Cationic group 3 alkyl complexes with isopropyl-substituted triazacyclononane-amide ligands: Synthesis, structure, and thermal decomposition processes

Article abstract of DOI:10.1021/om060278l

Yttrium and lanthanum dialkyl complexes with the isopropyl-substituted triazacyclononane-amide monoanionic ligands [iPr₂TACN-(B)-NrBu] (B = (CH₂)₂, L1; SiMe₂, L2) are described. For Y, these were obtained by reaction of Y(CH₂SiMe₃) ₂(THF)₂ with HL, whereas for La in situ peralkylation of LaBr₃(THF)₄ preceded reaction with HL. In C ₆D₅Br solvent, reaction of LMR₂ with [PhNMe₂H][B(C₆F₅)₄] results in rapid decomposition involving loss of propene from the ligand. This decomposition is prevented (Y) or retarded (La) in THF solvent. For yttrium, salts of the cations [LYR(THF)]⁺ were isolated and structurally characterized. ES-MS of these cations revealed facile desolvation. At increased nozzle voltages, fragmentation is observed with initial loss of SiMe₄, followed by loss of propene. Thus decomposition is likely to involve initial cyclometalation of a ligand iPr group, followed by propene extrusion. Decomposition of [L2LaR(THF)_x]⁺ in THF solution yields the dinuclear dication {[tBuN(Me₂Si)N-(C₂H₄) ₂N(C₂H₄)NiPr]₂La₂(THF) ₂}²⁺, which was structurally characterized. Kinetic data of the decomposition suggest that the process involves initial THF dissociation.

Full text of DOI:10.1021/om060278l

3486
Organometallics 2006, 25, 3486-3495
Cationic Group 3 Alkyl Complexes with Isopropyl-Substituted
Triazacyclononane-amide Ligands: Synthesis, Structure, and
Thermal Decomposition Processes
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
Andries P. Bruins
Center for Pharmacy, UniVersity of Groningen, Anthonius Deusinglaan 1,
9713 AW Groningen, The Netherlands
ReceiVed March 30, 2006
Yttrium and lanthanum dialkyl complexes with the isopropyl-substituted triazacyclononane-amide
monoanionic ligands [iPr2TACN-(B)-NtBu] (B ) (CH2)2, L1; SiMe2, L2) are described. For Y, these
were obtained by reaction of Y(CH2SiMe3)2(THF)2 with HL, whereas for La in situ peralkylation of
LaBr3(THF)4 preceded reaction with HL. In C6D5Br solvent, reaction of LMR2 with [PhNMe2H][B(C6F5)4]
results in rapid decomposition involving loss of propene from the ligand. This decomposition is prevented
(Y) or retarded (La) in THF solvent. For yttrium, salts of the cations [LYR(THF)]+ were isolated and
structurally characterized. ES-MS of these cations revealed facile desolvation. At increased nozzle voltages,
fragmentation is observed with initial loss of SiMe4, followed by loss of propene. Thus decomposition
is likely to involve initial cyclometalation of a ligand iPr group, followed by propene extrusion.
Decomposition of [L2LaR(THF)x]+ in THF solution yields the dinuclear dication {[tBuN(Me2Si)N-
(C2H4)2N(C2H4)NiPr]2La2(THF)2}2+, which was structurally characterized. Kinetic data of the decomposi-
tion suggest that the process involves initial THF dissociation.
system by intra- or intermolecular metalation reactions involving
the reactive metal-alkyl bond of the catalyst species. In one of
the families of catalysts developed in our group, bearing
monoanionic tetradentate 1,4,7-triazacyclononane-amide4a,9 and
bis(2-dimethylamino)amine-amide10 ancillary ligands, we have
observed evidence for the occurrence of ligand metalation
reactions. In particular, the cationic yttrium alkyl species {[iPr2-
TACN(CH2)2NtBu]YCH2SiMe3}+ was found to decompose
rapidly by loss of SiMe4 and propene,4a a reaction proposed to
be initiated by intramolecular metalation of one of the ligand
Introduction
Cationic electron-deficient transition-metal alkyl complexes
have been extensively studied for their efficiency in catalytic
olefin polymerization processes.1 In contrast, cationic alkyl
complexes of the group 3 metals and lanthanides, [LLnR]+, have
only relatively recently been explored as olefin polymerization
catalysts. Although several families of compounds of this type
have now been found to be active catalysts for olefin
polymerization,2-8 much of their properties still need to be
explored. An important feature in determining potential useful-
ness in catalysis is catalyst stability. A potential source of
catalyst deactivation is the degradation of the ancillary ligand
(6) L ) Crown-ether or THF: (a) Arndt, S.; Spaniol, T. P.; Okuda, J.
Chem. Commun. 2002, 896. (b) Arndt, S.; Zeimentz, P. M.; Spaniol, T. P.;
Okuda, J.; Honda, M.; Tatsumi, K. J. Chem. Soc., Dalton Trans. 2003,
3622. (c) Arndt, S.; Spaniol, T. P.; Okuda, J. Organometallics 2003, 22,
775. (d) Arndt, S.; Spaniol, T. P.; Okuda, J. Angew. Chem., Int. Ed. 2003,
42, 5075.
(7) L ) Amidinate: (a) Bambirra, S.; van Leusen, D.; Meetsma, A.;
Hessen, B.; Teuben, J. H. Chem. Commun. 2003, 522. (b) Bambirra, S.;
Bouwkamp, M. W.; Meetsma, A.; Hessen, B. J. Am. Chem. Soc. 2004, 26,
9182. (c) Hessen, B.; Bambirra, S. World Pat. WO2004000894, 2003.
(8) Other cationic rare earth metal alkyl systems: (a) Luo, Y.; Baldamus,
J.; Hou, Z. J. Am. Chem. Soc. 2004, 126, 13910. Zhang, L.; Luo, Y.; Hou,
Z. J. Am. Chem. Soc. 2005, 127, 14562. (b) Ward, B. D.; Bellemin-
Laponnaz, S.; Gade, L. H. Angew. Chem., Int. Ed. 2005, 44, 1668 (c)
Henderson, L. D.; MacInnis, G. D.; Piers, W. E.; Parvez, M. Can. J. Chem.
2004, 82, 162. (d) Hayes, P. G.; Welch, G. C.; Emslie, D. J. H.; Noack, C.
L.; Piers, W. E.; Parvez, M. Organometallics 2003, 22, 1577. (e) Hayes, P.
G. Ph.D. Dissertation, University of Calgary, Canada, 2004. (f) Arndt, S.;
Spaniol, T. P.; Okuda, J. Organometallics 2003, 22, 775. (g) Cameron, T.
M.; Gordon, J. C.; Michalczyk, R.; Scott, B. L. Chem. Commun. 2003,
2282. (h) Schaverien, C. J. Organometallics 1992, 11, 3476.
* To whom correspondence should be addressed. E-mail: B.Hessen@
rug.nl.
(1) (a) Bochmann, M. J. Chem. Soc., Dalton Trans. 1996, 255. (b)
Brintzinger, H. H.; Fischer, D.; Mu¨lhaupt, R.; Rieger, B.; Waymouth, R.
M.; Angew. Chem., Int. Ed. Engl. 1995, 34, 1143. (c) Guram, A. S.; Jordan,
R. F In ComprehensiVe Organometallic Chemistry II; Lappert, M. F., Ed.;
Elsevier Scientific Ltd: Oxford, 1995; Vol. 4, p 589. (d) McKnight, A. L.;
Waymouth, R. M. Chem. ReV. 1998, 98, 2587. (e) Resconi, L.; Cavallo,
L.; Fait, A.; Piemontesi, F. Chem. ReV. 2000, 100, 1253. (f) Gibson, V. C.;
Spitzmesser, S. K. Chem. ReV. 2003, 103, 283. (g) McKnight, A. L.;
Waymouth, R. M. Chem. ReV. 1998, 98, 2587.
(2) L ) TACN: (a) Hajela, S.; Schaefer, W. P.; Bercaw, J. E. J.
Organomet. Chem. 1997, 532, 45. (b) Lawrence, S. C.; Ward, B. D.;
Dubberley, S. R.; Kozak, C. M.; Mountford, P. Chem. Commun. 2003, 2880.
(3) L ) â-diketiminate: (a) Hayes, P. G.; Piers, W. E.; McDonald, R.
J. Am. Chem. Soc. 2002, 124, 2132. (b) Hayes, P. G.; Piers, W. E.; Parvez,
M. J. Am. Chem. Soc. 2003, 125, 2132.
(4) L ) TACN-amide: (a) Bambirra, S.; van Leusen, D.; Meetsma, A.;
Hessen, B.; Teuben, J. H. Chem. Commun. 2001, 637. (b) Hessen, B.;
Bambirra, S. World Pat. WO02/32909, 2002.
(9) Tazelaar, C. G. J.; Bambirra, S.; Van Leusen, D.; Meetsma, A.;
Hessen, B.; Teuben, J. H. Organometallics 2004, 23, 936.
(5) L ) Cp-amine: Canich, J. A. M.; Schaffer, T. D.; Christopher, J.
N.; Squire, K. R. World Pat. WO00/18808, 2000.
(10) Bambirra, S.; Boot, S. J.; van Leusen, D.; Meetsma, A.; Hessen, B.
Organometallics 2004, 23, 1891.
10.1021/om060278l CCC: $33.50 © 2006 American Chemical Society
Publication on Web 06/09/2006

Cationic Group 3 Alkyl Complexes
Organometallics, Vol. 25, No. 14, 2006 3487
Scheme 1
Scheme 2
cold (-20 °C) pentane, providing the complexes [L1]Y(CH2-
SiMe3)2 (1) and [L2]Y(CH2SiMe3)2 (2) as white microcrystalline
solids in about 75% yield.
