Lithium and potassium amides of sterically demanding aminopyridines

Article abstract of DOI:10.1002/ejic.200400228

The reaction of Grignard compounds of 1-bromo-2,4,6-diisopropylbenzene (1) or 1-bromo-2,6-dimethylbenzene (2), formed in situ, with 2,6-dibromopyridine in the presence of a catalytic amount of [(dme)NiBr₂] (dme = 1,2-dimethoxyethane) and tricyc

Full text of DOI:10.1002/ejic.200400228

FULL PAPER
Lithium and Potassium Amides of Sterically Demanding Aminopyridines
Natalie M. Scott,[a] Thomas Schareina,[b] Oleg Tok,[a] and Rhett Kempe*[a]
Keywords: Amido ligands / Coordination polymers / Lithium / N ligands / Potassium
The reaction of Grignard compounds of 1-bromo-2,4,6-diiso-
propylbenzene (1) or 1-bromo-2,6-dimethylbenzene (2), less crystalline material. X-ray structural analysis reveals it
formed in situ, with 2,6-dibromopyridine in the presence of to be a monomeric three-coordinate lithium aminopyridinate.
a catalytic amount of [(dme)NiBr2] (dme = 1,2-dimethoxy- In toluene solution, an equilibrium between [(Ap*Li)2] (in ex-
ethane) and tricyclohexylphosphane (1:2 ratio) leads to the cess at room temperature) and [Ap*Li(OEt2)] (prominent at
corresponding monoarylated bromopyridines. These bromo- low temperature) is observed. Reaction of ApЈH with BuLi in
ether using BuLi results (after workup in hexane) in a colour-
pyridines
undergo
Pd-catalysed
aryl
amination
diethyl ether gives rise to [Ap*LiAp*Li(OEt2)]. Deprotonation
of Ap*H and ApЈH using KH leads to [Ap*K]n and [ApЈK]ϱ,
respectively. [ApЈK]ϱ is a rare example of a crystalline or-
ganometallic polymer, as determined by X-ray analysis.
( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2004)
(Buchwald−Hartwig amination) with 2,6-diisopropylaniline
giving rise to (2,6-diisopropylphenyl)[6-(2,4,6-triisopropyl-
phenyl)pyridin-2-yl]amine (Ap*H) and (2,6-diisopropyl-
phenyl)[6-(2,6-dimethylphenyl)pyridin-2-yl]amine
(Ap = aminopyridinate). Deprotonation of Ap*H in diethyl
(ApЈH)
Introduction
During the renaissance[1] of (amido)metal[2] chemistry,
aminopyridinato ligands[3] have been used extensively to
stabilise early transition metal and lanthanide ions
(Scheme 1).
Scheme 2. Ap*H (5) and ApЈH (6)
The syntheses and structures of alkali metal aminopyridi-
nates were described first by Clegg and Snaith et al.[5] These
compounds are remarkable examples of the diversity metal
amides can show in terms of binding and aggregation
modes.[6] One of the most common structures observed is a
dimer containing two coordinated solvent molecules
(Scheme 3).[7]
Scheme 1. Aminopyridinato ligand ([M] ϭ early transition metal
moiety; R ϭ aryl, silyl or alkyl substituent)
The aminopyridinato ligands used thus far have exhibited
a relatively low steric demand, especially in the plane per-
pendicular to the pyridine moiety. This characteristic has
restricted the chemistry of the corresponding metal com-
plexes so far, leading to the formation of ‘‘ate’’ species, for
example.[3,4] In order to minimise this feature, we became
interested in designing bulkier aminopyridinato ligands by
the introduction of 2,6-alkylphenyl (alkyl ϭ methyl or iso-
propyl) substituents at the amido N atom as well as the 6-
position of the pyridine ring. Here, we report on the syn-
thesis and structure of the lithium and potassium amides of
Ap*H and ApЈH (Scheme 2).
Scheme 3. The dimeric bis(solvent)-coordinated structure motive
(M ϭ alkali metal; R, RЈ ϭ alkyl, aryl or silyl substituent; S ϭ
mono- or bidentate donor solvent molecule)
[a]
Lehrstuhl für Anorganische Chemie II, Universität Bayreuth,
95440 Bayreuth, Germany
Furthermore, structurally diverse alkali metal aminopyri-
dinates have been found in aminopyridinato ‘‘ate’’ com-
plexes[8] and in main group amides.[9]
E-mail: kempe@uni-bayreuth.de
[b]
Leibniz-Institut für Organische Katalyse,
Buchbinderstrasse 5Ϫ6, 18055 Rostock, Germany
Eur. J. Inorg. Chem. 2004, 3297Ϫ3304
DOI: 10.1002/ejic.200400228
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N. M. Scott, T. Schareina, O. Tok, R. Kempe
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Results and Discussion
Synthesis of the Ligands
The reaction of in situ formed Grignard compounds of
1-bromo-2,4,6-diisopropylphenyl or 1-bromo-2,6-dimeth-
ylphenyl (1, 2) with 2,6-dibromopyridine in the presence of
a catalytic amount of [(dme)NiBr2] and tricyclohexylphos-
phane (1:2 ratio) leads to the bromopyridines 3 and 4
(Scheme 4). The catalyst system was chosen on the basis of
results of parallel screening experiments with various phos-
phane/group 10 metal combinations. The best combination
also turned out to be optimal in terms of material avail-
ability (both components can be obtained commercially),
selectivity and activity.[10]
Figure 1. Molecular structure of 7 (ellipsoids correspond to the
˚
50% probability level); selected bond lengths [A] and angles [°]:
LiϪO 1.903(5), LiϪN1 1.987(5), LiϪN2 2.020(5); OϪLiϪN1
150.4(3), OϪLiϪN2 132.9(3), N1ϪLiϪN2 69.28(16)
protonated 5 is large. The maximum atomϪatom distances
˚
of deprotonated 5 in 7 are a ϭ 15 A (Scheme 6) and, ap-
˚
proximately perpendicular to it, b ϭ 8 A (Scheme 6). Com-
parison of these distances with those of the bulky, η5-coor-
dinated Cp* ligand[13] (Cp*
tadienyl), which has a distance of a ϭ b ϭ 6.2 A for both
directions, indicates that deprotonated 5 should be effective
for the protection of large metal ions.
