Group 3 dialkyl complexes with tetradentate (L, L, N, O; L = N, O, S) monoanionic ligands: Synthesis and reactivity

Article abstract of DOI:10.1021/om0608612

Tripodal, tetradentate phenols, (LCH₂)₂NCH ₂-C₆H₂-3,5-(CMe₃)₂-2-OH (L = CH₂OCH₃ (1), CH₂NEt₂ (2), 2-C₅H₄N (3), C

Full text of DOI:10.1021/om0608612

1178
Organometallics 2007, 26, 1178-1190
Group 3 Dialkyl Complexes with Tetradentate (L, L, N, O; L ) N,
O, S) Monoanionic Ligands: Synthesis and Reactivity
Smaranda C. Marinescu, Theodor Agapie, Michael W. Day, and John E. Bercaw*
Arnold and Mabel Beckman Laboratories of Chemical Synthesis, California Institute of Technology,
Pasadena, California 91125
ReceiVed September 21, 2006
Tripodal, tetradentate phenols, (LCH2)2NCH2-C6H2-3,5-(CMe3)2-2-OH (L ) CH2OCH3 (1), CH2NEt2
(2), 2-C5H4N (3), CH2SCMe3 (5), CH2NMe2 (6)), were synthesized, and metalations were performed via
alkane elimination from yttrium and scandium trialkyl complexes to generate the corresponding dialkyl
complexes [(LCH2CH2)2NCH2-C6H2-3,5-(CMe3)2-2-O]MR2 (M ) Y, L ) OCH3, R ) CH2SiMe2Ph (7a);
M ) Y, L ) NEt2, R ) CH2SiMe2Ph (7b); M ) Sc, L ) OCH3, R ) CH2SiMe2Ph (8a); M ) Sc, L )
SCMe3, R ) CH2SiMe2Ph (8b); M ) Y, L ) OCH3, R ) CH2SiMe3 (9); M ) Sc, L ) OCH3,
R ) CH2SiMe3 (10)). X-ray crystallographic studies show that 7a,b and 8a adopt, in the solid
1
state, mononuclear structures of C1 symmetry. The H NMR spectra of these dialkyl complexes in
benzene-d6 at high temperatures reveal exchange processes involving the ether groups and the alkyl
groups. The dynamic behavior of species 7a, 8a, and 10 in toluene-d8 was investigated by variable-
1
temperature H NMR spectroscopy. The activation parameters of the fluxional processes for 7a, 8a,
and 10 were determined by line-shape and Eyring analyses (for 7a, ∆Hq ) 7.3 ( 0.3 kcal/mol
and ∆Sq ) -16 ( 1.4 cal/(mol K); for 8a, ∆Hq ) 9.9 ( 0.5 kcal/mol and ∆Sq ) -15.3 ( 1.8 cal/
(mol K); for 10, ∆Hq ) 10.8 ( 0.6 kcal/mol and ∆Sq ) -11.4 ( 1.9 cal/(mol K)). These data establish
that the dialkyl complexes 7a, 8a, and 10 undergo a nondissociative exchange process. The
scandium dialkyl complex [(C5H4N-2-CH2)2NCH2-C6H2-3,5-(CMe3)2-2-O]Sc(CH2SiMe2Ph)2 (11) was
found to undergo clean activation of a C-H bond of a methylene linking a pyridine to the central nitrogen
donor. This process follows first-order kinetics (k ) [2.8(3)] × 10-4 s-1 at 0 °C). The yttrium dialkyl
complexes 7a and 9 react with 1 equiv of [PhNHMe2]+[B(C6F5)4]- in chlorobenzene-d5, to generate a
solution that slowly polymerizes ethylene. Compounds 7-10 also polymerize ethylene with low activity
upon activation with MAO.
However, group 3 still remains a relatively unexplored
part of the transition series in the context of olefin polymeri-
zation.2,3
As part of our continuing interest in developing novel
polymerization catalysts, we have explored new ligand designs
to support cationic group 3 alkyl complexes. Accordingly, a
Introduction
Cationic alkyl complexes of group 4 metals are the most
common single-site olefin polymerization catalysts.1-3 Isoelec-
tronic, neutral alkyl complexes of group 3 metals generally show
much lower polymerization activity.4 One approach to increasing
polymerization activity involves the generation of cationic alkyl
species. The most common route to cationic alkyl species
involves alkide abstraction from neutral dialkyl or trialkyl
complexes. Over the past few years the synthesis of dialkyl and
trialkyl complexes of group 3 metals supported by multidentate
ligands has been an area of increasing interest.5-21 Recent reports
indicate that, upon activation, the resulting cationic alkyl
complexes display promising polymerization activities.8-10,13,20
(9) Bambirra, S.; van Leusen, D.; Meetsma, A.; Hessen, B.; Teuben, J.
H. Chem. Commun. 2003, 522.
(10) Bambirra, S.; van Leusen, D.; Meetsma, A.; Hessen, B.; Teuben, J.
H. Chem. Commun. 2001, 637.
(11) Lee, L. W. M.; Piers, W. E.; Elsegood, M. R. J.; Clegg, W.; Parvez,
M. Organometallics 1999, 18, 2947.
(12) Lee, L.; Berg, D. J.; Einstein, F. W.; Batchelor, R. J. Organometallics
1997, 16, 1819.
(13) Hajela, S.; Schaefer, W. P.; Bercaw, J. E. J. Organomet. Chem.
1997, 532, 45.
(14) Fryzuk, M. D.; Giesbrecht, G.; Rettig, S. J. Organometallics 1996,
15, 3329.
(15) Skinner, M. E. G.; Tyrrell, B. R.; Ward, B. D.; Mountford, P. J.
Organomet. Chem. 2002, 647, 145.
(16) Evans, W. J.; Broomhall-Dillard, R. N. R.; Ziller, J. W. Organo-
metallics 1996, 15, 1351.
(17) Emslie, D. J. H.; Piers, W. E.; Parvez, M.; McDonald, R.
Organometallics 2002, 21, 4226.
(18) Bambirra, S.; Brandsma, M. J. R.; Brussee, E. A. C.; Meetsma, A.;
Hessen, B.; Teuben, J. H. Organometallics 2000, 19, 3197.
(19) Hayes, P. G.; Piers, W. E.; Lee, L. W. M.; Knight, L. K.; Parvez,
M.; Elsegood, M. R. J.; Clegg, W. Organometallics 2001, 20, 2533.
(20) Ward, B. D.; Bellemin-Laponnaz, S.; Gade, L. H. Angew. Chem.,
Int. Ed. Engl. 2005, 44, 2.
* To whom correspondence should be addressed. E-mail: bercaw@
caltech.edu.
(1) McKnight, A.; Waymouth, R. M. Chem. ReV. 1998, 98, 2587.
(2) Gibson, V. C.; Spitzmesser, S. K. Chem. ReV. 2003, 103, 283.
(3) Britovsek, G. J. P.; Gibson, V. C.; Wass, D. F. Angew. Chem., Int.
Ed. 1999, 38, 428.
(4) Shapiro, P. J.; Schaefer, W. P.; Labinger, J. A.; Bercaw, J. E.; Cotter,
W. D. J. Am. Chem. Soc. 1994, 116, 4623.
(5) Zeimentz, P. M.; Arndt, S.; Elvidge, B. R.; Okuda, J. Chem. ReV.
2006, 106, 2404-2433.
(6) Arndt, S.; Okuda, J. AdV. Synth. Catal. 2005, 347, 339-354.
(7) Gromada, J.; Carpentier, J. F.; Mortreux, A. Coord. Chem. ReV. 2004,
248, 397-410.
(8) Hayes, P. G.; Piers, W. E.; McDonald, R. J. Am. Chem. Soc. 2002,
124, 2132.
(21) Bambirra, S.; Boot, S.; van Leusen, D.; Meetsma, A.; Hessen, B.
Organometallics 2004, 23, 1891.
10.1021/om0608612 CCC: $37.00 © 2007 American Chemical Society
Publication on Web 02/01/2007

Group 3 Dialkyl Complexes
Scheme 1
Organometallics, Vol. 26, No. 5, 2007 1179
Results and Discussion
Ligand and Metal Dialkyl Complex Syntheses. (a) Syn-
thesisof(LCH2)2NCH2-C6H2-3,5-(CMe3)2-2-OH(L)CH2OCH3,
CH2NEt2, 2-C5H4N). A modification of the Mannich condensa-
tion used by Kol et al. to synthesize tetradentate diphenolate
ligands was employed for the synthesis of tetradentate monophe-
nolate ligands 1 and 2 (eq 1).39 Using a related strategy,
series of [L2NO] (L ) neutral donor; N ) tertiary amine; O )
phenolate) monoanionic, tripodal ligands was targeted. There
is precedent in the literature for related [N3O] monoanionic
ligands to support zinc(II) and copper(I) complexes22-25 as well
as for [S2NO] ligands to support copper(II) complexes.26
Complexes supported by triazacyclononanes functionalized with
one pendant phenolate arm have been reported as well.15,27
Furthermore, related tetradentate amino phenolate ligands have
beenrecentlyshowntosupportgroup3-5alkylcomplexes.15,28-34
Group 4 dialkyls supported by diphenolate ligands were reported
to be active olefin polymerization catalysts when activated, and
in some cases, isotactic poly-1-hexene and polypropylene are
obtained.34-36 These reports indicate that monoanionic [L2NO]
frameworks could be used as robust ancillary ligands. Inspired
by the promising precedents, we prepared a new series of [L2-
NO] ligands, and the ability of these to support group 3 dialkyl
species was investigated (see below). This report describes the
synthesis and reactivity of a series of yttrium and scandium alkyl
complexes with such tetradentate phenolate ligands. After we
started work on this project, two of the ligands described herein
were reported by others to support early-metal complexes.
Ligand 1, (CH3OCH2CH2)2NCH2-C6H2-3,5-(CMe3)2-2-OH, was
recently reported by Kol et al. as part of a study of a number of
zirconium complexes,37 while ligand 2, (Et2NCH2CH2)2NCH2-
C6H2-3,5-(CMe3)2-2-OH, was reported by Arnold et al. as part
of a study of group 3 catalysts for the polymerization of lactide
and ꢀ-caprolactone.38
compound 3 was prepared from the corresponding benzyl
bromide and secondary amine (eq 2). Compounds 1-3 were
synthesized using commercially available or easily accessible
starting materials. These procedures afford the desired products
in close to quantitative yields. The phenols obtained in this
fashion do not require additional purification before metalation.
(b) Synthesis of (LCH2CH2)2NCH2-C6H2-3,5-(CMe3)2-2-
OH (L ) SCMe3, NMe2). An alternative route to [L2NO] ligand
frameworks involves nucleophilic substitution on dichloride 4
(Scheme 1). This synthetic route was developed to gain access
to ligand precursors for which the appropriate secondary amine
starting materials required for the Mannich condensation are
not commercially available. Compound 4 has been readily
prepared in two steps from commercially available starting
materials via Mannich condensation followed by chlorination
with thionyl chloride. The nucleophilic substitution step could
present a problem due to the unprotected phenol functionality;
however, the example shown affords the desired product 5
cleanly upon purification by precipitation from CH3OH and
compound 6 upon purification by column chromatography.
The ligand syntheses described here offer the possibility of
altering the nature of the two L groups. Such ligand architecture
allows for steric and electronic variations on both the phenol
and the L donor fragments.
(22) Trosch, A.; Vahrenkamp, H. Eur. J. Inorg. Chem. 1998, 827.
(23) Trosch, A.; Vahrenkamp, H. Inorg. Chem. 2001, 40, 2305.
(24) Abufarag, A. V., H. Inorg. Chem. 1995, 34, 329.
(25) Inoue, Y.; Matyjaszewski, K. Macromolecules 2003, 36, 7432-
7438.
(26) Takahashi, K.; Ogawa, E.; Oishi, N.; Nishida, Y.; Kida, S. Inorg.
Chim. Acta 1982, 66, 97.
(27) Bylikin, S. Y.; Robson, D. A.; Male, N. A. H.; Rees, L. H.;
Mountford, P.; Schroder, M. Dalton Trans. 2001, 170.
(28) Groysman, S.; Goldberg, I.; Kol, M.; Goldschmidt, Z. Organome-
tallics 2003, 22, 3793-3795.
(29) Groysman, S.; Goldberg, I.; Kol, M.; Genizi, E.; Goldschmidt, Z.
Organometallics 2004, 23, 1880-1890.
(30) Tshuva, E. Y.; Goldberg, I.; Kol, M.; Goldschmidt, Z. Chem.
Commun. 2001, 2120-2121.
(31) Tshuva, E. Y.; Goldberg, I.; Kol, M.; Goldschmidt, Z. Inorg. Chem.
2001, 40, 4263-4270.
(32) Tshuva, E. Y.; Goldberg, I.; Kol, M.; Goldschmidt, Z. Organome-
tallics 2001, 20, 3017-3028.
(33) Tshuva, E. Y.; Groysman, S.; Goldberg, I.; Kol, M.; Goldschmidt,
Z. Organometallics 2002, 21, 662-670.
(c)SynthesisofMetalDialkylComplexes[(LCH2CH2)2NCH2-
C6H2-3,5-(CMe3)2-2-O]MR2 (M ) Y, Sc; L ) OCH3, NEt2,
SCMe3; R ) CH2SiMe2Ph, CH2SiMe3). Using in situ gener-
ated yttrium and scandium trialkyl starting materials, the
preparation of target metal dialkyl complexes was accomplished
(34) Tshuva, E. Y.; Goldberg, I.; Kol, M. J. Am. Chem. Soc. 2000, 122,
10706-10707.
(35) Segal, S.; Goldberg, I.; Kol, M. Organometallics 2005, 24, 200-
202.
(36) Busico, V.; Cipullo, R.; Ronca, S.; Budzelaar, P. H. M. Macromol.
Rapid Commun. 2001, 22, 1405-1410.
(37) Groysman, S.; Sergeeva, E.; Goldberg, I.; Kol, M. Inorg. Chem.
2005, 44, 8188-8190.
(39) Tshuva, E. Y.; Goldberg, I.; Kol, M.; Goldschmidt, Z. Organome-
tallics 2001, 20, 3017.
(38) Westmoreland, I.; Arnold, J. Dalton Trans. 2006, 4155-4163.