Since a related lanthanum tris(alkyl) La(CH2SiMe3)3(THF)x
is not available, we followed the in situ approach we described
before for TACN-amide and amidinate dialkyl complexes of
the larger lanthanide metal ions.7b,9 In a single-pot procedure,
a suspension of LaBr3(THF)4 in THF was reacted with 3 equiv
of LiCH2SiMe3 at ambient temperature for 30 min, after which
HL1 or HL2 was added. After removal of the volatiles the
residues were extracted with hexanes/toluene (1:1, at -0 °C)
to afford the complexes [L]La(CH2SiMe3)2 (L ) L1, 3; L2, 4)
in moderate yields of about 45%. It is noteworthy that the
lanthanum dialkyl 4, with the SiMe2-bridged ligand, can be
isolated under these conditions. Earlier we reported that the
related complex with the 4,7-dimethyl-substituted TACN-amide
ligand undergoes rapid ligand NMe metalation at low temper-
ature to produce the dinuclear species {[Me(µ-CH2)TACN-
(SiMe2)NtBu]La(CH2SiMe3)}2.9 Apparently, the iPr substituents
on the ligand sufficiently shield the metal-alkyl bonds to
prevent intermolecular C-H activation. It will be seen later that
the iPr substituents do give rise to intramolecular C-H
activation processes.
iPr substituents. In this paper we describe the synthesis and
characterization of neutral dialkyl and cationic monoalkyl
species of yttrium and lanthanum with the [iPr2TACN(B)NtBu]-
(B ) (CH2)2, SiMe2) ligand and a study of their thermal
decomposition.
Results and Discussion
Ligand Synthesis. The ligands employed in this study are
N-tert-butyl-2-(4,7-diisopropyl-1,4,7-triazanon-1-yl)ethylamine
(HL1) and N-tert-butyl(4,7-diisopropyl-1,4,7-triazanon-1-yl)-
dimethylsilylamine (HL2). HL1 is prepared by reaction of
known 1,4-diisopropyl-1,4,7-triazacyclononane11 with N-tert-
butylchloroacetamide in refluxing actonitrile, with a catalytic
amount of NaI, yielding the corresponding N-tert-butyl-(4,7-
diisopropyl-1,4,7-triazacyclonon-1-yl)acetamide. This was then
reduced at the carbonyl function with LiAlH4 in refluxing
dibutyl ether (nBu2O) instead of diglyme as previously reported,9
affording HL1 in 89% yield after hydrolysis and acid-base
extraction (Scheme 1). Ligand HL2 can be prepared either by
treating neat Me2SiC12 first with Li[4,7-iPr2-TACN]12 and then
with lithium tert-butylamide or by reacting [4,7-iPr2-TACN]Li
with ClSiMe2NHtBu in hexanes (Scheme 1). The latter proce-
dure affords HL2 spectroscopically pure (by 1H NMR) as a light
yellow oil in 84% yield.
Synthesis and Characterization of TACN-amide Yttrium
and Lanthanum Dialkyls. Yttrium dialkyl complexes [L]Y-
(CH2SiMe3)2 were made via the well-established alkane elimi-
nation route,13 by reaction of the yttrium tris(alkyl) Y(CH2-
SiMe3)3(THF)214 with the neutral ligand HL1 or HL2 in toluene
at ambient temperature (Scheme 2). After evaporation of the
volatiles under reduced pressure the residue was washed with
NMR Spectroscopic Data of [LM(CH2SiMe3)2]. Com-
pounds 1-4 were studied by NMR spectroscopy. At ambient
temperature, yttrium compound 1 (with the C2-bridged ligand)
displays 1H and 13C NMR spectra consistent with an asymmetric
structure, e.g., showing four doublets for the alkyl methylene
protons and two resonances for the alkyl methylene carbons.
The latter are found at δ 33.7 (JYC ) 37 Hz; JCH ) 95 Hz) and
31.0 ppm (JYC ) 39 Hz; JCH ) 95 Hz). In contrast, the other
three complexes display room-temperature spectra suggesting
(averaged) Cs symmetry. At lower temperatures, all compounds
give spectra consistent with an asymmetric ground-state struc-
ture. Variable-temperature 1H NMR spectra in THF-d8 solvent
allowed us to estimate the symmetrization barrier for all four
compounds from the coalescence behavior of the alkyl SiMe3
resonances.15 Coalescence temperatures Tc and calculated free
energies of activation ∆Gq (in kcal mol-1) are as follows: 1
Tc
(44.6 °C, 17.0), 2 (-25.7 °C, 12.6), 3 (-12.2 °C, 13.4), 4 (-37.4
°C, 11.9). From these data it is clear that the highest activation
barriers are found for the C2-bridged ligand L1, due to the
conformation of the backbone, and for the metal with the smaller
ionic radius (Y3+: 1.04 Å, La3+: 1.17 Å), due to the increased
steric congestion around the metal center. Also notable is that
there are considerable differences in chemical shifts between
the lanthanum complexes and their yttrium congeners in the
13C NMR spectra. For complexes 3 and 4 the M-CH2 carbon
(11) Houser, R. P.; Halfen, J. A.; Young, V. G., Jr.; Blackbum, N. J.;
Tolman, W. B. J. Am. Chem. Soc. 1995, 117, 10745. (b) Halfen, J. A.;
Tolman, W. B. Inorg. Synth. 1998, 32, 75.
(12) (a) Giesbrecht, G. R.; Gebauer, A.; Shafir A.; Arnold, J. J. Chem.
Soc., Dalton Trans. 2000, 4018. (b) Qian, B. X.; Henling, L. M.; Peters, J.
C. Organometallics 2000, 19, 2805.
(13) (a) Mu, Y.; Piers, W. E.; MacQuarrie, D. C.; Zaworotko, M. J.;
Young, V. G. Organometallics 1996, 15, 2720. (b) Hultzsch, K. C.; Spaniol,
T. P.; Okuda, J. Angew. Chem., Int. Ed. 1999, 38, 227. (c) Emslie, D. J.
H.; Piers, W. E.; Parvez, M.; McDonald, R. Organometallics 2002, 21,
4226.
(14) Lappert, M. F.; Pearce, R. J. Chem. Soc., Chem. Commun. 1973,
126.
(15) Hesse, M.; Meier, H.; Zeeh, B. Spekroskopische Methoden in der
Organischen Chemie; Georg Thieme Verlag: Stuttgart, 1995.

3488 Organometallics, Vol. 25, No. 14, 2006
Bambirra et al.
Figure 1. First-order plot for the thermal decomposition of 4 at
different temperatures in C6D6.
Figure 3. Molecular structure of [iPr2TACN(CH2)2NtBu]Y(CH2-
SiMe3)2 (1) (ellipsoid probability level at 50%).
Figure 2. Eyring plot for the thermal decomposition of 4 in C6D6.
resonances are found approximately 15 ppm downfield relative
to those in 1 and 2.
Thermal Stability of the Dialkyl Complexes. Complexes
1-4 decompose gradually at ambient temperature in C6D6
solution. Compound 4 is the least stable of the series, with a
half-life at 35 °C of 30 min. The La compounds 3 and 4 are
also insufficiently stable in the solid state to be subjected to
elemental analysis. The decomposition is accompanied by the
release of equimolar amounts of SiMe4 and propene. Neverthe-
less, a well-defined organometallic product could not be
identified, and at higher temperatures the second alkyl group is
also liberated as SiMe4 in a subsequent process. The thermolysis
of 4 in C6D6 solvent was followed at four different temperatures
by NMR spectroscopy. The reaction was found to follow simple
first-order kinetics, indicative of an intramolecular process
(Figure 1). Activation parameters of ∆Hq ) 54.6 ( 0.5 kJ mol-1
and ∆Sq ) 27 ( 20 J K-1 mol-1 were derived from the Eyring
plot (Figure 2). Interestingly, 4 seems to be somewhat more
stable in THF-d8 solvent. A similar analysis of the decomposi-
tion on this solvent yields the (apparent) activation parameters
∆Hq ) 69 ( 2 kJ mol-1 and ∆Sq ) 71 ( 19 J K-1 mol-1. The
significantly positive entropy of activation in THF solvent may
indicate that, although isolated 4 is free from coordinated THF
(even when obtained from THF-containing media), in neat THF
some additional solvation takes place.
Figure 4. Molecular structure of [iPr2TACN(SiMe2)NtBu]Y(CH2-
SiMe3)2 (2) (ellipsoid probability level at 50%).
Crystal Structures of the Dialkyl Complexes. Crystalliza-
tion of the dialkyl complexes from pentane or toluene/pentane
mixtures provides large, clear crystals of the compounds. The
structures of 1, 2, and 4 were determined by single-crystal X-ray
diffraction (shown in Figures 3-5, respectively). All three
compounds show a distorted octahedral geometry, with the three
nitrogen atoms of the TACN moiety in facial arrangement. The
sterically demanding ligand iPr groups and the metal-bound
alkyl groups are staggered, and the compounds are asymmetric
due to the bridge between the TACN and amide ligand moieties.
This asymmetry is reflected for example in the large difference
Figure 5. Molecular structure of [iPr2TACN(SiMe2)NtBu]La(CH2-
SiMe3)2 (4) (ellipsoid probability level at 50%).
between the two Namide-M-CH2 angles within each complex,
for instance, 98.22(13)° for C19 and 118.12(13)° for C23 in
complex 2.
As reported in the previous paragraph, the fluxional behavior
of the complexes is strongly influenced by the nature of the
bridge in the ligand and the size of the metal center. It is
therefore useful to compare some of the metrical parameters
for the complexes in the solid state. The effect of the bridging

Cationic Group 3 Alkyl Complexes
Organometallics, Vol. 25, No. 14, 2006 3489
Scheme 3
moiety of the TACN-amide ligand can be seen in comparing
the structures of 1 and 2. The Namido-Y-Nbridgehead ligand “bite”
angle for the (CH2)2 bridge in 1 of 72.4(2)° is noticeably larger
than for the SiMe2 bridge in 2 (64.5(1)°), indicating the greater
geometric constraint in the latter. Nevertheless, the effect of
this constraint on the Y-N-C angle of the amido substituent
is only modest, as this increases by only 1.3° upon changing
from the (CH2)2 bridge to the SiMe2 bridge. This effect is
significantly smaller than that of 4.0° observed in the “con-
strained geometry” cyclopentadienyl-amide titanium complexes
[C5H4(bridge)NtBu]TiCl2.16 A possible reason for this is that
the TACN ligand moiety has many more degrees of freedom
available to relax geometrical constraints than the planar
conjugated cyclopentadienyl moiety. A comparison of the
(isomorphous) structures of 2 and 4 shows the effects of the
increase in metal ionic radius. In the La complex 4, the increased
metal-N distances not only lead to a smaller Namido-Y-
Nbridgehead “bite” angle of 60.8(1)° but also to smaller M-N-
CiPr angles, one of which is as small as 102.9(3)°. This
orientation of the ligand iPr substituent relative to the La-alkyl
bond may facilitate C-H activation of the iPr methyl groups
as a thermal decomposition route of the complex.
