Nickel-catalysed hydrodimerization of unactivated terminal alkenes

Site-selective homo- and cross-hydrodimerization of terminal alkenes has remained a long-standing challenge in organic synthesis. Metal-hydride-catalysed selective dimerization, oligomerization or polymerization methods are often limited to electronically biased or small alkene substrates. Here we report the development of a nickel-catalysed protocol that enables selective homo- and cross-dimerization of unactivated linear and sterically congested terminal alkenes to afford linear alkyl-alkyl products in good yields and high linear/branched selectivity. The process is tolerant of a range of functionalities including heteroatoms, saturated heterocycles and bioactive motifs. Mechanistic experiments reveal that the co-oxidants we used, CuBr2 and di-tert-butyl peroxide, probably convert dialkyl-Ni(II) intermediates to the corresponding Ni(III) species through a single-electron-transfer process. This oxidative step avoids decomposition of thermally labile dialkyl-Ni(II) intermediates and promotes the formation of hydrodimerization products by reductive elimination of the Ni(III) complex. Without CuBr2, high branched selectivity was achieved, affording the methyl-branched products-which are typically difficult to synthesize-in good yields. Site-selective cross- and homo-hydrodimerization of terminal alkyl alkenes is a synthetic challenge. Now, a nickel-catalysed redox cross- and homo-hydrodimerization process is reported, providing selective access to linear alkyl-alkyl coupled products. Branched dimers can be formed by removing co-oxidant CuBr2 from the reaction mixture.