6- -2,2 -bipyridine cyclometalated complexes

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. 

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... 

More recent work include examples from several groups. Neve, Cam-pagna et al. and Quid, Campagna et al. have investigated the systems displayed in Fig. 23 [120,123]. A heterometallic cyclometalated complex [(PPy)2lr( x-L-0C(0)-L)Re(C0)3Br]+ with L-OC(O) - L = 4- (6 -phen-yl-2,2/-bipyridine-4/-yl)benzoyloxy]phenyl -6/phenyl-2,2/-bipyridine,... 

Organoruthenium and organoosmium compounds of polypyridine ligands offer alternative coordination modes of these ligands. In the cyclometalated complexes the ri (Ni, C2) coordination mode occurs. In some clusters the ri (Ni, C2) donor function is manifested. The latter becomes possible in clusters of 4,4 -bipyridine ligands, which otherwise play their traditional bridging function. 

Cyclometallated complexes have also been prepared using bipyridines which cannot form a chelate ring, as for example, 2,4 -bpy [47] ... 

In recent years, square planar platinum(II) systems bearing cyclometalating tridentate ligands based on 6-phenyl-2,2 -bipyridine have been demonstrated to offer favorable photophysical characteristics compared to 2,2 6, 2"-terpyridine analogues, and interest in these luminescent cyclometalated complexes has proliferated [16, 17, 38]. Like tris(2,2 -bipyridine)rutheni-... 

The 2-phenylpyridine-based cyclometallated complexes with bidentate pyridine ligands, such as bipyridine derivatives and o-phenanthroline (Ru-54 and Ru-55), were also accessible for the polymerization of styrene. Although an osmium homolog was inactive, Ru-54 and Ru-55 successfully induced the controlled polymerization of styrene even in the absence of the additives = The... 

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. 

Mdssbauer spectra of bonding and structure in, 15 184-187 reactions with diborane, 16 213 stabilization of, 5 17, 18-19 cyanates, 17 297, 298 cyanide complexes of, 8 143-144 cyclometallated bipyridine complex, 30 76 diazene complexes, 27 231-232 dinitrogen complexes, 27 215, 217 diphosphine complexes of, 14 208-219 dithiocarbamates, 23 253-254 -1,2-dithiolene complexes, 22 323-327 hydrogen bonding, 22 327 halide complexes with phosphine, etc., 6 25 hexaflouride, structure, 27 104 hydride complexes, 20 235, 248-281, see also Transition metal-hydride complexes... 

Il)cycles formed with 2,2 -bipyridine or 1,10-phenanthroline type ligands to give a variety of target compounds (Scheme 18). These syntheses are more feasible than previous, where the complexes cis-[RuCl2(bpy)2] or fRuCl .(tpy)] have been used to cyclometalate 2-phenyl-pyridine and its derivatives (230-233). A bunch of diverse compounds have been prepared in good yields. Crystal structures of some of them are shown in Fig. 21 and their useful properties are summarized in Table IX. 

In this article the results of a detailed optical spectroscopic investigation of a series of related bis-cyclometalated Rh3+ and Ir3 + complexes of the general formula [M(CnN),NnN]+, M = Rh3+, Ir3+ (HCnN = 2-phenylpyridine or 2-(2-thienyl) pyridine NnN = 2,2 -bipyridine or ethylenediamine) are summarized. The nature of the lowest excited states of the compounds is... 

A dozen years ago, the optical properties of a very few cases of Ir(III) complexes were known [1,2]. In the same period, Ru(II)-, Os(II)- and Re(I)-polyimine complexes, for instance, were comparatively much more popular as a consequence of research efforts related to the theme of the interconversion between light and chemical energy [3-5]. In early times, the tricationic Ir(bpy)33+ species proved difficult to prepare, and was clearly identified only after closely related species were studied [ 1,6,7] bpy is 2,2 -bipyridine, Fig. 1. At the same time, the neutral/ac-Ir(ppy)3 species initially appeared as a side-product of dichloro-bridged dimers of the type [Ir(ppy)2Cl]2 [8] ppy is the cyclometalating anion from Hppy, Fig. 1. Today, we witness an impressive expansion of the literature on the luminescence of Ir(III) complexes, as illustrated by Fig. 2. 

To date, the cyclometallated bonding mode has not been directly observed in complexes of terpy or higher oligopyridines. However, the unequivocal demonstration of a cyclometallated 2,2 -bipyridine moiety in iridium complexes suggests that such a possibility exists 71,130,131,145,233,419, 420, 478). There is H NMR and kinetic evidence to suggest that cyclometallated intermediates are not involved in the deuteration of [Rufterpylj] at the 3, 3, 5, and 5" positions 138). 

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. 

Cationic complexes of cyclometallated Ir (ppy)2 (ppy = 2-phenylpyridine) with chelated diimine ligands, such as bipyridines (bipy) and phenan-throlines (phen), have interesting phosphorescent properties with potential applications in electroluminescent devices. Such compounds show at rather high energy MLCT transitions (2,nax = 340-380 nm) from the [Ir° (ppy)2]-based HOMOs to the LUMOs based on the n -orbitals of the phen (or bipy) ligands. Thus, these complexes can be considered as push-pull molecules in which the Ir° (ppy)2 moiety acts as the donor and the diimine as the acceptor part. 

To examine the relationship between the low-energy luminescence and intramolecular metal-metal distances, a series of [Pt2(CANAN)2(/U-L)]n+ (HCANAN=4-(aryl)-6-phenyl-2,2 -bipyridine) derivatives supported by different bridging ligands (L) have been prepared by Che and coworkers [17]. Subsequent spectroscopic assignments of cyclometalated platinum(II) or palladium(II) derivatives were made by comparing their emission energies with those of the [Pt2(CANAN)2(//-L)]n+ complexes. 

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