Selective alkylation of 2,6-diiminopyridine ligands by dialkylmanganese reagents: A one-pot synthetic methodology

Article abstract of DOI:10.1021/om0609517

A one pot synthesis of new 2,6-diimine-4-alkylpyridines is reported. The addition of 2,6-[2,6-ⁱPr₂C₆H ₃N= C(Me)]₂C₅H₃N to the preformed MnR₂(THF)_n (R = CH₂CMe₂Ph, CH ₂Ph, CH₂CH=CH₂), followed by hydrolysis affords a mixture of 4-alkyl 2,6-bis(imino) derivatives of pyridine and 1,4-dihydropyridine in a variable ratio. Treatment of the mixture with a substoichiometric amount of CrO₂/K₂CO₃ in THF provides the 4-alkyl-2,6-diiminopyridines in good isolated yields and in a highly selective manner.

Full text of DOI:10.1021/om0609517

1104
Organometallics 2007, 26, 1104-1107
Selective Alkylation of 2,6-Diiminopyridine Ligands by
Dialkylmanganese Reagents: A “One-Pot” Synthetic Methodology
Juan Ca´mpora,* Carmen M. Pe´rez, Antonio Rodr´ıguez-Delgado, A. Marcos Naz,
Pilar Palma, and Eleuterio AÄ lvarez
Instituto de InVestigaciones Qu´ımicas, CSIC-UniVersidad de SeVilla, c/ Ame´rico Vespucio,
49, SeVilla, Spain
ReceiVed October 16, 2006
Summary: A “one pot” synthesis of new 2,6-diimine-4-alkyl-
pyridines is reported. The addition of 2,6-[2,6-iPr2C6H3Nd
C(Me)]2C5H3N to the preformed MnR2(THF)n (R ) CH2CMe2Ph,
CH2Ph, CH2CHdCH2), followed by hydrolysis affords a mixture
of 4-alkyl 2,6-bis(imino) deriVatiVes of pyridine and 1,4-
dihydropyridine in a Variable ratio. Treatment of the mixture
with a substoichiometric amount of CrO3/K2CO3 in THF
proVides the 4-alkyl-2,6-diiminopyridines in good isolated yields
and in a highly selectiVe manner.
interaction of the π-electron system with the partially filled metal
d orbitals.9 There are few examples of such substituted ligands
in the literature, these being hitherto limited to a 4-tert-butyl-
2,6-diiminopyridine derivative, prepared by Grassi through a
radical substitution reaction.10 Herein we report the use of
dialkylmanganese(II) reagents for the direct alkylation of the
pyridine ring in a highly selective manner. Monoalkylmanganese
species, usually formulated as Mn(X)R, have been used as mild
nucleophiles for selective C-C bond forming reactions.11
Although the nature of these paramagnetic species is not
precisely known, a number of Mn(II) dialkyl complexes have
been structurally characterized.12 However, the latter compounds
have not found practical applications.
Introduction
2,6-Diiminopyridines (PDI) are versatile ligands that have
found wide applications in coordination chemistry1,2 and
catalysis.3-6 Despite being known for more than 30 years, these
6-electron donors have received considerable attention over the
past decade, mainly due to the discovery of the high catalytic
activity of their Fe and Co complexes in olefin polymerization
catalysis.3 Moreover, these ligands have found use in many other
catalytic processes, such as olefin epoxidation,4 hydrogenation
and hydrosilation,5 and aerobic oxidation reactions.6 In part, the
success of diiminopyridine ligands stems from the ready
availability of their derivatives with different kinds of substit-
uents at the terminal imine nitrogen atoms and their straight-
forward synthesis from condensation reactions. Nevertheless,
structural modification of the central pyridine ring is a more
challenging task, despite the extensive nucleophilic substitution
chemistry of electron-deficient pyridines.7 In fact, it is now
known that the reaction of PDI ligands with main-group
organometallics often cause deprotonation,8a,b reduction,8c or
complex addition patterns.8b,d-f Introducing different substituents
in the pyridine ring may lead to significant changes in the
catalyst performance, since these depend on the extensive
Results and Discussion
The reaction of the homoleptic manganese alkyl [Mn(CH2-
CMe2Ph)2]2 with 2,6-[(2,6-iPr2C6H3)NdC(Me)]2C5H3N (ab-
breviated as iPrPDI) in toluene leads to a dark red solution, from
which a microcrystalline burgundy compound, 1, can be isolated.
