Nucleophilic degradation of a β-diketiminato ancillary by a transient scandium hydride intermediate

Article abstract of DOI:10.1021/om900700d

Reactions of a β-diketiminato-supported scandium dichloride LScCl ₂ (L = (Ar)NC(^tBu)CHC(^tBu)N(Ar); Ar = 2,6- ⁱPr₂-C₆H₃) with boro- and aluminohydride reagents result in transient

Full text of DOI:10.1021/om900700d

6228 Organometallics 2009, 28, 6228–6233
DOI: 10.1021/om900700d
Nucleophilic Degradation of a β-Diketiminato Ancillary by a Transient
Scandium Hydride Intermediate
Korey D. Conroy, Warren E. Piers,* and Masood Parvez
University of Calgary, 2500 University Drive N.W., Calgary, Canada, T2N 1N4
Received August 7, 2009
Reactions of a β-diketiminato-supported scandium dichloride LScCl2 (L = (Ar)NC(tBu)CHC-
(tBu)N(Ar); Ar = 2,6-iPr2-C6H3) with boro- and aluminohydride reagents result in transient
scandium hydrides, which undergo hydride transfer to the ligand backbone, inducing fragmentation
of the ancillary. The products of this fragmentation have been characterized and include an organic
enamine (2) and scandium imido containing clusters. One such product, formed via reaction with
LiBEt3H and LScCl2, is the trimer [ArNScCl(THF)]3[LiH(THF)], 1, which includes an occluded
molecule of lithium hydride. The reactions involving LiAlH4, along with labeling studies, helped to
clarify the fragmentation pathway and account for the observed products.
Introduction
cycles dominated by σ-bond metathesis and migratory in-
sertion reactions.2 For example, Cp*2Sc-H1a has been shown
by Tilley to mediate hydromethylation of olefins3 and de-
hydrosilylation of alkanes,4 albeit with low turnovers. Aside
from Cp*2Sc-H and Ind*2YH(THF),1b group 3 hydrides are
typically dimeric,5 oligomeric,6 or heteromultimetallic,7
although reactivity may be funneled through highly active
monomeric species. Most of the known examples of group 3
hydrides are stabilized by cyclopentadienyl-type donors;8
given their demonstrated potential for hydrocarbon functio-
nalization, new examples supported by other ancillary ligand
frameworks9 are of considerable interest.
Well-defined, monomeric hydrides of the group 3 metals
are rare,1 but potentially useful as mediators of catalytic
*To whom correspondence may be addressed. Tel: 403-220-5746.
E-mail: wpiers@ucalgary.ca.
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Maron, L.; Tilley, T. D. Organometallics 2008, 27, 2252.
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We,10 and others,11 have utilized the β-diketiminato ligand
framework to develop the chemistry of dialkyl organo group
3 compounds, and a logical extension of this work is to
explore the suitability of this ancillary for supporting reac-
tive scandium hydrides. Typically, early transition metal
hydrides are generated from alkyl precursors via hydrogeno-
lysis; in early studies, we found the dialkyl complexes I
(R = Me, CH2SiMe3) to react only slowly with H2 (4 atm)
and generate a complex mixture of products. Thus, we
turned to another more classical method,12 that of treatment
of scandium chloride antecedents with LiMH4 (M = B, Al),
to generate the desired hydride derivatives. While this tech-
nique has been utilized extensively to generate hydrides for
most metals in the d-block,13 typically group 3 hydridoborate
or hydridoaluminate complexes arise from such reactions. For
(8) For recent reviews, see: (a) Zeimentz, P. M.; Arndt, S.; Elvidge,
B. R.; Okuda, J. Chem. Rev. 2006, 106, 2404. (b) Arndt, S.; Okuda, J.
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Parvez, M.; Elsegood, M. R. J.; Clegg, W. Organometallics 2001, 20,
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McDonald, R. Organometallics 2004, 23, 2087. (c) Knight, L. K.; Piers,
W. E.; McDonald, R. Organometallics 2006, 25, 3289.
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Organometallics 2003, 22, 4705.
