Novel saccharinate-bridged palladium complexes for efficient C-O bond activation displaying promising luminescence properties.

The synthesis of mono- and dinuclear cyclometallated palladium(II) complexes with deprotonated saccharinate ligands displaying different coordination modes is described. The new compounds were prepared by direct reaction between saccharine and the corresponding hydroxo-complexes [{Pd(µ-OH)(C^N)}(2)] (C^N = 2-(2-pyridyl)phenyl (Phpy) I; = 7,8-benzoquinolyl (Bzq) II), showing a general formula [{Pd(µ-sac)(C^N)}(2)] with saccharinate 1 displaying a bridging -NCO-coordination mode. Bridge splitting with neutral ligands (L = pyridine (py) 2, quinoline (quinol) 3 or acridine (acrid) 4) yielded new mononuclear derivatives with saccharinate acting as an N-monodentated ligand. Structural characterization by X-ray diffraction of complexes I1, I2 and II2 confirmed the proposed formulae. All complexes emit in the solution and solid state at room temperature. Emission features between 640-680 nm in the solid state for complexes I1 and II1 are significantly red-shifted if compared to the emission in solution. These broad emissions are consistent with the simultaneous presence of (3)ππ* and (3)MMLCT transitions indicating the existence of a strong intramolecular Pd-Pd ground state interaction. The dimeric complexes have also shown to catalyze Suzuki-Miyaura cross-coupling of coumaryl tosylate and aryl boronic acids under phosphine-free conditions. Initial studies suggest the involvement of palladium nanoparticles, which has been further investigated using mercury-drop test and poisoning experiments.

Synthesis and luminescence properties of cyclopalladated complexes with S

The direct reaction between the hydroxo-complexes [{Pd(µ-OH)(C^N)}(2)] and protonated S^N-donor ligands to yield new dinuclear cyclometallated palladium(ii) complexes containing -NCS- bridging heterocyclic thionates of general formula [{Pd(µ-N^S)(C^N)}(2)] (C^N = 2-(2-pyridyl)phenyl (Phpy) I; = 7,8-benzoquinolyl (Bzq) II; N^S = pyrimidine-2-thionate (Spym) 1, benzoimidazolidine-2-thionate (Sbimid) 2, 1-methylimidazoline-2 thionate (Smeimid) 3) is described. The related mononuclear complexes [Pd(N^S)(C^N)] N^S = 2-aminothiophenolate (Atph) 4) were prepared in a similar way. Photophysical properties were investigated together with those of complexes with related ligands pyridin-2-thionate (Spy) 5 and pyrrole-2-carboxaldehydate (2-pcal) 6. All the compounds absorb intensely below 300 nm via(1)LC transitions located in Bzq or Phpy ligands, and display additional low energy absorptions of mixed (1)MLCT-(1)LC character. In the solid state diffuse reflectance UV-vis spectra, the differences are notable for dinuclear complexes. The complexes under study are quite unusual in terms of luminescence behaviour, since most of them are emissive in solution at room temperature and all display intense emissions in frozen CHCl(3) solution, but also in the solid state at 298 and 77 K. Emission quantum yields are in the range 2.52-0.14%, similar to that of related complexes. Structural characterisation by X-ray diffraction of complexes II3 and II6 confirmed the proposed formula.

Mono- and bidentate imidates of five-coordinate nickel(II) with macrocyclic ligands: spectroscopic and photophysical properties.

The hydroxo-complexes [Ni(2)(mcN(3))(2)(mu-OH)](2)(PF(6))(2)] [mcN(3) = 2,4,4-trimethyl-1,5,9-triazacyclododec-1-ene (Me(3)-mcN(3)) or 2,4,4,9-tetramethyl-1,5,9-triazacyclododec-1-ene (Me(4)-mcN(3))] react with imides (Him) in 1 : 2 (succinimide, glutarimide, saccharine and 1,8-naphthalimide) or 1 : 1 (pyromellitic diimide) molar ratio, leading to the formation of the imidate complexes: [Ni(mcN(3))(H(2)O)(Im)](+) (Im = succi, gluti, sac), [Ni(mcN(3))(naphthi)](+) and [Ni(mcN(3))(H(2)O)](2)(mu-pyrdi)](2+). The single crystal structures of [Ni(Me(3)-mcN(3))(H(2)O)(sac)](PF(6)) (3a) and [Ni(Me(4)-mcN(3))(H(2)O)(sac)](sac) (3b) show that, in 3a, sac exhibits a N-monodentate coordination mode, while in 3b the coordination is through oxygen. X-Ray structure of [Ni(Me(4)-mcN(3))(naphthi)](PF(6)) (4b) shows N,O-bonded 1,8-naphthalimidate ligand. The VT (1)H NMR study, carried out on this complex, suggests that the rotation around the Ni-N bond is hindered by ca. 11.6 kcal mol(-1). These species exhibit blue luminescence which arises from a mixed MLCT and LC excited state, and these properties may be useful for structural predictions in the solid state of complexes for which crystal structures have not been established.

Luminescence of five-coordinated nickel(ii) complexes with substituted-8-hydroxyquinolines and macrocyclic ligands.

A series of heteroleptic quinolinolate pentacoordinated nickel(ii) complexes, [Ni(mcN(3))(R(1),R(2),R(3)-8-hq)](PF(6)), were synthesized and characterized by spectroscopic methods. Single-crystal X-ray diffraction studies for [(Me(3)-mcN(3))Ni(N,O-2-CN-8-hq)][PF(6)] (6a), [(Me(4)-mcN(3))Ni(N,O-8-hq)][PF(6)] (2b) and [(Me(4)-mcN(3))Ni(N,O-5,7-I(2)-8-hq)][PF(6)] (5b) indicate that these complexes consist of a square-pyramidal ligand arrangement containing one chelating quinolinolate and one macrocyclic ligand (mcN(3)). Variation of the substituents on quinolinolate ligands imposes obvious electronic or structural effects on the nickel atom. These chromophores absorb moderately in the visible region and emit in the yellowish-green spectral region from a quinolinolate-centered intraligand charge-transfer excited state. The emission maxima are in the range 520-548 nm, with quantum yields between 0.11 and 1.63%, in deoxygenated organic solvents at room temperature. TD-DFT calculations allow exploration of the photophysical properties of complex [(Me(4)-mcN(3))Ni(N,O-8-hq)][PF(6)] and reveal the influence of the quinolinolate ligand on the HOMO/LUMO energies and oscillator strengths.