Structural Characterization of a Boron(III) η²-σ-Silane-Complex

Abstract

to unsaturated element centers, forming η 2 -σ-complexes, is a crucial step in H−E bond activations which are involved in numerous chemical transformations. Structural characterization of σ-complexes has provided invaluable insight into the σ-bond activation process. While numerous η 2 -σ-complexes of lowoxidation-state transition metals have been isolated and thoroughly studied, those based on d 0 metals or high-oxidation-state main group elements still remain elusive, despite their suggested role as key intermediates in σ-bond metathesis. Here we report the synthesis of a highly electrophilic o-carboranyl-substituted hydroborenium and its η 2 -σ-(H−Si)-complex, the latter of which was characterized by X-ray analysis. Unlike previous known σ-(H−Si)complexes in which back-donation contributes significantly to their stability, our computational studies revealed that no backdonation takes place between the borenium and silane moieties, and the key factors for the stability of this silane-borenium complex are (1) the strong interaction between the empty p orbital of the boron center and the bonding σ orbital of H−Si and (2) steric accessibility of the boron center due to the presence of a hydrogen substituent.

An isolable, crystalline complex of square-planar silicon(IV)

“…Such observations, although weak in this case, are characteristic for C–H agostic interactions in transition metal complexes 53 , 54 but unusual as the source of structural deformation in p-block element chemistry. E–H σ-bond donor-acceptor interactions in the p-block were only observed for combinations of more hydridic bonds with the most Lewis acidic boranes, 55 , 56 silylium ions, 2 , 57 anagostic, 9 or structurally enforced. 58…”

Understanding chemical reactivity using the activation strain model

“…The ASM can be applied to all unimolecular and bimolecular reactions in both homogeneous and heterogeneous systems and has been used routinely by theoretical and experimental chemists [28][29][30][31][32][33][34][35][36][37][38][39][40][41][42] . We provide specific examples of the ASM being applied to understand inorganic, organic, and supramolecular chemistries, namely, the transition metal-mediated oxidative addition of C-X bonds in cross-coupling reactions, the reactivity of cycloalkynes in 1,3-dipolar cycloadditions, the reactivity of dihalogen-catalyzed Michael addition reactions, and the bonding mechanism in hydrogen-bonded systems.…”

Metathesis by Partner Interchange in σ‐Bond Ligands: Expanding Applications of the σ‐CAM Mechanism

“…An intriguing main group s-bond complex, [IMe 4 -(Cb)(m-H)(HSiEt 3 )][B(C 6 F 5 ) 4 ], (IMe 4 = 1,3,4,5-tetramethylimidazol-2-ylidene,C b = 1,2-dicarba-closo-dodecaborane) has been described in which as ilane (HSiEt 3 )i sp roposed to engage with the empty p-orbital of ac ationic borenium center in aB ( h 2 -Si-H) s-interaction (Figure 5). [65] Other complexes have been reported where Si À H•••B [66] or C À H•••Si bonds [67] are invoked. It will be interesting to see if s-CAM is extended to reactions involving only main group elements.…”