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Azadiboriridine-Borane a Non-Classical Acid-Base Adduct.

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Since the course of the reaction with dimethyl maleate was
largely influenced by its coordination and the isomerization
to dimethyl fumarate, 2 was also allowed to react with the
cyclic, poorly coordinating N-methylmaleimide. The reaction carried out in n-dodecane gave as sole product (93%)
the exo-cycloadduct 10 corresponding to 4,E51whose exo-
Azadiboriridine-Borane:
a
Non-Classical Acio-Base AddUCt **
By Peter Paetzold,* Burkhard Redenz-Stormanns,
Roland Boese,* Michael Biihl, and Paul yon Rogue SchEeyer
*
In the reaction of the azadiboriridine 1 a['] with THF .
BH, we expected the Lewis acid BH, to add at the N atom.
Surprisingly, however, 1 a displays its Lewis basicity across
the B-B bond, and as a consequence the bicyclic 2, a colorless liquid, was obtained in accordance with Equation (a).
configuration was confirmed by an NOE experiment. Apparently, the attack of the non-coordinating dienophile takes
place exclusively from the side of the diene away from the
metal atom, which is consistent with the postulated reaction
course (Scheme 1).
The reactions of the cobalt complex 2 presented here represent the first cases in which a ring-slippage reaction
(q5--t q3 -+ q5)leads to breakage of one, and formation of
two new C-C bonds. The driving force behind this reaction
could be the ring strain in the educt and the individual transformations of 7c-bonds into o-bonds of each Diels-Alder reaction. The similarity to the chemistry of cyclobutabenzene
is unmistakable; an essential difference lies, however, in the
breaking of a symmetry plane in the educt and in the orthoquinodimethane-analogous intermediates by coordination
to a transition metal. Recent findings by Kiindig et al. are
also of interest in this connection."']
I
R
R
2
1
a, R = R ' = R " = fBu
b. R = R = t E u , R " = i P r
c, R=R':R"=H
d, R = H , R = R " = M e
The constitution of 2a in solution follows from the NMR
spectra."] The "B-NMR signal at 6 = 51.9 would have been
shifted to lower field if the ring x-electron pair had been
employed for the formation of a B-N adduct, but actually a
high field shift to 6 = 32.9 was observed with retention of the
equivalence of both B-atoms. Moreover, it can be concluded
from the 2D-COSY-"B-' 'B-NMR spectrum that the B
Received: April 17, 1990 [Z 3914 IEI
atom
of the BH, group directly interacts with each of the two
German version: Angew Chem. 102 (1990) 1058
other B atoms. A notable feature of 2 a is the rigid conformation of the BH, group, which leads to two quartets (I :l :l :l )
CAS-Regis t ry n um bers :
1,128382-90-1 ;2,128632-33-7; 3,128632-34-8;4,128706-21-8; 5,128706-22-9;
in the 'H-NMR spectrum and to a doublet/triplet pattern
10, 128632-35-9: dimethyl fumarate, 624-49-7; dimethyl maleate, 624-48-6.
with coupling constants of 131 Hz (BH) and 68 Hz (BH,) in
the "B-NMR spectrum. The 2:l non-equivalence of the
BH, protons is retained even at 90 "C in toluene. The NMR
H. G. Schuster-Woldan, F. Basolo, J. Am. Chem. Soc. 88 (1966) 1657.
findings in solution are also confirmed for the solid state by
J. M. OConnor. C. P. Casey, Chem. Rep. 87 (1987) 307, and references
an X-ray structure analysis at 120 K (Fig.
cited therein.
The almost equilateral triangles Bl-B2-B3 and N-B2-B3
G. Huttner, H. H. Brintzinger, L. G. Bell, P. Friedrich, V. Bejenke, D.
enclose an angle of 42.6'. The markedly large ring angle of
Neugebauer, J. Organomei. Chem. 145 (1978). 329.
