Reactivity of tris(allyl)aluminum toward pyridine: Coordination versus carbometalation

Article abstract of DOI:10.1021/om200492f

Tris(allyl)aluminum as its THF adduct, [Al(η¹-C ₃H₅)₃(THF)] (1), reacted with pyridine either under substitution to give [Al(η¹-C₃H ₅)₃(py)] (7) (py = pyridine) or under carbometalation to give N-metalated 2-allyldihydropyridine depending on the solvent. The substituent pattern of the pyridine substrate and the aluminum center's electrophilicity in [Al(η¹-C₃H₅) ₃(L)] (L = neutral ligand) influenced the outcome of the reaction. Reactions of one N-metalated dihydropyridine with electrophiles have been studied. A crystalline derivative of tris(allyl)aluminum, [Al(η¹- C₃H₅)₃(OPPh₃)] (2), and tetrakis(allyl)aluminate in the ion pair [K(15-crown-5)₂] [Al(η¹-C₃H₅)₄] (4) were characterized by single-crystal X-ray diffraction and shown to contain four-coordinate aluminum centers.

Full text of DOI:10.1021/om200492f

ARTICLE
pubs.acs.org/Organometallics
Reactivity of Tris(allyl)aluminum toward Pyridine: Coordination versus
Carbometalation
Crispin Lichtenberg, Thomas P. Spaniol, and Jun Okuda*
Institute of Inorganic Chemistry, RWTH Aachen University, Landoltweg 1, D-52056 Aachen, Germany
S Supporting Information
b
ABSTRACT: Tris(allyl)aluminum as its THF adduct, [Al(η1-
C3H5)3(THF)] (1), reacted with pyridine either under sub-
stitution to give [Al(η1-C3H5)3(py)] (7) (py = pyridine) or
under carbometalation to give N-metalated 2-allyldihydropyr-
idine depending on the solvent. The substituent pattern of the
pyridine substrate and the aluminum center’s electrophilicity in
[Al(η1-C3H5)3(L)] (L = neutral ligand) influenced the out-
come of the reaction. Reactions of one N-metalated dihydropyridine with electrophiles have been studied. A crystalline derivative of
tris(allyl)aluminum, [Al(η1-C3H5)3(OPPh3)] (2), and tetrakis(allyl)aluminate in the ion pair [K(15-crown-5)2][Al(η1-C3H5)4] (4)
were characterized by single-crystal X-ray diffraction and shown to contain four-coordinate aluminum centers.
’ INTRODUCTION
[Al(η1-C3H5)3(THF)] (1) and triphenylphosphine oxide,
OPPh3. Similar to the THF ligand in 1, the stronger donor
OPPh3 in 2 is also labile and undergoes rapid exchange in C6D6
or THF-d8 solution upon addition of another equivalent of
OPPh3 as evident from 1H and 31P NMR spectroscopy
(Scheme 2). The rate constant for this ligand exchange reaction
in THF solution was estimated by 31P VT NMR spectroscopy to
be kC = 6 ꢁ 103 sꢀ1 at the coalescence temperature TC = 296 K.23
Single crystals of 2 were obtained from a saturated solution
in diethyl ether/pentane (1:7) upon cooling to ꢀ30 °C.
The aluminum atom in 2 is found in a slightly distorted
tetrahedral coordination geometry.24 The CꢀAlꢀO bond
angles (103.4(2)ꢀ106.7(2)°) are significantly smaller than the
CꢀAlꢀC bond angles (111.4(2)ꢀ114.5(2)°), reflecting the
weaker donor ability of the neutral ligand. The metalꢀcarbon
bonds show a mean length of 1.999(7) Å. They are considerably
longer than the corresponding mean bond lengths in four-
coordinate cationic [Al(η1-C3H5)2(THF)2]+ (1.960(2) Å) or
five-coordinate cationic [Al(η1-C3H5)2(THF)3]+ (1.981(4) Å),
providing evidence for a higher extent of electronic saturation of
the Al center in neutral 2.22 They are also significantly longer
than mean AlꢀC bond lengths in R3Al(OPPh3) (R = Me:
1.965(3) Å, R = Ph: 1.986(2) Å) due to the weaker σ-donor
character of the allyl ligand.5 The AlꢀOꢀP angle of 159.0(2)° is
bent, which hints at triphenylphosphine oxide acting as a purely
σ-donating ligand.25 All allyl ligands in 2 coordinate to the metal
center in an η1-fashion.
Organoaluminum compounds are well known to form 1:1
adducts with a wide range of neutral donor ligands owing to their
Lewis acidity.1 Such Lewis acidꢀbase complexes are kinetically
stable, even if the neutral ligand contains acidic protons,2 a
nitrile,3 imine, or carbonyl functionality,4 or an activated
(hetero)aromatic ring.5,6 The insertion of pyridine derivatives
into the metalꢀcarbon bond of organometallic compounds to
give metalated 1,2- or 1,4-dihydropyridines (DHPs) is of interest
in organic chemistry, since 1,4-DHPs are well-known calcium
antagonists7 and 1,2-DHPs have been shown to also inhibit the
calcium channel.8 Whereas organometallic compounds of groups
1 and 2,9 many transition metals,10 lanthanides,11 and actinides12
react with pyridine under insertion, metalation, or ring cleavage,
the reactivity of group 13 organometallics is largely dominated by
adduct formation (Scheme 1: aꢀd).6,13ꢀ16
Only few examples for pyridine insertion using allyl boron
compounds have been reported.17 In the case of tris(organyl)-
aluminum reagents, there are no examples for insertion or
metalation products formed from reactions with pyridine. Two
cases of insertion products obtained from reactions with more
complex chelating ligands bearing a pyridine core motif (a
diiminopyridine and an iminophosphoranoquinoline) have been
reported.18ꢀ21 Recently we have reported on the reactivity of the
isolable THF adduct of tris(allyl)aluminum [Al(η1-C3H5)3-
(THF)] (1) along with its cationic and anionic derivatives.22
Here we report a crystalline adduct of tris(allyl)aluminum,
[Al(η1-C3H5)3(OPPh3)] (2), and the reactivity of Lewis base
adducts of tris(allyl)aluminum toward pyridine derivatives.
Recently, we reported the synthesis of aluminate K[Al(η1-
C3H5)4] (3).22 Reactivity studies involving 3 raised the question
whether the allyl ligands bound to the aluminum center also
interact with the potassium counterion.22 To further investigate
’ RESULTS AND DISCUSSION
[Al(η1-C3H5)3(OPPh3)] (2) and [K(15-c-5)2][Al(η1-C3H5)4]
(4). Compound 2 was obtained from an equimolar mixture of
Received: June 7, 2011
Published: July 25, 2011
r
2011 American Chemical Society
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|

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Scheme 1. Typical Products of Reactions of Organometallic
Compounds “MR” with Pyridine: (a) Adduct Formation; (b)
N-Metalated 1,2-DHP; (c) N-Metalated 1,4-DHP; (d) ortho-
Metalated Pyridinea
Scheme 3. Reaction of K[Al(η1-C3H5)4] (3) with Neutral
Chelating Ligands
a The special case of cleavage of the pyridine ring is not illustrated.10f,l
M = organometallic fragment; R = organic fragment.
