KINETICS OF IODINATION OF SOME AMINE-BORANES WITH MOLECULAR-IODINE INTOLUENE

R(3)N.BH3 (R=Me, Et, Pr-n) at room temperature reacts with I-2 in tolu ene quantitatively to produce R(3)N.BHI2 when concentrations of the re actants are kept low. But with reactant concentrations greater than or equal to 50 mmol dm(-3), R(3)N.BH2I and H-2 are produced as observed earlier (Inorg Synth, 12 (1970) 120). A reaction scheme has been propo sed to explain this difference. Production of R(3)N.BHI, from R(3)N.BH 3 proceeds in two consecutive steps: R(3)N.BH3<(k1)under right arrow>R (3)N.BH2I<(k2)under right arrow>R(3)N.BHI2. Both steps are first order each in [borane] and [I-2]. k(1) is greater than k(2) but both increa se in the order Et > Me > Pr-n. The secondary amine-borane (Et)(2)NH.B H3 reacts with I-2 much faster than any of the three tertiary amine-bo ranes studied. The observed order of reactivity of amine-boranes with homopolar I-2 is the same as that observed by earlier workers with het eropolar HOCl A bimolecular mechanism with a four-membered transition state and pentacoordinate B is proposed and the sequence of reactivity appears to; be primarily a result of steric influence, though electro nic effects might have a modifying role.