Formation and selective trapping of 2,5-dihydropyridine and its isopropylidene derivative by tungsten(0) alkylidene complexes. X-ray structure of the 5-isopropylidene-2,5-dihydropyridine adduct

Article abstract of DOI:10.1021/om9708079

A mixture of 1,2- and 2,5-dihydropyridines and 5-isopropylidene-2,5-dihydropyridine, obtained from 1-(methoxycarbonyl)-1,2-dihydropyridine and methyllithium followed by protonation, reacts with a series of pentacarbonyl tungsten(0) alkoxycarbene complexes to afford, besides the expected pyridinium ylide complexes 7, the 2,5-dihydropyridinium ylide complexes 6 together with the 5-isopropylidene-2,5-dihydropyridinium ylide complexes 5, which could be separated and fully characterized by X-ray analysis.

Full text of DOI:10.1021/om9708079

Organometallics 1998, 17, 361-366
361
F or m a tion a n d Selective Tr a p p in g of
2,5-Dih yd r op yr id in e a n d Its Isop r op ylid en e Der iva tive
by Tu n gsten (0) Alk ylid en e Com p lexes. X-r a y Str u ctu r e
of th e 5-Isop r op ylid en e-2,5-d ih yd r op yr id in e Ad d u ct
Henri Rudler,*,† Blanca Mart´ın-Vaca,† Muriel Nicolas,† Max Audouin,† and
J acqueline Vaissermann‡
Laboratoire de Synthe`se Organique et Organome´tallique, UMR 7611, and Laboratoire de
Chimie des Me´taux de Transition, URA 419, Universite´ Pierre et Marie Curie, T 44-45,
4 place J ussieu, 75252 Paris Cedex 5, France
Received September 11, 1997
A mixture of 1,2- and 2,5-dihydropyridines and 5-isopropylidene-2,5-dihydropyridine,
obtained from 1-(methoxycarbonyl)-1,2-dihydropyridine and methyllithium followed by
protonation, reacts with a series of pentacarbonyl tungsten(0) alkoxycarbene complexes to
afford, besides the expected pyridinium ylide complexes 7, the 2,5-dihydropyridinium ylide
complexes 6 together with the 5-isopropylidene-2,5-dihydropyridinium ylide complexes 5,
which could be separated and fully characterized by X-ray analysis.
Sch em e 1
In tr od u ction
Very recently we described the reduction of alkoxy-
carbene complexes of tungsten and chromium with 1,2-
and 1,4-dihydropyridines, a reaction which opened the
way to the synthesis and use as cyclopropanation and
cycloaddition reagents of protected alkylidene complexes
of W(0) and Cr(0) in the form of pyridinium ylides.1,2
A tentative mechanism explaining this transforma-
tion, which is akin to the dihydropyridine-induced
reductions of carbonyl compounds in biological systems
and involves a hydride transfer from dihydropyridine
to the carbene carbon with formation of pyridinium, has
been suggested. This transfer is probably followed by
a pyridinium-induced elimination of alcohol and of a
recoordination of the pyridine thus formed on the highly
electrophilic intermediate alkylidene complex 2 (Scheme
1). The formation and isolation of a second complex,
which could also be established as being an ylide of 2,5-
dihydropyridine, was briefly mentioned, but its origin
remained intriguing, since no 2,5-dihydropyridine was
supposed to be formed upon reduction of pyridinium
chloroformate by sodium borohydride.3
trapped with acetone and isolated as a new isopropyl-
idene-substituted 2,5-dihydropyridinium ylide complex
of W(0).
Resu lts a n d Discu ssion
F or m a tion of 2,5-Dih yd r op yr id in e a n d of 5-Iso-
p r op ylid en e-2,5-d ih yd r op yr id in e fr om P r otected
1,2-Dih yd r op yr id in e a n d Th eir Tr a p p in g b y
(OC)5WdC(CH3)H. When an excess of dihydropyri-
dine, prepared according to the literature3 from 1-(meth-
oxycarbonyl)-1,2-dihydropyridine and methyllithium fol-
lowed by protonation, was added to complex 1a , a
mixture of four complexes was obtained. Careful silica
gel chromatography allowed their separation in the
following order of elution: yellow W(CO)5(pyridine) (4),
the new orange complex 5a (8.5%) having almost the
same polarity as complex 4, 2,5-dihydropyridinium ylide
complex 6a (20%), and the pyridinium ylide complex 7a
(50%) having almost the same polarity as complex 6a .
1H and 13C NMR experiments on complex 5a (R )
Me) confirmed the presence of a CH3CH group as for
complexes 6a and 7a , giving respectively a quartet for
one proton at δ 3.86 ppm and a doublet for three protons
Herewith we provide evidence for the generality of
the formation of 2,5-dihydropyridinium ylide complexes,
starting from a series of ethoxycarbene complexes of
tungsten, and demonstrate that indeed a mixture of 1,2-
and 2,5-dihydropyridines is formed from the lithio amide
of 1,2-dihydropyridine during the deprotection reaction
of the 1-(methoxycarbonyl)-1,2-dihydropyridine precur-
sor. The intermediate in this transformation could be
† Laboratoire de Synthe`se Organique et Organome´tallique, URA
408.