Scheme 2. Synthesis of 2 from [Al(η1-C3H5)3(THF)] (1)
and OPPh3 and Rapid Exchange of OPPh3 Ligand in 2 in
C6D6 or THF-d8 Solution upon Addition of Another
Equivalent of OPPh3
Figure 2. Molecular structure of (a) cationic part and (b) anionic part
of [K(15-c-5)2][Al(η1-C3H5)4] (4), between which no interactions are
observed. 4 crystallized with two chemically identical but crystallogra-
phically independent formula units in the asymmetric unit. Only one of
them is discussed, as they do not differ significantly. Thermal ellipsoids
are shown at the 50% probability level. Hydrogen atoms are omitted for
clarity. Selected bond lengths [Å] and angles [deg]: Al1ꢀC1, 2.014(3);
Al1ꢀC4, 2.020(3); Al1ꢀC7, 2.021(3); Al1ꢀC10, 2.018(3); C1ꢀC2,
1.465(4); C2ꢀC3, 1.320(4); C4ꢀC5, 1.451(4); C5ꢀC6, 1.312(5);
C7ꢀC8, 1.473(4); C8ꢀC9, 1.323(4); C10ꢀC11, 1.483(4); C11ꢀC12,
1.295(5); K1ꢀO1ꢀ5, 2.845(2)ꢀ2.993(2); K1ꢀO6ꢀ10, 2.830-
(2)ꢀ2.935(2); C1ꢀAl1ꢀC4, 106.2(1); C1ꢀAl1ꢀC7, 112.6(1);
C1ꢀAl1ꢀC10, 107.4(1); C4ꢀAl1ꢀC7, 106.8(1); C4ꢀAl1ꢀC10,
113.7(1); C7ꢀAl1ꢀC10, 110.2(1); C1ꢀC2ꢀC3, 128.1(3);
C4ꢀC5ꢀC6, 128.8(3); C7ꢀC8ꢀC9, 127.9(3); C10ꢀC11ꢀC12,
127.6(3).
Figure 1. Molecular structure of 2. Thermal ellipsoids are drawn at the
30% probability level. Hydrogen atoms have been omitted for clarity.
The C8ꢀC9 bond appears short due to pronounced libration of the C9
atom. Bond lengths [Å] and angles [deg]: Al1ꢀC1, 1.979(5); Al1ꢀC4,
2.033(7); Al1ꢀC7, 1.985(6); Al1ꢀO1, 1.813(4); C1ꢀC2, 1.476(7);
C2ꢀC3, 1.31(1); C4ꢀC5, 1.425(8); C5ꢀC6, 1.295(9); C7ꢀ
C8, 1.47(1); C8ꢀC9, 1.18(1); P1ꢀO1, 1.511(3); average (C1/4/
7ꢀAl1ꢀC1/4/7), 113.1(2); average (C1/4/7ꢀAl1ꢀO1), 105.5(2);
Al1ꢀO1ꢀP1, 159.0(2); C1ꢀC2ꢀC3, 127.0(6); C4ꢀC5ꢀC6, 128.6(6);
C7ꢀC8ꢀC9, 140.1(9); average (C15/C17/C23ꢀP1ꢀC15/C17/
C23), 108.0(2); average (C15/C17/C23ꢀP1ꢀO1), 110.9(2).
(2.014(3) Å),26 but is longer than that in neutral 2 (vide supra).
The latter fact was ascribed to the enhanced σ-donor ability of
the (C3H5)ꢀ ligand compared to OPPh3. No interactions of the
allyl ligands in the anionic part of 4 with the potassium counter-
ion are observed. This is due to effective shielding of the
potassium center, which is coordinated by two 15-c-5 molecules
adopting a coordination number of 10 in a pentagonal antipris-
matic coordination geometry. Bond lengths and angles in the
[K(15-c-5)2]+ moiety compare well to the literature.27 Reaction
of 3 with 1 equiv of (18-c-6) also gave the expected adduct
[K(18-c-6)][Al(η1-C3H5)4] (5). In contrast to the two (15-c-5)
moieties in 4, the chelating ligand in 5 does not shield the
entire coordination sphere, but merely the equatorial plane of
the potassium ion. Therefore, interactions between the alumi-
nate and the potassium counterion are more likely in this case.
Single crystals of compound 5 were obtained by different
this point, 3 was reacted with neutral chelating ligands. Reaction
of 3 with 2 equiv of 15-crown-5 (15-c-5) gave the expected
adduct 4 in high yield (top part, Scheme 3). Single crystals were
obtained by cooling a saturated solution of 4 in THF/pentane
(2:1) to ꢀ30 °C. The aluminum atom in 4 adopts a tetrahedral
coordination geometry (CꢀAlꢀC, 106.2(1)ꢀ112.6(1)°)
(Figure 2). The allyl ligands coordinate to the metal center in
an η1-fashion. The mean metal carbon distance of 2.018(3) Å in
4 compares well to the corresponding value in [Al(nBu)4]ꢀ
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ARTICLE
Scheme 4. Solvent Dependence of the Reaction of Al(η1-
C3H5)3(THF) (1) with Pyridine
the same carbon atom as the aluminum center owing to the
conjugate π-electron system of the allyl ligand. The fact that 5
was isolated donor-solvent-free further supports the presence of
interactions between the allyl ligands and the potassium ion.
[K(dibenzo-18-c-6)][Al(η1-C3H5)4] was prepared in an analo-
gous manner and was also isolated without further donor ligands
bound to the potassium center.
Reaction of [Al(η1-C3H5)3(THF)] (1) with Pyridine. When
the ligand exchange in [Al(η1-C3H5)3(THF)] (1) by pyridine
was investigated, subsequent formation of small amounts of the
N-metalated 1,2-DHP 6 (Scheme 4) was observed.22,30 This
reaction can be interpreted as a metala Claisen rearrangement,
which explains why only aluminum allyl compounds undergo
this type of transformation with pyridine.31 Under the chosen
reaction conditions a conversion of only 13% is observed, after
which thermodynamic equilibrium is reached. Adding excess
pyridine increased the conversion to up to 76%, but no full
conversion was obtained even in neat pyridine (for details see
Supporting Information). With increasing amounts of pyridine
the formation of increasing amounts of byproduct was observed
(up to 15%), presumably due to further insertion reactions of 6
with pyridine (formation of [Al(η1-C3H5)3ꢀn(NC5H5(C3H5))n(L)];
n = 2ꢀ3, L = neutral ligand). Once a reaction mixture of 1 and
excess pyridine had reached thermodynamic equilibrium at room
temperature, heating to 60 °C for up to 3 d favored the reverse
reaction.32 The reversibility of metala Claisen rearrangements
has been observed before for reactions of allyl calcium and boron
compounds with pyridine derivatives.9i,17
The reaction of 1 with pyridine shows a pronounced solvent
dependence. Whereas coordination followed by insertion is
observed in polar solvents such as THF, the latter reaction is
inhibited in nonpolar solvent such as pentane (Scheme 4) even
after reaction times of up to four weeks. The coordination
compound [Al(η1-C3H5)3(Py)] (7) was obtained in quantitative
yield. In THF solution 7 undergoes insertion as observed for an
equimolar mixture of 1 and pyridine (right part, Scheme 4).
