Iron-Catalysed Hydrofunctionalisation of Alkenes and Alkynes

Abstract

The iron-catalysed hydrofunctionalisation of alkenes and alkynes has been developed to give a range of functionalised products with control of regio-, chemo-and stereochemistry. Using a bench-stable iron(II) pre-catalyst, the hydrosilylation, hydroboration, hydrogermylation and hydromagnesiation of alkenes and alkynes has been achieved.Iron-catalysed hydrosilylation, hydroboration and hydrogermylation of terminal, 1,1-and 1,2-disubstituted alkyl and aryl alkenes and alkynes was developed, in which the active iron catalyst was generated in situ (Scheme A1). Alkyl and vinyl silanes and pinacol boronic esters were synthesised in good to excellent yield in the presence of a range of functional groups. Catalyst loadings as low as 0.07 mol% were demonstrated, along with catalyst turn-over frequencies of up to 60 000 mol h −1 . Scheme A1. Iron-catalysed hydrosilylation and hydroboration of alkenes and alkynesThe iron-catalysed formal hydrocarboxylation of a range of styrene derivatives has been developed for the synthesis of -aryl carboxylic acids using carbon dioxide and ethylmagnesium bromide as the stoichiometric hydride source (Scheme A2). Detailed mechanistic studies have shown this reaction proceeds by iron-catalysed hydromagnesiation to give an intermediate benzylic organomagnesium reagent. The nature of the active catalyst and reaction mechanism have been proposed. Scheme A2. Iron-catalysed hydromagnesiation of styrene derivatives I would firstly and foremostly like to thank Steve for the past 4 years for making my PhD a thoroughly enjoyable experience. The amount of time he has invested in helping, advising and inspiring me has been truly remarkable and I genuinely could not be more thankful. I will certainly miss our 'discussions' about chemistry, and would finally like to admit that Steve is often right. I am very thankful for having had the chance to meet and work with various people over the years, both here in Edinburgh and in Bristol. I would like to thank the members of the Aggarwal and Pringle groups in Bristol, and all current and past members of the Thomas group. In particular I would like to thank Nick Barron for those days when we were the Thomas group, and Dominik Frank who always knew when it was time for a beer. I am also grateful for all those who have specifically worked with me on projects during my PhD: Dominik Frank, Fern Sinclair, Adam Kolodiej and Jonathan Kwan. I wish everybody the best for the future. I would like to thank the University of Bristol for financial support and those who worked on the Chemical Synthesis DTC (CDT now), in particular Eoghan McGarrigle, Mar and Kevin Booker-Milburn. I would also like to thank Paul Pringle for the time I spent working in his group. I am thankful to the University of Edinburgh for providing the financial support to allow me to move north of the border with Steve. I would also like to thank the RSC for financing my trip to speak at the J-NOST conference in India, despite the food poisoning. The technical and analytical staff at both Bristol and E...

Earth-Abundant Metal Catalysis Enabled by Counterion Activation

“…[7][8][9][10][11][12] Great progress has been made towards operationally simple iron-and cobalt-catalyzed alkene hydroboration methods, but the state-of-the-art remains exogenous activation strategies where a bench-stable pre-catalyst is activated using an organometallic reagent (Scheme 1A). [12][13][14][15][16][17][18][19][20][21][22][23] The use of an alkoxide in place of the organometallic activator further simplified these catalytic manifolds, but still required an external reagent. 24,25 Recently, endogenous (activator free) protocols have been reported using cobalt acetylacetonate complexes to catalyze eneyne cyclisation-borylation 26,27 and alkene diborylation, 28,29 and iron-and cobalt carboxylate complexes to catalyse alkene hydrosilylation.…”

Catalytic Organic Transformations Mediated by Actinide Complexes

“…The hydrosilylation of terminal alkynes can proceed to give three different isomeric products (Scheme 7), which comprise the cis, and trans vinylsilanes, and the geminal vinylsilane, which are obtained due to the 1,2 syn and anti and the 2,1-insertion modes, respectively. The product distribution obtained has been shown to depend strongly on the nature of the metal catalyst, the substrates and the reaction conditions [56][57][58][59]. Several actinide complexes have been explored as catalysts in the hydrosilylation of terminal acetylenes and olefins with PhSiH3, displaying different chemo-and regio-selectivities in dependence of the actinide center, the ancillary ligands, the substrates used and the reaction conditions.…”

In Situ Infrared Spectroscopic Study of Iron-Catalyzed Hydromagnesiation of Vinyl Arenes

“…For reagents containing aromatic olefins, α-silylation (Markovnikov substitution, Scheme 1.9A) is favored; whereas, aliphatic olefins favor β-silylation (Anti-Markovnikov substitution, Scheme 1.9B). 95,111,[113][114][115][116]120,170 Based upon known limitations of iron-catalyzed hydrosilylation, future methodology development is a necessity to improve regioselectivity, reduce side product pathways, and provide catalyst control by using redox-active ligands. Iron-catalyzed hydrosilylation side reactions.…”

“…The trend in lower yields and sparse mechanistic studies for transfer hydrometallation has introduced the need to have a better understanding of this catalytic process overall. 12,13,153,170,194,195 Scheme 2.1: Synthetic utility of (aryl)ethyl Grignards. A.)…”

“…153 The subsequent mechanistic analysis in Scheme 2.2B revealed: 1) complex kinetic regimes were evident for the catalyst and each substrate; 2) DHT (Scheme 2.2A steps 2-3), not BHE/MI (Scheme 2.2A steps 5-6), is the likely elementary catalytic step based upon deuterium labeling studies (Scheme 2.3B); 3) the resting state, as well as off cycle catalytic intermediates, are characterized as iron(0)-ate species. 170,195 Up to this point in the literature, the mechanistic investigations described above have not defined the further complex kinetic behavior nor do they take into account the role of the formation of the linear regioisomer. In this chapter, in situ infrared spectroscopy will be used to aid in the mechanistic developments of iron-catalyzed hydromagnesiation.…”