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Mechanism of the Reaction of the [W 3 S 4 H 3 (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
Author(s) -
Basallote Manuel G.,
Feliz Marta,
FernándezTrujillo M. Jesús,
Llusar Rosa,
Safont Vicent S.,
Uriel Santiago
Publication year - 2004
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200305376
Subject(s) - protonation , chemistry , hydride , solvent , halide , cluster (spacecraft) , molecule , reaction mechanism , reaction intermediate , kinetic isotope effect , medicinal chemistry , crystallography , metal , computational chemistry , inorganic chemistry , deuterium , catalysis , organic chemistry , ion , physics , quantum mechanics , computer science , programming language
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 WH 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 MH bonds but also by breakage of the HX or H + solvent bonds. It also indicates that the latter process can be more important in determining the rate of protonation.