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Mechanism of the Hetero-DielsЦAlder Reaction of Oxadienes and Alkenes Calculation of the AcroleinEthene System.

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determination["] revealed that the bis(dipheny1phosphino)ytterbocene acts as a chelating phosphane ligand to platinum (Fig. 1). Ytterbium has pseudo-tetrahedral eight com C 4 2
C36
c39
Fig. 1. Crystal structure of 4 (H atoms and T H F of solvation omitted for
clarity) Selected bond distances [A] and angles I"] (CT1 and CT2 denote the
centroids of cyclopentadienyl rings C1-C5 and C20-C24. respectively): Yb-CT1
2.422(8). Yb-CT2 2.434(9), mean Yb-C (Cl-C5, C20-C24) 2.71, Yb-01
2.428(8). Yb-02 2.379(6). Pt-Pi 2.288(3). PI-P2 2.290(3), Pt-C18 2.10(1),
Pt-Cl9 2.12( 1); CTI-Yb-CT2 133.6(3). 0 1 -Yb-02 93.7(3), CTI -Yb-01
104.30). CTI -Yb-O2 106.5(3). CT2-Yb-01 106.2(4). CT2-Yb-02 105.5(4).
C18-Pt-Cl9 82.2(5), Pl-Pt-P2 99.4(1). C18-Pt-PI 92.1(4). C19-Pt-PI 174.2(4).
CIX-Pt-P2 168.5(4), C19-Pt-P2 8 6 3 4 ) .
191 T. G. Appleton, H. C. Clark. L. E. Manzer, Coord. Chem. R e , . /(I (1973)
335.
[lo] 4, air-sensitive red plates, C,,H,,O,P,PtYb, M , = 1113.1. triclinic. space
group PT. u = 14.181(4). h = 14.927(5). c = 12.701(3) J = 100.34(2),
[I = 106.87(2), '; = 112.78(3), V = 2238.6 A3, 2 = 2, p ',,,Ld =
1.651 gem--', F(000) 1096, Mo,, radiation 0.71069 8.graphite monochromator, 8- 2 0 scans in the range 1 < 2 0 I 52" at 140(5) K. 8462 independent reflections, 6798 observed (Fo 2 4u(F,>)).Data corrected for
Lorentz and polarization effects, and an empirical absorption correction
applied (min./max. transmission 0 SSjl.17). Solution by Patterson and
Fourier techniques and refinement by blocked-matrix least-squares methods. One coordinated T H F ( 0 2 , C41 -C44) is disordered with two preferred positions for C41, C42. C41 -C44 and other non-hydrogen atoms
were refined with isotropic and anisotropic temperature factors. respectively. Hydrogen atoms were inserted in calculated ( d ( C H) = 1.08 A)
positions with a common isotropic temperature factor. Unit weights were
used throughout the refinement (maximum ratio of shift to error, 0.014)
giving R = 0.038. Two peaks of 3.64 and 3.56 e; A' electron dcnsity in the
final difference Fourier map are associated with the T H F moleculc of
solvation. Calculations with SHELX-76 and anomalous dispersion terms
applied [I 11. Further details of the crystal structure investigation may be
obtained from the Fachinforniationszentrum Karlsruhe. Gcsellschaft fur
wissenschaftlich-technische Information mbH. D-7514 EggensteinLeopoldshafen 2 (FRG), on quoting the depository number CSD-54051,
the names of the authors, and the journal citation.
1111 G. M. Sheldrick: SHELX-76 Progrum fiw C r ~ x t o lS/ruc/urc Dcwrmma/ion, University of Cambridge (UK).
[12] M. F. Lappert, P. I. W. Yarrow, J. L. Atwood. R. Shakir. J. Holton. J.
Chem. Soc. Chem. Cummun. 19x0, 987.
1131 J. M. Wisner, T. J. Bartczuk. J. A. lbers, Organomr/ulltc.v 5 (1986) 2044.
A.