1180 Organometallics, Vol. 26, No. 5, 2007
Marinescu et al.
Figure 1. Structural drawing of [(CH3OCH2CH2)2NCH2-C6H2-3,5-
(CMe3)2-2-O]Y(CH2SiMe2Ph)2 (7a) with thermal ellipsoids at the
50% probability level. Selected bond lengths (Å) and angles
(deg): Y-O3, 2.1140(11); Y-O1, 2.4038(11); Y-O2, 2.5040(11);
Y-N, 2.5345(14); Y-C22, 2.4453(19); Y-C31, 2.4557(19); N-Y-
O1, 69.30(4); N-Y-O2, 65.89(4); N-Y-O3, 78.55(4); N-Y-C22,
99.28(6); O3-Y-C22, 94.48(6).
Figure 2. Structural drawing of [(CH3OCH2CH2)2NCH2-C6H2-3,5-
(CMe3)2-2-O]Sc(CH2SiMe2Ph)2 (8a) with thermal ellipsoids at the
50% probability level. Selected bond lengths (Å) and angles
(deg): Sc-O1, 1.9702(10); Sc-O2, 2.3494(11); Sc-O3, 2.3028-
(11); Sc-N, 2.3721(13); Sc-C22, 2.2698(16); Sc-C31, 2.2636(16);
N-Sc-O1, 82.50(4); N-Sc-O2, 71.98(4); N-Sc-O3, 70.16(4);
N-Sc-C22, 99.58(5); O1-Sc-C22, 95.90(5).
Chart 1
via alkane elimination (eq 3). The starting materials, M(THF)2-
(CH2SiMe2Ph)3 (M ) Y, Sc) were expected to give more
crystalline products,17 while M(THF)2(CH2SiMe3)3 were pre-
ferred for ease of byproduct removal. For all compounds (eq
3) metalations occur cleanly with elimination of 1 equiv of
1
SiMe3Ph or SiMe4, on the basis of the H NMR spectrum of
Figure 3. Structural drawing of [(Et2NCH2CH2)2NCH2-C6H2-3,5-
(CMe3)2-2-O]Y(CH2SiMe2Ph)2 (7b), with thermal ellipsoids at the
50% probability level. Selected bond lengths (Å) and angles
(deg): Y-O1, 2.104(4); Y-N1, 2.538(4); Y-N2, 2.832(5); Y-N3,
2.594(5); Y-C28, 2.425(5); Y-C37, 2.430(5); N1-Y-O1, 76.55-
(13); N1-Y-N2, 66.81(14); N1-Y-N3, 71.62(14); N1-Y-C28,
114.41(16); O1-Y-C37, 112.95(16). Only one of the two positions
calculated for the ethyl methyl groups is shown.
the crude reaction mixture. The isolated yields are somewhat
low, due to the high solubility of the products. In general, the
reactions occur more cleanly when the reaction is started at low
temperatures (<-70 °C) and then warmed to room temperature.
Dialkyl complexes 7a,b and 8a,b can be separated from the
alkane byproduct by recrystallization from petroleum ether-
diethyl ether mixtures. On the other hand, when the more volatile
byproduct SiMe4 is formed, the purification is accomplished
by removing the volatile materials under vacuum. All complexes
are air- and water-sensitive.
The reactions of the yttrium and scandium trialkyl complexes
M(THF)2(CH2SiMe2Ph)3 with the ligand (Me2NCH2CH2)2-
NCH2-C6H2-3,5-(CMe3)2-2-OH (6) generate multiple, as yet

Group 3 Dialkyl Complexes
Organometallics, Vol. 26, No. 5, 2007 1181
1
Figure 4. Experimental (left) and simulated (right) variable-temperature H NMR spectra of [(CH3OCH2CH2)2NCH2-C6H2-3,5-(CMe3)2-
2-O]Y(CH2SiMe2Ph)2 (7a), showing the OCH3 (δ 2.94 and 2.8) resonances (toluene-d8, 500 MHz). Best-fit first-order rate constants (k) are
illustrated with the simulated spectra.
unidentified, products according to 1H NMR spectroscopy. One
possible decomposition pathway is the C-H activation of the
methyl groups. A recent report indicates that group III com-
plexes with pendant tertiary amine donors can undergo ligand
C-H activation reactions.21 The authors of this report state that
the rate of this process is dependent on subtle ligand changes.
If the reactions shown in eq 3 are similarly very dependent on
ligand structure, we may reconcile why in some, but not all,
cases the targeted dialkyl product (7b) can be isolated with
pendant amine donors. Reaction of phenol 3 with metal trialkyls
will be discussed in a later section.
Assuming the formation of hexacoordinate metal complexes,
the dialkyl species could present C1 or Cs symmetry (Chart 1).
In order to determine the favored geometry in the solid state as
well as in solution, single-crystal X-ray diffraction studies as
well as variable-temperature 1H NMR spectroscopic studies were
performed. These are discussed in the following sections.
Solid-State Structures of Dialkyl Complexes. The solid-
state structures of 7a,b and 8a were determined by single-crystal
X-ray diffraction studies (Figures 1-3). In all three cases, a
six-coordinate, distorted-octahedral, monomeric, C1-symmetric
structure is displayed. One alkyl group is trans to the linking
(axial) nitrogen and the other trans to a pendant neutral donor,
rather than a phenolate oxygen, possibly to avoid greater trans
influence in the latter case. The metal-ether oxygen distances
are larger that the metal-phenolate oxygen distances by 0.3-
0.4 Å. Moreover, the M-O bonds to the ethers trans to the
alkyls are longer than to the ethers trans to the phenolates by
0.05-0.1 Å, as anticipated for a greater trans influence for the
alkyls. A similar trend is observed for the pendant amines, with
a difference of more than 0.2 Å between the amine trans to the
alkyl vs the amine trans to the phenolate. An analogous
substantial bond length difference was observed for a related
yttrium dialkyl triaminoamide complex reported recently.21
Solution Structure of Dialkyl Complexes. Despite their C1
1
solid-state structures, the room-temperature (294 K) H NMR
spectra for both 7a and 8a, [(CH3OCH2CH2)2NCH2-C6H2-3,5-
(CMe3)2-2-O]M(CH2SiMe2Ph)2 (M ) Y, Sc), in toluene-d8
feature, among other peaks, a singlet corresponding to Si(CH3)2-
Ph, a singlet corresponding to MCH2 (M ) Y, Sc) and a singlet

