N ‐Methyl‐anilinoborane: Monomer, Dimers, Molecular Structure, and Rearrangement into μ‐( N ‐Methyl‐anilino)diborane(6). A Convenient Route to μ‐(Amino)diboranes(6)

N ‐Methyl‐anilinoborane exists as a dimer in the solid state, shown by X‐ray structural analysis, whereas in solution, a monomer–dimer equilibrium is present ( 1 H, 11 B and 13 C NMR spectroscopy). The phenyl groups are in trans positions in the crystalline dimer. In solution, both possible isomers of the dimer exist in a trans / cis ratio of 3:2, in agreement with the energies for calculated optimized geometries [B3LYP/6‐311+G(d,p) level of theory]. In solution, the monomer is rather reactive and disproportionates completely after several days to give a 1:1 mixture of bis( N ‐methyl‐anilino)borane and μ‐(N‐methyl‐anilino)diborane(6). This observation led to a convenient high yield synthesis of μ‐(amino)diborane(6) derivatives, starting from bis(amino)boranes and borane/THF.