Iron-Catalyzed Vinylsilane Dimerization and Cross-Cycloadditions with 1,3-Dienes: Probing the Origins of Chemo- and Regioselectivity

Abstract

The selective, intermolecular homodimerization and cross-cycloaddition of vinylsilanes with unbiased 1,3-dienes, catalyzed by a pyridine-2,6-diimine (PDI) iron complex are described. In the absence of a diene coupling partner, vinylsilane hydroalkenylation products were obtained chemoselectively with unusual head-to-head regioselectivity (up to >98% purity, 98:2 E/ Z). In the presence of a 4-or 2-substituted diene coupling partner, under otherwise identical reaction conditions, formation of valueadded [2+2]-and [4+2]-cycloadducts, respectively, was observed. The chemoselectivity profile was distinct from that observed for analogous α-olefin dimerization and cross-reactions with 1,3-dienes. Mechanistic studies conducted with well-defined, singlecomponent precatalysts ( Me PDI)Fe(L 2 ) (where Me PDI = 2,6-(2,6-Me 2 -C 6 H 3 NCMe) 2 C 5 H 3 N; L 2 = butadiene or 2(N 2 )) provided insights into the kinetic and thermodynamic factors contributing to the substrate-controlled regioselectivity for both the homodimerization and cross-cycloadditions. Diamagnetic iron diene and paramagnetic iron olefin complexes were identified as catalyst resting states, were characterized by in situ nuclear magnetic resonance and Mossbauer spectroscopic studies, and were corroborated with density functional theory calculations. Stoichiometric reactions and computational models provided evidence for a common mechanistic regime where competing steric and electronic requirements dictate the regioselectivity of oxidative cyclization. Although distinct chemoselectivity profiles were observed in cross-cycloadditions with the vinylsilane congeners of α-olefins, these products arose from metallacycles with the same connectivity. The silyl substituents ultimately governed the relative rates of β-H elimination and C−C reductive elimination to dictate final product formation.

On the Realties of Base Metal Catalysis: An Overview

“…Specifically, head-to-head vinylsilane dimerization, cross-[2+2]-cycloaddition, and cross-[4+2]cycloaddition with 4 and 2-substituted 1,3-dienes, respectively. 98 The products of these reactions have potential for various applications but, more crucially, these works contribute to the development of a broadly applicable catalytic method which is compatible with abundant, unactivated alkenes. 99 Figure 6.…”

“…99 Figure 6. Examples of reactions catalyzed by an Fe PDI catalyst developed by Chirik et al 95,96,98 4. Conclusions and Future Perspectives While the definition of a base metal catalyst is still broad, we conclude with some of the following take-aways: base metals and first-row transition metals are not synonymous, and if base metals are considered inherently sustainable, clearly some points for consideration need to be established.…”

Catalyst Design Principles Enabling Intermolecular Alkene-Diene [2+2] Cycloaddition and Depolymerization Reactions

“…A related reaction is the iron-catalyzed intermolecular [2 + 2] cycloaddition of dienes and alkenes to form vinylcyclobutanes (Figure B). Like the synthesis of DVOCB, [(PDI)­Fe] complexes are unique catalysts for promoting these transformations selectively, in high yields and under mild conditions. − While previous studies have expanded the understanding of the kinetics and scope of [2 + 2] cycloaddition reactions, ,, there are limited insights into what features of the catalyst promote this unique reactivity. This lack of precatalyst structure–activity relationships hinders the design of next generation of precatalysts that exhibit higher activity for the production of vinylcyclobutane and DVOCB.…”

Mechanistic study of cobalt(I)‐catalyzed asymmetric coupling of ethylene and enynes to functionalized cyclobutanes

“…19,20 For the cycloaddition reactions of alkenes or alkynes, the efficient catalysts could be photoinduction, [21][22][23][24] Lewis acids 25 or transition metal compounds. [26][27][28] However, the direct use of ethylene for synthesizing cyclobutane was hardly reported except for the reported Fe(0)-catalyzed the cycloaddition reaction of butadiene and ethylene giving the achiral cyclobutene. 29 For the enantioselective functionalization of cyclobutane derivatives or cyclobutane carboxylic acid derivatives, [30][31][32] the efficient catalysts could be either organic molecules or transition metals complexes.…”

“…Generally, there are two approaches for generating cyclobutane derivatives with stereocenters, including the enantioselective ring closure reactions 16–18 and the enantioselective functionalization of prochiral cyclobutane or cyclobutene speices 19,20 . For the cycloaddition reactions of alkenes or alkynes, the efficient catalysts could be photo‐induction, 21–24 Lewis acids 25 or transition metal compounds 26–28 . However, the direct use of ethylene for synthesizing cyclobutane was hardly reported except for the reported Fe(0)‐catalyzed the cycloaddition reaction of butadiene and ethylene giving the achiral cyclobutene 29 .…”