Despite being weak attractive forces, closed‐shell metallophilic interactions play important roles in the Group 11 metal complexes on their diverse structural and physical features. A plethora of experimental and computational studies has thus been dedicated to such weak attractive d10–d10 interactions, particularly aurophilic and argentophilic interactions. Although d10–d10 CuI–CuI forces had been recognized for four decades, cuprophilic interactions are less explored and they are best evidenced by single‐crystal X‐ray crystallographic analysis on CuI complexes and aggregates thereof, by which precise information about the Cu⋅⋅⋅Cu contacts, shorter than the sum of two van der Waals radii (3.92 Å) between the copper centers concerned can be obtained. Based on recently compelling experimental and spectroscopic evidence for intra‐ and intermolecular cuprophilic interactions in copper chemistry, the present Minireview summarizes recent progress in the past three decades in the synthesis and structures of multinuclear homometallic copper complexes, whereby supported and unsupported d10–d10 CuI–CuI interactions are at work.

Synthesis and characterization of two dodecacopper(I) extended metal atom chains (EMAC) assembled by two hexadentate bis(pyridylamido)amidinate-supported hexacopper(I) string complexes (monomers) via the ligand-unsupported cuprophilicity are described. In addition to short unsupported Cu-Cu contacts, two hexacopper fragments in these two dodecacopper EMACs show a bent conformation based on X-ray crystallography. Compared with their THF-bound hexacopper(I) monomers and protonated ligands, these ligand-unsupported cuprophilic interactions are shown to be weak by Raman spectroscopy. DFT calculations suggest the ligand-unsupported cuprophilicity originate from weak attractive orbital interactions, and the strength is estimated to be 2.4 kcal mol .

Although the field of metal-to-metal multiple bonding has been considered as mature, it was recently reinvigorated by the discovery of quintuple bonded dinuclear complexes. Initiated by theoretical studies, quintuple bonding was promoted by the recognition of the first isolable quintuple bonded chromium phenyl dimer Ar'CrCrAr' (Ar' = 2,6-(2,6-(i)Pr2C6H3)2C6H3) by Power and co-workers in 2005. Soon afterwards, many dinuclear group VI metal-to-metal quintuple bonded complexes stabilized by sterically hindered N-based bidentate ligands were subsequently characterized. All these remarkable compounds feature two or three bridging ligands, so each metal is two to three coordinate with respect to the ligands. Of particular interest is that they all have extremely short metal-metal bond lengths. These low-coordinate homo-univalent quintuple bonded dinuclear species not only display remarkable bonding schemes between two metal atoms, but also show interesting reaction chemistry with unsaturated hydrocarbons and small inorganic molecules. Herein, we review recent advances in quintuple bond chemistry including the synthesis, characterization and reactivity of quintuple bonded complexes.

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This perspective reviews recent advances in the newly discovered metal-to-metal quintuple bonded complexes. The idea of the structures of the metal-metal quintuple bonded complexes was initiated by theoreticians in 1979 and 2001 based on two types of model compounds, the D3h M2L6 and trans-bent M2H2, respectively. This theoretical hypothesis was put into practice in 2005 with the preparation of the first isolable quintuple bonded chromium terphenyl dimer Cr2Ar'2 (Ar' = 2,6-(2,6-i-Pr2C6H3)2C6H3). After this landmark discovery, many N-based donor-stabilized dinuclear group 6 quintuple bonded complexes with very short metal-metal separations have been identified by X-ray crystallography, and their quintuple bonding was corroborated by magnetic measurements and theoretical calculations. Unlike the quadruple bonded bimetallic units uniformly supported in a tetragonal environment, the configuration of the characterized quintuple bonded dinuclear complexes varies with the ligands and metals. Three types of quintuple bonded complexes have been identified to date. In addition to their geometry variation and interesting bonding schemes, these low-valent and low-coordinate quintuple bonded complexes are highly reducing and have been shown to be reactive towards small inorganic molecules and unsaturated organics.