Platinum carbene complexes with one heteroatom bonded to carbene carbon: Synthesis and mechanisms

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Xiang, Ke
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University of Guelph

Reactions of (η\sp4-1,5-cyclooctadiene-)(chloromethyl-)dichloroplatinum(II) ((COD) Pt(CH\sb2Cl)(Cl))), N,N,N′,N′-tetramethyldiaminomethane (Me\sb2NCH\sb2NMe\sb2) and ligands of type AB\sb3 (A = P, B = Ph, Et, 4-FC\sb6H\sb4, 4-MeOC\sb6H\sb4; A = As, B = Ph) were investigated. In all these cases, carbene complexes of type cis-[(L)Pt(CHNMe\sb2)(Cl)\sb2] are formed via a chelate ring complex of type trans-(L,N)[(L)Pt(CH\sb2NMe\sb2CH\sb2N―Me\sb2)(Cl)][Cl]. The relative reaction rates with different ligands are compared. The reactions are considered in two stages. First, the formation of the chelate ring complexes trans-(L,N)[(L)Pt(CH\sb2NMe\sb2CH\sb2N―Me\sb2)(Cl)][Cl]; second, the breakdown of these complexes. It has been found that in the first stage, the reaction rates decrease in the order L=AsPh\sb3>PPh\sb3>PEt\sb3; in the second stage, the rates decrease in the order L=PPh\sb3>AsPh\sb3. A mechanism for the formation of the chelate ring complexes trans-(L,N)[(L)Pt(CH\sb2NMe\sb2CH\sb2―NMe\sb2)(Cl)][Cl] is proposed. Reactions of [COD]Pt(CH\sb2Cl)(Cl)], triphenylphosphine and the bis(nucleophiles) MeSCH\sb2SMe and Me\sb2NCH\sb2OEt have also been investigated. The chelate ring complex trans-(P,S)[(Ph\sb3P)Pt(CH\sb2SCH\sb2S―Me)(Cl)][Cl] is formed from the bis(sulfide)ligand. Like the nitrogen analogue, this complex decomposes upon standing in solution, but the products have not been characterized. The aminoether ligand gives the complex cis-[(Ph\sb3P)Pt(CH\sb2NMe\sb2CH\sb2OEt)Cl\sb2], which is stable to decomposition in solution.

platinum carbene complexe, heteroatom, bond, carbene carbon, synthesis, mechanisms