‡ Laboratoire de Chimie des Me´taux de Transition, URA 419.
(1) Rudler, H.; Audouin, M.; Parlier, A.; Mart´ın-Vaca, B.; Goumont,
R.; Durand-Re´ville, T.; Vaissermann, J . J . Am. Chem. Soc. 1996, 118,
12045.
(2) Mart´ın-Vaca, B.; Rudler, H. J . Chem. Soc., Perkin Trans. 1 1997,
3119.
(3) Fowler, W. F. J . Org. Chem. 1972, 37, 1321.
1
at δ 2.18 ppm in the H NMR spectrum and signals at
δ 52.6 and 30.1 ppm in the 13C NMR spectrum.
S0276-7333(97)00807-8 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 01/07/1998

362 Organometallics, Vol. 17, No. 3, 1998
Rudler et al.
Moreover, signals for a methylene group at δ 53.0 ppm,
three methine groups at δ 144.1, 120.9, and 120.6 ppm,
two quaternary carbons at δ 147.7 and 121.8 ppm, and
two methyl groups at δ 22.2 and 20.9 ppm were also
observed. Altogether, these data suggested a structure
such as 5a (R ) Me), which could indeed be confirmed
by an X-ray analysis.
F igu r e 1. Molecular structure of C15H15O5NW showing
the atomic numbering scheme.
Ta ble 1. In ter a tom ic Dista n ces (Å) for
[W(CO)5(C10H15N)]
X-r a y Cr ysta l Str u ctu r e of th e 5-Isop r op ylid en e-
2,5-Dih yd r op yr id in iu m Com p lex. The CAMERON
drawing of the molecular structure of 5a is shown in
Figure 1. Interatomic distances and bond angles are
listed in Tables 1 and 2; crystallographic data are given
in Table 4. Noteworthy are the W(1)-C(1) and C(1)-
N(1) single bonds (2.381(9) and 1.45(1) Å, respectively)
which can be compared and are very close to those in
complex 6a , the carbon-carbon double bonds C(9)-C(10)
(1.31(1) Å) and C(11)-C(13) (1.35(1) Å), and the carbon-
nitrogen double bond N(1)-C(12) (1.29(1) Å); moreover,
as for complex 6a , the sum of the angles around N(1) is
equal to 360°. The atoms of the pyridinium ring and
C(1), C(13), and C(14) are in the same plane, with C(15)
slightly above the mean plane. No appreciable differ-
ences in the bond distances of the coordinated carbonyl
groups indicating a preferential delocalization of the
negative charge from the metal to these groups have
been detected however.
Or igin of th e New Dih yd r op yr id in es a n d of
Th eir Com p lexes. An important observation, besides
the fact that 1,2-dihydropyridine is able to reduce
carbene complexes, is the fact that two unexpected 2,5-
dihydropyridine complexes are also formed in this
reaction. This means that 2,5-dihydropyridines are
formed during the deprotection reaction and, moreover,
that these dihydropyridines are stable enough to be
trapped as such before their oxidation.
W(1)-C(1)
W(1)-C(4)
W(1)-C(6)
N(1)-C(1)
N(1)-C(12)
O(4)-C(4)
O(6)-C(6)
C(1)-C(2)
C(9)-C(10)
C(11)-C(12)
C(13)-C(14)
2.381(9)
2.03(1)
2.030(9)
1.45(1)
1.29(1)
1.14(1)
1.13(1)
1.51(1)
1.31(1)
1.42(1)
1.49(1)
W(1)-C(3)
W(1)-C(5)
W(1)-C(7)
N(1)-C(8)
O(3)-C(3)
O(5)-C(5)
O(7)-C(7)
C(8)-C(9)
C(10)-C(11)
C(11)-C(13)
C(13)-C(15)
2.03(1)
1.98(1)
2.055(9)
1.48(1)
1.13(1)
1.15(1)
1.12(1)
1.47(1)
1.47(1)
1.35(1)
1.48(1)
Ta ble 2. Bon d An gles (d eg) for [W(CO)5(C10H15N)]
C(1)-W(1)-C(3)
C(3)-W(1)-C(4)
C(3)-W(1)-C(5)
C(1)-W(1)-C(6)
C(4)-W(1)-C(6)
C(1)-W(1)-C(7)
C(4)-W(1)-C(7)
C(6)-W(1)-C(7)
C(1)-N(1)-C(12)
W(1)-C(1)-N(1)
N(1)-C(1)-C(2)
W(1)-C(4)-O(4)
W(1)-C(6)-O(6)
N(1)-C(8)-C(9)
C(9)-C(10)-C(11)
86.8(3)
88.6(4)
96.4(4)
83.7(3)
90.4(3)
96.1(3)
170.6(4)
91.3(4)
125.4(7)
114.1(5)
112.3(8)
C(1)-W(1)-C(4)
C(1)-W(1)-C(5)
C(4)-W(1)-C(5)
C(3)-W(1)-C(6)
C(5)-W(1)-C(6)
C(3)-W(1)-C(7)
C(5)-W(1)-C(7)
C(1)-N(1)-C(8)
C(8)-N(1)-C(12)
W(1)-C(1)-C(2)
W(1)-C(3)-O(3)
93.3(4)
175.8(3)
84.0(4)
170.4(4)
93.0(4)
91.2(4)
86.6(4)
114.4(7)
120.1(7)
113.2(6)
175.8(8)
178.5(9)
