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, [Et4 N][Ta(CO)6 ], with 1.1 equivalents of molecular iodine (I2 ) 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(C13 H17 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 (CsC8 ), 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(C13 H17 N)7 ][Ta(C13 H17 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, [MLx ]+ , and a homoleptic anion, [MLy ]- , 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 TaL6 complex of Ta0 .