β-diketiminato scandium chemistry: Attempted deprotonation of cationic amido complexes

Article abstract of DOI:10.1021/om060197p

Treatment of the β-diketiminato-supported scandium amido methyl derivatives [ArNC(^tBu)CHC(^tBu)NAr]Sc(Me)-(NHR) (Ar = 2,6-ⁱPr₂-C₆H₃; R = ^tBu, 2,6-ⁱPr₂-C

Full text of DOI:10.1021/om060197p

Organometallics 2006, 25, 3289-3292
3289
â-Diketiminato Scandium Chemistry: Attempted Deprotonation of
Cationic Amido Complexes
Lisa K. Knight,† Warren E. Piers,*,† and Robert McDonald‡
Departments of Chemistry, UniVersity of Calgary, 2500 UniVersity DriVe, N.W., Calgary,
Alberta, Canada T2N 1N4, and UniVersity of Alberta, Edmonton, Alberta, Canada T6G 2G2
ReceiVed March 1, 2006
Summary: Treatment of the â-diketiminato-supported scandium
amido methyl deriVatiVes [ArNC(tBu)CHC(tBu)NAr]Sc(Me)-
complex that implied the intermediacy of a monomeric scan-
dium imido species and suggests that, with the appropriate level
of steric support, such species might be prevented from
dimerizing.6
t
(NHR) (Ar ) 2,6-iPr2-C6H3; R ) Bu, 2,6-iPr2-C6H3) with 1
equiV of tris(pentafluorophenyl)borane resulted in the formation
of scandium amido ion pairs, 1a and 1b, respectiVely, in good
yields. A single-crystal X-ray analysis of 1a was undertaken,
and two crystallographically independent molecules were
obserVed in which one contains an N-H‚‚‚F-C hydrogen bond
while the other does not. SeVeral attempts to deprotonate the
amido ligand to yield a neutral imido species resulted in either
attack of the base at the metal center or deprotonation of the
â-diketiminato ligand. For example, treatment of 1a with tert-
butyllithium gaVe [ArNC(tBu)CHC(tBu)NAr]Sc(CMe3)(NHtBu)
(2), while treatment with the phosphazene base [(Me2N)3-
PdN]3PdNtBu gaVe the preViously characterized metalated
complex 3.
Recently, bulky N-aryl â-diketiminato7 and related8 ligands
have been demonstrably effective at stabilizing low-coordinate
environments.9 In particular, monomeric imides for the group
13 metals aluminum10 and gallium11 as supported by these
ligands have been prepared. For this reason, we felt it would
be a useful template from which to develop the chemistry of
terminal scandium imido complexes. However, despite the
availability of a wide variety of â-diketiminato (“nacnac”)-
supported scandium bis(alkyl),12 bis(amido)13,14 and mixed
alkyl-amido complexes, [ArNC(R)CH(R)CNAr]ScR′(R′′)
t
(Ar ) 2,6-iPr2-C6H3; R ) Me, Bu; R′ ) R′′ ) Me, Et, Bn,
CH2SiMe3, CH2CMe3 or R′ * R′′, R′ ) Me and R′′ ) NHtBu,
NHAr), we could not induce formation of “LScdNR” by the
classical thermal pathways developed by Bergman2a and
Wolczanski2b for group 4 congeners. In all instances, metalation
of the o-isopropyl groups was observed rather than loss of alkane
or amine, and labeling studies negated the possibility of the
Introduction
Terminal imido ligands (dNR) are playing an increasingly
important role in early-transition-metal chemistry as reactive
intermediates or spectator ligands. As bulky imido ligands are
isoelectronic with Cp ligands, they have been employed as
ancillary ligands with group 5 and 6 metals for metal-based
olefin polymerization, resulting in molecular fragments that are
isolobal with group 4 metallocenes.1 In addition, highly reactive
group 4 LnMdNR species are known to activate C-H bonds
of alkanes via a 1,2-addition across the MdN functionality.2
Also, these kinds of species are considered to be key intermedi-
ates in the catalytic hydroamination of allenes and alkynes by
titanium- and zirconium-based catalyst precursors.3 Experimental
and kinetic evidence suggests that the first step of the catalytic
cycle is the generation of the LnMdNR species from the metal
amido precursors, followed by 2 + 2 cycloaddition with
substrate, resulting in the formation of the C-N bond.