1182 Organometallics, Vol. 26, No. 5, 2007
Marinescu et al.
Dynamic Processes in 7a, 8a, and 10. In order to determine
exchange rate constants, line-shape analyses were performed
for 7a (Figure 4), 8a, and 10. As shown in Figure 4, increasing
the temperature from 203 to 273 K results in broadening and
coalescence of the OCH3 resonances followed by sharpening
of the resulting coalesced signal. For 7a and 8a, line-shape
analyses were performed only for the ether methyl groups. The
activation parameters for exchange of methoxy groups were
obtained from Eyring plots (Figures 7 and 8) over a temperature
range of greater than 60 K: ∆Hq ) 7.3 ( 0.3 kcal/mol and
∆Sq ) -16.2 ( 1.4 cal/(mol K) for 7a and ∆Hq ) 9.9 ( 0.5
kcal/mol and ∆Sq ) -15.3 ( 1.8 cal/(mol K) for 8a. Compound
10, [(CH3OCH2CH2)2NCH2-C6H2-3,5-(CMe3)2-2-O]Sc(CH2-
SiMe3)2, provides an opportunity to inspect independently the
exchange rates for both the ether methyl groups and the silicon
methyl groups, because both display only two singlets in the
slow exchange limit. The activation parameters determined for
the exchange of the ether methyl groups are ∆Hq ) 10.6 ( 0.4
kcal/mol and ∆Sq ) -12.3 ( 1.4 cal/(mol K), and those for
the silicon methyl groups are ∆Hq ) 11.1 ( 0.7 kcal/mol and
∆Sq ) -10.4 ( 2.3 cal/(mol K), values that are not significantly
different and indicative of a single process for exchange of both
methoxy and alkyl groups.
The substantially negative values of the entropy of activation
suggest that 7a, 8a, and 10 undergo a nondissociative exchange
process. The proposed mechanism that accommodates the
dynamic NMR behavior involves twisting of the trigonal faces
of the pseudo-octahedron (Scheme 2), resulting in the inter-
conversion of three facial groups via trigonal-prismatic inter-
mediates. This type of mechanism has previously been proposed
for dynamic processes in pseudo-octahedral complexes of
titanium.40
Figure 5. Variable-temperature 1H NMR spectra of [(CH3OCH2-
CH2)2NCH2-C6H2-3,5-(CMe3)2-2-O]Y(CH2SiMe2Ph)2 (7a) showing
the Si(CH3)2Ph peaks (toluene-d8, 500 MHz).
corresponding to OCH3. At temperatures below 203 K, the 1H
NMR spectra feature two singlets corresponding to the OCH3
groups (Figure 4), along with four singlets for Si(CH3)2Ph
(Figure 5) and four doublets for MCH2 (some overlapping).
When the temperature is increased, the peaks corresponding to
the Si(CH3)2Ph groups collapse first into two singlets and then,
at higher temperatures, into one singlet. Similar behavior is
observed for 8b, [(Me3CSCH2CH2)2NCH2-C6H2-3,5-(CMe3)2-
2-O]Sc(CH2SiMe2Ph)2 (Figure 6). For compounds 9 and 10,
[(CH3OCH2CH2)2NCH2-C6H2-3,5-(CMe3)2-2-O]M(CH2-
SiMe3)2 (M ) Y, Sc), with a different alkyl, the methyls bound
to each silicon are equivalent and give rise to only two singlets
at low temperature and one singlet at high temperature. At room
temperature, compound 7b, [(Et2NCH2CH2)2NCH2-C6H2-3,5-
(CMe3)2-2-O]Y(CH2SiMe2Ph)2, displays only one set of peaks
for the metal-bound alkyl groups; moreover, the four ethyl
groups display only one broad triplet/quartet combination.
Given the small number of peaks corresponding to the [CH2-
SiMe2Ph] groups, the room-temperature spectra for 7a and 8a
are consistent neither with Cs nor with C1 structures (Chart 1).
For the Cs structure, the two metal alkyl groups are chemically
different and distinct peaks are expected in the 1H NMR
spectrastwo singlets for the Si(CH3)2Ph protons and two
singlets for MCH2 (M ) Y, Sc). On the other hand, for the C1
structure, the silicon methyls are diastereotopic and should
display four singlets. Furthermore, the Sc- or Y-bound meth-
ylene groups present diastereotopic hydrogens and should
display four doublets in the 1H NMR spectrum. The ether
methyls are chemically different and should display two distinct
singlets. Hence, the variable-temperature 1H NMR spectroscopy
data are indicative of an exchange process. The 1H NMR spectra
at low temperatures (vide infra) do indicate that the lowest
energy structure is that having C1 symmetry, as established for
Two reaction pathways are required from the ground-state
structure (A): one involves rotation around the pseudo-C3 axis
passing through the [R1R2O] and [NL2L1] trigonal faces, and a
second involves rotation around the pseudo-C3 axis passing
through the [R1R2L2] and [NOL1] trigonal faces followed by
rotation around the pseudo-C3 axis passing through the [R1L1R2]
and [NL2O] trigonal faces. Other possible pseudo-C3 rotations
would necessarily change the nature of the tetradentate [ONL1L2]
coordination (N axial with O, L1 and L2 cis to N) and, thus,
need not be considered for nondissociative processes. Twisting
of the [R1R2O] face (red-arrow pathway) leads to the C1
structure C via the trigonal-prismatic intermediate B. This
process affords simultaneous exchange of the ligands L1 and
L2 together with alkyls R1 and R2. However, this process does
not exchange the diastereotopic groups of the alkyls (CH2 and
Si(CH3)2Ph). A pathway that interconverts these diastereotopic
protons involves twisting of the [R1R2L2] face (green-arrow
pathway) to access the Cs structure E, which, upon subsequent
twisting of the [R1L1R2] face (blue-arrow pathway), gives G
(an enantiomer of A). This process also interchanges L1 and L2
but does not change the chemical environment of the alkyl
groups R1 and R2. Hence, either pathway can interconvert the
neutral ligands L1 and L2, but neither one alone can exchange
both the metal alkyl groups and the diastereotopic groups on
each of the metal alkyls.
Significantly, for 7a, [(CH3OCH2CH2)2NCH2-C6H2-3,5-
(CMe3)2-2-O]Y(CH2SiMe2Ph)2, exchange of [Si(CH3)2Ph] meth-
yl hydrogens occurs in two stages; first the four singlets collapse
into two singlets and, at higher temperatures, into one singlet
(Figure 5). This stepwise behavior suggests that the exchange
involves two processes with different activation barriers. The
1
the solid-state structures. The H NMR spectroscopy data for
8b, 9, and 10 indicate the presence of a similar exchange process
and a C1-symmetric ground-state structure.
(40) Fay, R. C.; Lindmark, A. F. J. Am. Chem. Soc. 1983, 105, 2118.

Group 3 Dialkyl Complexes
Organometallics, Vol. 26, No. 5, 2007 1183
1
Figure 6. Selected aliphatic region of the H NMR spectra of [(Me3CSCH2CH2)2NCH2-C6H2-3,5-(CMe3)2-2-O]Sc(CH2SiMe2Ph)2 (8b) at
different temperatures (toluene-d8, 300 MHz).
that the stepwise exchange of diastereotopic [Si(CH3)2Ph] groups
gives rise to a similar situation: four singlets in slow exchange,
followed by rapid alkyl exchange with slow diastereotopic
[Si(CH3)a(CH3)bPh] methyl exchange at intermediate temper-
atures giving rise to two singlets, and rapid alkyl and diaste-
reotopic methyl exchange at high temperatures exhibiting one
singlet. We attempted to simulate the observed spectra using
two independent exchange rate constants at each temperature
for the four peaks due to the Si(CH3)2Ph group of 7a, but even
for this relatively simple case we have been unsuccessful. Thus,
we can conclude that the interconversion A S C is sometimes
faster than A S E S G (this is the case for 8b), but we are
unable to quantify the differences in rates and barriers.
The activation enthalpy for the yttrium complex 7a is smaller
than that for the scandium analogue 8a. Assuming that bond
strengths are affected in a similar fashion along the reaction
coordinate, it is likely that the larger yttrium center renders the
Figure 7. Eyring plot for [(CH3OCH2CH2)2NCH2-C6H2-3,5-
complex more sterically open, facilitating access to the strained
(CMe3)2-2-O]Y(CH2SiMe2Ph)2 (7a) (toluene-d8, 500 MHz).
trigonal-prismatic intermediates. Supporting this hypothesis,
increased steric bulk around the metal center has been shown
to increase the activation enthalpy for a series of titanium/acac
complexes that exchange via a similar mechanism.40
Interestingly, the room-temperature 1H NMR spectrum of 7b,
[(Et2NCH2CH2)2NCH2-C6H2-3,5-(CMe3)2-2-O]Y(CH2SiMe2-
Ph)2, shows only one set of peaks for the ethyl groups,
suggesting fast exchange of ethyls bound to the same nitrogen.
The mechanism proposed here for the complexes with ether
donors (Scheme 2) cannot account for this exchange. However,
a mechanism involving amine dissociation followed by inversion
and recoordination would provide a pathway for exchanging
the ethyl groups on each pendant nitrogen donor. This type of
mechanism has been proposed recently for a related yttrium
dialkyl triaminoamide complex.21 Furthermore, a related yttrium
complex supported by the same ligand but with bulkier amide
ligands (N(SiMe2H)2 instead of CH2SiMe2Ph) has been reported
to coordinate only via one of the two pendant amines, suggesting
that the amine coordination is not very strong.38
Figure 8. Eyring plot for [(CH3OCH2CH2)2NCH2-C6H2-3,5-
(CMe3)2-2-O]Sc(CH2SiMe2Ph)2 (8a) (toluene-d8, 300 MHz).
Metalation of (C5H5N-2-CH2)2NCH2-C6H2-3,5-(CMe3)2-2-
OH (3) with a Scandium Trialkyl. Reaction of the scandium
diastereotopic methylene hydrogens for these alkyls (both CH2-
SiMe3 and CH2SiMe2Ph derivatives) appear to also exhibit
stepwise exchange behavior that in some cases changes from
four doublets to a singlet by way of two doublets, although in
most cases it is not possible to unambiguously identify these
small signals at intermediate temperatures. The 263 K spectrum
for 8b [(Me3CSCH2CH2)2NCH2-C6H2-3,5-(CMe3)2-2-O]Sc(CH2-
SiMe2Ph)2 (Figure 6) does clearly show one set of these two
resonances as an AB quartet indicative of the alkyls being in
rapid exchange, but the individual diastereotopic hydrogens on
the two methylenes Sc(CHaHb)2SiMe2Ph are in slow exchange
and thus are still coupled to each other.41 We infer, therefore,
trialkyl Sc(THF)2(CH2SiMe2Ph)3 with the ligand (C5H5N-2-
CH2)2NCH2-C6H2-3,5-(CMe3)2-2-OH (3) in diethyl ether, at
room temperature, generates first a green solution that, within
(41) Cationic Zr species generated from the ligand precursor 1 were
reported, at room temperature, to display 1H NMR spectroscopy charac-
teristics related to the phenomena reported heresthe ether CH3 groups show
only one singlet, while the metal-bound benzyl group shows two doublets
for the methylene groups.33 This is consistent both with the Cs structure
proposed by Kol et al., with the two benzyls reflecting into each other via
the mirror plane, and with a dynamic process which, in this case, exchanges
the ether groups (via B), but not the diastereotopic hydrogens (via D-F).
A variable-temperature 1H NMR spectroscopy study would distinguish
between the two possibilities.

1184 Organometallics, Vol. 26, No. 5, 2007
Marinescu et al.
Scheme 2
Scheme 3
not consistent with the observed coupling constant. The THF
peak is broadened and shifted, indicating ether coordination.
These data are consistent with the decomposition of 11 via C-H
activation of a methylene group linking a pyridine to the central
nitrogen to give 12 with loss of another 1 equiv of silane.
Confirmation that the activated methylene position does link a
pyridine arm was made by quenching a THF solution of 12
with methanol-d4 and checking for deuterium incorporation (2H
NMR spectroscopy) in the phenol found in the resulting mixture.
A similar activation of a ligand benzylic C-H bond was
reported as well for a tantalum system supported by a related
tetradentate diphenolate ligand.29 However, a scandium alkyl
complex supported by a dianionic ligand displaying the same
pyridine arm as that here was stable enough for isolation at
room temperature.15 THF may be displaced by addition of
pyridine to afford 13 (Scheme 3), but not by softer donors such
as ethylene, 2-butyne, and trimethylphosphine.42b Compound
12 is thermally unstable, decomposing in solution even at -35
°C over a few days.
seconds, becomes deep red. The reaction occurs cleanly; only
one set of peaks corresponding to the multidentate ligand is
observed in the 1H NMR spectrum at room temperature after 1
h. The reaction was repeated at low temperature (-45 °C) and
the outcome investigated using 1H, 1H-1H COSY, 13C, DEPT,
and HETCOR NMR spectroscopic studies. At -45 °C, the 1H
NMR spectrum shows only one set of peaks corresponding to
the multidentate ligand, along with four singlets corresponding
to Si(CH3)2Ph and four doublets corresponding to ScCH2. The
benzylic hydrogen atoms, [(C5H5N-2-CH2)2NCH2-C6H2-3,5-
(CMe3)2-2-O], show six doublets (two distinct doublets and four
overlapped) that correlate with three CH2 peaks (DEPT study)
with chemical shifts between δ 60 and 63 ppm. One equivalent
of PhSiMe3, along with free THF released from the starting
material, is observed as well. These data are consistent with
the formation of dialkyl species 11 having a C1 symmetry
structure at -45 °C (Scheme 3), similar to the structures above.
The reaction mixture generated at -45 °C was warmed to
room temperature and, after 1 h, was interrogated by NMR
spectroscopy. The formation of an additional 1 equiv of PhSiMe3
was observed. The 1H NMR spectrum shows two singlets
corresponding to Si(CH3)2Ph and two doublets corresponding
to ScCH2. In the benzylic region, four doublets and one singlet
are observed. This singlet correlates with a methine carbon at
100.9 ppm, as determined by a HETCOR experiment. The 1JC-H
1
Transformation of 11 into 12 was monitored by H NMR
spectroscopy in toluene-d8 at 0 °C. Both the disappearance of
11 and the formation of 12 were followed over time by
measuring the integrals for selected, baseline-separated proton
peaks. As expected, these processes were found to follow first-
order kinetics with similar rate constants (Figure 9 in the
Supporting Information; k ) [2.8(3)] × 10-4 s-1 for the decay
of 11 and k ) [2.3(1)] × 10-4 s-1 for the formation of 12).
Attempts to cleanly metalate 3 with Y(THF)2(CH2SiMe2Ph)3
have been unsuccessful. NMR-scale reactions of the yttrium
trialkyl complex and compound 3, in toluene-d8, when moni-
1
tored by H NMR spectroscopy at -35 °C, reveal multiple,
unidentified products.
Generation of Cationic Alkyls for Ethylene Polymeriza-
tions. Generation and characterization of cationic monoalkyl
(42) (a) Silverstein, R. M.; Webster, F. X. Spectroscopic Identification
of Organic Compounds, 6th ed; 1998. (b) Dialkyl complexes 7a and 8a do
not show a reaction upon treatment with pyridine, suggesting that the
intramolecular ether donors are preferred to the added base. While no
reactivity was observed toward ethylene, 7b reacts with acetonitrile and
diphenylacetylene to afford multiple unidentified products.
value of 170 Hz is indicative of an sp2 hybridized carbon.42a
tautomeric binding mode through the carbon is possible, but
A

