Preparation and Properties of Perarylated 3,4-Disila-1,5-hexadienes. A Fluorescent Disilane Accommodated in the Crystal Lattice

Abstract

A dinickel complex with bridging silyl ligands, [{Ni(PCy3)}2(μ-SiHPh2)2] (1), prepared from [Ni(cod)2], PCy3, and H2SiPh2, underwent exchange of the PCy3 ligands with 1,2-bis(dimethylphosphino)ethane (dmpe) to yield a complex coordinated by the two bidentate ligands, [{Ni(dmpe)}2(μ-SiHPh2)2]. Reactions of diarylacetylenes, ArC≡CAr (Ar = C6H5, C6H4OMe-4, C6H4Me-4, C6H4F-4, C6H4CF3-4, C6H4CN-4), with 1 in a 4/1 ratio afforded 1,2-bis{(E)-1,2-diarylethenyl}-1,1,2,2-tetraphenyldisilanes via addition of the Si–H bond of the bridging silyl ligand to the alkynes and subsequent coupling of the resulted tertiary silyl ligand. X-ray crystallography of the dialkenyldisilanes resulted in three kinds of conformation of the C═C–Si–Si–C═C chain depending on the aryl group at the vinyl carbon. The disilane with phenyl substituents, 4a (Ar = C6H5), contained a planar C═C–Si–Si–C═C alignment with small Si–Si–C═C torsion angles (1.7(5) and 6.9(5)°). The other dialkenyldisilanes, 4b,c,e,f, had much larger torsion angles (30.9(3)–49.2(3)°), and the twisted conformation of the molecules was classified into two types. Compound 4a exhibited a fluorescence maximum at 488 nm in the solid state, while 4b–f showed peaks at 393–427 nm. The red shift in the emission of 4a is ascribed to orthogonal intramolecular charge transfer (OICT) from the electron-donating Si–Si to accepting C═C bonds.