Mechanism of the Hetero-DielsAlder Reaction
of Oxadienes and Alkenes: Calculation
of the AcroleinlEthene System **
By Lutz E Tietze,* Jens Fennen, and Ernst Anders*
ordination (two staggered cyclopentadienyl ligands and
two tetrahydrofuran oxygens), while platinum has approximately square-planar stereochemistry. The Pt . . . Y b distance (5.01 A) precludes any interaction. There is a marked
similarity between the ytterbium geometry of 4 and that of
[Yb(thf),(C,H,SiMe,)2]"21 and between the platinum
stereochemistry in 4 and that for other cis-PtMe,P, complexes.[' 31 Thus, coordination of the organoytterbium ligand
1 to the dimethylplatinum(n) complex to give 4 does not
cause major disruption of the parent structures.
Received: April 19, 1989 [Z 3300 IE]
German version: Angew. Chem. 101 (1989) 1374
CAS registry numbers:
I , 122425-14-3; 2, 122425-15-4; 3, 122425-16-5; 4. 122443-09-8; 4 (without
THF). 122425-17-6; Yb(C,F,),.
66080-22-6; C,H,PPh,,
58109-48-1 ;
PtMe,(cod). 12266-92-1.
[I] D. L. Dubois. C. W. Eigenbrot, A. Miedaner, J. C. Smart, R. C. Haltiwanger. 0rgunornrluNic.v 5 (1986) 1405; R. M. Bullock, C. P. Casey, Ace.
Chem. Res. 20 (1987) 167 and references therein.
121 H. Schumann, Angeu. Chem. 96 (1984) 475; Angew. Chem. In/. Ed.,Engl.
23 (1984) 474.
[3] W. J. Evans. Poljhedron 6 (1987) 403.
[4] C. J. Burns. R. A. Andersen, J. Am. Chem. Sor. 109 (1987) 915.
151 F. Mathey. J. P. Lampin, Tetrahedron 31 (1975) 2685.
[6J G. 8. Deacon. W D. Raverty, D. G. Vince, J. Orgunomrt. Chcm. 135
(1977) 103.
171 1 (yield 46%) and 2 (yield 80%) were characterized by elemental analysis
and spectroscopy. UVjVIS: I (Nujol): i.,,, = 430, 590 nm, (THF): 400,
520 nm; 2(Nujol): 390,510 nm; ' H NMR: 1 (C&D,O,TMS int.): 6 = 5.87
(t. br.. C,H,P), 5.95 (t, J = 3 Hz, C,H,P), 7.17 (m, br., Ph);
"Pi'H) NMR: 1 (THF, 85% H,PO, ext.): 6 = - 20.5.
[XI 3 (yield 79%) was characterized by elemental analysis and spectroscopy.
'H NMR (C,D,O. TMS int.): 6 = 0.22 (t. 3J(HP) = 8 Hz, 'J(HPt) =
68 H7. MePt). 2.30 (s, MePh), 5.74 (s, br., C,H,P), 5.81 (s, br., C,H,P),
7.08 7.21 (m. PhP PhMe), 7.49 (t. 'J(HH) = XHz, PhP).
"P( ' H i NMR (THE 85% H,PO, ext.): b = 17.1 (t. 'J(PtP) = 1920 Hz.
+
A n g w . Chcm. In(. Ed. Engl. 28 (1989) No. 10
Dedicated to Projessor Christoph Riichardt on the occasion qf
his 60th birthday
The Diels-Alder reaction is still--more than 60 years after
its discovery--of special preparative value, since it not only
offers an approach to carbocyclic compounds, but also to a
variety of heterocycles. Furthermore, it is often characterized by high selectivity. The theoretical discussion of this
reaction has focused above all on whether it proceeds by a
synchronous, a concerted two-stage, o r a two-step mechanism involving diradicals o r zwitterions as intermediates."]