Although its elemental analysis agrees with the composition
MnR2(iPrPDI), its color and magnetic susceptibility (4.7 µB) are
reminiscent of those of the Mn(I) methyl derivative MeMn-
(iPrPDI), reported by Gambarotta et al.13 On controlled metha-
nolysis under an inert atmosphere, 1 quantitatively yields the
(7) (a) Katritzky, A. R.; Pozharskii, A. F. Handbook of Heterocyclic
Chemistry, 2nd ed.; Pergamon: Oxford, U.K., 2000; pp 195-221. (b) Smith,
D. M. In ComprenhensiVe Organic Chemistry. The Synthesis and Reactions
of Organic Compounds; Barton, D., Ollis, W. D., Eds.; Sammes, P. G.,
Vol. Ed.; Pergamon: Oxford, U.K., 1979; Vol. 4, pp 20-34.
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Thiele, S. K. H. Organometallics 2004, 23, 5054. (b) Blackmore, I. J.;
Gibson, V. C.; Hitchcock, P. B.; Rees, C. W.; Williams, D. J.; White, A.
J. P. J. Am. Chem. Soc. 2005, 127, 6012. (c) Scott, J.; Gambarotta, S.;
Korobkov, I.; Knijnenburg, Q.; de Bruin, B.; Budzelaar, P. H. M. J. Am.
Chem. Soc. 2005, 127, 17204. (d) Knijnenburg, Q.; Smits, J. M. M.;
Budzelaar, P. H. M. Organometallics 2006, 25, 1036. (e) Khorobkov, I.;
Gambarotta, S.; Yap, G. P. A.; Budzelaar, P. H. M. Organometallics 2002,
21, 3088. (f) Blackmore, I. J.; Gibson, V. C.; Hitchcock, P. B.; Rees, C.
W.; Williams, D. J.; White, A. J. P. J. Am. Chem. Soc. 2005, 127, 6012.
(9) (a) Knijnenburg, Q.; Hetterscheid, D.; Kooistra, T. M.; Budzelaar,
P. H. M. Eur. J. Inorg. Chem. 2004, 1204. (b) Vidyaratne, I.; Gambarotta,
S.; Korobkov, I.; Budzelaar, P. H. M. Inorg. Chem. 2002, 44, 1187. (c)
Bart, S. C.; Chlopek, K.; Bill, E.; Bouwkamp, M. W.; Lobkovsky, E.; Neese,
F.; Wieghardt, K.; Chirik, P. J. J. Am. Chem. Soc. 2006, 128, 13901.
(10) Milione, S.; Cavallo, C.; Tedesco, C.; Grassi, A. Dalton Trans. 2002,
1839.
(11) (a) Organometallics in Synthesis, 2nd ed.; Schlosser,, M., Ed.;
Wiley: Chichester, U.K.,, 2002; pp 788-791. (b) Suh, Y.; Lee, J.-S..; Kim,
S.-H.; Rieke, R. D. J. Organomet. Chem. 2003, 684, 20.
(12) (a) Andersen, R. A.; Carmona-Guzma´n, E.; Gibson, J. F.; Wilkinson,
G. J. Chem. Soc., Dalton Trans. 1976, 2204. (b) Treichel, P. M. In
ComprehensiVe Organometallic Chemistry; Wilkinson, G., Stone, F. G. A.,
Abel, E. W., Eds.; Pergamon: Oxford, U.K., 1982; Vol. 4. (c) Girolami,
G. S.; Morris, R. J. In ComprehensiVe Organometallic Chemistry II;
Wilkinson, G., Stone, F. G. A., Abel, E. W., Eds.; Casey, C. P., Vol. Ed.;
Pergamon: Oxford, 1995; Vol. 5.
(1) (a) Alyea, E. C.; Ferguson, G.; Restivo, R. J. Inorg. Chem. 1975,
14, 2941. (b) Alyea, E. C.; Merrel, P. H. Inorg. Met.-Org. Chem. 1974, 4,
535. (c) Bruin, B.; Bill, E.; Bothe, E.; Weyhermuller, T.; Wieghardt, K.
Inorg. Chem. 2000, 39, 2936.
(2) Knijnenburg, Q.; Gambarotta, S.; Budzelaar. P. H. M. Dalton Trans.
2006, 5442.
(3) (a) Small, B. L.; Brookhart, M.; Bennett, A. A. J. Am. Chem. Soc.
1998, 120, 4049. (b) Britovsek, G. J. P.; Gibson, V. C.; Kimberley, B. S.;
Maddox, P. J.; McTavish, S. J.; Solan, G. A.; White, A. J. P.; Williams, D.