Figure 6. Molecular structure of 5 (ellipsoid probability level at
50%). Anion is omitted.
Figure 7. Molecular structure of 6 (ellipsoid probability level at
50%). Anion is omitted.
A feature that is common to all three structures is that one of
the nitrogen atoms of the TACN moiety shows a significantly
longer M-N bond distance than the other two, by as much as
0.12 (1) to 0.17 Å (4). This nitrogen atom invariably is the one
that is essentially trans to one of the metal-bound alkyl groups
(N-M-C angles of 151-155°). Earlier we observed in an
yttrium dialkyl complex with a noncyclic triamino-amide that,
in the absence of the geometric constraint of the cyclic nature,
this effect is even more pronounced, with a bond length
difference of 0.28 Å.17
Table 1. Selected Bond Lengths and Angles for 1, 2, and 4
1 (M ) Y)
2 (M ) Y)
4 (M ) La)
Bond Lengths (Å)
M-C19
M-C23
M-N1
M-N2
M-N3
M-N4
2.476(5)
2.421(7)
2.231(5)
2.541(5)
2.618(5)
2.740(5)
2.420(4)
2.599(5)
2.616(4)
2.388(4)
2.771(3)
2.727(4)
2.902(3)
2.465(4)
2.271(3)
2.574(4)
2.595(4)
2.747(3)
Bond Angles (deg)
Generation and Characterization of the Ionic Species
[LMCH2SiMe3(THF)]+[B(Ar)4]- (M ) Y, La; Ar ) Ph,
C6F5). Upon reaction of the dialkyl complexes 1-4 with the
Brønsted acid [PhNMe2H][B(C6F5)4] in C6D5Br solvent, in-
stantaneous liberation of 2 equiv of Me4Si and 1 equiv of
propene is observed by 1H NMR spectroscopy. This is in
contrast to earlier observations on related complexes with Me2-
TACN-amide ligands, where the formation of relatively stable
cationic monoalkyl species [(TACN-amide)M(CH2SiMe3)]+ was
seen.4 This decomposition of the cationic alkyl species can be
prevented (Y) or substantially retarded (La) when the reaction
is performed in THF-d8 solvent (Scheme 3). For yttrium, cationic
alkyl species [LYCH2SiMe3(THF-d8)]+ (L ) L1, 5; L2, 6)
appear to be stable in THF-d8 at ambient temperature for several
days, whereas for lanthanum the cationic [LLaCH2SiMe3(THF-
d8)x]+ (L ) L1, 7; L2, 8) species can be readily observed by
N1-M-N2
72.38(17)
113.8(2)
95.9(2)
155.3(2)
129.8(4)
110.8(4)
112.1(4)
64.47(12)
60.84(12)
100.24(16)
121.50(12)
151.35(14)
125.7(3)
N1-M-C19
N1-M-C23
N4-M-Calkyl-trans
M-N1-Camido
M-N3-CiPr
M-N4-CiPr
98.22(13)
118.12(13)
152.87(12)
131.1(3)
108.4(3)
112.0(2)
102.9(3)
108.8(2)
1H NMR, but gradually decompose with release of SiMe4 and
propene (vide infra).
The cationic yttrium alkyl species 5 and 6 were isolated as
their BPh4 salts, in single crystalline form in about 70% yield,
from the reaction of dialkyls 1 and 2 with equimolar amounts
of [PhNMe2H][B(C6H5)4] in THF, followed by layering with
hexanes at ambient temperature. Figures 6 and 7 show the
molecular structures of 5 and 6, respectively, and selected bond
lengths and angles are compiled in Table 2. The geometry
around the yttrium center in the cations is again distorted
octahedral, as in the corresponding neutral dialkyls. The
differences in Y-N and Y-CH2 distances between the neutral
and cationic species are relatively small, with one exception.
(16) Carpenetti, D. W.; Kloppenburg, L.; Kupec, J. T.; Petersen, J. L.
Organometallics 1996, 15, 1572.
(17) Bambirra, S.; Boot, S. J.; van Leusen, D.; Meetsma, A.; Hessen, B.
Organometallics 2004, 23, 1891.

3490 Organometallics, Vol. 25, No. 14, 2006
Bambirra et al.
Table 2. Selected Bond Lengths and Angles for 5 and 6
5 (bridge ) (CH2)2)
6 (bridge ) SiMe2)
Bond Lengths (Å)
2.4466(18)
2.3721(11)
2.5211(14)
2.5999(14)
2.5630(14)
2.2333(14)
Y-C19
Y-O
Y-N1
Y-N2
Y-N3
Y-N4
2.459(3)
2.379(3)
2.530(4)
2.568(4)
2.502(4)
2.242(3)
Bond Angles (deg)
73.56(5)
111.31(5)
88.76(4)
155.23(4)
N4-Y-N1
N4-Y-C19
N4-Y-O
N2-Y-O
65.90(13)
110.71(12)
89.83(12)
155.34(11)
The position taken in the neutral dialkyl complexes by the alkyl
group with the largest C-Y-NiPr angle (around 150°) is
occupied in 5 and 6 by the coordinated THF molecule. The
Y-N distance trans to it is considerably shorter than in the
neutral dialkyl complexes, so that the difference between the
two Y-NiPr distances in these complexes is only 0.036 (5) to
0.066 (6) Å instead of the 0.12-0.14 Å in the dialkyls 1 and 2.
This shows that the Y-N(amine) distance in these complexes
is very sensitive to the nature of the group trans to it.
Figure 8. ES-MS of {[iPr2TACN(CH2)2NtBu]Y(CH2SiMe3)-
(THF)}+ (5) in THF as a function of the nozzle voltage (40 V,
top; 160 V, bottom). *Background impurities.
1
In the room-temperature H NMR spectra (THF-d8 solvent)
of the yttrium cations 5 and 6 only a single M-CH2 resonance
is seen. Cooling the solutions induces decoalescence to reveal
the separate resonances for the diastereotopic alkyl protons: for
SiMe3(THF)][B(C6F5)4] in THF. Even at low nozzle voltages
(40 V), only the unsolvated alkyl cations [LYR]+ (5a: m/z
487.2; 6a: m/z 517.2) are observed (see Figure 8, top). In
addition, a trace of the H2O adduct is observed (5a‚H2O m/z
505.2; 6a‚H2O m/z 535.2). This indicates that the THF molecule
is only relatively loosely bound to the metal center in these
species. Increasing the nozzle voltage to 160 V leads to collision-
induced decay (CID) and gives spectra in which the [LYR-
SiMe4-C3H6]+ species (5b: m/z 356.9; 6b: m/z 386.9) are now
dominant. For the C2-bridged ligand system L1, closer inspec-
tion reveals a small peak at m/z 399.2 for the [LYR-SiMe4]+
(A) species (along with its water adduct, A‚H2O: [LYR‚H2O-
SiMe4]+ ) m/z 517.2) (Figure 8, bottom), suggesting that
decomposition may involve initial C-H activation of one of
the NiPr methyl groups, followed by rapid propene elimination.
For complex 6 (with L2), a corresponding peak was not
observable under the same conditions, suggesting that the
subsequent propene elimination is even faster in this system.
Whereas the yttrium alkyl cations 5 and 6 are quite stable at
ambient temperature in THF solution, the corresponding lan-
thanum derivatives decompose in this solvent at rates that allow
a kinetic evaluation of the process. For complex 8, with the
SiMe2-bridged ligand, the disappearance from a THF-d8 solution
was monitored by 1H NMR spectroscopy at four different
temperatures (see Supporting Information). This decomposition
follows clean first-order kinetics, and from an Eyring plot the
activation parameters ∆Hq ) 94 ( 3 kJ mol-1 and ∆Sq )
164 ( 7 J K-1 mol-1 were obtained. The large positive entropy
of activation for this process suggests that dissociation of a THF
molecule from the metal center is involved in the rate-
determining step. As the activation parameters of the thermal
decomposition of the neutral lanthanum dialkyl complex 4 in
C6D6 and THF-d8 solvent suggest that already in this case
additional solvation by THF is possible, we do not wish to
speculate on the number of THF molecules effectively coordi-
nated to the cation 8 in neat THF solvent.
5 (-10 °C) at δ -1.14 and -1.17 ppm (JYH ) 2.9 Hz, JHH
10.7 Hz), for 6 (-20 °C) at δ -0.90 and -0.95 ppm (JYH
)
)
2.7 Hz, JHH ) 11.0 Hz). In the 13C NMR spectra the YCH2
resonances for the cations are found approximately 4 ppm
downfield from those in the neutral dialkyl precursors, while
the JYC coupling constant increases by about 5 Hz.
Reaction of the lanthanum dialkyls 3 and 4 with equimolar
amounts of [PhNMe2H][B(C6F5)4] in THF-d8 solvent was
monitored by 1H NMR spectroscopy (20 °C). Formation of the
cationic lanthanum monoalkyl complexes [LLaCH2SiMe3(THF-
d8)x]+ (L ) L1, 7; L2, 8), together with SiMe4, is instantaneous.
Interestingly, also a small amount of propene is detected,
suggesting a ligand metalation process, as observed for the
neutral precursors 3 and 4. At low temperature (-50 °C)
decomposition is slowed and the alkyl methylene group now
shows resonances for the two diastereotopic protons: 7 (-0.93
and -1.10 ppm, JHH ) 9.4 Hz); 8 (-0.82 and -0.90 ppm,
JHH ) 10.2 Hz). Unfortunately, at that temperature the 13C NMR
spectra of both complexes show severe broadening, precluding
the extraction of chemical shifts and coupling constants for 7
and 8.
Thermal Decomposition of [LMCH2SiMe3(THF)] Cations.