H. Butenschon, P. Betz, J. Chem. Soc. Chem. Commun. 1990, 500.
78.1" at the N atom provides optimal clearance for the bulky
Consistent spectroscopic data and correct elemental analyses were obligands. The NB, skeleton can be regarded as a nido-fragtained. 2 . 'H-NMR (200MHz, CDCI,): 6 = 2.30, 2.68 (AAB B sysment of a trigonal bipyramid, and, indeed, 2 a fulfills the
J3,4 = 9.6 Hz), 4.34 (t. l H , 3-H,
tem, 4H. endo-6(7)-H, exo-6(7)-H,
electron count rules for a nido-compound. The Bl-Hl2 and
'J,,,,,, = 2.2 Hz), 4.48 (d, 2H, 2(4)-H), 7.23 (m, 12H, meia-Hi, para-H),
7.44 (m, 8 H . orrho-H).-3: (200 MHz, C,D,): d = 2.08 (m, 1 H, exo-5-H,
Bl-HI3 distances (each 1.16 A) are significantly greater
2J,,, s.cr,, = - 15.9 Hz, 3J4,ex0 = 12.4 Hz), 2.20 (m, 1 H, endo-2-H,
than B1-HI (1.10 A), but the B2-HI2and B3-HI3 distances
'Jend. 2.sr,, = - 15.8 Hz, 'JSnd,.1.3 = 11.9 Hz), 2.38 (m, 1 H, exo-2-H,
(ca. 1.67 A) are too large to assume a bridge position of
'Jex0 2 . 3 = 6.1 Hz), 2.54 (m, 2H. 4-H, endo-5-H. 3J4,ando.s
= 4.9 Hz,
HI2 and H13. The structure of 2 a is, in principle, reminis,J,,, = 11.6 Hz), 2.76 (m, 1 H, 3-H), 3.27 (s, 3H, exo-COOCH,), 3.29 (s.
3 H , endo-COOCH,), 4.24 (m, 1 H, 7-H 0.9-H, 3J,.w = 'J8,9 = 2.5 Hz,
cent of that of the anion [Fe(CO),B,H,,]@, which is formed
4 J , , , = 1.5Hz),4.30(m,lH,7-Ho.9-H),4.36(dd,1H,8-H),7.1(m,12H,
by the addition of BH, to a B-B bond of the anion
mcra-H. paru-H). 7.56 (m, 8 H , ortho-H).--lO:
(200 MHz, CDCI,):
[Fe(CO),B,H,]@ in the pentagonal base of the pyramidal
6 = 2.14 (m,1 H. endo-2(5)-H9 Jendo -21s).3(41~ 7 . Hz,
3 2Jendo.2(S,.exo
=
B,
- 15.1 Hz),2.60(dd,1H,exo-2(5)-H,J,,,.,~,,,,,,,~3.1
Hz),2.73(m,lH.
2(s1
3(4)-H).2.?6(~,3H,CH,),4.32(t.lH,S~H,~J,,,,,,=2.6Hz).4.57(d,2H,
7(9)-H), 7.23 (m, 12H, meru-, para-H), 7.41 (m, 8 H , oriho-H).
A. Nakamurd, N. Hagihara, Bull. Chem. Sac. Jpn. 34 (1961) 452; G. A.
Ville. K . P. C. Vollhardt, M. J. Winter, Organometal[ics 3 (1984) 1177; A.
Efraty. Chem. Rev. 77 (1977) 691, and references cited therein.
Cf. J. W. Pattiasina. C. E. Hissink, J. L. de Boer, A. Meetsma, J. H. Teuben,
J. Am. Chem. Soc. 107 (1985) 7758; F. G. N. Cloke, J. C. Green, M. L. H.
Green, C. P. Morley, J. Chem. Soc. Chem Commun. 1985. 945.
Taking into account the 100-fold excess of dimethyl maleate used compared to 2, this corresponds to approximately three catalytic cycles.
1. Sauer. D. Lang, H. Wiest, Chem. Ber. 97 (1964) 3208.
E. P. Kundig, G. Bernardinelli, J. Leresche, P. Romanens, Angeu. Chem.
102 (1990) 421: Angtw. Chem. f n l . Ed Engl. 29 (1990) 407.
Angeu. Chpm
Int.
Ed. EngI. 29 (1990) No. 9
[*] Prof. Dr. P. Paetzold. B. Redenz-Stormanns
Institut fur Anorganische Chemie der Technischen Hochschule
Templergraben 55, D-5100 Aachen (FRG)
[**I
Dr. R. Boese
Institut fur Anorganische Chemie der Universitat-Gesarnthochschule
Universitatsstrasse 5-7, D-4300 Essen (FRG)
Prof. Dr. P. von R. Schleyer, M. Buhl
Institut fur Organische Chemie der Universitat Erlangen-Nurnberg
Henkestrasse 42. D-8520 Erlangen (FRG)
This work was supported by the Deutsche Forschungsgemeinschaft.
