Flexible Bidentate Ligand Research Articles

A Mössbauer and electrochemical study of mononuclear iron(III) complexes with benzimidazole-based flexible bidentate ligands

A series of FeIII complexes of stoichiometry [FeLX3].nH2O have been synthesized, where X=Cl−, HCO−2 and L is a flexible bidentate ligand, 1,3(bis-benzimidazolyl) propane and 1,4(bis-benzimidazolyl)butane. Mossbauer data reveals that the isomer shift values lie in the range typically observed for high spin FeIII complexes, while the slightly large quadrupole splitting parameter indicates a rhombically distorted FeIII centre. Cyclic voltammetric studies reveal that the E1/2 for the FeIII/FeII couple for the formate complex shifts more cathodically than for the chloride complex; implying that HCO−2 is more effective at lowering the Lewis acidity of the FeIII centre.

Self-Assembly of Infinite Double Helical and Tubular Coordination Polymers from Ag(CF3SO3) and 1,3-Bis(4-pyridyl)propane

Three 1D coordination polymers were obtained from Ag(CF3SO3) and the conformationally flexible bidentate ligand 1,3-bis(4-pyridyl)propane (bpp), [Ag(bpp)](CF3SO3)·EtOH (1), [Ag(bpp)](CF3SO3) (2), and [Ag2(bpp)4](CF3SO3)2·bpp (3), the latter two exhibiting quite uncommon structural motifs. 2 contains an infinite double helical polymer, comprised of two chains of the type present in 1, and is the first example of a cationic infinite discrete double helix in coordination polymer chemistry. 3 contains a novel 1D polymer, comprised of interconnected macrocycles to give an infinite tubular shape. Uncoordinated bpp molecules are located inside the tubules, threading the rings in a pseudorotaxane-like manner.

Ruthenium clusters with nitrogen ligands V 1. Pyridyl ligands on triruthenium cores. X-ray structures of Ru 3(μ-H) 2 (μ-NC 5H 4) 2(CO) 8 and Ru 3( μ3- η2-PPhCH 2PPh 2) (μ-NC 5H 4)(CO) 8

The reaction between Ru 3(CO) 12 and pyridine affords a mixture of Ru 3(μ-H)(μ-NC 5H 4)(CO) 10 ( 1) and Ru 3(μ-H) 2 (μ-NC 5H 4) 2(CO) 8 ( 2). Cluster 2 is the first crystallographically-verified triruthenium cluster with two orthometalated N-heterocycles; these ligands occupy edge-bridging diaxial sites on two of the three RuRu bonds, one on each side of the triruthenium plane, with the hydrido ligands bridging the same RuRu bonds as the pyridyls. Reaction of 1 with dppm gives Ru 3( μ 3- η 2-PPhCH 2PPh 2)( μ-NC 5H 4)(CO) 8 ( 3) in low yield amongst a mixture of products. The structural study confirms that 3 results from dephenylation of the dppm ligand; concomitant loss of the hydrido ligand suggests reductive elimination of benzene. Formal electron counting on this electron precise cluster shows that Ru(1) and Ru(3) are each 0.5e deficient, and Ru(2) is 1e rich; two “semibridging” carbonyls in the triruthenium plane redistribute electron density from Ru(2) to Ru(1) and Ru(3). Reaction of Ru 3(μ-dppm)(CO) 10 with pyridine also affords 3 in low yield. Related reactions with the more flexible bidentate ligand dppe afford more complex mixtures of products. Whereas thermolysis of 1 affords [Ru 2(μ-H)(μ-NC 5H 4) 2(CO) 4(NC 5H 5) 2][Ru 10( μ-H)( μ 6-C)(CO) 24], thermolyses of 2 or 3 do not lead to tractable products.

Complexes of Copper with a Flexible Bis-benzimidazole Ligand

The flexible bidentate ligand 1,3-bis(benzimidazol-2-yl)propane, L3, and its N-methylated derivative L4, form complexes with CUI and CUII. The X-ray crystal structure of [Cu(L4)(MeCN)] (PF6) (1) shows a trigonal coordination of the CuI with the eight-membered chelate ring adopting a half-chair conformation. With CuII in EtOH, L3 forms dimeric [(L3)Cu(μ-EtO)2Cu(L3)](ClO4)2 · 2EtOH (2) whose X-ray crystal structure shows CuII in a distorted square-planar environment with one bidentate ligand and two bridging ethoxides. The chelate ring now has a boat-chair conformation which forms a hydrophobic pocket around the metal.

Trimethylpalladium(IV) complexes of flexible bidentate ligands. Conformational and fluxional effects in related Me 3Pd IV and Me 3Pt IV systems

A comparison of variable temperature 1H NMR spectra for stable complexes fac-Me 3Pt(L 2)I with low temperature spectra obtained after addition of iodomethane to Me 2Pd(L 2) allows assignment of structure for unstable organopalladium(IV) complexes of the flexible bidentate ligands (py) 2CHMe and (py)(pz)CH 2 (py = pyridin-2-yl, pz = pyrazol-1-yl), together with the first comparison of conformational effects and fluxional processes for organo-palladium(IV) and -platinum(IV) systems. Oxidative addition of CD 3I at −50°C occurs with scrambling of CD 3 and Me positions in fac-Me 2(CD 3)Pd(L 2)I, but for the platinum analogues the CD 3 and iodo ligands remain trans until scrambling occurs on warming to ca. −10°C.

Possible isomerism in octahedral metal complexes containing three flexible bidentate ligands

For octahedral complexes containing three flexible bidentate ligands we distinguish five sources of isomerism - metal and ligand asymmetry, conformational, orientation and sequential isomerism. By using the “C 3” projection and simple permutation concepts it is possible to account for, name, total and inter-relate all isomers in this system. The example shows how in a typical system 2244 isomers are distinguished and uniquely named in a simple table. The gaps in the table are also simply explained. Whereas permutation group theory goes straight to totals and “Herumprobieren” counts heads, this is enlightened Herumprobieren which factorizes, permutes and identifies.