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.

Several mono- or bis-alkynyl derivatives of general formula Pt6(μ-PBu(t)2)4(CO)4X(C[triple bond, length as m-dash]C-R), Pt6(μ-PBu(t)2)4(CO)4(C[triple bond, length as m-dash]C-R)2 or Pt6(μ-PBu(t)2)4(CO)4(C[triple bond, length as m-dash]C-R)(C[triple bond, length as m-dash]C-R') were obtained under Sonogashira type conditions. The new clusters have been characterized with microanalysis and using IR and multinuclear NMR spectroscopy. The crystal and molecular structures of Pt6(μ-PBu(t)2)4(CO)4(C[triple bond, length as m-dash]C-R)2 (R = H, C6H4-4-n-C5H11) are presented and electrochemical and spectroelectrochemical studies of some representative compounds are also reported.

The monochloro derivative {Pt3}Cl [(1), {Pt3} = Pt3(μ-PBu(t)2)3(CO)2] was reacted with one equiv. of 4-ethynylbenzaldehyde under Sonogashira dehydrohalogenation conditions to afford {Pt3}CC-(1,4)C6H4-CHO, (3). Under analogous conditions, the condensation of the dichloride {Pt6}Cl2 [(2), {Pt6} = Pt6(μ-PBu(t)2)4(CO)4] with two equiv. of 4-ethynyl-benzaldehyde provided {Pt6}(CC-(1,4)C6H4-CHO)2, (4). The fulleropyrrolidine derivatives {Pt3}CC-(1,4)C6H4-C2H3N(C8H17)C60, (5), and {Pt6}(CC-(1,4)C6H4-C2H3N(C8H17)C60)2, (6), were obtained by reacting the formyl clusters 2 and 4 with an appropriate amount of N-octylglycine and C60. Cyclovoltammetric and IR, UV and NIR spectroelectrochemical data suggest the absence of a significant communication between the cluster and the fullerene units in covalent assemblies 5 and 6. The crystal and molecular structure of compound 3 is also reported.

The hexanuclear cluster {Pt(6)}H(2) (2) contains a sterically hindered and chemically stable {Pt(6)} = Pt(6)(mu-PtBu(2))(4)(CO)(4) core, with the six metals forming an edge-bridged tetrahedron. The two hydrides are the reactive sites of the cluster and lie on opposite sides of the cluster, terminally bonded to the two "apical" edge-bridging platinum centres. Indeed, cluster 2 reacts with acids of different acidity (HA = CF(3)SO(3)H, HBF(4), p-CH(3)-C(6)H(4)-SO(3)H, CF(3)COOH, PhCOOH and CH(3)COOH), affording, after evolution of two equivalents of dihydrogen, the corresponding anion-substituted clusters {Pt(6)}A(2) (4). We suggest that the reaction proceeds through a mechanism similar to the one generally accepted for the analogous protonation of mononuclear hydrides, with some of the intermediates partially characterised at low temperature. Interestingly, the reverse reaction, the heterolytic splitting of H(2) by clusters 4, occurs readily under mild conditions. The anions in clusters 4a and 4b (4a: A = CF(3)SO(3), 4b: A = BF(4)) are bonded in the solid state but very easily dissociate in solution and may be substituted under mild conditions by weak ligands, such as CH(2)Cl(2) or CH(3)CN. With dialkyl ethers, the reaction proceeds further with the heterolytic splitting of a C-H bond of the ethereal ligand. This process allowed us to isolate the polymer [{Pt(6)}(CH(2)OCH(2)CH(2)OCH(2))](x) (8), in which the {Pt(6)} cluster units are connected by insulating spacers arising from dimethoxyethane. The results of single-crystal X-ray diffraction studies on 4a and 8 are also reported.