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Formation of a 2 5-Diborabicyclo[2.1

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f ) K. A. Caldwell, D. E. Giblin, M. L. Gross, ibid., in press; g) E. E. B.
Campbell, R. Ehrlich, A. Hielscher, J. M. A. Frazar, I. V. Hertel, 2.Phys.
D.,in press; h) T. Weiske, J. HruSak, D. K. Bohme, H. Schwarz, Helv.
Chim. Actn 1992, 75, 79; i) R. C. Mowrey, M. M. Ross, J. H. Callahan, J.
Phys. Chem., in press; j) Z. Wan, J. F. Christian, S. C. Anderson, .
Chem.,in press; k) J. HruSak, D. K. Bohme, T. Weiske, H. Schwarz, Chem.
Phys. Lett., in press.
[5] T. Weiske, T. Wong, W. Kratschmer, J. K. Terlouw, H. Schwarz, Angew.
Cheni. 1992, 102, 180; Angew. Chem. Int. Ed. Engl. 1992, 31, 183.
[6] a) R. F. Curl, R. E. Smalley, Spektr. Wissensch. 1991, No. 12, p. 88; Sci.
Am. 1991, 265, No. 4, p. 32; b) R. E. Smalley in Large Carbon Clusters
[ACS Symp. Ser. 48f (Eds.: G. S. Hammond, V. J. Kuck)], Am. Chem.
SOC.,Washington, DC, 1992, p. 141.
[7] The negligible insertion of two 4He atoms in C;: under multiple-collision
conditions in one collision cell was described by Gross et al. [see 4e].
[XI a) R. Srinivas, D. Siilzle, T. Weiske, H. Schwarz, Int. .IMass Spectrom. Ion
Processes 1991, 107, 369; b) R. Srinivas, D. Siilzle, W. Koch, C. H. DePuy,
H . Scbwarz, J. Am. Chem. SOC.1991, 113, 5970.
[9] a) C. G. Macdonald, M. J. Lacey, Org. Muss Spectrom. 1984, f 9 , 5 5 ; b)
J. R. Chapman, Practical Organic Mass Spectrometry, Wiley, Chichester,
1985, Chapter 6.
[lo] We have also carried out the reverse sequence, i.e. initial insertion of 4He
and then 'He (C;' triplets with Am = 4, 7). As a result of the energetics
of the inelastic collisions [see 4 f,rj] we were not surprised to observe that
the relative transmittances for the production of [3He4He(@C,]'t are different from those for [4He3@C,rt ( x = 60-52). Analogous considerations are also valid for the production of [4He,(a',Cxr+ (C;' triplet with
Am = 4, 8).
2,4-position and by H migration, the carborane 2 with an
isopropyl and an isopropenyl substituent is formed, whose
constitution was determined by the measurement of nuclear
Overhauser effects (NOE) in the proton NMR.
Scheme 1. "B NMR data for 1: 6 = 33, 66; for 2: 6 = -42, 24
Whereas amino-substituted diallenylborane and diallenyldiborane(4) derivatives are
the bicycle 1 is unexpectedly formed from the reaction of 1,2-di-tert-butyl-l,2di~hlorodiborane(4)[~1
with 3,3-dimethylallenyllithium in
48% yield. The crystal structure analysis of 1 (Fig.
shows a I-boretane bridged in the 2,4-position. The strong
Formation of a 2,5-DiborabicycIo[2.l.l]hexane
Derivative and Its Conversion
to a Tetracarbahexaborane**
By Markus Enders, Hans Pritzkow, and Walter Siebert*
Dedicated to Professor Worfsang Beck
on the occasion of his 60th birthday
Preparative and theoretical investigations into the stability of the C,B, compounds A,['] B,['I and CI3I have shown
that the conversion of the organoborane into the carborane
structure is controlled by the substituents R bound to boron.
