LUBRICANTS FOR RIGID MAGNETIC MEDIA BASED UPON CYCLOTRIPHOSPHAZENES -INTERACTIONS WITH LEWIS-ACID SITES

Lubricants such as polyperfluorinated ethers are used topically on rig id magnetic media, or computer disks, to provide a low friction interf ace. These materials are subject to degradation particularly in the pr esence of Lewis acids; however, the degradation may in part be mitigat ed by the addition of additives such as is(3-(trifluoromethyl)phenoxy) cyclotriphosphazene, [(NP)(3)(OC6H4CF3)(4)(OC6H4F)(2)], or X-1P. This report explores how X-1P may preferentially interact with Lewis acid s ites to impart protection to the host lubricant. Therefore, ab initio theoretical studies on the Lewis acid-base interactions between cyclot riphosphazene derivatives and AlF3 are performed. The theoretical resu lts indicate that the strongest binding between X-1P and AlF3 is achie ved when the endocyclic nitrogen atom bonds to the aluminum, providing a binding energy of the order of -55 kcal/mol. The magnitude of the b inding energy indicates significant bonding as opposed to a dipole-dip ole attraction. The lone pair of electrons on the phenoxy substituents also provide strong binding to AlF3, although not to the extent the n itrogen atoms do, with binding energies near -37 kcal/mol. Binding to fluorine is considerably smaller, near -8 kcal/mol. The population ana lyses indicate that the preferred nitrogen interaction involves the p- orbital that contains the in-plane lone pair of electrons. A computed reaction coordinate with [NPH2](3) and AlF3 gives every indication tha t the in-plane interaction is strongest and most stable on the potenti al energy surface. There is little desire on the part of the N3P3 ring itself to interact with Lewis acid sites parallel to the plane of the ring, i.e., with the p-orbitals housing the lone pair of electrons pe rpendicular to the plane of the ring. These orbitals instead provide w eak pi bonding with the phosphorus d-orbitals and are energetically we ll below the HOMO. The reason for the strong binding between AlF3 and the ring nitrogen atom originates from the polar, almost zwitterionic character of the endocyclic P-N bond, which polarizes the nitrogen ato m negatively. All data lead to the conclusion that if the ring nitroge n in X-1P is sterically accessible, this will be the preferred binding site.