Labile Substitution Reactions in Diamagnetic tetrakis(Alkylisocyanide)bis(triarylphosphine)cobalt(III) Complexes by Tri‐n‐propylphosphine

Abstract

The diamagnetic alkylisocyanide‐triarylphosphine Co(III) complexes [Co(CNC6H11)4{P(C6H4OMe‐p)3}2](ClO4)3, [Co(CNC6H11)4{P(C6H4Me‐p)3}2](ClO4)3, [Co(CNC6H11)4(PPh3)2](ClO4)3, and [Co(CNCH2Ph)4{P(C6H4OMe‐p)3}2](BF4)3, are investigated in substitution reactions with the trialkylphosphine ligand P(C3H7‐n)3, in the solvents CF3CH2OH, CH2Cl2, and CH3NO2. Eleven of the 12 reactions are labile, resulting in formation of the complexes [Co(CNR)4{P(C3H7‐n)3}2]X3; only [Co(CNC6H11)4{P(C6H4OMe‐p)3}2](ClO4)3 in CF3CH2OH failed to undergo substitution. Some yields are low due to reduction of the Co(III) in solution, and some reaction times exceed the suggested t 1/2<1 min criterion for labile behavior. Reactions in CH3NO2 were performed at lowered temperatures to minimize reduction of Co(III). Correlation of reactivity with observation of an “extra” Co(III) band in the solution IR spectra, suggesting the presence of a second Co(III) species, is partially successful in providing a mechanism for these unexpected reactions.