Structural studies on alkene binding and hydroamination of platinum complexes
Pryadun, Ruslan S
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A sequence of simple and conjugated alkene complexes of platinum has been prepared, cis -PtCl 2 (PPh 3 )(alkene). These complexes are characterized by NMR, including assignment of each proton, and X-ray crystallography. Each complex with bound alkene was reacted with diethylamine. For 1-hexene, 1-octene and 1-decene the amine displaces the alkene. For the smaller alkenes (ethylene, propene, 1-butene, 2-butene) the diethylamine nucleophilically attacks the coordinated alkene. For propene and 1-butene low temperature (-78°C) addition gives anti-Markovnikoff nucleophilic attack from which the product slowly converts at room temperature to the Markovnikoff product. The transformation from anti-Markovnikoff to Markovnikoff addition occurs without diethylamine dissociation. All adducts were defined by detailed NMR analysis including assigning each proton. Reaction of a bound butadiene complex with diethylamine yielded a diamination product with anti-Markovnikoff stereochemistry complexed to platinum. An attempt at binding cis -butyne to the metal center resulted in metal-assisted formation of 1,2,3,4-tetramethylcyclobutadiene with previously unreported geometry as shown by a crystal structure determination.