c> VCH Verlagsgtsellschafi mbH, D-6940 Weinheim. 1990
0570-0833_7190j0909-1059
3 3.50f.25/0
1059
The azadiboriridine 1 b can be prepared analogously to 1 a
from CI-B(tBu)-N(tBu)-B(ir)-ClL'~
b y dehalogenation
with Na/K if the reaction is carried out at - 78 " C ; on allowing to warm to room temperature, 1 b dimerizes to the nidocluster compound N,B,tBu,iPr, .[IJ If, however, 1 b is treat-
UI
Fig. 1. Molecular structure of Za in the crystal. Selected bond lengths, angles,
and torsion angles ([A] and ['I, resp., standard deviations in brackets): Bl-B2
1.770(2), B1-B3 1.752(2), B2-B3 1.785(2), Bl-N 2.484(2), B2-N 1.412(2), B3-N 1.421(2), B2-Cl 1.590(2), B3-CS 1.592(2), N-CY 1.480(2), Bl-HI 1.098(17).
Bl-Hl2 1.158(17), Bl-Hl3 1.155(15), B2-Hl2 1.686(18), B3-Hl3 1.653(17);
B2-Bl-B3 60.9(1), Bl-B2-B3 59.1(1), Bl-B3-B2 60.0(1), N-B2- B3 51.2(1),
N-B3-B2 50.7(1), B2-N-B3 78.1(1), BI-B2-CI 120.9(1), N-B2-C1 136.9(1),
Bl-B3-C5 120.9(1), N-B3-CS 135.8(1), B2-N-CY 140.8(1), B3-N-C9 140.3(1),
HI-Bl-B2 127.2(8), Hl-Bl-B3 124.8(8), H1-Bl-HI2 119.6(11). HI-Bl-Hl3
118.3(11); HI-B1-B2-N 142.4, HI-Bl-B3-N -145.9. Hl-Bl-B2-B3 113.5,
Hl-Bl-H12-B2 120.8, Hl-Bl-H13-B3 -117.9, Cl-B2-B3-C5 -2.7, C1B2-N-CY 27.7, CS-B3-N-C9 -33.2, H12-B2-B3-B1 -25.8. H13-Bl-B2-B3
-44.2.
ence of the alkyl substituents on the "B-NMR signals of
B2/B3 is made clear on going from 2 c (8 = 22) to 2 d
(6 = 29).-Based on the calculated bond order of 0.39 a
weak B2.. .H I 2 interaction becomes apparent in 2c, in spite
of the relatively long distance of more than 1.6
This
may be a further explanation for the observed conformationa1 rigidity of the complexed BH, group in addition to steric
reasons. The enthalpy of formation of -45.7 kcal mol- for
the formation of 2c from BH, and NB,H, is significantly
greater than the value of -28.5 kcdl mol-' calculated for
the formation of H,B-NH, from BH, and NH, [calculated
for both at MP4sdtq(FC)/6-31 G**//MP2//(Full)/6-3lG* +
ZPE(6-31G*) level]. Hence, azadiboriridines are stronger
bases towards BH, than amines, but the weak B-B bondr9]
and not the nitrogen represents the basic center. This is
also true for the protonation: the proton affinity of
-21 1.5 kcal mol-' calculated for NB,H, (with formation
of a three-center B-H-B bond) is greater than that for ammonia, with a value of -206.8 kcal mol [calculated for both
at MP4sdtq(FC)/6-31 + G**//6-31G* + ZPE(6.31G*) level].
Experimental
1.2,3-Tri-leri-butyl-nido-l-azatetraborane(6) (tri-rerr-butylazadiboriridineborane) 2a: A solution of l a (1.08 g) in T H F (15 mL) was treated at O'C with
5.9 mL of a 0.83 M solution of BH, in THF. The mixture was stirred for 30 min
at room temperature. After removal of solvent and distillation at 45°C
(0.3 torr) we obtained 1.10 g (95%) of La, m.p. - 10'12.
Received May 2, 1990 f Z 3939 IE]
German version: Angew. Chem. 102 (1990) 1059
CAS-Registry numbers:
l a , 109976-00-3; l b , 128497-14-3; Za, 128497-15-4; Zb, 128497-16-5; Zc,
128497-17-6; Zd, 128497-18-7; BH,, 13283-31-3.
ed with THF . BH, at -78"C, 2 b can be isolated in 3 4 %
yield as a colorless liquid, and can be characterized N M R
spectros~opically.[~~The
l 1 B-NMR signal of the BH, group,
at room temperature a doublet-triplet pattern at 6 = - 17.8
( J = 131 and 69 Hz, respectively), is converted into a quartet
at 6 = - 17.2 ( J = 88 Hz) upon heating to 90 "C in toluene,
an indication that the conformational rigidity of the BH,
group in 2a has, inter alia, steric origin.