Group 3 Dialkyl Complexes
Organometallics, Vol. 26, No. 5, 2007 1185
Table 1. Crystal and Refinement Data for Complexes 7a,b
and 8a
atm) led to the isolation of small amounts of polymer upon
workup with MeOH/HCl. The polymerization was repeated as
above, but with addition of excess MAO, as well as with MAO
as sole activator. Only minor changes in polymerization activity
arose on changing the nature of activator. Polymerization trials
with dialkyls 7a,b, 8a,b, 9, and 10 were performed upon
activation with excess MAO (500 equiv), under 5 bar of
ethylene, using 3.3 × 10-4 M concentrations of precatalyst.
Under these conditions, all complexes serve as sluggish po-
lymerization precatalysts, displaying productivities between 0.5
and 2.5 kg of PE/(mol M bar) (M ) Y, Sc), after 1 h reaction
times. The very low polymerization activities in these systems
with pendant, unconstrained, donor groups may relate to the
results reported by Hessen et al., who studied tetradentate
monoanionic ligands based on one amide donor and three amine
donors.21 A system competent for ethylene polymerization was
obtained when the neutral donors were linked in a macrocycle
(1,4,7-triazacyclononane), but the polymerization activity de-
creases 20-fold when the NN macrocyclic linkage is removed.
This reduction in activity was attributed to a reduced stability
of the complexes with “open” triamine ligands, and, indeed,
that may well be the case here.
7a
7b
8a
empirical formula C39H62NO3-
Si2Y
C45H76N3O-
Si2Y
C39H62NO3-
Si2Sc
formula wt
T (K)
737.99
98(2)
820.18
100(2)
694.04
100(2)
a, Å
b, Å
c, Å
11.3640(4)
14.2999(5)
25.4993(9)
18.3292(16)
10.1929(8)
28.733(2)
12.8434(5)
18.7067(7)
33.6484(12)
R, deg
â, deg
γ, deg
V, Å3
100.2310(10)
103.571(2)
4077.9(2)
4
5218.2(8)
4
8084.3(5)
8
Z
cryst syst
space group
d
monoclinic
P21/n
1.202
monoclinic
P21/c
1.044
orthorhombic
Pbca
1.140
calcd, g/cm3
θ range, deg
µ, mm-1
abs cor
1.62-28.41
1.46-22.49
1.99-28.50
1.523
1.194
0.276
none
none
none
GOF
1.446
2.059
2.272
R1,a wR2b
(I > 2σ(I))
0.0323, 0.0535 0.0640, 0.1126 0.0447, 0.0693
2
2
a R1 ) ∑||Fo| - |Fc||/∑|Fo|. b wR2 ) [∑[w(Fo2 - Fc )2]/∑[w(Fo )2]1/2
.
Conclusions
yttrium species was attempted. In order to allow character-
1
ization by H NMR spectroscopy, a stoichiometric activator,
Yttrium and scandium dialkyl complexes supported by readily
available tetradentate, monoanionic phenolate ligands can be
prepared by alkane elimination from trialkyl precursors. H
[PhNHMe2]+[B(C6F5)4]-, was utilized (eq 4). NMR-scale reac-
1
NMR spectroscopy studies show fluxional behavior in solution.
C1-Symmetric structures are favored for all alkyls in the solid
state as well as in solution. The dynamic behavior of dialkyl
complexes with pendant ether donors was investigated by
1
variable-temperature H NMR spectroscopy, and the fluxional
rates and activation parameters were determined by line-shape
analysis. A mechanism involving nondissociative ligand ex-
change was found, likely via trigonal-prismatic intermediates
generated via twists of pseudooctahedral trigonal faces contain-
ing both alkyls and another donor ligand. The ligand with
pendant pyridine donors (C5H4N-2-CH2)2NCH2-C6H2-3,5-
(CMe3)2-2-OH (3) presents a different reactivity. Low-temper-
ature NMR studies indicate intermediate formation of dialkyl
species at -45 °C, which decomposes cleanly by activation of
a C-H bond of a methylene connecting the pyridine to the
nitrogen linker position at 0 °C. The yttrium dialkyl complexes
7a and 9 react quite cleanly (1H NMR spectroscopy), at low
temperatures with 1 equiv of [PhNHMe2]+[B(C6F5)4]- in
chlorobenzene-d5 to generate 1 equiv of alkane and, presumably,
a cationic monoalkyl species. Solutions of these cations
slowly polymerize ethylene. Compounds 7-10 also
polymerize ethylene upon activation with MAO, but with very
low activities.
tions of [(CH3OCH2CH2)2NCH2-C6H2-3,5-(CMe3)2-2-O]YR2
(R ) CH2SiMe2Ph (7a), CH2SiMe3 (9)) with 1 equiv of
anilinium salt in chlorobenzene-d5 occur with formation of a
major new species, but not cleanly (see the Supporting Informa-
tion for the 1H NMR spectrum) at -35 °C. For 9, formation of
SiMe4 is observed, along with one major set of peaks corre-
sponding to the phenoxide C(CH3)3 groups. The metal-bound
alkyl group displays two doublets for YCH2, while the ether
groups display two singlets for the OCH3 protons. Upon
warming to room temperature, the doublets for the metal-bound
methylene group collapse into a singlet, as do the two peaks
for the ether methyl groups. These observations are consistent
with the protonation of one of the alkyl groups to generate a
C1-symmetric monoalkyl species (15) at -35 °C. The N(CH3)2
resonances are shifted from those of free dimethylaniline,
suggesting coordination to the metal center. Compound 15 seems
to be involved in a dynamic process that exchanges the ether
groups and the diastereotopic YCH2 protons. The cationic
species decomposes within hours at room temperature. Slow
consumption of ethylene (7.5 equiv in 7 h) was observed with
15 generated at low temperature.
Experimental Section
General Considerations and Instrumentation. All air- and
moisture-sensitive compounds were manipulated using standard
vacuum line, Schlenk, or cannula techniques or in a drybox under
a nitrogen atmosphere. Solvents for air- and moisture-sensitive
reactions were dried over sodium benzophenone ketyl or by the
method of Grubbs.43 Benzene-d6 was purchased from Cambridge
Isotopes and distilled from sodium benzophenone ketyl. Chloro-
form-d and chlorobenzene-d5 were purchased from Cambridge
Isotopes and distilled from calcium hydride. 2-Hydroxy-3,5-di-tert-
The dialkyl complexes were investigated for ethylene po-
lymerization activity more generally. Medium-scale polymeriza-
tions with 7a or 9 and activation with [PhNHMe2]+[B(C6F5)4]-
in a closed system with excess ethylene (initial pressure of 4
(43) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;
Timmers, F. J. Organometallics 1996, 15, 1518.

