文摘
Reaction of the incomplete cuboidal [W3S4H3(dmpe)3]+ cluster with a Pd(0) complex under a CO atmosphere producesa rare example of a heterodimetallic hydrido cluster of formula [W3PdS4H3(dmpe)3(CO)]+ ([1]+). There are notsignificant changes in the W-W bond lengths on going from the trinuclear to the tetranuclear cluster. The averageW-W and W-Pd bond distances of 2.769[10] and 2.90[2] Å, respectively, are consistent with the presence ofsingle bonds between metal atoms. The heterodimetallic [1]+ complex is easier to oxidize and more difficult toreduce than its trinuclear precursor, which reflects the electron-donating capability of the Pd(CO) fragment. However,mechanistic studies on the reaction of [1]+ with acids show a lower basicity for this complex in comparison withthat of its trinuclear precursor, so there is a major electron-density rearrangement within the cluster core uponPd(CO) coordination. This rearrangement is also reflected in an unusual expansion of the sulfur tetrahedron withinthe W3PdS4 core with the concomitant elongation of the W-S bond distances by 0.04 Å with respect to the analogousbond lengths in the trinuclear precursor. For those thermodynamically favored proton-transfer processes, the reactionmechanism of [1]+ with acids is quite similar to that observed for the incomplete trinuclear cluster, with only smallchanges in the rate constants. The reaction of [1]+ with HCl in acetonitrile/water mixtures produces [W3PdS4Cl3(dmpe)3(CO)]+ ([2]+) in two kinetically distinguishable steps. Proton transfer occurs in the initial step, in which theW-H bonds are attacked by the acid to yield dihydrogen-bonded adducts that are further attacked by an acetonitrilemolecule to give [W3PdS4(CH3CN)3(dmpe)3(CO)]4+ and dihydrogen. The nature of processes involved in the secondstep are not well-understood with the present data, although it is very likely that these correspond to some secondaryprocesses. In the third resolved step, the coordinated CH3CN ligands in [W3PdS4(CH3CN)3(dmpe)3(CO)]4+ aresubstituted by Cl- to afford the final [2]+ product. No reaction is observed between [1]+ and HCl in neat acetonitrile,whereas the product of the reaction of [1]+ with HBF4 or Hpts (pts- = p-toluenesulfonate) in this solvent is[W3PdS4(CH3CN)3(dmpe)3(CO)]4+. The reaction occurs in a single kinetic step with a first- (Hpts) or second-order(HBF4) dependence with respect to the acid. The first- and second-order acid dependences can be interpretedthrough the initial formation of dihydrogen adducts with one or two acid molecules, respectively.