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The search for efficient and selective methods for the divergent synthesis of multi‐substituted aminotetralins is of much interest and importance. We report herein for the first time the diastereoselective [4+2] annulation of 2‐methyl aromatic aldimines with alkenes via benzylic C(sp3)−H activation by half‐sandwich rare‐earth catalysts, which constitutes an efficient route for the divergent synthesis of both trans and cis diastereoisomers of multi‐substituted 1‐aminotetralin derivatives from readily accessible aldimines and alkenes. The use of a scandium catalyst bearing a sterically demanding cyclopentadienyl ligand such as C5Me4SiMe3 or C5Me5 exclusively afforded the trans‐selective annulation products in the reaction of aldimines with styrenes and aliphatic alkenes. In contrast, the analogous yttrium catalyst, whose metal ion size is larger than that of scandium, yielded the cis‐selective annulation products. This protocol features 100 % atom‐efficiency, excellent diastereoselectivity, broad substrate scope, and good functional group compatibility. The reaction mechanisms have been elucidated by kinetic isotope effect (KIE) experiments and the isolation and transformations of some key reaction intermediates. [ABSTRACT FROM AUTHOR]

The creation of self‐healing polymers from commodity olefins is of great interest and importance but has remained a challenge to date. We report here for the first time the synthesis of self‐healing polymers by catalyst‐controlled polymerization of a simple commodity diene, isoprene. We found that polyisoprenes having an appropriate mixture (ca. 70/30) of 3,4‐ and cis‐1,4‐microstructures synthesized by using a half‐sandwich scandium catalyst could act as excellent self‐healing elastomers without any external intervention. The unprecedented self‐healability could be ascribed to nanoscale heterogeneities formed by microphase separation of the relatively hard 3,4‐segments from a flexible cis‐1,4‐segment matrix. The hydrogenated polyisoprenes (without C=C bonds) with the analogous microstructures also exhibited excellent mechanical and self‐healing properties, further demonstrating that even simple polyolefins can be made self‐healable if the microstructures are appropriately regulated. [ABSTRACT FROM AUTHOR]

The ortho-selective benzylic C(sp3)–H alkenylation of 2-methyl tertiary anilines with internal alkynes has been achieved for the first time by using a half-sandwich scandium catalyst. This protocol provides a straightforward route for the synthesis of a new family of 2-allylaniline derivatives, featuring broad substrate scope, 100% atom-efficiency, high yields, and high chemo-, regio-, and stereoselectivity. [ABSTRACT FROM AUTHOR]

Here we report for the first time the regio‐ and diastereoselective [3+2] annulation of a wide range of aliphatic aldimines with alkenes via the activation of an unactivated β‐C(sp3)−H bond by half‐sandwich scandium catalysts. This protocol offers a straightforward and atom‐efficient route for the synthesis of a new family of multi‐substituted aminocyclopentane derivatives from easily accessible aliphatic aldimines and alkenes. The annulation of aldimines with styrenes exclusively afforded the 5‐aryl‐trans‐substituted 1‐aminocyclopentane derivatives with excellent diastereoselectivity through the 2,1‐insertion of a styrene unit. The annulation of aldimines with aliphatic alkenes selectively gave the 4‐alkyl‐trans‐substituted 1‐aminocyclopentane products in a 1,2‐insertion fashion. A catalytic amount of an appropriate amine such as adamantylamine (AdNH2) or dibenzylamine (Bn2NH) showed significant effects on the catalyst activity and stereoselectivity. [ABSTRACT FROM AUTHOR]

The terpolymerization of a non‐polar olefin (such as ethylene) and two different polar functional olefins in a controlled fashion is of great interest and importance but has hardly been explored to date. We report for the first time the terpolymerization of ethylene (E) and two different methoxyaryl‐substituted propylenes (AR1P=hexylanisyl propylene; AR2P=methoxynaphthyl propylene or methoxypyrenyl propylene) by a half‐sandwich scandium catalyst. The terpolymerization took place in a sequence‐controlled fashion, affording unique multi‐block copolymers composed of two different ethylene‐alt‐methoxyarylpropylene sequences E‐alt‐AR1P (soft segments) and E‐alt‐AR2P (hard segments) and relatively short ethylene–ethylene (EE) blocks (crystalline segments). The terpolymers exhibited excellent elasticity and unprecedented self‐healing as a result of microphase separation of nanodomains of the crystalline EE segments and the hard amorphous E‐alt‐AR2P segments from a very flexible E‐alt‐AR1P matrix, demonstrating unique synergy of the three different components. [ABSTRACT FROM AUTHOR]

