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Bis(tetramethylbutynediol)nickel(0) the First Pure Monoalkyne Complex of Nickel and Its Chemistry.

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lengthened and the C-C bonds shortened, from which a charge
delocalization in the ligand may be concluded. The EPR spectrum
of the crystalline compound displays an intense signal without
fine structure (g = 2.004), which suggests that 2 is paramagnetic.
The spectrum does not change on dissolving the compound in
nonpolar solvents ( g = 2.006). Since in the EPR spectrum of 2 no
half field signal is observed, the dad ligands are independent
radical anions each with spin S = 1/2, and the Be atom is in the
oxidation state 11. Analogous ions also exist in diazadiene complexes of aluminum and gallium. In these compounds only one diazadiene ligand is present as radical ion; the other can be formulated as a n enediamide ion.[to.''I Comparable with 2 are diazddienelanthanide complexes of the type [Ln(NR=CH-CH=NR),]
containing exclusively radical anions on the metal atom. Because the solubility of 2 is too small and its nature is paramagnetic, no interpretable 'HN M R spectrum could be obtained in
[D,]toluene. Surprisingly, however? sharp signals are observed
in the spectrum recorded in [DJTHF. Under the influence of the
donor. 2 is converted into the diamagnetic compound 3 accord-
R'
R'
I
R'
2 THF
R\'
-2
?
THF " N y R
\ /
(b)
RxN-R'
N-
&F
R+N'
R'-N
R
R
\
R'
3
2
ing to Equation (b): an intramolecular disproportionation takes
place in which one of the radical anions transfers its electron to
the other ligand at the Be atom to form a free dad ligand and an
enediamide ion. Possibly a beryllium enediamide intermediate is
formed first and stabilizes by dimerizing with the formation of
enediamide bridging ligands to yield 3. In the 'H N M R spectrum
this reaction can be monitored by the appearance of a singlet for
the methyl protons of the free ligand 1 at S = 2.16 and two
singlets for the methyl groups of the nonequivalent p-tolyl
groups of the enediamide ions at 6 = 2.24 and 2.26. Analogously the 13CN M R spectrum of 1, recorded in [DJTHF, displays the
CH, signal of 1 at 6 = 20.93 and two singlets at 6 = 23.19 and
14.34 for the CH, groups of the enediamide ligands of 3. Similar
structures with enediamide bridging ligands were discussed for
Mg complexes on the basis of N M R data, and were proven for
the Mn complex [{Mn(NPh-CPh=CPh-NPh).THF),] by Xray structure analysis.[41 Dimeric structures and indications of
equilibria in solution are also prevalent in the conversions of
dialkylberyllium compounds with other chelating ligands like
N,N.N',N'-tetramethylethylenediamine, 2,2'-bipyridyl, and
dimethoxyethane." 31
E2yperirnentuI Procedure
2: Anhydrous BeCI, (0.77 g, 9.66 mmol) were added to a solution of 1 (7.5 g,
lY.3 mmol) in toluene (200 mL) at 20'C. The mixture was stirred for 24 h. after
which sodium (0.44 g. 19.3 mmol) was added, and the mixture again stirred for 3
days. during which time the color changes from the initial orange-yellow to deep red
and finall) dark brown. After the solvent was removed under vacuum. the residue
was extracted in a continuous extractor with hot toluene. Compound 2 separates as
a black-green. microcrystalline substance. Yield 3.5 g (46%). Repeated recrystallization from hot toluene produces crystals suitable for X-ray structure analysis.
Correct eleinental analysis ( C , H , N ) ; El-MS (70eV): m;;("A):
786 (75) [ M ' ] . 388
(45) [ d a d ' ] . 194 (100) [Me-4-C,H4N=CPh+].
Ari,q<m.C h i w h i . Ed. €nji/. 1994, 33. N o . 13
sn
3: ' H NMK (300 MHz, [DJTHF, 25 C ) : 6 =7.85- 6.40 (m, C,H,. C6H,-4-Me).
2.26. 2.24 (s. C6H,-4-Me); "C NMK (75 MHz [DJTHF. 25 C ) : 6 = I 5 0 120
(C,H,. C6H,-4-Me). 23.2. 14.3 (C6H,-4-.Me).
1: ' H N M R (200 MHz. [DJTHF. 25 C ) : 6 = 2.16 (a. 6 H . C,H4-4-Mr). 6.82 (d.