ϭ
pentamethylcyclopen-
˚
Scheme 4. Synthesis of 3 and 4 (3 with R, RЈ ϭ iPr; 4 with R ϭ
CH3, RЈ ϭ H)
Compounds 3 and 4 undergo Pd-catalysed aryl amin-
ation (BuchwaldϪHartwig amination) with 2,6-diisopro-
pylaniline giving rise to 5 and 6, respectively.[11] Despite the
steric demands of the reactants, good yields have been ob-
served for these two reactions.
Synthesis, Structure and Dynamic Behaviour of the
Aminopyridinates
Deprotonation of 5 in diethyl ether using BuLi gave rise
(after workup in hexane) to a colourless crystalline material
(compound 7) in about 80% yield (Scheme 5). X-ray crystal
structure analysis of 7 revealed it to be a monomeric three-
coordinated lithium aminopyridinate in the solid state (Fig-
ure 1).
Scheme 6. Description of the steric demand of deprotonated 5
1H NMR spectroscopy of 7 at room temperature revealed
it to be dynamic (Figure 2). One possibility is that the iso-
propyl groups of the aniline moiety and the pyridine sub-
stituent have restricted rotation due to the strained η2-coor-
dination mode [angle N1ϪLiϪN2 ϭ 69.28(16)°]. Alterna-
tively, two different compounds (e.g. isomers) could exist
in solution. Cooling of the NMR sample resulted in the
formation of signals from a second compound (Figure 2). A
characteristic of this ‘‘room-temperature compound’’ (7a) is
that ether coordination is not observed as evidenced by the
matching of the well-resolved ether signals to those of ‘‘free
ether’’ in C7D8. In accordance with the structure of 8 (see
discussion below) we propose a ‘‘solvent-free’’ dimeric
structure for 7a (Scheme 7)
The nearly equivalent LiϪN distances [LiϪN1 1.987(5),
[12]
˚
LiϪN2 2.020(5) A] indicate a delocalised binding mode.
The coordination of the lithium ion is approximately trig-
onal-planar (sum of angles ϭ 353°; deviation of Li out of
˚
the plane N1ϪN2ϪO ϭ 0.26 A). The steric demand of de-
Cooling down to Ϫ30 °C results in a change in the ratio
of 7/7a from 2:1 to 3:1. Precipitation of 7 starts at Ϫ50 °C
(broad signals). Signal resolution occurs with the addition
Scheme 5. Synthesis of 7 (Tip ϭ 2,4,6-triisopropylphenyl)
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Lithium and Potassium Amides of Sterically Demanding Aminopyridines
FULL PAPER
Reaction of 6 with BuLi in diethyl ether gave (after work
up in hexane) a crystalline material (8) in good yield
(Scheme 8).
Scheme 8. Synthesis of 8 (Dmp ϭ 2,6-dimethylphenyl)
X-ray crystal structure analysis of 8 revealed a dimeric
structure in the solid state (Figure 3). Both Li atoms are
coordinated in an almost trigonal-planar manner. The devi-
ations of the lithium atoms out of the coordination planes
˚
˚
are 0.43 A (Li1) and 0.23 A (Li2). One of the two ApЈ
ligands acts as a bridge (bridging binding mode) with a sig-
nificantly longer NpyridineϪLi than NamidoϪLi bond, indica-
tive of a localisation of the anionic charge of this ligand at
the amido nitrogen atom. The second ApЈ ligand binds one
of the lithium atoms in the strained η2-binding mode
[N4ϪLi2ϪN3 65.82(14)°] whereas the Namido lone pair acts
as a bridge to the second lithium atom. The steric demands
of this new ligand can be described as mentioned above for
Ap* (Scheme 6). The maximum atomϪatom distances are
˚
˚
a ϭ 13 A and, perpendicular to it, b ϭ 8 A. NMR studies
reveal a similar dimeric structure in toluene solution as
found in the solid state.
Figure 2. 1H NMR of 7 in C7D8 at different temperatures; the two
last spectra show signals after addition of [D8]THF
Scheme 7. Equilibrium between 7a (dominant at room tempera-
ture) and 7 (low-temperature ether adduct)
Figure 3. Molecular structure of 8 (ellipsoids correspond to the
˚
50% probability level); selected bond lengths [A] and angles [°]:
of an excess of [D8]THF at this temperature with the forma-
tion of a THF adduct analogous to 7. This is indicated by
a new, third signal set accompanied by the signals of ‘‘free
ether’’. Raising the temperature to 25 °C causes only mar-
ginal changes of the signal set, which is in accordance with
the expected temperature dependence. Furthermore, the sig-
nals observed for the pyridine protons suggest a delocalised
binding mode in solution for both 7 and 7a.[12]
N4ϪLi2 1.922(4), N3ϪLi1 2.023(3), N3ϪLi2 2.271(5), N2ϪLi1
2.005(3), O1ϪLi1 2.013(4), N1ϪLi2 1.907(4); N2ϪLi1ϪO1
112.85(15), N2ϪLi1ϪN3 129.09(16), O1ϪLi1ϪN3 104.09(14),
N1ϪLi2ϪN4 164.4(5), N1ϪLi2ϪN3 119.1(3), N4ϪLi2ϪN3
65.82(14)
The reactions of 5 and 6 with KH lead to crystalline 9
and 10, respectively, according to Scheme 9. Crystals of 10
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N. M. Scott, T. Schareina, O. Tok, R. Kempe
FULL PAPER
coordinatively saturating the potassium atoms and owing
to geometric restrictions, the transoid-bridging binding
mode is favoured. A detailed discussion of bond lengths
and angles of 10 is precluded by the high disorder in the X-
ray structure and grown-together twinned crystals. Despite
the fact that a potassiumϪarene interaction is a common
phenomenon, polymeric structures based on these are ra-
rely observed[14] and homoleptic systems are almost un-
known.[15]
Scheme 9. Synthesis of 9 (R, RЈ ϭ iPr) and 10 (R ϭ CH3, RЈ ϭ H)
Conclusions
Grignard coupling and palladium-catalysed aryl amin-
ation are efficient methods for the preparation of sterically
encumbered aminopyridines. The steric coverage of depro-
tonated aminopyridines (aminopyridinato ligands) ap-
proaches the nanometer range and the cover area is about
3.3 and 2.8 times larger for deprotonated 5 and depro-
tonated 6, respectively, than for Cp*. The structural and
dynamic behaviour of the lithium and potassium amides in
solution differ significantly. Compound 10 is a rare example
of an Ap complex exhibiting the transoid-bridging binding
mode.
