Contacted ion-pair lithium alkylamidoaluminates: Intramolecular alumination (Al-H exchange) traps for TMEDA and PMDETA

Article abstract of DOI:10.1021/om900736a

Exploring the reactivity of mixed-metal synergic bases, it is found that the lithium TMP aluminate ⁱBu₃ Al(TMP)Li functions as a dual TMP/alkyl base, exhibiting 2-fold AMM Al (alkali-metal-mediated alumination) toward TMEDA to yield the heterobimetallic bis-(deprotonated TMEDA) derivative [Li{Me₂NCH₂CH₂N(Me)CH ₂}₂Al(ⁱBu)₂] (2). In contrast, the amide enriched aluminate ⁱBu₂Al(TMP)₂Li acts as only a single-fold amido base toward TMEDA or PMDETA to afford the aminedeprotonated derivatives [Li{Me₂NCH₂CH ₂N(Me)CH₂}(TMP)Al(ⁱBu)₂] (4) and [Li{Me₂NCH₂CH₂N(Me)CH₂CH ₂N(Me)CH₂}(TMP)Al(ⁱBu)₂] (5), respectively. On their own, the aluminum compounds ⁱBu₃Al or ⁱBu₂Al(TMP) are not sufficiently strong bases to metalate TMEDA or PMDETA, so in 2, 4, and 5, the α-deprotonations of TMEDA and PMDETA are synergic in origin, as the intramolecular communication between Li and Al appears to activate the TMP and ⁱBu bases. This special behavior can be attributed to intramolecular proximity effects between the active base component (TMP or ⁱBu) and the ligating TMEDA or PMDETA molecule. X-ray crystallography studies reveal 2 is a contacted ion-pair ate containing two a-aluminated TMEDA ligands, which chelate the lithium cation which is linked to the distorted tetrahedral Al center by two N bridges from the metalated junction of the TMEDA molecules. In contrast, 4 and 5 have a mixed NCH₂-TMP bridging ligand set, completed by two terminal ⁱBu ligands on Al and a chelating metalated TMEDA or PMDETA ligand attached to Li, respectively. In addition, the ¹H, ⁷Li, and ¹³C{¹H} spectra of 2 (recorded in C₆D ₆ solutions), 4, and 5 (recorded in cyclohexane solutions-d ₁₂) are disclosed.

Full text of DOI:10.1021/om900736a

6462 Organometallics 2009, 28, 6462–6468
DOI: 10.1021/om900736a
Contacted Ion-Pair Lithium Alkylamidoaluminates: Intramolecular
Alumination (Al-H Exchange) Traps for TMEDA and PMDETA
,‡
†
†
Ben Conway,† Joaquı
n Garcıa-Alvarez,* Eva Hevia, Alan R. Kennedy,
ꢀ
´ ´
Robert E. Mulvey,*,† and Stuart D. Robertson†
†WestCHEM, Department of Pure and Applied Chemistry, University of Strathclyde,
‡
Glasgow G1 1XL, U.K., and Departamento de Quımica Organica e Inorganica, Instituto Universitario de
´
Quımica Organometalica “Enrique Moles” (Unidad Asociada al CSIC), Facultad de Quımica,
ꢀ
ꢀ
´
ꢀ
´
Universidad de Oviedo, E-33071 Oviedo, Spain
Received August 24, 2009
Exploring the reactivity of mixed-metal synergic bases, it is found that the lithium TMP aluminate
iBu3Al(TMP)Li functions as a dual TMP/alkyl base, exhibiting 2-fold AMMAl (alkali-metal-mediated
alumination) toward TMEDA to yield the heterobimetallic bis-(deprotonated TMEDA) derivative
i
[Li{Me2NCH2CH2N(Me)CH2}2Al(iBu)2] (2). In contrast, the amide enriched aluminate Bu2Al-
(TMP)2Li acts as only a single-fold amido base toward TMEDA or PMDETA to afford the amine-
deprotonated derivatives [Li{Me2NCH2CH2N(Me)CH2}(TMP)Al(iBu)2] (4) and [Li{Me2NCH2-
CH2N(Me)CH2CH2N(Me)CH2}(TMP)Al(iBu)2] (5), respectively. On their own, the aluminum com-
pounds iBu3Al or iBu2Al(TMP) are not sufficiently strong bases to metalate TMEDA or PMDETA, so
in 2, 4, and 5, the R-deprotonations of TMEDA and PMDETA are synergic in origin, as the
intramolecular communication between Li and Al appears to activate the TMP and iBu bases. This
special behavior can be attributed to intramolecular proximity effects between the active base
i
component (TMP or Bu) and the ligating TMEDA or PMDETA molecule. X-ray crystallography
studies reveal2 isacontacted ion-pair atecontainingtwoR-aluminated TMEDA ligands, whichchelate
the lithium cation which is linked to the distorted tetrahedral Al center by two N bridges from the
metalated junction of the TMEDA molecules. In contrast, 4 and 5 have a mixed NCH2-TMP bridging
i
ligand set, completed by two terminal Bu ligands on Al and a chelating metalated TMEDA or
1
7
PMDETA ligand attached to Li, respectively. In addition, the H, Li, and 13C{1H} spectra of 2
(recorded in C6D6 solutions), 4, and 5 (recorded in cyclohexane solutions-d12) are disclosed.
Introduction
ortho-metalation (DoM) reactivity.2-4 Furthermore, on the
basis of our synthetic, reactivity, NMR spectroscopic, and
X-ray crystallographic studies, a reaction scheme involving
previously unconsidered solvent-separated ion-pair species
and a dismutation process was postulated.5 In addition, we
First reported in 2004 by Uchiyama et al., lithium TMP-
aluminate “iBu3Al(TMP)Li” (where TMP is the sterically
demanding amide 2,2,6,6-tetramethylpiperidide) is an excel-
lent base reagent in THF, realizing highly chemo- and
regioselective deprotonative aluminations of functionalized
aromatic and heteroaromatic compounds as well as of
functionalized allylic compounds.1 Theoretical and experi-
mental studies have revealed that this TMP-aluminate
acts as an amido base, exhibiting only single-step directed
were able to report5 the complex [(THF)3 Li{O(dC)-
3
N(iPr)2(C6H4)}Al(iBu)3] as the first tangible metallo inter-
mediate of a direct alumination reaction (performed in THF
solutions) of N,N-diisopropylbenzamide, or indeed of any
functionalized aromatic compound, to be structurally de-
fined and fully characterized.6 We also described that carry-
ing out the same reaction in a nonpolar solvent (hexane)
*To whom correspondence should be addressed. E-mail: r.e.mulvey@
strath.ac.uk (R.E.M.) and garciajoaquin.uo@uniovi.es (J.G.-A.).
(1) (a) Uchiyama, M.; Naka, H.; Matsumoto, Y.; Ohwada, T. J. Am.
Chem. Soc. 2004, 126, 10526. (b) Naka, H.; Uchiyama, M.; Matsumoto, Y.;
Wheatley, A. E. H.; McPartlin, M.; Morey, J. V.; Kondo, Y. J. Am. Chem.
