Introduction of Bulky Substituents at the Bridgehead Position of a 9-Silatriptycene:  Pentacoordinate Hydridoorganylsilicates as Intermediates

Abstract

The reaction of 10-phenyl-10-germa-9-silatriptycene (1b) with phenyllithium in THF/HMPA produced 9,10-diphenyl-10-germa-9-silatriptycene (1a), which had hitherto not been accessible. The reaction proceeds by attack of the phenyl anion on 1b via the intermediate silicate anion 7, which was identified by 29 Si NMR spectroscopy. The structure of 1a was confirmed by X-ray crystallography. As a model reaction, the attack of phenyllithium on triphenylsilane (8) and diphenylsilane ( 14) was investigated by 29 Si NMR spectroscopy, revealing the formation of a number of novel hydridosilicates analogous to 7.

Hypervalent Hydrosilicates Connected to Light Alkali Metal Amides: Synthesis, Structure, and Hydrosilylation Catalysis

“…Although fluoride‐containing organosilicates can be readily isolated, reports of fully characterized hydridosilicates remain scarce. By reacting phenyllithium with H 2 SiPh 2 , Bickelhaupt and co‐workers generated highly colored solutions containing [Li(H 2 SiPh 3 )] and other species, which were characterized in situ by their characteristic 29 Si NMR shifts and coupling constants 1 J Si−H . The first examples of hypervalent hydridosilicates with crown ether adducts of sodium and potassium counterions were isolated and structurally characterized by Steed and co‐workers .…”

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?

“…Since the bridgehead atoms can adopt approximately tetrahedral arrangements in all of 3, no drastic change is observed when going from 3 a to the heavier congeners, in contrast to the case of 1. The species 3 b-3 d are structurally similar to Group 14 9,10-dimetallatriptycenes, [27,28] compounds that are handled by standard laboratory techniques. The measured strain energy of 3 a is 7.4 kcal mol À1 , [49] that is, 4 kcal mol Figure 8 and Table 2), but shorter than the sum of the van der Waals radii.…”

“…However, with different Group 14 elements in tethers and at bridgeheads, these species cannot display such homology. The 9,10-dimetallatriptycenes of Takahashi et al [27] and Bickelhaupt et al [28] are the bicyclic species with the shortest C-based tethers linking bridgehead Si, Ge, and Sn atoms. This near lack of Group 14 1,(n+2)-dimetalla[n.n.n]propellanes and 1,(n+2)-dimetallabicyclo-[n.n.n]alkanes with n = 3 (Scheme 1) led us to probe computationally which of these are realistic synthetic targets.…”

Unexpected Formation of the First Doubly Benzylic 1,1-Di-Grignard Reagent

“…Alternatively, 11 may react by attack of its carbanion functionality on silicon under formation of the silicate intermediate 12. Recently, there have been several pieces of evidence for such silicates involving pentacoordinate silicon with four or five carbon ligands [25][26][27]. Silicate 12 will preferentially cleave the benzylic bond [28] because this leads to the stable benzylic carbanion 13, which finally combines with MgX + to furnish 4.…”