Efficient and selective alkene hydrosilation promoted by weak, double Si–H activation at an iron center

Smith, Patrick W.; Dong, Yuyang; Tilley, T. Don

doi:10.1039/d0sc01749c

Cited by 15 publications

(15 citation statements)

References 46 publications

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“…While previous work disclosed a variety of mechanistically diverse catalytic cycles, ,− we aimed here to shed some light on the mode of activation of these carbene iron catalysts in hydrosilylation. Therefore, a set of stoichiometric experiments was conducted as well as some tailored modifications of the catalyst precursor in order to facilitate the activation process.…”

Section: Resultsmentioning

confidence: 99%

Highly Modular Piano-Stool N-Heterocyclic Carbene Iron Complexes: Impact of Ligand Variation on Hydrosilylation Activity

2021

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The piano-stool configuration combined with N-heterocyclic carbene (NHC) ligation constitutes an attractive scaffold for employing iron in catalysis. Here, we have expanded this scaffold by installing a pentamethyl cyclopentadienyl (Cp*) ligand as a strong electron donor compared to the traditionally used unsubstituted cyclopentadiene (Cp). Moreover, decarboxylation is introduced as a method to prepare these iron(II) NHC complexes, which avoids the isolation of air-sensitive free carbenes. In addition to the Cp/ Cp* variation, the complexes have been systematically modulated at the NHC scaffold, the NHC wingtip groups, and the ancillary ligands in order to identify critical factors that govern the catalytic activity of the iron center in the hydrosilylation of aldehydes. These modulations reveal the importance of steric tailoring and optimization of electron density for high catalytic performance. The data demonstrate a critical role of the NHC scaffold with triazolylidenes imparting consistently higher activity than imidazolylidenes and a correlation between catalytic activity and steric rather than electronic factors. Moreover, the implementation of steric bulk is strongly dependent on the nature of the NHC and severely limited by the Cp* iron precursor. The best performing catalytic systems reach turnover frequencies, TOF max 's, of up to 360 h −1 at 60 °C. Mechanistic investigations by 1 H NMR and in situ IR spectroscopies indicate a catalyst activation that involves CO release and aldehyde coordination to the [Fe(Cp)(NHC)I] fragment.

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Section: Resultsmentioning

confidence: 99%

Highly Modular Piano-Stool N-Heterocyclic Carbene Iron Complexes: Impact of Ligand Variation on Hydrosilylation Activity

2021

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“…Focusing on bis(σ-SiH) coordination, Tilley has recently reported that the [Cp*Fe(H)(N 2 )(P i Pr 2 Me)] iron complex ( 38 ) can form cationic complexes [Cp*Fe(H 2 SiHR)(P i Pr 2 Me)][BAr F ] ( 39 ) in the presence of primary silanes and the hydride abstractor [Ph 3 C][BAr F ] (Scheme 40). 89…”

Section: Catalytic Silylation Reactionsmentioning

confidence: 99%

“…Focusing on bis(s-SiH) coordination, Tilley has recently reported that the [Cp*Fe(H)(N 2 )(P i Pr 2 Me)] iron complex (38) can form cationic complexes [Cp*Fe(H 2 SiHR)(P i Pr 2 Me)][BAr F ] (39) in the presence of primary silanes and the hydride abstractor [Ph 3 C][BAr F ] (Scheme 40). 89 Once formed, these cationic systems are involved in hydrosilylation reactions of a variety of terminal and internal alkenes and some internal alkynes. The catalytic procedure involves the use of only 0.1 mol% of the catalyst at room temperature.…”

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confidence: 99%

Activation of Si–H and B–H bonds by Lewis acidic transition metals and p-block elements: same, but different

2022

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“…Note that RajanBabu and co-workers reported the Co-catalyzed reactions of ( E )-dodeca-1,3-diene with HSiPh 3 dominantly gave the reduction product, ( E )-3-dodecene, and those with H 2 SiPh 2 and H 3 SiPh gave a 1,2- E - anti -Markovnikov selective product, ( E )-1-silyldodec-3-ene . Formation of a silylene species has been reported in the Ru-, Ir-, and Fe-catalyzed hydrosilylation using a primary silane, and the present catalyst may have reacted with a primary silane and changed the course of the reaction.…”

Section: Resultsmentioning

confidence: 99%

Ligand-Controlled Regiodivergent Hydrosilylation of Conjugated Dienes Catalyzed by Mono(phosphine)palladium(0) Complexes

et al. 2020

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Mono(phosphine)palladium(0) complexes, [Pd(η2:η2-C6H10O)(PR3)] (1), catalyze hydrosilylation of electron-deficient conjugated dienes with HSiPh3. Hydrosilylation of methyl penta-2,4-dienoate with HSiPh3 catalyzed by [Pd(η2:η2-C6H10O)(PR3)] (R = Me (1a), Et (1b), OEt (1d), O i Pr (1e)) proceeds to give the 1,2-E product in quantitative yield with exclusive Markovnikov selectivity. In contrast, their triphenylphosphine and -phosphite analogues, [Pd(η2:η2-C6H10O)(PR3)] (R = Ph (1f), OPh (1g)), mainly produce the 1,4-Z product (1,2-E/1,4-Z = 3/7). The regioselectivity in the hydrosilylation of methyl 2,4-pentadienoate is also controlled by organosilanes. Mechanistic studies suggest that the reaction using a compact and basic mono-phosphorus complex proceeds by the Chalk–Harrod mechanism involving the reductive elimination from an (η3-allyl)(silyl)palladium(II). A poor electron-donating mono-phosphorus ligand such as P(OPh)3 destabilizes a Pd(II) species and promotes direct reductive elimination to give the 1,4-Z product. On the other hand, a compact and electron-donating phosphorus ligand, such as PMe3, PEt3, and P(OMe)3, favors to give the more stable (η3-allyl)(silyl)palladium(II) intermediate by the allyl rotation, followed by reductive elimination to give the 1,2-E product.

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Efficient and selective alkene hydrosilation promoted by weak, double Si–H activation at an iron center

Abstract: Cationic iron complexes [Cp*(iPr2MeP)FeH2SiHR]+, generated and characterized in solution, are very efficient catalysts for the hydrosilation of terminal alkenes and internal alkynes by primary silanes at low catalyst loading (0.1 mol%) and ambient temperature.

Cited by 15 publications

References 46 publications

Highly Modular Piano-Stool N-Heterocyclic Carbene Iron Complexes: Impact of Ligand Variation on Hydrosilylation Activity

Highly Modular Piano-Stool N-Heterocyclic Carbene Iron Complexes: Impact of Ligand Variation on Hydrosilylation Activity

Activation of Si–H and B–H bonds by Lewis acidic transition metals and p-block elements: same, but different

Ligand-Controlled Regiodivergent Hydrosilylation of Conjugated Dienes Catalyzed by Mono(phosphine)palladium(0) Complexes

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