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Cendrowski-Guillaume, S. M.; Ephritikhine, M. J. Chem. Soc., Dalton
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W. J.; Ziller, J. W. J. Am. Chem. Soc. 1990, 112, 5674. (g) Baudry, D.;
Ephritikhine, M. J. Organomet. Chem. 1986, 311, 189. (h) Evans, W. J.;
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r
pubs.acs.org/Organometallics
Published on Web 10/09/2009
2009 American Chemical Society

Article
Organometallics, Vol. 28, No. 21, 2009 6229
Scheme 1
Chart 1
Results and Discussion
Clean reaction of the β-diketiminato scandium dichloride
(LScCl2) depicted in Scheme 1 with LiBEt3H occurs when
carried out with 1.3 equiv of the borohydride reagent in
toluene over the course of 12 h, yielding the scandium-
containing product 1 and the organic ene-amine 2. Initial
experiments utilized equimolar amounts of LScCl2 and
LiBEt3H led to more complex product mixtures from which
the unusual cluster 1 was isolated and characterized by X-ray
crystallography (see below). The occluded LiH evident in
this structure, present in a 1/3 ratio with scandium, suggested
that its clean production required an extra 0.33 equiv of
LiBEt3H, which was experimentally borne out in subsequent
preparations.
example, Morris and Smith reported the preparation of
14
Sc(BH4)3 THFn via reaction of anhydrous ScCl3 with a
3
slight excess of LiBH4 in THF. The first structurally char-
acterized borohydride of scandium, [Sc{η5-C5H3(Si-
Me3)2}2(BH4)], was prepared a decade later by Lappert
and co-workers,15 and several other examples of scandium
BH4 compounds have been subsequently identified.16
These compounds can be viewed as masked scandium
hydrides, protected by “BH3”; removal by treatment with a
Lewis base could potentially liberate a reactive scandium
hydride. Indeed, this was apparently observed by Fryzuk
et al. in the reaction of a PNP pincer ligand stabilized
scandium borohydride with PMe3, although the chemistry
was not clean enough to allow for exploration of the chem-
istry of the resulting scandium hydride.16c Furthermore,
Mindiola et al. have demonstrated that BEt3 is labile in
the complex II, prepared via reaction of LSc(NHAr)Cl
(Ar = 2,6-diisopropylphenyl) with NaHBEt3, liberating a
putative Sc-H species, which was trapped with a series of
oxygen-containing substrates.11
With these precedents in mind, we report the reactions of
the well-defined, monomeric, and base-free scandium
dichloride precursor to dialkyls I, in which the nacnac ligand
bears tert-butyl substituents, with the boro- and alumino-
hydride reagents LiHBEt3 and LiAlH4. These studies show
that this nacnac ligand framework does not support scan-
dium hydrides but undergoes fragmentation to yield imide-
containing clusters.
The ene-amine product 2 arises from the β-diketiminate
scaffold and was identified by GC/MS (m/z = 327 g/mol)
1
and H NMR spectroscopy. Characteristic resonances in
C6D6 include a well-resolved AB quartet centered at 5.80
ppm corresponding to the trans-coupled olefinic protons
(3JHH = 16.7 Hz) and two signals at 1.40 and 0.77 ppm for
the inequivalent tBu groups. Loss of this fragment necessa-
rily leaves “ArNdScCl”, which apparently assembles into
the trinuclear cluster 1, templated around LiH and stabilized
by THF molecules present since LiBEt3H is administered as
a 1.0 M solution in THF. Product 1 is isolated by precipita-
tion and washing with cold pentane; its 1H NMR spectrum
indicates the presence of two types of coordinated THF
ligands in a 3:1 ratio, assignable to the THF ligated to
scandium and lithium, respectively. In addition, signals for
one NAr group with diastereotopic isopropyl groups are
present in this C3v symmetric molecule. A singlet at -1.7 ppm
7
in the Li{1H} NMR spectrum is suggestive of an anionic
scandium “ate” complex9a and confirms the presence of
lithium in the cluster. No spectroscopic signature for the
central Sc3HLi hydride was observed, presumable due to
severe quadrupolar broadening.