175.5(9)
123.3(8)
175.6(10) W(1)-C(5)-O(5)
178.4(8)
114.2(7)
121.4(8)
W(1)-C(7)-O(7)
C(8)-C(9)-C(10)
C(10)-C(11)-C(12) 114.3(8)
C(12)-C(11)-C(13) 122.0(8)
C(11)-C(13)-C(14) 122.3(9)
C(14)-C(13)-C(15) 113.2(9)
C(10)-C(11)-C(13) 123.6(8)
N(1)-C(12)-C(11) 126.5(8)
C(11)-C(13)-C(15) 124.5(9)
that delocalization of the negative charge in the lithio
amide 9 exists and that protonation can occur both at
nitrogen and at carbon C-11: a mixture of 1,2- and 2,5-
dihydropyridines 10 and 11 can thus be formed (Scheme
2). Whereas 10 can act as a reducing agent on complex
1 to give 7 as the expected complex, 11 could be trapped,
at least in part, by the alkylidene complex 2 to give
complex 6. Second, the origin of complex 5a and
especially of the extra isopropylidene group can be
explained in the following way: it is known that N,N-
disubstituted carbamates react with 2 mol of an alkyl-
lithium reagent to give symmetrical ketones in which
both alkyl groups are derived from the organometallic
compound.4,5 Thus, during the reaction of 2 equiv of
methyllithium with the protected dihydropyridine 8
acetone is formed together with the delocalized anion
That complexes 5 and 6 had the same origin, the lithio
amide of 1,2-dihydropyridine 9, formed upon interaction
of the protected dihydropyridine 8 and methyllithium,
has been established in the following way. First,
protected 1,2-dihydropyridine 8D6 was prepared from
perdeuterated pyridine and NaBD4. After its deprotec-
tion as above (MeLi followed by protonation), it reacted
with complex 1a to give inter alia the new complex 6a D7
1
(eq 2). According to its H NMR spectrum, this complex
surprisingly bore hydrogen at C-11 (numbering scheme
as in Figure 1 for the sake of simplicity). This indicates
(4) Michael, U.; Ho¨rnfeldt, A. B. Tetrahedron Lett. 1970, 5219.
(5) Scilly, N. F. Synthesis 1973, 160.

Trapping of 2,5-Dihydropyridine by W(0) Complexes
Organometallics, Vol. 17, No. 3, 1998 363
Sch em e 2
tion step, the hydrogen atoms at this position being
rather labile. Second, the fact that, unexpectedly,
several different dihydropyridines are formed from the
protected 1,2-dihydropyridine 8 renders the analysis of
the data obtained from labeled compounds more com-
plicated, since both 1,2- and 2,5-dihydropyridines are
able to reduce the alkoxycarbene complexes. This was
1
experimentaly confirmed. Indeed, according to the H
2
and H NMR spectra of the labeled complexes 6a D7 and
7a D6, 20-25% of hydrogen is present at C-1, where only
deuterium was expected in the case of the reduction due
to 1,2-dihydropyridine 10D6. Since exchange at this
position seems unlikely under the reaction conditions,
it means that the alkylidene complex 2a , which traps
1,2-dihydropyridine and pyridine to form 6a D7 and
7a D6, is 20-25% 2a (1-H) and results from the reduction
of complex 1a with the labeled 2,5-dihydropyridine
Ta ble 3. H/D Ra tio fr om NMR La belin g
Exp er im en ts
6
11D6 (eq 4).
complex
posi-
tion
C-1 0.75/0.25 0.78/0.22 0.70/0.30 0.75/0.25 0.25/0.75 0.20/0.80
C-11 2.00/0 1.75/0.25 1.85/0.15
6a D2
7a D1
6a D6
7a D5
6a D7
7a D6
9. Reaction of 9 with acetone (alkylation at C-11) can
then lead to 12 and, after a proton shift via 13 followed
by dehydration, can give the new isopropylidene-2,5-
dihydropyridine 14. Finally, the reaction of the latter
with complex 2 might give complex 5 (Scheme 2).
Confirmation of this assumption could be assessed by
the use of perdeuterated methyllithium to carry out the
deprotection reaction: in that case, the labeled complex
5a D6 was obtained in addition to the other complexes.
