Communications
EI) m/z (%): 722 (0.5) [M+], 649 (0.35) [M+ꢀSi(CH3)3], 477 (54)
The structure was solved by direct methods and refined to F2
anisotropically, the H atoms were refined with a riding model.
The final quality coefficient wR2(F2) for all data was 0.0750, with
a conventional R(F) = 0.0258 for 118 parameters. CCDC-216013
(4[Li(dme)]2) contains the supplementary crystallographic data
for this paper. These data can be obtained free of charge via
bridge Crystallographic Data Centre, 12 Union Road, Cam-
bridge CB21EZ, UK; fax: (+ 44)1223-336-033; or deposit@
ccdc.cam.ac.uk).
[M+ꢀMes*], 73 (100) (Si(CH3)3+).
4[Li(dme)]2: An orange suspension of 1b (0.72 g, 1.0 mmol) in
DME (15 mL) and lithium (0.07 g, 10.0 mmol) were stirred at room
temperature for 3 h, forming a light red solution. The reaction
mixture was filtered to remove residual metal, and the solvent was
removed in vacuo. Yield 396 mg (93%); NMR ([D8]THF, 258C):
31P NMR: d = 200.3 ppm (s); 1H NMR: d = 0.0 (s, Si(CH3)3), 1.3 (s,
Mes*), 3.4 (s, DME), 3.5 (s, DME), 7.3 ppm (s, Mes*); 7Li NMR: d =
3
ꢀ4.6 ppm (s); 13C NMR: d = 0.0 (t, JC,P = 2.4 Hz, Si(CH3)3), 56.3 (s,
DME), 69.4 (s, DME), 126.0 ppm (t, 1JC,P = 59.2 Hz, PCP); 29Si NMR:
d = ꢀ17.3 ppm (t, 2JSi,P = 18.3 Hz, Si(CH3)3). The pale yellow solid was
then dissolved in a mixture of hexane (5 mL) and DME (0.2 mL) and
the solution was stored at ꢀ308C. Yellow crystals of 4[Li+(dme)]2
formed over a period of 2 days.
[10] a) P. Binger, R. Milczarek, R. Mynott, M. Regitz, W. Rösch,
Angew. Chem. 1986, 98, 645; Angew. Chem. Int. Ed. Engl. 1986,
25, 644; b) P. B. Hitchcock, M. J. Maah, J. F. Nixon, J. Chem. Soc.
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[11] a) J. Lynam, M. Copsey, M. Green, J. Jeffery, J. McGrady, C.
Russell, J. Slattery, A. Swain, Angew. Chem. 2003, 115, 2884;
Angew. Chem. Int. Ed. 2003, 42, 2778; b) M. D. Francis, P. B.
Hitchcock, Chem. Commun. 2002, 86; c) G. Anderson, J. C.
Green, M. D. Francis, Organometallics 2003, 22, 2897.
[12] a) A. Sekiguchi, T. Matsuo, H. Watanabe, J. Am. Chem. Soc.
2000, 122, 5652; b) A. Sekiguchi, M. Tanaka, T. Matsuo, H.
Watanabe, Angew. Chem. 2001, 113, 1721; Angew. Chem. Int. Ed.
2001, 40, 1675; c) A. Sekiguchi, T. Matsuo, M. Tanaka,Organo-
metallics 2002, 21, 1072.
4[K(dme)2]2: Potassium (0.39 g, 10.0 mmol) was added to an
orange suspension of 1b (0.72 g 1.0 mmol) in DME (15 mL), and the
mixture was stirred for 3 h at room temperature. The solution became
dark red, as the reaction proceeded. The reaction mixture was filtered
to remove residual metal, and the solvent was then removed in
vacuum. The residue was washed with hexane (20 mL). Yield: 471 mg
(96%); NMR ([D8]THF, 258C): 31P NMR: d = 217.3 ppm (s);
1H NMR: d = 0.0 (s, Si(CH3)3), 1.4 (s, Mes*), 3.3 (s, DME), 3.4 (s,
DME), 7.4 ppm (s, Mes*); 13C NMR: d = 0.0 (t, 3JC,P = 2.6 Hz,
Si(CH3)3), 55.5 (s, DME), 69.4 (s, DME), 125.5 ppm (s, PCP); 29Si
[13] F. G. N. Cloke, P. B. Hitchcock, J. F. Nixon, D. J. Wilson, Organo-
metallics 2000, 19, 219.
2
NMR: d = ꢀ22.5 ppm (t, JSi,P = 20.7 Hz, Si(CH3)3).
[14] F. Tabellion, C. Peters, U. Fischbeck, M. Regitz, F. Preuss, Chem.
Eur. J. 2000, 6, 4558.