Figure 4. Part of the molecular structure of 10 (ellipsoids corre-
˚
spond to the 50% probability level); selected bond lengths [A] and
angles [°]: C1ϪK1 3.125(9), C2ϪK1 3.218(10), C3ϪK1 3.260(10),
C4ϪK1 3.260(10), C5ϪK1 3.187(9), C6ϪK1 3.137(9), C12ϪK1
3.292(9), C17ϪK1 3.341(9), N3ϪK1 2.815(7), N4ϪK1 2.739(7);
N4ϪK1ϪN3 157.2(2)
Experimental Section
General Procedures: All reactions and manipulations with air-sensi-
tive compounds were performed under dry argon, using standard
Schlenk and drybox techniques. Solvents were distilled from so-
dium benzophenone ketyl. Deuterated solvents were obtained from
Cambridge Isotope Laboratories and were degassed, dried (CaH2)
and distilled prior to use. NMR spectra were obtained using either
a Bruker ARX 250 or Bruker DRX 500 spectrometer. Chemical
shifts are reported in ppm relative to the deuterated solvent. nBuLi,
KH, 1-bromo-2,4,6-triisopropylbenzene, 1-bromo-2,6-dimeth-
ylbenzene, NiBr2(dme), tricyclohexylphosphane, 2,6-diisopro-
pylaniline, 3-bis(diphenylphosphanyl)propane, sodium tert-butox-
ide, 1,2-dibromoethane and tris(dibenzylideneacetone)dipallad-
ium(0) were purchased from commercial suppliers. X-ray crystal
structure analyses were performed by using a STOE-IPDS I or II
equipped with an Oxford Cryostream low-temperature unit. Struc-
ture solution and refinement were accomplished using SIR97,[16]
SHELXL-97[17] and WinGX.[18] Crystallographic details are sum-
marised in Table 1. CCDC-231858 (for 10), -231859 (for 8) and -
231860 (for 7) contain the supplementary crystallographic data for
this paper. These data can be obtained free of charge at
www.ccdc.cam.ac.uk/conts/retrieving.html [or from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ,
UK; Fax: ϩ 44-1223-336-033; E-mail: deposit@ccdc.cam.ac.uk]
suitable for X-ray analysis were grown from diethyl ether
(crystal structure: Figure 4).
The structure of 10 is best described as a coordinative
one-dimensional polymer. (The amidoaryl groups appear
on the same side in successive ‘‘monomer residues’’ Ϫ
pseudo-isotactic.) The amido N atom coordinates one pot-
assium atom and the pyridine function binds the next. The
coordination thus can be described as a transoid-bridging
binding mode (Scheme 10).
Scheme 10. transoid- (left) and cisoid-bridging binding (right) mode
of aminopyridinato ligands ([M] metal moiety)
The binding situation observed for 10 might be helpful
in explaining the mechanism of polymeric by-product for-
mation found during aminopyridinato early transition me-
tal complex syntheses.[3] The transoid-bridging binding
Preparation of 1-MgBr-[2,4,6-(iPr)3C6H2] (1): THF (30 mL) was
added to magnesium turnings (0.94 g, 38.7 mmol). 1-Br-2,4,6-
(iPr)3C6H2 (35.2 mmol, 9.97 g, 8.86 mL) was then added and the
resulting suspension stirred and activated using 1,2-dibromoethane.
mode formed by a two-coordinate potassium ion would be An exothermic reaction took place and an ice bath was used to
cool the reaction mixture when the reaction became too vigorous.
After 1 h, the cooled reaction mixture was stirred at 50 °C over-
night. The reaction mixture was filtered and the filtrate directly
used in the preparation of 3.
unstable without the π-coordination of the electron-rich
phenyl substituents which coordinatively saturate the sys-
tem. From an alternative viewpoint it could be said that
the electron-rich arene functions of 5 and 6 are ideal for
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Lithium and Potassium Amides of Sterically Demanding Aminopyridines
FULL PAPER
Table 1. Details of the X-ray crystal structure analyses
7
8
10
Crystal system
Space group
monoclinic
P21/c
monoclinic
P21/n
orthorhombic
Pbca
12.669(1)
37.704(5)
18.694(1)
Ϫ
˚
a [A]
18.235(4)
19.007(4)
10.013(2)
95.70(3)
3453.2(5)
4
10.780(5)
17.869(5)
25.205(5)
91.49(5)
4854(3)
4
˚
b [A]
˚
c [A]
β [°]
3
˚
V [A ]
8929.6(15)
8
Z
Crystal size [mm]
0.18 ϫ 0.16 ϫ 0.08
1.592
0.060
0.5 ϫ 0.4 ϫ 0.3
1.099
0.064
0.4 ϫ 0.2 ϫ 0.2
1.180
0.250
ρcalcd. [g cmϪ3
]
µ [mmϪ1] (Mo-Kα)
T [K]
193(2)
193(2)
193(2)
θ range [°]
2.14Ϫ26.07
6405
3076
361
0.170
1.40Ϫ26.03
9521
7740
551
0.149
1.08Ϫ20.56
4511
3477
489
0.242
No. of unique reflections
No. of reflections observed [I Ͼ 2σ(I)]
No. of parameters
wR2 (all data)
R value [I Ͼ 2σ(I)]
0.059
0.050
0.097
Preparation of 1-MgBr-[2,6-(Me)2C6H3] (2): THF (30 mL) was ad-
ded to magnesium turnings (0.94 g, 38.7 mmol). 1-Br-2,6-Me2C6H3
(35.2 mmol, 6.50 g, 4.69 mL) was then added and the resulting sus-
pension stirred. The reaction mixture was activated using 1,2-dibro-
moethane (approx. 0.4 mL). An exothermic reaction took place
and an ice bath was used to cool the reaction mixture when the
reaction became too vigorous. After 2 h, the cooled reaction mix-
ture was stirred at 50 °C for 12 h. The reaction mixture was filtered
and the filtrate directly used in the preparation of 4.