1186 Organometallics, Vol. 26, No. 5, 2007
Marinescu et al.
butylbenzylbromide,44 LiCH2SiMe2Ph,17 andM(THF)2(CH2SiMe2Ph)317
reaction mixture was stirred at room temperature overnight. The
volatile materials were removed via rotary evaporation. A solution
of NaOH was added to the reaction mixture, and the organic phase
was extracted with CH2Cl2. The organic phase was dried over
anhydrous MgSO4. The volatile materials were removed via rotary
evaporation to yield a golden oil (1.77 g, 4.2 mmol, 84%). HRMS
(M ) Sc, Y) were prepared according to the literature procedures.
1
Other materials were used as received. H and 13C NMR spectra
were recorded on Varian Mercury 300 and Varian INOVA-500
spectrometers at room temperature, unless otherwise indicated.
1
Chemical shifts for H and 13C data are reported with respect to
1
(m/z): calcd, 418.2858 (MH+); found, 418.2852. H NMR (500
internal solvent: 7.16 and 128.38 (t) ppm (C6D6); 7.27 and 77.23
(t) ppm (CDCl3). 1H NMR data recorded in C6D5Cl were referenced
with respect to the most upfield peak for Ph2CH2 (3.8 ppm) or with
respect to the alkane byproduct, Si(CH3)4 (0 ppm), where appropri-
ate. 2H NMR spectra were recorded on a Varian INOVA-500
spectrometer, the chemical shifts being reported with respect to an
external D2O reference (4.8 ppm).
MHz, C6D6; δ): 1.36 (s, 9H, C(CH3)3), 1.77 (s, 9H, C(CH3)3), 3.68
(s, 2H, aryl CH2N), 3.82 (s, 4H, NCH2C5H4N), 6.52-6.56 (m, 2H,
aryl H), 6.95-7.01 (m, 3H, aryl H), 7.12 (d, 2H, aryl H), 7.53 (d,
J ) 2.4 Hz, 1H, aryl H), 8.41-8.44 (m, 2H, aryl H), 11.07 (s, 1H,
OH). 1H NMR (300 MHz, CDCl3; δ): 1.28 (s, 9H, C(CH3)3), 1.48
(s, 9H, C(CH3)3), 3.82 (s, 2H, aryl CH2N), 3.89 (s, 4H, NCH2C5H4N),
6.90 (d, J ) 2.4 Hz, 1H, aryl H), 7.13-7.19 (m, 2H, aryl H), 7.22
(d, J ) 2.4 Hz, 1H, aryl H), 7.39 (d, 2H, aryl H), 7.60-7.67 (m,
Synthesis of (MeOCH2CH2)2NCH2-C6H2-3,5-(CMe3)2-2-OH
(1). A methanol (10 mL) solution of 2,4-di-tert-butylphenol (2 g,
9.7 mmol, 1 equiv), bis(2-methoxyethyl)amine (1.3 g, 9.7 mmol, 1
equiv), and formaldehyde (3.5 g of a 37% aqueous solution, 38.9
mmol, 4 equiv) was refluxed. After the mixture was cooled to room
temperature, volatile material was removed via rotary evaporation.
The resulting pale yellow oil was placed under high vacuum for
6 h to remove remaining excess amine. The resulting material was
1
2H, aryl H), 8.57 (m, 2H, aryl H), 10.66 (s, 1H, OH). H NMR
(300 MHz, CD2Cl2; δ): 1.26 (s, 9H, C(CH3)3), 1.44 (s, 9H,
C(CH3)3), 3.78 (s, 2H, aryl CH2N), 3.83 (s, 4H, NCH2C5H4N), 6.90
(d, 1H, aryl H), 7.13-7.21 (m, 3H, aryl H), 7.33 (d, 2H, aryl H),
7.63 (td, 2H, aryl H), 8.54 (m, 2H, aryl H), 10.67 (s, 1H, OH). 13
C
NMR (75 MHz, CDCl3; δ): 29.8 (C(CH3)3), 31.9 (C(CH3)3), 34.3
(CMe3), 35.2 (CMe3), 58.4 (NCH2), 59.7 (NCH2), 121.8 (aryl),
122.4 (aryl-H), 123.3 (aryl-H), 123.8 (aryl-H), 124.7 (aryl-
H), 135.7 (aryl), 136.8 (aryl-H), 140.5 (aryl), 149.2 (aryl-H),
154.0 (aryl), 158.3 (aryl).
1
pure by H NMR spectroscopy (3.08 g, 8.7 mmol, 90%). HRMS
(m/z): calcd, 351.2773 (M+); found, 351.2766. 1H NMR (300 MHz,
C6D6; δ): 1.37 (s, 9H, C(CH3)3), 1.73 (s, 9H, C(CH3)3), 2.60 (t,
4H, J ) 5.7 Hz, NCH2CH2O), 3.21 (t, 4H, J ) 5.7 Hz,
NCH2CH2O), 3.01 (s, 6H, OCH3), 3.63 (s, 2H, aryl CH2), 6.94 (d,
1H, J ) 2.4 Hz, aryl H), 7.51 (d, 1H, J ) 2.4 Hz, aryl H), 10.91
(s, 1H, OH). 1H NMR (300 MHz, CDCl3; δ): 1.29 (s, 9H, C(CH3)3),
1.43 (s, 9H, C(CH3)3), 2.82 (t, 4H, J ) 5.7 Hz, NCH2CH2O),
3.54 (t, 4H, J ) 5.7 Hz, NCH2CH2O), 3.33 (s, 6H, OCH3), 3.85
(s, 2H, aryl CH2), 6.74 (d, 1H, J ) 2.4 Hz, aryl H), 7.21 (d, 1H,
J ) 2.4 Hz, aryl H), 10.59 (br s, 1H, OH). 13C NMR (75 MHz,
CDCl3; δ): 29.8 (C(CH3)3), 31.9 (C(CH3)3), 34.3 (CMe3), 35.0
(CMe3), 53.5 (CH2), 59.0 (OCH3), 59.7 (CH2), 70.6 (CH2), 121.7
(aryl), 123.0 (aryl-H), 123.7 (aryl-H), 135.8 (aryl), 140.5 (aryl),
154.5 (aryl).
Synthesis of (ClCH2CH2)2NCH2-C6H2-3,5-(CMe3)2-2-OH (4).
A methanol (40 mL) solution of 2,4-di-tert-butylphenol (20.3 g,
98.3 mmol, 1 equiv), diethanolamine (15.5 g, 147.4 mmol, 1.5
equiv), and formaldehyde (31.9 g of a 37% aqueous solution, 393.1
mmol, 4 equiv) was refluxed overnight. After the mixture was
cooled to room temperature, the volatile material was removed via
rotary evaporation. The oily residue was dissolved in 200 mL of
diethyl ether and treated with 14 mL of concentrated hydrochloric
acid (37%). Abundant precipitation of a white solid was observed.
The product was collected on the sintered-glass funnel and washed
with diethyl ether and water. The solid prepared by the above
procedure was dissolved in CH2Cl2. Thionyl chloride (46.5 mL,
75.8 g, 637.5 mmol, 6.5 equiv) was added via volumetric pipet,
and the reaction mixture was stirred overnight. A 10% solution of
KOH was added to the reaction mixture until basic pH. The organic
phase was extracted with CH2Cl2 (3 × 400 mL). The organic phase
was dried over anhydrous MgSO4. The volatile materials were
removed via rotary evaporation to yield a yellowish solid (26.7 g,
74.2 mmol, 75%). HRMS (m/z): calcd, 359.1783 (M+); found,
Synthesis of (Et2NCH2CH2)2NCH2-C6H2-3,5-(CMe3)2-2-OH
(2). A methanol (15 mL) solution of 2,4-di-tert-butylphenol (3.68
g, 17.8 mmol, 1.1 equiv), N,N,N′,N′-tetraethyldiethylenetriamine
(3.9 g, 90% purity, 16.2 mmol, 1 equiv), and formaldehyde (5.3 g
37% aqueous solution, 64.8 mmol, 4 equiv) was refluxed for 14 h.
After the mixture was cooled to room temperature, volatile material
was removed via rotary evaporation. An 8 mL portion of HCl
(36.5%) was added to the reaction mixture. The aqueous phase was
washed with petroleum ether (3 × 50 mL). The aqueous layer was
neutralized with KOH solution and extracted with diethyl ether (3
× 50 mL). The organic phase was dried over anhydrous MgSO4.
The volatile materials were removed via rotary evaporation to yield
1
359.1765. H NMR (300 MHz, C6D6; δ): 1.35 (s, 9H, C(CH3)3),
1.68 (s, 9H, C(CH3)3), 2.28 (t, 4H, J ) 6.6 Hz, NCH2CH2Cl), 2.97
(t, 4H, J ) 6.6 Hz, NCH2CH2Cl), 3.22 (s, 2H, aryl CH2), 6.82 (d,
1H, J ) 2.7 Hz, aryl H), 7.50 (d, 1H, J ) 2.7 Hz, aryl H), 9.61 (s,
1H, OH). 1H NMR (300 MHz, CDCl3; δ): 1.31 (s, 9H, C(CH3)3),
1.45 (s, 9H, C(CH3)3), 3.00 (t, 4H, J ) 6.6 Hz, NCH2CH2Cl), 3.64
(t, 4H, J ) 6.6 Hz, NCH2CH2Cl), 3.87 (s, 2H, aryl CH2), 6.87 (d,
1H, J ) 2.4 Hz, aryl H), 7.28 (d, 1H, J ) 2.4 Hz, aryl H), 9.45 (br
s, 1H, OH). 13C NMR (75 MHz, CDCl3; δ): 29.8 (C(CH3)3), 31.9
(C(CH3)3), 34.4 (CMe3), 35.1 (CMe3), 41.2 (CH2), 55.9 (CH2), 59.5
(CH2), 120.8 (aryl), 123.8 (aryl-H), 123.9 (aryl-H), 136.4 (aryl),
141.3 (aryl), 153.9 (aryl).
1
the desired product as a yellow oil (6.56 g, 15.2 mmol, 94%). H
NMR data in C6D6 match those in the literature report.38 1H NMR
(300 MHz, CDCl3; δ): 0.97 (t, J ) 7.1 Hz, 12H, CH2CH3), 1.27
(s, 9H, C(CH3)3), 1.41 (s, 9H, C(CH3)3), 2.48 (q, J ) 7.1 Hz, 8H,
CH2CH3), 2.57-2.64 (m, 8H, NCH2CH2N), 3.73 (s, 2H, aryl CH2),
6.83 (d, J ) 2.3 Hz, 1H, aryl H), 7.18 (d, J ) 2.3 Hz, 1H, aryl H),
10.56 (br s, 1H, OH). 13C NMR (75 MHz, CDCl3; δ): 11.8
(NCH2CH3), 29.8 (C(CH3)3), 31.9 (C(CH3)3), 34.3 (C(CH3)3), 35.0
(CMe3), 47.4 (NCH2), 50.6 (NCH2), 52.3 (NCH2), 59.0 (NCH2),
122.0 (aryl), 122.9 (aryl-H), 123.9 (aryl-H), 135.7 (aryl), 140.4
(aryl), 154.3 (aryl).
Synthesis of (Me3CSCH2CH2)2NCH2-C6H2-3,5-(CMe3)2-2-OH
(5). A THF (∼50 mL) solution of Me3CSH (3.3 g, 36.7 mmol, 3.3
equiv) was added under an argon atmosphere to a suspension of
sodium hydride (1.3 g, 53.3 mmol, 4.8 equiv) in THF (∼50 mL).
A THF (∼60 mL) solution of 4 (4 g, 11.1 mmol, 1 equiv) was
added to the reaction mixture, and this mixture was stirred overnight.
The reaction mixture was quenched with distilled water (150 mL)
and extracted with diethyl ether (3 × 100 mL). The organic fraction
was dried over MgSO4 and filtered. Volatile materials were removed
via rotary evaporation. The resulting yellow solid was recrystallized
from methanol to give a white solid (2.8 g, 6.1 mmol, 55%). HRMS
Synthesis of (C5H4N-2-CH2)2NCH2-C6H2-3,5-(CMe3)2-2-OH
(3). A THF (20 mL) solution of 2-hydroxy-3,5-di-tert-butylbenzyl
bromide (1.49 g, 5.0 mmol, 1 equiv) was added dropwise to a THF
(20 mL) solution of bis(2-picolyl)amine (0.99 g, 5.0 mmol, 1 equiv)
and N,N-diisopropylethylamine (0.62 g, 5.0 mmol, 1 equiv). The
(44) Sokolowski, A.; Muller, J.; Weyhermuller, T.; Schnepf, R.; Hilde-
brandt, P.; Hildenbrand, K.; Bothe, E.; Wieghardt, K. J. Am. Chem. Soc.
1997, 119, 8889-8900.

