Sterically hindered diazabutadienes (DABs): Competing reaction pathways with MeLi

Article abstract of DOI:10.1021/om100850p

Treatment of N,N′-bis(2,6-diisopropylphenyl)-1,4-diaza-2,3-dimethyl- 1,3-butadiene with MeLi results in carbon-carbon bond formation and selective reduction of one of the imine arms to give the N-lithiated salt of the imine/amine, N,N′-bis(2,6-diisopropyl

Full text of DOI:10.1021/om100850p

Organometallics 2010, 29, 6509–6517 6509
DOI: 10.1021/om100850p
Sterically Hindered Diazabutadienes (DABs): Competing Reaction
Pathways with MeLi
†
Mohan Bhadbhade, Guy K. B. Clentsmith,* and Leslie D. Field
,‡
‡
†
‡
University of New South Wales Analytical Centre and School of Chemistry, University of New South Wales,
Sydney, New South Wales 2052, Australia
Received September 2, 2010
0
Treatment of N,N -bis(2,6-diisopropylphenyl)-1,4-diaza-2,3-dimethyl-1,3-butadiene with MeLi
results in carbon-carbon bond formation and selective reduction of one of the imine arms to give the
N-lithiated salt of the imine/amine, N,N -bis(2,6-diisopropylphenyl)-1,4-diaza-2,3,3-trimethyl-
0
1
solution and the solid state, and features a three-coordinate lithium nucleus that is chelated to
-butene. This compound crystallizes from Et O as a solvent adduct, exists as a monomer both in
2
0
oxygen, amido, and imino donors. In contrast, treatment of N,N -bis(2,4,6-trimethylphenyl)-
1
trimethylphenyl)-1-aza-2-methyl-3-N -(2,4,6-trimethylphenyl)-1,3-butadiene, as the ether adduct, by
,4-diaza-2,3-dimethyl-1,3-butadiene with MeLi gives the N-lithiated imine anion N-(2,4,6-
0
0
proton abstraction. With a more hindered base, N,N -bis(2,6-diisopropylphenyl)-1,4-diaza-2,3-dimethyl-
1,3-butadiene undergoes proton abstraction with lithium diisopropylamide to give the N-lithiated imine
anion of the ene/amine, N-(2,6-diisopropylphenyl)-1-aza-2-methyl-3-N -(2,6-diisopropylphenyl)-1,3-
0
butadiene, again isolated as the ether adduct. A further equiv of MeLi LiBr added to N-(2,4,6-
0
3
trimethylphenyl)-1-aza-2-methyl-3-N -(2,4,6-trimethylphenyl)-1,3-butadiene gives the doubly N-lithiated
0
salt of the diene/diamide, 2,3-N,N -bis(2,4,6-trimethylphenyl)-1,3-butadiene, in which both nitrogen centers
have been reduced, and which adopts a cisoid stereochemistry with respect to the butadiene unit in
the solid state.
1
. Introduction
ketimine donors such as the imino-substituted pyridines 2
4
and 3, where the pyridyl donors introduce another poten-
5
tially reactive site in the heterocyclic ring. In the context of
olefin polymerization, such reactivity is often exploited to
1
when bound to middle- and late-transition-metal centers,
,4-Diaza-1,3-butadiene (DAB or R-diimine) ligands,
1
boast an impressive array of reactivity and sometimes
impart useful catalytic activities in a variety of chemical
4b
elaborate from the neutral precursor new anionic ligands,
whose charge lends itself to subsequent reaction with Lewis
2
transformations. While some work points to the relative
innocence of DAB ligands upon coordination, even in the
acidic metal centers. For example, imine-based ligands 1-3
i
(typically Ar = 2,6-Pr C H , 2,4,6-Me C H ) are methylated
with 1 equiv of trimethylaluminum at the imine carbon with
2
6
3
3
6
2
3
presence of strong nucleophiles, the ketimine moiety is
nevertheless able to undergo reaction at any of the enolizable
β-hydrogens and also at the electrophilic carbon of the imine
group. This is also true for related multidentate ligands with
carbon-carbon bond formation to give an imine/amido
system with geminal dimethyl groups (Scheme 1). Likewise
4
ligands such as ArNdCHCHdNAr (1) will undergo reac-
tions with Lewis acidic metal alkyls M(CH Ph) (M=Zr,
2
4
(
1) (a) Vrieze, K. J. Organomet. Chem. 1986, 300, 307–326. (b) van
Koten, G.; Vrieze, K. Adv. Organomet. Chem. 1982, 21, 151–239.
c) Klerks, J. M.; Stufkens, D. J.; van Koten, G.; Vrieze, K. J. Organomet.
Chem. 1979, 181, 271–283.
2) (a) Gottfried, A. C.; Brookhart, M. Macromolecules 2003, 36,
085–3100. (b) Grasa, G. A.; Singh, R.; Stevens, E. D.; Nolan, S. P.
Hf) to give an anionic imine/amido ligand bound in situ to
6
the group 4 metal center.
(
0
i
In the case of 1, N,N -(2,6-Pr C H ) -1,4-diaza-1,3-buta-
2
6
3 2
(
diene, such reactivity gives rise to a chiral center at the point
4
of addition; however, hydride migration from the adjacent
b
3
J. Organomet. Chem. 2003, 687, 269–279. (c) Heumann, A.; Giordano,
L.; Tenaglia, A. Tetrahedron Lett. 2003, 44, 1515–1518. (d) Gottfried,
A. C.; Brookhart, M. Macromolecules 2001, 34, 1140–1142. (e) Ittel, S. D.;
Johnson, L. K.; Brookhart, M. Chem. Rev. 2000, 100, 1169–1203. (f) van
Belzen, R.; Hoffmann, H.; Elsevier, C. J. Angew. Chem., Int. Ed. Engl.
1c
position can occur to give an achiral species (Scheme 2).
(5) (a) Clentsmith, G. K. B.; Gibson, V. C.; Hitchcock, P. B.;
Kimberley, B. S.; Rees, C. W. Chem. Commun. 2002, 1498–1499.
(b) Khorobkov, I.; Gambarotta, S.; Yap, G. P. A.; Budzelaar, P. H. M.
Organometallics 2002, 21, 3088–3090.
(6) (a) De Waele, P.; Jazdzewski, B. A.; Klosin, J.; Murray, R. E.;
Theriault, C. N.; Vosejpka, P. C.; Petersen, J. L. Organometallics 2007,
26, 3896–3899. For activation of diacetyl-based DAB ligands by Mn(II)
hydrocarbyls see: (b) Riollet, V.; Coperet, C.; Basset, J. M.; Rousset, L.;
Bouchu, D.; Grosvalet, L.; Perrin, M. Angew. Chem., Int. Ed. 2002, 41,
3025–3027. For activation of glyoxal-based DAB ligands by Group 3 metal
hydrocarbyls see: (c) Kaneko, H.; Tsurugi, H.; Panda, T. K.; Mashima, K.
Organometallics 2010, 29, 3463–3466.
1
997, 36, 1743–1745.
3) Bart, S. C.; Hawrelak, E. J.; Schmisseur, A. K.; Lobkovsky, E.;
Chirik, P. J. Organometallics 2004, 23, 237–246.
4) (a) Nienkemper, K.; Kehr, G.; Kehr, S.; Fr o€ hlich, R.; Erker, G.
(
(
J. Organomet. Chem. 2008, 693, 1572–1589. (b) Gibson, V. C.; Redshaw,
C.; White, A. J. P.; Williams, D. J. J. Organomet. Chem. 1998, 550, 453–456.
