Mechanism of the Reaction of the [W3S4H3(dmpe)3]+ Cluster with Acids: Evidence for the Acid-Promoted Substitution of Coordinated Hydrides and the Effect of the Attacking Species on the Kinetics of Protonation of the Metal-Hydride Bonds

✍ Scribed by Manuel G. Basallote; Marta Feliz; M. Jesús Fernández-Trujillo; Rosa Llusar; Vicent S. Safont; Santiago Uriel

• Publisher: John Wiley and Sons
• Year: 2004
• Tongue: English
• Weight: 187 KB
• Volume: 10
• Category: Article
• ISSN: 0947-6539
• DOI: 10.1002/chem.200305376

✦ Synopsis

Abstract

The cluster [W~3~S~4~H~3~(dmpe)~3~]^+^ (1) (dmpe=1,2‐bis(dimethylphosphino)ethane) reacts with HX (X=Cl, Br) to form the corresponding [W~3~S~4~X~3~(dmpe)~3~]^+^ (2) complexes, but no reaction is observed when 1 is treated with an excess of halide salts. Kinetic studies indicate that the hydride 1 reacts with HX in MeCN and MeCN–H~2~O mixtures to form 2 in three kinetically distinguishable steps. In the initial step, the WH bonds are attacked by the acid to form an unstable dihydrogen species that releases H~2~ and yields a coordinatively unsaturated intermediate. This intermediate adds a solvent molecule (second step) and then replaces the coordinated solvent with X^−^ (third step). The kinetic results show that the first step is faster with HCl than with solvated H^+^. This indicates that the rate of protonation of this metal hydride is determined not only by reorganization of the electron density at the MH bonds but also by breakage of the HX or H^+^solvent bonds. It also indicates that the latter process can be more important in determining the rate of protonation.