Deprotonation versus Nucleophilic Substitution in Some Platinum(II) Coordinated Olefins Containing an Electron Withdrawing Group

Two new cationic olefin complexes of platinum(II) with electron-withdrawing substituents on the allylic carbon, [PtCl(η 2 -CH 2 ═CHCH 2 X)(tmeda)] + (X = −C(O)OCH 3 ( 1a ), −OC(O)CH 3 ( 1b )) have been synthesized and their reactivity toward nucleophiles investigated. The reaction of 1a with various nucleophiles, including water, causes allylic deprotonation and formation of the η 3 -allyl complex [Pt{η 3 -CH 2 CHCHC(O)OCH 3 }(tmeda)] + ( 4a ). In nonaqueous media it was possible to identify also a transient alkenyl species, [PtCl{η 1 -CH═CHCH 2 C(O)OCH 3 }(tmeda)] ( 2a ), formed by loss of a vinylic proton. In contrast, the reaction of 1b with nucleophiles does not lead to deprotonation but to substitution of the acetate group followed by addition to the olefinic double bond. The latter can be intramolecular, as in the case of acetylacetonate, leading to [PtCl{η 1 -CH 2 CHCH 2 C[C(O)CH 3 ]═C(CH 3 ) O}(tmeda)] ( 5b ) or requires a second molecule of nucleophile, as in the case of secondary amines, leading to the Markovnikov and anti-Markovnikov addition products (e.g., [PtCl{η 1 -CH 2 CH(NEt 2 )CH 2 NEt 2 }(tmeda)] ( 6b′ ) and [PtCl{η 1 -CH(CH 2 NEt 2 ) 2 }(tmeda)] ( 6b )).