As mentioned above, the thermal decomposition of the unsol-
vated cations [LMCH2SiMe3]+, generated in situ, is fast and
releases equimolar amounts of SiMe4 and propene. As attempts
to observe well-defined products or intermediates of this process
in solution by NMR spectroscopy were unsuccessful, the
decomposition process was studied in the gas phase for M )
Y. To this end, ES-MS (electrospray mass spectrometry)18-20
was applied to freshly prepared 10-3 M solutions of [LYCH2-
(18) (a) Whitehouse, C. M.; Dreyer, R. N.; Yamashita, M.; Fenn, J. B.
Anal. Chem. 1985, 57, 675. (b) Fenn, J. B. Angew. Chem., Int. Ed. 2003,
42, 3871;
(19) (a) Evans, W. J. Johnston, M. A.; Fujimoto, C. H.; Greaves J.
Organometallics 2000, 19, 4258. (b) Traeger, J. C. Int. J. Mass Spectrom.
2000, 200, 387.
(20) For recent reviews in this field see: (a) Plattner, D. A. Int. J. Mass
Spectrom. 2001, 207, 125. (b) Chen, P. Angew. Chem., Int. Ed. 2003, 42,
2832.
After full decomposition of 8 in THF-d8, the 1H NMR
spectrum of the remaining inorganic species looks complex, but
not ill-defined. In an attempt to obtain the decomposition product
in crystalline form, a THF solution of 8 with the BPh4 anion as

Cationic Group 3 Alkyl Complexes
Organometallics, Vol. 25, No. 14, 2006 3491
described above, is short-lived and undergoes a four-center
electron rearrangement, liberating propene. Two cationic di-
amine-diamide lanthanum species then combine to form dimer
9.
Conclusions
The isopropyl-substituted monoanionic iPr2TACN-amide
ligands L1 and L2 can be used to obtain neutral TACN-amide
dialkyl complexes of yttrium and of lanthanum, the largest rare
earth metal. The isopropyl substituents improve the thermal
stability of the neutral La dialkyl derivatives over those with
the Me2TACN-amide ligands: the latter suffers from rapid NMe
metalation when the bridging moiety in the ligand is SiMe2.9
Nevertheless, the isopropyl substituents also open up another
decomposition route: intramolecular cyclometalation of the
isopropyl methyl group followed by propene loss. This makes
the derived cationic iPr2TACN-amide monoalkyl species dis-
tinctly less stable than their analogues with Me2TACN-amide
ligands. This decomposition can be retarded by interaction of
the metal center with Lewis bases (as shown for THF).
Figure 9. Molecular structure of 9 (ellipsoid probability level at
10%). Anions are omitted.
Scheme 4
As the decomposition of the cationic monoalkyl complexes
by iPr metalation and propene extrusion eliminates the last
metal-carbon bond in the complex, it is also a possible catalyst
deactivation mechanism when these species are employed in
catalytic ethene polymerization. Apparently, the balance between
the tendency toward metalation and the stabilization of the
cationic alkyl species by the Lewis basic alkene substrate is
delicate: in ethene polymerization studies involving the four
metal-ligand combinations described,4b only the yttrium catalyst
with the least constraining ligand bridge, [iPr2TACN(CH2)2-
NtBu]Y(CH2SiMe3)+ (i.e., the cation derived from 1), was found
to be competent in catalytic ethene polymerization.
Experimental Section
counterion (to improve crystallization behavior) was generated
by the reaction of dialkyl 4 with [PhNMe2H][BPh4]. Layering
the solution with hexanes, and allowing it to stand overnight at
ambient temperature, yielded crystals that appeared suitable for
single-crystal X-ray diffraction. Despite considerable problems
associated with the modest crystal quality and what appears to
be a low-temperature phase transition, a structure determination
at a temperature of 200 K allowed an unambiguous identification
of the product as the tetraphenylborate salt of the dinuclear
General Considerations. All preparations were performed under
an inert nitrogen atmosphere, using standard Schlenk or glovebox
techniques, unless mentioned otherwise. Toluene, pentane, and
hexane (Aldrich, anhydrous, 99.8%) were passed over columns of
Al2O3 (Fluka), BASF R3-11-supported Cu oxygen scavenger, and
molecular sieves (Aldrich, 4 Å). Diethyl ether and THF (Aldrich,
anhydrous, 99.8%) were dried over Al2O3 (Fluka). All solvents were
degassed prior to use and stored under nitrogen. Deuterated solvents
(C6D6, C7D8, C4D8O; Aldrich) were vacuum transferred from Na/K
alloy, prior to use. Reagents Me3SiCH2Li,21 YCl3(THF)3.5, Y(CH2-
SiMe3)3(THF)2,22 iPr2-TACNH,23 iPr2-TACNLi,24 and ClSiMe2-
NHtBu,25 were prepared according to published procedures.
[PhNMe2H][B(C6F5)4] (Strem) was used as received. NMR spectra
were recorded on Varian Gemini VXR 300 or Varian Inova 500
spectrometers in NMR tubes equipped with a Teflon (Young) valve.
2+
dicationic species {[iPrTACN(SiMe2)NtBu]La(THF)}2 (9,
Figure 9). From each of the TACN-amide ligands in this
complex, one of the iPr groups has been lost from one of the
TACN nitrogen atoms, resulting in a dianionic diamine-diamide
ligand. The nitrogen that has lost its substituent is now bridging
between the two metal centers in the dinuclear complex. The
NMR spectra of the isolated product in THF are also in
agreement with the stoichiometry and the symmetry of the
compound in the crystal. The yttrium analogue of 9 could be
obtained in a similar manner in 85% isolated yield, but now
the reaction was performed in bromobenzene (to induce
decomposition) to which some THF was added after 1 hr.
Thus it appears that the general reaction scheme for the
thermolysis of the cationic monoalkyl complexes can be
described as summarized in Scheme 4.
We conclude that the formation of 9 is the result of ligand
metalation at one of the nitrogen isopropyl (methyl) substituents
with concomitant protonolysis of the metal-bound alkyl (CH2-
SiMe3) that is eliminated as SiMe4, generating a cationic
cyclometalated species A (Scheme 4). This species A, also
proposed in the decomposition of the yttrium analogues
1
The H NMR spectra were referenced to resonances of residual
protons in deuterated solvents. The 13C NMR spectra were
referenced to carbon resonances of deuterated solvents and reported
in ppm relative to TMS (δ 0 ppm).
The electrospray ionization mass spectrometry (ES-MS) experi-
ments were conducted on a Nermag R3010 triple quadrupole MS
system with a custom-built IonSpray (pneumatically assisted
(21) Lewis, H. L.; Brown, T. L. J. Am. Chem. Soc. 1970, 92, 4664.
(22) Lappert, M. F.; Pearce, R. J. Chem. Soc., Chem. Commun. 1973,
126.
(23) (a) Halfen, J. A.; Tolman, W. B. Inorg. Synth. 1998, 32, 75. (b)
Houster, R. P.; Halfen, J. A.; Young, V. G.; Blackburn, N. J.; Tolman, W.
B. J. Am. Chem. Soc. 1995, 117, 10745.
(24) (a) Qian, B.; Henling, M.; Peters, J. C. Organometallics 2000, 19,
2805. (b) Giesbrecht, G. R.; Gebauer, A.; Shafir, A.; Arnold, J. 2000, 4018.
(25) Wannagat, U.; Schreiner, G. Monatsh. Chem. 1965, 96, 1889

3492 Organometallics, Vol. 25, No. 14, 2006
Bambirra et al.
electrospray) source26 equipped with a gas curtain, which are
contained in a closed chamber that can be evacuated, flushed, and
maintained under nitrogen. Typical sample preparation: in a
glovebox, a sample of 10 µmol of the yttrium dialkyl and 10 µmol
of [Me2NPhH][B(C6F5)4] or alternatively 10 µmol of the isolated
ion pairs [{(iPr)2-TACN-SiMe2NtBu}Y(CH2SiMe3)(THF)][BPh4]‚
(THF), [{(iPr)2-TACN-CH2NtBu}Y(CH2SiMe3)(THF)][BPh4]‚(THF)
were dissolved in 1 mL of solvent (THF or C6H5Br) and diluted
10-fold with THF, generating a 10-3 M solution. The samples were
taken up into a 500 µL syringe (Model 1750 RNR, Hamilton) and
electrosprayed via a syringe pump operating at 10 µL/min. The
capillary voltage was 3.5 kV. Mass spectra were recorded from
m/z 200 to 900 at 10 s per scan under control of the Sciex API 3
data system. The sampling orifice (nozzle) voltage was increased
from +40 to +160 V to induce ion fragmentation. The skimmer
located behind the sampling orifice was at +25 V in all experiments.
Elemental analyses were performed at the Microanalytical Depart-
ment of H. Kolbe (Mu¨lheim an der Ruhr).
Method b. A solution of ClSiMe2NHtBu (0.98 g, 5.92 mmol)
in hexanes (10 mL) was added dropwise at ambient temperature to
a solution of Li[TACN(iPr)2] (1.30 g, 5.92 mmol) in hexanes (50
mL). The precipitated LiCl was filtered off, and the filtrate was
evaporated to dryness, yielding the product, spectroscopically pure
1
(NMR) as a light yellow oil (1.70 g, 4.95 mmol, 84%). H NMR
(300 MHz, 25 °C, C6D6): δ 3.01 (m, 4H, NCH2), 2.74 (sept,
3JHH ) 6.3 Hz, 2H, iPr CH), 2.68 (m, 4H, NCH2), 2.50 (s, 4H,
NCH2), 2.34 (s, 1H, NH) 1.18 (s, 9H, tBu Me), 0.93 (d, 3JHH ) 6.3
Hz, 12H, iPr Me), 0.22 (s, 6H, Me2Si). 13C NMR (75.4 MHz, 25
°C, C6D6): δ 54.5 (t, JCH ) 127.3 Hz, NCH2), 54.2 (d, JCH ) 141.2,
iPr CH), 53.5 (t, JCH ) 129.6 Hz, NCH2), 51.5 (t, JCH ) 130.7 Hz,
NCH2), 46.3 (tBu C), 33.8 (q, JCH ) 124.4, tBu Me), 18.4 (q,
JCH ) 124.3 Hz, iPr Me), 1.6 (q, JCH ) 117.5 Hz, SiMe2).
