Reactivity and Mechanism
in the Oxidative Addition
of Allylic Halides to a Dimethylplatinum(II) Complex
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Abstract
The complex [PtMe<sub>2</sub>(2,2′-bipyridine)], <b>1</b>, reacts with allyl chloride and allyl bromide, to give [PtXMe<sub>2</sub>(CH<sub>2</sub>CHCH<sub>2</sub>)(2,2′-bipyridine)], <b>2</b>, X = Cl; <b>3</b>, X = Br, with 2-methylallyl chloride
to give [PtClMe<sub>2</sub>(CH<sub>2</sub>CMeCH<sub>2</sub>)(2,2′-bipyridine)], <b>4</b>, and with crotyl chloride
(a mixture of <i>trans</i>- and <i>cis</i>-MeCHCHCH<sub>2</sub>Cl), to give a mixture of [PtClMe<sub>2</sub>(<i>trans-</i>CH<sub>2</sub>CHCHMe)(2,2′-bipyridine)], <b>5</b>, and [PtClMe<sub>2</sub>(<i>cis-</i>CH<sub>2</sub>CHCHMe)(2,2′-bipyridine)], <b>6</b>. The complexes are formed mostly by <i>trans</i> oxidative addition and, for the crotyl complexes, without allylic
rearrangement. Complex <b>1</b> reacts with CH<sub>2</sub>CHCHMeCl,
mostly with allylic rearrangement, to give complex <b>5</b>,
with complexes <b>6</b> and [PtClMe<sub>2</sub>(CHMeCHCH<sub>2</sub>)(2,2′-bipyridine)], <b>7</b>, as minor products.
The reactions of <b>1</b> with CH<sub>2</sub>CHCH<sub>2</sub>X (X = Cl or Br) and MeCHCHCH<sub>2</sub>Cl follow
second-order kinetics (first-order in both reagents), but <b>1</b> reacts with CH<sub>2</sub>CHCHMeCl by third-order kinetics
(first-order in <b>1</b>, second-order in CH<sub>2</sub>CHCHMeCl)
and with CH<sub>2</sub>CMeCH<sub>2</sub>Cl by a mixture of
second- and third-order kinetics. The second-order reactions are proposed
to occur by the S<sub>N</sub>2 mechanism, and potential mechanisms
of the third-order reactions are discussed
