An MO-theoretical Interpretation of the Reductive Cleavage of Organic Halides by Pentacyanocobaltate(II)

Abstract

The mechanism of the reductive cleavage of organic halides (RX) by pentacyanocobaltate(II) Co(CN)53− was investigated by means of the extended Hückel MO theory. First, the molecular structure of Co(CN)53− was considered to be the square-pyramidal C4V configuration, without H2O as its sixth ligand. Secondly, the order of the observed rate constants for the Co(CN)53−+RX→Co(CN)5X3−+R. reaction was found to be in satisfactory accordance with that of the calculated binding energies of the R-X bond. Thirdly, the reductive cleavage of RX by Co(CN)53− proceeds by the aid of the predominant electron-migration from the highest-occupied, lone-pair halogen-orbital to the singly-occupied dz2 Co-orbital and from the highest-occupied dxz (or dyz) Co-orbital to the lowest-unoccupied, antibonding pσ* orbital of the R–X bond. Finally, the mode of the interaction between Co(CN)53− and RX was precisely discussed in terms of the homolytic cleavage of the R–X bond.

Bonding capabilities of transition metal carbonyl fragments

“…51 We should also mention here the important recent theoretical study of the approach of RX to Co(CN)s3™. 52 A square-pyramidal MLs system with five d electrons would have a low-spin configuration (b2)2(e)3 for < 110°. The matrix isolation of V(CO)s has recently been reported.…”