Synthesis of [(iPr)2TACN(CH2)2NtBu]Y(CH2SiMe3)2 (1). At
ambient temperature, a solution of HL1 (0.32 g, 1.00 mmol) in
toluene (2 mL) was added dropwise to a solution of Y(CH2SiMe3)3-
(THF)2 (0.49 g, 1.00 mmol) in toluene (5 mL). The reaction mixture
was stirred for 2 h, after which the volatiles were removed under
reduced pressure. The residue was washed with cold pentane (-20
°C, 5 mL) and subsequently dried in a vacuum, yielding the title
compound (0.45 g, 0.78 mmol, 78%). This material is pure by NMR
spectroscopy, identical to the crystallized material communicated
previously.4a Full NMR spectroscopic data can be found in the
Supporting Information.
Synthesis of (iPr)2TACN(CH2)2NHtBu (HL1). (a) N-tert-
Butyl-(4,7-diisopropyl-1,4,7-triazanon-1-yl)acetamide. To a solu-
tion of 4,7-diisopropyl-1,4,7-triazacyclononane (1.30 g, 6.30 mmol)
in acetonitrile (20 mL) were added N-tert-butylchloroacetamide
(0.95 g, 6.30 mmol) and NaI (100 mg). After 6 h of reflux the
brownish solution was diluted with water (100 mL) acidified with
concentrated hydrochloric acid (pH ≈ 2) and washed with ether
(3 × 100 mL), made basic with KOH (pH ≈ 9) and extracted with
CH2Cl2 (3 × 100 mL). The combined extracts were dried over Na2-
SO4 and filtrated, and solvent was removed by a rotary evaporator,
yielding the product as a dark yellow oil (1.65 g, 5.0 mmol, 80%).
1H NMR (CDCl3): δ 7.9 (br, NH), 3.04 (s, 2H, NCH2CO), 2.83
(sept, 2H, JHH ) 6.6 Hz, iPr CH), 2.64-2.58 (m, 8H, NCH2), 2.56
(s, 4H, NCH2), 1.30 (s, 9H, tBu), 0.91 (d, JHH ) 6.6 Hz, 12H,
iPrMe).
Synthesis of [(iPr)2TACN(SiMe2)NtBu]Y(CH2SiMe3)2 (2). At
ambient temperature, a solution of HL2 (0.34 g, 1.00 mmol) in
pentane (10 mL) was added dropwise to a solution of Y(CH2SiMe3)3-
(THF)2 (0.49 g, 1.00 mmol) in pentane (30 mL). The reaction
mixture was stirred for 3 h (20 °C), after which the volatiles were
removed in a vacuum. The residue was stripped of remaining THF
by stirring with 5 mL of pentane, which was subsequently removed
under reduced pressure. The resulting sticky solid was then extracted
with pentane (20 mL). Cooling the extract to -30 °C produces
analytically pure crystalline product in modest yield (0.21 g, 0.34
mmol, 34%) due to its high solubility. A higher yield (75%) of
material, pure by NMR spectroscopy, can be obtained by simple
evaporation of the solvent from the reaction mixture, followed by
rinsing of the solid with cold pentane (-20 °C, 5 mL) and drying
(b) N-tert-Butyl-2-(4,7-diisopropyl-1,4,7-triazanon-1-yl)ethyl-
amine. Solid LiAlH4 (2.5 g) was added to a solution of N-tert-
butyl-(4,7-diisopropyl-1,4,7-triazanon-1-yl)acetamide (1.60 g, 5.0
mmol) in 30 mL of di-n-butyl ether (nBu2O). After refluxing for 5
h the mixture was cooled with an ice bath and diethyl ether (100
mL) was added to allow for a controlled hydrolysis of excess
LiAlH4 with water (which was added dropwise via a mounted
cooler). The white solids were filtered off and washed with diethyl
ether (2 × 100 mL). The combined ether fractions were dried over
Na2SO4 and filtrated, and the solvent was removed by rotary
evaporation, yielding the product as a yellow oil (1.40 g, 4.4 mmol,
1
in vacuo. H NMR (500 MHz, -50 °C, THF-d8): δ 4.01 (sept,
JHH ) 6.6 Hz, 1H, iPr CH), 3.69 (sept, JHH ) 6.6 Hz, 1H, iPr CH),
3.31 (m, 1H, NCH2), 3.10 (m, 1H, NCH2), 3.02 (m, 1H, NCH2),
2.93 (m, 2H, NCH2), 2.84 (m, 2H, NCH2), 2.73 (m, 3H, NCH2),
2.60 (m, 2H, NCH2), 1.47 (d, JHH ) 6.6 Hz, 3H, iPr Me), 1.36 (d,
JHH ) 6.6 Hz, 3H, iPr Me), 1.32 (s, 9H, NtBu), 1.05 (d, JHH ) 6.6
Hz, 3H, iPr Me), 1.01 (d, JHH ) 6.6 Hz, 3H, iPr Me), 0.33 (s, 3H,
Me2Si), 0.16 (s, 3H, Me2Si), 0.03 (s, 9H, Me3SiCH2), -0.06 (s,
1
3
89%). H NMR (300 MHz, C6D6, δ): 2.82 (sept, JHH ) 6.6 Hz,
2H, iPr CH), 2.76-2.73 (m, 4H, NCH2), 2.62-2.54 (m, 8H, NCH2),
2.51(s, 4H, NCH2N), 1.06 (s, 9H, NHtBu), 0.91 (d, 3JHH ) 6.6 Hz,
6H, NCHMe2). 13C NMR (75.4 MHz, C6D6, δ): 58.7 (d, JCH
130.32 Hz, NCHMe2), 56.1 (t, JCH ) 131.7, NCH2), 54.6 (t, JCH
132.42 Hz, NCH2), 52.8 (t, JCH ) 128.1 Hz, NCH2), 52.6 (t, JCH
)
)
)
9H,
Me3SiCH2),
-0.59
(dd,
JHH
)
10.5
Hz,
JYH ) 2.7 Hz, 1H, YCH2), -0.79 (dd, JHH ) 10.5 Hz, JYH ) 2.0
Hz, 1H, YCH2), -1.03 (dd, JHH ) 10.5 Hz, JYH ) 2.1 Hz, 1H,
YCH2), -0.12 (dd, JHH ) 10.4 Hz, JYH ) 2.2 Hz, 1H, YCH2). 13
C
128.1 Hz, NCH2), 49.9 (NCMe3), 40.3 (t, JCH ) 133.0 Hz, NCH2),
29.0 (q, JCH ) 124.4 Hz, NCMe3), 18.3 (q, JCH ) 124.4 Hz,
NCHMe2).
NMR (125.7 MHz, -50 °C, THF-d8): δ 58.1 (t, JCH ) 136.1 Hz,
NCH2), 57.1 (d, JCH ) 133.7, iPr CH), 57.0 (t, JCH ) 138.2 Hz,
NCH2), 56.6 (t, JCH ) 138.8 Hz, NCH2), 56.1 (t, JCH ) 136.0 Hz,
NCH2), 53.5 (NtBu C), 44.9 (t, JCH ) 137.9 Hz, NCH2), 43.8 (t,
JCH ) 135.8 Hz, NCH2), 37.7 (q, JCH ) 125.0, NtBu Me), 33.1
(dt, JCH ) 95.4 Hz, JYH ) 34.8 Hz, YCH2), 32.8 (dt, JCH ) 94.8
Hz, JYH ) 35.5 Hz, YCH2), 25.7 (q, JCH ) 126.0 Hz, iPr Me),
24.6 (q, JCH ) 126.0 Hz, iPr Me), 14.0 (q, JCH ) 125.1 Hz, iPr
Me), 13.8 (q, JCH ) 125.5 Hz, iPr Me), 6.0 (q, JCH ) 116.7 Hz,
Me3SiCH2), 5.5 (q, JCH ) 117.1 Hz, Me2Si), 3.9 (q, JCH ) 117.1
Hz, Me2Si). Anal. Calcd for C26H61N4Si3Y (604.34): C, 51.62; H,
10.50; N, 9.26; Y, 14.70. Found: C, 49.21; H, 10.15; N, 8.78; Y,
14.22. Elemental analysis values for 2 (several batches) show
inconsistencies that appear not to be associated with carbide
formation and that we have been unable to trace to soluble or
insoluble impurities.
Synthesis of (iPr)2TACN(SiMe2)NHtBu (HL2). Method a. To
30 mL of pure Me2SiCl2 was added Li[TACN(iPr)2] (0.92 g, 4.24
mmol in portions) at ambient temperature. The reaction mixture
turned yellow and was stirred for 4 h. The excess Me2SiCl2 was
removed under reduced pressure, and the remainder was dissolved
in toluene (30 mL). Subsequently, LiNHtBu (0.33 g, 4.24 mmol)
was added to the solution at room temperature. After 18 h the
toluene was removed under vacuum. The remaining sticky residue
was extracted with pentane (2 × 100 mL). Evaporation of the
pentane yielded 0.98 g (68%) of the title compound as a brownish
1
oil (95% by H NMR).
(26) Bruins, A. P.; Covey, T. R. Henion, J. D. Anal. Chem. 1987, 59,
2642.

Cationic Group 3 Alkyl Complexes
Organometallics, Vol. 25, No. 14, 2006 3493
Synthesis of [(iPr)2TACN(CH2)2NtBu]La(CH2SiMe3)2 (3).
Solid LaBr3(THF)4 (0.66 g, 1.00 mmol) and LiCH2SiMe3 (0.28 g,
3.00 mmol) were dissolved in THF (30 mL). The solution was
stirred for 30 min (RT), after which HL1 (0.31 g, 1.00 mmol,
dissolved in 5 mL of THF) was added. The yellowish reaction
mixture was stirred for 1 h, after which the volatiles were removed
under reduced pressure. The residue was stripped of remaining THF
by stirring twice with 5 mL of pentane (0 °C), which was
subsequently removed under reduced pressure. The solid was
extracted with a hexane/toluene mixture (25 mL each, 0 °C). The
filtrate was dried in a vacuum, affording 0.36 g of the crude product.
