Cyclometallating units

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 Rh(III) and Ir(III) cyclometallated units present in some of our compounds show (1) intense LC absorption bands in the UV region and weak bands, mainly of MLCT character, in the visible region of the spectrum (2) irreversible, presumably metal-based oxidation processes and (3) reversible one-electron reduction of... 

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... 

The tetrahedral [160-163] and cis-planar [100,134,164-167] structures are characteristic for chelates of type 874 with coordination units NiN4 and MN2S2, respectively, as well as chelates 868 discussed above. Original polyhedral forms were discovered by x-ray diffraction for nickel and palladium ICC of the discussed type 874. It is accepted that, in case of a nickel complex, the compound with a carbon-carbon bond 875 is formed [165,166] formation of palladium chelates is accompanied by the cyclometallation reaction leading to tetranuclear clusters 876, where the tridentate ligand behaves as C,N,S-donor [168]. 

Recently An et al. disclosed a palladium(II)-catalyzed bis(peroxidation)/cycli-zation method for the synthesis of 3-(peroxymethyl)-3-peroxyoxindoles 209 from N - ar y 1 aery I a m i d e s 208 (Fig. 52) [235]. Using 5 mol% of Pd(OAc)2 in the presence of terf-butyl hydroperoxide, 46-96% of products 209 were obtained. The reactions were proposed to involve a Pd-catalyzed radical bis(peroxidation) of the acrylic unit [236] followed by a two-electron directed cyclometalation/reductive elimination reaction of intermediate bis(peroxide) 208A. 

Four luminescent cyclometallated iridium(III) diimine complexes [Ir(ppy-spacer-biotin)2(NAN)]+ (NAN = Me4-phen, Ph2-phen) (38), each containing two biotin units, have been synthesised and characterised by Lo and co-workers [79], Photoexcitation of these iridium(III) diimine bis(biotin) complexes in fluid solutions at 298 K and in alcohol glass at 77 K results in intense and long-lived 3MLCT (djr(Ir) — ti (NaN))/3IL (ir —> ji ) (Me4-phen) emission. HABA assays and emission titrations indicate that the two biotin moieties of each complex are functional. RET-based emission-quenching experiments, microscopy studies using avidin-conjugated microspheres, and HPLC analysis all reveal that the complexes with a... 

A dinuclear cyclometalated platinum(II) complex [Pt2L2 (dppm)] + (L = 4-(jo-diethylphosphonophenyl)-6-phenyl-2, 2 -bipyridine) has been employed as a luminescent probe for SDS micelles. Addition of SDS micelles to an aqueous solution of the complex led to an entission band at 530 mn, which was similar to the MLCT emission of mononuclear species. The observations were attributed to the absence of intramolecular and/or intermolecular Pt(II) Pt(II) interactions when the complex was incorporated in the SDS nticelles. Addition of NaCl solution into a micellar solution of the complex resulted in an additional MMLCT ((da )— (tt )) emission band at 650 nm. It was suggested that addition of sodium cations would force two cyclometalated platinum(II) units sufficiently close for intramolecular metal-metal and/or ligand-ligand interactions to occur, and thus the observation of MMLCT luminescence. 

Figure 14. Kb values, from intervalence measurements, on a log scale, as a function of the through-space metal-metal distance +, ruthenium bipyridylpolyene complexes (series 1) , ruthenium bis(terpyridyl) complexes (series 2) , ruthenium bis(cyclometallated) complexes, dipyridylbenzene family (series 3) , ruthenium bis(cyclometallated) complexes, phenylpyridine family (series 4) A, bis(ferrocenyl)polyenes (series 5). Additional measurements a, bis(cyclometallated) complexes, phenylpyridine family with diethynylanthracene as spacer b, bis(ferrocene) with three phenylene and four vinylene units as spacer c, bis[ruthenium(trisbipyridyl)] with five double bonds as spacer. Note that the Cp (dppe)Fe system bridged by octatetrayne (13 A, 0.32 eV) is outside the graph.

In a similar way the pinene-phenylpyridine H[46] was prepared. Thus upon treatment of 4,5-(/f,/f)-pinene-2-phenylpyridine H[46] with IrCls.SHaO, the HEXOL-type tetranuclear iridium complexes [Ir IrCl2(46)2 3] were obtained as two isomers (5.67ab) in a ratio of 5 3 (Scheme 5.25). Each complex can be described as an inner core of HEXOL-type [Ir(IrCl2)3] units and a surface of six chiral bidentate cyclometallated ligands (46). 

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