STEPWISE MECHANISM FOR OXIDATIVE ADDITION OF IODINE TO ORGANOTELLURIUM(II) COMPOUNDS AS OBSERVED BY STOPPED-FLOW SPECTROSCOPY

The reaction of iodine with a series of diorgano tellurides was monito red by stopped-flow spectroscopy. For dihexyl telluride (1), diphenyl telluride (2), di-p-anisyl telluride (3), and phenyl 2-((dimethylamino )methyl)phenyl telluride (4), an initial ''fast'' reaction was first o rder in substrate and second order in iodine. For 2,6-di-tert-butyltel luropyran-4-one (5), the ''fast'' reaction was second order overall an d first order in iodine. The ''fast'' reaction is actually two reactio ns: the addition of iodine to the tellurium atom to form an eta(1)R(2) Te-I-2 complex followed by the addition of a second iodine to form pre sumably an eta(1)-R(2)Te-I-4 complex. The first reaction is faster tha n the second leading to a rapid preequilibrium and apparent inverted A rrhenius behavior in the temperature dependence of the rate constants. The ''fast'' reaction(s) is followed by a ''slow'' reaction, which is first order overall and independent of iodine concentration. The rate constant for the ''slow'' reaction increases with increasing solvent polarity, which is consistent with a dissociative process leading to i onic intermediates.