Inorganic Cobalt Sandwich Complex [(η 5 -P 5 )Co(η 3 -P 3 )] −

High Resolution Image Download MS PowerPoint Slide 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.