Silole Dianions Research Articles

Three-membered cyclic digermylenes stabilised by an N-heterocyclic carbene

Treatment of potassium salts of silole dianions with donor stabilised germanium dichlorides gave the anticipated silagermafulvenylidenes R2Si = Ge(Do) (R2Si = 1-silacyclopentadiendiyl, Do = N-heterocyclic carbene (NHC)) only as transient intermediates in a side reaction. They were detected by NMR spectroscopy and, in one case, the formal dimer, 2,4-disila-1λ3,3λ3-digermetane, was isolated. The main products of these reactions are sila-bis-λ3-germiranes, i.e. directly interconnected digermylenes that are part of a three-membered ring. The structural data, supported by the results of density functional calculations confirm the digermylene nature of these products with a long inner cyclic Ge–Ge bond that decreases the inherent high ring strain in silagermiranes.

Synthesis of 1,1'-Bis(1-Methyl/Chloro-2,3,4,5-Tetraphenyl-1-Silacyclopentadienyl) [Ph4C4Si(Me/Cl)-(Me/Cl)SiC4Ph4] from Silole Anion [MeSiC4Ph4]-•[Li+ or Na+] and Silole Dianion [SiC4Ph4]2-•2[Li+]; Oxidative Coupling of Silole Anion [MeSiC4Ph4]-•[Li+ or Na+] by Ferrous Chloride (FeCl2) and Oxidative Coupling and Chlorination of Silole Dianion [SiC4Ph4]2-•2[Li+] by Cupric Chloride (CuCl2).

A reaction of silole anion {[MeSiC4Ph4]−•[Li+ or Na+] (1) with anhydrous ferrous chloride (FeCl2) in THF (tetrahydrofuran) gives 1,1′-bis(1-methyl-2,3,4,5-tetraphenyl-1-silacyclopentadienyl) [Ph4C4Si(Me)-(Me)SiC4Ph4] (2) with precipitation of iron metal in high yield. Silole dianion {[SiC4Ph4]2−•2[Li+] (3) is added to anhydrous cupric chloride (CuCl2) in THF at −78 °C, then the dark red solution changes into a greenish solution. From the solution, a green solid is isolated, and stirring it in toluene at room temperature provides quantitatively 1,1′-bis(1-chloro-2,3,4,5-tetraphenyl-1-silacyclopentadienyl) [Ph4C4Si(Cl)-(Cl)SiC4Ph4] (4) with precipitation of copper metal in toluene. The green solid is suggested to be 1,1′-bissilolyl bisradical [Ph4C4Si-SiC4Ph4]2• (8), and lithium cuprous chloride salts {[Li2CuICl2]+•[CuICl2]−}. Both reactions are initiated by single-electron transfer (SET) from the electron-rich anionic silole substrates (1 and 3) to iron(II) and copper(II).

Trialkylsilyl-Substituted Silole and Germole Dianions

The synthesis of dipotassio-2,5-bis(trialkylsilyl)silacyclopentadienediides K2[3] and germacyclopentadienediides K2[4] is reported. The prepared silole dianions, 3, are characterized by a significantly deshielded silicon nuclei with 29Si NMR signals at very unusual low field positions for silicon anions (δ29Si = 148–169). The results of DFT calculations revealed that this deshielding is a consequence of the silylene-like frontier orbitals of silole dianions 3 and efficient hyperconjugation between the trialkylsilyl-substituents and the cyclic delocalized π-system. Solid-state structure determinations of potassium salts of silole and germole dianions revealed a novel polymeric bis-η5,bis-η1-coordination mode between heterole and potassium ions.

Isolable 1,1-Disubstituted Silole Dianion: a Homogeneous Two-Electron-Transfer Reducing Reagent

The 1,1-disubstituted silole dianion 2 has been isolated and characterized by single-crystal X-ray analysis for the first time. 2 can be used as a two-electron-transfer reducing reagent for the reduction of organic compounds and inorganic salts with regeneration of the corresponding neutral silole in nearly quantitative yields, indicating that it is an excellent reducing reagent. Reduction of (Mes)2SiCl2 with 2 selectively yielded the cyclotrisilane (Mes2Si)3 in high yield, which has not been isolated in pure form with the existing methods.

