Intramolecular dihydrogen bonding in main group elements. Connection with dehydrogenation reactions

The existence of intramolecular dihydrogen bonding in the main group elemen ts is investigated at the ab initio level of theory. The AH(n)-XHm complexe s (with A = Li/B/Al and X= F/O/N/Cl/S/P) in general do not show intramolecu lar dihydrogen bond (DHB) in their equilibrium structures; however, it is o bserved in the transition state for the dehydrogenation reaction AH(n)-XHm --> AH(n-1)-XHm-1 + H-2. The barriers to these reactions have been calculat ed and are found to be least for the complexes having DHB in the equilibriu m structure or having eclipsed geometry favorable for DHB formation. The to pological analysis of electron density distribution provides crucial inform ation on the existence of DHB as well as on the extent of the dehydrogenati on reaction. The above features indicate that the motivation for the format ion of intramolecular DHB is likely to facilitate the dehydrogenation react ion from complexes similar to AH(n)-XHm.