Synthesis, DFT studies, and reactions of scandium and yttrium dialkyl cations containing neutral fac-N3 and fac-S3 donor ligands

Article abstract of DOI:10.1021/om800279d

Reaction of Sc(CH₂SiMe₃)₃(THF)₂ with 1,4,7-trithiacyclononane gave Sc([9]aneS₃)(CH ₂SiMe₃)₃, the first organometallic group 3 complex of [9]aneS₃ ([9]aneS₃ = 1,4,7-trithiacyclononane). The corresponding reaction for yttrium gave equilibrium mixtures of Y([9]aneS₃)(CH₂SiMe₃)₃ and starting materials. Density functional theory (DFT) was used to compare the energies of formation and metal-ligand interaction energies for M([9]aneS₃)R ₃ with those for the previously reported fac-N₃ donor complexes M(fac-N₃)R₃ (R = Me or CH₂SiMe ₃; fac-N₃ = 1,4,7-trimethyltriazacyclononane (Me ₃[9]aneN₃) or HC(Me₂pz)₃). Reaction of M(CH₂SiMe₃)₃(THF)₂ with [NHMe₂Ph] [BAr^F₄] (Ar^F = C ₆F₅) in the presence of a face-capping ligand L (L = HC(Me₂pz)₃, Me₃[9]aneN₃, or [9]aneS₃) gave the cationic complexes [M(L)(CH₂SiMe ₃)₂(THF)]₊, which has been structurally characterized for M = Sc and L = [9]aneS₃. The corresponding base-free cations [M(L)(CH₂SiMe₃)₂]⁺ were studied by ²⁹Si NMR spectroscopy and/or DFT and found to possess β-Si-C agostic alkyl groups in most instances. The isolated cations [Sc(fac-N₃)(CH₂SiMe₃)₂(THF)] ⁺ underwent THF substitution reactions with OPPh₃ or pyridine, Sc - alkyl migratory insertion with carbodiimides, and C-H bond metathesis with PhCCH. The olefin polymerization capabilities of a series of complexes M(L)R₃ have been determined. The scandium complexes were found to be very productive for ethylene polymerization for L = HC(Me ₂pz)₃, Me₃[9]aneN₃, or [9]aneS ₃ and R = CH₂SiMe₃ when activated with 1 equiv of [CPh₃][BAr^F₄]. When activated with 2 equiv of [CPh₃][BAr^F₄], the compounds were also very active for the polymerization of 1-hexene.

Full text of DOI:10.1021/om800279d

3458
Organometallics 2008, 27, 3458–3473
Synthesis, DFT Studies, and Reactions of Scandium and Yttrium
Dialkyl Cations Containing Neutral fac-N3 and fac-S3 Donor
Ligands
Cara S. Tredget,† Eric Clot,*,‡ and Philip Mountford*,†
Chemistry Research Laboratory, UniVersity of Oxford, Mansfield Road, Oxford OX1 3TA, U.K., and
Institut Charles Gerhardt Montpellier, UMR 5253 CNRS-UM2-UM1-ENSCM, cc 1501, Place Euge`ne
Bataillon, 34095 Montpellier Cedex 5, France
ReceiVed March 30, 2008
Reaction of Sc(CH2SiMe3)3(THF)2 with 1,4,7-trithiacyclononane gave Sc([9]aneS3)(CH2SiMe3)3, the
first organometallic group 3 complex of [9]aneS3 ([9]aneS3 ) 1,4,7-trithiacyclononane). The corresponding
reaction for yttrium gave equilibrium mixtures of Y([9]aneS3)(CH2SiMe3)3 and starting materials. Density
functional theory (DFT) was used to compare the energies of formation and metal-ligand interaction
energies for M([9]aneS3)R3 with those for the previously reported fac-N3 donor complexes M(fac-N3)R3
(R ) Me or CH2SiMe3; fac-N3 ) 1,4,7-trimethyltriazacyclononane (Me3[9]aneN3) or HC(Me2pz)3).
Reaction of M(CH2SiMe3)3(THF)2 with [NHMe2Ph][BArF ] (ArF ) C6F5) in the presence of a face-
4
capping ligand L (L ) HC(Me2pz)3, Me3[9]aneN3, or [9]aneS3) gave the cationic complexes
[M(L)(CH2SiMe3)2(THF)]+, which has been structurally characterized for M ) Sc and L ) [9]aneS3.
The corresponding base-free cations [M(L)(CH2SiMe3)2]+ were studied by 29Si NMR spectroscopy and/
or DFT and found to possess ꢀ-Si-C agostic alkyl groups in most instances. The isolated cations [Sc(fac-
N3)(CH2SiMe3)2(THF)]+ underwent THF substitution reactions with OPPh3 or pyridine, Sc-alkyl
migratory insertion with carbodiimides, and C-H bond metathesis with PhCCH. The olefin polymerization
capabilities of a series of complexes M(L)R3 have been determined. The scandium complexes were found
to be very productive for ethylene polymerization for L ) HC(Me2pz)3, Me3[9]aneN3, or [9]aneS3 and
R ) CH2SiMe3 when activated with 1 equiv of [CPh3][BArF ]. When activated with 2 equiv of
4
[CPh3][BArF ], the compounds were also very active for the polymerization of 1-hexene.
4
Introduction
In the last 10 years in particular, noncyclopentadienyl group
3 and lanthanide compounds have attracted an increasing amount
of attention.1–4 Some of this work has been focused toward
catalytic transformations, and in particular olefin polymerization.5–8
In the latter regard, several research groups have recently
targeted mono- or dicationic alkyl derivatives as analogues of
the well-known cationic group 4 Ziegler-type polymerization
catalysts.9–11 In our laboratory12–23 we have been developing
the stoichiometric and catalytic reactions of early transition metal
organometallic complexes containing fac-coordinating N3-donor
ligands (Figure 1) such as 1,3,5-trimethyltriazacyclohexane
(Me3[6]aneN3), 1,4,7-trimethyltriazacyclonane (Me3[9]aneN3),
and tris(3,5-dimethyl)pyrazolylmethane (HC(Me2pz)3, a neutral
analogue of the anionic tris(pyrazolyl)hydroborate family
[HB(R2pz)3]-). These readily prepared chelating ligands provide
Figure 1. fac-N3 donor ligands used in this contribution.
well-defined coordination environments and have been widely
exploited in coordination chemistry in general. The “hard”
nitrogen donors are highly compatible with the “hard” early
transition metals and group 3/lanthanide elements.
Bercaw was the first to report organometallic Me3[9]aneN3
complexes of group 3, namely, M(Me3[9]aneN3)Me3 (M ) Sc
(9) Arndt, S.; Okuda, J. AdV. Synth. Catal. 2005, 347, 339.
(10) Zeimentz, P. M.; Arndt, S.; Elvidge, B. R.; Okuda, J. Chem. ReV.
2006, 106, 2404.
(11) Hou, Z.; Luo, Y.; Li, X. J. Organomet. Chem. 2006, 691, 3114.
(12) Wilson, P. J.; Blake, A. J.; Mountford, P.; Schro¨der, M. Chem.
Commun. 1998, 1007.
* Corresponding authors. E-mail: philip.mountford@chem.ox.ac.uk; clot@
univ-montp2.fr.
† University of Oxford.
‡ Institut Charles Gerhardt Montpellier.
(13) Wilson, P. J.; Blake, A. J.; Mountford, P.; Schro¨der, M. J.
Organomet. Chem. 2000, 600, 71.
(1) Piers, W. E.; Emslie, D. J. H. Coord. Chem. ReV. 2002, 131, 233–
234.
(14) Male, N. A. H.; Skinner, M. E. G.; Bylikin, S. Y.; Wilson, P. J.;
Mountford, P.; Schro¨der, M. Inorg. Chem. 2000, 39, 5483.
(15) Adams, N.; Arts, H. J.; Bolton, P. D.; Cowell, D.; Dubberley, S. R.;
Friederichs, N.; Grant, C.; Kranenburg, M.; Sealey, A. J.; Wang, B.; Wilson,
P. J.; Cowley, A. R.; Mountford, P.; Schro¨der, M. Chem. Commun. 2004,
434.
(16) Bolton, P. D.; Clot, E.; Cowley, A. R.; Mountford, P. Chem.
Commun. 2005, 3313.
(17) Tredget, C. S.; Lawrence, S. C.; Ward, B. D.; Howe, R. G.; Cowley,
A. R.; Mountford, P. Organometallics 2005, 24, 3136.
(2) Mountford, P.; Ward, B. D. Chem. Commun. 2003, 1797.
(3) Edelmann, F. T.; Freckmann, D. M. M.; Schumann, H. Chem. ReV.
2002, 102, 1851.
(4) Marques, N.; Sella, A.; Takats, J. Chem. ReV. 2002, 102, 2137.
(5) Gibson, V. C.; Spitzmesser, S. K. Chem. ReV. 2003, 103, 283.
(6) Hou, Z.; Wakatsuki, Y. Coord. Chem. ReV. 2002, 231, 1.
(7) Nakayama, Y.; Yasuda, H. J. Organomet. Chem. 2004, 689, 4489.
(8) Gromada, J.; Carpentier, J.-F.; Mortreux, A. Coord. Chem. ReV. 2004,
248, 397.
10.1021/om800279d CCC: $40.75
2008 American Chemical Society
Publication on Web 07/03/2008

Scandium and Yttrium Dialkyl Cations
Organometallics, Vol. 27, No. 14, 2008 3459
or Y).24 Their reactions with [NHMe2Ph][BArF ] or BArF3 were
provided extensive structural and spectroscopic evidence for rare
earth alkyl and aryl dications, some of which are active for olefin
polymerization.36,39–42
4
also described (ArF ) C6F5). For M ) Y the reaction with
[NHMe2Ph][BArF ] led to decomposition and loss of
4
Me3[9]aneN3. For M ) Sc, the corresponding reaction in THF
Recently it has been reported that the presence of neutral
S-donor groups may be beneficial to the performance of certain
group 4 alkyl polymerization catalysts.43 Unsurprisingly, the
non-cyclopentadienyl organometallic chemistry of the group 3
metals is dominated by “hard” N- and O-donor ligands.1–4
Although some noteworthy examples are known of anionic
bis(phenolate) ligands incorporating additional neutral thioether
donors,44,45 neutral or cationic organometallic complexes based
entirely on “soft” sulfur-donor ligands have yet to be described.
The commercially available macrocycle 1,4,7-trithiacy-
clononane ([9]aneS3) is the all-sulfur donor analogue of
Me3[9]aneN3. [9]aneS3 has an extensive coordination chemistry
of the later transition and p-block metals (ca. 250 organometallic
complexes alone have been reported).46–48 However, apart from
our recent communication,49 no organometallic rare earth
compounds (or indeed organotransition metal compounds before
group 6) containing [9]aneS3 have so far been reported. The
only rare earth complexes reported so far for [9]aneS3 are
La([9]aneS3)I3(MeCN)2 and U([9]aneS3)I3(MeCN)2.50
We recently described the synthesis and structures of a range
of group 3 fac-N3-coordinated complexes M(fac-N3)X3 (M )
Sc, Y; X ) Cl or CH2SiMe3; fac-N3 ) Me3[6]aneN3,
Me3[9]aneN3, or HC(Me2pz)3).17 In this contribution we report
the first rare earth organometallic complexes of [9]aneS3 along
with a number of well-defined, THF-stabilized cationic dialkyl
complexes containing neutral fac-N3 or -S3 donor ligands. DFT
studies comparing the ligand complexation energetics of
Me3[9]aneN3, HC(Me2pz)3, and [9]aneS3 are reported, together
with related studies of the structures of the base-free dialkyl
cations [M(L)(CH2SiMe3)2]+ (which could also be observed by
NMR spectroscopy in some instances). Selected C-H activation
and migratory insertion reactions of well-defined scandium
dialkyl cations are reported. The abilities of the complexes
M(L)(CH2SiMe3)3 to act as precatalysts for the polymerization
of ethylene and 1-hexene are also disclosed. Part of this work
has been communicated.49,51
gave a product tentatively formulated as [Sc(Me3[9]aneN3)-
Me2(THF)][BArF ]. Activation of Sc(Me3[9]aneN3)Me3 with
4
BArF on the NMR tube scale in THF-d8 provided a system
3
competent for ethylene polymerization at 80 °C, but no well-
defined compound was isolated. Hessen subsequently found that
tetradentate triazacyclononane-based ligands containing chelat-
ing amide groups formed very active, well-defined ethylene
polymerization catalysts for group 3 and lanthanide metals.25–29
Other group 3 catalyst systems based on fac-N3-type neutral
and monoanionic ligands have also been reported recently by
the same group.30,31 Related open-chain systems have also
recently been described.32
In other work with fac-N3-type monoanionic ligands, Piers33
and Bianconi34 reported scandium and yttrium tris(pyrazolyl)-
hydroborate complexes of the type M{HB(R2pz)3}(CH2SiMe3)2-
t
(THF)n (R ) Me or Bu, n ) 1 or 0), but these showed either
no (Sc) or negligible activity toward ethylene polymerization.
Okuda et al. were the first to report structurally authenticated
(but catalytically inactive) rare earth alkyl cations based on
O-donor crown ethers.35,36 Very recently Gade and co-workers
reported a series of C3-symmetric rare earth complexes M(iPr-
trisox)(CH2SiMe2R)3 (R ) Me or Ph) capable of the isospecific
polymerization of 1-hexene and other R-olefins.37,38 Interest-
ingly, based on in situ NMR experiments, alkyl dications of
the type “[M(iPr-trisox)(CH2SiMe2R)]2+” were proposed to be
the active species in these systems. Indeed, Okuda et al. have
(18) Adams, N.; Arts, H. J.; Bolton, P. D.; Cowell, D.; Dubberley, S. R.;
Friederichs, N.; Grant, C. M.; Kranenburg, M.; Sealey, A. J.; Wang, B.;
Wilson, P. J.; Zuideveld, M. A.; Blake, A. J.; Schro¨der, M.; Mountford, P.
Organometallics 2006, 25, 3888.
(19) Bolton, P. D.; Adams, N.; Clot, E.; Cowley, A. R.; Wilson, P. J.;
Schro¨der, M.; Mountford, P. Organometallics 2006, 25, 5549.
(20) Bolton, P. D.; Clot, E.; Adams, N.; Dubberley, S. R.; Cowley, A. R.;
Mountford, P. Organometallics 2006, 25, 2806.
(21) Bolton, P. D.; Clot, E.; Cowley, A. R.; Mountford, P. J. Am. Chem.
Soc. 2006, 128, 15005.
(22) Bigmore, H. R.; Dubberley, S. R.; Kranenburg, M.; Lawrence, S. C.;
Sealey, A. J.; Selby, J. D.; Zuideveld, M.; Cowley, A. R.; Mountford, P.
Chem. Commun. 2006, 436.
(23) Bigmore, H. R.; Zuideveld, M.; Kowalczyk, R. M.; Cowley, A. R.;
Kranenbrug, M.; McInnes, E. J. L.; Mountford, P. Inorg. Chem. 2006, 45,
6411.
(24) Hajela, S.; Schaefer, W. P.; Bercaw, J. E. J. Organomet. Chem.
1997, 532, 45.
(25) Bambirra, S.; van Leusen, D.; Meetsma, A.; Hessen, B.; Teuben,
J. H. Chem. Commun. 2001, 637.
(26) Tazelaar, C. G. J.; Bambirra, S.; van Leusen, D.; Meetsma, A.;
Hessen, B.; Teuben, J. H. Organometallics 2004, 23, 936.
(27) Bambirra, S.; Boot, S. J.; van Leusen, D.; Meetsma, A.; Hessen,
B. Organometallics 2004, 23, 1891.
Results and Discussion
Trithiacyclononane Complexes: Synthesis and Structures.
Reaction of Sc(CH2SiMe3)3(THF)2 with 1 equiv of [9]aneS3 in
cold toluene followed by removal of the volatiles under reduced
pressure gave Sc([9]aneS3)(CH2SiMe3)3 (1) as an air-sensitive,
white solid in 75% isolated yield (eq 1). Prolonged exposure to
(39) Arndt, S.; Spaniol, T. P.; Okuda, J. Angew. Chem., Int. Ed. 2003,
42, 5075.
(28) Bambirra, S.; Meetsma, A.; Hessen, B.; Bruins, A. P. Organome-
tallics 2006, 25, 3486.
(29) Bambirra, S.; van Leusen, D.; Tazelaar, C. G. J.; Meetsma, A.;
Hessen, B. Organometallics 2007, 26, 1014.
(40) Arndt, S.; Beckerle, K.; Zeimentz, P. M.; Spaniol, T. P.; Okuda, J.
Angew. Chem., Int. Ed. 2005, 44, 7473.
(41) Arndt, S.; Elvidge, B. R.; Zeimentz, P. M.; Spaniol, T. P.; Okuda,
J. Organometallics 2006, 25, 793.
(30) Ge, S.; Bambirra, S.; Meetsma, A.; Hessen, B. Chem. Commun.
2006, 3320.
(31) Ge, S.; Meetsma, A.; Hessen, B. Organometallics 2007, 26, 5278.
(32) Marinescu, S. C.; Agapie, T.; Day, M. W.; Bercaw, J. E.
Organometallics 2007, 26, 1178.
(33) Blackwell, J.; Lehr, C.; Sun, Y.; Piers, W. E.; Pearce-Batchilder,
S. D.; Zaworotko, M. J.; Young, V. G., Jr, Can. J. Chem. 1997, 75, 702.
(34) Long, D. P.; Bianconi, P. A. J. Am. Chem. Soc. 1996, 118, 12453.
(35) Arndt, S.; Spaniol, T. P.; Okuda, J. Chem. Commun. 2002, 896.
(36) Elvidge, B. R.; Arndt, S.; Zeimentz, P. M.; Spaniol, T. P.; Okuda,
J. Inorg. Chem. 2005, 44, 6777.
(42) Zeimentz, P. M.; Okuda, J. Organometallics 2007, 26, 6388.
(43) Oakes, D. C. H.; Kimberley, B. S.; Gibson, V. C.; Jones, D. J.;
White, A. J. P.; Williams, D. J. Chem. Commun 2004, 2174.
(44) Ma, H.; Spaniol, T. P.; Okuda, J. Dalton Trans. 2003, 4770.
(45) Ma, H. Y.; Spaniol, T. P.; Okuda, J. Angew. Chem., Int. Ed. 2006,
45, 7818.
(46) Blake, A. J.; Schro¨der, M. AdV. Inorg. Chem. 1990, 35, 1.
(47) Rawle, S. C.; Cooper, S. R. Struct. Bonding (Berlin) 1990, 72, 1.
(48) Levason, W.; Reid, G. J. Chem. Soc., Dalton Trans. 2001, 2953.
(49) Tredget, C. S.; Bonnet, F.; Cowley, A. R.; Mountford, P. Chem.
Commun. 2005, 3301.
(37) Ward, B. D.; Bellemin-Laponnaz, S.; Gade, L. H. Angew. Chem.,
Int. Ed. 2005, 44, 1668.
(38) Lukesova, L.; Ward, B. D.; Bellemin-Laponnaz, S.; Wadepohl, H.;
Gade, L. H. Organometallics 2007, 26, 4652.
(50) Karmazin, L.; Mazzanti, M.; Pecaut, J. Chem. Commun. 2002,
654.
(51) Lawrence, S. C.; Ward, B. D.; Dubberley, S. R.; Kozak, C. M.;
Mountford, P. Chem. Commun. 2003, 2880.