J. Chem. Commun. 1998, 849. (c) Small, B. L.; Brookhart, M. J. Am. Chem.
Soc. 1998, 120, 7143. (d) Britovsek, G. J. P.; Bruce, M.; Gibson, V. C.;
Kimberley, B. S.; Maddox, P. J.; Mastroianni, S.; McTavish, S. J.; Redshaw,
C.; Solan, G. A.; Stro¨mberg, S.; White, A. J. P.; Williams, D. J. J. Am.
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A. L.; Kranenburg, M.; Kooijman, H.; Veldmann, N.; Spek, A. L.; Elsevier,
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10.1021/om0609517 CCC: $37.00 © 2007 American Chemical Society
Publication on Web 01/20/2007

Notes
Organometallics, Vol. 26, No. 4, 2007 1105
Scheme 1
Figure 1. ORTEP drawing of compound 2a.
4-alkylated 2,6-diiminopyridine derivative 2a. Therefore, we
tentatively assign 1 the structure shown in Scheme 1. The
migration of the alkyl group to position 4 of the pyridine ring
finds precedents in related transformations involving Cr14 and
Al8b alkyl complexes. However, these reactions lead either to
dimeric compounds or to mixtures of products, whose trans-
formations into free organic compounds have not been explored.
The clean production of compound 2a suggested to us that
the reaction in Scheme 1 could provide the basis for a convenient
synthetic methodology for the selective alkylation of 2,6-
diiminopyridine derivatives, if the experimental difficulties
associated with the isolation and manipulation of the highly air-
sensitive manganese dialkyl species could be avoided.
Not surprisingly, attempts to separate the products by fraction-
al crystallization in air caused the slow aerobic oxidation of 3a
to 2a, and pure samples of the latter were isolated. 1,4-Dihydro-
pyridine aromatization is generally a facile process, and a num-
ber of oxidizing reagents can be used for this transformation.15
We found that 3a is efficiently converted into 2a when the
organic extract is treated with a catalytic amount of CrO3/K2CO3
in air. It is worth mentioning the convenience of removing the
inorganic manganese compounds prior to this oxidative treat-
ment, as they may interfere with the aromatization reaction.
This methodology has been successfully applied to the
synthesis of other 4-alkylated iPrPDI derivatives, even when the
corresponding MnR2 precursors have never been isolated. Thus,
with the benzyl or allyl Grignard reagents as starting materials,
the corresponding 2 + 3 mixtures were produced, from which
the derivatives 2b and 2c were obtained in excellent yields by
aerobic oxidation in the presence of CrO3/K2CO3. It is worth
noting that the intermediate bis(allyl)manganese complex ap-
pears to be thermally sensitive, as standing at room temperature
for more than 40 min results in substantially decreased yields
of 2c.
An X-ray diffraction study of 2a (Figure 1) confirmed the
structure proposed for the alkylated diiminopyridine compounds.
Apart from the expected CH2CMe2Ph group in the position 4
of the pyridine ring, its structural features are unexceptional
and show no significant differences from those of the unsub-
stitituted iPrPDI ligand.16
From a mechanistic point of view, the identification of the
dihydropyridine derivatives 3 as the major products is consistent
with an intramolecular alkyl migration process that involves the
initial formation of a unstable MnR2(iPrPDI) species (A), which
undergoes two consecutive 1,3-alkyl shifts, leading to a Mn(II)
alkyl dihydropyridine amide (C) (Scheme 3). Cope´ret has
observed that similar 1,3-alkyl migrations take place in related
MnR2(R-diimine) complexes.17 Interestingly, the species C tends
to spontaneously dehydrogenate in solution, leading to 1, which
is the only organometallic species isolated (in 67% yield), from
the reaction of [Mn(CH2CMe2Ph)2]2 with iPrPDI.
For synthetic purposes, Mn(X)R reagents are usually gener-
ated in situ by reacting the corresponding organolithium or
-magnesium reagents with anhydrous manganese chloride in
ethereal solvents.10a Mn(II) dialkyls can be formed in a similar
fashion. Thus, the reaction of MnCl2 with 2 equiv of Mg(Cl)CH2-
CMe2Ph proceeds readily, producing a pale brown solution. On
addition of iPrPDI at -78 °C, a rapid sequence of color changes
ensues, ending up in a deep red color, similar to that of complex
1. Quenching this reaction with a small amount of water or
methanol under inert atmosphere, followed by a standard workup
for the separation of paramagnetic Mn species, provides an
extract which contains the organic product of the reaction.