K[Al(η1-C3H5)4] (3), crown ether adducts of 3, and [Al(η1-
C3H5)2(THF)2][BPh4]22 react with pyridine under insertion
but with low selectivity, probably due to increased reactivity as a
result of the charged allylaluminum fragments.33
Table 1. Reaction of 1 with Pyridine (Derivatives) in Dif-
ferent Solventsa
1,2-insertion (conversion/%;
selectivity/%)
pyridine
ligand substituion
(compd no.)
pentane/
C6D6
entry
compound
THF
1
2
3
4
5
pyridine
7
no
13; >99
no
R-picoline
β-picoline
γ-picoline
3,5-lutidine
8
no
9
no
no
10
11
12
no
no
yesc
no
no
no
no
6b DMAP
no
no
Reaction of [Al(η1-C3H5)3(L)] with Pyridine Derivatives.
Pyridine derivatives with electron-donating groups Me or NMe2
underwent ligand substitution reactions with 1 (Table 1, entries
2ꢀ6). Bulky 2,6-lutidine did not react with 1 (entry 7), even
though adducts of this pyridine derivative with a number of
tris(alkyl)aluminum compounds, such as Al(nBu)3, are known in
the literature.6c,e Not only an increase of steric bulk around the
nitrogen atom of the pyridine derivative but also a strong
decrease in electron density prevented coordination of the
neutral donor to the aluminum center, as shown by the use of
C6F5N (entry 8). Change of reaction conditions from a nonpolar
solvent such as pentane to a polar solvent such as THF resulted in
carbalumination in the case of pyridine (Scheme 2 and Table 1,
entry 1). This type of reactivity was not observed for all the other
pyridine derivatives mentioned above. Methyl substitution not
only at the ortho-position of the pyridine substrate (entry 2) but
also at the meta- or para-position (entries 3ꢀ5) blocked the
pyridine insertion reaction. Whereas in the first case steric
contributions could play a role, the latter cases demonstrate that
increase of electron density in the heteroaromatic system results
in a lack of insertion reactivity. In agreement with this, the
electron-rich 4-(N,N-dimethylamino)pyridine (DMAP) was not
7
8
9
2,6-lutidine
no
no
pentafluoropyridine
4-(CF3)-pyridine
no
no
76; 75
90; 90
a Lack of reactivity, adduct formation, or insertion is observed dependent
on the steric and electronic properties of the heteroaromatic compound.
DMAP
= N,N-dimethylaminopyridine; L = THF or pyridine
(derivative) i: pentane or C6D6 as a solvent: entries 1ꢀ8: 30 min, rt
then 60 °C, > 1 d; entry 9: C6D6, rt, 75 min; ii: THF as a solvent: entries
1ꢀ8: rt to 60 °C, > 1 d; entry 9: rt, 0.5 h. Entry 9: formation of side
products is presumably due to further insertion reactions of pyridine
with desired N-metalated 1,2-DHPs and/or ligand scrambling
(formation of [Al(η1-C3H5)3ꢀn(NC5H5(C3H5))n(L)]; n = 2ꢀ3, L =
neutral ligand). b Solvent: pentane/Et2O (1:1). c Precoordination is
assumed, but could not be proved due to subsequent formation of
N-metalated 1,2-DHP.
methods, but invariably gave weak diffractions at high diffraction
angles when subjected to X-ray.28 Therefore bond lengths and
angles in 5 are not discussed, but connectivities are definite. Most
importantly, there are interactions between the allyl ligands and
potassium centers (Scheme 3, bottom part). In contrast to other
tetrakis(alkyl)aluminates,29 the cation in 5 does not interact with
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carbometalated by tris(allyl)aluminum (entry 6).34 Accordingly,
reaction of 1 with electron-poor 4-(trifluoromethyl)pyridine led
mainly to the metalated 1,2-DHP (entry 9).
tives 15 and 16 were isolated as oils in quantitative yields
(Table 2).35 The reactivity of tris(allyl)aluminum compounds
[Al(η1-C3H5)3(L)] (L = neutral ligand) toward pyridine deri-
vatives is summarized in Scheme 5.
In the reaction of [Al(η1-C3H5)3(L)] (L = neutral ligand)
with 4-(trifluoromethyl)pyridine, the influence of the neutral
ligand L could be investigated (Table 2). Increasing the σ-donor
strength of L (i.e., increasing the electronic saturation of the
metal center) resulted in decreasing reactivity. Lower reactivity
led to higher selectivity toward formation of N-metalated 1,2-
DHPs (Table 2, entries 1a, 2a, 3a). Using an excess of the
pyridine reactant led to higher conversions (entries 1b, 2b, 3b),
but lower selectivities were observed in some cases (entries 1b,
2b). An appropriate balance between reactivity and selectivity
was achieved by combining strong donors at the aluminum
center with an excess of the pyridine reactant (entries 3b, 4).
The optimized reaction protocol allowed for the first ortho-
allylation of a pyridine derivative with an aluminum reagent.
Thus, the insertion reactivity of the heavier group 13 homologue
toward heteroaromatic compounds is similar to that of allylboron
reagents17 previously observed. The metalated 1,2-DHP deriva-
Reaction of Metalated 1,2-DHP Derivative 15 with Allyl
Iodide. Compound 15 was reacted with 4 equiv of allyl iodide, a
substrate highly susceptible to nucleophilic substitution
(Scheme 6). The three different types of ligands in 15—(i) two
allyl ligands, (ii) DMAP, and (iii) an N-metalated 1,2-DHP—
each react with allyl iodide: (i) reaction with one allyl ligand gives
1
1,5-hexadiene (17) as detected by H NMR spectroscopy; (ii)
DMAP in 15 reacts with allyl iodide to give the N-allylated
pyridinium salt 18, which was isolated in moderate yield, while 1
equiv of allyl iodide was not converted even after a reaction time
of 12 d; (iii) aqueous workup followed by HR-ESI-MS analysis
revealed that the 1,2-DHP core is allylated twice, presumably by
reaction with allyl iodide and by carbalumination through the
1
remaining allylaluminum moiety. According to H NMR anal-
yses, a mixture of isomers and/or diastereomers rather than
a single compound was formed (Scheme 6). A sequence of
reactions leading to the observed products is suggested in the
Supporting Information.
