Stereochemistry of the Transmetalation of Grignard Reagents to Copper (I) and Manganese (II)

Transmetalation of a chiral secondary Grignard reagent to Cu(I) or Mn(II) occurs with partial racemization in a manner that suggests the sequence of two transmetalation cycles, one with racemization (caused by ET ?) and the other one with (predominant) retention of configuration.