Site Selectivity in the Reactions of the Hexanuclear Platinum Cluster [Pt₆(μ‐PtBu₂)₄(CO)₆][CF₃SO₃]₂

Abstract

The previously reported hexanuclear cluster [Pt(6)(mu-PtBu(2))(4)(CO)(6)](2+)[Y](2) (1-Y(2): Y=CF(3)SO(3) (-)) contains a central Pt(4) tetrahedron bridged at each of the opposite edges by another platinum atom; in turn, four phosphido ligands bridge the four Pt-Pt bonds not involved in the tetrahedron, and, finally, one carbonyl ligand is terminally bonded to each metal centre. Interestingly, the two outer carbonyls are more easily substituted or attacked by nucleophiles than the inner four, which are bonded to the tetrahedron vertices. In fact, the reaction of 1-Y(2) with 1 equiv of [nBu(4)N]Cl or with an excess of halide salts gives the monochloride [Pt(6)(mu-PtBu(2))(4)(CO)(5)Cl](+)[Y], 2-Y, or the neutral dihalide derivatives [Pt(6)(mu-PtBu(2))(4)(CO)(4)X(2)] (3: X=Cl; 4: X=Br; 5: X=I). Moreover, the useful unsymmetrically substituted [Pt(6)(mu-PtBu(2))(4)(CO)(4)ICl] (6) was obtained by reacting equimolar amounts of 2 and [nBu(4)N]I, and the dicationic derivatives [Pt(6)(mu-PtBu(2))(4)(CO)(4)L(2)](2+)[Y](2) (7-Y(2): L=(13)CO; 8-Y(2): L=CNtBu; 9-Y(2): L=PMe(3)) were obtained by reaction of an excess of the ligand L with 1-Y(2). Weaker nitrogen ligands were introduced by dissolving the dichloride 3 in acetonitrile or pyridyne in the presence of TlPF(6) to afford [Pt(6)(mu-PtBu(2))(4) (CO)(4)L(2)](2+)[Z](2) (Z=PF(6) (-), 10-Z(2): L=MeCN; 11-Z(2): L=Py). The "apical" carbonyls in 1-Y(2) are also prone to nucleophilic addition (Nu(-): H(-), MeO(-)) affording the acyl derivatives [Pt(6)(mu-PtBu(2))(4)(CO)(4)(CONu)(2)] (12: Nu=H; 13: Nu=OMe). Complex 12 is slowly converted into the dihydride [Pt(6)(mu-PtBu(2))(4)(CO)(4)H(2)] (14), which was more cleanly prepared by reacting 3 with NaBH(4). In a unique case we observed a reaction involving also the inner carbonyls of complex 1, that is, in the reaction with a large excess of the isocyanides R-NC, which form the corresponding persubstituted derivatives [Pt(6)(mu-tPBu(2))(4)(CN-R)(6)](2+)[Y](2), (15-Y(2): R=tBu; 16-Y(2) (2-): R=-C(6)H(4)-4-C triple bond CH). All complexes were characterized by microanalysis, IR and multinuclear NMR spectroscopy. The crystal and molecular structures of complexes 3, 5, 6 and 9-Y(2) are also reported. From the redox viewpoint, all complexes display two reversible one-electron reduction steps, the location of which depends both upon the electronic effects of the substituents, and the overall charge of the original complex.

Synthesis and Electrochemical Characterization of Halide, Isocyanide, and Alkynyl Synthons Containing the Encumbered Triangular Cluster Unit Pt3(μ-PtBu2)3

“…Indeed, a comparison of the redox potentials of the isocharged 1 + , 18 + , and 19 + suggests that they are more sensitive to the nature of the terminal ligands, and that Coulombic effects exerted by the decrease of the overall positive charge in 2 − 10 have only a minor effect. A similar behavior has been recently observed in the family of hexanuclear platinum clusters [{Pt 6 }(L) 6− n (X) n ] (2− n )+ , in which the replacement of one or two apical carbonyl ligands produces significant cathodic shifts of all of the redox changes and causes the appearance of a new oxidation process in the experimental window …”

A molecular wire incorporating a robust hexanuclear platinum cluster

“…Significant IR and NMR parameters for 3 and 4 (see Experimental) compare well with corresponding data for analogous derivatives characterized by X-ray diffraction. 7 These data, together with satisfactory microanalyses, support the structures shown in Scheme 1. As expected on the basis of the general redox behaviour of the family of clusters {Pt 6 }X 2 , 7 compound 3 undergoes a chemically-reversible one-electron reduction at E1 = À1.49 V, and a second, less reversible reduction at À1.64 V vs. saturated calomel electrode (SCE; CH 2 Cl 2 , 0.2 M Bu 4 NPF 6 ; Pt, Au or ITO working electrode).…”

“…Recently, a family of remarkably stable, redox-active clusters with unusual reactivity, [Pt 6 (CO) 4 (P t Bu 2 ) 4 L 2 ] x+ , hereinafter referred to as {Pt 6 }L 2 x+ , has been described. [5][6][7] These have the structure indicated in Scheme 1. The dication {Pt 6 }(CO) 2 2+ readily undergoes substitution of two terminal carbonyl ligands on the peripheral Pt atoms, to give {Pt 6 }L 2 x+ (x = 2, L = inter alia RNC, RCN, PMe 3 ; x = 0, L = Cl [1], I).…”

“…The dication {Pt 6 }(CO) 2 2+ readily undergoes substitution of two terminal carbonyl ligands on the peripheral Pt atoms, to give {Pt 6 }L 2 x+ (x = 2, L = inter alia RNC, RCN, PMe 3 ; x = 0, L = Cl [1], I). 7 The {Pt 6 } cluster unit is stable enough to permit the synthesis of multicluster dendrimers with s-alkynyl spacers, 8 and alternating cluster-phenyleneethynylene oligomers, 9,10 by Cu(I)-mediated reaction of 1 with terminal alkynes. Such supramolecular metal cluster systems could be of interest in molecular-scale electronics, providing that they can be shown to be stable enough to be incorporated intact into devices.…”

Synthesis and characterization of non-bridging mono- and bis-σ-η1-alkynyl derivatives of the phosphido-bridged hexaplatinum core [Pt6(μ-PBut2)4(CO)4]2+

“…11 Other bonding modes, in which the alkynyl ligand bridges four or more metal centres, are far less represented. 12 We have already shown 13 that hexanuclear clusters of general formula [Pt 6 (μ-PBu t 2 ) 4 (CO) 4 L n X 2−n ] n+ , sterically protected by the bulky bridging phosphides, have a thermally and chemically stable [Pt 6 (μ-PBu t 2 ) 4 (CO) 4 ] 2+ core (hereafter shortly represented by the notation {Pt 6 }) and two reactive positions located at the two opposite extremes of the major longitudinal molecular axis. These are useful pre-requisites for the construction of ordered covalent structures containing {Pt 6 } subunits connected to each other, or to other cluster units, by bis-or tris-alkynyl spacers.…”