Boron-nitrogen compounds: CXX. Complexes of B-triethylboroxin with ethylenediamine and derivatives thereof☆

B-Triethylboroxin forms colorless 11 molar complexes of the type (C2H5BO)3·L with L = ethylenediamine (1) and various derivatives of the latter, i.e., N,N-dimethylethylenediamine (2), N,N,N′,N′-tetramethylethylenediamine (3, piperazine (4), 1,4-diazabicyclo[2.2.2]octane (5), diethylenetriamine (6), and tris(2-aminoethyl)amine (7). The cited boroxin also forms 21 molar complexes, 2(C2H5BO)3·L, with L = ethylenediamine (8) and those derivatives of the latter which may be considered as symmetrical species, i.e., N,N,N′,N′-tetramethylethylenediamine (9), piperazine (10), 1,4-diazabicyclo[2.2.2]octane (11), and diethylenetriamine (12). NMR spectroscopic data suggest that the complexes are fluxional in solution at room temperature with a single nitrogen coordinating to the three boron atoms of a given boroxin ring and where, in solution, the 11 molar complexes of symmetrical amines appear to exchange their donor sites. There seem to be no principal differences in the complexing of (RBO)3 with R = C2H5 or C6H5. Two species of the unusual composition 3(RBO)3·2H2NCH2NH2 were also identified.