The syntheses and molecular structures of four compounds are reported: 1 (RBBr3), 2 (R(H)(2)B-B(H)(2)R), 3 (R(H)B=B(H)R), and 4 (RBH3) (R = :C{N(2,6-Pr-i 2C6H3)CH}(2)).These compounds were characterized by single-crystal X-ray diffraction, H-1 and B-11 NMR, and elemental analyses. Compounds 2 and 3 were prepared by the KC8 reduction of I in Et2O Compound 3 is the first structurally characterized neutral diborene (mean B=B: 1.560(18) A). The nature of the B=B double bond in 3 was delineated by DFF computations.