Information on the rate-determining step and on the
nature of the transition state in the transformation of
alkylalkoxycarbene complexes into pyridinium ylide
complexes might be obtained by the determination of
the kinetic isotopic effect by means of suitably labeled
dihydropyridines. It is assumed (vide supra) that the
key step in the transformation of carbene complexes into
alkylidene complexes under the influence of di-
hydropyridines is the transfer of a hydride from di-
hydropyridine to the carbene carbon according to Scheme
1.
Preferential hydrogen over deuterium transfers dur-
ing these transformations might be observed, as for the
reduction of organic substrates with dihydropyridines
and especially carbonyl compounds.7 For that purpose,
the two additional labeled and protected 1,2-dihydro-
pyridines 8D5 and 8D1 were synthesized as above by
using an excess of methyllithium in order to avoid the
formation of complexes 5a . Whereas 8D5 led to 10D5
and 11D5, 8D1 led to 10D1 and 11D1. At first glance,
according to the results of eqs 5 and 6, an isotopic effect
close to 3 is detected during the formation of complexes
6a D6 and 7a D5 and of 6a D2 and 7a D1. However, and
as already mentioned, the result of eq 4 indicates that
around 20% of the transferred hydrogens is due to a
secondary reaction, the oxidation of hydrogen-containing
2,5-dihydropyridine 11D6 into pyridine with preferential
transfer of hydrogen to the carbene complex 1a . Thus,
the overall isotopic effect is rather close to 2, a result
1
The H and 13C NMR spectra clearly show the presence
of deuterium at C-14 and C-15 with an almost complete
disappearance of the signals at δ 2.09 and 2.06 ppm in
the 1H NMR spectrum and with broad but weak
multiplets due to carbon-deuterium couplings at δ 22.2
and 20.9 in the 13C NMR spectrum.
Utilization of more than 2 equiv of MeLi suppressed
the formation of complex 5a , acetone being transformed
into tBuOH.
Kin etic Isotop ic Effect d u r in g th e Tr a n sfor m a -
tion of Alk oxyca r ben e Com p lexes in to P yr id in iu m
Ylid e Com p lexes. As the first result of the labeling
experiments (vide supra) we could establish the intro-
duction of a hydrogen atom at C-11 upon deprotection
of perdeuterated 1,2-dihydropyridine and thus demon-
strate the formation of 2,5-dihydropyridine. However,
this experiment led to several additional observations
which warrant mention. First, in the new complex
6a D7, obtained from perdeuterated pyridine, NaBD4,
and complex 1a , close to two hydrogen atoms are
present at C-11, (Table 3, H/D ) 1.85/0.15) where only
one was expected: this means that both atoms at this
position are exchangeable. This might occur either on
2,5-dihydropyridine during the deprotection process or
within the complex 6a D7 during the silica gel purifica-
(6) According to theoretical calculations, 2,5-dihydropyridines are
more stable (less oxidable) than 1,2 and 1,4-dihydropyridines, a result
which explains why they survive in part and why they can be trapped
by the alkylidene complexes (Hamon, L. Private communication).
(7) Verhoeven, J . W.; van Gerresheim, W.; Martens, F. M.; van der
Kerk, S. M. Tetrahedron 1986, 42, 975.

364 Organometallics, Vol. 17, No. 3, 1998
Rudler et al.
Exp er im en ta l Section
Gen er a l Meth od s. 1H, 2H, and 13C NMR spectra were
recorded on Bruker AC-200 or AMX-400 instruments. Column
chromatography was performed with Merck silica gel (70-230
mesh) using various dichloromethane/light petroleum ether
mixtures as eluent. All reagents were obtained from com-
mercial suppliers and used as received. Reactions were
performed under an argon atmosphere in carefully dried
glassware. Solvents were dried by distillation from a drying
agent: THF and Et2O from Na/benzophenone; CH2Cl2 from
CaH2 and P2O5.
Carbene complexes 1a and 1b were prepared according to
published methods.9
Syn th esis of (CO)5WdC(OEt)(CH2)3CtCP h (1c). This
complex was obtained from W(CO)6 (5.2 g, 14 mmol) in a
mixture of pentane (135 mL) and diethyl ether (90 mL) and
PhCtC(CH2)3Li (from the corresponding iodide (4 g, 14.8
mmol) and tBuLi in hexanes (18 mL, 31.1 mmol)) as a yellow
oil (4.0 g, 55%) after filtration on silica gel with petroleum
ether as eluent. Spectral data: 1H NMR (CDCl3) δ 7.46-7.32
(m, 5H, Ar), 4.94 (q, 2H, J ) 7.1 Hz, OCH2), 3.44 (m, 2H,
dCCH2), 2.50 (t, 2H, J ) 6.9 Hz, tCCH2), 1.86 (m, 2H, CH2),
1.66 (t, 3H, J ) 7.1 Hz, CH3); 13C NMR (CDCl3) δ 332.80
(WdC), 203.41, 197.40 (CO), 131.69, 128.38, 127.91 (Ar), 88.66
(CtC), 82.00 (OC), 80.92 (tCPh), 64.28 (tCCH2), 25.27 (2
CH2), 14.85 (CH3). MS (EI 70 eV; m/ e) 524. Anal. Calcd for
which points toward the conclusions that the carbon-
hydrogen bond rupture might be, as in the case of
carbonyl compounds, the rate-determining step in these
complex transformations of alkoxycarbene complexes of
tungsten (and chromium) into pyridinium ylide com-
plexes.
