Predetermined Chirality in Mono- and Dinuclear Cyclometalated Rhodium(III) Complexes

Abstract

Dinuclear and polynuclear metal complexes with octahedral eluent contains NaCl. Modeling the ΛΛ and the ∆Λ isomers of the dinuclear species shows crowding of the pinene centers coordinated to di-or polydentate ligands are often obtained as complicated mixtures of various stereoisomers. groups in both cases; however, the strain can be released by relatively small distortions only in the case of the ΛΛ isomer. Stereospecific synthesis of such species is therefore of high current interest. Chiral derivatives of pyridine can be used NO 3 -cleaves the dichloro bridge, yielding the mononuclear species ∆[Rh(L 2 ) 2 (NO 3 )] (2) in a completely stereoselective for this purpose. Dinuclear µ-chloro-bridged Rh III complexes with two didentate, cyclometalated thienylpyridine-type manner when NaCl is replaced by KNO 3 in the eluent mixture. The molecular structure has been determined by Xligands at each metal center are formed stereoselectively when pinene groups are fused to the pyridine rings. The two ray structure analysis for both the ∆∆ and the mononuclear complex ∆[Rh(L 2 ) 2 (NO 3 )] (2) in order to confirm the octahedral Rh III centers have homochiral configurations, ∆∆ and ΛΛ. The heterochiral diastereomer ∆Λ is not observed. configuration at the metal center.1 H-NMR, 13 C-NMR and CD spectra were measured and the latter shows that the CD With (8R,10R)-2-(2Ј-thienyl)-4,5-pinenopyridine [Hth4,5-(R,R)ppy] the ∆∆ to ΛΛ ratio is 9:1 when the separation activity is solely due to the chirality at the metal center.

Di-μ-chloro-bis{bis[4-(2-pyridyl)benzaldehyde-κ2C2,N′]iridium} dichloromethane sesquisolvate

“…The chloride ligands reside in the equatorial plane trans to the fppy C atoms and the fppy N atoms occupy the apical sites with trans geometry. This is consistent with other dinuclear iridium(III) and rhodium(III) complexes of this type (Fronczek et al, 1982;Steel, 1991;Garces et al, 1993;Ghisdavu et al, 1999). However, the IrÐCl bond lengths fall into two groups, differing by approximately 0.1 A Ê , with both IrÐCl1 bonds shorter than the IrÐCl2 bonds (Table 1).…”

Syntheses, Spectroscopy, and Structural Analyses of Dinuclear Chiral‐at‐Metal μ‐Aqua‐tetrakis[(R or S)‐N‐1‐(Ar)ethylsalicylaldiminato]di‐Λ‐ or ‐Δ‐nickel(II) Complexes

“…This phenomenon has also been observed in bridged dinuclear octahedral complexes using suitable chiral building blocks in the solid state 2a,2b,4. A pronounced diastereoselectivity was reported in dinuclear ΔΔ[Rh(L) 2 (μ‐Cl)] 2 [L = th4,5( R , R )ppy] with ΔΔ/ΛΛ = 9:1 and in ΛΛ[Rh(L′) 2 (μ‐Cl)] 2 [L′ = th4,5( S , S )ppy] with ΛΛ/ΔΔ = 9:1, according to the results of X‐ray studies 17a…”

Asymmetric Halogeno-Bridged Complexes of the Late Transition Metals − A Computational and Experimental Study

“…The homochiral complexes are energetically favoured by 7.77 kcal/mol at HartreeϪFock level. On the basis of molecular modelling studies of [(ppy) 2 Rh(µ-Cl)] 2 [19] and closely related complexes, [20] it has previously been suggested that the meso form is less stable due to interligand steric repulsion. Accordingly, for this class of compounds only ∆∆/ΛΛ complexes have been structurally characterized.…”

“…Accordingly, for this class of compounds only ∆∆/ΛΛ complexes have been structurally characterized. [20,21] A common feature of all the symmetrical complexes is a planar M(µ-Cl) 2 M unit (Table 2, Entries 1Ϫ11), the only exception being [(PPh 3 ) 2 Pd(µ-Cl)] 2 2ϩ , which displays a slightly bent chloro bridge in the crystal. This characteristic is also observed for most other halo-bridged complexes of d 8 transition metal ions.…”