(Oligo)aromatic species with one or two conjugated Si[double bond, length as m-dash]Si bonds: near-IR emission of anthracenyl-bridged tetrasiladiene.

A series of aryl disilenes Tip2Si[double bond, length as m-dash]Si(Tip)Ar (2a-c) and para-arylene bridged tetrasiladienes, Tip2Si[double bond, length as m-dash]Si(Tip)-LU-Si(Tip)[double bond, length as m-dash]SiTip2 (3a-d) are synthesized by the transfer of the Tip2Si[double bond, length as m-dash]SiTip unit to aryl halides and dihalides by nucleophilic disilenides Tip2Si[double bond, length as m-dash]SiTipLi (Tip = 2,4,6-iPr3C6H2, Ar = aryl substituent, LU = para-arylene linking unit). The scope of the nucleophilic Si[double bond, length as m-dash]Si transfer reaction is demonstrated to also include substrates of considerable steric bulk such as mesityl or duryl halides Ar-X (Ar = Mes = 2,4,6-Me3C6H2; Ar = Dur = 2,3,5,6-Me4C6H, X = Br or I). Bridged tetrasiladienes Tip2Si[double bond, length as m-dash]Si(Tip)-LU-Si(Tip)[double bond, length as m-dash]SiTip2 with more extended linking units surprisingly exhibit fluorescence at room temperature, albeit weak. DFT calculations suggest that partial charge transfer character of the excited state is a possible explanation.

Transfer of a disilenyl moiety to aromatic substrates and lateral functional group transformation in aryl disilenes.

The reaction of 1 equiv of the disilenide Tip2Si═Si(Tip)Li (5; Tip = 2,4,6-(i)Pr3C6H2) with para-substituted phenyl iodides, 4-X-PhI, transfers the Tip2Si═Si(Tip) moiety with elimination of lithium iodide to yield the laterally functionalized disilenes Tip2Si═Si(Tip)(4-X-Ph) [X = H (6a), F (6b), Cl (6c), Br (6d), I (6e)]. The UV-vis absorptions of 6a-d suggest a linear correlation with electronic Hammett parameters. In addition, X-ray structural analyses of 6a-d verified the theoretically predicted linear dependence of the Si═Si bond length and trans-bent angles. The p-bromophenyl-substituted disilene 6d undergoes a metal-halogen exchange reaction to give 6f (X = Li), which was trapped with Me3SiCl to afford 6g (X = SiMe3). In the case of simple phenyl halides PhX without additional functionality, the reaction with 5 proceeded smoothly for X = Br, but phenyl chlorides and fluorides did not react at room temperature even after one week, hinting at an S(N)2-type aromatic substitution mechanism. Reactions of p- and m-diiodobenzene with 5 afford the corresponding phenylene-bridged tetrasiladienes p-7 and m-7. While red p-7 (λ(max) = 508 nm) exhibits efficient conjugation of the two Si═Si bonds with the phenylene linker, the conjugation in yellow m-7 (λ(max) = 449 nm) is much less effective. Electrochemical studies of m-7 and p-7 as well as density functional theory calculations and electron paramagnetic resonance studies of their respective radical anions provided further support for the notion of conjugation.