(5) Beetstra, D. J.; Meetsma, A.; Hessen, B.; Teuben, J. H. Organome-
tallics 2003, 22, 4372.
(6) Chan, H.-S.; Li, H.-W.; Xie, Z. Chem. Commun. 2002, 652.
(7) Budzelaar, P. H. M.; van Oort, A. B.; Orpen, A. G. Eur. J. Inorg.
Chem. 1998, 1485.
(8) (a) Hayes, P. G.; Welch, G. C.; Emslie, D. J. H.; Noack, C. L.; Piers,
W. E.; Parvez, M. Organometallics 2003, 22, 1577. (b) Reynolds, A. M.;
Gherman, B. F.; Cramer, C. J.; Tolman, W. B. Inorg. Chem. 2005, 44,
6989. (c) Liu, X.; Gao, W.; Mu, Y.; Li, G.; Ye, L.; Xia, H.; Ren, Y.; Feng,
S. Organometallics 2005, 24, 1614. (d) Lee, B. Y.; Kwon, H. Y.; Lee, S.
Y.; Na, S. J.; Han, S.; Yun, H.; Lee, H.; Park, Y.-W. J. Am. Chem. Soc.
2005, 127, 3031. (e) Gao, H.; Guo, W.; Bao, F.: Gui, G.; Zhang, J.; Zhu,
F.; Wu, Q. Organometallics 2004, 23, 6273. (f) Porter, R. M.; Winston, S.;
Danopoulos, A. A.; Hursthouse, M. B. Dalton Trans. 2002, 3290. (g) Welch,
G. C.; Piers, W. E.; Parvez, M.; McDonald, R. Organometallics 2004, 23,
1811.
(9) (a) Bouget-Merle, L.; Lappert, M. F.; Severn, J. R. Chem. ReV. 2002,
102, 3031. (b) Basuli, F.; Bailey, B. C.; Tomaszewski, J.; Huffman, J. C.;
Mindiola, D. J. J. Am. Chem. Soc. 2003, 125, 6052. (c) Basuli, F.;
Tomaszewski, J.; Huffman, J. C.; Mindiola, D. J. J. Am. Chem. Soc. 2003,
125, 10170. (d) Basuli, F.; Bailey, B. C.; Baik, H.-H.; Mindiola, D. J. J.
Am. Chem. Soc. 2004, 126, 1924. (e) Basuli, F.; Bailey, B. C.; Brown, D.;
Tomaszewski, J.; Huffman, J. C.; Baik, M.-H.; Mindiola, D. J. J. Am. Chem.
Soc. 2004, 126, 10506.
Given the well-developed imido chemistry of the metals in
groups 4-6, it is surprising that the imido chemistry of the group
3 metals (and indeed the lanthanides) is still rather limited. To
the best of our knowledge, a monomeric, discrete LnMdNR
complex for group 3 has not yet been prepared.4 However,
Hessen et al. recently reported5 a dimeric scandium imido
* To whom correspondence should be addressed. Tel: 403-220-5746.
E-mail: wpiers@ucalgary.ca. S. Robert Blair Professor of Chemistry (2000-
2010).
(10) Zhu, H.; Chai, J.; Chandrasekhar, V.; Roesky, H. W.; Magull, J.;
Vidovic, D.; Schmidt, H.-G.; Noltemeyer, M.; Power, P. P. J. Am. Chem.
Soc. 2004, 126, 9472.
(11) Hardman, N. J.; Cui, C.; Roesky, H. W.; Fink, W. H.; Power, P. P.
Angew. Chem., Int. Ed. 2001, 40, 2172.
† University of Calgary.
‡ University of Alberta.
(1) Gade, L. H.; Mountford, P. Coord. Chem. ReV. 2001, 216-217, 65.
(2) (a) Walsh, P. J.; Hollander, F. J.; Bergman, R. G. J. Am. Chem. Soc.
1988, 110, 8729. (b) Cummins, C. C.; Baxter, S. M.; Wolczanski, P. T. J.
Am. Chem. Soc. 1988, 110, 8731. (c) Hoyt, H. M.; Micheal, F. E.; Bergman,
R. G. J. Am. Chem. Soc. 2004, 126, 1018.
(3) Bytschkov, I.; Doye, S. Eur. J. Org. Chem. 2003, 935.
