Oligosilyl substituent

Figure 10.6 shows three possible isomers for 4. Isomer II (Cs symmetry) can be ruled out on the basis of steric arguments as the size of the oligosilyl substituents is too large. In isomer III, all seven phosphorus atoms are nonequivalent and hence seven resonances would be expected. For isomer I (Cs symmetry) with two pairs of equivalent phosphorus atoms, five resonances with an intensity ratio I I I 2 2 would be expected, in accordance with observation. There is no evidence for the formation of isomer III. The formation of the anion upon reaction of 1 with tert-BuOK proceeds with a simultaneous inversion of one of the phosphorus atoms. 

Dzambasky A, Baumgartner J, Hassler K (2009) Phosphanes with bulky oligosilyl substituents. J Organomet Chem 694 757... 

Noblet P, Cappello V, Tekautz G, Baumgartner J, Hassler K (2011) Heptaphosphanortri-eyclenes with oligosilyl substituents syntheses and reactions. Eur J Inorg Chem 101... 

Summary A series of mono- and dimetalated oligosilyl compounds with trimethylsilyl- and phenyl substituents has been prepared. Multinuclear NMR spectroscopic data and crystal structures are compared. Trends concerning chemical shift Jt-polarization effects are pointed out. 

Summary The use of oligosilyl dianions greatly facilitates the synthesis of cyclohexasilanes with a specific substituent pattern. A number of such conqiounds differently substituted in 1,4-positions are compared according to their stractural data. While almost all cyclohexasilanes studied so far prefer a chair conformation, we find the unusual example of a twist conformation for l,l,4,4-tetrakis(trimefliylsilyl)-octamethyl-cyclohexasilane (2). 

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