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Although the application of cationic aluminum complexes in catalysis has been extensively investigated, the incorporation of an aluminum cation into a chiral environment is less explored. In this s...

The chemistry of the boron cation has been revitalized in the past decade due to its newfound application in stoichiometric and catalytic organic reactions. To extend the frontier of boron cation c...

In an attempt to prepare the heavier analogue of NHC-stabilized borenium cation, we have prepared a silylene-coordinated borenium equivalent (1a), which can be viewed as a contact ion pair of borenium and triflate. The triflate anion coordinates to the oxophilic silicon center, leaving the boron center existing in a trigonal-planar geometry in the solid state and in solution. Nucleophilic substitution reactions of 1a all result in the release of free silylene ligand, demonstrating the borenium-ion-like reactivity of 1a. Chemical reduction of 1a leads to a neutral radical possessing a partial Si–B double bond.

A series of five- and six-membered-ring Al complexes bearing Schiff bases was synthesized and their application to the ring-opening polymerization of e-caprolactone (CL) was studied. The five-membered-ring Al complexes have been shown to have a significantly higher polymerization rate than six-membered-ring Al complexes (2–3 fold for CL polymerization). The X-ray data revealed that the Al center of a five-membered-ring Al complex is farther from the Schiff base ligand than is that of a six-membered-ring Al complex. The results of density functional theory calculations also suggest that more space around the Al center of five-membered-ring Al complexes may reduce the steric repulsion in CL polymerization and increase the catalytic activity of five-membered-ring Al complexes.

The reaction mechanism of the [Et3BH]−-induced conversion of a dicationic boron compound ([Cp*B-IMes]2+, [1]2+) to a planar neutral carbene-coordinated borabenzene (2) is investigated experimentally and theoretically. Owing to the steric congestion around the boron center, bulky [Et3BH]− attacks the less encumbered carbon atom of Cp*, leading to a metastable 5-borabicyclo[2.1.1]hex-2-ene borenium cation ([3-CH]+) at low temperature. Upon raising the temperature, the bicyclic-borenium ion undergoes sequential pericyclic reactions, including suprafacial [1,3]-sigmatropic shift, two-electron electrocyclic ring opening, and then [1,2]-hydrogen shift to a planar cyclic borenium ion, [4-CH]+, which can then be deprotonated to yield the neutral aromatic borabenzene. The attack of hydride at the boron center of [1]2+ was excluded through the preparation and isolation of 6-borabicyclo[3.1.0]hexenylium, [3-BH]+, which could not be transformed into [3-CH]+ or [4-CH]+. The borenium ion rearrangement follows first-ord...

Redox behavior of Fe(I) complexes bearing a PNP-pincer-type phosphaalkene ligand, 2,6-bis[1-phenyl-2-(2,4,6-tri-tert-butylphenyl)-2-phosphaethenyl]pyridine (BPEP-Ph), is reported. The four-coordinate Fe(I) complex [FeBr(BPEP-Ph)] (1) readily reacts with 1 equiv of tBuNC in toluene at −35 °C to give [FeBr(tBuNC)(BPEP-Ph)] (2) with a 17e configuration. Complex 2 is fairly stable in neat benzene at room temperature, but smoothly undergoes disproportionation in the presence of added tBuNC to afford the Fe(0) complex [Fe(tBuNC)2(BPEP-Ph)] (3) and the Fe(II) complex [FeBr2(tBuNC)4] (4) along with free BPEP-Ph. The single-crystal X-ray diffraction studies of 3 and 4 reveal distorted trigonal bipyramidal and square pyramidal arrangements around Fe, respectively. The yield of 3 increases up to 50%/2 when 2 equiv of tBuNC is added to the system. A disproportionation process involving a 19e intermediate is proposed.