Angewandte
Chemie
dilithiobenzene (1.24 g, 5 mmol) in ether (30 mL) at À788C. The
mixture was warmed to room temperature and stirred overnight. All
the volatiles were removed in vacuo and the residue was extracted
with toluene (40 mL). Yield: (p-1: 1.72 g, 75%; m-1: 2.08 g, 91%;). p-
1: 1H NMR (300 MHz, CDCl3): d = 7.27 (s, 4H, CHaro), 2.95, 2.91, 2.90
and 2.77 ppm (s, 6H, NMe2); 13C{1H} NMR (75.5 MHz, CDCl3): d =
130.8 (s, CHaro), (Cipso not observed), 44.6, 43.2, 40.4 and 29.5 ppm (s,
NMe2); 11B{1H} NMR (CDCl3): d = 44.88, 41.45. m-1: 1H NMR
(300 MHz, CDCl3): d = 7.21 (m, 4H, CHaro), 2.89, 2.88, 2.85 and
2.71 ppm (s, 6H, NMe2); 13C{1H} NMR (CDCl3): d = 134.5, 130.1 and
126.7 (s, CHaro), (Cipso not observed), 44.8, 42.3, 40.2 and 37.8 ppm (s,
NMe2); 11B{1H} NMR (160.5 MHz, CDCl3): d = 40.3 ppm (br).
p-2 and m-2: 5.01 mL of tBuLi (1.5m, pentane) were added
dropwise to a solution of p-1 or m-1 (1.72 g, 3.76 mmol) in hexane
(20 mL) at À788C. The mixture was warmed to room temperature
and stirred for 6 h. All the solvents were then removed in vacuo.
Toluene was added and the salts were removed by filtration. Yield:
(p-2: 1.39 g, 90%; m-2: 1.23 g, 80%). p-2: 1H NMR (300 MHz,
CDCl3): d = 7.25 (s, 4H, CHaro), 2.97, 2.93, 2.85 and 2.84 (s, 6H,
NMe2), 0.93 ppm (s, 18H, tBu); 13C{1H} NMR (75.5 MHz, CDCl3):
d = 131.3 (s, CHaro; Cipso not observed), 46.8, 45.5, 40.3 and 39.9 (s,
NMe2), 29.6 ppm (s, tBu); 11B{1H} NMR (160.5 MHz, CDCl3): d =
44 ppm (br). m-2: 1H NMR (CDCl3) d = 7.10 (m, 4H, CHaro), 2.87 and
2.85 (s, 3H, NMe2), 2.84 (s, 6H, NMe2), 2.79 and 2.78 (s, 3H, NMe2),
2.73 (s, 6H, NMe2), 0.80 (s, 9H, tBu), 0.79 ppm (s, 9H, tBu); 13C{1H}
NMR (CDCl3: d = 136.5, 130.3 and 126.2 (s, CHaro; Cipso not
observed), 46.7, 45.5, 40.3 and 39.8 (s, NMe2), 29.5 ppm (s, tBu);
11B{1H} NMR (160.5 MHz, CDCl3): d = 52 ppm (br).
[1] a) J. A. Berson in Reactive Intermediate Chemistry (Eds.: R. A.
Moss, M. S. Platz, M. Jones, Jr.), Wiley-Interscience, Hoboken,
NJ, 2004, pp. 165 – 204; b) W. T. Borden in Encyclopedia of
Computational Chemistry (Ed.: P. v. R. Schleyer), Wiley, New
York, 1998, pp. 708 – 722; c) J. A. Berson, Acc. Chem. Res. 1997,
30, 238; d) D. A. Dougherty, Acc. Chem. Res. 1991, 24, 88.
[2] Conjugated Polymers and Related Material (Eds.: W. R. Sala-
neck, L. Lundstrom, B. Ranby), Oxford, New York, 1993.
[3] H. S. M. Lu, J. A. Berson, J. Am. Chem. Soc. 1997, 119, 1428;
H. S. M. Lu, J. A. Berson, J. Am. Chem. Soc. 1996, 118, 265.
[4] For recent work on carbon-based 1,3-diradicals: a) A. C. Goren,
D. A. Hrovat, M. Seefelder, H. Quast, W. T. Borden, J. Am.
Chem. Soc. 2002, 124, 3469; b) M. Abe, W. Adam, T. Minamoto,
Y. Ino, M. Nojima, J. Org. Chem. 2003, 68, 1796; c) M. Abe, W.
Adam, W. T. Borden, M. Hattori, D. A. Hrovat, M. Nojima, K.