This material was recrystallized from hexane/toluene (10:1, 5.0 mL,
-30 °C), yielding colorless crystals of the title compound (0.27 g,
(q, JCH ) 123.3, tBu Me), 24.1 (q, JCH ) 125.2 Hz, iPr Me), 23.2
(q, JCH )124.5 Hz, iPr Me), 17.4 (q, JCH )124.0 Hz, iPr Me),
14.0 (q, JCH )124.0 Hz, iPr Me), 6.1 (q, JCH ) 118.2 Hz, Me3-
SiCH2La), 5.4 (q, JCH ) 117.5 Hz, Me2Si), 5.5 (q, JCH ) 117.5
Hz, Me2Si). The compound is thermally too unstable to be sent
out for elemental analysis.
Reaction of [(iPr)2TACN(CH2)2NtBu]Y(CH2SiMe3)2 with
[HNMe2Ph][B(C6F5)4]. (a) In the Absence of THF. A solution
of 1 (12 mg, 20.8 µmol) in C6D5Br (0.6 mL) was added to [HNMe2-
Ph][B(C6F5)4] (17 mg, 20.8 µmol). The obtained solution was
transferred to an NMR tube and analyzed by NMR spectroscopy,
which showed the evolution of 2 equiv of SiMe4 and 1 equiv of
propene. Resonances of the yttrium species are broad and could
not be interpreted.
43%). 1H NMR (500 MHz, -50 °C, THF-d8): δ 3.91 (sept, JHH
)
6.3 Hz, 1H, iPr CH), 3.51 (sept, JHH ) 5.9 Hz, 1H, iPr CH), 3.40-
3.30 (m, 3H, NCH2), 3.16-3.04 (m, 2H, NCH2), 2.99-2.89 (m,
4H, NCH2), 2.83-2.74 (m, 3H, NCH2), 2.68 (m, 2H, NCH2), 2.49
(d, JHH ) 12.2, 1H, NCH2), 2.13 (d, JHH ) 11.5, 1H, NCH2), 2.51
(d, JHH ) 6.3 Hz, 3H, iPr Me), 1.36 (d, JHH ) 6.3 Hz, 3H, iPr
Me), 1.33 (s, 9H, tBu), 1.06 (d, JHH ) 5.9 Hz, 3H, iPr Me), 0.99
(d, JHH ) 5.9 Hz, 3H, iPr Me), -0.06 (s, 9H, Me3SiCH2), -0.09
(s, 9H, Me3SiCH2), -0.60 (d, JHH ) 10.5 Hz, 1H, LaCH2), -1.09
(d, JHH ) 10.5 Hz, 1H, LaCH2), -1.13 (d, JHH ) 10.0 Hz, 1H,
LaCH2), -1.32 (d, JHH ) 10.0 Hz, 1H, LaCH2). 13C NMR (125.7
MHz, -50 °C, THF-d8): δ 59.3 (t, JCH ) 127.0 Hz, NCH2), 58.2
(t, JCH ) 129.2 Hz, NCH2), 56.1 (t, JCH ) 127.1 Hz, NCH2), 55.9
(d, JCH ) 136.5 Hz, iPr CH), 55.5 (d, JCH ) 136.4 Hz, iPr CH),
55.4 (t, JCH ) 133.0 Hz, NCH2), 53.1 (t, JCH ) 135.7 Hz, NCH2),
(b) In the Presence of THF. A solution of 1 (24 mg, 41.6 µmol)
in C6D5Br (0.6 mL) with three drops of additional THF-d8 was
added to [HNMe2Ph][B(C6F5)4] (34 mg, 41.6 µmol). The obtained
solution was transferred into a NMR tube and analyzed by NMR
spectroscopy, which showed full conversion to the ionic monoalkyl
species [L1YCH2SiMe3(THF-d8)][B(C6F5)4], SiMe4, and free Ph-
1
NMe2. H NMR (500 MHz, -30 °C, C6D5Br): δ 7.23 (t, JHH
)
7.5 Hz, 2H, m-H PhNMe2), 6.77 (t, JHH ) 7.5 Hz, 1H, p-H
PhNMe2), 6.58 (d, JHH ) 7.5 Hz, 2H, o-H PhNMe2), 3.48 (sept,
JHH ) 6.0 Hz, 1H, iPr CH), 3.40 (t, JHH ) 13.0 Hz, 1H, NCH2),
2.79-2.75 (m, 2H, NCH2), 2.72 (s, 6H, PhNMe2), 2.68-2.59 (m,
3H, NCH2), 2.57 (br, 1H, iPr CH), 2.55-2.48 (m, 2H, NCH2),
2.42-2.29 (m, 3H, NCH2), 2.25-2.17 (m, 3H, NCH2), 1.18 (d,
JHH ) 6.0 Hz, 6H, iPr Me), 1.15 (s, 9H, tBu), 0.84 (d, JHH ) 5.5
Hz, 3H, iPr Me), 0.80 (d, JHH ) 5.5 Hz, 3H, iPr Me), 0.09 (s, 9H,
Me3SiCH2), 0.07 (s, 12H, Me4Si), -1.29 (dd, JHH ) 11.0 Hz,
JYH ) 3.0 Hz, 1H, YCH2), -1.35 (dd, JHH ) 11.0 Hz, JYH ) 3.0
Hz, 1H, YCH2).
52.9 (s, tBu C), 52.8 (t, JCH ) 137.4 Hz, NCH2), 48.3 (t, JCH
101.4 Hz, LaCH2), 46.7 (t, JCH ) 129.4 Hz, NCH2), 46.5 (t, JCH
100.3 Hz, LaCH2), 43.1 (t, JCH ) 132.3 Hz, NCH2), 42.9 (t, JCH
135.0 Hz, NCH2), 31.8 (q, JCH ) 122.8, tBu Me), 24.5 (q, JCH
)
)
)
)
126.3 Hz, iPr Me), 24.2 (q, JCH ) 126.2 Hz, iPr Me), 14.1 (q,
JCH ) 125.0 Hz, iPr Me), 13.8 (q, JCH ) 125.0 Hz, iPr Me), 6.4
(q, JCH ) 117.0 Hz, Me3SiCH2La), 6.2 (q, JCH ) 117.0 Hz, Me3-
SiCH2La). The compound is thermally too unstable to be sent out
for elemental analysis.
Synthesis of [{(iPr)2TACN(CH2)2NtBu}Y(CH2SiMe3)(THF)]-
[BPh4]‚(THF) (5). THF (0.5 mL) was added to a mixture of 100
mg (173 µmol) of 1 and 76 mg (173 µmol) of [HNMe2Ph][BPh4].
The resulting yellowish solution was layered with 2 mL of hexanes.
Upon standing overnight at ambient temperature, colorless crystals
formed. The mother liquor was decanted, and the crystals were
washed with hexanes. Drying in a vacuum yielded 141 mg of the
Synthesis of [(iPr)2TACN(SiMe2)NtBu]La(CH2SiMe3)2 (4).
Solid LaBr3(THF)4 (0.66 g, 1.00 mmol) and LiCH2SiMe3 (0.28 g,
3.00 mmol) were dissolved in THF (30 mL). The solution was
stirred for 30 min (RT), after which L2H (0.34 g, 1.00 mmol,
dissolved in 5 mL of THF) was added. The yellowish reaction
mixture was stirred for 1 h, after which the volatiles were removed
under reduced pressure. The residue was stripped of remaining THF
by stirring twice with 5 mL of pentane (0 °C), which was
subsequently removed under reduced pressure. The solid was
extracted with a hexane/toluene mixture (25 mL each, 0 °C). The
filtrate was dried in a vacuum, affording 0.40 g of the crude product.
This material was recrystallized from hexane/toluene (10:1, 5 mL,
-30 °C), yielding colorless crystals of the title compound (0.29 g,
1
title compound (148 µmol, 86%). H NMR (500 MHz, -10 °C,
THF-d8): δ 7.25 (br, 8H, o-H BPh4), 6.87 (t, JHH ) 6.9 Hz, 8H,
m-H BPh4), 6.74 (t, JHH ) 6.9 Hz, 4H, p-H BPh4), 3.50 (sept,
JHH ) 6.5 Hz, 1H, iPr CH), 3.15 (t, JHH ) 11.5 Hz, 2H, NCH2),
2.86-2.70 (m, 9H, NCH2), 2.65 (sept, JHH ) 6.5 Hz, 1H, iPr CH),
2.51 (d, JHH ) 11.8 Hz, 1H, NCH2), 2.40 (t, JHH ) 11.5 Hz, 2H,
NCH2), 2.11 (t, JHH ) 12.3 Hz, 1H, NCH2), 2.01 (t, JHH ) 11.6
Hz, 1H, NCH2), 1.34 (d, JHH ) 6.5 Hz, 3H, iPr Me), 1.30 (d,
JHH ) 6.5 Hz, 3H, iPr Me), 1.14 (s, 9H, tBu Me), 0.93 (d, JHH
)
6.5 Hz, 3H, iPr Me), 0.91 (d, JHH ) 6.5 Hz, 3H, iPr Me), -0.15
(s, 9H, Me3SiCH2), - 1.14 (dd, JYH ) 2.8 Hz, JHH ) 10.7 Hz, 1H,
44%). 1H NMR (500 MHz, -60 °C, THF-d8): δ 4.03 (sept, JHH
)
YCH2), - 1.17 (dd, JYH ) 2.8 Hz, JHH ) 10.7 Hz, 1H, YCH2). 13
C
6.0 Hz, 1H, iPr CH), 3.59 (sept, JHH ) 6.1 Hz, 1H, iPr CH), 3.21
(m, 1H, NCH2), 3.06-2.90 (m, 4H, NCH2), 2.78-2.70 (m, 4H,
NCH2), 2.62-2.50 (m, 3H, NCH2), 1.46 (d, JHH ) 6.0 Hz, 3H, iPr
Me), 1.33 (s, 9H, tBu), 1.28 (d, JHH ) 6.0 Hz, 3H, iPr Me), 1.03
(d, JHH ) 6.1 Hz, 3H, iPr Me), 0.97 (d, JHH ) 6.1 Hz, 3H, iPr
Me), 0.28 (s, 3H, Me2Si), 0.08 (s, 3H, Me2Si), -0.10 (s, 9H, Me3-
SiCH2), -0.13 (s, 9H, Me3SiCH2), -0.67 (d, JHH ) 10.5 Hz, 1H,
NMR (125.7 MHz, 25 °C, THF-d8): δ 165.7 (q, 49.8 Hz, ipso-
BPh4), 138.0 (dt, J ) 153.2 Hz, 6.96 Hz, o-BPh4), 126.8 (d, J )
153.0 Hz, m-BPh4), 123.0 (dt, J ) 156.8 Hz, 7.55 Hz, p-BPh4),
59.8 (t, JCH ) 140.2 Hz, NCH2), 57.6 (d, JCH ) 138.4 Hz, iPr
CH), 57.3 (d, JCH ) 138.4 Hz, iPr CH), 56.5 (t, JCH ) 137.0 Hz,
NCH2), 56.0 (t, JCH ) 137.2 Hz, NCH2), 55.3 (s, tBu C), 54.0 (t,
JCH ) 136.0 Hz, NCH2), 53.7 (t, JCH ) 139.6 Hz, NCH2), 46.3 (t,
JCH ) 133.5 Hz, NCH2), 44.6 (t, JCH ) 138.3 Hz, NCH2), 44.1 (t,
JCH ) 137.8 Hz, NCH2), 38.3 (dt, JYC ) 40.4 Hz, JCH ) 92.1 Hz,
YCH2), 32.4 (q, JCH ) 123.8, tBu Me), 24.5 (q, JCH )126.7 Hz,
iPr Me), 24.2 (q, JCH )125.8 Hz, iPr Me), 15.9 (q, JCH )126.7
Hz, iPr Me), 14.5 (q, JCH )126.7 Hz, iPr Me), 5.5 (q, JCH ) 117.0
Hz, Me3SiCH2Y). Anal. Calcd for [C26H58N4OSiY]‚[C24H20B]
(879.00): C, 68.32; H, 8.94; N, 6.37. Found: C, 68.06; H, 8.98;
N, 5.73.
