Cyclometallated complexes

Recently, three classes of cyclometallated complexes have been reported to show interesting second-order NLO properties, therefore opening a novel route for the design of new efficient second-order NLO chromophores. 

New orthopalladated NLO chromophores based on a parallel alignment of two different push-pull ligands have been synthesized by Centore et al. [153] and their second-order NLO activity has been measured by the EFISH technique working in CHCI3 with an incident wavelength of 1.907 pm. The maximum value of p Si.9i(EFISH) (610 x 10 esu) was obtained for the NLO chromo- 

Corona-poled thin polymeric films of 44 containing as guests this kind of NLO chromophores are characterized by large macroscopic NLO coefficients (25 pm V ), as determined by means of SHG measurements working with an incident wavelength of 1.064 pm [154]. 

Recently, Labat et al. [155] studied the second-order NLO properties of a new cyclometallated complex (45) for which the HRS technique, working in acetonitrile, gives a ySo(HRS) value of 230 x 10 ° esu. In this particular NLO chromophore the Ru moiety seems to act as the donor group of a push-pull system. 

LUMOs Ji orbitals of the phenanthroline [161]. Therefore, the secraid-order NLO response is strongly cOTitroUed by the donor or acceptor properties of the substituent on the phenanthroline ligand. 

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Reaction of the cyclometallated complexes 244-246 with pyrazole and excess sodium hydride affords cyclic dimers 247 (990M3991), where C N denotes the corresponding cyclometallated ligand in accordance with structures 244-246. The [Pt2(thienylpyridine)2(/j.-pz)](C104)3] is known as well. 

Diphenylimidazole with palladium acetate forms the cyclometallated complex 80 (X = OAc) (97AOC491). The acetate group is replaced by chloride or bromide when 80 (X = OAc) reacts with sodium chloride or lithium bromide, respectively, to give 80 (X = C1, Br). Bromide with diethyl sulfide forms the mononuclear complex 81. Similar reactions are known for 1 -acetyl-2-phenylimidazole (96JOM(522)97). 1,5-Bis(A -methylimidazol-2-yl)pen-tane with palladium(II) acetate gives the cyclometallated complex 82 (OOJOM (607)194). 

Treatment of the cyclometallated complexes [Au(N,N,C)Cl][PF6] [N,N,CH = 6-methylbenzyl- (a) or 6-(l,l-dimethylbenzyl)-2,2 -bipyridine (b)] [20] with KOH or Ag20 in aqueous media affords the hydroxo complexes [Au(N,N,C)(OH)][PF6] (36) in fairly good yields [45b, 101] these are air-stable white solids, quite soluble in water and in many organic solvents. When refluxed in anhydrous THF they condense to give the oxo-bridged complexes [Au2(N,N,C)2( J--0)] (37) (Equation 2.10 in Scheme 2.5) which, in turn, can be obtained by a different route [102] (see Section 3.2) the reaction can be reversed by refluxing the 0x0 complex in water. 

The terdentate cyclometalated complexes [Ir(L)(L )]2+ and [Ir(L )2]1, L = 2,6-bis(7 -methyl-4 -phenyl-2 -quinoyl)pyridine (233), L = monoanion of L (234), luminesce at 77 K in MeOH/EtOH (lmax = 592 nm, r =20 ps) and at room temperature in deoxygenated acetonitrile (imax 620 nm, r = 325 ns).405 Both compounds undergo four reversible, ligand-centered, one-electron reduction processes. 

Treatment of the cyclometallated complex [Au(C,N,N)C1]PF6 (I IC,N,/V zyl)-2,2 -bipyridine) with KOH in aqueous media gave the hydroxo xrvnmiPK, 1777,177s... 

The ruthenium(II) polypyridyl complexes are also popular but the brightnesses do not exceed 15,000 and thermal quenching is rather significant. This property can be utilized to design temperature-sensitive probes providing that the dyes are effectively shielded from oxygen (e.g., in polyacrylonitrile beads). Despite often very high emission quantum yields the visible absorption of cyclometallated complexes of iridium(III) and platinum(II) is usually poor (e < 10,000 M-1cm-1), thus,... 