As alluded to above, the nature of complex 1 was con-
firmed initially via X-ray crystallography. The compound is
highly soluble in aromatic and coordinating solvents and
moderately soluble in aliphatic solvents; thus, X-ray quality
crystals were grown by slow evaporation from concentrated
pentane solutions. The solid-state structure of 1 is shown in
Figure 1 along with selected metrical data. The Sc3N3 core
(14) Morris, J. H.; Smith, W. E. J. Chem. Soc., Chem. Commun. 1970,
245.
(15) Lappert, M. F.; Singh, A.; Atwood, J. L.; Hunter, W. E. J. Chem.
Soc., Chem. Commun. 1983, 206.
(16) (a) Mancini, M.; Bougeard, P.; Burns, R. C.; Mlekuz, M.; Sayer,
B. G.; Thompson, J. I. A.; McGlinchey, M. J. Inorg. Chem. 1984, 23,
1072. (b) Hagadorn, J. R.; Arnold, J. Organometallics 1996, 15, 984.
(c) Fryzuk, M. D.; Giesbrecht, G. R.; Rettig, S. J. Can. J. Chem. 2000, 78, 1003.

6230 Organometallics, Vol. 28, No. 21, 2009
Conroy et al.
Figure 2. Thermal ellipsoid diagram of 3 at 50% probability. All
hydrogen atoms except those associated with Al1 and most of the
carbon atoms of the aryl group attached to N1 are removed for
Figure 1. Thermal ellipsoid diagram of 1 at 50% probability.
All isopropyl groups, carbons of THF groups, and hydrogen
atoms except H1 are removed for clarity. Selected bond lengths
˚
clarity. Selected bond lengths (A): Sc1-N1, 2.122(2); Sc1-N2,
˚
(A): Sc1-N1, 2.037(2); Sc1-N2, 2.046(2); Sc1-O1, 2.166(2);
2.208(1); Sc1-Cl1, 2.416(1); Sc1-H01, 1.94(2); Sc1-H02, 1.92(2);
Sc1-H03, 1.97(2); Al1-O1, 1.978(1); Al1-O2, 1.985(1); Al1-
H01, 1.70(2); Al1-H02, 1.70(2); Al1-H(03), 1.71(2); Al1-H(04),
1.54(2). Selected bond angles (deg): N1-Sc1-N2, 92.95(5);
N1-Sc1-Cl1, 105.24(4); N2-Sc1-Cl1, 104.79(4); Cl1-Sc1-
H03, 157.0(5); O2-Al1-H02, 164.9(6). Selected torsion angles
(deg): N1-C3-C4-C5, 15.9(3); N2-C5-C4-C3, 29.6(3).
Sc1-Cl1, 2.443(1); Sc1-H1, 2.02(2); Sc2-N2, 2.038(2);
Sc2-N1, 2.040(2); Sc2-O2, 2.157(2); Sc2-Cl2, 2.485(1);
Sc2-H1, 2.00(2); Sc3-N3, 2.028(2); Sc3-N2, 2.037(2);
Sc3-O3, 2.157(2); Sc3-Cl3, 2.460(1); Sc3-H1, 1.98(2);
Li1-Cl1, 2.528(5); Li1-Cl2, 2.494(5); Li1-Cl3, 2.476(5);
Li1-O4, 1.963(5); Li1-H1, 2.11(3). Selected bond angles
(deg): N1-Sc1-N3, 122.05(8); N2-Sc2-N1, 118.78(8); N3-
Sc3-N2, 121.11(8); Sc1-N1-Sc2, 102.24(8); Sc2-N2-Sc3,
102.57(9); Sc3-N3-Sc1, 102.80(9).
