Insights into Rare-Earth Metal Complex-Mediated Hydroamination

Acetate Assistance in Regioselective Hydroamination of Allenamides: A Combined Experimental and Density Functional Theory Study

A key factor in the development of selective nucleophilic addition to allenamides is controlling the reactivity of electrophilic intermediates, which is generally achieved using an electrophilic activator via conjugated iminium intermediates. In this combined experimental and computational study, we show that a general and highly chemoselective hydroamination of allenamides can be accomplished using a combination of 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) and NaOAc. Experimental mechanistic studies revealed that HFIP mediates proton transfer to activate the allenamide, while the acetate additive significantly contributes to N-selective interception. This strategy enables a general hydroamination of allenamides without the use of metals. We demonstrated that various functionalized 1,3-diamines could be readily synthesized and diversified into value-added structural motifs. Detailed mechanistic investigations using the density functional theory revealed the role of NaOAc in the formation of reactive electrophilic intermediates, which ultimately governed the selective formation of 1,3-diamine products. Critically, calculations of the potential energy surface around the proton-transfer transition state revealed that two different reactive electrophilic intermediates were formed when NaOAc was added.

Sc and Y bis(alkyl) complexes supported by bidentate and tridentate amidinate ligands. Synthesis, structure and catalytic activity in polymerization of isoprene and 1-heptene

A series of bis(alkyl) complexes {(tBu)C[N(2,6-Me₂C₆H₃)]₂}Ln(CH₂SiMe₃)₂(THF)_n (Ln = Y, n = 1 (1); Ln = Sc, n = 1 (2)), {2-[Ph₂P(O)]C₆H₄NC(tBu)N(2,6-Me₂C₆H₃)}Sc(CH₂SiMe₃)₂ (3), {2-[Ph₂P(NPh)]C₆H₄NC(tBu)N(2,6-Me₂C₆H₃)}Sc(CH₂SiMe₃)₂ (4) coordinated by bidentate (N,N) and tridentate (N,N,O; N,N,N) amidinate ligands are synthesized using an alkane elimination approach. Yttrium complex 1 demonstrated a half-life of ∼2.5 days at room temperature in benzene-D6 (C₆D₆) solution, whereas scandium complexes proved to be much more stable (25 d (2), 30 d (3) and 42 d (4)). Complexes 1-4 as a part of ternary catalytic systems 1-4/TB, HNB/AlR₃ (AlR₃ = AliBu₃, AliBu₂H; TB = [Ph₃C][B(C₆F₅)₄], HNB = [PhNHMe₂][B(C₆F₅)₄]) demonstrated high catalytic activity in isoprene polymerization and enable 80%-100% conversion of 1000 equivalents of monomer into polymer at 25 °C within 3-180 min. The isolated polyisoprenes feature predominantly cis-1,4-regularity (69.2%-87.3%) and polydispersities M_w/M_n = 2.26-8.92. Moreover, the binary (2/TB) and ternary (1-4/TB/10 AliBu₃) systems initiate 1-heptene polymerization providing 40%-100% conversion of 500 equivalents of monomer in 24 h at 25 °C giving polymer samples with M_n = 1.55-190.2 × 10³ and M_w/M_n = 1.55-3.87.