Stable Silenolates and Brook-Type Silenes with Exocyclic Structures

The
first silenolates with exocyclic structures [(Me3Si)2Si­(Si2Me4)2SiC­(R)­O]−K+ (2a: R = 1-adamantyl; 2b:
mesityl; 2c: o-tolyl) were
synthesized by the reaction of the corresponding acylcyclohexasilanes 1a–c with KOtBu. NMR
spectroscopy and single-crystal X-ray diffraction analysis suggest
that the aryl-substituted silenolates 2b,c exhibit increased character of functionalized silenes as compared
to the alkyl-substituted derivative 2a due to the different
coordination of the K+ counterion to the SiC­(R)O moiety. 2b,c, thus, reacted with ClSiiPr3 to give the exocyclic silenes (Me3Si)2Si­(Si2Me4)2SiC­(OSiiPr3)­R (3b: R = Mes; 3c: o-Tol), while 2a afforded the Si-silylated
acylcyclohexasilane 1d. The thermally remarkably stable
compound 3b, which is the first isolated silene with
the sp2 silicon atom incorporated into a cyclopolysilane
framework, could be fully characterized structurally and spectroscopically.