The complexes [Ru(1-C⋮C−1,10-C2B8H9)(dppe)Cp*] (3a), [Ru(1-C⋮C−1,12-C2B10H11)(dppe)Cp*] (3b), [{Ru(dppe)Cp*}2{μ-1,10−(C⋮C)2−1,10-C2B8H8}] (4a) and [{Ru(dppe)Cp*}2{μ-1,12−(C⋮C)2−1,12-C2B10H10}] (4b), which form a representative series of mono- and bimetallic acetylide complexes featuring 10- and 12-vertex carboranes embedded within the diethynyl bridging ligand, have been prepared and structurally characterized. In addition, these compounds have been examined spectroscopically (UV−vis−NIR, IR) in all accessible redox states. The significant separation of the two, one-electron anodic waves observed in the cyclic voltammograms of the bimetallic complexes 4a and 4b is largely independent of the nature of the electrolyte and is attributed to stabilization of the intermediate redox products [4a]+ and [4b]+ through interactions between the metal centers across a distance of ca. 12.5 Å. The mono-oxidized bimetallic complexes [4a]+ and [4b]+ exhibit spectroscopic properties consistent with a description of these species in terms of valence-localized (class II) mixed-valence compounds, including a unique low-energy electronic absorption band, attributed to an IVCT-type transition that tails into the IR region. DFT calculations with model systems [4a-H]+ and [4b-H]+ featuring simplified ligand sets reproduce the observed spectroscopic data and localized electronic structures for the mixed-valence cations [4a]+ and [4b]+.

Reactions of [L 2 Rh(acac)] (L = alkene or phosphine) with B 2 cat 3 yield the zwitterionic complexes [L 2 Rh(h 6 -catBcat)] and [(acac)Bcat] cleanly; [(dppm)Rh(h 6 -catBcat)], the X-ray structure of which is reported, is an excellent catalyst for the diboration of vinylarenes and unstrained internal alkenes cis-and trans-stilbene and trans-b-methylstyrene.