For the reaction between trimethylaluminum and the related acenapthene-1,2-
bis-imine, see: (c) Tishkina, A. N.; Lukoyanov, A. N.; Morozov, A. G.; Fukin,
G. K.; Lyssenko, K. A.; Fedushkin, I. L. Russ. Chem. Bull., Int. Ed. 2009, 58,
2
250–2257.
r 2010 American Chemical Society
Published on Web 11/02/2010
pubs.acs.org/Organometallics

6
510 Organometallics, Vol. 29, No. 23, 2010
Bhadbhade et al.
Scheme 1
Scheme 4
0
i
ligand, N,N -(2,6-Pr C H ) -1,4-diaza-2,3-dimethyl-1,3-
2
6
3 2
butadiene (7), treatment with MeLi results in C-C bond
formation and gives the lithiated imine/amide 13 directly. In
0
contrast, the mesityl derivative N,N -(2,4,6-Me C H ) -1,4-
6
3
2 2
diaza-2,3-dimethyl-1,3-butadiene (8) undergoes a stepwise
deprotonation to give the singly reduced imine/ene-amide 15
and then the doubly reduced diene/diamide 16 after reaction
with successive equivalents of MeLi (Scheme 4).
Single-crystal X-ray diffraction structures have been
i
reported here for the lithiated compounds (2,6-Pr C H )NdC-
2
6 3
i
Scheme 2
(Me)C(CH ) N(Li)(2,6-Pr C H ) (13), (2,4,6-Me C H )-
3 2 2 6 3 3 6 2
NdC(Me)C(dCH )N(Li)(2,4,6-Me C H ) (15), and (2,4,6-
2
3
6
2
Me C H )(Li)NC(dCH )C(dCH )N(Li)(2,4,6-Me C H )(LiBr)
2
3
6
2
2
2
3
6
2
i
(16), and for the compound (2,6-Pr C H )NdC(Me)-
2 6 3
C(dCH )N(Li)(2,6-Pr C H ) (17) as well, which is the 2,6-
i
2
2
6
3
diisopropylphenyl-substituted analogue of 15. The struc-
i
tures of the dimethylaluminum derivatives (2,6-Pr C H )-
2
6
3
i
Scheme 3
NdC(Me)C(CH ) N(AlMe )(2,6-Pr C H ) (9) and (2,4,6-
3 2 2 2 6 3
Me C H )NdC(Me)C(CH ) N(AlMe )(2,4,6-Me C H ) (10)
3
6
2
3 2
2
3
6
2
i
2
and that of the free amine (2,6-Pr C H )NdC(Me)C(CH ) -
3 2
N(H)(2,6-Pr C H ) (11) will be reported elsewhere.
6
6
3
i
2
8
3
2. Results and Discussion
i
The diazabutadiene precursors (2,6-Pr C H )NdC(Me)C-
6
2
3
i
(Me)dN(2,6-Pr C H ) (7) and (2,4,6-Me C H )NdC(Me)-
C(Me)dN(2,4,6-Me C H ) (8) can be synthesized in gram
2 6 3 3 6 2
3
6
2
quantities by prolonged stirring of stoichiometric amounts
of diacetyl with the appropriate aniline in methanol at room
temperature. Small quantities of formic acid catalyze the
condensation, and both DAB ligands precipitate from solu-
9
tion as yellow crystalline materials in high yields. The 2,6-
diisopropylphenyl-substituted compound 7 was recrystal-
lized quantitatively from hot EtOH; the mesityl derivative
8, which is much less soluble in alcohol, was washed with cold
0
i
Related DAB ligands, N,N -(2,6-Pr C H ) -1,4-diaza-
2
6
3 2
0
,3-dimethyl-1,3-butadiene (7) and N,N -(2,4,6-Me C H ) -
3 6 2 2
,4-diaza-2,3-dimethyl-1,3-butadiene (8), are also reactive
2
1
EtOH and used directly in further reactions.
i
2
toward trimethylaluminum to give products analogous to 5
and 6. For compound 7, some of this chemistry has been
The addition of 1-2 equiv of MeLi to (2,6-Pr
C
6
H )NdC-
3
i
(Me)C(Me)dN(2,6-Pr C H ) (7) in Et O solution at ice-
2 6 3 2
7
reported in the patent literature (Scheme 3). The methylated
bath temperature rapidly discharged the yellow color of the
1
starting material and generated an exotherm. The H NMR
products 9 and 10 are readily hydrolyzed to give the parent
imine/amines 11 and 12, and lithiation by standard means
allows for isolation of lithiated imine/amides 13 and 14.
Compounds 7 and 8 both have methyl groups attached to
the imine carbon, and the pseudoallylic protons of the
methyl substituents are susceptible to hydrogen abstraction
by strongly basic reagents to give imine anions, a process
which has some precedent in the chemistry of 2 and which
features strongly in the chemistry of 8. This means that there
are competing reaction pathways that can occur when DAB
compounds such as 7 and 8 are treated with reagents that are
nucleophilic and/or basic.
spectrum of the reaction mixture in THF-d
quantitative formation of a C -symmetric product, as evi-
results in
8
s
denced by the appearance of two sets each of aryl, methyl,
and methine protons. The added MeLi reduces one of the
donor arms of the starting ligand so that the halves of the
molecule are differentiated in solution. The evidence that
C-C bond formation has occurred includes (i) appearance
of a singlet (6H integrand) at δ 1.30 ppm attributable to a
gem-dimethyl group, (ii) the persistence of a methyl singlet at
δ 1.81 ppm (3H) arising from the backbone methyl group of
the unperturbed imine arm, and (iii) the absence of any
5
b
While the DAB compounds 7 and 8 display similar reactiv-
ity toward trimethylaluminum, they undergo different reac-
tions with MeLi. With the sterically more encumbered
(8) Bhadbhade, M.; Clentsmith, G. K. B.; Field, L. D. Manuscript in
preparation.
(
9) (a) T u€ rkmen, H.; C- etinkaya, B. J. Organomet. Chem. 2006, 691,
749–3759. (b) tom Dieck, H.; Svoboda, M.; Greiser, T. Z. Naturforsch., B:
3
(7) Murray, R. E. US6562751 B2 20011218, 2002.
Chem. Sci. 1981, 36, 823–832.

Article
Organometallics, Vol. 29, No. 23, 2010 6511
i
2
i
2
Figure 1. ORTEP representation of [(2,6-Pr
ellipsoids. Hydrogen atoms have been omitted for clarity.
C
6
H
3
)NdC(Me)C(CH
3
)
2
N(Li)(2,6-Pr
C
H
6 3
)] Et O (13 Et
2
2
O) with 50% probability
3
3
˚
Table 1. Selected Bond Lengths (A) and Bond Angles (deg) for
resonances attributable to vinylic protons, with the resulting
i
reduction at a single imine function to give (2,6-Pr C H )-
i
i
(2,6-Pr
(13 3 Et
2,4,6-Me
C(dCH )N(Li)(2,4,6-Me C H ) (16 3Et O 2LiBr), and
2
C
6
H
3
)NdC(Me)C(CH
O), (2,4,6-Me )NdC(Me)C(dCH
2
) (15 Et O), (2,4,6-Me )(Li)NC(dCH )-
3 2 2 6 3
) N(Li)(2,6-Pr C H )
2
6
3
i
NdC(Me)C(CH ) N(Li)(2,6-Pr C H ) (13) (Scheme 3). The
3
2
3
C
6
H
2
)N(Li)-
2
3
2
2
6
(
3
C
6
H
2
2
3
C
H
6 2
structure of 13 is also consistent with the appearance of
1
3
3
1
singlets at δ 67.9 and 199.1 ppm in the C{ H} NMR
2
3
6
2
3
2
3
i
i
(
2,6-Pr
2
C
H
6 3
)NdC(Me)C(dCH
(
2
2 6 3
)N(Li)(2,6-Pr C H )
spectrum in THF-d , and these resonances can be attributed
to the quaternary carbon N-C(Me ) and CdN carbon
8
17 Et O)
2
3
2
nuclei in the structure. Yellow crystals of 13 were grown
from Et O solution at -15 ꢀC in 75-80% overall yields as
13
15
16
17
2
the ether solvate, 13 Et O. C-C bond formation was un-
Bond Lengths
1.912(10)
3
2
equivocally confirmed by a single-crystal X-ray diffraction
experiment (Figure 1). Selected data appear in Table 1.
