Iron‐Catalysed Chemo‐, Regio‐, and Stereoselective Hydrosilylation of Alkenes and Alkynes using a Bench‐Stable Iron(II) Pre‐Catalyst

Abstract

The chemo-, regio-, and stereoselective iron-catalysed hydrosilylation of alkenes and alkynes with excellent functional group tolerance is reported (34 examples, 41-96% yield). The catalyst and reagents are commercially available and easy to handle, with the active iron catalyst being generated in situ, thus providing a simple and practical methodology for iron-catalysed hydrosilylation. The silane products can be oxidised to the anti-Markovnikov product of olefin hydration, and the one-pot iron-catalysed hydrosilylation-oxidation of olefins to give silane(di)ols directly is also reported. The iron pre-catalyst was used at loadings as low as 0.07 mol%, and displayed catalyst turnover frequencies (TOF) approaching 60,000 mol h À1. Initial mechanistic studies indicate an iron(I) active catalyst.Keywords: catalysis; hydrosilylation; iron; olefins; synthetic methods Iron offers significant advantages as a catalyst over precious metals due to its low toxicity, low cost, natural abundance and sustainable long-term commercial availability.[1] Although iron catalysis is well established for cross-coupling [2] and redox reactions, [3] the hydrofunctionalisation of olefins has been less developed. In part, this can be attributed to the procedurally challenging reaction conditions and catalyst syntheses required, in comparison to the simplicity of ironcatalysed cross-coupling reactions. Building upon our work, [4] and previous work of others, [5] in which lowvalent iron catalysts were generated in situ, we sought to develop an operationally simple iron-catalysed hydrosilylation of olefins, in which all reagents were inexpensive, widely available and bench-stable. Furthermore, we sought to use this method for the introduction of silyl groups which could undergo further synthetic transformations (Figure 1).The hydrosilylation of alkenes and alkynes can produce alkyl-, allyl-, and vinylsilanes, [6] which are used in fine chemical synthesis for stereospecific oxidation [7] and cross-coupling reactions, [8] amongst other applications (Figure 1).[9] The cross-linking of silicone polymers by hydrosilylation represents one of the largest applications of homogeneous catalysis on an industrial scale.[6] To date, hydrosilylation has been dominated by precious metal catalysts such as platinum, palladium, ruthenium and rhodium, however these catalysts can suffer from competitive alkene isomerisation, dehydrosilylation reactions, and incompatibility with amino-substituted olefins.

Efficient and selective catalysis for hydrogenation and hydrosilation of alkenes and alkynes with PNP complexes of scandium and yttrium

“…The unsymmetric, internal alkyne methylphenylacetylene allows for an interesting probe for regioselectivity, since the product with the silyl group trans to the methyl group ( 2 ) is electronically preferred, while the product with the silyl group trans to the phenyl group ( 3 ) is sterically preferred. 15 Complex 1-Y affords the electronically-preferred product in about 90% selectivity (Table 3, entries 7, 8), similar to previously reported catalysts. 15 In contrast, 1-Sc exhibits the opposite preference, producing the sterically-preferred product with about 66% selectivity (Table 3, entries 2, 3).…”

“…15 Complex 1-Y affords the electronically-preferred product in about 90% selectivity (Table 3, entries 7, 8), similar to previously reported catalysts. 15 In contrast, 1-Sc exhibits the opposite preference, producing the sterically-preferred product with about 66% selectivity (Table 3, entries 2, 3). This difference may be attributed to the different radii of the metal centers, and a more crowded scandium center that exerts greater steric control.…”

Chemoselective Alkene Hydrosilylation Catalyzed by Nickel Pincer Complexes

“…Reported herein is that well-defined bis(amino)amide nickel pincer complexes are efficient catalysts for anti-Markovnikov hydrosilylation of terminal alkenes with turnover frequencies of up to 83 000 per hour and turnover numbers of up to 10 000. [8][9][10] While this modification improved the stability of the catalysts,f unctional-group compatibility remains to be improved. As light modification of reaction conditions allows tandem isomerization/hydrosilylation reactions of internal alkenes using these nickel catalysts.…”

Iron‐Catalysed Hydrofunctionalisation of Alkenes and Alkynes

“…with respect to iron) gave an iron catalyst that could be used for the hydrosilylation of terminal and disubstituted alkenes 184 and alkynes 185 using primary, secondary and tertiary silanes (Scheme 39). [98] Scheme 37. Hydrosilylation of alkenes using a bis(imino)pyridine iron (bis)dinitrogen complex pre-catalyst: A) reaction scope, B) resonance structures of bis(imino)pyridine iron (bis)dinitrogen complex and C) stoichiometric reactions of 170 with diphenylacetylene and phenylsilane.…”