Preparation of 4: 2,6-Dibromopyridine (7.91 g, 33.4 mmol), diox-
ane (35 mL), tricyclohexylphosphane (0.075 mmol, 1.5 mL (0.05 
in THF) and [NiBr2(dme)] (0.012 g, 0.0375 mmol) were combined
in a Schlenk flask and cooled to 0 °C. Compound 2 was then slowly
added dropwise to the cooled, stirred suspension. A beige precipi-
tate resulted and the resulting mixture was then warmed to room
temperature where a moderate exothermic reaction took place.
Once the reaction mixture was cooled to room temperature, it was
stirred and after 1 h heated to 50 °C for 72 h. Water (50 mL) and
CH2Cl2 (50 mL) were added and the resulting suspension trans-
ferred to a 2-L separating funnel. The organic phase was collected
and the inorganic phase washed with CH2Cl2 and extracted. The
combined organic phases were washed with a saturated sodium
chloride solution and dried with Na2SO4. The organic phase was
concentrated to dryness under vacuum resulting in a red-orange
oily product. The reddish oil was purified using silica chromatogra-
phy (dichloromethane) and then crystallised from pentane at Ϫ20
°C. Yield 7.80 g (89%). M.p. 62Ϫ63 °C. C13H12BrN (262.1): calcd.
Preparation of 3: 2,6-Dibromopyridine (7.91 g, 33.4 mmol), diox-
ane (35 mL), tricyclohexylphosphane [0.075 mmol, 1.5 mL (0.05
 in THF)] and [NiBr2(dme)] (0.012 g, 0.0375 mmol) were added
together in a Schlenk flask under argon; 1 was then added to the
stirred suspension resulting in a beige precipitate. The reaction mix-
ture was warmed to 50 °C and stirred for 72 h. Water and CHCl3
were added and the resulting suspension transferred to a 2-L separ-
ating funnel. The organic phase was collected and the inorganic
phase washed with CHCl3 and extracted. The combined organic
phases were washed with a saturated sodium chloride solution and
dried with Na2SO4. The solvent was removed to afford a white
precipitate. The precipitate was recrystallised from hot n-octane
and washed with n-pentane (20 mL). Yield 7.05 g (58%). M.p.
232Ϫ233 °C C20H26BrN (360.3): calcd. C 66.67, H 7.27, N 3.89;
found C 67.56, H 7.48, N 3.78. 1H NMR (250 MHz, CDCl3,
298 K): δ ϭ 1.00Ϫ1.30 [m, 18 H, CH(CH3)2], 2.44 [sept, 2 H,
CH(CH3)2], 2.88 [sept, 1 H, CH(CH3)2], 7.02 (s, 2 H, 9,11-H), 7.21
(d, 1 H, 3-H), 7.45 (d, 1 H, 5-H), 7.59 (br. dd, 1 H, 4-H) ppm. 13C
NMR (250 MHz, CDCl3, 298 K): δ ϭ 23.85 [2 CH3, (CH3)2CH],
24.06 [2 CH3, (CH3)2CH], 24.17 [2 CH3, (CH3)2CH], 30.41
[CH(CH3)2, C-13,-15], 34.44 [CH(CH3)2, C-14], 120.76 (CH, C-
9,11), 123.94 (CH, C-3/5), 125.90 (CH, C-3/5), 134.88 (C, C-7),
137.93 (CH, C-4), 141.46 (C, C-2), 146.12 (C, C-8,12), 149.29 (C,
C-10), 161.30 (C, C-6) ppm.
1
C 59.56, H 4.61, N 5.34; found C 60.30, H 4.74, N 5.28. H NMR
(250 MHz, CDCl3, 298 K): δ ϭ 1.91 (s, 6 H, CH3), 6.92 (s, 2 H,
9,11-H), 6.86Ϫ7.35 (m, 3 H, Ar, 3,5,10-H), 7.44 (br. dd, 1 H, 4-H)
ppm. 13C NMR (250 MHz, CDCl3, 298 K): δ ϭ 20.17 (2 CH3, C-
13,14), 123.41 (CH, C-3/5), 126.03 (CH, C-3/5), 127.52 (CH, C-
9,11), 128.21 (C, C-10), 135.64 (C, C-8,12), 138.91 (CH, C-4),
140.73 (C, C-2/7), 141.71 (C, C-2/7), 160.88 (C, C-6) ppm.
