Reductive cross-electrophile coupling reactions have recently been developed to a versatile and sustainable synthetic tool for selective C-C bond formation. The employment of cheap and abundant electrophiles avoids the pre-formation and handling of organometallic reagents. In situ reductive coupling is effected in the presence of a transition-metal catalyst (Ni, Co, Pd, Fe) and a suitable metallic reductant (Mn, Zn, Mg). This Concept article assesses the current state of the art and summarizes recent protocols with various combinations of alkyl, alkenyl, allyl, and aryl reagents and highlights key mechanistic studies.

This tutorial review is intended to provide the reader with a timely review of major developments and the current state-of-the-art of palladium-catalyzed cross-coupling reactions with Grignard reagents. Organomagnesium reagents, the most reactive and most easily accessible nucleophiles for carbon-carbon bond forming cross-coupling reactions, were the first nucleophiles ever employed in cross-coupling reactions, but have only recently been re-discovered for highly efficient and (stereo)selective coupling reactions. This is mostly a consequence of improved catalyst systems with bulky phosphine, phosphonate or carbene ligands and new metal-halogen exchange procedures for the generation of functionalized Grignard reagents.

Scheme 2. Mechanistic dichotomy: Oxidative acylation of nucleophiles (A, top); oxygenative acylation of electrophiles (B, bottom). Scheme 1. NHC-catalyzed acylations with aldehydes (Nu = nucleophile, El = electrophile). Scheme 15. NHC-catalyzed oxidative Michael addition-lactonization (oxidant=quinone shown in Scheme 14). Scheme 16. Enantioselective oxidative Michael-Michael-cyclization cascade by Studer et al. lactonization (oxidant = quinone shown in Scheme 14).

We report the synthesis of LH2-like supramolecular double- and triple-stranded complexes based upon porphyrin nanorings. Energy transfer from the antenna dimers to the π-conjugated nanoring occurs on a subpicosecond time scale, rivaling transfer rates in natural light-harvesting systems. The presence of a second nanoring acceptor doubles the transfer rate, providing strong evidence for multidirectional energy funneling. The behavior of these systems is particularly intriguing because the local nature of the interaction may allow energy transfer into states that are, for cyclic nanorings, symmetry-forbidden in the far field. These complexes are versatile synthetic models for natural light-harvesting systems.

Quantum information processing (QIP) would require that the individual units involved—qubits—communicate to other qubits while retaining their identity. In many ways this resembles the way supramolecular chemistry brings together individual molecules into interlocked structures, where the assembly has one identity but where the individual components are still recognizable. Here a fully modular supramolecular strategy has been to link hybrid organic–inorganic [2]- and [3]-rotaxanes into still larger [4]-, [5]- and [7]-rotaxanes. The ring components are heterometallic octanuclear [Cr7NiF8(O2CtBu)16]– coordination cages and the thread components template the formation of the ring about the organic axle, and are further functionalized to act as a ligand, which leads to large supramolecular arrays of these heterometallic rings. As the rings have been proposed as qubits for QIP, the strategy provides a possible route towards scalable molecular electron spin devices for QIP. Double electron–electron resonance experiments demonstrate inter-qubit interactions suitable for mediating two-qubit quantum logic gates.