Table 2. Influence of Neutral Donor Bound to Tris(allyl)
aluminum Moiety on Reactivity and Selectivity in Formation
of N-Metalated 1,2-DHP Speciesa
Scheme 6. Reaction of 15 with Allyl Iodidea
entry
L
Al reactant t/h n conversion/% selectivity/% product
1a THF
1
0.5
2.7
1
3
90
>99
88
90
26
13
13
14
14
15
15
16
1b THF
1
2a 3-Me-Py
2b 3-Me-Py
3a DMAP
3b DMAP
9
0.67 1
96
9
1.8
18
3
1
3
3
>99
55
58
12
12
2
96
20
18
>99
>99
>99
>99
4
OPPh3
a When reactions were carried out at ꢀ78 °C, no significant increase in
selectivity was observed. Formation of side products is presumably due
to further insertion reactions of 4-(trifluoromethyl)pyridine with
a 1,5-Hexadiene (17), N-allylated DMAP ligand 18, and, after quenching
with water, a (mixture of) tris(allylated) tetrahydropyridine(s) were
obtained. One of all possible isomers for [(C3H5)3-(CF3)-tetrahydro-
Py] is depicted; [Al] = aluminum species; i: aqueous workup.
13ꢀ16 and/or ligand scrambling (formation of [Al(η1-C3H5)3ꢀn
(NC5H5(C3H5)(CF3))n(L)]; n = 2, 3, L = neutral ligand).
-
Scheme 5. Reactivity of Lewis Base Adducts of Tris(allyl)aluminum toward Pyridine Derivativesa
a EWG = electron-withdrawing group; EDG = electron-donating group.
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Scheme 7. Reaction of 15 with Benzophenonea
measurements are reported relative to external standards, CFCl3, an
aqueous solution of Al(NO3)3, and phosphoric acid (85%), respectively.
The metal content of organoaluminum compounds was determined by
titration.37 Compounds 1 and 3 were prepared according to literature
procedures.22
[Al(η1-C3H5)3(OPPh3)] (2). A solution of [Al(η1-C3H5)3(THF)]
(1) (100 mg, 0.45 mmol) in diethyl ether (2 mL) was added to a
suspension of triphenylphosphine oxide (125 mg, 0.45 mmol) in diethyl
ether (2 mL) at ambient temperature. The volume of the yellowish
solution was reduced in vacuo by three-quarters. Upon addition of
pentane (2.8 mL), a colorless solid precipitated, which was isolated
by filtration and dried in vacuo. Yield: 150 mg, 0.35 mmol, 78%.
3
1H NMR (400.1 MHz, C6D6): δ 1.65 (br d, JHH = 8.8 Hz, 6H,
AlꢀCH2ꢀCHdCH2), 4.75 (ddt, 2JHH = 3.0 Hz, 3JHH = 10.0 Hz, 4JHH
=
2
0.8 Hz, 3H, AlꢀCH2ꢀCHdCHcisHtrans), 4.86 (ddt, JHH = 3.0 Hz,
3JHH = 16.8 Hz, 4JHH = 1.4 Hz, 3H, AlꢀCH2ꢀCHdCHcisHtrans), 6.50
3
3
3
(ddt, JHH = 8.8 Hz, JHH = 10.0 Hz, JHH = 16.8 Hz, 3H,
AlꢀCH2ꢀCHdCH2), 6.91ꢀ6.96 (m, 6H, m-Ph), 7.00ꢀ7.04 (m, 3H,
p-Ph), 7.53ꢀ7.58 (m, 6H, o-Ph) ppm. 1H NMR (400.1 MHz, THF-d8):
δ 0.99 (br d, 3JHH = 8.7 Hz, 6H, AlꢀCH2ꢀCHdCH2), 4.17 (ddt, 2JHH
a NꢀC bond cleavage in the assumed intermediate yields the mixed
aluminum alcoholate 19 and pyridine derivative 20.
3
4
= 3.0 Hz, JHH = 10.0 Hz, JHH = 0.8 Hz, 3H, AlꢀCH2ꢀ
CHdCHcisHtrans), 4.27 (ddt, JHH = 3.0 Hz, JHH = 16.8 Hz, JHH
=
2
3
4
Reaction of Metalated 1,2-DHP Derivative 15 with Benzo-
phenone. Reaction of 15 with 3 equiv of benzophenone did not
allow for isolation of the expected insertion product (shown as an
intermediate in Scheme 7). Instead, the mixed aluminum alkoxy
species 19 and a solution of the ortho-allylated pyridine derivative
20 were isolated as products of a rearomatization process.9h,i,36
1.5 Hz, 3H, AlꢀCH2ꢀCHdCHcisHtrans), 5.90 (ddt, 3JHH = 8.8 Hz, 3JHH
= 10.0 Hz, 3JHH = 16.8 Hz, 3H, AlꢀCH2ꢀCHdCH2), 7.58ꢀ7.63 (m,
6H, m-Ph), 7.71ꢀ7.79 (m, 9H, o-, p-Ph) ppm. 13C NMR (100.6 MHz,
C6D6): δ 21.95 (br s, AlꢀCH2ꢀCHdCH2), 104.37 (s, AlꢀCH2ꢀ
CHdCH2), 129.13 (d, 3JCP = 13.3 Hz, m-Ph), 132.76 (d, 2JCP = 11.3 Hz,
o-Ph), 133.74 (d, 4JCP = 2.5 Hz, p-Ph), 143.68 (s, AlꢀCH2ꢀCHdCH2)
ppm. 13C NMR (100.6 MHz, THF-d8): δ 21.71 (br s, AlꢀCH2ꢀ
Hz, m-Ph), 133.56 (d, 2JCP = 11.3 Hz, o-Ph), 134.67 (br s, p-Ph), 143.68
(s, AlꢀCH2ꢀCHdCH2) ppm. The ipso-C atom could not be de-
tected at concentrations up to 0.2 mol/L and high numbers of scans
(up to 8000). For comparable compounds known in the literature, no
13C NMR data were reported5a or the corresponding resonance was not
detected.5b 27Al NMR (104.3 MHz, C6D6): δ 157.85 (br s) ppm. 27Al
NMR (104.3 MHz, THF-d8): δ 149.02 (br s) ppm. 31P NMR (162.0
MHz, C6D6): δ 51.97 (s) ppm. 31P NMR (162.0 MHz, THF-d8): δ
36.96 (s) ppm. Anal. Calcd for C27H30AlOP (428.48 g/mol): Al, 6.30.
Found: Al, 6.27.
’ CONCLUSION
3
CHdCH2), 103.77 (s, AlꢀCH2ꢀCHdCH2), 129.95 (d, JCP = 13.2
Reactions of Lewis base adducts of tris(allyl)aluminum with
pyridine derivatives have been studied. The outcome of these
reactions depends on the electronic and steric properties of the
pyridine substrates as well as the electrophilicity of the aluminum
center: (i) Pyridine derivatives with a high steric bulk around the
N atom (2,6-lutidine) or highly electron poor pyridine deriva-
tives (C5F5N) do not react with [Al(η1-C3H5)3(THF)] (1); (ii)
electron-rich pyridines (picolines, 3,5-lutidine, DMAP) undergo
ligand substitution with 1 in quantitative yields; (iii) electron-
poor 4-(trifluoromethyl)pyridine reacts with [Al(η1-C3H5)3-
(OPPh3)] (2) or [Al(η1-C3H5)3(DMAP)] (12) under carbo-
metalation to give N-metalated 1,2-dihydropyridine derivatives
quantitatively. This type of carbometalation reactivity is rare for
organoaluminum reagents18 and so far known only for allyl
boron compounds among the group 13 homologues.17 The
reactivity of one N-metalated 1,2-dihydropyridine toward elec-
trophiles susceptible to substitution or insertion reactions re-
vealed carbaluminations and rearomatizations.
