Boron(III) cations are widely used as highly Lewis acidic reagents in synthetic chemistry. In contrast, boron(II) cations are extremely rare and their chemistry almost completely unknown. They are both Lewis acids and electron donors, properties that are commonly associated with catalytically active late-transition-metal complexes. This double reactivity pattern ensures a rich and diverse chemistry. Herein we report the facile synthesis of several new boron(II) cations starting with a special diborane with two easily exchangeable triflate substituents. By increasing the π-acceptor character of the neutral σ-donor reaction partners, first reactions were developed in which the combined Lewis acidity and electron-donor properties of boron(II) cations are applied for the reduction of organic molecules. The results of our study pave the way for applications of these unusual compounds in synthetic chemistry.

Starting with electron-rich ditriflato-diborane B2(hpp)2(OTf)2 (hpp = 1,3,4,6,7,8 hexahydro-2H-pyrimido[1,2-α]pyrimidinate), novel symmetric and unsymmetric diboranes B2(hpp)2X2 and B2(hpp)2XY with X,Y = Br, NCS, N3 or OTf are synthesized by substitution reactions...

The complexation and reduction of a series of diones with different redox-potentials in a dicationic diborane are analysed.

The introduction of electron‐donating, bridging guanidinate substituents in diborane(4) compounds allows the synthesis of a variety of new cationic diborane(4) compounds. In this work, strategies for the directed synthesis of cationic di‐ and tetraboron compounds are presented, leading to the synthesis and complete characterization of several new compounds with distinct structural motifs, all exhibiting BII atoms directly bound to each other. Hence, we report on tetracationic donor‐acceptor cyclophanes with diboron donor linkers and organic π‐acceptor units, on paddlewheel‐type cationic diboranes, and on unsymmetrically‐substituted monocationic diboranes.