C
19H16O6W: C, 43.52; H, 3.05. Found: C, 43.57; H, 3.09.
Gen er a l P r oced u r e for th e Rea ction of Ca r ben e Com -
p lexes w ith th e Mixtu r es of Dih yd r op yr id in es: Rea ction
of (CO)5WdC(CH3)OE t (1a ). Freshly prepared dihydro-
pyridines (obtained from 1-carbomethoxy dihydropyridine (24.6
mmol) and methyllithium (50 mmol) in diethyl ether (100 mL))
were added at room temperature to the carbene complex 1a
(3.6 g, 8.22 mmol) in diethyl ether (20 mL). The solution
turned rapidly from orange to red. Evaporation of the solvent
gave a residue which was rapidly chromatographed on silica
gel. Elution with dichloromethane/petroleum ether (20/80)
gave (CO)5W(pyridine) (4).1 Elution with dichloromethane/
petroleum ether (25/75) gave complex 5a (0.33 g, 8.5%), mp
112 °C. Elution with dichloromethane/petroleum ether (30/
70) gave complex 6a (0.7 g, 20%). Elution with dichloro-
methane/petroleum ether (40/60) gave complex 7a (1.75 g,
50%). Spectral data for 5a (R ) Me): 1H NMR (CDCl3) δ 8.21
(br s, 1 H, 12-H), 6.59 (ddd, 1H, J ) 10.6, 3.9, and 1.9 Hz,
10-H), 5.91 (ddd, 1H, J ) 10.6, 3.5, and 3.5 Hz, 9-H), 5.43 (br
d, 1H, J ) 22.7 Hz, 8-H), 4.43 (br d, 1H, J ) 22.7 Hz, 8-H),
3.86 (q, 1H, J ) 6.6 Hz, 1-H), 2.18 (d, 3H, J ) 6.6 Hz, 2-H3),
2.09 and 2.06 (2 s, 3H, 14- and 15-H3); 13C NMR (CDCl3) δ
204.1 (CO trans), 202.41 (CO cis), 147.7 (C-11), 144.1 (C-12),
121.8 (C-13), 120.9 and 120.6 (C-9, C-10), 53.0 (C-8), 52.6 (C-
1), 30.1 (C-2), 22.2 and 20.9 (dCMe2). Anal. Calcd for
Exten sion of th e Red u ction Rea ction to Oth er
Ca r ben e Com p lexes. The same types of complexes
were isolated and characterized by starting from the
alkylalkoxycarbene complexes 1b (R ) Bu) and 1c (R
) 5-phenylpent-4-ynyl) which contains a γ triple bond
with respect to the carbene carbon. Thus, the reaction
of complex 1b with an excess of protected 1,2-dihydro-
pyridine and 2 equiv of MeLi led to four new complexes.
Besides W(CO)5Py (4), complexes 5b, 6b, and 7b were
isolated after silica gel chromatography in respectively
3.5, 4.6, and 12.8% yield and were characterized by their
physical data (see the Experimental Section). Similarly,
the reaction of the mixture of dihydropyridines with
complex 1c gave, under the same conditions as above,
a mixture of complexes 4, 6c, and 7c in 10, 14, and 20%
yields. In this latter case, complex 5c, formed in a too
low yield, could not be obtained in a pure state.
Finally, it is important to notice that complexes 5 and
6 were not observed when the reduction of 1 was carried
out with 1,4-dihydropyridine.
C
15H15O5NW: C, 38.08; H, 3.20; N, 2.96. Found: C, 38.16; H,
3.20; N, 2.97.
R ea ct ion of (CO)5WdC(Bu )OE t (1b ) w it h Dih yd r o-
p yr id in es. Under the same conditions as above, complex 1b
gave a mixture of complexes 5b (0.15 g, 3.5%; mp 125 °C), 6b
(0.18 g, 4.6%; mp 85 °C), and 7b (0.5 g, 12.8%). Spectral data
for 5b (R ) Bu): 1H NMR (CDCl3) δ 8.25 (br s, 1H, C-12 H),
6.56 (m, 1H, 10-H), 5.87 (m, 1H, 9-H), 4.85 (br d, 1H, J ) 23.0
Hz, 8-H), 4.46 (br d, 1H, J ) 23 Hz, 8-H), 3.79 (m, 1H, 1-H),
2.30 (m, 2H, 2-H2), 2.05 and 2.00 (s, 3H, 14- and 15-H3), 1.40-
1.15 (m, 4H, 2CH2), 0.90 (t, 2H, J ) 6.7 Hz, 2-H3); 13C NMR
(CDCl3) δ 204.1 (CO), 202.5 (CO), 148.2 (C-11), 145.7 (C-12),
121.7 (C-13), 120.7 and 121.0 (C-10 and C-9), 60.6 (C-1), 52.1
(C-8), 42.34 (C-2), 31.05 (C-16), 22.4 (C-17), 20.9 and 22.3 (C-
14 and C-15), 14.2 (C-18); MS (EI 70 eV; m/ e) 516. Spectral
data for 6b (R ) Bu): 1H NMR (CDCl3) δ 7.85 (br s, 1H, 12-H),
Con clu sion
Although 2,5-dihydropyridine has been detected by
NMR spectroscopy, together with 1,2- and 1,4-dihydro-
pyridines, during the reduction of pyridine with LiAlH4
followed by protonation,8 to the best of our knowledge
the results described herein constitute the first success
in trapping it selectively. Complexes 5 and 6 are thus
best described as the result of the reciprocal stabiliza-
tion of two unstable species, 2,5-dihydropyridines and
(pentacarbonyl)tungsten(0) alkylidene complexes.