(4) (a) Emslie, D. J. H.; Piers, W. E. Coord. Chem. ReV. 2002, 233-
234, 131. (b) Giesbrecht, G. R.; Gordon, J. C. Dalton Trans. 2004, 2387.
(12) (a) Lee, L. W. M.; Piers, W. E.; Elsegood, M. R. J.; Clegg, W.;
Parvez, M. Organometallics 1999, 18, 2947. (b) 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.
(13) Knight, L. K.; Piers, W. E.; Fleurat-Lessard, P.; Parvez, M.;
McDonald, R. Organometallics 2004, 23, 2087.
(14) Basuli, F.; Tomaszewski, J.; Huffman, J. C.; Mindiola, D. J.
Organometallics 2003, 22, 4705.
10.1021/om060197p CCC: $33.50 © 2006 American Chemical Society
Publication on Web 05/24/2006

3290 Organometallics, Vol. 25, No. 13, 2006
Notes
involvement of a terminal imide in the metalation product-
forming process.13
Another strategy involves the deprotonation of primary amido
complexes,6,15 a process that should be thermodynamically more
favorable if the amido starting material is cationic. Given that
the nacnac scandium bis(alkyl) compounds readily undergo
alkide abstraction to form well-defined organoscandium cat-
ions,16 we surmised that nacnac amido cations should be
accessible from mixed alkyl-amido complexes. Herein we
describe the synthesis of such cations and their reaction with
various bases in attempts to uncover deprotonative routes to
terminal scandium imido complexes.
Results and Discussion
The amido methyl complexes [ArNC(tBu)CHC(tBu)NAr]Sc-
(Me)(NHR) (R ) tBu, 2,6-iPr2-C6H3) were prepared as described
previously and treated with 1 equiv of the strong organometallic
17
Lewis acid B(C6F5)3 in order to effect abstraction of the
methide anion.18 When it is carried out in hexanes, this reaction
results in nearly quantitative precipitation of the contact ion pairs
[ArNC(tBu)CHC(tBu)NAr]Sc(NHR)]+[MeB(C6F5)3]- (Ar )
2,6-iPr2-C6H3; R ) tBu (1a), 2,6-iPr2-C6H3 (1b)) as pale yellow
microcrystalline solids, as shown in eq 1. Cation formation is
Figure 1. Crystalmaker thermal ellipsoid diagram (50%) of
molecule A of 1a. all but the ipso carbons of the N-aryl 2,6-di-
isopropyl groups have been removed for clarity. For all of the
following data, analogous values for molecule B are given in italics.
Selected bond distances (Å): Sc-N(1), 2.121(2), 2.095(3);
Sc-N(2), 2.078(2), 2.112(2); Sc-N(3), 1.969(3), 1.943(3);
Sc-C(40), 2.521(3), 2.537(3); C(40)-B, 1.675(4), 1.679(4). Non-
bonded distance (Å): F(42)-N(3), 3.162. Closest N(3)-F contact
in molecule B: 3.996 Å. Distance of Sc from N(1)-C(3)-C(2)-
C(1)-N(2) mean plane (Å); 1.257(3), 1.234(3). Selected bond
angles (deg): N(1)-Sc-N(2), 94.8(1), 95.0(1); C(40)-Sc-N(3),
103.3(1), 96.6(2); Sc-N(3)-C(36), 141.2(2), 152.9(4).
signaled by several spectroscopic features present in the NMR
spectra of compounds 1 obtained in d8-toluene. The 11B NMR
resonances appear at -15.1 and -14.9 ppm for 1a and 1b,
respectively, typical of anionic four-coordinate borate centers.19
This is supported by 19F NMR spectroscopic data, which show
the separation between the resonances for the meta and para
fluorines as being 4.6 ppm (1a) and 4.1 ppm (1b), values typical
of the weakly coordinating methyl borate counteranion.20 In the
1H NMR spectra, the resonances for the N-H protons shift
significantly downfield (5.39 ppm for 1a and 7.54 ppm for the
anilido cation 1b) relative to the positions of these signals in
the neutral methyl amido starting materials (3.54 and 5.44 ppm).