LaCH2), -0.77 (d, JHH ) 10.5 Hz, 1H, LaCH2), -1.04 (d, JHH
)
C
10.5 Hz, 1H, LaCH2), -1.12 (d, JHH ) 10.5 Hz, 1H, LaCH2). 13
NMR (125.7 MHz, -60 °C, THF-d8): δ 58.2 (t, JCH ) 133.0 Hz,
NCH2), 57.0 (t, JCH ) 134.2 Hz, NCH2), 55.8 (d, JCH ) 136.4 Hz,
iPr CH), 55.6 (d, JCH ) 136.4 Hz, iPr CH), 55.5 (t, JCH ) 133.6
Hz, NCH2), 52.4 (s, tBu C), 50.3 (t, JCH ) 97.6 Hz, LaCH2), 48.0
(t, JCH ) 100.8 Hz, LaCH2), 44.9 (t, JCH ) 131.0 Hz, NCH2), 43.5
(t, JCH ) 131.5 Hz, NCH2), 43.1 (t, JCH ) 134.2 Hz, NCH2), 36.5

3494 Organometallics, Vol. 25, No. 14, 2006
Table 3. Crystal Data and Collection Parameters of Complexes 1, 2, and 4
Bambirra et al.
1
2
4
formula
fw
C26H61N4Si2Y
574.87
C26H63N4Si3Y
604.98
C26H63LaN4Si3
654.98
cryst color
cryst size (mm)
cryst syst
space group
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
colorless
0.05 × 0.10 × 0.30
triclinic
P1h
9.815(1)
9.859(1)
17.291(3)
95.60(1)
90.68(1)
98.63(1)
1645.7(4)
2
1.160
18.6
624
1.64, 26.0
0.0731
colorless
0.47 × 0.39 × 0.34
triclinic
colorless
0.26 × 0.21 × 0.16
triclinic
P1h (No. 2)
9.9434(6)
17.752(1)
19.563(1)
91.197(1)
94.254(1)
91.353(1)
3441.8(3)
4
1.168
18.18
1312
2.30, 26.73
0.0637
P1h (No. 2)
10.0781(5)
17.8056(8)
19.7373(9)
90.996(1)
94.522(1)
91.577(1)
3528.8(3)
4
1.233
13.32
1384
2.20, 28.28
0.0537
Z
F
calcd (g cm-3
)
µ (cm-1
)
F(000), electrons
θ range (deg)
R1
wR2(all data)
index ranges (h, k, l)
T (K)
0.1800
0f12, (12, (21
130
0.1516
(12, (22, (24
100
0.1307
(13, (23, (24
100
GOF
1.016
1.069
1.004
Table 4. Crystal Data and Collection Parameters of Complexes 5, 6, and 9
5
6
9
formula
[C26H58N4OSiY]+[C24H20B]-
[C26H60N4OSi2Y]+[C24H20B]-‚C4H8O
0.5[C38H84La2N8O2Si2]2+
[C24H20B]-‚0.5(C6H12)
807.87
‚
fw
879.00
981.21
cryst color
cryst size (mm)
cryst syst
space group
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
colorless
0.45 × 0.39 × 0.17
triclinic
colorless
0.42 × 0.21 × 0.03
orthorhombic
Pbca (No. 61)
17.775(2)
20.181(2)
30.309(3)
90.00(1)
90.00(1)
90.00(1)
10872(2)
8
1.199
11.59
4224
2.42, 25.35
0.0622
colorless
0.31 × 0.12 × 0.09
monoclinic
P1h (No. 2)
12.1829(6)
13.6520(7)
14.8613(8)
86.335(1)
88.358(1)
78.635(1)
2418.0(2)
2
1.207
12.7
944
2.11, 28.28
0.0335
P21/n (No. 14)
14.573(1)
16.465(1)
18.963(1)
96.348(1)
4522.2(5)
4
1.279
12.79
1824
2.24, 25.68
0.1099
0.2929
(17, (19, (23
200
Z
F
calcd (g cm-3
)
µ (cm-1
)
F(000), electrons
θ range (deg)
R1
wR2(all data)
index ranges (h, k, l)
T (K)
0.0852
(16, (16, (19
100
0.1637
(21, (20, (36
100
GOF
1.009
0.972
1.521
Reaction of [(iPr)2TACN(SiMe2)NtBu]Y(CH2SiMe3)2 with
[HNMe2Ph][B(C6F5)4]. (a) In the Absence of THF. A solution
of 2 (12 mg, 19.9 µmol) in C6D5Br (0.6 mL) was reacted with
[HNMe2Ph][B(C6F5)4] (16 mg, 19.9 µmol). The obtained solution
was transferred to an NMR tube and analyzed by NMR spectros-
copy, which showed the evolution of 2 equiv of SiMe4 and 1 equiv
of propene. Resonances of the yttrium species are broad and could
not be interpreted.
(s, SiMe4), - 0.02 (s, 9H, YCH2SiMe3), -0.84 (d, JHH ) 11.5 Hz,
1H, YCH2), -0.91 (d, JHH ) 11.0 Hz, 1H, YCH2).
Synthesis of [{(iPr)2TACN(SiMe2)NtBu}Y(CH2SiMe3)(THF)]-
[BPh4]‚(THF) (6). THF (0.5 mL) was added to a mixture of 100
mg (165 µmol) of [(iPr)2TACNSiMe2NtBu]Y(CH2SiMe3)2 and 73
mg (165 µmol) of [HNMe2Ph][BPh4]. The resulting yellowish
solution was layered with 2 mL of hexanes. Upon standing
overnight at ambient temperature, colorless crystals formed. The
mother liquor was decanted and the crystals were washed with
hexanes. Drying in a vacuum yielded 126 mg of the title compound
(128 µmol, 78%). 1H NMR (500 MHz, -50 °C, THF-d8): δ 7.23
(br, 8H, o-H BPh4), 6.86 (t, 3J ) 7.0 Hz, 8H, m-H BPh4), 6.73 (t,
3J ) 7.0 Hz, 4H, p-H BPh4), 3.00 (br, 1H, iPr CH), 2.88 (sept,
JHH ) 6.5 Hz, 1H, iPr CH), 2.73-1.57 (m, 8H, NCH2), 2.42 (m,
3H, NCH2), 2.23 (m, 1H, NCH2), 1.39 (br, 6H, iPr Me), 1. 62 (s,
9H, NtBu), 1.01 (d, JHH ) 6.5 Hz, 3H, iPr Me), 0.98 (d, JHH ) 6.5
Hz, 3H, iPr Me), 0.28 (s, 6H, Me2Si), -0.04 (s, 9H, Me3SiCH2),
-0.06 (s, 9H, Me3SiCH2), -0.86 (d, JYH ) 2.9 Hz, 2H, YCH2).
13C NMR (125.7 MHz, -50 °C, THF-d8): δ 165.7 (q, 48.8 Hz,
ipso-BPh4), 137.9 (d, J ) 154.0 Hz, o-BPh4), 126.7 (d, J ) 150.5
(b) In the Presence of THF. A solution of 2 (24 mg, 39.8 µmol)
in C6D5Br (0.6 mL) with a drop of added THF-d8 was reacted with
[HNMe2Ph][B(C6F5)4] (32 mg, 39.8 µmol). The obtained solution
was transferred to an NMR tube and analyzed by NMR spectros-
copy, which showed full conversion to the ionic monoalkyl species
{[L2Y(CH2SiMe3)(THF-d8)}[B(C6F5)4], SiMe4, and free PhNMe2.
1H NMR (500 MHz, -30 °C, C6D5Br): δ 7.23 (t, JHH ) 7.5 Hz,
2H, m-H PhNMe2), 6.77 (t, JHH ) 7.5 Hz, 1H, p-H PhNMe2), 6.58
(d, JHH ) 7.5 Hz, 2H, o-H PhNMe2), 3.30 (sept, JHH ) 6.0 Hz,
2H, iPr CH), 2.76-2.69 (m, 4H, NCH2), 2.63 (s, 6H, PhNMe2),
2.56-2.24 (m, 8H, NCH2), 1.12 (d, JHH ) 6.0 Hz, 6H, iPr Me),
1.10 (s, 9H, tBu), 0.72 (br, 6H, iPr Me), 0.22 (s, 6H, SiMe2), 0.01

Cationic Group 3 Alkyl Complexes
Organometallics, Vol. 25, No. 14, 2006 3495
Hz, m-BPh4), 123.0 (d, J ) 154.1 Hz, p-BPh4), 57.6 (d, JCH
135.1, iPr CH), 57.4 (t, JCH ) 141.1 Hz, NCH2), 56.9 (d, JCH
)
)
Synthesis of {[iPrTACN(SiMe2)NtBu]La(THF)}2[BPh4]2 (C6-
H12) (9). A solution of 4 (61 mg, 100 µmol) in THF (1 mL) was
reacted with [HNMe2Ph][BPh4] (44 mg, 100 µmol). The obtained
solution was layered with hexanes (2 mL). Upon standing overnight
at ambient temperature, colorless crystals formed. The mother liquor
was decanted, and the crystals were washed with hexanes. Drying
in a vacuum yielded 118 mg of the title compound (68 µmol, 68%).
