Kinga Leszczyńska

Reversible Base Coordination to a Disilene

During the last few decades, alkene and alkyne analogues of the heavier Group 14 elements have attracted considerable interest. Their isolation as stable derivatives has become possible by the use of carefully designed bulky substituents that provide kinetic (and to some extent thermodynamic) stabilization. The considerable differences in structure, bonding, and reactivity of such compounds in comparison to the carbon-based species have prompted various experimental and theoretical studies. By and large, the lower electronegativity of heavier elements and the increasing spatial extension of their valence electron shells are responsible for many of these differences. One of several rationalizations for structure and reactivity of such doubly and triply bonded species is based on zwitterionic (Ib and IIb in Scheme 1) and

The Pentamethylcyclopentadienylsilicon(II) Cation as a Catalyst for the Specific Degradation of Oligo(ethyleneglycol) Diethers

Covalent silicon(IV) compounds of the type R3SiX (R= organic substituent, X= electronegative group) have long been used as catalysts for several organic reactions, mainly in carbon–carbon bond-forming processes (such as Diels–Alder reactions, aldol condensations). Some ionic silicon(IV) compounds containing R3Si + cations have also been applied as catalysts in C C bond formation reactions and in some other transformations. The most important examples are collected in Scheme 1.

Isolation and Versatile Derivatization of an Unsaturated Anionic Silicon Cluster (Siliconoid).

Abstract The characteristic features of bulk silicon surfaces are echoed in the related partially substituted—and thus unsaturated—neutral silicon clusters (siliconoids). The incorporation of siliconoids into more‐extended frameworks is promising owing to their unique electronic features, but further developments in this regard are limited by the notable absence of functionalized siliconoid derivatives until now. Herein we report the isolation and full characterization of the lithium salt of an anionic R5Si6‐siliconoid, thus providing the missing link between silicon‐based Zintl anions and siliconoid clusters. Proof‐of‐principle for the high potential of this species for the efficient transfer of the intact unsaturated R5Si6 moiety is demonstrated by clean reactions with representative electrophiles of Groups 13, 14, and 15.

The Cp*Si+ cation as a stoichiometric source of silicon

The Cp*Si(+) cation acts as a stoichiometric source of silicon in the reaction with the disilenide Tip(2)Si=Si(Tip)Li (Tip = 2,4,6-(i)Pr(3)C(6)H(2)) affording known neutral unsaturated silicon clusters. It thereby provides a conceptually different approach to this novel class of compounds. The proposed mechanism involves a Cp*-substituted cyclotrisilene in which Cp*(-) acts as a leaving group upon single electron reduction or in a nucleophilic substitution step.

Disilenyl Silylene Reactivity of a Cyclotrisilene

The highly reactive silicon congeners of cyclopropene, cyclotrisilenes (c-Si3 R4 ), typically undergo either π-addition to the Si=Si double bond or σ-insertion into the Si-Si single bond. In contrast, treatment of c-Si3 Tip4 (Tip=2,4,6-i Pr3 C6 H2 ) with styrene and benzil results in ring opening of the three-membered ring to formally yield the [1+2]- and [1+4] cycloaddition product of the isomeric disilenyl silylene to the C=C bond and the 1,2-diketone π system, respectively. At elevated temperature, styrene is released from the [1+2]-addition product leading to the thermodynamically favored housane species after [2+2] cycloaddition of styrene and c-Si3 Tip4 .