A Study of the Cis‐Trans Isomerization of a Square Planar pt Ylide Complex

The isomerization of cis ‐Pt(PPh 3 ) 2 (I)(CH 2 P(O)(OCH 3 ) 2 ), 1 , was studied by an NMR technique. An Arrhenius plot for the isomerization gives an activation energy of 99.2 KJ/mol , Δ H ≠ = 97 KJ/mol and Δ S ≠ = −8.3 J/mol‐K. Under a CO atmosphere the cis isomer catalytically isomerized to its trans form. Free PPh 3 did not catalyze the cis‐trans isomerization. In the proposed isomerization mechanism the reaction goes through an intramolecular assisted phosphine dissociation, followed by dimer formation. The addition of phosphine to the dimer then completes the isomerization of the original monomer from cis to trans.