= 8 Hz, C6H,-4-Me). 6.44(d. 4 H . ' 4,,,,, = 8 Hz. C6H,-4-Me), 7.82 (m,
4H.
4H. C,H,). 7.32 (m, 4H. C,H,).
Received: December 27. 1993 [Z65781E]
German version: Anjiew. Chwi?. 1994. 106. 1461
[ I ] J. Scholz. M. Dlikan. D. Strohl. A. Dietrich. H. Schumann. K -H. Thiele.
Chein. Bw. 1990, 123. 2279 2285.
[2] .I.Scholz. A. Dietrich. H. Schumann, K.-H. Thiele. Chcm. Bcr. 1991. 124.
1035-1039.
131 a ) P. Clopath. A. von Zelewsky. J. Chmm. Soc. C'hrm. Conirnun. 1971. 47 48:
b) P. Clopath, A. von Zelewsky. Hdi,. Cliim. A c t a 1972. 52-67.
[4] D. Walter. U. Ritter. R Kempe. J. Sieler. 6. Undeutsch, Cheni. Brr. 1992, 125.
1529-1 536.
[S] M. Rieckhoff, U. Pieper, D. Stalke. F. T. Edelmann. A n p i c . Chcin. 1993. 105.
1102-1104, Angew. Cliein. 1171. Ed. Engl. 1993. 32. 1079-1081.
[6] X-ray crystal structure analysis for 2 (BeN,C,,H,,): M = 786.03. black-green.
dense crvstalO.8 x0.5 x0.5 mm. mounted in a auarz tube under nitrozen with
two-component adhesive. data collection temperature 20' C, monoclinic, space
group P2,:c (no. 141, u =1284.0(5), h =1530.8(4), c = 2353.9(4) pm. [j =
101.54-. V = 4530.1 A3, Z = 4,p,,,,, = 1.152 gcm-'. 20,,,, = 50 , Mo,, radiation,;. =71.069 pm,d2Uscan.Ir = 0.070 mm-'.F(000) =1664.0.X660reflections 111 the range 20 = 2 - W , reflections with 0 z 18 consistently will1
I < 2 u ( 1 ) ,3111 independent reflections with I > 2 4 1 ) . 194 parameters. residual electron density + 0.41;-0.31 e k 3 , K = 0.086. R, = 0.083. Enraf-Nonius CAD4 diffractometer; solution and refinement with SHELXTL-PC. The H
atoms were positioned geometrically (riding model) and the phenyl groups
were refined as rigid groups. Further details of the crystal structure investigation may bc obtained from the Fachinformationszentrum Karlsruhe. Gesellschaft fur wissenschaftlich-technischeInformation mbH. D-76344 EggensteinLeopoldshafen (FRG) on quoting the depository number CSD-581X7 and thc
journal citation.
J. L. Atwood. G. D. Stucky, J A m . Chein. Soc. 1969. 91. 4426-4430.
A. H. Clark, A. Haaland. Acra Chrm. Scund. 1970. 24. 3025 3(130.
J. Wunderle. J. Scholz, R. Frohlich. Z. Kri.md/oxr. 1993, 208. 277-279.
F. G . N. Cloke. G. R. Hanson. M. J. Henderson, P. B. Hitchcock. C. L.
Kaston. J Chrni. SOC.Chiwn. Commun. 1989, 1002-1003.
F. G. N . Cloke, Ch. I. Dalby, P. J. Daff. J. C. Green. J. C h ~ ~ i Sn .w . Ilo//on
Truns. 1991, 181 -184.
a) F. G . N. Cloke. H. C. de Lemos, A. A. Sameh, J. Chrm. So(.. Chcni. Cni77mun. 1986, 1344-1345; h) F. G N. Cloke. Chem. Soc RFI.. 1993. 17 24.
