Tantalum isocyanide complexes: Tai(CNDipp)6 (dipp is 2,6-diisopropylphenyl) and ionic [ta(CNDipp)7][ta(CNDipp)6], a formal disproportionation product of the 17-electron ta ⁰ metalloradical ta(CNDipp)6

Treatment of tetraethylammonium hexacarbonyltantalate, [Et ₄ N][Ta(CO) ₆ ], with 1.1 equivalents of molecular iodine (I ₂ ) in tetrahydrofuran (THF) at 200 K, followed by the addition of 6.0 equivalents of 2,6-diisopropylphenyl isocyanide (CNDipp) and slow warming to 293 K over a 24 h period gave the tantalum(I) iodide derivative hexakis(2,6-diisopropylphenyl isocyanide-κC)iodidotantalum(I), [TaI(C ₁₃ H ₁₇ N) ₆ ] or TaI(CNDipp) ₆ , 1. Recrystallization of this substance from pentane provided deep-red nearly black parallelepipeds of the product, which was characterized by single-crystal X-ray diffraction. Addition of 1 in THF at 200 K to a suspension of an excess (5.8 equivalents) of caesium graphite (CsC ₈ ), followed by warming, filtration, and solvent removal, afforded a dark-green oily solid of unknown composition, from which several red–brown rhombohedral plates of the ditantalum salt heptakis(2,6-diisopropylphenyl isocyanide-κC)tantalum hexakis(2,6-diisopropylphenyl isocyanide-κC)tantalate, [Ta(C ₁₃ H ₁₇ N) ₇ ][Ta(C ₁₃ H ₁₇ N) ₆ ] or [Ta(CNDipp) ₇ ][Ta(CNDipp) ₆ ], 2, were harvested. Salt 2 is a unique substance, as it is the only known example of a salt containing a homoleptic cation, [ML _x ] ⁺ , and a homoleptic anion, [ML _y ] ⁻ , with the same transition metal and π-acceptor ligand L. In solution, 2 undergoes full comproportionation to afford the recently reported 17-electron paramagnetic zerovalent tantalum complex Ta(CNDipp) ₆ , the only known isolable TaL ₆ complex of Ta ⁰ .