Olefin hydroborations with diamidocarbene-BH3 adducts at room temperature

An isolable N,N???-diamidocarbene (DAC) was previously shown to promote the B-H bond activation of various BH3 complexes. The resultant DAC-BH3 adducts facilitated olefin hydroborations under mild conditions and in the absence of exogenous initiators. The substrate scope for such transformations was further explored and is described herein. While organoboranes were obtained in quantitative yields from various terminal and internal olefins, use of the latter substrates resulted in intramolecular ring-expansion of the newly formed DAC-borane adducts.ope

Diamidocarbene Induced B-H Activation: A New Class of Initiator-Free Olefin Hydroboration Reagents

Enabled by its enhanced electrophilicity and attenuated nucleophilicity, an N,N'-diamidocarbene (DAC) was found to promote the B-H bond activation of various BH3 complexes and the B-B bond of bis(pinacolato)diboron, constituting the first such examples for an isolable carbene. The resultant DAC-BH3 adducts datively coordinated to Lewis bases (i.e., dimethyl sulfide, trimethylamine, or pyridine) and facilitated the hydroboration of various olefins under mild conditions and in the absence of exogenous initiators. © 2016 American Chemical Society111101sciescopu

Diamidocarbene Induced B-H Activation: A New Class of Initiator-Free Olefin Hydroboration Reagents

Enabled by its enhanced electrophilicity and attenuated nucleophilicity, an N,N'-diamidocarbene (DAC) was found to promote the B-H bond activation of various BH3 complexes and the B-B bond of bis(pinacolato)diboron, constituting the first such examples for an isolable carbene. The resultant DAC-BH3 adducts datively coordinated to Lewis bases (i.e., dimethyl sulfide, trimethylamine, or pyridine) and facilitated the hydroboration of various olefins under mild conditions and in the absence of exogenous initiators.clos

A cyclic (alkyl)(amido)carbene: synthesis, study and utility as a desulfurization reagent

The synthesis and study of a cyclic (alkyl)(amido) carbene is described. The carbene was found to undergo C-H insertion at low temperatures, formed cyclopropenes upon exposure to alkynes, and facilitated desulfurization reactions. Spectroscopic studies revealed that the carbene is strongly pi-accepting but retains a complimentary degree of sigma-donating properties.clos

Switchable Polymerization Catalysts

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Synthesis and crystal structures of 5,5′-(propane-2,2-diyl)bis(2-hydroxybenzaldehyde) and 5,5′-(propane-2,2-diyl)bis(2-hydroxyisophthalaldehyde)

The title compounds 5,5′-(propane-2,2-diyl)bis(2-hydroxybenzaldehyde), C17H16O4, (1), and 5,5′-(propane-2,2-diyl)bis(2-hydroxyisophthalaldehyde), C19H16O6, (2), crystallize with one molecule in the asymmetric unit. In molecule (1), a >C(CH3)2 group bridges two nearly planar salicylaldehyde groups [r.m.s deviations = 0.010 (1) and 0.025 (2) Å], each comprising a planar phenyl ring bonded with a hydroxyl and an aldehyde group. Similarly, compound (2) has the same bridging group, but it connects two nearly planar appendants [r.m.s deviations = 0.034 (1) and 0.035 (1) Å], each comprising a phenyl ring bonded with a hydroxyl and two aldehyde groups. Molecule (1) exhibits a bridge angle of 109.5 (2)° with the salicylaldehyde planes subtending a dihedral angle of 88.4 (1)°. In contrast, molecule (2) presents a bridge angle of 108.9 (2)° with its appendants subtending a dihedral angle of 79.6 (3)°. Both molecules exhibit two intramolecular O—H...O hydrogen bonds involving the phenolic H atoms and carboxyl O-atom acceptors. In the crystal of (2), O—H...O hydrogen bonds between one of the hydroxyl H atoms and a carboxyl O atom from a symmetry-related molecule form a chain along [10\overline{1}]. In addition, (2) exhibits a strong visible luminescence when excited with ultraviolet radiation

A Ring-Opening Metathesis Polymerization Catalyst That Exhibits Redox-Switchable Monomer Selectivities

A ring-opening metathesis polymerization catalyst supported by a redox-active N-heterocyclic carbene was synthesized and found to undergo reversible reduction. In its neutral form, the catalyst polymerized 1,5-cis,cis-cyclooctadiene at a higher rate than that of a norbornene derivative; however, upon reduction, the selectivity was found to reverse. Utilizing this oxidation state dependent selectivity, a series of copolymers with controlled compositions, microstructures, and physical properties were prepared by redox-switching the catalyst over the course of a series of polymerization reactions.clos

A redox-switchable ring-closing metathesis catalyst

A Ru(II) complex ligated to a quinone-annulated N-heterocyclic carbene (NHC) was synthesized as a redox-active analogue of the Hoveyda-Grubbs II generation catalyst. The complex exhibited a single reversible reduction with a E-1/2 of -0.63 V (vs. SCE), and was successfully reduced and then oxidized with high fidelity using chemical reagents. While the catalyst facilitated a range of ring-closing metathesis (RCM) reactions in its neutral state, its activity was inhibited upon the introduction of a suitable reducing reagent. A series of density functional theory calculations revealed that the differences in catalytic activity may be attributed to the stronger donating ability of the reduced NHC ligand which stabilized a ruthenacyclobutane intermediate and thus suppressed the rate-determining retro-[2 + 2] cycloaddition step of the underlying RCM mechanism