 Hz, Ph-p),
1
1
96.6 (d, 1JCH ) 154.2 Hz, γ-C), 70.3 (t, 1JCH ) 130.6 Hz, LaCH2),
Hz, BPh4-m), 123.3 (d, JCH ) 156.2 Hz, Ar CH), 120.7 (d, JCH
) 152.1 Hz, Bz CH), 118.2 (d, 1JCH ) 160.3 Hz, Bz CH), 81.2 (b,
1
1
30.3 (d, JCH ) 126.8 Hz, CHMe2), 26.4 (q, JCH ) 127.5 Hz,
Me), 26.3 (q, JCH ) 127.1 Hz, CHMe2). Anal. Calcd for
1
1
LaCH2), 47.0 (s, tBu C), 32.0 (d, JCH ) 125.5 Hz, iPr CH), 30.5
(q, 1JCH ) 125.4 Hz, iPr Me), 28.0 (q, 1JCH ) 125.2 Hz, iPr Me).
C47H63LaN2O [810.92]: C, 69.61; H, 7.83; N, 3.45. Found: C, 70.10;
H, 8.13; N, 3.43.
1
245. (q, JCH
) 126.2 Hz, tBu Me). Anal. Calcd for
C76H102LaBN2O4 [1257.3]: C, 72.60; H, 8.18; N, 2.23. Found: C,
71.60; H, 8.23; N, 2.51. For this material we consistently obtained
analyses with a relatively low carbon content, but could not detect
specific impurities.
Synthesis of {[µ-η2:η1-ArNC(Me)CHC(CH2)NAr]2La[K-
(THF)4]}∞ (8). To a solution of 6 (172 mg, 0.2 mmol) in THF (2
mL) was added a THF (5 mL) solution of KCH2Ph (52 mg, 0.4
mmol). The dark orange solution was stirred at 80 °C for 24 h,
allowed to cool to ambient temperature, and filtered. The filtrate
was layered with hexanes (5 mL) and left to stand overnight,
whereupon the title compound crystallized as colorless needles (92
mg, crude yield 70%). Its structure was corroborated by X-ray
diffraction analysis. Elemental analysis of the bulk solid revealed
significantly lower C and H values than expected for pure 8,
indicating the presence of coprecipitated metal salt. 1H NMR (500
MHz, THF-d8, 20 °C): δ 6.97 (d, 3JHH ) 7.5 Hz, 2H, C6H3), 6.94
Synthesis of KL1. To a stirred solution of HL1 (2.0 g, 5 mmol)
in toluene (20 mL) was added solid KCH2Ph (0.65 g, 5 mmol).
The initially orange suspension formed a yellow solution within 5
min. The solvent was removed and the residue was rinsed with
cold (0 °C) pentane, yielding the title compound (2.2 g, 4.8 mmol,
1
96%). H NMR (300 MHz, THF-d8, 20 °C): δ 5.89 (d, 4H, J )
7.6 Hz, C6H3), 6.68 (t, 2H, J ) 7.6 Hz, C6H3), 4.19 (s, 1H, γ-CH),
3.28 (sept, 4H, J ) 6.8 Hz, CHMe2), 1.48 (s, 6H, Me), 1.11 (d,
12H, J ) 6.8 Hz, CHMe2), 1.03 (d, 12H, J ) 6.8 Hz, CHMe2). 13
C
3
3
(d, JHH ) 7.5 Hz, 2H, C6H3), 6.84 (t, JHH ) 7.5 Hz, 2H, C6H3),
NMR (300 MHz, THF-d8, 20 °C): δ 161.5 (C-N), 154.0 (ipso, Ar,
C-N), 144.1 (ipso, Ar, C-iPr), 124.0 (d, J ) 151.6 Hz, Ar), 121.9
(d, J ) 158.6 Hz, Ar), 91.7 (d, J ) 150.8 Hz, γ-C), 29.0 (d, J )
131.2 Hz, CHMe2), 25.8 (q, J ) 126.0 Hz, Me), 25.4 (q, J ) 125.3
Hz,CHMe2), 25.2 (q, J ) 122.6 Hz, CHMe2). Anal. Calcd for
C29H41N2K [456.7]: C, 76.26; H, 9.05; N, 6.13. Found: C, 76.55;
H, 9.38; N, 6.13.
