Reactivity in the periphery of functionalised multiple bonds of heavier group 14 elements

Abstract

Heavier group 14 multiple bonds have intrigued chemists since more than a century. The synthesis of stable compounds with double and triple bonds with silicon, germanium, tin and lead had considerable impact on modern ideas of chemical bonding. These developments were made possible by the use of bulky substituents that provide kinetic and thermodynamic protection. Since about a decade the compatibility of heavier multiple bonds with various functional groups has moved into focus. This review covers multiply bonded group 14 species with at least one additional reactive site. The vinylic functionalities of groups 1 and 17, resulting in nucleophilic and electrophilic disila vinyl groups, respectively, are the most prevalent and well-studied. They have been employed repeatedly for the transfer of heavier multiple bonds to yield low-valent group 14 compounds with novel structural motifs. Vinylic functionalities of groups 2 to 16 and a few σ-bonded transition metal complexes are experimentally known, but their reactivity has been studied to a lesser extent. Donor-coordinated multiple bonds are a relatively new field of research, but the large degree of unsaturation as isomers of alkynes (as well as residual functionality in some cases) offers considerable possibility for further manipulation, e.g. for the incorporation into more extended systems. Heavier allyl halides constitute the major part of heavier multiple bonds with a functional group in allylic position and some examples of successful transformations are given. At present, remote functionalities are basically limited to para-phenylene functionalised disilenes. The reported use of the latter for further derivatisation might encourage investigations in this direction. In summary, the study of peripherally functionalised multiple bonds with heavier group 14 elements is already well beyond its infancy and may be an instrumental factor in awakening the potential of group 14 chemistry for applications in polymers and other materials.

A Fully Phosphane‐Substituted Disilene

“…However, the solid‐state cross‐polarization magic angle spinning (CP‐MAS) 31 P{ 1 H} NMR spectrum of 7 consists of a pair of singlets at −55.9 and −77.9 ppm, consistent with the two distinct phosphorus environments observed by X‐ray crystallography (see proceeding text), while the solid‐state CP‐MAS 29 Si{ 1 H} NMR spectrum of 7 consists of a broad singlet at 111.7 ppm; 31 P– 29 Si coupling is not resolved. The 29 Si chemical shift of 7 is in the typical range for disilenes;2, 3 the observed 31 P{ 1 H} and 29 Si{ 1 H} chemical shifts correlate reasonably well with those obtained from DFT calculations (Supporting Information).…”

“…The major disorder component has a strongly trans ‐bent geometry (40.6° deviation of the SiP 2 mean plane from the Si−Si vector). This contrasts with the near‐planar geometries adopted by most silicon‐substituted disilenes,2, 3 although a few carbon‐substituted disilenes do exhibit large trans ‐bending angles 19. The trans ‐bending angle in the major disorder component of 7 is similar to those observed in a few heteroatom‐substituted systems; for example in (Trip) 2 Si=Si(Trip){P(N i Pr 2 ) 2 } the trans ‐bending angle at the phosphorus‐substituted silicon center is 30.8°,4 while the trans ‐bending angles in (Bbt)BrSi=SiBr(Bbt) are 32.4 and 39.8° (Bbt=2,6‐{(Me 3 Si) 2 CH} 2 ‐4‐{(Me 3 Si) 3 C}C 6 H 2 ) 10…”

“…Nevertheless, there is continuing interest in these compounds and recent attention has turned to functionalized species, which provide fascinating opportunities for tuning the physical and chemical properties of the E=E bond 3, 4, 5, 6, 7, 8, 9, 10, 11, 12…”

Synthesis and Functionalization of a 1,2-Bis(trimethylsilyl)-1,2-disilacyclohexene That Can Serve as a Unit of cis-1,2-Dialkyldisilene

“…All operations were carried out in a glove box. In a Schlenk tube (50 mL), 3 (1.26 g, 1.45 mmol), KC 8 (825 mg, 6.10 mmol) and THF (70 mL) were placed. After stirring the mixture at room temperature for three hours, the volatiles were removed under reduced pressure.…”

“…Because such silicon π-electron systems have an intrinsically higher π-orbital level and a narrower HOMO (highest occupied molecular orbital)-LUMO (lowest unoccupied molecular orbital) gap compared to those of the corresponding organic π-electron systems, extended π-electron systems that include the Si=Si double bond(s) should be anticipated to be unprecedented functional π-electron materials. In this context, the reactions of disilenide (a disilicon analogue of vinyl anion [R 2 Si=SiR] − ) with electrophiles is one of the promising routes to introduce a functional group into the silicon π-electron systems [4][5][6][7][8][9]. Disilenides have been synthesized by reductive dehalogenation of the corresponding trihalodisilane [10] or reductive cleavage of R-Si(sp 2 ) bond on the Si=Si double bond in a stable disilene [11][12][13][14][15].…”