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-iPr3C6H2) 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 SN2-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 (λmax = 508 nm) exhibits efficient conjugation of the two SiSi bonds with the phenylene linker, the conjugation in yellow m-7 (λmax = 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.