Preparation of single enantiomers of chiral at metal bis-cyclometallated iridium complexes

Abstract

) with enantiopure X^Y ligands. However, these complexes have chirality at the ligand as well as the metal; hence, the aim of this work was to prepare, on a synthetically useful scale, homochiral cyclometallated Ir(III) complexes which are only chiral at the metal.Our strategy was to prepare diastereomeric complexes [Ir(C^N) 2 (X^Y*)], separate the diastereomers, then remove the chiral auxiliary by protonation and replace it with another bidentate ligand. A similar strategy has recently been applied by Meggers for the synthesis of homochiral trisbidentate ruthenium complexes, 10 and in 2012 was applied to iridium complexes for the first time. 5The dimer [Ir(ppz) 2 Cl] 2 (a, Hppz = phenylpyrazole) was reacted with 2.2 equiv. of (S)-Na(L1) 11,12 in a mixture of DCMmethanol (2 : 1) at room temperature for 2-4 hours, to give 1a as a (1 : 1) mixture of diastereomers, DS and LS, in good combined yields (>75%) (Scheme 1). The reaction was repeated with only 0.8 equiv. of (S)-Na(L1) per dimer and the 1 H NMR spectrum of the product showed a 1 : 1 ratio of the two diastereomers along with the unreacted excess dimer. This suggests that there is no diastereoselectivity in the synthesis and there is an equal probability for the formation of the two diastereomers. The diastereomers of 1a could be separated by crystallisation from different solvents and they do not interconvert in solution, suggesting the chirality at the metal is stable at room temperature. The absolute configuration of both diastereomers was determined by X-ray crystallography 13 and the structures of LS-and DS-1a are shown in Fig. 1. 14 The structures show that both isomers have cis carbon atoms and trans nitrogen atoms for the C^N ligands and S configuration at the chiral carbon atom of the oxazoline ligand; one isomer has a L configuration at the Ir centre (Fig. 1, left), whereas the other isomer shows a D configuration (Fig. 1, right). The change in chirality at the metal leads to different orientations of L1 with respect to the

Remote control: stereoselective coordination of electron-deficient 2,2′-bipyridine ligands to Re(i) and Ir(iii) cores

“…Whilst both isomers might be expected to form, inspection of the solid-state structure shows the presence of only the Δ R,S isomer and, given that the yield of the initially isolated solid was 71%, the complex is clearly formed diastereoselectively (see later). Similar discrimination has been observed in related systems 9 but remains rare 10 and, in this case given the remote position of the asymmetric unit, somewhat unexpected.…”

Rational design of iridium–porphyrin conjugates for novel synergistic photodynamic and photothermal therapy anticancer agents

“…Separation of the enantiomers of an Ir complex is rarely accomplished and is beyond the scope of the present work. 56 Tetraphenylporphyrin (TPP), a standard PS, [42][43][44][45][46] is studied as a comparison to 1-Ir and 4-Ir. The detailed synthetic procedures and spectroscopic characterization of TPP, 1-Ir and 4-Ir are reported in the ESI (Fig.…”

Chiral‐at‐Metal Octahedral Iridium Catalyst for the Asymmetric Construction of an All‐Carbon Quaternary Stereocenter

“…In this respect, it is our opinion that cyclometalated iridium(III) complexes are especially suitable metal-based scaffolds because of their high substitutional inertness and configurational stability, [23,24] as well as the ability to conveniently access stereoisomers in a nonracemic fashion. [25,26] Received: August 9, 2013 Revised: September 9, 2013 Published online: November 8, 2013 . Keywords: asymmetric catalysis · chirality · hydrogen bonds · iridium · quaternary stereocenter…”