Synthesis and characterization of orthopalladated complexes containing tridentate C, N, O-oxazolones

The (Z)-4-aryliden-2-(2-acetoxyphenyl)-5(4H)oxazolones 1a-1c react with H2SO4 to give the corresponding (Z)-4-aryliden-2-(2-hydroxyphenyl)-5(4H)oxazolones 2a-2c.The molecular structures of 1c and 2a have been determined by X-ray diffraction methods, and show planar skeletons. Oxazolones 2a-2c are potential C, N, O-tridentate ligands towards transition metals, and their molecular design obeys to the search of a rigid environment around the metal. The reaction of Pd(OAc)2 with oxazolones 2a-2c (1:1 M ratio) in CF3CO2H or NCMe as solvents results in the synthesis of diverse complexes (3–7). As a function of the reaction conditions, two different bonding modes have been characterized: N, O-chelate in the dinuclear complexes Pd(¿2-N, O-2b, c)(µ -O2CCF3)]2 (3b, c), as a result of the N-coordination and deprotonation of the hydroxy group; and C, N, O-tridentate in mononuclear complexes Pd(¿ 3-C, N, O-2a, b)(L)] (L = CF3CO2H 4a, b; dmso-d6 5a, b; NCMe 6b; pyridine 7b), obtained after N-bonding, OH deprotonation and C–H bond activation. All complexes have been fully characterized by HRMS and NMR methods, showing the high stability of the C, N, O-tridentate bonding mode

Fluorescent Orthopalladated Complexes of 4-Aryliden-5(4H)-oxazolones from the Kaede Protein: Synthesis and Characterization

The goal of the work reported here was to amplify the fluorescent properties of 4-aryliden-5(4H)-oxazolones by suppression of the hula-twist non-radiative deactivation pathway. This aim was achieved by simultaneous bonding of a Pd center to the N atom of the heterocycle and the ortho carbon of the arylidene ring. Two different 4-((Z)-arylidene)-2-((E)-styryl)-5(4H)-oxazolones, the structures of which are closely related to the chromophore of the Kaede protein and substituted at the 2- and 4-positions of the arylidene ring (1a OMe; 1b F), were used as starting materials. Oxazolones 1a and 1b were reacted with Pd(OAc)2 to give the corresponding dinuclear orthometalated palladium derivates 2a and 2b by regioselective C-H activation of the ortho-position of the arylidene ring. Reaction of 2a (2b) with LiCl promoted the metathesis of the bridging carboxylate by chloride ligands to afford dinuclear 3a (3b). Mononuclear complexes containing the orthopalladated oxazolone and a variety of ancillary ligands (acetylacetonate (4a, 4b), hydroxyquinolinate (5a), aminoquinoline (6a), bipyridine (7a), phenanthroline (8a)) were prepared from 3a or 3b through metathesis of anionic ligands or substitution of neutral weakly bonded ligands. All species were fully characterized and the X-ray determination of the molecular structure of 7a was carried out. This structure has strongly distorted ligands due to intramolecular interactions. Fluorescence measurements showed an increase in the quantum yield (QY) by up to one order of magnitude on comparing the free oxazolone (QY < 1%) with the palladated oxazolone (QY = 12% for 6a). This fact shows that the coordination of the oxazolone to the palladium efficiently suppresses the hula-twist deactivation pathway

Organometallic Fluorophores of d8 Metals (Pd, Pt, Au)

International audienceIn this contribution, we review the state-of-the-art in the field of the synthesis and luminescent properties of cyclometalated complexes of noble d8 metals Pd(II), Pt(II), and Au(III), with a large variety of organic ligands. For platinum and gold complexes, special emphasis has been done in the last 3 years (2015–17), because a huge number of outstanding contributions of academic and even industrial interest have appeared in this short period of time, while cyclopalladated complexes have been analyzed with a wider temporal perspective. The intrinsic properties of the metals (oxidation state, geometry, electrophilic character, redox behavior) and the ligands (type of donor atoms, σ-donating strength, π-accepting ability, planarity, rigidity) have been analyzed to determine their influence in the synthesis, through different methods, of the respective cyclometalated complexes, and also in the photophysical properties (type of transitions, tuning as a function of the substituents, etc.). In some selected cases, the application of these complexes to industrial optical devices is presented

Saccharinate as a versatile polyfunctional ligand. Four distinct coordination modes, misdirected valence, and a dominant aggregate structure from a single reaction system

The reaction system consisting of copper, saccharinate, and the auxiliary ligands H 2O, PPh 3, and NH 3 produces a sequence of compounds in which saccharinate is coordinated to copper in four distinct manners. The complex trans-[Cu(sacch) 2(H 2O) 4] (2) (produced by thermal dehydration of trans-[Cu(sacch) 2(H 2O) 4] ·2H 2O (1)) reacts with triphenylphosphine in CH 2Cl 2 to produce any or all of three Cu(I) complexes, depending upon conditions. The three Cu(I) compounds are Cu(sacch)(PPh 3) 3 (3), in which saccharinate binds to copper through the carbonyl group of the ligand, Cu(sacch)(PPh 3) 2 (4), in which sacch binds to Cu through its charge-bearing nitrogen atom; and [Cu(sacch)(PPh 3)] 2 (5), a dinuclear complex in which saccharinate bridges two Cu centers through its imidate nitrogen and carbonyl oxygen atoms. Complexes 3-5 can be isolated individually, although in solution they exist in a complex equilibrium which has been examined by NMR spectroscopy. Each of the three Cu(I) products reacts with NH 3 in CH 2Cl 2 solution to produce trans-[Cu(sacch) 2(NH 3) 4] (6), an unstable Cu(II) complex that exhibits misdirected valence at the Cu-N(sacch) bond. Complex 6 evolves spontaneously to [Cu(sacch)(NH 3) 4](sacch)·H 2O (7), which in the solid state is dominated by a supramolecular aggregate of two formula units, linked by hydrogen bonding in which the water molecule plays a central role. Alternative pathways exist to several of the products. The X-ray crystal structure analyses of 3-7 are reported and establish the coordination modes of saccharinate, the misdirected valence in 6, and the supramolecular aggregation in 7. The structure analysis of 7 by single-crystal neutron diffraction is reported and together with the previously reported neutron structure analysis of 1 establishes the substitution of the auxiliary ligand H 2O by NH 3 in the Cu(II) products