With one amino and one methyl substituent the carborane is
still stable; two amino substituents (R = N iF'r,) lead to the
bicycle D. The temperature-dependent 'H NMR spectra indicate that C and D are in e q ~ i l i b r i u m . ~ ~ '
Herein we report a new reaction path to the tetracarbahexaborane B from the unsaturated organoborane 1, a framework isomer of D (Scheme 1). In 1, as in D, two sp2 hybridized B and C atoms as well as two sp3 hybridized C
atoms are present in the C,B, framework; a nido-carborane
formation is not hindered by the substituent at boron but by
the two K systems. After rearrangement of 1 into a 1,3-diboretane bridged by the two isopropylidene groups in the
Prof. Dr. W. Siebert, DipLChem. M. Enders, Dr. H. Pritzkow
Anorganisch-Chemisches Institut der Universitat
Im Neuenheimer Feld 270, D-W-6900 Heidelberg (FRG)
This work was supported by the Deutsche Forschungsgemeinschaft (SFB
247), the Fonds der Cbemischen Industrie, and the BASF AG.
Fig. 1. Molecular structure of 1. Selected distances [A] and angles ["I: B1-C3
1.744(9), B1-C2 1.658(8),B1-C4 1.595(9), C2-C3 1.491(7),C3-C4 1.501(7), C3C31 1.370(6), C2-B5 1.521(7), C4-C6 1.483(7), B5-C6 1.584(8), C6-C61
1.344(6); C2-Bl-C4 86.1(5), C2-C3-C4 95.9(5) BI-C2-C3 67.0(4), BI-C4-C3
0 VCH Verlagsgesellschuft mbH, W-6940 Weinheim, 1992
folding of the four-membered ring (angle between the planes
C4-BI-C2 and C2-C3-C4 is l0S0) leads to a short distance
between B1 and C3 of 1.74 A. This indicates a 1,3-transannular interaction between the free p orbital at B1 and the
exocyclic double bond at C3, which also explains the remarkable high-field shift in the "B NMR spectrum (6 = 33).
A comparable interaction is found in the Diels-Alder dimer
of 2,3,4,5-tetramethyl-l-phenylb0role.~~~
Also in agreement
with this is the fact that the exocyclic substituents (C11 at BI,
C31 at C3) do not lie in a plane with the other substituents
at B1 and C3 (as is expected by sp2 hybridized atoms), but
are bent toward the center of the ring (8 and 16", respectively), which favors a transannular interaction.
In the 'H NMR spectrum of 1 the hydrogen atoms of the
boretane give rise to two doublets (6 = 3.62, 3.90,
OS70-0833/92/050S-0606$3.50+ .25/0
Angew. Chem. Int. Ed. Engl. 31 (1992) No. 5
4J(H,H) = 5.6 Hz), and for two of the four inequivalent
methyl groups of the isopropylidene substituents a quartet
(4J(H,H) = 0.6 Hz) is observed. In the I3C NMR spectrum
at room temperature six primary and three quarternary C
atoms are observed, and the B-CH atoms show two broad
signals at 6 = 73.1 and 56.6. Additionally, the quaternary C3
atom at 6 = 141 and a broad signal for the C atoms of the
tert-butyl groups bound to boron are observed on cooling to
250 K.
By framework rearrangement and migration of a hydrogen atom from one isopropylidene group to the other and
simultaneously raising the coordination numbers of the
boron atoms from three to four and six, respectively, the
racemate of 2 is formed. The "B NMR spectrum shows two
signals at 6 = 24.1 and -41.9 for the basal and apical boron
atom, respectively. The existence of an isopropenyl unit
(6=5.20 (m,lH), 5.05 (m,lH), 1.85 (m,3H)) and a
diastereotopic isopropyl group (6 = 3.01 (sept,l H), 1.02
(d,3H), 0.99 (d,3H)) in the 'H NMR spectrum proves that
the H migration has occurred. The two H atoms on the
carborane framework produce two doublets at 6 = 4.38 and
If the methyl protons of the isopropyl group are irradiated, one H atom (6 = 4.38) of the basal CH groups and one
H atom of the isopropenyl group (6 = 5.20) show an NOE
(8% and 3%). When the CH, group of the isopropenyl
substituent is irradiated, it is exactly the other way around
(NOE at 6 = 4.33 (9%) and 5.05 (6 %)>. This shows that the
C,H, and C,H, groups are adjacent and have one H substituent each as a neighbor.
