RESUMEN
Ir-catalyzed arene C-H borylations (CHB) of anilines can be highly ortho selective by using a small B2eg2 (eg = ethane-1,2-diol) as the borylating reagent. Unfortunately, the products are prone to decomposition, and transesterification with pinacol is required prior to isolation. This work offers a solution by adjusting the size of the diboron reagent. Based on our evaluation, we conclude that B2bg2 (bg = butane-1,2-diol) achieves an optimal balance between CHB regioselectivity and stability for the borylated products.
RESUMEN
Ir-catalyzed C-H borylations of fluorinated and cyanated arenes with high meta-to-F/CN are described. Use of a dipyridyl hydrazone framework as the ancillary ligand and pinacolborane (HBpin) as the functionalizing reagent generates catalysts that are significantly more active and selective than 4,4'-di-tert-butyl-2,2'-bipyridine (dtbpy) for both electron-deficient and electron-rich substrates. Investigation of the ligand framework resulted in the observation of formal N-borylation of the hydrazone by HBpin, as evidenced by NMR spectroscopy and X-ray crystallography. Subsequent stoichiometric reactions of this adduct with an iridium precatalyst revealed the formation of an unusual IrI hydrazido. Isolation and use of this hydrazido reproduce the selectivity of in situ generated catalysts, suggesting that it leads to formation of the active species.
RESUMEN
Hydrofluoroolefins (HFOs) constitute the newest generation of fluorocarbon refrigerants and foam-blowing agents due to their reduced global warming potential vs their saturated analogues. To identify new synthetic routes to HFOs, we show that reactions of bulky Ni(0) phosphine and -NHC complexes with vinylidene difluoride (VF2) afford µ-fluoro-1,1,3-trifluorobut-3-enyl Ni complexes. Moreover, addition of triisopropylsilane allows for reductive elimination of the reduced productâ2,4,4-trifluoro-1-buteneâdemonstrating the Ni-catalyzed hydrodefluorodimerization of VF2. Accompanying DFT calculations identify the T-shaped nickelacyclopentane intermediate that spontaneously undergoes selective intramolecular ß-F (vs ß-H) elimination.
Asunto(s)
Níquel , CatálisisRESUMEN
Manganese, the third most abundant transition-metal element after iron and titanium, has recently been demonstrated to be an effective homogeneous catalyst in numerous reactions. Herein, the preparation of silica-supported MnII sites is reported using Surface Organometallic Chemistry (SOMC), combined with tailored thermolytic molecular precursors approach based on Mn2 [OSi(OtBu)3 ]4 and Mn{N(SiMe3 )2 }2 â THF. These supported MnII sites, free of organic ligands, efficiently catalyze numerous reactions: hydroboration and hydrosilylation of ketones and aldehydes as well as the transesterification of industrially relevant substrates.
RESUMEN
Silica-supported copper nanoparticles prepared via surface organometallic chemistry are highly efficient for the selective hydrogenation of various α,ß-unsaturated carbonyl compounds yielding the corresponding saturated esters, ketones, and aldehydes in the absence of additives. High conversions and selectivities (>99%) are obtained for most substrates upon hydrogenation at 100-150 °C and under 25 bar of H2.
RESUMEN
High ortho selectivity for Ir-catalyzed C-H borylations (CHBs) of anilines results when B2eg2 (eg = ethylene glycolate) is used as the borylating reagent in lieu of B2pin2, which is known to give isomeric mixtures with anilines lacking a blocking group at the 4-position. With this modification, high selectivities and good yields are now possible for various anilines, including those with groups at the 2- and 3-positions. Experiments indicate that ArylN(H)Beg species are generated prior to CHB and support the improved ortho selectivity relative to B2pin2 reactions arising from smaller Beg ligands on the Ir catalyst. The lowest-energy transition states (TSs) from density functional theory computational analyses have N-H···O hydrogen-bonding interactions between PhN(H)Beg and O atoms in Beg ligands. Ir-catalyzed CHB of PhN(H)Me with B2eg2 is also highly ortho-selective. 1H NMR experiments show that N-borylation fully generates PhN(Me)Beg prior to CHB. The TS with the lowest Gibbs energy was the ortho TS, in which the Beg unit is oriented anti to the bipyridine ligand.
