ARE PHOSPHATETRAHEDRANE AND DIPHOSPHATETRAHEDRANE PHOSPHORUS OR CARBON BASES

The protonation processes of phosphotetrahedrane (PTH) and diphosphate trahedrane (DPTH) were studied using density functional theory approac hes. The geometries of the neutrals and the protonated species were op timized at the B3LYP/6-31G(d) level and the final energies were obtain ed using the B3LYP/6-311+G(3df,2p) level of theory. Both PTH and DPTH are tetrahedral compounds which behave as carbon bases in the gas phas e. In contrast with what was found for other phosphorus-containing cag e structures such as tetraphosphacubane, the nature of the basic cente r does not change when the hydrogen atoms are substituted by bulky sub stituents. This is a consequence of the fact that both phosphorus and carbon protonation processes lead to C-P bond fission, so that the rep ulsive interactions between the susbtituents are not significantly dif ferent in carbon- or phosphorus-protonated structures. Protonation of DPTH at the P-P bond yields a local minimum with a P-H-P linkage simil ar to that described before for the most stable protonated form of Pq This seems to indicate that the existence of P-P linkages in strained structures clearly favors the formation of non-classical protonated sp ecies where the proton bridges the two phosphorus atoms. (C) 1998 John Wiley & Sons, Ltd.