The mechanism of the boron metathesis reaction of the transition-metal-aminoborylene complex Cp(CO)(2)FeBN(CH3)(2)(+) (8) with EX, where EX = H3PO (9ap), H3AsO (9bp), H3PS (9aq), H3AsS (9bq), CH3CHCH2 (9cr), (NH2)(2)CCH2 (9dr), H2CO (9ep), and (NH2)(2)CO (9dp) is investigated at the B3LYP/LANL2DZ level. The analysis of bonding and charge distribution shows that the Fe-borylene complex (8) is a Fischer-type carbene analogue. The attack of the olefin takes place at the metal end of the MC bond of the metal-carbene complex in olefin metathesis and proceeds via [2 + 2] cycloaddition, while in boron metathesis, the initial attack of the substrates takes place at the positively charged B atom of the Fe-borylene complex and forms the preferred acyclic intermediate. The energetics of boron metathesis is comparable to that of the olefin metathesis. Substrates that are polar and a have low-lying sigma* molecular orbital (weak sigma bond) prefer the boron metathesis reaction. The relative stability of the metathesis products is controlled by the strength of the Fe-E and B-X bonds of the products 13 and 14, respectively. We have also investigated the possibility of a beta-hydride-transfer reaction in the Fe-borylene complex.