Preparation of Ap*H (5): In a drybox the solids 3 (4.00 g,
11.12 mmol),
1,3-bis(diphenylphosphanyl)propane
(0.115 g,
0.279 mmol), tris(dibenzylideneacetone)dipalladium(0) (0.126 g,
0.139 mmol) and sodium tert-butoxide (0.90 g, 3.10 mmol) were
combined in a Schlenk flask. 2,6-Diisopropylaniline (11.12 mmol,
1.97 g, 2.10 mL) and toluene (40 mL) were added to the flask. The
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N. M. Scott, T. Schareina, O. Tok, R. Kempe
FULL PAPER
resulting mixture was heated at 95 °C for 48 h. The reaction mix-
23,24,25,26], 103.73 (CH, C-3), 114.08 (CH, C-5), 124.06 (CH, C-
ture was cooled to room temperature, and water (50 mL) and di- 17,19), 127.56 (CH, C-9,11), 127.70 (CH, C-10/18), 128.00 (CH, C-
ethyl ether (50 mL) were added. The organic phase was extracted
and the remaining inorganic phase was washed with diethyl ether
(3 ϫ 20 mL). The combined organic phases were washed with a
saturated sodium chloride solution and the organic phase was dried
with sodium sulfate. The solvent was removed under reduced press-
ure and the resulting red-orange solid was purified using silica
chromatography (dichloromethane). Yield 5.00 g (89%). M.p.
162Ϫ163 °C. C32H44N2 (456.7): calcd. C 84.16, H 9.71, N 6.13;
found C 83.94, H 9.75, N 5.71. 1H NMR (250 MHz, CDCl3,
298 K): δ ϭ 1.00Ϫ1.27 [m, 30 H, CH(CH3)2], 2.70 [sept, 2 H,
10/18), 134.18 (C, C-15), 135.75 (C, C-8,12), 138.04 (CH, C-4),
140.74 (C, C-7), 148.01 (C, C-16,20), 158.43 (C, C-2/6), 159.37 (C,
C-2/6) ppm.
CH(CH3)2], 2.90 [sept,
1 H, CH(CH3)2], 3.25 [sept, 2 H,
1
CH(CH3)2], 3.72 (br. s, 1 H, NH), 5.91 (br. d, J ϭ 8.30 Hz, 1 H,
3-H), 5.97 (br. s, 1 H, 4-H), 6.61 (br. d, 1J ϭ 7.2 Hz, 1 H, 5-H),
7.03Ϫ7.40 (m, Ar,
5
H, 9,11,18,19,20-H) ppm. 13C NMR
(250 MHz, CDCl3, 298 K): δ ϭ 22.43 [CH(CH3)2, C-22,23], 23.95
[2 CH(CH3)2, C-32,33/28,29/30,31], 24.14 [2 CH(CH3)2, C-32,33/
28,29/30,31], 24.51 [2 CH(CH3)2, C-32,33/28,29/30,31], 28.47
[CH(CH3)2, C-24,25,26,27], 30.33 [CH(CH3)2, C-13,14], 34.47
[CH(CH3)2, C-15], 103.64 (CH, C-3), 114.89 (CH, C-5), 120.74
(CH, C-9,11), 123.92 (CH, C-18,20), 127.90 (CH, C-19), 134.51 (C,
C-16), 136.61 (C, C-7), 137.35 (CH, C-4), 146.01 (C, C-8,12),
148.01 (C, C-17,21), 148.45 (C, C-10), 158.54 (C, C-2/6), 159.08 (C,
C-2/6) ppm.
Preparation of 7: nBuLi (1.38 mL, 1.6 , 2.20 mmol) was slowly
added to a stirred solution of Ap*H (1.00 g, 2.20 mmol) in diethyl
ether (40 mL) at 0 °C. After complete addition, the mixture was
stirred and warmed to room temperature (ca. 1 h). The reaction
mixture was concentrated to dryness and hexane (20 mL) added.
The solvent volume was reduced to ca. 2 mL in vacuo, and on
standing colourless crystals of the title complex formed. Yield
0.96 g (82%). C36H53LiN2O (536.8): calcd. C 80.56, H 9.95, N 5.22;
found C 79.85, H 9.66, N 4.90. 1H NMR (250 MHz, C7D8, 298 K):
δ ϭ 0.89 (br. m, 6 H, CH3, OEt2), 0.98Ϫ1.40 [m, 30 H, CH(CH3)2],
2.83 [br. m, 3 H, CH(CH3)2] 3.11 (m, 4 H, CH2, OEt2), 3.25 [br.
1
m, 2 H, CH(CH3)2], 5.61 (br. d, J ϭ 8.05 Hz, 1 H, 3-H), 5.92 (d,
1J ϭ 6.90 Hz, 1 H, 5-H), 6.95 (br. dd, 1 H, 4-H), 6.98Ϫ7.32 (m,
Ar, 5 H, 9,11,18,19,20-H) ppm. 13C NMR (250 MHz, C7D8,
298 K): δ ϭ 14.99 (2 CH3, Et2O), 24.37 [CH(CH3)2, C-22,23], 24.47
[CH(CH3)2, C-28,29,32,33], 24.88 [CH(CH3)2, C-30,31], 28.42
[CH(CH3)2, C-24,25,26,27], 30.66 [br., CH(CH3)2, C-13,14], 34.94
[br., CH(CH3)2, C-15], 66.17 (2 CH2, Et2O), 107.15 (br. CH, C-3),
108.58 (br., CH, C-5), 120.76, 120.97, 124.47, 137.88, 145.18 (br.,
CH, C-4), 146.70, 148.52, 157.32 (br., C, C-6), 169.56 (br., C, C-2)
1
ppm. H NMR (250 MHz, C7D8, 273 K): δ ϭ 0.92 (m, 6 H, CH3,
OEt2), 0.98Ϫ1.38 [m, 30 H, CH(CH3)2], 2.88 [v. br. m, 3 H,
CH(CH3)2], 3.05 (m, 4 H, CH2, OEt2), 3.36 [v. br. m, 1 H,
Preparation of ApЈH (6): In a drybox the solids 4 (2.00 g,
7.63 mmol),
1,3-bis(diphenylphosphanyl)propane
(0.115 g, CH(CH3)2], 3.76 [v. br. m, 1 H, CH(CH3)2], 5.62 (br. d, 1J ϭ
1
0.279 mmol), tris(dibenzylideneacetone)dipalladium(0) (0.126 g,
0.139 mmol) and sodium tert-butoxide (0.83 g, 8.6 mmol) were
combined in a Schlenk flask. 2,6-Diisopropylaniline (7.63 mmol,
8.50 Hz, 1 H, 3-H), 6.69 (v. br. d, 3-H*), 5.98 (d, J ϭ 6.80 Hz, 1
H, 5-H), 6.77 (br. dd, 1 H, 4-H), 6.90Ϫ7.32 (m, Ar, 5 H,
9,11,18,19,20-H) ppm. 13C NMR (250 MHz, C7D8, 273 K): δ ϭ
1.35 g, 1.43 mL) and toluene (30 mL) were added to the flask. The 14.45 (2 CH3, Et2O), 24.43 [CH(CH3)2, C-22,23], 24.62 [CH(CH3)2,
resulting mixture was heated at 95 °C for 72 h. The reaction mix- C-28,29,32,33], 24.97 [CH(CH3)2, C-30,31], 28.36 [CH(CH3)2, C-
ture was cooled to room temperature, and water (50 mL) and di- 24,25,26,27], 30.67 [br., CH(CH3)2, C-13,14], 37.00 [br., CH(CH3)2,
ethyl ether (50 mL) were added. The organic phase was extracted
and the remaining inorganic phase washed with diethyl ether (3 ϫ
20 mL). The combined organic phases were washed with a satu-
rated sodium chloride solution and the organic phase was dried
with sodium sulfate. The solvent was removed under reduced press-
ure and the resulting red solid was then purified using column chro-
matography (dichloromethane) and crystallised at Ϫ20 °C from
pentane to afford a white crystalline material. Yield 2.10 g (77%).