Table 1. Comparison of measured (2a) and calculated (Zc, d) distances and
"B-NMR chemical shifts.
[A]
BGB2
B1-B3
Za
ZC
Zd
1.770
1.752
1.716
1.724
[a]
Distances
82-83
B2-N
B3-N
1.785
1.758
1.766
1.421
1.412
1.421
1.424
B2-Hl2
B3-Hl3
1.653
1.686
1.599
1.627
B1
6 ("B) [hl
B2IB3
-14.1
32.9
-15.5
-18.9
22.1
28.8
[a] MP2/6-31G*-optimized (Zc, d). [b] IGLO (Individual Gauge for Localized
Orbitals) [S]; Double-Zeta Basis (Zc, d).
Ab initio calculationsr6]on the model systems 2c and 2 d
confirm the experimental findings. Optimizations in C, symmetry satisfactorily reproduce both the geometry as well
as the "B-NMR chemical shifts of 2 a (Table I). The influ1060
0 VCH
VerlugsgeseNschuft mhH. 0-6540 Weinheim. 1990
111 R. Boese, B. Krockert, P. Paetzold, Chem. Ber. 120 (1987) 1913.
[2] Z a : NMR (CDCI,): 6('H) = 0.92 (2H), 1.04 (18H), 1.36 (9H), 2.03 (1 H);
6("B) = -14.1 (1 B), 32.9 (2B). MS: m / z = 207 (21%, M e - BH,), 164
(100, M e - CbH9), 150 (91, Me - BH, - C,H,), 108 (32, Me - C,H,
-C
8 d
[3] Single crystal from the melt in a measuring tube; u = 12.143(2),
h = 8.644(1), L' = 15.637(3), p = 103.79(1)", V = 1594.0(4) A3, Z = 4,
e,,,, = 0.920 g cm-3, P2,/n (No. 14); crystal size d = 0.3 mm; measuring
range: 3 5 28 2 SO'; 2770 independent reflections, 2268 observed with
Fo t 4alF); anisotropic temperature factors for the non-hydrogen atoms;
160 refined parameters; R = 0.042, R , = 0.048. Further details of the crystal structure investigation are aVdibdbk on request from the Fachinformationszentrum Karlsruhe, Gesellschaft fur wissenschaftlich-technische Information mbH, D-7514 Eggenstein-Leopoldshafen 2 (FRG), on quoting the
depository number CSD-54561. the names of the authors, and the journal
citation.
[4] 0. Hollander, W. R. Clayton. S . G. Shore, J. Chem. Soc. Chem. Commun.
1974, 604; M. Mangion, W. R. Clayton, 0. Hollander, S. G. Shore, Inorg.
Chem. 16 (1977) 2110.
[S] 2b:NMR(CDC13):6('H) = 0.70(2H),0.90(d.J = 7.0 Hz.6H), 1.03(9H),
1.33(9H),1.64(sept,J=7.0Hz,lH)1.79(1H);6("B)=-17.8(1B),32.4
(1 B), 34.4 (1 B). MS: m / z = 193 (28%, Me-BH,), 178 (4. Me-BH,136 (100, Me-BH,-C,H,).
CH,). 150 (92, Me-C,H,),
[6] Standard procedures and basis sets were used, see, e.g., W Hehre, P. von R.
Schleyer, J. A. Pople, Ah Inirio Molecular Orhital Theory, Wiley, New York
1986. The scaled 6-31G* frequencies were used for the zero-point correction.
[7] From a population analysis of the natural orbitals (6-31G* basis set); for a
review see. A. E. Reed. L. A. Curtiss, F. Weinhold, Chem. Rev. 88 (1988)
899.
[8] W. Kutzelnigg, Isr. J Chem. 15 (1980) 193; M. Schindler, W. Kutzelnigg, J.
Chem. Phys. 76 (1982) 1919; review: W. Kutzelnigg, U. Fleischer. M. Schindler, N M R Basic Princ. Prog., in press.
[Y] P. H. M. Budzelaar, P. von R. Schleyer, J. Am. Chem. Soc. 108(1986) 3967.
0570-0833/90j0909-1060S 3.XJ-t .25//J
Angetr. Chem. Ini. Ed. EngI. 29 (1590) No. 9
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