(9) Darensbourg, M. Y.; Darensbourg, D. J . Inorg. Chem. 1970, 9,
32.
(8) Tanner, D. D.; Yang, C.-M. J . Org. Chem. 1993, 58, 1840.

Trapping of 2,5-Dihydropyridine by W(0) Complexes
Organometallics, Vol. 17, No. 3, 1998 365
Ta ble 4. Cr ysta l Da ta for C15H15O5NW
5.98-5.83 (m, 2H, 10-H, 9-H), 4.72 (m, 1H, 8-H), 4.22 (m, 1H,
8-H), 3.76 (m, 1H, 1-H), 3.40-3.05 (m, 2H, 11-H2), 2.30 (m,
2H, 2-H2), 1.40-1.15 (m, 4H, 2CH2), 0.91 (t, J ) 6.6 Hz, 15-
H3); 13C NMR (CDCl3) δ 203.8 (CO), 202.5 (CO), 151.5 (C-12),
120.9 and 119.1 (C-9 and C-10), 61.2 (C-1), 51.3 (C-8), 42.5
(C-2), 30.8 (C-11), 28.6 and 22.3 (2 CH2), 14.12 (CH3); MS (EI
70 eV, m/ e) 476. Spectral data for 7b (R ) Bu): 1H NMR
(CDCl3) δ 8.50 (m, 2H, H ortho Py), 7.83 (m, 1H, H para Py),
7.61 (m, 2H, H meta Py), 4.65 (dd, 1H, J ) 9.8 and 5.4 Hz,
1-H), 2.55 (m, 2H, 2-H2), 1.45-1.10 (m, 4H, 13-H2 and 14-H2),
0.85 (t, 3H, J ) 7.0 Hz, 15-H3); 13C NMR (CDCl3) δ 204.9 (CO),
202.2 (CO), 140.2, 136.8, and 127.0 (Py), 64.5 (C-1), 43.9 (C-
2), 31.9 (C-13), 22.3 (C-14), 14.2 (C-15). Anal. Calcd for
fw
473.1
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
6.809(2)
20.928(12)
11.611(4)
90
100.93(3)
90
1625(9)
4
cryst syst
monoclinic
space group
P21/n
72.8
1.93
linear abs coeff µ (cm-1
)
density F (g cm-3
diffractometer
radiation
)
CAD4 Enraf-Nonius
Mo KR (λ ) 0.710 69 Å)
ω/2θ
C
15H15O5NW: C, 38.08; H, 3.20; N, 2.96. Found: C, 38.15; H,
3.17; N, 2.96.
scan type
Rea ction of (CO)5WdC(CH2CH2CH2CtCP h )OEt (1c)
w ith Dih yd r op yr id in es. Under the same conditions as
above, complex 1c gave a mixture of complexes 5c (0.75 g, 14%)
scan range (deg)
θ limits (deg)
temp of measurement
octants collected
0.8 + 0.345 tan θ
1-25
room temp
and 7c (0.92 g, 20%). Spectral data for 5c (R
)
0-8; 0-24; -13 to 13
3208
5-phenyl-4-pentynyl): 1H NMR (CDCl3) δ 8.31 (br s, 1H, 12-
H), 7.35 (m, 5H, Ar), 6.54 (m, 1H, 10-H), 5.85 (m, 1H, 9-H),
4.86 (br d, 1H, J ) 23.0 Hz, 8-H), 4.45 (br d, 1H, J ) 23.0 Hz,
8-H), 3.90 (br s, 1H, 1-H), 2.66 and 2.46 (m, 4H, 2-H2 and 17-
H2), 1.95 (br s, 6H, 2CH3), 1.57 (m, 2H, 16-H2); 13C NMR
(CDCl3) δ 204.0 (CO), 202.3 (CO), 148.8 (C-11), 145.9 (C-12),
131.6, 128.3, 127.8, and 123.7 (Ar), 121.6 (C-13), 120.8 and
120.5 (C-9 and C-10), 89.7 and 81.3 (C-18 and C-19), 59.7 (C-
1), 52.0 (C-8), 41.5 (C-2), 27.6 (C-17), 22.2 and 20.7 (Me), 18.9
(C-16); MS (EI, 70 eV; m/ e) 587. Spectral data for 7c (R )
5-phenyl-4-pentynyl): 1H NMR (CDCl3) δ 8.51 (m, 2H, H ortho
Py), 7.81 (m, 2H, H para Py), 7.55 (m, 2H, H meta Py), 7.30
(m, 5H, Ar), 4.73 (dd, 1H, J ) 10.3, 5.4 Hz, 1-H), 2.72 (m, 2H,
no. of data collected
no. of unique data collected
no. of unique data used
for refinement
2851
2150 ((Fo)2 > 3σ(Fo)2)
R(int)
0.0487
R ()Σ||Fo| - |Fc||/Σ|Fo|
Rw ) [Σw(|Fo| - |Fc|)2/ΣwFo
abs cor
0.0299
2
1/2
]
0.0328 (w ) 1.0)
DIFABS (min 0.86, max 1.33)
extinction param
no. of variables
none
245
-1.11
0.75
∆Fmin (e Å-3
