Steric stabilization of homoleptic bis(pi-allyl) complexes of chromium(II) and iron(II)

Synthesis without solvent: consequences for mechanochemical reactivity

Solvents are so nearly omnipresent in synthetic chemistry that a classic question for their use has been: "What is the best solvent for this reaction?" The increasing use of mechanochemical approaches to synthesis-by grinding, milling, extrusion, or other means-and usually with no, or only limited, amounts of solvent, has raised an alternative question for the synthetic chemist: "What happens if there is no solvent?" This review focuses on a three-part answer to that question: when there is little change ("solvent-optional" reactions); when solvent needs to be present in some form, even if only in the amounts provided by liquid-assisted (LAG) or solvate-assisted grinding; and those cases in which mechanochemistry allows access to compounds that cannot be obtained from solution-based routes. The emphasis here is on inorganic and organometallic systems, including selected examples of mechanosynthesis and mechanocatalysis. Issues of mechanochemical depictions and the adequacy of LAG descriptions are also reviewed.

Advances in organometallic synthesis with mechanochemical methods

Solvent-based syntheses have long been normative in all areas of chemistry, although mechanochemical methods (specifically grinding and milling) have been used to good effect for decades in organic, and to a lesser but growing extent, inorganic coordination chemistry. Organometallic synthesis, in contrast, represents a relatively underdeveloped area for mechanochemical research, and the potential benefits are considerable. From access to new classes of unsolvated complexes, to control over stoichiometries that have not been observed in solution routes, mechanochemical (or 'M-chem') approaches have much to offer the synthetic chemist. It has already become clear that removing the solvent from an organometallic reaction can change reaction pathways considerably, so that prediction of the outcome is not always straightforward. This Perspective reviews recent developments in the field, and describes equipment that can be used in organometallic synthesis. Synthetic chemists are encouraged to add mechanochemical methods to their repertoire in the search for new and highly reactive metal complexes and novel types of organometallic transformations.

Direct synthesis of doubly deprotonated, dearomatised lutidine PNP Cr and Zr pincer complexes based on isolated K and Li ligand transfer reagents

Double deprotonation of a hybrid bis(phosphino)picoline ligand yields lithium or potassium pincer salts with dearomatised lutidine backbones that afford unusual chromium and zirconium complexes by transmetallation.