B−B Bond Nucleophilicity in a Tetraaryl μ‐Hydridodiborane(4) Anion

Abstract

The tetraaryl μ‐hydridodiborane(4) anion [2H]− possesses nucleophilic B−B and B−H bonds. Treatment of K[2H] with the electrophilic 9‐H‐9‐borafluorene (HBFlu) furnishes the B3 cluster K[3], with a triangular boron core linked through two BHB two‐electron, three‐center bonds and one electron‐precise B−B bond, reminiscent of the prominent [B3H8]− anion. Upon heating or prolonged stirring at room temperature, K[3] rearranges to a slightly more stable isomer K[3 a]. The reaction of M[2H] (M+=Li+, K+) with MeI or Me3SiCl leads to equimolar amounts of 9‐R‐9‐borafluorene and HBFlu (R=Me or Me3Si). Thus, [2H]− behaves as a masked [:BFlu]− nucleophile. The HBFlu by‐product was used in situ to establish a tandem substitution‐hydroboration reaction: a 1:1 mixture of M[2H] and allyl bromide gave the 1,3‐propylene‐linked ditopic 9‐borafluorene 5 as sole product. M[2H] also participates in unprecedented [4+1] cycloadditions with dienes to furnish dialkyl diaryl spiroborates, M[R2BFlu].

Small molecules (CO2, iPrNCO, and iPrNCNiPr) activation by the metallomimetics (μ‐Hydrido) diborane anion: A DFT investigation on mechanism and chemoselectivity controlling

“…The reaction center of [1aH] À has a B H bond at the end position, the ligand position of [1bH] À has changed, and there is still a hydrogen bridge bond. 49,50 Based on Wagner's experimental results, 30 the cycloaddition mechanisms of [1H] À with CO 2 , iPrNCO, and iPrNC-NiPr are determined. The optimized xyz coordinates of all these stationary points are listed in SI.…”

“…The former calculation study of M. Wagner et al shows that [1H] − has three isomers: [1H] − , [1aH] − , and [1bH] − (shown in Scheme 2). Among them, [1H] − is the most stable, and the relative energies of [1aH] − and [1bH] − are slightly higher than that of [1H] − ; only 5.1 kcal/mol and 6.6 kcal/mol 49 . [1H] − can be easily converted to [1aH] − and [1bH] − by Wagner–Meerwein rearrangement 28,29 .…”

“…Although the energies of [1aH] − and [1bH] − are slightly higher than [1H] − , they are structurally more conducive to the reaction. The reaction center of [1aH] − has a BH bond at the end position, the ligand position of [1bH] − has changed, and there is still a hydrogen bridge bond 49,50 . Based on Wagner's experimental results, 30 the cycloaddition mechanisms of [1H] − with CO 2 , iPrNCO, and iPrNCNiPr are determined.…”

“…47,48 [1aH] À and [1bH] À are slightly higher than that of [1H] À ; only 5.1 kcal/mol and 6.6 kcal/mol. 49 [1H] À can be easily converted to…”