An outer-sphere two-electron platinum reagent

Luminescent Platinum(II) Dimers with a Cyclometallating Aryldiamine Ligand

Triflate salts of three (Pt(pip2NCN))2(mu-L)2+ (pip2NCNH = 1,3-bis(piperidylmethyl)benzene) dimers bridged by a series of nitrogen-donor ligands (L = pyrazine (pyz), 1,2-bis(4-pyridyl)ethane (bpa), trans-1,2-bis(4-pyridyl)ethylene (bpe)) are reported. These complexes have been fully characterized by 1H NMR spectroscopy and elemental analysis. The X-ray crystal structures of [(Pt(pip2NCN))2(mu-pyz)](CF3SO3)2 and [(Pt(pip2NCN))2(mu-bpe)](CF3SO3)2 x 2CH2Cl2 are reported. [(Pt(pip2NCN))2(mu-pyz)](CF3SO3)2: triclinic, P, a = 12.5240(5) A, b = 14.1570(6) A, c = 14.2928(6) A, alpha = 106.458(1) degrees , beta = 92.527(1) degrees , gamma = 106.880(1) degrees , V = 2303.46(17) A(3), Z = 2. [(Pt(pip2NCN))2(mu-bpe)](CF3SO3)2 x 2CH2Cl2: monoclinic, P21/c, a = 10.1288(6) A, b = 16.3346(9) A, c = 17.4764(10) A, beta = 90.882(2) degrees , V = 2891.1(3) A3, Z = 2. These structures and solution measurements provide evidence for the strong trans-directing properties of the pip2NCN- ligand. The electronic structures of these complexes and those of the 4,4'-bipyridine (bpy) dimer, (Pt(pip2NCN))2(mu-bpy)2+, also have been investigated by UV-visible absorption and emission spectroscopies, as well as cyclic voltammetry. The accumulated data indicate that variations in the bridging ligands provide remarkable control over the electronic structures and photophysics of these complexes. Notably, the bpa dimer exhibits a broad, low-energy emission from a metal-centered 3LF excited state, whereas the bpe and bpy dimers exhibit structured emission from a lowest pyridyl-centered 3(pi-pi*) excited state. In contrast, the pyz dimer exhibits remarkably intense yellow emission tentatively assigned to a triplet metal-to-ligand charge-transfer excited state.

Vapochromism and Its Structural Basis in a Luminescent Pt(II) Terpyridine−Nicotinamide Complex

A novel Pt(II) terpyridine complex that has a nicotinamide moiety linked to the terpyridyl ligand has been synthesized in good yield and studied structurally and spectroscopically. The complex, [Pt(Nttpy)Cl](PF(6))(2) where Nttpy = 4'-(p-nicotinamide-N-methylphenyl)-2,2':6',2' '-terpyridine, is observed to be brightly luminescent in the solid state at room temperature and at 77 K. The complex exhibits reversible vapochromic behavior and crystallographic change in the presence of several volatile organic solvents. Upon exposure to methanol vapors, the complex changes color from red to orange, and a shift to higher energy is observed in the emission maximum with an increase in excited-state lifetime and emission intensity. The crystal and molecular structures of the orange and red forms, determined by single-crystal X-ray diffraction on the same single crystal, were found to be equivalent in the molecular sense and only modestly different in terms of packing. In both forms, the cationic Pt(II) complexes possess distorted square planar geometries. Analysis of the orange form's crystal packing reveals the presence of solvent molecules in lattice voids, Pt...Pt separations averaging 3.75 A and a zigzag arrangement between nearest neighbor Pt atoms, whereas the red form is devoid of solvent within the crystal lattice and contains complexes stacked with a nearly linear arrangement of Pt(II) ions having an average distance of 3.33 A. On the basis of the crystallographic data, it is evident that sorption of methanol vapor induces a change in intermolecular contacts and Pt...Pt interactions in going from red to orange. Disruption of the d(8)-d(8) metallophilic interactions consequently alters the emitting state from (3)[(d)sigma*-pi*(terpyridine)] that is formally a metal-metal-to-ligand charge transfer (MMLCT) state in the red form to one in which the HOMO corresponds to a more localized Pt(d) orbital in the red form ((3)MLCT).

A Platinum−Ruthenium Dinuclear Complex Bridged by Bis(terpyridyl)xanthene

4,5-Bis(terpyridyl)-2,7-di-tert-butyl-9,9-dimethylxanthene (btpyxa) was prepared to serve as a new bridging ligand via Suzuki coupling of terpyridin-4'-yl triflate and 2,7-di-tert-butyl-9,9-dimethylxanthene-4,5-diboronic acid. The reaction of btpyxa with either 1 equiv or an excess of PtCl(2)(cod) (cod = 1,5-cyclooctadiene) followed by anion exchange afforded mono- and dinuclear platinum complexes [(PtCl)(btpyxa)](PF(6)) ([1](PF(6))) and [(PtCl)(2)(btpyxa)](PF(6))(2) ([2](PF(6))(2)), respectively. The X-ray crystallography of [1](PF(6)).CHCl(3) revealed that the two terpyridine units in the ligand are nearly parallel to each other. The heterodinuclear complex [(PtCl)[Ru((t)Bu(2)SQ)(dmso)](btpyxa)](PF(6))(2) ([4](PF(6))(2)) (dmso = dimethyl sulfoxide; (t)Bu(2)SQ = 3,5-di-tert-butyl-1,2-benzosemiquinone) and the monoruthenium complex [Ru((t)Bu(2)SQ)(dmso)(trpy)](PF(6)) ([5](PF(6))) (trpy = 2,2':6',2' '-terpyridine) were also synthesized. The CV of [2](2+) suggests possible electronic interaction between the two Pt(trpy) groups, whereas such an electronic interaction was not suggested by the CV of [4](2+) between Pt(trpy) and Ru((t)Bu(2)SQ) frameworks.