The reaction introduced here is novel since the organoborane 1 can be isolated before the formation of the nido-tetracarbahexaborane 2 occurs. Compared with the endocyclic
ones in the 1,4-diboracycIohexadiene,the exocyclic double
bonds of 1 hinder a rapid rearrangement to the carborane.
Only after framework rearrangement and migration of a H
atom, one electron of each localized n bond can be made
available for cluster formation; thus 1 is kinetically stabilized. The surprising formation of 1 and the rearrangement
to 2 are subject to further investigations.
CAS Registry numbers:
1, 139565-05-2; 2, 139565-06-3; (CH,),CB(CI)B(CI)C(CH,),,
(CH,),C=C=CHBr, 6214-32-0.
[l] P. L. Timms, J. Am. Chem. Soc. 1968, 90,4585-4589; G. E. Herberich, B.
HeOner, J. Organomet. Chem. 1978, 161, C36-C40; Chem. Ber. 1982, 115,
[2] P. Binger, Tetrahedron L e f t . 1966,2675-2680; S. M. van der Kerk, P. H. M
Budzelaar, A.L.M. van Eekeren, G. J. M. van der Kerk. Polyhedron 1984,
3,271-280; R. N. Camp, D. S . Marynick, G. D. Graham, W. N. Lipscomb,
1 Am.Chem. SOC.1978, 100,6781 -6783.
f3] G. E. Herberich, H. Ohst, H. Mayer, Angew. Chem. 1984, 96, 975-976;
Angew. Chem. Int. Ed. Engl. 1984, 23,969.
[4] M. Enders, H. Pritzkow, W. Siebert, Chem. Ber., in press.
[5] W. Biffar, H. Noth, H. Pommerening, Angew. Chem. 1980, 92, 63-64;
Angew. Chem. Inf. Ed. Engl. 1980, 19, 56; H. Kluik, A. Berndt, 1
Organomet. Chem. 1982,234, C17-Cl9.
[6] 1: Space group P i , a = 9.123(6), b = 9.664(9), c = 12.261(10) A, a =
95.04(7), j = 91.82(6), x = 315.88(6)", V = 966 AS,Z = 2; 1347 observed
reflections ( I > 1.5u,, R = 0.089, Rw = 0.089. Further details of the crystal
structure investigation may be obtained from the Fachinformationszentrum Karlsruhe, Gesellschaft fur wissenschaftlich-technische Information
mhH, D-W-7514 Eggenstein-Leopoldshafen 2 (FRG) on quoting the depository number CSD-56006, the names of the authors, and the journal
[7] P. J. Fagan, E. G. Bums, J. C. Calabrese, J. Am. Chem. Sor. 1988, 110,
2979 - 2981.
Equilibria between Nonclassical and Classical
Boron Compounds, Competition between
Aromaticity in Two and Three Dimensions**
By Holger Michel, Dirk Seiner, Sigrid Wo&dfo,
Jiirgen Allwohn, Nicoluos Stamatis, Werner Massa,
and Armin Berndt*
Dedicated to Professor Anton Meller
on the occasion of his 60th birthda,v
Nonclassical boron compounds 2 are considerably lower
31 This can
in energy ['I than their classical isomers 1 and 3.[2*
be explained by the three-dimensional aromaticity of 2."-41
Conversion of the benzo derivatives 4 into 5, during which
the two-dimensional aromaticity of the fused benzene ring
would be lost, could not be observed for compounds of type
4."- 61 Therefore, is the three-dimensional aromaticity in
Experimental Procedure
1: To a solution of l-bromo-3,3-dimethylallene
(4.41 g, 30 mmol) in diethyl
solution, 12 mL) was added at -78 "C.