Additionally, the resonances for the Sc-CH3 protons broaden
and shift to the region characteristic of methyl borate anions
engaged in bridging interactions with the scandium center.16
Previously, we have shown that a variety of (nacnac)ScX2
species are fluxional in solution,12,13,21 manifested by exchange
between the diastereotopic endo (underneath the N2C3 ligand
plane) and exo positions; this process can be studied via
variable-temperature NMR experiments. The exchange process
occurs via a C2V-symmetric transition state wherein the Sc passes
through the N2C3 plane. In systems where the groups on
scandium are chemically distinct, as in compounds 1, two
diastereomers are potentially in exchange via this process.16b
Variable-temperature 1H NMR studies on both 1a and 1b,
however, indicated that only one isomer is present over the
accessible temperature range (200-360 K). By analogy to our
more detailed analysis of the neutral alkyl amido precursors,13
the isomer present is likely that in which the amido group
occupies the exo site, which is both sterically preferred and
electronically favorable for π-donating ligands.13
This assignment is borne out in the molecular structure of
1a, determined by X-ray crystallography on single crystals of
this derivative. There are two crystallographically independent
molecules in the unit cell; a diagram of molecule A is shown
in Figure 1, along with selected metrical data for both, and
crystal data and refinement details are given in Table 1. In both
molecules, the amide ligand occupies the exo site, while the
more sterically hindered endo site accommodates the methyl
borate anion, whose steric bulk is farther removed from the
scandium center. The two molecules differ mainly in the
orientation of the borate counteranion with respect to the amide
ligand. In molecule A, one of the C6F5 rings is oriented such
that the C(42)-F(42) axis is aligned with the N-H moiety of
the amide, forming a weak N-H′‚‚‚F hydrogen bond (the N(3)-
F(42) distance is 3.162 Å, which is close to the sum of the van
der Waals radii for N-F of 3.15 Å22). In molecule B, this ring
(15) (a) Kissounko, D. A.; Epshteyn, A.; Fettinger, J. C.; Sita, L. R.
Organometallics 2006, 25, 1076. (b) Knight, P. D.; Munslow, I.; O′Shaugh-
nessy, P. N. O.; Scott, P. Chem. Commun. 2004, 894.
(16) (a) Hayes, P. G.; Piers, W. E.; McDonald, R. J. Am. Chem. Soc.
2002, 124, 2132. (b) Hayes, P. G.; Piers, W. E.; Parvez, M. Organometallics
2005, 24, 1173.
(17) Piers, W. E. AdV. Organomet. Chem. 2005, 52, 1.
(18) Chen, E. Y.-X.; Marks, T. J. Chem. ReV. 2000, 100, 1391.
(19) Kidd, R. G. In NMR of the Newly Accessible Nuclei; Laszlo, P.,
Ed.; Academic: London, 1983; Vol. 2.
(20) Horton, A. D.; de With, J.; van der Linden, A. J.; van der Weg, H.
Organometallics 1996, 15, 2672.
(21) Knight, L. K.; Piers, W. E.; McDonald, R. Chem. Eur. J. 2000, 6,
4322.
(22) Huheey, J. E., Keiter, E. A., Keiter, R. L., Eds. Inorganic
Chemistry: Principles of Structure and ReactiVity, 4th ed.; Harper Collins
College: New York, 1993.

Notes
Organometallics, Vol. 25, No. 13, 2006 3291
Table 1. Summary of Data Collection and Structure
Refinement Details for 1a
Scheme 1
formula
fw
temp, °C
cryst syst
space group
a, Å
C
58.75H67.75N3ScBF15
1156.68
-80
triclinic
P1h (No. 2)
13.525(4)
22.096
b, Å
c, Å
22.507
R, deg
â, deg
γ, deg
V, Å3
65.395(5)
78.125(5)
87.470(5)
5978(3)
4
1.285
0.208
36364
15328
Z
d
calcd, g cm-3
µ, mm-1
no. of rflns measd
no. of unique rflns
R1/wR2
spectroscopy and elemental analysis (see Experimental Section).
A related compound, [ArNC(Me)CHC(Me)NAr]Sc(CMe3)-
(NHAr), was recently reported by Mindiola et al.,14 and 2 has
spectroscopic properties similar to those of this derivative.