C-bound K -phosphoramidite in addition to a K -phosphoramidite (Scheme 11). This cyclometalated complex was identified by NMR spectroscopy and X-ray crystallography [70]. A cyclometalated species had been proposed to form in reactions catalyzed by [lr(COD)Cl]2 and P(OPh)3. However, no complexes were isolated from this mixture or shown to be competent to catalyze allylic substitution [45]. 

The versatility of the quinolyl derivative (295) is exemplified in the complex [Ru(295-A,A )(295-A,A, A")C1]. The coordination behavior of (295) has been compared with those of (296) and (297) and factors influencing didentate vs. tridentate preferences have been examined. Perchlorate salts of [Ru(tpy)L)] " and [RUL2] where L = (298)-(300) have been synthesized and characterized, and their properties compared with those of [Ru(tpy)2] ". Complexation of Ru with 2,6-bis(4 -phenyl-2 -quinolyl)pyridine (L) affords [RUL2] , spectrosccmic properties of which have been discussed. " The bis(7 -methyl)-derivative of this ligand, L, has also been prepared and incorporated into the complexes [M(L )2f, [ (L CIs] (M = Ru, Os), and [Ru(L )(tppz)] + where tppz = 2,3,5,6-tetra(2 -pyridyl)pyrazine. Related cyclometallated complexes have also been studied. All the complexes luminesce at 77 K and [M(L )2] (M = Ru or Os), [Ru(L )(L )] , and two of the cyclometallated species are luminescent at room... 

The choice of an ionic liquid was shown to be critical in experiments with [NBuJBr (TBAB, m.p. 110°C) as a catalyst carrier to isolate a cyclometallated complex homogeneous catalyst, tra .s-di(ri-acetato)-bis[o-(di-o-tolylphosphino) benzyl] dipalladium (II) (Scheme 26), which was used for the Heck reaction of styrene with aryl bromides and electron-deficient aryl chlorides. The [NBu4]Br displayed excellent stability for the reaction. The recycling of 1 mol% of palladium in [NBu4]Br after the reaction of bromobenzene with styrene was achieved by distillation of the reactants and products from the solvent and catalyst in vacuo. Sodium bromide, a stoichiometric salt byproduct, was left in the solvent-catalyst system. High catalytic activity was maintained even after the formation of visible palladium black after a fourth run and after the catalyst phase had turned more viscous after the sixth run. The decomposition of the catalyst and the formation of palladium... 

Cyclobutanones, Solution Phase Photochemistry of (Morton and Turro). Cyclometallated Complexes, Photochemistry and Luminescence of (Maestri, Balzani, Deuschel-Cornioley, and von Zelewsky). 

Also cyclometallated complexes involving an additional C-M bond with a remote carbon atom are described (Equation 5) <2003JOM(688)112>. 

Dinuclear cyclometallated complexes are usually prepared starting from the metal chloride and the cyclometallating ligand (Figure 5, top). The same type of synthesis can be used to prepare cyclometallated complexes of high nuclearity. As an example, the recently reported synthesis of a hexanuclear cyclometallated complex is shown in Figure 5, bottom. ... 

Figure 5. (a) Metal chlorides can react with simple cyclometalating ligands to give dinuclear cyclometallated complexes, (b) Schematic representation of the synthesis of a hexanuclear complex containing cyclometallated units. ... 

The hexanuclear cyclometallated complex 61 (Scheme 1 and Table 1) shows a single reversible oxidation process at +1.31 V (Table 2), which involves four electrons. This process can be attributed to the oxidation of the four, almost noninteracting, peripheral Ru(ll) metals. The lack of other oxidation processes is an expected result since the increase (+4) in the charge of the complex displaces the oxidation of the core outside the accessible potential window. 

Extremely high ECL efficiencies seem to be a common feature of the homoleptic-IrL3 as well as the heteroleptic-L2Ir(X) iridium(III) cyclometallated complexes. Extremely high ECL efficiencies (up to 0.55) were observed via ion annihilation between the electrochemically generated L2Ir(acac)+ or L2Ir(pico) + cations (where... 

The complex Cp TaMe3(NMe2) undergoes loss of methane to generate a cyclometallated complex (equation 94).247 The reaction is first order with kHjkD = 9.7 at 34°C when using N(CD3)2 ligands.247... 

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