Aiding Factors in the Formation of Azaplatinacyclobutane Rings – X‐ray and Crystal Structure of [Pt{CH(Ph)CH₂NEt₂‐κC,κN}(<i>N</i>,<i>N</i>,<i>N′</i>,<i>N′</i>‐tetramethylethylenediamine)]⁺ and of Its Open‐Chain Precursor

Abstract

Abstract The addition products 2 of a secondary amine to a coordinated olefin, in the cationic complexes [PtCl(η 2 ‐CH 2 =CHR)(tmeda)] + (tmeda = N , N , N′ , N′ ‐tetramethylethylenediamine; R = Me, 1a ; Ph, 1b , H, 1c ), undergo in basic medium an intramolecular nucleophilic substitution with elimination of the chlorido ligand and formation of an azaplatinacyclobutane ring 3 . The ring‐closing process occurs notwithstanding the absence of a labilizing ligand trans to the leaving chlorido ligand and of bulky substituents on the amino–ethanide chain. If the addition product 2 is a mixture of Markovnikov and anti‐Markovnikov isomers, the ring‐closing reaction is faster for the anti‐Markovnikov form, and this leads to an increase of the relative amount of the anti‐Markovnikov isomer in the cyclized species 3 . The difference in the rate of formation of the azaplatinacyclobutane ring between the two isomers has been interpreted on the basis of a more favorable stereochemistry in the case of the anti‐Markovnikov form. The X‐ray crystal structures of [Pt{CH(Ph)CH 2 NEt 2 ‐κC,κN}(tmeda)] + ( 3bn ) and of its open‐chain precursor, [PtCl{CH(Ph)CH 2 NHEt 2 }(tmeda)] + ( 2bn ) fully support this hypothesis.(© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2007)