Aromatic Benzannulated Germole Dianions. The Dilithio and Disodio Salts of a Germaindenyl Dianion Seok-Bong Choi, Philip Boudjouk,* and Kun Qin Center for Main Group Chemistry, Department of Chemistry, North Dakota State University, Fargo, North Dakota 58105 Received December 14, 1999 Summary: Conversion of the neutral 1,1-dichloro-DPGI (1) (DPGI ) 2,3-diphenyl-1-germaindene) to the lithium dianion (2a) or sodium dianion (2b) leads to the highly unusual phenomenon of aromatization of the GeC 4 portion of 1-germaindene at the expense of the aromatic annulated C 6 ring. Treatment of 2a with trimethylchlo- rosilane gave the 1,1-bis(trimethylsilyl)-DPGI derivative (3) in high yield. The structure of 2a was determined by X-ray crystallography and found to possess two η 5 - coordinated lithium ions. The five-membered ring of the germaindenyl system undergoes significant carbon- carbon bond equalization upon formation of the dianion, while the remaining four carbon atoms become diene- like, exhibiting two short bonds separated by a long bond. Introduction The structural characterization of the dianionic siloles and germoles by West, 1 Tilley, 2 and our group 3,4 provide strong support for our initial postulation, based on NMR data, 5 that these species were aromatic. All the spec- troscopic data and the typical structures a and b in R 4 E 2- ‚2M + (E ) Si, Ge; M ) Li, Na, and K) have also been supported by calculations. 6 Recently we have reported the unique bonding struc- ture c providing the strong possibility for the intercon- version between the structures a and b in solution. 3 Moreover, we were also able to directly compare the aromaticity between the silole dianion and benzene in silaindenyl dianion molecule d, which indicates that the significant aromaticity in the silicon-containing ring is responsible for changing the fused benzene ring in the precursor to a cyclohexadiene moiety in the dianionic silaindene. 4 Herein we report the synthesis and characterization of the first benzannulated germole dianions, dilithium DPGI (2a) (DPGI ) 2,3-diphenyl-1-germaindene) and disodium DPGI (2b). To our surprise, we find that, upon formation of the dianion, the germanium-containing ring becomes aromatic, apparently at the expense of the fused benzene ring, which takes on the features of a conjugated diene (e). Result and Discussion Stirring of 1,1-dichloro-DPGI (1) 7 with excess lithium in THF produced a dark red solution. After removal of unreacted lithium, treatment of this solution with an excess of trimethylchlorosilane gave 1,1-bis(trimethyl- silyl)-DPGI (3) in high yields (eq 1). For comparative purposes, the molecular structure of 1,1-bis(trimethylsilyl)-DPGI (3) was determined. The X-ray structure of 1,1-bis(trimethylsilyl)-DPGI (3) is shown in Figure 1. The crystallographic data are in Table 1. Selected bond lengths and bond angles are listed in Table 2. The GeC 4 ring has inequivalent C-C distances, indicating isolated single (1.485 Å) and double (1) (a) West, R.; Sohn, H.; Bankwitz, U.; Calabrese, J.; Apeloig, Y.; Mueller, T. J. Am. Chem. Soc. 1995, 117, 11608. (b) West, R.; Sohn, H.; Bankwitz, U.; Powell, D. R.; Mueller, T.; Apeloig, Y. Angew. Chem., Int. Ed. Engl. 1996, 35, 1002. (2) (a) Freeman, W. P.; Tilley, T. D.; Yap, G. P. A.; Rheingold, A. L. Angew. Chem., Int. Ed. Engl. 1996, 35, 882. (b) Freeman, W. P.; Tilley, T. D.; Liable-Sands, L. M.; Rheingold, A. L. J. Am. Chem. Soc. 1996, 118, 10457. (3) Choi, S.-B.; Boudjouk, P.; Hong, J.-H. Organometallics 1999, 18, 2919. (4) Choi, S.-B.; Boudjouk, P.; Wei, P. J. Am. Chem. Soc. 1998, 120, 5814. (5) (a) Hong, J.-H.; Boudjouk, P.; Castellino, S. Organometallics 1994, 13, 3387. (b) Hong, J.-H.; Boudjouk, P. Bull. Chem. Soc. Fr. 1995, 132, 495. (6) (a) Goldfuss, B.; Schleyer, P. v. R.; Hampel, F. Organometallics 1996, 15, 1755. (b) Goldfuss, B.; Schleyer, P. v. R. Organometallics 1997, 16, 1543. (7) Kanj, A.; Meunier, P.; Gautheron, B. J. Organomet. Chem. 1993, 454, 51. (1) 1806 Organometallics 2000, 19, 1806-1809 10.1021/om990991t CCC: $19.00 © 2000 American Chemical Society Publication on Web 03/31/2000