3460 Organometallics, Vol. 27, No. 14, 2008
Tredget et al.
vacuum led to decomposition, possibly due to loss of [9]aneS3.
Compound 1 is the first organometallic derivative of [9]aneS3
for any group 3 or rare earth metal.
The solution NMR data and crystallographic data (see below)
are consistent with the six-coordinate structure illustrated in eq
1. The CH2SiMe3 groups appear as singlets in the 1H and
13C{1H} spectra with values in the expected ranges. The
inequivalent methylene hydrogens of [9]aneS3 (i.e., “up” and
“down” with respect to Sc) appear as two sets of multiplets
(relative integrals 6 H each) at ca. 2.25 and 1.45 ppm in the 1H
spectrum, consistent with coordination of the ligand to the
Sc(CH2SiMe3)3 moiety in solution. No exchange was observed
between free and coordinated [9]aneS3 on the NMR time scale.
When the reaction between Sc(CH2SiMe3)3(THF)2 and [9]aneS3
Figure 2. Displacement ellipsoid plot (20% probability) of
Sc([9]aneS3)(CH2SiMe3)3 (1). H atoms and toluene of crystallization
omitted for clarity. Selected distances (Å): Sc(1)-S(1) 2.7947(7),
Sc(1)-S(2) 2.7799(6), Sc(1)-S(3) 2.8039(6), Sc(1)-C(7) 2.250(2),
Sc(1)-C(11) 2.265(2), Sc(1)-C(15) 2.231(2). Selected angles
(deg): S(1)-Sc(1)-S(2) 74.439(18), S(1)-Sc(1)-S(3) 74.240(17),
S(2)-Sc(1)-S(3) 74.380(18), C(7)-Sc(1)-C(11) 109.66(9),
C(7)-Sc(1)-C(15) 106.75(8), C(7)-Sc(1)-C(15) 103.74(9).
1
was monitored by H NMR spectroscopy at 293 K in toluene-
d8, it was found to lead to only ca. 85% conversion to 1 and
THF, in a temperature-dependent equilibrium. Cooling the
sample to 241 K shifted the equilibrium slightly back toward
the starting materials (ca. 75% conversion at this temperature).
This is to be anticipated since formation of 1 requires one
[9]aneS3 ligand to displace two THF molecules from
Sc(CH2SiMe3)3(THF)2, which is an entropically favored process.
The reversibility of eq 1 was confirmed by the addition of 5
equiv of THF to a pure sample of 1, which led to complete
displacement of [9]aneS3. Furthermore, addition of 1 equiv of
the fac-N3 donor ligands HC(Me2pz)3 or Me3[9]aneN3 to 1 in
C6D6 also gave quantitative displacement of [9]aneS3 to form
the previously reported Sc(fac-N3)(CH2SiMe3)3 (2 or 3, respec-
tively).17 Addition of 1 equiv. of [9]aneS3 to pure samples of
either Sc(fac-N3)(CH2SiMe3)3 compound failed to give any
reaction, confirming that the positions of these equilibria are
governed by thermodynamic factors (eq 2). The ready displace-
ment of [9]aneS3 by THF and the fac-N3 species is consistent
with expectations based on the hardness of these O- and N-donor
ligands.
°C. The molecular structure is shown in Figure 2 together with
selected bond distances and angles. Molecules of 1 contain six-
coordinate scandium centers bound to three CH2SiMe3 ligands
and a fac-coordinated [9]aneS3. The Sc-S bonds lie in the range
2.7799(6)-2.8039(6) Å. Although there are very few previously
determined distances to compare these to, they are within the
range of those reported by Okuda for two six-coordinate thio-
ether-bridged scandium bis(phenolate) complexes (av 2.867,
range 2.744(2)-2.873(1) Å).44 The Sc-CH2 distances in 1 (av
2.249 Å) lie within the general range for compounds containing
a Sc-CH2SiMe2R (R ) Me or Ph) group (range 2.166-2.295,
av 2.232 Å).52,53 However, they are noticeably shorter than those
in the closely related fac-N3 complexes Sc{HC(Me2pz)3}(CH2-
SiMe3)3 (2, av 2.280 Å) and Sc(Me3[9]aneN3)(CH2SiMe3)3 (3,
av 2.281 Å).17 The shorter Sc-CH2 distances in 1 indicate that
the bonding to the alkyl ligands in this complex is less perturbed
by the fac-coordinated ligand compared to that in the N3-donor
complexes, again suggesting that [9]aneS3 bonds less well to
the Sc(CH2SiMe3)3 fragment than the analogous nitrogen
macrocycle Me3[9]aneN3 or related podand ligand HC(Me2pz)3.
Further examination of the geometry of the Sc(CH2SiMe3)3
fragments in the three complexes 1, 2, and 3 appears to confirm
this. Thus the C-Sc-C angles in 1 (av 106.7°) are significantly
less compressed than those in 2 (av 100.5°) and 3 (av 100.8°).
Accordingly, the displacement of Sc from the plane defined by
the three CH2SiMe3 methylene carbons in 1 (0.85 Å) is
significantly less than in 2 (1.05 Å) or 3 (1.04 Å).
DFT Studies of Ligand Binding Abilities. Compound 1 is
unique in group 3 organometallic chemistry, whereas complexes
of the type Sc(fac-N3)R3 based on Me3[9]aneN317 or other N3-
donor ligands17,30,33,34 are fairly well-established (as are O-donor
crown ether complexes35,36). The NMR tube experiments
described above (eqs 1 and 2) found that [9]aneS3 is displaced
by both THF and fac-N3 donor ligands. To gain further insight
into these processes, DFT calculations probing the underlying
The reaction between Y(CH2SiMe3)3(THF)2 and [9]aneS3 has
also been followed by NMR spectroscopy in toluene-d8 (eq 1).
At 293 K only ca. 60% conversion to the fac-coordinated
product Y([9]aneS3)(CH2SiMe3)3 (4) was observed, reducing
to ca. 50% at 241 K. Unfortunately, 4 could not be isolated on
1
the preparative scale, but was characterized in situ by H and
13C NMR spectroscopy. The NMR spectra of 4 were analogous
1
to those of 1, in particular showing two sets of H multiplets
for the coordinated [9]aneS3. 89Y coupling to the Y-bound CH2
groups was observed in the 13C spectrum.
(52) Fletcher, D. A.; McMeeking, R. F.; Parkin, D. J. Chem. Inf. Comput.
Sci. 1996, 36, 746. (The United Kingdom Chemical Database Service)
(53) Allen, F. H.; Kennard, O. Chem. Des. Automation News 1993, 8,
1 and 31.
Diffraction-quality crystals of Sc([9]aneS3)(CH2SiMe3)3 (1)
were grown from a toluene-pentane solvent mixture at -80

Scandium and Yttrium Dialkyl Cations
Organometallics, Vol. 27, No. 14, 2008 3461
former systems (cf. the larger d values computed in Table 1
and found experimentally, Vide supra). This presumably maxi-
mizes metal-ligand bonding interactions in the fac-N3 systems.
The consistently smaller ∆Edef(L) values for both Me3[9]aneN3
and [9]aneS3 compared to HC(Me2pz)3 are attributed to the well-
known “macrocyclic effect” for these highly preorganized
ligands.54
Figure 3. Thermodynamic cycle considered to analyze the forma-
tion energy ∆Eform of the M(L)R3 complexes as a sequence of three
steps: (i) deformation of the MR3 fragment, ∆Edef(M); (ii) deforma-
tion of the ligand, ∆Edef(L); (iii) interaction between the two
fragments in the geometry of the complex, ∆Eint(M · · · L). L )
Me3[9]aneN3, HC(Me2pz)3, or [9]aneS3; R ) Me or CH2SiMe3; M
) Sc or Y. ∆Eform ) ∆Edef(M) + ∆Edef(L) + ∆Eint(M · · · L). See
Table 1 for further details.
The general trends for the bulky Sc(L)(CH2SiMe3)3 systems
are found for the smaller trimethyl homologues Sc(L)Me3
(entries 4-6). The ∆Eform values are more favorable for all
ligands, which relates primarily to the smaller deformation
energies ∆Edef(M). In fact a pronounced ꢀ-Si-C agostic
interaction is present in the fragments M(CH2SiMe3)3 (M ) Sc
or Y), and this contributes to add extra stabilization. Thus
deformation of the fragment to accommodate the incoming L
ligand is energetically more costly compared to the same process
for ScMe3, where such an agostic interaction is absent.
For the yttrium congeners (entries 7-9) there is a somewhat
larger difference between the ∆Eform value for the [9]aneS3
complex 4 and both fac-N3 complexes. Again, this does not
relate primarily to the intrinsic ∆Eint(M · · · L) values (which vary
by no more than ca. 10 kJ mol-1 from Sc to Y), but to the
different extents of stabilization of the M(CH2SiMe3)3 deforma-
tion energies for the larger metal center. Thus for Me3[9]aneN3
and HC(Me2pz)3 the deformation energies decrease by ca. 31
electronic energies of the reactions in eqs 1 and 2 were carried
out for a series of model systems M(L)R3 (M ) Sc or Y, R )
Me or CH2SiMe3; L ) Me3[9]aneN3, HC(Me2pz)3, or [9]aneS3;
see Computational Details for further information).
Figure 3 assesses the formation energies, ∆Eform, of various
model complexes M(L)R3 from the separated hypothetical
fragments MR3 and free ligands L. The overall formation
energies (see Table 1) have been decomposed into three main
parts: (i) the energy, ∆Edef(M), required to deform the free MR3
fragment to its geometry in the M(L)R3 complex; (ii) the
corresponding preorganization energy for the ligand, ∆Edef(L);
(iii) the interaction energy, ∆Eint(M · · · L), between the preor-
ganized MR3 and L moieties. Table 1 also gives the distance d
of M in M(L)R3 above the plane defined by the M-CH2 or
M-CH3 carbons of the alkyl ligands. This is a measure of the
extent of deformation (pyramidalization) of the MR3 fragments
from their equilibrium geometries (d ≈ 0.4 Å, see Table 1).
Table 1 also provides the calculated electronic energy ∆Eexch
for the substitution of two THFs in MR3(THF)2 by L (R ) Me
or CH2SiMe3; eq 3). We have not attempted to estimate
entropies for the processes, which, to a first approximation are
assumed to be effectively constant within the two different
systems (i.e., Figure 3 and eq 3). Where the experimental data
are available, the agreement between the calculated and observed
geometries of the various complexes M(L)(CH2SiMe3)3 is very
good.
Entries 1-3 of Table 1 list the energetic parameters for ligand
bonding to Sc(CH2SiMe3)3. The ∆Eform values predict that both
Me3[9]aneN3 and HC(Me2pz)3 form stronger complexes with
Sc(CH2SiMe3)3 than [9]aneS3 does, in accord with eq 2 and
our previous report that Me3[9]aneN3 displaces HC(Me2pz)3
from M{HC(Me2pz)3}(CH2SiMe3)3 (M ) Sc or Y).17 However,
although the difference in ∆Eform between 2 and 1 is only 14.3
kJ mol-1, this is not a direct reflection of the differences in the
metal-ligand interaction energy (∆Eint(M · · · L)) for the
HC(Me2pz)3 and [9]aneS3 ligands themselves. As shown in
Table 1, the ∆Eint(M · · · L) values for the two fac-N3 donors
(-260.4 and -236.6 kJ mol-1) are considerably more favorable
than for [9]aneS3 (-156.7 kJ mol-1). The origin of the
unexpectedly small difference in the overall ∆Eform between 2
and 1 is instead attributed to the higher preorganization energy
of both the Sc(CH2SiMe3)3 (95.0 vs 62.0 kJ mol-1) and ligand
(35.8 vs 3.3 kJ mol-1) fragments for the N3-donor case. The
higher ∆Edef(M) value for 2 (and 3) compared to 1 relates to
the more extensive pyramidalization of Sc(CH2SiMe3)3 in the
and 26 kJ mol-1
, respectively, whereas for M([9]-
aneS3)(CH2SiMe3)3 the decrease from M ) Sc to Y is only ca.
17 kJ mol-1. This is because the deformation of the MR3
fragment in all three compounds M([9]aneS3)R3 (1, 7, and 4)
is systematically lower (as indicated by the smaller d values)
than for the corresponding fac-N3 systems.
The calculated ∆Eexch values for THF displacement from
M(CH2SiMe3)3(THF)2 according to eq 3 follow the same trends
as the ∆Eform values for M ) Sc and Y. For Me3[9]aneN3 the
formation of 3 or 8 from the bis(THF) species is exothermic.
In contrast, for both HC(Me2pz)3 and [9]aneS3 it is endothermic,
but for different reasons as discussed above. In both of the latter
cases it appears that entropic contributions are essential for the
formation of the M(L)(CH2SiMe3)3 complexes. The more
positive ∆Eexch for the formation of 4 compared to that for 1 is
consistent with the lower extent of conversion of
Y(CH2SiMe3)3(THF)2 to Y([9]aneS3)(CH2SiMe3)3 as found in
the NMR experiments. It is also interesting to note that although
HC(Me2pz)3 reacts with Sc(CH2SiMe3)3(THF)2 in C6D6 or
CD2Cl2 to quantitatively form M{HC(Me2pz)3}(CH2SiMe3)3 (2)
(despite the positive calculated ∆Eexch value),17 when pure 2 is
dissolved in THF-d8, an equilibrium mixture of 2, HC(Me2pz)3,
and Sc(CH2SiMe3)3(THF-d8)2 is formed. However, Me3[9]aneN3
is not displaced from 3 under the same conditions, again in
agreement with Table 1. The ∆Eexch values for the hypothetical
trimethyl complexes MMe3(THF)2 follow the same trend as for
M(CH2SiMe3)3(THF)2.
Synthesis and Reactivity of THF-Stabilized Dialkyl
Cations. The remainder of this contribution is concerned with
the synthesis, bonding, and reactivity of cationic complexes.
Scheme 1 shows the preparative-scale syntheses of the new
THF-stabilized cations [M{HC(Me2pz)3}(CH2SiMe3)2(THF)]+
(M ) Sc (10+) or Y (11+)). They were isolated in 71-73%
yield in analytically pure form as their [BArF ]- salts (ArF )
4
C6F5) by precipitation from THF solution on addition of pentane,
the SiMe4 and NMe2Ph side-products remaining in the super-
natants. NMR tube experiments in CD2Cl2 showed that 10+ or
(54) Lindoy, L. F. The Chemistry of Macrocyclic Ligand Complexes;
Cambridge University Press: Cambridge, 1989.