[K(15-crown-5)2][Al(η1-C3H5)4] (4). Solutions of 1 (50 mg, 0.22
mmol) and 15-crown-5 (99 mg, 0.45 mmol) in THF (400 μL each) were
subsequently added to a solution of allylpotassium (18 mg, 0.22 mmol)
in THF (400 μL). The reaction mixture was filtered. After removal of all
volatiles from the colorless filtrate under reduced pressure, a colorless
solid was obtained, which was washed with pentane (5 ꢁ 2 mL) and
dried in vacuo. Yield: 135 mg, 0.20 mmol, 91%. 1H NMR (400.1 MHz,
a,b
THF-d8): δ 0.85ꢀ0.99 (m, 8H, CH2 ꢀCHdCH2), 3.64 (s, 40H,
O(CH2CH2)O), 4.01 (br s, 4H, CH2ꢀCHCdHcisHtrans), 4.24 (br d,
3
4H, JHH = 16.3 Hz, CH2ꢀCHdCHcisHtrans), 6.00ꢀ6.13 (m, 4H,
’ EXPERIMENTAL SECTION
CH2ꢀCHdCH2) ppm. 13C NMR (100.6 MHz, THF-d8): δ 22.98
1
(sext, JAlC = 63.6 Hz, CH2ꢀCHdCH2), 68.33 (s, O(CH2CH2)O),
General Remarks. All operations were carried out under argon
using standard Schlenk-line and glovebox techniques. Starting materials
were purchased from ABCR Chemicals or Sigma Aldrich and purified
following standard laboratory procedures. Nondeuterated solvents were
purified using an MB SPS-800 solvent purification system. Benzene-d6
and THF-d8 were distilled from sodium benzophenone ketyl. NMR
spectra were recorded at ambient temperature using a Varian Mercury-
200 or a Bruker Avance II 400 MHz spectrometer. The chemical shifts of
1H and 13C NMR spectra were referenced internally using the residual
solvent resonances and are reported relative to the chemical shift of
70.49 (s, O(CH2CH2)O), 99.09 (br s, CH2ꢀCHdC1H2), 99.29 (br s,
CH2ꢀCHdC2H2), 147.60 (s, CH2ꢀC1HCH2), 147.81 (s, CH2ꢀ
C2HdCH2) ppm. Anal. Calcd for C32H60AlKO10 (590.77 g/mol):
Al, 4.02. Found: 3.98.
[K(18-crown-6)][Al(η1-C3H5)4] (5). 18-Crown-6 (31 mg, 0.12
mmol) was added to a solution of 3 (27 mg, 0.12 mmol) in THF
(0.5 mL) to give a colorless solution. Upon addition of pentane (7 mL),
a colorless oil precipitated. The supernatant was decanted and the
residue washed with pentane (4 ꢁ 2 mL) to give a colorless solid, which
was dried in vacuo. Yield: 54 mg, 0.11 mmol, 92%. 1H NMR (400.1 MHz,
1
tetramethylsilane. The resonances in H and 13C NMR spectra were
a,b
23 °C, THF-d8): δ 0.84ꢀ0.98 (m, 8H, CH2 ꢀCHdCH2), 3.63 (s,
assigned on the basis of two-dimensional NMR experiments (COSY,
HMQC, HMBC). The resonances recorded in 19F, 27Al, and 31P NMR
24H, O(CH2)2O), 4.00 (br s, 4H, CH2ꢀCHCdHcisHtrans), 4.23 (br d,
4413
dx.doi.org/10.1021/om200492f |Organometallics 2011, 30, 4409–4417

Organometallics
ARTICLE
1
3JHH = 14.8 Hz, 4H, CH2ꢀCHdCHcisHtrans), 6.00ꢀ6.12 (m, 4H,
Yield: 20 mg, 48 μmol, 100%. H NMR (400.1 MHz, THF-d8): δ 1.25
1
3
CH2ꢀCHdCH2) ppm. H NMR (400.1 MHz, ꢀ80 °C, THF-d8): δ
(br d, JHH = 8.6 Hz, 4H, AlꢀCH2ꢀCHdCH2), 1.96ꢀ2.02 (m, 1H,
a
b
0.84 (br s, 4H, CH2 ꢀCHdCH2), 0.91 (br s, 4H, CH2 ꢀCHdCH2),
CꢀCHH0ꢀCHdCH2), 2.34ꢀ2.42 (m, 1H, CꢀCHH0ꢀCHdCH2),
3.12 (s, 6H, NMe2), 3.98 (br dt, 3JHH = 6.2 Hz, 3JHH = 7.0 Hz, 1H, H2),
3
3.62 (br s, 24H, O(CH2)2O), 4.02 (br d, JHH = 9.0 Hz, 4H,
2
3
4
CH2ꢀCHCdHcisHtrans), 4.21 (br d, JHH = 16.6 Hz, 4H, CH2ꢀ
3
4.40 (ddt, JHH = 2.7 Hz, JHH = 10.0 Hz, JHH = 1.0 Hz, 2H,
AlꢀCH2ꢀCHdCHcisHtrans), 4.53 (ddt, 2JHH = 2.7 Hz, 3JHH = 16.8 Hz,
4JHH = 1.4 Hz, 2H, AlꢀCH2ꢀCHdCHcisHtrans), 4.89 (dd, 3JHH = 6.8 Hz,
4JHH = 2.1 Hz, 1H, H5), 4.91ꢀ4.98 (m, 2H, CꢀCH2ꢀCHdCH2), 5.24
(dm, 3JHH = 6.2 Hz, 1H, H3), 5.79(ddt, 3JHH =7.4Hz, 3JHH = 10.3 Hz, 3JHH
= 17.0 Hz, 1H, CꢀCH2ꢀCHdCH2), 5.97(ddt, 3JHH =8.6Hz, 3JHH = 10.0
Hz, 3JHH = 16.8 Hz, 2H, AlꢀCH2ꢀCHdCH2), 6.51 (dd, 3JHH = 6.8 Hz,
CHdCHcisHtrans), 6.02 (br ddt, 3JHH = 9.0 Hz, 3JHH = 9.0 Hz, 3JHH
=
16.6, 4H, CH2ꢀCHdCH2) ppm. 13C NMR (100.6 MHz, 23 °C,
1
THF-d8): δ 22.79 (sext, JAlC = 63.6 Hz, CH2ꢀCHdCH2), 71.23
(s, O(CH2)2O), 98.94 (br s, CH2ꢀCHdC1H2), 99.13 (br s, CH2ꢀ
CHdC2H2), 147.44 (s, CH2ꢀC1HCH2), 147.62 (s, CH2ꢀC2HdCH2)
ppm. 27Al NMR (104.3 MHz, 23 °C, THF-d8): δ 144.62 (s) ppm. Anal.
Calcd for C24H44AlKO6 (494.68 g/mol): Al, 5.45. Found: 5.07.
