Silylenes decamethylsilicocene

Following a number of stable Si-N silylenes301 and the stable hapto bonded silylene decamethylsilicocene (Me5C5)2Si 107,265 Kira et al. have described the preparation of the first stable sigma-bonded dialkylsilylene,... 

After a decade of research the basic principles in the chemistry of decamethylsilicocene (1) seem to be understood. This compound shows the reactivity of a nucleophilic silylene due to the fact that the Tt-bonded pentamethylcyclopentadienyl ligands are easily transferred to a-bonded substituents during the reaction. The steric requirements of these substituents permit reactions with bulky substrates. The migratory aptitude and the leaving-group character of the pentamethylcyclopentadienyl groups... 

The presently known silicon chemical shift range is 990 ppm. This includes the Dsd form of decamethylsilicocene 28 (5 Si = —423 (solid state)), which is the most shielded resonance reported to date and the alkyl-substituted silylene 45, which presently defines the high-frequency end of the spectrum at 5 Si = 567. Most silicon chemical shifts occur, however, in a much smaller range from 5 Si = +50 to —190. This includes hexa-, penta- and tetracoordinated silicon compounds and for trivalent, positively charged silicon a significant low-field shift compared to comparable tetravalent silicon species is expected. 

The reaction of decamethylsilicocene, Si(Cp )2, with Au(PPh3)Cl, in toluene, resulted in insertion of the silylene into the Au-Cl bond and isolation of (Ph3P) AuSiCl(Cp )2 77. The compound is molecular, with a -interaction between a silicon-bound Cp substituent and the central gold atom [Au(l)-Cp centroi[Pg.221]

Although silylenes have been known for a long time as transient intermediates in thermal, photochemical or dehalogenation reactions, stable species have become available only recently. Si(II) compounds with coordination number larger than two have already been isolated in the late eighties, i.e., decamethylsilicocene prepared by Jutzi et al [1] and the tetracoordinated phosphine derivative obtained by Karsch et al [2]. 

Keywords Decamethylsilicocene / Silanone / Silathione / Silylene / Transition metal hydride... 

Summary Decamethylsilicocene (1), the first Si(II) compound stable under ordinary conditions [1], is a h5 ercoordinated nucleophilic silylene, which reacts preferentially with electrophilic substrates [2], In the reaction of 1 with the electrophilic heterocumulenes CO2, COS and RNCS (R = Me, Ph), double bond species of the type Cp 2Si=X (X = O, S) are formed, which are stabilized via different routes to the silaheterocycles I-IV [3], Multistep rearrangement processes are postulated to explain the formation of the dithiasiletane derivatives V and VI in the reaction of 1 with CS2. A surprising polycyclic silaheterocycle VII is obtained in the reaction of 1 with hexafluorobutyne. With HMn(CO)s 1 reacts to the dimanganese-substituted silane VIII. In all reactions, the lone pair at silicon is involved, an r) -ri - rearrangement of the Cp ligands take place, and the formal oxidation state at Si changes to +4 in the final products. 

Usually silylenes are highly reactive due to unoccupied orbital at silicon. In the last years by steric shielding of these reactive centers highly coordinated decamethylsilicocene [1], [2] or silylene complexes with donor and revealed that silylenes are stabilized also by and a free electron pair of donor substituents,... 

Recently the chemistry of nucleophilic silylenes has received a lot of attention. Decamethylsilicocene (1) can be considered as a hypercoordinated nucleophilic silylene [1]. Here we report on reactions of 1 with Lewis-acidic compounds of elements of groups 13 to 15. 

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