A novel semi‐aliphatic diamine with bulky cyclohexyl and ortho‐substituted tertiary butyl groups (4,4'‐(cyclohexylmethylene)bis(2‐(tert‐butyl)aniline), CHMBTBA) is synthesized via Mannich and rearrangement reactions of cyclohexanecarboxaldehyde and 2‐tert‐butylaniline. Afterward, several semi‐aliphatic polyimides are prepared by the high‐temperature one‐pot polymerization of CHMBTBA with various aromatic dianhydrides respectively. The resulting PIs exhibit outstanding solubility in common organic solvents (i.e., trichloromethane, etc.) and are easily processed into light color or colorless transparent films (thickness: 25 ± 1 µm) by the blade coating of polymer solution. The transmittance of all resulting films is above 86% in the visible light region (400–760 nm). Their glass transition temperatures exceed 310 °C and reach even to 374 °C (by differential scanning calorimetry). They also display low water absorption (0.29–0.87%) and good mechanical properties (tensile strength: 50.9–87.7 MPa, Young's modulus: 2.0‐2.5 GPa, elongation at break: 3.8–7.6%). Thus, they are promising potential candidates for flexible display substrates.
Dinuclear
transition-metal catalysis is a distinctive approach
for cross-coupling reactions, but Rh(I)–Rh(III) redox catalysis
has rarely been considered. Here, a dinuclear Rh(III)–Rh(III)
redox catalytic cycle for [Rh(coe)2Cl]2-catalyzed
remote terminal arylation of activated olefins is proposed and validated
by density functional theory. Calculations reveal that the catalytic
cycle of terminal arylation involves phosphine-directed oxidative
addition of the indole C7(aryl)–H bond, alkene insertion, Rh-walking,
and reductive elimination. Throughout the catalytic cycle, the dinuclear
rhodium complex remains intact, and each of the rhodium atoms have
important roles. One acts as the active catalytic center and undergoes
Rh(I)–Rh(III) redox cycles; the other remains in the +3 oxidation
state after the pre-catalytic cycle and is not directly involved in
the reactions but affects the chemoselectivity by adjusting the coordination
environment of the active rhodium atom. The hydroarylation regioselectivity
is controlled by steric effects, which distinguish different reactive
sites in the dinuclear rhodium pathway. The mononuclear rhodium catalytic
cycle is unfavorable because of the endothermic monomerization process.
A tether effect in the reductive elimination step also restricts generation
of the δ-arylation product in the mononuclear pathway.
Silanes are important in chemistry and material science. The self-redistribution of HSiCl 3 is an industrial process to prepare SiH 4 , which is widely used in electronics and automobile industries. However, selective silane cross-redistribution to prepare advanced silanes is challenging. We now report an enthalpy-driven silane cross-redistribution to access bis-silanes that contain two different types of SiÀ H bonds in the same molecule. Compared with entropy-driven reactions, the enthalpy-driven reaction shows high regioselectivity, broad substrate scope (62 examples) and high atom economy. Our combined experimental and computational study indicates that the reaction proceeds through a Ni 0 -Ni II -Ni IV catalytic cycle.
Density functional theory (DFT) calculations have been performed to provide mechanistic insight into the Rh/Cu co-catalyzed multicomponent annulation of indoles, diazo compounds, and α,β-unsaturated esters.
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