Synthesis of a Hybrid m‑Terphenyl/o‑Carborane Building Block: Applications in Phosphine Ligand Design

A hybrid terphenyl/o-carborane ligand building block is synthesized by the reaction of m-terphenylalkyne with B10H14. This sterically demanding substituent can be installed into ligands, as demonstrated by the preparation of carboranylphosphine. The bulky phosphine reacts with [ClRh­(CO)2]2 to produce monophosphine complex ClRhL­(CO)2, which subsequently extrudes CO under vacuum to afford the dimeric species [ClRhL­(CO)]2. The latter complex does not react with excess phosphine and is resistant toward cyclometalation, which is in contrast to related o-carborane phosphine complexes. Data from a single-crystal X-ray diffraction study are utilized to quantify the steric impact of the ligand via the percent buried volume approach.