Decamethylsilicocene Chemistry:  Reaction with Representative Aldehydes and Ketones

Abstract

Reactions of decamethylsilicocene, (Me5C5)2Si (1), with representative organic carbonyl compounds are described. They proceed via [2 + 1] cycloaddition products of the oxasilirane type as reactive intermediates to give different types of compounds. The formal oxidation state of silicon is changed from +II in the substrate to +IV in the final products; at the same time the hapticity of the pentamethylcyclopentadienyl ligands changes from η5 to η1. In the reaction of 1 with aldehydes such as benzaldehyde and trans-cinnamaldehyde as well as with acetone, formation of the respective dioxasilolane derivatives 2, 3, and 5 takes place. Here, C−C bond formation is observed for the first time in the reaction of a divalent silicon compound; reaction with the aldehydes is stereospecific. In the reaction of 1 with acetophenone or benzophenone, the bicyclic ring systems 6 and 7, respectively, containing an oxasilacyclopentene unit are formed by rearrangement of the transient oxasiliranes. The 1,3,2-dioxasilole 9 is the product of the reaction of 1 with benzil. The new compounds are characterized by NMR (1H, 13C, 29Si) spectroscopy and by mass spectrometry and microanalytical data. The X-ray crystal structure analysis of 2 is presented.

Stabilization of Silicon–Carbon Mixed Oxides

“…The −91.5 ppm 29 Si NMR resonance of 4 is comparable to those for 6 (−100.7 and −101.6 ppm). 26 The carbonyl 13 C NMR resonance (142.5 ppm, in THF-d 8 ) of 4 is similar to that for [(Me 5 C 5 ) 2 SiO 2 CO] 2 (143.9 ppm) 24 and for 6 (148.8 and 148.9 ppm). 26 While the infrared (IR) absorption of the SiO stretch in 4 (1165 cm −1 ) is similar to that of the 4-Ph model (1169 cm −1 ), the ν (CO) band is red-shifted from the (SiO 2 ) 2 CO 2 model (1911 cm −1 ) to the 4-Ph model (1806 cm −1 ), and then to 4 (1751 cm −1 ).…”

“…Since the discovery of carbon dioxide oxidation of decamethylsilicocene nearly two decades ago, 24 CO 2 has been utilized as an oxidant for various low oxidation state group 14 compounds [i.e., disilenes, 25 coordinated disilyne (5 in Scheme 1), 26 amido-digermyne (7 in Scheme 1), 27 and silylenes 28,29 ].…”

Versatile Reactivity of a Zwitterionic Isolable Silylene toward Ketones: Silicon‐Mediated, Regio‐ and Stereoselective CH Activation

“…However, the latter product does not undergo re-aromatization and formation of the corresponding analogue of 3. [20] Although the mechanism is still unknown, it is proposed that the 1,4-dipolar nature of 1 plays an important role in the reaction: First, the charge separation in 1 favors a nucleophilic attack of the oxygen atom in benzophenone at the positively charged, divalent Si atom, leading to the donoracceptor adduct A as an initial product (Scheme 3). Owing to the high Lewis basicity of the Si II lone pair electrons, the formation of a [2 + 1] cycloaddition compound in the following step seems possible but unlikely due to steric congestion and strain energy of the Si-O-C three-membered ring.…”

“…The collected colorless crystals amounted to 0.76 g (1. 20 (d, 3 JA C H T U N G T R E N N U N G (H,H) = 6.5 Hz, 2 H; C 6 H 4 ), 6.32 (d, 3 JA C H T U N G T R E N N U N G (H,H) = 7. …”

“…In the latter case, merely one isolable Nheterocyclic silylene, [16] transient silylenes generated in situ either by thermolysis [17] or photolysis of the corresponding precursors, [18] and decamethylsilocene [19,20] were employed to study the reactivity of divalent silicon toward ketones. The conversions led to unexpected new SiÀC-and SiÀO-functionalized products, including siloxindanes [17][18][19][20] and silyl enol ethers, [17] depending on the electronic nature of the applied silylenes and the ketones. The mechanism is unknown and intermediates could not be observed but it has been proAbstract: Reactions of the isolable, ylide-like silylene LSi: 2 , Ar= 2,6-iPr 2 C 6 H 3 ) with different ketones (benzophenone, benzylideneaceton, acetophenone) have been investigated.…”