Soc. 2007, 129, 1921.
(2) Naka, H.; Morey, J. V.; Haywood, J.; Eisler, D. J.; McPartlin, M.;
Garcia, F.; Kudo, H.; Kondo, Y.; Uchiyama, M.; Wheatley, A. E. H.
J. Am. Chem. Soc. 2008, 130, 16193.
(4) For an authoritative review on “complex-induced proximity effect
(CIPE)” in DoM see: Whisler, M. C.; MacNeil, S.; Snieckus, V.; Beak, P.
Angew Chem., Int. Ed. 2004, 43, 2206. For reviews in DoM of aromatic
systems through alkali-metal-mediated alumination (and metalation in gen-
eral), see: (a) Mulvey, R. E.; Mongin, F.; Uchiyama, M.; Kondo, Y. Angew.
Chem., Int. Ed. 2007, 46, 3802. (b) Mulvey, R. E. Acc. Chem. Res. 2009, 42,
743.
(3) This is in contrast to most TMP-zincate bases which exhibit two-
step DoM, see: Nobuto, D.; Uchiyama, M. J. Org. Chem. 2008, 73, 1117,
although the second step can be inhibited by coordination saturation at the
zinc center, see: Clegg, W.; Conway, B.; Graham, D. V.; Hevia, E.; Kennedy,
A. R.; Mulvey, R. E.; Russo, L.; Wright, D. S. Chem.;Eur. J. 2009, 15,
7074.
(5) Conway, B.; Hevia, E.; Garcia-Alvarez, J.; Graham, D. V.;
Kennedy, A. R.; Mulvey, R. E. Chem. Commun. 2007, 5241.
(6) Crystal structures of three different Lewis base-stabilized deriva-
tives [L Li(μ-TMP)(μ-iBu)(iBu)2] have been previously described by us
3
in: Garcia-Alvarez, J.; Hevia, E.; Kennedy, A. R.; Klett, J.; Mulvey,
R. E. Chem. Commun. 2007, 2402.
r
pubs.acs.org/Organometallics
Published on Web 10/09/2009
2009 American Chemical Society

Article
Organometallics, Vol. 28, No. 22, 2009 6463
the regioselectivity of which depends on the identity of
t
the deprotonating agent. Thus, by means of BuLi14a or
nBuLi,14b,c lithiation of TMEDA in the terminal methyl
group is achieved, while its methylene metalation is observed
when the superbase LICKOR is used,14a followed by elim-
ination of potassium dimethylamide. Only a select few
methods have been proven to be effective in direct deproto-
nation of other nonfunctionalized amines. To date,
these include deprotonation of: (i) monodentate amines as
N-methylpiperidine (metalated at a CH3 position by the
Lochmann-Schlosser base),15 (ii) bidentate amines as
1,3-dimethyl-1,3-diazacyclohexane (deprotonated at the
disfavored position between the two nitrogen atoms with
tBuLi)16a,b and N,N,N0,N0-tetramethylcyclohexane-1,2-dia-
mine ((R,R)-TMCDA, lithiated at a terminal CH3 group by
tBuLi),17 (iii) tridentate amines as N,N0,N00-trimethyl-1,4,7-
triazacyclononane18 (lithiated at a CH3 position by nBuLi),
MeN[(CH2)2NMe2]2 (N,N,N0,N00,N00-pentamethyldiethyle-
netriamine, PMDETA, lithiated at a terminal or central
CH3 group depending on the concentration of the alkyl
lithium reagent),19 and 1,3,5-trimethyl-1,3,5-triazacyclohex-
ane (TMTAC, deprotonated at a methylenic (CH2) group
Figure 1. Structure of [{PhC(dO)N(iPr)2} Li{2-[1-C(dO)N-
3
(iPr)2]C6H4}{Me2NCH2CH2N(Me)CH2}Al(iBu)2] (1).
instead of THF, the aforementioned LiTMP-aluminate can
function as a dual TMP/alkyl base in the synthesis of the
complex [{PhC(dO)N(iPr)2} Li{2-[1-C(dO)N(iPr)2]C6H4}-
3
{Me2NCH2CH2N(Me)CH2}Al(iBu)2] (1) (see Figure 1) that
combines ortho-alumination of N,N-diisopropylbenzamide
with methyl-alumination of TMEDA (N,N,N0,N0-tetra-
methylethylenediamine, Me2NCH2CH2NMe2).7 As pre-
viously noted by Clayden,8 “direct deprotonation R to
nitrogen is usually impossible to achieve (except for superba-
sic reagents) unless the lone pair of the nitrogen atom is
involved in conjugation with a carbonyl group or delocalized
around an aromatic ring.” This general process, direct R-
metalation of tertiary amines, is a desirable synthetic route to
polar heteroatom-containing organometallics but is ham-
pered due, as previously mentioned, to the destabilization of
the developing carbanions by the repulsion with the lone pair
electron density of the adjacent nitrogen atom.9 Usually,
multistep procedures such as BF3-activation of amines,10
transmetalation (in particular, tin/lithium exchange),11 or
C-S/C-Te bond breakages12 are necessary to access these
useful synthetic reagents, but generally these provide only
moderate yields. Only a few examples exist for which direct
deprotonation of otherwise nonfunctionalized amines has
been demonstrated. Although TMEDA’s primary role in
organometallic chemistry13 is as a bidentate N donor ligand,
it does, on prolonged exposure to certain organoalkali
reagents, undergo different direct R-metalation reactions,
t
between the two nitrogen atoms with BuLi),16a,b and (iv)
tetradentate amines as bis(3-methyl-1,3-diazacyclohex-1-
yl)methane and its five-ring analogue (regioselectively de-
protonated at both endocyclic NCH2N units by tBuLi).16c
In this work, we present the regioselective direct lithium-
mediated methyl-alumination of TMEDA by two different
i
LiTMP-aluminates. Thus, Bu3Al(TMP)Li is capable of
metalating two molecules of TMEDA in a one-pot reaction,
establishing, as previously described in a communication by
us,7 that this TMP-aluminate can function as a dual TMP/
alkyl base, while moving to the dialkyl-diamido aluminate
iBu2Al(TMP)2Li only one molecule of TMEDA could be
metalated. Significantly, this dialkyl-diamido aluminate
iBu2Al(TMP)2Li can also undergo lithium-mediated meth-
yl-alumination of a terminal CH3-group of PMDETA.
Results and Discussion
As we have previously described, mixing LiTMP, iBu3Al,
TMEDA, and N,N-diisopropylbenzamide in bulk hydrocar-
bon solvent generates the heterobimetallic trianionic
(7) Garcia-Alvarez, J.; Graham, D. V.; Kennedy, A. R.; Mulvey, R.
E.; Weatherstone, S. Chem. Commun. 2006, 3208.
(8) Clayden, J. In Organolithiums: Selectivity for Synthesis, Tetrahe-
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P. v. R. in Lithium Chemistry; John Wiley & Sons: New York, 1995, p. 195.
