AB-INITIO MOLECULAR-ORBITAL STUDY OF MECHANISMS OF THE REACTION OF B2H6 WITH SH2

The potential energy surface for the reaction of diborane with sulfur dihydride has been calculated by using MP4/6-31+G(2d,p)//MP2(FULL)/6-3 1G(d) method with zero-point energy corrections. The proposed mechanis m of formation of mercaptoborane, BH2SH, from the reaction includes as initial step the bimolecular addition of SH2 to B2H6 to form the B2H7 - like complex, H2S-B2H6. Then this complex can either eliminate BH3 o r rearrange into SH2(BH3)2, complex of H2S With two BH3's. The latter can be also transformed by two different ways, elimination of BH3 or H -2. The second pathway with formation of B2H5.SH complex is more favor able thermodynamically but is forbidden by a high barrier of H-2 elimi nation. Removal of BH3 gives BH3.SH2 Species. Since H-2 elimination fr om BH3SH2 also has a high activation barrier, it is suggested to occur at higher temperatures in the observed reaction. Calculated vibration al frequencies (MP2(FULL)/6-31G(d)) are compared with experimental val ues for BH2SH and HBS and are predicted for SH2B2H6, SH2(BH3)2, and B2 H5SH. Comparison of mechanisms of the reactions of diborane with SH2 a nd NH3 is performed.