3462 Organometallics, Vol. 27, No. 14, 2008
Tredget et al.
Table 1. Formation Energies, ∆Eform, of the M(L)R3 Complexes and Energetic Contributions Defined According to the Thermodynamic Cycle
Shown in Figure 3 (parameter “d” is the distance between the metal atom and the plane of the three C atoms bonded to the metal; 4Eexch
ligand exchange energy defined according to eq 3; all energies given in kJ mol-1
)
)
entry
compound
∆Eform
∆Eint(M · · · L)
∆Edef(M)
∆Edef(L)
d (Å)a
∆Eexch
1
2
3
4
5
6
7
8
9
Sc(Me3[9]aneN3)(CH2SiMe3)3 (3)
Sc{HC(Me2pz)3}(CH2SiMe3)3 (2)
Sc([9]aneS3)(CH2SiMe3)3 (1)
Sc(Me3[9]aneN3)Me3 (5)
Sc{HC(Me2pz)3}Me3 (6)
Sc([9]aneS3)Me3 (7)
Y(Me3[9]aneN3)(CH2SiMe3)3 (8)
Y{HC(Me2pz)3}(CH2SiMe3)3 (9)
Y([9]aneS3)(CH2SiMe3)3 (4)
-138.6
-105.8
-91.5
-211.6
-177.0
-135.0
-172.5
-146.2
-109.0
-260.4
-236.6
-156.7
-263.5
-243.2
-149.9
-260.2
-249.2
-156.0
102.2
95.0
62.0
33.9
27.2
11.9
71.2
68.7
45.0
19.5
35.8
3.3
18.0
39.1
3.0
16.5
34.2
2.0
1.002
1.031
0.807
0.997
0.949
0.757
0.991
1.083
0.762
-10.5
22.3
36.6
-4.8
-0.2
40.0
-18.3
7.9
45.1
a Values for the MR3 fragment: Sc(CH2SiMe3)3, 0.459 Å; ScMe3, 0.379 Å; Y(CH2SiMe3)3, 0.354 Å.
Scheme 1. Synthesis of THF-Stabilized Dialkyl Cations with
resonances at 3.99 and 2.03 ppm, consistent with it remaining
coordinated in solution). The nature of the fluxional process
has not been established but appears to be effectively an in-
place rotation of the fac-N3 ligand as reported previously for
fac-N3 Donor Ligandsa
related systems.13 Addition of OPPh3 (1 equiv) to 11-BArF
4
gave the adduct [Y{HC(Me2pz)3}(CH2SiMe3)2(OPPh3)][BArF ]
4
(12-BArF ) in reasonable isolated yield. In this case the Cs-
4
symmetric cation 12+ showed the expected resonances (e.g.,
two Me2pz ring environments and doublets of doublets for the
methylene linkages of the neosilyl ligands).
As mentioned in the Introduction, Bercaw has reported the
reactions of the trimethyl complexes M(Me3[9]aneN3)Me3 (M
) Sc or Y) with [NHMe2Ph][BArF ].24 In the case of yttrium
4
only decomposition products were obtained; for scandium no
well-defined compound could be isolated. Encouraged by the
results for the tris(3,5-dimethylpyrazolyl)methane systems 10+
and 11+, we turned to the triazacyclononane-supported neosilyl
analogues. As for M{HC(Me2pz)3}(CH2SiMe3)3, reaction of
M(Me3[9]aneN3)(CH2SiMe3)3 (M ) Sc (3) or Y (8)17) with
[Ph3C][BArF ] in CD2Cl2 in the presence of THF gave quantita-
4
tive conversion to well-defined cations [M(Me3[9]aneN3)-
(CH2SiMe3)2(THF)]+ (M ) Sc (13+) or Y (14+). However, as
for the tris(3,5-dimethyl)pyrazolylmethane systems, the com-
pounds 13-BArF and 14-BArF are most cost-effectively and
F
-
a
[BAr
] anions omitted for clarity.
4
4
4
11+ can also be formed quantitatively by reaction of
M{HC(Me2pz)3}(CH2SiMe3)3 (M ) Sc (2) or Y (9)17) with
conveniently prepared using one-pot reactions (Scheme 1)
starting from M(CH2SiMe3)3(THF)2, [NHMe2Ph][BArF ], and
4
[Ph3C][BArF ] in the presence of THF, forming the expected
Me3[9]aneN3 which affords them in ca. 50% isolated yield. In
contrast to the tris(3,5-dimethylpyrazolyl)methane reactions,
which work best in THF solution, the Me3[9]aneN3 complexes
are most cleanly prepared in chlorobenzene. The analytically
pure compounds 13-BArF and 14-BArF have been fully
4
Ph3CCH2SiMe3 side-product.20 However, it is more convenient
and efficient to use the “one-pot” route in Scheme 1, as this
avoids the need to isolate and purify the intermediate tris(alkyl)
species. Attempts to grow diffraction-quality crystals of 10-
BArF or 11-BArF were unsuccessful. An alternative anion
4
4
characterized and their NMR spectra are comparable to those
4
4
of 10-BArF and 11-BArF .
[BPh4]- was used in the reaction of 2 with [NHEt3][BPh4],
which formed [Sc{HC(Me2pz)3}(CH2SiMe3)2(THF)][BPh4] (10-
BPh4) in 43% isolated yield, but again diffraction-quality
crystals could not be obtained. However, the X-ray structure of
a [9]aneS3 analogue of [M{HC(Me2pz)3}(CH2SiMe3)2(THF)]+
has been obtained and is discussed below.
4
4
The 1H and 13C NMR spectra of 10-BArF showed the
4
expected resonances for the THF-stabilized Cs-symmetric cation
illustrated in Scheme 1. In particular, two sets of Me2pz group
resonances were seen (2:1 intensity ratio for the groups trans
to CH2SiMe3 and THF, respectively), and the diastereotopic
methylene protons of the alkyl ligands appeared as a pair of
mutually coupled doublets. The 19F NMR spectrum showed no
evidence for anion coordination in CD2Cl2 for 10+ or any of
In
a
similar manner, the one-pot reaction of
Sc(CH2SiMe3)3(THF)2, [NHMe2Ph][BArF ], and [9]aneS3 in
4
chlorobenzene afforded the cationic fac-S3 complex
[Sc([9]aneN3)(CH2SiMe3)2(THF)][BArF ] (15-BArF ) in ca.
4
4
50% yield (eq 4). When followed on the NMR scale in CD2Cl2
the conversion is quantitative with no unreacted [9]aneS3.
Analogous experiments found that 15-BArF4 can also be formed
from previously isolated Sc([9]aneN3)(CH2SiMe3)3 and
1
the species reported herein. In contrast to 10+, the H and 13C
NMR spectra of 11+ in CD2Cl2 showed only one Me2pz group
environment, even at low temperatures, and the alkyl methylene
protons appeared as a broad doublet (2JYH ) 2.9 Hz) indicative
of a dynamic process (the THF gave rise to 1H multiplet
[NHMe2Ph][BArF ] in the presence of THF (1 equiv). The NMR
4
data are consistent with the structure shown in eq 4, although

Scandium and Yttrium Dialkyl Cations
Organometallics, Vol. 27, No. 14, 2008 3463
as illustrated in eq 5. The spectra are unchanged at -80 °C. As
for 15+ the [9]aneS3 ligand gives rise to two sets of methylene
1H signals for the hydrogens positioned “up” and “down” with
regard to the metal center. However, due to the rapid in-place
rotational fluxional process, only one type of 13CH2 resonance
is observed for the methylene carbons even at -80 °C. In
principle the NMR data for 16+ could also be consistent with
a six-coordinate cation [Y([9]aneS3)(CH2SiMe3)2(THF)]+ (analo-
gous to 15+) undergoing fast exchange with the remaining THF
molecule. It is not possible to exclude this possibility on the
available evidence. We note, however, that Okuda has reported
structural evidence for both the eight-coordinate [Y(12-crown-
4)(CH2SiMe3)(THF)3]2+ and [Y(12-crown-4)Me2(THF)2]+ and
seven-coordinate [YMe2(THF)5]+ cations.36,40 As in the case
of 15+ and the neutral M([9]aneS3)(CH2SiMe3)3 systems,
addition of an excess of THF to 16+ causes complete displace-
ment of the [9]aneS3 ligand. It was not possible to isolate 16-
BArF on the preparative scale.
4
Figure 4. Displacement ellipsoid plot (25% probability) of
Synthesis and NMR and DFT Studies of Base-Free
[Sc([9]aneS3)(CH2SiMe3)2(THF)]+ (15+). H atoms and [BArF ]-
Cations. Addition of [Ph3C][BArF ] (1 equiv) to a solution of
4
4
anion omitted for clarity. Selected distances (Å): Sc(1)-S(1)
2.7696(10),Sc(1)-S(2)2.7623(10),Sc(1)-S(3)2.6920(9),Sc(1)-C(7)
2.154(2), Sc(1)-C(11) 2.175(2), Sc(1)-O(1) 2.150(2). Selected
angles (deg): S(1)-Sc(1)-S(2) 73.77(3), S(1)-Sc(1)-S(3) 76.41(3),
S(2)-Sc(1)-S(3)76.83(3),C(7)-Sc(1)-C(11)111.19(15),C(7)-Sc(1)-O(1)
97.92(13), C(11)-Sc(1)-O(1) 103.26(12).
Sc(Me3[9]aneN3)(CH2SiMe3)3 (3) in CD2Cl2 formed the base-
free cation [Sc(Me3[9]aneN3)(CH2SiMe3)2]+ (17+), which is
stable for several hours at -80 °C (although is less stable at
room temperature). Addition of THF quantitatively forms the
adduct [Sc(Me3[9]aneN3)(CH2SiMe3)2(THF)]+ (13+). The 19F
NMR spectrum of 17+ is consistent with a noncoordinated
[BArF ]- anion. The cation 17+ is highly fluxional even at -80
4
the coordinated [9]aneS3 appears to be undergoing fast in-place
rotation on the NMR time scale even at -80 °C in CD2Cl2. As
for neutral 1, the [9]aneS3 ligand can be displaced from the
scandium on the addition of an excess of THF.
°C, showing one N-Me group signal for the macrocyclic ligand
and one set of alkyl group resonances. Analogous results were
found for Sc{HC(Me2pz)3}(CH2SiMe3)3 (2), which formed the
fluxional cation [Sc{HC(Me2pz)3}(CH2SiMe3)2]+ (19+) on
reaction with [Ph3C]+. Neither 19-BArF nor 17-BArF could
Singlecrystalsof15-BArF4 weregrownfromapentane-chloro-
benzene solution. The molecular structure of 15+ is shown in
Figure 4 along with selected bond distances and angles.
Compound 15-BArF4 contains the first structurally characterized
group 3 or rare earth cation containing a thioether donor ligand.
The cation 15+ contains an approximately octahedral scandium
center with a fac-κ3-coordinated [9]aneS3 ligand, two neosilyl
groups, and a THF. The Sc-S distances trans to the alkyl groups
(2.7704(10) and 2.7617(10) Å) are longer than that trans to THF
(2.6921(9) Å) but shorter than those in 1 (av 2.793 Å), consistent
with the formal cationic charge for scandium and the reduced
steric crowding in 15+. The Sc-C distances (2.154(2) and
2.175(2) Å) are also shorter than in 1 (av 2.249 Å), for the
same reason. One other cation containing a Sc-CH2SiMe3 group
has been structurally characterized, namely, the five-coordinate
4
4
be isolated in the solid state. Attempts to form [Sc([9]aneS3)(CH2-
SiMe3)2]+ or the corresponding yttrium cations from [Y(fac-
N3)(CH2SiMe3)2]+ (fac-N3 ) Me3[9]aneN3, HC(Me2pz)3) at low
temperature in either CD2Cl2 or C6D5Br gave mixtures of
products or oily precipitates.
The low valence electron counts and coordination numbers
for 17+ and 19+ suggest the possibility of agostic bonding, most
likely via ꢀ-Si-C · · · Sc interactions, which are widespread
throughout the rare earth and electron-deficient early transition
metals.56–65 Of particular relevance to 17+ and 19+ is our recent
report of the macrocycle-supported titanium imido cation
[Ti(Me3[9]aneN3)(NtBu)(CH2SiMe3)]+ (18+), which possesses
a ꢀ-Si-C agostic alkyl group.20 The agostic interaction was
detected by 29Si NMR spectroscopy through an upfield-shifted
resonance of -15.9 ppm (cf. the nonagostic neutral precursor
Ti(Me3[9]aneN3)(NtBu)(CH2SiMe3)2 with δ ) -1.8 ppm,
CD2Cl2). DFT calculations found a ꢀ-Si-C agostic structure
and reproduced the 29Si shifts very well indeed,20 thus showing
i
[Sc{PhC(NAr)2}(CH2SiMe3)(THF)2]+ (Ar ) 2,6-C6H3 Pr2,
Sc-CH2 ) 2.165(2) Å).55
(56) Nikonov, G. I. J. Organomet. Chem. 2001, 635, 24.
(57) Clot, E.; Eisenstein, O. Struct. Bonding (Berlin) 2004, 113, 1.
(58) Scherer, W.; McGrady, G. S. Angew. Chem., Int. Ed. 2004, 43,
1782.
(59) Eisch, J. J.; Piotrowski, A. M.; Brownstein, S. K.; Gabe, E. J.; Lee,
F. L. J. Am. Chem. Soc. 1985, 107, 7219.
(60) Horton, A. D.; Orpen, A. G. Organometallics 1991, 10, 3910.
(61) Beswick, C. L.; Marks, T. J. J. Am. Chem. Soc. 2000, 122, 10358.
(62) Clark, D. L.; Gordon, J. C.; Hay, P. J.; Martin, R. L.; Poli, R.
Organometallics 2002, 21, 5000.
(63) Brady, D. E.; Clark, D. L.; Gordon, J. C.; Hay, P. J.; Keogh, D. W.;
Poli, R.; Scott, B. L.; Watkin, J. G. Inorg. Chem. 2003, 6682.
(64) Perrin, L.; Maron, L.; Eisenstein, O.; Lappert, M. F. New J. Chem.
2003, 27, 121.
The NMR tube-scale reaction of Y(CH2SiMe3)3(THF)2 with
[NHMe2Ph][BArF ] and [9]aneS3 in CD2Cl2 appears to form
4
the seven-coordinate cation [Y([9]aneS3)(CH2SiMe3)2(THF)2]+
(16+, eq 5). Cation 16+ contains two coordinated THF ligands
and two CH2SiMe3 groups, the methylene protons of which
appear as doublets (2JHY ) 3.2 Hz), suggesting Cs symmetry
(65) Song, F.; Lancaster, S. J.; Cannon, R. D.; Schormann, M.;
Humphrey, S. M.; Zuccaccia, C.; Macchioni, A.; Bochmann, M. Organo-
metallics 2005, 24, 1315.
(55) Bambirra, S.; Bouwkamp, M. W.; Meetsma, A.; Hessen, B. J. Am.
Chem. Soc. 2004, 126, 9182.

3464 Organometallics, Vol. 27, No. 14, 2008
Tredget et al.
how 29Si NMR can be a diagnostic tool bridging experiment
and theory in these types of systems.
features one ꢀ-Si-C agostic alkyl group with a compressed
Sc-CH2-Si bond angle of 100.6° and a closest Sc · · · Me
contact of 2.877 Å. Within this SiMe3 group the Si-C distance
for the methyl closest to Sc is 1.944 Å, which is lengthened in
comparison with the other two Si-Me distances (1.900, 1.897
Å) as noted previously for ꢀ-Si-C agostic systems.20,60,64 The
nonagostic alkyl group serves as a reference point with a
Sc-CH2-Si bond angle of 138.2° and Si-Me distances of
1.898, 1.899, and 1.905 Å. The computed 29Si values for 17+
are 3.6 (nonagostic ligand) and -13.0 (agostic group), giving
an averaged calculated shift of -4.7 ppm, which is in good
agreement with the experimental value of -2.2 ppm. Taken
together, the experimental NMR data and DFT calculations
suggest that the real cation 17+ possesses a ꢀ-Si-C agostic
ground state, but that the two alkyl groups are in fast exchange
on the NMR time scale.
The cation [Sc(Me3[9]aneN3)(CH2SiMe3)2]+ (17+) could in
principle exist as one of three main isomers: nonagostic (17a+);
ꢀ-Si-C agostic (17b+); doubly agostic (17c+). An analogous
situation could arise for 19+ (and, by analogy, all other
[(L)M(CH2SiMe3)2]+ species). To explore these possibilities
further, a series of 29Si NMR measurements and DFT calcula-
tions were carried out.
The tris(alkyl) compounds Sc{HC(Me2pz)3}(CH2SiMe3)3 (2)
and Sc(Me3[9]aneN3)(CH2SiMe3)3 (3) have nonagostic ground
states according to X-ray crystallography17 and serve as
benchmarks for the 29Si NMR and DFT studies. The observed
29Si NMR resonances are -3.9 and -3.5 ppm, respectively
(CD2Cl2). The computed structures show good agreement with
those determined by X-ray crystallography. The computed
average 29Si shifts are -2.5 and -2.4 ppm, respectively,
showing excellent agreement with experiment and validating
the methodology (the individual values for the independent alkyl
groups range from -0.6 to -3.7 ppm).
At first sight, the similarity of the observed 29Si NMR shifts
for 17+ and 19+ suggests that the cationic tris(3,5-dimeth-
ylpyrazolyl)methane system might also possess one agostic and
one nonagostic alkyl ligand. However, the full DFT-computed
structure of [Sc{HC(3,5-Me2pz)3}(CH2SiMe3)2]+ (19+, Figure
5) adopts an approximately trigonal-bipyramidal, nonagostic
ground state with Sc-CH2-Si angles of 121.8° and 133.4°,
Si-Me distances in the range 1.895-1.911 Å, and a closest
Sc · · · Me separation of 3.805 Å. The calculated 29Si NMR shifts
for the two independent alkyl ligands of 19+ are -0.4 and -0.6
ppm. The calculated average shift of -0.5 ppm is again
comparable within error to that observed experimentally (-3.4
ppm). To test whether the HC(3,5-Me2pz)3 ligand 3-position
methyl groups were sterically impeding the development of an
agostic interaction in 19+, the hypothetical 4,5-ring substituted
The dialkyl cations 17+ and 19+ each show only a single
29Si NMR resonance at -80 °C, which appear at -2.2 and -3.4
ppm, respectively. In the case of 17+, for example, these data
might be equally consistent with a nonagostic ground state
(17a+) or a fluxional monoagostic system 17b+ with a time-
averaged 29Si chemical shift. A doubly agostic species (e.g.,
17c+) appears to be inconsistent with the -2.2 ppm 29Si shift
observed.
The DFT-computed structure of [Sc(Me3[9]aneN3)(CH2-
SiMe3)2]+ (17+) is shown in Figure 5 along with selected
parameters. Cation 17+ has a pseudo-octahedral Sc center and
Figure 5. DFT-computed structure of [Sc(Me3[9]aneN3)(CH2SiMe3)2]+ (17+) and [Sc{HC(3,5-Me2pz)3}(CH2SiMe3)2]+ (19+). Selected
parameters for 17+: (i) for the ꢀ-Si-C agostic alkyl group Si-Me ) 1.944 (closest to Sc), 1.893, 1.890 Å, closest Sc · · · Me ) 2.877 Å,
Sc-CH2-Si ) 100.6°; (ii) for the nonagostic alkyl group Si-Me ) 1.898, 1.899, 1.905 Å, Sc-CH2-Si ) 138.2°. Selected parameters for
19+: Si-Me distances 1.895-1.911 Å, Sc-CH2-Si ) 121.8° and 133.4°, Sc · · · Me ) 3.805 and 4.209 Å. Key: Sc, red; Si, yellow; N,
blue; C and H, white.