1
Unexpectedly, the H NMR spectrum of the crude mixture is
complex and indicates that compound 2a is formed together
with a second organic product, 3a. The 2a/3a ratio varies
appreciably from one experiment to another, but 3a is invariably
the major product. In spite of the apparent complexity of the
NMR spectra of this mixture, it can be readily deduced that,
like 2a, 3a displays a symmetric substitution pattern. A
1
combination of 13C, H, and two-dimensional NMR spectros-
copy allowed the identification of the major product as a 1,4-
dihydropyridine derivative (Scheme 2). Accordingly, the EI-
MS spectrum of the crude reaction mixture consists of two signal
clusters corresponding to the molecular ions [2a + H]+ and
[3a + H]+, confirming that only these two organic products
are formed in significant amounts (Scheme 2).
Scheme 2

1106 Organometallics, Vol. 26, No. 4, 2007
Notes
Scheme 3
a crystalline red-purple solid. Yield: 2.32 g. 67%. IR (Nujol
mull): ν (CdN) 1640, 1589 cm-1. Anal. Calcd for C47H56MnN3:
C, 75.45; H, 7.18; N, 5.87. Found: C: 75.42, H: 6.91, N: 6.00.
µeff (20 °C, magnetic susceptibility balance): 4.70 µB.
Methanolysis of Compound 1. Anhydrous methanol (5 mL)
was added to a 20 mL hexane solution of 1 (0.15 g, 0.19 mmol) at
room temperature. The resultant mixture turned instantaneously
from a purple solution to a green suspension with a brown
precipitate. The solution was filtered through a pad of silica
previously treated with Et3N, and after solvent evaporation a yellow
solid was obtained, which was identified as 2a. Yield: 0.10 g. 86%.
“One Pot” Synthesis of iPrPDI-4-CH2CMe2Ph (2a). A pink
suspension of MnCl2 (187 mg, 1.48 mmol) in 20 mL of THF was
mixed with 2.1 equiv of a colorless 1.3 M Et2O solution of
(PhCMe2CH2)MgCl (2.43 mL) at -78 °C. The reaction mixture
was stirred for 10 min and then warmed gradually, while it turned
from pale green to brown. After 10-15 min at room temperature,
the mixture became pale brown. The solution was transferred over
a cold (-78 °C) suspension of iPrPDI (580 mg, 1.19 mmol) in
hexane. A thick, dark brown solution formed instantaneously, which
was vigorously stirred for 10 min at -78 °C and then warmed to
room temperature. The stirring was continued for 90 min, during
which time the color changed again to deep purple. Then, an excess
of anhydrous methanol (8-10 mL) was added to quench the
reaction. After solvent and volatiles were removed from the resultant
clear red solution, an orange oil was isolated, which was extracted
with 3 × 25 mL of hexane and 2 × 20 mL of toluene, leaving
behind a pale brown precipitate. The orange oil isolated after solvent
removal (0.65 g. 89%) was identified as a 1:2 mixture of 2a and
3a. Then, the oily mixture was redissolved in THF and, in air,
treated with a catalytic amount of CrO3 (ca. 10 mg, 10 mol %) and
1.5 g of K2CO3 for 1 h at room temperature. The solvent and
volatiles were removed under reduced pressure, and 2a was
extracted in hexane (2 × 15 mL). A yellow solid was isolated,
after filtration and solvent evaporation. Yield: 0.52 g. 71%.
In summary, the reaction of manganese dialkyls with iPrPDI
leads initially to unstable organomanganese(II) compounds,
which evolves via consecutive 1,3-alkyl shifts to 4-substituted
2,6-diiminopyridine alkylmanganese complexes. On the basis
of this reaction, we have designed a one-pot synthetic methodol-
ogy that allows the selective alkylation of the diiminopyridines
at the position 4 in the pyridine ring. We are currently testing
the performance of the new alkylated ligands in olefin polym-
erization, using the corresponding complexes of Fe, Co, and
Cr. The introduction of suitably functionalized alkyl groups in
the 2,6-diiminopyridine system may find interesting applications.
For example, these may be used as attaching points to anchor
the complexes at surfaces (immobilization) while the active site
is kept isolated from the influence of the solid support. In
addition, the alkyl group can be used as a tether to connect the
pyridine diimine moiety to other potentially interesting mol-
ecules.