G. E. Coates. S. I. E. Green, J. Cken7. So<. A 1962, 3340-3348.
-
Bis(tetramethylbutynediol)nickel(o) , the First
Pure Monoalkyne Complex of Nickel and Its
Chemistry**
Dirk Walther,* Andreas Schmidt, Thomas Klettke,
Wolfgang Imhof, and Helmar Gorls
"Pure" alkyne complexes of nickel, which exclusively contain
monoalkynes as ligands can be considered an attractive goal in
organometallic synthesis as numerous catalytic transformations
of alkynes on nickel(0) centers are known. The simplest stable
compound should be of the type [Nio(alkyne),]; however. such
complexes have not previously been isolatedr'] even though
stable platinum(0) complexes of this type exist.[*]
[*] Prof. Dr. D. Walther. Dip1.-Chem. A. Schmidt. T. Klettke
Iiistitut fur Anorganische und Analytische Cheinie der Universitit
August-Bebel-Strasse 2, D-07743 Jena (FRG)
Telefax: Int. code + (3641)6-35538
Dr. W. Irnhof. Dr. H. Gorls
Max-Planck-Gruppe C0,-Chemie, Jena
[**I
This work was supported by the Dsutsche Forschungsgemeinschaft (SFB 247.
Heidelberg). the Max-Planck-Gesellschaft (Arbeitsgruppe C0,-Chemie) and
the Fonds der Chemischen Industrie.
VCH Ver/ujis,ocse//.rchuffmhH. 0.69451 Weinheim,1994
0570-0833/Y4i1313-/373 .%
10.00
+ .25:0
1373
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We report here on the synthesis of bis(tetramethy1butynediol)nickel(O) ( I ) the first stable alkyne-nickel complex, which
contains solely monoalkynes as ligands and which is formed
surprisingly easily by treating [Ni(cod),] (cod : cycloocta-I .5-diene) with alkyne [Eq. (a)] in boiling T H F (reaction time 6 h).
Compound 1 can be obtained from THF/hexane as lemon yellow crystals.
CH,
CH,
I
I
[ N i ( ~ o d )+~ ]2 HO-C-C=C-C-OH
-’
CH,
I
[Ni((HO-C-C+2j,]
I
I
I
CH,
CH,
CH3
1.86 A-that the alkyne ligand acts as a four-electron donor.[’I
In contrast, the alkyne has to be considered a two-electron ligand in compounds of type [NiL,(butynediol)], where the solidstate structure is also influenced by hydrogen bonding.[41
Compound 1 shows a rich chemistry, which will be illustrated
by three examples : Addition of N,N,N‘,N‘-tetramethylethylenediamine (tmeda) to 1 results in displacement of one alkyne ligand and formation of an intermediate, which, however, is not
isolated but instead reacts further with 1 [Eq. (b)] to yield the
(a)
1
1
+ tmedd
-
’
[Nl(trnedd)(~~-(HOC(CH,)~C$~)1
f
[(tineda)Ni :/I-(HOC(CH 3)zC$ z)Ni [(HOC(CH,),C +,)I
(b)
L
According to the results of the crystal structure analysis[3]
(Fig. 1) the nickel(o) center is surrounded by four C atoms of the
alkyne groups in a distorted tetrahedral fashion. Ni-C and
C-C bond lengths as well as the C=C-C bond angles lie within
the expected range. N o agostic interactions are observed for the
H atoms of the CH, groups and the nickel center; hence, compound 1 truly is an alkyne-nickel(0) complex.
deep red, binuclear complex 2. Binuclear nickel(o) complexes
stabilized by phosphane-containing bridging and terminal alkyne
ligands are already known for e t h ~ n e . [ ~ ’
The crystal structure analysis of 2 showed that the molecules
are connected by four intermolecular hydrogen bonds to give a
double-stranded structure (Fig. 2) .[31 Furthermore, there are
two intramolecular hydrogen bonds between bridging alkynes
and between bridging and terminal alkynes. In contrast to 1, the
two O H groups of the terminal alkyne are far appart.
%P
c1
Fig. 1. Structure of molecules 1 and their packing in the crystal (the methyl groups
were omitted for clarity). 0 : 0. a:Ni. 0 : C. ---: H bonds. Selected bond lengths
(A] and angles I1: Ni-Cl 1.90(1), Ni-CZ 1.851(9j, Ni-C9 1.905(7). Ni-CIO 1.82(1),
C K 2 1.278(7). C9-CI0 1.21(1). 0 1 - 0 3 A 2.74, 0 1 - 0 4 A 2.76. 0 2 - 0 3 A 2.72. 0 2 0 4 A 2.81 ; CI-Ni-C2 39.8(2). C9-Ni-CIO 37.7(3), C2-C1-Ni 68.1(8). Ni-CZ-Cl
72 l(7). CIO-C9-Ni 67.3(7). Ni-ClO-C9 75.0(8). CZ-Cl-C3 156(1). CI-C2-Ch
154(1). ClO-C9-C11158(1). C9-CtO-Cl4 152(1).