A series of half-sandwich scandium-dialkyl complexes that bear various auxiliary ligands have been examined for the copolymerization of isoprene (IP) with nonconjugated α,ω-dienes such as 1,5-hexadiene (HD) and 1,6-heptadiene (HPD). Significant ligand influence on the catalytic activity and selectivity has been observed. The thf-coordinated complex [(C5Me4SiMe3)Sc(CH2SiMe3)2(thf)] ( 2) and the methoxy side arm containing the half-sandwich complex [(C5Me4C6H4OMe- o)Sc(CH2SiMe3)2] ( 3), in combination with an equivalent of [Ph3C][B(C6F5)4], can serve as excellent catalysts for the random cyclocopolymerizations of IP with HD and HPD. The resulting random HD-IP copolymers contain five-membered-ring methylene-1,3-cyclopentane (MCP), 3,4-polyisoprene (3,4-IP), and 1,4-polyisoprene (1,4-IP) units with controllable HD incorporation in a range of 17-82 mol %. The random HPD-IP copolymers possess six-membered-ring methylene-1,3-cyclohexane (MCH), 1,4-IP, and 3,4-IP units with HPD incorporation in a range of 11-55 mol %. By use of a catalyst that bears a phosphine oxide group [{C5Me4SiMe2CH2P(O)Ph2}Sc(CH2SiMe3)2] ( 5), the alternating copolymerizations of IP with HD and HPD have been achieved for the first time in which HD and HPD are completely cyclized to the MCP and MCH units, respectively. More remarkably, in the alternating copolymerization of HPD and IP by 5, the regio- and stereospecific cis-MCH selectivity reached as high as 99 %. The microstructures and compositions of these copolymers showed significant influences on their mechanical properties. [ABSTRACT FROM AUTHOR]

The living isospecific-cis-1,4-polymerization and block-copolymerization of (E)-1,3-pentadiene with 1,3-butadiene have been achieved for the first time by using cationic half-sandwich scandium catalysts. [ABSTRACT FROM AUTHOR]

A series of half-sandwich fluorenyl (Flu′) scandiumdialkyl complexes Flu′Sc(CH2SiMe3)2(THF)n(1, Flu′= C13H9, n= 1; 2, Flu′ = 2,7-tBu2C13H7, n= 1; 3, Flu′= 9-SiMe3C13H8, n= 1; 4, Flu′ = 2,7-tBu2-9-SiMe3C13H6, n= 1; 5, Flu′ = 9-CH2CH2NMe2C13H8, n= 0; 6, Flu′ = 2,7-tBu2-9-CH2CH2NMe2C13H6, n= 0) have been synthesizedand structurally characterized. In comparison with the well-knowncyclopentadienyl-ligated scandium catalyst system [(C5Me4SiMe3)Sc(CH2SiMe3)2(THF)]/[Ph3C][B(C6F5)4], the analogous combinations of the fluorenyl-ligated, THF-containingcomplexes 1–4with [Ph3C][B(C6F5)4] show relatively lowactivities, albeit with similar syndioselectivities for styrene polymerizationand styrene–ethylene copolymerization. However, on treatmentwith 15 equiv of AliBu3, the 1–4/[Ph3C][B(C6F5)4] combinations show a dramatic increase in catalyticactivity without changes in the stereoselectivity. In contrast, thecombinations of complexes 5and 6, whichhave an amino group attached to the fluorenyl ring and intramolecularlybonded to the metal center, exhibit very low activity, no matter whetheror not AliBu3is present, affordingsyndiotactic polystyrenes with broad molecular weight distributions.The DFT calculations of the activation mechanism by using the representativecatalysts suggest that AliBu3can capture the THF molecule from the catalyst precursors 1–4at first,and then the new, THF-freecationic half-sandwich scandium active species [Flu′Sc(CH2SiMe3)][B(C6F5)4] with less steric hindrance around the metal center is generatedin the presence of an activator such as [Ph3C][B(C6F5)4]. The DFT calculations on the syndioselectivityof styrene (co)polymerization catalyzed by [Flu′Sc(CH2SiMe3)][B(C6F5)4] havealso been carried out, thus shedding new light on the mechanisticaspects of the (co)polymerization processes. [ABSTRACT FROM AUTHOR]