Compound 2 is also the major product when 1a is first treated
with 1 equiv of pyridine to block the scandium center, although
the reaction in this case is both slower and less selective. Further
heating of 2 resulted in loss of isobutane and formation of the
previously characterized metalated complex 3,13 likely formed
by prior isomerization of the tert-butyl to the sec-butyl derivative
before σ-bond metathetical loss of the alkyl group. Thus, it
appears that even with these nonnucleophilic or sterically bulky
bases, attack at the electrophilic and relatively accessible metal
center is kinetically (and perhaps even thermodynamically)
favored.
We therefore turned to the commercially available phos-
phazene superbase [(Me2N)3PdN]3PdNtBu as a base that has
great thermodynamic strength but poor nucleophilicity.25 Sita
et al. have had success with the deprotonation of a cationic
zirconium amido species with a similar base.15 Unfortunately,
reaction of 1a with 1 equiv of [(Me2N)3PdN]3PdNtBu led
rapidly to the metalated product 3 (Scheme 1). The reaction
was also performed with d-1a, selectively deuterated in the
amido NH position, and the product was d-3, indicating that 3
is produced via direct deprotonation of the aryl isopropyl group
and not via a transient scandium imido derivative.26 Since it is
difficult to see how the isopropyl methyl protons could be more
acidic than the amido proton, this pathway must be kinetically
and statistically favored. Thus, while the deprotonation of a
cationic primary amido species is perhaps yet a potentially viable
route to the elusive scandium imido function, the search for a
suitable supporting ligand framework and base continues.
0.0714/0.2136
0.986
+0.911/ -0.831
GOF
resid density, e/Å3
is twisted out of this alignment, such that the closest N(3)-F
contact is 3.996 Å. This change in orientation also has an impact
on the Sc-N(3)-C(36) and C(40)-Sc-N(3) angles, which
differ by several degrees in the two molecules. For the rest, the
metrical data is quite similar between the two molecules and
we will refer only to that for molecule A for the remainder of
the discussion. The abstracted methyl group is now 2.521(3) Å
away from the scandium center, as opposed to 2.229(2) Å
in the starting methyl amide.13 The B(1)-C(40) distance of
1.675(4) Å is typical of such anions;18 the hydrogens of this
methyl group are placed in idealized positions based on C(40).
The Sc-N(3) distance of 1.969(3) Å is only slightly contracted
from the observed length of 2.000(2) Å in the neutral precursor
complex [ArNC(tBu)CHC(tBu)NAr]Sc(Me)(NHtBu), indicating
that cation formation does not significantly impact the extent
of π bonding between Sc and N,23 and is consistent with the
notion that π bonding is already quite significant in the neutral
amido alkyl compounds.13
Our interest in these compounds stems from their potential
as precursors to heretofore unknown group 3 metal imido
complexes via deprotonation. While several strategies to depro-
tonate the neutral precursors to cations 1 failed to yield imido-
containing products, we felt that deprotonation of the presumably
more acidic cationic primary amido ligand would be more
thermodynamically favored if a suitable base could be found
to favor this pathway kinetically. Selective deprotonation of a
cationic zirconium amide has recently been realized, but these
reactions are extremely sensitive to the nature of the base and
the ligand environments employed.15
Experimental Section
Treatment of 1a or 1b with various anionic bases (LDA, LiN-
(TMS)2, LiCMe3) at ambient or low temperature and in the
presence or absence of coordinating bases (THF, pyridine)
invariably resulted in attack of the nucleophile at the scandium
center and elimination of [Li][MeB(C6F5)3] (Scheme 1). The
latter product was identified by matching 19F NMR signals with
an authentic sample, prepared in situ from B(C6F5)3 and MeLi.24
In the case of the tert-butyllithium reaction, preparative-scale
experiments allowed for isolation of [ArNC(tBu)CHC(tBu)NAr]-
Sc(CMe3)(NHtBu) (2), which was fully characterized by NMR
General procedures and the syntheses of compounds 1 and their
precursors have been described in detail elsewhere.13 tert-Butyl-
lithium was purified by filtering commercial 1.7 M solutions in
pentane and removing the solvent in vacuo and was used as a
solid.27 Solvent was removed under reduced pressures from the 1.0
M hexane solution of [(Me2N)3PdN]3PdNtBu (Aldrich-Sigma),
(25) (a) Swesinger, R.; Schlemper, H.; Hasenfratz, C.; Willaredt, J.;
Dambacher, T.; Breuer, T.; Ottaway, C.; Fletschinger, M.; Boele, J.; Fritz,
H.; Putzas, D.; Rotter, H. W.; Bordwell, F. G.; Satish, A. V.; Ji, G.-Z.;
Peters, E.-M.; Peters, K.; von Schnering, H. G.; Walz, L. Liebigs Ann. Chem.
