Easy-to-prepare η -coordinated phosphine-borane ligands are demonstrated to liberate hydrogen upon treatment with different σ-donor/π-acceptor ligands (CO, tBuNC, CN ). Depending on the utilized ancillary ligand, different reaction pathways are observed, ranging from simple hydride protonation to iron-boron bond formation and subsequent rearrangement to pincer-type ligands based on a tricoordinate boron centre. The last-named reactivity is in line with a formal umpolung at the boron centre from a Lewis acidic borane to a Lewis basic boron-based donor ligand.

The transposition of a homoallyl pinacol boronic ester was realized by a highly reactive nickel-catalyst system comprising NiCl2(dppp), zinc powder, ZnI2, and Ph2PH. The in situ generated Z-crotyl pinacol boronic esters were reacted with various aldehydes to form syn-homoallylic alcohols in high diastereoselectivities. The present nickel-catalyzed reaction is complementary to the iridium-catalyzed transposition reported by Murakami leading to the corresponding anti-homoallylic alcohols. Also, the multiple transposition of pentenyl pinacol boronic ester was realized.

The nickel-catalysed transposition of a carbon?carbon double bond of N-allyl and N-homoallyl amides is described. While the transposition of acyclic amides gave very high Z-selectivity of the enamides, corresponding cyclic N-allyl amides led exclusively to the E-configured products. Thereby, we realised a stereodivergent approach to enamides that is dependent on the structure of the amide substituents. When homoallylic substrates are used, a temperature-controlled single transposition to a Z-allylic amide derivative at low temperature or a double transposition to an E-enamide at elevated temperature could be achieved.

A cobalt-catalysed 1,4-hydrovinylation reaction is successfully applied in a sequential three-component transformation of unsaturated phosphonium bromides, 1,3-dienes, and aldehydes leading to non-conjugated products with a 1,4-diene subunit in good to excellent yields. The hydrovinylation provides regioselectively diene structures with one exo double bond whereas the third double bond can be introduced via an in situ Wittig or Horner–Wadsworth–Emmons olefination leading to 1,4,7-trienes suitable for further double bond functionalisations.

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