2a: 1H NMR (C6D6, 298 K, 500 MHz) δ 1.15 (d, 12H, 3JHH
)
)
Experimental Section
All preparations were carried out under oxygen-free nitrogen by
conventional Schlenk techniques unless otherwise stated. Solvents
were rigorously dried and degassed before use. Microanalyses were
performed by the Microanalytical Service of the Instituto de
Investigaciones Qu´ımicas (Sevilla, Spain). Infrared spectra were
recorded on a Bruker Vector 22 spectrometer and NMR spectra on
6.9 Hz, CHMe2), 1.17 (s, 6H, CH2CMe2Ph), 1.22 (d, 12H, 3JHH
6.9 Hz, CHMe2), 2.27 (s, 6H, CH3CdN), 2.65 (s, 2H, CH2CMe2Ph),
2.89 (sept, 4H, 3JHH ) 6.9 Hz, CHMe2), 7.13-7.02 (m, 6H, CHar),
7.22-7.16 (m, 5H, CHar(Ph)), 8.22 (s, 2H, CH(py)); 13C{1H} NMR
δ 16.9 (CH3CdN), 23.0, 23.2 (CHMe2), 26.9 (CH2CMe2Ph), 28.4
(CHMe2), 38.3 (CH2CMe2Ph), 49.9 (CH2CMe2Ph), 123.2 (3,5-Car),
123.9 (4-Car), 124.3 (s, 3,5-Car(py)), 125.8 (4-Car(Ph)), 125.9 (2,6-
Car(Ph)), 128.0 (3,5-Car(Ph)), 135.6 (Car), 146.8 (Car), 147.2
(Car(py)), 148.9 (Car), 154.6 (Car(py)), 166.8 (CH3CdN); IR (Nujol
mull) ν(CdN) 1641, 1590, 1553 cm-1; ESI-MS (m/z) 614.4 (M +
1).
1
Bruker DRX 300, 400, and 500 MHz spectrometers. The H and
13C{1H} resonances of the solvent were used as the internal
standard, but the chemical shifts are reported with respect to TMS.
MnCl2 was obtained from Sigma Aldrich and Co. and purified by
11a
methods described in the literature.18 [Mn(CH2CMe2Ph)2]n was
prepared according to literature methods. The iPrPDI ligand and
Grignard reagents RMgCl (R ) PhCMe2CH2, PhCH2, CH2CHd
CH2) were prepared following conventional synthetic methods.
Synthesis of Complex 1. A 20 mL toluene solution of
[Mn(CH2CMe2Ph)2]n (1.41 g, 4.39 mmol) was added dropwise to
a 20 mL toluene suspension of iPrPDI (2.06 g, 4.29 mmol) at -40
°C. The resultant mixture turned instantaneously from yellow to
dark red. The mixture was stirred vigorously for 5 min at -40 °C
and for 1 h at room temperature. Then, solvents and volatiles were
removed under reduced pressure to obtain an oily solid residue,
which was extracted with 3 × 20 mL of pentane. The filtrate was
cooled at -80 °C for several days, and complex 1 was isolated as
1
3
3a: H NMR (CDCl3, 298 K, 300 MHz) δ 0.970 (d, 6 H, JHH
3
) 6.9 Hz, CHMe2), 1.05 (d, 12 H, JHH ) 6.9 Hz, CHMe2), 1.23
3
(d, 6 H, JHH ) 6.9 Hz, CHMe2) 1.42 (s, 6H, CH2CMe2Ph), 1.60
3
(s, 6H, CH3CdN), 2.04 (d, 2H, JHH ) 6 Hz, CH2CMe2Ph), 2.60
3
3
(sept, 4H, JHH ) 6.9 Hz, CHMe2), 3.33 (q, 1H, JHH ) 4.5 Hz,
4-CH(py)), 4.71 (bs, 2H, 3,5-CH(py)), 7.14-6.95 (m, 6H, CHar),
7.47-7.13 (m, 5H, CHar(Ph)), 8.17 (bs, H, NH); 13C{1H} NMR δ
15.0 (CH3CdN), 22.5, 22.6 (CHMe2), 23.1 (CH2CMe2Ph), 28.34
(CHMe2), 28.8 (4-CH(py)) 29.4 (CH2CMe2Ph), 32.5 (CH2CMe2Ph),
37.2 (CH2CMe2Ph), 55.2 (CH2CMe2Ph), 106.4 (3,5-C(py)), 123.7
(3,5-Car), 123.8 (4-Car), 124.9 (3,5-Car(py)), 125.1 (4-Car(Ph)), 125.5
(2,6-Car(Ph)), 128.0 (3,5-Car(Ph)), 134.59 (Car), 135.5 (Car), 136.46
(Car), 146.3 (Car), 149.4 (Car), 159.5 (CH3CdN); IR (Nujol mull)
ν(H-N) 3376 cm-1, ν(CdN) 1637, 1589, 1555 cm-1; ESI-MS (m/
z) 616.4 (M + 1).