structural motif; direct analogues appear to be absent from
the literature, but related examples in which the Li-H parti-
cipates in three-center-two-electron bonding arrangements
with other metals are known.18
adopts a six-membered chair conformation with the three
˚
scandium-bound chlorine atoms (Sc-Clav = 2.464(1) A) all
occupying axial positions in a cis arrangement. This posi-
A plausible sequence for the production of products 1 and
2 is shown in Scheme 1. The reaction likely proceeds through
initial salt metathesis to form a scandium borohydride
intermediate akin to II as observed by Mindiola et al.11 Since
II is an isolable species, it is likely that liberation of BEt3 is
facile in the present system; the greater steric demands of the
nacnac ligand featuring tert-butyl substituents may encou-
rage loss of triethylborane. In any event, the resulting
scandium hydrido chloride rapidly converts to the diamide
intermediate proposed via hydride transfer to the imine
carbon of the nacnac ligand. This intermediate undergoes
fragmentation via C-N bond cleavage to form 2 and a
scandium imide, which assembles into 1 in the presence of
a slight excess of LiBEt3H. Although unanticipated, related
fragmentations in titanium β-diketiminato complexes result-
ing in d0 imide19 and phosphinidene20 complexes provide
precedence for such behavior.
Further support for this proposal, in the form of spectro-
scopic observation of the diamide intermediate of Scheme 1,
was found in studying the reactions of LScCl2 with lithium
aluminum hydride. Reaction with 1 equiv of purified LiAlH4
in THF at -35 °C produces a new Cs symmetric β-diketimi-
nato-ligated scandium complex with no evidence for ligand
degradation, assigned as the aluminohydride adduct, 3
(Scheme 2). The effective C2v ligand symmetry present in
tions each chloride to effectively bind to Li(1) with average
˚
Cl-Li contacts of 2.499(5) A. Each scandium adopts a
distorted trigonal-bipyramidal geometry, with the encapsu-
lated hydride and oxygen from THF occupying the apical
positions. The hydride was crystallographically located and
is symmetrically bound to the three scandium centers with an
˚
average Sc-H bond length of 2.00(2) A. The tetrahedral
coordination sphere of H(1) is completed with a lithium ion,
˚
which features a Li(1)-H(1) distance of 2.11(3) A. All three
imide nitrogens are trigonal planar, and the Dipp groups
align essentially orthogonal to the Sc-N-Sc planes. The
structural rigidity imposes asymmetry on the top and bottom
isopropyl groups, which is borne out in the 1H NMR
˚
spectrum of 1. The Sc-N bond lengths average 2.038(2) A,
which are in good agreement with other bridging scandium
imides.17 The average N-Sc-N bond angles are larger than
the corresponding Sc-N-Sc angles by almost 15° presum-
ably due to the greater steric bulk at scandium versus
nitrogen. The encapsulated Li-H moiety is an unusual
(17) Beetstra, D. J.; Meetsma, A.; Hessen, B.; Teuben, J. H. Organo-
metallics 2003, 22, 4372.
(18) (a) Sellmann, D.; Hille, A.; Heinemann, F. W.; Moll, M.; Reiher,
M.; Hess, B. A.; Bauer, W. Chem.-Eur. J. 2004, 10, 4214. (b) Sellmann,
D.; Gottschalk-Gaudig, T.; Heinemann, F. W. Inorg. Chem. 1998, 37, 3982.
(c) Bazhenova, T. A.; Kachapina, L. M.; Shilov, A. E.; Antipin, M. Y.;
Struchtov, Y. T. J. Organomet. Chem. 1992, 428, 107. (d) Bohra, R.;
Hitchcock, P. B.; Lappert, M. F.; Au-Yeung, S. C. F.; Leung, W.-P. J. Chem.
Soc., Dalton Trans. 1995, 2999. (e) Dawson, D. M.; Meetsma, A.; Roedelof,
J. B.; Teuben, J. H. Inorg. Chem. Acta 1997, 259, 237. (f ) Etkin, N.; Hoskin,
A. J.; Stephan, D. W. J. Am. Chem. Soc. 1997, 119, 11420. (g) Lukens,
W. W. Jr.; Matsunaga, P. T.; Anderson, R. A. Organometallics 1998, 17,
5240. (h) Dube, T.; Gambarotta, S.; Yap, G. Organometallics 2000, 19, 121.