Scandium and Yttrium Dialkyl Cations
Organometallics, Vol. 27, No. 14, 2008 3465
isomer [Sc{HC(4,5-Me2pz)3}(CH2SiMe3)2]+ (20+) was evalu-
ated by DFT. Although a slightly more strongly agostic structure
was found, as judged for example by 29Si shifts of 0.0 and -4.3
ppm and Sc-CH2-Si angles of 121.5° and 113.5°, it appears
that such tris(pyrazolyl)methane-type fac-N3 ligands may be
better donors to the metal centers than Me3[9]aneN3 and inhibit
the formation of additional interactions.
Scheme 2. Selected Reactions of [Sc{HC(Me2pz)3}(CH2Si-
a
Me3)2(THF)][BArF4] (10-BArF
)
4
Although we were not able to observe the base-free [9]aneS3
or yttrium cations [M(L)(CH2SiMe3)2]+ (M ) Sc, L ) [9]aneS3;
M ) Y, L ) Me3[9]aneN3 or HC(Me2pz)3) experimentally, we
computed their ground-state structures at the DFT level for the
purposes of comparing the effect of varying the donor ligand L
and metal. All three cations [Sc([9]aneS3)(CH2SiMe3)2]+ (21+)
and [Y(fac-N3)(CH2SiMe3)2]+ (fac-N3 ) Me3[9]aneN3 (22+)
or HC(Me2pz)3 23+)) feature ꢀ-Si-C agostic interactions. For
21+ computed 29Si shifts of -21.9 (agostic) and 3.3 ppm were
found. The geometry of 21+ is similar to that of the Me3[9]aneN3
analogue, 17+, but (as suggested by the more negative 29Si shift)
the ꢀ-Si-C agostic interaction is even more pronounced. The
Sc-CH2-Si (agostic) bond angle is 92.9° (cf. 100.6° in 17+)
and the longest Si-C distance is 1.978 Å (methyl closest to
Sc, cf. 1.944 Å in 17+). For the yttrium cations 22+ and 23+
the computed 29Si shifts for the agostic alkyls are -15.3 and
-13.5 ppm, respectively, and 1.3 and -0.5 ppm for the
nonagostic alkyls. In both yttrium cations the agostic interactions
appear to be more strongly developed than for their scandium
congeners, as judged by M-CH2-Si bond angles of 96.4° and
100.8° and Si-C distances of 1.971 and 1.949 Å (methyls
closest to Y) for the agostic CH2SiMe3 groups. Again it appears
that it is the tris(pyrazolyl)methane complex (23+) that forms
the less strong ꢀ-Si-C interaction.
F
-
a
[BAr
]
anions are omitted for clarity.
4
Scheme 3. Selected Reactions of [Sc(Me3[9]aneN3)(CH2Si-
Me3)2(THF)][BArF4] (13-BArF
)
a
4
These calculations show that both the fac-N3 or fac-S3 ligand
and the metal in the base-free cations [(L)M(CH2SiMe3)2]+ have
significant effects on their ability to develop ground-state
ꢀ-Si-C agostic interactions. In particular, [9]aneS3 appears to
result in the most developed ꢀ-Si-C agostic interaction among
the [Sc(L)(CH2SiMe3)2]+ cations, presumably to compensate
for the fac-S3 ligand’s weaker donor ability. However, in these
fluxional dialkyl systems, the 29Si data alone are insufficient to
distinguish between agostic and nonagostic ground states.
Selected Stoichiometric Reactions: Lewis Base Adducts,
Carbodiimide Insertion, and C-H Bond Activation. The
reaction chemistry of group 3 alkyl cations is in its infancy,
and so we report here a brief account of selected stoichiometric
reactions of [Sc{HC(Me2pz)3}(CH2SiMe3)2(THF)]+ (10+) and
[Sc(Me3[9]aneN3)(CH2SiMe3)2(THF)]+ (13+). We focused par-
ticularly on these two fac-N3 systems because of the higher
stability of the scandium cations compared to the yttrium ones
and the higher stability of the N3 donor complexes compared
to their [9]aneS3 analogues. Schemes 2 and 3 summarize the
results of reactions with Lewis bases, phenyl acetylene, and
carbodiimides. The reactions of neutral group 3 alkyls with
alkynes66–69 and carbodiimides69,70 are well-established. In
contrast, the first reactions of alkynes with rare earth alkyl
F
-
a
[BAr
]
anions are omitted for clarity.
4
cations have only very recently been described,71 and reactions
with carbodiimides remain unexplored. Several substrates of this
type were therefore selected for investigation.
Addition of OPPh3 (1 equiv) to 10-BArF gave the adduct
4
[Sc{HC(Me2pz)3}(CH2SiMe3)2(OPPh3)][BArF ] (24-BArF ), the
4
4
(66) Den Haan, K. H.; Wielstra, Y.; Teuben, J. H. Organometallics 1987,
6, 2053.
(67) Burger, B. J.; Thompson, M. E.; Cotter, W. D.; Bercaw, J. E. J. Am.
Chem. Soc. 1990, 112, 1566.
(68) Deelman, B.-J.; Stevels, W. M.; Teuben, J. H.; Lakin, M. T.; Spek,
A. L. Organometallics 1994, 13, 3881.
(69) Zhang, W.-X.; Nishiura, M.; Hou, Z. J. Am. Chem. Soc. 2005, 127,
16788.
analogue of 12-BArF4 mentioned above. The formation of 10+
and all the new compounds in Schemes 2 and 3 were
quantitative by H NMR spectroscopy in CD2Cl2, but variable
yields were obtained on the preparative scale owing to the
1
(70) Zhang, J.; Ruan, R.; Shao, Z.; Cai, R.; Weng, L.; Zhou, X.
Organometallics 2002, 21, 1420.
(71) Ge, S.; Norambuena, V. F. Q.; Hessen, B. Organometallics 2007,
26, 6508.

3466 Organometallics, Vol. 27, No. 14, 2008
Tredget et al.
a
Table 2. Ethylene Polymerization Data for the Tris(alkyl) Complexes Sc(L)R3 Activated by [CPh3][BArF
]
4
PE yield
(g)
productivity
precatalyst
(kg mol-1 h-1 bar-1
)
Mw
Mn
Mw/Mn
Sc{HC(Me2pz)3}(CH2SiMe3)3 (2)
Sc(Me3[9]aneN3)(CH2SiMe3)3 (3)
Sc(Me3[6]aneN3)(CH2SiMe3)3 (30)
Sc([9]aneS3)(CH2SiMe3)3 (1)
Sc(Me3[9]aneN3)Me3 (5)
7.9
7.1
0.1
8.4
0.4
9.1
0
830
730
10
860
40
297 000
532 000
243 000
187 000
433 000
421 000
7920
6820
3780
2245
4590
9090
37
78
64
83
95
46
Sc(Me3[9]aneN3)(CH2SiMe3)3 (3)b
Sc(CH2SiMe3)3(THF)2
910
0
a Conditions unless otherwise stated: 6 bar of C2H4; 250 mL of toluene; run time ) 10 min; activation temperature 33-36 °C; Sc:B ) 1:1; catalyst
loading ) 5 or 10 µmol; Sc:Al ) 1:500; productivity data are for duplicate runs. b Sc:B ) 1:2.
sometimes oily nature of the products. Similarly, 10-BArF
BArF3 as a cocatalyst were disclosed in a recent communication
and are consistent with the wider study reported here.51
High productivities were found for Sc{HC(Me2pz)3}(CH2-
SiMe3)3 (2) and Sc(Me3[9]aneN3)(CH2SiMe3)3 (3) (ca. 830 and
730 kg mol-1 h-1 bar-1, respectively). These are competitive
with the best values previously described in the literature for
this metal, but fall some way short of the highest described for
cationic lanthanide systems in general (up to ca. 3000 kg mol-1
h-1 bar).5–8 Changing from Sc(Me3[9]aneN3)(CH2SiMe3)3 (3)
to the previously reported Sc(Me3[6]aneN3)(CH2SiMe3)3 (30)17
with a smaller triazacyclic ligand showed negligible productivity
under these conditions.
4
reacts with pyridine to form [Sc{HC(Me2pz)3}(CH2SiMe3)2-
(py)][BArF ] (25-BArF ). Pyridine adducts of group 3 and 4
4
4
alkyl species are often unstable to alkane elimination via
metalation of the ortho-C-H bond.20,41,72,73 However, even after
prolonged gentle heating (ca. 50 °C), cation 25+ does not show
any signs of SiMe4 elimination or degradation.
Cation 10+ reacts with di-p-tolyl carbodiimide in CD2Cl2 to
give the amidinate product [Sc{HC(Me2pz)3}(CH2SiMe3)-
{TolNC(CH2SiMe3)NTol}]+ (26+) as judged by 1H NMR and
13C NMR spectroscopy. Attempts to isolate 26-BArF or its
4
homologues on a preparative scale were unsuccessful. However,
reaction of 13-BArF with di-isopropyl carbodiimide gave
4
quantitative formation of [Sc(Me3[9]aneN3)(CH2SiMe3)-
{iPrNC(CH2SiMe3)NiPr}][BArF ] (27-BArF ) which was iso-
4
4
lated and fully characterized. An imido titanium analogue of
27+, [Ti(Me3[9]aneN3)(NtBu){iPrNC(CH2SiMe3)NiPr}]+, was
recently prepared by an analogous route. Hou et al. reported
the first carbodiimide insertion into a (neutral) rare earth
metal-alkyl bond in 2002,70 but ours is the first example of
the corresponding reaction for an alkyl cation.
Addition of PhCCH (1 equiv) to 10-BArF gave SiMe4 (as
In this context we note that titanium catalyst systems of the
type Ti(fac-N3)(NR)Cl2/MAO also showed productivity de-
pendencies in the order fac-N3 ) Me3[6]aneN3 , Me3[9]aneN3
≈ HC(Me2pz)3.18,22,74 On the other hand, while the vanadium
tris(pyrazolyl)methane systems V{HC(Me2pz)3}(NR)Cl2/MAO
were able to polymerize ethylene, the corresponding macrocyclic
systems V(Me3[9]aneN3)(NR)Cl2/MAO were totally inactive.23
It is also interesting to compare the performances of the very
productive scandium precatalysts 2 and 3 with those of the
yttrium systems 8 and 9, which were inactive. Hessen has
reported very active, related yttrium catalysts supported by
triazacyclonane ligands that contain additional pendant anionic
donors.25,27–29 It would appear that these “anchor points” are
important in imparting stability on the catalytic systems for the
larger metal.
Interestingly, the thioether complex Sc([9]aneS3)(CH2SiMe3)3
(1) was also highly productive, with a figure of merit comparable
to both 2 and 3. Although sulfur donors are generally viewed
as being detrimental for later transition metal catalysts, in the
case of these group 3 cationic systems the change from
Me3[9]aneN3 to [9]aneS3 does not damage productivity. This
is apparently in accord with recent reports for certain cationic
group 4 Ziegler-type catalyst systems.43
4
judged by an NMR tube-scale reaction in CD2Cl2) and the
acetylide complex [Sc{HC(Me2pz)3}(CH2SiMe3)(CCPh)-
(THF)][BArF ] (28-BArF ) via a C-H bond activation reaction.
4
4
Products of alkyne insertion into a Sc-CH2SiMe3 bond were
not observed. The NMR spectra of 28+ feature six distinct
pyrazolyl ring methyl carbons, confirming the unsymmetric
nature of 28+. Reaction of 13-BArF4 with PhCCH (Scheme 3)
gave an analogous product, [Sc(Me3[9]aneN3)(CH2SiMe3)-
(CCPh)(THF)][BArF ] (29-BArF ), showing three inequivalent
4
4
macrocycle N-Me groups. No reaction was observed between
10-BArF4 or 13-BArF4 and PhCCMe. No further Sc-CH2SiMe3
bond substitution or other reaction was observed between 28-
BArF4 or 29-BArF4 and an additional equivalent of PhCCH, in
contrast to very recent results from Hessen et al. for a cationic
organo-yttrium system supported by a triamine-amide ligand.71
Ethylene Polymerization Studies. As mentioned in the
Introduction, olefin polymerization by cationic group 3 and
lanthanide compounds is an area of ongoing interest.5–10 Table
2 summarizes the ethylene polymerization results obtained for
a series of scandium tris(alkyl) complexes activated with
[Ph3C][BArF ] (TB) in the presence of AliBu3 as scavenger.
4
Negligible activity was found for either of the yttrium com-
pounds Y(fac-N3)(CH2SiMe3)3 (8 or 9) or the bis(THF) complex
Sc(CH2SiMe3)3(THF)2, which was assessed as a control experi-
ment. Preliminary results for some of the compounds using
Bercaw has previously reported that mixtures of scandium
trimethyl complex Sc(Me3[9]aneN3)Me3 (5) and BArF3 in THF-
d8 were competent for the polymerization of ethylene at 80 °C
on the NMR scale. To make a quantitative comparison between
5 and the other tris(trimethylsilyl) systems in Table 2, we
assessed 5 under the same conditions. Compound 5 reproducibly
(72) Jordan, R. F.; Taylor, D. F.; Baenziger, N. C. Organometallics 1990,
9, 1546.
(73) Jantunen, K. C.; Scott, B. L.; Gordon, J. C.; Kiplinger, J. L.
Organometallics 2007, 26, 2777.
(74) Bolton, P. D.; Mountford, P. AdV. Synth. Catal. 2005, 347, 355.

