Diborane(4) compounds are versatile reagents in synthetic chemistry. Generally, diboranes(4) with sp-hybridized boron atoms react as electrophiles. By contrast, the chemistry of nucleophilic diborane(4) compounds with two sp-hybridized boron atoms is very much underdeveloped. In this work, we systematically vary the substituents of electron-rich diborane(4) compounds with bridging guanidinate substituents. In this way, five new diboranes are synthesized and fully characterized. Using quantum chemical computations, we show that the electronic properties and reactivity of these compounds can be rationally varied by the choice of substituents. The HOMO energies, adiabatic ionization energies and proton affinities are considered as parameters to compare the chemical properties of these unusual compounds.

Hydroboration generally requires the presence of a catalyst to lower the barrier for hydride transfer. This work reports on the first catalyst-free CO hydroboration with a neutral boron compound, the nucleophilic diborane [HB(hpp)] , 1 (hpp=1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidinate). Further hydroboration reactions to bis(boryl)acetals are possible. In acetonitrile, but not in dichloromethane solutions, hydroboration of a first CO is followed by hydroboration of a second CO molecule. Detailed kinetic measurements for both hydroboration steps were carried out and the influence of the solvent and the addition of a Lewis base on the rate constants analyzed. In contrast to catalyst-free hydroboration of CO , hydroboration of the less electrophilic acetone requires the presence of an activating Lewis acid.

Redox reactions compete with coordination and polymerization reactions when the organic electron donor and ligand, 1,2,4,5‐tetrakis(tetramethylguanidino)benzene (1), is dissolved together with silver halides AgX (X = Cl, Br or I) in solvents of different polarity. The complex results obtained for the relatively simple system 1/AgX highlight the importance of solvent effects. A variety of chain polymers have been synthesized in which the guanidine electron‐donor building blocks are connected by silver halide clusters of different sizes.