Li1-N1
Li2-N1
Li1-N2
Li1-O1
Li3-O2
C1-N1
C2-N2
C1-C2
C1-C3
C2-C4
C2-C5
1.977(5)
2.128(6)
1.955(5)
1.907(5)
i
As seen in Figure 1, the lithium nucleus of (2,6-Pr C H )-
2
6
3
1.858(5)
1.899(5)
1.956(9)
1.904(8)
1.989(4)
1.911(7)
i
NdC(Me)C(CH ) N(Li)(2,6-Pr C H ) (13 Et O) is three-
coordinate, with two longer coordinate-covalent bonds
1.968(4)
1.943(5)
1.371(3)
3
2
2
6
3
3
2
1.281(3)
1.458(3)
1.521(3)
1.503(3)
1.549(4)
1.547(4)
1.432(3)
1.403(3)
1.342(6)
1.317(7)
1.488(7)
1.408(7)
1.448(7)
1.362(12)
1.257(13)
1.544(14)
1.385(13)
1.558(14)
˚
˚
(
(
Li-N1=1.977 A, Li-O=1.899 A) and a covalent bond
˚
Li-N2=1.858 A). From the point of view of ligand struc-
1.366(4)
ture, this is reasonable, given that it is this nitrogen that has
been reduced with respect to the starting material by addition
of a methyl group to the imine carbon and, therefore, it is this
N2 center that is formally anionic. Significantly, 13 Et O is a
N1-Cipso-aryl
N2-C
1.416(6)
1.427(6)
1.423(3)
1.425(13)
1.420(13)
3
2
ipso-aryl
0
monomer in the solid state, and presumably the bulky aryl
substituents, whose planes are canted normal to the plane
containing the lithium nucleus and the donor atoms, act to
C1-C1
1.522(5)
2.319(3)
2.512(5)
2.578(5)
2.388(3)
Li3-C2
Li3-Br1
Li3-Br2
˚
˚
suppress aggregation. C2-C4 (1.548 A), C2-C5 (1.547 A),
0
0
Li2-Br2
˚
and C2-N2 (1.458 A) are all consistent with C-C or C-N
single bonds, whereas the bond length C1-N1 (1.281 A) is
typical of a CdN double bond and is quite comparable with
˚
Bond Angles
N1-Li1-O1
N2-Li1-O1
N1-Li1-N2
N1-Li1-N1
N1-Li2-N1
C2-C1-C3
122.4(2)
139.0(3)
87.38(19)
137.2(6)
135.3(5)
86.9(4)
127.3(5)
137.27(12)
135.44(12)
85.61(9)
the CdN bond lengths measured in the structures of the
precursor ligands 7, and 8. The sums of the bond angles
1
0
P
0
0
75.0(2)
83.0(3)
around the backbone C1 and C2 centers (
=360.0ꢀ,
—
C1
2
P
3
=
C2
441.5ꢀ) also argue strongly for sp - and sp -
hybridized carbon centers at C1 and C2, respectively.
—
118.3(2)
119.2(5)
119.4(10)
0
C2-C1-C1
121.35(17)
1
The H NMR spectrum of (2,6-Pr C H )NdC(Me)C-
i
2
6
3
i
(
CH ) N(Li)(2,6-Pr C H ) (13 Et O) in THF-d , after
3 2 2 6 3 2 8
3
recrystallization from Et O, highlights the diastereotopic
2
nature of the methyl groups of the 2,6-diisopropyl substitu-
ents on the aniline rings. The isopropyl methyls of the aryl
substituents on the amide side of the reduced DAB system
(
10) (a) Schaub, T.; Radius, U. Z. Anorg. Allg. Chem. 2006, 632, 807–
8
13. (b) Cope-Eatough, E. K.; Mair, F. S.; Pritchard, R. G.; Warren, J. E.;
Woods, R. J. Polyhedron 2003, 22, 1447–1454.

6
512 Organometallics, Vol. 29, No. 23, 2010
Bhadbhade et al.
Scheme 5
Scheme 6
give rise to a pair of doublets at δ 1.20 and 1.12 ppm (12H)
and at δ 1.30 and 1.28 ppm (12H) for the imine side of the
reduced DAB. In addition to two signals for the aryl protons
of each donor arm, the spectrum also exhibits two clearly
distinct septet absorptions due to the methine protons of the
i
(dCH )N(Li)(2,6-Pr C H ) (17) was recrystallized from
2
2
6
3
Et O in high yield. When 7 was treated with 2 equiv of
2
i
2
Pr NLi in THF, deprotonation of both methyl groups
occurred to give the known, symmetrical diene/diamide
3
i
i
2-
þ
[(2,6-Pr C H )NC(dCH )C(dCH )N(2,6-Pr C H )] Li
2
isopropyl group at δ 4.23 and 3.06 ppm (4H, J = 6.8 Hz).
2
6
3
2
3
2
2
6
3
3
1
The upfield absorption corresponds to the methine proton
on the imine side of the reduced DAB. Resonances attribu-
table to the ether of crystallization (δ 3.39 ppm, q, 4H; δ
4THF (19) (Scheme 6).
On the other hand, reduction of (2,6-Pr C H )Nd
C(Me)C(Me)dN(2,6-Pr C H ) (7) with Li, Mg, or Na metal
i
2
6
3
i
2
6
3
3
1
1
.10, t, J = 6.9 Hz, 6H) are also observed in the H NMR
in THF or Et O gives moderate yields of [ArN(CH )Cd
2
3
2
-
þ
spectrum. In previous examples of carbo-metalations of
diketimines, the presence of stereocenters on the carbon
C(CH )NAr]
M (M = Li, Na) or [ArN(CH )CdC(CH )-
NAr] Mg , in which both imine groups have been reduced
3
2
3
3
2
-
2þ
4
b,11
backbone indicates the molecularity in solution.
t
Thus,
the Bu Li adduct of N,N -(Bu ) -1,4-diaza-1,3-butadiene, a
but the central C-C bond has been oxidized to form an
3 2
0
t
14
olefinic bond. The putative 1,2-diamine ArN(H)C(CH ) C-
2
dimer in the solid state, preserves this structure in benzene
solution as the diastereomers observed in solution are ne-
(CH ) N(H)Ar, in which both imine donors have been
3
2
reduced and both amino groups are protected by adjacent
geminal dimethyl groups, has yet to be synthesized.
1
cessarily aggregated. Likewise, the aluminum compound 4
1
i
Ar = 2,6-Pr ), which is a monomer in the solid state, does
i
The lithiated imine/ene-amide (2,6-Pr C H )NdC(Me)C-
(
not aggregate in solution, as argued by the absence of fea-
2
2
6
3
i
(dCH )N(Li)(2,6-Pr C H ) (17) was characterized by its
2 2 6 3
H NMR spectrum in THF-d . The molecule is unsymme-
8
1
tures attributable to diastereomers in its solution H NMR
1
4
b
spectrum.
