Closely Related Benzylene-Linked Diamidophosphine Scaffolds and Their Zirconium and Hafnium Complexes: How Small Changes of the Ligand Result in Different Complex Stabilities and Reactivities

The closely related benzylene-linked diaminophosphines PhP­(CH2C6H4-o-NHPh)2 ([PhA]­H2) and PhP­(C6H4-o-CH2NHXyl)2 ([B]­H2) were prepared as robust alternatives to the previously reported N,N′-bis­(trimethylsilyl)-substituted derivative PhP­(CH2C6H4-o-NHSiMe3)2 ([SiA]­H2). Upon reaction of [PhA]­H2 and [B]­H2 with M­(NMe2)4 (M = Zr, Hf), the respective dimethylamido complexes [PhA]­M­(NMe2)2 and [B]­M­(NMe2)2 ([PhA]-1-M and [B]-1-M, M = Zr, Hf) were isolated in high yields and converted to the corresponding diiodo derivatives [PhA]­MI2 and [B]­MI2 ([PhA]-2-M and [B]-2-M, M = Zr, Hf). In contrast to [SiA]­ZrI2, these thermally robust diiodo complexes were found to react cleanly with Bn2MgL2 (L = THF or Et2O), resulting in the corresponding dibenzyl species [PhA]­MBn2 and [B]­MBn2 ([PhA]-4-M and [B]-4-M, M = Zr, Hf). Upon addition of [B]­H2 to [B]­ZrBn2, the related homoleptic species [B]2Zr ([B]-5-Zr) was generated. Similar 2:1 complexes have not been observed for the hafnium homologue bearing the latter ligand or for [SiA]- or [PhA]-coordinated complexes. The former dibenzyl complexes were reacted with 2,6-xylylisonitrile, and clean conversions to the bis-η2-iminoacyl complexes [B]-6-Hf and [PhA]-6-M were observed for [B]-4-Hf and [PhA]-4-M (M = Zr, Hf). For [SiA]­HfBn2 ([SiA]-4-Hf) only one equivalent of the former isonitrile was inserted into one of the hafnium carbon bonds, which is in line with the steric differences between [SiA] and [PhA].