Nozaki, J. Wirz, J. Am. Chem. Soc. 2004, 126, 574.
[5] Several heterocyclobutane-1,3-diyls that contain Group 14 and/
or Group 15 elements confined by a trans-annular antibonding
p-overlap, which makes the thermal ring closure forbidden have
been isolated: a) E. Niecke, A. Fuchs, F. Baumeister, M. Nieger,
W. W. Schoeller, Angew. Chem. 1995, 107, 640; Angew. Chem.
Int. Ed. Engl. 1995, 34, 555; b) O. Schmidt, A. Fuchs, D. Gudat,
M. Nieger, W. Hoffbauer, E. Niecke, W. W. Schoeller, Angew.
Chem. 1998, 110, 995; Angew. Chem. Int. Ed. 1998, 37, 949; c) E.
Niecke, A. Fuchs, M. Nieger, Angew. Chem. 1999, 111, 3213;
Angew. Chem. Int. Ed. 1999, 38, 3028; d) W. W. Schoeller, C.
Begemann, E. Niecke, D. Gudat, J. Phys. Chem. A 2001, 105,
10731; e) H. Sugiyama, S. Ito, M. Yoshifuji, Angew. Chem. 2003,
115, 3932; Angew. Chem. Int. Ed. 2003, 42, 3802; f) M. Sebastian,
M. Nieger, D. Szieberth, L. Nyulaszi, E. Niecke, Angew. Chem.
2004, 116, 647; Angew. Chem. Int. Ed. 2004, 43, 637; g) C. Cui,
P. P. Power, Abstr. Am. Chem. Soc. Meet. 2004, 801; h) M. F.
Lappert, Abstr. Am. Chem. Soc. Meet. 2004, 427.
[6] For reviews on diradicals based on main group elements see:
a) H. Grützmacher, F. Breher, Angew. Chem. 2002, 114, 4178;
Angew. Chem. Int. Ed. 2002, 41, 4006; b) P. P. Power, Chem. Rev.
2003, 103, 789.
[7] D. Scheschkewitz, H. Amii, H. Gornitzka, W. W. Schoeller, D.
Bourissou, G. Bertrand, Angew. Chem. 2004, 116, 595; Angew.
Chem. Int. Ed. 2004, 43, 585.
[8] For discussions on the diradical character of derivatives of type
A: a) M. Seierstad, C. R. Kinsinger, C. J. Cramer, Angew. Chem.
2002, 114, 4050; Angew. Chem. Int. Ed. 2002, 41, 3894; b) W. W.
Schoeller, A. Rozhenko, D. Bourissou, G. Bertrand, Chem. Eur.
J. 2003, 9, 3611; c) Y. Jung, M. Head-Gordon, J. Phys. Chem. A
2003, 107, 7475; d) M. J. Cheng, C. H. Hu, Mol. Phys. 2003, 101,
1319.
[9] a) D. Scheschkewitz, H. Amii, H. Gornitzka, W. W. Schoeller, D.
Bourissou, G. Bertrand, Science 2002, 295, 1880; b) H. Amii, L.
Vranicar, H. Gornitzka, D. Bourissou, G. Bertrand, J. Am.
Chem. Soc. 2004, 126, 1344.
p-3 and m-3: A solution of BBr3 (1.27 mL, 13.48 mmol) in hexane
(20 mL) was added dropwise to a solution of p-2 or m-2 (1.39 g,
3.37 mmol) in hexane (40 mL) at À788C. After the solution had been
stirred for 30 min, all the volatiles were removed in vacuo and the
residue was treated with hexane (20 mL), filtered and used for the
next step without further purification. p-3: 1H NMR (300 MHz,
CDCl3): d = 7.8 (s, 4H, CHaro), 1.1 ppm (s, 18H, tBu). m-3: 1H NMR
(300 MHz, CDCl3): d = 8.4 (s, 1H, CHaro), 8.2 (d, JHH = 7.2, 2H,
CHaro), 7.6 (t, JHH = 7.2, 1H, CHaro), 1.20 ppm (s, 18H, tBu).