Group 3 Dialkyl Complexes
Organometallics, Vol. 26, No. 5, 2007 1187
(m/z): calcd, 466.3177 ([MH+] - H2); found, 466.3161. 1H NMR
(300 MHz, C6D6; δ): 1.13 (s, 18H, SC(CH3)3), 1.36 (s, 9H, aryl
C(CH3)3), 1.70 (s, 9H, aryl C(CH3)3), 2.46-2.61 (m, 8H,
NCH2CH2S), 3.43 (s, 2H, aryl CH2), 6.88 (d, J ) 2.4 Hz, 1H, aryl
H), 7.48 (d, J ) 2.4 Hz, 1H, aryl H), 10.39 (s, 1H, OH). 1H NMR
(300 MHz, CDCl3; δ): 1.26 (s, 18H, SC(CH3)3), 1.28 (s, 9H, aryl
C(CH3)3), 1.43 (s, 9H, aryl C(CH3)3), 2.62-2.82 (m, 8H,
NCH2CH2S), 3.80 (s, 2H, aryl CH2), 6.84 (d, J ) 2.6 Hz, 1H, aryl
H), 7.22 (d, J ) 2.6 Hz, 1H, aryl H), 10.20 (br s, 1H, OH). 13C
NMR (75 MHz, CDCl3; δ): 25.8 (CH2), 29.8 (C(CH3)3), 31.2
(C(CH3)3), 31.9 (C(CH3)3), 34.3 (CMe3), 35.0 (CMe3), 42.5 (CMe3),
54.7 (CH2), 59.3 (CH2), 121.4 (aryl), 123.3 (aryl-H), 123.7 (aryl-
H), 136.0 (aryl), 141.0 (aryl), 154.2 (aryl).
C(CH3)3), 1.39, 2.24, 2.33, 2.60 (br m, 8H, NCH2CH2O), 3.24 (br
s, 2H, aryl CH2), 2.94 (s, 6H, OCH3), 6.86 (d, 1H, J ) 2.4 Hz,
aryl H), 7.59 (d, 1H, J ) 2.4 Hz, aryl H), 7.23 (t, 2H, p-Ph H),
7.31 (t, 4H, m-Ph H), 7.88 (d, 4H, o-Ph H). 13C NMR (75 MHz,
C6D6; δ): 3.5 (s, Si(CH3)2), 27.6 (d, YCH2, 1JYC ) 39.8 Hz), 30.6
(C(CH3)3), 32.6 (C(CH3)3), 34.6 (CMe3), 36.0 (CMe3), 52.6, 61.3,
63.6, 72.0 (OCH3, aryl CH2, NCH2CH2O), 123.7, 125.1, 125.9,
2
127.9, 128.0, 134.3, 136.8, 137.5, 148.3 (aryls), 162.2 (d, JYC
)
3.1 Hz, COY). 1H NMR (500 MHz, C6D5CD3, -75 °C; δ): -0.51
(br app d, 1H, YCH2), -0.35 (br app t, 2H, YCH2), -0.24 (br app
d, 1H, YCH2), 0.63 (s, 3H, SiCH3), 0.67 (s, 3H, SiCH3), 0.75 (s,
3H, SiCH3), 0.95 (s, 3H, SiCH3), 1.51 (s, 9H, C(CH3)3), 1.92 (s,
9H, C(CH3)3), 1.06, 1.37, 1.74, 2.20, 2.36, 2.47, 2.70 (m, 9H,
NCH2CH2O and aryl CH2), 2.80 (br s, 3H, OCH3), 2.94 (br s, 3H,
OCH3), 3.84 (br app d, 1H, aryl CH2), 6.92 (s, 1H, aryl H), 7.23
(br s, 4H, aryl H), 7.40 (br s, 2H, aryl H), 7.62 (s, 1H, aryl H),
7.73 (br s, 2H, aryl H), 8.00 (br s, 2H, aryl H).
Synthesis of (Me2NCH2CH2)2NCH2-C6H2-3,5-(CMe3)2-2-OH
(6). Compound 4 (4 g, 11.2 mmol, 1 equiv) and lithium dimethy-
lamide (2.9 g, 56.2 mmol, 5 equiv) were placed in a Schlenk tube,
in the drybox. THF (∼50 mL) was vacuum-transferred over the
starting materials. The reaction mixture was warmed to room
temperature and stirred overnight. The reaction mixture was then
quenched with water and extracted with diethyl ether. The organic
fraction was dried over MgSO4 and filtered. Volatile materials were
removed via rotary evaporation. The resulting oil consists of three
species. A diethyl ether solution of the product mixture was acidified
with hydrochloric acid. The aqueous layer was washed with diethyl
ether and then basified with sodium hydroxide and extracted with
diethyl ether. The organic fraction was dried over MgSO4 and
filtered, and then the volatile materials were removed via rotary
evaporation. The resulting material consists of a mixture of only
two species. Purification by column chromatography with ethyl
acetate as eluent provided pure product (0.4 g, 0.9 mmol, 8%).
Because this phenol did not give clean metalation reactions, no
optimization was attempted. HRMS (m/z): calcd, 332.2828 (M -
Synthesis of [(Et2NCH2CH2)2NCH2-C6H2-3,5-(CMe3)2-2-O]Y-
(CH2SiMe2Ph)2 (7b). Recrystallization from petroleum ether,
followed by collection on a sintered-glass funnel and washing with
cold petroleum ether, provides the desired product as a white solid
(32% yield) carrying only traces of alkane residue. Anal. Calcd
for C45H76ON3Si2Y: C, 65.90; H, 9.34; N, 5.12. Found: C, 66.20;
H, 8.85; N, 5.49. 1H NMR (300 MHz, C6D6, 40 °C; δ): -0.21 (d,
2JYH ) 2.7 Hz, 4H, YCH2), 0.57 (s, 12H, Si(CH3)2), 0.68 (t, 12H,
NCH2CH3), 1.43 (s, 9H, C(CH3)3), 1.81 (s, 9H, C(CH3)3), 2.36 (q,
8H, NCH2CH3), 1.20-1.32, 1.88-2.10, 2.14-2.22 (m, 8H,
NCH2CH2N), 3.34 (br s, 2H, aryl CH2), 6.95 (d, J ) 2.6 Hz, 1H,
aryl H), 7.58 (d, J ) 2.6 Hz, 1H, aryl H), 7.18-7.30 (m, 6H, p-Ph
H and m-Ph H), 7.80 (d, 4H, o-Ph H). 13C NMR (75 MHz, C6D6,
1
40 °C; δ): 3.4 (Si(CH3)2), 9.7 (NCH2CH3), 31.4 (d, JYC ) 41.9
Hz, YCH2), 31.0 (C(CH3)3), 32.5 (C(CH3)3), 34.6 (CMe3), 36.1
(CMe3), 46.4 (NCH2), 49.3 (NCH2), 51.0 (NCH2), 61.4 (NCH2),
123.4, 125.1, 125.7, 127.9, 128.0, 134.3, 137.3, 138.0, 147.9 (aryls),
1
[HNMe2]); found, 332.2818. H NMR (300 MHz, C6D6; δ): 1.39
(s, 9H, C(CH3)3), 1.75 (s, 9H, C(CH3)3), 1.86 (s, 12H, NCH3), 1.96
(t, 4H, J ) 5.7 Hz, NCH2CH2N), 2.24 (t, 4H, J ) 5.7 Hz,
NCH2CH2N), 3.59 (s, 2H, aryl CH2), 6.93 (d, 1H, J ) 2.4 Hz, aryl
2
1
161.5 (d, JYC ) 3.3 Hz, COY). H NMR (300 MHz, C6D5CD3,
-75 °C, selected peaks; δ): -0.52 (br app d, 1H, YCH2), -0.33
(br app d, 1H, YCH2), -0.13 (br app d, 1H, YCH2), 0.10 (br app
d, 1H, YCH2), 1.50 (s, 9H, C(CH3)3), 1.95 (s, 9H, C(CH3)3).
1
H), 7.52 (d, 1H, J ) 2.4 Hz, aryl H), 11.61 (br s, 1H, OH). H
NMR (300 MHz, CDCl3; δ): 1.27 (s, 9H, C(CH3)3), 1.41 (s, 9H,
C(CH3)3), 2.18 (s, 12H, NCH3), 2.45 (t, 4H, J ) 5.9 Hz,
NCH2CH2N), 2.65 (t, 4H, J ) 5.9 Hz, NCH2CH2N), 3.73 (s, 2H,
aryl CH2), 6.83 (d, 1H, J ) 2.4 Hz, aryl H), 7.18 (d, 1H, J ) 2.4
Hz, aryl H), 10.51 (br s, 1H, OH). 13C NMR (75 MHz, CDCl3; δ):
29.8 (C(CH3)3), 31.9 (C(CH3)3), 34.3 (CMe3), 35.0 (CMe3), 45.6
(NCH3), 46.1 (NCH2), 53.6 (NCH2), 58.4 (NCH2), 122.3 (aryl),
122.9 (aryl-H), 123.3 (aryl-H), 135.9 (aryl), 140.4 (aryl),
155.0 (aryl).
Synthesis of [(MeOCH2CH2)2NCH2-C6H2-3,5-(CMe3)2-2-O]-
Sc(CH2SiMe2Ph)2 (8a). Recrystallization from diethyl ether, fol-
lowed by collection on a sintered-glass funnel and washing with
cold diethyl ether, provides the desired product as a white solid
(26% yield) carrying only traces of alkane byproduct. Anal. Calcd
for C39H62NO3Si2Sc: C, 67.49; H, 9.00; N, 2.02. Found: C, 67.81;
H, 8.66; N, 2.31. 1H NMR (300 MHz, C6D6, 55 °C; δ): -0.03 (s,
4H, ScCH2), 0.59 (s, 12H, Si(CH3)2), 1.40 (s, 9H, C(CH3)3), 1.81
(s, 9H, C(CH3)3), 1.43-1.54, 2.33-2.59, 2.72-2.80, 3.21-3.44
(m, 10H, NCH2CH2O and aryl CH2), 3.07 (s, 6H, OCH3), 6.83 (d,
J ) 2.4 Hz, 1H, aryl H), 7.56 (d, J ) 2.4 Hz, 1H, aryl H), 7.17-
7.24 (m, 2H, p-Ph H), 7.25-7.32 (m, 4H, Ph H), 7.82 (m, 4H, Ph
H). 13C NMR (75 MHz, C6D6, 55 °C; δ): 3.1 (Si(CH3)2), 30.7
(ScCH2), 30.8 (C(CH3)3), 32.5 (C(CH3)3), 34.6 (CMe3), 36.0
(CMe3), 53.4 (br s, OCH3), 61.9 (CH2), 64.1 (CH2), 71.9 (CH2),
123.9, 124.9, 125.3, 127.9, 128.0, 134.4, 136.7, 138.2, 148.0 (aryls),
Synthesis of [(LCH2CH2)2NCH2-C6H2-3,5-(CMe3)2-2-O]M-
(CH2SiMe2Ph)2 (M ) Y, Sc; L ) OMe, NEt2, SCMe3). In a
typical procedure, a THF (5 mL) solution of phenol (1 equiv) was
added dropwise to an in situ generated THF (5 mL) solution of
M(THF)2(CH2SiMe2C6H5)3 (1 equiv) and stirred for 4 h at room
temperature. 1H NMR spectra of the crude reaction mixtures show
clean formation of the desired yttrium and scandium dialkyl
products along with SiMe3Ph. The volatile materials were removed
under vacuum. Diethyl ether (5 mL) was added, and the mixture
was filtered through Celite to remove insoluble salts. The filtrate
was concentrated under vacuum.
1
161.8 (COSc). H NMR (300 MHz, C6D5CD3, -60 °C, selected
peaks; δ): -0.22 (br app d, 1H, ScCH2), -0.05 (br app d, 1H,
ScCH2), 0.16 (br app d, 1H, ScCH2), 0.70 (br app d, 1H, ScCH2),
0.53 (s, 3H, SiCH3), 0.62 (s, 3H, SiCH3), 0.80 (s, 3H, SiCH3), 0.90
(s, 3H, SiCH3), 1.48 (s, 9H, C(CH3)3), 1.92 (s, 9H, C(CH3)3), 2.80
(s, 3H, OCH3), 3.10 (s, 3H, OCH3).
Synthesis of [(MeOCH2CH2)2NCH2-C6H2-3,5-(CMe3)2-2-O]Y-
(CH2SiMe2Ph)2 (7a). Recrystallization from petroleum ether or
petroleum ether/diethyl ether mixtures, followed by collection on
a sintered-glass funnel and washing with cold petroleum ether,
provided the desired product as a white solid (57% yield) carrying
only traces of alkane impurity. Anal. Calcd for C39H62NO3Si2Y:
C, 63.47; H, 8.47; N, 1.90. Found: C, 64.46; H, 9.01; N, 2.08. 1H
NMR (300 MHz, C6D6; δ): -0.38 (d, 2JYH ) 2.9 Hz, 4H, YCH2),
0.65 (s, 12H, Si(CH3)2), 1.43 (s, 9H, C(CH3)3), 1.82 (s, 9H,
Synthesis of [(Me3CSCH2CH2)2NCH2-C6H2-3,5-(CMe3)2-2-O]-
Sc(CH2SiMe2Ph)2 (8b). Recrystallization from petroleum ether,
followed by collection on a sintered-glass funnel and washing with
cold petroleum ether, provides desired product as a white solid
(16% yield) carrying only traces of alkane residue. Anal. Calcd
for C45H74NOS2Si2Sc: C, 66.70; H, 9.20; N, 1.73. Found: C, 67.70;