The observation that the lithium derivative (2,6-Pr C H )-
trical, and there are clearly two vinylic signals at δ 3.94 and
i
2
6
3
3.14 ppm (2H) correlated to signals at δ 78.0 (CdCH ), and
2
i
NdC(Me)C(CH ) N(Li)(2,6-Pr C H ) (13) may be gener-
ated in usable yields by the simple addition of MeLi to the
13
1
3
2
2
6
3
δ 59.1 ppm (CdCH ) in the C{ H} NMR spectrum. The
2
structure of 17 Et O was obtained by single-crystal X-ray
3
2
i
DAB compound (2,6-Pr C H )NdC(Me)C(Me)dN(2,6-
2
6
3
diffraction and appears in Figure 2. Selected structural data
are given in Table 1.
The structure of 17 Et O is monomeric, with the bulky
i
Pr C H ) (7) in Et O is remarkable. While addition of
2
6
3
2
2
equiv of MeLi is known to accomplish double reduction
i.e., dual carbo-lithiation) of less substituted DAB ligands
3
2
(
such as N,N -(Bu ) -1,4-diaza-1,3-butadiene, the more
aryl arms again perpendicular to the plane of the lithium-
nitrogen core. Bond distances C4-C2 (1.479 A) and C3-C1
(1.352 A
0
t
11
˚
2
highly substituted, diacetyl-based diketimines rarely under-
go nucleophilic addition with C-C bond formation, and
under equivalent conditions, MeLi merely abstracts one of
the backbone β-hydrogens of pyridyl imines such as 2 and 3
to give methane and the lithiated imine/ene-amide in an
˚
) clearly represent a C-C single bond and a double
bond, respectively, as anticipated for an imine/ene-amide
structure. The C-N bond distances reinforce these metrics
˚
˚
, C1-N1=1.315 A), which clearly reflect
(C2-N2=1.262 A
an imine bond and a C-N single bond, respectively; the
C1-N1 single bond is attached to the C3-C1 methylene
unit, and conversely the C2-N2 double bond connects to the
C4-C2 single bond, in accord with its simple formula
representation.
5
b,12
acid-base reaction.
metric amount of Bu Li to 7 in Et O affords low yields of the
Likewise, addition of a stoichio-
n
2
related, racemic lithiated imine/amide 18, whose structure
appears in the Supporting Information and in which the
lithium reagent simply adds as a nucleophile to accomplish
C-C bond formation (Scheme 5); quantities of the product
Under conditions identical with those for the synthesis
i
i
of (2,6-Pr C H )NdC(Me)C(CH ) N(Li)(2,6-Pr C H ) (13)
2
6
3
3 2
2
6
3
i
0
from 7, when N,N -(2,4,6-Me C H ) -1,4-diaza-2,3-dimethyl-
3 6 2 2
of proton abstraction, (2,6-Pr C H )NdC(Me)C(dCH )N-
2
6
3
2
i
Li)(2,6-Pr C H ) (17), are also observed as the major
(
product in the reaction mixture.
1,3-butadiene (8) is treated with MeLi, C-C bond formation
occurs and MeLi acts simply as a strong base to abstract
one of the backbone methyl protons to give methane and
the lithium-bound ene-amide (2,4,6-Me C H )NdC(Me)C-
2
6
3
While MeLi adds to the imine with C-C bond formation,
i
the methyl protons of (2,6-Pr C H )NdC(Me)C(Me)dN-
2
6
3
3
6
2
i
2,6-Pr C H ), (7) can be abstracted quantitatively if a non-
(
nucleophilic base such as Pr NLi is used, and the resultant
(dCH )N(Li)(2,4,6-Me C H ) (15), with a coordinated
2 3 6 2
2
6
3
i
2
imine arm (Scheme 7). As anticipated, the same product is
i
isolated when 8 is treated with Pr NLi.
i
singly deprotonated species (2,6-Pr C H )NdC(Me)C-
2
6
3
2
The structure of the resultant imine/ene-amide (2,4,6-
Me C H )NdC(Me)C(dCH )N(Li)(2,4,6-Me C H ) (15 Et O)
(
11) (a) Gardiner, M. G.; Raston, C. L. Inorg. Chem. 1995, 34, 4206–
3
6
2
2
3
6
2
3
2
4
212. For other examples of carbo-metalation of bis-imines by lithium or
magnesium reagents see: (b) Fedushkin, I. L.; Hummert, M.; Schumann, H.
Eur. J. Inorg. Chem. 2006, 3266–3273. (c) Fedushkin, I. L.; Makarov, V. M.;
Rosenthal, E. C. E.; Fukin, G. K. Eur. J. Inorg. Chem. 2006, 827–832.
(13) Yu, L. B.; Yao, Y. M.; Shen, Q.; Sun, J. Inorg. Chem. Commun.
2004, 7, 542–544.
(14) (a) Mahrova, T. V.; Fukin, G. K.; Cherkasov, A. V.; Trifonov,
A. A.; Ajellal, N.; Carpentier, J. F. Inorg. Chem. 2009, 48, 4258–4266.
(b) Liu, Y.; Yang, P. J.; Yu, J.; Yang, X. J.; Zhang, J. D.; Chen, Z. F.; Schaefer,
H. F.; Wu, B. Organometallics 2008, 27, 5830–5835.
(
5
2
d) Neumann, W. L.; Rogic, M. M.; Dunn, T. J. Tetrahedron Lett. 1991, 32,
865–5868. (e) Stamp, L.; tom Dieck, H. J. Organomet. Chem. 1984, 277,
97–309.
(
12) N u€ ckel, S.; Burger, P. Organometallics 2000, 19, 3305–3311.

Article
Organometallics, Vol. 29, No. 23, 2010 6513
i
2
i
2
Figure 2. ORTEP representation of (2,6-Pr C H )NdC(Me)C(dCH )N(Li)(2,6-Pr C H ) (17 Et O) with 50% probability ellipsoids.
6
3
2
6
3
3
2
Disordered ethyl groups bound to the oxygen atom and hydrogen atoms have been omitted for clarity.
Scheme 7
polymeric structure, in which a terminal lithium nucleus
00
(
Li2) is loosely bound to the bromide nucleus (Br2 ) of an
adjacent formula unit, as shown in Figure 4. The C1-C2
˚
bond length is 1.365(4) A, which is consistent with an olefinic
0
˚
bond. On the other hand, the C1-C1 (1.522 A) and C1-N1
(
˚
1.373 A) bond lengths clearly represent single bonds. The
subsidiary LiBr units, whose origin is easily traced to the
LiBr present in the ethereal solution of the MeLi used to
prepare this species, interact loosely with the methylene units
is shown in Figure 3. This structure again features a discrete
monomer whose lithium metal is again three-coordinate with
˚
P
of the backbone (C2-Li3 = 2.319 A) and act to bridge the
formula units with the unsolvated lithium nucleus, Li2,
a capping Et O molecule (
2
= 359.6ꢀ). Here, the
—Li-O/N
identity of single and double bonds is less apparent than in
the other structures; however, the sum of the bond angles
around the backbone carbons, C1 and C2, clearly point to
00
˚
acting as the junction (Li2-Br2 = 2.388(3) A). In solution,
while there is no way to determine the molecularity of this
1
species, the observed H NMR signals clearly point to a
P
P
2
sp -hybridized centers (
= 360.0ꢀ,
= 359.9ꢀ).