(b) Bordwell, N. R.; Vanler, R.; Zhang, X. J. Am. Chem. Soc. 1991, 113,
9856. (c) Schlosser, M., Ed. Organometallics in Synthesis;A Manual 2nd
ed.; Wiley: New York, 2002.
complex [{PhC(dO)N(iPr)2} Li{2-[1-C(dO)N(iPr)2]C6H4}-
3
{Me2NCH2CH2N(Me)CH2}Al(iBu)2] (1) (see Figure 1). At-
tempting to shed more light on this unexpected R-alumina-
tion of TMEDA, the same reaction methodology was
employed but avoiding the addition of the aromatic amide.
(10) Kessar, S. V.; Singh, P. Chem. Rev. 1997, 97, 721.
(11) (a) Seyferth, D.; Weiner, M. A. J. Org. Chem. 1959, 24, 1395.
(b) Peterson, D. J. J. Organomet. Chem. 1970, 21, 63. (c) Peterson, D. J. J.
Am. Chem. Soc. 1971, 93, 4027. (d) Tian, X.; Woski, M.; Lustig, C.; Pape, T.;
(15) (a) Schlosser, M.; Hartmann, J. Angew. Chem. 1973, 85, 544.
Angew. Chem., Int. Ed. 1973, 12, 508. (b) Bauer, W.; Lochmann, L. J. Am.
Chem. Soc. 1992, 114, 7482.
€
Frohlich, R.; Le Van, D.; Bergander, K.; Mitzel, N. W. Organometallics
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€
2005, 24, 82. (e) Tian, X.; Frohlich, R.; Pape, T.; Mitzel, N. W. Organome-
(16) (a) Bojer, D.; Kamps, I.; Tian, X.; Hepp, A.; Pape, T.; Frohlich,
€
tallics 2005, 24, 5294. (f) Tian, X.; Frohlich, R.; Mitzel, N. W. Dalton Trans.
R.; Mitzel, N. W. Angew. Chem. 2007, 119, 4254. Angew. Chem., Int. Ed.
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2007, 46, 4176. (b) See also: Kohn, R. D.; Seifert, G.; Kociok-Kohn, G.
Chem. Ber. 1996, 129, 1327. (c) Kamps, I.; Mix, A.; Berger, R. J. F.;
Neumann, B.; Stammler, H.-G.; Mitzel, N. W. Chem. Commun. 2009, DOI:
10.1039/b909561f.
(12) (a) Gawley, R. E.; Zhang, Q. J. Org. Chem. 1995, 60, 5763.
(b) Quintard, J.-P.; Elissondo, B.; Jousseaume, B. Synthesis 1984, 495. (c)
Trost, B. M., Fleming, I., Eds. in Comprehensive Organic Synthesis;
Pergamon Press: New York, 1991. (d) Strohmann, C.; Abele, B. C. Angew.
Chem., Int. Ed. Engl. 1996, 35, 2378.
(13) For an enlightening discussion on the role of TMEDA in group 1
chemistry, see: (a) Collum, D. B. Acc. Chem. Rev. 1992, 25, 448. See also:
(b) Langer, A. W. Polyamine-Chelate Alkali Metal Compounds; Advances in
Chemistry Series; American Chemical Society: Washington, DC, 1974; p 130.
(14) (a) Kohler, F. H.; Hertkorn, N.; Blumel, J. Chem. Ber. 1987, 120,
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(c) Hildebrand, A.; Lonnecke, P.; Silaghi-Dumitrescu, L.; Silaghi-Dumitrescu,
I.; Hey-Hawkins, E. Dalton Trans. 2006, 967. (d) Gessner, V. H.; Strohmann,
C. J. Am. Chem. Soc. 2008, 130, 14412.
(17) (a) Strohmann, C.; Gessner, V. H. Angew. Chem. 2007, 119, 8429
(b) Angew. Chem., Int. Ed. 2007, 46, 8281.
(18) Arnold, J.; Knapp, V.; Schmidt, J. A. R.; Shafir, A. J. Chem.
Soc., Dalton Trans. 2002, 3273.
(19) (a) Schakel, M.; Aarnts, M. P.; Klumpp, G. W. Recl. Trav. Chim.
Pays-Bas 1990, 109, 305. (b) Klumpp, G. W.; Luitjes, H.; Schakel, M.; de
Kanter, E. J. J.;Schmitz, R. F.;vanEikemaHommes, N. J. R.C. Angew. Chem.
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€
€

6464 Organometallics, Vol. 28, No. 22, 2009
Conway et al.
P21/c, can be considered a contacted ion pair, with both N
atoms of the metalated junction of TMEDA chiral as each is
attached to four different substituents, although overall the
crystals are racemic. The anionic moiety comprises a dis-
torted tetrahedral Al center (range of C-Al-C bond angles
101.78(9)-117.29(10)°) made up of four C atoms, from two
terminal iBu ligands (with the shortest Al-C bonds
(Al(1)-C(13) 2.017(2) A, Al(1)-C(17) 2.013(2) A]) and
two R-deprotonated TMEDA molecules (with the longest
Al-C bonds (Al(1)-C(1) 2.032(2) A, Al(1)-C(7) 2.029(2)
A), in the same range as the Al-C bond length found in the
metalated TMEDA units of 1 (2.0327(17) A)).7 Contact to
the cationic moiety is through the two N atoms from the
metalated junction of the TMEDA molecules, which bind to
Li to complete a distorted tetrahedral coordination sphere of
N atoms (range of N-Li-N bond angles 87.35(13)-128.38-
(17)°), the remaining two of which belong to the unmetalated
end of TMEDA. The Li-N bonds involving the metalated
part of TMEDA (Li(1)-N(1) 2.060(3)A, Li(1)-N(3)
2.045(3) A)) are significantly shorter than the Li-N bonds
in the unmetalated part (Li(1)-N(2) 2.198(3) A, Li(1)-N(4)
2.182(4) A). Overall, the Al and Li centers are held together
in an irregularly shaped 12-membered LiNCCN-
CAlCNCCN tricyclic ring, containing a smaller six-mem-
bered AlNCLiNC ring, which, surprisingly, does not have
the expected chair conformation but displays a boat-shape
conformation. This probably occurs because this six-mem-
bered ring is also attached to another two five-atom rings
(LiNCCN) to build together the larger dodecatricyclic ring.
1H, 13C, and 7Li NMR spectra recorded in benzene-d6
solution were obtained for 2 with only one set of resonances,
supporting the diastereoselective formation of this com-
pound (note that two stereogenic centers are generated,
namely both N atoms of the metalated junction of TMEDA).