Scandium and Yttrium Dialkyl Cations
Organometallics, Vol. 27, No. 14, 2008 3467
a
Table 3. 1-Hexene Polymerization Data for the Tris(alkyl) Complexes Sc(fac-N3)R3 Activated by [CPh3][BArF
]
4
c
precatalyst
Sc:TBb
temp (°C)
time
24 h
30 min
18 h
10 min
10 min
10 min
10 min
10 min
20 min
2.5 h
conversion (%, NMR)
isolated yield (g)
0
Mn(calcd)
Mn(GPC)
Mw/Mn
Sc{HC(Me2pz)3}(CH2SiMe3)3 (2)
Sc(Me3[9]aneN3)(CH2SiMe3)3 (3)
Sc(Me3[6]aneN3)(CH2SiMe3)3 (30)
Sc{HC(Me2pz)3}(CH2SiMe3)3 (2)
Sc(Me3[9]aneN3)(CH2SiMe3)3 (3)
Sc(Me3[9]aneN3)Me3 5)
Sc(Me3[6]aneN3)(CH2SiMe3)3 (30)
Sc([9]aneS3)(CH2SiMe3)3 (1)
Sc{HC(Me2pz)3}(CH2SiMe3)3 (2)
Sc(Me3[9]aneN3)(CH2SiMe3)3 (3)
Sc(Me3[6]aneN3)(CH2SiMe3)3 (30)
Sc(CH2SiMe3)3(THF)2
1:1
1:1
1:1
1:2
1:2
1:2
1:2
1:2
1:2
1:2
1:2
1:2
22
22
22
22
22
22
22
22
0
0
88
34
100
100
95
76
46
85
20
58
0
0.5
22 220
8590
5 980
12.2
d
d
d
0.6
0.8
0.7
0.7
0.3
0.6
0.1
0.3
0
50 500
50 500
47 970
38,380
23,290
42,920
10,100
29,290
11 140
29 610
16 000
36 290
13 280
46 120
35 440
102 220
2.6
2.3
2.3
2.2
5.8
1.7
7.3
3.6
0
0
22
7 h
24 h
a Conditions: 600 equiv of 1-hexene, 20 µmol of precatalyst, 5 mL of C6H5Cl. b TB ) [Ph3C][BArF4]. c Assuming 2 PH (for Sc:TB ) 1:1) or 1 PH
(Sc:TB ) 1:2) chains per metal center at the given NMR % conversions and that all of the precatalyst is activated. d Polymer could not be isolated.
showed a much lower productivity (ca. 40 kg mol-1 h-1 bar-1
)
R-olefin using Sc(L)(CH2SiMe3)3 (L ) HC(Me2pz)3 (2),
Me3[9]aneN3 (3), Me3[6]aneN3 (30), or [9]aneS3 (1)) and
Bercaw’s Sc(Me3[9]aneN3)Me3 (5) for comparison. No activity
was found for either of the yttrium complexes Y(fac-
N3)(CH2SiMe3)3 (8 or 9) under any of the conditions assessed.
By way of a control experiment, no activity was found for the
THF complex Sc(CH2SiMe3)3(THF)2 under our conditions.
Initial polymerization studies were carried out in C6H5Cl
using 1 equiv of [Ph3C][BArF ] (TB) or [NHMe2Ph][BArF ]
than 3 on activation with TB/AliBu3. Analogous results were
found using BArF3 as an activator. The reasons for the difference
between 3 and 5 are unclear. It is conceivable that the more
sterically accessible first-formed cation [Sc(Me3[9]aneN3)Me2]+
might more readily undergo homo- or heterobimetallic deactiva-
tion reactions of the type well-established for group 4 metal-
locenium and related cations.75,76
Finally we evaluated the productivity of Sc(Me3[9]aneN3)-
(CH2SiMe3)3 (3) using 2 equiv of TB. As discussed below, 3
and a number of other rare earth compounds of the type Ln(fac-
N3)(CH2SiMe3)3 polymerize 1-hexene to a significant extent only
when 2 equiv of activator are employed.37,38 In group 4 Ziegler
catalyst systems an increase in productivity has also been
reported when an excess of activator has been employed.77,78
However, although the productivity of the 3/2 TB/AliBu3 system
(ca. 910 mol-1 h-1 bar-1) was reproducibly somewhat higher
than for 3/1 TB/AliBu3, we did not observe the same kind of
dramatic increase in performance noted for 1-hexene polym-
erization below.
Table 2 also summarizes the PE molecular weight charac-
teristics as determined by GPC. The Mn values in all instances
are very low (indicative of facile chain transfer processes), and
the polydispersity indices (PDI, Mw/Mn) are very broad indeed.
Such large PDI values may imply that multiple active species
are present or several chain transfer modes are operative.
Analysis of the PE formed with 2 or 3 by NMR spectroscopy
(100 °C, 1,2-C6D4Cl2) showed linear PE with only saturated
(methyl group) end groups. Isopropyl end groups (such as might
arise from chain transfer to AliBu379,80) were not detected,
indicating that chain transfer is probably taking place through
an uncontrolled homolytic process. Unfortunately, attempts to
run the polymerization experiments at lower temperatures gave
negligible productivity.
4
4
activator. No activity was found with the anilinium activator,
presumably due to coordination of the NMe2Ph side-product to
the so-formed alkyl cations. NMR tube-scale reactions (C6D5Br)
between 2 and [NHMe2Ph][BArF ] supported this hypothesis,
4
the spectra being consistent with the formation of
[Sc{HC(Me2pz)3}(CH2SiMe3)2(NMe2Ph)]+, the analogue of
[Sc{HC(Me2pz)3}(CH2SiMe3)2(L)]+ (L ) THF (10+), OPPh3
(24+), or py (25+)). No polymerization was found with 2 and
TB (1 equiv), whereas the triazacyclononane-supported 3
achieved 88% conversion of 1-hexene to polyhexene (PH)
within 30 min. However, analysis of the PH by GPC found a
broad PDI of 12.2 and a very low Mn value of ca. 6000
compared to that expected for one (44 440) or two (22 220)
chains per precatalyst metal center, suggesting that some form
of chain transfer process is taking place under these conditions.
1H NMR analysis of the PH from these experiments found only
saturated (methyl) end groups, indicating the chain transfer
probably involves noncontrolled radical cleavage. 13C NMR
analysis found that the PHs formed in all of these systems are
predominantly atactic. The sterically more “open” triazacyclo-
hexane complex 30 does not lead to higher productivity, as
might have been hoped for, achieving only 34% conversion by
NMR after 18 h. This could be consistent with more effective
binding of the solvent and/or anion to the dialkyl cation. It was
not possible to isolate the PHs in this case due to their apparent
low molecular weights.
1-Hexene Polymerization Studies. Relatively few examples
of the polymerization of R-olefins by cationic group 3 complexes
have been reported to date.5–8,37,38,40,81,82 Table 3 summarizes
our results for the polymerization of 1-hexene as a representative
(75) Bochmann, M. J. Chem. Soc., Dalton Trans. 1996, 255.
(76) Bochmann, M. J. Organomet. Chem. 2004, 689, 3982.
(77) Al-Humydi, A.; Garrison, J. C.; Youngs, W. J.; Collins, S.
Organometallics 2005, 24, 193.
(78) Song, F.; Cannon, R. D.; Lancaster, S. J.; Bochmann, M. J. Mol.
Catal. A: Chem. 2004, 218, 21.
(79) Small, B. L.; Brookhart, M. Macromolecules 1999, 32, 2120.
(80) Kretschmer, W. P.; Meetsma, A.; Hessen, B.; Schmalz, T.; Qayyum,
S.; Kempe, R. Chem.-Eur. J. 2006, 12, 8969–8978.
(81) Li, X.; Baldamus, J.; Hou, Z. Angew. Chem., Int. Ed. 2005, 44,
962.
(82) Li, X.; Nishiura, M.; Mori, K.; Mashiko, T.; Hou, Z. Chem.
Commun. 2007, 4137.
Following on from Okuda’s reports of well-defined dicationic
lanthanide polymerization catalysts,39,40 Gade showed that
activation of the complex Sc(iPr-trisox)(CH2SiMe3)3 (31) with
2 equiv of TB gave a very productive 1-hexene polymerization

3468 Organometallics, Vol. 27, No. 14, 2008
Tredget et al.
catalyst system.37 We therefore assessed the polymerization
capabilities of the Sc(L)R3 complexes using a Sc:TB ratio of
1:2. Again neither of the Y(fac-N3)(CH2SiMe3)3 were active
under these conditions.
conducted parallel NMR studies in C6D5Cl, which is also a better
mimic of the chlorobenzene polymerization solvent. Analogous
results were found for 2 and 3, and so we focused on the former
since the 2/2 TB catalyst system gave the best agreement
between found and expected molecular weight at 0 °C.
Furthermore, the podand ligand HC(Me2pz)3 is a closer match
Activation of Sc{HC(Me2pz)3}(CH2SiMe3)3 (2) and
Sc(Me3[9]aneN3)(CH2SiMe3)3 (3) with 2 equiv of TB under
conditions otherwise identical to those used for the 1 equiv
experiments gave much higher productivities (100% conversion
within 10 min). GPC analysis of the resultant PHs revealed
improved molecular weight distributions of 2.6 and 2.3,
respectively (cf. 12.2 for the 3/1 TB catalyst system), but the
Mn values of 11 140 and 29 610 were still lower than that
expected (50 500) assuming all of the metal centers were
activated to a species of the type “[Sc(L)R]2+” (R ) CH2SiMe3
or polyhexyl). The trimethyl complex Sc(Me3[9]aneN3)Me3 (5)
exhibited similar behavior to that of 3, in contrast to the situation
found for the ethylene polymerization studies (Table 2). The
triazacyclohexane complex 30 also catalyzes the production of
PHs on activation with 2 equiv of TB. The productivity (76%
conversion after 10 min) is lower than that of the larger
macrocycle analogue 3 or 5. The agreement between the found
(36 290) and calculated (38 380) Mn values was much better,
but the PDI of 2.2 is far from that expected (1.0) for a well-
defined system forming 1 PH chain per metal center. The
[9]aneS3 complex 1 was also productive upon activation with
2 equiv of TB. However, the conversion of 1-hexene (46%)
was significantly lower than found using the fac-N3-supported
catalysts, and the PDI of the PHs produced (5.8) was also much
poorer. No further experiments were performed using 1.
i
to Pr-trisox and offers the best chance of comparing the data
for Gade’s 31/2 TB system with ours.
Reaction of Sc{HC(Me2pz)3}(CH2SiMe3)3 (2) with 1 equiv
of TB in C6D5Cl formed the previously mentioned dialkyl
monocation [Sc{HC(Me2pz)3}(CH2SiMe3)2]+ (19+). This reac-
tion was slower than the corresponding one in CD2Cl2. Addition
of 1-hexene to an NMR tube containing 19+ (in either CD2Cl2
or C6D5Cl) gave no reaction even after 24 h, consistent with
the results shown in Table 3. Addition of 2 or 3 equiv of TB to
a solution of 2 in C6D5Cl showed only formation of the dialkyl
monocation 19+ and unreacted [CPh3]+. The same reaction in
CD2Cl2 again showed only formation of 19+, but in this case
the decomposition of 19+ to an unknown mixture was somewhat
faster than in the 1 equiv of TB case (t1/2 ≈ 30 min). Finally
we found that addition of TB (1 equiv) to an NMR sample
containing the preformed dialkyl monocation 19+ and unreacted
1-hexene (prepared as above, in either C6D5Cl or CD2Cl2) gave
rapid conversion of the 1-hexene to PHs. After all the 1-hexene
had been polymerized, ca. 80% of the original 19+ still remained
(as judged against an internal standard). No evidence for a new
HC(Me2pz)3-containing species was found.
It appears from the NMR tube experiments that formation of
a simple monoalkyl dication [Sc(L)(CH2SiMe3)(solvent)n]2+
under these conditions does not readily occur. Nonetheless, it
is evident that a second equivalent of TB is essential for the
efficient polymerization of 1-hexene. Although the relative rates
would vary depending on reaction conditions, it appears that
propagation of chain growth may be fast compared to initiation.
This would account for the relatively high Mn values found in
some of our own systems (Table 3) and also in the lower
temperature polymerization experiments on the Sc(iPr-
trisox)(CH2SiMe3)3 (31) system. Further work is clearly needed
before a satisfactory understanding emerges of the various
M(L)R3/2 TB/R-olefin polymerization systems reported to date.
As expected, reducing the polymerization temperature to 0
°C gave a reduction in productivity (85% conversion within 20
min for 2/2 TB and only 20% for 3/2 TB after 2.5 h). For 2 the
experimental Mn value of 46 120 was in good agreement with
that expected (42 920) and the PDI was 1.7, indicating that 2/2
TB gives the best “control” of the molecular weights and their
distribution at this temperature. In contrast, 3/2 TB afforded
PHs with a high PDI of 7.3 and a Mn of 35 440, which is higher
than that expected (10 100). Similarly, 30/2 TB gave PHs with
a PDI of 3.6 (cf. 2.2 at 22 °C) and a very high Mn of 102 220
compared with that expected (29 290). Therefore it is certainly
clear that not all of the metal centers are activated (or active)
in these last two instances. Indeed, the apparently good
agreement between found and calculated Mn values in the cases
of 2/2 TB (0 °C) and 30/TB (22 °C) may be fortuitous given
the PDIs of 1.7 and 2.2, respectively, and possibly result from
a combination of chain transfer processes and less than 100%
precatalyst activation.
It is interesting to compare our data in Table 3 with those
described by Gade for the Sc(iPr-trisox)(CH2SiMe3)3 (31)/2 TB
catalyst system. At 21, 0, and -30 °C, conversions of 88% (PDI
) 2.22), 64% (PDI ) 2.36), and 30% (PDI ) 1.18) were found.
However, as for our systems, chain transfer and/or incomplete
activation is clearly evident in these systems with ca. 3 PH
chains formed per precatalyst center at 21 °C and only 0.16
chain per metal at -30 °C (based on the reported Mn values).
Similarly, all of the PHs produced by 31 possessed saturated
end groups according to NMR spectroscopy.
Conclusions
The neutral face-capping (fac-N3) ligands Me3[9]aneN3 and
HC(Me2pz)3 are effective supporting groups for developing the
stoichiometric and catalytic chemistry of cationic scandium, but
are somewhat less suitable for yttrium with regard to polym-
erization catalysis. This larger metal appears to require either a
larger ring size (cf. the crown ether complexes of Okuda35,36
)
or an anionic “anchoring” pendant arm as reported by Hessen.27–29
Interestingly, the “soft” ligand [9]aneS3 can also be used to
stabilize both neutral and cationic organoscandium complexes,
despite the low intrinsic metal-ligand binding energy. This is
attributed to the well-known “macrocycle effect” (a combination
of enthalpic and entropic contributions) associated with such
cyclic ligands and the smaller reorganization energy of the
Sc(CH2SiMe3)3 fragment in the case of Sc([9]aneS3)-
(CH2SiMe3)3. Lewis base-stabilized dialkyl cations using fac-
N3 donor ligands are readily accessible for both scandium and
yttrium and in the former case undergo stoichiometric ligand
substitution or Sc-alkyl bond reactions. According to DFT, the
electron-deficient base-free dialkyl cations [M(L)(CH2SiMe3)2]+
are usually stabilized by a ꢀ-Si-C agostic interaction, but the
extent of this depends on both the metal center and the ligand
L. Experimentally, it was not possible to obtain direct 29Si NMR
Encouraged by Gade’s report of the observation of a red
dialkyl cation “[Sc(iPr-trisox)(CH2SiMe3)(solvent)n]2+” in
CD2Cl2 at room temperature on treating 31 with 2 equiv of TB,
we set out to investigate analogous behavior for our systems.
However, since our dialkyl monocations [Sc(fac-
N3)(CH2SiMe3)2]+ (fac-N3 ) HC(Me2pz)3 or Me3[9]aneN3)
slowly decomposed in CD2Cl2 at room temperature, we also

