Synthesis of Tetrakis(Cyclohexylisocyanide)Bis(Tri-Phenylphosphine)Cobalt(II) Perchlorate. Isolation of Cohalt(II) in an Unstable Stereochemistry

Abstract

Tetrakis(cyclohexylisocyanide)bis(triphenylphosphine)cobalt(II) perchlorate, [Co(CNC₆H₁₁)₄(PPh₃)₂](ClO₄)₂. was synthesized and limitedly characterized. This complex was isolated by rapid precipitation and immediate filtration. Under even the most favorable reaction conditions this intrinsically unstable six-coordinate Co(II) complex is still the minor product relative to the thermodynamically-favored five-coordinate Co(I) complex, [Co(CNC₆H₁₁)₃(PPh₃)₂]ClO₄. Attempted recrystallization of [Co(CNC₆H₁₁)₄(PPh₃)₂(ClO₄)₂ yields the five-coordinate Co(II) complex, [Co(CNC₆H₁₁)₃(PPh₃)₂](ClO₄)₂. Analogous reactions of P(C₆H₄Me-p)₃ and P(C₆H₄OMe-p)₃ with [Co(CNC6H₁₁)₅](ClO₄)₂ in ethanol produced only the [Co(CNC6H₁₁)₃(PR₃)₂]ClO₄ complexes. This six-coordinate Co(II) complex may be an intermediate in the reduction/ligand-substitution reactions for pentakis(organoisocyanide)cobalt(II) complexes.