Competition for Hydride Between Silicon and Boron: Synthesis and Characterization of a Hydroborane‐Stabilized Silylium Ion

Abstract

Potent main-group Lewis acids are capable of activating element-hydrogen bonds. To probe the rivalry for hydride between silylium-and borenium-ion centers, a neutral precursor with the hydrosilane and hydroborane units in close proximity on a naphthalene-1,8-diyl platform was designed. Abstraction of one hydride leads to a hydroborane-stabilized silylium ion rather than a hydrosilane-coordinated borenium ion paired with [B(C 6 F 5 ) 4 ] À or [HCB 11 Cl 11 ] À as counteranions. Characterization by multinuclear NMR spectroscopy and X-ray diffraction supported by DFT calculations reveals a cationic, unsymmetrical open three-center, twoelectron (3c2e) SiÀ HÀ B linkage.

Catalyst-free diboration and silaboration of alkenes and alkynes using bis(9-heterofluorenyl)s

“…Its well-resolved shape points against a bonding interaction with the adjacent B atom in solution, even though B(μ-H)Si structural motifs are known. 21 The pronounced shielding of the 11 B nucleus in 6(thf) (13.6 ppm) is therefore likely due to thf coordination. In line with this, 1 H NMR spectra (THF- d 8 ) recorded on a sample of 6(thf) isolated from THF- h 8 revealed the presence of 1 equiv.…”

Incipient Nucleophilic Attack on a Carbonyl Group Adjacent to a Stereogenic Centre in Peri Naphthalene Derivatives

“…[43] The small difference in size of the two exo angles at the ring fusion in the naphthalene skeleton is also intermediate between those for the methyl and isopropyl ketone derivatives, suggesting that repulsion between the peri phenyl and hydrogen groups does not exert a significant distorting effect on these angles. In contrast, for molecule 8, which has two peri diphenyl groups, repulsion between these groups widens the exo angle (ψ) between them to 124.39 (12)°and this narrows the opposite exo angle (φ) between the dimethylamino and carbonyl functionalities to 119.57 (13)°and so reduces the N•••C(=O) separation to 2.4893( 19) Å (Table 1). Conversely, in the acenaphthene analogue 9, the ethylene bridge tightens the exo angle (ψ) within 1).…”

“…Peri ‐naphthalenes have been used widely since in investigations of interactions and bond formation. Examples include a NMe 2 or OMe group with an aldehyde, alkene, alkyne or nitrile, [5–8] hydrogen bonding to an amide nitrogen atom [9,10] or to a π‐surface, [11] novel Si−H⋅⋅⋅B bonds, [12] construction of abnormally long bonds, [13] methods for determining the degree of bonding between peri‐ groups, [14] and the promotion of reactions between groups held close together [15] . Peri‐ naphthalenes also occur in some proton sponges, [16] and systems with frustrated lone pairs, [17] while peri ‐acenaphthenes have been used to investigate interactions between the heavier main group elements [18,19] .…”