(19) (a) Basuli, F.; Bailey, B. C.; Tomaszewski, J.; Huffman, J. C.;
Mindiola, D. J. J. Am. Chem. Soc. 2003, 125, 6052. (b) Bailey, B. C.;
Basuli, F.; Huffman, J. C.; Mindiola, D. J. Organometallics 2006, 25, 3963.
(20) (a) Basuli, F.; Tomaszewski, J.; Huffman, J. C.; Mindiola, D. J.
J. Am. Chem. Soc. 2003, 125, 10170. (b) Zhao, G.; Basuli, F.; Kilgore, U. J.;
Fan, H.; Aneetha, H.; Huffman, J. C.; Wu, G.; Mindiola, D. J. J. Am. Chem.
Soc. 2006, 128, 13575.

Article
Organometallics, Vol. 28, No. 21, 2009 6231
Scheme 2
10
LScCl2 is disrupted in 3, indicating replacement of one
scandium chloride with a new ligand. In addition to two new
isopropyl septets at 3.80 and 3.27 ppm signaling the lowered
symmetry, a broad resonance at 3.07 ppm integrating to four
hydrogens was observed. The concomitant presence of a
broad singlet at 99.1 ppm12 in the 27Al{1H} NMR spectrum
is fully consistent with a scandium aluminohydride complex.
X-ray quality crystals of 3 were obtained by slow evapora-
tion of THF solutions at -35 °C, and the molecular structure
is shown in Figure 2 along with selected metrical data. The
four aluminum hydride atoms were located in the difference
map and refined in the solid-state structure, and the AlH4
unit is coordinated to scandium in the exo position10 through
three bridging hydrides with average Sc-H bond lengths of
imine carbon of the β-diketiminato framework are observed
during the course of the reaction (Figure 3). Excess LiAlH4
liberates the scandium hydrido chloride through the forma-
tion of LiAl2H7 (observed in the 27Al NMR spectrum δ = 87
ppm),21 which leads to diamide production. The presence of
the intermediate is indicated by two characteristic upfield
doublets at 4.91 and 4.53 ppm (3JHH = 5.6 Hz) correspond-
ing to the olefinic and aliphatic protons of the ligand back-
bone, respectively. When the analogous reaction is
performed with LiAlD4, the furthest upfield doublet is no
longer observed and the downfield signal becomes a 1:1:1
triplet (3JH-D = 1.3 Hz). On the basis of the NMR data, it
appears that C-N cleavage is rate limiting in this system, as
the concentration of the diamide increases over time at the
expense of 3, reaching a maximum before eventually con-
verting entirely to a new scandium-containing product con-
comitant with production of 2. Stoichiometry dictates that
this new scandium product is “ArNdScCl”, which in the
absence of LiBEt3H forms a cluster of undefined nuclearity
and THF incorporation. 1H NMR spectroscopy indicates a
symmetrical product on the basis of a single isopropyl group,
but all attempts to obtain X-ray quality crystals from the
product mixture were unsuccessful, as the material consis-
tently forms extremely thin crystalline plates that were
not suitable for diffraction. Efforts are continuing to charac-
terize this potentially useful synthon for scandium imido
derivatives.
˚
1.94(2) A, which are slightly shorter than the analogous
distances in the solid-state structure of 1. The trio of three-
center-two-electron bonds serve to elongate the Al-H01-03
˚
bonds by 0.16 A relative to the nonbridging Al-H04, which is
1.54(2) A. Two THF molecules complete the coordination
˚
sphere of aluminum with Al-O bond lengths of 1.978(1) and
1.985(1) A. The β-diketiminato ligand deviates noticeably
from planarity, with backbone torsion angles of 15.9(3)°
and 29.6(3)°, with the backbone C4 residing below the
plane formed by N1-C3-C5-N2. The Sc-N contacts
˚
˚
˚
(Sc1-N1 = 2.122(2) A; Sc1-N2 = 2.208(1) A) are also
˚
asymmetric, differing by almost 0.1 A. A weak interaction
appears present between C4 and Cl1, as the endo chloride is
10
canted further under the ancillary than in LScCl2 The
N-Sc-Cl bond angles at 105.24(4)° and 104.79(4)° are
significantly smaller in 3 than in the dichloride precursor
(cf. 113.5(2)° and 116.0°),10 which supports this weak in-
tramolecular interaction.
