Selective Incorporation Of Primary Amines Into A Trizirconium Imido System And Catalyic Cyclization Of Aminoalkynes

The trinuclear zirconium imido complex [{LZr(NMe2)}(3)] (2, L = C5Me4CH2CH2N) was synthesized by amine elimination between Zr(NMe2)(4) and endo-olefinic isomers of (tetramethylcyclopentadienyl)ethanamine (LH3) (1). To study the fundamental reactivity of the trizirconium system, reactions of 2 with primary amines were examined. Selective incorporations of the primary amines were observed, depending on steric and electronic natures of the amine substrates. The amine-incorporated complexes [(LZrNHR)(LHZrNHR)(LHZr)(-NHR)((3)-NR)] (3, R = Pr, Et), [(LZrNHR)(2)(LHZr)(-NR)] (4, R = Pr, i-Bu), [(LZr)(2)(LZrNMe2)(-NR)] (5, R = neo-Pen), and [(LZr)(LZrNHAr)(LH2Zr)(-NAr)(2)] (6, Ar = Ph, C6H4-4-Br, C6H4-4-OMe) were structurally characterized by NMR and XRD analysis and showed several coordination modes of the substrate nitrogen ligands: i.e., terminal amides, bridging amides, and bridging imides but not terminal imides. Thermolysis of a mixture of 3 and 4 led to CH bond activation, giving rise to the zirconaaziridines [{LZr(eta(2)-NCHR)}(LZr)(LHZr)(-NHCH2R)] (12, R = Et, Me). Complex 2 proved to be a competent precatalyst in the hydroamination of the aminoalkynes ((H2NCH2CR2CH2C)-C-1 CR2) (13, R-1 = H, R-2 = Bu, Ph, t-Bu; 14, R-1 = Me, R-2 = Et, Ph). Stoichiometric or semicatalytic reactions of 2 and the aminoalkynes were studied to explore the reactivity of in situ formed Zr-3 species.