—C2
—
C1
species with C geometry, as suggested by the crystallo-
s
graphic symmetry: one set of aryl protons (δ 6.62 ppm,
˚
The carbon-nitrogen bond distances (C1-N1=1.341(7) A,
C2-N2 = 1.318(6) A) are barely differentiated, as are the
˚
4
4
H) and two distinct vinyl resonances (δ 3.08, 2.13 ppm,
H), and methyl resonances (δ 2.19, 2.14 ppm, 18H) are
lithium-nitrogen and the carbon-carbon distances (Li-N1 =
.911(10) A, Li-N2 = 1.956(10) A; C1-C2 = 1.488(7) A,
˚
˚
˚
1
observed, along with resonances due to the ether of crystal-
7
lization. The Li NMR spectrum of 16 3Et O 2LiBr reveals
˚
˚
C1-C3 = 1.408(7) A; C2-C4 = 1.448(7) A). Nevertheless,
from these data it is clear that the N2-C2 and C1-C3
linkages represent a pair of conjugated double bonds and
that it is the N1 center that is the formal anion. Unsaturation
is more evident from the solution data, where the H NMR
spectrum exhibits a pair of vinylic protons at δ 3.79 and 2.97
3
2
3
several chemically distinct lithium environments at low
temperature; however, it has not been possible to establish
their identities. If lithium reagents without stoichiometric
LiBr are employed in reaction with 8 (i.e., if bromide-free
MeLi is used), signals attributable to 16 can be observed in
1
13
1
ppm (2H) and the C{ H} NMR spectrum features a down-
field singlet at δ 176.6 ppm, consistent with the imino carbon.
Likewise, signals due to the ortho and para methyl groups of
the mesityl rings (δ 2.14 and 2.04 ppm, 12H; δ 2.24, 1.92 ppm,
1
the H NMR spectrum; however, crystalline material has not
been isolated.
i
The two diazabutadienes (2,6-Pr C H )NdC(Me)-
2
6
3
i
C(Me)dN(2,6-Pr C H ) (7) and (2,4,6-Me C H )Nd
2
6
3
3
6
2
6
H) as well as the unperturbed methyl group (C4) at
1
C(Me)C(Me)dN(2,4,6-Me C H ) (8) thus follow different
3 6 2
δ 2.15 ppm are also clearly distinguishable in the H NMR
spectrum.
When (2,4,6-Me C H )NdC(Me)C(Me)dN(2,4,6-Me C H )
paths when treated with MeLi. For 7, nucleophilic attack
occurs at the imine carbon, whereas with 8, proton abstrac-
tion occurs at the methyl group attached to the imine carbon.
Both of these reaction pathways are not unreasonable, and
since MeLi is potent as both a base and a nucleophile, the
reactions with MeLi are probably under kinetic control
linked to the ease of proton abstraction. With both 7 and
8, the product of reaction contains a five-membered, un-
saturated ring with lithium bound to amido, imino, and
oxygen donors; therefore, the thermodynamic course of each
3
6
2
3 6 2
(
alternatively, when a further 1 equiv of MeLi LiBr was
8) was treated with >2 equiv of MeLi LiBr in Et O (or,
2
3
3
added to (2,4,6-Me C H )NdC(Me)C(dCH )N(Li)(2,4,6-
2
3
6
2
Me C H ) (15)), stoichiometric proton abstraction occurred
3
6
2
to give the dilithiated diamido/diene (2,4,6-Me C H )-
6
3
2
(Li)NC(dCH )C(dCH )N(Li)(2,4,6-Me C H ) (16), with
a cisoid structure in the solid state (Scheme 8). This com-
2 2 3 6 2
pound has the formulation 16 3Et O 2LiBr and comprises a
2
3
3

6
514 Organometallics, Vol. 29, No. 23, 2010
Bhadbhade et al.
Figure 3. ORTEP representation of (2,4,6-Me
ellipsoids. Hydrogen atoms have been omitted for clarity.
3
C
6
H
2
)NdC(Me)C(dCH
2
)N(Li)(2,4,6-Me
3
C
6
2
H ) (15 Et
3
2
O), with 50% probability
Scheme 8
Scheme 9
electron-releasing substitution on the aryl group acts to
decrease the acidity of the hydrogens on the methyl sub-
stituent on the imine carbon.
To test this proposal, the deuterium-labeled starting material
2,4,6-Me C H )NdC(Me-d )C(Me-d )dN(2,4,6-Me C H )
(
3 6 2 3 3 3 6 2
Figure 4. ORTEP representation of (2,4,6-Me C H )(Li)NC-
3
(8-d ) was prepared from diacetyl-d and mesitylaniline.
6 6
6
2
(
5
dCH
0% probability ellipsoids. Hydrogen atoms and ethyl groups
attached to oxygen have been omitted for clarity.
2
)C(dCH
2
)N(Li)(2,4,6-Me
3
C
6
H
2
) (16 3Et
2
O 2LiBr) with
protio-Diacetyl undergoes slow deuteration in D O at reflux
2
3
3
with a trace of DCl, and the degree of deuteron incorpora-
1
tion was increased by several cycles at reflux. Upon con-
7
densation with mesitylaniline in methyl alcohol-d in the
3
presence of catalytic formic acid-d, 8-d
reaction is reasonably similar. Little data exist on the pK
1
a
5
6
was obtained in
reasonable purity (approximately 85%, as determined by
values of simple imines and aldimines, and there are no
data for the diketimines studied in this work. A more recent
1
integration of the H NMR spectrum in benzene-d
1
6
). Signifi-
6
study of imine metalation, which dealt solely with lithium
dialkylamides as the basic reagent but which also considered
the effect of chelation of the alkali metal by pendant groups
on the starting imine, concluded that increased steric bulk
around the starting imine raised activation enthalpies with
respect to proton abstraction and metalation. Thus, while
the bulkier isopropyl substitution on 7 sterically shields the
imine carbon from prospective attack by a nucleophile, the
cantly, the reaction of 8-d with 1 equiv of MeLi in Et O at
2
6
ice-bath temperature proceeds with no loss of intensity of the
yellow color of the ketimine starting material, as occurs when
protio-8 is treated with this reagent. Yellow crystals of (2,4,6-
Me C H )NdC(Me-d )C(Me-d )(Me)N(Li)(2,4,6-Me C H )
3
6
2
3
3
3
6
2
(
14-d Et O) were obtained from THF/hexanes in moderate
6 2
3
yield, and the solution spectroscopic data are entirely consistent
with the product of carbon-carbon bond formation (Scheme 9).
In THF-d solution, 14-d Et O displays (i) two signals for
8
6
3
2
(
15) Fraser, R. R.; Bresse, M.; Chuaqui-Offermanns, N.; Houk,
K. N.; Rondan, N. G. Can. J. Chem. 1983, 61, 2729–2734.
16) Romesberg, F. E.; Collum, D. B. J. Am. Chem. Soc. 1995, 117,
166–2178.
(
(17) Plouzennec-Houe, I.; Lemberton, J. L.; Perot, G.; Guisnet, M.
Synthesis 1983, 659–661.
2

Article
Organometallics, Vol. 29, No. 23, 2010 6515
the aryl protons on two different aromatic rings (δ 6.83,
NMR spectra of known volumes against accurate masses of 1,5-
1
8
6
.63 ppm, 4H), (ii) the sets of signals for the methyl groups
substituting the two different aryl groups (δ 2.23 and 2.20,
H; δ 2.09 and 2.06 ppm, 9H), and (iii) an upfield singlet
δ 1.31 ppm, 3H), which represents the methyl group added
cyclooctadiene; a trace of benzene-d was added to the solu-
6
1
13
1
tions to facilitate assignment. H and C{ H} NMR spectra
were obtained on a Bruker Avance III 400 instrument operating
9
(
2
1
at 400.13 and 100.61 MHz, respectively; H{ H} NMR spectra
were obtained on a Bruker Avance II 300 instrument operating
at 46.1 MHz. NMR spectra were referenced to the residual
to the imine carbon and is now part of a d -gem dimethyl
3
group. The deuterium labels of 14-d Et O can be observed
6
3
2
2
solvent resonances. X-ray diffraction experiments for 13 Et O
2
3
directly in the H NMR spectrum at δ 2.2 and 1.3 ppm.
