n-alkyl fluorenyl phases in chromatography. I. Synthesis and characterization

A new class of silica gel-bound fluorene phases is described. The compounds are synthesized via reaction of fluorenyl lithium with omega-alkenyl bromides leading to 9-(5'-hexenyl)-9H- and 9-(9'-decenyl)-9H-fluorene (1 and 2), followed by hydrosilation reactions with different hydrosilanes. The resulting omega-functionalized silylalkyl fluorenes 3a(T0), 3b(T0), 4a(T0), 4b(T0) and 4c(M0) (Scheme 1) react with surface silanol groups of silica gel to generate the new fluorene phases 3a(Tn)(Qm)y, 3b(Tn)(Qm)y, 4a(Tn)(Qm)y, 4b(Tn)(Qm)y and 4c(M1)(Qm)y. The phases are characterized by employing 1H, 13C and 29Si solid-state nuclear magnetic resonance spectroscopy. Their applicability in high-performance liquid chromatography is proved by the Sander and Wise test (SRM 869). In contrast to conventional n-alkyl phases, pi-pi interactions are additionally involved in the separation process and, therefore, the retention times of the polycyclic aromatic hydrocarbons sample molecules depend on the ligand densities of the applied fluorene phases.