Alkyl arenes are used in a wide range of industrial products including plastics, detergents, fuels and fine chemicals. However, the synthesis of truly linear 1-phenylalkanes is not accessible with current industrial synthetic routes. Alkyl benzene surfactant precursors are produced from benzene and α-olefins using acid-based catalysis, which primarily results in a distribution of 2- and 3-phenyl alkanes. Transition metal mediated hydroarylation of olefins that circumvents the formation of carbocation intermediates is an alternative to acid-based catalysis for alkyl arene synthesis. This process couples olefin insertion into metal-aryl bonds and metal mediated C−H activation. By controlling the regioselectivity of the olefin insertion step (i.e., 1,2- vs 2,1-insertion), it is possible to selectively produce 1-phenylalkanes. The simple rhodium complex, [Rh(m-OAc)(h2-C2H4)2]2, selectively catalyzes oxidative hydroarylation of α-olefins using Cu(II) as the oxidant to generate alkenyl arenes that produce straight-chain alkyl arenes upon hydrogenation. Upon optimization of the reaction, a linear to branched ratio of 10:1 and turnover numbers &gt; 1000 have been achieved. The development of oxidatively resistant ligands that cap and protect the Rh center has overcome the instability of the Rh system towards O2 or reactive Cu-peroxo intermediates. Not only has the longevity of the catalyst been enhanced, but the Cu(II) oxidant can now be recycled in situ. These ligands provide Rh catalysts that can maintain activity over month long reactions with multiple Cu(II) regeneration steps using O2 and acid, while retaining linear product selectivity and high turnover numbers.

Catalytic synthesis of linear alkenyl arenes using capping arene ligand supported Rh(I) catalysts

254th National Meeting (2017)

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