All the anticipated different types of hydrogen atoms in 2 are
Figure 2. Molecular structure of [Li{Me2NCH2CH2N(Me)-
CH2}2Al(iBu)2] (2) with selective atom labeling. Hydrogen
atoms have been omitted for clarity. Selected bond lengths (A)
and angles (deg): Al(1)-C(1) 2.032(2), Al(1)-C(7) 2.029(2),
Al(1)-C(13) 2.017(2), Al(1)-C(17) 2.013(2), Li(1)-N(1)
2.060(3), Li(1)-N(2) 2.198(3), Li(1)-N(3) 2.045(3), Li(1)-N(4)
2.182(4); C(1)-Al(1)-C(7) 103.83(9), C(1)-Al(1)-C(13)
109.89(9), C(1)-Al(1)-C(17) 117.29(10), C(7)-Al(1)-C(13)
113.91(10), C(7)-Al(1)-C(17) 101.78(9), C(13)-Al(1)-C(17)
109.92(10), N(1)-Li(1)-N(2) 87.85(13), N(1)-Li(1)-N(3)
113.48(16), N(1)-Li(1)-N(4) 127.99(17), N(2)-Li(1)-N(3)
128.38(17), N(2)-Li(1)-N(4) 116.61(16), N(3)-Li(1)-N(4)
87.35(13).
Scheme 1. Lithium-Mediated Alumination of Two Molecules of
TMEDA
1
accounted for and well-resolved in its H NMR spectrum,
nBuLi was converted to LiTMP by initial addition of the
amine TMP(H) followed by TMEDA (or vice versa), and
the reaction (see Scheme 1) was completed by addition of
the trialkylaluminium (iBu3Al) reagent. Surprisingly, the
crystalline product obtained [Li{Me2NCH2CH2N(Me)-
CH2}2Al(iBu)2] (2) contains two molecules of methyl-alumi-
nated TMEDA, which bridge both metals in a contacted ion-
pair type molecular structure (Figure 2). Moreover, as 2 was
still obtained even when a deficiency of TMEDA was
employed (in the 1:1 stoichiometric reaction), it can be
inferred that the putative intermediate [Li{Me2NCH2CH2-
N(Me)CH2}(iBu)Al(iBu)2] or [Li{Me2NCH2CH2N(Me)-
CH2}(TMP)Al(iBu)2] (products of amido and alkyl basicity,
respectively) is more reactive than the initial lithium TMP-
aluminate “iBu3Al(TMP)Li”. Thus, the reaction was there-
fore repeated in line with the stoichiometry found in 2 by
adding an extra molar equivalent of TMEDA and this
caused an increase in the yield of 2 (from 15 to 48%, see
Scheme 1). This result establishes that TMP-aluminates can
function as dual alkyl/amido bases7 even with relatively
nonacidic (N)C-H bonds as ultimately one methyl group
from each of two molecules of TMEDA are deprotonated in
this one-pot reaction. It is important to note that on its own
iBu3Al is not a strong enough base to metalate TMEDA, so
both deprotonations of this reaction are synergic in origin, as
the contacted Li appears to activate the Al-attached TMP
the most significant features being the two doublet signals
(AB spin system, JHA, HB = 12.9 Hz) at 1.15 and 2.02 ppm
for both protons of the metalated NCH2 unit of TMEDA.
The Me2N and Me0N resonances appear at 1.63 and 2.27
ppm, respectively, while all four H atoms of the two unique
CH2 groups are inequivalent, having separate resonances at
1.53, 1.80, 2.21, and 2.53 ppm, consistent with the rigid,
tricyclic conformation of the structure. Similarly, the 13C
NMR spectrum of 2 is easily fully assignable (see Experi-
mental Section for details). The reaction filtrate that re-
mained after isolating the crystalline product 2 was also
1
probed by NMR techniques. The H NMR spectrum in-
dicated that the oily filtrate appeared to contain the afore-
mentioned signals for 2 and free TMP(H) (consistent with
the amido basicity of 2) but accompanied with a complicated
mixture of products in minor yield.
As we have previously demonstrated, deprotonations of
both TMEDA molecules in 2 are synergic in origin, as the
contacted Li appears to activate the Al-attached TMP and
iBu bases. To probe whether the remaining terminal two iBu
ligands in 2 were able to bring about a metalation of a third
(or even fourth) TMEDA molecule, we decided to repeat the
synthetic process for 2 (see Scheme 1) but adding an extra
excess (3 or 4 mol equiv) of TMEDA. However, this made no
difference as we always recover from these reactions
[Li{Me2NCH2CH2N(Me)CH2}2Al(iBu)2] (2) as a crystalline
solid in similar yields to those found when the reaction
is carried out with 2 equiv of TMEDA. Furthermore, the
i
and one of the Bu groups of the base. The molecular
structure of 2 (see Figure 2), belonging to the space group

Article
Organometallics, Vol. 28, No. 22, 2009 6465
Scheme 2. Lithium-Mediated Alumination of One Molecule of
TMEDA by a Dialkyldiamidoaluminate Base
1H NMR analysis of the filtrate revealed the presence of
nonmetalated TMEDA and free TMP(H), showing that the
two remaining iBu groups in 2 fail to metalate any additional
molecule of TMEDA or even the more acidic amine TMP-
(H). This lack of basicity could be related to the fact that in
compound 2, lithium is coordinatively saturated and there-
fore it cannot bind to another molecule of TMEDA, which
we believe should be the first step to induce an intramolecular
R-deprotonation (vide infra, Scheme 3). This was supported
by our findings when we investigated the deprotonation of
TMEDA using an alternative solvent-separated ion-pair
Figure 3. Molecular structure of [Li{Me2NCH2CH2N(Me)-
CH2}(TMP)Al(iBu)2] (4) with selective atom labeling. Hydro-
gen atoms have been omitted for clarity. Selected bond lengths
(A) and angles (deg): Al(1)-N(3) 1.9869(13), Al(1)-C(12)
2.0658(17), Al(1)-C(30) 2.0340(16), Al(1)-C(40) 2.0319(17),
Li(1)-N(1) 2.000(3), Li(1)-N(2) 2.086(3), Li(1)-N(3) 2.035(3);
N(3)-Al(1)-C(12) 99.57(6), N(3)-Al(1)-C(30) 121.47(7),
N(3)-Al(1)-C(40) 115.57(6), C(12)-Al(1)-C(30) 106.57(7),
C(12)-Al(1)-C(40) 110.56(7), C(30)-Al(1)-C(40) 102.71(7),
N(1)-Li(1)-N(2) 88.58(12), N(1)-Li(1)-N(3) 114.87(14),
N(2)-Li(1)-N(3) 151.46(15).
i
lithium aluminate. Thus, we prepared Bu3Al(TMP)Li in
THF solution following literature procedures,1 which
was proposed to contain solvent-separated ion pairs of
general formula [{Li(THF)x}þ{Al(TMP)n(iBu)4-n}-]5 then
added an equimolar amount of TMEDA to the reaction
mixture. However, this procedure gave only a white oily
heterotrianionic complex [Li{Me2NCH2CH2N(Me)CH2}-
(TMP)Al(iBu)2] (4) in an isolated crystalline yield of 55%.