Since the temporal sequence of bond breaking and bond
formation is difficult to determine experimentally, quantumchemical calculations have been used to analyze the mechanism of the Diels-Alder reaction.[21The a b initio calculations carried out for the butadiene/ethene system [Eq. (a)] by
E
[*I
[**I
P
Prof. Dr. L. F. Tietze. J. Fennen
lnstitut fur Organische Chemie der Universitit
Tammannstrasse 2, D-3400 Gottingen (FRG)
Prof. Dr. E. Anders
lnstitut fur Organische Chemie der Universitbt Erlangen-Nurnberg
Henkestrasse 42. D-8520 Erlangen (FRG)
Inter- and Intramolecular Hetero-Diels-Alder Reactions. Part 27. This
work was supported by the Deutsche Forschungsgemeinschaft and the
Fonds der Chemischen Industrie. We thank Prof. Dr. P. von R. Schlqvr,
Dr. ?: Clark (Universitbt Erlangen-Nurnberg),and Prof. Dr. M. C. Zo.nrr
(University of Florida, Gainsville, USA) for helpful discussions. Part 26:
M. Buback. W. Tost, T. Hiibsch, E. VoB, L. F. Tietze, Chem. Bcr. 122 ( 1 989)
1 1 7 9 ~1186.
$> VC'H VerlagsgeseNsrhufi mhH, 0.6940 Wcmheim,I989
0570-11833/H9/1010-1371 $02.50/0
1371
Houk et al.,[zblOrtegu et aI.,["l Bernardiet al.,['*] and Gajew-
ski et al.iz'l gave a symmetrical transition state, whereas
Dewur et al.,l'fl using the semiempirical AM IjCI method
(half electron approximation), found an unsymmetrical
diradicaloid intermediate. Calculations for Diels-Alder
reactions of heterodienes such as acrolein have been performed only once, without considering the problem of diradicaloid intermediate^.'^]
In our studies of intramolecular Diels-Alder reactions[41
of heterodienes such as I , readily accessible in situ by condensation of an aldehyde with a 1,3-dioxo compound, we
were able to show that cycloaddition to give 2 [Eq. (b)] very
2
1
likely proceeds in a concerted fashion without the intermediacy of diradi~aloids.~~]
Moreover, we obtained the first experimental proof that this type of reaction proceeds via an
unsymmetrical transition state.[61Here we present the results
of a theoretical study, using the AM1 method, of the intramolecular cycloaddition of acrolein and ethene [Eq. (c)],
E
P
300-
the parent reaction of (b), and we compare the results with
those obtained for the butadiene/ethene system [Eq. (a)].
Our goal was to develop a theoretical framework for understanding the stereoselectivity of the reaction. The most important results of the calculations for reaction (c) are summarized in Table 1.
The assessment of the radicaloid character of intermediates requires quantum-chemical methods capable of treating
Tahle 1. Characteristic data for the hetero-Diels-Alder systems acrolein/
ethene; AM 1 results for reaction (c).
Methodspecies AH,
IkJ
S2
r(C-C) r ( C - 0 )
Ipml
[pml
Coefficients
of the configurations [a]
a'h'
a'
h2
mol-'1
RHF
UHF
CI
TS [b] 126.3 198.7
E
0.7 85.5 194.7
TS1
IN
4.6 152.2
TS2
126.3 198.7
P
-159.3
148.2
E
-33.6
TSl
99.4 184.0
IN
49.0 151.7
TS2
123.7 198.6
P
-182.2
148.1
200.8
~
-
-
-
-
-
-~
354.5
364.2
200.8
137.7
0.836 1.050 0.000 0.000 -
-
-
265.8
358.3
200.9
137.1
-
-
-
-
-
-
-
-
-
0.055 [c]
0.953 -0.298
0.319 [c] -0.656
0.654
0.041 [c]
0.989 -0.142
0.014
0.985 -0.172
[a]a indicates the HOMO, h the LUMO. [h]Dipole moment, 2.104D; charge
separation; arcolein/ethene, - 0.1 3/+ 0.13. For comparison. butadiene/ethene
[2Q: 0.560D. - O.OO/+O.OO. (c]For comparison, a'h' values for hutadienel
ethene [2Q: TS 1 , O.OS5; IN, 0.872; TS2, - 0.241.