RESUMEN
A new low-spin (LS) cobalt(II) outer-sphere redox shuttle (OSRS) [Co(PY5Me2)(CN)]+, where PY5Me2 represents the pentadentate ligand 2,6-bis(1,1-bis(2-pyridyl)ethyl)pyridine, has been synthesized and characterized for its potential application in dye-sensitized solar cells (DSSCs). Introduction of the strong field CN- ligand into the open axial coordination site forced the cobalt(II) complex, [Co(PY5Me2)(CN)]+, to become LS based upon the complex's magnetic susceptibility (1.91 ± 0.02 µB), determined by the Evans method. Interestingly, dimerization and subsequent cobalt hexacyanide cluster formation of the [Co(PY5Me2)(CN)]+ monomer was observed upon long-term solvent exposure or addition of a supporting electrolyte for electrochemical characterization. Although long-term stability of the [Co(PY5Me2)(CN)]+ complex made it difficult to fabricate liquid electrolytes for DSSC applications, short-term stability in neat solvent afforded the opportunity to isolate the self-exchange kinetics of [Co(PY5Me2)(CN)]2+/+ via stopped-flow spectroscopy. Use of Marcus theory provided a smaller than expected self-exchange rate constant of 20 ± 5.5 M-1 s-1 for [Co(PY5Me2)(CN)]2+/+, which we attribute to a Jahn-Teller effect observed from the collected monomer crystallographic data. When compared side-by-side to cobalt tris(2,2'-bipyridine), [Co(bpy)3]3+, DSSCs employing [Co(PY5Me2)(CN)]2+ are expected to achieve superior charge collection, which result from a smaller rate constant, ket, for recombination based upon simple dark J- E measurements of the two redox shuttles. Given the negative redox potential (0.254 V vs NHE) of [Co(PY5Me2)(CN)]2+/+ and the slow recombination kinetics, [Co(PY5Me2)(CN)]2+/+ becomes an attractive OSRS to regenerate near IR absorbing sensitizers in solid-state DSSC devices.
RESUMEN
Catalytic C-H borylation using the five-coordinate tris-boryl complex (dippe)Ir(Bpin)3 (5a, dippe = 1,2-bis(diisopropylphosphino)ethane) has been examined using 31P{1H} and 1H NMR spectroscopy. Compound 5a was shown to react rapidly and reversibly with HBpin to generate a six-coordinate borylene complex, (dippe)Ir(H)-(Bpin)2(BOCMe2CMe2OBpin) (6), whose structure was confirmed by X-ray crystallography. Under catalytic conditions, the H2 generated from C-H borylation converted compound 6 to a series of intermediates. The first is tentatively assigned from 31P{1H} and 1H NMR spectra as (dippe)Ir(H2B3pin3) (7), which is the product of formal H2 addition to compound 5a. As catalysis progressed, compound 7 was converted to a new species with the formula (dippe)Ir(H3B2pin2) (8), which arose from H2 addition to compound 7 with loss of HBpin. Compound 8 was characterized by 31P{1H} and 1H NMR spectroscopy, and its structure was confirmed by X-ray crystallography, where two molecules with different ligand orientations were found in the unit cell. DFT calculations support the formulation of compound 8 as an IrIII agostic borane complex, (dippe)IrH2(Bpin)(η2-HBpin). Compound 8 was gradually converted to (dippe)Ir(H4Bpin) (9), which was characterized by 31P{1H} and 1H NMR spectroscopy and X-ray crystallography. DFT calculations favor its formulation as an agostic borane complex of IrIII with the formula (dippe)IrH3(η2-HBpin). Compound 9 reacted further with H2 to afford the dimeric structure [(dippe)IrH2(µ2-H)]2 (10), which was characterized by 1H NMR and X-ray crystallography. Compounds 7-10 are in equilibrium when H2 and HBpin are present.
RESUMEN
Ir catalysts supported by bidentate silyl ligands that contain P- or N-donors are shown to effect ortho borylations for a range of substituted aromatics. The substrate scope is broad, and the modular ligand synthesis allows for flexible catalyst design.
Asunto(s)
Compuestos de Boro/síntesis química , Quelantes/síntesis química , Complejos de Coordinación/química , Nitrógeno/química , Compuestos Organofosforados/síntesis química , Compuestos de Organosilicio/síntesis química , Compuestos de Boro/química , Catálisis , Quelantes/química , Iridio/química , Estructura Molecular , Compuestos Organofosforados/química , Compuestos de Organosilicio/químicaRESUMEN
With the aid of high-throughput screening, the efficiency of Ir-catalyzed C-H borylations has been assessed as functions of precatalyst, boron reagent, ligand, order of addition, temperature, solvent, and substrate. This study not only validated some accepted practices but also uncovered unconventional conditions that were key to substrate performance. We anticipate that insights drawn from these findings will be used to design reaction conditions for substrates whose borylations are difficult to impossible using standard catalytic conditions.