1996, 1055. (b) Swesinger, R.; Schlemper, H. Angew. Chem., Int. Ed. Engl.
1987, 26, 1167. (c) Swesinger, R.; Hasenfratz, C.; Schlemper, H.; Walz,
L.; Peters, E.-M.; Peters, K.; von Schnering, H. G. Angew. Chem., Int. Ed.
Engl. 1993, 32, 1361.
(23) Interestingly, the analogous distance in molecule B, which does not
feature the N-H‚‚‚F hydrogen bond, is slightly more contracted, to 1.943-
(3) Å, consistent with the expectation that hydrogen bonding would render
the amide a poorer π donor to scandium.
(24) Caution! Dry [Li][MeB(C6F5)3] is prone to detonation: Beck, S.;
Lieber, S.; Schaper, F.; Geyer, A.; Brintzinger, H. H. J. Am. Chem. Soc.
2001, 123, 1483.
(26) No evidence for the scrambling of the N-D deuteron into the
isopropyl groups of the nacnac N-aryl groups was observed, suggesting
that 3 is not in equilibrium with the elusive scandium imido isomer.

3292 Organometallics, Vol. 25, No. 13, 2006
Notes
which was then utilized as a solid without further purification. Tris-
(pentafluorophenyl)borane was purchased from Boulder Scientific,
purified by treatment with Me2SiH(Cl) in hexanes to remove water,
and sublimed (120 °C, dynamic vacuum). In the following, Ar )
2,6-diisopropylphenyl.
Yield: 0.054 g, 87%. 1H NMR: δ 7.13-7.00 (m, 6H, C6H3), 5.55
(s, 1H, CH), 4.30 and 3.03 (m, 2 × 2H, CH(CH3)2, JH-H ) 6.8 or
7.2 Hz), 3.51 (br s, 1H, NH), 1.62, 1.45, 1.28, and 1.24 (d, 4 ×
6H, CH(CH3)2, JH-H ) 6.8 or 7.2 Hz), 1.32 (s, 9H, NHC(CH3)3),
1.14 (s, 18H, NCC(CH3)3), 0.75 (s, 9H, ScC(CH3)3). 13C{1H}
NMR: δ 175.1 (NCC(CH3)3), 145.4, 143.3, 142.4, 126.7, 125.2,
and 124.6 (C6H3), 95.1 (CH), 54.6 (NHC(CH3)3), 45.2 (NCC-
(CH3)3), 35.6 (NHC(CH3)3), 33.4 (NCC(CH3)3), 32.2 (ScC(CH3)3),
29.4 and 28.2 (CH(CH3)2), 28.0, 26.4, 25.3, and 25.2 (CH(CH3)2).
Note: ScC(CH3)3 was not visible in the 13C{1H} NMR spectrum,
and this phenomenon was most likely due to the quadrupolar nature
of scandium, where I ) 7/2. Anal. Calcd for C40H66N3Sc: C, 75.78;
H, 10.49; N, 6.63. Found: C, 75.72; H, 10.31; N, 6.58.
Synthesis of 1a. The tert-butylamido methyl complex [ArNC-
(tBu)CHC(tBu)NAr]Sc(Me)(NHtBu) (0.152 g, 0.240 mmol) and
B(C6F5)3 (0.123 g, 0.240 mmol) were weighed out separately and
dissolved in hexane. A solution of B(C6F5)3 was added dropwise
to the stirred solution of the amido methyl reagent. The reaction
mixture was stirred for 2 h at room temperature, and then it was
left overnight at -36 °C. The supernatant was decanted off of the
pale yellow precipitate of 1a, and the solid was dried in vacuo.