In the solid state the molecules are connected by four intermolecular hydrogen bonds between neighboring, coordinated
butynediols. The resulting polymer-like chain structure consists
of C, tetrahedra that surround the coordinated nickel(0) and 0,
tetrahedra; the two types of tetrahedra are separated by CMe,
“spacer” groups. (Fig. 1, bottom).
As expected, two signals (for CH, and OH) are observed in
the ‘H N M R spectrum ([DJTHF) of I . In addition to the signals for the C(CH,), groups. the I3C NMR spectrum exhibits
one signal for the coordinated alkyne carbon atoms at 6 = 206.
This strong deshielding of the alkyne carbon atoms in 1 indicates- in conjunction with the short average Ni-C distance of
c5
o2
c7
Fig. 2. Structure ofmoleculeh 2 and their packing in the crystal ( d . Fig. I ) . Selected
bond lengths [A] and angles I ] :Nil-Ni2 2.449(1). Nil-CI 1.879(2). Nil-C2
1.907(2). Ni2-Ci 1.968(3). NiZ-CZ 1 938(3j, Cl-C2 1.344(3). Nil-NI 2.024(2), NilN2 2.035(2). N G C 9 1.847(2), N i l - C l 0 1.876(3). C9-ClO 1.268(3), 0 1 - 0 2 2.727.
0 1 - 0 3 2.900. 0 1 - 0 3 A 2.735. 0 3 - 0 1 A 2.735. 0 2 - 0 4 B 2 726. 0 4 - 0 2 C 2.726; Nil49.86(7).
CI-Ni? 79.04(9). Nil-C?-NiZ 7 9 . l ( l ) . Nil-Ni2-CI 48.86(7). Nil-NiZ-CZ
NiI-C2-C1 68 l ( 1 ) . Ni2-CI-C2 68.7(1). Ni2-Nil-Cl 52.10(7). Ni?-Nil-C:! 51.01(8).
C1-Nil-C? 41.59(9), Ni2-C2-C1 71.1(1). CI-Ni2-C2 40.24(9). Nil-CI-CZ 70.3(1),
N1 -Nil - N 2 87.25(9), C3-CI -C2 136.9(2). C6-C2-C 1 138.4(2), C11 -C9-ClO
152.1(2). C14-C10-C9 149 6 ( ? ) .
As the catalytic cyclotetramerization of alkynes probably proceeds via binuclear nickel species,r612 can be regarded as a model
compound for the initial steps of this reaction. Its structure
makes it plausible that O H groups-fixed in distinct positions
by hydrogen bonds--can influence the selectivity of C-C bond
formations (cf. Ref. [7]).
COMMUNICATIONS
Substitution of an alkyne in 1 by a ligand without functional
groups yields compound 3 [Eq. (c)] in which the OH groups
I
+ cod
[Ni(cod)j(HOC(CH,),CSzl]
3
(c)
form both intra- and 3 intermolecular hydrogen bonds to neighboring complex molecules. This leads to a third "connecting"
principle in the crystal, which results in a polymeric chain with
helical structure for the coordinated alkynols (Fig. 3) .[31
Fig. 4. Structure of molecules 4 and their packing in the crystal (for clarity the
phenyl groups are represented in the figure by the ipso carbon atoms). Selected bond
lengths [A] and angles 1 I: Ni-PI 2.1892(8), NI-PZ 2.1895(8), Ni-Cl 1.8X. Ni-C2
1.914(2),Cl-C2 1.260(4).01-022.640.01~N2.911,01X-022.~05.02-02A
2.828.
P1-Ni-P2 101.86(3), CI-Ni-C2 38.7(1), C3-CLC2 142.2(1). C6-C2-C1 139.9(2).
P
thermal stability of the solid-state structures but are also of
significance in solution.
Fig. 3. Structure of molecules 3 and their packing in the crystal (cf. Fig. I . in the
bottom figure the cod ligand is represented by its center of gravity. 0 3 and 0 4
represent the hydroxyl groups of the second symmetry-independent molecule of 3).