[K(dibenzo-18-crown-6)][Al(η1-C3H5)4]. Allylpotassium (36
mg, 0.45 mmol) and dibenzo-18-crown-6 (162 mg, 0.45 mmol) were
subsequently added to a solution of 1 (100 mg, 0.45 mmol) in THF
(2.0 mL) to give a slightly yellow solution. After removal of all volatiles
under reduced pressure, a slightly yellow oil was obtained. The oil was
washed with pentane (7 ꢁ 2 mL) to give a colorless solid, which was
4JHH = 0.7 Hz, 1H, H6), 6.79 (dm, JHH = 7.4 Hz, 2H, 3,5-DMAP),
3
7.60ꢀ7.62 (m, 2H, 2,6-DMAP) ppm. 13C NMR (100.6 MHz, THF-d8): δ
18.91 (br s, AlꢀCH2ꢀCHdCH2), 39.27 (s, NMe2), 39.45 (s,
CꢀCH2ꢀCHdCH2), 52.73 (s, C2), 91.65 (q, JCF = 2.4 Hz, C5),
3
106.47 (s, AlꢀCH2ꢀCHdCH2), 107.72 (s, 3,5-DMAP), 108.30 (q, 3JCF
=
5.5 Hz, C3), 117.06 (s, CꢀCH2ꢀCHdCH2), 125.34 (q, 1JCF = 271.2 Hz,
CF3), 128.78 (q, JCF = 31.0 Hz, C4), 135.69 (s, CꢀCH2ꢀCHdCH2),
2
141.54 (s, AlꢀCH2ꢀCHdCH2), 142.65 (s, C6), 146.99 (s, 2,6-DMAP),
157.24 (s, 4-DMAP) ppm. 19F NMR (188.1 MHz, THF-d8): δ ꢀ64.11 (s)
ppm. 27Al NMR (104.3 MHz, THF-d8): δ = 142.06 (br s) ppm. Anal.
Calcd. for C22H29AlF3N3 (419.46 g/mol): Al, 6.43. Found: Al, 6.17.
[Al(η1-C3H5)2(j-N-2-(C3H5)-4-(CF3)-1,2-dihydro-Py)(OPPh3)] -
(16). 4-(Trifluoromethyl)pyridine (52 mg, 0.35 mmol) was added to a
solution of 1 (50 mg, 0.12 mmol) in THF (2.0 mL) to give a colorless
solution. After 18 h all volatiles were removed from the reaction
mixture under reduced pressure to give a yellow oil, which was dried
in vacuo for 2 h. Yield: 68 mg, 0.12 mmol, 100%. 1H NMR (400.1 MHz,
dried in vacuo. Yield: 261 mg, 0.44 mmol, 98%.
1H NMR (400.1 MHz, 23 °C, THF-d8): δ 0.87ꢀ1.01 (m, 8H, CH2
ꢀ
a,b
CHdCH2), 3.99ꢀ4.01 (m, 8H, O(CH2CH2)O), 4.03 (br s, 4H,
CH2ꢀCHCdHcisHtrans), 4.24ꢀ4.26 (m, 8H, O(CH2CH2)O), 4.25 (br
s, 4H, CH2ꢀCHdCHcisHtrans), 6.02ꢀ6.14 (m, 4H, CH2ꢀCHdCH2)
6.93ꢀ6.97 (m, 4H, Ph3,6), 7.01ꢀ7.05 (m, 4H, Ph4,5) ppm. 13C NMR
1
(100.6 MHz, THF-d8): δ 23.01 (sext, JAlC = 64.2 Hz, CH2ꢀ
CHdCH2), 68.33 (s, O(CH2CH2)O), 70.49 (s, O(CH2CH2)O), 99.18
(br s, CH2ꢀCHdC1H2), 99.35 (br s, CH2ꢀCHdC2H2), 112.36 (s,
Ph3,6), 122.51 (s, Ph4,5), 147.62 (s, CH2ꢀC1HCH2), 147.80 (s,
CH2ꢀC2HdCH2), 148.05 (s, Ph1,2) ppm. 27Al NMR (104.3 MHz,
THF-d8): δ 144.63 (s) ppm. Anal. Calcd for C32H44AlKO6 (590.77 g/
mol): Al, 4.57. Found: 4.17.
3
THF-d8): δ 1.05 (br d, JHH = 8.7 Hz, 4H, AlꢀCH2ꢀCHdCH2),
1.84ꢀ1.90 (m, 1H, CꢀCHH0ꢀCHdCH2), 2.32ꢀ2.39 (m, 1H,
3
3
CꢀCHH0ꢀCHdCH2), 3.88 (br dt, JHH = 6.2 Hz, JHH = 7.5 Hz,
1H, H2), 4.30 (br ddt, 2JHH = 2.8 Hz, 3JHH = 10.0 Hz, 4JHH = 0.8 Hz, 2H,
AlꢀCH2ꢀCHdCHcisHtrans), 4.43 (ddt, 2JHH = 2.8 Hz, 3JHH = 16.8 Hz,
4JHH = 1.4 Hz, 2H, AlꢀCH2ꢀCHdCHcisHtrans), 4.73 (dd, 3JHH = 6.7
Hz, 4JHH = 2.1 Hz, 1H, H5), 4.86 (ddt, 2JHH = 2.4 Hz, 3JHH = 17.0 Hz,
4JHH = 1.4 Hz, 1H, CꢀCH2ꢀCHdCHcisHtrans), 4.88ꢀ4.89 (m, 1H, H3,
overlapped by parts of signals due to CꢀCH2ꢀCHdCH2), 4.90 (ddt,
[Al(η1-C3H5)3(py)] (7). A solution of 1 (106 mg, 477 μmol) in
pentane (2.0 mL) was treated with a solution of pyridine (38 mg, 480
μmol) in pentane (2.0 mL) to immediately give a yellow solution. After
30 min all volatiles were removed in vacuo to give a yellow oil, which was
dried in vacuo for 2 h. Yield: 109 mg, 475 μmol, 100%. 1H NMR (400.1
2
3
MHz, C6D6): δ 1.56 (dd, JHH = 1.0 Hz, JHH = 8.7 Hz, 3H,
AlꢀCHH0ꢀCHdCH2), 1.56 (dd, 2JHH = 1.0 Hz, 3JHH = 8.7 Hz, 3H,
2JHH = 2.4 Hz, JHH = 10.1 Hz, JHH = 0.2 Hz, 1H, CꢀCH2ꢀ
3
4
2
3
3
3
3
CHdCHcisHtrans), 5.71 (ddt, JHH = 7.3 Hz, JHH = 10.1 Hz, JHH
=
=
=
AlꢀCHH0ꢀCHdCH2), 4.76 (ddt, JHH = 2.7 Hz, JHH = 10.0 Hz,
4JHH = 1.0 Hz, 3H, AlꢀCH2ꢀCHdCHcisHtrans), 4.82 (ddt, 2JHH = 2.7
Hz, 3JHH = 16.8 Hz, 4JHH = 1.4 Hz, 3H, AlꢀCH2ꢀCHdCHcisHtrans),
17.0 Hz, 1H, CꢀCH2ꢀCHdCH2), 5.92 (ddt, JHH = 8.7 Hz, 3JHH
3
10.0 Hz, 3JHH = 16.8 Hz, 2H, AlꢀCH2ꢀCHdCH2), 6.41 (dd, 3JHH
3
3
3
6.7 Hz, 4JHH = 0.5 Hz, 1H, H6), 7.56ꢀ7.61 (m, 6H, m-Ph), 7.68ꢀ7.74
(m, 9H, m-, o-Ph) ppm. 13C NMR (100.6 MHz, THF-d8): δ 19.82 (br s,
AlꢀCH2ꢀCHdCH2), 39.38 (s, CꢀCH2ꢀCHdCH2), 52.55 (s, C2),
90.55 (q, 3JCF = 2.4 Hz, C5), 105.82 (s, AlꢀCH2ꢀCHdCH2), 107.51
(q, 3JCF = 5.7 Hz, C3), 116.70 (s, CꢀCH2ꢀCHdCH2), 125.41 (q, 1JCF
= 271.3 Hz, CF3), 128.54 (q, 2JCF = 31.0 Hz, C4), 130.02 (d, 3JCP = 13.1
Hz, m-Ph), 133.55 (d, 2JCP = 11.3 Hz, o-Ph), 134.96 (br s, p-Ph), 135.79
(s, CꢀCH2ꢀCHdCH2), 142.24 (s, AlꢀCH2ꢀCHdCH2), 143.00 (s,
C6) ppm. No resonance due to the ipso-Ph carbon atom was detected;
compare compound 2. 19F NMR (188.1 MHz, THF-d8): δ ꢀ63.93 (s)
ppm. 27Al NMR (104.3 MHz, THF-d8): δ 132.74 (br s) ppm. 31P NMR
(162.0 MHz, THF-d8): δ 40.39 (br s) ppm. Anal. Calcd for C33H34AlF3-
NOP (575.58 g/mol): Al, 4.69. Found: Al, 4.22.
