Dodecahedryl Anion Formation and an Experimental Determination of the Acidity and C−H Bond Dissociation Energy of Dodecahedrane

Abstract

Dodecahedryl anion (1a) was generated in a Fourier transform mass spectrometer by deprotonation of dodecahedrane (1). Examination of the acid and base behavior of 1 and 1a, respectively, enabled the acidity of 1 to be determined (∆H°a cid ) 402 ( 2 kcal/mol). Good agreement is found with the 298 K computed MP2/6-31+G(d)//HF/6-31+G(d) value of 405.1 kcal/mol. In a similar manner, the electron affinity of dodecahedryl radical was measured (EA ) 4 ( 2 kcal/mol). These results were combined in a thermodynamic cycle to afford the C-H bond dissociation energy of dodecahedrane (BDE ) 92 ( 3 kcal/mol), which is reasonably well reproduced (96.7 kcal/mol) at the MP2//HF level but leads to the suggestion that the reported heat of hydrogenation of dodecahedrene is in error. The DePuy kinetic method for measuring the acidity of 1 also was explored. It was found that this approach works well with triphenylsilyldodecahedrane but gives poor results with triethylsilyldodecahedrane. This latter failure is attributed to steric effects, and provides a rationale for several problem cases and a means to overcome these difficulties.

Organosilicon-Based Multifunctional β-Diketones and their Rhodium and Iridium Complexes

“…Multifunctional ligands with approximately tetrahedral angles between the ligand moieties can be derived from di-, tri-, and tetraphenylmethane. However, the Si analogues (i.e., di-, tri-, and tetraphenylsilanes; see Figure ) are generally easier to synthesize, because of the availability of coupling reactions between aryllithium compounds and chlorosilanes. − Thus, tetraphenylsilane is considerably easier to prepare than tetraphenylmethane. Still, even among the oligoarylsilanes, some derivatives have presented synthetic challenges: for example, Wuest et al reported that tetrakis(4-formylphenyl)silane was difficult to prepare in pure form .…”

Fluorotrimethylsilane affinities of anionic nucleophiles: A study of fluoride-induced desilylation

“…Calculated energy differences between the axial (1a) and equatorial (1b) geometries are typically 3-4 kcal/mol. Kass and coworkers have previously shown that bulky substituents tend to occupy the axial position in pentavalent siliconates [75], and it has also been suggested that the substituents may prefer the axial position because they are more electronegative than the methyl groups [76].…”

Fundamentals of Organic Chemistry

“…What are the ring strain energies of the simple hydrocarbon rings, cyclopropane (28) and cyclobutane (29)? These rings are made up of methylene groups, CH 2 fragments, just like the interior carbons in straight-chain, unstrained alkanes.…”

“…For this discussion, we will determine the RSE of cyclobutane (29), cyclobutene (30), and oxetane (31). Three methods for generating an appropriate chemical reaction have found utility: the isodesmic reaction, the homodesmotic reaction, and the group equivalent reaction.…”