(C 4 Me 4 )Co-containing triple-decker complexes with bridging heterocyclic ligands

(C 4 Me 4 )Co-containing triple-decker complexes with bridging boron and phosphorus heterocyclic ligands [(C 4 Me 4 )Co(μ-η:η-L)MCp*] + ( 1 : M = Fe, L = C 5 H 5 BMe; 2 : M = Fe, L = C 4 Me 4 P; 3a : M = Fe, L =  cyclo -P 5 ; 3b : M = Ru, L =  cyclo -P 5 ) were synthesized by photochemical reaction of [(C 4 Me 4 )Co(C 6 H 6 )] + with sandwich compounds Cp*ML. They were isolated as salts with PF 6 − anion, and the structures of 1 PF 6 , 2 PF 6 , and 3a PF 6 were determined by X-ray diffraction. The μ-pentaphospholyl complex 3a was also synthesized by exchange of sandwich compounds in the μ-cyclopentadienyl triple-decker complexes [(μ-η:η-Cp){Co(C 4 Me 4 )} 2 ] + or [(C 4 Me 4 )Co(μ-η:η-Cp)FeCp] + . Complexes 1 , 2 , and 3a undergo nucleophilic degradation by acetone and acetonitrile with selective elimination of the [(C 4 Me 4 )Co] + fragment giving the starting sandwich compounds. The rate of the nucleophilic degradation depends on the nature of the bridging ligand and decreases in the following order: C 4 Me 4 P ≥ C 5 H 5 BMe >  cyclo -P 5 . The bonding in 1 , 2 , and 3a was analyzed and compared with that in the cyclopentadienyl analog [(C 4 Me 4 )Co(μ-η:η-Cp)FeCp*] + using energy decomposition analysis.