6.33 (ddt, JHH = 8.7 Hz, JHH = 10.0 Hz, JHH = 16.8 Hz, 3H,
AlꢀCH2ꢀCHdCH2) 6.35ꢀ6.38 (m, 2H, 3,5-Py, partially overlapped
3
by resonances due to AlꢀCH2ꢀCHdCH2), 6.68 (tt, JHH = 7.7 Hz,
4JHH = 1.6 Hz, 1H, 4-Py), 8.10 (br d, 3JHH = 4.9 Hz, 2H, 2,6-Py) ppm.
1H NMR (400.1 MHz, THF-d8): δ 1.20 (br d, JHH = 8.7 Hz, 6H,
3
AlꢀCH2ꢀCHdCH2) 4.33 (ddt, 2JHH = 2.8 Hz, 3JHH = 10.0 Hz, 4JHH
=
1.0 Hz, 3H, AlꢀCH2ꢀCHdCHcisHtrans), 4.45 (ddt, 2JHH = 2.8 Hz, 3JHH
= 16.8 Hz, 4JHH = 1.4 Hz, 3H, AlꢀCH2ꢀCHdCHcisHtrans), 5.98 (ddt,
3
3
3JHH
= 8.7 Hz, JHH = 10.0 Hz, JHH = 16.8 Hz, 3H,
AlꢀCH2ꢀCHdCH2), 7.61ꢀ7.64 (m, 2H, 3,5-Py), 8.03ꢀ8.08 (m,
1H, 4-Py), 8.58ꢀ8.69 (m, 2H, 2,6-Py) ppm (when the NMR is not
measured immediately after dissolving 7 in THF-d8, resonances due to
the ortho-allylated product 3 are also observed). 13C NMR (100.6 MHz,
C6D6): δ 19.82 (br s, AlꢀCH2ꢀCHdCH2), 105.76 (s, AlꢀCH2ꢀ
CHdCH2), 124.79 (s, 3,5-Py), 140.94 (s, 4-Py), 141.94 (s,
AlꢀCH2ꢀCHdCH2), 148.34 (s, 2,6-Py) ppm. 27Al NMR (104.3
MHz, C6D6): δ 157.08 (br s) ppm. Anal. Calcd for C14H20AlN
(229.30 g/mol): Al, 11.77. Found: Al, 11.80.
Reaction with Allyl Iodide. 15 (18 mg, 43 μmol) was dissolved in
THF-d8 (600 μL), and allyl iodide (29 mg, 173 μmol) was added, giving
a slightly yellowish solution. After 3 h small amounts of 1,5-hexadiene
(17) could be detected.38 After 6 d a colorless solid had precipitated,
which after decantation of the liquid phase was washed with diethyl ether
(3 ꢁ 1 mL) and dried in vacuo. A second crop was isolated from the
reaction mixture after a total reaction time of 12 d. Overall yield of
18: 6.3 mg, 22 μmol, 51%. The filtrate was quenched with water (1 mL)
and extracted with pentane (1.5 mL). The organic phase was separated
and analyzed by means of mass spectrometry.
[Al(η1-C3H5)2(j-N-2-(C3H5)-4-(CF3)-1,2-dihydro-Py)(DMAP)]
(15). A solution of 1 (13 mg, 48 μmol) in THF-d8 (300 μL) was treated
with a solution of 4-(trifluoromethyl)pyridine (21 mg, 143 μmol) in THF-
d8 (300μL). After 20 h all volatiles were removed in vacuo from the colorless
reaction mixture to give a yellow oil, which was dried in vacuo for 2 h.
4414
dx.doi.org/10.1021/om200492f |Organometallics 2011, 30, 4409–4417

Organometallics
ARTICLE
[N-(C3H5)DMAP]+Iꢀ (18). 1H NMR (400.1 MHz, CDCl3): δ 3.29
(s, 6H, NMe2), 5.00 (br d, 3JHH = 6.2 Hz, 2H, NꢀCH2ꢀCHdCH2),
CHdCH2), 147.46 (s, 2,6-DMAP), 150.08 (s, CH(ipso-Ph)2OR),
151.82 (s, C(C3H5)(ipso-Ph1)2OR), 151.90 (s, C(C3H5)(ipso-Ph2)2OR),
156.84 (s, 4-DMAP) ppm. 27Al NMR (104.3 MHz, THF-d8): δ 59.24 (br s)
ppm. Anal. Calcd for C52H51AlN2O3 (778.95 g/mol): Al, 3.46. Found:
Al, 3.08. ESI-MS: exact mass calcd. for C16H16NaO+ m/z = 247.1099,
5.43 (br d, 3JHH = 10.2 Hz, 1H, NꢀCH2ꢀCHdCHcisHtrans), 5.43 (br d,
3
3JHH = 17.0 Hz, 1H, NꢀCH2ꢀCHdCHcisHtrans), 6.03 (ddt, JHH
=
6.2 Hz, 3JHH = 10.2 Hz, 3JHH = 17.0 Hz, 1H, NꢀCH2ꢀCHdCH2), 6.99
(br d, 3JHH = 7.8 Hz, 2H, 3,5-DMAP), 8.38 (br d, 3JHH = 7.8 Hz, 2H, 2,6-
DMAP) ppm. 13C NMR (100.6 MHz, CDCl3): δ 40.91 (s, NMe2),
60.14 (s, NꢀCH2ꢀCHdCH2), 108.58 (s, 3,5-DMAP), 122.34
(s, NꢀCH2ꢀCHdCH2), 130.91 (s, NꢀCH2ꢀCHdCH2), 142.49
(s, 2,6-DMAP), 156.54 (s, 4-DMAP) ppm. ESI-MS: exact mass calcd
+
found (%) m/z = 247.1098 (51) [(C(C3H5)Ph2OH) + Na+]+; C11H13
m/z = 167.0855, found (%) m/z = 167.0858 (7) [(CHPh2OH +
H+ ꢀ H2O)]+.
