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

Abstract

Addition of formate on the dicationic cluster [Pd(3)(dppm)(3)(mu(3)-CO)](2+) (dppm=bis(diphenylphosphinomethane) affords quantitatively the hydride cluster [Pd(3)(dppm)(3)(mu(3)-CO)(mu(3)-H)](+). This new palladium-hydride cluster has been characterised by (1)H NMR, (31)P NMR and UV/Vis spectroscopy and MALDI-TOF mass spectrometry. The unambiguous identification of the capping hydride was made from (2)H NMR spectroscopy by using DCO(2) (-) as starting material. The mechanism of the hydride complex formation was investigated by UV/Vis stopped-flow methods. The kinetic data are consistent with a two-step process involving: 1) host-guest interactions between HCO(2) (-) and [Pd(3)(dppm)(3)(mu(3)-CO)](2+) and 2) a reductive elimination of CO(2). Two alternatives routes to the hydride complex were also examined : 1) hydride transfer from NaBH(4) to [Pd(3)(dppm)(3)(mu(3)-CO)](2+) and 2) electrochemical reduction of [Pd(3)(dppm)(3)(mu(3)-CO)](2+) to [Pd(3)(dppm)(3)(mu(3)-CO)](0) followed by an addition of one equivalent of H(+). Based on cyclic voltammetry, evidence for a dual mechanism (ECE and EEC; E=electrochemical (one-electron transfer), C=chemical (hydride dissociation)) for the two-electron reduction of [Pd(3)(dppm)(3)(mu(3)-CO)(mu(3)-H)](+) to [Pd(3)(dppm)(3)(mu(3)-CO)](0) is provided, corroborated by digital simulation of the experimental results. Geometry optimisations of the [Pd(3)(H(2)PCH(2)PH(2))(3)(mu(3)-CO)(mu(3)-H)](n) model clusters were performed by using DFT at the B3 LYP level. Upon one-electron reductions, the Pd--Pd distance increases from a formal single bond (n=+1), to partially bonding (n=0), to weak metal-metal interactions (n=-1), while the Pd--H bond length remains relatively the same.

Synthesis, structure and gas-phase reactivity of the mixed silver hydride borohydride nanocluster [Ag3(μ3-H)(μ3-BH4)LPh3]BF4(LPh= bis(diphenylphosphino)methane)

“…[33][34][35][36][37] As expected, a transition metal centre with a d 10 Å), where the corresponding anti-bonding skeletal molecular orbitals are also fully occupied. 38 With regards to the unimolecular fragmentation chemistry, the calculations indicate that the first loss of the ligand, L (eqn (12)), from [Ag 3 (H)(BH 4 )L Me 3 ] + results in transferring the hydride to Ag 2 and causes this centre to adopt a mainly linear structure with a very weak interaction with Ag 1 (Fig. 5).…”

MALDI‐TOFMS analysis of coordination and organometallic complexes: a nic(h)e area to work in

“…Since 2005 many other systems have been investigated. These include, but are not limited to, porphyrins and phthalocyanines,26–37 other nitrogen heterocycles,26, 38–46 other nitrogen ligands,47–53 metallocenes/aryl ligands,26, 54–60 phosphorus ligands,26, 44, 57, 59, 61–63 hydrazones,64 carboxylates,51, 54, 65 thiophenes,66, 67 acetylacetonates,59, 68 ethers,69, 70 polyynes/cumulenes,71 acetohydrazides,72 octreotate,73 tripsalen,74 thiols75 and quinolates 76. Successfully characterised compounds have contained, but are not limited to, magnesium,37 the first‐row transition metals in general,63, 68 specifically vanadium,59 chromium,74 manganese,28, 74 iron,26, 35, 40, 54, 59, 60, 63, 66, 74 cobalt,28, 29, 31, 33, 34, 40, 42, 64, 72 nickel,29, 33, 40, 64, 67, 72 copper,26, 29, 31, 33, 34, 39, 52, 64, 71, 72 zinc,26, 28, 29, 31–34, 40, 45, 48, 55, …”

“…Successfully characterised compounds have contained, but are not limited to, magnesium,37 the first‐row transition metals in general,63, 68 specifically vanadium,59 chromium,74 manganese,28, 74 iron,26, 35, 40, 54, 59, 60, 63, 66, 74 cobalt,28, 29, 31, 33, 34, 40, 42, 64, 72 nickel,29, 33, 40, 64, 67, 72 copper,26, 29, 31, 33, 34, 39, 52, 64, 71, 72 zinc,26, 28, 29, 31–34, 40, 45, 48, 55, 64, 65, 72 gallium,26, 42 the Group 4 metals,58 ruthenium,26, 44, 46, 53, 57, 73 rhodium,26 palladium,28, 41, 49, 50, 53, 55, 61–63, 67 silver,28, 29, 52, 71 cadmium,40, 43, 47, 72 indium,42 tin,38, 51, 54, 69, 70 rhenium,26 osmium,26 iridium,39, …”

The free-energy barrier to hydride transfer across a dipalladium complex

“…Catalysts of this type may range from long established systems such as Wilkinson's catalyst for alkene hydrogenation 13 to multinuclear clusters with known or potential use for the catalysis of hydrogen transfer reactions. 14,15 Solution 1 H NMR spectroscopic studies of MesPdH suggested the occurrence of a uxional process, which was thought to involve the hydride ligand exchanging between the palladium centres (Fig. 1).…”

“…Previous experimental studies on palladium hydride clusters have shown/ suggested that hydride transfer processes between metal centres can occur either with the Pd-Pd bond remaining intact, or with cleavage of the Pd-Pd via a Pd-H-Pd geometry. 14,15 These studies are mostly based on the interpretation of solution phase uxionality investigated by variable temperature NMR spectroscopy. The presence of good NMR probes in the clusters, phosphine ligands, can be invaluable in discriminating between mechanistic pathways.…”