1188 Organometallics, Vol. 26, No. 5, 2007
Marinescu et al.
1
H, 8.99; N, 1.76. H NMR (300 MHz, C6D6; δ): 0.49 (br d, J )
(m, 8H, NCH2CH2O), 3.56 (br s, 2H, aryl CH2), 3.19 (s, 6H, OCH3),
6.89 (d, J ) 2.7 Hz, 1H, aryl H), 7.54 (d, J ) 2.7 Hz, 1H, aryl H).
13C NMR (75 MHz, C6D6, 60 °C; δ): 4.7 (Si(CH3)3), 30.7 (ScCH2),
30.9 (C(CH3)3), 32.5 (C(CH3)3), 34.6 (CMe3), 36.0 (CMe3), 53.5
(br s, OCH3), 61.9 (CH2), 64.3 (CH2), 72.0 (CH2), 123.8, 125.0,
12 Hz, 2H, ScCH2), 0.58 (br d, J ) 12 Hz, 2H, ScCH2), 0.62 (s,
6H, Si(CH3)2), 0.64 (s, 6H, Si(CH3)2), 1.01 (s, 18H, SC(CH3)3),
1.40 (s, 9H, C(CH3)3), 1.81 (s, 9H, C(CH3)3), 1.93-2.16, 2.19-
2.32, 2.34-2.47 (m, 8H, NCH2CH2N), 3.17 (br s, 2H, aryl CH2),
6.85 (d, J ) 2.4 Hz, 1H, aryl H), 7.54 (d, J ) 2.4 Hz, 1H, aryl H),
7.19-7.29 (m, 6H, Ph H), 7.79 (m, 4H, Ph H). 1H NMR (300 MHz,
C6D6, 70 °C; δ): 0.48 (br s, 4H, ScCH2), 0.55 (s, 12H, Si(CH3)2),
1.06 (s, 18H, SC(CH3)3), 1.38 (s, 9H, C(CH3)3), 1.76 (s, 9H,
C(CH3)3), 2.07-2.43, 2.45-2.60 (m, 8H, NCH2CH2N), 3.23 (s,
2H, aryl CH2), 6.84 (d, J ) 2.4 Hz, 1H, aryl H), 7.51 (d, J ) 2.4
Hz, 1H, aryl H), 7.17-7.26 (m, 6H, Ph H), 7.74 (m, 4H, Ph H).
13C NMR (75 MHz, C6D6, 70 °C; δ): 3.1 (s, Si(CH3)2), 27.6
(ScCH2), 31.0 (C(CH3)3), 31.1 (C(CH3)3), 32.5 (C(CH3)3), 34.7
(CMe3), 36.0 (CMe3), 40.5 (br s, SCMe3), 46.3 (CH2), 51.6 (CH2),
60.8 (CH2), 123.3 (aryl), 124.9 (aryl-H), 125.4 (aryl-H), 128.0
(aryl-H), 128.1 (aryl-H), 134.4 (aryl-H), 137.5 (aryl), 146.9
1
125.3, 136.8, 138.0 (aryls), 162.0 (COSc). H NMR (300 MHz,
C6D5CD3, -50 °C, selected peaks; δ): -0.35 (br app d, 1H,
ScCH2), -0.22 (br app d, 1H, ScCH2), -0.15 (br app d, 1H,
ScCH2), -0.08 (br app d, 1H, ScCH2), 0.45 (s, 9H, Si(CH3)3), 0.64
(s, 9H, Si(CH3)3), 1.46 (s, 9H, C(CH3)3), 1.89 (s, 9H, C(CH3)3),
2.85 (s, 3H, OCH3), 3.20 (s, 3H, OCH3), 6.93 (br d, 1H, aryl H),
7.61 (br d, 1H, aryl H).
Synthesis of [(C5H4N-2-CH2)2NCH2-C6H2-3,5-(CMe3)2-2-O]-
Sc(CH2SiMe2Ph)2 (11). Under a nitrogen atmosphere, a toluene-
d8 solution (0.4 mL) of Sc(CH2SiMe2Ph)3(THF)2 (68.4 mg, 0.1074
mmol, 1 equiv) was frozen in a J-Young tube. Toluene-d8 (0.1 mL)
was added to separate the toluene-d8 solution (0.4 mL each) of the
trialkyl complex from the phenol (C5H4N-2-CH2)2NCH2-C6H2-3,5-
(CMe3)2-2-OH (3) (44.8 mg, 0.1074 mmol, 1 equiv). Before the
1H NMR spectrum was recorded, the sample was warmed for 5-10
1
(aryl), 160.8 (COSc). H NMR (300 MHz, C6D5CD3, -50 °C,
selected peaks; δ): 0.35 (br app d, 1H, ScCH2), 0.55 (br s, 3H,
SiCH3), 0.66 (br s, 3H, SiCH3), 0.75 (br s, 3H, SiCH3), 0.88 (s,
9H, SC(CH3)3), 1.01 (s, 9H, SC(CH3)3), 1.42 (s, 9H, C(CH3)3), 1.86
(s, 9H, C(CH3)3).
1
s and mixed. After the H and 13C NMR spectra were recorded,
the sample was warmed up room temperature and stirred for 1 h.
The 1H NMR spectrum shows formation of one species containing
the phenolate ligand. The kinetics of this process were studied by
1H NMR spectroscopy at 0 °C. NMR spectra used to characterize
Synthesis of [(MeOCH2CH2)2NCH2-C6H2-3,5-(CMe3)2-2-O]Y-
(CH2SiMe3)2 (9). A thawing THF (5 mL) solution of the phenol
(MeOCH2CH2)2NCH2-C6H2-3,5-(CMe3)2-2-OH (0.36 g, 1.0 mmol,
1 equiv) was added dropwise to an in situ generated thawing THF
(5 mL) solution of Y(THF)2(CH2SiMe3)3 (1 equiv), and the mixture
was stirred for 4 h at room temperature. The volatile materials along
with the byproduct, tetramethylsilane, were removed under vacuum.
1H NMR spectra of the crude reaction mixtures show clean
formation of the desired yttrium dialkyl product. Diethyl ether (5
mL) was added, and the mixture was filtered through Celite to
remove insoluble salts. The filtrate was concentrated under vacuum.
Recrystallization from petroleum ether, followed by collection on
a sintered-glass funnel and washing with cold petroleum ether,
provided the desired product as a white solid (0.24 g, 0.4 mmol,
38%). Anal. Calcd for C29H58NO3Si2Y: C, 56.74; H, 9.52; N, 2.28.
Found: C, 55.62; H, 9.34; N, 2.36. 1H NMR (300 MHz, C6D6, 40
1
11 and 12 are presented in the Supporting Information. H NMR
(300 MHz, C6D5CD3, -45 °C; δ): 0.21 (s, 9H, PhSi(CH3)3, 1
equiv), -0.09 (br app d, J ) 11.2 Hz, 1H, ScCHH), 0.17 (br app
d, J ) 11.2 Hz, 1H, ScCHH), 0.45 (br app d, J ) 11.2 Hz, 1H,
ScCHH), 0.64 (br app d, J ) 11.2 Hz, 1H, ScCHH), 0.29 (s, 3H,
SiCH3), 0.54 (s, 3H, SiCH3), 0.92 (s, 3H, SiCH3), 0.96 (s, 3H,
SiCH3), 1.40 (m, 17H, C(CH3)3 and O(CH2CH2)2, THF, 2 equiv),
1.65 (s, 9H, C(CH3)3), 3.57 (t, 8H, O(CH2CH2)2, THF, 2 equiv),
2.60-2.83 (m, 4H, NCH2), 4.01 (d, J ) 14.4 Hz, 1H, NCH2), 4.37
(d, J ) 11.1 Hz, 1H, NCH2), 5.76 (d, 1H, aryl H), 6.21 (t, 1H, aryl
H), 6.36-6.48 (m, 4H, aryl H), 6.72-7.63 (15H, aryl H), 8.17 (d,
2H, aryl H), 8.66 (d, 1H, aryl H), 8.91 (d, 1H, aryl H). 13C NMR
(75 MHz, C6D5CD3, -45 °C; δ): -1.3 (PhSi(CH3)3), 2.3 (SiCH3),
2.6 (SiCH3), 2.7 (SiCH3), 3.8 (SiCH3), 25.6 (O(CH2CH2)2, THF),
28.7 (br, ScCH2), 30.3 (br, ScCH2), 30.5 (C(CH3)3), 32.1 (C(CH3)3),
34.0 (CMe3), 35.3 (CMe3), 60.3 (NCH2), 61.9 (NCH2), 62.3
(NCH2), 67.6 (O(CH2CH2)2, THF), 119.9, 121.8, 122.7, 123.4,
123.5, 127.9, 129.0, 133.4, 133.5, 133.8, 134.1, 134.3, 135.1, 136.4,
136.9, 137.7, 138.8, 139.9, 147.4, 147.6, 149.5, 156.6, 156.7, 161.3
(aryls and C6H5SiMe3).
2
°C; δ): -0.58 (d, JYH ) 2.7 Hz, 4H, YCH2), 0.44 (s, 18H, Si-
(CH3)3), 1.41 (s, 9H, C(CH3)3), 1.79 (s, 9H, C(CH3)3), 1.56-1.67,
2.44-2.58, 2.76-2.85 (m, 8H, NCH2CH2O), 3.48 (br s, 2H, aryl
CH2), 3.19 (s, 6H, OCH3), 6.90 (d, J ) 2.6 Hz, 1H, aryl H), 7.56
(d, J ) 2.6 Hz, 1H, aryl H). 13C NMR (75 MHz, C6D6, 40 °C; δ):
5.1 (Si(CH3)3), 30.8 (d, YCH2, JYC ) 40.1 Hz), 30.7 (C(CH3)3),
32.6 (C(CH3)3), 34.6 (CMe3), 36.0 (CMe3), 52.9 (br s, OCH3), 61.4
1
1
(CH2), 63.8 (CH2), 72.1 (CH2), 123.5, 125.2, 125.9, 137.0, 137.4
(aryls), 162.4 (d, JYC ) 3.3 Hz, COY).
Spectroscopic Characterization of 12. H NMR (300 MHz,
2
C6D5CD3; δ): 0.20 (s, 18H, PhSi(CH3)3, 2 equiv), 0.27 (d, J ) 11
Hz, 1H, ScCHH), 0.41 (d, J ) 11 Hz, 1H, ScCHH), 0.61 (s, 3H,
SiCH3), 0.62 (s, 3H, SiCH3), 1.36 (m, 17H, C(CH3)3 and
O(CH2CH2)2, THF, 2 equiv), 1.65 (s, 9H, C(CH3)3), 3.72 (br s,
8H, O(CH2CH2)2, THF, 2 equiv), 2.91 (d, J ) 14.8 Hz, 1H, NCHH),
3.32 (d, J ) 13.5 Hz, 1H, NCHH), 3.86 (d, J ) 13.5 Hz, 1H,
NCHH), 4.19 (d, J ) 14.8 Hz, 1H, NCHH), 4.08 (s, 1H, NCH),
5.01 (t, 1H, aryl H), 5.74 (d, 1H, aryl H), 6.05-6.12 (m, 1H, aryl
H), 6.16-6.24 (d, 1H, aryl H), 6.24-6.30 (t, 1H, aryl H), 6.56-
6.63 (td, 1H, aryl H), 7.02 (d, 1H, aryl H), 7.16-7.23 (m, 7H, aryl
H), 7.28-7.35 (t, 2H, aryl H), 7.39-7.46 (m, 5H, aryl H), 7.52 (d,
1H, aryl H), 7.90 (dd, 2H, aryl H), 8.72 (d, 1H, aryl H). 13C NMR
(75 MHz, C6D5CD3; δ): -1.2 (PhSi(CH3)3), 3.0 (SiCH3), 3.1
(SiCH3), 25.6 (O(CH2CH2)2, THF), 27.7 (ScCH2), 30.3 (C(CH3)3),
32.1 (C(CH3)3), 34.3 (CMe3), 35.5 (CMe3), 62.1 (NCH2),
64.4 (NCH2), 68.8 (br s, O(CH2CH2)2, THF), 96.6 (aryl-H),
100.9 (NCH, 1JC-H ) 170 Hz), 114.0 (aryl-H), 122.3, 122.5, 123.7,
123.9, 124.9, 127.7, 127.8, 128.0, 129.0, 131.0, 133.5, 136.6, 137.9,
138.3, 140.2, 143.5, 143.8, 146.9, 149.0, 151.9, 159.8, 160.3 (aryls
Synthesis of [(MeOCH2CH2)2NCH2-C6H2-3,5-(CMe3)2-2-O]-
Sc(CH2SiMe3)2 (10). A thawing THF (5 mL) solution of the phenol
(MeOCH2CH2)2NCH2-C6H2-3,5-(CMe3)2-2-OH (1; 0.30 g, 0.9
mmol, 1 equiv) was added dropwise to the in situ generated thawing
THF (5 mL) solution of Sc(THF)2(CH2SiMe3)3 (1 equiv), and the
mixture was stirred for 4 h at room temperature. The volatile
materials along with the byproduct, tetramethylsilane, were removed
under vacuum. 1H NMR spectra of the crude reaction mixtures show
clean formation of the desired yttrium dialkyl product. Diethyl ether
(5 mL) was added, and the mixture was filtered through Celite to
remove insoluble salts. The filtrate was concentrated under vacuum.
Recrystallization from petroleum ether, followed by collection on
a sintered-glass funnel and washing with cold petroleum ether,
provided the desired product as a white solid (0.22 g, 0.4 mmol,
45%). Anal. Calcd for C29H58NO3Si2Sc: C, 61.12; H, 10.26; N,
2.46. Found: C, 58.66; H, 9.01; N, 2.22. 1H NMR (300 MHz, C6D6,
60 °C; δ): -0.22 (s, 4H, ScCH2), 0.38 (s, 18H, Si(CH3)3), 1.39 (s,
9H, C(CH3)3), 1.79 (s, 9H, C(CH3)3), 1.62-1.72, 2.63, 2.86-2.95