)
∆Fmax (e Å-3
)
mixture of hexadeuterated dihydropyridines (prepared from
pyridine-d5, methyl chloroformate, NaBD4, methyllithium, and
H2O) to give complexes 6a D7 (4%) and 7a D6 (18%). Spectral
data for 6a D7: 1H NMR (CDCl3) δ 4.87 (m, 0.1H, 8-H), 4.19
(m, 0.1H, 8-H), 3.81 (m, 0.25H, 1-H), 3.21 (m, 1.85H, 11-H),
2-H2), 2.43 (t, 2H, J ) 6.0 Hz, 14-H2), 1.49 (m, 2H, 13-H2); 13
C
NMR (CDCl3) δ 204.6 (CO), 201.9 (CO), 140.0, 136.9, and 131.6
(Py), 127.8, 126.9, and 123.8 (Ar), 89.7 and 81.3 (C-15 and
C-16), 63.4 (C-1), 43.2 (C-2), 28.4 (C-14), 16.9 (C-13H); MS (EI,
70 eV; m/ e) 559. Anal. Calcd for C22H17O5NW: C, 47.24; H,
3.04; N, 2.50. Found: C, 47.27; H, 3.11; N, 2.51.
2
2.11 (d, 3H, J ) 6.5Hz, 2-H3); H NMR (CHCl3) δ 7.82 (br s,
1D, 12-D), 5.90 (m, 2D, 9-D/10-D), 4.87 (m, 0.9D, 8-D), 4.19
(m, 0.9D, 8-D), 3.81 (m, 0.75D, 1-D), 3.21 (m, 0.15D, 11-D).
Spectral data for 7a D6: 1H NMR (CDCl3) δ 8.53 (s, 0.1H, H
ortho Py), 4.90 (q, 0.2H, J ) 7.0Hz, 1-H), 2.35 (d, 3H, J )
7.0Hz, 2-H3); 2H NMR (CHCl3) δ 8.5 (sl, 1.9D, ortho Py), 7.82
(br s, 1D, D para Py), 7.59 (br s, 2D, D meta Py), 4.90 (br s,
0.8D, 1-D).
Rea ction of th e Ca r ben e Com p lex (CO)5WdC(CH3)OEt
(1a ) w ith Mixtu r es of Deu ter a ted Dih yd r op yr id in es.
Rea ction w ith Mon od eu ter a ted Dih yd r op yr id in es. Un-
der the same conditions as above, complex 1a reacts with a
mixture of monodeuterated dihydropyridines (prepared from
pyridine, methyl chloroformate, NaBD4, methyllithium, and
H2O) to give the complexes 6a D2 (20%) and 7a D1 (49%).
Spectral data for 6a D2: 1H NMR (CDCl3) δ 7.82 (br s, 1H, 12-
H), 5.91 (m, 2H, 9-H/10-H), 4.87 (m, 0.6H, 8-H), 4.19 (m, 0.6H,
8-H), 3.81 (m, 0.75H, 1-H), 3.21 (m, 2H, 11-H), 2.11 (d, 3H, J
) 6.5Hz, CH3); 2H NMR (CHCl3) δ 4.87 (br s, 0.4D, C-8D), 4.19
(br s, 0.4D, C-8D). Spectral data for 7a D1: 1H NMR (CDCl3)
δ 8.55 (d, 1.6H, J ) 6.0Hz, H ortho Py), 7.82 (m, 1H, H para
Py), 7.59 (m, 2H, H meta Py), 4.90 (q, 0.78H, J ) 7.0Hz, C-1H),
Rea ction of (CO)5WdC(CH3)OEt (1a ) w ith a Mixtu r e
of Dih yd r op yr id in es P r ep a r ed w ith CD3Li. Freshly pre-
pared dihydropyridines (obtained from 1-carbomethoxy dihy-
dropyridine and perdeuterated methyllithium (2 equiv) in
diethyl ether (20 mL)) was added at room temperature to the
carbene 1a (1 g, 2.7 mmol) in diethyl ether (10 mL). The
solution was worked up as above to give, besides complexes
6a and 7a , 5a D6. Spectral data for 5a D6: 1H NMR (CDCl3) δ
8.21 (br s, 1 H, C-12H), 6.59 (ddd, 1H, J ) 10.6, 3.9, and 1.9Hz,
C-10H), 5.91 (ddd, 1H, J ) 10.6, 3.5, and 3.5Hz, C-9H), 5.43
(br d, 1H, J ) 22.7Hz, C-8H), 4.43 (br d, 1H, J ) 22.7Hz,
C-8H), 3.86 (q, 1H, J ) 6.6Hz, C-1H), 2.18 (d, 3H, J ) 6.6Hz,
C-2H3); 13C NMR (CDCl3) δ 204.1 (CO trans), 202.41 (CO cis),
147.7 (C-11), 144.1 (C-12), 121.8 (C-13), 120.9 and 120.6 (C-9,
C-10), 53.0 (C-8), 52.6 (C-1), 30.1 (C-2), 22.2 and 20.9 (m,
dC(CD3)2).
