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Two aryl amino borinium cations derived from Cl(Mes)B-NR2 (NR2 = TMP, HMDS) faced divergent outcomes. As the HMDS-substituted one underwent methyl migration from silicon to boron transforming the putative borinium ion to a silylium ion, [Mes-B-TMP]+ can initiate cyanosilylation and catalyse hydrosilylation of ketones and aldehydes. [ABSTRACT FROM AUTHOR]

A twisted mono-cationic bis-benzimidazolium salt was serendipitously isolated from the dehydrative condensation of 5,6-dihydroxyl-1,3- dimesityl-benzimidazolium and 1,4-benzenediboronic acid. Subsequent deprotonation of the benzimidazolium salt led to the formation of a spiroborate-linked free bis-NHC, which was further transformed into the corresponding diborane adduct and the di-Rh complex. [ABSTRACT FROM AUTHOR]

The reaction of [Li(THF)4][1,8-μ-(Mes2B)C10H6] with HgCl2 affords [1,1′-(Hg)-[8-(Mes2B)C10H6]2] (3) or [1-(ClHg)-8-(Mes2B)C10H6] (4), depending on the stoichiometry of the reagents. These two new compounds have been characterized by 1H, 13C, 11B and 199Hg NMR, elemental analysis and X-ray crystallography. The cyclic voltammogram of 3 in THF shows two distinct waves observed at E1/2 −2.31 V and −2.61 V, corresponding to the sequential reductions of the two boron centers. Fluoride titration experiments monitored by electrochemistry suggest that 3 binds tightly to one fluoride anion and more loosely to a second one. Theses conclusions have been confirmed by a UV-vis titration experiment which indicates that the first fluoride binding constant (K1) is greater than 108 M−1 while the second (K2) equals 5.2 (± 0.4) × 103 M−1. The fluoride binding properties of 3 have been compared to those of [1-(Me2B)-8-(Mes2B)C10H6] (1) and [1-((2,6-Me2-4-Me2NC6H2)Hg)-8-(Mes2B)C10H6] (2). Both experimental and computational results indicate that its affinity for fluoride anions is comparable to that of 2 but significantly lower than that of the diborane 1. In particular, the fluoride binding constants of 1, 2 and 3 in chloroform are respectively equal to 5.0 (± 0.2) × 105 M−1, 1.0 (± 0.2) × 103 M−1 and 1.7 (± 0.1) × 103 M−1. Determination of the crystal structures of the fluoride adducts [S(NMe2)3][1–μ2-F] and [S(NMe2)3][3–μ2-F] along with computational results indicate that the higher fluoride binding constant of 1 arises from a strong chelate effect involving two fluorophilic boron centers. [ABSTRACT FROM AUTHOR]

While we have previously reported that [1-(Mes2B)-8-(Me3NCH2)-C10H6]+ ([2]+) complexes fluoride ions to form [1-(Mes2FB)-8-(Me3NCH2)-C10H6] (2-F), we now show that this cationic borane also complexes cyanide to form [1-(Mes2(NC)B)-8-(Me3NCH2)-C10H6] (2-CN). This reaction also occurs under biphasic conditions (H2O–CHCl3) and may serve to transport cyanide in organic phases. The zwitterionic cyanoborate 2-CN has been fully characterized and its crystal structure determined. UV-vis titration experiments carried out in THF indicate that [2]+ has a higher affinity for fluoride (K > 108 M−1) than cyanide (K = 8.0 (±0.5) × 105 M−1). Steric effects which impede cyanide binding to the sterically congested boron center of [2]+ are most likely at the origin of this selectivity. Finally, electrochemical studies indicate that [2]+ is significantly more electrophilic than its neutral precursor 1-(Mes2B)-8-(Me2NCH2)-(C10H6) (1). These studies also show that reduction of [2]+ is irreversible, possibly because of elimination of the NMe3 moiety under reductive conditions. In fact, [2]OTf reacts with NaBH4 to afford 1-(Mes2B)-8-(CH3)-(C10H6) (4) which has also been fully characterized. [ABSTRACT FROM AUTHOR]