Group 3 Dialkyl Complexes
Organometallics, Vol. 26, No. 5, 2007 1189
and C6H5SiMe3). A diethyl ether solution of 12 was quenched with
mg, 0.015 mmol, 1 equiv) was frozen in a J-Young tube. A
chlorobenzene-d5 solution (0.3 mL) of diphenylmethane (2.5 mg,
0.015 mmol, 1 equiv) was added as an internal standard and to
separate the chlorobenzene-d5 solution (0.4 mL each) of the yttrium
dialkyl complex from the stoichiometric activator [PhNHMe2]+-
[B(C6F5)4]- (11.9 mg, 0.015 mmol, 1 equiv). Before the 1H NMR
spectrum was recorded, the sample was warmed for 5-10 s and
mixed. The 1H NMR spectrum shows the formation of mainly one
species containing the phenolate ligand, along with the alkane
byproduct. After activation, ethylene (0.166 mmol, 11.1 equiv) was
condensed into the J-Young tube. Using diphenylmethane as an
internal standard, slow consumption of ethylene (<7.5 equiv) was
observed over 7 h.
CD3OD and filtered through alumina. The volatile materials
1
were removed under vacuum. H NMR (500 MHz, CDCl3, peaks
in the 3.5-4.0 ppm region; δ): 3.80 (d, J ) 13.5 Hz, 1H, aryl
CHH), 3.83 (d, J ) 13.5 Hz, 1H, aryl CHH), 3.86 (br s, 1H,
NCHDC5H4N), 3.88 (br s, 2H, NCH2C5H4N). 2H NMR (75 MHz,
CH2Cl2; δ): 3.83.
Synthesis of 13. Under a nitrogen atmosphere, dry pyridine (10.7
µL, 0.13 mmol, 1 equiv) was added dropwise to a diethyl ether
solution (3 mL) of 12 (1 equiv) previously generated. The reaction
mixture was stirred for 5 min. The volatile materials were removed
1
under vacuum. The H NMR spectrum shows formation of one
species containing the phenolate ligand. 1H NMR (300 MHz, C6D5-
CD3; δ): 0.42 (d, J ) 11 Hz, 1H, ScCHH), 0.60 (d, J ) 11 Hz,
1H, ScCHH), 0.31 (s, 3H, SiCH3), 0.38 (s, 3H, SiCH3), 1.33 (m,
9H, C(CH3)3), 1.73 (s, 9H, C(CH3)3), 2.98 (d, J ) 14.4 Hz, 1H,
NCHH), 3.12 (br d, J ) 14.4 Hz, 1H, NCHH), 3.61 (br d, J )
14.4 Hz, 1H, NCHH), 4.20 (d, J ) 14.4 Hz, 1H, NCHH), 4.07 (s,
1H, NCH), 5.07 (br t, 1H, aryl H), 5.78 (d, 1H, aryl H), 6.12-6.23
(m, 2H, aryl H), 6.30 (t, 1H, aryl H), 6.48 (br t, 2H, C5H5N), 6.63
(t, 1H, aryl H), 6.78 (br t, 1H, C5H5N), 6.88 (br s, 1H, aryl H),
7.17-7.46 (m, 4H, aryl H), 7.65 (br s, 1H, aryl H), 7.73 (br s, 2H,
aryl H), 8.77 (d, 1H, aryl H), 8.97 (br s, 2H, C5H5N). 13C NMR
(75 MHz, C6D5CD3; δ): -1.2 (PhSi(CH3)3), 2.3 (SiCH3), 2.5
(SiCH3), 30.4 (C(CH3)3), 32.0 (C(CH3)3), 32.2 (ScCH2), 34.2
(CMe3), 35.6 (CMe3), 62.7 (NCH2), 64.4 (NCH2), 101.4 (NCH),
96.9 (aryl-H), 114.2 (aryl-H), 122.3, 122.5, 123.8, 124.9, 125.2,
127.6, 128.0, 129.0, 131.1, 133.5, 133.8, 135.7, 136.6, 137.9, 138.3,
138.6, 140.2, 144.0. 146.9, 149.0, 150.8, 151.8, 152.7, 159.8, 160.4
(aryls, C5H5N, and C6H5SiMe3).
1
Spectroscopic Characterization of 15. H NMR (300 MHz,
C6D5Cl, -40 °C; δ): tentatively assigned to the activated species
(major), -0.98 (br d, J ) 11.1 Hz, 1H, YCHH), -0.77 (br d, J )
11.1 Hz, 1H, YCHH), 0.19 (br s, 9H, Si(CH3)3), 1.30 (s, 9H,
C(CH3)3), 1.60 (s, 9H, C(CH3)3), 1.70-3.00 (br m, NCH2CH2O
and aryl CH2), 3.15 (s, 3H, OCH3), 3.37 (s, 3H, OCH3), 2.59 (s,
6H, C6H5N(CH3)2); not assigned, 0.83 (m), 1.22 (s), 6.54-7.62 (aryl
H peaks for C6H2-OY, and C6H5NMe2). 1H NMR (300 MHz, C6D5-
Cl; δ): tentatively assigned to the activated species (major), -0.81
(br s, 2H, YCH2), 0.15 (br s, 9H, Si(CH3)3), 1.30 (s, 9H, C(CH3)3),
1.58 (br s, 9H, C(CH3)3), 1.80-4.00 (br m, NCH2CH2O and aryl
CH2; overlapping broad peaks), 3.33 (s, 6H, OCH3), 2.69 (s, 6H,
C6H5N(CH3)2); not assigned, 0.84 (m), 1.22, 6.67-7.51 (aryl H
peaks for C6H2-OY, and C6H5NMe2).
Line Shape and Eyring Analysis. NMR spectral simulations
were performed using gNMR version 3.6. The chemical shifts
observed in the slow limit exchange (203 K) were used to set up
the spin systems. The relative population ratio was fixed at 1:1 for
7a, 8a, and 10. Lorentzian line shapes with line widths of 2 Hz
were utilized. Small changes to the line width did not visibly
affect the activation parameters of the exchange process. As the
chemical shifts of the different hydrogens vary slightly with
temperature, the difference in the chemical shifts was used to
compare simulated with experimental spectra. For different tem-
peratures, the exchange rate was varied to get the best fit between
the simulated and the experimental spectra. Activation parameters
were determined by a standard Eyring analysis, and the standard
deviations from the ø2 fit were used to estimate the uncertainties
in ∆Hq and ∆Sq.
Ethylene Polymerizations. Ethylene polymerizations were
performed in a high-pressure glass vessel equipped with a magnetic
stirrer. In a typical procedure, under a nitrogen atmosphere, solid
MAO (48.3 mg, 0.833 mmol, 500 equiv) was added to 4.5 mL of
chlorobenzene. The mixture was pressurized to 1 bar of ethylene.
A chlorobenzene (0.5 mL) solution of catalyst precursor (1.67 µmol,
1 equiv) was added by syringe. The ethylene pressure was
immediately increased to 5 bar, and the solution was stirred for 1
h. The polymerization was stopped by venting of the vessel and
quenching with a mixture of 37% HCl solution and methanol (1:
12 v/v). The polymer was collected by filtration, washed with
methanol (3 × 10 mL), and dried under high vacuum overnight.
The amounts of polymer obtained are tabulated in the Supporting
Information.
Activation of 7a with [PhNHMe2]+[B(C6F5)4]- and NMR-
Scale Ethylene Polymerizations. Under a nitrogen atmosphere, a
chlorobenzene-d5 solution (0.4 mL) of an yttrium dialkyl complex
(13.5 mg, 0.018 mmol, 1 equiv) was frozen in a J-Young tube. A
chlorobenzene-d5 solution (0.3 mL) of diphenylmethane (3.1 mg,
0.018 mmol, 1 equiv) was added as an internal standard and to
separate the chlorobenzene-d5 solution (0.4 mL each) of the yttrium
dialkyl complex from the solution of the stoichiometric activator
[PhNHMe2]+[B(C6F5)4]- (14.6 mg, 0.018 mmol, 1 equiv). Before
1
the H NMR spectrum was recorded, the sample was warmed for
1
5-10 s and mixed. The H NMR spectrum shows formation of
mainly one species containing the phenolate ligand along with the
alkane byproduct. After activation, ethylene (0.166 mmol, 9.3 equiv)
was condensed in the J-Young tube. Using diphenylmethane as
internal standard, slow consumption of ethylene (<4 equiv) was
observed over 6 h.
1
Spectroscopic Characterization of 14. H NMR (300 MHz,
C6D5Cl, -40 °C; δ): tentatively assigned to the activated species
(major), -0.75 (br d, J ) 10.8 Hz, 1H, YCHH), -0.54 (br d, J )
10.8 Hz, 1H, YCHH), 0.37 (br s, 3H, SiCH3), 0.49 (br s, 3H,
SiCH3), 1.36 (s, 9H, C(CH3)3), 1.68 (s, 9H, C(CH3)3), 2.09-3.50
(m, NCH2CH2O and aryl CH2; overlapping broad peaks), 3.11 (s,
3H, OCH3), 3.38 (s, 3H, OCH3), 2.62 (s, 6H, C6H5N(CH3)2); not
assigned, 0.85 (t, 1H), 0.89 (t, 1H), 1.61 (s, not C(CH3)3 from the
starting material), 6.55-7.79 (aryl H peaks for YCH2SiMe2C6H5,
C6H2-OY, C6H5SiMe3, and C6H5NMe2). 1H NMR (300 MHz, C6D5-
Cl; δ): tentatively assigned to the activated species (major), -0.60
(br s, 2H, YCH2), 0.40 (br s, 6H, Si(CH3)2), 1.32 (s, 9H, C(CH3)3),
1.57 (br s, 9H, C(CH3)3), 2.08-3.08 (br m, 10H, NCH2CH2O and
aryl CH2), 3.23 (s, 6H, OCH3), 2.65 (s, 6H, C6H5N(CH3)2),
remaining peaks are broad and overlapped; not assigned, 0.85 (m,
∼2H), 1.22 (s, not C(CH3)3 from the starting material), 6.67-7.71
(aryl H peaks for YCH2SiMe2C6H5, C6H2-OY, C6H5SiMe3, and
C6H5NMe2).
X-ray Crystal Data: General Procedure. Crystals grown from
diethyl ether (7a and 8a) or a mixture of diethyl ether and petroleum
ether (7b) at -35 °C were removed quickly from a scintillation
vial to a microscope slide coated with Paratone N oil. Samples
were selected and mounted on a glass fiber with Paratone N oil.
Data collection was carried out on a Bruker Smart 1000 CCD
diffractometer. The structures were solved by direct methods. All
non-hydrogen atoms were refined anisotropically. Some details
regarding refined data and cell parameters are available in Table
1. Selected bond distances and angles are supplied in the captions
of Figures 3-5.
Activation of 9 with [PhNHMe2]+[B(C6F5)4]- and NMR-Scale
Ethylene Polymerizations. Under a nitrogen atmosphere, a chlo-
robenzene-d5 solution (0.4 mL) of an yttrium dialkyl complex (9.1

1190 Organometallics, Vol. 26, No. 5, 2007
Marinescu et al.
Acknowledgment. This work has been supported by US-
DOE Office of Basic Energy Sciences (Grant No. DE-FG03-
85ER13431) and the National Science Foundation (Grant
No. CHE-0131180). S.C.M. thanks Caltech’s Summer Under-
graduate Research Fellowship program for funding. We
thank Mr. Lawrence Henling for assistance in obtaining the
X-ray crystal structures and Ms. Mona Shahgholi for help
with HRMS. We thank Prof. John Arnold for an insightful
personal communication regarding the structures of some related
complexes supported by ligand 3, particularly one related to
12.
Supporting Information Available: NMR spectra for experi-
ments involving 7a, 8a, 10-12, and 15, kinetic plots for the
conversion of 11 into 12, tabulated results of the ethylene
polymerization trials, Eyring plots for 10, and CIF files giving X-ray
crystallographic data. This material is available free of charge via
the Internet at http://pubs.acs.org.
OM0608612