Scandium and Yttrium Dialkyl Cations
Organometallics, Vol. 27, No. 14, 2008 3469
In Situ Synthesis of Y([9]aneS3)(CH2SiMe3)3 (4). A solution
of Y(CH2SiMe3)3(THF)2 (5.0 mg, 0.01 mmol) in toluene-d8 was
added to solid [9]aneS3 (1.8 mg, 0.01 mmol) to give a clear colorless
solution. The 1H NMR spectrum showed a mixture of 4, THF, and
evidence of a “frozen out” ꢀ-Si-C agostic species. The
scandium complexes Sc(L)(CH2SiMe3)3 (L ) [9]aneS3,
Me3[9]aneN3, HC(Me2pz)3) were all very productive precatalysts
for the polymerization of ethylene, but the polymer properties
as assessed by GPC indicate the presence of very poorly defined
active species. Changing from Sc(Me3[9]aneN3)(CH2SiMe3)3 to
Y(Me3[9]aneN3)(CH2SiMe3)3, Sc(Me3[9]aneN3)Me3, or Sc(Me3-
[6]aneN3)(CH2SiMe3)3 gave inactive catalyst systems, showing
how delicately balanced this polymerization system is in terms
of metal, macrocycle ring size, and initiating alkyl group. A
range of complexes Sc(L)R3 were also active for the polymer-
1
the starting materials, with ca. 50% conversion to 4 at 241 K. H
NMR (toluene-d8, 299.9 MHz, 241 K): 1.97 (6 H, m, SCH2), 1.23
(6 H, m, SCH2), 0.35 (27 H, s, SiMe3), -0.53 (6 H, br s, YCH2).
13C{1H} NMR (toluene-d8, 75.5 MHz, 241 K): 36.6 (YCH2, d, 1JCY
) 35 Hz), 30.5 (SCH2), 4.6 (SiMe3) ppm.
[Sc{HC(Me2pz)3}(CH2SiMe3)2(THF)][BArF4] (10-BArF4). To
a cold (-78 °C) Schlenk tube containing Sc(CH2SiMe3)3(THF)2
(0.20 g, 0.44 mmol) and [NHMe2Ph][BArF ] (0.36 g, 0.44 mmol)
ization of 1-hexene in the presence of 2 equiv of [CPh3][BArF ]
4
4
was added THF (5 mL). To this solution was added a solution of
HC(Me2pz)3 (0.13 g, 0.44 mmol) in THF (5 mL). The solution was
stirred at -78 °C for 2 h, after which time it was allowed to warm
to RT and concentrated in Vacuo to ca. 2 mL; then pentane (10
mL) was added. The supernatant was carefully decanted away to
activator. No direct evidence for the formation of a dication of
the type [Sc{HC(Me2pz)3}(CH2SiMe3)]2+ could be gained using
NMR spectroscopy, although it is clear that both equivalents
of [CPh3][BArF ] activator are required for high (or in some
4
instances, any) productivity.
leave a pale oil, which upon drying in Vacuo gave 10-BArF as a
4
spongy cream solid. Yield: 0.40 g (71%). 1H NMR (CD2Cl2, 299.9
MHz, 293 K): 7.90 (1 H, s, HC(Me2pz)3), 6.19 (1 H, s,
4-HC(Me2pz)3 trans THF), 6.08 (2 H, s, 4-HC(Me2pz)3 trans
CH2SiMe3), 4.24 (4 H, m, OCH2CH2), 2.76 (3 H, s, 3-HC(Me2pz)3
trans THF), 2.60 (3 H, s, 5-HC(Me2pz3)3 trans THF), 2.54 (6 H, s,
3-HC(Me2pz)3 trans CH2SiMe3), 2.37 (6 H, s, 5-HC(Me2pz)3 trans
CH2SiMe3), 2.16 (4 H, m, OCH2CH2), 0.35 (2 H, d, 2J ) 11.7 Hz,
CH2SiMe3), 0.11 (2 H, d, 2J ) 11.7 Hz, CH2SiMe3), -0.23 (18 H,
s, SiMe3) ppm. 13C{1H} NMR (CD2Cl2, 75.4 MHz, 293 K): 155.5
(3-HC(Me2pz)3, trans THF), 154.5 (3-HC(Me2pz)3 trans
CH2SiMe3), 147.6 (br d, 2-C6F5), 141.6 (5-HC(Me2pz)3 trans
CH2SiMe3), 141.4 (5-HC(Me2pz)3 trans THF), 137.8 (br d, 4-C6F5),
135.9 (br d, 3-C6F5), 109.1 (4-Me2pz trans CH2SiMe3), 108.9 (4-
HC(Me2pz)3 trans THF), 73.3 (OCH2CH2), 68.1 (HC(Me2pz)3, 25.4
(OCH2CH2), 16.4 (5-HC(Me2pz)3 trans THF), 15.0 (3-HC(Me2pz)3
trans CH2SiMe3), 11.5 (3-HC(Me2pz)3 trans CH2SiMe3), 11.2 (5-
Experimental Section
General Methods and Instrumentation. All manipulations were
carried out using standard Schlenk line or drybox techniques under
an atmosphere of argon or dinitrogen. Protio- and deutero-solvents
were predried over activated 4 Å molecular sieves and were refluxed
over the appropriate drying agent, distilled, and stored under
dinitrogen in Teflon valve ampules. NMR samples were prepared
under dinitrogen in 5 mm Wilmad 507-PP tubes fitted with J. Young
Teflon valves. 1H, 13C{1H}, 19F, and 29Si NMR spectra were
recorded on Varian Mercury-VX 300, Varian Unity Plus 500, and
Bruker AV500 spectrometers. 1H and 13C assignments were
confirmed when necessary with the use of DEPT-135, DEPT-90,
1
1
and two-dimensional H-1H and 13C-1H NMR experiments. H
and 13C spectra were referenced internally to residual protio-solvent
(1H) or solvent (13C) resonances and are reported relative to
tetramethylsilane (δ ) 0 ppm). 19F and 29Si spectra were referenced
externally to CFCl3 and tetramethylsilane, respectively. Chemical
shifts are quoted in δ (ppm) and coupling constants in hertz. Infrared
spectra were prepared as Nujol mulls between NaCl plates and were
recorded on Perkin-Elmer 1600 and 1710 series FTIR spectrometers.
Infrared data are quoted in wavenumbers (cm-1). Mass spectra were
recorded by the mass spectrometry service of Oxford University’s
Department of Chemistry and elemental analyses by the analytical
services of the University of Oxford Inorganic Chemistry Labora-
tory or by the Elemental Analysis Service at the London Metro-
politan University.
HC(Me2pz)3 trans CH2SiMe3), 3.5 (SiMe3), 1.1 (ScCH2) ppm. 19
F
NMR (CD2Cl2,, 282.2 MHz, 293 K): -133.5 (d, 2-C6F5), -164.1
(t, 4-C6F5), -67.9 (app. t, 3-C6F5) ppm. IR (NaCl plates, Nujol
mull): 1643 (w), 1514 (m), 1306 (w), 1240 (w), 1085 (s), 1035
(m), 979 (s), 861 (m), 768 (w), 774 (w), 156 (w) cm-1. Anal. Found
(calcd for C52H52BF20N6OScSi2): C 49.2, (49.2); H 4.1, (4.1); N
6.6, (6.6).
[Sc{HC(Me2pz)3}(CH2SiMe3)2(THF)][BPh4] (10-BPh4). To a
cold (-78 °C) Schlenk tube containing Sc(CH2SiMe3)3(THF)2 (0.10
g, 0.22 mmol), HC(Me2pz)3 (0.07 g, 0.22 mmol), and
[NHEt3][BPh4] (0.09 g, 0.22 mmol) was added THF (20 mL). The
orange suspension was stirred at -78 °C for 30 min and then
allowed to warm to RT, giving a clear orange solution. This was
allowed to stir for a further 30 min, after which time the mixture
was concentrated in Vacuo to 2 mL and pentane (20 mL) added. A
pale oil formed and was isolated by carefully decanting away the
supernatant. Upon drying in Vacuo 10-BPh4 was obtained as a
spongy cream solid. Yield: 87 mg (43%). 1H NMR (CD2Cl2, 299.9
MHz, 293 K): 7.78 (1 H, s, HC(Me2pz)3), 7.30 (8 H, m,
m-B(C6H5)4), 6.98 (8 H, t, 3J ) 7.3 Hz, o-B(C6H5)4), 6.83 (4 H, t,
3J ) 7.0 Hz, p-B(C6H5)4), 6.15 (1 H, s, 4-HC(Me2pz)3, trans THF),
6.01 (2 H, s, 4-HC(Me2pz)3, trans CH2SiMe3), 4.21 (4 H, m,
OCH2CH2), 2.75 (3 H, s, 3-HC(Me2pz)3 trans THF), 2.47 (3 H, s,
5-HC(Me2pz)3 trans THF), 2.39 (6 H, s, 3-HC(Me2pz)3 trans
CH2SiMe3), 2.34 (6 H, s, 5-HC(Me2pz)3 trans CH2SiMe3), 2.13 (4
H, m, OCH2CH2), 0.34 (2 H, d, 1J ) 11 Hz, ScCH2), 0.09 (2 H, d,
1J ) 11 Hz, ScCH2), -0.23 (18 H, s, SiMe3) ppm. 13C{1H} NMR
NMR (CD2Cl2, 75.5 MHz, 293 K): 155.3 (3-HC(Me2pz)3 trans
THF), 154.4 (3-HC(Me2pz)3 trans CH2SiMe3), 141.7 (5-
HC(Me2pz)3 trans CH2SiMe3), 141.3 (5-HC(Me2pz)3 trans THF),
136.2 (m-B(C6H5)4), 125.8 (o-B(C6H5)4), 122.0 (p-B(C6H5)4), 109.1
(4-HC(Me2pz)3 trans CH2SiMe3), 108.9 (4-HC(Me2pz)3 trans THF),
73.2 (OCH2CH2), 68.0 (HC(Me2pz)3), 25.8 (OCH2CH2), 15.1 (3-
Starting Materials. The compounds M(CH2SiMe3)3(THF)2 (M
) Sc or Y),83 M{HC(Me2pz)3}(CH2SiMe3)3 (M ) Sc or Y),17
Sc(Me3[9]aneN3)Me3,24 M(Me3[9]aneN3)(CH2SiMe3)3 (M ) Sc or
Y),17 and Sc(Me3[6]aneN3)(CH2SiMe3)317 were prepared according
to the literature methods. Other reagents were purchased and used
without further purification.
Sc([9]aneS3)(CH2SiMe3)3 (1). To a solution of Sc(CH2SiMe3)3-
(THF)2 (400 mg, 0.88 mmol) in cold (0 °C) toluene (20 mL) was
added a solution of [9]aneS3 (160 mg, 0.88 mmol) in toluene (20
mL). The solution was stirred at 0 °C for 5 h, after which time the
volatiles were removed under reduced pressure to afford 1 as a
1
white solid. Yield: 321 mg (75%). H NMR (C6D6, 299.9 MHz,
293 K): 2.25 (6 H, m, SCH2), 1.45 (6 H, m, SCH2), 0.47 (27 H, s,
SiMe3), 0.15 (6 H, s, ScCH2) ppm. 13C{1H} NMR (C6D6, 75.5
MHz, 293 K): 43.0 (ScCH2), 31.2 (SCH2), 4.3 (SiMe3) ppm. IR
(NaCl plates, Nujol mull): 1413 (w), 1234 (w), 1246 (s), 875 (s),
823 (m), 745 (m) cm-1. EI-MS: m/z ) 225.3 (12%) [M -
3CH2SiMe3]+, 179.8 (100%) [[9]aneS3]+. Anal. Found (calcd for
C
1 8H45S3ScSi3): C, 44.1 (44.0); H, 9.2 (9.3).
(83) Lappert, M. F.; Pearce, R. J. Chem. Soc., Chem. Commun. 1973,
126.

3470 Organometallics, Vol. 27, No. 14, 2008
Tredget et al.
HC(Me2pz)3 trans CH2SiMe3), 14.9 (3-HC(Me2pz)3 trans THF),
11.8 (5-HC(Me2pz)3 trans THF), 11.3 (5-HC(Me2pz)3 trans
CH2SiMe3), 3.5 (SiMe3) ppm. IR (NaCl plates, Nujol mull): 1567
(m), 1416 (m), 1305 (m), 1239 (m), 1094 (m), 1035 (s), 1018 (s),
981 (w), 861 (s), 733 (m), 705 (s), 732 (m), 666 (w) cm-1. Anal.
Found (calcd for C52H72BN6OScSi2): C 68.8, (68.7); H 7.9, (7.9);
N 9.2, (9.2).
pentane (20 mL) added. An off-white oil precipitated and was
isolated by carefully decanting away the supernatant. Upon drying
in Vacuo the 13-BArF4 formed as a spongy off-white solid. Yield:
1
0.22 g (43%). H NMR (CD2Cl2, 299.9 MHz, 293 K): 4.45 (4 H,
m, br, OCH2CH2), 3.25 (2 H, m, NCH2), 3.15 (3 H, s, NCH3, trans
THF), 3.0-2.7 (10 H, m, NCH2), 2.6 (6 H, s, NCH3, trans
2
CH2SiMe3), 0.01 (18 H, s, SiMe3), -0.12 (2 H, d, J ) 11.9 Hz,
ScCH2), -0.18 (2 H, d, 2J ) 11.9 Hz, ScCH2) ppm. 13C{1H} NMR
(CD2Cl2, 75.5 MHz, 293 K): 147.6 (br d, 2-C6F5), 137.8 (br d,
4-C6F5), 135.9 (br d, 3-C6F5), 74.8 (OCH2CH2), 55.9 (NCH2), 55.8
(NCH2), 55.2 (NCH3, trans THF), 50.9 (NCH2), 49.7 (NCH3, trans
CH2SiMe3), 25.5 (OCH2CH2), 3.3 (SiMe3) ppm. 19F NMR (CD2Cl2,
282.2 MHz, 293 K): -133.5 (d, 2-C6F5), -164.1 (t, 4-C6F5), -167.9
(app. t, 3-C6F5) ppm. IR (NaCl plates, Nujol mull): 1643 (w), 1601
(w), 1514 (m), 1299 (w), 1273 (m), 1259 (m), 1241 (m), 1153 (w),
1084 (s), 1003 (m), 978 (s), 899 (w), 846 (m), 817 (m) cm-1. Anal.
Found (calcd for C45H51BF20N3OScSi2): C 47.3, (47.3); H 4.6, (4.5);
N 3.6, (3.7).
[Y{HC(Me2pz)3}(CH2SiMe3)2(THF)][BArF4] (11-BArF4). To
a cold (-78 °C) Schlenk tube containing Y(CH2SiMe3)3(THF)2
(0.20 g, 0.40 mmol) and [NHMe2Ph][BArF ] (0.32 g, 0.40 mmol)
4
was added THF (5 mL). To this was added a solution of
HC(Me2pz)3 (0.12 g, 0.40 mmol) in THF (5 mL). The solution was
stirred at -78 °C for 1.5 h, after which time it was allowed to
warm to RT and concentrated in Vacuo to ca. 2 mL. Pentane (10
mL) was added to give a pale oil, from which the supernatant was
decanted. Upon drying in Vacuo 11-BArF4 formed as a spongy off-
1
white solid. Yield: 0.39 g (73%). H NMR (CD2Cl2, 299.9 MHz,
293 K): 7.92 (1 H, s, HC(Me2pz)3), 6.12 (3 H, s, 4-HC(Me2pz)3),
3.99 (4 H, m, br, OCH2CH2), 2.56-2.49 (18 H, s, br, HC(Me2pz)3),
2.03 (4 H, m, br, OCH2CH2), -0.17 (18 H, s, SiMe3), -0.42 (4 H,
d, 2JHY ) 2.9 Hz, YCH2) ppm. 13C{1H} NMR (CD2Cl2, 75.5 MHz,
293 K): 154.7 (3-HC(Me2pz)3), 147.6 (br d, 2-C6F5), 142.3
(5-HC(Me2pz3)3), 137.8 (br d, 4-C6F5), 135.9 (br d, 3-C6F5), 108.9
(4-HC(Me2pz3)3), 71.0 (OCH2CH2), 68.7 (HC(Me2pz)3), 38.6 (d,
1JCY ) 40 Hz, YCH2), 25.8 (OCH2CH2), 15.0 (HC(Me2pz)3), 11.5
(HC(Me2pz)3), 3.9 (SiMe3) ppm. 19F NMR (CD2Cl2, 282.2 MHz,
293 K): -133.5 (d, 2-C6F5), -164.0 (t, 4-C6F5), -167.9 (app. t,
3-C6F5) ppm. IR (NaCl plates, Nujol mull): 1642 (m), 1601 (w),
1568 (m), 1513 (s), 1391 (m), 1376 (s), 1306 (m), 1238 (w), 1086
(s), 1035 (m), 979 (s), 859 (m), 774 (m), 768 (w) cm-1. Anal.
Found (calcd for C52H52BF20N6OSi2Y): C 47.6, (47.6); H 3.9, (3.9);
N 6.4, (6.4).
[Y(Me3[9]aneN3)(CH2SiMe3)2(THF)][BArF4] (14-BArF4). To
a Schlenk tube containing Y(CH2SiMe3)3(THF)2 (0.20 g, 0.40
mmol) and [NHMe2Ph][BArF ] (0.32 g, 0.40 mmol) was added
4
C6H5Cl (15 mL). To this stirring solution was added Me3[9]aneN3
(78 µL, 0.40 mmol) via a microlitre syringe. The solution was
allowed to stir at RT for 2 h, after which time it was concentrated
to 2 mL and pentane (20 mL) added. An off-white oil formed, which
was isolated by carefully decanting away the supernatant. Upon
drying in Vacuo 14-BArF4 formed as a spongy solid. Yield: 0.26 g
(54%). 1H NMR (CD2Cl2, 299.9 MHz, 263 K): 4.32 (4 H, m,
OCH2CH2), 3.20-2.20 (12 H, m, NCH2), 2.87 (3 H, s, NCH3, trans
THF), 2.56 (6 H, s, NCH3, trans CH2SiMe3), -0.10 (18 H, s,
SiMe3), -0.77 (4 H, s, br s, YCH2) ppm. 13C{1H} NMR (CD2Cl2,
75.5 MHz, 263 K): 147.6 (br d, 2-C6F5), 137.8 (br d, 4-C6F5), 135.9
(br d, 3-C6F5), 72.6 (OCH2CH2), 47.5 (NCH3, trans THF), 47.0
[Y{HC(Me2pz)3}(CH2SiMe3)2(OPPh3)][BArF ] (12-BArF ). To
4
4
1
((NCH3, trans CH2SiMe3), 39.5 (d, JCY ) 43 Hz, YCH2), 25.1
a
Schlenk tube containing [Y{HC(Me2pz)3}(CH2SiMe3)2-
(THF)][BArF ] (0.10 mg, 0.08 mmol) and PPh3O (0.02 g, 0.08
(OCH2CH2), 2.9 (SiMe3) ppm. NCH2 resonances obscured by
CD2Cl2. 19F NMR (CD2Cl2, 282.2 MHz, 263 K): -133.8 (d,
2-C6F5), -162.9 (t, 4-C6F5), -166.9 (app. t, 3-C6F5) ppm. IR (NaCl
plates, Nujol mull): 1643 (m), 1601 (w), 1514 (s), 1376 (s), 1300
(w), 1274 (m) 1240 (m), 1152 (w), 1085 (s), 1003 (s), 978 (s), 850
(m), 768 (m) cm-1. Anal. Found (calcd for C45H51BF20N3OSi2Y):
C 45.5, (45.6); H 4.2, (4.3); N 3.4, (3.5).
4
mmol) was added CH2Cl2 (15 mL). The off-white solution was
stirred at RT for 1 h. The volatiles were removed under reduced
pressure to leave 12-BArF4 as a spongy white solid. Yield: 64 mg
(56%). 1H NMR (CD2Cl2, 299.9 MHz, 293 K): 7.89 (1 H, s,
HC(Me2pz)3), 7.69-7.47 (15 H, m, PPh3O), 6.13 (1 H, s, 4-Me2pz3
trans PPh3O, 5.85 (2 H, s, 4-HC(Me2pz)3 trans CH2SiMe3), 2.90
(3 H, s, 3-HC(Me2pz)3 trans PPh3O), 2.58 (3 H, s, 5-HC(Me2pz)3
trans PPh3O), 2.53 (6 H, s, 3-HC(Me2pz)3 trans CH2SiMe3), 1.75
(6 H, s, 5-HC(Me2pz)3 trans CH2SiMe3), -0.34 (18 H, s, SiMe3),
[Sc([9]aneS3)(CH2SiMe3)2(THF)][BArF4] (15-BArF4). To a
Schlenk tube containing Sc(CH2SiMe3)2(THF)2 (0.1 g, 0.22 mmol),
[NHMe2Ph][BArF ] (0.18 g, 0.22 mmol), and [9]aneS3 (0.04 g, 0.22
4
2
2
mmol) was added C6H5Cl (10 mL). The solution was stirred at RT
for 2 h, after which time it was concentrated under reduced pressure
to 1 mL. Pentane (15 mL) was added to the reaction mixture, which
caused an oil to precipitate. The oil was isolated by carefully
-0.47 (2 H, dd, J ) 11.0 Hz, JHY ) 2.1 Hz, YCH2), -0.64 (2
H, dd, 2J ) 10.6 Hz, 2JHY ) 3.2 Hz) ppm. 13C{1H} NMR (CD2Cl2,
75.5 MHz, 293 K): 154.6 (3-HC(Me2pz)3 trans PPh3O), 153.8 (3-
HC(Me2pz)3 trans CH2SiMe3), 147.6 (br d, 2-C6F5), 141.2 (5-
HC(Me2pz)3 trans PPh3O), 141.1 (5-HC(Me2pz)3 trans CH2SiMe3),
137.8 (br d, 4-C6F5), 135.9 (br d, 3-C6F5), 134.3 (PPh3O), 132.6
(PPh3O), 132.4 (PPh3O), 129.4 (PPh3O), 129.3 (PPh3O), 108.1 (4-
HC(Me2pz)3 trans PPh3O), 107.9 (4-HC(Me2pz)3 trans CH2SiMe3),
decanting away the pentane layer. Drying the oil gave 15-BArF
4
as an off-white solid. Care must be taken not to expose the product
to prolonged periods under dynamic vacuum. Yield: 123 mg (48%).
1H NMR (CD2Cl2, 299.9 MHz, 293 K): 4.38 (4 H, m, OCH2CH2),
3.26 (6 H, m, SCH2, down), 3.02 (6 H, m, SCH2, up), 2.20 (4 H,
m, OCH2CH2), 0.31 (2 H, d, 2J ) 12 Hz, ScCH2), 0.49 (2 H, d, 2J
) 12 Hz, ScCH2), -0.04 (18 H, s, ScCH2SiMe3) ppm. 13C{1H}
NMR (CD2Cl2, 75.5 MHz, 198 K): 147.6 (br d, 2-C6F5), 137.8 (br
d, 4-C6F5), 135.9 (br d, 3-C6F5), 74.6 (OCH2CH2), 32.9 (SCH2),
32.5 (ScCH2), 25.8 (OCH2CH2), 3.1 (ScCH2SiMe3) ppm. 19F NMR
(CD2Cl2, 282.2 MHz, 293 K): -133.8 (d, 2-C6F5), -162.9 (t,
4-C6F5), -166.9 (app. t, 3-C6F5) ppm. IR (NaCl plates, Nujol mull):
XXXXX cm-1. Anal. Found (calcd For C42H42BF20OS3ScSi2): C,
42.9 (42.8); H, 3.7 (3.7).
1
67.9 (HC(Me2pz)3), 32.9 (d, JCY ) 38 Hz, YCH2), 15.5 (3-
HC(Me2pz)3 trans PPh3O), 14.2 (3-HC(Me2pz)3 trans CH2SiMe3),
11.4 (5-HC(Me2pz)3 trans PPh3O), 11.2 (5-HC(Me2pz)3 trans
CH2SiMe3), 3.5 (SiMe3) ppm. 19F NMR (CD2Cl2, 282.2 MHz, 293
K): -133.8 (d, 2-C6F5), -162.9 (t, 4-C6F5), -166.9 (app. t, 3-C6F5)
ppm. IR (NaCl plates, Nujol mull): 1643 (w), 1569 (w), 1513 (m),
1308 (w), 1236 (w), 1140 (m), 1122 (m), 1085 (s), 1035 (m), 979
(s), 903 (w), 861 (m), 802 (m), 774 (w) cm-1. Anal. Found (calcd
for C66H59BF20N6OPYSi2): C 52.2, (52.2); H 3.9, (3.9); N 5.5, (5.5).
[Sc(Me3[9]aneN3)(CH2SiMe3)2(THF)][BArF4] (13-BArF4). To
a Schlenk tube containing Sc(CH2SiMe3)3(THF)2 (0.20 g, 0.44
In Situ Synthesis of [Y([9]aneS3)(CH2SiMe3)2(THF)2]-
[BArF4] (16-BArF4). A solution of Y(CH2SiMe3)3(THF)2 (5.0 mg,
0.01 mmol) in CD2Cl2 (0.7 mL) was added to solid
mmol) and [NHMe2Ph][BArF ] (0.36 g, 0.44 mmol) was added
4
C6H5Cl (15 mL). To this stirring solution was added Me3[9]aneN3
(86 µL, 0.44 mmol) via microlitre syringe. The solution was stirred
at RT for 2 h, after which time it was concentrated to 2 mL and
[NHMe2Ph][BArF ] (8.1 mg, 0.01 mmol). This solution was added
4
1
to solid [9]aneS3 (1.8 mg, 0.01 mmol). The H NMR spectrum of

