[3+2] versus [2+2] addition of metal oxides across C=C bonds. reconciliation of experiment and theory

The mechanism of the addition of osmium tetra oxide, and rhenium (VII) oxides across C=C bonds was controversial. Early work indicated a [3+2] addition, and later kinetic studies suggested, an initial [2+2] addition, whereas recent quantum-chemical calculations showed the [3+2] addition to be favored.