For the mesityl-substituted DAB (2,4,6-Me C H )Nd
C(Me)C(Me)dN(2,4,6-Me C H ) (8), the backbone methyl
and and 15-18 Et O were performed on a Bruker Kappa
3
2
3
6
2
APEX-II CCD instrument at 150 K with graphite-monochro-
mated Mo KR radiation (λ = 0.710 75 A). All crystals, mounted
˚
3
6
2
protons are sufficiently acidic to be abstracted by added
MeLi to give 15 Et O; however, for the deuterated analogue
on the goniometer with cryo loops for intensity measurements,
were coated with Paratone-N oil and then quickly transferred to
the cold stream maintained by an Oxford Cryo stream attach-
ment. Symmetry-related absorption corrections were applied by
the SADABS program, and the data were corrected for
Lorentz and polarization effects with the Bruker APEX2 soft-
3
2
8
-d , proton (or more precisely deuteron) abstraction is
6
turned off and nucleophilic attack at the imine carbon is
the preferred reaction pathway. It is reasonable to conclude
then that there are two competing reaction pathways for the
reaction of diacetyl-based DABs with MeLi: (i) proton
abstraction from the methyl group or (ii) nucleophilic methyla-
tion at the imine carbons. The reactions are similar in energy,
with proton abstraction being the kinetically favored path-
way, but factors which make this pathway more difficult
1
9
1
9,20
ware suite.
and full-matrix least-squares refinements were carried out with
All structures were solved by direct methods,
21
SHELXL. Three of the crystals (13 Et
8 Et O) contain two crystallographically independent mole-
2
2
O, 17 Et
3
2
O, and
3
1
3
cules in their asymmetric units, and almost all the structures
gave rise to either rotational disorder in the isopropyl groups or
conformational disorder in the coordinated diethyl ether mole-
cule or in both positions. In each case, the disordered groups
were refined using PART instruction and their geometries and
thermal parameters were restrained by means of the DFIX,
DELU, and SIMU options available in SHELXL. Structure
solution and refinement of 17 Et O was attempted in tetragonal
P4 ), orthorhombic (P2 2 2 ), and monoclinic (P2 ) space
(such as deuteration, steric loading, and the introduction
of electron-rich substituents) switch the reaction to make
nucleophilic addition the preferential pathway.
21
3. Conclusion
3
2
(
Selected diazabutadiene ligands derived from diacetyl
were selectively reduced by lithium reagents to give new
3
1
1
1
1
groups, with the same cell parameters. On the basis of refine-
ment parameters (lowest R value, 0.16), geometry of molecules,
and behavior of anisotropic thermal parameters of atoms, the
n
anionic ligands. Both MeLi and Bu Li can react with N,N -
0
i
2,6-Pr C H ) -1,4-diaza-2,3-dimethyl-1,3-butadiene (7) by
(
nucleophilic attack at one of the imine carbon atoms. In con-
2 6 3 2
1
monoclinic space group P2 was adopted. An examination of
reciprocal lattice plots indicated the possibility of twinning in
these crystals, which could give rise to higher (pseudo) symme-
try. In all cases, the non-hydrogen atoms were refined aniso-
tropically. The hydrogen atoms, located in the difference
Fourier maps, were refined isotropically under the riding model
0
trast, with N,N -(2,4,6-Me C H ) -1,4-diaza-2,3-dimethyl-
3
6
2 2
1
,3-butadiene (8), MeLi acts simply as a base and abstracts
a proton from one of the methyl groups attached to the imine
carbon. The kinetic acidity of the protons attached to the
imine carbon is the likely factor which determines whether
reaction with alkyllithiums occurs by nucleophilic attack or
with proton abstraction. Both deuteron incorporation and
steric loading serve to decrease the kinetic acidity of the
2
1
option in SHELXL. The details of the crystal parameters, data
collection, and refinements are summarized in Table 2. The
Supporting Information contains CIF files for all the crystal-
lographic data.
i
i
(
2,6-Pr C H )NdC(Me)C(Me) N(Li)(2,6-Pr C H ) (13 Et O).
2 6 3 2 2 6 3 2
1
starting imine, and this in turn makes it more susceptible to
i
a MeLi nucleophile. Both lithiated species, (2,6-Pr C H )-
3
-
2 2
MeLi in Et O (1.4 mL, 1.50 mol L MeLi in Et O, 1.1 equiv) was
added to a solution of (2,6-Pr C H )NdC(Me)C(Me)dN(2,6-
2
6
3
i
i
NdC(Me)C(CH ) N(Li)(2,6-Pr C H ) (13) and (2,4,6-
2 6 3
3
2
2
6
3
i
2
-3
Pr C H ) (7; 0.777 g, 1.92 ꢀ 10 mol) in Et O (20 mL) at ice-bath
6
3
2
Me C H )NdC(Me)C(CH ) N(Li)(2,4,6-Me C H ) (14),
2
3
6
2
3 2
3
6
temperature. The yellow color of the initial solution intensified, and an
exotherm was noted. The solution was warmed to room temperature,
filtered, and concentrated to 7 mL. The solution deposited yellow
have the potential to be useful ligands for stabilizing transi-
tion-metal centers. Preliminary reactions with a range of
selected metal precursors are underway.
crystals of 13 Et O upon standing at -15 ꢀC (0.721 g, 75% yield).
3
2
Anal. Calcd for C33
2
H53LiN O: C, 79.16; H, 10.67; N, 5.60. Found: C,
1
79.00; H, 10.91; N, 5.50. H NMR (400.13 MHz, 300 K, THF-d
4
. Experimental Section
8
):
3
δ 7.14, 6.85 (d, 4H, aryl, JH,H
0
= 8.0 Hz), 7.06, 6.59 (t, 2H, aryl,
0
3
3
= 8.0 Hz), 4.23, 3.06 (sept, 4H, CH(CH ) , J
Unless otherwise stated, all experiments and manipulations
have been performed under an atmosphere of pure argon or
dinitrogen by Schlenk and cannula techniques. The DAB ligands
JH,H
0
= 6.8 Hz),
=7.0 Hz), 1.81 (s, 3H, CH CdN),
3 2
H,H
3
3.39 (q, 4H, OCH CH , J
0
2
3
H,H
3
3
1.30 (s, 6H, (CH ) CN), 1.20, 1.18 (d, 24H, CH(CH ) , J
0
=
= 7.0 Hz). C{ H} NMR
3
2
3 2
H,H
9
3
6.8 Hz), 1.10 (t, 6H, OCH CH , J
13
1
used in this work were prepared according to the literature.
Small quantities of diacetyl-d were prepared by the literature
0
2
3
H,H
6
(100.61 MHz, 300 K, THF-d ): δ 193.8 (CdN), 158.0, 149.0,
8
17
method and used to prepare (2,4,6-Me C H )NdC(CD )-
3
147.4, 138.9, 124.9, 124.1, 122.3, 118.3 (aryl), 68.4 (C(CH ) N),
66.4 (OCH ), 31.1, 28.5, 28.0, 24.4, 24.3, 18.7 (peak assignment is
6
2
3
3 2
3
) by standard means. All
C(CD
3
)dN(2,4,6-Me
solvents were dried over and distilled from appropriate drying
3
C
6
H
2
) (8-d
6
2
ambiguous due to coincidence of chemical shifts), 15.8 (OCH CH ).
