Group-4 η1-Pyrrolyl Complexes Incorporating N,N-Di(pyrrolyl-α-methyl)-N-methylamine

Syntheses and properties of group-4 complexes incorporating the tridentate, dianionic ligand N,N-(dipyrrolyl-α-methyl)-N-methylamine, dpma, have been investigated. Addition of 1 equiv of H2dpma to Ti(NMe2)4 and Zr(NMe2)4 results in transamination with 2 dimethylamides providing Ti(NMe2)2(dpma) and Zr(NMe2)2(NHMe2)(dpma), respectively. Addition of 2 equiv of H2dpma to Zr(NMe2)4 and Hf(NMe2)4 results in production of the homoleptic complexes Zr(dpma)2 and Hf(dpma)2. Conversely, treatment of Ti(NMe2)4 with 2 equiv of H2dpma does not provide Ti(dpma)2, which was available by addition of 2 Li2dpma to TiCl4. The properties of the isostructural series M(dpma)2 were investigated by single crystal X-ray diffraction, cyclic voltammetry, 14N NMR, and other techniques. By 14N NMR, it was found that the pyrrolyl resonance chemical shift changes approximately linearly with the electronegativity of the metal center, which was attributed to π-interaction between the pyrrolyl nitrogen lone pair and the metal. Other complexes produced during this study include Ti(CH2SiMe3)(NMe2)(dpma), TiCl2(THF)(dpma), and Ti(OCH2CF3)2(THF)(dpma). Two isomers for Ti(CH2SiMe3)(NMe2)(dpma) were isolated and characterized.