The Structure of ([W₃Q₄X₃(dmpe)₃]⁺, Y^-) Ion Pairs (Q = S, Se; X = H, OH, Br; Y = BF₄, PF₆, dmpe = Me₂PCH₂CH₂PMe₂) in Dichloromethane Solution and the Effect of Ion-Pairing on the Kinetics of Proton Transfer to the Hydride Cluster [W₃S₄H₃(dmpe)₃]⁺

Abstract

The 1H,19F HOESY spectra of the title compounds in CD2Cl2 solution indicate that the cluster cations form ion pairs with the BF4- and PF6- anions with a well-defined interionic structure that appears to be basically determined essentially by the nature of the X- ligand. For the clusters with X = H and OH, the structure of the ion pairs is such that the counteranion (Y-) and the X- ligands are placed close to each other. However, when the size and electron density of X- increase (X = Br), Y- is forced to move to a different site, far away from X-. The relevance of ion-pairing on the chemistry of these compounds is clearly seen through a decrease in the rate of proton transfer from HCl to the hydride cluster [W3S4H3(dmpe)3]+ in the presence of an excess of BF4-. The kinetic data for this reaction can be rationalized by considering that the ([W3S4H3(dmpe)3]+, BF4-) ion pairs are unproductive in the proton-transfer process. Theoretical calculations indicate that the real behavior can be more complex. Although the cluster can still form adducts with HCl in the presence of BF4-, the structures of the most-stable BF4--containing HCl adducts show H...H distances too large to allow the subsequent release of H2. In addition, the effective concentration of HCl is also reduced because of the formation of adducts as ClH...BF4-. As a consequence of both effects, the proton transfer takes place more slowly than for the case of the dihydrogen-bonded HCl adduct resulting from the unpaired cluster.

The Role of Solvent on the Mechanism of Proton Transfer to Hydride Complexes: The Case of the [W3PdS4H3(dmpe)3(CO)]+ Cubane Cluster

“…[14] Thus, although no definitive conclusions can be obtained for the last two resolved steps in the kinetics of reaction in Equation (3), comparison with its closely related analogue makes reasonable the assumption that all the three steps are second-order with respect to HCl. In any case the value of k 1 above is close to that found for the reaction of […”

“…In addition, the kinetics and mechanism of proton transfer in dichloromethane are largely affected by the formation of ([W 3 S 4 H 3 A C H T U N G T R E N N U N G (dmpe) 3 ] + , BF 4 À ) ion pairs, in which BF 4 À approaches the cluster at the proximities of one of the coordinated hydrides. [14] Proton transfer in these ion pairs takes place more slowly than for the case of W À H···H À Cl adducts resulting from the unpaired cluster.…”

Synthesis and Structure of Trinuclear W3S4Clusters Bearing Aminophosphine Ligands and Their Reactivity toward Halides and Pseudohalides

“…Those structures indicate the formation of outer sphere complexes between the cluster and the anion, in agreement with previous reports on related systems. 56 The stability of the different outer-sphere complexes can be estimated from the relative energy values, listed in Table 5, with regard to those of the separated ions. In general, free energies are close to zero, except for the Figure 12), which is significantly more stable than the other outer-sphere complexes.…”

“…However, it must be noted that the outer-sphere complexes commented above correspond to Y -approaching the W center in a particular orientation that favors the substitution process, but other orientations are also possible for the entering anions, as experimentally found for related systems. 56 As outer-sphere complexes with these alternative structures are usually unable to evolve to the substitution product, they would represent dead-end species that would simply compete with productive outer-sphere complexes and make reaction to slow down. Although the formation of these alternative outer-sphere complexes has not been Table 5) for various productive and unproductive outer-sphere complexes are similar in most cases.…”

Enantioselective synthesis of tungsten trimetallic cluster chalcogenides

“…HS; diphosphine=dmpe, dppe, dhmpe, dhprpe, dhbupe, Me-BPE, TTF-dppe) [14][15][16][17][18][19][20][21]. The specific coordination of the bidentate ligand to the incomplete cubane-type M 3 S 4 unit, with one phosphorus atom located trans to the capping sulfur and the other trans to the bridging sulfur, results in C 3 -symmetry trimetallic complexes with backbone chirality, as represented in Scheme 1.…”