1372
open-shell systems. In carrying out these calculations, we
found it advantageous to determine approximately the geometries of the transition states TS or intermediates IN by
using an MMX force field[7a1and to use the results as starting points for the restricted Hartree-Fock (RHF) optimization of the geometries with initially fixed C-C and C-0 bond
lengths. This approach saves CPU time and proved to be
widely applicable.
The enthalpies of formation AH, of starting materials E
and products P were calculated by using the AMPAC[7b1or
VAMP program
All structures were completely
optimized without symmetry restrictions. After the RHF optimization of the geometry, the RHF transition state TS was
completely calculated (NSOIA routine[7d1of the VAMP
program package). Its structure then served as the starting
geometry for calculating the two unrestricted Hartree-Fock
(UHF) transition states TS 1 and TS 2. The determination of
the configuration interaction (CI) transition states TS 1 and
TS 2 is generally straightforward when the UHF transition
states are known and the NSOIA routine is used. The NSOlA
geometries were refinedf7'] and then characterized by a
FORCE calculation.~7f1
NSOI A and SADDLE routine~[~g]
were generally found to give nearly identical results. For
relatively long partial bonds (starting at ca. 240 pm) and
only insignificantly differing heats of formation, NSOI A
afforded somewhat deviating structural parameters. This
may be explained by the overall very flat potential energy
surfaces close to the first transition state TS 1.
For the two reactions (a) and (c), both the UHF and the
CI approximation revealed the existence of an intermediate
IN and thus indicated a two-step mechanism. However, the
energy profiles of reactions (a) and (c) are fundamentally
different both qualitatively and quantitatively (Fig. 1, left
and right, respectively).
$3
VCH ~rlagsgcseilschaflmhH. 04940 Wemheirn,1989
I
AH,
250200-
184.6
IkJ mol -11
148.6
150-
100
-05
-159.33
-182 2
-42.3%
-65 7
~
E
TSI
IN TS2 P
E
TS1 IN
TS2
Fig. 1. Reaction profile for cyclodddition calculated with the semiempirical
methods AM l / U H F (---) and AM l/CI (-). Left: Reaction (a) [2Q. Right:
Reaction (c).
Thus, the second transition state in (c) is higher in energy
than the first and therefore rate-determining. In reaction (a),
the first-nonradicaloid-transition
state initially appears
to be rate-determining owing to its higher energy. The AH,
value of the second transition state must be corrected, however, because of its radicaloid character (see be1ow);I'gI the
resulting increased importance of TS 2 in reaction (a) makes
it impossible to determine which transition state is ratedetermining.
The AH, values calculated by the two open-shell approximations (UHF and CI) differ by only ca. 13 kJ mol-' for
both TS 1 and TS 2 in reaction (c); this value is much smaller
than that calculated for cycloaddition (a) (Fig. 1, left,
AAH'(TS1) = 25.5,AAHf(TS2) = 33.5kJmol-'; the higher
value in each case was obtained from the CI calculation[2g1).
The C-C bonds being formed in the two transition states
0570-0R33/89/folO-r3728 02.SOj0
Angrw. Chem. Int. Ed. Engl. 28 (1989) N o . 10
P
TS 1 and TS 2 of reaction (c) are more similar in length (I 84.0
and 198.6 pm, respectively) than those of reaction (a) (193
and 153.2 pm, respectively). The C-0 bond being formed in
TS 1 of (c) is only 265.8 pm, a very short value compared
with that of the second C-C bond in TS 1 of (a) (498.9 pm).
Comparison of the TS 2 bond lengths in cycloadditions
(c) and (a) shows that the rate-determining transition state
T S 2 of (c) (r(C-C) = 198.6 pm, r(C-0) = 200.9 pm) is surprisingly "symmetric" (TS2 of (a): r(C-C) = 153.2 and
290.3 pm).
