A Solid-State NMR and ab Initio Study of Sodium Metallocenes

Abstract

Sodium metallocenes (sodocenes) are a fascinating class of molecules that form polymeric chains of repeating [Cp‘Na]n units. A variety of sodium metallocenes have been studied by 23Na (I = 3/2) and 13C solid-state NMR, where Cp‘ = Cp (C5H5-), CpMe (C5H4Me-), CpiPr (C5H4iPr-), and Cp* (C5Me5-). Simulations of 23Na MAS NMR spectra yield the 23Na quadrupolar coupling constants (CQ) and asymmetry parameters (ηQ) for all compounds. Values of CQ range from 2.97 to 3.89 MHz for the linear Cp‘Na compounds. A new bent base-substituted species, CpNa·THF (THF = tetrahydrofuran), is identified which has CQ = 1.82(2) MHz. The sodium nuclei in sodocenes are extremely shielded with respect to the standard sodium chemical shift range, with chemical shifts (δiso) ranging from −45.5 to −61.9 ppm. All of the linear base-free compounds exhibit values of ηQ near zero, which reflect the axial symmetry of the sodium environments, while the nonlinear CpNa·THF has ηQ = 0.39(2), indicative of the electronic asymmetry about the sod...