Silyliumylidene

The sharply increasing interest in the chemistry of monovalent silyliumylidene ion derivatives of the type RSi stimulated a great number of experimental studies in this field, which recently culminated in the synthesis of the very remarkable (Tl -Me5C5)Si+ cation 25+ TPFPB- (Scheme 2.21). A stable 25+ TPFPB- was obtained by the oxidation of decamethylsilicocene 26 with (Me5C5H2) TPFPB in CH2CI2 (Scheme 2.21). 

Jutzi et al. synthesized an (/ )-A BSi = SiAB-type disilene by the reaction of stable silyliumylidene cation Me5C5Si + 83 with lithium bis(trimethylsilyl)amide 84.19 Formation of disilene 44 is explained by the dimerization of the initially formed (Me5C5)[(Me3Si)2N]Si ... 

Keywords silyliumylidene, Si(II)-cation, divalent silicon, pentamethylcyclopentadienylsilicon cation... 

The even more reactive SiH" cation ( silyliumylidene ) has been observed in the laboratory by discharge of SilL [7] and also in the solar spectrum. If there is at all a chance to prepare a persistent derivative, then this would probably be with pentamethylcyclopentadienyl as Ji-bonded substituent (Fig. 1). 

Silyliumylidene (179) has been accessed from dibenzo-7-silanorbornadienes (178) by hydride abstraction forming the silylium cation, followed by a-elimination of anthracene.The silyliumylidene has been shown to react with the reaction solvent (namely benzene or toluene) via C-H insertion and Friedel-Craft-type reaction to yield the corresponding triarylsilylium (180). 

A silyliumylidene cation possesses a silicon center that bears a positive charge, a lone pair, and not one but two vacant orbitals (1). Such species are highly unstable and several factors should be considered for the successful isolation of these compounds. The silicon center in these compoimds is stabilized either by intramolecular electron donation or by the use of various donor substituents. The synthetic methods involve multiple step synthesis and usually a low-valent silicon precursor is involved in the synthesis of silyliumylidenes (2—8). 

Scheme 6.3.2.1 Synthesis of NHC-Stabilized Silyliumylidene Ion [m-TerSi( NHC)2lCI m-Ter = 2,6-Mes2C6H3, Mes = 2,4,6-Me3C6H2, NHC = 1,3,4,5-tetramethylimidazol-2-ylidene. ...

This method can be used for the synthesis of NHC-stabilized silyliumylidene ions with various size and functionality of organyl substituents as well as a variety of the NHCs (11). The modification of substituents at the silicon center may lead to different reactivity based on reaction kinetics. The described silyliumylidene cation can activate CO2 and lead to the formation of a sila-acylium ion (12). 

The newly synthesized chlorosilyliumylidene possesses both the HOMO as well as the LUMO mainly on the silicon center according to the DFT calculations promising versatile reactivity. An aspect highlighting the promising nature of the chlorosilyliumylidene [ClSi ] is the substitution of chlorine atom with suitable nucleophiles R that can lead to the generation of silyliumylidene derivatives [RSi ]". The synthesis of a novel cyclic silylone by the reduction of the chlorosilyliumylidene cation is described underneath (7). 

An iminosilylene (LSiCp ) with a bulky bis 2,6-diisopropylphenyl)imidazolin-2-iminato substituent and an electron-donating Cp (Cp = MesCs) group is described (1). The iminosilylene LSiCp is accessible in reasonable yield of 57% (method 1) through the salt metathesis reaction of Jutzi s silyliumylidene cation (2) with the imidazolin-2-iminato lithium salt LIT L = bis 2,6-diisopropylphenyl)imidazolin-2-iminato. An alternate approach is the reduction of the dibromosilane precursor, however, the yield is low in this reaction (Scheme 6.4.2.1). 

Keywords Bond activation Silicon NMR Silylium ion Lewis acid XRD Low coordinated compounds Main group chemistry Organosilicon chemistry Hydrosilylation Silicon cation Small-molecule activation Silyliumylidene... 

Scheme 45 Attempts to synthesize terphenyl-substituted silyliumylidene 132 (anions are omitted) [76]...

Gerdes C, Saak W, Haase D, Muller T (2013) Dibenzosilanorbomadienyl cations and their fragmentation into silyliumylidenes. J Am Chem Soc 135 10353... 

Xiong Y, Yao S, Inoue S, Irran E, Driess M (2012) The elusive silyliumylidene [ClSi ] and silathionium [ClSi=S] cations stabilized by bis(iminophosphorane) chelate ligand. Angew Chem Int Ed 51 10074... 

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