A mild, efficient, and regiospecific catalytic cyclotrimerization of alkynes to form 1,2,4-substituted arenes has been discovered. From a cheap and air-stable [Fe(salen)] 2 -μ-oxo complex and readily available pinacol borane (HBpin), a monomeric [FeH(salen)]•Bpin species formed in situ acts as the active catalyst. This species is shown to feature a hemilabile salen ligand stabilized via interactions with the boron entity. The formation, identity, and reaction mechanism of the active species are supported by complementary kinetic, spectroscopic, and computational data. The active catalyst undergoes hydrometallation of a coordinated alkyne to form a vinyl iron species, stepwise additions of two more alkynes across the Fe−C bond to form a pendant triene, which upon ring-closure forms the arene product. The catalytic cycle is closed by substitution of the product with the alkyne substrate. With the active [FeH(salen)]•Bpin catalyst, atom-efficient, intermolecular trimerization is shown with high regioselectivity for a diverse range of substrate substitution patterns and presence of functional groups.
The hydroboration of aldehydes and ketones is demonstrated using a cheap and air stable [Fe(salen)]2-µ-oxo pre-catalyst with pinacolborane (HBpin) as the reductant under mild conditions. This catalyst system chemoselectively hydroborates...
A rapid method for the reduction of secondary phosphine oxides under mild conditions has been developed, allowing simple isolation of the corresponding free phosphines. The methodology involves the use of pinacol borane (HBpin) to effect the reduction while circumventing the formation of a phosphine borane adduct, as is usually the case with various other commonly used borane reducing agents such as borane tetrahydrofuran complex (BH3•THF) and borane dimethyl sulfide complex (BH3•SMe2). In addition, this methodology requires only a small excess of reducing agent and therefore compares favourably not just with other borane reductants that do not require a metal cocatalyst, but also with silane and aluminium based reagents.
A method
has been developed to reliably quantify the isotopic composition
of liquid water, requiring only immersion of a “ReactIR”
probe in the sample under test. The accuracy and robustness of this
method has been extensively tested using a deuterium/protium system,
and substantial improvements in sensitivity were obtained using highly
novel chemical signal amplification methods demonstrating a standard
deviation of 247 ppb D (a δD of 1.6 ‰). This compares
favorably with other more costly and time-consuming techniques and
is over 20 times more sensitive than any previously published FTIR
study. Computational simulations of a model system match the experimental
data and show how these methods can be adapted to a tritium/protium
system.
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