A Luminescent Platinum(II) 2,6-Bis(N-pyrazolyl)pyridine Complex

Four platinum(II) cationic complexes were prepared with the mer-coordinating tridentate ligands 2,6-bis(N-pyrazolyl)pyridine (bpp) and 2,6-bis(3,5-dimethyl-N-pyrazolyl)pyridine (bdmpp): [Pt(bpp)Cl]Cl.H(2)O; [Pt(bdmpp)Cl]Cl.H(2)O; [Pt(bpp)(Ph)](PF(6)); [Pt(bdmpp)(Ph)](PF(6)). The complexes were characterized by (1)H NMR spectroscopy, elemental analysis, and mass spectrometry, and the structures of the bpp derivatives were determined by X-ray crystallography. [Pt(bpp)Cl]Cl.2H(2)O: monoclinic, P2(1)/n, a = 11.3218(5) A, b = 6.7716(3) A, c = 20.6501(6) A, beta = 105.883(2) degrees, V = 1522.73(11) A(3), Z = 4. The square planar cations stack in a head-to-tail fashion to form a linear chain structure with alternating Pt...Pt distances of 3.39 and 3.41 A. [Pt(bpp)(Ph)](PF(6)).CH(3)CN: triclinic, P, a = 8.3620(3) A, b = 10.7185(4) A, c = 13.4273(5) A, alpha = 96.057(1) degrees, beta = 104.175(1) degrees, gamma = 110.046(1) degrees, V = 1072.16(7) A(3), Z = 2. Cyclic voltammograms indicate all four complexes undergo irreversible reductions between -1.0 and -1.3 V vs Ag/AgCl (0.1 M TBAPF(6)/CH(3)CN), attributable to ligand- and/or metal-centered processes. By comparison to related 2,2':6',2' '-terpyridine complexes, the electrochemical and UV-visible absorption data are consistent with bpp being both a weaker sigma-donor and pi-acceptor than terpyridine. Solid samples of [Pt(bpp)(Ph)](PF(6)) at 77 K exhibit a remarkably intense, narrow emission centered at 655 nm, whereas the other three complexes exhibit only very weak emission.

Tuning the Electronic Structures of Platinum(II) Complexes with a Cyclometalating Aryldiamine Ligand

Triflate salts of four platinum(II) pyridyl complexes with a mer-coordinating tridentate pincer ligand, pip(2)NCN(-) (pip(2)NCNH = 1,3-bis(piperidylmethyl)benzene), are reported: Pt(pip(2)NCN)(L)(+) (2, L = pyridine; 3, L = 4-phenylpyridine; 5, L = 2,6-pyridinedimethanol) and [(Pt(pip(2)NCN))(2)(micro-4,4'-bipyridine)](2+) (4). The complexes have been fully characterized by (1)H NMR spectroscopy, elemental analysis, and X-ray crystallography. Compound 2(CF(3)SO(3)(-)): triclinic, P1, a = 9.7518(6) A, b = 12.0132(8) A, c = 12.6718(9) A, alpha = 114.190(2) degrees, beta = 100.745(3) degrees, gamma = 103.545(2) degrees, V = 1247.95(14) A(3), Z = 2. Compound 3(CF(3)SO(3)(-)): monoclinic, P2(1)/c, a = 15.550(2) A, b = 9.7386(11) A, c = 18.965(3) A, beta = 92.559(7) degrees, V = 2869.1(6) A(3), Z = 4. Compound 4(CF(3)SO(3)(-))(2).1/2(CH(3))(2)CO: monoclinic, I2/a, a = 21.3316(5) A, b = 9.6526(2) A, c = 26.1800(6) A, beta = 96.4930(10) degrees, V = 5356.0(2) A(3), Z = 4. Compound 5(CF(3)SO(3)(-)).3/2CHCl(3): monoclinic, P2(1)/n, a = 17.1236(10) A, b = 9.3591(5) A, c = 21.3189(11) A, beta = 96.11(3) degrees, V = 3397.2(3) A(3), Z = 4. The accumulated data indicate that the phenyl group of pip(2)NCN(-) labilizes the trans pyridyl ligand. The electronic structures were investigated using cyclic voltammetry, as well as UV-visible absorption and emission spectroscopies. Red emission from 2 in rigid media originates from a lowest triplet ligand field excited state, whereas yellow-green emissions from 3 and 4 originate from a lowest pyridyl ligand-centered triplet pi-pi state, indicating that substitution of the pyridyl ligand results in a dramatic change in the orbital character of the emissive state.