Activation of Small Molecules by Compounds that Contain Triple Bonds Between Heavier Group‐14 Elements

Abstract

According to quantum chemicalp redictions, [5] linear isomer A (Scheme 1), which is analogous to HCCH, does not occupy am inimum on the potentiale nergy surfacef or the isomerization of A into E,f or which two imaginary frequencies were discovered. In contrast, trans-bent model B was identified as am inimum, albeit that its structure is very different from the linear symmetry of HCCH (D 1h ), despite the factt hat the Si atom also exhibits s 2 p 2 valence electrons similar to carbon. According to theoretical calculations, trans-bent disilyne B shouldn ot to be stable and easily isomerize into the more stable 1,2-H-shifted C.D i-bridged E was identified as ag lobal minimum for Si 2 H 2 ,w hile isomer D is al ocal minimum that exhibits the second-lowest energy.T he predicted results were furtherc onfirmed by subsequent experiments, i.e.,b oth D [6a] and E [6b-d] were observedu sing millimeter-and submillimeterwave rotationals pectroscopy.A dditional studies [6e-j] revealed that Ge 2 H 2 ,S n 2 H 2 ,a nd Pb 2 H 2 follow the same trend as Si 2 H 2 , i.e.,their di-bridged formsrepresent globalminima.These studies indicate that efficient steric protection is necessary to prevent isomerizationsvia 1,2-shifts and exergonic dimerizationsi no rder to isolate stable dimetallynes (Scheme2).Recently the idea of kinetic stabilization has been proventob e very effective fort he isolation of stable dimetallynes with an E Et riple bond. Although this review focuses on the reactivity of isolated dimetallynes, their structural features and recent [a] Prof.

Cycloaddition Chemistry of a Silylene‐Nickel Complex toward Organic π‐Systems: From Reversibility to C−H Activation

“…[7,8] Nevertheless, examples of cycloaddition chemistry of these moieties are somewhat sparse. [11,12] Well-defined examples of the cycloaddition chemistry of SiÀMd ouble bonds are limited to reports from Sekiguchi et al (Figure 1), in the [2+ +2] addition of alkynesa nd benzonitrile to aS i =Ti bond. [11,12] Well-defined examples of the cycloaddition chemistry of SiÀMd ouble bonds are limited to reports from Sekiguchi et al (Figure 1), in the [2+ +2] addition of alkynesa nd benzonitrile to aS i =Ti bond.…”

“…Addition of alkynes and phosphalkynes to threefold-bonded SiÀOs, [9] and ketones and carbodiimides to threefold-bonded SiÀWs pecies have been reported, [10] somewhat comparable with the wide-ranging andv ersatile cycloaddition chemistry of homonuclear EÀE multiple bonds (E = Si, Ge, Sn). [11,12] Well-defined examples of the cycloaddition chemistry of SiÀMd ouble bonds are limited to reports from Sekiguchi et al (Figure 1), in the [2+ +2] addition of alkynesa nd benzonitrile to aS i =Ti bond. [13] These remarkable reports are reminiscent of keys teps in the metathesis reactions of classical Schrock-type carbene complexes.…”

Main Group Multiple Bonds for Bond Activations and Catalysis

“…Homodiatomic E 14 multiple bonds have been shown to react with a number of substrates including small molecules [97] . It was the latter that first drew the comparisons to transition metals, [14–15] as digermyne showed ambient temperature reactivity towards dihydrogen [98] .…”

“…[96] Homodiatomic E 14 multiple bonds have been shown to react with an umber of substrates including small molecules. [97] It was the latter that first drew the comparisons to transition metals, [14][15] as digermyne showeda mbient temperature reactivity towards dihydrogen. [98] Even thoughd isilenes are arguably the most studied E 14 multiple bond, it was only recently that dihydrogen activation was achieved.…”

An Update on Multiple Bonding between Heavier Main Group Elements: The Importance of Pauli Repulsion, Charge-Shift Character, and London Dispersion Force Effects

“…Earlier comprehensive reviews , of heavier main group multiple bonded species listed all such compounds that had been isolated under ambient conditions along with some discussion of their physical, structural, and bonding properties. The bonding discussion was exclusively focused on the direct element–element interaction between the heavier main group element atoms in these compounds . It was assumed that the stabilizing ligands, which were generally σ-bonded (e.g., alkyl groups) to the main group element, were “innocent”, without any further direct electronic interaction with the protected bond.…”