Synthesis and Spectroscopic and Spectroelectrochemical Characterization of a New Family of 44e^– Tris-Phosphido-Bridged Palladium Triangles

Abstract

Triangular clusters containing a [M3(μ-PR2)3](+) core are very common in platinum chemistry but were virtually unknown for M = Pd. Herein we describe the synthesis and characterization of several palladium derivatives belonging to this class. The trinuclear monohalide clusters {Pd3}(CO)2X [{Pd3} = Pd3(μ-PBu(t)2)3; X = Br, I] were prepared by reacting [(n)Bu4N]X or KX with the dinuclear complex [Pd(PBu(t)2H)(μ-PBu(t)2)]2 and H2O under an atmosphere of CO. The reaction of {Pd3}(CO)2I with CNBu(t) leads to the substitution of all the terminal ligands to afford the symmetrical cluster [{Pd3}(CNBu(t))3]I. The latter reacts with TlPF6 (excess) or AgCF3SO3 (1:1 ratio) to give anion metathesis, whereas the addition of a second equivalent of Ag(+) causes cluster oxidation to the thermally stable paramagnetic 43e(-) dication [{Pd3}(CNBu(t))3](2+). The cationic clusters [{Pd3}(CO)2(L)]PF6 (L = NCCH3, Py or CO) were obtained by reacting {Pd3}(CO)2I with TlPF6, under nitrogen in acetonitrile or in pyridine or under 1 atm of carbon monoxide in THF. Finally, {Pd3}(CO)2Cl was achieved by the reaction of [{Pd3}(CO)3]PF6 with [(PPh3)2N]Cl. All clusters have been obtained in good yields and purity and have been characterized by microanalysis and IR and multinuclear NMR spectroscopy. Single crystal X-ray diffraction studies on {Pd3}(CO)2Br and [{Pd3}(CNBu(t))3]CF3SO3 are also reported. The cyclovoltammetric profile exhibited by the palladium clusters prepared in this work is characterized by the presence of two monoelectronic oxidation processes whose reversibility and potentials depend on the nature of the ligands. Moreover, the UV-vis and IR spectroelectrochemical analysis of {Pd3}(CO)2I, [{Pd3}(CO)3]PF6 and [{Pd3}(CNBu(t))3]PF6 allowed the spectroscopical characterization of some electrogenerated oxidized species and provided some detail for the redox-coupled reactions of metastable products.

Multinuclear Solid-State NMR and DFT Studies on Phosphanido-Bridged Diplatinum Complexes

“…Platinum diorganophosphanido complexes have been the object of intense study in the last years due to the rich chemistry they exhibit. − NMR spectroscopy is a powerful technique for investigating the structure and dynamics in solution of such complexes, owing to the presence of several different spin 1/2 nuclei in these molecules ( 1 H, 31 P, 195 Pt, 13 C, and in several cases 19 F). Although NMR studies on this kind of complexes have been performed for several decades, some issues about 195 Pt NMR and 31 P NMR remain unclear.…”

Low Valent Palladium Clusters: Synthesis, Structures and Catalytic Applications

“…Leoni and co‐workers prepared and synthesized a sequence of unusual [Pd 3 ( μ ‐PR 2 ) 3 ] + complexes. [ 59 ] Firstly, a promising air‐stable precursor [Pd 3 ( μ ‐P t Bu 2 ) 3 (CO) 2 X] (X = Br, I) has been obtained by adding H 2 O, KX or [ n Bu 4 N]X to dipalladium complex [Pd(P t Bu 2 H)( μ ‐P t Bu 2 )] 2 in the presence of CO. Then several Pd 3 clusters could be gained through the substitution reactions of terminal ligands step by step. In addition, the treatment of [Pd 3 ( μ ‐P t Bu 2 ) 3 (CN t Bu) 3 ][I] with 2 equiv AgCF 3 SO 3 resulted in the invention of a 43e – dication cluster [Pd 3 ( μ ‐P t Bu 2 ) 3 (CN t Bu) 3 ] 2+ .…”

Bridging molecular clusters and fullerene

“…17a,b,f,32d Apparatus and techniques for the electrochemical measurements and in situ spectroelectrochemistry have been described previously. 38 The cyclic voltammetries of sparingly soluble compounds (C 60 and 6) were performed using a platinum disk with a diameter of 6.0 mm as the working electrode. Electrochemical measurements were performed in dichloromethane solutions containing [ n Bu 4 N]PF 6 (0.2 mol dm −3 ) as the supporting electrolyte and all the potential values were determined using the decamethylferrocenium-decamethylferrocene couple as an internal standard.…”