1
Thermolysis of 2. 2 was dissolved in C6D6 and heated to 60 °C
for approximately 4 h, and then the temperature was raised to 70
°C for 17 h. At this point, the reaction was about 50% complete
and the resonances for the product 3 and HC(CH3)3 were present
Yield: 0.267 g, 97%. H NMR (T ) 248 K, toluene-d8): δ 6.96
and 6.82 (m, 6H, C6H3), 5.54 (s, 1H, CH), 5.39 (br s, 1H, NH),
2.56 (m, 4H, CH(CH3)2), 1.53 (br s, 3H, CH3B(C6F5)3), 1.41, 1.17,
1.10, and 1.02 (d, 4 × 6H, CH(CH3)2, JH-H ) 6.5 or 6.6 Hz),
0.85 (s, 18H, NCC(CH3)3), 0.58 (s, 9H, NHC(CH3)3). 13C{1H}
NMR (T ) 239 K, toluene-d8): δ ) 175.7 (NCC(CH3)3), 149.9,
147.5, 140.4, 136.1, 123.0, and 122.8 (C6F5), 143.1, 140.3, 139.0,
127.2, 124.6, 124.3 (C6H3), 86.4 (CH), 55.9 (NHC(CH3)3), 44.9
(NCC(CH3)3), 32.6 (NHC(CH3)3), 31.0 (NCC(CH3)3), 28.7 and 25.5
(CH(CH3)2), 25.2, 24.2, 24.1, and 23.2 (CH(CH3)2), 24.9 (CH3B).
19F NMR: δ -132.6 (d, 6F, o-F, JF-F ) 23.3 Hz ), -159.8 (br s,
3F, p-F), -164.4 (br s, 6F, m-F). 11B NMR: δ -15.1 (s, CH3B).
Anal. Calcd for C58H66N3F15BSc: C, 60.79; H, 5.81; N, 3.67.
Found: C, 60.70; H, 5.75; N, 3.55.
1
in the 400 MHz H NMR spectrum.
In Situ Synthesis of the Pyridine Adduct of 1a. The scandium
ion pair 1a (0.020 g, 0.0175 mmol) was dissolved in toluene-d8
and placed in an NMR tube; pyridine (1.4 µL, 0.0175 mmol) was
syringed into the tube. The NMR tube was briefly shaken, and then
the reaction mixture was characterized by 1H and 19F NMR
spectroscopy. 1H NMR (toluene-d8): δ 8.40 (m, 2H, NC5H5), 7.44
(m, 1H, NC5H5), 6.96 and 6.82 (m, 8H, C6H3 and NC5H5), 5.92
(s, 1H, CH), 4.52 (br s, 1H, NH), 2.64 and 2.30 (m, 2 ×
2H, CH(CH3)2), 1.24 (br s, 6H, CH(CH3)2), 1.20-0.91 (m, 21H,
CH(CH3)2 and CH3B(C6F5)3), 1.01 (s, 18H, NCC(CH3)3), 0.63 (s,
9H, NHC(CH3)3). 19F NMR (toluene-d8): δ -131.4 (d, 6F, o-F,
JF-F ) 19.1 Hz), -164.3 (t, 3F, p-F, JF-F ) 20.7 Hz), -166.5 (m,
6F, m-F).
Synthesis of 1b. The compound [ArNC(tBu)CHC(tBu)NAr]Sc-
(Me)(NHAr) (0.074 g, 0.100 mmol) and B(C6F5)3 (0.051 g, 0.100
mmol) were combined to synthesize 1b using the same method as
that employed to produce 1a. Yield: 0.103 g, 82%. 1H NMR (T )
228 K, toluene-d8): δ 7.65 (br s, 1H, NH), 6.85 (t, 2H, 3 × C6H3,
JH-H ) 7.7 Hz), 6.68 (m, 7H, 3 × C6H3), 6.10 (s, 1H, CH), 2.97
and 2.71 (m, 2 × 2H, CH(CH3)2, JH-H ) 6.4 Hz), 1.39 (br m, 5H,
NH-2,6-(CH(CH3)2)2C6H3 and CH3B(C6F5)3), 1.15, 1.09, 1.01, and
0.78 (d, 4 × 6H, CH(CH3)2, JH-H ) 6.4 Hz), 0.98 (s, 18H, NCC-
(CH3)3), 0.63 (d, 12H, NH-2,6-(CH(CH3)2)2C6H3, JH-H ) 6.4 Hz).