1H, 13C, and 7Li NMR spectra recorded in cyclohexane-d12
solution were obtained for 4. The 1H NMR spectrum clearly
shows the expected pattern for methyl-aluminated TMEDA,
mimicking that previously described for 2 (NCH2Al 1.39 and
1.58 (1H each, AB spin system, d, JHA, HB = 14.0 Hz) ppm;
NCH2 1.96 (2H, m), 2.73 and 2.94 (1H each, m) ppm;
1
product. Its H NMR spectrum indicates that the oil con-
tains unmetalated TMEDA. Thus, this observation seems to
rule out the use of separated ion pairs of general formula
[{Li(THF)x}þ{Al(TMP)n(iBu)4-n}-] to achieve metalation
of TMEDA, as the aforementioned close proximity between
the substrate TMEDA and the Al(TMP)n(iBu)4-n fragment,
thought necessary to promote the intramolecular deproto-
nation, is no longer present.
1
N(CH3)2 (2.24, 2.73, and 2.74 (3H each, s) ppm). This H
NMR spectrum also reveals the presence of two iBu groups
and one TMP ligand (see Supporting Information). The
reaction filtrate that remained after isolating the crystalline
1
The success in the metalation of TMEDA observed in 2 by
i
using Bu3Al(TMP)Li prompted us to investigate its amide
product 4 was also probed by NMR techniques. The H
NMR spectrum indicated that this reaction is almost quan-
titative, as the oily filtrate appears to contain only the
aforementioned signals for 4 and free TMP(H). Thus, to-
ward TMEDA, the lithium dialkyldiamidoaluminate
iBu2Al(TMP)2Li acts as an amido base, exhibiting only
single-step AMMAl (alkali-metal-mediated alumination)
reactivity in contrast to the dual amido/alkyl basicity of
enriched congener, that is, iBu2Al(TMP)2Li (previously pro-
posed as a component in the dismutation process of iBu3Al-
(TMP)Li in pure THF),5 obtained by mixing LiTMP with
iBu2Al(TMP) (3). Organoaluminum amides (R2AlNR02)20
can be easily prepared from the metathesis reaction of
the corresponding lithium amide and the dialkylaluminum
halide. For iBu2Al(TMP) 3, even though it was pre-
viously found to be highly effective for the Fischer indole
synthesis21a and asymmetrization of meso-cyclic ketones,21b
to the best of our knowledge, no NMR spectroscopic data
for it have been reported. We report such data here. In
particular, the 1H NMR spectrum is very informative,
showing the presence of two well-defined sets of signals,
one for the iBu groups (0.17 (4H, d, CH2-Al iBu), 1.01 (12H,
d, CH3-iBu), and 1.94 (2H, sept, CH-iBu) ppm) and the other
for the amide TMP (1.29 (12H, s, CH3 of TMP), 1.31 (4H, m,
β-TMP), 1.72 (2H, m, γ-TMP) ppm), in a 2:1 ratio. By simply
mixing together a hexane solution of freshly prepared
i
the trialkylamidoaluminate Bu3Al(TMP)Li. It should be
i
noted that, as aforementioned for 2 with Bu3Al, the orga-
noaluminium amide iBu2Al(TMP) (3) is not a strong enough
base to metalate TMEDA, so the deprotonation observed in
this reaction is also synergic in origin, as the contacted Li
appears to activate one of the Al-attached TMP ligands. The
molecular structure of 4 (Figure 3) features a five-atom, four-
element LiNCAlN ring, with a mixed NCH2-TMP bridging
ligand set, and is completed by two terminal iBu ligands on
Al and a chelating metalated TMEDA (N,N-attached) to Li.
Overall, the Al and Li centers are held together in an
irregularly shaped octa-LiNCCNCAlN bycyclic ring, with
a Li-N hinge. The Al center displays a distorted tetrahedral
geometry (subtending bond angles from 99.57(6)°
{N(3)-Al(1)-C(12)} to 121.47(6)° {N(3)-Al(1)-C(30)})
i
LiTMP with the diisobutylaluminium amide Bu2Al(TMP)
before a molar equivalent of the Lewis base (TMEDA)
was introduced, we obtained the heterobimetallic-
i
made up of three C atoms, from two terminal Bu ligands
(20) (a) Mole, T.; Jeffrey, E. A. In Organoaluminium Compounds;
Elsevier: Amsterdam, 1972. (b) Ooi, T.; Maruoka, K. Sci. Synth.s 2004, 7,
225.
(21) (a) Naruse, Y.; Yamamoto, H. Tetrahedron 1988, 44, 6021.
(b) Maruoka, K.; Oishi, M.; Yamamoto, H. J. Org. Chem. 1993, 58, 7638.
(with the shortest Al-C bonds {Al(1)-C(40) 2.0319(17) A,
Al(1)-C(30) 2.0340(16) A}) and one deprotonated TMEDA
molecule (with the longest Al-C bonds {Al(1)-C(12)
2.0658(17) A}), as previously reported for 2, with the fourth

6466 Organometallics, Vol. 28, No. 22, 2009
Scheme 3. Proposed Stepwise Reaction Pathway for the Formation of 2
Conway et al.
atom the N of the amido TMP (Al(1)-N(3) 1.9869(13) A),
with a bond length in the same range as the Al-N distances
the smaller size of lithium, that in the lithium case TMEDA
will be in closer proximity to the TMP bridge to facilitate a
subsequent intramolecular Me deprotonation. In the first
step, TMEDA is intramolecularly R-aluminated by activated
TMP, with concomitant elimination of TMPH to yield the
intermediate A (not isolated or detected), which is more
reactive than the initial lithium TMP-aluminate “iBu3Al-
(TMP)Li” as 2 was still obtained even when a deficiency of
TMEDA was employed. This putative intermediate can
react now in two different ways: (i) With an additional
equivalent of TMEDA (pathway a), where the chelating
found in other structures of general formula (donor
3
Li(TMP)Al(iBu)3).1b,6 The wide Al(1)-C(12)-N(1) bond
angle at 116.86(10)° is marginally less than those in 2 (Al(1)-
C(1)-N(1), 118.28(13)°; Al(1)-C(7)-N(3), 120.06(13)°) and
these fall in a similar range to those reported in the
closely related terminally dialuminated TMEDA comp-
lexes R2AlCH2N(Me)CH2CH2N(Me)CH2AlR2 (R = Me,
113.9(1)°; R = tBu, 116.3(2)/116.2(2)°), which in contrast to
2 and 4 were prepared by a conventional metathesis approach
from the corresponding dilithium complex.11e Note that an
even wider Al-C(H)2-N bond angle (121.5(2)°) is found in
diamine could coordinate to lithium, because the Li iBu
3 3 3
contact in A can be expected to be relatively weak,23 allowing
the formation of intermediate24 B (not isolated or detected).
