Sandwich compounds are foundational to organometallic chemistry, yet carbon-free analogs remain exceptionally rare. We report the all-phosphorus heteroleptic cobalt sandwich anion (η5-P5) Co (η3-P3) - (4), obtained via a stepwise P4 activation/unmasking sequence in which (nacnac') SiP4 serves as a controllable, silicon-protected P4 synthon. Reaction with the cobalt (-I) complex K (THF) 0. 2Co (η2: η2-cod) 2 furnishes a bis (silatetraphosphacyclopentadienyl) cobaltate anion (1), and successive cleavage of the Si (nacnac') units delivers the "naked" cyclo-P5/cyclo-P3 sandwich framework via monosilylated intermediates 2 and 3. The cryptate salts M (crypt-222) 4 (M = Na, K) were characterized by 31P1H 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 (η4-P5) Co (η3-P3) 2- (5), isolated as K (crypt-222) 25 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.
Trabitsch et al. (Fri,) studied this question.