p-4 and m-4: A suspension of iPr2PLi (prepared by adding nBuLi
(4.80 mL, 2.5m, pentane) to iPr2PH (12.04 mmol) in ether (20 mL) at
À788C and subsequent stirring at room temperature for 1 hour) was
added to a solution of p-4 or m-4 (1.66 mL, 3.01 mmol) in hexane
(20 mL) at À788C. The reaction mixture was warmed to room
temperature within 1 hour and the solvents were removed in vacuo.
Toluene was added and the salts were filtered off. Violet crystals of p-
4 were obtained by cooling a saturated boiling toluene solution to
room temperature, Yield: (0.96 g, 43%). Colorless crystals of m-4
1
were obtained in THF at À308C. Yield: (2.41, 41%). p-4: H NMR
(300 MHz, C6D6): d = 7.67 (s, 4H, CHaro), 2.06 (m, 8H, PCH), 1.36 (s,
18H, tBu), 1.22 (dd, JHH = 16.5 Hz, JHP = 7.2 Hz, 24H, CHCH3),
1.13 ppm (dd,
J
HH = 15.9 Hz,
JHP = 7.2 Hz, 24H, CHCH3);
13C{1H} NMR (75.5 MHz, C6D6): d = 134.9 (s, CHaro), (Cipso not
observed), 34.5 (s, tBu), 21.9 (t, JPC = 22.6 Hz, PCH), 21.4 ppm (d,
J
PC = 14.3 Hz, CHCH3); 11B{1H} NMR (C6D6): d = 2.67, À2.80 ppm;
[10] a) A. Rajca, Chem. Rev. 1994, 94, 871; b) C. Rovira, D. Ruiz-
Molina, O. Elsner, J. Vidal-Gancedo, J. Bonvoisin, J. P. Launay, J.
Veciana, Chem. Eur. J. 2001, 7, 240.
31P{1H} NMR (C6D6: d = À22.40 ppm. m-4: 1H NMR (300 MHz,
C6D6): d = 7.88 (s, 1H, CHaro), 7.51 (d, JHH = 7.5, 2H, CHaro), 7.30 (t,
J
J
HH = 7.5, 1H, CHaro), 2.01 (m, 8H, PCH), 1.41 (s, 18H, tBu), 1.22 (dd,
HH = 16.2 Hz , JHP = 6.9 Hz, 24H, CHCH3), 1.10 ppm (dd, JHH
[11] 1,2-diphenyl-1,2-dichloro-diborane is known to be highly unsta-
ble: H. Hommer, H. Nöth, J. Knizek, W. Ponikwar, H. Schwenk-
Kircher, Eur. J. Inorg. Chem. 1998, 1519.
=
16.0 Hz, JHP = 7.8 Hz, 24H, CHCH3); 13C{1H} NMR (75.5 MHz,
C6D6): d = 143.9, 133.3 and 127.0 (s, CHaro), (Cipso not observed),
34.7 (s, tBu), 28.8 (t, JPC = 21.9 Hz, PCH), 21.4 ppm (d, JPC = 11.6 Hz,
CHCH3); 11B{1H} NMR (160.5 MHz, C6D6): d = À3.7, À8.0 ppm;
31P{1H} NMR (C6D6): d = À28.4 ppm.
[12] As observed for related carbon-based singlet 1,3-diradicals,[4]
derivatives of type
A are strongly colored, whereas the
bicyclic[1.1.0] isomers B are colorless.
[13] The Bruker SMART-1000[19a] X-ray diffraction instrument with
Mo-radiation was used for data collection of compounds p-4 and
m-4. All data frames were collected by using w-scan mode (À0.38
w-scan width, hemisphere of reflections) and integrated by using
the Bruker SAINTPLUS program.[19b] The intensity data were
corrected for Lorentzian polarization and absorption corrections
Received: April 28, 2004
Keywords: boron · magnetic properties · phosphorus · radicals
.
Angew. Chem. Int. Ed. 2004, 43, 4876 –4880
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4879