Cyclometalations, bis

Fig. 18 Schematic structures of cyclometalated bis-terdentate complexes the two terdentate planar systems are roughly perpendicular to each other...

The reaction of [CsF SiMesXhTi- -TdCsFrXSiMesXk with the diazoalkane Me3SiGHN2 leads to the isolation of a double cyclometallated bis-Cp complex, arising from facile intramolecular C-H activation of the Cp substituent by a transient titanocene alkylidene (Scheme 552), while treatment with the diazoalkane Ph2GN2 affords the corresponding diazoalkane compound.1443... 

Regioselective C-H Activation of Cyclometalated Bis-Tridentate Ruthenium Complexes... 

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). 

Rh(COE)2Cl]2 in the presence of IMes, MA -bis-[2,4,6-(trimethyl)phenyl]imi-dazol-2-ylidene, reacted with at room temperature to give the trigonal bipyrami-dal [Rh(H)2Cl(IMes)2] 6 (which is analogons to 3) via intermediate formation of the isolable cyclometallated 5 (Scheme 2.2) [3],... 

Further examples of emissive cyclometallated gold(III) complexes are [Au(L)Cl] (L = tridentate carbanion of 4 -(4-methoxyphenyl)-6 -phenyl-2,2 -bipyridine) [53], as well as mono- and binuclear bis-cyclometallated gold(III) complexes, namely [Au (C N C )L ]" (C N C = tridentate dicarbanion of 2,6-diphenylpyridine L = depro-tonated 2-mercaptopyridine (2-pyS ), n = 0 L = PPh3 or 1-methylimidazole, n = 1) and [Au2(C N C )2(P P)](C104)2 (P P = dppm, dppe) respectively [54]. The crystal structures of the binuclear derivatives show intramolecular interplanar separations of 3.4 A between the [Au(C N C)] moieties, implying the presence of weak n-n interactions. The mononuclear complexes show absorption with vibronic structure at 380-405 nm (e > 10 cm ), attributed to metal-perturbed intraligand transition. 

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. 

A trinuclear system, whose structure was published,555 was formed in high yield by the cyclometalation of a l,3-bis(alkylbenzimidazol-2-yl)benzene ligand, followed by the trimerization of the unit, which possesses a vacant coordination site on the palladium atom and a pendant noncoordinated benzimidazole moiety. The resulting product forms a cup-shaped trimer or tricorn, presented in Figure 46, that includes a molecule of acetonitrile in the crystal structure.556... 

A trinuclear system, formed in high yield by the cyclometalation of a l,3-bis(alkylbenzimidazol-2-... 

Colombo, M. G., Hauser, A., and Giidel, H. U. Competition Between Ligand Centered and Charge Transfer Lowest Excited States in bis Cyclometalated Rh3+ and Ir3+ Complexes. 171, 143-172(1994). 

Very recently, Ma has reported a rhodium-catalyzed route to 18,19-norsteroid skeletons from bis-allenes, involving a cyclometallation-carbometallation-reductive elimination-Diels-Alder reaction cascade process.410... 

This two-step synthetic method can thus be extended to the synthesis of bis-cyclometalated Ir(III) complexes (CAN)2Ir(LX) (249) (Scheme 3.77) [290],... 

S Lamansky, P Djurovich, D Murphy, F Abdel-Razzaq, HE Lee, C Adachi, PE Burrows, SR Forrest, and ME Thompson, Highly phosphorescent bis-cyclometalated iridium complexes synthesis, photophysical characterization, and use in organic light-emitting diodes, J. Am. Chem. Soc., 123 4304-4312, 2001. 

A wide range of carbon, nitrogen, and oxygen nucleophiles react with allylic esters in the presence of iridium catalysts to form branched allylic substitution products. The bulk of the recent literature on iridium-catalyzed allylic substitution has focused on catalysts derived from [Ir(COD)Cl]2 and phosphoramidite ligands. These complexes catalyze the formation of enantiomerically enriched allylic amines, allylic ethers, and (3-branched y-8 unsaturated carbonyl compounds. The latest generation and most commonly used of these catalysts (Scheme 1) consists of a cyclometalated iridium-phosphoramidite core chelated by 1,5-cyclooctadiene. A fifth coordination site is occupied in catalyst precursors by an additional -phosphoramidite or ethylene. The phosphoramidite that is used to generate the metalacyclic core typically contains one BlNOLate and one bis-arylethylamino group on phosphorus. 

The preparation of carbonyl-lr—NHC complexes (Scheme 3.1) and the study of their average CO-stretching frequencies [7], have provided some of the earliest experimental information on the electron-donor power of NHCs, quantified in terms of Tolman s electronic parameter [8]. The same method was later used to assess the electronic effects in a family of sterically demanding and rigid N-heterocyclic carbenes derived from bis-oxazolines [9]. The high electron-donor power of NHCs should favor oxidative addition involving the C—H bonds of their N-substituents, particularly because these substituents project towards the metal rather than away, as in phosphines. Indeed, NHCs have produced a number of unusual cyclometallation processes, some of which have led to electron-deficient... 

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... 

Addition of dmpe (Me2PCH2CH2PMe2) leads to a bis-cyclometallated complex.253 Some insight into how the metal interacts with, and eventually activates, the y-CH bonds of NfSiMe groups has come from the observation of a significant ground state interaction between the metal center and these methyl groups in the complex Yb[N(SiMe3)2]2(dmpe).254... 

Competition Between Ligand Centered and Charge Transfer Lowest Excited States in bis Cyclometalated Rh3+ and Ir3 Complexes... 

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