Preparation of all N-coordinated zirconium amide amidinates and studies of their reactions with dioxygen and water

Zr(NR2)2[MeC(NiPr)2]2 (R = Me, 1; Et, 2) have been prepared through aminolysis and their reactions with O2 and water have been studied. Two major products from the reactions are the oxo dimer {(μ-O)Zr[MeC(NiPr)2]2}2 (3) and its insoluble polymer {(μ-O)Zr[MeC(NiPr)2]2}n (4). Over time the dimer 3 polymerizes to 4. Zr peroxo trimer {(μ-η2:η2-O2)Zr[MeC(NiPr)2]2}3 (5) was also observed from the reaction of 1 with O2 and its crystal structure is reported. DFT calculations show that the reaction of 1 with O2 follows a radical process, yielding the peroxo trimer 5. Mass spectrometric studies of the reactions of water in air with 1 and 2 show the formation of the oxo monomer (O=)Zr[MeC(NiPr)2]2 (6), oxo dimer {(μ-O)Zr[MeC(NiPr)2]2}2 (3), and the dihydroxy monomer (HO)2Zr[MeC(NiPr)2]2 (7). In addition, the cations {Zr(NR2)[MeC(NiPr)2]2}+ (R = Me, Et) were observed. 2 revealed an interesting dynamic NMR behavior. Variable-temperature (VT) NMR spectroscopy has been used to study the Bailar twist process in 2, giving activation parameters ΔH‡ = 10.9(1.1) kcal mol−1, ΔS‡ = −11(4) eu and ΔG‡303 K = 14(2) kcal mol−1.

Zr(NMe2)2[MeC(NiPr)2]2 (1) reacts with O2 forming peroxo trimer {(μ-η2:η2-O2)Zr[MeC(NiPr)2]2}3 and then oxo dimer {(μ-O)Zr[MeC(NiPr)2]2}2 and its insoluble polymer {(μ-O)Zr[MeC(NiPr)2]2}n through a radical process, as DFT studies show. Reaction of 1 with H2O yields dihydroxy monomer (HO)2Zr[MeC(NiPr)2]2, oxo monomer (O=)Zr[MeC(NiPr)2]2, and the dimer, as revealed by MS.Figure optionsDownload as PowerPoint slide