The insertion reaction of bis(pinacolato)diborane(4) [(Me4C2O2)BB(O2C2Me4 ), 1] with various diazoalkanes provided novel representatives of a new class of substituted C1-bridged bis(pinacolato)diborane(4) derivatives 5a, 5b, 5c, and 5d in a range of 75-78% isolated yields. The reaction was efficiently catalyzed by Pt(PPh3)4 in toluene at 110 °C. Single-crystal X-ray diffraction, GCMS, and NMR multinuclear spectroscopies fully confirmed the structure and configuration of the new compounds. Crystals of 5a and 5c are centrosymmetric, while those of 5d are chiral. 5b crystallized with a somewhat unusual Fdd2 space symmetry. While its crystals are noncentrosymmetric, they contain mirror-related species. The degree of puckering of the five-membered C2O2B rings, as well as the dihedral angles between the mean planes of these rings, vary from one compound to another and to some extent from one ring to another within the same compound.