3
3
6.73 (t, JHH ) 7.5 Hz, 2H, C6H3), 6.70 (d, JHH ) 7.5 Hz, 2H,
3
C6H3), 6.69 (d, JHH ) 7.5 Hz, 2H, C6H3), 5.18 (s, 2H, γ-CH),
3.61 (sept, JHH ) 7.0 Hz, 2H, CHMe2), 3.48 (sept, JHH ) 7.0
Hz, 2H, CHMe2), 3.14 (sept, JHH ) 7.0 Hz, 2H, CHMe2), 2.95
(sept, JHH ) 7.0 Hz, 2H, CHMe2), 2.78 (d, JHH ) 2.4 Hz, 2H,
3
3
3
3
3
3
NCCH2), 2.07 (d, JHH ) 2.4 Hz, 2H, NCCH2), 1.67 (s, 6H, Me),
3
3
1.45 (d, JHH ) 7.0 Hz, 12H, CHMe2), 1.22 (d, JHH ) 7.0 Hz,
Synthesis of (L1)LaBr2(THF)2 (6). To a suspension of
LaBr3(THF)4 (1330 mg, 2.00 mmol) in THF (30 mL) was added a
THF (5 mL) solution of KL1 (0.91 g, 2 mmol). The yellowish
reaction mixture was stirred for 2 h and centrifuged to separate
formed KBr. The clear yellow solution was evaporated to dryness
to afford a sticky solid, which was subsequently rinsed with hexanes
(10 mL) to yield 6 as a yellowish microcrystalline solid (1300 mg,
1.5 mmol, 76%). 1H NMR (500 MHz, THF-d8, 20 °C): δ 7.20–7.14
(m, 6H, C6H3), 5.01 (s, 1H, γ-CH), 3.48 (sept, 4H, J ) 6.6 Hz,
CHMe2), 1.68 (s, 6H, Me), 1.32 (d, 12H, J ) 6.6 Hz, CHMe2),
1.07 (d, 12H, J ) 6.6 Hz, CHMe2). 13C NMR (125.8 MHz, THF-
d8, 20 °C): δ 166.7 (C-N), 146.7 (ipso, Ar, C-iPr), 144.1 (ipso, Ar,
C-N), 127.8 (d, J ) 160.0 Hz, Ar), 126.1 (d, J ) 156.7 Hz, Ar),
100.6 (d, J ) 149.5 Hz, γ-C), 30.3 (d, J ) 129.3 Hz, CHMe2),
26.5 (q, J ) 127.0 Hz, Me), 26.4 (q, J ) 126.1 Hz,CHMe2), 26.3
(q, J ) 126.1 Hz, CHMe2). Anal. Calcd for C37H57Br2N2LaO2
[860.75]: C, 51.64; H, 6.68; N, 3.26. Found: C, 51.58; H, 6.63; N,
3.25.
Reaction of 6 with MeMgCl. To a solution of (L1)LaBr2(THF)2
(6, 860 mg, 1.00 mmol) in THF (10 mL) was added a THF solution
(3 M) of MeMgCl (0.70 mL, 2 mmol). The yellow solution was
stirred for 2 h, after which the solvent was removed under reduced
pressure. The residue was extracted with a hexane/THF mixture
(9:1, 10 mL) and filtrated. The filtrate cooled to -30 °C yielded
(L1)MgMe(THF),25 identified by NMR spectroscopy, as white
crystals (370 mg, 70%).
12H, CHMe2), 1.08 (d, 3JHH ) 7.0 Hz, 12H, CHMe2), 0.97 (d, 3JHH
3
) 7.0 Hz, 12H, CHMe2), 0.91 (d, JHH ) 7.0 Hz, 12H, CHMe2),
3
3
0.88 (d, JHH ) 7.0 Hz, 12H, CHMe2), 0.41 (d, JHH ) 7.0 Hz,
12H, CHMe2), 0.11 (d, JHH ) 7.0 Hz, 12H, CHMe2). 13C NMR
3
(125.7 MHz, THF-d8, 20 °C): δ 164.5 (C-N), 154.0 (ipso, C6H3),
149.4 (ipso, C6H3), 146.9 (ipso, C6H3), 145.9 (ipso, C6H3), 143.3
(ipso, C6H3) 142.4 (ipso, C6H3), 127.0 (d, 1JCH ) 160.2 Hz, C6H3),
1
1
124.8 (d, JCH ) 160.9 Hz, C6H3), 124.5 (d, JCH ) 156.0 Hz,
1
1
C6H3), 124.0 (d, JCH ) 155.6 Hz, C6H3), 123.6 (d, JCH ) 158.2
Hz, C6H3), 122.4 (d, JCH ) 158.6 Hz, C6H3), 100.6 (d, JCH
152.2 Hz, γ-C), 77.0 (t, JCH ) 153.4 Hz, NCCH2), 33.3 (d, JCH
) 126.8 Hz, CHMe2), 29.3, 29.2, 29.1 (d, JCH ) 127.8 Hz,
1
1
)
1
1
1
CHMe2), 28.7, 27.9, 26.8, 26.7, 26.5, 25.5, 24.8, 22.4 (Me, CHMe2).