Scandium and Yttrium Dialkyl Cations
Organometallics, Vol. 27, No. 14, 2008 3471
the reaction mixture was recorded immediately, showing 100%
mmol) via microlitre syringe. After 30 min the solution was
concentrated to 2 mL and pentane (15 mL) was added. An off-
white oil precipitated and was isolated by carefully decanting the
1
conversion to 16-BArF4. H NMR (CD2Cl2, 299.9 MHz, 213 K):
4.04 (8 H, m, OCH2CH2), 3.21 (6 H, m, SCH2, down), 3.01 (6 H,
m, SCH2, up), 2.06 (8 H, m, OCH2CH2), -0.04 (18 H, s,
YCH2SiMe3), -0.7 (4 H, d, 2JHY ) 3.2 Hz, YCH2) ppm. 13C{1H}
NMR (CD2Cl2, 75.5 MHz, 213 K): 147.6 (br d, 2-C6F5), 137.8 (br
d, 4-C6F5), 135.9 (br d, 3-C6F5), 71.3 (OCH2CH2), 39.7 (YCH2,
1JYC ) 35 Hz), 32.6 (SCH2), 25.6 (OCH2CH2), 3.9 (YCH2SiMe3)
ppm. 19F NMR (CD2Cl2, 282.2 MHz, 293 K): -133.8 (d, 2-C6F5),
-162.9 (t, 4-C6F5), -166.9 (app. t, 3-C6F5) ppm.
supernatant. Drying the oil in Vacuo gave 25-BArF as a spongy
4
off-white solid. Yield: 37 mg (37%). 1H NMR (CD2Cl2, 299.9 MHz,
293 K): 8.69 (2 H, app. s, br, o-C5H5N), 8.12 (1 H, tt, 3J ) 7.7 Hz,
4J ) 1.5 Hz, p-C5H5N), 7.99 (1 H, s, HC(Me2pz)3), 7.63 (2 H,
app.t, 3J ) 6.4 Hz), 6.24 (1 H, s, 4-HC(Me2pz)3 trans py), 6.03 (2
H, s, 4-HC(Me2pz)3, trans CH2SiMe3), 2.83 (3 H, s, 3-HC(Me2pz)3
trans py), 2.64 (3 H, s, 5-HC(Me2pz)3, trans py), 2.57 (6 H, s,
3-HC(Me2pz)3 trans CH2SiMe3), 1.76 (6 H, s, 5-HC(Me2pz)3, trans
CH2SiMe3), 0.53 (2 H, d, 2J ) 11 Hz, ScCH2), 0.28 (2 H, s, 2J )
11.7 Hz, ScCH2), -0.26 (18 H, SiMe3) ppm. 13C{1H} NMR
(CD2Cl2, 75.5 MHz, 293 K): 155.5 (3-HC(Me2pz)3 trans py), 154.9
(3-HC(Me2pz)3 trans CH2SiMe3), 147.6 (br d, 2-C6F5), 149.7 (p-
C5H5N), 141.6 (5-HC(Me2pz)3 trans CH2SiMe3), 141.5 (5-
HC(Me2pz)3 trans py), 137.8 (br d, 4-C6F5), 135.9 (br d, 3-C6F5),
126.1 (m-C5H5N), 109.2 (4-HC(Me2pz)3 trans CH2SiMe3), 109.1
(4-HC(Me2pz)3 trans py), 68.3 (HC(Me2pz)3), 34.5 (ScCH2), 14.6
(3-HC(Me2pz)3 trans CH2SiMe3), 14.2 (3-HC(Me2pz)3 trans py),
11.5 (5-HC(Me2pz)3 trans py), 11.3 (4-HC(Me2pz)3 trans
CH2SiMe3), 3.4 (SiMe3) ppm. 19F NMR (CD2Cl2, 282.2 MHz, 293
K): -133.8 (d, 2-C6F5), -162.9 (t, 4-C6F5), -166.9 (app. t, 3-C6F5)
ppm. IR (NaCl plates, Nujol mull): 1643 (w), 1606 (w), 1569 (w),
1514 (s), 1306 (m), 1240 (w), 1086 (m), 1040 (m), 979 (s), 861
(m), 774 (w) cm-1. Anal. Found (calcd for C53H49BF20N7-
ScSi2 · 1.5(CH2Cl2)): C 47.0, (46.6); H 3.7, (3.8); N 7.4, (7.0).
In Situ Synthesis of [Sc(Me3[9]aneN3)(CH2SiMe3)2][BArF
]
4
(17-BArF4). A solution of Sc(Me3[9]aneN3)(CH2SiMe3)3 (0.01 g,
0.02 mmol) in CD2Cl2 was added to solid [Ph3C][BArF ] (0.02 g,
4
0.02 mmol) to give a yellow solution. NMR analysis showed
immediate quantitative conversion to 17-BArF4. 1H NMR (CD2Cl2,
299.9 MHz, 193 K): 2.98-2.89 (12 H, m, br, NCH2), 2.74 (9 H,
br s, NCH3), 0.02 (4 H, s, ScCH2), -0.08 (18 H, s, SiMe3) ppm.
19F NMR (CD2Cl2, 282.2 MHz, 193 K): -133.8 (d, 2-C6F5),
-162.9 (t, 4-C6F5), -166.9 (app. t, 3-C6F5) ppm. 29Si NMR
1
(HMQC H-observed, CD2Cl2, 299.9 MHz, 193 K): -3.4 ppm.
In Situ Synthesis of [Sc{HC(Me2pz)3}(CH2SiMe3)2][BArF
]
4
(19-BArF4). A solution of Sc{HC(Me2pz)3}(CH2SiMe3)3 (0.01 g,
0.017 mmol) in CD2Cl2 was added to solid [CPh3][BArF ] (0.015
4
g, 0.017 mmol) to give a yellow solution. NMR analysis showed
immediate quantitative conversion to 19-BArF4. 1H NMR (CD2Cl2,
299.9 MHz, 193 K): 7.89 (1 H, s, HC(Me2pz)3), 6.16 (3 H, s,
4-HC(Me2pz)3), 2.61 (9 H, s, HC(Me2pz)3), 2.56 (9 H, s,
HC(Me2pz)3), 0.70 (4 H, s, br, ScCH2), -0.02 (18 H, s, SiMe3)
ppm. 13C{1H} NMR (CD2Cl2, 75.5 MHz, 193 K): 153.6 (3-
HC(Me2pz)3), 147.6 (br d, 2-C6F5), 142.6 (5-HC(Me2pz)3), 137.8
(br d, 4-C6F5), 135.9 (br d, 3-C6F5), 109.4 (4-HC(Me2pz)3), 68.5
(HC(Me2pz)3), 15.4 (HC(Me2pz)3), 11.4 (HC(HC(Me2pz)3), 3.0
(SiMe3) ppm. 19F NMR (CD2Cl2, 282.2 MHz, 193 K): -133.8 (d,
2-C6F5), -162.9 (t, 4-C6F5), -166.9 (app. t, 3-C6F5) ppm. 29Si NMR
In Situ Synthesis of [Sc{HC(Me2pz)3}(CH2SiMe3){TolNC-
(CH2SiMe3)NTol}][BArF
] a solution of
(26-BArF4). To
4
[Sc{HC(Me2pz)3}(CH2SiMe3)2(THF)][BArF ] (15 mg, 0.012 mmol)
4
in CD2Cl2 (0.7 mL) was added TolNCNTol (2.6 mg, 0.012 mmol).
The 1H NMR spectrum showed quantitative conversion to 26-
BArF . 1H NMR (CD2Cl2, 299.9 MHz, 293 K): 7.9 (1 H, s,
4
HC(Me2pz)3), 7.13 (4 H, d, 3J ) 7.8 Hz, 2,6-NC6H4CH3), 6.85 (4
3
1
H, d, J ) 8.3 Hz, 3,5-NC6H4CH3), 6.06 (2 H, s, 4-HC(Me2pz)3,
(HMQC H-observed, CD2Cl2, 299.9 MHz, 193 K): -2.2 ppm.
[Sc{HC(Me2pz)3}(CH2SiMe3)2(OPPh3)][BArF ] (24-BArF ). To
trans TolNC(CH2SiMe3)NTol), 6.04 (1 H, s, 4-HC(Me2pz)3 trans
4
4
CH2SiMe3),
2.58
(6
H,
s,
5-HC(Me2pz)3,
trans
a
Schlenk tube containing [Sc{HC(Me2pz)3}(CH2SiMe3)2-
(THF)][BArF ] (0.10 mg, 0.08 mmol) and PPh3O (0.02 g, 0.08
TolNC(CH2SiMe3)NTol), 2.49 (3 H, s, 5-HC(Me2pz)3, trans
CH2SiMe3), 2.43 (3 H, s, 3-HC(Me2pz)3, trans CH2SiMe3), 2.32
(6 H, s, NCC6H4CH3), 1.96 (6 H, s, 3-HC(Me2pz)3, trans
TolNC(CH2SiMe3)NTol), 0.33 (2 H, s, CH2SiMe3), -0.13 (9 H, s,
ScCH2SiMe3), -0.65 (9 H, s, TolNC(CH2SiMe3)NTol) ppm.
13C{1H} NMR (CD2Cl2, 75.5 MHz, 293 K): 179.3
4
mmol) was added CH2Cl2 (15 mL). The off-white solution was
stirred at RT for 1 h, and then the volatiles were removed in Vacuo
to give 24-BArF as a spongy white solid. Yield: 70 mg (60%).
4
1H NMR (CD2Cl2, 299.9 MHz, 293 K): 7.90 (1 H, s, HC(Me2pz)3),
7.68-7.47 (15 H, m, PPh3O), 6.15 (1 H, s, 4-HC(Me2pz)3 trans
PPh3O), 5.80 (2 H, s, 4-HC(Me2pz)3 trans CH2SiMe3), 2.73 (3 H,
s, 3-HC(Me2pz)3 trans PPh3O), 2.59 (3 H, s, 5-HC(Me2pz)3 trans
PPh3O), 2.54 (6 H, s, 3-HC(Me2pz)3 trans CH2SiMe3), 1.74 (6 H,
(TolNC(CH2SiMe3)NTol),
155.5
(3-HC(Me2pz)3
trans
TolN(CH2SiMe3)NTol), 154.4 (3-HC(Me2pz)3, trans CH2SiMe3),
147.6 (br d, 2-C6F5), 144.3 (1-NC(CH2SiMe3)NC6H4CH3), 142.2
(5-HC(Me2pz)3, trans TolNC(CH2SiMe3)NTol), 141.4 (5-HC(Me2-
pz)3, trans CH2SiMe3), 137.8 (br d, 4-C6F5), 135.9 (br d, 3-C6F5),
2
s, 5-HC(Me1pz)3 trans CH2SiMe3), 0.22 (2 H, d, J ) 11.8 Hz,
ScCH2), 0.15 (2 H, d, 2J ) 11.8 Hz, ScCH2), -0.32 (18 H, s, SiMe3)
ppm. 13C{1H} NMR (CD2Cl2, 75.5 MHz, 293 K): 153.5 (3-
HC(Me2pz)3 trans PPh3O), 154.4 (3-HC(Me2pz)3 trans CH2SiMe3),
147.6 (br d, 2-C6F5), 140.6 (5-Me2pz3 trans PPh3O), 140.5
(5-HC(Me2pz)3 trans CH2SiMe3), 137.8 (br d, 4-C6F5), 135.9 (br
d, 3-C6F5), 133.2 (OPPh3), 133.0 (OPPh3), 129.6 (OPPh3), 129.5
(OPPh3), 108.7 (4-HC(Me2pz)3 trans PPh3O, 108.5 (4-HC(Me2pz)3
trans CH2SiMe3), 68.1 (HC(Me2pz)3), 16.5 (3-HC(Me2pz)3 trans
PPh3O), 14.9 (3-HC(Me2pz)3 trans CH2SiMe3), 11.4 (5-HC(Me2pz)3
trans PPh3O), 11.2 (5-HC(Me2pz)3 trans CH2SiMe3), 3.5 (SiMe3)
ppm. 19F NMR (CD2Cl2, 282.2 MHz, 293 K): -133.8 (d, 2-C6F5),
-162.9 (t, 4-C6F5), -166.9 (app. t, 3-C6F5) ppm. IR (NaCl plates,
Nujol mull): 1643 (w), 1592 (w), 1571 (w), 1513 (s), 1308 (m),
1237 (w), 1142 (m), 1121 (s), 1085 (s), 1035 (m), 979 (s), 863
134.5
(4-NC(CH2SiMe3)C6H4CH3),
130.1
((6-
NC(CH2SiMe3)C6H4CH3), 125.3 (5-NC(CH2SiMe3)C6H4CH3), 108.9
(4-HC(Me2pz)3 trans TolNC(CH2SiMe3)NTol), 108.7 (4-
HC(Me2pz)3 trans CH2SiMe3), 68.5 (HC(Me2pz)3), 20.9
(NC6H4CH3), 14.0 (3-HC(Me2pz)3, trans CH2SiMe3), 13.9 (3-
HC(Me2pz)3, trans TolNC(CH2SiMe3)NTol), 11.3 (5-HC(Me2pz)3,
trans TolNC(CH2SiMe3)NTol), 11.2 (5-HC(Me2pz)3, trans
CH2SiMe3), 2.7 (NC(CH2SiMe3), 0.0 (ScCH2SiMe3) ppm. 19F NMR
(CD2Cl2, 282.2 MHz, 293 K): -133.8 (d, 2-C6F5), -162.9 (t,
4-C6F5), -166.9 (app. t, 3-C6F5) ppm.
[Sc(Me3[9]aneN3)(CH2SiMe3){iPrNC(CH2SiMe3)NiPr}][BArF
]
4
(27-BArF4). To a Schlenk tube containing Sc(CH2SiMe3)3(THF)2
(0.10 g, 0.22 mmol) and [NHMe2Ph][BArF ] (0.18 g, 0.22 mmol)
4
(m), 774 (w), 660 (m)cm-1
.
Anal. Found (calcd for
was added C6H5Cl (15 mL). To this stirring solution was added
1,4,7-Me3[9]aneN3 (43 µL, 0.22 mmol) via microlitre syringe. The
solution was stirred at RT for 30 min (generating 13-BArF4 in situ),
C66H59BF20N6OPScSi2 · 0.5(CH2Cl2)): C 52.7, (52.6); H 4.1, (4.0);
N 5.5, (5.5).
[Sc{HC(Me2pz)3}(CH2SiMe3)2(py)][BArF4] (25-BArF4). To a
after which time PrNCNiPr (34 µL, 0.22 mmol) was added. The
i
solution of [Sc{HC(Me2pz)3}(CH2SiMe3)2(THF)][BArF ] (0.10 g,
solution was stirred for a further 30 min, and then pentane (25 mL)
was added. An oil formed, which was isolated by carefully
4
0.08 mmol), in CH2Cl2 (10 mL), was added pyridine (13 µL, 0.16

