Angewandte
Chemie
Table 1: Selected physical and spectroscopic properties of 1a, 2a, and
4a.
[1] R. Hoffmann, R. G. Alder, C. F. Wilcox, J. Am. Chem. Soc. 1970,
92, 4992; J. B. Collins, J. D. Dill, E. D. Jemmis, Y. Apeloig,
P. von R. Schleyer, R. Seeger, J. A. Pople, J. Am. Chem. Soc.
1976, 98, 5419.
1a: yield estimated by NMR spectroscopy 75%; 1H NMR (500 MHz,
[D8]THF, ꢀ908C): d=6.88, 6.87 (each s, each 1H, p-H), 3.40 (s, 4H,
DME), 3.24 (s, 6H, DME), 2.28, 2.18, 2.15, 2.12, 1.97, 1.84, 1.24, 1.00
(each s, each 3H, o- and m-Me), 1.21, 0.73 (each d, each 1H, B-CH2Si),
1.10 (s, 3H, B-Me), 0.23, 0.03 ppm (each s, each 9H, SiMe3); 13C NM R
(125 MHz, [D8]THF, ꢀ908C): d=143.7 (br.s, 1C, CB3), 139.7, 139.6,
138.2, 137.6, 134.5, 134.4, 134.2, 134.0, 133.3, 132.5 (each s, each 1C, o-
and m-C), 133.4, 132.5 (each d, each 1C, p-C), 133.2, 126.4 (each br.s,
each 1C, i-C), 72.4, 58.8 (each 2C, DME), 22.0, 21.8, 21.3, 12.1, 20.9,
20.1, 19.6, 19.4 (each q, each 1C, o- and m-Me), 16.6 (br.q, 1C, MeB), 9.1
(br.t, 1C, BCH2Si), 1.1, 1.0 ppm (each q, each 3C, SiMe3)
[2] D. Rˆttger, G. Erker, Angew. Chem. 1997, 109, 841; Angew.
Chem. Int. Ed. Engl. 1997, 36, 812, and references therein; W.
Siebert, A. Gunale, Chem. Soc. Rev. 1999, 28, 367; M. Driess, J.
Aust, K. Merz, C. van W¸llen, Angew. Chem. 1999, 111, 3967;
Angew. Chem. Int. Ed. 1999, 38, 3677; Y. Sahin, M. Hartmann, G.
Geiseler, D. Schweikart, C. Balzereit, G. Frenking, W. Massa, A.
Berndt, Angew. Chem. 2001, 113, 2725; Angew. Chem. Int. Ed.
2001, 40, 2662, and references therein.
[3] a)K. Krogh-Jespersen, D. Cremer, D. Poppinger, J. A. Pople,
P. von R. Schleyer, J. Chandrasekhar, J. Am. Chem. Soc. 1979,
101, 4843; b)K. Sorger, P. von R. Schleyer, THEOCHEM 1995,
338, 317, and references therein; Z.-X. Wang, P. von R. Schleyer,
J. Am. Chem. Soc. 2001, 123, 994, and references therein; c)S.
Fau, G. Frenking, THEOCHEM 1995, 338, 117.
2a: colorless crystals; m.p. 1098C (decomp); yield 78%; 1H NM R
(500 MHz, [D8]THF, ꢀ908C): d=6.90 (s, 2H, p-H), 2.24, 2.23, 2.16 (each
s, in total 24H, o- and m-CH3), 0.88 (br.s, 2H, BCH2), 0.76 (br.s, 3H,
BCH3), ꢀ0.04, ꢀ0.5 ppm (each s, each 9H, Me3Si); 13C NMR (125 MHz,
[D8]THF, ꢀ908C): d=137.2, 137.1, 134.8, 134.7 (each s, each 2C, o- and
m-C), 134.2 (br.s, 2C, i-C), 133.0 (br.s, 1C, CB2), 132.3 (d, 2C, p-C), 22.6,
20.1, 20.0 (in total 8C, o- and m-CH3), 19.8 (br.t, 1C, BCH2), 13.4 (br.q,
1C, BCH3), 0.9, 0.4 ppm (each q, each 3C, Me3Si); 11B NMR (96 MHz,
[D10]Et2O, 278C): d=80 (1B), 40 ppm (2B)
[4] M. Menzel, D. Steiner, H.-J. Winkler, D. Schweikart, S. Mehle, S.
Fau, G. Frenking, W. Massa, A. Berndt, Angew. Chem. 1995, 107,
368; Angew. Chem. Int. Ed. Engl. 1995, 34, 327.
[5] All geometries were optimized by employing the B3LYP hybrid
functional together with the 6-31G(d)basis set. The transition
state TS1b/2b was characterized by its intrinsic reaction
coordinate. Relative energies are corrected for zero-point
energies and are based on energy computations with 6-311 +
G(d,p), likewise the computed chemical shifts (GIAO-NMR).
a)Gaussian98 (RevisionA.7), M. J. Frisch, G. W. Trucks, H. B.
Schlegel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, V. G.
Zakrzewski, J. A. Montgomery, R. E. Stratmann, J. C. Burant, S.
