Heavier Ester analogues : synthesis of amidinate-stabilized aryloxo silanechalcogenones
Date of Issue2016
School of Physical and Mathematical Sciences
The first amidinate-stabilized aryloxosilylene [LSi(OAr)] (II, L = PhC(NtBu)2, Ar = 2,6-tBu2-4-MeC6H2) was synthesized by the reaction of the amidinate-stabilized chlorosilylene I with lithium 2,6-di-tert-butyl-4-methylphenyloxide in E120. After that, the amidinate-stabilized aryloxosilylene-borane adduct [L(ArO)Si~BH3] (III) and the amidinate-stabilized aryloxosilanechalcogenones [L(ArO)Si=E] [E = S (IV) and Se (V)] were synthesized by treatment of II with BH3, elemental sulfur and elemental selenium, respectively. The structures of the amidinate-stabilized aryloxosilylene, aryloxosilylene-borane adduct and aryloxosilanechalcogenones were determined by X-ray crystallography, and NMR spectroscopy. The 29Si NMR results showed that the amidinate-stabilized aryloxo silanechalcogenones [L(ArO)Si=E] [E = S (IV) and Se (V)] are upfield shifted compared with those of three-coordinate silanechalcogenones with Si=E double bond. However, the coupling constant of the silicon atom with the selenium atom in V is larger than that in the silaneselenide containing bridging Si-Se bonds. In the solid state, the four-membered Si-N-C-N rings in compounds II, III, IV and V are planner, and the phenyl rings are orthogonal to these planes. In addition, the bond lengths of C-N bonds are intermediate between single and double bond lengths, which indicate that the N-C-N skeletons are partially conjugated and there are electron delocalizations. From the X-ray crystallographic data, the bond lengths of the Si=E bonds [E = S (IV) and Se (V)] are intermediate between double and single bond due to the resonance structures between the Si=E double bond structure and the strongly delocalized Si+-E- single bond structure.