1H NMR (500 MHz, 20 °C, THF-d8): δ 7.25 (br, 8H, o-H BPh4),
6.85 (t, 3J ) 7.0 Hz, 8H, m-H BPh4), 6.71 (t, 3J ) 7.0 Hz, 4H, p-H
BPh4), 3.83 (m, 1H, NCH2), 3.28 (m, 1H, NCH2), 3.18 (m, 1H,
NCH2), 3.03-2.84 (m, 5H, NCH2), 2.76 (sept, JHH ) 6.5 Hz, 1H,
iPr CH), 2.58 (m, 2H, NCH2), 2.46 (m, 1H, NCH2), 2.39 3.28 (m,
1H, NCH2), 1.25 (s, 12H, C6H12), 1.19 (d, JHH ) 6.5 Hz, 3H, iPr
Me), 1.16 (s, 9H, NtBu), 0.97 (d, JHH ) 6.5 Hz, 3H, iPr Me), 0.23
(s, 3H, Me2Si), 0.17 (s, 3H, Me2Si). 13C NMR (125.7 MHz, 20 °C,
THF-d8): δ 165.9 (q, 49.0 Hz, ipso-BPh4), 137.9 (d, J ) 152.0
Hz, o-BPh4), 126.7 (d, J ) 150.9 Hz, m-BPh4), 123.0 (d, J ) 155.4
Hz, p-BPh4), 57.0 (d, JCH ) 132.5, NCHMe2), 56.8 (NtBu C), 55.0
(t, JCH ) 138.9 Hz, NCH2), 54.8 (t, JCH ) 135.0 Hz, NCH2), 54.0
(t, JCH ) 136.3 Hz, NCH2), 50.9 (t, JCH ) 138.4 Hz, NCH2), 49.6
(t, JCH ) 134.6 Hz, NCH2), 48.3 (t, JCH ) 136.8 Hz, NCH2), 36.9
(q, JCH ) 123.4, NtBu Me), 21.7 (q, JCH ) 126.7 Hz, iPr Me),
18.7 (q, JCH ) 124.7 Hz, iPr Me), 5.7 (q, JCH ) 117.5 Hz, Me2Si),
4.6 (q, JCH ) 117.9 Hz, Me2Si). Anal. Calcd for [C38H84N8O2Si2-
La]‚[C24H20B](C6H12) (1741.75): C, 63.44; H, 7.87; N, 6.43.
Found: C, 63.32; H, 7.97; N, 6.19.
134.2, iPr CH), 56.2 (t, JCH ) 133.0 Hz, NCH2), 56.3 (NtBu C),
45.0 (t, JCH ) 140.3 Hz, NCH2), 44.3 (t, JCH ) 135.4 Hz, NCH2),
42.9 (t, JCH ) 137.8 Hz, NCH2), 37.2 (q, JCH ) 122.5, NtBu Me),
37.3 (dt, JCH ) 94.1 Hz, JYH ) 41.0 Hz, YCH2), 24.9 (q, JCH
)
124.7 Hz, iPr Me), 24.3 (q, JCH ) 127.0 Hz, iPr Me), 14.7 (q,
JCH ) 124.8 Hz, iPr Me), 14.0 (q, JCH ) 126.5 Hz, iPr Me), 5.6
(q, JCH ) 117.3 Hz, Me3SiCH2), 4.5 (q, JCH ) 118.1 Hz, Me2Si),
4.3 (q, JCH ) 117.9 Hz, Me2Si). Anal. Calcd for [C26H60N4OSi2Y]‚
[C24H20B]‚(C4H8O) (981.21): C, 66.10; H, 9.04; N, 5.71. Found:
C, 65.42; H, 9.25; N, 5.66.
Reaction of [(iPr)2TACN(CH2)2NtBu]La(CH2SiMe3)2 with
[HNMe2Ph][B(C6F5)4]. A solution of 3 (25 mg, 40.0 µmol) in THF-
d8 (0.6 mL) was added to [HNMe2Ph][B(C6F5)4] (32 mg, 40.0
µmol). The obtained solution was transferred into a NMR tube and
analyzed by NMR spectroscopy, which showed full conversion to
the ionic monoalkyl species {L1La(CH2SiMe3)(THF-d8)}[B(C6F5)4]
(7), SiMe4, and free PhNMe2. 1H NMR (500 MHz, -50 °C, THF-
d8): δ 7.14 (t, JHH ) 6.7 Hz, 2 H, m-H PhNMe2), 6.71 (t, JHH
)
7.6 Hz, 1 H, p-H PhNMe2), 6.60 (d, JHH ) 6.7 Hz, 2H, o-H
PhNMe2), 4.01 (sept, JHH ) 6.4 Hz, 1H, iPr CH), 3.83 (sept,
JHH ) 6.4 Hz, 1H, iPr CH), 3.62 (m, 2 H, NCH2), 3.45-3.30 (m,
4H, NCH2), 3.13 (m, 2H, NCH2), 2.91 (s, 6H, PhNMe2), 2.80-
2.70 (m, 4H, NCH2), 2.65-2.52 (m, 4H, NCH2), 1.47 (d, JHH
)
6.4 Hz, 3H, iPr Me), 1.44 (d, JHH ) 6.4 Hz, 3H, iPr Me), 1.31 (s,
9H, tBu), 1.10 (d, JHH ) 6.4 Hz, 3H, iPr Me), 1.06 (d, JHH ) 6.4
Hz, 3H, iPr Me), 0.00 (s, 12H, SiMe4), -0.13 (s, 9H, Me3SiCH2),
-0.93 (d, JHH ) 9.4 Hz, 1H, LaCH2), -1.10 (d, JHH ) 9.4 Hz,
1H, LaCH2).
Preparation of [{(iPr)TACN(SiMe2)NtBu}Y(THF)][BPh4]. A
solution of 2 (60 mg, 100 µmol) in C6H5Br (2 mL) was reacted
with [HNMe2Ph][BPh4] (44 mg, 100 µmol). The solution was
allowed to stand at ambient temperature for 1 h, after which THF
(0.5 mL) was added. The solution was then layered with hexanes
(2 mL). Upon standing overnight at ambient temperature, colorless
crystals formed. The mother liquor was decanted, and the crystals
were washed with hexanes. Drying in a vacuum yielded 66 mg of
the title compound (85 µmol, 85%). Anal. Calcd for [C19H42N4-
OSiY][C24H20B] (778.79): C, 66.32; H, 8.02; N, 7.19. Found: C,
66.18; H, 8.11; N, 7.06. Resonances in the 1H and 13C NMR spectra
(THF-d8 solvent) are very broad and could not be interpreted.
Reaction of [(iPr)2TACN(SiMe2)NtBu]La(CH2SiMe3)2 with
[HNMe2Ph][B(C6F5)4]. A solution of 4 (26 mg, 40.0 µmol) in THF-
d8 (0.6 mL) was added to [HNMe2Ph][B(C6F5)4] (32 mg, 40.0
µmol). The obtained solution was transferred into a NMR tube and
analyzed by NMR spectroscopy, which showed full conversion to
the ionic monoalkyl species {L2La(CH2SiMe3)(THF-d8)}[B(C6F5)4]
(8), SiMe4, and free PhNMe2. As propene is gradually released upon
1
standing in solution (as detected by H NMR), indicating ther-
molysis of the title compound, NMR spectroscopy was performed
at low temperatures, at which the 13C NMR spectra are uninter-
pretable due to severe broadening of the resonances. 1H NMR (500
MHz, -50 °C, THF-d8): δ 7.14 (t, JHH ) 6.7 Hz, 2H, m-H
PhNMe2), 6.71 (t, JHH ) 7.6 Hz, 1H, p-H PhNMe2), 6.60 (d,
JHH ) 6.7 Hz, 2H, o-H PhNMe2), 3.76 (sept, JHH ) 6.5 Hz, 1H,
iPr CH), 3.29 (sept, JHH ) 6.3 Hz, 1H, iPr CH), 3.19 (m, 2H,
NCH2), 3.10-3.00 (m, 4H, NCH2), 2.96 (m, 2H, NCH2), 2.91 (s,
6H, PhNMe2), 2.86-2.75 (m, 3H, NCH2), 2.46 (m, 1H, NCH2),
1.49 (d, JHH ) 6.5 Hz, 3H, iPr Me), 1.45 (d, JHH ) 6.5 Hz, 3H, iPr
Me), 1.34 (s, 9H, tBu), 1.12 (d, JHH ) 6.3 Hz, 3H, iPr Me), 1.08
(d, JHH ) 6.3 Hz, 3H, iPr Me), 0.25 (s, 3H, SiMe2), 0.20 (s, 3H,
SiMe2), 0.00 (s, 12H, SiMe4), -0.12 (s, 9H, Me3SiCH2), -0.82
(d, JHH ) 10.2 Hz, 1H, LaCH2), -0.90 (d, JHH ) 10.2 Hz, 1H,
LaCH2).
Acknowledgment. We thank E. Otten and Dr. D. J. Beetstra
for help in acquiring kinetic data and the National Research
School Combination-Catalysis for financial support.
Supporting Information Available: Crystallographic data for
1, 2, 4, 5, 6, and 9 including atomic coordinates, full bond distances,
and bond angles as well as anisotropic thermal parameters (CIF),
fits used for determination of rate constants and Eyring plot of
thermal decomposition of 4 and 8 in THF, and text of full NMR
data of various compounds (PDF). This material is available free
of charge via the Internet at http://pubs.acs.org.
OM060278L