The hydroboration of RN:C:NR (R = cyclohexyl) with (9H-9-BBN)2 gives RN:C(H)N(R)BC8H14 (1), which reacts with 9H-9-BBN to form the six-membered heterocycle mixed dimer I. I crystallizes in the monoclinic space group C 2/c, a = 27.776(3), b = 17.140(2), c = 12.302(2) .ANG., b = 113.31 Deg (at 120 K). On heating, I is transformed by intramol. hydroboration into H2[C(R)B(C8H14)]2. 1 Reacts with Et2O-BF3 to give 9F-9-BBN and (cyclic) RN:C(H)N(R)BF2. The total hydroboration of PhN:C:NPh with (9H-9-BBN) affords H2C[N(Ph)B(C8H14)14]2.