2
3
agents and degassed after distillation. MeLi and MeLi LiBr
3
3 6 2 3 3 3 6 2
(2,4,6-Me C H )NdC(CD )C(CD )(Me)N(Li)(2,4,6-Me C H )
n
were obtained from Aldrich or Fisher in ether solution; Bu Li
-1
6 2
(14-d Et O). An ether solution of MeLi (1.9 mL, 1.0 mol L MeLi
3
was obtained from Fisher in hexanes. Concentrations of the
alkyllithium solutions were assessed by integration of the H
1
(19) SADABS; Bruker Analytical X-ray Instruments Inc., Madison, WI,
001.
20) SAINT; Bruker Analytical X-ray Instruments Inc., Madison, WI,
2007.
(21) Sheldrick, G. M. Acta Crystallogr., Sect. A 2008, 64, 112–122.
2
(
(18) Hoye, T. R.; Eklov, B. M.; Voloshin, M. Org. Lett. 2004, 6, 2567–
2570.

6
516 Organometallics, Vol. 29, No. 23, 2010
Bhadbhade et al.
O), (2,4,6-Me )NdC-
i
2
i
Table 2. Crystal and Refinement Data for (2,6-Pr
(
C
6
H
3
)NdC(Me)C(CH
3
)
Me)C(dCH )N(Li)(2,4,6-Me C H ) (15 Et O), (2,4,6-Me C H )(Li)NC(dCH )C(dCH )N(Li)(2,4,6-Me C H )
2
N(Li)(2,6-Pr
2
C
6
H
3
) (13 Et
2
3 6 2
C H
3
2
3
6
2
3
2
3
6
2
2
2
3
6
2
i
i
(
16 (Et
3
2
O)
3
(LiBr)
2
), and (2,6-Pr
2
C
6 3
H )NdC(Me)C(dCH
2
)N(Li)(2,6-Pr
2
C
H
6 3
), (17 Et
3
2
O)
1
3 Et
3
2
O
15 Et
3
2
O
16 3Et
3
2
O 2LiBr
3
2
17 Et O
3
empirical formula
fw
C
500.73
150(2)
33.1529(10)
9.7406(3)
19.9215(6)
90.00
92.984(2)
90.00
6424.5(3)
8
monoclinic
P2
1.035
33
H
53LiN
2
O
C
26
H
37LiN
2
O
C
359.15
150(2)
9.3319(4)
22.4980(10)
10.1430(4)
90.00
112.340(2)
90.00
17
H
23Br
2
Li
2
NO3/2
32 2
C H49LiN O
484.69
150(2)
10.017(14)
30.64(6)
10.062(13)
90.00
90.00
90.00
400.53
150(2)
16.436(3)
8.7758(17)
17.154(4)
90.00
90.00
90.00
2474.3(9)
4
T, K
˚
a, A
˚
b, A
˚
c, A
R, deg
β, deg
γ, deg
3
˚
V, A
Z
1969.68(14)
4
monoclinic
3089(9)
4
monoclinic
cryst syst
space group
orthorhombic
Pca2
1.075
1
/c
1
P2
1.211
1
/m
P2
1.042
1
-
3
dcalcd, g cm
θ range, deg
2.328-21.708
0.061
1.012
0.0601, 0.1399
0.1093, 0.1669
2.63-19.16
0.064
0.869
0.0614, 0.1414
0.1641, 0.1950
2.352-29.125
2.088
1.068
2.454-20.183
0.061
2.023
0.1633, 0.2126
0.3774, 0.3952
-1
μ, mm
GOF
a
b
c
R1 , wR2 [(I > 2σ(I ))
R1, wR2 (all data)
0.0350, 0.0873
0.0457, 0.0930
P
P
P
P
P
a
2
1/2
b
c
|. wR2 = [ w(|F
2
o
2
c
2
2 2 1/2
| ]
GOF = [ w(|F
o
| - |F
c
|) /(Nobs - Nparam)]
.
R1 = ||F
o
| - |F
c
||/ |F
o
| - |F
|) / w|F
o
.
in Et O, 1.1 equiv) was added to a slurry of (2,4,6-Me
2
3
C
6
H
2
)Nd
The yellow starting material dissolved to give a caramel-colored
solution, from which an ocher material precipitated after
20 min. The slurry was stirred overnight, and volatiles were
removed under reduced pressure. The ocher residue was recrys-
-
3
C(CD )C(CD )dN(2,4,6-Me C H ) (8-d ; 0.567 g, 1.74 ꢀ 10 mol)
3
3
3
6
2
6
in Et
give a clear, yellow solution, and after 10 min, a yellow solid
deposited. Et O was removed under reduced pressure, and the
2
O (20 mL) at ice-bath temperature. The slurry dissolved to
tallized from Et
Me )(Li)NC(dCH
(16 3Et O 2LiBr) were deposited (2.32 g, 55% yield). Anal.
2
O (15 mL), from which ocher crystals of (2,4,6-
2
residue was redissolved in THF (5 mL) to give a bright yellow
solution that was layered with hexanes (10 mL). The mixture
was allowed to stand at -15 ꢀC, and yellow crystals appeared
3
C
6
H
2
2
)C(dCH )N(Li)(2,4,6-Me
2
C H )
3 6 2
3
2
3
Calcd for C30
C, 55.30; H, 7.18; N, 4.32. H NMR (400.13 MHz, 300 K, THF-
2 4 2 2
H46Br Li N O : C, 55.19; H, 7.11; N, 4.29. Found:
1
(
0.250 g, 34% yield). Anal. Calcd for C H D LiN O: C,
27 35 6 2
1
3
7
NMR (400.13 MHz, 300 K, THF-d
6.74; H, 8.35; N, 6.63. Found: C, 77.05; H, 9.00; N, 6.73. H
): δ 6.83, 6.63 (s, 4H, aryl),
d ): δ 6.62 (s, 4H, aryl), 3.38 (q, 8H, OCH CH , J
0
= 7.0 Hz),
0
8
2
3
H,H
0
8
3.08 (s, 2H, CdCHH ), 2.19 (s, 12H, CH ), 2.14 (s, 6H, CH ),
3
0
2.13 (s, 2H, CdCHH ), 1.10 (t, 12H, OCH CH , J = 7.0
H,H
Hz). C{ H} NMR (100.61 MHz, 300 K, THF-d ): δ 153.7,
3
3
0
3
3
2
.39 (q, 4H, OCH
0
2
CH
.20 (s, 3H, CH ), 2.09 (s, 3H, CH ), 2.06 (s, 6H, CH ), 1.31
3
, JH,H
0
= 7.0 Hz), 2.23 (s, 6H, CH
0
3
),
2
3
13
1
3
3
3
8
3
(
s, 3H, CD
3
CH
C{ H} NMR (100.61 MHz, 300 K, THF-d
47.9, 135.7, 132.4, 131.5, 129.6 129.0, 128.7 127.7 (aryl),
9.1 (C(CH N), 66.5 (OCH ), 32.0 (CD CH ), 22.7,
1.2, 21.0, 18.7 (CH ), 15.9 (OCH ). H{ H} NMR (46.1
), 1.3 (s, N-C-
3
), 1.10 (t, 6H, OCH
2
CH
3
, JH,H
0
= 7.0 Hz).
