Cyclometallated complexes structures

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. 

Fig. 1. Schematic structures of the bis-cyclometalated complexes treated in this article. The abbreviations refer to Table 1...

Some properties of Ir(III) complexes of (NANAN) ligands are listed in Table 11 [25,65,90,91] Fig. 16 displays schematic structures of the complexes. As noted above, for these non-cyclometalated complexes, the metal-centered oxidation step is difficult and is not observed in the usually explored potential range [25]. 

Berenguer et al. also investigated the photophysical properties of cyclometallated complexes, but focused their attention on the CANAC platform, studying the anionic acetylide derivatives as well as other related structures, 3.12 [67], Contrary to the results obtained by Che in the NANAC structures, these complexes do not display photoluminescence in solution at RT. The absorption spectra in all cases are dominated by IL n-n and CT transitions. To the best of our knowledge these are the only reports on the photophysics of cyclometallated Ptn acetylide complexes to date. 

Most cyclometallated compounds of Pt and Pd contain the metals in the + 2 oxidation state (d8 configuration) with its strong tendency for planar coordination. Other oxidation states, notably +4, are also possible. A series of Pt(IV)-cyclometallated complexes have been obtained [55] from Pt(II) compounds through oxidative addition reactions. Details of the photochemical and photophysical properties of these systems are discussed later in this review. Here we restrict ourselves to the discussion of the structural aspects of the Pt(IV) and, as far as applicable, to Pd(IV) compounds. 

Constable, E.C. Eeese. T.A. Tocher, D.A. Polynuclear 7E intermediates in the synthesis of cyclometallated complexes and molecular structure of (2-pyridylphenyl)mer-cury(II) chloride tetramer. J. Chem. Soc., Dalton Trans. 

The dinuclear cyclometalated complexes act as building blocks for the formation of tetranuclear species with the olefinic pyridyl ligands providing a stable coordination geometry and structural stability for these coordination compounds. The reaction of the racemic mixture of the homochiral dimers with configuration R, R)- and (S, S)- at the metal in the presence of bridging ligands... 

Bis(iminophosphoranyl)methyl complexes of Ni, prepared by a transmetallation procedure, display an unusual structure with a central Ni-C bond and therefore can be formally regarded as cyclometallated complexes (Equation (61)). The crystal structure of one derivative (Ar = 2,6-diisopropylphenyl) exhibits a planar PGP unit, approximately perpendicular to the coordination plane, and relatively short P-G bonds. These features have been interpreted in terms of resonance between sigma and r/-ylidic canonic forms. " ... 

Carbene complex 138 has been isolated under considerably less extreme conditions/" The air and water stable complex 138 is isolated from the reaction of potassium tetrachloroplatinate with a free pyridine in ethanoic acid, even though a cyclometallated complex coordinated to the platinum through a nitrogen might have been anticipated. In principle, the carbene structure of 138 could be redrawn as the ionic structure 139 (Scheme 34) however, a short Pt-G distance of 1.952(7) A in the X-ray structure and a solution G chemical shift of 324 ppm for the carbon bonded to platinum confirms that carbene form 138 more accurately represents the molecular form present. 

In an attempt to evaluate the impact of chelation, the Albrecht group observed that cyclometalated complex 29 underwent acidolysis of the Cph-Ir bond in the presence of HCl [eqn (3.6)]. The formed complex 30 was stable over several days and no traces of triazolium salt were observed. According to these results, the Cafyi-Ir bond would be substantially less stable than the Ctrz-Ir bond. Despite the lack of support through chelation, the Ct -Ir bond resisted cleavage, suggesting that the bond might be intrinsically more stable than imidazolylidene iridium bonds [see eqn (3.4)] and does not need to be supported in a metalacyclic structure for acid resistance. 

Kitadai, K., Takahashi, M., Takeda, M., Bhargava, S.K., Priver, S.Fl. and Bennett, M.A. (2006) Synthesis, structures and reactions of cyclometalated gold complexes containing (2-diphenylarsino-n-methyl)phenyl (n = 5, 6). Dalton Transactions, (21), 2560—2571. 

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. 

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