Oxidative addition of iodo-acetonitrile and of elemental halogens to [Pt3(µ-CO)3(PCy3)3]

Abstract

The reaction of [Pt₃(µ-CO)₃(PCy₃)₃] (1) with one mole-equivalent of iodo-acetonitrile was quantitative at −70 °C giving the oxidative addition product [Pt₃(µ-CO)₃(PCy₃)₃(I)(CH₂CN)] (2). Fragmentation of 2 was observed in solution giving [Pt₂I(CH₂CN)(CO)₂(PCy₃)₂] (3) which is the major product at room temperature if the starting cluster/reactant ratio is equal to or less than 1 to 1.5. Dimer 3 decomposes slowly in solution giving [Pt₂I₂(CO)₂(PCy₃)₂] ( 4a) and succinonitrile. Monomer [PtI(CH₂CN)(CO)(PCy₃)] was the final product of the reaction when using excess of iodo-acetonitrile. The reactions of 1 with one mole-equivalent of halogens X₂ gave the new 44-electron clusters [Pt₃X(µ-CO)₂(µ-X)(PCy₃)₃] (X = I₂ ( 7a) or Br₂ ( 7b)) by oxidative addition followed by substitution of CO by X⁻. Fragmentation of 7a and 7b took place in solution when using one and a half mole-equivalents of X₂ giving dimers 4a and [Pt₂Br₂(CO)₂(PCy₃)₂] ( 4b) as well as [Pt₂X₂(µ-X)₂(CO)₂(PCy₃)₂]. Monomers cis-[PtX₂(CO)(PCy₃)] were the final products of the reaction of 1 with excess of halogens. Insertion of SnCl₂ was observed into the Pt–Pt bond but not into the Pt–X bond, when equimolar amounts of SnCl₂·2H₂O were added to a solution of 4a or its chloro-analogue giving [Pt₂X₂(µ-SnCl₂)(CO)₂(PCy₃)₂]. The Pt(I) dimers have unusually small J(Pt–Pt) values as observed by ¹⁹⁵Pt NMR and calculated by DFT. These values showed periodic changes comparing 4a and its analogues with other halides and mixed halide dimers.