Abstract
Sandwich compounds are foundational to organometallic chemistry, yet carbon-free analogs remain exceptionally rare. We report the all-phosphorus heteroleptic cobalt sandwich anion [(η(5)-P(5))Co(η(3)-P(3))](-) (4), obtained via a stepwise P(4) activation/unmasking sequence in which (nacnac')SiP(4) serves as a controllable, silicon-protected P(4) synthon. Reaction with the cobalt(-I) complex [K(THF)(0.2)][Co(η(2):η(2)-cod)(2)] furnishes a bis(silatetraphosphacyclopentadienyl) cobaltate anion (1), and successive cleavage of the Si(nacnac') units delivers the "naked" cyclo-P(5)/cyclo-P(3) sandwich framework via monosilylated intermediates 2 and 3. The cryptate salts [M(crypt-222)]4 (M = Na, K) were characterized by (31)P{(1)H} NMR spectroscopy, ESI-MS, and single-crystal X-ray diffraction (scXRD) for [Na(crypt-222)]4. In solution, 4 undergoes slow disproportionation to give the paramagnetic dianion [(η(4)-P(5))Co(η(3)-P(3))](2-) (5), isolated as [K(crypt-222)](2)5 and authenticated by scXRD and EPR spectroscopy. Complexes 4 and 5 establish a deliberate strategy for accessing inorganic sandwich architectures and extend carbon-free metallocene chemistry to cobalt in two different oxidation states.