Stereospecific Attack on Complexed Double Bonds

In contrast to the trans addition observed for irreversible nucleophilic attack on tricarbonyliron dienylium cations and olefins complexed to Fp (Section III,A), irreversible nucleophilic attack (e.g., by carbon nucleophiles) on olefins coordinated to Pt(II) and Pd(II) appears to result in cis addition, presumably via initial attack at the coordinatively unsaturated Pt(II) or Pd(II), followed by intramolecular transfer of the coordinated nucleophile to the double bond (Section III,A). 

Reversible nucleophilic attack (e.g., by nitrogen and oxygen nucleophiles) usually results in trans addition, presumably reflecting thermodynamic control. The mechanism in this latter case could involve the ping-pong effect suggested in Section IV,A. 

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