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A crucial step in the formation of mono-aminoboranes (R2N–BH2) from the corresponding imine–BH3 adducts, under mild reaction conditions, is the 1,3-hydride shift. We offer experimental and theoretical insights into this molecular rearrangement according to two mechanistic pathways: intra-molecular (unimolecular) and inter-molecular (bimolecular). Even though a few experimental observations were inconclusive, an isotope-based experiment suggested that the 1,3-hydride shift occurs bimolecularly. In addition, the shape of the potential energy landscape, generated via the computational means, strongly suggests that these reactions are bimolecular. Relative energy gradient analysis enabled to identify the driving forces according to both scenarios and to explain the unusual shape of the minimum energy path in a unimolecular process. Our results imply that elevated temperature (60 °C) supplies the reactants with sufficient energy to cross the barrier, whereby each collision with properly oriented reactants results in mono-aminoborane formation. [ABSTRACT FROM AUTHOR]

We report on the synthesis and structural features of NMe2-modified β-diketiminate-supported boron difluoride compounds (LArBF2 : LAr = [HC(NAr)2(CNMe2)2]–; LPh : Ar = Ph; LTol : Ar = p -tolyl; LXyl : Ar = m -xylyl). The title compounds were prepared in moderate yields (~65 %) by in situ deprotonation of the corresponding ligands LArH using KH, followed by the addition of BF3OEt2. According to solid-state and theoretical analyses of the BF2 compounds, the lone pair at each NMe2 group is involved in electron delocalization within the central BC3N2 ring. As a result, the N -aryl substituents sterically clash with the NMe2 groups, causing this central ring to pucker. Several attempts were made to prepare heavy analogues (e.g. LArBX2 , X = Cl, Br, I) but only unidentifiable product mixtures were observed. It appears that the observed steric clash between the N -aryl substituents and the NMe2 groups prevented the formation of these heavy analogues. Electronic delocalization involving NMe2 groups and the central six-membered ring resulted in a steric clash between the NMe2 groups and Ar substituents. This steric clash was identified as the main reason for these ligand systems being able to stabilize only a BF2 fragment, while attempts to prepare heavy analogues resulted in product mixtures. [ABSTRACT FROM AUTHOR]

A β-diketiminate-supported aluminum bistriflate complex (DipLAl(OTf)2·Na[BArCl4]; DipL = CH(CMe)2(N-C6H3-iPr2)2; Tf = O2SCF3; ArCl = 3,5-Cl2-C6H3) has been identified as an efficient Lewis acid catalyst for Michael additions involving numerous electron-rich (hetero)aromatic substrates and several α,β-unsaturated carbonyl compounds. In a vast majority of the attempted Michael reactions our catalytic system was significantly superior over the currently used methods for the same transformations in terms of reaction times and temperatures, catalyst loadings, isolated product yields, and/or selectivity. [ABSTRACT FROM AUTHOR]

The reactivity of phosphenium dication [(Ph3P)2C-P-NiPr2]2+, 12+, towards pyridine N-oxide (O-py) has been investigated. The resulting oxophosphonium dication [(Ph3P)2C(NiPr2)P(O)(O-py)]2+, 22+, was surprisingly stabilized by a less nucleophilic O-py ligand instead of pyridine (py). This compound was then identified as an analogue of the elusive Criegee intermediate as it underwent oxygen insertion into the P–C bond through a mechanism usually observed for Baeyer-Villiger oxidations. This oxygen insertion appears to be the first example of a Baeyer-Villiger oxidation involving O-py. [ABSTRACT FROM AUTHOR]

The synthesis, characterization and X-ray analysis of dichloro- and dibromo-borenium cations stabilized by a 4-membered carbene are reported. The ligand's structural changes, atypical for similar systems, were caused by coordination to electron deficient fragments and its CN2P ring strain. [ABSTRACT FROM AUTHOR]

Although there exists a variety of different catalysts for hydroboration of organic substrates such as aldehydes, ketones, imines, nitriles etc., recent evidence suggests that tetra-coordinate borohydride species, formed by activation, redistribution, or decomposition of boron reagents, are the true hydride donors. We then proposed that Me2S-BH3 could also act as a hydride donor for the reduction of various imines, as similar compounds have been observed to reduce carbonyl substrates. This boron reagent was shown to be an effective and chemoselective hydroboration reagent for a wide variety of imines. [ABSTRACT FROM AUTHOR]

The reactivity of nucleophilic carbodiphosphorane (C(PPh3)2, 1) and carbodicarbene (C(C(NMe)2C6H4)2, 2) towards various dichlorophosphines has been explored. In most cases the expected carbone-for-chloride ligand exchange was observed. However, the use of MeN(PCl2)2 resulted in a unique P–N bond cleavage that, according to computational studies, occurred via an SN2′-like mechanism. [ABSTRACT FROM AUTHOR]