A Potassium Diboryllithate: Synthesis, Bonding Properties, and the Deprotonation of Benzene

Abstract

A potassium diboryllithate (B2LiK) was synthesized and structurally characterized. DFT calculations, including NPA and AIM analyses of B2LiK, revealed ionic interactions between the two bridging boryl anions and Li+ and K+. Upon standing in benzene, B2LiK deprotonated the solvent to form a hydroborane and a phenylborane. On the basis of DFT calculations, a detailed reaction mechanism, involving deprotonation and hydride/phenyl exchange processes, is proposed. An NBO analysis of the transition state for the deprotonation of benzene suggests that the deprotonation should be induced by the coordination of benzene to the K+.

Easy access to nucleophilic boron through diborane to magnesium boryl metathesis

“…Although this latter feature also ensures that the electropositive boron centre retains a significant partial positive charge (for 1 ; calculated natural population analysis charge on B=+0.072), these species behave as boron-centred nucleophiles by dint of a net polarization of the boron–lithium bond (in effect, B δ+ –Li δ++ ) induced by the even lower effective nuclear charge of lithium (for 1 ; calculated natural population analysis charge on Li=+0.755)913. Although a rich and varied chemistry has since arisen from the reactivity of compound 1 and related N- heterocyclic boryl anions with organic914, transition metal15161718 and main group electrophiles1419202122232425, alternative nucleophilic boron reagents remain very rare species262728293031. Notable exceptions are Braunschweig's dimetalloborylene and borolyl anions (for example, 2 and 3 )3233 Bertrand and Kinjo's carbene-stabilised monovalent boron species (for example, 4 )3435363738 and a remarkable tricyanoborandiyl dianion394041.…”

Arene C−H Activation at Aluminium(I): meta Selectivity Driven by the Electronics of SNAr Chemistry

“…In previous work we showed by quantum chemical methods that C−H activation in benzene (Scheme 1) proceeds via nucleophilic attack by the aluminyl, generating a Meisenheimer type transition state which collapses by C‐to‐Al hydride migration [11e, 16, 17] . A similar concerted S N Ar (cS N Ar) mechanism has also been advanced by Fernandez and Cabrera‐Trujillo for arene C−H activation in benzene and extended arenes by aluminyl reagents [18–20] . That said, the relatively close approach of the H atom of the C−H bond to the aluminium centre in the transition state (ca.…”

A meta‐Selective C−H Alumination of Mono‐Substituted Benzene by Using An Alkyl‐Substituted Al Anion through Hydride‐Eliminating SNAr Reaction

“…The solid‐state structure of 2 is similar to the previously reported (hydrido)(phenyl)aluminate [12j] generated by a reaction of 1 with benzene. Considering the low electronegativity of Al (1.61) [15] and the similar reactivity of diaminoboryl anion toward benzene, [16] we originally assumed alumanyl anion 1 has a high Brønsted basicity to deprotonate benzene [12j] . However, the present meta ‐selective C−H cleavage by 1 is completely different from the reactivity of diaminoboryl anion that deprotonates benzylic C−H bond of toluene [17] .…”