Conclusions
While scandium alkyls are tolerated by β-diketiminato
ligands, hydrides rapidly transfer from the metal to the imine
carbon of the ligand. This results in a transiently observed
intermediate in which the nacnac ligand is transformed to a
chelate of amide-enamide character; this species fragments
via C-N bond cleavage to yield an enamine organic product
(2) and a scandium imido fragment that assembles into
higher nuclearity products. Thus, although the nacnac ligand
proves unsuitable for supporting scandium hydrides, their
transient generation here points to their potentially high
reactivity. With ligands less prone to nucleophilic reduction,
perhaps this reactivity can be harnessed. Another avenue for
investigation that arises from these studies is the possibility
Although stable indefinitely at -35 °C in solution, 3 does
decompose when warmed to room temperature to a mixture
of products, including a small amount of the ene-imine
ligand fragment 2; this, in addition to the high solubility of
the compound, contributes to its low isolated yield of 47%.
In an effort to study the decomposition, LScCl2 was treated
with an excess (2.5 equiv) of LiAlH4 at -35 °C in a J-Young
NMR tube and slowly warmed to room temperature in the
NMR probe. Monitoring the reaction over 24 h reveals
clean, quantitative conversion of LScCl2 through 3 en route
to a new scandium imide product and loss of the ene-imine
fragment 2 (Scheme 2). Interestingly, in this system signals
for an intermediate assignable to the proposed diamide
intermediate formed as a result of hydride transfer to the
(21) Atwood, J. L.; Hrncir, D. C.; Rogers, M. J.; Howard, J. A. K.
J. Am. Chem. Soc. 1981, 103, 4277.

6232 Organometallics, Vol. 28, No. 21, 2009
Conroy et al.
Figure 3. Series of 400 MHz 1H NMR spectra monitoring reaction of LScCl2 with 2.5 equiv of LiAlH4 in d8-THF at 25 °C.
of using the scandium-containing imido cluster products as
synthons for well-defined, monomeric scandium imides.22
CFCl3 using an external standard of hexafluorobenzene
(δ -163.0 ppm) in C6D6. NMR data are provided in ppm.
The coupling constants (i.e., 3JH-H) for the isopropyl groups on
the ligand range between 6.4 and 7.2 Hz and, thus, are not
reported in the NMR analysis of the compounds. Elemental
analyses were performed by Mrs. Dorothy Fox and Mr. John-
son Li in the microanalytical laboratory at the University of
Calgary. Complexes containing scandium have been routinely
found to be low in carbon, possibly as a result of metal-catalyzed
carbide formation, leading to incomplete combustion.25 X-ray
data were collected on a Bruker P4/RA/SMART 1000 CCD
diffractometer using Mo KR radiation at -100 °C.
Experimental Section
General Procedures. All manipulations were performed either
in an Innovative Technologies System One inert atmosphere
glovebox or on greaseless vacuum lines equipped with Teflon
needle valves (Kontes) using swivel-frit-type glassware. Tolu-
ene, THF, and hexanes were dried and purified using the
Grubbs/Dow purification system23 and stored in evacuated
bombs. Bromobenzene and d5-bromobenzene were predried
over CaH2, and d8-THF, d6-benzene, and d8-toluene were dried
and stored over sodium/benzophenone. All were distilled prior
to use. I-Cl was synthesized using a literature procedure.9
LiAlH4 was extracted into anhydrous ether and recrystallized
prior to use, and LiBEt3H was used as a 1.0 M solution in THF
from Aldrich, and the 1H and 11B NMR spectra were obtained
to assess purity; no evidence for LiBEt4 or LiBEt2H2 was
found.24
Synthesis of [ClScNDipp(THF)]3[LiH(THF)], 1. A 100 mL
two-neck flask was charged with LScCl2 (1.510 g, 2.44 mmol)
dissolved in 60 mL of toluene added in vacuo at -78 °C. The
solution was warmed to room temperature, and LiBEt3H (1.0 M
in THF, 3.66 mL) was added dropwise via syringe through a
rubber septum. The reaction mixture was stirred overnight,
whereupon a cloudy dark yellow solution was obtained. Tolu-
ene was removed in vacuo, and the flask was attached to a swivel
frit apparatus in the glovebox. The assemblage was evacuated,
and fresh toluene (50 mL) was vacuum distilled into the flask.