Selected bond lengths [A] and angles ['I. Nil-Cl 1.6:68(6), Nil-C2 1.854(6). Nil-C9
2.079(9). Nil-C10 2.064(8). Nil-C13 2.06:0(6:),Nil-C14 2.055(6:), CI-C2 1.251(9),
0 1 - 0 2 2.75, 01-04.4 2.74.02-03B 2.79; Cl-Nil-C2 39.3(3), C9-Nil-C10 37.4(3),
CIO-Nil-C13 84.6(4), C13-Nil-Cl4 3X.3(4), C14-Nil-C9 X6.X(5). C3-CI-C2
144.5(6). C6-C2-C1 142.X(6).
Rupture of the polymeric structure can be achieved by compounds that can interact with the O H groups of the alkynes but
do not possess element-H bonds suitable for hydrogen bonding. For example, compound 4, formed by treating 1 with Ph,P
in acetonitrile [Eq. (d)], has a dimeric structure in the crystal.
1
+ PPh,
+
[Ni(PPh,),i(HOC(CH,),~,)]
(a
4
Acetonitrile is disordered in the crystal and binds to one OH
group of the alkynediol. An intermolecular hydrogen bond between neighboring monomers and two intramolecular hydrogen
bonds complete the binucledr structure (Fig. 4) .I3]
The special significance of the OH groups becomes apparent
when comparing the formation reactions of 1-3 with the reaction of the diinethoxy derivative of tetramethylbutynediol with
[Ni(cod),]. When using this alkyne under the reaction conditions which otherwise cleanly yield 1. thermal decomposition to
elemental nickel is observed. Therefore, attempts to synthesize
a binuclear complex analogous to 2 yielded only decomposition
products.
This strengthens the notion that peripheral influences (here
hydrogen bonds) d o not only play a role in the formation and
Experimental Procedure
All reactions were carried out under an inert argon atmosphere.
1: 10 mmol [Ni(cod),] and 20 mmol tetramethylbutynediol were relluxed in 30 m L
T H F for 6 h. After removal of T H F and cod by vacuum destillation followed by
addition of ether, the reaction product was collected on a filter and washed with
hexane. Yield. approximately 60%, lemon yellow powder; single crystals were
obtained from THF:hexdne. IR (Nujol) i =1889cm-' ( C = C ) , 3271 c m - ' (OH)
' H N M R ([DJTHF): 6 =1.36 (s. CH,). 2.08 ( s , O H ) . I3C N M R ([DJTHF).
6 = 32.1 (CH,), 69.9 (CMe20H). 206.3 (C-C) [XI.
2: To a solution of 1. prepared in situ by treating 2.6: mmol [Ni(cod),] with 5.6 mmol
alkyne. was added 10 mmol tmeda, and the mixture was stirred for 2 h. The solution
was reduced in volume, and after layering with hexane. red crystals of 2 werc
obtained. IR (Nujol)? =1573cm-' ( C s C ) . 1842cm-' (C-C), 3266cm-l ( O H ) .
' H N M R ([DJTHF): 6 =1.30-1.60 (m. CH,), 2.13-2.29 (m. CH,), 2.50 (s,
N-CH,), 2.78 (5. N-CH,). 3.44 (s, OH), 3.83 (s, OH), 4.20 (s. O H ) . "C NMR
([DJTHF): ii = 32.7 (CH,), 33.5 (CH,). 46.1 (CH,), 49.3 (N-CH,). 50.6
(N-CH,). 58.9 (CMe,OH). 59.5 (CMe,OH), 117.9 ( C = ) [8].
3: Compound 3 is prepared as described above for 1 from equimolar amounts of
[Ni(cod),] and alkyne. Orange powder: ~inglecrystals were obtained from THF,'
'HNMR([D,]THF):
hexane. IR(Nujol)? =1807cm-'(C~C).3?47cm-'(OH).
6 =1.2X (s. CH,), 2.0-2.4 (m, CH,). 4.24 (s. OH). 5 39 (s. C H = ) . " C N M R
([DJTHF): 6 = 30.8 (CH,), 32.0 (CH,), 70.0 (CMe,OH), 94.7 (CH=). 137.1
(C-C) [8].
4: Compound 4 WAS prepared from [Ni(Ph,P),(tetramethylbutynediol)] [4c] in hot
acetonitrile. I R (Nujol) ? =1770cm-' (C-C). 2 2 1 5 c m - ' ( C = N ) . 32X6cni ~'
(OH) PI.