Synthesis and NMR-Study of 1-Trimethylsilyl Substituted Silole Anion [Ph4C4Si(SiMe3)]−•[Li]+ and 3-Silolenide 2,5-carbodianions {[Ph4C4Si(n-Bu)2]−2•2[Li]+, [Ph4C4Si(t-Bu)2]−2•2[Li]+} via Silole Dianion [Ph4C4Si]−2•2[Li

1-Trimethylsilyl, 1-R (R = Me, Et, i-Bu)-2,3,4,5-tetraphenyl-1-silacyclopentadiene [Ph4C4Si(SiMe3)R] are synthesized from the reaction of 1-trimethylsilyl,1-lithio-2,3,4,5-tetraphenyl-1-silacyclopentadienide anion [Ph4C4SiMe3]−•[Li]+ (3) with methyl iodide, ethyl iodide, and i-butyl bromide. The versatile intermediate 3 is prepared by hemisilylation of the silole dianion [Ph4C4Si]−2•2[Li]+ (2) with trimethylsilyl chloride and characterized by 1H-, 13C-, and 29Si-NMR spectroscopy. 1,1-bis(R)-2,3,4,5-tetraphenyl-1-silacyclopentadiene [Ph4C4SiR2] {R = n-Bu (7); t-Bu (8)} are synthesized from the reaction of 2 with n-butyl bromide and t-butyl bromide. Reduction of 7 and 8 with lithium under sonication gives the respective 3-silolenide 2,5-carbodianions {[Ph4C4Si(n-Bu)2]−2•2[Li]+ (10) and [Ph4C4Si(t-Bu)2]−2•2[Li]+ (11)}, which are characterized by 1H-, 13C-, and 29Si-NMR spectroscopy. Polarization of phenyl groups in 3 is compared with those of silole anion/dianion, germole anion/dianion, and 3-silolenide 2,5-carbodianions 10 and 11.

Synthesis of 1,1-Bis(n-butyl, t-butyl)-2,3,4,5-Tetraphenyl-1-Silacyclopentadiene and NMR Study of Their 2,5-Carbodianions

Abstract1,1-Bis(n-butyl)-2,3,4,5-tetraphenyl-1-silacyclopentadiene (3) and 1,1-bis(t-butyl)-2,3,4,5-tetraphenyl-1-silacyclopentadiene(4) are synthesized from the reaction of the versatile silole dianion (2) with n-butyl bromide and t-butyl bromide. Reductionof (3) and (4) with an excess of lithium to give 1,1-bis(n-butyl)-2,5-dilithio-2,3,4,5-tetraphenyl-1-silacyclopenta-3-enide(6) and 1,1-bis(t-butyl)-2,5-dilithio-2,3,4,5-tetraphenyl-1-silacyclopenta-3-enide (7). 13 C-NMR study of two 2,5-carbodianions (6 and 7) shows tert-carbanion at 73.18 and 78.12 ppm respectively. Two bulky tert-butyl groups in (7)increase the inversion barrier at the tert-carbanion, line broadenings of tert-butyl groups in 1 H and 13 C-NMR spectrumare observed.Key words: Silole, tert-Carbanion, 2,5-Carbodianion, Inversion 1. Introduction In last decades a lot of group 14 metalloles have beenprepared [1-6] . Especially their anions/dianions have beenreported to be aromatic systems in experimental [7-25] andtheoretical studies

Synthesis and NMR-Study of the 2,3,4,5-Tetraethylsilole Dianion [SiC4Et4]2−•2[Li

The previously unknown silole dianion [SiC4Et4]2−•2[Li]+ (3) was prepared by the sonication of 1,1-dichloro-2,3,4,5-tetraethyl-1-silacyclopentadiene [Cl2SiC4Et4, 2] with more than four equivalent of lithium in THF. 1H-, 13C-, and 29Si-NMR data of 3 are compared with those of the reported silole dianion [SiC4Ph4]2−. Trapping of 3 with trimethylchlorosilane gave 1,1-bis(trimethylsilyl)-2,3,4,5-tetraethyl-1-silacyclopentadiene [(Me3Si)2SiC4Et4, 4] in high yield. The silole of 2 was synthesized in high yield in three steps by a modified procedure using Cp2ZrCl2 via Cp2ZrC4Et4 and 1,4-dibromo-1,2,3,4-tetraethyl-1,3-butadiene.

Reduction of 1-chloro-1,2,3,4,5-pentaphenylsilole: formation of silole monoanion and dianion

The reduction of 1-chloro-1,2,3,4,5-pentaphenylsilole, (C 4Ph 4SiPhCl, 1) with 2 equiv lithium gave the pentaphenylsilole anion [C 4Ph 4SiPh] − ( 2), silole dianion [C 4Ph 4Si] 2− ( 3), and hexaphenylsilole C 4Ph 4SiPh 2 ( 4). 2, 3, and 4 from the reaction mixture were characterized by 29Si NMR spectroscopy. The 29Si chemical shift of 3.7 ppm for 2 is shifted upfield as compared to that of previously reported t -butyltetraphenylsilole anion Li[C 4Ph 4Si tBu], but shifted downfield compared to that of the other silole monoanion such as Li[C 4Me 4SiSiMe 3], indicating the delocalization of silole anion through the 5-membered ring. Derivatization of the reaction mixture with iodomathane gave C 4Ph 4SiPh 2 ( 4), C 4Ph 4SiMePh ( 5), and C 4Ph 4SiMe 2 ( 6), which were characterized by 1H, 13C, and 29Si NMR spectroscopy. The silole dianion 3 could be either from the continuous reduction of 1 with lithium or from the disproportionation of 2. The reduction of 1 with excess lithium in THF gave the silole dianion [C 4Ph 4Si] 2− in about 70% yield.