In a final step, one of the neighboring iBu groups attached to
Al intramoleculary deprotonates one NMe2 arm of the
TMEDA, to close a six-member {LiNCAlCN} ring, afford-
(tBu2AlCH2NiPr2 LiCl)2.11f Contact from aluminum to the
3
lithium atom in 4 is through one amido (TMP) nitrogen atom
(Li(1)-N(3) 2.035(3) A) and one nitrogen of the metalated
junction of TMEDA (Li(1)-N(1) 2.000(3) A). The remaining
nitrogen atom of TMEDA also binds to Li, displaying the
longest Li-N bond distance (Li(1)-N(2) 2.086(3) A) to
complete a distorted trigonal coordination sphere of N atoms
(subtendingbond anglesfrom 88.58(12)° {N(1)-Li(1)-N(2)}
to 151.46(15)° {N(2)-Li(1)-N(3)}).
i
ing compound 2 and releasing BuH. (ii) Alternatively, A
could react with the concomitant TMP(H) formed during the
metalation of the first equivalent of TMEDA (pathway b),
affording compound 4. In this compound, the TMP ligand
forms a strong bridge between Li and Al, which is retained in
solution as evidenced by the inequivalence of the four methyl
groups of the TMP ligand in the 1H and 13C{1H} spectra (see
Experimental Section). As above-mentioned, our reactivity
After the successful isolation of the monometalated TME-
DA compound 4, which established that the lithium dialkyl-
diamidoaluminate iBu2Al(TMP)2Li acts as only a single-step
amido base, we investigated whether the remaining amido
bridging ligand or the terminal iBu groups were able to bring
about a metalation of a second TMEDA molecule as seen in
compound 2. Thus, we repeated the aforementioned synth-
esis of 4 but adding an extra molar equivalent of TMEDA.
However, this led only to recovery of [Li{Me2NCH2CH2-
N(Me)CH2}(TMP)Al(iBu)2] (4) as a crystalline solid with the
excess of unmetalated TMEDA and free TMP(H) observed
in the filtrate, even when more drastic reaction conditions
were employed.22 This observation apparently rules out 4 as
an intermediate in the formation of 2 and suggests that the
presence of an additional bridging TMP ligand in 4 inhibits
the metalation of a second molar equivalent of TMEDA.
A reaction sequence can be proposed (see Scheme 3) to
rationalize the formation of 2. While the structure of the
starting complex is as yet not known, the sodium congener
has been found to adopt this structure and it is likely given
i
studies show that 4 (prepared by reacting Bu2Al(TMP)2Li
with 1 equiv of TMEDA) fails to metalate TMEDA. This can
now be rationalized in terms of the coordination sphere of Li,
which forms three strong Li-N bonds (Li-N bond dis-
tances: 2.000(3), 2.086(3), and 2. 0340(16) A), making the
alkali-metal coordinatively and electronically saturated and
leaving no place for the coordination of an additional
molecule of TMEDA. Because this precoordination seems
to be crucial for the deprotonation to take place, the forma-
tion of 2 must occur through the alternative reaction path-
way a. The stronger Lewis basicity of TMEDA versus that of
(23) NMR studies on the related [(THF) Li(TMP)Al(iBu3)] showed
that in solution the three isobutyl groups appear equivalent, suggesting
3
that these Li C bonds are forming/breaking fast in the NMR time
3 3 3
scale, see ref 1b.
(24) A similar open contacted ion-pair motif with a tetracoordinated
lithium bridged to aluminium by an ortho-metalated benzamide in
(22) Long reaction times at room temperature (48 h) or refluxing
conditions (hexane or toluene) only yield 4 as the major product.
compound [(THF)3 Li{O(dC)N(iPr)2(C6H4)}Al(iBu)3] has been pre-
viously reported by us in ref 5.
3

Article
Organometallics, Vol. 28, No. 22, 2009 6467
Scheme 4. Lithium-Mediated Alumination of One Molecule of
PMDETA by a Dialkyldiamidoaluminate Base
Figure 4. Structure of [Li{Me2NCH2CH2N(Me)CH2CH2N(Me)-
CH2}(TMP)Al(iBu)2] (5).
bulky TMP(H) and also its bidentate nature may be impor-
tant factors in favoring this reaction pathway.
filtrate appears to contain only the aforementioned reso-
nances for 5 and free TMP(H). Again, we decided to check if
i
the remaining amido bridging ligand or the terminal Bu
After the success in the R-metalation of TMEDA by means
of lithium(TMP)aluminates, we decided to extend this chem-
istry to the tridentate ligand PMDETA, which is commonly
used as a coordinating additive to break up organolithium
aggregates and thus to aid solubility and reaction kinetics.25
As previously mentioned, PMDETA is lithiated at a terminal
or central CH3 group depending on the concentration of the
alkyllithium compound.19,26 Thus, attempting to achieve R-
alumination of PMDETA, the same reaction methodology
used in the synthesis of 2 was employed but substituting
TMEDA by PMDETA. However, this procedure gave only
a white oily product. In this case, a 1H NMR spectrum
indicates that the oil appeared to contain metalated PMDE-
TA but accompanied with a complicated mixture of pro-
ducts. As no useful structural information could be gleaned
from this oil, we decided to utilize the lithium dialkyldiami-
doaluminate iBu2Al(TMP)2Li in anticipation of a directed R-
alumination of PMDETA (see Scheme 4). This was indeed
realized as the solid product of the reaction was the hetero-
bimetallic-heterotrianionic complex [Li{Me2NCH2CH2-
N(Me)CH2CH2N(Me)CH2}(TMP)Al(iBu)2] (5) obtained in
a crystalline yield of 47%.
groups were able to bring about a second metalation of
another methyl group of PMDETA. Therefore, we repeated
the aforementioned synthesis of 5 but employed more drastic
reaction conditions (refluxing the mixture in toluene solution
for 2 h). However, even by using 2 equiv of PMDETA, we
always recovered only [Li{Me2NCH2CH2N(Me)CH2-
CH2N(Me)CH2}(TMP)Al(iBu)2] (5) as a crystalline materi-
al. It should be mentioned that, as aforementioned for 4,
i
the organoaluminium amide Bu2Al(TMP) (3) is not a
powerful enough base to metalate PMDETA, so the
deprotonation observed in this reaction is also synergic in
origin, as the contacted Li appears to activate one of the Al-
attached TMP ligands. A low resolution crystal structure of 5
confirmed its previously discussed components and their
connectivity, featuring an undeca LiNCCNCCNCAlN tri-
cyclic ring, containing two five-atom, three-element
LiNCCN rings and a five-atom, four-element LiNCAlN
ring, with a mixed NCH2-TMP bridging ligand set com-
i
pleted by two terminal Bu ligands on Al and a chelating
metalated PMDETA (N,N,N-attached) to Li, in agreement
with findings from the aforementioned NMR spectroscopic
studies (Figure 4).