ether (20 mL), n-butyllithium ( 2 . 5 ~
After 30 min 1,2-di-tert-butyl-l,2-dichlorodiborane(4)
(3.10 g, 15 mmol) in
pentane (30 mL) was added dropwise. This was warmed to room temperature,
filtered, and after the removal of the solvent distilled as a green-yellow liquid.
Yield 1.93 g (47.6%), b.p. 70"C/10-3 Torr, m.p. 65"C(pentane). 'H NMR
3H, 4J(H,H) = 0.6Hz), 1.85 (s, 3H), 1.98 (s, 3H), 3.62 (d, 1 H. "J(H,H) =
5.6H~),3.90(d,lH,~J(H,H)= 5.6Hz).-"BNMR(C6D,):6 = 33,66(1:1).
NMR ([D,Jtoluene, 250 K): 6 = 18.5 (8-C,), 22.6 (CH,C), 22.7 (CH,C),
23.9 (CH,C), 26.5 (CH,C), 29.2 ((CH,),C), 29.3 ((CH,),C), 56.5 (B-CH), 73.4
(B-CH), 115.7 (CJ, 126.3(Cq),141 (B-C,), 148.2 (CJ. - El-MS: m/z270 (Me,
3.0), 57 (C,H;, 85.6), 56 (C,H:, loo), 41 (C,H:, 88.2).
2: A solution of 1 (30mg, 0.11 mmol) in [D,]toluene was heated in an NMR
tube to 100 "C. After 90 minutes only the signals of the carborane 2 are present
in the 'H NMR spectrum. The reaction half-time is approximately IS minutes.
'H NMR(C6DJ: 6 = 0.85 (s, 9H), 0.99 (d, 3H, 3J(H,H) = 6.7 Hz), 1.02 (d,
6.7 Hz). 4.33 (d, 1 H, 4J(H,H) = 3.5 Hz), 4.38 (d, 1 H, 4J(H,H) = 3.5 Hz), 5.05
(m,l H), 5.20 (m,l H). - IlB NMR(C,D,): 6 = 24.1, -41.9 (1:l). - 13CNMR
[*] Prof. Dr. A. Berndt, H. Michel, D.Steiner, S . WaEadlo, Dr. J. Allwohn, N.
([DJtoluene, 230K):S =12 (B-C,), 17.5 (B-C,), 21.5 (CH,), 24.2 (CH,), 24.4
Stamatis, Prof. Dr. W. Massa
(CHA 26.4 (CH(CHA), 31.7 ((CH,),C), 32.1 ((CH3),C), 79.5 (B-CH), 80.5
Fachbereich Chemie der Universitat
(B-CH), 110.1 (Cq),117.3 (=CH,), 119.7 (Cq), 136.8 (CCH,).-EI-MS: m/z270
Hans-Meerwein-Strasse, D-W-3550 Marburg (FRG)
( M e , loo), 255 ( M e - CH,, 22.1), 227 ( M e - C,H,, 26.9), 213 ( M e - C,H,,
[**I This work was supported by the Deutsche Forschungsgemeinschaft and
the Fonds derchemischen Industrie. We thank Prof. B. BogdanoviC,MaxReceived: October 18, 1991 [Z4975IE]
Planck-Institut fur Kohlenforschung, Mulheim, for information concerning the production of highly reactive magnesium (cf. [l 11).
German version: Angew. Chem. 1992, 104,628
Angen. Chem. Int. Ed. Engl. 31 (1992) No. 5
Verlagsgesellschaft mbH, W-6940 Weinheim, 1992
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