The C1-B bond length in 3a (1.671(3) Å) is almost identical to those reported for known carbeneborane adducts (ca. 1.66~1.70 Å) that mediate, via regeneration of frustrated Lewis pairs, the heterolytic cleavage of H2 at room temperature or under heating conditions. The N=P bond lengths commonly fall in the range 1.53~1.62 Å, 5a and little difference was found for 3a (1.541(2) Å), 3b