Catalytic hydrogenation or transfer hydrogenation of quinolines was thought to be a direct strategy to access dihydroquinolines. However, the challenge is to control the chemoselectivity and regioselectivity. Here we report an efficient partial transfer hydrogenation system operated by a cobalt-amido cooperative catalyst, which converts quinolines to 1,2-dihydroquinolines by the reaction with H 3 N•BH 3 at room temperature. This methodology enables the large scale synthesis of many 1,2-dihydroquinolines with a broad range of functional groups. Mechanistic studies demonstrate that the reduction of quinoline is controlled precisely by cobalt-amido cooperation to operate dihydrogen transfer from H 3 N•BH 3 to the N=C bond of the substrates.
To determine the reaction pathways at a metal-ligand site in enzymes, we incorporated a terminal thiolate site into a diiron bridging hydride. Trithiolato diiron hydride, (μ-H)Fe(pdt)(dppbz)(CO)(SR) (1(μ-H)) [pdt = 1,3-(CH)S, dppbz = 1,2-CH(PPh), RS = 1,2-CyPCHS)], was synthesized directly by photoassisted oxidative addition of 1,2-CyPCHSH to Fe(pdt)(dppbz)(CO). The terminal thiolate in 1(μ-H) undergoes protonation, affording a thiol-hydride complex [1(μ-H)H]. Placing an acidic SH site adjacent to the Fe-H-Fe site allows intramolecular thiol-hydride coupling and releases H from [1(μ-H)H]. A diiron η-H intermediate in the formation of H is proposed, and is evidenced by the H/D exchange reactions of [1(μ-H)H] with D, DO, and CDOD. Isotopic exchange in [1(μ-D)H] is driven by an equilibrium isotope effect with 2.1 kJ/mol difference in free energy that favors [1(μ-H)D]. [1(μ-H)H] catalyzes H/D scrambling between H and DO or CDOD to produce HD. The reactions based on such a "proton-hydride" model provide insights into the reversible heterolytic cleavage of H by Hases.
This paper describes a well-defined cobalt(II) half-sandwich complex bearing a phosphinoaminato ligand, Cp*Co(1,2-Ph2PC6H4NH) (1), that can activate pinacolborane (HBpin) for catalytic terminal hydroboration of olefins. The cooperative cobalt(II)–amido reactivity in 1 enables the B–H bond cleavage, affording the 17-electron cobalt(II) hydride Cp*Co(1,2-Ph2PC6H4NH(Bpin)), abbreviated H1(Bpin), in which the borenium ion is captured by the uncoordinated nitrogen atom of the phosphinoaminato ligand. Hydroboration of the CC bond can be promoted by a heteroatom such as N or O at the β-position of terminal alkenes. The mechanism of such hydroboration was established by various stoichiometric reactions based on the cobalt(II) hydride. With cooperative CoII–N reactivity for the B–H bond cleavage, our catalysis depends on the CoII–H hydride generated by the system itself.
Drosera is a small insectivorous plant whose antennae can fold up, encircle, and prey. The rapid movement of the antennae is achieved by the synergistic effect of a double‐layer structure with the antennae contracts on the front and expands on the back. In this work, a drosera‐inspired dual‐actuating double‐layer hydrogel actuator is proposed, in which the temperature‐responsive poly(N, N‐diethyl acrylamide) (PDEAAm) layer acts as the main actuation layer and a moisture‐responsive poly(acrylamide) (PAAm) layer acts as the auxiliary actuation layer. In a water environment with low temperature, both the PAAm and PDEAAm layers absorb water and expand with a swelling property. When the temperature exceeds the lower critical solution temperature of PDEAAm, the PDEAAm layer undergoes a hydrophilic–hydrophobic transition and shrinks rapidly. Therefore, the synergistic effect of the double‐layer hydrogel enables the double‐layer hydrogel to achieve a large bending angle at high temperature. In addition, when designing and fabricating shape‐patterned double‐layer hydrogels, complex shape changes can be achieved. Due to the physical and chemical properties, the actuator can be used to grab, transport, and release objects. This drosera‐inspired double‐layer hydrogel actuator has high practical value, which may provide new insights for the design and manufacture of artificial intelligence materials.
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