The involvement of radicaloids in reaction (c) is usually
expressed by the coefficient contributions to the singlet CI
eigenfunction, composed of the configurations a'b', a2,and
b2 (Table I). though there are a number of other criteria for
determining the extent of mixing of singly excited states;"]
the a 1b' coefficient is particularly suitable. The rate-determining transition state TS2 (a'b' = 0.041) in (c), in contrast
to TS2 of (a) (a'b' = - 0.241), displays almost no radicaloid character, but does exhibit a certain degree of polarity, as revealed by comparison of the dipole moments of the
R H F transition states (footnote [b] in Table 1). An only
slightly higher a ' b ' contribution (0.055) is obtained for transition state TS 1 of (c), whereas the radicaloid character of
intermediate IN is pronounced (a'b' = 0.319). Since the stability of these species is overestimated by the use of such
calculation methods, however, it is necessary to correct the
calculated heats of formation to a more positive value.12']
Although the amount of this correction is somewhat uncertain,'2b,2f1evenan increase ofonly a few kJ mol-' in the heat
of formation of I N in (c) decreases its importance as a sufficiently long-lived and therefore significant intermediate for
the reaction."] Our experimental finding that the configuration of the dienophilic moiety of 1 is retained in the intramolecular hetero-Diels-Alder reaction (b) may thus be
explained on the basis of this A M 1 study.
The essential difference between reactions (a) and (c) lies
in the finding that the total course of the hetero-Diels-Alder
reaction (c) is governed by the structural and energetic properties of transition state TS2. Of particular importance is
the fact that, in contrast to reaction (a), all methods employed here (RHF, UHF, CI) gave very similar results for
TS 2 of (c). Therefore, the much less time-consuming R H F
method may be used for calculating the hetero-Diels-Alder
reaction of oxadienes. Thus, it should also be possible to
describe---at least roughly-more complex transition-state
structures containing substituents of practical relevance with
the R H F method.
Received: June 8, 1989 [Z 3386 IE]
German version: Angew. Chem. 101 (1989) 1420
IS]
[6]
[7]
[XJ
[9]
Kiedrowski. K. Harms, W. Clegg, G. Sheldrick, AngPn.. Chrm. 92 (1980)
130-131; Angeiv. Chem. Int. Ed. Engl. 19 (1980) 134-135.
L. F. Tietze. M. Bratz, R. Machinek, G. von Kiedrowski, J. Org. Chem. 52
(1987) I638 - 1640.
L. F. Tietze. T. Brumby. S. Brand, M. Bratz, Chrm. Ber. 121 (1988) 499506.
a) MMX: K. Steliou, unpublished; b) AMPAC: J. J. P. Stewart, QCPE
No. 506; c) VAMP (T. Clark, Universitat Erlangen-Numberg. unpublished)
is a "vectorized" version of AMPAC 1.0, updated for MOPAC 4.0 and the
CONVEX-C computer series; d) NSOIA is a gradient optimmation routine
described by M. J. D. Poivrll and modified by J. Chundrmrkur, P. H. M.
Budzelaur, and Z Clark (Universitit Erlangen-Nurnberg) for the VAMP
program package; e) PRECISE option of the AMPAC and VAMP program
package; f) only one negative eigenvalue (frequency analysis) is obtained for
all the transition states described here;compare J. W. McIver, A. Kormonicki. J. Am. Chem. SOC.94 (1972) 2625-2633. g) M. J. S. Dewar. E. F. Haley.
J. J. P. Stewart, J. Chen?.Sor. Furudaj. Trans. 2 80 (1984) 227 333.
P. M. Lahti, A. S. Ichimura, J. A. Berson. J. Org. Chew. 54 ( 1 989) 958. 965.
On the basis of ah initio calculations, L. Sukm et al. obtained a comparable
result for substituted reactants in reaction (a). In this case. too. thc existence
of an experimentally hardly detectable. radicaloid intermediate cannot be
ruled out; see R. E. Townshend, G. Ramunni, G.Segal, W. J. Hehrc, L.
Salem, J. Am. C'hem.Sol. 98(1976) 2190- 2198, thestatement o n page 2197.