(14) Sugiyama, H.; Aharonian, G.; Gambarotta, S.; Yap, G. P. A.;
Budzelaar, P. H. M. J. Am. Chem. Soc. 2002, 124, 12268.
(15) (a) See ref 7a, p 241. (b) Fukuzumi, S.; Tokuda, Y.; Kitano, T.;
Okamoto, T.; Otera, J. J. Am. Chem. Soc. 2005, 115, 8960.
(16) CCDC 116252 (HORSEM). Yap, G. P. A.; Gambarotta, S. Private
communication, 1999.
(17) Riollet, V.; Cope´ret, C.; Basset, J.-M.; Rousset, L.; Bouchu, D.;
Grosvalet, L.; Perrin, M. Angew. Chem., Int. Ed. 2002, 41, 3025.
(18) So, J.-H.; Boudjouk, P. Inorg. Chem. 1990, 29, 1592.
Synthesis of iPrPDI-4-CH2Ph (2b). To a fine pink suspension
of MnCl2 in THF (150 mg, 1.19 mmol) stirred at -78 °C was added
2.1 equiv (2.49 mmol, 2.5 mL) of a 0.97 M solution of Mg(CH2Ph)Cl
in Et2O. After 10 min the cooling bath was removed and the mixture
was stirred for 60 min more. The resultant solution was added to

Notes
Organometallics, Vol. 26, No. 4, 2007 1107
a suspension of iPrPDI (0.46 g, 0.952 mmol) in toluene (30 mL) at
-78 °C. Color changes were similar to those observed in the
previous case. After quenching with anhydrous methanol and
evaporation, a yellow solid was obtained (0.41 g 92%), composed
mainly of the dihydropyridine derivative 3b. A 0.10 g portion of
this solid was dissolved in THF and the solution stirred in an air
atmosphere together with CrO3 (ca. 10 mol %) and K2CO3 (1 g)
for 1 h at room temperature. The volatiles were removed under
reduced pressure, and the residue was extracted with 20 mL of
hexane. After concentration and cooling, 2b was isolated as a yellow
crystalline solid. Yield: 0.09 g. 81%.
(CH3CdNAr); IR (Nujol mull): ν(H-N) 3377 cm-1, ν(CdN)
1643, 1589, 1556 cm-1; ESI-MS (m/z) 524.4 (M + 1).
3
3c: 1H NMR (CDCl3, 298 K, 500 MHz) δ δ 1.01 (d, 6H, JHH
) 7.0 Hz, CHMe2), 1.03 (d, 6H, 3JHH ) 7.0 Hz, CHMe2), 1.08 (d,
6H, 3JHH ) 7.0 Hz, CHMe2), 1.10 (d, 6H, 3JHH ) 7.0 Hz, CHMe2),
3
1.84 (s, 6H, CH3CdN), 2.39 (t, 2H, JHH ) 7.0 Hz, CH2) 2.59
(sept, 2H, 3JHH ) 7.0 Hz, CHMe2), 2.62 (sept, 2H, 3JHH ) 7.0 Hz,
CHMe2), 3.6 (q, 3JHH ) 7.0 Hz, 1H 4-CH(py)), 5.10-5.11 (m, 2H,
CHdCH2), 5.12-5.14 (m, 2H, 3,5-CH(py)), 5.87-5.92 (m, 1H,
CHdCH2), 6.92-7.01 (m, 6H, CH), 8.33 (bs, 1H, N-H); 13C{1H}
NMR (CDCl3, 298 K, 75 MHz) δ 15.5 (CH3CdNAr), 22.6
(CHMe2), 23.1 (CHMe2), 28.2 (CHMe2), 35.6, (4-C(py)), 43.9
(CH2CHdCH2), 104.3 (3,5-C(py)), 116.6 (CH2CHdCH2), 122.7
(Car), 123.0 (2,4-C(py)) 123.3 (Car), 135.7 (CH2CHdCH2), 135.9,
137.3 (Car), 145.9 (Car), 159.14 (CH3CdNAr); IR (Nujol mull)
ν(H-N) 3377 cm-1; ν(CdN) 1644, 1592, 1559 cm-1; ESI-MS (m/
z): 524.4 (M + 1).