C-15], 66.24 (2 CH2, Et2O), 107.29 (br., CH, C-3), 108.59 (br., CH,
C-5), 120.43, 121.06, 123.63, 124.59, 137.25, 137.09, 144.63 (br.,
CH, C-4), 145.23, 146.64, 148.65, 157.36 (br., C, C-6), 169.51 (br.,
1
C, C-2) ppm. H NMR (250 MHz, C7D8, 243 K): δ ϭ 0.86 (m, 6
H, CH3, OEt2), 0.95Ϫ1.40 [m, 30 H, CH(CH3)2], 2.89 [m, 3 H,
CH(CH3)2], 3.25 [br. m, 1 H, CH(CH3)2], 3.39 (m, 4 H, CH2, OEt2),
1
3.70 [br. m, 1 H, CH(CH3)2], 5.64 (br. d, J ϭ 8.50 Hz, 3-H), 5.69
(v. br. d, 1J ϭ 8.30 Hz, 3-H*), 6.04 (d, 1J ϭ 6.90 Hz, 1 H, 5-H),
M.p. 106Ϫ107 °C. C25H30N2 (358.5): calcd. C 83.75, H 8.43, N 6.75 (br. dd, 1 H, 4-H), 6.98Ϫ7.40 (m, Ar, 5 H, 9,11,18,19,20-H)
ppm. 13C NMR (250 MHz, C7D8, 243 K): δ ϭ 14.44 (2 CH3,
1
7.81; found C 83.37, H 8.54, N 7.72. H NMR (250 MHz, CDCl3,
298 K): δ ϭ 0.88Ϫ1.20 [m, 12 H, CH(CH3)2], 2.09 (s, 6 H, CH3), Et2O), 24.53 [CH(CH3)2, C-22,23], 24.64 [CH(CH3)2, C-
3.25 [sept, 2 H, CH(CH3)2], 3.76 (v. br. s, 1 H, NH), 5.86 (br. d, 28,29,32,33], 24.88 [CH(CH3)2, C-30,31], 28.46 [br., CH(CH3)2, C-
1J ϭ 8.30 Hz, 1 H, 3-H), 5.98 (br. s, 1 H, 4-H), 6.49 (br. d, J ϭ 24,25,26,27], 30.86 [br., CH(CH3)2, C-13,14], 35.29 [CH(CH3)2, C-
1
7.2 Hz, 1 H, 5-H), 7.03Ϫ7.35 (m, Ar, 6 H, 9,10,11,17,18,19-H)
15], 66.20 (2 CH2, Et2O), 104.72 (br., CH, C-3*), 104.98 (br., CH,
C-5*), 107.29 (br., CH, C-3), 108.59 (br., CH, C-5), 120.53 (br.*),
ppm. 13C NMR (250 MHz, CDCl3, 298 K): δ ϭ 20.10 (CH3, C-
13,14), 23.75 [CH(CH3)2, C-21,22], 28.44 [CH(CH3)2, C- 121.06, 122.47 (br.*), 123.88 (br.*), 124.75, 137.37, 138.36 (*),
3302  2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim www.eurjic.org
Eur. J. Inorg. Chem. 2004, 3297Ϫ3304

Lithium and Potassium Amides of Sterically Demanding Aminopyridines
FULL PAPER
139.49 (*), 143.40 (CH, C-4), 144.79 (CH, C-4*), 145.28, 146.64 (*
Preparation of 9: Diethyl ether (50 mL) was added to the solids KH
), 146.78 (br.), 147.96 (*), 148.60 (*), 148.84, 157.01 (C, C-6*),
(0.09 g 2.19 mmol) and Ap*H (1.00 g, 2.19 mmol) and the reaction
1
157.47 (C, C-6), 169.64 (C, C-2), 169.92 (C, C-2*) ppm. H NMR mixture stirred for 12 h. The mixture was filtered and the filtrate
(250 MHz, C7D8, 223 K): δ ϭ 0.69 (v. br. s, 6 H, CH3, OEt2), concentrated to dryness under vacuum. The resulting off-white
0.95Ϫ1.50 [v. br. m, 30 H, CH(CH3)2], 2.77 [v. br. m, 3 H, residue was washed with hexane (30 mL) and the resulting white
CH(CH3)2], 3.15 [v. br. m, 1 H, CH(CH3)2], 3.36 (v. br. m, 4 H, precipitate dried under vacuum. Yield 0.86 g (79%). [C32H43KN2]n:
1
CH2, OEt2), 3.79 [v. br. m, 1 H, CH(CH3)2], 5.64 (v. br. d, 3-H), calcd. C 77.68, H 8.76, N 5.66; found C 77.39, H 8.94, N 5.34. H
5.69 (v. br. d, 3-H*), 6.14 (v. br. s, 1 H, 5-H), 6.85 (v. br. s, 1 H, 4-