Received: August 29, 2003 [Z52746]
[15] Further cooling to ꢀ908 results in a signal broadening because of
quadrupolar relaxation: O. Howarth in Multinuclear NMR
Spectroscopy, (Ed.: J. Mason), Plenum, New York, 1987, pp. 133.
[16] The aromatic character of the cyclobutadiene dianion together
with other possibly aromatic dianions has recently been studied
in detail. a) T. Sommerfeld, J. Am. Chem. Soc. 2002, 124, 1119;
b) S. Feuerbacher, A. Dreuw, L. S. Cederbaum, J. Am. Chem.
Soc. 2002, 124, 3163; c) S. Feuerbacher, L. S. Cederbaum, J. Am.
Chem. Soc. 2003, 125, 9531; d) A. Dreuw, L. S. Cederbaum,
Chem. Rev. 2002, 102, 181. The interesting conclusion of these
studies is that the increasing conjugation destabilizes the
dianions against electron loss, thus reducing their lifetimes.
Note that these conclusions do not refer to the ion-pair-
stabilized anions.
Keywords: density functional calculations · dianions ·
fragmentation · phosphorus heterocycles · radical anions
.
[1] A. Fuchs, F. Baumeister, M. Nieger, W. W. Schoeller, E. Niecke,
Angew. Chem. 1995, 107, 640 – 642; Angew. Chem. Int. Ed. Engl.
1995, 34, 555.
[2] W. W. Schoeller, C. Begemann, E. Niecke, D. Gudat, J. Phys.
Chem. A 2001, 105, 10731.
[3] Very recently a stable 1,3-diphosphetane-2,4-diyl was obtained
exhibiting a large red shift: H. Sugiyama, S. Ito, M. Yoshifuji,
Angew. Chem. 2003, 115, 3932; Angew. Chem. Int. Ed. 2003, 42,
3802.
[17] L. Nyulµszi, T. VeszprØmi, J. RØffy,J. Phys. Chem. 1993, 97, 4011.
[18] Calculations were carried out by using the Gaussian 98 package.
(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. Unless otherwise
stated the geometries were optimized first at the B3LYP3-
21G(*) level of theory, and at the optimized structures second
derivatives were calculated to show, whether minimum (positive
eigenvalues only) or transition structure (a single negative
eigenvalue of the hessian matrix) has been obtained. Further
optimization was performed at the B3LYP6-31 + G* level of the
theory. Magnetic shieldings were calculated by using the GIAO
method, at the B3LYP6-311 + G**//B3LYP6-31 + G* level. To
calculate the thermodynamic functions the B3LYP3-21G(*)
[4] Similar biradicaloid features have been demonstrated for a 1,3-
diphospha-2,4-diboracyclobutane-2,4-diyl: D. Scheschkewitz, H.
Amii, H. Gornitzka, W. W. Schoeller, D. Bourissou, G. Bertrand,
Science 2002, 295, 1880.
[5] a) A. Fuchs, O. Schmidt, D. Gudat, M. Nieger, W. Hoffbauer,
W. W. Schoeller, E. Niecke, Angew. Chem. 1998, 110, 995;
Angew. Chem. Int. Ed. 1998, 37, 949; b) A. Fuchs, M. Sebastian,
O. Schmidt, M. Nieger, L. Nyulµszi, E. Niecke, unpublished
results.
[6] A. Fuchs, M. Nieger, E. Niecke, Angew. Chem. 1999, 111, 3213;
Angew. Chem. Int. Ed. 1999, 38, 3028.
[7] a) Presented at the 10th International Symposium on Inorganic
Ring Systems: M. Sebastian, M. Nieger, L. Nyulaszi, E. Niecke
(Vermont, USA, August 2003); b) M. Sebastian, O. Schmidt, M.
Nieger, L. Nyulµszi, E. Niecke, unpublished results.
[8] P. Maslak, Top. Curr. Chem. 1993, 168, 1; J.-M. SavØant, Acc.
Chem. Res. 1993, 26, 455.
[9] X-ray structure analysis of 4[Li(dme)]2: C16H38Li2O4P2Si2:
yellowish crystals, crystal dimension 0.15 0.20 0.50 mm3;
Mr = 426.46; monoclinic, space group P21/n (No. 14), a =
11.1755(2), b = 10.9568(2), c = 11.1966(2) , b = 105.786(1)8,
V= 1319.29(4) 3, Z = 2, m(MoKa) = 0.270 mmꢀ1, T= 123(2) K,
F(000) = 460. 26387 reflection up to 2qmax. = 508 were measured
on a Nonius KappaCCD diffractometer with MoKa radiation,
2329 of which were independent and used for all calculations.
640
ꢀ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2004, 43, 637 –641