Zirconium-Nitrogen Intermolecular Frustrated Lewis Pairs

A series of intermolecular transition metal frustrated Lewis pairs (FLPs) based on zirconocene alkoxide complexes ([Cp₂Zr(OMes)]⁺ 1 or ([Cp*₂Zr(OMes)]⁺ 2) with nitrogen Lewis bases (NEt₃, NEtⁱPr₂, pyridine, 2-methylpyridine, 2,6-lutidine) are reported. The interaction between Zr and N depends on the specific derivatives used, in general more sterically encumbered pairs leading to a more frustrated interaction; however, DOSY NMR spectroscopy reveals these interactions to be dynamic in nature. The pairs undergo typical FLP-type reactivity with D₂, CO₂, THF, and PhCCD. The catalytic dehydrocoupling of Me₂NH·BH₃ is also reported. Comparisons can be made with previous work employing phosphines as Lewis bases suggesting that hard–hard or hard–soft acid–base considerations are of little importance compared to the more prominent roles of steric bulk and basicity.