Studies of chelation. Part III. Complexes of chromium and molybdenum tetra- and penta-carbonyls with S-substituted 1,2-dimercaptoethane compounds. Electronic influences on chelate-ring formation

Abstract

Complexes in the classes [M(CO)₅L], [{(OC)₅M}₂L], and [M(CO)₄L]{M = Cr or Mo; L = RSCH₂CH₂SR, R =p-XC₆H₄[X = NO₂(nte), Cl(cte), H(pte), Me(tte), OMe(mte), and NMe₂(dte)] and CMe₃(bte)} have been prepared and characterised by i.r., mass, u.v.–visible, and n.m.r. spectroscopy and by analysis. The rate of chelate-ring formation increases with electron donation to the nucleophile and is subject to steric retardation, indicating an important associative contribution to the process. Comparison with analogous tertiary phosphine complexes shows that the stability and reactivity of the complexes is influenced both by the metal atom and the ligand-donor atom in a previously unrecognised manner. The aryl dithioether ligand is displaced from [M(CO)₅L] complexes by ditertiary phosphines under mild conditions.