Ligand isomerism

Since many ligands are organic compounds which have possibilities for isomerism, the resulting complexes can show isomerism from this source. Examples of isomeric ligands are 1,2-diaminopropane ( propylenediamine, pn) and 1,3-diaminopropane C trimethylenediamine, tn) or ortho-, meta-, and pcra-toluidine fCH3C6H4NH2). 

The reaction proceeds almost exclusively by direct substitution (ipso), as shown by reactions of isomeric chlorotoluene complexes (Scheme 4).so The relative rates of substitution of the isomeric ligands are similar, in the order 1.0 1.4 2.4 for o m p.50 A version of cine substitution is possible under special conditions, as discussed below. 

The two enantiomeric forms of the diethyl tartrate ligand in Sharpless oxidation lead to epoxy alcohols 22 and 24. Which of the isomeric ligands is required for the present reaction ... 

The low temperature process is obviously intramolecular because all intermole-cular rearrangements would result in geometric isomerization. Ligand exchange has been observed in these complexes and occurs at a much slower rate than either the low or high temperature processes so the high temperature process is intramolecular as well. 

Complexes of 82 have also been formed by the reaction of 2,6-diacetylpyridine and Af.Af-hwQ-aminopropyOamine in the presence of nickel(II) chloride and copper(II) chloride50). Other metals that have been used include copper(II) 63,64), nickel64165), cobalt(II) 66), manganese(II)73>, cobalt(I)69), eobalt(III)68,70-72), zinc(II)73>, and ruthenium(II)74). Kam and Busch 51 have reported the catalytic hydrogenation of the nickel(II) perchlorate complex of 82 to afford two nickel(II) complexes of 83 a yellow minor component and a red major component which preliminary studies indicate to be the meso form (84). The isomeric ligands can be displaced from the respective reduced complexes by cyanide ion. Ligand 84 has also been isolated and characterized as the cobalt(III) 67), iron(II)61,62), iron(III) 62>, and copper(II) complex 75,76). Dehydro — 82 has also been synthesized and complexed with nickel(II) 65,65a), and nickel(III)65 a. ... 

Rule 10. Designation of Structural Isomerism in the Ligand. Ligand isomerism is indicated by separate names for the isomeric ligands -SCN, thiocyanato vs. -NCS, isothiocyanato -NO2, nitro vs. -ONO, nitrito. 

Attempts to introduce a larger poly(pyrazolyl)borate ligand have demonstrated the steric limits of this system. Reaction of UCI4 with one equivalent of the thallium salt of [HB(3-Mspz)3] (Ms = mesityl) generates only the product containing an isomerized ligand, UCl3[[HB(3-Mspz)2(5-Mspz)]. ... 

Geometric isomerism ligands assume different relative positions in the coordination sphere examples are cis and trans isomers... 

Tauchert, M.E. (2009) Nickel-catalyzed hydrocyanation and pentenenitrile isomerization ligand design and mechanistic studies. Dissertation. Universitat Heidelberg. 

Geest and Steel synthesized N,G palladacycles of the two isomeric ligands 2,2 -diphenyl-4,4 bipyridine and 3,3 -di(2-pyridyl)biphenyl. 

Fig. 3.2s The bidentate ligands are shown here very schematically. If in one complex they represent a particular ligand but in another complex an isomeric ligand, then the two complexes provide an example of ligand isomerism.

Solvent Exchange, Racemization, Isomerization, Ligand Exchange 169... 

Use of structural differences between the two isomeric ligand syntones 396 and 397 allowed obtaining [196] both the non-intertwined Pd2L4 coordination capsule 775 and its intertwined PdsLe analog 776, respectively (Scheme 4.190). The double trefoil knot-mimicking capsule 776... 

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