Received: February I . 1994
Revised: March 11. 1994 [Z6661 IE]
German version. An,qen.. Chew. 1994, 106. 1421
[ l ] a) E. L. Muetterties, W. R. Pretzer. M. G. Thomas, B. F. Beier. D. L. Thorn,
V. W. Day, A. B. Anderson. J. A m Chrw. Soc. 1978, 100, 2090 2096: b) G. A.
Orin, D. F. McIntosh, W. J. Power. R. P. Messmer, Inor,q. Cl7en7. 1981.20.17821792: c) A Ni(o) chelate containing macrocyclic trisalkyne ligand has been reported: J. D. Ferrara. C. Tessier-Youngs. W. J. Youngs, J. A m < ' / i c m i . Soc. 1985.
107. 6719-6721.
COMMUNICATIONS
121 F D Rochon. T. Theophanides, Cwr. J. Chew 1972. SO. 1325-1327: b) R. J
Dube).. , 4 c / f / .C ~ I ~ . S / ~ /Set-i.
/~J,~
B / -197s.
.
31, 1860- 1x64: c ) N. M. Boag. M
Green, D. M. Grove. J. A . K. Howard. J. L. Spencer. F G. A. Stone. J. C'licwi
Soc. D ~ l i f~i r~mn. 1980. 2170-2190.
[3] Ci-ystal data. Ma,, .; = 0.71069 A. <r)-?it-scan.structure solution: direct methods (SHELXS-86). refinement on IF1 (SHELXLY?). hydrogen atoms were
calculated in idealized positions unless otherwise noted. 1. 0.2 x 0 . 2 0.1
~ mm.
monoclinic. Cc, i/=15.524(3). / I = X.520(2). < =15.5XX(3) A. /I =108.64(3) .
C =1953.6(7)A3. L = 4 . pc,,,cc,=l166gcm-'. T = 2 9 3 K . ~ 1 = 1 . 0 1 1 m m ~ ' .
4262 measured reflections (triclinic). 2578 sbmmetry-independent reflections. of
which 2014 were observed ( I > 2 0 ( / ) ) . 206 parameters relined. R, = 0.0477.
ii R2 = 0 1020. residual electron density 0.234 e k ' . 2 . 0 6 x 0.4 x 0.3 inm. triclinic. PT. o = 9.418(4). h = 9.601(5). c =15.508(6) A. Y = 103 54(3), [j =
9?.?9(4), ; ' = 1 0 2 . 7 7 ( 5 ) . l~~'=l320(1),&.",Z = 2 .
=1.303gcm-'. T =
193 K. 11 = 1.463 mm I . 4807 meatured reflections, 4616 symmetry-independent reflection\ of which 4199 Bere obserbed ( I > 2u(1)).292 parameters refined,
R , = 0.0299. ii.R2 = 0.0751. residual electron density 0.591 e k ' . 3:
0.4 x 0 3 x 0.1 mm. monoclinic. P
. (I = 9.450(2). h = 23 159(5). ( =
15.522(3)A./j=102.77(3). V = 3 3 1 3 ( 1 ) ~ ' , ~ = 8 . ~ ~ , , , , , = 1 . ? 3 9 g c m
T=
~~.
293 K. 11 = 1.176 mm-'. 5419 measured retlections. 5208 symmetry-independent reflections of which 3710 were observed ( I > 2 u ( I ) ) .408 parameters refined.
R, = 0.0765. wRZ = 0.1505, retidual electron density 0.481 e k ' . The unit cell
contains t w o independent molecules of 3 pcr asymmetric unit. The olefinic
hydrogen atoms of the cod ligand were determined by difference Fourier analysis and refined uithout parainetric constraints Because of poor crystal quality
and disorder problems with the cod Iigands. thcir C atoms could only partially
be refined isotropicall>. 4: 0.4:0.38;0.36 min. monoclinic. c'2;~.,(1 = 19.809(4),
/ J =12.564(3). c = ~ ? . ~ x x ( ~/j )=10?.9s(3)
A.
, v=7953(3)A3. Z = X. p,,$,,,, =
1.246 Fcm-', T = 293 K , 11 = 0.605 m m - l . 9207 measured reflections. 9046
aymmetr?-independeiit retlections. of ~ h i c h7012 were observed ( I 2 u ( / ) ) ,
449 parameters refined. R, = 0.0469. 11 R , = 0.1170, residual electron densit)
0.46 e k ' Further detail? of the crbstal structure investigation may be obtained
from the FachinthrmationsLentrum Karlsruhe. D-76?44 Eggenstein-Leopoldshafen (FRG). o n quoting the depository number CSD-58133.