Dapprich, J. M. Millam, A. D. Daniels, K. N. Kudin, M. C. Strain,
O. Farkas, J. Tomasi, V. Barone, M. Cossi, R. Cammi, B.
Mennucci, C. Pomelli, C. Adamo, S. Clifford, J. Ochterski, G. A.
Petersson, P. Y. Ayala, Q. Cui, K. Morokuma, D. K. Malick,
A. D. Rabuck, K. Raghavachari, J. B. Foresman, J. Cioslowski, J.
V. Ortiz, B. B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I.
Komaromi, R. Gomperts, R. L. Martin, D. J. Fox, T. Keith, M. A.
Al-Laham, C. Y. Peng, A. Nanayakkara, C. Gonzalez, M.
Challacombe, P. M. W. Gill, B. G. Johnson, W. Chen, M. W.
Wong, J. L. Andres, M. Head-Gordon, E. S. Replogle, J. A.
Pople, Gaussian, Inc., Pittsburgh, PA, 1998; b)A. D. Becke, J.
Chem. Phys. 1993, 98, 1372; A. D. Becke, J. Chem. Phys. 1993, 98,
5648; c)C. Lee, W. Yang, R. G. Parr, Phys. Rev. B 1988, 37, 785.
[6] Y. Sahin, C. Pr‰sang, P. Amseis, M. Hofmann, G. Geiseler, W.
Massa, A. Berndt, Angew. Chem. 2003, 115, 693; Angew. Chem.
Int. Ed. 2003, 42, 669.
1
4a: colorless crystals; m.p. 1188C; yield ca. 50%; H NMR (500 MHz,
CD2Cl2, ꢀ408C): d=7.10 (s, 2H, p-H), 2.52, 2.46, 2.20(each s, in total
24H, o- and m-Me), 0.23, 0.03, (each s, each 2H, H2CSi, localized by C/H
correlation), 0.08, ꢀ0.04, ꢀ0.57 ppm (each s, each 9H, Me3Si); 13C NM R
(125 MHz, CD2Cl2, ꢀ408C): d=142.2, 140.5, 133.7, 133.6 (each s, each
2C, o- and m-C), 135.0 (d, 2C, p-C), 132.1 (br.s, 2C, i-C), 73.3 (br.s, 1C,
CB3), 21.4, 21.1, 20.3, 20.2 (each q, in total 8C, o- and m-Me), 18.1, 12.8
(each br.t, each 1C, CH2Si), 2.1, 1.1, 0.2 ppm (each q, each 3C, Me3Si);
11B NMR (96 MHz, CDCl3, ꢀ208C): d=58 (br.s, 3B), 5.8 ppm (1B).
Above ꢀ208C 4a is converted partly to an isomer with d(11B) =
ꢀ1.0 ppm, crystallization of the mixture leads to the re-formation of 4a
[7] The methylating reagent was added to a solution of 3a in
[D8]THF at ꢀ1208C, which had been frozen in an NMR tube
with the aid of liquid nitrogen. Thereafter the components were
warmed to ꢀ908C in the NMR spectrometer.
Figure 2. Section (145 to 125.5 ppm) of the 13C NMR spectrum of a
3:1 mixture of 1a and 2a. The insert shows an expansion of the region
between d=133.2 and 136.6 ppm. The signals of 2a are marked by an
[8] The structure of 2a in the crystal resembles that of the starting
material of 3a,[6] which bears a chlorine atom instead of the
methyl group at the boron atom of the boryl bridge of 2a.
asterisk ( ); their intensities increase as the temperature is raised,
*
ꢀ
ꢀ
Selected distances in 2a [pm]: C1 B1 145.5(7), C1 B2 143.9(8),
those of the other signals decrease: after 30 min at ꢀ658C only the
signals of 2a are observed.
ꢀ
ꢀ
ꢀ
B1 B2 167.7 (10), B1 B3 192.4(9), B2 B3 192.8(8).
[9] Crystal structure analysis of 4a: A colorless crystal (0.60 î 0.30 î
0.05 mm3)was measured on at 193 K on an IPDS area detector
is planar-tetracoordinate. DFT computations[5] for the models
1b, 2b, and the transition state TS1b/2b of the isomerization
1b!2b reveal that 2b is 11.6 kcalmolꢀ1 lower in energy than
1b[11] and that the barrier of the isomerization
(20.6 kcalmolꢀ1)is low. [12] The facile isomerization to 2a thus
provides additional support for the structure of 1a.
system (Stoe)with Mo
radiation. C32H57B4ClSi3, monoclinic,
Ka
space group P2/c, Z = 4, a = 1186.3(1), b = 1185.9(1), c =
2697.2(1)pm, b = 91.55(1)8, V= 3793.1(5)î 10ꢀ30 m3, 1calcd
=
1.059 Mgmꢀ3, 29451 reflections up to q = 25.948, 6979 independ-
ent (Rint = 0.0584), 4901 with I > 2s(I). The structure was solved
with direct methods and refined against all F2 data with full
matrix, wR2 = 0.0997 for all reflections, R = 0.0391 for the
observed reflections. CCDC-185030 (4a)contains the supple-
mentary crystallographic data for this paper. These data can be
Received: August 6, 2002 [Z19909]
Angew. Chem. Int. Ed. 2003, 42, No. 6
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