H), 6.98Ϫ7.45 (v. br. m, Ar, 5 H, 9,11,18,19,20-H) ppm. H NMR
NMR (250 MHz, C6D6, 298 K): δ ϭ 1.10Ϫ1.30 [m, 30 H,
CH(CH3)2], 2.85 [sept, H, CH(CH3)2], 3.18 [sept, H,
CH(CH3)2], 3.33 [sept, 2 H, CH(CH3)2], 5.76 (v. br. d, 1 H, 3-H),
1
1
2
(250 MHz, C7D8 {addition of two drops of C4D8O} 298 K): δ ϭ
1.07 (m, 6 H, CH3, OEt2), 1.20Ϫ1.40 [m, 30 H, CH(CH3)2], 2.84 5.92 (br. d, 1J ϭ 6.80 Hz, 1 H, 5-H), 6.93 (br. dd, 1 H, 4-H),
[m, 1 H, CH(CH3)2], 3.23 (m, 4 H, CH2, OEt2), 3.35 [m, 2 H, 6.90Ϫ7.21 (m, Ar,
5
H, 9,11,18,19,20-H) ppm. 13C NMR
1
CH(CH3)2], 3.65 [m, 2 H, CH(CH3)2], 5.66 (br. d, J ϭ 8.60 Hz, 1 (250 MHz, C6D6, 298 K): δ ϭ 24.15 [CH(CH3)2, C-28,29,32,33],
1
H, 3-H), 5.86 (d, J ϭ 6.90 Hz, 1 H, 5-H), 6.91 (br. dd, 1 H, 4-H), 24.46 [CH(CH3)2, C-30,31], 25.11 [CH(CH3)2, C-22,23], 28.38
6.98Ϫ7.26 (m, Ar,
5
H, 9,11,18,19,20-H) ppm. 13C NMR
[CH(CH3)2, C-13,14], 30.44 [CH(CH3)2, C-24,25,26,27], 34.93
(250 MHz, C7D8 {addition of two drops of C4D8O}, 298 K): δ ϭ [CH(CH3)2, C-15], 106.58 (CH, C-3), 120.73 (CH, C-9,11), 121.93
15.45 (2 CH3, Et2O), 23.99 [CH(CH3)2, C-22*,23*], 24.31 (CH, C-5), 123.82 (CH, C-18,20), 125.84 (CH, C-19), 136.26 (CH,
[CH(CH3)2, C-28*,29*,32*,33*], 24.94 [CH(CH3)2, C-30*,31*], C-4), 139.96 (C, C-7), 143.49 (C, C-16), 146.54 (C, C-8,12), 146.77
28.20 [CH(CH3)2, C-24*,25*,26*,27*], 30.38 [CH(CH3)2, C-13* (C, C-10), 147.99 (C, C-17,21), 154.05 (C, C-6), 157.81 (C, C-2)
,14*], 34.88 [CH(CH3)2, C-15*], 65.91 (2 CH2, Et2O), 104.71 (CH, ppm.
C-3*/5*), 104.82 (CH, C-3*/5*), 120.20 (CH, C-9*,11*), 121.40
(CH, C-19*), 123.44 (CH, C-18*,20*), 136.44 (CH, C-4*), 140.00
(C, C-10*), 143.10 (C, C-8*,12*), 146.61 (C, C-17*,21*), 147.40 (C,
Preparation of 10: Diethyl ether (50 mL) was added to the solids
KH (0.09 g 2.19 mmol) and ApЈH (1.00 g, 2.19 mmol) and the reac-
tion mixture stirred for 12 h. The mixture was filtered and the fil-
C-7*), 149.75 (C, C-16*), 156.95 (C, C-6*), 169.10 (C, C-2*) ppm.
trate concentrated to dryness under vacuum. The resulting off-
1H NMR (250 MHz, C7D8 {addition of two drops of C4D8O},
white residue was washed with hexane (30 mL) and the resulting
223 K): δ ϭ 1.06 (m, 6 H, CH3, OEt2), 1.16Ϫ1.33 [m, 30 H,
white precipitate dried under vacuum. Yield 0.86 (79%). Crystals
CH(CH3)2], 2.84 [br. m, 1 H, CH(CH3)2], 3.26 (m, 4 H, CH2, OEt2),
of 6 were grown from diethyl ether. C25H29KN2 (396.6): calcd. C
3.35 [br. m, 2 H, CH(CH3)2], 3.65 [br. m, 2 H, CH(CH3)2], 5.67 (d,
75.71, H 7.37, N 7.06; found C 75.45, H 7.63, N 6.63. 1H NMR
1J ϭ 8.60 Hz, 1 H, 3-H), 5.87 (d, 1J ϭ 6.90 Hz, 1 H, 5-H), 6.91
(250 MHz, C6D6, 298 K): δ ϭ 1.11Ϫ1.16 [m, 12 H, CH(CH3)2],
(br. dd, 1 H, 4-H), 6.98Ϫ7.26 (m, Ar, 5 H, 9,11,18,19,20-H) ppm.
