Chemical behavior of acylpolysilanes, (Me3Si)3SiCOR (1a, R = Mes; 1b, R = o-Tol; 1c, R = Ad; 1d, R = t-Bu; 1g, R = Ph; 1h, R = Me), toward silyllithium reagents has been studied. Reactions of 1a−d with [tris(trimethylsilyl)silyl]lithium gave the corresponding lithium silenolates, (Me3Si)2SiCROLi (5a, R = Mes; 5b, R = o-Tol; 5c, R = Ad; 5d, R = t-Bu), in high yield by removal of a trimethylsilyl group from the acylpolysilane. However, a similar reaction of 1g gave an unstable lithium silenolate, which undergoes dimerization and then further reactions under the conditions used. Acetylpolysilane 1h did not afford the lithium silenolate but gave lithium [tris(trimethylsilyl)silyl]ethenolate. Lithium silenolate 5a was produced also by treating 1a with (dimethylphenylsilyl)lithium. The reactions of 1b,c with (dimethylphenylsilyl)lithium proceed in a different fashion from that of 1a to afford products arising from addition of the silyllithium to the carbonyl bond as major products. Lithium silenolates 5a,c,d are stable at low temperature in THF solution and can be characterized by NMR spectroscopy. Silenolates 5a−d reacted with alkyl halides to afford Si-alkylated products in high yield. Treatment of 5a,b with chlorotriethylsilane led to the formation of silenes arising from O-silylation of the lithium silenolates, almost quantitatively, while 5c,d gave the corresponding acylpolysilanes by Si-silylation in high yield. Results of theoretical studies which were carried out using the reaction of (H3Si)3SiCOCH3 with H3SiLi as a model also are described.

The chemical behavior of lithium silenolates, (Me3Si)2SiC(OLi)R (1a, R = Mes; 1b, R = t-Bu), toward carbonyl compounds was studied. Treatment of lithium silenolates 1a and 1b with benzaldehyde and then with chlorotriethylsilane afforded products derived from the reactions of the lithium silenolates with 2 equiv of benzaldehyde, followed by coupling of the resulting anions with chlorotriethylsilane, in good yields. Treatment of 1a and 1b with mesityl aldehyde under the same conditions proceeded similarly to give the respective adducts in high yields, while the reaction of 1a with acetophenone gave the adduct only in low yield. Similar reactions of 1a and 1b with mesityl methyl ketone, however, afforded no adducts but produced lithium 1-mesitylethenolate and the respective acylbis(trimethylsilyl)silanes.

No abstract

The chemical properties of lithium silenolates toward dienes were studied. The reaction of lithium 2-tert-butyl-1,1-bis(trimethylsilyl)silen-2-olate (1a) with butadiene at −40 °C, followed by hydrolysis, afforded 2-tert-butyl-1,1-bis(trimethylsilyl)silacyclohex-4-en-2-ol, derived from [2 + 4] cycloaddition of 1a with butadiene, in 94% yield. Similar treatment of lithium 2-adamantyl-1,1-bis(trimethylsilyl)silen-2-olate (1b) gave the respective adduct in 87% yield. The reactions of lithium silenolates 1a,b with 2,3-dimethylbutadiene, isoprene, and 1,3-pentadiene proceeded in a fashion similar to those with butadiene to give the [2 + 4] cycloadducts in high yields. The reactions of 1a,b with 2,3-dimethylbutadiene and butadiene at room temperature gave the products originated from 1,1-bis(trimethylsilyl)silacyclohexa-1,4-diene intermediates. The crystal structure of 10-adamantyl-2,3,6,7-tetramethyl-9-(trimethylsilyl)-9-silabicyclo[4.4.0]deca-2,6-diene (6b), which was obtained from the reaction of 1b with 2,3-dimethylbutadiene at room temperature, was determined by a single-crystal X-ray diffraction study.

Treatment of lithium 2-mesityl-, adamantyl-, and tert-butyl-1,1-bis(trimethylsilyl)-1-silen-2-olate with 0.5 equiv of palladium dichloride afforded the corresponding coupling products, 1,2-bis(acyl)tetrakis(trimethylsilyl)disilanes (3a−c), in high yields. The molecular structure of compound 3b was established by single-crystal X-ray diffraction study.