7
1H, 13C, and Li NMR spectra recorded in cyclohexane-
d12 solution were obtained for 5 with only one set of
resonances, supporting the diastereoselective formation of
this compound (note that two stereogenic centers are gener-
ated, namely the two N atoms of the metalated junction of
PMDETA). The 1H NMR spectrum clearly shows the
expected pattern for methyl-aluminated PMDETA, similar
to that for TMEDA previously described for 2 and 4
In conclusion, this work establishes that lithium TMP
i
aluminates can function as dual TMP/alkyl (for Bu3Al-
i
(TMP)Li) or as mono amido bases (for Bu2Al(TMP)2Li)
exhibiting two-fold or single-fold AMMAl (alkali-metal-
mediated alumination), respectively, toward TMEDA or
i
i
PMDETA. On their own, Bu3Al or Bu2Al(TMP) are not
sufficiently strong bases to metalate TMEDA or PMDETA,
so in 2, 4, and 5, the R-deprotonations of TMEDA and
PMDETA are synergic based, as the intramolecular com-
munication between Li and Al appears to activate the TMP
(NCH2Al 1.07 and 1.82 (d, AB spin system, JHA, HB
=
13.4 Hz, ppm; NCH2 1.98, 2.12, and 2.95 (1H, m), 2.42 (3H,
m), and 2.73 (2H, m) ppm; N(CH3)2 2.22 (6H, s), 2.34, and
2.37 (3H each, s) ppm). This 1H NMR spectrum also shows
the presence of two iBu groups and one TMP ligand in 5 (see
Supporting Information). Thus, again, the lithium dialkyl-
diamidoaluminate iBu2Al(TMP)2Li acts as only a single-step
amido base toward PMDETA. The reaction filtrate that
remained after isolating the crystalline product 5 was also
checked by NMR spectroscopy. A 1H NMR spectrum
indicates that this reaction is almost quantitative as the oily
i
and Bu bases. Finally, it further establishes that by using
AMMAl the normal patterns of reactivity can be reversed
with a TMEDA nonacidic C-H bond breaking in preference
to an acidic TMP(H) N-H bond. This special behavior can
be attributed to intramolecular proximity effects between the
i
active base component (TMP or Bu) and the ligating
TMEDA molecule. It remains to be established whether
these bimetallic alumination traps can be utilized to depro-
tonate other donor ligand molecules usually resistant to
conventional organometallic bases.
€
(25) See for example: (a) Schumann, U.; Kopf, J.; Weiss, E. Angew.
Chem. 1985, 97, 222. Angew. Chem., Int. Ed. Engl. 1985, 24, 215.
(b) Engelhardt, L. M.; Leung, W.-P.; Raston, C. L.; Salem, G.; Twiss, P.;
White, A. W. J. Chem. Soc., Dalton Trans. 1988, 2403. (c) Karsch, H. H.;
Zellner, K.; Mikulcik, P.; Lachmann, J.; M€uller, G. Organometallics 1990, 9,
190. (d) Lappert, M. F.; Engelhardt, L. M.; Raston, C. L.; White, A. H.
J. Chem. Soc., Chem. Commun. 1982, 1323.
Experimental Section
General Procedures. All reactions were carried out under a
protective argon atmosphere using standard Schlenk techni-
ques. Hexane was dried by heating to reflux over sodium
benzophenone ketyl and distilled under nitrogen prior to use.
(26) Polar metalation of PMDETA has been described in: (a) Eller-
€
man, J.; Schutz, M.; Heinemann, F. W.; Moll, M.; Bauer, W. Chem. Ber.
i
i
nBuLi, Bu3Al, and Bu2AlCl were purchased from Aldrich
1997, 130, 141. (b) Izod, K.; Steward, J. C.; Clegg, W.; Harrington, R. H.
Dalton Trans. 2007, 257.
Chemicals and used as received. NMR spectra were recorded

6468 Organometallics, Vol. 28, No. 22, 2009
Conway et al.
on a Bruker DPX 400 MHz spectrometer, operating at 400.15
MHz for 1H, 150.32 MHz for 7Li, and 100.62 MHz for 13C.
X-ray Crystallography. Crystal data for 2: C20H48AlLiN4,
M = 378.54, monoclinic, P21/c, a = 9.2581(3), b= 15.4470(5),
c= 18.2432(5) A, β = 99.457(2)°, V = 2573.50(14) A3, Z = 4,
T = 223 K. Data were collected on a Nonius Kappa CCD
diffractometer with Mo KR radiation (λ = 0.71073 A), 31196
reflections collected, 5063 were unique, Rint 0.053. Final refine-
ment27 to convergence was on F2, R = 0.0501 (F, 3351 obsd
data only) and Rw = 0.1291, F2 all data), GOF = 1.013, 293
refined parameters, residual electron density max and min
0.294 and -0.224 e A-3. Crystal data for 4: C23H51AlLiN3,
M = 403.59, monoclinic, P21/n, a = 10.3165(4), b= 15.3891(6),
c= 17.0248(7) A, β = 105.505(4)°, V = 2604.52(18) A3, Z = 4,
T = 123 K. Data were collected on an Oxford Diffraction
Gemini S diffractometer with Mo KR radiation (λ = 0.71073
A), 23211 reflections collected, 5742 were unique, Rint 0.0441,
R = 0.0457 (F, 4043 obsd data only), and Rw = 0.1136, F2 all
data), GOF = 0.999, 287 refined parameters, residual electron
Synthesis of [Li{Me2NCH2CH2N(Me)CH2}(TMP)Al(iBu)2]
(4). Bu2Al(TMP) was synthesized as above and added via
i
canula to a freshly prepared solution of LiTMP in 10 mL of
hexane (from a mixture of nBuLi (2 mmol, 1.25 mL of a 1.6 M
solution in hexane) and TMPH (2 mmol, 0.34 mL) to give an
homogeneous solution. Finally, 0.30 mL (2 mmol) of TMEDA
were injected and the reaction mixture left to stir for 30 min
before the Schlenk tube was placed in the freezer overnight
(-28 °C). A crop (0.44 g, 55%) of colorless crystals formed in
solution that were suitable for X-ray crystallographic analysis.
1H NMR (400.13 MHz, cyclohexane-d12, 300 K): 0.17 (4H, m,
i
CH2-Al Bu), 0.76 and 0.89 (1H each, m, β-TMP), 0.90, 0.94,
0.99, and 1.00 (3H each, d, 3JHH = 6.4 Hz, CH3-iBu), 1.31 (6H,
s, 2 CH3 of TMP), 1.34 and 1.44 (3H each, s, CH3 of TMP), 1.39
and 1.58 (1H each, d, AB spin system, JHA, HB = 14.0 Hz,
Al-CH2N of TMEDA), 1.69 (2H, m, β-TMP), 1.80 (1H, sept,
3JHH = 6.4 Hz, CH-iBu), 1.96 (5H, m, 2H CH2-TMEDA, 2H γ-
TMP, and 1H CH-iBu), 2.24, 2.73, and 2.74 (3H each, s, CH3-
TMEDA), 2.73 and 2.94 (1H each, m, CH2-TMEDA). 13C{H}
NMR (100.63 MHz, cyclohexane-d12, 300 K): 18.10 (γ-TMP),
26.08 (CH of iBu), 27.06, 27.16, 27.45, and 27.67 (CH3 of iBu),
28.68, 28.80, and 29.59 (CH3-TMP), 35.39 and 36.34 (β-TMP),
45.34, 46.43, and 48.07 (CH3 TMEDA), 47.39 (Al-CH2N
TMEDA), 51.36 and 52.30 (R-TMP), 56.36 and 59.9 (CH2-
TMEDA). Signal for Al-CH2 of iBu was not observed. 7Li NMR
(155.50 MHz, cyclohexane-d12, 300 K, reference LiCl in D2O at
0.00 ppm): 1.20.
density max and min 0.337 and -0.242 e A-3
.