Generation and Ionization Pattern
of the Iso(va1ence)electronic Compounds
ClP( = 0), and CIP( = S)z**
By Manfred Meisel,* Hans Bock,* Bahman Solouki,
and Matthias Kremer
Dedicated to Professor Christoph Ruchardl on the occasion
of his 60th birthday
According to the "classical" Walsh rules['] tetraatomic
chalcogen-element halides Hal,E = X and HalE( = X), with
24 valence electrons are planar, and in the case of the main
group elements E they form a link between the likewise
planar iso(va1ence)electronic molecules F,B and SO,. In
spite of their fundamental importance as K / G bond models,
only the (diamagnetic) neutral compounds Hal,C = 0
(Hal = F,CI,Br),r21 Hal,C=S (Hal = F,CI),r21 F,C=Se[21
and HalN( = 0),(Hal = F,CI)['] have thus far been characterized by their ionization patterns, since unsaturated derivatives such as F2Si=0[3a1 tend to oligomerize and can frequently only be generated and investigated in noble gas
matrices at low temperatures. The same applies for
CIP( = 0),, which previously had to be either cold-trapped
from rather non-selective gas reactions r3b1 or generated from
~ " ~ in a joint matrix r3d1
CIP = 0 by p h ~ t o l y z i n g ~ozone
(Scheme 1).
+ ;02
CAS Registry numbers:
acrolein. 107-02-8; ethene, 74-85-1
[l] J. Sauer. R. Sustmann,Angew. Chem. 92(1980)773-801; Angew. Chem. I n f .
Ed. EngI. 19 (1980) 779-807.
[2] a) R. Sustmann, P. Daute, R. Sauer, W. Sicking, TetrahedronLett. 29(1988)
4699 4702; b) K. N. Houk, Y. Lin, E K. Brown, J. Am. Chem. SOC.108
(1986) 554-556; c) M. Ortega, A. Oliva, J. M. Lluch, J. Bertran, Phys. Lett.
fff2 (1983) 317-326; d) F. Bernardi, A. Bottoni,.M. A. Rott. M. J. Field,
I. H. Hillier, M. E J. Guest, J. Chrm. Soc. Chem. Commun. 1985, 10511052; e) J. J. Gajewski, K. B. Peterson, J. R. Kagel, J. Am. Chem. SOC.109
(1987) 5545-5546; fi M. J. S . Dewar. S. Olivella, J. J. P. Stewart, ibid. /OX
(1986) 5771 -5779.
[3] 1. Lee. E. S. Han. J. J. Choi, J. Comput. Chem. 5 (1984) 606-61 1 ;see also X.
Balcells, M. Duran. A. Ledos, J. Bertran, J. Mnl. S/ruct. (THEOCHEM)
149 (1987) 153-160.
[4] Review: L. F. Tietze in W. Bartmann, B. M. Trost (Eds.): Selerrivily-A
Goal for Synrhefic Efficiency, Verlag Chemie, Weinheim 1984. p. 299; see
also D. L. Boger. S. M. Weinreb, Hetero-Di~ls-AlderMrthodologs in Organic ~Synrhrsir,Academic Press, New York 1987; 1.F. Tietze, G. von
A n g r n . Chem. In(. Ed. En&. 28 (19891 No. 10
((3
Scheme 1 .
[*I
[**I
(Ar matrix)
Prof. Dr. M. Meisel
Zentralinstitut fur Anorganische Chemie
der Akademie der Wissenschaften
Rudower Chaussee 5 , DDR-1199 Berlin
Prof. Dr. H. Bock, Dr. B. Solouki, Dip1.-Chem. M. Kremer
Institut fur Anorganische Chemie der UniversitZt
Niederurseler Hang, D-6000 Frankfurt am Main 50 (FRG)
Gas-Phase Reactions, Part 76. This work was supported by the Deutsche
Forschungsgemeinschaft, the Fonds der Chemischen Industrie, and by the
Land Hessen. Part 75: H. Bock, M. Bdnkmann, A n g w . Chrm. 101 (1989)
950; Angew. Chem. Int. Ed. Engl. 28 (1989) 91 1.
VCH VerIagsge.~ellvcha~
mhH, 0-6940 Weinhcim, 1989
0570-ff833/#9/fff10-1373 $02.50/0
1313
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