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Electrochemical synthesis can provide more sustainable routes to industrial chemicals 1 – 3 . Electrosynthetic oxidations may often be performed ‘reagent-free’, generating hydrogen (H 2 ) derived from the substrate as the sole by-product at the counter electrode. Electrosynthetic reductions, however, require an external source of electrons. Sacrificial metal anodes are commonly used for small-scale applications 4 , but more sustainable options are needed at larger scale. Anodic water oxidation is an especially appealing option 1 , 5 , 6 , but many reductions require anhydrous, air-free reaction conditions. In such cases, H 2 represents an ideal alternative, motivating the growing interest in the electrochemical hydrogen oxidation reaction (HOR) under non-aqueous conditions 7 – 12 . Here we report a mediated H 2 anode that achieves indirect electrochemical oxidation of H 2 by pairing thermal catalytic hydrogenation of an anthraquinone mediator with electrochemical oxidation of the anthrahydroquinone. This quinone-mediated H 2 anode is used to support nickel-catalysed cross-electrophile coupling (XEC), a reaction class gaining widespread adoption in the pharmaceutical industry 13 – 15 . Initial validation of this method in small-scale batch reactions is followed by adaptation to a recirculating flow reactor that enables hectogram-scale synthesis of a pharmaceutical intermediate. The mediated H 2 anode technology disclosed here offers a general strategy to support H 2 -driven electrosynthetic reductions. A quinone-mediated hydrogen anode design shows that hydrogen can be used as the electron source in non-aqueous reductive electrosynthesis, for a more sustainable way to make molecules at larger scale.

The reaction of PEt 2 OH with K 2 PtCl 4 yields [PtCl{(PEt 2 O) 2 H}] 2 ( 2 ). The X-ray crystal structure of 2 shows that the two chloride ligands bridge the two Pt atoms. The structure is unusual in that the PtCl 2 Pt unit is bent, which is the first example of a platinum phosphinito chloride-bridged dimer that is bent. Dimer 2 is a poor catalyst for the hydration of acetonitrile (and presumably other nitriles). Likewise, the monomeric catalyst that results from the reaction of 2 with sodium hydroxide is not a good hydration catalyst. In an attempt to form a more reactive monomeric catalyst, PtCl(PMe 2 OH){(PMe 2 O) 2 H} ( 1) was reacted with sodium hydroxide. This reaction resulted in the formation of two species, tentatively characterized as Na[PtCl(PMe 2 O){(PMe 2 O) 2 H}] ( 5 ) and Na[PtCl(OH){(PMe 2 O) 2 H}] ( 6 ). Complexes 5 and 6 could not be separated. However, the mixture of the two complexes quickly hydrated acetonitrile. The catalyst mixture of 5 and 6 was efficiently poisoned by cyanide, which prevented its use as a catalyst for the hydration of cyanohydrins.