Stable Silapyramidanes

Abstract

Starting from tetrakis(trimethylsilyl)cyclobutadiene and an amidinate-supported silylene of the Roesky-type, a sequence of addition and reduction cleanly gives the elusive silapyramidane via an isolable cyclobutene intermediate with an exocyclic SiC bond. The silapyramidane features an unusually shielded 29Si NMR resonance at −448.3 ppm for the apex silicon atom. Treatment with Fe2(CO)9 results in the formation of the corresponding silapyramidane–iron complex. Silapyramidane also reacts with the cyclobutadiene starting material to cleanly afford a fluorescent spirobis(silole).

Pyramidanes: newcomers to the anti-van’t Hoff–Le Bel family

“…The structural characteristics of 42 are also highly reminiscent to those of its heavier congeners 11ac: stretched Si-C pyramidal bonds of 2.027(1)-2.037(2) Å that are notably longer than the standard Si-C single bonds (1.91 Å), and near-square shape of the C 4 -base with the basal C-C bonds of 1.483(2)-1.490(2) Å. 98 Similar to its heavier analogues 11a-c, (sila)pyramidane 42 revealed NBO charge separation within the molecule (+0.71e on Si and À0.71e on the cyclobutadiene fragment), high s-character (84.7%) lone pair at the Si apex, and relatively small bond order for the pyramidal Si-C bonds (0.48-0.49, WBI) [DFT BP86-D3(BJ)/def2-SVP level]. The AIM topological analysis of 42 revealed, again in accord with the results reported for other pyramidanes, a significant degree of ionic contribution for the apical Si-C bonds.…”

“…At first, they prepared a (sila)pyramidane precursor, namely, cyclobutene 41 featuring an exocyclic SiQC bond, unexpectedly formed upon the reaction of the tetrakis(trimethylsilyl)cyclobutadiene with Roesky's silylene PhC(N t Bu) 2 SiCl (Scheme 28). 98 Being an intramolecularly donor-stabilzied silene, 41 exhibited a high-field 29 Si NMR signal observed at À35.3 ppm. The SiQC double bond in 41 of 1.736(2) Å was in the range expected for amidinate-supported silenes.…”

A donor-supported silavinylidene and silylium ylides: boroles as a flexible platform for versatile Si(ii) chemistry

“…Almost coinciding with this study, the Scheschkewitz and Nakamoto groups reported the highly related reaction involving trimethylsilyl migrations of a cyclobutadiene with Roesky's PhC(NtBu)2SiCl 38 to give a donorstabilized silene which can be reduced to give access to silapyramidane. 39 We recently reported a synthetic route to a series of 2,5-disilyl-3,4-diaryl boroles [(Ar2TMS2C4)B-R, A/B-R] (backbone system A: Ar = Xyl = 3,5-Me2(C6H3); B: Ar = Ph* = 3,5-t Bu2(C6H3), Chart 1) and successfully applied boroles as a dianionic, [Cp] --mimicking ligand for E(+II) coordination chemistry. 17,[40][41][42][43] In the following discussion of compounds, all product numbers will be accompanied by the borole identifier from which they derive.…”

Cyclobutenylidene: A Multifaceted Two-Coordinate Carbon Species Obtained via Skeletal Editing of a Cyclopropenylidene

“…CBY-transition metal complexes have also been sought as intermediates for metathesis reactions; , however, no free CBY has been synthesized as a persistent or isolable species up to date. In fact, while the chemistry of heavier group-14 element analogue of vinyl carbenes − has shown considerable development, vinyl carbenes are still regarded as challenging species to synthesize due to their high tendency to cyclize to cyclopropenes. − …”