Bis pyridyl ligands

The aforementioned polymer-supported bis-pyridyl ligand has also been applied in microwave-assisted asymmetric allylic alkylation [140], a key step in the enantio-selective synthesis of (R)-baclofen (Scheme 7.118), as reported by Moberg and coworkers. The ( (-enantiomer is a useful agonist of the GABAb (y-aminobutyric acid) receptor, and the racemic form is used as a muscle relaxant (antispasmodic). Under microwave heating, the enantioselectivity could be improved to 89% when using toluene as solvent (see also Scheme 6.52) [140],... 

A similar mechanism could operate also for bis(imino)pyridyl Fe(II)-based catalysts which have been reported to afford isospecific chain-end controlled propene polymerization occurring through secondary monomer insertion.138139 In fact, preliminary calculations indicate that the chirality of the growing chain would determine a chiral conformation of the bis-pyridyl ligand, which in turn would discriminate between the two monomer enantiofaces. 

A second example is the recently reported singlet-triplet equilibrium in a Mo(II) complex, cis-[Mo(bipy)2(OPri)2] (31). The interpretation of the magnetism is complicated by the possibility that the equilibrium is not entirely metal centered, but involves charge transfer to the bi-pyridyl ligands. Because a strong field is required to spin pair the d4 configuration, however, it is not impossible that examples exist among Mo(II) chemistry. The possible dynamics are subject to considerations similar to those which apply to Mn(III). 

Banerjee S, Adarsh NN, Dastidar P (2010) Selective separation of the sulfate anion by in situ crystallization of Cd-II coordination compounds derived from bis(pyridyl) ligands equipped with urea/amide hydrogen-bonding backbone. Eur J Inorg Chem 3770-3779... 

Because asymmetric catalysis enables access to several synthetically important compounds, microwave-assisted molybdenum-catalyzed allylic allylation has been studied using both free and polymer-supported bis-pyridylamide ligands [134]. The microwave-assisted catalytic reaction of 3-phenylprop-2-enyl methyl carbonate with dimethyl malonate in the presence of N,0-bis(trimethylsilyl)acetamide (BSA) and a polymer-bound bis-pyridyl ligand was rather slow, however. 

The microwave-induced reaction with a polymer-supported bis-pyridyl ligand (Scheme 16.87) was also slow, presumably because the insoluble resin-bound ligand makes the catalyst heterogeneous. After microwave irradiation at 160 °C for 30 min, however, the reaction was complete and the branch-to-linear ratio of the product was 35 1, an enantiomeric excess of 97%. The polymer-supported ligand has obvious advantages over its unsupported analogue because it could be reused at least seven times without any loss of activity [134]. 

This polymer-supported bis-pyridyl ligand (Scheme 16.87) has also been used in microwave-assisted asymmetric allylic alkylation [134], a key step in the enantio-selective synthesis of (R)-baclofen. 

What has been achieved with coordination polymers in going from innocent 4,4 -bipyridine to bis-pyridyl ligands having a non-innocent backbone 12CSR3039. 

Bis-pyridyl ligands with cmijugated dienes are indeed interesting since they can undergo double [2+2] cycloaddition reactions. Once such ligand was the bis-pyridyl... 

The PdeLn cubic coordination capsule 495 has been formed in a quantitative yield by coordination-driven self-assembly of a bis-pyridyl ligand syntone 261 having a bend angle... 

Coordination-driven self-assembly of a rigid angular bis-pyridyl ligand syntone 264 with palladium(II) ions by Scheme 4.22 afforded a cuboctahedral M12L24 capsule 499 in quantitative... 

Guest-template self-assembly of tris- and bis-pyridyl ligand syntones 241 and 291 with palladium(II) ions by Scheme 4.46 on the corresponding aromatic molecules as a matrix afforded 1 1 cage complexes of the heterotopic Me L2 L3 ligand 552 with encapsulated coronene and pyrene molecules in quantitative yield [45]. These DjA-symmetric coordination capsules have been characterized by NMR and CSI-MS methods ... 

A coordination-driven guest-templated self-assembly of rigid triazine and bis-pyridyl ligand... 

Self-assembly of four polyaromatic bis-pyridyl ligand syntone 577 with two palladium(II) ions by Scheme 4.164 gave a C4-symmetric macrotricyclic coordination capsule 733 encapsulating one nitrate anion to give a 1 1 cage complex [166]. 

An imidazole/pyridyl ligand (4) coordinates to a copper(II) center and on deprotonation the imidazole reacts with bis(hexafluoroacetylacetonato)zinc to form a trimeric Cu2Zn species bridged by imidazoles. The zinc ion is in an octahedral coordination environment with Zn-N distances of 2.029(2) A.116... 

Chelating bis(imine) ligands such asA-alkyl(2-pyridyl)methanimine (AlkPMI) have also been successfully utilized in copper-mediated ATRP [74,75,76,77,78]. In... 

Kinetic parameters k, often also and AS, occasionally AV ) for formation and dissociation of several pentacyanoferrate(II) complexes [Fe(CN)5L]" have been established. Ligands L include several S- and A-donor heterocycles,4-methyl- and 4-amino-pyridines, a series of alkylamines, 3- and 4-hydroxy- and 3- and 4-methoxy-pyridines, several amino acids, nicotinamide, " 4-pyridine aldoxime, 3-Me and 3-Ph sydnones, several bis-pyridine ligands,neutral, protonated, and methylated 4,4 -bipyridyl, 1,2-bis(4-pyridyl)ethane and traTO-l,2-bis0-pyridyl)ethene, pyrazine- 4,4 -bipyridyl- and bis(4-pyridyl)ethyne-pentaammine-cobalt(III), edta-ruthenium(III), and pentaammineruthenium-(II)and-(III) complexes of... 

Kinetic studies of the reaction of a CH2S(CH2)3SCH2-linked bis-terpyridyl ligand (bterpy) with [Fe(terpy)2] revealed a very slow two-step process. The mechanism suggested consists of slow loss of one terpy, rapid formation of [Fe(terpy)(bterpy)], and finally slow displacement of the second terpy as the partially bonded bterpy becomes hexadentate. " Replacement of the 2,4,6-tri(2 -pyridyl)-l,3,5-triazine, 2,4,6-tptz (66), in [Fe(2,4,6-tptz)2] " " by phen or bipy is alleged to occur by an associative mechanism. ... 

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