ChemInform Abstract: Synthesis and Characterization of Dibenzannulated Silole Dianions. The 1,1-Dilithiosilafluorene and 1,1′-Dilithiobis(Silafluorene) Dianions.

Abstract Stirring of 1,1-dichloro-SiFl ( 1 ), (SiFl, silafluorene) in THF with excess lithium for 1 h gave a dark green solution of 1,1-dilithio-SiFl ( 2 ) in high yield. The dark red solution of the intermediate 1,1′-dilithio-(SiFl) 2 ( 3 ) was also observed from this reaction within 10 min. Treatment of 2 with excess trimethylchlorosilane gave the 1,1-bis(trimethylsilyl)-SiFl derivative ( 4 ) in 95% yield. Treatment of the dark red solution of 3 and 2 with excess methyliodide gave the 1,1′-dimethyl-bis(SiFl) ( 5 ) and 1,1-dimethyl-SiFl ( 6 ) derivatives in a 4:1 ratio. The upfield locations of the 29 Si resonances of dianions 2 and 3 (−1.09 ppm and −39.25 ppm, respectively) are consistent with π-electron localization on the silicon atoms.

Synthesis and characterization of dibenzannulated silole dianions. The 1,1-dilithiosilafluorene and 1,1′-dilithiobis(silafluorene) dianions

Stirring of 1,1-dichloro-SiFl ( 1), (SiFl, silafluorene) in THF with excess lithium for 1 h gave a dark green solution of 1,1-dilithio-SiFl ( 2) in high yield. The dark red solution of the intermediate 1,1′-dilithio-(SiFl) 2 ( 3) was also observed from this reaction within 10 min. Treatment of 2 with excess trimethylchlorosilane gave the 1,1-bis(trimethylsilyl)-SiFl derivative ( 4) in 95% yield. Treatment of the dark red solution of 3 and 2 with excess methyliodide gave the 1,1′-dimethyl-bis(SiFl) ( 5) and 1,1-dimethyl-SiFl ( 6) derivatives in a 4:1 ratio. The upfield locations of the 29Si resonances of dianions 2 and 3 (−1.09 ppm and −39.25 ppm, respectively) are consistent with π-electron localization on the silicon atoms.

Aromatic Benzannulated Silole Dianions. The Dilithio and Disodio Salts of a Silaindenyl Dianion1

Aromatic Benzannulated Silole Dianions. The Dilithio and Disodio Salts of a Silaindenyl Dianion¹

Aromaticity in Silole Dianions: Structural, Energetic, and Magnetic Aspects

Structural, energetic, and magnetic criteria confirm that the silole dianion (CH)4Si2- (7) and its alkali-metal ion pairs, e.g. (CH)4SiLi- (7a), (CH)4SiLi2 (7b), (CH)4SiNa2 (13), and (CH)4SiK2 (14), are highly aromatic. Inverse sandwich structures and strongly delocalized silole rings are prefered by 7b, 13, and 14. The degree of aromaticity in [η5-(CH)4Si]Li- (7a) exceeds that of the isoelectronic third-period heterocycles (CH)4PLi (5a) and (CH)4SLi+ (6a) and even approaches that of (CH)5Li (3a).

Synthesis and Study of Cyclic π-Systems Containing Silicon and Germanium. The Question of Aromaticity in Cyclopentadienyl Analogues

Synthetic routes to the metallole species C4Me4E(H)R (9, E = Si, R = Si(SiMe3)3; 10, E = Si, R = Mes (mesityl); 11, E = Ge, R = Si(SiMe3)3; 12, E = Ge, R = Mes), C4R4E(SiMe3)2 (13, E = Si, R = Me; 14, E = Ge, R = Me; 19, E = Si, R = Et; 20, E = Ge, R = Et), and C4Me4E(R)E(R)Me4C4 (15, E = Si, R = SiMe3; 16, E = Si, R = Me; 17, E = Ge, R = SiMe3; 18, E = Ge, R = Me) are described. In the presence of 18-crown-6, dihalides 1 and 2 are reduced by potassium in tetrahydrofuran to give crystalline samples of the silole dianion [K(18-crown-6)+]2[C4Me4Si2-] (21) and the germole dianion [K4(18-crown-6)3][C4Me4Ge]2 (22). Compound 21 adopts an inverse-sandwich geometry, while 22 is a dimer with a bridging [K(18-crown-6)K]2+ group and η5-binding modes for all of the potassium atoms. The metallole dianions in these structures appear to possess delocalized π-systems, as evidenced by nearly equivalent C−C bond lengths in the five-membered rings. Silolyl and germolyl anions have been obtained by various methods involving ...