Synthesis of zirconium complexes containing the tridentate diamido ligands [(t-Bu-d6-N-o-C6H4)2S]2- and [(i-PrN-o-C6H4)2S]2-

The thioethers (t-Bu-d(6)-NH-o-C6H4)(2)S (H-2[t-BuNSN]) and (i-PrNH-o-C6H4)(2)S (H-2[i-PrNSN]) have been prepared in three steps in good yield. Zirconium complexes that contain the [t-BuNSN](2-) ligand ([t-BuNSN]Zr(NMe2)(2), [t-BuNSN]ZrCl2, and [t-BuNSN]ZrMe2) were prepared readily, but the last is unstable, and no higher alkyl homologues could be prepared. In contrast, [i-PrNSN]ZrMe2 and [i-PrNSN]Zr(CH2CHMe2)(2) are both stable, even at elevated temperatures. An X-ray study of [t-BuNSN]ZrCl(NMe2) showed it to have a geometry about zirconium that is approximately trigonal bipyramidal with the chloride and sulfur atoms in the axial positions. An X-ray study of [i-PrNSN]ZrMe2 showed it to have approximately a square-pyramidal structure with a methyl group in the apical position. Low-temperature solution H-1 and C-13 NMR spectra of [t-BuNSN](2-) and [i-PrNSN](2-) species are consistent with the solid-state structures, although inversion at sulfur on the NMR time scale results in equilibration of the two metal substituents (e.g., methyl groups). Cationic complexes prepared from [RNSN]ZrMe2 precursors (R = t-Bu, i-Pr) were neither stable at 22 degrees C nor active for the controlled polymerization of 1-hexene.