Synthesis of [Li{Me2NCH2CH2N(Me)CH2}2Al(iBu)2] (2). In
a Schlenk tube, 4 mmol of TMEDA (0.60 mL) were added to a
hexane solution of LiTMP (prepared freshly from a mixture of
nBuLi (2 mmol, 1.25 mL of a 1.6 M solution in hexane) and
TMPH (2 mmol, 0.34 mL)) to give a yellow solution. After the
solution had been stirred for 30 min, iBu3Al (2 mmol, 2 mL of a 1
M solution in hexane) was introduced and the mixture changed
from a yellow to a slightly cloudy yellow solution. This mixture
was heated gently to form a yellow solution, which was allowed
to cool to ambient temperature. Freezer cooling of this solution
at -27 °C afforded colorless crystals of 2 (0.37 g, 48%). Note
that adding only 1 mol equiv of TMEDA also produced 2, but in
a smaller yield. 1H NMR (400.13 MHz, benzene-d6, 300 K): 0.43
(4H, m, CH2-Al iBu), 1.15 and 2.02 (2H each, d, AB spin system,
Synthesis of [Li{Me2NCH2CH2N(Me)CH2CH2N(Me)CH2}-
(TMP)Al(iBu)2] (5). Complex 5, isolated as colorless crystals
(0.43 g, 47%), was prepared as previously described for 4 but
using the N-donor ligand PMDETA (2 mmol, 0.42 mL) instead
of TMEDA. 1H NMR (400.13 MHz, cyclohexane-d12, 300 K):
0.23 (4H, m, CH2-Al iBu), 0.91 and 0.95 (3H each, d, 3JHH = 6.4
Hz, CH3-iBu), 0.99 (6H, d, 3JHH = 6.4 Hz, CH3-iBu), 1.07 and
1.82 (1H each, d, AB spin system, JHA, HB = 13.4 Hz, Al-CH2N
of PMDETA), 1.18 and 1.71 (2H each, m, β-TMP), 1.34 and
1.37 (6H each, s, CH3 of TMP), 1.71 (m, 2H, γ-TMP), 1.87 (1H,
m, CH-iBu), 1.98 (2H, m, 1H of CH2-PMDETA and 1H of
CH-iBu), 2.12 and 2.95 (1H each, m, CH2-PMDETA), 2.27 (6H,
CH3-PMDETA), 2.34 and 2.37 (3H each, CH3-PMDETA), 2.42
(3H, m, CH2-PMDETA), 2.73 (2H, m, CH2-PMDETA). 13C-
{H} NMR (100.63 MHz, cyclohexane-d12, 300 K): 18.32
JHA, HB = 12.9 Hz), Al-CH2N of TMEDA), 1.46 and 1.48 (6H
each, d, 3JHH = 6.8 Hz, CH3-iBu), 1.53, 1.80, 2.21, and 2.53 (2H
each, m, 4 CH2-TMEDA), 1.63 (12H, broad s, 4 CH3-TMEDA),
2.27 (6H, s, 2 Al-CH2N(CH3) of TMEDA), 2.45 (2H, sept, 3JHH
= 6.8 Hz, CH-iBu). 13C{H} NMR (100.63 MHz, benzene-d6,
300 K): 29.87 (CH of iBu), 30.36 and 30.58 (CH3 of iBu), 31.10
(Al-CH2N TMEDA), 46.87 (Al-CH2N(CH3) TMEDA), 49.92
(CH3 TMEDA), 58.87 and 61.96 (CH2-TMEDA). Signal for Al-
CH2 of iBu was not observed. 7Li NMR (155.50 MHz, benzene-
d6, 300 K, reference LiCl in D2O at 0.00 ppm): -0.13.
i
(γ-TMP), 26.08 (CH of Bu), 27.14, 27.22, 27.53, and 27.77
i
(CH3 of Bu), 29.19 and 29.76 (CH3-TMP), 32.58 (b, CH2 of
Synthesis of iBu2Al(TMP) (3). Ten mL of hexane were added
to an oven-dried Schlenk tube. Next, 1.25 mL (2 mmol) of 1.6 M
solution of nBuLi were added, followed by 0.34 mL (2 mmol) of
TMP(H) at room temperature. The reaction mixture was left to
stir for 30 min and then 0.38 mL (2 mmol) of iBu2AlCl were then
injected into the Schlenk tube, producing a white suspension
almost immediately. The reaction mixture was left to stir for 45
min and was then filtered through celite and glasswool, which
was then washed with a further 10 mL of hexane. The solvent
was then removed in vacuo to yield a clear oil (quantitative yield
iBu), 44.35 (2C, β-TMP), 46.38, 48.64, and 51.96 (CH3
PMDETA), 47.28 (Al-CH2N PMDETA), 51.96 (2C, R-TMP),
54.10, 57.26, 59.00, and 61.15 (CH2-PMDETA). 7Li NMR
(155.50 MHz, cyclohexane-d12, 300 K, reference LiCl in D2O
at 0.00 ppm): 0.43.
Acknowledgment. We thank the EPSRC and the Royal
Society (International Travel Grant to E.H. and J.G.-A.
and a Wolfson merit award to R.E.M.) for sponsoring
this research. In addition, E.H. thanks the Royal Society
for a University Research Fellowship and J.G-A. thanks
the Ministerio de Ciencia y Educacion (MEC) of Spain
and the European Social Fund for the award of a “Juan
de la Cierva” contract.
1
by NMR). H NMR (400.13 MHz, cyclohexane-d12, 30 0K):
0.17 (4H, d, 3JHH = 6.8 Hz, CH2-Al iBu), 1.01 (12H, d, 3JHH
=
6.8 Hz, CH3-iBu), 1.29 (12H, s, CH3 of TMP), 1.31 (4H, m,
β-TMP), 1.72 (2H, m, γ-TMP), 1.94 (1H, sept, 3JHH = 6.8 Hz,
CH-iBu). 13C{H} NMR (100.63 MHz, cyclohexane-d12, 300 K):
i
i
18.85 (γ-TMP), 25.81 (CH2 of Bu), 27.68 (CH3 of Bu), 28.44
(CH of iBu), 32.45 (CH3-TMP), 39.08 (β-TMP), 50.87 (R-TMP).
Supporting Information Available: NMR spectra for 2, 3, 4,
and 5 and CIF file giving crystallographic data for compounds 2
and 4. This material is available free of charge via the Internet at
http://pubs.acs.org.
(27) Sheldrick, G. M. Acta Crystallogr., Sect. A: Found. Crystallogr.
2008, 64, 112.