Tetraaza macrocycles as ancillary ligands in early metal alkyl chemistry. Synthesis and characterization of out-of-plane (Me4taen)ZrX2 (X = alkyl, benzyl, NMe2, Cl) and (Me4taen)ZrX2(NHMe2) (X = Cl, CCPh) complexes

Article abstract of DOI:10.1021/om00007a062

The objectives of the present work were to develop efficient routes to (Me₄taen)ZrR₂ compounds and a general understanding of their structures and properties. The chemistry of cationic derivatives will be discussed in a subsequent paper. Alkane elimination reactions of the neutral macrocycle (Me₄taen)H₂ (1) and homoleptic ZrR₄ compounds provide the most efficient approach to (Me₄taen)ZrR₂ complexes. Compound 1 reacts readily with ZrR₄ (R = CH₂Ph, CH₂SiMe₃) in pentane at 23°C affording (Me₄taen)ZrCH₂Ph)₂ (2) and (Me₄taen)Zr(CH₂SiMe₃)₂ (3) in high yield. Complexes 2 and 3 are isolated as orange solids after recrystallization and have been characterized by ¹H and ¹³C NMR and analysis. Complex 2 is sparingly soluble, 3 is quite soluble in benzene, and both are soluble and stable in THF and CH₂Cl₂. The ¹H NMR spectra of 2 and 3 contain singlets for the Me₄taen methyl and methine hydrogens, and two multiplets for the -CH₂CH₂- hydrogens. These data are consistent with cis C_2v-symmetric structures, in which the `upper' and `lower' -CH₂CH₂- hydrogens are inequivalent. The ZrCH₂ J_CH values for 2 (106 Hz) and 3 (105 Hz) are at the low end of the normal range observed for alkyl complexes of electropositive metals, and indicate that the hydrocarbyl ligands are not significantly distorted by non-classical η²-benzyl or α-agostic interactions.