Fine tunable metal assemblies constrained by multidentate phosphine ligands

Abstract

Structurally constrained multinuclear metal assemblies are fascinating building blocks for atomically precise nano-structured molecular devices with a variety of functions from electronic, magnetic, photophysical, and catalytic properties arising from cooperative effects of proximate metal centers. Finely tuned structures and electronic states of metal assemblies are in debt to design of multidentate guiding and supporting ligands, and aiming to develop low valent metal assemblies as molecular miniatures of metallic materials, those with a pair of soft donors connected by a single atom, namely, bearing short bite units, are highly desired. In this regard, this review surveys the studies over a couple of decades on multinuclear metal complexes constrained by linear and branched tri-, tetra-, and polydentate phosphine ligands with short bite distances between the two donor atoms possessing P3, P4, and P6 donor sets. Those with mixed donor phosphines having PCP, PNP, PAsP, PNNP, and N(P3) donor sets, are also explained because the hetero soft donors of carbene, imino-nitrogen, and arsine enable fine stepwise syntheses of heterometal assemblies through metallomacrocyclic and metallocage precursors. Multinuclear complexes supported by non-phosphino multidentate ligands and by mono- and diphosphines are not included. This contribution focuses not only on 1D metal chains but on other 2D and 3D topological arrangements, and in particular, highlights the recently developed Pt and Pd based metal strings organized by linear tri- and tetraphosphine ligands, photo- and electroluminescent coinage metal assemblies in linear, ring, planar, and polyhedral metal arrangements, and copper hydride multinuclear complexes showing attractive hydride reactivity. These compounds of subnano- to nano-scaled building blocks will provide useful platforms to develop further assembled nano-molecular devices with structurally and atomically controlled synthetic strategies.