A Bicyclo[1.1.1]pentasilane Derivative. Synthesis, Molecular Structure, and Comments on Structural Homology

Abstract

fact enolization, we can estimate a hydronium-ion catalytic coefficient of ka, = 4 x M -' s-' for the enohation reaction at 25 "C. Combination of this with the hydroniumion catalytic coefficient for ketonization measured at 25 "C, k,!& = 9.3 x lo3 M -' s -' , [ '~] then leads to the keto-enol equilibrium constant pKE = 15.4.This keto-enol equilibrium [Eq. (f)] and the acid ionization of the enol, [Eq. (d)] form two branches of a thermodynamic cycle whose third member is the deprotonation of mandelic acid 5 as a carbon acid [Eq. (g)]. The equilibrium constant for this reaction may therefore be calculated from the other two: pKf = pK, i pKB = 22.0.These three equilibrium constants, pKE, pKF, and pKF, are the first ever measured for a simple carboxylic acid ketoenol system in aqueous They show the enol content to be very low-orders of magnitude less than of simple aldehydes and ketones-as expected from stabilization of the keto tautomer of the carboxylic acid system through conjugative interaction of its carbonyl and hydroxyl groups. The carboxylic acid enol, on the other hand, is more acidic than those of simple aldehydes and ketones, and that makes the carbon acidity of this carboxylic acid greater than it would otherwise be. Received: March 27, 1990 [Z 3881 IE] German version: Angew. Chem. 102 (1990) 810 CAS Registry numbers: 2, 127645-81-2; 5, 90-64-2.4 3 R)SiCI, P Scheme 1. Synthesis of la-c (Ar = aryl).excess dichlorosilane (Sa-c) to provide l a in 31 %, l b in 12 Yo, and lc in 15 % yield, respectively. The spectral data of these compounds (Table 1) are consistent with the proposed structures. Particularly revealing are the 29Si-NMR spectra,

Heavy Group 14 1,(n+2)‐Dimetallabicyclo[n.n.n]alkanes and 1,(n+2)‐Dimetalla[n.n.n]propellanes: Are They All Realistic Synthetic Targets?

“…[31] When comparing strain energies of 1 a-1 d calculated with the inexpensive MP2 and B3LYP methods with those from CCSD(T)/cc-pVTZ(SDB)//MP2/cc-pVTZ(SDB), MP2 produces the best agreement (Figure 1), even though B3LYP properly describes the trend and magnitude of the change in strain. [25] bicyclo[1.1.1]pentastannane, [5,24] as well as 2,4,5-trithia-and 2,4,5-triselena-1,3-disilabicyclo-[1.1.1]pentanes, [26] [a]…”

In search of 1,3-disila/germa/stannabicyclo[1.1.1]pentanes with short bridgehead-bridgehead distances and low ring strain energies

“…We also calculated the pentatetrelbicyclo[1.1.1]pentanes (12E), since both Si-and Snrepresentatives of this category have been generated before [10][11][12].…”

“…Masamune and co-workers formed three pentasilabicyclo[1.1.1]pentanes with combinations of H, methyl, iso-propyl and phenyl substituents on the Si bridge atoms and more bulky 4-tert-butyl-2,6-isopropylphenyl substitituents at the two bridgehead atoms [10]. They structurally characterized one of these and found a Si,Si through-space distance of 2.98Å which is longer than our calculated value of 12Si by ∼0.09Å (Figure 1).…”

Persilastaffanes: Design, Synthesis, Structure, and Conjugation between Silicon Cages

“…(Figure 1 a) has a three-fold axis through the bridgehead silicon atoms in the solid state. Similarly to Masamune's bicyclopentasilanes 1 and all-carbon bicyclo[1.1.1]pentanes, [10] 3 has a short nonbonded distance between bridgehead silicon atoms (Si2···Si2*) of 2.9768 (5) , which is much shorter than the sum of van der Waals radii of two silicon atoms (4.20 ) and close to that of 1 a (2.98 ), [12] and considerably acute intracage SiÀSiÀSi angles (Si3ÀSi2À Si4(*) and Si4ÀSi2ÀSi4* angles) at the bridgehead silicon atom Si2 (84.68 on average). The exocyclic Si1 À Si2 distance of 3 (2.3429(6) ) is slightly shorter than the endocyclic Si À Si distances of 3 (2.3622(6)-2.3626(6) for Si2 À Si3 and Si2 À Si4), which are lying in the range of those of 1 a (2.32(2)-2.38(1) ).…”

“…[7] The corresponding all-carbon [n]staffanes B have been studied extensively by Michl and co-workers. [10,11] Although stable bicyclo[1.1.1]pentasilanes bearing aryl substituents 1 [12] and 2 [13] have been synthesized by the Masamune and Breher, [14] no catenated bicyclo[1.1.1]pentasilanes (persila[n]staffanes, n ! 2) have been reported.…”