Thermodynamic  and  Kinetic  Control  over  the  Reduction  Mechanism  of  the Pd₃(dppm)₃(CO)(I)⁺ Cluster

Abstract

The reduction mechanism of the title cluster has been investigated by means of cyclic voltammetry (CV), rotating disk electrode (RDE) voltammetry, and coulometry. The 2-electron reduction proceeds via two routes simultaneously. The first one involves two 1-electron reduction steps, followed by an iodide elimination to form the neutral Pd(3)(dppm)(3)(CO)(0) cluster (EEC mechanism). The second one is a 1-electron reduction process, followed by an iodide elimination, then by a second 1-electron step (ECE mechanism) to generate the same final product. Control over these two competitive mechanisms can be achieved by changing temperature, solvent polarity, iodide concentration, or sweep rate. The reoxidation of the Pd(3)(dppm)(3)(CO)(0) cluster in the presence of iodide proceeds via a pure ECE pathway. The overall results were interpreted with a six-member square scheme, and the cyclic and RDE voltammograms were simulated, in order to extract the reaction rate and equilibrium constants for iodide exchange for all three Pd(3)(dppm)(3)(CO)(I)(n)() (n = +1, 0, -1) adducts.

New Insights into the Stoichiometric and Catalytic Reactivity of Unsaturated Pd3(dppm)3COn+ Clusters (n = 0, 1) Towards Halocarbons – First Evidence for Inorganic By‐Products

“…This latter process is well known and has been previously established for X -= Br -and I -. [8,22] Finally, the paramagnetic Pd 3 + cluster undergoes reactions (2) and (3). A second mechanism can also be considered and this involves the heterolytic C-X bond cleavage of the species Pd 3 ···(RX) 0 followed by the reductive elimination of "R · "; see reactions (8) and (9).…”

“…Its RDE voltammogram is depicted in Figure 1 (trace a) and exhibits two closely spaced waves for oxidation and reduction labelled AЈ 1 + can be seen (δ = -6.4 ppm). [20][21][22] 31 P NMR spectroscopic data (δ = -6.14 ppm in [D 6 ]acetone) as well as the formation of Bz 2 (44 % based upon GCMS data) and PhMe. [23] During the course of this investigation, crystals of Pd 3 (Br) + suitable for X-ray analysis were obtained and investigated (see below).…”

Unexpected Reaction of the Unsaturated Cluster Host and Catalyst [Pd3(μ3‐CO)(dppm)3]2+ with the Hydroxide Ion: Spectroscopic and Kinetic Evidence of an Inner‐Sphere Mechanism

“…This result is consistent with the decrease in the binding constant between halides and [Pd 3 ] n (n = 0-2). [8,15] These effects are also anticipated for the OH adduct.…”

“…The kinetics were resolved by means of stoppedflow experiments and are consistent with the proposed mechanism. In the presence of an excess of Bu 4 NOH, an electrocatalytic process was observed with modest turnover numbers (7)(8).…”

Generation, Characterization, and Electrochemical Behavior of the Palladium–Hydride Cluster [Pd3(dppm)3(μ3‐CO)(μ3‐H)]+ (dppm=Bis(diphenylphosphinomethane)

“…The double-layer capacitance value was estimated as C dl /A = 1.7.10 À4 F cm 2 + (D = 2.5.10 À6 cm 2 s À1 ) were evaluated previously. [34] The charge transfer coefficients a i was arbitrarily set at 0.5. The standard potential (E Theoretical computations: Calculations with the density functional theory (DFT) approximation were performed by using the commercially available Gaussian 98 software.…”