Reaction mechanism of transmetalation between tetraorganostannanes and platinum(II) aryltriflate complexes. Mechanistic model for stille couplings
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The complexes trans-[PtPh(OTf)(PMe2Ph)(2)] (1) and trans- [PtPh(OTf)(PPh3)(2)] (4) were synthesized from the corresponding chloro complexes in moderate yields. Complex I is slowly hydrolyzed in solution, giving the dinuclear hydroxo-bridged complex [Pt(mu-OH)(PMe2Ph)(2)](2)(CF3SO3)(2) (6), which was characterized by X-ray crystallography. In solution I and 4 undergo fast solvolysis to give the corresponding solvento cations. The reactivities of 1 and 4 with Me3SnPh were investigated in different solvents, and with 1 two products, trans- [PtPh2(PMe2Ph)(2)] (8) and cis-[PtPh2(PMe2Ph)(2)] (9), were always formed simultaneously. In THF an intermediate, trans- [PtPhMe(PMe2Ph)(2)] (14), was characterized on the path to 9. The kinetics for these reactions were evaluated numerically, and on the basis of rate laws, activation parameters, and reactivity trends a mechanism involving parallel equilibria to 8 and 9 with associative activation in all steps is proposed. In this mechanism the initial attack always takes place trans to the phenyl group, giving 8 and 14, respectively, via an open transition state. In a subsequent reaction, 14 reacts with another molecule of stannane, giving 9 as the final product via a cyclic transition state. Complex 4 gives exclusive formation of cis products: cis-[PtPhMe(PPh3)2] (12) and cis-[PtPh2(PPh3)2] (13). These results are discussed in relation to the reaction mechanism of the transmetalation step in the Stille reaction.
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Ämnesklassifikation (UKÄ) – OBLIGATORISK
|Status||Published - 2006|
|Peer review utförd||Ja|