X-ray Crystal Structure Determination. X-ray diffraction data
were collected on a Bruker CCD area-detector diffractometer with Mo
KR radiation (graphite monochromator, λ = 0.71073 Å) using j and ω
scans. The SMART program package was used for the data collection
and unit cell determination; processing of the raw frame data was
performed using SAINT; absorption corrections were applied with
SADABS.39 The structures were solved by direct methods and refined
against F2 using all reflections with the SHELXL-97 software. The non-
hydrogen atoms were refined anisotropically, and hydrogen atoms were
placed in calculated positions.40
+
for C10H15N2 m/z = 163.1230, found (%) m/z = 163.1224 (25)
+
[(M ꢀ Iꢀ)+]; C7H9N2 m/z = 121.0760, found (%) m/z = 121.0756
(100) [(M ꢀ Iꢀ ꢀ (C3H6))+]; C6H7N2+ m/z = 107.0604, found (%)
m/z = 107.0600 (20) [(M ꢀ Iꢀ ꢀ (C4H8))+].
[(C3H5)3-(CF3)-tetrahydro-Py]. ESI-MS: exact mass calcd for
C18H25F3N+ m/z = 312.1934, found (%) m/z = 312.1931 (6)
[((C3H5)4-(CF3)-tetrahydro-Py)
+ =
H+]+; C15H21F3N+ m/z
272.1621, found (%) m/z = 272.1621 (100) [((C3H5)3-(CF3)-tetra-
hydro-Py) + H+]+; C12H15F3N+ m/z = 230.1151, found (%) m/z =
230.1151 (5) [((C3H5)2-(CF3)-dihydro-Py) + H+]+; C18H25F3N+ m/z
= 163.1230, found (%) m/z = 163.1229 (12) [((C3H5)-(NMe2)-Py)+]+.
Reaction with Benzophenone. Benzophenone (31 mg, 170 μmol)
was added to a solution of 15 (24 mg, 57 μmol) in THF-d8 (600 μL) at
ambient temperature to give a colorless solution. After 5 d volatiles were
removed from the reaction mixture under reduced pressure and collected
in a cold trap at ꢀ196 °C. The residue, a colorless oil, was dissolved in
THF (1 mL) and filtered. All volatiles were removed from the filtrate to
give a colorless oil, which was dried in vacuo for 4 h. Yield of 19: 44 mg,
56 μmol, 98%.
’ ASSOCIATED CONTENT
S
Supporting Information. CIF file giving crystallographic
b
data for compounds 2 and 4; analytical data for 8ꢀ12; data on
dependence of the formation of 6 on stoichiometry; analytical
data for nonisolated compounds; rationalization of reaction of 15
with allyl iodide. This material is available free of charge via the
Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION
Condensate: Solution of 2-(C3H5)-4-CF3-Py (20) in THF. 1H
3
Corresponding Author
*Fax: +49 241 80 92644. E-mail: jun.okuda@ac.rwth-aachen.de.
NMR (400.1 MHz, THF-d8): δ 3.65 (br d, JHH = 6.9 Hz, 2H,
CꢀCH2ꢀCHdCH2), 5.10 (ddt, 2JHH = 1.7 Hz, 3JHH = 10.1 Hz, 4JHH
=
=
1.3 Hz, 1H, CꢀCH2ꢀCHdCHcisHtrans), 5.16 (ddt, 2JHH = 1.7 Hz, 3JHH
4
17.1 Hz, JHH = 1.6 Hz, 1H, CꢀCH2ꢀCHdCHcisHtrans), 6.08 (ddt,
’ ACKNOWLEDGMENT
3
3
3JHH = 6.9 Hz, JHH = 10.1 Hz, JHH = 17.1 Hz, 1H, CꢀCH2ꢀ
CHdCH2), 7.44 (br d, 3JHH = 5.1 Hz, 1H, H5), 7.49 (s, 1H, H3), 8.71
(d, 3JHH = 5.1 Hz, 1H, H6) ppm. 13C NMR (100.6 MHz, THF-d8): δ
43.39 (s, CꢀCH2ꢀCHdCH2), 117.25 (s, CꢀCH2ꢀCHdCH2), 117.4
Financial support by the Deutsche Forschungsgemeinschaft is
gratefully acknowledged. C.L. is grateful for a Kekulꢀe scholarship
kindly provided by the Fonds der Chemischen Industrie.
(q, 3JCF = 3.8 Hz, C5), 118.80 (q, 3JCF = 3.6 Hz, C3), 124.27 (q, 1JCF
=
272.8 Hz, CF3), 136.33 (s, CꢀCH2ꢀCHdCH2), 138.92 (q, 2JCF = 33.7
Hz, C4), 151.48 (s, C6), 163.04 (s, C2) ppm. 19F NMR(188.1MHz, THF-
d8): δ ꢀ62.02 (s) ppm. ESI-MS: exact mass calcd for C9H9F3N+ m/z =
188.0682, found (%) m/z = 188.0680 (100) [(M + H+)+]; C7H7F3NO+
m/z = 178.0474, found (%) m/z = 178.0474 (9) [(M + MeOH ꢀ
(C3H5ꢀ))+]; C7H5F3N+ m/z = 160.0369, found (%) m/z = 160.0367 (8)
[(M ꢀ (C2H3ꢀ))+]; C6H5F3N+ m/z = 148.0369, found (%) m/z =
148.0368 (1) [(M ꢀ (C3H4ꢀ))+].
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=
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17.2 Hz, 1H,
3
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(30) 6 contains a stereocenter, and the formation of a racemic
mixture of this complex can be expected.
(31) Control experiments showed that AlMe3 did not react with
stoichimetric amounts or an excess of pyridine in THF solution at
ambient temperature, not even when reaction times of up to 2 d were
applied. This is in good agreement with the literature.
(32) After keeping the same reaction mixture at ambient temperature
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(33) Side reactions such as subsequent reaction of desired products
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(34) A referee noted that coordination of the NMe2 group to the metal
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(35) 13ꢀ16 contain a stereocenter, and the formation of racemic
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(36) Re-aromatization is a known phenomenon in the chemistry
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(37) (a) W€anninen, E.; Ringbom, A. Anal. Chim. Acta 1955, 12,
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