화학공학소재연구정보센터
Journal of the American Chemical Society, Vol.132, No.48, 17306-17315, 2010
Transfer of a Disilenyl Moiety to Aromatic Substrates and Lateral Functional Group Transformation in Aryl Disilenes
The reaction of 1 equiv of the disilenide Tip(2)Si=Si(Tip)Li (5; Tip = 2,4,6-(Pr3C6H2)-Pr-i) with para-substituted phenyl iodides, 4-X-Phl, transfers the Tip(2)Si=Si(Tip) moiety with elimination of lithium iodide to yield the laterally functionalized disilenes Tip(2)Si=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 (lambda(max) = 508 nm) exhibits efficient conjugation of the two Si=Si bonds with the phenylene linker, the conjugation in yellow m-7 (lambda(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.