Dynamics of the reactions of pentakis(t-octylisocyanide)cobalt(II) complex with triarylphosphines

Abstract

The reactions of freshly prepared solutions of [Co(CNC₈H₁₇-t)₅](ClO₄)₂ with three triarylphosphines, PR₃ (R = Ph, C₆H₄Me-p, C₆H₄OMe-p), were investigated in dichloromethane under pseudo-first-order conditions and with temperatures maintained at  ± 0.1 °C. Addition of each of the phosphines to the Co(II) complex solutions results in a shift in the λ _max of the electronic spectra accompanied by a change in color of the solution. The shift is attributed to ligand substitution. Analyses of the kinetic data suggest a general rate law given by: Rate =

. Overall, the reactions of the cobalt(II) complex [Co(CNC₈H₁₇-0t)₅]²⁺ with the triarylphosphines are proposed to proceed via substitution/reduction mechanisms with final formation of disubstituted Co(I) complexes. The order of reactivity of the complex with the triarylphosphines was P(C₆H₄OMe-p)₃ > P(C₆H₄Me-p)₃ > PPh₃. This order is explained in terms of the electron donating/π-acceptor properties of the phosphines.

Keywords:

• Pentakis(t-octylisocyanide)cobalt(II) complex
• Triarylphosphines
• Rate constants
• Infrared spectra
• Kinetics

Acknowledgments

The authors wish to acknowledge University of Botswana Office of Research and Development for funding and University of Botswana Foundation for partial scholarship to G. Ramokongwa.