New Element‐Carbon (p‐p)π Bonds

Abstract

Recent years have seen the preparation of π systems containing novel (p‐p)π bonds between carbon and elements from the third, fourth, and fifth Main Groups of the Periodic Table; most of these compounds are predicted to be incapable of existence according to the classical concepts of the double bond. (p‐p)π. Bonds between carbon and phosphorus, arsenic, and antimony have been successfully stabilized in resonance‐stabilized colored compounds of the cyanine and triphenylmethane type, and also in aromatic systems deriving from benzene, naphthalene, and anthracene. Bismuth‐carbon and boron‐carbon (p‐p)π bonds have likewise been confirmed in aromatic systems. Silicon‐carbon and germanium‐carbon (p‐p)π bonds have been detected in extremely reactive derivatives of silaethylene and germaethylene, respectively. The present report describes characteristic reactions of the new π systems. Their bonding follows from X‐ray structure analysis, from photoelectron, UV, and NMR spectra, and from calculations. Criteria for the existence of π systems which are not allowed by the classical double bond rule are discussed; these criteria remain valid on generalization.

Polyanionic Hexagons: X6n– (X = Si, Ge)

“…The multiple-bond rule took a dogma-status as the golden rule in silicon and germanium chemistry for a long time [14]. The rule states that heavier Group 14 elements such as silicon and germanium cannot form multiple bonds because of the considerable Pauli repulsion between the electrons of inner shells.…”

“…The hexagons are coordinated on both sides by barium. Planar hexasilylhexasilacyclohexene anions (Si 12 ) containing Si 6 -ring system of approximate D 6h symmetry was obtained in unusual Zintl phase (Ca 7 Mg 7.5± Si 14 ) with metallic conductivity [11], but the Si 6 ring is nonaromatic. The first flat aromatic D 6h -symmetric Si 6 and Ge 6 rings with six  electrons were computationally designed by us as polyanionic clusters [12,13].…”

Construction of Building Blocks for Highly Functional π-Electron Silicon Nanomaterials by First-Principles Calculations

“…The multiple-bond rule took a dogma-status as the golden rule in silicon chemistry for a long time (Jutzi 1975 (West et al 1981); this is the dawn of the unsaturated silicon chemistry. The X-ray crystallographic measurement of tetramesityldisilene revealed an astonishing fact (Fink et al 1983): tetramesityldisilene adopts a -bent geometry at the silicon-silicon double bond in crystal.…”

Syntheses of elusive unsaturated silacycles

“…The base induced elimination of HCl from 1-chloro-l-alkyl-l-silacyclohexa-2,4-dienes was reported in 1974 by P. Jutzi (26) to yield only polymeric material. Similarly, the elimination of HCl from 9-R-9-chloro-10-R'-9,10-dihydro-9-silaanthracenes ^ were reported to proceed via intermolecular substitution leading to dimeric and polymeric materials (37)(38)(39).…”

“…Since that report, all of the Group V heterobenzenes (X = As, Sb, Bi) and borabenzene (X=B) have been prepared and characterized (26). They are all reasonably stable species either in solution or at low temperatures.…”