[en] It is reasonable to consider that this is a weak agostic interaction based on the distance of Tm to α-hydrogen H9 which is not as short as that observed for other systems with the agostic interaction between the lanthanide metal and α-hydrogen. Abundant studies on transition metal organohydroborate complexes have been reported. However, lanthanide metal organo-hydroborate derivatives have received less attention. We have been involved in the chemistry of the cyclic organohydroborate anions, and their transition metal derivatives. Recently, a series of group 4 metallocene organohydroborate complexes were synthesized. The M-H-B (M: transition metal) three center two electron bond is present in the organohydro-borate metal complexes in which B-H or M-H bond may serve as the electron pair donor to an unsaturated metal center or a trivalent boron to form the hydrogen-bridged bond. In an effort to extend lanthanide organohydroborate chemistry, the complexes have been investigated. Here we describe the detail of the synthesis and crystal structure of a novel thulium cyclic organohydroborate complex, (THF)₃Tm{(μ-H)₂BC₈H₁₄}, which was prepared in the reaction of TmCl₃ with K[H₂BC₈H₁₄]. This thulium complex has electron deficient, three center two electron bonds Tm-H-B. An interesting feature in the molecular structure of the complex is the existence of an agostic interaction between Tm(III) and the α-C-H bond of the cyclic organohydroborate H₂BC₈H₁₄ group