Selective Oligomerization and [2 + 2 + 2] Cycloaddition of Terminal Alkynes from Simple Actinide Precatalysts

Abstract

A catalyzed conversion of terminal alkynes into dimers, trimers, and trisubstituted benzenes has been developed using the actinide amides U[N(SiMe 3 ) 2 ] 3 (1) and [(Me 3 Si) 2 N] 2 An[κ 2 -(N,C)-CH 2 Si(CH 3 )N(SiMe 3 )] (An = U (2), Th (3)) as precatalysts. These complexes allow for preferential product formation according to the identity of the metal and the catalyst loading. While these complexes are known as valuable precursors for the preparation of various actinide complexes, this is the first demonstration of their use as catalysts for C−C bond forming reactions. At high uranium catalyst loading, the cycloaddition of the terminal alkyne is generally preferred, whereas at low loadings, linear oligomerization to form enynes is favored. The thorium metallacycle produces only organic enynes, suggesting the importance of the ability of uranium to form stabilizing interactions with arenes and related π-electroncontaining intermediates. Kinetic, spectroscopic, and mechanistic data that inform the nature of the activation and catalytic cycle of these reactions are presented.

Examining the Factors That Govern the Regioselectivity in Rhodium-Catalyzed Alkyne Cyclotrimerization

“…The phenyl group has a weak π-donor and inductive withdrawing character 12 that makes phenylacetylene a mild electron deficient alkyne. 13 The Gibbs energy profile obtained for the [2+2+2] cyclotrimerisation of phenylacetylene catalysed by [Rh(BIPHEP)] + is shown in Scheme 3. There is a preactivation scenario that transforms A0 to A2 in an exergonic process by ca.…”

Catalytic insertion of E–H bonds (E = C, N, P, S) into heterocumulenes by amido–actinide complexes

“…Attempts to isolate the intermediates generated and characterisation by crystallisation were unsuccessful, however previous studies have shown that activation of the thorium complex 3 with terminal alkyne similarly results in complete displacement of the amido moieties. 53 It is worth note that the order of addition of the reagents to the precatalyst solution did not markedly affect the reaction rate or product distribution. The nature of the REH substrate additionally affects the outcome of the insertion product ( Fig.…”

“…Recently, we have shown that a series of simple amido–actinide complexes of the formula U[N(SiMe 3 ) 2 ] 3 ( 1 ) and [(Me 3 Si) 2 N] 2 An[κ 2 -( N , C )–CH 2 Si(CH 3 ) 2 N(SiMe 3 )] (An = U ( 2 ), Th ( 3 )) ( Fig. 1 ) are capable of effecting the efficient oligomerisation or cyclotrimerisation of terminal alkynes, 53 the sole example of a catalytic transformation employing this class of complexes prior to the work described in this study. These complexes are generated in a one-pot process using readily available starting materials and have already shown impressive stoichiometric reactivity, 54 , 55 making them exceptionally attractive in their use as catalysts.…”

Actinide (Th4+ and UO22+) assisted oxidative coupling of ortho-phenylenediamine in the presence of oxygen

“…11,15 For example, Arnold and coworkers have used an organothorium metallacycle precatalyst, [(Me 3 Si) 2 N]Th[k 2 -(N,C)-CH 2 Si(CH 3 )N(SiMe 3 )], to regioselectively oligomerize terminal alkynes producing organic enynes and this demonstrates the first example of using a Th catalyst such as this in C-C bond formation. 18 Although all of these methods have aided in the understanding of the chemistry of the actinides, they require laborious preparation and, being either air or moisture sensitive, have short shelf-lives. In contrast to these organoactinide catalysts, actinide salts offer longer shelf-lives and increased ease of use.…”

“…Of note, simple, sterically unencumbered actinide centers have rarely been reported in the literature. 17,18 Few reactions have been reported with simple actinide salts, 17,18,26 and no catalytic reactions have been reported using simple thorium salts. …”