Generation of [(L1)La(CH2Ph)(THF)x][BPh4] (9). A solution
of 7 (26 mg, 0,032 mmol) in THF-d8 (0.6 mL) was added to
[HNMe2Ph][B(C6H5)4] (14 mg, 32.0 µmol). The obtained solution
was transferred into a NMR tube and analyzed by NMR spectros-
copy, which showed full conversion to the ionic monoalkyl species
1
9, toluene, and free PhNMe2. H NMR (500 MHz, 20 °C, THF-
3
d8): δ 7.23 (br, 8H, o-H BPh4), 6.81 (t, JHH ) 7.8 Hz, 8H, m-H
BPh4), 6.68 (t, 3JHH ) 7.8 Hz, 4H, p-H BPh4), 6.56 (t, 3JHH ) 6.60
Hz, 2H, Ph-m), 6.47 (t, 3JHH ) 6.60 Hz, 1H, Ph-p), 6.05 (t, 3JHH
)
6.60 Hz, 2H, Ph-o), 5.3 (s, 1H, γ-CH), 2.80 (sept, 3JHH ) 6.8 Hz,
4H, CHMe2), 1.83 (s, 6H, Me), 1.61 (s, 2H, LaCH2), 1.23 (d, 3JHH
3
) 6.8 Hz, 12H, CHMe2), 1.17 (d, JHH ) 6.8 Hz, 12H, CHMe2).
13C NMR (500 MHz, THF-d8, 20 °C): δ 167.7 (C-N), 166.0 (q,
49.0 Hz, ipso-BPh4), 150.7 (ipso, Ph), 145.0 (ipso, Ar, C-N), 143.9
(ipso, Ar, C-iPr), 137.9 (d, J ) 152.0 Hz, o-BPh4), 133.4 (d, 1JCH
) 162.9 Hz, Ph-m), 128.7 (d, 1JCH ) 158.7 Hz, Ar), 126.7 (d, J )
150.9 Hz, m-BPh4), 125.8 (d, 1JCH ) 155.6 Hz, Ar), 123.5 (d, 1JCH
) 152.7 Hz, Ph-o), 123.0 (d, J ) 155.4 Hz, p-BPh4), 121.0 (d,
Synthesis of (L1)La(CH2Ph)2THF (7). To a solution of 6 (172
mg, 0.2 mmol) in THF (2 mL) was added a THF (4 mL) solution
of KCH2Ph (52 mg, 400 µmol). The orange solution was stirred
for 1 h, filtered, and evaporated to dryness. The residue was
dissolved in a mixture of hexane/THF (3:1, 4 mL total volume)
and cooled to -30 °C, yielding 7 as yellow crystals (75 mg, 0.09
1
1JCH ) 164.7 Hz, Ph-p), 96.8 (d, JCH ) 155.2 Hz, γ-C), 77.2 (t,
1
mmol, 46%). H NMR (500 MHz, THF-d8, 20 °C): δ 7.16–7.08
1
(m, 6H, C6H3), 6.66 (t, 3JHH ) 7.5 Hz, 4H, Ph-m), 6.25 (t, 3JHH
)
1JCH ) 133.8 Hz, LaCH2), 31.2 (d, JCH ) 126.8 Hz, CHMe2),
7.5 Hz, 2H, Ph-p), 6.15 (d, 3JHH ) 7.5 Hz, 4H, Ph-o), 5.25 (s, 1H,
26.1 (q, 1JCH ) 127.0 Hz, Me), 25.0 (q, 1JCH ) 127.0 Hz,CHMe2).

712 Organometallics, Vol. 27, No. 4, 2008
Bambirra et al.
Crystallographic data for 2, 3b, 4, 6, and 8 including atomic
coordinates, full bond distances, and bond angles as well as
anisotropic thermal parameters (CIF). This material is available free
of charge via the Internet at http://pubs.acs.org.
Acknowledgment. Financial support from National Re-
search School Combination-Catalysis (NRSC-C) is gratefully
acknowledged. The authors would like to dedicate this work
to Dr. Karel Mach, on the occasion of his 70th birthday.
Supporting Information Available: Experimental details of the
reaction of LaBr3(THF)4 with varying amounts of LiCH2SiMe3.
OM700919H