Structure and Chemistry of 1-Silafluorenyl Dianion, Its Derivatives, and an Organosilicon Diradical Dianion

Abstract

1-Silafluorene dianion was synthesized by potassium reduction of 1,1-dichloro-1-silafluorene in refluxing THF. The X-ray structure of 1,1-dipotassio-1-silafluorene (3b) shows C−C bond length equalization in the five-membered silole ring and C−C bond length alternation in the six-membered benzene rings, indicating aromatic delocalization of electrons in the silole ring. The downfield 29Si chemical shift at 29.0 ppm and theoretical calculations also support electron delocalization in the silole ring of 3b. Dianion salt 3b underwent nucleophilic reactions with Me3SiCl and EtBr to form the corresponding disubstituted products. Benzaldehyde underwent reductive coupling in the presence of 3b. Slow oxidation of 3b yielded 1,1‘-dipotassio-1,1‘-bis(silafluorene) (16). The X-ray structure and 29Si chemical shift (−38.0 ppm) of 16 indicate localized negative charges at the silicon atoms and no aromatic character. Heating a DME/hexane solution of 3b in the presence of 18-crown-6 led to a novel diradical dianion salt.

Synthesis and Reactions of Dibenzo[a,e]pentalenes

“…The X-ray crystallographic analysis of 26a revealed that the fivemembered rings contain nearly equalized CC bond lengths, whereas a slight bond alternation in those of the six-membered ring is found, suggesting preferable aromatic delocalization in the five-membered ring over benzenoid delocalization. Similar trends were also found in some benzannulated anions [50][51][52][53][54][55][56]. Dianion 26a was also synthesized by the reaction of the corresponding dibenzopentalene 1aa with lithium (Scheme 31) [57].…”

Tetramer and Polymer of 2,7-Dialkoxy-9H-9-silafluorene Composed of Si Backbone and π-Stacked Biphenylene Groups

“…Corey, 3 Tanaka, 4 and West 5 reported SiSi coupling reactions of 9H-9-silafluorene and dichlorosilafluorene to obtain new polymers, which have a main chain composed of Si atoms and have a biphenylene group in each repeating unit. The obtained polymers, however, are not soluble in common organic solvents, and hence are not suited for detailed studies on molecular structures and film fabrication.…”

Unusual Reaction of 1,1‐Dilithio‐2,3,4,5‐tetraphenylsilole with 1,3‐Dienes Yielding Spirosilanes and Elemental Lithium

“…2 (20 %) was detected by 1 H NMR spectroscopy. 5: Compound 4 was prepared from 9,9-dichloro-9-silafluorene and lithium as described by Liu et al [7] A solution of DMB (2.2 mmol) in toluene (10 mL) was added at À78 8C to a solution of 4 (2.2 mmol) in toluene (10 mL). The reaction mixture was worked up as described above for 2.…”