131.6, 129.0, 126.1 (aryl), 66.4 (OCH CH ), 58.6 (CdCH ,
2
3
2
1
3
1
8
): δ 193.7 (CdN),
quaternary vinyl could not be located), 21.2 (p-Me), 19.8
(o-Me), 15.8 (OCH CH ).
(2,6-Pr C H )NdC(Me)C(dCH )N(Li)(2,6-Pr C H ),
1
6
2
2
3
i
i
3
)
2
2
3
3
2 6 3 2 2 6 3
2
1
i
CH
3
(17 Et O). An ether/hexane solution of Pr
2 2
n
NLi (prepared
from 5.0 mL of a 1.57 mol L Bu Li solution in hexanes added
3
2
3
-
1
MHz, 300 K, THF/hexanes): δ 2.20 (s, NdCCD
(
3
i
2
CH )(CD )).
to 1.1 mL of Pr O at -50 ꢀC, 1.1 equiv) was
added to a solution of (2,6-Pr C H )NdC(Me)C(Me)dN(2,6-
2 6 3
NH in 20 mL of Et
2
3
3
i
(
2,4,6-Me
3
C
6
H
2
)NdC(Me)C(dCH
2
)N(Li)(2,4,6-Me
15 Et O). An ether solution of MeLi (12.9 mL, 1.0 mol L
3
C
6
H
2
)
-
1
i
2
-3
(
MeLi in Et O, 1.05 equiv) was added to a slurry of (2,4,6-
2
Pr C H ) (7; 2.88 g, 7.12 ꢀ 10 mol) in Et O (50 mL) at ice-
3
6
3
2
2
bath temperature, and the mixture was warmed to room tem-
perature. The solution became a more intense yellow, and the
solution was stirred overnight. The solution was concentrated to
Me
3
C
6
H
2
)NdC(Me)C(Me)dN(2,4,6-Me
3 6 2
C H ) (8;10g,0.0128mol)
in Et O (40 mL) at ice-bath temperature. The slurry dissolved as the
2
MeLi was added, and a clear, orange solution was obtained. The
solution was stirred for 4 h and then concentrated to 15 mL. Upon
i
2
a 10 mL volume, and yellow crystals of (2,6-Pr C H )Nd
3
2
C(Me)C(dCH )N(Li)(2,6-Pr C H ) (17 Et O) appeared after
standing at 5 ꢀC (2.20 g, 65% yield). Anal. Calcd for C H Li-
N O: C, 79.30; H, 10.19; N, 5.78. Found: C, 79.50; H, 10.01; N,
2
6
i
2
6
3
3
2
standing at -5 ꢀC, yellow crystals of (2,4,6-Me
dCH )N(Li)(2,4,6-Me ) (15 Et O) were deposited (3.05 g,
0% yield). Anal. Calcd for C26 37LiN O: C, 77.97; H, 9.31; N,
.00. Found: C, 78.16; H, 9.02; N, 6.70. H NMR (400.13 MHz, 300
K, THF-d ): δ 6.84, 6.77 (s, 4H, aryl), 3.79, 2.96 (s, 2H, dCH ), 3.38
3
C
6
H
2
)NdC(Me)C-
3
2
49
(
6
7
2
3
C
6
H
2
2
3
1
H
2
6.00. H NMR (400.13 MHz, 300 K, THF-d ): δ 7.17, 6.95
8
1
3
3
= 7.8 Hz), 7.07, 6.75 (t, 2H, aryl, JH,H
(d, 4H, aryl, JH,H
0
0
=
7.8 Hz), 3.94, 3.14 (s, 2H, CdCHH ), 3.51, 3.04 (sept, 4H, CH-
0
8
2
3
3
3
(
q, 4H, OCH CH
2
3
, JH,H
0
= 7.0 Hz), 2.23 (s, 3H, CH ), 2.14 (s, 6H,
3
(CH
7.0 Hz), 2.02 (s, 3H, CH
3
)
2
, JH,H
0
= 6.8 Hz), 3.39 (q, 4H, OCH
CdN), 1.20, 1.16, 1.12, 0.98 (d, 24H,
2 3
CH , JH,H =
0
0
0
CH
CH
100.61 MHz, 300 K, THF-d ): δ 176.6 (CdN), 155.9, 154.0, 147.9,
3
), 2.15 (s, 3H, CH
3
CdN), 2.04 (s, 6H, CH
3
), 1.91 (s, 3H,
3
3
13
1
3
3
3
), 1.10 (t, 6H, OCH
2
CH
3
, JH,H
0
= 7.0 Hz). C{ H} NMR
CH(CH
3
)
2
, JH,H
0
= 6.8 Hz), 1.10 (t, 6H, OCH
7.0 Hz). C{ H} NMR (100.61 MHz, 300 K, THF-d
(CdN), 157.5, 141.9, 136.7, 122.8, 121.9, 121.1, 118.3, 117.5
(aryl), 78.0 (CdCH ), 64.2 (OCH ), 59.1 (CdCH ), 44.0
(NdCCH ), 26.7, 26.4, 23.7, 23.0 (CH(CH
(CH ), 15.8 (OCH CH ).
(2,6-Pr )NdC(Me)C(Me)(C
(18 Et
2 3
CH , JH,H =
0
1
3
1
(
8
): δ 175.3
8
1
5
1
32.5, 129.3, 128.9, 127.7, 126.9 (aryl), 76.0 (CdCH
9.1 (CdCH ), 43.8 (CH CdN), 26.6, 26.4, 22.3, 22.2, 18.7 (CH
5.9 (OCH CH ).
2,4,6-Me
16 3Et O 2LiBr). An ether solution of MeLi LiBr (15.0 mL,
2
), 64.3 (OCH
2
),
3
),
2
3
2
2
2
3
3
)
2
), 22.3, 22.2 (CH-
2
3
(
3
C
6
H
2
)(Li)NC(dCH
2
)C(dCH
2
)N(Li)(2,4,6-Me
3
C
6
H
2
)
3
)
2
2
3
i
i
(
0
2
C
6
H
3
4
H
9
)N(Li)(2,6-Pr
2
C
6
H
3
)
3
2
3
3
-
1
n
-1
n
.89 mol L MeLi in Et
2
O, 2.3 equiv) was added to a slurry of
) (8; 1.85
O (60 mL) at ice-bath temperature.
2
O). Bu Li in hexanes (7.25 mL, 1.5 mol L Bu Li in
3
i
(
2,4,6-Me
3
C
6
H
2
)NdC(Me)C(Me)dN(2,4,6-Me
3
C
6
H
2
hexanes,1.05 equiv) was added to a slurry of (2,6-Pr
2
C
6
H
3
)-
-
3
i
-3
g, 5.77 ꢀ 10 mol) in Et
2
2 6 3
NdC(Me)C(Me)dN(2,6-Pr C H
) (7; 4.16 g, 10.3 ꢀ 10 mol)

Article
in Et O (50 mL) at ice-bath temperature. The resultant orange
solution was concentrated to 40 mL and filtered from the
Organometallics, Vol. 29, No. 23, 2010 6517
2
spectroscopy revealed the presence of signals attributable to
17 Et O, and no further characterization was attempted.
2
3
residue, and orange and yellow crystals deposited at 5 ꢀC. While
i
an orange crystal corresponding to (2,6-Pr
2
C
6
H
3
)NdC(Me)C-
Supporting Information Available: CIF files giving crystal-
lographic data for 13 Et O and and 15-18 Et O. This material
is available free of charge via the Internet at http://pubs.acs.org.
i
2
(
Me)(C
H
4 9
)N(Li)(2,6-Pr O) was selected for
X-ray diffraction and characterized by these means, H NMR
C
6
H
3
) (18 Et
2
2
2
3
3
3
1