;i) R. Diercks. J. Kopf. H. tom Dieck. .4cin c ' r ~ . v d / o g rSwi.
.
c' 1984, 40. 363365: our own m;ilysrs o f rhe 3tructure data show the presence ofdiiners, which
are as i n 1 connected by lour hydrogen bonds: b) H. Gorls, B. Schula, U.
Rosenthal. W. SchulL. C,:l..u. Ro.. f i , d i f i d 1988. 13. 25 33: c) U. Rosenthal, H.
Gdrls. J. Or,qmrmw/.c ' l w f ~ i .1988. 348. 135- 138.
K.-R. Porschke. J Ani. C'herri. Sot, 1989. / / / , 5691-3699.
G. Wilke. Pure Appl. Ckcw 1978. 60. 677-690.
H. tom Dieck. A . M. Lauer. L. Slamp. R. Diercks. J. Mol. Cuiul. 1986. 3S.
317 325: b) D Walther. D . Braun. W. Schulz. U . Rosenthal, Z. Airorg A//g.
C h r . 1989. 577. 270-282.
Correct elemental analyses (C. H. Ni).
J. Templeton. MI,.Orgorroriiei Chwrr IY8Y. 1 Y , I .
~
been suggested that thermal pericyclic reactions take place preferentially through aromatic transition states.15] Although the
parent Diels-Alder reaction between butadiene and ethylene is
taken as the prototype of pericyclic processes.[6J the energy of
concert is relatively small.[']
We now apply magnetic properties as criteria[+
' I b ]to
investigate the nature of concerted transition states for the first
time specifically for the Diels-Alder reactions of ethylene both
with butadiene and cyclopentadiene. While the magnetic properties of transition states cannot be measured, both chemical
shifts and magnetic susceptibilities can be computed conveniently. The accuracy of the IGLO" l a ] results for ground states
suggest that they may be applied to analyze the nature of transition structures as well. Moreover, we examine the changes of
chemical shifts and magnetic susceptibilities along the reaction
path for the reaction of ethylene with butadiene. These results
are presented in Figures 1 and 2.
The geometries of the individual points on the reaction coordinate were optimized at the ab initio RHF/3-21G level['21within the C, point group. and were employed for IGLO calculations
with a Huzinaga DZ basis
During the reaction (read
Figures from right to left), eight of the ten olefinic protons of
''3
8-
i
L
7 --
6 -5 --
t 1:
2.1 --
1
-'
-2
Magnetic Properties of Aromatic Transition
States: The Diels-Alder Reactions**
Rainer Herges,* Haijun Jiao,
and Paul von R a p e Schleyer
r1A1
30
-
Fig. 1. Calculated ' H chemical shifts in the retro-Diels-Alder reaction of cyclohexene as a function of the ofreaction coordinate I'. The total energy curve €,,,(reaction
profile) is depicted with a broken line [8a]
-1004
Dctlicnted to Professor Werner Kutzehigg
011 tiii. occavon of hi^ 60th birthdo).
Evans et al. first recognized the analogy between the n electrons
of benzene and the six electrons in the cyclic transition state of
the Diels-Alder reaction of butadiene and ethylene."] Generalized through the Woodward - Hoffmann rules[21and the HiickelMobius m e t h ~ d ' ~to
. ~many
'
pericyclic reactions. it has often
[*IPriv.-DoL. Dr.
R. Herges. Dip[.-Chem H. J i m , Prof. Dr. P. v. R . Schleyer
Computer-Cheniie-Centrum
lnstitut fur Organische Chemie der Universitit Erlangen-Nurnberg
Henkestrasse 42. D-91054 Erlangen ( F R G )
Telefiix: Int. code + (9131385.9132
[**IThis work u a s supported by the Deutsche Forschungsgemeinschaft and the
Fonds der Chemischcii Industrie. The authors thank Prof. W. Kutzelnigg for
suggesting that magnetic susceptibility might be used to characterize aromatic
transition states. Dr. U. Fleischer also provided helpful comments. H. J. 17
grateful for a fellowship of the Shnnxi Normal University.
L, 1.6.
18
2
22
rlAl
2.4
2.6
Z.-.O
Fig. 2. Calculated diamagnetic susceptibility and total energy E,,,, of the reaction
in Fig. 1 as a function of the reaction coordinate r
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