The mixture was sonicated for 30 min at room temperature and
filtered, and solvent removed under vacuum to afford a dark
orange oil. Pentane (25 mL) was added and the mixture soni-
cated for 20 min, then cooled to -35 °C and back-filtered. The
off-white solid was washed with 3 Â 5 mL of pentane
and evacuated to dryness. X-ray quality crystals were grown
from concentrated pentane solutions at -35 °C (0.620 g, 1.76
Samples were analyzed by NMR spectroscopy on Bruker
AMX-300 and DRX-400 spectrometers at room temperature
1
unless otherwise specified. H and 13C were referenced to Si-
(CH3)4 through the residual peaks of the employed solvent, 11
B
spectra to external BF3 OEt2 at 0.0 ppm, and 19F spectra to
3
(22) (a) Scott, J.; Basuli, F.; Fout, A. R.; Huffman, J. C.; Mindiola,
D. J. Angew. Chem., Int. Ed. 2008, 47, 8502. (b) Giesbrecht, R. R.; Gordon,
J. C. Dalton Trans. 2004, 2387.
(23) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;
Timmers, F. J. Organometallics 1996, 15, 1518.
1
mmol, 72%). H NMR (C6D6): δ 7.24 (d, 3H; C6H3), 7.12 (d,
3H; C6H3), 6.83 (t, 3H; C6H3), 4.71 (sp, 3H; CHMe2), 4.05
(24) (a) Fryzuk, M. D.; Lloyd, B. R.; Clentsmith, G. K. B.; Rettig,
S. J. J. Am. Chem. Soc. 1994, 116, 3804. (b) Fryzuk, M. D.; Lloyd, B. R.;
Clentsmith, G. K. B.; Rettig, S. J. J. Am. Chem. Soc. 1991, 113, 4332.
(25) Fryzuk, M. D.; Giesbrecht, G. R.; Rettig, S. J. Organometallics
1996, 15, 3329.

Article
Organometallics, Vol. 28, No. 21, 2009 6233
Table 1. Data Collection and Refinement Details for 1 and 3
Characterization of DippNC(tBu)CHCH(tBu), 2. 1H NMR
(C6D6): δ 7.19 (d, 2H; C6H3), 7.04 (t, 1H; C6H3) 5.80 (dd, 2H;
CHdCHtBu), 3.02 (sp, 2H; CHMe2), 1.40 (s, 9H; NCCMe3),
1.28 (ov d, 12H; CHMe2), 0.77 (s, 9H; NCCMe3). 13C{1H}
NMR (C6D6): δ 172.4 (NCCMe3), 150.3 (Me3CCH), 148.4,
133.9, 122.7, 122.6 (C6H3), Me3CHCHCCMe3) 41.3, 37.1
(CMe3), 28.5, 28.4 (CMe3), 28.2 (CHMe2) 23.2, 22.1
(CHMe2). GC-MS (m/z): 327 g/mol.