2.25 (s, 6 H, CH3), 3.32 [m, 2 H, CH(CH3)2], 5.85 (v. br. d, 1 H,
13C NMR (250 MHz, C7D8 {addition of two drops of C4D8O},
3-H), 6.23 (br. d,
1 H, 5-H), 7.00Ϫ7.45 (m, Ar, 7 H,
223 K): δ ϭ 15.46 (2 CH3, Et2O), 23.99 [CH(CH3)2, C-22*,23*],
24.18 [CH(CH3)2, C-28*,29*,32*,33*], 24.94 [CH(CH3)2, C-30*
,31*], 28.20 [CH(CH3)2, C-24*,25*,26*,27*], 30.38 [CH(CH3)2, C-
13*,14*], 34.88 [CH(CH3)2, C-15*], 65.91 (2 CH2, Et2O), 104.18
(CH, C-3*,5*), 120.12 (CH, C-9*,11*), 121.21 (CH, C-19*), 123.36
(CH*, C-18,20*), 136.56 (CH, C-4*), 139.67 (C, C-10*), 142.74 (C,
C-8*,12*), 146.24 (C, C-17*,21*), 147.25 (C, C-7*), 149.39 (C, C-
16*), 156.78 (C, C-6*), 168.40 (C, C-2*) ppm. * ϭ monomeric iso-
mer.
4,9,10,11,17,18,19-H) ppm. 13C NMR (250 MHz, C6D6, 298 K):
δ ϭ 20.47 (CH3, C-13,14), 24.11 [CH(CH3)2, C-23,24,25,26], 28.53
[CH, CH(CH3)2, C-21,22], 121.42 (1 CH, C-3/4/5), 123.09, 123.97
(CH, C-17,19), 124.40, 127.26 (CH, C-9,11), 135.65, 135.83 (C, C-
1
8,12), 137.07 (1 CH, C-3/4/5), 150.07 (C, C-16,20) ppm. H NMR
(250 MHz, C4D8O, 298 K): δ ϭ 1.08Ϫ1.12 [m, 12 H, CH(CH3)2],
2.20 (s, 6 H, CH3), 3.39 [m, 2 H, CH(CH3)2], 5.34 (v. br. d, 1 H,
3-H), 5.51 (br. d, 1 H, 5-H), 6.76 (br. dd, 1 H, 4-H), 6.95Ϫ7.02 (m,
Ar, 6 H, 9,10,11,17,18,19-H) ppm. 13C NMR (250 MHz, C4D8O,
298 K):
δ ϭ 20.45 (CH3, C-13,14), 24.51 [CH(CH3)2, C-
Preparation of 8: nBuLi (0.63 mL, 1.6 , 1.00 mmol) was slowly
added to a stirred solution of ApЈH (0.36 g, 1.00 mmol) in diethyl
ether (40 mL) at 0 °C. After complete addition, the mixture was
stirred and warmed to room temperature (ca. 1 h). The reaction
mixture was reduced to dryness and hexane (20 mL) added. The
solvent volume was reduced to ca. 10 mL in vacuo, and on standing
colourless crystals of the title complex formed. Yield 0.35 g (88%).
C54H68Li2N4O (803.0): calcd. C 80.76, H 8.53, N 6.98; found C
79.18, H 8.20, N 6.95; the slightly too low C value is due to removal
of the coordinated ether during the drying process. 1H NMR
(500 MHz, C7D8, 298 K): δ ϭ 0.99 (br. m, 6 H, CH3, OEt2),
0.92Ϫ1.10 [m, 24 H, CH(CH3)2], 1.92 (s, 12 H, CH3), 3.19 (m, 4 H,
CH2, OEt2), 3.27 [sept, 4 H, CH(CH3)2], 5.58 (br. d, 1J ϭ 8.05 Hz, 2
H, 3-H), 5.76 (d, 1J ϭ 6.90 Hz, 2 H, 5-H), 6.83 (br. dd, 2 H, 4-
H), 6.98Ϫ7.10 (m, Ar, 12 H, 9,10,11,17,18,19-H) ppm. 13C NMR
(250 MHz, C7D8, 298 K): δ ϭ 15.32 (2 CH3, Et2O), 20.08 (2 CH3,
C-13,14), 24.18 [2 CH3, CH(CH3)2, C-23,25/24,26], 24.58 [2 CH3,
CH(CH3)2, C-23,25/24,26], 28.44 [2 CH3, CH(CH3)2, C-23,25/
24,26], 65.88 (2 CH2, Et2O), 106.19 (CH, C-3/5), 107.46 (CH, C-3/
5), 124.90 (CH, C-17,19), 127.30Ϫ128.40 (CH, C-9,10,11,18),
135.78 (C, C-8,12), 138.53 (CH, C-4), 141.13 (C, C-7), 143.86 (C,
C-15), 144.89 (C, C-16,20), 157.16 (C, C-6), 169.19 (C, C-2) ppm.
23,24,25,26], 28.90 [CH, CH(CH3)2, C-21,22,], 101.92 (v. br., 1 CH,
C-3/4/5), 104.21 (1 CH, C-3/4/5), 119.77 (v. br., 1 CH, C-3/4/5),
122.58 (CH, C-17,19), 126.29 (CH, C-10), 126.79 (CH, C-9,11),
135.03 (CH, C-18), 135.50 (C, C-8,12), 142.82 (v. br., C, C-16,20),
144.82 (br., C, C-7), 157.74 (C, C-6), 165.71 (v. br., C, C-2) ppm;
C-15 signal could not be observed.
Acknowledgments
We thank Wolfgang Milius for his support in the X-ray laboratory
and Elena Klimkina for her help with the assignment of the NMR
spectroscopic data. Financial support from the Alexander von
Humboldt Stiftung (N. M. S.), the Deutsche Forschungsgemeinsch-
aft (Schwerpunktprogramm 1166 ‘‘Lanthanoidspezifische Funk-
tionalitäten in Molekül und Material’’) and the Fonds der Chem-
ischen Industrie is gratefully acknowledged.
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www.eurjic.org
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
3303

N. M. Scott, T. Schareina, O. Tok, R. Kempe
FULL PAPER
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