13C{1H} NMR (T ) 228 K, toluene-d8): δ 178.4 (NCC(CH3)3),
150.0, 147.7, 138.5, 138.1, and 136.0 (1 signals was unobserved
for C6F5), 147.5, 144.4, 141.9, 141.2, 141.1, 133.9, 133.8, 124.8,
123.4, and 120.5 (10 of 12 signals were observed for 3 × C6H3),
93.0 (CH), 44.5 (NCC(CH3)3), 32.2 (NH-2,6-(CH(CH3)2)2C6H3),
31.1 (NCC(CH3)3), 29.1 and 28.4 (CH(CH3)2), 28.6, 25.64,
25.59, and 24.1 (CH(CH3)2), 23.9 (NH-2,6-(CH(CH3)2)2C6H3), 19.4
(CH3B(C6F5)3). 19F NMR: δ -131.7 (d, 6F, o-F, JF-F ) 21.2 Hz),
Deprotonation of 1a with [(Me2N)3PdN]3PdNtBu. Complex
1a was prepared in situ by dissolving [ArNC(tBu)CHC(tBu)NAr]-
Sc(Me)(NHtBu) (0.006 g, 9.46 × 10-6 mol) and B(C6F5)3 (0.005
g, 9.77 × 10-6 mol) in C6D6 in a vial. To ensure the reaction went
to completion, the reaction mixture was stirred for 2 min. The
phosphazene base (0.006 g, 9.56 × 10-6 mol) was dissolved in a
separate vial in the same solvent. While the mixture was stirred
continuously, the phosphazene base solution was added dropwise
to the yellow solution of 1a. After approximately 10 min, the
reaction was complete and the known metalated neutral scandium-
amido species 3 and the new ion pair [[(Me2N)3PdN]3PdN(H)tBu]-
[MeB(C6F5)3] were present. The reaction went quantitatively to
completion, as shown by 1H, 19F, and 31P NMR spectroscopy.
Compound 3 was never isolated on a large scale by this method.
19F NMR: δ -131.9 (br s, 6F, o-F), -165.1 (br s, 3F, p-F), -167.3
-160.5 (t, 3F, p-F, JF-F ) 20.7 Hz), -164.6 (t, 6F, m-F, JF-F
)
2
(br s, 6F, m-F). 31P{1H} NMR: δ 10.9 (d, P[N(Me2)3]3, JP-P
)
20.7 Hz). 11B NMR (C6D5Br): δ -14.9 (s, CH3B). Anal. Calcd
for C66H74N3ScF15B: C, 63.42; H, 5.97; N, 3.36. Found: C, 63.03;
H, 6.01; N, 3.30.
2
47.6 Hz), -25.1 (q, PdNtBu, JP-P ) 47.6 Hz).
X-ray Crystallography for 1a. Measurements were made on a
Bruker PLATFORM/SMART 1000 CCD diffractometer using
graphite-monochromated Mo KR (0.710 73 Å) radiation. Crystal
data and refinement details are given in Table 1, and the crystal-
lographic information file is available as Supporting Information
and from the Cambridge Database (CCDC 299421).
Synthesis of 2. 1a (0.107 g, 0.0934 mmol) and tBuLi (0.007 g,
0.109 mmol) were weighed into a vial and dissolved in hexane (5
mL). The reaction mixture consisted of a yellow solution with
yellow-orange powder, and it was stirred overnight at room
temperature. The light orange precipitate was filtered off, and the
precipitate was washed with hexane (4 × 1 mL). (Caution! Dry
[Li][MeB(C6F5)3] has been known to detonate.) Following filtration,
the light orange precipitate of [Li][MeB(C6F5)3] was immediately
dissolved in toluene and water was added to the solution to
deactivate any remaining [Li][MeB(C6F5)3]. The four hexane
fractions and the filtrate were combined, and the solvent was
removed under reduced pressure, producing a yellow powder of 2.
Acknowledgment. Funding for this work came from the
Natural Sciences and Engineering Research Council of Canada
in the form of a Discovery Grant (to W.E.P.).
Supporting Information Available: A CIF file giving crystal-
lographic data and ORTEP diagrams for both molecules of 1a.
This material is available free of charge via the Internet at
http://pubs.acs.org.
(27) Peterson, T. H.; Golden, J. T.; Bergman, R. G. J. Am. Chem. Soc.
2001, 123, 455.
OM060197P