2
2.35 (d, 3H, J ) 7.0Hz, C-2H3); H NMR (CHCl3) δ 8.5 (br s,
0.4D, D ortho Py), 4.90 (br s, 0.22D, C-1D).
Rea ction w ith P en ta d eu ter a ted Dih yd r op yr id in es.
Under the same conditions as above, complex 1a reacts with
a mixture of pentadeuterated dihydropyridines (prepared from
pyridine-d5, methyl chloroformate, NaBH4, methyllithium, and
H2O) to give complexes 6a D6 (7%) and 7a D5 (27%). Spectral
data for 6a D6: 1H NMR (CDCl3) δ 4.87 (m, 0.45H, 8-H), 4.19
(m, 0.5H, 8-H), 3.81 (m, 0.7H, 1-H), 3.21 (m, 1.75H, 11-H), 2.11
X-r a y Str u ctu r e Deter m in a tion . X-ray-quality crystals
were obtained by slow evaporation of dichloromethane from a
solution of complex 4a (R ) Me) in a mixture of dichloro-
methane and hexane. Data were collected at room tempera-
ture on a Nonius CAD4 diffractometer (Table 4). Empirical
absorption correction using DIFABS (minimum 0.86, maxi-
mum 1.33) was applied. Anomalous dispersion terms were
applied, there was no correction of secondary extinction. The
structure was solved by standard Patterson-Fourier techniques
and refined by least-squares analysis using anisotropic
2
(d, 3H, J ) 6.5Hz, 2-H3); H NMR (CHCl3) δ 7.82 (br s, 1D,
12-D), 5.90 (m, 2D, 9-D/10-D), 4.87 (m, 0.5D, 8-D), 4.19 (m,
0.5D, 8-D), 3.81 (m, 0.3D, 1-D), 3.21 (m, 0.3D, 11-D). Spectral
data for 7a D5: 1H NMR (CDCl3) δ 8.55 (s, 0.25H, H ortho Py),
4.90 (q, 0.75H, J ) 7.0Hz, 1-H), 2.35 (d, 3H, J ) 7.0Hz, 2-H3);
2H NMR (CHCl3) δ 8.5 (br s, 1.7D, ortho Py), 7.82 (br s, 1D, D
para Py), 7.59 (br s, 2D, D meta Py), 4.90 (br s, 0.25D, 1-D).
Reaction with Hexadeu ter ated Dih ydr opyr idin es. Un-
der the same conditions as above, complex 1a reacts with a

366 Organometallics, Vol. 17, No. 3, 1998
Rudler et al.
thermal parameters for all non-hydrogen atoms. H atoms
were located on a difference Fourier map, and their coordinates
were refined with an overall isotropic thermal parameter. A
total of 2851 reflections, with I > 3σ(I), were used to solve and
refine the structure to R ) 0.0299 and RW ) 0.0328 (unit
weights; 245 least-squares parameters). The programs used
were Crystals and Cameron.10,11
Ack n ow led gm en t. This research was supported by
the Ministerio de Educacio´n y Cultura (Spain) (post-
doctoral grant to B.M.-V.), the Centre National de la
Recherche Scientifique, and the Ministe`re de
l’Enseignement Supe´rieur et de la Recherche Scienti-
fique. We thank the Laboratoires des Douanes for 2H
NMR facilities.
Su p p or tin g In for m a tion Ava ila ble: Tables of atomic
positional and thermal parameters (2 pages). Ordering infor-
mation is given on any current masthead page.
(10) Watkin, D. J .; Prout, C. K.; Carruthers, J . R.; Betteridge, B.
W. Crystals Issue 10; Chemical Crystallography Laboratory, University
of Oxford, Oxford, U.K., 1996.
(11) Watkin, D. J .; Prout, C. K.; Pearce, L. J . Cameron; Chemical
Crystallography Laboratory; University of Oxford, Oxford, U.K., 1996.
OM9708079