2b: 1H NMR (C6D6, 298 K, 500 MHz) δ 1.15 (d, 12H, 3JHH
)
3
6.9 Hz, CHMe2), 1.17 (d, 12H, JHH ) 6.9 Hz, CHMe2), 2.29 (s,
6H, CH3CdNar), 2.91 (sept, 4H, 3JHH ) 6.9 Hz, CHMe2), 3.59 (s,
2H, CH2(benc)), 6.90-7.12 (m, 6H, CHar), 7.21-7.19 (m, 5H,
CHar(Ph)), 8.53 (s, 2H, 3-CHar(py)); 13C{1H} NMR δ 17.0 (CH3Cd
NAr), 22.9, 22.6 (CHMe2), 28.5 (CHMe2), 41.2 (CH2(benc)), 122.7
(Car), 123.2 (Car), 124.0 (Car), 126.4 (Car), 128.5 (Car), 129.0 (Car),
135.6 (Car), 146.7 (Car), 147.7 (Car), 151.7 (Car), 155.6 (Car), 166.8
X-ray Structural Determination. One crystal coated with dry
perfluoropolyether was mounted on a glass fiber and fixed in a
cold nitrogen stream (T ) 100(2) K). Intensity data were collected
on a Bruker-Nonius X8Apex-II CCD diffractometer equipped with
a Mo KR1 radiation (λ ) 0.710 73 Å) source and graphite
monochromator. The data were reduced (SAINT)20 and corrected
for Lorentz-polarization and absorption effects by multiscan
methods (SADABS).21 The structure was solved by direct methods
(SIR-2002)22 and refined against all F2 data by full-matrix least-
squares techniques (SHELXTL-6.12),23 minimizing w[Fo2 - Fc2]2.
All non-hydrogen atoms were refined with anisotropic thermal
parameters. Hydrogen atoms were included in calculated positions
and refined riding on the carbon atoms which they are bonded,
with the isotropic temperature factors (Uiso values) fixed at 1.2 times
(1.5 times for methyl groups) those Ueq values of the corresponding
carbon atoms. Crystal data for 2a: C46H55D3N3 (C43H55N3‚0.5C6D6),
Mr ) 655.97, yellow plate (0.44 × 0.16 × 0.08 mm3) from
deuterated benzene, triclinic, space group P1h (No. 2), a ) 8.6811(6)
Å, b ) 15.1172(14) Å, c ) 16.2449(16) Å, R ) 73.095(3)°, â )
(CH3CdNAr); IR (Nujol mull) ν(CdN) 1644, 1592, 1554 cm-1
;
ESI-MS (m/z) 572.5 (M + 1).
3
3b: 1H NMR (CDCl3, 298 K, 300 MHz) δ 0.970 (d, 6 H, JHH
3
) 6.9 Hz, CHMe2), 1.05 (d, 12 H, JHH ) 6.9 Hz, CHMe2), 1.23
3
(d, 6 H, JHH ) 6.9 Hz, CHMe2), 1.42 (s, 6H, CH2CMe2Ph), 1.60
3
(s, 6H, CH3CdN), 2.04 (d, 2H, JHH ) 6 Hz, CH2CMe2Ph), 2.60
3
3
(sept, 4H, JHH ) 6.9 Hz, CHMe2), 3.33 (q, 1H, JHH ) 4.5 Hz,
4-CH(py)), 4.71 (bs, 2H, 3,5-CH(py)), 7.14-6.95 (m, 6H, CHar),
7.47-7.13 (m, 5H, CHar(Ph)), 8.17 (bs, H, NH); 13C{1H} NMR δ
15.0 (CH3CdN), 22.5, 22.2 (CHMe2), 27.7 (4-CH(py)), 37.2
(CH2Ph), 106.4 (3,5-C(py)), 123.7 (3,5-Car), 123.8 (4-Car), 124.9
(3,5-Car(py)), 125.1 (4-Car(Ph)), 125.5 (2,6-Car(Ph)), 128.0 (3,5-
Car(Ph)), 134.59 (Car), 135.5 (Car), 136.46 (Car), 138.5 (Car(Ph)),
146.3 (Car), 149.4 (Car(py)), 159.5 (CH3CdN); IR (Nujol mull)
ν(H-N) 3377 cm-1, ν(CdN) 1630, 1587, 1554 cm-1; ESI-MS (m/
z): 574.4 (M + 1).
85.004(3)°, γ ) 77.590(4)°, V ) 1991.4(3) Å,3 Z ) 2, Fcalcd
)
Synthesis of iPrPDI-4-CH2CHdCH2 (2c). A fine pink suspen-
sion of MnCl2 (200 mg, 1.58 mmol) in THF (20 mL) was cooled
to -78 °C, and 2.1 equiv of a cold (0 °C) 2 M THF solution (1.66
mL) of allylmagnesium chloride was slowly added to the vigorously
stirred suspension via syringe. The resultant mixture was dark brown
when the addition was complete. The cold bath was removed, and
the mixture was warmed for 15 min. After 10 min at room
temperature, it was transferred to a flask containing a cold (-78
°C) suspension of iPrPDI. The color of the resultant mixture was
dark brown. The cold bath was then removed after 10 min. The
reaction mixture stirred at room temperature for 50 min, and the
resulting dark purple solution was quenched with 5 mL of MeOH.
