Chelated Diborenes and Their Inverse-Electron-Demand Diels-Alder Reactions with Dienes.

A doubly base-stabilised diborane based on a benzylphosphine linker was prepared by a salt elimination reaction between 2-LiC6 H4 CH2 PCy2 ⋅Et2 O and B2 Br4 . This compound was reduced with KC8 to its corresponding diborene, with the benzylphosphine forming a five-membered chelate. The diborene reacts with butadiene, 2-trimethylsiloxy-1,3-butadiene, and isoprene to form 4,5-diboracyclohexenes, which interconvert between their 1,1- (geminal) and 1,2- (vicinal) chelated isomers. The 1,1-chelated diborene undergoes a halide-catalysed isomerisation into its thermodynamically favoured 1,2-isomer, which undergoes Diels-Alder reactions more slowly than the kinetic product.

Dynamic, Reversible Oxidative Addition of Highly Polar Bonds to a Transition Metal.

The combination of Pt0 complexes and indium trihalides leads to compounds that form equilibria in solution between their In-X oxidative addition (OA) products (PtII indyl complexes) and their metal-only Lewis pair (MOLP) isomers (LnPt→InX3). The position of the equilibria can be altered reversibly by changing the solvent, while the equilibria can be reversibly and irreversibly driven toward the MOLP products by addition of further donor ligands. The results mark the first observation of an equilibrium between MOLP and OA isomers, as well as the most polar bond ever observed to undergo reversible oxidative addition to a metal complex. In addition, we present the first structural characterization of MOLP and oxidative addition isomers of the same compound. The relative energies of the MOLP and OA isomers were calculated by DFT methods, and the possibility of solvent-mediated isomerization is discussed.

Formation of a stable radical by oxidation of a tetraorganoborate.

Herein, we describe the selective formation of a stable neutral spiroborate radical by one-electron oxidation of the corresponding tetraorganoborate salt Li[B(C4Ph4)2], formally containing a tetrahedral borate centre and a s-cis-butadiene radical cation as the spin-bearing site. Spectroscopic and computational methods have been used to determine the spin distribution and the chromism observed in the solid state.

New outcomes of Lewis base addition to diboranes(4): electronic effects override strong steric disincentives.

Two surprising new outcomes of the reaction of Lewis bases with dihalodiboranes(4) are presented, including sp(2)-sp(3) diboranes in which the Lewis base unit is bound to a highly sterically congested boron atom, and a rearranged double base adduct. The results provide a fuller understanding of the reactivity of diboranes, a poorly-understood class of molecule of critical importance to synthetic organic chemistry.

Dative Bonding between Group†13 Elements Using a Boron-Centered Lewis Base.

An electron-rich monovalent boron compound is used as a Lewis base to prepare adducts with Group 13 Lewis acids using both its boron and nitrogen sites. The hard Lewis acid AlCl3 binds through a nitrogen atom of the Lewis base, while softer Lewis acids GaX3 (Cl, Br, I) bind at the boron atom. The latter are the first noncluster Lewis adducts between a boron-centered Lewis base and a main-group Lewis acid.