3472 Organometallics, Vol. 27, No. 14, 2008
Tredget et al.
Table 4. X-ray Data Collection and Processing Parameters for
decanting away the supernatant. The oil was carefully dried in Vacuo
to give 27-BArF as an off-white oil. Care must be taken not to
Sc([9]aneS3)(CH2SiMe3)3 · 0.5(C7H8) (1 · 0.5(C7H8)) and
4
[Sc([9]aneS3)(CH2SiMe3)2(THF)][BArF4] (15-BArF
)
4
leave the product under dynamic vacuum for long periods. Yield:
125 mg (47%). 1H NMR (CD2Cl2, 299.9 MHz, 293 K): 3.65 (2 H,
sept, 3J ) 6.5 Hz, NC(H)(CH3)2), 3.34-2.73 (12H, m, NCH2), 3.05
(6 H, s, NCH3 trans CH2SiMe3), 2.49 (3 H, s, NCH3 trans
parameter
1 · 0.5(C7H8)
15-BArF
4
empirical formula
fw
C
21.5H49S3ScSi3
C42H42BF20OS3ScSi2
1150.89
533.04
i
iPrNC(R)NiPr), 2.17 (2 H, s, PrNC(CH2SiMe3)NiPr), 1.34 (6 H,
temp/K
150
150
d, 3J ) 6.5 Hz, NCH(CH3)2), 1.30 (6 H, d, 3J ) 6.5 Hz,
NCH(CH3)2), 0.18 (9 H, s, iPrNC(CH2SiMe3)NiPr), -0.09 (9 H, s,
ScCH2SiMe3), -0.30 (2 H, s, ScCH2SiMe3) ppm. 13C{1H} NMR
(CD2Cl2, 75.5 MHz, 293 K): 147.6 (br d, 2-C6F5), 137.8 (br d,
4-C6F5), 135.9 (br d, 3-C6F5), 135.0 (B(C6F5)4), 55.8 (NCH2), 55.3
(NCH2), 55.0 (NCH2), 49.6 (NCH3), 49.45 (NCH3), 48.6 (NCH3),
26.6 (NCH(CH3)2), 25.8 (NCH(CH3)2), 18.5 (NC(CH2SiMe3)), 3.5
(ScCH2SiMe3), -0.0 (NC(CH2SiMe3)) ppm. 19F NMR (CD2Cl2,
282.2 MHz, 293 K): -133.8 (d, 2-C6F5), -162.9 (t, 4-C6F5), -166.9
(app. t, 3-C6F5) ppm. IR (NaCl plates, Nujol mull): 1642 (m), 1513
(s), 1463 (s), 1379 (s), 1257 (m), 1211 (w), 1179 (w), 1083 (s),
1003 (m), 978 (s), 910 (w), 854 (m), 774 (m), 756 (m) cm-1. Anal.
Found (calcd for C49H61BF20N5ScSi: C 48.7, (48.6); H 4.9, (5.1);
N 5.9, (5.8).
wavelength/Å
space group
a/Å
b/Å
c/Å
0.71073
C2/c
20.0776(4)
15.6656(3)
20.0619(4)
90
100.0286(9)
90
6213.6(2)
8
1.140
0.562
R1 ) 0.0350
Rw ) 0.0436
0.71073
P1
j
10.7691(2)
12.7989(3)
17.9114(4)
81.1573(8)
86.3644(9)
86.7330(10)
2431.73(9)
2
1.572
0.440
R1 ) 0.0514
Rw ) 0.0637
R/deg
ꢀ/deg
γ/deg
V/Å3
Z
d(calcd)/Mg · m-1
abs coeff/mm-1
R indicesa
[I > 3σ(I)]
a R1 ) ∑|Fo| - |Fc|/∑|Fo|; Rw ) ꢀ{∑w(|Fo| - |Fc|)2/∑w|Fo|2}.
[Sc{HC(Me2pz)3}(CH2SiMe3)(CCPh)(THF)][BArF
]
(28-
of
4
NCH2), 2.78 (3 H, s, NCH3), 2.71 (3 H, s, NCH3), 2.43 (4 H, m,
OCH2CH2), -0.08 (9 H, s, ScCH2SiMe3), 0.00 (1 H, d, 2J ) 11.7
Hz, ScCH2), -0.15 (1 H, d, 2J ) 11.9 Hz, ScCH2) ppm. 13C{1H}
NMR (CD2Cl2, 75.5 MHz, 293 K): 147.6 (br d, 2-C6F5), 137.8 (br
d, 4-C6F5), 135.9 (br d, 3-C6F5), 131.7 (ScCCC6H5), 130.1
(ScCCC6H5), 128.8 (ScCCC6H5), 128.6 (ScCCC6H5), 75.4
(OCH2CH2, 56.4 (NCH2), 56.1 (NCH2), 55.4 (NCH2), 51.4 (NCH3),
50.4 (NCH3), 49.0 (NCH3), 25.6 (OCH2CH2), 3.2 (ScCH2SiMe3)
ppm. 19F NMR (CD2Cl2, 282.2 MHz, 293 K): -133.8 (d, 2-C6F5),
-162.9 (t, 4-C6F5), -166.9 (app. t, 3-C6F5) ppm. IR (NaCl plates,
Nujol mull): 2071 (w, Ct C), 1643 (m), 1514 (s), 1201 (w), 1085
(s), 1001 (m), 978 (s), 888 (m), 852 (w), 775 (m), 756 (m), 723
(m) cm-1. Anal. Found (calcd for C43H40BF20N3OScSi): C 48.0,
(47.9); H 3.7, (3.7); N 3.9, (3.9).
Crystal Structure Determinations of Sc([9]aneS3)(CH2Si-
Me3)3 · 0.5(C7H8) (1 · 0.5(C7H8)) and [Sc([9]aneS3)(CH2SiMe3)2-
(THF)][BArF4] (15-BArF4). Crystal data collection and processing
parameters are given in Table 4. Crystals were mounted on glass
fibers using perfluoropolyether oil and cooled rapidly in a stream
of cold N2 using an Oxford Cryosystems Cryostream unit. Dif-
fraction data were measured using an Enraf-Nonius KappaCCD
diffractometer. As appropriate, absorption and decay corrections
were applied to the data and equivalent reflections merged.84 The
structures were solved by direct methods (SIR9285), and further
refinements and all other crystallographic calculations were per-
formed using the CRYSTALS program suite.86 Other details of
the structure solution and refinements are given in the Supporting
Information (CIF data). A full listing of atomic coordinates, bond
lengths and angles, and displacement parameters for all the
structures have been deposited at the Cambridge Crystallographic
Data Centre. See Notice to Authors, Issue No. 1.
BArF4).
To
a
solution
4
[Sc{HC(Me2pz)3}(CH2SiMe3)2(THF)][BArF ] (0.20 g, 0.16 mmol)
in CH2Cl2 (10 mL) was added PhCCH (17.4 µL, 0.16 mmol) via
microlitre syringe. The light green solution was stirred at RT for
30 min, and the volatiles were removed in Vacuo to give 28-BArF
4
as a spongy off-white solid. Yield: 131 mg (64%). 1H NMR
(CD2Cl2, 299.9 MHz, 293 K): 7.90 (1 H, s, HC(Me2pz)3), 7.33 (2
H, m, o-C6H5), 7.23 (3 H, m, o,p-C6H5), 6.17 (1 H, s,
4-HC(Me2pz)3), 6.18 (1 H, s, 4-HC(Me2pz)3), 6.04 (1 H, s,
4-HC(Me2pz)3), 4.51 (2 H, m, OCH2CH2), 4.25 (2 H, m,
OCH2CH2), 2.92 (3 H, s, 3-HC(Me2pz)3), 2.59 (3 H, s,
5-HC(Me2pz)3), 2.58 (3 H, s, 5-HC(Me2pz)3), 2.54 (3 H, s,
3-HC(Me2pz)3), 2.51 (3 H, s, 5-HC(Me2pz)3), 2.49 (3 H, s,
3-HC(Me2pz)3), 2.18 (4 H, m, OCH2CH2), 0.42 (1 H, d, 2J ) 11.7
2
Hz, ScCH2), 0.31 (1 H, d, J ) 11.7 Hz, ScCH2), -0.14 (9 H, s,
ScCH2SiMe3) ppm. 13C{1H} NMR (CD2Cl2, 75.5 MHz, 293 K):
156.2 3-HC(Me2pz)3), 155.3 (3-HC(Me2pz)3), 154.8 (3-
HC(Me2pz)3), 147.6 (br d, 2-C6F5), 137.8 (br d, 4-C6F5), 135.9 (br
d, 3-C6F5), 131.8 (ScCCC6H5), 128.5 (ScCCC6H5), 127.2
(ScCCC6H5), 109.1 (4-HC(Me2pz)3), 109.0 (4-HC(Me2pz)3), 73.6
(OCH2CH2), 68.2 (HC(Me2pz)3), 25.8 (OCH2CH2), 15.6 (3-
HC(Me2pz)3), 14.9 (3-HC(Me2pz)3), 14.6 (3-HC(Me2pz)3), 11.4 (5-
HC(Me2pz)3), 11.3 (5-HC(Me2pz)3), 11.1 (5-HC(Me2pz)3), 3.42
(ScCH2SiMe3) ppm. 19F NMR (CD2Cl2, 282.2 MHz, 293 K):
-133.8 (d, 2-C6F5), -162.9 (t, 4-C6F5), -166.9 (app. t, 3-C6F5)
ppm. IR (NaCl plates, Nujol mull): 2071 (w, Ct C), 1643 (m), 1596
(w), 1568 (m), 1513 (s), 1305 (m), 1262 (s), 1201 (w), 1086 (s),
1039 (m), 979 (s), 859 (s), 775 (m), 756 (m) cm-1. Anal. Found
(calcd for C56H46BF20N6OScSi2.CH2Cl2): C 50.6, (50.1); H 3.8,
(3.5); N 6.4, (6.1).
[Sc(Me3[9]aneN3)(CH2SiMe3)(CCPh)(THF)][BArF
]
(29-
Procedure for the Polymerization of Ethylene. A typical
ethylene polymerization run was carried out as follows with all
manipulations under ethylene (∼1 atm) working gas until the
mixture was quenched. Stock solutions of Sc{HC(Me2pz)3}(CH2Si-
4
BArF4). To a Schlenk tube containing Sc(CH2SiMe3)3(THF)2 (0.10
g, 0.22 mmol) and [NHMe2Ph][BArF ] (0.18 g, 0.22 mmol) was
4
added C6H5Cl (15 mL). To this stirring solution was added 1,4,7-
Me3)3 (6 mg, 10 µmol in 25 mL of toluene) and [Ph3C][BArF ]
4
Me3[9]aneN3 (43 µL, 0.22 mmol) via microlitre syringe. The
solution was stirred at RT for 1 h (generating 13-BArF in situ),
(9.2 mg, 10 µmol in 20 mL of toluene) were made up. Toluene
(225 mL) was added to AliBu3 (1 M toluene solution, 5 mL, 5
mmol) and transferred to the reactor, which was fitted with an
external heat bath set to 40 °C. The mixture was stirred for 10 min
4
after which time PhCCH (24 µL, 0.22 mmol) was added. After a
further 30 min the volume was reduced to 1 mL and pentane (15
mL) was added. A dark oil formed, which was isolated by carefully
decanting away the supernatant. Upon drying in Vacuo the 29-BArF
4
(84) Otwinowski, Z.; Minor, W. Processing of X-ray Diffraction Data
Collected in Oscillation Mode; Academic Press: New York, 1997.
(85) Altomare, A.; Cascarano, G.; Giacovazzo, G.; Guagliardi, A.; Burla,
M. C.; Polidori, G.; Camalli, M. J. Appl. Crystallogr. 1994, 27, 435.
(86) Betteridge, P. W.; Cooper, J. R.; Cooper, R. I.; Prout, K.; Watkin,
D. J. J. Appl. Crystallogr. 2003, 36, 1487.
formed as a spongy off-white solid. Care must be taken not to leave
the product under dynamic vacuum for extended periods of time.
Yield: 125 mg (52%). 1H NMR (CD2Cl2, 299.9 MHz, 293 K):
7.35-7.25 (5 H, m, ScCCC6H5), 4.78 (2 H, m, OCH2CH2), 4.60
(2 H, m, OCH2CH2), 3.23 (3 H, s, NCH3), 2.9 - 2.6 (12 H, m, br,

Scandium and Yttrium Dialkyl Cations
Organometallics, Vol. 27, No. 14, 2008 3473
(1000 rpm) to scrub the apparatus and allow the toluene solution
to equilibrate to approximately 35 °C. Sc{HC(Me2pz)3}(CH2SiMe3)3
(6 mg, 10 µmol in 25 mL of toluene) was added to the reactor,
effective core potential (RECP) from the Stuttgart group and the
associated basis sets.90 The Si and S atoms were represented by
RECP from the Stuttgart group and the associated basis sets,91
augmented by a d polarization function.92 The remaining atoms
(C, H, N, O) were represented by a 6-31G(d,p) basis set.93 Full
optimizations of geometry without any constraint were performed,
followed by analytical computation of the Hessian matrix to confirm
the nature of the located extrema as minima on the potential energy
surface. NMR chemical shifts were computed using the GIAO
method94,95 at the B3PW91 level. For the NMR parameters, all
electron calculations were considered where the basis set for Sc
was the TZP basis set of Ahlrichs,96 and all the other atoms were
described with the IGLOO-II basis set.97 For the NMR calculations
on Y complexes, the Y atom was described with the RECP from
Dolg et al. and the associated basis set.
followed by [Ph3C][BArF ] (10 µmol in 20 mL of toluene). A
4
dynamic ethylene pressure of 6 bar was applied. The temperature
and ethylene uptake were monitored and the reaction was run for
10 min, after which the ethylene flow was stopped and the pressure
carefully released. The reactor lid was removed and the reaction
mixture quenched by the careful dropwise addition of MeOH
(approximately 10 mL). Distilled water (50 mL) was then added
and the mixture acidified to pH 1 (10% HCl in MeOH) (ap-
proximately 25 mL). The reaction mixture was stirred for 16 h and
then filtered. The solid PE was washed with distilled water (1000
mL) and dried at approximately 60 °C to constant weight.
Procedure for the Polymerization of 1-Hexene. A typical
1-hexene polymerization run was carried out as follows. To a
stirring solution of Sc{HC(Me2pz)3}(CH2SiMe3)3 (12 mg, 20 µmol)
in C6H5Cl (2.5 mL) was added 1-hexene (1.48 mL, 12 mmol). To
Acknowledgment. We thank the EPSRC, St. Edmund
Hall, Oxford, the CNRS, and the British Council for support,
this mixture was added a solution of [CPh3][BArF ] (40 mg, 40
and DSM Research for gifts of [CPh3][BArF ] and
4
4
[NHMe2Ph][BArF ]. We thank Dr. A. R. Cowley for col-
µmol) in C6H5Cl (2.5 mL). The reaction mixture became extremely
viscous almost immediately. After 10 min the reaction mixture was
quenched with wet THF. The polyhexene was isolated by precipita-
tion in EtOH and was dried in Vacuo.
Computational Details. All the calculations have been per-
formed with the Gaussian03 package87 at the B3PW91 level.88,89
The scandium and yttrium atoms were represented by the relativistic
4
lecting the X-ray data.
Supporting Information Available: X-ray crystallographic data
in CIF format for the structure determinations of 1 · 0.5(C7H8) and
15-BArF4. Cartesian coordinates for the molecules optimized and
electronic energies (au) at the B3PW91 level for the neutral
molecules. This information is available free of charge via the
Internet at http://pubs.acs.org.
(87) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb,
M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.; Kudin, K. N.;
Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.;
Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.;
Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.;
Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li,
X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Bakken, V.; Adamo, C.;
Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.;
Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.;
Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich,
S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A. D.;
Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.;
Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz,
P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.;
Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson,
B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian 03,
Revision C.02; Gaussian, Inc.: Wallingford, CT, 2004.
OM800279D
(90) Andrae, D.; Haussermann, U.; Dolg, M.; Stoll, H.; Preuss, H. Theor.
Chim. Acta 1990, 77, 123.
(91) Bergner, A.; Dolg, M.; Kuchle, W.; Stoll, H.; Preuss, H. Mol. Phys.
1993, 30, 1431.
(92) Hollwarth, A.; Bohme, H.; Dapprich, S.; Ehlers, A. W.; Gobbi,
A.; Jonas, V.; Kohler, K. F.; Stagmann, R.; Veldkamp, A.; Frenking, G.
Chem. Phys. Lett. 1993, 203, 237.
(93) Hariharan, P. C.; Pople, J. A. Theor. Chim. Acta 1973, 28, 213.
(94) Lee, A. M.; Handy, N. C.; Colwell, S. M. J. Chem. Phys. 1995,
103, 10095.
(95) Ditchfiled, R. J. Chem. Phys. Lett. 1972, 56, 5688.
(96) Scha¨fer, A.; Huber, C.; Ahlrichs, R. J. Chem. Phys. Lett. 1994,
100, 5829.
(88) Becke, A. D. J. Chem. Phys. 1993, 98, 5648.
(89) Perdew, J. P.; Wang, Y. Phys. ReV. B 1992, 45, 13244.
(97) Kutzelnigg, W.; Fleischer, U.; Schindler, M.; NMR Basic Principles
and Progress; Springer-Verlag: Berlin, 1990; p 165.