The solvent and volatiles were removed, leaving a brown oil, which
was extracted with hexane (3 × 30 mL). Vacuum evaporation left
470 mg (88%) of a yellow foam, composed almost exclusively of
the dihydropyridine 3c. A 0.10 g portion of this product was
dissolved in THF, and this solution was exposed to the atmosphere
and stirred for 1 h with a catalytic amount of CrO3 (ca. 10 mol %)
and 1 g of K2CO3 at room temperature. After the solvent and
volatiles were removed under reduced pressure, 2c was extracted
with hexane (20 mL). A yellow powdery solid was isolated, after
filtration and solvent evaporation. Yield: 0.082 g. Total yield: 72%.
1.094 g cm-3, F(000) ) 710, µ ) 0.063 mm-1, 16 455 reflections
were collected in the range 5.54 < 2θ < 52.76°, index ranges -10
e h e 10, -17 e k e 18, -20 e l e 20, 8002 independent
reflections (Rint ) 0.0706), 4336 reflections observed with I > 2σ(I),
final R1 (I > 2σ(I)) ) 0.0691, wR2 (all data) ) 0.2133, w )
2
2
[σ2(Fo ) + (0.0775P)2 + 0.1648P]-1, P ) (Fo + 2Fc2)/3; 8002/
0/442 data/restraints/parameters, goodness of fit on F2 1.030. In
the final difference map, the highest residual peaks, those above
0.2 e Å-3, were located close to the isopropyl groups and have no
chemical meaning.
Acknowledgment. Financial support from the DGI (Project
PPQ2003-000975) and Junta de Andaluc´ıa is gratefully ac-
knowledged. A.R.-D. thanks the Ministerio de Educacio´n y
Ciencia for a Ramo´n y Cajal fellowship, and C.M.P. acknowl-
edges a research grant from Repsol-YPF.
Supporting Information Available: Text giving experimental
procedures and characterization data for all new complexes and a
CIF file giving crystallographic data for 2a. This material is
available free of charge via the Internet at http://pubs.acs.org.
OM0609517
2c: 1H NMR (CDCl3, 298 K, 300 MHz) δ δ 1.14 (d, 12H, 3JHH
(19) (a) Van Koten, G.; Vrieze, K. AdV. Organomet. Chem. 1982, 21,
151. (b) Laine, T. V.; Piironen, U.; Lappalainen, K.; Klinga, M.; Aitola,
E.; Leskela¨, M. J. Organomet. Chem. 2000, 606, 112. (c) Laine, T. V.;
Klinga, M.; Leskela¨, M. Eur. J. Inorg. Chem. 1999, 959. (d) Meneghetti,
S. P.; Lutz, P. J.; Kress, J. Organometallics, 1999, 18, 2734.
(20) SAINT 6.02; Bruker-AXS, Inc., Madison, WI, 1997-1999.
(21) Sheldrick, G. SADABS; Bruker AXS, Inc., Madison, WI, 1999.
(22) Burla, M. C.; Camalli, M.; Carrozzini, B.; Cascarano, G. L.;
Giacovazzo, C.; Polidori, G.; Spagna, R. SIR2002: the program. J. Appl.
Crystallogr. 2003, 36, 1103.
) 6.6 Hz, CHMe2), 1.16 (d, 12H, 3JHH ) 6.6 Hz, CHMe2), 2.25 (s,
3
6H, CH3CdN), 2.76 (sept, 4H, JHH ) 6.6 Hz, CHMe2), 3.56 (d,
2H, 3JHH ) 6.6 Hz CH2), 5.18 (m, 2H, CHdCH2), 6.05-5.99 (m,
1H, CHdCH2), 7.17-7.04 (m, 6H, CH), 8.30 (s, 2H, 3,5-CHar(py));
13C{1H} NMR (CDCl3, 298 K, 75 MHz) δ 17.6 (CH3CdNAr),
23.3 (CHMe2), 22.5 (CHMe2), 28.5 (CHMe2), 40.1 (CH2CHdCH2),
117.7 (CH2CHdCH2), 122.56 (Car), 123.3 (Car), 135.6 (CH2CHd
CH2), 136.1 (Car), 146.7 (Car), 150.5 (Car), 155.6 (Car), 167.4
(23) SHELXTL 6.14; Bruker AXS, Inc., Madison, WI, 2000-2003.