Redox-Active Metallodithiolene Groups Separated by Insulating Tetraphosphinobenzene Spacers

Compounds of the type [(S₂C₂R₂)M(μ-tpbz)M(S₂C₂R₂)] (R = CN, Me, Ph, p-anisyl; M = Ni, Pd, Pt; tpbz = 1,2,4,5-tetrakis(diphenylphosphino)benzene) have been prepared by transmetalation with [(S₂C₂R₂)SnR'₂] reagents, by direct displacement of dithiolene ligand from [M(S₂C₂R₂)₂] with 0.5 equiv of tpbz, or by salt metathesis using Na₂[S₂C₂(CN)₂] in conjunction with X₂M(μ-tpbz)MX₂ (X = halide). X-ray crystallography reveals a range of topologies (undulating, chair, bowed) for the (S₂C₂)M(P₂C₆P₂)M(S₂C₂) core. The [(S₂C₂R₂)M(μ-tpbz)M(S₂C₂R₂)] (R = Me, Ph, p-anisyl) compounds support reversible or quasireversible oxidations corresponding to concurrent oxidation of the dithiolene terminal ligands from ene-1,2-dithiolates to radical monoanions, forming [(^-S^•SC₂R₂)M(μ-tpbz)M(^-S^•SC₂R₂)]²⁺. The R = Ph and p-anisyl compounds support a second, reversible oxidation of the dithiolene ligands to their α-dithione form. In contrast, [(S₂C₂(CN)₂)Ni(tpbz)Ni(S₂C₂(CN)₂)] sustains only reversible, metal-centered reductions. Spectroscopic examination of [(^-S^•SC₂( p-anisyl)₂)Ni(μ-tpbz)Ni(^-S^•SC₂( p-anisyl)₂)]²⁺ by EPR reveals a near degenerate singlet-triplet ground state, with spectral simulation revealing a remarkably small dipolar coupling constant of 18 × 10^-4 cm^-1 that is representative of an interspin distance of 11.3 Å. This weak interaction is mediated by the rigid tpbz ligand, whose capacity to electronically insulate is an essential quality in the development of molecular-based spintronic devices.

Coordination chemistry and applications of versatile 4,5-diazafluorene derivatives

This review article highlights the versatile nature of 4,5-diazafluorene derivatives as ligands, and details some recent advances made using this ligand family.

An Extended Chain and Trinuclear Complexes Based on Pt(II)-M (M = Tl(I), Pb(II)) Bonds: Contrasting Photophysical Behavior

The syntheses and structural characterizations of a Pt-Tl chain [{Pt(bzq)(C6F5)2}Tl(Me2CO)]n 1 and two trinuclear Pt2M clusters (NBu4)[{Pt(bzq)(C6F5)2}2Tl] 2 and [{Pt(bzq)(C6F5)2}2Pb] 3 (bzq = 7,8-benzoquinolinyl), stabilized by donor-acceptor Pt → M bonds, are reported. The one-dimensional heterometallic chain 1 is formed by alternate "Pt(bzq)(C6F5)2" and "Tl(Me2CO)" fragments, with Pt-Tl bond separations in the range of 2.961(1)-3.067(1) Å. The isoelectronic trinuclear complexes 2 (which crystallizes in three forms, namely, 2a, 2b, and 2c) and 3 present a sandwich structure in which the Tl(I) or Pb(II) is located between two "Pt(bzq)(C6F5)2" subunits. NMR studies suggest equilibria in solution implying cleavage and reformation of Pt-M bonds. The lowest-lying absorption band in the UV-vis spectra in CH2Cl2 and tetrahydrofuran (THF) of 1, associated with (1)MLCT/(1)L'LCT (1)[5dπ(Pt) → π*(bzq)]/(1)[(C6F5) → bzq], displays a blue shift in relation to the precursor, suggesting the cleavage of the chain maintaining bimetallic Pt-Tl fragments in solution, also supported by NMR spectroscopy. In 2 and 3, it shows a blue shift in THF and a red shift in CH2Cl2, supporting a more extensive cleavage of the Pt-M bonds in THF solutions than in CH2Cl2, where the trinuclear entities are predominant. The Pt-Tl chain 1 displays in solid state a bright orange-red emission ascribed to (3)MM'CT (M' = Tl). It exhibits remarkable and fast reversible vapochromic and vapoluminescent response to donor vapors (THF and Et2O), related to the coordination/decoordination of the guest molecule to the Tl(I) ion, and mechanochromic behavior, associated with the shortening of the intermetallic Pt-Tl separations in the chain induced by grinding. In frozen solutions (THF, acetone, and CH2Cl2) 1 shows interesting luminescence thermochromism with emissions strongly dependent on the solvent, concentration, and excitation wavelengths. The Pt2Tl complex 2 shows an emission close to 1, ascribed to charge transfer from the platinum fragment to the thallium [(3)(L+L')MM'CT]. 2 also shows vapoluminescent behavior in the presence of vapors of Me2CO, THF, and Et2O, although smaller and slower than those of 1. The trinuclear neutral complex Pt2Pb 3 displays a blue-shift emission band, tentatively assigned to admixture of (3)MM'CT (3)[Pt(d) → Pb(sp)] with some metal-mediated intraligand ((3)ππ/(3)ILCT) contribution. In contrast to 1 and 2, 3 does not show vapoluminescent behavior.

Interaction of organoplatinum(II) complexes with monovalent coinage metal triflates

The organoplatinum(II) complexes [(NN)PtMe(2)] and [(NN)PtPh(2)] (NN = ArNC(Me)C(Me)NAr, Ar = 2,6-dichlorophenyl) can act as donor ligands for copper(I) and silver(I) triflates, affording a series of homo- and heteroleptic complexes which were characterized by X-ray diffraction. [(NN)PtMe(2)] binds to the coinage metals through short, ligand-unsupported d-d(10) contacts that are best described as Pt-->M dative bonds (M = Cu, Ag), in which the d(z(2)) orbital of the square-planar Pt(II) center donates electron density to the Lewis-acidic metal. Spectroscopic studies in solution and DFT calculations corroborate this description. [(NN)PtPh(2)] binds preferentially by eta(1) or eta(2) complexation of the ipso carbon atoms of the phenyl groups to the coinage metal, affording homoleptic complexes {[(NN)PtPh(2)](2)M}(+){TfO}(-) in the solid state. The 1:1 adducts of formula {[(NN)PtPh(2)]M(OTf)}(n) (M = Cu, n = 1; M = Ag, n = 2) are observed in solution, and a 1:2 adduct of formula {[(NN)PtPh(2)]Ag(2)(OTf)(2)(C(6)H(6))}(n) was characterized in the solid state, showing that unsupported Pt-->M bonds are also accessible for [(NN)PtPh(2)]. The thermolyses of the complexes [(NN)PtMe(2)]MOTf in benzene affords moderate yields of [(NN)PtPh(2)] through an oxidatively induced double C-H activation process.