1
3
formula
C
52H84Cl3LiN3O4Sc3
C43H73AlClN2-
O2Sc 0.5C4H8O
793.48
triclinic
P1
9.698(1)
13.072(3)
19.616(4)
82.282(10)
79.336(14)
68.963(13)
2274.7(7)
2
173(2)
0.71073
1.158
864
0.277
0.22 Â 0.07 Â 0.06
0.9836-0.9415
2.60-27.49
10 365/6/542
3
fw
cryst syst
space group
1063.39
monoclinic
P21/c
14.195(1)
14.779(3)
27.634(4)
90
100.489(9)
90
5700.4(15)
4
173(2)
˚
a, A
Synthesis of [LScCl][AlH4(THF)2], 3. A 20 mL vial was
charged with LScCl2 (0.250 g, 0.405 mmol) and LiAlH4 (0.017
g, 0.445 mmol), and 5 mL of THF was added. The vessel was
shaken vigorously for 5 min and then cooled to -35 °C for
7 days, over which time large colorless needles were obtained.
The supernatant was removed, and the solid was dried in vacuo
˚
b, A
˚
c, A
R, deg
β, deg
γ, deg
3
˚
V, A
Z
T, K
1
to afford pure 3 (0.144 g, 0.190 mmol, 47%). H NMR (d8-
THF): δ 6.95 (m, 6H; C6H3), 5.73 (s, 1H; CH), 3.78 (sp, 2H;
CHMe2), 3.27 (sp, 2H; CHMe2), 3.07 (br s, 4H; AlH4), 1.39 (d,
6H; CHMe2), 1.31 (d, 6H; CHMe2), 1.24 (ov d, 12H; CHMe2),
1.16 (s, 18H; NCCMe3), THFAl resonances were not observed
due to scrambling with d8-THF. 13C{1H} NMR (d8-THF): δ
173.7 (NCCMe3), 148.0 (Cipso), 146.5, 143.0, 141.6 (C6H3), 140.4
(Cipso), 124.3, 123.5, 123.1 (C6H3), 94.3 (CH), 44.4 (CMe3), 32.2
(CHMe2), 32.0 (CMe3), 29.8 (CHMe2), 27.9, 27.7, 26.3, 25.2
(CHMe2). 27Al NMR (d8-THF): 99.1. Anal. Calcd for
C43H73AlClN2O2Sc: C, 68.18; H, 9.71; N, 3.70. Found: C,
67.23; H, 10.02; N, 3.58.
˚
λ, A
0.71073
1.239
2264
F
calc, g/cm3
F(000)
μ, mm-1
0.530
cryst size, mm3
transmn factors
θ range, deg
no. of data/restraints/
params
0.22 Â 0.20 Â 0.10
0.9489-0.8923
2.66-27.46
12 871/0/602
GoF
1.013
0.0476
0.0729
0.492 and -0.440
1.019
0.0416
0.0697
0.392 and -0.361
R1 (I > 2σ(I))
wR2 (all data)
residual density, e/A
3
˚
Acknowledgment. Funding for this work was provided
by the National Science and Engineering Research Coun-
cil in the form of a Discovery Grant to W.E.P. and
scholarships to K.D.C. (PGS-A and CGS-D). K.D.C.
also acknowledges Alberta Ingenuity for a Studentship
Award. The authors also thank Prof. Paul G. Hayes
(Lethbridge) for preliminary experiments.
(sp, 3H; CHMe2), 3.98 (br s, 4H; THFLi), 3.27 (br m, 12H;
THFSc), 1.58 (d, 18H; CHMe2), 1.42 (d, 18H; CHMe2), 1.25 (m,
4H; THFLi), 0.88 (m, 12H; THFSc), Li-H not observed. 13C-
{1H} NMR (C7D8): δ 153.8, 137.6, 134.4, 124.1, 122.1, 117.3
(C6H3), 71.1 (THFSc), 33.4 (THFLi), 28.3 (CHMe2), 26.5
(THFSc), 25.2, 24.5 (CHMe2), 22.4 (THFLi), 13.9 (CHMe2).
7Li NMR (C6D6): δ -1.7. Anal. Calcd for C52H84Cl3Li-
N3O4Sc3: C, 58.73; H, 7.96; N, 3.95. Found: C, 58.25; H, 8.20;
N, 4.19.
Supporting Information Available: Crystallographic data
(CIF) for 1 and 3. This information is available free of charge
via the Internet at http://pubs.acs.org.